1-07.6(2)3_SWPPP_20260414_261-1128_45th_Ave_SW_Culvert_Replacement_(PW#2025-017).pdf

F o r m e r l y D C G / W a t e r s h e d

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SPU 45th Ave SW Culvert Replacement

Stormwater Pollution Prevention Plan ( S W P P P )

A P R I L 1 4 , 2 0 2 6

Prepared for: Prepared on behalf of:

Washington Department of Ecology Northwest Region Shoreline Office

Seattle Public Utilities Seattle, Washington Justin Record

F o r m e r l y D C G / W a t e r s h e d

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Prepared by:

Tracey Belding, PE Principal of Civil Engineering, Project Manager TBelding@FacetNW.com

9706 4th Ave NE, Suite 300 Seattle, WA 98115 206.523.0024 www.facetnw.com mailto:TBelding@FacetNW.com

Stormwater Pollution Prevention Plan (SWPPP)

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Construction Stormwater General Permit (CSWGP)

Stormwater Pollution Prevention Plan

(SWPPP)

for 45th Ave SW Culvert Replacement and Habitat Restoration

Prepared for:

Department of Ecology Northwest Region Shoreline Office

Permittee / Owner Developer Operator / Contractor Seattle Public Utilities Seattle Public Utilities TBD

Fauntleroy Creek crossing 45th Ave SW, Seattle, WA 98136

Certified Erosion and Sediment Control Lead (CESCL) Name Organization Contact Phone Number

TBD TBD TBD

SWPPP Prepared By Name Organization Contact Phone Number

Tracey Belding, PE Facet 206.523.0024 ext. 106

SWPPP Preparation Date 09 / 1 / 2025

Project Construction Dates Activity / Phase Start Date End Date

Construction 05 / 01 / 2026 12 / 01 / 2028

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Table Of Contents Project Information (1.0)

Existing Conditions (1.1)

Proposed Construction Activities (1.2)

Construction Stormwater Best Management Practices (BMPs) (2.0) The 12 Elements (2.1)

Element 1: Preserve Vegetation / Mark Clearing Limits (2.1.1)

Element 2: Establish Construction Access (2.1.2)

Element 3: Control Flow Rates (2.1.3)

Element 4: Install Sediment Controls (2.1.4)

Element 5: Stabilize Soils (2.1.5)

Element 6: Protect Slopes (2.1.6)

Element 7: Protect Drain Inlets (2.1.7)

Element 8: Stabilize Channels and Outlets (2.1.8)

Element 9: Control Pollutants (2.1.9)

Element 10: Control Dewatering (2.1.10)

Element 11: Maintain BMPs (2.1.11)

Element 12: Manage the Project (2.1.12)

Element 13: Protect Low Impact Development (LID) BMPs (2.1.13)

Pollution Prevention Team (3.0) Monitoring and Sampling Requirements (4.0)

Site Inspection (4.1)

Stormwater Quality Sampling (4.2)

Turbidity Sampling (4.2.1) pH Sampling (4.2.2)

Discharges to 303(d) or Total Maximum Daily Load (TMDL) Waterbodies (5.0) 303(d) Listed Waterbodies (5.1)

TMDL Waterbodies (5.2)

Reporting and Record Keeping (6.0) Record Keeping (6.1)

Site Log Book (6.1.1)

Records Retention (6.1.2)

Updating the SWPPP (6.1.3)

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Reporting (6.2)

Discharge Monitoring Reports (6.2.1)

Notification of Noncompliance (6.2.2)

Appendices A. Site Map

B. BMP Detail

C. Correspondence

D. Site Inspection Form

E. Construction Stormwater General Permit (CSWGP)

F. 303(d) Listed Waterbodies & TMDL Waterbodies Information

G. Contaminated Site Information

List of Tables

Table 1 - Summary of Site Pollutant Constituents Table 2 – Pollutants Table 3 – pH-Modifying Sources Table 4 – Dewatering BMPs Table 5 – Management Table 6 – BMP Implementation Schedule Table 7 – Team Information Table 8 – Turbidity Sampling Method Table 9 – pH Sampling Method

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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

CO2 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

GULD General Use Level Designation

NPDES National Pollutant Discharge Elimination System

NTU Nephelometric Turbidity Units

NWRO Northwest Regional Office of the Department of Ecology pH Power of Hydrogen

RCW Revised Code of Washington

SPCC Spill Prevention, Control, and Countermeasure su Standard Units

SWMMEW Stormwater Management Manual for Eastern Washington

SWMMWW Stormwater Management Manual for Western Washington

SWPPP Stormwater Pollution Prevention Plan

TESC Temporary Erosion and Sediment Control

SWRO Southwest Regional Office of the Department of Ecology

TMDL Total Maximum Daily Load

VFO Vancouver Field Office of the Department of Ecology

WAC Washington Administrative Code

WSDOT Washington Department of Transportation

WWHM Western Washington Hydrology Model

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Project Information (1.0) Project/Site Name: 45th Ave SW Culvert Replacement and Habitat Restoration Street/Location: 45th Ave SW City: Seattle State: Washington Zip code: 98136 Subdivision: N/A Receiving waterbody: Fauntleroy Creek (tributary to Puget Sound)

Existing Conditions (1.1) Total acreage (including support activities such as off-site equipment staging yards, material storage areas, and borrow areas).

