Impact of service line replacement on lead, cadmium, and other drinking water quality parameters in Flint, Michigan

In April 2014, Flint, MI switched its drinking water source from water treated in Detroit to Flint River water without applying corrosion control. This caused lead and other metals to leach into drinking water. To mitigate lead exposure, Flint began to replace lead service lines and galvanized iron service lines in March 2016. In this study, the short- and long-term impact of service line replacement on Flint drinking water quality was investigated. In particular, lead and other metal concentrations, chlorine residual, and levels of select microbial populations were examined before and two and five weeks after SL replacement in water collected from 17 Flint homes. Overall, lead levels in premise plumbing water did not change significantly within five weeks of replacement, however, significant reductions were observed two weeks after service line replacement in flushed samples representative of distribution system water (pre-replacement median = 0.98 mu g L-1; two-week post-replacement median = 0.11 mu g L-1). Multiple sequential samplings from one Flint residence before and 11 months after service line replacement revealed large reductions in lead levels in all samples, indicating long-term benefits of service line replacement. Cadmium was also detected at levels at or above the federal maximum contaminant level. Microbial analyses established that 100%, 21%, and 52% of samples had quantifiable concentrations of total bacteria, Legionella spp., and Mycobacterium spp. as measured by quantitative PCR, while Legionella pneumophila was not detected in any samples. Our results provide evidence that both lead service line and galvanized service line replacement benefit consumers in the long term by reducing drinking water lead concentrations, while short-term advantages of service line replacement in sites with prior lead seeding of in-home plumbing are less apparent.