Radon Testing & Mitigation in Adams County, PA
Radon in Adams County: 44% of the 16,613 basement tests reported to PA DEP measured 4.0 pCi/L or higher, EPA's action level, 7 points above the 37% statewide share and below all three counties Adams borders. The median result is 3.4 pCi/L. Adams is EPA Zone 1, and Gettysburg-area homes should be tested regardless of the county figure.
Radon Testing in Adams County
A test is the only way to learn a specific Adams County home's radon level. The share of basement tests at or above 4.0 pCi/L, 44% of 16,613 reported to PA DEP, describes the county, not any one house. Short-term tests run 48–96 hours and give a first reading; long-term tests run 90 days or longer and better reflect the annual average.
EPA's action level is 4.0 pCi/L. At or above it, confirm with a follow-up test or move to mitigation, then retest once a system is installed and at least every two years after. Under 25 Pa. Code § 240, anyone testing for radon as a service in Pennsylvania must hold current DEP certification; homeowners may test their own home with a kit from a DEP-certified laboratory. Buying or selling? See radon testing in Pennsylvania real estate transactions.
Above the Statewide Share, Below Every Neighbor
Adams County has 16,613 basement radon tests on record with PA DEP, and 44% of them measured 4.0 pCi/L or higher, the level at which EPA recommends mitigation. That is 7 points above the 37% statewide share. The median result is 3.4 pCi/L, and Adams ranks 40th highest of 67 counties — above the state as a whole without approaching the extremes.
The comparison that matters is local. Adams borders three counties, and all three are higher: Franklin at 59%, York at 57%, and Cumberland at 55%. A homeowner who has read about South Central Pennsylvania radon has almost certainly encountered numbers from those three counties. Adams is more than ten points below each of them, though more than four basement tests in ten here still reached the action level.
The first-floor number reinforces it. Of 2,679 first-floor tests in Adams, 18% measured 4.0 pCi/L or higher, against 44% of basement tests, and the first-floor median is 1.4 pCi/L. In Adams the elevated concentrations are concentrated below grade, which is a more tractable mitigation problem than a county where the exposure has already worked its way into the living space.
Diabase Contact Zones Under the Gettysburg Basin
Adams County sits on the Gettysburg Basin — a Triassic complex of shale and siltstone cut by diabase intrusions. The Gettysburg diabase is a Jurassic-age igneous body that pushed up through those sedimentary rocks, and uranium concentrates at the contact zones where the diabase meets the surrounding shale and siltstone. Those contact zones weather into uranium-enriched soils, and uranium-enriched soil is what produces radon.
This is geology you can see. The diabase surfaces as the dark, rocky ridges across the battlefield landscape around Gettysburg. Homes built on or near those ridges and outcrops sit closest to the contact zones and carry the highest local risk.
The practical consequence is variability rather than uniform elevation. A county built on a single uniform formation produces a tight distribution of results; a county built on intrusions cutting through sedimentary rock produces a wide one, because the distance from a given house to the nearest contact zone can change over a few hundred yards. The 3.4 pCi/L county median is the midpoint of a genuinely wide spread: 44% of basement tests reached 4.0 pCi/L, and 6% measured 20 pCi/L or higher.
Two Housing Stocks, Two Mitigation Problems
Adams County has the newest housing stock of the counties profiled on this page: a Census-reported median year built of 1980 for owner-occupied housing, against 1960 in Armstrong and 1957 in Allegheny. Gettysburg borough, at a median year built of 1942, is 38 years older than the county around it. Adams is a Civil War-era core surrounded by four decades of newer construction.
Those two stocks fail differently. Post-1970 construction across the county was built to tighter thermal specifications — better insulation and reduced air infiltration raise the stack effect during the heating season, which pulls more soil gas across the slab. A modern Adams County home is not protected by its age; its envelope is doing the opposite.
The borough core is the other problem. Historic stone and brick homes from the Civil War era frequently have fieldstone foundations, exposed dirt basements, and minimal vapor barriers, all of which increase radon entry. These structures need mitigation designs that achieve depressurization without damaging original masonry or requiring visible exterior piping — a specialist scope, and one worth naming when requesting a proposal.
