What is recommended if the average of the initial and second short-term results is equal to or greater than 4 pCi/L?

When the average of the initial and second short-term radon measurement results is equal to or greater than 4 pCi/L, it indicates that there is a significant level of radon present in the environment. This level is considered above the EPA's action level for radon in indoor air. At this point, taking action becomes crucial to ensure the safety of individuals who may be exposed to this hazardous gas, which can increase the risk of lung cancer over prolonged exposure.

Radon mitigation involves implementing strategies to reduce the radon concentration indoors. Common methods include improving ventilation, sealing cracks in floors and walls, and installing radon reduction systems that actively draw radon from beneath the building and vent it outside. Therefore, the recommended action is to carry out radon mitigation to decrease the radon levels in the home or building, thereby protecting the health of the occupants.

Other options, such as taking no action or opting for further testing, may lead to continued exposure at unsafe levels, while lowering ventilation would likely worsen the situation by allowing radon to accumulate further. Thus, mitigation is the most responsible and effective response to elevated radon levels.