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The Massachusetts Water Resources Authority (MWRA) operates the wastewater collection and treatment system for 43 communities in the Boston area. Four of these communities have combined sewer systems with combined sewer overflows (CSOs). In the early 1990s, to support the development of a CSO long term control plan, the MWRA developed a detailed collection system model using the EPA's Stormwater Management Model (SWMM). Since then the MWRA has used this model extensively in the planning and design of projects to improve operation of its collection system. However, the existing SWMM model was limited in its ability to simulate all of the hydraulic elements in the system, as well as complex real-time control alternatives. The SWMM model also had constraints relating to stability, which required schematization of the system. Therefore, to support its continued efforts to optimize the use of its collection and treatment systems, MWRA decided to develop a new state-of-the-art model.

The new model was developed using the InfoWorks CS software package, which allows linkage with GIS and data base systems. The framework for the new MWRA model was developed from MWRA's Oracle and GIS database. The community system networks, which tie into MWRA's interceptor system, were added using information from the previous SWMM model. Additional information was added to simulate structures, such as pump stations, in significant detail. This included the addition of screens and gates as well as implementing RTC rules to simulate operator controls at facilities. The resulting model includes every manhole and hydraulic structure in the MWRA's regional interceptor system. As a result, the model is an excellent tool for bridging the gap between system operators and engineers. Operational and field inspection staff can easily identify and discuss system knowledge of particular locations in the system, while the engineers can perform simulations to determine the cause of observed problems and devise remedial measures.

The InfoWorks model was calibrated to over 200 flow meters and 88 CSO locations for three typical storm events and one extreme storm event. Radar rainfall data were utilized to better characterize the calibration storms.

The new model is being used to explore possible optimization alternatives to improve wastewater conveyance during wet weather conditions. Optimization alternatives are being evaluated for both normal operations and for extreme events that have caused flooding in the past. The metrics used for the optimization include CSO activations, system surcharging, flooding control, and costs. Alternatives to optimize operations under typical wet weather conditions focused primarily on pumping strategies to lower upstream hydraulic grade lines; real-time controls for CSO facility influent gates to fully utilize in-system storage prior to and during activation; and hydraulic relief or flow diversions to help balance system capacity. Alternatives to optimize operations under extreme wet weather conditions focus on transferring flows from the MWRA's South System to the North System, to take advantage of variations in timing and duration of peak flows; optimization of wet weather pump station operations; construction of relief points to direct and manage overflows; and the potential to route diverted flows to an existing CSO treatment facility.

Document Type: Research Article


Publication date: January 1, 2004

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