Hydrogeochemical assessment of groundwater in transboundary aquifers along the US-Mexico border and drinking water quality implications for Texas colonias

The groundwater resources in transboundary aquifers are crucial to the development of involved nations. A unified governance strategy based on scientific data is essential for the management of transboundary aquifers. This study presents a comprehensive geochemical analysis of the groundwater quality of private wells along the US-Mexico border in Texas across three transboundary aquifer types. The concentrations of dissolved major ions, trace, and rare earth elements (REE) were measured, and the dissolved organic matter was spectroscopically characterized to evaluate the prevailing water-rock interactions, biogeochemical reactions, and anthropogenic contamination in the groundwater and their susceptibility to future contamination. Groundwater samples were collected from private wells (n = 22) from four representative counties within a section of the Texas-Mexico border (Maverick, Kinney, Dimmit, and Webb Counties). Three distinct aquifer types were revealed from the major ion composition, e.g., a carbonate aquifer within Kinney County (a part of Edwards-Trinity aquifer), an alluvial aquifer with prevailing reducing conditions within Dimmit and Webb Counties (a part of Carrizo-Wilcox aquifer), and an evaporite-rich aquifer within Maverick County. The concentrations of trace elements in the groundwater of each aquifer type were below the MCL of USEPA, however, excessive Sr concentrations were evident mostly in the evaporite-rich aquifer. Our results indicate dissolution of evaporites, and possible anthropogenic contamination may be responsible for the degradation of groundwater quality in Maverick County, raising concern for the viability of the aquifer in the future.