Processes Controlling Groundwater Quality Research Articles

Hydrochemical Characteristics and Formation Mechanism of Groundwater in the Western Region of Hepu Basin, Beihai City

Beihai City is a typical coastal city where groundwater provides a strong support for social and economic development. Studies on the hydrochemical characteristics and formation mechanism in Beihai City play an important role in the scientific management of water resources and coastal ecological environment protection. In this study, we revealed the main hydrogeochemical processes controlling groundwater quality by means of groundwater survey and water sample collection in the western region of Hepu Basin, Beihai City, combined with hydrochemistry and isotope theories and methods. The results showed that groundwater had the remarkable features of low pH value and low mineralization degree. For pore water, hydrochemistry type by primarily NO3 type water and concentrations of Na+ and Cl- were modestly increased along the flow path. Ca-HCO3, Ca-Cl·HCO3, Ca·Na-HCO3, and Na-Cl·HCO3 types were predominant in fissure water. The groundwater was of meteoric origin, hydrogeochemical evolutions were mainly affected by water-rock interactions, cation exchange, and anthropogenic activities. Na+, K+, and Cl- were mainly derived from evaporite and silicate rocks; Ca2+, Mg2+, HCO3-, and SO42- were from carbonatite and evaporite; and NO3- principally arose from anthropogenic activities. This study suggests that the groundwater pollution prevention and control should be carried out as soon as possible in the area where the NO3 type water occurs to avoid the further deterioration of water quality.

Compositional data analysis (CoDA) and geochemical signatures of the terminal complex aquifer in an arid zone (northeastern Algeria)

The Biskra region, one of the arid regions in North-East Algeria, has known remarkable agricultural development, necessitating additional mobilization of groundwater resources, which are almost the only source of water in the region. In the long term, this heavy mobilization may threaten the quantity and quality of groundwater. This study was carried out to gain a better understanding of groundwater quality in the Terminal Complex (TC) aquifer of the Biskra region, to determine the hydrogeochemical processes controlling water mineralization, and further to investigate the suitability of the groundwater for consumption. For this purpose, multivariate statistical analysis, based on compositional data analysis (CoDA), including robust PCA, cluster analysis (HCA), ilr-ion diagram, and correlation analysis as well as graphical approaches, was carried out on the hydrochemical results of forty-four (44) groundwater samples analysed by standard methods. The results showed that most groundwater parameters exceeded WHO-recommended safe limits for drinking water. Robust CoDA revealed three distinct processes controlling groundwater hydrochemistry: the first “carbonate link” [NO3−, HCO3−, pH] at the northern boundary, which was progressively replaced by the second link [Ca2+, Mg2+, SO42−], and the third “mineralization link” [Na+, Cl−, K+, EC, TDS], located on the Outaya, Biskra, Sidi Okba, and El-Houche axes. In addition, around 93% of samples were within the geochemical zone [SO42− +Cl− >CO32-- HCO3−], while only 7% fell within the [CO32− - HCO3−> SO42− + Cl−] zone, with the following chemical facies dominating: Ca–SO4 (52.27%), Ca–Mg–SO4 (22.72%), Na–Cl (20.45%), and Ca–HCO3 (4.56%). The modified water quality index (WQI) revealed five quality classes: excellent (9.10%), good (11.36%), poor (65.90%), very poor (11.36%), and unsuitable quality (2.28%), with an apparent deterioration in water quality from north to south, following the same direction of groundwater flow. Finally, the use of CoDA with isometric log-ratio plotting, for the first time in the study area, has enabled a more thorough and reliable assessment of the processes controlling groundwater quality, which is valuable for rationalizing pumping and can help decision-makers to plan current and future water resource management practices.

Assessing the geochemical processes controlling groundwater quality and their possible effect on human health in Patna, Bihar.

