Geochemical process regulating groundwater quality in a coastal region with complex contamination sources: Barka,Sultanate of Oman

An investigation was carried out to evaluate the geochemical processes regulating groundwater quality in a coastal region, Barka, Sultanate of Oman. The rapid urban developments in Barka cause depletion of groundwater quantity and deterioration of quality through excessive consumption and influx of pollutants from natural and anthropogenic activities. In this study, 111 groundwater samples were collected from 79 wells and analysed for pH, EC, DO, temperature, major ions, silica and nutrients. In Barka, water chemistry shows large variation in major ion concentrations and in electrical conductivity, and implies the influence of distinguished contamination sources and hydrogeochemical processes. The groundwater chemistry in Barka is principally regulated by saline sources, reverse ion exchange, anthropogenic pollutants and mineral dissolution/precipitation reactions. Due to ubiquitous pollutants and processes, groundwater samples were classified into two groups based on electrical conductivity. In group1, water chemistry is greatly influenced by mineral dissolution/precipitation process and lateral recharge from upstream region (Jabal Al-Akdar and Nakhal mountains). In group 2, the water chemistry is affected by saline water intrusion, sea spray, reverse ion exchange and anthropogenic pollutants. Besides, high nitrate concentrations, especially in group 2 samples, firm evidence for impact of anthropogenic activities on groundwater quality, and nitrate can be originated by the effluents recharge from surface contamination sources. Ionic ratios such as SO₄/Cl, alkalinity/Cl and total cation/Cl indicate that effluents recharged from septic tank, waste dumping sites and irrigation return flow induce dissolution of carbonate minerals, and enhances solute load in groundwater. The chemical constituents originating from saline water sources, reverse ion exchange and mineral dissolution are successfully differentiated using ionic delta, the difference between the actual concentration of each constituent and its theoretical concentration for a freshwater–seawater mix calculated from the chloride concentration of the sample, and proved that this approach is a promising tool to identify and differentiate the geochemical processes in coastal region. Hence, both regular geochemical methods and ionic delta ensured that groundwater quality in Barka is impaired by natural and human activities.     

Hydrogeochemistry of the Saloum (Senegal) superficial coastal aquifer

Seawater has entered and concentrated in the Saloum hydrologic system up to 100 km upstream, contaminating both the surface water and the superficial 'Continental terminal' (CT) groundwater resources, and large proportions of cultivated lands. In the areas affected by saltwater contamination, chloride concentrations as high as 3,195 mg/l have been measured in the groundwater samples collected from wells located in the vicinity of the Saloum River, making the water inadequate for drinking water purposes. This paper presents the results of a study designed to characterise the current extent of the saline groundwater and the mechanism of saline surface water body/fresh groundwater mixing in relation to the groundwater flow trends. It also describes the groundwater chemical and isotopic composition and geochemical processes controlling the chemical patterns. Four major water types occur in the study area, namely Na-rich saline groundwater, Ca-Na-rich saline groundwater, Na-dominant fresh groundwater and Ca-dominant fresh groundwater. A hydrogeochemical zonation of the aquifer, based on the presence of different water families and on the groundwater flow, led to the identification of the main processes controlling the groundwater chemistry. Cation exchange reactions on the kaolinite clay mineral, calcite dissolution in the eastern zone where calcite minerals have been identified, reverse cation exchange reactions in the saline-contaminated band along the Saloum River and, to a lesser extent, a gypsum dissolution are the predominant processes. Results of i¹⁸O and iD analysis in 15 groundwater samples compared with the local meteoric line indicate that the groundwater has been affected by evaporation, and the groundwater is isotopically lighter as the depth of water table increases. In this study, i¹⁸O data were used in conjunction with chloride data to identify the source of high chloride. Results show a departure of the contaminated water samples from the seawater mixing line, which indicates that other processes rather than mixing between modern seawater and native groundwater alone increase the chloride concentrations.     

Hydrochemical evolution and variation of groundwater and its environmental impact at Sohag, Egypt

Groundwater resources of Sohag, Egypt are currently threatened by contamination from agricultural and urbanization activities. Groundwater in Sohag area has a special significance where it is the second source for fresh water used for agricultural, domestic, and industrial purposes. Due to growing population, agriculture expansion, and urbanization, groundwater quality assessment needs more attention to cope with the increasing water demand in this arid zones and limited water resources. The aim of this paper is to address the integrated role of geochemical processes, agriculture and urbanization in evolution of groundwater composition, and their impact on groundwater quality to help in management and protection of groundwater resources of study area using geochemical modeling techniques and geographical information systems. Spatial variation of groundwater hydrochemical properties, rock–water interaction, ion exchange, and assessment of groundwater quality were investigated. Results indicated that groundwater properties are varied spatially and its evolution in the study area is generally controlled by the prevailed geochemical processes represented by leaching, dissolution, and precipitation of salts and minerals, ion exchange, in addition to human activities represented by agriculture and urbanization as well as climatic and poor drainage conditions. Management alternatives should be followed in the study area to avoid degradation of groundwater quality and provide sustainable development.     

