Hydrogeochemical processes in groundwater in Uganda: a national-scale analysis

Hydrogeochemical studies were carried out in the Penna-Chitravathi river basins to identify and delineate the important geochemical processes which were responsible for the evolution of chemical composition of groundwater. The area is underlain by peninsular gneissic complex of Archaean age, Proterozoic meta-sediments, and strip of river alluvium. Groundwater samples were collected covering all the major hydrogeological environs in pre- and post-monsoon seasons. The samples were analyzed for major constituents such as Ca2+, Mg2+, Na+, K+, CO3-, HCO3-, Cl-, SO2(-4), NO3-, and F-. The groundwater in general is of Na+-Cl-, Na+-HCO3-, Ca2+-Mg2+-HCO3-, and Ca2+-Mg2+-Cl- types. Na+ among cations and Cl- and/or HCO3- among anions dominate the water; Na+ and Ca2+ are in the transitional state with Na+ replacing Ca2+ and HCO3- Cl- due to physiochemical changes in the aquifer and water-rock interactions. The Ca2+-Mg2+-Cl- HCO3- type water in one third samples suggest that ion exchange and dissolution processes are responsible for its origin. Change in storage of aquifer in a season does not influence the major geochemical makeup of groundwater. Gibbs plots indicate that the evolution of water chemistry is influenced by water-rock interaction followed by evapotranspiration process. The aquifer material mineralogy together with semiarid climate, poor drainage system, and low precipitation factors played major role in controlling groundwater quality of the area.

The objective of this work was to evaluate the influence of the natural degradation of the leachate organic fraction from the Belo Horizonte landfill on groundwater chemical evolution. The work focused on the modifications introduced by redox reactions in the presence of terminal electron acceptors. Twenty-one sampling points distributed along 13 monitoring wells were selected for the analysis of the chemical indicators of interest (TDS, SO4−2, Fe+2, Ba, pH and Eh). The behaviour of the variables involved in the alteration of the water quality was assessed by the spatial distribution of target parameters, elaboration of redox diagrams and chemical modelling that focused on the determination of mineral saturation indexes. The study showed a trend toward pyrite precipitation, which leads to the removal of chemical species such as divalent iron and sulphur as sulphide from the system. This removal disturbs the chemical equilibrium, typically by moving the reactions to replenish the sulphate concentration present in the groundwater. This process occurs primarily through the dissolution of compounds that have sulphate in their chemical composition, such as barite, suggesting that part of the barium concentration in the subsurface can be of geogenic origin. This study demonstrated the importance of knowing the nature of the geochemical processes in groundwater contaminated by urban solid waste.

The Fengfeng mining area is in the transition zone between the North China Plain and the Taihang Mountains, and groundwater is the main source of water supply in the district. Under the combined influence of human activities and natural geological conditions, the quality of different types of groundwater varies greatly, posing a potential threat to the safety of drinking water. In this study, hydrogeochemical processes in different types of groundwater were analyzed using multivariate statistical analysis methods with ion–ratio relationships, and a groundwater quality and health risk assessment model was developed. The research findings show that the main chemical components and TDS in the groundwater have obvious spatial distribution characteristics, i.e., the content of deep karst water (DKW) in the west is significantly lower than that of shallow pore water (SPW) in the east, and the hydrochemical type has changed from HCO3–Ca to SO4–Ca. The chemical components of SPW and DKW are mainly derived from silicates and carbonates, accompanied by weathering dissolution of sulphidic minerals, especially SPW. The chemical components of the groundwater was also influenced by the cation exchange reaction and human activities. The quality of the SPW was significantly worse than that of the DKW, and the nitrates in SPW carry a high non-carcinogenic risk, especially to children. The shallow pore water is not suitable for drinking water. This study can provide guidance on the safety of drinking water in the Fengfeng coal mining area and other areas with intensive industrial, mining, and agricultural activities.

