SW 142nd Street & 6th Avenue SW Environmental Investigation & Infiltration Evaluation

Burien, Washington

HWA was contracted by the City of Burien to perform an environmental investigation and infiltration evaluation. The site is in a topographic depression, has been subject to flooding, and is also reported to contain some surficial soil contamination. The City plans to construct a stormwater infiltration facility at the site to accommodate storm drainage and reduce flooding.

HWA's scope of work was designed to investigate the potential presence of contamination and evaluate site infiltration capacity. HWA excavated and logged backhoe test pits and collected soil samples for physical and chemical testing. We delineated contamination, estimated infiltration rates, and provided recommendations for soil cleanup and stormwater infiltration designs. Site geology indicated more favorable infiltration receptor soils at depth, therefore HWA's recommendations included the use of drywells, stone columns, deep trenches or galleries to increase infiltration capacity by accessing the more permeable soils.