The Edwards Aquifer

Abstract

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Hydrogeochemical Evaluation of Aquifer Storage and Recovery in Edwards Aquifer, New Braunfels, Texas

“…Carbonate rocks of the Edwards aquifer in the vicinity New Braunfels were deposited in Early Cretaceous time in the shallow subtidal to tidal flat marine San Marcos platform developed behind the shelf‐edge Stuart City reef (Rose 1972; Sharp Jr. 1990). Cretaceous depositional processes resulted in variable rock fabrics with a stacked pattern of beds of distinctive properties mapped as formations and hydrostratigraphic zones (Lindgren et al 2004).…”

“…The 25 to 30 km wide Balcones Fault Zone(Figure 3)—separating the Edwards Plateau from the Gulf Coastal Plain in South Texas—controls the hydrogeology and geochemistry of the Edwards aquifer by (1) thinning or offsetting aquifer strata, thus disrupting fault block communication (Allan 1989; Maclay 1989), and (2) creating barriers and/or pathways for fluid flows (Maclay 1995; Caine et al 1996). While the juxtaposition of less permeable zones impedes flow across faults, flow across faulted blocks is favored by the juxtaposition of permeable beds (Sharp Jr. 1990). The Edwards aquifer water quality is dictated by aquifer stratigraphy, structure, lithology, geomorphology, cross‐formational flow, mixing with saline formation waters, and water‐rock interactions (Sharp Jr. 1990).…”

“…While the juxtaposition of less permeable zones impedes flow across faults, flow across faulted blocks is favored by the juxtaposition of permeable beds (Sharp Jr. 1990). The Edwards aquifer water quality is dictated by aquifer stratigraphy, structure, lithology, geomorphology, cross‐formational flow, mixing with saline formation waters, and water‐rock interactions (Sharp Jr. 1990). A combination of these factors makes the Edwards aquifer an anisotropic medium (e.g., Maclay 1995; Lindgren et al 2004).…”

“…The badwater zone is defined by an isoconcentration line commonly known as the “badwater line,” which separates freshwater from water exceeding 1000 mg/L TDS (Figure 3). The badwater line demarcates the updip and rapidly circulating (90 to 900 cm/day) freshwater portion of the Edwards from the downdip slowly migrating (1 to 2 cm/day) basinal fluid, hence marking a significant decline in permeability (Maclay and Small 1986; Maclay and Land 1988; Clement 1989; Sharp Jr. 1990). The permeability in the badwater zone is estimated to be 2 to 3 orders of magnitude less than the permeability in the freshwater zone (Maclay and Land 1988).…”