GROUNDWATER CHEMISTRY IN RELATION TO AQUIFER … · Groundwater Chemistry in Relation to Aquifer...

Emirates Journal for Engineering Research, 12 (2), 75-88 (2007) (Regular Paper)

75

GROUNDWATER CHEMISTRY IN RELATION TO AQUIFER MINERALOGY OF THE EOCENE AQUIFER, KUWAIT

F.M. Al-Ruwaih1, K.M. Hadi2 and M. Shehata3 1Department. of Earth & Environmental Sciences, Kuwait University, Safat-13060, Kuwait, [email protected]

2Hydrology Department, Kuwait Institute of Scientific Research, Safat, Kuwait, [email protected] 3Department of Geology, Faculty of Science, Zagazig University, Egypt, [email protected]

(Received May 2006 and accepted March 2007)

إن تركيز األيونات . جودة المياه الجوفية ھي عالقة تفاعالت ما بين صخور الخزان المائي والمياه المتدفقة خاللهالتركيب المعدني لصخور الخزان المائي الذي من خالله تتحرك المياه في اتجاه حركة في المياه الجوفية يعتمد على

وعليه فإن التركيب المعدني والمعادن المتبقية غير الذائبة والتركيب الكيميائي لخزان تكوين الدمام . المياه الجوفيةستخدام تقنية االنكسار اإلشعاعي قد تم دراستھا من خالل تحليل العينات الصخرية على أعماق مختلفة وذلك با

XRD وتقنية االنكسار الفلوروسينسيXRF . كذلك تم استخدام تقنية االتزان الكتلي باستعمال برنامجWATEVAL لتتبع نشأة صخور خزان تكوين الدمام ، والتعرف على أھم العمليات الجيوكيميائية التي تؤثر على جودة المياه

لقياس درجة تشبع أو عدم تشبع المياه الجوفية بالنسبة WATEQ4Fاستخدام برنامج ھذا باإلضافة إلى. الجوفيةتدل نتائج ھذه الدراسة على أن الجزء العلوي لتكوين الدمام يتكون من دولوميت . إلى بعض المعادن الشائعة

من الفحم النباتي طباشيري ، والجزء السفلي يتكون من حجر جيري دولوميتي فيه بعض األحافير ، مع شريط دقيقلقد وجد أن التركيب المعدني لصخور تكوين الدمام يتكون . ، أما الجزء السفلي فيتكون من حجر جيري نيولوميتي

أجزاء صدفية % 3.7أراجونيت و % 0.2كوارتز % 1.5طين ، % 2.6كالسيت ، % 41دولوميت ، % 51من صخور تكوين الدمام ھي مصدر الكالسيوم والماغنسيوم دلت دراسة نشأة صخور تكوين الدمام أن ذوبان . وفوسفات

في مياه الخزان المائي ، بينما المعادن الطينية ھي التي تزود المياه بأيونات الصوديوم وتستھلك الكالسيوم من خالل لسيوم الصوديوم على سيادة عملية اإلذابة الطبيعية من خالل نقصان الكا/ دلت نسبة كلور . عملية التبادل األيوني

لقد وجد أن األنواع الكيميائية للمياه الجوفية السائدة ھي كلوريد .وزيادة الصوديوم في الخزان المائي لتكوين الدمامكما دلت دراسة درجة تشبع المياه على أن المياه الجوفية . الكالسيوم ، كبريتات الصوديوم وكبريتات الكالسيوم

معادن األنھيدرايت ، الجبس والھاليت ، كما أنھا مشبعة بالنسبة إلى معادن لتكوين الدمام غير مشبعة بالنسبة إلى وھذا يدل على أن عملية ذوبان الدولوميت ھي العملية األساسية في خزان . الكالسيت ، الدولوميت ، والكوارتز

خزان المائي كما تبين من دراسة حساب متوسط الضغط الجزئي لثاني أكسيد الكربون على أن ال. تكوين الدمام .لتكوين الدمام يمثل بيئة ترسيبية مغلقة

The water quality is a function of the interactions between aquifer material and the water flowing through them. The concentrations of ions in groundwater depend on the rock mineralogy through which the water passes along the path flow. Accordingly, the mineralogical, insoluble residue and chemical composition of the Dammam Formation aquifer have been investigated by analyzing samples collected at different depths, using the XRD and XRF methods. Also, a mass-balance technique using WATEVAL program has been utilized to deduce the source rock of the Dammam Formation aquifer water, and to identify the main geochemical processes that influence the groundwater quality. In addition, WATEQ4F speciation model has been used to calculate the saturation indices, which helps in determining the equilibrium condition of groundwater with respect to given minerals. The results of the present study indicate that the Dammam Formation is mainly massive chalky dolomite as the upper member; fossiliferous laminated limestone and dolomicrite with lignite seams as the middle member, and nummulitic limestone as the lower member. The mineralogical composition of the rocks is as follows: 51% dolomite, 41% calcite, 2.6% clay, 1.5% quartz, 0.2% aragonite and 3.7% shell fragments and phosphates. The groundwater source-rock deduction indicates that dissolution of the Dammam Formation aquifer carbonate rocks maintains the concentrations of Ca2+ and Mg2+ in this aquifer water, while the clay mineral provides the aquifer water with Na+ ions, and consume Ca2+ ions through the cation exchange process. The Cl/Na ratio indicates the occurrence of a natural softening process, which depletes the Ca2+ and increases the Na+ ions in the Dammam Formation aquifer. The groundwater chemical types CaCl2, Na2SO4 and CaSO4 are the dominant types. The calculated saturation indices indicate that the groundwater is undersaturated with respect to anhydrite, gypsum and halite, and supersaturated with respect to calcite, dolomite and quartz. This indicates that the incongruent dissolution of dolomite is the major controlling process in the Dammam Formation aquifer. The calculated PCO2 indicates that the aquifer is a closed system.

Keywords: Carbonate aquifer, mineralogical composition, chemical composition, source-rock, satuation index, chemical coefficients, water types

F.M. Al-Ruwaih, K.M. Hadi and M. Shehata

76 Emirates Journal for Engineering Research, Vol. 12, No.2, 2007

1. INTRODUCTION

The study area, Umm-Gudair, is located in the southwest of Kuwait near the Kuwait–Saudi Arabia border. It occupies an area of 450 km2. The Umm-Gudair field includes 41 production water wells screened in the Kuwait Group and the Dammam Formation (dual-completion well) aquifers (Fig. 1). The field production started with 54,550 m3/day which increased to the present production of 113,650 m3/day. In the study area the drilling program was conducted in two stages. In the first stage, the Kuwait Group aquifer was drilled to a depth of 228.6 m, after which a pumping test program was made and groundwater samples were collected. In the second stage, drilling was continued in the same wells to penetrate the Dammam Formation, in which a pumping test program was also done, as well as groundwater samples collected for hydrogeological and hydrochemical evaluation. In countries located in arid and semi-arid regions such as Kuwait, groundwater is a major water supply source. The Dammam Formation is considered the most potential aquifer in Kuwait. The Dammam Formation was deposited on a shallow marine shelf experiencing minor fluctuations from lagoon to tidal flat and swamp environments. This tectonically stable period was interrupted by small pulses in the source land and minor fluctuations in the sea level, which caused alternating transgressive and regressive cycles[1].

