Ex-situ Groundwater

The ROD identifies ex-situ treatment of the 1,4-dioxane and VOC plume as a remedial component of the RD/RA. Due to the mobility of 1,4-dioxane and an inherit threat to a downgradient municipal well, USEPA elected to accelerate the cleanup efforts through a Non-Time Critical Removal Action for Groundwater (GW NTCRA), effective July 2016. In order to isolate the plume and cutoff the migration towards Assabet 1A supply well, a temporary treatment system was installed in May 2017 and operated through May 2019.

Operations of the temporary system proved that pumping the extraction well at ~20 gallons permit successfully achieved hydraulic containment of the plume and cutoff migration of contaminated groundwater downgradient to the extraction well. The final groundwater treatment system was designed to operate at the same extraction rate and includes an innovative Advanced Oxidation Process (AOP) that successfully treats 1,4-dioxane and VOCs to non-detectable concentrations. The final groundwater treatment system has been in operation since April 2019 and will continue in perpetuity until site remedial goals in overburden are met.

Groundwater Treatment Monitoring Performance Objectives

Maintain Hydraulic Capture

by extracting at the designed rate of approximately 20 gpm and monitoring groundwater elevations.

Hydraulic Capture

continues to be maintained and monitored monthly.

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Observe Decreasing Concentration Trends

by tracking 1,4-dioxane concentration over time.

Decreasing Concentration Trends

decreasing 1,4-dioxane concentrations have been seen in wells downgradient from the extraction well.

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Monitor Treatment System Effectiveness

by tracking the overall influent and effluent 1,4-dioxane over time.

Treatment System Effectivness

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