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<br />Secondary Treatment <br />Secondary treatment consists of two trains of aeration basins, eight secondary clarifiers, and <br />the associated blowers and pumps that function to treat and remove organic loading (BOD) <br />and to a lesser extent TSS from the wastewater. On a functional basis, secondary treatment <br />is regarded as removing roughly twice as much BOD relative to TSS. <br />For the design criteria basis, typical secondary treatment sizing is governed by both average <br />and peak flow, but for MWMC, where the parallel primary/secondary approach (or high- <br />rate clarification approach as a second choice) is proposed for peak flow management, the <br />peak flows will be split between primary treatment and secondary treatment. Therefore, <br />only average flow is considered in the cost allocation. <br />Combining the functional basis with the design criteria basis, the following allocation is for <br />secondary treatment: <br />? <br />Average Flow - 1/4 <br /> <br />? <br />BOD - 1/2 <br /> <br />? <br />TSS - 1/4 <br /> <br />Disinfection/Outfall <br />Following secondary treatment, the wastewater is disinfected (chlorinated and <br />dechlorinated) and discharged to the Willamette River through an outfall pipe. Both the <br />function and sizing of these facilities are entirely based on flow. The relationship between <br />the functional basis and design criteria is identical to that for the collection system facilities <br />and, therefore, the following allocation is for disinfection/outfall: <br />? <br />Average Flow - 1/4 <br /> <br />? <br />Peak Flow - 3/4 <br /> <br />Biosolids <br />Biosolids are a byproduct of wastewater treatment and are produced during the primary <br />treatment, secondary treatment, and to a lesser degree tertiary treatment processes. The <br />three subcomponents used to allocate biosolids treatment, handling, and disposal/reuse <br />costs for purposes of SDC calculations are: <br />? <br />General <br /> <br />? <br />Dewatering <br /> <br />? <br />Biocycle Farm <br /> <br />The definitions of these subcomponents are presented in Appendix C, Growth Capacity <br />Allocation Documentation. The three subcomponents were developed for the SDC update <br />because of the differing available capacities and growth percentages associated with <br />facilities in the subcomponents. However, in terms of allocating the facility components to <br />the wastewater parameters, the methodology is identical—independent of which <br />subcomponent is being considered. <br />Page 25 OF 39 <br /> <br /> <br />