Manganese and arsenic are widespread in Marion County wells.
2 widespread, 3 rare out of 5 health checks.
From 94 wells tested in Marion County since 2000; your own well needs its own test. How to read this
Not charted, because fewer than 10 wells were tested: fluoride (2).
Rare: under 5%Worth checking: 5 to 15%Widespread: 15%+
Lab results: Water Quality Portal (USGS and EPA)
Who drinks from a well here
1 in 4 people 85,562 people
Nobody else tests these wells. Only you do.
People on wells: EPA researchers' 2020 estimate
How deep wells go here
Middle depth: some shelter from the surface, not complete.
Well depths: US Groundwater Well Database
Radon risk (a gas from rock)
Less likely, but the EPA still says test your air.
Radon zones: EPA map
Here's how Marion County compares with Oregon and the counties around it.
Each result puts Marion County next to the 6 counties that border it, on the chart's 0 to 50% scale.
These 2 are widespread in Marion County wells.
Manganese36 of 77 wells over
Too few tested to show: Jefferson.
Arsenic13 of 77 wells over
Too few tested to show: Jefferson.
These 3 are rare in Marion County.
Lead4 of 86 wells over
Too few tested to show: Jefferson.
Nitrate2 of 90 wells over
Too few tested to show: Jefferson.
Uranium0 of 68 wells over
Too few tested to show: Jefferson.
Too few Marion County wells were tested for this one.
Fluoride2 wells tested
Coliform bacteria turned up in 20 of 49 tested Marion County wells, so test for it every year.
Coliform bacteria20 of 49 wells had it
Too few tested to show: Jefferson, Wasco.
E. coli6 of 51 wells had it
Too few tested to show: Jefferson, Wasco.
E. coli means human or animal waste is getting in, so if a test of your Marion County well finds it, boil drinking water until the well is fixed.
Iron reached staining levels in 43 of 76 tested wells, and it isn't a health risk.
Iron stains43 of 76 wells had it
Too few tested to show: Jefferson.
Marion County has 94 tested wells, and the busiest decade for testing was the 2010s.
Only 13 of the 94 wells have a test from 2020 or later, so a fresh test of your own well tells you more than any of these.
Most Marion 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 4 things to check in Marion County.
- Bacteria
- Nitrate
- Manganese
- Arsenic
What Oregon offers well owners
- Free testingWe didn't find a free program for all of Oregon. Oregon's private well page
- Certified labsOregon's list of certified labs
- Well recordsOregon's well record search
- New wellsUnder the Domestic Well Testing Act, sellers must test the well for arsenic, nitrate and total coliform bacteria during a real estate transaction and send the results to the buyer and OHA within 90 days.
Half the household wells here are shallower than 133 feet.
That comes from 19,378 household wells in Oregon's drilling records. Most wells of every kind here are 80 to 220 feet deep. Wells as deep as Marion County's are usually better protected from fertilizer and bacteria at the surface, but they can pick up more of what's in the rock, like arsenic and uranium. Typical household wells here are shallower than in 23 of the 35 other Oregon counties with enough drilling records.
Look up your own well's depth in Oregon'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 Marion County.
Marion County is in the EPA's lowest radon zone, so radon from well water is unlikely to be a problem. Radon guide
Between 2023 and 2025 the EPA had 11 town water systems in Marion County test for PFAS. 1 found some PFAS, all below the new limits. No well in Marion 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 Marion County
Is well water in Marion County safe to drink?
36 of 77 wells tested in Marion County had manganese over the limit, about 5 in 10. Across Oregon it's about 2 in 10. That's a bigger share than in 19 of the 25 other Oregon counties with 10 or more tested wells, leaving out 2 counties whose results are likely overstated. So test your own well for manganese before you count on it.
Where can I get my well tested in Marion County?
Use a lab Oregon has certified for drinking water. Oregon's list is linked above, in the box about testing. Ask for bacteria, nitrate, manganese and arsenic, the tests that matter most in Marion County.
How deep are wells in Marion County?
Half the household wells here are shallower than 133 feet. Typical household wells here are shallower than in 23 of the 35 other Oregon counties with enough drilling records.
How does Marion County compare with the counties around it?
For manganese, the share of tested wells over the limit: Marion County, at 47%, had a higher share than all 5 neighboring counties with data. Groundwater doesn't stop at county lines, so Yamhill's 46% is worth knowing about if you live near it.
How often should I test my well in Marion County?
In Marion County, 20 of 49 tested wells had coliform bacteria, so the CDC's advice matters here: 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 Marion County numbers come from
- People on wells: 85,562 in Marion County, from EPA estimates built on the 2020 Census (Murray et al.).
- Lab tests: 884 well water samples from 94 wells in the Water Quality Portal, run by the USGS and EPA, 2000 to 2026.
- Well depths: 19,378 Oregon drilling records for Marion County, gathered in the US Groundwater Well Database (Lin and others, 2024).
- Neighboring counties: the 6 counties that share a border with Marion County, from the Census Bureau's county adjacency file.
- PFAS: EPA tests of 11 town water systems in Marion County under the Fifth Unregulated Contaminant Monitoring Rule, 2023 to 2025.
- Radon: Marion County is zone 3 on the EPA Map of Radon Zones.
- State programs and links: Oregon Health Authority, checked November 1, 2026.