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Res 2098 - DOCUMENT - 2024 Surface Water Comprehensive Plan
CITY OF TUKWILA SURFACE WATER COMPREHENSIVE PLAN 2024 UPDATE Adopted City of Tukwila Surface Water Comprehensive Plan 2024 Update Prepared for City of Tukwila, Washington Prepared February 2013 by Updated June 2024 by Acknowledgments m� � "�.��������n�������������s �� C�'-� ������ Sherry Edquid,Project K4anager Mike Perfetti' Surface Water Program Manager Russell Betteridge' NPOES[oordinator Joshua Hopkins, Surface Water Project Manager Jeff Heg|und,Sewer lkSurface Water Superintendent (forrner) Pat Bradley, Sewer & Surface Water Superintendent Nancy E[Wund,Long Range Planning Manager Project Development Team: Thsta Kob|uskie, SeniorStonnvvater Planner & Project Manager Cara Donovan, Environmental Planner Tyson HOuns8[PE, Senior Engineer Shai|ee]8in, PE, Project Engineer Rose Horton, PE, Project Engineer Frank S0ttOsant0,PE, Project Engineer Charles Dewey, PE, Project Engineer Sara K4andani,Engineering Designer Micha|Tutka, Engineering Designer John Rogers, Senior G|SSpecialist _-_^-- __^ -U������^^������^K: Thomas McLeod, Mayor Mohamed Abdi,Council President TOShSharp Armen Papyan Hannah Hedrick Dennis Martinez ]ovitaK4cConneU De'Sean Quinn Contents Executive Summary E-1 1.0 Introduction 1-1 11 Background 1-2 12 Plan Objective 1-5 1.2.1 City Comprehensive Plan Goals and Policies 1-7 2,0 Drainage Basin and Watershed Characteristics 2-1 2.1 General Description 2-1 22 Population, Existing Land Use and Future Development 2-4 2.3 Drainage Basins 2-10 24 Drainage System Characterization 2-12 2.5 Water Quality Characterization 2-13 2.5.1 Superfund 2-14 2.52 Washington State Water Quality Standards 2-14 2.5.3 Benthic Index ofBiotic Integrity 2-15 2.54 Water Quality Sampling and Anecdotal Reports 2-15 2.6 Aquatic Habitat Characterization 2-18 2.61 Green/OuvvannishRiver 2-18 2.62 Gilliam Creek 2-20 2.63 Riverton Creek 2-21 2.64 Southgate Creek 2-22 2.65 Johnson Creek 2-23 2.66 Mill Creek 2-24 3.0 Regulations and City Policies 3-1 3] Applicable Surface Water Regulations 3-1 3.2 Potential Regulatory Changes 3-2 4.0 Coordination with Regional Plans and Tribes 4-1 4.1 Lower Green River Corridor Flood Hazard Management Plan 4-1 42 Salmon Habitat Plan 4-2 4.3 Our Green [}uvvannish Implementation Plan 4-3 4.4 Action Agenda for Puget Sound 4-4 4.5 Ouvvannish Blueprint: Salmon Habitat inthe OuvvannishTransition Zone 4-4 4.6 ZUZ0State ofour Watershed 4-4 4.7 StornnvvaterParks 4-4 4.8 Coordinating with Tribes 4-5 5.0 Surface Water Known Issues and Solutions 5-1 5] Available Data and Information 5-1 52 Surface Water Known Issues 5-2 5.3 Menu ofSolutions toAddress Surface Water Issues 5-5 / CONTENTS 5.3.1 Programmatic Solutions 5-6 5.3.2 Capital Project Solutions 5-11 5.4 Solutions to Tukwila's Surface Water Issues 5-17 5.5 Issue and Solution Prioritization and Selection 5-27 6.0 Capital Improvement Projects and Studies 6-1 7.0 Operations and Maintenance 7-1 8.0 Recommendations 8-1 8.1 Recommended Activities 8-1 8.1.1 Capital Projects 8-1 8.1.2 Programmatic Solutions and Policies 8-1 8.2 Implementation 8-5 8.2.1 Funding and Partnerships 8-5 8.2.2 Prioritization and Scheduling 8-8 8.3 Conclusion 8-10 9.0 References 9-1 Tables Table E-1 High Priority Capital and Programmatic Recommendations E-1 Table E-2 Medium Priority Capital and Programmatic Recommendations E-3 Table 2-1 Tukwila Zoning and Land Use by Basin (2022) 2-6 Table 2-2 Drainage Basin Areas Summary 2-10 Table 2-3 Surface Water Pump Stations 2-13 Table 5-1 Surface Water Known Issue Summary 5-3 Table 5-2 Known Issue Types Addressed by Programmatic Solutions 5-6 Table 5-3 Surface Water Issue Types Addressed by Capital Projects 5-12 Table 5-4 Recommended Solutions 5-19 Table 5-5 Known Issue Screening Factors 5-27 Table 5-6 Project Prioritization Weights 5-28 Table 6-1 Recommended Capital Projects and Studies 6-1 Table 8-1 Recommended Priority for Implementing Recommendations 8-8 Figures Figure 2-1 City of Tukwila Vicinity Map 2-3 Figure 2-2 City of Tukwila Zoning 2-5 Figure 2-3 Infiltration Not Allowed 2-8 Figure 2-4 Flow Control Standards 2-9 Figure 2-5 City of Tukwila Drainage Basins 2-11 CONTENTS Figure 2-0 30](d) Listed Water Bodies 2-17 Figure 5-1 Known Issues 5-4 Figure 6-1 Individual Capital Improvement Projects and Studies 6'3 Figure 8-1 Surface Water Capital Program Funding 2023-2024 8-6 Appendices Appendix StorrnvvaterSvstern Maps by Basin Appendix 8 Drainage, Water Quality, and Fish Habitat Characterization Appendix [ Surface Water Regulations and Policies Appendix [> Surface Water Issues and Solutions Appendix ESurface Water Capital Projects and Studies Appendix FSupporting Studies for Programmatic QPs Appendix GPublic Comments CONTENTS Acronyms and Abbreviations 6pP[} N-(1,3-dinnethy|butv|)-N'-phenyl-p-pheny|enediannine 6PPO-q 0PPO-quinnne 8-|8| Benthic Index OfBiotic Integrity BK4P Best Management Practice CB[} Southeast Central Business District [BP] Community -Based Public -Private Partnerships CCTV Closed Circuit Television CTP Cooperative Technical Partners Ecology Washington State Department ofEcology EK4P Enhanced Maintenance Plan EPA U.S. Environmental Protection Agency ESA Endangered Species Act FEK4A Federal Emergency Management Agency G|S Geographic Information System HAHD Howard A.Hanson Dam |LA |nter|Oca|Agreennent KCFCD King County Flood Control District LF linear feet L|[} Low Impact Development nng/L milligrams per liter MS4 Municipal Separate Storm Sewer System NK4FS National Marine Fisheries Service N[)AA National Oceanic and Atmospheric Administration NPDES National Pollutant Discharge Elimination System NPOES Phase|| Permit NP[)ESPhase || Municipal StorrnvvaterPerrnit {)8{K4 Operations and maintenance PE|S Programmatic Environmental Impact Statement R{}VV right-of-way SEPA State Environmental Policy Act SK4AP Storrnvvater Management Action Plan STORM StorrnvveterOutreach for Regional Municipalities SVVCP Surface Water Comprehensive Plan TK4[}L total nnaxirnunn daily load TSS total suspended solids TUC Tukwila Urban Center VV[)FVV Washington Department ofFish and Wildlife VVR|A Water Resource Inventory Area VVSOC)T State OfWashington Department 0fTransportation iv CONTENTS The City of Tukwila acknowledges the land and water addressed in this 2024 Surface Water Comprehensive Plan is the ancestral lands and water of the Coast Salish people of past and present who have been living and working here since time immemorial. The City recognizes and honors with gratitude their elders past and present. This acknowledgement does not take the place of authentic relationships with tribal communities but serves as a first step in honoring the land we are on and the people and the cultures it has nurtured. Executive Summary This 2024 Surface Water Comprehensive Plan (SWCP) is an update to the SWCP prepared in 2013. The purpose of this Surface Water Comprehensive Plan is to provide a strategic framework for the management of surface water within the City of Tukwila. The 2024 SWCP strives to have a multi -benefit approach to surface water management by: • Protecting the public's health and safety • Protecting public property, private property, and roads from localized flooding from stormwater drainage • Conserving and enhancing the natural aquatic systems within the City • Restoring salmon habitat and improving access to salmon habitat • Coordinating with Tribes within whose ancestral lands the City of Tukwila is located • Aligning with regional surface water plans and projects • Having a clear understanding of the existing stormwater system • Maintaining compliance with local, state, and federal regulations related to surface water The recommendations outlined in the 2024 SWCP consist of programmatic solutions and policies, studies, and capital projects. Not all capital improvement projects (CIPs) are recommended for implementation in this surface water planning window, due to funding availability. The tables below outline the recommendations by priority. Table E-1 High Priority Capital and Programmatic Recommendations Recommendation Reason Implementation In -progress Surface Water CIPs identified in the City's 2023-2028 Capital Improvement Program Ongoing Prior years — 2025 or beyond Programmatic changes pursuant to 2024-2029 NPDES Phase II permit requirements - TBD Maintain regulatory compliance 2025-2029 CIP-1 Norfolk Outfall Trunkline Sewer Separation Preliminary Feasibility Study Reduce potential City liability for combined sewer overflows and responsibility for Superfund site cleanup 2025 E-1 EXECUTIVE SUMMARY Table E-1 High Priority Capital and Programmatic Recommendations Recommendation Reason Implementation CIP 91241202 Stormwater Outfalls Water Quality Retrofit Program Grant award received; meets regional priorities for reducing harmful effects of urban runoff on water bodies; completes programmatic CIP begun in 2017 2024 CIP 99441202 Soil Reclamation Facility / Enhanced Maintenance Program and Decant Facility Design — Part 1 Grant award received; supports NPDES Phase II permit requirements; meets regional priorities for reducing harmful effects of urban runoff 2024-2025 Stormwater Management Action Program (SMAP) CIPs Meets expected requirement of 2024- 2029 NPDES Phase II permit; meets regional priorities for reducing harmful effects of urban runoff on water bodies; eligible for grant funding Begin 2025, then ongoing every 2-3 years WSDOT Retrofit Program Required in order to charge surface water management fee to WSDOT; meets regional priorities for reducing harmful effects of urban runoff on water bodies; funded by WSDOT 2024 and annually CIP-102 Middle Fork Southgate Creek — Stream and Slope Stability Study Stream condition severely degraded and private property at risk. Coordinates with ongoing Southgate Hydraulic Study encompassing Normed Facility and could make use of findings from City's successful FEMA-funded landslide study. 2026 OP-3 Fort Dent Park Water Quality Retrofit, Alternative 1 Meets regional priorities for reducing harmful effects of urban runoff on water bodies; low-cost alternative that can be implemented by City crews. 2027 CIP-2 S Ryan Way Pipe Rehabilitation Collaboration with City Transportation Department; preventive repair and replacement; reduce sheet flow on steep high -traffic roadway Coordinate timing with City Transportation Department MS4 mapping and documentation programmatic recommendations City risks permit non-compliance. Barriers to information sharing hinders stormwater planning, regulatory review of development and construction, inspection and enforcement, and capital project development. 2025-2029 E-2 EXECUTIVE SUMMARY Table E-1 High Priority Capital and Programmatic Recommendations Recommendation Reason Implementation Apply for grant funding for eligible phases of programmatic water quality CIPs and medium priority projects identified below Allows City to continue to fund higher levels of capital investments without impacting surface water utility rates 2024-2034 Ecosystem Services Conservation Program Reduces disparities in access to healthy environments, improves interdepartmental coordination in working on regional priorities such as reducing harmful effects of urban runoff, increasing access to fish habitat, and increasing quality of fish habitat Begin 2025 Regulatory and Policy change - omit the current regulatory enforcement procedure which permits temporary gravel parking lots to be constructed without stormwater drainage and runoff treatment facilities and then effectively to become permanent untreated impervious surfaces. City risks permit non-compliance. Strategically time interdepartmental negotiations and policy -setting with reissuance of NPDES Phase II permit in 2024. 2025 OP-104 Tukwila Master Plan for the Lower Green River Levee Projects Flood protection projects sponsored by KCFCD and federal partners are imminent. City will need to begin master planning immediately in order to guide aesthetic and community considerations of these projects. Begin 2025 Table E-2 Medium Priority Capital and Programmatic Recommendations Recommendation Reason Implementation CIP 98641222 S 143rd St Storm Drain System Longstanding drainage / flooding issue which may be eligible for grant funding from KCFCD 2027 CIP 99441202 Soil Reclamation Facility / Enhanced Maintenance Program and Decant Facility Design — Part 2 Increase efficiency and effectiveness of operations and maintenance program 2026 E-3 EXECUTIVE SUMMARY Table E-2 Medium Priority Capital and Programmatic Recommendations Recommendation Reason Implementation CIP 98741202 Nelson/Longacres — Phase II Longstanding drainage / flooding issue which requires coordination with railroad and may be eligible for grant funding from KCFCD 2028 OP-6 Johnson Creek Fish Barrier Mitigation Alternatives Analysis Meets regional priorities to increase access to fish habitat; ensures balanced portfolio of CIP projects by including fish barrier removals at regular intervals 2026 OP-90341214 S 146th St and 35th Ave S Drainage Longstanding drainage / flooding issue which may be eligible for grant funding from KCFCD 2029 The 2024 SWCP provides a strategic framework for the management of surface water within the City of Tukwila. It is an ambitious proposal for tackling drainage issues, water quality issues, erosion/sedimentation issues, habitat loss, and maintenance and condition of the stormwater system. The 2024 SWCP recognizes that City of Tukwila can be a key partner with state agencies, King County, Tribes, and organizations in reaching toward regional priorities to protect and restore the region's cherished natural resources. The City of Tukwila Public Works Department asserts that the 2024 Surface Water Comprehensive Plan would not have significant adverse impacts on the environment. The attached SEPA Environmental Checklist provides more information related to this 2024 Surface Water Comprehensive Plan. E-4 1.0 Introduction The City of Tukwila's Surface Water Management Program in the Public Works Department serves Tukwila rate payers in managing storm water and protecting surface waters that are important for fish and wildlife and for people as recreational amenities for boating, fishing, and enjoyment. The Surface Water Management Program plans and implements projects that manage flood hazards, improve water quality, restore habitat, and often serve as public amenities. These multi -beneficial projects are capable of garnering broad support from granting agencies, working in tandem to support Tribal treaty rights, Federal Clean Water Act and Endangered Species Act requirements, while addressing a variety of City Comprehensive Plan goals and regional goals. Tukwila is an integral member of WRIA 9, a keystone city where salt water of Elliott Bay and fresh water from the Green and Black Rivers mix in the transition zone of the Duwamish River. Water quality impairments and loss of aquatic and riparian habitat due to flood control projects and land development have degraded the Green/Duwamish River and threaten the existence of Chinook salmon, steelhead, and the iconic Southern Resident Killer Whales (Orca) that depend on Chinook salmon for food. The Surface Water Management Program works in partnership with Water Resource Inventory Area 9 (WRIA 9), the King County Flood Control District, Our Green- Duwamish Partnership, non -governmental organizations, and others to create a resilient, equitable and sustainable future centered around a vision of a community connected to its river. Section 1.0 Introduction introduces the topics and concepts that will be explored in further detail in the plan within the following sections. Section 2.0 Drainage Basin and Watershed Characteristics summarizes the existing conditions of the waters and watersheds within the City, and how their conditions have been influenced by local and regional changes to rivers and streams, vegetation cover, and land cover. Section 3.0 Regulations and City Policies summarizes the surface water regulations from federal and state agencies which guide the City's surface water compliance activities, and it introduces the City policies pertinent to regulating surface water. Section 4.0 Coordination with Regional Plans describes regional efforts and plans to address widespread and systemic problems such as salmon recovery, Puget Sound recovery, flood protection, and watershed protection which are supported by the City. 1-1 1.0 INTRODUCTION Section 5.0 Surface Water Known Issues and Solutions identifies the numerous specific drainage, erosion, water quality, and habitat issues within the city limits and presents a menu of solutions to address the types of problems identified. The section also prioritizes the issues and solutions. Section 6.0 Capital Improvement Projects and Studies describes the projects and studies selected to solve the priority issues identified in Section 5.0. Section 7.0 Operations and Maintenance was not updated for the 2024 Surface Water Comprehensive Plan and will likely be reinstated in the next 10-year update. Section 8.0 Recommendations proposes an implementation plan which discusses funding, partnerships, and priorities. 1.1 Background The purpose of this Surface Water Comprehensive Plan is to provide a strategic framework for the management of surface water within the City of Tukwila. It further serves as a guidebook for City staff to define and build upon for capital projects, work programs, and strategies for meeting existing and future surface water management needs. The 2024 Surface Water Comprehensive Plan (2024 SWCP) is intended to be a flexible document that may be revised should priorities or regulatory requirements change. It can also serve as a reference for City departments whose activities may impact surface water drainage, water quality, or aquatic habitat. This 2024 SWCP is an update to the Surface Water Comprehensive Plan prepared in 2013 (CH2MHILL, 2013). Previous surface water plans were prepared in 2003 and 1993. The 2024 SWCP addresses changes that have taken place since 2013, including addition of new positions, stormwater planning, emerging pollutants, changing regulatory requirements, and strengthening partnerships to address regional goals. See Section 3.0 for more information on the changing regulations and Section 4.0 for more about regional partnerships. The 2024 SWCP also reflects the surface water capital and non-structural investments that the City of Tukwila has made since the 2013 Surface Water Comprehensive Plan, including addressing priority drainage, water quality, and aquatic habitat issues identified in that plan. The City has made significant progress since the 2013 Surface Water Comprehensive Plan was drafted. Tukwila completed numerous projects identified in that plan, some projects are in progress in 2024, and some projects were identified subsequent to that plan and have been started or completed. 1-2 1.0 INTRODUCTION The following are completed or resolved projects that were identified in previous surface water plans: • East Marginal Way S Stormwater Outfall and Conveyance Inspection (91041204) • 53rd Ave S Storm Drain System (90341213) • Gilliam Creek 42nd Ave S Culvert (99341208) • Christensen Rd Pipe Replacement (98941202) • Storm Lift Station No. 15 Improvements (91041203) • Foster Golf Course Riverbank (90330106) • Riverton Creek Flapgate Removal (99830103) • Duwamish Gardens (90630102) • Minkler Boulevard Culvert Replacement (90341208) o Note: This project was intended to address local flooding. It was not completed because a redevelopment project upstream resolved the issue. The following projects identified in previous planning documents are now in -process: • Gilliam Creek Fish Barrier Removal (99830105) • Lower Gilliam Creek Channel Improvements (90330116) • Nelsen Side Channel Habitat Assessment (90330104) • Duwamish Riverbank Stabilization 1B at S 104th St (99441205) • Duwamish Riverbank Stabilization II near S 115th St (99441209) • Northwest Gilliam Storm Drainage System (90341206) o Note: A portion of this project has been completed. The remaining portion is on the 2024 Small Drainage Project List. • Water Quality Retrofit Program (91241201) o Note: One of three identified project locations, S 122nd St, is not complete. The following projects and changes to the Surface Water Management Program were identified or implemented following the completion of the 2013 Surface Water Comprehensive Plan as priorities and regulations changed and opportunities arose: • The Surface Water Management Program added staff to support regulatory compliance and expanding program goals: o In accordance with the 2013 recommendation, the City added a Habitat Project Manager position to the Surface Water Management Program in 2015 1-3 1.0 INTRODUCTION to manage time -sensitive and critical habitat restoration projects. The position has been reclassified to a Surface Water Project Manager, which allows the position to manage a range of multi -beneficial projects. o The City added a Levee Project Manager position to the Surface Water Management Program in 2021 to manage and facilitate levee projects in partnership with the King County Flood Control District and the U.S. Army Corps of Engineers. The position also manages the effort to get the Tukwila 205 levee certified and ultimately accredited by the Federal Emergency Management Agency (FEMA) and oversees the City's Floodplain Permit requirements for development. o In 2022, the City expanded the Surface Water Management Program workload by adding business source control inspections and fats -oils -grease (FOG) compliance inspections. As a result, a second inspector was added to the Surface Water Management Program. The positions are classified Environmental Compliance Inspector to reflect the broader scope of work. • Completed the Stormwater Management Action Plan (SMAP) for Riverton Creek (see Appendix F). • Completed Stormwater Outfall Water Quality Retrofit Project Design Report (for four projects in the Green/Duwamish Basin). o Stormwater Outfalls Water Quality Retrofit Project (for four projects along the Green/Duwamish River). Two sites along Tukwila International Boulevard and Interurban Avenue South are under construction as of the writing of this plan. • Ongoing programmatic changes as a result of reissuance of the National Pollutant Discharge Elimination System Phase II Permit (NPDES Phase II Permit) in 2019. • Began a sediment transport and flooding study along the main stem of Southgate Creek. • Obtained a grant to begin a City-wide Landslide Study with a grant from FEMA. • Created the "Green the Green" Program to fund shoreline revegetation projects on public lands and through public -private partnerships. The City is in the maintenance phase of two installed projects at NC Machinery and the Southcenter Office Park and is working with MidSound Fisheries on a shoreline revegetation and depaving project on West Valley Highway. • Identified and began the S 131st PI Drainage Improvements project (91641204). 