PFAS in Well Water: Testing, Limits & Removal

What PFAS Is, and How It Gets Into a Well

PFAS is a family of more than 14,000 human-made chemicals built around a carbon-fluorine bond so strong that nothing in nature breaks it down. That is why they are called forever chemicals - and why, unlike arsenic or radon, they never come out of the ground on their own.

This is the single most important thing for a well owner to understand: PFAS is not a geological contaminant. Arsenic, radon, uranium, and iron all leach naturally from certain bedrock. PFAS does not. If a lab finds PFAS in your well - even a deep, drilled well in a rural area - it got there because human contamination on the surface migrated down into your aquifer. There is always a source, and it is always man-made.

Practically all PFAS in groundwater traces back to four kinds of surface sources:

• AFFF firefighting foam: aqueous film-forming foams used since the 1960s at military bases, civilian airports, and fire-training centers are a leading cause of large groundwater plumes.
• Industrial manufacturing sites: plants that made or used PFAS for nonstick coatings, waterproof textiles, food packaging, and semiconductors discharged it into air and wastewater that settled into local soil and groundwater.
• Landfills and leachate: PFAS-laden consumer goods end up as trash; rainwater filtering through creates leachate that escapes failing or unlined liners into the aquifer below.
• Wastewater and biosolids: treatment plants cannot break PFAS down, so treated effluent and the sludge (biosolids) sold as farm fertilizer carry it right back into the water table.

Shallow dug and driven wells are the most exposed to recent surface contamination, but even a deep drilled well can be compromised - through a cracked casing, a poorly sealed annulus, or a well screen that intersects a contaminated fracture. PFAS is also a close cousin in behavior to other man-made well contaminants like VOCs (volatile organic compounds), which arrive through the same kinds of industrial and landfill pathways.

Where the Risk Is Highest

In October 2024 the USGS published the first national map of PFAS in untreated groundwater. The headline is sobering: an estimated 71 to 95 million people - more than a fifth of the U.S. population - draw water from aquifers with detectable PFAS before any treatment.

The USGS model analyzed 1,238 groundwater samples for 24 PFAS compounds and predicted contamination from factors like urban land use, well depth, soil clay content, septic nitrogen loading, and distance to known sources such as airports and fire-training areas. Urban land use turned out to be the single strongest predictor - which is exactly why "rural and deep" does not guarantee "safe."

Michigan shows both ends of the spectrum. At one rural Belmont property, a private well hit a catastrophic 24,000 ppt from 1970s tannery waste - proof that rural does not mean safe. Elsewhere, in Cadillac, the state found pervasive low-level PFAS across many private wells but could not pin down the industrial source, leaving it an "orphan" site where the cleanup burden falls entirely on individual homeowners. The state has spent roughly $125 million identifying more than 266 active contamination sites.

The most useful next step is to check your own neighborhood. The USGS publishes an interactive PFAS probability map down to a 1x1 kilometer grid, and you can see how deep neighboring wells run - a strong hint at how exposed your aquifer is to the surface - on the DrillerDB well map.

Health Effects and the EPA Limit (and Why It Is in Flux)

PFAS bioaccumulates - it builds up in the body and clears extremely slowly. Long-term exposure is linked to kidney and testicular cancer, thyroid disease, high cholesterol, a weakened immune response, and reproductive and developmental harm.

Because PFAS causes harm at almost unimaginably low concentrations, the limits are tiny. One part per trillion is roughly one drop of water in 20 Olympic swimming pools - and the federal drinking-water limit for PFOA and PFOS is just four of those drops.

In April 2024 the EPA finalized the nation's first legally enforceable drinking-water standards for six PFAS compounds:

• PFOA: 4.0 parts per trillion (ppt)
• PFOS: 4.0 ppt
• PFHxS, PFNA, and HFPO-DA (GenX): 10.0 ppt each
• Mixtures: a "Hazard Index" of 1.0 (a combined-risk calculation)

The original rule gave public water systems until April 2029 to comply. It immediately drew lawsuits from water utilities and industry groups (American Water Works Association v. EPA, D.C. Circuit), who argued the EPA skipped required cost-benefit steps and that the rule would cost utilities far more than the EPA's $1.5 billion estimate.

Where things stand in 2026: after a change in administration, the EPA moved to reconsider the rule. On May 18, 2026 it published two proposed rules - one to rescind the limits for PFHxS, PFNA, GenX, and the Hazard Index, and another to keep the 4.0 ppt limit for PFOA and PFOS but push the utility compliance deadline from 2029 to April 2031. The public comment period ran through July 20, 2026, and the D.C. Circuit case remains pending.

