SOUTH LAKE TAHOE - Elevated levels of radon pose a significant health risk to California residents around Lake Tahoe, according to a report released by the California Geological Survey.
An estimated 23,400 people live in homes were radon is likely to equal or exceed the U.S. Environmental Protection Agency's recommended action level of 4 picocuries per liter, the agency reported.
The survey found about 40 percent of California homes around Tahoe are at or above that level, and that the basement measurement from one house was more than 20 times that level.
"The highest radon potential areas ... are located in the South Lake Tahoe area, the Truckee area and in an area immediately north of Emerald Bay," El Dorado County's Department of Environmental Management said in a news release.
The prevalence of radon can vary from house to house, depending on differences in home construction, a home's age and the type of soil it is built on, said Ginger Huber, Tahoe division manager for the department.
"It's important that you test your home because you might have radon where your neighbor doesn't," Huber said.
While the study covered only the California side of Tahoe, the University of Nevada Cooperative Extension reported earlier this year that nearly 60 percent of homes in Stateline, Glenbrook and Zephyr Cove on the lake's Nevada side have elevated radon levels.
Radon is produced naturally by decaying uranium in granitic soils. The colorless, odorless gas usually dissipates into the air, but can enter buildings through crawl spaces. According to the EPA, long-term exposure to the gas is the leading cause of lung cancer among nonsmokers.