1-4 1.0 INTRODUCTION • Identified the need for improving the surface water inventory and committed funding for it (90241201 and 80241201). • Started the Chinook Wind Trail Project and completed Chinook Wind Public Access Project to connect the Chinook Wind Mitigation Site (by King County's Mitigation Reserve Program) to the Duwamish Gardens, which began as a Surface Water Management Program habitat restoration initiative in 2015. 1.2 Plan Objective As documented within this 2024 SWCP and in numerous regional studies and plans, Puget Sound, the Green River, the Duwamish River, and local streams have been extensively impacted by various and interrelated human alterations of the water bodies and lands that drain to them. Impacts include, but are not limited to, direct loss of habitat for salmon due to construction of levees and bank armoring, reduction of fish access to portions of the water bodies due to construction of impoundments such as dams and floodgates, introduction of pollutants that kill or damage fish and other aquatic life from agriculture, industry, and urban stormwater runoff, and loss of vegetation which absorbs and evaporates rain and shades streams and rivers to provide cool temperatures needed by many native aquatic species and salmon. The overarching goal of the 2024 SWCP is to advocate for Tukwila's strong participation with county, state, and federal partners to address regional surface water goals while providing high quality stormwater drainage and water quality service to the citizens of Tukwila. In service of the overarching goal, the objectives of this 2024 SWCP include providing a surface water management framework that will protect the public's health and safety, protect both public and private property, conserve and enhance the natural aquatic systems within the City, participate in regional restoration of salmon habitat, coordinate with regional surface water plans and projects, have a clear understanding of the existing stormwater system, and maintain compliance with local, state, and federal regulations related to surface water. This Plan is also intended to support Tukwila's elected officials in advocating for the City's identified priorities and needs in a regional setting. The 2024 SWCP strives to have a multi -benefit approach to surface water management. As a result, where possible, the projects and programs identified serve multiple purposes, including, but not limited to, water quality improvement, flood risk reduction, habitat restoration, community amenities, recreation, and equitable distribution of resources. An outcome of the 2024 SWCP is to acknowledge and support the City's active role in addressing regional and watershed -wide problems, and to document how the City can 1-5 1.0 INTRODUCTION leverage regional programs to address local needs. Current City program guidance comes from the following: • Flood Control — the City has an Interlocal Agreement (ILA) with the King County Flood Control District (KCFCD) in which the KCFCD manages, maintains, repairs and funds levee projects, along with the US Army Corps of Engineers (for Federally - authorized levees), along the Green River. The Tukwila Levee Accreditation Phase 1 (NHC, 2015) & Phase 2 (NHC, 2019) as well as the Green River System Wide Improvement Framework (SWIF) (KCFCD, 2019) are guiding documents for City flood hazard management priorities and recommendations for implementation. KCFCD Motion 20-07 declared the King County Flood Control District's commitment to integrated floodplain management and multi -benefit projects and to the principles of environmental stewardship, equity, social justice, and environmental justice, and it redefined how the District plans capital projects and reimagined how the District designs projects. • Water Quality — the City is a member of Our Green Duwamish Partnership, which is an emerging group among jurisdictions in the watershed and partners to address regional water quality issues. This group is working to establish a formal framework for membership similar to WRIA 9 or KCFCD. • Habitat Restoration — the City is a paying jurisdictional member of WRIA 9, formed to guide recovery of the ESA -listed Puget Sound Chinook salmon, listed as threatened in 1999. Steelhead, bull trout, and Southern Resident killer whales have been listed since then. The WRIA 9 Salmon Habitat Plan includes projects along the Green/Duwamish River within the City of Tukwila; when the City to sponsors habitat projects, the City may qualify for funding from various sources for project implementation. • NPDES Phase II Permit — this City-wide permit, issued by the Washington State Department of Ecology (Ecology), is coordinated through the Surface Water Management Program. The permit, reissued and expanded every five years, places increasingly greater emphasis on, and requirements of, permittees to make measurable improvements in water quality through actions like water quality retrofits, regional partnerships to address large- scale water quality problems, source control, urban forestry, stormwater planning, mapping, and policy implementation. • Move Ahead Washington's Stormwater Retrofit Proviso, 2022 provides funding for water quality retrofits on priority state highways for 16 years. Several state highways cross the Green/Duwamish River and tributaries in Tukwila, and the state's preliminary draft prioritization of state highways segments for runoff treatment 1-6 1.0 INTRODUCTION includes several highway segments in Tukwila. Proving treatment for runoff from state highways before it enters surface waters is a state priority and a local priority for Tukwila. 1.2.1 City Comprehensive Plan Goals and Policies This 2024 SWCP supports the draft 2024-2044 Tukwila Comprehensive Plan and the Washington State Growth Management Act (GMA) which requires the City to develop a comprehensive plan. The GMA has several goals which are relevant to this 2024 SWCP. The GMA aims to protect the environment, water quality, and shorelines of the state. It seeks to ensure that cities provide adequate public facilities and services, including stormwater conveyance and facilities, necessary to support development. The City's capital plans, including this 2024 SWCP, are integrated into the City's Capital Facilities element of the Comprehensive Plan. The Capital Facilities element is required to include an inventory of capital facilities, a forecast of future needs, proposed expanded or new capital facilities, and a six -year plan to finance capital facilities projects. One of the key links between the two plans is the following policy: • Use the Surface Water Fund to retrofit surface water systems to improve water quality, support forest conservation and restoration, restore aquatic and riparian habitat and enhance fish passage by establishing an urban canopy preservation program that emphasizes support for Citywide canopy preservation policies and strategies. The 2024 Comprehensive Plan also informs this 2024 SWCP. The draft Comprehensive Plan outlines several key ideas that are important to surface water management, including but not limited to: • Tukwila is envisioned as a high -performing, service- and results -oriented government that recognizes and solves problems. • Growth is managed in a way that protects the environment. • Ensuring plans, such as the Surface Water Comprehensive Plan, benefit existing and future populations in an equitable manner. • Promote affordable and equitable access to public services to all communities, especially underserved communities. • Retention and planting of trees. • Increasing resiliency to climate change. • Functional, healthy water resources for fish, wildlife, human safety, and recreation. 1-7 1.0 INTRODUCTION • Vital and self-sustaining fish and wildlife habitat areas and corridors that are protected and restored. • An open space network that is protected and expanded through acquisition, donation, easements, partnerships, and regulation. 1-8 2.0 Drainage Basin and Watershed Characteristics This section contains a description of the physical characteristics of the City of Tukwila. Drainage, water quality, and aquatic habitat conditions are also presented. Appendix A contains maps of the City's public stormwater system by basin. Appendix B contains the detailed information in support of this section. 2.1 General Description The City of Tukwila encompasses approximately 9.7 square miles straddling the Green and Duwamish Rivers (Figure 2-1). The climate is strongly influenced by the Pacific Ocean with wet and mild winters with temperatures varying from 30°F to 50°F and dry and cool summers with temperatures typically less than 80°F. The average annual precipitation is between 32 and 38 inches. The Green and Duwamish Rivers, tributaries, and associated floodplains dominate the geography and topography of Tukwila. Relatively flat, and poorly drained floodplains exist adjacent to the rivers and steep valley walls dominate the areas on the west side of Tukwila along the 1-5 corridor. Soils in the valley floor tend to be fine sandy loam and silty clay loam (Newberg and Woodinville Series, respectively). The valley walls typically are comprised of soils from the Alderwood Series (interbedded silts and clays) and are characterized by numerous hillside springs and the accompanying potential for instability. All of the surface waters in the City of Tukwila eventually discharge to the Green/Duwamish River. In Tukwila, the Green/Duwamish River flows northward along 14 river miles, meandering through the entire length of the City, from river mile 17.3 at Kent city limits to river mile 3.3 at Seattle city limits. The Green/Duwamish River is tidally influenced within the Tukwila city limits. Tidal fluctuations are recorded as far upstream as the Auburn stream gauge, upstream of the City of Kent. The salinity transition zone occurs from river mile 1 to 10, located downstream of the 1-5 crossing in Tukwila. The historic Black River confluence with the Green/Duwamish River at river mile 11 defines the transition zone from the Green River to the Duwamish River. Tukwila's hydrology today is vastly different from its historic state, when forested floodplains spanned the valley, which was flattened during glacial recession and overlain with deposits from Mount Rainier's volcanic activity. At that time the White River, which now flows west and south into the Puyallup River and into Commencement Bay, met the Green River south of Tukwila and flowed north to Elliot Bay. In 1906, a large debris jam diverted the White River at Auburn towards the south, reducing the volume of the Green River. Historically, Lake 2-1 2.0 DRAINAGE BASIN AND WATERSHED CHARACTERISTICS Washington drained into the Black River, which flowed south, meeting the White River (now the Green River) at Tukwila, and forming the Duwamish River. The Black River dried up in the early 20th Century after extensive changes to regional hydrology for the purposes of industry and flood control, including the following: construction of the Lake Washington Ship Canal, which moved the outlet of Lake Washington to the north, and diversion of the Cedar River from the Black River to Lake Washington to avoid flood risk in Renton. Construction of the Howard A. Hanson Dam changed the flow regime and transport of sediment from the Upper Green River into the Middle and Lower Green River segments by retaining snow melt and precipitation and controlling flows. The culmination of these regional changes to hydrology has led to a much -altered hydrologic character in Tukwila. 2-2 FIGURE 2-1 VICINITY MAP TUKWILA SWCP 133383 TUKWILA, WASHIINGTGN Legend © City Boundary I Neighboring Cities Streams and Rivers Da;a Su0n:es Kirp Ca0rty City of Iuukwr e ( iolllj 0 Maps tia+a 1l2G+2004 Grsch rrrs Ths ep'a 1s,ot "uvey 0003:a y and u macn) fol plan'it 1p pr.ra.rses rrr�v [:33311,0)333888A0()tGMAPRKs) 33381 tu. Wr n SWCP S 0uma33183 SWf:P <•a 0oo aprc Q CITY OF C BELLEVUE 5 Miles Otak 2.0 DRAINAGE BASIN AND WATERSHED CHARACTERISTICS 2.2 Population, Existing Land Use and Future Development The City of Tukwila's population in 2023 was 22,780, with an estimated with an estimated 46,000 people employed at businesses located within the city limits. The resident population of Tukwila is expected to increase by approximately 17,000 by 2044. Any further increase in residents would be due to redevelopment that may increase residential densities. Tukwila's Southcenter Urban Center and the undeveloped Tukwila South area is expected to accommodate the majority of this residential growth. Additional employees working in the City of Tukwila are expected to be accommodated in the Southcenter Urban Center and the Tukwila Manufacturing and Industrial Center. The 2044 targets for additional housing units and employees are 6,500 and 15,890, respectively. The City of Tukwila has relatively few areas of undeveloped land which are not significantly encumbered by critical areas. The remaining large tracts of developable undeveloped land are located in the Tukwila South area. The City's remaining undeveloped land are in sensitive areas and in locations that are difficult to build on, such as wetlands, floodplains, seeps, steep slopes, and buffers. Figure 2-2 shows the zoning within the City of Tukwila in 2024 and Table 2-1 lists the distribution of land uses by drainage basin. Land use, re -development, and future development are pertinent to the Surface Water Management Program because urbanization and development create impacts on surface waters such as: • Polluted stormwater runoff that contributes to poor water quality in streams, lakes, rivers, and Puget Sound which impacts fish, wildlife, and human health. • Changes to stream flow due to placement of culverts, levees, or bank armoring that can prevent fish from accessing or using streams and rivers for migration, spawning, and rearing. • Loss of riparian vegetation to shade streams, lakes, and rivers, which keeps them cool and helps maintain adequate dissolved oxygen levels for fish. • Increase in velocity, volume, and duration of stormwater flows in streams that can lead to erosion and accelerated rates of sediment transport, with impacts both to municipal infrastructure and to aquatic habitat. • Increase in velocity and volume of stormwater flows in streams that can reduce ability of fish to rest, forage for food, survive, or use the stream. 2-4 CITY OF BURIEN Legend c3 City Boundary r J Neighboring Cities — Streams and Rivers Zoning Description (2015) CLI,Commercial Light Industrial HDR,High Density Residential HI,Heavy Industrial DR,Low Density Residential LDR,Manufacturing Industrial Center/Light I,Light Industrial MDR,Medium Density Residential MIC/H,Manufacturing Industrial Center/Heavy IC/L,Manufacturing Industrial Center/Light UO,Mixed Use Office NCC,Neighborhood Commercial Center O,Office RC,Regional Commercial RCC,Residential Commercial Center RCM,Regional Commercial Mixed Use TUC-CC,Commercial Corridor TUC-P,Pond TUC-RC,Regional Center TUC-TOD,Transit Oriented Development 1 TUC-WP,Workplace TVS,Tukwila Valley South CITY OF SEATAC CITY OF, KENT FIGURE 2-2 CITY ZONI''' IIG TUKWILA SWCP 133383 TUKWILA, WASHIINGTON Q 1 Mile Data rttorrms K,r3CuJrty City data from 201.5 Date 3r1rf12a2a rYsctarr or Tris cea is 8.4 to srrvay a,, orary anti ,s meant for Clanoaq W rrorso, or y t) \(',Kar[ C,1,331$04333R,nGN)1)K;IS\ 83RXr, ;3383 "(yaw, d SWG13 t 5010s33338310w is 0W200 r quro, aprx Otak 2.0 DRAINAGE BASIN AND WATERSHED CHARACTERISTICS Table 2-1 (Revised 3/4/2025) Tukwila Zoning and Land Use by Basin (2022) Basin Name Low -Density Multi -Family Residential Residential Industrial Commercial Wetland or Park Right -Of -Way' Other % of % of % of % of % of % of % of Acres Basin2 Acres Basin2 Acres Basin2 Acres Basin2 Acres Basin2 Acres Basin2 Acres Basin2 Gilliam Creek 433 33% 127 10% 9 1% 232 18% 58 4% 383 29% 73 6% Green/Duwamish 492 19% 31 1% 638 25% 424 16% 206 8% 449 17% 350 14% River Johnson3 31 11% 0 0% 0 0% 203 70% 21 7% 34 12% 0 0% Mill Creek 0 0% 0 0% 5 5% 68 78% 0 0% 12 14% 2 3% Nelsen 3 3% 0 0% 21 19% 38 35% 1 1% 24 22% 22 20% P17 47 6% 4 0.5% 33 4% 445 55% 33 4% 94 12% 152 19% Riverton Creek 106 26% 1 0.3% 9 2% 148 37% 14 4% 100 25% 25 6% Southgate Creek 249 50% 35 7% 1 0.3% 56 11% 29 6% 107 21% 27 5% Springbrook Creek 0 0% 0 0% 23.8 51% 0 0% 23.2 49% 0 0% 0 0% 'ROW boundaries used for this analysis are imprecise; these values are approximate. 2 % of Basin calculated on area within city limits only. 3 Wetland or Park boundaries for Johnson are estimated; this value is approximate. 2-6 2.0 DRAINAGE BASIN AND WATERSHED CHARACTERISTICS Stormwater management on re -development and future development sites is undertaken in accordance with the City's storm drainage manual, which is the latest version of the King County Surface Water Design Manual (2021, at the time of writing of this plan) and the latest version of the City's Infrastructure Design and Construction Standards (2019, at the time of writing). The City has identified areas where infiltration is not allowed as a surface water management approach due to steep slopes and/or high groundwater table (Figure 2-3). The City of Tukwila has established three levels of flow control standards covering different basins plus one area with a basin -specific standard established in a developer agreement for the Tukwila South project (Figure 2-4). Tukwila has established Basic Flow Control, Conservation Flow Control, and Flood Flow Control areas. Chapter 5 of the City's Infrastructure Design and Construction Standards (City of Tukwila, 2019) includes descriptions of each of the flow control levels applicable within the city limits. The basin - specific flow control requirement, which is located in the southern portion of the P17 Basin and in the Johnson Creek Basin, will revert to the Conservation Flow Control level when the developer agreement expires in December 2024. Upon expiration of the developer agreement, the City will regulate new development in the undeveloped portions of the P17 Basin and Johnson Creek Basin using the Conservation Flow Control standard. The 2024 SWCP uses basin boundaries which were updated based on current drainage patterns during the development of the SMAP. Because of the basin boundary changes developed pursuant to the SMAP, the basin boundaries used in the 2019 Infrastructure Design and Construction Standards to define the areas where various flow control levels apply are now outdated. The City will update the Infrastructure Design and Construction Standards in 2025. The boundaries of the flow control levels should be updated at that time. Figure 4 is labeled with the basin names that match current basins in Table 5.0.1 — Flow Control Standards by Drainage Basin — in the Infrastructure Design and Construction Standards as well as the basin names used in the 2024 SWCP in parenthesis. 