Assessing the Impact of Water Reuse on Water Quality in the Los Angeles River

Abstract:

Water reuse through water reclamation plants (WRPs) is an approach used by Los Angeles to reduce dependence on imported water. Three WRPs in the Los Angeles River (LAR) watershed, located in southern California, contribute up to 70% of the river discharge during dry weather periods. Thus, the hydrology and ecology may be sensitive to alterations in water reuse. Increasing water reuse may lead to reductions to in-stream flow volume and negatively affect water quality of the LAR. The purpose of this research is to identify the impact of water reuse on metals, total suspended solids, and specific conductance during dry weather periods in the LAR. A water quality baseline is established by collecting monitoring data from LA County and other programs and statistically analyzing the data. A water quality module is then added to a calibrated and validated EPA-SWMM hydrologic model for water years 2011 to 2017 on a daily time-step, which was built in prior work. Land use characteristics, event mean concentrations, water quality concentrations during dry weather flow, and WRP water quality concentrations are used as inputs for the simulations. Water reuse scenarios are applied to the calibrated water quality model and the simulated daily loads are assessed using Total Maximum Daily Load compliance criteria approved by the California Water Boards for dry weather periods. Initial results will be summarized for representative wet, dry and average water years and evaluated to help water managers make informed decisions for the LAR.