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MSD McKnight Sewer

New Storm Sewer System in St. Louis

As part of the Metropolitan St. Louis Sewer District’s ongoing CIRP program, Farnsworth Group was selected to provide engineering services for the rehabilitation and reconstruction of an existing combined sewer system and construction of a new storm sewer system.

The project included 9,000 LF of sanitary sewer rehabilitation ranging in size from 8-inch to 21-inch pipe, 2,000 LF of sanitary sewer reconstruction ranging in size from 8-inch to 15-inch pipe, and 5,500 LF of proposed storm sewer ranging in size from 12-inch to 36-inch pipe and 4-feet x 3-feet box culvert. Public inflow sources were removed from the downstream sanitary sewer system by constructing a new storm sewer parallel to the existing combined sewer and reusing the combine sewer as the sanitary sewer system.

In addition, private inflow and infiltration sources were removed using the District's Private Inflow Reduction Report (PIRR) process. This process included inspecting private properties for I/I sources, determining solutions for the removal of the I/I and working with the property owners to get approval of the solutions. Of the ninety-six (96) properties identified with I/I sources, sixty-seven (67) properties, or 70%, agreed to participate in the program.

Additional culvert modifications were designed to improve the hydraulics of the downstream storm sewer system. The storm sewer system was modeled using Storm CAD software, while the sanitary sewer was modeled using Hydra software.