Assessment of the geochemical evolution of groundwater quality near the El Kharga Oasis, Egypt using NETPATH and water quality indices

Abstract

The Nubian Sandstone Aquifer (NSA) has been the main source of water in the western desert of Egypt since 1985. This aquifer is subject to excessive groundwater withdrawal in the region, causing declines in potentiometric heads and a deterioration of groundwater quality. Consequently, investigations were undertaken to provide baseline water quality information for groundwater management. Water quality data from wells in the study area were manipulated using a Geographic Information System (GIS), statistical analyses (SPSS), graphical simulations (such as Piper and Gibbs diagrams), water quality index (WQI) and a simple geochemical model (NETPATH). This assessment and the use of hydrochemical indices indicated that chemical reactions between the aquifer matrix and groundwater are likely to be the main factors controlling the chemical composition of groundwater in the area. Also, the results of WQI showed that the majority of the collected water points (about 89%) were unsuitable for potable use due to elevated iron concentrations. The NETPATH modeling results suggest that dedolomitization, silicate weathering and dissolution of halite processes are the main geochemical processes that influence changes in the chemical composition along groundwater flow-paths.