Factors Controlling Groundwater Quality Research Articles

Factors controlling groundwater quality and salinization near the salt playa of Kavir-e Daranjir, central part of Iran

Factors controlling groundwater quality and salinization near the salt playa of Kavir-e Daranjir, central part of Iran

An appraisal to hydrochemical characterization, source identification, and potential health risks of sulfate and nitrate in groundwater of Bemetara district, Central India.

Gypsum-enriched aquifers (GEA) and intensive agriculture regions (IAR) in semi-arid regions are responsible for very high amounts of sulfate and nitrate in many groundwater systems of the world, respectively. However, in such regions, the problem of nitrate pollution and its associated health risk has been increasing and emerging as a global issue. However, along with nitrate, sulfate contamination and its potential health risks are often neglected worldwide in these regions. Therefore, considering sulfate along with nitrate as a significant threat to water quality in such regions, this study aimed to characterize hydrochemistry, factors controlling groundwater quality, and assessment of risk to human health. To accomplish this objective, 116 groundwater samples were collected over pre-monsoon (PRM) and post-monsoon (POM) (2019) seasons in Bemetara district. As per Bureau of Indian standards (BIS) for drinking, SO42- (28 and 19%) and NO3- (7 and 35%) exceeded the permissible limits in PRM and POM seasons, respectively; thereby, groundwater was not suitable for drinking. SO42- and NO3- pollution sources were identified and mainly attributed to gypsum dissolution and agricultural activities as well as domestic sewage discharge, respectively. In addition, SO42-and NO3- risk assessment results show that total 20% to 46% of all samples surpassed the permissible limit (HQ = 1) of risk to children and adults, over both seasons. To ensure drinking water security in this region, sustainable management of agricultural activities and treatment should be done to reduce the potential health risks due to SO42- and NO3-.

Hydrochemistry and quality appraisal of groundwater in Birr River Catchment, Central Blue Nile River Basin, using multivariate techniques and water quality indices

Due to the continuous population growth and the expansion of industry and agriculture in Ethiopia, groundwater demand has been increasing to supplement the erratic surface water. Therefore, the availability of sufficient and clean groundwater should be appraised and tracked regularly to secure its multi-purposes. This work aims to assess the appropriateness of groundwater for drinking, and irrigation uses and identifies the key factors controlling groundwater quality in the Birr River Catchment (BRC), Blue Nile River Basin, Ethiopia. For this purpose, a total of 79 groundwater samples were assessed for physicochemical parameters. Major ion analysis, multivariate techniques (MCA, HCA, and PCA), and multi-hydrochemical indices wereapplied in the analysis of groundwater quality data. Hydrochemical analysis indicated that the principal cation and anion were Ca2+ and HCO3-, respectively. The spatial analysis of the major ions revealed a positive trend for Mg2+, Na+, K+, HCO3-, Cl-, and SO42- along the groundwater flow path from the upland to the Birr river valley. Conversely, Ca2+ shows a deleterious tendency along the groundwater flow direction. The aquifer has three principal hydrochemical facies: Ca-HCO3, Ca/Mg-HCO3, and Na-HCO3. The water quality analysis indicates that with the exception of TDS, Ca2+, Mg2+, and HCO3- in a few locations, most of the parameters analyzed are within the WHO allowable limits and are thus considered suitable for drinking water. The combined use of Gibbs and ionic ratio plots confirmed that silicate weathering was invariably prevailing in the region. The Chloro-Alkali Indices (CAIs) have indicated that cation exchange occurs in more than 85% of groundwater samples. However, there were indications of the influence of reverse ion exchange in the rest of the data. The MCA, PCA, and HCA disclosed that geo-genic sources accompanied by human activities mainly control the groundwater quality of the catchment. However, water quality assessment indices show that groundwater in the highest proportion of the catchment is suitable for human consumption and agricultural use.

