Hydrogeochemical characterization and quality assessment of groundwater using self-organizing maps in the Hangjinqi gasfield area,Ordos Basin,NW China

Water resources are scarce in arid or semiarid areas,which not only limits economic development,but also threatens the survival of mankind.The local communities around the Hangjinqi gasfield depend on groundwater sources for water supply.A clear understanding of the groundwater hydrogeochemical characteristics and the groundwater quality and its seasonal cycle is invaluable and indispensable for groundwater protection and management.In this study,self-organizing maps were used in combination with the quantization and topographic errors and K-means clustering method to investigate groundwater chemistry datasets.The Piper and Gibbs diagrams and saturation index were systematically applied to investigate the hydrogeochemical characteristics of groundwater from both rainy and dry seasons.Further,the entropy-weighted theory was used to characterize groundwater quality and assess its seasonal variability and suitability for drinking purposes.Our hydrochemical groundwater dataset,consisting of 10 parameters measured during both dry and rainy seasons,was classified into 6 clusters,and the Piper diagram revealed three hydrochemical facies:Cl-Na type(clusters 1,2 and 3),mixed type(clusters 4 and 5),and HCO3-Ca type(cluster 6).The Gibbs diagram and saturation index suggested thatweathering of rock-forming mineralswere the primary process controlling groundwater chemical composition and validated the credibility and practicality of the clustering results.Two-thirds of 45 groundwater samples were categorized as excellent-or good-quality and were suitable as drinking water.Cluster changes within the same and different clusters from the dry season to the rainy season were detected in approximately 78%of the collected samples.The main factors affecting the groundwater quality were hydrogeochemical characteristics,and dry season groundwater quality was better than rainy season groundwater quality.Based on this work,such results can be used to investigate the seasonal variation of hydrogeochemical characteristics and assess water quality accurately in the others similar area.     

Groundwater recharge in suburban areas of Hanoi,Vietnam: effect of decreasing surface-water bodies and land-use change

Over-exploited groundwater is expected to remain the predominant source of domestic water in suburban areas of Hanoi, Vietnam. In order to evaluate the effect on groundwater recharge, of decreasing surface-water bodies and land-use change caused by urbanization, the relevant groundwater systems and recharge pathways must be characterized in detail. To this end, water levels and water quality were monitored for 3 years regarding groundwater and adjacent surface-water bodies, at two typical suburban sites in Hanoi. Stable isotope (δ¹⁸O, δD of water) analysis and hydrochemical analysis showed that the water from both aquifers and aquitards, including the groundwater obtained from both the monitoring wells and the neighboring household tubewells, was largely derived from evaporation-affected surface-water bodies (e.g., ponds, irrigated farmlands) rather than from rivers. The water-level monitoring results suggested distinct local-scale flow systems for both a Holocene unconfined aquifer (HUA) and Pleistocene confined aquifer (PCA). That is, in the case of the HUA, lateral recharge through the aquifer from neighboring ponds and/or irrigated farmlands appeared to be dominant, rather than recharge by vertical rainwater infiltration. In the case of the PCA, recharge by the above-lying HUA, through areas where the aquitard separating the two aquifers was relatively thin or nonexistent, was suggested. As the decrease in the local surface-water bodies will likely reduce the groundwater recharge, maintaining and enhancing this recharge (through preservation of the surface-water bodies) is considered as essential for the sustainable use of groundwater in the area.

     

Hydrogeochemistry and groundwater quality assessment of the multilayered aquifer in Lower Kelantan Basin,Kelantan, Malaysia

Continual expansion of population density, urbanization, agriculture, and industry in most parts of the world has increased the generation of pollution, which contributes to the deterioration of surface water quality. This causes the dependence on groundwater sources for their daily needs to accumulate day by day, which raises concerns about their quality and hydrogeochemistry. This study was carried out to increase understanding of the geological setup and assess the groundwater hydrogeochemical characteristics of the multilayered aquifers in Lower Kelantan Basin. Based on lithological data correlation of exploration wells, the study area can be divided into three main aquifers: shallow, intermediate and deep aquifers. From these three aquifers, 101 groundwater samples were collected and analyzed for various parameters. The results showed that pH values in the shallow, intermediate and deep aquifers were generally acidic to slightly alkaline. The sequences of major cations and anions were Na⁺ > Ca²⁺ > Mg²⁺ > K⁺ and HCO₃^? > Cl^? > SO₄^2? > CO₃^2?, respectively. In the intermediate aquifer, the influence of ancient seawater was the primary factor that contributed to the elevated values of electrical conductivity (EC), Cl^? and total dissolved solids (TDS). The main facies in the shallow aquifer were Ca–HCO₃ and Na–HCO₃ water types. The water types were dominated by Na–Cl and Na–HCO₃ in the intermediate aquifer and by Na–HCO₃ in the deep aquifer. The Gibbs diagram reveals that the majority of groundwater samples belonged to the deep aquifer and fell in the rock dominance zone. Shallow aquifer samples mostly fell in the rainfall zone, suggesting that this aquifer is affected by anthropogenic activities. In contrast, the results suggest that the deep aquifer is heavily influenced by natural processes.     