This research was conducted in the urban area of Patna region, the capital and largest city of Bihar, which is part of the Indo-Gangetic alluvium plain. This study aims to identify the sources and processes controlling groundwater's hydrochemical evolution in the Patna region's urban area. In this research, we evaluated the interplay between several measures of groundwater quality, the various possible causes of groundwater pollution, and the resulting health risks. Twenty groundwater samples were taken from various locations and examined to determine the water quality. The average EC of the groundwater in the investigated area was 728 ± 331.84 µS/cm, with a range of around 300-1700 µS/cm. Positive loadings were seen for total dissolved solids (TDS), electrical conductivity (EC), calcium (Ca2+), magnesium (Mg2+), sodium (Na+), chloride (Cl-), and sulphate (SO42-) in principal component analysis (PCA), demonstrating that these variables accounted for 61.78% of the total variance. In the groundwater samples, the following main cations are the most prevalent such as Na+ > Ca2+ > Mg2+ > K+, while the dominant anions are HCO3- > Cl- > SO42-. The elevated HCO3- and Na+ ions indicate that carbonate mineral dissolution might affect the study area. The result demonstrated that 90% of samples fall into the Ca-Na-HCO3 type, remaining in the mixing zone. The presence of the NaHCO3 kind of water is suggestive of shallow meteoric water, which may have originated from the river Ganga that is located nearby. The results show that a multivariate statistical analysis and graphical plots successfully identify the parameters controlling groundwater quality. In accordance with guidelines for safe drinking water, the electrical conductivity and potassium ion concentrations in the groundwater samples are 5% higher than acceptable levels. People who take large amounts of salt replacements report feeling tight in the chest, vomiting, having diarrhoea, developing hyperkalaemia, having trouble breathing, and even experiencing heart failure.

Geochemical characteristics and evaluation of the potentially toxic metals in surface and groundwater in Akamkpa-Biase, southeastern Nigeria

This study investigated water quality using geochemical characteristics and potentially toxic metals in surface water and groundwater in Akamkpa-Biase, southeastern Nigeria. Mean concentrations of potentially toxic elements are within permissible limits for potable water, but pH (6.42) and Ba (0.093ppm) mean levels exceeded levels recommended for potable water by WHO (2009). Silicate and carbonate weathering, precipitation, and ion exchange are dominant geochemical processes controlling groundwater quality in the study area. Cations trend as Na > Ca > Mg and anion HCO3 > Cl > SO4 in water. Piper plot shows that Ca + Mg, HCO3 dominate the water type. ANOVA test revealed streams and groundwater sources contributed significantly to elemental concentrations in water. Silicate and carbonate weathering and anthropogenic inputs from mining and agricultural practices are the factors controlling water chemistry. Water sample classification based on metal load shows a dominance of near neutral low metal. Borehole water sources recorded near neutral/high metal classification were compared to shallow water sources. Mineral saturation indices (SI) at equilibrium (SI=0) were more than oversaturated (SI>0) and under saturated (SI 3). Contamination index possesses a mean value of 0.39. Heavy metal evaluation index and heavy metal pollution index attained mean values of 6.99 and 17.68, respectively. These values are below 100, which is the critical value for water pollution. This study provides vital information in environmental management strategies for water quality investigations in Nigeria and other parts of the world.

Using geochemical techniques to identify the origin of ions and processes controlling groundwater quality of Shahrood aquifer

