ASSESSMENT OF ARSENIC AND BROMIDE IN WATERS AT DOS PALMAS NATURAL PRESERVE, SALTON SEA, SOUTHERN CALIFORNIA

Dos Palmas Spring and Natural Preserve (DPSNP) an oasis primarily managed by the Bureau of Land Management (BLM) functions as a sanctuary to native flora and fauna of the region as well as human recreation. Yet, water quality is not fully characterized. Previous water analyses have indicated relatively high concentrations of bromide (up to 3 ppm) and arsenic (up to 40 ppb) following an earthquake swarm of 2016, suggesting the possibility of deep basin brine of marine origin migrating to shallow aquifers. As a result, this project assesses arsenic, bromide, and other basic water quality parameters at DPSNP. Located in the arid Coachella Valley, Southern California, it is positioned in a tectonically active zone, the Salton Trough, that is bounded by geologic features; Orocopia and Chocolate mountains, the San Andreas Transform fault, Hidden Springs Fault and Poweline Fault; as possible conduits for fluid flow. DPSNP has three possible sources of water that may contribute to the abnormal concentrations of arsenic and bromide: 1) The All-American Coachella Canal, that diverts imported water from the Colorado River that recharges water into the preserve, 2) natural meteoric groundwater from surrounding mountains via hydraulic gradient, 3) possible deep ancient basin brines of marine origin that travel along present faults. Water samples have been collected from springs, ponds, and groundwater in several occasions since 2013 and most recently in 2019. Anions (F, Cl, Br, NO₃, and SO₄) were analyzed by ion chromatography and total alkalinity was titrated in the Hydrogeology laboratory at Cal Poly Pomona. Cations, including Arsenic, and oxygen and hydrogen isotopes were measured at the Environmental Chemistry Laboratory at UC Riverside. Measurements of pH, electrical conductivity, and temperature were measured at the time of sampling. Preliminary result from 2019 indicate bromide concentrations ranging between non-detect to 0.78 mg/L. Arsenic, from non-detect to 8.76 μg/L. Chloride and sulfate concentrations were as high as 1000 mg/L and 863 mg/L, respectively. Bromide and arsenic are apparently lower in concentration compared to previous sampling pre-earthquake swarm sampling.