Hydrogeochemical stratification of the unconfined Samobor aquifer (Zagreb,Croatia)

In the western part of the city of Zagreb, Croatia, hydrogeochemical and isotopic investigations of the Samobor aquifer were carried out with the aim of determining the differences in hydrogeochemical characteristics at increasing aquifer depths. The aquifer comprises 40-m thick gravelly–sandy deposits, with lenses and interlayers of silt and clay. The analyses have proven that with increasing aquifer depth, there are decreases in groundwater temperature and the values of electrical conductivity and increases in the sodium, iron and manganese concentrations. The δ¹³C distribution shows an evident increase in biogenic carbon concentrations with increasing aquifer depth. The measured specific ¹⁴C activities showed that the deeper part of the aquifer is characterized by slow water exchange, while the shallower part is influenced by current recharge, although the pumping wells located on the well-field downstream penetrate the aquifer fully. A direct exchange of water from the Sava River and groundwater occurs in the near vicinity of the river. This exchange weakens further away, while the difference in hydrogeochemical characteristics between the Sava River water and groundwater increases.     

Holocene estuarine sediments as a source of arsenic in Pleistocene groundwater in suburbs of Hanoi,Vietnam

Groundwater pollution by arsenic is a major health threat in suburban areas of Hanoi, Vietnam. The present study evaluates the effect of the sedimentary environments of the Pleistocene and Holocene deposits, and the recharge systems, on the groundwater arsenic pollution in Hanoi suburbs distant from the Red River. At two study sites (Linh Dam and Tai Mo communes), undisturbed soil cores identified a Pleistocene confined aquifer (PCA) and Holocene unconfined aquifer (HUA) as major aquifers, and Holocene estuarine and deltaic sediments as an aquitard layer between the two aquifers. The Holocene estuarine sediments (approximately 25–40 m depth, 9.6–4.8 cal ka BP) contained notably high concentrations of arsenic and organic matter, both likely to have been accumulated by mangroves during the Holocene sea-level highstand. The pore waters in these particular sediments exhibited elevated levels of arsenic and dissolved organic carbon. Arsenic in groundwater was higher in the PCA (25–94 μg/L) than in the HUA (5.2–42 μg/L), in both the monitoring wells and neighboring household tubewells. Elevated arsenic concentration in the PCA groundwater was likely due to vertical infiltration through the arsenic-rich and organic-matter-rich overlying Holocene estuarine sediments, caused by massive groundwater abstraction from the PCA. Countermeasures to prevent arsenic pollution of the PCA groundwater may include seeking alternative water resources, reducing water consumption, and/or appropriate choice of aquifers for groundwater supply.     

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

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

Estimated volume of water in shallow wells of Ekiti State,Southwestern Nigeria: implications on groundwater sustainability

Volumes of water in shallow wells of Ekiti State Southwestern Nigeria was estimated during the rainy and dry seasons of 2017 to categorize the area into different groundwater potential zones and to scrutinize it for groundwater sustainability and development. Locations of the wells were measured using etrex 12 Channel GPS while dip meter was employed for the water levels and depths of wells. The volume of water in a well was estimated employing V = πr²h (r and h are radius and water column of well, respectively). The wells in the area have low water storage (av. 6.91m³ and 2.70m³ in rainy and dry seasons, respectively). The study area had sufficient quantity of water in the rainy season to meet domestic, agricultural, and industrial requirements as deficiency was met from rainfall replenishment. Groundwater potential evaluation revealed that majority of the study area fell into very poor to poor water categories. Groundwater sustainability and development in the study area is a herculean task due to uncoordinated sitting of wells, low storage of water in the aquifers, and erratic occurrence of the groundwater. Hygiene education should be intensified in the area to forestall the risks post by the principal elements of fecal oral disease transmission.     

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.     

