Three Night-Time pH Excursions, a Missing Notification and Eight Calibration Sheets
Kestrel Foods runs a ready-meal factory whose on-site effluent plant discharges to the River Tarn under a permit limiting pH to 6.0–9.0, COD to 125 mg/L and flow to 900 m³/day. A continuous pH meter with a data logger monitors the final discharge, and a contract laboratory takes one 24-hour composite sample per month. You are the lead auditor with eight hours on site, of which four are allocated to effluent control. Reviewing twelve months of logger data, you find three pH excursions below 6.0 on consecutive nights in June, with a minimum of 4.7. The permit requires the regulator to be notified 'without delay and in any event within 24 hours'. Only one notification letter is on file, dated five days after the third excursion. The effluent plant is run by a single contract operator, Marek, who tells you the probe 'drifts after a storm' and that he recalibrates it every Monday. Calibration sheets exist for 8 of the 26 weeks. The EHS manager says monthly laboratory results have never exceeded the COD limit, 'so the pH issue is a meter problem, not a real discharge problem'.
1. Set out the sampling plan you would follow in the remaining four hours: what you would select, how much, and why. Include how you would handle the calibration-record gap.
Read the worked answer
Treat this as two populations with different sampling logic: records that should exist continuously, and events.
1. Records that should exist. Do not 'sample' the 18 missing calibration weeks - verify the absence. That means testing the sample frame first: is there a second file, an electronic log, a contractor's copy? Ask Marek to show you where he would record a calibration. Look for indirect evidence: probe purchase invoices, laboratory calibration certificates, service visit reports, a spare probe in stores. Absence of a record only becomes a finding once you are satisfied it was required (7.5.3) and was not produced.
2. The excursions. Examine all three June dates - this is a 100 % selection because they are the highest-risk events. Trace backwards: logger data → alarm set points and who can change them → probe calibration status at the time → the operating instruction → the operator's competence record. Trace forwards: excursion → decision → notification letter → regulator response.
3. Representative sample. Take five or six ordinary weeks spread across the year, including one immediately after a probe replacement, to test whether the control works when nothing has gone wrong. This is how you separate a systemic failure from an isolated event.
4. Context documents. Request the permit, the notification procedure, and the contract with the effluent contractor, including the competence requirements it specifies (8.1 for outsourced processes, 7.2).
Record what you selected and why; sampling must be defensible if the client challenges a finding.
2. How would you interview Marek and the EHS manager to test competence and the notification process? Give the sequence and types of question and how you would corroborate answers.
Read the worked answer
Sequence matters: open questions first, then probe, then verify.
With Marek:
- Opening (open): 'Walk me through a normal night shift - what do you check, and when?'
- Focused (open): 'What happened on the nights of 11–13 June?'
- Probing: 'The alarm went off. What did you do next? Who did you call?'
- Verifying (closed): 'Did you recalibrate on 14 June?' - then, critically, 'Show me.'
- Hypothetical: 'It is 02:00, the meter reads 4.7 and the permit minimum is 6.0. What do you do?'
Ask him to demonstrate the calibration on the probe and to find the entry in the log rather than describe it. Note whether he knows the permit limits, the notification route and the escalation contact - 7.2 competence and 7.3 awareness.
With the EHS manager, interview separately so the answers are independent. Ask how the notification decision is made and who authorises it, then test it against the single letter on file: 'Show me the record of the decision not to notify on the first two nights.'
Corroborate everything against records and against the contract. Where answers conflict - Marek says weekly calibration, only eight sheets exist - do not resolve the conflict by preferring one person. Record both statements and the documentary evidence, and base the finding on the evidence. Do not carry one interviewee's answers into the other interview.
3. The client asserts the excursions are a meter fault. What evidence would confirm or refute this, and how would you record your conclusion?
Read the worked answer
Test the assertion; do not arbitrate it. A meter fault, if true, is still relevant, because 9.1.1 requires monitoring and measuring equipment to be calibrated or verified and the organisation to act on unreliable data. The question splits into three: is the data valid, was the notification obligation met, and was the equipment controlled?
Evidence supporting a meter fault: calibration certificates showing the probe failed a post-event check; a service report or probe replacement dated just after 13 June; buffer-solution records with slope or asymmetry outside acceptance criteria; a maintenance log showing the same drift complaint before June; rainfall or storm data if the logger enclosure flooded.
Evidence against: the probe passed the calibrations that do exist; spot samples taken at the time show higher pH; the excursions coincide with a process change (a new cleaning chemical, a batch discharge) rather than with weather; logger diagnostics show no fault.
Whatever the outcome, the 18 missing calibration records remain a finding, and the late notification is assessed separately against the permit and the organisation's own procedure. Record the objective evidence and the client's explanation in the report. The lead auditor should not write 'meter fault confirmed' unless the evidence supports it. If the client cannot demonstrate the data are invalid, evaluate fulfilment of compliance obligations (9.1.2) on the basis that the recorded values are real, and consider a legal-compliance finding.