Identification and evolution of hydrogeochemical processes in the groundwater environment in an area of the Palar and Cheyyar River Basins,Southern India

The Palar and Cheyyar River Basins in Tamil Nadu state of Southern India are characterised by different geological formations, and groundwater is the major source for domestic, agricultural and other water-related activities. Hydrogeochemical studies were carried out in this area with the objective of identifying the geochemical processes and their relation to groundwater quality. Groundwater samples were collected once a month from 43 groundwater wells in this area from January 1998 to July 1999. Sampling procedures and chemical analysis were carried out as per the standard methods. Chemical data are used for mathematical calculations and graphical plots to understand the chemical process and its relation to the groundwater quality. The chemical composition of groundwater in the central part of the study area mainly depends on the recharge from lakes and the river, which is explained by a mixing mechanism. In addition, weathering of silicate minerals controls the concentration of major ions such as sodium, calcium, magnesium and potassium in the groundwater of this area. Further, the activity ratios indicate that the groundwater is in equilibrium with kaolinite, smectite and montmorrillonite. The reverse ion exchange process controls the concentration of calcium, magnesium and sodium in hard rock formations, and dissolution of carbonate minerals and accessory minerals is the source of Ca and Mg, in addition to cation exchange in the sedimentary formations. In general, the chemical composition of the groundwater in this area is influenced by rock–water interaction, dissolution and deposition of carbonate and silicate minerals, ion exchange, and surface water interactions.     

Integrating multivariate statistical analysis with GIS for geochemical assessment of groundwater quality in Shiwaliks of Punjab,India

The dependency of people on groundwater has increased in the past few decades due to tremendous increase in crop production, population and industrialization. Groundwater is the main source of irrigation in Shiwaliks of Punjab. In the present study the samples were collected from predetermined location as was located on satellite image on basis of spectral reflectance. Global positioning system was used to collect samples from specific locations. Principal components analysis (PCA) together with other factor analysis procedures consolidate a large number of observed variables into a smaller number of factors that can be more readily interpreted. In the present study, concentrations of different constituents were correlated based on underlying physical and chemical processes such as dissociation, ion exchange, weathering or carbonate equilibrium reactions. The PCA produced six significant components that explained 78% of the cumulative variance. The concentration of the few trace metals was found to be much higher indicating recharge due to precipitation as main transport mechanism of transport of heavy metals in groundwater which is also confirmed by PCA. Piper and other graphical methods were used to identify geochemical facies of groundwater samples and geochemical processes occurring in study area. The water in the study area has temporary hardness and is mainly of Ca–Mg–HCO₃ type.     

Evidence for the occurrence of hydrogeochemical processes in the groundwater of Khoy plain,northwestern Iran,using ionic ratios and geochemical modeling

Rapid population growth, industrialization, and agricultural expansion in the Khoy area (northwestern Iran) have led to its dependence on groundwater and degradation of groundwater quality. This study attempts to decipher the major processes and factors that degrade the groundwater quality of the Khoy plain. For this purpose, 54 groundwater samples from unconfined and confined aquifers of the plain were collected in July 2017 and analyzed for major cations and anions (Na, K, Ca, Mg, HCO₃, SO_4, and Cl), minor ions (NO₃ and F), and Al. Magnesium and bicarbonate were identified as the dominant cation and anion, respectively. Several ionic ratios and geochemical modeling using PHREEQC indicated that the most important hydrogeochemical processes to affect groundwater quality in the plain were weathering and dissolution of evaporitic and silicate minerals, mixing, and ion exchange. There were smaller effects from evaporation and anthropogenic factors (e.g., industries). Results showed that the high salinity of the groundwater in the northeast area of the plain was due to the high solubility of the evaporitic minerals, e.g., halite and gypsum. Reverse ion exchange and the contribution of mineral dissolution were more significant than ion exchange in the northeastern part of the plain. Elevated salinity of the groundwater in the southeast was attributed mostly to reverse ion exchange and somewhat to evaporation.     

