Well water in Portage County, Wisconsin
In Portage County, 21% of 3,842 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.
3,842 private wells tested 1988 to 2025 in state summaries; 67 individual samples from 35 wells, 1953 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.
What individual samples found
Each row summarizes every public sample for that contaminant inside Portage 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 | |
|---|---|---|---|---|---|---|---|
| Nitrate 1973 to 2004 | 32 | 91% | 31% | 4.3 | 44 | 10 mg/L EPA limit | |
| Uranium 1994 to 2024 | 67 | 96% | 0% | 1.37 | 8.16 | 30 ug/L EPA limit | |
| Radium (226 + 228) 2003 to 2014 | 18 | 72% | 0% | 0.205 | 0.82 | 5 pCi/L EPA limit | |
| Arsenic 1973 to 2015 | 15 | 73% | 0% | 0.43 | 2 | 10 ug/L EPA limit | |
| Sodium 1974 to 2017 | 12 | 100% | no limit | 1.85 | 10 | 20 mg/L health guideline |
Sampled fewer than 10 times, too few to summarize: Lead (4), Fluoride (3), Copper (2), Manganese (9), Chloride (7), Iron (5), Radon (3).
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What this means
Among homeowners in Portage County who sent a sample to the state lab, the health-based limits most often exceeded were nitrate (21% of 3,842 wells), total coliform (10% of 1,284 wells), and E. coli (3% of 122 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 and sodium exceed the state's advisory level in a sizable share of wells; these are mostly a taste, staining or diet issue rather than a toxicity one.
What to test for in Portage County
- Volatile organic compounds (VOCs)163 leaking underground storage tank sites on record locally.
- Iron19% of 247 local wells tested were above the Wisconsin nuisance level.
- Sodium10% of 219 local wells tested were above the EPA advisory level.
- Total coliform10% of 1,284 local wells tested were above the Wisconsin limit (any detection).
- E. coli3% of 122 local wells tested were above the Wisconsin limit (any detection).
- Manganese3% of 307 local wells tested were above the Wisconsin enforcement standard.
- Lead2% of 279 local wells tested were above the Wisconsin enforcement standard.
- Chloride1% of 1,312 local wells tested were above the Wisconsin nuisance level.
- Copper1% of 274 local wells tested were above the Wisconsin enforcement standard.
Contamination sources on record in Portage County
Wisconsin DNR records 163 leaking underground storage tank sites in Portage County, among 433 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.
- 163
- leaking underground storage tank sitesGasoline and heating oil that leaked from tanks move through groundwater as benzene, MTBE and other volatile organic compounds.
- 37
- lined landfills and transfer facilities
- 233
- 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
- Iron
- Oxidizing filter whole-house; Water softener (low levels); Aeration plus filtration
- Sodium
- Point-of-use reverse osmosis; Distillation
- Fluoride
- Point-of-use reverse osmosis; Activated alumina; Distillation
- Manganese
- Oxidizing filter (greensand, birm) whole-house; Water softener (low levels); Point-of-use reverse osmosis
Get your Portage County water tested at home
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Common questions
Is there arsenic in well water in Portage County?
Arsenic was detected in 73% of 15 public well samples in Portage 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 Portage County?
The median radon level across 3 public samples in Portage County was 260 pCi/L, with a high of 660 pCi/L. New Hampshire recommends treatment above 2,000 pCi/L.
How often should I test a private well in Portage 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 Portage County
- Alban20% nitrate
- Almond38% nitrate
- Almond village12% nitrate
- Amherst22% nitrate
- Amherst Junction village10% nitrate
- Belmont15% nitrate
- Buena Vista45% nitrate
- Carson22% total coliform
- Dewey14% total coliform
- Eau Pleine24% total coliform
- Grant8% nitrate
- Hull16% nitrate
- Lanark12% total coliform
- Linwood16% total coliform
- Nelsonville village32% nitrate
- New Hope16% nitrate
- Pine Grove62% nitrate
- Plover45% nitrate
- Plover village22% nitrate
- Rosholt village26% nitrate
- Sharon19% nitrate
- Stevens Point14% nitrate
- Stockton34% nitrate
5 towns have fewer than 30 public samples and are included in the Portage County totals above rather than shown separately: Amherst village, Junction City village, Milladore village, Park Ridge village, Whiting village.
Sources
- USGS Water Quality Portal: 177 samples in Portage 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 Portage County, up to 3,842 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: 433 regulated sites located in Portage 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.