Search for New Ground Water Sources in the Basin and Range Region of the Southwestern United States

The need to develop additional supplies of water to satisfy the demands of the rapidly growing urban communities of the arid Southwestern USA is prompting the search for new water sources. For decades ground water from alluvial aquifers was the principal source for cities like Phoenix, Tucson and Las Vegas.Ground water continues to be an important and essential component of their water supply.Imported water from the Colorado River, managed aquifer recharge,water re-use, along with improved management of the limited and climate sensitive surface water resources have substantially contributed to augment their supply during the last two decdes. However, as the population continues to grow and with the concerns of potential impacts from climate change new water sources will be required. Fractured bedrock aquifers (FBA) associated with tectonic features of the Western Cordillera are an untested potential source for ground water.Accumulated tectonic knowledge during the last twenty five years of the Basin and Range region has provided an adequate interpretation of its structural framework that can be applied to the exploration of FBA. Thrusts, detachment faults with their associated listric faults and high angle normal faults generated during the three most recent orogenic episodes (Laramide, Mid-Tertiary and Basin and Range) are potential FBA.The location of fractured rock masses associated with these tectonic features can be realized with detailed geologic mapping assisted with indirect detection methods mainly geophysical. Electromagnetic soundings of which controlled source audio frequency magnetotellurics (CSAMT) is a very cost effective and high resolution method. As an example of this exploration and its feassibility was the discovery of a deep FBA in a granite of Precambrian age hosted in a possible detachment fault. Exploratory drilling confirmed the occurrence of this aquifer at a depth of 300 meters in an area of the City of Phoenix.