School Testing on a Summer Budget: 24 Detectors for 40 Rooms
A K-8 school requests radon testing before a bond vote. The building has 40 ground-contact rooms: six classrooms and a gym on a below-grade basement level, 20 classrooms on a slab-on-grade first floor, and 14 rooms over a crawl space. The budget covers 24 detectors for a 48-hour test during the last week of June, when only summer staff are present, the HVAC is shut down for coil cleaning, and custodians prop exterior doors open for deliveries. Your plan places detectors in the six basement classrooms, the gym, and 17 first-floor classrooms. On day 2 a custodian opens windows in two basement classrooms 'to clear gym floor refinishing fumes.' Results: two basement rooms at 3.9 and 4.2 pCi/L, one first-floor room at 2.7 pCi/L, the rest 0.4–1.3 pCi/L, and the two window-opened rooms at 0.3 and 0.5 pCi/L. The district wants a one-page 'we are safe' letter before the vote.
1. Critique the sampling plan and the test conditions against the purpose of school testing.
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The purpose is to find rooms where occupants may be exposed, so testing should cover frequently occupied, ground-contact rooms, starting with the lowest level.
Plan problems:
- Testing 17 of 20 first-floor classrooms leaves three rooms uncharacterized.
- The 14 crawl-space rooms are untested, so the district cannot conclude anything about them.
- The gym is intermittently occupied and a lower priority than a classroom. Under a 24-detector budget, swap it for a classroom.
Condition problems, which are more serious:
- Propped exterior doors and open windows violate closed-building conditions.
- The HVAC is offline.
- The building is unoccupied.
June results under those conditions do not represent occupied winter conditions and probably understate concentrations. A defensible plan either tests all occupied ground-contact rooms or phases the work with a documented rationale and completes the rest before anyone draws conclusions.
2. How do you treat the two window-opened rooms and the summer conditions when reporting?
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The 0.3 and 0.5 pCi/L results from the two rooms with open windows are invalid. Ventilation with outdoor air near 0.4 pCi/L drives the reading down, which is exactly what the data show. Do not report them as results. Report them as invalid, state the reason, and schedule retests.
The remaining results are valid for the conditions tested, but those conditions were not representative: HVAC off, doors open at times, summer leakage. A 4.2 pCi/L result still exceeds the 4 pCi/L action level and warrants follow-up regardless of season; 3.9 pCi/L is close enough to justify retesting rather than dismissing.
Low values from a ventilated summer test cannot be used to certify a building. The report should say this plainly, in the same document that presents the numbers, so the caveat travels with the data.
3. What can the letter say, and what follow-up do you recommend?
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The letter can state what was measured, where, when, and under what conditions; list the valid results; identify the two invalid rooms; and state clearly that the scope covered 24 of 40 ground-contact rooms and that results may not represent occupied winter conditions.
It cannot say 'we are safe.'
Recommended follow-up:
- Retest the two invalid rooms.
- Test the three untested first-floor classrooms and the crawl-space rooms.
- Run retests during occupancy, with HVAC operating normally and closed-building conditions for 12 hours before and throughout.
- Treat any room at or above 4 pCi/L as requiring mitigation or confirmatory testing.
If the district wants one defensible basis for the bond discussion, a building-wide plan covering all occupied ground-contact rooms is the only honest option. Offering that plan is more useful to the district than a letter that will not survive scrutiny.