Officials say permeable reactive barrier and monitoring have sharply reduced PFAS migration at former fire training site

Paul Rosala, identified in the transcript as the county assets and infrastructure manager, told the Cape Cod Regional Government Assembly of Delegates on Dec. 3 that county staff and consultants are making measurable progress addressing a PFAS release from a former municipal fire training facility. The county has completed a permeable reactive barrier (PRB) installation this year and is continuing Phase 2 site delineation to define the plume and its sources.

Rosala said the PRB project—funded in part with ARPA dollars—was finished in October and that the county is operating a groundwater pump-and-treat system and performing ongoing monitoring and required reporting under the Massachusetts Contingency Plan (MCP). "We have a groundwater pump and treat system that's currently active at the site," Rosala said, and noted the county carries budgets for operation, oversight, legal services and MassDEP fees.

John Paquin, the licensed site professional from consulting firm GZA, described the MCP's risk-based approach: "The goal of that plan is really to address the site as necessary to remove unacceptable risk," he said. GZA presented results from ecological and human-health sampling. The ecological risk assessment, Paquin said, produced values "very, very much less than 1" overall; the consultants reported two slight exceedances that could affect individual animals but not populations. Paquin added that human ingestion risk has been largely controlled by early wellhead treatment installed on the Mary Dunn public-supply wells.

Paquin and Rosala also described complexities at the site: multiple municipal wells (the Mary Dunn wells and seasonal Airport 1 well), the nearby airport's separate PFAS plume, and a so-called "mystery plume" whose source is not yet determined. To help distinguish contributions, Paquin said GZA has requested permission to sample older airport wells and will split samples with airport staff; the team also plans to test for sucralose as a tracer of wastewater-derived contributions. "We're starting sampling next week," Paquin said.

On the remedy, Paquin described the PRB installation method and early performance: the full-scale injection used roughly 247 probe locations along a ~600-foot alignment, about 600,000 gallons of mixed product (reported as the diluted volume) and the equivalent of approximately 400,000 pounds of activated carbon. Pilot testing showed a reduction of groundwater concentrations from about 4,500 parts per trillion to near nondetect at downgradient monitoring points shortly after injection. Paquin said early full-scale monitoring results have been positive so far.

County staff cautioned that final remediation cost estimates remain uncertain. Rosala and Paquin explained a conservative long-range planning number of $60 million was retained in some scenarios to account for the possibility of a large-scale pump-and-treat remedy, but both consultants emphasized that pump-and-treat can be inefficient and long-running. Rosala noted current pump-and-treat operating costs on the site are roughly $400,000 per year and said the PRB strategy is intended to stabilize the site and reduce long-term operating expense.

Paquin said the DEP has been involved and that state officials are evaluating whether it would be technically feasible to trace low-level contributions across the town's many PFAS sources; the DEP has used the term "infeasibility" in internal discussions. Rosala and Paquin also noted the county is a potential claimant in manufacturer litigation for property damages, which could yield additional funds but remains uncertain in timing and amount.

Next steps outlined to the assembly included completing Phase 2 delineation, splitting and analyzing the newly collected airport and wastewater-relevant samples, refining the groundwater model, completing the PRB performance verification and then discussing with DEP whether the pump-and-treat system can be scaled back once the PRB's containment performance is confirmed. "Once we know that the PRB is working as designed," Paquin said, the county will engage DEP on whether continuing pump-and-treat is necessary.

The assembly's discussion included questions about historical records of firefighting foam usage (consultants said documentation is incomplete and that individual fire departments procured foam independently), airport responsibility (the airport is listed as a responsible party and is conducting its own assessment and mitigation), and whether wastewater treatment plant discharges could have contributed to the mystery plume (testing for sucralose and additional sampling were planned to address that possibility).

The county presentation and consultant remarks were technical and emphasized the MCP risk-driven standard: the initial priority is to reduce exposure and ecological risk, then to evaluate longer-term cost-effective remedies once the plume extent and likely contributors are better defined.