Deer Island Waste Water Treatment Plant

[2] The plant is a key part of the program to protect Boston Harbor from pollution from sewer systems in eastern Massachusetts, mandated by a 1984 federal court ruling by Judge Paul G. Garrity, in a case brought under the Clean Water Act.

[3][4] These lawsuits culminated in Federal District Judge A. David Mazzone’s 1985 ruling that made the cleanup of the Boston Harbor a non-voluntary, court-ordered mandate.

Over the next fifteen years, the agency built one of the finest regional sewerage systems in the country, although it still discharged the raw sewage into the ocean.

[1][2][6] After nearly a decade of construction the project was capped-off by the deaths of two divers deep under the earth and sea in the narrowing anoxic outfall tunnel ten miles from land.

[7][8][9] In 2017, MWRA, Massport, the US Army Corps of Engineers, and Eversource reached a settlement[10] to re-lay the Deer Island power cable that was blocking bigger ships from docking at Conley Terminal.

In August 2019, a new cable was energized, requiring Deer Island to run on backup power for a few days but adding a redundant fiber optic line from South Boston.

Three pump stations with a combined capacity of 1270 million gallons per day (mgd) lift the wastewater about 150 feet to primary treatment clarifiers that use gravity to remove about half of the pollutants.

Sludge and scum from the primary and secondary treatment stages are thickened and fed to twelve 130 foot high egg-shaped digesters.