A Benefit-Cost Framework for Evaluating Alternative Real Time Control Strategies in Louisville, Kentucky

The Louisville and Jefferson County Metropolitan Sewer District (MSD) operates and maintains combined and sanitary sewer systems that serve over 700,000 people in Louisville and its surrounding areas. The MSD service area encompasses 11 watersheds in the Ohio River Watershed spanning approximately 385 square miles. Real Time Control (RTC) has been a critical part of MSD's control strategy for more than a decade and will continue to be going forward. At present, MSD employs a Global Optimal Predictive (GOP) RTC system that currently services nine RTC sites distributed throughout the system that utilize in-line storage, off-line storage, and flow diversion to minimize flooding, minimize combined and sanitary sewer overflows, maximize treatment and minimize energy costs. Smart use of RTC technology has allowed MSD to enhance the sustainability of their sewer systems, by improving the water quality of surrounding waterways.In December, 2008, MSD submitted their Integrated Overflow Abatement Plan (IOAP), as part of their Amended Consent Decree (ACD) requirements, to the US EPA and Kentucky Environmental and Public Protection Cabinet. The IOAP includes provision for the design and construction of a number of new facilities that will incorporate an RTC component. As MSD embarks on expansion of their RTC system, they are developing a holistic operating and control strategy for MSD's facilities. Developing this strategy has provided MSD with an opportunity to take a step back, three years into running their RTC system, and evaluate the lessons learned thus far. In so doing, MSD has been able to identify ways in which their RTC system can be improved to help them better manage and operate their sewer system. As part of the study MSD also took time to re-evaluate the RTC strategy currently employed and, at the same time, consider alternative RTC strategies. In order to achieve this, a benefit/cost framework was developed and applied to determine the most sustainable RTC strategy for their current and future facilities. In addition, MSD has developed a set of RTC design standards to be used in the design of future RTC facilities and has identified ways to modify their internal organizational structure to ensure the sustainability of RTC operation and management.This paper will highlight the lessons learned from MSD's experience with RTC thus far and describe the benefit-cost framework and its application in Louisville. Together, these will demonstrate how this process has helped enhance the sustainability of the MSD sewer system.