Lead Action Level Exceedance and Sampling Errors
A 4,200-service-connection system completed its lead and copper tap sampling. Sixty samples were collected; the 90th percentile lead is 0.019 mg/L, above the 0.015 mg/L action level. Six of the samples came from sites that had lead service lines but were sampled after only 4 hours of stagnation instead of the required 6 hours, and two samples were taken from a kitchen faucet with a point-of-use filter. The current corrosion-control treatment is pH adjustment to 7.3 with a target of 7.5; alkalinity averages 38 mg/L and the water is moderately hard. The system has no lead service line inventory and is due to submit its annual consumer confidence report in three months. The mayor asks whether the utility can simply resample the noncompliant sites and delay public education until after the CCR. The state has not yet reviewed the sampling paperwork.
1. Is the 90th percentile result valid for compliance? What must you do about invalid samples?
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I would not treat the 90th percentile as final until the sampling paperwork is reviewed. Sampling after 4 hours instead of 6, and sampling a point-of-use filtered faucet, are protocol errors that can make those eight results invalid for compliance. I would recalculate the 90th percentile using only valid samples, but I would not discard high results simply because they are inconvenient. Invalid sites must be resampled using approved methods and stagnation times, and the state must be informed. The action level is based on the valid 90th percentile, not on whether the utility likes the answer. If the valid recalculated result remains above 0.015 mg/L, an action-level exceedance exists and the regulatory clock starts. I would review all sites for lead service lines, first-draw protocol, and resident instructions, and I would keep the original results in the record.
2. How should you respond to the mayor's request to delay public education until after the CCR?
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I would tell the mayor that public education cannot be delayed until the CCR. The lead action level has its own public-education requirement, typically within 60 days after the end of the monitoring period, and the CCR is not a substitute. Delaying would violate the rule and increase the risk that families with lead service lines or high lead levels do not get timely information. I would explain the health basis: infants, children, and pregnant women are most vulnerable, and corrosion control may need to change. I would give the mayor a short timeline, the required message content, and the cost of the education, and I would coordinate the content with the state. If the mayor still objects, I would document the advice in writing. Resampling is allowed only under the proper protocol; it is not a way to avoid an exceedance.
3. What corrosion control and lead service line steps would you evaluate?
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I would start a corrosion-control study rather than simply raising pH blindly. The water is moderately hard with alkalinity near 38 mg/L, so pH 7.3 to 7.5 may not be enough to form a stable passivating layer. The study should evaluate pH and alkalinity adjustment and possibly orthophosphate, with pipe-loop or coupon testing and careful attention to lead and copper release. I would build a lead service line inventory from records, field verification, and customer surveys, and prioritize replacement where children are present or lead results are highest. I would revise the tap monitoring plan to target high-risk sites, verify stagnation times, and train residents. Public education should include flushing, filters, and replacement options. I would also coordinate with the state on lead service line replacement funding and confirm that any treatment change does not create a new problem, such as increased copper corrosion.