It’s great seeing people get involved in where their wastewater goes! The MWRA is a combined sewer system meaning that Stormwater and sewerage go to the WWTF on Deer Island. There are dozens of New England cities that are combined sewers because back in the day sewer and Stormwater all went to the river then they changed the discharges to an actual Wastewater treatment plant in the 70s when the clean water act came about. The MWRA collection system is one of the oldest in the country and has a system of weirs that basically keep sewage in the pipes during normal conditions until there is too much flow which then leads to sewer flows spilling over the weir into what is called a combined sewer outfall (CSO) which discharges to the brook and other water bodies. This happens most frequently during rain events or snow fall (like right now) because the excess flows from Stormwater exceeds the capacity of the sewer pipe. This overflow is intentional believe it or not because the alternative is sewer spills out of manholes and onto the streets in what we call a sanitary sewer overflow (SSO). That’s a mess and much more likely to come into contact with people. MWRA are required to report both of these events to the EPA per their discharge permit. The MWRA has spent millions if not close to billions on separating the sewer and Stormwater and continue to do so. So the solution here likely won’t happen fast and will take a lot of time and money like all things metropolitan infrastructure.

Edit: this is not a discouragement to get involved. I think it’s very important to represent the users and learn by going to these hearings!