SECTION 1:  Chapter 21 of the General Laws, as appearing in the 2020 Official Edition, is hereby amended by adding the following section:

Section 27B

a) As used in this Section, the following words and phrases shall have the following meanings unless the context clearly requires otherwise:

“Combined Sewer System” is a wastewater collection system of a municipality or of a Publicly Owned Treatment Works that conveys sanitary wastewaters (domestic, commercial, and industrial wastewaters) and storm water through a single-pipe system to a treatment plant.

“Combined Sewer Overflow” is a discharge or release from a Combined Sewer System directly or indirectly to a water of the commonwealth at a point prior to a Publicly Owned Treatment Works Treatment Plant.

“Publicly Owned Treatment Works” is a treatment works as defined by Section 212 of the Clean Water Act that is owned by a state or municipality as defined by Section 502(4) of the Clean Water Act, which includes the treatment works of the Massachusetts Water Resources Authority. This definition includes any devices and systems used in the storage, treatment, recycling, and reclamation of municipal sewage or industrial wastes of a liquid nature. It also includes sewers, pipes, and other conveyances that convey wastewater to a sewage treatment plant.

“Publicly Owned Treatment Works Treatment Plant” is that portion of the Publicly Owned Treatment Works that is designed to provide at least secondary treatment, including recycling and reclamation, of municipal sewage and industrial waste. That includes the Massachusetts Water Resources Treatment Plant at Deer Island.

“Untreated Combined Sewer Overflow” is a discharge or release that does not include at least the removal of solids and treatment to deactivate bacteria.

b) Beginning on January 1, 2035, in the Massachusetts Water Resources Authority sewer service areas set forth in Acts of 1984, chapter 372, Section 8(c), there shall be no untreated Combined Sewer Overflow in any 25-year 24-hour storm event or smaller storm event.

c) Within 18 months, the Department of Environmental Protection shall adopt regulations to implement this Section that shall include, but not be limited to, the definition of a 25-year 24-hour storm event, which it shall update from time to time as the climate changes, and a definition of Combined Sewer Overflow treatment that shall include at a minimum removal of solids and treatment to deactivate bacteria, which it shall update from time to time as technology changes.