Investigation of the hydrogeochemical processes in an alluvial channel aquifer located in a typical Karoo Basin of Southern Africa

An investigation was conducted to assess the hydrogeochemical processes of an alluvial channel aquifer located in a typical Karoo Basin of Southern Africa. The investigation was aimed at identifying and describing the groundwater chemistry evolution and its contribution to the overall groundwater quality. X-ray fluorescent spectrometry (XRF) and X-ray diffractometry (XRD) analyses were performed on geological samples to identify and quantify the major element oxides and minerals. The study utilises the conventional Piper diagram, bivariate plots and PHREEQC hydrogeochemical model to analyse groundwater chemistry data obtained during the wet (February and May) and dry seasons (August and December) of 2011. The XRF and XRD results show that the channel deposits are dominated by SiO₂ element oxides and quartz minerals, thus elevated concentrations of silicon (Si⁴⁺) were found in the groundwater. Dolomite and calcite minerals were also detected in the unconsolidated aquifer sediments. The detailed study of the alluvial aquifer system has shown that dissolution of dolomite and calcite minerals and ion exchange are the dominant hydrogeochemical processes influencing the groundwater quality. The groundwater evolves from Ca²⁺–Mg²⁺–HCO₃ ^? recharge water that goes through ion exchange with Na⁺ in the clay-silt sediment to give a Na⁺–HCO₃ ^? water type. The groundwater is supersaturated with respect to quartz, dolomite and calcite minerals. The study shows the potential usefulness of simple bivariate plots as a complimentary tool to the conventional methods for analyzing groundwater hydrogeochemical processes.     

Inverse geochemical modeling of groundwater salinization in Azraq Basin,Jordan

The aim is to define the mechanism of chemical reactions that are responsible for the salinization of the Azraq basin along groundwater flow path, using inverse modeling technique by PHREEQC Interactive 2.8 for Windows. The chemical analysis of representative groundwater samples was used to predict the causes of salinization of groundwater. In addition, the saturation indices analysis was used to characterize the geochemical processes that led to the dissolution of mineral constituents within the groundwater aquifer system. According to the modeling results, it was noted that the groundwater at the recharge area was undersaturated with respect to calcite, dolomite, gypsum, anhydrite, and halite. Thus, the water dissolved these minerals during water rock interaction, and therefore, the concentration of Ca, Mg, Na, and SO₄ increased along the groundwater flow path. Furthermore, the groundwater at the discharge area was oversaturated with respect to calcite and dolomite. This meant that the water would precipitate these minerals along the flow path, while the water was undersaturated with respect to gypsum and halite throughout the simulated path; this showed the dissolution processes that take place during water-rock interaction. Therefore, the salinity of the groundwater increased significantly along the groundwater flow paths.     

Desalination of a sedimentary rock aquifer system invaded by Pleistocene Champlain Sea water and processes controlling groundwater geochemistry

The objective of this study was to identify geochemical processes and Quaternary geological events responsible for the variations in groundwater geochemistry observed in a sedimentary rock aquifer system, including brackish to saline groundwater. Inorganic constituents and environmental isotopes were analyzed for 146 groundwater samples. Dissolution of carbonates dominates in recharge areas, resulting in Ca-, Mg-HCO₃ groundwater. Further along flow paths, under confined conditions, Ca²⁺–Na⁺ ion exchange causes groundwater evolution to Na-HCO₃ type. Na-Cl groundwater is also found and it falls on a seawater mixing line. Using conservative tracers, Cl⁻ and Br⁻, the original Champlain Sea water is shown to have been, in the region, a mixture of about 34% seawater and 66% freshwater, a composition still retained by some groundwater. Na-Cl groundwater thus results from mixing with former Champlain Sea water and also from solute diffusion from overlying marine clay. The system is thus found to be at different stages of desalinization, from the original Champlain Sea water still present in hydraulically stagnant areas of the aquifer to fully flushed conditions in parts, where more flow occurs, especially in recharge zones. The geochemical processes are integrated within the hydrogeological context to produce a conceptual geochemical evolution model for groundwater of the aquifer system.     

