In 2014, a routine federal testing program called UCMR3 delivered a gut punch to the suburbs north of Philadelphia. Five of fourteen public drinking water wells in Horsham Township, Pennsylvania were contaminated with PFAS — the so-called "forever chemicals" that don't break down in nature or the human body. Two of those wells weren't just contaminated. They were among the worst in the country.
Well 26 tested at 700 parts per trillion (ppt) of PFOS and 290 ppt of PFOA. Well 40 was even worse: 1,000 ppt of PFOS. Today's EPA maximum contaminant level for PFOS in drinking water is 4 ppt. Those wells were delivering water at 175 to 250 times the current federal safety limit.
The source was no mystery. Three Department of Defense facilities — the former Naval Air Station Joint Reserve Base Willow Grove, the Naval Air Warfare Center in Warminster, and the Horsham Air Guard Station — had used aqueous film-forming foam (AFFF) for decades of firefighting training and emergency response. AFFF is extremely effective at suppressing fuel fires. It is also loaded with PFOS and PFOA, which leached through the soil and into the groundwater that fed the community's drinking water wells.
The Scale of the Problem
As testing expanded, the picture got worse. In Warminster, public water showed PFOS at 1,100 ppt and PFOA at 350 ppt — the third-highest public water PFOS level ever recorded in the United States. An on-base supply well at Willow Grove tested at approximately 19,000 ppt of PFOS, more than 4,700 times today's federal limit. Groundwater near the base hit 329,500 ppt. Soil samples showed PFAS at 98,000 parts per billion.
The contamination wasn't limited to public systems. By March 2018, the Department of Defense and EPA had tested more than 650 private wells in the Horsham, Warminster, and Warrington area. Of those, 169 exceeded the then-current EPA health advisory of 70 ppt for combined PFOA and PFOS. Another 70 private wells showed PFAS between 40 and 70 ppt — below the advisory but well above what anyone would consider safe, especially under today's 4 ppt standard.
Two Mothers Who Wouldn't Wait
The federal response in the early days was methodical but slow. Residents didn't have the luxury of patience — they were drinking the water, bathing in it, cooking with it. That urgency drove the formation of the Buxmont Coalition for Safe Water, co-founded by Joanne Stanton and Hope Grosse, two Bucks County residents who understood that contamination data on a government spreadsheet means nothing if nobody reads it.
Stanton and Grosse organized affected families across Bucks and Montgomery Counties. They compiled contamination data into formats residents could understand. They showed up at every public meeting. And critically, they testified — Stanton submitted formal written comments to the Pennsylvania Independent Regulatory Review Commission urging the state to adopt enforceable PFAS drinking water standards, invoking the coalition's representation of families whose water had been poisoned by military operations on their doorstep.
Grosse pushed relentlessly for the region to be included in the federal government's national PFAS health study. That effort succeeded: Bucks and Montgomery Counties were selected as one of seven national study sites, receiving $5 million over five years from the CDC and Agency for Toxic Substances and Disease Registry (ATSDR). The study, conducted by the Pennsylvania Department of Health, RTI International, and Temple University, recruited over 1,000 local adults and children to examine the relationship between PFAS exposure and thyroid function, cholesterol, kidney and liver function, immune response, and childhood developmental outcomes.
What the Blood Tests Showed
A 2018 pilot study of 235 residents near the three military facilities found what the community already suspected: their PFAS blood levels were elevated compared to national averages. The full multi-site ATSDR study — spanning seven communities across the country — has continued to gather data on long-term health effects. While the study does not include cancer as a primary endpoint, the scientific literature has established associations between PFAS exposure and kidney cancer, testicular cancer, thyroid disease, elevated cholesterol, ulcerative colitis, and reproductive complications including preeclampsia and low birth weight.
For the families of Horsham and Warminster, these aren't abstract epidemiological findings. They're the backdrop to a decade of worry about what the water may have already done.
The Cleanup: Shutdowns, Carbon Filters, and New Wells
The Horsham Water and Sewer Authority (HWSA) acted quickly once the UCMR3 results came in. Wells 26 and 40 were shut down immediately in consultation with EPA and the Pennsylvania Department of Environmental Protection. But shutting down contaminated wells in a system that depends almost entirely on groundwater creates its own crisis — where does the water come from?
HWSA redesigned its supply system. Some wells were taken offline permanently. Others were fitted with granular activated carbon (GAC) treatment systems capable of stripping PFAS from the water. The authority expanded its interconnections with neighboring water suppliers to bring in treated surface water. By the time the engineering was complete, HWSA had reduced system-wide PFAS in finished drinking water to approximately 4 ppt combined PFOA and PFOS — right at today's federal MCL.