Behaviour of chromium VI in a multilayer aquifer in the industrial zone of Annaba,Algeria

Industrial wastewater is characterised by the presence of a great quantity of metallic micro-pollutants, among which chromium by its mobility, contaminates the surface and groundwater. The study of different aquifers within the area of Annaba (Algeria) shows extremely variable chromium concentrations in the unconfined aquifer (0–0.22 mg l⁻¹), which becomes practically null in dry period; on the other hand, they remain relatively constant in the deep confined aquifer (about 0.04 mg l⁻¹). To specify the mechanisms of chromium migration in the aquifer system, a study of space–time evolution of chromium concentrations in unconfined aquifer was undertaken, while considering the kinetics of diffusion in the deeper aquifer. Chromium, indirectly reduced microbiologically by sulphate-reducer bacteria in the upper aquifer, is likely to anticipate the auto-depuration capacity of the ground and to reduce the quality of groundwater.     

Hydro-environmental status and soil management of the River Nile Delta,Egypt

The sea level rise has its own-bearing on the coastal recession and hydro-environmental degradation of the River Nile Delta. Attempts are made here to use remote sensing to detect the coastal recession in some selected parts and delineating the chemistry of groundwater aquifers and surface water, which lie along south-mid-northern and coastal zone of the Nile Delta. Eight water samples from groundwater monitoring wells and 13 water samples from surface water were collected and analyzed for various hydrochemical parameters. The groundwater samples are classified into five hydrochemical facies on Hill-Piper trilinear diagram based on the dominance of different cations and anions: facies 1: Ca–Mg–Na–HCO₃–Cl–SO₄ type I; facies 2: Na–Cl–HCO₃ type II; facies 3: Na–Ca–Mg–Cl type III, facies 4: Ca–Na–Mg–Cl–HCO₃ type IV and facies 5: Na–Mg–Cl type V. The hydrochemical facies showed that the majority of samples were enriched in sodium, bicarbonate and chloride types and, which reflected that the sea water and tidal channel play a major role in controlling the groundwater chemical composition in the Quaternary shallow aquifers, with a severe degradation going north of Nile Delta. Also, the relationship between the dissolved chloride (Cl, mmol/l), as a variable, and other major ion combinations (in mmol/l) were considered as another criterion for chemical classification system. The low and medium chloride groundwater occurs in southern and mid Nile Delta (Classes A and B), whereas the high and very high chloride (classes D and C) almost covers the northern parts of the Nile Delta indicating the severe effect of sea water intrusion. Other facets of hydro-environmental degradation are reflected through monitoring the soil degradation process within the last two decades in the northern part of Nile Delta. Land degradation was assessed by adopting new approach through the integration of GLASOD/FAO approach and Remote Sensing/GIS techniques. The main types of human induced soil degradation observed in the studied area are salinity, alkalinity (sodicity), compaction and water logging. On the other hand, water erosion because of sea rise is assessed. Multi-dates satellite data from Landsat TM and ETM+ images dated 1983 and 2003 were used to detect the changes of shoreline during the last two decades. The obtained results showed that, the eroded areas were determined as 568.20 acre; meanwhile the accreted areas were detected as 494.61 acre during the 20-year period.     

Methodology of hydrogeological characterization of deep carbonate aquifers as potential reservoirs of groundwater. Case of study: the Jurassic aquifer of <Emphasis Type="Italic">El Maestrazgo</Emphasis> (Castellón,Spain)

A methodology for the characterization of deep carbonate aquifers has been developed and applied to El Maestrazgo Jurassic aquifer in Castellón, Spain. Characterization of these aquifer formations, located at more than 300 m deep, consisted of a previous phase of compilation, analysis and synthesis of the existing information about the area, followed by a coordinated combination of different speciality studies: geology, stratigraphy, structural analysis, hydrogeology, hydrochemistry, geophysics and remote sensing. Geological studies included geological mapping, definition of stratigraphical units and facies and structural analysis. The aim of the hydrogeology study was to define aquifer formations, recharge area, aquifer points inventory and groundwater flow directions for the establishment of piezometric and water quality observation nets. Special techniques were applied, like thermal infrared aerial images and the evaluation of submarine groundwater discharge by means of natural radium isotopes. Hydrochemical techniques, including majority elements characterization and stable isotopes (¹⁸O, ²H and ³H) determination, allowed classifying hydrochemical facies and establishing a renewal pattern for water within the system. Geophysics was useful in determining the aquifer geometry, the features of the basement and the petrophysical characteristics of the geological formations. Preliminary results show an important tectonic complexity and the possibilities for groundwater uses in the area of study.     

