What is the recommended action if the radon levels exceed acceptable levels after mitigation?

When radon levels exceed acceptable levels after mitigation, the recommended action is to review and adjust the mitigation system accordingly. This response is critical because it addresses the potential inadequacies or failures of the current radon mitigation measures. Mitigation systems are designed to reduce radon levels; however, their effectiveness can be influenced by various factors such as building changes, seasonal variations, or system malfunctions. By reviewing the system, professionals can determine if adjustments are needed, which may involve enhancing ventilation, sealing cracks, or upgrading the radon extraction system to ensure that radon levels are effectively reduced to safe thresholds.

In contrast, the other options do not provide appropriate responses to the situation. Assuming that the levels will normalize without action ignores the possibility of persistent high radon concentrations, which can be detrimental to health. Immediate evacuation is an extreme measure and may not be necessary if a plan to improve the mitigation system is enacted. Increasing air circulation in the building could help temporarily, but it is not a comprehensive solution and does not address the root cause of high radon levels. Therefore, a careful review and adjustment of the mitigation system is the most reliable approach to ensure long-term safety and compliance with health standards.