Conceptual Value Engineering Study Yields Significant Cost Savings on Interceptor Relief Project

The East Branch of the Muddy Creek Interceptor (EBMCI) runs along the north bank of the Ohio River west of the downtown Cincinnati area. The approximately 32,000 foot long interceptor serves a combined sewer system, and 11 outfalls along the interceptor currently discharge approximately 460 million gallons of CSO in a typical year. In 2000, a study of the EBMCI by the Metropolitan Sewer District of Greater Cincinnati (MSDGC) concluded that the interceptor had insufficient capacity, and should be replaced. The proposed location of the new interceptor was intended to facilitate future sewer separation, and the work would have included replacement of four existing small pump stations along the route of the interceptor that were in poor condition. The plan recommended increasing the size of the existing interceptor from 15 to 24-inch diameter, with an estimated construction cost of 12.5 million.As design proceeded on the interceptor relief project, the estimated construction cost climbed to approximately 97 million. The increase in estimated construction cost was driven by numerous utility conflicts, soil conditions, and changes to design criteria for peak flow capacity. These conditions required the invert elevation of the new interceptor to be lower than previously planned, resulting in the need to install much of the interceptor by microtunneling, and also increased the diameter of the interceptor.As a result of the significant increase in project cost, MSDGC undertook a conceptual value engineering study to identify and evaluate potential alternatives to the current interceptor relief plan. The intent was to think “outside the box”, to identify alternative solutions to control CSO discharge volumes and improve the existing infrastructure. An initial range of alternatives was subjected to a series of screening steps involving sequentially more detailed evaluations. This approach encouraged innovative thinking, while preserving analysis budget for the more feasible alternatives. The initial brainstorming resulted in the identification of 39 alternatives, which were subsequently screened to 16 alternatives, and then to seven and finally to four, from which the preferred alternative was selected.The alternative selected by MSDGC included the following elements:Rehabilitate the existing interceptor by CIPPReplace the four existing pump stations with four new pump stations with increased capacityImplement sewer separation along the interceptorImplement river inflow prevention measuresThe selected alternative had an estimated construction cost of approximately 48 million, representing a savings of approximately 50 million over the previous plan. This plan would reduce the annual CSO discharge volume by approximately 96 percent in a typical rainfall year.