SECAP IS THE C IN CMOM FOR MMSD: CONDUCTING LOCAL SYSTEM CAPACITY ASSESSMENTS IN A REGIONAL WASTEWATER SYSTEM

In 2004, the Milwaukee Metropolitan Sewerage District (MMSD) launched a project to conduct capacity analyses for the 28 satellite municipalities contributing sanitary sewer flow to the MMSD regional collection system. The capacity analyses will play a role in both the development of the regional 2020 Facilities Plan and development of the satellite municipalities' capacity assurance, management, operation and maintenance programs (CMOMs). Extensive hydraulic modeling of the regional metropolitan interceptor sewer (MIS) system has been conducted over the years, but coordinated modeling of the satellite municipal systems had not been previously undertaken. Activities within the satellite municipal systems, such as land use development and system improvements, are a principal factor to the operation of downstream MMSD conveyance and treatment systems.The purpose of the satellite municipality system evaluation and capacity assurance plan (SECAP) analyses was to construct computer hydraulic models capable of identifying and quantifying capacity deficiencies within the 28 satellite municipality systems. As part of the creation of the most recent generation of MMSD facilities plans, the satellite system hydraulic models and flow development were calibrated for year 2000 conditions, several historic wet weather events and historic bypass occurrences. The calibrated hydraulic models were then used to simulate the satellite systems with year 2020 flows. The SECAP analyses determined the cause of the deficiencies to be either the satellite sanitary sewer system or the MIS system. The quantified deficiencies will be included in the regional 2020 Facilities Plan, in which satellite and MIS system improvements will be recommended, along with a cost of implementing the recommended improvement.Analyses of satellite municipality sanitary sewer systems were funded and managed by the regional government agency of MMSD. Examples of the challenges faced by the SECAP project included:Maintaining a standardized approach while working with different raw data formats. Satellite municipality system data was provided in paper, CAD, GIS, and proprietary hydraulic model formats. Differing data formats required corresponding data processing and extraction methods.Identifying key system elements in a consistent manner, while also considering the unique features within each satellite system. Key system elements included pumps and overflow locations, in addition to areas having historic capacity-related problems.Applying a flow development method on a satellite municipality basis utilizing the regional flows developed by a larger planning effort. The application of regionally-developed flows to these more local and detailed hydraulic models required re-calibration of the previously developed flows.Defining a system deficiency and an approach to determine the cause of the deficiency. The hydraulic models were revised to eliminate potential capacity constraints and to determine whether the cause of the system deficiency was a satellite or regional system component.To meet the challenges noted above, several protocols applicable to each of the 28 satellite municipalities were created. The protocols outlined guidelines for identification of key system elements, development of sewershed sub-basins for flow development, and definition of system deficiencies.In addition to providing MMSD with more information about the systems contributing flow to the regional MIS, the resulting hydraulic models for the 28 satellite municipalities will provide the opportunity for the local municipalities to efficiently identify potential local system improvements. The hydraulic models can also serve as starting points for development of more detailed models to aid the municipalities in future decision making.