2a Areas where infiltration not allowed Drainage Basins N 0 1 2 11111111111 Miles FIGURE 2-3 Infiltration Not Allowed City of Tukwila 2012 Surface Water Comprehensive Plan SEA \\SIMBA\PROD\TUKWILAWACITYOF\412954SWCOMPPL\GIS\LAYOUT\FIGURE4_NOINFILTRATION.MXD TJANTZEN 4/2/2013 10 27 31 CH2MHILL CITY OF DES FIGURE 2-4 FL W CONT'u L STANDAR S BY BASIN TUKWILA SWCP 133383 TIKWIILA, WASH NGTON Legend ® City Boundary J Neighboring Cities - Streams and Rivers Dab 31?5f2f1P4 Daschu, ar i[ rs ta'n is ;,t'n a, auy a • ura a and r, rr r not far pl„nrr ry purp,)r©s ar ry t�4'RU11 (, rr333lC\333533^,N)[))Crsa rrXaar383 rrxxwr a SWCP rr raa\Yraa3Jr!karja SWrrrr array rrrx CITY OF RENTON Nelsen Place ong Acres Basin, (Nelsen)°;� StranderPum Station Basin, :4> (Green/Duwamish) Lower Mill Creek Basin, (Mill Creek) CITY OF.KENT .'Gilliam'", Creek Basin, East of I-5,,''' (Gilliam) Basin; Flow Control Standard Conservation FC Area iIIIM Basic FC Area Basin Specific Flood FC Area (Existing) 0 Mile Otak 2.0 DRAINAGE BASIN AND WATERSHED CHARACTERISTICS 2.3 Drainage Basins The City is divided into nine drainage basins (Figure 2-5): • Gilliam Creek • Green/Duwamish River Mainstem • Johnson Creek • Mill Creek • Nelsen • P17 • Riverton Creek • Southgate Creek • Springbrook Creek Portions of these basins are located outside city limits as shown in Table 2-2. The basin boundary delineations are based on information from field visits, the City Geographic Information System (GIS), and previously developed basin plans, including the Stormwater Management Action Plan (Appendix F). Table 2-2 Drainage Basin Areas Summary Basin Name Area of Basin in Percent of Basin Total Basin Area City of Tukwila in City of (Square Miles) (Square Miles) Tukwila Gilliam Creek 2.9 2.1 71.0% Green/Duwamish River 465.0 4.0 0.9% Johnson Creek 2.7 0.5 16.5% Mill Creek 8.0 0.1 1.7% Nelsen 0.2 0.2 98.7% P17 2.4 1.3 53.3% Riverton Creek 0.8 0.6 78.3% Southgate Creek 0.8 0.8 99.6% Springbrook Creek 3.6 0.1 2.0% Total 486.4 9.7 2-10 FIGURE 2-5 DRAINAGE BASINS TUKWILA SWCP 133383 TUKWILA, WASFflNGTON Cora Soi r es Kirp [,o arty fit rai Tr kwI P t'nor a Mnps D 3,2 ociPi Disrhimrr Fins moo/ 2r'7 io rpoont for pian , ip p rp isp, w`iY Legend © City Boundary r I Neighboring Cities Q Drainage Basins — Streams and Rivers OrP,,Oh Ci,1;3/fn333&1C,N1CPCIS•APRXsi,MP; 1rsxwrrr SWC3'SWCP a rrs oprx 0 Mile Otak 2.0 DRAINAGE BASIN AND WATERSHED CHARACTERISTICS 2.4 Drainage System Characterization All of the surface water in the City of Tukwila eventually discharges to the Green and Duwamish Rivers. The Green/Duwamish River is called the Duwamish below the confluence with the Black River and is called the Green River upstream of that point. Tukwila's drainage network consists of both closed -pipe and open channel conveyance. Numerous outfalls discharge directly to the river, while other outfalls discharge to creeks and some to wetlands. The outfalls with the largest discharge are typically associated with the creek systems located entirely or partially within the City, including Riverton Creek, Gilliam Creek, Southgate Creek, and Johnson Creek. Several of the creeks are fitted with tide gates or flapgates at the mouth, preventing river and tidal flows from flowing up into the drainage basins. The City has removed the flapgate at the mouth of Riverton Creek to increase access to salmon habitat. The City plans to evaluate and remove other tide gates and flapgates, if feasible. Tukwila's stormwater assets include pipes, manholes, ditches, ponds, culverts, detention facilities, runoff treatment facilities, and surface water pump stations. The City aims to update the inventory of stormwater assets routinely as projects are built which change the system. The data used in the 2024 SWCP was current as of 2021. Table 2-3 lists each of the City -owned surface water pump stations (also shown in Figure 2-5). Outfalls, tide gates, pump stations, and other drainage assets are shown in the Stormwater System Maps in Appendix A. Note that King County owns and operates a pump station (P17) within the City of Tukwila's P17 drainage basin, which is also shown on Figure 2-5 and in Appendix A. 2-12 2.0 DRAINAGE BASIN AND WATERSHED CHARACTERISTICS Table 2-3 Surface Water Pump Stations Station Name Physical Location Drainage Basin Ownership P17 Pump Minkler Public Works Facility P17 King County Flood Station Control District' Sta #15 5880 S 180th Street — P17 City of Tukwila near Claim Jumper Restaurant Stormwater Utility Sta #16 7420 S. 180t" Street — Springbrook Creek, City of Tukwila underpass Green/ Duwamish River Stormwater Utility Sta #17 530 Strander Boulevard — Bicentennial Park Sta #18 4225 S. 122nd Street — Allentown Sta #19 Fort Dent Park Green/ Duwamish River Green/ Duwamish River Green/ Duwamish River City of Tukwila Stormwater Utility City of Tukwila Stormwater Utility City of Tukwila Parks Department 1 This pump station is owned and operated by the KCFCD and manages City of Tukwila stormwater systems draining to the P17 pond. Supporting information for the drainage system, water quality, and aquatic habitat characterizations located in Sections 2.4, 2.5, and 2.6, respectively, was developed for the 2013 Surface Water Plan and is contained in Appendix B. Updates for the 2024 SWCP have been incorporated directly into the sections. Appendix B has not been updated except for the fish barrier inventory (Attachment A to Appendix B). Appendix B otherwise remains unchanged for reference. 2.5 Water Quality Characterization This section contains a description of the water quality characteristics of Tukwila's receiving waters, all of which flow to the Green/Duwamish River. Water quality assessments of the receiving waters is assessed based on reports of historical contamination, Washington State water quality standards, biological conditions of streams, water quality sampling, and anecdotal reports. Overall, the water quality of the Green/Duwamish River and its tributaries is poor with a designated Superfund site, state water quality standards not being met, poor to very poor aquatic biological conditions, observed salmon mortality, and ongoing concerns with trash, pollutants, and sedimentation. 2-13 2.0 DRAINAGE BASIN AND WATERSHED CHARACTERISTICS 2.5.1 Superfund The northern -most portion of the City of Tukwila lies within the Lower Duwamish Waterway Superfund Site, designated by the U.S. Environmental Protection Agency (EPA) in 2001. King County, the Port of Seattle, and the cities of Seattle and Tukwila are working with Ecology and the EPA to control sources of pollution in the Lower Duwamish Waterway. Ecology is the lead agency for implementing source controls in the Lower Duwamish Waterway. In 2002 the City of Seattle, King County, and the Boeing Company developed a public -private partnership called the Lower Duwamish Waterway Group to coordinate source control activities. Five Early Action Area cleanups have focused on areas of highly contaminated mud on the river bottom which were predicted to reduce average PCB levels by 50% across the Lower Duwamish Waterway. Two early action sites in Tukwila and are at, or near, completion as of 2024. The Jorgensen Forge site in Tukwila is partially cleaned up with some pollution stabilized and left in place. The other, Boeing Plant 2, is a former industrial site. The cleanup effort involved dredging and removing contaminated sediments. Today, the waterfront is an award -winning new habitat area. 2.5.2 Washington State Water Quality Standards In 2003, Ecology adopted a water use -based classification for state surface waters (RCW 173-201A, Table 602) that determines the surface water quality standards applicable for that water body (RCW 173-201A-600(1)). The available classifications of designated uses, or beneficial uses, include, but are not limited to, aquatic life uses such as salmonid spawning, rearing, and migration, recreational uses, water supply uses, and miscellaneous uses. The designated uses Ecology has established for the Duwamish River in Tukwila are Salmonid Rearing/Migration Only and Primary Contact Recreation. The designated uses Ecology has established for the portion of the Green River in Tukwila are Salmonid Spawning/Rearing and Primary Contact Recreation. Ecology sets state water quality standards for water bodies based on their established uses. None of the tributaries to these rivers within Tukwila is called out in Table 602. Therefore, the uses defined for tributaries are the same as the river to which they discharge. Riverton Creek and Southgate Creek discharge to the Duwamish River so they have a use -based classification of Salmonid Rearing/Migration and Primary Contact Recreation. Gilliam Creek, Johnson Creek, Springbrook (Mill Creek), and P17 drainage basins have a use -based classification of Salmonid Spawning/Rearing and Primary Contact Recreation. Ecology maintains a list of water bodies that do not meet water quality standards, known as the 303(d) list. The water quality assessment and 303(d) list for the state of Washington were updated in 2022. Figure 2-6 shows the 303(d) listed water bodies in Tukwila. The Green/Duwamish River within the City of Tukwila does not meet water quality standards 2-14 2.0 DRAINAGE BASIN AND WATERSHED CHARACTERISTICS according to the 2022 303(d) list. Both the Green River and Duwamish River are listed as Category 5 (at least one designated use is impaired) for dissolved oxygen, temperature, and pH, based on water sampling and analysis. There are Category 5 listings for Gilliam Creek for bioassessment, Johnson Creek (Angle Lake) for bacteria, Springbrook (Mill) Creek for bacteria, zinc, dissolved oxygen, and bioassessment, and Riverton Creek for bioassessment. 2.5.3 Benthic Index of Biotic Integrity Stream quality is also assessed using the Benthic Index of Biotic Integrity (B-IBI) data. The B- IBI scoring system is a quantitative method for determining and comparing the biological condition of streams with a higher B-IBI score out of 100 indicating better stream ecological health. A score lower than 20 is considered very poor, 20-40 is considered poor, 40-60 is considered fair, 60-80 is considered good, and 80-100 is considered excellent. The B-IBI score for Gilliam Creek is very poor (9.1), Mill Creek is poor (30.5) and very poor (14.5), and Riverton Creek is poor (28.9). No B-IBI sample locations were found inside the Green/Duwamish River, P17, Johnson Creek, Nelsen, Southgate Creek, or Springbrook basins. 2.5.4 Water Quality Sampling and Anecdotal Reports In a study conducted in June and September 1997, two Gilliam Creek samples were collected during summer baseflow conditions. Several samples taken during these months did not meet the then -current state dissolved oxygen water quality standard, with one sample recorded at 3.2 mg/L, well below the state water quality standard of 6 mg/L. These samples also fell slightly below the pH state water quality standard. In September, the measured stream temperature of 17.5 degrees Celsius barely fell below the state water quality standard of 18 degrees. Two years later water quality sampling was performed during storm runoff events in the fall of 1999 as part of the Gilliam Creek Stormwater Management Plan (Herrera Environmental Consultants, 2001). Temperature, dissolved oxygen, and pH (the latter with the exception of one sample) all met then -current state water quality standards during this sampling. Turbidity was somewhat elevated, generally ranging from 25 to 50 NTUs. Similarly suspended solids were also only modestly elevated, generally ranging from 20 to 60 milligrams per liter (mg/L). Dissolved lead met applicable water quality criteria, as did nearly 90% of the dissolved zinc samples. About half of the samples failed to meet the dissolved copper criteria. Finally, nearly all of the fecal coliform samples exceeded the state water quality standards. 2-15 2.0 DRAINAGE BASIN AND WATERSHED CHARACTERISTICS City -collected data from the lower reach of Gilliam Creek in 2018-2020 indicated concerns with pH, turbidity, and total suspended solids. Metals, dissolved oxygen, and temperature met then -current water quality standards in Gilliam Creek. Data from 2019 testing in Riverton Creek indicated there are concerns with dissolved oxygen. Temperature and pH met state water quality standards in Riverton Creek. Fish mortality due to urban runoff in Riverton Creek has been observed by City staff. Agricultural activities in the City of Kent likely contribute fecal coliform to Johnson Creek. City data in Southgate Creek basin from 1994 and 1995 indicates there are moderate concerns with dissolved oxygen and pH. In addition, Southgate Creek has sediment issues due to bank stabilization. Permitted (Hydraulic Project Approval) dredging maintenance is often required to manage sediment. Hydraulic Project Approvals from the Washington Department of Fish and Wildlife (WDFW) are required in or near state waters to ensure work activities, in this case dredging maintenance, is done in a manner that protects fish and their aquatic habitat. There are homeless encampments along the Green/Duwamish riverbanks that are prone to winter flooding and could contribute unknown debris and contaminants. In addition, Fort Dent Park has synthetic turf sports fields that could potentially be a source of 6PPD-quinone. However, further research is needed to determine if either of these situations pose a threat to water quality in the river. 2-16 FIGURE 2-6 ECOLOGY 303(D) LISTE WATER BOA IhS TUKWILA SWCP 133383 TUK nn Ay ASHNINGTON Ua'n_inl.lcry Ktrvy Cuarly City of 11.1,wtr 5n0r3'c Niop, I;a`e 312(I202C Ctschor r;t tp ccr,trpry arc] is rnranl fur pldncn ig pUrp.xs3s o55y Legend 0 City Boundary r J Neighboring Cities --- Streams and Rivers 0\PRo1FCls}31110\13383[CA[)13\CPSAPRXs\33383 Tuxwta SWOP F tgientt31383 Ti.kw,ta SWCP t p n., 303d anru Receiving Water Impairment Bioassessment Bacteria pH Dissolved Oxygen MI Temperature a Mile (t 1 Otak 2.0 DRAINAGE BASIN AND WATERSHED CHARACTERISTICS 2.6 Aquatic Habitat Characterization This section contains a summary of the existing conditions of the City's rivers and streams and their use by fish and other aquatic life. Anadromous fish such as various salmon species are the primary focus of this inquiry. Salmon and other anadromous fish spend a part of their life cycle in fresh waters such as streams and rivers, migrate to ocean waters, and typically migrate back to fresh waters to reproduce. Supporting information for the aquatic habitat characterization located in this section is contained in Appendix B. A detailed fish -blocking culvert inventory, updated in 2024, is included as Attachment A to Appendix B. 2.6.1 Green/Duwamish River Productive, good quality fish habitat, both in the main channel and in off -channel tributaries, is generally lacking along the Green/Duwamish River. Several factors explain the existing lack of fish habitat. The Green/Duwamish River course and flows have been significantly altered as described in Section 2.0 in ways that affect the presence of, and access to, aquatic habitat regionally. Significantly, regulation of flow in the Green River at the Howard A. Hanson Dam (HAND) has reduced seasonal flows and lowers the river elevation enough to disconnect it from its floodplain and tributaries, which historically provided rearing and high flow refuge. Little, if any, historical rearing habitat occurs in the City. The Green/Duwamish River channel has also been significantly altered from its natural condition along many reaches in the City of Tukwila. Development within the floodplain and buffers and construction of levees and revetments along the river shoreline disconnect critical floodplain and tributary habitat that support all salmon life stages, and in particular juvenile salmon during their out -migration through Tukwila. Levees and revetments are maintained free of tree canopy that would produce shade to cool the river and assist in maintaining healthy dissolved oxygen levels to support fish. Juvenile fish are particularly vulnerable to environmental conditions, and the absence of habitat that supports juvenile fish limits the population size that can survive and reach the Duwamish Estuary, Puget Sound, and the Pacific Ocean. Currently, most of the juveniles are being flushed down the Green/Duwamish River too quickly because they do not have places to rest, forage, and shelter from predation in the river. The absence of this type of habitat leads to mortality and/or arriving in the Duwamish Estuary underdeveloped and ill-equipped to survive the saline conditions. WDFW studies have shown that Chinook salmon that are able to find habitat and rear in the river and tributaries make up 93-95% of the adult salmon that return. 2-18 2.0 DRAINAGE BASIN AND WATERSHED CHARACTERISTICS On the contrary, salmonids that do not find adequate habitat only make up 5% of returning adults. Non-native and other less desirable trees and shrubs such as blackberry have replaced native riparian vegetation along the Green/Duwamish River. Riprap also borders the river along many reaches. While habitat conditions along the Green/Duwamish River are still poor a number of projects along the mainstem have improved pockets of habitat in Tukwila. Codiga Park (Army Corps, 2005), the first off channel habitat restoration project in the City, is a natural area that is a partially restored tidal wetland that now provides shelter for juvenile salmon. The Chinook Wind Mitigation project (King County Mitigation Reserves Program, 2023), Duwamish Gardens (City of Tukwila, 2016), North Wind's Weir (King County, 2009), and Cecil Moses Memorial Park (King County, ca. 2006) also provide habitat for juvenile salmon. A number of the more recent habitat projects are well -used, as documented by UW Wetland Ecosystem student study of "Juvenile Chinook Salmon Effectiveness Monitoring of Duwamish Shallow Water Restoration Sites." Despite these projects in Tukwila, numerous other levee setbacks, shoreline restoration in Puget Sound, and revegetation in the watershed, Chinook salmon numbers continue to decline in the watershed and region. In a 2019 Biological Opinion, the National Marine Fisheries Service (NMFS) identified the lack of fish passage at HARD upstream of Tukwila as a jeopardy to the viability of ESA -listed Chinook salmon, steelhead, and Southern Resident killer whales. In December 2023, Tukwila Mayor Allan Ekberg joined 32 other governments, organizations, and business in signing a letter supporting the HAHD downstream fish passage project, a project of regional and national significance that received $220 million in funding allocated through the federal government in 2022. The HARD downstream fish passage project would restore access to over 100-miles of salmon spawning habitat in the upper watershed and is believed to be the largest single opportunity to increase salmon production in the Puget Sound. The HAHD fish passage project has been a top priority of WRIA 9 since the 2005 Salmon Habitat Plan was published. The broad -based show of support over the last five years has been critical to continuing to advance this regionally significant project. There are restoration efforts addressing invasive species, such as Himalayan blackberries, along the Duwamish River shoreline to improve habitat. The Green the Green Program is working in concert with the Muckleshoot Indian Tribe to prioritize canopy restoration at specific locations to maximize shade, especially where there is an absence of shade at southern and western exposures. 2-19 2.0 DRAINAGE BASIN AND WATERSHED CHARACTERISTICS In summary, productive, good quality fish habitat, both in the main channel and in off - channel tributaries, is generally lacking along the Green/Duwamish River. Significant investment is needed to improve habitat and increase access to existing habitat. In addition to the mainstem Green/Duwamish River channel, aquatic habitat is provided in the five tributaries that drain most of Tukwila to the Green Duwamish River. These tributaries include Gilliam Creek, Riverton Creek, Southgate Creek, Johnson Creek, and Mill Creek. The remainder of this section includes a description of the aquatic habitat available to fish in these creek systems. 2.6.2 Gilliam Creek To access Gilliam Creek from the Green/Duwamish River anadromous fish need to first pass through the Gilliam Creek flapgate. The flapgate is inaccessible other than during high flow events in Gilliam Creek which force the flapgate open. While several species of anadromous fish are reported to make use of the lower reach of Gilliam Creek, along the south shoulder of 1-405 between the Green River and the 1-5/1-405 interchange, their numbers are small despite habitat availability. The fish present include Chinook salmon, coho salmon, and cutthroat trout. The lower reach of Gilliam Creek provides mostly rearing and possibly some scattered spawning habitat. Spawning gravels are covered by sediments deposited by upstream erosion and by historical construction activities. Habitat in the lower reach of Gilliam Creek is available to fish through the flapgate at the outlet of Gilliam Creek only under certain conditions, when the Green River water level is elevated but remains lower than the water level in Gilliam Creek. At the time of writing, the City is advancing a project that will replace the existing flapgate with a fish friendly flapgate. If the project is funded, it will also provide rearing habitat and flood refugia. These actions are intended to benefit Puget Sound Chinook salmon in the juvenile life stage during the out -migration, to support survival and development during the sensitive, and vulnerable life stage transition from parr to fry. Other fish and marine life in Puget Sound will also benefit. There are more than 10 additional total and partial fish passage barriers along Gilliam Creek both upstream and downstream of the 1-5/1-405 interchange limiting fish movement (see Appendix B for more information). These barriers are privately -owned, City -owned, and owned by the State of Washington Department of Transportation (WSDOT). WDFW determined that several of the tributaries to upper Gilliam Creek provide some rearing habitat (WSDOT, 2007). Since there are culverts underneath the 1-5/1-405 interchange that are total barriers to anadromous fish, it is likely that only resident fish such as cutthroat 2-20 2.0 DRAINAGE BASIN AND WATERSHED CHARACTERISTICS trout and sculpin are utilizing the available habitat in the upper reaches of Gilliam Creek at this time. Fish barriers will need to be addressed to provide anadromous fish access to this rearing habitat. Fish barriers also exist in the upper reaches of Gilliam Creek, including a WSDOT-owned culvert beneath SR 518 that conveys a tributary that is identified as a total fish passage barrier. 