How did PFAS from the Willow Grove and Warminster bases reach local drinking water?
Health agencies name firefighting foam from two former Navy bases in Pennsylvania as the likely source of here. The chemicals reached public and private wells in Horsham and Warrington and in Warminster. From 2014, local utilities began shutting down affected wells or treating the water.
Jump to: the bases · results before 2018 · results since 2021 · water systems · health findings · what to bring to a lawyer
health consultation for the Willow Grove base, March 2020
Before 2014, drinking the water near the base may have raised the risk of harmful health effects. Some people on private wells had some of the highest exposures off the base.
Which bases does this page cover?
The lists its off-base test results under three names in this area. Its data names the branch and type of each base:
| Base | Branch | Name in the Department's data |
|---|---|---|
| Former Naval Air Station Joint Reserve Base Willow Grove | Navy, listed as | Willow Grove NASJRB |
| Biddle Air National Guard Base | Air Force, Air National Guard | Biddle ANGB (formerly Horsham/Willow Grove ANG) |
| Former Naval Air Warfare Center Warminster | Navy, listed as BRAC | Warminster NAWC AD |
The Warminster center covered 824 acres. From 1944 to 1996 it was used for aircraft research and testing. It has been on the since 1989. It was listed for other chemicals, not for PFAS.
Why do the three bases share one page?
The Navy tests off-base wells near both of its former bases. A 2022 Navy report cites one sampling plan from October 2020 for both sites. The Department's data fits that. In our download, 44 laboratory report numbers appear for both Navy bases. 29 match exactly. For 15, the two numbers differ only by a final letter. Similar numbers alone do not prove the same report. Together with the shared plan, they point to one program. The Air National Guard's results come from other laboratories.
This page cannot tell you which base affected a specific home. The records do not say, and neither do we. The Department assigns each sample to a base. We keep that assignment as it is.
Why is firefighting foam named as the source?
Firefighting foam of this kind is called . ATSDR reviewed the Willow Grove base in 2020. It assumed that the PFAS came from this foam. A fire training area on the base was used from 1942 to 1976. ATSDR names it as the likely source for the wells of the Horsham water authority.
The Navy lists the areas it is cleaning up. They include hangars with foam tanks, the fire station, the fire training area, a landfill and aircraft parking areas. From 2014 to 2019, the Navy sampled 38 on the base. PFAS were found in every sample. Levels were highest near the hangars and the fire training area.
For Warminster, ATSDR reports that the foam was used in training for decades.
"Assumed" and "likely" are the agencies' own words. We do not state the source more firmly than they do.
What happened, and what has been done since?
Foam use and contamination found Steps that ended or treated it
- 1942–1976The fire training area on the Willow Grove base was in use. ATSDR
- 1944–1996The Warminster center was in operation. Foam was used in training. ATSDR
- 2011PFAS were found in groundwater on the Willow Grove base. The base emptied its foam tanks. ATSDR
- 2013In summer, PFAS were found in groundwater on the Warminster base. In November, Warminster well 26 had 791 of . ATSDR
- 2014Federal testing under found PFAS in public wells off the base. ATSDR
- 2014Warminster shut wells 13 and 26 in June and well 10 in September. ATSDR Warrington shut wells 1, 2 and 6 in October. The drinking water wells on the Willow Grove base stopped being used for drinking in September. ATSDR
- 2016Warrington shut wells 3 and 9 after the EPA's new advisory in May. ATSDR
- 2020In March, a pilot plant began treating groundwater at Hangar 680 on the base. Navy
- 2022In January, a second pilot plant began at the fire training area. Both plants treat groundwater on the base, not drinking water. Navy
- 2023In September, Warrington wells 3, 5, 8, 9 and 11 were cleared for use again. Treatment had been built first. Warrington water report
- 2024The Horsham authority reports permanent PFAS treatment at several wells. Horsham water report The Navy reports it has paid the authority more than $25 million. Navy In September, the Department set an action level for private wells. Department of War memo
- 2026On September 9, the Navy broke ground on a system to remove PFAS from the groundwater at the former base. It is designed for more than 400 gallons a minute. The Navy expects it to run in 2027. Navy
Some entries name a month, others only a year. That is how precisely the records state it. The Navy also reports removing more than 4,400 tons of soil from the base.
What was measured before the wells were treated?
