Radon in well water in York County, PA

Is radon in well water dangerous?

Radon in well water is mainly a breathing risk. Most of the risk comes from radon released into the air when the water is used for showering and other household purposes, and the EPA says the lung cancer risk from breathing radon in air is much larger than the stomach cancer risk from swallowing water with radon in it.

Based on a National Academy of Sciences report, the EPA estimates that radon in drinking water causes about 168 cancer deaths a year in the United States. Of those, 89 percent are lung cancers from radon released into indoor air and 11 percent are stomach cancers from drinking the water.

Soil gas is usually the bigger source. The EPA puts the share of indoor radon that comes from drinking water at about 1 to 2 percent, and its consumer guide calls radon from water a small risk in most homes compared with radon from the soil. Where the water itself runs high, southern York County is the clearest case in the USGS data.

Sources: EPA, A Consumer's Guide to Radon Reduction (2016); EPA, basic information about radon in drinking water (archived page, 2014).

How common is radon in well water in York County?

Radon in well water is common across Pennsylvania, and parts of southern York County sit on the rock with the highest median in the USGS study. Wells on the Peters Creek Schist, a rock unit under parts of southern York, Lancaster and Chester counties, had a median of 4,300 pCi/L, the highest of the 16 rock units studied.

All 51 samples from that schist exceeded 300 pCi/L, and 55 percent reached 4,000 or more. The same area had the highest indoor air median of the 16 units, 6.4 pCi/L, and the USGS estimates that 81 percent of the people living on it draw their water from their own wells. Statewide, 87 percent of the 1,041 samples had 300 pCi/L or more and 14 percent had 4,000 or more.

Source: USGS, Evaluation of Radon Occurrence in Groundwater from 16 Geologic Units in Pennsylvania, 1986 to 2015 (Scientific Investigations Report 2017-5018).

The USGS attaches a warning to its own numbers: the data are not meant to predict the radon in an individual well, because levels vary widely even within one rock unit. Only a test of your own water shows what your well carries, and the next sections cover how the radon gets there and when to test.

How does radon get into well water?

Radon gets into well water from the rock around the well. Uranium in the bedrock decays to radon, groundwater moving through the rock dissolves the gas, and the USGS found the highest concentrations in the schists, gneisses and quartzites of the Piedmont, the region the Peters Creek Schist belongs to.

Surface water is a different story. The EPA says radon in water is not usually a problem when the source is surface water, and the DEP notes that many public supplies draw on surface water, which tends to have lower radon. Private wells are not regulated under the federal Safe Drinking Water Act, so testing a well is up to its owner.

Radon leaves the water when it is heated or agitated, and the USGS names showering, washing clothes and washing dishes as the household routes into indoor air. That is why the question of when to test starts with the air.

When should you test your well water for radon?

Test your well water for radon when an air test in the house comes back above 4 pCi/L. The Pennsylvania DEP recommends a water test for any home with that result that is served by a private well or a community well.

That trigger is common in York County. In the DEP record of 98,845 York County air tests, 52.5 percent were at or above 4 pCi/L, so many well owners who test the air will meet the DEP's condition for testing the water too.

The EPA suggests that well owners who are concerned test both the air and the water, so the results show which source needs treatment. The page on testing for radon in York County covers the air test, and the water test works differently.

How do you test well water for radon?

Well water is tested for radon by a certified laboratory. The DEP says a radon water test can be requested from a certified lab, and its 2014 fact sheet put the cost at about $25 to $50. The EPA notes that the devices and procedures differ from those for an air test, so an air test kit cannot measure water.

Radon decays by half in 3.8 days, so a sample is collected as the lab instructs and returned without delay. The result comes back in pCi/L, like an air result, but water numbers run far higher, which is why the next section translates them.

What level of radon in well water is too high?

No legal limit applies to radon in a private well. The DEP says private wells are not regulated under the federal Safe Drinking Water Act, and the EPA's proposed limit of 300 pCi/L for public water has not been adopted. The same proposal included an alternative limit of 4,000 pCi/L for states with an approved indoor radon program, Pennsylvania among them.

The DEP's rule of thumb turns a water result into its effect on the air: every 10,000 pCi/L of radon in the water adds about 1 pCi/L to the air of the house.

Source: PA DEP, Radon in Water (fact sheet 2940-FS-DEP4429, 2014).

On the Peters Creek Schist, the USGS estimates that well water adds 0.2 to 0.9 pCi/L to indoor air, against a York County basement average of 11.79 pCi/L in the DEP record. In most York County houses on a well, the soil under the floor still decides whether the air needs a radon mitigation system, and the water result decides whether the water needs treatment of its own. The DEP adds that the proposed public water limit, if adopted, may give private well owners useful guidance.

How do you remove radon from well water?

Radon is removed from well water by a whole-house system where the water enters the house. Aeration mixes the water with air and vents the radon outdoors, while granular activated carbon holds the radon in a bed of carbon.

Sources: EPA, A Consumer's Guide to Radon Reduction (2016) for reduction, use and upkeep; DEP fact sheet for carbon replacement.

A filter at the kitchen sink is not an option for radon. The DEP says treating water at the tap would not reduce the radon that enters the home, and the EPA says point-of-use devices treat only a small share of the water. The EPA suggests discussing aeration against carbon with the state radon office or a water treatment professional; the DEP Radon Division is on 800-237-2366.

How much does it cost to remove radon from well water?

Removing radon from well water with aeration cost $5,279 to $7,750 in the five Pennsylvania installations the DEP recorded from 2019 to 2023, with a median of $5,470. The three carbon systems in the same register, from 2015 to 2018, cost $925 to $2,670.

Source: PA DEP radon mitigation dataset on the PA Open Data Portal, retrieved 2 October 2026. The register lists nine water treatment systems statewide since 1987 and none in York County, so these are Pennsylvania examples rather than York County prices.

The DEP's own fact sheet, from 2014, put aeration at about $3,000 to $4,000 and charcoal systems at about $1,000 to $1,500. Penn State Extension describes aeration as one of the most expensive home water treatments, at several thousand dollars. Carbon costs less to buy, but the EPA notes that the filters collect radioactivity and may need special disposal, which belongs in the comparison.

A quote should name the system, where the radon vents, the maintenance schedule and whether a follow-up water test is included. With no York County installations in the register, a local quote is the only York County price. What an air system costs in the county is on the page about radon mitigation cost in York County.

Common questions about radon in well water