Stormwater Action Monitoring - Effectiveness studies

Study questions

• How effective is each individual best management practices (BMP) at treating stormwater under this large retrofit project?
• What well does the entire retrofit protect Echo Lake from pollutants?
• What is the potential protection to the lake itself?

Scope of work; Amendment 1

Study findings

Individual BMPs — bioretention and proprietary devices — provided significant reductions in common pollutants carried by stormwater. A system-wide analysis showed the detection tank provided additional pollutant treatment, but flow control and pre- vs. post- retrofit comparison were not possible due to challenges discovered during the study. 

• The sampling phase was completed in early 2017, see Quality Assurance Project Plan (QAPP)
• Retrofit Preliminary Results at Echo Lake SAM Symposium (June 2017)
• Short Report: Monitoring Stormwater Retrofits in the Echo Lake Drainage Basin  and Final Report: Appendices

King County's website for this project.

State and local governments want to learn about source control undertaken by small business owners to prevent pollutants from entering stormwater runoff.

Source control activities — such as common practices, techniques, or devices —  are collectively termed as best management practices (BMPs) and are employed at small businesses across the region. 

This City of Lakewood lead study gathered survey responses in 2016 from NPDES stormwater permittees. The final report for Business Inspection Stormwater Source Control Effectiveness Study (Aspect, 2017) summarizes responses from Phase I and II permittees on the types of businesses, frequencies of inspections, and source control BMPs employed. Recommendations for municipal stormwater permittees, Ecology's permit writers, and future study questions are provided. 

• SAM Fact Sheet #007 Business inspection stormwater source control effectiveness study

Study questions

• Does the default bioretention soil mix reduce Polycyclic Aromatic Hydrocarbons
  (PAH), metal, fecal coliforms, and nutrient pollution from highway runoff?
• Does the default bioretention soil mix reduce toxicity to adult and embryonic Coho salmon?

Study findings

This SAM Effectiveness study funded ongoing work to evaluate the effectiveness of bioretention soils to reduce the toxicity of urban stormwater to Coho. 

State and local governments are relieved to learn that the default 60:40 bioretention soil mix given in the Stormwater Management Manual for Western Washington is capable of removing acute toxicity to adult and embryonic Coho salmon. U.S. Fish and Wildlife partnered with Suquamish Tribe and Washington State University-Puyallup to specifically test the default mix (60 percent sand and 40 percent compost) for toxicity treatment.

What does it tell us?

This new information on the default bioretention soil mix helps inform stormwater managers across Washington as they adaptively manage stormwater runoff in urbanizing watersheds. The study also found that the default soil mix we specified for bioretention is effective at reducing metals, PAHs and fecal coliform concentrations.

Ecology’s stormwater management manual will continue to specify the 60:40 mix as the standard BSM for bioretention. 

• SAM Fact Sheet on Bioretention toxicity prevention
• SAM Final Report
• Media coverage on this ongoing research topic​: WSU press release and NOAA Fisheries. 

This new information on the bioretention soil mix informs stormwater managers across Washington as they adaptively build bioretention facilities to manage stormwater runoff in urbanizing watersheds.