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Other Sources of Salt. Subsurface inflow from the mesa area to the west may add salt to the Subarea. The tributary area, known as the Mule Area, is bounded on the west by the Mule Mountains and the Palo Verde Mountains, and has an area of about 80 square miles. Much of the area's 4-inch annual rainfall occurs as thundershowers and may exit as surface runoff. Assuming that, after evaporation and use by vegetation, 1/100 of the rainfall ends up as subsurface discharge, the inflow to the Palo Verde Subarea is about 150 acre-feet per year. Its salinity is unknown, but water well data from Chuckwalla Valley [7] lying to the northeast of the Mule Mountains, and a comparison of the respective terrains, suggest that the salinity of the ground water may range from 1,000 to 2,000 mg/L. Assuming a salinity of 1,500 mg/L, the salt inflow to the Subarea would be about 300 tons per year, which is insignificant. It may also be possible that salt is entering with some subsurface inflow from the Rannells Subarea to the north. The bound- ary between the two subareas was drawn perpendicul ar to ground-water contours as much as possible to minimize such inflow. It is likely that such inflow is offset by subsurface outflow at the south end of the Palo Verde Subarea, and if anything, the net effect is likely to be a salt loss since the ground-water sa 1 i ni ty is hi ghest in the southern part of the Subarea. These effects were ignored. Fert il i zers carri ed down be 1 ow the root zone may also be contributing to salt discharge. Such an effect was not evaluated. Total Excess Salt. For purposes of this analysis, the total amount of excess salt underlying the Palo Verde Subarea is taken to be 7.0 million tons--6.65 in the ground water and 0.35 in the unsaturated soi 1. It wi 11 be treated as though it is all in the ground water because the amount in the unsaturated soil is such a small part of the total and will probably discharge slowly. 002861 18