Case Study: Permeable Reactive Barrier, Market Street Property

Client: Confidential Location: King County (Seattle), WA Contact for environmental projects: Doug Hillman

Project Background & Challenges

As a result of historical plating operations in an industrial area of Seattle, metals and chlorinated solvents were released to soil and groundwater, impacting properties owned by four separate parties. The solvent plume in groundwater threatened to reach the Lake Washington Ship Canal; furthermore, because of the complicated subsurface geology, an existing pump-and-treat system installed by a former consultant had become ineffective. In addition to the plating-related issues, a separate release of PCBs in a carrier solution also threatened the Ship Canal.

Solution

After evaluating groundwater conditions and transport pathways, Aspect designed two subsurface treatment walls to passively treat the releases. We prepared two separate cleanup action plans and helped the property owner implement them. The first wall featured a zero-valent iron funnel-and-gate system for remediating chlorinated solvents in groundwater. The second was a reactive/sorptive curtain containing both zero-valent iron and activated carbon, a mixture required to destroy residual solvents while adsorbing dissolved PCBs. Both walls are working as designed and reducing contaminant concentrations by 99 percent. Ecology has granted a No Further Action letter for the funnel-and-gate system.