Evaluation of Changes in Lead Levels in Drinking Water Due to Replacement of Water Mains: A Comprehensive Study in Chicago, Illinois.

Disturbances to water treatment and distribution systems using lead service lines have been reported to increase water lead levels. This study evaluates effects from one type of physical disturbance, namely, water mains replacement. Lead concentrations at 542 homes in Chicago, Illinois were measured using partial profile sampling (1st, 4th, 6th and 5th min 1-L samples) after 6-h stagnation, both before and after mains replacement; a subset had monthly follow-up sampling for an additional 12 months. Concentrations were correlated from month-to-month and depended on household water consumption, temperature, residence age, and other factors. The sampling event maximum yielded considerably higher concentrations than first-draw samples, and 5 min flush samples had the lowest concentration at nearly all homes. Mains replacement was associated with less than a 1 μg/L increase in median and 90th percentile concentrations; changes were smaller or not seen after controlling for other factors. Transient lead peaks were identified in a subset of residences and visits. These findings in Chicago indicate that mains replacement did not produce large changes in Pb concentrations in samples collected 1 to 12 months following the disturbance. We recommend continued outreach to promote flushing and other actions to minimize lead exposure, and routine use of profile sampling.