Regional specific yield of the Edwards and associated limestones in the San Antonio, Texas, area

Abstract

The regional specific yield in the recharge area of the Edwards and associated limestones, the principal aquifer in the San Antonio, Texas, area, is estimated to be about 0.025. This estimate is based on annual differences between recharge and discharge and on the averages of annual water-level changes in 10 observation wells in and near the outcrop area. HYDROGEOLOGY OF THE AREA The Edwards and associated limestones o2 Early Cretaceous age consist of the Comanche Peak, Edwards, and Georgetown Limestones (fig. 1). These light-gray limestones form a single hydrologic unit and generally hard, dense, and fine grained. They are characterized by numerous solution-enlarged openings at various depths. The total thickness of the limestones is 400 to 500 feet in the artesian area and about 400 feet in the water-table or recharge area. The artesian part of the aquifer is confined by the Del Rio Clay above and the Glen Rose Limestone below. In the San Antonio area, the limestone aquifer dips south and southeast towards the Gulf of Mexico at a rate of 10 to 20 feet per mile. The Balcones Fault Zone, an area of moderate to intense block faulting within the study area, is characterized by high-angle normal faults, downthrown to the south or southeast, with displacements oL as much as 500 feet (fig. 2). The faults provide passageways for circulating ground water, which in turn enlarges the openings by dissolving the limestone. The effective porosity (precentage of total pore volume occupied by interconnected interstices available for fluid flow)

The Edwards Aquifer

“…Slade and others (1985) estimated a mean specific yield of 0.017 for the Barton Springs segment. Lindgren and others (2004), Maclay and Rettman (1973), and Maclay and Small (1984) give ranges of specific yield (0.025 to 0.200) and storativity (10 -5 to 810 -4 ) for the San Antonio segment.…”

Hydrogeologic settings and groundwater-flow simulations for regional investigations of the transport of anthropogenic and natural contaminants to public-supply wells—Investigations begun in 2004

“…Because the quantity of leakage from the Albuquerque water-distribution and sewer systems has been uncertain, leakage was assumed to be 10 percent of the City of Albuquerque annual groundwater withdrawals for each stress period of this simulation. GIS databases of the extent of the Albuquerque Metropolitan area in the years 1935, 1951, 1973, and 1991(Feller and Hester, 2001 were intersected with GIS databases of the City of Albuquerque water-distribution and sewage-pipe systems to generate geospatial data of the areas susceptible to pipe leakage at those times. Although the spatial distributions of water-pipe leaks (New Mexico Environmental Finance Center, 2006) and sewer-pipe leaks (Camp Dresser & McKee, 1998) have been correlated with material pipe types, the leaky-pipe recharge flux was homogeneously specified over areas designated as susceptible to pipe leakage in each stress period (fig.…”

“…Transmissivity=39,947 to 204,380 m 2 /d Horizontal hydraulic conductivity= 3.05x10 -4 to 3.05x10 4 m/d Storage coefficient=1x10 -5 to 8x10 -4 (San Antonio segment); Specific storage=3.28x10 -6 to 9.51x10 -2 m -1 (Barton Springs segment); Specific yield=0.005 to 0.20; porosity =0.04 to 0.42 (Hovorka and others, 1996;Hovorka and others, 1998;Maclay and Land, 1988;Maclay and Rettman, 1973;Maclay and Small, 1984;Senger and Kreitler, 1984;Sieh, 1975;Slade and others, 1985;Scanlon and others, 2002).…”

“…The effective porosity generally ranges from 2 to 14 percent (Maclay and Small, 1976); 6 percent is considered to be average (Maclay, 1995). Reported estimates of specific yield for the San Antonio segment of the Edwards aquifer range from 0.025 to 0.20, and reported estimates of storage coefficient range from 1x10 -5 to 8x10 -4 (Maclay and Rettman, 1973;Sieh, 1975;Klemt and others, 1979;Maclay and Small, 1984;Maclay and Land, 1988;Hovorka and others, 1993). Reported estimates of specific yield for the Barton Springs segment range from 0.005 to 0.06, and reported specific storage ranges from 3.28x10 -6 to 9.51x10 -2 m -1 (Brune and Duffin, 1983;Senger and Kreitler, 1984;Slade and others, 1985;Scanlon and others, 2002).…”

Stream and aquifer biology of south-central Texas — A literature review, 1973-97

“…In general, the movement in the aquifer is from the west to the east or northeast. Numerous publications discuss the hydrology of the aquifer specifically and include water levels, recharge, discharge, amounts of precipitation, and other hydrologic properties (Follett, 1956;Garza, 1966;Lang, 1954;Maclay and Rettman, 1973;Puente, 1974;Rappmund, 1975Rappmund, , 1977Rettman, 1969;Sieh, 1975). Hydrologic models have been developed for predictive purposes on the basis of increased population and subsequent increased water use.…”