آب زیرزمینی در مسیر جریان خود از محل تغذیه تا محل تخلیه، با مواد مختلفی در تماس بوده و واکنش‌های متعددی را متحمل می‌شود. طی این مسیر برخی از مواد در آب حل شده و برخی دیگر در آن رسوب می‌کنند و کیفیت آب در آبخوان دچار تغییراتی می‌شود. تعیین و شناخت عوامل مؤثر بر تغییرات کیفیت آب، می‌تواند گامی مؤثر در راستای مدیریت کیفی آبخوان‌ها باشد. آب زیرزمینی در شمال آبخوان شاهرود، داری تیپ بی‌کربناته و کیفیتی مطلوب با EC حدود (µs/cm) 671 است، که به تدریج در روندی رو به جنوب کیفیت آب کاهش یافته و در نهایت به آبی شور با تیپ کلراید سدیم و میزان EC (µs/cm) 11210 تبدیل می‌گردد. پژوهش حاضر به منظور شناسایی منشأ یون‌ها و فرآیندهای مهم کنترل کننده کیفیت آب آبخوان شاهرود صورت گرفته است. به منظور بررسی فرآیندهای ژئوشیمـیایی حاکم بر این آبخوان، با استفاده از نتایج آنالیز 120 نمونه آب زیرزمینی برداشت شده در خرداد 1397، نقشه‌های پراکندگی EC، تیپ آب، غلظت یون‌ها، و نمودارهای دو متغیره Ca2+Mg2 در برابر HCO3+SO4، Ca+Mg در برابر TDS، Na در برابرCl وCa در مقابل HCO3 و نمودارهای تبادلات یونی و شاخص‌های اشباع کانی‌های هالیت، ژیپس، کلسیت، دولومیت و آراگونیت ترسیم و استفاده گردید. براساس نتایج این پژوهش فـرآیندهای انحلال هالیت و ژیپس، رسوبگذاری کلسیت و دولومیت و تبادلات کاتیونی مستقیم و معکوس، از مهم‌ترین فرآیندهای کنترل کننده کیفیت آب آبخوان شاهرود هستند. خط تقسیم آب زیرزمینی باعث تغییراتی در روند کلی جهت جریان آب زیرزمینی گردیده و با جلوگیری از نفوذ آب شور وارد شده از بخش‌های شرقی و جنوب شرقی، به بخش‌های مرکزی و غربی آبخوان، باعث شده این توده‌های آب شور، تأثیر چندانی بر هیدروشیمی آبخوان شاهرود نداشته باشند.

Identification of the processes controlling groundwater quality in shallow aquifers of Moradabad city, west Uttar Pradesh, India

Present study has been carried out to identify the processes controlling groundwater quality of Moradabad city, Uttar Pradesh. A total 188 groundwater samples were collected and analyzed for major ions in pre- and post-monsoon seasons of years 2012 and 2013. Analysis results showed higher concentration of Na, K, Cl, SO4 and NO3. LL diagram showed dominance of alkalis and Cl + SO4, in three sampling seasons except in post-monsoon 2012, when Na + K–Cl + SO4 facies is recorded in 50% samples. There is dearth of HCO3 complexes in the pre-monsoon season of 2012, and then, their appearance in the post-monsoon season with alkali bicarbonates being 50%. This trend is reversed in 2013. Groundwater composition showed potential impact of varying rainfall pattern suggesting that chemistry of groundwater is intimately related to meteorological parameters. To predict minerals and their reactivity in groundwater, saturation index (SI) was calculated for pre- and post-monsoon of 2012. Groundwater is highly under-saturated with respect to halite, sulphates of Ca and fluorite and super-saturated with respect to chalcedony, quartz and talc, and these minerals may possibly be precipitated out. Relationship of SiO2 with Cl and TDS gives unequivocal evidence of anthropogenic factors having significant effect in determining the chemical characteristics of groundwater. Groundwater chemistry of the area is sum total of factors, such as, meteorological, hydrological and lithological and a set of processes related to various domains of anthropogenic activities, where variation in intensity and distribution of rainfall seems to be one of the driving factors responsible for overall temporal variations in groundwater chemistry.

EFFECTIVENESS OF A MODERN LANDFILL LINER SYSTEM IN CONTROLLING GROUNDWATER QUALITY OF AN OPEN HYDROGEOLOGICAL SYSTEM, SE LITHUANIA

The work analyzes data of environmental geological mapping, groundwater monitoring of the region municipal waste landfill. This study examines the effectiveness of a modern landfill liner system in minimizing migration of pollutants in the groundwater of an open hydrogeological system. The results showed that dissolution of carbonates and dilution were the major processes controlling groundwater quality. In the landfill’s direct impact zone, groundwater was only weakly polluted with biogenic components. Increase in concentrations of these chemical components in this zone was related with the groundwater and surface runoff water flowing from adjacent areas. We can state that the modern landfill liner system we analysed is efficient and has no adverse effects on groundwater quality under hydrogeological conditions favourable for the spread of pollutants. However, in case of an accident, pollutants might pose a great threat on the safety of groundwater. Therefore, even modern landfill liner systems are not recommended to be constructed in open hydrogeological systems.

