Interpreting Results and Reporting
This domain tests whether a result is interpreted with the right comparison, uncertainty, and reporting language-not just whether it is above or below 4 pCi/L.
Interpreting a result
A radon result is a concentration at the device location during the test period. Short-term tests are snapshots; radon varies hourly, daily, and seasonally. EPA's action level is 4 pCi/L; EPA also suggests considering mitigation if a long-term result is between 2 and 4 pCi/L. If an initial short-term result is at or above 4 pCi/L, a follow-up short-term test or a long-term test is normally used before a final decision. If the follow-up is also at or above 4 pCi/L, mitigation is indicated.
Reporting
Report the value with units, test method, device ID, start and end dates/times, duration, location, closed-house confirmation, calibration/chain-of-custody information, and any deviations. State the detection limit and uncertainty if the lab provides them. Avoid writing "safe" or "unsafe"; describe the result against the action level and recommend follow-up or mitigation as appropriate.
Worked example
An initial 48-hour test in a basement family room reports 5.2 pCi/L. The report should not say "mitigate immediately" or "average it with a previous 3.0." The correct reasoning is that the result is above 4 pCi/L, so a follow-up test is performed. If the follow-up long-term result is 4.8 pCi/L, mitigation is indicated. If it is 2.6 pCi/L, the home is below the action level but still in the 2–4 range where EPA suggests considering mitigation.
Traps
Averaging an initial and follow-up result without a protocol; rounding 3.9 up to 4; treating a long-term result as directly comparable to a 48-hour result; reporting a number without units, location, or test conditions; and declaring a home "safe" because one short test was low.