Conflicting Cathodic Protection Readings on a Municipal Watermain
You are the field technologist on a 2.4 km ductile iron watermain replacement in an Ontario municipality. The contract specifies a polyethylene wrap and a 30-millivolt cathodic protection criterion measured against a copper-copper sulfate reference electrode. During backfill inspection on lot 7, you record pipe-to-soil potentials of -0.62 V at station 0+400 and -0.48 V at station 0+650. The contractor's technician used a high-impedance meter but did not calibrate it that morning, and two readings were taken within 90 seconds of backfilling while the trench was still wet from dewatering discharge. The contractor argues the readings pass and asks you to sign the inspection sheet so backfill can proceed on lots 8 through 12 before the weekend. Your supervisor is unreachable. The specification also requires a 24-hour stabilization period before acceptance readings.
1. Should you sign the inspection sheet? Identify the technical and ethical issues and state what you do next.
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No. Signing would certify a test that was not performed to the specified method. Three technical defects exist: the meter was uncalibrated, so the absolute values are not traceable; readings were taken during an abnormal wet condition that temporarily lowers soil resistivity and shifts potentials; and the 24-hour stabilization period was skipped. The criterion is also ambiguous as written (30 mV shift versus an absolute -0.85 V style criterion), so the pass/fail basis itself must be clarified with the designer.
Ethically, signing a false or premature acceptance record is a integrity breach regardless of schedule pressure. The correct sequence: (1) decline to sign and document the refusal factually in the daily report; (2) request meter calibration records and re-test after stabilization; (3) issue a non-conformance report to the contractor and copy the contract administrator; (4) request written clarification of the acceptance criterion from the designer; (5) if schedule relief is needed, propose that the contractor proceed on lots 8-12 at their own risk with a hold on final acceptance, documented in writing. Escalate to your supervisor and, if unresolved, to the engineer of record.
2. The contractor says wet-trench readings are conservative and therefore acceptable. Evaluate that argument.
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The argument is not reliable in either direction. Saturated backfill lowers soil resistivity, which generally makes the pipe easier to polarize, so readings can appear more protective than the dry-soil steady state; that is optimistic, not conservative. Conversely, recent disturbance and mixed electrolytes can produce stray current effects and unstable potentials. Because the direction of error is not predictable without baseline data, wet-trench readings cannot substitute for stabilized measurements. The defensible position is to treat them as screening data only, record them as such, and require post-stabilization verification before acceptance.