The chloride to bromide ratio as an environmental groundwater tracer, with a field study at the Wellton-Mohawk Irrigation and Drainage District

Abstract

The purpose of this study was to determine if the chloride to bromide ratio (Cl/Br) of water imported via interbasin transfer can be used to trace the mixing of imported water with native ground water. Laboratory experiments and a chemical literature review indicate that chloride's and bromide's properties should make the Cl/Br a useful environmental ground-water tracer. This study has shown that the Cl/Br can be accurately quantified at environmental levels, is not attenuated by aquifer or soil media, is chemically stable, and is present in different levels in waters from different sources. Infiltration and mixing of irrigation water from the Colorado River (Cl/Br = 1300) with native ground water (Cl/Br = 630) was investigated at the Wellton-Mohawk Irrigation and Drainage District near Yuma, Arizona. The downgradient increase in the Cl/Br is correlated with distance from the upgradient limit of irrigation (r =.83), reflecting the chemical influence of infiltrating irrigation water.