The county carries 107,914 residents, a median owner-occupied home value of $256,100, and a Gettysburg-area median sale price of $320,000. Radon testing is standard in Adams County real estate transactions, and tourist-area rental properties around the battlefield warrant testing on the same basis as owner-occupied homes.
Measured Radon Data for Adams County
Source: PA Department of Environmental Protection, Radon Test Results, data.pa.gov. Tests through July 2026. Retrieved September 29, 2026. Figures count tests, not homes. A home tested more than once is counted each time, and tests run after a mitigation system was installed are included because the dataset does not separate them.
Adams is a mid-sample county: 28th of 67 by basement test volume, with 16,613 basement and 2,679 first-floor tests on record. ZIP 17325, the Gettysburg area, accounts for 5,568 of the basement tests, and 40% of those measured 4.0 pCi/L or higher.
1 DEP-certified mitigation firm is physically based in Adams County. Firms from adjacent counties routinely serve here as well.
Source: PA DEP Certified Mitigation Firms Directory, July 2026. This reflects business address only — firms based elsewhere may also serve Adams County.
Cities and Boroughs in Adams County
Gettysburg is the Adams County municipality with its own PA Radon Hub page. It holds the Gettysburg-area figures, guidance for historic fieldstone-foundation properties, and connections to DEP-certified professionals serving the county.
Adjacent Counties
All three counties Adams borders have a higher share of basement tests at or above 4.0 pCi/L — Franklin at 59%, York at 57%, and Cumberland at 55%, against 44% in Adams. That contrast is the clearest argument against applying regional South Central Pennsylvania radon figures to an Adams County address.
Comparing radon risk across the wider Commonwealth? Browse All 67 Pennsylvania county radon pages for EPA zone classification and measured basement averages statewide.
Connect with a DEP-Certified Radon Professional
Submit your request and we will connect you with a DEP-certified professional serving Adams County. All providers verified against the PA Department of Environmental Protection Bureau of Radiation Protection directory.
(717) 461-2427Connect with a DEP-certified radon proPA Radon Hub is an independent informational resource. We do not perform radon testing or mitigation. We connect Pennsylvania property owners with independent, DEP-certified professionals — verify any contractor's certification at dep.pa.gov/radon before hiring.
Testing and Mitigation Options in Adams County
Testing a County Where Basement and First-Floor Results Diverge
In Adams, 44% of basement tests measured 4.0 pCi/L or higher, against 18% of first-floor tests. Test the basement, and treat a first-floor result as a separate question rather than a proxy. Short-term charcoal canisters and continuous monitors run 48–96 hours at $15–$50; long-term alpha-track detectors run 90 days or more and average out the heating-season stack effect, which matters more than usual in the county's post-1970 housing because tighter envelopes amplify that seasonal swing.
If the property sits on or near a diabase ridge, a long-term test is the better first instrument. Proximity to a contact zone drives a wide range of possible results, and a 48-hour snapshot in that setting is a weaker basis for a decision than a 90-day average.
Historic Foundations Change the Cost Picture
Active sub-slab depressurization systems in the Gettysburg area run $900–$2,400, and where a property falls in that band is mostly a function of when it was built. A post-1970 home on a poured-concrete slab is a routine installation at the lower end. A Civil War-era property with a fieldstone foundation and an exposed dirt basement needs sub-membrane depressurization, sealing work that respects original masonry, and often concealed routing in place of exterior piping — all of which push toward the upper end.
One Firm in County, Several Across the Line
The PA DEP Certified Mitigation Firms Directory lists one mitigation firm with a business address in Adams County. Cumberland County lists seven and York two, and firms from both routinely work in Adams. For a historic Gettysburg property it is worth asking specifically about prior work on fieldstone foundations before comparing proposals. Certification under 25 Pa. Code § 240 is required statewide — confirm the certification number is current before signing a contract or accepting payment.
Frequently Asked Questions
What share of radon tests in Adams County are at or above the EPA action level?
