Brown County Brackish-Water Project: Ellenburger and Hickory Aquifers as a Public Water Supply

Abstract

The purpose of this study was to determine favorable locations for test brackish water wells tapping the Hickory and Ellenburger aquifers in Brown County, Central Texas. We determined that the best location is close to the southwest tip of the county (Figure ES1), where (1) total dissolved solids (TDS) concentration is relatively low (~3,000 mg/L), (2) the aquifers are relatively thick (~350 ft for the Hickory and ~1100 ft for the Ellenburger-San Saba), and (3) the recharge zone is reasonably close (20-30 miles to the South). Another location close to the City of Brownwood will test the Ellenburger-San Saba, which is ~1200 ft thick there. Despite potentially good yield (>500 gpm), the TDS concentration is much higher at the second location, 10,000 to 15,000 mg/L in the Ellenburger and likely even higher in the Hickory, which is thinner there and more removed from recharge areas. The test wells would reach a depth of 3,000 to 3,500 ft. Both Hickory and Ellenburger exhibit relatively high levels of radium and other radionuclides: regionally, 30% of the wells have measurements above the radium maximum contaminant limit (15 pCi/L). The focus of the study was on the Hickory and Ellenburger-San Saba aquifers because they represent the most extensive water sources in the county, even if they are not fresh. Other water-bearing formations include the Mid-Cambrian/Welge aquifer, the Marble Falls aquifer, several mostly brackish upper Paleozoic aquifers of limited extent, the Trinity aquifer, and alluvial aquifers along rivers. The alluvial aquifers are limited in extent and capacity. The Trinity aquifer exists only in the eastern third of the county and consists of three individual sands that can provide limited amounts of fresh water. The upper Paleozoic aquifers occur across the whole county where not covered by Trinity sediments, but in a fragmented way, with no communication between them. In addition, they quickly become brackish with depth, even if the shallow part of the aquifer is tapped for fresh water to meet local domestic and irrigation needs. The Marble Falls and Welge aquifers could supplement wells drilled to tap the Ellenburger or the Hickory.

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