Ground Zero
Willow Grove Naval Air Station / Joint Reserve Base — Horsham Township, Montgomery County, Pennsylvania. The fire training area where it started. The aquifer it entered. The wells it reached. The community that still lives in its plume.
13,700
ppt PFOS — on-base wells
EPA advisory: 70 ppt
5,200
ppt — peak private well
74× the advisory level
46,000
Public water users exposed
Horsham & Warrington Twp
2014
First PFAS detection
35 years after 3M's warning
What Happened Here
The Base
Naval Air Station Joint Reserve Base Willow Grove (NASJRB) operated in Horsham Township, Montgomery County, Pennsylvania for decades. It served as both an active reserve base and a training facility. AFFF — aqueous film-forming foam — was used extensively in fire training exercises from the 1970s onward. Site 5, the Fire Training Area, became the primary contamination source.
In 1995, the base was added to the EPA National Priorities List under Superfund for groundwater contamination — at that time, from volatile organic compounds (VOCs). PFAS was not part of the Superfund investigation. It was not in the regulatory vocabulary for military site reviews at that time.
The Numbers
When PFAS was finally tested in 2011 as part of a five-year review, PFOS and PFOA were identified as a concern. Full testing of off-base public water supplies began in 2014. What they found:
- → On-base supply wells: PFOS up to 13,700 ppt (EPA advisory: 70 ppt)
- → Private wells near base: PFOS/PFOA up to 5,200 ppt
- → Warrington Township public wells: 3 of 8 wells above EPA advisory — removed from service Oct 2014
- → Horsham tap water: PFOS exceeded ATSDR child exposure limits in 24% of samples
ATSDR Health Consultation — Updated (2020)
"Based on the available limited sampling information, there was a past exposure pathway to PFAS in drinking water for civilian employees, service members, and their families on-base. The maximum levels of PFAS detected in on-base drinking water supply wells (not delivered water at the tap) exceeded ATSDR's EMEGs for PFOS and PFOA for adults and children."
EMEG = Emergency Minimum Exposure Guideline — the threshold at which exposure is considered a public health concern requiring immediate action.
The Site Timeline
3M's AFFF used in fire training at Site 5 (Fire Training Area) and for fire suppression. PFAS compounds soak into soil and begin migrating toward the water table beneath Horsham and Warrington Townships.
NASJRB added to EPA's National Priorities List for groundwater contamination — but from volatile organic compounds. PFAS not part of the investigation framework.
ATSDR conducts two site evaluations. Reviews drinking water, soil, surface water, sediment, fish. Identifies TCE/PCE contamination. Concludes no immediate public health hazards. PFAS is not tested. Not mentioned. Not in the assessment framework.
By this date, 3M had known for 17–21 years that PFOS was toxic. The question was never asked.
ATSDR publishes the Willow Grove Public Health Assessment — the most comprehensive federal health review the base has ever received. Evaluates drinking water, soil, surface water, sediment, and fish tissue. PFAS is not in the document.
The ATSDR's own 2020 update states plainly: "This public health evaluation pre-dated the site monitoring and detection of PFAS."
BRAC 2005 recommends closure. Airfield closes March 31, 2011. Final closure September 15, 2011. Through the entire period from 1996 to closure — 15 years — no PFAS testing conducted on base drinking water or surrounding wells.
2011: limited groundwater sampling during Five-Year Review identifies PFOS/PFOA as a potential concern. October 2014: PFOS and PFOA detected in multiple public water supply wells in the Warrington Township Water Supply District. Three wells removed from service immediately. Private well owners notified and offered bottled water.
The gap from 3M's 1979 internal toxicity finding to the 2014 detection at Willow Grove: 35 years.
Following the EPA's May 2016 Health Advisory release, additional wells taken offline. Horsham Township takes remediation measures — interconnections, purchased water, new filtration. By 2018, system-wide combined PFOS/PFOA averages reduced to ~0.004 µg/L. The Navy and Air National Guard continue site investigation and cleanup under a Federal Facility Agreement. As of 2020, a small number of private well properties still awaited public water connection.
Who Was Exposed
~46,000
Public water users
Horsham and Warrington Township residents served by contaminated public water supply wells. Exposure continued from at least the 1990s until wells were taken offline in 2014–2016.
Hundreds
Private well users
Private drinking water well owners in the area — many of whom were not identified until after initial public well testing in 2014, meaning years of additional undetected exposure.
20,000+
On-base personnel
Active duty reserve, retired personnel, and their family members receiving care and services at the base. A daycare center for 96 children was located on-site. On-base supply wells showed the highest contamination levels detected anywhere at the site.
Primary Source Documents
ATSDR Public Health Assessment — NASJRB Willow Grove (2002)
The comprehensive federal health assessment that pre-dated PFAS detection at the site. The document that proves the institutional blind spot was real.
ATSDR Health Consultation — Former NASJRB Willow Grove (Updated 2020)
The updated health evaluation including PFAS contamination data, exposure pathway conclusions, and the explicit acknowledgment of the pre-2014 data gap.
EPA Superfund Site Profile — Former NASJRB Willow Grove
Current remediation status, site history, and cleanup actions. Ongoing investigation under the Federal Facility Agreement.
Navy BRAC PMO — Former NASJRB Willow Grove
Base history, closure timeline, and current property transfer status.