Groundwater chemistry and redox processes: Depth dependent arsenic release mechanism

Patchy occurrences of elevated As are often encountered in groundwater from the shallow aquifers (<50 m) of the Bengal Delta Plain (BDP). A clear understanding of various biogeochemical processes, responsible for As mobilization, is very important to explain this patchy occurrence and thus to mitigate the problem. The present study deals with the periodical monitoring of groundwater quality of five nested piezometeric wells between December 2008 and July 2009 to investigate the temporal changes in groundwater chemistry vis-a-vis the prevalent redox processes in the aquifer. Geochemical modeling has been carried out to identify key phases present in groundwater. A correlation study among different aqueous redox parameters has also been performed to evaluate prevailing redox processes in the aquifer. The long term monitoring of hydrochemical parameters in the multilevel wells together with hydrogeochemical equilibrium modeling has shown more subtle differences in the geochemical environment of the aquifer, which control the occurrence of high dissolved As in BDP groundwater. The groundwater is generally of Ca-HCO₃ type. The dissolved As concentration in groundwater exceeded both WHO and National drinking water standard (Bureau of Indian Standards; BIS, 10 μg L⁻¹) throughout the sampling period. The speciation of As and Fe indicate persistent reducing conditions within the aquifer [As(III): 87-97% of As_T and Fe(II): 76-96% of Fe_T]. The concentration of major aqueous solutes is relatively high in the shallow aquifer (wells A and B) and gradually decreases with increasing depth in most cases. The calculation of SI indicates that groundwater in the shallow aquifer is also relatively more saturated with carbonate minerals. This suggests that carbonate mineral dissolution is possibly influencing the groundwater chemistry and thereby controlling the mobilization of As in the monitored shallow aquifer. Hydrogeochemical investigation further suggests that Fe and/or Mn oxyhydroxide reduction is the principal process of As release in groundwater from deeper screened piezometric wells. The positive correlations of U and V with As, Fe and Mn indicate redox processes responsible for mobilization of As in the deeper screened piezometric wells are possibly microbially mediated. Thus, the study advocates that mobilization of As is depth dependent and concentrations of As in groundwater depends on single/combined release mechanisms.     

Preliminary evaluation of hydrochemistry of the Kalambaina Formation, Sokoto Basin, Nigeria

Hydrochemical investigations in the Kalambaina Formation have been initiated to determine potability and suitability of the shallow groundwater for domestic and agricultural uses. This limestone formation is an extensive aquifer supplying water to livestock and domestic wells in its outcrop areas. The aquifer is recharged by rainfall and discharges mainly into the Sokoto–Rima River system and lakes at Kware, Gwadabawa and Kalmalo in Nigeria. Because recharge to the aquifer is mainly from rainfall, the quality of the groundwater is controlled essentially by chemical processes in the vadose zone and locally by human activities. Water samples were taken at 11 sites comprising boreholes, dug wells and a spring and were chemically analysed for their major ion components. Hydrochemical results show water of fairly good quality. It is, however, hard and generally of moderate dissolved solids content. Concentration of the total dissolved solids is between 130 and 2,340 mg/l. Concentrations of ions vary widely but a high concentration of K⁺ is found in places. NO₃⁻ is on the higher side of the World Health Organization (WHO) permissible limits, indicating pollution in such areas. Groundwater chemistry is predominantly of two facies, namely the calcium–magnesium–bicarbonate and calcium–magnesium–sulphate–chloride facies. These facies probably evolved primarily as a result of dissolution of calcium and magnesium carbonates as well as some human/land-use activities.     

Hydrogeochemical characteristics and its role in controlling arsenic mobilization in a shallow aquifer

The relevance of groundwater hydrogeochemistry to explain the occurrence and distribution of arsenic in groundwater is of great interest. The insightful discussions on the control of shallow groundwater (< 50 m) hydrogeochemistry in arsenic mobilization are known to be a viable tool to explain the arsenic menace in shallow groundwater. The present investigation emphasizes the hydrogeochemical driver and/or control over the reductive dissolution of Fe-bearing host minerals and thereby releasing arsenic into the shallow groundwater of the study area. The study suggests that hydrogeochemical evolution is mainly governed by carbonate minerals dissolution, silicate weathering, and competitive ion-exchange processes in the shallow aquifers (< 50 m). The present study also indicates the prevalence of carbonate minerals dissolution over silicate weathering. The emergence of Cl⁻ concentration in the shallow groundwater founds the possibilities of anthropogenic inputs into the shallow aquifers (< 50 m). The reducing environment in shallow aquifers (< 50 m) of the study area is evident in the reductive dissolution of Fe- bearing shallow aquifer minerals which absorb arsenic in the solid phase and mobilize arsenic onto shallow groundwater. The study opted for many statistical approaches to delineate the correlation among major and minor ionic constituents of the groundwater which are very helpful to understand the comprehensive mechanism of arsenic mobilization into shallow groundwater.

