Resolution No. 4793 - Laserfiche WebLink

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IVlWMC FACILITIES PLAN Alternative 1 would not increase capacity through the primary clanfiers. Alternative 2 is expected to increase the allowable SOR of the existing clarifiers, and thus the primary clarifier capadty, by approxLmately 20 percent. Although it will not be adequate to fully address the peak flow issue with respect to blending while meeting the NPDES permit, this alternative does provide an excellent increase in capacity using existing h~asb'ucture and can be done at a reasonable cost. It also provides increased reliability in performance; however, sludge blanket washout would still occur at peak flows, and eventual perm/t violations would be anticipated. Alternative 3 is anticipated to increase the allowable SOR of the existing cla~Lfiers, and thus the clarifier capacity, by up to 100 percent over Alternative 1. The resulting capacity of the primary clarffiers would be comparable to the proposed secondary treatment capacity. Alternative 3 is recommended because it would increase the existing primary clarffier capacity and improve the reliability of effluent quahty. Although it is the highest-cost alternative, most of the capacity gained is through existing infrastructure, wt'dch maximizes the plant's existing investment while occupying very little site space. The eqrdpment associated with the elimination of the sludge blanket in the primary clarif/er accounts for much of the cost. This alternative provides all the capacity and performance reliabiI/ty benefits of Alternative 2, plus 60 percent increased capacity, excellent operational flexibility,. high-quality PE at h/gh SORs, and meets all the primary clarification needs of the proposed secondary treatment system. Baffling improvements, new primary sludge pumps, two new pr/mary sludge thickeners, and a primary sludge pump station will be requLred for this alternative. 6.2.4 Preliminary Treatment The existing pretreatment facility at the WPCF has a peak capacity of 175 mgd. This is based on having one of the six screening channels and one of the four aerated grit chambers out of service during peak flow events. Equipment in the existing pretreatment fadlity is outlined in Table 3.2.2-1. The projected 2025 PWWF flow being used for facility planrdng analysis is 277 mgd. Pretreatment facilities, at a minimum, must be expanded to accommodate additional flows with the largest traits out of service. Two alternatives have been evaluated to expand the existing pretreatment capacity, both of which are based on an expanded capacity of 160 mgd. An expanded capacity of 160 mgd is necessary to accommodate the projected peak dry weather flow. It was used as the design basis so that the expanded facility capacity would match the capacity of modified secondary treatment facilities. Using this approach, the new facilities would be used to treat normal plant flows and the existing pretreatment facility would be brought online ordy as necessary during wet weather events to t~eat peak Alternative I - Expand Existing Pretreatment Facility Alternative 1 looks at expanding the existing pretreatment facility. New grit and screenings handling equipment would be located in a new building south of the existing pretreatment area. The influent channels of the expanded facilities would be hydraulically connected to the existing facilities so that flow could be transferred between them. The expanded facilities would use fine screening technology and the screenings would be handled separately from the existing facilities by new washer/compactors. This is necessary because the