In Warminster, the situation required even more aggressive intervention. At one point, eight of the municipality's fourteen wells were offline due to PFAS contamination. The Navy committed $18 million to install treatment systems on five Warminster wells and extend water mains to nearly 100 contaminated private wells. Warminster itself built additional treatment capacity, including Well 10, a new facility equipped with GAC treatment that takes incoming water at 250 ppt of PFAS and delivers finished water at non-detectable levels.
For private well owners who couldn't be connected to municipal systems immediately, the response included bottled water delivery and point-of-use treatment filters. By 2018, 81 of the 95 most-affected private wells had been converted to municipal water, with 14 still receiving bottled water while awaiting connection.
The Regulatory Domino Effect
Communities like Horsham and Warminster didn't just clean their own water. They helped change the rules for everyone.
In April 2024, EPA finalized enforceable Maximum Contaminant Levels for PFOA and PFOS at 4 ppt each — the first-ever legally binding federal limits on forever chemicals in drinking water. These weren't arbitrary numbers. They were informed by a decade of contamination data, health studies, and community testimony from places like Bucks County, where residents had been living the evidence.
The Department of Defense, confronted with PFAS contamination at 723 military installations, BRAC sites, and National Guard facilities as of September 2025, updated its cleanup protocols accordingly. At 55 installations where PFOS and PFOA exceeded the old 70 ppt advisory in drinking water, DoD reports having taken "immediate action" to address exposure. Under the new MCL framework, DoD must now initiate interim actions — point-of-use treatment, alternate water, or connection to public systems — for any private well impacted by military-related PFAS at concentrations three times the MCL or above (12 ppt).
Meanwhile, the national PFAS litigation reached a watershed. 3M agreed to a settlement of approximately $10.3 billion with U.S. public water systems for PFAS contamination, much of it linked to AFFF. The settlement, which received final court approval and entered implementation by 2025, established a claims program for eligible water systems to offset treatment costs. Utilities like those in Horsham and Warminster — which have spent millions on GAC systems, new wells, and supply reconfiguration — are among the systems the settlement was designed to help.
Where Things Stand Today
The drinking water in Horsham and Warminster is clean. HWSA's system delivers water at approximately 4 ppt combined PFOA and PFOS. Warminster's GAC-treated wells produce water at non-detectable PFAS levels. Public utilities continue to test regularly, and ATSDR confirms that treated drinking water near both Willow Grove and Warminster meets or exceeds the new federal standards.
But clean water today doesn't erase decades of exposure. The groundwater beneath and around the former military facilities remains contaminated. A 2023 study published in Environmental Science & Technology on the persistence of PFAS at military fire training areas concluded that, without aggressive source remediation, elevated PFAS in groundwater can persist for decades to centuries. The contamination isn't going away on its own. Long-term treatment and monitoring will be necessary for generations.
The Buxmont Coalition for Safe Water continues its work — educating residents, pushing for stronger enforcement, and ensuring that the community's voice remains part of every decision about the water they drink.
What This Case Teaches Us
The Horsham-Warminster story carries lessons that extend far beyond southeastern Pennsylvania:
Testing reveals what inaction hides. PFAS had been in the groundwater for decades before UCMR3 sampling found it in 2014. Without systematic testing of unregulated contaminants, the contamination would have continued undetected. Thousands of communities across the country still rely on private wells that have never been tested for PFAS.
Community organizing accelerates government action. The Buxmont Coalition didn't have legal authority to shut down a well or install a treatment system. What they had was the ability to make contamination data visible, hold agencies accountable, and ensure that affected families weren't forgotten between budget cycles. That matters.
Treatment works, but it isn't free. GAC systems, new wells, supply interconnections, and private well conversions cost tens of millions of dollars in Horsham and Warminster alone. The Navy's $18 million commitment was significant, but it didn't cover everything. Public water systems need sustained funding — from settlements, federal infrastructure dollars, and responsible-party payments — to maintain treatment for the long term.
Enforceable standards change behavior. The 70 ppt health advisory that existed from 2016 to 2024 was a guideline, not a mandate. When EPA set legally binding MCLs at 4 ppt in 2024, it changed the calculus for every water utility and every polluter in the country. Standards with teeth drive action that advisories alone cannot.
At EPR Foundation, we believe that the story of Horsham and Warminster represents what's possible when communities, science, and government work in the same direction. Clean water isn't a partisan issue. It's a promise — and it's one worth keeping.
Sources: EPA UCMR3 monitoring data; Horsham Water and Sewer Authority PFAS technical presentation (NJWEA, 2019); ATSDR PFAS site assessments, Region 3; EPA Horsham community engagement presentation (July 2018); WHYY reporting on Warminster treatment costs and PFAS health study funding; Buxmont Coalition for Safe Water; Pennsylvania IRRC public comments; NBC News investigation of military PFAS contamination; Philadelphia Inquirer PFAS health study reporting; DoD PFAS cleanup status report (2025); Environmental Science & Technology, "Centurial Persistence of Forever Chemicals at Military Fire Training Areas" (2023).