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6 DEVELOPMENT AND EVALUATION OF ALTERNA~VES <br /> <br />treatment capacity has kistorically been estimated at 103 mgd. Above 103 mgd the existing <br />secondary effluent (SE) quality begins to degrade rapidly, limited by the capacity of the <br />ex~stJng secondary clarffiers. The result is a SE with a higher effluent TSS than is acceptable. <br /> <br />Alternatives for increasing the secondary clarification capacity include constructing new <br />secondary clarifiers and enhancing the performance of the exist~g secondary clarffiers. <br />Before considering construction of new secondary darifiers, alternatives that evaluate <br />optimizing the exLst~g secondary clarifiers should be considered. Tiffs approach will <br />maximize the facility's exist~g investment in secondary clarifiers. <br /> <br />Alternative 1: Partia~ Retrofit: Baffling and I~lechanism Retrofit <br />This alternative represents the minknum modifications required to achieve the operational <br />performance results des[red. It includes a new energy dissipating inlet (EDI) installed on the <br />existing influent colunm to address the inlet velocity issues. A new flocculation well sled to <br />accommodate the larger influent flows would redirect surface velocity currents. This <br />alternative would retain the exist~g inboard launder. The outboard weir of this launder <br />would need to be either blocked or baffled to prevent density currents from pushing <br />suspended solids over the outside of the weir. Ring and density cm~ent baffles may redirect <br />suspended solids toward an inboard launder, which is more than 12 feet off the perimeter <br />wall, and are not recommended. Retrofitting the exis~ng suction tubes to a single suction <br />manifold with adjustable orifices would address the issues associated with the existing <br />mechanism dragging on the floor, reduce the radial density currents associated with the <br />horLzontal suction [-t~bes, improve the sludge withdrawal distribution, and increase the <br />available head for sludge withdrawal. <br /> <br />Alternative 2 - Partia~ Retrofit: Baffling and Mechanism Retrofit, New Effluent Launders <br />This alternative would provide the same EDI, flocculation well, axtd mechanism retrofit as <br />described in Alternative t. In addition, this alternative proposes to remove the corroded <br />inboard launder and locate a new launder at the exterior of the clar~fier. The relocated <br />launder would be fabricated steel, either painted or stainless. With the reloca~on of the <br />launder a new scum baffle, as well as new scum skimmer arms, would be required. For <br />outboard launders a density current baffle is recommended for density currents. This baffle <br />could be either fiberglass reinforced plastic (FRP) or stainless steel. <br /> <br />Alternative 3 - Compete Retrofit: Baffling Retrofit, ~techanism Replacement, l'{ew Effluent <br />Launders <br />This alternative would provide the same EDI, flocculation well, new outboard launder, <br />skimmer arms, scum baffle, and density current baffle as described in Alternative 2. In <br />addition, this alternative proposes to remove and replace the entire existing Lrffluent colunm <br />and drive mecharfism. This alternative also proposes to replace the existing clarifier bridges. <br /> <br />Results <br />The capital cost comparison is summarized in Table 6.2.2-1. A non-monetary comparison <br />was not performed because each of the alternatives was assumed to result in the same level <br />of operational performance and effluent TSS reliability. <br /> <br /> MW~C_6 9_REV11 DOC 6-1 ~ <br /> <br /> <br />