The Borderline Wipe
You receive laboratory results for a post-abatement clearance. One floor wipe in a bedroom reports a lead loading of 41 µg/ft². The applicable clearance threshold for floors is 40 µg/ft². The laboratory's reporting limit is 10 µg/ft², and its uncertainty at this concentration is approximately ±15%. The abatement contractor argues the result is 'within analytical error' and should be treated as a pass. The client wants the unit reoccupied tomorrow. Your report is due in the morning.
1. How should you interpret a result that is marginally above the clearance threshold given the stated uncertainty, and what should your report say?
Read the worked answer
A result above the threshold is a failure of clearance as reported. Analytical uncertainty does not convert a reported exceedance into a pass; it means the true value is likely close to the threshold, but the decision rule is applied to the reported result. The correct response is not to argue the number away but to re-clean and re-sample the location.
In the report:
- State the result and the threshold.
- Note the laboratory's uncertainty so the reader understands the margin is small.
- Conclude that clearance is not achieved for that location and specify the corrective action (re-clean, re-wipe, re-evaluate).
- Do not certify occupancy.
2. The contractor asks you to 'just round it down.' What is your professional and ethical obligation?
Read the worked answer
Decline. Rounding a reported result to fit a threshold is falsification of data, regardless of intent. Your obligation is to report what the laboratory reported, with its qualifiers, and to let the decision follow from the data.
You may explain to the contractor that the path forward is corrective action, not arithmetic. Document the request in your file. If pressed, state that altering a result would violate the integrity requirements of the program and your professional ethics, and that you will not do it.