Chemometric analysis to infer hydro-geochemical processes in a semi-arid region of India

Groundwater exploitation in Punjab has increased in last few decades due to rapid increase in industrialization, population, crop production, and erratic monsoon. In the present study, groundwater samples from 29 locations were collected and analyzed for almost all major anions, cations, and heavy metals. The analyzed parameters formed the attribute database for statistical analysis. The study approach included multivariate statistical analysis of hydro-chemical data to identify hydro-geochemical processes occurring in the study area and its relation to groundwater quality. The principal component analysis produced seven significant factors that explained nearly 77 % of the cumulative variance. Factor 1 explained nearly 22.05 % of dataset with variables loading indicating mineralization of geological component of soil. Trilinear plot and other graphical methods were also used to identify chemical facies of groundwater and geochemical processes occurring in study area. The water type in the study area is of Na/K–Mg–HCO₃ type. It was found that the general hydro-geochemistry of groundwater in the study area dominated is by the processes such as carbonate/silicate weathering, ion-exchange, and dissolution. Thus, statistical methods can prove to be an effective tool understanding hydro-geochemistry of a region along with conventional graphical methods.     

Groundwater quality assessment using integrated geochemical methods,multivariate statistical analysis,and geostatistical technique in shallow coastal aquifer of Terengganu,Malaysia

Extensive agricultural, residential, and industrial activities have increased demand for water supplies, which can lead to groundwater quality degradation. The integration of geochemical methods, multivariate statistical analysis, and geostatistical approaches were carried out on 169 groundwater samples to elucidate the regional factors and processes that influencing the geochemical composition of groundwater in coastal shallow aquifer of Terengganu, Malaysia. Hydrochemical modelling revealed that the abundance of Ca and Mg was contributed by carbonate and silicate weathering while higher HCO₃ and Cl were resulted from reverse ion exchange reaction. Therefore, the dominant hydrogeochemical facies of groundwater was Ca-Mg-HCO₃-Cl type. The influence of salinization resulting from seawater mixing to the groundwater was corroborated by Cl/HCO₃ ratio, which affected around 50.9% of the groundwater samples slightly or moderately. Spatial mapping using ordinary kriging found that the threat of sea water intrusion is more prominent in the major river confluence especially around Terengganu and Marang River in the northeast and Dungun and Kemaman River confluence in southeast of study area. Moreover, factor analyses concluded that salinization, anthropogenic activities, reverse ion exchange, weathering processes, agricultural impact, and seasonal variations were the factors that regulate 63% of the major ion chemistry in study area. Finally, these findings showed the importance of understanding the hydrochemical characteristics for effective utilization, aquifer protection, and prediction of changes to minimize the effects of salinization and reduce human pollution such as agriculture and urbanization. It is essential steps in order to safeguard the utilization of groundwater resources for future generations.     

广汉市平原区浅层地下水化学演化及其控制因素

为在广汉市城乡规划过程中提供地下水资源开发利用的基础信息,采用矿物风化系统分析、相关性分析、主成分分析和PhreeQC反向水文地球化学模拟等方法对广汉市平原区的浅层地下水的地下水水化学组分进行分析,确定了浅层地下水的水化学演化及控制因素,完成了地下水资源的质量及时空分布特征分析。分析表明：Gibbs图显示岩石风化主导该区地下水水化学特征,风化过程产生离子和次生矿物又经历水解作用,在矿物风化系统稳定场图中显示水样中铝硅酸盐矿物逐渐趋于溶解,碳酸盐矿物处于饱和状态;PhreeQC反向水文地球化学模拟结果显示在水流模拟路径上主要发生了钙蒙脱石、钾长石溶解和高岭石、石英、钠长石的沉淀,以及Ca-Na₂之间的阳离子交换吸附作用;离子相关性和主成分分析进一步的验证了溶滤作用、蒸发浓缩作用和阳离子交换吸附作用是引起浅层地下水水化学过程和矿物组成改变的主要原因。研究区地下水水质总体不会对人体健康造成不良影响。     

Chemical evolution of groundwater in the River Danube deposits in the southern part of the Pannonian Basin (Hungary)

Processes controlling the groundwater chemical composition were studied in the River Danube deposits, in the southeastern part of Hungary. PHREEQM, a combined geochemical and one-dimensional transport model and PHREEQE, NETPATH and WATEQF geochemical computer codes were used to simulate these processes. The main processes controlling water chemistry are equilibrium with calcite, undersaturation in dolomite and albite weathering in the recharge area, ion exchange along the flow path, and ion exchange and mixing with old water at the end of the flow path. Ion exchange seems to be the most important process controlling groundwater chemistry along the flowpath in the fluvial sediments studied. Isotopic data support the geochemical model. The groundwater ages, adjusted for the modeled C mass transfer range from 3300 to 20 200 a B.P. Cation exchange suggests that displacement of a former aqueous solution by the present groundwater occurred. This displacement is attributed to tectonic and paleoclimatic events at the end of the Pleistocene.     

