Item 4 - PH on MWMC Reg. SDCs - Laserfiche WebLink

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APPENDIX B Capacity Parameter Allocation Basis System Capacity Parameters are based on permitting requirements. Facility process components (defined in Appendix A) are allocated to each of the system capacity parameters, as described below. Collection System Pipelines This category consists of major gravity sewer pipelines and force mains (pressure lines) that convey flow for the regional wastewater collection system. Since the primary function of the pipelines is to convey flow, the allocation is assigned to either average or peak flow and none to wastewater strength parameters (i.e., BOD and TSS). The majority of the time the conveyance system is carrying average flows. However, the limiting design criteria when sizing pipelines is based on peak flows. An assessment of the wet season I/I, which is the key driver in determining the peak flows, can be used as a guide in determining the average/peak allocation breakdown. Table B-1 presents the wet season I/I as a percentage of total peak flow for existing capacity, current loading, and future required capacity. TABLE B-I Design Criteria Basis For Unit Processes Driven By Peak Flow Average Wet Weather I/I as a Flow Wet Weather I/I Total Peak Flow Percentage of Total Peak (mgd) (mgd) (mgd) Flow, % Existing capacity 49 126 175 72% Current loading (current 43.8 220.2 264 83% capacity required) Projected 2025 loading 59.3 218.7a 277 79% (future capacity required) Notes: a) Net reduction in total I/I occurs between now and 2025 as a result of I/I reduction efforts by the cities. The range of wet weather I/I as a percentage of total peak flow for these three scenarios ranges from 72 to 84 percent. The arithmetic average of these three values is 78 percent. Therefore, a reasonable approach is to allocate a quarter to functional use basis, or average flow; and three quarters to the design criteria sizing basis, or peak flow. · Average Flow - 1/4 · Peak Flow-3/4 SEA31003271388(DG).DOC/041040034