International Journal of Geosciences, 2012, 3, 71-80 Published Online February 2012 (
Potentiality of Secondary Aquifers in Saudi Arabia:
Evaluation of Groundwater Quality in Jubaila Limestone
Mohammed Tahir Hussein1, Mazin M. Al Yousif2, Hussein S. Awad1
1SGSRC, Department of Geology, College of Science, King Saud University, Riyadh, Saudi Arabia
2KACST, Riyadh, Saudi Arabia
Received September 11, 2011; revised October 16, 2011; accepted November 18, 2011
Groundwater scarcity in arid regions may hinder development plans and cause many inconveniences for the population
and authorities. Saudi Arabia has limited groundwater resources stored in the sedimentary sequence of the Arabian
Shelf. Some of these resources were classified as major aquifers, secondary and minor aqu ifers, and some were consid-
ered as aquicludes. The Jubaila Limestone is one of the secondary aquifers of Saudi Arabia. The main purpose of this
paper is to evalu ate the groundwater re sources of the Jubaila Limestone in Riyadh area, with emphasis on groundwater
quality. Groundwater was found to occur in fractures and within solution openings of the Jubaila Limestone at depths
which range between 19 an d 210 m. The transmissivity value was 1.7 × 10 –3 to 7.2 × 10–3 m2/s; the storag e coefficient
was of 1.3 × 10–4. The electrical conductivity for collected water samples ranged between 831 and 7670 µS/cm. The
major ionic relationships were Na > Ca > Mg and SO4 > Cl > HCO3. The groundwater evolves from NaCl dominated at
the southern end of the study area, into Ca, MgSO4 water in the north. The main chemical process responsible of this
variation was found to be dissolution of anhydrite and gypsum. The groundwater was not found suitable for drinking
purposes but can be used by livestock and for some agricultural purposes.
Keywords: Saudi Arabia; Riyadh; Jubaila Limestone; Groundwater Quality; Dissolution
1. Introduction
Saudi Arabia, is by far the largest country in the Arabian
Peninsula. It occupies a surface area of about 2.15 mil-
lion km². It is bordered in the north by Jordan, Iraq and
Kuwait, in the east by the Persian Gulf with a coastline
of 480 km, in the south-east and south by Qatar, the
United Arab Emirates, Oman and Yemen, and in the west
by the Red Sea with a coastline of some 1750 km. The
country can be divided into 4 main physiographic units
(Figure 1): the Western Mountains, the Central Hills, the
Desert Regions, and the Coastal Regions.
Saudi Arabia has a desert climate characterized by ex-
treme heat during the day, an abrupt drop in temperature
at night, and slight, erratic rainfall. Because of the influ-
ence of a subtropical high-pressure system and the many
fluctuations in elevation, there is considerable variation
in temperature and humidity. A uniform climate prevails
in Riyadh area. The average summer temperature is 45
degrees Centigrade, but readings of up to 54 degrees are
common. The heat becomes intense shortly after sunrise
and lasts until sunset, followed by comparatively cool
nights. In the winter, the temperature seldom drops be-
low 0 degree Centigrade but the almost total absence of
humidity and the high wind-chill factor make a bitterly
Figure 1. Map of Saudi Arabia illustrating the main physi-
ographic features and the location of Riyadh.
opyright © 2012 SciRes. IJG
cold atmosphere. In the spring and autumn, temperatures
average 29 degree Centigrade. The entire year’s rainfall
may consist of one or two torrential outbursts that flood
the wadies and then rapidly disappear into the soil to be
trapped above the layers of impervious rock. This is suf-
ficient, however, to sustain forage growth. Although the
average rainfall is 100 - 150 millimeters per year, the
area may not experience rainfall for several years.
