Geochemical evolution and tracing of groundwater salinization using different ionic ratios, multivariate statistical and geochemical modeling approaches in a typical semi-arid basin

Delineation of groundwater potential zones and its extent of contamination from the hard rock aquifers in west-Bengal, India

This study evaluates the groundwater potential and quality in the parts of Chhotanagpur Gneissic Complex situated in the East Indian Shield. The region has faced groundwater development challenges for several decades. Therefore, in the study area, it is crucial to address the depletion of both groundwater quality and quantity, as this facilitates the identification of potential uncontaminated groundwater zones. The present study interprets the groundwater potential zones (GWPZ) utilizing an analytical hierarchical process (AHP) integrated with hydrogeochemical analysis. Several thematic maps were prepared to delineate the GPWZ. It has been found that ∼0.6% of the study area has a very good potential zone, 14.4% has good, 52% has moderate, and approximately 32% and 0.9% have low to very low prospective groundwater resources, respectively. The authentication of results was found to be excellent (91.4%) with the Area Under Curve (AUC). Analysis of hydrogeochemical data suggests that Mixed Ca-Na-HCO3, Mixed Ca-Mg-Cl, Ca-HCO3, and Na-Cl are the dominant water types in the study area. The principal component analysis suggests that Na+, Mg2+, Cl-, NO3-, and SO42- significantly contribute to groundwater chemistry. The K-means clustering and hierarchical cluster analysis classified groundwater samples into three clusters based on the hydrogeochemical characteristics. It is inferred that silicate weathering and reverse ion reactions through rock-water interaction control geogenic processes for groundwater chemistry. It is also inferred that regions with poor to unsuitable water quality indexes also have low GWPZ. Further, groundwater for irrigation is also accessed and found unsuitable at some locations. This research contributes to comprehending groundwater characteristics in analogous geological regions globally. Additionally, it assists in implementing preventive actions to mitigate groundwater contamination, consequently lowering health risks and formulating sustainable plans for the future.

Anthropogenic processes drive spatiotemporal variability of sulfate in groundwater from a multi-aquifer system: Dilution caused by mine drainage

The water quality evolution of surface and groundwater caused by mining activities and mine drainage is a grave public concern worldwide. To explore the effect of mine drainage on sulfate evolution, a multi-aquifer system in a typical coal mine in Northwest China was investigated using multi-isotopes (δ34SSO4, δ18OSO4, δD, and δ18Owater) and Positive Matrix Factorization (PMF) model. Before mining, the Jurassic aquifer was dominated by gypsum dissolution, accompanied by cation exchange and bacterial sulfate reduction, and the phreatic aquifers and surface water were dominated by carbonate dissolution. Significant increase in sulfate in phreatic aquifers due to mine drainage during the early stages of coal mining. However, in contrast to common mining activities that result in sulfate contamination from pyrite oxidation, mine drainage in this mining area resulted in accelerated groundwater flow and enhanced hydraulic connections between the phreatic and confined aquifers. Dilution caused by the altered groundwater flow system controlled the evolution of sulphate, leading to different degrees of sulfate decrease in all aquifers and surface water. As the hydrogeochemical characteristic of Jurassic aquifer evolved toward phreatic aquifer, this factor should be considered to avoid misjudgment in determining the source of mine water intrusion. The study reveals the hydrogeochemical evolution induced by mine drainage, which could benefit to the management of groundwater resources in mining areas.

Identification of groundwater pollution sources and health risk assessment in the Fengshui mining area of Central Shandong, China

The crux of groundwater protection lies in a profound understanding of the sources of pollutants and their impacts on human health. This study selected 47 groundwater samples from the Fengshui mining area in central Shandong Province, China, employing advanced hydrogeochemical techniques, positive matrix factorization (PMF), and Monte Carlo analysis methods, aimed at unveiling the characteristics, origins, and health risks of water pollutants. The results indicated that the majority of samples exhibited a slightly alkaline nature. Notably, the concentrations of fluoride (F-) and nitrate (NO3-) exceeded China's safety standards in 40.43% and 23.40% of the samples, respectively. Moreover, a water quality index (WQI) below 50 was observed in approximately 68.09% of the sites, suggesting that the water quality in these areas generally met acceptable levels. However, regions with higher WQI values were predominantly located in the northern and southern parts of the mining area. PMF analysis revealed that regional geological and industrial activities were the primary factors affecting water quality, followed by mining discharges, fundamental geological and agricultural processes, and leachate enrichment activities. The health risk assessment highlighted the heightened sensitivity of the youth demographic to fluoride, with a more pronounced non-carcinogenic risk compared to nitrate, affecting about 31.89% of the youth population. Hence, it is imperative for local authorities and relevant departments to take prompt actions to remediate groundwater contamination to minimize public health risks.

FlowSOM clustering - A novel pattern recognition approach for water research: Application to a hyper-arid coastal aquifer system

Monitoring and understanding of water resources have become essential in designing effective and sustainable management strategies to overcome the growing water quality challenges. In this context, the utilization of unsupervised learning techniques for evaluating environmental tracers has facilitated the exploration of sources and dynamics of groundwater systems through pattern recognition. However, conventional techniques may overlook spatial and temporal non-linearities present in water research data. This paper introduces the adaptation of FlowSOM, a pioneering approach that combines self-organizing maps (SOM) and minimal spanning trees (MST), with the fast-greedy network clustering algorithm to unravel intricate relationships within multivariate water quality datasets. By capturing connections within the data, this ensemble tool enhances clustering and pattern recognition. Applied to the complex water quality context of the hyper-arid transboundary Caplina/Concordia coastal aquifer system (Peru/Chile), the FlowSOM network and clustering yielded compelling results in pattern recognition of the aquifer salinization. Analyzing 143 groundwater samples across eight variables, including major ions, the approach supports the identification of distinct clusters and connections between them. Three primary sources of salinization were identified: river percolation, slow lateral aquitard recharge, and seawater intrusion. The analysis demonstrated the superiority of FlowSOM clustering over traditional techniques in the case study, producing clusters that align more closely with the actual hydrogeochemical pattern. The outcomes broaden the utilization of multivariate analysis in water research, presenting a comprehensive approach to support the understanding of groundwater systems.

