The new Deer Island Plant set a new one-day record for flows at 1.14 billion gallons and an instantaneous rate record of 1.24 billion gallons. The new plant and 9.5 mile outfall tunnel to Massachusetts Bay have greatly increased the capacity of MWRA to remove wastewater from communities and provide treatment to meet federal and state regulations. The new facilities likely saved thousands of homes from sewer backups. MWRA sewer facilities remained 100% operational throughout the storm and MWRA crews provided assistance to community sewer departments.

All flows to the Deer Island plant received full primary treatment using 42 of the plant’s 48 clarifiers. A record 456 Million gallons per day (40%) of the total plant flows received full secondary treatment. All three batteries of secondary were operated during the event. The plant was able to disinfect all flows with chlorine to meet discharge permit requirements and then dechlorinate all flows before final discharge to the outfall tunnel.
See Deer Island Treatment Plant for further details on plant operation and performance.

Even with the new modernized facilities, the massive amount of rainfall and stream flooding taxed the capacity of the MWRA sewer system as well as the 5,000 miles of community managed sewer lines. The MWRA and community systems ran full into the weekend with limited overflows continuing. By Monday, March 26, flows at Deer Island are still at 700 million gallons, about twice the average flow.