Union County Well Water Testing
Private-well guidance for Union County, South Dakota: USGS area-risk estimates for arsenic and nitrate, a recommended test panel, and how to get your own well tested at a South Dakota-certified lab.
Union County groundwater risk (area estimates)
These are modeled USGS estimates for the county area — not a measurement of your specific well.
Arsenic
area estimate4%
modeled chance a well in this area exceeds 10 µg/L (the EPA limit).
10% chance of exceeding 5 µg/L.
Most-probable concentration category: <=5 ug/L.
Nitrate
area estimate1.99 mg/L
predicted nitrate (as N) for domestic-supply depth.
This estimate is below the 10 mg/L EPA limit, but individual wells can still exceed it.
Private wells
area estimate2,952
people on private wells in Union County.
Roughly 1,181 households, estimated from the USGS modeled domestic-supply population.
Area context
Additional state-only or optional layers for Union County, shown where the data exists.
Uranium
area estimateA state-only uranium model is not available for South Dakota. See observed samples and test your own well to learn its uranium level.
Radon
area estimateA state-only radon model is not available for South Dakota. See observed samples and test your own well to learn its radon level.
Agricultural land use
area contextAbout 74% of the Union County area is row-crop farmland (USDA Cropland Data Layer). Intensively farmed row-crop land raises the likelihood of elevated nitrate in nearby groundwater, so it is a reason to include nitrate in your test panel. This is land-use context for the county area — not a measurement of nitrate in any well.
These figures are USGS area estimates: statistical groundwater models describing how likely elevated contaminant levels are across a county. They are not designed to predict the concentration in any single well. Only testing your own well reveals its water quality.
Recommended test panel for Union County
- coliform
- nitrate
Coliform bacteria is recommended for every private well as the universal baseline test. Nitrate is recommended because about 74% of this county area is row-crop land (USDA CDL), a land-use predictor of elevated groundwater nitrate — this is area context, not a measured concentration. The federal loan minimum (FHA, VA, USDA) tests for coliform, nitrate, nitrite, lead.
Federal FHA, VA, and USDA home loans require testing for coliform, nitrate, nitrite, lead at the point of a federally-backed loan. See the program-specific rules: FHA well test, VA well test, USDA well test.
Already have lab results? Interpret your well water test results to see how your own numbers compare to EPA limits.
How Union County compares across South Dakota
Where Union County's modeled area estimates sit relative to the other South Dakota counties in our analysis.
- Arsenicabove the South Dakota median
Union County: 4% · South Dakota median: 4% · flagged in 3 of 66 counties.
See all South Dakota arsenic data → - Nitrateabove the South Dakota median
Union County: 1.99 mg/L · South Dakota median: 0.33 mg/L · flagged in 0 of 66 counties.
See all South Dakota nitrate data →
Municipal (public) water in Union County
Most Union County residents are served by a public water system, not a private well. If that's you, open your city's tap-water quality report:
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Volatile Organic Compounds (VOC) Test
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Find a state-certified lab
Test your Union County well through a lab certified by the South Dakota Department of Agriculture & Natural Resources — find one in the official directory (Website with links to certified laboratory information).
Recognize & research well-water problems
Notice a problem? Diagnose it by symptom
Learn about these contaminants in drinking water
Data sources
Union County's estimates are modeled from public federal datasets. See the data & methodology for how we build, source, and validate them.
- USGS arsenic probability-of-exceedance model
- USGS nitrate predicted concentration, domestic-supply depth
- USGS domestic (private) well population density
- USDA NASS Cropland Data Layer (CDL) 30m
- EPA/USGS Water Quality Portal (waterqualitydata.us)
- US Census TIGER/Line county polygons
By TapWaterData Editorial · Last updated June 26, 2026.
Union County well water FAQ
How do I test my well water in Union County?
Order a sample kit covering the recommended panel for Union County (coliform, nitrate), then send it to a South Dakota-certified drinking-water laboratory. Certified labs use EPA-approved methods, so the results are defensible for a federally-backed home loan. You can also use a mail-in test kit for a convenient EPA-certified analysis.
What does the USGS arsenic estimate mean for my well?
It is an area estimate, not a prediction for your specific well. The USGS model describes how likely elevated arsenic is across Union County as a whole; an individual well in the county can be much higher or much lower. Only testing your own well reveals its actual arsenic level.
How often should a private well be tested?
The CDC recommends testing private wells at least once a year for total coliform bacteria and nitrate, and more often if you notice a change in taste, color, or odor, or after flooding or nearby construction.
Does South Dakota require well testing?
Federal FHA, VA, and USDA home-loan programs require a private-well water test at the point of a federally-backed loan. A state sale, rental, or recurring testing mandate was not independently verified for this state — consult your state's program.
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