Faisal K. Zaidi

Reverse ion exchange as a major process controlling the groundwater chemistry in an arid environment: a case study from northwestern Saudi Arabia

Assessment of groundwater quality is of utmost significance in arid regions like Saudi Arabia where the lack of present-day recharge and high evaporation rates coupled with increasing groundwater withdrawal may restrict its usage for domestic or agricultural purposes. In the present study, groundwater samples collected from agricultural farms in Hail (15 samples), Al Jawf (15 samples), and Tabuk (30 samples) regions were analyzed for their major ion concentration. The objective of the study was to determine the groundwater facies, the main hydrochemical process governing the groundwater chemistry, the saturation index with respect to the principal mineral phases, and the suitability of the groundwater for irrigational use. The groundwater samples fall within the Ca–Cl type, mixed Ca–Mg–Cl type, and Na–Cl type. Evaporation and reverse ion exchange appear to be the major processes controlling the groundwater chemistry though reverse ion exchange process is the more dominating factor. The various ionic relationships confirmed the reverse ion exchange process where the Ca and Mg in the aquifer matrix have been replaced by Na at favorable exchange sites. This phenomenon has accounted for the dominance of Ca and Mg ions over Na ion at all the sites. The process of reverse ion exchange was further substantiated by the use of modified Piper diagram (Chadha’s classification) and the chloro-alkaline indices. Evaporation as a result of extreme aridity has resulted in the groundwater being oversaturated with aragonite/calcite and dolomite as revealed by the saturation indices. The groundwater samples were classified as safe (less than 10) in terms of sodium adsorption ratio (SAR) values, good (less than 1.25) in terms of residual sodium carbonate (RSC) values, and safe to moderate (between 0 and 3) in terms of Mg hazard for irrigation purposes. Though the high salinity groundwater in the three regions coupled with low SAR values are good for the soil structure, it can have a negative impact on the crop production by adversely affecting the crop physiology. Cultivation of high-salinity-resistant varieties of crops is recommended for maximum agricultural productivity.

Hydrogeological vulnerability and pollution risk mapping of the Saq and overlying aquifers using the DRASTIC model and GIS techniques, NW Saudi Arabia

AbstractSaq and overlying aquifers serve as important sources of water supply for agricultural and domestic usage in Saudi Arabia. Due to urbanization and growth in the agricultural sector, groundwater resources are over-exploited and are prone to quality deterioration. The aquifer vulnerability technique helps delineate areas according to the susceptibility to groundwater contamination. Various parameters pertaining to the surface and subsurface environment were synthesized to represent the data variation in the 3D horizon. Estimates of the parameters, such as recharge, soil media, and vadose zone, were obtained based on modified criteria to account for data variability. Statistical analysis indicates that the input parameters are independent and contribute individually to the vulnerability index. For vulnerability assessment, the DRASTIC model was considered due to the large number of data input parameters. Based on the vulnerability index, the study area is classified into low to very high vulnerability classes. To assess the human interaction on the groundwater environment, the land-use pattern was included as an additional input layer. Sensitivity analyses helped to compute the influence of the input layers on the vulnerability index and the model calibration through revised weights. The model validity tests were performed by comparing the NO3, SO4 and Cl concentration with the different vulnerability zones. The aquifer vulnerability maps developed in the present study may serve as an important tool for effective groundwater resource management.

A combined hydrochemical-statistical analysis of Saq aquifer, northwestern part of the Kingdom of Saudi Arabia

