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[VlWMC FACILITIES PLAN TABLE 6.2.4-1 Summary of Pretreatment Expansion Alternatives Comparison MWMC Facilities Plan, Eugene-Springfield Capital Cost Alternative (millions of dollars) Non-Monetary Ratinga I - Expand Existing Pretreatment Facility $12.8 21 2 - Construct New Pretreatment Facility $17 19 Notes: a Non-monetary score is out of a possible maximum score of 30 points. Capital costs associated with construction of a new pretreat~nent facility are approximately 30 percent higher than for the expansion of the existing facility. The non-monetary evaluation of the two alternatives indicates that expansion of the existing pretreatment facility is slightly more favorable than constructing a new facility. Both alternatives will have 160 mgd of capacity to minimize operation of the existing pretreatment facility, which would only need to be brought online for peak flows. It was assumed that the new pretreatment facility would have full grit removal capacity. As more detailed planning and design efforts proceed for the expansion of the existing pretreatment facility, both of these assumptions should be evaluated more closely. It may be more cost-effective to provide only the required 102 mgd of additional capacity and provide flexibility to bring the existing pretreatment facility online and offlLne more frequently, although this would be extremely labor-intensive from an O&M standpoint. An alternative to providing grit removal during pretreatment would be to degrit thin primary sludge from the primary clarifiers. This may avoid construction of grit removal facilities in the pretreatment expansion. As part of the approach to expand primary clarifier capacity, the ability to pump thin sludge and thicken the primary sludge outside of the clarifiers will be assessed. Grit accumulation in the primary clarifier centerwells is an issue of concern that would have to be addressed if the degritting primary sludge approach is pursued. Based on the alternatives analysis, it is recommended that Alternative 1, expansion of the existing pretreatment facility, be carried forward for facility planning purposes. Further investigation of pretreatment capacity and grit removal will be carried out during predesign. Upon further refinement of the pretreatment expansion, selection and comparison of specific equipment associated with the selected alternative will be evaluated more comprehensively. 6.2.5 Odor Control It is anticipated that the WPCF will need to increase its odorous air treatment system to address the projected increase in air flow rates resulting from the addition of new process units throughout the plant. The existing odor control system consists of a three-cell, organic media biofilter with a design capacity of 18,000 cubic feet per minute (ft3/minute) and a connected capacity of 15,000 ft3/minute. The new odor control system would have sufficient capacity to treat the existing odorous air flow rates and an additional 23,000 ft3/minute anticipated for the new process units. Representative sizes for new facilities requiring odor control have been selected and the resulting air flow rates calculated using the applicable 6-16 MWMC_6.0_REV11.DOC