Mitigation Basics and Professional Standards
This domain tests the mitigation options a tester should understand well enough to report and refer responsibly, plus the professional boundaries around testing.
Mitigation basics
The most common and reliable method is active sub-slab depressurization (SSD): a fan draws soil gas from beneath the slab through a suction pit and piping, venting it above the roof. A manometer confirms suction. Sealing cracks and openings can improve performance but is not a stand-alone mitigation method. Crawlspace depressurization, block-wall suction, and sub-membrane systems are used for specific foundations. Radon in water is treated by aeration or, in some cases, granular activated carbon; water treatment is considered when water concentrations are high.
Post-mitigation and standards
After installation, the system should run continuously and a post-mitigation test should be performed under closed-house conditions after the system has operated long enough for stable conditions-commonly at least 24 hours, following EPA/state guidance. The tester should follow the applicable standards of practice, state licensing rules, and a code of ethics; use calibrated devices; maintain chain of custody; and disclose conflicts of interest, such as testing and mitigating the same property where that is restricted.
Worked example
A basement test is 12 pCi/L. An SSD system is installed with a suction pit, 4-inch piping, an inline fan, and a manometer. A post-mitigation test after continuous operation reports 1.8 pCi/L. The reasoning is that the result is below 4 pCi/L and the system is performing, but the homeowner should still monitor the manometer and retest periodically or after major renovations.
Traps
Recommending sealing alone as mitigation; testing immediately after the fan is switched on; accepting a post-mitigation result with the fan off; treating a water softener as radon water treatment; and performing mitigation without the required license or without disclosing a conflict.