The present study aims to use the Water Quality Index (WQI) modeling method to know about groundwater hydrochemistry and drinking suitability in and around (5 km) the Peenya industrial area/estate in Bengaluru city. For this research study, 116 bore well samples were collected and examined for the pre (dry) and post (wet) monsoon seasons in 2021, following APHA standard procedures. According to the BIS standard, the TH, Ca, Mg, NO3, and TDS exceed the desirable limits in both seasons. The water quality examination data shows that TDS concentration is found to be higher above the desired limit (500 mg/l) during the pre- (63%) and post- (45%) monsoon seasons. Furthermore, 55% (pre-monsoon) and 15% (post-monsoon) of the groundwater samples exceed the BIS’s nitrate allowable limit (45 mg/l). Among the analyzed samples, the calcium content in 19% and 20% of samples exceeded the desirable limit (75 mg/l), and magnesium content in 87% and 83% exceeded the desirable limit (30 mg/l) in pre- and post-monsoon seasons. In 95% of samples, TH content exceeded the desirable limit (200 mg/l) in both pre- and post-monsoon seasons. Piper diagram plots were utilized to determine sources of dissolved constituents, rock-water interaction, and other factors that influenced the region’s groundwater composition. Based on hydro-chemical facies the Ca-Mg-HCO3 type of water predominates in the study area during pre (dry) and post (wet)-monsoon seasons of the year 2021. The chemistry of groundwater has deteriorated significantly because of several industrial and anthropogenic activities. The WQI spatial distribution map shows that groundwater quality has the greatest impact in the west and a few places in the north and south regions of the research area. This study was conducted in Bangalore’s Peenya industrial area to determine whether groundwater is suitable for drinking, identify the mechanisms governing groundwater’s geochemistry, and evaluate the effects of an industrial area on groundwater quality. The primary focus of this study is the major ion chemistry in this field.

Groundwater quality assessment is critical due to its susceptibility to a range of natural and anthropogenic influences, which, if unmanaged, can pose serious environmental and public health risks. This study investigates the hydrogeochemical characteristics and groundwater quality evaluation in the southwestern districts of Punjab, India, with a focus on sustainable resource management. A total of 242 groundwater samples were systematically collected during the summer of 2019 across the districts of Mansa, Fazilka, Muktsar, Bathinda, Firozpur, and Faridkot. The samples were analyzed for almost all major cations, anions and other physicochemical parameters. Relative abundance of cations was Na+ > Mg2+ > Ca2+ > K & anions were SO42− > HCO3− > Cl− > NO3− > F. Elevated concentrations of sulphate & nitrate were detected, highlighting the impact of agrochemical inputs. The plots of Wilcox and USSL plots revealed a declining trend in groundwater suitability for irrigation, affecting both shallow and deep aquifer sources, due to increasing salinity and sodium hazards. Hydrochemical data was interpreted using Gibbs diagram, Piper’s trilinear plot and Durov diagram to understand the various geochemical processes affecting the groundwater quality. Hydrochemical analysis indicates that rock–water interactions, evaporation & anthropogenic processes predominantly control groundwater composition, as evidenced by high levels of sodium and chloride. This study is significant as the surface water resources are limited and the quality and quantity of groundwater are deteriorating with time due to anthropogenic inputs. These findings underscore the necessity of continuous monitoring and informed groundwater management strategies to mitigate contamination and ensure long-term sustainability.

Groundwater hydrogeochemical processes, water quality index, and probabilistic health risk assessment in an arid and semi-arid environment (Hamedan, Iran)

