HYDROGEOLOGICAL AND HYDROCHEMICAL SETTINGS OF THE QUATERNARY AND PRE-QUATERNARY AQUIFERS IN THE SOUTHWESTERN PART OF THE MESOPOTAMIA – IRAQ

Abstract

The spatial variation of the hydrogeological and hydrochemical characteristics of the main upper aquifers in southwestern part of the Mesopotamia is investigated, based on sampling from sixteen groundwater wells of different depths and locations, drilled by Iraq Geological Survey (GEOSURV) during dry season of 2011. Pumping tests were conducted to evaluate the hydrogeological parameters in these wells. The suitability of groundwater for different uses and the hydrochemical evolution of groundwater were evaluated using the field measurement of the physiochemical parameters (pH and EC) and analyzing the groundwater samples for major cations and anions. The hydrochemical and hydrogeological results were compared with previous hydrogeological data in the area and found them compatible. The Quaternary sediments cover most of the study area and represent the main intergranular-type aquifer, whereas the carbonate rocks of the Euphrates Formation (Lower Miocene) and the Dammam Formation (Upper Eocene) represent the main fracture-type aquifers in the southwestern parts of the area. In general, the groundwater quality in the shallow aquifer of the Quaternary sediments is saline to brine water of chloridic type, except for the zones along the rivers and stream where the groundwater is brackish. The groundwater in the fracture aquifer in the southwestern parts is of sulfate type, brackish to highly brackish water. There is a significant spatial variation in the hydrogeological parameters due to the lateral variation in the Quaternary sediments and the variation in the permeability of the pre-Quaternary sediments. This variation influences the hydrochemical properties of the groundwater in the study area. The main factor that affects the evolution and quality of chloride-type groundwater in the Quaternary aquifer is evaporation, while in Pre-Quaternary fracture-type aquifer the chemical evolution of the groundwater is controlled by the dissolution of the evaporate rocks (gypsum and anhydrite) and the weathering of the carbonate rocks. The groundwater in the Quaternary sediments is not suitable for any use due to the high salinity; whereas the groundwater of the Pre-Quaternary fracture-type aquifer can be used for livestock drinking and to irrigate some salt tolerant crops especially when considering the high infiltration capacity of the sediments.