What would be an appropriate action for a single point sub-slab depressurization system that reduces radon but not below 4.0?

Choosing to seal excess air entry points is a strategic approach to improving the effectiveness of a single point sub-slab depressurization system, particularly when radon levels are not reduced below 4.0 pCi/L. When radon enters a home, it often does so through various entry points, including cracks in the foundation, gaps around service pipes, and other openings. By sealing these potential pathways, you can reduce the amount of radon that infiltrates the living spaces, thus allowing the existing mitigation system to work more efficiently.

Sealing these air entry points can also enhance the negative pressure created by the mitigation system, which can contribute to a greater suction effect, promoting further reduction in radon concentrations. This action can be particularly beneficial before making more expensive adjustments, such as installing additional suction points or increasing the suction power, since it may yield significant improvements in radon reduction without the need for more complex solutions.

In summary, sealing excess air entry points addresses the root of the problem by limiting radon entry, potentially improving the effectiveness of the current system and helping to achieve lower radon levels.