Values-Based CSO LTCP Project Selection Process
Abstract:Louisville and Jefferson County Metropolitan Sewer District (MSD) entered into a Consent Decree with the Kentucky Department of Environmental Protection and EPA Region IV on August 12, 2005. As part of the response to this Consent Decree, a final CSO Long Term Control Plan (LTCP) was completed and submitted to the regulatory agencies prior to the December 31, 2008, deadline. The final CSO LTCP is one of two major plans prepared to resolve water quality, public health and regulatory issues related to sanitary and combined sewer overflows. The CSO LTCP was combined with a Sanitary Sewer Discharge Plan and a Green Infrastructure Plan to form a consolidated approach to address Consent Decree requirements, called the Integrated Overflow Abatement Plan (IOAP).
MSD's sewer system consists of over 3,200 miles of sewer, with 111 active combined sewer overflow locations that may overflow as often as 60 times per year. For development of this LTCP, over 400 projects were evaluated, including a variety of technologies, several consolidation and clustering approaches, and four different levels of site-specific residual overflow frequency. The final CSO LTCP consists of 23 “gray infrastructure” projects, including a mix of sewer separation, off-line storage, in-line storage, storage controls, and “equivalent primary” treatment. Green infrastructure was incorporated as an integral component of the CSO LTCP.
The process used to evaluate and select projects was based on a benefit/cost analysis. A unique feature of the analysis was the use of a multi-variable risk management approach to define the project benefits. The major steps in the project identification and selection process were:
Define a list of potential projects that could control each CSO location
Perform hydraulic modeling necessary to size facilities to control CSOs to four overflow events per year
Prepare conceptual designs and comparative cost estimates for these initial solutions
Calculate a “benefit“ score for each of the initial solutions using a multi-variable set of performance measures
Rank projects based upon benefit to cost ratios to pick the preferred projects.
Optimize the level of service for each of the preferred projects by re-sizing the solutions for 0, 2 and 8 combined sewer overflows per year, recalculating costs and benefit scores, and identifying the level of service with the highest benefit to cost ratio for each location.
Select final listing of projects.
A variety of planning tools were developed to ensure that this process was well
documented, repeatable, and practical given the large number of permutations evaluated. The tools include a planning-level cost development tool, a benefit scoring tool, and project fact sheet templates to uniformly summarize high level aspects of the projects.
The other major component of MSD's Consent Decree response is a Sanitary Sewer Discharge Plan. Development of this plan involved 5 separate watershed modeling teams. Each team used the same set of development and analysis tools, ensuring uniformity of approaches between the teams. Document management approaches to provide access to the evaluation models from each of the teams presented a significant challenge that required standardized naming conventions and file structures, since all deliverables were stored on MSD's internal servers.
Document Type: Research Article
Publication date: January 1, 2009
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