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. . UI. USDA TI1'I.EI ACTIVITIES 1\, USDA activities under Title I of the Colorado River Salinity Co~trol Act are <:) primarily related to improvi~g irrigatio~ efficie~cies, reducing deep N percolatio~, a~d reduci~g highly saline irrigatio~ a~d drai~age returu flows ,0) from the 65,000 acre Wellto~-Mohawk Irrigatio~ a~d Drai~age District in Yuma Cou~ty, Arizo~a. As farmers over-irrigate, excess a~d u~used irrigatio~ waters percolate down through the soil profile creati~g a high water table enriched with high salinity levels. To overcome the agricultural production problems caused by salinity build-up and poor drainage, pump-drai~age wells are used to lower the saline high water tables. This "pumped" drainage water', with salinity conce~trations ra~gi~g from 3,000 to 6,000 parts per million (PPM), is then removed from the Wel1ton-Mohawk area through drainage ca~als a~d ditches dischargi~g into the Colorado ,River. These highly sali~e return flows the~ cause increased salinity concentrations i~ the Colorado River waters delivered to Mexico. This highly sali~e drai~age return flow created the downstre~ salinity problems for Mexico i~ the 1960's which led to Mi~ute No. 242, and the passage of Public Law 93-320, the Colorado River Basin Salinity Control Act. I~ co~junction with the DR planning for.the desalting plant authorized in Title I of the Act, an Advisory Committee on Irrigation Efficiency and a support Technical Field Committee on Irrigation EffiCiency were created. The interagency committees were formed to develop alternatives to i~prove irrigation efficiencies and to reduce drainage return flows. This would ultimately reduce the size and costs of building and operating a large desalting plant. A 1974 "Special Report: ,Mea~ures for Reducing Return Flows from the Wellton-Mohawk Irrigation and Drainage District" includes the specific recoll1lllendations for installing onfarm. measures and technical assistance. The recommended onfarm. program essentially included structural onfarm improvement measures, technical assistance through SCS, and Federal cost-share through individual conservation plans and long-term contracts. The initial program established in 1974 included irrigation system improvements and water management on 23,800 acres in a five-year period. Recommended cost-sharing was established at 75 percent Federal and 25 percent landowner or farm operator. The combined impact of the USDA onfarm program, the DR Irrigation Management Scheduling program, and the DR 10,000 acre acreage reduction program were projected to increase district-wide irrigation efficiencies from 55 percent up to 72 percent. Drainge return flows were also projected to be reduced from approximately 200,000 acre-feet per year down to 136,000 acre-feet. In 1979, the Technical Field Committee on Irrigation Efficiencies recommended the onfarm program be expanded to include treatment on an additional 19,000 acres with all other irrigation lands being eligible for a water management plan. The Advisory Committee's recommended implementation program to improve onfarm irrigation efficiencies will further reduce return flows to 108,000 acre-feet per year. The implementation program is scheduled to continue through 1986. The Well ton-Mohawk onfarm program is fully funded by the DR. Under authority of the USDI and USDA Memorandum of Understanding (November 1974) and a DR-SCS Title I Memorandum of Agreement (December 1974), the DR periodically reimburses the SCS for cost-sharing expenditures and technical assistance costs. The SCS e~ters into direct landown~r or operator contracts to install conservation practices that contribute directly to the objectives of the B