Total acreage: 1.55 acres

Disturbed acreage: 1.25 acres

Existing structures: Within the project limits there is an existing 24-inch culvert to be replaced, a concrete panel roadway, walkways, driveways, and concrete/asphalt parking.

Landscape topography: The roadbed of 45th Ave SW is on top of a 35 to 40-foot-high embankment that spans the ravine through which Fauntleroy Creek flows. Fauntleroy Creek flows through an existing 24-inch culvert at the bottom of the embankment. The site generally slopes from east to west. The project is bounded to the north and south by multi-family residential buildings and bounded to the east and west by Fauntleroy Creek.

Drainage patterns: Fauntleroy Creek flows within a ravine that is conveyed through a 24-inch culvert beneath the 45th Ave SW roadway. The Fauntleroy Creek drainage basin is approximately 150 acres, and it originates to the east of the site with much of the drainage area within Fauntleroy Park. Surface runoff within 45th Ave SW is collected in gutters and conveyed to existing public conveyance systems. Drainage from the existing buildings to the north of the culvert flows into the sanitary sewer main in 45th Ave SW which outlets to Puget Sound after treatment at a the King County West Point Treatment Plant. South of the culvert, runoff from the 9212 45th Ave SW building drains through a detention pipe that outlets to Fauntleroy Creek upstream of the culvert. Runoff from 4502 SW Wildwood Pl located south of the culvert is collected in onsite drainage infrastructure and discharged to a storm drain main in SW Wildwood Pl that outfalls to Puget Sound.

Existing Vegetation: Existing vegetation within the ravine is forested with invasive groundcover (e.g., English ivy), existing vegetation within the 45th Ave SW ROW is lawn and street trees. The site contains 33 trees which will be removed to complete the proposed construction (top-down excavation). All other trees in the vicinity will be protected during construction.

Critical Areas: The site contains four Environmentally Critical Areas (ECAs): Steep Slope, Riparian Corridor, Wetlands, and a Potential Liquefaction area.

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List of known impairments for 303(d) listed or Total Maximum Daily Load (TMDL) for the receiving waterbody:

Water – Bacteria, Enterococci (Listing ID: 84187)

Sediment – Dibenzo(a,h)anthracene (Listing ID: 506771)

Sediment – Acenaphthene (Listing ID: 506779)

Sediment – Bis(2-ethylhexyl)phthalate (Listing ID: 506783)

Sediment – Benzo(a)anthracene (Listing ID: 506784)

Sediment – Benzo(a)pyrene (Listing ID: 506785)

Sediment – Benzoic Acid (Listing ID: 506786)

Sediment – Benzo(g,h,i)perylene (Listing ID: 506788)

Sediment – Butyl benzyl phthalate (Listing ID: 506789)

Sediment – Chrysene (Listing ID: 506792)

Sediment – Indeno(1,2,3-c,d)pyrene (Listing ID: 506801)

Sediment – Benzofluoranthenes, Total (b+k+j) (Listing ID: 506812)

TMDL – Fecal Coliform

Washington State Department of Ecology Confirmed and Suspected Contaminated Sites in the vicinity of the project:

Tacoma Smelter Plume: According to Washington State Department of Ecology’s (Ecology) Dirt Alert website (Dirt Alert), the site is located in an area that may have been contaminated by air emissions originating from the Asarco smelter in Tacoma, Washington. The Washington State Department of Ecology (Ecology) recommended soil sampling in the project area to evaluate the levels of arsenic and lead in the soil prior to project commencement. Arsenic and lead were evaluated as part of project site characterization; results are summarized in Appendix G. Arsenic was not detected in soil; lead was either non-detect or detected within the natural background range (Natural Background Soil Metals Concentrations in Washington State, Puget Sound region, Washington State Department of Ecology publication #94-115, October 1994.)

Results were shared with Ecology, and Ecology confirmed soil remediation associated with the Tacoma Smelter Plume is not needed for this project site. In groundwater, arsenic was detected at a maximum concentration of 6.4 micrograms per liter (µg/L) below the natural background level of 8 µg/L as defined by Ecology in the Natural Background Groundwater Arsenic Concentrations in Washington State published in January 2022 (Publication No. 14-09-044).

Dissolved lead was not detected; total lead was non-detect in two wells and detected at trace concentrations of 2.3 µg/L in a third well.

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45th Ave SW Apartments: Ecology records indicate a historical localized UST release on an adjacent parcel. The UST(s) were removed in 1989, and the affected soils were limited to an area less than 350 square-feet in size, located in the west-central portion of the parcel, which is presently overlaid with impervious pavement and a building. The affected area is outside of the present project’s construction limits. A chemical oxidation and ORC injection program was performed at the site in 2018. Compliance monitoring results empirically demonstrated that the soil-to-groundwater pathway was addressed, and Ecology granted the site No Further Action status (source: 2024 Remedial Action Report). Site characterization completed for this project included soil and groundwater sampling in the project area; petroleum constituents were not detected in groundwater monitoring wells installed for the project. Site characterization data are included in Appendix G.

