The overall goal of this project was to develop new recommendations for a bioretention soil media (BSM) that protects beneficial uses of receiving waters and does not export nutrients and dissolved copper as is the case with the current BSM specification of 60 percent sand/ 40 percent compost (60/40). The project entailed selecting and testing media components, combining components in various ratios and placing the BSMs in columns for water quality testing, flushing and dosing the columns with stormwater to assess performance, conducting toxicological testing of influent and effluent stormwater, and finally recommending the best performing BSM. The best performing BSM consisted of a 2-inch compost blanket, underlain by 18 inches of a sand/ coconut coir/high carbon wood ash blend, underlain by 12 inches of a sand/ activated alumina/ iron filings blend. The BSMs were similarly able to prevent expected toxic impacts including acute lethality and reproductive impairment in C. dubia, and reduced growth and pericardial edema in D. rerio. However, collectively, the bioassays showed a reduced ability of all of the tested BSMs to prevent toxicity during the final dosing event (Event 5).
Bioretention Media Blends to Improve Stormwater Treatment: Final Phase of Study to Develop New Specifications Final Report
Reference: Herrera. 2020. Bioretention Media Blends to Improve Stormwater Treatment: Final Phase of Study to Develop New Specifications Final Report. Prepared for King County Department of Natural Resources and Parks, by Herrera Environmental Consultants, Inc., Seattle, Washington.