Well water in Penobscot County, Maine
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Testing recommended
private wells tested in Penobscot County had arsenic above the Maine guideline (10 ug/L), according to Maine CDC.
The strongest signal is PFOA: 18% of 294 local samples were above the limit, too few samples to carry the headline but first on the test list below.
3,177 private wells tested in state summaries; 1,565 test results across 17 contaminants from at least 294 wells, 1941 to 2026; PFOA has the most at 294. Data refreshed September 15, 2026.
Compiled by Nick at Well Water Nerd from public records. How these pages are built
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.
An estimated 81,251 people in Penobscot County get their drinking water from a private well, per USGS 2015 county water use. That is about 53% of residents.
Separately, the USGS national arsenic model estimates that 23% of the 81,251 people on private wells in Penobscot County draw water above 10 ug/L (the model's range is 19% to 27%), from geology and well depth rather than local tests.
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 | Above limit | Samples | Detected | Median | Highest | Limit |
|---|---|---|---|---|---|---|
| PFOA 2020 to 2026 | 294 | 51% | 0.265 | 493 | 4 ng/L EPA limit | |
| PFOS 2020 to 2026 | 294 | 41% | 0 | 96 | 4 ng/L EPA limit | |
| Nitrate 1941 to 2023 | 72 | 76% | 0.35 | 45 | 10 mg/L EPA limit | |
| PFHxS 2020 to 2026 | 294 | 26% | 0 | 54.6 | 10 ng/L EPA limit | |
| PFNA 2020 to 2026 | 294 | 12% | 0 | 158 | 10 ng/L EPA limit | |
| Fluoride 1948 to 2023 | 55 | 64% | 0.1 | 0.6 | 4 mg/L EPA limit | |
| Arsenic 1999 to 2023 | 14 | 64% | 0.2 | 9 | 10 ug/L EPA limit | |
| Radium (226 + 228) 1999 to 2014 | 12 | 92% | 0 | 2 | 5 pCi/L EPA limit | |
| Uranium 1999 to 2023 | 11 | 82% | 0.625 | 5.11 | 30 ug/L EPA limit | |
| Copper 1999 to 2023 | 11 | 73% | 0.001 | 0.014 | 1.3 mg/L EPA limit | |
| Lead 1999 to 2023 | 11 | 55% | 0.019 | 4.9 | 15 ug/L EPA limit | |
| Chloride 1941 to 2023 | no limit | 64 | 100% | 6.1 | 88 | 250 mg/L nuisance level |
| Iron 1942 to 2023 | no limit | 64 | 84% | 110 | 93,000 | 300 ug/L nuisance level |
| Manganese 1949 to 2023 | no limit | 59 | 80% | 50 | 18,000 | 300 ug/L health guideline |
Sampled fewer than 10 times, too few to summarize: E. coli (7), Radon (6), Sodium (3).
Closer than the county
See the sampled wells near your address
The same records, drawn around one point: which wells within a few miles were sampled and what they found, how deep the wells next to you were drilled, and any leaking tank or cleanup site within a mile.
Check my addressWhat 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
- 1PFOA18% of 294 local samples were above the limit.
- 2PFOS10% of 294 local samples were above the limit.
- 3Arsenic8% of 2,501 local wells tested were above the Maine guideline.
- 4Nitrate6% of 72 local samples were above the limit.
- 5PFHxS1% of 294 local samples were above the limit.
- 6Uranium<1% of 2,167 local wells tested were above the Maine guideline.
- 7PFNA<1% of 294 local samples were above the limit.
- 8Fluoride<1% of 3,177 local wells tested were above the Maine guideline.
- 9Volatile organic compounds (VOCs)176 leaking underground storage tank sites on record locally.
- 10PFAS53 unlined landfills on record locally.
- 11Metals panel57 hazardous waste sites on record locally.
Test your Penobscot County well for PFOA, PFOS and arsenic
Certified lab analysis of your own tap water, bottles and prepaid return shipping included. The Essential well panel covers arsenic, uranium, nitrate, lead, copper, manganese, iron, sodium and bacteria; radon and PFAS are add-ons.
