Improving Wet Weather Capture Through “Intelligent Wet Weather Management”: Louisville’s Success Story

Written by Angela Akridge, PE, Diana Qing Tao, M.Eng.

Collection Systems – April 19 – 22, 2009

As part of its on-going efforts to reduce combined sewer overflows, the Louisville & Jefferson County Metropolitan Sewer District (MSD) has pioneered the implementation of “intelligent real time control” (RTC) in the United States to operate and manage its complex sewer network.

While in-line storage of wet weather flows has been practiced for decades in many locations around the world, intelligent real time control adds forward-looking rainfall prediction to the control algorithm, allowing system-wide optimization of flow routing and storage in MSD’s complex system.

MSD’s implementation of RTC began with a series of feasibility studies that showed cost effective benefits of optimization intelligence to sewer flow management. Louisville MSD was particularly interested in taking advantage of the potential for rapid implementation of CSO control measures leading to significant overflow reduction through the use of existing large diameter sewers and other infrastructure.

The first phase of the intelligent RTC system went into operation in April 2006, which had an immediate impact on CSO volumes with annual average reduction of over 600 million gallons, representing a system-wide overflow reduction of 14%. Modeled comparisons of the actual performance of the intelligent RTC system compared to a conventional in-line storage system showed a 26% improvement in wet weather capture attributable to the intelligent optimization feature of the RTC system. The cost of implementing the Phase 1 system was $13 M, resulting in a control cost of $0.012 to $0.021/gallon AAOV removed based on actual costs and actual performance of the system, in region 3 and region 1 respectively. The success of the first phase of RTC implementation supported immediately moving forward with the planned second phase of the overall program, incorporating four additional sites into the intelligent RTC system and in service before the end of 2008. The Phase 2 sites have an expected cost of implementation of $0.02/gallon AAOV removed using inline storage with intelligent control.

In parallel with implementation of the first and second phases of RTC implementation, MSD developed an Integrated Overflow Abatement Plan to address system-wide CSO and SSO issues. A comprehensive decision support process was used in developing this plan, based on a risk management-based benefit/cost evaluation. The successes of the first phase of RTC implementation and the expected effectiveness of the second phase supported the development of RTC project alternatives at several additional sites in the system. In head-to-head comparisons with more conventional overflow abatement approaches, RTC alternatives were selected at 12 additional sites, either as the sole method of CSO control, or as an integral part of a more extensive CSO control system.

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Diana Tao

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