Well water in Maine
In Maine, 17% of 27,616 private wells tested had arsenic above the Maine guideline (10 ug/L), according to Maine CDC.
31,960 private wells tested in state summaries; 3,567 individual samples from 3,567 wells, 1941 to 2026. Data refreshed September 3, 2026.
Maine DEP samples private wells near fields where sludge or septage was spread and near other known PFAS sources, and resamples detections. PFAS shares describe wells that were tested for a reason, not every well in the area. In that targeted sampling, 19% of 3,567 PFOA results in Maine were above the EPA limit of 4 ng/L. In that targeted sampling, 11% of 3,567 PFOS results in Maine were above the EPA limit of 4 ng/L.
What homeowner tests found
Maine Tracking Network private well summaries: private wells tested and reported to the state. Shares are against the level the state applies to each contaminant, named in the last column; several are stricter than EPA. County and state figures combine the town summaries, weighted by wells tested; medians are not combined.
What individual samples found
Each row summarizes every public sample for that contaminant inside Maine. Above limit means above the EPA maximum contaminant level; where EPA has no enforceable limit, the row shows a health guideline or nuisance level instead.
| Contaminant | Samples | Detected | Above limit | Median | Highest | Limit | |
|---|---|---|---|---|---|---|---|
| Arsenic 1977 to 2023 | 528 | 89% | 56% | 20 | 3,000 | 10 ug/L EPA limit | |
| PFOA 2017 to 2026 | 3,567 | 58% | 19% | 0.396 | 7,590 | 4 ng/L EPA limit | |
| PFOS 2017 to 2026 | 3,567 | 44% | 11% | 0 | 17,200 | 4 ng/L EPA limit | |
| Nitrate 1941 to 2023 | 1,154 | 81% | 10% | 0.51 | 162 | 10 mg/L EPA limit | |
| Uranium 1958 to 2023 | 227 | 82% | 10% | 1.16 | 960 | 30 ug/L EPA limit | |
| PFNA 2017 to 2026 | 3,566 | 16% | 2% | 0 | 1,830 | 10 ng/L EPA limit | |
| Fluoride 1956 to 2019 | 84 | 76% | 1% | 0.1 | 4.9 | 4 mg/L EPA limit | |
| PFHxS 2017 to 2026 | 3,562 | 30% | 1% | 0 | 489 | 10 ng/L EPA limit | |
| Radium (226 + 228) 1958 to 2019 | 112 | 89% | <1% | 0 | 57 | 5 pCi/L EPA limit | |
| Copper 1953 to 2023 | 187 | 67% | 0% | 0 | 0.63 | 1.3 mg/L EPA limit | |
| Lead 1977 to 2023 | 64 | 42% | 0% | 0 | 6.3 | 15 ug/L EPA limit | |
| E. coli 2011 to 2019 | 59 | 0% | 0% | 0 | 0 | 0 MPN/100mL EPA limit | |
| Chloride 1941 to 2023 | 1,169 | 99% | no limit | 9.13 | 2,020 | 250 mg/L nuisance level | |
| Sodium 1958 to 2023 | 89 | 100% | no limit | 6.6 | 814 | 20 mg/L health guideline | |
| Manganese 1956 to 2011 | 88 | 85% | no limit | 45 | 5,200 | 300 ug/L health guideline | |
| Iron 1942 to 2007 | 87 | 89% | no limit | 80 | 110,000 | 300 ug/L nuisance level | |
| Radon 1999 to 2014 | 46 | 100% | no limit | 2,020 | 102,000 | 2,000 pCi/L health guideline |
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What this means
Among homeowners in Maine who sent a sample to the state lab, the health-based limits most often exceeded were arsenic (17% of 27,616 wells), uranium (7% of 23,366 wells), and fluoride (2% of 31,960 wells). These are ordinary wells tested by their owners, so the shares are the best available picture of a typical well here, with one caveat: people test more often when they suspect a problem.
What to test for in Maine
- Volatile organic compounds (VOCs)1,177 leaking underground storage tank sites on record locally.
- PFAS500 unlined landfills on record locally.
- Metals panel570 hazardous waste sites on record locally.
- PFOA19% of 3,567 local samples were above the limit.
- PFOS11% of 3,567 local samples were above the limit.
- Manganese5% of 25,764 local wells tested were above the Maine guideline.
- PFNA2% of 3,566 local samples were above the limit.
- Nitrite<1% of 31,613 local wells tested were above the Maine guideline.
Wells in Maine
90,708 domestic wells in Maine are on record with the state since 1970. 98% are drilled into bedrock, and the typical well is 240 feet deep (one in ten goes past 455 feet).
