What best describes the requirements for post-mitigation testing in accordance with AARST soil gas mitigation standard?

The best choice for describing the post-mitigation testing requirements according to the AARST soil gas mitigation standard is a short-term test lasting at least 48 hours, conducted under closed building conditions. This approach is crucial because it accurately reflects the effectiveness of the radon mitigation system in reducing radon levels.

Conducting the test under closed building conditions ensures that external factors do not influence the indoor radon levels, providing a true representation of the system's performance. A testing duration of at least 48 hours allows for the collection of reliable data, as radon levels can fluctuate based on daily and seasonal changes. This duration is specifically recommended by the AARST guidelines to ensure that the testing captures a stable measurement of radon levels rather than a snapshot that might be affected by transient conditions.

In contrast, other options describe testing scenarios that do not align with the established standards for post-mitigation effectiveness verification. For example, a long-term test lasting 30 days with unrestricted building access would not provide accurate results since the presence of open windows or doors could alter the indoor air flow and radon concentrations. Similarly, conducting a test without prior conditions disregards the necessary controlled environment that is essential for accurate monitoring. Lastly, waiting a year after