Geological and geophysical studies of the structure and stratigraphy of the northwestern Hueco Bolson Aquifer, El Paso, Texas

Abstract

The Hueco Bolson Aquifer contributes between 30% and 60% of the yearly drinking water supply for El Paso's population, depending on surface-water availability from the Rio Grande. The aquifer contains both freshwater and brackish water. We used microgravity and well-log data in a highly urbanized area of the northwestern Hueco Bolson Aquifer, where the majority of currently operating water wells are located, to demarcate subsurface faults that may control the locations of the freshwater and brackish water. Our results extend the length of some previous mapped faults, as well as identifying several new faults. Because of the large distance between individual wells, well-log correlations themselves do not resolve the individual faults; however, structural cross sections suggest that at least some faults inferred from the microgravity surveys are present between the wells. The depositional environments inferred from the gamma-log responses and their stacking patterns are consistent with braided stream, alluvial-fan, playa-margin, delta, and sheetflood deposits. Faults in the western portion of the study area, in a region where the East Franklin Mountains fault steps over 2 km to the west, appear to serve as conduits for upwelling of deeper brackish water, while in the eastern study area, faults appear to serve as barriers to the flow of brackish water into the shallower portion of the aquifer. The thickest region of freshwater correlates with the deepest portion of the basin as delineated by the gravity data. PREVIOUS STUDIES The Hueco Bolson is one of a series of north-trending, interconnected asymmetrical grabens that form the Rio Grande rift system (

Current Status and Future Directions in Modeling a Transboundary Aquifer: A Case Study of Hueco Bolson

“…The Hueco Bolson follows the structural depression associated with the Rio Grande Rift. The northern part is dominated by north striking faults, whereas the southern part, mainly located in Mexico, is characterized by northwest-striking faults [39]. The main aquifer is of unconfined and semiconfined nature and consists of basin-fill deposits up to 2500 m thickness [10].…”

“…The groundwater chemistry and isotope study of Anderholm and Heywood [38] indicated that the infiltration of precipitation and the runoff from the Franklin Mountains is the main source of groundwater along the ridge, and dilute recharge water mixes with sodium chloride brine as groundwater moves away from the recharge area. The location of fresh and brackish groundwater seems to be controlled by stratigraphic and structural changes in the El Paso area of the Hueco Bolson [39]. In some parts of the basin, the deeper-lying saline groundwater [32] can upwell through fractures due to fault step-overs [39].…”

“…The location of fresh and brackish groundwater seems to be controlled by stratigraphic and structural changes in the El Paso area of the Hueco Bolson [39]. In some parts of the basin, the deeper-lying saline groundwater [32] can upwell through fractures due to fault step-overs [39]. Effects of the surrounding land-use activities, i.e., agriculture and wastewater treatment systems, are reflected in the lower groundwater quality near the Rio Grande than farther away from the river [40].…”