Hydrochemistry of Umm Er Radhuma Groundwater

摘要

Umm Er Radhuma Aquifer (UER) is the most important groundwater aquifer in Saudi Arabia, extending over 1.6 M · km~( 2 ) in the eastern part of the Arabian Peninsula, forming the main aquifer throughout the Rub’ Al-Khali (RAK). Groundwater salinity increased from west to east, reaching more than 27,000 mg/L near the border with the United Arab Emirates, where a Na ~( + ) -Ca ~( 2+ ) Cl ˉ - ? water type dominated. Gibbs diagrams indicated that the dissolution/precipitation of carbonates and evaporation/precipitation of minerals, especially anhydrite, gypsum, and halite account for the solutes and salinity in groundwater. Most of the samples plot above the 1:1 line of (Ca ~( 2+ ) + Mg ~( 2+ ) ) against , indicating other sources of Ca ~( 2+ ) and Mg ~( 2+ ) in the groundwater along with dolomite and calcium carbonate minerals. Phreeqc model indicated that the main clay minerals are kaolinite and gibbsite which had major effect on the cation exchange process as indicated by the Chloro-Alkaline index (CAI), where most of groundwater samples had values greater than zero which indicated the occurrence of reverse ion exchange between the groundwater and its host aquifer. The water type Na ~( + ) -Ca ~( 2+ ) Cl ~( ˉ ) - dominated in the eastern part of the aquifer as the anaerobic conditions prevailed and the reduction of sulphate took place.