Multivariate statistical and hydrochemical approaches for evaluation of groundwater quality in north Bahri city-Sudan

Groundwater has recently been considered one of the primary sources of water supply in Sudan. However, groundwater quality is continuously degraded due to overexploitation and long-term agricultural operations. The fossilized Cretaceous Nubian sandstone is the principal aquifer in the study area. This research aims to determine the major factors influencing groundwater quality and detect the suitability of groundwater for drinking and irrigation purposes by integrating hydrochemical and multivariate statistical methods. Hydrochemical plots such as Piper, Chadha, and Durov diagrams were applied to detect the groundwater facies and hydrochemical processes controlling the groundwater quality. They indicated Ca–Mg–HCO3 water type as a dominant groundwater facies followed by Na–HCO3 and Na–Cl types. Gibbs plots suggested that the dissolution of the minerals is the main factor influencing the water quality. The results of the Gibbs plot were further interpreted using saturation indices (SI). The SI values indicated that aragonite, calcite, and dolomite precipitated respectively in 58.33%, 75%, and 75% of groundwater samples. Multivariate statistical analyses, including Pearson's correlation analysis, hierarchical cluster analysis (HCA), and principal component analyses (PCA), were jointly employed to identify the structure of water quality data and deduce the main factors controlling groundwater quality. The statistical analysis revealed the effect of the physical and human-induced activities as the main factors influencing groundwater chemistry. These factors are rock-water interaction, agricultural practice, and organic contamination from septic tanks. Further, the suitability of groundwater for irrigation is determined using sodium adsorption ratio (SAR) and sodium percent (Na+%) indices. They carefully indicated that 75% of the groundwater samples in the study area are excellent for irrigation except for some sample location where the salinity hazard is stimulated by ion exchange. This integrated approach was effective in calibrating water quality assessment methodologies. The current research concluded that the implication of a groundwater quality monitoring scheme is crucial to ensure water supply sustainability in north Bahri city.

Origin and Implications of Pollution in Coastal Groundwater of the Guangdong Province

The groundwater resource is crucial to the urbanization and industrialization in the Guangdong coastal area; the rapid development of Daya Bay has presented a challenge for the management of the groundwater quantity and quality. Therefore, a novel approach to hydrochemical analysis, which, combined with the health risk model and the water quality index (WQI), was used to explain the hydrochemistry characteristics and risks to human health of groundwater in the Guangdong coastal areas in addition to investigating the factors controlling groundwater quality. The results showed that the average concentration of total dissolved solids (TDS) in groundwater was 1935.26 mg/L and the quality of water was weakly alkaline. The dominant hydrochemical types of groundwater were identified to be Mg-HCO3 and Na-Cl·HCO3. The main factor influencing the hydrochemical composition was rock weathering, while the result of principal component analysis (PCA) shows seawater intrusion and anthropogenic inputs also have an effect on the water quality. The conclusions of the water quality assessment indicated that most of the groundwater samples were acceptable for drinking. However, both WQI and the non-carcinogenic hazard quotient (HQ) values indicated unacceptable risks in any area of Maoming, Zhanjiang and Shantou, and, according to the hazard index (HI) value, children in the study area are at more danger to health risks than adults. It is suggested that both groundwater salinization and nitrate pollution should be paid attention to when improving groundwater quality and exploring the sustainable utilization of groundwater resources.

A GIS-Based Spatiotemporal Impact Assessment of Droughts in the Hyper-Saline Urmia Lake Basin on the Hydro-Geochemical Quality of Nearby Aquifers

