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Officials say pump‑and‑treat is reducing 1,4‑dioxane at Asabet 1A; cleanup level cited at 0.46 ppb
Summary
Project managers reported that extraction and treatment of groundwater downgradient of the Nuclear Metals site reduced 1,4‑dioxane concentrations at the Asabet 1A monitoring well below the cleanup level of 0.46 parts per billion, and additional extraction wells and system tuning are improving capture and mass removal.
Officials at the April 2026 public meeting described progress on groundwater remedies designed to limit migration of the 1,4‑dioxane plume and to treat contaminated water.
Bruce Thompson, project coordinator for the settling defendants, highlighted the pump‑and‑treat system installed to prevent plume migration beneath the Asabet River toward municipal wells. "Our cleanup level for this particular flavor of contamination is 0.46 parts per billion," Bruce said while showing historical data for the Asabet 1A monitoring well. He noted that influent concentrations in extraction wells were near 30 ppb when operations began and have dropped to the low single digits at some wells.
Project managers described an initial extraction well (EW1) placed and operated in 2017, later augmented by additional wells on both sides of the river to increase capture and remove more contaminant mass. The team said EW1 and the additional extraction wells are tied to permitted treatment systems; treated water is discharged to the Asabet River under those permits and is monitored monthly to verify compliance.
Presenters showed time‑series data indicating a downward trend at the Asabet 1A well since system operation began, while cautioning that some data spikes are artifacts of laboratory detection limits. Officials said the system's capture zone and performance are continually evaluated and that additional bedrock remedy work remains to be defined.
The project team committed to continued annual groundwater reporting and invited the public to review the recently posted 2023–2024 groundwater report on EPA’s website, which includes trend analyses and cross‑sections of the plume.
