The historical use of lead in potable water plumbing systems has caused significant public health challenges. The Lead and Copper Rule requires utilities to take action if the 90^th percentile lead concentration exceeds the action level (AL) of 15 ppb. Assessment of the AL is based on a sample of homes representing a relatively small fraction of connections. Due to the intentional nonrepresentative sampling approach, the full set of conditions influencing lead concentrations in a large distribution system may be poorly characterized. Further, there is uncertainty in assessing statistical parameters such as the 90^th percentile concentration. This work demonstrates methods to compute the uncertainty in the 90^th percentile statistic and assesses the associated effect on compliance outcomes. The method is demonstrated on four utilities in southwest Pennsylvania (referred to as A, B, C, and D). For Utility A, evaluation of the 90^th percentile showed an increase over time in observed and estimated values and the value’s uncertainty. This type of change in the uncertainty might have served as an early warning of the exceedance that followed. This could have triggered more timely review of operational changes in order to avoid the effects of noncompliance on utility costs and consumer confidence.

中文翻译：

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使用合规性数据了解宾夕法尼亚州西南部地区饮用水中铅含量的不确定性。

饮用水管道系统中铅的历史使用已引起重大的公共卫生挑战。的铅和铜规则需要实用程序，如果90采取行动^个百分铅浓度超过15 PPB的作用电平（AL）。对AL的评估基于代表相对较小连接比例的房屋样本。由于有意采取的非代表性抽样方法，影响大型配电系统中铅浓度的整套条件可能无法很好地描述。此外，评估统计参数（例如第90^个百分位数浓度）存在不确定性。这项工作表明方法计算在90中的不确定性^日百分比统计，并评估对合规性结果的相关影响。该方法在宾夕法尼亚州西南部的四个公用事业公司（称为A，B，C和D）上得到了证明。对于公用事业A，对第90^个百分位数的评估显示观察值和估计值以及该值的不确定性随时间增加。不确定性的这种类型的变化可能已作为随后的超标的预警。这可能会触发对运营变更的更及时审查，从而避免违规对公用事业成本和消费者信心的影响。