Why is it so unusually expensive to replace lead pipes in Chicago?

Chicago has the largest inventory of lead water service lines in the U.S., with over 400,000 lines. Replacing each line costs an average of $31,000, more than six times the EPA’s national estimate of $4,700. High costs are attributed to inefficient contracts, permitting delays, and fragmented replacement strategies, with total replacement estimated at over $12 billion under a federal mandate.