NHDES announces Ambient Groundwater Quality Standard changes effective September 1, 2018

August 28, 2018


Upcoming Changes to NH Water Standards and Anticipated Impacts for Naphthalene, 1,4-Dioxane, and Perfluorooctanesulfonic Acid (PFOS)

The New Hampshire Department of Environmental Services (NHDES) has announced changes to its Ambient Groundwater Quality Standards (AGQS), effective September 1, 2018.  Some of the standards are increased while others are lowered. Not all of these chemicals are often detected at sites, but there are a few changes that will impact activities ranging from real estate due diligence to monitoring remediation results at New Hampshire sites, in particular for naphthalene, 1,4-dioxane, and perfluorooctanesulfonic acid (PFOS).


Naphthalene is of particular interest as it is commonly detected in groundwater at aboveground storage tank (AST) and underground storage tank (UST) release sites.  Furthermore, naphthalene can hinder site closures as it does not degrade easily in groundwater.  The proposed AGQS for naphthalene is increasing from 20 ug/L to 100 ug/L.  For any project in New Hampshire, it would be worthwhile to evaluate recent groundwater data to see if this change might result in closure.

The Oil Remediation and Compliance Bureau (ORCB) is gearing up for a wave of site closures where naphthalene concentrations in ground water have been above the current AGQS of 20 µg/L but below the new standard of 100 µg/L.  While the ORCB has not developed a standard pathway to closure for these sites yet, they are working on a standard approach that will be released in the near future.  We expect that part of the proposed standards will include evaluating soil data to ensure they pass the new Method-1 soil standard for naphthalene, which is expected to change from the current 5 mg/kg to something within the 20-30 mg/kg range.

1,4-Dioxane is common in industrial production where chlorinated solvents are present. The updated AGQS lowers the existing limit significantly from 3 ug/L to 0.32 ug/L. Sites that are working to mitigate this pollutant may need to expand their monitoring programs to meet the new limits. Here are some anticipated impacts for 1,4-dioxane:

  • The NHDES does not plan to open old sites that were closed under the old standard, unless there is new information that necessitates further evaluation—for example, new data from a real estate transaction assessment.
  • Sites with a Groundwater Management Zone (GMZ) that has the boundary defined under the old standard, but not under the new standard, may be required to re-define a new GMZ boundary; however, the NHDES will consider this requirement on a case-by-case basis, with the presence or absence of sensitive receptors being a significant determining factor.

In conjunction with AGQS, NHDES will also be enacting new amendments relative to Groundwater Discharges of Wastewater containing 1,4-dioxane, and the required responses necessary for exceedances to AGQS.

The NHDES has also provided clarification to the AGQS for PFOS, specifying that the 0.07 parts per billion includes the total of all PFOS isomers (PFOS is manufactured in linear and branched isomer structures); therefore, it is required that laboratories test for all isomers. PFOS is a part of a larger group of chemicals known as poly- and perfluoroalkyl substances (PFAS). Across New Hampshire, PFAS has been detected at industrial sites, landfills, and car washes. Moreover, they are often found in products with oil and stain resistant properties, household cleaning agents, fire-fighting foam, food packaging, and more.

In May 2016, the United States EPA issued a health advisory for PFAS, PFOS, and perfluorooctanoic acid (PFOA) chemicals of 0.07 parts per billion (70 parts per trillion). In October 2016, the USEPA standards were adopted by the NHDES as AGQSs for each compound and as a combination of PFOA and PFOS. We are keeping a close eye on the developments around all PFAS chemicals, as detection limits and testing requirements are still being formalized while new data about health effects is presented.

NHDES will also be revising and publishing the soil remediation standards for these chemicals to be current with the AGQS updates.

If you are concerned about any of these changes and how they could impact your site, call us – 603.314.0820. We can help you navigate the ever-changing landscape of environmental regulations.  

Get In Touch:

If you have questions, get in touch with our experts:

GeoInsight's Team of New Hampshire Environmental Experts:


Brian D. Kisiel, PG | President


Contact Brian Kisiel


Michael F. Dacey, PG, LSP | Senior Consultant / Senior Hydrogeologist


Contact Mike Dacey


Dave A. Maclean, PG, LSP, LEP | Director of Water Supply


Contact Mike Dacey