Well water in Columbia County, Wisconsin

In Columbia County, 18% of 2,862 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.

2,862 private wells tested 1988 to 2025 in state summaries; 12 individual samples from 7 wells, 1945 to 2024. 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	2,862	18%	48.1	10 mg/L
E. coli	34	12%
Sodium	239	10%	145	20 mg/L
Total coliform	388	9%
Iron	235	9%	30,876	300 ug/L
Copper	277	2%	1.63	1.3 mg/L
Lead	277	2%	111	15 ug/L
Arsenic	446	2%	247	10 ug/L
Manganese	277	1%	2,746	300 ug/L
Chloride	384	<1%	404	250 mg/L

What individual samples found

Each row summarizes every public sample for that contaminant inside Columbia 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 1980 to 2024	12	92%	0%		0.49	0.904	30 ug/L EPA limit

Sampled fewer than 10 times, too few to summarize: Radium (226 + 228) (8), Nitrate (7), Fluoride (2), Arsenic (1), Lead (1), Manganese (5), Radon (3), Iron (2), Chloride (2), Sodium (2).

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What this means

Among homeowners in Columbia County who sent a sample to the state lab, the health-based limits most often exceeded were nitrate (18% of 2,862 wells), E. coli (12% of 34 wells), and total coliform (9% of 388 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 Columbia County

Volatile organic compounds (VOCs)93 leaking underground storage tank sites on record locally.
Nitrate18% of 2,862 local wells tested were above the Wisconsin enforcement standard.
E. coli12% of 34 local wells tested were above the Wisconsin limit (any detection).
Sodium10% of 239 local wells tested were above the EPA advisory level.
Total coliform9% of 388 local wells tested were above the Wisconsin limit (any detection).
Iron9% of 235 local wells tested were above the Wisconsin nuisance level.
Copper2% of 277 local wells tested were above the Wisconsin enforcement standard.
Lead2% of 277 local wells tested were above the Wisconsin enforcement standard.
Arsenic2% of 446 local wells tested were above the Wisconsin enforcement standard.

Contamination sources on record in Columbia County

Wisconsin DNR records 93 leaking underground storage tank sites in Columbia County, among 404 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.

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

Treatment that fits the local profile

Nitrate: Point-of-use reverse osmosis; Anion exchange; Distillation
E. coli: Shock chlorination and fix the well cap or casing; UV disinfection whole-house; Chlorination system
Total coliform: Inspect and repair the well cap and casing, then shock chlorinate and retest; 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 Columbia County water tested at home

A licensed local water treatment company tests your tap water in your home, walks you through the numbers, and quotes treatment only if something needs fixing. Free, about 30 minutes, no obligation. Tell us what you need and we match you with a company that serves Columbia County.

Common questions

Is there arsenic in well water in Columbia County?

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

The median radon level across 3 public samples in Columbia County was 310 pCi/L, with a high of 310 pCi/L. New Hampshire recommends treatment above 2,000 pCi/L.

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

Arlington46% nitrate
Caledonia8% nitrate
Columbus15% nitrate
Courtland20% nitrate
Dekorra12% nitrate
Fort Winnebago7% nitrate
Fountain Prairie10% nitrate
Hampden39% nitrate
Leeds62% nitrate
Lewiston7% nitrate
Lodi16% nitrate
Lowville27% nitrate
Marcellon30% nitrate
Newport10% nitrate
Otsego32% nitrate
Pacific6% nitrate
Randolph29% nitrate
Scott41% nitrate
Springvale30% nitrate
West Point11% nitrate
Wyocena8% nitrate

14 towns have fewer than 30 public samples and are included in the Columbia County totals above rather than shown separately: Arlington village, Cambria village, Columbus, Doylestown village, Fall River village, Friesland village, Lodi, Pardeeville village, Portage, Poynette village, Randolph village, Rio village, Wisconsin Dells, Wyocena village.

Sources

USGS Water Quality Portal: 45 samples in Columbia 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 Columbia County, up to 2,862 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: 404 regulated sites located in Columbia 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.