Geologically, the Kingdom of Saudi Arabia is divided
into the Arabian Shield and the Arabian Shelf. The
Shield is composed mainly of crystalline and crystallo-
phyllian rocks primarily of Precambrian-Cambrian ages
with volcanic lava flows of Tertiary-Quaternary age ex-
tending to recent years. Groundwater in the Arabian
Shield occurs within the wadi deposits and in restricted
area within the basaltic lava flows. The Arabian Shelf is
mainly occupied by a sedimentary sequence lying un-
comfortably on the basement rocks of the Shield and
dipping towards the east and northeast. The sedimentary
sequence starts with deposits of Cambrian ages and ends
with Quaternary-recent deposits [1]. The sequence had
been interrupted by a number of uncomformities during
Phanerozoic. Table 1 summarizes the sedimentary se-
quence of the Jurassic Formations on the Arabian Shelf
[2]. Within the Arabian Shelf groundwater is obtained
from a number of aquifers ranging through Cambrian up
to the Pliocene formations. The principal aquifers are the
Saq, Wajiid, Qassim, Minjur, Dhurma, Wasia and Bayad,
Umm er Radhuma, Dammam and Neogene aquifers. The
Jubaila Limestone, according to the Water Atlas of Saudi
Arabia [3] is classified as one of the secondary aquifers
in Riyadh area. A. Al-Bassam, [4] considered the Jubaila
Limestone as a moderate aquifer both as regards its
quantitative and qualitative properties.
The water scarcity and the limited resources of water
within the country make it necessary to look into the po-
tentialities of the secondary aquifers and try to character-
ize its properties as possible. The main purpose of this
study is to evaluate the groundwater quality in Jubaila
Limestone, north of Riyadh between latitudes 24˚45' -
24˚55'N and longitudes 46˚20' - 46˚30'E. The evaluation
includes groundwater occurrences, movement, ground-
water quality variation, chemical processes responsible
for these quality variations and the suitability of water for
various purposes.
2. Methodology
Based on the above-mentioned concerns, the methods
used in this study included both field and laboratorial
methods. Field methods included both geological and
hydrogeological methods. The geological methods fo-
cused on identifying rock types, measurement and ob-
servation of geological features in the study area. The
hydrogeological methods were concerned with preparing
a well inventory sheet for all wells drilled in the study
area. The collected information included well location
using a GPS, measurements of static and pumping water
levels using water-level sounders, discharge rate meas-
urements using both containers and stopwatches, and
collection of groundwater samples for analyzing their
major, minor and trace elements. The laboratorial meth-
ods included the analyses of the collected groundwater
samples and the data processing using AquaChem and
PHREEQ softwares [5]. The analyses were performed
according to APH/AWWA/WPCF [6]. Thirty wells were
inventoried, sampled and analyzed for this study.
3. Geology of the Study Area
The study area is mainly occupied by the Shaqra Group
sedimentary rocks. The Shaqra Group lies unconform-
ably upon the Minjur Formation, of Late Triassic age,
and is overlain by the Sulaiy Formation, of Berriasian
age (Table 1). It is comprised of, in ascending strati-
graphic order, the Marrat, Dhruma, Tuwaiq Mountain,
Hanifa, Jubaila, Arab and Hith formations. These forma-
tions are separated by hiatuses of which the duration
progressively decreases, as displayed on Table 1, where
they are calibrated with the latest [7-9]. The Jurassic
formations consist predo minantly of carbon ates, alth ough
evaporitic sediments become more prevalent in the
Kimmeridgian and Tithonian Arab and Hith formations.
Unlike the underlying red sandstone-dominated Minjur
Formation, siliciclastics are uncommon in the carbon-
ate-dominated Shaqra Group and mostly confined to the
northern and southern margins of the outcrop belt where
near-shore palaeoenvironments are inferred.
The Lower Jurassic succession includes the Marrat
Formation, 102.5 m thick, that lies unconf ormably on the
Triassic Minjur Formation, and consists of interbedded
marine sandstone, carbonate and claystone deposits that
are Toarcian or older in age. It is informally subdivided
into lower (36.5 m), middle (41.8 m) and upper Marrat
(24.2 m).
The Middle Jurassic is represented by the Dhruma and
Tuwaiq Mountain formations. The Dhruma Formation,
as defined here, is 336 m thick and lies unconformably
on the Marrat Formation. It is mainly composed of car-
bonate in the subsurface, carbonate and claystone in the
central part of the outcrop area, and siliciclastics in out-
crops to the north and south. Tuwaiq Mountain Forma-
tion lies unconformably on the Dhruma Formation and
consists mostly of shallow-marine lagoon and stro-
matoporoid carbonates of Middle to Late Callovian age
with a combined thickn ess of 295 m.
