Three installations, one groundwater problem
The former Naval Air Station Joint Reserve Base Willow Grove in Horsham Township, the Horsham Air Guard Station next to it, and the former Naval Air Warfare Center Warminster across the Bucks County line all used aqueous film-forming foam. ATSDR states that the source of PFAS in groundwater near these bases is assumed to be that past use.
The base’s former fire-fighting training area, Site 5, was used from 1942 to 1976, and ATSDR calls it a likely source of the PFOS and PFOA found in downgradient water authority wells. Runways, hangars and plane crash sites are named as other possible source areas. Nobody should publish a start date for the foam itself: ATSDR says plainly that although the product has been commercially available since the mid-1960s or 1970s, it is unknown when it was first used at the site. Every AFFF storage tank and line on the base was emptied, cleaned and closed in place in 2011.
The installation has been on the Superfund National Priorities List since 1995, listed originally for volatile organic compounds in groundwater, years before PFAS was on anybody’s list. It carries EPA facility ID PAD987277837, and a Federal Facilities Agreement among EPA, the Pennsylvania Department of Environmental Protection and the Navy governs the cleanup.
One geographical note that trips up every out-of-town search: the air station everyone calls Willow Grove is in Horsham Township.
What the federal limits are, as of today
EPA’s PFAS National Primary Drinking Water Regulation is a final rule, published 26 April 2024 and effective 25 June 2024:
| Compound | Maximum contaminant level |
|---|---|
| PFOA | 4.0 ppt |
| PFOS | 4.0 ppt |
| PFHxS | 10 ppt |
| PFNA | 10 ppt |
| HFPO-DA (GenX) | 10 ppt |
| Mixtures of PFHxS, PFNA, HFPO-DA and PFBS | Hazard Index of 1 |
Initial monitoring runs to 2027 and compliance with the limits is required by 2029.
You will read that this was all undone in 2026. It was proposed, and nothing more. EPA announced two rules on 18 May 2026 and published both on 20 May 2026, with comment periods that closed on 20 July 2026 after a hearing on 7 July. One proposes to rescind the determinations and limits for PFHxS, PFNA, HFPO-DA and the Hazard Index. The other proposes a federal exemption that would move the PFOA and PFOS compliance date from 26 April 2029 to 26 April 2031 — and only for systems that submit a request, so it would not be automatic even if it landed.
As of 26 August 2026 neither proposal has been finalised. The 2024 limits, including the 10 ppt figures and the Hazard Index, are still on the books. A challenge is also running — American Water Works Association v. EPA in the D.C. Circuit, where the court denied EPA’s request for summary vacatur on 12 January 2026 and merits briefing resumed that March.
Pennsylvania has its own limits, published in the Pennsylvania Bulletin on 14 January 2023: PFOA at 14 ppt and PFOS at 18 ppt. Because those are less strict than the federal 4.0 ppt, the federal figure is the one that governs.
What the Navy has paid for, and what has been connected
From the Navy’s Restoration Advisory Board presentation of 16 July 2026:
- The Navy has provided over $25 million to the Horsham Water and Sewer Authority — filtration on ten municipal wells, plus funding for up to 225 public water connections for properties on private wells.
- Over 600 private wells have been sampled.
- Over 460 have already been connected to municipal water under earlier actions.
- 120 were connected for exceeding three times the EPA limits.
- Four more are awaiting connection.
The earlier round is worth knowing about too. Between September 2014 and April 2017, EPA sampled 640 residential private wells in Horsham, Warrington and a small part of Warminster on behalf of the Navy and the Air National Guard. 166 of them, about 26%, came back above the 70 parts per trillion lifetime health advisory then in force for PFOA and PFOS combined. Some owners never granted access, so the population is incompletely characterised — and those are exactly the parcels where nobody knows.
The aquifer and the tap are two different answers
The Horsham Water and Sewer Authority serves about 26,000 people from fifteen wells, with interconnections to North Wales Water Authority and Aqua Pennsylvania’s main system. It adopted a non-detect policy in October 2019, stricter than any state or federal limit, and reports eleven PFAS removal systems installed.
Its 2025 consumer confidence report puts both numbers side by side. Raw water at Well 26 averaged 417.2 ppt PFOS and 305.5 ppt PFOA across the year; Well 40 averaged 388.8 ppt PFOS. Treated water was non-detect at every entry point in 2025, with one exception — a 3.6 ppt PFOA maximum at Well 19. The detection limit is roughly 2.5 ppt per compound.
So the groundwater under Horsham is still contaminated, and the water coming out of the authority’s pipes in 2025 was not. Both of those are the authority’s own published figures for the same year, and a buyer deserves to hear them together.
Around the edges, the picture changes by system. Willow Grove and Upper Moreland Township are served by Aqua Pennsylvania, so none of the Horsham results transfer — ask for Aqua’s own consumer confidence report. Warminster Municipal Authority is adding ion exchange treatment at ten more wells, construction running October 2026 to October 2027, funded by the Department of Defense, the Navy and the state remediation authority. Warrington Township sold its water system to North Wales Water Authority in October 2019.
And one wrinkle specific to Horsham: a property can be on a private well and public sewer at the same time. The authority’s rate schedule carries dedicated line items for metered and unmetered private wells under sewer customers. Verify the water source and the wastewater disposal for the parcel, never for the ZIP.
What this does to an appraisal and to underwriting
The appraisal report names the water source, so a private well in this area is going to be on the record. What the lender then asks for depends on the loan program, and that is a question worth answering before the appraisal is ordered instead of three weeks later. The lender who calls you back can tell you what the program requires on a well and on documented treatment.
The seller’s side of it is prescribed by regulation. Pennsylvania’s Seller’s Property Disclosure Statement sits at 49 Pa. Code § 35.335a. Section 8 asks for the drinking water source, and for anything other than public water it asks when the water was last tested and what the result was, whether the pump works, and whether there is a softener, filter or other purification system — and whether that system is owned or leased. Section 14 asks whether the seller is aware of underground tanks or hazardous substances and whether the property has ever been tested.
Say the limit of that out loud, because it matters here: the form asks what the seller knows. A seller who never tested a well has nothing to report, and Pennsylvania does not require a private well to be tested before a sale.
Which is why the paperwork trail is the thing to chase. With over 460 wells in this area already connected to municipal water at Navy expense and 120 more connected for exceeding three times the limits, the answer for a specific parcel may already exist. Ask whether the well was sampled in the EPA, Navy and Air National Guard program, what the result was, whether the property was connected to public water or given a treatment system, and who maintains it now.
What to do next
Find out first whether the address is on public water or a well, and which authority serves it, because that single fact reorders every other question. Then call and say the township and the water source, and one licensed Pennsylvania mortgage lender calls you back — usually the same working day, and by the end of the next working day at the outside. Or put the address and what you know about the well in the form and send it along. This is a question with public documents behind it, and finding them beats guessing.