International Journal of Geosciences, 2012, 3, 71-80 http://dx.doi.org/10.4236/ijg.2012.31009 Published Online February 2012 (http://www.SciRP.org/journal/ijg) 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 Email: [email protected] Received September 11, 2011; revised October 16, 2011; accepted November 18, 2011 ABSTRACT 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 aquifers, 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 evaluate the groundwater resources 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 and 210 m. The transmissivity value was 1.7 × 10–3 to 7.2 × 10–3 m2/s; the storage 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 Figure 1. Map of Saudi Arabia illustrating the main physi- humidity and the high wind-chill factor make a bitterly ographic features and the location of Riyadh. Copyright © 2012 SciRes. IJG 72 M. T. HUSSEIN ET AL. cold atmosphere. In the spring and autumn, temperatures a well inventory sheet for all wells drilled in the study average 29 degree Centigrade. The entire year’s rainfall area. The collected information included well location may consist of one or two torrential outbursts that flood using a GPS, measurements of static and pumping water the wadies and then rapidly disappear into the soil to be levels using water-level sounders, discharge rate meas- trapped above the layers of impervious rock. This is suf- urements using both containers and stopwatches, and ficient, however, to sustain forage growth. Although the collection of groundwater samples for analyzing their average rainfall is 100 - 150 millimeters per year, the major, minor and trace elements. The laboratorial meth- area may not experience rainfall for several years. ods included the analyses of the collected groundwater Geologically, the Kingdom of Saudi Arabia is divided samples and the data processing using AquaChem and into the Arabian Shield and the Arabian Shelf. The PHREEQ softwares [5]. The analyses were performed Shield is composed mainly of crystalline and crystallo- according to APH/AWWA/WPCF [6]. Thirty wells were phyllian rocks primarily of Precambrian-Cambrian ages inventoried, sampled and analyzed for this study. with volcanic lava flows of Tertiary-Quaternary age ex- tending to recent years. Groundwater in the Arabian 3. Geology of the Study Area Shield occurs within the wadi deposits and in restricted area within the basaltic lava flows. The Arabian Shelf is The study area is mainly occupied by the Shaqra Group mainly occupied by a sedimentary sequence lying un- sedimentary rocks. The Shaqra Group lies unconform- comfortably on the basement rocks of the Shield and ably upon the Minjur Formation, of Late Triassic age, dipping towards the east and northeast. The sedimentary and is overlain by the Sulaiy Formation, of Berriasian sequence starts with deposits of Cambrian ages and ends age (Table 1). It is comprised of, in ascending strati- graphic order, the Marrat, Dhruma, Tuwaiq Mountain, with Quaternary-recent deposits [1]. The sequence had Hanifa, Jubaila, Arab and Hith formations. These forma- been interrupted by a number of uncomformities during tions are separated by hiatuses of which the duration Phanerozoic. Table 1 summarizes the sedimentary se- progressively decreases, as displayed on Table 1, where quence of the Jurassic Formations on the Arabian Shelf they are calibrated with the latest [7-9]. The Jurassic [2]. Within the Arabian Shelf groundwater is obtained formations consist predominantly of carbonates, although from a number of aquifers ranging through Cambrian up evaporitic sediments become more prevalent in the to the Pliocene formations. The principal aquifers are the Kimmeridgian and Tithonian Arab and Hith formations. Saq, Wajiid, Qassim, Minjur, Dhurma, Wasia and Bayad, Unlike the underlying red sandstone-dominated Minjur Umm er Radhuma, Dammam and Neogene aquifers. The Formation, siliciclastics are uncommon in the carbon- Jubaila Limestone, according to the Water Atlas of Saudi ate-dominated Shaqra Group and mostly confined to the Arabia [3] is classified as one of the secondary aquifers northern and southern margins of the outcrop belt where in Riyadh area. A. Al-Bassam, [4] considered the Jubaila near-shore palaeoenvironments are inferred. Limestone as a moderate aquifer both as regards its The Lower Jurassic succession includes the Marrat quantitative and qualitative properties. Formation, 102.5 m thick, that lies unconformably on the The water scarcity and the limited resources of water Triassic Minjur Formation, and consists of interbedded within the country make it necessary to look into the po- marine sandstone, carbonate and claystone deposits that tentialities of the secondary aquifers and try to character- are Toarcian or older in age. It is informally subdivided ize its properties as possible. The main purpose of this into lower (36.5 m), middle (41.8 m) and upper Marrat study is to evaluate the groundwater quality in Jubaila (24.2 m). Limestone, north of Riyadh between latitudes 24˚45' - The Middle Jurassic is represented by the Dhruma and 24˚55'N and longitudes 46˚20' - 46˚30'E. The evaluation Tuwaiq Mountain formations. The Dhruma Formation, includes groundwater occurrences, movement, ground- as defined here, is 336 m thick and lies unconformably water quality variation, chemical processes responsible on the Marrat Formation. It is mainly composed of car- for these quality variations and the suitability of water for bonate in the subsurface, carbonate and claystone in the various purposes. central part of the outcrop area, and siliciclastics in out- crops to the north and south. Tuwaiq Mountain Forma- 2. Methodology tion lies unconformably on the Dhruma Formation and Based on the above-mentioned concerns, the methods consists mostly of shallow-marine lagoon and stro- used in this study included both field and laboratorial matoporoid carbonates of Middle to Late Callovian age methods. Field methods included both geological and with a combined thickness of 295 m. hydrogeological methods. The geological methods fo- The Upper Jurassic succession consists of the Hanifa, cused on identifying rock types, measurement and ob- Jubaila, Arab and Hith formations. servation of geological features in the study area. The The Hanifa Formation lies disconformably upon the hydrogeological methods were concerned with preparing Tuwaiq Mountain Formation, is 126 m thick and consists Copyright © 2012 SciRes. IJG M. T. HUSSEIN ET AL. 73 Table 1. Jurassic stratigraphic column of Saudi Arabia (after Al Husseini, 2009). of a lower muddy carbonate unit and an upper stromato- faulting, jointing, solution cavities and fractures. In areas poroid and lagoonal carbonate lithofacies. The Jubaila well yields is found to be of high quantities and espe- Limestone lies disconformably upon the Hanifa Forma- cially when these solution cavities are connected to tion and consists of moderately deep marine carbonates wadies in the area [3]. The aquifer properties were esti- in the lower part that is overlain by a shallow marine mated [1,10-12]. The Transmissivity was estimated dur- –3 stromatoporoid-associated assemblage. In the outcrop ing this study to be in the range between 1.7 × 10 and –3 belt, the carbonates pass into sandstones to the south and 7.2 × 10 m/s, and the Storage Coefficient was in the –4 northwest. The Arab Formation is approximately 54 m order of 1.3 × 10 . thick in outcrop. The Hith Anhydrite, consists mostly of Depth to water in the study area varied from some 19 m anhydrite but has an upper carbonate unit, as described in wells nos., 21 and 22 to 210 m in well no.