Radon is worth checking in St. Lawrence County wells.

1 worth checking, 6 rare out of 7 health checks.

From 43 wells tested in St. Lawrence County since 2005; your own well needs its own test. How to read this

Tested wells over the limit St. LawrenceNew York

Radon7%3 of 42 Manganese5%2 of 43 Nitrate2%1 of 43 Uranium2%1 of 43 Arsenic0%0 of 43 Lead0%0 of 43 Fluoride0%0 of 43

GermsTest every year, whatever the chart says

Coliform bacteria20%8 of 41 E. coli12%5 of 41

StainsNot a health risk

Iron stains28%12 of 43

Rare: under 5%Worth checking: 5 to 15%Widespread: 15%+

Lab results: Water Quality Portal (USGS and EPA)

Show bacteria and iron

Who drinks from a well here

5 in 10 people 56,842 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)

LowMiddleHigh

Possible here. A home air test is inexpensive.

Radon zones: EPA map

Here's how St. Lawrence County compares with New York and the counties around it.

Each result puts St. Lawrence County next to the 5 counties that border it, on the chart's 0 to 50% scale.

This one is worth checking in St. Lawrence County.

Radon in water3 of 42 wells over

3 of 42 wells tested here from 2005 to 2020 were over 4,000 pCi/L, a level the EPA proposed, against under 1 in 50 across New York. Half the results were under 600 pCi/L, and the top 1 in 10 were 2,620 pCi/L or more. That's a bigger share than in 41 of the 45 other New York counties with 10 or more tested wells.

St. Lawrence and its neighbors

Hamilton12%

St. Lawrence7%

Herkimer4%

Franklin0%

Jefferson0%

Lewis0%

Radon guide

These 6 are rare in St. Lawrence County.

Manganese2 of 43 wells over

2 of 43 wells tested here from 2005 to 2020 were over the EPA health advisory of 0.3 mg/L, against about 1 in 7 across New York. Half the results were under 0.0085 mg/L, and the top 1 in 10 were 0.12 mg/L or more. That's a smaller share than in 30 of the 50 other New York counties with 10 or more tested wells, leaving out 1 county whose results are likely overstated.

St. Lawrence and its neighbors

Hamilton12%

St. Lawrence5%

Lewis5%

Herkimer4%

Franklin0%

Jefferson0%

Manganese guide

Nitrate1 of 43 wells over

1 of 43 wells tested here from 2005 to 2020 was over the EPA limit of 10 mg/L, against about 1 in 35 across New York. Half the results were under 0.06 mg/L, and the top 1 in 10 were 1.6 mg/L or more. That's a bigger share than in 43 of the 51 other New York counties with 10 or more tested wells.

St. Lawrence and its neighbors

St. Lawrence2%

Franklin0%

Hamilton0%

Herkimer0%

Jefferson0%

Lewis0%

Nitrate guide

Uranium1 of 43 wells over

1 of 43 wells tested here from 2005 to 2020 was over the EPA limit of 30 µg/L, against under 1 in 100 across New York. Half the results were under 0.47 µg/L, and the top 1 in 10 were 4.4 µg/L or more. That's a bigger share than in 44 of the 46 other New York counties with 10 or more tested wells.

St. Lawrence and its neighbors

Hamilton12%

Herkimer4%

St. Lawrence2%

Franklin0%

Jefferson0%

Lewis0%

Uranium guide

Arsenic0 of 43 wells over

None of the 43 wells tested here from 2005 to 2020 were over the EPA limit of 10 µg/L, against about 1 in 28 across New York. At least half the results were too low for the lab to measure, and the top 1 in 10 were 1.8 µg/L or more. St. Lawrence County had none, while 23 of the 49 other New York counties with 10 or more tested wells had at least one.

St. Lawrence and its neighbors

Franklin0%

Hamilton0%

Herkimer0%

Jefferson0%

Lewis0%

St. Lawrence0%

Arsenic guide

Lead0 of 43 wells over

None of the 43 wells tested here from 2005 to 2020 were over the EPA action level of 15 µg/L, against about 1 in 40 across New York. Half the results were under 0.14 µg/L, and the top 1 in 10 were 1.3 µg/L or more. St. Lawrence County had none, while 3 of the 51 other New York counties with 10 or more tested wells had at least one.

St. Lawrence and its neighbors

Franklin0%

Hamilton0%

Herkimer0%

Jefferson0%

Lewis0%

St. Lawrence0%

Lead guide

Fluoride0 of 43 wells over

None of the 43 wells tested here from 2005 to 2020 were over the EPA limit of 4 mg/L, against under 1 in 100 across New York. Half the results were under 0.28 mg/L, and the top 1 in 10 were 0.75 mg/L or more. St. Lawrence County had none, while 2 of the 51 other New York counties with 10 or more tested wells had at least one.

St. Lawrence and its neighbors

Franklin0%

Hamilton0%

Herkimer0%

Jefferson0%

Lewis0%

St. Lawrence0%

Coliform bacteria turned up in 8 of 41 tested St. Lawrence County wells, so test for it every year.

