Tunneling a Solution: Storage tunnels keep overflows at bay

A detailed groundwater monitoring and management plan is required to be developed and implemented early in a design phase of a tunnel system and periodically updated throughout design, construction, and long-term operations. The project team should devote special attention to strategies and controls to limit infiltration and to control exfiltration for projects that encompass storage and conveyance of combined sewer overflows (CSOs) and sanitary sewer overflows (SSOs). A detailed evaluation of the geology and hydrogeology of the tunnel alignment corridor, construction, and project considerations, risk management strategies are key for meeting storage and conveyance goals. Controlling the hydraulic gradient line during operation of the tunnel system will drastically reduce the potential for exfiltration and subsequent higher infiltration rates.