What EPA's radon map says about Calvert County

Calvert County is mapped as Zone 1 - Highest Potential by EPA — meaning the county-wide average indoor level is predicted above 4 pCi/L. That puts Calvert County in the 93rd percentile nationally for radon potential — higher than 93% of the counties EPA has rated.

Calvert County by the numbers

About 94,913 people live in Calvert County, Maryland, spread over 213.19 square miles. Population density there runs about 445 people per square mile. Among counties sharing Calvert County's EPA zone, it outranks 81% of them by population. EPA's geology-based Region 3 groups Calvert County with 244 other counties nationally sharing its underlying rock and soil profile.

What this actually means for a house in Calvert County

Outdoor air nationally averages about 0.4 pCi/L, indoor air about 1.3 pCi/L — Calvert County's Zone 1 prediction clears both of those and EPA's fix-it threshold besides. Being in Zone 1 raises the odds Calvert County homes test above the action level, but it does not mean any specific house does — EPA recommends every home be tested, in every zone, because the only way to know is to test.

If Calvert County tests above the action level

Mitigation cost doesn't depend on Calvert County's zone — it depends on the house's foundation. A typical system runs $800–$2,500 (about $1,200 typical), and testing first is what tells you whether that's needed at all.

Find Maryland's state radon program

Calvert County's test kit answers today; a Airthings radon monitor keeps answering for Calvert County over time. Affiliate link, RadonZoneCheck earns a commission there, at no extra cost to you. Code RADONZONE-10OFF takes 10% off at checkout.

More on how this number was built

Calvert County's zone, rank and region all trace back to named EPA and Census sources — the methodology guide lists exactly which ones. Whatever zone Calvert County carries, the zone explainer covers what it does and doesn't tell you about any one house.