Behind the $740M: Building a Technical Consensus for Indianapolis Consent Decree Amendment No. 2

The February 2011 Engineering News Record article “With a Modified Consent Decree, Indianapolis Is Cleaning Up” (ENR, 2011) provided a high-level summary of Amendment No. 2 to the Indianapolis Consent Decree (CD), which reduced estimated CSO program costs by $740 million. The CD modification has been celebrated by U.S. EPA as a “win-win” since it resulted in cost savings for the city and additional capture of CSO discharges.In May 2009, Indianapolis DPW and RebuildIndy program management team staff proposed to U.S. EPA Region 5 a modification of the CD for 14 of the 31 combined sewer control measures in the consent decree, including the deep tunnel system and the Southport advanced wastewater treatment (AWT) plant expansion, which are the two largest components of the consent decree. The amendment was formally approved and entered in December 2010. In order to be recommended for approval by EPA and DOJ staff, it was necessary for Indianapolis to demonstrate that the proposed modifications had better environmental benefits than the original CD that was entered in January 2007. The technical basis for proving the environmental benefits to EPA and DOJ included:• Hydraulic Modeling: A more detailed evaluation of the CSO system determined that average annual CSO volumes are approximately 30% lower than understood at the time of the original CD. This finding, in conjunction with the first CD amendment, allowed for smaller facilities to achieve the same performance criteria. The expansion and calibration of the hydraulic model since January 2007 was presented in detail to EPA to confirm the updated facility sizes.• Sustainability: The accepted modifications to the CD included a more sustainable plan, not from the standpoint of green infrastructure, but from the standpoint of shifting CSO control measures away from shallow interceptors, in-line storage, pump stations, and treatment expansions, and towards storage facilities with a longer service life, better reliability, and lower electrical and chemical usage.• Sewage Out Sooner: The accepted modifications to the CD included a lower average annual CSO discharge after full implementation than the original CD, and also allowed for accelerating key projects to capture an additional 3.5 billion gallons of CSO by full implementation.