You Can Dig It, But Can You Operate It? Proactive CSO Tunnel Operational Planning

In 2011, Citizens Energy Group began construction of the Dig Indy Deep Rock tunnel system, which includes 47 km (29 miles) of tunnels with a finished internal diameter of 5.5 meters (18 feet). This system is the critical part of Citizens’ combined sewer overflow (CSO) consent decree, which is required to be fully operational by the end of 2025. Due to the phased implementation of tunnel design and construction, Citizens initiated a focused, proactive operational planning to ensure that there are no loose ends between multiple design contracts and construction phases. The operational planning included:Development of a SCADA strategy to connect all drop shaft sites to the treatment plant network via fiber optic cable;Development of an instrumentation strategy to reliably monitor the tunnel as part of surge mitigation;Development of a conceptual tunnel dewatering strategy;Physical modeling of drop and ventilation shafts;Development of an air management tool to evaluate forward air induction, air pocket pressurization, and air pocket migration based on current research.Development of a tunnel ventilation strategy based on the physical modeling and air management tool. The strategy focuses on routing air to working and retrieval shafts that are larger than the tunnel diameter;Odor Dispersion analysis for both H2S and ammonia for the end shaft of the Eagle Creek tunnel branch that will be located in a city park; andTours of established CSO tunnel systems and collaboration with other design and operations professionals.The work in developing the Dig Indy operational plan is derived both from highly technical sources, as well as boots-on-the-ground practical experience. Each element of the plan has helped to minimize Citizens’ long-term risk in operating the tunnel system.