The present study includes detailed hydrochemical assessment of groundwater resources of Saq aquifer. The Saq aquifer covers a large area (about 375,000 km2) and lies in the arid region with low annual rainfall and extremely high evaporation. In the study area, groundwater serves as the major source for agricultural activity and for domestic usages. A total of 295 groundwater samples collected and were analyzed for physico-chemical parameters such as hydrogen ion concentration (pH), total dissolved solids (TDS) and electrical conductivity (EC), sodium (Na+), potassium (K+), magnesium (Mg2+), and calcium (Ca2+), bicarbonate (HCO3) chloride (Cl−), sulfate (SO42−) and nitrate (NO3). The goal and challenge for the statistical overview was to delineate chemical distributions in a complex, heterogeneous set of data spanning over a large geographic range. After de-clustering to create a uniform spatial sample distribution with 295 samples, histograms and quantile-quantile (Q-Q) plots were employed to delineate subpopulations that have coherent chemical affinities. The elements showing significantly higher positive correlation are: TDS with EC; Ca with EC, TDS; Mg and EC, TDS, Ca, K; Cl and EC, TDS, Mg, Na, Ca; SO4 and EC, TDS, Ca, Cl, Na, Mg. The distribution of major ions in the groundwater is Na+ > Ca++ > Mg++ > K+ and Cl− > SO4−2>HCO3−>NO3−. Ionic abundance plot of alkalis with Ca and Mg is suggestive of mix type trends of concentrations as evident by moderate correlation (r = 0.57). About 60% of the total samples have alkalis abundance and rests have more Ca + Mg concentrations than alkalis. Taking both results of cluster tree and geochemical features of variables into consideration, the authors classify the elements into two major groups, the first includes TDS, Na, EC, Cl, Ca, SO4, and Mg, where the relationship within the group are strong. The second group includes K, HCO3, pH, and NO3. This group has close relationship with group 1 demonstrate that, the increase in the concentration to some elements could be the same. Some of the analyzed parameters approach a normal distribution, as both their skewnesses and kurtoses reach close to “0”. The study revealed that, all of the element pairs exhibit positive relations.

Hydrochemical characteristics and evaluation of the granite aquifer in the Alwadeen area, southwest Saudi Arabia

This study was carried out in the Alwadeen area of Khamis Mushayt district of southwestern Saudi Arabia to evaluate the hydrochemical characteristics of the shallow hard rock aquifers. These hard rock aquifers mostly comprise granites and contain significant quantities of groundwater that complement the available groundwater from the unconsolidated alluvial sediments in the nearby wadis. The field investigation indicates two main fracture sets which intersect each other and are oriented in the west-northwest and east-west directions. The granitic rocks in the area are intruded by coarse-grained and quartz-rich monzogranite and pegmatite veins. Hydrogeologically, the fracture systems are important since they facilitate the groundwater storage and assume the transmissive function during times of groundwater abstraction. Given the fact that groundwater in the fractured rock aquifers generally occurs at shallow depths, it may be exposed to contamination from surface and/or near-surface sources, and it is therefore important to evaluate its quality. To this end, a hydrochemical analysis was carried out on six groundwater samples collected from the area. The hydrochemistry revealed that the groundwater is fairly fresh, and facies analysis reveals mixed Na-Cl and Ca-Mg-Cl-SO4 types. Overall, the results reveal that the groundwater is saturated with calcite and dolomite, but unsaturated with gypsum and halite. The degree of salinity increases in the direction of the groundwater flow due to increased rock-water interaction.

Evaluation of metals that are potentially toxic to agricultural surface soils, using statistical analysis, in northwestern Saudi Arabia

Abstract Heavy metals in agricultural soils enter the food chain when taken up by plants. The main purpose of this work is to determine metal contamination in agricultural farms in northwestern Saudi Arabia. Fifty surface soil samples were collected from agricultural areas. The study focuses on the geochemical behavior of As, Cd, Co, Cr, Cu, Hg, Pb and Zn, and determines the enrichment factor and geoaccumulation index. Multivariate statistical analysis, including principle component analysis and cluster analysis, is also applied to the acquired data. The study shows considerable variation in the concentrations of the analyzed metals in the studied soil samples. This variation in concentration is attributed to the intensity of agricultural activities and, possibly, to nearby fossil fuel combustion activities, as well as to traffic flows from highways and local roads. Multivariate analysis suggests that As, Cd, Hg and Pb are associated with anthropogenic activities, whereas Co, Cr, Cu and Zn are mainly controlled by geogenic activities. Hg and Pb show the maximum concentration in the analyzed samples as compared to the background concentration.