Geochemical and isotopic characterization of groundwater in the alluvial aquifer of Guelma (north-eastern Algeria)

This study aims at determining the factors and the processes controlling groundwater quality, origin, and chemistry in the alluvial aquifer of Guelma northeastern of Algeria. Hydrochemical and isotopic investigations were carried out on 21 points, including boreholes, wells, springs, and surface waters in June 2016. A thorough hydrogeological investigation has revealed that groundwater is Ca–Mg/SO4–Cl facies. The combined use of geochemical tools and multivariate statistical analysis indicates that groundwater composition is largely governed by water-rock interactions, particularly the dissolution of evaporitic minerals as well as ion exchange processes. This study reports for the first time the isotopic contents (δ18O, δ2H) of the alluvial aquifer and the surface water. The stable isotope composition for the ground- and surfacewater samples has shown a homogeneous isotopic signature and reveals non-evaporated waters in the northern and central parts of the aquifer. This is the indication of the presence of a significant recharge by modern rainfall. Evaporated waters that are characterized by relatively enriched δ18O and δ2H contents are located in the western part of the plain. This suggests the occurrence of partial evaporation at the surface prior to, during, or after infiltration through the unsaturated zone.

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.

Identification of hydrogeochemical processes controlling groundwater quality in Tripura, Northeast India using evaluation indices, GIS, and multivariate statistical methods

Tripura is a water-rich administrative state in the Northeastern part of India. Though groundwater is the main source of drinking water, groundwater monitoring and historical data on the groundwater quality of this state is relatively scarce. This study aims to identify the sources and processes controlling the hydrochemical evolution of groundwater in Hezamara block in Tripura. Interpretation of measured parameters using geochemical plots, analysis of ionic ratios, multivariate statistical techniques, and spatial interpolation methods indicated both natural and anthropogenic sources. Results show that precipitation is the dominant process controlling the groundwater quality followed by rock–water interaction. Carbonate dissolution and silicate weathering were the major geochemical processes. The findings showed that the concentration of few heavy metals (iron, manganese, and lead) exceeded the drinking water quality standards. Evaluation of the results through various heavy-metal indices showed that several locations exceeded the limits and pose a risk to humans. Potential non-carcinogenic risk through the drinking water pathway was also identified. Pollution mapping indicates that only less than 1 km2 of the study area is suitable for drinking use. This study recommends installation of public drinking water supply in this area to reduce the impact of heavy-metal contamination on human health. Moreover, the water should be treated before supplying for public use.

Factors affecting groundwater quality in the area between Safaga and El Quseir, Eastern Desert, Egypt

The current study objective is to identify the hydro-geochemical processes and their relation with the groundwater quality in Safaga-El Quseir District, Egypt. The study approach includes conventional graphical plots and geochemical modeling of the hydrochemical data to define the evaluation of aquifer systems based on the ionic constituents, hydrochemical facies, and physiochemical processes controlling groundwater quality. The results suggest that different natural hydrogeochemical processes like simple dissolution, mixing, evaporation, weathering of carbonate minerals, silicate, and sulfate as well as ion exchange are the key factors controlling the groundwater quality at Safaga-El Quseir District. The results of geochemical modeling simulation show that the processes of evaporation, mixing, and water–rock interactions are the most effective processes governing the groundwater quality (composition) in study area. The mixing ratio of 90:10 (rain/Nubian) with evaporation of 90% gives a similar composition to Miocene groundwater, while a mixing ratio of 80:20 (rain/ Nubian) with evaporation of 90% lead to a composition similar to the Oligocene groundwater. As the contribution from the Nubian water component increase (becomes 50% or more), the simulation of mixing accompanied with evaporation of 90% gives a similar composition to both of the Alluvium and fractured basement aquifers which contain more mineralized water. The simulation of mixing in combination with evaporation gives results more comparable with the final compositions of the different samples collected from the study area than the simulation of evaporation alone. This is because both of evaporation and mixing have some bearings on the groundwater quality in Safaga-El Quseir District. The geochemical modeling results of the current study can be applied on similar localities along the Red Sea Coast in Egypt and Sudan.

