Res 2015-012/Wastewater Master Plan

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Wastewater Master Plan City of San Marcos Executive Summary The hydraulic model was used to evaluate the existing collection system to assess the ability of the system to adequately convey wastewater without excessively surcharging or overflowing. The analysis was performed to determine if there are any existing system deficiencies and also to provide a baseline for the current level of service. The results of the analysis are summarized below: • Lift Station #11 and the upstream and downstream piping do not have sufficient capacity to adequately convey existing peak flows. • The 8 -inch wastewater line along the north side of Spring Lake experiences significant surcharging due to insufficient pipe capacity. • The 12 -inch wastewater lines near the railroad and Gravel Road experience significant surcharging during the existing system analysis. The model indicates that the line is exceeding capacity and is nearly overflowing under design storm conditions at the intersection where the 10 -inch and 12- inch wastewater lines convey flow into a single 12 -inch line crossing the railroad. • Several pipe segments in flow monitoring basin SM -12 experience surcharging due to pipe capacity deficiencies. Based on the results of the flow monitoring, this basin experienced an 11.28 wet weather to dry weather peaking factor. • The 8 -inch wastewater line owned by Gary Job Corp south of the City airport experienced surcharging due to insufficient pipe capacity during the existing system analysis. While this wastewater line is not owned by the City, wastewater flows for the City airport are conveyed through the Gary Job Corp wastewater lines. Once the existing system was evaluated, hydraulic analyses were performed on the collection system under future peak flow conditions. Wastewater system improvements were developed to accommodate residential and non - residential growth through 2035. To serve the growth, the City must rehabilitate, replace, or upsize existing infrastructure and provide additional service to areas of growth. Key observations and recommendation resulting from modeling and evaluation are: • Ground elevations and recommended improvements revealed a change in the delineation of wastewater basin service areas. • It is recommended that the City continue to limit and /or reduce the number of lift station where possible due to the cost of operating and maintaining the facilities. Recommended improvements would allow for the decommissioning of six lift stations across the City, including Oakridge Dr. 206 ES -5