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Massachusetts Water Resources Authority


January 6, 2022


Ria Convery
(617) 788-1105,

Public Briefing on MWRA’s CSO Post-Construction Monitoring and Performance Assessment, Final Report

The Massachusetts Water Resources Authority (MWRA) will hold a virtual public briefing on the findings of its Combined Sewer Overflow (CSO) Post-Construction Monitoring and Performance Assessment on Thursday, February 17, 2022, starting at 10:00 AM.

The virtual meeting site link and login information are below:

Link to virtual meeting site:
Access Code: 2331 962 5386
Password: February17

In November 2017, MWRA commenced a multi-year study to measure the performance of its CSO Long-Term Control Plan (the “LTCP”). MWRA conducted the study in accordance with the final milestone in the nearly 35-year-old Federal District Court Order in the Boston Harbor Case (U.S. v. M.D.C., et al, No. 85-0489 MA). In December 2021, MWRA submitted the results of its CSO post-construction monitoring and performance assessment to the U.S. Environmental Protection Agency and the Massachusetts Department of Environmental Protection, fulfilling the final milestone. The report presents the results of field investigations and modeling assessments undertaken to assess the level of performance achieved by the MWRA’s LTCP program and includes the following key findings: 

• From 1987 through 2015, MWRA addressed 182 CSO-related court schedule milestones, including completing the construction of the 35 wastewater system projects that comprised the LTCP by December 2015.  MWRA’s ratepayers across the sewer service area have made a substantial investment in the elimination or control of CSO discharges to protect the environment and public health.
• The total typical year discharge volume has been decreased by 87% from 3,300 MG to 414 MG, within 1% of the LTCP goal.  93% of remaining CSO receives treatment.
• In both the Charles River and Alewife Brook/Upper Mystic River, the predominant source of bacteria loading was demonstrated to be non-CSO sources.  Under current conditions, CSOs alone would only contribute to annual non-attainment of the E. coli criterion less than 0.1% percent of the time for the Charles River, and approximately 2% of the time for the Alewife Brook/Upper Mystic River, consistent with the targets established in previous CSO planning efforts. 

.The public briefing will present the findings of the Post Construction Monitoring Program and Performance Assessment report issued on December 30, 2021, copies of which can be reviewed at The briefing will include opportunity for questions and comments.

For additional information, contact Jeremy Hall, MWRA Project Manager, at 617-759-0340 or


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Updated January 6, 2022