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<br />w <br />00 <br />00 <br />(D <br /> <br />depletion schedules were used: the Bureau of Reclamation's schedule <br />, and the low depletion schedule developed by the Forum. <br /> <br />Five d'ifferent salinity control project scenarios that were evaluated: <br /> <br />1. Base Case. Assumes that no more funds will be expended on salinity <br />control. OnlY the completed Reclamation and USDA portions of the Grand <br />Valley and Uinta Basin Units and the Meeker Dome Unit are included in <br />this case. <br /> <br />Figure 5 represents the average base case projection of salinity at <br />Imperial Dam using natural hydrology from 1906 to 1983 (taking the mean <br />of 15 sequences) and Reclamation's depletion schedule (approximating the <br />Forum's high depletion schedule). Essentially, the "target load estimates" <br />(the estimate of necessary salt load reduction) were derived to meet the <br />standard with a maximum TDS projection at Imperial Dam of 1005 mg/L by the <br />year 2020. The target load is the equivalent amount of salt to be removed <br />from the river system to offset expected increases in salinity above the <br />standard caused by depletions. <br /> <br />Scenarios 2, 3, 4, and 5 summarize salt tonnage removal assumptions for <br />the CRSS salinity projections. The comparative effects of these salt <br />removal assum~tions are shown on figure 6. <br /> <br />2,.'$cenari'o 2. The salt removal assumptions (input data to, the CRSS <br />model) consist of the presently completed units plus completion of only <br />the remainder of Reclamation's presently authorized and planned salinity <br />control project5--namely, Grand Valley, Paradox Valley, and Las Vegas <br />Wash. No further USDA work in the Grand Valley and Uinta Basin Units is <br />included. The assumptions are that no further authori2ing legislation <br />will be forthcbming and that USDA projects will not be funded. <br /> <br />Figure 7 summarizes the salt tonnage removal assumptions made in scenario <br />2 for Interior, USDA, and total program effects. <br /> <br />3. Scenario,3lc This scenario assumes that only the USDA legislation <br />is passed (H.Rr 3903). This alternative encompasses scenario 2 plus <br />the entire USDA onfarm program and results in the tonnage reductions <br />as shown on figure 8. <br /> <br />For the USDA onfarm program, there is some uncertainty regarding the <br />long-term salt load reduction benefits after the specified useful onfarm <br />practice life. This relates to the overall operations, maintenance, and <br />subsequent replacement of onfarm practices. Unti 1 there is further <br />clarification of this matter by USDA, for this evaluation, the assump- <br />tions are that practice life is 20 years and that long-term salt load <br />reduction beneflts then diminish to 50 percent of the original benefits. <br />These assumptions explain why the salt load reduction tonnage from the <br />USDA program drbps off after the year 2000 in scenarios 3, 4, and 5. <br />If followup work prevents the reduction in benefits, there will be <br />additional costs associated with all followup work. <br /> <br />26 <br /> <br />i~ _-" _ <br /> <br />n <br />,{is. <br />