The highest results come from 2013 to 2017. Wells were then shut down, treated or replaced. The reports from that time count wells, so this section does too. Results in ng/L:
| Where | When | Highest PFOS | Highest | Source |
|---|---|---|---|---|
| Private wells near Willow Grove (640 wells) | 2014 to April 2017 | 5,200 | 5,000 | ATSDR 2020 |
| Drinking water wells on the Willow Grove base | 2014–2015 | above 10,000 | 8,100 | ATSDR 2020 |
| Horsham authority, well 40 | 2014 | 1,000 | — | ATSDR 2020 |
| Warrington, well 2, untreated | October 2014 | 1,600 | — | ATSDR 2020 |
| Warminster authority, well 26 | Summer 2014 | 1,090 | 349 | ATSDR 2016 |
| Private home wells near Warminster (94 wells) | July–Nov 2014 | 729 | — | ATSDR 2016 |
A dash means we do not show a value for that chemical in this row. For the base wells, the 2020 report gives two different highest PFOS values. Both are above 10,000 ng/L. One well near Willow Grove held 8,100 ng/L of PFOS and PFOA combined.
How many wells were above the values used at the time?
Near Willow Grove, about half of the 640 wells were above ATSDR's PFOS comparison value for children. About a quarter were above the 's 2016 . The report gives two slightly different counts for that, so we round.
Near Warminster, 118 samples were taken from 100 private wells in 2014. 94 of them served homes. ATSDR counted 11 home wells above the EPA's provisional PFOS advisory in use in 2014, 200 ng/L. Under the rounding rule used then, that included results from 152 ng/L up. Of the other six wells, one industrial well had 1,510 ng/L.
These comparison values are dated. Today's limits are far lower; see how today's limits compare.
The Department of War's data in the next section starts in 2021. It does not show these earlier peaks.
What has the Department of War measured off base since 2021?
The Department publishes its test results for off-base drinking water. For these three bases, it lists 803 samples without a treatment system. They run from August 2021 to September 2025. The Navy describes its program as sampling private drinking water wells, at an outside tap. We do not know whether every sample in the data comes from a private well.
Highest results, in ng/L. " estimate" is a value the laboratory flagged as estimated:
| Chemical | Willow Grove | J estimate | Biddle | J estimate | Warminster | J estimate |
|---|---|---|---|---|---|---|
| PFOS | 864 | 36.2 | 26.0 | 17.8 | 93.5 | 42.1 |
| PFOA | 27.8 | 34.5 | 17.1 | 14.8 | 91.7 | 21.0 |
| 470 | 24.3 | 10.5 | 8.9 | 27.5 | 22.3 | |
| 51.2 | 4.51 | 2.0 | 2.6 | 21.6 | 3.69 | |
| Samples | 220 | 48 | 535 | |||
| Period | Aug 2021 – Sept 2024 | Jan 2022 – Nov 2024 | Aug 2021 – Sept 2025 |
The first column per base is the highest result without a laboratory qualifier. Twice, an estimate is higher than that: PFOA at Willow Grove and PFNA at Biddle. That is why estimates get their own columns. PFOS was found in 189 of 220 samples at Willow Grove. At Biddle it was 45 of 48, at Warminster 531 of 535. One Warminster sample listed with a treatment system is left out.
These are samples, not wells. The data carries no address and no well number. The same well can appear many times, and we cannot tell which samples belong together. We also show no trend. The data cannot follow the same well from year to year.
Why does one Willow Grove result stand out?
Sample F4983-FS from October 29, 2021 had 864 ng/L of PFOS and 470 ng/L of PFHxS. The next highest PFOS result at Willow Grove is 51.1 ng/L, from October 2023. For these two chemicals, the sample's detection limit is far higher than usual, about 27 ng/L. We assume the sample was diluted and measured again, a normal step for high values. The export has no laboratory note that confirms this. We show it as a real result, but a single one.
Why are some chemicals left out before April 2022?
For the two Navy bases, the data labels results up to April 1, 2022 as . From April 20, 2022, it says Method 537.1. Method 537.1 lists 18 chemicals. One of them is . Four of them were added with Method 537.1. Yet the data lists all 18 for the earlier samples too, as not detected.
A 2022 Navy report says that in 2019, Method 537 covered six chemicals in this program. We cannot resolve this from the data. So for the four newer chemicals, we use only results from April 20, 2022 on. PFOS, PFOA, PFHxS and PFNA are covered by both methods.