In this study, 176 groundwater samples were collected along the floodplain of the Kherlen River to assess seasonal variations in groundwater quality. Sampling was conducted three times: twice during the spring and once during the autumn. The analysis included the use of a Piper diagram, a Gibbs diagram, and correlation analysis to evaluate temporal and spatial variations in groundwater hydrochemistry. The results revealed significant seasonal fluctuations in the concentrations of HCO₃⁻, Ca²⁺, Na⁺, Fe, F⁻, and NO₃⁻, with more pronounced spatial variations during the spring due to the dilution effect of precipitation. In both seasons, the majority of groundwater samples were classified under the Ca-HCO₃ hydrochemical type, while a few samples were identified as Na-HCO₃ and Mixed-HCO₃ types. The findings indicated that the groundwater in the study area mainly originated from rock-water interactions, with only a few samples linked to evaporation mechanisms. High Na⁺/(Na⁺+Ca²⁺) ratios and low Cl⁻/(Cl⁻+HCO₃⁻) ratios suggest that groundwater chemistry is primarily influenced by the weathering of carbonate and silicate minerals. Additionally, cation exchange processes, specifically the replacement of Ca²⁺ by Na⁺, were found to actively contribute to the hydrogeochemical evolution of the aquifer system. Correlation analysis further demonstrated that groundwater salinity is predominantly controlled by dissolved ions, as evidenced by strong positive correlations between EC and TDS. Significant associations among major ions, including Ca²⁺, Mg²⁺, Na⁺, and HCO₃⁻, highlight the influence of geochemical processes such as dolomite dissolution and the weathering of sodium-rich minerals. The positive correlation between nitrate and Ca²⁺/Mg²⁺, along with its negative correlation with HCO₃⁻, points to anthropogenic impacts-particularly from agricultural inputs-as significant contributors to groundwater contamination. These findings underscore the need for improved land and water management practices to safeguard groundwater quality in the region.

Groundwater hydrochemistry, source identification and pollution assessment in intensive industrial areas, eastern Chinese loess plateau.

Mountainous catchments are one of the world’s important water sources that sustains a major portion of global population and a rich biodiversity. The groundwater quantity and quality of mountainous watersheds depend generally on the geologic characteristics and climate gradients. Although many groundwater studies have been carried out in the midlands and lowlands of many river basins, not enough focus has been paid to the mountainous catchments of tropical watersheds. Here we report a case study on groundwater quality and controlling factors of a mountainous catchments of the Western Ghats mountain ranges of peninsular India—the Bhavani river basin, which is identified as a testbed for long-term monitoring of the Critical Zone process. A total of 88 water samples were collected seasonally for assessing various physico-chemical parameters, solute contents and scaling properties. Standard methods were followed for the estimation of various hydrochemical parameters in the open and borewell samples. The results of the study revealed that higher pH and Total Dissolved Solids (TDS) are noticed in the talc-tremolite dominated central zone whereas low values are recorded in the charnockite dominated areas. The major cations in the water samples are of the order Ca2+ > Mg2+ > Na+ > K+ and the anions are of the order HCO3− > Cl− > SO42−. The content of Cl− shows higher values in areas close to agricultural/settlement areas. An overall evaluation shows that the hydrochemistry of groundwater in the study area is influenced by both silicate and carbonate weathering. Mineral stability indices computed for the groundwater reveal that about 52% of the samples are supersaturated with carbonate minerals and often exhibit scaling due to solute overloading. Saturation Index and mineral stability diagram also support that the incongruent dissolution of aluminosilicate minerals (silicate weathering) is an important hydrochemical process controlling the chemistry of groundwater. Langelier saturation index (LSI) and Puckorius scaling index (PSI) show that a significant number of open well and borewell samples exhibit scaling tendency. Among the contributing factors that determine water quality of groundwaters, chemical weathering and anthropogenic activities play a significant role.

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.

The combined use of self-organizing map technique and fuzzy c-means clustering to evaluate urban groundwater quality in Seoul metropolitan city, South Korea

