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<br />u <br />u <br />u <br />U <br />I <br />n <br />n <br />n <br />n <br />u <br />u <br />D <br />n <br />ti <br />D <br />. <br />~ <br />m <br />ti <br /> <br />.... <br /> <br />C) <br />OJ <br />~ <br />~ <br /> <br />-212- <br /> <br />load from the Lower Gunnison at 1.0 x 106 Mgm for a total <br />average salt load of about 13.5 Mgm/ha. The EPA (1971) <br />computed the salt load from the areas above the Curecanti <br />Project to vary from 0.67 Mgm/ha to about 2.25 Mg/ha, and <br />that the irrigation of 66,420 hectares in the Lower Gunnison <br />Valley annually contributed about 15 Mgm/ha. Primarily as a <br />result of agricultural activities, the average flow weighted <br />concentration of the Uncompahgre River rises from about <br />200 mg/l at Ouray to over 1,100 mg/l near Delta. <br />A memorandum of the USDI, BR (1978) calculated the two <br />year average (1976-77) of irrigation-related salinity con- <br />tribution for the area. . The Mancos shale soils on the east <br />side of the Uncompahgre River contributed a total of approxi- <br />mately 253,000 Mgm or average of 15 Mgm/ha of salt to the <br />river, while the terrace deposits on the west side annually <br />contributed about 100,000 Mgm or an average of about 4.5 <br />Mgm/ha. This difference is due to low amounts of salt <br />inherent in the soils of the terraces, and relatively short <br />travel times for the groundwater to be in contact with the <br />underlying Mancos shales. Figure 2-3 illustrates the <br />extent of the Mancos shale and terrace deposits in the area. <br />The numbers and letters on Figure 2-3 correspond to the same <br />designations on Table 2-5. <br />The WPRS is presently only investigating lands under <br />the Uncompahgre Project which is about one-half of the total <br />irrigated area and accounts for about one-third of the <br />salinity. The majority of the remaining irrigated lands are <br /> <br />~:_~- <br />