Contaminated site screening and site characterization: Laboratory analytical data collected for the project are provided in Appendix G. Groundwater sampling did not detect BTEX/VOCs, PAHs, or petroleum-range hydrocarbons; detected analytes were limited to low concentrations of metals below background-scale concentrations (see Appendix G). Soil analytical results are included in Appendix G; constituents detected in soil are addressed through the SWPPP’s erosion and sediment control BMPs to prevent mobilization and off-site transport. Table 1 summarizes screening constituents evaluated based on site screening and project-specific characterization and presents groundwater results.

Table 1 - Summary of Site Pollutant Constituents

Constituent (Pollutant) Location Depth Concentration

Petroleum hydrocarbons / VOCs Gasoline-Range Organics

(GRO)

B-202, B-501, and B-502

Groundwater depth varies

Not detected in groundwater (B-202 <100 µg/L; B-501 <100 µg/L)

Diesel-Range Organics

(DRO)

B-202, B-501, and B-502

Groundwater depth varies

Not detected in groundwater (B-202 <250 µg/L; B-501 <0.2 µg/L)

Motor Oil-Range Organics B-202, B-501, and B-502

Groundwater depth varies

Not detected in groundwater (B-202 <250 µg/L; B-501 <0.2 µg/L)

BTEX (benzene, toluene, ethylbenzene, total xylenes)

B-202, B-501, and B-502

Groundwater depth varies

Not detected in groundwater (benzene <0.2 µg/L; toluene <1 µg/L; ethylbenzene <0.2 µg/L; total xylenes <0.4 µg/L in B-202 and B-501)

PAHs/cPAHs B-202, B-501, and B-502

Groundwater depth varies

Not detected in groundwater (B-202

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<0.011 µg/L; B-501 <0.0096 µg/L)

Metals Arsenic (dissolved) B-202, B-501, and

B-502 Groundwater depth varies

Detected in B-501 at

6.4 µg/L; non-detect in B-202 and B-502 (<3 µg/L)

Arsenic (total) B-202, B-501, and B-502

Groundwater depth varies

5.7–5.8 µg/L in B-202 and B-501; non-detect in B-502 (<3.3 µg/L)

Lead (dissolved) B-202, B-501, and B-502

Groundwater depth varies

Non-detect in all wells (<1 µg/L)

Lead (total) B-202, B-501, and B-502

Groundwater depth varies

Detected at 2.3 µg/L in B-202; non-detect in B- 501 and B-502 (<1.1 µg/L)

Note: Washington’s surface water quality toxics criteria for aquatic life are provided in WAC 173- 201A-240 (Table 240). For arsenic, the freshwater aquatic life criteria are 300 µg/L (acute) and 130 µg/L (chronic). The maximum dissolved arsenic detected in groundwater (6.4 µg/L) is below these aquatic-life criteria. Freshwater aquatic-life criteria for lead are hardness-dependent (Table 240 footnotes q and r); dissolved lead was non-detect (<1 µg/L) in all groundwater samples, and total lead was detected at 2.3 µg/L in one well, non-detect in the other two wells.

Petroleum-related constituents (TPH ranges, BTEX/VOCs, and PAHs) were not detected in groundwater, which does not indicate petroleum is present in the mobile dissolved phase at sampled locations within the project site. Soil analytical results are included in Appendix G; for soil-associated constituents, the primary transport mechanism to receiving waters is sediment;

accordingly, the SWPPP focuses on preventing sediment mobilization and managing discharges to meet applicable criteria through BMPs, monitoring, and treatment where required to comply with the requirements of the discharge permit.

Proposed Construction Activities (1.2) Description of site development:

This Fish Habitat Enhancement Project (FHEP) involves the removal of a failing 24-inch culvert and replacement with a fish-passable culvert structure and associated habitat restoration of disturbed creek and riparian areas. Surface improvements in the right-of-way include installing a paved landing area, driveways, asphalt and concrete street surfaces, sidewalks, maintenance access stairs, fencing, drainage collection, landscaped areas, and street trees.

Description of construction activities:

• Fish exclusion

• Cofferdams

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• Fauntleroy Creek pumped bypass system implementation (regulated by Washington Department of Fish and Wildlife (WDFW) under the Hydraulic Project Approval)

• Site preparation

• Soldier pile installation

• Culvert trench excavation

• Culvert trench dewatering

• Culvert construction

• Creek and fish habitat restoration

• Trench backfill

• Stormwater facilities construction (detention pipe and stormwater quality GSI)

• Site grading and restoration planting

• Asphalt and concrete removal and final surface restoration paving

Description of construction phase site drainage including flow from and onto adjacent properties:

During the construction phase of this project, 45th Ave SW will have a 17-ft wide shored trench open to a depth of up to 40-feet to construct the new fish-passable culvert structure through an existing roadway embankment. Discussion of construction phase stormwater is separated by areas of the site that receive rainfall north of the trench, in the trench and ravine system, and south of the trench.

