Memorandum on ground-water irrigation in Mitchell County, Texas

Abstract

Although ground water is generally available in most parts of Mitchell County, Tex., for stock and domestic use, wells of large yield have not been reported until recently. In the past, Colorado City has had considerable difficulty in obtaining enough water for public supply from ground water in the immediate vicinity of the city. Reports of irrigation wells yielding more than 1,000 gallons a minute in east-central Mitchell County, therefore, have attracted considerable interest, particularly as the water was discovered during a period of severe drought. This memorandum is based on a brief investigation made in May 1953. Pre vious investigations have been made in various parts of Mitchell County, particularly in the vicinity of Colorado City, but this investigation is concerned mainly with irrigation wells in the northeastern piart of the county. There are about 65 to 70 irrigation wells in Mitchell County Records were obtained for 48 of these wells, samples of water were taken from 21 wells for chemical analyses, and drillers' logs of 19 wells were Obtained, These data are recorded in tables at the end of this memorandum The irrigation wells range in depth from 115 to 315 feet but most of them are 150 to 200 feet deep. The groundwater reservoir is composed of sand and gravel beds of Triassic age. In most places aquifers are found at two different depths, the upper between depths of 20 and 50 feet, and the lower between 100 and 200 feet" Some of the water is obtained from alluvium. No large quantity of water has been found below 300 feet. The cost of irrigation wells has been relatively small because the cost of drilling is about $1.50 per foot and not much casing is required. Many wells have 20 to 50 feet of casing in them but some wells have no casing at alL It was not possible to measure static water levels in many of the wells because most of the wells had been pumping continuously for about 3 months. Static levels for a number of wells were measured in January 1953= It is reported that the static water levels in January, before pumping started, ranged from about 15 feet below the land surface in the northern part of the area to about 65 feet in the southern part. Most of the wells yield 200 to 250 gallons a minute, but the Granite 25