Order the Tap Score well water test kit, from $209Already tested? Upload the report
Just want bacteria checked first? Tap Score coliform and E. coli test, $99. Coliform and E. coli are the tests every well needs every year.
Want a quick look before paying for a lab? Home well water test strips on Amazon check hardness, iron, pH and nitrate in minutes. They are a screen, not a result: arsenic, bacteria, uranium and PFAS need a certified lab.
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Where to get a well tested in Maine: certified labs, state programs and prices.
Already have results back? Get your lab report read against the Penobscot County numbers, $29. Every line explained, ranked by what matters, with the fix for each.
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.
The rock under Penobscot County
Not a principal aquifer
The USGS map places this area outside any principal aquifer, which usually means wells here draw from fractured bedrock or thin local deposits rather than a large regional aquifer. Bedrock wells of that kind are where arsenic, radon and uranium turn up, and yields vary from well to well.
Classification from the USGS Principal Aquifers of the United States (national map, 2003 edition, GIS release 2015), read at the county centroid. A single well can sit in a different unit, especially near a boundary.
Official help in Maine
Two places to start that are not selling anything: the state program that answers private well questions, and its list of labs certified to run drinking water tests. A certified lab is the difference between a result you can act on and a number.
- Private Well Water, Maine CDC
- Laboratory Accreditation, Maine CDC
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
Systems we would look at first
Some links below are affiliate links. If you buy through one, the merchant pays us a commission at no extra cost to you. It does not change which products we list or what the data says.
For arsenic
Under-sink reverse osmosis system
under-sink or countertop, about $300
Look for NSF/ANSI 58 certification listing the contaminant you need removed.
For arsenic
Whole-house arsenic and uranium filter
whole-house, at the point of entry, about $2,500
Adsorptive iron-based media; sized to your well yield.
For arsenic
Aquasana SmartFlow reverse osmosis
under-sink or countertop, about $225
Certified to NSF/ANSI 58 and 53 to reduce arsenic (96%, pentavalent), fluoride (90%), lead (99%), nitrate, nitrite and PFOA/PFOS at the kitchen tap, with a remineralizer.
For PFOA
Aquasana Claryum 3-Stage under-sink filter
under-sink or countertop, about $175
Certified to NSF/ANSI 53 to reduce 99% of lead and 99.7% of PFOA and PFOS at the tap. Not a fix for arsenic, nitrate or bacteria.
For PFOA
Whole-house PFAS carbon system
whole-house, at the point of entry, about $3,000
Granular activated carbon certified to NSF/ANSI 53 for PFOA and PFOS; replace media on schedule.
For PFOA
Aquasana HealthShield whole-house filter
whole-house, at the point of entry, about $2,099
Whole-house carbon system the maker certifies to reduce PFAS (PFOA and PFOS) and VOCs at every tap; a UV option adds bacteria protection.
Free, no obligation
Get on the list for a free in-home water test in Penobscot County
No water treatment company serves Penobscot County through Well Water Nerd yet. We are signing licensed companies on county by county: they test at your tap for free, walk you through the numbers, and quote treatment only if something needs fixing. Leave your details and you are first in line. Nothing is shared until a company joins for Penobscot County, and you get an email naming it first.
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 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.
Counties near Penobscot County
Closest first. Groundwater does not stop at a line on a map, so the next county over is a fair second opinion.
Want the numbers themselves? Download the Maine dataset as CSV, every county and town, with the sources named.
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: 389 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.
- USGS national arsenic model (Ayotte 2017): estimated share of 81,251 people on private wells in Penobscot County above 10 ug/L of arsenic, from geology, well depth and land use. County estimates of domestic well users with arsenic above 10 ug/L from the USGS national logistic regression model (Ayotte, Medalie and Qi, 2017), with private well population from the USGS 2015 county water-use compilation (Dieter and others, 2018). Retrieved September 15, 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.