The Upper Jurassic succession consists of the Hanifa,
Jubaila, Arab and Hith formations.
The Hanifa Formation lies disconformably upon the
Tuwaiq Mountain Formation, is 126 m thick and consists
Copyright © 2012 SciRes. IJG
Copyright © 2012 SciRes. IJG
Table 1. Jurassic stratigraphic column of Saudi Arabia (after Al Husseini, 2009).
of a lower muddy carbonate unit and an upper stromato-
poroid and lagoonal carbonate lithofacies. The Jubaila
Limestone lies disconformably upon the Hanifa Forma-
tion and consists of moderately deep marine carbonates
in the lower part that is overlain by a shallow marine
stromatoporoid-associated assemblage. In the outcrop
belt, the carbonates pass into sand stones to the south and
northwest. The Arab Formation is approximately 54 m
thick in outcrop. The Hith Anhydrite, consists mostly of
anhydrite but has an upper carbonate unit, as described
by Hughes [9]. It is 90 m thick at the outcrop [1].
4. Groundwater in the Study Area
Groundwater occurs in the Hubaila Limestone in zones
characterized with secondary porosity created due to
faulting, jointing, solution cavities an d fractures. In areas
well yields is found to be of high quantities and espe-
cially when these solution cavities are connected to
wadies in the area [3]. The aquifer properties were esti-
mated [1,10-12]. The Transmissivity was estimated dur-
ing this study to be in the range between 1.7 × 10–3 and
7.2 × 10–3 m/s, and the Storage Coefficient was in the
order of 1.3 × 10–4.
De p t h to water in the study area varied fro m some 19 m
in wells nos., 21 and 22 to 210 m in well no. 10. Ac-
cordingly the elevation of the water table varied from
705 m above mean sea level, at well no. 30, in the north-
west part of the study area to about 437 m at well no. 10.
Figure 2 shows the water table distribution in the study
area and the direction of groundwater flow. In the northern
part of the study area the groundwater flow followed
Figure 2. The red points are the locations of the inventored wells.
that of Wadi Hanifa as shown by the flow lines. At about
the center of the study area a cone of depression was no-
ticed around well no. 10. At the southern end of the area
the direction of groundwater flow was towards the
southeast and the south direction. The average hydraulic
gradient is about 0.005.
4.1. Groundwater Quality Variation
Groundwater quality in th e stud y area varies gr eatly in its
Electrical Conductivity (EC) from 831 to 7670 mS/cm.
This variation is due to interaction between hydraulic
gradient, the nature of the water-bearing rocks and the
chemical processes in action. Figure 3 shows the areal
distribution of the EC in the study area. The general in-
crease in EC is from the south towards the north of the
study area where two major anomalies were noticed
around the contour 6000 mS/cm and the contour 5000
mS/cm. This corresponds to the general direction of
groundwater flow.
The main chemical composition of groundwater in the
study area is summar ized on Table 2. The pH measured in
the field is between 6.01 and 8.30, i.e. it ranges from acidic
Copyright © 2012 SciRes. IJG
Figure 3. Spatial distribution of electerical conductivity (uS/cm).
water to alkaline. The same wide range in the composi-
tion was found in all of the major ions, the minor ions
and the total hardness of groundwater as shown (Table
2). Table 3 shows the correlation Matrix of the analyzed
chemical constituents. The EC was found to be mainly
correlated with Hardness, 4
, Ca, Mg and Cl. These
ions seem to be the most responsible of the chemical
composition and variation in the water quality in Jubaila
Limestone. This is understood as the occurrence of
groundwater in this aquifer is mainly due to solution
openings and fractures within the formation. Harness is
strongly correlated with the Ca, . The Ca is, in turn
correlated with the Cl and 4 concentrations, Mg is
strongly correlated with , and, Na is strongly re-
lated to Cl.
The ionic relationship, using the units of milliequiva-
lent per litre (meq/L), in the Jubaila Limeston e is charac-
terized with the following:
Na+ > Ca2+ > Mg2+
4 > Cl >
To understand more the chemical variations in the
groundwater system within the study area, a hydro-
chemical section was constructed. The location of this
section is along the flow path from the south towards the
Copyright © 2012 SciRes. IJG
Table 2. Summary statistics of groundwater composition in the study are a.
