If the average of the first and second short-term test for radon is above the EPA action level of 4.0 pCi/L, what action should be taken?

When the average of the first and second short-term radon tests exceeds the EPA's action level of 4.0 pCi/L, the recommended course of action is to consider mitigation. This is important because prolonged exposure to radon levels above the action level increases the risk of lung cancer. Mitigation involves implementing strategies to reduce the radon concentration in the home or building, which can include techniques like increasing ventilation, sealing cracks and openings in the foundation, or installing a radon mitigation system.

In this context, it's critical to act on radon levels that surpass the established safety threshold rather than simply testing further or ignoring the results, as doing so would not address the health risks posed by high radon levels. Consulting a medical professional may be wise in some contexts, but it is primarily the environmental risk posed by radon exposure that necessitates immediate action through mitigation measures.