HomeMy WebLinkAbout20250807_PWD3985_SWPPP LAND TECHNOLOGIES, INC.
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PLANNING • PERMITTING • ENGINEERING
MAKING A"WAY"OUT OF"NO WAY"
Harmony at Arlington
7417 204th St NE, Arlington, WA 98223
3985
July 2025
Construction Stormwater
Pollution Prevention Plan
for
Harmony at Arlington
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Prepared by:
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Tyler Foster, P.E. RF-- Eo
360-652-9727 0N ALE��'
Email:Tyler@landtechway.com
18820 Third Avenue NE, Arlington WA 98223 voice: 360.652-9727 fax:360.652.7553
CONTENTS
Section 3 -Stormwater Pollution Prevention Plan .......................................................................................1
3.1 MR-2 -Construction Stormwater Pollution Prevention......................................................................1
3.1.1 Project Data Summary:................................................................................................................1
3.2 Introduction:.......................................................................................................................................2
3.2.1 Element 1: Preserve Vegetation/Mark Clearing Limits................................................................2
3.2.2 Element 2: Establish Construction Access ...................................................................................3
3.2.3 Element 3: Control Flow Rates.....................................................................................................3
3.2.4 Element 4: Install Sediment Controls...........................................................................................3
3.2.5 Element 5: Stabilize Soils .............................................................................................................4
3.2.6 Element 6: Protect Slopes............................................................................................................5
3.2.7 Element 7: Protect Permanent Drain Inlets.................................................................................5
3.2.8 Element 8: Stabilize Channels and Outlets ..................................................................................6
3.2.9 Element 9: Control Pollutants......................................................................................................6
3.2.10 Element 10: Control Dewatering...............................................................................................7
3.2.11 Element 11: Maintain Best Management Practices...................................................................7
3.2.12 Element 12: Manage the Project. ..............................................................................................7
3.2.13 Element 13: Protect On-site Stormwater Management BMPs for Runoff from Roofs and
otherHard Surface................................................................................................................................8
3.3 Sequence of BMP Implementation.....................................................................................................9
3.4 BMP Specifications and Details.........................................................................................................10
FIGURES
Figure1 -Seed Mixes....................................................................................................................................5
SWPPP Harmony at Arlington 28-Jul-2025 i
Section 3 - Stormwater Pollution Prevention Plan
3.1 MR-2 - Construction Stormwater Pollution Prevention
3.1.1 Project Data Summary:
Existing and proposed project areas are presented for determination of stormwater management
requirements based on prescribed thresholds as outlined on the City of Arlington Municipal Code.
Project Location Data: I
Applicant Harmony at Arlington LLC I
Site Owner Harmony at Arlington LLC I
Project Name Harmony at Arlington I
Project T.S.R. Location Section 11,Township 31 N, Range 5 W I
Project Address 7417 204th St NE, Arlington, WA 98223 I
Parcel ID(s) 310511-003-040-00,-004-007-00
Watershed Mainstem Stillaguamish
WRIA number 5
Basin Stillaguamish
Sub-Basin Portage Creek
Disturbance Area Data
Total Site Area 190,958 sf (4.38 cc) I
Total Disturbance Area 146,070 sf (3.35 cc) I
Total Proposed Impervious Area 102,572 sf (2.36 cc) I
SWPPP Harmony at Arlington 28-Jul-2025 3-1
3.2 Introduction:
This document is part of the Stormwater Site Plan for the Harmony at Arlington LLC Permit Application.
The Stormwater Pollution Prevention Plan (SWPPP) fulfills Minimum Requirement 2 of the drainage
requirement as outlined in the Stormwater Management Manual for Western Washington (SMMWW).
It has been prepared for NPDES stormwater permit requirements for site improvements on Harmony at
Arlington LLC Parcel No. 310511-003-040-00, -004-007-00 located at 7417 204th St NE, Arlington, WA
98223.
Construction Activities
The SWPPP describes proposed construction activities, all erosion and sediment control measures,
pollution prevention measures, inspection/monitoring activities, and recordkeeping that will be
implemented during the proposed construction project.
The objective of the SWPPP is to:
a) Implement Best Management Practices (BMPs) to prevent erosion and sedimentation, and to
identify, reduce, eliminate or prevent stormwater contamination and water pollution from
construction activity.
b) Prevent violations of surface water quality, ground water quality, or sediment management
standards.
c) Prevent, during the construction phase, adverse water quality impacts including impacts on
beneficial uses of the receiving water by controlling peak flow rates and volumes of stormwater
runoff at the Permittee's outfalls and downstream of the outfalls.