North of the trench:

The existing drainage patterns will not be altered over the course of the approximately 2-year construction period. During that time, existing impervious pavements will remain intact, isolating drainage from underlying soils. Pavements will only be demolished and replaced in the final activity of construction, projected to span the final summer month of the 2-year construction period. Per the existing condition, drainage will follow existing pavement gradients to public and private collection systems, which convey flows to an existing SPU-owned sanitary sewer in 45th Ave SW. This sanitary sewer conveys flows to the West Point Wastewater Treatment Plant for treatment. During the primary construction phases, this area is not proposed to discharge construction stormwater to Fauntleroy Creek or any other water of the state.

South of the trench:

Like the area north of the trench, existing pavements will remain intact through construction, and existing drainage patterns will remain as existing pavement gradients direct drainage north. The trench will be protected from receiving drainage from this area, and temporary drainage structures (StormFilter® Stormwater Treatment Device or approved equivalent) will be installed at the low points of existing pavements to intercept surface water drainage before it reaches the open trench. Once this surface drainage (which will be isolated from underlying soils by maintaining existing impervious pavements) is treated through a StormFilter® Stormwater Treatment Device or approved equivalent, drainage will be pumped to the 12-inch storm drain main in 45th Ave SW approximately 50-ft south of the project site. Discharge from the temporary system will be monitored and managed in accordance with the CSWGP and the applicable discharge authorization requirements. Pavements will be removed and replaced during the final

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Trench and upper (east) ravine system:

Precipitation that falls within the culvert trench (excavation) will enter the trench’s dewatering collection system. Precipitation that falls within the upper ravine area east of the culvert trench will either infiltrate and drain toward the trench or flow as overland drainage to the trench collection system. Dewatering water (including groundwater and collected drainage from within the isolated construction footprint) will be conveyed to a Baker tank/treatment system, where it will be monitored and treated as necessary to comply with the CSWGP and applicable discharge authorization requirements. Prior to initiating routine discharge, treated effluent will be batch sampled as required by Ecology; if results indicate additional treatment is necessary, the treatment train will be adjusted accordingly. Discharge monitoring, BMP maintenance activities, and sampling results will be documented and retained in the project records in accordance with the CSWGP and discharge authorization.

A cofferdam will be constructed at the uppermost region of the ravine within the project limits to hydraulically isolate the active construction area from upstream creek flows. An impervious creek bypass system will convey creek flows around the isolated construction area to the downstream channel, with outlet protection and erosion control measures installed and maintained to prevent scour and sediment transport. The creek bypass system and outlet protection inspection and testing for downstream turbidity are under the project’s approved and issued WDFW HPA permit.

Lower (west) ravine region:

The lower (west) ravine region is currently vegetated; during most of the construction phase, and after construction, it will remain vegetated. Like the pavements described above, this area will remain largely intact through construction until (1) creek and fish habitat restoration is completed after the culvert is work is complete and (2) upland ravine areas undergo invasives removal and final restoration planting near the end of construction during summertime. This area will be isolated from the active construction footprint and creek flows by a downstream cofferdam location such that there is no uncontrolled connectivity between the construction area and downstream receiving waters. Where temporary ground disturbance occurs in this area, BMPs will be installed, inspected, and maintained in accordance with the SWPPP’s 12 Elements to prevent sediment mobilization and off-site transport.

Description of final site drainage including flow from and onto adjacent properties:

The final stormwater condition will be unchanged from the existing condition, with all existing stormwater points of discharge reestablished and/or maintained.

45th Ave SW drainage will be collected in inlets and catch basins and routed to the 8” Public Sanitary Sewer within 45th Ave SW. 9144 45th Ave SW drainage will be collected in inlets and catch basins and routed to the 8” Public Sanitary Sewer in 45th Ave SW. SW Barton St ROW drainage will be collected in catch basins and routed east to the ravine through a non-infiltrating

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Description of final stabilization:

Final stabilization includes approximately:

• 10,828 SF of concrete and asphalt paving (driveways, roadways, parking, curb and gutter, landing)

• 2,900 SF of concrete sidewalks

• 990 SF of ROW landscaping strips (lawn)

• 17,935 SF of native plant restoration

• 4,500 SF of creek channel

Contaminated Site Information:

Proposed activities regarding contaminated soils or groundwater (example: on-site treatment system, authorized sanitary sewer discharge):

Project groundwater analytical data have not indicated petroleum-impacted groundwater is present within the project area; petroleum-range hydrocarbons and VOCs were not detected in groundwater (Appendix G), indicating petroleum is not present in the mobile dissolved phase at sampled locations across the project site (east, within, and west of 45th Ave SW). Soil analytical results are included in Appendix G; soil-associated constituents are addressed through implementation and maintenance of the SWPPP Elements 1–12 to prevent sediment mobilization and off-site transport. In addition, a downstream cofferdam will be installed to isolate the active construction area from creek flow as described in Section 1.2. Construction-related water discharged to waters of the state will be captured at defined discharge points and will be tested and treated, as required by the CSWGP and applicable discharge authorization.