Generally, the Dammam Formation appears to be low in its effective primary porosity and its variation in hydrological characteristics, mostly related to the degree of karstification and silicification. The effective secondary porosity value is relatively high in the dolomitic limestone and it gradually decreases in the lateral flow direction towards southwest-northeast trend. Related to the recharge-discharge regime and to the relatively high vertical hydraulic resistance of this formation, the piezometric head increases with depth, while it gradually decreases towards the discharge area approximately southwest-northeast direction. The average piezometric level of the Dammam Formation aquifer is 82.69 m from MSL. The hydraulic gradient is 1.5x10-3, which yields a groundwater flow of 10,450 m3/day to the Umm-Gudair field through the Dammam Formation. For the Kuwait Group, the hydraulic gradient is 1.7 x 10-3 and the groundwater flow across the Umm-Gudair field is 4550 m3/day[2].

The Dammam Formation is a semi-confined to confined aquifer, with an average transmissivity and effective permeability of 328.45 m2/d and 2.53 m/d, respectively. The estimated values of the storage coefficient of the Dammam Formation aquifer range between 5.28 x 10-4 and 6.7 x 10-4, with an average value of 5.86x 10-4 [2,3].

The objectives of this piece of research are to describe the relationship between the groundwater chemistry and aquifer mineralogical composition.

Figure 1. Location map of the Umm-Gudair field showing distribution of the production and observation wells.

Since groundwater geochemistry depends on the chemical composition of the groundwater and aquifer materials, therefore, determination of petrological and mineralogical composition of the aquifer material and an application of geochemical modeling studies on the Dammam Formation aquifer are important to deduce source-rock and to elucidate the major geochemical processes which control the quality of the aquifer.

2. SPECIFIC BASIS FOR GEOCHEMICAL MODELING ACTIVITIES

The relationships between the chemical composition of groundwater and the environmental factors, which include climate, geologic effects of the aquifer material, biochemical factors, sources of solutes in the atmosphere, composition of recharge water (e.g. precipitation) and the influence of human activities, can be evaluated and understood by groundwater geochemical modeling investigations. However, the widest spread applications of geochemical modeling are the evaluation of groundwater chemistry in the aquifer system and the investigations of the geochemical processes that govern the chemical composition of the aquifers water, which have been applied in this study. Examples of this type of study can be found in the work

Groundwater Chemistry in Relation to Aquifer Mineralogy of the Eocene Aquifer, Kuwait

Emirates Journal for Engineering Research, Vol. 12, No.2, 2007 77

of several hydrologists, including Langmuir[4], who studied the geochemistry of carbonate groundwater in central Pennsylvania by considering the effect of CaSO4 and MgSO4, Mg(HCO3)2 ion pairs in the calculation of groundwater saturation with calcite and dolomite.

In general the application of geochemical modeling in studying the evolution of groundwater chemistry, facilitates the determination of the prevailing geochemical reactions, quantification of the extent to which these reactions occur, prediction of the fate of inorganic contaminants, and estimation of the direction and rate of groundwater flow[5]. Plummer[6] divided geochemical modeling into two general approaches, inverse modeling and forward modeling. The WATEQ4F[7] speciation model and the WATEVAL program[8] mass-balance model, as an inverse geochemical modeling approach, are used in the current work in order to study the geochemical evolution of the groundwater in the Dammam Formation aquifer in the Umm-Gudair area. Particular emphasis will be placed on the complexes and their relationships with the saturation indices of the relevant minerals and phases in the aquifers water and materials, and subsequently their sources.

3. DATA COLLECTION The geological and geochemical investigations of the Umm-Gudair area’s geological sequences, which include the Dammam Formation, are mainly based on the collected data and reports from different sources. These sources include the Groundwater Administration of the Ministry of Energy (MOE) and the National Scientific and Technical Information Center (NSTIC) in the Kuwait Institute for Scientific Research (KISR). These data include the well construction reports and core samples, as well as the technical reports on the geology and hydrochemistry of the study area. The core samples were examined in the core house of KISR, and the Dammam Formation representative core samples were selected in order to investigate the geochemistry of these materials by different laboratory analysis. The selected samples were also investigated megascopiclaly to describe the various lithotypes of these geological sequences. On the other hand, the groundwater hydrochemistry investigation in the Umm-Gudair area is based on the initial chemical data which was collected during the construction of the water wells.

4. LABORATORY INVESTIGATIONS 4.1 Determination of Insoluble Residue

A total of 24 samples were selected from the Dammam Formation core samples, in order to determine their insoluble residue. These samples represent different depths and lithotypes in this formation. The procurement of this analysis is done by leaching out

carbonate from the samples by using 10% HCl. The residues are then washed, dried, and weighed. The types of these residues were investigated by binocular microscope, and the clay fractions were separated for further investigation.

4.2 X-Ray Diffraction (XRD)

A total of 19 samples were selected from the Dammam Formation core samples, in order to determine their gross mineralogical composition by XRD. These samples were cleaned, powdered, and dried before they were sent to the Central Analytical Laboratory (CAL) at Kuwait Institute for Scientific Research, where a nickel-filtered Cuα radiation was used for XRD analysis. A further 17 samples of clay fractions from the insoluble residue were selected, in order to identify the types of clay and to estimate their percentages in each sample, by XRD. These samples were collected by separation from the insoluble residues of the Dammam Formation selected samples, using sieve with a 0.063 μm mesh.

4.3 X-Ray Fluorescence (XRF)

A total of 48 samples were selected from different depths of the Dammam Formation, from the KISR core house, and analysed by XRF in order to determine the chemical composition of the aquifer’s materials. The samples were cleaned, powdered, and dried at 110oC for one hour before they were analysed by a Phillips PW 1410 X-ray fluorescence spectrophotometer at CAL.

5. REGIONAL GEOLOGICAL CONTEXT Kuwait State is located at the north-western tip of the Arabian Gulf, forming part of the Arabian Peninsula. It occupies an area of approximately 18, 000 km2, and is mainly low relief desert with several low, flat islands. It is bordered by Saudi Arabia in the south and by Iraq in the north and west.

The geological history of Kuwait State relates to that of the Arabian Shield, which was formed from igneous and metamorphic rocks during Pre-Cambrian times. This Shield was divided into a stable region in the western part of the Arabian Peninsula and an unstable region on the eastern side (adjacent to Kuwait).

