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HomeMy WebLinkAbout17327 67th Ave NE_PWD1860_2026 Centennial Park 18386.20 June 30,2020 Drainage Report Section V,Page 5 Construction Stormwater General Permit Stormwater Pollution Prevention Plan (SWPPP) for Centennial Park Prepared for: The Washington State Department of Ecology Northwest Regional Office Permittee/Owner Developer Operator/Contractor Williams Investments Williams Investments Exxel Pacific 67th Ave and 172"d Street NE,Arlington,WA 98223 Certified Erosion and Sediment Control Lead (CESCL) Name Organization Contact Phone Number Joshua Taylor Taylor Excavating 360.629.3078 SWPPP Prepared By Name Organization Contact Phone Number Darina Litushko CG Engineering 425.778.8500 SWPPP Preparation Date July 2019 Project Construction Dates Activity/ Phase Start Date End Date Construction August 2019 December 2020 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Section V,Page 6 Table of Contents 1 Project Information.............................................................................................................. 9 1.1 Existing Conditions........................................................................................................................9 1.2 Proposed Construction Activities................................................................................................10 2 Construction Stormwater Best Management Practices (BMPs)........................................ 11 2.1 The 13 Elements..........................................................................................................................11 2.1.1 Element 1: Preserve Vegetation/Mark Clearing Limits.................................................... 11 2.1.2 Element 2: Establish Construction Access.......................................................................... 12 2.1.3 Element 3: Control Flow Rates........................................................................................... 13 2.1.4 Element 4: Install Sediment Controls................................................................................. 14 2.1.5 Element 5:Stabilize Soils.................................................................................................... 15 2.1.6 Element 6: Protect Slopes .................................................................................................. 16 2.1.7 Element 7: Protect Drain Inlets..........................................................................................17 2.1.8 Element 8:Stabilize Channels and Outlets.........................................................................18 2.1.9 Element 9:Control Pollutants ............................................................................................19 2.1.10 Element 10: Control Dewatering........................................................................................22 2.1.11 Element 11: Maintain BMPs...............................................................................................23 2.1.12 Element 12: Manage the Project........................................................................................24 2.1.13 Element 13: Protect Low Impact Development(LID) BMPs...............................................27 3 Pollution Prevention Team................................................................................................. 28 4 Monitoring and Sampling Requirements........................................................................... 29 4.1 Site Inspection.............................................................................................................................29 4.2 Stormwater Quality Sampling.....................................................................................................29 4.2.1 Turbidity Sampling..............................................................................................................29 4.2.2 pH Sampling...........--.... ... ............................................................................................31 5 Discharges to 303(d) or Total Maximum Daily Load (TMDL) Waterbodies ....................... 32 5.1 303(d) Listed Waterbodies..........................................................................................................32 5.2 TMDL Waterbodies.....................................................................................................................32 6 Reporting and Record Keeping........................................................................................... 33 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Section V,Page 7 6.1 Record Keeping...........................................................................................................................33 6.1.1 Site Log Book......................................................................................................................33 6.1.2 Records Retention..............................................................................................................33 6.1.3 Updating the SWPPP..........................................................................................................33 6.2 Reporting.....................................................................................................................................34 6.2.1 Discharge Monitoring Reports ...........................................................................................34 6.2.2 Notification of Noncompliance ..........................................................................................34 List of Tables Table 1—Summary of Site Pollutant Constituents.......................................................................................9 Table2—Pollutants.....................................................................................................................................19 Table3—pH-Modifying Sources.................................................................................................................19 Table4—Dewatering BMPs........................................................................................................................22 Table5—Management...............................................................................................................................24 Table 6—BMP Implementation Schedule...................................................................................................25 Table7—Team Information........................................................................................................................28 Table 8—Turbidity Sampling Method.........................................................................................................29 Table9—pH Sampling Method...................................................................................................................31 List of Appendices Appendix/Glossary A.Site Map B. BMP Detail C. Correspondence D.Site Inspection Form E. Construction Stormwater General Permit (CSWGP) F.303(d) List Waterbodies/TMDL Waterbodies Information G.Contaminated Site Information H. Engineering Calculations C 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Section V,Page 8 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 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineeri ng.com Centennial Park 18386.20 June 30,2020 Drainage Report Section V,Page 9 Acronym/Abbreviation Explanation WSDOT Washington Department of Transportation WWHM Western Washington Hydrology Model 1. Project Information Project/Site Name: Centennial Park Street/Location: 18506 Smokey Point Blvd. City: Arlington State: WA Zip code: 98223 Subdivision: N/A Receiving waterbody: Creek 1.1 Existing Conditions Total acreage (including support activities such as off-site equipment staging yards, material storage areas, borrow areas). Total acreage: 8.81 ac Disturbed acreage: 6.36 ac Existing structures: 0 ac Landscape 0ac Drainage patterns: The site generally slopes downward from the E to the W. Grades are moderate too steep on the east side of the property and mostly flat otherwise. Existing Vegetation: Bushes,shrubs,grass,wetland,trees Critical Areas (wetlands, streams, high erosion risk, Slopes on east property line, Relict Stream steep or difficult to stabilize slopes): Channel, Category IV Wetland List of known impairments for 303(d) listed or Total Maximum Daily Load (TMDL) for the receiving waterbody: Edgecomb Creek is not listed as having impairments on the EPA website. Table 1 includes a list of suspected and/or known contaminants associated with the construction activity. No known or suspected contaminants are associated with the site. 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Section V,Page 10 Table 1—Summary of Site Pollutant Constituents Constituent(Pollutant) Location Depth Concentration 1.2 Proposed Construction Activities Description of site development(example:subdivision): Multi-family residential. The project will add 15 buildings. These include one mixed use building, two common buildings, and 12 apartment buildings. Description of construction activities(example:site preparation,demolition,excavation): Clearing and grubbing of existing forested and brushed areas; excavating, filling, and grading; utility installation, parking lot surfacing, building construction and frontage improvements. Description of site drainage including flow from and onto adjacent properties. Must be consistent with Site Map in Appendix A: The site generally slopes downward from the east to the west and drainage in the developed condition is expected to flow in the same direction. Description of final stabilization (example:extent of revegetation,paving, landscaping): Buildings, parking lots and driveways will cover about 50%of the site,with approximately 20%of the site being landscaping and the remaining 30% being encumbered by critical areas (Category IV wetland and stream). Contaminated Site Information: Proposed activities regarding contaminated soils or groundwater(example: on-site treatment system, authorized sanitary sewer discharge): N/A 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineeri ng.com Centennial Park 18386.20 June 30,2020 Drainage Report Section V,Page 11 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. 2.1 The 13 Elements 2.1.1 Element 1: Preserve Vegetation/ Mark Clearing Limits To protect adjacent properties and to reduce the area of soil exposed to construction, the limits of construction will be clearly marked before land-disturbing activities begin.Trees that are to be preserved, as well as all sensitive areas and their buffers, shall be clearly delineated in the field. In general, natural vegetation and native topsoil shall be retained in an undisturbed state to the maximum extent possible. A protective barrier shall be placed around the protected trees prior to land preparation or construction activities and shall remain in place until all construction activity is terminated. No equipment, chemicals, soil deposits or construction materials shall be placed within the protective barriers. Any landscaping activities subsequent to the removal of the barriers shall be accomplished with light machinery or hand labor. High Visibility Fence will be placed around the entire site running along the property lines. List and describe BMPs: • BMP C101: Preserving Natural Vegetation • BMP C102: Buffer Zones • BMP C103: High Visibility Plastic or Metal Fence • BMP C233:Silt Fence Installation Schedules: Install BMPs prior to clearing and grading. Inspection and Maintenance plan:As needed. Responsible Staff: CESCL. C 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Section V,Page 12 2.1.2 Element 2: Establish Construction Access Limit vehicle access to one route, if possible. Construction access or activities occurring on unpaved areas shall be minimized, yet where necessary, access points shall be stabilized to minimize the tracking of sediment onto public roads. Street sweeping,street cleaning, orwheel wash/tire baths may be necessary if the stabilized construction access is not effective. If sediment is tracked off site,clean the affected roadway thoroughly at the end of each day, or more necessary as needed. All wheel wash wastewater shall be controlled on-site and CANNOT be discharged into waters of the State. Stabilized construction entrances will be added along the west edges of the site at the locations of the proposed entrances to the complex.This will help to prevent sediment tracking into the right of way. List and describe BMPs: • BMP C105:Stabilized Construction Entrance/Exit • BMP C107:Construction Road/Parking Area Stabilization Installation Schedules: Install BMPs prior to clearing and grading. Inspection and Maintenance plan:As needed. Responsible Staff:CESCL. C 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cge ngi n e e ri n g.co m Centennial Park 18386.20 June 30,2020 Drainage Report Section V,Page 13 2.1.3 Element 3: Control Flow Rates The project site has a gentle slope from east to west for most of the site (<2%).There is a moderate slope near the west side of the site (12%). Stormwater will be directed to a temporary detention pond at the northwest corner of the site,and flow rates will be controlled per the BMPs listed below.The construction of the temporary sediment pond must be done as one of the first steps in grading. Infiltration facilities will be constructed for permanent stormwater control. Stormwater should not be directed to these facilities until the site has been stabilized. Protect Low Impact Development BMPs from compaction and sedimentation per Element 13. Flow rates around the rest of the site will be controlled by the silt fence that will be placed around the entire site. 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: • BMP C207:Check Dams • BMP C209:Outlet Protection • BMP C241:Temporary Sediment Pond Installation Schedules: Install BMPs prior to grading. Inspection and Maintenance plan:As needed. Responsible Staff:CESCL. C 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Section V,Page 14 2.1.4 Element 4: Install Sediment Controls Stormwater must be filtered prior to being discharged to an infiltration system or leaving the construction site. Sediment control BMPs will be installed as one of the first steps of grading. These BMPs must be functional before other land-disturbing activities, especially grading and filling,take place. A silt fence will be installed around the perimeter of the developed site areas.A temporary sediment pond will be installed at the northwest corner of the site where some sediment will be able to settle out prior to discharge to the public storm system. If sediment controls are ineffective and turbid water is observed discharging from the site, additional energy dissipation BMPs and sediment control BMPs should be installed such as wattles. It may also be necessary to stabilize soils per Element 5 that are not being worked on. List and describe BMPs: • BMP C233:Silt Fence • BMP C235:Wattles • BMP C241:Temporary Sediment Pond Installation Schedules: Install BMPs prior to clearing and grading. Inspection and Maintenance plan: Repair sediment controls as needed. Remove sediment from pond as needed. Responsible Staff:CESCL. 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Section V,Page 15 2.1.5 Element 5: Stabilize Soils Stabilize exposed and unworked soils by the BMPs listed below to prevent erosion. Protect stockpiles with plastic covering or other approved sediment trapping measures. Stabilize exposed soils with Temporary and Permanent Seeding, Mulching, Sodding, Top soiling/Compost, or Surface Roughening. Minimize soil compaction by applying gravel base early on areas to be paved. The ESC Supervisor shall be familiar with BMPs for soil stabilization and dust control and implement these BMPs where needed on the proposed site. 