Back Cove South Storage Facility

[1][2] Centered on Back Cove Park,[3] between Preble Street to the southwest, Franklin Street to the northeast and Interstate 295 to the southeast, the project—a combined sewer and stormwater overflow (or CSO)—is estimated to cost $40 million, and is the city's largest such project to date.

[2] It is designed to reduce combined sewage overflow into both Back Cove and Portland's harbor by 40%.

In 2013, the city had built two conduits, each capable of capturing one million gallons of sewer and stormwater to prevent overflow from entering the cove.

[2] The project's completion date was extended by two years to the summer of 2025 due to the discovery of soft clay.

[6] The underground storage tank will collect the first flow of stormwater—the equivalent of 1 inch (25 mm) of rainfall containing the highest concentration of pollution—during heavy rainfalls and raw sewage from three of the city’s CSOs and store it until it can be pumped to the East End Treatment Plant, located around 0.7 miles (1.1 km) to the northeast, beside Tukey's Bridge.