Abstract

In 2005, the City of Columbus, Ohio submitted a plan to the Ohio Environmental Protection Agency (EPA) to manage its wet weather flow which includes a list of proposed improvements to eliminate or mitigate combined sewer overflows (CSOs). Critical components of the plan are the Olentangy Scioto interceptor sewer (OSIS) augmentation relief sewer (OARS), the construction of CSO high rate treatment, and a 10 MG storage facility to meet the desired level of control of zero overflow in a typical year. The total estimated cost of these three components in 2005 dollars was $396 million.

During the design phases of OARS, the city expressed interest in increasing the level of control of the downtown CSOs. A value engineering team favoured a deep tunnel option for OARS. A hydraulic SWMM model was developed to optimize the size of OARS through examining the capability of the collection system to meet the higher level of control of the downtown CSOs.

Modeling showed there was flexibility to allow the implementation of different methods of flow control in the collection system by adjusting gate settings, the operational rates of pump stations, and different tunnel sizes and numbers of shafts, all of which was reflected in cost savings of $103 million. The modeling also identified constraints of the wastewater treatment plant (WWTP) capacities and limitations of the existing collection system.

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