2.6.3 Riverton Creek Both west and east forks of Riverton Creek are characterized by narrow, straight channels and long sections of culverts in their lower reaches. Both forks are considered fish -bearing. Coho salmon, fall Chinook salmon, fall chum, and resident coastal cutthroat trout are potentially present in Riverton Creek. Overall, Riverton Creek provides some limited rearing habitat for salmon, but no longer provides substantial spawning habitat. Additionally, City staff may have witnessed urban runoff mortality of salmon in Riverton Creek. There are more than 80 culverts and more than 10 total or partial fish passage barriers along Riveron Creek. Up until 2021, there were two culverts with flapgates at the outlet of Riverton Creek to the Duwamish River, built by WSDOT in the 1960s, which were impassable to fish during low flows plus somewhat impassable all other times, with one gate fixed open. Hydraulic analysis showed that the flapgates did not provide upstream flood protection, and so through the Riverton Flapgate Removal Project, the City removed the two culverts and flapgates, daylit the creek, installed a trail bridge, and improved habitat and plantings along 1,200 linear feet of the creek. The East Fork of Riverton Creekjust upstream of the SR 599 culvert is characterized by a wide, exposed, sandy, and silty streambed which provides fish passage but no spawning or rearing habitat. This section of Riverton Creek is part of a wetland complex. Upstream of that reach, a more than 2,000 linear feet (LF) culvert likely prevents at least some anadromous fish from accessing suitable habitat located in the upper reach between S 126' Street and S 128" Street, where good overhead cover from riparian plants, sufficient flows, and streambed gravels appears suitable for coho salmon spawning. Anecdotal evidence from a local resident during a February 2011 site visit suggests that anadromous salmon can and do access the east fork up to S 128" Street. The gradient upstream of S 128" Street is likely too steep for anadromous fish. Approximately 2,000 LF of restored channel in the West Fork of Riverton Creekjust upstream of SR 599 has provided some spawning and rearing habitat. The culverts within this restored reach could fill with sediment from upper watershed erosion and surface water runoff, which 2-21 2.0 DRAINAGE BASIN AND WATERSHED CHARACTERISTICS could potentially block fish passage. Just upstream of the restored reach, a 20-foot-tall manmade waterfall prevents fish from passing upstream to S 126th Street. A private property owner owns and operates a fish hatchery and releases juvenile salmon at the base of the waterfall into the west fork at the upper end of the restored reach. A King County Metro project for the South Annex Base expansion will improve the east and west forks of Riverton Creek. The project plans to daylight portions of both Riverton Creek branches and install three fish -passable culverts on the project site. The first culvert will be under S 120' PI along the east fork. The second and third culverts will be beneath the internal access drive and parking long along the west fork. Approximately 940 linear feet of Riverton Creek will be daylit, 328 linear feet of the west fork and 612 linear feet of the east fork, 0.5 acres of riparian vegetation will be restored, and the wetland the east fork runs through will be restored. This project will improve instream habitat, water quality, and fish passage along both forks of Riverton Creek. Upstream of the waterfall on the west fork up to S 126th Street, there is about 500 feet of potential fish habitat, though that reach also includes additional fish passage barriers. Fish would likely not be able pass upstream of S 126' Street because of a steep gradient, even if the waterfall and other nearby barriers were removed. However, this upper reach beyond S 126th Street has a cobble streambed that is likely supporting macroinvertebrates, a food source for fish downstream of the barriers. 2.6.4 Southgate Creek The east fork of Southgate Creek begins as a relatively small channel just south of S 137th Street and flows north through a steep ravine, several culverts, and ditches before it merges with the west fork. The west fork begins as three smaller tributaries that collect flow from the hillside just west of 40th Avenue S and merge just upstream of S 133rd Street. The west fork then passes underneath S 133' Street and Macadam Road S through more than 500 feet of culvert and merges with the east fork coming from a ditch along S 133rd Street. From there, the main stem of Southgate Creek extends under SR 599 through about 320 feet of culvert, a fish ladder, and large arch culvert into the Duwamish River downstream of the Black River confluence. Bank erosion from the combination of steep gradients and surface water runoff from urban development have deposited sediments in the lower reach, which have reduced effective culvert conveyance capacities and covered up salmon spawning gravels. The section of the main stem just downstream of the confluence of the west and east Forks is often completely blocked by sediment and debris. An upcoming sediment and hydraulic study in Southgate 2-22 2.0 DRAINAGE BASIN AND WATERSHED CHARACTERISTICS Creek will provide more information on how the City can reduce sedimentation in Southgate Creek. As in other urbanized streams, development has altered Southgate Creek's riparian buffer and natural channel alignment, resulting in increased channel incision, stream bank erosion, and degraded water quality. Rearing habitat is available in the main stem between SR 599 and S 132nd Street culvert. Rearing habitat is available in some small sections of the east fork along S 1315t Place and S 134th Place. Rearing and some spawning habitat is available in the recently restored section of the west fork just upstream of S 133rd Street. Coho salmon, fall chinook, fall chum, resident coastal cutthroat, and winter steelhead are potentially present in Southgate Creek. The fish ladder at Interurban Ave S is a barrier to anadromous fish during low stream flows. Two additional total barriers are located at S 132nd Street and S 133rd Street/E Marginal Way, both along the main stem of Southgate Creek. During a February 2011 site visit, juvenile salmon were observed in the section of the east fork along S 131st Place, which are regularly released into the stream by a nearby homeowner, according to local residents and City of Tukwila staff. Fish are unlikely to be present in the west fork of Southgate Creek upstream of Macadam Way S due to the steep gradient. Some resident fish may use the upper reaches of the east fork within Southgate Park. 2.6.5 Johnson Creek Johnson Creek in Tukwila is an intermittent stream that flows east and discharges to the Green River. There are two likely tributaries to Johnson Creek in the City of Tukwila, Ditches C and J2, which both flow south. Coho salmon, fall chinook, fall chum, resident coastal cutthroat, and winter steelhead are potentially present in Johnson Creek. Tributaries in this section of the Green River are often used by out -migrating Chinook for rearing and flood refugia. The Johnson Creek flapgate and outfall to the Green River, once partial blockages to fish passage, were replaced in 2011 as part of the mitigation for the proximate commercial development. As part of the commercial development, the lower reach of Johnson Creek was reconstructed and now provides aquatic habitat opportunities. This flapgate was considered fish -passable when it was installed in 2011. However, a recent King County study documented no fish in Johnson Creek, possibly due to debris clogging the debris rack, low elevation placement of the flapgate, which causes it to be closed during the Chinook outmigration period, low water velocity, which likely impedes the ability of juvenile salmonids to pass through the flapgate, or a combination of these conditions. Another potential barrier was identified in 2011 at S 204th Street along Johnson Creek. 2-23 2.0 DRAINAGE BASIN AND WATERSHED CHARACTERISTICS In 2023, King County purchased 30 acres of land, which includes an equestrian track and several residences on the Kent side of S. 204' Street. With this acquisition, there is interest and opportunity for multi jurisdictional collaboration to remedy the fish barrier at Johnson Creek and improve floodplain connectivity and habitat conditions in the lower Johnson Creek basin. Because development in the basin may change the habitat conditions, a revised aquatic habitat assessment should be performed after the commercial development in the Johnson Creek Basin has been completed. 2.6.6 Mill Creek The Mill Creek drainage basin is the area east of the Green River north of S 190' Street and west of 72nd Avenue South. This area flows into the Duwamish River and/or south and east into the Mill Creek basin within the City of Kent. All drainage conveyance is piped. No natural channels exist in this basin within the City of Tukwila. Mill Creek flows north from the City of Kent into the City of Renton, then discharges into the Green/Duwamish River within the City of Renton. Habitat opportunities and problems within the Mill Creek drainage within the City of Kent are identified in the Kent Surface Water Comprehensive Plan, likewise for those opportunities and problems within the City of Renton. 2-24 3.0 Regulations and City Policies This section contains a brief description of the current and anticipated future surface water regulations applicable to the City of Tukwila. The City's Surface Water Management Program coordinates compliance and reporting for the surface water regulations, which are applicable to all City departments and operations. Appendix C contains the detailed information in support of this Section 3. 3.1 Applicable Surface Water Regulations Since preparation of the 2013 Surface Water Comprehensive Plan, the NPDES Phase II Permit has been reissued to Tukwila by Ecology. The current permit became effective on August 1, 2019, and will expire on July 31, 2024. Regulations currently applicable to the City of Tukwila are described in detail in Appendix C. (Note that Green and Duwamish River flooding and flood protection are outside the scope of this Plan.) The City conducted an evaluation, or gap analysis, of Tukwila's Surface Water Management Program against the 2019-2024 permit in 2020 and implemented the recommendations in it to maintain compliance with the permit. Specific actions recommended to continue to maintain regulatory compliance are presented in Section 8 of this Plan. At the time of writing, the City is nearing completion of an assessment of its NPDES compliance program, which will provide program recommendations and actions both near -term and long-term. The Endangered Species Act (ESA) establishes protections for fish, wildlife, and plants and that are listed as threatened or endangered and their habitat. A species may be listed as threatened or endangered under the ESA because of any of the following five factors: • present or threatened destruction, modification, or curtailment of its habitat or range; • over -utilization of the species for commercial, recreational, scientific, or educational purposes; • disease or predation; • inadequacy of existing regulatory mechanisms; and • other natural or manmade factors affecting its continued existence. The Puget Sound Chinook salmon, Puget Sound Steelhead, and Bull Trout were listed as threatened in 1999, 2007, and 1998, respectively. In 2005, the Southern Resident Orcas were designated as endangered. The WRIA 9 Salmon Habitat Plan was a Green/Duwamish River 3-1 3.0 REGULATIONS AND CITY POLICIES watershed -based response tothe Puget Sound Chinook salmon being listed asthreatened under the ESA. 3,2 Potential Regulatory �Chan�s ~* A number ofchanges in regulations relevant to surface water management are expected to occur in the 10-yeartirnefnarne covered by the 2024 S\NCP. Ecology will reissue the NP[}ES permit in 2024. A draft of the NPDES Phase 112024-2029 Permit has been reviewed, and the anticipated changes and key requirements include: w Adopt tree canopy goals and policies to support stornlvvator management and water quality improvements and begin mapping tree canopy. ° Implement projects recommended by the SMAP Orother water quality projects and ° Develop a3MAPfor another basin. ° Increase detail 0f5tOrnlvv8t8rsystem mapping. w Update illicit discharge prohibitions and source control requirements to incorporate limitations on discharge ofPCBs and other emerging pollutants. w Adopt an updated stormwater management manual which includes new thresholds for providing runoff treatment facilities on development sites with multiple threshold discharge areas and new thresholds for requiring stormwater management on road - related redevelopment projects and commercial or industrial redevelopment projects. Changes to the associated Total Maximum Daily Load [[K4OU program are possible, as well as the possibility of additional listings (or downgrading of existing listed species) under the ESA. |ngeneral, these changes are expected tOincrease the CitV'sobligations for surface water management, water quality, and aquatic habitat protection and restoration. Tukwila will need to accommodate such changes in its Surface Water Management Program, possibly with additional financial resources and/or additional staff time. Section 8 includes a section on recommendations to address these regulatory requirements anticipated in this next surface water planning cycle. 3-2 4.0 Coordination with Regional Plans and Tribes The City of Tukwila is committed to working in partnership with other jurisdictions and community partners to address shared regional goals including the following: • Improving water quality in the Green/Duwamish River and tributaries in Tukwila; • Restoring habitat conditions in the Green/Duwamish Watershed and the Puget Sound; and • Reducing flood risk along the Green and Duwamish Rivers. • Protecting and ensuring access to historical and tribal sites and access to the river. The City partners with other jurisdictions and coordinates with regional efforts, including those described below, to realize the City's objectives and support progress toward regional goals. 4.1 Lower Green River Corridor Flood Hazard Management Plan The Lower Green River, between river miles 11 and 32, which flows through the southern portion of Tukwila, is at risk of severe flooding. The King County Flood Control District (KCFCD) will develop a Lower Green River Corridor Flood Hazard Management Plan. This plan will be developed to guide investments to reduce flood risk over the next 30 to 50 years. At the time of writing KCFCD has finalized a Programmatic Environmental Impact Statement (PEIS) which will inform when the plan is drafted, and which approach is taken to reduce flood risk and other objectives. The City and many other stakeholders commented on the Draft PEIS' three alternatives. In 2019, the City requested the inclusion of the following ten flood control projects in KCFCD's capital construction budget over the following ten years: • Gaco-Mitchell-Segale Levee • S. 180th Bridge to Pedestrian Bridge • Christensen Rd. Levee • Ratolo Levee • Van Warden Levee • Christensen Rd. Levee • Segale-Green Levee 4-1 4.0 COORDINATION WITH REGIONAL PLANS AND TRIBES • Gunter Levee • Christensen Rd. Levee • Cross Levee The City continues to coordinate with KCFCD and has supported two additional flooding control projects within the City limits which are on the KCFCD's current six -year CIP: the Desimone Levee Repair and the Fort Dent Levee Repair. 4.2 Salmon Habitat Plan Tukwila falls within the Duwamish and Lower Green River sub -watersheds within Water Resource Inventory Area 9 (WRIA 9). WRIA 9 developed a Salmon Habitat Plan, most recently updated in 2021, which focuses on identifying, prioritizing, and implementing salmon recovery actions. WRIA 9 Salmon Habitat Plan 2021 Update is an addendum to the 2005 WRIA 9 Salmon Habitat Plan. The 2021 Update is a status update for the Green River Chinook salmon population for which the long-term goal is to achieve self-sustaining levels of Puget Sound Chinook numbers, distribution, and diversity. The Plan Update introduces new 10-year habitat goals for "necessary future conditions" for achieving a viable salmon population. The prioritized actions in the plan align with creating supportive rearing and high -flow refuge habitat in the lower basins to support increased spawning habitat in the upper watershed that will become available with the Howard A. Hanson Dam downstream fish passage project planned for 2030 (see Section 2.6.1). There are two 10-year goals for the Duwamish River Sub Basin. The first is creation of 40- acres of shallow water habitat between river mile 1 and 10. The second is revegetating 170- acres/9.8 miles of streambank. The plan has several goals related to off -channel habitat, riparian forest, large woody debris, and bank armor in the Lower Green River Sub Basin. The off -channel habitat goals include restoring 240-acres of floodplain habitat, restoring 550 feet of high flow channels and 3,470 feet of low flow channels, and re -connecting 75-acres of backwater habitat, 66-acres of floodplain wetland, and 99-acres of other 100-year floodplain. The riparian goal includes revegetating 250-acres/8.52 miles of high -priority unforested shoreline. The large woody debris goal includes achieving the installation of 425 pieces/mile. The bank armor goal includes setting back one mile of levee. A total of 127 projects were identified and ranked into three tiers. Tier 1 projects have significant potential to advance salmon recovery and contribute to habitat goals. Tier 2 and 4-z 4.0 COORDINATION WITH REGIONAL PLANS AND TRIBES Tier 3 projects have moderate to limited potential, respectively, to advance recovery and achieve habitat goals. The projects identified in the Salmon Habitat Plan are opportunistic and rely on willing landowners; the plan has a long horizon, allowing proponents to act on opportunities when they arise. Numerous Tier 1 projects are within the City of Tukwila: • Project number DUW-2 (Rendering Plant): Acquire and restore approximately seven acres with side channel and backwater habitat enhancements and reforestation. • Project number DUW-7 (Chinook Wind): Expand and enhance low velocity, shallow water rearing habitat (shallow subtidal and intertidal) in the Duwamish transition zone. This project was constructed in 2021 and created more than four acres of estuarine wetland, aquatic, and riparian habitat area which provides off -channel habitat. • Project number DUW-7a (Chinook Wind Extension): Expand and enhance the land between Chinook Wind Mitigation and Duwamish Gardens to create a unified park and restoration site. This project is currently in design and is on the City's 2023-2028 Capital Improvement Program. • Project number DUW-25 (Desimone Oxbow Restoration): Acquire and restore 45.4- acre site resulting in 23.6 acres of marsh created, 10.8 acres of vegetation, and 34.4 acres refuge habitat created. This project is unlikely to take place in the near future, despite WRIA and government coordination efforts. An Amazon warehouse and shoreline restoration was completed in 2021 on this parcel. • Project number DUW-64 (U-Haul River Project): Acquire and restore an approximate four -acre parcel by creating off -channel mudflat, marsh, and riparian habitat. • Project number LG-35 (P-17 Pond Connection Reconnection): Relocate the City of Tukwila's stormwater pond; clean and connect the existing pond to the river, setback the levee to create up to seven acres off -channel habitat. 4.3 Our Green Duwamish Implementation Plan The City of Tukwila is a partner with Our Green Duwamish which strives to improve air, land, and water conditions in the Green/Duwamish River watershed. The Our Green Duwamish Implementation Plan is a coordinated regional effort to restore stormwater quality and control stormwater quantity. The City of Tukwila has committed to numerous actions to achieve the plan's goals and objectives. 4-3 4.0 COORDINATION WITH REGIONAL PLANS AND TRIBES 4.4 Action Agenda for Puget Sound Puget Sound Partnership is a Washington state agency leading the regional effort to restore and protect Puget Sound. The City of Tukwila falls within the Puget Sound National Estuary Program area, and the City supports the Partnership's Action Agenda for Puget Sound. At the time of writing the Action Agenda is a 2022-2026 plan that outlines a set of strategies to achieve 23 desired outcomes that will have multi -benefit results. As a recovery partner the City is committed to implementing specific projects, programs, and actions to advance recovery of Puget Sound. 