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MWMC FACILITIES PLAN TABLE $.2.2-1 Summary of Secondary Clarifier Baffling and Mechanism Improvements - Alternatives Comparison MWMC Facilities Plan, Eugene-Springfield Capital Cost Alternative (millions of dollars) 1 - Partial Retrofit - Baffling and Mechanism Retrofit $2.9 2 - Partial Retrofit - Baffling and Mechanism Retrofit with $5.5 New Effluent Launder 3 - Complete Retrofit - Baffling with Complete $7.0 Mechanism Replacement and New Effluent Launders The baffling and associated miscellaneous improvements for each alternative are anticipated to result in an increased secondary clarifier capacity of 20 to 30 percent. A capacity increase of 40 percent has been observed in some installations; however, in the absence of stress testing data for an WPCF secondary clarifier, a conservative assumption of the increase in clarifier capacity is estimated at a minimum of 20 percent. This translates to a sustained peak surface overflow rate (SOR) of 1260 gpd/sf for each secondary clarifier and a total sustained peak flow capacity of 134 mgd with all eight secondary clarifiers on line. The three alternatives and their costs were presented at an October 2003 workshop with Eugene-Springfield staff and CH2M HILL staff. Eugene-Springfield staff unanimously chose to proceed with Alternative 2 as the preferred alternative. Stress testing of the retrofitted secondary clarifiers can be conducted to determine the actual estimated capacity increase resulting from the modifications. 6.2.3 Primary Clarification Enhancements The WPCF currently uses a total of four primary clarifiers to treat screened and degritted raw sewage. The existing primary clarifiers are circular, have outboard launders, and are 135 feet in diameter with 12-foot sidewater depths. The primary sludge is accumulated at the bottom of the clarifier and thickened through compaction. Primary sludge solids are drawn off with intermittent sludge pumping, and a sludge blanket is maintained within the clarifier. Equipment for the existing primary treatment facilities is outlined in Table 3.2.2-2 in Chapter 3.0. Plant operations personnel have observed that when the total plant flow exceeds approximately 72 mgd, the primary clarified effluent quality rapidly deteriorates. At flows around 86 mgd the primary sludge blanket begins to be washed out of the clarifier, resulting in negative TSS removals. An increase in primary clarification capacity is necessary to address both current and future PWWFs. Currently, all of the plant influent, including the PWWFs, must pass through the existing primary clarification facilities, which are limited in capacity. It is prudent to look at alternatives to optimize the performance of the existing primary clarifiers before considering the construction of new primary clarifiers. This approach will maximize the facility's existing investment in primary treatment facilities. 6-12 MWMC_6.0_REV1 LDOC