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

摘要

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. 2to the Indianapolis Consent Decree (CD), which reduced estimated CSO program costs by $740million. The CD modification has been celebrated by U.S. EPA as a “win-win” since it resultedin cost savings for the city and additional capture of CSO discharges.In May 2009, Indianapolis DPW and RebuildIndy program management team staff proposed toU.S. EPA Region 5 a modification of the CD for 14 of the 31 combined sewer control measuresin the consent decree, including the deep tunnel system and the Southport advanced wastewatertreatment (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 berecommended for approval by EPA and DOJ staff, it was necessary for Indianapolis todemonstrate that the proposed modifications had better environmental benefits than the originalCD that was entered in January 2007. The technical basis for proving the environmental benefitsto EPA and DOJ included:1 Hydraulic Modeling: A more detailed evaluation of the CSO system determined thataverage annual CSO volumes are approximately 30% lower than understood at the timeof the original CD. This finding, in conjunction with the first CD amendment, allowed forsmaller facilities to achieve the same performance criteria. The expansion and calibrationof the hydraulic model since January 2007 was presented in detail to EPA to confirm theupdated facility sizes.2 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 CSOcontrol measures away from shallow interceptors, in-line storage, pump stations, andtreatment expansions, and towards storage facilities with a longer service life, betterreliability, and lower electrical and chemical usage.3 Sewage Out Sooner: The accepted modifications to the CD included a lower averageannual CSO discharge after full implementation than the original CD, and also allowedfor accelerating key projects to capture an additional 3.5 billion gallons of CSO by fullimplementation.