Resolution No. 4793 - Laserfiche WebLink

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6 DEVELOPMENT AND EVALUATION OF ALTERNATIVES 6.1 Conveyance System Alternatives A rigorous analysis was made of potential wastewater collection system flow management alternatives as part of the September 2000 MWMC Wet Weather Flow Management Plan (WWFMP) [CH2M HILL, 2000]. The results of that analysis are summarLzed below. 6.1.1 Basic A tematives The W-W~P considered several technologies £or managing wet weather flow ~-~ the wastewater collection system: system rehabilitation to reduce RDII; storage; conveyance; and wet weather ~reatment. This section summarizes the analysis, evaluates the four technologies and combinations oJ~ the four, and develops solutions for most cost-effectively managing wet weather flow. The analysis included many iterations of hydraulic model simulations, as well as economic optimization coupling hydraulic modeling results (flow management effectiveness) and cost estimates. The WWFMP analysis primarily- addressed ~vo objectives: - Object~ve 1: Manage flows and water surface elevations in ma,_holes in the collection system to eliminate overflows and basement flooding. Objective 2: Provide the most cost-effective means to manage excess flow rates at the WPCF. The alternatives analysis/system optimization proceeded in two phases directed at these two objectives. In the first phase, sub-area alternatives and solutions were developed and evaluated to elm~nate basement flooding and overflows in the collection system. With implementation oJ~ successful sub-area solutions, the flow arriving at the WPCF was estimated to still exceed the maximum primary treatment capacity. Therefore, the second phase dealt with additional effort beyond the sub-area solutions to manage the excess peak flow arriving at the WPCF. To meet Objective 1 (described above) city staff used the hydraulic model and local knowledge to evaluate sub-area alternatives and develop sub-area solutions that would reduce maximum hydraulic grade (water surface elevatiorrs in manholes) to acceptable levels. Because potential problems were location-specific, alternatives and solutions to address them were re£erred to as "sub-area" alternatives and solutions. Sub-area alternatives were comprised of one or more of three technologies: system rehabffitation to reduce RDIL ~-lLqe and off-line storage facilities, and additional conveyance capacity. System rehabilitation was considered separately as either public only or public and private. Public only consisted of rehabilitation that would occur only in the public right-of-way. Public and private Lqcluded system rehabffitation on portions of the private system within sub-basirm identified for public rehabilitation. Once sub-area alternatives were re~ed such that they adequately accomplished Objective 1, they became sub-area solutions. To facilitate analysis of sub-area alternatives, the collection system was di,~dded into East and West portions. The East portion comprised the entire system upstream of the Willakenzie pump station. This included all of Springfield and Eugene's WJllakenzie sub- basins. The West portion included the rest of Re Eugene system. Sub-area alternatives were evaluated for both the East and West Each separately portions. sul~area alternative ~,ras MWMC_6 O_RE'V11.DOC