SOUTH LAKE TAHOE, Calif.—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.

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