A high-storage cavernous aquifer has developed in the Cretaceous Edwards Limestone within the Miocene Balcones fault zone. The trend of the fault system, and that of its contained aquifer, cuts across the depositional facies of the Edwards Limestone. Measured sections in the Edwards Limestone west of the fault zone and in a core east of the down-dip boundary (“bad-water line”) of the main aquifer contain significantly higher percentages of dolomite than do similar depositional facies within the fault zone aquifer. It appears that the large amount of high Ca/Mg-ratio ground water, which has passed through the artesian aquifer in the Edwards Group, has calcitized many of the dolomite beds.

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