Combined Sewer Overflow – Long Term Control Plan, Muncie, Indiana

Introduction The Muncie Sanitary District (MSD), a special sewer district formed under Indiana statute guidelines, serves nearly 40,000 residents of the City of Muncie and adjacent Delaware County. It has experienced negative press from the local news media regarding the cause of pollution entering the West Fork of the White River that cuts through the downtown of the City of Muncie and serves as a community recreational greenway. In the seventies, the newspaper blamed much of the pollution of the river on the CSOs and the lack of pollution control of industries as a whole.HNTB Corporation was selected to provide a CSO Reduction Study and Long Term Control Plan to fulfill a requirement of the MSD's discharge permit. The project characterized Muncie's combined sewer system, evaluated CSO reduction alternatives, recommended a 20-year plan to achieve the state's 85% volume reduction goal, and participated with the local Citizen Advisory Committee that reviewed the findings and recommendations of the report. A preliminary report to the LTCP was a District-developed study called a Stream Reach Characterization and Evaluation Report (SRCER) that provided a break-through in information about the source of E-Coli in the river and its tributary streams. In dry weather and wet weather, the sampling efforts of the SRCER identified that the river reaches upstream of the District's CSOs were already laden with E-Coli and other pollution contaminants. Complexity The LTCP preparation involved a complex set of criteria and challenges to solve. The EPA's Storm Water management Model (SWMM) was developed to better understand the operation of the collection system and to evaluate the performance of proposed alternatives. The model required the following data:Accurate sewer system maps describing location, depth, and size of pipe in the combined sewer areasFlow monitoring data from 25 meter stations that collected three consecutive months of continuous data that included 10 significant rainfall eventsCSO discharge sampling data that included analytical results for CBOD, Total Suspended Solids, Ammonia, and E-ColiForty-seven years of historical rainfall and temperature dataThe goal of the study was to find the alternative that produced the most CSO reduction for the least cost, while complying with the goals of the IDEDM. Deductive reasoning and careful screening was conducted to reduce the number of alternatives for comparison. As a result,eight alternative composed of various combinations of corrective measures were analyzed for their individual cost/benefit ration. The SWMM quickly and simultaneously calculated resultant flows in the collection system and the river for every option HNTB evaluated as a cost-effective tool of reducing discharges. Unique Techniques The study represents a mix of different techniques and equipment for solving a long-standing problem of poor water quality in the West Fork of the White River. The plan includes a unique mix of sewer separation, in-system storage, plant-site storage pond, and increased wetweather treatment capacity at the MSD facility. The innovative treatment equipment includes:An interceptor sized for capture and storage of the average annual CSO event for its collection zone (approximately 2 million gallons) that also serves sanitary service to nonsewered areas, and to eliminate two siphon river crossings and a pump stationA hydraulically-operated, flow-control gate on the in-system storage pipeline“Floatables” screening systems on three major CSO structuresHigh-rate primary treatment facility rated at 25 million gallons per day (mgd) providing a higher level of treatment in a smaller space than conventional primary treatment technologyOn-site gas chlorine generation system rated for 50 mgd plant flow to minimize risk of neighbors to stored gas cylindersPlant headworks and CSO structure to provide a common control point for maximizing the quantity of combined sewer flow captured, stored, and partially and/or fully treated, and to provide screening, grit removal and flow measurement of CSO discharge to the riverSocial/Economic Considerations The solutions provided by the study brought a number of benefits to the community, including reduced surface flooding, improving pavement and curb conditions, increased value of property, and improvement to the recreational value of the river for hiking, biking, fishing, and feeding water fowl. The screening of the CSOs, unsightly views of sanitary sewage in the river was eliminated, ultimately benefiting the health, safety and welfare of the community.Meeting and Exceeding Client's Needs and IDEM's goals While the 24 million proposed plan to reduce CSO discharges will increase the District's sewer rate by 36%, they will remain in the lower one-third of the rates for like service in Indiana. The original budget for meeting the District's goal of reducing CSO discharge by 85% was 35 million, but after review with the Citizen Advisory Committee and District staff it was lowered by 33% to the final 24 million level. The other benefit was that CSO discharges would be reduced by 96%, an eleven percent increase over the state's goal of 85%,with only four to six events per year occurring during an average rainfall year.