Hydrologically the most important depositional period was the Tertiary, which includes reasonably good aquifers in its sedimentary sequences in the Arabian Peninsula. Tertiary sediment sequences have been divided into two main groups[9]. These are from the bottom, the Hasa Group, overliad by the Kuwait Group. The Hasa Group comprises three formations. In a descending order these are Dammam, Rus and Umm Er-Radhuma. The Dammam Formation will be discussed in detail as it represents the potential aquifer in the study area.



5.1 Stratigraphy and Petrology of the Dammam Formation

Geological and geophysical studies of the Dammam Formation[9-16], suggested that this formation comprises of three members, which can be further sub-divided into several litho-types. Petrographical and mineralogical investigations of each member have been carried out during this study using various analytical methods.

Gross Lithology

Upper member

This member has a massive tan, porous chalky dolomite layer with some chert in few samples. The carbonates of this layer are predominant dolomite, with only traces of calcite and aragonite as a result of dolomitisation processes which affected most of the original deposit. This layer is underlain by massive layers of variously-coloured dolomite. These layers are very porous and uniform in mineralogical composition of the Dammam.

Middle member

This member is composed of alternating hard, gray, and dense limestone with massive, generally dense, dolomite. Lignitic material and small black silica nodules also occur in this member. The rocks of this member compose of dolomite and calcite as the main minerals. Phosphatic particles are also found as golden pellets. Barite is found in this member as cavity-fills inside the rock matrix.

Lower member

This member comprises bioclastic limestone and dolomite and the rock is generally tan in colour, hard, dense and laminated. The member is also characterized by occurrences of different fossiliferous limestone types. Biosparite and biomicrite are recognized in this member, where the calcite cement has precipitated in the pore spaces between grains and larger cavities. Laminated biomicrite occurs within this member. This type of rock is generally rich in spherical pellets of phosphate fragments.

The thickness of the Dammam Formation increases from south to north and ranges from 122 to 300 meters, where the depth of this formation also increases from south to north and ranges from near surface to a maximum of 550 meters at the north-east of the country.

5.2 Mineralogical Composition of the Dammam Formation

Three different types of analysis were used in order to determine the mineralogical composition of the rocks of the Dammam Formation in Umm-Gudair area. These are the compositional analysis, insoluble residues, and X-ray diffraction (XRD). Compositional analysis was carried out on 38 samples from the Dammam Formation to identify the chemical components of the rocks at

different depths. The results are tabulated in Table 1. From Table 1 it can be seen that an average of almost 44% of each sample weight was lost as a result of heating the sample from 25 to 1050oC during the analysis. The remaining weights are dominated by CaO and MgO at different proportions in each member. The upper member shows a higher MgO than the other member, which may reflect the abundance of dolomite. Also, SiO2 was detected in relatively higher amounts in the middle and lower members than the upper member, who means that clastic sediment may occur in those members more than the upper member. Other chemical components are also present in trace amounts, but less in the upper member than the middle and lower members. These are P2O5, Fe2O3, K2O and Al2O3.

The carbonate contents of 24 samples were leached out by 10% HCl and the residues were subject to further analysis by microscope and X-ray diffraction. These samples were taken from different depths and members. The percentage of the insoluble residues depend on the rock type in the formation and not on the member type, as demonstrated by the results in Table 2.

The insoluble residues of the Dammam Formation were investigated by microscope. The investigation revealed that they are composed of clay minerals, quartz, phosphate and silicified fragments. Two different types of sample sets from the Dammam Formation were analysed by XRD. The first set were whole sediment samples for determining the mineralogical composition of the Dammam Formation rocks. From the cores, 19 samples at different depths were selected for this set and analysed by XRD. The results are illustrated in Table 3. The results confirmed the first analysis conclusion. They showed that on average 96% of the upper member of the Dammam Formation is composed of dolomite and only 1% calcite. The middle member is composed of, on average, 84% dolomite and 6% calcite. The lower member is dominated by 89.5 % of calcite, while the dolomite does not exceed 1.8% in average. Silica, which is present as quartz, palygorskite, and other minerals are also present in the Dammam Formation in different percentages from the upper member to the lower one. Furthermore, one sample showed that 0.5 % aragonite was also present in the lower member.

The second set of samples was collected by separating the clay fractions from the insoluble residue using the 0.063 μm mesh. These samples were analysed by XRD in order to detect the types of clay present in the Dammam Formation. Table 4 shows that the clay fraction is almost completely composed of palygorskite, with most samples containing low percentages of illite, montmorillonite and kaolinite.

Table 5 shows the residual resolution analysis results of observation well no.7, where as the stratigraphic sequence of the upper part of Dammam Formation as well as the XRD diffraction chart of the OW-7 at a depth of 910 ft are shown in Figs. 2 and 3 respectively.



Table 1. Compositional analysis results of different core samples from different depths from the Dammam Formation in Umm-Gudair area.

Member Well No. Sample Depth (m) M.S.L

SiO2 %

Al2O3 %

CaO %

K2O %

Fe2O3 %

MgO %

P2O5 %

L.O.I %

Uppe

r Mem

ber

OW-1 -40 1.13 0.28 30.21 0.02 0.14 21.35 0.013 46.78 OW-2 -53 4.08 0.8 28.6 0.06 0.36 20.6 0.022 45.4 OW-4 -109 1.36 0.4 29.91 0.2 0.16 21.3 0.015 46.54 OW-5 -21 3.29 0.63 29.08 0.07 0.3 20.79 0.013 45.68 OW-8 -21 0.9 0.14 31.4 0.04 0.21 21 0.013 47.2 OW-8 -15 1.01 0.3 30.43 0.03 0.14 21.24 0.006 46.67 OW-8 -10 0.76 0.2 30.45 0.01 0.13 21.4 0.013 46.82 OW-8 -14 1.1 0.21 30.8 0.04 0.22 21.2 0.005 47.1 OW-9 -2 0.8 0.17 31.3 0.04 0.22 21.2 0.005 47.3 OW-9 -25 0.41 0.16 30.6 0.01 0.1 21.5 0.01 47.03

Average 1.48 0.33 30.3 0.05 0.2 21.2 0.012 46.7

Midd

le Me

mbe

r

OW-4 -164 4.84 0.73 30 0.04 0.31 19.31 0.04 44.55 OW-4 -166 2.46 0.45 40.41 0.02 0.16 11.2 0.015 45 OW-8 -49 1 0.17 30.9 0.04 0.21 21.5 0.009 47.2 OW-8 -97 1.4 0.27 33.3 0.04 0.21 18 0.006 46.9 OW-8 -98 5.42 1.22 45.95 0.32 0.39 3.81 0.02 41.51 OW-8 -100 1.6 0.31 33 0.047 2.1 17.6 0.006 47.2 OW-8 -106 2.44 0.25 46.75 0.07 0.09 5.47 0.02 44.02 OW-9 -48 4.6 0.79 28.5 0.04 0.33 20.6 0.007 45.6 OW-9 -71 4.7 0.81 31.2 0.07 0.37 17.3 0.026 44.6 OW-9 -82 1.4 0.3 32.3 0.06 0.27 19.5 0.009 46.6 OW-9 -113 1.9 0.36 36.3 0.04 0.35 14 0.067 45.7 OW-9 -122 1.12 0.24 45.55 0 0.12 8.23 0.004 44.25 OW-9 -128 0.8 0.13 36.1 0.04 0.18 16.3 0.012 46.7