4.5 Duwamish Blueprint: Salmon Habitat in the Duwamish Transition Zone The Duwamish Blueprint: Salmon Habitat in the Duwamish Transition Zone document originated from a program in the 2005 WRIA 9 Salmon Habitat Plan. The Duwamish Blueprint Working Group finalized the current working draft in 2014. The document provides guidance to improve the aquatic ecosystem of the Duwamish Estuary which extends from Kellogg Island in the City of Seattle to the I-5/SR-599 interchange in Tukwila. This estuarine habitat is particularly important for migrating juvenile salmon which need food, shelter, and habitat to osmoregulate as they transition to saltwater fish. Several of the projects sponsored by the City of Tukwila in the Duwamish Blueprint are now projects outlined in the WRIA 9 Salmon Habitat plan. Several more projects have already been completed within the city limits. 4.6 2020 State of our Watershed The Northwest Treaty Tribes' State of Our Watersheds Report was most recently released in 2020. The City of Tukwila falls within the Muckleshoot Tribe's geographic area of interest which includes WRIAs 8, 9, and 10. The report illustrates the need to continue to protect habitat and achieve restoration goals. The report specifically notes the need to establish a riparian shade corridor along the Green River, including through Tukwila, to address water temperatures. 4.7 Stormwater Parks King County published a provisional goal of implementing 30 stormwater parks throughout the County in partnership with municipalities and organizations. Stormwater parks are facilities that serve to both treat stormwater from a larger area, such as a regional treatment facility, and provide recreational opportunities, such as parks, trails, or community gardens). Stormwater parks can provide numerous benefits, including but not limited to equity, climate resilience, green space, wildlife habitat, and educational opportunities. Puget Sound 4-4 4.0 COORDINATION WITH REGIONAL PLANS AND TRIBES Regional Council provides guidance related to the siting and design of stormwater parks. The 2024 SWCP recommends implementing multi -benefit stormwater parks in Tukwila where feasible. 4.8 Coordinating with Tribes City of Tukwila Surface Water Program is committed to coordinating protection of surface waters and river -adjacent cultural resources with the Duwamish Tribe and the Muckleshoot Indian Tribe. A representative of the Duwamish Tribe commented on a draft of the 2024 SWCP (Appendix G), and the Surface Water Program will integrate the following considerations into plans when implementing projects and programs: • Protect cultural resources during groundbreaking activities. • Support access to the Duwamish River for the Tribe and other local community members. • Where outdoor lighting is planned, consider responsible outdoor lighting that protects the night skies. • Observe stream and wetland buffers. • Use woody debris where sensible in urban streams to slow down flows. • Consult with the Duwamish Tribe on Lushootseed signage around their sacred sites. 4-5 5.0 Surface Water Known Issues and Solutions This section summarizes surface water known issues discovered during preparation of the 2024 SWCP. These known issues are organized by type of surface water issue: drainage, water quality, erosion, maintenance, or habitat. Appendix D contains the detailed information in support of this section. 5.1 Available Data and Information Known issues identified in the 2013 Surface Water Comprehensive Plan were evaluated and kept if still relevant. The following sources of information were used to identify known issues in the 2013 Plan: • Anecdotal and recorded information provided by City staff. • Observations made during field visits by CH2M HILL and City staff. • 2003 City of Tukwila Comprehensive Surface Water Management Plan. • The following drainage studies: O 1993 Surface Water Management Comprehensive Plan. O 1994 Gilliam Creek Detention and Water Quality Enhancements. O 1996 Fostoria Basin Stormwater Quality Management Plan. O 1997 Southgate Creek By -Pass Study. O 2001 Gilliam Creek Basin Storm Water Management Plan. In addition to these sources, the 2024 SWCP references the following to identify known issues: • Anecdotal and recorded information provided by City staff, including: o List of polluting gravel yards O 2022 Small Drainage Project List o Flood Patrol Assets List o Sites catalogued during fieldwork and workshops in 2022 and 2023 • 2013 Surface Water Comprehensive Plan. • Juvenile Chinook Use of Non -natal Tributaries in the Lower Green River (2019). • Gilliam Creek Water Quality Assessment and Report (2019). 5-1 5.0 SURFACE WATER KNOWN ISSUES AND SOLUTIONS • Riverton Sampling Report from the Riverton Flapgate Removal Project (2020). • Tukwila Pond Park Master Plan (2022). • Technical Information Report for Starfire Fields at Fort Dent Park (2003). • Citizen reports at an open house in 2023. 5.2 Surface Water Known Issues The 2024 SWCP has identified 169 specific surface water known issues within the City of Tukwila. Localized drainage problems are the one primary surface water concern for the residents of the City of Tukwila. Drainage issues arise on both public and private property where there are no storm drainage systems, the existing conveyance systems are damaged or in need of maintenance, or the existing conveyance systems have inadequate hydraulic capacity. Much of the development in Tukwila occurred before current stormwater flow control standards. In addition, as impervious surfaces are added, more stormwater runs off during storms, exacerbating existing problems. Water quality problems are evident in the Green and Duwamish River system and in each of the major creek systems within Tukwila. The Green River and Duwamish River are listed as impaired on the 2022 Ecology 303(d) list for the following pollutants associated with stormwater runoff and reduction in riparian cover: dissolved oxygen, temperature, and pH. Untreated runoff from arterial streets with intensive traffic usage, areas of dense commercial development, parking lots, and 1-5 and 1-405 contributes to these problems. All of Tukwila's creek systems are also affected. Runoff conveyed to the river via these creeks is contributing to impairment of the Green and Duwamish Rivers. Bacteria and poor bioassessment are also issues in Tukwila's streams. A new chemical called 6PPD (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) that causes acute death of coho salmon was identified in 2020. 6PPD is used in all tires as a rubber preservative to increase the lifespan of the tire. 6PPD is also found in all recycled tire products. When exposed to air this chemical reacts with ozone to create 6PPD-quinone (6PPD-q) which contaminates stormwater runoff and is lethal to coho salmon even in small quantities, less than one part per billion. Stormwater managers are researching best management practices (BMPs) that manage 6PPD-q contaminants in stormwater runoff. At the time of writing research indicates that BMPs that use infiltration, sorption, and/or filtration are expected to reduce the concentrations of 6PPD-q in runoff. Additionally, it is expected that preventive maintenance, such as street sweeping or catch basin cleaning, prevent runoff of 6PPD-q to receiving waters. 6PPD-q is a regional, statewide, and citywide concern. 5-2 5.0 SURFACE WATER KNOWN ISSUES AND SOLUTIONS Available aquatic habitat has been significantly reduced in the creeks that drain Tukwila due to the effects of development and the loss of riparian buffer areas. Uncontrolled runoff flows coupled with steep slopes in the upper reaches of Gilliam, Southgate, Riverton, and Johnson Creeks cause channel erosion that in turn delivers sediments to the lower -gradient downstream reaches of these streams. Other causes such as landslides may be contributing to the sedimentation in the lower stream reaches. Sediment deposition significantly reduces the conveyance capacity of the channels, restricts fish passage, and hinders the potential for salmonid spawning in these lower reaches. Better quality aquatic habitat in the lower reaches of Tukwila's streams and changes to river velocity at the confluences would provide refuge to salmonids from high flows and predators in the Green and Duwamish Rivers. Several culverts are blockages to fish passage from the lower reaches to the upper reaches of several creek systems. Addressing these blockages to fish passage would provide salmonids access to aquatic habitat in the middle and upper reaches of these systems. In addition, restoration of riparian buffer areas both in the upper and lower reaches of these creeks would reduce water temperatures, which is better for salmonids at all life cycles. Many opportunities for salmon habitat restoration (and protection) are outlined in the WRIA 9 Salmon Habitat Plan (WRIA 9 2021). Table 5-1 summarizes the surface water known issues by type. Individual surface water issues are shown on Figure 5-1 and discussed in detail in Appendix D. Table 5-1 Surface Water Known Issue Summary Type of Surface Water Issue Number Water Erosion / Drainage Basin of Issues' Drainage Quality Sediment Maintenance Habitat' Gilliam 64 27 10 0 27 0 Green/Duwamish 62 16 32 0 13 1 Johnson 4 0 3 0 0 1 Mill Creek 0 0 0 0 0 0 Nelson 8 1 5 0 2 0 P17 15 4 5 0 5 1 Riverton 34 11 11 1 10 1 Southgate 49 18 18 1 12 0 Springbrook 1 0 0 0 1 0 Totals 237 77 84 2 70 4 ' 169 total known issues were documented. Many issues are categorized into multiple types, therefore the total count by issue type (237) exceeds the total number of issues documented (169). 2 Number of habitat known issues exceed totals documented in this table. Findings of the separate Fish Passage Barrier Update memorandum are not documented here. See Appendix B. 5-3 Known Issues Types - Citywide Count Erosion I Habitat aintainabiif Flooding Water ©ual ty 20 40 60 Count FIGURE 5-1 II II OW ISSUES TUKWILA SWCP 133383 TUKWILA, WASHiIING°NN Legend © City Boundary Known Issue Point ! j Neighboring Cities Water Quality — Streams and Rivers • Flooding ■ Erosion Maintainability • Habitat Mile 0 1 Data Sol rrns Kr^q County Cdy of Tukwila, Googlo Maps Date 9.29/2024 DrucUumer This dnt fa survey accuracy and is meant for ptrrnrrg porprr € nnfy o\PROJF=C1\33:300\333&f\GADD\GfSW'RXS\rr338rf Tukvrfa owcp i rqures\3J303 Tukwila SWCf gu'es aprr Otak 5.0 SURFACE WATER KNOWN ISSUES AND SOLUTIONS 5.3 Menu of Solutions to Address Surface Water Issues This section outlines the menu of solutions that could be used to address the surface water issues identified in the City of Tukwila. No single type of action, activity, or project is a "one size fits all" fix to all of these identified problems. Some surface water problems have structural solutions, while others have programmatic (non-structural) solutions, and many have both programmatic and structural solutions. Implementing a diverse portfolio of solutions allows for different aspects of the issues to be addressed by different solutions. Potential solutions are divided into actions that would not involve construction or land acquisition, collectively referred to as programmatic approaches, and projects that would require construction or land acquisitions and would be listed in the City of Tukwila Capital Improvement Program. The programmatic activities have the benefit of often being strategic rather than reactionary. Instead of fixing a single problem with a structural solution, programmatic alternatives often address a series of existing problems and are effective at preventing future problems. Often, capital (structural) solutions are most effective for single -location surface water problems and programmatic solutions are most effective for watershed -wide or other large- scale problems. Regulatory requirements (such as the NPDES Phase II Permit) emphasize programmatic approaches to problems. Also, water quality problems can be targeted successfully using programmatic means such as source control measures. Sub -basin- or watershed -wide water quantity problems, such as increase in impervious surface runoff, can be addressed with programmatic solutions. Location -specific known issues can be addressed with capital projects. Using capital projects and programmatic solutions in tandem is the most effective method of addressing problems comprehensively. Because multiple sources contribute to the problems, multiple solutions targeting different sources and different aspects of sources are appropriate. Programmatic actions can provide overlapping benefits, thus addressing several pollution sources at once. However, capital projects can yield immediate, measurable results in a specific location, such as reduction of sediment load to the Green River from a specific parking lot. An additional benefit of capital projects is that the City can implement any number of individual capital projects in any given year depending upon funding availability. A programmatic capital improvement program is a hybrid approach combining the programmatic and capital solution types described above. A programmatic capital improvement program acknowledges that the solution to intractable or widespread surface water issues requires coordinated and prioritized capital investments over a long period of time and/or large geographic area. As examples, programmatic CIPs may be employed to 5-5 5.0 SURFACE WATER KNOWN ISSUES AND SOLUTIONS improve water quality in a full stream system, to restore access to fish habitat in several stream systems, or to address widespread small drainage issues over an entire City. Programmatic CIPs often rely on studies or alternatives analyses to evaluate the most effective capital projects and the most effective order in which to implement projects. As City of Tukwila participates more vigorously in reaching regional goals such as salmon recovery, protection of Puget Sound, and protection of developed lands and people from severe flooding of the Green River and Duwamish River, programmatic CIPs are useful in identifying and prioritizing projects that the City can implement to realize progress toward regional goals. In addition, the next issuance of the NPDES Phase II Permit may require permittees such as Tukwila to implement water quality retrofit projects identified in the SMAP. The SMAP for Riverton Creek Basin can be considered, in part, as a programmatic CIP with the goal of improving water quality in Riverton Creek for fish and people, as can the Water Quality Retrofit Program and Green the Green Program, which endeavor to provide structural retrofits and shoreline revegetation, respectively. 5.3.1 Programmatic Solutions One objective of the Surface Water Comprehensive Plan is to comprehensively address drainage, water quality, erosion, maintenance, and habitat issues identified in the City of Tukwila. Another is to coordinate with regional efforts to improve water quality, fish passage and habitat, and flood protection in and along the region's streams, rivers, lakes, and Puget Sound. The type(s) of surface water issues that could be addressed by individual programmatic solutions are summarized in Table 5-2. Note that many of these activities are required in whole or in part by the City's NPDES Phase II Permit. The remainder of this sub- section discusses each of programmatic solutions in further detail. Table 5-2 Known Issue Types Addressed by Programmatic Solutions Known Issue Type Required Erosion / by NPDES Water Sedimen Mainten Phase II Program Element Drainage Quality tation ance Habitat Permit* Stormwater Planning x x x x Regulatory and x x x x x Policy Changes Inspection and x x x x Enforcement Operations and x x x x x x Maintenance 5.6 5.0 SURFACE WATER KNOWN ISSUES AND SOLUTIONS Table 5-2 Known Issue Types Addressed by Programmatic Solutions Known Issue Type Required Erosion / by NPDES Water Sedimen Mainten Phase II Program Element Drainage Quality tation ance Habitat Permit* MS4 Mapping and x x x x x x Documentation Public Education and x x Outreach Public Involvement x x and Participation x x x x x * Required in whole or in part 5.3.1.1 Stormwater Planning Stormwater planning is an NPDES Phase II Permit requirement. In part, stormwater planning requires the City to cooperate interdepartmentally to ensure the protection of water quality and compliance with the NPDES Phase II Permit. Stormwater planning improves water quality by developing a set of policies and strategies to implement based on receiving water conditions. The City has developed an inter -disciplinary team to inform stormwater planning in Tukwila and coordinates with other planning efforts in the City to ensure water quality is taken into account. The City has adopted Low Impact Development (LID) regulations and BMPs which reduce the impact of new development and redevelopment projects on surface waters. The City will continue to review and revise these regulations as new information becomes available. Among other collaborative, regional stormwater planning efforts described in Section 4, the City completed a Stormwater Management Action Plan (SMAP) for Riverton Creek in 2023 which can be found in Appendix F. This SMAP identifies stormwater retrofits, land management and development strategies, customized stormwater management actions, and instream improvements to protect and restore water quality in the Riverton Creek basin. Stormwater planning benefits water quality, erosion/sedimentation, and habitat. 5.3.1.2 Regulatory and Policy Changes There are two broad categories of water quality problems in Tukwila: 1) non -point source pollution, which include contaminants coming from roads, vehicles, parking lots and buildings and 2) point source pollution, which is identifiable and traceable to a particular 5-7 5.0 SURFACE WATER KNOWN ISSUES AND SOLUTIONS source. Sources include illicit discharges of material into storm drains or permitted industrial discharges. Regulations prohibit the illicit discharge of contaminants to stormwater runoff, and protection of water quality is dependent on improved regulations to address the source of the pollutants so that stormwater runoff entering the City's storm drains is as clean as possible. Programmatic solutions can be used to prevent future drainage and water quality problems by managing how new development and redevelopment is conducted. The Tukwila Municipal Code, the 2019 Infrastructure Design Standards, and the 2021 King County Surface Water Design Manual regulate stormwater management for development and redevelopment projects. The Surface Water Management Program staff is aware of frequent use of the nonconforming parking lot standards in TMC 18.70.080, which permit temporary gravel parking lots to be constructed without drainage and water quality treatment facilities. Many of these lots have since effectively become permanent installations and may contribute to localized flooding and water quality issues. The City has identified 65 gravel parking lots without drainage or treatment facilities. The nonconforming parking lot standards have not been updated since 1997. Changes to City policies and regulations would have drainage, water quality, erosion/ sedimentation, and aquatic habitat benefits. 5.3.1.3 Inspection and Enforcement Inspection and enforcement meet the requirements of the NPDES Phase II Permit. The City conducts various surface water -related inspections. The following types of inspections are conducted by City of Tukwila's Surface Water Management Program or by the Department of Community Development: • Inspections to detect, remove, and prevent illicit connections, discharges, and improper disposal of non-stormwater runoff, including spills, into the surface water system. • Construction site erosion and sedimentation control inspections and pollution control inspections to reduce sources of pollution in stormwater runoff. • Development site stormwater facility inspections to review construction of required stormwater management facilities on permitted development and redevelopment sites. 5-8 5.0 SURFACE WATER KNOWN ISSUES AND SOLUTIONS • Private stormwater facility maintenance inspections to review maintenance condition of required privately -operated stormwater facilities. • Public stormwater facility and catch basin maintenance inspections to review maintenance condition of the City's stormwater facilities and refer required facility maintenance tasks to other personnel. • Business source control inspections to reduce sources of pollutants in stormwater. • As -needed closed-circuit television (CCTV) inspections of stormwater conveyance pipes to assess both structural condition and maintenance condition. Possible changes to inspections and enforcement include: • Prioritizing business source control inspections in a single drainage basin to make measurable progress toward water quality improvement in a high -priority stream system (see the SMAP in Appendix F). • Escalating enforcement when violations are found. Note that the NPDES Phase II Permit requires each permittee to include escalating enforcement procedures and actions as part of its illicit discharge prohibition regulations by July 1, 2027. • Incorporating information about PCBs and other emerging pollutants of concern into inspection training materials, inspection checklists, and technical assistance materials. Inspection and enforcement activities have drainage, water quality, and maintenance benefits. 