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  • Expert Witness and Remediation

    WET was hired to conduct a field investigation, provide expert witness testimony, and design and implement remedial measures to address historical releases of volatile organic compounds (VOCs) at a large industrial maintenance facility in Montana. The historical source area contains dissolved VOCs in groundwater in both the surficial alluvial aquifer, as well as the underlying fractured bedrock, with the likely presence of dense non-aqueous phase liquid (DNAPL) in the fractured bedrock.

     

    Field investigation work to date has helped to further characterize VOCs in groundwater at the Facility and has identified VOCs, primarily tetrachloroethene, or PCE, in groundwater, soil gas, and indoor air at several private properties downgradient of the Facility. WET utilized several investigative methods including depth-integrated soil gas characterization using a GeoProbe direct-push drill rig and mobile gas chromatograph/mass spectrometer (GC/MS); indoor air and sub-slab soil gas sampling; and construction of soil gas monitoring points and groundwater monitoring wells.

    The WET team is providing remedial design and construction in a two-pronged approach. Pilot testing is underway in the historical source area to evaluate treatment options in the fractured bedrock aquifer, and a large Air Sparge/Soil Vapor Extraction (AS/SVE) curtain was constructed immediately downgradient of the historical source area to intercept VOCs diffusing from the deeper bedrock to the alluvial groundwater.

    Bedrock testing included slug tests and tracer testing to determine the bedrock’s hydraulic conductivity; the degree of connectivity between the bedrock and alluvial units; and the feasibility of chemical injection or groundwater recirculation to remediate VOCs in bedrock.

     

    To address the downgradient alluvial plume, WET designed and constructed an AS/SVE curtain consisting of multiple parallel rows of air injection wells to strip VOCs from the groundwater, vapor extraction wells to capture the volatilized chemicals, and a granular activated carbon (GAC) filtration system to remove the captured VOCs from the gas stream.

     

    Project activities were conducted in accordance with Montana’s Comprehensive Environmental Cleanup and Responsibility Act (CECRA) and other applicable environmental requirements.