Arsenic and manganese are widespread in Park County wells.
2 widespread, 1 worth checking, 2 rare out of 5 health checks.
From 22 wells tested in Park County since 2000; your own well needs its own test. How to read this
Not charted, because fewer than 10 wells were tested: uranium (9), radon (9).
Rare: under 5%Worth checking: 5 to 15%Widespread: 15%+
Lab results: Water Quality Portal (USGS and EPA)
Who drinks from a well here
5 in 10 people 14,935 people
Nobody else tests these wells. Only you do.
People on wells: EPA researchers' 2020 estimate
How deep wells go here
Shallow wells: watch for fertilizer and germs from above.
Well depths: US Groundwater Well Database
Radon risk (a gas from rock)
Likely here. Test your home's air first.
Radon zones: EPA map
Here's how Park County compares with Wyoming and the counties around it.
Each result puts Park County next to the 8 counties that border it, on the chart's 0 to 50% scale.
These 2 are widespread in Park County wells.
Arsenic4 of 14 wells over
* Likely overstated, so we don't rank it.
Too few tested to show: Big Horn, Hot Springs, Park, MT.
Manganese3 of 14 wells over
* Likely overstated, so we don't rank it.
Too few tested to show: Big Horn, Hot Springs, Park, MT.
This one is worth checking in Park County.
Fluoride2 of 14 wells over
Too few tested to show: Big Horn, Gallatin, MT, Hot Springs, Park, MT.
These 2 are rare in Park County.
Nitrate1 of 22 wells over
* Likely overstated, so we don't rank it.
Too few tested to show: Park, MT.
Lead0 of 14 wells over
Too few tested to show: Big Horn, Fremont, Gallatin, MT, Hot Springs, Park, MT.
Too few Park County wells were tested for these 2.
Uranium9 wells tested
Radon in water9 wells tested
Every well needs a bacteria test every year.
No bacteria tests from Park County wells are in the public data. Test every year anyway.
Iron reached staining levels in 5 of 14 tested wells, and it isn't a health risk.
Iron stains5 of 14 wells had it
Too few tested to show: Big Horn, Hot Springs, Park, MT.
Most of the 22 wells tested in Park County were last tested before 2010.
An old result shows the water as it was then, so treat these 22 wells as a starting point and test your own.
Most Park County wells in these records were tested for research or because someone suspected a problem, which can push the shares above what a typical home well would show (how we read the numbers).
One mail-in lab test covers the 5 things to check in Park County.
- Bacteria
- Nitrate
- Arsenic
- Manganese
- Fluoride
What Wyoming offers well owners
- Free testingWe didn't find a free program for all of Wyoming. Wyoming's private well page
- Certified labsWyoming's list of certified labs
- Well recordsWyoming's well record search
Half the household wells here are shallower than 57 feet.
That comes from 3,230 household wells in Wyoming's drilling records. Most wells of every kind here are 22 to 105 feet deep. Wells as shallow as Park County's pick up bacteria and nitrate from the surface more easily, so the yearly test matters even more here. Typical household wells here are shallower than in 20 of the 22 other Wyoming counties with enough drilling records.
Look up your own well's depth in Wyoming's well record search, or see how to find it.
Well depths: US Groundwater Well Database
Here's what we know about radon and PFAS in Park County.
Park County is in the EPA's highest radon zone. Radon from well water adds to the radon in your indoor air, so test your air first, and your water too if the air is high. Radon guide
Between 2023 and 2025 the EPA had 4 town water systems in Park County test for PFAS. None found any. No well in Park County has public PFAS results, so the town systems are the best clue to what's in the groundwater nearby. PFAS guide
Radon zones: EPA Map of Radon Zones. PFAS: EPA tests of town water systems, 2023 to 2025
Questions people ask about well water in Park County
Is well water in Park County safe to drink?
4 of 14 wells tested in Park County had arsenic over the limit, about 3 in 10. Across Wyoming it's about 1 in 18. That's the highest share among the 16 Wyoming counties with 10 or more tested wells. So test your own well for arsenic before you count on it.
Where can I get my well tested in Park County?
Use a lab Wyoming has certified for drinking water. Wyoming's list is linked above, in the box about testing. Ask for bacteria, nitrate, arsenic, manganese and fluoride, the tests that matter most in Park County.
How deep are wells in Park County?
Half the household wells here are shallower than 57 feet. Typical household wells here are shallower than in 20 of the 22 other Wyoming counties with enough drilling records.
How does Park County compare with the counties around it?
For arsenic, the share of tested wells over the limit: 1 of the 5 neighboring counties with data had a higher share than Park County, at 29%. Gallatin, MT had the most, at 52%. Groundwater doesn't stop at county lines, so Gallatin, MT's 52% is worth knowing about if you live near it.
How often should I test my well in Park County?
Park County has no public bacteria results for wells, so follow the CDC's advice: test for bacteria and nitrate every year, and right away after a flood, a repair, or any change in taste or smell.
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Where the Park County numbers come from
- People on wells: 14,935 in Park County, from EPA estimates built on the 2020 Census (Murray et al.).
- Lab tests: 144 well water samples from 22 wells in the Water Quality Portal, run by the USGS and EPA, 2000 to 2023.
- Well depths: 3,230 Wyoming drilling records for Park County, gathered in the US Groundwater Well Database (Lin and others, 2024).
- Neighboring counties: the 8 counties that share a border with Park County, from the Census Bureau's county adjacency file.
- PFAS: EPA tests of 4 town water systems in Park County under the Fifth Unregulated Contaminant Monitoring Rule, 2023 to 2025.
- Radon: Park County is zone 1 on the EPA Map of Radon Zones.
- State programs and links: Department of Environmental Quality (DEQ), Know Your Well program, checked November 1, 2026.