Urmia Lake is a hyper-saline lake in northwestern Iran that has been drying up since 2005. The main objective of this study was to evaluate the water quality in aquifers that are the main source of fresh water for the eastern plains Urmia Lake, which has been drying up due to intensive land use/cover changes and climate change. We evaluated hydro-geochemical data and factors contributing to aquifer pollution and quality variation for nine aquifers in the vicinity of Urmia Lake during the dry and wet seasons from 2000–2020. Our methodology was based on the analysis of 10 years of data from 356 deep and semi-deep wells using GIS spatial analysis, multivariate statistical analysis, and agglomerative hierarchical clustering. We developed a Water Quality Index (WQI) for spatiotemporal assessment of the status of the aquifers. In doing so, we highlighted the value of combining Principal Component Analysis (PCA), WQI, and GIS to determine the hydro-geochemical attributes of the aquifers. We found that the groundwater in central parts of the study area was unsuitable for potable supplies. Anthropogenic sources of contamination, such as chemical fertilizers, industrial waste, and untreated sewage water, might be the key factors causing excessive concentrations of contaminants affecting the water quality. The PCA results showed that over 80% of the total variance could be attributed to two principal factors for most aquifers and three principal factors for two of the aquifers. We employed GIS-based spatial analysis to map groundwater quality in the study area. Based on the WQI values, approximately 48% of groundwater samples were identified as poor to unsuitable for drinking purposes. Results of this study provide a better hydro-geochemical understanding of the multiple aquifers that require preventive action against groundwater damage. We conclude that the combined approach of using a multivariate statistical technique and spatial analysis is effective for determining the factors controlling groundwater quality.

An investigation into the hydrochemistry, quality and risk to human health of groundwater in the central region of Shandong Province, North China

This study aimed to characterize the hydrochemistry and risk to human health of groundwater in the central region of Shandong Province (CRSP) as well as to investigate the factors controlling groundwater quality. Methods applied included traditional hydrochemical analysis methods, the water quality index (WQI) and a health risk model. The results showed that groundwater of the CRSP is weakly alkaline, with average concentrations of total dissolved solids (TDS) over the wet and dry seasons of 666.2 mg·L−1 and 653.9 mg·L−1, respectively. The southeast part of the study region and Laiwu, Xintai and Taian showed higher concentrations of TDS and NO3−. The dominant hydrochemical types of groundwater in the CRSP were identified to be HCO3–Ca·Mg and SO4·Cl–Ca·Mg. The main factors influencing the hydrochemical composition of groundwater in CRSP were identified to include rock weathering, cation exchange and anthropogenic inputs, and the main source of nitrate in groundwater was identified as agricultural activities. The results of the water quality evaluation showed that most groundwater samples of the CRSP were suitable for drinking and agricultural irrigation. However, the non-carcinogenic risk index (HQ) values calculated for groundwater of the CRSP over both the dry and wet seasons indicated unacceptable risk to the health of both children and adults. The contradicting results between the water quality evaluation and health risk assessment were due to differences in the water quality standard limits used. It is suggested that permissible limits of water quality variables be adjusted according to local conditions and that a water quality evaluation system be established that is suitable for Chinese residents, so as to ensure the sustainable management of groundwater and the safety of drinking water.

Hydrogeochemical and isotopic assessment for characterizing groundwater quality and recharge processes in the Lower Anayari catchment of the Upper East Region, Ghana

The Lower Anayari Catchment (LAC) groundwater system of the upper east region contributes substantially to the populace’s socioeconomic development. LAC is well distinguished for intense farming activities. This study sought to assess the quality and processes/activities that impact on the groundwater chemistry in the catchment. Forty-one (41) samples, comprising boreholes and hand-dug wells were sampled from six (6) prime communities (Kulwase, Manyoro, Mirigu, Nakolo, Paga and Pungu) for physico-chemical and stable isotopes analysis. Hydrochemistry, ionic ratios, principal component analysis (PCA), geostatistics and stable isotopes (δ18O and δ2H) approaches were applied to construe the hydrogeochemistry of the groundwater system. Utilizing PCA and geostatistics, two factors controlling groundwater quality were depicted as; (a) V1- the dissolution of silicate minerals and (b) V2- agrochemicals/domestic waste. Piper Trilinear plot identified two hydrochemical facies, namely, Ca-Na-HCO3 and Na-Ca-HCO3. Cation exchange processes and silicate weathering/dissolutions are main drivers of the groundwater chemistry. Stable isotopes suggests groundwater in LAC is mainly of meteoric origin and a well-mixed system. However, few deviations of groundwater isotopic signatures from GMWL were observed suggesting evaporation before recharge or recharge occurring from an enriched source.