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:August 2019 End date: December 2020 Will you construct during the wet season? ®Yes ❑ No List and describe BMPs: • BMP C120:Temporary and Permanent Seeding • BMP C121: Mulching • BMP C123: Plastic Covering • BMP C124:Sodding • BMP C125:Top soiling/Composting • BMP C130:Surface Roughening • BMP C131: Gradient Terraces • BMP C140: Dust Control Installation Schedules:As needed as soil is exposed. Inspection and Maintenance plan: End of the shift before a holiday or weekend and prior to forecasted rain events. Responsible Staff:CESCL. C 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Section V,Page 16 2.1.6 Element 6: Protect Slopes All cut and fill slopes will be designed, constructed, and protected in a manner that minimizes erosion. The interceptor swale and check dams will be located along the west side of the site as needed. Will steep slopes be present at the site during construction? ❑Yes ® No (temporary excavations may create brief temporary slopes during wall construction) List and describe BMPs: • BMP C120:Temporary and Permanent Seeding • BMP C121: Mulching • BMP C123: Plastic Covering • BMP C124:Sodding • BMP C130:Surface Roughening • BMP C200: Interceptor Dike and Swale • BMP C201: Grass-Lined Channels • BMP C207: Check Dams Installation Schedules: Install BMPs prior to grading and as needed to minimize erosion. Inspection and Maintenance plan:As needed. Responsible Staff:CESCL. 250 4th Avenue South,Suite 200 CM Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cge ngi n e e ri ng.co m Centennial Park 18386.20 June 30,2020 Drainage Report Section V,Page 17 2.1.7 Element 7: Protect Drain Inlets All storm drain inlets and culverts made operable during construction shall 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 street wash water 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 and nearthe project site. Inlet protection should be provided as shown on the C2.1 Plan. Inlet protection devices will be cleaned (or removed and replaced), when sediment has filled the device by one third (1/3) or as specified by the manufacturer. List and describe BMPs: • BMP C220:Storm Drain Inlet Protection Installation Schedules: Before land disturbance for existing catch basins and as new catch basins are made operable. Inspection and Maintenance plan: Inlets will be inspected weekly at a minimum and daily during storm events. Responsible Staff:CESCL. C250 4th Avenue South,Suite 200 CM Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Section V,Page 18 2.1.8 Element 8: Stabilize Channels and Outlets Where site runoff is to be conveyed in channels or discharged to a stream or some other natural drainage point, efforts will be taken to prevent downstream erosion. The project site is located west of the Cascade Mountain Crest. As such,all temporary on-site conveyance channels 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. Alternatively,the 10-year, 1-hour peak flow rate indicated by an approved continuous runoff simulation model, increased by a factor of 1.6,shall be used. 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: • BMP C202: Channel Lining • BMP C207: Check Dams • BMP C209: Outlet Protection Installation Schedules: Install BMPs prior to grading. Inspection and Maintenance plan:As needed. Responsible Staff:CESCL. 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Section V,Page 19 2.1.9 Element 9: Control Pollutants The following pollutants are anticipated to be present on-site: Table 2—Pollutants Pollutant (List pollutants and source, if applicable) Concrete Concrete process water Concrete slurry Asphalt materials Utility Materials List and describe BMPs: • BMP C151: Concrete Handling • BMP C152:Sawcutting and Surfacing Pollution Prevention • BMP C153: Material Delivery,Storage and Containment Installation Schedules:As needed as pollutant source materials are used on-site. Inspection and Maintenance plan:As needed. Responsible Staff:CESCL. Will maintenance,fueling, and/or repair of heavy equipment and vehicles occur on-site? [:]Yes ® No Will wheel wash or tire bath system BM Ps be used during construction? [:]Yes ® No Will pH-modifying sources be present on-site? ®Yes ❑ No Table 3—pH-Modifying Sources ❑ None ® Bulk cement Z Cement kiln dust ® Fly ash ® Other cementitious materials U New concrete washing or curing waters 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Section V,Page 20 ❑ 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 C 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Section V,Page 21 2.1.10 Element 10: Control Dewatering Dewatering is not anticipated to be associated with this construction project. Most excavations are intended to occur in the dry seasons above the groundwater table, although several instances of "perched"groundwater were found in the geotechnical test pits. If necessary,only clean,non-turbid dewatering water(such as well-point groundwater)may 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. Table 4—Dewatering BMPs Infiltration ® Transport off-site in a vehicle (vacuum truck for legal disposal) Ecology-approved on-site chemical treatment or other suitable treatment technologies Sanitary or combined sewer discharge with local sewer district approval (last resort) U Use of sedimentation bag with discharge to ditch or swale (small volumes of localized dewatering) List and describe BMPs: N/A. Installation Schedules: N/A. Inspection and Maintenance plan: N/A. Responsible Staff:CESCL. 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Section V,Page 22 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. C250 4th Avenue South,Suite 200 CM Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Section V,Page 23 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 5— 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 Z Retain sediment on-site ® Thoroughly monitor site and maintain all ESC measures ® Schedule major earthwork during the dry season ❑ Other(please describe) C 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Section V,Page 24 Table 6— BMP Implementation Schedule In general, it is expected that most early grading will occur in the dry season of 2019 and be picked up again in dry season of 2020. Phase of Wet/Dry Construction Stormwater BMPs Date Season Project Pre-construction Preserving Natural Vegetation (BMP C101) 8/19/2019 Dry Pre-construction High Visibility Fence(BMP C103) 8/21/2019 Dry Pre-construction Silt Fence(BMP C233) 8/21/2019 Dry Land disturbance Stabilized Construction Entrance/Exit(BMP 8/23/2019 Dry C105) Land disturbance Sediment Trap (BMP C240) NA Dry Land disturbance Temporary Sediment Pond (BMP C241) 8/26/2019 Dry Land disturbance Temporary and Permanent Seeding(BMP Throughout project Dry C120) as needed Land disturbance Mulching(BMP C121) Throughout project Dry as needed Land disturbance Nets and Blankets (BMP C122) NA Dry Land disturbance Plastic Covering(BMP C123) 10/15/2019 Dry Land disturbance Sodding(BMP C124) Throughout project Dry as needed Land disturbance Topsoiling/Composting(BMP C125) Throughout project Dry as needed Land disturbance Surface Roughening (BMP C130) Throughout project Dry as needed Land disturbance Dust Control (BMP C140) Throughout project Dry as needed Land disturbance Interceptor Dike and Swale(BMP C200) 8/23/2019 Dry Land disturbance Channel Lining(BMP C202) 8/23/2019 Dry Land disturbance Check Dams (BMP C207) 8/23/2019 Dry Land disturbance Outlet protection (BMP C209) 8/26/2019 Dry Land disturbance Storm Drain Inlet Protection (BMP C220) 8/19/19 Dry Construction Wattles (BMP C235) NA Dry Construction Concrete handling(BMP C151) NA Dry Construction Sawcutting and Surfacing Pollution 4/30/2020 Dry Prevention (BMP C152) Construction Material Delivery,Storage and Containment 8/26/19 Dry (BMP C153) 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Section V,Page 25 2.1.13 Element 13: Protect Low Impact Development(LID) BMPs Gravel Infiltration Trenches (SWMMWW Section 3.3.11) will be the primary means of stormwater mitigation for the roofs and other hard surfaces on this project. The infiltration trenches will need to be protected from compaction during construction. This can be done by placing orange protective fencing around the trenches as they are constructed in order to avoid compaction from vehicle traffic. 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Section V,Page 26 3 Pollution Prevention Team Table 7—Team Information Title Name(s) Phone Number Certified Erosion and Sediment Control Joshua Taylor 360.629.3078 Lead (CESCL) Resident Engineer CG Engineering 425.778.8500 Emergency Ecology Contact Jess Eakens 360.407.6442 Emergency Permittee/Owner Contact Ryan Kilby 425.750.7926 Non-Emergency Owner Contact Ryan Kilby 425.750.7926 Monitoring Personnel TBD TBD Ecology Regional Office Northwest Regional Office 425.649.7000 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Section V,Page 27 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 logbook.Asite logbook 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 File a blankform under Appendix D. The site logbook 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 maybe 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: Table 8—Turbidity Sampling Method ® Turbidity Meter/Turbidimeter(required for disturbances 5 acres or greater in size) ❑ I Transparency Tube (option for disturbances less than 1 acre and up to 5 acres in size) { The benchmark for turbidity value is 25 nephelometric turbidity units (NTU) and a transparency less than 33 centimeters. 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Section V,Page 28 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 logbook. 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 or http://www.ecy.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 logbook. 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Section V,Page 29 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. 0 1-5 NTU over background turbidity, if background is less than 50 NTU 0 1%-10%over background turbidity, if background is 50 NTU or greater • The discharge stops or is eliminated. C250 4th Avenue South,Suite 200 CM Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778,5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Section V,Page 30 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 priorto the use of chemical treatment other than CO2 sparging or dry ice. Method for sampling pH: Table 9—pH Sampling Method pH meter U pH test kit U Wide range pH indicator paper C250 4th Avenue South,Suite 200 CM Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Section V,Page 31 5 Discharges to 303(d) or Total Maximum Daily Load (TMDL) Waterbodies 5.1 303(d) Listed Waterbodies Is the receiving water 303(d) (Category 5) listed for turbidity,fine sediment, phosphorus, or pH? ❑yes ® No List the impairment(s): N/A 5.2 TMDL Waterbodies Waste Load Allocation for CSWGP discharges: N/A List and describe BMPs: N/A 1 Discharges to TMDL receiving waterbodies will meet in-stream water quality criteria at the point of discharge. The Construction Stormwater General Permit Proposed New Discharge to an Impaired Water Body form is included in Appendix F. 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Section V,Page 32 6 Reporting and Record Keeping 6.1 Record Keeping 6.1.1 Site Logbook A site logbook 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 Logbook 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. 6.2 Reporting 6.2.1 Discharge Monitoring Reports Cumulative soil disturbance is one (1) acre or larger; therefore, Discharge Monitoring Reports (DMRs) will be submitted to Ecology monthly. If there was no discharge during a given monitoring period the DMR will be submitted as required, reporting"No Discharge".The DMR due date is fifteen (15) days following the end of each calendar month. C 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Section V,Page 33 DMRs will be reported online through Ecology's WQWebDMR System. 6.2.2 Notification of Noncompliance 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 SS.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 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Section V,Page 34 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 In accordance with Special Condition S4.D.5.b of the CSWGP,the Ecology Regional office will be notified if chemical treatment other than CO2 sparging is planned for adjustment of high pH water. 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Section V,Page 35 Appendix/Glossary A. Site Map D 8 Plcki Pull Cash m Fa Junk Cars 8 € m s z m d Wilcox B Flegel9 m m rmeru rre. lui ran Church PROJECT The Suite Satin And Spa Q SITE Wash ingf-9 y Trucking,lu 7 `� z m O O —10000 Figure A-1.Site map. 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Section V,Page 36 B. BMP Detail BMP details are shown on the approved TESC plan. Additional/alternative BMPs are listed below and available for download from the Ecology Construction Stormwater website: http://www.ecy.wa.gov/programs/wq/stormwate r/construction/index.htm I Element#1-Mark Clearing Limits • BMP C101: Preserving Natural Vegetation • BMP C102: Buffer Zones • BMP C103: High Visibility Plastic or Metal Fence • BMP C233:Silt Fence Element#2-Establish Construction Access • BMP C105:Stabilized Construction Entrance/Exit • BMP C107: Construction Road/Parking Area Stabilization Element#3-Control Flow Rates • BMP C207:Check Dams • BMP C209:Outlet Protection • BMP C241:Temporary Sediment Pond Element#4-Install Sediment Controls • BMP C233:Silt Fence • BMP C235:Wattles • BMP C241:Temporary Sediment Pond Element#5-Stabilize Soils • BMP C120:Temporary and Permanent Seeding • BMP C121: Mulching • BMP C123: Plastic Covering • BMP C124:Sodding • BMP C125:Topsoiling/Composting • BMP C130:Surface Roughening • BMP C131: Gradient Terraces • BMP C140: Dust Control Element#6-Protect Slopes • BMP C120:Temporary and Permanent Seeding • BMP C121: Mulching • BMP C123: Plastic Covering • BMP C124:Sodding • BMP C130:Surface Roughening • BMP C200: Interceptor Dike and Swale 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Section V,Page 37 • BMP C201: Grass-Lined Channels • BMP C207: Check Dams Element#7-Protect Drain Inlets • BMP C220:Storm Drain Inlet Protection Element#8-Stabilize Channels and Outlets • BMP C202:Channel Lining • BMP C207:Check Dams • BMP C209:Outlet Protection Element#9—Control Pollutants • BMP C151:Concrete Handling • BMP C152:Sawcutting and Surfacing Pollution Prevention • BMP C153: Material Delivery, Storage and Containment • See Volume IV—Source Control BMPs Element#10-Control Dewatering NA Element#11: Maintain BMPs • BMP C150: Materials On Hand • BMP C160:Certified Erosion and Sediment Control Lead Element#12: Manage the Project • BMP C150: Materials On Hand • BMP C160: Certified Erosion and Sediment Control Lead • BMP C162:Scheduling Element#13: Protect LID BMPs • BMP C103: High Visibility Fence C 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Section V,Page 38 C. Correspondence 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Section V,Page 39 D. Site Inspection Form Permit# Inspection Time Project Date Name 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 Ei Fog A.Type of inspection: Weekly Post Storm Event Other B. Phase of Active Construction (check all that apply): Pre-Construction/installation of Clearing/Demo/Grading Infrastructure/storm/roads erosion/sediment controls Concrete pours Vertical Utilities �] Construction/buildings Offsite improvements LiSite 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, Yes No or oil sheen 3. Was a water quality sample taken during inspection? (refer to permit Yes No conditions S4&S5) 4. Was there a turbid discharge 250 NTU or greater, or Transparency 6 cm or Yes No less?* 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 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Section V,Page 40 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/ i transparency is 33 cm or greater. Sampling Date: Results: Parameter Method (circle one) Result Other/Note NTU cm pH Turbidity tube, meter, laboratory pH Paper, kit, meter D. Check the observed status of all items. Provide"Action Required "details and dates. Element# Inspection BMPs BMP BMP Action Inspected needs failed required yes no n/a maintena (describe nce 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 BM Ps? (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 roadway was cleaned thoroughly at the end of the day or more frequent as necessary. 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Section V,Page 41 3 Are flow control measures Control Flow installed to control stormwater Rates volumes and 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. 