What Can Utilities Expect from New Lead Fifth-Liter Sampling Based on Historic First-Draw Data?

The United States Environmental Protection Agency recently released their most sweeping overhaul to the Lead and Copper Rule in three decades. One of the most significant changes is requiring a fifth-liter (L5) sample at homes with lead service lines (LSLs) rather than the original first-liter (L1) sample for a demonstration of compliance with water lead level (WLL) limits. We analyzed sequential sampling data from three large water systems and compliance data from Michigan utilities-which base compliance on the 90th percentile of the greater of L1 and L5 samples-to evaluate whether L5 WLLs better represent water in contact with LSLs and to explore regulatory impacts of including L5 samples in compliance monitoring. The sequential sampling data demonstrated that it is impossible to use a single sample volume within a sequential profile to universally capture the volume of water in an LSL. While L5 is not always a reliable indicator of water in contact with an LSL, Michigan compliance data showed that the L5 sample is more likely to be from an LSL and can identify utilities that benefit from an improved corrosion control treatment. Michigan compliance data indicate that it is likely that L5 sampling will result in more systems having a higher 90th percentile WLL and that a high proportion of the systems likely to exceed regulatory action levels based on L5 samples can be identified through a retrospective analysis of historic L1 data. The impact of the switch to L5 sampling on the effectiveness of corrosion control treatment over time has yet to be determined.