Pipe Considerations for Deep St. Louis LMRDP CSO Tunnel Dewatering Pump Station

This paper will discuss the challenges of designing pipe from a deep tunnel pump station and the solutions developed in the design to accommodate them. The LMRDP CSO Tunnel Dewatering Pump Station will dewater a nine (9) mile long, 30-foot diameter tunnel with a storage capacity of about 240 MG. Located 250 feet below grade, the cavern-style pump station piping required complex design considerations including differential head in discharge piping, space limitations in the tunnel and shafts, pipe coatings and linings for buried and exposed piping, constructability, and pipe joint design for buried pipe in fill and piping in the tunnel and shafts. The improvements are part of the Metropolitan St. Louis Sewer District’s (MSD) implementation of Project Clear, a program to reduce combined sewer overflows (CSO), and eliminate sanitary system overflows (SSO) in compliance with their EPA consent decree. The 100 MGD pump station will contain four (4) 20 MGD pumps, three (3) 10 MGD pumps, and two (2) 5 MGD pumps, with the ability to accommodate a future capacity of 150 MGD. Discharge piping within the pump station and shaft consists of eleven (11) pipes ranging from 30-inch to 4-inch diameter. Buried forcemains are 54-inch and 24-inch. Suction pipes range from 84-inch to 30-inch diameter.