5 Have exposed un-worked soils Stabilize Soils been stabilized with effective BMP to prevent erosion and sediment deposition? Are stockpiles stabilized from erosion, protected with sediment trapping 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 Slopes disturbed areas with interceptor dikes, pipes and or swales? C 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Section V,Page 42 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? Wheel wash wastewater is handled and disposed of properly. 10 Concrete washout in designated Control areas. No washout or excess concrete Dewatering on the ground. C 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Section V,Page 43 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 BMP erosion and sediment control BMPs 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 B M Ps? 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. C 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineer*ing.com Centennial Park 18386.20 June 30,2020 Drainage Report Section V,Page 44 E. Check all areas that have been inspected. ✓ All in place All disturbed All concrete wash out All material storage BMPs soils area areas All discharge All equipment storage All construction locations areas entrances/exits 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: (Signature) Date: (print) Title/Qualification of Inspector: 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Section V,Page 45 E. Construction Stormwater General Permit (CSWGP) 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengi nee ri ng.com Centennial Park 18386.20 June 30,2020 Drainage Report Section V,Page 46 F. 303(d) List Waterbodies /TMDL Waterbodies Information C 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Section V,Page 47 G. Contaminated Site Information 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Section V,Page 48 H. Engineering Calculations Sediment Pond Calculations-Surface Area SA!:FS(Q/Vs) Water surface area FS= 2 Factor of Safety Q2= 3.031 cfs 2-yr developed peak from WWH M Vs= 0.00096 ft/s Settling Velocity Side Slopes= 3 HAV Depth= 3.S ft Minimum 10-year Trap Geometry SA= 6314 sf Min,Pond Dimensions= 78.9 by 80-0 ft LN=3:1 to 6:1 Volume= 17,029 d Sediment Pond Calculations DLL Nte 12/7/2018 Surface Area °1d pate ENGINEERING sc , r0w,No. 1 250 4th Ave.South N.T.S. Edmonds,WA98020 Centennial Park Job NO. 18386.20 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengi neeri ng.com Centennial Park 18386.20 June 30,2020 Drainage Report Section VI,Page 1 Section VI — Special Reports and/or Studies Section VI Summary Narrative The following reports are included in this section: 1. Geotechnical Engineering Report by Geotest, dated May 17, 2019. 2. Wetlands Delineation and Fish and Wildlife Habitat Report and Buffer Enhancement Plan by Soundview Consultants dated June 28, 2019. 3. As Built Drawings from Edgecomb Creek Rerouting 4. Supplemental Infiltration Report by Geotest, dated March 6, 2020 5. Cutoff Trench, Rev 1 by Geotest, dated March 17,2020 6. Hydrogeological Assessment Report by GeoEngineers, dated June 29, 2020 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Section VII,Page 1 Section VII — Other Permits Section VII Summary Narrative This project will require the following additional permits/approvals beyond those required by the City of Arlington. 1. Construction Stormwater General Permit by the Washington State Department of Ecology. 2. The potentially unregulated channel needs to be approved as unregulated by the Department of Natural Resources prior to any work occurring within the buffer or channel.The current proposal does not include this work. 250 4th Avenue South,Suite 200 CM Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Section VIII,Page 1 Section VIII — Operation and Maintenance Manual Section VIII Summary Narrative The Operation and Maintenance Manual is a standalone document that will be given to the property manager following the construction of the project.The contractor will be responsible forthe maintenance and operation of all stormwater structures and BMPs requiring maintenance during construction and, after construction, responsibility will pass to the property management company. The manual shall be kept in the offices of the proposed buildings. Upon request by the City, it shall be made available for their inspection. It is generally expected that few to none of these defects will be present upon the yearly inspection of each facility. 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Section VIII,Page 2 Centennial Park 67th Ave and 172nd Street NE Arlington,WA 98223 OPERATION AND MAINTENANCE MANUAL Date:June 2020 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Section VIII,Page 3 Operation and Maintenance Manual This Operation and Maintenance Manual has been created for Centennial Park, a 8.81 ac site located at 67th Ave and 172"d Street NE Arlington, WA 98223. The proposed stormwater management system consists of catch basins, water quality systems, and conveyance pipes that collect runoff from roofs, parking, and new landscaping, and route them to gravel infiltration trenches under parking lots throughout the site. Included in this Operation and Maintenance Manual is an 11" x 17" grading and drainage plan sheet showing the locations of the infiltration system and catch basins. Please note that this map is generated during the design phase and may not reflect all changes made in permitting and construction. CG Engineering may be contacted for an updated copy of this map once the as-built drawings are completed for the site. Maintenance sheets from the 2014 Stormwater Management Manual for Western Washington are included for the following facilities: Catch Basins: Concrete structures with steel grates that collect stormwater runoff from the site and act as junctions for storm conveyance pipes. See"No. 5"for maintenance. Gravel Infiltration Trench:Subsurface trenches backfilled with a coarse stone aggregate,allowing for temporary storage of stormwater runoff in the voids of the aggregate. Runoff is distributed through the trench with a perforated pipe and gradually infiltrates into the surrounding soil. Vegetation Management: Landscaping can include grading, soil transfer, vegetation removal, pesticide and fertilizer applications,and watering.Stormwater contaminants include toxic organic compounds, heavy metals, oils, total suspended solids, coliform bacteria, fertilizers, and pesticides. Water Quality System: Two Modular Wetland System Catch Basins have been chosen and sized as the water quality system to treat stormwater runoff from pollution-generating hard within the driveway entrances,which bypass the infiltration.The project site is required to treat runoff to an "Enhanced Treatment" standard per the 2014 Washington State Department of Ecology Stormwater Management Manual. Facilities shall be inspected for defects listed in the following facility sheets. Most maintenance tasks are generally reactionary to a defect being found, rather than a matter of constant upkeep. It is generally expected that few to none of these defects will be present upon the yearly inspection of each facility.The facility sheets list the potential conditions warranting maintenance and the expected result following any maintenance. Several engineer's notes for specific tasks are provided within the facility sheets. Unless otherwise noted on the facility sheets the maintenance tasks should be performed on an "as needed" basis: (a) When the described defect is visible to whomever performs the yearly inspection, (b) Should any defect become apparent between inspections. 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Section Vill,Page 4 SAMPLE ACTIVITY LOG DATE FACILITY MAINTENANCE PERFORMED RESULTS/NOTES 1 C250 4th Avenue South,Suite 200 CM Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com No. 2—Infiltration Maintenance Defect Conditions When Maintenance Is Results Expected When Component Needed Maintenance Is Performed General Trash&Debris See"Detention Ponds"(No. 1). See"Detention Ponds" (No. 1). Poisonous/Noxious See"Detention Ponds"(No. 1). See"Detention Ponds" Vegetation (No. 1). Contaminants and See"Detention Ponds"(No. 1). See"Detention Ponds" Pollution (No. 1). Rodent Holes See"Detention Ponds"(No. 1). See"Detention Ponds" (No. 1) Storage Area Sediment Water ponding in infiltration pond after Sediment is removed rainfall ceases and appropriate time and/or facility is cleaned allowed for infiltration.Treatment basins so that infiltration system should infiltrate Water Quality Design Storm works according to Volume within 48 hours,and empty within design. 24 hours after cessation of most rain events. (A percolation test pit or test of facility indicates facility is only working at 90%of its designed capabilities.Test every 2 to 5 years. If two inches or more sediment is present,remove). Filter Bags(if Filled with Sediment and debris fill bag more than 1/2 Filter bag is replaced or applicable) Sediment and full. system is redesigned. Debris Rock Filters Sediment and By visual inspection, little or no water flows Gravel in rock filter is Debris through filter during heavy rain storms. replaced. Side Slopes of Erosion See"Detention Ponds"(No. 1). See"Detention Ponds" Pond (No. 1). Emergency Tree Growth See"Detention Ponds"(No. 1). See"Detention Ponds" Overflow Spillway (No. 1). and Berms over 4 feet in height. Piping See"Detention Ponds"(No. 1). See"Detention Ponds" (No. 1). Emergency Rock Missing See"Detention Ponds"(No. 1). See"Detention Ponds" Overflow Spillway (No. 1). Erosion See"Detention Ponds"(No. 1). See"Detention Ponds" (No. 1). Pre-settling Facility or sump 6"or designed sediment trap depth of Sediment is removed. Ponds and Vaults filled with Sediment sediment. and/or debris Volume V—Runoff Treatment BMPs—December 2014 4-35 No. 5—Catch Basins Maintenance Defect Conditions When Maintenance is Needed Results Expected When Component Maintenance is performed General Trash& Trash or debris which is located immediately No Trash or debris located Debris in front of the catch basin opening or is immediately in front of blocking inletting capacity of the basin by catch basin or on grate more than 10%. opening. Trash or debris(in the basin)that exceeds 60 No trash or debris in the percent of the sump depth as measured from catch basin. the bottom of basin to invert of the lowest pipe into or out of the basin, but in no case less than a minimum of six inches clearance from the debris surface to the invert of the lowest pipe. Trash or debris in any inlet or outlet pipe Inlet and outlet pipes free blocking more than 1/3 of its height. of trash or debris. Dead animals or vegetation that could No dead animals or generate odors that could cause complaints vegetation present within or dangerous gases(e.g., methane). the catch basin. Sediment Sediment(in the basin)that exceeds 60 No sediment in the catch percent of the sump depth as measured from basin the bottom of basin to invert of the lowest pipe into or out of the basin, but in no case less than a minimum of 6 inches clearance from the sediment surface to the invert of the lowest pipe. Structure Top slab has holes larger than 2 square Top slab is free of holes Damage to inches or cracks wider than 1/4 inch and cracks Frame and/or (Intent is to make sure no material is running Top Slab into basin). Frame not sitting flush on top slab, i.e , Frame is sitting flush on separation of more than 3/4 inch of the frame the riser rings or top slab from the top slab. Frame not securely and firmly attached. attached Fractures or Maintenance person judges that structure is Basin replaced or repaired Cracks in unsound. to design standards. Basin Walls/ Bottom Grout fillet has separated or cracked wider Pipe is regrouted and than 1/2 inch and longer than 1 foot at the secure at basin wall. joint of any inlet/outlet pipe or any evidence of soil particles entering catch basin through cracks. Settlement/ If failure of basin has created a safety, Basin replaced or repaired Misalignment function, or design problem. to design standards. Vegetation Vegetation growing across and blocking more No vegetation blocking than 10%of the basin opening. opening to basin. Vegetation growing in inlet/outlet pipe joints No vegetation or root that is more than six inches tall and less than growth present. six inches apart. Contamination See"Detention Ponds"(No 1). No pollution present. and Pollution Volume V—Runoff Treatment BMPs—December 2014 4-38 No. 5—Catch Basins Maintenance Defect Conditions When Maintenance is Needed Results Expected When Component Maintenance is performed Catch Basin Cover Not in Cover is missing or only partially in place. Catch basin cover is Cover Place Any open catch basin requires maintenance. closed Locking Mechanism cannot be opened by one Mechanism opens with Mechanism maintenance person with proper tools. Bolts proper tools. Not Working into frame have less than 1/2 inch of thread. Cover Difficult One maintenance person cannot remove lid Cover can be removed by to Remove after applying normal lifting pressure. one maintenance person. (Intent is keep cover from sealing off access to maintenance.) Ladder Ladder Rungs Ladder is unsafe due to missing rungs, not Ladder meets design Unsafe securely attached to basin wall, standards and allows misalignment, rust, cracks, or sharp edges. maintenance person safe access. Metal Grates Grate opening Grate with opening wider than 7/8 inch. Grate opening meets (If Applicable) Unsafe design standards. Trash and Trash and debris that is blocking more than Grate free of trash and Debris 20%of grate surface inletting capacity. debris. Damaged or Grate missing or broken member(s)of the Grate is in place and Missing. grate. meets design standards. No. ebris Barriers(e.g., Trash Racks) Maintenance tenance efect Condition When Maintenance is Results Expected When Components Needed Maintenance is Perfor General Trash and as or debris that is plugging more Barrier cle o design flow Debris tha %of the openings in the barrier. CaIDO Metal Damaged/ Bars are ben of shape more th Bars in place with no bends more Missing inches. than 3/4 inch. Bars. Bars are g or entire barrier Bars in place according to design. mis ' Bars are loose and rust is causing 50% Barrie laced or repaired to deterioration to any part of barrier. design sta ds. Inlet/Outlet Debris barrier missing or not attached to Barrier firmly attache �ipe Pipe pipe Volume V—Runoff Treatment BMPs—December 2014 4-39 Applicable Operational BMPs: • Eliminate unpermitted wastewater discharges to storm sew , ground water, or surface water. • Convey unpermitted discharges to a sanitary sewer • allowed by the cal sewer authority, or to other approved treat nt. • Obt in appropriate state and local permits fo• ese discharges. Recomme ed Additional Operational B s: At commercial and industrial faci ' ies, conduct a survey of w tewater discharge connections to storm drains a d to surface water as Ilows: • Conduct a fields rvey of build' gs,particularly older buildings, and other industrial are to loca storm drains from buildings and paved surfaces.Note where e join the public storm drain(s). • During non-stormwa c ditions inspect each storm drain for non- stormwater discha aes. Reco the locations of all non-stormwater discharges. Incl a all permitte discharges. • If useful, pr are a map of each ar . Show on the map the known location storm sewers, sanitary se rs, and permitted and unper itted discharges. Aerial photos be useful. Check records suc as piping schematics to identify kno side sewer connections d show these on the map. Consider using s oke, dye, or chemical analysis tests to detect connections between two onveyance systems (e.g.,process water and stormwater). If desirable, nduct TV inspections of the storm drains and record the footag n videotape. • Compare the observed locations of connections with th information on the map and revise the map accordingly. Note suspect nnections that are inconsistent with the field survey. • Identify all connections to storm sewers or to surface water an ke the actions specified above as applicable BMPs. S411 BMPs for Landscaping and Lawn/ Vegetation Management Description of Pollutant Sources: Landscaping can include grading, soil transfer, vegetation removal,pesticide and fertilizer applications, and watering. Stormwater contaminants include toxic organic compounds, heavy metals, oils, total suspended solids, coliform bacteria, fertilizers, and pesticides. Lawn and vegetation management can include control of objectionable weeds, insects, mold, bacteria, and