At Biddle, 12 samples from 2022 were tested for six chemicals only. The data lists a detection limit of about 4 ng/L for PFOS and PFOA there. Two lower values were still reported. So "not detected" there does not mean zero.
What else did the tests find?
HFPO-DA was found twice at Willow Grove, both times as an estimate. The higher value was 0.40 ng/L. It was not found at the other two bases. Three Warminster samples from October 2024 contained . Two results had no qualifier, 7.05 and 3.86 ng/L. The third was an estimate of 0.737 ng/L. The data does not say where it came from.
How we got these numbers. We downloaded the full result files from the Department of War's off-base testing tool on September 29, 2026. We used Advanced Search: State = Pennsylvania, one query per base name as listed above, all analytes, no date filter. The tool gives no permanent link to a result set. To check our figures, download our copies of the three files or run the same queries. What we changed in the files and how we count is on its own page.
Each laboratory sample ID counts as one sample. No sample lists the same chemical twice. Some pairs of samples are nearly identical and may be field duplicates. For highest values, that makes no difference. Samples listed with a treatment system are left out. The data does not call the other samples untreated, so neither do we.
How do these results compare with today's limits?
Pennsylvania set its own PFAS limits for public water systems in January 2023. They are 14 ng/L for PFOA and 18 ng/L for PFOS. A system meets them on a running annual average, measured where water enters the system. A single result from a private well does not break these limits in the legal sense. So we say such a result is above the value Pennsylvania set for public systems.
Federal limits and the Department of War's action level for private wells may change. We keep them on one page: How do PFAS results compare with the limits? None of these values decides whether someone has a legal claim. What the lawsuits ask for is a separate question.
How many samples reached the action level for a single chemical?
We counted samples in which at least one chemical reached its own action level, as set in September 2024. Without estimates: 101 of 220 at Willow Grove, 26 of 48 at Biddle, and 364 of 535 at Warminster. Including estimates: 110, 29 and 380. Almost all of these samples reached the level through PFOA or PFOS.
Read these numbers with care. They count samples, not homes. Some wells were sampled many times. From 2017 to 2020, wells with higher results were retested more often. The sampled homes lie near the bases. They are not a random selection.
We used the values the Department of War lists for its September 2024 policy. For PFOA or PFOS, that is 12 ng/L. For PFHxS, PFNA or HFPO-DA, it is 30 ng/L, each on its own. The action level also includes a for mixtures. Our counts leave it out. A rough check with the reported values added no further samples.
Which public water systems serve the area?
Your provider's name was on your bill. Each public system also has a . The table shows what each system's latest report says:
| System | PWSID | What its annual report says |
|---|---|---|
| Horsham Water and Sewer Authority | PA1460033 | 15 wells, plus connections to North Wales Water Authority and Aqua. Ten wells and the Aqua connection have PFAS treatment. In 2025, treated water from well 19 had up to 3.6 ng/L PFOA. All other treated results for PFOA and PFOS were not detected. Untreated water from well 26 had up to 630 ng/L PFOS. |
| Warminster Municipal Authority | PA1090069 | In 2025, it bought 87 % of its water from North Wales Water Authority. PFOA and PFOS were not detected in water from its own wells. At the connections to North Wales, PFOA was 2.58 ng/L and PFOS 1.22 ng/L, a J estimate. |
| Warrington Township service area, run by North Wales Water Authority | PA1090070 | In 2025, Forest Park water had PFOA from not detected to 2.8 ng/L. The highest running annual average was 1.9. The report lists PFOA for Forest Park water and names PFOS among substances not detected there. It gives no PFOA or PFOS results for the Warrington wells. |
| North Wales Water Authority | PA1460048 | Supplies most of the water for Warminster and Warrington. About 4 % of its water came from its own wells in 2025. There, PFOA reached 14.7 ng/L in one result, with a highest running annual average of 12.6. That is below Pennsylvania's 14. PFOS reached 12.2, with a highest annual average of 10.5. The wells lie across its whole service area. |
| Aqua Pennsylvania Main System | PA1460073 | Connected to the Horsham system. Aqua's own report for 2025 is printed in Horsham's report. Across the whole Aqua Main System, PFOA reached 13 ng/L and PFOS 7.9 ng/L. That is not the water at the Horsham connection, which has its own PFAS treatment. |
| Private wells | — | No utility, so no PWSID and no annual report. A test result for the well helps, if one exists. See what to bring to a lawyer. |
The Warminster and Warrington reports print their numbers without the letters PA, as 1090069 and 1090070. All reports in the table cover 2025. Utilities publish a new report every year.
