Item 2C: Adoption of Resolution Amending MWMC Regional Wastewater SDC Methodology

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Collection System Pump Stations The category collection system pump stations consist of pump stations that impart additional head or pressure to the wastewater so that the flow is conveyed to the WPCF. An example of such a facility is the Wilakenzie Pump Station. These regional pump stations have the same functional and design criteria basis as the regional collection system pipelines, and, therefore, the allocations are: ? Average Flow - 1/4 ? Peak Flow - 3/4 Preliminary Treatment Preliminary treatment facilities are located between the pump stations and primary treatment, consisting of screenings and grit removal facilities. Minimal organic matter (BOD) is removed during preliminary treatment. Also, solid materials removed during preliminary treatment tend to be large and heavy in nature; these materials are not typically considered a “suspended” material (or TSS). Consequently, the loading parameters of BOD and TSS generally do not apply to preliminary treatment, and the unit process category is entirely flow based. The functional and design criteria basis for preliminary treatment are very similar to that of the collection system facilities, and, therefore, the allocation is identical to the preceding categories. The split between average and peak flow is as follows: ? Average Flow - 1/4 ? Peak Flow - 3/4 Primary Treatment Primary treatment consists of the four, large, circular concrete basins (primary clarifiers) and the associated equipment used to remove solids that settle to the bottom of the basins. The purpose of primary treatment from a functional basis is to remove TSS and to a lesser degree BOD. Typical percent removal across primary treatment for TSS and BOD are 60 and 30 percent, respectively. In other words, twice as much TSS is removed relative to BOD. For the design criteria basis, typical primary clarifiers sizing is governed by both average and peak flow, but for MWMC, where the parallel primary/secondary approach is proposed for peak flow management, the peak flow will be split between primary treatment and secondary treatment. Likewise, if the high-rate clarification peak flow management is ultimately implemented (because regulatory approval is not obtained for the parallel primary/secondary approach), the peak flow will be split between the primary treatment and the high-rate clarification. Therefore, only average flow is considered in the cost allocation. Combining the functional basis with the design criteria basis, the following allocation is for primary treatment: ? Average Flow - 1/4 ? BOD - 1/4 ? TSS - 1/2 Page 24 OF 39