Of the 16,613 basement tests reported to PA DEP from Adams County, 44% measured 4.0 pCi/L or higher, against 37% statewide. The median result is 3.4 pCi/L, and 6% of tests measured 20 pCi/L or higher. First-floor tests run lower: 18% of 2,679 measured 4.0 pCi/L or higher. Adams ranks 40th highest of 67 counties.
Why does Adams County read lower than York and Cumberland?
In Adams, 44% of basement tests measured 4.0 pCi/L or higher, against 59% in Franklin, 57% in York, and 55% in Cumberland. Adams sits on the Gettysburg Basin, a Triassic shale and siltstone complex cut by diabase intrusions, where radon production concentrates at the contact zones between the igneous rock and the surrounding sediments rather than being generated uniformly across the county. That is consistent with a lower county share and a wide spread between individual properties.
How does Gettysburg diabase affect radon levels?
The Gettysburg diabase is a Jurassic-age igneous intrusion that penetrated the Triassic sedimentary rocks of the Gettysburg Basin. Uranium concentrates at the contact zones where the diabase meets the surrounding shale and siltstone, and those zones weather into uranium-enriched soils that generate elevated radon. The diabase is visible as the dark, rocky terrain across the battlefield area. Homes near those ridges and outcrops carry the highest local risk, which is why Adams County results vary widely between properties a short distance apart.
Do historic Gettysburg homes need different radon mitigation?
Often, yes. Civil War-era stone and brick homes frequently have fieldstone foundations, exposed dirt basements, and minimal vapor barriers, all of which increase radon entry. Mitigating them typically means sub-membrane depressurization, sealing that respects original masonry, and concealed routing rather than visible exterior piping. DEP-certified contractors experienced with historic preservation can design systems that reach the required depressurization without altering the structure. Expect these properties toward the upper end of the $900–$2,400 Adams County range.
Does newer construction in Adams County have lower radon risk?
No. Adams County has a Census-reported median year built of 1980 — newer than most Pennsylvania counties — and post-1970 construction is not protective. Tighter insulation and reduced air infiltration raise the stack effect during the heating season, drawing more soil gas across the slab. Sump pits, plumbing chases, and slab penetrations remain entry paths regardless of construction era. Test the house, not the build year.
Is radon testing expected in Adams County real estate transactions?
Radon testing is standard in Adams County real estate transactions, against a county median owner-occupied home value of $256,100 and a Gettysburg-area median sale price of $320,000. Pennsylvania's Real Estate Seller Disclosure Law (68 Pa.C.S. §§ 7301–7315) requires sellers to disclose known material defects (§ 7303), with radon recorded on the state disclosure form under 'presence of hazardous substances' at § 7304(b)(14); § 7308 imposes no duty to test. Tourist-area rental properties around the battlefield warrant testing on the same basis as owner-occupied homes.
Which ZIP codes does the Adams County radon data cover?
The Adams County figures on this page count every test reported to PA DEP with an Adams County address: 16,613 basement tests and 2,679 first-floor tests. 16 ZIP codes have at least 20 basement tests on record in the county. The largest is 17325, the Gettysburg area, with 5,568 basement tests, of which 40% measured 4.0 pCi/L or higher.
Does Adams County's Zone 1 classification match its measured data?
EPA Zone 1 predicts a county-wide average indoor radon level above 4.0 pCi/L. The PA DEP record shows 44% of the 16,613 basement tests from Adams County at or above 4.0 pCi/L, with a median of 3.4 pCi/L. The zone is a 1993 prediction of an average and the record is a count of measured results, so they are not the same kind of figure. Both support testing Adams County homes; neither predicts what any individual property will read, which in a county whose radon is driven by proximity to diabase contact zones can vary widely between neighboring addresses.
Related Reading
Independent resource — we do not perform testing. PA Radon Hub is an independent informational resource connecting Pennsylvania property owners with independent, DEP-certified radon professionals. We do not perform radon testing or mitigation. Verify contractor certification against the PA DEP Radon Services Directory before hiring.