Uranium in Maine well water
In Maine, 7% of 23,366 private wells tested had uranium above the Maine guideline (30 ug/L), according to Maine CDC.
Uranium in well water comes from granite bedrock. Its main health effect is chemical toxicity to the kidneys rather than radiation. It is common in the same areas where radon and arsenic occur.
By county, from homeowner tests
Share of private wells above the state guidance level (30 ug/L) in tests homeowners sent to the state lab, to .
| County | Wells tested | Above state level | Highest | |
|---|---|---|---|---|
| Cumberland | 3,441 | 20% | ||
| Androscoggin | 1,016 | 14% | ||
| Oxford | 953 | 9% | ||
| Hancock | 2,264 | 8% | ||
| Lincoln | 1,490 | 7% | ||
| Waldo | 1,191 | 6% | ||
| Kennebec | 4,005 | 6% | ||
| Franklin | 645 | 4% | ||
| Knox | 548 | 2% | ||
| Somerset | 811 | 2% | ||
| Washington | 1,067 | 2% | ||
| York | 1,835 | 2% | ||
| Sagadahoc | 876 | 1% | ||
| Penobscot | 2,167 | <1% | ||
| Aroostook | 772 | <1% |
Towns with the highest share above the state level
- Naples, Cumberland County56% of 163 wells
- Prospect, Waldo County51% of 49 wells
- Sebago, Cumberland County45% of 51 wells
- Casco, Cumberland County44% of 100 wells
- Raymond, Cumberland County43% of 162 wells
- Gray, Cumberland County34% of 235 wells
- Dedham, Hancock County34% of 71 wells
- New Gloucester, Cumberland County34% of 179 wells
- Otis, Hancock County33% of 36 wells
- Rome, Kennebec County32% of 62 wells
- Swanville, Waldo County32% of 56 wells
- Poland, Androscoggin County31% of 123 wells
- Cumberland, Cumberland County30% of 164 wells
- Minot, Androscoggin County30% of 71 wells
- Bridgton, Cumberland County28% of 125 wells
- Waldoboro, Lincoln County28% of 107 wells
- Falmouth, Cumberland County27% of 144 wells
- Fryeburg, Oxford County26% of 38 wells
- Denmark, Oxford County26% of 35 wells
- Standish, Cumberland County26% of 235 wells
- Farmingdale, Kennebec County24% of 79 wells
- North Yarmouth, Cumberland County24% of 126 wells
- Ellsworth, Hancock County22% of 287 wells
- Orland, Hancock County20% of 86 wells
- Smithfield, Somerset County19% of 36 wells
By county, from individual samples
Public monitoring samples against the EPA limit (30 ug/L); counties with at least 30 samples.
| County | Samples | Detected | Above EPA limit | Median | Highest |
|---|---|---|---|---|---|
| Cumberland | 32 | 78% | 25% | 2.57 | 960 ug/L |
| Kennebec | 48 | 81% | 10% | 1.69 | 320 ug/L |
Sources
- Maine Tracking Network private well summaries: 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.
- Individual samples from the USGS Water Quality Portal and state monitoring, summarized per geography. uranium counts and shares are listed on each county and town page with their sources.