Construction Stormwater Best Management Practices (BMPs) (2.0) 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.

The 12 Elements (2.1) Element 1: Preserve Vegetation / Mark Clearing Limits (2.1.1) List and describe BMPs:

• BMP C101: Preserving Natural Vegetation Natural vegetation will be retained to the maximum extent feasible while site clearing and grading occurs. Clearing and grading will be phased throughout areas onsite to

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Native topsoil will be retained and stockpiled onsite where it is feasible for reuse for site grading and landscaping. The native soils are suitable for reuse as structural fill if the required compaction limits are achieved. While the entire site will be cleared for construction, natural vegetation surrounding the site will be retained to the maximum extent feasible.

• BMP C103: High Visibility Fence A high visibility fence or temporary chain link construction fencing will be installed around the perimeter of the project limits prior to commencement of site clearing and grading.

Installation Schedules:

• BMP C101: Preserving Natural Vegetation Measures for protecting natural vegetation will be implemented through the site during the clearing and grading phase(s) of the project to the maximum extent feasible and trees to be retained will be surrounded with tree protection fencing in accordance with the project’s landscape plans.

• BMP C103: High Visibility Fence A high visibility fence or temporary chain link construction fencing will be installed around the perimeter of the project limits prior to commencement of site clearing and grading and will remain throughout the duration of the project.

Inspection and Maintenance plan: To be determined by the project CESCL (TBD). See BMP details in Appendix B for inspection and maintenance standards.

Responsible Staff: Contractor provided CESCL (TBD)

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Element 2: Establish Construction Access (2.1.2) List and describe BMPs:

• BMP C105: Stabilized Construction Entrance/Exit One stabilized construction entrance/exit will be installed to provide access to the staging yard located at 9131 California Ave SW (with access from SW Director St).

Construction entrances on 45th Ave SW are paved in the existing condition such that stabilization is not required. Construction entrances on 45th Ave SW may be installed as necessary to reduce sediment tracked from the work area. The location of construction access may be modified as necessary to accommodate phasing of the site work.

• BMP C107: Construction Road/Parking Area Stabilization Onsite areas of frequent construction traffic and/or parking will be stabilized.

Street sweeping and street cleaning will be performed as necessary to remove sediment tracked from the project site. If sediment is tracked off site, public roads shall be cleaned thoroughly at the end of each day minimum, or more frequently during wet weather. Sediment shall be removed from roads by shoveling or sweeping and transporting to a controlled sediment disposal area. All wheel wash wastewater shall be controlled on-site and is not permitted to be discharged into waters of the State.

Street washing is not permitted, even after shoveling or sweeping. During construction, if material is being deposited on off-site streets, additional strategies may be required including:

• Regenerative-type vacuum sweepers and repeated or continuous sweeping.

• Wheel wash (or an improved wheel wash is one already exists).

• Special site procedures and provisions (such as transferring haul-outs to trucks that travel only on paved and maintained surfaces in the site).

• Suspension of work until dry weather.

Installation Schedules:

• BMP C105: Stabilized Construction Entrance/Exit Construction access shall be established prior to beginning site clearing and grading activities.

• BMP C107: Construction Road/Parking Area Stabilization Construction road/parking area stabilization shall be established prior to beginning construction traffic.

Inspection and Maintenance plan: To be determined by the project CESCL (TBD). See BMP

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Element 3: Control Flow Rates (2.1.3) Will you construct stormwater retention and/or detention facilities?

☒ Yes ☐ No A detention facility will be installed to replace an existing detention CMP in-kind. This facility will not be used for flow control during construction. Flow control will be provided as necessary by on-site sedimentation tanks to reduce discharge flowrates to the storm drain system.

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

• BMP C235: Coir Logs Coir logs shall be placed contouring site slopes to control erosion, stabilize banks, and to minimize drainage velocities and provide opportunity to capture sediment.

• BMP C202: Riprap Channel Lining A riprap mat will be constructed within the Fauntleroy Creek channel at the outlet of the creek bypass to reduce the bypass flow’s velocity, energy, and ability to scour the channel.

Installation Schedules: All BMPs to control flowrates shall be installed prior to beginning site clearing and grading activities.

Inspection and Maintenance plan: To be determined by the project CESCL (TBD). See BMP

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Element 4: Install Sediment Controls (2.1.4)

• BMP C235: Coir Logs Coir logs shall be placed contouring site slopes to control erosion, stabilize banks, and to minimize drainage velocities and provide opportunity to capture sediment.

• BMP C220: Storm Drain Inlet Protection Inlet protection will be placed throughout the site and at all inlets and catch basins downstream of any areas that could release or sediments as a result of project activities.

