Well water in Pennington County, South Dakota
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Testing recommended
tested well samples in Pennington County exceeded the EPA limit for arsenic (10 ug/L), based on public data from USGS Water Quality Portal.
4,438 test results across 14 contaminants from at least 434 wells, 1935 to 2026; nitrate has the most at 628. Data refreshed September 15, 2026.
Compiled by Nick at Well Water Nerd from public records. How these pages are built
An estimated 9,835 people in Pennington County get their drinking water from a private well, per USGS 2015 county water use. That is about 9% of residents.
Separately, the USGS national arsenic model estimates that 3% of the 9,835 people on private wells in Pennington County draw water above 10 ug/L (the model's range is 3% to 5%), from geology and well depth rather than local tests.
What individual samples found
Each row summarizes every public sample for that contaminant inside Pennington 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 |
|---|---|---|---|---|---|---|
| Arsenic 1974 to 2024 | 349 | 56% | 0 | 282 | 10 ug/L EPA limit | |
| Uranium 1954 to 2024 | 260 | 88% | 3.15 | 190 | 30 ug/L EPA limit | |
| Radium (226 + 228) 1979 to 2002 | 70 | 56% | 0.195 | 66 | 5 pCi/L EPA limit | |
| Nitrate 1935 to 2026 | 628 | 84% | 0.32 | 91.9 | 10 mg/L EPA limit | |
| Fluoride 1935 to 2024 | 399 | 97% | 0.4 | 21 | 4 mg/L EPA limit | |
| Lead 1974 to 2024 | 110 | 38% | 0 | 30 | 15 ug/L EPA limit | |
| Copper 1978 to 2024 | 327 | 44% | 0 | 0.52 | 1.3 mg/L EPA limit | |
| Chloride 1935 to 2024 | no limit | 624 | 87% | 8.4 | 3,080 | 250 mg/L nuisance level |
| Iron 1935 to 2024 | no limit | 551 | 68% | 20 | 93,000 | 300 ug/L nuisance level |
| Sodium 1935 to 2024 | no limit | 550 | 100% | 19.1 | 2,450 | 20 mg/L health guideline |
| Manganese 1938 to 2024 | no limit | 527 | 67% | 0 | 3,050 | 300 ug/L health guideline |
| Radon 1988 to 1992 | no limit | 39 | 74% | 190 | 5,800 | 2,000 pCi/L health guideline |
Sampled fewer than 10 times, too few to summarize: PFOS (2), PFOA (2).
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 | <1%405 samples | 12%179 samples | n/a | 2%44 samples |
| Fluoride | 1%342 samples | 0%35 samples | n/a | 0%22 samples |
| Arsenic | 3%283 samples | n/a | 89%36 samples | 21%24 samples |
| Copper | 0%266 samples | n/a | 0%35 samples | 0%24 samples |
| Uranium | 10%240 samples | n/a | n/a | 22%18 samples |
| Lead | 1%90 samples | n/a | n/a | 0%18 samples |
Nitrate above the limit in Pennington County fell from 12% of 179 samples in the 2000s to 2% of 44 in the 2020s.
Arsenic above the limit in Pennington County fell from 89% of 36 samples in the 2010s to 21% of 24 in the 2020s.
Fluoride, copper have 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 arsenic (14% of 349 samples), uranium (11% of 260 samples), and radium (226 + 228) (10% of 70 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 Pennington County
- 1Arsenic14% of 349 local samples were above the limit.
- 2Uranium11% of 260 local samples were above the limit.
- 3Radium (226 + 228)10% of 70 local samples were above the limit.
- 4Nitrate4% of 628 local samples were above the limit.
- 5Fluoride1% of 399 local samples were above the limit.
- 6Lead<1% of 110 local samples were above the limit.
- 7Coliform bacteriaRecommended for every private well, every year.
- 8Volatile organic compounds (VOCs)1,266 reported spills and releases on record locally.
Test your Pennington County well for arsenic, uranium and radium (226 + 228)
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 South Dakota: certified labs, state programs and prices.
Already have results back? Get your lab report read against the Pennington County numbers, $29. Every line explained, ranked by what matters, with the fix for each.
Wells in Pennington County
2,899 domestic wells in Pennington County are on record with the state since 1970. the typical well is 180 feet deep (one in ten goes past 640 feet).
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 DANR well completion reports and choose Water Well.
- It lists depth, aquifer, static water level and the driller.
South Dakota has required reports since 1986.
The rock under Pennington 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 South Dakota
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.
- Test a Private Well, South Dakota Department of Health
- Drinking Water Program - Laboratory Certification, South Dakota DANR
Contamination sources on record in Pennington County
South Dakota DANR tank facilities and spills records 1,266 reported spills and releases in Pennington County, among 1,731 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.
- 1,266
- reported spills and releasesMost spills are fuel; a few are solvents or chemicals that reach the water table.
- 343
- registered underground storage tank sitesRegistered tanks are regulated and inspected; they matter most when they are old or near a shallow well.
- 122
- other solid waste facilities
Treatment that fits the local profile
Arsenic
Point-of-use reverse osmosis; Adsorptive media (iron-based) whole-house; Anion exchange
Uranium
Point-of-use reverse osmosis; Anion exchange; Whole-house anion exchange
Radium (226 + 228)
Water softener (cation exchange); Point-of-use reverse osmosis
Nitrate
Point-of-use reverse osmosis; Anion exchange; Distillation
Fluoride
Point-of-use reverse osmosis; Activated alumina; Distillation
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 lead
Aquasana Claryum 3-Stage under-sink filter
under-sink or countertop, about $175
Certified to NSF/ANSI 53 to reduce 99% of lead and 99.7% of PFOA and PFOS at the tap. Not a fix for arsenic, nitrate or bacteria.
For lead
Acid neutralizing filter
whole-house, at the point of entry, about $1,200
Raises pH so plumbing stops leaching lead and copper.
Free, no obligation
Get on the list for a free in-home water test in Pennington County
No water treatment company serves Pennington 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 Pennington County, and you get an email naming it first.
Common questions
How deep are wells in Pennington County?
The typical domestic well in Pennington County is 180 feet deep, based on 2,899 wells reported to the state since 1970. One in ten is deeper than 640 feet.
Is there arsenic in well water in Pennington County?
Arsenic was detected in 56% of 349 public well samples in Pennington County, and 14% 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 Pennington County?
The median radon level across 39 public samples in Pennington County was 190 pCi/L, with a high of 5,800 pCi/L. New Hampshire recommends treatment above 2,000 pCi/L.
How often should I test a private well in Pennington 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 Pennington 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 South Dakota dataset as CSV, every county and town, with the sources named.
Sources
- USGS Water Quality Portal: 4,438 samples in Pennington 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 9,835 people on private wells in Pennington 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.
- South Dakota DANR well completion reports: 6,095 well records in Pennington County, 2,899 domestic. Well completion reports filed with the South Dakota Department of Agriculture and Natural Resources. Only aggregates are shown; owner names and addresses are never stored. Retrieved September 18, 2026.
- South Dakota DANR tank facilities and spills: 1,731 regulated sites located in Pennington County. Regulated tank facilities and spill reports from the South Dakota Department of Agriculture and Natural Resources. Retrieved September 18, 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.