Resolution No. 4793 - Laserfiche WebLink

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MWMC FACILmE$ PLAN anticipated NPDES permit requirements. However, HRC is being cor~idered for application as equivalent secondary treatment. If equivalent secondary treatment status is gained for this technology, the effluents would no longer be considered blended and the regulatory uncertainty would no longer be an issue. This alternative is feasible cost-wise and should be considered further for permit compliance. Figure 6.6.3-4 shows a potential site layout for system alternative 5. In addition to those facilities required for all alternatives, fids alternative includes the construction of a new primary diversion pump station and a new secondary diversion pump station. Thickening of primary sludge outside the existing primary clarifiers would be required with this alternative. The hydraulic control strategy associated with system alternative 5 would be more complicated to operate than the other system alternatives because of the complexity of achieving proper flow splitting and balancing using two pump stations. Blending would be required for this alternative to meet the anticipated NPDES permit requirements. System alternative 5 might present a greater challenge from a regulatory standpoint as state and federal blending policies are still evolving. This alternative is feasible cost-wise and should be considered further for permit compliance. 6,6.4 Permit Compliance Assessment System alternatives 3, 4, and 5 were selected for further analysis regarding permit compliance relative to cost. These system alternatives were analyzed usLng a spreadsheet model developed to simulate the projected peak flows and estimate the resulting effluent BOD and TSS concentrations. The model used historical urtit process performance data from peak flow events in conjunction with anticipated unit process performance to simulate worst-case average weekly and monthly values for BOD and TSS. Compliance with the monthly average 85 percent removal requirement was also assessed. The results of each model run were compared with current NPDES BOD and TSS permit requirements to evaluate a system alternative's ability to meet both current and potential future effluent limits. Figures 6.6.4-1 and 6.6.4-2 show the results of the permit compliance analysis relative to cost for each alternative. These figures illustrate that the predicted effluent loadings are comparable for each alternative even though the construction costs vary considerably. All three alternatives would be able to meet the current and future peak week and peak month effluent requirements, provided the mass limits remain constant. In a worst-case scenario, assuming that the ?WWF occurs during the peak week flow and the peak week flow occurs during the peak month (likely in May), the 85 percent monthly removal requirement specified in the NPDES permit for BOD would require filtration of a portion of the SE. This is the case for all of t_he alternatives, and it was assumed that filtration would be available because it will be required for TSS removal reliability during the dry season. Filtered flow required trader this worst-case scenario would be 10 mgd at 2010, and 30 mgd at 2025. System alternative 5 - Parallel Primary and Secondary treatment is recommended for treating PWWFs at the WPCF. Although the three alternatives had similar non-cost evaluation results and all system altematives were anticipated to meet future NPDES permits, system alternative 5 provides MWMC with the most cost-effective solution to treating infrequent PWWFs with no environmental impacts to the receiving stream. However, there is some regulatory uncertainty regarding blending policy that puts system NIWIVlC_6 O_RE-Vi 1 DOC