Design and Construction of the South Hartford CSO Tunnel

The South Hartford CSO Tunnel (South Tunnel) project is a significant component of the Metropolitan District’s SSO/CSO control program in Hartford, CT. The South Tunnel is a 4-mi.-long, 18-ft internal diameter wet weather tunnel that will eliminate sanitary sewer overflows (SSOs) and control combined sewer overflows (CSOs). Sewer diversion structures will be constructed at each CSO and SSO to replicate or intercept overflows and divert them to near-surface consolidation sewers. These consolidation sewers will in turn, discharge to one of eight hydraulic tangential vortex drop shafts which will convey the flow to the deep rock tunnel. Once in the tunnel, the sewer overflows will be stored and then pumped to receive proper treatment. The project was split into five construction contracts totalling approximately $410 MM. Advanced utility relocation and electrical upgrades have been completed. Construction of the deep rock tunnel, shafts, and deep rock connector tunnels are underway. The 35-ft diameter launch shaft has been excavated. The 70-ft diameter pump station shaft has been excavated to 80 ft below grade. The tunnel boring machine (TBM) has arrived onsite and is being assembled. By July 2018, the launch shaft, pump station shaft, fifteen drilled shafts, and the starter and tail tunnels should all be excavated and the TBM should be beginning its journey. This paper and presentation will focus on the design basis, progress to date, and lessons learned.