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Bioretention alternative blends

Ecology's stormwater management manuals describe a default 60/40 bioretention soil mix (BSM) and list soil specifications for designers to create a custom filtration mix. In this project, collaborators from municipalities, academia, and the private sector will continue work to develop alternative BSM blends that do not leach phosphorus.

Study questions

  • Are there alternative mixtures for the bioretention soil mix (BSM) that will meet basic, enhanced, and phosphorus treatment objectives?
  • Do these alternative mixes prevent toxicity to aquatic organisms?
  • Are these mixes affordable and available to permittees in Washington state?

Study findings

This study continues work done under an Ecology grant to develop and test eight media blends to find a high performing alternative soil mix to provide stormwater treatment, particularly to areas draining to phosphorus sensitive water bodies.

Project tasks and deliverables

1. Project management
  • Deliverable 1.1 Semi-annual progress report
  • Deliverable 1.2 Semi-annual progress report
  • Deliverable 1.3 Semi-annual progress report
  • Deliverable 1.4 Semi-annual progress report
2. Project advisory team
  • Deliverable 2.1 April 2018 kickoff meeting agenda and notes
  • Deliverable 2.2 Meeting agenda and notes on media components and blend
  • Deliverable 2.3 Meeting agenda and notes on results and selecting the highest performing blends
  • Deliverable 2.4 Meeting agenda and notes on blends physical and chemical characteristics
3. Quality Assurance Project Plan (QAPP)
  • Deliverable 3.1 Draft QAPP 
  • Deliverable 3.2 Final QAPP
4. Testing of alternative bioretention media blends
  • Deliverable 4.1 Results from four clean water flushing events for water quality and saturated hydraulic conductivity. Water quality results from eight stormwater dosing events.
  • Deliverable 4.2 Physical and chemical characteristics: nine metrics for developing specifications of six components of the media blend.
  • Deliverable 4.3 Physical and chemical characteristics: nine metrics for developing specifications for the final three highest performing media blends.
5. Evaluate ability of media blends to protect aquatic organisms
  • Deliverable 5.1 Acute toxicity results
6. Distribution of findings
  • Deliverable 6.1 Draft Report
  • Deliverable 6.2 Presentation to SWG
  • Deliverable 6.3 SAM Fact Sheet
  • Deliverable 6.4 Final Report