A study was made of an irrigated area in Arizona to evaluate costs and benefits associated with desalting saline ground water from seven wells as an improved water source for irrigation. Both multistage flash distillation (MSF) and electrodialysis (ED) processes were evaluated. The study area involved 1376 acres near Buckeye, Arizona. Well water quality varied from 1580 to 4600 ppm. Irrigation water qualities of 400, 900, and 1500 ppm are developed by the two processes. Adaptable cropping patterns are selected for maximum returns. A total of six alternative plans are compared. Direct, indirect, and public benefits for the projected year of 1990 are generated by shifts to higher value crops, intensive double cropping, increased crop yields, reduced water use, reduced fertilizer costs, reduced irrigation labor, and from increased flow of farm products. Costs are based on such features as the desalting facilities, well water collection system, product storage reservoir, conveyance and distribution system, brine disposal system, blending facilities (MSF only), gypsum addition system (ED only), and water treatment facilities. Benefit-cost ratios increased with improved water quality. Investment costs per acre were found to be high. The most favorable benefitcost ratio involved use of the ED process at a water quality level of 400 ppm.

.A case study was performed to evaluate potential applications of desalted saline water for agriculture using 2 distillation type processes and 2 membrane type processes. The investigation determined the costs and benefits associated with desalting saline water at concentrations of 1,500, 900, 400, 200, and 50 ppm. Benefits from desalting are generated by shifts to more profitable crops, reduced costs for drainage, and reduction in fertilizer and labor requirements with better quality water. Costs are based on the project features such as desalting plants, raw water diversion facilities, storage reservoirs, conveyance and distribution systems, brine disposal, blending facilities, and gypsum addition systems. Hydrologic studies determined the crop irrigation requirements, water demand schedules, desalted water storage requirements, brine disposal requirements, and size of facilities required. Reconnaissance design layouts were made for producing desalted water using a combination of 14 schemes. The study also included a review of irrigation practices. The benefit‐cost ratios range from 0.4 to 1.0 for 1,500 ppm irrigation water to 0.8 to 1.0 for 50 and 200 ppm water. Investment costs per acre are high, ranging from $12,900 to $20,900. Irrigation benefits are based on the increase in production from a desert condition with no water supply to the irrigation conditions studied.

No abstract

The Office of Saline Water, which has federal responsibility for developing low‐cost, saline sources of fresh water, has recognized the need for an improved method of forecasting the future potential of desalting in this country. The magnitude of the role of desalting will influence the plans of federal, state, and local water resource agencies and the research and development programs of manufacturers. A dynamic simulation model has been developed by Arthur D. Little, Inc. under contract by OSW to translate relevant factors of water supply and demand into a forecast of desalting potential. The model projects the needs for desalting in 20 hydrologic regions of the U.S. Model performance has thus far been demonstrated by the development of a forecast and a battery of related sensitivity tests. Current results indicate the following potential desalting capacities: 225 MGD in 1980; 2,250 MGD in 2000; and 7,000 MGD in 2020. Significant improvements in desalting economics promise to increase these potentials by a factor of four or five by 2000‐2020. Model inputs and results are continuing to be refined. When completed, OSW will have a dynamic tool with which to guide its R&D program.

No abstract