Devised to tackle sewer overflows in the Lemay/South St. Louis County region, the Jefferson Barracks Tunnel is set to span from just south of I-255 at Koch Road to the Lemay Wastewater Treatment Plant, situated at the confluence of the River des Peres and the Mississippi River.
Displaying signs of aging, the original system could no longer cope with demand during moderate to heavy rainfall. The forthcoming tunnel, along with additional construction, will replace the outdated system, augmenting its capacity to collect, transport, and store wastewater. This proactive measure aims to prevent overflows that pose a threat to the contamination of our waterways.
Extending over 17,800 feet (equivalent to 3.37 miles) alongside the Mississippi River, the tunnel will boast a diameter of 7 feet and will be lined with fiberglass pressure pipe. Adding a layer of intricacy to the project, the chosen route traverses an area of river bluff karst—an absorbent limestone featuring numerous caves and sinkholes formed by erosion. Careful alignment was crucial to circumvent the challenges posed by this terrain, leading engineers to determine that the optimal solution involved boring below the limestone and karst, tunneling into rock at depths ranging from 150 to 230 feet below the surface.