Radon in York County: why levels run high, and radon in well water

A third of York County homes fail the test. The rock, the houses and the wells that explain it, and what to do about radon in your water.

York County is one of the places in Pennsylvania where the question is less whether you have radon than how much. This guide explains why, and covers the separate problem of radon in well water that the standard slab system does not touch.

The numbers

Pennsylvania as a whole has about 40 percent of homes over the EPA action level of 4.0 pCi/L, one of the highest shares in the country. York County's share of tested homes over 4.0 is close to a third, and the average basement reading in the county is well above the action level. The EPA maps York, Lancaster, Adams, Cumberland and Dauphin Counties as Zone 1, its highest-potential band.

The rock

• The Piedmont carbonate belt. Limestone and dolomite under York city, the Codorus valley and the eastern townships. Limestone is porous and fractured, and radon moves through it easily.
• Peach Bottom slate. The slate belt across southern York County around Delta, Peach Bottom and the townships toward Shrewsbury and Glen Rock. Slate and the associated schist carry more uranium than average and produce some of the county's highest readings.
• Triassic shale and sandstone. The Gettysburg basin under the northern and western townships, Dover included. Moderate on average with local hot spots.
• The Reading Prong. Not in York County; the extreme readings from the Lehigh Valley and Berks County that make the news come from there. York's problem is broader and less spectacular: a lot of houses moderately high, rather than a few extremely high.

The houses

Geology sets the supply; the house sets how much gets in. Older borough houses on stone and block foundations leak soil gas through the walls. Newer subdivisions on tight, well-insulated foundations trap what comes through the slab. Finished basements put people in the room with the highest concentration. Forced-air furnaces in the basement pull soil gas in as they run. None of this can be judged from the street, which is why the only way to know is to test.

Radon in well water

About a fifth of York County households are on private wells, mostly in the rural southern and northern townships. Groundwater in the same rock carries dissolved radon, which is released into the air when water is run for showers, laundry and dishwashing. The rule of thumb is that 10,000 pCi/L in water adds about 1 pCi/L to indoor air. Water radon is a smaller contributor than soil gas in most houses, but in a rural house with a high water number it can keep the air over 4.0 even after a good slab system is installed.

• Testing. A water sample to a lab, $30 to $100. Do it if you are on a well and your air test is high or your slab system did not get you under 4.0.
• Treatment. Aeration systems strip the radon from the water and vent it outdoors, $3,000 to $6,000, and are the right choice above about 5,000 pCi/L. Granular activated carbon (GAC) tanks absorb it, $1,000 to $2,500, and suit lower levels but concentrate radioactivity in the carbon over time.
• Who does it. Water treatment companies and some mitigators; see radon in well water. Air mitigation and water mitigation are different jobs and usually different contractors.

What to do

Test the air first, in winter. If it is over 4.0, call a DEP-certified mitigator from the directory. If you are on a well and the air result is stubborn, test the water. And whatever the result, re-test every two years; the rock is not going anywhere.

Last updated 2026-09-28. General information for the York area, not professional advice; confirm specifics with a qualified contractor or your insurer.