Biofiltration swales, or bioswales, use vegetated soil substrates to filter contaminants from stormwater, decrease sediment load, and reduce erosion. Following a storm, runoff moves slowly through the swale at a shallow depth. While stormwater is retained in the bioswales, pollutants are removed by the combined effects of filtration, infiltration, settling, and biotransformation. The system currently being evaluated at the Washington State University (WSU) Puyallup Research and Extension Center (PREC) uses compost to further enhance the ability of bioswales to remove toxicants. WSDOT has created guidelines for constructing compost amended biofiltration swales (CABS) and implemented a field test for CABS along Washington State Route (SR) 518 in 2009. As part of an ongoing study, influent and effluent samples are currently being collected at the field site during storm events and tested for metals, PAHs, pesticides, phthalates, and unknowns (LC-QTOF). Acute toxicity and sub-lethal effects of stormwater were also measured using zebrafish (Danio rerio) bioassays. Along with researchers from University of Washington (UW) we created a laboratory model for CABS at the WSU PREC to verify field test results in a controlled setting and identify ways that the WSDOT design could be improved. This system is exposed to highway runoff from a previously studied high volume source off SR 520 and tested at different flow rates, swale lengths, and slope gradients. Paired chemistry and toxicology data show how stormwater treatment by CABS differ from traditional soil biofiltration methods. Results presented at Salish Sea show how zebrafish developmental biology is affected by stormwater treatments and how CABS design impacts toxicant treatment efficacy