Variable Mean Minimum Maximum Range Std. Dev. Skewness Kurtosis
Temperature (˚C) 25.033 17.6 30 12.4 2.487 –0.815 2.466
pH 7.215 6.01 8.38 2.37 0.435 0.49 2.99
EC (mS/cm) 4001.37 831 7670 6839 1717.26 0.287 –0.782
Hardness (mg/L) 1477.17 610 2740 2130 594.39 0.291 –1.001
Ca (mg/L) 308.733 92 608 516 148.012 0.172 –0.995
Mg (mg/L) 172.823 46.3 298 251.7 68.308 0.048 –1.084
Na (mg/L) 680.243 365.45 1075.22 710.77 225.336 0.137 –1.37
K (mg/L) 8.967 3 24 21 5.288 1.661 2.162
HCO3 (mg/L) 180.433 90 392 302 6 6.884 1.732 3.279
SO4 (mg/L) 1057.47 197 1822 1625 341.95 0.065 0.434
Cl (mg/L) 1193.33 500 2050 1550 479.355 0.168 –1.42
NO3 (mg/L) 18.233 1.25 37.5 36.25 10.157 0.211 -0.59
SiO2 (mg/L) 12.708 5 42.5 37.5 7.536 2.362 7.666
Fe (mg/L) 0.168 0.001 0.088 0.879 0.188 1.963 5.991
B (mg/L) 0.565 0.1117 0.9846 0.8729 0.279 –0.139 –1.142
Mn (mg/L) 0.004 0.00239 0.01581 0.01342 0.003 2.936 8.422
Table 3. Correlation matrix.
Variable EC
(mS/cm) Hardness
(mg/L) Ca
(mg/L) Mg
(mg/L) Na
(mg/L) K
(mg/L) HCO3
(mg/L) SO4
(mg/L) Cl
(mg/L) NO3
(mg/L) SiO2
(mg/L) Fe
(mg/L) B (mg/L)Mn
EC (mS/cm) 1 0.975 0.908 0.867 0.730.0170.1370.9320.8750.5320.153 0.182 0.1660.123
(mg/L) 1 0.939 0.882 0.656–0.0710.0640.8990.8660.5560.111 0.218 0.2410.135
Ca (mg/L) 1 0.669 0.653–0.226–0.0530.8110.8610.5540.13 0.304 0.2880.028
Mg (mg/L) 1 0.5210.1580.2110.8410.6930.4450.063 0.052 0.1440.246
Na (mg/L) 1 0.1280.0110.7460.9020.2950.545 0.075 0.0420.19
K (mg/L) 1 0.3930.099–0.04–0.0160.26 –0.239 0.0470.215
HCO3 (mg/L) 1 0.183–0.11–0.248–0.047 0.177 0.2360.073
SO4 (mg/L) 1 0.7850.4640.268 0.054 0.16 0.096
Cl (mg/L) 1 0.4610.358 0.196 0.1220.194
NO3 (mg/L) 1 0.018 –0.156 0.2790.115
SiO2 (mg/L) 1 0.127 –0.061–0.14
Fe (mg/L) 1 0.121–0.08
B (mg/L) 1 0.31
Mn (mg/L) 1
north. Ca2+, Mg2+, Na+ (Figure 4(a)) illustrate a gradual
increase in their concentrations with the flow line, the
same is shown for the 4 and the Cl evolution (Fig-
ure 4(b)). The HCO3 exhibits a different trend, not re-
lated with the flow direction. It can be related to very
limited rainfall in the study area. These findings reflect
the effect of dissolution of gypsum and anhydrite miner-
als within the Jubaila Limestone.
4.2. Hydrochemical Facies
Hydrochemical facies are bodies of water with separate
but distinct chemical compositions contained in an aqui-
fer. Each hydrochemical facies defines a group of
groundwater with similar composition. Each facies typi-
cally has a unique origin and or pattern of evolution [13].
Hydrochemical Facies provides some insight into the
environmental processes that have affected a site and that
Copyright © 2012 SciRes. IJG
Figure 5. Trilinear diagram.
