Water lead exposure risk in Flint, Michigan after switchback in water source: Implications for lead service line replacement policy.

In February of 2016, the City of Flint, Michigan commenced the FAST start initiative with the aim "to get the lead out of Flint" by replacing lead and galvanized steel service lines throughout the city. An estimated 29,100 parcels are scheduled for service line replacement (SLR) at an expected cost of $172 million. The lead exposure benefits of SLR are evaluated by analyzing Sentinel data on hundreds of repeatedly sampled homes in Flint from February 16, 2016 to July 21, 2017, comparing water lead (WL) in homes with and without lead service lines. Samples taken from homes with lead service lines were significantly more likely to exceed specified thresholds of WL than homes without lead service lines. Second, regardless of service line material type, sampled homes experienced significant reductions in WL with elapsed time from Flint's switchback to water provided by the Detroit Water and Sewage Department. Third, the risk of exceedance of WL > 15 μg/L was uncorrelated with service line material type. These results are robust to sample restrictions, period stratification, time operations, reference group definitions, and statistical modeling procedures. On the question of what is gained from SLR over optimal corrosion control techniques, we simulated age-specific lead uptake (μg/day) and blood lead levels (μg/dL) for children in Flint at 16 and 90 weeks of elapsed time from Flint's switchback to Detroit water. At 90 weeks from the switchback in water source, the quantity of water lead consumed by children in homes with lead service lines decreased 93%, as compared to 16 weeks. Lead exposure benefits of SLR have declined in time, with modest differences in lead uptake across homes with different service lines. In light of results, policy considerations for Flint and nationwide are discussed.