Additionally, sediment will be removed from paved areas in and adjacent to construction work areas manually or using mechanical sweepers, as needed, to minimize tracking of sediments on vehicle tires away from the site and to minimize wash off sediments from adjacent streets in runoff. Whenever possible, sediment laden water shall be discharged into onsite, relatively level, vegetated areas (BMP C240 paragraph 5, page 4-102).

Alternate sediment control BMPs are included in Appendix B as a quick reference tool for the onsite inspector in the event the BMP(s) listed herein are deemed ineffective or inappropriate during construction to satisfy the requirements set forth in the General NPDES Permit (Appendix E). To avoid potential erosion and sediment control issues that may cause a violation of the NPDES Construction Stormwater permit (as provided in Appendix E), the Certified Erosion and Sediment Control Lead will promptly initiate the implementation of one or more of the alternative BMPs listed in Appendix B after the first sign that existing BMPs are ineffective or failing. If the standards are not met, additional BMPs (including site-specific designs) shall be implemented.

Installation Schedules: Prior to any significant clearing and grading activities and as needed. If determined necessary by the project CESCL, a sediment tank shall be installed prior to beginning site clearing and grading and/or dewatering activities.

Inspection and Maintenance plan: To be determined by the project CESCL (TBD). See BMP

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Element 5: Stabilize Soils (2.1.5) 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: 04/22/2026 End date: 07/05/2028

Will you construct during the wet season?

☒ Yes ☐ No

• BMP T5.13 Post Construction Soil Quality and Depth (required of all projects)

• BMP C120: Temporary and Permanent Seeding

Large areas of exposed soils that are anticipated to remain unworked for a long period of time shall be stabilized by using temporary seeding.

• BMP C121: Mulching Exposed soils that are anticipated to remain unworked for shorter periods of time shall be stabilized. This can be accomplished by use of several BMPs, including mulching.

• BMP C122: Nets and Blankets Exposed soils that are anticipated to remain unworked for shorter periods of time shall be stabilized. This can be accomplished by use of several BMPs, including nets and blankets. This BMP is particularly useful for the stabilization of temporary soil stockpiles.

• BMP C123: Plastic Covering Exposed soils that are anticipated to remain unworked for shorter periods of time shall be stabilized. This can be accomplished by use of several BMPs, including plastic covering. If plastic covering is used, ensure that the increase in runoff from plastic-covered areas can be accommodated by downstream sediment controls.

• BMP C125: Topsoiling / Composting Topsoiling and composting shall be completed over exposed soils if deemed necessary by the site CESCL.

• BMP C130: Surface Roughening Surface roughening shall be used in areas of significant slope that are to be stabilized by use of temporary and permanent seeding. Surface roughening techniques, such as the use of tracked construction vehicles to create surface depressions and control flowrates, shall also be used.

• BMP C140: Dust Control

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Dust control shall be performed during site clearing, excavation, and grading.

Installation Schedules: Stabilize Soils BMPs shall be installed on exposed soils in accordance with the schedule shown in the table at the beginning of this section. Note that the requirement of stabilizing stockpiles also applies to any stockpiles of noxious weeds or organic material.

Inspection and Maintenance plan: To be determined by the project CESCL (TBD). See BMP

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Element 6: Protect Slopes (2.1.6)

Will steep slopes be present at the site during construction?

☒ Yes ☐ No

• BMP C120: Temporary and Permanent Seeding Large areas of exposed soils that are anticipated to remain unworked for a long period of time shall be stabilized by using temporary seeding as determined necessary by the on-site CESCL.

• BMP C121: Mulching Exposed soils that are anticipated to remain unworked for shorter periods of time shall be stabilized as determined necessary by the on-site CESCL. This can be accomplished by use of several BMPs, including mulching.

• BMP C122: Nets and Blankets Exposed soils that are anticipated to remain unworked for shorter periods of time shall be stabilized as determined necessary by the on-site CESCL. This can be accomplished by use of several BMPs, including nets and blankets. This BMP is particularly useful for the stabilization of temporary soil stockpiles.

• BMP C123: Plastic Covering Exposed soils that are anticipated to remain unworked for shorter periods of time shall be stabilized as determined necessary by the on-site CESCL. This can be accomplished by use of several BMPs, including plastic covering. If plastic covering is used, ensure that the increase in runoff from plastic-covered areas can be accommodated by downstream sediment controls.

If temporary steep slopes are created during site grading activities, refer to the BMPs listed in Section 2.1.5 in addition to this section. Additionally, the following BMPs may be employed:

• BMP C203: Water Bars

• BMP C204: Pipe Slope Drains

Clearing/grading work shall comply with the Stormwater Manual, geotechnical recommendations, State Environmental Policy Act conditions, and other applicable regulations and standards. These project-specific requirements are in addition to and take priority over general standards.

Inspection and Maintenance plan: To be determined by the project CESCL (TBD). See BMP

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Element 7: Protect Drain Inlets (2.1.7)

• BMP C220: Storm Drain Inlet Protection Storm drain inlet protection shall be installed on all existing storm drain inlets in the project vicinity, and on all proposed inlets once installed. Refer to the project TESC plan for inlet protection locations.

