Well water in Mellette County, South Dakota

1in11

Testing recommended

tested well samples in Mellette County exceeded the EPA limit for nitrate (10 mg/L), based on public data from USGS Water Quality Portal.

600 test results across 9 contaminants from at least 98 wells, 1954 to 1996; nitrate has the most at 126. Data refreshed September 15, 2026.

Compiled by Nick at Well Water Nerd from public records. How these pages are built

An estimated 1,155 people in Mellette County get their drinking water from a private well, per USGS 2015 county water use. That is about 56% of residents.

Separately, the USGS national arsenic model estimates that <1% of the 1,155 people on private wells in Mellette County draw water above 10 ug/L, from geology and well depth rather than local tests.

What individual samples found

Each row summarizes every public sample for that contaminant inside Mellette 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
Nitrate 1954 to 1996	10%	126	82%	0.54	438	10 mg/L EPA limit
Fluoride 1954 to 1996	4%	97	92%	0.4	4.6	4 mg/L EPA limit
Arsenic 1974 to 1996	0%	23	70%	2	10	10 ug/L EPA limit
Lead 1976 to 1990	0%	15	27%	0	2	15 ug/L EPA limit
Chloride 1954 to 1996	no limit	110	100%	26	860	250 mg/L nuisance level
Sodium 1957 to 1996	no limit	107	100%	140	1,290	20 mg/L health guideline
Iron 1954 to 1996	no limit	63	92%	80	8,700	300 ug/L nuisance level
Manganese 1957 to 1996	no limit	58	84%	100	1,500	300 ug/L health guideline

Sampled fewer than 10 times, too few to summarize: Copper (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 address

What this means

The contaminants most often above their limit here are nitrate (10% of 126 samples) and fluoride (4% of 97 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 Mellette County

1
Nitrate
10% of 126 local samples were above the limit.
2
Fluoride
4% of 97 local samples were above the limit.
3
Coliform bacteria
Recommended for every private well, every year.
4
Copper
Detected in 100% of local samples.
5
Chloride
Detected in 100% of local samples.
6
Iron
Detected in 92% of local samples.
7
Manganese
Detected in 84% of local samples.
8
Volatile organic compounds (VOCs)
40 reported spills and releases on record locally.

Test your Mellette County well for nitrate, fluoride and coliform bacteria

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 $209 Already 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 Mellette County numbers, $29. Every line explained, ranked by what matters, with the fix for each.

Wells in Mellette County

80 domestic wells in Mellette County are on record with the state since 1971. the typical well is 163 feet deep (one in ten goes past 2,446 feet).

1970s

1980s

1990s

2000s

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 Mellette 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 Mellette County

South Dakota DANR tank facilities and spills records 40 reported spills and releases in Mellette County, among 60 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.

40: reported spills and releasesMost spills are fuel; a few are solvents or chemicals that reach the water table.
17: registered underground storage tank sitesRegistered tanks are regulated and inspected; they matter most when they are old or near a shallow well.
3: other solid waste facilities

Treatment that fits the local profile

Nitrate

Point-of-use reverse osmosis; Anion exchange; Distillation

Fluoride

Point-of-use reverse osmosis; Activated alumina; 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

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 nitrate

Under-sink reverse osmosis system

under-sink or countertop, about $300

Look for NSF/ANSI 58 certification listing the contaminant you need removed.

For nitrate

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 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

Get on the list for a free in-home water test in Mellette County

No water treatment company serves Mellette 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 Mellette County, and you get an email naming it first.

Common questions

How deep are wells in Mellette County?

The typical domestic well in Mellette County is 163 feet deep, based on 80 wells reported to the state since 1971. One in ten is deeper than 2,446 feet.

Is there arsenic in well water in Mellette County?

Arsenic was detected in 70% of 23 public well samples in Mellette County, and 0% 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 Mellette 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 Mellette 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: 600 samples in Mellette 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 1,155 people on private wells in Mellette 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: 222 well records in Mellette County, 80 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: 60 regulated sites located in Mellette 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.