Water from fossil aquifers as a potential supply source for solar desalination plants on a regional scale

Abstract

Research carried out on the hydrogeology and hydrogeochemistry of the water in the Judea Kurnuk and Arad Group aquifers in the Negev (Cenomanian. Lower Cretaceous and Jurassic) reveals that under a large area of the Negev an aquiferous section 1000 m to 1500 m thick is saturated with brackish water. Data derived from oil and water wells enabled the mapping of the distribution of the various water groups, which in turn made it possible to map the chemical composition of the water in the different regions. Thus, southeast of the line running from Masada on the Dead Sea to Ayun Musa on the Suez Gulf, water of approximately 5 g/l TDS can be found in the Judean (Cenomanian) and Kurnuk (Lower Cretaceous) Groups and of about 10 g/l TDS in the Arad Group (Jurassic). The potential quantities of water, from the point of view of storage, are in the order of magnitude of hundreds of billions of cubic meters. Annual pumping amounts, however, are a function of management policy. According to recent research, the annual pumping potential for the next thirty years from the Kurnub Group (Lower Cretaceous) is about 60 to 100 million cubic meters, with an allowance of 20–100 meters for the reduction of head. The Judea Group (Cenomanian Turonian) and Arad Group (Jurassic) can be reached in the northern Negev and still another potential Paleozoic aquifer (with water of about 12 g/l TDS) is available in the southern Arava. Quantitative pumping potential figures are not yet available for these aquifers. However, a very rough estimate suggests that the potential may amount to several tens of millions of cubic meters over the next fifty years. In addition to the direct use of this water for agriculture and industry (Arava farms, Phosphate and Dead Sea Works), as well as desalination by the RO method, it is suggested that the possibility of using this water for solar energy desalination be investigated on a regional scale. The cost of desalination may be reduced if one takes water whose salinity is a little above the threshhold of direct application for agricultural use and mixes it with the distilled water supplied by the solar distiller. The chances of achieving even lower costs for distilled water are promising as the water pumped has an average temperature of 40°C. Thus, the efficiency of the solar still may be greater, and may even enable night distillation to take place. The application of solar distillation thus appears promising in the Arava, where the special climatic conditions give a marginal benefit value of $1.00 per cubic meter of water for winter for winter vegetables. Along the dead Sea coast, this looks even better.