Hydrochemical Assessment of Groundwater from the Harrat Khyber Flood Basalts, Northwest Saudi Arabia.

The present study was carried out in the Harrat Khyber region of the Madinah province in Western Saudi Arabia. The objective of the study was to determine the main factors affecting groundwater chemistry and assess the impact of groundwater quality on human health with respect to nitrate, fluoride, and heavy metals (arsenic, chromium, copper, nickel, selenium, and zinc). Hydrochemical data for 70 groundwater samples from dug wells and bore wells from Harrat Khyber were interpreted to achieve the research objective. The groundwater chemistry is influenced by ion-exchange and the evaporation process. A wide variation in the concentration of various major ions is observed primarily due to the varied nature of the aquifer system which includes the unconsolidated wadi deposits, weathered-fractured basaltic aquifer system, and subbasaltic sedimentary aquifer system. The total hazard quotient (THQ) with respect to NO3 and F was determined. Although the F values are well within the limits of human consumption in water prescribed by WHO, the values of NO3 exceed the allowable limits in 50% of the groundwater samples. The average THQ values are 2.16, 2.92, and 2.34 for adults, children, and infants, respectively, which makes the water unsafe for human consumption. Six heavy metals (arsenic, chromium, copper, nickel, selenium, and zinc) were used to calculate the heavy-metal contamination index (HCI). The average HCI value is 19.505. Overall HCI calculation shows that the groundwater is unpolluted with respect to heavy metals. The heavy metals in water are mainly of geogenic origin.

Evaluation of heavy metal contamination and groundwater quality along the Red Sea coast, southern Saudi Arabia.

To evaluate the heavy metal contamination and groundwater quality in southern Saudi Arabia, 105 groundwater samples were analyzed for EC, pH, TDS, major ions (NO3-, Cl-, HCO3-, SO42-, F-, Ca2+, Mg2+, Na+, and K+), and heavy metals (Fe, Li, As, B, Al, Cr, Cu, Mo, Ni, Se, Sr, V, Zn, and Mn). Groundwater quality index (GWQI), degree of contamination (Cd), heavy metal pollution index (HPI), ecological risks of heavy metals (ERI), salinity hazard (EC), sodium adsorption ratio (SAR), sodium percentage (Na%), and Kelly's ratio (KR) were calculated and compared, and multivariate statistical techniques were applied. The results revealed that the major cations and anions followed the orders of Na+ > Ca2+ > Mg2+ > K+ and Cl- > SO42- > HCO3- > NO3- > F-, respectively. The maximum values of As, Mn, Cr, Ni, Se, and Zn were above the permissible limits for drinking water purposes. Pollution indices indicated that 20 to 52% of the groundwater samples were suitable for agricultural and domestic purposes. The unsuitable samples were distributed mostly in the western part along the Red Sea coast. Multivariate statistical analyses revealed that the dissolution of halite and gypsum (in sabkha deposits), carbonates, and the agricultural activities were the possible sources of the major cations and anions, and heavy metals in the study area.

Assessment of hydrological processes operating in a multi-layered sedimentary aquifer system in Saudi Arabia using integrated chemical and statistical approach.

Hydrochemical processes have a great influence on the groundwater quality especially in arid regions where groundwater is the single most important source of water supply. The present study was carried out in the Wadi Ad Dawasir region of Saudi Arabia. The objective of this study was to determine the processes influencing the groundwater composition in the region by integrated hydrochemical and statistical assessment. Hydrochemical data from 140 groundwater samples were interpreted using hydrochemical and statistical techniques. Evaporation, mineral dissolution, reverse ion exchange, and chloride/nitrate contamination from irrigation return flows were the main geogenic and anthropogenic sources influencing the groundwater composition. Principal component analysis was carried out to determine the component showing the maximum variability in the data. Two principal components were extracted. The first principal component representing gypsum dissolution and anthropogenic pollution (chloride and nitrate pollution from agricultural farms) was more pronounced in the western part of the study area whereas the second principal component representing silicate weathering process was more dominant in the eastern part. Total dissolved solid was found to be the single most important hydrochemical parameter showing the maximum variation in the analyzed data set. This study demonstrates that the loadings of the individual hydrochemical parameters in the extracted principal component and the component scores of the individual samples for each extracted principal component can be effectively used for determining the hydrochemical processes influencing the groundwater chemistry in an area.

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.

A pragmatic approach to study the groundwater quality suitability for domestic and agricultural usage, Saq aquifer, northwest of Saudi Arabia.

The present study deals with detailed hydrochemical assessment of groundwater within the Saq aquifer. The Saq aquifer which extends through the NW part of Saudi Arabia is one of the major sources of groundwater supply. Groundwater samples were collected from about 295 groundwater wells and analyzed for various physico-chemical parameters such as electrical conductivity (EC), pH, temperature, total dissolved solids (TDS), Na(+), K(+), Ca(2+), Mg(2+), CO3 (-), HCO3 (-), Cl(-), SO4 (2-), and NO3 (-). Groundwater in the area is slightly alkaline and hard in nature. Electrical conductivity (EC) varies between 284 and 9,902 µS/cm with an average value of 1,599.4 µS/cm. The groundwater is highly mineralized with approximately 30 % of the samples having major ion concentrations above the WHO permissible limits. The NO3 (-) concentration varies between 0.4 and 318.2 mg/l. The depth distribution of NO3 (-) concentration shows higher concentration at shallow depths with a gradual decrease at deeper depths. As far as drinking water quality criteria are concerned, study shows that about 33 % of samples are unfit for use. A detailed assessment of groundwater quality in relation to agriculture use reveals that 21 % samples are unsuitable for irrigation. Using Piper's classification, groundwater was classified into five different groups. Majority of the samples show Mix-Cl-SO4- and Na-Cl-types water. The abundances of Ca(2+) and Mg(2+) over alkalis infer mixed type of groundwater facies and reverse exchange reactions. The groundwater has acquired unique chemical characteristics through prolonged rock-water interactions, percolation of irrigation return water, and reactions at vadose zone.