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20251017_PLN1416_SSP
BARGWAUS EN CORE STATES • � • GROUP .* Cn � .WASI 10/06/2025 EL Stormwater Site Plan PREPARED BY Visconsi Development Alex White, P.E. Senior Civil Project Manager PREPARED FOR CLIENT ADDRESS Visconsi Companies, Ltd. 30050 Chagrin Boulevard, Suite 360 Pepper Pike, OH 44124 SITE ADDRESS PROJECT NO. DATE JURISDICTION NWC - 212th Street & 24413 10/06/2025 City of Arlington Medical Center Drive Arlington, WA U J J � L L C: w � N L L �Vcoo M U) V o C) � O O� E (� L U) 0 � ♦+ M M m TABLE OF CONTENTS 1.0 PROJECT OVERVIEW Figure 1.1 —Vicinity Map 2.0 CONDITIONS AND REQUIREMENTS SUMMARY 2.1 Analysis of the Minimum Requirements Figure 2.1.1 — Flow Chart for Determining Requirements for Redevelopment 3.0 EXISTING CONDITIONS SUMMARY Figure 3.1 —Assessor Map Figure 3.2— FEMA Map Figure 3.3—Soil Survey Map Figure 3.4—Sensitive Areas Map 4.0 OFF-SITE ANALYSIS REPORT 5.0 PERMANENT STORMWATER CONTROL PLAN 5.1 Existing Site Hydrology Figure 5.1.1 — Existing Basin Map 5.2 Developed Site Hydrology Figure 5.2.1 — Developed Basin Map 5.3 Performance Standards and Goals 5.4 Low Impact Development Features Figure 5.4.1 — Flow Chart for Determining MR No. 5 Requirements 5.5 Flow Control System Figure 5.5.1 —As-built Drainage Report File No. S-04-033 Figure 5.5.2—As-built Drainage Report Basin Maps 5.6 Runoff Treatment System 5.7 Conveyance System Analysis and Design Figure 5.7.1 — Pipe Conveyance Calculations 6.0 CONSTRUCTION STORMWATER POLLUTION PREVENTION PLAN Figure 6.1 —Construction Stormwater Pollution Prevention Plan 7.0 SPECIAL REPORTS AND STUDIES Figure 7.1 — DRAFT Geotechnical Engineering Report prepared by Terra Associates dated August 19, 2025 8.0 OTHER PERMITS 9.0 OPERATIONS AND MAINTENANCE MANUAL Figure 9.1 —O&M Manual 10.0 DECLARATION OF COVENANT FOR PRIVATELY MAINTAINED FLOW CONTROL AND TREATMENT FACILITIES 11.0 DECLARATION OF COVENANT FOR PRIVATELY MAINTAINED ON-SITE STORMWATER MANAGEMENTBMPS 12.0 BOND QUANTITIES WORKSHEET 24413.002-SSP.doc Tab 1 . 0 1.0 PROJECT OVERVIEW The new development project proposes to construct a medical building located on Tax Parcel No. 31051200200400. The site does not currently have an address but is located on the northwest corner of 212th Street N.E. and Medical Center Drive, Arlington, Washington 98223, and is situated within the Section 12, Township 31 North, Range 5 East, Willamette Meridian, Snohomish County, Washington. Please see Figure 1.1, Vicinity Map, for a graphical description of the site's location. The project site is currently undeveloped and consists of mainly vegetation. The project site has significant grade change, with slopes ranging from 1 to 50 percent generally sloping down from the northwest to the southeast. Along with the proposed building, this project proposes associated paving for parking and vehicle circulation, landscaping, new utilities, and stormwater improvements. The project proposes greater than 5,000 square feet of new and replaced hard surfaces and therefore, must address Minimum Requirement Nos. 1 through 9 of the 2024 Department of Ecology Stormwater Management Manual for Western Washington (2024 SWMMWW); refer to Figure 2.1.1. Please see the remainder of this report for a discussion on how this project intends to comply with all Minimum Requirements of the applicable stormwater manual. 24413.002-SSP.doc Figure 1 . 1 Vicinity Map Presidents Elementary Scnool E 3rd St el a' v Eagle Creek Elementary 4 School V O N E 2nd St Z 4 A x Y Q1 r r 3 IE C Z vt � � Z Z W z E 1st St E 1st St c A Q x h lapse-'t v1 pd t > 215th St NE Q E Maple St Arlington High '_chool n J M Z 2131h St NW in n Medical Ctv Cascade Valley Hospi!al SITE .z E Highla�Dr 12th St NE cc Y N L �0 a 81st Dr NE 1A - � •_ ......•........BAN Patage St L 2071h St NE _ r " 7Son r a � �y KeitA Cn Qa REFERENCE: Geomap(2025) Scale: For. Job Number Horizontal: N.T.S. Vertical: N/A Arlington Medical Center Arlington, Washington24413 Barghausen 9 Consulting Engineers,LLC. Title: 18215 72nd Avenue South VICINITY MAP Kent,WA 98032 425.251.6222 barghausen.com DATE:9/05/25 P:124000s1244131exhibitlgraphicsl24413 vmap.cdr Tab 2 . 0 2.0 CONDITIONS AND REQUIREMENTS SUMMARY 2.1 Analysis of the Minimum Requirements Minimum Requirement No. 1: Preparation of Stormwater Site Plan: Response: This Minimum Requirement has been fulfilled by the preparation and completion of this Stormwater Site Plan. Minimum Requirement No. 2: Construction Stormwater Pollution Prevention: Response: The Construction Stormwater Pollution Prevention Plan (SWPPP) for this project has been provided. See Section 6 of this report. Minimum Requirement No. 3: Source Control Prevention: Response: All known available and reasonable Source Control BMPs will be applied to this project in accordance with those applicable to the proposed development. At a minimum, the parking lot will be swept on a regular basis, and the proper spill prevention and cleanup techniques will be implemented. Minimum Requirement No. 4: Preservation of Natural Drainage System and Outfalls: Response: The project proposes to maintain the existing drainage patterns and continue draining to the existing detention pond constructed under City File No. S-04-033, which was intended to collect the runoff from the future buildout of this project site; therefore, this development is not anticipated to negatively impact the existing drainage patterns. Minimum Requirement No. 5: On-Site Stormwater Management: Response: The on-site portion of this project triggers Minimum Requirements Nos. 1 through 9 and is on a parcel inside the UGA; therefore, this project must either apply the Low Impacted Development Performance Standard and BMP T5.13: Post Construction Soil Quality and Depth; or evaluate the feasibility of the BMPs in List No. 2. This project will choose to evaluate the feasibility of BMPs from List No. 2 and apply them to the maximum extent feasible, refer to Section 5.4 of this report. Minimum Requirement No. 6: Runoff Treatment: Response: The project proposes more than 5,000 square feet of new and replaced pollution- generating hard surfaces, and therefore, triggers the requirements to provide runoff treatment. This project will utilize the existing detention pond constructed under City File No. S-04-033 to meet runoff treatment requirements. Please see Section 5.6 of this report for a more detailed discussion. Minimum Requirement No. 7: Flow Control: Response: This project proposes more than 10,000 square feet of new and replaced pollution- generating hard surfaces and therefore triggers the requirements to provide flow control. This project proposes to utilize the existing detention pond constructed under City File No. S-04-033 to meet flow control requirements. Please see Section 5.5 for further information. Minimum Requirement No. 8: Wetland Protection: Response: There are no wetlands or wetland buffers located within the project site. 24413.002-SSP.doc Minimum Requirement No. 9: Operation and Maintenance Response: An Operations and Maintenance Manual has been provided. Refer to Section 9 of this report. 24413.002-SSP.doc Figure 2. 1 . 1 Flow Chart for Determining Requirements for Redevelopment Figure 1-3.1: Flow Chart for Determining Requirements for New Development Start Does all stormwater runoff Yes The UIC Rule (Chapter 173-218 WAC) Here from the Project Site discharge applies. Refer to 1-4 UIC Program to a Class V UIC Well? Guidelines for UIC Program Requirements. No IF See Redevelopment Project ro oes the Site have 35% Yes r more of existing hard Thresholds and the Figure "Flow surface coverage? Chart for Determining Requirements for Redevelopment". $N Does the Project result in 2,000 square feet or more of new plus replaced hard surface area? OR Does the land disturbing activity total 7,000 square feet or greater? es No Minimum Requirements#1 IF through#5 apply to the new and replaced hard surfaces Minimum Requirement#2 applies. and the land disturbed. Next Question Does the Project add 5,000 square feet or more of new plus replaced hard surfaces? OR Convert Y4 acres or more of vegetation to lawn or landscaped areas? OR Convert 2.5 acres or more of native vegetation to pasture? es No IF All Minimum Requirements apply to the new and replaced No additional requirements hard surfaces and converted vegetation areas. r►� Flow Chart for Determining Requirements for DEPARTMENT OF New Development ECOLOGY State of Washington Revised September2022 2024 Stormwater Management Manual for Western Washington Volume I-Chapter 3-Page 109 Tab 3 . 0 3.0 EXISTING CONDITIONS SUMMARY The existing site is bordered by developed paved roads, Medical Center Dr. to the north and east and 212th Street N.E. to the south, and an existing partially developed site to the west. The site slopes vary from 1 to 50%, with a significant slope on the eastern portion of the property. Existing conditions include overgrown grass and shrubs covering most of the site, and therefore, this project is defined as a new development project. An existing asphalt parking lot, helicopter landing pad, and vegetation is located on the parcel to the west, Parcel No. 31051200200700. 24413.002-SSP.doc Figure 3. 1 Assessor Map 00 - -- Z-Ulb:1-U1� 3' ;5 Yb 3 2 218-TH-PL NE i 1 25 = 1 03 4: 62 01 6 e s 7 8 g 10 Z 24 01 i ..1—_ --- -1ST -ST- � i - 23 Sp 1£ 2 i 19 i 2Q PIED PIPER 12 13 12 11 22 3 18 i 3 iY 5 6 TR 99.7 14 4 111 7 i� 4 Q 15 217TH PtN(c s 16 »»»tea HEIGH -S (5430) 11 ? EAGJLE 16 21 = TR 999 5LL CREAK r. 7 00 14 w 6 7 10 PLACE 17 19 20 8 13 Q 02 9 12 2 i s 01 8 00 i g (94'33) 18 R 998 i 10 11 cn 8 a i — 2- 2-017 BLAAFN 2001©6135 — Q2-034 2-040 d5 0 2 SP 26 8 3 4 S KENTJID 2-020 Q TR 4 2 10012 1314 g�2 ROS FIN.,. 9Z 9011015003 +3 y 2 11 10i.9 8 7 6 5 2-018 2-031 2.033 2-03C __-MAPLE--_ST__. 215TH 00 , 01 01 02 U1: R NEI 3 5; ElCztiT (4962) 12 +'IXI.Y h'l.'M111111/,A'I.YhV.V .�N4N4H Z 11"00 f-yh°i�1y,. 9 IHIHNt1IINIl1.; I " 11 01 1-040 I 2-022 4 = 6 7 10 01 ,...»,,»„ LU -042 B o2 z THE44.:/N4NIN N/-N 1:1NtN N111/N 2-022 1 CASCADE MEDICAL PH 2 6 1 CENTER CONDO PH 3 YAFAMI.1•T 8niAl 5 2 f' PLAT - -- - - - - - -- , NORWOOD GLEN 4 :::.. 1-029 i _ - --------- CONDO (10466) (8499) 3 '' E\j i A RdS AFN 840330503 SITE 9°NN BLA--Z-I -027-BLA A PH 1 i 2-006 z 0� ----- p,0 A -------' j 2-004 z � TR .,..,..., �H 2 p� `: 2-005 Q 1 F1-031 2-0 7 0) TR: i z 212TH —ST— NE — WHITEHORSE MEDICAL 4 C � I c T �h..,l.•I CONDO 2 n 3-006 (8127) I WESLEY---ST- - `. O REFERENCE: Snohomish County Department of Assessments(Dec.2024) Scale: For. Job Number Horizontal: N.T.S. Vertical: N/A Arlington Medical Center Arlington, Washington24413 Barghausen g Consulting Engineers,LLC. Title: 18215 72nd Avenue South ASSESSOR MAP Kent,WA 98032 425.251.6222 barghausen.com DATE:9105/25 P:124000sl244131exhibitlgraphicsl24413 amap.cdr Figure 3 .2 FEMA Map 3T I < o �oCity of Arlington �3 7N�D T � Q z > > 0 Ua r z w LU cn Q N - 218 TUj H Q cn ig Z pL NE Z 217TH p Q Q o PL NE ST E 1ST ST _ �E MAPLE S HAML 245 H DR ST NE ST ST 1j.,* ' E UNION 215TH ST pL NE MF°, 87 T H Q► E JACKSON ST CrR �,,�, AVE NE p n/E/T RD E HIGHLAND DR ZI I r-I ST NE .� SLEY:ST H ND DR - !10TH 81 ST I �L NE DR S STILLAGUAMISH - AUE LEGEND 9TH PORTAGE ST Without Base Flood Elevation(BFE) :;a.1_V.AQQ 'E NE With BFE or Depth%one At,Ao,Ari,VE,AR 207TH SPECIAL FLOOD Regulatory Floodway 209TH ST NE pL NE HAZARD AREAS g 0.2%Annual Chance Flood Hazard,Areas N of 1%annual chance flood with average depth less than one foot or with drainage LOIS LN areas of less than one square mile — Future Conditions 1%Annual Chance Flood Hazard KEITH LN OTHER AREAS OF — Area with Reduced Flood Risk due to Levee FLOOD HAZARD See Notes.Znne.x 81 ST NO SCREEN Areas Determined to be Outside the DR NE OTHER 0.2%Annual Chance Floodplain AREAS Area of Undetermined Flood Hazard -,e D REFERENCE: Federal Emergency Management Agency(Portion of Map 53061C0405F, June 2020) Scale: For: Job Number Horizontal. N.T.S. Vertical: N/A Arlington Medical Center Arlington, Washington24413 Barghausen g Consulting Engineers,LLC. Title: 18215 72nd Avenue South FEMA MAP Kent,WA 98032 425.251.6222 barghausen.com DATE:9105/25 P:124000sl244131exhibitlgraphicsl24413 fema.cdr Figure 3.3 Soil Survey Map , A ar Lim. � 1 l.;l�•►+IEirls + • I. REFERENCE: USDA, Natural Resources Conservation Service LEGEND: HSG 1 =Alderwood gravelly sandy loam, 0-8%slopes B 57 = Ragnar fine sandy loam, 0-8%slopes A Scale: For. Job Number Horizontal: N.T.S. vertical: N/A Arlington Medical Center Arlington, Washington24413 Barghausen 9 Consulting Engineers,LLC. Title: 18215 72nd Avenue South SOIL SURVEY MAP Kent,WA98032 425.251.6222 barghausen.com DATE:9/05/25 P:124000s1244131exhibitlgraphicsl24413 soil.cdr Figure 3.4 Sensitive Areas Map 1 Critical Areas Geohazard Layers Geohazard - Landslides Snohomish County Landslides CAR LCSPI Model , SITE Site Visits- Michael Braaten;et,al. NE WA DNR Landslides P TV- Forest Practices ' Miscellaneous Reconnaissance-level Mapping Watershed Analysis itot 71 aGeohazard - Steep Slopes E ST 9. Steep Slopes(> 33 percent slope) Wetlands and Hydric Soils Hydric Soils Wetlands (Modeled) REFERENCE: Snohomish County PDS Map Portal (2025) Scale: For: Job Number Horizontal: N.T.S. Vertical: N/A Arlington Medical Center Arlington, Washington24413 Barghausen 9 Consulting Engineers,LLC. Title: 18215 72nd Avenue South SENSITIVE AREAS Kent,WA 98032 425.251.6222 barghausen.com MAP DATE:9/05/25 P:124000s1244131exhibitlgraphicsl24413 sens.cdr Tab 4 . 0 4.0 OFF-SITE ANALYSIS REPORT Based on existing topography and survey, flows from Medical Center Drive and 212th Street N.E. appear to sheet flow into their respective flowlines and are captured within the existing stormwater conveyance system; and therefore, the site does not experience stormwater run-on from the bordering streets. It appears that the site experiences a portion of stormwater run-on from the parcel to the west, however, the majority of the run-on is from the adjacent parcel's landscaping. The runoff generated on the existing parking lot to the northwest is captured and conveyed to the existing conveyance system within Medical Center Drive. It is anticipated that the portion of run-on that does enter the project limits is either dispersed in the existing vegetation or sheet flows into the existing conveyance system within 212th Street N.E. and discharges into an existing privately owned detention pond, located on Parcel No. 31051200200400, east of Medical Center Drive. Based on the approved drainage report and as-builts under City File No. S-04-033, it appears that the existing stormwater detention pond has been constructed and sized to include the stormwater runoff generated from the proposed project site. At the time of this report preparation, there does not appear to be any identified drainage problems within the project's vicinity. This project proposes to meet runoff treatment and flow control requirements by utilizing the existing stormwater detention pond. It is anticipated that this development will not negatively affect the surrounding parcels. 24413.002-SSP.doc Tab 5 . 0 5.0 PERMANENT STORMWATER CONTROL PLAN This section contains the following information: 5.1 Existing Site Hydrology 5.2 Developed Site Hydrology 5.3 Performance Standards and Goals 5.4 Low Impact Development Feature 5.5 Flow Control System 5.6 Runoff Treatment System 24413.002-SSP.doc 5.1 Existing Site Hydrology The existing land cover consists entirely of vegetation on the project site. The site slopes vary from 1 to 50%, with a significant slope on the eastern portion of the property. Site stormwater runoff is assumed to disperse into the existing vegetation or to sheet flow into the adjacent roads, ultimately being captured by the existing conveyance system located along 212th Street N.E. and Medical Center Drive. As previously mentioned, the existing stormwater conveyance system appears to discharge into a privately owned stormwater detention pond located on Parcel No. 31051200200400, east of Medical Center Drive. According to the Soil Survey Map in Figure 3.3, the site consists of Alderwood gravelly sandy loam and Ragnar fine sandy loam. Refer to Figure 5.1.1 for the Existing Basin Map. A geotechnical report has been prepared that provides greater detail of the site- specific soil conditions. Refer to Figure 7.1. 24413.002-SSP.doc Figure 5. 1 . 1 Existing Basin Map PREDEVELOPED BASIN MAP N FOR PROJECT LAND COVERAGE MEDICAL CENTER n SEC. 12,TWP. 31 N., RGE 5 E., W. M. cQc PRIVATE PROPERTY G z CITY OF ARLINGTON SNOHOMISH COUNTY WASHINGTON PARCEL#31051200200400 z Q O Q EXISTING IMPERVIOUS AREA 61 SF(0.001 AC) m Z w EXISTING PERVIOUS AREA 75,159 SF(1.73 AC) Z PARCEL#31051200200400 TOTAL AREA 75,220 SF±(1.73 AC) ° C/) LZ O Lu PARCEL#31051200200700 -o d = C) n EXISTING IMPERVIOUS AREA 4,920 SF(0.11 AC) I 0 15 30 60 O ~ J _Vz N89°32'11"E 418.39' � -J N Q EXISTING PERVIOUS AREA 24,209 SF(0.56 AC) 0 - - - - - - - w U TOTAL PROJECT AREA 29,129±(0.67 AC) I /�- SCALE-9 =30 w U Q_ PUBLIC ROW PROPERTY _______ ______________ ____1________ ____- _______--©11 80 <��X69Z9.) / >> w 0 o N89, ,.E .74'- -_, Z6 .p 3, C) EXISTING IMPERVIOUS AREA 2,187 SF(0.05 AC) ® N89"32'11"E 310.28' - ��90.9\60 O // Lu z C EXISTING PERVIOUS AREA 1,364 SF(0.03 AC) 0 / < 00. TOTAL AREA 3,551 SF(0.08 AC) 15'EXISTING DRAINAGE EASEMENT PER AFN 200407265279 ° \ '.° NOT INCLUDED IN TITLE REPORT . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 0 o J LL o w > ° z a °` Q _ ° ° o p g - U ¢� ° ° 1 Z i C cl) J ° El , N ° .PARCEL N0.-3105120020?400. v O O O ° ° ('y "VEX W MITF J v FWAcc"" Z D �O ynjy O O Ir c o Q O a 3 O G�n� _ - n b O ` m 77�o e w d e ° Z 9 G/STEP G\� 370NAL EN c I O O m z O O O - PARCEL N0.31051200200700 I O O - 0 i 0 0 0 0'p r ---- 0 3 3 j Q ® u E J 8 j I J Vl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i d L 7 _ 3 L I •. L—---- .-.-.-.-... C r N C 3 C W C N , prom ® •.,: � �� � Pta/ POWER EASEMENT '� Prom W ENT • - - - N89"58'14"W 343.66' O'SEWER EASEMENT N89°58.14"W 213.7 00 N a H - - AFN 9207230118 ---- 21'X32'GAS REGULATOR 10 POWER EASEMENT _ AFN 200407265279 AF POWER EASEMENT . i 3 -a.N --- STATION EASEMENT AFN 9207230118 - -- AFN 9207230118 - M — C Q Cp $ _________________ ___ AFN 9207230118 -_____________ _______ _______ _- ____________ in C Ln 2 1 2 T H S T NE 589°58'14"E 1305.69' O N C O 12 - - - - - - - - - - - - - - - - - - - - - - - - m V r°Y o a -- - - - - - - - -- - - - - TEL RISER�o 0 M E r m o N r S 5.2 Developed Site Hydrology The proposed development consists of a medical facility building, paved parking area and drive aisles, and landscaping. Proposed surfaces will include new roofing, asphalt and concrete pavement, and landscaping. In addition to these features, new catch basins will be installed to capture the runoff generated from the new hard surfaces and convey the runoff into the existing public conveyance system. Runoff generated from the new and replaced hard surfaces within the right-of-way along Medical Center Drive and 212th Street N.E. will continue to flow into the existing public stormwater conveyance system. The stormwater runoff generated from both the private property and right-of-way work will continue being conveyed to the existing privately owned detention pond located on Parcel No. 31051200200400. Refer to Figure 5.2.1 for the Developed Basin Map. 24413.002-SSP.doc Figure 5.2 . 1 Developed Basin Map DEVELOPED BASIN MAP N FOR PROJECT LAND COVERAGE MEDICAL CENTER SEC. 12,TWP. 31 N., RGE 5 E., W. M. a p PRIVATE PROPERTY Q z CITY OF ARLINGTON, SNOHOMISH COUNTY, WASHINGTON NEWPAR IMPERVIOUS ERV0 US SURFACES (AFTER BSP) z LLJ � NEW IMPERVIOUS SURFACE$ 72,713 SF(1.67 AC) � LQT B � (� z W PAVEMENT/CURBS/WALL 62,545 SF(1.44 AC) ® - ROOF 10,168 SF(0.23 AC) 0 � o m w Z O _____1-1_ ---____--__________________________________________________ ____ PROPOSED PERVIOUS 30.368 SF(0.70 AC) 0 -"--- NORWOOD GLEN � = LJJ U TOTAL PARCEL AREA(AFTER BSP) 103,081 SFm(2.37 AC) I _ CONDOWOOD PHASE// 0 15' 30' 60' ~CN J Z N89°3 _39' - — ___-- _ _ AFN200704035004 a r Q PARCEL#31051200200700 I ' - - - - - 0 -\ ° SCALE:1-30' O N U J N89°32'11"E 80.74' 4x NEW AND REPLACED IMPERVIOUS AREA 19 SF(0.0004 AC) q`9p, // L.L� U 0 Q ____ __ ___________________________1___ _________ _ _____.d=90°29' <x 166,Z9.9 / LLI PROPOSED UTILITY TRENCHING 1,253 SF(0.03 AC) o o - < > Lij TOTAL PROJECT AREA 1,272 SFt(0.03 AC) y R 111' 0' ds p. d , 0 Z N89°32'11"E 310.28' L D0' 06 D p Z NORWOODGLEN CONDOMINIUM PHASE IMPROVEMENTS / AFN 200610315003 NEW AND REPLACED IMPERVIOUS AREA 2,686 SF(0.06 AC) ® IT EXISTING DRAINAGE EASEMENT PER y . . y a O AFN 200407265279 . . . . . LOTD PROPOSED PERVIOUS 1,159 SF(0.03 AC) 0 - NOT INCLUDED IN TITLE REPORT - TOTAL AREA 3,845 SF(0.09 AC) _ $ \ 0 > ° r" ° z Q o' d O O c7 ° ) z it J o n° D C) J ° n LL o 0 0 o N89°58'14-W 112.00' ° m M ❑ w O O O O p O a�F w a /rF j O O r M� O 8 O G O m n/ w b d �e O �. O o APN 31051200200400 z I APN3105 11 0 02 02 70 0 O O N LOTC ._y LOTS 00 _ gO _ 3-STORY BLDG LL _ O O 00 n 335�+57 00 30,000 S.F. o S78'3 W i O of a 2 F 8 v .�.`. .'. .` J t> N o POWER EASEMENT N89°58'14'W 343.66' EASEMENT N89°58'14"W 213.74' N C Q co N 0'SEWER EASEME 10'POWER EASEMENT AFN 200407265279 10'POWER EASEMENT j -a Ql N w --- AFN 9207230118 ------- --- ---------AFN 9207230118 -- ----- V P AFN 9207230118 f0 -5 C Q N a _ N 21'X32'GAS REGULATOR 212TH ST NE 589°58'14'E 1305.69' / i 5 cN STATION EASEMENT —- - - - - - - - - - - - - - - - - m 0 O AFN 9207230118 m V -Y m s -----------------------________________ ----------------------- -----------------------_----- o I 3 = � v ❑o 0 S M r E r m o N r S 5.3 Performance Standards and Goals This project is required to meet Flow Control and Runoff Treatment Standards per the 2024 Stormwater Management Manual for Western Washington. The following is a full discussion of how this project intends to meet the required performance objectives. 24413.002-SSP.doc 5.4 Low Impact Development Feature This project triggers Minimum Requirements Nos. 1 through 9 and must either use on-site stormwater management BMPs from List No. 2, or demonstrate compliance with the LID Performance Standard and BMP T5.13. This project will choose to evaluate the feasibility of on-site stormwater management BMPs from List No. 2. Lawn and Landscaped Areas 1. Soil preservation and Amendment BMP in Volume III, Section 3.1. Feasible: Post Construction Soil Quality and Depth in accordance with BMP T5.13 in Chapter 5 Volume V of the SWMMWW will be applied to all proposed landscaping areas. Roofs: 1. Full Dispersion in accordance with BMP T5.30 in Chapter 5 of Volume V of the SWMMWW, or Downspout Full Infiltration Systems in accordance with BMP T5.10A in Section 3.1.1 of Volume III of the SWMMWW. Infeasible: This project will not preserve 65 percent of the site area as forest or native vegetation. Additionally, the geotechnical engineering study indicated that due to the soil conditions of this site, infiltration will not be feasible. Refer to Figure 7.1 for the Geotechnical Report. 2. Bioretention (See Chapter 7 of Volume V of the SWMMWW) facilities that have a minimum horizontally projected surface area below the overflow, which is at least 5 percent of the total surface area draining to it. Infeasible: The geotechnical engineering study has indicated that due to the soil conditions of this site, infiltration will not be feasible. Refer to Figure 7.1 for the Geotechnical Report. 3. Downspout Dispersion Systems in accordance with BMP T5.10B in Section 3.1.2, Volume III, of the SWMMWW. Infeasible: Downspout dispersion systems are infeasible due to the lack of available vegetated area and flow path space. 4. Perforated Stub-out Connections in accordance with BMP T5.10C in Section 3.1.3, Volume III, of the SWMMWW. Infeasible: Perforated Stub-out Connections are infeasible. All rooftop runoff is proposed to be collected and discharged to the existing stormwater detention pond that has been designed to meet Minimum Requirement No. 7 of the Flow Control Requirements. Other Hard Surfaces: 1. Full Dispersion in accordance with BMP T5.30 in Chapter V, of the SWMMWW. Infeasible: This project will not preserve 65 percent of the site area as forest or native vegetation. 24413.002-SSP.doc 2. Permeable Pavement No. 2 is in accordance with BMP T5.15 in Chapter 5, Volume V, of the SWMMWW. Infeasible: The geotechnical engineering study indicated that due to the soil conditions of this site, infiltration will not be feasible. Refer to Figure 7.1 for the Geotechnical Report. Bioretention (See Chapter 7, Volume V of the SWMMWW) facilities that have a minimum horizontally projected surface area below the overflow which is at least 5 percent of the total surface area draining to it. Refer to Figure 7.1 for the Geotechnical Report. Infeasible: The geotechnical engineering study indicated that due to the soil conditions of this site, infiltration will not be feasible. 3. Sheet Flow Dispersion in accordance with BMP T5.12, or Concentrated Flow Dispersion in accordance with BMP T5.11 in Chapter 5, Volume V, of the SWMMWW. Infeasible: The site lacks the available vegetated flow path space for sheet flow dispersion per BMP T5.12, or concentrated flow dispersion per BMP T5.11. 24413.002-SSP.doc Figure 5.4. 1 Flow Chart for Determining MR No. 5 Requirements Figure 1-3.3: Flow Chart for Determining MR #5 Requirements Does the entire project qualify as Flow Control exempt(per MR#7)? Yes �E] Did the project developer choose to meet Does the project trigger NO the LID Performance Standard? only MRs#1 -#5?(Per (the project triggers Is the project outside the Project Thresholds in MRs#1 -#9) the UGA on a parcel NO Applicability of the that is 5 acres or larger? Minimum Requirements Yes Section). REQUIRED:For each surface,consider the BMPs Yes in the order listed in List#3 NO for that type of surface.Use the first BMP that is Did the project considered feasible. developer choose to meet the LID Yes NOT REQUIRED: Performance Did the project Achievement of the LID Standard? developer choose to Performance Standard. NO meet the LID Performance Standard? REQUIRED:For each Yes Yes surface,consider the NO BMPs in the order listed in List#1 for that type of surface.Use the first BMP that is considered feasible. NOT REQUIRED: Achievement of the LID Performance Standard. REQUIRED:Meet the LID REQUIRED:Meet the LID Performance REQUIRED:For each Performance Standard through Standard through the use of any Flow Control surface,consider the BMPs the use of any Flow Control BMP(s)in this manual. in the order listed in List#2 BMP(s)in this manual. for that type of surface.Use REQUIRED:Apply BMP T5.13 Post the first BMP that is REQUIRED:Apply BMP T5.13 Construction Soil Quality and Depth. considered feasible. Post-Construction Soil Quality and Depth. NOT REQUIRED:Applying the BMPs in Lists NOT REQUIRED: #1,#2,or#3. Achievement of the LID NOT REQUIRED:Applying the Performance Standard. BMPs in Lists#1,#2,or 43. r►� Flow Chart for Determining MR #5 DEPARTMENT OF Requirements ECOLOGY State of Washington Revised March 2019 2024 Stormwater Management Manual for Western Washington Volume I-Chapter 3-Page 126 5.5 Flow Control System This project proposes more than 10,000 square feet of new and replaced hard surfaces and therefore must provide flow control per the 2024 DOE SWMMWW. This project proposes to utilize the existing stormwater detention pond constructed under City File No. S-04-033 to meet flow control requirements. Per the 2024 DOE SWMMWW Appendix I-D.3, if the regional facility is privately owned and specifies the ultimate construction of all the areas it was designed to serve, it is all considered as one project, and therefore, may be utilized for the project. Based on as-builts and the approved drainage report, the existing detention pond was sized to meet the flow control requirements for the surrounding development, including the project site in the developed condition. Please refer to Figure 5.5.1 and 5.5.2 for the approved Drainage Report and figures discussing the design of the existing stormwater detention pond. As noted in Figure 5.5.2, the pond was sized to accommodate the developed condition of Lot A and C (Parcel Nos. 31051200200700 and 31051200200400, respectively) assuming that the impervious coverage was 90%. The proposed impervious coverage of the developed site will not exceed 90% and therefore, the existing detention pond will continue to be adequately sized to provide flow control for this project. 24413.002-SSP.doc Figure 5.5. 1 As-built Drainage Report File No. S-04-033 • • Northwest Corp. • • • . - S-04-033 AuguA 11 2004- r9 y � '•ice ..:•`�":`'�'.� :r" # •�'�' t„�y..��� ` `�� CITY OF ARLINGTON I + q •l35715li l �\ 10NAL 1 1• Prepared , Cascade Surveying • i t �' - , �. I �. � �' -� t - ' I F Project Summary Erosion Control Risk Assessment Upstream & Downstream Analysis Stormwater Quantity Control & Water Quality BMP's Appendix BASIN MAPS DRAINAGE CALCULATIONS 1 4 Project Summary PROPERTY DESCRIPTION The site of proposed development is located in a portion of the SW `/ of the NW '/ of Section 12, Township 31 N, Range 5 E, W.M. The property is 5.17-acres in size and is located just east of the intersection of Stillaguamish Ave. and 212th St. N.E. (Tveit Rd). The project site is identified as new Lot D of the Hospital District#3 B.L.A., Project File No. Z-04-027-BLA. (See Vicinity Map below). QUFfrLR SECf1U�l tUl':NSI Ii`11.V10.L S1PN(iL L.1- - NW 12 31 5 Nn.• _:..... . ti1N-1-.77 i 06 KUNZE'ACREAGE iRAf.i# (4868) JC- 14i1 i p a Yl$ p 2003 ' O1 Mw' e9S.« nl 19 I ♦ ec 014.�nreTn n3a m 7 01 e e N if yi- nrz 00 { Y O' ae a I27 .. - Ia 'r :._,at7e(67y^ u' 10 -- P1ED.;P1 U ��f) n s = - 04 'i •�1'T'-4 HEKiN�S I., " �EAGI.E i +> s CREEK' N 1 �� ' o .''•. j j r .�..`..__ r_., In _ PLACE 'I''m - "I Or Y 11 Y�- n'y r )•Ora 8LII AFN OIIeteet KfNf Nlll 1 r UFO 1y{{ G fR t 12 Ito N ♦ a A[{y- OJ U.r __— MO r�tl 11D tlT[OYa U4 Ir '1e e 8 7(6'b a 2018' 2031 1S71t�19 MAME .QT ' m i Of r Of 2 oa• ?+ Ole .r Nis (490) 2 rn rrf„_ _ THE 1 ' �AT� y1NY 'ARUNc:)Rti CASCAOEM. ICAL CENTER C DO YAi{MUTI! ON (8016) PLAT ... ' 2 V. tflP L\l+lF7 T93 (51991 •a !.l .�Iyt1L'��M,,,���,ppr%L E 6 '. N� _ Y 'S 7oOS 11 1, 12' - 10 14� 037 7t TN $T FC (TWIT eW Dr a WHITFHORSF Figure 1: Vicinity Map. Not to scale. 2 ._,1 I i I I EXISTING CONDITIONS New Lot D is approximately 5.17-acres of undeveloped land. The site is second growth forest with the exception of the southern tip of the property where there is pasture. Along and parallel to the east boundary is a 100-ft Puget Sound Power& Light Transmission Line Easement. Passing through this easement at the southeast corner of the site is a sewer line coming from the direction of the Yarmuth Plat, through the subject property in a south westerly direction to a manhole onsite. From the angle point, the sewer line continues in a southerly direction along the existing detention pond offsite. The site generally slopes downhill in a south easterly direction to an existing detention pond within New Lot C. Onsite slopes range from 2-40%. Any stormwater runoff generated on site sheet/shallow flows downhill to the detention pond. Stormwater runoff generated upstream of New Lot D (i.e., New Lots A, B & C) is piped to or naturally drains to an interceptor ditch along the west boundary of New Lot D and the south boundary of New Lot C before out-falling into the existing detention pond. The drainage area tributary to the existing detention pond is approximately 15.42-acres. In addition to surface water runoff, groundwater is also a source of stormwater on this site. Currently, groundwater is picked up by existing drainage systems throughout the pond's watershed and directed to the pond creating a constant base flow. The base flow is evident throughout most of the year when the water table is up. According to the SCS of Snohomish County, onsite soils are Ragnar fine sandy loam (hydrologic group A) along the very southerly edges of the site and Alderwood gravelly sandy loam (hydrologic group C) throughout the remainder. DEVELOPED CONDITIONS The proposal is to build eight 5-plex condominiums for a total of 40-dwelling units. In addition, this development will require the dedication of 2131h Place NE to the public and the extension of said road to 212`h St NE. The road will be built with full improvements, i.e., 40-ft of driving surface, curb and gutter, 5-ft landscaping strips and 5-ft sidewalks on both sides of the road. Three 25-ft wide paved driveways will be built to provide access to each of the buildings. Stormwater generated by the proposed development will be collected by catch basins throughout the site and conveyed to the existing detention pond before being released downstream. The existing detention pond will be re-constructed to provided water quality treatment via a wetpool. Additional storage will be provided above the wetpool for quantity control detention storage. The combination wetpool/detention pond will be redesigned and reconstructed to accommodate the full development of New Lots A, B, C & D, 2131h Place NE, and that portion of 2121h St and Stillaguamish Ave that currently drains to the existing pond. In the design of the pond, Lots A, B & C are assumed to have 90% maximum impervious cover and Lot D to have 75%maximum impervious allowed by the zoning code. See the Impervious Area Basin Map on pg. 16 for the breakdown of impervious area assumed for the drainage basin. The drainage area tributary to the 3 i proposed detention pond is approximately 16.12-acres. Based on the preliminary calculations, there is sufficient area within the pond tract to provide for all required treatment. Pond reconstruction will include deepening, berm construction and possible walls. Actual redesign to be finalized during construction plan approval process. Due to development, groundwater will be intercepted by footing drains and utility trenches and directed to the detention pond. Combined with groundwater intercepted elsewhere in the pond's basin, a small stream of water will be draining to the pond throughout most of the year. Since the groundwater flow is bypass flow and small in comparison to the surface water runoff, the actual amount of groundwater will have little or no impact on the pond design other than the orifice sizing. Therefore, after site improvements are in place, we propose to measure the actual rate of groundwater flow and adjust the orifice sizing at that time. 4 i i Erosion Sedimentation Control Notes Although the risk of erosion is low,erosion control should be taken seriously. The following list is an example of typical erosion control notes. (a) Erosion On-and Off-Site. During and after construction, all persons engaging in developing activities shall prevent or minimize erosion and sedimentation on-site and shall protect properties and water courses downstream from the site from erosion due to increases, in the volume, velocity and peak flow rate of storm water runoff from the site: (b) Transport of Sediment onto Adjacent Properties. The applicant shall prevent the transport of sediment onto adjacent properties. (c) Transport of Sediment onto Paved Surfaces. The applicant shall apply BMP's from the City of Arlington Construction Standards or as approved by the City, to prevent or minimize the transport of sediment onto paved surfaces during construction. If sediment is transported onto a paved surface the contractor is to clean the paved surface at the end of each day. (d) Stabilizing Exposed soil. The applicant shall stabilize denuded areas and soil stockpiles as follows: (i) From October 1 to April 30,no soil may remain exposed for more than 2 days. From May 1 to September 30,no soil may remain exposed for more than 7 days. On portions of the site where active grading is in progress, the City may extend the deadline for soil stabilization upon determining that the likelihood of erosion impacts is low. Reasons for this determination may include, but are not limited to the following, the type and amount of soil exposed, site topography, or the potential for discharge to critical areas and lakes. Upon finding a risk of erosion, the applicant shall immediately apply soil stabilization, regardless of any previously established deadline, and the City may require immediate stabilization at any time for this purpose. The applicant shall keep materials, equipment, and other resources on site at all times,in adequate quantities to immediately stabilize all soil. (ii) Denuded areas shall be covered with mulch, sod, plastic, or other BMP's described in City of Arlington Construction Standard G-4 or as approved by the City. (iii) Soil stockpiles shall be stabilized or protected with sediment retention BMPs within 24 hours of formation to prevent soil loss; and (iv) Grading and construction shall be timed and conducted in stages to minimize soil exposure. (e) Removal of Temporary Erosion and Sedimentation Control Measures. The applicant may remove all temporary erosion and sedimentation control BMPs within 30 days after final site stabilization or after they are no longer necessary. (f) Permanent Vegetative Cover. Before construction acceptance by the City, the applicant shall establish a permanent vegetative ground cover to control soil erosion and to survive severe weather conditions on all areas of land disturbance not otherwise permanently stabilized by impervious surfaces or other means. (g) Maintenance and Repair of Erosion and Sedimentation Control Measures. The applicant shall maintain and repair as necessary all temporary and permanent erosion and sedimentation control BMPs to assure their continued performance through construction acceptance and the potential for on site erosion has passed. (h) Field Marking. Before performing any grading or clearing, the applicant shall mark, in the filed, the limits of all proposed clearing and grading,critical areas and their buffers,trees to be retained, and drainage courses. 6 I I I 1 I I (i) Protecting Storm Sewer Inlets. The applicant shall protect storm sewer inlets receiving storm water runoff during construction so that water will not enter the inlet without first being filtered or otherwise treated to minimize the amount of sediment entering the inlet. (j) Sediment Retention. The applicant shall route storm water runoff from disturbed areas of the site through sediment ponds, traps or other sediment retention BMPs prior to discharge from the site. The BMPs shall be installed as the first step in grading, and shall be in operation before any other site disturbance occurs. The applicant shall stabilize temporary earth structures within the time period specified in subparagraph(d)(i). If site conditions warrant, the City may require additional sediment controls, including but not limited to, preserving a vegetated buffer strip around the lower perimeter of the site. (k) Temporary Sediment Ponds and Traps shall be constructed per City of Arlington Construction Standard (G- 5). Periodic removal of trapped sediments shall be performed as necessary, however trapped sediment may also be permanently stabilized onsite. (1) The applicant shall design and construct temporary and permanent BMPs adequate to prevent erosion of outlets,adjacent stream banks,slopes and downstream reaches. (m) The installation of underground utility lines shall be subject to the following additional requirements. (i) Between October 1 and March 31, no more than 500 feet of continuous trench may remain open at one time unless check dams to reduce flow velocities and prevent erosion are installed. (ii) Excavated material shall be placed on the uphill side of trenches, unless inconsistent with safety or site constraints. (n) Water from a de-watering device shall discharge into a sediment-retention BMP. The applicant shall implement fully the erosion and sedimentation control plan at each stage of site development. 7 Upstream & Downstream Analysis UPSTREAM ANALYSIS The detention pond drainage basin is limited to New Lots A-D, portions of Tveit Rd and Stillaguamish Ave and all of 213"' Place NE. Also draining to the pond is approximately 2.33- acres of land to the north that naturally slopes towards the project site. Within the offsite area are 4-houses with driveways and that portion of Hamlin Street south of Maple Street. The total offsite impervious area to the north is 0.81-acres (approximately 3 5% of the total offsite area based on aerial photographs and CAD aerials). The remaining offsite area consists of landscaping. Tveit Rd to the south drains into the existing detention pond. The eastern half of Stillaguamish Ave from it's intersection with Medical Center Drive to it's intersection with Tveit Rd gutter flows to catch basins on Tveit Rd. The land east of the site is downhill sloping away from the property. See Basin Maps pp. 14-16. DOWNSTREAM ANALYSIS Stormwater exits the detention pond via an 18-inch CMP that outfalls into a catch basin a short distance away along Tveit Rd. An 18-inch CMP exits the structure in a south easterly direction to an unknown structure under Tveit Rd. At this point, the piping changes over to an 18-inch DIP and outfalls at a drainage crossroads along side the north side of Tveit Rd. Here, a ditch coming from the north, an 18-inch DIP from the south and our 18-inch from the west out fall at this point before draining into another 18-inch CMP that ties into a catch basin adjacent to the Tveit Rd. north sidewalk. At this point stormwater continues in an easterly direction to a catch basin at the NW corner of the intersection of 871" Ave NE and Tveit Rd. Continuing east to another structure at the NE corner of the intersection, stormwater passes through the catch basin and out via an 18-inch CMP that out falls at the north end of a creek crossing under Tveit Rd. The creek travels in a northerly direction eventually draining into the Stillaguamish River. >eSS c Ag Figure 2: Existing detention pond looking NW. 8 i t vii" '-��"'�i"'v1'.�"`a ��..(•� 'SF7�y�•�4�",{��ylr:,t `�'�-M��^Z" 'a' � .+$C ��i!•"7wi��� ��'•Y.4.�� •_.�'•C.. Y-rj�'LwJlq't„JOyis'�Cvw,Gr TF? �- bill rV'�r�i'r J' �+.�y:.o � `A�- 'r..�-:,�,.a.�•a:i�lv�i;•', 3frv�,����'��-..yyr"�.•+�.r-; ^' •'Y tr tawcVt ` '�"' V,.?^7- y ,��s '���1K'.'> > t Ar.,� s+•.t .. t%h \la�i�tis1:�••c _ Figure 3: 18-inch pipe (right side) from unknown structure in Tveit Rd. Looking South. ` •Y - t Figure 4: 18-inch CMP outlet to a catch basin in north sidewalk of Tveit Rd. Looking South. 9 1 I •r 'wY Figure 5: Tveit Rd looking East. Note 18-inch CMP goes to CB in the sidewalk, then heads east to another structure at 87th Ave NE via 18-inch CMP. t Figure 6: Catch basins at NW and NE corner of the intersection of 87"Ave and Tveit Rd before out falling into the creek beyond the upper left corner of the photo. Looking East 10 i Stormwater Quantity Control & Water Quality B.M.P.'s STORMWATER QUANTITY CONTROL BMP The stormwater quantity control BMP specified for this site is a detention pond. The existing pond will be re-graded as necessary to accommodate the full development of New Lots A-D, 213th Place NE, that portion of Tveit Rd and Stillaguamish Ave that already drains to the pond, and the offsite area to the north. Flow out of the new pond will be controlled to match the existing 2-yr, 10-yr and 100-yr release rates out of the existing pond. The actual pond configuration and calculated release rates will be finalized during the construction plan approval process (See pg. 12 for current design rates). WATER QUALITY BMP The water quality BMP proposed for this site is a wetpool. The existing detention pond will be deepened to provide a dead storage volume equivalent to the developed 6-month runoff volume of 47,237-cf. The available dead storage capacity at a depth of 4.5-ft is 48,125-cf. The bottom of the dead pool is at an elevation of 150-ft. The top of the dead pool is at an elevation of 154.5- ft. J Basin Data I Pery CN I Pery TC Impery CN] Impery TC Compute Design Event 1 Select Design Event: F'mo Compute Computational Results for this event: Peak Flow Rate 3.0868 cfs Peak Time(hrs) 470.0000 min-7.8333 hr Peak Volume 47236.7054 of-1.0844 acft OK Cancel Help Figure 7: StormSHED model of the developed 6-month runoff volume. 