Identifying susceptible groundwater contamination zones in western Odisha of India using hydro-geochemical and geospatial approaches

Nuapada is one of the most drought-affected and fluoride-contaminated districts in Odisha, India. The presence of various dissolved substances, evapotranspiration, and lowering water table during pre- and post-monsoon (PRM and POM) seasons are responsible for declining groundwater (GW) quality over the Nuapada region. To comprehend the contaminated GW zones over the Nuapada and Komna blocks of the northern Nuapada district during the seasons, integration of hydrogeochemistry and statistical approaches using GW sample data on a geospatial platform have been done. The analysis exhibits that the major source of groundwater contamination is mostly geogenic with little anthropogenic impact. The cumulative impact of fluoride (F-), iron (Fe2+), and nitrate (NO₃-) contents are noticed in great-depth zones of the water table in the north and south parts of Nuapada and Komna blocks, respectively. The dominant hydro facies, such as Na-Cl (41.77%) and Ca-Cl (25.31%) types exist over both blocks during PRM and POM seasons, respectively. Demarcation of contaminant and susceptible zones over the study area using geospatial analysis and groundwater quality indices (GWQI) were done. About 3% of the total area, in the north and middle parts of the Nuapada and Komna blocks, falls under contamination zones and is unfit for drinking purposes, and about 35% of the region is susceptible to future contamination. The outcome of the result analysis will enhance the scope for researchers, policymakers, and water managers to regulate emerging health, agricultural, and industrial issues in the stressed aquifer system in India and the world.

Groundwater heavy metal(loid)s risk prediction based on topsoil contamination and aquifer vulnerability at a zinc smelting site

Groundwater pollution is a recurrent problem in abandoned non-ferrous metal smelting sites, and its severity is influenced by topsoil contamination, hydrogeological characteristics, and hydrogeochemical conditions. In such unique areas, traditional methods for evaluating groundwater pollution risk are biased, as the long production history of these sites have led to highly polluted and heterogeneous soil and groundwater. Herein, based on a typical lead-zinc smelting site, As, Pb, Zn, Cd, Mn, and Ni were found to be the predominant heavy metal (loid)s in groundwater, with respective exceedance rates of 44.4%, 50.0%, 72.2%, 88.9%, 88.9%, and 61.1%. Combined with the groundwater pollution characteristics, the representative hydrogeochemical factors were screened out to optimize the following aquifer vulnerability evaluation using the AHP-DRASTICH method. A comprehensive evaluation model (DI-NCPI) for groundwater pollution risk was established by combining the DRASTICH index (DI) obtained after optimization and the Nemerow comprehensive contamination index (NCPI) of topsoil. The fit between DI-NCPI and groundwater heavy metal (loid) pollution index reached 0.956, which laterally confirms that the model has some reference value. In terms of distribution, the high-risk and very high-risk zones were mainly concentrated in the zinc smelting system, located in the southeastern and central-western parts of the site. These areas have relatively high levels of topsoil contamination and aquifer vulnerability and require focused attention in site remediation. This research highlights the importance of combining topsoil contamination and aquifer vulnerability to evaluate groundwater pollution risk in smelting areas. It provides a more targeted reference for groundwater remediation strategies in abandoned smelting sites, as well as severely polluted industrial areas.

Spatio-temporal variability of seawater mixing in the coastal aquifers based on hydrogeochemical fingerprinting and statistical modeling

This study discusses monitoring and characterization of spatial and temporal variability to comprehend groundwater salinization based on hydrogeochemical fingerprinting and statistical modeling in the coastal belt of Digha-Shankarpur-Tajpur-Mandarmani, West Bengal, India. An integrated study of hydrogeochemical, bulk magnetic susceptibility, multivariate statistical, and geochemical modeling methods is implemented. The major cationic and anionic concentrations in groundwater are in the order Na+ > Ca2+ > Mg2+ > K+ and Cl- > HCO3- > SO4- > NO3- > F- respectively. The major water types are dominated by (Ca2+ - HCO3-) followed (Ca2+ - Mg2+ - Cl-), (Ca2+ - Na+ - HCO3-), (Na+ - HCO3-), and (Na+ - Cl). The results showed that the groundwater quality continuously declined steadily from pre-monsoon 2020 to pre-monsoon 2022. The deterioration of groundwater is due to an interplay of multiple factors, i.e., water-rock interaction, including ion-exchange, seawater mixing, and anthropogenic actions. Furthermore, it is also found that the regions showing higher seawater mixing index and oversaturated with carbonate minerals are also areas where groundwater is unsuitable for irrigation. The findings are beneficial in assisting local communities and legislators in designing appropriate management and mitigation techniques to arrest seawater intrusion in coastal regions.

