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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 />Ground water underlies approximately two million acres of the San Luis <br />Valley [19J. For an average aquifer thickness of 5,000 feet with a specific <br />yield of 0.2, the amount of water in storage is estimated to be about two <br />billion acre-feet. Transmissivities in the unconfined aquifer are commonly <br />in excess of 5,000 gallons per day per foot (g/d/ft.) and range upward to <br />225,000 g/d/ft. Transmissivities in the upper 1,500 feet of the confined <br />aquifer range as high as 1.2 million g/d/ft. Transmissivities and potential <br />yields from wells are highest in the western half of the Valley [20J. <br /> <br />New Mexico <br /> <br />Ground water in New Mexico occurs primarily along the valley of the Rio <br />Grande mainstem, in the Pecos River basin, and in several of the closed <br />basins (bo1sons) between the Rio Grande and the Pecos River and to the west <br />of the Rio Grande. Generally, the structural basins in which the ground <br />water occurs conform to the topographically-defined river basins. Principal <br />aquifers from which fresh and slightly saline water is obtained include <br />unconsolidated valley fill, limestone and dolomite, and volcanic rocks <br />(basalt). <br /> <br />Rio Grande Mainstem - Ground water in the Rio Grande valley between the <br />Colorado state line and Elephant Butte Reservoir (WAU's 130201 and 130202) <br />occurs primarily in unconsolidated valley fill. The maximum thickness of the <br />valley fill aquifer is unknown, but it is probably about 9,000 feet; its <br />average thickness is probably about 4,000 feet [19J. This is the thickest <br />known aquifer in New Mexico. With the exception of the Rio San Jose Valley <br />near Grants, New Mexico, where yields of more than 2,000 GPM have been <br />obtained from individual wells in a limestone aquifer, the consolidated sedi- <br />mentary and crystalline rocks along the periphery of the Rio Grande valley <br />are poor aquifers. Locally, volcanic rocks serve as aquifers. <br /> <br />Recharge to the valley fill aquifer is from direct precipitation in the <br />valley, from percolation of surface water diverted for irrigation, and from <br />.0 <br />~~unoff that emerges from steep mountain streams after intense rain storms. <br />~ the northern part of the valley (WAU 130201), snowmelt contributes some <br />recharge. Ground water movement is toward the center of the valley, where <br /> <br />28 <br />