table 1

Table 1. Summary of the lithologic and hydrogeologic properties of the hydrogeologic subdivisions of the Glen Rose Limestone and associated units that crop out, Camp Stanley Storage Activity and immediately adjacent area, Bexar County, Texas.

[Groups, formations, and members modified from Forgotson (1956), Rose (1972), Ashworth (1983); hydrogeologic subdivisions (aquifers, zones, intervals) from Maclay (1995), Barker and Ardis (1996); Clark (2003); lithologic terminology modified from Dunham (1962); and porosity type modified from Choquette and Pray (1970). AQ, aquifer; CU, confining unit; *, not exposed in the study area]

Group, formation, member			Hydro- geologic subdivision			Hydro- logic function	Thickness (feet)	Lithology	Field identification	Karst features	Porosity type/ permeability
Edwards Group	Kainer Formation	Basal Nodular member	Edwards aquifer		VIII¹	AQ karst; CU not Karst,	50–60	Shaly, nodular limestone, mudstone, and miliolid grainstone	Massive, nodular, and mottled; abundant gastropods and Exogyra texana	Large lateral caves at surface	Fabric; stratigraphically controlled/large conduit flow at surface
Glen Rose Limestone		Upper member	Trinity aquifer	Upper Zone	Interval A	AQ associated with fractures and karst; CU if not	²30–120	Alternating and interfingering medium-bedded mudstone, wackestone, and packstone with solution zones locally	Near contact with Edwards Group; stair-step topography; devoid of fossils; evaporite beds locally	Some caves below contact with Edwards Group. Caves associated with fractures and bedding planes	At surface, not-fabric selective fracture and cavern porosity; probably very permeable near contact with Edwards Group, which decreases with depth, breccia porosity associated with collapse resulting from dissolution of evaporite beds
					Interval B	CU; AQ associated with fractures and karst	120–150	Alternating and interfingering mudstones, clays, wackestone, and packstones	Devoid of fossils; stair-step topography; evaporite bed at top of zone	Few caves	Fabric selective interparticle porosity and not-fabric selective fracture and some cavernous porosity; generally low permeability away from caves and solutionally enlarged fractures.
					Interval C	AQ	10–20	Yellow to white calcareous mud and vuggy mudstone	Yellow calcareous mud, with springs and seeps; topography tends to be flat; few fossils	No known caves	Fabric selective, breccia and moldic (boxwork) porosity
					Interval D	AQ associated with bioherms; CU above and below bioherms	135–180	Alternating beds of wackestone, packstone, and marl; thin-bedded “platy” mudstone; thick-bedded biostromes locally	Profuse Orbitolina texana; “platy” mudstone bed; generally low relief; stair-step topography not well defined	Relative abundance of caves related to fractures and bedding planes	Both fabric and not-fabric selective porosity; vug, fracture, cavern, and moldic porosity within biostrome; in lower 90 feet very low porosity, primarily fracture related
					Interval E	AQ	7–10	Yellow-to-white calcareous mud and vuggy mudstone	Yellow-to-white calcareous mud, with springs and seeps; topography tends to be flat; Corbula bed at base separating upper and lower Glen Rose Limestone; numerous fossils	No known caves	Fabric selective, breccia and moldic (boxwork) porosity
		Lower member		Middle Zone		AQ in bioherms and evaporite bed; also associated with karst and fractures; CU elsewhere	320–340	Thick-bedded mudstone; thin-to-medium-bedded mudstone, wackestone, packstone, and grainstone	Massive mudstone	Relatively more caves than in other subdivisions except interval D	Both fabric and not-fabric selective porosity; large fracture, cavern, and moldic porosity within bioherms; mudstones and marls primarily fracture porosity; low permeability in mudstones and marls; good permeability in bioherms
Pearsall Formation		Bexar Shale member		Middle Zone		CU	60–70	Dark mudstone, clay, and shale	*	*	*