GROUNDWATER RESISTIVITY SURVEY, TDEM AND WELL ANALYSIS IN THE LOWER MESILLA VALLEY, NEW MEXICO AND TEXAS

In 1973 the U. S. Geological Survey (USGS), in cooperation with the Texas Water Development Board, made sixty five Schlumberger resistivity soundings in the lower Mesilla Valley. The survey area includes the westernmost edge of Texas in El Paso County and part of Dona Ana County, New Mexico. This study was made to estimate and delineate the volume of fill containing fresh groundwater (Zohdy, 1976). A re-interpretation of the resistivity data was subsequently made by Al-Garni (1996). Some of the resistivity models proposed in the more recent work do not fit the observed sounding curves well and the cross-sections based on these models show extremely low resistivity values (from 3 to 10 ohm-m) at depths of approximately 500 m. After 40 years of other geological and geophysical studies made in this area, it is known that those low resistivity values do not correspond to the actual structure of the basin. This could be a problem since a recent regional groundwater report uses these interpretations. The main objectives of this project are: to reprocess the USGS resistivity data, conduct new resistivity surveys, analyze data from more recent TDEM surveys and integrate these with existing geophysical logs and water quality data to create a more accurate model of the basin and evaluate strategies for managing the aquifer.