Well water in Marshall County, South Dakota
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Testing strongly recommended
tested well samples in Marshall County exceeded the EPA limit for fluoride (4 mg/L), based on public data from USGS Water Quality Portal.
1,800 test results across 13 contaminants from at least 353 wells, 1938 to 2024; chloride has the most at 452. Data refreshed September 3, 2026.
Compiled by Nick at Well Water Nerd from public records. How these pages are built
What individual samples found
Each row summarizes every public sample for that contaminant inside Marshall 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 |
|---|---|---|---|---|---|---|
| Fluoride 1938 to 2024 | 138 | 100% | 0.4 | 9.3 | 4 mg/L EPA limit | |
| Uranium 1978 to 2024 | 91 | 74% | 0.6 | 78 | 30 ug/L EPA limit | |
| Nitrate 1953 to 2024 | 172 | 85% | 1.04 | 770 | 10 mg/L EPA limit | |
| Arsenic 1970 to 2024 | 100 | 48% | 0 | 14 | 10 ug/L EPA limit | |
| Copper 1970 to 2024 | 96 | 36% | 0 | 0.31 | 1.3 mg/L EPA limit | |
| Lead 1970 to 2024 | 11 | 64% | 0 | 0 | 15 ug/L EPA limit | |
| Chloride 1938 to 2024 | no limit | 452 | 97% | 38 | 2,640 | 250 mg/L nuisance level |
| Sodium 1953 to 2024 | no limit | 273 | 100% | 200 | 2,600 | 20 mg/L health guideline |
| Iron 1938 to 2024 | no limit | 262 | 76% | 160 | 16,600 | 300 ug/L nuisance level |
| Manganese 1953 to 2024 | no limit | 200 | 87% | 40 | 2,980 | 300 ug/L health guideline |
Sampled fewer than 10 times, too few to summarize: Radium (226 + 228) (3), E. coli (1), Radon (1).
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 fluoride (31% of 138 samples), uranium (7% of 91 samples), and nitrate (6% of 172 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 Marshall County
- 1Fluoride31% of 138 local samples were above the limit.
- 2Uranium7% of 91 local samples were above the limit.
- 3Nitrate6% of 172 local samples were above the limit.
- 4Arsenic1% of 100 local samples were above the limit.
- 5Coliform bacteriaRecommended for every private well, every year.
- 6RadonMedian local reading is 239 pCi/L.
- 7ChlorideDetected in 97% of local samples.
- 8Volatile organic compounds (VOCs)147 reported spills and releases on record locally.
Test your Marshall County well for fluoride, uranium and nitrate
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 Marshall County numbers, $29. Every line explained, ranked by what matters, with the fix for each.
Wells in Marshall County
589 domestic wells in Marshall County are on record with the state since 1970. the typical well is 692 feet deep (one in ten goes past 1,053 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 Marshall 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 Marshall County
South Dakota DANR tank facilities and spills records 147 reported spills and releases in Marshall County, among 198 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.
- 147
- reported spills and releasesMost spills are fuel; a few are solvents or chemicals that reach the water table.
- 25
- registered underground storage tank sitesRegistered tanks are regulated and inspected; they matter most when they are old or near a shallow well.
- 26
- other solid waste facilities
Treatment that fits the local profile
Fluoride
Point-of-use reverse osmosis; Activated alumina; Distillation
Uranium
Point-of-use reverse osmosis; Anion exchange; Whole-house anion exchange
Nitrate
Point-of-use reverse osmosis; Anion exchange; Distillation
Arsenic
Point-of-use reverse osmosis; Adsorptive media (iron-based) whole-house; Anion exchange
Chloride
Point-of-use reverse osmosis; 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 fluoride
Under-sink reverse osmosis system
under-sink or countertop, about $300
Look for NSF/ANSI 58 certification listing the contaminant you need removed.
For fluoride
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 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 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
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No water treatment company serves Marshall 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 Marshall County, and you get an email naming it first.
Common questions
How deep are wells in Marshall County?
The typical domestic well in Marshall County is 692 feet deep, based on 589 wells reported to the state since 1970. One in ten is deeper than 1,053 feet.
Is there arsenic in well water in Marshall County?
Arsenic was detected in 48% of 100 public well samples in Marshall 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 often should I test a private well in Marshall 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 Marshall 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: 1,800 samples in Marshall 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.
- South Dakota DANR well completion reports: 958 well records in Marshall County, 589 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: 198 regulated sites located in Marshall 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.