Geochemical controlling mechanisms and quality of the groundwater resources in El Fayoum Depression, Egypt

Abstract

The main groundwater aquifer in El Fayoum region is a Quaternary aquifer. It shows increasing signs of groundwater quality deterioration. Therefore, a comprehensive assessment of groundwater quality has been performed for determining the geochemical processes affecting the groundwater quality evolution and assessing groundwater quality for drinking and irrigation uses. Physicochemical parameters, geochemical model (NETPATH), and water quality indices (WQIs) are applied to improve water quality assessment and controlling mechanisms with help of statistical analysis and GIS techniques. Thirty-eight groundwater samples from the Quaternary aquifer at depths less than 60 m and 12 irrigation drainage samples were collected. Thirteen physicochemical parameters including temperature (°C), TDS, pH, EC, K+, Na+, Ca+2, Mg2+, HCO3−, Cl−, SO42−, CO32−, and NO3− were measured by standard analytical techniques. The analytical findings reveal that the groundwater facies are Na-Cl, mixed Ca-Mg-Cl, and Na-Ca-HCO3 water types. In addition, the minerals saturation indices (SI) estimated by a geochemical model revealed that the groundwater samples are supersaturated by kaolinite, Ca-montmorillonite, dolomite, gibbsite, calcite, quartz, and aragonite and are unsaturated by gypsum, anhydrite, and partial pressure of CO2. The drinking water quality index (DWQI) results revealed that 58% of the groundwater samples are very poor quality, while 42% of samples are unsuitable for drinking uses. The irrigation water quality index (IWQI) results revealed that all groundwater samples range from 26.1 to 36.1, indicating a medium class of quality for irrigation purposes. These results reflect the influences of the high mineralization processes, cumulative effect of cation exchange, leaching processes from aquifer materials, contamination by irrigation return flow, and seepage from drains on the groundwater quality. In conclusion, utilization of physicochemical parameters, geochemical model, and WQIs can be considered as a promising and applicable approach to determine the controlling geochemical mechanisms and for assessing of groundwater quality in El Fayoum Depression, Egypt.