Well water in Fremont County, Wyoming
In Fremont County, 4% of 451 tested well samples exceeded the EPA limit for nitrate (10 mg/L), based on public data from USGS Water Quality Portal.
The strongest signal is uranium: 9% of 23 local samples were above the limit, too few samples to carry the headline but first on the test list below.
1,818 test results across 13 contaminants from at least 288 wells, 1945 to 2020; nitrate has the most at 451. Data refreshed September 15, 2026.
Compiled by Nick at Well Water Nerd from public records. How these pages are built
An estimated 11,845 people in Fremont County get their drinking water from a private well, per USGS 2015 county water use. That is about 29% of residents.
Separately, the USGS national arsenic model estimates that 12% of the 11,845 people on private wells in Fremont County draw water above 10 ug/L (the model's range is 10% to 15%), from geology and well depth rather than local tests.
What individual samples found
Each row summarizes every public sample for that contaminant inside Fremont 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 |
|---|---|---|---|---|---|---|
| Uranium 1984 to 2016 | 23 | 70% | 1.48 | 1,730 | 30 ug/L EPA limit | |
| Nitrate 1945 to 2020 | 451 | 75% | 0.3 | 281 | 10 mg/L EPA limit | |
| Fluoride 1945 to 2016 | 310 | 98% | 0.8 | 9.3 | 4 mg/L EPA limit | |
| Arsenic 1984 to 2016 | 33 | 67% | 0.48 | 5 | 10 ug/L EPA limit | |
| Lead 1984 to 2012 | 27 | 15% | 0 | 2 | 15 ug/L EPA limit | |
| Copper 1984 to 2012 | 26 | 81% | 0.003 | 0.072 | 1.3 mg/L EPA limit | |
| Radium (226 + 228) 1984 to 2012 | 11 | 36% | 0 | 0.23 | 5 pCi/L EPA limit | |
| E. coli 2001 | 10 | 0% | 0 | 0 | 0 MPN/100mL EPA limit | |
| Sodium 1945 to 2016 | no limit | 328 | 100% | 175 | 4,320 | 20 mg/L health guideline |
| Chloride 1945 to 2016 | no limit | 318 | 99% | 15 | 2,000 | 250 mg/L nuisance level |
| Iron 1945 to 2016 | no limit | 187 | 89% | 100 | 19,000 | 300 ug/L nuisance level |
| Manganese 1957 to 2016 | no limit | 83 | 93% | 43.8 | 2,020 | 300 ug/L health guideline |
| Radon 2001 to 2012 | no limit | 11 | 100% | 1,390 | 4,370 | 2,000 pCi/L health guideline |
Over time
Share of samples above the limit by period. A cell needs ten samples to show; a comparison needs twenty in each period. Later periods sample fewer wells, and often the ones already known to have a problem.
| Contaminant | before 2000 | 2000s | 2010s | 2020s |
|---|---|---|---|---|
| Nitrate | 3%407 samples | 0%20 samples | 25%16 samples | n/a |
| Fluoride | <1%296 samples | 0%10 samples | n/a | n/a |
| Arsenic | 0%19 samples | 0%10 samples | n/a | n/a |
| Lead | 0%15 samples | 0%10 samples | n/a | n/a |
| Copper | 0%14 samples | 0%10 samples | n/a | n/a |
Nitrate has held within a few points between the two most recent periods with enough samples.
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
The contaminants most often above their limit here are uranium (9% of 23 samples), nitrate (4% of 451 samples), and fluoride (<1% of 310 samples). A well next door can differ sharply from yours because bedrock fractures, well depth and plumbing all matter, so these rates describe the area, not your tap.
Chloride, Iron, and Manganese are widespread in local groundwater. They are mainly a staining and taste problem, but high manganese also carries a health advisory for infants.
What to test for in Fremont County
- 1Uranium9% of 23 local samples were above the limit.
- 2Nitrate4% of 451 local samples were above the limit.
- 3Fluoride<1% of 310 local samples were above the limit.
- 4Coliform bacteriaRecommended for every private well, every year.
- 5RadonMedian local reading is 1,390 pCi/L.
- 6ChlorideDetected in 99% of local samples.
- 7ManganeseDetected in 93% of local samples.
Test your Fremont County well for uranium, nitrate and fluoride
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 Wyoming: certified labs, state programs and prices.
Already have results back? Get your lab report read against the Fremont County numbers, $29. Every line explained, ranked by what matters, with the fix for each.
The rock under Fremont 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 Wyoming
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.
- Know Your Well, Wyoming DEQ
- Certified Drinking Water Laboratories for Systems in Wyoming (EPA Region 8), EPA Region 8
Treatment that fits the local profile
Uranium
Point-of-use reverse osmosis; Anion exchange; Whole-house anion exchange
Nitrate
Point-of-use reverse osmosis; Anion exchange; 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
Iron
Oxidizing filter whole-house; Water softener (low levels); Aeration plus filtration
Systems we would look at first
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For uranium
Under-sink reverse osmosis system
under-sink or countertop, about $300
Look for NSF/ANSI 58 certification listing the contaminant you need removed.
For uranium
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 nitrate
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 iron
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 Fremont County
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Common questions
Is there arsenic in well water in Fremont County?
Arsenic was detected in 67% of 33 public well samples in Fremont 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 Fremont County?
The median radon level across 11 public samples in Fremont County was 1,390 pCi/L, with a high of 4,370 pCi/L. New Hampshire recommends treatment above 2,000 pCi/L.
How often should I test a private well in Fremont 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.
Counties near Fremont 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 Wyoming dataset as CSV, every county and town, with the sources named.
Sources
- USGS Water Quality Portal: 1,818 samples in Fremont 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.
- USGS national arsenic model (Ayotte 2017): estimated share of 11,845 people on private wells in Fremont 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.
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.