PFAS in Pennsylvania Groundwater and Factors Influencing Occurrence

Overview of PFAS

Per- and poly-fluoroalkyl substances (PFAS) exposure is of growing concern due to the potential negative health impacts. This diverse family of organic chemicals has gained significant awareness over the last few decades as laboratory methods of testing continue to improve. PFAS are of concern because they have been associated with negative human health impacts. Some examples of PFAS sources into the environment include airports, military stations, and other areas where some types of fire suppressants were used in the past, landfills, application of PFAS-contaminated residual wastes to agricultural lands (i.e., treated wastewater and biosolids), and chemical manufacturing discharges. Depending on the proximity to potential sources and a variety of environmental factors, PFAS can accumulate in drinking water, soil, farm produce, and air. Therefore, we can be exposed to PFAS by consuming contaminated food and drinking water, or by inhaling contaminated particles. To learn more about the chemistry of PFAS, exposure pathways, and health impacts, refer to Penn State Extension's article "Understanding PFAS- What They Are, Their Impact, and What We Can Do".

Among these exposure pathways, drinking water is particularly important. We consume water daily, often from the same source. Because of human health risks through drinking water, some PFAS are regulated in states like Pennsylvania, and the US EPA also finalized federal regulations for six PFAS compounds that will be implemented in 2031. Five compounds are regulated individually: perfluorooctanoic acid (PFOA), perfluorooctanesulfonic acid (PFOS), perfluorohexanesulfonic acid (PFHxS), perfluorononanoic acid (PFNA), and hexafluoropropylene oxide dimer acid (HFPO-DA or "Gen-X"). PFOA and PFOS are regulated at a particularly low level of 4 ng/L. PFHxS, PFNA, and HFPO-DA are regulated at 10 ng/L. Perfluorobutanesulfonic acid (PFBS) is also regulated, but as a unitless hazard index when co-occurring as a mixture with PFHxS, PFNA, and/or HFPO-DA.

Public versus Private Water Systems

What is the difference between public water systems (PWS) and private systems? Public water systems provide drinking water to residents and businesses in most towns or cities. They can also serve campgrounds, service stations, mobile home parks, schools, and hospitals. The water typically comes from local surface water (lakes and rivers) or groundwater (e.g., wells) sources and is treated at a drinking water treatment plant to remove any present contamination. Treated water is then distributed to customers through a series of underground pipes or other methods. Public water systems must have at least 15 service connections or serve a minimum of 25 people for at least 60 days a year. To ensure they meet state and federal drinking water standards, public water systems treat the water, frequently test its quality, and report water quality conditions to the regulatory bodies. Customers can also find water quality reports known as Consumer Confidence Reports (CCRs) from their provider. 

Private water systems typically serve only one household and the water can come from wells, springs, or cisterns. There are over one million private wells in PA that serve a population of over 3.5 million people. Private systems owners and users are responsible for all of the testing, monitoring, and maintenance. Both state and federal drinking water regulations only apply to public water systems. However, private water system users are encouraged to ensure their drinking water meets these safety standards. 

Both public and private water systems may be more vulnerable to elevated PFAS levels depending on nearby land uses.

PFAS Monitoring across PA

Kosiarski et al. (2025) incorporated PFAS monitoring data from both public and private supply wells across Pennsylvania. In total, there were 167 private wells monitored by Penn State researchers from 2021-2023. Private well study participants were recruited from the Master Well Owner Network (MWON). Monitoring data from 406 public supply wells studied by the Pennsylvania Department of Environmental Protection (PADEP) from 2021-2022 were also included. The sampling campaign done by the PADEP prioritized groundwater sources but included some surface water sources. Using both PA DEP and Penn State monitoring datasets provides a broader picture of the occurrence of PFAS in groundwater used as drinking water sources across PA.  

Summary of PFAS Levels in Drinking Water Sources Across PA

The number of samples varied by county. Data collected through the MWON by Penn State covered 46 of the counties and samples from PA DEP monitoring included 66 counties. There was no data collected from Greene County from either monitoring programs. Sample numbers across counties may influence how representative the results are across the state.

