Santa Clara County, CA Radon Zone Data

Santa Clara County, CA: EPA's radon zone, explained

EPA's own radon map rates Santa Clara County zone 2 - moderate potential, predicting a county-wide average indoor level between 2 and 4 pCi/L. Nationally that's the 66th percentile for radon potential — Santa Clara County outranks 66% of every county EPA has rated.

Santa Clara County by the numbers

Santa Clara County, California is home to about 1,926,325 people across 1,291.084 square miles. Population density there runs about 1,492 people per square mile. By population, Santa Clara County is the 7th largest of every county sharing its EPA zone — the 99th percentile by population within that zone. Santa Clara County falls in EPA Radon Region 9, one of 95 counties nationally EPA assigns to that same geologic province.

Zone vs. an actual test

Call it a middle case: above the 1.3 pCi/L most US homes average, below the 4 pCi/L line EPA uses to recommend mitigation — that's Santa Clara County's Zone 2 prediction. Middle-of-the-pack doesn't mean risk-free for any one Santa Clara County address — a moderate county average still leaves individual homes to test either side of it.

Testing and mitigation in Santa Clara County

For a Santa Clara County homeowner, the order is simple: test first, since a kit costs a small fraction of what mitigation would. Only if the result clears 4 pCi/L does a system — typically $800–$2,500, about $1,200 for a common install — become worth pricing out.

Find California's state radon program

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

Where Santa Clara County's figures come from

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