This study was designed to meet the specific needs of the Environmental Protection Agency consistent with the interests and research goals of the ARS. The specific objectives of the study are: (1) to identify variables needed to predict effects of deep percolation, tailwater runoff, and lateral seepage on the quality of return flows. Includes evaluation of quantity and quality of various components of field water balance. (2) To define the effect of irrigation water management on the quality of runoff and deep percolation leaving the farm unit, and determine the reduction in both water and salt losses achievable through improved irrigation technology. (3) To identify mechanisms by which the salt load of return flow water is modified after it leaves the farm unit and moves toward the Colorado River; to attempt to determine the most practicable control methods for salt accretion. (4) To evaluate the experimental methods used in the above studies with regard to their applicability in other similar irrigated river valleys.