Installation Schedules:

• BMP C220: Storm Drain Inlet Protection Inlet protection shall be installed on existing inlets within the project vicinity prior to beginning site clearing and grading activities and shall be replaced and maintained throughout the duration of construction. Inlet protection shall be installed on proposed inlets as soon as the inlets are installed and connected to the storm system. Alternatively, inlet protection installation for proposed inlets can be delayed until the inlets begin receiving runoff if all sediment is removed from the structure prior to installation. The Contractor shall remove inlet protection at the end of the project without releasing captured sediment into the storm system.

Inspection and Maintenance plan: To be determined by the project CESCL (TBD). See BMP

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Element 8: Stabilize Channels and Outlets (2.1.8) 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 C122: Nets and Blankets Fauntleroy Creek will be bypassed for the duration of construction as approved by WDFW. The channel bottom at the outlet of the bypass pipe shall be stabilized. This can be accomplished by use of several BMPs, including nets and blankets.

• BMP C202: Riprap Channel Lining Fauntleroy Creek will be bypassed for the duration of construction. The channel bottom at the outlet of the bypass pipe shall be stabilized. This can be accomplished by use of several BMPs, including riprap channel lining.

• BMP C209: Outlet Protection Outlet protection shall be used at all outlets of pipes, ditches, or other conveyances that discharge to a natural/constructed drainage feature such as a stream, wetland, or ditch.

Installation Schedules:

• BMP: C122 Nets and Blankets Nets and Blankets (Scour control mat) will be installed at the downstream outlet of the bypass pipe during the creek dewatering phase of the project and will remain while the creek bypass is in operation.

• BMP: C202 Riprap Channel Lining Riprap channel lining will be installed at the downstream outlet of the bypass pipe during the creek dewatering phase of the project and will remain while the creek bypass is in operation.

• BMP: C209 Outlet Protection Outlet protection will be installed on existing outlets prior to clearing and grading. Outlet protection will be installed on all new outlets as they become operational.

Inspection and Maintenance plan: To be determined by the project CESCL (TBD). See BMP

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Element 9: Control Pollutants (2.1.9) The following pollutants are anticipated to be present on-site:

Table 2 – Pollutants

Pollutant (and source, if applicable) Petroleum products (construction vehicles, equipment) Chemicals (fertilizer/pesticides, cleaning supplies) Dust (demolition activities, excavation and backfill, and site grading) Process water (concrete removal and pouring) Solid waste (Materials packaging)

For the majority of construction, existing impervious pavements and vegetated groundcover will remain intact to the greatest extent practical to separate drainage from underlying soils; the primary pollutant transport concern is sediment from disturbed areas, which shall be managed via the 12 Elements BMPs.

All pollutants, including waste materials and demolition debris, that occur onsite shall be handled and disposed of in a manner that does not cause contamination of stormwater. Good house-keeping and preventative measures will be taken to ensure that the site will be kept clean, well-organized, and free of debris. Dust is controlled and is in compliance with the Puget Sound Clean Air Agency and Work in Critical Areas conforms to requirements of the City’s Critical Areas Ordinance (CAO). If required, BMPs to be implemented to control specific sources of pollutants are discussed below.

Vehicles, construction equipment, and/or petroleum product storage/dispensing:

• All vehicles, equipment, and petroleum product storage/dispensing areas will be inspected regularly to detect any leaks or spills, and to identify maintenance needs to prevent leaks or spills.

• On-site fueling tanks and petroleum product storage containers shall include secondary containment.

• Spill prevention measures, such as drip pans, will be used when conducting maintenance and repair of vehicles or equipment.

• To perform emergency repairs on site, temporary plastic will be placed beneath and, if raining, over the vehicle/equipment.

• Contaminated surfaces shall be cleaned immediately following any discharge or spill incident.

Chemical storage:

• Any chemicals stored in the construction areas will conform to the appropriate source control BMPs listed in Volume IV of the Ecology stormwater manual. In Western Washington, all chemicals shall have cover, containment, and protection provided on site, per BMP C153 for Material Delivery, Storage and Containment in the SWMMWW.

• Application of agricultural chemicals, including fertilizers and pesticides, shall be conducted in a manner and at application rates that will not result in loss of chemical to

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Demolition:

• Dust released from demolished sidewalks, buildings, or structures will be controlled using Dust Control measures (BMP C140).

• Storm drain inlets vulnerable to stormwater discharge carrying dust, soil, or debris will be protected using Storm Drain Inlet Protection (BMP C220 as described above in Section 2.1.7).

• Process water and slurry resulting from sawcutting and surfacing operations will be prevented from entering the waters of the State by implementing Sawcutting and Surfacing Pollution Prevention measures (BMP C152).

Concrete and grout:

• Process water and slurry resulting from concrete work will be prevented from entering the waters of the State by implementing Concrete Handling measures (BMP C151).

• A CO2 system will be implemented to mitigate any high pH water that may be encountered

(requires DOE approval).

Sanitary wastewater:

• Portable sanitation facilities will be firmly secured, regularly maintained, and emptied when necessary.

