The Origin of Badwater in the Edwards Aquifer, Texas: An Integrated Approach to Regional Flow Systems in a Carbonate Aquifer

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This research seeks to evaluate the processes responsible for natural saline groundwaters in a regional carbonate aquifer--the Edwards aquifer of Texas. These waters are present in what is locally referred to as the badwater zone (salinities of greater than 1000 mg/1). Despite the environmental importance of this aquifer and many previous studies here, hypotheses for the origin and evolution of the badwater zone hydrochemical facies remain numerous and speculative. This research will integrate a range of conventional and newly developed analytical techniques in a hydrological and geochemical study of the Edwards aquifer both along and normal to the boundary between the badwater and freshwater zones. The data base will include potentiometric and major-element (rare-earth elements), and stable (H, O, B, S) and radiogenic (Sr, Nd, U and Ra) isotope data that will be acquired on new samples. This study will also include petrologic and geochemical analyses of lower Cretaceous carbonate rocks that constitute the aquifer. These data will be used in quantitative models that simulate fluid flow, fluid-rock interaction, and fluid mixing within aquifers. The elemental and isotopic parameters to be studied have a wide range of geochemical behavior, which will be critical for the application of theoretical models to constraining the processes involved in the origin of each of five distinct hydrochemical facies. This study will bear on our understanding of regional flow systems in the Gulf of Mexico sedimentary basin, and will have broader implications for the chemical and structural controls on the development of regional carbonate aquifers and the evolution of saline groundwaters.