The results came in while I was in Little Rock. We have a measured 17.8 pCi/L (picocuries per liter) in the basement, where the test packet was hung. This is over four times the recommended maximum.
We'll be re-testing in a couple of weeks. If it turns out to be that high again, we'll have to do something. I don't know what, but I expect it to be expensive.
This is new to me. Radon isn't much of a problem in Houston, since houses there don't have basements: the ground there is mainly clay gumbo, and the water table is typically 4 feet below the surface. The first skyscraper built there, the Exxon Building (built as the Humble Building), literally floats. (I don't know how they handle the problem for newer, larger buildings.)
Isn't owning a house fun?