vii

2. Future Quality of Water Delivered to Mexico. The water to be delivered to Mexico under Phases 1 and 2 of the proposed program will not have any deleterious effect on soil productivity insofar as exchangeable sodium levels are concerned. The sodium adsorption ratio under Phase 1 will range from 4.7 to 6.5 and from 5.3 to 5.9 under Phase 2. The dissolved mineral content of water delivered to Mexico will be approximately 2,000 ppm and 1,800 ppm after construction under Phases 1 and 2, respectively, is completed. At the present time, the unfavorable salt balance in the Mexicali Valley is primarily due to the lack of adequate leaching of excess soluble salts from overextension of the cropped area. The situation in the Mexicali Valley today was not brought about by a year of Wellton-Mohawk drainage operations but, rather, it is the accumulation of irrigation practices over an extended period of time. The water available under the treaty is not sufficient to irrigate the present acreage and maintain the proper salt balance. Even curtailment of the present acreage would require that adequate leaching and drainage be provided to prevent waterlogging and surface accumulation of harmful salts. Initially, the total quantity of dissolved solids contained in Colorado River water delivered under the proposed plans will remain approximately the same on an annual basis but will be reduced as refreshing of the Wellton-Mohawk aquifer progresses. If Mexico carries out accepted irrigation and leaching procedures the salt concentrations will not be detrimental to the crops that are presently being grown. Neither will these concentrations of salt be detrimental to soils in the irrigable classes. A number of irrigated areas in viiEpson Perfection 4870 Photo, 400 dpi, 8 bit, 8,817,664 byte