Across Bucks and Montgomery Counties, Pennsylvania is dealing with one of the nation's more recognizable AFFF contamination clusters. Firefighting foam used at the former Naval Air Station Willow Grove, the Horsham Air Guard Station, and the Naval Air Warfare Center in Warminster left PFAS in the groundwater feeding Warminster, Warrington, and Horsham. Private wells close to those bases came back with PFAS thousands of times over the 4 ppt reference point, and some PFOS results ran near 5,000 ppt.

The human side is on the record as well. A health study of area residents found nearly everyone carrying elevated PFAS in their blood, with about 30% high enough to qualify for medical monitoring, according to the USGS, NBC News, and the PFAS Project Lab. This is a bona fide hotspot, and the numbers make that unmistakable.

Part of what makes the Bucks-Montgomery cluster so instructive is how densely populated it is. Unlike a remote installation, these former bases sit inside a suburban stretch of greater Philadelphia where public systems, private wells, and thousands of homes overlap the same groundwater. When contamination surfaced, it did not touch a handful of isolated properties — it prompted well closures, bottled-water programs, and new treatment at the municipal scale, and it turned this corner of the state into a closely watched case study for how communities respond when a plume reaches a crowded aquifer.

State and federal limits

Pennsylvania wrote its own enforceable drinking-water limits — 14 ppt for PFOA and 18 ppt for PFOS (per PA DEP and BCLP). Those state MCLs now run alongside the stricter 2024 federal standards: 4 ppt each for PFOA and PFOS, and 10 ppt each for PFNA, PFHxS, and GenX, with mixtures graded by a hazard index. A public system has to satisfy whichever rule is more protective, which in day-to-day terms means the federal 4 ppt floor for PFOA and PFOS.

Testing near the bases and beyond

If your home taps a private well anywhere in the affected corridor — or you simply want to be sure — a certified-lab PFAS test using EPA Method 537.1 or 533 is the reliable path. Follow the sampling kit closely, since PFAS can leach out of everyday materials and compromise a sample that would otherwise be sound.

Three removal methods

• Granular activated carbon (GAC): a carbon bed adsorbs PFAS from flowing water — the standard for whole-house systems.
• Strong-base anion exchange: resin that captures charged PFAS and frequently outdoes carbon on short-chain compounds.
• Reverse osmosis (RO): a membrane that strips out PFAS and much more at your drinking tap.

With levels this high near the bases, a whole-house GAC or anion system covering every fixture is a sensible call for many households. An under-sink RO unit layers on a focused final barrier for drinking and cooking water. Stacking both is a common choice in the Warminster and Horsham area.

When source concentrations climb into the hundreds or thousands of ppt seen near these installations, media life shrinks and correct sizing becomes make-or-break — an undersized bed can break through far ahead of schedule. That makes a lab result and a realistic replacement plan essential rather than optional. Even homes now hooked to municipal water may still want point-of-use RO as a last safeguard, because one tested tap gives you direct proof your drinking water clears the 4 ppt federal floor. Wiring verification into the plan turns a serious local problem into a managed one.

Systems for Pennsylvania homes

Our PFAS water filter removal guide helps you match test results to the right treatment. Test first, then choose.