other pests with pesticides. Examples include weed control on golf course lawns, access roads, and utility corridors and during landscaping; sap stain and insect control on lumber and logs; rooftop moss removal; killing nuisance rodents; fungicide application to patio decks, and residential lawn/plant care. It is possible to Volume IV-Source Control BMPs—December 2014 2-21 i release toxic pesticides such as pentachlorophenol, carbamates, and organometallics to the environment by leaching and dripping from treated parts, container leaks,product misuse, and outside storage of pesticide contaminated materials and equipment. Poor management of the vegetation and poor application of pesticides or fertilizers can cause appreciable stormwater contamination. Pollutant Control Approach: Control of fertilizer and pesticide applications, soil erosion, and site debris to prevent contamination of stormwater. Develop and implement an Integrated Pest Management Plan (IPM) and use pesticides only as a last resort. Carefully apply pesticides/herbicides, in accordance with label instructions. Maintain appropriate vegetation, with proper fertilizer application where practicable, to control erosion and the discharge of stormwater pollutants. Where practicable grow plant species appropriate for the site, or adjust the soil properties of the subject site to grow desired plant species. Applicable Operational BMPs for Landscaping: • Install engineered soil/landscape systems to improve the infiltration and regulation of stormwater in landscaped areas. • Do not dispose of collected vegetation into waterways or storm sewer systems. Recommended Additional Operational BMPs for Landscaping: Conduct mulch-mowing whenever practicable ! • Dispose of grass clippings, leaves, sticks, or other collected vegetation, ' by composting, if feasible. • Use mulch or other erosion control measures on soils exposed for more than one week during the dry season or two days during the rainy season. • Store and maintain appropriate oil and chemical spill cleanup materials in readily accessible locations when using oil or other chemicals. Ensure that employees are familiar with proper spill cleanup procedures. Till fertilizers into the soil rather than dumping or broadcasting onto the surface. Determine the proper fertilizer application rate for the types of soil and vegetation encountered. • Till a topsoil mix or composted organic material into the soil to create a well-mixed transition layer that encourages deeper root systems and drought-resistant plants. • Use manual and/or mechanical methods of vegetation removal rather than applying herbicides, where practical. Volume IV-Source Control BMPs—December 2014 2-22 Applicable Operational BMPs for the Use of Pesticides: Develop and implement an IPM (See section on IPM in Applicable Operational BMPs for Vegetation Nfana erg nent) and use pesticides only as a last resort. Implement a pesticide-use plan and include at a minimum: a list of selected pesticides and their specific uses; brands, formulations, application methods and quantities to be used; equipment use and maintenance procedures; safety, storage, and disposal methods; and monitoring, record keeping, and public notice procedures. All procedures shall conform to the requirements of Chapter 17.21 RCW and Chapter 16-228 WAC(Appendix IV-D R.7). Choose the least toxic pesticide available that is capable of reducing the infestation to acceptable levels. The pesticide should readily degrade in the environment and/or have properties that strongly bind it to the soil. Conduct any pest control activity at the life stage when the pest is most vulnerable. For example, if it is necessary to use a Bacillus thurin iens application to control tent caterpillars, apply it to the material before the caterpillars cocoon or it will be ineffective.Any method used should be site-specific and not used wholesale over a wide area. • Apply the pesticide according to label directions. Do not apply pesticides in quantities that exceed manufacturer's instructions. • Mix the pesticides and clean the application equipment in an area where accidental spills will not enter surface or ground waters, and will not contaminate the soil. i • Store pesticides in enclosed areas or in covered impervious containment. Do not discharge pesticide contaminated stormwater or spills/leaks of pesticides to storm sewers. Do not hose down the paved areas to a storm sewer or conveyance ditch. Store and maintain appropriate spill cleanup materials in a location known to all near the storage area. • Clean up any spilled pesticides. Keep pesticide contaminated waste materials in designated covered and contained areas. The pesticide application equipment must be capable of immediate shutoff in the event of an emergency. • Spraying pesticides within 100 feet of open waters including wetlands, ponds, and rivers, streams, creeks, sloughs and any drainage ditch or channel that leads to open water may have additional regulatory requirements beyond just following the pesticide product label. Additional requirements may include: • Obtaining a discharge permit from Ecology. • Obtaining a permit from the local jurisdiction. • Using an aquatic labeled pesticide. Volume IV-Source Control BMPs—December 2014 2-23 • Flag all sensitive areas including wells, creeks, and wetlands prior to spraying. Post notices and delineate the spray area prior to the application, as required by the local jurisdiction or by Ecology. • Conduct spray applications during weather conditions as specified in the label direction and applicable local and state regulations.Do not apply during rain or immediately before expected rain. Recommended Additional Operational BMPs for the use of pesticides: • Consider alternatives to the use of pesticides such as covering or harvesting weeds, substitute vegetative growth, and manual weed control/moss removal. Consider the use of soil amendments, such as compost,that are known to control some common diseases in plants, such as Pythium root rot, ashy stem blight, and parasitic nematodes. The following are three possible mechanisms for disease control by compost addition (USEPA Publication 530-F-9-044): 1. Successful competition for nutrients by antibiotic production; 2. Successful predation against pathogens by beneficial microorganism; and 3. Activation of disease-resistant genes in plants by composts. Installing an amended soil/landscape system can preserve both the plant system and the soil system more effectively. This type of approach provides a soil/landscape system with adequate depth,permeability, and organic matter to sustain itself and continue working as an effective stormwater infiltration system and a sustainable nutrient cycle. • Once a pesticide is applied, evaluate its effectiveness for possible improvement. Records should be kept showing the effectiveness of the pesticides considered. Develop an annual evaluation procedure including a review of the effectiveness of pesticide applications, impact on buffers and sensitive areas (including potable wells), public concerns, and recent toxicological information on pesticides used/proposed for use. If individual or public potable wells are located in the proximity of commercial pesticide applications, contact the regional Ecology hydrogeologist to determine if additional pesticide application control measures are necessary. Rinseate from equipment cleaning and/or triple-rinsing of pesticide containers should be used as product or recycled into product. For more information, contact the Washington State University (WSU) Extension Home-Assist Program, (253) 445-4556, or Bio-Integral Resource Center (BIRO), P.O. Box 7414, Berkeley, CA.94707, or EPA to Volume IV-Source Control BMPs—December 2014 2-24 obtain a publication entitled "Suspended, Canceled, and Restricted Pesticides"which lists all restricted pesticides and the specific uses that are allowed. Applicable Operational BMPs for Vegetation Management: • Use at least an eight-inch "topsoil" layer with at least 8 percent organic matter to provide a sufficient vegetation-growing medium. Amending existing landscapes and turf systems by increasing the percent organic matter and depth of topsoil can substantially improve the permeability of the soil,the disease and drought resistance of the vegetation, and reduce fertilizer demand. This reduces the demand for fertilizers, herbicides, and pesticides. Organic matter is the least water-soluble form of nutrients that can be added to the soil. Composted organic matter generally releases only between 2 and 10 percent of its total nitrogen annually, and this release corresponds closely to the plant growth cycle. Return natural plant debris and mulch to the soil, to continue recycling nutrients indefinitely. • Select the appropriate turfgrass mixture for the climate and soil type. Certain tall fescues and rye grasses resist insect attack because the symbiotic endophytic fungi found naturally in their tissues repel or kill common leaf and stem-eating lawn insects. However,they do not, repel root-feeding lawn pests such as Crane Fly larvae, and are toxic to ruminants such as cattle and sheep. The fungus causes no known adverse effects to the host plant or to humans. Endophytic grasses are commercially available; use them in areas such as parks or golf courses where grazing does not occur. Local agricultural or gardening resources such as Washington State University Extension office can offer advice on which types of grass are best suited to the area and soil type. • Use the following seeding and planting BMPs, or equivalent BMPs to } obtain information on grass mixtures, temporary and permanent seeding procedures, maintenance of a recently planted area, and fertilizer application rates: Temporary and Permanent Seeding, Mulching,Plastic Covering, and Sodding as described in Volume II. • Adjusting the soil properties of the subject site can assist in selection of desired plant species. For example, design a constructed wetland to resist the invasion of reed canary grass by layering specific strata of organic matters (e.g., composted forest product residuals) and creating a mildly acidic pH and carbon-rich soil medium. Consult a soil restoration specialist for site-specific conditions. • Aerate lawns regularly in areas of heavy use where the soil tends to become compacted. Conduct aeration while the grasses in the lawn are growing most vigorously. Remove layers of thatch greater than 3/4-inch deep. Volume IV-Source Control BMPs—December 2014 2-25 • Mowing is a stress-creating activity for turfgrass. Grass decreases its productivity when mown too short and there is less growth of roots and rhizomes. The turf becomes less tolerant of environmental stresses, more disease prone and more reliant on outside means such as pesticides, fertilizers, and irrigation to remain healthy. Set the mowing height at the highest acceptable level and mow at times and intervals designed to minimize stress on the turf. Generally mowing only 1/3 of the grass blade height will prevent stressing the turf. Irrigation: • The depth from which a plant normally extracts water depends on the rooting depth of the plant. Appropriately irrigated lawn grasses normally root in the top 6 to 12 inches of soil; lawns irrigated on a daily basis often root only in the top 1 inch of soil. Improper irrigation can encourage pest problems, leach nutrients, and make a lawn completely dependent on artificial watering. The amount of water applied depends on the normal rooting depth of the turfgrass species used, the available water holding capacity of the soil, and the efficiency of the irrigation system. Consult with the local water utility, Conservation District, or Cooperative Extension office to help determine optimum irrigation practices. Fertilizer Management: • Turfgrass is most responsive to nitrogen fertilization, followed by potassium and phosphorus. Fertilization needs vary by site depending on plant, soil, and climatic conditions. Evaluation of soil nutrient levels through regular testing ensures the best possible efficiency and economy of fertilization. For details on soils testing, contact the local Conservation District, a soils testing professional, or a Washington State University Extension office. • Apply fertilizers in amounts appropriate for the target vegetation and at the time of year that minimizes losses to surface and ground waters. Do not fertilize when the soil is dry. Alternatively, do not apply fertilizers within three days prior to predicted rainfall. The longer the period between fertilizer application and either rainfall or irrigation, the less fertilizer runoff occurs. • Use slow release fertilizers such as methylene urea, IDBU, or resin coated fertilizers when appropriate, generally in the spring. Use of slow release fertilizers is especially important in areas with sandy or gravelly soils. • Time the fertilizer application to periods of maximum plant uptake. Ecology generally recommends application in the fall and spring, although Washington State University turf specialists recommend four fertilizer applications per year. Volume IV-Source Control BMPs—December 2014 2-26 • Properly trained persons should apply all fertilizers. Apply no fertilizer at commercial and industrial facilities, to grass swales, filter strips, or buffer areas that drain to sensitive water bodies unless approved by the local jurisdiction. Integrated Pest Management An IPM program might consist of the following steps: l Step 1: Correctly identify problem pests and understand their life cycle Step 2: Establish tolerance thresholds for pests. Step 3: Monitor to detect and prevent pest problems. Step 4: Modify the maintenance program to promote healthy plants and discourage pests. Step 5: Use cultural,physical, mechanical or biological controls first if pests exceed the tolerance thresholds. Step 6: Evaluate and record the effectiveness of the control and modify maintenance practices to support lawn or landscape recovery and prevent recurrence. For an elaboration of these steps, refer to Appendix IV-F. S4 BMPs for Loading and Unloading Areas for Liquid or Solid Material Description of Pollutant Sources: Operators typically condu loading/unloading of liquid and solid materials at industri nd commercial facilities at shipping and receiving, outsid torage, fueling reas, etc. Materials transferred can include produc , raw materials, in mediate products, waste materials, fuels, sc p metals, etc. Leaks and spills fuels, oils,powders, organics, heav etals, salts, acids, alkalis, etc. duri transfer may cause stormwate contamination. Spills from hydraulic lin breaks are a common blem at loading docks. Pollutant Contr Approach: ver and contain the loading/unloading area where necess o prev t run-on of stormwater and runoff of contaminated stormwat Applicable Operat' al B s: At All Loadin nloading Area . • A Sig ' scant amount of debris can cumulate at outside, uncovered to ng/unloading areas. Sweep these rfaces frequently to remove ose material that could contaminate stor water. Sweep areas temporarily covered after removal of the con 'ners, logs, or other material covering the ground. • Place drip pans, or other appropriate temporary conta ent device, at locations where leaks or spills may occur such as hose co ections. hose reels and filler nozzles. Always use drip pans when ma •ig and Volume IV-Source Control BMPs—December 2014 2-27 WETLANDS Maintenance Guidelines for Modular Wetland System - Linear Maintenance Summary o Remove Trash from Screening Device-average maintenance interval is 6 to 12 months. • (5minute average service time). o Remove Sediment from Separation Chamber-average maintenance interval is 12 to 24 months. • (10 minute average service time). o Replace Cartridge Filter Media—average maintenance interval 12 to 24 months. ■ (10-15 minute per cartridge average service time). o Replace Drain Down Filter Media—average maintenance interval is 12 to 24 months. ■ (5 minute average service time). o Trim Vegetation—average maintenance interval is 6 to 12 months. ■ (Service time varies). System Diagram Access to screening device, separation chamber and cartridge filter Access to drain Inflow Pipe - down filter (optional) Pre-Treatment Chamber Biofiltration Chamber � J Outflow Discharge Pipe Chamber www.modularwetiands.com WETLANDS- Maintenance Procedures Screening Device 1. Remove grate or manhole cover to gain access to the screening device in the Pre- Treatment Chamber. Vault type units do not have screening device. Maintenance can be performed without entry. 