     

The groundwater age in the Middle-Upper Devonian aquifer system, Lithuania

³H, δ¹³C and hydrochemical data were used to estimate the corrected groundwater age derived from conventional ¹⁴C age of dissolved inorganic carbon (DIC). The Middle-Upper Devonian aquifer system from the Baltic upland recharge area in eastern Lithuania towards the discharge area on the Baltic Sea coast in the west was considered. The concentration of total dissolved solids (TDS) in groundwater changes from 300 to 24,000  mg/L and increases downgradient towards the coast. The other major constituents have the same trend as the TDS. The hydrochemical facies of groundwater vary from an alkali-earth carbonates facies at the eastern upland area to an alkali-earth carbonate-sulfate and chloride facies at transit and discharge areas. Meteoric water percolating through the Quaternary and Devonian aquifers regulate the initial ¹⁴C activities of groundwater involving two main members of DIC: soil CO₂ with modern ¹⁴C activity uptake and dissolution of ¹⁴C-free aquifer carbonates. Other sources of DIC are less common. ¹⁴C activity of DIC in the groundwater ranged from 60 to 108 pMC at the shallow depths. With an increase of the aquifers depth the dolomitization of aqueous solution and leakage of the “old” groundwater from lower aquifers take place, traced by lower activities (7–30 pMC).     

Investigating the hydrogeological properties of springs in a karstic aquifer in Dorfak region (Guilan Province,Iran)

Karstic aquifers are considered as the main sources of groundwater in the northeast of Rudbar, Iran. The present study was conducted to evaluate the hydrogeological properties of karstic springs in this region. For this purpose, saturation indices (SI values) were calculated using the geochemical PHREEQC model for a number of minerals in the groundwater in the karstic aquifer. Moreover, AqQA-RockWare software packages were used to prepare hydrogeochemical plots for the aquifer, using which the sources of the ions in the water were identified. The origin of bicarbonate, calcium, and magnesium ions in water was determined using chloro-alkaline indices. Moreover, through plotting a Piper diagram for spring water samples, it was discovered that water type of all springs is the Ca-HCO₃ type, confirming the karstic characteristic of springs in the area. A Durov diagram also suggests that the water composition of the springs is of the bicarbonate type with the dominant Ca cation, suggesting the calcareous effects of the region on the quality of groundwater and exhibiting a single source for the springs. The calculated saturation indices show that most of the water samples are undersaturated with respect to calcite, dolomite, and CO₂. The stable isotopes (δ¹⁸O and δ²H) and deuterium excess values were used to get information about transport pathways in groundwater, atmospheric moisture, and the degree of interaction between these reservoirs. The degree of karstification of the recharge area of the karst aquifer was determined to be 5.5 from an analysis of the hydrograph Sefidab Spring.     

Groundwater arsenic in the Chaco-Pampean Plain,Argentina: case study from Robles county,Santiago del Estero Province

In large parts of rural Argentina people depend on groundwater whose As content exceeds the Argentine drinking water standards (0.05 mg l⁻¹). The most affected areas are located in the Chaco-Pampean Plain, where aquifers comprise Tertiary loess deposits (in the Pampean Plain) and Tertiary and Quaternary fluvial and aeolian sediments (in the Chaco Plain). Robles county is located in the alluvial cone of the Dulce River consisting of loess (aeolian), and gravel, silt, sand and clay (alluvial) deposits. In the shallow aquifers, more than 48% of the 63 studied wells show As at toxic levels (maximum 4.8 mg l⁻¹), while in the deep groundwater the concentration is below 0.05 mg l⁻¹. The pH of the shallow groundwaters range between 6.5 and 9 and generally have high electrical conductivity with mean values of 2072 and 1693 μS/cm⁻¹ in the years 1998 and 1999, respectively. Arsenic concentrations are high in the alkaline Na–HCO₃ type groundwaters, where As correlates positively with Na⁺ and HCO₃⁻. Moreover, As correlates positively with Mo, U, and V, while a negative correlation was observed with Ca²⁺ and Mg²⁺. The potential sources of groundwater As are: (i) layers of volcanic ash with 90% of rhyolitic glass; (ii) volcanic glass dispersed in the sediments; and (iii) clastic sediments of metamorphic and igneous origin. Great lateral variability in the concentration of groundwater As is caused by several hydrogeological and hydrogeochemical factors.     

