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ATTACHMENT 4 To 05-06-04 Draft MWMC Minutes was growth's contribution t° 298 mgds of peak flow which would include all of the average flow that we are paying for under average flow. [glo, incorrect. Once project costs are allocated to average flow they are no longer available to be allocated to peak flow and vice versa.] Thc 29% cun'ently allocated to growth for peak flow isn't supported by the data. [The 29% or 30 mgd of 102 mgd is derived in Table C-2 of the SDC methodology and is supported by data. The I/I assumed to be generated by growth is less than 30% of the !/I generated by existing MWMC users. Some communities in the Willamette Valley corridor are using 35%.] I. How Much Capacity Do We Have? General Facility Capacity Information: The MWMC treatment facility was designed in 1977 and became operational twenty years ago, in 1984. It was designed to serve a population of 277,100 persons and it was estimated in 1977 that number of persons served by the facility would be reached in 2005. The current number of persons served by MWMC in 2004 is 217,690 persons, so · the initial 1977 population projection that the facility would reach its service capacity next year was substantially in err. Based solely on population to be served, the facility would currently be used at 72.5% of its capacity [This assumption only works if ' you assume that the level of treatment required in 1977 is the same as the level of treatment required in 2025 which is not a correct assumption] is is based solely on the original design. "Design of the original WPCF (Water Pollution Control Facility) was based on demographic and population data established in the mid-1970's. The facility was designed to provide adequate sewerage capacity through the year 2005 for a projected population of 277,100. This projection was made for the sewer service area that existed in the 1970s. However, the growth rate during the 1980s was significantly less than projected. This trend in the growth rate was common throughout much of Oregon because of depressed economic conditions during the mid-1980s (April, 2004 Draft MWMC Facilities Plan, page 1-6). In addition, LCOG population projections for the 1990s were higher than the actual numbers provided by the 2000 US Census. Another factor significantly affected the projected use of the facility's capacity- water conservation efforts. A substantial part of our wastewater, both dry weather flows and wet weather flows, is just What the name suggests - water. I am not referring now to inflow and infiltration (I/I), but rather the composition of the wastewater that is released from homes, businesses, and industrial plants. Whether the wastewater originates from the shower we take in the morning, the dishwashers at a restaurant, or a car wash, the vast majority of our wastewater is simply water. The amount ofwastewater sent from homes and businesses to the sanitary sewer pipes correlates so closely to our actual water usage that our winter water consumption is the basis upon which our MWMC sewer bill is Attachment 4 Page 5 of 17 4-8