A 9.1 Spike, a Motion Flag, and a Landlord's Request
A certified tester deploys a continuous radon monitor in the basement unit of a duplex for a 48-hour real estate test. The report shows a 48-hour average of 4.3 pCi/L, with hourly values ranging from 1.9 to 9.1; the 9.1 reading coincides with a six-hour period overnight. The monitor's tamper log records a motion event at hour 18, and the tester's field notes show the tenant's basement window was open when the device was retrieved. The landlord, who is not selling, wants the report to state "no mitigation required" so he can re-lease the unit. The tenant has two young children and asks for the raw data. The duplex shares a common basement wall with the adjoining unit, where a separate monitor previously read 5.6 pCi/L.
1. Is the test valid? What do the open window and the motion event do to the report?
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No, this cannot be reported as a valid closed-house short-term test.
The open window. Closed-house conditions require exterior doors and windows closed for 12 hours before and throughout the deployment. A basement window open at retrieval is direct evidence of a breach, and the monitor cannot prove how long it was open. That alone is enough to qualify or invalidate the result.
The motion event. A continuous monitor's tamper log exists to show the device was not moved or disturbed. An unexplained motion event at hour 18 means placement cannot be verified for the full 48 hours. Without an explanation documented in the field notes, the data are compromised.
The adjacent unit. A shared basement wall next door previously reading 5.6 pCi/L makes retesting more important, not less - common-wall and shared-soil conditions are exactly where one unit's number predicts the other's.
The defensible report states the measurement, the hourly data, the deviation and the motion flag, and concludes that the test does not meet closed-house protocol and should not be used as a decision basis. Then retest under correct conditions. Acknowledge the protocol failure plainly rather than burying it.
2. The landlord wants "no mitigation required" written into the report. How do you handle that?
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The report cannot say that. Two separate reasons.
First, it would be false on the data. The 48-hour average is 4.3 pCi/L, above the 4 pCi/L action level, and the test is invalid on top of that. "No mitigation required" contradicts both facts.
Second, it is not the tester's decision to make. A tester reports measurements and recommendations; whether to mitigate is the owner's decision informed by those measurements and by state requirements. Writing an owner-directed conclusion into a measurement report turns an instrument reading into an opinion for sale.
What the report can say is factual: the average, the range, the deployment location, the conditions observed, the deviations, and a recommendation to retest and to consider mitigation. If the landlord pushes, explain that a report written to order is worthless the moment a tenant or a future buyer tests independently, and that misrepresenting a radon result creates real liability for him as well as for the tester.
Tenant-occupied units add a wrinkle: the tester reports to whoever contracted the work, but the occupant has a legitimate interest, and many states impose disclosure or landlord-action duties at certain levels. Follow state rules, and at minimum do not conceal a result from the person living above it.
3. How do you explain the 4.3 average with a 9.1 peak to the tenant, and what do you recommend?
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The average and the peak answer different questions.
4.3 is the 48-hour arithmetic mean, and that is what the action level is compared against.
9.1 is a real six-hour excursion, typically from a pressure change - a weather front, a furnace or exhaust fan cycling, wind - that pulled more soil gas in overnight. It raises the average but does not replace it. It is also a signal that the house can go well above 4 under the wrong conditions, which means a single low retest would not reassure me either.
What I would tell the tenant: the number is above the level EPA says to fix; the test itself had protocol problems, so it must be repeated; and given two young children, the 9.1 is a reason to move promptly rather than wait a year. Long-term testing over 90 days or more gives the best estimate of the annual average, and a short-term retest under proper closed-house conditions gives a faster answer.
I would give the tenant the raw hourly data they asked for - it is their home and their exposure. Withholding data from occupants while giving a summary to the owner is not a defensible position for a certified tester.