2. Remove all pollutants collected by the screening device. Removal can be done manually or with the use of a vacuum truck. The hose of the vacuum truck will not damage the screening device. 3. Screening device can easily be removed from the Pre-Treatment Chamber to gain access to separation chamber and media filters below. Replace grate or manhole cover when completed. Separation Chamber 1. Perform maintenance procedures of screening device listed above before maintaining the separation chamber. 2. With a pressure washer spray down pollutants accumulated on walls and cartridge filters. 3. Vacuum out Separation Chamber and remove all accumulated pollutants. Replace screening device, grate or manhole cover when completed. Cartridge Filters 1. Perform maintenance procedures on screening device and separation chamber before maintaining cartridge filters. 2. Enter separation chamber. 3. Unscrew the two bolts holding the lid on each cartridge filter and remove lid. 4. Remove each of 4 to 8 media cages holding the media in place. 5. Spray down the cartridge filter to remove any accumulated pollutants. 6. Vacuum out old media and accumulated pollutants. 7. Reinstall media cages and fill with new media from manufacturer or outside supplier. Manufacturer will provide specification of media and sources to purchase. 8. Replace the lid and tighten down bolts. Replace screening device, grate or manhole cover when completed. Drain Down Filter 1. Remove hatch or manhole cover over discharge chamber and enter chamber. 2. Unlock and lift drain down filter housing and remove old media block. Replace with new media block. Lower drain down filter housing and lock into place. 3. Exit chamber and replace hatch or manhole cover. www.modularwetlands.com 1�-- WETLANDS- Maintenance Notes 1. Following maintenance and/or inspection, it is recommended the maintenance operator prepare a maintenance/inspection record. The record should include any maintenance activities performed, amount and description of debris collected, and condition of the system and its various filter mechanisms. 2. The owner should keep maintenance/inspection record(s) for a minimum of five years from the date of maintenance. These records should be made available to the governing municipality for inspection upon request at any time. 3. Transport all debris, trash, organics and sediments to approved facility for disposal in accordance with local and state requirements. 4. Entry into chambers may require confined space training based on state and local regulations. 5. No fertilizer shall be used in the Biofiltration Chamber. 6. Irrigation should be provided as recommended by manufacturer and/or landscape architect. Amount of irrigation required is dependent on plant species. Some plants may require irrigation. www.modularwetlands.com WETLANDS- Maintenance Procedure Illustration Screening Device The screening device is located directly _ under the manhole or grate over the Pre-Treatment Chamber. It's mounted directly underneath for easy access and cleaning. Device can be cleaned by hand or with a vacuum truck. ' Separation Chamber The separation chamber is located directly beneath the screening device. It can be quickly cleaned using a vacuum truck or by hand. A pressure washer is useful to assist in the cleaning process. �OY_t• 1f� T�� � .'fBG� TI 4 � www.modularwetlands.com lik WETLANDS- Cartridge Filters The cartridge filters are located in the Pre-Treatment chamber connected to the wall adjacent to the biofiltration chamber. The cartridges have removable tops to access the individual media filters. Once the cartridge is open media can be easily removed and replaced by hand or a vacuum truck. S. V Drain Down Filter The drain down filter is located in the Discharge Chamber. The drain filter unlocks from the wall mount and hinges up. Remove filter block and replace with new block. a www.modularwetlands.com M O D U L A R WETLANDS Trim Vegetation Vegetation should be maintained in the same manner as surrounding vegetation and trimmed as needed. No fertilizer shall be used on the plants. Irrigation per the recommendation of the manufacturer and or landscape - architect. Different types of vegetation requires different amounts of irrigation. j www.modularwetiands.com WETLANDS- Inspection Form 4 r • n Modular Wetland System, Inc. P. 760.433-7640 F. 760-433-3176 E. lnfo@modularwetiands.com www.modularwetiands.com B� CLEAN Inspection Report ENVIXONMENTAt 1EAVrEE3.INC Modular Wetlands System WETLANDS Project Name For Office Use Only Project Address (city) (Zip Code) (Renewed By) l Owner/Management Company (Date) Office personnel to complete section to Contact Phone( ) — the left- Inspector Name Date / / Time AM/PM Type of Inspection ❑ Routine ❑ Follow Up ❑ Complaint ❑ Storm Storm Event in Last 72-hours? ❑ No ❑ Yes Weather Condition Additional Notes Inspection Checklist Modular Wetland System Type(Curb, Grate or UG Vault): Size (22', 14'or etc.): Structural Integrity: Yes No Comments Damage to pre-treatment access cover(manhole cover/grate)or cannot be opened using normal lifting pressure? Damage to discharge chamber access cover(manhole cover/grate)or cannot be opened using normal lifting pressure? Does the MWS unit show signs of structural deterioration(cracks in the wall,damage to frame)? Is the inlet/outlet pipe or drain down pipe damaged or otherwise not functioning properly? Working Condition: Is there evidence of illicit discharge or excessive oil,grease,or other automobile fluids entering and clogging th unit? Is there standing water in inappropriate areas after a dry period? Is the filter insert(if applicable)at capacity and/or is there an accumulation of debris/trash on the shelf system? Does the depth of sediment/trash/debris suggest a blockage of the inflow pipe,bypass or cartridge filter? If yes Depth: specify which one in the comments section. Note depth of accumulation in in pre-treatment chamber. Chamber: Does the cartridge filter media need replacement in pre-treatment chamber and/or discharge chamber? .Any signs of improper functioning in the discharge chamber? Note issues in comments section. Other Inspection Items: Is there an accumulation of sediment/trash/debris in the wetland media(if applicable)? Is it evident that the plants are alive and healthy(if applicable)?Please note Plant Information below. Is there a septic or foul odor coming from inside the system? Waste: Yes No Recommended Maintenance Plant Information Sediment/Silt/Clay No Cleaning Needed Damage to Plants Trash/Bags/Bottles Schedule Maintenance as Planned Plant Replacement Green Waste/Leaves/Foliage Needs Immediate Maintenance Plant Trimming Additional Notes: 2972 San Luis Rey Road,Oceanside,CA 92058 P(760)433-7640 F(760)433-3176 -]L- WETLANDS- Maintenance Report y B10 C14�. I U60)433.1640 Jt �14 ! Zvi y� � ��'� •}�•i..`� S { � .1 � },.��� k,i �!��. 1 ..fir Y�S ���j` '�` �•y4'j�4 � ,\ �b �i '�i x, �j�' \ Modular Wetland System, Inc. P. 760.433-7640 F. 760-433-3176 E. Info@modularwetlands-com www.modularwetiands.com B� CLEAN Cleaning and Maintenance Report Modular Wetlands System WETLANDS CI`)nlA 11 W ENVIRONMENTAL SERVICES.INC. ETLANDS 1 Project Name For Office Use Only Project Address (city) (zip code) (Reviewed By) Owner/Management Company (uate) Office personnel to complete section to Contact Phone( ) — the len 1 Inspector Name Date 1 1 Time AM/PM 1 Type of Inspection ❑ Routine ❑ Follow Up ❑ Complaint ❑Storm Storm Event in Last 72-hours? ❑ No ❑ Yes r Weather Condition Additional Notes Condition of Media Operational Per Site GPS Coordinates Manufacturer/ Trash Foliage Sediment Total Debris 25/50/75/100 Manufactures' Map# of Insert Description/Sizing Accumulation Accumulation Accumulation Accumulation (will be changed Specifications @ 75%) (If not,why?) Lat: M W S Catch Basins Lon a: MWS Sedimentation Basin Media Filter Condition Plant Condition Drain Down Media Condition Discharge Chamber Condition Drain Down Pipe Condition Inlet and Outlet Pipe Condition Comments: 2972 San Luis Rey Road,Oceanside,CA 92058 P.760-433 7640 F.760.433.3176 Centennial Park 18386.20 June 30,2020 Drainage Report Appendix A,Page 1 Appendix A — WWHM Reports Appendix A Summary A-1 Narrative A-2 Bypass Calculation A-10 Sub-Basin 2 Infiltration Trench Verification Calculation& LID Performance Calculation A-28 Drawdown Volume Calculation A-29 Water Quality Flows for MWS Catch Basins A-33 Conveyance Analysis A-35 Wetland Input Analysis Calculations in this section start with a global look at the site to verify compliance with the Flow Control Standard and the Low Impact Development (LID) Standard. The majority of developed areas on the site area fully infiltrated, but the area on the western side of the site is bypassed at allowable rates. The bypassed area is referred to in the forthcoming calculations as Sub-Basin 1.The infiltrated area is Sub- Basin 2. By 100% infiltrating Sub-Basin 2, the bypassed area is small enough that when added together, the LID and flow control standards are met. Following this, it was important to break Sub-Basin 2 into further Sub-Basins. This is because the infiltration trenches are at different elevations, and we wanted to verify that there was not an imbalance that would lead to overflows from one trench that would not be caught on the overall calculation. Following this, water quality calculations discussed in Section IV area provided. This includes the Drawdown time and water quality volume, along with the water quality treatment flows for the Pollution Generating hard surfaces flowing toward the right of way within the bypass basin. 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineeri ng.com Centennial Park 18386.20 June 30,2020 Drainage Report Appendix A,Page 2 WWHM2012 PROJECT REPORT 501 POC 1 Predeveloped 0.77`' 801 PCIC 1 Hiria-d'�d fhwn n 4- 0.61 0.44 ems, 0 `` IL 0.28 0.12 10E-5 10E-4 10E-3 10E-2 10E-1 1 10 100 P-E2,rce"t Time Exce�dirmg FIGURE A-1 Bypass Point of Compliance Graph(Flow Control) 501 POC 1 Predeveloped 0.12'' 691 POC 1 bfiti]at<d flan n rA 1- 0.10 D V 0.07 0 IL 0.04 0.02 10E-5 10E-4 10E-3 10E-2 10E-1 1 10 100 Perce"t Time Exceedi"g FIGUREA-1 Bypass Point of Compliance Graph(Low Impact Development) 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Appendix A,Page 3 WWHM2012 PROJECT REPORT Project Name:Centennial Park Bypass Calculation Site Name: Site Address:6711 and 172nd City : Arlington Report Date:6/19/2020 Gage : Everett Data Start:1948/10/01 Data End :2009/09/30 Precip Scale: 1.20 Version Date:2018/10/10 Version :4.2.16 Low Flow Threshold for POC 1:50 Percent of the 2 Year High Flow Threshold for POC 1:50 year PREDEVELOPED LAND USE Name : Predeveloped Site Bypass: No GroundWater: No Pervious Land Use acre C,Forest,Flat 4.222 C,Forest,Mod .783 C,Forest,Steep 1.324 Pervious Total 6.329 Impervious Land Use acre Impervious Total 0 Basin Total 6.329 Element Flows To: Surface Interflow Groundwater C 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Appendix A,Page 4 MITIGATED LAND USE Name : Developed Site(BYPASS AREA ON WEST SIDE ONLY) Bypass: No GrounclWater:No Pervious Land Use acre C,Lawn,Flat .32 Pervious Total 0.32 Impervious Land Use acre SIDEWALKS FLAT 0.326 PARKING FLAT 0.115 Impervious Total 0.441 Basin Total 0.761 Element Flows To: Surface Interflow Groundwater ANALYSIS RESULTS Stream Protection Duration Predeveloped Landuse Totals for POC#1 Total Pervious Area:6.329 Total Impervious Area:O Mitigated Landuse Totals for POC#1 Total Pervious Area:0.32 Total Impervious Area:0.441 Flow Frequency Return Periods for Predeveloped. POC#1 Return Period Flow cfs 2 year 0.241736 5 year 0.378011 10 year 0.484637 C 250 4th Avenue South,Suite 200 Edmonds,WA 98020 eNGIN&RING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Appendix A,Page 5 25 year 0.638926 50 year 0.768682 100 year 0.911671 Flow Frequency Return Periods for Mitigated. POC#1 Return Period Flow cfs 2 year 0.276088 5 year 0.393177 10 year 0.482248 25 year 0.608712 50 year 0.71355 100 year 0.827948 Stream Protection Duration POC#1 The Facility PASSED The Facility PASSED. Flow(cfs)Predev Mit Percentage Pass/Fail 0.1209 16010 1373 8 Pass 0.1274 13503 1135 8 Pass 0.1340 11644 998 8 Pass 0.1405 9768 841 8 Pass 0.1470 8147 714 8 Pass 0.1536 7007 628 8 Pass 0.1601 5858 546 9 Pass 0.1667 5067 467 9 Pass 0.1732 4348 402 9 Pass 0.1798 3790 361 9 Pass 0.1863 3189 325 10 Pass 0.1928 2789 295 10 Pass 0.1994 2413 257 10 Pass 0.2059 2160 231 10 Pass 0.2125 1889 198 10 Pass 0.2190 1626 182 11 Pass 0.2256 1470 167 11 Pass 0.2321 1303 156 11 Pass 0.2387 1166 147 12 Pass 0.2452 1031 129 12 Pass 0.2517 965 120 12 Pass 0.2583 900 108 12 Pass 0.2648 840 100 11 Pass 0.2714 778 90 11 Pass 0.2779 742 84 11 Pass 0.2845 693 78 11 Pass 0.2910 641 73 11 Pass 0.2975 609 69 11 Pass 0.3041 581 66 11 Pass 0.3106 560 63 11 Pass 0.3172 544 58 10 Pass 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Appendix A,Page 6 0.3237 528 55 10 Pass 0.3303 504 49 9 Pass 0.3368 465 44 9 Pass 0.3433 442 43 9 Pass 0.3499 423 39 9 Pass 0.3564 402 35 8 Pass 0.3630 384 33 8 Pass 0.3695 367 31 8 Pass 0.3761 350 28 8 Pass 0.3826 338 24 7 Pass 0.3892 328 22 6 Pass 0.3957 321 21 6 Pass 0.4022 310 18 5 Pass 0.4088 304 16 5 Pass 0.4153 295 14 4 Pass 0.4219 286 13 4 Pass 0.4284 275 8 2 Pass 0.4350 266 8 3 Pass 0.4415 254 8 3 Pass 0.4480 241 8 3 Pass 0.4546 234 8 3 Pass 0.4611 218 8 3 Pass 0.4677 211 8 3 Pass 0.4742 203 7 3 Pass 0.4808 193 6 3 Pass 0.4873 174 6 3 Pass 0.4939 168 6 3 Pass 0.5004 160 5 3 Pass 0.5069 153 5 3 Pass 0.5135 146 5 3 Pass 0.5200 138 5 3 Pass 0.5266 132 5 3 Pass 0.5331 123 5 4 Pass 0.5397 115 5 4 Pass 0.5462 98 5 5 Pass 0.5527 83 5 6 Pass 0.5593 70 5 7 Pass 0.5658 59 5 8 Pass 0.5724 51 4 7 Pass 0.5789 46 4 8 Pass 0.5855 40 4 10 Pass 0.5920 37 4 10 Pass 0.5985 35 4 11 Pass 0.6051 29 4 13 Pass 0.6116 26 4 15 Pass 0.6182 19 4 21 Pass 0.6247 16 4 25 Pass 0.6313 15 4 26 Pass 0.6378 11 4 36 Pass 0.6444 7 4 57 Pass 0.6509 6 4 66 Pass C250 4th Avenue South,Suite 200 CM Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengi neeri ng.co m Centennial Park 18386.20 June 30,2020 Drainage Report Appendix A,Page 7 0.6574 4 4 100 Pass 0.6640 4 4 100 Pass 0.6705 4 4 100 Pass 0.6771 4 3 75 Pass 0.6836 4 3 75 Pass 0.6902 4 3 75 Pass 0.6967 3 3 100 Pass 0.7032 3 3 100 Pass 0.7098 3 3 100 Pass 0.7163 3 3 100 Pass 0.7229 3 3 100 Pass 0.7294 3 3 100 Pass 0.7360 3 3 100 Pass 0.7425 3 2 66 Pass 0.7491 3 2 66 Pass 0.7556 3 2 66 Pass 0.7621 2 2 100 Pass 0.7687 2 2 100 Pass LID Duration POC#1 The Facility PASSED The Facility PASSED. Flow(cfs) Predev Mit Percentage Pass/Fail 0.0193 284899 73898 25 Pass 0.0204 273563 69813 25 Pass 0.0214 262868 66027 25 Pass 0.0224 252816 62519 24 Pass 0.0234 243191 59290 24 Pass 0.0245 234207 56188 23 Pass 0.0255 225652 53344 23 Pass 0.0265 217524 50713 23 Pass 0.0275 209653 48189 22 Pass 0.0286 202124 45772 22 Pass 0.0296 194980 43505 22 Pass 0.0306 188243 41345 21 Pass 0.0316 181676 39227 21 Pass 0.0327 175324 37366 21 Pass 0.0337 169357 35527 20 Pass 0.0347 163560 33794 20 Pass 0.0357 158063 32190 20 Pass 0.0368 152780 30586 20 Pass 0.0378 147690 29132 19 Pass 0.0388 142770 27805 19 Pass 0.0398 138022 26458 19 Pass 0.0409 133466 25153 18 Pass 0.0419 129103 24020 18 Pass 0.0429 124932 22886 18 Pass 250 4th Avenue South,Suite 200 Edmonds,WA 98020 GMIN&NNG ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Appendix A,Page 8 0.0440 120889 21817 18 Pass 0.0450 117018 20826 17 Pass 0.0460 113296 19922 17 Pass 0.0470 109767 19017 17 Pass 0.0481 106367 18148 17 Pass 0.0491 103158 17316 16 Pass 0.0501 100078 16489 16 Pass 0.0511 97084 15719 16 Pass 0.0522 94089 15066 16 Pass 0.0532 91266 14399 15 Pass 0.0542 88592 13787 15 Pass 0.0552 85983 13152 15 Pass 0.0563 83438 12557 15 Pass 0.0573 80957 12001 14 Pass 0.0583 78625 11475 14 Pass 0.0593 76358 11000 14 Pass 0.0604 74134 10515 14 Pass 0.0614 71973 10042 13 Pass 0.0624 69899 9586 13 Pass 0.0634 67931 9174 13 Pass 0.0645 65920 8778 13 Pass 0.0655 64038 8412 13 Pass 0.0665 62199 8068 12 Pass 0.0675 60488 7734 12 Pass 0.0686 58734 7392 12 Pass 0.0696 57087 7099 12 Pass 0.0706 55504 6817 12 Pass 0.0716 53985 6509 12 Pass 0.0727 52552 6239 11 Pass 0.0737 51098 5989 11 Pass 0.0747 49729 5736 11 Pass 0.0757 48360 5499 11 Pass 0.0768 47013 5268 11 Pass 0.0778 45751 5067 11 Pass 0.0788 44531 4853 10 Pass 0.0798 43398 4693 10 Pass 0.0809 42200 4532 10 Pass 0.0819 41109 4363 10 Pass 0.0829 39997 4205 10 Pass 0.0839 38992 4066 10 Pass 0.0850 37944 3925 10 Pass 0.0860 36981 3784 10 Pass 0.0870 36019 3647 10 Pass 0.0881 35078 3521 10 Pass 0.0891 34158 3399 9 Pass 0.0901 33302 3296 9 Pass 0.0911 32447 3191 9 Pass 0.0922 31613 3093 9 Pass 0.0932 30800 2992 9 Pass 0.0942 30051 2885 9 Pass 0.0952 29303 2798 9 Pass 250 4th Avenue South,Suite 200 GM Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineeri ng.com Centennial Park 18386.20 June 30,2020 Drainage Report Appendix A,Page 9 0.0963 28575 2704 9 Pass 0.0973 27827 2620 9 Pass 0.0983 27121 2541 9 Pass 0.0993 26437 2451 9 Pass 0.1004 25795 2374 9 Pass 0.1014 25153 2297 9 Pass 0.1024 24490 2220 9 Pass 0.1034 23913 2156 9 Pass 0.1045 23335 2095 8 Pass 0.1055 22779 2036 8 Pass 0.1065 22202 1971 8 Pass 0.1075 21645 1921 8 Pass 0.1086 21139 1865 8 Pass 0.1096 20659 1815 8 Pass 0.1106 20114 1766 8 Pass 0.1116 19654 1715 8 Pass 0.1127 19186 1665 8 Pass 0.1137 18749 1622 8 Pass 0.1147 18257 1584 8 Pass 0.1157 17817 1546 8 Pass 0.1168 17353 1503 8 Pass 0.1178 16946 1460 8 Pass 0.1188 16519 1422 8 Pass 0.1198 16093 1384 8 Pass 0.1209 15682 1355 8 Pass This program and accompanying documentation are provided'as-is'without warranty of any kind. The entire risk regarding the performance and results of this program is assumed by End User. Clear Creek Solutions Inc.and the governmental licensee or sublicensees disclaim all warranties,either expressed or implied,including but not limited to implied warranties of program and accompanying documentation. In no i event shall Clear Creek Solutions Inc.be liable for any damages whatsoever(including without limitation to damages for loss of business profits, loss of business information,business interruption,and the like)arising out of the use of,or inability to use this program even if Clear Creek ' Solutions Inc.or their authorized representatives have been advised of the possibility of such damages. Software Copyright©by:Clear Creek Solutions,Inc.2005-2020;All Rights Reserved. 