Quality of Urban Runoff in the Tijuana River Watershed

A sampling program was conducted to assess the quality of runoff associated with a variety of land uses in the Tijuana River watershed, a binational river basin on the U.S. Mexican border. Generally, metal concentrations in samples collected during the first two to four hours of runoff (early storm) were higher than those in samples collected 24 36 hours into the rain event (late storm). A notable exception to this pattern was observed for the site on Tecate Creek, where levels of cadmium, chromium, copper, and nickel were higher in the latestorm sample. This is possibly due to the point source discharge of wastewater effluent from the Tecate Municipal Wastewater Treatment Plant just one mile upstream. At the industrial site, concentrations of lead and zinc in samples of early-storm runoff fell in the 85th percentile range (80th percentile for copper) of a U.S. industrial runoff dataset (Line et al. 1997). Other urban land-use sites (including residential and commercial) were generally comparable to the 90th percentile values for wet-weather runoff in an urban watershed of Los Angeles County. The resulting data suggest that nonpoint source pollution arising from a variety of land uses in the Tijuana River watershed will continue to enter the Tijuana Estuary and near-shore ocean during wet weather, arguing for basin-wide wastewater and stormwater management in this urban watershed.