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In the Mexicali Valley, the area presently under Irrigation is between 500,000 and 600,000 acres. This area is irrigated both by Colorado River water and by wells. Since 1957, there have been 490 relatively large wells (3 to 10 cubic feet per second capacity, depths from 200 to 300 feet) in operation, which in 1961 yielded 730,000 acre feet of water. The salinity of the water produced by the wells used for irrigation varies in general from 800 parts per million to 1,800 parts per million. About 5% of the wells show salinity concentrations of 2,000 to 2,400 parts per million. These high salinity wells are operated only occasionally for irrigation, but are used, together with surface drains, to regulate the level of the water table. Up until the fall of 1961, the well water for irrigation was mixed in the irrigation canal with Colorado River water (salinity 910 ppm) to obtain irrigation water of 1,100 to 1,200 parts per million. To avoid sea water intrusion, the drawdown of the wells are regulated. Because of the relatively large amount of land under cultivation, and the limited water supply. the allotment of water per acre has been only 3.9 to 4.3 feet, and consequently there has been a tendency for salt accumulation in the soil and sub-soil. This situation can be alleviated by reducing the acreage under irrigation, and by improved drainage. But the predominant fine texture of the soils of the Mexicali Valley provides as inherent difficulty to the improvement of Icaching and drainage conditions. According to Dr. C. A. Bower, Director of the Salinity Laboratory of the Department of Agriculture at Riverside, and one of the United States members of the Panel, it is doubtful whether Mexico. "can physically improve irrigation practices and drainage conditions in the Mexicali Valley sufficiently to obtain the same crop yields with water having a salt content of 2,500 to 3,000 parts per million and a sodium adsorption ratio of 8 to 10, as with water having a salt content of 900 to 1,000 parts per million and a sodium adsorption ratio of about 3." In their consideration of possible solutions to the problem, the United States members of the Joint Panel adopted the following constraints: (1) The provisions of the 1944 Water Treaty must be adhered to, and, specifically, nothing must be done to reduce the amount of water usable in the United States under the terms of the Treaty: (2) there must be no impairment of the Wellton- Mohawk District: (3) there must not be included any guarantee of quality or usability of waters delivered to Mexico. -2-Epson Perfection 4870 Photo, 400 dpi, 24 bit, 10,656,768 byte