1 C 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Appendix A, Page 10 BAST 2A �107, 111) B SIN 2B 10 B SIN IC 10 -106 A� 109 Al 07, 1 1 01-1 0 FIGURE A-2 DEVELOPED BASIN 2 FLOW CHART WWHM2012 PROJECT REPORT Project Name:2020.06.15 CP Ph1 Site Name:CP-Phase 1—Basin 2 Site Address: City : Report Date:6/19/2020 Gage : Everett Data Start: 1948/10/01 Data End:2009/09/30 Precip Scale: 1.20 Version Date:2018/10/10 Version :4.2.16 Low Flow Threshold for POC 1:50 Percent of the 2 Year High Flow Threshold for POC 1:50 year PREDEVELOPED LAND USE 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Appendix A,Page 11 Name : Basin 1 Bypass: No GroundWater: No Pervious Land Use acre C,Forest,Flat 3.461 C,Forest,Mod .783 C,Forest,Steep 1.324 Pervious Total 5.568 Impervious Land Use acre Impervious Total 0 Basin Total 5.568 Element Flows To: Surface Interflow Groundwater MITIGATED LAND USE Name : Basin 2C(101-106) Bypass: No GroundWater:No Pervious Land Use acre C,Lawn,Flat .601 Pervious Total 0.601 Impervious Land Use acre ROOF TOPS FLAT 0.63 SIDEWALKS FLAT 0.42 PARKING FLAT 0.939 Impervious Total 1.989 Basin Total 2.59 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cge ngi n ee ri ng.co m Centennial Park 18386.20 June 30,2020 Drainage Report Appendix A,Page 12 Element Flows To: Surface Interflow Groundwater Gravel Trench Bed 101-Gravel Trench Bed 101- Name : Basin 2A(107/11) Bypass: No GroundWater: No Pervious Land Use acre C,Lawn,Flat .874 Pervious Total 0.874 Impervious Land Use acre ROOFTOPS FLAT 0.549 SIDEWALKS FLAT 0.401 PARKING FLAT 0.433 Impervious Total 1.383 Basin Total 2.257 Element Flows To: Surface Interflow Groundwater Gravel Trench Bed 107,Gravel Trench Bed 107, Name : Basin 2B(109) Bypass: No GroundWater: No Pervious Land Use acre_ C,Lawn,Flat .09 Pervious Total 0.09 mpervious Land Use acre ROOF TOPS FLAT 0.284 SIDEWALKS FLAT 0.081 PARKING FLAT 0.25 Impervious Total 0.615 C 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cge ngi n ee ri n g.co m Centennial Park 18386.20 June 30,2020 Drainage Report Appendix A,Page 13 Basin Total 0.705 Element Flows To: Surface Interflow Groundwater Gravel Trench Bed 109 Gravel Trench Bed 109 Name :Gravel Trench Bed 107, 111 Bottom Length:545.00 ft. Bottom Width: 10.00 ft. Trench bottom slope 1:0 To 1 Trench Left side slope 0:0 To 1 Trench right side slope 2:0 To 1 Material thickness of first layer: 1.5 Pour Space of material for first layer: 0.35 Material thickness of second layer: 1.5 Pour Space of material for second layer: 0.33 Material thickness of third layer: 0 Pour Space of material for third layer: 0 Infiltration On Infiltration rate:5 Infiltration safety factor: 1 Total Volume Infiltrated(ac-ft.):362.047 Total Volume Through Riser(ac-ft.):0 Total Volume Through Facility(ac-ft.):362.047 Percent Infiltrated:100 Total Precip Applied to Facility:0 Total Evap From Facility:0 Discharge Structure Riser Height:3 ft. Riser Diameter: 12 in. Element Flows To: Outlet 1 Outlet 2 Gravel Trench Bed Hydraulic Table StaKe feet) Area(ac.l_Volume(ac-ft.)Discharge(cfs)Infilt(cfs) 0.0000 0.125 0.000 0.000 0.000 0.0333 0.125 0.001 0.000 0.630 0.0667 0.125 0.002 0.000 0.630 0.1000 0.125 0.004 0.000 0.630 0.1333 0.125 0.005 0.000 0.630 0.1667 0.125 0.007 0.000 0.630 C 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Appendix A,Page 14 0.2000 0.125 0.008 0.000 0.630 0.2333 0.125 0.010 0.000 0.630 0.2667 0.125 0.011 0.000 0.630 0.3000 0.125 0.013 0.000 0.630 0.3333 0.125 0.014 0.000 0.630 0.3667 0.125 0.016 0.000 0.630 0.4000 0.125 0.017 0.000 0.630 0.4333 0.125 0.019 0.000 0.630 0.4667 0.125 0.020 0.000 0.630 0.5000 0.125 0.021 0.000 0.630 0.5333 0.125 0.023 0.000 0.630 0.5667 0.125 0.024 0.000 0.630 0.6000 0.125 0.026 0.000 0.630 0.6333 0.125 0.027 0.000 0.630 0.6667 0.125 0.029 0.000 0.630 0.7000 0.125 0.030 0.000 0.630 0.7333 0.125 0.032 0.000 0.630 0.7667 0.125 0.033 0.000 0.630 0.8000 0.125 0.035 0.000 0.630 0.8333 0.125 0.036 0.000 0.630 0.8667 0.125 0.038 0.000 0.630 0.9000 0.125 0.039 0.000 0.630 0.9333 0.125 0.040 0.000 0.630 0.9667 0.125 0.042 0.000 0.630 1.0000 0.125 0.043 0.000 0.630 1.0333 0.125 0.045 0.000 0.630 1.0667 0.125 0.046 0.000 0.630 1.1000 0.125 0.048 0.000 0.630 1.1333 0.125 0.049 0.000 0.630 1.1667 0.125 0.051 0.000 0.630 1.2000 0.125 0.052 0.000 0.630 1.2333 0.125 0.054 0.000 0.630 1.2667 0.125 0.055 0.000 0.630 1.3000 0.125 0.056 0.000 0.630 1.3333 0.125 0.058 0.000 0.630 1.3667 0.125 0.059 0.000 0.630 1.4000 0.125 0.061 0.000 0.630 1.4333 0.125 0.062 0.000 0.630 1.4667 0.125 0.064 0.000 0.630 1.5000 0.125 0.065 0.000 0.630 1.5333 0.125 0.067 0.000 0.630 1.5667 0.125 0.068 0.000 0.630 1.6000 0.125 0.069 0.000 0.630 1.6333 0.125 0.071 0.000 0.630 1.6667 0.125 0.072 0.000 0.630 1.7000 0.125 0.073 0.000 0.630 1.7333 0.125 0.075 0.000 0.630 1.7667 0.125 0.076 0.000 0.630 1.8000 0.125 0.078 0.000 0.630 1.8333 0.125 0.079 0.000 0.630 1.8667 0.125 0.080 0.000 0.630 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Appendix A,Page 15 1.9000 0.125 0.082 0.000 0.630 1.9333 0.125 0.083 0.000 0.630 1.9667 0.125 0.084 0.000 0.630 2.0000 0.125 0.086 0.000 0.630 2.0333 0.125 0.087 0.000 0.630 2.0667 0.125 0.089 0.000 0.630 2.1000 0.125 0.090 0.000 0.630 2.1333 0.125 0.091 0.000 0.630 2.1667 0.125 0.093 0.000 0.630 2.2000 0.125 0.094 0.000 0.630 2.2333 0.125 0.095 0.000 0.630 2.2667 0.125 0.097 0.000 0.630 2.3000 0.125 0.098 0.000 0.630 2.3333 0.125 0.100 0.000 0.630 2.3667 0.125 0.101 0.000 0.630 2.4000 0.125 0.102 0.000 0.630 2.4333 0.125 0.104 0.000 0.630 2.4667 0.125 0.105 0.000 0.630 2.5000 0.125 0.106 0.000 0.630 2.5333 0.125 0.108 0.000 0.630 2.5667 0.125 0.109 0.000 0.630 2.6000 0.125 0.111 0.000 0.630 2.6333 0.125 0.112 0.000 0.630 2.6667 0.125 0.113 0.000 0.630 2.7000 0.125 0.115 0.000 0.630 2.7333 0.125 0.116 0.000 0.630 2.7667 0.125 0.117 0.000 0.630 2.8000 0.125 0.119 0.000 0.630 2.8333 0.125 0.120 0.000 0.630 2.8667 0.125 0.122 0.000 0.630 2.9000 0.125 0.123 0.000 0.630 2.9333 0.125 0.124 0.000 0.630 2.9667 0.125 0.126 0.000 0.630 3.0000 0.125 0.127 0.000 0.630 Name :Gravel Trench Bed 109 Bottom Length:215.00 ft. Bottom Width: 10.00 ft. Trench bottom slope 1:0 To 1 Trench Left side slope 0:0 To 1 Trench right side slope 2:0 To 1 Material thickness of first layer: 1.5 Pour Space of material for first layer: 0.35 Material thickness of second layer: 1.5 Pour Space of material for second layer: 0.33 Material thickness of third layer: 0 Pour Space of material for third layer: 0 Infiltration On Infiltration rate:5 Infiltration safety factor: 1 250 4th Avenue South,Suite 200 C CM Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Appendix A,Page 16 Total Volume Infiltrated(ac-ft.): 128.504 Total Volume Through Riser(ac-ft.):0 Total Volume Through Facility(ac-ft.): 128.504 Percent Infiltrated: 100 Total Precip Applied to Facility:0 Total Evap From Facility:0 Discharge Structure Riser Height:3 ft. Riser Diameter: 12 in. Element Flows To: Outlet 1 Outlet 2 Gravel Trench Bed Hydraulic Table Stage(feet) Area(ac.) Volume(ac-ft.)DischarKe(ds)Infilt(ds) 0.0000 0.049 0.000 0.000 0.000 0.0333 0.049 0.000 0.000 0.248 0.0667 0.049 0.001 0.000 0.248 0.1000 0.049 0.001 0.000 0.248 0.1333 0.049 0.002 0.000 0.248 0.1667 0.049 0.002 0.000 0.248 0.2000 0.049 0.003 0.000 0.248 0.2333 0.049 0.004 0.000 0.248 0.2667 0.049 0.004 0.000 0.248 0.3000 0.049 0.005 0.000 0.248 0.3333 0.049 0.005 0.000 0.248 0.3667 0.049 0.006 0.000 0.248 0.4000 0.049 0.006 0.000 0.248 0.4333 0.049 0.007 0.000 0.248 0.4667 0.049 0.008 0.000 0.248 0.5000 0.049 0.008 0.000 0.248 0.5333 0.049 0.009 0.000 0.248 0.5667 0.049 0.009 0.000 0.248 0.6000 0.049 0.010 0.000 0.248 0.6333 0.049 0.010 0.000 0.248 0.6667 0.049 0.011 0.000 0.248 0.7000 0.049 0.012 0.000 0.248 0.7333 0.049 0.012 0.000 0.248 0.7667 0.049 0.013 0.000 0.248 0.8000 0.049 0.013 0.000 0.248 0.8333 0.049 0.014 0.000 0.248 0.8667 0.049 0.015 0.000 0.248 0.9000 0.049 0.015 0.000 0.248 0.9333 0.049 0.016 0.000 0.248 0.9667 0.049 0.016 0.000 0.248 1.0000 0.049 0.017 0.000 0.248 1.0333 0.049 0.017 0.000 0.248 1.0667 0.049 0.018 0.000 0.248 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Appendix A,Page 17 1.1000 0.049 0.019 0.000 0.248 1.1333 0.049 0.019 0.000 0.248 1.1667 0.049 0.020 0.000 0.248 1.2000 0.049 0.020 0.000 0.248 1.2333 0.049 0.021 0.000 0.248 1.2667 0.049 0.021 0.000 0.248 1.3000 0.049 0.022 0.000 0.248 1.3333 0.049 0.023 0.000 0.248 1.3667 0.049 0.023 0.000 0.248 1.4000 0.049 0.024 0.000 0.248 1.4333 0.049 0.024 0.000 0.248 1.4667 0.049 0.025 0.000 0.248 1.5000 0.049 0.025 0.000 0.248 1.5333 0.049 0.026 0.000 0.248 1.5667 0.049 0.027 0.000 0.248 1.6000 0.049 0.027 0.000 0.248 1.6333 0.049 0.028 0.000 0.248 1.6667 0.049 0.028 0.000 0.248 1.7000 0.049 0.029 0.000 0.248 1.7333 0.049 0.029 0.000 0.248 1.7667 0.049 0.030 0.000 0.248 1.8000 0.049 0.030 0.000 0.248 1.8333 0.049 0.031 0.000 0.248 1.8667 0.049 0.031 0.000 0.248 1.9000 0.049 0.032 0.000 0.248 1.9333 0.049 0.032 0.000 0.248 1.9667 0.049 0.033 0.000 0.248 2.0000 0.049 0.034 0.000 0.248 2.0333 0.049 0.034 0.000 0.248 2.0667 0.049 0.035 0.000 0.248 2.1000 0.049 0.035 0.000 0.248 2.1333 0.049 0.036 0.000 0.248 2.1667 0.049 0.036 0.000 0.248 2.2000 0.049 0.037 0.000 0.248 2.2333 0.049 0.037 0.000 0.248 2.2667 0.049 0.038 0.000 0.248 2.3000 0.049 0.038 0.000 0.248 2.3333 0.049 0.039 0.000 0.248 2.3667 0.049 0.040 0.000 0.248 2.4000 0.049 0.040 0.000 0.248 2.4333 0.049 0.041 0.000 0.248 2.4667 0.049 0.041 0.000 0.248 2.5000 0.049 0.042 0.000 0.248 2.5333 0.049 0.042 0.000 0.248 2.5667 0.049 0.043 0.000 0.248 2.6000 0.049 0.043 0.000 0.248 2.6333 0.049 0.044 0.000 0.248 2.6667 0.049 0.044 0.000 0.248 2.7000 0.049 0.045 0.000 0.248 2.7333 0.049 0.046 0.000 0.248 2.7667 0.049 0.046 0.000 0.248 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Appendix A,Page 18 2.8000 0.049 0.047 0.000 0.248 2.8333 0.049 0.047 0.000 0.248 2.8667 0.049 0.048 0.000 0.248 2.9000 0.049 0.048 0.000 0.248 2.9333 0.049 0.049 0.000 0.248 2.9667 0.049 0.049 0.000 0.248 3.0000 0.049 0.050 0.000 0.248 Name :Gravel Trench Bed 101-106 Bottom Length:465.00 ft. Bottom Width:40.00 ft. Trench bottom slope 1:0 To 1 Trench Left side slope 0:0 To 1 Trench right side slope 2:0 To 1 Material thickness of first layer: 1.5 Pour Space of material for first layer: 0.33 Material thickness of second layer: 0 Pour Space of material for second layer: 0 Material thickness of third layer: 0 Pour Space of material for third layer: 0 Infiltration On Infiltration rate:0.94 Infiltration safety factor: 1 Total Volume Infiltrated(ac-ft.):450.107 Total Volume Through Riser(ac-ft.):0 Total Volume Through Facility(ac-ft.):450.107 Percent Infiltrated: 100 Total Precip Applied to Facility:0 Total Evap From Facility:0 Discharge Structure Riser Height:1.5 ft. Riser Diameter: 12 in. Element Flows To: Outlet 1 Outlet 2 Gravel Trench Bed Hydraulic Table stage(feet) Area(ac.) volume(ac-ft.)Discharge(ds)Infilt(ds) 0.0000 0.427 0.000 0.000 0.000 0.0167 0.427 0.002 0.000 0.404 0.0333 0.427 0.004 0.000 0.404 0.0500 0.427 0.007 0.000 0.404 0.0667 0.427 0.009 0.000 0.404 0.0833 0.427 0.011 0.000 0.404 0.1000 0.427 0.014 0.000 0.404 0.1167 0.427 0.016 0.000 0.404 0.1333 0.427 0.018 0.000 0.404 C � 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Appendix A,Page 19 0.1500 0.427 0.021 0.000 0.404 0.1667 0.427 0.023 0.000 0.404 0.1833 0.427 0.025 0.000 0.404 0.2000 0.427 0.028 0.000 0.404 0.2167 0.427 0.030 0.000 0.404 0.2333 0.427 0.032 0.000 0.404 0.2500 0.427 0.035 0.000 0.404 0.2667 0.427 0.037 0.000 0.404 0.2833 0.427 0.039 0.000 0.404 0.3000 0.427 0.042 0.000 0.404 0.3167 0.427 0.044 0.000 0.404 0.3333 0.427 0.047 0.000 0.404 0.3500 0.427 0.049 0.000 0.404 0.3667 0.427 0.051 0.000 0.404 0.3833 0.427 0.054 0.000 0.404 0.4000 0.427 0.056 0.000 0.404 0.4167 0.427 0.058 0.000 0.404 0.4333 0.427 0.061 0.000 0.404 0.4500 0.427 0.063 0.000 0.404 0.4667 0.427 0.065 0.000 0.404 0.4833 0.427 0.068 0.000 0.404 0.5000 0.427 0.070 0.000 0.404 0.5167 0.427 0.072 0.000 0.404 0.5333 0.427 0.075 0.000 0.404 0.5500 0.427 0.077 0.000 0.404 0.5667 0.427 0.079 0.000 0.404 0.5833 0.427 0.082 0.000 0.404 0.6000 0.427 0.084 0.000 0.404 0.6167 0.427 0.086 0.000 0.404 0.6333 0.427 0.089 0.000 0.404 0.6500 0.427 0.091 0.000 0.404 0.6667 0.427 0.093 0.000 0.404 0.6833 0.427 0.096 0.000 0.404 0.7000 0.427 0.098 0.000 0.404 0.7167 0.427 0.101 0.000 0.404 0.7333 0.427 0.103 0.000 0.404 0.7500 0.427 0.105 0.000 0.404 0.7667 0.427 0.108 0.000 0.404 0.7833 0.427 0.110 0.000 0.404 0.8000 0.427 0.112 0.000 0.404 0.8167 0.427 0.115 0.000 0.404 0.8333 0.427 0.117 0.000 0.404 0.8500 0.427 0.119 0.000 0.404 0.8667 0.427 0.122 0.000 0.404 0.8833 0.427 0.124 0.000 0.404 0.9000 0.427 0.126 0.000 0.404 0.9167 0.427 0.129 0.000 0.404 0.9333 0.427 0.131 0.000 0.404 0.9500 0.427 0.133 0.000 0.404 0.9667 0.427 0.136 0.000 0.404 0.9833 0.427 0.138 0.000 0.404 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cge ngi n ee ri n g.co m Centennial Park 18386.20 June 30,2020 Drainage Report Appendix A,Page 20 1.0000 0.427 0.140 0.000 0.404 1.0167 0.427 0.143 0.000 0.404 1.0333 0.427 0.145 0.000 0.404 1.0500 0.427 0.148 0.000 0.404 1.0667 0.427 0.150 0.000 0.404 1.0833 0.427 0.152 0.000 0.404 1.1000 0.427 0.155 0.000 0.404 1.1167 0.427 0.157 0.000 0.404 1.1333 0.427 0.159 0.000 0.404 1.1500 0.427 0.162 0.000 0.404 1.1667 0.427 0.164 0.000 0.404 1.1833 0.427 0.166 0.000 0.404 1.2000 0.427 0.169 0.000 0.404 1.2167 0.427 0.171 0.000 0.404 1.2333 0.427 0.173 0.000 0.404 1.2500 0.427 0.176 0.000 0.404 1.2667 0.427 0.178 0.000 0.404 1.2833 0.427 0.180 0.000 0.404 1.3000 0.427 0.183 0.000 0.404 1.3167 0.427 0.185 0.000 0.404 1.3333 0.427 0.187 0.000 0.404 1.3500 0.427 0.190 0.000 0.404 1.3667 0.427 0.192 0.000 0.404 1.3833 0.427 0.194 0.000 0.404 1.4000 0.427 0.197 0.000 0.404 1.4167 0.427 0.199 0.000 0.404 1.4333 0.427 0.202 0.000 0.404 1.4500 0.427 0.204 0.000 0.404 1.4667 0.427 0.206 0.000 0.404 1.4833 0.427 0.209 0.000 0.404 1.5000 0.427 0.211 0.000 0.404 ANALYSIS RESULTS Stream Protection Duration Predeveloped Landuse Totals for POC#1 Total Pervious Area:5.568 Total Impervious Area:O Mitigated Landuse Totals for POC#1 Total Pervious Area:1.565 Total Impervious Area:3.987 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Appendix A,Page 21 Flow Frequency Return Periods for Predeveloped. POC#1 Return Period Flow cfs 2 year 0.21617 5 year 0.338953 10 year 0.43522 25 