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SAM's effectiveness studies measure the stormwater management actions in Western Washington and communicate useful findings on what works and what doesn't work. The Stormwater Work Group (SWG) organizes permittees and stakeholders to select the SAM study topics.
SAM effectiveness projects can occur at site or regional scales and the results can be used across jurisdictions.
A two-phased study of the bioretention best managment practices (BMP) was completed to assess hydrologic performance to capture infiltrate stormwater runoff in Western Washington using multiple design models. The City of Bellingham led the first phase of the study to evaluate bioretention designed prior to the 2012 Western Washington Hydrologic Model (WWHM) and the City of Olympia led the second phase evaluating those designed using WWHM2012 to the current standard required in the Stormwater Managment Manual for Western Washington (SWMMWW).
Based on the 20 bioretention sites evaluated across Western Washington, most met the hydrologic performance targets established by the stormwater permits minimum requirements for the LID standard and flow control. Some of the bioretention facilities were built as retrofits, which are not held to the performance thresholds of new and re-development as they are often limited to the size of the available property. The pre-2012 designs were adequate but were often built larger and with coarser substrate than designed. These two factors combined accounted for the more than adequate hydrologic performance to control stormwater flows, design constraints, and exceeded modeled expectations.
The report summarizes the findings, provides reasons and data for observed differences in performance and expectations, and makes recommendations for engineers, jurisdictions, and model development.
U.S. Fish & Wildlife partnered with Washington State University-Puyallup to evaluate improvements in the default bioretention soil mix capability to reduce nutrient, bacteria, and metal pollutants when amended with fungal spores and plants. The default mix is 60 percent sand and 40 percent compost per Ecology's Stormwater Management Manual for Western Washingotn.
This two-year field scale evaluation gathered new information about how local plants and mulch inoculated with S. rugosoannulata affect water quality and other bioretention performance parameters.
King County evaluated the capture and treatment of polychlorinated biphenyls (PCBs) in bioretention mesocosms using stormwater gathered from Interstate 5 near the Ship Canal in Seattle.
Scope of Work, Amendment 1
This field study provides much needed information on treatment of polychlorinated biphenyls (PCBs) transported by stormwater. PCBs are a significant pollutant to Puget Sound and responsible for many fish consumption advisories. Despite being banned in Washington there are still ongoing PCB sources from wash-off of products or paints, transport of contaminated soils, or low-level arial deposition. Bioretention columns (55-gallon drums) were built using the default bioretention soil mix (60% sand and 40% compost) and tested quarterly for two years of natural rainfall in a Seattle neighborhood. The key findings are:
State and local governments, academia, and the private sector worked together to develop and test several alternative bioretention soil mix (BSM) blend that does not export phosphorus, like Ecology's stormwater management manuals default 60/40 BSM, for use in areas near sensitive surface waterbodies.
Scope of Work
This bench-scale study successfully tested the performance of eight experimental BSM treatments over five storm events using highway runoff stormwater. Influent stormwater was compared to effluent from each BSM blend for total suspended solids (TSS), total and dissolved copper (Cu), lead (Pb) and zinc (Zn), total phosphorus (TP), ortho phosphorus (ortho-P), nitrate+nitrite, fecal coliform bacteria, polycyclic aromatic hydrocarbons (PAHs), and total petroleum hydrocarbons. Pollutant reduction targets were defined by Ecology's TAP-E treatment goals for TSS, metals, and phosphorus.
One experimental BSM (treatment #4) accomplished all the experimental pollution reduction goals including export of phosphorus, but was able to reduce phosphorus carried in the influent. Treatment 4 consisted of several layers (primary, polishing, and compost mulch) that when used in combination, could be anticipated to meet basic, enhanced, and phosphorus reduction goals. The study recommendations provide the specifications for Ecology to adopt the combination or component parts of the treatment 4 experimental blend as a new Washignton bioretention media. A bioretention media specification that meets Ecology’s basic, enhanced and phosphorus treatment objectives will greatly increase the surface water settings where designers and jurisdictions can confidently apply bioretention systems to manage stormwater runoff.
State and local governments want to learn and share effectiveness of catch basin cleaning programs to prevent pollution in stormwater. King County led an effort to collect, assemble and analyze local government catch basin cleaning data.
The City of Puyallup partnered with Washington State University Extension and Stewardship Partners to create an easy-to-use field protocol to assess rain gardens and bioretention facilities function and maintenance needs.
King County evaluated how effectively a large improvement project treats stormwater at a regional water detention facility in Federal Way.
King County's website for this project.
The City of Lakewood and consultants lead this SAM study (Scope of Work, Amendment 1, and Amendment 2) to look at permittees efforts for source control. This study gathered survey responses in 2016 from NPDES stormwater permittees. 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.
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.
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.
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.
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.
Stormwater Action Monitoring Coordinator