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ATTACHMENT 4 To 05-06-04 Draft MWMC Minutes (maximum month basis). Even if the constant concentration limits for CBOD and TSS are met, the mass limits imply a lower concentration requirement if the wastewater flows exceed the current dry weather design capacity or if the future dry weather design capacity of the facility is increased. Concentration limits was well as percent removal requirements are also specified in the NPDES permit... Permit removal limits apply; however, they are not a factor during the dry season because the mass and concentration limits are significantly more stringent (page 5-4). The question arises again. Why measure things differently than DEQ does? DEQ, in the permit, provides three different means to measure the CBOD and TSS in both the dry season and the wet weather seasons. Why convert to a fourth measurement that is not proVided by DEQ? Since DEQ refers to the average monthly dry weather design Capacity of the facility of 49 mgds and provides a limit for monthly average flow, why not use monthly average flow to arrive at your capacity (apples to apples)? By converting to Maximum Week, I/I is again included in the flow but not in the design capacity, which is · automatically going to skewer the measurement and result in a significant loss of facility capacity. As a result, CH2MHill determined in the System Development Charge Methodology that the facility is now operating at 83% of our BOD capacity and at 90.4% of our TSS capacity. Seven years ago, when CH2MHill prepared the Master Plan, they concluded that we had a great deal of effluent BOD and TSS capacity. "The remaining treatment capacity of the E/SWPCF is substantial for average dry and wet weather flow conditions and conventional pollutants (BOD and TSS) (page 450). DEQ, as you will recall, placed the capacity used for effluent organic loads at 60%. It also said: "The current permit contains CBOD and TSS removal efficiency limits of 85 percent. The facility has been able to comply with the permit limits and has not had any violations even during the extremely wet months (page 4 of the Fact Sheet and evaluation)." As you recall,.DEQ also concluded that Our current facilities would allow us to continue to remain in compliance with our permit. A second decision made by CH2MHill and .MWMC staff also affected the amount of BOD and TSS capacity reportedly available. When calculating BOD capacity, for example, CH2MHill used the following formula for the System Development Charge Methodology: cUrrent BOD = (0.!9 x 217,690 x 1.3) + 2,402 = 54~800 lbs/day where 0.19 r, 0.185 us the correct nurnberJ is the selected pounds per capita per day based on dry season values from 1990 to 2002 217,690 is the population served in 2002 Attachment 4 Page 14 of 17 4-17