After installing a mitigation system, if a short-term test shows an average result of 1.5 pCi/L and a subsequent independent test shows 4.5 pCi/L, what is the appropriate response?

The appropriate response in this scenario is to inspect the system for failures and discuss findings with the client. A significant discrepancy between the short-term test result of 1.5 pCi/L after installation and a subsequent independent test result of 4.5 pCi/L raises concerns about the effectiveness of the mitigation system.

Investigating the system allows for the identification of potential issues, such as improper installation, malfunctioning components, or changes in conditions that might have led to the increased radon levels. It is crucial to address these findings promptly and discuss them with the client to ensure transparency and to develop a plan for ensuring long-term effectiveness of the mitigation system.

Such an approach not only ensures that the mitigation system is functioning as intended but also reinforces trust with the client, as they are involved in the process of understanding and addressing the issue. The other options, while they may seem practical at first glance, do not adequately address the need for immediate inspection and communication necessary to assess and rectify any potential problems with the mitigation system.