Evaluation of Perchlorate Sources in the Rialto-Colton and Chino California Subbasins using Chlorine and Oxygen Isotope Ratio Analysis

Perchlorate in groundwater can be from synthetic or natural sources. the latter of which include both historical application of imported nitrate fertilizers from the Atacama Desert of Chile and atmospheric perchlorate. The objective of this study was to evaluate the use of isotopic data to distinguish sources of perchlorate in groundwater in a specific region of the Rialto-Colton and Chino. CA groundwater subbasins. Perchlorate extracted from wells in this region was analyzed for chlorine and oxygen stable isotope ratios and radioactive chlorine-36 isotopic abundance. along with other geochemical. isotopic. and hydrogeologic data. The stable isotope and chlorine-36 data provided relatively unambiguous discrimination of synthetic and Atacama perchlorate sources in most wells having relatively high concentrations. providing regional perspective on anthropogenic perchlorate contamination in the Rialto-Colton and Chino subbasins. Where indigenous natural perchlorate was indicated as a substantial component. total perchlorate concentrations were low and concentrations of anthropogenic components were near background levels. The original document contains color images.