The lower Mesilla Valley extends southward from the vicinity of Anthony, Tex., to the gorge of the Rio Grande north of El Paso and westward from the Franklin Mountains to the east edge of La Mesa. The increase in the use of ground water for the public water supply of El Paso and for supplemental irrigation, when the surface-water allotments were inadequate, emphasized the need for an investigation of the groundwater resources of the lower Mesilla Valley. The deep and medium aquifers in the Santa Fe group, whose maximum thickness is at least 2,000 feet, are the major sources of ground water for public supply. The alluvium (shallow aquifer), which supplies water chiefly for irrigation and to a lesser extent for industrial and municipal supply, has a maximum thickness of about 150 feet. The Santa Fe group is recharged by precipitation on the surface of the uplands. The alluvium is recharged by seepage from drains, irrigation canals, and the river, from excess surface water applied to the land, from precipitation on the valley floor, and from the upward movement of water from the Santa Fe group. Ground water is discharged by evapotranspiration in areas of high water table, by seepage to the drains and river, by underflow at the south end of the valley, and by wells. Except in the uplands, water in the Santa Fe is under confined (artesian) conditions; water in the alluvium is under unconflned (water-table) conditions. Pumpage of ground water for irrigation and for the public supply of El Paso increased from 1951 through 1956. Irrigation pumpage decreased in 1957 and 1958, when surface-water allotments were increased. In 1958 the city of El Paso wells pumped an average of 6.8 million gallons per day from the deep and medium aquifers of the Santa Fe, an increase of 4.3 million gallons per day from the quantity pumped in 1957. The 1958 pumpage from the medium and deep aquifers is estimated to be about 50 percent of the annual recharge to the Santa Fe. Aquifer tests in the El Paso city well field northwest of Canutillo indicate substantial leakage between the shallow, medium, and deep aquifers. The coefficients of transmissibility averaged about 60,000 gallons per day per foot in the deep aquifer, 35,000 in the medium aquifer, and 150,000 in the shallow aquifer. The quantity of fresh water in storage in the Texas part of the valley is estimated to be 560,000 acre-feet, of which 150,000 acre-feet is in the alluvium. AA1 AA2 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES Less than half the fresh water in storage however, may be recovered by wells, owing to the possibility of saltwater contamination. North and west of Canutillo, water in the medium and deep aquifers of the Santa Fe is satisfactory for municipal use. The water in the alluvium is relatively fresh but more mineralized than that in the Santa Fe. South of Canutillo, the water in the alluvium is highly mineralized but, generally, is of better quality than the water in the underlying Santa Fe. Pumping from the medium and deep aquifers may result in the percola...
