Potential aquifer mapping for cost-effective groundwater reverse osmosis desalination in arid regions using integration of hydrochemistry, environmental isotopes and GIS techniques

In arid regions, water resources are scarce; therefore, sea and brackish groundwater desalination using reverse osmosis (RO) techniques is commonly used to provide freshwater for potable purposes. El-Moghra Oasis, a case study of an inland depression, represents an arid region in the Western Desert of Egypt. The oasis relies mainly on the brackish groundwater in El-Moghra Aquifer for salt-tolerant crop irrigation and feeding desalination plants. The RO brackish groundwater desalination conserves about 75% of the total cost compared to seawater as feed water. Accordingly, the main target of the present work is to allocate cost-effective sites for constructing desalination plants to solve freshwater shortages. The hydrogeochemical and isotopic techniques have been applied to understand the aquifer recharge mechanism and the main factors that deteriorate the groundwater quality. Additionally, an Analytical Hierarchy Process (AHP) relying on the geographic information systems (GIS) utilized to delineate the promising desalination sites. Four main criteria linked with the cost of RO groundwater desalination were investigated, including aquifer hydraulic parameters, hydrogeochemical characteristics, recharge indicators based on isotopic tracers, and other miscellaneous parameters related to the site accessibility and environmental issues. These four main criteria include fourteen sub-criteria; depth to water (DTW), aquifer saturated thickness (ST), transmissivity (T), total dissolved solids (TDS), iron (Fe), total groundwater hardness (TH), calcium sulfate (CaSO₄), silica (SiO₂), strontium (Sr), oxygen-18 (δ¹⁸O), global solar radiation (GSR), land slope (LS) and distance to roads (D). The final suitability map identifies the most favorable locations for constructing a desalination plant is in the northeast, which comprises 64.5% of the study area. The locations with low appropriateness are concentrated in the west and southwest and account for 35.5% of the area.