Item 5: Resolution Adopting Amended SDC Methodologies and Rates

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. . APPENDIX B Capacity Parameter Allocation Basis System Capacity,Parameters.arebased on permitting requirements. Facility process components (defined in Appendix A) are allocated to' each of the system capacity parameters, as described below. CollecUon System Pipelines This category consists of major gravity sewer pipelines and force mains (pressure ~es) that convey flow for the regional wastewater collection systeIlL Since the primary function af the pipelines is to convey flow, the allocation is assigned to either average ~r peak flow and none to wastewater strengt!l 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 1/1, which is the key driver in determining the peak flows, can be 'used as a guide in determining the average/peak allocation bre*down.Table B-1 . presents the wet season 1/1 as a percentage of total peak flow for existing capacity, cUrrent loading, and future required capacity. TABLE B-1 Design Criteria Basis For Unit Pr~sses Driven By Peak Flow Existing capacity Current loading (current capacity required) Projected 2025 loading (future capacity required) Notes: a) Net reduction in. total III occurs between now and 2025 as ,a result of III reduction efforts by th.e cities. Average Wet Weather 111 as a Flow Wet Weather III Total Peak Flow Percentage of Total Peak (mgd) (mgd) (mgd) PI'ow, .% 49 126 175 720/0 43.8 220.2 264 83% 59.3 218.78 277 79% The range of wet weather III as a percentage of total pe.ak 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