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Testing Removal of 6PPDQ and Coho Salmon Lethality by High-performance Bioretention Media Blends: Final King County Report

Testing Removal of 6PPDQ and Coho Salmon Lethality by HPBSM The extreme toxicity of the tire chemical, 6PPD-quinone (6PPDQ) to salmon has spurred an urgent regional need to identify stormwater treatment technologies that remove 6PPDQ and protect salmon from acutely toxic stormwater. Bioretention is expected to be one of the best treatments for 6PPDQ because of its proven effectiveness for protecting coho salmon from toxic stormwater and its flexibility as a stormwater best management practice (BMP). The purpose of this study was to determine the 6PPDQ treatment effectiveness of three configurations of high performance bioretention soil mixes (HPBSMs) that are newly adopted by the Washington State Department of Ecology (Ecology) and King County and compare these to the default sand and compost-based bioretention soil mix (BSM) widely used in Washington. This is the first study to quantify 6PPDQ treatment by bioretention soil mixes used in Washington State. The major findings of this study are: • All tested HPBSM configurations and the default BSM completely protected juvenile coho salmon from acutely toxic stormwater. • While all tested media reduced 6PPDQ concentrations by at least 10-fold, the HPBSMs provided small, significant improvements in 6PPDQ treatment. • Stormwater filtered through the HPBSMs always had 6PPDQ concentrations below Ecology’s adopted acute aquatic life criteria for 6PPDQ of 12 ng/L (12 parts per trillion). This was not the case for the default soil mix.

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    Testing Removal of 6PPDQ and Coho Salmon Lethality by HPBSM

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