Deep Tunnel Hydraulic Optimization and Stakeholder Coordination: Pleasant Run Deep 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 44.8-km long network of six 5.4-m diameter tunnels. Beginning near the Indiana State Fairgrounds on the north, and ending on the south side of Indianapolis, DigIndy is the largest public works project in the city’s history. The tunnel system will capture up to 97% of CSOs along six Indianapolis waterways, reducing overflows to less than four per year, the maximum allowed by the U.S. Environmental Protection Agency (EPA). The final segment of the system is pleasant run deep tunnel, a 11,970-m long tunnel. Final planning optimized the conceptual design to achieve CSO capture objectives while eliminating expensive components and saving millions of dollars. After the elimination of several drop shafts from the original plan, final design included identifying potential revised locations of drop shafts. The project design faced challenges of construction in an urban environment around numerous utilities. Sizes of the near surface consolidation sewers range from 61- to 274-cm and are planned to be installed through various construction methods including traditional open cut and trenchless bore and jack. Outreach with city stakeholders and land owners of future developments for municipal and private projects led to relocations of shafts including a large diameter intermediate shaft. Citizens and the design team continued to optimize the tunnel alignment and near surface components to minimize consolidation sewer lengths. Recently, the collection system model was expanded, leading to updated flow data resulting in investigation of additional cost savings.