Average 2.6 0.46 36.2 0.064 0.39 14.8 0.019 45.4

Lowe

r Mem

ber

OW-1 -181 09.86 0.18 51.31 0.05 0.05 3.54 0.008 43.57 OW-2 -174 3.01 0.2 49.78 0.09 0.11 3.42 0.04 42.9 OW-4 -175 2.83 0.25 48.44 0.04 0.09 3.65 0.07 43.73 OW-7 -173 1.42 0.35 50.57 0.14 0.1 3.47 0.013 43.59 OW-7 -189 4.42 0.89 47.36 0.15 0.32 3.7 0.007 41.88 OW-8 -123 0.5 0.05 54.2 0.04 0.17 0.8 0.005 44.4 OW-8 -131 0.8 0.15 54.2 0.04 0.19 0.8 0.015 44 OW-8 -134 2.85 0.72 49.41 0.19 0.19 3.54 0.05 42.64 OW-9 -135 0.6 0.07 55 0.04 0.17 0.6 0.007 43.9 OW-9 -137 1 0.06 54.3 0.03 0.17 0.7 0.017 43.8 OW-9 -159 0.3 0.05 54.1 0.037 0.17 0.8 0.005 44.75 OW-9 -166 9.4 1.88 43.8 0.18 0.55 2 0.008 40.7 OW-9 -187 5.2 1.04 47 0.19 0.35 1.4 0.063 43.5 OW-9 -189 11.86 2.28 41.46 0.26 0.91 4.44 0.03 37.59 OW-9 -191 12 2.66 41.3 0.25 0.75 2.3 0.01 38.6

Average 3.8 0.72 49.5 0.115 0.29 2.3 0.023 42.6



Table 2. Insoluble residue percentages in different samples from the Dammam Formation in Umm-Gudair area and the percentage of their concentrations.

Mem

ber

Well

No.

Sam

ple D

epth

(m

) M.S

.L.

% o

f Ins

olub

le

Resid

ue

% of Insoluble Residue

Constituent

Clay

%

Quar

tz %

Orga

nic

Debr

is %

Phos

phat

es

Uppe

r Mem

ber

OW-1 -36 13 60 20 20 0 OW-1 -66 15 50 0 50 0 OW-1 -68 18 80 0 20 0 OW-1 -69 34 55 30 15 0 OW-1 -101 15 55 30 0 15 OW-1 -106 25 45 45 0 10 OW-1 -110 40 50 0 50 0 OW-9 -40 24 0 100 0 0 OW-9 -49 35 80 0 0 20 OW-9 -50 29 50 15 35 0 OW-9 -68 33 55 0 15 30

Average 25.5 52.7 21.8 18.6 6.8

Midd

le Me

mbe

r

OW-1 -165 15 30 55 15 0 OW-1 -167 27 50 0 50 0 OW-1 -177 5 0 0 0 100 OW-1 -184 4 0 0 0 100 OW-9 -108 28 60 0 40 0 OW-9 -110 34 60 0 40 0 OW-9 -133 20 60 40 0 0

Average 19 37.1 13.6 20.7 28.6

Lowe

r Mem

ber OW-1 -214 19 0 0 40 60

OW-1 -218 12 0 0 100 0 OW-1 -222 13 0 0 0 100 OW-1 -226 8 0 0 100 0 OW-9 -166 28 55 30 0 15 OW-9 -171 24 80 0 20 0

Average 17.3 22.5 5 43.3 29.2 Table 3. Mineralogical composition of different samples from different

core intervals from the Dammam Formation in Umm-Gudair area as identified by XRD analysis.

Mem

ber

Well

No.

Sam

ple D

epth

(m

) M.S

.L

Dolo

mite

Calci

te

Quar

tz

Arag

onite

Palyg

orsk

ite

% o

f oth

er

min

erals

Upper Member

OW-8 - 21 96 2 0 0 1 1 OW-8 -14 96 0 1 0 1 2 OW-8 -20 97 1 0 0 0 2

Average 96 1 0.3 0 0.7 1.7

Middle Member

OW-8 -49 98 0 1 0 0 1 OW-8 -97 90 0 1.5 0 0 8.5 OW-8 -100 86 0 1 0 2 11 OW-9 -48 94 0 2.5 0 3.5 0 OW-9 -71 78 0 0 0 9 13 OW-9 -82 91 4.5 0.5 0 2 2 OW-9 -113 64 30 0 0 3 3 OW-9 -128 78 14 0.4 0 1 6.6

Average 84 6 0.9 0 2.6 2.6

Lower Member

OW-8 -123 2 96 0 0 1 1 OW-8 -131 0 97 0.5 0 1 2.5 OW-9 -135 0 94 0 0 0 2 OW-9 -137 1 96 0.8 0 0 2.2 OW-9 -159 0 96 0 0 0 4 OW-9 -166 4 78 6 0 8 4 OW-9 -187 4 82 4 0 4 6 OW-9 - 191 0 77 6 0 13 4

Average 1.8 89.5 2.2 0.5 3.4 3.2

Table 4. Mineralogical composition of different samples from different core intervals from the Dammam Formation in Umm-Gudair area as identified by XRD analysis.

Mem

ber

Well

No.

Sam

ple d

epth

(

m) M

.S.L

.

Inso

lubl

e R

esid

ue (%

)

% Of Clay types

Clay

Mon

tmor

illoni

te

Paly

gors

kite

Illit

e

Kao

linite

Upper Member

OW-1 - 36 13 60 60 0 40

OW-1 - 66 15 50 25 70 5

OW-1 - 68 18 80 95 5

OW-1 - 69 34 55 100

OW-1 - 101 15 55 95 5

OW-1 - 106 25 45 100

OW-1 - 110 40 50 97 3

OW-9 - 49 35 80 20 80

OW-9 - 50 29 50 80 20

OW-9 - 68 33 55 100

Middle Member

OW-1 - 165 15 30 100

OW-1 - 167 27 50 95 5

OW-9 - 108 28 60 80 20

OW-9 - 110 34 60 95 5

OW-9 - 133 20 60 100

Lower Member

OW-9 - 166 28 55 15 75 10

OW-9 - 171 24 80 10 90

6. GROUNDWATER CHEMISTRY The groundwater in the Dammam Formation is of brackish type. A total of 39 samples were analyzed for basic cations and anions. The total dissolved solids range between 2798 and 5534 mg/l with an average value of 3480 mg/l (selected groundwater samples are presented in Table 6), and show an increasing trend towards the northeast as shown in Figure 4. The pH value ranges between 6.7 and 8.1 with an average value of 7.53.

