OVERVIEW ON INTEGRATING REMOTE SENSING WITH TRADITIONAL METHODS IN HYDROLOGIC, GEOLOGIC, AND WATER-EXPLORATION STUDIES AT FORT IRWIN NATIONAL TRAINING CENTER IN THE MOJAVE DESERT, CALIFORNIA

The U.S. Army Fort Irwin National Training Center (NTC), in the Mojave Desert, obtains all of its potable water supply from three groundwater basins within the NTC boundaries. Based on hydrographs, groundwater withdrawals from these basins exceed recharge. To plan for the long-term water availability and sustainability at the NTC, water resources were evaluated in 7 undeveloped groundwater basins underlying the NTC. Most of the undeveloped basins have little to no lithologic or historical hydrologic data. As part of a multi-faceted NTC-wide study, traditional data-collection methods used include lithologic and geophysical logging at newly drilled borehole, hydrologic (water-level, water-quality, aquifer tests, wellbore flow) data collection, and geologic, gravity and aeromagnetic mapping. These data cover a small portion of the 1,177 square-mile NTC. To obtain subsurface information on a regional scale for hydrogeologic framework and groundwater-flow models, airborne and transient electromagnetic surveys were conducted. Integration of the remote sensing and traditional methods indicated that the NTC is a heavily-faulted and geologically-complex area, bounded by the Garlock fault to the north and is in the Eastern California Shear Zone. The hydrogeology of the NTC is typical of many alluvial basins in the Mojave Desert. Basins are underlain by pre-Tertiary basement complex of consolidated plutonic and metamorphic rocks. Volcanic rocks, predominantly in western basins, are highly variable, ranging from welded to highly fractured, and may yield water. The basins fill consists of semi-consolidated to unconsolidated Tertiary and Quaternary deposits derived from the surrounding terrain. Surface runoff from storms occurs primarily in the volcanic highlands in the west and local mountains. Recharge from these storms occurs along perennial washes and near the base of local mountains. Groundwater flows from recharge areas toward the low areas in the basins, the playas. The depth to groundwater and direction of groundwater flow is important which is controlled by the distribution of faults, recharge, discharge, and aquifer hydraulic properties within the basins. Discharge by subsurface flow occurs between some of the basins through saddles and along faulted or fractured zones in bedrock.