If an initial short-term test result is 4 pCi/L (0.02 WL) or higher, what should be done next?
The EPA recommends a follow-up measurement be used to confirm whether radon levels are high enough to warrant mitigation. There are two types of follow-up measurements that may be conducted. The choice depends, in part, on the results of the initial test.
An initial measurement result of 10 pCi/L (or 0.05 WL) or greater should be quickly followed by a second short-term test under closed-building conditions. If the average of the initial and second short-term results is equal to or greater than 4 pCi/L (0.02 WL), radon mitigation is recommended. If the average of the short-term test results is less than 4 pCi/L, consider testing again sometime in the future.
If the result of the initial measurement is between 4 pCi/L (or 0.02 WL) and 10 pCi/L (or 0.05 WL), the follow-up test may be made with either a short-term or a long-term method. If a long-term follow-up test result is 4 pCi/L (0.02 WL) or higher, the EPA recommends remedial action. If the long-term follow-up test result is less than 4 pCi/L, consider testing again sometime in the future.
If a short-term follow-up test is done and the result is 4 pCi/L or higher, radon mitigation is recommended. If the average of the initial and follow-up short-term tests is less than 4 pCi/L, consider testing again sometime in the future.
In certain instances, such as may occur when measurements are performed in different seasons or under different weather conditions, the initial and follow-up tests may vary by a considerable amount. Radon levels can vary significantly between seasons, so different values are to be expected.