11 i DRAINAGE MODEL SUMMARY The storm drainage modeling software used is StormSHED Rel. 6.1.6.8. The following table summarizes the results of the drainage model. EXISTING DETENTION MAX ALLOWED DEV POND DEV PO?JD STORM POJJD PEAK DEVELOPED PEAK �EAY ?E! A S E DEV PO?VD STORAGE EVENT RELEASE DiSCHf-,RGE RATE STAGE VOLUME CFS CES CPS Pr CF EX 2-YR 0 93 EX I 0-YR 2 43 EX I00-YR 5 40 DEV 6-MO 0 65 55 97 3,608 DEV 2-Y.R 0 93 0 92 157 46 29,048 DEV 10-YR 2 43 2 42 1 58 53 40,764 DEV 100-YR 5 40 5 39 159 44 51,283 Table 1: Calculations Summary. VOLUME CORRECTION FACTOR According to the 1992 D.O.E. Stormwater Manual, streambank erosion control BMP's require a volume correction factor to be applied to the 100-yr. design volume when the SCS method of analysis is used. According to Figure III-1.1 on pg. III-1-3 of the D.O.E. Stormwater Manual, with a site impervious of 79%, a VCF of 1.42 must be applied. With a 100-yr storage volume of 51,283-cf, the corrected volume to be stored will be 1.42 x 51,283 = 72,822-cf. The available live storage of the design pond is 72,825-cf at an elevation of 159.44-ft. CONTROLSTRUCTURE The existing control structure will be replaced with a new control structure inside the pond. The control will be housed inside a type II 54-inch catch basin. The primary orifice of the control structure will be a 4-7/16-inch diameter horizontal orifice. Out flow through the control structure will occur at the existing elevation of 154.50-ft. The secondary orifices will provide additional release for the larger storm events, i.e., the 10 & 100-yr 24-hr storms. The secondary orifice is a 7-inch diameter horizontal orifice at an elevation of 157.50-ft. Additional release will be provided by a 1'-1"rectangular weir notched at an elevation of 158.6-ft. The top of the control structure riser will act as an emergency overflow path for the pond water as well as a separate structure. The separate structure will act as the primary emergency overflow spillway. The primary overflow structure will consist of an open-topped type II 54-inch CB in—line and downstream of the control structure. Both the top of the riser pipe control structure and the crest of the type II structure will be at an elevation of 160-ft. 12 EXISTING DRAINAGE MODEL REPORT SWALE BASIN SWALE EX. DET. POND � P - mp EX CB TVEIT B" M 17 EXISTING 2-YR CALCULATIONS 160.324 ft 1.24 cfs 155.992 ft cfs 0.5Qfis 153.560 ft 158.1�-ft rt M ROUTEHYD []THRU [EXISTING] USING TYPE1A AND [2 yr] NOTZERO RELATIVE Reach Area Flow Full Q % Full nDepth Size nVel fVel Cl3asin/Hyd ----- ac cfs cfs ratio ft ---- ft/s ft/s ------------ 12"PVC 3.7400 0.5619 9.4084 0.06 0.1658 12"Diam 6.5811 11.9791 TVIET ROAD BASIN SWALE 5.2800 1.2427 ---- 1.00 0.2013 Ditch 5.1390 ----- BIOSWALE BASIN Routing thru RI-Pool Node EX. DET. POND; 2 yr event 2 yr Match Q: 0.0000 cfs Peak Out Q: 0.9331 cfs -Peak Stg: 155.99 ft-Active Vol: 0.1183 acft 18"CMP 15.4200 0.9331 7.3947 0.13 0.3598 18"Diam 2.8633 4.1846 DET.POND BASIN ---- Rch App Bend Junct HW Max EII .__._ ----- Loss Head Loss Loss Elev Rim El From Node To Node ft ft ft ft ft ft EX CB 153.5600 EX.DET.POND EX CB 154.5767 --na-- --na-- --na-- 155.9919 158.6000 TVEIT RD EX.DET.POND 158.1094 ------ ------ ------ 158.1095 162.7100 SWALE BASIN EX.DET.POND 160.3241 --na-- --na-- --na-- 160.3241 204.0000 18 EXISTING 10-YR CALCULATIONS 160.439 ft • 2.b8 cfs ~' '157.026 ft .`..-4 cfs 1.08_-Cf> 153.560 ft 158.304-ft �J ROUTEHYD []THRU [EXISTING] USING TYPE1A AND [10 yr] NOTZERO RELATIVE Reach Area Flow Full Q % Full nDepth Size nVel Wel CBasin/ Hyd -- ac cfs cfs ratio ft ---- ft/s ft/s ------------ 12"PVC 3.7400 1.0848 9.4084 0.12 0.2292 12"Diam 7.9860 11.9791 TVIET ROAD BASIN SWALE 5.2800 2.0820 ---- 1.00 0.2718 Ditch 6.0218 ----- BIOSWALE BASIN Routing thru RI-Pool Node EX. DET. POND; 10 yr event 10 yr Match Q: 0.0000 cfs Peak Out Q: 2.4289 cfs -Peak Stg: 157.03 ft-Active Vol: 0.2883 acft 18"CMP 15.4200 2.4289 7.3947 0.33 0.5917 18"Diam 3.7491 4.1846 DET.POND BASIN ----- ----- Rch App Bend Junct HW Max EI/ ..... ----- Loss Head Loss Loss Elev Rim El From Node To Node ft ft ft ft ft ft EX CB 153.5600 EX.DET.POND EX CB 155.0191 --na-- --na-- --na-- 157.0261 158.6000 TVEIT RD EX.DET.POND 158.3041 ------ ------ ------ 158.3041 162.7100 SWALE BASIN EX.DET.POND 160.4394 --na-- --na-- --na-- 160.4394 204.0000 19 i EXISTING 100-YR CALCULATIONS 160.542 ft • 3.b0 cfs 157.265 ft ~dt�cfs 153.560 ft 158.5171 if ROUTEHYD []THRU [EXISTING] USING TYPE1A AND [100 yr] NOTZERO RELATIVE Reach Area Flow Full Q % Full nDepth Size nVel fVel CBasin/ Hyd ---- ac cfs cfs ratio ft ---- ft/s ft/s ------------ 12"PVC 3.7400 1.6866 9.4084 0.18 0.2867 12"Diam 9.0670 11.9791 TVIET ROAD BASIN SWALE 5.2800 3.0001 ---- 1.00 0.3351 Ditch 6.7061 ----- BIOSWALE BASIN Routing thru RI-Pool Node EX. DET. POND; 100 yr event 100 yr Match Q: 0.0000 cfs Peak Out Q: 5.4023 cfs-Peak Stg: 157.27 ft-Active Vol: 0.3309 acft 18"CMP 15.4200 5.4023 7.3947 0.73 0.9518 18"Diam 4.5682 4.1846 DET.POND BASIN Rch App Bend Junct HW Max EII ----- ----- Loss Head Loss Loss Elev Rim El From Node To Node ft ft ft ft ft ft EX CB 153.5600 EX.DET.POND EX CB 155.5379 --na-- --na-- --na-- 157.2653 158.6000 TVEIT RD EX.DET.POND 158.5011 ------ ------ ------ 158.5011 162.7100 SWALE BASIN EX.DET.POND 160.5417 --na-- --na-- --na-- 160.5417 204.0000 20 EXISTING MODEL DATA REPORT SWALE BASIN SWALE ,EX. DET. POND 12"WC EX CB TVEIT IT M Project Precips [6 mo] 1.15 in [2 yr] 1.80 in [10 yr] 2.75 in [25 yr] 3.20 in [100 yr] 3.75 in Reach Records Reach ID:12"PVC Section Properties: Shape: Circular Routing Method: Travel Time Translation Size Material Mannings n Hyd params By 12"Diam Smooth CDEP 0.0120 Mannings Formula Length Slope Entrance Loss 43.0000 ft 5.91% Square Edge w/Headwall Diam 1.0000 ft Up Node Dn Node Up Invert Dn Invert TVEIT RD EX.DET.POND 157.7100 ft 155.1690 ft Conduit Constraints: Min Vel Max Vel Min Cov Min Slope Max Slope Min drop 2.0000 ft 15.0000 ft 3.0000 ft 0.5000 ft 2.0000 ft 0.0000 ft In/Exfil Hold Up Hold Dn Match Inv Allow Smaller 0.0000 in/hr NO NO YES NO Conduit Summary: Trib Area Flow Capacity Velocity Normal Depth 3.7400 ac 1.6866 cf 9.4084 cf 9.0670 ft/s 0.2867 ft Ent Loss Exit Loss Frict Loss Start TW 0.035803 ft 0.071606 ft 0.081644 ft 157.2653 ft Reach ID:18"CMP Section Properties: Shape: Circular Routing Method: Travel Time Translation Size Material Mannings n Hyd params By 18"Diam Corr Metal-nonnal 0.0240 Mannings Formula Length Slope Entrance Loss 34.0000 ft 1.68% Headwall 21 Diam 1.5000 ft Up Node Dn Node Up Invert Dn Invert EX.DET.POND EX CB 154.1000 It 153.5290 ft Conduit Constraints: Min Vel Max Vel Min Cov Min Slope Max Slope Min drop 2.0000 ft 15.0000 ft 3.0000 ft 0.5000 ft 2.0000 ft 0.0000 ft In/Exfil Hold Up Hold Dn Match Inv Allow Smaller 0.0000 in/hr NO NO YES NO Conduit Summary: Trib Area Flow Capacity Velocity Nonnal Depth 15.4200 ac 5.4023 cf 7.3947 cf 4.5682 ft/s 0.9518 ft Ent Loss Exit Loss Frict Loss Start TW 0.162021 ft 0.324042 ft 0.304776 ft 154.4808 ft Reach ID:SWALE Section Properties: Shape: Ditch Routing Method: Travel Time Translation Size Material Mannings n Hyd params By Corr Metal-normal 0.0250 Mannings Formula Length Slope Entrance Loss 0.0010 ft 9.00% Width Bank Hgt ss l ss2 1.0000 ft 3.0000 ft 1.00h:1 v 1,00h:l v Up Node Dn Node Up Invert Dn Invert SWALE BASIN EX.DL F.POND 160.0000 It 160.0000 ft Conduit Constraints: Min Vel Max Vel Min Cov Min Slope Max Slope Min drop 2.0000 ft 15.0000 ft 3.0000 ft 0.5000 ft 2.0000 ft 0.0000 ft In/Exfil Hold Up Hold Dn Match Inv Allow Smaller 0.0000 in/hr NO NO YES NO Conduit Summary: Trib Area Flow Capacity Velocity Nonnal Depth 5.2800 ac 3.0001 cf 3.0001 of 6.7061 ft/s 0.3351 ft Ent Loss Exit Loss Frict Loss Start TW 0.000000 ft 0.000000 ft 0.000000 ft 160.5417 ft 22 Node Records Node ID:EX CB Start El: 153.5600 ft Max El: 158.7100 ft Contrib Basin: Contrib Hyd: Hgl Elev: 153.5600 ft Struct Type: CB-TYPE 1 Classification Catch Basin Ke Descrip: CMP:Headwall or Headwall&Wingwall sq edge;.ke=0.5 Catch Depth: 1.4160 ft Bot Area: 3.9700 sf Condition: No particular shape. Status: Existing Structure Approach Credit: 0.0000 ft Node ID:EX.DET.POND Start El: 154.1000 ft Max El: 158.6000 ft Contrib Basin: DET.POND BASIN Contrib Hyd: Hgl Elev: 157.2653 It Storage Id: EX.STORAGE Discharge ld: EX COMBO Node ID:EX.STORAGE Start El: 154.1000 ft Max El: 158.6000 ft Contrib Basin: Contrib Hyd: Stage Area Volume Volume 154.10 2.00 0.00 cf 0.0000 acft 154.50 42.00 8.80 cf 0.0002 acft 155.00 1068.00 286.30 cf 0.0066 acft 155.50 5944.00 2039.30 cf 0.0468 acft 156.00 6725.00 5206.55 cf 0.1195 acft 156.50 7153.00 8676.05 cf 0.1992 acft 157.00 7566.00 12355.80 cf 0.2837 acft 157.50 7965.00 16238.55 cf 0.3728 acft 158.00 8349.00 20317.05 cf 0.4664 acft 158.50 8719.00 24584.05 cf 0.5644 acft 158.60 8795.00 25459.75 cf 0.5845 acft Control Structure ID:EX COMBO-Combination Control Structure Start El Max El Increment 154.1000 ft 158.9100 ft 0.10 ID List: EX CONTROL EX OVERFLOW Control Structure ID:EX CONTROL-Multiple Orifice Structure Start El Max El Increment 154.1000 ft 155.6000 ft 0.10 Orif Coeff: 0.62 Bottom El: 152.10 ft Lowest Diam: 5.0000 in Control Structure ID:EX OVERFLOW-Overflow riser Start El Max El Increment 156.8300 ft 158.9100 ft 0.10 Riser Dia: t 8.00 in Orif Coeff: 3.78 Weir Coeff: 9.74 Node ID:SWALE BASIN Start El: 160.0000 ft Max El: 204.0000 ft Contrib Basin: BIOSWALE BASIN Contrib Hyd: Hgl Elev: 160.5417 ft Node ID:TVEIT RD Start El: 157.7100 ft Max El: 162.7100 ft Contrib Basin: TVIET ROAD BASIN Contrib Hyd: Hgl Elev: 158.5011 R Struct Type: CB-TYPE 1 Classification Catch Basin Ke Descrip: CMP:Headwall or Headwall&Wingwall sq edge;.ke=0.5 Catch Depth: 1.4160 ft Bot Area: 3.9700 sf Condition: No particular shape. Status: Existing Structure Approach Credit: 0.0000 ft 23 Contributing Drainage Areas Drainage Area:BIOSWALE BASIN Hyd Method: SBUH Hyd Loss Method: SCS CN Number Peak Factor: 484.00 SCS Abs: 0.20 Storm Dur: 24.00 hrs Intv: 10.00 min Area CN TC Pervious 2.3000 ac 83.66 1.28 hrs Impervious 2.9800 ac 98.00 0.09 hrs Total 5.2800 ac Supporting Data: Pervious CN Data: FOREST 81.00 0.7700 ac PASTURE 85.00 1.5300 ac Impervious CN Data: EX.BUILDINGS,P-LOTS,213TH PLACE 98.00 2.9800 ac Pervious TC Data: Flow type: Description: Length: Slope: Coeff: Travel Time Sheet FOREST 200.00 ft 3.00% 0.8000 73.80 min Channel SWALE 450.00 ft 3.00% 20.0000 2.17 min Channel SWALE 180.00 ft 9.00% 17.0000 0.59 min Impervious TC Data: Flow type: Description: Length: Slope: Coeff: Travel Time Sheet PARKING LOT 100.00 ft 2.00% 0.0110 1.62 min Channel DRAIN PIPE 440.00 ft 1.80% 42.0000 1.30 min Channel SWALE 450.00 ft 3.00% 20.0000 2.17 min Channel SWALE 180.00 ft 9.00% 17.0000 0.59 ruin Drainage Area:DET.POND BASIN Hyd Method: SBUH Hyd Loss Method: SCS CN Number Peak Factor: 484.00 SCS Abs: 0.20 Stone Dur: 24.00 hrs Intv: 10.00 min Area CN TC Pervious 5.4800 ac 82.88 0.91 hrs Impervious 0.9200 ac 98.46 0.17 hrs Total 6.4000 ac Supporting Data: Pervious CN Data: FOREST 81.00 3.4700 ac OFFSITE LANDSCAPE 86.00 1.5200 ac PASTURE 85.00 0.3000 ac SEWER GRAVEL RD 89.00 0.0900 ac OFFSITE GRAVEL DRIVEWAY 89.00 0.1000 ac Impervious CN Data: DETENTION POND 100.00 0.2100 ac OFFSITE HOUSES,DRIVES,HAMLIN ST 98.00 0.7100 ac Pervious TC Data: Flow type: Description: Length: Slope: Coeff: Travel Time Sheet OFFSITE LAWN 300.00 ft 0.75% 0.1500 46.58 min Shallow ALONG GRAVEL DRIVE 100.00 ft 4.00% 11.0000 0.76 min Shallow FOREST 525.00 ft 7.00% 5.0000 6.61 min Shallow FOREST 75.00 ft 19.00% 5.0000 0.57 min Impervious TC Data: Flow type: Description: Length: Slope: Coeff: Travel Time Sheet ACROSS HAMLIN ST 12.00 ft 2.00% 0.0110 0.30 min Shallow GUTTER FLOW HAMLIN ST 250.00 ft 3.00% 27.0000 0.89 rein Shallow FOREST 655.00 ft 7.00% 5.0000 8.25 min Shallow FOREST 75.00 ft 19.00% 5.0000 0.57 ruin Drainage Area:TVIET ROAD BASIN Hyd Method: SBUH Hyd Loss Method: SCS CN Number Peak Factor: 484.00 SCS Abs: 0.20 Storm Dur: 24.00 hrs Intv: 10.00 min Area CN TC Pervious 2.7100 ac 85.00 0.68 hrs Impervious 1.0300 ac 98.00 0.04 hrs Total 3.7400 ac Supporting Data: Pervious CN Data: PASTURE 85.00 2.7100 ac Impervious CN Data: 24 i MET RD&STILLIGUAMISH 98.00 1.0300 ac Pervious TC Data: Flow type: Description: Length: Slope: Coeff: Travel Time Sheet PASTURE 300.00 ft 3.00% 0.2400 38.96 min Shallow PASTURE 90.00 ft 4.00% 11.0000 0.68 min Channel GUTTER FLOW 50.00 ft 2.00% 42.0000 0.14 min Channel DRAIN PIPE 665.00 ft 5.00% 42.0000 1.18 min Impervious TC Data: Flow type: Description: Length: Slope: Coeff: Travel Time Sheet ACROSS STILLIGUAMISH 2O.00 ft 2.00% 0.0110 0.45 min Channel GUTTER 520.00 ft 5.00% 42.0000 0.92 min Channel DRAIN PIPE 665.00 ft 5.00% 42.0000 1.18 min 25 Layout Hydrographs Hydrograph ID:EX CB-2 yr Area: 15.4200 ac Hyd Int: 10.00 min Base Flow: Pending tt translation: 0.20 min Peak Flow: 0.9331 cfs Peak Time: 10.17 hrs Hyd Vol: 1.1661 acft Time Flow Time Flow Time Flow hr cfs hr cfs hr cfs 1.33 0.0299 11.83 0.9080 22.00 0.5035 1.50 0.0296 12.00 0.9041 22.17 0.5017 1.67 0.0636 12.17 0.9001 22.33 0.4963 1.83 0.0670 12.33 0.8959 22.50 0.4899 2.00 0.0948 12.50 0.8916 22.67 0.4848 2.17 0.0971 12.67 0.8872 22.83 0.4814 2.33 0.1272 12.83 0.8825 23.00 0.4788 2.50 0.1272 13.00 0.8778 23.17 0.4764 2.67 0.1469 13.17 0.8730 23.33 0.4750 2.83 0.1499 13.33 0.8684 23.50 0.4736 3.00 0.1628 13.50 0.8637 23.67 0.4731 3.17 0.1669 13.67 0.8591 23.83 0.4722 3.33 0.1774 13.83 0.8542 24.00 0.4722 3.50 0.1811 14.00 0.8493 24.17 0.4467 3.67 0.1943 14.17 0.8444 24.33 0.2120 3.83 0.2055 14.33 0.8396 24.50 0.1896 4.00 0.2109 14.50 0.8348 24.67 0.1357 4.17 0.2283 14.67 0.8301 24.83 0.1307 4.33 0.2472 14.83 0.8251 25.00 0.0924 4.50 0.2526 15.00 0.8201 25.17 0.0924 4.67 0.2698 15.17 0.8151 25.33 0.0636 4.83 0.2907 15.33 0.8102 25.50 0.0670 5.00 0.2938 15.50 0.8053 25.67 0.0417 5.17 0.3130 15.67 0.7987 25.83 0.0496 5.33 0.3325 15.83 0.7897 26.00 0.0272 5.50 0.3379 16.00 0.7807 26.17 0.0367 5.67 0.3548 16.17 0.7719 26.33 0.0182 5.83 0.3757 16.33 0.7633 26.50 0.0280 6.00 0.3792 16.50 0.7551 26.67 0.0116 6.17 0.4133 16.67 0.7472 26.83 0.0211 6.33 0.4345 16.83 0.7395 27.00 0.0072 6.50 0.4437 17.00 0.7322 27.17 0.0166 6.67 0.4625 17.17 0.7250 27.33 0.0038 6.83 0.4972 17.33 0.7175 27.50 0.0128 7.00 0.5313 17.50 0.7099 27.67 0.0025 7.17 0.5689 17.67 0.7026 27.83 0.0101 7.33 0.6185 17.83 0.6955 28.00 0.0000 7.50 0.6479 18.00 0.6887 28.17 0.0098 7.67 0.6749 18.17 0.6819 28.33 0.0000 7.83 0.7365 18.33 0.6747 28.50 0.0067 8.00 0.8079 18.50 0.6674 28.67 0.0000 8.17 0.8431 18.67 0.6603 28.83 0.0048 8.33 0.8657 18.83 0.6534 29.00 0.0000 8.50 0.8818 19.00 0.6468 29.17 0.0036 8.67 0.8957 19.17 0.6241 29.33 0.0000 8.83 0.9061 19.33 0.5894 29.50 0.0027 9.00 0.9146 19.50 0.5625 29.67 0.0000 9.17 0.9215 19.67 0.5434 29.83 0.0020 9.33 0.9260 19.83 0.5300 30.00 0.0000 9.50 0.9289 20.00 0.5208 30.17 0.0015 9.67 0.9311 20.17 0.5145 30.33 0.0000 9.83 0.9324 20.33 0.5104 30.50 0.0011 10.00 0.9331 20.50 0.5075 30.67 0.0000 10.17 0.9331 20.67 0.5055 30.83 0.0000 10.33 0.9324 20.83 0.5044 31.00 0.0012 10.50 0.9311 21.00 0.5035 31.17 0.0000 10.67 0.9294 21.17 0.5030 31.33 0.0000 10.83 0.9271 21.33 0.5026 31.50 0.0000 11.00 0.9245 21.50 0.5026 31.67 0.0012 11.17 0.9216 21.67 0.5028 31.83 0.0000 11.33 0.9185 21.83 0.5030 32.00 0.0000 11.50 0.9152 22.00 0.5035 32.17 0.0000 26 11.67 0.9117 22.17 0.5017 32.33 0.0000 27 Hydrograph 1D:EX CB-100 yr Area: 15.4200 ac Hyd Int: 10.00 min Base Flow: Pending tt translation: 0.12 min Peak Flow: 5.4023 cfs Peak Time: 8.33 hrs Hyd Vol: 3.3017 acft Time Flow Time Flow Time Flow lir cfs lir cfs hr cfs 0.83 0.0703 11.83 2.1688 22.67 1.2212 1.00 0.0848 12.00 2.1264 22.83 1.2117 1.17 0.1722 12.17 2.0895 23.00 1.2038 1.33 0.1977 12.33 2.0498 23.17 1.1970 1.50 0.2631 12.50 2.0144 23.33 1.1913 1.67 0.2828 12.67 1.9826 23.50 1.1868 1.83 0.3392 12.83 1.9465 23.67 1.1827 2.00 0.3522 13.00 1.9145 23.83 1.1794 2.17 0.3955 13.17 1.8905 24.00 1.1768 2.33 0.4197 13.33 1.8718 24.17 1.1450 2.50 0.4332 13.50 1.8578 24.33 1.1173 2.67 0.4409 13.67 1.8408 24.50 1.1077 2.83 0.4512 13.83 1.8166 24.67 1.0964 3.00 0.4621 14.00 1.7937 24.83 1.0840 3.17 0.4722 14.17 1.7763 25.00 1.0705 3.33 0.4821 14.33 1.7633 25.17 1.0562 3.50 0.4908 14.50 1.7533 25.33 1.0407 3.67 0.5026 14.67 1.7400 25.50 1.0242 3.83 0.5189 14.83 1.7194 25.67 1.0073 4.00 0.5355 15.00 1.6985 25.83 0.9899 4.17 0.5565 15.17 1.6828 26.00 0.9721 4.33 0.5871 15.33 1.6710 26.17 0.9540 4.50 0.6185 15.50 1.6615 26.33 0.9357 4.67 0.6451 15.67 1.6493 26.50 0.9155 4.83 0.6531 15.83 1.6297 26.67 0.8950 5.00 0.6633 16.00 1.6095 26.83 0.8743 5.17 0.6757 16.17 1.5938 27.00 0.8535 5.33 0.6911 16.33 1.5822 27.17 0.8326 5.50 0.7082 16.50 1.5728 27.33 0.8115 5.67 0.7272 16.67 1.5656 27.50 0.7805 5.83 0.7487 16.83 1.5601 27.67 0.7421 6.00 0.7717 17.00 1.5558 27.83 0.7037 6.17 0.7970 17.17 1.5475 28.00 0.6651 6.33 0.8159 17.33 1.5308 28.17 0.5455 6.50 0.8339 17.50 1.5136 28.33 0.0000 6.67 0.8541 17.67 1.4999 28.50 0.0182 6.83 0.8779 17.83 1.4891 28.67 0.0000 7.00 0.9037 18.00 1.4803 28.83 0.0128 7.17 0.9317 18.17 1.4693 29.00 0.0000 7.33 0.9611 18.33 1.4507 29.17 0.0101 7.50 0.9921 18.50 1.4313 29.33 0.0000 7.67 1.0385 18.67 1.4160 29.50 0.0072 7.83 1.1104 18.83 1.4035 29.67 0.0000 8.00 3.3596 19.00 1.3937 29.83 0.0048 8.17 5.3684 19.17 1.3815 30.00 0.0000 8.33 5.4023 19.33 1.3625 30.17 0.0046 8.50 5.0184 19.50 1.3427 30.33 0.0000 8.67 4.7715 19.67 1.3270 30.50 0.0031 8.83 4.4432 19.83 1.3136 30.67 0.0000 9.00 4.1876 20.00 1.3031 30.83 0.0023 9.17 3.9748 20.17 1.2943 31.00 0.0000 9.33 3.7063 20.33 1.2872 31.17 0.0017 9.50 3.4804 20.50 1.2814 31.33 0.0000 9.67 3.3150 20.67 1.2769 31.50 0.0013 9.83 3.1592 20.83 1.2727 31.67 0.0000 10.00 3.0325 21.00 1.2697 31.83 0.0000 10.17 2.9212 21.17 1.2670 32.00 0.0015 10.33 2.8004 21.33 1.2653 32.17 0.0000 10.50 2.6959 21.50 1.2635 32.33 0.0000 10.67 2.6074 21.67 1.2626 32.50 0.0010 10.83 2.5163 21.83 1.2615 32.67 0.0000 11.00 2.4386 22.00 1.2609 32.83 0.0000 11.17 2.3737 22.17 1.2569 33.00 0.0000 11.33 2.3129 22.33 1.2458 33.17 0.0000 28 i I I 11.50 2.2611 22.50 1.2326 33.33 0.0012 11.67 2.2157 22.67 1.2212 33.50 0.0000 Hydrograph ID:EX CB-10 yr Area: 15.4200 ac Hyd Int: 10.00 min Base Flow: Pending tt translation: 0.15 min Peak Flow: 2.4289 cfs Peak Time: 9.17 hrs Hyd Vol 2.1658 acft Time Flow Time Flow Time Flow hr cfs hr cfs hr cfs 1.00 0.0437 11.83 1.4454 22.50 1.0231 1.17 0.0535 12.00 1.4208 22.67 1.0193 1.33 0.1141 12.17 1.3988 22.83 1.0154 1.50 0.1199 12.33 1.3755 23.00 1.0116 1.67 0.1722 12.50 1.3546 23.17 1.0078 1.83 0.1799 12.67 1.3350 23.33 1.0040 2.00 0.2223 12.83 1.3140 23.50 1.0002 2.17 0.2283 13.00 1.2946 23.67 0.9965 2.33 0.2698 13.17 1.2793 23.83 0.9928 2.50 0.2715 13.33 1.2670 24.00 0.9892 2.67 0.2983 13.50 1.2574 24.17 0.9837 2.83 0.2983 13.67 1.2472 24.33 0.9742 3.00 0.3187 13.83 1.2342 24.50 0.96,18 3.17 0.3201 14.00 1.2209 24.67 0.9481 3.33 0.3339 14.17 1.2105 24.83 0.9333 3.50 0.3365 14.33 1.2018 25.00 0.9163 3.67 0.3573 14.50 1.1949 25.17 0.8986 3.83 0.3721 14.67 1.1872 25.33 0.8803 4.00 0.3792 14.83 1.1768 25.50 0.8615 4.17 0.4067 15.00 1.1659 25.67 0.8423 4.33 0.4298 15.17 1.1572 25.83 0.8227 4.50 0.4340 15.33 1.1498 26.00 0.8028 4.67 0.4442 15.50 1.1439 26.17 0.7665 4.83 0.4630 15.67 1,1374 26.33 0.7297 5.00 0.4816 15.83 1.1297 26.50 0.6927 5.17 0.5017 16.00 1.1230 26.67 0.6554 5.33 0.5275 16.17 1.1206 26.83 0.4913 5.50 0.5533 16.33 1.1197 27.00 0.0000 5.67 0.5806 16.50 1.1187 27.17 0.0437 5.83 0.6130 16.67 1.1177 27.33 0.0000 6.00 0.6439 16.83 1.1168 27.50 0.0317 6.17 0.6509 17.00 1.1158 27.67 0.0000 6.33 0.6621 17.17 1.1147 27.83 0.0232 6.50 0.6757 17.33 1.1132 28.00 0.0000 6.67 0.6926 17.50 1.1116 28.17 0.0166 6.83 0.7146 17.67 1.1100 28.33 0.0000 7.00 0.7393 17.83 1.1083 28.50 0.0124 7.17 0.7670 18.00 1.1065 28.67 0.0000 7.33 0.7998 18.17 1.1046 28.83 0.0089 7.50 0.8209 18.33 1.1024 29.00 0.0000 7.67 0.8550 18.50 1.1000 29.17 0.0066 7.83 0.9158 18.67 1.0976 29.33 0.0000 8.00 0.9851 18.83 1.0950 29.50 0.0048 8.17 1.0453 19.00 1.0925 29.67 0.0000 8.33 1.0873 19.17 1.0898 29.83 0.0037 8.50 1.1205 19.33 1.0868 30.00 0.0000 8.67 1.7543 19.50 1.0835 30.17 0.0027 8.83 2.2432 19.67 1.0802 30.33 0.0000 9.00 2.4139 19.83 1.0769 30.50 0.0021 9.17 2.4289 20.00 1.0735 30.67 0.0000 9.33 2.3299 20.17 1.0701 30.83 0.0015 9.50 2.2180 20.33 1.0667 31.00 0.0000 9.67 2.1247 20.50 1.0634 31.17 0.0012 9.83 2.0336 20.67 1.0600 31.33 0.0000 10.00 1.9585 20.83 1.0567 31.50 0.0000 10.17 1.8931 21.00 1.0534 31.67 0.0013 10.33 1.8221 21.17 1.0502 31.83 0.0000 10.50 1.7605 21.33 1.0468 32.00 0.0000 10.67 1.7073 21.50 1.0434 32.17 0.0000 10.83 1.6534 21.67 1.0401 32.33 0.0013 11.00 1.6064 21.83 1.0369 32.50 0.0000 29 i 11.17 1.5677 22.00 1.0337 32.67 0.0000 11.33 1.5313 22.17 1.0304 32.83 0.0000 11.50 1.4999 22.33 1.0269 33.00 0.0000 11.67 1.4729 22.50 1.0231 33.17 0.0000 30 DEVELOPED DRAINAGE MODEL REPORT PRO DET POND p DEV OUTtFT PIPE EX CB M1, M 31 S 6-MONTH CALCULATIONS 155.966 ft p 0:� rrfis 1153.826 ft L'�t ROUTEHYD []THRU [DEVELOPED] USING TYPE1A AND [6 mo] NOTZERO RELATIVE Reach Area Flow Full Q % Full nDepth Size nVel Wel Cl3asin/ Hyd ----- ac cfs cfs ratio ft ---- ft/s ft/s ------------ Routing thru RI-Pool Node PRO DET POND; 6 mo event 6 mo Match Q: 0.0000 cfs Peak Out Q: 0.6470 cfs- Peak Stg: 155.97 ft-Active Vol: 0.3124 acft DEV OUTLET PIPE 16.1200 0.6470 8.8935 0.07 0.2738 18"Diam 2.9313 5.0327 DEV SITE ----- ----- Rch App Bend Junct HW Max EI/ ----- ----- Loss Head Loss Loss Elev Rim El From Node To Node ft ft ft ft ft ft EX CB 153,8265 PRO DET POND EX CB 154.8855 --na-- --na-- --na-- 155.9661 162.0000 32 2-YR CALCULATIONS 157.462 ft p 0."r 2 CIS 153.885 ft -.t ROUTEHYD []THRU [DEVELOPED] USING TYPE1A AND [2 yr] NOTZERO RELATIVE Reach Area Flow Full Q % Full nDepth Size nVel Wel CBasin/Hyd ----- ac cfs cfs ratio ft ---- ft/s ft/s ------------ Routing thru RI-Pool Node PRO DET POND; 2 yr event 2 yr Match Q: 0.0000 cfs Peak Out Q: 0.9197 cfs- Peak Stg: 157.46 ft-Active Vol: 0.6668 acft DEV OUTLET PIPE 16.1200 0.9197 8.8935 0.10 0.3257 18"Diam 3.2500 5.0327 DEV SITE ----- ----- Rch App Bend Junct HW Max EI/ ----- ----- Loss Head Loss Loss Elev Rim El From Node To Node ft ft ft ft ft ft EX CB 153.8852 PRO DET POND EX CB 154.9673 --na-- --na-- --na-- 157.4621 162.0000 33 I0-YR CALCULATIONS 158.530 f# p 2 =4? cfs 154.117 f# H ROUTEHYD []THRU [DEVELOPED] USING TYPE1A AND [10 yr] NOTZERO RELATIVE Reach Area Flow Full Q % Full nDepth Size nVel Wel Cl3asin I Hyd ----- ac cfs cfs ratio ft ---- ft/s ft/s ------------ Routing thru RI-Pool Node PRO DET POND; 10 yr event 10 yr Match Q: 0.0000 cfs Peak Out Q: 2.4224 cfs - Peak Stg: 158.53 ft-Active Vol: 0.9358 acft DEV OUTLET PIPE 16.1200 2.4224 8.8935 0.27 0.5349 18"Diam 4.2839 5.0327 DEV SITE ----- ----- Rch App Bend Junct HW Max EI/ ----- ----- Loss Head Loss Loss Elev Rim El From Node To Node ft ft ft ft ft ft EX CB 154.1170 PRO DIET POND EX CB 155.3052 --na-- --na-- --na-- 158.5302 162.0000 34 I I00-YR CALCULATIONS 159.437 ft p 5. cfs 154.423 ft ROUTEHYD []THRU [DEVELOPED] USING TYPE1A AND [100 yr] NOTZERO RELATIVE Reach Area Flow Full Q % Full nDepth Size nVel Wel Cl3asin/ Hyd ----- ac cfs cfs ratio ft ---- ft/s ft/s ------------ Routing thru RI-Pool Node PRO DET POND; 100 yr event 100 yr Match Q: 0.0000 cfs Peak Out Q: 5.3890 cfs - Peak Stg: 159.44 ft-Active Vol: 1.1773 acft DEV OUTLET PIPE 16.1200 5.3890 8.8935 0.61 0.8426 18"Diam 5.2725 5.0327 DEV SITE ----- ----- Rch App Bend Junct HW Max EU Loss Head Loss Loss Elev Rim El From Node To Node ft ft ft ft ft ft EX CB 154.4225 PRO DIET POND EX CB 155.8222 —na-- --na-- --na-- 159.4370 162.0000 35 DEVELOPED MODEL DATA REPORT PRO DET POND P DEV OUTLET PIPE EX CB Project Precips [6 mo] 1.15 in [2 yr] 1.80 in [10 yr] 2.75 in [25 yr] 3.20 in [100 yr] 3.75 in Reach Records Reach ID:DEV OUTLET PIPE Section Properties: Shape: Circular Routing Method: Travel Time Translation Size Material Mannings n Hyd paiams By 18"Diam Con•Metal-normal 0.0240 Mannings Formula Length Slope Enhance Loss 40.0000 ft 2.43% Headwall Diam 1.500011 Up Node Dn Node Up Invert Dn Invert PRO DET POND EX CB 154.5000 ft 153.5280 ft Conduit Constraints: Min Vel Max Vel Min Cov Min Slope Max Slope Min drop 2.0000 ft 15.0000 ft 3.0000 ft 0.5000 ft 2.0000 ft 0.0000 ft In/Exfil Hold Up Hold Dn Match Inv Allow Smaller 0.0000 in/fir NO NO YES NO Conduit Summary: Trib Area Flow Capacity Velocity Normal Depth 16.1200 ac 5.3890 cf 8.8935 cf 5.2725 ft/s 0.8426 ft Ent Loss Exit Loss Frict Loss Start TW 0.215830 ft 0.431661 ft 0.356794 ft 154.4225 ft comment: 36 I I � - Node Records Node ID:EX CB Start El: 153.5600 ft Max El: 158.7100 ft Contrib Basin: Contrib Hyd: Hgl Elev: 154.4225 ft Struct Type: CB-TYPE I Classification Catch Basin Ke Descrip: CMP:Headwall or Headwall&Wingwall sq edge;.ke=0.5 Catch Depth: 1.4160 ft Bot Area: 3.9700 sf Condition: No particular shape. Status: Existing Structure Approach Credit: 0.0000 ft Node ID:PRO DET POND Start El: 154.5000 ft Max El: 162.0000 ft Contrib Basin: DEV SITE Contrib Hyd: Hgl Elev: 159.4370 ft Storage Id: POND STORE Discharge Id: DEV COMBO Node ID:POND STORE Start El: 154.5000 ft Max El: 162.0000 ft Contrib Basin: Contrib Hyd: Stage Area Volume Volume 154.50 8835.00 0.00 cf 0.0000 acft 156.00 9727.00 13921.50 cf 0.3196 acft 158.00 10964.00 34612.50 cf 0.7946 acft 160.00 12237.00 57813.50 cf 1.3272 acft 162.00 13542.00 83592.50 cf 1.9190 acft Control Structure ID:DEV COMBO-Combination Control Structure Start El Max El Increment 154.5000 ft 162.0000 ft 0.10 ID List: PRIMARY WEIR Control Structure ID:PRIMARY-Multiple Orifice Structure Start El Max El Increment 154.5000 ft 156.0000 ft 0.10 Orif Coeff: 0.62 Bottom El: 152.50 ft Lowest Diam: 4.4375 in out to 2nd: 3.0000 ft Diam: 7.0000 in Control Structure ID:WEIR-Rectangular weir Start El Max El Increment 158.6000 ft 162.0000 ft 0.10 Length: 1.0833 ft 37 �l I Contributing Drainage Areas Drainage Area:DEV SITE Hyd Method: SBUH Hyd Loss Method: SCS CN Number Peak Factor: 484.00 SCS Abs: 0.20 Stonn Dur: 24.00 hrs lnty: 10.00 min Area CN TC Pervious 3.3800 ac 86.00 0.81 hrs Impervious 12.7400 ac 98.12 0.07 hrs Total 16.1200 ac Supporting Data: Pervious CN Data: LOT A 10%PERVIOUS 86.00 0.2700 ac LOT B 10%PERVIOUS 86.00 0.1700 ac LOT C 10%PERVIOUS 86.00 0.1700 ac LOT D 25%PERVIOUS 86.00 1.0500 ac OFFSITE EXISTING PERVIOUS 86.00 1.5200 ac 213TH PLACE 10%PERVIOUS 86.00 0.1200 ac DETENTION TRACT 10%PERVIOUS 86.00 0.0800 ac Impervious CN Data: LOT A 90%IMPV 98.00 2.4700 ac LOT B 90%IMPV 98.00 1.6000 ac LOT C 90%IMPV 98.00 1.5600 ac LOT D 75%IMPV 98.00 3.1600 ac 213TH PLACE 90%IMPV 98.00 1.1000 ac TVEIT RD 100%IMPV 98.00 1.3000 ac DETENTION TRACT 90%IMPV 100.00 0.7400 ac OFFSITE EXISTING IMPV 98.00 0.8100 ac Pervious TC Data: Flow type: Description: Length: Slope: Coeff: Travel Time Sheet OFFSITE LAWN 300.00 R 0.75% 0.1500 46.58 min Shallow ALONG EX GRAVEL DRIVE 100.00 ft 4.00% 11.0000 0.76 min Channel DRAIN PIPE 880.00 R 5.50% 42.0000 1.49 min Impervious TC Data: Flow type: Description: Length: Slope: Coeff: Travel Time Sheet PARKING LOT 100.00 ft 2.00% 0.0110 1.62 min Channel DRAIN PIPE 440.00 ft 1.80% 42.0000 1.30 min Channel DRAIN PIPE 750.00 ft 5.50% 42.0000 1.27 min 38 •�I I Layout Hydrographs Hydrograph ID:EX CB-2 yr Area: 16.1200 ac Hyd Int: 10.00 min Base Flow: Pending tt translation: 0.21 min Peak Flow: 0.9197 cfs Peak Time: 13.67 hrs Hyd Vol: 1.8548 acft Time Flow Time Flow Time Flow hr cfs hr cfs hr cfs 1.33 0.0232 13.00 0.9186 24.33 0.8157 1.50 0.0394 13.17 0.9189 24.50 0.8081 1.67 0.0559 13.33 0.9192 24.67 0.8004 1.83 0.0724 13.50 0.9195 24.83 0.7926 2.00 0.0885 13.67 0.9197 25.00 0.7847 2.17 0.1042 13.83 0.9196 25.17 0.7767 2.33 0.1199 14.00 0.9195 25.33 0.7686 2.50 0.1351 14.17 0.9194 25.50 0.7606 2.67 0.1496 14.33 0.9192 25.67 0.7525 2.83 0.1634 14.50 0.9191 25.83 0.7443 3.00 0.1766 14.67 0.9189 26.00 0.7362 3.17 0.1893 14.83 0.9184 26.17 0.7280 3.33 0.2015 15.00 0.9178 26.33 0.7198 3.50 0.2132 15.17 0.9173 26.50 0.7115 3.67 0.2248 15.33 0.9167 26.67 0.7033 3.83 0.2366 15.50 0.9162 26.83 0.6951 4.00 0.2482 15.67 0.9155 27.00 0.6868 4.17 0.2600 15.83 0.9146 27.17 0.6786 4.33 0.2725 16.00 0.9136 27.33 0.6703 4.50 0.2850 16.17 0.9127 27.50 0.6621 4.67 0.2975 16.33 0.9117 27.67 0.6537 4.83 0.3106 16.50 0.9107 27.83 0.6445 5.00 0.3237 16.67 0.9098 28.00 0.6353 5.17 0.3367 16.83 0.9088 28.17 0.6261 5.33 0.3503 17.00 0.9079 28.33 0.6169 5.50 0.3637 17.17 0.9069 28.50 0.6076 5.67 0.3771 17.33 0.9056 28.67 0.5984 5.83 0.3909 17.50 0.9042 28.83 0.5892 6.00 0.4046 17.67 0.9029 29.00 0.5800 6.17 0.4187 17.83 0.9016 29.17 0.5707 6.33 0.4342 18.00 0.9002 29.33 0.5615 6.50 0.4498 18.17 0.8988 29.50 0.5523 6.67 0.4662 18.33 0.8971 29.67 0.5431 6.83 0.4844 18.50 0.8954 29.83 0.5338 7.00 0.5030 18.67 0.8936 30.00 0.5246 7.17 0.5223 18.83 0.8919 30.17 0.5154 7.33 0.5435 19.00 0.8902 30.33 0.5061 7.50 0.5651 19.17 0.8883 30.50 0.4969 7.67 0.5992 19.33 0.8863 30.67 0.4877 7.83 0.6553 19.50 0.8841 30.83 0.4784 8.00 0.7108 19.67 0.8820 31.00 0.4692 8.17 0.7542 19.83 0.8798 31.17 0.4600 8.33 0.7808 20.00 0.8777 31.33 0.4508 8.50 0.8002 20.17 0.8756 31.50 0.4415 8.67 0.8178 20.33 0.8735 31.67 0.4323 8.83 0.8314 20.50 0.8714 31.83 0.4231 9.00 0.8431 20.67 0.8693 32.00 0.4138 9.17 0.8535 20.83 0.8673 32.17 0.4046 9.33 0.8613 21.00 0.8652 32.33 0.3954 9.50 0.8680 21.17 0.8632 32.50 0.3861 9.67 0.8742 21.33 0.8612 32.67 0.3769 9.83 0.8796 21.50 0.8592 32.83 0.3677 10.00 0.8845 21.67 0.8572 33.00 0.3584 10.17 0.8890 21.83 0.8552 33.17 0.3492 10.33 0.8928 22.00 0.8533 33.33 0.3400 10.50 0.8962 22.17 0.8512 33.50 0.3308 10.67 0.8993 22.33 0.8489 33.67 0.3215 10.83 0.9018 22.50 0.8465 33.83 0.3123 11.00 0.9042 22.67 0.8442 34.00 0.3031 11.17 0.9063 22.83 0.8418 34.17 0.2938 11.33 0.9083 23.00 0.8395 34.33 0.2846 11.50 0.9100 23.17 0.8371 34.50 0.2754 11.67 0.9117 23.33 0.8348 34.67 0.2662 11.83 0.9131 23.50 0.8325 34.83 0.2569 39 i 12.00 0.9143 23.67 0.8302 35.00 0.2477 12.17 0.9155 23.83 0.8279 35.17 0.2385 12.33 0.9164 24.00 0.8257 35.33 0.2292 12.50 0.9172 24.17 0.8220 35.50 0.2200 12.67 0.9178 24.33 0.8157 35.67 0.2108 12.83 0.9183 24.50 0.8081 35.83 0.2016 40 i Hydrograph ID:EX CB-6 mo Area: 16.1200 ac Hyd Int: 10.00 min Base Flow: Pending tt translation: 0.23 min Peak Flow: 0.6470 cfs Peak Time: 11.50 hrs Hyd Vol: 1.0843 acft Time Flow Time Flow Time Flow hr cfs hr cfs hr cfs 1.83 0.0182 12.33 0.6454 22.67 0.5195 2.00 0.0286 12.50 0.6447 22.83 0.5168 2.17 0.0394 12.67 0.6439 23.00 0.5141 2.33 0.0503 12.83 0.6429 23.17 0.5114 2.50 0.0608 13.00 0.6418 23.33 0.5088 2.67 0.0708 13.17 0.6407 23.50 0.5062 2.83 0.0804 13.33 0.6397 23.67 0.5037 3.00 0.0897 13.50 0.6387 23.83 0.5012 3.17 0.0987 13.67 0.6376 24.00 0.4987 3.33 0.1073 13.83 0.6363 24.17 0.4946 3.50 0.1157 14.00 0.6349 24.33 0.4875 3.67 0.1240 14.17 0.6335 24.50 0.4789 3.83 0.1326 14.33 0.6322 24.67 0.4702 4.00 0.1411 14.50 0.6309 24.83 0.4614 4.17 0.1498 14.67 0.6294 25.00 0.4525 4.33 0.1591 14.83 0.6278 25.17 0.4435 4.50 0.1684 15.00 0.6261 25.33 0.4346 4.67 0.1779 15.17 0.6245 25.50 0.4255 4.83 0.1878 15.33 0.6228 25.67 0.4164 5.00 0.1977 15.50 0.6212 25.83 0.4074 5.17 0.2076 15.67 0.6195 26.00 0.3982 5.33 0.2180 15.83 0.6176 26.17 0.3891 5.50 0.2283 16.00 0.6156 26.33 0.3800 5.67 0.2386 16.17 0.6137 26.50 0.3708 5.83 0.2492 16.33 0.6117 26.67 0.3616 6.00 0.2598 16.50 0.6098 26.83 0.3524 6.17 0.2707 16.67 0.6079 27.00 0.3432 6.33 0.2827 16.83 0.6061 27.17 0.3341 6.50 0.2947 17.00 0.6042 27.33 0.3249 6.67 0.3074 17.17 0.6023 27.50 0.3157 6.83 0.3216 17.33 0.6002 27.67 0.3064 7.00 0.3360 17.50 0.5980 27.83 0.2972 7.17 0.3509 17.67 0.5958 28.00 0.2880 7.33 0.3674 17.83 0.5936 28.17 0.2788 7.50 0.3840 18.00 0.5915 28.33 0.2696 7.67 0.4113 18.17 0.5893 28.50 0.2603 7.83 0.4572 18.33 0.5869 28.67 0.2511 8.00 0.5070 18.50 0.5843 28.83 0.2419 8.17 0.5447 18.67 0.5818 29.00 0.2327 8.33 0.5666 18.83 0.5794 29.17 0.2235 8.50 0.5818 19.00 0.5770 29.33 0.2142 8.67 0.5955 19.17 0.5744 29.50 0.2050 8.83 0.6054 19.33 0.5717 29.67 0.1958 9.00 0.6138 19.50 0.5688 29.83 0.1865 9.17 0.6210 19.67 0.5660 30.00 0.1773 9.33 0.6260 19.83 0.5633 30.17 0.1681 9.50 0.6299 20.00 0.5605 30.33 0.1588 9.67 0.6335 20.17 0.5578 30.50 0.1496 9.83 0.6365 20.33 0.5551 30.67 0.1404 10.00 0.6391 20.50 0.5525 30.83 0.1312 10.17 0.6413 20.67 0.5499 31.00 0.1219 10.33 0.6429 20.83 0.5473 31.17 0.1126 10.50 0.6442 21.00 0.5447 31.33 0.1034 10.67 0.6453 21.17 0.5422 31.50 0.0942 10.83 0.6460 21.33 0.5397 31.67 0.0850 11.00 0.6465 21.50 0.5373 31.83 0.0757 11.17 0.6468 21.67 0.5349 32.00 0.0665 11.33 0.6470 21.83 0.5325 32.17 0.0572 11.50 0.6470 22.00 0.5301 32.33 0.0481 11.67 0.6470 22.17 0.5277 32.50 0.0389 11.83 0.6467 22.33 0.5250 32.67 0.0295 12.00 0.6464 22.50 0.5222 32.83 0.0205 12.17 0.6460 22.67 0.5195 33.00 0.0110 41 Hydrograph ID:EX CB-100 yr Area: 16.1200 ac Hyd Int: 10.00 min Base Flow: Pending tt translation: 0.13 min Peak Flow: 5.3890 cfs Peak Time: 8.67 hrs Hyd Vol: 4.3404 acft Time Flow Time Flow Time Flow hr cfs hr cfs hr cfs 0.83 0.0383 12.83 2.5317 24.67 0.9164 1.00 0.0680 13.00 2.4994 24.83 0.9091 1.17 0.0992 13.17 2.4766 25.00 0.9017 1.33 0.1311 13.33 2.4629 25.17 0.8941 1.50 0.1616 13.50 2.4496 25.33 0.8864 1.67 0.1908 13.67 2.4355 25.50 0.8786 1.83 0.2192 13.83 2.4197 25.67 0.8707 2.00 0.2464 14.00 2.4034 25.83 0.8627 2.17 0.2724 14.17 2.3875 26.00 0.8547 2.33 0.2981 14.33 2.3720 26.17 0.8466 2.50 0.3228 14.50 2.3569 26.33 0.8385 2.67 0.3461 14.67 2.3412 26.50 0.8304 2.83 0.3682 14.83 2.3237 26.67 0.8222 3.00 0.3893 15.00 2.3056 26.83 0.8140 3.17 0.4093 15.17 2.2881 27.00 0.8058 3.33 0.4286 15.33 2.2711 27.17 0.7976 3.50 0.4470 15.50 2.2546 27.33 0.7894 3.67 0.4652 15.67 2.2373 27.50 0.7811 3.83 0.4836 15.83 2.2182 27.67 0.7729 4.00 0.5017 16.00 2.1986 27.83 0.7646 4.17 0.5201 16.17 2.1796 28.00 0.7564 4.33 0.5394 16.33 2.1611 28.17 0.7481 4.50 0.5587 16.50 2.1432 28.33 0.7399 4.67 0.5782 16.67 2.1259 28.50 0.7316 4.83 0.5984 16.83 2.1091 28.67 0.7233 5.00 0.6187 17.00 2.0929 28.83 0.7151 5.17 0.6390 17.17 2.0760 29.00 0.7068 5.33 0.6595 17.33 2.0570 29.17 0.6985 5.50 0.6784 17.50 2.0374 29.33 0.6902 5.67 0.6974 17.67 2.0186 29.50 0.6820 5.83 0.7170 17.83 2.0003 29.67 0.6737 6.00 0.7366 18.00 1.9827 29.83 0.6654 6.17 0.7569 18.17 1.9642 30.00 0.6571 6.33 0.7787 18.33 1.9436 30.17 0.6482 6.50 0.8009 18.50 1.9202 30.33 0.6390 6.67 0.8240 18.67 1.8972 30.50 0.6297 6.83 0.8495 18.83 1.8752 30.67 0.6205 7.00 0.8755 19.00 1.8540 30.83 0.6113 7.17 0.9024 19.17 1.8319 31.00 0.6021 7.33 1.1736 19.33 1.8073 31.17 0.5928 7.50 1.5621 19.50 1.7818 31.33 0.5836 7.67 1.9106 19.67 1.7575 31.50 0.5744 7.83 2.3085 19.83 1.7341 31.67 0.5651 8.00 3.1369 20.00 1.7118 31.83 0.5559 8.17 4.4192 20.17 1.6905 32.00 0.5467 8.33 5.0229 20.33 1.6702 32.17 0.5375 8.50 5.2585 20.50 1.6511 32.33 0.5282 8.67 5.3890 20.67 1.6330 32.50 0.5190 8.83 5.3320 20.83 1.6160 32.67 0.5098 9.00 5.2132 21.00 1.6000 32.83 0.5005 9.17 5.0638 21.17 1.5850 33.00 0.4913 9.33 4.8359 21.33 1.5712 33.17 0.4821 9.50 4.6040 21.50 1.5581 33.33 0.4728 9.67 4.4004 21.67 1.5462 33.50 0.4636 9.83 4.2032 21.83 1.5350 33.67 0.4544 10.00 4.0277 22.00 1.5249 33.83 0.4452 10.17 3.8690 22.17 1.5128 34.00 0.4359 10.33 3.7101 22.33 1.4967 34.17 0.4267 10.50 3.5669 22.50 1.4793 34.33 0.4175 10.67 3.4399 22.67 1.4631 34.50 0.4082 10.83 3.3170 22.83 1.4479 34.67 0.3990 11.00 3.2076 23.00 1.4338 34.83 0.3898 11.17 3.1123 23.17 1.4208 35.00 0.3805 11.33 3.0247 23.33 1.4088 35.17 0.3713 11.50 2.9478 23.50 1.3979 35.33 0.3621 11.67 2.8794 23.67 1.3878 35.50 0.3529 42 I I 11.83 2.8147 23.83 1.3789 35.67 0.3436 12.00 2.7569 24.00 1.3707 35.83 0.3344 12.17 2.7049 24.17 1.3254 36.00 0.3251 12.33 2.6548 24.33 1.1896 36.17 0.3159 12.50 2.6100 24.50 0.9234 36.33 0.3067 12.67 2.5699 24.67 0.9164 36.50 0.2975 43 Hydrograph ID:EX CB-10 yr Area: 16.1200 ac Hyd Int: 10.00 min Base Flow: Pending tt translation: 0.16 min Peak Flow: 2.4224 cfs Peak Time: 9.67 hrs Hyd Vol: 3.0360 acft Time Flow Time Flow Time Flow hr ofs hr cfs hr cfs 1.00 0.0289 12.83 2.0680 24.50 0.9111 1.17 0.0521 13.00 2.0410 24.67 0.9037 1.33 0.0771 13.17 2.0148 24.83 0.8961 1.50 0.1012 13.33 1.9893 25.00 0.8884 1.67 0.1246 13.50 1.9646 25.17 0.8806 1.83 0.1477 13.67 1.9395 25.33 0.8727 2.00 0.1698 13.83 1.9100 25.50 0.8648 2.17 0.1913 14.00 1.8806 25.67 0.8567 2.33 0.2124 14.17 1.8523 25.83 0.8487 2.50 0.2329 14.33 1.8251 26.00 0.8406 2.67 0.2522 14.50 1.7990 26.17 0.8324 2.83 0.2706 14.67 1.7726 26.33 0.8243 3.00 0.2881 14.83 1.7446 26.50 0.8161 3.17 0.3049 15.00 1.7165 26.67 0.8079 3.33 0.3209 15.17 1.6898 26.83 0.7997 3.50 0.3363 15.33 1.6643 27.00 0.7915 3.67 0.3514 15.50 1.6399 27.17 0.7832 3.83 0.3668 15.67 1.6152 27.33 0.7750 4.00 0.3818 15.83 1_5885 27.50 0.7667 4.17 0.3970 16.00 1.5617 27.67 0.7585 4.33 0.4129 16.17 1.5363 27.83 0.7502 4.50 0.4289 16.33 1.5122 28.00 0.7420 4.67 0.4449 16.50 1.4897 28.17 0.7337 4.83 0.4617 16.67 1.4684 28.33 0.7254 5.00 0.4784 16.83 1.4487 28.50 0.7172 5.17 0.4951 17.00 1.4304 28.67 0.7089 5.33 0.5126 17.17 1.4114 28.83 0.7006 5.50 0.5299 17.33 1.3895 29.00 0.6923 5.67 0.5473 17.50 1.3670 29.17 0.6841 5.83 0.5652 17.67 1.3463 29.33 0.6758 6.00 0.5831 17.83 1.3275 29.50 0.6675 6.17 0.6015 18.00 1.3101 29.67 0.6592 6.33 0.6215 18.17 1.2917 29.83 0.6505 6.50 0.6416 18.33 1.2691 30.00 0.6413 6.67 0.6619 18.50 1.2462 30.17 0.6321 6.83 0.6828 18.67 1.2253 30.33 0.6229 7.00 0.7043 18.83 1.2066 30.50 0.6136 7.17 0.7266 19.00 1.1900 30.67 0.6044 7.33 0.7510 19.17 1.1718 30.83 0.5952 7.50 0.7760 19.33 1.1476 31.00 0.5859 7.67 0.8143 19.50 1.1223 31.17 0.5767 7.83 0.8765 19.67 1.1007 31.33 0.5675 8.00 1.3988 19.83 1.0824 31.50 0.5582 8.17 1.8855 20.00 1.0674 31.67 0.5490 8.33 2.0711 20.17 1.0559 31.83 0.5398 8.50 2.1799 20.33 1.0471 32.00 0.5306 8.67 2.2682 20.50 1.0410 32.17 0.5213 8.83 2.3248 20.67 1.0370 32.33 0.5121 9.00 2.3668 20.83 1.0340 32.50 0.5029 9.17 2.3985 21.00 1.0319 32.67 0.4936 9.33 2.4128 21.17 1.0309 32.83 0.4844 9.50 2.4190 21.33 1.0304 33.00 0.4752 9.67 2.4224 21.50 1.0298 33.17 0.4659 9.83 2.4204 21.67 1.0298 33.33 0.4567 10.00 2.4158 21.83 1.0298 33.50 0.4475 10.17 2.4086 22.00 1_0293 33.67 0.4382 10.33 2.3965 22.17 1.0210 33.83 0.4290 10.50 2.3824 22.33 0.9972 34.00 0.4198 10.67 2.3668 22.50 0.9710 34.17 0.4106 10.83 2.3482 22.67 0.9568 34.33 0.4013 11.00 2.3284 22.83 0.9488 34.50 0.3921 11.17 2.3081 23.00 0.9511 34.67 0.3829 11.33 2.2866 23.17 0.9488 34.83 0.3736 11.50 2.2646 23.33 0.9488 35.00 0.3644 11.67 2.2423 23.50 0.9488 35.17 0.3552 11.83 2.2189 23.67 0.9488 35.33 0.3459 44 12.00 2.1951 23.83 0.9464 35.50 0.3367 12.17 2.1711 24.00 0.9488 35.67 0.3275 12.33 2.1459 24.17 0.9237 35.83 0.3183 12.50 2.1205 24.33 0.9183 36.00 0.3090 12.67 2.0949 24.50 0.9111 36.17 0.2998 45 J 1S` I fi �. Figure 5.5.2 As-built Drainage Report Basin Maps 0, I • 1 1 � ■ EXISTING CONDITIONS ■ BASIN MAP ■ 1 ■ 15. 42 ACRES TOTAL ■ ■ ■ I • I i . I 1 I 1 I SCALE: V-100' . - .,-■■� -•■�-'-'"' • 1 DETENTION POND 1 s • 4BASIN NEW • 3 6. 40 ACRES 87,119 SQ. FT. ` ■ 11 ■ 1 1 iIl .•. .TM ��► ~��� NEW D ■ '1 �\ 225,357 SQ. FT. ■ � 1 1 BIOSWALE BASI ' j ��� ♦♦♦ ' 5. 28 ACRES `' ♦♦ NEW ~ � 41t� 129,638 SQ. FT, NEW A 128,783 SQ. FT. �� • TVEIT RD BASIN 3. 74 ACRES �♦ 1 ' � 1 r , 1 \--& 1 1 r vm �"'" ----------- -- 1 1 ______-__ ___ 1 I ----- 1 1 ♦ - - - - - - ■ 0 0a -z-a-■f■ I NEW mat* �II • f j DEVELOPED CONDITIONS o 1 ■ I � 1 ■ SCALE: 1'�100' BASIN MAP ! ■ 1 I ' 16 . 12 ACRES I � •�4` 1 ''r 1 _ -- I ' i NEW B I 87,119 SQ. FT. ! i I I I � I - 1 SEWS 225,357 SQ. FT ; (MEDICAL CENTER DR) � l � ' 1 � \ 1 i \\ I ^1 i I ti 1 1 i NEW C 1 129,638 SQ. FT. F 1 NEW A Lu 1 128,783 SQ. FT. I c 1 WN I I t52 1 5. - 1 -tom i5fi j l CO 1 � _ - - I ' - - - - - - - 211th ST ACE ITVEIT BDI mill . I i � • I �_��11 ■ II V IMPERVIOUS OFFS ATE (35% IMPV) OFFS ACRES TOTAL I AREA BASIN A 1. ACRES IMPV ■ .52 52 ACRES PERV ■ h ■ Qt MAP SCALE: 1'=100' it 16 . 12 ACRES TOTAL ` j' 1 NEW B i 87,119 SQ. FT. it r� i; LOT B (90% IMPV) Ii 1.77 ACRES TOTAL ' 1.60 ACRES IMPV E i.i?J D (75% i; 4.21 0.17 ACRES PERV 3.16 'RES 1 1' ACR- PEW, I ■ Ii 11EWCAL CENTER DRIVE 190% 1N1 V 1.22 A('RF,S TOTAL \ 22.357 SO. FTF 1.10 ACRES IMPV t).12 ACRES PERV (MEDICAL CENTER DR) 1• itiliilll, 'i i i i i i NEW C l 129,638 SQ. FT. o I = ' W NEW A 128.783 SQ. FT. LOT C (90% IMPV) 1.73 ACRES TOTAL 1.56 ACRES IMPV ' i LOT A (90% IMPV) 0.17 ACRES PERV - DETENTION (90% IMP I 2.74 ACRES TOTAL 0. ACRES TOTAL ' 0.74 ACRES I11IPV 2.47 ACRES IMPV 0.08 ACRES PERV ' 0.27 ACRES PERV ------------ --------------- - ' ----- •--------------- XL T1'Ell RD (100% IMPV) 1.30 ACRES TOTAL _ _ _ _ - - - - 212th ST NE IT EEIT BDI -# ' I 1.30 :(CRES IMPV 0.00 ACRE- 'L•':\' - - - 5.6 Runoff Treatment System This project proposes 5,000 square feet of new pollution-generating hard surfaces, and must therefore provide runoff treatment. This project proposes utilizing the existing combined wetpool/detention pond constructed under City File No. S-04-033 to meet runoff treatment requirements. Per the 2024 DOE SWMMWW Appendix I-D.3, if the regional facility is privately owned and specifies the ultimate construction of all the areas it was designed to serve, it is all considered as one project, and therefore, may be utilized for the project. Based on as-builts and the approved drainage report, the existing combined wetpool/detention pond was sized to meet the runoff treatment requirements for the surrounding development, including the project site in the developed condition. Please refer to Figure 5.5.1 and 5.5.2 for the approved Drainage Report and figures discussing the design of the existing combined wetpool/detention pond. As previously mentioned, and noted in Figure 5.5.2, the pond was sized to accommodate the developed condition of Lot A and C, assuming an impervious coverage of 90%. The proposed impervious coverage of the developed site will not exceed 90% and therefore, the existing combined wetpool/detention pond will continue to be adequately sized to provide runoff treatment for this project. 24413.002-SSP.doc 5.7 Conveyance System Analysis and Design Conveyance calculations for the proposed storm drain system and the existing conveyance system within 212th Street N.E. to the existing detention pond have been provided within this section of the report. Please refer to Figure 5.7.1 for Pipe Conveyance Calculations. Per Section 3-3.02 of the City of Arlington Engineering Stormwater Standards, pipes shall be sized to convey the 25-year storm. The provided capacity calculations analyze the design using the 100-year storm event and therefore, the proposed pipes are adequately sized to meet the City's requirements. 24413.002-SSP.doc Figure 5.7. 1 Pipe Conveyance Calculations PIPE CONVEYANCE SUBBASINS N FOR MEDICAL CENTER z SEC. 12,TWP. 31 N., RGE 5 E., W. M. p CITY OF ARLINGTON, SNOHOMISH COUNTY, WASHINGTON - m Z p Q pwQ� � c/) zw w z U C/) z O z , i 0 20' 40' 80' Q = U V I— I Z SCALE:1-40' ; N U EXISTING ASPHALT PARKING LOT DRAINS TO L CONVEYANCE SYSTEM WITHIN MEDICAL --_ sr_ •- xnus1 Q CENTER DRIVE.PER THE AS-BUILTS,THIS Lu U Z Lu CONVEYANCE IS SEPARATE FROM THE N89°32-11"1418.39' /� CONTRIBUTING AREAS TO CATCH BASINS w CONVEYANCE WITHIN 212TH ST.NE. _ _ _ HOWEVER,BOTH IS CONVEYED TO THE s 4 CB#10 11,162 SF(0.26 AC) — N89'3211"E 80.74' v d=90, / �Q 9019.i' / ® m EXISTING DETENTION POND. --- ° R 135�•3g• / <,Z76S0 a3 CB#9 19,373 SF(0.44 AC) ® o d N89°32'11"E 310.28' _..._° EX CB ,:. ° - -- -2/3,�2, -\` �060 ' .° ,. i/ CB#7 10,168 5� 0.23 AC N ( ) CB#6 10,588 SF(0.24 AC) AREA IS CAPTURED BY CONVEYANCE CB#5 8,488 SF(0.19 AC) / SYSTEM WITHIN MEDICAL CENTER DRIVE. CB#3 14,643 SF(0.34 AC) ® p Q I - /hv ;s\PER THE AS-BUILTS,THIS CONVEYANCE IS ZURN#1 8,737 SF(0.20 AC) 0 J - SEPARATE FROM THE CONVEYANCE WITHIN 212TH ST.NE.HOWEVER,BOTH N / __ '. IS CONVEYED TO THE EXISTING EX CB#4 74,195 SF(1.70 AC) ® W DETENTION POND. EX CB#3 11,771 SF(0.27 AC) ® Z EX CB#2 15,159 SF(0.35 AC) ® Q CB#8 CB#11 EX CB#1 10,916 SF(0.25 AC) TOTAL 4.47 AC m a CB#10 N89°58 O v)+ c6#9 S '14"W 112.00' Il° U H 0 n(_ o LL > IL 913#7 o rnW z Z ° � w p�EX W H/TF CB#6 I I APN 3>OS>7 002 02 700 O (,�_ � S APN 3>05>1001004�0�0� o I CB#4 ni �e II N 578°33'35'W57.00' CB#5 3�'000S.F. I I i... s''iONALEN��� I v I - r = AREA IS CAPTURED BY WALL FOOTING DRAINS AND DRAINS TO CONVEYANCE SYSTEM WITHIN MEDICAL \ CENTER DRIVE.PER THE AS-BUILTS,THIS 3 CONVEYANCE IS SEPARATE FROM THE CONVEYANCE of 3 of WITHIN 212TH ST.NE.HOWEVER,BOTH IS ICB#3 a o I CB#2 CONVEYED TO THE EXISTING DETENTION POND. ZURN 41 c .- N89°5814"W 343.66' N89°58'14"W 213 74 --- pE J c I EX CB#4 CB#1 EX CB#3 589°5814 E 1305..9' _2 T H o N E EX CB#2 EX CB#1 d e — — — -- N C In Ol w N M Qacooci M + N JC y Ln �ri m 0 N m U r°Yv 3 0 s M E � ^ o CV r S Autodesk® Storm and Sanitary Analysis 2024 - Version 13.6.323 (Build 0) ----------------------------------------------------------------------------------------- Project Description File Name ................. Pipe Conveyance Calcs.SPF Analysis Options Flow Units .............. . . cfs Subbasin Hydrograph Method. Santa Barbara UH Time of Concentration.... . . SCS TR-55 Link Routing Method ....... Hydrodynamic Storage Node Exfiltration.. Constant flow Starting Date ............. SEP-22-2025 00:00:00 Ending Date ............... SEP-23-2025 00:00:00 Report Time Step .......... 