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Page 28 <br />Section D: PLANT OPBRATLONS <br />• Biochemical Oxygen Demand <br />The average BOD concentration over the pastfive <br />years has been 144 mg/L. The lowest was 60 mg/L <br />and the highest was 266 mg/L. A typical national <br />average is 100 to 300 mg/L. BOD concentrations <br />in the Northwest are usually lower than in other <br />parts of the country because of the higher flow <br />attributed to inflow and infiltration. <br />The low BOD concentrations result in low "food- <br />to-microorganism (F/M) ratios" in the activated <br />sludgeprocess. Thisfacilitates thegrow~hoflowF/ <br />M filament bacteria, which can lead to excess foam <br />accumulation and/or sludge settling problems if <br />not held in check. <br />DISCHARGE PERMIT MONITORING <br />AND LIMITATION PARAMETERS <br />The following information shows the results and <br />treatment performance of the plant in relation to <br />waste discharge permit parameters. <br />• Total Flow <br />Daily monitoring and reporting of total plant flow <br />is required. The discharge permit allows an aver- <br />age dry weather flow of 49 MGD. The average <br />total flow in the pasC six years for May through <br />October was 23.6 MGD. The maximum monthly <br />average for the same period was 36 MGD. The <br />average total flow for November through April <br />(wetweather months) was 40.2 MGD. The maxi- <br />mum monthly weC weather average for the same <br />period was 74.6 MGD. <br />• Influent pH <br />Influent pH must be monitored daily. Influent pH <br />normally ranges between 6.5 and 8.0, and rarely <br />shows extreme fluctuations beyond this range. <br />• Effluent pH <br />The year-round limit for effluent pH is 6.0 to 9.0. <br />The planthas consistentlymaintainedeffluentpH <br />levels within a range of 6.6 to 8.0. <br />• Effluent BOD/Dry Weather Average <br />The maximum allowable monthly average of of <br />fluent BOD concentration for the dry weather <br />months May through October is 10 mg/L. The <br />maximum allowable weekly average of effluent <br />BOD concentration is 15 mg/L. The maximum <br />allowable monthly average of total pounds of BOD <br />discharged is 4,085. The maximum allowable <br />weekly average is 6,122, and the daily average is <br />8,170. <br />Plant Effluent BOD Concentrations/May <br />through October (Limits: 10 mg/I- monthly, <br />15 mg/L weekly): <br />Peak Peak <br />Daily Monthly Weekly <br />Average Average Average <br />1984 6 mg/L 9 mg/L 11 mg/L <br />1985 6 mg/L 8 mg/L 12 mg/L <br />1986 7 mg/L 9 mg/L 13 mg/L <br />1987 8 mg/L 8 mg/L 10 mg/L <br />1988 7 mg/L 9 mg/L 14 mg/L <br />1989 7 mg/L 9 rng/L 14 mg/L <br />1990 4 mg/L 6 mg/L 9 mg/L <br />1991 5 mg/L 6 mg/L 10 mg/L <br />PlantEffluent BOD Pounds Discharged/May <br />through October (Limits: 4,0851bs. monthly, <br />6,1221bs. weekly, 8,1701bs. daily): <br /> Peak Peak Peak <br /> Monthly Weekly Daily <br /> Average Average Average <br />1984 1,9221bs 2,7391bs 4,5831bs <br />1985 1,4001bs 2,3201bs 3,6301bs <br />1986 2,6801bs 2,8531bs 4,6901bs <br />1987 1,5601bs 2,2731bs 2,8301bs <br />1988 2,0601bs 3,0801bs 4,3001bs <br />1989 1,7901bs 2,9201bs 3,9401bs <br />1990 1,4501bs 1,6431bs 4,4501bs <br />1991 2,4801bs 6,4601bs 14,8301bs <br />• E f f luent TSS, Dry Weather Average <br />The maximum allowable monthly average for ef- <br />fluentTSS in the waste discharge limitation per- <br />mitfordry weather months May through October <br />is 10 mg/L. The maximum allowable weekly aver- <br />