Hydrochemical and isotopic characterization of groundwater in the southeastern part of the Plateaux Region,Togo

Hydrochemical, inverse geochemical modelling and isotopic approaches are used to assess the hydrogeochemical evolution of groundwater from the basement aquifers in the southeastern part of the Plateaux Region, Togo. Groundwater originates from present-day rainwater infiltration and is mostly fresh and slightly acidic to neutral. Hydrochemical facies are predominantly mixed cations-HCO₃ associated with Ca/Mg-Cl, Na-HCO₃ and Na-Cl water types in equilibrium with kaolinite and Ca/Mg-smectites. They are related to silicates hydrolysis, anthropogenic contamination, nitrification/denitrification, mixing along flowpaths and dissolution/precipitation of secondary minerals. The pattern of flow paths is in accordance with an increasing trend in total dissolved solids (TDS) toward the potentiometric depression located in the central and southern parts of the aquifer system. Inverse geochemical modelling using the NETPATH-WIN model showed the relative importance of biotite, plagioclase and amphibole weathering and dissolution of secondary carbonate minerals along the flowpath, suggesting that an abundance of minerals is not necessarily the main factor controlling the groundwater chemistry evolution.     

Application of inverse geochemical modelling for predicting surface water chemistry in Ekbatan watershed,Hamedan, western Iran

ABSTRACT

A study of surface water chemistry evolution was conducted by multivariate statistical analysis and inverse geochemical modelling using the PHREEQC computer program. Using hierarchical cluster analysis the 14 sampling sites were classified into three groups (recharge, transition and discharge areas). Water chemistry changed along a flow path so that waters with Ca–HCO₃ and Mg–Cl composition changed to Mg–Cl–HCO₃ waters. The order of abundance of the major cations was Mg > Ca > Na > K. Their average concentrations were 21, 19, 3.6 and 2.5 mg L^-1, respectively. Inverse geochemical modelling along flow paths indicated that the dissolution of sylvite and kaolinite, and precipitation of feldspars and andalusite, happened with Na entering the solution and Ca, Mg and K leaving the solution.

Editor D. Koutsoyiannis; Associate editor not assigned     

Hydrogeochemical Evolution Along Groundwater Flow Paths in the Manas River Basin,Northwest China

The impacts of long-term pumping on groundwater chemistry remain unclear in the Manas River Basin, Northwest China. In this study, major ions within five surface water and 105 groundwater samples were analyzed to identify hydrogeochemical processes affecting groundwater composition and evolution along the regional-scale groundwater flow paths using the multivariate techniques of hierarchical cluster analysis (HCA) and principal components analysis (PCA) and traditional graphical methods for analyzing groundwater geochemistry. HCA classified the groundwater samples into four clusters (C1 to C4). PCA reduced the dimensionality of geochemical data into three PCs, which explained 86% of the total variance. The results of HCA and PCA were used to identify three zones: “recharge,” “transition,” and “discharge.” In the recharge zone the groundwater type is Ca-HCO₃-SO₄ and is primarily impacted by the dissolution of calcite and silicate weathering. In the transition zone the groundwater type is Ca-HCO₃-SO₄-Cl and is impacted by rock dissolution and reverse ion exchange. In the discharge zone the groundwater type is Na-Cl and is impacted by evaporation and reverse ion exchange. In addition, anthropogenic activities impact the groundwater chemistry in the study area. The groundwater type generally changes from Ca-HCO₃-SO₄ in the recharge area to Na-Cl in the discharge area along the regional-scale groundwater flow paths. This study provides a process-based knowledge for understanding the interaction of groundwater flow patterns and geochemical evolution within the Manas River Basin.     

Using multivariate statistical techniques and geochemical modelling to identify factors controlling the evolution of groundwater chemistry in a typical transitional area between Taihang Mountains and North China Plain

Identifying the key factors controlling groundwater chemical evolution in mountain-plain transitional areas is crucial for the security of groundwater resources in both headwater basins and downstream plains. In this study, multivariate statistical techniques and geochemical modelling were used to analyse the groundwater chemical data from a typical headwater basin of the North China Plain. Groundwater samples were divided into three groups, which evolved from Group A with low mineralized Ca-HCO₃ water, through Group B with moderate mineralized Ca-SO₄-HCO₃ water, to Group C with highly saline Ca-SO₄ and Ca-Cl water. Water-rock interaction and nitrate contamination were mainly responsible for the variation in groundwater chemistry. Groundwater chemical compositions in Group A were mainly influenced by dissolution of carbonates and cation exchange, and suffered less nitrate contamination, closely relating to their locations in woodland and grassland with less pronounced human interference. Chemical evolution of groundwater in Groups B and C was gradually predominated by the dissolution of evaporites, reverse ion exchange, and anthropogenic factors. Additionally, the results of the inverse geochemical model showed that dedolomitization caused by gypsum dissolution, played a key role in the geochemical evolution from Group A to Group B. Heavy nitrate enrichment in most groundwater samples of Groups B and C was closely associated with the land-use patterns of farmland and residential areas. Apart from the high loads of chemical fertilizers in irrigation return flow as the main source for nitrate contamination, the stagnant zones, flood irrigation pattern, mine drainage, and groundwater-exploitation reduction program were also important contributors for such high mineralization and heavy NO₃⁻ contents in Group C. The important findings of this work not only provide the conceptual framework for the headwater basin but also have important implications for sustainable management of groundwater resources in other headwater basins of the North China Plain.     

