Granite counter tops can emit radiation and radon gas. Many homeowners worry about their granite. Many more homeowners have radon coming from their soil.
A homeowner in Menlo Park, CA recently discovered that his home had 14 picoCuries/liter of radon, three times the EPA action level of 4 picoCuries/liter (pCi/L). He tested his home for radon because he was concerned about his new granite counters. However, his granite was not the source of the radon. He had “geologic” radon coming from the soil beneath his house.
Homeowners in Atherton, CA and Carmel, CA both learned last year that they had 8 pCi/L of radon, twice the EPA action level. The homeowners in Atherton tested their home because they were concerned about their granite. They discovered they had geologic radon instead. The family in Carmel had some radon emitted by their granite, but the majority of their radon was coming from the soil.
Homeowners in Redding, CA and Davis, CA also learned recently that they have elevated radon. Both homeowners originally assumed their radon was coming from granite. Nevertheless, in both homes, the radon was entering from the soil.
Many real estate agents tell their clients that California does not have any radon. The Natural Hazard Disclosure (used by most real estate agents) claims that no counties in California have elevated radon. JCP Geologists, the company that provides many of the reports, has the following misinformation on their website:Only 10 counties in the state, all of them rural, have an estimated mean annual radon level above 1.0pCi/L.
Some homes in Silicon Valley have more than 50 pCi/L of radon. That is more than ten times the EPA action level. Other Silicon Valley cities with elevated radon are Palo Alto, Sunnyvale, and Saratoga. Overall, about one in twelve Santa Clara County homes can expect to have radon above the EPA action level.
California’s Santa Barbara County and Ventura County are in EPA Radon Zone 1. The average home in those counties has radon above 4 pCi/L, the EPA action level. The same is true for homes around Tahoe.
Radon comes from the soil in most cases. Granite counters can also contribute to indoor radon, but those cases are rare. We have seen many homes with radon from the soil. We have only seen a few homes where granite contributed substantially to the radon concentration.
Testing a home for radon is inexpensive and easy. Californians can get radon test kits for $5 from the Department of Public Health. Testing granite requires equipment that measures radiation, but it is a relatively quick and easy process. Look for an industrial hygienist or a health physicist to test granite for radiation.
California Radon Map courtesy of California Department of Public Health