There are thirteen elements presented in the 2024 SMMWW Volume II, Chapter 3. Each element is
addressed in this document for the project site and was prepared per the requirements set forth in the
current Drainage Manual (2024 SMMWW).
NOTES:
1. BMPs referred to in this document are those specified in the 2024 SMMWW. A copy of Volume
2 of the 2024 SMMWW should be acquired and made available at the construction site.
2. NOTE: Siting, sizing, materials, and other specifications for all BMPs offered in this SWPPP are
presented in the Stormwater Site Plan Set as the 'SWPPP PLAN" sheet.
3.2.1 Element 1: Preserve Vegetation/Mark Clearing Limits
The guideline is to minimize removal of existing trees and disturbance and compaction of native soils,
except as needed for building purposes. The goal is to retain any duff layer, native top soil, and natural
vegetation in an undisturbed state to the maximum degree practicable.
Relevant BMPs:
• BMP C101: Preserving natural vegetation
SWPPP Harmony at Arlington 28-Jul-2025 3-2
3.2.2 Element 2: Establish Construction Access
Construction vehicle ingress and egress shall be limited to one route if possible. A stabilized
construction entrance or other equivalent BMP shall be installed to prevent sediment transport onto
roads. The location is shown on the SWPPP plan.
It is recommended that early on, the entire access road be stabilized as it is developed. The proposed
parking and development area is a logical location for equipment parking, material storage/transfer, and
will require regular inspection and maintenance. Contractor shall work to limit disruption of the
neighboring businesses.
Streets shall be cleaned at the end of each day during dry weather and more frequently during wet
weather. Street washing is only allowed after sediment is removed by shoveling or pick-up sweeping and
transported to a controlled disposal area. Street wash wastewater shall be controlled by pumping it
back on site or otherwise preventing its discharge into systems tributary to the waters of the state or
waters that would otherwise require enhanced treatment.
Relevant BMPs:
• BMP C105: Stabilized Construction Entrance
• BMP C107: Construction Parking Area Stabilization
3.2.3 Element 3: Control Flow Rates
The purpose of element 3 is to protect properties and waterways downstream to the project from soil
erosion due to increases in the velocity and peak volumetric flow rate of stormwater runoff from the
project site. Stormwater retention or detention facilities can be needed to comply with this
requirement, and are required to be constructed as one of the first steps in grading the site.
In the primary development area, a sediment trap should be located at the downstream edge of the site
away from bioretention and infiltration areas if necessary. Once the site has been stabilized, all
collected sediments are to be removed.
Relevant BMPs:
• BMP C207: Check Dams
• BMP C234: Vegetated Strip
• BMP C240: Sediment Trap
3.2.4 Element 4: Install Sediment Controls
Remove sediment from construction site runoff by using appropriate sediment removal BMPs. Runoff
from fully stabilized areas may be discharged without a sediment removal BMP.
It is best to avoid sediment generation in the first place, but methods must be employed to treat
sediment laden surface runoff when it occurs.
SWPPP Harmony at Arlington 28-Jul-2025 3-3
In the primary development area, the bio-swale and infiltration trench areas as specified in the
stormwater management plan shall be avoided as a sediment trap. Brush barriers of alternative forms of
capture shall be employed in the infiltration zones of the site. The facility is to be excavated to within
one foot of depth of the proposed design. Once the site has been stabilized, all collected sediments are
to be removed and the facility completed to the design specification.
Relevant BMPs:
• BMP C230: Straw Bale Barrier
• BMP C231: Brush Barrier
• BMP C233: Silt Fence (or preserve natural vegetation—see Element 1)
• BMP C234: Vegetated Strip
• BMP C235: Straw Wattles
• BMP C240: Sediment Trap
3.2.5 Element 5: Stabilize Soils
Exposed and unworked soils and soil stockpiles shall be stabilized. Soil stockpiles shall be located away
from storm drain inlets, drainage channels and other waters.
Mandatory: The time period of soil exposure allowed depends on the season. No soil shall remain
exposed and unworked for more than seven days during the dry season, May 1 through September 30,
or two days during the wet season, October 1 through April 30, unless the SWPPP places other
restrictions on the project.
