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SYSTEM DEVELOPMENT CHARGE METHODOLOGY Biosolids facilities at the WPCF and the BMF are both sized and function to treat the BOD and TSS removed during the treatment process; therefore, their allocation is split equally between BOD and TSS. · BOD-1/2 · TSS-1/2 Tertiary Filters The existing WPCF does not have tertiary filters. The 20-year project list recommends that tertiary filters be installed to enable the WPCF to consistently meet the NPDES permit discharge requirements. The permit includes mass limits for BOD and TSS. As influent flows to the WPCF increase in the future, the effluent concentration required to meet the mass limits decreases. Addition of the filters will assist with meeting these more stringent effluent concentrations. From a functional basis, the main purpose of the filters is to remove TSS, and to a lesser degree BOD. From a design criteria sizing basis, average flow is used to determine the size of the facilities. In the wet weather season, a portion of the peak flow may be routed to the filters for additional treatment. However, the associated peak flow loading rate onto the filters will not be the limiting factor in terms of design criteria sizing. Following is the allocation for the tertiary filter treatment category: · Average Flow- 1/4 · BOD- 1/4 · TSS- 1/2 Reuse Facilities Reuse facilities may be constructed to comply with more stringent regulatory requirements related to temperature and/or thermal load restrictions of Willamette River discharges. Reuse facilities would allow flow to be diverted from the river by reusing plant effluent for irrigation. The basic design criterion used to size reuse facilities is average flow; so this parameter receives 100 percent of the allocation. · Average Flow - 100 percent Odor Control Odor control facilities function by collecting odorous air from preliminary/primary liquids treatment processes and biosolids treatment/handling processes and treating the air to remove the odors. Odor generation is dependent on the influent loading levels and, therefore, the allocation is split equally between BOD and TSS because both parameters contribute to the sizing and function of the odor control systems. · BOD- 1/2 · TSS- 1/2 Peak Flow Management There are a number of future capital improvement projects that specifically function to convey, treat, and discharge the wet season peak flow. For example, the parallel primary/secondary peak flow management approach is proposed solely to address peak SEA31003271388{DG).DOC/041040034