Geochemical processes controlling groundwater quality under semi arid environment: A case study in central Morocco

Bahira plain is an important area for Morocco due to its agriculture and mining activities. Situated in a sub-arid to arid climate, this plain hosts an aquifer system that represents sequences of carbonates, phosphates, evaporates and alluvial deposits. Groundwater flows from Ganntour plateau (recharge area) to the basin-fill deposits and Zima Lake and Sed Elmejnoun where water evaporates. The objective of this study was to characterize the chemical properties of the groundwater and to assess the processes controlling the groundwater's chemistry. We can divide water samples into three hydrochemical water groups: recharge waters (Ca/Mg–HCO3), transition zone waters (Ca–HCO3–SO4/Cl) and discharge waters (Na-Cl/SO4). Accordingly, compositions of waters are determined by the availability of easily soluble minerals like calcite (Ca–HCO3 dominant), halite (Na–Cl dominant) and gypsum (Ca–SO4 dominant). Cl/Br ratios show that Cl concentration increases from dissolution of natural halite. When groundwater is affected by extreme evaporation Cl/Br ratios may increase up to 1900. High fluoride concentrations are associated with low Ca2+ concentrations (<100mg/L). That means when recharge waters enter the aquifer, it starts dissolving fluorite since the Ca2+ concentration is low. Once groundwater becomes saturated with Ca2+, the immobilization of fluoride is occurring by precipitation of fluoride-rich minerals like fluoro-apatite. According to the environmental isotope (18O and 2H) analyses, they are three potential processes affecting groundwater: 1. Evaporation as verified by low slope value, 2. Water-rock interaction, 3. admixture of waters showed different stable isotope compositions and salinities.

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.

Spatiotemporal variation of groundwater quality in an arid area experiencing long-term paper wastewater irrigation, northwest China

Groundwater is crucial for multiple uses over the world, especially in arid and semiarid regions. However, human activities significantly decreased groundwater quality. In this study, the spatiotemporal variation of groundwater quality was evaluated in an arid area where long-term paper wastewater irrigation has been implemented. For this study, seven wells were regularly monitored for physicochemical parameters over a period of 1 year. Statistical and graphical approaches were applied to interpret the spatiotemporal variation of groundwater quality parameters in the wastewater irrigation zone. Correlation analysis was also carried out to reveal the sources of some major ions. The results indicate that the groundwater type in the study area is dominated by the Cl–Na, followed by the HCO3–Na, the HCO3–Ca·Mg, and the SO4·Cl–Ca·Mg types. Groundwater in the area is significantly contaminated locally with fluoride, nitrite and ammonia, and the chemical oxygen demand levels were increased in some groundwater monitoring wells. Most contaminants showed an increasing trend from the Yellow River water irrigation zone toward the wastewater irrigation zone. Rock weathering, mineral dissolution, and cation exchange are important processes controlling groundwater quality, but human activities, such as wastewater irrigation, play an undeniable role in affecting groundwater quality in this area. The results of this study contribute to the understanding of the formation and circulation of groundwater under human activities and provide a scientific basis for regional water quality evaluation, water quality improvement, and protection.