Figure 2. X-Ray diffraction chart of the sample at a depth of 910 ft (OW-7).



Table 5. Residual resolution analysis results of well no. OW-7, Umm-Gudair.

Sam

ple N

o.

Dept

h (ft

) M.S

.L.

Sam

ple W

t. (g

)

Resid

ual W

t. (g

)

Carb

onat

e Wt.

(g)

Clas

tic %

Carb

onat

e %

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41

492 500 508 510 515 516 521 528 531 538 544 551 555 560 564 568 576 581 582 585 587 588 589 590 591 593 596 603 604 607 612 613 615 616 617 650 652 654 663 664 910

5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5

4.92 4.74 4.62 4.33 3.04 4.78 5.39 4.93 4.75 3.97 4.73 4.72 4.92 2.15 1.89 3.07 3.92 1.92 4.16 4.83 3.45 2.68 0.22 2.36 3.91 3.85 3.73 3.25 2.38 2.02 1.98 0.56 0.49 0.23 1.21 0.07 0.12 0.04 0.06 0.14 0.36

0.08 0.26 0.38 0.67 1.96 0.22 0.61 0.07 0.25 1.03 0.27 0.28 0.08 2.85 3.11 1.93 1.08 3.08 0.84 0.17 1.55 2.33 5.78 2.64 1.09 1.15 1.27 1.75 2.62 2.98 3.02 4.44 4.51 4.77 3.79 4.93 4.88 4.96 4.94 4.86 4.64

98.4 94.8 92.4 86.6 60.8 95.6 87.8 98.6 95.0 79.4 94.6 94.4 98.4 43.0 37.8 61.4 78.4 38.4 83.2 96.6 69.0 53.6 4.4 74.2 78.2 77.0 74.6 65.0 47.6 40.4 39.6 11.2 9.8 4.6 24.2 1.4 2.4 0.8 1.2 2.8 7.2

1.6 5.2 7.6 13.4 39.2 4.4 12.2 1.4 5.0 20.6 5.4 5.6 1.6 57.0 62.2 36.6 21.6 61.6 16.8 3.4 31.0 46.6 95.6 52.8 21.8 23.0 25.4 35.0 52.4 59.6 60.4 88.8 90.2 95.4 75.8 98.6 97.6 99.2 98.8 99.2 92.8

By the application of the hydrochemical facies method[17], the groundwater is characterized by a calcium-sodium cation facies and chloride-sulphate anion facies as shown in Fig. 5. According to Haddad method[18] four groundwater chemical types were determined. These are: CaSO4 water type in which the cations sequence is Ca2+ > (Na+K)+ > Mg2+ and the anions sequence is SO4

2- > Cl- > HCO3-, with Cl- >

Figure 3. Stratigraphic sequence of the Upper part of the Dammam

Formation, O.W.7 in Umm-Gudair area. (Na+K)+; CaCl2 water type with a cations sequence of Ca2+ > (Na+K)+ > Mg2+ and an anions sequence of Cl- > SO4

2- >HCO3- with Cl- >(Na+K)+; Na2SO4 water

type where the cations sequence is (Na+K)+ > Ca2+ > Mg2+ and the anions sequence is SO4

2- > Cl- > HCO3-

with (Na+K)+ > Cl- and Na2SO4 water type with a cation sequence of (Na+K)+ > Ca2+ > Mg2+ and anions sequence of SO4

2- >Cl- > HCO3- where Cl- > (Na+K)+.

Figure 6 represents the areal distribution of the groundwater chemical types. It is clear from Figure 6 that the CaSO4 type occupies the central and the lower southwest parts of the aquifer, while the CaCl2 water type is located in the lower south part with a trend towards SW-NE and also in the upper northwest part. The Na2SO4 type where (Na+K)+ > Cl- is concentrated along the upper northwest part with a trend of SW-NE. Finally, the Na2SO4 type in which Cl- > (Na+K)+ is scattered in the lower southeast part and in the upper northwest part also.



In cation exchange the divalent ions are more strongly bonded to a solid surface such that the divalent ions tend to replace monovalent ions. The monovalent ions have a small energy of adsorption and therefore more likely to remain in solution. As a result of a large energy of adsorption, divalent ions are more abundant as an exchangeable cations. Ca2+ is typically more abundant as an exchangeable cation than Mg2+, K+ or Na+. The energy absorption sequence is Ca2+ > Mg2+ > K+ > Na+ and this provides a general ordering of cation exchangeability for common ions in groundwater. The removal of Ca2+ by cation exchange causes calcite dissolution to occur to restore carbonate[19]. When seawater intrudes a coastal freshwater aquifer, the following cation exchange reaction can occur:

Na+ + ½ Ca – X → Na – X + ½ Ca2+

where X indicates the exchange material. As the exchanger takes up Na+, Ca2+ is released and the hydrochemical water type evolves from Na–Cl to Ca–Cl. The reverse reaction can occur when fresh water flushes a saline aquifer:

½ Ca2+ + Na – X → ½ Ca – X + Na+

where Ca2+ is taken up from water in return for Na+ resulting in a Na – HCO3 water type.

It is suggested that the groundwater in the Dammam aquifer is completely replaced by the lateral flow of meteoric water of an SO4–Na genetic water type, while in the north to east direction it is partially flushed, as indicated by the dominance of a Cl–Mg water type. Therefore, the reasons behind these different chemical groundwater types can be referred to the active ion exchange between the groundwater and the Dammam aquifer formation[20]. Moreover, by the application of the ionic concentration percentage-frequency relationship method[21], it was found that SO4

2- and Cl- are the dominant anions with no dominant cations. The pair-wise comparison of the dominance zones indicates that there is no dominant water type in Figure 7. The anion relation all over the study area is SO4

2- > Cl- > HCO3-. Generally, the

predominant order of cations is Na+ > Ca2+ > Mg2+ in the NW and Ca2+ > Na+ > Mg2+ in the S and SE.

Table 6. Chemical analysis data of Dammam Formation in Umm-Gudair (in mg/l).

