Holding-Time and Container Deviation in an Outfall Sample
A junior technician collects a grab sample from an industrial outfall for residual chlorine and sulfide. The method requires chlorine to be determined within 15 minutes and sulfide within 15 minutes, with samples kept in amber glass, headspace-free, and cooled to 4 °C. The technician uses a clear plastic bottle, leaves about 20% headspace, and places the bottle on the dashboard of the sampling vehicle. At the laboratory, 60 minutes after collection, the sample temperature is 22 °C. The technician analyzes chlorine and gets 0.05 mg/L, below the permit limit of 0.10 mg/L, and wants to report the result as compliant. The laboratory's quality manual requires deviations to be documented and the data qualified. The outfall is upstream of a municipal intake, and the client is waiting for the compliance report.
1. Assess the validity of the 0.05 mg/L chlorine result and decide whether it can be reported as compliant.
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The result cannot be reported as a valid compliance determination. Residual chlorine is highly reactive and volatile. A 60-minute hold exceeds the 15-minute requirement by 45 minutes; the sample is at 22 °C rather than 4 °C; the bottle is clear plastic rather than amber glass; and the 20% headspace allows volatilization and reaction. Sunlight and warmth accelerate chlorine loss. Each deviation biases the result low, and the combined effect is likely to be substantial and unquantified. A low result therefore cannot demonstrate compliance; it may be a false negative. Reporting 0.05 mg/L as compliant would understate the chlorine concentration and could create a public-health risk upstream of the municipal intake.
The correct action is to qualify or invalidate the result, not to report it as compliant. If the data are needed, report them as estimated with a clear qualifier and explain the deviation. Notify the client and the responsible regulatory contact according to the laboratory's procedures. The sulfide result is also suspect because sulfide oxidizes and volatilizes under the same conditions. A resample is required.
2. Describe the resampling and corrective-action plan, including documentation and communication steps.
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Resample as soon as practicable using the method-specified containers and preservation. Collect in amber glass with no headspace, chill to 4 °C, protect from light, and analyze chlorine and sulfide within 15 minutes. If on-site analysis is not possible, use a validated field analyzer or a fixed laboratory with documented transport time that meets the holding time. Record collection time, analysis time, temperature, container type, and analyst.
Document the original deviation in a nonconformance or deviation record: the clear plastic bottle, headspace, dashboard storage, temperature, and the 60-minute delay. Link the record to the affected sample and to the qualified or invalidated result. Perform root cause analysis: the likely causes are inadequate training, an incomplete sampling kit, and unclear field instructions. Corrective actions include retraining the technician, issuing amber glass bottles and coolers in the sampling kit, adding a field checklist with holding times, and verifying competence before independent sampling.
Communicate promptly with the client and, where required by permit or regulation, with the authority. Explain that the original result is not valid for compliance, provide the resample plan and timeline, and do not wait for the final report to disclose the deviation. If the resample cannot be done before the reporting deadline, report the original result as qualified and explain why.