5.3.1.4 Operations and Maintenance Operations and maintenance are essential to maintaining a functional drainage network, removing pollution, managing erosion and sedimentation, and supporting aquatic habitat. Elements of operations and maintenance duties are spelled out in the NPDES Phase II Permit requirement. Currently, Tukwila City maintenance staff maintain the surface water system, including but not limited to pipes, manholes, inlets and catch basins, ditches, open streams, and pump stations. The City implements maintenance standards in the latest version of the King County Surface Water Design Manual. The City has also developed a program for long-term operations and maintenance for City facilities. By conducting proactive maintenance Tukwila may benefit water quality and habitat by reducing pollutant and total sediment load to creeks. An example of this is cleaning out catch basins more often than required by the NPDES Phase II Permit in sensitive areas such as near salmon -bearing creeks. Another example is street sweeping. 5-9 5.0 SURFACE WATER KNOWN ISSUES AND SOLUTIONS The City has two upcoming projects that will adjust the existing operations and maintenance program: an Enhanced Maintenance Plan (EMP) and NPDES Program Assessment. Developing an EMP is a requirement of the Department of Ecology in order for the City to obtain funding for its future decant facility. The EMP will describe the City's current surface water maintenance program and develop recommendations for maintenance procedures that will further improve water quality. The NPDES Program Assessment provides a gap analysis with both short-term and long-term programmatic improvements including operations and maintenance. Tukwila is also required to inspect private stormwater facilities according to the NPDES Phase II Permit. The City must have a regular inspection plan for both public and private facilities. Maintenance benefits drainage, water quality, erosion/sedimentation, maintenance, and habitat. 5.3.1.5 MS4 Mapping and Documentation Municipal Separate Storm Sewer System (MS4) mapping and documentation is an NPDES Phase 11 Permit requirement. MS4 mapping is an important tool for engineering staff and operations and maintenance staff to visualize what and where stormwater assets are, to delineate what assets belong to the City as opposed to adjacent cities, other agencies, or private properties. The tool is used by staff to locate assets for both routine maintenance and repair as well as detection of illicit discharges and illicit connections. The information is referenced by in-house and consulting designers and engineers and is often the subject of requests by the public and by developers. As such, it is important to keep the MS4 mapping as up-to-date and accessible as possible. At the time of this writing, the Technology and Information Services Department is in the process of creating a self-service portal for stormwater assets so that the public may directly access this information, saving them time and staff time. City staff have experienced challenges to maintaining an accurate and updated MS4 mapping system. In 2023, Public Works hired a GIS Field Technician to collect in -field utility data, support Lucity software integration for operations and maintenance work order management, and support the Technology and Information Services Department to integrate field data and as -built information into the GIS MS4 map. MS4 mapping benefits drainage, water quality, erosion/sedimentation, maintenance, and habitat. 5-10 5.0 SURFACE WATER KNOWN ISSUES AND SOLUTIONS 5.3.1.6 Public Education and Outreach Public education and outreach is an NPDES Phase 11 Permit requirement. Many surface water issues in Tukwila are caused by the everyday actions of people that live in or visit the City. Educating the public about the link between human actions and activities and their effect on watershed and ecosystem health is a key component to restoring water quality. The City's current efforts are strategically driven to deliver effective personal messaging to residents, property owners, fixed and mobile businesses, to build general awareness, effect behavior change, and create stewardship opportunities for residents and interested outside parties. The City uses regional resources and public partnerships to implement the program including Stormwater Outreach for Regional Municipalities (STORM), Washington Stormwater Center, Municipal Resource Service Center/Washington Cities Insurance Agency, and regional meetings. Public education and outreach have drainage, water quality, and habitat benefits. 5.3.1.7 Public Involvement and Participation Public involvement and participation are an NPDES Phase II Permit requirement. Public involvement can promote awareness of and foster a sense of responsibility for the health of the watersheds of Tukwila and of the greater Puget Sound, and it can help identify problems and solutions. Engaging people in the reporting and documenting of surface water problems through phone hotlines increases detection of problems. A technique for reducing impervious surfaces, which may improve drainage, water quality, and habitat indirectly, is to remove existing unneeded pavement, also known as 'depaving.' Depaving is an established community partnership model used in Washington and Oregon to replace unwanted impervious surface with healthy urban tree canopy in support of adopted City goals and regulations around surface water management, the environment, livability, health, and equity. Public involvement activities can be coordinated with the educational activities mentioned previously. Public involvement benefits drainage, water quality, and habitat. 5.3.2 Capital Project Solutions Capital projects implemented as part of a comprehensive capital improvement program (CIP) can together address many of the surface water problems identified in the City of Tukwila often resulting in multiple benefits. Capital projects have the potential to reduce and/or store stormwater volumes, reduce peak flows, improve water quality, reduce erosion, 5-11 5.0 SURFACE WATER KNOWN ISSUES AND SOLUTIONS reduce maintenance demand, restore habitat, and provide a public amenity. This section includes descriptions of the methods that can be utilized to address these surface water issues using capital projects. The type(s) of known issues that could be addressed by capital projects are summarized in Table 5-3. The remainder of this sub -section discusses each of the types of capital projects in further detail. Capital project types are organized by known issue type (drainage, water quality, erosion/sedimentation, maintenance, and habitat). Table 5-3 Surface Water Issue Types Addressed by Capital Projects Surface Water Issue Type Water Erosion/ Capital Project Type Drainage Quality Sedimentation Maintenance Habitat Increase conveyance capacity* x x Provide drainage system (or x x re-route existing) Infiltration* x x x x On -site detention/retention x x x Regional detention/retention x x x Velocity reduction (check x x x x x dams, etc.) * High flow bypass x x Impervious surface reduction* x x x x Point source control x x Water quality treatment* x x Conveyance system cleaning x x x x and inspection* Capital repair & replacement x of stormwater facilities Land acquisition* x x x Sanitary sewer separation x x x Riparian buffer restoration / x x x x protection* Channel stabilization* x x x Channel physical habitat x restoration Fish passage barrier removal* x * These capital project types were marked as a priority by the Duwamish Tribe. 5-12 5.0 SURFACE WATER KNOWN ISSUES AND SOLUTIONS There is increasing emphasis on providing larger -scale, collaborative stormwater capital projects, and a variety of the capital project solution types described below are candidates for procurement and implementation using Community -Based Public -Private Partnerships (CBP3). See Section 8.2.1 for more about CBP3 as an implementation strategy for surface water capital improvements. 5.3.2.1 Drainage Capital projects meant to address altered hydrology (that is, water quantity) include infiltration, regional detention/retention, onsite detention/retention, reductions in impervious surface, velocity reduction, high -flow bypass facilities, dispersion, stream buffer restoration, and land purchase. The effectiveness of any of these alternatives can be limited by physical space constraints. The feasibility of any of these alternatives is also often limited by topography, soil conditions, and the presence of sensitive areas. Increasing Conveyance Capacity of a drainage network is often performed to alleviate localized drainage issues. Pipes are removed and replaced with a larger diameter pipe. Hydraulic and hydrologic analysis should be performed in order to assess upstream and downstream impacts of proposed conveyance capacity changes. Providing a drainage network where there is currently no formal system will provide conveyance of stormwater away from a location. Lack of a formal (that is engineered or planned) drainage network is common in areas developed before current stormwater standards. Infiltration is an extremely effective method to reduce stormwater runoff volumes and peak flows. Under pre -development conditions, a significant portion of the annual precipitation infiltrated into the ground. After development, and the corresponding increase in impervious surfaces that prevents infiltration, much more of the annual precipitation runs off as stormwater, a generally warm, chemically compounded water, which moves quickly across the landscape, through pipes and ditches, into receiving waters or downstream conveyances that may flood or scour as a result. Promoting infiltration is a method to reduce the impacts of development by mimicking natural hydrologic processes, capturing pollutants, and slowly releasing the water through the subterranean hyporheic zone, which in turn, supplies streams and rivers with cool water through warmer and drier months. Infiltration effectiveness is a function of soil infiltration capacity. Many areas of Tukwila have topsoil that is conducive to infiltration. When local soils are not conducive to infiltration, soils amended with organic material can be brought in and placed over native soils. Even if the native underlying soils have low infiltration capacity, the infiltrated water will use the storage 5-13 5.0 SURFACE WATER KNOWN ISSUES AND SOLUTIONS available in the soil column of the amended soil layer until infiltration into the underlying layer is possible. Moisture retained in the amended soil layer is available for plant uptake, including lawns. During construction activities, it is common for the native top layer of soil to be stripped away. In this case, amended soils should be introduced rather than relying on the remaining native soils. Planting, then maintaining, a lawn on the remaining native soil will require watering and fertilizing that would not be necessary if the native top layer were still in place or if amended soils were used. Regional detention/retention is a plausible structural solution. Regional detention could be used to detain erosive peak flows. Total volumes of stormwater runoff and the duration of erosive flows to streams can be reduced through retention via evaporation, plant uptake, and infiltration. In addition to implementation of new facilities, existing regional detention facilities can be retrofitted to promote capacity and capability. A more recent advance is to provide real-time control of releases from regional detention facilities based on weather predictions; a proprietary version of this technology is known as Continuous Monitoring and Adaptive Control (CMAC) by OptiRTC, Inc. Real-time control may be used to retrofit existing detention facilities for better performance and may also be used in the design of new regional detention. Onsite detention/retention and other site -specific measures are also effective at detaining peak flows, decreasing total volumes of stormwater runoff, and reducing the duration of erosive flows to streams. Onsite detention and other site -specific measures on public, City -owned property is considered capital projects and are therefore discussed in this section. Onsite detention and other site -specific measures on private property are discussed in the programmatic solutions section under education and regulations. That said, it may be feasible to use public funds to fund on -site detention on private property if the benefit is shared by a larger group than just the private property owner. Dispersion, for purposes of this discussion, is considered a type of on -site stormwater management. Reductions in impervious surface can reduce runoff volumes and velocities. Low Impact Development (LID) regulations can promote reduced widths of newly constructed roadways and is covered in the regulations section (programmatic), but retrofitting existing infrastructure is a structural solution. Pilot projects for reducing road widths and using permeable pavements can be implemented within the City to address water quantity concerns. Conveyance system cleaning and inspection provides information as to the condition of the stormwater conveyance system that allows for prioritization of rehabilitation, repair, or 5-14 5.0 SURFACE WATER KNOWN ISSUES AND SOLUTIONS replacement efforts. In addition, cleaning of the conveyance system can increase the effective conveyance capacity by removing accumulated sediment and other material. Water quality benefits may also be obtained by removing that sediment from the stormwater system. Stormwater runoff velocities can be reduced using check dams and vegetation in existing ditches. In addition, high -flow bypass facilities can be installed in areas that are prone to erosion under high flow regimes. Stream buffer restoration can reduce stormwater volumes via plant uptake and reduce stormwater velocities by adding roughness to the flow path. Land acquisition can be an effective method to reduce developed land surface and therefore reduce impervious surface, promote infiltration, and retain the natural tree canopy. Sanitary sewer separation can ensure stormwater runoff does not mix with sanitary sewerage and discharge untreated sewage to surface waters. 5.3.2.2 Water Quality The most effective methods to reduce pollutant loading to the City of Tukwila's receiving waters are controlling pollutants at the source and controlling stormwater flows (that is, peak flows, volumes, and durations of erosive flows). Water quality treatment can also be an effective method, but effectiveness is often limited by available technology. Channel stabilization also has water quality benefits. Source control measures tend to be programmatic in nature rather than structural and are therefore addressed in the programmatic solution section. However, control of point source water quality problems is covered in this section. Alternatives geared towards reducing volumes, peaks, and durations of stormwater runoff discussed in the drainage section also have positive impacts on pollutant inputs by reducing erosion and erosive capabilities of stormwater and by reducing total stormwater inputs to receiving water bodies. These solutions include infiltration, regional or on -site detention or retention, impervious surface reduction, velocity reduction, stream buffer restoration, and land purchase. The effectiveness of water quality treatment as an alternative is limited by available technology. Total suspended solids (TSS) are relatively easy to remove but other pollutants such as nutrients and heavy metals are not. Particulate -bound copper can be removed via treatment, but dissolved copper is difficult to remove. Though particulate -bound copper can be removed using sedimentation and filtration, dissolved copper requires adsorption, precipitation, or separation. 6PPD-q is an emerging pollutant of concern that can early studies are showing can be removed from stormwater runoff using infiltration, sorption, 5-15 5.0 SURFACE WATER KNOWN ISSUES AND SOLUTIONS and/or filtration. Water quality treatment best management practices (BMPs) are available to remove each of these pollutants at varying costs. The pollutant removal capabilities of stormwater treatment is dependent upon the concentrations of pollutants entering the treatment facility. The lower the influent concentration, the harder it is to remove. The term "irreducible limits" refers to the concentration at which no more of a constituent can be removed. The irreducible limit depends on available technology. The higher the influent concentration, the easier the constituent is to remove. Channel stabilization can be used to reduce channel erosion propagated by increasing stormwater peak flows and volumes, in that it can minimize erosion and total suspended solids contributions. However, the use of channel stabilization needs to be weighed against risk when working in -stream since channel migration is an important stream forming process that supports off -channel rearing, refuge and food production for migratory salmon and other aquatic species. This structural solution can prevent significant erosion and minimize the risk of increasing channel incision (that is, down -cutting). The selection of a preferred water quality solution is dependent upon pollutants of concern in the receiving water body. 5.3.2.3 Erosion/Sedimentation Stream buffer restoration can reduce stormwater volumes via plant uptake and reduce stormwater velocities by adding roughness to the flow path. Velocity reduction can reduce erosion of the streambank and sedimentation downstream. Channel stabilization can be used to reduce channel erosion propagated by increasing stormwater peak flows and volumes. This structural solution can prevent significant erosion and minimize the risk of increasing channel incision (that is, down -cutting). 5.3.2.4 Maintenance Project types that improve conveyance, drainage, and facility design or condition have the possibility of decreasing maintenance frequency by reducing service calls for localized flooding and stormwater facility condition. These project types include increasing conveyance capacity, providing drainage system, velocity reduction within existing facilities that have been damaged by improperly managed inputs, conveyance system cleaning and inspection, and capital repair and replacement of stormwater facilities. 5-16 5.0 SURFACE WATER KNOWN ISSUES AND SOLUTIONS 5.3.2.5 Habitat Direct structural solutions aimed at aquatic habitat restoration include replacing culverts, flapgates, or other structures that block fish passage, restoration of physical features of creek and river channels, and riparian buffer restoration and protection. Any of these solutions can aid in aquatic habitat restoration. The 2024 SWCP contains an inventory of blockages to fish passage in Tukwila. Restoring physical features of creek channels and protecting and restoring stream buffers also have water quantity and water quality benefits, in addition to aquatic habitat benefits. Note that habitat restoration or protection projects on the Green or Duwamish Rivers will require significant partnerships with regulatory agencies and with other municipalities such as King County. Land acquisition can be an effective and often necessary method to restore habitat, particularly critically -needed off -channel rearing habitat, which requires enough space to restore floodplain that supports shallow -gradient, slow water with sufficient space for the necessary earthwork and riparian buffer restoration. With Tukwila highly urbanized, and with older development encroaching well within historic buffers, and an extensive levee system along the Green River, there is insufficient space available along the river and its tributaries to create this off -channel habitat. Acquisition is an important tool to reduce developed land surface and therefore promote infiltration, retain the natural tree canopy, and restore stream buffers. Retention of the natural tree canopy and restoration of stream buffers promote improvement of aquatic habitat through shading. Several other types of stormwater management solutions can indirectly improve fish habitat by reducing high stormwater flows that make it difficult for fish to conduct their lifecycle activities and by reducing stormwater pollution that affects water chemistry, such as infiltration, velocity reduction, impervious surface reduction, point source control, water quality treatment, conveyance system cleaning and inspection, and sanitary sewer separation. 5.4 Solutions to Tukwila's Surface Water Issues The purpose of this sub -section is to specify individual solutions to the surface water issues outlined earlier in this section in Table 5-3. Table 5-4 outlines all major surface water issues identified during this planning effort. All of the surface water issues identified have been assigned one or more possible solutions. Each issue can be wholly or partially addressed by that, or those, solutions. Note that some City-wide problems such as the creation of temporary gravel parking lots without stormwater facilities will need to be addressed by either a programmatic activity (such as a regulatory change) or a programmatic CIP. Problems identified at specific locations may be addressed by a capital project, a 5-17 5.0 SURFACE WATER KNOWN ISSUES AND SOLUTIONS programmatic action, or a combination of both programmatic and capital investment. A recommended solution is also shown in Table 5-4. Note that both the programmatic activities and capital projects recommended as part of the 2024 SWCP are described in Section 8 (Recommendations). Section 6 provides a listing of the capital projects. 