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<br />Biosolids facilities at the WPCF and the BMF are both sized and function to treat the BOD <br />and TSS removed during the treatment process; therefore, their allocation is split equally <br />between BOD and TSS. <br />? <br />BOD - 1/2 <br /> <br />? <br />TSS - 1/2 <br /> <br />Tertiary Filters <br />The existing WPCF does not have tertiary filters. The 20-year project list recommends that <br />tertiary filters be installed to enable the WPCF to consistently meet the NPDES permit <br />discharge requirements. The permit includes mass limits for BOD and TSS. As influent <br />flows to the WPCF increase in the future, the effluent concentration required to meet the <br />mass limits decreases. Addition of the filters will assist with meeting these more stringent <br />effluent concentrations. From a functional basis, the main purpose of the filters is to remove <br />TSS, and to a lesser degree BOD. From a design criteria sizing basis, average flow is used to <br />determine the size of the facilities. In the wet weather season, a portion of the peak flow <br />may be routed to the filters for additional treatment. However, the associated peak flow <br />loading rate onto the filters will not be the limiting factor in terms of design criteria sizing. <br />Following is the allocation for the tertiary filter treatment category: <br />? <br />Average Flow – 1/4 <br /> <br />? <br />BOD – 1/4 <br /> <br />? <br />TSS – 1/2 <br /> <br />Reuse Facilities <br />Reuse facilities may be constructed to comply with more stringent regulatory requirements <br />related to temperature and/or thermal load restrictions of Willamette River discharges. <br />Reuse facilities would allow flow to be diverted from the river by reusing plant effluent for <br />irrigation. The basic design criterion used to size reuse facilities is average flow; so this <br />parameter receives 100 percent of the allocation. <br />? <br />Average Flow – 100 percent <br /> <br />Odor Control <br />Odor control facilities function by collecting odorous air from preliminary/primary liquids <br />treatment processes and biosolids treatment/handling processes and treating the air to <br />remove the odors. Odor generation is dependent on the influent loading levels and, <br />therefore, the allocation is split equally between BOD and TSS because both parameters <br />contribute to the sizing and function of the odor control systems. <br />? <br />BOD – 1/2 <br /> <br />? <br />TSS – 1/2 <br /> <br />Peak Flow Management <br />There are a number of future capital improvement projects that specifically function to <br />convey, treat, and discharge the wet season peak flow. For example, the parallel <br />primary/secondary peak flow management approach is proposed solely to address peak <br />Page 26 OF 39 <br /> <br /> <br />