Radon Testing & Mitigation in Williamsport, PA
High radon risk from Devonian and Silurian shale and limestone formations in the Susquehanna West Branch valley. Lycoming County's EPA Zone 1 classification reflects consistently elevated testing data, with USGS studies confirming high radon-222 concentrations in both indoor air and groundwater.
High Radon Risk Area
Williamsport sits in EPA Zone 1 — testing is recommended for every home regardless of age or foundation type.
Radon Testing in Williamsport
In Williamsport-area ZIP codes, 39% of 6,120 basement tests reported to PA DEP measured 4.0 pCi/L or higher, with a median of 2.9 pCi/L. Readings differ from house to house, so each home needs its own test. Start with a short-term test of 48–96 hours on the lowest lived-in level. A long-term test of 90 days or more averages out seasonal swings.
A result at or above EPA's 4.0 pCi/L action level calls for a confirming test or mitigation. Retest after a mitigation system goes in, and at least every two years from then on. Pennsylvania requires DEP certification for anyone who tests as a paid service; you may test your own home with a kit from a DEP-certified laboratory. For a home sale, read the Pennsylvania real estate radon testing guide.
Local Geology & Risk Factors
Williamsport is located in an area with Appalachian Plateau / Susquehanna West Branch Valley geology, which contributes to elevated radon levels. The Pennsylvania DEP identifies this region as having significant radon potential due to uranium-bearing rock formations.
Testing is essential because radon levels can vary significantly between neighboring homes based on construction, soil permeability, and ventilation.
See Pennsylvania radon levels and EPA radon zone classifications →
Downtown Williamsport and the historic West Fourth Street corridor — known as Millionaires' Row for its concentration of Victorian-era mansions built by lumber barons in the 1860s–1890s — sits on the valley floor directly over the most uranium-productive formations in the county. The Victorian housing stock is the architectural equivalent of Lancaster's stone farmhouses in terms of radon vulnerability: deep basements with stone foundations, unsealed mortar joints, no vapor barriers, and in some cases direct contact between occupied basement spaces and the underlying soil. These homes are architecturally magnificent and structurally challenging to mitigate. Stone foundation walls require extensive sealing before ASD can establish an effective pressure field. Multi-point suction systems are common due to the compartmentalized foundation geometry of large Victorian homes with additions built across different decades.
Quick Facts
- Median home value: $146,500 · Median year built: 1938
- Population: 27,629
- Foundation types: Basement (most common); Stone foundation (older Victorian homes); Crawlspace (flood-plain properties)
Lycoming County Context
Williamsport is a municipality of Lycoming County, EPA Zone 1. Zone designation is assigned at the county level, so Williamsport inherits its classification; countywide aggregate figures live on the county page.
See Lycoming County radon aggregate data →Measured Radon Data for Williamsport
These figures cover every test whose ZIP code is listed above. ZIP codes do not follow municipal lines, so the figures describe Williamsport-area ZIP codes, not the municipal boundary of Williamsport. They count tests, not homes.
Source: PA Department of Environmental Protection, Radon Test Results, data.pa.gov. Tests through July 2026. Retrieved September 29, 2026.
Ready to move forward? Talk to a DEP-certified pro.
Radon Mitigation Cost in Williamsport
Active sub-slab depressurization (ASD) systems in Williamsport typically cost $900–$2,300. Standard basement installs on modern poured concrete fall at the lower end; historic foundations, block-wall depressurization, multi-point suction, and crawlspace encapsulation push costs higher.
Foundations covered locally
- Basement (most common)
- Stone foundation (older Victorian homes)
- Crawlspace (flood-plain properties)
Systems used in the region
- Active sub-slab depressurization
- Block wall depressurization
- Sump pit depressurization
Certification & Compliance
All Pennsylvania radon testing and mitigation professionals must hold active PA DEP certification. Ask any contractor for their certification number and verify it before signing.
Pennsylvania's Real Estate Seller Disclosure Law (68 Pa.C.S. §§ 7301–7315) requires sellers to disclose known material defects to buyers under § 7303; the mandated disclosure form records radon under § 7304(b)(14). Sellers who have never tested are not compelled to test — § 7308 imposes no affirmative duty to investigate — but pre-listing testing is standard practice across most PA markets.