Geochemistry and associated human health risk through potential harmful elements (PHEs) in groundwater of the Indus basin, India

Inorganic contamination in groundwater has become a major health concern because of its acute and chronic health impacts. To investigate the major hydro-geochemical processes controlling groundwater quality in a part of the Indus river basin, 29 groundwater samples were collected and tested for major ions and potentially harmful elements (PHEs) including Mn, Cu, Cd, Cr, Pb, Fe, and Zn. The cations and PHEs were measured using the atomic absorption spectrophotometer and the anions were analyzed using ion chromatograph. Anthropogenic activities and rock–water interactions are the major factors controlling groundwater quality, along with silicate weathering and evaporation. Ca–HCO3 is the dominant water facies, followed by Na–HCO3 and Na–Cl water facies. Among PHEs, Pb is the most dominant contaminant with 21 samples exceeding WHO guidelines followed by Cr and Fe in 27% and 24% of samples, respectively. Health risk to the population for both dermal and direct ingestion was assessed by calculating chronic dose index (CDI), hazardous quotient (HQ), and hazardous index (HI) for children and adults. HQ through ingestion was highest for Cd because of its low reference dose value. HI for dermal exposure was found to be safe for both children and adults, with values below 1; for ingestion 14 samples had high HI > 1 for adults, and 27 samples for children. High HI values indicate that at a few locations, the groundwater is not suitable for consumption and can cause serious health implications. Proper planning for mitigation is required and large-scale testing along with sharing of wells among neighbors is recommended for reducing exposure.

Groundwater pollution by trace metals and human health risk assessment in central west part of Bangladesh

To evaluate the trace element contamination level and human health risk in study area, a total of twenty groundwater samples were collected and analyzed for pH, EC, Cu, Cd, Fe, Mn, Ni, and Zn. The results revealed that, groundwater is slightly acidic in nature with the mean conductance of 686.10 μs/cm. Heavy metal evaluation index (HEI), the degree of contamination (Cd) and nemerow pollution index (NI) were employed to estimate the pollution load, and it was found 5%, 95%, and 75% of samples exhibits the high degree of pollution respectively. According to the spatial analysis it was found that, south-central part of the study area is highly contaminated with trace elements. Moreover, Pearson correlation, principal component analysis (PCA) and cluster analysis (CA) were applied to identify the pollution source and factors controlling groundwater quality, and the results indicates that groundwater of the study area were influenced by both natural and anthropogenic factors. Chronic health risk via exposure of both oral and dermal routes were also determined by calculating the hazard quotient (HQ) and hazard index (HI), for both adults and children. In case of oral exposure, almost 85% of samples suggest the medium category of chronic risk for adult, and 50% of samples were found at high risk for children. Again, dermal exposure showed comparatively lower risk than oral exposure, and 55% and 80% of samples attributed medium chronic risk for adult and children respectively. However, the carcinogenic risk of cadmium (Cd) via oral exposure pathway suggest, all of the samples are at high risk for both adults and children. Average lifetime cancer risks (LTCR) of Cd for both adult and children were found to be 4.55E-4 and 5.59E-4 respectively, that indicated high carcinogenic risk. Results of sensitivity analysis specified concentration has high impact on carcinogenic risk both for adult and children.

