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. . . o c.o ~ ~ SPECIAL STUDIES (Continued) drainage system. This model can be interfaced with the conjunctive use model mentioned above to provide basin wide simulation capabilities. Information concerning these models are included in final reports dated August 1977, (EPA-600l2-77-l79c and 17ge). With these models the implication for water resource projects is that farm operation could be designed to use the least amount of water and return the smallest amount of salt to the river while permitting the farmer to obtain the greatest possible return from his farm. The salt load reductions expected from irrigation scheduling and management could also be verified on the Vernal Unit in the Uinta Basin. 2. Florida Project Area Study Flow and quality data were collected at several points in the Florida Project area beginning in 1958 before the project was con- structed. A study of these data for the period 1958-63 show the effect of irrigation of these lands on the quality of return flows leaving the area. Results show that there has been a very small amount of pickup measured in the river downstream from the irrigated area. The concen- tration of total dissolved solids in the in flowing water ranges from 0.14 to 0.17 ton per acre-foot (103 to 125 mg/l), and that of the out- flowing water ranges from 0.17 to 0.30 ton per acre-foot (125 to 221 mg/l). About 13,720 acres (5,550 ha) were irrigated at the time the measurements were made. Other areas in the Colorado River Basin with similar type soils and underlying aquifers would yield only minor amounts of salt. 3. Grand Valley Area A.R.S. The Agricultural Research Service is doing a research study in the Grand Valley with regards to irrigation efficiencies. This is further covered in Part VIII. 4. Montezuma Valley The Soil Conserva tion Service has conducted a study of on farm improvements in the Montezuma Valley in Colorado. 5. Other Studies Considerable variation in the effects of irrigation return flow on water quality is to be expected. D1fferences arise due to the size of the irrigated areas, the number of times the return flow is reused, properties of the soils and drainage area, number of years land has been 122