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amount of salt from other subareas diverted to the Sundesert Plant would increase by 1,800 tons, because of changes in the proportions of drainage among subareas. The net effect would be to reduce the ini- tial excess salt discharge to the river by 67,400 tons, and the resulting discharge to the river would be 53,400 tons, as shown on Table 2. The long-term salt discharge to the river with 60-percent effi- ciency is plotted on Figure 6. The upper plot shows that the salt discharge begins initially at 53,400 tons per year and decreases gradually with time. Also shown is the discharge of excess salt to the ri ver wi th the Sundesert Pl ant. A compari son between the plot with Sundesert and the plot with 60-percent efficiency indicates the reducti on in annual salt di scharge resulting from 60-percent effi- ciency. The plots of excess salt content show that with salinity control measures the reduction of excess salt from the Subarea would be more gradual and prolonged. It also shows a peculiarity of the concept of excess salt. When the efficiency changes to 60 percent, there is a shift in the initial quantity of excess salt. Under present condi- tions the nonexcess salt was 3.1 million tons because the average sa 1 i ni ty of perco 1 at i ng seepage and 1 eachi ng fraction was 1,230 mg/L TDS. When the efficiency increases, the average salinity of percolat- i ng agri cul tura 1 drai nage increases, whi ch increases the amount of salt considered to be nonexcess. And since the absolute tonnage of salt remains the same, the excess salt is reduced a corresponding amount. The important thing with respect to the Colorado River is not the amount of excess salt, but the change in salt pickup that would occur. An increase in the salinity of the percolating water has an effect on the apparent salt discharge. As the salinity of the percolating water increases, there will be less difference between it and the salinity of the ground water that it flushes out. This will cause an apparent decrease in the salt pickup per acre-foot of drainage. 002873 29