Assessment of the factors controlling groundwater quality in a coastal aquifer adjacent to the Bay of Bengal, India

A study has been conducted in the heavily populated coastal areas of the Puri district (Odisha, India) with the aim to: (1) identify the factors that influence the major ion composition and concentrations of trace elements in groundwater; (2) determine the spatial distribution of the water-quality parameters and how they vary on a seasonal basis. To do this, groundwater samples were collected from 60 shallow tube wells located along the Puri coast during the pre-monsoon and post-monsoon seasons. Based on their TDS content, 52% of the collected groundwater samples were identified as being brackish-to-saline and unsuitable for drinking purposes in both the pre- and post-monsoon seasons. Significant concentrations of trace elements including Ba, Br, F, Fe, Mn, and Sr were detected in most of the samples. Iron concentrations were found to be higher than the WHO drinking water guideline value (0.3 mg/l) in 92% of the samples irrespective of seasons. Elevated Mn concentrations were observed in 37% and 40% of samples during the pre-monsoon and post-monsoon seasons, respectively. In addition, fluoride concentrations in excess of the WHO limit (1.5 mg/l) were found in 15% of samples during the pre-monsoon and 23% of samples during the post-monsoon season. The concentrations of major and trace elements show wide spatial and minor temporal variations. Large spatial and limited temporal variations in Cl and Na concentrations along with considerable Br and Sr concentrations in groundwater suggest that saltwater intrusion is the dominant process controlling groundwater quality in the study area, although other processes including ion exchange, the precipitation and dissolution of minerals, microbial activity, and the weathering of aquifer material also play roles to some extent in determining the spatial and seasonal distribution of the major and trace elements in coastal groundwater. Grouping of various water-quality parameters related to these processes by principal component analysis and their linking to one cluster in the hierarchical cluster analysis further supports the view that these processes control the groundwater chemistry in the coastal aquifer.

Factors controlling groundwater quality in the Yeonjegu District of Busan City, Korea, using the hydrogeochemical processes and fuzzy GIS.

The hydrogeochemical processes and fuzzy GIS techniques were used to evaluate the groundwater quality in the Yeonjegu district of Busan Metropolitan City, Korea. The highest concentrations of major ions were mainly related to the local geology. The seawater intrusion into the river water and municipal contaminants were secondary contamination sources of groundwater in the study area. Factor analysis represented the contamination sources of the mineral dissolution of the host rocks and domestic influences. The Gibbs plot exhibited that the major ions were derived from the rock weathering condition. Piper's trilinear diagram showed that the groundwater quality was classified into five types of CaHCO3, NaHCO3, NaCl, CaCl2, and CaSO4 types in that order. The ionic relationship and the saturation mineral index of the ions indicated that the evaporation, dissolution, and precipitation processes controlled the groundwater chemistry. The fuzzy GIS map showed that highly contaminated groundwater occurred in the northeastern and the central parts and that the groundwater of medium quality appeared in most parts of the study area. It suggested that the groundwater quality of the study area was influenced by local geology, seawater intrusion, and municipal contaminants. This research clearly demonstrated that the geochemical analyses and fuzzy GIS method were very useful to identify the contaminant sources and the location of good groundwater quality.

Integrated approach for identifying the factors controlling groundwater quality of a tropical coastal zone in Kerala, India