Soil piles should be covered until the soil is either used or removed. Plastic covering will likely be the
best option. Backfill exploration holes or any deeper excavated areas as soon as possible and rough
grade the site. This will eliminate large soil mounds, which are highly erodible, and prepares the site for
temporary cover, to further reduce erosion potential.
Remove excess soil from the site as soon as possible after backfilling. This will eliminate any sediment
loss from surplus fill.
Relevant BMPs:
• BMP C120:Temporary and Permanent Seeding
• BMP C121: Mulching
• BMP C123: Plastic Covering
• BMP C124: Sodding
• BMP C125:Topsoiling (to be used for soil stabilization only, not soil amendment)
• BMP C140: Dust Control
SWPPP Harmony at Arlington 28-Jul-2025 3-4
TABLE 1 -Bio-Cell Detention&Bio-Cell Swale Grass Seed Mix APPLICATION:
Evenly disperse seed mix by
SPECIES WGT.PERCENT hand-operated Spreader at the
Hard Fescue 45 rate of 2 lb per 1,000 sf.
Hydro-mulch at the rate of 2,000 Ibs
Creeping Meadow Foxtail 20 fiber mulch per acre over the seed.
Creeping Red Fescue 10 Hydroseed tanks and equipment to
Poo Trivialis 10 be cleaned of all prior seed and
Dutch White Clover** 15 other materials before use.
Pre-Mix Options
Pro-Time Rough & Ready Low Profile Mix 100 Sources:
w/Microclover(or equivalent) [I] Hobbs and Hopkins,Portland,
**recommend ProTime Microclover[3),Trifolium repens'Pipolina' Oregon, 503-239-7518
www.protimelawnseed.com
120 SEED MIXES FOR BIO-CELLS AND FILTER STRIPS
SCALE: N.T.S.
Figure 1 -Seed Mixes
3.2.6 Element 6: Protect Slopes
Cut and fill slopes shall be designed and constructed in a manner that will minimize erosion and comply
with the SWPPP's applicable critical area regulations. Cut and fill slopes shall be protected from erosive
flows and concentrated flows until permanent cover and drainage conveyance systems are in place.
Excavated material shall be placed on the uphill side of trenches, consistent with safety and space
considerations.
While there are no cut and fill slopes of significant size to be concerned about erosion damage, the
following measure should be applied if such protection is warranted.
Relevant BMPs:
• BMP C123: Plastic Covering
• BMP C130: Surface Roughening
• BMP C200: Interceptor Dike and Swale
• BMP C201: Grass-Lined Channels
• BMP C206: Level Spreader
• BMP C207: Check Dams
• BMP C208:Triangular Silt Dike (Geotextile-Encased Check Dam)
3.2.7 Element 7: Protect Permanent Drain Inlets.
This element provides guidance and means to protect permanent storm drain inlets from sediment and
silt-laden water. Permanent storm drain inlets operable on the site during construction shall be
protected so that stormwater runoff does not enter the conveyance system without first being filtered
or treated to remove sediment. Inlet protection devices shall be cleaned or removed and replaced when
SWPPP Harmony at Arlington 28-Jul-2025 3-5
sediment has filled one-third of the available storage or as specified by the product manufacturer. They
may be removed once the site is stabilized.
Relevant BMPs:
• none
3.2.8 Element 8: Stabilize Channels and Outlets
This element provides guidance and means for stabilization of temporary and permanent (both
proposed and pre-existing) conveyance systems for the prevention of erosion during and after
construction. Stabilization includes armoring material, adequate to prevent erosion of outlets, adjacent
stream banks, slopes, and downstream reaches and outlets of all conveyance systems.
The site will infiltrate a majority of stormwater during the construction phase. The sediment trap will
have an installed Emergency Overflow routed to the downstream parcel at the natural discharge
location.
Relevant BMPs:
• None
3.2.9 Element 9: Control Pollutants
Appropriate pollution source control measures shall be implemented as applicable in areas of:
construction equipment maintenance or fueling; handling or storage of waste materials, construction
debris,fertilizers, chemicals; and other activities that may contribute pollutants to stormwater.
The following specific requirements apply.
• Cover, containment, and protection from vandalism shall be provided for all chemicals, liquid
products, petroleum products, and other materials that have the potential to pose a threat to
human health or the environment.