00:00:10 ************* Element Count ************* Number of rain gages ...... 1 Number of subbasins ....... 11 Number of nodes ........... 15 Number of links ........... 14 Raingage Summary Gage Data Data Recording ID Source Type Interval min ------------------------------------------------------------ 100-year 100-year CUMULATIVE 15.00 Subbasin Summary Subbasin Total Imperv. Raingage Area Area ID acres a ---------------------------------------------------- CB#10 0.26 100.00 100-year CB#3 0.34 100.00 100-year CB#5 0.19 100.00 100-year CB#6 0.24 100.00 100-year CB#7 0.23 100.00 100-year CB#9 0.44 100.00 100-year EXCB#1 0.25 100.00 100-year EXCB#2 0.35 100.00 100-year EXCB#3 0.27 100.00 100-year EXCB#4 1.70 100.00 100-year ZURN#1 0.20 100.00 100-year Node Summary Node Element Invert Maximum Ponded External ID Type Elevation Elev. Area Inflow Autodesk Storm and Sanitary Analysis ft ft ft2 ------------------------------------------------------------------------------ CB1 JUNCTION 188.15 191.97 0.00 CB10 JUNCTION 197.84 200.61 0.00 CB2 JUNCTION 188.87 193.21 0.00 CB3 JUNCTION 194.98 198.34 0.00 CB4 JUNCTION 196.45 200.66 0.00 CB5 JUNCTION 196.74 199.78 0.00 CB6 JUNCTION 196.93 200.36 0.00 CB7 JUNCTION 197.10 200.69 0.00 CB9 JUNCTION 197.44 200.79 0.00 EX-CB#1 JUNCTION 161.46 166.46 0.00 EX-CB#2 JUNCTION 171.43 176.20 0.00 EX-CB#3 JUNCTION 183.46 188.78 0.00 EX-CB#4 JUNCTION 188.70 192.36 0.00 ZURN JUNCTION 188.94 192.64 0.00 Out-01 OUTFALL 160.75 161.75 0.00 ************ Link Summary ************ Link From Node To Node Element Length Slope Manning's ID Type ft % Roughness -------------------------------------------------------------------------------------------- Link-02 EX-CB#3 EX-CB#2 CONDUIT 224.0 5.3705 0.0150 Link-03 EX-CB#2 EX-CB#1 CONDUIT 198.0 5.0354 0.0150 Link-04 EX-CB#1 Out-01 CONDUIT 56.0 1.2679 0.0150 Link-05 CB10 CB9 CONDUIT 80.0 0.5000 0.0150 Link-06 CB9 CB7 CONDUIT 68.0 0.5000 0.0150 Link-07 CB6 CB5 CONDUIT 37.0 0.5135 0.0150 Link-08 CB5 CB4 CONDUIT 58.0 0.5000 0.0150 Link-11 CB4 CB3 CONDUIT 80.0 1.8375 0.0150 Link-12 CB7 CB6 CONDUIT 35.0 0.4857 0.0150 Link-13 CB3 CB2 CONDUIT 50.0 12.2200 0.0150 Link-14 CB2 CB1 CONDUIT 13.0 5.5385 0.0150 Link-15 CB1 EX-CB#3 CONDUIT 164.0 2.8598 0.0150 Link-16 EX-CB#4 CB1 CONDUIT 19.0 2.8947 0.0150 Link-17 ZURN CB2 CONDUIT 7.0 1.0000 0.0150 ********************* Cross Section Summary ********************* Link Shape Depth/ Width No. of Cross Full Flow Design ID Diameter Barrels Sectional Hydraulic Flow Area Radius Capacity ft ft ftz ft cfs ------------------------------------------------------------------------------------------------- Link-02 CIRCULAR 1.00 1.00 1 0.79 0.25 7.16 Link-03 CIRCULAR 1.00 1.00 1 0.79 0.25 6.93 Link-04 CIRCULAR 1.00 1.00 1 0.79 0.25 3.48 Link-05 CIRCULAR 1.00 1.00 1 0.79 0.25 2.18 Link-06 CIRCULAR 1.00 1.00 1 0.79 0.25 2.18 Link-07 CIRCULAR 1.00 1.00 1 0.79 0.25 2.21 Autodesk Storm and Sanitary Analysis Link-08 CIRCULAR 1.00 1.00 1 0.79 0.25 2.18 Link-11 CIRCULAR 1.00 1.00 1 0.79 0.25 4.19 Link-12 CIRCULAR 1.00 1.00 1 0.79 0.25 2.15 Link-13 CIRCULAR 1.00 1.00 1 0.79 0.25 10.79 Link-14 CIRCULAR 1.00 1.00 1 0.79 0.25 7.27 Link-15 CIRCULAR 1.00 1.00 1 0.79 0.25 5.22 Link-16 CIRCULAR 1.00 1.00 1 0.79 0.25 5.25 Link-17 CIRCULAR 0.67 0.67 1 0.35 0.17 1.05 ************************** Volume Depth Runoff Quantity Continuity acre-ft inches ************************** Total Precipitation ...... 1.483 3.981 Surface Runoff ........... 1.397 3.749 Continuity Error (%) ..... 0.000 ************************** Volume Volume Flow Routing Continuity acre-ft Mgallons ************************** External Inflow .......... 0.003 0.001 External Outflow ......... 1.395 0.454 Initial Stored Volume .... 0.001 0.000 Final Stored Volume ...... 0.004 0.001 Continuity Error (%) ..... 0.000 ****************************************** Composite Curve Number Computations Report ****************************************** ----------------- Subbasin CB#10 ----------------- Area Soil Soil/Surface Description (acres) Group CN ---------------------------------------------------------------------------------------- Composite Area & Weighted CN 0.26 98.00 ---------------- Subbasin CB#3 ---------------- Area Soil Soil/Surface Description (acres) Group CN ---------------------------------------------------------------------------------------- Composite Area & Weighted CN 0.34 98.00 ---------------- Subbasin CB#5 ---------------- Area Soil Soil/Surface Description (acres) Group CN ---------------------------------------------------------------------------------------- Composite Area & Weighted CN 0.19 98.00 ---------------- Subbasin CB#6 ---------------- Autodesk Storm and Sanitary Analysis Area Soil Soil/Surface Description (acres) Group CN ---------------------------------------------------------------------------------------- Composite Area & Weighted CN 0.24 98.00 ---------------- Subbasin CB#7 ---------------- Area Soil Soil/Surface Description (acres) Group CN ---------------------------------------------------------------------------------------- Composite Area & Weighted CN 0.23 98.00 ---------------- Subbasin CB#9 ---------------- Area Soil Soil/Surface Description (acres) Group CN ---------------------------------------------------------------------------------------- Composite Area & Weighted CN 0.44 98.00 ------------------ Subbasin EXCB#1 ------------------ Area Soil Soil/Surface Description (acres) Group CN ---------------------------------------------------------------------------------------- Composite Area & Weighted CN 0.25 98.00 ------------------ Subbasin EXCB#2 ------------------ Area Soil Soil/Surface Description (acres) Group CN ---------------------------------------------------------------------------------------- Composite Area & Weighted CN 0.35 98.00 ------------------ Subbasin EXCB#3 ------------------ Area Soil Soil/Surface Description (acres) Group CN ---------------------------------------------------------------------------------------- Composite Area & Weighted CN 0.27 98.00 ------------------ Subbasin EXCB#4 ------------------ Area Soil Soil/Surface Description (acres) Group CN ---------------------------------------------------------------------------------------- Composite Area & Weighted CN 1.70 98.00 ------------------ Subbasin ZURN#1 ------------------ Area Soil Soil/Surface Description (acres) Group CN ---------------------------------------------------------------------------------------- Composite Area & Weighted CN 0.20 98.00 ************************************** Runoff Coefficient Computations Report ************************************** ----------------- Subbasin CB#10 Autodesk Storm and Sanitary Analysis ----------------- Area Soil Runoff Soil/Surface Description (acres) Group Coeff. ----------------------------------------------------------------------------------------- 5.00 - 0.72 Composite Area & Weighted Runoff Coeff. 5.00 0.72 ---------------- Subbasin CB#3 ---------------- Area Soil Runoff Soil/Surface Description (acres) Group Coeff. ----------------------------------------------------------------------------------------- 0.32 - 0.72 Composite Area & Weighted Runoff Coeff. 0.32 0.72 ---------------- Subbasin CB#5 ---------------- Area Soil Runoff Soil/Surface Description (acres) Group Coeff. ----------------------------------------------------------------------------------------- 5.00 - 0.72 Composite Area & Weighted Runoff Coeff. 5.00 0.72 ---------------- Subbasin CB#6 ---------------- Area Soil Runoff Soil/Surface Description (acres) Group Coeff. ----------------------------------------------------------------------------------------- 0.47 - 0.72 Composite Area & Weighted Runoff Coeff. 0.47 0.72 ---------------- Subbasin CB#7 ---------------- Area Soil Runoff Soil/Surface Description (acres) Group Coeff. ----------------------------------------------------------------------------------------- 0.23 - 0.72 Composite Area & Weighted Runoff Coeff. 0.23 0.72 ---------------- Subbasin CB#9 ---------------- Area Soil Runoff Soil/Surface Description (acres) Group Coeff. ----------------------------------------------------------------------------------------- 0.43 - 0.72 Composite Area & Weighted Runoff Coeff. 0.43 0.72 ------------------ Subbasin EXCB#1 ------------------ Area Soil Runoff Soil/Surface Description (acres) Group Coeff. ----------------------------------------------------------------------------------------- 0.24 - 0.72 Composite Area & Weighted Runoff Coeff. 0.24 0.72 ------------------ Subbasin EXCB#2 ------------------ Area Soil Runoff Soil/Surface Description (acres) Group Coeff. ----------------------------------------------------------------------------------------- Autodesk Storm and Sanitary Analysis 5.00 - 0.72 Composite Area & Weighted Runoff Coeff. 5.00 0.72 ------------------ Subbasin EXCB#3 ------------------ Area Soil Runoff Soil/Surface Description (acres) Group Coeff. ----------------------------------------------------------------------------------------- 5.00 - 0.72 Composite Area & Weighted Runoff Coeff. 5.00 0.72 ------------------ Subbasin EXCB#4 ------------------ Area Soil Runoff Soil/Surface Description (acres) Group Coeff. ----------------------------------------------------------------------------------------- 4.62 - 0.72 Composite Area & Weighted Runoff Coeff. 4.62 0.72 ------------------ Subbasin ZURN#1 ------------------ Area Soil Runoff Soil/Surface Description (acres) Group Coeff. ----------------------------------------------------------------------------------------- 0.15 - 0.72 Composite Area & Weighted Runoff Coeff. 0.15 0.72 *************************************************** SCS TR-55 Time of Concentration Computations Report *************************************************** Sheet Flow Equation ------------------- Tc = (0.007 * ((n * Lf)^0.8)) / ((P^0.5) * (Sf^0.4)) Where: Tc = Time of Concentration (hrs) n = Manning's Roughness Lf = Flow Length (ft) P = 2 yr, 24 hr Rainfall (inches) Sf = Slope (ft/ft) Shallow Concentrated Flow Equation ---------------------------------- V = 16.1345 * (Sf^0.5) (unpaved surface) V = 20.3282 * (Sf^0.5) (paved surface) V = 15.0 * (Sf^0.5) (grassed waterway surface) V = 10.0 * (Sf^0.5) (nearly bare & untilled surface) V = 9.0 * (Sf^0.5) (cultivated straight rows surface) V = 7.0 * (Sf^0.5) (short grass pasture surface) V = 5.0 * (Sf^0.5) (woodland surface) V = 2.5 * (Sf^0.5) (forest w/heavy litter surface) Tc = (Lf / V) / (3600 sec/hr) Where: Tc = Time of Concentration (hrs) Lf = Flow Length (ft) V = Velocity (ft/sec) Sf = Slope (ft/ft) Autodesk Storm and Sanitary Analysis Channel Flow Equation --------------------- V = (1.99 * (R^(2/3)) * (Sf^0.5)) / n R = Aq / Wp Tc = (Lf / V) / (3600 sec/hr) Where: Tc = Time of Concentration (hrs) Lf = Flow Length (ft) R = Hydraulic Radius (ft) Aq = Flow Area (ft2) Wp = Wetted Perimeter (ft) V = Velocity (ft/sec) Sf = Slope (ft/ft) n = Manning's Roughness ----------------- Subbasin CB#10 ----------------- Total TOC (minutes) : 0.00 ------------------------------------------------------------------------------------------------ ---------------- Subbasin CB#3 ---------------- Total TOC (minutes) : 0.00 ------------------------------------------------------------------------------------------------ ---------------- Subbasin CB#5 ---------------- Total TOC (minutes) : 0.00 ------------------------------------------------------------------------------------------------ ---------------- Subbasin CB#6 ---------------- Total TOC (minutes) : 0.00 ------------------------------------------------------------------------------------------------ ---------------- Subbasin CB#7 ---------------- Total TOC (minutes) : 0.00 ------------------------------------------------------------------------------------------------ Autodesk Storm and Sanitary Analysis ---------------- Subbasin CB#9 ---------------- ------------------------------------------------------------------------------------------------ Total TOC (minutes) : 0.00 ------------------ Subbasin EXCB#1 ------------------ ------------------------------------------------------------------------------------------------ Total TOC (minutes) : 0.00 ------------------ Subbasin EXCB#2 ------------------ ------------------------------------------------------------------------------------------------ Total TOC (minutes) : 0.00 ------------------ Subbasin EXCB#3 ------------------ ------------------------------------------------------------------------------------------------ Total TOC (minutes) : 0.00 ------------------ Subbasin EXCB#4 ------------------ ------------------------------------------------------------------------------------------------ Total TOC (minutes) : 0.00 ------------------ Subbasin ZURN#1 ------------------ ------------------------------------------------------------------------------------------------ Total TOC (minutes) : 0.00 Subbasin Runoff Summary -------------------------------------------------------------------------- Autodesk Storm and Sanitary Analysis Subbasin Total Total Peak Weighted Time of ID Precip Runoff Runoff Curve Concentration in in cfs Number days hh:mm:ss -------------------------------------------------------------------------- CB#10 3.98 3.75 0.25 98.000 0 00:05:00 CB#3 3.98 3.75 0.33 98.000 0 00:05:00 CB#5 3.98 3.75 0.18 98.000 0 00:05:00 CB#6 3.98 3.75 0.23 98.000 0 00:05:00 CB#7 3.98 3.75 0.22 98.000 0 00:05:00 CB#9 3.98 3.75 0.42 98.000 0 00:05:00 EXCB#1 3.98 3.75 0.24 98.000 0 00:05:00 EXCB#2 3.98 3.75 0.34 98.000 0 00:05:00 EXCB#3 3.98 3.75 0.26 98.000 0 00:05:00 EXCB#4 3.98 3.75 1.63 98.000 0 00:05:00 ZURN#1 3.98 3.75 0.19 98.000 0 00:05:00 -------------------------------------------------------------------------- Node Depth Summary ----------------------------------------------------------------------------------------- Node Average Maximum Maximum Time of Max Total Total Retention ID Depth Depth HGL Occurrence Flooded Time Time Attained Attained Attained Volume Flooded ft ft ft days hh:mm acre-in minutes hh:mm:ss ----------------------------------------------------------------------------------------- CB1 0.28 0.64 188.79 0 08:00 0 0 0:00:00 CB10 0.11 0.23 198.07 0 08:00 0 0 0:00:00 CB2 0.18 0.45 189.32 0 08:01 0 0 0:00:00 CB3 0.13 0.26 195.24 0 08:01 0 0 0:00:00 CB4 0.20 0.43 196.88 0 08:01 0 0 0:00:00 CB5 0.27 0.60 197.34 0 08:01 0 0 0:00:00 CB6 0.25 0.59 197.52 0 08:01 0 0 0:00:00 CB7 0.22 0.54 197.64 0 08:01 0 0 0:00:00 CB9 0.18 0.39 197.83 0 08:00 0 0 0:00:00 EX-CB#1 1.85 5.00 166.46 0 00:00 0.00 0 0:00:00 EX-CB#2 0.25 0.55 171.98 0 08:01 0 0 0:00:00 EX-CB#3 0.23 0.52 183.98 0 08:00 0 0 0:00:00 EX-CB#4 0.20 0.49 189.19 0 08:00 0 0 0:00:00 ZURN 0.12 0.40 189.34 0 08:01 0 0 0:00:00 Out-01 2.39 2.39 163.14 0 00:00 0 0 0:00:00 ***************** Node Flow Summary ***************** ------------------------------------------------------------------------------------ Node Element Maximum Peak Time of Maximum Time of Peak ID Type Lateral Inflow Peak Inflow Flooding Flooding Inflow Occurrence Overflow Occurrence cfs cfs days hh:mm cfs days hh:mm ------------------------------------------------------------------------------------ CB1 JUNCTION 0.00 3.40 0 08:00 0.00 CB10 JUNCTION 0.25 0.25 0 08:00 0.00 CB2 JUNCTION 0.00 1.79 0 08:01 0.00 CB3 JUNCTION 0.33 1.60 0 08:01 0.00 CB4 JUNCTION 0.00 1.28 0 08:01 0.00 CB5 JUNCTION 0.18 1.29 0 08:00 0.00 CB6 JUNCTION 0.23 1.11 0 08:00 0.00 CB7 JUNCTION 0.22 0.88 0 08:00 0.00 CB9 JUNCTION 0.42 0.67 0 08:00 0.00 EX-CB#1 JUNCTION 0.24 4.21 0 08:01 1.77 0 00:00 EX-CB#2 JUNCTION 0.34 3.99 0 08:00 0.00 EX-CB#3 JUNCTION 0.26 3.66 0 08:00 0.00 Autodesk Storm and Sanitary Analysis EX-CB#4 JUNCTION 1.63 1.63 0 08:00 0.00 ZURN JUNCTION 0.19 0.19 0 08:00 0.00 Out-01 OUTFALL 0.00 4.21 0 08:01 0.00 *********************** Outfall Loading Summary *********************** ----------------------------------------------- Outfall Node ID Flow Average Peak Frequency Flow Inflow M cfs cfs ----------------------------------------------- Out-01 98.91 1.12 4.21 ----------------------------------------------- System 98.91 1.12 4.21 ***************** Link Flow Summary ***************** ------------------------------------------------------------------------------------------------- ------------------------------- Link ID Element Time of Maximum Length Peak Flow Design Ratio of Ratio of Total Reported Type Peak Flow Velocity Factor during Flow Maximum Maximum Time Condition Occurrence Attained Analysis Capacity /Design Flow Surcharged days hh:mm ft/sec cfs cfs Flow Depth minutes ------------------------------------------------------------------------------------------------- ------------------------------- Link-02 CONDUIT 0 08:00 8.56 1.00 3.66 7.16 0.51 0.54 0 Calculated Link-03 CONDUIT 0 08:01 6.08 1.00 3.98 6.93 0.57 0.78 0 Calculated Link-04 CONDUIT 0 08:01 5.37 1.00 4.21 3.48 1.21 1.00 1439 SURCHARGED Link-05 CONDUIT 0 08:00 1.21 1.00 0.25 2.18 0.11 0.31 0 Calculated Link-06 CONDUIT 0 08:00 1.86 1.00 0.67 2.18 0.30 0.46 0 Calculated Link-07 CONDUIT 0 08:01 2.27 1.00 1.11 2.21 0.50 0.60 0 Calculated Link-08 CONDUIT 0 08:01 3.16 1.00 1.28 2.18 0.59 0.51 0 Calculated Link-11 CONDUIT 0 08:01 5.35 1.00 1.28 4.19 0.31 0.34 0 Calculated Link-12 CONDUIT 0 08:00 1.91 1.00 0.88 2.15 0.41 0.57 0 Calculated Link-13 CONDUIT 0 08:01 6.36 1.00 1.60 10.79 0.15 0.36 0 Calculated Link-14 CONDUIT 0 08:01 4.08 1.00 1.79 7.27 0.25 0.55 0 Calculated Link-15 CONDUIT 0 08:00 7.22 1.00 3.40 5.22 0.65 0.58 0 Calculated Link-16 CONDUIT 0 08:00 3.56 1.00 1.63 5.25 0.31 0.56 0 Calculated Link-17 CONDUIT 0 08:00 0.83 1.00 0.19 1.05 0.18 0.64 0 Calculated Autodesk Storm and Sanitary Analysis Highest Flow Instability Indexes All links are stable. WARNING 107 Initial water surface elevation defined for Junction CB1 is below junction invert elevation. Assumed initial water surface elevation equal to invert elevation. WARNING 108 Surcharge elevation defined for Junction CB1 is below junction maximum elevation. Assumed surcharge elevation equal to maximum elevation. WARNING 107 : Initial water surface elevation defined for Junction CB10 is below junction invert elevation. Assumed initial water surface elevation equal to invert elevation. WARNING 108 : Surcharge elevation defined for Junction CB10 is below junction maximum elevation. Assumed surcharge elevation equal to maximum elevation. WARNING 107 Initial water surface elevation defined for Junction CB2 is below junction invert elevation. Assumed initial water surface elevation equal to invert elevation. WARNING 108 Surcharge elevation defined for Junction CB2 is below junction maximum elevation. Assumed surcharge elevation equal to maximum elevation. WARNING 107 Initial water surface elevation defined for Junction CB3 is below junction invert elevation. Assumed initial water surface elevation equal to invert elevation. WARNING 108 Surcharge elevation defined for Junction CB3 is below junction maximum elevation. Assumed surcharge elevation equal to maximum elevation. WARNING 107 Initial water surface elevation defined for Junction CB4 is below junction invert elevation. Assumed initial water surface elevation equal to invert elevation. WARNING 108 Surcharge elevation defined for Junction CB4 is below junction maximum elevation. Assumed surcharge elevation equal to maximum elevation. WARNING 107 Initial water surface elevation defined for Junction CB5 is below junction invert elevation. Assumed initial water surface elevation equal to invert elevation. WARNING 108 Surcharge elevation defined for Junction CB5 is below junction maximum elevation. Assumed surcharge elevation equal to maximum elevation. WARNING 107 Initial water surface elevation defined for Junction CB6 is below junction invert elevation. Assumed initial water surface elevation equal to invert elevation. WARNING 108 Surcharge elevation defined for Junction CB6 is below junction maximum elevation. Assumed surcharge elevation equal to maximum elevation. WARNING 107 Initial water surface elevation defined for Junction CB7 is below junction invert elevation. Assumed initial water surface elevation equal to invert elevation. WARNING 108 Surcharge elevation defined for Junction CB7 is below junction maximum elevation. Assumed surcharge elevation equal to maximum elevation. WARNING 107 Initial water surface elevation defined for Junction CB9 is below junction invert elevation. Assumed initial water surface elevation equal to invert elevation. WARNING 108 Surcharge elevation defined for Junction CB9 is below junction maximum elevation. Assumed surcharge elevation equal to maximum elevation. WARNING 107 : Initial water surface elevation defined for Junction EX-CB#1 is below junction invert elevation. Assumed initial water surface elevation equal to invert elevation. WARNING 108 : Surcharge elevation defined for Junction EX-CB#1 is below junction maximum elevation. Assumed surcharge elevation equal to maximum elevation. WARNING 107 : Initial water surface elevation defined for Junction EX-CB#2 is below junction invert elevation. Assumed initial water surface elevation equal to invert elevation. WARNING 108 : Surcharge elevation defined for Junction EX-CB#2 is below junction maximum elevation. Assumed surcharge elevation equal to maximum elevation. WARNING 107 : Initial water surface elevation defined for Junction EX-CB#3 is below junction invert elevation. Assumed initial water surface elevation equal to invert elevation. WARNING 108 : Surcharge elevation defined for Junction EX-CB#3 is below junction maximum elevation. Assumed surcharge elevation equal to maximum elevation. WARNING 107 : Initial water surface elevation defined for Junction EX-CB#4 is below junction invert elevation. Autodesk Storm and Sanitary Analysis Assumed initial water surface elevation equal to invert elevation. WARNING 108 : Surcharge elevation defined for Junction EX-CB#4 is below junction maximum elevation. Assumed surcharge elevation equal to maximum elevation. WARNING 107 : Initial water surface elevation defined for Junction ZURN is below junction invert elevation. Assumed initial water surface elevation equal to invert elevation. WARNING 108 : Surcharge elevation defined for Junction ZURN is below junction maximum elevation. Assumed surcharge elevation equal to maximum elevation. WARNING 116 : Conduit inlet invert elevation defined for Conduit Link-02 is below upstream node invert elevation. Assumed conduit inlet invert elevation equal to upstream node invert elevation. WARNING 117 : Conduit outlet invert elevation defined for Conduit Link-03 is below downstream node invert elevation. Assumed conduit outlet invert elevation equal to downstream node invert elevation. Analysis began on: Wed Oct 8 12:33:09 2025 Analysis ended on: Wed Oct 8 12:33:10 2025 Total elapsed time: 00:00:01 Autodesk Storm and Sanitary Analysis Profile Plot Main Street Storm Sewer 212- r----------------------------- ------------------- ------------------ -------------------- ------------------- ----------------I------------------------------------- -------------------T------------------ P O210 --------- ---------- ---------- ------------- -------------- ------------- -------------- ---------- - - - - - -------------- -------- ------------------------- --------------------------------- ------------- -------------- ------------- -------------- --------------------------------------------------------- --------- V 0 � W - ----------------------------- ----------- - --------------------------- --------------- 208- ----- ------------------ VV_L%_ ------------M --------------•---------------I-------------1.---------------I-------------I---------------I----------------------------I----------------------------I---------- L) 206- ------0.0----------------- Q X3- "I M. E P U', 0 ------------------ ----------------------------------------------------------------------------------------------------------------------------------------------------- H 0 ----r-r P-i------------R ----rr 10-----------r 4------------ ---------------------------------------r--------------- T I T ----------- N W '4 Link ID Link,05 w 0-irilk ID Link-06 -!�JR nk 16 E ink f 1--- -------- ----- ------- -------------- ---------------------------- -------------- ------------- -------------- ------------- -------------- ---------------------------- ---------------------------- --------- 204 ------V 9L Length 80-.W It----a--.ry I 0 .14 1 Link-4j!4w J� ink- lkink--W-c W A OL Aga 35.OQL :37.0(911t� Dia 12.00(in Dia 12.00 in Length t8.00 It Lbngth 80.00 ft a -A-*ID Link-13- -----4----------------r----------------------------------------------------------------------------------------------------------r---------------------------- ----------------------------4---------- 202 ------- ----Siope 0-.005b wit--------Src�p�-O 00- -------Dia 12.00 in '7bia 14.00 in--- --------bia-fibb-16------ 4 ;0 ft/ft Sh�pe 0 0049'A$e obm ft yt�,,t, 11:1 ;jAgth 50.00 e-ff A SI pe 0.01 Myt---:- -- - . , -------------------------------------------------- ----------------------------------------------------- ------------------ -Dia Q.004n:6'r -4--------------------- Dn Invert 197.1 eirt 113990 200 ------ Ili�Invert 19 .�4 It vent ert 196.45 If Slope Fl_ c� 9 , M OD 198 .9 Invert-1-94.9 .................. ---------------------- --- -------------------------------------------------------------------------------------------------------------------------------------------------- ert 188.8* a M 4.) 196--------- � W--- I ---i-A;� -ir n,--------------Ir----------------------X-W-c4T--------------r-------------I-------------- -------------I-------------- ---------------------------- ---------------------------- --------- W r- OD- eng h A Link ID Link-1 5 . _i: OD 19 ------- I in--------------Length 1-114-00 A---------------Q .. ............. ------------- -------------- ------------- -------------- ---------------------------- ---------------------------- --------- K Dia 1�2.00 in 5 4 ftfit : 0 192- ------ e -----------Slope OJ02116=------- 'cr .... --------- ---------------------------- ----------------------------I----------------I----------------------------*-----------------------------I---------- e 8 188.15 It 04 Link ID LInk-02 190 ------ I --------------T--------------I------L------ -------------- ---------------------------------------------------------T----------------------------11--------- ength 2�4.00 It lee- ------ ........Die 12,qq in----------- ------------- ---------------L-------------- -------------a--------------------------- ---------- Slope 0.0535 Wit 186 ------ --- .....Up Invert 183.42 ft :,---e-------- r ----------------------- ------------- ------------------------- ---------------------------- --------- Dn Invert 1711.43 ft 0 M 4) c) 184 ------- tj � V ---------------------------------------r----r-------X 0 ----------------------------T----------------------------I---------- -4 Lu P4 N r 182 ------- ------I-------------J. ----------------------------I----------------------------1.--------- A.W..k St-and S. yA-1yj. 180 ------- ------------- -------I------------------------------I-----------------------------I--------- 14 1 Link JD Link-03 178 ------ --------L---------- - - ------ ---------------------------- Lenglh 198.00 It Die 12.00 in 176 ------ ------------ --- - ------------------------ ------------ --------- Slope:0.0510 Itift .% p 0 'D Up Invbrt 171.43 ft L) . V 'a-- - ------------------ 174- ------ --------b n--in-Vid-1-61-.55_W---- ---------------X j � 04 V m 172 ------ ----- -------------- -------- 0 LO 170 ------ -----------------:1$--01 -------- -r-L- :4 a Lmk ID Link-Q40 ZD 168 ------ -------- ------ Leihgtli 96.0 it-A Die 12.00 i6 166 ------ _T_ e 0.0127 ft. 164 ------- _Z. p 161:46 n 162- ------- ---- Tail water elevation was set to the 1 00-Yea r 160 Storm event within the existing detention pond. ----- 159.44 Accounting 158 ------- for the datum shift of approx.3.7' ----- 1+00 1+50 3+00 3+50 4+1-11-1 41 u 5+00 5+50 5+1_1111 6+50 7+00 7+51-1 9+00 1 00-Year Elevation=159.44+3.7=163.14 1+_O 11+_dl Slalio I I tl I Node ID: CB10 CB9 C137 CB6 CH CB4 CK CB2 CB1 EX-CB113 EX_CB#2 EX-CB#f\ Out-01 Rim(ft): 200.61 200.79 200.69 200.36 199.78 200.66 198.34 193.391.97 188.78 176.20 166.46 Invert(ft): 197.84 197.44 197.10 196.93 196.74 196.45 194.98 188.888.15 183.46 171.43 161.46 160.75 Min Pipe Cover(ft): 1.77 2.35 2.59 2.43 2.04 3.21 2.36 3.342.82 4.32 3.77 4.00 Max HGL(ft): 198.07 197.83 197.64 197.52 197.34 196.88 195.24 189.3218.79 183.98 171.98 166.46 163.14 Link ID: Link-05 Link-06 Link-1 2 Link-07 Link-08 Link-1 1 Link-1 3 L nk-1 Link-1 5 Link-02 Link-03 Link-04 Length(ft): 80.00 68.00 35.00 37.00 58.00 80.00 50.00 3.0( 164.00 224.00 198.00 56.00 Dia(in): 12.00 12.00 12.00 12.00 12.00 12.00 12.00 2.0( 12.00 12.00 12.00 12.00 Slope(ft/ft): 0.0050 0.0050 0.0049 0.0051 0.0050 0.0184 0.1222 C 055 0.0286 0.0535 0.0510 0.0127 Up Invert(ft): 197.84 197.44 197.10 . 196.93 196.74 196.45 194.98 138.8 188.15 183.42 171.43 161.46 Dn Invert(ft): 197.44 197.10 196.93 196.74 196.45 194.98 188.87 138.1 i 183.46 171.43 161.33 160.75 Max Q 0.25 0.67 0.88 1.11 1.28 1.28 1.60 �.791 3.40 3.66 3.98 4.21 (cf:, �.081 7.22 8.56 6.08 Max Vel(ft,)! 1.21 1.86 1.91 2.27 3.16 5.35 6.36 F_ ::I_ 5.37 Max Depth(ft): 1 1 0.31 0.46 0.57 0.60 0.51 1 0.34 0.36 P.551 0.58 1 0.54 1 0.78 1.00 Tab 6 . 0 6.0 CONSTRUCTION STORMWATER POLLUTION PREVENTION PLAN A Construction Stormwater Pollution Prevention Plan is provided in this section. Refer to Figure 6.1. 24413.002-SSP.doc Figure 6. 1 Construction Stormwater Pollution Prevention Plan Construction Stormwater General Permit Stormwater Pollution Prevention Plan (SWPPP) for Visconsi Companies, LTD Prepared for: The Washington State Department of Ecology Northwest Regional Office 15700 Dayton Avenue N Shoreline, WA 98133 (206) 594-0000 Permittee / Owner Developer Operator/ Contractor Visconsi Companies, LTD Visconsi Companies, LTD TBD NWC 212th Street N.E. and Medical Center Drive Arlington, WA 98223 Certified Erosion and Sediment Control Lead (CESCL) Name Organization Contact Phone Number TBD TBD TBD SWPPP Prepared By Name Organization Contact Phone Number Alex White, P.E. Barghausen Consulting (425) 251-6222 Engineers, LLC. SWPPP Preparation Date October 3, 2025 Project Construction Dates Activity / Phase Start Date End Date TBD TBD TBD Table of Contents 1 Project Information.............................................................................................................. 4 1.1 Existing Conditions ...................................................................................................... 4 1.2 Proposed Construction Activities.................................................................................. 4 2 Construction Stormwater Best Management Practices (BMPs)........................................... 5 2.1 The 13 Elements.......................................................................................................... 6 2.1.1 Element 1: Preserve Vegetation / Mark Clearing Limits ........................................ 6 2.1.2 Element 2: Establish Construction Access............................................................ 7 2.1.3 Element 3: Control Flow Rates ............................................................................. 8 2.1.4 Element 4: Install Sediment Controls .................................................................... 9 2.1.5 Element 5: Stabilize Soils ....................................................................................10 2.1.6 Element 6: Protect Slopes....................................................................................11 2.1.7 Element 7: Protect Drain Inlets ............................................................................12 2.1.8 Element 8: Stabilize Channels and Outlets ..........................................................13 2.1.9 Element 9: Control Pollutants...............................................................................14 2.1.10 Element 10: Control Dewatering ..........................................................................16 2.1.11 Element 11: Maintain BMPs.................................................................................17 2.1.12 Element 12: Manage the Project..........................................................................18 2.1.13 Element 13: Protect Low Impact Development (LID) BMPs .................................19 3 Pollution Prevention Team.................................................................................................20 4 Monitoring and Sampling Requirements ............................................................................21 4.1 Site Inspection ............................................................................................................21 4.2 Stormwater Quality Sampling......................................................................................21 4.2.1 Turbidity Sampling ...............................................................................................21 4.2.2 pH Sampling ........................................................................................................24 5 Discharges to 303(d) or Total Maximum Daily Load (TMDL) Waterbodies .........................25 5.1 303(d) Listed Waterbodies..........................................................................................25 6 Reporting and Record Keeping..........................................................................................26 6.1 Record Keeping..........................................................................................................26 6.1.1 Site Log Book ......................................................................................................26 6.1.2 Records Retention ...............................................................................................26 6.1.3 Updating the SWPPP...........................................................................................26 6.2 Reporting....................................................................................................................27 6.2.1 Discharge Monitoring Reports (DMRs).................................................................27 6.2.2 Notification of Noncompliance..............................................................................27 Page I 1 List of Tables Table 1 — pH-Modifying Sources............................................................................................14 Table2 — Management............................................................................................................18 Table 3 —Team Information....................................................................................................20 Table 4—Turbidity Sampling Method....................................................................................21 Table 5 — pH Sampling Method ..............................................................................................24 List of Appendices Appendix/Glossary A. Site Map B. BMP Detail C. Site Inspection Form D. Engineering Calculations Page 12 List of Acronyms and Abbreviations Acronym /Abbreviation Explanation 303(d) Section of the Clean Water Act pertaining to Impaired Waterbodies BFO Bellingham Field Office of the Department of Ecology BMP(s) Best Management Practice(s) CESCL Certified Erosion and Sediment Control Lead COz Carbon Dioxide CRO Central Regional Office of the Department of Ecology CSWGP Construction Stormwater General Permit CWA Clean Water Act DMR Discharge Monitoring Report DO Dissolved Oxygen Ecology Washington State Department of Ecology EPA United States Environmental Protection Agency ERO Eastern Regional Office of the Department of Ecology ERTS Environmental Report Tracking System ESC Erosion and Sediment Control GUILD General Use Level Designation NPDES National Pollutant Discharge Elimination System NTU Nephelometric Turbidity Units NWRO Northwest Regional Office of the Department of Ecology pH Power of Hydrogen RCW Revised Code of Washington SPCC Spill Prevention, Control, and Countermeasure sU Standard Units SWMMEW Stormwater Management Manual for Eastern Washington SWMMWW Stormwater Management Manual for Western Washington SWPPP Stormwater Pollution Prevention Plan TESC Temporary Erosion and Sediment Control SWRO Southwest Regional Office of the Department of Ecology TMDL Total Maximum Daily Load VFO Vancouver Field Office of the Department of Ecology WAC Washington Administrative Code WSDOT Washington Department of Transportation WWHM Western Washington Hydrology Model Page 13 1 Project Information Project/Site Name: Arlington Medical Center Street/Location: NWC 212th St. NE and Medical Center City: Arlington State: WA Zip code: 98223 Subdivision: NA Receiving waterbody: Stillaguamish River 1.1 Existing Conditions Total acreage (including support activities such as off-site equipment staging yards, material storage areas, borrow areas). Total acreage: 2.37 acres Disturbed acreage: 2.49 acres Existing structures: The project site is undeveloped consisting of existing vegetation. Landscape The site slopes range from 1 to 50% sloping north to southeast. Topography: Drainage patterns: Runoff is assumed to either disperse into the existing soils or sheet flow into the existing public stormwater conveyance system. Existing Vegetation: The majority of the site consists of overgrown grass and shrubs. Critical Areas (wetlands, streams, high erosion This site is located outside of any critical risk, steep or difficult to stabilize slopes): areas. List of known impairments for 303(d) listed or Total Maximum Daily Load (TMDL) for the receiving waterbody: NA Currently no pollutants contaminants exist on-site. 1.2 Proposed Construction Activities Description of site development (example: subdivision): This project proposes a medical facility building, parking stalls, and landscaping. Description of construction activities (example: site preparation, demolition, excavation): Construction activities will include, clearing and grubbing entire site, grading, and excavations. Description of site drainage including flow from and onto adjacent properties. Must be consistent with Site Map in Appendix A: Drainage currently flows across the site from north to southeast or is infiltrated into the existing vegetation. Description of final stabilization (example: extent of revegetation, paving, landscaping): Final site stabilization will include paving and landscaping. Contaminated Site Information: Proposed activities regarding contaminated soils or groundwater (example: on-site treatment system, authorized sanitary sewer discharge): N/A Page 14 2 Construction Stormwater Best Management Practices (BMPs) The SWPPP is a living document reflecting current conditions and changes throughout the life of the project. These changes may be informal (i.e., hand-written notes and deletions). Update the SWPPP when the CESCL has noted a deficiency in BMPs or deviation from original design. Page 15 2.1 The 13 Elements 2.1.1 Element 1: Preserve Vegetation / Mark Clearing Limits List and describe BMPs: In order to protect adjacent properties and to reduce the area of soil exposed to construction, the limits of construction will be clearly marked and enclosed within a construction fence prior to any land disturbing activities. This fence will encompass all areas subject to construction, as well as delineate all areas where no construction is to take place. A silt fence will also be placed in certain areas as shown on the accompanying Site Plan, in order to protect the soil and vegetation outside the construction area. Refer to Appendix B: Construction BMPs for detailed drawings of the proposed BMPs. The proposed BMPs relevant to vegetation preservation/clearing limits are: • BMP C103: High Visibility Plastic or Metal Fence • BMP C233: Silt Fence Installation Schedules: BMPs listed above (Silt Fence and High Visibility Plastic or Metal Fence) will be installed prior to any land disturbing activity Inspection and Maintenance plan: Inspect weekly and after storm events. Provide maintenance as needed to ensure proper function of BMPs listed above. Responsible Staff: TBD. Page 16 2.1.2 Element 2: Establish Construction Access List and describe BMPs: In order to protect the adjacent existing asphalt pavement from dirt and debris, the project will construct a Construction Entrance. See Appendix A: Site Plan for the proposed location of the construction entrance. • BMP C105: Construction Access Installation Schedules: Construction Entrance shall be installed prior to the commencement of construction activities. Inspection and Maintenance plan: Inspect weekly and after storm events. Provide maintenance as needed to ensure proper function of BMPs listed above. Responsible Staff: TBD Page 17 2.1.3 Element 3: Control Flow Rates Will you construct stormwater retention and/or detention facilities? ❑ Yes® No Will you use permanent infiltration ponds or other low impact development (example: rain gardens, bio-retention, porous pavement) to control flow during construction? ❑ Yes® No List and describe BMPs: A sediment trap and rock check dams will be installed for purposes of controlling flow rates during construction. See Appendix A for the location of the sediment pond and rock check dams, Appendix B for detailed drawings of the proposed BMPs, and Appendix D for engineering calculations for the sediment pond. The proposed BMP relevant to flow control is: • BMP C240: Sediment Trap • BMP C207: Rock Check Dams Installation Schedules: The BMP listed above will be installed prior to any land disturbing activity. Inspection and Maintenance plan: Inspect weekly and after storm events. Provide maintenance as needed to ensure proper function of BMPs listed above. Responsible Staff: TBD Page 18 2.1.4 Element 4: Install Sediment Controls List and describe BMPs: On-site sediment contamination shall be controlled by the implementation of silt fences and/or straw wattles. Silt fences will be placed in the necessary areas where soil from the areas marked for excavation may interfere and contaminate with soils located either off site or adjacent. Moreover, wattles are suggested in disturbed area that require immediate erosion protection and on exposed soils during the period of short construction interruptions or over winter months. See Appendix A for the location of silt fences on site and Appendix B for detailed drawings of the proposed BMPs. The proposed BMP that will be installed for sediment control is: • BMP C233: Silt Fence • BMP C235: Wattles Installation Schedules: Sediment Controls will be installed prior to any land disturbance activity. Inspection and Maintenance plan: Inspect weekly and after storm events. Provide maintenance as needed to ensure proper function of BMPs listed above. Responsible Staff: TBD Page 19 2.1.5 Element 5: Stabilize Soils West of the Cascade Mountains Crest Season Dates Number of Days Soils Can be Left Exposed During the Dry Season May 1 — September 30 7 days During the Wet Season October 1 —April 30 2 days Soils must be stabilized at the end of the shift before a holiday or weekend if needed based on the weather forecast. Anticipated project dates: Start date: TBD End date: TBD Will you construct during the wet season? TBD List and describe BMPs: Soils exposed and unworked for the time period specified above shall be stabilized with the application of effective BMPs to prevent erosion throughout the duration of the project. Soil stockpiles shall be stabilized or covered using plastic sheeting and where possible, located away from storm inlets, waterways, and drainage channels. The practice of Dust Control is also recommended to prevent wind transport of dust onto roadways and drainage ways. Refer to Appendix B for detailed drawings of the BMPs used. The proposed BMPs specific to Soil Stabilization are: • BMP C123: Plastic Covering • BMP C140: Dust Control Installation Schedules: BMPs shall be implemented as soon as land disturbing activity begins and installed where applicable for the duration of the project. Inspection and Maintenance plan: Inspect weekly and after storm events. Provide maintenance as needed to ensure proper function of BMPs listed above. Responsible Staff: TBD Page 1 10 2.1.6 Element 6: Protect Slopes Will steep