Assessment of Groundwater Quality and Mapping Human Health Risk in Central Ganga Alluvial Plain, Northern India

The present paper deals with the assessment of hydrogeochemical processes controlling groundwater quality in Lucknow urban area located in an alluvial plain of Ganga-Gomti interfluve, India. Physico-chemical data were derived from 42 groundwater samples, and were further used to map human health risk in Lucknow monitoring area. The analysis reveals that the carbonate and silicate weathering along with reverse ion exchange, cation exchange, sulphide oxidation, dissociation of residual halides are the major solute processes controlling the ionic concentration of groundwater in Lucknow. Groundwater is predominantly of Na+-Ca2+-HCO3 − type having all cations and anions within prescribed WHO limits except for Fe2+ and NO3 −. Ionic concentrations of groundwater were combined to derive a Water Quality Index (WQI) using spatial overlay in Geographic Information Systems (GIS). WQI reveals that about 47.8% of the total 133.52 km2 area covering Cis-Gomti localities of the city has nearly poor water quality for drinking use which is possibly due to high Fe2+ and NO3 − influx in shallow unconfined aquifers. WQI is integrated with urban population density index data to map spatial distribution of human health risk due to consumption of poor water quality. Results reveal that the sites located in and around the vicinity of Alambagh, Kaiserbagh and Hazratganj, covering 9.81% of the total area, are potential ‘hot spot’ at moderate to high health risk, and require substantial remediation measures to control the anthropogenic influx on a long-term basis.

Hydrogeochemical processes controlling groundwater quality around Bomboré gold mineralized zone, Central Burkina Faso

This study investigates the processes that control dug well and borewell water chemistry in crystalline basement aquifers in semi-arid environment. Changes in SO42− and NO3− were observed in both dug well and borewell samples. Six dug wells and seven borewells had high NO3− concentrations relative to SO42− suggesting prevailing oxidizing redox conditions in these samples. The highest NO3− and SO42− concentrations were found in few borewells. These high concentrations could be attributed to low recharge rates and chemical weathering of sulfide minerals. The acidic conditions may have promoted AsT adsorption in the majority of dug wells. The saturation indices and correlation coefficients showed that most dug wells and some borewells were supersaturated with respect to Fe-bearing minerals, implying that trace elements such as AsT, Cu, Cr, Ni and Zn were likely to coprecipitate with residual Fe minerals. The low mobility of AsT in dug wells could be also explained by the limited carbonate mineral abundance in the weathered layer. By contrast, the elevated AsT concentrations observed in the majority of borewells reflected an extended water–rock interaction that had led to deportonation of surface charges of the aquifer minerals, thereby inhibiting AsT adsorption. The average concentration of FeT and total coliform content of dug well samples exceeded the World Health Organization (WHO) limits for drinking waters. Likewise, the average concentrations of FeT, AsT (~55% of samples) and Pb in borewells were higher than the WHO permissible limits. The study showed that the local groundwater resources are exposed to both anthropogenic and geogenic sources of pollution.

Geochemical influences on the quality of groundwater in eastern part of Semnan Province, Iran

To identify the principal geochemical processes controlling groundwater quality in eastern part of Semnan Province, a total of 257 groundwater samples from wells and springs were collected. Since groundwater is the only source of water for various purposes, preservation of the quality of available groundwater resources in this region is of great importance. The order of abundance of anions was Cl−>SO4 2−>HCO3 −>NO3 −>F−, and for them the average values were 509.41, 404.24, 120.48, 14.51, 0.59 mg/l, respectively. On the other hand, for cations, Na+ and Ca2+ with average values of 442.10 and 135.09 mg/l were the most abundant parameters. Geochemical characteristics based on bivariate diagrams indicated that Na release from silicate weathering is an important process whereas the dissolution of dolomite and the effect of silicate materials on the aquifer were other determinative processes influencing the quality of groundwater in the area. In order to predict the overall quality of groundwater with respect to a calculated water quality index (WQI), support vector machine (SVM) and artificial neural network (ANN) were utilized. The correlation coefficients between the predicted and observed WQI for the training and test data set related to SVM were 0.97 and 0.96, respectively. On the contrary, the results of ANNs with early stopping showed roughly the same performance resulting in correlation coefficients of 0.98 and 0.96 for the training and test data set, respectively. As a whole, the WQI for 8 % of the sampling stations was <50 and for 17 %, the calculated index was <60 which are important concerns.