Hydrogeochemical evolution of groundwater impacted by acid mine drainage (AMD) from polymetallic mining areas (South China)

Mining activities have long-term impacts on the groundwater of surrounding areas and deserve in-depth analysis and study. Herein, the geochemical mechanisms of acid mine drainage (AMD)-affected groundwaters were examined, and groundwater quality was assessed through water quality indices. 15 water samples from 7 domestic and 4 groundwater monitoring wells were tested for physical and chemical parameters in 2022, and multivariate statistical analysis was carried out with monitoring data from 21 domestic wells in 2010. The groundwater chemical composition varied from a predominantly Ca-HCO3 type in 2010 to a Ca-SO4 type in 2022. The isotopic values of δ18O and δD indicate that groundwater has not been significantly affected by evaporation. Changes in groundwater sulfate and total dissolved solids (TDS) levels over the twelve-year period confirmed the AMD infiltration impact on groundwater quality. The groundwater chemical properties changed more slowly than those of surface waters affected by AMD based on a cumulative increase in sulfate concentration of 29.94 mg/L. Changes in groundwater quality were investigated, namely, the spatiotemporal distribution of potentially toxic elements (PTEs), including Fe, Mn, Cd, Pb, and As. Mn concentrations in upstream groundwater areas near the mine decreased by 61.8% between 2010 and 2022. Conversely, groundwater in midstream areas had Mn concentrations of 2.25 mg/L and arsenic concentrations of 11.8 μg/L, both exceeding the WHO, 2022 standard. According to multivariate statistical analysis, Mn, Cd, and Pb originated from polymetallic minerals, whereas As was likely derived from the reduction of Fe/Mn hydroxyl oxides. AMD remediation improved contaminated upstream groundwater quality over 12 years, with a 36.8% improvement in WQI values. PTE distribution determined water quality changes; therefore, PTE contamination should be treated in mid- and downstream regions while contaminated groundwater should be treated upstream.

Using stable isotopes (δ2H and δ18O) and hydrochemistry to understand the genesis and hydrochemical processes of groundwater in Chongming Island, Yangtze Estuary

Groundwater is an indispensable freshwater resource and its quality is significant in supporting sustainable social and economic development, particularly in estuarine islands where aquifers are complicated. In this study, a total of 19 groundwater and 4 surface water samples were collected in September 2022 to identify the origin and hydrogeochemical evolution processes of groundwater using stable isotopes and hydrochemistry in Chongming Island, which is the largest estuarine alluvial island in the world. The stable isotopic composition indicated that shallow groundwater and surface water are all derived from precipitation recharge under a humid climate, and the evaporative effect incurs the enrichment of isotopic compositions. The shallow groundwater and surface water were primarily of Ca-HCO₃ type. Gibbs diagram, ionic correlation analysis, ionic ratios analysis, and mineral saturation indices suggested that water-rock interactions like carbonate and silicate weathering play a vital role in groundwater chemistry, but cation exchange reactions are weak. Revelle index (RI) result indicated that 10.5% of shallow groundwater samples were found to suffer seawater intrusion. The NO₃^- concentrations were between l2.0 and 180.8 mg/L with 31.6% of groundwater samples exceeding the World health organization (WHO) standards (50 mg/L). Agricultural activities and industrial activities were found to be mainly responsible for groundwater pollution in shallow groundwater. The findings of this study provide a scientific basis for better managing groundwater resources on coastal estuarine islands.

Surface water quality for irrigation and industrial purposes: a comparison between the south and north sides of the Wei River Plain (northwest China)

Surface water is extensively used for irrigation and industrial purposes in the Wei River Plain. However, the surface water shows different characteristics in the southern and northern zones of the Wei River Plain. This study aims to investigate the differences in surface water quality between the southern and northern zones of the Wei River Plain and their influencing factors. To ascertain the hydrochemistry and its governing factors, graphical methods, ion plots, and multivariate statistical analyses were employed. The quality of the irrigation water was assessed using various irrigation water quality indices. In addition, water foaming, corrosion, scaling, and incrustation risks were determined to evaluate water quality for industrial uses. The spatial distribution of water quality was done using GIS models. This research revealed that the concentrations of EC, TH, TDS, HCO₃^-, Na⁺, Mg²⁺, SO₄^2- and Cl^- on the north side of the plain were twice as high as those on the south side. On both sides of the Wei River Plain, water‒rock interactions, ion exchange, and considerable evaporation were observed. Gypsum, halite, calcite, and dolomite all dissolve to produce significant anions and cations in the water, according to ion correlation analysis. However, additional sources of contaminants led to higher concentrations in the surface water on the north side than on the south side. Surface water in the south of the Wei River Plain has superior quality to that in the north, according to the overall findings of irrigation water and industrial water quality assessments. The findings of this study will boost better water resource management policies for the plain.

Appraisal of groundwater quality with WQI and human health risk assessment in Karamık wetland and surroundings (Afyonkarahisar/Turkey)

Groundwater in Karamık wetland and surroundings, which is one of the important wetlands in Turkey, was examined and the chemical properties and quality of groundwater were determined in the present study. In addition, the possible risks to human health as a result of groundwater usage were investigated along with spatial analyses carried out using Geographic Information Systems (GIS). Physicochemical analyses were carried out on 25 samples taken from groundwater. The dominant ions in the study area are Ca, Mg, and HCO₃. When the results are compared with the limit values in the valid drinking water guidelines such as TSI-266 (Standards for drinking waters, 2005) and WHO (Guidelines for drinking-water quality, 2011), the groundwaters were not suitable for use as drinking water in terms of NO₃, Fe, Pb and As. The analysis results were evaluated together with GIS and Water Quality Index (WQI) methods. In the evaluations with the WQI method, 76% of the samples were in the "poor water" class. The groundwater in the study area is polluted by both geogenic and anthropogenic sources. For this reason, health risk assessment was performed due to the use of groundwater in the region by the local people in different areas, especially as drinking water, and the negative effects of water quality. Accordingly, there are non-carcinogenic negative effects on health in terms of NO₃, As, Pb and Fe parameters from the use of groundwater by children. In addition, Pb and As concentrations are at carcinogenic levels for both children and adults in all groundwater samples collected from the study area. Therefore, it is not recommended to use groundwater as drinking water without treatment.