Characterisation of groundwater chemistry in an eastern coastal area of Cuddalore district,Tamil Nadu

The groundwater quality detoriation due to various geochemical processes like saline water intrusion, evaporation and interaction of groundwater with brines is a serious problem in coastal environments. Understanding the geochemical evolution is important for sustainable development of water resources. A detailed investigation was carried out to evaluate the geochemical processes regulating groundwater quality in Cuddalore district of Tamilnadu, India. The area is entirely underlined by sedimentary formations, which include sandstone, clay, alluvium, and small patches of laterite soils of tertiary and quaternary age. Groundwater samples were collected from the study area and analyzed for major ions. The electrical conductivity (EC) value ranged from 962 to 11,824 μS/cm, with a mean of 2802 μS/cm. The hydrogeochemical evolution of groundwater in the study area starts from Mg-HCO₃ type to Na-Cl type indicating the cation exchange reaction along with seawater intrusion. The Br/Cl ratio indicates the evaporation source for the ion. The Na/Cl ratios indicate groundwater is probably controlled by water-rock interaction, most likely by derived from the weathering of calcium-magnesium silicates. The plot of (Ca+Mg) versus HCO₃ suggests ions derived from sediment weathering. The plot of Na+K over Cl reflects silicate weathering along with precipitation. Gibbs plot indicates the dominant control of rock weathering. Factor analysis indicates dominance of salt water intrusion, cation-exchange and anthropogenic phenomenon in the study.     

Evaluation of hydrogeochemical characteristics of groundwater in parts of the lower Benue Trough, Nigeria

The aim of this work is to evaluate the hydrogeochemical characteristics of groundwater in parts of the lower Benue Through in Nigeria as well as to evaluate the variation in groundwater chemistry data and the suitability of the groundwater for drinking and other domestic purposes. This was based on chemical analyses of 44 water samples from existing wells and boreholes in the study area. From the statistical analysis (wide ranges, median and standard deviation), it is obvious that there are significant variations in the quality/composition of groundwater in the period of sampling. The calculated SAR, Na% and RSC values indicated that the water is of excellent to good quality and is suitable for irrigation. Na and HCO₃ are dominant with respect to the chemical composition of the groundwater. On the basis of water chemistry, hydrochemical indices and factor analysis the dominant controls or processes affecting the distribution of geochemical variables in the study area have been shown to be water/rock interaction which is mainly controlled by carbonate and silicate dissolution as well as anthropogenic influence to a lesser extent. Additional processes include cation exchange reactions and reverse ion exchange to a minor extent.     

Isotope hydrogeochemical models for assessing the hydrological processes in a part of the largest continental flood basalts province of India

Continental Flood Basalts (CFB) occupy one fourth of the world’s land area. Hence, it is important to discern the hydrological processes in this complex hydrogeological setup for the sustainable water resources development. A model assisted isotope, geochemical, geospatial and geophysical study was conducted to understand the monsoonal characteristics, recharge processes, renewability and geochemical evolution in one of the largest continental flood basalt provinces of India. HYSPLIT modelling and stable isotopes were used to assess the monsoonal characteristics. Rayleigh distillation model were used to understand the climatic conditions at the time of groundwater recharge. Lumped parameter models (LPM) were employed to quantify the mean transit time (MTT) of groundwater. Statistical and geochemical models were adopted to understand the geochemical evolution along the groundwater flow path. A geophysical model was used to understand the geometry of the aquifer. The back trajectory analysis confirms the isotopic finding that precipitation in this region is caused by orographic uplifting of air masses originating from the Arabian Sea. Stable isotopic data of groundwater showed its meteoric origin and two recharge processes were discerned; (i) quick and direct recharge by precipitation through fractured and weathered basalt, (ii) low infiltration through the clayey black cotton soil and subjected to evaporation prior to the recharge. Tritium data showed that the groundwater is a renewable source and have shorter transit times (from present day to <30 years). The hydrogeochemical study indicated multiple sources/processes such as: the minerals dissolution, silicate weathering, ion exchange, anthropogenic influences etc. control the chemistry of the groundwater. Based on the geo-electrical resistivity survey, the potential zones (weathered and fractured) were delineated for the groundwater development. Thus, the study highlights the usefulness of model assisted isotopic hydrogeochemical techniques for understanding the recharge and geochemical processes in a basaltic aquifer system.