4.3. Saturation Index
is the logarithm of the quotient
P/K a solution is in equilibrium, under-
r the minerals
Figure 4. Hydrochemical crossection showing major ion
evolution along flow line.
might continue its effect in future. For defining the hyd-
rochemical facies present in the Jubaila Limestone aqui-
fer, Piper Diagram has been constructed for the collected
samples [14,15]. The plots of the collected and analyzed
groundwater samples is shown on Figure 5. 50% of the
collected samples belong to the hydrochemical facies:
Na+-Ca2+-Mg2+-Cl-4. 27% of the samples belong
to the hydrochemical facies: Na+- Mg2+-Cl-4
17% are Na+-Mg2+-Ca2+-Cl-. The hydrochemical
facies Na+-Ca2+-Cl-4 r epresent only 7% of the ana-
lyzed samples. The spatial distribution of these facies is
illustrated on Figure 6. The groundwater evolves from
NaCl dominated at the southern end of the study area,
into Ca, Mg SO4 water in the north i.e. in the down-
stream direction of the flow line. The main process re-
sponsible for this evolution is mainly dissolutio n of min-
eral as stated above. The dissolution of the minerals cal-
cite and dolomite, dominant in the Jub aila Limestone can
take place as:
2CaSO4·2H2O Ca2 + SO4 + 2H2O
2CaCO3 + H2CO3 Ca2 + 2HCO3
2Ca, Mg(CO3)2 + 2H2CO3 Ca2 + Mg2 +4HCO3
The dissolution of halite and gypsum are as follows:
NaCl Na+ + Cl
The saturation index (SI)
of the ion-activity product (IAP) and the solubility prod-
uct (K). The IAP is the product of element activity. Ana-
lytically determined concentrations have to be trans-
formed to activities considering ionic strength, tempera-
ture and complex fo rmation. The solub ility-produ ct is the
maximum possible solubility at the respective water
SI = log IA
SI indicates if
turated or super-saturated with regard to a solid phase.
A value of 1 signifies a tenfold super-saturation, a value
of –2 a hundred fold under-saturation in relation to a cer-
tain mineral phase. Equilibrium can be assumed for a
range of –0.5 to 0.5. If the SI value is below –0.5, the
solution is under-saturated with regard to the corre-
sponding mineral, if the SI exceeds +0.5 the water is su-
per-saturated with respect to this mineral.
Table 4 shows the saturation indices fo
lcite, dolomite, gypsum and anhydrite in the collected
water samples. Most of the samples were found in equi-
librium or super- saturated with calcite and dolomite. The
SI for calcite ranges between 0.93 to 0.99 (Figure 7), and
that for dolomite is between 1.8 and 2.93 (Figure 8).
77% of the samples were found in equilibrium for calcite
and 84% were found in equilibrium with dolomite i.e.
groundwater is saturated with respect to calcite and
dolomite. The SI for gypsum and anhydrite were found
in the ranges of –1.51 to –0.71 and –1.72 to –0.39, re-
spectively. These findings explain why the major ions
dissolve in the groundwater are Ca2+, Mg2+, 2
is still the groundwater is able to dissolve anhe and
gypsum. ydrit
Copyright © 2012 SciRes. IJG
Copyright © 2012 SciRes. IJG
Figure 6. Spatial distribution of hydrochemical facies.
.4. Suitability of Groundwater
the suitability for
with Boron over 0.5 mg/L. Thus the groundwater is not
, Na, SO, and hardness.
The availability of groundwater and
various uses are inextricably intertwined. The results of
the physical and chemical parameters of groundwater
within the Jubaila Limestone were thus compared with
the WHO standards and guidelines of 1993 [16]. It was
found that the EC and the major ions exceed the stan-
dards for drinking and public health purposes. The TDS
exceed the maximum limit, the Na in all samples exceeds
200 mg/L, the Cl is above 250 mg/L stated by the stan-
dard. All samples except three have SO4 concentration
above 500 mg/L. 50% of the samples were characterized
suitable for drinking purposes.
To determine suitability for livestock, the following
parameters were considered: EC4
ese are the parameters most likely to limit the use of
water by livestock, other factors not tested can also cause
the water to be unfit. When the EC is less than 1000
mS/cm, it is unlikely that individual salts would cause
health problems and no further analysis for salts is nec-
essary. However, as the concentration of salts increases,
the risk of health problems and/or reduced productivity
may occur.
