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Massachusetts Water Resources Authority


May 1, 2019


Ria Convery
(617) 788-1105,

Combined Sewer Overflow Control
Public Briefing on the Progress of MWRA’s CSO
Post-Construction Monitoring and Performance Assessment

The Massachusetts Water Resources Authority (MWRA) will hold a public briefing on its Combined Sewer Overflow (CSO) Post-Construction Monitoring and Performance Assessment on Friday, May 31, 2019, at 1:00 PM in MWRA’s Chelsea Administration Building, 2 Griffin Way, Chelsea, MA.

In November 2017, MWRA commenced a three-year study to measure the performance of its CSO Long-term Control Plan (the “LTCP”). The study is intended to demonstrate whether the goals of the LTCP have been met 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). The milestone requires MWRA to submit to the U.S. Environmental Protection Agency and the Massachusetts Department of Environmental Protection by December 2020 the results of CSO post-construction monitoring and assessments demonstrating whether it has achieved the levels of CSO control including frequencies of activation and discharge volumes specified in the LTCP. MWRA’s study includes the following key elements:

  • Inspections at all CSO regulators/outfalls addressed in the LTCP to confirm closed or active status and confirm or update physical understanding of overflow structures
  • Collection of extensive meter/overflow data at remaining active CSO regulators/outfalls
  • Configuration updates and recalibration of MWRA’s hydraulic model of the wastewater system using recent inspection information and meter/overflow data
  • Assessments of system performance for CSO control against the LTCP levels of control
  • Assessments of the water quality impacts of remaining CSOs and compliance with Massachusetts Water Quality Standards, with emphasis on the CSO variance waters of Lower Charles River/Charles Basin and Alewife Brook/Upper Mystic River.

The public briefing will address the progress of the MWRA study as reported in semiannual progress reports MWRA issued in November 2018 and April 2019, 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 617-570-5461 or


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Updated May 1, 2019