The DigIndy CSO Tunnel System

In accordance with a Federal Consent Decree, Citizens Energy Group is implementing a long term control plan to address combined sewer overflows (CSOs) in Indianapolis. Included in the “DigIndy” plan are provisions for a series of CSO diversion structures, consolidation sewers, drop shafts, and a 28-mile long network of six 18-foot diameter tunnels. Beginning near the Indiana State Fairgrounds on the north, and ending on the south side of Indianapolis, DigIndy will be the largest public works project in the city’s history. The tunnel system will capture up to 95 percent of CSOs along seven Indianapolis waterways, reducing overflows to less than four per year, the maximum allowed by the US Environmental Protection Agency (EPA). With a volume of more than 250 million gallons, the tunnel system will extend along Fall Creek, White River, Pogues Run, Pleasant Run and Bean Creek to create a collective, underground storage and transport facility for combined sewer overflows. All CSOs captured, stored, and transported in the tunnel system will be treated at one of the City’s advanced wastewater treatment plants. The White River Tunnel is designed to be approximately 5.3 miles, capture 9 combined sewer overflows in 7 vertical drop shafts and contain nearly 5,000 feet of consolidation sewer at the near surface. When incorporated with other improvements in the White River watershed, White River Tunnel will achieve 95 percent CSO capture and limit overflows to an average of 4 events per year. The Fall Creek Tunnel is designed to be approximately 3.7 miles, capture 26 combined sewer overflows in 13 vertical drop shafts and contain nearly 5,100 feet of consolidation sewer at the near surface. When incorporated with other improvements in the fall creek watershed, fall creek tunnel will achieve 97 percent CSO capture and limit overflows to an average of 2 events per year. Sizes of the near surface consolidation sewers range from 24-inch to 108-inch and are planned to be installed through various construction methods including traditional open cut and trenchless bore and jack. The paper and presentation will discuss the overall tunnel system and highlight the near surface sites constructed to date. Also the challenges of managing design of a large system with multiple construction packages, coordination with multiple stakeholders and community neighborhoods, and managing project risks and schedule.