Washington County, MD radon potential

EPA places Washington County in Zone 1 - Highest Potential — a predicted county-wide average indoor radon level above 4 pCi/L, based on the geology, soil and aerial radioactivity data behind EPA's national map. Nationally, Washington County ranks higher in radon potential than 96% of rated counties (the 96th percentile).

How Washington County compares

Washington County, Maryland is home to about 157,228 people across 457.789 square miles. That works out to roughly 343 people per square mile. Within its own EPA zone, Washington County is bigger by population than 88% of the counties that share it. Washington County falls in EPA Radon Region 3, one of 245 counties nationally EPA assigns to that same geologic province.

Zone vs. an actual test

Outdoor air nationally averages about 0.4 pCi/L, indoor air about 1.3 pCi/L — Washington County's Zone 1 prediction clears both of those and EPA's fix-it threshold besides. A Zone 1 rating means testing is worth doing sooner rather than later, but it is still county-wide average, not a reading for any single house — some homes in Washington County will test well under the action level, and EPA's guidance is to test regardless of zone.

Next steps for a home in Washington County

A short-term test kit is the standard first step and typically costs far less than mitigation itself. If a test comes back at or above 4 pCi/L, a radon mitigation system for a typical home runs roughly $800–$2,500 (around $1,200 for a common single-family install), driven mainly by foundation type, not by county.

Find Maryland's state radon program

For Washington County, an ongoing number beats a one-time test - a Airthings radon monitor tracks Washington County's levels over time. RadonZoneCheck earns a commission there, at no extra cost to you. Use code RADONZONE-10OFF at checkout for 10% off.

Where Washington County's figures come from

The methodology guide shows exactly which EPA and Census sources feed Washington County's numbers. The guide to what a radon zone actually means covers why testing matters in every zone, not just Zone 1.