slopes be present at the site during construction? ® Yes❑ No List and describe BMPs: All cut and fill slopes will be designed, constructed, and protected in a manner that minimizes erosion. Temporary and permanent seeding shall be used at all exposed areas pursuant to the prior mentioned schedule (seasonal restrictions). Soil stockpiles shall be stabilized or covered using plastic sheeting and where possible, located away from storm inlets, waterways, and drainage channels. The proposed BMPs specific to Slope Protection are: • BMP C120: Temporary and Permanent Seeding • BMP C123: Plastic Covering Installation Schedules: BMPs shall be implemented as soon as land disturbing activity begins and installed where applicable for the duration of the project. Implementation of one or more of alternative BMPs may be necessary after the first sign that existing BMPs are ineffective or failing. Inspection and Maintenance plan: Inspect weekly and after storm events. Provide maintenance as needed to ensure proper function of BMPs listed above. Responsible Staff: TBD Page 1 11 2.1.7 Element 7: Protect Drain Inlets List and describe BMPs: All storm drain inlets, both existing and those installed during construction must be protected to prevent unfiltered or untreated water from entering the drainage conveyance system; however, the first priority is to keep all access roads clean of sediment and keep water from washing streets separate from entering storm drains until treatment can be provided. Storm Drain Inlet Protection will be implemented for all drainage inlets and culverts that could potentially be impacted by sediment-laden runoff on or near the project site. This includes inlets and culverts located offsite. Inlet protection devices shall be cleaned and replaced or removed when sediment has filled a third of the available storage (unless a different standard is specified by the product manufacturer). The following inlet protection measures will be proposed for this project: • BMP C220: Storm Drain Inlet Protection Installation Schedules: Storm Drain Inlet Protection will be provided at the start of the project and will be maintained for the duration of the project. Inspection and Maintenance plan: Inspect weekly and after storm events. Provide maintenance as needed to ensure proper function of BMPs listed above. Responsible Staff: TBD Page 112 2.1.8 Element 8: Stabilize Channels and Outlets Provide stabilization, including armoring material, adequate to prevent erosion of outlets, adjacent stream banks, slopes, and downstream reaches, will be installed at the outlets of all conveyance systems. List and describe BMPs: The project site is located west of the Cascade Mountain Crest. As such, where there are any temporary on-site conveyance channels,they shall be designed, constructed, and stabilized to prevent erosion from the expected peak 10-minute velocity of flow from a Type 1A, 10-year, 24-hour recurrence interval storm for the developed condition. An on-site sediment pond is proposed for this project along with a temporary conveyance channel, therefore an Outlet Control BMP is proposed. The following outlet protection measures will be proposed for this project: • BMP C209: Outlet Protection Installation Schedules: Outlet Protection will be provided at the start of the project and will be maintained for the duration of the project. Inspection and Maintenance plan: Inspect weekly and after storm events. Provide maintenance as needed to ensure proper function of BMPs listed above. Responsible Staff: TBD Page 113 2.1.9 Element 9: Control Pollutants List and describe BMPs: All pollutants, including waste materials and demolition debris, which occur on site will be handled and disposed of in a manner that does not cause contamination of stormwater. Good housekeeping and preventative measures will be taken to ensure that the site will be kept clean, well-organized, and free of debris. The following practices will be implemented: • All vehicles, equipment, and petroleum product storage/dispensing areas will be inspected regularly to detect any leaks or spills, and to identify maintenance needs to prevent leaks or spills. • In order to perform emergency repairs on site, temporary plastic will be placed beneath and, if raining, over the vehicle. • Any chemicals stored in the construction areas will conform to the appropriate source control BMPs listed in Volume IV of the Ecology stormwater manual. All chemicals shall have cover, containment, and protection provided on site, pursuant to BMP C153 for Material Delivery, Storage and Containment. Proposed BMPs applicable to Pollutant Control: • BMP C140: Dust Control • BMP C151: Concrete Handling • BMP C152: Sawcutting and Surface Pollution Prevention • BMP C153: Material Delivery, Storage, and Containment • BMP C154: Concrete Washout Area Installation Schedules: BMPs shall be installed as necessary to control pollutants for the duration of construction. Inspection and Maintenance plan: Inspect weekly and after storm events. Provide maintenance as needed to ensure proper function of BMPs listed above. Responsible Staff: Pennon Construction Will maintenance, fueling, and/or repair of heavy equipment and vehicles occur on-site? ❑ Yes® No Will wheel wash or tire bath system BMPs be used during construction? ® Yes❑ No Will pH-modifying sources be present on-site? ® Yes❑ No Table 1 — pH-Modifying Sources Page 114 ❑ None ® Bulk cement ❑ Cement kiln dust ❑ Fly ash ❑ Other cementitious materials ❑ New concrete washing or curing waters ❑ Waste streams generated from concrete grinding and sawing ❑ Exposed aggregate processes ❑ Dewatering concrete vaults ❑ Concrete pumping and mixer washout waters ❑ Recycled concrete ❑ Recycled concrete stockpiles ❑ Other (i.e., calcium lignosulfate) [please describe: ] Concrete trucks must not be washed out onto the ground, or into storm drains, open ditches, streets, or streams. Excess concrete must not be dumped on-site, except in designated concrete washout areas with appropriate BMPs installed. Will uncontaminated water from water-only based shaft drilling for construction of building, road, and bridge foundations be infiltrated provided the wastewater is managed in a way that prohibits discharge to surface waters? ❑ Yes❑ No Page 1 15 2.1.10 Element 10: Control Dewatering List and describe BMPs: • Discharge clean, non-turbid de-watering water, such as well-point groundwater, to systems tributary to, or directly into surface waters of the state, provided that the de- watering flow does not cause erosion or flooding of receiving waters or interfere with the operation of the system. Do not route clean dewatering water through stormwater sediment ponds. Note that "surface waters of the state" may exist on a construction site as well as off site; for example, a creek running through a site. • Highly turbid or contaminated dewatering water shall be handled separately from stormwater. • Clean, non-turbid dewatering water, such as well-point ground water, can be discharged to systems tributary to, or directly into surface waters of the state, provided the dewatering flow does not cause erosion or flooding of receiving waters. Clean dewatering water should not be routed through stormwater sediment ponds. • Other dewatering disposal options may include: o Transport off site in a vehicle, such as a vacuum flush truck, for legal disposal in a manner that does not pollute state waters. o Infiltration. o Ecology-approved on-site chemical treatment or other suitable treatment technologies. o Sanitary sewer discharge with local sewer district approval, if there is no other option. o Use of a sedimentation bag with outfall to a ditch or swale for small volumes of localized dewatering. Depending on the time of year, dewatering activities will occur during the installation of on-site stormwater conveyance systems and excavation activities. Installation Schedules: Dewatering controls will be installed prior to any significant excavation activities. Inspection and Maintenance plan: Inspect weekly and after storm events. Provide maintenance as needed to ensure proper function of BMPs listed above. Responsible Staff: TBD Page 1 16 2.1.11 Element 11: Maintain BMPs All temporary and permanent Erosion and Sediment Control (ESC) BMPs shall be maintained and repaired as needed to ensure continued performance of their intended function. Maintenance and repair shall be conducted in accordance with each particular BMP specification (see Volume 11 of the SWMMWW or Chapter 7 of the SWMMEW). Visual monitoring of all BMPs installed at the site will be conducted at least once every calendar week and within 24 hours of any stormwater or non-stormwater discharge from the site. If the site becomes inactive and is temporarily stabilized, the inspection frequency may be reduced to once every calendar month. All temporary ESC BMPs shall be removed within 30 days after final site stabilization is achieved or after the temporary BMPs are no longer needed. Trapped sediment shall be stabilized on-site or removed. Disturbed soil resulting from removal of either BMPs or vegetation shall be permanently stabilized. Additionally, protection must be provided for all BMPs installed for the permanent control of stormwater from sediment and compaction. BMPs that are to remain in place following completion of construction shall be examined and restored to full operating condition. If sediment enters these BMPs during construction, the sediment shall be removed and the facility shall be returned to conditions specified in the construction documents. Page 117 2.1.12 Element 12: Manage the Project The project will be managed based on the following principles: • Projects will be phased to the maximum extent practicable and seasonal work limitations will be taken into account. • Inspection and monitoring: o Inspection, maintenance and repair of all BMPs will occur as needed to ensure performance of their intended function. o Site inspections and monitoring will be conducted in accordance with Special Condition S4 of the CSWGP. Sampling locations are indicated on the Site Map. Sampling station(s) are located in accordance with applicable requirements of the CSWGP. • Maintain an updated SWPPP. o The SWPPP will be updated, maintained, and implemented in accordance with Special Conditions S3, S4, and S9 of the CSWGP. As site work progresses the SWPPP will be modified routinely to reflect changing site conditions. The SWPPP will be reviewed monthly to ensure the content is current. Table 2 — Management ® Design the project to fit the existing topography, soils, and drainage patterns ® Emphasize erosion control rather than sediment control ® Minimize the extent and duration of the area exposed ® Keep runoff velocities low ® Retain sediment on-site ® Thoroughly monitor site and maintain all ESC measures ® Schedule major earthwork during the dry season ❑ Other (please describe) Page 1 18 2.1.13 Element 13: Protect Low Impact Development (LID) BMPs The project does not propose any Low Impact Development BMPs to be implemented as part of this proposal. Page 119 3 Pollution Prevention Team Table 3—Team Information Title Names Phone Number Certified Erosion and TBD TBD Sediment Control Lead (CESCL) Resident Engineer Alex White, P.E. (425) 251-6222 Emergency Ecology Staff on Duty (425) 649-7130 Contact Emergency Permittee/ TBD TBD Owner Contact Non-Emergency Owner TBD TBD Contact Monitoring Personnel TBD TBD Ecology Regional Office Northwest Regional Office (206) 549-0000 Page 120 4 Monitoring and Sampling Requirements Monitoring includes visual inspection, sampling for water quality parameters of concern, and documentation of the inspection and sampling findings in a site log book. A site log book will be maintained for all on-site construction activities and will include: • A record of the implementation of the SWPPP and other permit requirements • Site inspections • Stormwater sampling data Create your own Site Inspection Form or use the Construction Stormwater Site Inspection Form found on Ecology's website. http://www.ecy.wa.gov/programs/wq/stormwater/construction/i ndex.htm I File a blank form under Appendix C. The site log book must be maintained on-site within reasonable access to the site and be made available upon request to Ecology or the local jurisdiction. Numeric effluent limits may be required for certain discharges to 303(d) listed waterbodies. See CSWGP Special Condition S8 and Section 5 of this template. 4.1 Site Inspection Site inspections will be conducted at least once every calendar week and within 24 hours following any discharge from the site. For sites that are temporarily stabilized and inactive, the required frequency is reduced to once per calendar month. The discharge point(s) are indicated on the Site Map (see Appendix A) and in accordance with the applicable requirements of the CSWGP. 4.2 Stormwater Quality Sampling 4.2.1 Turbidity Sampling Requirements include calibrated turbidity meter or transparency tube to sample site discharges for compliance with the CSWGP. Sampling will be conducted at all discharge points at least once per calendar week. Method for sampling turbidity: Check the analysis method you will use: Table 4—Turbidity Sampling Method ® Turbidity Meter/Turbidimeter (required for disturbances 5 acres or greater in size) ❑ Transparency Tube (option for disturbances less than 1 acre and up to 5 acres in size) Page 121 The benchmark for turbidity value is 25 nephelometric turbidity units (NTU) and a transparency less than 33 centimeters. If the discharge's turbidity is 26 to 249 NTU or the transparency is less than 33 cm but equal to or greater than 6 cm, the following steps will be conducted: 1. Review the SWPPP for compliance with Special Condition S9. Make appropriate revisions within 7 days of the date the discharge exceeded the benchmark. 2. Immediately begin the process to fully implement and maintain appropriate source control and/or treatment BMPs as soon as possible. Address the problems within 10 days of the date the discharge exceeded the benchmark. If installation of necessary treatment BMPs is not feasible within 10 days, Ecology may approve additional time when the Permittee requests an extension within the initial 10-day response period. 3. Document BMP implementation and maintenance in the site log book. If the turbidity exceeds 250 NTU or the transparency is 6 cm or less at any time, the following steps will be conducted: 1. Telephone or submit an electronic report to the applicable Ecology Region's Environmental Report Tracking System (ERTS) within 24 hours. • Central Region (Benton, Chelan, Douglas, Kittitas, Klickitat, Okanogan, Yakima): (509) 575-2490 or http://www.ecy.wa.gov/programs/spills/forms/nerts online/CRO nerts online.html • Eastern Region (Adams, Asotin, Columbia, Ferry, Franklin, Garfield, Grant, Lincoln, Pend Oreille, Spokane, Stevens, Walla Walla, Whitman): (509) 329-3400 orhttp://www.ecV.wa.gov/programs/spills/forms/nerts online/ERO nerts online.html • Northwest Region (King, Kitsap, Island, San Juan, Skagit, Snohomish, Whatcom): (425) 649-7000 or http://www.ecy.wa.gov/programs/spills/forms/nerts online/NWRO nerts online.html • Southwest Region (Clallam, Clark, Cowlitz, Grays Harbor, Jefferson, Lewis, Mason, Pacific, Pierce, Skamania, Thurston, Wahkiakum,): (360) 407-6300 or http://www.ecy.wa.gov/programs/spills/forms/nerts online/SWRO nerts online.html 2. Immediately begin the process to fully implement and maintain appropriate source control and/or treatment BMPs as soon as possible. Address the problems within 10 days of the date the discharge exceeded the benchmark. If installation of necessary treatment BMPs is not feasible within 10 days, Ecology may approve additional time when the Permittee requests an extension within the initial 10-day response period 3. Document BMP implementation and maintenance in the site log book. 4. Continue to sample discharges daily until one of the following is true: • Turbidity is 25 NTU (or lower). • Transparency is 33 cm (or greater). • Compliance with the water quality limit for turbidity is achieved. o 1 - 5 NTU over background turbidity, if background is less than 50 NTU Page 122 o 1% - 10% over background turbidity, if background is 50 NTU or greater • The discharge stops or is eliminated. Page 123 4.2.2 pH Sampling pH monitoring is required for "Significant concrete work" (i.e., greater than 1000 cubic yards poured concrete over the life of the project). The use of recycled concrete or engineered soils (soil amendments including but not limited to Portland cement-treated base [CTB], cement kiln dust [CKD] or fly ash) also requires pH monitoring. For significant concrete work, pH sampling will start the first day concrete is poured and continue until it is cured, typically three (3)weeks after the last pour. For engineered soils and recycled concrete, pH sampling begins when engineered soils or recycled concrete are first exposed to precipitation and continues until the area is fully stabilized. If the measured pH is 8.5 or greater, the following measures will be taken: 1. Prevent high pH water from entering storm sewer systems or surface water. 2. Adjust or neutralize the high pH water to the range of 6.5 to 8.5 su using appropriate technology such as carbon dioxide (CO2) sparging (liquid or dry ice). 3. Written approval will be obtained from Ecology prior to the use of chemical treatment other than CO2 sparging or dry ice. Method for sampling pH: Check the analysis method you will use: Table 5— pH Sampling Method ❑ pH meter ® pH test kit ❑ Wide range pH indicator paper Page 124 5 Discharges to 303(d) or Total Maximum Daily Load (TMDL) Waterbodies 5.1 303(d) Listed Waterbodies Circle the applicable answer, if necessary: Is the receiving water 303(d) (Category 5) listed for turbidity, fine sediment, phosphorus, or pH? ❑ Yes❑ No Page 125 6 Reporting and Record Keeping 6.1 Record Keeping This section does not need to be filled out. It is a list of reminders for the permittee. 6.1.1 Site Log Book A site log book will be maintained for all on-site construction activities and will include: • A record of the implementation of the SWPPP and other permit requirements • Site inspections • Sample logs 6.1.2 Records Retention Records will be retained during the life of the project and for a minimum of three (3) years following the termination of permit coverage in accordance with Special Condition S5.0 of the CSWGP. Permit documentation to be retained on-site: • CSWGP • Permit Coverage Letter • SWPPP • Site Log Book Permit documentation will be provided within 14 days of receipt of a written request from Ecology. A copy of the SWPPP or access to the SWPPP will be provided to the public when requested in writing in accordance with Special Condition S5.G.2.b of the CSWGP. 6.1.3 Updating the SWPPP The SWPPP will be modified if: • Found ineffective in eliminating or significantly minimizing pollutants in stormwater discharges from the site. • There is a change in design, construction, operation, or maintenance at the construction site that has, or could have, a significant effect on the discharge of pollutants to waters of the State. The SWPPP will be modified within seven (7) days if inspection(s) or investigation(s) determine additional or modified BMPs are necessary for compliance. An updated timeline for BMP implementation will be prepared. Page 126 6.2 Reporting 6.2.1 Discharge Monitoring Reports (DMRs) Discharge monitoring reports will be submitted to Ecology monthly. If there was no discharge during a give monitoring period the DMR will be submitted as required, reporting "No Discharge". The DM due date is fifteen (15) days following the end of each calendar month. 6.2.2 Notification of Noncompliance DMRs will be reported online through Ecology's WQWebDMR System. If any of the terms and conditions of the permit is not met, and the resulting noncompliance may cause a threat to human health or the environment, the following actions will be taken: 1. Ecology will be notified within 24-hours of the failure to comply by calling the applicable Regional office ERTS phone number (Regional office numbers listed below). 2. Immediate action will be taken to prevent the discharge/pollution or otherwise stop or correct the noncompliance. If applicable, sampling and analysis of any noncompliance will be repeated immediately and the results submitted to Ecology within five (5) days of becoming aware of the violation. 3. A detailed written report describing the noncompliance will be submitted to Ecology within five (5) days, unless requested earlier by Ecology. Anytime turbidity sampling indicates turbidity is 250 NTUs or greater, or water transparency is 6 cm or less, the Ecology Regional office will be notified by phone within 24 hours of analysis as required by Special Condition S5.A of the CSWGP. • Central Region at (509) 575-2490 for Benton, Chelan, Douglas, Kittitas, Klickitat, Okanogan, or Yakima County • Eastern Region at (509) 329-3400 for Adams, Asotin, Columbia, Ferry, Franklin, Garfield, Grant, Lincoln, Pend Oreille, Spokane, Stevens, Walla Walla, or Whitman County • Northwest Region at (425) 649-7000 for Island, King, Kitsap, San Juan, Skagit, Snohomish, or Whatcom County • Southwest Region at (360) 407-6300 for Clallam, Clark, Cowlitz, Grays Harbor, Jefferson, Lewis, Mason, Pacific, Pierce, Skamania, Thurston, or Wahkiakum Include the following information: 1. Your name and / Phone number 2. Permit number 3. City/ County of project 4. Sample results 5. Date /Time of call 6. Date /Time of sample 7. Project name Page 127 In accordance with Special Condition S4.D.5.b of the CSWGP, the Ecology Regional office will be notified if chemical treatment other than COz sparging is planned for adjustment of high pH water. Page 128 Appendix/Glossary A. Site Map B. BMP Detail C. Site Inspection Form D. Engineering Calculations Page 129 Appendix A Site Map ®- TESC CONSTRUCTION NOTES: TESC PLAN 1. APPROXIMATE LOCATION OF CONSTRUCTION STAGING AREA.CONTRACTOR TO TESC LEGEND: FOR USE THIS AREA FOR TEMPORARY STOCKPILE STORAGE AND CONCRETE WASHOUT.ADJUST SIZE AND LOCATION OF AREA AS NEEDED DURING MEDICAL CENTER CONSTRUCTION. SAWCUT LINE 2. INSTALL TEMPORARY CONSTRUCTION FENCE AND SITE ACCESS GATE)6' LIMITS OF DISTURBANCE SEC. 12,TWP. 31 N., RGE 5 E., W. M. HIGH-CHAINLINK WITH LOCKING DEVICE)AT TEMPORARY CONSTRUCTION ENTRANCE.SEE DETAILS/C2.2. SILT FENCE CITY OF ARLINGTON, SNOHOMISH COUNTY, WASHINGTON = Z Ir 3. APPROXIMATE LIMITS OF DISTURBANCE. TEMPORARY CONSTRUCTION FENCE I Q Q W ' 4. INSTALL AND MAINTAIN TEMPORARY SILT FENCE FOR DURATION OF ® TEMPORARY ROCK CHECK DAM ]I - _ _--s„r3 RuE) {(y8 Q Z W CONSTRUCTION ACTIVITIES.PLACEMENT6 OF SILT FENCE SHALL BE INSTALLED AS - J N Z Z SHOWN ON THIS PLAN OR AS DIRECTED BY CITY INSPECTOR.SEE DETAIL 3/C2.2. ® CATCH BASIN PROTECTION 4'�' - 5. CONSTRUCT TEMPORARY CONSTRUCTION ENTRANCE.COORDINATE PLACEMENT --� w w •_ =w w-w w wy =w--_ ��o :) U = ULLJ F_ WITH CITY INSPECTOR.MOVE TEMPORARY CONSTRUCTION ENTRANCE AS p6\ 6 „� �s'e'. 0 15' 30' 60' 1--- J NECESSARY OVER COURSE OF CONSTRUCTION.SEE DETAIL 1/C2.2. _ N89°3T�39' - S'EXISTING DRAINAGE EASEMENT PER_ asp., 6 W N Q J 200407265279 6. INSTALL TEMPORARY INLET SEDIMENT PROTECTION AT ALL EXISTING AND AFN/ ° ~ .SCALE:1 U NOT INCLUDED IN TITLE REPORT U Q Q PROPOSED CATCH BASINS AS NECESSARY TO PREVENT SILT-LADEN WATER FROM ENTERING STORM DRAINAGE SYSTEM PER BMP C220 OF THE 2024 SWMMWW AND _ _ N89°3211E 80 74'_ ___ ___ _ " 6 / Iy CWC WSDOT STD PLAN 1.40.20-00.COORDINATE PLACEMENT WITH PROPERTY =- - /zw ?66'rpp33 Z G i OWNERS AND AS DIRECTED BY CITY INSPECTOR.SEE DETAIL 2 AND 8/C2.2. _ P o_z sc rr / p60 7. PROPOSED SEDIMENT TRAP PER BMP C240 OF THE 2024 SWMMWW.MINIMUM AREA OF THE TRAP SHALL BE 2,770 SF.CONTRACTOR TO ENSURE MAXIMUM SIDE 8--- - Rape Sr Po SLOPE OF SEDIMENT TRAP 15 3H:1V.SEE DETAIL 7/C2.2. 1'' 2 / w<a7j�SOp�O'' TOP ELEVATION:190.00 ° BOTTOM ELEVATION:186.50 J /a 1Z. r- l � 6 0 8. TEMPORARY DITCH.SEE DETAIL 6/C2.2. 9. APPROXIMATE LOCATION OF TEMPORARY ROCK CHECK DAM PER BMP C207 OF g % o J THE 2024 SWMMWW.SEE DETAIL 4/C2.2. ` < \\\\\ ss\ \ �� o W 6 / �� �qb�\ J fV LLI 6 d," Q > o LLT 9A am 50 ° 2 U Ed w V) < �io 4 I� 1 1 z Z d U U W 6 �p I >` 5 O d / I III Ln DUST CONTROL NOTES: 0_ - ^' _// �/ I I I I I I 3 w 14 6 o CONTRACTOR SHALL DETERMINE THE APPLICABILITY OF DUST CONTROL AND APPLY Ni I p�-� / o I I I o APPROPRIATE DUST CONTROL MEASURES AS NEEDED. I �\ o r 0 9 581 1N 112. /� I I I I _N - 19 ^o 1. WATER ALL ACTIVE CONSTRUCTION AREAS AT LEAST TWICE DAILY. I I / v./ —� �� g 0 / II I I I I I I I D w II pP WAByF L o �/ 2. WATER OR COVER STOCKPILES OF DEBRIS,SOIL,SAND OR OTHER MATERIALS THAT : oy 1 I p o - CANBEBLOWNBYTHEWIND. .u� I --------- _ 3. COVER ALL TRUCKS HAULING SOIL,SAND,AND OTHER LOOSE MATERIALS OR I'm° \ b 3 /I,"� / I I I 9 I I '� rn I 21036]]] e REQUIRE ALL TRUCKS TO MAINTAIN AT LEASTTWO FEETOFFREEBOARD. -� I IN '� / / �lO �� v /I / / I I I I I : F� Z o ,V� S/ONAL I(CAUTION I I EN 4. SWEEP DAILY(PREFERABLY WITH WATER SWEEPERS)ALL PAVED ACCESS ROADS, ° n I / OV' Q �� 0 1 I IT7�18 PARKING AREAS AND STAGING AREAS AT CONSTRUCTION SITES. REFER 70 HELICOPTER // 10/1/25 5. SWEEP STREETS DAILY(PREFERABLY WITH WATER SWEEPERS)IF VISIBLE SOIL ' PAD PROTECTION NOTE O - �— - / / I I I I ' MATERIAL IS CARRIED ONTO ADJACENT PUBLIC STREETS. L7.1 I / / THIS SHEET. 0 -aQ �� /� I I III I 9 _ �� O 578°3335'W 57.E 6. CITY STREETS ARE TO BE KEPT CLEAR OF DIRT AND DEBRIS AT ALL TIMES DURING NI I Q + } 0 d 0 0� CONSTRUCTION.DUST SUPPRESSION AND STREET CLEANING MUST OCCUR AS DIRECTED BY THE PUBLIC WORKS INSPECTOR. ��� EROSION CONTROL NOTES 1. ALL NECESSARY EQUIPMENT AND MATERIALS SHALL BE AVAILABLE ON SITE TOI FACILITATE RAPID INSTALLATION OF EROSION AND SEDIMENT CONTROL BMPS —��/ / �� I WHEN RAIN IS IMMINENT. � " V. . I ,qb/ J I 2 \ w I w 2. THE CONTRACTOR SHALL RESTORE ALL EROSION CONTROL DEVICES TO I ' WORKING ORDER TO THE SATISFACTION OF THE AUTHORITY HAVING N -U ! �/ __-.�/ TOP JURISDICTION AFTER EACH RUN-OFF PRODUCING RAINFALL. /� b `�\ o - ��/ .. \ J I I 4 I J tCc 1 / q4- I 3 �; 3. THE CONTRACTOR SHALL INSTALL ADDITIONAL EROSION CONTROL MEASURES AS I—� o -� i1 \ \ J� i �... N 3 MAY BE REQUIRED BY THE AUTHORITY HAVING JURISDICTION DUE TO �° �I �"' "�"' 7 H I o UNCOMPLETED GRADING OPERATIONS OR UNFORESEEN CIRCUMSTANCES WHICH 21 X32 GAS REGULATOR _ / H.1 BTM._O I I ; 0 L H:1V� J MAY ARISE. I STATION EASEMENT T - 9� ��� - 'AFN 9207230118 ___ N / EMERGENCY �190� 6 •� N 4. ADEQUATE EROSION AND SEDIMENT CONTROL AND PERIMETER PROTECTION / �— 6 6 _ 7 �19 OVERFLOW SPILLWAY �� 1 LU C BEST MANAGEMENT PRACTICE MEASURES MUST BE INSTALLED AND MAINTAINED. v 1 __1 - /� C M Pwro—Pccro P:o �} - � O) — ro —Prom - _ - - C Q 5. CONTRACTOR TO IMPLEMENT SLOPE STABILIZATION MEASURES AS NECESSARY , ° ° c—c-c—o- N89"5814Y✓343.66' _ - N89°5814 W 213.74' °itW� 8 75 -�"c c-cc c c c __ 'XS'POWER EASEMENT z =_ _ 1U P AFN 9207230118--- - so-so i3 - - - "S 1 10'POWER EASEMENT AF SEWER EASEMENT _c v _\ C Q 00 FOR EXPOSED SLOPES DURING CONSTRUCTION.MEASURES CAN INCLUDE AFN 92072301, CAUTION AFN 200407265279 ` ° c c w-r± TEMPORARY AND PERMANENT SEEDING PER DOE BMP C120. N -- - - -- "TO BE RELEASED _ I I CATO TIOEAD __ N �—- =AFN 9 2 072 3 011 8 ffi=_ 3 t II II ` 6 � —so— o—so 3 I1 I! N 6.. - 3 C Ln4in I A _ _ s _ _1 2 T H S T N E �sa9°581a E 13os.69' _ _�T _ c fV SEDIMENT CONTROL NOTE, POWER PROTECTION IXISTING GAS MAIN.REFER ROW CENTERLINE I m V w Y 0 19/ 6 B 192/ TO GAS MAIN PROTECTION 0b ^qC. 1/ y 1Q, _,(y---- -- -_--- ' NOTE THIS SHEET. A CONTRACTOR TO MAINTAIN SEDIMENT CONTROL BMP'S TO ENSURE THAT THE SITE CONTAINS ALL / __ NOTE THIS SHEET - ___ -- _s�-- -_ _-- __'� __ ------------- WHAT _ SURFACE STORM WATER RUNOFF AND SEDIMENT. ADDITIONAL TESC CONTROL MAY BE REQUIRED. __ --- ._ �_-�_ -_- - � HAS BEEN DEPICTED ON THESE PLANS IS ONLY THE MINIMUM REQUIRED TO CONTAIN SILT LADEN STORM WATER.CONTRACTOR MAY BE REQUIRED TO MODIFY OR IMPLEMENT ADDITIONAL TESC ` v CONTROLS THROUGHOUT CONSTRUCTION. s UTILITY CONFLICT NOTE: TEMPORARY EXCAVATION SLOPE NOTE: CITY OFARLINGTON THE CONTRACTOR SHALL BE RESPONSIBLE FOR VERIFYING THE LOCATION,DIMENSION,AND DEPTH CONTRACTOR TO ENSURE TEMPORARY SLOPES HAVE A MAXIMUM SLOPE INCLINATION OF GAS MAIN PROTECTION NOTE: CONSTRUCTION DRAWING REVIEW APPROVAL $ OF ALL EXISTING UTILITIES WHETHER SHOWN ON THESE PLANS OR NOT BY POTHOLING THE 1.5H:1V.CONTRACTOR TO REFER TO THE GEOTECHNICAL ENGINEERING STUDY % UTILITIES AND SURVEYING THE HORIZONTAL AND VERTICAL LOCATION PRIOR TO CONSTRUCTION. l., PREPARED BY TERRA ASSOCIATES,INC.DATED AUGUST 19,2025 FOR EXCAVATION AND THE EXISTING GAS MAIN SHALL BE PROTECTED TO REMAIN.CONTRACTOR TO THIS PLAN SHEET HAS BEEN REVIEWED AND APPROVED PER THE THIS SHALL INCLUDE CALLING UTILITY LOCATE AT 81148 HOURS IN ADVANCE AND THEN POTHOLING p Know what's b@IOW. SLOPE REQUIREMENTS. POTHOLE EXISTING GAS MAIN TO VERIFY THE HORIZONTAL AND VERTICAL LOCATION. CONDITIONS ON THE TITLE SHEET. ALL OF THE EXISTING UTILITIES AT LOCATIONS OF NEW UTILITY CROSSINGS TO PHYSICALLY VERIFY C111 before you dig. OVERHEAD POWER PROTECTION NOTE: RESEEDING NOTE: HELICOPTER PAD PROTECTION NOTE: BY: E _M M M WHETHER OR NOT CONFLICTS EXIST.LOCATIONS OF SAID UTILITIES AS SHOWN ON THESE PLANS ARE Dial 811 ALL EXPOSED GROUND MUST BE RESEEDED WITHIN 30 DAYS OF THE COMPLETION OF THE CONTRACTOR SHALL ENSURE THE EXISTING HELICOPTER PAD 15 PROTECTED DURING Development Services Manager o S BASED UPON THE UNVERIFIED PUBLIC INFORMATION AND ARE SUBJECT TO VARIATION.IF CONFLICTS THE CONTRACTOR SHALL CONTACT SNOHOMISH COUNTY PUD PRIOR TO CONSTRUCTION CONSTRUCTION.IF RESEEDING IS NOT PRACTICAL DUE TO WEATHER OR SEASON CONSTRUCTION.THE HELICOPTER PAD WILL REMAIN IN USE DURING CONSTRUCTION AND SHOULD OCCUR,THE CONTRACTOR SHALL NOTIFY BARGHAUSEN CONSULTING ENGINEERS,LLC.TO TO CONFIRM OVERHEAD POWER CLEARANCE REQUIREMENTS,AND ANY RESTRICTIONS OR RESTRAINTS,THE GROUND MUST BE COVERED WITH MULCH AS DIRECTED BY THE THEREFORE,THE CONTRACTOR SHALL ENSURE CONSTRUCTION DOES NOT INTERFERE WITH DATE: THIS APPROVAL VALID FOR 18 MONTHS lV RESOLVE ALL PROBLEMS PRIOR TO PROCEEDING WITH CONSTRUCTION. REQUIREMENTS RELATING TO GRADING ACTIVITIES. N $ CITY ENGINEER. THE OPERATION OF THE HELICOPTER PAD. TESC DETAILS FOR MEDICAL CENTER SEC. 12,TWP. 31 N., RGE 5 E., W. M. CITY OF ARLINGTON, SNOHOMISH COUNTY, WASHINGTON - Z Ir cl) Figure 11-3.1:Stabilized Construction Access Figure 11-3.17:Block and Gravel Filter Figure 11-3.22:Silt Fence Figure 11.4.16:Rock Check Dam J LU Z tY NOT TO SCALE A Q LLJ Drain grate Jotmsin geotexfl.fab6caha11 be View Looking Upstream W N Z 0 spliced at posts.Use staples,wire rings LLJ '�•.° or egamatem m anaen rabrc o pose A 6 �` Q U ~ oo��$° Co is ale block Reny�- We�o ° 2 k2'by 14 G e or equ vakm, 1P• �I(U.Sm) U N J Z '�1Y .•.Q O� standardat ngtn fabrk uses "so mm) �n Q LLjP9�Gad :Q°s 4�g Gravel bacll Note ✓,/7A•i0.em)C / ff V�J VC14 Q Q Key yaame ao mlentala mnmummie�lt LLJ s ° ������ .O• o.sm to tfimarounddarn Z .op I I ( ) preven A z AOa °o �• ?ice, ° ry Section A-A /J JA Minimum J II tr may —I / 4'k4'trench lu 24•(0 .1 1 ) Post spacing may be increased c Plan View to 8'nwire backing is used p equivalent Install driuewar 2•Y2•Hood poste,steel ------- culven inhere is a fence Data,or roadside ditch present 4"-8"quarry Conoreteblock lhlre screen or \��/j spells filter fabric CD Grovel backfill Ov BaloN wat P-ding height Q M 2 X2•by 14 Ga.wire or equivalent, Geotextile Water •� 8 standard strength fabric used LLJ inlet \�\//\����/ /'� \\ Spacing Between Check Dams � — 1 GeDtextik fabric NIT vv/v� v ��/� .�/i\✓ �\\ 2•ram •L•=1ne distance such that points w T 'A'and'B'are of equal elevation. Z 0 Notes: J \ 15'min. L' Q > 0 1. Driveway span meal \\\I,/ Section A-A \/� PcinrB• J 12'minimum thickness Back6Il trench wfh / Pdm'A' d the requirements of the "\ ` m LL native soil or Y4•- pennining agency. Notes: /• - 1. Drop inlet sediment baniers are to be used for small,Hearty level drainage areas.(less 1.5'washed gravel \'12'min /\\�\ Q Z Y 2. Itre recommended that Providefullwidth than 5%) /�'/\/\//\/.' \ \ the access be crowned of in ss/e Minimum \\�\ \/\/./j�,/,/ ,( _— U gre grass t E---teabasinofsugicient sizeadjacemtothedmpinlet. 4'x4^trench " `l` \j�\�\\/�\\ _ �r1 so that mnog drains off area 3- The top of the slmcture(ponding hag ht)must be well below the ground elevation V the Pad. downslope to prevent runoff from bypassing the inlet.Atemporary dike may be Z 2'k2•wood posts,sleet Q LLJ necessary on the downsbpe side of the atmaure. NOT TO SCALE fence p eq osts,or uivalem NOT TO SCALE NOT TO SCALE O Z = d � V vUio a Stabilized Construction Access Block and Gravel Filter Silt Fence Rock Check Dam QL > o Revised June 2018 Revised June 2016 Revised July 2017 {� o DEPARTMENT OF DEPARTMENT OF DEPARTMENT OF DEPARTMENT OF M ECOLOGY pl ease see hnplAAvw.ecy. gw1bop"ht.hhmforcopyrightnmkeincludingWamissions, ECOLOGY pleases-e UpYA ..ec.vm. /co hthfMform htnotceincludin ECOLOGY ECOLOGY p' y gov pyTlg pyrig gpermissbns, Pleasiono httplNmw.d di.we.go/pyTlghthmgforcopynght notice including permissbns, Stale of Washington Revised June 2016 State of Washington limkatbn of liability,and dixleimer. State of Washington limitation of liability,and disclaimer. Stale of Washington limitation or liability,end disclaimer. PVEX -%W H/TF OF CONSTRUCTION ACCESS INLET PROTECTION 3 SILT FENCE a ROCK CHECK DAM C2.2 SCALE:NTS Cz.2 SCALE:NITS Cz.z SCALE:NTS \a.2,j SCALE:NITS 1-5/8"0-D.GALVANIZED Figure 11-4.26:Cross Section of Sediment Trap /STEP 9O HF 10SO' �e AF. O STRETCHER BAR(NP) a, DRAINAGE GRATE SS/OVA L ENG 4 GRATE -RECTANGULAR GRATE SHOWN RETRIEVAL SYSTEM(TYP.) DRAINAGE GRATE TRIM 10/1/25 GRATE FRAME 0 Ti D \SEDIMENT AND DEBRIS {7\ d of a a OVERFLOW BYPASS Surface area determined v BELOW INLET GRATE DEVICE p U o � at top of war II.4'Merin. tI g \\*~ j��,y\/• %\\ \\ �\\\ 1'Min. Overlbw 2 X 2 MESH 11 GAUGE MIN PROVIDE _ _ 1,Min I FILTERED BELOW INLET GRATE DEVICE OVERFLOW BYPASS CONCRETE BLOCK SECURE ATTACHMENT AROUND ENTIRE �— T ———S�� - - WATER t�Tt J pE MIN 80 LBS J 8 FENCE PANEL T 7'Min. C L 3.5'-5' 5 TEMPORARY CONSTRUCTION FENCE Fiat �-- d '�" STATE OF ' Washed gravel MSHINGTON A� t D2.2 SCALE:NT$ Discharge b �V �Q REGISTERED Note:Trap may be formed by bean or by Georl mil mn yadiced A A LANDSCAPE ARCHITECT s�w N partial or complete excevation. 2'-4-Rode outleLco level -01 spreader MARK W.MAURER lU Rip Rap 0 0 ISOMETRIC VIEW CERTIFICATE NO.DODS98 C LUCal _ NOTES N DO N =III- nNX 1. Size the Below Inlet Grate Device(BIGD)for the storm water structure it ill service. STORM DRAIN SECTION VIEW 1:y 1'• w t y MdX F INLET PROTECTION 0) w i C to w 2. The BIGD shall have abuilt-in high-flow relief system(overflow bypass). C NOT scuE STANDARD PLAN I-40.20-00 N O —III— 3. The retrieval system must allow removal of the BIGD without spilling the SHEET 1 OF 1 SHEET m U Y\t a Collected material. APPROVED FOR PUBLICATION 4_ Perform maintenance in accordance with Standard Specification B-01.3(15). Pasco BakodCh It/ 09-2"7 s TEMPORARY"T DITCH NOT TO SCALE _ s*n osaox voixa a \ c2.2 SCALE:NIS ..a B WSDOT INLET PROTECTION �we n„aan sa.D.P>mw„alT myaMm 3 Cross Section of Sediment Trap Cz'2 SCALE: CITY OFARLINGTON CONSTRUCTION DRAWING REVIEW APPROVAL S DEPARTMENT OF ECOLOGY THIS PLAN SHEET HAS BEEN REVIEWED AND APPROVED PER THE State of Washington Revised June 2016 CONDITIONS ON THE TITLE SHEET. _ M M BY: SEDIMENT TRAP E M Development Services Manager N o S C2.2 SCALE:NiS DATE: THIS APPROVAL VALID FOR 18 MONTHS o lV N $ Appendix B BMP Detail burying and smothering vegetation. . Vegetative buffer zones for streams, lakes or other waterways shall be established by the local permitting authority or other state or federal permits or approvals. Maintenance Standards Inspect the area frequently to make sure flagging remains in place and the area remains undis- turbed. Replace all damaged flagging immediately. Remove all materials located in the buffer area that may impede the ability of the vegetation to act as a filter. BMP C103: High-Visibility Fence Purpose High-visibility fencing is intended to: . Restrict clearing to approved limits. • Prevent disturbance of sensitive areas,their buffers,and other areas required to be left undis- turbed. • Limit construction traffic to designated construction entrances, exits,or internal roads. • Protect areas where marking with survey tape may not provide adequate protection. Conditions of Use To establish clearing limits plastic,fabric,or metal fence may be used: . At the boundary of sensitive areas,their buffers, and other areas required to be left uncleared. . As necessary to control vehicle access to and on the site. Design and Installation Specifications High-visibility plastic fence shall be composed of a high-density polyethylene material and shall beat least four feet in height. Posts for the fencing shall be steel or wood and placed every 6 feet on center (maximum)or as needed to ensure rigidity.The fencing shall be fastened to the post every six inches with a polyethylene tie. On long continuous lengths of fencing, a tension wire or rope shall be used as a top stringer to prevent sagging between posts.The fence color shall be high-visibility orange.The fence tensile strength shall be 360 Ibs/ft using the ASTM D4595 testing method. If appropriate install fabric silt fence in accordance with BMP C233: Silt Fence to act as high-visibility fence. Silt fence shall be at least 3 feet high and must be highly visible to meet the requirements of this BMP. Metal fences shall be designed and installed according to the manufacturer's specifications. Metal fences shall be at least 3 feet high and must be highly visible. Fences shall not be wired or stapled to trees. 2019 Stormwater Management Manual for Western Washington Volume//-Chapter 3-Page 274 Maintenance Standards If the fence has been damaged or visibility reduced, it shall be repaired or replaced immediately and visibility restored. BMP C105: Stabilized Construction Access Purpose Stabilized construction accesses are established to reduce the amount of sediment transported onto paved roads outside the project site by vehicles or equipment.This is done by constructing a sta- bilized pad of quarry spalls at entrances and exits for project sites. Conditions of Use Construction accesses shall be stabilized wherever traffic will be entering or leaving a construction site if paved roads or other paved areas are within 1,000 feet of the site. For residential subdivision construction sites, provide a stabilized construction access for each res- idence, rather than only at the main subdivision entrance. Stabilized surfaces shall be of sufficient length/width to provide vehicle access/parking, based on lot size and configuration. On large commercial, highway, and road projects,the designer should include enough extra mater- ials in the contract to allow for additional stabilized accesses not shown in the initial Construction SWPPP. It is difficult to determine exactly where access to these projects will take place; additional materials will enable the contractor to install them where needed. Design and Installation Specifications See Figure I I-3.1: Stabilized Construction Access for details. Note:the 1 00'minimum length of the access shall be reduced to the maximum practicable size when the size or configuration of the site does not allow the full length (100'). Construct stabilized construction accesses with a 12-inch thick pad of 4-inch to 8-inch quarry spalls, a 4-inch course of asphalt treated base(ATB),or use existing pavement. Do not use crushed con- crete, cement, or calcium chloride for construction access stabilization because these products raise pH levels in stormwater and concrete discharge to waters of the State is prohibited. A separation geotextile shall be placed under the spalls to prevent fine sediment from pumping up into the rock pad.The geotextile shall meet the standards listed in Table I I-3.2: Stabilized Con- struction Access Geotextile Standards. Table II-3.2: Stabilized Construction Access Geotextile Standards Geotextile Property Required Value Grab Tensile Strength(ASTM D4751) 200 psi min. 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 275 Table II-3.2: Stabilized Construction Access Geotextile Standards (continued) Geotextile Property Required Value Grab Tensile Elongation(ASTM D4632) 30% max. Mullen Burst Strength(ASTM D3786-80a) 400 psi min. AOS(ASTM D4751) 20-45(U.S. standard sieve size) . Consider early installation of the first lift of asphalt in areas that will be paved;this can be used as a stabilized access.Also consider the installation of excess concrete as a stabilized access. During large concrete pours, excess concrete is often available for this purpose. • Fencing (see BMP C103: High-Visibility Fence)shall be installed as necessary to restrict traffic to the construction access. . Whenever possible,the access shall be constructed on a firm, compacted subgrade.This can substantially increase the effectiveness of the pad and reduce the need for maintenance. . Construction accesses should avoid crossing existing sidewalks and back of walk drains if at all possible. If a construction access must cross a sidewalk or back of walk drain,the full length of the sidewalk and back of walk drain must be covered and protected from sediment leaving the site. Alternative Material Specification WSDOT has raised safety concerns about the Quarry Spall rock specified above.WSDOT observes that the 4-inch to 8-inch rock sizes can become trapped between Dually truck tires, and then released off-site at highway speeds.WSDOT has chosen to use a modified specification for the rock while continuously verifying that the Stabilized Construction Access remains effective.To remain effective,the BMP must prevent sediment from migrating off site.To date,there has been no per- formance testing to verify operation of this new specification.Jurisdictions may use the alternative specification, but must perform increased off-site inspection if they use,or allow others to use, it. Stabilized Construction Accesses may use material that meets the requirements of WSDOT's Stand- ard Specifications for Road, Bridge, and Municipal Construction Section 9-03.9(1) (WSDOT, 2016) for ballast except for the following special requirements. The grading and quality requirements are listed in Table II-3.3: Stabilized Construction Access Alternative Material Requirements. Table II-3.3: Stabilized Construction Access Alternative Material Requirements Sieve Size Percent Passing 2'/2" 99-100 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 276 Table II-3.3: Stabilized Construction Access Alternative Material Requirements (continued) Sieve Size Percent Passing 2" 65-100 3/4" 40-80 No. 4 5 max. No. 100 0-2 % Fracture 75 min. . All percentages are by weight. . The sand equivalent value and dust ratio requirements do not apply. . The fracture requirement shall beat least one fractured face and will apply the combined aggregate retained on the No.4 sieve in accordance with FOP for AASHTO T 335. Maintenance Standards Quarry spalls shall be added if the pad is no longer in accordance with the specifications. . If the access is not preventing sediment from being tracked onto pavement,then alternative measures to keep the streets free of sediment shall be used.This may include replace- ment/cleaning of the existing quarry spalls, street sweeping,an increase in the dimensions of the access,or the installation of BMP C106:Wheel Wash. . Any sediment that is tracked onto pavement shall be removed by shoveling or street sweep- ing.The sediment collected by sweeping shall be removed or stabilized on site.The pavement shall not be cleaned by washing down the street,except when high efficiency sweeping is inef- fective and there is a threat to public safety. If it is necessary to wash the streets,the con- struction of a small sump to contain the wash water shall be considered.The sediment would then be washed into the sump where it can be controlled. • Perform street sweeping by hand or with a high efficiency sweeper. Do not use a non-high effi- ciency mechanical sweeper because this creates dust and throws soils into storm systems or conveyance ditches. . Any quarry spalls that are loosened from the pad,which end up on the roadway shall be removed immediately. . If vehicles are entering or exiting the site at points other than the construction access(es), BMP C103: High-Visibility Fence shall be installed to control traffic. 