• On-site fueling tanks shall include secondary containment.
• Maintenance, fueling and repair of heavy equipment and vehicles shall be conducted using spill
prevention and control measures consistent with the SMMWW.
• Contaminated surfaces shall be cleaned immediately following any spill incident.
• Application of fertilizers and pesticides shall be conducted in a manner and at application rates
that will not result in loss of chemical to stormwater runoff. Manufacturers' label requirements
for application rates and procedures shall be followed
• BMPs shall be used to prevent contamination of stormwater runoff by pH modifying sources.
These sources include, but are not limited to, bulk cement, cement kiln dust, fly ash, new
concrete washing approved treatment, curing waters, waste streams generated from concrete
grinding and sawing, exposed aggregate processes, dewatering concrete vaults, concrete
pumping and mixer washout waters.
Relevant BMPs:
• BMP C151: Concrete Handling
• BMP C152: Sawcutting and Surfacing Pollution Prevention
SWPPP Harmony at Arlington 28-Jul-2025 3-6
• BMP C153: Material Storage, Delivery, and Containment
Also see SWMM Volume II for additional BMPs that may apply.
3.2.10 Element 10: Control Dewatering
Turbid or contaminated dewatering water shall be handled separately from stormwater, and shall be
collected for off-site disposal in a legal manner, or discharged to a sanitary sewer contingent on local
sewer district approval. Uncontaminated or clean water from dewatering systems for trenches, vaults
and foundations may be disposed by on-site infiltration or use of a catch basin insert or with outfall to a
ditch or swale for small volumes of dewatering water.
The need for dewatering is not anticipated for this project.
Relevant BMPs:
• None
3.2.11 Element 11: Maintain Best Management Practices.
The Best Management Practices (BMPs) are activities, protective measures, and maintenance
procedures that, when used singly or in combination, prevent or reduce the impacts of erosion and
sediment transport.
All temporary and permanent erosion and sediment control BMPs shall be maintained and repaired as
needed by the project manager/property owner/contractor to assure continued performance of their
intended function. Sediment control BMPs shall be inspected weekly or after a runoff-producing storm
event during the dry season and daily during the wet season.
All temporary erosion and sediment control 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
removed or stabilized on site. Disturbed soil areas resulting from removal of BMPs or vegetation shall be
permanently stabilized.
3.2.12 Element 12: Manage the Project.
The SWPPP shall be fully implemented at all times and modified whenever 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 following principles should be forefront in the management and application of erosion and
sediment control BMPs
SWPPP Harmony at Arlington 28-Jul-2025 3-7
• Emphasize erosion control rather than sediment control.
• Minimize the extent and duration of the area exposed.
• Trend toward methods that have low runoff velocities.
Quantities of erosion prevention and sediment control materials shall be kept on the project site at all
times to be used for emergency situations such as unexpected heavy summer rains. Having these
materials on-site reduces the time needed to implement BMPs when inspections indicate that existing
BMPs are not meeting the SWPPP requirements
• BMP C150: Materials on Hand
Phasing of Construction - Development projects shall be phased where feasible in order to prevent, to
the maximum extent practicable, the transport of sediment from the development site during
construction. Revegetation of exposed areas and maintenance of that vegetation shall be an integral
part of the clearing activities for any phase. Clearing and grading activities shall minimize removal of
existing trees and minimizing disturbance/compaction of native soils except as needed for building
purposes. If clearing and grading are proposed between October 1 and April 30, silt-laden runoff will be
prevented from leaving the construction site by application of erosion and sediment control measures.
3.2.13 Element 13: Protect On-site Stormwater Management BMPs for Runoff from
Roofs and other Hard Surface
On-site Stormwater Management BMPs shall be protected at all times during the construction process.
This may mean that stormwater management BMPs will be installed towards the end of the
construction process to avoid siltation and compaction. BMPs include but are not limited to: full
dispersion, roof downspout full infiltration or dispersion systems, perforated stubout connections, rain
gardens, bioretention systems, permeable pavement, sheetflow dispersion, and concentrated flow
dispersion. Additional requirements for on-site stormwater management BMPs are included in their
respective sections of Volume V.
In particular, BMP T7.30 Bioretention Cells, Swales, and Planter Boxes in Section 7.3, Vol. V of the 2024
SMMWW. Areas to be used for Bio-retention shall be protected during construction and after
construction.These areas are to be protected from compaction, siltation, and degradation.
