AN INTEGRATED GEOCHEMICAL, GEOPHYSICAL AND SEDIMENTOLOGICAL APPROACH TO DELINEATE FRESHWATER-BRACKISH WATER INTRUSION FROM WELL LOGS OF HUECO BOLSON, EL PASO AREA

The El Paso-Juarez region is located at the southern end of the tectonically active Rio Grande Rift. This region includes basins that contain alluvial aquifers which are the sources of water for the municipal needs of El Paso and Ciudad Juarez, Mexico. The Hueco Bolson, an asymmetrical basin that covers approximately 1.6 million acres, is located east of the Franklin Mountains, west of the Hueco Mountains, south of Sierra el Presidio, and north of the Sierra de Guadalupe. The Hueco Bolson Aquifer (HBA) contains both fresh and brackish water. El Paso Water Utilities (EPWU) has drilled many wells up to 1000 ft (305 m) deep into this aquifer that provides about 40% of El Paso’s water supply. The HBA is cut by faults that serve as important barriers to regional groundwater flow. Many of these faults cannot be traced at the surface, especially in the more urbanized areas of El Paso-Juarez. A previous study has shown the success of using a combination of water well logs, well cuttings and microgravity data to locate faults that appear to separate zones of fresh and saline water in the HBA within south-central El Paso. The logs and cuttings from this previous study also helped to define a sedimentological and stratigraphic framework that could be applied to other parts of the HBA. In our current study we have collected additional information from 10 water wells and microgravity data from the north-central and northwestern HBA in an effort to trace the faults and stratigraphic facies across the basin. Initial geochemical data show that total dissolved solids (TDS) in these wells progressively increase towards the north, but decrease towards the northwest. Our goal is to better understand the structural and stratigraphic mechanisms controlling these observed differences.