Geologic framework and hydrogeologic characteristics of the Edwards Aquifer outcrop, Comal County, Texas

Water-Resources Investigations Report 94-4117




All of the hydrogeologic subdivisions within the Edwards aquifer outcrop in Comal County have some porosity and permeability. The most porous and permeable appear to be hydrogeologic subdivision VI, the Kirschberg evaporite member of the Kainer Formation; hydrogeologic subdivision III, the leached and collapsed members, undivided; and hydro- geologic subdivision II, the cyclic and marine members, undivided, of the Person Formation. The two types of porosity in the Edwards aquifer outcrop are fabric selective, which is related to depositional or diagenetic elements and typically exists in specific stratigraphic horizons; and not fabric selective, which can exist in any litho- stratigraphic horizon. Two faults, Comal Springs and Hueco Springs, completely, or almost completely, offset the Edwards aquifer along much of their respective traces across Comal County. Porous and permeable Edwards aquifer limestones are juxtaposed against impermeable upper confining beds along all, or most of their traces across Comal County. These faults could be barriers, or partial barriers, to ground-water flow where the aquifer is offset. In Comal County, the Edwards aquifer is probably most vulnerable to surface contamination in the rapidly urbanizing areas on the Edwards aquifer outcrop. Possible contamination can result from spills, leakage of hazardous materials, or runoff onto the intensely faulted and fractured, karstic limestone outcrops characteristics of the recharge zone.

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Geologic framework and hydrogeologic characteristics of the Edwards Aquifer outcrop, Comal County, Texas
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Water-Resources Investigations Report
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U.S. Geological Survey ; USGS Earth Science Information Center, Open-File Reports Section [distributor],
iii, 10 p. :maps (some col.) ;28 cm.