I recently purchased a home. During the inspection there was measured radon levels of 6.3 PiC/L.
After having a professionally installed radon mitigation system, an electronic sensor indicates an unchanged level of 6.3. The system was installed 5 days ago.
The contractor noted clay soil underneath the basement slab.
What strategies can I employ to reduce my radon levels further? Should remain optimistic about reducing the levels below the WHO guideline of 2.7?