Relevant BMPs:
• BMP C102: Buffer Zone
• BMP C103: High Visibility Fence
• BMP C201: Grass-lined Channels
• BMP C208:Triangular Silt Dike
• BMP C231: Brush Barrier
• BMP C233: Silt Fence
• BMP C234: Vegetated Strip
SWPPP Harmony at Arlington 28-Jul-2025 3-8
3.3 Sequence of BMP Implementation
Implementation and sequence of Erosion Control BMPs is presented along with construction sequence:
1) Arrange and attend a pre-construction meeting with City staff, the on-site erosion control specialist,
the design engineer, and owner.
2) Delineate or mark the following areas and features on the site:
a) Clearing limits;
b) Critical areas and their buffers;
c) Erosion or landslide hazard areas and their setbacks;
d) Easements;
e) Required landscaping, and tree retention and replacement areas;
f) Other areas on the site required preservation or protection;
3) Install construction zone road signs.
4) Grade and install construction entrance(s) and provide parking area stabilization.
5) Establish areas for storage and handling of polluted materials at each pollution source.
6) Control BMPs will be implemented.These include:
a) Placement of silt fence, straw wattles, etc.;
b) Excavation of temporary sediment pond;
c) Install temporary sedimentation measures;
7) Carefully remove trees and vegetative materials from areas to be graded. Grind clearing debris to
create a fine-grade chip. Save clean chips for trails and put "sawdust" and finer debris back over
areas to be stripped of organic surface soils.
8) Carefully strip areas to be graded of only the upper organic surface soils being cautious not to mix
weathered mineral soils with organic surface soils. In un-forested areas the chip cover may be
disked into the surface soils before stripping. Stockpile and protect these organic soils as BMP T5.13
Soils for use in yards and other drainage features.
9) Complete mass grading. Reconstruct sediment-trapping measures as grading progresses. Relocate
surface water controls and erosion control measures, or install new measures as site conditions
change so as to maintain compliance with City standards.
10) Install Sewer and Water Main to onsite roads.
11) As construction proceeds, install appropriate sediment controls. Grade and stabilize roads and
interceptor swales in conjunction with the clearing and grading activity.
12) Implement stabilization measures for disturbed areas, slopes, and material stockpiles.
13) Locate and install infiltration system trench. Plug outlets of catch basins with pipes leading to
infiltration systems. Prop solid lids to allow for flow exit and surround with wattles or vegetative
berms. Clean pipes and CBs after paving and site is fully stabilized before unplugging the conveyance
to the infiltration system.
14) Seed and mulch areas to be vegetated using low growing seed mixes as specified.
15) Maintain BMPs until final site stabilization.
16) Final grade, construct and pave roadways. Ensure that the permanent drainage system is complete
and functional.
17) Remove any temporary sediment controls when permanent drainage is complete and erosion
measures are in place and functional. Add topsoil to roadside flow control BMPs.
18) Unplug pipe system to allow stormwater from fully stabilized site to enter infiltration system.
SWPPP Harmony at Arlington 28-Jul-2025 3-9
3.4 BMP Specifications and Details
Reproduction pages of the Construction Stormwater Pollution Prevention BMPs as taken from the 2024
DOE SWMM as noted below,follow this page. This is a recommended list and not all listed measures
are necessarily required. The project's CECSL shall determine which measures are applicable. Sheet
numbers shown are those from the manual.
List of BMPs referenced by this document:
• C101 Preserving Natural Vegetation
• C105 Stabilized Construction Entrance
• C107 Construction Road/Parking Area Stabilization
• C120 Temporary& Permanent Seeding
• C121 Mulching
• C122 Nets and Blankets
• C123 Plastic Covering
• C140 Dust Control
• C150 Materials on Hand
• C151 Concrete Handling
• C153 Material Delivery,Storage and Containment
• C160 Certified Erosion &Sediment Control Lead
• C162 Scheduling
• C200 Interceptor Dike and Swale
• C206 Level Spreader
• C207 Check Dam
• C208 Triangular Silt Dike
• C209 Outlet Protection
• C220 Storm Drain Inlet Protection
• C233 Silt Fence
• C234 Vegetated Strip
• C235 Straw Wattles
• C240 Sediment Trap
SWPPP Harmony at Arlington 28-Jul-2025 3-10