Support for Mitigating Contaminated Transboundary Flows in the Tijuana River Watershed

Raw sewage and other waste flow from Tijuana, Mexico, into Southern California, closing beaches, threatening public health, negatively impacting coastal and marine water bodies, and depriving communities of recreational and economic opportunities. To address these transboundary water quality issues, the U.S. Environmental Protection Agency was considering several water infrastructure projects in the San Diego-Tijuana area of the Tijuana River Watershed, including trash capture, water reuse, river water diversion and treatment, and expanding and upgrading wastewater conveyance and treatment. To select among these projects, EPA turned to ERG for support in assessing their effectiveness for improving water quality in the watershed. ERG evaluated the potential effectiveness of these projects, including their ability to reduce transboundary flows, reduce sewage and sediment discharged from the Tijuana River to the Pacific Ocean, and reduce sewage discharged from Mexico into the Pacific Ocean, and we reported the results to EPA to inform project selection. Following implementation, the selected projects are expected to improve water quality in the area, resulting in reduced beach closures in Southern California and safer public health conditions along the international border.