Well water in Penobscot County, Maine
In Penobscot County, 8% of 2,501 private wells tested had arsenic above the Maine guideline (10 ug/L), according to Maine CDC.
3,177 private wells tested in state summaries; 294 individual samples from 294 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, 18% of 294 PFOA results in Penobscot County were above the EPA limit of 4 ng/L. In that targeted sampling, 10% of 294 PFOS results in Penobscot County 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 Penobscot County. 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 | |
|---|---|---|---|---|---|---|---|
| PFOA 2020 to 2026 | 294 | 51% | 18% | 0.265 | 493 | 4 ng/L EPA limit | |
| PFOS 2020 to 2026 | 294 | 41% | 10% | 0 | 96 | 4 ng/L EPA limit | |
| Nitrate 1941 to 2023 | 42 | 88% | 10% | 1.2 | 45 | 10 mg/L EPA limit | |
| PFHxS 2020 to 2026 | 294 | 26% | 1% | 0 | 54.6 | 10 ng/L EPA limit | |
| PFNA 2020 to 2026 | 294 | 12% | <1% | 0 | 158 | 10 ng/L EPA limit | |
| Arsenic 1999 to 2023 | 14 | 64% | 0% | 0.2 | 9 | 10 ug/L EPA limit | |
| Radium (226 + 228) 1999 to 2014 | 12 | 92% | 0% | 0 | 2 | 5 pCi/L EPA limit | |
| Copper 1999 to 2023 | 11 | 73% | 0% | 0.001 | 0.014 | 1.3 mg/L EPA limit | |
| Uranium 1999 to 2023 | 11 | 82% | 0% | 0.625 | 5.11 | 30 ug/L EPA limit | |
| Chloride 1941 to 2023 | 64 | 100% | no limit | 6.1 | 88 | 250 mg/L nuisance level |
Sampled fewer than 10 times, too few to summarize: Fluoride (9), E. coli (7), Lead (3), Manganese (8), Iron (7), Radon (6), Sodium (3).
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What this means
Among homeowners in Penobscot County who sent a sample to the state lab, the health-based limits most often exceeded were arsenic (8% of 2,501 wells), uranium (<1% of 2,167 wells), and nitrate (<1% of 3,022 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 Penobscot County
- Volatile organic compounds (VOCs)176 leaking underground storage tank sites on record locally.
- PFAS53 unlined landfills on record locally.
- Metals panel57 hazardous waste sites on record locally.
- PFOA18% of 294 local samples were above the limit.
- PFOS10% of 294 local samples were above the limit.
- Arsenic8% of 2,501 local wells tested were above the Maine guideline.
- Manganese4% of 2,436 local wells tested were above the Maine guideline.
- PFHxS1% of 294 local samples were above the limit.
- Uranium<1% of 2,167 local wells tested were above the Maine guideline.
- PFNA<1% of 294 local samples were above the limit.
- Fluoride<1% of 3,177 local wells tested were above the Maine guideline.
Wells in Penobscot County
7,366 domestic wells in Penobscot County are on record with the state since 1970. 99% are drilled into bedrock, and the typical well is 200 feet deep (one in ten goes past 400 feet).
In a typical Penobscot County well, bedrock starts about 16 feet down, the median yield is 6 gallons per minute, 18% 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 Penobscot County
Maine DEP records 176 leaking underground storage tank sites, 53 unlined landfills, and 57 hazardous waste sites in Penobscot County, among 632 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.
- 176
- leaking underground storage tank sitesGasoline and heating oil that leaked from tanks move through groundwater as benzene, MTBE and other volatile organic compounds.
- 53
- unlined landfillsOlder unlined landfills are a leading source of PFAS, VOCs and metals in nearby wells.
- 57
- hazardous waste sitesSolvents, degreasers and metals from industrial sites can travel far in fractured bedrock.
- 346
- other remediation projects
Treatment that fits the local profile
- Arsenic
- Point-of-use reverse osmosis; Adsorptive media (iron-based) 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
- PFHxS
- Granular activated carbon whole-house; Point-of-use reverse osmosis; Anion exchange
- PFNA
- Granular activated carbon whole-house; Point-of-use reverse osmosis; Anion exchange
Book a free water test in Penobscot County
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Common questions
How deep are wells in Penobscot County?
The typical domestic well in Penobscot County is 200 feet deep, based on 7,366 wells reported to the state since 1970. One in ten is deeper than 400 feet. 99% are drilled into bedrock.
Is there arsenic in well water in Penobscot County?
Arsenic was detected in 64% of 14 public well samples in Penobscot County, and 0% 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 Penobscot County?
The median radon level across 6 public samples in Penobscot County was 1,220 pCi/L, with a high of 2,530 pCi/L. New Hampshire recommends treatment above 2,000 pCi/L.
How often should I test a private well in Penobscot County?
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.
Towns in Penobscot County
- Alton17% arsenic
- Bangor2% arsenic
- Bradford15% arsenic
- Bradley3% arsenic
- Brewer0% fluoride
- Carmel9% arsenic
- Charleston12% arsenic
- Clifton6% fluoride
- Corinna17% arsenic
- Corinth9% arsenic
- Dexter4% nitrate
- Dixmont0% arsenic
- Eddington8% arsenic
- Enfield18% arsenic
- Exeter15% arsenic
- Garland3% nitrate
- Glenburn8% arsenic
- Greenbush13% arsenic
- Hampden6% arsenic
- Hermon8% arsenic
- Holden4% uranium
- Hudson2% arsenic
- Kenduskeag3% arsenic
- Lagrange10% arsenic
- Lee0% arsenic
- Levant8% arsenic
- Lincoln11% uranium
- Medway3% arsenic
- Milford14% arsenic
- Newburgh0% arsenic
- Newport24% arsenic
- Old Town10% arsenic
- Orono4% arsenic
- Orrington5% arsenic
- Plymouth7% arsenic
- Stetson7% arsenic
31 towns have fewer than 30 public samples and are included in the Penobscot County totals above rather than shown separately: Argyle UT, Burlington, Carroll plantation, Chester, Drew UT, East Central Penobscot UT, East Millinocket, Edinburg, Etna, Howland, Kingman UT, Lakeville, Lowell, Mattawamkeag, Maxfield, Millinocket, Mount Chase, North Penobscot UT, Passadumkeag, Patten, Penobscot Indian Island Reservation, Prentiss UT, Seboeis plantation, Springfield, Stacyville, Twombly Ridge UT, Veazie, Webster plantation, Whitney UT, Winn, Woodville.
Sources
- Maine DEP PFAS investigation: 1,176 samples in Penobscot County. PFAS results for private wells sampled by the Maine Department of Environmental Protection. Retrieved September 3, 2026.
- USGS Water Quality Portal: 197 samples in Penobscot County. 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 Penobscot County, up to 3,177 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: 7,632 well records in Penobscot County, 7,366 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: 632 regulated sites located in Penobscot County. 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.