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<br />For convenience in this report, the concept of "excess salt" <br />will be used. Excess salt is defined as the amount of salt in the <br />ground water in excess of that which would be present if the ground- <br />water salinity were the same as the salinity of the leaching fraction <br />plus seepage. For example, if the ground water under the Subarea had <br />an average salinity of 1,230 mg/L, it would contain approximately <br />3.1 mill i on tons of salt. The excess salt in the ground water is <br />approximately 6.65 million tons (9.75 million minus 3.1 million). <br /> <br />Salt in Unsaturated Soil. Prior to irrigation, the unsatu- <br />rated. soils of the Subarea contained soluble salts deposited throug~ <br />water use by natural vegetation and evaporation from sloughs and bare <br />soil. The water table was relatively shallow. Salt leaching activi- <br />ties and crop irrigation have probably removed most but not all of <br />this preexisting salt. <br />A limited program of soil sampling was carried out in the <br />Subarea in the summer of 1977 to determine the approximate amount of <br />soluble salt in the unsaturated soil profile, which averaged 7 feet in <br />depth. Soil samples were obtained from 22 holes dug with a 3-inch <br />di ameter hand auger to depths of 7 feet to 11 feet, until water <br />impeded sample recovery. The samples were tested for total soluble <br />salts. The results, converted to percent soluble salt, varied from <br />.02 percent in sandy, we ll-dra i ned soil s to over 2 percent in tight <br />soils under bypassed areas not farmed. A common salt percentage for <br />well drained soils seemed to be .08 percent. <br />Using the results of this survey, it was estimated that the <br />soluble salt content of the unsaturated soil was approximately 500,000 <br />tons, including a few bypassed parcels of land unsuitable for agri- <br />cul ture. In maki ng the estimate a sal t content of .08 percent was <br />selected as an irreducible minimum, and that anything greater was <br />assumed to be subject to removal. This produced a quantity of salt to <br />be leached of approximately 350,000 tons. <br /> <br />002860 <br /> <br />17 <br />