Parts of Massachusetts have combined sewer systems, in which surface runoff is put through the same pipes as sewage. Somerville’s Water and Sewer Department says the issue came up because water meters were not sending the appropriate water usage data to the billing department. For the "2050 Typical Year" level of control, alternatives also include "regional tunnel solutions and full sewer separation of combined areas tributary to the variance water CSO outfalls." The MWRA estimated that planning level capital costs for the CSO control alternatives under consideration range from approximately about $400 million to $5.6 billion. The plan is to file the draft updated CSO control plan "in December 2025," MWRA said, before a series of public meetings and hearings.