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Metropolitan Wastewater Management Commission ATTACHMENT D partners in wastewater management MEMORANDUM DATE: June 11, 2004 TO: Lane County Commissioners FROM: Peter Ruffler, Director, Wastewater Division Susie Smith, General Manager, MWMC SUBJECT: Peak Wastewater Flows, Response to Public Hearing on the Regional Wastewater Facilities Plan On June 9, 2004 the Lane County Board of Commissioners held a public hearing on the Facilities Plan adopted by the Metropolitan Wastewater Management Commission(MWMC) for the regional wastewater treatment facilitiesserving the Eugene/Springfield metropolitan area. During this hearing questions were raised about the number ofwastewater overflows that have occurred from the regional facilities. This memo isprovided in response to these questions. Since '1995 there have been 7 separate wastewater overflow events reported to the Department of Environmental Quality (DEQ), as requiredby the NPDES permit regulating the regional wastewater facilities. Each of these eventswas associated with a period of significant rainfall, and involved the discharge of untreated sewage to the Willamette River from multiple discharge locations (which, depending upon the event, may have includedthe Old Springfield Plant Site Pump Station at Aspen and Walnut in Springfield; the Glenwood Pump Station in Glenwood; the Fillmore Pump Station in Maurie Jacobs Park, Eugene; and the Willakenzie Pump Station on Goodpasture Lakes Loop Road in Eugene, as well as the surcharging of individual manholes in each of the cities' sanitary sewer collection system). The total volume of the overflows associated with these events has been estimated at over 260,000,000 gallons. It is important to note that most of the years since 1995 have been part of a drought cycle, and that during this period the Eugene-Springfield area has experienced some of the driest years on record. The State of Oregon has established a standard that requires the conveyance and treatment of all sanitary sewer flows that occur during a 5-year, 24-hour rainfall event.~ Modeling done for the Facilities Plan estimates that the peak flows from the Eugene/Springfield system associated with the 5 year storm event will reach a peak of 277 million gallons per day (MGD) by the year 2025 (based upon the assumption of continuing rehabilitation of public sewer pipe by Eugene and Springfield). The existing rated peak flow capacity of the Eugene/Springfield Water Pollution Control Facility is 175 MGD. Statistical analysis of the historical flow record also indicates that the 175 MGD current rated capacity will be exceeded 4 days per year underexistin.q conditions. While there is not a direct correlation between flows exceeding the rated capacity and overflows from the system since the use of redundant pumping and treatment equipment, precipitation ~ Note: The U.S. EPA is in the process of developing a national standard for overflow events. The current proposal is more stringent than the Oregon standard, and would prohibit any overflow events except in exceptional circumstances such as earthquakes, tsunamis, or severe, widespread flooding. L:\CMO~2004 Council Agendas~,1040628\S0406287-attD.doc