Stormwater runoff is just as certain as the rain that falls in the Puget Sound. When rain falls on impervious surfaces, like roads and rooftops, it picks up pollution and carries the pollution on a journey that ends in our waterways and ecosystems. This pollution is a lethal threat to salmon and contaminates our environment and food. One of mother nature’s invisible superpowers, infiltration, has inspired a type of nature-based solution called Green Stormwater Infrastructure (GSI). Infiltration is when water on top of the ground flows into the soil – just like when rain falls in our forests and grasslands. The soil acts like a filter and many contaminants are removed through different biological and physical processes. GSI removes pollution from stormwater by filtering the water through a designed mix of soil and other media tailored for the pollutants found in stormwater and offers promise for restoring our critical systems.
WHY WE NEED TO ACCELERATE GSI
One of the most dangerous pollutants stormwater carries into our ecosystems is 6PPD-quinone (6PPD-q). 6PPD is a tire preservative that reacts in the atmosphere over time to form 6PPD-q and is then shed in tiny particles from cars, trucks and buses as they drive along our roads and highways. When it rains, 6PPD-q flows to the nearest waterway. This chemical is known to cause mortality in coho salmon – killing them before they get the chance to lay eggs for the next generation. While there are efforts underway to eliminating 6PPD-q from tires and replace it with a safer alternative, this could take decades. Shorter-term solutions are needed to address this pollutant and support the health of coho salmon. This is where GSI promises hope – pollution can be alleviated by directing stormwater through infrastructure that mimic nature’s processes refined over millenia, like the bioswales you see along roadsides and development that often look like beautiful planted areas or grassy slopes, but are really are engineered treatment areas.
GSI promises hope – pollution can be alleviated by directing stormwater through infrastructure that mimic nature’s processes refined over millenia
The benefits of GSI go beyond pollution mitigation, too. GSI can be designed to provide a multi-use space for community, such as parks or walking trails, as well as provide habitat for birds, bees and more.
New Tool in our Conservation Toolbelt
While the benefits may be known, communities still run into challenges as they work to identify optimal locations (site), design, fund and construct multi-benefit green stormwater infrastructure. To support communities, The Nature Conservancy in Washington (TNC) has invested in a suite of tools and resources to accelerate the treatment of polluted stormwater over the past 8 years. Some of these resources include TNC’s Retrofitting Our Legacy report and the Stormwater Heatmap. These tools and resources were developed in collaboration with partners form municipalities, non-profits and scientists throughout the Puget Sound region.
The latest tool in this toolbox is a Scope of Work (SOW) Template for Siting and Selecting GSI published with some helpful case studies (PDF). The template provides practitioners with a step-by-step guide to help organizations and communities identify, prioritize, and site high-impact stormwater treatment facilities designed to benefit people and nature. Using a template saves time and money in the planning process.
How the SOW and Case Studies Help
As they work to make progress on projects to address stormwater pollution, Jurisdictions, municipalities, and other organizations often have to navigate competing priorities and limited resources. The template aims to efficiently identify high-impact GSI opportunities and provide the foundation to seek grant funding for feasibility studies, design, and construction of stormwater infrastructure.
Tasks:
Agreement on project goals and desired outcomes
Select a target waterway or reach within project boundaries
Gather detailed information about the preferred waterway or reach
Identify potential sites for intervention
Screen site and select a preferred project location
The template includes 5 main groups of activities, called tasks, that begin at the regional or watershed scale and sequentially move toward the selection of one or more preferred site(s). At the conclusion, practitioners will be well-prepared to begin an initial design or pursue supplemental funding through grants or larger initiatives. Depending on prior work in the watershed, current initiatives, or other priorities, the practitioner may choose to skip portions of a task or whole tasks entirely.
As part of developing the template and to continue to support acceleration of high-impact stormwater in our home, TNC collaborated with two jurisdictions, the City of Tacoma and the City of Kent, to pilot the template. These case studies also demonstrate the customizable nature of the template, enabling practitioners to only utilize the portions of the template relevant to their projects.
For example, working with Tacoma it was clear an existing sub-area plan provided most of the information that Task 2 and 3 of the Scope of Work template were designed to produce. With this as the foundation, TNC worked in partnership with the City of Tacoma’s stormwater planners on Tasks 4 and 5 to complete a technical engineering feasibility study of potential stormwater sites in the south part of Tacoma. The final sites selected used engineering criteria like pollutant removal and hydraulic feasibility while also looking at the potential community benefits. A final report produced showed significant opportunity at multiple sites in the community and illustrated the potential for GSI to capture a large amount of stormwater pollution. Ultimately, the project team focused in on a final site for a GSI project that could provide multiple community benefits. There is continued discussion about this potential site.
The template and associated case studies are just one piece of the puzzle when considering green stormwater infrastructure projects to address threats to salmon and ecosystems in the Puget Sound. These documents offer concrete first steps and examples of what to consider when engaging in project design. Using the template tasks, jurisdictions, municipalities, and other organizations can work to build projects that provide the most impact while supporting salmon, ecosystems, and our communities.
ACCESSING THE SOW TEMPLATE
The template is available in two formats, a PDF with example deliverables and a fully modifiable plain text document intended to be customized by the practitioner with their community’s values and priorities.
SOW Template: https://www.cityhabitats.org/wp-content/uploads/2024/03/SOW-Template-Final.pdf
Case Studies: https://www.cityhabitats.org/wp-content/uploads/2024/03/Case-Studies-Document-Final-compressed-2.pdf
Modifiable Template: https://www.cityhabitats.org/wp-content/uploads/2024/03/Plain-Text.Site-Screening-and-Selection-SOW-for-Stormwater-Treatment.docx
Please contact Kate Sievers at k.w.sievers@tnc.org with any questions or feedback.
Feature photo of bioswale © Hannah Letinich
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