Well water in Shoshone County, Idaho
In Shoshone County, 2% of 43 tested well samples exceeded the EPA limit for arsenic (10 ug/L), based on public data from Idaho statewide ground water quality monitoring (IDWR EDMS) and USGS Water Quality Portal.
48 individual samples from 13 wells, 1952 to 2023. Data refreshed September 9, 2026.
What individual samples found
Each row summarizes every public sample for that contaminant inside Shoshone 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 | |
|---|---|---|---|---|---|---|---|
| Arsenic 1990 to 2023 | 43 | 37% | 2% | 0 | 10.4 | 10 ug/L EPA limit | |
| Fluoride 1952 to 2023 | 45 | 44% | 0% | 0 | 1.05 | 4 mg/L EPA limit | |
| Nitrate 1990 to 2023 | 43 | 72% | 0% | 0.074 | 0.6 | 10 mg/L EPA limit | |
| Nitrite 1992 to 2011 | 32 | 6% | 0% | 0 | 0.004 | 1 mg/L EPA limit | |
| Copper 1990 to 2018 | 29 | 45% | 0% | 0 | 0.012 | 1.3 mg/L EPA limit | |
| E. coli 1990 to 2008 | 29 | 0% | 0% | 0 | 0 | 0 MPN/100mL EPA limit | |
| Uranium 2002 to 2023 | 17 | 18% | 0% | 0 | 0 | 30 ug/L EPA limit | |
| Lead 1990 to 2002 | 17 | 24% | 0% | 0 | 1 | 15 ug/L EPA limit | |
| Sodium 1978 to 2023 | 48 | 100% | no limit | 4.05 | 48 | 20 mg/L health guideline | |
| Chloride 1990 to 2023 | 47 | 91% | no limit | 1.35 | 13.9 | 250 mg/L nuisance level | |
| Iron 1990 to 2023 | 44 | 82% | no limit | 23.5 | 639 | 300 ug/L nuisance level | |
| Manganese 1990 to 2023 | 44 | 75% | no limit | 3.3 | 150 | 300 ug/L health guideline |
Sampled fewer than 10 times, too few to summarize: Radon (4).
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What this means
The contaminants most often above their limit here are arsenic (2% of 43 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 Shoshone County
- Arsenic2% of 43 local samples were above the limit.
- Coliform bacteriaRecommended for every private well, every year.
- RadonMedian local reading is 1,010 pCi/L.
- NitrateRecommended for every private well, especially near farms or septic systems.
- ChlorideDetected in 91% of local samples.
- IronDetected in 82% of local samples.
- ManganeseDetected in 75% of local samples.
Treatment that fits the local profile
- Arsenic
- Point-of-use reverse osmosis; Adsorptive media (iron-based) whole-house; Anion exchange
- Chloride
- Point-of-use reverse osmosis; Distillation
- Iron
- Oxidizing filter whole-house; Water softener (low levels); Aeration plus filtration
- Manganese
- Oxidizing filter (greensand, birm) whole-house; Water softener (low levels); Point-of-use reverse osmosis
Get your Shoshone 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 Shoshone County.
Common questions
Is there arsenic in well water in Shoshone County?
Arsenic was detected in 37% of 43 public well samples in Shoshone County, and 2% 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 Shoshone County?
The median radon level across 4 public samples in Shoshone County was 1,010 pCi/L, with a high of 1,300 pCi/L. New Hampshire recommends treatment above 2,000 pCi/L.
How often should I test a private well in Shoshone 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): 427 samples in Shoshone 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: 15 samples in Shoshone 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.