A 1.1-Inch U-Tube and a 4.9 Upstairs
A homeowner hires a contractor to fix a 7.2 pCi/L basement reading in a 1970s split-level with a block-wall foundation, a sump pit with a perforated liner, and a forced-air furnace whose return duct runs through the basement. The contractor drills one suction point in the slab near the sump, pipes it to a 3-inch PVC stack with an inline centrifugal fan, and seals the sump lid with silicone. The u-tube reads 1.1 inches of water column. A 48-hour post-mitigation test returns 1.5 pCi/L in the basement and 4.9 pCi/L in an upstairs bedroom. The homeowner reports the system is noisy and has been switching the fan off at night. The contractor offers a written "lifetime guarantee of 2 pCi/L" and says the upstairs number "doesn't count because the system is a basement system." The house also has a second slab section under a 1990s addition with no suction point.
1. Why is the upstairs bedroom reading higher than the basement after mitigation? Work through the likely causes.
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Several causes, and the fan being switched off is the first.
Fan off at night. Sub-slab depressurization works only while the fan runs. A homeowner turning it off overnight means the house is unmitigated during the hours when stack effect is strongest - exactly when the 4.9 would be expected to appear.
Pressure-field extension. One suction point near a sump in a block-wall foundation, plus a 1990s addition slab with no suction point at all, is a design that may never have reached the addition or the far side of the block walls. A 1.1-inch u-tube reading proves the fan is moving air; it does not prove the vacuum reaches the whole slab. Hollow block walls often need dedicated wall depressurization. One suction point is a starting point, not a guaranteed field.
The basement return duct. A forced-air return in the basement can depressurize that space relative to the soil and can pick up soil gas and distribute it upstairs. That produces exactly this pattern: a low basement and an elevated bedroom. Duct sealing and return placement matter.
The perforated sump liner. Sealing the lid helps only if the pit itself is under suction; an open, perforated liner can short-circuit the field.
Conclusion: this is not a completed mitigation, and the diagnosis comes before adding equipment.
2. Evaluate the contractor's "lifetime guarantee of 2 pCi/L" and the claim that the upstairs result "doesn't count."
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Both statements are wrong.
"Upstairs doesn't count" is false. Post-mitigation testing is performed in the lowest livable level of the home, but an occupied bedroom is a living space. A system that leaves 4.9 pCi/L where someone sleeps has not done its job. Occupants do not live in the sump.
A "lifetime guarantee of 2 pCi/L" is a marketing claim, not a standard. ANSI/AARST SGM-SF expects guarantees to be in writing, to state specific performance criteria and the conditions under which they are verified - fan operating, closed-house conditions, which locations, what timeframe - and to be tied to a valid post-installation test. An unconditional lifetime number with no testing conditions attached is not something a certified professional should sign, because radon levels in a house change with weather, occupancy, and building modifications.
Worth checking independently: whether the contractor holds current certification through NRPP or NRSB, whether state licensure applies, whether the fan is listed for radon service, and whether a permit or inspection was required.
The tester's role is to report measurements, not to referee a contract - but these claims belong in the written report as observations, because the homeowner will rely on them.
3. What should the post-mitigation report and recommendations contain?
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The report should contain:
- Method and device, location by location, with dates and duration.
- System status during the test - and here, the fact that the homeowner reported switching the fan off at night, which means the system was not operating continuously during the measurement.
- Both results, labeled by location, with the basement identified as the lowest livable level and the bedroom identified as an occupied space.
- Diagnostic observations: no documented pressure-field verification, one suction point serving two slab sections, a basement return duct, a perforated sump liner.
- A clear conclusion that the home does not meet the 4 pCi/L action level on the basis of the upstairs result, and that the system needs corrective work.
- Recommendations: run the fan continuously; have a qualified mitigation professional perform pressure-field diagnostics and add suction and/or block-wall depressurization and duct sealing as needed; re-test at least 24 hours after corrective work with the system running; then test periodically - annually, and at minimum every two years per EPA guidance.
I would not issue a clearance. The 1.5 in the basement is real, but it is not the number that matters to the people sleeping upstairs, and a clearance report based on it would mislead the homeowner about the house they are living in.