Overall, considering both data sets, PFAS were detected in 47 counties across PA. Detection frequencies show us how often different PFAS compounds were found in collected samples. As shown in Figure 1, detection frequencies varied significantly across the counties. Samples collected from 19 counties did not have any detectable PFAS, while in 4 counties, PFAS was detected in every sample. It is important to note that detection frequencies may appear higher due to a small sample size in some counties that only had a few samples taken. Average total PFAS concentrations were calculated for each county by summing up the concentration of individual PFAS compounds and dividing the total samples collected from that county. Averages ranged from 0.28 to 289.80 ng/L. Some county averages appear high because they are based on only one or very few samples with detectable PFAS.

To better understand where PFAS levels may pose concern, we also looked at how often individual samples exceeded the EPA’s new maximum contaminant levels (MCLs) for PFAS. Samples most commonly exceeded the drinking water standards set for PFOS and PFOA. Out of the 579 combined public and private water system samples, 16.8% (97) samples exceeded the MCL for PFOS and 17.8% (103) samples exceeded the MCL for PFOA. Also, samples that exceeded a drinking water standard for one compound often exceeded another drinking water standard for a different compound. As shown in Figure 2, the counties that had the highest exceedances of drinking water standards were mainly located in the Southeastern portion of the state (Blair, Bucks, Chester, Montgomery, and York). For more detailed results on detection frequency, exceedance of drinking water standards, and sample counts by county, please explore our interactive map tool.

Factors Influencing PFAS Occurrence in Groundwater

Land use: Land use refers to how we use the land around us and the impact the activities may have on our environment. Developed land refers to areas that are no longer in their natural state and have been either cleared and constructed to support residential areas, businesses, industries, among other infrastructure and community amenities.  Agricultural land is used for cultivating crops and raising animals to produce food and other products. These land uses may be classified as point-source and non-point sources of pollution. A point source is a single, identifiable source of pollution that releases contaminants into the environment, while non-point sources are often scattered within an area. Pollution from non-point sources is usually transported through surface runoff following rainfall or snowmelt. Some point source pollution for PFAS in developed land uses can include discharges from industries, manufacturing factories, landfills, discharges from wastewater treatment plants, and military bases, or firefighting training sites where PFAS-containing firefighting foam was used in the past. Non-point pollution sources for PFAS can include farmlands where PFAS-contaminated biosolids were applied and domestic septic systems.

Water sources located near potential point or non-point sources of PFAS are likely to have detectable levels of PFAS in them. As you explore the map on Figure 1 and the interactive tool, you may notice that PFAS detections and exceedances of current US EPA MCLs tend to cluster in Southeastern portions of the state. These regions are highly developed and likely to have a wide variety of point and non-point sources of PFAS, which indicates that the water sources may be vulnerable to PFAS contamination (Kosiarski et al., 2025). Similar studies at a national level have also found percent developed land use in a region to be an important predictor of PFAS levels in water (Smalling et al., 2023). We also found that drinking water sources in agricultural cropland that utilize certain pesticides or highly contaminated biosolids may be vulnerable to elevated PFAS levels (Kosiarski et al., 2025). While we did not evaluate the influence of septic system density in our study in Pennsylvania, other researchers have found that domestic septic systems can have an impact on overall PFAS occurrences in private water wells and local groundwater supplies (Schaider et al., 2015; Tokranov et al., 2024).

PFAS chemical properties: The chemistry of individual PFAS can influence their presence in the environment after they are released from different sources. Some PFAS are hydrophobic, meaning they do not dissolve easily in water and will bind to soil particles and organic matter. Because hydrophobic PFAS don't move easily through the soil, they can build up in the soil over time. Eventually, they can contaminate groundwater and surface water sources through surface runoff. Other PFAS are hydrophilic, meaning they mix easily with water and can move through the soil, increasing the risk of reaching groundwater and surface water sources. Due to the chemical stability of PFAS, they are very persistent in the environment and do not readily break down. This can also contribute to their accumulation in environmental matrices such as soil, water, and crops.