5-18 5.0 SURFACE WATER KNOWN ISSUES AND SOLUTIONS Table 5-4 Recommended Solutions ID Problem Description Location Issue Type Possible Solutions Recommended Solution KI-1 Sediment/clogging issues along all of Southgate Creek including Normed Drainage Issue KI-2* Gilliam Creek dissolved oxygen issue Southgate Creek Drainage, water quality Gilliam Creek Water quality KI-3 Gilliam Creek turbidity issue Gilliam Creek Water quality KI-4 Gilliam Creek low pH issue KI-5 Gilliam Creek Sediment (PAHs) Issue Gilliam Creek Gilliam Creek Water quality Water quality Studies followed by Capital and/or Programmatic Capital (infiltration, retention, riparian buffer restoration, channel stabilization, sanitary sewer separation), or programmatic (education, source control) Capital (all BMPs for Water Quality and Erosion/Sedimentation issue types), or programmatic (ed- ucation, inspections, source control) Programmatic (education, source control) Capital (water quality treatment, impervious surface reduction, point source control) or programmatic (education, inspection for source control) Study (in progress) Programmatic Capital and programmatic Programmatic Capital and programmatic 5-19 5.0 SURFACE WATER KNOWN ISSUES AND SOLUTIONS Table 5-4 Recommended Solutions ID Problem Description Location Issue Type Possible Solutions Recommended Solution KI-6* Riverton Creek Sediment (Metals) Issue KI-7* Riverton Creek dissolved oxygen Issue KI-8* Fort Dent Park 6PPD- quinone issue Riverton Creek Water quality Riverton Creek Water quality Fort Dent Park Water quality KI-9* Runoff damaging private Beacon Ave S Drainage septic system and S 103 St Mul- tiple Mul- tiple 2022 Small Drainage Program List: KI-10 to KI-18 and KI-70 to KI-73 and KI-81, KI-87 Various Flood Patrol Assets — long list Various of stormwater system locations City staff checks Drainage, Maintenance Drainage, Maintenance Capital (water quality treatment, impervious surface reduction, riparian buffer restoration) or programmatic (education, operations and maintenance) Capital (infiltration, retention, riparian buffer restoration, channel stabilization, sanitary sewer separation), or programmatic (education, source control) Study to confirm issue, or Capital (infiltration, water quality treatment) Capital (provide drainage system) Capital (increase conveyance capacity, provide drainage system, velocity reduction, capital repair & replacement) Programmatic (operations and maintenance) Programmatic SMAP for Riverton Creek Basin CIP and programmatic Programmatic SMAP for Riverton Creek Basin CIP CIP-3 Fort Dent Park Water Quality Retrofit Programmatic Annual Small Drainage Program CIP Programmatic Annual Small Drainage Program CIP Programmatic (operations and maintenance) 5-20 5.0 SURFACE WATER KNOWN ISSUES AND SOLUTIONS Table 5-4 Recommended Solutions ID Problem Description Location Issue Type Possible Solutions Recommended Solution during all storms: KI-19 to KI- 69 KI-74* Fish mortality in Riverton Creek KI-75* KI-76 Lack of off -channel salmon habitat along lower Duwamish River: Issue ID 4 in 2013 Plan Fish habitat accessibility issues in Riverton Creek culvert: Issue ID 4 in 2013 Plan KI-77 Dumping Riverton Creek Water quality Duwamish Habitat River near light rail crossing E Marginal Habitat Way south of SR599 Citywide Water quality KI-78 Ponding in low spot, possible 49th Ave S and Drainage ponding on the east side of S Hazel Street road: Issue ID 2 in 2013 Plan Study to confirm issue, or Capital (all BMPs for Water Quality issue types), or programmatic (education, operations for street sweeping) Capital (physical habitat restoration) Capital (barrier removal, physical habitat restoration) Programmatic (education, illicit discharge detection, maintenance, enforcement) Capital (increase capacity) Programmatic SMAP for Riverton Creek Basin CIP and study to confirm issue Capital (physical habitat restora- tion) — Duwamish Gardens Phase II Capital — King County Metro Base redevelop- ment project includes daylighting Riverton Creek Programmatic (education, illicit discharge detection, maintenance, enforce- ment) Solved 5-21 5.0 SURFACE WATER KNOWN ISSUES AND SOLUTIONS Table 5-4 Recommended Solutions ID Problem Description Location Issue Type Possible Solutions Recommended Solution KI-79 Tukwila stormwater line dis- charges to WSDOT pipe, no access due to 1-405 widening: Issue ID 10 in 2013 Plan KI-80 Historical landslide: Issue ID 10 in 2013 Plan KI-82 Andover Park 48-inch storm - water pipe in poor condition, possibly damaged: Issue ID 11 in 2013 Plan KI-83 34th Ave S Water-logged Property KI-84 Water Quality in Tukwila Pond KI-85 Cascade view/S 128' St Landslide Known Issue Andover Park Drainage/ W at Gilliam Maintenance Creek S 137" St at 44th Ave S Water quality/ Drainage / Erosion/Sedimentation Andover Park Drainage W 34th Ave S north of S 135th St Drainage Tukwila Pond Water quality Military Rd S and S 128th St Water quality, Drainage, Erosion/ Sedimentation Capital (increase conveyance capacity, replacement of culvert to be fish -passable) Study Capital (conveyance system repair & replacement) Capital (provide drainage system) or Programmatic (technical assistance) Capital (water quality treatment) Study Capital CIP-4 Tukwila Parkway / Gilliam Creek Outfalls Study CIP-102 Middle Fork of Southgate Creek — Stream and Slope Stability Study Capital (conveyance system repair & replacement) None — private responsibility2 CIP-5 Tukwila Pond Water Quality Improvement Landslide study grant from Federal Emergency Management Agency (FEMA) 5-22 5.0 SURFACE WATER KNOWN ISSUES AND SOLUTIONS Table 5-4 Recommended Solutions ID Problem Description Location Issue Type Possible Solutions Recommended Solution KI-86 Unauthorized encampment in Parcel 3747 Mul- Pollution -generating gravel tiple parking lots: KI-88 to KI-154 KI-155 Springbrook Maintenance KI-156 S Ryan Way Drainage and Pipe Condition Issues KI-157 Erosion at inlet of 108" diameter culvert carrying Gilliam Creek under 66th Ave S and the Green River Trail KI-158 Foster Heights erosion problem in Southgate Hwy 99 and S 146th St Citywide Water quality Drainage, Water quality Springbrook Maintenance S Ryan Way between Beacon Ave S and Martin Luther King Way S 66th Ave S and 1-405 Drainage, Maintenance Drainage, Maintenance 43rd Ave S just Erosion north of S 137th St Capital (land acquisition) Programmatic (regulatory and policy changes, inspection, and enforcement) Programmatic (operation and maintenance) Capital (repair & replacement of stormwater facilities) Capital (velocity reduction, channel stabilization, repair & replacement) Study N/A — parcel subsequently sold Programmatic (regulatory and policy changes, inspection, and enforcement) Programmatic (operation and maintenance)2 City of Renton is responsible. CIP-2 S Ryan Way Pipe Rehabilitation Capital (velocity reduction, channel stabilization, repair & replacement) — project in progress Study CIP-102 Middle Fork Southgate Creek Stream and Slope Stability Study 5-23 5.0 SURFACE WATER KNOWN ISSUES AND SOLUTIONS Table 5-4 Recommended Solutions ID Problem Description Location Issue Type Possible Solutions Recommended Solution KI-159 Norfolk Trunkline Sewer Separation KI-160 KI-161* KI-162 General Water Quality and Flow Control Issues in Southgate Creek — Opportunity for Stormwater Park Barriers to fish passage (citywide) and Johnson Creek Flapgate Fish Passage Barrier Incomplete transfers of responsibility of old WSDOT stormwater facilities to City KI-163 S 180th Pump Station Capacity Concern KI-164 Minkler Property Sale and P17 Pond Replacement East Marginal Way and S Norfolk St Water quality 44th Ave S and Water quality S 131st PI Near Frager Rd Habitat S and S 204th St Interurban Ave Water quality, S and South- Maintenance west Grady Way & others S 180th St just Drainage, east of South- Maintenance center Pkwy Minkler Blvd Habitat, Drainage, east of Maintenance Industry Rd Capital (provide drainage system, sanitary sewer separation) Capital (regional detention/retention, water quality treatment, land acquisition) Capital (fish passage barrier removal, channel physical habitat restoration) Programmatic (policy changes) Study Study CIP-1 Norfolk Outfall Trunkline Sewer Separation Preliminary Feasibility Study Capital (regional detention/retention, water quality treatment, land acquisition) CIP-6 Johnson Creek Fish Barrier Mitigation Alternatives Analysis and Study CIP-101 Fish Passage Barrier Prioritization Programmatic (policy changes) Study CIP-103 P17 Pond and Southcenter Subarea Hydraulic Study Study CIP-103 P17 Pond and Southcenter Subarea Hydraulic Study 5-24 5.0 SURFACE WATER KNOWN ISSUES AND SOLUTIONS Table 5-4 Recommended Solutions ID Problem Description Location Issue Type Possible Solutions Recommended Solution KI-165 KI-166 KI-167 KI-168* KI-169 ROW and private property flooding in Southgate Creek basin. Issue ID 24 in 2013 Plan. Unknown condition of storm system in Southcenter Subarea. ROW and private property drainage issues occur along S 143rd St. Issue ID 9 in 2013 Plan. No functional outlet to drainage network at Nelsen/Longacres. Issue ID 19 in 2013 Plan. Permanent home for soils reclamation facility (decant facility). Issue ID 18 in 2013 Plan. along Green/ Duwamish River S 146' St and Drainage 35' Ave S Southcenter Maintenance Subarea S 143rd east of Drainage Interurban Ave Area bounded Drainage by SR 181, Green River, BNRR, and Strander Blvd. TBD Water quality Capital (increase conveyance capacity) Programmatic (operation and maintenance) Capital (provide drainage system) Capital (provide drainage system) Capital (land acquisition and site development for decant facility) CIP 90341214 S 146" St Pipe and 35th Ave Drainage System CIP 91241203 Tukwila Urban Center Conveyance Inspections CIP 98641222 S 143rd St Drainage System CIP 98741202 Nelson/Longacres Drainage Improvement, Phase II CIP 99441202 Soil Reclamation Decant Facility 5-25 5.0 SURFACE WATER KNOWN ISSUES AND SOLUTIONS Table 5-4 Recommended Solutions ID Problem Description Location Issue Type Possible Solutions Recommended Solution N/A** Addressing flood protection River corridor, Major flooding** along the Green/Duwamish citywide River within the City, including the need to certify the Tukwila 205 Levee for accreditation from the Federal Emergency Management Agency (FEMA) Capital (flood protection)** CIP-104 Tukwila Master Plan for the Lower Green River Levee Projects * These issues and solutions have been recognized as priorities by the Duwamish Tribe. ** This issue was added near the end of planning. The major flooding issue and flood protection capital solution type are not discussed extensively elsewhere in this document and are primarily the responsibility of the KCFCD. 5-26 5.5 Issue and Solution Prioritization and Selection The planning process for the 2024 SWCP identified more issues that require a capital improvement than the City could afford to construct over the next 10 years. As a result, the issues were screened to identify the most important issues to address first. For the most important issues, potential capital improvement projects were prioritized based on a variety of factors. In addition to selecting capital improvement projects based on individual characteristics, the process also ensured that the City's portfolio of surface water CIPs and studies in the 2024 SWCP would solve a comprehensive set of surface water issue types and would address regional priorities. Table 5-5 describes the known issue screening factors, and Table 5-6 describes project prioritization weighting. Table 5-5 Known Issue Screening Factors Issue Type Audience City Regional Priority Public Input Intractable, severe, or widespread issue within City Localized drainage Issues x x Degraded water quality from urban x x x pollutants Degraded water quality from erosion x and landslides Flow control x x Degraded or lack of off -river fish x x x habitat Barriers to fish passage x x x Poor condition and aging of storm x x sewer system 5-27 5.0 SURFACE WATER KNOWN ISSUES AND SOLUTIONS Table 5-6 Project Prioritization Weights Project Characteristics Relative Weight High Medium Low Multi -beneficial project which combines solutions to x multiple problems Multi -beneficial project which coordinates with efforts of x other Tukwila departments and divisions (e.g., Parks, Transportation) or other agencies Project addresses a regional priority or anticipated x regulatory requirement Project is eligible for grant funding x Project received favorable public input x Previously identified project not yet implemented x Standalone water quality project x Standalone habitat / fish barrier removal project x Standalone flooding / drainage project, high severity x Standalone erosion / sedimentation project x Tukwila Surface Water Management Program is not the lead x agency and does not control timing of multi -benefit project' Standalone maintainability or capital repair/replacement x Standalone flooding / drainage project, low or medium x severity ' Change priority to "high" when another department or agency is ready to advance the project 5-28 6.0 Capital Improvement Projects and Studies This section summarizes the individual capital improvement projects, programmatic CIPs, and studies recommended for inclusion into the City of Tukwila's capital improvement program. The capital projects are listed in Table 6-1. Figure 6-1 shows the locations of each individual capital project. Appendix E contains the details for each capital project, programmatic CIP, and study, including cost estimates. Projects that are already in -process or have funding committed are listed in Section 1.1. Table 6-1 Recommended Capital Projects and Studies Estimated Total Project ID Project Name Project History Cost (2023 dollars) Individual Capital Projects 98641222 S 143rd St storm drain system 98741202 Nelsen/Longacres — Phase II 99441202 Soil Reclamation Facility / Decant Facility Design — Phase I 90341214 S 146th St pipe and 35th Ave S drainage 91241203 Tukwila Urban Center Conveyance Inspections CIP-1 Norfolk Outfall Trunkline Sewer Separation Preliminary Feasibility Study CIP-2 S Ryan Way Pipe Rehabilitation CIP-3 Fort Dent Park Water Quality Retrofit CIP-4 Tukwila Pkwy/Gilliam Cr Outfalls 2003 and 2013 Plans $1,410,000 2013 Plan $1,000,000 2003 and 2013 Plans; $540,000 City will study cost under Enhanced Maintenance Planning grant in 2024 2003 and 2013 Plans 2003 and 2013 Plans New New New 2013 Plan ID 91241202; 2023 Tukwila CIP ID 91241205; CIP-4 is a redesign $1,290,000 $790,000 $155,000 Alt. 1: $840,000 Alt. 2: $680,000 Alt. 1: 90,000 Alt. 2: $1,745,000 $1,240,000 6-1 6.0 CAPITAL IMPROVEMENT PROJECTS AND STUDIES Table 6-1 Recommended Capital Projects and Studies Estimated Total Project ID Project Name Project History Cost (2023 dollars) CIP-5 Tukwila Pond Water Quality New $940,000 Improvement CIP-6 Johnson Creek Fish Barrier New $280,000 Mitigation Alternatives Analysis Programmatic CIPs 81241207 Annual Small Drainage Ongoing, Annual Avg. $950,000 / year Program 91241202 Stormwater Outfalls Water 2013 Plan (ID Varies by project Quality Retrofit Program 91241201); some projects in program have been completed. TBD SMAP Program CIP New $3,640,000 TBD Green Infrastructure Program New TBD TBD WSDOT Stormwater Retrofit Ongoing Varies by project and Maintenance Program Studies and Plans CIP-101 Fish Passage Barrier New $147,000 Prioritization Study CIP-102 Middle Fork of Southgate New $200,000 Creek — Stream and Slope Stability Study CIP-103 P17 Pond and Southcenter New $300,000 Subarea Hydraulic Study CIP-104 Tukwila Master Plan for the New $275,000 Lower Green River Levee Projects 6-2 FIGURE 6-1 CAPITAL IMPROVE AND STUDIES TUKWILA SWCP 133383 TUKWILA, WAHIT4��N T PROJECTS Data Sources King County Gdy of Tukwia Google Maps Date 6/5i2024 D,sdamer Ms data is not to survey accuracy and IS meant for piannuog purposes only 0 \ PROJECT /33300\33383\CADD\GIS\APFXr\33383 Tukwila SWCP Fioures\33383 Tukwila SWGP Figures TMK aprx Legend ® City Boundary r J Neighboring Cities - Streams and Rivers ' Capital Improvement Projects ',.CITY OF,RENTON Y3 Ax =98741,202= Q Mile Otak 7.0 Operations and Maintenance In the 2013 SWCP, this section contained a description of the operations and maintenance activities applicable to the City of Tukwila's Surface Water Management Program. This section has not been updated for the 2024 SWCP, and the content has been omitted from the plan. Two significant studies are already underway which will soon provide the City guidance for updating Surface Water Management Program O&M. These are 1) an Enhanced Maintenance Plan (EMP) and 2) NPDES Program Assessment. The EMP will describe, assess, and recommend updates to the City's operations and maintenance program. The NPDES Program Assessment will evaluate the current operations and maintenance program to identify gaps and where the City can improve compliance with the Phase II NPDES Permit. Section 7.0 has been retained in the 2024 SWCP as a placeholder for the next plan update, expected in about 10 years. At that time, updated information about the Surface Water Management Program operations and maintenance program should be re -integrated into the plan document. 7-1 8.0 Recommendations This section describes the recommendations made in the 2024 SWCP for the City of Tukwila's Surface Water Management Program and an implementation plan, which considers funding, partnerships, prioritization, and scheduling. 8.1 Recommended Activities 8.1.1 Capital Projects Section 6 outlines the individual capital projects, programmatic CIPs, and studies proposed in this plan. Not all capital projects are recommended for implementation in the 10-year planning window, due to funding availability. The remaining capital projects represent the continuing need for capital improvements in the City of Tukwila in order to achieve surface water goals. The City of Tukwila should consider this list of unfunded capital projects when making investments in other arenas (such as transportation) or when outside funding sources are identified (such as grants or loans). This list will likely be a starting point for the next round of comprehensive surface water planning. To implement capital project recommendations, the City will need to proceed with a thorough design and permitting process for each project. The capital project design process will consider the possibility of encountering Duwamish Tribe or Muckleshoot Indian Tribe cultural resources or archaeological deposits, conflicts with other utilities, presence of critical areas such as wetlands and steep slopes, and other factors to be assessed during the design and permitting process. 8.1.2 Programmatic Solutions and Policies Subsequent to the 2013 Surface Water Comprehensive Plan, the City made substantial improvements to the Surface Water Management Program within the Public Works Department in order to comply with the then -current NPDES Phase II Permit. The current programmatic recommendations are comparatively modest and are tailored primarily toward voluntary programmatic actions to participate in regional water quality and aquatic habitat improvement efforts. This sub -section contains a summary of the recommended improvements to Tukwila's Surface Water Management Program needed in order to more fully comply with applicable regulations or to voluntarily improve efficiency, performance, or outcomes. 9-1 8.0 RECOMMENDATIONS The City should continue to comply with the NPDES Phase II Permit and continue to implement its required annual NPDES Stormwater Management Program. The recommendations below are limited to new programs or substantial changes to programs. 8.1.2.1 Stormwater Planning To protect water quality and prepare for anticipated requirements in the next NPDES Phase II Permit cycle, the City should adopt and implement its Stormwater Management Action Plan (SMAP) for Riverton Creek (Appendix F) as part of the implementation plan for the 2024 SWOP. It is also recommended that the City develop an asset management system to inform stormwater planning efforts and operation and maintenance of the stormwater system. Capital projects and programmatic solutions are informed by data the City or partners collect. A dashboard would track all metrics related to surface water issues within the city limits and receiving waters. 8.1.2.2 Regulatory and Policy Changes The City should respond to any new and additional requirements in the next NPDES Phase II Permit cycle, which will likely include changes to thresholds for providing stormwater management facilities on development and redevelopment sites and a requirement to preserve and increase forest cover as a stormwater management BMP. To protect water quality and maintain compliance with the NPDES Phase II Permit, the City should consider changing policies, regulations, or enforcement, include the following: • Study whether to update nonconforming parking lot standards in TMC 18.70.080 to modify redevelopment thresholds for nonconforming parking areas. The temporary gravel parking areas developed under this standard have effectively become permanent impervious surfaces which can contribute to surface water pollution. Another option is to change enforcement procedures to ensure that temporary nonconforming lots do not become effectively permanent. A change in policy or enforcement will require coordination between the Public Works and Community Development departments. • Establish a policy to preserve and increase forest cover in the City in coordination with the draft Comprehensive Plan Goal 13 to increase tree cover at least by the time a policy is required by the 2024-2029 NPDES Phase II Permit in 2028. • Require annual inspections and corrections for septic systems (where applicable). • Allow new roads, driveways, parking areas and walkways to be constructed of pervious materials such as pervious asphalt, concrete, or pavers where infiltration is feasible. 