Finding Solutions to Sanitary Sewer System Capacity Deficiencies
In 2000, the Metropolitan Sewer District of Greater Cincinnati (MSDGC) initiated the development of a system-wide computer model (SWM) of their wastewater collection system to assist the agency in the assessment of the hydraulic performance of its system and in the prioritization of short- and long-term system improvements. The 42,000-node SWM was developed and calibrated, using EPA SWMM 4, over a three-year period and represents over 1,500 miles of pipe (CDM, 2003).
In response to Consent Decree requirements, the SWM was used to perform a comprehensive hydraulic capacity assessment to identify system deficiencies of the wastewater collection system under both dry- and wet-weather flow conditions. More recently, the SWM has been applied to find solutions to hydraulic deficiencies in order to provide adequate system capacity under present and future conditions.
This chapter presents the process used to develop a solution to hydraulic capacity deficiencies in the Mill Creek Basin of the MSDGC sanitary service area. The general approach using SWMM modeling techniques to screen alternatives and find cost-effective solutions are discussed, including a tool created to read SWMM output files and generate planning level costs. The costing is based on agreed upon costing curves for the project and is applied for a particular scenario based on the difference in pipe sizes needed for various scenarios. The costing tool provided an efficient means to estimate costs and expedited the alternative screening process. The process led to approximately $300M in sanitary sewer capital improvement projects that are currently being considered as a component to the agency’s Wet Weather Improvement Plan.
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