Well # EC TDS pH Na K Ca Mg Cl SO4 HCO3 SiO2 NO3 Ca/Mg * Cl/Na * 1 3720 2945 8 440 15 293 105 588 1260 136 25 7 1.69 0.87 2 3670 2861 7.9 370 12 300 120 500 1230 151 28 9 1.52 0.88 4 3503 2903 7.9 370 13 324 112 552 1284 155 24 8 1.75 0.97 6 3560 2856 7.5 425 12 308 114 584 1043 152 26 9 1.64 0.89 7 3970 3343 7.2 425 15 375 158 728 1260 232 22 10 1.44 1.11 9 3729 2881 7.7 380 14 309 120 560 1212 157 24 7 1.56 0.96 10 4880 3712 6.7 450 14 443 170 967 1170 240 23 27 1.58 1.39 11 3505 2798 7.9 410 12 303 108 528 1069 122 26 13 1.70 0.84 17 3785 3127 7.8 430 14 341 131 640 1230 147 26 18 1.58 0.97 19 4140 3278 7.3 425 16 375 135 780 1140 192 24 31 1.69 1.19 22 4030 3396 7.6 370 17 540 143 804 1290 185 26 23 2.29 1.41 24 4210 3838 7.1 450 15 450 173 736 1380 151 24 26 1.58 1.06 25 4410 3675 8 450 19 443 173 753 1275 180 22 15 1.55 1.09 28 4760 3884 7.7 470 20 454 188 871 1320 171 22 20 1.46 1.20 29 4170 3323 7.2 490 17 390 150 730 1280 152 23 4 1.58 0.97 31 4930 4084 7.5 430 17 488 193 1082 1260 203 15 42 1.53 1.63 34 6250 5534 6.8 590 19 623 218 1627 1200 137 23 56 1.73 1.79 36 4220 3484 7.2 435 19 383 225 779 1260 184 23 10 1.03 1.16 39 6370 5107 8.2 550 18 623 210 1671 1020 124 25 58 1.80 1.97 41 5050 4141 7 440 18 503 203 1056 1260 186 26 17 1.50 1.56

* milliequivalents per litre (meq/l)



Figure 4. Isosalinity map of the Dammam Formation aquifer in the study area

Figure 5. Back diagram for representing groundwater analyses of

the Dammam Formation aquifer in the study area.

7. GROUNDWATER SOURCE-ROCK DEDUCTION OF DAMMAM FORMATION

The concentration of Ca2+, Mg2+, Na+, Cl-, SO42-,

HCO3- and SiO2 ions depends on the rock mineralogy

that the water encounters and its rapidity along the flow path. Accordingly, rock composition may be

Figure 6. Areal distribution map of the groundwater chemical types of the Dammam Formation aquifer in the study area.

deduced from the water composition. Hounslow[8]

introduced a helpful approach to deduce the source-rock for a given water by applying the mass-balance approach to water quality data, using the WATEVAL, which is a water quality evaluation program used to evaluate water quality data from several points of view, such as: (a) an intensive evaluation of the analysis for determination of its reliability, and (b) a deduction of the aquifer mineralogy from the analysis[22]. Hounslow[8] approach was applied to 39 groundwater samples of the Dammam Formation aquifer. pH values of the samples collected from the Dammam Formation aquifer have a range of 6.7 to 8.1 with an average of 7.53. This range allows the Hounslow[8] approach to be applied in this aquifer to deduce source-rock types. By assuming that the primary source of Cl- in the aquifer is from sodium chloride (from direct halite dissolution), the Na+ concentration should be equal to a Cl- concentration. Figure 8 shows that all the samples from this aquifer had different Cl- and Na+ concentrations. Out of 39 samples, 13 showed that there are other sources of Na+ other than halite since Na+ > Cl-. These sources could be ion exchange or plagioclase minerals (such as albite) weathering,



2NaAlSi3O3+2CO2+11H2O→Al2Si2O5(OH)4+2Na++ 4H4SiO4+2HCO3

-

This can be checked by comparing nonhalite Na+ with SiO2 contents, where Nonhalite Na+ = (Na+K)+ - Cl-

SiO2 contents in these samples are less than nonhalite Na+, which suggests that natural softening is more likely to occur rather than plagioclase weathering as shown in Fig. 9. The remaining samples show that Cl- > Na+ indicating that reverse ion exchange is likely to occur in these locations. According to Albarède[22], the various forms of silica (SiO2) are stable at different pressures. Silica solubility in hydrous fluid increases with temperature and with pH. Warm diagenetic fluids carry silica which precipitates in the upper sedimentary layers, and constitute the familiar flintstones that grow on fossils and pebbles occurring in limestone. When the replacement of the initial sediment is total, a siliceous rock known as chert is attained. As a result of the very low solubility of silica at the ambient temperature quartz is left essentially untouched by erosion and form the familiar sands that, upon diagenetic cementation become sandstone.

SO42- ions concentration can be compared with

Ca2+ ions concentration assuming that the primary sources of these ions are gypsum or anhydrite dissolution. Only sample No. 22 showed that there was no excess source of Ca2+ ions rather than an assumed source (Fig. 10), while samples No. 39 and 34 showed that Ca2+ ions exceeded SO4

2- ions indicating that there is another source of Ca2+ ions which may be carbonate or silicate. The most likely source in this environment is carbonate. The other samples show SO4

2- > Ca2+ which indicates the removal of Ca2+ by either ion exchange or calcite precipitation. By inspecting the relationship between the non gypsum Ca2+ (i.e. Ca2+ - SO4

2-) and the nonhalite Na+ (i.e. {Na+K}+ – Cl-) shown in the graph in Fig. 11, we find that the ion exchange process is likely to occur in this aquifer since non-gypsum Ca2+ increases with decreasing nonhalite Na+. Figure 12 illustrates that there is a systematic increase in Mg2+ and Ca2+ which indicates that the dissolution of dolomite is likely to occur in this aquifer. Fig. 13 represents the areal distribution of the Ca/Mg ratio in the Dammam Formation, which ranges from 1.03 to 2.88, and this is most likely due to the presence of dolomite and limestone as the aquifer materials. Therefore, the main outcome of the application of Hounslow approach for deducing the main rock source of the Dammam Formation aquifer is that the clay minerals are present in the aquifer, providing the aquifer water with Na+ ion, while consuming Ca2+ ions. In addition, the Ca2+ and Mg2+ ion concentrations are relatively high in the groundwater samples indicating that the carbonate rocks in the aquifer maintain these concentrations with respect to certain carbonate minerals such as dolomite and calcite.

Figure 7. Ion-concentration percentage frequencies relationship of the Dammam Formation aquifer water sample.



0

5

10

15

20

25

30

35

1 2 3 4 5 6 7 8 9 10 11 12 13 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 34 35 36 37 38 39 40 41

Conc

entra

tions

(meq

/l)

Well No.

Ca SO4

0

5

10

15

20

25

30

35

40

45

50

1 2 3 4 5 6 7 8 9 10 11 12 13 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 34 35 36 37 38 39 40 41

Conc

entra

tions

(m

eq/l)

Well No.

Fig. 8. Bar diagram showing the concentration of chloride and sodium in the Dammam Formation aquifer in each well.

Na Cl

-20

-15

-10

-5

0

5

10

1 2 3 4 5 6 7 8 9 10 11 12 13 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 34 35 36 37 38 39 40 41

Con

cent

ratio

ns (m

eq/l)

Well No.