The groundwater quality of the Indus basin of Punjab, India, is a serious concern due to the existence of toxic contaminants. Although, this contamination has been documented in some studies, some part of this basin is scantily explored. This is true for the Fazilka district of Malwa region, Punjab. In the present study, a total of 78 groundwater samples were collected from this district to evaluate their suitability for drinking and irrigation purpose, to understand the current hydrogeochemical processes involved and assess the human health risk status of the region. The results of the water quality index (WQI) revealed that majority of the groundwater samples were of poor quality with U, F−, SO4 2−, and NO3 − exceeding the BIS limit in 60%, 94%, 43%, and 19% of samples, respectively. The groundwater geochemistry is mainly influenced by rock-water interaction. Ca-Mg-Cl water type is identified as the dominant hydrogeochemical facies, followed by Ca-Mg-SO4 2− and Na-Cl types. The Mg2+ and Na+ were identified as the major cations, while SO4 2− and HCO3 − existed as the dominant anions. Furthermore, the results of Principal Component Analysis (PCA), Hierarchical cluster and Pearson correlation matrix (PCM) analyses corroborated the elevated level of U, F−, SO4 2− with geogenic activity supplemented with agrochemical activities. The annual effective intake dose of U exceeded the WHO recommended mean annual effective dose of U (100 µSv y−1) for all age groups with infants recording the highest dose of U (151 µSv y−1). Moreover, the non-cancer risk of U and F− exceeded the USEPA limit (HQ-1) in majority of the sites. The high cumulative risk of non-carcinogenic contaminants (HI-4.6) in the entire study area is a matter of grave concern.

Salinity and sodicity of groundwater are the principal water quality concerns in irrigated areas of arid and semi-arid regions. The hydrochemical characteristics and sodicity of groundwater in the Shirin Sou area, western Iran were investigated in this study by chemical analyses of groundwater samples from 49 wells. Chemical analysis of the groundwater showed that the mean concentration of the cations was in the order: Na+ > Ca2+ > Mg2+ > K+, while that for anions was SO32− > Cl− > HCO3− > NO3−. The most prevalent water type is Na–SO4 followed by water types Na–Cl and Ca–SO4. The chemical evolution of groundwater is primarily controlled by water–rock interactions: mainly weathering of aluminosilicates, dissolution of sulfate minerals, and cation exchange reactions. Sulfate dissolution and pyrite weathering may both contribute to the SO42− load of the groundwater. High Na+ concentrations in groundwater participate in ion-exchange processes, resulting in the displacement of base cations into solution and raised concentrations in groundwater. The principal component analysis (PCA) performed on groundwater identified three principal components controlling variability of groundwater chemistry. Electrical conductivity, Ca2+, Mg2+, Na+, SO42−, and Cl− content were associated in the same component (PC1) (salinity), most likely linked to anthropogenic activities.

Groundwater is the most important source of water supply in Tchamba prefecture. Groundwater quality contaminations have emerged in many geographical areas due to natural environmental processes and human intervention in the geosystems. Hydrochemical evolution of groundwater quality in the study area was investigated. The physicochemical parameters such as major ions were determined. Factor analysis was used to identify key parameters that described groundwater quality in the study area. The first two factors were considered: Factor 1 explained 53.43% of the total variance and translates the natural rainwater recharge and water-soil/rock interaction process. The second factor (F2) explained 22.05% of the total variance and expresses the anthropogenic pressure such as domestic sewage, uncontrolled landfill waste, fertilizers, and wastewater. The results showed that silicate mineral dissolution and cation exchange in aquifers play an important role in groundwater chemistry evolution.

Knowledge of mechanism controlling the hydrochemistry of groundwater are crucial requirement to understand the hydrochemical evolution and evaluate the water quality of subsurficial water resources. Thus, to understand the process governing the hydrochemistry variability and flow dynamics of the Parecis and Ronuro Aquifers, the use of statistical analysis and isotopic characterization were combined. In the correlation matrix it was found that the highest correlation coefficient was observed for HCO3-, Ca2+, Mg2+, Sr2+, SO42-, and F-, which suggested that these parameters are derived from the same source, most likely from rock–water interactions. Additionally, we noticed moderate to high correlation among NO3-, Cl-, Na+, K+, and Ba2+, which collectively are indicative of domestic sewage contamination. Finally, a principal component analysis (PCA) identified that the most variance in hydrochemistry from the evaluated samples was controlled by HCO3-, Ca2+ and Mg2+, which is associated with rock–water interaction. Regarding the 18O and 2H isotope values, it could be observed that the aquifer recharges were of meteoric origin and that the Ronuro Aquifer samples were more enriched than the PAS samples. This work reinforces the capability of multivariate statistics to discern the main process that controls the variability of groundwater hydrochemistry.