In a typical Maine well, bedrock starts about 15 feet down, the median yield is 6 gallons per minute, 22% of wells yield under 3 gallons per minute and usually need a storage tank.
Bedrock wells are where arsenic, uranium and radon come from: the water sits in fractures in granite and metamorphic rock and picks up whatever the rock carries. That is why testing for those three matters more here than in a dug or gravel well.
Contamination sources on record in Maine
Maine DEP records 1,177 leaking underground storage tank sites, 500 unlined landfills, and 570 hazardous waste sites in Maine, among 4,871 regulated sites in total. Groundwater does not follow property lines, so a well within a few hundred feet of one of these is worth testing for what that site could release.
- 1,177
- leaking underground storage tank sitesGasoline and heating oil that leaked from tanks move through groundwater as benzene, MTBE and other volatile organic compounds.
- 500
- unlined landfillsOlder unlined landfills are a leading source of PFAS, VOCs and metals in nearby wells.
- 570
- hazardous waste sitesSolvents, degreasers and metals from industrial sites can travel far in fractured bedrock.
- 2,624
- other remediation projects
Treatment that fits the local profile
- Arsenic
- Point-of-use reverse osmosis; Adsorptive media (iron-based) whole-house; Anion exchange
- Uranium
- Point-of-use reverse osmosis; Anion exchange; Whole-house anion exchange
- PFOA
- Granular activated carbon whole-house; Point-of-use reverse osmosis; Anion exchange
- PFOS
- Granular activated carbon whole-house; Point-of-use reverse osmosis; Anion exchange
- Nitrate
- Point-of-use reverse osmosis; Anion exchange; Distillation
Common questions
How deep are wells in Maine?
The typical domestic well in Maine is 240 feet deep, based on 90,708 wells reported to the state since 1970. One in ten is deeper than 455 feet. 98% are drilled into bedrock.
Is there arsenic in well water in Maine?
Arsenic was detected in 89% of 528 public well samples in Maine, and 56% were above the EPA limit of 10 ug/L. Arsenic has no taste or smell; a lab test is the only way to know your level.
How high is radon in well water in Maine?
The median radon level across 46 public samples in Maine was 2,020 pCi/L, with a high of 102,000 pCi/L. New Hampshire recommends treatment above 2,000 pCi/L.
How often should I test a private well in Maine?
Test for bacteria and nitrate every year. Test once for arsenic, uranium, radon, fluoride, manganese and PFAS, then again every three to five years or after any change in taste, color, or plumbing.
Counties in Maine
- Androscoggin15% arsenic
- Aroostook4% nitrate
- Cumberland20% uranium
- Franklin10% arsenic
- Hancock22% arsenic
- Kennebec28% arsenic
- Knox17% arsenic
- Lincoln7% uranium
- Oxford9% uranium
- Penobscot8% arsenic
- Piscataquis12% arsenic
- Sagadahoc5% arsenic
- Somerset18% arsenic
- Waldo9% arsenic
- Washington17% arsenic
- York23% arsenic
Sources
- Maine DEP PFAS investigation: 14,254 samples in Maine. PFAS results for private wells sampled by the Maine Department of Environmental Protection. Retrieved September 3, 2026.
- USGS Water Quality Portal: 3,902 samples in Maine. Data from the Water Quality Portal, a service of USGS, EPA and USDA; groundwater samples collected by USGS and cooperators. Retrieved September 3, 2026.
- Maine Tracking Network private well summaries: summaries for 6 contaminants in Maine, up to 31,960 wells each. Town summaries of private well tests run by the Maine Health and Environmental Testing Laboratory, published by Maine CDC through the Maine Tracking Network. Shares are against Maine's guideline for each analyte (arsenic 10 ug/L, uranium 30 ug/L, fluoride 2 mg/L, manganese 0.3 mg/L, nitrate 10 mg/L, nitrite 1 mg/L). Towns with too few tests are suppressed (NR). Only the share above the guideline and wells tested are published; no medians. Retrieved September 3, 2026.
- Maine Geological Survey well database: 95,597 well records in Maine, 90,708 domestic. Well construction records reported to the Maine Geological Survey by licensed well drillers. Only aggregates are shown; owner names and addresses are never stored. Retrieved September 3, 2026.
- Maine DEP regulated sites: 4,871 regulated sites located in Maine. Remediation sites, leaking underground storage tanks and closed municipal landfills from the Maine Department of Environmental Protection. Retrieved September 3, 2026.
Non-detects count as samples and are treated as zero when computing medians. Exactly at the limit counts as not above it. A sample belongs to the town containing the well's reported coordinates.