PEAK FLOW TREATMENT ALTERNATIVES EVALUATED FOR THE EUGENE-SPRINGFIELD WATER POLLUTION CONTROL FACILITY, OREGON

A comprehensive facilities plan was developed for the Metropolitan Wastewater Management Commission (MWMC) in 2004 and included an evaluation of the regional wastewater treatment facilities serving the Eugene-Springfield (E-S) metropolitan area. A previous study, the 2001 Wet Weather Flow Management Plan (WWFMP), modeled the collection system, determined what rainfall dependent infiltration and inflow (RDII) was cost effective to remove and identified an implementation plan for removing that RDII, and concluded that a “convey and treat” approach was the most cost effective solution for addressing the remaining peak flows in the system.One of the key focuses of the newly developed MWMC Facilities Plan was to determine a more detailed solution for implementing the “convey and treat” approach. Early-out efforts of the 2004 planning confirmed that efforts to remove/reduce RDII were being realized as assumed in the WWFMP and that the convey and treat approach was still valid. Alternatives were evaluated for increasing the peak flow treatment capacity at the Eugene-Springfield Water Pollution Control Facility (WPCF) from 175 million gallons per day (mgd) to 277 mgd by 2025. This increase in peak flow capacity is necessary to comply with the Oregon Department of Environmental Quality's (DEQ's) requirement that the wet season flow associated with the 5-year, 24-hour rainfall event be accommodated by MWMC's facilities without resulting in sanitary sewer overflows (SSOs).The alternatives evaluated use a combination of primary treatment and secondary treatment in conjunction with effluent blending to treat the peak flows. Operating the primary and secondary facilities in parallel during infrequent wet season peak flow events is cost effective while protective of effluent receiving water and is the preferred approach. Federal blending policy is still evolving; however, so the use of a high rate clarification process has been retained as the next best alternative for treating the peak wet weather flows.