RMS Post-Mitigation Testing 2 — Questions and Answers
Question 1: How soon after a sub-slab depressurization system is installed should post-mitigation testing begin?
- Immediately after installation
- At least 24 hours after installation with the system running (Correct answer)
- 30 days after installation
- 90 days after installation
Correct answer: At least 24 hours after installation with the system running
EPA guidelines recommend waiting at least 24 hours after system activation before conducting post-mitigation testing to allow radon levels to stabilize.
Question 2: Which type of test device is considered the gold standard for post-mitigation confirmation testing?
- Electret ion chamber (E-PERM)
- Short-term charcoal canister
- Long-term alpha track detector (ATD) (Correct answer)
- Continuous radon monitor (CRM)
Correct answer: Long-term alpha track detector (ATD)
Long-term alpha track detectors provide a 90-day or longer average, which is the most reliable measure of actual radon exposure after mitigation.
Question 3: A post-mitigation test result of 3.8 pCi/L is obtained. What is the recommended action?
- No action needed; result is below 4.0 pCi/L
- Inform the client the system is working and suggest a follow-up test (Correct answer)
- Immediately redesign the mitigation system
- Recommend sealing all floor cracks before retesting
Correct answer: Inform the client the system is working and suggest a follow-up test
A result just below 4.0 pCi/L is technically within EPA guidance but warrants informing the client and suggesting continued monitoring since it is close to the action level.
Question 4: During post-mitigation testing, closed-house conditions are required for at least how long prior to and during the test?
- 6 hours
- 12 hours
- 24 hours (Correct answer)
- 48 hours
Correct answer: 24 hours
EPA protocols require closed-house conditions for at least 12 hours prior to and throughout a short-term radon test, though 24 hours is the practical standard for post-mitigation tests.
Question 5: What does a post-mitigation diagnostic pressure field extension (PFE) measurement confirm?
- That the fan is operating at the correct CFM rating
- That the sub-slab communication is adequate to depressurize the affected area (Correct answer)
- That radon entry points have been sealed
- That indoor radon levels have dropped below 2 pCi/L
Correct answer: That the sub-slab communication is adequate to depressurize the affected area
PFE measurements verify that the suction applied through the pipe extends sufficiently under the slab to capture radon-bearing soil gas.
Question 6: A homeowner replaces a failed mitigation fan and asks when to retest. Which answer reflects best practice?
- Retest immediately after fan replacement
- Retest after 24–48 hours of continuous operation of the new fan (Correct answer)
- No retest is needed if the same fan model is used
- Retest only if the original post-mitigation level was above 2 pCi/L
Correct answer: Retest after 24–48 hours of continuous operation of the new fan
After any significant system change, radon levels should be re-measured after at least 24–48 hours of continuous system operation to confirm performance.
Question 7: Which radon test placement rule applies during post-mitigation testing in a home with a finished basement?
- Test only on the first floor above grade
- Test in the lowest livable area of the home (Correct answer)
- Test in the bedroom with the highest occupancy
- Test at the geometric center of the house
Correct answer: Test in the lowest livable area of the home
Post-mitigation testing should be conducted in the lowest livable level to capture worst-case radon concentrations where occupants spend time.
RMS Post-Mitigation Testing 2
How soon after a sub-slab depressurization system is installed should post-mitigation testing begin?