City of Morgan Hill Sewer System Master Plan 2017

2017 City of Morgan Hill

7.0 CHAPTER 7 - EVALUATION AND PROPOSED IMPROVEMENTS This section presents a summary of the sanitary sewer system capacity evaluation during peak dry weather flows and peak wet weather flows for the existing and buildout flows. The recommended sanitary sewer system improvements needed to mitigate capacity deficiencies are also discussed in this chapter. 7.1 OVERVIEW The calibrated hydraulic model was used for evaluating the sanitary sewer system for capacity deficiencies during peak dry weather flows (PDWF) and peak wet weather flows (PWWF). Since the hydraulic model was calibrated for dynamic modeling, the analysis duration was established at 24 hours for most analyses. The criteria used for evaluating the capacity adequacy of the wastewater collection system facilities (gravity mains, force mains, and lift stations) were discussed and summarized in the System Performance and Design Criteria chapter. 7.2 EXISTING SEWER SYSTEM CAPACITY EVALUATION The system performance and design criteria summarized, on Table 3.1 , were used as a basis to judge the adequacy of capacity for the existing sanitary sewer system. The design flows simulated in the hydraulic model for existing conditions were summarized on Table 5.4 and are listed as follows: During the peak dry weather simulations, the maximum allowable pipe d/D criteria for new pipes (d/D ratio of 0.75) for was used. For existing pipes, the criteria was relaxed to allow a maximum d/D ratio of 0.90 (full pipe capacity) to prevent unnecessary pipe replacements. During the peak wet weather simulations, capacity deficiencies included pipe segments with a hydraulic grade line (HGL) that rises within three feet of the manhole rim elevation. In general, the hydraulic model indicated that the sanitary sewer system exhibited acceptable performance to service the existing customers during both peak dry weather flows ( Figure 7.1 ) and peak wet weather flows ( Figure 7.2 ), with exceptions noted in the following sections. 7.2.1 Existing Peak Dry Weather Flows Capacity Evaluation The existing dry weather flow analysis indicated several areas where pipelines experienced deficiencies, which are documented on Figure 7.1 . Additionally, this figure documents pipelines x Existing PDWF = 5.4 mgd x Existing PWWF = 7.7 mgd

August 2017

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City of Morgan Hill Sewer System Master Plan