Stormwater Action Monitoring - Effectiveness studies

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.

Study questions

• What can municipalities learn from existing catch basin cleaning programs?
• Which alternative inspection schedules and frequencies are most efficient?
• What is a standard list of data to be collected across programs?

Scope of work

Study findings

The high variability in not only the data that is collected across the many jurisdictions in Puget Sound, but also the lack of a standard catch basin definition precluded accomplishing the original goals for this project.  With assistance from the project technical advisory committee, alternate goals were established based on the information collected on catch basin cleaning from municipal stormwater permittees. Recommendations on the type and quality of data collection and efficiencies to reduce costs are made. Based on data from seven permittees, it appears that over 80 percent of catch basins do not require more frequent cleaning than the standard inspection schedule. Revisit the definition of a circuit to consider if the circuit option will work either alone or in combination with other schedules.

• Survey and data request of municipal catch basin maintenance programs
• Survey responses technical memorandum
• Data analysis plan
• CB programs summary and costs
• Final report "Using Western Washington Catch Basin Inspection and Maintenance Data to Predict Maintenance Schedules and Identify Cost-Efficiencies"
• Final database (available upon request)
• Presentation to SWG November 2018

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.

Study questions

• What attributes can be measured by volunteers and staff through visual observation or simple tests that reliably predict the functional success of rain gardens and bioretention facilities?
• What construction and maintenance activities contribute most to the overall success of a rain gardens and bioretention facilities and can they be easily measured?
• What attributes of rain garden/bioretention facilities contribute most to a landowner's perception of functional success?

Scope of work

Study findings

The Raingarden and Bioretention Assessment Protocol was developed that provides replicable results and gives an overall indication of the current state of a rain garden or bioretention facility. Training is not necessary, but is suggested (even if self-directed). Data collected will provide sufficient detail to indicate if a site needs further actions for the functional aspects related to maintenance, hydrology, and vegetation.

Protocol Development:

• Literature review for protocol creation
• Final Report on social science results and recommendations
• Summary of first two versions's experiences

Final Protocol:

• Rain Garden & Bioretention Assessment Protocol, functional assessment form, data input spreadsheet, training webinar, and handouts
• Protocol assessment findings
• Presentation to SWG Jan 16, 2019 on protocol development and implementation
• Proposal for regional implementation

King County evaluated how effectively a large improvement project treats stormwater at a regional water detention facility in Federal Way.

Study question

• How well does each individual practice treat stormwater in this large retrofit?
• What about combinations of treatments?
• What is the overall flow control and pollutant reduction to the stream?

Scope of Work and Amendment 1

The study evaluated two new bioretention facilities, an expanded and new combined detention stormwater treatment wetlands (wetland complex), and the regional facility as a whole, for their ability to improve water quality and to reduce peak flows of stormwater runoff. The study also evaluated the in-stream water quality and benthic macro-invertebrates in North Fork West Hylebos Creek before and after the retrofit.

Study findings

Eighteen storms between March 2016 and April 2017 were sampled using compositors. Flows were measured continuously. Both bioretention facilities, the expanded wetland complex, and the system as a whole reliably attenuated stormwater flows by reducing and delaying the timing of peak flows. The bioretention facilities and the wetland complex had mixed water quality treatment results, they were able to treat some targeted pollutants but not others. The system as a whole reduced total suspended solids, organic contaminants, and total metals (zinc, lead, copper and cadmium). However, the system increased concentrations of nutrients and dissolved lead. The bioretention facilities were a source of nutrients.

Water quality and benthic community data from the North Fork of West Hylebos Creek were collected downstream of the retrofit and expansion before and after the project to assess overall performance of the system. Turbidity improved, though the data were not significant, and no changes in the benthic community were not observed. It is likely too early to detect a change in the benthic communities in the creek.

• Final Quality Assurance Project Plan (QAPP)
• Final project report and appendices
• Presentation to SWG Jan 16, 2019
• King County's website on this Regional Retrofit Project
• SAM Fact Sheet #013 Regional stormwater facility study in Federal Way

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.