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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />it discharges into the Rio Grande. Ground and surface water in this area are <br />considered to be hydraulically connected. Yields from high capacity wells in <br />the valley fill aquifer range from 240 GPM to 2,000 GPM. The estimated <br />volume of recoverable fresh ground water in storage is 2.3 billion acre-feet <br />and there is an additional half billion acre-feet of slightly saline ground <br />water in storage [15,19]. <br /> <br />Bedrock in the vicinity of Elephant Butte Reservoir restricts the width <br />of the Rio Grande valley and partially separates the ground water aquifers <br />to the north (WAU 130202) from those to the south (WAU 130301). As in the <br />San Luis Valley in Colorado and in the Rio Grande valley north of Elephant <br />Butte, the principal aquifer in WAU 130301 is unconsolidated sand and gravel <br />valley fill with interbedded volcanic rocks. The thickness of the fill near <br />Las Cruces ranges up to 5,000 feet, and it probably averages about 3,000 <br />feet. The southern terminus of the bolson occurs near El Paso, where the <br />structural and topographic valleys again narrow. Recharge is by direct pre- <br />cipitation on the valley floor, by runoff from bounding mountaneous areas, <br />and, especially, by leakage of irrigation water from croplands and con- <br />veyance facilities, but it is limited because of the small size of the <br />bolson. Ground water movement is toward the center of the basin where, <br />under normal streamflow conditions, subsurface discharge to the Rio Grande <br />occurs. There are between 200 and 300 million acre-feet of fresh to <br />slightly saline water in storage. Individual wells in this area yield up to <br />3,000 GPM [15,19]. <br /> <br />Pecos River - The ground water situation in ~he Pecos River valley of <br />New Mexico (WAU 130600), particularly the interrelationship between the <br />aquifers and the Pecos itself, is extremely complex. Aquifers comprise con- <br />solidated sandstone, limestone, gypsum, basalt, and unconsolidated valley <br />fill. The valley fill is a productive aquifer where it is fairly thick. <br />There are both unconfined and confined aquifers in the basin with exchange <br />between the aquifers and the Pecos River occurring as both recharge and <br />discharge. <br /> <br />\(l <br />dO The aquifers in the south central portion of the New Mexico Pecos River <br />o <br />~alley immediatelysouth of the city of Roswell, a geologic structural area <br /> <br />29 <br />