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MWMC FACILITIES PLAN 3.1.6 Summary of Previous Collection System Modeling The WWFMP provided the MWMC, Eugene, and Springfield with a plan to identify the immediate rehabilitative needs of the wastewater conveyance system, and recommended a proactive approach to future wastewater management. The basis of these recommendations is the DHI MOUSE hydraulic model, which simulates unsteady flows in pipe networks. To meet the objectives of the WWFMP, it was not necessary to include every pipe of the service area in the model. Because flows were analyzed at a subbasin level, the model network needed only to be similarly detailed. In general, pipes 12 inches in diameter and larger were included in the model, as well as major pump stations and force mains. However, where necessary to maintain continuity in a series of pipes within a conveyance reach, pipes with smaller diameters were included. Figure 3.1.4-1 shows the modeled portions of the wastewater collection system. As part of the WWFMP, the hydraulic model was calibrated to flow data from extensive flow monitoring conducted between 1997 and 1999 throughout the wastewater collection system and from the WPCF. In accordance with DEQ guidelines, the 10-year summer and the 5-year winter rainfall events were compared to determine which storm produced the defining (i.e., worst-case) flow condition in the wastewater collection system. The 10-year summer rainfall event is typically of shorter sustained duration and higher intensity compared to the 5-year winter event. The 2000 WWFMP modeling effort concluded that the 5-year winter event was more critical and the buildout flow rate for the WPCF was estimated at 290 mgd. The collection system model would be subsequently updated for this Facility Plan to define the 2025 peak flow rate. That analysis is presented in section 5.4.1. 3.2 Wastewater Treatment Facility 3.2.1 Facility History The WPCF officially began operation in April 1984. Most of the planning and design of the original facility took place in 1979. The majority of the construction for the major treatment facilities took place between 1983 and 1985. Table 3.2.1-1 summarizes the construction of the original major treatment facilities, notes the year that construction took place, and briefly describes the facilities constructed. TABLE 3.2.1-1 Original Plant Construction and Facilities MWMC Facilities plan, Eugene-Springfield Construction Project Year Description Pretreatment 1984 Influent pump station, five screening channels with comminutors, four aerated grit chambers, four preaeration chambers, and two carbon odor control scrubbers Primary Treatment 1984 Four primary clarifiers and primary sludge pump station Aeration Basins 1984 Eight aeration basins with course bubble diffuser aeration Secondary Clarifiers 1984 Eight secondary clarifiers 3-6 MWMC_3.0_REV11.DOC