Maine Radon Zones: Which Counties Have the Highest Risk?

# Maine Radon Zones: Which Counties Have the Highest Risk? Radon is a problem throughout Maine, but the risk isn't uniform. The EPA divides counties into three radon zones based on predicted indoor radon levels. Understanding your county's zone helps set expectations — though every home should still be tested individually. ## Maine's EPA Radon Zone Map **Zone 1 — Highest Predicted Average (above 4 pCi/L):** - Androscoggin - Aroostook - Franklin - Kennebec - Oxford - Penobscot - Piscataquis - Somerset - Waldo - Washington - York (partially) **Zone 2 — Moderate Predicted Average (2–4 pCi/L):** - Cumberland - Hancock - Knox - Lincoln - Sagadahoc No Maine counties are classified Zone 3. ## Why Does Geology Matter? Radon comes from uranium decay in rock and soil. Maine's bedrock is dominated by granite and metamorphic rock — both of which are relatively uranium-rich compared to sedimentary geology found in other parts of the country. As uranium breaks down into radium and then radon gas, that gas migrates upward through fractures and soil and can accumulate in homes. Zone 1 counties tend to have more granitic bedrock close to the surface and older, more fractured rock formations. Zone 2 coastal counties have some granite but also more varied geology including marine sediments and glacial till. ## Zone 2 Doesn't Mean Safe Here's the critical caveat: **a Zone 2 county can have Zone 1-level homes**. The EPA zones are statistical averages based on regional geology. Individual homes vary dramatically depending on: - Foundation type (block vs. poured concrete vs. crawlspace) - Soil permeability beneath the foundation - How well-sealed the basement or slab is - Home age and construction style We've mitigated homes in Cumberland County (Zone 2) that tested at 15+ pCi/L. The zone tells you about regional risk — not your specific home. ## The Only Way to Know: Test Radon test kits are available at most Maine hardware stores and online for $15–$30. Place the kit in your lowest livable space (usually the basement) for 48–96 hours, then mail it to the lab. Results come back within a week. If you test above 4 pCi/L, contact a certified mitigator. If you test between 2 and 4 pCi/L, the EPA recommends retesting — and many homeowners choose to mitigate anyway given the low cost of protection. ## We Serve All of Maine's High-Risk Zones Central Maine Radon & Water Mitigation is NRPP certified and serves customers throughout central, southern, and coastal Maine — including the highest-risk Zone 1 counties. [Request a free estimate](/get-a-quote) or call us at (207) 483-5637.