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6. DEVELOPMENT AND EVALUATION OF ALTERNATIVES treatment capacity has historically been estimated at 103 mgd. Above 103 mgd the existing secondary effluent (SE) quality begins to degrade rapidly, limited by the capacity of the existing secondary clarifiers. The result is a SE with a higher effluent TSS than is acceptable. Alternatives for increasing the secondary clarification capacity include constructing new secondary clarifiers and enhancing the performance of the existing secondary clarifiers. Before considering construction of new secondary clarifiers, alternatives that evaluate optimizing the existing secondary clarifiers should be considered. This approach will maximize the facility's existing investment in secondary clarifiers. Alternative 1: Partial Retrofit: Baffling and Mechanism Retrofit This alternative represents the minimum modifications required to achieve the operational performance results desired. It includes a new energy dissipating inlet (EDI) installed on the existing influent column to address the inlet velocity issues. A new flocculation well sized to accommodate the larger influent flows would redirect surface velocity currents. This alternative would retain the existing inboard launder. The outboard weir of this launder would need to be either blocked or baffled to prevent density currents from pushing suspended solids over the outside of the weir. Ring and density current baffles may redirect suspended solids toward an inboard launder, which is more than 12 feet off the perimeter wall, and are not recommended. Retrofitting the existing suction tubes to a single suction manifold with adjustable orifices would address the issues associated with the existing mechanism dragging on the floor, reduce the radial density currents associated with the horizontal suction tubes, improve the sludge withdrawal distribution, and increase the available head for sludge withdrawal. Alternative 2 - Partial Retrofit: Baffling and Mechanism Retrofit, New Effluent Launders This alternative would provide the same EDI, flocculation well, and mechanism retrofit as described in Alternative 1. In addition, this alternative proposes to remove the corroded inboard launder and locate a new launder at the exterior of the clarifier. The relocated launder would be fabricated steel, either painted or stainless. With the relocation of the launder a new scum baffle, as well as new scum skimmer arms, would be required. For outboard launders a density current baffle is recommended for density currents. This baffle could be either fiberglass reinforced plastic (FRP) or stainless steel. Alternative 3 - Compete Retrofit: Baffling Retrofit, Mechanism Replacement, New Effluent Launders This alternative would provide the same EDI, flocculation well, new outboard launder, skimmer arms, scum baffle, and density current baffle as described in Alternative 2. In addition, this alternative proposes to remove and replace the entire existing influent column and drive mechanism. This alternative also proposes to replace the existing clarifier bridges. Results The capital cost comparison is summarized in Table 6.2.2-1. A non-monetary comparison was not performed because each of the alternatives was assumed to result in the same level of operational performance and effluent TSS reliability. MWMC_6.0_REV11 .DOC 6-11