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DES adopts PFAS soil standards; asks Saint‑Gobain to address excess soil and continues site work
Summary
DES outlined how December 2024 soil remediation standards were derived and described initial implementation steps around the Saint‑Gobain site, including a letter requiring the company to address a stockpile of soil, demolition activities, point‑of‑entry system installations and ongoing groundwater monitoring.
The New Hampshire Department of Environmental Services has finalized soil remediation standards (SRS) for regulated PFAS compounds and has begun applying the new standards to sites tied to the Saint‑Gobain Performance Plastics contamination in Merrimack, DES staff told the House study commission.
Jeff Martz, administrator of DES’s Hazardous Waste Remediation Bureau, said state statute RSA 45‑H:13 (enacted July 22, 2022) directed rulemaking that led to PFAS soil remediation standards effective December 2024. Martz described the multi‑factor methodology DES used: direct‑contact risk‑based values, leaching‑based values to protect vulnerable groundwater, natural background screening values, laboratory quantitation limits, and a ceiling concentration where applicable.
Why it matters: the new SRS establish enforceable soil thresholds that aim to prevent further leaching of PFAS from soil to drinking water. DES staff said the rules change how the department evaluates where soil must be removed, contained or otherwise managed during redevelopment and site work.
Martz summarized the USGS‑DES statewide soil survey that informed the rulemaking: DES and the USGS collected shallow (0–6 inch) samples in 100 grid cells across the state and deeper profiles in a subset, showing most PFAS detections concentrated in the first foot of soil for background locations. Those data, along with laboratory method limits (EPA Method 1633), informed SRS numeric thresholds.
Martz said DES used a leaching model (CSoil) tailored to New Hampshire soils to derive values protective of groundwater, and that the department selected protective values using the lower of the leaching result or a laboratory quantitation limit. The SRS Martz cited in the meeting include a PFOA SRS of 0.4 parts per billion (ppb) and a PFNA SRS of 1.3 ppb; for PFOS DES used a leaching‑based value of 0.5 ppb as the protective threshold.
DES staff described early implementation actions around the Saint‑Gobain site. Andy Fuller, project manager for the Saint‑Gobain Performance Plastics site, said Saint‑Gobain has removed above‑ground structures and is scarifying the remaining concrete floor and that the company has been shipping demolition debris with high PFAS concentrations to out‑of‑state hazardous waste landfill disposal. Fuller said Saint‑Gobain’s current plan is to remove above‑ground structures and leave the concrete foundation in place after scarification and stated the company expects demolition activities to be complete in 2025.
Fuller told the commission that DES recently issued a written request to Saint‑Gobain asking the company to address an off‑site stockpile of excess soil generated during a nearby development at 702 Daniel Webster Highway; the company was given a deadline to respond. "We've asked Saint‑Gobain to address that soil pile," Fuller said, noting DES would review the company's proposed response.
On drinking water response and monitoring, Fuller said Saint‑Gobain contractors have been installing point‑of‑entry treatment systems (POETs) for eligible properties inside the consent decree area and conducting ongoing maintenance under a submitted work plan. DES and Saint‑Gobain are also extending municipal water lines and connecting eligible properties in Litchfield, Bedford, Londonderry and Merrimack; Fuller said Hillcrest Road work is complete and bottled‑water deliveries were discontinued to properties now on municipal water. Fuller reported Saint‑Gobain’s long‑term groundwater monitoring plan will target eligible properties for periodic sampling (about six samples per eligible property by the end of 2026) and that the company has been sampling under that plan since January 2025.
DES said it reviewed Saint‑Gobain’s remedial action plan (RAP) and wrap addendum and found deficiencies; Saint‑Gobain has told DES it will submit a revised addendum and a work plan to fill data gaps and address remedial alternatives, with the addendum expected in the second quarter of 2025.
Commission members pressed DES about demolition dust, concrete sampling and the adequacy of leaving the concrete foundation in place. Fuller said DES has asked for concrete scarification sampling results from Saint‑Gobain and is awaiting the data; he acknowledged analytical methods and interpretation are complex and that DES will follow up to determine how to interpret the results and what remediation obligations apply. Jeff Martz recommended that residents report visible dust off property to DES’s Air Resources Division so inspectors can investigate.
Ending: DES officials said the newly adopted soil remediation standards change how the department evaluates soil management and that initial enforcement and implementation steps — letters to Saint‑Gobain, expanded monitoring, POET installation and waterline extensions — are underway while the department awaits additional data and revised remedial plans from the company.