Improving the Hydrogeological Conceptual Model of the Sidi Merzoug-Sbiba Aquifer System (North-West of Tunisia) Using Hydrochemistry and Isotopic Tools

The aim of the study is to improve the knowledge of the hydrogeological systems in the Sidi Merzoug Sbiba Basin (Northwestern Tunisia), using chemical and isotopic tools. Three major aquifers have been identified in this semi-arid region by previous hydrogeological studies: the Cretaceous, the Miocene and the Plio-Quaternary aquifers. Its hydrodynamic regime is largely influenced by tectonics, lithology and recharge conditions. Given the heterogeneity of the multilayer aquifer system in a complex fractured zone, an hydrochemical and environmental isotope (2H, 18O,3H and14C) data were used to caracterised the groundwater flow and provide valuable information about the geochemical processes controlling groundwater quality and the circulation patterns of the different groundwater bodies. Three major processes control the chemical composition: i) dissolution of carbonate minerals, ii) cation exchange reactions and iii) evaporation process. Stable isotopes indicate that most groundwater samples originate from infiltration of modern precipitation. A significant infiltration before evaporation takes place, indicating a major recharge directly from Cretaceous and Miocene formations of surrounding mountains and infiltration of surface water in the El Breck and Sbiba rivers. Downstream, the isotopic signature of evaporated water clearly indicates a recharge from rivers, irrigation fields or Sbiba dam. Tritium and 14C contents confirm the existence of modern groundwaters in the South-Western border and in the North -Eastern part of the basin and confirm the stratification of the system.

Chemical Evolution of the Continental Terminal Shallow Aquifer in the South of Coastal Sedimentary Basin of Benin (West-Africa) Using Multivariate Factor Analysis

In southern Benin, where population is growing and water demand for domestic activities is increasing, water balance assessment constitutes a serious concern about sustainability of water resources. Major ions have been employed with statistical methods to identify geochemical processes controlling groundwater quality. Multivariate statistical analysis (principal component analysis “PCA” and hierarchical cluster analysis “HCA”) revealed the main sources of groundwater mineralization. According to the hydrochemical data and the methods of treatment, groundwater mineralization in the investigated aquifer is caused by four main processes: 1) mixing with Nokoue lake and Porto-Novo lagoon salt water causing salinity to increase in the southern part of the aquifer; 2) anthropogenic activities; 3) cation exchange process; and 4) soil CO2 diffusion providing a large proportion of bicarbonates.

Hydrochemical Studies of Ground Water in Parts of Lagos, Southwestern Nigeria

Abstract Groundwater samples were randomly collected from forty-five protected dug wells and thirteen boreholes in parts of Lagos, Southwestern Nigeria. Samples were analysed for pH, electrical conductivity and total dissolved solids in situ. Cations (calcium, magnesium, potassium and sodium) and anions (chloride, bicarbonate, sulphate and carbonates) were determined in the laboratory after standard procedure. The study is aimed at examining the extent of groundwater pollution and its possible sources using multivariate and graphical techniques. Rockware software was used to characterize groundwater composition while the sample locations were mapped with ArcMap 9.3 software. The results show high mean value in the groundwater characteristics of the protected dug wells compared to the boreholes. A significant relationship exists among EC/ TDS and major ions indicating the influence of sea water on the groundwater quality. The dominant cations and anions are in the order of: Ca2+ &gt; Mg2+ &gt;Na+ &gt; K+; and Cl- &gt;HCO3 - &gt; SO42+ respectively. Factor analysis extracted two major sources of pollution (sea water and industrial) responsible for the processes controlling groundwater quality in the area. The Piper plot revealed seven distinct water types including Ca-HCO3, Ca-Cl, Mg-HCO3, Na-SO4, Mg-Cl, Na-HCO3 and Na-Cl representing 44.8%, 25%, 15.5%, 5.2%, 3.4%, 3.4%, and 1.7% respectively. The paper recommended monitoring of groundwater abstraction and treatment of industrial effluent before being released into the subsurface to prevent salinization and quality deterioration in the study area.