Groundwater quality for irrigation in an arid region-application of fuzzy logic techniques

Groundwater is the main source to answer the irrigation supply in several arid and semi-arid areas. In the present work, groundwater quality for irrigation purposes in the arid region of Menzel Habib (Tunisia) for thirty-six groundwater samples is assessed considering the application of different conventional water quality indicators, particularly, electrical conductivity (EC), sodium absorption ratio (SAR), soluble sodium percentage (SSP), magnesium adsorption ratio (MAR), Kelly ratio (KR), and permeability index (PI). The results obtained indicate a variability for EC: 3.06 to 14.98 mS.cm^-1; SAR: 4.08 to 19.30; SSP: 35.78 to 71.53%; MAR: 34.19 to 56.01; PI: 38.47 to 72.74; and KR: 0.56 to 2.47. These results suggest that groundwater from Menzel Habib aquifer system is classified between excellent to unsuitable according to the applied water quality indices. Furthermore, the groundwater samples are also plotted in the Richards diagram classification system, based on the relation between SAR and EC, suggesting that almost groundwater samples present a harmful quality. Moreover, fuzzy logic model has been proposed and created to assess groundwater quality for irrigation. The membership functions are constructed for six significant parameters such as EC, SAR, SSP, MAR, KR, and PI and the rules are, then, fired to get a simple Fuzzy Irrigation Water Quality Index (FIWQI). The obtained groundwater quality results suggest that 3% of the samples from Menzel Habib region are considered as "good" for irrigation, 3% are classified as "good to permissible", 33% with a "permissible" quality, 36% "permissible to unsuitable", while 25% of groundwater present an "unsuitable" quality. Thus, the use of fuzzy logic techniques has more reliable and robust results by overcoming the uncertainties in the decision-making attributed to the conventional methods by the creation of new classes (excellent to good, good to permissible, and permissible to unsuitable) in addition to the classes proposed by Richards diagram classification (excellent, good, permissible, and unsuitable) to assess the groundwater quality suitability for irrigation purposes.

Identifying the geochemical evolution and controlling factors of the shallow groundwater in a high fluoride area, Feng County, China

Understanding how groundwater is formed and evolves is critical for water resource exploitation and utilization. In this study, hydrochemistry and stable isotope tracing techniques were adopted to determine the key factors influencing groundwater chemical evolution in Feng County. A total of fourteen wells and five surface water samples were investigated in November 2021. The δD and δ¹⁸O compositions show that both surface water and groundwater are recharged from atmospheric precipitation. The dominating order of cations and anions in groundwater appears to be Na⁺ > Mg²⁺ > Ca²⁺ > K⁺ and HCO₃^- > SO₄^2- > Cl^- > NO₃^- > F^-, respectively. The groundwater hydrochemical facies are mainly characterized by HCO₃-Ca-Mg and SO₄-Cl-Na types. The chemical evolution of groundwater is dominated by water-rock interaction and cation exchange reactions. The major ions in groundwater are mainly controlled by various geogenic processes including halite, gypsum, calcite, dolomite, Glauber's salt, feldspar, and fluorite dissolution/precipitation. Furthermore, the abundant fluoride-bearing sediments, together with low Ca²⁺, promote the formation of high F^- groundwater. Approximately 85.7% and 28.6% of groundwater samples exceeded the permissible limit for F^- and NO₃^- respectively. Apart from geogenic F^-, human interventions (i.e., industrial fluoride-containing wastewater discharge and agricultural phosphate fertilizer uses) also regulate the F^- enrichment in the shallow groundwater. Nitrate pollution of the groundwater may be attributed to domestic waste and animal feces. Our findings could provide valuable information for the sustainable exploitation of groundwater in the study area and the development of effective management strategies by the authorities.

Geophysical investigation for seawater intrusion in the high-quality coastal aquifers of India: a review

Around the globe, seawater intrusion in the coastal aquifer is a significant problem. Excessive groundwater extraction because of population growth, industrialization, tourism, and other anthropogenic activities and geogenic processes initiates and accelerates this problem. The contaminated groundwater impacts the health, economic activities, and social and cultural development of coastal regions. This work aims to explore the current status and a holistic comprehending review of geophysical studies applied to delineate the seawater intrusion in the high-quality coastal aquifers in India, as well as its origin and causes, mitigation strategies, and recent advancements in geophysical techniques to access the qualitative and quantitative properties of the complex aquifer system. In the future, it is recommended to do a detailed subsurface imaging of the entire coastal belt of India to decipher the lateral and vertical variation of the lithological conditions and seawater intrusion in space and time with improved/advanced geophysical techniques, which can lead toward sustainable development.

