County updates technical plan for PFAS cleanup at former municipal fire training site; PRB pilot advance funded with ARPA money

Barnstable County staff and consultants on Feb. 25 gave a technical briefing on the former municipal fire training site and ongoing PFAS remediation planning. Paul Rosala, the county’s assets and infrastructure manager, and consultants from GZA GeoEnvironmental described a coordinated, multi‑track program of additional investigation, numerical groundwater modeling, forensic source analysis, and pilot testing in advance of larger remediation steps.

GZA principals David Leone and John (last name recorded variously) said the county’s strategy is to close key data gaps, refine a conceptual site model and use a numerical groundwater flow model (built from a USGS Cape‑wide model and supplemented with higher‑resolution local data) to assess plume pathways, the influence of pumping wells, and remedial scenarios. The consultants said new work includes a geophysical survey to map a low‑permeability silty‑clay layer beneath the site, targeted soil and groundwater sampling to the north and downgradient directions, and installation of monitoring wells aligned with a planned permeable reactive barrier (PRB).

GZA described the PRB approach as an in situ containment measure using injected activated carbon (a “colloidal carbon” curtain) to sorb PFAS as groundwater moves through the injected zone. GZA said the PRB method can avoid deep trenching and reduce the volume of groundwater that would otherwise be pumped, treated, and reinjected—a costly process that can produce large secondary waste streams (iron sludges and spent carbon). The PRB pilot has regulatory support from MassDEP, GZA said, and the county has a vendor contract and an ARPA set‑aside to install a PRB once final design details—principally the mapped top of the silty‑clay confining layer—are confirmed.

Rosala reviewed existing and planned obligations: the county has a settlement with the town of Barnstable for drinking‑water impacts (the county estimated settlement damages at approximately $3,600,000 over the period 2017–2037), ongoing operations and maintenance agreements for point‑of‑use and wellhead treatment, the site capping already completed to limit infiltration, and contracts for professional services and legal work tied to Massachusetts Contingency Plan (MCP) compliance. Earlier, higher‑level cleanup cost estimates cited to the county (previously $10 million–$60 million or more) were labeled “to be determined” as the county narrows remedial options.

GZA emphasized the need to understand whether several off‑site plumes are connected to the training site, to evaluate contribution from the airport and other nearby industrial activity, and to assess how pumping from Mary Dunn wells and other high‑capacity producers affect contaminant migration. The consultants have compiled a regional database that includes historic well logs and monitoring results and are using the model to run particle‑tracking scenarios that suggest the highest hydraulic connection is toward Mary Dunn Pond and the Mary Dunn wellfield; reverse particle tracking indicated potential contributions from sources to the west of the site.

Planned near‑term work includes geophysical mapping of the lower clay unit, installation of additional monitoring and PRB performance wells (using an S/MBE‑compliant driller to meet funding requirements), expanded ecological assessments (pond and wetland biota sampling and moth/light‑trap surveys) and a Phase II MCP report targeted for completion in 2025 pending data flow. County staff said quick turnaround analysis through a county lab arrangement will speed field decision‑making during drilling and sampling.

County and consultant remarks stressed coordination with MassDEP, the USGS and local stakeholders (town, airport, fire district and community groups), and the need to clarify responsibility for remediation costs and potential recoveries through ongoing litigation or third‑party settlements. Commissioners said they expect the county to press for cost‑sharing where appropriate and to keep the public informed as the technical work proceeds.

Why it matters: the training site sits near multiple public drinking‑water wells, the Hyannis water system, and sensitive wetlands. A successful containment strategy that reduces contaminant migration and lowers wellhead loading would reduce ongoing treatment costs for municipal suppliers and reduce long‑term public‑health and environmental risks.

Next steps: complete geophysical mapping, install targeted monitoring and PRB performance wells, execute the PRB pilot and monitor performance; finish the Phase II report in 2025 and continue coordination with MassDEP and other stakeholders.