Oyster shell retrofits in catch basins

King County evaluates the effectiveness of stormwater treatment by oyster shell. This study compares water quality in two groups of catch basins in the City of Mercer Island — one with crushed oyster shell retrofit and the other without them. Visit King County's project webpage for detailed information.


Study questions

  • Does oyster shell provide treatment for dissolved metals?
  • Can catch basins with oyster shell retrofits reduce stormwater pollutants significantly more than catch basins without oyster shell?

Study findings

Initial data gathering showed no treatment effect by oyster shell retrofit in catchbasins. This is likely due to limited contact time and oystershell amount to treat high volume of stormwater discharge from large contributing basins in the study area.

While we originally planned for the study to end April 2022, this will now happen March 2021. We expect the final study report November 2020.

Project tasks and key deliverables

  1. Project management 
  2. Planning and Quality Assurance Project Plan 
  3. Field sampling and analysis
  4. Final report 
  5. Communication of findings 
    • Presentation 
    • Fact sheet