Coliform bacteria8 of 41 wells had it

About 2 in 10 wells tested here from 2005 to 2020 had coliform bacteria, against about 1 in 4 across New York.

St. Lawrence and its neighbors

Herkimer24%

Jefferson21%

St. Lawrence20%

Hamilton18%

Lewis14%

Franklin12%

Bacteria guide

E. coli5 of 41 wells had it

About 1 in 8 wells tested here from 2005 to 2020 had E. coli, against about 1 in 26 across New York.

St. Lawrence and its neighbors

Jefferson12%

St. Lawrence12%

Franklin0%

Hamilton0%

Herkimer0%

Lewis0%

E. coli means human or animal waste is getting in, so if a test of your St. Lawrence County well finds it, boil drinking water until the well is fixed.

Bacteria guide

Iron reached staining levels in 12 of 43 tested wells, and it isn't a health risk.

Iron stains12 of 43 wells had it

About 3 in 10 wells tested here from 2005 to 2020 had enough iron to stain (0.3 mg/L), against about 4 in 10 across New York.

St. Lawrence and its neighbors

St. Lawrence28%

Lewis27%

Herkimer22%

Jefferson20%

Franklin18%

Hamilton6%

Iron guide

About 3 in 10 of the 43 wells tested in St. Lawrence County have a test from 2020 or later.

13 wells had a test in the 2000s, 20 in the 2010s and 15 since 2020.

With 15 wells tested since 2020, age matters less here than who did the testing and why.

Most St. Lawrence 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 St. Lawrence County.

Bacteria
Nitrate
Radon in water
Arsenic

What New York offers well owners

Free testingThe Private Well PFAS Testing and Mitigation Rebate Pilot Program offers limited free PFAS testing and treatment rebates in Dutchess, Orange, Putnam, Suffolk, Ulster and Westchester counties. See the program
Certified labsNew York's list of certified labs
Well recordsNew York's well record search

Half the household wells here are shallower than 120 feet.

That comes from 2,836 household wells in New York's drilling records. Most wells of every kind here are 85 to 176 feet deep. Wells as deep as St. Lawrence 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 33 of the 56 other New York counties with enough drilling records.

Look up your own well's depth in New York'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 St. Lawrence County.

St. Lawrence County is in the EPA's middle radon zone. An indoor air test is cheap and tells you whether to look at your water. Radon guide

Between 2023 and 2025 the EPA had 5 town water systems in St. Lawrence County test for PFAS. 1 found some PFAS, all below the new limits. No well in St. Lawrence 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

Next door to St. Lawrence County

Jefferson

Elsewhere in New York

Orange Ulster Saratoga Oneida Oswego Rensselaer Steuben

All of New York

Questions people ask about well water in St. Lawrence County

Is well water in St. Lawrence County safe to drink?

3 of 42 wells tested in St. Lawrence County had radon in water over the limit, about 1 in 14. Across New York it's under 1 in 50. That's a bigger share than in 41 of the 45 other New York counties with 10 or more tested wells. So test your own well for radon in water before you count on it.

Can I get my well tested for free in St. Lawrence County?

The Private Well PFAS Testing and Mitigation Rebate Pilot Program offers limited free PFAS testing and treatment rebates in Dutchess, Orange, Putnam, Suffolk, Ulster and Westchester counties. If not, use a lab New York has certified for drinking water. Ask for bacteria, nitrate, radon in water and arsenic, the tests that matter most in St. Lawrence County.

How deep are wells in St. Lawrence County?

Half the household wells here are shallower than 120 feet. Typical household wells here are shallower than in 33 of the 56 other New York counties with enough drilling records.

How does St. Lawrence County compare with the counties around it?

For radon in water, the share of tested wells over the limit: 1 of the 5 neighboring counties with data had a higher share than St. Lawrence County, at 7%. Hamilton had the most, at 12%. Groundwater doesn't stop at county lines, so Hamilton's 12% is worth knowing about if you live near it.

How often should I test my well in St. Lawrence County?

In St. Lawrence County, 8 of 41 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.

By the Tested Water teamData from the USGS, EPA and Department of HealthUpdated November 8, 2026

If you buy something through our links, we may earn a commission. We'd recommend the same thing either way, and we'll tell you when a free option exists. How we make money

Where the St. Lawrence County numbers come from

People on wells: 56,842 in St. Lawrence County, from EPA estimates built on the 2020 Census (Murray et al.).
Lab tests: 485 well water samples from 43 wells in the Water Quality Portal, run by the USGS and EPA, 2005 to 2020.
Well depths: 2,836 New York drilling records for St. Lawrence County, gathered in the US Groundwater Well Database (Lin and others, 2024).
Neighboring counties: the 5 counties that share a border with St. Lawrence County, from the Census Bureau's county adjacency file.
PFAS: EPA tests of 5 town water systems in St. Lawrence County under the Fifth Unregulated Contaminant Monitoring Rule, 2023 to 2025.
Radon: St. Lawrence County is zone 2 on the EPA Map of Radon Zones.
State programs and links: Department of Health, checked November 1, 2026.

Download this county's data (CSV)How we read these numbers Report an error