Overview
The River Des Peres in southwest St. Louis City is a channelized tributary to the Mississippi River extending nearly 9 miles to “The Hill” neighborhood. Like many older communities throughout the US, the area is served by a combined sewer system where wastewater and stormwater are collected in the same pipe. During heavy rain events these pipes can generate combined sewer overflows (CSOs) that release the mixed wastewater and stormwater directly into River Des Peres.
At a depth of 200 feet below ground, the project will generally follow the River Des Peres so that it can capture the mixed wastewater and stormwater before it enters the river. Tangential vortex drop shafts will transfer the mixed water from shallow pipes (sewers) to the tunnel. The tunnel will store the water until it can be treated at the Lemay Wastewater Treatment Plant near the Mississippi River.
The project consists of the following key elements:
- Main tunnel: Approximately 9-miles long, 30-ft inside diameter
- Two (2) connecting tunnels: Each approximately 1/2-mile in length with 12-ft to 14-ft inside diameter
- Five (5) large diameter construction shafts
- A large (150-ft long by 58-ft wide by 84-ft high) excavation for a future cavern-style pump station
- Thirty-four (34) intake structures, including the 20-ft diameter drop shaft on the Forest Park Intake.
Lower & Middle River Des Peres Storage Tunnel Fast Facts
Length: approximately 9 miles
Estimated Construction Cost: $995 million
Construction Start (anticipated): 2029
Construction Completion (anticipated): 2038
Design Engineer: Jacobs
Construction Manager: Black & Veatch