Project Completion Report, OWRT Project No. A-050-ARIZ. / Agreement No. 14-31-0001-5003 / Project Dates: July 1974 - June 1976. / The work upon which this publication was based was supported in part by funds provided by the Office of Water Research and Technology (A-050-ARIZ), U.S. Department of the Interior, Washington, D.C., as authorized by the Water Research and Development Act of 1978. / INTRODUCTION: The use of treated sewage effluent by the Buckeye Irrigation Company began with 800 acre -feet in 1962 and had increased to 40,000 a.f. by 1968. The effluent was diverted by the Buckeye Irrigation Company from the Gila River approximately seven miles below the City of Phoenix 91st Avenue treatment plant, as it became available at their diversion point. Natural streamflow, used in earlier years, had virtually stopped due to upstream development except in heavy runoff years such as 1941. The ground water in the district of the Buckeye Irrigation Company is relatively high in dissolved solids. The quality of the treated effluent is better. In 1971 the company signed a 40 -year contract with Phoenix to assure its use of 30,000 a.f. of effluent per year. The effluent is mixed with native ground water to bring the total water applied on the 18,000-acre district up to approximately 90,000 a.f. (Halpenny, 1973). The treated effluent use by the Buckeye Irrigation Company is the largest in the State of Arizona and one of the largest land applications of treated effluent in the United States. It is unique in that it is being utilized by an irrigation district. Most other uses have been by city operated farms or private farms under a single ownership. In spite of its uniqueness the effects of effluent use by the Buckeye Irrigation District had not, prior to this research, been well documented. This documentation was made in order to improve the general knowledge needed to extend this type of use to other areas in the state and nation. "Widespread consideration and utilization of land application cannot be made until such time as adequate information concerning the technique involved is made available. The experience gained by those who have successfully utilized this wastewater management should be used... specific evaluation of established systems in the various climatic zones would appear to be more fruitful than new research installations for determining long term effects on soils, vegetation, ground water and the indigenous ecology..." (Sullivan, et al., 1973). During the two year research period most of the initial objectives were achieved. The original specific objectives were: 1. To identify changes during an extended period of application of treated wastewater to irrigated fields in: a. irrigation practices b. cropping patterns c. fertilization practices d. crop yield response and quality e. quality of irrigation water, and f. soil properties. 2. To make a preliminary evaluation of the effects of the use of effluent on ground-water conditions. 3. To make a preliminary evaluation of changes in water costs and farm profits.