The Road to 700 Million Gallons: Helping SPU and WTD Reach GSI Goals

Seattle Public Utilities (SPU) and King County Wastewater Treatment Division’s (WTD) 2020 Green Stormwater Infrastructure (GSI) Progress Report is now available! This report provides insight into current GSI goals and initiatives around the Seattle area.

Over the past 20 years, the use of GSI implementation has grown through SPU and WTD-led projects, updated stormwater codes, and public-private partnerships. In this timeframe, the millions of gallons of water managed per year through GSI has increased from 10 million gallons in 2000 to 410 million gallons in 2020. With this, SPU and WTD are on track to naturally control 700 million gallons of stormwater annually by 2025.

SPU and WTD’s GSI Program focuses on four main growth areas: expanding the GSI toolbox, growing partnerships, supporting the community, and removing barriers. As a lead consultant for the GSI Program, Herrera is dedicated to assisting SPU and WTD with these initiatives, further advancing green stormwater infrastructure throughout the Seattle area.

GSI on Private Properties
As part of the GSI Program work, Herrera supported SPU and WTD in developing RainWise; a program that provides rebates to property owners for rain gardens and cisterns to manage roof runoff in neighborhoods where storm and sewer systems share the same pipes. Since the program’s inception, RainWise has completed over 2,200 projects throughout Seattle, including more than 1,000 rain gardens. RainWise also provides opportunities for contractors in landscaping and other GSI-related fields, offering multilingual, virtual, and small business training options.

In addition to single-family residences, RainWise actively recruits “Big Roof” projects, providing rebates to community centers, religious organizations, apartment buildings, and businesses for the installation of cisterns or rain gardens. These projects benefit large properties by saving property owners money, promoting environmental stewardship, and creating volunteer opportunities for community education and engagement. Herrera continues to support RainWise on single-family residence and Big Roof projects by leading technical support for these initiatives.

GSI in the Right-of-Way
SPU and WTD lead large capital projects to integrate GSI in the public right-of-way to manage roadway runoff using natural drainage systems. There are multiple NDS projects currently underway.  Herrera is proud to be leading design for 12th Avenue NDS and North Thornton NDS, in addition to providing design review, monitoring support, and construction support for BSM on Longfellow Creek NDS and South Thornton NDS projects.

In addition to NDS work, Herrera is the Green Design Lead for Longfellow Starts Here– SPU’s community-centered project in the South Delridge neighborhood. Through this project, SPU plans to improve water quality in Longfellow Creek by investing in sewer system improvements and stormwater treatment. The project is centered on racial and social equity to determine how and where investments should be made to maximize community benefits.

GSI Innovations
Green stormwater infrastructure continues to evolve with the emergence of new technologies and tools. Notably, Herrera’s water quality scientists supported SPU in developing a “polishing layer” for bioretention soil to improve treatment performance and eliminate phosphorus export from the soil. SPU is conducting the first full-scale field deployment of the polishing layer at the Swale on Yale project.

Constructed floating wetlands (CFW) have also emerged as a new tool for improving water quality. These man-made water structures support wetland ecosystems by providing habitat for fish and wildlife while supporting clean water. The WTD WaterWorks Grant Program funded two CFW projects for construction on the Duwamish River and the Washington Lake Ship Canal. Herrera is currently working with the Seattle-based organization Friends of Green Lake, which plans to build constructed floating wetlands at Green Lake to support ecosystem vitality.

In collaborating with SPU on what it means to deliver a community-centered infrastructure project, Herrera has developed several innovations and tools for Longfellow Starts Here.

The Water Game: The Water Game is a calculator that allows the community to explore the water quality performance and costs of infrastructure options in real-time. This tool intends to facilitate simple, iterative planning so that community members can collaborate with SPU to “co-create” the project and engage in dialogue around trade-offs and benefits of various scenarios.

GSI Mapping Tool: Herrera developed a new mapping tool designed to center community needs in the City’s infrastructure planning process. Through a series of “heat” maps, users can identify the feasibility of GSI in streets and on parcels. The second series of “heat” maps show gaps in accessible green open space, prioritized mobility routes, and existing infrastructure risks. Users of this tool can overlay maps to identify opportunities for the project to address multiple needs at once and maximize community benefits.

SPU and WTD’s GSI efforts remain instrumental in fostering a healthy community that supports public and environmental health. Herrera looks forward to continuing our support in these initiatives as they align with our organizational mission of creating economic vitality and community in a sustaining environment.