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Happy Valley Water & Sewer Study Technical Memorandum 4 Sewer System Evaluation This section describes the evaluation process and results for extending sewer mains and associated facilities to parcels within the Study Area but outside current City limits. The capacity of the existing sewer col Iection system to the sewer trunk on Sunol Boulevard has also been evaluated to determine any necessary improvements, including two existing pump stations: 5 -12 and 5 -14. There is currently sufficient capacity available in all trunk sewers downstream of the Sunol Boulevard connection, including sewer flows from the Happy Valley study area. 4.1 Evaluation Criteria Evaluation criteria used in the development of facilities and cost estimates for the sewer system are described in this section. 4.1.1 Sizing and Siting Criteria Pipe sizing and flow criteria are summarized in Table 4, and are based on the City's 1984 Sewer System Design Standards and recommendations included in the 2007 Wastewater Master Plan. Pipeline alignments are based on siting information from the Happy Valley Specific Plan and discussions with City staff. The firm capacities of pump stations 5 -12 and 5 -14 were also compared to the potential peak wet weather flow (PWWF) rates. Existing sewer facilities in the Study Area are shown in Figure 5. 4.1.2 Cost Criteria Similar to the water system evaluation, planning -level construction cost estimates for each sewer collection system component have been developed to the same level of accuracy as the water system (AACE Class 4). Costs are indexed to the February 2016 Engineering News Record Construction Cost Index 20 Cities Average (10,182). Costs for new sewer construction were estimated based on RMC's experience with similar projects and recent bids. Cost criteria include baseline fully burdened unit construction costs for gravity sewers. Costs associated with pipeline construction, including excavation, street reconstruction, and manholes are included in the unit cost for sewer pipeline construction. Allowances have been added to the baseline construction cost for project - specific costs (such as mobilization and demobilization, remove and replace construction, and traffic control for work in roadways). Open -cut construction methods are assumed for all pipeline improvements. Costs for gravity sewers vary with pipe diameter and depth. Depth has been estimated based on the City's minimum depth of cover (five feet), appropriate pipe slopes, and topographic data provided by the City. Implementation allowances are the same factors that were applied for the water system cost estimates evaluation, and are summarized in Table 2. November 2016 11