The present study examined the factors controlling shallow groundwater quality in two coastal panchayaths (viz., Chennam-Pallippuram and Thykkattussery) of Alappuzha district, Kerala, India, for three sampling seasons: pre-monsoon, monsoon and post-monsoon. The hydrochemical analysis shows significant seasonal fluctuations in groundwater quality, which are principally controlled by the climatic seasonality, contributed by the monsoon phenomenon. The groundwater is highly polluted due to organic load, which is manifested as high total and fecal coliform (TC and FC) contents, especially during MON. Fresh water recharge during MON contributes Ca–Mg–HCO3 type waters, whereas Ca–Mg–Cl and mixed cations-Cl types during PRM imply interaction between groundwater and saline/brackish water of the lake surrounding the study area. Such interaction is also evident by various ionic ratios (e.g., Mg2+/Ca2+, Na+/Cl−) as well as the correlation between Cl− and SO4 2−. The Ca2++ Mg2+ versus TZ+ relationship indicates significance of weathering of carbonate and silicate minerals as well as interaction between groundwater and aquifer matrix, which is also supported by the positive chloro-alkaline indices. Isotopic composition of the groundwater and lake water also suggests the influence of fresh water recharge (mainly during monsoon) as well as interaction of groundwater with lake water in controlling groundwater quality. Factor analysis proposes three dominant processes controlling groundwater quality of the region: (1) interaction of groundwater with brackish water of the Vembanad Lake, (2) geogenic/atmospheric sources, such as weathering, groundwater interaction with aquifer matrix, atmospheric inputs and fresh water recharge and (3) diverse anthropogenic sources of contamination (e.g., domestic waste, septic tanks, and agricultural residues). However, relative influence of these factors on groundwater quality varies temporally to form groundwater with differing chemical composition among the seasons. The present study underscores the exigency to ensure availability of safe drinking water for the coastal zones.

Multivariate statistical analysis and geochemical modeling for geochemical assessment of groundwater of Delhi, India

Groundwater is the most important source of drinking waters supply in the National Capital Territory (NCT) of, New Delhi, India. A diverse geological and topographical set up along with the fast growing population and anthropogenic activities has created a need of groundwater quality assurance for drinking and domestic water supply in the region. The major hydro-geochemical process and impacts of anthropogenic activities can be deciphered using multivariate statistical analysis, conventional graphical plots and saturation indices. Groundwater samples were collected from 170 locations spread over entire region and were analysed for a total of 12 water quality physico-chemical parameters. It is observed that the groundwater is neutral to alkaline in nature with electrical conductivity (EC) value ranging from 460 to 8980μs/cm. Chemometric analysis was performed along with geochemical modeling. The 3 clusters obtained through HCA were clearly differentiated based on their chemical characteristics i.e. concentration of major ions. High concentration of nitrate (NO3−) and fluoride (F−) exceeding WHO standards was found in 29% and 27% of the water samples respectively. It is observed that semi-arid climatic conditions along with rock-water interaction, weathering and ion-exchange are the major factors controlling groundwater quality in the region. Oversaturation of fluorite and gypsum has resulted into high concentration of F− in study area. It is found that the results from statistical and geochemical models compliment the findings using conventional plots and are able to decipher comprehensive geochemistry of groundwater in the region.

Natural and anthropogenic factors affecting groundwater quality in the eastern region of the United Arab Emirates

Groundwater contamination is a serious health and environmental problem in the eastern region of the United Arab Emirates. Factors affecting groundwater quality are known to be natural and anthropogenic, but the process through which it is being released is poorly understood. In this study, an attempt has been made to map and spatially correlate factors controlling groundwater quality using a combination of remote sensing and geographic information system technology. Factors, which might have spatial relation with groundwater quality, namely flow direction, host rock, land use and topographic slope, were selected as essential factors. Factor thematic maps were extracted from remote sensing data using deterministic eight-node and fuzzy logic algorithms. The obtained maps were correlated with groundwater data collected from groundwater wells. The results show that pollutants resulting from intensive agriculture and human activities and carbonate rocks in the Al Ain area are likely to contribute significantly to the degradation of groundwater quality. The results also show that the salinity in groundwater ranges from 100 mg/L at the foot of the Oman Mountain to 5,343 mg/L at Al Ain city.

