Radon in Washington County, PA: ZIP Results and Costs

Washington County shows why a zone label is not the whole story. EPA's 1993 map rates it Zone 2, a predicted county average of 2 to 4 pCi/L, yet in the 40 ZIP codes centered in the county with at least 30 basement tests, 13,528 of 39,398 basement tests (34.3%) were at or above 4 pCi/L in PA DEP data, by our count through July 2026.

Across all floors, DEP's data set holds 43,589 Washington County tests with 33.0% at or above the action level. Of the county's 56 ZIP areas in the Census Bureau file, 5 also take in Zone 1 land in a neighboring county.

HomeGuide's Feb 2026 survey puts a standard sub-slab system at $1,200 to $2,000 installed, the range most Pittsburgh-suburb basement homes fall into.

Licensing and permits

Pennsylvania DEP certification applies statewide, Zone 2 counties included: paid testing or mitigation requires it under 25 Pa. Code Chapter 240.

Municipal permits: Washington County's townships and boroughs handle construction code permits locally or through an agency; some want an electrical permit for the fan. HomeGuide reports $25 to $150 for radon permits where required.

New construction: the fast-growing townships around Canonsburg and Peters see many new homes. A passive pipe installed during construction can be activated with a fan later, about $300 in EPA's 2010 guide (2010 dollars).

Keep the DEP-filed post-mitigation result.

Local conditions

The county sits on the Appalachian Plateau, layered sedimentary rock: shale, sandstone, limestone and coal seams including the Pittsburgh coal, cut by stream valleys such as Chartiers Creek and the Monongahela River along the eastern edge.

DEP basement data by ZIP: Canonsburg's 15317 was 29.7% at or above 4 pCi/L across 13,231 tests; the city of Washington's 15301 35.1% across 7,395; Venetia's 15367 33.3% across 3,630; McDonald's 15057, on the Allegheny County line, 38.6% across 3,581 (PA DEP data, our count).

Monongahela's 15063, along the river, was 38.0% across 1,414 tests and Charleroi's 15022 37.3% across 1,156 (PA DEP data). In this Zone 2 county, about a third of basement tests still exceed the action level.

Former mining areas deserve a mention because homeowners ask. Coal itself is not a notable radon source, but deep mine workings and subsidence cracks can change how soil gas moves under a foundation, so homes over old workings near the Monongahela River towns should test like everyone else. The fix is the same sub-slab approach, sometimes with more sealing.

What drives local prices

Newer slab and basement homes in the northern townships usually take a single sub-slab point, $1,200 to $2,000 based on HomeGuide's published survey.
Hillside lots: walk-out basements with part slab and part crawlspace can need a second suction area, an est. ×1.5 in our calculator.
Older homes in the Monongahela River towns often have block or stone foundations; block-wall work runs $1,800 to $3,000 (HomeGuide).
Permit $25 to $150 and professional retest $125 to $400 (HomeGuide).
Activating a passive system in new construction: about $300 in EPA's 2010 guide.

Common jobs

Sub-slab systems in Peters, North Strabane and Cecil Township subdivisions.
Fan activation of passive pipes in newer homes.
Block-wall systems in older river-town houses.
Tests and fixes during sales in the Canonsburg and Washington markets.

From test to fixed, and where we cover

Step 1: test even though the county is Zone 2; a third of basement tests here exceed 4 pCi/L. Step 2: at 4 pCi/L or above, get two DEP-certified bids.

Step 3: hold each bid against the calculator. Step 4: retest after installation.

We cover Canonsburg, McMurray, Venetia, Washington, McDonald, Monongahela, Charleroi and Burgettstown, along I-79, I-70 and US 19.

Communities: Canonsburg, McMurray, Venetia, Washington, McDonald, Monongahela, Charleroi, Burgettstown

Before you sign

A Zone 2 label is not a pass. EPA's guidance is to test every home and fix at 4 pCi/L or higher, on a timeline of weeks, not hours (EPA Citizen's Guide).

Questions about Washington County

Washington County is EPA Zone 2. Do I still need to test?

Yes. In PA DEP data, 34.3% of basement tests in the county's ZIPs read 4 pCi/L or higher, and EPA finds elevated homes in every zone.

Which Washington County ZIPs test highest?

Among ZIPs with a thousand or more basement tests in DEP data, McDonald's 15057 led at 38.6%, then Monongahela's 15063 at 38.0%.

What does a radon system cost near Canonsburg?

HomeGuide's published range is $1,200 to $2,000 for a sub-slab system; walk-out and mixed foundations can cost more.

Does the installer need DEP certification?

Yes, under 25 Pa. Code Chapter 240, regardless of the county's zone.

Sources

Nearby counties

Rules and fees change; confirm with the state radon office. Price your own system with the radon mitigation cost calculator, read the radon mitigation cost guide, or check any ZIP with the radon levels by ZIP tool.