Longevity of biological protection using bioretention

The U.S. Fish and Wildlife Service, in collaboration with Washington State University, is testing how long a bioretention soil mix can be used to reduce pollution and toxicity from urban stormwater. This builds on the findings from a previous SAM study showing that filtration through bioretention reduces stormwater toxicity and protects sensitive fish-coho salmon (see factsheet).  

The current study continues to use the standard bioretention soil mix in experimental columns to evaluate its effectiveness of bioretention in treating stormwater for 13 water years. Ecology funds added by Amendment 2 add 3 water years and direct testing for the contaminant 6PPD-q in the influent and effluent for 2022-2023 testing.

Study questions

  • How long can the 60:40 standard bioretention soil media prevent acute toxicity from urban stormwater?
  •  What soil depths are necessary to provide sufficient biological protection and water quality treatment?

Study findings

The study will continue until November 2024.

Project tasks and key deliverables

Phase I: Contract IAA & Scope of Work, Amendment 1

Phase II: Contract IAA & Scope of Work, Amendment 1, Amendment 2

  1. Develop Quality Assurance Project Plan
  2. Prepare experimental columns
  3. Conditioning experimental columns
  4. Bioretention performance throughout accelerated aging 
    • Progress reports: Report 1, Report 2, Report 3, Report 4, Report 5, Report 6, Report 7, Report 8, Report 9 
      • Note: During 10th water year (Report 5) stormwater dosing experiment, some bioretention experienced surface soil layer clogging. Top 1-3 inch of surface soil and fine particles has been removed as part of bioretention maintenance. 
      • Note: Report 6 covers the last water year (#13) of the experiment.
  5. Communication & Outreach