Well water in St. Croix County, Wisconsin

In St. Croix County, 11% of 3,738 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.

3,738 private wells tested 1988 to 2025 in state summaries; 18 individual samples from 7 wells, 1957 to 2018. Data refreshed September 9, 2026.

What homeowner tests found

Wisconsin Well Water Quality Viewer samples: private wells tested and reported to the state, 1988 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
Nitrate	3,738	11%	40.4	10 mg/L
Total coliform	486	9%
Sodium	196	8%	76.1	20 mg/L
Iron	192	7%	6,433	300 ug/L
E. coli	45	7%
Copper	270	3%	2.52	1.3 mg/L
Lead	271	2%	1,266	15 ug/L
Manganese	270	1%	1,391	300 ug/L
Arsenic	512	<1%	24.6	10 ug/L
Chloride	641	0%	185	250 mg/L

What individual samples found

Each row summarizes every public sample for that contaminant inside St. Croix 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 1957 to 2018	18	67%	0%		0.143	1.22	30 ug/L EPA limit
Radium (226 + 228) 2007 to 2018	12	75%	0%		0.085	0.7	5 pCi/L EPA limit

Sampled fewer than 10 times, too few to summarize: Nitrate (5), Fluoride (3), Arsenic (1), Radon (7), Manganese (3), Chloride (2), Iron (1), Sodium (1).

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What this means

Among homeowners in St. Croix County who sent a sample to the state lab, the health-based limits most often exceeded were nitrate (11% of 3,738 wells), total coliform (9% of 486 wells), and E. coli (7% of 45 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 St. Croix County

Volatile organic compounds (VOCs)82 leaking underground storage tank sites on record locally.
Nitrate11% of 3,738 local wells tested were above the Wisconsin enforcement standard.
Total coliform9% of 486 local wells tested were above the Wisconsin limit (any detection).
Sodium8% of 196 local wells tested were above the EPA advisory level.
Iron7% of 192 local wells tested were above the Wisconsin nuisance level.
E. coli7% of 45 local wells tested were above the Wisconsin limit (any detection).
Copper3% of 270 local wells tested were above the Wisconsin enforcement standard.
Lead2% of 271 local wells tested were above the Wisconsin enforcement standard.
Manganese1% of 270 local wells tested were above the Wisconsin enforcement standard.

Contamination sources on record in St. Croix County

Wisconsin DNR records 82 leaking underground storage tank sites in St. Croix County, among 321 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.

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

Treatment that fits the local profile

Nitrate: Point-of-use reverse osmosis; Anion exchange; Distillation
Total coliform: Inspect and repair the well cap and casing, then shock chlorinate and retest; UV disinfection whole-house; Chlorination system
E. coli: Shock chlorination and fix the well cap or casing; UV disinfection whole-house; Chlorination system
Sodium: Point-of-use reverse osmosis; Distillation
Iron: Oxidizing filter whole-house; Water softener (low levels); Aeration plus filtration
Fluoride: Point-of-use reverse osmosis; Activated alumina; Distillation

Get your St. Croix County water tested at home

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Common questions

Is there arsenic in well water in St. Croix County?

Arsenic was detected in 0% of 1 public well samples in St. Croix 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 St. Croix County?

The median radon level across 7 public samples in St. Croix County was 360 pCi/L, with a high of 580 pCi/L. New Hampshire recommends treatment above 2,000 pCi/L.

How often should I test a private well in St. Croix 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 St. Croix County

Baldwin0% nitrate
Cady2% nitrate
Eau Galle4% nitrate
Emerald6% nitrate
Erin Prairie36% nitrate
Forest5% nitrate
Glenwood13% nitrate
Hammond14% nitrate
Hudson11% total coliform
Kinnickinnic13% nitrate
Pleasant Valley7% nitrate
Richmond26% nitrate
Rush River11% nitrate
Somerset6% total coliform
Springfield8% nitrate
Stanton15% nitrate
Star Prairie3% nitrate
St. Joseph13% total coliform
Troy12% nitrate
Warren22% nitrate

15 towns have fewer than 30 public samples and are included in the St. Croix County totals above rather than shown separately: Baldwin village, Cylon, Deer Park village, Glenwood City, Hammond village, Hudson, New Richmond, North Hudson village, River Falls, Roberts village, Somerset village, Spring Valley village, Star Prairie village, Wilson village, Woodville village.

Sources

USGS Water Quality Portal: 53 samples in St. Croix 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 St. Croix County, up to 3,738 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: 321 regulated sites located in St. Croix 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.