Hydrogeochemical evolution and assessment of groundwater quality for drinking and irrigation purposes in the Gushegu Municipality and some parts of East Mamprusi District, Ghana

The Gushegu Municipality and the East Mamprusi District in Ghana are dominated by the Oti/Pendjari Group within the Voltaian Supergroup. The major rock types found in the area are quartzites, siltstones, conglomerates, and shales with minor occurrences of tillites, silexites, limestones, and barite-rich dolomites. The inhabitants of the area are mainly peasant farmers, and their activities might be influencing the groundwater chemistry, but little is known about the quality of the groundwater. Therefore, this study evaluated the suitability of groundwater resources in the Gushegu Municipality, and some parts of the East Mamprusi District in Ghana for domestic and irrigation uses, employing hydrogeochemical graphing, geochemical modelling, multivariate statistical analysis, and computation of water quality indices. Sodium (Na⁺), with concentrations ranging from 4.93 to 323 mg/L and a mean of 169 mg/L, is found to be the major cation in the groundwater, while bicarbonate (HCO₃^-), with concentrations ranging from 19.9 to 685 mg/L and a mean of 397 mg/L, is the major anion in the area. The dominant hydrochemical facies is the Na-HCO3 type, accounting for about 72.7% of the study area's groundwater and is influenced by silicate weathering, carbonate mineral dissolution, and ion exchange reactions. Other factors accounting for this dominance may be anthropogenic activities, including the dissolution and leaching of fertilizers from farmlands. Overall, this study reveals that the groundwater in the area is suitable for drinking based on the WQI classification. There are localized contaminations with respect to B and F^-, making the water in those areas unsuitable for drinking. Also, the groundwater in the area is unsuitable for irrigation purposes due to the high Na% values (43 to 99% with a mean of 86%), magnesium hazard values (1 to 312 with a mean of 88), and sodium adsorption ratio (0.57 to 42.4 with a mean of 12.7). All these indices exceed their respective standards for irrigation purposes.

Salinization of groundwater during 20 years of agricultural irrigation, Luxor, Egypt

Groundwater salinization is a global problem accounting for 11-30% of the world's irrigated areas. Luxor region in Upper Egypt is one of such areas affected by salinity. Multivariate statistics indicate that groundwater is affected by intermixed processes; mineralization (salinization), fertilization, domestic wastes, and meteoric recharge. Temporal change in salinity and hydrochemical facies during 1997-2017 revealed aquifer salinization, due to the dissolution of salts from overlain saline soil and marine deposits underneath as well as up-coning of deep saline water. Increasing salinity over time was statistically documented, exhibited temporally high significant differences (P < 0.05), where salinization consumed a quarter of the aquifer during 20 years. Evolution of water facies from less mineralized Ca-Cl, Mg-Cl to highly mineralized Na-Cl species explains the salinization process over time. Elevated content of Na and Cl is associated with the dissolution of marine sediments and saltwater intrusion. The shift from silicate weathering into evaporation dominance confirmed the saltwater intrusion. As a result, groundwater has a high degree of salinity, is not suitable for domestic and other uses. On other hand, fertilization and domestic sewage are probably responsible for the high NO₃^- and Cd content. Over 80% of Cd exists in mobile species facilitates Cd-plant uptake indicating an alarming environmental situation. Cd mobility is closely related to elevated salinity and chlorinity, allowing competition with major ions and forming of soluble complexes. The present approach will improve the uncertainties of environmental interpretation, as an initial step for aquifers management in reclaimed lands.

Insight into the Process and Mechanism of Water-Rock Interaction in Underground Coal Mine Reservoirs Based on Indoor Static Simulation Experiments

During the storage of underground water reservoirs in coal mines, water-rock interaction occurred between mine water and collapsed rocks, resulting in improved mine water quality, but the water-rock process and mechanism have not been clarified. In this study, six sets of simulated experiments were designed to investigate the water-rock interaction between two types of roof collapse rocks and different water samples in the Daliuta coal mine. The ion ratio method and multivariate statistics are used to reveal the process and mechanism of water-rock interaction during the experimental process from the perspective of input and output water chemical characteristics and rock properties, respectively. The results show that the ion concentration of the effluent water is controlled by water-rock interaction, and the water-rock process mainly involves the dissolution of halite, silicate, pyrite, calcite, dolomite, magnesia chlorite, and gypsum precipitation and is accompanied by ion exchange. Mineral dissolution and precipitation are the most important factors affecting the ion abundance in the effluent. There are differences in the reaction rate, degree of reaction, and dissolution process during the experimental process of fine sandstone and mudstone. Fine sandstone is more reactive than mudstone in terms of reaction rate and degree of reaction, and fine sandstone is dissolved from surface pores to inside and around, while mudstone is generated in new dissolved pores. We found that rock type, ion concentration in the input water, and rock reaction period influence the water-rock interaction during the experiment. The results provide a reference for clarifying the water-rock interaction during the storage of underground water reservoirs in coal mines and predicting the water quality of the effluent.

Hydrogeochemical assessment of carcinogenic and non-carcinogenic health risks of potentially toxic elements in aquifers of the Hindukush ranges, Pakistan: insights from groundwater pollution indexing, GIS-based, and multivariate statistical approaches

Globally, potentially toxic elements (PTEs) and bacterial contamination pose health hazards, persistency, and genotoxicity in the groundwater aquifer. This study evaluates PTE concentration, carcinogenic and noncarcinogenic health hazards, groundwater quality indexing (GWQI-model), source provenance, and fate distribution in the groundwater of Hindukush ranges, Pakistan. The new estimates of USEPA equations record new research dimensions for carcinogenic and noncarcinogenic hazards. The principal component analysis (PCA), mineral phases, and spatial distribution determine groundwater contamination and its impacts. The average concentrations of PTEs, viz., Cd, Cu, Co, Fe, Pb, and Zn, were 0.06, 0.27, 0.07, 0.55, 0.05, and 0.19 mg/L, and E. coli, F. coli, and P. coli were 27.5, 24.0, and 19.0 CFU/100 ml. Moreover, the average values of basic minerals, viz., anhydrite, aragonite, calcite, dolomite, gypsum, halite, and hydroxyl apatite, were 0.4, 2.4, 2.6, 5.1, 0.6, and - 4.0, 11.2, and PTE minerals like monteponite, tenorite, cuprite, cuprous ferrite, cupric ferrite, ferrihydrite, goethite, hematite, lepidocrocite, maghemite, magnetite, massicot, minium, litharge, plattnerite, and zincite were - 5.5, 2.23, 4.65, 18.56, 20.0, 4.84, 7.54, 17.46, 6.66, 9.67, 22.72, - 3.36, 22.9, 3.16, - 18.0, and 1.46. The groundwater showed carcinogenic and non-carcinogenic health hazards for children and adults. The GWQI-model showed that 58.3% of samples revealed worse water quality. PCA revealed rock weathering, mineral dissolution, water-rock interaction, and industrial effluents as the dominant factors influencing groundwater chemistry. Carbonate weathering and ion exchange play vital roles in altering CaHCO3 type to NaHCO3 water. In this study, E. coli, F. coli, P. coli, EC, turbidity, TSS, PO43─, Na+, Mg+2, Ca+2, Cd, Co, Fe, and Pb have exceeded the World Health Organization (WHO) guidelines. The carcinogenic and non-carcinogenic impacts of PTEs and bacterial contamination declared that the groundwater is unfit for drinking and domestic purposes.

