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ATTACHMENT 4 To 05-06-04 Draft MWMC Minutes The 2004 Draft'MWMC FaCilities Plan, also prepared by CH2MI-Iill, also identifies the ' dry weather average month design capacity as 49 mgds. However, the amount of monthly flow, either average month or maximum month is dependent upon population estimates. There is a serious discrepancy in the population estimates that CH2MHill provided on March 26, 2004, for the Draft System Development Charge Methodology, in which CH2MHill estimated the current population served in 2002 as 217,690, and the estimated 2005 population estimate of 229,145 found in the draft facilities plan. [This is incorrect. There is no discrepancy. One number is 2002 population and one is the estimated 2005 population. This represents roughly an additional 3,800 people served per year which is consistent with the population projections being used for this Facilities Plan.] Based on the latter 2005 population, CH2MHill estimates actual dry season average flows of 29.6 mgds and dry season maximum monthly flows of 46 mgds (page 4-13). That means we would be using 60.4% of our dry season average monthly capacity and 69.7% of our dry season maximum monthly capacity, Using the design capacities of 49 mgds and 66 mgds respectively./66 mgd is not the current maximum month rating of the plant, so these numbers have no value] CH2MHill identifies the projected 2025 dry season average floW at 38.4 mgds, still substantially below the 49 mgd average flow design capacity, and the 2025 dry weather maximum month flow at 59.3, also below the design capacity of 66 mgds. [66 mgd is not the current maximum month rating of the plant, so these numbers have no value] DEQ also provided an evaluation of the MWMC treatment facility in 2002 in conjunction with the renewal of our NPDES wastewater discharge permit. It noted: The design Average Dry Weather Flow (ADWF) for the facility is 49 million gallons per day (MGD). The ADWF is the estimated maximum flow during May 1 to October 31 (expressed as average daily flow), at which the design engineer expects the treatment facility can still meet all effluent limits. [The definition here states the point at hand. Th'e ADWF is the maximum flow at which the design engineer expects the facility can still meet all the effluent limits. This is 49 mgd under the current NPDES permit] The dry weather flOws do not contain the high levels of infiltration and inflow that are associated with the winter in Oregon. Therefore,' the design dry weather flows are used mostly to estimate how much treatment capacity there is for organic loads. The current actual dry weather flow for May 1 to October 31, for the past two years, is 28.6 MGD, [This was based on information supplied.in 1996, and does not reflect the last 7.5 years of data and the new NPDES permit] On the basis of the current flows, this facility is at approximately 60% of organic treatment capacity. Based on the current low flows compared to the design flows, and the lack of effluent violations, no expansion of the facility is needed at this time (page 2). Attachment 4 Page 8 of 17 4-11