Which scenario would necessitate a long-term radon test following an initial short-term test?

A long-term radon test is necessary in a scenario where the initial test result is just at the action level. This situation is critical because radon levels can fluctuate based on various factors such as weather, building occupancy, and time of year. A short-term test gives a snapshot of radon levels, but if a result is at the action level, it indicates the potential for elevated risk to health. Conducting a long-term test, which typically lasts over 90 days, provides a more accurate assessment of the radon levels in the environment over time, helping determine if mitigation is necessary.

In cases where the initial test result is below action level, it often indicates that the radon levels are not a concern, and there may be no immediate need for further testing. If the initial result is high but stable, ongoing monitoring might not be necessary if plans to mitigate the radon are already in place. Likewise, if significant fluctuation is noted in the short-term results, that does not directly necessitate a long-term test unless those results indicate average levels above the action level. Therefore, testing at the action level warrants further investigation with a long-term assessment to ensure reliable information about the radon concentration over time.