Extreme Natural Hazards, Disaster Risks and Societal Implications: Natural hazards in Saudi Arabia

As the name implies Natural Hazards are naturally occurring events that can endanger human lives and property. During the past few decades the losses to life and property from natural hazards have increased many folds mainly due to the increase in human population resulting in the inhabitation of areas prone to hazards. Saudi Arabia is quite prone to different kinds of natural hazards. The North western region of the kingdom is prone to earthquakes and volcanic hazards whereas the central and western region of the kingdom is exposed to floods especially during events of heavy rainfall. Landslides are a common phenomenon in the inhabited mountainous regions of the south west. Dust storms are quite common in the central and the eastern regions of the Kingdom. Pollution of natural resources specially groundwater has also been seen in the kingdom in the recent years especially around the wadis and agricultural farms where the extensive use of fertilizers for increasing agricultural yields have resulted in polluting the aquifers. Different government agencies and various universities having been working on these issues, to mitigate these hazards and also educate the people. The SGS Chair on Natural Hazards established at the King Saud University is one such effort in addressing this subject. Due to the 2009 Jeddah flood disaster more emphasis is being given to tackle the problems related to hydrological hazards. Similar events like this have the potential to affect other major cities of the Kingdom.

Structural analysis for metavolcanics and their metapyroclastics at gold deposit of the Mahd Ad Dahab Area, Arabian Shield, Saudi Arabia

The present study focuses on the gold mining in Mahd Ad Dahab region of Saudi Arabia. The study aims to assess the spatial relationship between tectonic contacts in Mahd Ad Dahab area and to provide a meaningful hypothesis relating gold metallogeny to the evolution of the Arabian Shield. Distribution and localization of gold occurrences in the study area was envisaged based on the different styles of microstructures and the major deformation phases affecting the area. The detailed petrographical and mineralogical investigations indicate that the metavolcanic rocks at the Mahd Ad Dahab gold mine area can be classified into metabasalt, metaandesite, and the felsic varieties (metadacite, metarhyodacite and metarhyolite) associating their metapyroclastics (conglomerate and tuffs). Furthermore, quartz forms allotriomorphic crystals which exhibit wavy extinction, deformational lamina and foliation due to subsequent deformations. Furthermore, we conclude that finite strain in the deformed rocks is of the same order of magnitude for all units of metavolcano-sedimentary rocks. Furthermore, contacts formed during intrusion of plutons with some faults in the Mahd Ad Dahab area under brittle to semi-ductile deformation conditions. In this case, finite strain accumulated during superimposed deformation on the already assembled nappe structure. It indicates that the contacts formed during the accumulation of finite strain.

Structural and Mechanical Controls on Intrusion Related to Mahd Ad Dahab Area, Arabian Shield, Saudi Arabia

Mahd Ad Dahab area is located on the western side of the Arabian Precambrian Shield. In the study area, Mahd group rocks are deposited along margin of active extensional volcanotectonic basin. These rocks are associated with the major geologic structures which are attributed to various deformational stages of the Precambrian basement. Field geology, finite strain and microstructural studies were carried out and the relationships between the lithological contacts and major/minor structures have been studied. The Rf/φ and Fry methods on the metavolcano-sedimentary samples from 3 andesite samples, 2 lower agglomerate samples, 7 lower rhyolite samples, 3 upper agglomerate, 1 upper tuff sample and 2 rhyolite porphyry samples were used in Mahd Ad Dahab area. Finite-strain data shows that a low to moderate range of deformation of the metavolcanosedimentary samples and axial ratios in the XZ section range from 1.10 to 2.50 for the Rf/φ method and from 1.15 to 2.35 for the Fry method. Furthermore, the short axes are subvertical associated with a subhorizontal foliation. We conclude that finite strain in the deformed rocks is of the same order of magnitude for all units of metavolcano-sedimentary rocks. Furthermore, contacts formed during intrusion of plutons with some faults in the Mahd Ad Dahab area under brittle to semi-ductile deformation conditions. In this case, finite strain accumulated during superimposed deformation on the already assembled nappe structure. It indicates that the nappe contacts formed during the accumulation of finite strain.