Under 25 Pa. Code § 240 — the Pennsylvania chapter governing radon certification — every radon service provider working in the Commonwealth must hold current DEP certification. Verify the contractor's status via the DEP Radon Services Directory before hiring.
Verify Contractor Certification — PA DEP Official Directory for Williamsport, Lycoming County
View PA DEP Certified Contractor DirectoryThe PA Department of Environmental Protection maintains the official list of certified radon testers and mitigators, sorted by county and updated monthly. Always verify certification before hiring any contractor.
Directory resource provided by PA DEP Bureau of Radiation Protection, Radon Division.
Frequently Asked Questions
Is radon a problem in Williamsport, PA?
Yes. Williamsport sits in the Susquehanna West Branch valley on Devonian and Silurian shale and limestone formations with elevated uranium content. Lycoming County is EPA Zone 1 — the highest radon potential classification. 39% of the 6,120 basement tests reported to PA DEP from Williamsport-area ZIP codes measured 4.0 pCi/L or higher. USGS studies have also confirmed elevated radon-222 in Lycoming County groundwater.
Does Williamsport have radon in well water?
Yes. USGS testing in Lycoming County found that two-thirds of private well water samples contained radon-222 levels exceeding the proposed drinking water standard of 300 picocuries per liter. Homes on private wells should test both indoor air and water for radon. Municipal water supplies are generally treated, but private wells require independent testing.
What does radon mitigation cost in Williamsport?
Williamsport area radon mitigation systems typically cost $900–$2,300. Older Victorian-era homes with stone foundations cost more due to sealing complexity. Standard poured-concrete basement ASD installations fall at the lower end. Request quotes from DEP-certified Lycoming County contractors.
What share of radon tests in Williamsport-area ZIP codes are at or above the EPA action level?
39% of the 6,120 basement tests reported to PA DEP from Williamsport-area ZIP codes measured 4.0 pCi/L or higher, in line with the 37% statewide share. The median result is 2.9 pCi/L. Of 1,181 first-floor tests, 16% measured 4.0 pCi/L or higher. The figures cover the ZIP codes listed on this page, not the municipal boundary, and they count tests, not homes.
Do homes in Williamsport need to be tested for radon?
Lycoming County is EPA Zone 1 — the highest radon-potential classification — so every home in Williamsport should be tested regardless of age, foundation type, or neighborhood. Short-term charcoal or continuous monitor tests take 48–96 hours and cost $15–$50; long-term alpha-track tests run 90 days and better represent annual averages. If the result meets or exceeds 4.0 pCi/L, mitigation by a DEP-certified professional is recommended.
How much does radon mitigation cost in Williamsport?
Active sub-slab depressurization (ASD) systems in the Williamsport area typically cost $900–$2,300. Standard basement installations on modern poured-concrete foundations fall at the lower end; historic foundations, block-wall depressurization, multi-point suction, and crawlspace encapsulation push costs toward the upper end. All work must be performed by a DEP-certified mitigation professional under 25 Pa. Code § 240.
Is radon disclosure required when selling a home in Williamsport?
Pennsylvania's Real Estate Seller Disclosure Law (68 Pa.C.S. §§ 7301–7315) requires residential sellers to disclose known material defects to buyers (§ 7303). The state-mandated disclosure form covers 'presence of hazardous substances' at § 7304(b)(14) — where any known elevated radon test result or existing mitigation system is recorded. Sellers who have never tested are not required to test: § 7308 imposes no affirmative duty to investigate. In Williamsport, the practical reality is that most buyers request radon testing during the inspection contingency period. Sellers who test and mitigate before listing eliminate the most common contract contingency and preserve negotiating position.
Which ZIP codes does the Williamsport radon data cover?
The Williamsport radon dataset on this page covers ZIP code 17701. These are the ZCTAs assigned to Williamsport in the Census 2020 ZCTA-to-Place relationship file, and the page counts every test in the PA DEP record on data.pa.gov that carries one of them. A ZIP code can reach into a neighboring municipality, so the figures describe these ZIP codes rather than Williamsport's municipal boundary.
Connect with a DEP-Certified Radon Pro in Williamsport
Submit your request and we will connect you with a DEP-certified professional serving Lycoming County.
(717) 461-2427Connect with a DEP-certified radon pro