Ground-water resources of the El Paso area, Texas

Abstract

El Paso, Tex., and Ciudad Juarez, Chihuahua, Mexico, and the industries in -that area draw their water supplies from wells, most of which are from 600 to 800 feet deep. In 1906, the estimated average pumpage there was about 1,000,000 gallons a day, and by 1935 it had increased to 15,400,000 gallons a day. The water-bearing beds, consisting of sand and gravel interbedded wire clay, tie in the deep structural trough known as the Hueco bolson, between the Organ and Franklin Mountains on the west, the Hueco, Finlay, and Malone Mountains on the east, the Tularosa Basin on the north, and the mountain ranges of Mexico on the south. From the gorge above El Paso to that beginning near Fort Quitman, about 90 miles southeast .of El Paso, the Rio Grande has eroded a flat-bottomed, steepwalled valley, 6 to 8 miles wide and 225 to 350 feet deep. No other large drainage channels have been developed on the bolson. The valley is known as the El Paso Valley, and the uneroded upland part of the bolson is called the Mesa. In the lowest parts of the El Paso Valley, the water-table is nearly at the surface. The quality of the underground water in the valley varies greatly both vertically and laterally. To a depth of about 400 to 500 feet it is in general too highly mineralized for municipal use, but between about. 500 and 900 feet good water may be obtained from several beds. In the beds between 500 and 900 feet the water level in wells is in places as. much as 20 feet lower than that in the shallow beds. Beneath the Mesa the water level .varies from about 200 feet beneath the surface, where the ground elevation is least, to about 400 feet. where it is highest. The water beneath the Mesa in general is of satisfactory quality and contains less than 500 parts per million of dissolved solids. Two cones of depression in the water table have been formed by the pumping near El Paso--one m the vicinity of the Mesa well field, the other around the Montana well field in the valley. The water released from storage by the formation of the cone centering in the Mesa field was calculated at 22,000 acre-feet, but the total pumpage was estimated to have been 90,000 acre-feet. Thus, about one-fourth of the total pumpage was taken from storage; the remaining three-fourths and apparently was taken from recharge. About 210,000 acre-feet of water has been pumped from the cone of depression in the El Paso Valley in and near El Paso. The volume of this cone could not be determined because there are artesian conditions in this area. Computations were made of the amount of water that would be recovered from storage if, for a distance of 10 miles north of the Mesa well field, the water level in a series of wells were drawn down the same amount as the present drawdown in the wells in that field. The water that would be recovered from storage in the formation 0f this depression in the ground water surface was calculated at about 130,000 acre-feet, the equivalent of about 70 years' supply at the 1935 rate of pumping.It is, of course, available in addition to the annual recharge. The sudden increase in 1924 in the saltwater content of the water from El Paso well 3 (well 52), in the Montana well field, was shown to be the result of a leak in the casing at a depth of about 127 feet, and the well was successfully repaired during the investigation. However, the chloride content of all of the wells in the field has been increasing gradually. This may indicate that salty water is being pulled in from considerable distances or that the barriers between the fresh-water-bearing beds and the saltwater-bearing beds above-them are not capable of preventing vertical movement of the ground water. The fact that in the valley the static water level in the shallow beds yielding poor water is higher than that in the deeper beds is disquieting, and if the level in the lower beds continues to decline, seepage from the river will eventually force the shallow highly mineralized water