Identifying Major Factors Controlling Groundwater Quality in Semiarid Area Using Advanced Statistical Techniques

There are many factors controlling groundwater pollution and vulnerability. However, the factors’ weights are still not reasonably investigated. In order to assess groundwater quality and the controlling factors in semiarid region, 178 groundwater samples were collected and analyzed for salinity and nitrate content. New statistical techniques of prediction profiler and hierarchical cluster combined with geographic information systems (GIS) were used to assess the groundwater quality based on three categorical controlling factors; landuse/ land cover (LULC), soil texture, and aquifer type. It is hypothesized these factors are controlling groundwater quality with various weights. Groundwater salinity across the study area varied from 327.0 to 9110.0 mg/L, while nitrate ranged from 0.2 mg/L to 339.6 mg/L. Both prediction profiler and cluster analyses provided excellent tools for quantifying the pollution magnitudes, weighing the controlling factors, and visualizing the pollution zones. Prediction profiler showed high capability to predict groundwater pollution (P < 0.0001 and 0.0038 for salinity and nitrate, respectively) where LULC was the most effective factor, followed by aquifer type and soil texture class. According to desirability function analysis, maximum salinity and nitrate pollution was predicted to be associated with irrigated agriculture lands at shallow aquifers with silty clay loam soils. Hierarchical cluster analysis combined with GIS mapping was able to group the controlling factors into six vulnerability zones. The generated groundwater spatial pollution map allowed for potential pollution sources identification (e.g. fertilizer use, treated waste water, overdrafting). This paper also offers detailed mapping for decision makers to allow further ecosystem restoration and rehabilitation planning.

Geochemistry and assessment of hydrogeochemical processes in groundwater in the southern part of Bathinda district of Punjab, northwest India

Hydrogeochemistry of groundwater is important for sustainable development and effective management of the groundwater resource. Fifty-six groundwater samples were collected from shallow tube wells of the intensively cultivated southern part of district Bathinda of Punjab, India, during pre- and post-monsoon seasons. Conventional graphical plots were used to define the geochemical evaluation of aquifer system based on the ionic constituents, water types, hydrochemical facies and factors controlling groundwater quality. Negative values of chloroalkaline indices suggest the prevalence of reverse ion exchange process irrespective of the seasons. A significant effect of monsoon is observed in terms chemical facies as a considerable amount of area with temporary hardness of Ca2+–Mg2+–HCO3− type in the pre-monsoon switched to Ca2+–Mg2+–Cl− type (18%) followed by Na+–HCO3− type (14%) in the post-monsoon. Evaporation is the major geochemical process controlling the chemistry of groundwater process in pre-monsoon; however, in post-monsoon ion exchange reaction dominates over evaporation. Carbonate weathering is the major hydrogeochemical process operating in this part of the district, irrespective of the season. The abundance of Ca2+ + Mg2+ in groundwater of Bathinda can be attributed mainly to gypsum and carbonate weathering. Silicate weathering also occurs in a few samples in the post-monsoon in addition to the carbonate dissolution. Water chemistry is deteriorated by land-use activities, especially irrigation return flow and synthetic fertilisers (urea, gypsum, etc.) as indicted by concentrations of nitrate, sulphate and chlorides. Overall, results indicate that different natural hydrogeochemical processes such as simple dissolution, mixing, weathering of carbonate minerals locally known as ‘‘kankar’’ and silicate weathering are the key factors in both seasons.

Hydrogeochemistry of groundwaters in a semi-arid region. El Ma El Abiod aquifer, Eastern Algeria

In this work, we present results of the hydrogeochemical and isotopic studies on groundwater samples from the El Ma El Abiod Sandstone aquifer, in Tebessa, Algeria. Chemical and environmental isotope data are presented and discussed in order to identify the geochemical processes and their relation with groundwater quality as well as to get an insight into the hydrochemical evaluation, in space and time, of groundwater and of the origin of dissolved species. A combined hydrogeologic and isotopic investigation have been carried out using chemical and isotopic data to deduce a hydrochemical evaluation of the aquifer system based on the ionic constituents, water types, hydrochemical facies, and factors controlling groundwater quality. All of the investigated groundwaters are categorized into two chemical types: low mineralized water type and relatively high mineralized water type. Interpretation of chemical data, based on thermodynamic calculations and geochemical reaction models of selected water groups constructed using PHREEQC, suggest that the chemical evolution of groundwater is primarily controlled by water–rock interactions, involving (1) acidic weathering of aluminosilicates, (2) dissolution of secondary carbonate minerals, and (3) cation exchange of Na+ for Ca2+. However, the original composition of groundwater may have been modified by further secondary processes such as mixing of chemically different water masses. The combined use of SI and mass-balance modeling has shown to be a useful approach in interpreting groundwater hydrochemistry in an area where large uncertainties exist in the understanding of the groundwater flow system. Interpretation of 18O and 2H, suggest that the recharge of the investigated groundwaters may result from different mechanisms.

