2. Hydrogeology

The northeastern part of Arabian Peninsula is characterized by four major systems of aquifers. These are (1) The Paleozoic-Triassic System, (2) The Cretaceous System, (3) The Eocene System, and (4) The Neogene-Quaternary System. The last two aquifers contain usable water, while the other deeper aquifers have connate water. Thus, the principle aquifer system in Kuwait consists of the Kuwait Group and the Dammam Formation of the Hasa Group. Many hydrological and hydrochemical evidences indicate local hydraulic connection between the Kuwait Group and the Dammam Formation aquifers in which both aquifers are considered as one complex system forming the main potential aquifers in Kuwait. Basically, the saturated part of the Kuwait Group and the Dammam Formation aquifers are replenished by infiltration on the outcrop area of Hasa Group at the eastern-northeastern part of Saudi Arabia and groundwater is discharged in Shatt Al-Arab and the Arabian Gulf [5]. Potentiometric level maps of the Kuwait Group and the Dammam Formation aquifers indicate a direction of groundwater movement from southwest to northeast direction. Due to the variations of clay percentage and cementation degree, the Kuwait Group is divided into two aquifers separated by an aquitard formation of clay and sand. Accordingly, the Kuwait Group appears to be semi-confined aquifer with a free water surface in the uppermost horizons. The saturated thickness of the Kuwait Group aquifer gradually increases toward northeast direction, as related to the structure of the Dammam Formation, where the groundwater in the aquifer becomes very saline.

The Kuwait Group aquifer is hydraulically connected with the underlying Dammam Formation aquifer under natural hydrological conditions; the flow occurs in a dynamic equilibrium

state, in SW-NE direction, to be discharged finally by seepage into Kuwait Bay and the Arabian Gulf [6]. The Kuwait Group aquifer gains part of its water by leakage from the Dammam Formation aquifer. The other sources of aquifer replenishment are the infiltration through the well-developed wadies and depression system, and lateral flow coming from Saudi Arabia. It is generally estimated that the hydraulic conductivity in the aquifer conjunctively decreases with depth by the increase of cementation degree. The hydraulic conductivity is relatively high in the upper saturated zones of the aquifer.
