Res 2015-012/Wastewater Master Plan

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Wastewater Master Plan City of San Marcos Executive Summary during the study period. This effect could be the result of RDII, Texas State University flows, or a combination of the two. If the extended recovery from Sites SM10 and SM14 is a result of high RDII entering the system after a rainfall event, these flow monitoring basins would have a higher rehabilitation priority. It is recommended that the location of the Texas State University flows be verified to determine if this effect is partially the result of changing student populations between Spring and Summer semesters. 6.0 HYDRAULIC MODEL DEVELOPMENT & CALIBRATION The City of San Marcos selected Infoworks CS hydraulic modeling software to evaluate the wastewater collection system. The City's geographic information system (GIS) provided the basis for constructing the hydraulic model. This will provide for greater ease in updating the model in the future. FNI calibrated the hydraulic model to specific dry and wet weather events experienced during the flow monitoring period. A properly calibrated model serves as the foundation for any future modeling scenarios. Dry weather calibration model results for flow, depth, and velocity closely matched the observed data on May 3, 2012 for each flow meter site with the difference between modeled and observed flow within 5 %. This indicates that the model is properly matching the residential and non- residential wastewater loads. The wet weather calibration was performed for the rain event that occurred onMay10,2012. Modeled wet weather flows were generally within 15% of the observed flows, indicating that the model is accurately predicting the wastewater system's response to rain events. The dry and wet weather calibration results correlated well to the recorded data and therefore provides a high level of confidence that the model is accurately reflecting the characteristics of the actual collection system. 7.0 WASTEWATER SYSTEM ANALYSIS & HYDRAULIC MODELING Hydraulic analyses were conducted to identify deficiencies in the City of San Marcos's existing wastewater collection system and to establish a capital improvements plan to improve the existing system and accommodate projected wastewater flows through 2035. Various combinations of improvements and modifications were investigated to determine the most appropriate approach for conveying projected flows. Parameters used in developing the improvements plan included increasing system reliability, simplifying system operations, conveying peak wet weather flows, maintaining proper velocities, and reducing surcharging and sanitary sewer overflows. ES -4