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 277 Upon project completion and site stabilization, all construction accesses intended as per- manent access for maintenance shall be permanently stabilized. 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 278 Figure 11-3.1: Stabilized Construction Access NOT TO SCALE a �X�St�rg boa � 100'min. Install driveway culvert if there is a roadside ditch present 4"-8"quarry spat is Geotextile Notes: 15'min. 1. Driveway shall meet the requirements of the 12"minimum thickness permitting agency. 2. It is recommended that Provide full width the access be crowned of ingress/egress so that runoff drains off area the pad. Stabilized Construction Access Revised June 2018 DEPARTMENT OF ECOLOGY Please see http:Owww.ecy.wa.gov/copyrrghthtml for copyright notice including permissions, State of Washington limitation of liability,and disclaimer. 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 279 Crushed rock, gravel base, etc.,shall be added as required to maintain a stable driving surface and to stabilize any areas that have eroded. Following construction,these areas shall be restored to pre-construction condition or better to pre- vent future erosion. Perform street cleaning at the end of each day or more often if necessary. BMP C120: Temporary and Permanent Seeding Purpose Seeding reduces erosion by stabilizing exposed soils.A well-established vegetative cover is one of the most effective methods of reducing erosion. Conditions of Use Use seeding throughout the project on disturbed areas that have reached final grade or that will remain unworked for more than 30 days. The optimum seeding windows for western Washington are April 1 through June 30 and September 1 through October 1. Between July 1 and August 30 seeding requires irrigation until 75 percent grass cover is established. Between October 1 and March 30 seeding requires a cover of mulch or an erosion control blanket until 75 percent grass cover is established. Review all disturbed areas in late August to early September and complete all seeding by the end of September. Otherwise,vegetation will not establish itself enough to provide more than average pro- tection. Mulch is required at all times for seeding because it protects seeds from heat, moisture loss, and transport due to runoff. Mulch can be applied on top of the seed or simultaneously by hydroseeding. See BMP C121: Mulching for specifications. Seed and mulch all disturbed areas not otherwise vegetated at final site stabilization. Final sta- bilization means the completion of all soil disturbing activities at the site and the establishment of a permanent vegetative cover, or equivalent permanent stabilization measures(such as pavement, riprap, gabions, or geotextiles)which will prevent erosion. See BMP T5.13: Post-Construction Soil Quality and Depth. Design and Installation Specifications General . Install channels intended for vegetation before starting major earthwork and hydroseed with a Bonded Fiber Matrix. For vegetated channels that will have high flows, install erosion control blankets over the top of hydroseed. Before allowing water to flow in vegetated channels, establish 75 percent vegetation cover. If vegetated channels cannot be established by seed 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 284 before water flow; install sod in the channel bottom—over top of hydromulch and erosion con- trol blankets. . Confirm the installation of all required surface water control measures to prevent seed from washing away. • Hydroseed applications shall include a minimum of 1,500 pounds per acre of mulch with 3 per- cent tackifier. See BMP C 121: Mulching for specifications. . Areas that will have seeding only and not landscaping may need compost or meal-based mulch included in the hydroseed in order to establish vegetation. Re-install native topsoil on the disturbed soil surface before application. See BMP T5.13: Post-Construction Soil Quality and Depth. . When installing seed via hydroseeding operations, only about 1/3 of the seed actually ends up in contact with the soil surface.This reduces the ability to establish a good stand of grass quickly.To overcome this, consider increasing seed quantities by up to 50 percent. • Enhance vegetation establishment by dividing the hydromulch operation into two phases: • Phase 1- Install all seed and fertilizer with 25-30 percent mulch and tackifier onto soil in the first lift. • Phase 2- Install the rest of the mulch and tackifier over the first lift. Or, enhance vegetation by: • Installing the mulch, seed,fertilizer, and tackifier in one lift. • Spread or blow straw over the top of the hydromulch at a rate of 800-1000 pounds per acre. • Hold straw in place with a standard tackifier. Both of these approaches will increase cost moderately but will greatly improve and enhance vegetative establishment.The increased cost may be offset by the reduced need for: • Irrigation. • Reapplication of mulch. • Repair of failed slope surfaces. This technique works with standard hydromulch (1,500 pounds per acre minimum)and Bon- ded Fiber Matrix/Mechanically Bonded Fiber Matrix(BFM/MBFMs)(3,000 pounds per acre minimum). Seed may be installed by hand if: • Temporary and covered by straw, mulch,or topsoil. • Permanent in small areas(usually less than 1 acre)and covered with mulch,topsoil, or erosion blankets. . The seed mixes listed in Table 11-3.4:Temporary and Permanent Seed Mixes include 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 285 recommended mixes for both temporary and permanent seeding. . Apply these mixes,with the exception of the wet area seed mix, at a rate of 120 pounds per acre.This rate can be reduced if soil amendments or slow-release fertilizers are used.Apply the wet area seed mix at a rate of 60 pounds per acre. . Consult the local suppliers or the local conservation district for their recommendations.The appropriate mix depends on a variety of factors, including location, exposure,soil type,slope, and expected foot traffic.Alternative seed mixes approved by the local authority may be used, depending on the soil type and hydrology of the area. Table 11-3.4: Temporary and Permanent Seed Mixes Common Name Latin Name % Weight % Purity % Germination Temporary Erosion Control Seed Mix A standard mix for areas requiring a temporary vegetative cover. Chewings or Festuca rubra var. annual blue grass commutata or Poa 40 98 90 anna Perennial rye Lolium perenne 50 98 90 Redtop or colonial Agrostis alba or 5 92 85 bentgrass Agrostis tenuis White dutch clover Trifolium repens 5 98 90 Landscaping Seed Mix A recommended mix for landscaping seed. Perennial rye blend Lolium perenne 70 98 90 Chewings and red Festuca rubra var. fescue blend commutata or Fes- 30 98 90 tuca rubra Low-Growing Turf Seed Mix A turf seed mix for dry situations where there is no need for watering. This mix requires very little main- tenance. Dwarf tall fescue Festuca arundin- 45 98 90 (several varieties) acea var. Dwarf perennial Lolium perenne 30 98 90 rye(Barclay) var. barclay Red fescue Festuca rubra 20 98 90 Colonial bentgrass Agrostis tenuis 5 98 90 Bioswale Seed Mix A seed mix for bioswales and other intermittently wet areas. Tall or meadow fes- Festuca arundin- 75-80 98 90 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 286 Table II-3.4: Temporary and Permanent Seed Mixes (continued) Common Name Latin Name % Weight % Purity % Germination acea or Festuca cue elatior Seaside/Creeping Agrostis palustris 10-15 92 85 bentgrass Redtop bentgrass Agrostis alba or 5-10 90 80 Agrostis gigantea Wet Area Seed Mix A low-growing, relatively non-invasive seed mix appropriate for very wet areas that are not regulated wet- lands. Consult Hydraulic Permit Authority(H PA)for seed mixes if applicable. Tall or meadow fes- Festuca arundin- acea or Festuca 60-70 98 90 cue elatior Seaside/Creeping Agrostis palustris 10-15 98 85 bentgrass Meadow foxtail Alepocurus praten- 10-15 90 80 s/s Alsike clover Trifolium hybridum 1-6 98 90 Redtop bentgrass Agrostis alba 1-6 92 85 Meadow Seed Mix A recommended meadow seed mix for infrequently maintained areas or non-maintained areas where col- onization by native plants is desirable. Likely applications include rural road and utility right-of-way. Seed- ing should take place in September or very early October in order to obtain adequate establishment prior to the winter months. Consider the appropriateness of clover, a fairly invasive species, in the mix.Amending the soil can reduce the need for clover. Redtop or Oregon Agrostis alba or bentgrass Agrostis ore- 20 92 85 gonensis Red fescue Festuca rubra 70 98 90 White dutch clover Trifolium repens 10 98 90 Roughening and Rototilling . The seedbed should be firm and rough. Roughen all soil no matter what the slope.Track walk slopes before seeding if engineering purposes require compaction. Backblading or smoothing of slopes greater than 4H:1 V is not allowed if they are to be seeded. • Restoration-based landscape practices require deeper incorporation than that provided by a simple single-pass rototilling treatment.Wherever practical, initially rip the subgrade to improve long-term permeability, infiltration, and water inflow qualities.At a minimum, 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 287 permanent areas shall use soil amendments to achieve organic matter and permeability per- formance defined in engineered soil/landscape systems. For systems that are deeper than 8 inches complete the rototilling process in multiple lifts, or prepare the engineered soil system per specifications and place to achieve the specified depth. Fertilizers . Conducting soil tests to determine the exact type and quantity of fertilizer is recommended. This will prevent the over-application of fertilizer. • Organic matter is the most appropriate form of fertilizer because it provides nutrients(includ- ing nitrogen, phosphorus, and potassium) in the least water-soluble form. . In general, use 10-4-6 N-P-K(nitrogen-phosphorus-potassium)fertilizer at a rate of 90 pounds per acre.Always use slow-release fertilizers because they are more efficient and have fewer environmental impacts. Do not add fertilizer to the hydromulch machine, or agit- ate, more than 20 minutes before use. Too much agitation destroys the slow-release coating. . There are numerous products available that take the place of chemical fertilizers. These include several with seaweed extracts that are beneficial to soil microbes and organisms. If 100 percent cottonseed meal is used as the mulch in hydroseed, chemical fertilizer may not be necessary. Cottonseed meal provides a good source of long-term, slow-release, available nitrogen. Bonded Fiber Matrix and Mechanically Bonded Fiber Matrix • On steep slopes use Bonded Fiber Matrix(BFM)or Mechanically Bonded Fiber Matrix (MBFM) products.Apply BFM/MBFM products at a minimum rate of 3,000 pounds per acre with approximately 10 percent tackifier.Achieve a minimum of 95 percent soil coverage during application. Numerous products are available commercially. Most products require 24-36 hours to cure before rainfall and cannot be installed on wet or saturated soils. Generally, products come in 40-50 pound bags and include all necessary ingredients except for seed and fertilizer. • Install products per manufacturer's instructions. • BFMs and MBFMs provide good alternatives to blankets in most areas requiring vegetation establishment.Advantages over blankets include: • BFM and MBFMs do not require surface preparation. • Helicopters can assist in installing BFM and MBFMs in remote areas. • On slopes steeper than 2.5H:1 V, blanket installers may require ropes and harnesses for safety. • Installing BFM and MBFMs can save at least$1,000 per acre compared to blankets. 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 288 BMP C123: Plastic Covering Purpose Plastic covering provides immediate,short-term erosion protection to slopes and disturbed areas. Conditions of Use Plastic covering may be used on disturbed areas that require cover measures for less than 30 days, except as stated below. • Plastic is particularly useful for protecting cut and fill slopes and stockpiles. However,the rel- atively rapid breakdown of most polyethylene sheeting makes it unsuitable for applications greater than six months. • Due to rapid runoff caused by plastic covering, do not use this method upslope of areas that might be adversely impacted by concentrated runoff. Such areas include steep and/or unstable slopes. • Plastic sheeting may result in increased runoff volumes and velocities, requiring additional on- site measures to counteract the increases. Creating a trough with wattles or other material can convey clean water away from these areas. . To prevent undercutting,trench and backfill rolled plastic covering products. . Although the plastic material is inexpensive to purchase,the cost of installation, maintenance, removal, and disposal add to the total costs of this BMP. . Whenever plastic is used to protect slopes, install water collection measures at the base of the slope.These measures include plastic-covered berms,channels,and pipes used to convey clean rainwater away from bare soil and disturbed areas. Do not mix clean runoff from a plastic covered slope with dirty runoff from a project. • Other uses for plastic include: • Temporary ditch liner. • Pond liner in temporary sediment pond. • Liner for bermed temporary fuel storage area if plastic is not reactive to the type of fuel being stored. • Emergency slope protection during heavy rains. • Temporary drainpipe("elephant trunk")used to direct water. Design and Installation Specifications Plastic slope cover must be installed as follows: 1. Run plastic up and down the slope, not across the slope. 2. Plastic maybe installed perpendicular to a slope if the slope length is less than 10 feet. 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 298 3. Provide a minimum of 8-inch overlap at the seams. 4. On long or wide slopes, or slopes subject to wind,tape all seams. 5. Place plastic into a small (12-inch wide by 6-inch deep)slot trench at the top of the slope and backfill with soil to keep water from flowing underneath. 6. Place sand filled burlap or geotextile bags every 3 to 6 feet along seams and tie them together with twine to hold them in place. 7. Inspect plastic for rips,tears, and open seams regularly and repair immediately.This prevents high velocity runoff from contacting bare soil,which causes extreme erosion. 8. Sandbags may be lowered into place tied to ropes. However, all sandbags must be staked in place. • Plastic sheeting shall have a minimum thickness of 0.06 millimeters. . If erosion at the toe of a slope is likely, a gravel berm, riprap, or other suitable protection shall be installed at the toe of the slope in order to reduce the velocity of runoff. Maintenance Standards . Torn sheets must be replaced and open seams repaired. . Completely remove and replace the plastic if it begins to deteriorate due to ultraviolet radi- ation. . Completely remove plastic when no longer needed. • Dispose of old tires used to weight down plastic sheeting appropriately. Approved as Functionally Equivalent Ecology has approved products as able to meet the requirements of this BMP. The products did not pass through the Technology Assessment Protocol—Ecology(TAPE) process. Local jurisdictions may choose not to accept these products, or may require additional testing prior to consideration for local use. Products that Ecology has approved as functionally equivalent are available for review on Ecology's website at: https:Hecology.wa.gov/Regulations-Permits/Guidance-technical-assistance/Stormwater-per- mittee-guidance-resources/Emerging-stormwater-treatment-technologies BMP C124: Sodding Purpose The purpose of sodding is to establish turf for immediate erosion protection and to stabilize drainage paths where concentrated overland flow will occur. 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 299 BMP C140: Dust Control Purpose Dust control prevents wind transport of dust from disturbed soil surfaces onto roadways, drainage ways,and surface waters. Conditions of Use Use dust control in areas(including roadways)subject to surface and air movement of dust where on-site or off-site impacts to roadways, drainage ways, or surface waters are likely. Design and Installation Specifications . Vegetate or mulch areas that will not receive vehicle traffic. In areas where planting, mulching, or paving is impractical, apply gravel or landscaping rock. • Limit dust generation by clearing only those areas where immediate activity will take place, leaving the remaining area(s) in the original condition. Maintain the original ground cover as long as practical. • Construct natural or artificial windbreaks or windscreens.These may be designed as enclos- ures for small dust sources. • Sprinkle the site with water until the surface is wet. Repeat as needed. To prevent carryout of mud onto the street, refer to BMP C105: Stabilized Construction Access and BMP C106: Wheel Wash. . Irrigation water can be used for dust control. Irrigation systems should be installed as a first step on sites where dust control is a concern. • Spray exposed soil areas with a dust palliative,following the manufacturer's instructions and cautions regarding handling and application. Used oil is prohibited from use as a dust sup- pressant. Local governments may approve other dust palliatives such as calcium chloride or PAM. • PAM (BMP C126: Polyacrylamide(PAM)for Soil Erosion Protection)added to water at a rate of 0.5 pounds per 1,000 gallons of water per acre and applied from a water truck is more effect- ive than water alone.This is due to increased infiltration of water into the soil and reduced evaporation. In addition,small soil particles are bonded together and are not as easily trans- ported by wind.Adding PAM may reduce the quantity of water needed for dust control. Note that the application rate specified here applies to this BMP, and is not the same application rate that is specified in BMP C 126: Polyacrylamide(PAM)for Soil Erosion Protection, but the downstream protections still apply. Refer to BMP C126: Polyacrylamide(PAM)for Soil Erosion Protection for conditions of use. PAM shall not be directly applied to water or allowed to enter a water body. • Contact your local Air Pollution Control Authority for guidance and training on other dust con- trol measures. Compliance with the local Air Pollution Control Authority constitutes 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 313 compliance with this BMP. . Use vacuum street sweepers. . Remove mud and other dirt promptly so it does not dry and then turn into dust. . Techniques that can be used for unpaved roads and lots include: • Lower speed limits. High vehicle speed increases the amount of dust stirred up from unpaved roads and lots. • Upgrade the road surface strength by improving particle size, shape, and mineral types that make up the surface and base materials. • Add surface gravel to reduce the source of dust emission. Limit the amount of fine particles(those smaller than .075 mm)to 10 to 20 percent. • Use geotextile fabrics to increase the strength of new roads or roads undergoing recon- struction. • Encourage the use of alternate, paved routes, if available. • Apply chemical dust suppressants using the admix method, blending the product with the top few inches of surface material. Suppressants may also be applied as surface treatments. • Limit dust-causing work on windy days. • Pave unpaved permanent roads and other trafficked areas. Maintenance Standards Respray area as necessary to keep dust to a minimum. BMP C150: Materials on Hand Purpose Keep quantities of erosion prevention and sediment control materials on the project site at all times to be used for regular maintenance and emergency situations such as unexpected heavy rains. Hav- ing these materials on-site reduces the time needed to replace existing or implement new BMPs when inspections indicate that existing BMPs are not meeting the Construction SWPPP require- ments. In addition, contractors can save money by buying some materials in bulk and storing them at their office or yard. Conditions of Use . Construction projects of any size or type can benefit from having materials on hand.A small commercial development project could have a roll of plastic and some gravel available for immediate protection of bare soil and temporary berm construction.A large earthwork project, such as highway construction, might have several tons of straw, several rolls of plastic,flexible 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 314 pipe,sandbags, geotextile fabric and steel"T" posts. • Materials should be stockpiled and readily available before any site clearing,grubbing,or earthwork begins.A large contractor or project proponent could keep a stockpile of materials that are available for use on several projects. . If storage space at the project site is at a premium,the contractor could maintain the materials at their office or yard.The office or yard must be less than an hour from the project site. Design and Installation Specifications Depending on project type, size, complexity, and length, materials and quantities will vary.A good minimum list of items that will cover numerous situations includes: . Clear Plastic, 6 mil • Drainpipe, 6 or 8 inch diameter . Sandbags,filled . Straw Bales for mulching . Quarry Spalls . Washed Gravel . Geotextile Fabric . Catch Basin Inserts . Steel"T"Posts • Silt fence material . Straw Wattles Maintenance Standards . All materials with the exception of the quarry spalls,steel"T" posts,and gravel should be kept covered and out of both sun and rain. • Re-stock materials as needed. BMP C151 : Concrete Handling Purpose Concrete work can generate process water and slurry that contain fine particles and high pH, both of which can violate water quality standards in the receiving water. Concrete spillage or concrete dis- charge to waters of the State is prohibited. Use this BMP to minimize and eliminate concrete, con- crete process water, and concrete slurry from entering waters of the State. 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 315 Conditions of Use Any time concrete is used, utilize these management practices. Concrete construction project com- ponents include, but are not limited to: . Curbs • Sidewalks • Roads • Bridges . Foundations • Floors • Runways Disposal options for concrete, in order of preference are: 1. Off-site disposal 2. Concrete wash-out areas(see BMP C 154: Concrete Washout Area) 3. De mini mus washout to formed areas awaiting concrete Design and Installation Specifications . Wash concrete truck drums at an approved off-site location or in designated concrete washout areas only. Do not wash out concrete trucks onto the ground (including formed areas awaiting concrete), or into storm drains,open ditches,streets, or streams. Refer to BMP C 154: Concrete Washout Area for information on concrete washout areas. o Return unused concrete remaining in the truck and pump to the originating batch plant for recycling. Do not dump excess concrete on site,except in designated concrete washout areas as allowed in BMP C 154: Concrete Washout Area. . Wash small concrete handling equipment(e.g. hand tools, screeds, shovels, rakes,floats, trowels, and wheelbarrows)into designated concrete washout areas or into formed areas awaiting concrete pour. . At no time shall concrete be washed off into the footprint of an area where an infiltration fea- ture will be installed. . Wash equipment difficult to move, such as concrete paving machines, in areas that do not dir- ectly drain to natural or constructed stormwater conveyance or potential infiltration areas. • Do not allow washwater from areas, such as concrete aggregate driveways,to drain directly (without detention or treatment)to natural or constructed stormwater conveyances. . Contain washwater and leftover product in a lined container when no designated concrete washout areas(or formed areas, allowed as described above)are available. Dispose of con- tained concrete and concrete washwater(process water) properly. 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 316 . Always use forms or solid barriers for concrete pours, such as pilings,within 15-feet of surface waters. • Refer to BMP C252:Treating and Disposing of High pH Water for pH adjustment require- ments. • Refer to the Construction Stormwater General Permit(CSWGP)for pH monitoring require- ments if the project involves one of the following activities: Significant concrete work(as defined in the CSWGP). The use of soils amended with(but not limited to)Portland cement-treated base, cement kiln dust or fly ash. Discharging stormwater to segments of water bodies on the 303(d)list(Category 5)for high pH. Maintenance Standards Check containers for holes in the liner daily during concrete pours and repair the same day. BMP C152: Sawcutting and Surfacing Pollution Prevention Purpose Sawcutting and surfacing operations generate slurry and process water that contains fine particles and high pH (concrete cutting), both of which can violate the water quality standards in the receiving water. Concrete spillage or concrete discharge to waters of the State is prohibited. Use this BMP to minimize and eliminate process water and slurry created through sawcutting or surfacing from enter- ing waters of the State. Conditions of Use Utilize these management practices anytime sawcutting or surfacing operations take place. Saw- cutting and surfacing operations include, but are not limited to: . Sawing • Coring . Grinding • Roughening • Hydro-demolition . Bridge and road surfacing 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 317 Design and Installation Specifications . Vacuum slurry and cuttings during cutting and surfacing operations. . Slurry and cuttings shall not remain on permanent concrete or asphalt pavement overnight. . Slurry and cuttings shall not drain to any natural or constructed drainage conveyance includ- ing stormwater systems.This may require temporarily blocking catch basins. • Dispose of collected slurry and cuttings in a manner that does not violate ground water or sur- face water quality standards. • Do not allow process water generated during hydro-demolition, surface roughening or similar operations to drain to any natural or constructed drainage conveyance including stormwater systems. Dispose of process water in a manner that does not violate ground water or surface water quality standards. . Handle and dispose of cleaning waste material and demolition debris in a manner that does not cause contamination of water. Dispose of sweeping material from a pick-up sweeper at an appropriate disposal site. Maintenance Standards Continually monitor operations to determine whether slurry, cuttings, or process water could enter waters of the state. If inspections show that a violation of water quality standards could occur, stop operations and immediately implement preventive measures such as berms, barriers, secondary containment, and/or vacuum trucks. BMP C153: Material Delivery, Storage, and Containment Purpose Prevent, reduce, or eliminate the discharge of pollutants to the stormwater system or watercourses from material delivery and storage. Minimize the storage of hazardous materials on-site, store mater- ials in a designated area, and install secondary containment. Conditions of Use Use at construction sites with delivery and storage of the following materials: • Petroleum products such as fuel, oil and grease . Soil stabilizers and binders(e.g., Polyacrylamide) . Fertilizers, pesticides and herbicides . Detergents . Asphalt and concrete compounds 2019 Stormwater Management Manual for Western Washington Volume//-Chapter 3-Page 318 • Hazardous chemicals such as acids, lime, adhesives, paints,solvents, and curing compounds . Any other material that maybe detrimental if released to the environment Design and Installation Specifications . The temporary storage area should be located away from vehicular traffic, near the con- struction entrance(s), and away from waterways or storm drains. • Safety Data Sheets(SDS)should be supplied for all materials stored. Chemicals should be kept in their original labeled containers. . Hazardous material storage on-site should be minimized. • Hazardous materials should be handled as infrequently as possible. • During the wet weather season(Oct 1 —April 30), consider storing materials in a covered area. • Materials should be stored in secondary containments,such as an earthen dike, horse trough, or even a children's wading pool for non-reactive materials such as detergents, oil,grease, and paints. Small amounts of material may be secondarily contained in"bus boy"trays or con- crete mixing trays. • Do not store chemicals, drums, or bagged materials directly on the ground. Place these items on a pallet and,when possible,within secondary containment. . If drums must be kept uncovered, store them at a slight angle to reduce ponding of rainwater on the lids to reduce corrosion. Domed plastic covers are inexpensive and snap to the top of drums, preventing water from collecting. • Liquids, petroleum products, and substances listed in 40 CFR Parts 110, 117, or 302 shall be stored in approved containers and drums and shall not be overfilled. Containers and drums shall be stored in temporary secondary containment facilities. . Temporary secondary containment facilities shall provide for a spill containment volume able to contain 10%of the total enclosed container volume of all containers,or 110%of the capa- city of the largest container within its boundary,whichever is greater. . Secondary containment facilities shall be impervious to the materials stored therein for a min- imum contact time of 72 hours. • Sufficient separation should be provided between stored containers to allow for spill cleanup and emergency response access. • During the wet weather season(Oct 1 —April 30), each secondary containment facility shall be covered during non-working days, prior to and during rain events. • Keep material storage areas clean, organized and equipped with an ample supply of appro- priate spill clean-up material (spill kit). . The spill kit should include,at a minimum: 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 319 1-Water Resistant Nylon Bag 3-Oil Absorbent Socks 3"x 4' 2-Oil Absorbent Socks 3"x 10' 12-Oil Absorbent Pads 17"x19" 1-Pair Splash Resistant Goggles o 3-Pair Nitrile Gloves 10-Disposable Bags with Ties Instructions Maintenance Standards . Secondary containment facilities shall be maintained free of accumulated rainwater and spills. In the event of spills or leaks, accumulated rainwater and spills shall be collected and placed into drums.These liquids shall be handled as hazardous waste unless testing determines them to be non-hazardous. • Re-stock spill kit materials as needed. BM C154: Concrete Washout Area Purpose Prevent or reduce the discharge of pollutants from concrete waste to stormwater by conducting washout off-site, or performing on-site washout in a designated area. Conditions of Use Concrete washout areas are implemented on construction projects where: . Concrete is used as a construction material . It is not possible to dispose of all concrete wastewater and washout off-site(ready mix plant, etc.). . Concrete truck drums are washed on-site. Note that auxiliary concrete truck components(e.g. chutes and hoses)and small concrete handling equipment(e.g. hand tools, screeds, shovels, rakes,floats,trowels, and wheel- barrows)may be washed into formed areas awaiting concrete pour. At no time shall concrete be washed off into the footprint of an area where an infiltration feature will be installed. 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 320 Design and Installation Specifications Implementation • Perform washout of concrete truck drums at an approved off-site location or in designated con- crete washout areas only. • Do not wash out concrete onto non-formed areas,or into storm drains,open ditches,streets, or streams. . Wash equipment difficult to move, such as concrete paving machines, in areas that do not dir- ectly drain to natural or constructed stormwater conveyance or potential infiltration areas. . Do not allow excess concrete to be dumped on-site, except in designated concrete washout areas as allowed above. . Concrete washout areas may be prefabricated concrete washout containers,or self-installed structures(above-grade or below-grade). • Prefabricated containers are most resistant to damage and protect against spills and leaks. Companies may offer delivery service and provide regular maintenance and disposal of solid and liquid waste. . If self-installed concrete washout areas are used, below-grade structures are preferred over above-grade structures because they are less prone to spills and leaks. • Self-installed above-grade structures should only be used if excavation is not practical. . Concrete washout areas shall be constructed and maintained in sufficient quantity and size to contain all liquid and concrete waste generated by washout operations. Education • Discuss the concrete management techniques described in this BMP with the ready-mix con- crete supplier before any deliveries are made. • Educate employees and subcontractors on the concrete waste management techniques described in this BMP. . Arrange for the contractor's superintendent or Certified Erosion and Sediment Control Lead (CESCL)to oversee and enforce concrete waste management procedures. . A sign should be installed adjacent to each concrete washout area to inform concrete equip- ment operators to utilize the proper facilities. Contracts Incorporate requirements for concrete waste management into concrete supplier and subcontractor agreements. 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 321 Location and Placement • Locate concrete washout areas at least 50 feet from sensitive areas such as storm drains, open ditches,water bodies, or wetlands. . Allow convenient access to the concrete washout area for concrete trucks, preferably near the area where the concrete is being poured. . If trucks need to leave a paved area to access the concrete washout area, prevent track-out with a pad of rock or quarry spalls(see BMP C 105: Stabilized Construction Access).These areas should be far enough away from other construction traffic to reduce the likelihood of acci- dental damage and spills. . The number of concrete washout areas you install should depend on the expected demand for storage capacity. • On large sites with extensive concrete work, concrete washout areas should be placed in mul- tiple locations for ease of use by concrete truck drivers. Concrete Truck Washout Procedures . Washout of concrete truck drums shall be performed in designated concrete washout areas only. . Concrete washout from concrete pumper bins can be washed into concrete pumper trucks and discharged into designated concrete washout areas or properly disposed of off-site. Concrete Washout Area Installation . Concrete washout areas should be constructed as shown in the figures below,with a recom- mended minimum length and minimum width of 10 ft, but with sufficient quantity and volume to contain all liquid and concrete waste generated by washout operations. • Plastic lining material should be a minimum of 10 mil polyethylene sheeting and should be free of holes,tears, or other defects that compromise the impermeability of the material. • Lath and flagging should be commercial type. • Liner seams shall be installed in accordance with manufacturers'recommendations. • Soil base shall be prepared free of rocks or other debris that may cause tears or holes in the plastic lining material. Maintenance Standards Inspection and Maintenance . Inspect and verify that concrete washout areas are in place prior to the commencement of con- crete work. • Once concrete wastes are washed into the designated washout area and allowed to harden, 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 322 the concrete should be broken up, removed, and disposed of per applicable solid waste reg- ulations. Dispose of hardened concrete on a regular basis. • During periods of concrete work, inspect the concrete washout areas daily to verify continued performance. • Check overall condition and performance. • Check remaining capacity(%full). • If using self-installed concrete washout areas, verify plastic liners are intact and side- walls are not damaged. • If using prefabricated containers, check for leaks. • Maintain the concrete washout areas to provide adequate holding capacity with a minimum freeboard of 12 inches. . Concrete washout areas must be cleaned, or new concrete washout areas must be con- structed and ready for use once the concrete washout area is 75%full. • If the concrete washout area is nearing capacity, vacuum and dispose of the waste material in an approved manner. • Do not discharge liquid or slurry to waterways, storm drains or directly onto ground. • Do not discharge to the sanitary sewer without local approval. • Place a secure, non-collapsing, non-water collecting cover over the concrete washout area prior to predicted wet weather to prevent accumulation and overflow of pre- cipitation. • Remove and dispose of hardened concrete and return the structure to a functional con- dition. Concrete may be reused on-site or hauled away for disposal or recycling. • When you remove materials from a self-installed concrete washout area, build anew struc- ture; or, if the previous structure is still intact, inspect for signs of weakening or damage, and make any necessary repairs. Re-line the structure with new plastic after each cleaning. Removal of Concrete Washout Areas • When concrete washout areas are no longer required for the work, the hardened concrete, slurries and liquids shall be removed and properly disposed of. • Materials used to construct concrete washout areas shall be removed from the site of the work and disposed of or recycled. • Holes, depressions or other ground disturbance caused by the removal of the concrete washout areas shall be backfilled, repaired, and stabilized to prevent erosion. 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 323 Figure II-3.7: Concrete Washout Area with Wood Planks 3m Minimum Lath and flagging on 3 sides �J Sandbag Berm Sandbag 10 mil plastic lining Varies � A [� A 1m ,r '-��• �- Berm Section A-A 10 mil plastic lining Plan Notes: 1. Actual layout determined in the field. Type "Below Grade" 2. A concrete washout sign shall be installed within 10 m of the 3m Minimum temporary concrete washout facility. Wood frame B B securely fastened around entire perimeter with two stakes Varies 10 mil plastic lining Stake(typ.) Section B-B 10 mil plastic lining Two-stacked 2x12 rough Plan wood frame Type "Above Grade" with Wood Planks NOT TO SCALE Concrete Washout Area with Wood Planks Revised June 2016 DEPARTMENT OF ECOLOGY Please see http://www.ecy.wa.gov/copyrighthtml for copyright notice including permissions, State of Washington limitation of liability,and disclaimer. 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 324 Figure II-3.8: Concrete Washout Area with Straw Bales Straw bale 10 mil plastic lining Binding wire Staples Native material (2 per bale) (optional) Wood or Plywood metal stakes 1200 mm x 610 mm Wood post (2 per bale) painted white (89 mm x 89 mm Lag screws x 2.4 m) Section B-B (12.5 mm) iCONCRETEI Black letters WASHOUT 150 mm height 915 mm 915 mm Stake(typ) 3m Minimum Concrete Washout Sign Detail (or equivalent) B B Varies - 50 mm 200 mm �` 3.05 mm dia. T— steel wire ■ ■ Staple Detail Straw bale 10 mil plastic lining Notes: 1. Actual layout (typ-) determined in the field. Plan 2. The concrete washout sign shall be installed within 10 m of the temporary concrete washout facility. Type "Above Grade" with Straw Bales NOT TO SCALE Concrete Washout Area with Straw Bales Revised June 2016 DEPARTMENT OF ECOLOGY Please see http://www.ecy.wa.gov/copyrighthtml for copyright notice including permissions, State of Washington limitation of liability,and disclaimer. 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 325 Figure 11-3.9: Prefabricated Concrete Washout Container w/Ramp NOT TO SCALE Prefabricated Concrete Washout Container w/Ramp Revised June 2016 DEPARTMENT OF ECOLOGY Please see http://www.ecy.wa.gov/copyright.htm/for copyright notice including permissions, State of Washington limitation of liability,and disclaimer. 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 326 BMP C160: Certified Erosion and Sediment Control Lead Purpose The project proponent designates at least one person as the responsible representative in charge of erosion and sediment control(ESC), and water quality protection.The designated person shall be responsible for ensuring compliance with all local, state, and federal erosion and sediment control and water quality requirements. Construction sites one acre or larger that discharge to waters of the State must designate a Certified Erosion and Sediment Control Lead(CESCL)as the responsible representative. Conditions of Use A CESCL shall be made available on projects one acre or larger that discharge stormwater to sur- face waters of the state. Sites less than one acre may have a person without CESCL certification conduct inspections. The CESCL shall: . Have a current certificate proving attendance in an erosion and sediment control training course that meets the minimum ESC training and certification requirements established by Ecology. Ecology has provided the minimum requirements for CESCL course training, as well as a list of ESC training and certification providers at: https://ecology.wa.gov/Regulations-Permits/Permits-certifications/Certified-erosion-sed- iment-control OR • Bea Certified Professional in Erosion and Sediment Control (CPESC). For additional inform- ation go to: http://www.envirocertintl.org/cpesc/ Specifications . CESCL certification shall remain valid for three years. . The CESCL shall have authority to act on behalf of the contractor or project proponent and shall be available,or on-call, 24 hours per day throughout the period of construction. . The Construction SWPPP shall include the name,telephone number,fax number, and address of the designated CESCL. See II-2 Construction Stormwater Pollution Prevention Plans(Construction SWPPPs). . A CESCL may provide inspection and compliance services for multiple construction projects in the same geographic region, but must be on site whenever earthwork activities are 2019 Stormwater Management Manual for Western Washington Volume//-Chapter 3-Page 327 occurring that could generate release of turbid water. Duties and responsibilities of the CESCL shall include, but are not limited to the following: • Maintaining a permit file on site at all times which includes the Construction SWPPP and any associated permits and plans. • Directing BMP installation, inspection, maintenance, modification, and removal. • Updating all project drawings and the Construction SWPPP with changes made. • Completing any sampling requirements including reporting results using electronic Dis- charge Monitoring Reports(WebDMR). • Facilitate, participate in, and take corrective actions resulting from inspections per- formed by outside agencies or the owner. • Keeping daily logs,and inspection reports. Inspection reports should include: ■ Inspection date/time. ■ Weather information;general conditions during inspection and approximate amount of precipitation since the last inspection. ■ Visual monitoring results, including a description of discharged stormwater.The presence of suspended sediment,turbid water,discoloration,and oil sheen shall be noted, as applicable. ■ Any water quality monitoring performed during inspection. ■ General comments and notes, including a brief description of any BMP repairs, maintenance or installations made as a result of the inspection. ■ A summary or list of all BMPs implemented, including observations of all erosion/sediment control structures or practices.The following shall be noted: 1. Locations of BMPs inspected. 2. Locations of BMPs that need maintenance. 3. Locations of BMPs that failed to operate as designed or intended. 4. Locations of where additional or different BMPs are required. BMP C162: Scheduling Purpose Sequencing a construction project reduces the amount and duration of soil exposed to erosion by wind, rain, runoff, and vehicle tracking. 