Item B-MWMC Proposed SDC - Laserfiche WebLink

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SYSTEM DEVELOPMENT CHARGE METHODOLOGY Secondary Treatment Secondary treatment consists of two trains of aeration basins, eight secondary clarifiers, and the associated blowers and pumps that function to treat and remove organic loading (BOD) and to a lesser extent TSS from the wastewater. On a functional basis, secondary treatment is regarded as removing roughly twice as much BOD relative to TSS. For the design criteria basis, typical secondary treatment sizing is governed by both average and peak flow, but for MWMC, where the parallel primary/secondary approach (or high- rate clarification approach as a second choice) is proposed for peak flow management, the peak flows will be split between primary treatment and secondary treatment. Therefore, only average flow is considered in the cost allocation. Combining the functional basis with the design criteria basis, the following allocation is for secondary treatment: · Average Flow - 1/4 · BOD- 1/2 · TSS - 1/4 Disinfection/Outfall Following secondary treatment, the wastewater is disinfected (chlorinated and dechlorinated) and discharged to the Willamette River through an outfall pipe. Both the function and sizing of these facilities are entirely based on flow. The relationship between the functional basis and design criteria is identical to that for the collection system facilities and, therefore, the following allocation is for disinfection/outfall: · Average Flow - 1/4 · Peak Flow - 3/4 Biosolids Biosolids are a byproduct of wastewater treatment and are produced during the primary treatment, secondary treatment, and to a lesser degree tertiary treatment processes. The three subcomponents used to allocate biosolids treatment, handling, and disposal/reuse costs for purposes of SDC calculations are: · General · Dewatering · Biocycle Farm The definitions of these subcomponents are presented in Appendix C, Growth Capacity Allocation Documentation. The three subcomponents were developed for the SDC update because of the differing available capacities and growth percentages associated with facilities in the subcomponents. However, in terms of allocating the facility components to the wastewater parameters, the methodology is identical-independent of which subcomponent is being considered. SEA3100327 t388(DG).DOC/041040034