Well water in Mahnomen County, Minnesota
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Testing strongly recommended
private wells tested between 2008 and 2021 in Mahnomen County had arsenic above the EPA limit (10 ug/L), according to the Minnesota Department of Health.
267 private wells tested 2008 to 2021 in state summaries; 141 test results across 11 contaminants from at least 19 wells, 1964 to 1995; nitrate has the most at 23. Data refreshed September 15, 2026.
Compiled by Nick at Well Water Nerd from public records. How these pages are built
An estimated 3,757 people in Mahnomen County get their drinking water from a private well, per USGS 2015 county water use. That is about 69% of residents.
Separately, the USGS national arsenic model estimates that 5% of the 3,757 people on private wells in Mahnomen County draw water above 10 ug/L (the model's range is 4% to 7%), from geology and well depth rather than local tests.
What homeowner tests found
MDH new private well arsenic tests: private wells tested and reported to the state, 2008 to 2021. Shares are against the level the state applies to each contaminant, named in the last column; several are stricter than EPA.
| Contaminant | Above state level | Wells tested | Median | 95th pct | Highest | State level |
|---|---|---|---|---|---|---|
| Arsenic | 267 | 7.7 | 40 | 10 ug/L |
What individual samples found
Each row summarizes every public sample for that contaminant inside Mahnomen 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 | Above limit | Samples | Detected | Median | Highest | Limit |
|---|---|---|---|---|---|---|
| Nitrate 1964 to 1995 | 23 | 43% | 0 | 16.7 | 10 mg/L EPA limit | |
| Fluoride 1964 to 1995 | 13 | 100% | 0.3 | 0.64 | 4 mg/L EPA limit | |
| Copper 1984 to 1995 | 10 | 20% | 0 | 0 | 1.3 mg/L EPA limit | |
| Lead 1984 to 1995 | 10 | 60% | 0 | 0 | 15 ug/L EPA limit | |
| Manganese 1964 to 1995 | no limit | 19 | 100% | 170 | 740 | 300 ug/L health guideline |
| Iron 1964 to 1995 | no limit | 19 | 100% | 1,000 | 4,800 | 300 ug/L nuisance level |
| Chloride 1964 to 1995 | no limit | 18 | 100% | 2.21 | 18 | 250 mg/L nuisance level |
| Sodium 1964 to 1995 | no limit | 13 | 100% | 15 | 102 | 20 mg/L health guideline |
Sampled fewer than 10 times, too few to summarize: Arsenic (8), Uranium (4), Radon (4).
Closer than the county
See the sampled wells near your address
The same records, drawn around one point: which wells within a few miles were sampled and what they found, how deep the wells next to you were drilled, and any leaking tank or cleanup site within a mile.
Check my addressWhat this means
Among homeowners in Mahnomen County who sent a sample to the state lab, the health-based limits most often exceeded were arsenic (42% of 267 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 Mahnomen County
- 1Arsenic42% of 267 local wells tested were above the EPA limit.
- 2Nitrate4% of 23 local samples were above the limit.
- 3Coliform bacteriaRecommended for every private well, every year.
- 4RadonMedian local reading is 315 pCi/L.
- 5FluorideDetected in 100% of local samples.
- 6ManganeseDetected in 100% of local samples.
- 7IronDetected in 100% of local samples.
- 8Volatile organic compounds (VOCs)38 leaking underground storage tank sites on record locally.
Test your Mahnomen County well for arsenic, nitrate and coliform bacteria
Certified lab analysis of your own tap water, bottles and prepaid return shipping included. The Essential well panel covers arsenic, uranium, nitrate, lead, copper, manganese, iron, sodium and bacteria; radon and PFAS are add-ons.
Order the Tap Score well water test kit, from $209Already tested? Upload the report
Just want bacteria checked first? Tap Score coliform and E. coli test, $99. Coliform and E. coli are the tests every well needs every year.
Want a quick look before paying for a lab? Home well water test strips on Amazon check hardness, iron, pH and nitrate in minutes. They are a screen, not a result: arsenic, bacteria, uranium and PFAS need a certified lab.
Affiliate links: the merchant pays us a commission and the price is the same for you. It does not change what the data above says. As an Amazon Associate we earn from qualifying purchases.
Where to get a well tested in Minnesota: certified labs, state programs and prices.
Already have results back? Get your lab report read against the Mahnomen County numbers, $29. Every line explained, ranked by what matters, with the fix for each.
Wells in Mahnomen County
223 domestic wells in Mahnomen County are on record with the state since 1920. <1% are drilled into bedrock, and the typical well is 112 feet deep (one in ten goes past 204 feet).
In a typical Mahnomen County well, bedrock starts about 285 feet down.
Find your own well's report
The state keeps the driller's report for most wells drilled since 1984. It tells you how deep your well is, where bedrock starts, and how much water it makes, which decides what treatment can work.
- Open Minnesota Well Index and choose Water Well.
- The record shows depth, casing, depth to bedrock, aquifer, static water level and the driller; new wells since 2008 also show the arsenic test result.
Wells drilled since 1974 have records; older wells appear only if a later owner reported them.