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 328 Conditions of Use The construction sequence schedule is an orderly listing of all major land-disturbing activities together with the necessary erosion and sedimentation control measures planned for the project. This type of schedule guides the contractor on work to be done before other work is started so that serious erosion and sedimentation problems can be avoided. Following a specified work schedule that coordinates the timing of land-disturbing activities and the installation of control measures is perhaps the most cost-effective way of controlling erosion during construction.The removal of ground cover leaves a site vulnerable to erosion. Construction sequen- cing that limits land clearing, provides timely installation of erosion and sedimentation controls, and restores protective cover quickly can significantly reduce the erosion potential of a site. Design Considerations • Minimize construction during rainy periods. • Schedule projects to disturb only small portions of the site at anyone time. Complete grading as soon as possible. Immediately stabilize the disturbed portion before grading the next por- tion. Practice staged seeding in order to revegetate cut and fill slopes as the work progresses. 11-3.3 Construction Runoff BMPs BMP C200: Interceptor Dike and Swale Purpose Provide a dike of compacted soil or a swale at the top or base of a disturbed slope or along the peri- meter of a disturbed construction area to convey stormwater. Use the dike and/or swale to intercept the runoff from unprotected areas and direct it to areas where erosion can be controlled.This can prevent storm runoff from entering the work area or sediment-laden runoff from leaving the con- struction site. Conditions of Use Use an interceptor dike or swale where runoff from an exposed site or disturbed slope must be con- veyed to an erosion control BMP which can safely convey the stormwater. • Locate upslope of a construction site to prevent runoff from entering the disturbed area. . When placed horizontally across a disturbed slope, it reduces the amount and velocity of run- off flowing down the slope. • Locate downslope to collect runoff from a disturbed area and direct it to a sediment BMP (e.g. BMP C240: Sediment Trap or BMP C241: Sediment Pond (Temporary)). 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 329 Design and Installation Specifications • Dike and/or swale and channel must be stabilized with temporary or permanent vegetation or other channel protection during construction. • Steep grades require channel protection and check dams. • Review construction for areas where overtopping may occur. . Can be used at the top of new fill before vegetation is established. • May be used as a permanent diversion channel to carry the runoff. • Contributing area for an individual dike or swale should be one acre or less. • Design the dike and/or swale to contain flows calculated by one of the following methods: • Single Event Hydrograph Method:The peak volumetric flow rate calculated using a 10- minute time step from a Type 1 A, 10-year,24-hour frequency storm for the worst-case land cover condition. OR • Continuous Simulation Method:The 10-year peak flow rate, as determined by an approved continuous runoff model with a 15-minute time step for the worst-case land cover condition. Worst-case land cover conditions(i.e., producing the most runoff)should be used for analysis (in most cases,this would be the land cover conditions just prior to final landscaping). Interceptor Dikes Interceptor dikes shall meet the following criteria: . Top Width: 2 feet minimum. • Height: 1.5 feet minimum on berm. • Side Slope: 2H:1 V or flatter. . Grade: Depends on topography, however, dike system minimum is 0.5%, and maximum is 1%. . Compaction: Minimum of 90 percent ASTM D698 standard proctor. • Stabilization: Depends on velocity and reach. Inspect regularly to ensure stability. . Ground Slopes<5%: Seed and mulch applied within 5 days of dike construction (see BMP C121: Mulching). . Ground Slopes 5-40%: Dependent on runoff velocities and dike materials. Stabilization should be done immediately using either sod or riprap, or other measures to avoid erosion. . The upslope side of the dike shall provide positive drainage to the dike outlet. No erosion shall 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 330 occur at the outlet. Provide energy dissipation measures as necessary. Sediment-laden runoff must be released through a sediment trapping facility. • Minimize construction traffic over temporary dikes. Use temporary cross culverts for channel crossing. . See Table II-3.8: Horizontal Spacing of Interceptor Dikes Along Ground Slope for recom- mended horizontal spacing between dikes. Table II-3.8: Horizontal Spacing of Interceptor Dikes Along Ground Slope Average Slope Slope Percent Flowpath Length 20H:1V or less 3-5% 300 feet (10 to 20)H:1V 5-10% 200 feet (4 to 1 Oft 1V 10-25% 100 feet (2 to 4)H:1V 25-50% 50 feet Interceptor Swales Interceptor swales shall meet the following criteria: • Bottom Width: 2 feet minimum;the cross-section bottom shall be level. • Depth: 1-foot minimum. . Side Slope: 2H:1 V or flatter. • Grade: Maximum 5 percent,with positive drainage to a suitable outlet(such as BMP C241: Sediment Pond (Temporary)). • Stabilization: Seed as per BMP C120: Temporary and Permanent Seeding, or BMP C202: Riprap Channel 1.ining, 12 inches thick riprap pressed into the bank and extending at least 8 inches vertical from the bottom. Maintenance Standards . Inspect diversion dikes and interceptor swales once a week and after every rainfall. Imme- diately remove sediment from the flow area. • Damage caused by construction traffic or other activity must be repaired before the end of each working day. . Check outlets and make timely repairs as needed to avoid gully formation.When the area below the temporary diversion dike is permanently stabilized, remove the dike and fill and sta- bilize the channel to blend with the natural surface. 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 331 BMP C207: Check Dams Purpose Construction of check dams across a swale or ditch reduces the velocity of concentrated flow and dis- sipates energy at the check dam. Conditions of Use Use check dams where temporary or permanent channels are not yet vegetated, channel lining is infeasible, and/or velocity checks are required. • Check dams may not be placed in streams unless approved by the State Department of Fish and Wildlife. • Check dams may not be placed in wetlands without approval from a permitting agency. • Do not place check dams below the expected backwater from any salmonid bearing water between October 1 and May 31 to ensure that there is no loss of high flow refuge habitat for overwintering juvenile salmonids and emergent salmonid fry. Design and Installation Specifications . Construct rock check dams from appropriately sized rock. The rock used must be large enough to stay in place given the expected design flow through the channel.The rock must be placed by hand or by mechanical means(do not dump the rock to form the dam)to achieve complete coverage of the ditch or swale and to ensure that the center of the dam is lower than the edges. • Check dams may also be constructed of either rock or pea-gravel filled bags. Numerous new products are also available for this purpose.They tend to be re-usable, quick and easy to install, effective, and cost efficient. • Place check dams perpendicular to the flow of water. • The check dam should form a triangle when viewed from the side.This prevents undercutting as water flows over the face of the check dam rather than falling directly onto the ditch bottom. • Before installing check dams, impound and bypass upstream water flow away from the work area. Options for bypassing include pumps, siphons,or temporary channels. . Check dams combined with sumps work more effectively at slowing flow and retaining sed- iment than a check dam alone.A deep sump should be provided immediately upstream of the check dam. . In some cases, if carefully located and designed, check dams can remain as permanent install- ations with very minor regrading. They may be left as either spillways, in which case accu- mulated sediment would be graded and seeded, or as check dams to prevent further sediment from leaving the site. • The maximum spacing between check dams shall be such that the downstream toe of the 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 351 upstream dam is at the same elevation as the top of the downstream dam. • Keep the maximum height at 2 feet at the center of the check dam. • Keep the center of the check dam at least 12 inches lower than the outer edges at natural ground elevation. • Keep the side slopes of the check dam at 2H:1 V or flatter. • Key the stone into the ditch banks and extend it beyond the abutments a minimum of 18 inches to avoid washouts from overflow around the dam. • Use filter fabric foundation under a rock or sand bag check dam. If a blanket ditch liner is used, filter fabric is not necessary.A piece of organic or synthetic blanket cut to fit will also work for this purpose. . In the case of grass-lined ditches and swales, all check dams and accumulated sediment shall be removed when the grass has matured sufficiently to protect the ditch or swale-unless the slope of the swale is greater than 4 percent.The area beneath the check dams shall be seeded and mulched immediately after dam removal. • Ensure that channel appurtenances,such as culvert entrances below check dams, are not subject to damage or blockage from displaced stones. . See Figure I I-3.16: Rock Check Dam. Maintenance Standards Check dams shall be monitored for performance and sediment accumulation during and after each rainfall that produces runoff. Sediment shall be removed when it reaches one half the sump depth. . Anticipate submergence and deposition above the check dam and erosion from high flows around the edges of the dam. . If significant erosion occurs between dams, install a protective riprap liner in that portion of the channel. See BMP C202: Riprap Channel Lining. Approved as Functionally Equivalent Ecology has approved products as able to meet the requirements of this BMP. The products did not pass through the Technology Assessment Protocol—Ecology(TAPE)process. Local jurisdictions may choose not to accept these products, or may require additional testing prior to consideration for local use. Products that Ecology has approved as functionally equivalent are available for review on Ecology's website at: https://ecology.wa.gov/Regulations-Permits/Guidance-technical-assistance/Stormwater-per- mittee-guidance-resources/Emerging-stormwater-treatment-technologies 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 352 Figure II-3.16: Rock Check Dam View Looking Upstream A 18„ 12" (0.5m) (150mm) (0.6m) Note: L Key stone into channel banks and extend it beyond the abutments a minimum of 18" (0.5m)to prevent flow around dam. A Section A-A FIB 24"(0.6m) a,o� O o0 rr (d ojX pp Opo 0 o 8'(2.4m) Spacing Between Check Dams 'L'=the distance such that points 'A'and'B'are of equal elevation. Point'A' Point'B' NOT TO SCALE Rock Check Dam Revised June 2016 DEPARTMENT OF ECOLOGY Please see http://www.ecy.wa.gov/copyrighthtml for copyright notice including permissions, State of Washington limitation of liability,and disclaimer. 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 353 and staples. In the case of grass-lined ditches and swales, check dams and accumulated sediment shall be removed when the grass has matured sufficiently to protect the ditch or swale unless the slope of the swale is greater than 4 percent.The area beneath the check dams shall be seeded and mulched immediately after dam removal. Maintenance Standards . Inspect TSDs for performance and sediment accumulation during and after each rainfall that produces runoff. Remove sediment when it reaches one half the height of the TSD. . Anticipate submergence and deposition above the TSD and erosion from high flows around the edges of the TSD. Immediately repair any damage or any undercutting of the TSD. BMP C209: Outlet Protection Purpose Outlet protection prevents scour at conveyance outlets and minimizes the potential for downstream erosion by reducing the velocity of concentrated stormwater flows. Conditions of Use Use outlet protection at the outlets of all ponds, pipes, ditches,or other conveyances that discharge to a natural or manmade drainage feature such as a stream,wetland, lake,or ditch. Design and Installation Specifications • The receiving channel at the outlet of a pipe shall be protected from erosion by lining a min- imum of 6 feet downstream and extending up the channel sides a minimum of 1—foot above the maximum tailwater elevation,or 1-foot above the crown,whichever is higher. For pipes lar- ger than 18 inches in diameter,the outlet protection lining of the channel shall be four times the diameter of the outlet pipe. • Standard wingwalls,tapered outlets,and paved channels should also be considered when appropriate for permanent culvert outlet protection (WSDOT, 2015). • BMP C122: Nets and Blankets or BMP C202: Riprap Channel Lining provide suitable options for lining materials. . With low flows, BMP C201: Grass-Lined Channels can be an effective alternative for lining material. • The following guidelines shall be used for outlet protection with riprap: • If the discharge velocity at the outlet is less than 5 fps, use 2-inch to 8-inch riprap. Min- imum thickness is 1-foot. • For 5 to 10 fps discharge velocity at the outlet, use 24-inch to 48-inch riprap. Minimum 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 355 thickness is 2 feet. • For outlets at the base of steep slope pipes(pipe slope greater than 10 percent), use an engineered energy dissipator. • Filter fabric or erosion control blankets should always be used under riprap to prevent scour and channel erosion. See BMP C122: Nets and Blankets. Bank stabilization, bioengineering, and habitat features maybe required for disturbed areas. This work may require a Hydraulic Project Approval (H PA)from the Washington State Depart- ment of Fish and Wildlife. See 1-2.11 Hydraulic Project Approvals. Maintenance Standards . Inspect and repair as needed. . Add rock as needed to maintain the intended function. . Clean energy dissipator if sediment builds up. BMP C220: Inlet Protection Purpose Inlet protection prevents coarse sediment from entering drainage systems prior to permanent sta- bilization of the disturbed area. Conditions of Use Use inlet protection at inlets that are operational before permanent stabilization of the disturbed areas that contribute runoff to the inlet. Provide protection for all storm drain inlets downslope and within 500 feet of a disturbed or construction area, unless those inlets are preceded by a sediment trapping BMP. Also consider inlet protection for lawn and yard drains on new home construction.These small and numerous drains coupled with lack of gutters can add significant amounts of sediment into the roof drain system. If possible, delay installing lawn and yard drains until just before landscaping, or cap these drains to prevent sediment from entering the system until completion of landscaping. Provide 18-inches of sod around each finished lawn and yard drain. Table II-3.10: Storm Drain Inlet Protection lists several options for inlet protection.All of the methods for inlet protection tend to plug and require a high frequency of maintenance. Limit contributing drain- age areas for an individual inlet to one acre or less. If possible, provide emergency overflows with additional end-of-pipe treatment where stormwater ponding would cause a hazard. 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 356 Table II-3.10: Storm Drain Inlet Protection Type of Inlet Pro- Emergency Applicable for tection Overflow Paved/ Earthen Sur- Conditions of Use faces Drop Inlet Protection Excavated drop Yes,temporary Applicable for heavy flows. Easy inlet protection flooding may Earthen to maintain. Large area requirement: occur 30'x30'/acre Block and gravel drop inlet pro- Yes Paved or Earthen Applicable for heavy concentrated flows. Will not pond. tection Gravel and wire drop inlet pro- No Paved or Earthen Applicable for heavy concentrated flows. Will pond. Can withstand traffic. tection Catch basin filters I Yes Paved or Earthen Frequent maintenance required. Curb Inlet Protection Curb inlet pro- Small capacity Used for sturdy, more compact install- tection with overflow Paved ation. wooden weir Block and gravel curb inlet pro- Yes Paved Sturdy, but limited filtration. tection Culvert Inlet Protection Culvert inlet sed- N/A N/A 18 month expected life. iment trap Design and Installation Specifications Excavated Drop Inlet Protection Excavated drop inlet protection consists of an excavated impoundment around the storm drain inlet. Sediment settles out of the stormwater prior to entering the storm drain. Design and installation spe- cifications for excavated drop inlet protection include: • Provide a depth of 1-2 ft as measured from the crest of the inlet structure. . Slope sides of excavation should be no steeper than 2H A V. • Minimum volume of excavation is 35 cubic yards. . Shape the excavation to fit the site,with the longest dimension oriented toward the longest inflow area. • Install provisions for draining to prevent standing water. . Clear the area of all debris. 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 357 • Grade the approach to the inlet uniformly. • Drill weep holes into the side of the inlet. . Protect weep holes with screen wire and washed aggregate. . Seal weep holes when removing structure and stabilizing area. • Build a temporary dike, if necessary,to the down slope side of the structure to prevent bypass flow. Block and Gravel Filter A block and gravel filter is a barrier formed around the inlet with standard concrete blocks and gravel. See Figure 11-3.17: Block and Gravel Filter. Design and installation specifications for block gravel fil- ters include: • Provide a height of 1 to 2 feet above the inlet. • Recess the first row of blocks 2-inches into the ground for stability. • Support subsequent courses by placing a pressure treated wood 2x4 through the block open- ing. • Do not use mortar. • Lay some blocks in the bottom row on their side to allow for dewatering the pool. • Place hardware cloth or comparable wire mesh with 1/2-inch openings over all block openings. • Place gravel to just below the top of blocks on slopes of 2H:1 V or flatter. . An alternative design is a gravel berm surrounding the inlet, as follows: Provide a slope of 3H:1 V on the upstream side of the berm. Provide a slope of 2H:1 V on the downstream side of the berm. Provide a 1-foot wide level stone area between the gravel berm and the inlet. Use stones 3 inches in diameter or larger on the upstream slope of the berm. Use gravel'/2-to%-inch at a minimum thickness of 1-foot on the downstream slope of the berm. 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 358 Figure II-3.17: Block and Gravel Filter A Drain grate o'p. �'Oo duod�ooa p�O Concrete block oo �° b op•DO o0 q a �o : 44 p o�o �000�0 Q �o o�10° �o .�o' ° Gravel backfill a� dd310 Nq po �p q Qffa O doOO./�JJ�CJo°O o�pp�p° o ++.• V o�Qa �Oq p�0 �0 6yr\Qe �a���Uvoo�oo� 0 Plan View Concrete block Wire screen or filter fabric Gravel backfill Overflow water o Ponding height Water . po Drop inlet Section A-A Notes: 1. Drop inlet sediment barriers are to be used for small,nearly level drainage areas.(less than 5%) 2. Excavate a basin of sufficient size adjacent to the drop inlet. 3. The top of the structure(ponding height)must be well below the ground elevation downslope to prevent runoff from bypassing the inlet.A temporary dike may be necessary on the downslope side of the structure. NOT TO SCALE Block and Gravel Filter Revised June 2016 DEPARTMENT OF ECOLOGY Please see http://www.ecy.wa.gov/copyrighthtml for copyright notice including permissions, State of Washington limitation of liability,and disclaimer. 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 359 Gravel and Wire Mesh Filter Gravel and wire mesh filters are gravel barriers placed over the top of the inlet.This method does not provide an overflow. Design and installation specifications for gravel and wire mesh filters include: • Use a hardware cloth or comparable wire mesh with'/2-inch openings. • Place wire mesh over the drop inlet so that the wire extends a minimum of 1-foot bey- ond each side of the inlet structure. • Overlap the strips if more than one strip of mesh is necessary. • Place coarse aggregate over the wire mesh. Provide at least a 12-inch depth of aggregate over the entire inlet opening and extend at least 18-inches on all sides. Catch Basin Filters Catch basin filters are designed by manufacturers for construction sites.The limited sediment stor- age capacity increases the amount of inspection and maintenance required,which may be daily for heavy sediment loads.To reduce maintenance requirements, combine a catch basin filter with another type of inlet protection.This type of inlet protection provides flow bypass without overflow and therefore may be a better method for inlets located along active rights-of-way. Design and install- ation specifications for catch basin filters include: • Provides 5 cubic feet of storage. • Requires dewatering provisions. • Provides a high-flow bypass that will not clog under normal use at a construction site. . Insert the catch basin filter in the catch basin just below the grating. Curb Inlet Protection with Wooden Weir Curb inlet protection with wooden weir is an option that consists of a barrier formed around a curb inlet with a wooden frame and gravel. Design and installation specifications for curb inlet protection with wooden weirs include: • Use wire mesh with '/2-inch openings. • Use extra strength filter cloth. . Construct a frame. . Attach the wire and filter fabric to the frame. • Pile coarse washed aggregate against the wire and fabric. • Place weight on the frame anchors. 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 360 Block and Gravel Curb Inlet Protection Block and gravel curb inlet protection is a barrier formed around a curb inlet with concrete blocks and gravel. See Figure II-3.18: Block and Gravel Curb Inlet Protection. Design and installation spe- cifications for block and gravel curb inlet protection include: • Use wire mesh with '/2-inch openings. • Place two concrete blocks on their sides abutting the curb at either side of the inlet opening. These are spacer blocks. • Place a 2A stud through the outer holes of each spacer block to align the front blocks. • Place blocks on their sides across the front of the inlet and abutting the spacer blocks. • Place wire mesh over the outside vertical face. • Pile coarse aggregate against the wire to the top of the barrier. 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 361 Figure II-3.18: Block and Gravel Curb Inlet Protection A Catch basin Back of sidewalk //2x4 Wood stud Back of curb Curb inlet Concrete block Q QQ• aPP�. Wire screen or filter fabric %4 inch (20 mm) Concrete block Drain gravel Plan View Ponding height 3/4 inch(20 mm) Drain gravel Overflow Curb inlet Wire screen or filter fabric 2x4 Wood stud (100x50 Timber stud) Catch basin \j Concrete block Section A-A Notes: 1. Use block and gravel type sediment barrier when curb inlet is located in gently sloping street segment,where water can pond and allow sediment to separate from runoff. 2. Barrier shall allow for overflow from severe storm event. 3. Inspect barriers and remove sediment after each storm event.Sediment and gravel must be removed from the traveled way immediately. NOT TO SCALE Block and Gravel Curb Inlet Protection Revised June 2016 DEPARTMENT OF ECOLOGY Please see http://www.ecy.wa.gov/copyrighthtml for copyright notice including permissions, State of Washington limitation of liability,and disclaimer. 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 362 Curb and Gutter Sediment Barrier Curb and gutter sediment barrier is a sandbag or rock berm(riprap and aggregate)3 feet high and 3 feet wide in a horseshoe shape. See Figure 11-3.19: Curb and Gutter Barrier. Design and installation specifications for curb and gutter sediment barrier include: . Construct a horseshoe shaped berm,faced with coarse aggregate if using riprap, 3 feet high and 3 feet wide, at least 2 feet from the inlet. • Construct a horseshoe shaped sedimentation trap on the upstream side of the berm. Size the trap to sediment trap standards for protecting a culvert inlet. 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 363 Figure II-3.19: Curb and Gutter Barrier Back of sidewalk Burlap sacks to overlap onto curb Back of curb Runoff Curb inlet Runoff Spillway Catch basin Plan View Gravel filled sandbags stacked tightly Notes: 1. Place curb type sediment barriers on gently sloping street segments,where water can pond and allow sediment to separate from runoff. 2. Sandbags of either burlap or woven'geotextile'fabric,are filled with gravel,layered and packed tightly. 3. Leave a one sandbag gap in the top row to provide a spillway for overflow. 4. Inspect barriers and remove sediment after each storm event.Sediment and gravel must be removed from the traveled way immediately. NOT TO SCALE Curb and Gutter Barrier Revised June 2016 DEPARTMENT OF ECOLOGY Please see http://www.ecy.wa.gov/copyrighthtml for copyright notice including permissions, State of Washington limitation of liability,and disclaimer. 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 364 BMP C233: Silt Fence Purpose Silt fence reduces the transport of coarse sediment from a construction site by providing a temporary physical barrier to sediment and reducing the runoff velocities of overland flow. Conditions of Use Silt fence may be used downslope of all disturbed areas. . Silt fence shall prevent sediment carried by runoff from going beneath,through, or over the top of the silt fence, but shall allow the water to pass through the fence. . Silt fence is not intended to treat concentrated flows, nor is it intended to treat substantial amounts of overland flow. Convey any concentrated flows through the drainage system to a sediment trapping BMP. • Do not construct silt fences in streams or use in V-shaped ditches. Silt fences do not provide an adequate method of silt control for anything deeper than sheet or overland flow. 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 370 Figure II-3.22: Silt Fence Joints in geotextile fabric shall be spliced at posts.Use staples,wire rings or equivalent to attach fabric to posts 2"x2"by 14 Ga.wire or equivalent, K standard strength fabric used Minimum I I 6'max 4"x4"trench I � I u Post spacing may be increased to 8'if wire backing is used 2"x2"wood posts,steel fence posts,or equivalent 2"x2"by 14 Ga.wire or equivalent, if standard strength fabric used �j\\\ Geotextile fabric -I\, -r \��\\ 2'min Backfill trench native soil or 3/" 1.5"washed gravel \\12"mm\ Minimum 4"x4"trench 2"x2"wood posts,steel fence posts, or equivalent NOT TO SCALE Silt Fence Revised July 2017 DEPARTMENT OF ECOLOGY Please see http:Owtrow.ecy.wa.gov/copyrrghthtml for copyright notice including permissions, State of Washington limitation of liability,and disclaimer. 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 371 Design and Installation Specifications • Use in combination with other construction stormwater BMPs. • Maximum slope steepness(perpendicular to the silt fence line) 1 H:1 V. • Maximum sheet or overland flow path length to the silt fence of 100 feet. • Do not allow flows greater than 0.5 cfs. • Use geotextile fabric that meets the following standards.All geotextile properties listed below are minimum average roll values(i.e.,the test result for any sampled roll in a lot shall meet or exceed the values shown in Table 11-3.11: Geotextile Fabric Standards for Silt Fence): Table II-3.11: Geotextile Fabric Standards for Silt Fence Geotextile Property Minimum Average Roll Value Polymeric Mesh AOS 0.60 mm maximum for slit film woven(#30 sieve). (ASTM D4751) 0.30 mm maximum for all other geotextile types(#50 sieve). 0.15 mm minimum for all fabric types (#100 sieve). Water Permittivity 0.02 sec-1 minimum (ASTM D4491) Grab Tensile Strength 180 lbs. Minimum for extra strength fabric. (ASTM D4632) 100 Ibs minimum for standard strength fabric. Grab Tensile Strength 30% maximum (ASTM D4632) Ultraviolet Resistance 70% minimum (ASTM D4355) . Support standard strength geotextiles with wire mesh, chicken wire,2-inch x 2-inch wire, safety fence,or jute mesh to increase the strength of the geotextile. Silt fence materials are available that have synthetic mesh backing attached. • Silt fence material shall contain ultraviolet ray inhibitors and stabilizers to provide a minimum of six months of expected usable construction life at a temperature range of 0°F to 120°F. . One-hundred percent biodegradable silt fence is available that is strong, long lasting,and can be left in place after the project is completed, if permitted by the local jurisdiction. • Refer to Figure 11-3.22: Silt Fence for standard silt fence details. Include the following Stand- ard Notes for silt fence on construction plans and specifications: 1. The Contractor shall install and maintain temporary silt fences at the locations shown in the Plans. 2. Construct silt fences in areas of clearing, grading, or drainage prior to starting those activities. 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 372 3. The silt fence shall have a 2-feet min.and a 2'/2-feet max. height above the original ground surface. 4. The geotextile fabric shall be sewn together at the point of manufacture to form fabric lengths as required. Locate all sewn seams at support posts.Alternatively,two sections of silt fence can be overlapped, provided that the overlap is long enough and that the adjacent silt fence sections are close enough together to prevent silt laden water from escaping through the fence at the overlap. 5. Attach the geotextile fabric on the up-slope side of the posts and secure with staples, wire,or in accordance with the manufacturer's recommendations.Attach the geotextile fabric to the posts in a manner that reduces the potential for tearing. 6. Support the geotextile fabric with wire or plastic mesh, dependent on the properties of the geotextile selected for use. If wire or plastic mesh is used,fasten the mesh securely to the up-slope side of the posts with the geotextile fabric up-slope of the mesh. 7. Mesh support, if used, shall consist of steel wire with a maximum mesh spacing of 2- inches,or a prefabricated polymeric mesh.The strength of the wire or polymeric mesh shall be equivalent to or greater than 180 lbs.grab tensile strength.The polymeric mesh must be as resistant to the same level of ultraviolet radiation as the geotextile fabric it supports. 8. Bury the bottom of the geotextile fabric 4-inches min. below the ground surface. Backfill and tamp soil in place over the buried portion of the geotextile fabric,so that no flow can pass beneath the silt fence and scouring cannot occur.When wire or polymeric back-up support mesh is used,the wire or polymeric mesh shall extend into the ground 3-inches min. 9. Drive or place the silt fence posts into the ground 18-inches min.A 12—inch min.depth is allowed if topsoil or other soft subgrade soil is not present and 18-inches cannot be reached. Increase fence post min. depths by 6 inches if the fence is located on slopes of 3H:1 V or steeper and the slope is perpendicular to the fence. If required post depths cannot be obtained,the posts shall be adequately secured by bracing or guying to pre- vent overturning of the fence due to sediment loading. 10. Use wood, steel or equivalent posts.The spacing of the support posts shall be a max- imum of 6-feet. Posts shall consist of either: . Wood with minimum dimensions of 2 inches by 2 inches by 3 feet.Wood shall be free of defects such as knots,splits, or gouges. • No. 6 steel rebar or larger. . ASTM A 120 steel pipe with a minimum diameter of 1-inch. • U,T, L,or C shape steel posts with a minimum weight of 1.35 lbs./ft. . Other steel posts having equivalent strength and bending resistance to the post sizes listed above. 11. Locate silt fences on contour as much as possible, except at the ends of the fence, 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 373 where the fence shall be turned uphill such that the silt fence captures the runoff water and prevents water from flowing around the end of the fence. 12. If the fence must cross contours,with the exception of the ends of the fence, place check dams perpendicular to the back of the fence to minimize concentrated flow and erosion.The slope of the fence line where contours must be crossed shall not be steeper than 3H:1 V. . Check dams shall be approximately 1-foot deep at the back of the fence. Check dams shall be continued perpendicular to the fence at the same elevation until the top of the check dam intercepts the ground surface behind the fence. . Check dams shall consist of crushed surfacing base course, gravel backfill for walls, or shoulder ballast. Check dams shall be located every 10 feet along the fence where the fence must cross contours. Refer to Figure 11-3.23: Silt Fence Installation by Slicing Method for slicing method details.The following are specifications for silt fence installation using the slicing method: 1. The base of both end posts must be at least 2-to 4-inches above the top of the geo- textile fabric on the middle posts for ditch checks to drain properly. Use a hand level or string level, if necessary,to mark base points before installation. 2. Install posts 3-to 4-feet apart in critical retention areas and 6-to 7-feet apart in standard applications. 3. Install posts 24-inches deep on the downstream side of the silt fence, and as close as possible to the geotextile fabric, enabling posts to support the geotextile fabric from upstream water pressure. 4. Install posts with the nipples facing away from the geotextile fabric. 5. Attach the geotextile fabric to each post with three ties, all spaced within the top 8- inches of the fabric.Attach each tie diagonally 45 degrees through the fabric,with each puncture at least 1-inch vertically apart. Each tie should be positioned to hang on a post nipple when tightening to prevent sagging. 6. Wrap approximately 6-inches of the geotextile fabric around the end posts and secure with 3 ties. 7. No more than 24-inches of a 36-inch geotextile fabric is allowed above ground level. 8. Compact the soil immediately next to the geotextile fabric with the front wheel of the tractor, skid steer,or roller exerting at least 60 pounds per square inch. Compact the upstream side first and then each side twice for a total of four trips. Check and correct the silt fence installation for any deviation before compaction. Use a flat-bladed shovel to tuck the fabric deeper into the ground if necessary. 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 374 Figure II-3.23: Silt Fence Installation by Slicing Method Ponding height max.24" POST SPACING: 7'max.on open runs Attach fabric to 4'max.on pooling areas Top of Fabric ` upstream side of post Belt I# FLOW POST DEPTH: top 8" Drive over each side of As much below ground silt fence 2 to 4 times as fabric above ground with device exerting 60 p.s.i.or greater Diagonal attachment 100%compaction 100%compaction doubles strength =1 =1 LIL =1 III=1 III 11=111=i I I=1 11=1 11=1 11=1 1=1 11=1 11=1 11=1 11=1 11- -III—III—III—III III—III—III—III—III—I IIIIIIIIIIIIIIIIIIIIIII N 1111111111111111111111111111111- 1=1 1=1 1=1 1= -III=111=111=1I rQ I I1=1I1=111=III=III= Attachment Details: I I El I I1111111�1 Q II 11=1 11=1 11=1 11=1 I II I I posts,if needed. _ • Gather fabric at =III=1 =11 N I=1 I=I I=111=III=11' . Utilize three ties per post,all within top 8" 11=III—III— — III=III III III III- -I 11=111=111=11 =111=III=111a I 1=1 I of fabric. 11=1I1=1I 1=1I1= I1=1I1=1 I1=1I1=1I . Position each tie diagonally,puncturing III—III—III=11I 1=III=III=11I—I i,l holes vertically a minimum of 1"apart. I—III=III=III= III=III=III=III=1 ;I II-III,-III III, -111 III II1=1i Hang each tie on a post nipple and tighten No more than 24"of a 36" securely.Use cable ties(50 Ibs)or soft fabric is allowed above ground wire. Operation Roll of silt fence � Post Kx� installed Fabric after above compaction Oground Silt Fence III—III—I 1=1 1=1 1=1 1=1 1=1 200- -I 11=1 11=1 11=1 11=1 11=1 11=1 I I 11= i I 1=1 11=1 III—I�' III-1 -1 1 300mm —III I=1 I; - 1 I' =1 1= —III-III-III-111,;,111— I,;,III-III,,, 11-III; - —11i- � ';III 11i1 1—' Horizontal chisel point Slicing blade (76 mm width) (18 mm width) Completed Installation Vibratory plow is not acceptable because of horizontal compaction NOT TO SCALE Silt Fence Installation by Slicing Method Revised June 2016 DEPARTMENT OF ECOLOGYPlease see http://www.ecy.wa.gov/copyrighthtm!for copyright notice including permissions, State of Washington limitation of liability,and disclaimer. 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 375 Maintenance Standards • Repair any damage immediately. • Intercept and convey all evident concentrated flows uphill of the silt fence to a sediment trap- ping BMP. • Check the uphill side of the silt fence for signs of the fence clogging and acting as a barrier to flow and then causing channelization of flows parallel to the fence. If this occurs, replace the fence and remove the trapped sediment. • Remove sediment deposits when the deposit reaches approximately one-third the height of the silt fence, or install a second silt fence. • Replace geotextile fabric that has deteriorated due to ultraviolet breakdown. BMP C234: Vegetated Strip Purpose Vegetated strips reduce the transport of coarse sediment from a construction site by providing a physical barrier to sediment and reducing the runoff velocities of overland flow. Conditions of Use . Vegetated strips may be used downslope of all disturbed areas. . Vegetated strips are not intended to treat concentrated flows, nor are they intended to treat substantial amounts of overland flow.Any concentrated flows must be conveyed through the drainage system to BMP C241: Sediment Pond (Temporary)or other sediment trapping BMP. The only circumstance in which overland flow can be treated solely by a vegetated strip, rather than by a sediment trapping BMP, is when the following criteria are met(see Table 1I- 3.12: Contributing Drainage Area for Vegetated Strips): Table II-3.12: Contributing Drainage Area for Vegetated Strips Average Contributing Area Average Contributing Area Per- Max Contributing area Flowpath Slope cent Slope Length 1.5H : 1V orflatter 67% orflatter 100 feet 2H : 1V orflatter 50% orflatter 115feet 4H : 1 V or flatter 25% or flatter 150 feet 6H : 1 V or flatter 16.7%or flatter 200 feet 10H : lV orflatter 10% orflatter 250 feet 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 376 Design and Installation Specifications . The vegetated strip shall consist of a continuous strip of dense vegetation with topsoil for a min- imum of a 25-foot length along the flowpath. Grass-covered, landscaped areas are generally not adequate because the volume of sediment overwhelms the grass. Ideally,vegetated strips shall consist of undisturbed native growth with a well-developed soil that allows for infiltration of runoff. . The slope within the vegetated strip shall not exceed 4H:1 V. . The uphill boundary of the vegetated strip shall be delineated with clearing limits. Maintenance Standards . Any areas damaged by erosion or construction activity shall be seeded immediately and pro- tected by mulch. . If more than 5 feet of the original vegetated strip width has had vegetation removed or is being eroded, sod must be installed. . If there are indications that concentrated flows are traveling across the vegetated strip, storm- water runoff controls must be installed to reduce the flows entering the vegetated strip,or addi- tional perimeter protection must be installed. BM P C235: Wattles Purpose Wattles are temporary erosion and sediment control barriers consisting of straw, compost,or other material that is wrapped in netting made of natural plant fiber or similar encasing material.They reduce the velocity and can spread the flow of rill and sheet runoff, and can capture and retain sed- iment. Conditions of Use . Wattles shall consist of cylinders of plant material such as weed-free straw, coir,wood chips, excelsior,or wood fiber or shavings encased within netting made of natural plant fibers unaltered by synthetic materials. • Usewattles: • In disturbed areas that require immediate erosion protection. • On exposed soils during the period of short construction delays, or over winter months. • On slopes requiring stabilization until permanent vegetation can be established. . The material used dictates the effectiveness period of the wattle. Generally,wattles are effect- ive for one to two seasons. 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 377 Prevent rilling beneath wattles by entrenching and overlapping wattles to prevent water from passing between them. Design Criteria . See Figure 11-3.24: Wattles for typical construction details. • Wattles are typically 8 to 10 inches in diameter and 25 to 30 feet in length. • Install wattles perpendicular to the flow direction and parallel to the slope contour. • Place wattles in shallow trenches, staked along the contour of disturbed or newly constructed slopes. Dig narrow trenches across the slope(on contour)to a depth of 3-to 5-inches on clay soils and soils with gradual slopes. On loose soils, steep slopes, and areas with high rainfall, the trenches should be dug to a depth of 5-to 7-inches, or 1/2 to 2/3 of the thickness of the wattle. • Start building trenches and installing wattles from the base of the slope and work up. Spread excavated material evenly along the uphill slope and compact it using hand tamping or other methods. . Construct trenches at intervals of 10-to 25-feet depending on the steepness of the slope, soil type, and rainfall. The steeper the slope the closer together the trenches. • Install the wattles snugly into the trenches and overlap the ends of adjacent wattles 12 inches behind one another. . Install stakes at each end of the wattle, and at 4-foot centers along entire length of wattle. . If required, install pilot holes for the stakes using a straight bar to drive holes through the wattle and into the soil. . Wooden stakes should be approximately 0.75 x 0.75 x 24 inches min.Willow cuttings or 3/8- inch rebar can also be used for stakes. . Stakes should be driven through the middle of the wattle, leaving 2 to 3 inches of the stake pro- truding above the wattle. 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 378 Figure II-3.24: Wattles 3'-4' Overlap adjacent \Y rolls 12"behind one another Straw rolls must be N placed along slope contours �1tIW �Y 1 10'-25' 3-8m �9 Spacing depends on soil type and slope steepness �� Sediment,organic matter, and native seeds are captured behind the rolls. 3"-5"(75-125mm) 8"-10"Dia. (200-250mm) Live Stake :Ty'// 1"x 1"Stake l/ (25 x 25mm) NOTE: r 1. Straw roll installation requires the placement and secure staking of the roll in a trench,3"-5"(75-125mm)deep,dug on contour. Runoff must not be allowed to run under or around roll. NOT TO SCALE Wattles Revised December 2016 DEPARTMENT OF ECOLOGY Please see http://www.ecy.wa.gov/copyrighthtml for copyright notice including permissions, State of Washington limitation of liability,and disclaimer. 