What does this mean for today's water?
For public systems, the utility's annual report is the current record. For private wells, the Department of War starts interim action at or above its action level. That applies where it is the known source. For a well that was never part of the program, a test is the only way to know.
Two questions are separate here. What came out of the tap in the years someone lived there? And what does the water contain today? The reports above answer the second one only for public systems. For a private well that was never tested, neither has an answer yet.
What did health agencies conclude for this area?
Willow Grove, 2020. ATSDR reached six conclusions. In short:
- Before 2014, drinking the water may have raised the risk of harmful health effects.
- The cancer risk from PFOA alone was low to very low. For mixtures of PFAS, it is uncertain.
- Some people on private wells had some of the highest exposures off the base.
- For the water supplies ATSDR reviewed, harm is not expected after treatment or replacement.
- People whose private wells were never tested may still be at risk.
- People on the base were exposed in the past through its drinking water wells.
- Fish from nearby waters may carry PFAS, but were not sampled.
- For breastfeeding, the benefits outweigh the risks.
Warminster, 2016. ATSDR looked at the highest PFOS results in private and public wells. It called past exposure to those levels a public health hazard. ATSDR says it based this on the maximum values, a cautious approach. It did not estimate a cancer risk.
Were people's blood levels tested?
Yes. A Pennsylvania Department of Health pilot tested 235 people. PFOS was found in all of them. A larger federal study followed. In Pennsylvania, it reports PFAS results for 1,253 adults and 89 children. The study spans several states. Across all sites, adults had higher PFOA and PFHxS levels on average than the general US population. Children had higher PFHxS on average.
What about showering and cancer ratings?
Drinking and cooking are the routes that matter most. The EPA says showering and washing are unlikely to add much to your risk. The has rated both chemicals. It classifies PFOA as carcinogenic to humans and PFOS as possibly carcinogenic. The wider research, and where it is unsettled, is on one page: What does PFAS exposure do to health?
Three things are easy to mix up. A cancer rating says whether a chemical can cause cancer at all. A study link says how often an illness occurs in exposed groups. Neither says what caused one person's illness. Having been exposed does not mean a person will become ill.
How do the AFFF lawsuits apply here?
The AFFF cases are grouped before one federal judge as 2873. Handling the foam at work and drinking contaminated water are separate exposure routes. Near these bases, both can apply. The bases trained with the foam, and it reached public and private wells. People who served at Willow Grove may also have drunk its well water until 2014; see the timeline.
Which conditions the lawsuits cover, and which are under review, is kept on one page: What are the AFFF lawsuits? What the work route asks for is explained under What if you handled the foam at work?
What else do people ask?
Can I find out which base affected my home?
Not from these records. The results carry no address. The two Navy bases share one sampling program. We keep the Department's assignment and add nothing to it.
Why are the 2014 numbers so much higher than the Department's data?
They come from before most wells were shut down or treated. The Department's published data starts in 2021. The two sets also come from different wells and programs. So they cannot be compared directly.
Does "not detected" mean my well had no PFAS?
No. It means the amount was below what the test could report. That limit differs between tests. At Biddle in 2022, the listed limit was about 4 ng/L.
My water tested fine — does that rule me out?
Not by itself. A clean result today cannot rule out contamination in earlier years. That is especially true after a switch of water source or new treatment.
What if I served at a base but lived off it?
Both routes can apply. They are assessed separately. What the work route asks for is explained under handling the foam at work.
Does this page sign me up for anything?
No. There is no form here.
What should you bring to a lawyer?
A lawyer will ask for records that show your history. For the drinking water route, that includes the water system at each address. The table above names the public systems and PWSIDs for this area.
On a private well, there is no PWSID. A test result for the well helps, if you have one. Without one, a lawyer can say which other records may show the contamination. The Navy's published reports do not name addresses, so a well owner cannot look up a result there. If the Navy or the Air National Guard sent you a result, keep your copy.
The full list of what the court asks for, by route, is kept on one page. It also covers medical records, finding a lawyer and fees: What should you bring to a lawyer?
Where does this page's information come from?