Soil characteristics: Proximity to a potential PFAS source alone does not absolutely mean that the drinking water source will have elevated PFAS. Soil characteristics also play a role in how PFAS are transported to groundwater and nearby surface water sources. In this study, we found that groundwater underlying sandy soils can be more vulnerable to elevated PFAS. Sandier soils don’t retain PFAS due to their higher permeability, lower organic matter, and fewer adsorption sites for PFAS. Soils with high sand content can allow PFAS to be transported easily through the soil column to groundwater or be washed off to surface water sources through surface runoff. Clayey soils with high organic carbon content and less water movement can trap PFAS in soil particles

Groundwater and well characteristics: Groundwater recharge is the process where water travels downward towards groundwater aquifers following rainfall events, snowmelt, or irrigation activities. Groundwater age can vary depending on the amount of time that recharge water has been underground. Because PFAS are human-made chemicals that have been in use since the 1940s, they are more likely to be present in groundwater sources with recent recharge events that are impacted by PFAS sources as opposed to older groundwater sources recharged thousands of years ago (like the Pleistocene-age) (Tokranov et al., 2024). Similarly, shallower wells have been found to be more susceptible to PFAS than deeper wells, because they are more likely to receive PFAS-contaminated recharge, whereas deeper groundwater typically reflects older, less impacted recharge (McMahon et al., 2023; Tokranov et al., 2024). In the present study, we did not find any correlation between PFAS detections and concentrations and reported well depth. This could be due to the limited variability in well depths we assessed and other factors, such as groundwater recharge, that may also dilute PFAS concentrations.

In addition to groundwater age and depth, the physical construction of a well plays a critical role in protecting against elevated PFAS levels. Wells with poor construction and/or deterioration of well casings and grout may be more vulnerable to PFAS infiltration from shallow or surface sources (VanDerwerker et al., 2024). PFAS are used in a wide variety of consumer products, including construction materials. Wells may also be impacted depending on the type of PFAS that may be present in the construction materials used. While some PFAS (e.g. PFOA and PFOS) have been phased out in consumer products since the early 2000s, some older wells may have PFAS detections if these products were used in construction materials.

Activities in the wellhead protection zone may also contribute to the contamination of a well. Penn State Extension recommends designating a minimum of a 100-foot radius around the well as a wellhead protection zone. Private well owners are advised to avoid the following near their well head: dumping or burning waste, storing or mixing chemicals and pesticides, vehicle maintenance activities or parking, spreading manure, fertilizer, compost, or biosolids, etc. These activities can introduce a wide range of chemical contaminants into the water supply.

Socioeconomic factors: Our analysis also found associations between socioeconomic indicators and PFAS occurrence, suggesting that PFAS use patterns and exposure may vary with community-level characteristics. In particular, areas with higher socioeconomic scores were typically correlated with higher concentrations of PFAS, and PFOA was found to be positively associated with areas that had a higher percentage of non-white individuals.  These patterns can reflect differences in land use intensity, types of industry present, proximity to potential point sources, and PFAS usage within the community.

If you are interested in reading more about the environmental and socioeconomic factors that shape PFAS presence in private wells please refer to the paper "Geospatial and socioeconomic factors of PFAS contamination in private drinking water wells: Insights for monitoring and management". This paper provides a more in-depth, technical perspective on the dataset.

What can you do as a Private Water System Owner/User?

