Wisconsin DNR finds PFAS in 71% of shallow groundwater samples


Nov. 07, 2023

The Wisconsin Department of Natural Resources has released the results of a study reviewing PFAS concentrations in 450 samples from shallow private wells. The study detected PFAS in 71% of the samples, with certain samples exceeding the Environmental Protection Agency’s proposed maximum contaminant levels for certain substances.

PFAS and the Wisconsin DNR

  • Per- and polyfluoroalkyl substances (PFAS) are wide class of synthetic organic chemicals that have been used since the 1940s in many different applications. PFAS resist many environmental stressors, including heat, oil, water, and grease, which has led to applications in textiles, coatings, and lubricants. However, this ability to resist stressors generally means that PFAS will persist in the environment and may bioaccumulate in organisms including humans.
  • The Environmental Protection Agency (EPA) has released proposed regulations that would restrict concentrations of six PFAS in drinking water. The proposed National Primary Drinking Water Regulation (NPDWR) would cover perfluorooctanoic acid (PFOA), perfluorooctane sulfonic acid (PFOS), perfluorononanoic acid (PFNA), hexafluoropropylene oxide dimer acid (HFPO-DA or GenX), perfluorohexane sulfonic acid (PFHxS), and perfluorobutane sulfonic acid (PFBS) [for an analysis of the proposed NPDWR, see the AgencyIQ analysis here]. PFOA and PFOS limits would be set at 4 parts per trillion (ng/L or ppt) individually. The remaining four would be set via a Hazard Index (HI) that would take concentrations of all four into account when determine whether a water source was above the limit. The agency expects to release the finalized rule in January 2024.
  • The Wisconsin Department of Natural Resources (DNR) is the state’s agency tasked with protecting and enhancing the resources of the state, with its authority covering hunting, fishing, state parks, as well as climate and environment regulations. The state regulations cover PFAS, and the state considers that the discharge of PFAS into the environment is subject to the state’s hazardous substance regulations. In 2022, DNR advanced new regulations that set maximum contaminant limits (MCLs) for PFOS and PFOA in drinking water. The department based these values, at 70 ng/L both individually and combined, on the EPA’s 2016 Lifetime Health Advisories for the chemicals (notably, the EPA updated these drinking water health advisories at .004 ng/L for PFOA and .02 ng/L for PFOS in 2022).

Insights from the study

  • On November 3, 2023, DNR announced the results of a study reviewing PFAS in ambient shallow groundwater in the state. The department utilized EPA funding to collect samples from 450 locations in summer and fall 2022 from private wells in the state. The department utilized an “equal area grid” methodology for dividing the state into cells of equal area and identified private water supply wells from each of the 450 cells. The state targeted wells that had available well construction reports as well as casing that extended at least to the static water level, but no deeper than 40 feet below the static water level.
  • Water samples were taken from the home plumbing system and from an outdoor faucet if possible. Prior to sample collection, the department asked homeowners about any treatment systems, and would attempt to bypass any treatment system to sample untreated water. The samples were extracted by the Wisconsin State Laboratory of Hygiene and were tested utilizing the ISO 21675 draft method, which reviews for 44 individual PFAS substances.
  • At least one PFAS was detected in approximately 71% of the 450 samples. Perfluorobutanoic acid (PFBA) was the most frequently detected PFAS and was found in 46% of samples, followed by PFOA which was detected in 45% of samples. The agency stated that because PFBA has a higher detection limit than PFOA, the relative presence of PFBA in groundwater may be “much higher” than PFOA.
  • Of the samples collected, 13 had concentrations above the EPA’s proposed MCL for PFOA, and 11 were above the proposed MCL For PFOS. The testing method had a variety of detection limits, which the department combined into a median detection limit of .181 ng/L to create a baseline level to determine PFAS incidence at a constant concentration. Under this limit, the department detected a PFAS in approximately 65% of the study samples, with inferred prevalence peaking at four-carbon chains (PFBA is a C4 PFAS). Although the testing contained a list of 16 precursors for perfluoroalkyl acids, the department only detected four precursors in its analysis.

Next steps

  • DNR conducted the study to characterize the levels of PFAS in shallow groundwater in the state, which is consumed by approximately 70% of the state’s population as drinking water. As this groundwater may move deeper with time, it is also possible that PFAS may move with it and this would become an issue for municipal water systems that draw from deeper wells and groundwater.
  • DNR may seek to add additional regulation for PFAS based on the results of the study. Despite the low incidence of detected samples over the EPA’s proposed MCLs for drinking water, the state may choose to focus on remediation or source reduction for introducing PFAS into the environment. The use of the equal area grid may also provide the agency with insight into the sources of these various PFAS.
  • The results of the study mirror a recent Pennsylvania study that identified PFAS in about 76% of tested streams in the state [an AgencyIQ analysis of the study is available here]. Both of the studies seem to indicate that the commonality of PFAS contamination in the United States may be much higher than a recent U.S. Geological Survey study that estimated that at least 45% of tap water contains measurable levels of PFAS [an AgencyIQ analysis of the study is available here]. Although the levels for the Wisconsin study are mostly below the EPA’s action levels, the sheer prevalence of PFAS in groundwater and surface water could have significant implications for PFAS regulations in the future. However, additional testing may find significant differences between PFAS incidence in surface water, groundwater, and drinking water overall.

To contact the author of this analysis, please email Walker Livingston.

To contact the editor of this analysis, please email Patricia Iscaro.

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