INVESTIGATION OF ANOMALOUS SULFATE CONCENTRATIONS WITHIN THE SAN ANTONIO CANYON WATERSHED OF THE SAN GABRIEL MOUNTAINS, CALIFORNIA

The objective of this research is to analyze various streams and springs, as well as local rocks, to deduce the source of these anomalous concentrations of sulfate within San Antonio watershed of the eastern san Gabriel Mountains. Drainages of interest include the main San Antonio Canyon, along with some of its tributaries, Evey Canyon, North and South forks of Barrett Canyon, and Cascade Canyon. In the past, sulfate has been as high 1,706 ppm in Cascade Canyon (Yaralian, 2017).

We collected water samples bi-weekly from November 2018 to August 2019, although some sites had flowing water only during the wet season. Samples were analyzed for alkalinity, pH, oxidation-reduction potential, and concentrations of anions (ion chromatograph at CPP) and cations (ICP-OES, at UC Riverside). Current results show sulfate as high as 836 ppm in Cascade Canyon, with elevated values of 164 ppm and 58 ppm in Barrett and Evey canyons, respectively, that exceed background values of 25 - 30ppm. Hydrochemical data from past research by alumni and faculty is also be included in this study, as well as precipitation records from 2017 to 2019. Most samples appear to exhibit seasonal fluctuations in sulfate concentration, with a decrease during the wet season and in increase during the dry season.

Sulfate in water systems has three main sources; the decomposition of organic matter via microbes, precipitation from environmentally impacted areas, and local geology. The latter source is hypothesized to play a more significant role, due to abundance of hematite- and limonite-stained, hydrothermally altered and mineralized bedrock in the headwaters of Cascade and Barrett canyons. Spring Hill landslide is of special interest as it contributes groundwater to the Barrett and Cascade watersheds, and sulfur-bearing horizons are locally exposed. The most ubiquitous sulfide mineral present in the area is pyrite, that releases high amounts of sulfate and iron as it weathers. We will analyze local rock samples on the XRF to supplement the water data and narrow down the sulfate source to a specific area or rock unit. Although water supply is regularly tested in North Fork Barrett Canyon, this study is imperative to the residents who tap directly from the local streams and springs, and recreation visitors or animals that drink from the water.