• Assess if there are potential PFAS sources nearby: Private water supplies that are adjacent to potential PFAS sources mentioned above may be at risk of PFAS contamination.
• Consider testing your drinking water source: If there is a confirmed PFAS contamination source or investigation near you, testing is the only way to know if your source is impacted. The Pennsylvania Department of Environmental Protection (PA DEP) has state-accredited labs for PFAS testing in potable water. Current labs with PFAS testing capabilities are summarized in this Penn State Extension article: PFAS Drinking Water Standards, Testing, and Treatment. For an up-to-date list of laboratories, visit and search through the PA DEP Accredited Environmental Laboratories Database. Instructions for using the laboratory database can be found on the DEP website.
• Compare your test results with drinking water standards: Although private water systems are not regulated, owners/users are encouraged to ensure their source meets current drinking water safety standards. Recently finalized federal MCLs for the six PFAS can be used as a reference point when reviewing your test results. You can use this Drinking Water Interpretation Tool to interpret your results or contact a local Extension Educator to help.
• Explore if water treatment may be necessary: In the case of elevated PFAS, there are some steps you can take to reduce PFAS levels in drinking water. Commonly used and efficient treatment technologies include reverse osmosis filtration, ion exchange, and granular carbon filtration devices (GAC). These can be point-of-use (POU) systems that are designed to only treat water at a certain location in the house, such as the kitchen faucet. Or they can be point-of-entry (POE) systems which treat the water in the entire house. For more information about PFAS action items, please see "Home Water Treatment for PFAS". Beyond drinking water, there are things you can do to reduce PFAS exposure through consumer products. In your kitchen, for example, consider switching non-stick cookware to cast iron or switching plastic food storage containers for glass. For more tips, refer to our article "Reducing Exposure to PFAS at Home".
• Protect your water supply: Prevent activities near your wellhead that can unintentionally contaminate your drinking water source. Maintain your septic system to ensure that it is functioning properly.

References

Kosiarski, K., Veith, T. L., Kibuye, F. A., Fetter, J., Boser, S., Vanden Heuvel, J. P., Thompson, C. L., Preisendanz, H. E. (2025). Geospatial and socioeconomic factors of PFAS contamination in private drinking water wells: Insights for monitoring and management. J Environ Manage., 388, 125863. doi.org/10.1016/j.jenvman.2025.125863

McMahon, P. B., Tokranov, A. K., Bexfield, L. M., Lindsey, B. D., Johnson, T. D., Lombard, M. A., Watson, E. (2022). Perfluoroalkyl and Polyfluoroalkyl Substances in Groundwater Used as a Source of Drinking Water in the Eastern United States. Environ Sci Technol., 56, 4, 2279-2288. doi.org/10.1021/acs.est.1c04795

Tokranov, A. K., Ransom, K. M., Bexfield, L. M., Lindsey, B. D., Watson, E., Dupuy, D. I., Stackelberg, P. E., Fram, M. S., Voss, S. A., Kingsbury, J. A., Jurgens, B. C., Smalling, K. L., Bradley, P. M. (2024). Predictions of groundwater PFAS occurrence at drinking water supply depths in the United States. Science, 386, 6723, 748-755. doi.org/10.1126/science.ado6638

Schaider, L. A., Ackerman, J. M., Rudel, R. A. (2016). Septic systems as sources of organic wastewater compounds in domestic drinking water wells in a shallow sand and gravel aquifer. Sci Total Environ, 547, 470-481. doi.org/10.1016/j.scitotenv.2015.12.081

Smalling, K. L., Romanok, K. M., Bradley, P. M., Morriss, M. C., Gray, J. L., Kanagy, L. K., Gordon, S. E., Williams, B. M., Breitmeyer, S. E., Jones, D. K., DeCicco, L. A., Eagles-Smith, C. A., Wagner, T. (2023). Per- and polyfluoroalkyl substances (PFAS) in United States tapwater: Comparison of underserved private-well and public-supply exposures and associated health implications. Environ Int., 178, 108033. doi.org/10.1016/j.envint.2023.108033

VanDerwerker, T. J., Knappe, D. R. U., Genereux, D. P. (2024). Adapting to PFAS contamination of private drinking water wells near a PFAS production facility in the US Atlantic Coastal Plain of North Carolina. Water Environ Res., 96, 8, e11091. doi.org/10.1002/wer.11091