Somerville outlines CSO plan, proposes stormwater enterprise and parcel-based fees

Richard Raich, Somerville's director of infrastructure and asset management, told the City Council on May 20 that the city is carrying out a comprehensive update to its long-term control plan for combined sewer overflows (CSOs) and is proposing a new stormwater enterprise and parcel-based billing system to help pay for capital work.

The update, Raich said, is built on unified hydraulic modeling with the Massachusetts Water Resources Authority (MWRA) and Cambridge and is the first regionwide plan the presenters know of to explicitly incorporate climate-change projections into planning. "We are the first in the nation to incorporate climate change into that regulatory framework," Raich said as he described revised typical-year metrics and conceptual alternatives for separation, storage, and tunnels.

Why it matters: CSOs discharge untreated or partially treated sewage and stormwater to local waterways during heavy rain. Somerville officials said the city still discharges treated and untreated flows to the Mystic River and Alewife Brook in larger storms and that climate change increases both the frequency and volume of discharges. The scale of infrastructure needed under the updated scenario makes clear the city must coordinate regionally and change how it funds stormwater management.

Key facts from the presentation

- Regional framing: the long-term…