A Storm Series Provides Central San a Flood of Ideas to Optimize Storage

Presentation Description: A series of atmospheric river events that inundated California in January 2023 imposed significant burden on Northern California water resource recovery facilities (WRRFs). Central Contra Costa Sanitary District's (Central San's) WRRF, in particular, grappled with an extensive two-week storm event spanning from December 31, 2022, to January 16, 2023. Such consecutive storm occurrences have the tendency to strain the treatment and wet weather capacity limits of WRRFs. This scenario, exemplified by the experience of Central San, underscores the need to address the implications of storm series on WRRFs. Despite maintaining an independent sanitary sewer system distinct from the storm sewer system, Central San witnessed a fivefold surge in flow rates to the plant.

Central San employed a network of wet weather basins to manage excess wet weather flow beyond the WRRF's processing capabilities. Remarkably, Central San successfully navigated the 2023 winter storms without any overflows. Post-event, Central San aimed to dissect the storm occurrences and their wet weather infrastructure to enhance preparedness for future extreme events. Central San engaged Brown and Caldwell to address pivotal questions: What magnitude or sequence of storm events could lead to an overflow? Are operational adjustments and capital enhancements feasible to optimize the system?

In collaboration, Central San and Brown and Caldwell embarked on a comprehensive study of the wet weather basin system. The objectives encompassed the identification of operational lessons and improvements from the 2023 storms, the creation and calibration of hydraulic and hydrologic models mimicking basin fill and drain dynamics, as well as influent flow patterns utilizing local rainfall data. Statistical analysis would then quantify basin utilization frequencies and overflow risks in extreme circumstances. Furthermore, the initiative aimed to outline high-level concepts for improving the wet weather basin system.

This presentation will delve into Central San's experience during the 2023 winter storms, provide insights gleaned from operations and maintenance, upcoming capital enhancements, and the intricate hydraulic and hydrologic models fashioned for a more profound analysis of the WRRF's wet weather system.