What could cause a home's radon level to return to pre-mitigation levels after a successful mitigation?

The reason the chosen answer is correct lies in the way renovations, particularly in the basement, can impact the home’s radon levels. When a homeowner renovates a basement and installs air returns, the airflow dynamics within the home change significantly. These alterations can inadvertently introduce new pathways for radon gas to enter the living spaces, especially if the sealed areas around the mitigation system are disturbed or if the renovation creates unsealed gaps or holes that allow radon to seep in.

Air returns can also create pressure changes that could potentially pull in additional radon from soil beneath the house or other areas that might not have been exposed before. The introduction of new materials and changes in ventilation can lead to an increase in radon levels, causing them to return to pre-mitigation levels despite previous successful mitigation efforts.

Natural fluctuations in radon levels happen regularly due to various factors, including weather changes and seasonal variations, but this option does not specifically tie to a physical change in the home's structure that would effectively facilitate an increase in radon levels.

Increased radon levels outdoors might correlate with high outdoor readings but does not directly cause a home’s indoor levels to revert back. The installation of a radon remediation system should theoretically reduce radon levels, hence would