MONITORING AND MODELING OF WATER QUALITY IN THE TIJUANA RIVER WATERSHED (Project WQ PP96II-10)

The Tijuana River Watershed (TRW) is a binational watershed on the westernmost portion of the US Mexico border, encompassing much of the City of Tijuana in Mexico and portions of the City and County of San Diego in the US (Figure 1). The basin contains three surface water reservoirs, various flood control works, and a National Estuarine Sanctuary which is home to several endangered species and is protected by the US federal government. For decades, raw sewage from the city of Tijuana, Mexico has flowed into the Tijuana River and across the international border into the Tijuana Estuary. This problem has worsened in recent years with the substantial growth of Tijuana’s population, along with intensive industrial development associated with the maquiladora (in-bond manufacturing and assembly plants) program in Mexico. Unfortunately, due to many factors, an industrial pretreatment program similar to one implemented in the United States, has not been initiated in Mexico. Moreover, in Mexico there is no program equivalent to the U.S. EPA’s National Pollutant Discharge Elimination System (NPDES ) stormwater permitting program, so the threat of chemical contamination of the Tijuana Estuary is pronounced. Additionally, inadequate infrastructure for the collection, treatment, and disposal of sewage originating in Tijuana has long plagued the watershed, as wastewater flows have chronically outpaced the ability of the infrastructure to handle them. These elements yield transboundary and cross-cultural water quality management challenges.