SiO (Na+K)-Cl2

Figure 8. Bar diagram showing the concentration ofchloride and sodium in the Dammam Formation aquifer in each well.

Figure 9. Bar diagram comparing the nonhalite sodium [(Na+K)+-Cl-] with SiO2 in the Dammam Formation aquifer.

Figure 10. Bar diagram showing the concentrations of sulphate and calcium in the Dammam Formation aquifer in each well.

1 2 3 4 5 6 7 8 9 10 11 12 13 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 34 35 36 37 38 39 40 41

Well No.

1 2 3 4 5 6 7 8 9 10 11 12 13 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 34 35 36 37 38 39 40 41

Ca SO4

SiO2



8. SOLUBILITY PRODUCT AND SATURATION INDEX

The dynamic equilibrium between a mineral and its saturation solution when no further dissolution occurs is quantified by the thermodynamic equilibrium constant. The equilibrium constant for a reaction between a solid and its saturated solution is known as the solubility product Ksp. The solubility product can be used to calculate the solubility (mol L-1) of a mineral in pure water. The state of saturation of a mineral in aqueous solution can be expressed using a saturation index[24].

where S.I. = log10

(IAP/Ksp)

in which IAP is the ion activity product of the ions in solution obtained by analysis. The value of S.I. equal to zero indicates the mineral saturation (equilibrium) has been reached, with positive values indicating supersaturation and negative values undersaturation. By calculating saturation indices, it’s possible to determine from hydrochemical data the equilibrium condition of groundwater with respect to a given mineral. The calculated S.I. values for the Dammam Formation in the study area are listed in Table 7, which reveals that the groundwater is undersaturated with respect to anhydrite, gypsum, halite and

palygorskite; and supersaturated with respect to calcite, dolomite and quartz.

On the basis of the thermodynamic calculation, it is likely that anhydrite dissolves irreversibly in most of the aquifer systems, whereas the water remains at or near saturation with calcite and dolomite. When the groundwater nears saturation with calcite and dolomite, the dissolution of anhydrite adds calcium to the groundwater, causing the pH to decrease (due to H+ released from HCO3

- during incorporation of CO32-

in calcite). The decrease in pH increases the proportion of H2CO3 in solution and thus increases the PCO2. The decrease in CO3

2- concentration with decreasing pH results in the water becoming undersaturated with respect to dolomite, which leads to dolomite dissolution and an increase in dissolved magnesium. The dissolution of anhydrite and dolomite in this de-dolomitization process exceeds the calcite precipitated, resulting in a net increase in dissolved calcium[25].

Cation exchange could contribute further HCO3-, in

addition to the de-dolomitization reaction. In this case, the uptake of Ca2+ and Mg2+ and release of Na+ from exchange sites on clay minerals causes dissolution of carbonate minerals. The additional CO3

2- released from the dissolution of carbonate minerals reacts with dissolved H2CO3 resulting in excess of HCO3

-, which is balanced by Na+ released from cation exchange.

Figure 11. The relationship between nonhalite sodium and nongypsum calcium im the Dammam Formation aquifer.

Figure 12. The relationship between calcium and magnesium in the Dammam Formation aquifer.

Figure 13. Ca/Mg ratio of the Dammam Formation aquifer in Umm-Gudair.



Table 7. Saturation indices of Dammam Formation in Umm-Gudair.

Well No. Anhydrite Calcite Dolomite Gypsum Halite Quartz

Paly- gorskite PCO2

1 -0.63 0.75 0.84 -0.41 -5.27 0.599 0.37 1.09E-03 2 -0.63 0.72 0.82 -0.41 -5.41 0.650 0.24 1.54E-03 4 -0.59 0.75 0.83 -0.37 -5.37 0.583 -0.21 1.58E-03 6 -0.67 0.36 0.08 -0.46 -5.28 0.621 -1.43 4.00E-03 7 -0.57 0.30 0.01 -0.35 -5.20 0.551 -2.60 1.21E-02 9 -0.62 0.56 0.49 -0.40 -5.35 0.585 -0.93 2.58E-03 10 -0.56 -0.11 -0.85 -0.34 -5.06 0.572 -4.48 3.92E-02 11 -0.66 0.65 0.63 -0.45 -5.34 0.617 0.09 1.24E-03 17 -0.60 0.66 0.69 -0.38 -5.24 0.619 -0.15 1.88E-03 19 -0.60 0.33 0.01 -0.38 -5.17 0.589 -2.20 7.95E-03 22 -0.44 0.74 0.70 -0.22 -5.22 0.622 -0.90 3.69E-03 24 -0.49 0.08 -0.47 -0.27 -5.17 0.590 -3.02 9.79E-03 25 -0.52 1.03 1.44 -0.30 -5.16 0.545 0.43 1.37E-03 28 -0.51 0.72 0.86 -0.29 -5.08 0.550 -0.45 2.68E-03 29 -0.55 0.13 -0.36 -0.33 -5.14 0.571 -2.58 7.90E-03 31 -0.51 0.64 0.66 -0.29 -5.03 0.385 -1.97 5.09E-03 34 -0.48 0.26 -0.15 -0.26 -4.73 0.575 -3.10 6.73E-03 36 -0.59 0.21 -0.03 -0.38 -5.16 0.571 -2.44 9.43E-03 39 -0.54 1.16 1.66 -0.32 -4.75 0.599 -3.01 5.27E-04 41 -0.50 0.12 -0.37 -0.28 -5.03 0.626 -2.96 1.50E-02

Mean -0.56 0.50 0.37 -0.34 -5.16 0.58 -1.57 6.77E-03 Additional sodium and potassium are available from chloride sources in the aquifer system.

The calculated mean of PCO2 of the Dammam Formation aquifer is 6.77 x 10-3 atm., which is significantly above the PCO2 of the Earth’s atmosphere (10-3.5 atm.). This indicates that the groundwater in the aquifers became charged with CO2 during infiltration through the soil zones and probably now represents a deep closed environment system leading to low Ca2+ concentrations, low CO2 pressures in water and a higher pH[26].

9. CONCLUSIONS The Dammam Formation is the major brackish water supply aquifer in Kuwait. The Dammam Formation of the Hasa Group comprise carbonate sediments, mainly massive chalky dolomite as the upper member; fossiliferous laminated limestone and dolomicrite with lignitic seams as the middle member; and nummulitic limestone as the lower member. The modal mineralogical composition of these rocks is as follows: 51% dolomite, 41% calcite, 2.6% clay (13% montmorillonite, 59% palygorskite, 5% kaolinite and 23% illite), 1.5% quartz, 0.2% aragonite and 3.7% shell fragments and phosphates. The groundwater source-rock deduction indicates that dissolution of the Dammam Formation aquifer carbonate rocks maintains the concentrations of Ca2+ and Mg2+ in this aquifer water, while the clay minerals provide the

aquifer water with Na+ ions, and consume Ca2+ ions through the cation exchange process. Cl/Na ratio indicates the occurrence of a natural softening process which depletes the Ca2+ ions and increases the Na+ ions in the Dammam Formation aquifer.