8-z 8.0 RECOMMENDATIONS • Update thresholds for providing stormwater management facilities on development and re -development when required by the 2024-2029 NPDES Phase II Permit. • Update regulation to prohibit discharge of PCBs into stormwater from washdown of commercial and industrial buildings that date from 1950 to 1980 when required by the 2024-2029 NPDES Phase II Permit. Changes to policies or to regulations at the state or national level are outside the scope of this document. In addition, the City should keep track of possible modifications to its NPDES stormwater permit over future cycles to include TMDL requirements on the Green and Duwamish Rivers. 8.1.2.3 Inspection and Enforcement The City should complete as -needed CCTV inspections of the City's stormwater pipes where sedimentation or poor condition is suspected due to age, system design, or observed localized flooding. Complete cleaning of identified stormwater pipes in order to allow inspections to occur. The City should enhance its inspection program to reduce noncompliance with source control and private stormwater facility maintenance requirements to protect against the risk of water quality violations. The concurrent NPDES Program Assessment Project, ongoing as of the writing of the 2024 SWCP, may identify required changes to address requirements of the next NPDES Phase II Permit. 8.1.2.4 Operations and Maintenance The City should assess its maintenance program for opportunities to improve or increase services to improve stormwater quality. The concurrent NPDES Program Assessment Project, ongoing as of the writing of the 2024 SWCP, may identify required changes to address requirements of the next NPDES Phase II Permit. The City should build a permanent Vactor waste treatment facility (decant facility) to allow more frequent and thorough maintenance of the storm system. To voluntarily enhance the City's active commitment to protecting ESA -listed fish, the City should consider applying to the Regional Road Maintenance Program and formally adopting and following the Regional Road Maintenance Guidelines. The program and application of the guidelines ensure that road maintenance is conducted in a fashion that does not harm ESA -listed fish. 8-3 8.0 RECOMMENDATIONS 8.1.2.5 MS4 Mapping and Documentation To improve effectiveness in managing the stormwater system and prepare for anticipated requirements in the 2024-2029 NPDES Phase II Permit cycle the City should: • Develop an administrative policy from the City Administrator's office detailing responsibilities for coordinating the routing of information and updating the MS4 map cooperatively between Community Development, Technology and Innovation Services, and Public Works. The policy should also ensure adequate access to data for City staff end users. This action is not required by the NPDES Phase II Permit, but it could facilitate needed cooperation and understanding between departments. • Map additional characteristics of the MS4, such as connection points to private stormwater systems, when required by 2024-2029 NPDES Phase II Permit. • Map tributary basins to outfalls and discharge points, and document acreages that are not managed in a stormwater treatment or flow control facility when required by 2024-2029 NPDES Phase II Permit. • Begin mapping tree canopy when required by 2024-2029 NPDES Phase II Permit. • Reassess outfall identification after the Community Development Department revises the City's stream mapping and identification. It is thought that a more complete stream mapping will reveal that some stormwater system structures should be classified as outfalls to receiving waters. 8.1.2.6 Public Education and Outreach The City's existing public education and outreach activities appear adequate to meet requirements of the current NPDES Phase II Permit. The concurrent NPDES Program Assessment Project, ongoing as of the writing of the 2024 SWCP, may identify required changes to address requirements of the 2024-2029 NPDES Phase II Permit. The City may wish to expand the program offerings voluntarily. The educational topics listed below could supplement the current City of Tukwila education program: • Proper maintenance of septic systems (where applicable). • Stream reach needs — get to know your backyard, adding Adopt -a -Stream to the Adopt A Spot program. • Free "mutt mitts" for pet owners. 8-4 8.0 RECOMMENDATIONS • Free technical assistance for private property owners wishing to implement on -site surface water management (such as rain gardens or rain barrels). • Community Rain Garden Stewardship Program (see SMAP-20 in Appendix F). • Green Tukwila. • Tree giveaway. 8.1.2.7 Public Involvement and Participation Environmental stewardship activities should continue with a focus on overburdened communities, which the EPA defines as minority, low-income, and tribal populations that may experience disproportionate environmental harms and risks. Ecology may require increased emphasis on involvement of overburdened communities in the upcoming NPDES Phase 11 Permit, so The City should document its efforts to involve these communities. The concurrent NPDES Program Assessment Project, ongoing as of the writing of the 2024 SWCP, may identify required changes to address requirements of the next NPDES Phase II Permit. Green Tukwila presents an opportunity for the Surface Water Management Program to capitalize further on an existing City program. Green Tukwila aims to restore and maintain more than 100 acres of Tukwila's forested parks and natural land, ensure natural lands provide ecosystem benefits, and engage volunteers to lead restoration efforts. The program recognizes that natural lands reduce stormwater runoff, improve water quality, provide habitat, and much more. The program could also serve to improve public awareness of stormwater issues. 8.2 Implementation The 2024 SWCP is an ambitious proposal for tackling both regional and local issues. The City's prior surface water plans were comprised of capital and programmatic solutions targeting drainage concerns and minimum compliance with NPDES Phase II Permit requirements. The 2024 SWCP also emphasizes interdepartmental and regional cooperation to achieve multi -benefit solutions serving regional priorities to protect and restore the region's cherished natural resources. 8.2.1 Funding and Partnerships Projects implemented primarily for surface water management purposes are funded with the City's Fund 412, Surface Water Fund. Fund 412 is an enterprise account for utility operations which is self -supported through Surface Water rate charges. At the time of writing, the City has projected annual increases to surface water rates through 2028. Including both 8-5 8.0 RECOMMENDATIONS projected rate revenue and projected proceeds from grants, the City's 2023-2028 rate model analysis allows for slow growth in expenditures for programmatic elements such as operations and maintenance and permit compliance activities. It allows for variable annual funding for the CIP ranging from $1,965,000 at the lowest in 2027 to $12,995,000 at the highest in 2025. It should be noted that the projections are used for planning purposes and are not adopted City budgets. The City adopts a budget and a six -year CIP biennially. Grant and bond revenue is also deposited into Fund 412 when available. The City has made extensive use of grants from Ecology and KCFD for surface water capital projects. City Council approved $13.6 million in capital expenditures from the Surface Water Fund in the first two years of the adopted 2023-2028 Capital Improvement Program. Nearly half of the approved capital expenditures are from grants as illustrated in Figure 8-1. ooniRr Figure 8-1 Surface Water Capital Program Funding 2023-2024 The City has received approximately $3.2 million in grant funding for stormwater planning and stormwater retrofit CIPs from Department of Ecology between 2016 and 2023. The City has current agreements totaling $2.3 million in grant funding for the Enhanced Maintenance Program and Decant Facility Design (CIP 99341208) and the Stormwater Quality Retrofit Program Part 2 (91241202). The City has received a landside grant from FEMA Cooperative Technical Partners (CTP) to study existing landslides. The findings from the study could produce findings that assist with the Middle Fork Southgate Creek Stream Stability Study (CIP-102). The City has submitted an application for funding to FEMA CTP for P17 Pond and Southcenter Subarea Hydraulic Study (CIP-103). The City may qualify for grant funding from the King County Flood Control District for projects that reduce the impact of flooding. The program categories are Flood Reduction, Urban Streams, Coastal Erosion/Coastal Flooding, and Culvert Replacement/Fish Passage 8-6 8.0 RECOMMENDATIONS Restoration. Projects that achieve multiple benefits are encouraged. Eligible project types that are applicable to the City proposed CIPs are: • Upgrading aging or undersized stormwater systems in urban or suburban areas. o CIP-2 S Ryan Way Pipe Rehabilitation o CIP 90341214 S 146th St Drainage o CIP 98641222 S 143rd St Drainage o CIP 98741202 Nelsen Place/Longacres Phase 2 • Replacing culverts that block fish passage and restrict flows and undermine streambanks. o CIP-6 Johnson Creek Fish Barrier Mitigation Alternatives Analysis In addition, Ecology typically awards the City a Capacity Grant each year to support compliance with the Phase II NPDES Permit with activities such as education and outreach about stormwater, a volunteer Stream Team, charity car washes, technical assistance for stormwater source control, and other required compliance activities. Based upon the findings of the NPDES Program Assessment, expected to be complete in 2024, and the Enhanced Maintenance Program Analysis, expected to be complete in 2025, the City should reevaluate Operations & Maintenance expenditures and request budget increases and staffing increases if findings support those increases. This could require shifting some resources away from the CIP Program expenditures in order to maintain the Fund 412 balance required by the City's financial policies. The City intends to leverage partnerships to increase effectiveness of its programs and capital investments and to obtain grants to fund elements of the CIP. The City partners with Washington State to fund stormwater retrofit projects and certain maintenance activities with surface water management fees collected by the City from WSDOT. This partnership aims to retrofit limited -access state highways in Tukwila with water quality treatment BMPs. An annual retrofit plan and project status report must be submitted to and approved by WSDOT in order to collect a surface water management fee from WSDOT. See Appendix F for the Tukwila Retrofit and Maintenance Plan for WSDOT Facilities Memorandum. The 2024 SWCP recommends implementing Community -Based Public -Private Partnerships (CBP3) to plan, deliver, and/or maintain public stormwater projects. CBP3s are partnerships between a local government and a private entity to collaboratively plan, deliver, or maintain 8a 8.0 RECOMMENDATIONS public stormwater projects. These partnerships are intended to achieve community benefits beyond stormwater improvements and permit compliance through performance -based contracts and alternative procurement. CBP3 projects can vary greatly but are intended to achieve stormwater improvements in addition to community benefits. The Washington State Department of Commerce has developed a guidebook to assist local governments to more effectively achieve stormwater and community objectives. Ecology is also developing a program that will support jurisdictions, including Tukwila, in developing and implementing CBP3s. 8.2.2 Prioritization and Scheduling The City will determine a schedule for implementing the recommendations in the 2024 SWCP based on priority and availability of funding. Table 8-1 lists recommendations by priority. Table 8-1 Recommended Priority for Implementing Recommendations Recommendation Reason Schedule High Priority Ongoing CIPs identified in Table E- Ongoing 7 (Appendix E) Programmatic changes pursuant to 2024-2029 NPDES Phase II Permit requirements - TBD OP-1 Norfolk Outfall Trunkline Sewer Separation Preliminary Feasibility Study CIP 91241202 Stormwater Outfalls Water Quality Retrofit Program CIP 99441202 Soil Reclamation Facility / Enhanced Maintenance Program and Decant Facility Design — Part 1 SMAP Program CIPs Maintain regulatory compliance Prior years — 2025 or beyond 2025-2029 Reduce potential City liability for combined 2025 sewer overflows and responsibility for Superfund site cleanup Grant award received; meets regional 2024 priorities for reducing harmful effects of urban runoff on water bodies; completes programmatic CIP begun in 2017 Grant award received; supports NPDES Phase II Permit requirements; meets regional priorities for reducing harmful effects of urban runoff Meets expected requirement of 2024-2029 NPDES Phase II Permit; meets regional priorities for reducing harmful effects of urban runoff on water bodies; eligible for grant funding 2024-2025 Begin 2025, then ongoing every 2- 3 years 8-8 8.0 RECOMMENDATIONS Table 8-1 Recommended Priority for Implementing Recommendations Recommendation Reason Schedule WSDOT Retrofit Program OP-102 Middle Fork Southgate Creek — Stream and Slope Stability Study CIP-3 Fort Dent Park Water Quality Retrofit, Alternative 1 OP-2 S Ryan Way Pipe Rehabilitation MS4 mapping and documentation programmatic recommendations Apply for grant funding for eligible phases of programmatic water quality CIPs and medium priority projects identified below Green Infrastructure Program CIP-104 Tukwila Master Plan for the Lower Green River Levee Projects Required in order to charge surface water management fee to WSDOT; meets regional priorities for reducing harmful effects of urban runoff on water bodies; funded by WSDOT Stream condition severely degraded and private property at risk. Coordinates with ongoing Southgate Hydraulic Study encompassing Normed Facility and could make use of findings from City's successful FEMA-funded landslide study. Meets regional priorities for reducing harmful effects of urban runoff on water bodies; low-cost alternative that can be implemented by City crews. Collaboration with City Transportation Department; preventive repair and replacement; reduce sheet flow on steep high -traffic roadway City risks permit non-compliance. Barriers to information sharing hinders stormwater planning, regulatory review of development and construction, inspection and enforcement, and capital project development. Allows City to continue to fund higher levels of capital investments without impacting surface water utility rates Reduces disparities in access to healthy environments, improves interdepartmental coordination in working on regional priorities such as reducing harmful effects of urban runoff, increasing access to fish habitat, and increasing quality of fish habitat Flood protection projects sponsored by KCFCD and federal partners are imminent. City will need to begin master planning immediately in order to guide aesthetic considerations and community connections for these projects. 2024 and annually 2026 2027 Coordinate timing with City Transportation Department 2025-2029 2024-2034 Begin 2025 Begin 2025 8-9 8.0 RECOMMENDATIONS Table 8-1 Recommended Priority for Implementing Recommendations Recommendation Reason Schedule Regulatory and Policy change - study whether to update nonconforming parking lot standards in TMC 18.70.080 or update enforcement procedures. City risks permit non-compliance. Strategically time interdepartmental negotiations and policy -setting with reissuance of NPDES Phase II Permit in 2024. 2025 Medium Priority CIP 98641222 S 143rd St Storm Drain System CIP 99441202 Soil Reclamation Facility / Enhanced Maintenance Program and Decant Facility Design — Part 2 CIP 98741202 Nelson/Longacres — Phase II OP-6 Johnson Creek Fish Barrier Mitigation Alternatives Analysis OP-90341214 S 146th St and 35th Ave S Drainage Longstanding drainage / flooding issue 2027 which may be eligible for grant funding from KCFCD Increase efficiency and effectiveness of 2026 operations and maintenance program Longstanding drainage / flooding issue 2028 which requires coordination with railroad and may be eligible for grant funding from KCFCD Meets regional priorities to increase access 2026 to fish habitat; ensures balanced portfolio of CIP projects by including fish barrier removals at regular intervals Longstanding drainage / flooding issue 2029 which may be eligible for grant funding from KCFCD Low Priority Other programs and CIPs not listed 2030 and beyond above 8.3 Conclusion The 2024 SWCP proves a strategic framework for the management of surface water within the City of Tukwila. It is an ambitious proposal for tackling drainage issues, water quality, erosion / sedimentation issues, habitat loss, and maintenance and condition of the stormwater system. The 2024 SWCP recognizes that City of Tukwila can be a key partner with state agencies, King County, Tribes, and organizations in reaching toward regional priorities to protect and restore the region's cherished natural resources. 8-10 9.0 References Accola, Kerry, et. al. 2O24. Technical Report on Juvenile Chinook Salmon Effectiveness Monitoring of1Juw/mnvish Shallow Water Restoration Sites 2023. Prepared by Wetland Ecosystem Team and Fisheries Acoustics Lab, School of Aquatic and Fishery Sciences, University of Washington. Prepared forVVR|A 9. March. CH2MHILL. 2003.City of Tukwila Comprehensive Surface Water Management Plan. Prepared by CH2M HILL, Inc. Prepared for the City of Tukwila. November. CH2M HILL. 2013. City ofTukwila Surface Water Comprehensive Plan Prepared by CH2M HILL, Inc. Prepared for the City of Tukwila. February. City of Tukwila. 2019. Inhouse Baseline Water Quality Assessment and Report Riverton Flapgate Removal Project January 17. City ofTukwila. 2022. Tukwila Pond Park Master Plan. https://w/wmv.tukvvi|avva.gov/vvp- cnntent/up|Oads/Tukvvi|a-Pond-Park-Master-P|an 2OZ2-01-ZZ.pdfaccessed February 2OZ4. January. City ofTukwila. 2U24.Annual Small Drainage Program. https://vvvvvv.tukvvi|avva.gov/departnnents/pub|ic-vvorks/construction-pr jects-and transportation-irnpacts/annua|-srna||-drainaQe-pnoQrarn/accessedFebruary2O24. City of Tukwila. 2024. Chinook Wind. https://www.tukwi|awagov/departments/pub|ic- vvorks/cnnstruction-p jects-and-transpOrtation-irnpacts/chinnok-vvind/accessed February 2024. City ofTukwila. 2024.Green Tukwila Partnership. https://vvvvvv.tukvvi|avvagov/departnnents/parks-andrecneation/vO|unteering/green-tukvvi|a partnership/acces5ed February2024. City of Tukwila. 2024. Stornvm/oterManagement Program (5N/MP). https://vvvvvv.tukvvi|avvagov/vvp-content/up|oads/PVV-NPOES-2OZ4-S\NK4P-Dnaft- [onnrnent.pdfaccessed Feb/uaryZO24. [hv of Tukwila. 2024. Stornvm/oter Outfalls Water Quality Retrofit Project Report. https//vvvvvv.tukvvi|avvagov/departnnents/pub|ic-vvorks/cnnstruction-projects'and transportation-irnpacts/stornnvvater-outfa||s-vvater-qua|itv-retrofit-pnject/accessed February2U24. m 9.0 REFERENCES City ofTukwila. 2024. Tukwila Comprehensive Plan 2024-2044: Draft Plan Forwarded to City Council for Review. https://vvvvvv.tukvvi|avvagov/departnnents/connrnunitV- deve|Oprnent/cornprehensive-p|an/connprehensive-p|an-e|ernent-drafts/accessed March 2024. DuvvarnishAJive! Coalition. ZU24.Duw/omishSites. https://vvvvw.duvvarnisha|iveorg/duvvannish-sites/accessed February 2024. OuvvarnishBlueprint Working Group. ZO14. Salmon Habitat b7the Duw/on/ishTransition Zone. Prepared for the Gneen/Ouvvarnish and Central Puget Sound (WR|A9) Watershed Ecosystem Forum. https://vvvvvv.gov|ink.orq/watersheds/9/p|an innp|ennentation/duvvb|ueprint/duvvb|ueprint nov0 ZU14-fina|.pdfaccessed February2UZ4. Novennber0. Esseyons Consulting Engineers, Inc. 2003. Technical Information Report for Starfire Fields at Fort Dent Park. May 27. Forterna.Z017.Green Tukwila 20-Year Stewardship Pkzn h tukwilawo.govlwp- con ten t1uploodslPR- Green - Tukwila-20- Year- Ste wardship -P/on.pdfaccessed February Z024. Green/Ouvvarnishand Central Puget Sound Watershed Water Resource Inventory Area 9 (WR|AQ).2021. Salmon Habitat Plan. https://www.gov|ink.org/watersheds/9/pdf/2021 P|anUpdate.pdfaccessed February ZO24. February11. King County. 2O23.Provisional Regional Storn7w/uberAction Goals. April. King County Department of Natural Resources and Parks. 2019./uvenile Chinook Use ofNon- natal Tributaries in the Lower Green River. 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