Mass balance simulation and its application to refining flow field in Binchang area,China

Groundwater flow fields in aquifers are often determined by water level data measured in monitoring wells. The flow field can be further refined by mass balance simulations, especially when groundwater level data is limited. The mass balance simulation is based on the principle of mass conservation and relies on water quality data in the same aquifer. The approach is applied to the Luohe aquifer in the Binchang area, China. The water-rock interactions and the hydrogeochemical evolution were studied along four typical flow paths. The study indicates that groundwater in the Luohe formation flows from the southern border to the interior of the Ordos Basin. The southern border, approximately 1,400 km², is a recharge zone, where the Luohe formation outcrops. The total dissolved solids of the groundwater in the southern boarder are less than 1 g/l, and the hydrochemistry type is HCO₃–Na. This new finding refines the flow field of the water-bearing formation, and an additional 1,400 km² is included in the water resource planning of the area.     

Hydrogeochemical characterization and groundwater quality assessment in the intensive agricultural zone of the Upper Cheliff plain,Algeria

The alluvial aquifer of Upper Cheliff (northern Algeria) is known for its intensive agricultural activities, which is based especially on groundwater exploitation. This aquifer is now facing a dual problem of quantity and quality, with a decrease in the groundwater levels and an increase in mineralization. Twenty monitoring samples were collected and analyzed for major ion during the dry season 2014. In the present study, we try to characterize the hydrogeochemical processes and to assess the impact of natural and anthropogenic conditions on groundwater mineralization. The analytical results of the dry season 2014 show a groundwater quality slightly alkaline (pH > 7) and indicate that the majority of samples have a values exceeding the limits of potability fixed by WHO in 2008, due to the various sources of anthropogenic pollution. The Piper diagram shows the dominance of groundwater types: Ca–Cl, the mixed facies (Cl–SO₄–Ca–Mg), and Ca–HCO₃: The mineralization process in this aquifer is mainly controlled by the lithology of the aquifer (exchange water–rock and weathering of calcareous crust dissolution in the unsaturated zone), by anthropogenic factors (discharges of untreated urban sewage, intensive use of fertilizers in agriculture and the use of domestic septic tanks by rural inhabitants) and also by geoclimatic conditions (semiarid climate). Suitability of groundwater shows more than 80% of samples have very poor quality for drinking and more than 20% of samples indicate a quality unsuitable for irrigation.     

Carbonate and carbon isotopic evolution of groundwater contaminated by produced water brine with hydrocarbons

The major ionic and dissolved inorganic carbon (DIC) concentrations and the stable carbon isotope composition of DIC (δ¹³C_DIC) were measured in a freshwater aquifer contaminated by produced water brine with petroleum hydrocarbons. Our aim was to determine the effects of produced water brine contamination on the carbonate evolution of groundwater. The groundwater was characterized by three distinct anion facies: HCO₃⁻-rich, SO₄²⁻-rich and Cl⁻-rich. The HCO₃⁻-rich groundwater is undergoing closed system carbonate evolution from soil CO_2(g) and weathering of aquifer carbonates. The SO₄²⁻-rich groundwater evolves from gypsum induced dedolomitization and pyrite oxidation. The Cl⁻-rich groundwater is contaminated by produced water brine and undergoes common ion induced carbonate precipitation. The δ¹³C_DIC of the HCO₃⁻-rich groundwater was controlled by nearly equal contribution of carbon from soil CO_2(g) and the aquifer carbonates, such that the δ¹³C of carbon added to the groundwater was −11.6‰. In the SO₄²⁻-rich groundwater, gypsum induced dedolomitization increased the ¹³C such that the δ¹³C of carbon added to the groundwater was −9.4‰. In the produced water brine contaminated Cl⁻-rich groundwater, common ion induced precipitation of calcite depleted the ¹³C such that the δ¹³C of carbon added to the groundwater was −12.7‰. The results of this study demonstrate that produced water brine contamination of fresh groundwater in carbonate aquifers alters the carbonate and carbon isotopic evolution.