Fluoride enrichment mechanisms and related health risks of groundwater in the transition zone of geomorphic units, northern China

Although groundwater is the primary drinking water source in northern of China, little is known about generation mechanisms and related health risks of high fluoride groundwater at the geomorphic transition zones. Thus, 419 groundwater samples were collected from Zhangjiakou region, where is a typically geomorphic transition zone of the North China Plain and the Inner Mongolia Plateau, to conduct the hydrochemical analysis, geochemical modeling, multivariate statistical analysis, and health risks assessment. From the results, F^- concentration in groundwater had a range of 0.05-9.71 mg L^-1. About 37.1% and 26.2% of groundwater samples from Bashang region (BSR) and Baxia region (BXR), respectively, were over the 1.50 mg L^-1, which were mainly distributed in the groundwater flow retardation area and/or evaporation discharge area. Thermodynamic simulations demonstrated that F-bearing minerals dissolution and Ca²⁺/Mg²⁺ removal via calcite/dolomite precipitation primarily governed high-F^- groundwater formation in the whole study area. Competitive adsorption, evaporation, evaporites dissolution and salt-effect also affected F^- enrichment in BSR. Desorption in alkaline environment, ion exchange and human activities played a vital role in F^- enrichment at BXR. The multivariate statistical analysis revealed that the origin of F^- contamination was geogenic in BSR; whereas, it was geogenic and anthropogenic in BXR. Besides, more than 71.8%, 51.0%, 36.1% and 25.5% of the study area exceeded the acceptable level (health index>1) for infants, children, adult males, and females, respectively. The health risks for different groups of people varied significantly and ranked: infants > children > males > females, suggesting that younger people were more susceptible to fluoride contamination. Meanwhile, females were more resistant to fluoride contamination than males. These findings are vital to providing insights on high-F^- groundwater formation, investigate the situation of health risks, and conduct the integrated management for high fluoride groundwater in geomorphic transition zones at northern China.

Genesis of high hexavalent chromium groundwater in deep aquifers from loess plateau of Northern Shaanxi, China

Hexavalent chromium (Cr(VI)) groundwater usually exists in shallow aquifers related to ultramafic and serpentine formations, but knowledge of the genesis of dissolved Cr(VI) in deep sandstone aquifers is limited. Both groundwater and aquifer sediments were taken from the Jingbian County in the Loess Plateau of Northwestern Shaanxi to investigate distribution and genesis mechanism of high Cr(VI) groundwater in deep sandstone aquifers. Results showed that the Cr concentrations (median 142 μg/L) in groundwater from deep aquifers (>100 m) were relatively high, while the Cr concentrations in shallow groundwater were low (median 33.8 μg/L). Dissolved Cr mainly existed in the species of Cr(VI) (average, 90%). Deep groundwater with higher Cr(VI) concentrations generally had higher pH, Eh, and DO than shallow groundwater, indicating that the high Cr(VI) groundwater existed in relatively oxic environment. Cretaceous sandstones in deep aquifers had anomalously high contents of total Cr (average 115 mg/kg), where Cr was mainly present in silicates-bound form, and secondly in strongly adsorbed form. There were positive correlations between Mn and Cr in the unweathered silicate-bound form and adsorbed form, which were conducive to Cr(III) oxidation into Cr(VI) in an alkaline-oxic environment. The different ionic ratios (i.e. (Ca²⁺ + Mg²⁺)/(HCO₃^- + SO₄^2-)) also supported silicate weathering as the dominant rock-water interactions in the deep groundwater, which enhanced the release of the unweathered silicate-bound Cr. Relatively high pH and ionic strength mobilized the adsorbed Cr(VI) into groundwater. This investigation emphasizes the geological origin of high Cr(VI) groundwater in deep sandstone aquifers containing Mn oxides, which deserves more concerns for the purpose of drinking water supply.

