The Post-Mitigation Verification
A radon mitigation system was installed in a home with an initial radon level of 12 pCi/L. The system is an active soil depressurization (ASD) with a single suction point and a 4-inch PVC pipe. The post-mitigation test, conducted 24 hours after system start-up using a CRM for 48 hours, shows an average of 3.8 pCi/L. The homeowner is relieved but wants to know if the system is working properly. The professional must evaluate the system's performance and determine if further action is needed.
1. Is the post-mitigation radon level of 3.8 pCi/L acceptable? Explain the criteria for successful mitigation according to EPA standards and any additional checks needed.
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According to EPA standards, a successful mitigation system should reduce radon levels to below 4 pCi/L, and ideally below 2 pCi/L. The result of 3.8 pCi/L is below 4 pCi/L, so it meets the minimum criterion. However, EPA recommends considering further reduction if levels are between 2 and 4 pCi/L, especially if the initial level was high. Additionally, the professional should verify that the system is functioning correctly: check that the fan is operating, the u-tube manometer shows proper pressure differential (typically 0.5-1.5 inches water column for a 4-inch pipe), and that the system is properly labeled. A visual inspection for leaks and a communication test (if not done initially) could confirm effectiveness. The professional should also ensure that the post-mitigation test was conducted under closed-house conditions and that the CRM was calibrated. If all checks pass, the system is acceptable, but a follow-up test in 30 days and annually is recommended. If the level were above 4, additional suction points or sealing might be needed.
2. What if the post-mitigation test had been conducted only 12 hours after system start-up? How would that affect the validity of the results, and what should the professional do?
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A post-mitigation test conducted only 12 hours after start-up is not valid because the system needs time to stabilize and the soil gas concentrations to reach steady state. EPA protocols require waiting at least 24 hours after system installation before testing, and the test itself should be at least 48 hours. If the test was only 12 hours after start-up, the results may not represent long-term performance. The professional should invalidate the test and conduct a new test after the system has been running for at least 24 hours, with a 48-hour test duration. The professional should also check that closed-house conditions were maintained. If the 12-hour test showed 3.8 pCi/L, it might be artificially low or high, so a retest is necessary. The professional should communicate to the homeowner that the initial test was premature and schedule a proper verification test.