Well water in Grant County, Wisconsin

In Grant County, 6% of 1,466 private wells tested between 1988 and 2025 had nitrate above the Wisconsin enforcement standard (10 mg/L), according to the UWSP Well Water Quality Viewer.

1,466 private wells tested 2006 to 2025 in state summaries; 16 individual samples from 6 wells, 1944 to 2014. Data refreshed September 9, 2026.

What homeowner tests found

Wisconsin Well Water Quality Viewer samples: private wells tested and reported to the state, 2006 to 2025. 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.

Contaminant	Wells tested	Above state level	Highest	State level
E. coli	3	33%
Iron	19	11%	415	300 ug/L
Total coliform	29	10%
Nitrate	1,466	6%	33.8	10 mg/L
Arsenic	121	4%	82.9	10 ug/L
Chloride	29	0%	197	250 mg/L
Manganese	21	0%	26	300 ug/L
Lead	21	0%	11	15 ug/L
Copper	21	0%	0.163	1.3 mg/L
Sodium	19	0%	13.1	20 mg/L

What individual samples found

Each row summarizes every public sample for that contaminant inside Grant 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
Uranium 1961 to 2014	16	44%	0%		0	1	30 ug/L EPA limit

Sampled fewer than 10 times, too few to summarize: Fluoride (4), Lead (2), Radium (226 + 228) (2), Nitrate (2), Arsenic (1), Chloride (3), Iron (1), Manganese (1), Radon (1).

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What this means

Among homeowners in Grant County who sent a sample to the state lab, the health-based limits most often exceeded were total coliform (10% of 29 wells), nitrate (6% of 1,466 wells), and arsenic (4% of 121 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.

Iron exceeds the state's advisory level in a sizable share of wells; this is mostly a taste, staining or diet issue rather than a toxicity one.

What to test for in Grant County

Volatile organic compounds (VOCs)78 leaking underground storage tank sites on record locally.
Iron11% of 19 local wells tested were above the Wisconsin nuisance level.
Total coliform10% of 29 local wells tested were above the Wisconsin limit (any detection).
Nitrate6% of 1,466 local wells tested were above the Wisconsin enforcement standard.
Arsenic4% of 121 local wells tested were above the Wisconsin enforcement standard.
Coliform bacteriaRecommended for every private well, every year.
RadonMedian local reading is 52 pCi/L.
FluorideDetected in 100% of local samples.
ChlorideDetected in 100% of local samples.

Contamination sources on record in Grant County

Wisconsin DNR records 78 leaking underground storage tank sites in Grant County, among 310 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.

78: leaking underground storage tank sitesGasoline and heating oil that leaked from tanks move through groundwater as benzene, MTBE and other volatile organic compounds.
33: lined landfills and transfer facilities
199: other remediation projects

Treatment that fits the local profile

Total coliform: Inspect and repair the well cap and casing, then shock chlorinate and retest; UV disinfection whole-house; Chlorination system
Nitrate: Point-of-use reverse osmosis; Anion exchange; Distillation
Iron: Oxidizing filter whole-house; Water softener (low levels); Aeration plus filtration
Fluoride: Point-of-use reverse osmosis; Activated alumina; Distillation
Chloride: Point-of-use reverse osmosis; Distillation
Manganese: Oxidizing filter (greensand, birm) whole-house; Water softener (low levels); Point-of-use reverse osmosis

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Common questions

Is there arsenic in well water in Grant County?

Arsenic was detected in 100% of 1 public well samples in Grant 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 Grant County?

The median radon level across 1 public samples in Grant County was 52 pCi/L, with a high of 52 pCi/L. New Hampshire recommends treatment above 2,000 pCi/L.

How often should I test a private well in Grant 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 Grant County

Beetown3% nitrate
Bloomington26% nitrate
Ellenboro5% nitrate
Harrison4% nitrate
Hazel Green11% nitrate
Jamestown<1% nitrate
Liberty3% nitrate
Lima3% nitrate
Muscoda5% nitrate
North Lancaster19% nitrate
Paris2% nitrate
Platteville3% nitrate
Platteville0% nitrate
Potosi8% nitrate
Smelser13% nitrate
South Lancaster0% nitrate
Waterloo4% nitrate

35 towns have fewer than 30 public samples and are included in the Grant County totals above rather than shown separately: Bagley village, Bloomington village, Blue River village, Boscobel, Boscobel, Cassville, Cassville village, Castle Rock, Clifton, Cuba City, Dickeyville village, Fennimore, Fennimore, Glen Haven, Hazel Green village, Hickory Grove, Lancaster, Little Grant, Livingston village, Marion, Millville, Montfort village, Mount Hope, Mount Hope village, Mount Ida, Muscoda village, Patch Grove, Patch Grove village, Potosi village, Tennyson village, Watterstown, Wingville, Woodman, Woodman village, Wyalusing.

Sources

USGS Water Quality Portal: 33 samples in Grant 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.
Wisconsin Well Water Quality Viewer samples: summaries for 10 contaminants in Grant County, up to 1,466 wells each. Private well samples compiled by the UWSP Center for Watershed Science and Education from the DNR Groundwater Retrieval Network, DATCP surveys, the UWSP Water and Environmental Analysis Lab and county health programs, published in the Wisconsin Well Water Quality Viewer with Wisconsin DHS. Samples are located to the town, village or city they fall in; one result per well and parameter (the latest) so repeat samples do not double count; wells without a state well number are keyed by location. Shares are against Wisconsin NR 140 enforcement standards (arsenic 10 ug/L, nitrate 10 mg/L as N, manganese 300 ug/L, lead 15 ug/L, copper 1.3 mg/L) and the iron and chloride secondary levels. Many samples were submitted by homeowners with a reason to test, so shares can run above a random survey. Retrieved September 9, 2026.
Wisconsin DNR regulated sites: 310 regulated sites located in Grant County. Open and closed remediation activities (BRRTS, including leaking underground storage tanks and spills) and landfill and waste sites from the Wisconsin Department of Natural Resources. Retrieved September 9, 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.