GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 19-5
Presentation Time: 9:00 AM


HERNANDEZ, Brianda N., Department of Geological Sciences, California State Polytechnic University-Pomona, 3801 W Temple Ave, Pomona, CA 91768 and OSBORN, Stephen G., Geological Sciences Department, California State Polytechnic University, Pomona, 3801 W. Temple Avenue, Pomona, CA 91768

The Santa Ana River (SAR), at 154 km in total length, is the longest river in Southern California, with the head waters located in the San Bernardino mountains and ending at the delta at Huntington Beach. The river flows through a variety of different land uses (urban, rural, commercial) that may have an impact on the water quality. Though a significant topic, there is a general lack of publicly available research that addresses potential impacts. This project collected water samples along a 11.3 km stretch of the SAR that spans multiple land uses. SAR water samples were taken bi-weekly over a 7-month period from the August (dry season) into March (wet season). In the field, river metrics were taken to determine flow speed, pH, total dissolved solids (TDS), temperature and depth. Water samples were analyzed for anions (chloride, fluoride, bromide, nitrate, and sulfate) by an Ion Chromatograph, Dionex ICS-1100 at the Water Quality Laboratory at Cal Poly Pomona. Major, minor, and some trace cations were analyzed by a Perkin-Elmer Optima 7300DV ICP-OES at UC Riverside. Noticeable concentrations of chloride were observed and compared. The spatial effects had slight variability in the water chemistry from the sample spots upstream (158 ± 0.88 mg/L) to the sample spots downstream (161 ± 7.0 mg/L) within the 11.3 km. Variable changes due to the seasonal effects were much more pronounced for chloride from the dry (157 ± 10 mg/L) and wet seasons (132 ± 40 mg/L). Traces of arsenic, up to 15.3 μg/L, in some samples were detected during the wet season, above the EPA primary drinking water standards of 10.0 μg/L, while there was little to non-existent arsenic in the dry season. This suggests that wet season run-off may be the source of arsenic and should be tested further.