2019 Stormwater Management Manual for Western Washington Volume 11-Chapter 3-Page 379 Maintenance Standards • Monitor the spray field on a daily basis to ensure that over saturation of any portion of the field does not occur at any time. The presence of standing puddles of water or creation of concentrated flows visually signify that over saturation of the field has occurred. • Monitor the vegetated spray field all the way down to the nearest surface water, or farthest spray area, to ensure that the water has not caused overland or concentrated flows, and has not created erosion around the spray nozzle(s). • Do not exceed water quality standards for turbidity. • Ecology recommends that a separate inspection log be developed, maintained, and kept with the existing site logbook to aid the operator conducting inspections. This separate "Field Filtration Logbook"can also aid in demonstrating compliance with permit conditions. • Inspect the spray nozzles daily, at a minimum, for leaks and plugging from sediment particles. • If erosion, concentrated flows, or over saturation of the field occurs, rotate the use of branches or spray heads or move the branches to a new field location. • Check all branches and the manifold for unintended leaks. BMP C240: Sediment Trap Purpose A sediment trap is a small temporary ponding area with a gravel outlet used to collect and store sediment from sites during construction. Sediment traps, along with other perimeter controls, shall be installed before any land disturbance takes place in the contributing drainage area. Conditions of Use • Sediment traps are intended for use on sites where the contributing drainage area is less than 3 acres, with no unusual drainage features, and a projected build-out time of 6 months or less. The sediment trap is a temporary measure (with a design life of approximately 6 months)and shall be maintained until the contributing drainage area is permanently pro- tected against erosion by vegetation and/or structures. • Sediment traps are only effective in removing sediment down to about the medium silt size fraction. Runoff with sediment of finer grades (fine silt and clay)will pass through untreated, emphasizing the need to control erosion to the maximum extent first. • Projects that are constructing permanent Flow Control BMPs, or permanent Runoff Treat- ment BMPs that use ponding for treatment, may use the rough-graded or final-graded per- manent BMP footprint for the temporary sediment trap. When permanent BMP footprints are used as temporary sediment traps, the surface area requirement of the sediment trap must be met. If the surface area requirement of the sediment trap is larger than the surface area of the permanent BMP, then the sediment trap shall be enlarged beyond the 2024 Stormwater Management Manual for Western Washington Volume //-Chapter 4-Page 427 permanent BMP footprint to comply with the surface area requirement. • A floating pond skimmer may be used for the sediment trap outlet if approved by the Local Permitting Authority. • Sediment traps may not be feasible on utility projects due to the limited work space or the short-term nature of the work. Portable tanks may be used in place of sediment traps for util- ity projects. Design and Installation Specifications • See Figure II-4.26: Cross Section of Sediment Trap and Figure 11-4.27: Sediment Trap Out- let for details. • To determine the sediment trap geometry, first calculate the design surface area (SA)of the trap, measured at the invert of the weir. Use the following equation: SA= FS* (Q2/VS) where: SA= Design surface area of the trap(square feet) FS =A safety factor of 2 to account for non-ideal settling. Q2 =The peak volumetric flow rate (cubic feet per second), calculated using one of the fol- lowing options: o Option 1 -Single Event Hydrograph Method The peak volumetric flow rate calculated using a 10-minute time step from a Type 1 A, 2-year, 24-hour frequency storm for the developed condition. The 10-year peak volu- metric flow rate shall be used if the project size, expected timing and duration of con- struction, or downstream conditions warrant a higher level of protection. o Option 2-The Rational Method For construction sites that are less than 1 acre, the peak volumetric flow rate cal- culated using the Rational Method. VS=The settling velocity of the soil particle of interest. The 0.02 mm (medium silt) particle with an assumed density of 2.65 g/cm3 has been selected as the particle of interest and has a settling velocity(VS)of 0.00096 ft/sec. Therefore, the equation for computing sediment trap surface area becomes: SA=2 x Q2/0.00096 or 2080 square feet per cfs of inflow 2024 Stormwater Management Manual for Western Washington Volume 11-Chapter 4-Page 428 • Sediment trap depth shall be 3.5 feet minimum from the bottom of the trap to the top of the overflow weir. • To aid in determining sediment depth, all sediment traps shall have a staff gauge with a prominent mark 1 foot above the bottom of the trap. • Design the discharge from the sediment trap by using the guidance for discharge from tem- porary sediment ponds in BMP C241: Sediment Pond (Temporary). Maintenance Standards • Sediment shall be removed from the trap when it reaches 1 foot in depth. • Any damage to the trap embankments or slopes shall be repaired. 2024 Stormwater Management Manual for Western Washington Volume 11- Chapter 4-Page 429 Figure II-4.26: Cross Section of Sediment Trap Surface area determined 4'Min. at top of weir 1'Min. Overflow —�— 1'Min ��- � —� -:�•,"-�.°tr ' 1'Min. �L 3.5'-5' : 1.5'Min. Flat Bottom I Y4"-1.5" Washed gravel Discharge to Note:Trap may be formed by berm or by Geotextile stabilized partial or complete excavation. 2"-4"Rock conveyance, outlet,or level Rip Rap spreader NOT TO SCALE Cross Section of Sediment Trap DEPARTMENT OF ECOLOGY State of Washington Revised June 2016 2024 Stormwater Management Manual for Western Washington Volume 11-Chapter 4-Page 430 Figure II-4.27: Sediment Trap Outlet 6'Min. I I—I I—I I—III—III—I I— 1'Min.depth overflowill III—III—III—III—III—I I I— J I IJ I I-1 I I-1 I I-1 I I;it i1 I II I spillway I I II I VI I IJ I I-1 I I-1 I IJ I IJ 11= -III—I -S[.3�_��;;�. ���' ����•;': !,�=�-�_:,:>:C�'.i.�:. �—III- Min. 1'depth 2"-4"rock Native soil or —1 11-1 I I I I I-1 I I-1 I I-1 I I-1 Min. 1'depth 3/4° -1.5" compacted backfill washed gravel Geotextile NOT TO SCALE Sediment Trap Outlet DEPARTMENT OF ECOLOGY State of Washington Revised June2016 2024 Stormwater Management Manual for Western Washington Volume 11- Chapter 4-Page 431 Appendix C Site Inspection Form Construction Stormwater Site Inspection Form Project Name Permit# Inspection Date Time Name of Certified Erosion Sediment Control Lead (CESCL) or qualified inspector if less than one acre Print Name: Approximate rainfall amount since the last inspection (in inches): Approximate rainfall amount in the last 24 hours (in inches): Current Weather Clear ❑ Cloudy ❑ Mist ❑ Rain ❑ Wind ❑ Fog ❑ A.Type of inspection: Weekly ❑ Post Storm Event ❑ Other ❑ B. Phase of Active Construction (check all that apply): Pre Construction/installation of erosion/sediment controls Clearing/Demo/Grading Infrastructure/storm/roads Concrete pours Vertical Construction/buildings Utilities Offsite improvements Site temporary stabilized Final stabilization C. Questions: 1. Were all areas of construction and discharge points inspected? Yes No 2. Did you observe the presence of suspended sediment,turbidity, discoloration, or oil sheen Yes No 3. Was a water quality sample taken during inspection? (refer to permit conditions 54&55) Yes No 4. Was there a turbid discharge 250 NTU or greater, or Transparency 6 cm or less?* Yes No 5. If yes to#4 was it reported to Ecology? Yes No 6. Is pH sampling required? pH range required is 6.5 to 8.5. Yes No If answering yes to a discharge, describe the event. Include when, where, and why it happened; what action was taken, and when. *If answering yes to#4 record NTU/Transparency with continual sampling daily until turbidity is 25 NTU or less/transparency is 33 cm or greater. Sampling Results: Date: Parameter Method (circle one) Result Other/Note NTU cm pH Turbidity tube, meter, laboratory pH Paper, kit, meter Page 1 Construction Stormwater Site Inspection Form D. Check the observed status of all items. Provide "Action Required "details and dates. Element # Inspection BMPs BMP needs BMP Action Inspected maintenance failed required yes no n/a (describe in section F) 1 Before beginning land disturbing Clearing activities are all clearing limits, Limits natural resource areas(streams, wetlands, buffers, trees) protected with barriers or similar BMPs? (high visibility recommended) 2 Construction access is stabilized Construction with quarry spalls or equivalent Access BMP to prevent sediment from being tracked onto roads? Sediment tracked onto the road way was cleaned thoroughly at the end of the day or more frequent as necessary. 3 Are flow control measures installed Control Flow to control stormwater volumes and Rates velocity during construction and do they protect downstream properties and waterways from erosion? If permanent infiltration ponds are used for flow control during construction, are they protected from siltation? 4 All perimeter sediment controls Sediment (e.g. silt fence,wattles, compost Controls socks, berms, etc.) installed, and maintained in accordance with the Stormwater Pollution Prevention Plan (SWPPP). Sediment control BMPs (sediment ponds, traps,filters etc.) have been constructed and functional as the first step of grading. Stormwater runoff from disturbed areas is directed to sediment removal BMP. S Have exposed un-worked soils Stabilize been stabilized with effective BMP Soils to prevent erosion and sediment deposition? Page 2 Construction Stormwater Site Inspection Form Element # Inspection BMPs BMP needs BMP Action Inspected maintenance failed required yes no n/a (describe in section F) 5 Are stockpiles stabilized from erosion, Stabilize Soils protected with sediment trapping Cont. measures and located away from drain inlet,waterways,and drainage channels? Have soils been stabilized at the end of the shift, before a holiday or weekend if needed based on the weather forecast? Has stormwater and ground water 6 been diverted away from slopes and Protect disturbed areas with interceptor dikes, Slopes pipes and or swales? Is off-site storm water managed separately from stormwater generated on the site? Is excavated material placed on uphill side of trenches consistent with safety and space considerations? Have check dams been placed at regular intervals within constructed channels that are cut down a slope? 7 Storm drain inlets made operable Drain Inlets during construction are protected. Are existing storm drains within the influence of the project protected? 8 Have all on-site conveyance channels Stabilize been designed,constructed and Channel and stabilized to prevent erosion from Outlets expected peak flows? Is stabilization, including armoring material,adequate to prevent erosion of outlets,adjacent stream banks, slopes and downstream conveyance systems? 9 Are waste materials and demolition Control debris handled and disposed of to Pollutants prevent contamination of stormwater? Has cover been provided for all chemicals, liquid products, petroleum products,and other material? Has secondary containment been provided capable of containing 110% of the volume? Were contaminated surfaces cleaned immediately after a spill incident? Were BMPs used to prevent contamination of stormwater by a pH modifying sources? Page 3 Construction Stormwater Site Inspection Form Element # Inspection BMPs BMP needs BMP Action Inspected maintenance failed required yes no n/a (describe in section F) 9 Wheel wash wastewater is handled Cont. and disposed of properly. 10 Concrete washout in designated areas. Control No washout or excess concrete on the Dewatering ground. Dewatering has been done to an approved source and in compliance with the SWPPP. Were there any clean non turbid dewatering discharges? 11 Are all temporary and permanent Maintain erosion and sediment control BMPs BMP maintained to perform as intended? 12 Has the project been phased to the Manage the maximum degree practicable? Project Has regular inspection, monitoring and maintenance been performed as required by the permit? Has the SWPPP been updated, implemented and records maintained? 13 Is all Bioretention and Rain Garden Protect LID Facilities protected from sedimentation with appropriate BMPs? Is the Bioretention and Rain Garden protected against over compaction of construction equipment and foot traffic to retain its infiltration capabilities? Permeable pavements are clean and free of sediment and sediment laden- water runoff. Muddy construction equipment has not been on the base material or pavement. Have soiled permeable pavements been cleaned of sediments and pass infiltration test as required by stormwater manual methodology? Heavy equipment has been kept off existing soils under LID facilities to retain infiltration rate. E. Check all areas that have been inspected. ✓ All in place BMPs ❑ All disturbed soils ❑ All concrete wash out area All material storage areas All discharge locations All equipment storage areas All construction entrances/exits Page 4 Construction Stormwater Site Inspection Form F. Elements checked "Action Required" (section D) describe corrective action to be taken. List the element number; be specific on location and work needed. Document, initial, and date when the corrective action has been completed and inspected. Element Description and Location Action Required Completion Initials # Date Attach additional page if needed Sign the following certification: "I certify that this report is true, accurate, and complete, to the best of my knowledge and belief" Inspected by: (print) (Signature) Date: Title/Qualification of Inspector: Page 5 Appendix D Engineering Calculations SEDIMENT POND SIZING CALCULATIONS Project Name: Medical Center Date: 09/18/25 Street Location: NWC 212th St NE and Medical Center Dr. Our Job No.: 24413 Municipality: Arlington, WA Engineer: Aspen Lee FS= 2 SA , x Q,'D-00096 Q2= 1.3296 cfs WWHM OR Vs= 0.00096 ft/s 2,080 square feet per cubic feet per second of inflow SA= 2770.00 ft2 Minimum Area of Sediment Trap = 2,770 ft2 Page 1 of 1 24413-Sediment Trap Sizing ®Ana U Flow Frequency 10.0 Cumulative Probability 10.0 Flow(cfs) Predeveloped Mitigated x 2 Year = 0.0029 1.3296 xxx x x 5 Year = 0.0062 1.7932 ®c0°�0°0xxxx 10 Year = 0.0100 2.1314 1.0 xx�cxxxx� 1.0 25 Year = 0.0174 2.5957 50 Year = 0.0258 2.9692 100 Year = 0.0374 3.3673 O 0.1 + + + 5 1 Annual Peaks LL 1949 0.0019 1.4240 + A I 1950 0.0058 1.5288 0.01 +++++ 1951 0.0042 1.6496 +++ 1952 0.0019 1.2642 1953 0.0020 1.6106 + + + +++ 1954 0.0138 2.0150 0.001 0.001 1955 0.0104 1.6316 0.5 1 2 5 10 20 30 50 70 80 90 95 98 9999.51IN 1956 0.0020 0.7053 1957 0.0020 1.1586 Stream Protection Duration I LID Duration Flow Frequency I Water Quality I Hydrograph Duratio 1958 0.0020 2.9947 Wetland Input Volumes LID Report Recharge n Recharge Predeveloped Recharge Mitigated I 1959 0.0045 1.2104 1960 0.0037 1.2095 Analyze datasets Compact WDM Delete Selected r Monthly FF �] 1961 0.0094 3.8213 Duration Chart 1962 0.0020 1.5240 1963 0.0020 1.6468 1964 0.0065 0.9107 :1 1965 0.0020 1.1619 1966 0.0020 1.1636 1967 0.0039 2.5902 1968 0.0020 1.3687 1969 0.0020 2.6578 1970 0.0020 1.0555 All Datasets Flow Stage Precip Evap pOC_1,... 1971 0.0097 1.4447 Flood Frequency Method 1972 0.0020 1.8593 Log Pearson Type III 17B 1973 0.0020 1.5276 Weibull 1974 0.0053 1.8638 Cunnane 1975 0.0018 1.4642 Gringorten 1976 0.0045 1.0273 Page 1 of 1 24413-Sediment Trap Sizing Tab 7 . 0 7.0 SPECIAL REPORTS AND STUDIES The following special reports and studies are included: 7.1 Draft Geotechnical Engineering Report prepared by Terra Associates, Inc. dated August 19, 2025. 24413.002-SSP.doc Figure 7 . 1 Geotechnical Report DRAFT I GEOTECHNICAL REPORT NWC 212 Street. NE Medical Office Facility Snohomish County Tax Parcel 3105120020-0400 Arlington, Washington Project No. T-9205 Terra Associates, Inc. � • 4 AA Prepared for: Visconsi Companies Ltd. Pepper Pike, Ohio August 19, 2025 TERRA ASSOCIATES, Inc. . •; •• Consultants in Geotechnical Engineering, Geology and Environmental Earth Sciences August 19,2025 Project No. T-9205 Mr. Shawn A. Jurisch,P.E. DRAFT Visconsi Companies Ltd. 30050 Chagrin Blvd., Suite 360 Pepper Pike,Ohio 44124 Subject: Geotechnical Report NWC 212 Street NE Medical Office Facility Snohomish County Tax Parcel 3105120020-0400 Arlington,Washington Dear Mr. Jurisch: As requested,we conducted a geotechnical engineering study for the subject project. The attached report presents our findings and recommendations for the geotechnical aspects of project design and construction. Our field exploration indicates soil conditions observed in the test borings underlying several inches of organic topsoil and sod,consists of approximately 4.5 feet to 20 feet of loose to very dense silty sand with gravel overlying medium dense to very dense silty sand with gravel with interbedded sands up to several inches thick to the termination of the test borings. The soil formation is till-like in nature. In Test Borings B-2, B-4 and B-7 we observed approximately seven to ten feet of fill consisting of loose to dense silty sand with gravel overlying the native site soils. We observed light groundwater seepage in Test Borings B-5 and B-7 at depths of approximately 50 and 35 feet, respectively. The seepage was typically observed within interbedded sands in the lower till like deposits. In our opinion, the soil and groundwater conditions are suitable for the planned development provided the recommendations presented in this report are incorporated into project design and construction. We trust the information presented in this report is sufficient for your current needs. If you have any questions or require additional information,please call. Sincerely yours, TERRA ASSOCIATES,INC. Maxwell E. Price,L.G. Staff Geologist DRAFT Theodore J. Schepper, P.E. Senior Principal Engineer Project No. T-9205 12220—113th Avenue NE, Ste. 130, Kirkland, Washington 98034 Phone (425)821-7777 TABLE OF CONTENTS Page No. 1.0 Project Description.......................................................................................................... 1 2.0 Scope of Work................................................................................................................. 1 3.0 Site Conditions ................................................................................................................2 3.1 Surface.....................................................................................................................2 3.2 Soils.........................................................................................................................2 3.3 Groundwater............................................................................................................3 3.4 Geologic Hazards....................................................................................................3 3.4.1 Erosion Hazard Areas....................................................................................3 3.4.2 Landslide Hazard Areas.................................................................................4 3.4.3 Seismic Hazard Areas....................................................................................4 3.5 Seismic Site Class....................................................................................................5 4.0 Discussion and Recommendations..................................................................................5 4.1 General....................................................................................................................5 4.2 Site Preparation and Grading...................................................................................5 4.3 Excavations..............................................................................................................7 4.4 Foundations.............................................................................................................7 4.5 Slab-on-Grade Floors..............................................................................................8 4.6 Lateral Earth Pressures for Retaining Walls............................................................8 4.7 Stormwater Facilities/Infiltration Feasibility...........................................................9 4.8 Drainage................................................................................................................ 10 4.9 Utilities.................................................................................................................. 10 4.10 Pavements..............................................................................................................10 5.0 Additional Services........................................................................................................ 11 6.0 Limitations..................................................................................................................... 11 Fi ures VicinityMap.........................................................................................................................Figure 1 Exploration Location Plan....................................................................................................Figure 2 Typical Wall Drainage Detail...............................................................................................Figure 3 Appendix Field Exploration and Laboratory Testing.......................................................................Appendix A Geotechnical Report NWC 212 Street NE Medical Office Facility Snohomish County Tax Parcel 3105120020-0400 Snohomish, Washington 1.0 PROJECT DESCRIPTION The project consists of redeveloping the site with a 30,000 square foot medical office facility and associated infrastructure improvements. Based on a preliminary grading and drainage plan prepared by Barghausen Consulting Engineers, the building will be located in the southeastern portion of the site with access and paved parking to the north, west and south. Final design grades will require cuts on the order of one to five feet to the north and west with similar fill depths to the south and east. Up to 8 feet of fill will be required to achieve the finished floor elevation along the south side of the building. The preliminary grading and drainage plan also proposed using infiltration galleries installed below the western paved parking area for control of development stormwater. We expect that the building will be a three-story, steel-framed structure, with the main floor constructed at grade. Foundation loads are expected to be moderate, with interior columns carrying 300 to 400 kips and bearing walls carrying 6 to 8 kips per foot. The recommendations contained in the following sections of this report are preliminary and based on our understanding of the above design features. We should review design drawings as they become available to verify that our recommendations have been properly interpreted and incorporated into project design and to amend or supplement our recommendations,if required. 2.0 SCOPE OF WORK Our scope of work was completed in accordance with our authorized proposal dated April 2, 2025. Accordingly, on August 4th, 5th and 6th, 2025, nine test borings were advanced to depths of 10 to approximately 50 feet below existing grades. At completion, three of the test borings located in the proposed infiltration gallery area were converted into groundwater monitoring wells to allow for monitoring groundwater levels over the winter season. Using the results of our field study and laboratory testing, analyses were undertaken to develop geotechnical recommendations for project design and construction. Specifically,this report addresses the following: • Soil and groundwater conditions. • Geologic hazards per the City of Arlington Municipal Code (AMC). • Seismic site class per the 2021 International Building Code(IBC). • Site preparation and grading. • Excavations. • Foundations. August 19,2025 Project No. T-9205 • Slab-on-Grade floors. • Stormwater facilities/infiltration feasibility. • Utilities. • Pavements. It should be noted that recommendations outlined in this report regarding drainage are associated with soil strength, design earth pressures, erosion, and stability. Design and performance issues with respect to moisture as it relates to the structure environment are beyond Terra Associates' purview. A building envelope specialist or contactor should be consulted to address these issues, as needed. 3.0 SITE CONDITIONS 3.1 Surface The project site consists of an approximately 2.3-acre parcel (Snohomish County tax parcel 3 1 05 1 20020-0400) located northwest of the intersection of 212th Street Northeast and Medical Center Drive in Arlington,Washington. The approximate location of the site is shown on Figure 1. The site is currently undeveloped and covered with grass and several scattered small-to medium- sized trees. Site topography slopes gently to the south— southeast with about 20 feet of elevation relief carried over a gradient of about 5 percent. There is a ridge of higher elevation along the east side of the property with slopes off the ridge descending to the west and south. 3.2 Soils In general, soil conditions observed in the test borings underlying several inches of organic topsoil and sod, consist of approximately 4.5 feet to 20 feet of loose to very dense silty sand with gravel overlying medium dense to very dense silty sand with gravel with interbedded sands to the termination of the test borings. Sand interbeds were observed to be several inches thick. There were two exceptions to this general condition. In Test Borings B-2,B- 4 and B-7 we observed approximately seven to ten feet of fill soil,consisting of loose to dense silty sand with gravel overlying the native site soils. In Test Boring B-5 we observed very dense silt with sand and gravel near the 50- foot termination depth of the boring. The Geologic map of the Arlington East quadrangle, Snohomish County, Washington by J.P. Minard(1985)maps the site as Vashon recessional outwash known locally as Arlington Gravel Member (Qvra). Vashon recessional outwash is described as well-drained,stratified outwash sand and gravel deposited by meltwater from the stagnating and receding Vashon Glacier. The area immediately to the north and northwest of the subject site is mapped as Vashon till(Qvt). Vashon till is described as consisting of a non-sorted mixture of clay-silt, sand,pebbles,cobbles and boulders. The soil conditions observed in the test borings are generally more consistent with the description of the Qvt geologic map unit. Page No. 2 August 19,2025 Project No. T-9205 The preceding discussion is intended to be a general review of the soil conditions encountered. For more detailed descriptions,please refer to the Test Boring Logs in Appendix A. The approximate locations of the Test Borings are shown on Figure 2. 3.3 Groundwater We observed light groundwater seepage in Test Borings B-5 and B-7 at depths of approximately 50 and 35 feet, respectively. The seepage was typically observed within interbedded sands in the lower dense silty sand deposits. In addition, mottled soils were observed in all of the test borings within the upper weathered soil zone. Mottled soils typically indicate the presence of perched groundwater seepage throughout much of the site. The occurrence of shallow perched groundwater is typical for sites underlain by fine-grained soils. We expect perched groundwater levels and flow rates will fluctuate seasonally and will typically reach their highest levels during and shortly following the wet winter months (November through May). To evaluate the seasonal weather influence, three of the test borings were converted to observation wells. 3.4 Geologic Hazards Chapter 20.93.600.a of the City of Arlington Municipal Code (AMC) defines geologically hazardous areas as "...areas susceptible to erosion, sliding, earthquakes, liquefaction, or other geological events. Geologically hazardous areas shall be classified based upon the history or existence of landslides,unstable soils, steep slopes, high erosion potential or seismic hazards." Discussions related to erosion, landslide, mine, and seismic hazards are presented below. 3.4.1 Erosion Hazard Areas Chapter 20.93.600.b.I of the AMC defines erosion hazard areas as areas that are"... as defined by the USDA Soil Conservation Service,United States Geologic Survey, or by the Department of Ecology Coastal Zone Atlas. The following classes are high erosion hazard areas: a) Class 3, class U (unstable) includes severe erosion hazards and rapid surface runoff areas; b) Class 4, class UOS (unstable old slides) includes areas having severe limitations due to slope; and, c) Class 5, class URS (unstable recent slides)." We did not observe any indication of erosion or sediment deposition at the site. The vast majority of the site soils are mapped as Alderwood gravelly sandy loam,0 to 8 percent slopes by the United States Department of Agriculture Natural Resources Conservation Service (MRCS). A small portion at the southeast corner of the site is mapped as Ragnar fine sandy loam, 0 to 8 percent slopes. Over the site with existing slope gradients,both of these soils will have a slight potential for erosion when exposed. Therefore, the site is not an erosion hazard as defined by the AMC. Regardless, the site soils will be susceptible to erosion when exposed during construction. In our opinion, proper installation and maintenance of Best Management Practices (BMPs) for erosion prevention and sedimentation control would adequately mitigate the erosion potential in the proposed development areas. All BMPs for erosion prevention and sedimentation control should conform to the Snohomish County requirements. Page No. 3 August 19,2025 Project No. T-9205 3.4.2 Landslide Hazard Areas Chapter 20.93.600.b.2 of the AMC defines landslide hazard areas as "...areas subject to severe risk of landslide based on a combination of geologic, topographic and hydrologic factors. Some of these areas may be identified in the Department of Ecology Coastal Zone Atlas,or through site-specific criteria.Landslide hazard areas include any of the following: a) Areas characterized by slopes greater than fifteen percent and impermeable soils (typically silt and clay) frequently interbedded with permeable granular soils (predominantly sand and gravel) or impermeable soils overlain with permeable soils or springs or groundwater seepage; b) Any area that has exhibited movement during the Holocene epoch (from ten thousand years ago to present) or which is underlain by mass wastage debris of that epoch; c) Any area potentially unstable due to rapid stream incision, stream bank erosion or undercutting by wave action; d) Any area located on an alluvial fan presently subject to or potentially subject to inundation by debris flows or deposition of steam-transported sediments; e) Any area with a slope of thirty-three percent or greater and with a vertical relief of ten or more feet except areas composed of consolidated rock; f) Any area with slope defined by the United States Department of Agriculture Soil Conservation Service as having a severe limitation for building site development; and g) Any shoreline designated or mapped as class U, UOS, or URS by the Department of Ecology Coastal Zone Atlas." Site topography, as shown on the Snohomish County PDS Map Portal, slopes gently to the south—southeast with about 20 feet of elevation relief carried over a gradient of about 5 percent. There is a ridge of higher elevation along the east side of the property with slopes off the ridge descending to the west and south. None of the criteria listed above apply to the site, therefore, it is our opinion that slopes on the site show little to no risk of mass movement due to geologic,topography, or hydrologic factors and that a landslide hazard does not exist at the site. 3.4.3 Seismic Hazard Areas Chapter 20.93.600.b.4 of the AMC defines seismic hazard areas as "... areas subject to severe risk of earthquake damage as a result of seismic induced settlement, shaking, slope failure or soil liquefaction. These conditions occur in areas underlain by cohesion less soils of low density usually in association with a shallow groundwater table." A review of a map titled Faults and Earthquakes in Washington State, dated 2014 by Jessica L. Czajkowski and Jeffrey D. Bowman shows the site does not reside within any active fault zone. The nearest fault,which is a spur of the Darrington-Devils Mountain Fault, is categorized as"Class B" and is located approximately 5.8 miles north of the site. Accordingly,during a seismic event,the risk of ground rupture along a fault line at the site is low. Page No. 4 August 19,2025 Project No. T-9205 Liquefaction is a phenomenon where there is a reduction or complete loss of soil strength due to an increase in water pressure induced by vibrations. Liquefaction mainly affects geologically recent deposits of fine-grained sands underlying the groundwater table. Soils of this nature derive their strength from intergranular friction. The generated water pressure or pore pressure essentially separates the soil grains and eliminates this intergranular friction;thus, eliminating the soil's strength. Based on the soil and groundwater conditions observed, in our opinion, the potential for soil liquefaction and settlement within the native soils is negligible. Groundwater seepage was typically perched with minimal flow. Additionally,the site is rated as having very low potential for liquefaction on the Washington State Department of Natural Resources Natural Hazards Single-Topic Map. Therefore,the site would not meet the seismic hazard area criteria, as described above. 3.5 Seismic Site Class Based on soil conditions observed in the test pits, and our knowledge of the area geology, per Chapter 20 of the 2021 International Building Code(IBC), Site Class"D"should be used in structural design. 4.0 DISCUSSION AND RECOMMENDATIONS 4.1 General In our opinion, there are no geotechnical conditions that would preclude the planned development. The medical office building can be supported on conventional spread footings bearing on competent native soils below the organic topsoil layer or on structural fill placed above the competent native soils. Existing fill soils observed in the eastern ridge at test borings B-2,B-4 and B-7 are not suitable for building support in their current condition. Over excavation and structurally recompacting these existing fills will be required. Floor slabs and pavements can be similarly supported. The native and existing fill soils encountered at the site contain a significant amount of fines and will be difficult to compact as structural fill when too wet. The ability to use the existing fill and native soils from site excavations as structural fill will depend upon its moisture content and the prevailing weather conditions at the time of construction. If grading activities take place during winter, the owner should be prepared to import clean granular material for use as structural fill and backfill. The following sections provide detailed recommendations regarding the preceding issues and other geotechnical design and construction considerations. These recommendations should be incorporated into the final design drawings and construction specifications. 4.2 Site Preparation and Grading To prepare the site for construction, all vegetation, organic surface soils, and other deleterious material should be stripped and removed from the site. Surface stripping depths of approximately two to four inches should be expected to remove the organic surface soils and vegetation. Organic topsoil will not be suitable for use as structural fill but may be used for limited depths in nonstructural areas. Page No. 5 August 19,2025 Project No. T-9205 The existing fill soils observed in the upper ten feet in Test Borings B-4 and B-7 are currently in a very loose to loose condition and will need to be over excavated and recompacted structurally below all building elements. We recommend removing the existing fill to a depth that leaves two feet of the fill in place. At that depth the fill should be compacted structurally with the soils then replaced in uniform lifts and compacted structurally as recommended below. Once clearing and stripping operations are complete, cut and fill operations can be initiated to establish desired building grades. Prior to placing fill, all exposed bearing surfaces should be observed by a representative of Terra Associates, Inc. to verify soil conditions are as expected and suitable for support of new fill or building elements. Our representative may request a proofroll using heavy rubber-tired equipment to determine if any isolated soft and yielding areas are present. If excessively yielding areas are observed and they cannot be stabilized in place by compaction, the affected soils should be excavated and removed to firm bearing and grade restored with new structural fill. If the depth of excavation to remove unstable soils is excessive,the use of geotextile fabrics such as, Mirafi 500X or an equivalent fabric can be used in conjunction with clean granular structural fill. Our experience has shown, in general, a minimum of 18 inches of a clean, granular structural fill placed and compacted over the geotextile fabric should establish a stable bearing surface. Our study indicates that both the existing fill soils and native soils at the site contain a sufficient amount of soil fines that will make them difficult to compact as structural fill when too wet or too dry. The ability to use these soils from site excavations as structural fill will depend upon its moisture content,the prevailing weather conditions at the time of construction and the contractor's ability to compact the native silt soils. If wet soils are encountered, the contractor will need to dry the soils by aeration during dry weather conditions. Alternatively, the use of an additive, such as Portland cement or lime to stabilize the soil moisture can be considered. If the soil is amended, additional Best Management Practices (BMPs) addressing the potential for elevated pH levels will need to be included in the Stormwater Pollution Prevention Program (SWPPP) prepared with the Temporary Erosion and Sedimentation Control(TESC)plan. The relatively clean sand and gravels observed throughout the site, should be suitable to reuse as structural fill in most weather conditions. If grading activities are planned during the wet winter months,or if they are initiated during the summer and extend into fall and winter,the owner should be prepared to import wet-weather structural fill. For this purpose,we recommend importing a granular soil that meets the following grading requirements: U.S. Sieve Size Percent Passim 6 inches 100 No. 4 75 maximum No. 200 5 maximum* *Based on the 3/4-inch fraction. Prior to use, Terra Associates, Inc. should examine and test all materials imported to the site for use as structural fill. Page No. 6 August 19,2025 Project No. T-9205 Structural fill should be placed in uniform loose layers not exceeding 12 inches and compacted to a minimum of 95 percent of the soil's maximum dry density, as determined by American Society for Testing and Materials(ASTM) Test Designation D-1557(Modified Proctor). The moisture content of the soil at the time of compaction should be within two percent of its optimum, as determined by this ASTM standard. In nonstructural areas, the degree of compaction can be reduced to 90 percent. 4.3 Excavations All excavations at the site associated with confined spaces, such as lower-building level retaining walls, must be completed in accordance with local, state, and federal requirements. Based on the Washington State Safety and Health Administration (WSHA) regulations, the loose to dense fill and native weathered till soils would typically be classified as Type "C" soils. The native dense to very dense unweathered till would be classified as Type "A" soils. Accordingly, temporary excavations in Type C soils should have their slopes laid back at an inclination of 1.5:1 (Horizontal: Vertical)or flatter, from the toe to the crest of the slope. Side slopes in Type A soils can be laid back at a slope inclination of 0.75:1 or flatter. For temporary excavation slopes less than 8 feet in height in Type A soils, the lower 3.5 feet can be cut to a vertical condition, with a 0.75:1 slope graded above. For temporary excavation slopes greater than 8 feet in height up to a maximum height of 12 feet,the slope above the 3.5-foot vertical portion will need to be laid back at a minimum slope inclination of 1:1. No vertical cut with a backslope immediately above is allowed for excavation depths that exceed 12 feet. In this case, a four-foot vertical cut with an equivalent horizontal bench to the cut slope toe is required. All exposed temporary slope faces that will remain open for an extended period of time should be covered with a durable reinforced plastic membrane during construction to prevent slope raveling and rutting during periods of precipitation. Groundwater seepage may be encountered within excavations during the wet winter season. We anticipate that the volume of water and rate of flow into the excavation will be relatively minor and is not expected to impact the stability of the excavations when completed, as described. Conventional sump pumping procedures, along with a system of collection trenches, if necessary, should be capable of maintaining a relatively dry excavation for construction purposes. This information is provided solely for the benefit of the owner and other design consultants and should not be construed to imply that Terra Associates, Inc. assumes responsibility for job site safety. It is understood that job site safety is the sole responsibility of the project contractor. 4.4 Foundations The building may be supported on conventional spread footing foundations bearing on competent native soils or on structural fill placed above competent soils. Foundation subgrades should be prepared as recommended in Section 4.2 of this report. Foundations exposed to the weather should bear at a minimum depth of one and one-half feet below adjacent exterior grades for frost protection. Interior foundations should be supported at a minimum depth of one foot below the finished floor elevation. The existing fill soils and native soils will be easily disturbed by normal construction activity particularly when wet. Care will need to be exercised during construction to avoid excessively disturbing the subgrade. If disturbed, the material should be removed, and footings lowered to undisturbed material or grade restored with structural fill. During wet-weather conditions,to avoid disturbance,consideration should be given to protecting the fill foundation subgrade with a four-inch layer of crushed rock or lean mix concrete. Page No. 7 August 19,2025 Project No. T-9205 We recommend designing foundations bearing on competent structural fill soils for a net allowable bearing capacity of 3,000 pounds per square foot(psf). Foundations that are supported on competent native soils below the fills can be designed for and allowable bearing capacity of 5,000 psf. For short-term loads, such as wind and seismic,a one- third increase in this allowable capacity can be used. With the expected building loads and this bearing stress applied, in general, total, and differential settlements should not exceed one inch and one-half inch,respectively. Settlements will occur in and immediate nature as building loads are applied. The one-half inch differential settlement would be expected to occur between isolated interior columns and perimeter continuous footings. For designing foundations to resist lateral loads, a base friction coefficient of 0.35 can be used. Passive earth pressures acting on the sides of the footings should be considered. We recommend calculating this lateral resistance using an equivalent fluid weight of 350 pounds per cubic foot(pcf). We do not recommend including the upper 12 inches of soil in this computation because it can be affected by weather or disturbed by future grading activity. This value assumes the foundation will be backfilled with structural fill, as described in Section 4.2 of this report. The values recommended include a safety factor of 1.5. 