Allan K. Clark

Geologic Framework and Hydrostratigraphy of the Edwards and Trinity Aquifers Within Hays County, Texas

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Characterizing the subsurface geology in and around the U.S. Army Camp Stanley Storage Activity, south-central Texas

Figure 1. Location of the Camp Stanley Storage Activity study area, Bexar County, Texas (modified from Pantea and others, 2014). The geologic framework and hydrologic characteristics of aquifers are important components for understanding the Nation’s subsurface geology and predicting its hydraulic budgets. Integrating surface lithostratigraphic and hydrostratigraphic mapping can help characterize the spatial distribution and hydraulic connectivity of an aquifer’s permeable zones. Three-dimensional (3D) geologic modeling of an aquifer system can quantitatively characterize the connectedness of rock units across fault and fracture zones and enable geoscientists to visualize the spatial relations between the saturated and unsaturated stratigraphic units. Three-dimensional geologic framework model data can also be integrated into groundwater flow models, such as those constructed using MODFLOW (Christenson and others, 2011; Blome and Smith, 2012). Several U.S. Geological Survey (USGS) projects, supported by the National Cooperative Geologic Mapping Program (NCGMP), have used multidisciplinary approaches over a 14-year period to reveal the surface and subsurface geologic frameworks of the Edwards and Trinity aquifers of central Texas and the Arbuckle-Simpson aquifer of south-central Oklahoma (fig. 1). Some of the project achievements include advancements in hydrostratigraphic mapping, 3D subsurface framework modeling, and airborne geophysical surveys as well as new methodologies that link geologic and groundwater flow models (Blome and others, 2007; Blome and Smith, 2012). One area where some of these milestones were achieved was in and around the U.S. Army Camp Stanley Storage Activity (CSSA), located in northwestern Bexar County, Texas, about 19 miles northwest of downtown San Antonio (fig. 1).

Data Release of the bedrock geology and hydrostratigraphy of the Edwards and Trinity aquifers within the Driftwood and Wimberley 7.5-minute quadrangles, Hays and Comal Counties, Texas

The Edwards and Trinity aquifers are major sources of water in south-central Texas and are both classified as major aquifers by the State of Texas. The population in Hays and Comal Counties is rapidly growing, increasing demands on the areas water resources. To help effectively manage the water resources in the area, refined maps and descriptions of the geologic structures and hydrostratigraphic units (HSUs) of the aquifers are needed. This digital map database presents the detailed 1:24,000-scale bedrock hydrostratigraphic map as well as names and descriptions of the geologic and hydrostratigraphic units of the Driftwood and Wimberley 7.5-minute quadrangles in Hays and Comal Counties, Tex. These digital data accompany Clark, A.K., and Morris, R.R., 2017, Bedrock geology and hydrostratigraphy of the Edwards and Trinity aquifers within the Driftwood and Wimberley 7.5-minute quadrangles, Hays and Comal Counties, Texas: U.S. Geological Survey Scientific Investigations Map 3386, https://doi.org/10.3133/sim3386.