A confluence of least-cost solutions and complex objectives came together in South Bend.

South Bend applied Optimizer™ to its CSO Long Term Control Plan to reduce costs by $112 million, while reducing system-wide overflow volumes an additional 30%.

South Bend, Indiana is one of 772 U.S. communities served by a Combined Sewer System (CSS). In 2011, the City of South Bend was negotiating its Consent Decree with Federal and State regulators aimed at alleviating the frequency and volume of CSOs into the St. Joseph River. The City recognized the estimated $510 million cost of the planned Long Term Control Plan (LTCP) would burden its rate payers with rising monthly utility bills.


City of South Bend, Indiana



Combined Sewer Overflow Long Term Control Plan




  • Significant cost savings against baseline Long-Term Control Plan
  • Reduction in CSO frequency and volume and surcharge levels
  • Evaluate green technology alternatives

“When you are about to invest half a billion dollars over the next 20 years on a CSO Long Term Control Plan, you want to know it is the right plan – the smartest investment. This will be the largest environmental infrastructure program in our city history – this team has given us confidence we are on the best path making a sound investment that will achieve the stewardship and economic end in mind.”

Gary Gilot
Board of Public Works

The City took a decisive step to undertake an optimization study to review and modify its existing LTCP to reduce the Plan cost and to efficiently stage the LTCP improvements. The project team developed an extensive set of feasible improvement alternatives, unit cost rate estimates for each improvement option, and selected suitable design storm events from the typical-year rainfall data.

The comprehensive optimization was conducted in two phases. Phase 1 considered grey infrastructure alternatives and developed an optimized “grey-only” solution directly comparable to the existing LTCP. The existing LTCP cost was reduced from $412 million to $350 million (15% less). Phase 2 developed an optimized CSO LTCP that considered both grey infrastructure and green infrastructure alternatives. The cost then dropped from $412 million to $300 million (27% less).

The Optimizer benefits were not only avoided cost but also improved system performance. The grey-green optimized solution demonstrated a reduction in total overflow volume of more than 30%, a decrease in the number of CSO locations and CSO frequency, and significantly reduced surcharge levels to mitigate basement backups.


Prioritization of Projects for Maximum Impact.

Overflow volumes are for worst 10 rainfall events from typical year rainfall data and do not include controlled overflows (i.e., those with provisions for treatment).