The rock under Mahnomen County
Not a principal aquifer
The USGS map places this area outside any principal aquifer, which usually means wells here draw from fractured bedrock or thin local deposits rather than a large regional aquifer. Bedrock wells of that kind are where arsenic, radon and uranium turn up, and yields vary from well to well.
Classification from the USGS Principal Aquifers of the United States (national map, 2003 edition, GIS release 2015), read at the county centroid. A single well can sit in a different unit, especially near a boundary.
Official help in Minnesota
Two places to start that are not selling anything: the state program that answers private well questions, and its list of labs certified to run drinking water tests. A certified lab is the difference between a result you can act on and a number.
- Wells and Borings, Minnesota Department of Health
- Accredited Laboratories as Well Partners, Minnesota Department of Health
Contamination sources on record in Mahnomen County
MPCA records 38 leaking underground storage tank sites in Mahnomen County, among 85 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.
- 38
- leaking underground storage tank sitesGasoline and heating oil that leaked from tanks move through groundwater as benzene, MTBE and other volatile organic compounds.
- 34
- registered underground storage tank sitesRegistered tanks are regulated and inspected; they matter most when they are old or near a shallow well.
- 7
- lined landfills and transfer facilities
- 6
- other remediation projects
Treatment that fits the local profile
Arsenic
Point-of-use reverse osmosis; Adsorptive media (iron-based) whole-house; Anion exchange
Nitrate
Point-of-use reverse osmosis; Anion exchange; Distillation
Manganese
Oxidizing filter (greensand, birm) whole-house; Water softener (low levels); Point-of-use reverse osmosis
Iron
Oxidizing filter whole-house; Water softener (low levels); Aeration plus filtration
Systems we would look at first
Some links below are affiliate links. If you buy through one, the merchant pays us a commission at no extra cost to you. It does not change which products we list or what the data says.
For arsenic
Under-sink reverse osmosis system
under-sink or countertop, about $300
Look for NSF/ANSI 58 certification listing the contaminant you need removed.
For arsenic
Whole-house arsenic and uranium filter
whole-house, at the point of entry, about $2,500
Adsorptive iron-based media; sized to your well yield.
For arsenic
Aquasana SmartFlow reverse osmosis
under-sink or countertop, about $225
Certified to NSF/ANSI 58 and 53 to reduce arsenic (96%, pentavalent), fluoride (90%), lead (99%), nitrate, nitrite and PFOA/PFOS at the kitchen tap, with a remineralizer.
For manganese
Iron and manganese oxidizing filter
whole-house, at the point of entry, about $1,800
Air-injection or greensand media; fixes staining at the source.
Free, no obligation
Get on the list for a free in-home water test in Mahnomen County
No water treatment company serves Mahnomen County through Well Water Nerd yet. We are signing licensed companies on county by county: they test at your tap for free, walk you through the numbers, and quote treatment only if something needs fixing. Leave your details and you are first in line. Nothing is shared until a company joins for Mahnomen County, and you get an email naming it first.
Common questions
How deep are wells in Mahnomen County?
The typical domestic well in Mahnomen County is 112 feet deep, based on 223 wells reported to the state since 1920. One in ten is deeper than 204 feet. <1% are drilled into bedrock.
How often should I test a private well in Mahnomen 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 Mahnomen County
19 towns have fewer than 30 public samples and are included in the Mahnomen County totals above rather than shown separately: Beaulieu township, Bejou, Bejou township, Chief township, Clover township, Gregory township, Heier township, Island Lake township, La Garde township, Lake Grove township, Little Elbow township, Mahnomen, Marsh Creek township, Oakland township, Pembina township, Popple Grove township, Rosedale township, Twin Lakes township, Waubun.
Counties near Mahnomen County
Closest first. Groundwater does not stop at a line on a map, so the next county over is a fair second opinion.
Want the numbers themselves? Download the Minnesota dataset as CSV, every county and town, with the sources named.
Sources
- USGS Water Quality Portal: 141 samples in Mahnomen 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.
- MDH new private well arsenic tests: summaries for 1 contaminants in Mahnomen County, up to 267 wells each. Arsenic results for every new private well drilled and tested August 2008 to December 2021, reported to the Minnesota Department of Health by well contractors and published by county. Mandatory test on new wells only, so older wells are not represented; 64,793 wells statewide. Shares are against 10 ug/L, which MDH applies as its advice level. Median and 95th percentile published per county. Retrieved September 15, 2026.
- USGS national arsenic model (Ayotte 2017): estimated share of 3,757 people on private wells in Mahnomen County above 10 ug/L of arsenic, from geology, well depth and land use. County estimates of domestic well users with arsenic above 10 ug/L from the USGS national logistic regression model (Ayotte, Medalie and Qi, 2017), with private well population from the USGS 2015 county water-use compilation (Dieter and others, 2018). Retrieved September 15, 2026.
- Minnesota Well Index: 247 well records in Mahnomen County, 223 domestic. Well construction records from the Minnesota Well Index (Minnesota Department of Health), non-public-supply wells. Only aggregates are shown; owner names and addresses are never stored. Retrieved September 15, 2026.
- MPCA regulated sites: 85 regulated sites located in Mahnomen County. Tank, leak, remediation, Superfund and landfill sites from the Minnesota Pollution Control Agency What's In My Neighborhood database. Retrieved September 15, 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.