Well water in Fremont County, Idaho
In Fremont County, 28% of 65 tested well samples exceeded the EPA limit for total coliform (0 MPN/100mL), based on public data from Idaho statewide ground water quality monitoring (IDWR EDMS) and USGS Water Quality Portal.
313 individual samples from 211 wells, 1957 to 2025. Data refreshed September 9, 2026.
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 | Samples | Detected | Above limit | Median | Highest | Limit | |
|---|---|---|---|---|---|---|---|
| Total coliform 2009 to 2023 | 65 | 28% | 28% | 0 | 201 | 0 MPN/100mL EPA limit | |
| Nitrate 1976 to 2025 | 202 | 94% | 8% | 1.62 | 42.6 | 10 mg/L EPA limit | |
| E. coli 1991 to 2008 | 313 | 3% | 3% | 0 | 200 | 0 MPN/100mL EPA limit | |
| Arsenic 1991 to 2025 | 190 | 59% | <1% | 0.5 | 15 | 10 ug/L EPA limit | |
| Fluoride 1975 to 2025 | 225 | 94% | <1% | 0.645 | 6.98 | 4 mg/L EPA limit | |
| Nitrite 1991 to 2023 | 145 | 5% | 0% | 0 | 0.774 | 1 mg/L EPA limit | |
| Copper 1991 to 2020 | 117 | 66% | 0% | 0.002 | 0.15 | 1.3 mg/L EPA limit | |
| Lead 1991 to 2005 | 62 | 16% | 0% | 0 | 2.3 | 15 ug/L EPA limit | |
| Uranium 1957 to 2025 | 55 | 56% | 0% | 0.168 | 9.7 | 30 ug/L EPA limit | |
| Chloride 1991 to 2025 | 248 | 100% | no limit | 5.97 | 304 | 250 mg/L nuisance level | |
| Sodium 1991 to 2025 | 239 | 100% | no limit | 11 | 58 | 20 mg/L health guideline | |
| Iron 1991 to 2025 | 173 | 49% | no limit | 0 | 16,000 | 300 ug/L nuisance level | |
| Manganese 1991 to 2025 | 172 | 37% | no limit | 0 | 4,600 | 300 ug/L health guideline | |
| Radon 1991 to 1995 | 21 | 100% | no limit | 780 | 2,980 | 2,000 pCi/L health guideline |
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What this means
The contaminants most often above their limit here are total coliform (28% of 65 samples), nitrate (8% of 202 samples), and e. coli (3% of 313 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 is widespread in local groundwater. It is mainly a staining and taste problem, but high manganese also carries a health advisory for infants.
What to test for in Fremont County
- Total coliform28% of 65 local samples were above the limit.
- Nitrate8% of 202 local samples were above the limit.
- E. coli3% of 313 local samples were above the limit.
- Arsenic<1% of 190 local samples were above the limit.
- Fluoride<1% of 225 local samples were above the limit.
- RadonMedian local reading is 780 pCi/L.
- ChlorideDetected in 100% of local samples.
Treatment that fits the local profile
- Total coliform
- Inspect and repair the well cap and casing, then shock chlorinate and retest; UV disinfection whole-house; Chlorination system
- 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
- Arsenic
- Point-of-use reverse osmosis; Adsorptive media (iron-based) whole-house; Anion exchange
- Fluoride
- Point-of-use reverse osmosis; Activated alumina; Distillation
Get your Fremont County water tested at home
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Common questions
Is there arsenic in well water in Fremont County?
Arsenic was detected in 59% of 190 public well samples in Fremont County, and <1% 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 21 public samples in Fremont County was 780 pCi/L, with a high of 2,980 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.
Sources
- Idaho statewide ground water quality monitoring (IDWR EDMS): 1,968 samples in Fremont County. Ground water quality results from the Idaho Department of Water Resources statewide monitoring program and partner agencies (ISDA, IDEQ, INL), EDMS bulk download. Retrieved September 9, 2026.
- USGS Water Quality Portal: 259 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.
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.