Hydrogeochemical evolution and assessment of groundwater quality in the Togo and Dahomeyan aquifers, Greater Accra Region, Ghana

Groundwater quality is generally better than surface water quality but this is not sacrosanct because during recharge and abstraction, groundwater may be subjected to variations due to influence from natural and anthropogenic processes. The Togo and Dahomeyan aquifers are threatened by several anthropogenic activities like dumping of domestic and industrial wastes in open landfill sites. These activities can be sources of groundwater constituents and can pose adverse health effects on humans and the ecosystem but little is known about the hydrogeochemical characteristics of groundwater and its quality in the area. Therefore, the present study is aimed at unravelling the hydrogeochemical characteristics and quality of groundwater in the Togo and Dahomeyan aquifers in the Greater Accra Region of Ghana. A total of 37 groundwater samples were collected and analysed for the concentrations of major ions, minor ions, and trace elements. The results were used to compute water quality parameters like electrical conductivity, sodium adsorption ratio, sodium percent, and magnesium ratio to assess the quality of the water for irrigation purposes. Groundwater shows acidic to slightly alkaline pH and evolved from Mg-Na-HCO₃, Ca-Na-Mg-HCO₃, Na-Ca-Mg-HCO₃-Cl to Na-Mg-Ca-HCO₃ with other mixed water types, which reflect the local geology. Geochemical modelling indicates that groundwater is supersaturated with respect to goethite and hematite and saturated with respect to calcite, aragonite, and dolomite in some samples. Hydrochemical graphing and multivariate statistical analysis indicate that the chemistry of groundwater in the area is primarily controlled by an interplay of chemical weathering, mineral dissolution, ion exchange reactions, agricultural activities, and sewage disposal. The groundwater is not entirely suitable for drinking purposes because of high concentrations of EC, TDS, Na⁺, Cl^-, F^-, Fe, Mn, Pb, Cr, and Ni, which exceed their maximum permissible limits provided by the World Health Organization. The computed parameters for assessing the quality of the water for irrigation reveal that 64.9% of the samples are suitable for irrigation purposes. However, 35.1% of the samples show very high salinity and sodium hazard and thus, are unsuitable for irrigation purposes. Therefore, it is recommended that mixing of the high salinity and sodium water with low salinity and sodium water can improve crop yields.

An Integrated Approach for Deciphering Hydrogeochemical Processes during Seawater Intrusion in Coastal Aquifers

For managing the freshwater in the worldwide coastal aquifers, it is imperative to understand the hydrogeochemical processes and flow patterns in the mixing freshwater/saltwater zone. The Egyptian Nile Delta aquifer is a typical example. The management of seawater intrusion (SWI) requires detailed investigations of the intrusion wedge and the dynamic processes in the mixing zone. Thus, a multidisciplinary approach was applied based on holistic hydrogeochemical, statistical analysis, and DC resistivity measurements to investigate the lateral and vertical changes in groundwater characteristics undergoing salinization stressor. The results of cross plots and ionic deviations of major ions, hydrochemical facies evolution diagram (HFE-D), and seawater mixing index (SMI) were integrated with the resistivity results to show the status of the SWI where the intrusion phase predominates in ~2/3 of the study are (~70 km radius) and the compositional thresholds of Na, Mg, Cl, and SO4 are 600, 145, 1200, and 600 mg/L, respectively, indicating that the wells with higher concentrations than these thresholds are affected by SWI. Moreover, the results demonstrate the efficiency of combining hydrogeochemical facies from heatmap and resistivity investigations to provide a large-scale characterization of natural and anthropogenic activities controlling aquifer salinization to support decision-makers for the long-term management of coastal groundwater.

Integrating magnetic susceptibility, hydrogeochemical, and isotopic data to assess the seawater invasion in coastal aquifers of Digha, West Bengal, India

Seawater intrusion in coastal aquifers is a major concern due to geogenic and anthropogenic activities leading to declining groundwater quality. The present study focuses on deciphering the sea water intruded zones and its extent in the Quaternary alluvial aquifer system in the coastal belt of Digha, West Bengal, India. In this study, 36 groundwater samples were collected during pre-monsoon (2020). Subsequently, an integrated approach of hydrogeological, hydrogeochemistry, bulk magnetic susceptibility, isotopic, multivariate statistical, and geochemical modeling is adopted. Spatial distribution maps of hydrological parameters (salinity, conductivity, TDS) and major ion concentration (Na+, K+, Ca2+, Mg2+, Cl-, SO42-, F-, and Br-) suggest that the northern, south-west, and eastern parts of the study area are largely affected by saltwater intrusion and are corroborated with seawater mixing index (SMI). Based on sodium adsorption ratio (SAR), sodium percentage (Na%), and Permeability index (PI) distribution maps, the same locations are identified under critical condition for the suitability of groundwater for irrigation. The order of concentration of cations and anions in the water samples are Na+  > Ca2+  > Mg2+  > K+ and HCO3-  > SO4-  > Cl-  > Br-  > F- respectively. Piper diagram shows three principal hydrochemical water types with water composition changes from fresh (86%) to saline water mix (14%). The hydrochemical facies evolution diagram depicts 81% of water samples are in the freshening phase, and 19% are in the intrusion phase. The various bivariate plots revealed that ion exchange, reverse ion exchange, silicate weathering, seawater mixing, and anthropogenic inputs are the governing factors that control groundwater evolution. R-mode factor analysis, principal component analysis (PCA), and agglomerative hierarchical cluster (AHC) also indicate the influence on groundwater from seawater mixing and/or seawater intrusion. The superlativeness of bulk magnetic susceptibility (χ) analysis of water samples in delineating seawater intruded zones is elaborated. Saturation index (SI) shows that groundwater is saturated (> 0) with calcite, dolomite, and aragonite, plausibly due to seawater ingression. Stable isotopic analysis of δ2H (- 53.979 to - 16.9578‰) and δ18O (- 7.00183 to - 1.37 ‰) suggests precipitation recharge/paleo-water at some locations and evaporation enrichment of groundwater. It is recommended to increase groundwater recharge, reduce groundwater extraction at critically affected locations, and have regular monitoring and management to control seawater intrusion.

