4. Methodology

dry in the extreme southwest and is almost saturated with water along the coast of the Arabian Gulf. In the north of Kuwait, the Kuwait Group can be divided into three formations based on the presence of an intermediate evaporite development. These divisions are Dibdibba, Lower Fars, and Ghar Formations, arranged from top to bottom. The undivided Kuwait Group extends under all of Kuwait with an extension eastwards beneath the Arabian Gulf. The Dibdibba Formation was named after the type locality Al-Dibdibba Plain, which extends from Basra to the northern part of Kuwait. The Dibdibba Formation is overlain by unconsolidated Recent and sub-Recent sediments of varying lithologies. The Lower Fars Formation ranges in thickness from 61 m in the west to more than 100 m in the eastern area into the offshore and it is absent in the south. It consists of fine to coarse-grained conglomeratic sandstone, variegated shale, and thin, fossiliferous limestone. The outcrop thickness of the Ghar Formation is only 33 m but it increases in subsurface and ranges from 195 to 250 m of marine to terrestrial, coarse-grained, unconsolidated sandstone with a few thin, sandy limestone, clay and anhydrite layers. At the base of the formation, above the eroded top of the Dammam Formation, is a brown, marly, coarse-grained sandstone with white, crystalline limestone resting unconformably over the Dammam Formation, and in gradational contact

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

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

with the Lower Fars Formation.

2. Hydrogeology

110 Aquifers - Matrix and Fluids

becomes very saline.

Seventy-one groundwater samples have been collected and analyzed to determine physical parameters like pH, EC, TDS, total hardness (TH), total alkalinity, and SiO2. In addition, the chemical parameters of the major cations and anions such as Ca2+, Mg2+, Na+ , K+ , HCO3 , SO4 2, and Cl expressed in mg/l were analyzed and converted to equivalent per million (e.p.m), and % e.p.m. [7]. Ion balance equation was applied to validate the accuracy of the chemical analyses where 5% is acceptable [8]. The reaction error of all groundwater samples was less than the accepted limit of 10% [9].

A speciation model has been used to determine the degree of saturation of groundwater with respect to some minerals using WATEQ4F program [10]. A mass-balance modeling WATEVAL computer program [11] is used to reveal the major geochemical reactions that control the geochemistry of the study area, along with the application of Gibb's ratio to assess the functional sources of dissolved chemical constituents, and to recognize the main processes governing the groundwater chemistry of the study area [12]. Hydrochemical facies interpretation is used to determine flow pattern and origin of chemical histories of groundwater by plotting the major cations and anions on the Piper diagram [13]. The assessment of groundwater for irrigation purposes based on different irrigation indices is carried out which includes sodium adsorption ratio (SAR), residual sodium carbonate (RSC), %Na. permeability index (PI), potential salinity (PS), salinity hazard, magnesium ratio (MgR), Kelly's ratio (KR), and chloro-alkaline index [14].

Wilcox diagram Wilcox [15] and Doneen permeability index [16, 17] have also been utilized for classification of groundwater for irrigation.