Solid Waste:

• Solid waste will be stored in secure, clearly marked containers.

Other:

• Other BMPs will be administered as necessary to address any additional pollutant sources on site.

List and describe BMPs:

• BMP C151: Concrete Handling

• BMP C152: Sawcutting and Surfacing Pollution Prevention

• BMP C153: Material Delivery, Storage and Containment

• BMP C154: Concrete Washout Area

Installation Schedules:

• BMP C151: Concrete Handling This BMP shall be employed whenever concrete work is occurring.

• BMP C152: Sawcutting and Surfacing Pollution Prevention This BMP shall be employed whenever sawcutting of existing pavement is occurring.

• BMP C153: Material Delivery, Storage and Containment This BMP shall be employed throughout the life of the project for all materials.

• BMP C154: Concrete Washout Area This BMP shall be employed in areas of washing of concrete equipment.

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Inspection and Maintenance plan: To be determined by the project CESCL (TBD). See BMP

Responsible Staff: Contractor provided CESCL (TBD)

Will maintenance, fueling, and/or repair of heavy equipment and vehicles occur on-site?

☒ Yes ☐ No

Will wheel wash or tire bath system BMPs be used during construction?

☐ Yes ☒ No

Will pH-modifying sources be present on-site?

☒ Yes ☐ No If yes, check the source(s).

Table 3 – pH-Modifying Sources

☐ None ☒ Bulk cement ☐ Cement kiln dust ☐ Fly ash ☐ Other cementitious materials ☒ New concrete washing or curing waters ☒ Waste streams generated from concrete grinding and sawing ☐ Exposed aggregate processes ☐ Dewatering concrete vaults ☐ Concrete pumping and mixer washout waters ☐ Recycled concrete ☐ Other (i.e. calcium lignosulfate) [please describe]

Adjust pH of stormwater if outside the range of 6.5 to 8.5 su.

Obtain written approval from Ecology before using chemical treatment with the exception of CO2 or dry ice to modify pH.

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.

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Element 10: Control Dewatering (2.1.10) This element applies to construction-related dewatering and other captured construction water discharged to waters of the state. Creek bypass flows are conveyed around the isolated work area and are managed via erosion/outlet protection rather than treatment and are not considered construction stormwater. A dewatering system for the shored culvert trench such as a vacuum well system will be used to dewater the trench while the culvert is being constructed.

Captured construction water discharged to waters of the state will be managed through defined discharge points described in Section 1.2 and monitored/sampled in accordance with Section

4.0 and the applicable discharge authorization.

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) ☐ Use of sedimentation bag with discharge to ditch or swale (small volumes of localized dewatering) ☒ Other – settling, flocculation, and sand filtration

• Sedimentation Tank A sediment tank can be installed at the site with associated sumps, pipes, and pumps to collect and convey construction stormwater runoff to the sediment tank as deemed necessary by the on-site CESCL. Portable duplex pumps will lift drainage to the site’s sedimentation/storage tank as deemed necessary by the on-site CESCL.

• Onsite Chemical Treatment A natural, biodegradable chitosan polymer or approval equivalent treatment may be added to the sedimentation tank to aid coagulation and reduce turbidity and associated iron precipitation/discoloration.

All dewatering water shall be routed to the on-site dewatering treatment system. Dewatering water will be pumped to a treatment system that includes a sedimentation tank for gross particle settling. The outlet of the tank will be pumped through a pre-engineered flow-through structure where chitosan coagulant is added for turbidity reduction. After coagulant addition, the water is sent to a second tank where the coagulated particles flocculate and settle from the water column. Post settling, the clarified water is passed through a sand media filter and discharged.

Prior to initiating routine discharge to Fauntleroy Creek, treated effluent will be batch sampled at the treatment system discharge point for the analytical parameters required by Ecology under the CSWGP/discharge authorization. If results indicate additional treatment is required, the treatment train will be adjusted accordingly. Once routine discharge is authorized, the CESCL will implement ongoing field monitoring (turbidity and pH) and any required laboratory sampling

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As described above, dewatering water will be tested and treated before discharge to Fauntleroy Creek in a manner that does not cause erosion, flooding, or a violation of state water quality standards. Alternate dewatering control BMPs are included in Appendix B as a quick reference tool for the on-site inspector in the event the BMP(s) listed above are deemed ineffective or inappropriate during construction to satisfy the requirements set forth in the General NPDES Permit (Appendix E). To avoid potential erosion and sediment control issues that may cause a violation(s) of the NPDES Construction Stormwater permit (as provided in Appendix E), the Certified Erosion and Sediment Control Lead will promptly initiate the implementation of one or more of the alternative BMPs listed in Appendix B after the first sign that existing BMPs are ineffective or failing.

Installation Schedules:

• Sedimentation Tank A sedimentation tank shall be installed prior to groundwater dewatering activities.

• Onsite Chemical Treatment Biopolymer addition may be utilized as needed to reduce turbidity level to below the threshold discussed in Section 4.2 of this SWPPP.

Inspection and Maintenance plan: To be…