Does radon in my house come from my granite counter tops?
Yes, some granite contains uranium, the source of radioactive radon gas.
However, the occurrence of radon counter tops is quite rare. If your customer is concerned about radon from granite countertops, the customer should be concerned about the radon gas from soil gases. If you test for radon from granite counter tops, the customer should also be testing the basement for elevated radon levels. A reasonable approach for testing for radon from countertops should include three radon tests. The first is a radon test close to the granite counter tops. A second would be in a room on the same level as the kitchen. Third and most important simultaneous test would be done in the basement. If the basement test results show elevated radon level, the source is soil radon gases and not the granite countertop.
If the basement level is high and the kitchen is high, then the source of radon is from the soil gas.
If the basement is low and the kitchen is high, then the source is the granite counter tops.