Recharge and Geochemical Evolution of Groundwater in Fractured Basement Aquifers (NW India): Insights from Environmental Isotopes (δ18O, δ2H, and 3H) and Hydrogeochemical Studies

Considering water as a limiting factor for socio-economic development, especially in arid/semi-arid regions, both scientific communities and policymakers are interested in groundwater recharge-related data. India is fast moving toward a crisis of groundwater due to intense abstraction and contamination. There is a lack of understanding regarding the occurrence, movement, and behaviors of groundwater in a fractured basement terrane. Therefore, integrated environmental isotopes (δ18O, δ2H, and 3H) and hydrogeochemical studies have been used to understand the recharge processes and geochemical evolution of groundwater in the fractured basement terranes of Gujarat, NW India. Our results show that the relative abundance of major cations and anions in the study basin are Ca2+ > Na+ > Mg2+ > K+ and HCO3− > Cl− > SO42− > NO3−, respectively. This suggests that the chemical weathering of silicate minerals influences the groundwater chemistry in the aquifer system. A change in hydrochemical facies from Ca-HCO3 to Na-Mg-Ca-Cl. HCO3 has been identified from the recharge to discharge areas. Along the groundwater flow direction, the presence of chemical constituents with different concentrations demonstrates that the various geochemical mechanisms are responsible for this geochemical evolution. Furthermore, the chemical composition of groundwater also reflects that the groundwater has interacted with distinct rock types (granites/granulites). The stable isotopes (δ18O and δ2H) of groundwater reveal that the local precipitation is the main source of recharge. However, the groundwater recharge is affected by the evaporation process due to different geological conditions irrespective of topographical differences in the study area. The tritium (3H) content of groundwater suggests that the aquifer is mainly recharged by modern rainfall events. Thus, in semi-arid regions, the geology, weathering, and geologic structures have a significant role in bringing chemical changes in groundwater and smoothening the recharge process. The findings of this study will prove vital for the decision-makers or policymakers to take appropriate measures to design water budgets as well as water management plans more sustainably.

SWAT-SF: A flexible SWAT-based model for watershed-scale water and soil salinity modeling

Natural and anthropogenic complex processes release salts into the environment. These change the balances of natural systems in the watersheds. Models can assist study of salinity processes throughout watersheds. This study proposes a flexible water and soil salinity module for the Soil and Water Assessment Tool (SWAT) that can profitably incorporate expert scientific judgments into a deterministic salinity framework to adapt predicted salinity processes to actual salinity processes watershed-scale. The proposed flexible salinity model (SWAT-SF) was developed using new equations for salinity assessment and then successfully applied to the Dehram River Basin located south of Iran that endangers natural and anthropogenic salinity problems. The SWAT-SF model uses a general framework that can be utilized with/without the direct guidance of experts for the determination of salinity processes, the extent of the salinity, identification and investigation of the saline site, assessment and management of the salinity, and evaluation of salinity economics throughout the world.

Hydrogeochemical Assessment of Groundwater and Suitability Analysis for Domestic and Agricultural Utility in Southern Punjab, Pakistan

Groundwater is a critical water supply for safe drinking water, agriculture, and industry worldwide. In the Khanewal district of Punjab, Pakistan, groundwater has severely deteriorated during the last few decades due to environmental changes and anthropogenic activities. Therefore, 68 groundwater samples were collected and analyzed for their main ions and trace elements to investigate the suitability of groundwater sources for drinking and agricultural purposes. Principal component analysis (PCA) and cluster analysis (CA) were employed to determine the major factors influencing groundwater quality. To assess the groundwater’s appropriateness for drinking and irrigation, drinking and agricultural indices were used. The pH of the groundwater samples ranged from 6.9 to 9.2, indicating that the aquifers were slightly acidic to alkaline. The major cations were distributed as follows: Na+ > Ca2+ > Mg2+ > K+. Meanwhile, the anions are distributed as follows: HCO3− > SO42− > Cl− > F−. The main hydrochemical facies were identified as a mixed type; however, a mixed magnesium, calcium, and chloride pattern was observed. The reverse ion exchange process helps in exchanging Na+ with Ca2+ and Mg2+ ions in the groundwater system. Rock weathering processes, such as the dissolution of calcite, dolomite, and gypsum minerals, dominated the groundwater hydrochemistry. According to the Weight Arithmetic Water Quality Index (WAWQI), 50% of the water samples were unsafe for drinking. The Wilcox diagram, USSL diagram, and some other agricultural indices resulted in around 32% of the groundwater samples being unsuitable for irrigation purposes. The Khanewal’s groundwater quality was vulnerable due to geology and the influence of anthropogenic activities. For groundwater sustainability in Khanewal, management strategies and policies are required.

Hydrogeochemical Investigation of Elevated Arsenic Based on Entropy Modeling, in the Aquifers of District Sanghar, Sindh, Pakistan

Arsenic (As) contamination in drinking groundwater is a common environmental problem in Pakistan. Therefore, sixty-one groundwater samples were collected from various groundwater sources in District Sanghar, Sindh province, Pakistan, to understand the geochemical behavior of elevated As in groundwater. Statistical summary showed the cations and anions abundance in decreasing order of Na+ > Ca2+ > Mg2+ > K+, and HCO3− > Cl− > SO42− > NO3−. Arsenic was found with low to high concentration levels ranging from 5 µg to 25 µg/L with a mean value of 12.9 µg/L. A major water type of groundwater samples was mixed with NaCl and CaHCO3 type, interpreting the hydrochemical behavior of rock–water interaction. Principal component analysis (PCA) showed the mixed anthropogenic and natural sources of contamination in the study area. Moreover, rock weathering and exchange of ions controlled the hydrochemistry. Chloro-alkaline indices revealed the dominance of the reverse ion exchange mechanism in the region. The entropy water quality index (EWQI) exposed that 17 samples represent poor water, and 11 samples are not suitable for drinking.