Resolution No. 4793 - Laserfiche WebLink

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DEVELOPMENT AND EVALUATION OF ALTERNAllVES System alternative 1 does not increase treatment capacity or alter existing operations to system efficiency. Although cost is zero, the ability to meet future NPDES increase the permits and EPA requirements for projected plant capacities is unlikely, if not impossible, without substantial upgrades or improvements to existing facilities. Therefore, this alternative was eliminated for further consideration. Figure 6.6.3-1 shows a potential site layout for system alternative 2. In addition to those facilities required for all alternatives, this alternative includes the construction of four new primary clarifiers, a new aeration basin, and six additional new secondary clarifiers. This system alternative would result in the highest capital investment and requires the most site space. This is significant because the only available site space that could be used is reserved for future build-out of secondary treatment capacity. Additionally, the primary clarifiers would be located a long distance from the existing primary clarifiers, requiring separate primary sludge handling and odor control facilities. Thickening of primary sludge outside the primary darifier would not be required with this alternative; however, it is recommended. This system alternative would be capable of treating 100 percent of the projected PWWF thi'ough primary and secondary treatment and no blending would be required. However, all these additional new facilities would be constructed to mitigate PWWF that only occurs on a relatively infrequent basis. It is therefore recommended that this alternative be removed from further consideration because of its extremely high capital cost. Figure 6.6.3-2 shows a potential site layout for system alternative 3. In addition to those facilities required for all alternatives, this alternative includes the construction of four new primary clarifiers. Less costly than system alternative 2, this system alternative has the benefit of providing primary treatment for 100 percent of the PWWF. As in system alternative 2, this alternative provides redundant primary treatment capacity, because a total of eight prLmary clarifiers would be available. The new primary clarifiers will occupy excessive site space allocated to future expansion of secondary treatment facilities. Additionally, if these clanfiers were constructed they would be located a long distance from the existing primary clarifiers, further complicating primary sludge handling and odor control facilities. Thickening of primary sludge outside theprimary clarifier would not be required with this alternative; however, it is recommended. Blending would be required for this alternative to meet the anticipated NPDES permit requirements. This alternative is feasible cost-wise, and should be considered further for permit compliance. Figure 6.6.3-3 shows a potential site layout for system alternative 4. In addition to those facilities required for all alternatives, this alternative includes the construction of a new high-rate clarification pump station and new high-rate clarification facilities. System alternative 4 offers the greatest operational flexibility as it would allow the HRC to function as primary clarifiers and would allow the existing primaries to be taken off line if necessary. Thickening of primary sludge outside the existing primary clarifiers would be required with this alternative to reduce the overall HRC needs. HRC can function in multiple modes, either to treat base dry season flows or to treat WWPH flows. The HRC system would reqttire more extensive O&M than either system alternatives 1, 2, 3, and 5 because the monthly exercising of the system would be significantly more involved. This system would also experience higher operational costs because of chemical requirements and electrical costs associated with the would be for this alternative system. Blending required to meet the MWMC_60_REV11.DOC 6-55