Tracing the factors responsible for arsenic enrichment in groundwater of the middle Gangetic Plain, India: a source identification perspective

Arsenic contamination in groundwater is of increasing concern because of its high toxicity and widespread occurrence. This study is an effort to trace the factors responsible for arsenic enrichment in groundwater of the middle Gangetic Plain of India through major ion chemistry, arsenic speciation, sediment grain-size analyses, and multivariate statistical techniques. The study focuses on the distinction between the contributions of natural weathering and anthropogenic inputs of arsenic with its spatial distribution and seasonal variations in the plain of the state Bihar of India. Thirty-six groundwater and one sediment core samples were collected in the pre-monsoon and post-monsoon seasons. Various graphical plots and statistical analysis were carried out using chemical data to enable hydrochemical evaluation of the aquifer system based on the ionic constituents, water types, hydrochemical facies, and factors controlling groundwater quality. Results suggest that the groundwater is characterized by slightly alkaline pH with moderate to strong reducing nature. The general trend of various ions was found to be Ca(2+) > Na(+) > Mg(2+) > K(+) > NH(4) (+); and HCO(3) (-) > Cl(-) > SO(4) (2-) > NO(3) (-) > PO(4) (3-) > F(-) in both seasons. Spatial and temporal variations showed a slightly higher arsenic concentration in the pre-monsoon period (118 microg/L) than in the post-monsoon period (114 microg/L). Results of correlation analyses indicate that arsenic contamination is strongly associated with high concentrations of Fe, PO(4) (3-), and NH(4) (+) but relatively low Mn concentrations. Further, the enrichment of arsenic is more prevalent in the proximity of the Ganges River, indicating that fluvial input is the main source of arsenic. Grain size analyses of sediment core samples revealed clay (fine-grained) strata between 4.5 and 7.5 m deep that govern the vertical distribution of arsenic. The weathering of carbonate and silicate minerals along with surface-groundwater interactions, ion exchange, and anthropogenic activities seem to be the processes governing groundwater contamination, including with arsenic. Although the percentage of wells exceeding the permissible limit (50 microg/L) was less (47%) than that reported in Bangladesh and West Bengal, the percentage contribution of toxic As(III) to total arsenic concentration is quite high (66%). This study is vital considering that groundwater is the exclusive source of drinking water in the region and not only makes situation alarming but also calls for immediate attention.

The hydrogeochemical characterization of Morsott-El Aouinet aquifer, Northeastern Algeria

A study of the hydrogeochemical processes in the Morsott-El Aouinet aquifer was carried out with the objective of identifying the geochemical processes and their relation with groundwater quality as well as to get an insight into the hydrochemical evaluation of groundwater. The high salinity coupled with groundwater level decline pose serious problems for current irrigation and domestic water supplies as well as future exploitation. A combined hydrogeologic and isotopic investigation have been carried out using chemical and isotopic data to deduce a hydrochemical evaluation of the aquifer system based on the ionic constituents, water types, hydrochemical facies and factors controlling groundwater quality. The ionic speciation and mineral dissolution/precipitation was calculated by WATEQF package software. The increase in salinity is related to the dissolution and/or precipitation processes during the water–rock interaction and to the cationic exchange reactions between groundwater and clay minerals. The isotopic analysis of some groundwater samples shows a similarity with the meteoric waters reflect their short residence time and a lowest evaporation phenomenon of infiltrated groundwater.