year 0.574742 50 year 0.692241 100 year 0.821864 Flow Frequency Return Periods for Mitigated. POC#1 Return Period Flow cfs 2 year 0 5 year 0 10 year 0 25 year 0 50 year 0 100 year 0 Stream Protection Duration POC#1 The Facility PASSED The Facility PASSED. Flow(cfs)Predev Mit Percentage Pass/Fail 0.1081 15287 0 0 Pass 0.1140 13349 0 0 Pass 0.1199 11289 0 0 Pass 0.1258 9522 0 0 Pass 0.1317 7980 0 0 Pass 0.1376 6759 0 0 Pass 0.1435 5677 0 0 Pass 0.1494 4851 0 0 Pass 0.1553 4169 0 0 Pass 0.1612 3557 0 0 Pass 0.1671 3020 0 0 Pass 0.1730 2665 0 0 Pass 0.1789 2342 0 0 Pass 0.1848 2038 0 0 Pass 0.1907 1806 0 0 Pass 0.1966 1574 0 0 Pass 0.2025 1396 0 0 Pass 0.2084 1245 0 0 Pass 0.2143 1089 0 0 Pass 0.2202 994 0 0 Pass 0.2261 924 0 0 Pass 0.2320 878 0 0 Pass 0.2379 812 0 0 Pass 0.2438 756 0 0 Pass 0.2497 716 0 0 Pass 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Appendix A,Page 22 0.2556 670 0 0 Pass 0.2615 622 0 0 Pass 0.2674 589 0 0 Pass 0.2733 566 0 0 Pass 0.2792 548 0 0 Pass 0.2851 530 0 0 Pass 0.2910 513 0 0 Pass 0.2969 483 0 0 Pass 0.3028 448 0 0 Pass 0.3087 425 0 0 Pass 0.3146 403 0 0 Pass 0.3205 386 0 0 Pass 0.3264 369 0 0 Pass 0.3323 351 0 0 Pass 0.3382 336 0 0 Pass 0.3441 327 0 0 Pass 0.3500 321 0 0 Pass 0.3559 311 0 0 Pass 0.3618 304 0 0 Pass 0.3677 295 0 0 Pass 0.3736 287 0 0 Pass 0.3795 277 0 0 Pass 0.3854 265 0 0 Pass 0.3913 253 0 0 Pass 0.3972 241 0 0 Pass 0.4031 234 0 0 Pass 0.4090 219 0 0 Pass 0.4149 213 0 0 Pass j 0.4208 203 0 0 Pass 0.4267 191 0 0 Pass 0.4326 175 0 0 Pass 0.4385 168 0 0 Pass 0.4444 160 0 0 Pass 0.4503 151 0 0 Pass 0.4562 146 0 0 Pass 0.4621 136 0 0 Pass 0.4680 133 0 0 Pass 0.4739 124 0 0 Pass 0.4798 114 0 0 Pass 0.4857 97 0 0 Pass 0.4916 81 0 0 Pass 0.4975 68 0 0 Pass 0.5034 58 0 0 Pass 0.5093 50 0 0 Pass 0.5152 43 0 0 Pass 0.5211 38 0 0 Pass 0.5270 36 0 0 Pass 0.5329 35 0 0 Pass 0.5388 30 0 0 Pass 0.5447 24 0 0 Pass 0.5506 18 0 0 Pass C � 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Appendix A,Page 23 0.5565 16 0 0 Pass 0.5624 14 0 0 Pass 0.5683 9 0 0 Pass 0.5742 6 0 0 Pass 0.5801 6 0 0 Pass 0.5860 4 0 0 Pass 0.5919 4 0 0 Pass 0.5978 4 0 0 Pass 0.6037 4 0 0 Pass 0.6096 4 0 0 Pass 0.6155 4 0 0 Pass 0.6214 3 0 0 Pass 0.6273 3 0 0 Pass 0.6332 3 0 0 Pass 0.6391 3 0 0 Pass 0.6450 3 0 0 Pass 0.6509 3 0 0 Pass 0.6568 3 0 0 Pass 0.6627 3 0 0 Pass 0.6686 3 0 0 Pass 0.6745 3 0 0 Pass 0.6804 3 0 0 Pass 0.6863 2 0 0 Pass 0.6922 2 0 0 Pass LID Duration LID Duration Annual Peaks for Predeveloped and Mitigated. POC#1 Year Predeveloped Mitigated 1949 0.223 0.000 1950 0.237 0.000 1951 0.194 0.000 1952 0.163 0.000 1953 0.137 0.000 1954 0.752 0.000 1955 0.271 0.000 1956 0.234 0.000 1957 0.300 0.000 1958 0.411 0.000 1959 0.206 0.000 1960 0.199 0.000 1961 0.550 0.000 1962 0.201 0.000 1963 0.331 0.000 1964 0.238 0.000 1965 0.174 0.000 1966 0.109 0.000 C � 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Appendix A,Page 24 1967 0.219 0.000 1968 0.267 0.000 1969 0.684 0.000 1970 0.147 0.000 1971 0.248 0.000 1972 0.176 0.000 1973 0.162 0.000 1974 0.393 0.000 1975 0.160 0.000 1976 0.155 0.000 1977 0.130 0.000 1978 0.152 0.000 1979 0.435 0.000 1980 0.204 0.000 1981 0.152 0.000 1982 0.201 0.000 1983 0.358 0.000 1984 0.197 0.000 1985 0.252 0.000 1986 0.580 0.000 1987 0.268 0.000 1988 0.143 0.000 1989 0.164 0.000 1990 0.186 0.000 1991 0.194 0.000 1992 0.146 0.000 1993 0.137 0.000 1994 0.136 0.000 1995 0.197 0.000 1996 0.366 0.000 1997 0.699 0.000 1998 0.128 0.000 1999 0.161 0.000 2000 0.124 0.000 2001 0.051 0.000 2002 0.184 0.000 2003 0.144 0.000 2004 0.240 0.000 2005 0.171 0.000 2006 0.483 0.000 2007 0.381 0.000 2008 0.510 0.000 2009 0.150 0.000 LID Duration POC#1 The Facility PASSED The Facility PASSED. C � 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Appendix A,Page 25 Flow(cfs)Predev Mit Percentage Pass/Fail 1 0.0173 281263 0 0 Pass 0.0182 269713 0 0 Pass 0.0191 259232 0 0 Pass i 0.0200 249180 0 0 Pass 0.0210 239768 0 0 Pass 0.0219 230785 0 0 Pass 0.0228 222230 0 0 Pass -� 0.0237 214102 0 0 Pass 0.0246 206359 0 0 Pass 0.0255 198959 0 0 Pass 0.0265 191879 0 0 Pass 0.0274 185099 0 0 Pass 0.0283 178639 0 0 Pass 0.0292 172394 0 0 Pass 0.0301 166490 0 0 Pass 0.0310 160758 0 0 Pass 0.0320 155325 0 0 Pass 0.0329 150021 0 0 Pass 0.0338 145037 0 0 Pass 0.0347 140161 0 0 Pass 0.0356 135477 0 0 Pass 0.0366 130985 0 0 Pass 0:0375 126729 0 0 Pass 0.0384 122622 0 0 Pass 0.0393 118644 0 0 Pass 0.0402 114772 0 0 Pass 0.0411 111200 0 0 Pass 0.0421 107757 0 0 Pass 0.0430 104377 0 0 Pass 0.0439 101255 0 0 Pass 0.0448 98175 0 0 Pass 0.0457 95116 0 0 Pass 0.0466 92207 0 0 Pass 0.0476 89491 0 0 Pass 0.0485 86796 0 0 Pass 0.0494 84208 0 0 Pass 0.0503 81748 0 0 Pass 0.0512 79352 0 0 Pass 0.0521 77021 0 0 Pass 0.0531 74797 0 0 Pass 0.0540 72594 0 0 Pass 0.0549 70497 0 0 Pass 0.0558 68466 0 0 Pass 0.0567 66476 0 0 Pass 0.0576 64509 0 0 Pass 0.0586 62626 0 0 Pass 0.0595 60873 0 0 Pass 0.0604 59161 0 0 Pass 0.0613 57472 0 0 Pass 0.0622 55846 0 0 Pass 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Appendix A,Page 26 0.0631 54306 0 0 Pass 0.0641 52830 0 0 Pass 0.0650 51397 0 0 Pass 0.0659 49964 0 0 Pass 0.0668 48595 0 0 Pass 0.0677 47269 0 0 Pass 0.0687 45922 0 0 Pass 0.0696 44724 0 0 Pass 0.0705 43526 0 0 Pass 0.0714 42371 0 0 Pass 0.0723 41238 0 0 Pass 0.0732 40147 0 0 Pass 0.0742 39099 0 0 Pass 0.0751 38115 0 0 Pass 0.0760 37088 0 0 Pass 0.0769 36126 0 0 Pass 0.0778 35163 0 0 Pass 0.0787 34243 0 0 Pass 0.0797 33367 0 0 Pass 0.0806 32490 0 0 Pass 0.0815 31698 0 0 Pass 0.0824 30843 0 0 Pass 0.0833 30073 0 0 Pass 0.0842 29345 0 0 Pass 0.0852 28597 0 0 Pass 0.0861 27891 0 0 Pass 0.0870 27142 0 0 Pass 0.0879 26458 0 0 Pass 0.0888 25795 0 0 Pass 0.0897 25132 0 0 Pass 0.0907 24469 0 0 Pass 0.0916 23891 0 0 Pass 0.0925 23314 0 0 Pass 0.0934 22758 0 0 Pass 0.0943 22202 0 0 Pass 0.0952 21645 0 0 Pass 0.0962 21119 0 0 Pass 0.0971 20591 0 0 Pass 0.0980 20086 0 0 Pass 0.0989 19618 0 0 Pass 0.0998 19149 0 0 Pass 0.1007 18713 0 0 Pass 0.1017 18272 0 0 Pass 0.1026 17813 0 0 Pass 0.1035 17359 0 0 Pass 0.1044 16884 0 0 Pass 0.1053 16491 0 0 Pass 0.1063 16072 0 0 Pass 0.1072 15672 0 0 Pass 0.1081 15287 0 0 Pass 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Appendix A,Page 27 Water Quality BMP Flow and Volume for POC#1 on-line facility volume:0 acre-feet On-line facility target flow:0 cfs. Adjusted for 15 min:0 cfs. Off-line facility target flow:0 cfs. Adjusted for 15 min:0 cfs. LID Report LID Technique Used for Total Volume Volume Infiltration Cumulative Percent Water Quality Percent Comment Treatment? Needs Through Volume Volume Volume Water Quality Treatment Facility (ac-ft.) Infiltration Infiltrated Treated (ac-ft) (ac-ft) Credit Gravel Trench Bed 107,111 POC N 329.46 N 100.00 Gravel Trench Bed 109 POC N 116.94 N 100.00 Gravel Trench Bed 101-106 POC N 409.60 N 100.00 Total Volume Infiltrated 856.00 0.00 0.00 100.00 0.00 0% No Treat.Credit Compliance with LID Standard 8 Duration Analysis Result=Passed Perind and Impind Changes No changes have been made. This program and accompanying documentation are provided'as-is'without warranty of any kind. The entire risk re ardin the performance and results of this program is assumed by End User. Clear Creek Solutions Inc.and the governmental licensee or sublicensees disclaim all warranties,either expressed or implied,including but not limited to implied warranties of program and accompanying documentation. In no event shall Clear Creek Solutions Inc.be liable for any damages whatsoever(including without limitation to damages for loss of business profits, loss of business information,business interruption,and the like)arising out of the use of,or inability to use this program even if Clear Creek Solutions Inc.or their authorized representatives have been advised of the possibility of such damages. Software Copyright©by:Clear Creek Solutions,Inc.2005-2020;All Rights Reserved. } 1 1 J 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Appendix A,Page 28 WWHM2012 PROJECT REPORT Project Name infiltration drawdown calc(BASIN 2 ONLY) Site Name: Centennial Park Site Address: City : Report Date: 10/15/2019 Gage : Everett Data Start: 1948/10/01 Data End:2009/09/30 Precip Scale: 1.20 Version Date:2018/10/10 Version :4.2.16 MITIGATED LAND USE Pervious Land Use acre C,Lawn,Flat 1.565 Pervious Total 1.565 Impervious Land Use acre ROOF TOPS FLAT 1.463 SIDEWALKS FLAT 0.918 PARKING FLAT 1.622 Impervious Total 4.003 Basin Total 5.568 Water Quality BMP Flow and Volume for POC#1 On-line facility volume:0.5288 acre-feet On-line facility target flow:0.7526 cfs. Adjusted for 15 min:0.7526 cfs. Off-line facility target flow:0.425 cfs. Adjusted for 15 min:0.425 cfs. Perind and Impind Changes No changes have been made. This program and accompanying documentation are provided'as-is'without warranty of any kind. The entire risk regarding the performance and results of this program is assumed by End User. Clear Creek Solutions Inc.and the governmental licensee or sublicensees disclaim all warranties,either expressed or implied,including but not limited to implied warranties of program and accompanying documentation. In no event shall Clear Creek Solutions Inc.be liable for any damages whatsoever(including without limitation to damages for loss of business profits, loss of business information,business interruption,and the like)arising out of the use of,or inability to use this program even if Clear Creek Solutions Inc.or their authorized representatives have been advised of the possibility of such damages. Software Copyright©by:Clear Creek Solutions,Inc.2005-2019;All Rights Reserved. WWHM2012 C 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Appendix A,Page 29 PROJECT REPORT Project Name: Driveway WQ flow Sizing Site Name: Centennial Park Site Address: City : Arlington Report Date: 10/15/2019 Gage : Everett Data Start: 1948/10/01 Data End :2009/09/30 Precip Scale: 1.20 Version Date:2018/10/10 Version :4.2.16 PREDEVELOPED LAND USE Name : Basin 1-North Driveway Bypass: No GroundWater:No Pervious Land Use acre C,Forest,Flat .089 Pervious Total 0.089 Impervious Land Use acre Impervious Total 0 Basin Total 0.089 Element Flows To: Surface Interflow Groundwater Name : Basin 2—South Driveway Bypass: No GroundWater:No Pervious Land Use acre C,Forest,Flat .128 Pervious Total 0.128 Impervious Land Use acre C 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Appendix A,Page 30 Impervious Total 0 Basin Total 0.128 Element Flows To: Surface Interflow Groundwater MITIGATED LAND USE Name : Basin 1—North Driveway Bypass: No GroundWater:No Pervious Land Use acre C,Lawn,Flat .017 Pervious Total 0.017 Impervious Land Use acre DRIVEWAYS FLAT 0.049 SIDEWALKS FLAT 0.023 Impervious Total 0.072 Basin Total 0.089 Element Flows To: Surface Interflow Groundwater Name : Basin 2—South Driveway Bypass: No GroundWater: No Pervious Land Use acre C,Lawn,Flat .058 Pervious Total 0.058 Impervious Land Use acre DRIVEWAYS FLAT 0.047 SIDEWALKS FLAT 0.023 Impervious Total 0.07 Basin Total 0.128 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Appendix A,Page 31 Element Flows To: Surface Interflow Groundwater ANALYSIS RESULTS Stream Protection Duration Predeveloped Landuse Totals for POC#1—North Driveway Total Pervious Area:0.089 Total Impervious Area:O Mitigated Landuse Totals for POC#1—North Driveway Total Pervious Area:0.017 Total Impervious Area:0.072 Flow Frequency Return Periods for Predeveloped. POC#1 —North Driveway Return Period Flow cfs 2 year 0.040491 5 year 0.055638 10 year 0.066848 25 year 0.082414 50 year 0.095068 100 year 0.108663 Flow Frequency Return Periods for Mitigated. POC#1 —North Driveway Return Period Flow cfs 2 year 0.040491 5 year 0.055638 10 year 0.066848 25 year 0.082414 50 year 0.095068 100 year 0.108663 Water Quality BMP Flow and Volume for POC#1 -North Driveway On-line facility volume:0.0091 acre-feet On-line facility target flow:0.0136 cfs. Adjusted for 15 min:0.0136 cfs. Off-line facility target flow:0.0077 cfs. Adjusted for 15 min:0.0077 cfs. Stream Protection Duration Predeveloped Landuse Totals for POC#2—South Driveway Total Pervious Area:0.128 Total Impervious Area:O 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Appendix A,Page 32 Mitigated Landuse Totals for POC#2—South Driveway Total Pervious Area:0.058 Total Impervious Area:0.07 Flow Frequency Return Periods for Predeveloped. POC#2 —South Driveway Return Period Flow cfs 2 year 0.004301 5 year 0.006598 10 year 0.008369 25 year 0.010903 50 year 0.013014 100 year 0.015322 Flow Frequency Return Periods for Mitigated. POC#2 —South Driveway Return Period Flow cfs 2 year 0.04476 5 year 0.064193 10 year 0.079057 25 year 0.100253 50 year 0.117892 100 year 0.137198 Water Quality BMP Flow and Volume for POC#2 -South Driveway On-line facility volume:0.0102 acre-feet On-line facility target flow:0.0129 cfs. Adjusted for 15 min:0.0129 cfs. Off-line facility target flow:0.0072 cfs. Adjusted for 15 min:0.0072 cfs. Perind and Impind Changes No changes have been made. i This program and accompanying documentation are provided'as-is'without warranty of any kind. The entire risk regarding the performance and results of this program is assumed by End User. Clear Creek Solutions Inc.and the governmental licensee or sublicensees disclaim all warranties,either expressed or implied,including but not limited to implied warranties of program and accompanying documentation. In no event shall Clear Creek Solutions Inc.be liable for any damages whatsoever(including without limitation to damages for loss of business profits, loss of business information,business interruption,and the like)arising out of the use of,or inability to use this program even if Clear Creek Solutions Inc.or their authorized representatives have been advised of the possibility of such damages. Software Copyright©by:Clear Creek Solutions,Inc.2005-2019;All Rights Reserved. 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGN6MNS ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Appendix A,Page 33 Conveyance Sizing The conveyance pipes on the site were checked for the 25-year storm on the site.The table below reflects various pipe diameters,slopes and capacities. Runoff was calculated using 15-minute timesteps in WWHM. In general catch basins immediately connect to infiltration trenches without collecting significant runoff areas, but there are several places where this is not the case. In basin 2A extended runs of piping collecting roof drains from several buildings is needed. Conveyance Capacity 4-inch 6-inch 8-inch 10-inch 112-inch Slope (ft/ft) 0.005 0.13 0.40 0.87 1.55 2.52 0.010 0.19 0.56 1.23 2.20 3.57 0.015 0.23 0.69 1.50 2.69 4.37 0.020 0.27 0.79 1.74 3.11 5.05 0.025 0.30 0.89 1.94 3.47 5.65 0.030 0.33 0.97 2.13 3.81 6.18 0.035 0.36 1.05 2.30 4.11 6.68 0.040 0.38 1.12 2.46 4.39 7.14 0.045 0.40 1.19 2.60 4.66 7.57 0.050 0.43 1.26 2.75 4.91 7.98 0.055 0.45 1.32 2.88 5.15 8.37 0.060 0.47 1.38 3.01 5.38 8.75 0.065 0.49 1.43 3.13 5.60 9.10 0.070 0.50 1.49 3.25 5.81 9.45 0.075 0.52 1.54 3.36 6.02 9.78 0.080 0.54 1.59 3.47 6.21 10.10 0.085 0.56 1.64 3.58 6.40 10.41 0.090 0.57 1.68 3.68 6.59 10.71 0.095 0.59 1.73 3.78 6.77 11.01 0.100 0.60 1.78 3.88 6.95 11.29 Table A-1:Conveyance Capacity Table Basin 2 Overflow Sizing Flow Frequency Predeveloped Inflow to Mitigated Mitigated Flow(cfs) 050115m 070115m 080115m 25 Year = 0.6077 1.8815 0.0000 100 Year= 0.8553 2.3452 0.0000 Two 12" overflow pipes are provided from the infiltration trenches,with the minimum slope on either being 0.5%connecting from the site into the City storm system on 67th.The conveyance capacity of one 12" pipe at that flow (2.52 cfs) exceeds the 100-year mitigated flow for the site (2.34 cfs). 