Functional Design for the South Hartford CSO Storage Tunnel

This paper presents the functional design of the South Hartford Conveyance and Storage Tunnel in Hartford, CT. Functional design focuses on how excess wet weather flow is handled throughout the tunnel system, from the upstream conduits that convey flow to diversion structures, to the downstream pumping system used to empty the tunnel, following storm events. The South Tunnel is being built by Hartford’s Metropolitan District to reduce combined sewer overflows (CSOs) and eliminate sanitary sewer overflows (SSOs) to the Connecticut River and local tributaries. Consolidation conduits will pick up those overflows and convey them to diversion structures. The diversion structures will limit overflows to the capacity of the tunnel system and divert excess flows to existing CSO outfalls. Hydraulic drop shafts will convey flow in a controlled manner to the deep rock tunnel. Once in the tunnel, flow will eventually be pumped to the Hartford Water Pollution Control Facility (HWPCF). The tunnel system will be operated and controlled using a simple predictive control strategy designed to limit the admittance of 1-yr CSOs into the tunnel during large storms when capacity must be preserved for higher priority CSOs and SSOs.