What Do Radon Levels Look Like by York ZIP Code?

Quick Answer: York County is EPA Radon Zone 1, the highest-risk category, and PA DEP’s test data shows basement averages around 10 pCi/L in both the York city ZIPs and Hanover, more than double the 4.0 pCi/L action level. But ZIP code averages don’t predict your house. Two homes on the same street can test 2 and 25. The only number that matters is yours.

People search this question hoping for a map that says “your neighborhood is fine.” I understand the impulse. I’d want the same thing. But after years of watching radon crews work basements from Dillsburg down to the Maryland line, I can tell you the map doesn’t exist, and if it did, it wouldn’t tell you what you want to know. If your ZIP is 17401, 17403 or 17404, the radon mitigation York PA page goes deeper on the city numbers and what to do about them.

The numbers DEP actually has

Pennsylvania DEP keeps a public Radon Test Data by ZIP Code tool, built from short-term closed-house tests reported by certified testers and labs going back to 1990. It’s the only official local dataset, and it’s worth looking at before you look at anything else.

For the York city ZIPs (17401, 17403, 17404), DEP’s data through the end of 2025 shows a basement average of about 9.85 pCi/L across more than 10,000 tests, and a first-floor average around 6.7. The highest single reading on record in those ZIPs is 534 pCi/L. Hanover (17331) runs slightly higher, with a basement average near 11. Put the two together and you’re at roughly 10.3 pCi/L countywide across about 18,000 basement tests, with a single-home peak above 1,200 pCi/L. For what those numbers mean next to the EPA risk table, see our breakdown of what radon numbers mean in York County.

Read those again. The average basement in York is two and a half times the level at which the EPA says fix it. Roughly a third of tested homes in the York ZIPs come in over 4.0. And that’s the average, which means half the houses in the dataset are above it. If your own number came back over 4.0, our walkthrough of what to do after a failed radon test lays out the next steps in order.

Why the average is close to useless for your house

Here’s what a ZIP code number hides. York County isn’t one kind of ground. The middle of the county, York, Spring Grove, out toward Hanover, sits on a limestone and dolomite belt. Limestone dissolves. It’s full of fractures, voids, and in places outright karst, which gives soil gas open highways to travel through. The southeast corner, down around Peach Bottom and the river, is fractured slate. The north and west, up toward Dillsburg and the Gettysburg side, is Triassic red shale, which tends to test lower but not low.

Within any one of those zones, the variation from house to house is enormous. A slab poured over a limestone fracture pulls gas the neighbor’s house never sees. An old stone-and-rubble foundation in the city, like a lot of the housing stock from before the war, leaks soil gas through every joint. A newer poured basement two miles away might be tight. Same ZIP, different planet.

I’ve stood in two basements on the same road, one right after the other, on the same afternoon. One had a system humming along and had tested in the low 20s before it went in. The other had never tested and the owner figured they were fine because the first guy “had the radon and got it handled.” That’s not how it works. Your neighbor’s result is your neighbor’s result.

The other thing ZIP averages hide: the season

The DEP dataset is mostly closed-house testing, which is the right way to do it. But plenty of homeowners test once in July with the windows open, get a 2, and call it done. Come January, with the furnace running and the ground frozen so soil gas has nowhere to go but up under the slab, that same basement can read 10 or 12. A continuous monitor left running through a winter tells you more than any ZIP code lookup ever will.

What to actually do with this

Test your own house. That’s the whole answer, but here’s how to do it right in York County:

Test in the lowest lived-in level. If the basement is finished or you’re planning to finish it, test there. A converted basement bedroom or office is where exposure hours pile up.
Test in cold weather if you can. Closed-house conditions. If you’re testing in summer, a long-term test (90 days or more) smooths out the seasonal swing.
Don’t put the kit near a drafty window, an exterior door, or the sump. All three skew the reading low.
Retest. If it’s been ten years, a “clean” result isn’t a result anymore. Foundations crack, HVAC gets changed, basements get finished.
If you’re buying, especially in the southern commuter towns like Shrewsbury and New Freedom where inspection windows are short, get the test scheduled on day one of the contingency period, not day eight.

A basic kit runs $20 to $50. A digital monitor is a little more and gives you a running number all winter.

If the number comes back high

Above 4.0, the standard fix is an active sub-slab system. In the York area that generally runs $1,200 to $1,800 on a normal poured basement, and more, $2,500 and up, when a stone foundation, a finished basement, or deep limestone means multiple suction points or tricky venting. Every install needs a PA DEP certified mitigator, and you can check any contractor’s number against DEP’s directory in about five minutes.

You can look up your ZIP in DEP’s tool if you’re curious. Just don’t let it make the decision for you. The York PA Radon Pros list has vetted mitigation companies covering every ZIP in the county, and our testing guide walks through where to put the kit and how to read the result.