4.5 Slab-on-Grade Floors Slab-on-grade floors may be supported on a subgrade prepared as recommended in Section 4.2 of this report. Immediately below the floor slab,we recommend placing a four-inch-thick capillary break layer composed of clean, coarse sand or fine gravel that has less than five percent passing the No. 200 sieve. This material will reduce the potential for upward capillary movement of water through the underlying soil and subsequent wetting of the floor slab. The capillary break layer will not prevent moisture intrusion through the slab caused by water vapor transmission. Where moisture by vapor transmission is undesirable, such as covered floor areas, a common practice is to place a durable plastic membrane on the capillary break layer and then cover the membrane with a layer of clean sand or fine gravel to protect it from damage during construction, and aid in uniform curing of the concrete slab. It should be noted that if the sand or gravel layer overlying the membrane is saturated prior to pouring the slab, it will be ineffective in assisting uniform curing of the slab and can actually serve as a water supply for moisture seeping through the slab and affecting floor coverings. Therefore, in our opinion, covering the membrane with a layer of sand or gravel should be avoided if floor slab construction occurs during the wet winter months and the layer cannot be effectively drained. We recommend floor designers and contractors refer to the current American Concrete Institute(ACI)Manual of Concrete Practice for further information regarding vapor barrier installation below slab- on-grade floors. 4.6 Lateral Earth Pressures for Retaining Walls The magnitude of earth pressures developing on below-grade walls will depend upon the quality and compaction of the wall backfill. We recommend placing and compacting wall backfill as structural fill,as described in Section 4.2 of this report. To prevent overstressing the walls during backfilling,heavy construction machinery should not be operated within five feet of the wall. Wall backfill in this zone should be compacted with hand-operated equipment. To prevent hydrostatic pressure development, wall drainage must also be installed. A typical wall drainage detail is shown on Figure 3. Page No. 8 August 19,2025 Project No. T-9205 With wall backfill placed and compacted as recommended, and drainage properly installed, we recommend designing unrestrained walls for an active earth pressure equivalent to a fluid weighing 35 pounds per cubic foot (pcf). For restrained walls, an additional uniform load of 100 psf should be added to the 35 pcf. To account for typical traffic surcharge loading,the walls can be designed for an additional imaginary height of two feet(two-foot soil surcharge). For evaluation of wall performance under seismic loading, a uniform pressure equivalent to 8H psf,where H is the height of the below-grade portion of the wall, should be applied in addition to the static lateral earth pressure. These values assume a horizontal backfill condition and that no other surcharge loading, sloping embankments, or adjacent buildings will act on the wall. If such conditions exist, then the imposed loading must be included in the wall design. Friction at the base of foundations and passive earth pressure will provide resistance to these lateral loads. The values for these parameters are provided in Section 4.4 of this report. 4.7 Stormwater Facilities/Infiltration Feasibility Based on the preliminary grading and drainage plan by Barghausen Consulting Engineers,development stormwater will be routed to infiltration galleries located below the western pavement areas. In our subsurface exploration,we observed predominantly dense till like soils composed of silty sand with gravel to the termination of the test borings. The native weathered and unweathered till like deposits at the site contain a significant amount of soil fines and is a poorly drained soil unit. These soil conditions are not suitable for discharge of development stormwater using infiltration facilities. Conventional stormwater detention with controlled release to existing stormwater infrastructure should be used to manage development stormwater. Detention Vault If onsite detention is provided by a buried vault,we expect the bottom of the excavation would likely expose native, dense to very dense silty sand with gravel or very stiff to hard silt with sand and gravel. Vault foundations supported by these native soils may be designed for an allowable bearing capacity of 5,000 psf provided that the foundation subgrade is at least eight feet below current site grades. For short-term loads, such as seismic, a one-third increase in this allowable capacity can be used. Wet subgrade conditions that are easily disturbed by construction traffic will be exposed at the bottom of the vault excavation. Vault walls should be designed as below-grade retaining walls following the parameters outline in Section 4.6 of this report. Any portion of the wall for which drainage cannot be provided should be designed for an earth pressure equivalent to a fluid weighing 85 pcf. Where applicable, a uniform horizontal traffic value of 75 psf should be included in the design of vault walls. Detention Pond If fill berms are constructed,the berm locations should be stripped of topsoil,duff,and soils containing organic material prior to the placement of fill. The fill berms should be constructed by placing structural fill in accordance with recommendations outlined in Section 4.2 of this report. Material used to construct pond berms should consist predominately of granular soils with a maximum size of 3 inches and a minimum of 20 percent fines. Terra Associates, Inc. should examine and test all onsite or imported materials proposed for use as a fill berm prior to their use. Page No. 9 August 19,2025 Project No. T-9205 In our opinion,establishing the interior pond slopes at a 3:1 (Horizontal:Vertical)gradient will significantly reduce or eliminate the risk of periodic shallow instability or sloughing of the exposed soils due to fluctuating stored water levels. Finished slope faces should be thoroughly compacted and vegetated to guard against erosion. We should review the stormwater plans when they are completed and revise our recommendations, if required. 4.8 Drainage Surface Final exterior grades should promote free and positive drainage away from the building areas. We recommend providing a positive drainage gradient away from the building perimeters. If a positive gradient cannot be provided, provisions for collection and disposal of surface water adjacent to the structures should be provided. Subsurface We recommend installing a continuous drain along the outside lower edge of the perimeter building foundations. The drains can be laid to grade at an invert elevation equivalent to the bottom of footing grade. The drains can consist of four-inch diameter perforated PVC pipe that is enveloped in washed one half-to three-quarter-inch gravel- sized drainage aggregate. The aggregate should extend six inches above and to the sides of the pipe. The foundation drains and roof downspouts should be tightlined separately to an approved point of controlled discharge. All drains should be provided with cleanouts at easily accessible locations. These cleanouts should be serviced at least once each year. 4.9 Utilities Utility pipes should be bedded and backfilled in accordance with American Public Works Association(APWA) or City of Arlington specifications. At minimum,trench backfill should be placed and compacted as structural fill as described in Section 4.2 of this report. As noted, soils excavated onsite should generally be suitable for use as backfill material provided, they are near optimum moisture when excavated and are placed during dry weather conditions. However, the site soils are fine grained and moisture sensitive; therefore, moisture conditioning may be necessary to facilitate proper compaction. If utility construction takes place during the winter, it may be necessary to import suitable wet-weather fill for utility trench backfilling. 4.10 Pavements Pavements should be constructed on subgrades prepared as recommended in Section 4.2 of this report. Regardless of the degree of relative compaction achieved, the subgrade must be firm and relatively unyielding before paving. Proof-rolling the subgrade with heavy construction equipment should be completed to verify this condition. The pavement design section is dependent upon the supporting capability of the subgrade soils and the traffic conditions to which it will be subjected. Page No. 10 August 19,2025 Project No. T-9205 For traffic consisting mainly of light passenger vehicles with only occasional heavy traffic, and with a stable subgrade prepared as recommended,we recommend the following pavement sections: • Two inches of hot mix asphalt(HMA)over six inches of crushed rock base(CRB). • Four inches full depth HMA over prepared subgrade. The paving materials used should conform to the Washington State Department of Transportation (WSDOT) specifications for ''/z-inch class HMA and CRB. Long-term pavement performance will depend upon surface drainage. A poorly drained pavement section will be subject to premature failure as a result of surface water infiltrating into the subgrade soils and reducing their supporting capability. For optimum pavement performance, we recommend surface drainage gradients of at least two percent. Some degree of longitudinal and transverse cracking of the pavement surface should be expected over time. Regular maintenance should be planned to seal cracks when they occur. 5.0 ADDITIONAL SERVICES Terra Associates, Inc., should review the final designs and specifications in order to verify that earthwork and foundation recommendations have been properly interpreted and implemented in project design. We should also provide geotechnical services during construction in order to observe compliance with our design concepts, specifications,and recommendations. This will allow for design changes if subsurface conditions differ from those anticipated prior to the start of construction. 6.0 LIMITATIONS We prepared this report in accordance with generally accepted geotechnical engineering practices. No other warranty, expressed or implied, is made. This report is the copyrighted property of Terra Associates, Inc. and is intended for specific application to the NWC 212th St. NE Medical Office Facility project in Arlington, Washington. This report is for the exclusive use of Visconsi Companies. Ltd and their authorized representatives. No other warranty, expressed or implied,is made. The analyses and recommendations presented in this report are based on data obtained from our onsite test pits. Variations in soil conditions can occur,the nature and extent of which may not become evident until construction. If variations appear evident, Terra Associates, Inc. should be requested to reevaluate the recommendations in this report prior to proceeding with construction. Page No. I I 1§, Eagle Creek ElemEntary a '� Sthc!al 2-id Si Z as Era O Az < ro � U vi U. Z. uj f ¢5t # E fst 5t z o t? s ti 4' ati Cd r ) �+ m U E Maple St l5th S`NE Ariington High Schc)ol 13 r ii3th St N\N V7 Medical C. Cascade Valley Hospital SITE LU } C Hkjh7and_gr t12th Sr NE aO -17 C P a a E ro Bl p!NT —ir c� • .. Portage St ./� 2003 5t NE 0 500 1000 APPROXIMATE SCALE IN FEET ozozs Microsoft Corporation 2025 T..T.. �-Air-1 r" REFERENCE: https://www.bing.com/maps ACCESSED 2025 Terra VICINITY MAP NWC 212 ST. NE MEDICAL OFFICE FACILITY Associates, Inc. ARLINGTON, WASHINGTON Consultants in Geotechnical Engineering Geology and Environmental Earth Sciences Proj.No. T-9205 Date: AUG 2025 Figure 1 •� �,. MER 40 amp No vow I&A W,0Pdw 09w s' 0 -40 1j 1 21 Ali. NOTE: LEGEND: THIS SITE PLAN IS SCHEMATIC. ALL LOCATIONS AND & APPROXIMATE BORING LOCATION DIMENSIONS ARE APPROXIMATE. IT IS INTENDED FOR 0 80 160 M REFERENCE ONLY AND SHOULD NOT BE USED FOR DESIGN OR CONSTRUCTION PURPOSES. APPROXIMATE SCALE IN FEET REFERENCE:SITE PLAN PROVIDED BY BING MAPS. Terra EXPLORATION LOCATION PLAN NWC 212 ST. NE MEDICAL OFFICE FACILITY Associates, Inc. ARLINGTON, WASHINGTON Consultants in Geotechnical Engineering Geology and Pro .No. T-9205 Date: AUG 2025 Figure 2 Environmental Earth Sciences J 9 12" MINIMUM 3/4" MINUS WASHED GRAVEL SLOPE TO DRAIN 12" ............................................................... ............................................. j COMPACTED j n STRUCTURAL FILL / ..% i ... SEE NOTE "' EXCAVATED SLOPE EE REP (SORT TEXT FOR APPROPRIATE 6"(MIN.) ............................................... INCLINATIONS) G 0 0 0 0 0 12" OVER PIPE 3" BELOW PIPE 4" DIAMETER PERFORATED PVC PIPE NOT TO SCALE NOTE: MIRADRAIN G100N PREFABRICATED DRAINAGE PANELS OR SIMILAR PRODUCT CAN BE SUBSTITUTED FOR THE 12-INCH WIDE GRAVEL DRAIN BEHIND WALL. DRAINAGE PANELS SHOULD EXTEND A MINIMUM OF SIX INCHES INTO 12-INCH THICK DRAINAGE GRAVEL LAYER OVER PERFORATED DRAIN PIPE. Terra TYPICAL WALL DRAINAGE DETAIL NWC 212 ST. NE MEDICAL OFFICE FACILITY Associates, Inc. ARLINGTON, WASHINGTON Consultants in Geotechnical Engineering Geology and Environmental Earth Sciences Proj.No. T-9205 Date: AUG 2025 Figure 3 APPENDIX A FIELD EXPLORATION AND LABORATORY TESTING NWC 212 Street NE Medical Office Building Arlington,Washington On August 4, 5, and 6, 2025, we observed soil and groundwater conditions in nine test borings advanced with a hollow-stem auger to maximum depths of approximately 50 feet below existing site grades. The test boring locations were approximately determined in the field using GPS coordinates and by sighting and pacing from existing surface features. The approximate test boring locations are shown on Figure 2. The Test Boring Logs are presented as Figures A-2 through A-10. A geologist from our office conducted the field exploration. Our representative classified the soil conditions encountered, maintained a log of each test boring, obtained representative soil samples, and recorded water levels observed during drilling. During drilling, soil samples were obtained in general accordance with ASTM Test Designation D-1586. Using this procedure, a 2-inch(outside diameter) split barrel sampler is driven into the ground 18 inches using a 140-pound hammer free falling from a height of 30 inches. The number of blows required to drive the sampler 12 inches after an initial 6-inch set is referred to as the Standard Penetration Resistance value or N value. This is an index related to the consistency of cohesive soils and relative density of cohesionless materials.N values obtained for each sampling interval are recorded on the Test Boring Logs,Figures A-2 through A-10. All soil samples were visually classified in accordance with the Unified Soil Classification System (USCS) described on Figure A-1. Representative soil samples obtained from the test borings were placed in sealed plastic bags and taken to our laboratory for further examination and testing. The moisture content of each sample was measured and is reported on the individual Boring Logs. Grain size analyses were performed on select soil samples. The results are shown on Figures A-11 and A-12. Project No. T-9205 MAJOR DIVISIONS LETTER TYPICAL DESCRIPTION SYMBOL Clean GW Well-graded gravels, gravel-sand mixtures, little or no fines. GRAVELS Gravels (less cn More than 50% than 5% y g g g 2) fines) GP Poorly-graded raded ravels, ravel-sand mixtures, little or no fines. O ca N of coarse fraction Cl) To is larger than No. GM Silty gravels, gravel-sand-silt mixtures, non-plastic fines. w a) > 4 sieve Gravels with Z is .0 fines Q E (n GC Clayey gravels, gravel-sand-clay mixtures, plastic fines. o 0 N oLO o Clean Sands SW Well-graded sands, sands with gravel, little or no fines. Cn M z SANDS (less than QM More than 50% 5%fines) SP Poorly-graded sands, sands with gravel, little or no fines. O o — of coarse fraction :2 is smaller than SM Silty sands, sand-silt mixtures, non-plastic fines. No. 4 sieve Sands with fines SC Clayey sands, sand-clay mixtures, plastic fines. L ML Inorganic silts, rock flour, clayey silts with slight plasticity. ` .� SILTS AND CLAYS p To Liquid Limit is less than 50% CL Inorganic clays of low to medium plasticity. (Lean clay) G M U) OL Organic silts and organic clays of low plasticity. Z Eo _ o0 Q \o N MH Inorganic silts, elastic. � � o z SILTS AND CLAYS W M ° CH Inorganic clays of high plasticity. (Fat clay) Z . M Liquid Limit is greater than 50/° U_ o OH Organic clays of high plasticity. HIGHLY ORGANIC SOILS PT Peat. DEFINITION OF TERMS AND SYMBOLS co Standard Penetration 2"OUTSIDE DIAMETER SPILT SPOON SAMPLER w Density Resistance in Blows/Foot Z 2.4" INSIDE DIAMETER RING SAMPLER OR O Very Loose 0-4 SHELBY TUBE SAMPLER cn Loose 4-10 = Medium Dense 10-30 1 WATER LEVEL(Date) O Dense 30-50 U Very Dense >50 Tr TORVANE READINGS,tsf Standard Penetration Pp PENETROMETER READING, tsf Consistancy Resistance in Blows/Foot W DID DRY DENSITY, pounds per cubic foot cn Very Soft 0-2 W Soft 2-4 LL LIQUID LIMIT, percent 2 O Medium Stiff 4-8 U Stiff 8-16 PI PLASTIC INDEX Very Stiff 16-32 Hard >32 N STANDARD PENETRATION, blows per foot Terra UNIFIED SOIL CLASSIFICATION SYSTEM NWC 212 ST. NE MEDICAL OFFICE FACILITY Associates, Inc. ARLINGTON, WASHINGTON Consultants in Geotechnical Engineering Geology and Pro .No. T-9205 Date: AUG 2025 Figure A-1 Environmental Earth Sciences � g LOG OF BORING NO. B-1 Figure No.A-2 Project: NWC 212 St. NE Medical Office Facility Project No:T-9205 Date Drilled: August 5, 2025 Client:Visconsi Companies Ltd. Driller: BoreTec1 Logged By: MEP Location: Arlington, Washington Depth to Groundwater:N/A Approx. Elev: NA L 2 Soil Description Consistency/ SPT(N) Moisture a p Relative Density Blows/foot Content(%) Q E Q i) 10 30 50 0 Grayish-brown silty SAND with gravel,fine to coarse sand, fine to coarse gravel, moist, mottled. (SM) • 16 5 • 16 15.0 Medium Dense • 15 13.2 *Became wet at 7.5 feet. 10 • 13 9.5 Boring terminated at 10 feet. Minor perched seepage observed at approximately 10 feet. 15 . Terra NOTE:This borehole log has been prepared for geotechnical purposes. This information pertains only to this boring location and should not be interpeted as being indicative of ikOO Associates, Inc. other areas of the site Consultants in Geotechnical Engineering Geology and Environmental Earth Sciences LOG OF BORING NO. B-2 Figure No.A-3 Project: NWC 212 St. NE Medical Office Facility Project No:T-9205 Date Drilled: August 5, 2025 Client:Visconsi Companies Ltd. Driller: BoreTec1 Logged By: MEP Location: Arlington, Washington Depth to Groundwater:N/A Approx. Elev: NA L 2 Soil Description Consistency/ SPT(N) Moisture a p Relative Density Blows/foot Content(%) Q E Q i) 10 30 50 0 FILL?: Brown silty SAND with gravel,fine to coarse sand,fine to coarse gravel,dry to moist, scattered rootlets. (SM) Medium Dense • 13 20.8 5 • 7 9.0 Loose --------------------------------------------- Grayish-brown silty SAND with gravel,fine to coarse sand, . 16 18.5 fine to coarse gravel, moist, mottled. (SM) Medium Dense 10 49 12.0 Dense Boring terminated at 10 feet. Minor seepage observed at 10.5 feet deep. 15 . Terra NOTE:This borehole log has been prepared for geotechnical purposes. This information pertains only to this boring location and should not be interpeted as being indicative of ikOO Associates, Inc. other areas of the site Consultants in Geotechnical Engineering Geology and Environmental Earth Sciences LOG OF BORING NO. B-3 Figure No.A-4 Project: NWC 212 St. NE Medical Office Facility Project No:T-9205 Date Drilled: August 5, 2025 Client:Visconsi Companies Ltd. Driller: BoreTec1 Logged By: MEP Location: Arlington, Washington Depth to Groundwater:N/A Approx. Elev: NA L 2 Soil Description Consistency/ SPT(N) Moisture a p Relative Density Blows/foot Content(%) Q E Q i) 10 30 50 0 Brown silty SAND with gravel,fine to coarse sand,fine gravel, dry to moist,scattered rootlets (SM) Loose • 7 15.0 Grayish-brown silty SAND with gravel,fine to coarse sand, 5 fine to coarse gravel, moist, mottled. (SM) • 42 12.1 Dense 53 10.7 Very Dense 10 • 42 10.5 Dense Boring terminated at 10 feet. No groundwater seepage observed. 15 . Terra NOTE:This borehole log has been prepared for geotechnical purposes. This information pertains only to this boring location and should not be interpeted as being indicative of ikOO Associates, Inc. other areas of the site Consultants in Geotechnical Engineering Geology and Environmental Earth Sciences LOG OF BORING NO. B-4 Figure No.A-5 Project: NWC 212 St. NE Medical Office Facility Project No:T-9205 Date Drilled: August 5, 2025 Client:Visconsi Companies Ltd. Driller: BoreTec1 Logged By: MEP Location: Arlington, Washington Depth to Groundwater:N/A Approx. Elev: NA L 2 Soil Description Consistency/ SPT(N) Moisture a p Relative Density Blows/foot Content(%) Q E Q i) 10 30 50 0 FILL?: Brown silty SAND with gravel,fine to coarse sand,fine gravel, dry to moist. (SM) Dense 31 10.5 I *Scattered rootlets in the upper 4 feet. 5 T • 8 17.5 1 Loose 5 20.9 I 1 o T 6 20.9 1 (4-inches organic TOPSOIL with scattered straw) IGrayish-brown silty SAND with gravel,fine to coarse sand, Dense • 44 8.6 fine to coarse gravel, moist to wet, mottled. (SM) 15 T 50/3" 20.8 1 --------------------------------------------- Gray silty SAND with gravel,fine to coarse sand,fine to Very Dense 20 coarse gravel, moist. (SM) 65 10.3 25 T 20 10.1 1 Medium Dense 30 T Very Dense 50/6" 1 Boring terminated at 30 feet. No groundwater seepage observed. 35 40 . Terra NOTE:This borehole log has been prepared for geotechnical purposes. This information pertains only to this boring location and should not be interpeted as being indicative of ikOO Associates, Inc. other areas of the site Consultants in Geotechnical Engineering Geology and Environmental Earth Sciences LOG OF BORING NO. B-5 Figure No.A-6 Project: NWC 212 St. NE Medical Office Facility Project No:T-9205 Date Drilled: August 4, 2025 Client:Visconsi Companies Ltd. Driller: BoreTec1 Logged By: MEP Location: Arlington, Washington Depth to Groundwater:50 feet Approx. Elev: NA L 2 Soil Description Consistency/ SPT(N) Moisture a p Relative Density Blows/foot Content(%) Q E Q i) 10 30 50 0 Grayish-brown silty SAND with gravel,fine to coarse sand, fine to coarse gravel, dry to moist, mottled. (SM) Dense • 44 11.0 I 5 I *Scattered rootlets in the upper 4 feet. Very Dense 55 10.2 •I Medium Dense 25 11.7 10 I *Moist to wet below 7.5 feet. • 32 11.6 I Dense 50 9.5 15 I • 47 13.4 20 I --------------------------------------------- • 16 16.7 Gray silty SAND with gravel,fine to medium sand, fine to coarse gravel,wet. (SM) 25 I • 14 12.6 *1"interbeds of fine to medium sand at approximately 25 feet Medium Dense deep. 30 I • 18 11.7 35 I • 28 11.8 40 I Dense • 36 10.4 r------------------------------------------- 45 I Gray silty SAND,fine to coarse sand,wet, trace fine gravel. 50/6" 16.6 (SM) Very Dense s50 Gray SILT with sand and gravel,fine to medium sand,fine to 52 14.2 I coarse gravel,wet to saturated, 1-2-inch interbeds of medium to coarse sand. (ML) 55 Boring terminated at 50 feet. Groundwater seepage observed at 50 feet. 60 . Terra NOTE:This borehole log has been prepared for geotechnical purposes. This information pertains only to this boring location and should not be interpeted as being indicative of ikOO Associates, Inc. other areas of the site Consultants in Geotechnical Engineering Geology and Environmental Earth Sciences LOG OF BORING NO. B-6 Figure No.A-7 Project: NWC 212 St. NE Medical Office Facility Project No:T-9205 Date Drilled: August 6, 2025 Client:Visconsi Companies Ltd. Driller: BoreTec 1 Logged By: MEP Location: Arlington, Washington Depth to Groundwater:NA Approx. Elev: NA v Soil Description Consistency/ SPT(N) Moisture Observ. p Relative Density Blows/foot Content(%) Well a E o in 10 30 50 0 Grayish-brown silty SAND with gravel, fine to coarse sand,fine to coarse gravel, moist, mottled. (SM) *Scattered rootlets in the upper 4 feet. Very Dense 54 9.9 I 5 I • 23 10.8 • 27 12.1 I ---------------------------------------- Medium Dense 10— Gray silty SAND with gravel,fine to coarse sand, fine to • 16 16.0 coarse gravel,wet. (SM) • 26 13.0 I 15 50/4" 11.8 I Very Dense *2-3"interbeds of fine to medium sand at approximately 20 20 feet deep. Medium Dense . 17 14.2 I Test Boring terminated at approximately 20 feet. 2"PVC monitoring well constructed with a 0.010 slot screen from 10 to 20 feet. Samples collected by driving a 2.5 inch O.D. sampler 25 with a 140-pound hammer. Well Tag#BQU-132 No groundwater seepage observed. 30 Terra NOTE:This borehole log has been prepared for geotechnical purposes. This information Associates Inc. pertains only to this boring location and should not be interpeted as being indicative of 7 other areas of the site e Consultants in otechnical Engineering Geology and Environmental Earth Sciences LOG OF BORING NO. B-7 Figure No.A-8 Project: NWC 212 St. NE Medical Office Facility Project No:T-9205 Date Drilled: August 4, 2025 Client:Visconsi Companies Ltd. Driller: BoreTec1 Logged By: MEP Location: Arlington, Washington Depth to Groundwater:35 feet Approx. Elev: NA L 2 Soil Description Consistency/ SPT(N) Moisture a p Relative Density Blows/foot Content(%) Q E Q i) 10 30 50 0 FILL: Brown silty SAND with gravel,fine to coarse sand,fine I to coarse gravel, moist, occasional charcoal fragments, 8 5 scattered rootlets. (SM) Loose • 6 14.7 I FILL?: Light brown SILT, moist, mottled, scattered gravel. (ML) • 8 39.4 ---------------------------------------------- 10 I Grayish-brown silty SAND with gravel,fine to coarse sand, Very Dense 55 15.5 fine to coarse gravel, moist, mottled. (SM) • 23 14.1 I Medium Dense 15 I • 36 13.8 3-4-inch interbed of silt at 15 feet deep. 20 50 9.6 I Dense 25 Gray silty SAND with gravel,fine to coarse sand,fine gravel, 41 10.9 I moist to wet. (SM) 30 I 72 9.9 Very Dense =35 I 50/6" 12.6 40 I Medium Dense • 25 11.6 45 I Very Dense 52 10.3 50 Medium Dense • 25 12.6 I Boring terminated at 50 feet. 55 Light seepage observed at 35 feet. 60 . Terra NOTE:This borehole log has been prepared for geotechnical purposes. This information pertains only to this boring location and should not be interpeted as being indicative of ikOO Associates, Inc. other areas of the site Consultants in Geotechnical Engineering Geology and Environmental Earth Sciences LOG OF BORING NO. B-8 Figure No.A-9 Project: NWC 212 St. NE Medical Office Facility Project No:T-9205 Date Drilled: August 5, 2025 Client:Visconsi Companies Ltd. Driller: BoreTec1 Logged By: MEP Location: Arlington, Washington Depth to Groundwater:NA Approx. Elev: NA v Soil Description Consistency/ SPT(N) Moisture Observ. p Relative Density Blows/foot Content(%) Well a E o in 10 30 50 0 Grayish-brown silty SAND with gravel, fine to coarse sand,fine to coarse gravel, moist, mottled. (SM) Very Loose 2 19.8 T 5 I 20 11.9 I Medium Dense 16 12.1 10 I 30 12.3 T 50/6" *1-2-inch interbed of fine to medium sand at 13 feet. Very Dense 15 T Gray silty SAND with gravel,fine to coarse sand, fine 29 10.9 gravel, moist to wet. (SM) Medium Dense 20 I 29 10.2 25 I Very Dense 53 8.7 Test Boring terminated at approximately 25 feet. 2"PVC monitoring well constructed with a 0.010 slot screen from 15 to 25 feet. 30 Samples collected by driving a 2.5 inch O.D. sampler with a 140-pound hammer. Well Tag#BQU-131 No groundwater seepage observed. 35 Terra NOTE:This borehole log has been prepared for geotechnical purposes. This information Associates Inc. pertains only to this boring location and should not be interpeted as being indicative of 7 other areas of the site e Consultants in otechnical Engineering Geology and Environmental Earth Sciences LOG OF BORING NO. B-9 Figure No.A-10 Project: NWC 212 St. NE Medical Office Facility Project No:T-9205 Date Drilled: August 6, 2025 Client:Visconsi Companies Ltd. Driller: BoreTec1 Logged By: MEP Location: Arlington, Washington Depth to Groundwater:NA Approx. Elev: NA v Soil Description Consistency/ SPT(N) Moisture Observ. p Relative Density Blows/foot Content(%) Well a E o in 10 30 50 0 Grayish-brown silty SAND with gravel, fine to coarse sand,fine to coarse gravel, moist, mottled. (SM) Dense • 27 12.2 I 5 65 11.0 I Very Dense 67 9.4 --------------------------------------- 10 Gray silty SAND with gravel,fine to coarse sand, fine to • 45 10.8 I coarse gravel, moist to wet. (SM) • 32 11.8 I Dense 15 • 45 11.5 I Test Boring terminated at approximately 15 feet. 2"PVC monitoring well constructed with a 0.010 slot screen from 5 to 15 feet. Samples collected by driving a 2.5 inch O.D. sampler with a 140-pound hammer. 20 Well Tag#BQU-133 No groundwater seepage observed. 25 Terra NOTE:This borehole log has been prepared for geotechnical purposes. This information Associates Inc. pertains only to this boring location and should not be interpeted as being indicative of 7 other areas of the site e Consultants in otechnical Engineering Geology and Environmental Earth Sciences Particle Size Distribution Report C - C O O O C C C C C C co pp O O eOeyy QOQ O O_ a O to to " ` \ M iL at i[ 9! iL it ik Xk �k 100 I ! I I I I I I I I f I I I I I I I I I I I I 90 I I I I I I I 1 I I I I 80 I I I I I I I I 1 I I I I I I I I I I I I I I I I I I I I I 70 I I I I I I I I f I I I ! I I I I I I I I ( I I I I I I I I I I I I ( I I I W 60 I I I I I I I I I Z I I I I I I I I I LL I I I I I I I Z 50 I I I I I I I I w I I I I I I I I I I I a 40 I I I I I I I I I I I i I I I I I I AII I I I 30 I I I I I I I I I I I I I I I I I I I I I I I I 20 I I I I I I I I I I f l l I I I I I I I I I I I I I 10 I I I I I I I I I I I I I I I I I I I I I I I I I I I 0 100 10 1 0.1 0.01 0.001 GRAIN SIZE-mm. %+3" %Gravel %Sand %Fines Coarse Fine Coarse) Medium Fine Silt Clay o 0.0 1.6 18.2 8.2 14.0 21.1 36.9 ❑ 0.0 0.0 2.9 4.4 7.1 61.7 23.9 0 0.0 7.0 13.4 9.5 19.0 26.0 25.1 LL PL Dgr, Dan DS0 D3p D I r, Din C C 0 7.9936 0.5135 0.2292 7 0.3547 0.1966 0.1731 0.1197 0 8.2177 1 0.8276 0.4000 1 0.1457 Material Description USCS AASHTO o silty SAND with gravel SM ❑ silty SAND SM o silty SAND with gravel SM Project No. T-9205 Client: visconsi Companies Ltd. Remarks: Project: NWC 212 St NE Medical Office Facility oTested on August 13,2025 ❑Tested on August 13,2025 o Location: Test Boring B-4 Depth: 25 feet Sample Number: 8 oTested on August 13,2025 ❑ Location: Test Boring B-5 Depth: 45 feet Sample Number: 12 io Location: Test Boring B-6 Depth:20 feet Sample Number: 7 Terra Associates, Inc. 7 Kirkland WA Figure A-11 Tested By: ZA Particle Size Distribution Report C C O O O C C C C C C coO O C QG O G O (D M N -Z M A 3t U f 7i # ;L �k 100 I I I I I I I I I I I I I I I I I I I I I I I 90 I I I I I I I I I I I I I 80 I I I I I I I I ! I I I I I I I I I I I I I I I I I I I I I I I I I I I I 70 ! I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I ! I I I I I W 60 I I I I I I I I l l Z I I I I I I I I I I I I I U- l I I I I I Z 50 ! I I I I I I 1 wOf I I I I I I I I I I v I I I I I I I I I I I I a 40 I I I I I I I I I I I I I I I I I I I I I I I I I I I 30 I I I I I I I I I I I I I I I I I I I I I I ! I I I I I 20 I I I l l I I I I I I I I I I I I I I I I I I I I 10 I I I I I I I I I I I I I I I I I I I I I I I I I 0 100 10 1 0.1 0.01 0.001 GRAIN SIZE-mm. %+3„ %Gravel %Sand %Fines Coarse Fine Coarse] Medium Fine Silt Clay 0 0.0 0.8 17.3 14.8 19.2 16.8 31.1 ❑ 0.0 0.0 17.7 9.2 14.1 20.8 38.2 0 0.0 7.2 ! 12.9 6.8 11.5 20.5 41.1 LL PL D Drn D50 D D1 r, D10 cc C 0 6.0222 1.2156 0.5146 0 6.3012 0.4693 0.2149 0 8.8218 0.3575 0.1744 Material Description USCS AASHTO o silty SAND with gravel SM ❑ silty SAND with gravel SM A silty SAND with gravel SM Project No. T-9205 Client: Visconsi Companies Ltd. Remarks: Project: NWC 212 St NE Medical Office Facility oTested on August 13,2025 ❑Tested on August 13,2025 o Location: Test Boring B-7 Depth: 35 feet Sample Number: 9 oTested on August,13,2025 ❑ Location: Test Boring B-8 Depth: 25 feet Sample Number: 7 to Location: Test Boring B-9 Depth: 15 feet Sample Number: 6 Terra Associates, Inc. Kirkland WA Figure A-12 Tested By: ZA Tab 8 . 0 8.0 OTHER PERMITS Permits pertaining to this project will be provided in this section upon request. 24413.002-SSP.doc Tab 9 . 0 9.0 OPERATIONS AND MAINTENANCE MANUAL Refer to Figure 9.1 for the complete Operating and Maintenance Manuals for the proposed private stormwater infrastructure. 24413.002-SSP.doc Figure 9. 1 O&M Manual Table V-A.S: Maintenance Standards - Control Structures (continued) Maintenance Com- Defect Condition When Maintenance is Needed Results Expected When Maintenance is Performed ponent Clean-out gate is not watertight or is missing. Gate is watertight and works as designed. Clean-out Gate Damaged or Missing Gate cannot be moved up and down by one maintenance person. Gate moves up and down easily and is watertight. Chain/rod leading to gate is missing or damaged. Chain is in place and works as designed. Gate is rusted over 50%of its surface area. Gate is repaired or replaced to meet design standards. Orifice Plate Damaged or Missing Control device is not working properly due to missing,out of place,or bent orifice Plate is in place and works as designed. plate. Obstructions Any trash, debris, sediment, or vegetation blocking the plate. Plate is free of all obstructions and works as designed. Overflow Pipe Obstructions Any trash or debris blocking(or having the potential of blocking)the overflow pipe. Pipe is free of all obstructions and works as designed. Access Opening See V-A.5 Maintenance Standards-Tanks and Vaults Catch Basin See V-A.7 Maintenance Standards-Catch Basins V-A.7 Maintenance Standards - Catch Basins Table V-A.6: Maintenance Standards - Catch Basins Maintenance Defect Conditions When Maintenance is Needed Results Expected When Maintenance is per- Component formed Trash or debris which is located immediately in front of the catch basin opening or is blocking inletting capacity of the basin by more than 10%. No Trash or debris located immediately in front of catch basin or on grate opening. Trash or debris(in the basin)that exceeds 60%of the sump depth as measured from the bottom of basin to invert of the lowest pipe into or out of No trash or debris in the catch basin. Trash&Debris the basin, but in no case less than a minimum of 6 inches clearance from the debris surface to the invert of the lowest pipe. Trash or debris in any inlet or outlet pipe blocking more than 1/3 of its height. Inlet and outlet pipes free of trash or debris. Dead animals or vegetation that could generate odors that could cause complaints or dangerous gases(e.g. methane). No dead animals or vegetation present within the catch basin. Sediment Sediment(in the basin)that exceeds 60%of the sump depth as measured from the bottom of basin to invert of the lowest pipe into or out of the No sediment in the catch basin basin, but in no case less than a minimum of 6 inches clearance from the sediment surface to the invert of the lowest pipe. To slab has holes larger 2 square inches or cracks wider than 1/4 inch. Intent is to make sure no material is running into basin Top slab is free of holes and cracks. General Structure Damage to P g q ( g )� Frame and/or Top Slab Frame not sitting flush on top slab, i.e.separation of more than 3/4 inch of the frame from the top slab. Frame not securely attached. Frame is sitting flush on the riser rings or top slab and firmly attached. Maintenance person judges that structure is unsound. Fractures or Cracks in Basin replaced or repaired to design standards. Basin Walls/Bottom Grout fillet has separated or cracked wider than 1/2 inch and longer than 1 foot at the joint of any inlet/outlet pipe or any evidence of soil particles Pipe is regrouted and secure at basin wall. entering catch basin through cracks. Settlement/Mis- If failure of basin has created a safety,function,or design problem. Basin replaced or repaired to design standards. alignment Vegetation Vegetation growing across and blocking more than 10%of the basin opening. No vegetation blocking opening to basin. Vegetation growing in inlet/outlet pipe joints that is more than 6 inches tall and less than 6 inches apart. No vegetation or root growth present. Contamination and Pol- See V-A.2 Maintenance Standards-Detention Ponds No pollution present. 2024 Stormwater Management Manual for Western Washington Volume V-Appendix A -Page 1178 Table V-A.6: Maintenance Standards - Catch Basins (continued) Maintenance Defect Conditions When Maintenance is Needed Results Expected When Maintenance is per- Component formed lution Cover Not in Place Cover is missing or only partially in place.Any open catch basin requires maintenance. Cover/grate is in place, meets design standards, and is secured. Catch Basin Locking Mechanism Mechanism cannot be opened by one maintenance person with proper tools. Bolts into frame have less than 1/2 inch of thread. Mechanism opens with proper tools. Cover Not Working Cover Difficult to One maintenance person cannot remove lid after applying normal lifting pressure. Cover can be removed by one maintenance per- Remove (Intent is keep cover from sealing off access to maintenance.) son. Ladder Ladder Rungs Unsafe Ladder is unsafe due to missing rungs, not securely attached to basin wall, misalignment, rust, cracks,or sharp edges. Ladder meets design standards and allows main- tenance person safe access. Grate opening Unsafe Grate with opening wider than 7/8 inch. Grate opening meets design standards. Metal Grates Trash and Debris Trash and debris that is blocking more than 20%of grate surface inletting capacity. Grate free of trash and debris. (if applicable) Grate is in place, meets the design standards, and Damaged or Missing. Grate missing or broken member(s)of the grate. is installed and aligned with the flow path. V-A.8 Maintenance Standards - Debris Barriers (e.g. Trash Racks) Table V-A.7: Maintenance Standards - Debris Barriers (e.g. Trash Racks) Maintenance Components Defect Condition When Maintenance is Needed Results Expected When Maintenance is Performed General Trash and Debris Trash or debris that is plugging more than 20%of the openings in the barrier. Barrier cleared to design flow capacity. Bars are bent out of shape more than 3 inches. Bars in place with no bends more than 3/4 inch. Damaged/Missing Bars Bars are missing or entire barrier missing. Bars in place according to design. Metal Bars are loose and rust is causing 50%deterioration to any part of barrier. Barrier replaced or repaired to design standards. Inlet/Outlet Pipe Debris barrier missing or not attached to pipe Barrier firmly attached to pipe V-A.9 Maintenance Standards - Energy Dissipators Table V-A.8: Maintenance Standards - Energy Dissipators Maintenance Com- Defect Conditions When Maintenance is Needed Results Expected When Maintenance ponents is Performed External Missing or Moved Rock Only one layer of rock exists above native soil in area five square feet or larger, or any exposure of native soil. Rock pad replaced to design standards. Rock Pad Erosion Soil erosion in or adjacent to rock pad. Rock pad replaced to design standards. Dispersion Trench Pipe Plugged with Sediment Accumulated sediment that exceeds 20%of the design depth. Pipe cleaned/flushed so that it matches design. 2024 Stormwater Management Manual for Western Washington Volume V-Appendix A -Page 1179 Table V-A.27: Maintenance Standards - Downspout Full Infiltration (continued) Recommended Frequency a Maintenance Component Condition when Maintenance is Needed (Standards) Action Needed (Procedures) Inspection Routine Maintenance Source: (Herrera and W , 2013) V-A.29 Maintenance Standards - Post-Construction Soil Quality and Depth Table V-A.28: Maintenance Standards - Post-Construction Soil Quality and Depth Recommended Frequency a Condition when Maintenance is Maintenance Component Needed (Standards) Action Needed (Procedures) Inspection Routine Maintenance Vegetation not fully covering • Maintain 2 to 3 inches of mulch over bare areas in landscape beds A ground surface or vegetation health • Add plants if sufficient space is poor • Re-seed bare turf areas until the vegetation fully covers ground surface Ongoing None (routine maintenance) Return leaf fall and shredded woody materials from the landscape to the site when possible in order to replenish soil nutrients and structure Soil media (maintain high organic soil content) Ongoing None (routine maintenance) On turf areas, "grasscycle" (mulch-mow or leave the clippings)to build turf health Ongoing None (routine maintenance) Avoiding use of pesticides (bug and weed killers), like"weed &feed", which damage the soil • Where fertilization is needed (mainly turf and annual flower beds), a moderate fer- tilization program should be used which relies on compost, natural fertilizers or slow- A None (routine maintenance) release synthetic balanced fertilizers • Follow IPM protocols for fertilization procedures • To remediate compaction, aerate soil, till to at least 8-inch depth, or further amend soil with compost and re-till • If areas are turf, aerate compacted areas and topdress them with 1/4 to 1/2 inch of Soil media (maintain infilt- Ab Soils become waterlogged, do not compost to renovate them ration) appear to be infiltrating • If drainage is still slow, consider investigating alternative causes (e.g. high wet sea- son groundwater levels, low permeability soils) • Also consider site use and protection from compacting activities • Identify and address cause of erosion (e.g. concentrate flow entering area, chan- nelization of runoff) and stabilize damaged area (regrade, rock, vegetation, erosion Areas of potential erosion are vis- control matting) Erosion Scouring A, W, S ible • For deep channels or cuts (over 3 inches in ponding depth), temporary erosion con- trol measures should be put in place until permanent repairs can be made. Grass/Vegetation A Less than 75% of planted veget- . Take appropriate maintenance actions (e.g. remove/replace plants) ation is healthy with a generally 2024 Stormwater Management Manual for Western Washington Volume V-Appendix A -Page 1206 Table V-A.28: Maintenance Standards - Post-Construction Soil Quality and Depth (continued) Recommended Frequency a Maintenance Component Condition when Maintenance is Action Needed (Procedures) Inspection Routine Maintenance Needed (Standards) good appearance • If problem persists, evaluate if vegetation is appropriate for the location (e.g. expos- ure, soil, soil moisture) • By law, class A& B noxious weeds must be removed, bagged and disposed as garbage immediately • Reasonable attempts must be made to remove and dispose of class C noxious M weeds Listed noxious vegetation is present Noxious weeds (March—October, pre- (refer to current county noxious • Watch for and respond to new occurrences of especially aggressive weeds such as ceding seed dispersal) weed list) Himalayan blackberry, Japanese knotweed, morning glory, English ivy, and reed canary grass to avoid invasions • It is strongly encouraged that herbicides and pesticides not be used in order to protect water quality; use of herbicides and pesticides may be prohibited in some jur- isdictions M • Remove weeds with their roots manually with pincer-type weeding tools, flame weed- Weeds (March—October, pre- Weeds are present ers, or hot water weeders as appropriate ceding seed dispersal) I I • Follow IPM protocols for weed management Note that the inspection and routine maintenance frequencies listed above are recommended by Ecology.They do not supersede or replace the municipal stormwater permit requirements for inspection frequency required of municipal stormwater permittees for"stormwater treatment and flow control BMPs/facilities". a)Frequency:A=Annually; B=Biannually(twice per year); M= Monthly;W=At least one visit should occur during the wet season (for debris/clog related maintenance,this visit should occur in the early fall,after deciduous trees have lost their leaves); S= Perform inspections after major storm events(24-hour storm event with a 10-year or greater recurrence interval). b) Inspection should occur during a storm event. IPM- Integrated Pest Management Source: (Herrera and)ASC, 2013) 2024 Stormwater Management Manual for Western Washington Volume V-Appendix A -Page 1207 Tab 10 . 0 10.0 DECLARATION OF COVENANT FOR PRIVATELY MAINTAINED FLOW CONTROL AND TREATMENT FACILITIES The Declaration of Covenant for the Privately Maintained Flow Control and Treatment Facilities may be provided, if required by the City. 24413.002-SSP.doc Tab 11 . 0 11.0 DECLARATION OF COVENANT FOR PRIVATELY MAINTAINED ON-SITE STORMWATER MANAGEMENT BMPS The Declaration of Covenant for the Privately Maintained On-Site Stormwater Management BMPs may be provided, if required by the City. 24413.002-SSP.doc Tab 12 . 0 12.0 BOND QUANTITIES WORKSHEET Applicable Bond Quantities will be provided upon project acceptance and at the request of the City. 24413.002-SSP.doc