Barnstable County updates public on PFAS plume, begins full-scale carbon barrier after successful pilot

Barnstable County and consultants gave residents an update on ongoing investigations and remedial work at the former municipal fire training site in Barnstable on Oct. 12, 2025, and confirmed a full-scale permeable reactive barrier (PRB) is being installed after a pilot test sharply reduced groundwater PFAS concentrations.

The county’s Paul Rosala, Barnstable County assets and infrastructure manager, opened the meeting and said the session was “the former municipal fire training site, PFAS release response public update.” John Paquin, principal hydrogeologist with GZA GeoEnvironmental, told attendees the project is being executed under the requirements of the Massachusetts Contingency Plan. “We’re focused on complying with the requirements of the Massachusetts contingency plan,” Paquin said.

The update summarized recent field work, new groundwater monitoring, ecological sampling and a PRB pilot test that GZA said produced rapid declines in PFAS in downgradient monitoring wells. GZA reported adding 16 multilevel monitoring wells to fill data gaps, instrumenting ponds to measure groundwater–surface water interaction, collecting sediment, insect and upcoming fish samples for an ecological risk assessment, and performing PFAS “forensics” to compare chemical fingerprints across the site and neighboring properties.

Why this matters: the plume of regulated PFAS (PFAS-6) overlaps shallow and intermediate groundwater between the training site and municipal supply wells known as the Mary Dunn wells. GZA presented plume maps showing a PFAS-6 contour of 1,000 nanograms per liter (ng/L) near the site and 100 ng/L contours extending toward the Mary Dunn and nearby Air 1 supply wells. Jen McKechnie, GZA hydrogeologist, said groundwater flow in the shallow and intermediate zones generally trends southeast toward those public supply wells and that some deeper lobes of the plume extend past the wells.

GZA’s forensic analysis, led by Jeremiah Duncan, senior chemist, showed differences in PFAS compound patterns in groundwater samples that suggest more than one source of PFAS in the area. “There do seem to be potentially some other sources and some other things happening in this area that we didn’t fully understand when we started our investigation,” Duncan said, noting a fluoro-telomer signature that aligns with airport-related releases in parts of the plume and different fingerprints nearer the training site.

Remedial work: GZA and the county performed a pilot injection of colloidal activated carbon (PlumeStop) in a roughly 10-by-30-foot test area in late October 2024. The pilot used approximately 24,000 pounds of carbon. Dan Scanlon, GZA senior project manager and remediation engineer, said post-injection monitoring in February–April showed “a really significant decline” in PFAS concentrations in downgradient wells, with some samples falling below Massachusetts regulatory criteria. Based on those results, Regenesis was selected through competitive bid to inject the full-scale PRB. The county submitted an Interim Remedial Action (IRA) plan modification to the Massachusetts Department of Environmental Protection (MassDEP) in June; Paquin reported MassDEP issued a conditional approval.

The full-scale PRB alignment runs along the eastern and southern boundary of the former training facility. GZA said the design calls for roughly 250 injection points spaced about 5 feet apart and the injection of about 590,000 gallons of colloidal carbon solution, with a higher-dose zone in the southern portion where PFAS concentrations are greatest. Injection work began in July and is expected to continue on a roughly 12-week schedule, with a target completion in October. Post-injection performance will be tracked using multilevel “performance verification” wells installed in spring 2025.

Secondary system and incident: the county also operates a groundwater extraction and on-site granular activated carbon treatment system (pump-and-treat) that captures contaminated groundwater from extraction well PRW4 and reinjects treated water through an on-site reinjection gallery. Scanlon reported the system was taken offline after an operator’s inspection in June found evidence of vandalism at the recovery well control box and damage to the access gate. “They found the evidence that it had been burned,” Scanlon said. Repairs were completed and the system awaits reinspection to be returned to service.

Ongoing work and next steps: GZA said it will finish the PRB installation this fall, complete the ecological risk assessment for pond sediments, surface soils and biota, calibrate a numerical groundwater-flow and particle-tracking model that incorporates a confining silty-clay layer, and finish the Phase 2 comprehensive site assessment by late 2025 or early 2026. Paquin said technical working-group meetings that include the towns, the airport, MassDEP, U.S. Geological Survey and local stakeholders will continue.

Local water officials pressed for clarity about the conceptual site model and potential cross-connections from historical pumping and wastewater pathways. Hans Kaiser, town of Barnstable water-supply division, and Jim Begley, the town’s licensed site professional (LSP) engaged under a grant, requested the county explicitly assess whether historic pumping and treated wastewater infiltration could have redistributed PFAS to other areas. Begley said that possibility should be incorporated into the Phase 2 assessment. Paquin and GZA acknowledged the concern and said the model and ongoing data collection will be used to test those scenarios.

The county plans another public briefing within six months or when new, substantive results are available. Interim status reports will be issued to stakeholders in the meantime.

Ending note: the project team stressed that the data are preliminary and that work is data-driven; GZA said the evolving groundwater model, PFAS forensic results and field monitoring together will inform further remedial decisions.