Consultants: 1,4‑Dioxane exceeded Massachusetts guideline in five Gardner landfill monitoring wells

Civil Environmental Consultants told the Gardner Board of Health on Feb. 24 that recent groundwater sampling at the closed West Street landfill detected 1,4‑dioxane at concentrations ranging roughly from 1.5 to 8 parts per billion (ppb) in five of 11 monitoring wells, above Massachusetts' drinking‑water guideline of 0.3 ppb.

The finding matters because the 0.3 ppb value used by the state and referenced by the consultants is a drinking‑water guideline intended to limit lifetime cancer risk; the U.S. Environmental Protection Agency has a closely aligned value (about 0.35 ppb). John Tavolianza, a licensed site professional with Civil Environmental Consultants, said the wells that exceeded the guideline were primarily in the northwest portion of the property and that the detections resulted from a change in laboratory method that lowered the method detection limit.

CEC explained that the landfill has 11 groundwater monitoring wells and four surface‑water sample locations. The company said the historical laboratory method had a reporting limit around 250 ppb; at the DEP's request CEC used a method that reports down to less than 1 ppb, which is why 1,4‑dioxane showed up in wells that had not previously been tested to that lower limit. Phil Dugoda, the board's main point of contact at Civil Environmental Consultants, said the most recent annual sampling (collected in April 2024) produced the detections.

The consultants described relevant regulatory benchmarks: the Massachusetts contingency plan (MCP) and state drinking‑water guidance set a GW‑1 (drinking‑water) value for 1,4‑dioxane at 0.3 ppb; the MCP GW‑2 inhalation guidance is 5,000 ppb and the GW‑3 surface‑water discharge guidance is 50,000 ppb. Tavolianza emphasized that the GW‑1 standard is health‑based and conservative — it is set to limit lifetime cancer risk to roughly one in a million at that concentration.

Board members and consultants discussed the difficulty of identifying a source. Groundwater flow at the site generally trends from the southeast to the northwest, and the detections appeared in wells to the northwest of the landfill, which the consultants said could be consistent with the landfill as a source. However, the consultants also noted a nearby pond and wetland connections and said surface‑water flow patterns complicate simple source attribution. Tavolianza said one well had historical 1,4‑dioxane results consistent with the recent round, but most wells had not previously been analyzed using the lower detection limit.

Consultants recommended continued monitoring and additional data before taking remediation steps. Tavolianza told the board that the logical next steps are more frequent sampling or additional monitoring wells to delineate extent and any trend, then coordination with the Massachusetts Department of Environmental Protection (DEP) to determine regulatory response. Dugoda said sampling is typically annual in April or May; the board discussed the possibility of increased sampling frequency or adding wells to the northwest to confirm trends.

Board members and consultants also discussed exposure pathways. Consultants told the board there are no known private drinking wells within about 1,000 feet of the detections; the nearest private well in the likely flow direction was described as roughly 1,600 feet away. Consultants said the measured surface‑water concentrations, while above the drinking‑water guideline, are low and that incidental contact (such as swimming) would not likely produce the lifetime ingestion exposure the guideline addresses because 1,4‑dioxane is poorly absorbed through skin and the guideline assumes lifetime daily ingestion.

The board asked about remedies used elsewhere; Dugoda cited examples of point‑of‑use treatment (activated carbon systems) installed on private wells in other towns where detections occurred. He said regulatory decisions about corrective action would be guided by DEP given the limited exposure pathways at the moment.

Next steps recorded at the meeting: the consultants will continue annual sampling with the lower reporting limit, discuss additional monitoring options with DEP, and return data from the next sampling round for trend analysis. The consultants said that several years of comparable data may be needed to confirm trends.