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Tucson Electric Power (TEP) is carrying out subsurface investigations in order to locate more groundwater for cooling at the Sundt power-generating plant. To assist with this investigation, the University of Arizona GEN/GEOS 416/516 Field Studies in Geophysics class conducted geophysics surveys in an area just south of Davis-Monthan Air Force Base and between UTM coordinates 508,555 to 511,753 East and 3,553,705 to 3,556,895 North. Four geophysics methods (Gravity, Magnetics, Transient Electromagnetics (TEM), and Passive Seismic) were employed to locate a postulated fault, which may be correlated with ground water flow. A broad regional magnetic anomaly was mapped, as the magnetic field decreases steadily from NE to SW. There are no significant magnetic field anomalies that could be related to a potential fault. The Gravity results show a regional gravitational gradient, steadily decreasing from NE to SW, with a large isolated anomaly apparent around 1500m from the base station at the NE corner of the survey area. But, this large anomaly is a localized, and does not appear on the adjacent parallel survey lines, therefore it is not related to a potential fault contact. The Passive Seismic survey detected a deep boundary at 100m to 160m in elevation, but the depths interpreted from the 11 stations are scattered and do not show a clear trend. The Transient Electromagnetic (TEM) data show a consistent difference in depth to a low-resistivity layer along the profile line. The four TEM stations north of Interstate 10 (I10) have an average elevation for the 10 Ohm-m contour line of 720 meters. The four TEM stations south of I10 have an average elevation for the 10 Ohm-m contour line of 670 meters. This offset may be related to the postulated fault.

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A geophysical study of the Patagonia-Sonoita Nature Conservancy property was carried out to determine the depth to bedrock and the geometry of the underlying basin in the area. The survey was part of the ongoing U.S. Geological Survey studies of the region. CSAMT, TEM, DC Resistivity, Seismic, Gravity, and Magnetic surveys were performed. Many of the surveys were not able to map depth to bedrock because the depth of penetration of these surveys was less than the large depth to bedrock, which we encountered in this area. The best estimate of depth to bedrock in the center of the valley is of the order of one kilometer, as identified by the CSAMT surveys. The CSAMT survey found a significant low-resistivity anomaly in the vicinity of the Nature Conservancy Visitor Center. This low-resistivity anomaly could be due to clay-rich rocks or possibly mineralized rocks. Magnetic and TEM anomalies also occurred in the same area as the CSAMT low-resistivity anomaly. Seismic surveys showed a loosely consolidated surface layer above more consolidated alluvium. The model from the · Gravity survey shows an extensive alluvial basin overlying rhyolite with high and low-angle faults.

During the Spring semester, 2000, the University of Arizona Geophysics Field Camp (GEN/GEOS 416/516 class) conducted geophysical surveys in the vicinity of the United Musical Instruments facility near Nogales, Arizona. This site is a super-fund site, due to the presence of contaminants, including TCE, in the ground water. The contaminants are presumed to have come from cleaning and electroplating solutions, which had been dumped into a small pond on the UMI property. The U.S. Geological Survey provided the funding for our study. The objective was to determine subsurface structural information that would help interpret possible future movement of the contaminant plume. Transient electromagnetic (TEM) data were most useful for interpreting the subsurface geohydrology. Water table was found at a depth of approximately 30 meters, north of the UMI building. A particularly interesting feature in the TEM data was a high-resistivity anomaly and an associated low-resistivity anomaly 10 to 1 00 meters northeast of the UMI building. We interpret the high-resistivity anomaly as possibly being due to an impermeable levee that was associated with a buried stream channel and the low-resisitivity anomaly as possibly being due to the pooling of conductive contaminated fluids against the impermeable levee. DC resistivity surveys were dominated by cultural coupling, which was pervasive m the survey area. Magnetic readings were used to help locate potential cultural interference. Gravity surveys indicated a low-density anomaly, which may be due to a buried stream channel. This feature could be related to the features mapped with the TEM surveys. The seismic survey indicated progressively more compacted and cemented alluvium, overlying the Nogales formation. The seismic data did not provide any direct information about the geohydrology of the area

During the Spring semester, 2001, the University of Arizona Geophysics Field Camp (GEN/GEOS 416/516) conducted geophysical surveys near the San Pedro River, Arizona. This site is being investigated by the U.S. Geological Survey as part of a basinwide study of water resources. Our geophysical investigation was designed to provide information that will assist in this hydrogeological study. The surveys were conducted near Boquillas Ranch (approximately 2 km south of Fairbank, AZ) and approximately 2 km north of Hereford, AZ. Dipole-dipole and Schlumberger DC resistivity surveys were conducted at both the Boquillas Ranch and Hereford sites. Depth to water table was approximately 10-20 meters at the Boquillas Ranch site and 0-to-1 0 meters at the Hereford site. The electrical resistivities at depth at the Hereford site were unusually low for Arizona basin-fill sediments (less than 10 ohm-m). Transient electromagnetic (TEM) soundings were also recorded at both the Boquillas Ranch and Hereford sites. Electrical resistivity models were determined that were very similar to the DC resistivity models. In general, the TEM soundings were able to provide similar information to the DC resistivity soundings with greater data acquisition rates and with a smaller crew. Electromagnetic induction (EM31 and EM34) surveys were run at the Hereford site. Qualitatively, an electrical resistivity structure was found that was similar to the DC resistivity survey and the TEM survey results (i.e. the resistivity decreased with increasing depth of investigation).These data are not well suited, however, to quantitative modeling. Seismic, magnetic, and gravity surveys were run at the Boquillas Ranch site. These surveys provided useful background information on the geologic structure at this site. They did not provide direct information on the hydrogeology at the site.