- ATSDR — Letter Health Consultation, Willow Grove Naval Air and Air Reserve Station, March 13, 2020 (PDF)
Conclusions on pp. 2–7. Source and site history on pp. 15–18. Horsham wells on p. 27, Warrington wells on p. 35. Private wells on p. 40 (Table A-6), base wells on pp. 41–42 (Table A-7). The count above the 2016 advisory is 166 on p. 5 and 164 on p. 40. Page numbers as printed in the report. - Department of War (then Defense) — Memorandum on implementing the EPA limits, September 3, 2024 (PDF)
The action level for private wells where the Department is the known source. - Department of War — PFAS Task Force
Lists the action level values for each chemical. - ATSDR — Letter Health Consultation, Naval Air Warfare Center Warminster, January 20, 2016 (PDF)
History of the center, well shutdowns in 2014, and the public health finding. Private well results from 2014 on p. 8. - Navy — Restoration Advisory Board poster, Willow Grove, November 2024 (PDF)
Source areas, groundwater investigation, pilot plants and soil removal. Also payments to the Horsham authority, off-base well sampling. - Navy — Groundbreaking for the PFAS groundwater treatment system, September 2026
Start of construction on September 9, 2026, design capacity and the expected start of operation. - Navy — Final 2017 to 2020 Summary Report for Private Well Sampling, Naval Air Warfare Center Warminster, March 2022 (PDF)
Sampling rules and laboratory methods before 2021. Cites the shared 2020 sampling plan for both Navy bases. Sample locations are anonymized. - Department of War — Off-Base Drinking Water PFAS Testing Results
The measurement data for all three bases. Query results have no permanent link, so the full query is stated on this page. Retrieved September 29, 2026. Our copies of the files can be downloaded. - Horsham Water and Sewer Authority — 2024 Consumer Confidence Report (PDF)
PWSIDs of Horsham, North Wales and Aqua. Treatment at the wells, as of 2024. - Horsham Water and Sewer Authority — 2025 Water Quality Report (PDF)
Treated and untreated well results for 2025. Also includes Aqua's 2025 report for its Main System. - Warminster Municipal Authority — 2025 Annual Drinking Water Quality Report (PDF)
PWSID, share of purchased water, PFOA and PFOS from its own wells and the North Wales connections. - North Wales Water Authority — Warrington Township, 2025 Drinking Water Quality Report (PDF)
PFOA from Forest Park water, with running annual average. - North Wales Water Authority — Main System, 2025 Drinking Water Quality Report (PDF)
Share of well water, PFOA and PFOS from its own wells. We did not use its table of federal monitoring results. It lists some averages above their own maximum. - North Wales Water Authority — Warrington Township service area, 2023 Water Quality Report (PDF)
Wells returned to service in September 2023. - Pennsylvania Bulletin, Vol. 53, No. 2, January 14, 2023 — PFAS limits (PDF)
The Pennsylvania limits for PFOA and PFOS. - Pennsylvania Department of Environmental Protection — PFAS drinking water limits
How public systems must show they meet the limits. - EPA — Method 537.1, Version 2.0, March 2020 (PDF)
The 18 chemicals the method measures (Section 1.1). - EPA presentation on PFAS methods, hosted by the New Jersey Department of Environmental Protection, May 2020 (PDF)
The four chemicals added with Method 537.1. - ATSDR — PFAS Multi-site Study
The federal blood study that includes this area. - RTI International — Pennsylvania PFAS Multi-site Health Study
Participant numbers for the Pennsylvania site. - Multi-site Study results, Environment International (2025)
Peer-reviewed blood results across all study sites. - EPA — Steps you can take to reduce your risk
Showering and washing. - IARC — Monographs Volume 135: PFOA and PFOS
Cancer classification of PFOA and PFOS. - US District Court, District of South Carolina — MDL 2873
The court's page for the AFFF lawsuits. Conditions, exposure routes and proof requirements are set out on the PFAS topic page.
We link a source at the point each claim is made. One set of figures has no permanent link at its source: the Department of War's data. So we state the full query and publish our copy of the data. If a link is broken or a source has been superseded, tell us.
Found an error, or have a question?
Found an error? Have a question about something we published? Have a suggestion for a topic, the design, or anything else? Email feedback@tetonintake.com — we read everything. Corrections get priority: if something on this site is wrong, we want it fixed. One limit: we can't advise on individual cases — that's what lawyers, doctors, and other experts are for.