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The range in total dissolved solids is from about 2,000 to about 18,000 parts per million. Similarly, Drawing No. 998-303-108 shows the range and distribution of total dissolved solids in the shallow zone of the aquifer, as shown by samples from 324 shallow observation wells. High mineral concentrations in the ground water are principally due to the large amounts of sodium and chloride ions. C. Hydrology of the Wellton-Mohawk Area 1. Water Supply and Requirements. Importations of water for irrigation through the Wellton-Mohawk Canal represent practically all the surface-water inflows to the Wellton-Mohawk area. Total annual precipitation is only about three inches, and is not considered significant. Occasionally, runoff from storms on the upstream or tributary areas reaches the project. For the period 1951-60, the average runoff at the Dome gauging station was less than 5,000 acre-feet per year. Importations from the Colorado River during water year 1962 (October 1, 1961, to September 30, 1962) amounted to 405,750 acre-feet for approximately 57,000 acres of irrigated land. The 57,000 acres include 3,400 double-cropped acres and 800 acres of Bermuda grass not included in the crop census. (Crop census for 1962 is not yet available, and it is assumed for the purposes of this report that the area irrigated in 1962 was approximately the same as for 1961.) The unit gross diversion was about 7.1 acre-feet per acre. Alfalfa was the predominant crop and in 1961 accounted for more than 55 percent of total, followed by cotton, 13%; Bermuda grass, 11%; and about 5% each for barley, wheat, oats and sorghum. 47Epson Perfection 4870 Photo, 400 dpi, 8 bit, 8,979,968 byte