Hydrochemically, the salinity of the Dammam Formation aquifer increases from southwest to north-northeast, ranging generally from 2798 to 5534 mg/l, with an average value of 3480 mg/l and a pH of 7.5. Also, the groundwater is characterized by secondary salinity and a calcium-sodium cation facies with chlorite-sulphate anion facies. The groundwater chemistry shows that SO4

2- and Cl- are the dominant ions. Moreover, four chemical water types were determined. These are: CaCl2, Na2SO4 with (Na+K)+ > Cl-, Na2SO4 with Cl- > (Na+K)+, and CaSO4 water types. The anion relation all over the study area is SO4

2- > Cl- > HCO3-. Generally, the predominance

order of cations is Na+ > Ca2+ > Mg2+ in the NW and Ca2+ > Na+ > Mg2+ in the S and SE.

The calculated saturation index values revealed that the groundwater is undersaturated with respect to anhydrite, gypsum, halite and palygorskite. And supersaturated with respect to calcite, dolomite and quartz. This indicates that the incongruent dissolution of dolomite is the major controlling process in the Dammam Formation aquifer. Therefore, the chemistry of the Dammam Formation water is likely to be controlled by its mineralogical composition of calcite, dolomite, halite, gypsum and palygorskite.



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(1998). Stratigraphy of the Dammam Formation in Umm-Gudair area, Kuwait. Geologie Mediterraneenne Tome XXX (2),105-116.

2. Al-Ruwaih, F.M. (1998). Numerical modeling of Umm-Gudair field, Kuwait. Kuwait Journal of Science and Engineering 25, 231-248.

3. Abu Hijleh, A.S. (1988). Hydrogeological and hydrochemical study of Umm-Gudair area, southwest Kuwait. M.Sc. Thesis, Kuwait University, Kuwait [unpublished].

4. Langmuir, D. (1971). The geochemistry of some carbonate groundwaters in central Pennsylvania. Geochemica et Cosmochimica Acta (Journal of the Geochemical Society and the Meteorological Society) 35, 1023-1045.

5. Parkhurst, D.L. and Plummer, L.N. (1993). Geochemical models. In: Regional Groundwater quality. (Ed. Alley, W.M.) Chapter 9, New York, Van Nostrand Reinhold, 199-225.

6. Plummer, L.N. (1984). Geochemical modeling: A comparison of forward and inverse methods. Proceedings of First Canadian/American Conference on Hydrogeology: Practical applications of Groundwater Geochemistry, Canada. Hithon, B. and Wallick, E.I. editors. Worthington, OH: National Water Well Association.

7. Ball, J.W. and Nordstrom, D.K. (1992). User’s manual for WATEQ4F, with revised thermodynamic data base and test case for calculating speciation of major, trace and redox elements in natural waters. USGS, USA. Open-File Report, 91-183.

8. Hounslow, A.W. (1995). Water quality data: Analysis and interpretation. CRC Lewis, 397.

9. Owen, R.M. and Nasr, S.N. (1958). Stratigraphy of the Kuwait – Basrah area. In: Habitat of Oil. American Association of Petroleum Geologists 42, 1252-1278.

10. O’Brein, C.A.E. (1952). A stratigraphy study of the Eocene upper limestone in southern Kuwait. Mimeographed Report, Kuwait Oil Company, Kuwait [unpublished].

11. Saker, I.M.A. (1970). Geological and hydrological studies of the Shegaya area, Kuwait. M.Sc. Thesis, Kuwait University.

12. Omar, S.A., Al-Yacoubi, A. and Senay, Y. (1981). Geology and groundwater hydrology of the State of Kuwait. Journal of the Arabian Gulf and Peninsula Studies 1, 5-67.

13. Pasek, J. (1986). A lithological and stratigraphical study of the Eocene and post-Eocene deposits in the Umm-Gudair area in Kuwait. MEW, Kuwait [Unpublished].

14. Al-Awadi, E. (1988). Stratigraphic study of the Dammam Formation in the Umm-Gudair area, Kuwait. M.Sc. Thesis, Kuwait University, Kuwait [unpublished].

15. Khalaf, F., Mukhopadhyay, A., Naji, M. (1989). Geological assessment of the Eocene and Post-Eocene aquifers of Umm-Gudair, Kuwait. KISR Report 3176, Kuwait [unpublished].

16. Al-Sulaimi, J.S. and Al-Ruwaih, F.M. (2004). Geological, structural and geochemical aspects of the main aquifer systems in Kuwait. Kuwait Journal of Science and Engineering 31(1), 149-174.

17. Back, W. (1966). Hydrochemcial facies and groundwater flow patterns in north part of Atlantic Coastal Plain. US Geological Survey Professional paper, 498-A, USA.

18. Haddad, R.H. (1982). A proposed numerical approach to the classification of groundwater. Journal of the Gulf and Arabian Peninsula Studies 2, 47-68.

19. Hiscock, K. (2005). Hydrogeology - Principles and Practice. Blackwell Publishing, USA.

20. Hadi, K.M. and Al-Ruwaih, F.M. (2005). Impact of the environmental deposition on water quality of the limestone aquifer, Kuwait. Emirates Journal of Engineering Research, 10(2), 37-49.

21. Sen, Z. and Al-Dakhell, A. (1986). Hydrochemical facies evaluation in Umm er-Radhuma limestone, Eastern Saudi Arabia. Groundwater 24(5), 625–635.

22. Albarède, F. (2003). Geochemistry – an introduction. Cambridge University press. United Kingdom. 239.

23. Plummer, L.N., Prestemon, E.C. and Parkhurst, D.L. (1991). An interactive code (NETPATH) for modeling NET geochemical reactions along a flow path. USGS, Reston, Virginia, Water Resources Investigations, 91-4078.

24. Al-Ruwaih, F.M., Talebi, L. and Hadi, K.M. (2005). Major geochemical processes in the evolution of Eocene carbonate aquifer, Kuwait. Kuwait Journal of Science and Engineering 32(1), 119-144.

25. Drever, J.I. (1997). The Geochemistry of natural waters: surface and groundwater environments. 3rd Edition, Printice Hall, Englewood Cliffs.

26. Appelo, C.A.J. and Postma, D. (1994). Geo-chemistry, groundwater and pollution, AA Balkema, Rotterdam.

27. Edmunds, W.M. and Walton, N.G.R. (1983). The Lincolnshire Limestone-hydrogeochemical evolution over a ten-year period. Journal of Hydrology 156, 47-59.

28. Piper, A.M. (1944).Graphic procedure in the geochemical interpretation of water-analyses. American Geophysical Union Transactions 25, 914-923.

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