How to Test for PFAS

PFAS is tasteless, odorless, and invisible, so a certified laboratory test is the only way to know. There is no legitimate at-home kit - the chemistry simply cannot be done on a countertop.

Detecting parts per trillion requires liquid chromatography-tandem mass spectrometry (LC-MS/MS), available only at accredited environmental labs. Any product advertising an instant PFAS dipstick is fraudulent. You order a kit, collect carefully (PFAS is in so many household items that cross-contamination is the biggest risk), and ship it back.

Pick the right method: 537.1, not 1633

Two EPA methods come up when you call a lab. For a private well, you want 537.1.

Schedule: test a baseline now; if negative, retest every 3 to 5 years or immediately after a known spill, landfill failure, or new firefighting/military activity nearby. If you install treatment, test the treated water annually to catch filter breakthrough.

Reading Your Results

Lab reports use units that confuse a lot of homeowners. The short version: ng/L and ppt are the same thing, and you compare PFOA and PFOS against 4.0.

• Units: labs report PFAS in nanograms per liter (ng/L) or parts per trillion (ppt). They are identical - 1 ng/L = 1 ppt.
• Action level:compare your PFOA and PFOS numbers to the EPA's 4.0 ppt standard. A PFOA result of 5.0 ng/L exceeds the health threshold; switch to an alternate water source and plan long-term treatment.
• Mixtures: if your report lists several compounds, the 2024 rule also used a combined Hazard Index - but for a homeowner the simplest, most protective read is that any PFOA or PFOS at or above 4.0 ppt means act.

If Your Test Comes Back High: Do This Now

A result over 4.0 ppt calls for immediate, calm action. The single most important rule: do not try to fix it by boiling.

Treatment Options Compared

First, the bad news: softeners, UV, aeration, and standard iron filters do nothing to PFAS - the carbon-fluorine bond is unbreakable by oxidation. Only three technologies work, and which one you need depends on how high your numbers are.

The three proven residential methods are reverse osmosis (RO), granular activated carbon (GAC), and ion exchange (IX). They differ in how they capture PFAS and in which concentration range they handle best.

Match the system to your number. Under 50 ppt, an under-sink RO unit or a single GAC tank is plenty. From 50-200 ppt, a point-of-entry ion-exchange system (often with a GAC polishing filter behind it in a "lead-lag" design) is the recommended whole-house setup. Above 200 ppt, RO is the strictly advised method, and whole-house protection means redundant IX + GAC with monthly monitoring. The reason whole-house PFAS systems are so large and expensive is contact time: PFAS needs about 10 minutes of empty bed contact time, versus 2 minutes for chlorine, so the media tanks have to be big.

Prevention and Well Construction

Filtration treats a contaminated aquifer; good well construction keeps surface PFAS - from a nearby spill, septic field, or biosolids application - from getting in to begin with.

Keep high-risk activities at least 100 feet from the wellhead: chemical and fuel storage, fertilizer or biosolids application, equipment repair, and septic leach fields. Then make sure the well itself is sound. Casing must extend deep enough to seal off shallow, contaminated layers; the sanitary cap must be watertight with a downward-facing screened vent; and the pitless adapter (below the frost line) must keep shallow soil moisture out of the supply line. A cracked casing or a poorly sealed annulus lets surface PFAS run straight down the outside of the pipe and ruin an otherwise pristine deep aquifer - casing and cap work belongs to a licensed well contractor. For the full mechanical picture, see our well maintenance guide and well components guide.

Money to Help Pay: State Programs and Settlements

PFAS testing and treatment are expensive, but you may not be on the hook for all of it. Several states run direct rebate programs, and multi-billion-dollar settlements are expanding public water into formerly rural areas.

On top of state programs, major manufacturers have settled enormous national lawsuits - 3M for roughly $10.3-$12.5 billion and DuPont/Chemours/Corteva for about $1.185 billion - primarily to help public water systems. These funds mostly help municipalsystems, but they expand public water lines into formerly rural areas, which lets more well owners on the urban fringe qualify for state connection rebates. Localized settlements can reach individuals directly: the $17.5 million Tyco settlement in Marinette/Peshtigo, Wisconsin, requires the responsible party to provide deep drinking water and ongoing water service to affected residents for 20 years.

Keep reading

• Well Water Testing: labs, sampling, and what each panel costs
• VOCs in Well Water: the other man-made contaminant from industry and landfills
• Nitrates in Well Water: the contaminant boiling makes worse, too
• Well Water Upkeep: the year-round testing and treatment routine
• State-by-state well rules and testing programs