Table 4. Saturation indices of calcite, dolomite and anh-
Well Calcite Dolomite Gypsum Anhydrite
1 –0.1297 –0.2346 –0.4983 –0.7157
2 0.108 0.2488 –0.6882 –0.9102
3 0.388 0.6904 –0.5895 –0.8158
4 0.1649 0.2701 –0.4092 –0.6298
5 0.4568 1.0383 –0.9832 –1.2262
6 0.4842 0.455 –0.5003 –0.7214
7 0.9916 2.0308 –0.6631 –0.8813
8 0.4502 1.2715 –1.5102 –1.7238
9 0.1397 0.2441 –0.4458 –0.6601
10 –0.1642 –0.149 –0.6332 –0.8467
11 –0.2454 –0.5958 –0.5575 –0.7722
12 0.0794 0.2225 –0.3951 –0.6083
13 –0.1077 –0.1027 –0.4088 –0.6294
14 0.1361 0.5667 –0.6482 –0.8456
15 –0.9332 –1.8321 –0.2642 –0.4774
16 0.04 0.0704 –0.2468 –0.461
17 –0.1361 0.5017 –0.9741 –1.1711
Figure 7. Saturation index of calcite in the groundwater of
Jubaila limestone.
.07460.5192 –0.5613 –0.7664
19 –0.2759 –0.3595 –0.8162 –1.0358
20 –0.2065 –0.0405 –0.9284 –1.1488
21 0.1186 0.5221 –0.8481 –1.073
22 –0.1793 –0.0019 –0.8953 –1.1158
23 –0.0549 0.0972 –0.3959 –0.6077
24 0.2226 0.4716 –0.355 –0.5706
25 0.4284 0.9204 –0.385 –0.5992
26 0.349 0.6525 –0.2709 –0.5062
27 0.0606 0.162 –0.1752 –0.3912
28 0.2799–0.5958 –0.7535 –0.986
29 2495 –0.3619 –0.3613 –0.5771
30 –0.2006 –0.316 –0.529 –0.7558
Livk pr in ty arerepot
attle surviving on water o ver 7500 mS/cm EC. However
ion purposes.
as measured according to:
estocoducershe studa have rted adul
SO4 concentration above 500 mg/L may have laxative
effects and can cause diarrhea to livestock.
Two parameters were used to test the suitability of
Jubaila Limestone groundwater for irrigat
ese were the Magnesium Hardness (MH) and the So-
dium Adsorption Ratio (SAR). The MH is calculated
according to:
MH = Mg2+/(Ca2+ + Mg2+) * 100
The SAR w
SAR = Na+/[(Ca2+ + Mg2+)/2]1/2
Figure 8. Saturation index of dolomite in the groundwater
of Jubaila Limestone.
of Mg, Ca and Na were in mil-
equivalent/lit er (meq/L) in both equ a tions.
i.e. 40% of
rs in the Jubaila Jurassic Limestone in
hin solution openings. The aquifer
The concentrations 2+ 2++
li The MH was found to range b etween 18.8 and 80 with
an average of 49 for the collected samples,
e samples exceed the maximum limit for MH. The
SAR was found to be 3.9 to 14.6 with an average of 7.9.
When plotting the SAR against the Salinity Hazard on
Wilcox Diagram (Figure 9), most of the samples were
located in the C4-S3 and C4-S2 fields, i.e. with very high
salinity hazard and high sodium hazard, and very high
salinity hazard and moderate sodium hazard, respec-
5. Con
Groundwater occu
fractures and wit
properties were characterized with transmissivity values
of 1.7 × 10–3 to 7.2 × 10–3 m2/s, and storage coefficient of
1.3 × 10–4. The regional direction of groundwater flow in
the study area is from the south towards the north with
cones of depression around pumping centres. The ground-
water quality varies from nearly fresh to saline waters.
The main hydrochemical facies defining the groundwater
composition were Na-Ca-Mg-Cl-SO4, Na-Mg-Cl-SO4,
Copyright © 2012 SciRes. IJG
Copyright © 2012 SciRes. IJG
Figure 9. Wilcox diagram of SAR against salinity haz
ales were found to be in equilibrium with calcite and
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