Analysis
PFAS in private wells: what testing near known sources and routine testing each found
By Nick, Well Water Nerd. Published September 29, 2026, figures computed from data refreshed September 22, 2026.
PFAS results for private wells come from two very different kinds of testing, and mixing them up is how the headlines go wrong. Investigations sample the wells around a known source of contamination, and they find wells over the limit far more often. Routine programs test ordinary wells, and most of those come back under it. In New Jersey, which tests every private well at the sale of a home, 10% of 20,186 wells had PFOA above the EPA limit of 4 ng/L. In New Hampshire's sampling around known sources, 61% of 6,090 samples did.
Routine testing of ordinary wells
| Program | Wells | PFOA above 4 ng/L | Years |
|---|---|---|---|
| New Jersey, every private well at a home sale | 20,186 | 10% | 2002 to 2024 |
| Massachusetts, free program for towns and wells near suspected sources | 1,793 | 19% | 2020 to 2023 |
Massachusetts runs higher than New Jersey because its free program was offered to towns without public water and to wells near suspected sources, so it sits between the two kinds of testing.
Testing around known sources
| Investigation | Samples | Wells | PFOA above 4 ng/L | Highest |
|---|---|---|---|---|
| New Hampshire, NHDES sampling near known and suspected sources | 6,090 | 3,387 | 61% | 200 ng/L |
| Washington County, Ohio, around the Chemours Washington Works plant | 444 | 341 | 67% | 22,100 ng/L |
| Maine, DEP investigation of sludge-spread farmland and other sites | 3,567 | 3,567 | 19% | 7,590 ng/L |
| Kent County, Michigan, the North Kent study area around tannery waste sites | n/a | 1,595 | 26% | 16,000 ng/L |
These are the numbers to believe if a well sits near an airport, a military base, a landfill, a plant that made or used PFAS, or farmland where treated sludge was spread. They are not the numbers for a well chosen at random.
Even routine testing varies by county
Within New Jersey's program, the share of wells above the limit ranges from 1% in Monmouth County to 44% in Bergen County, among counties with at least 300 wells tested.
| County | Wells | PFOA above 4 ng/L |
|---|---|---|
| Bergen | 530 | 44% |
| Passaic | 931 | 31% |
| Sussex | 2,246 | 16% |
| Morris | 1,851 | 14% |
| Somerset | 911 | 14% |
| Cape May | 696 | 11% |
| Mercer | 302 | 11% |
| Salem | 951 | 6% |
| Burlington | 2,050 | 6% |
| Gloucester | 1,648 | 4% |
| Cumberland | 1,674 | 4% |
| Camden | 601 | 4% |
| Ocean | 751 | 4% |
| Hunterdon | 1,905 | 3% |
| Atlantic | 1,227 | 3% |
| Warren | 1,080 | 3% |
| Monmouth | 677 | 1% |
What it means for one well
For an ordinary well, the routine programs suggest roughly one in ten or better will test above the limit, more in some counties. For a well near a known source, the odds run several times higher. PFAS has no taste or smell and is not part of most standard lab panels, so it has to be ordered by name. Many states test wells near known sources for free; the state testing pages list them: well water testing by state. Where results come back high, reverse osmosis at the kitchen tap or whole-house carbon treatment brings PFOA and PFOS down.
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Method and sources
All shares are for PFOA against the EPA limit of 4 ng/L, finalized in 2024. Routine figures are the published summaries of the programs named. Investigation figures are every PFOA sample in the state or county from the programs named plus the USGS Water Quality Portal, with non-detects counted as samples; Michigan's North Kent figure is one highest reading per well. Samples taken after a treatment system are excluded where the source marks them.
New Jersey's program is the closest thing in the country to a random sample of private wells, because state law requires a test at the sale of any home with a well. Even it is not random: it covers homes that sold, in the years PFOA was on the test list.
The figures on this page are computed from the same records as the county and town pages, at the time the page is served. Download the data by state, or read how the site builds its numbers. Free to cite with a link.