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Appendix A,Page 34 6"Roof Drain Capacity Check Flow Frequency for 6,000 sf building Flow(cfs) Predeveloped Mitigated 25 Year = 0.0111 0.1350 100 Year= 0.0156 0.1751 6" conveyance pipes are shown on the plans for all roof drains around each building. With 6,000 sf of roof area used as a conservative typical condition,the roof drain tightlines will convey the 100-Year storm from each building even if the pipe is set at just 0.5%.The mitigated flow from this area is 0.17 cfs,while the 6" pipe can convey 0.40 cfs. Site Basin 2A, Upstream of Infiltration Areas In general catch basins on this site pick up small areas and immediately convey into the large infiltration beds distributed throughout the site, but Site Basin 2A includes a significant portion of the site where infiltration was not used due to infeasibility concerns noted in the geotechnical report. This area is on the easternmost side of the site 1.49 acres and includes buildings K, L and M. Total: 64,929 sf 1.490 ac Roof: 13,884 sf 0.318 ac Sidewalk: 9,069 sf 0.208 ac Parking: 15,666 sf 0.359ac Landscaping: 26,310 sf 0.605ac Flow Frequency Flow(cfs) Predeveloped Mitigated 25 Year = 0.1269 1.2030 100 Year= 0.1784 1.6322 Conveyance pipes in this basin were set at a 1.0% minimum and 8" in diameter to properly convey the 25-year design storm into the infiltration trenches. Another large portion includes the narrower site driveway between buildings F, G, and H. Due to tuck under parking running right up alongside the drive isle, adequate separation was not there for infiltration beds, leading to longer runs collection more area. Total: 20,516 sf 0.471 ac Roof: 5,837 sf 0.134 ac Sidewalk: 2,144 sf 0.049 ac Parking: 9,134 sf 0.209 ac Landscaping: 3,488 sf 0.079ac Flow Frequency Flow(cfs) Predeveloped Mitigated 25 Year = 0.0401 0.4425 100 Year= 0.0564 0.5821 The 8" pipes being collected flow into infiltration and will function as expected at 0.5%slope or more. 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Appendix A,Page 35 120 -------------W trncTS1---fV-I--es-FoU-T------------ -20D npuum Too 80 2 gp I .100 d? I li a 40 ly` / > 20 o .000 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec — Percent — Preed_vFbPed — M1b::B15d FIGURE A-3 Wetland Input Volumes Graph WWHM2012 PROJECT REPORT Project Name:2020.06.18 cpwetland calc Site Name: Site Address: City : Report Date:6/19/2020 Gage : Everett Data Start: 1948/10/01 Data End :2009/09/30 Precip Scale: 1.20 Version Date:2018/10/10 Version :4.2.16 Low Flow Threshold for POC 1:50 Percent of the 2 Year High Flow Threshold for POC 1:50 year PREDEVELOPED LAND USE Name :Centennial Existing On Site Bypass: No GrounclWater: No C 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Appendix A,Page 36 Pervious Land Use acre C,Forest,Mod 1.6 SAT,Forest,Flat .5 Pervious Total 2.1 Impervious Land Use acre Impervious Total 0 Basin Total 2.1 Element Flows To: Surface Interflow Groundwater Name :Centennital Off Site(Existing and Proposed) Bypass: No GroundWater:No Pervious Land Use acre C,Forest,Mod 7.9 C,Pasture,Mod 2.7 Pervious Total 10.6 Impervious Land Use acre ROOF TOPS FLAT 1.1 Impervious Total 1.1 Basin Total 11.7 Element Flows To: Surface Interflow Groundwater MITIGATED LAND USE 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Appendix A,Page 37 Name :Centennial Off site(existing and proposed) Bypass: No GroundWater: No Pervious Land Use acre C,Forest,Mod 7.9 C,Pasture,Mod 2.7 Pervious Total 10.6 Impervious Land Use acre ROOF TOPS FLAT 1.1 Impervious Total 1.1 Basin Total 11.7 Element Flows To: Surface Interflow Groundwater Name :wetland and buffer to remain Bypass:No GroundWater:No Pervious Land Use acre SAT,Forest,Flat .5 C,Forest,Mod .26 Pervious Total 0.76 Impervious Land Use acre Impervious Total 0 Basin Total 0.76 Element Flows To: Surface Interflow Groundwater G 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Appendix A,Page 38 Name :Groundwater(M,J Excluded) Bypass: No GroundWater: No Pervious Land Use acre C,Lawn,Flat .094 Pervious Total 0.094 Impervious Land Use acre ROOF TOPS FLAT 0.25 DRIVEWAYS FLAT 0.14 Impervious Total 0.39 Basin Total 0.484 Element Flows To: Groundwater ANALYSIS RESULTS Stream Protection Duration Predeveloped Landuse Totals for POC#1 Total Pervious Area:12.7 Total Impervious Area:1.1 Mitigated Landuse Totals for POC#1 Total Pervious Area:11.454 Total Impervious Area:1.49 Flow Frequency Return Periods for Predeveloped. POC#1 Return Period Flow cfs 2 year 1.02044 5 year 1.559036 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Appendix A,Page 39 10 year 1.991453 25 year 2.632819 50 year 3.185333 100 year 3.806914 Flow Frequency Return Periods for Mitigated. POC#1 Return Period Flow cfs 2 year 0.976538 5 year 1.486208 10 year 1.894192 25 year 2.497868 50 year 3.016818 100 year 3.59966 Wetlands Input Volume Average Annual Volume(acft) Series 1:501 POC 1 Predeveloped flow Series 2:801 POC 1 Mitigated flow Month Series 1 Series 2 Percent Pass/Fail Jan 4.9285 4.4703 90.7 Pass Feb 3.8597 3.4956 90.6 Pass Mar 3.7920 3.4349 90.6 Pass Apr 2.7648 2.5039 90.6 Pass May 1.7327 1.5753 90.9 Pass Jun 1.4786 1.3445 90.9 Pass Jul 0.9315 0.8451 90.7 Pass Aug 0.7339 0.6708 91.4 Pass Sep 0.7326 0.6765 92.3 Pass Oct 1.1425 1.0657 93.3 Pass Nov 3.0112 2.7687 91.9 Pass Dec 4.7036 4.2798 91.0 Pass Day Series 1 Series 2 Percent Pass/Fail Jan1 0.1708 0.1550 90.8 Pass 2 0.1581 0.1433 90.6 Pass 3 0.1508 0.1366 90.6 Pass 4 0.1705 0.1554 91.1 Pass 5 0.1659 0.1503 90.6 Pass 6 0.1642 0.1493 90.9 Pass 7 0.1827 0.1661 90.9 Pass 8 0.1754 0.1588 90.6 Pass 9 0.1585 0.1435 90.5 Pass 10 0.1404 0.1270 90.5 Pass 11 0.1392 0.1261 90.6 Pass 12 0.1391 0.1263 90.8 Pass 13 0.1644 0.1498 91.1 Pass 14 0.1693 0.1533 90.6 Pass 15 0.1641 0.1490 90.8 Pass 16 0.1646 0.1492 90.7 Pass 17 0.1810 0.1646 90.9 Pass 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Appendix A,Page 40 18 0.1758 0.1590 90.4 Pass 19 0.1582 0.1429 90.3 Pass 20 0.1463 0.1325 90.6 Pass 21 0.1460 0.1325 90.8 Pass 22 0.1578 0.1435 90.9 Pass 23 0.1738 0.1579 90.9 Pass 24 0.1522 0.1374 90.3 Pass 25 0.1391 0.1260 90.5 Pass 26 0.1290 0.1167 90.5 Pass 27 0.1400 0.1271 90.8 Pass 28 0.1603 0.1455 90.8 Pass 29 0.1636 0.1483 90.6 Pass 30 0.1544 0.1398 90.6 Pass 31 0.1480 0.1338 90.4 Pass Febl 0.1391 0.1257 90.4 Pass 2 0.1235 0.1116 90.4 Pass 3 0.1360 0.1233 90.7 Pass 4 0.1362 0.1235 90.6 Pass 5 0.1389 0.1257 90.5 Pass 6 0.1299 0.1176 90.5 Pass 7 0.1467 0.1330 90.7 Pass 8 0.1262 0.1139 90.2 Pass 9 0.1132 0.1025 90.5 Pass 10 0.1149 0.1041 90.6 Pass 11 0.1304 0.1185 90.9 Pass 12 0.1357 0.1231 90.7 Pass 13 0.1328 0.1203 90.6 Pass 14 0.1340 0.1214 90.6 Pass 15 0.1364 0.1238 90.7 Pass 16 0.1458 0.1323 90.7 Pass 17 0.1467 0.1332 90.8 Pass 18 0.1465 0.1324 90.4 Pass 19 0.1323 0.1197 90.5 Pass 20 0.1400 0.1272 90.9 Pass 21 0.1394 0.1261 90.4 Pass 22 0.1332 0.1205 90.5 Pass 23 0.1565 0.1419 90.7 Pass 24 0.1520 0.1377 90.6 Pass 25 0.1443 0.1304 90.4 Pass 26 0.1322 0.1195 90.4 Pass 27 0.1351 0.1225 90.7 Pass 28 0.1276 0.1157 90.7 Pass 29 0.1403 0.1272 90.6 Pass Marl 0.1401 0.1270 90.6 Pass 2 0.1419 0.1285 90.6 Pass 3 0.1398 0.1265 90.5 Pass 4 0.1257 0.1138 90.5 Pass 5 0.1073 0.0967 90.1 Pass 6 0.1159 0.1052 90.8 Pass 7 0.1144 0.1038 90.7 Pass 8 0.1409 0.1281 90.9 Pass 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Appendix A,Page 41 9 0.1319 0.1195 90.6 Pass 10 0.1363 0.1235 90.6 Pass 11 0.1307 0.1184 90.6 Pass 12 0.1257 0.1136 90.4 Pass 13 0.1186 0.1074 90.5 Pass 14 0.1212 0.1099 90.6 Pass 15 0.1198 0.1085 90.6 Pass 16 0.1185 0.1074 90.6 Pass 17 0.1224 0.1109 90.6 Pass 18 0.1187 0.1074 90.5 Pass 19 0.1186 0.1075 90.6 Pass 20 0.1052 0.0951 90.4 Pass 21 0.1185 0.1077 90.9 Pass 22 0.1259 0.1142 90.7 Pass 23 0.1221 0.1105 90.5 Pass 24 0.1194 0.1080 90.5 Pass 25 0.1252 0.1136 90.7 Pass 26 0.1134 0.1024 90.3 Pass 27 0.1152 0.1045 90.7 Pass 28 0.1092 0.0989 90.6 Pass 29 0.1029 0.0931 90.5 Pass 30 0.1064 0.0963 90.5 Pass 31 0.1058 0.0959 90.6 Pass Apr1 0.1027 0.0930 90.6 Pass 2 0.1028 0.0932 90.7 Pass 3 0.1104 0.1001 90.7 Pass 4 0.1098 0.0994 90.5 Pass 5 0.1039 0.0940 90.4 Pass 6 0.0927 0.0838 90.4 Pass 7 0.1048 0.0951 90.8 Pass 8 0.0972 0.0878 90.3 Pass 9 0.0939 0.0850 90.5 Pass 10 0.0995 0.0903 90.7 Pass 11 0.1041 0.0945 90.8 Pass 12 0.0986 0.0894 90.6 Pass 13 0.0886 0.0801 90.4 Pass 14 0.0908 0.0824 90.7 Pass 15 0.1056 0.0957 90.7 Pass 16 0.0971 0.0878 90.4 Pass 17 0.0861 0.0779 90.4 Pass 18 0.0971 0.0883 91.0 Pass 19 0.0966 0.0870 90.1 Pass 20 0.0735 0.0661 89.9 Pass 21 0.0691 0.0626 90.5 Pass 22 0.0867 0.0788 90.9 Pass 23 0.0885 0.0801 90.5 Pass 24 0.0781 0.0706 90.3 Pass 25 0.0684 0.0618 90.3 Pass 26 0.0752 0.0684 90.9 Pass 27 0.0833 0.0755 90.6 Pass 28 0.0768 0.0697 90.7 Pass C 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Appendix A,Page 42 29 0.0771 0.0698 90.5 Pass 30 0.0686 0.0620 90.4 Pass May1 0.0654 0.0593 90.7 Pass 2 0.0672 0.0610 90.8 Pass 3 0.0659 0.0597 90.5 Pass 4 0.0697 0.0633 90.8 Pass 5 0.0620 0.0561 90.5 Pass 6 0.0530 0.0478 90.1 Pass 7 0.0509 0.0462 90.7 Pass 8 0.0494 0.0449 90.9 Pass 9 0.0638 0.0582 91.2 Pass 10 0.0696 0.0634 91.2 Pass 11 0.0598 0.0541 90.4 Pass 12 0.0596 0.0542 90.9 Pass 13 0.0588 0.0536 91.0 Pass 14 0.0569 0.0515 90.6 Pass 15 0.0567 0.0516 91.0 Pass 16 0.0481 0.0436 90.5 Pass 17 0.0496 0.0451 90.9 Pass 18 0.0532 0.0485 91.2 Pass 19 0.0537 0.0489 91.1 Pass 20 0.0499 0.0454 90.9 Pass 21 0.0463 0.0420 90.7 Pass 22 0.0461 0.0418 90.8 Pass 23 0.0479 0.0437 91.2 Pass 24 0.0462 0.0420 90.9 Pass 25 0.0487 0.0445 91.3 Pass 26 0.0539 0.0495 91.8 Pass 27 0.0525 0.0478 91.1 Pass 28 0.0497 0.0455 91.5 Pass 29 0.0478 0.0436 91.2 Pass 30 0.0615 0.0567 92.1 Pass 31 0.0558 0.0506 90.7 Pass Jun1 0.0578 0.0526 91.0 Pass 2 0.0644 0.0587 91.2 Pass 3 0.0576 0.0522 90.7 Pass 4 0.0515 0.0468 90.8 Pass 5 0.0509 0.0463 90.9 Pass 6 0.0587 0.0534 90.9 Pass 7 0.0538 0.0488 90.7 Pass 8 0.0508 0.0461 90.8 Pass 9 0.0627 0.0576 91.8 Pass 10 0.0611 0.0555 90.9 Pass 11 0.0553 0.0505 91.2 Pass 12 0.0461 0.0419 90.9 Pass 13 0.0384 0.0347 90.3 Pass 14 0.0379 0.0345 90.8 Pass 15 0.0451 0.0411 91.3 Pass 16 0.0553 0.0504 91.2 Pass 17 0.0543 0.0493 90.9 Pass 18 0.0537 0.0487 90.7 Pass 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Appendix A,Page 43 19 0.0440 0.0397 90.2 Pass 20 0.0421 0.0381 90.5 Pass 21 0.0419 0.0382 91.1 Pass 22 0.0410 0.0373 90.8 Pass 23 0.0481 0.0440 91.6 Pass 24 0.0451 0.0411 91.3 Pass 25 0.0427 0.0387 90.8 Pass 26 0.0424 0.0386 91.0 Pass 27 0.0375 0.0340 90.6 Pass 28 0.0436 0.0397 91.1 Pass 29 0.0389 0.0353 90.8 Pass 30 0.0434 0.0397 91.5 Pass Jul1 0.0506 0.0461 91.0 Pass 2 0.0426 0.0388 91.0 Pass 3 0.0355 0.0322 90.5 Pass 4 0.0358 0.0327 91.2 Pass 5 0.0312 0.0282 90.4 Pass 6 0.0301 0.0272 90.5 Pass 7 0.0325 0.0297 91.1 Pass 8 0.0355 0.0324 91.3 Pass 9 0.0317 0.0285 90.1 Pass 10 0.0313 0.0284 90.8 Pass 11 0.0289 0.0261 90.3 Pass 12 0.0313 0.0286 91.1 Pass 13 0.0294 0.0266 90.6 Pass 14 0.0275 0.0248 90.3 Pass 15 0.0338 0.0311 92.1 Pass 16 0.0287 0.0261 90.8 Pass 17 0.0263 0.0237 90.2 Pass 18 0.0287 0.0262 91.2 Pass 19 0.0271 0.0246 90.7 Pass 20 0.0247 0.0222 89.8 Pass 21 0.0265 0.0241 90.7 Pass 22 0.0243 0.0219 90.0 Pass 23 0.0240 0.0216 90.1 Pass 24 0.0248 0.0224 90.5 Pass 25 0.0270 0.0246 91.3 Pass 26 0.0243 0.0219 90.4 Pass 27 0.0250 0.0227 90.7 Pass 28 0.0242 0.0219 90.5 Pass 29 0.0223 0.0201 89.8 Pass 30 0.0224 0.0201 90.0 Pass 31 0.0221 0.0199 89.9 Pass Aug1 0.0223 0.0201 90.1 Pass 2 0.0226 0.0204 90.3 Pass 3 0.0227 0.0205 90.4 Pass 4 0.0224 0.0203 90.4 Pass 5 0.0265 0.0244 91.9 Pass 6 0.0262 0.0241 91.8 Pass 7 0.0213 0.0192 90.0 Pass 8 0.0219 0.0198 90.4 Pass 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Appendix A,Page 44 9 0.0210 0.0189 90.1 Pass 10 0.0211 0.0191 90.3 Pass 11 0.0217 0.0196 90.6 Pass 12 0.0246 0.0225 91.7 Pass 13 0.0221 0.0201 90.9 Pass 14 0.0258 0.0238 92.2 Pass 15 0.0237 0.0217 91.5 Pass 16 0.0224 0.0204 91.1 Pass 17 0.0244 0.0224 91.9 Pass 18 0.0267 0.0247 92.5 Pass 19 0.0224 0.0203 90.9 Pass 20 0.0210 0.0190 90.6 Pass 21 0.0265 0.0246 92.6 Pass 22 0.0284 0.0265 93.1 Pass 23 0.0253 0.0233 92.2 Pass 24 0.0233 0.0214 91.6 Pass 25 0.0277 0.0257 92.8 Pass 26 0.0271 0.0251 92.6 Pass 27 0.0235 0.0215 91.7 Pass 28 0.0221 0.0202 91.4 Pass 29 0.0218 0.0199 91.4 Pass 30 0.0233 0.0214 92.0 Pass 31 0.0253 0.0234 92.6 Pass Sepl 0.0216 0.0198 91.4 Pass 2 0.0217 0.0198 91.5 Pass 3 0.0218 0.0200 91.6 Pass 4 0.0218 0.0200 91.5 Pass 5 0.0256 0.0237 92.9 Pass 6 0.0217 0.0199 91.7 Pass 7 0.0231 0.0214 92.3 Pass 8 0.0254 0.0235 92.7 Pass 9 0.0271 0.0252 93.2 Pass 10 0.0263 0.0244 92.8 Pass 11 0.0193 0.0175 90.5 Pass 12 0.0217 0.0199 91.8 Pass 13 0.0241 0.0223 92.7 Pass 14 0.0232 0.0214 92.3 Pass 15 0.0256 0.0239 93.2 Pass 16 0.0304 0.0285 93.8 Pass 17 0.0223 0.0204 91.6 Pass 18 0.0239 0.0221 92.5 Pass 19 0.0243 0.0225 92.8 Pass 20 0.0216 0.0198 91.8 Pass 21 0.0294 0.0274 93.3 Pass 22 0.0335 0.0309 92.3 Pass 23 0.0298 0.0274 92.0 Pass 24 0.0249 0.0228 91.8 Pass 25 0.0241 0.0223 92.3 Pass 26 0.0225 0.0207 92.2 Pass 27 0.0223 0.0206 92.2 Pass 28 0.0230 0.0212 92.2 Pass 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Appendix A,Page 45 29 0.0254 0.0236 93.0 Pass 30 0.0265 0.0246 92.9 Pass Octl 0.0248 0.0229 92.3 Pass 2 0.0251 0.0234 93.0 Pass 3 0.0274 0.0257 93.8 Pass 4 0.0256 0.0239 93.3 Pass 5 0.0389 0.0363 93.3 Pass 6 0.0339 0.0312 92.1 Pass 7 0.0347 0.0325 93.5 Pass 8 0.0307 0.0285 93.0 Pass 9 0.0291 0.0271 93.3 Pass 10 0.0294 0.0274 93.3 Pass 11 0.0264 0.0245 92.8 Pass 12 0.0270 0.0252 93.4 Pass 13 0.0271 0.0253 93.5 Pass 14 0.0254 0.0236 92.9 Pass 15 0.0292 0.0274 93.9 Pass 16 0.0362 0.0341 94.3 Pass 17 0.0364 0.0339 93.0 Pass 18 0.0414 0.0389 94.0 Pass 19 0.0485 0.0457 94.2 Pass 20 0.0437 0.0409 93.6 Pass 21 0.0412 0.0386 93.6 Pass 22 0.0444 0.0414 93.3 Pass 23 0.0481 0.0449 93.3 Pass 24 0.0490 0.0455 92.9 Pass 25 0.0514 0.0482 93.8 Pass 26 0.0519 0.0484 93.2 Pass 27 0.0540 0.0504 93.3 Pass 28 0.0440 0.0408 92.6 Pass 29 0.0481 0.0446 92.8 Pass 30 0.0430 0.0398 92.7 Pass 31 0.0488 0.0456 93.4 Pass Novl 0.0564 0.0522 92.5 Pass 2 0.0611 0.0571 93.3 Pass 3 0.0736 0.0685 93.1 Pass 4 0.0602 0.0558 92.7 Pass 5 0.0582 0.0540 92.8 Pass 6 0.0595 0.0552 92.8 Pass 7 0.0590 0.0548 92.8 Pass 8 0.0656 0.0610 93.0 Pass 9 0.0732 0.0682 93.2 Pass 10 0.0833 0.0773 92.8 Pass 11 0.1047 0.0969 92.5 Pass 12 0.1047 0.0966 92.2 Pass 13 0.0980 0.0900 91.8 Pass 14 0.0976 0.0897 91.9 Pass 15 0.1012 0.0929 91.8 Pass 16 0.0990 0.0911 92.0 Pass 17 0.0996 0.0916 91.9 Pass 18 0.1220 0.1126 92.3 Pass 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Appendix A,Page 46 19 0.1465 0.1346 91.9 Pass 20 0.1362 0.1242 91.2 Pass 21 0.1107 0.1010 91.2 Pass 22 0.1168 0.1070 91.7 Pass 23 0.1531 0.1402 91.6 Pass 24 0.1648 0.1509 91.6 Pass 25 0.1320 0.1199 90.9 Pass 26 0.1339 0.1223 91.3 Pass 27 0.1187 0.1081 91.0 Pass 28 0.1308 0.1195 91.4 Pass 29 0.1419 0.1299 91.5 Pass 30 0.1475 0.1348 91.4 Pass Dec1 0.1418 0.1294 91.3 Pass 2 0.1688 0.1543 91.4 Pass 3 0.1615 0.1471 91.1 Pass 4 0.1581 0.1444 91.3 Pass 5 0.1572 0.1430 91.0 Pass 6 0.1328 0.1206 90.9 Pass 7 0.1291 0.1175 91.0 Pass 8 0.1312 0.1198 91.3 Pass 9 0.1418 0.1294 91.3 Pass 10 0.1514 0.1380 91.2 Pass 11 0.1646 0.1500 91.1 Pass 12 0.1536 0.1393 90.7 Pass 13 0.1550 0.1413 91.2 Pass 14 0.1856 0.1691 91.1 Pass 15 0.1702 0.1547 90.9 Pass 16 0.1563 0.1417 90.7 Pass 17 0.1409 0.1279 90.8 Pass 18 0.1473 0.1341 91.0 Pass 19 0.1559 0.1417 90.9 Pass 20 0.1555 0.1413 90.9 Pass 21 0.1440 0.1308 90.8 Pass 22 0.1467 0.1335 91.0 Pass 23 0.1558 0.1416 90.9 Pass 24 0.1592 0.1445 90.8 Pass 25 0.1531 0.1390 90.8 Pass 26 0.1613 0.1466 90.9 Pass 27 0.1400 0.1269 90.7 Pass 28 0.1488 0.1353 90.9 Pass 29 0.1466 0.1329 90.6 Pass 30 0.1420 0.1290 90.8 Pass 31 0.1730 0.1574 91.0 Pass LID Report LID Technique Used for Total Volume Volume Infiltration Cumulative Percent Water Quality Percent Comment Treatment? Needs Through Volume Volume Volume Water Quality 250 4th Avenue South,Suite 200 Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com Centennial Park 18386.20 June 30,2020 Drainage Report Appendix A,Page 47 Treatment Facility (ac-ft.) Infiltration Infiltrated Treated (ac-ft) (ac-ft) Credit Total Volume Infiltrated 0.00 0.00 0.00 0.00 0.00 0% No Treat.Credit Compliance with LID Standard 8 Duration Analysis Result=Passed Perind and Impind Changes No changes have been made. This program and accompanying documentation are provided'as-is'without warranty of any kind.The entire risk regardingthe performance and results of this program is assumed by End User. Clear Creek Solutions Inc.and the governmental licensee or sublicensees disclaim all warranties, either expressed or implied,including but not limited to implied warranties of program and accompanying documentation. In no event shall Clear Creek Solutions Inc. be liable for any damages whatsoever(including without limitation to damages for loss of business profits,loss of business information,business interruption,and the like)arising out of the use of,or inability to use this program even if Clear Creek Solutions Inc.or their authorized representatives have been advised of the possibility of such damages. Software Copyright©by:Clear Creek Solutions, Inc.2005-2020;All Rights C250 4th Avenue South,Suite 200 CM Edmonds,WA 98020 ENGINEERING ph.425.778.8500 1 f.425.778.5536 www.cgengineering.com