Identification of hydrogeochemical processes in the Coimbatore district,Tamil Nadu,India

ABSTRACT

Hydrogeochemical investigations were carried out with an objective to identify the processes affecting the chemistry of groundwater in the Coimbatore district of Tamil Nadu, India. Thirty-three groundwater samples were collected from representative wells for chemical analysis. Groundwater types identified from piper plots were Ca-Mg-Cl and Na-Cl. The dominance of ions was in the order of Na>Ca>Mg>K and Cl>HCO₃>SO₄>CO₃. Spatial variation diagrams of ions were generated using the geostatistical analyst tool ArcGIS 9.3. According to these diagrams, most of the ions were higher in the northeast and southeast regions. This is attributed to the flow direction of the groundwater and high residence times. Gibbs diagrams identified rock–water interaction as an important geochemical process in the district. Evaporation, ion exchange, silicate weathering and dissolution of carbonate minerals were identified as other important hydrogeochemical processes which influence the groundwater chemistry of the study area.

EDITOR D. Koutsoyiannis ASSOCIATE EDITOR M. Besbes     

Seawater–freshwater mixing and resulting calcite dissolution: an example from a coastal alluvial aquifer in eastern South Korea

Abstract

In order to evaluate groundwater quality and geochemical reactions arising from mixing between seawater and dilute groundwater, we performed a hydrochemical investigation of alluvial groundwater in a limestone-rich coastal area of eastern South Korea. Two sites were chosen for comparison: an upstream site and a downstream site. Data of major ion chemistry and ratios of oxygen–hydrogen isotopes (δ¹⁸O, δD) revealed different major sources of groundwater salinity: recharge by sea-spray-affected precipitation in the upstream site, and seawater intrusion and diffusion zone fluctuation in the downstream site. The results of geochemical modelling showed that Ca²⁺ enrichment in the downstream area is caused by calcite dissolution enhanced by the ionic strength increase, as a result of seawater–groundwater mixing under open system conditions with a constant P_CO2 value (about 10^?1.5 atm). The results show that, for coastal alluvial groundwater residing on limestone, significant hydrochemical change (especially increased hardness) due to calcite dissolution enhanced by seawater mixing should be taken into account for better groundwater management. This process can be effectively evaluated using geochemical modelling.

Editor D. Koutsoyiannis; Associate editor Y. Guttman

Citation Chae, G.-T., Yun, S.-T., Yun, S.-M., Kim, K.-H., and So, C.-S., 2012. Seawater–freshwater mixing and resulting calcite dissolution: an example from a coastal alluvial aquifer in eastern South Korea. Hydrological Sciences Journal, 57 (8),1–12.     

Hydrogeochemical evaluation of high-fluoride groundwaters: a case study from Mehsana District,Gujarat, India

Abstract

Groundwater quality problems have emerged in many geographical areas due to natural environmental processes and human intervention in the geosystems. Hydrogeochemical appraisal of fluoride contaminated groundwater in Mehsana District, Gujarat State, India is carried out by means of groundwater quality investigations together with X-ray diffraction analysis of soil samples in the delineated high fluoride areas. Results show that fluoride has negative relationships with calcium, whereas relationships with sodium, alkalinity and sulphate are positive. Results obtained from aqueous speciation modelling using PHREEQC reveal that the groundwater is undersaturated with fluorite and oversaturated with calcite. The factor analysis indicates that sodium plus potassium bicarbonate groundwater have high factor loading for fluoride, whereas that for calcium chloride and magnesium chloride groundwater is low. The plausible geochemical reactions in the study area are precipitation of calcite and dissolution of dolomite, carbon dioxide and sulphate minerals with ion exchange.     

Acquisition de salinité et qualité des eaux d’une nappe profonde en Tunisie: approche statistique et géochimique

Abstract

The multi-layered Jeffara de Gabes aquifer system is greatly influenced by tectonics. This system is limited at the base and laterally by evaporite layers and has lateral contacts with the sebkhas (salt flats). The groundwater in this aquifer is characterized by high salinity (3–10 g L^-1). Multivariate statistical analysis and a geochemical approach were applied to determine the influence of the evaporite layers and sebkhas on the hydrochemical quality of the Jeffara de Gabes aquifer, and to understand the processes governing its salinity. According to these methods, and based in part on the Sr²⁺/Ca²⁺ ratio, it is demonstrated that the strong salinity of the groundwater is due to interactions between water and the evaporite layers that act as a substratum of this aquifer, as well as saltwater intrusion from the sebkhas. Moreover, the medium- to poor-quality groundwaters are characterized by geochemical interactions: cationic exchange and the precipitation/dissolution process of minerals in the aquifer formations.

Editeur Z.W. Kundzewicz

Citation Ben Alaya, M., Zemni, T., Mamou, A. et Zargouni, F., 2014. Acquisition de salinité et qualité des eaux d’une nappe profonde, Tunisie: approche statistique et géochimique. Hydrological Sciences Journal, 59 (2), 395–419.     

Genesis of arsenic in groundwater of North Bengal Plain using PCA: A case study of English Bazar Block,Malda District,West Bengal,India

The study area is located on the western part of the alluvium‐filled gap between the Rajmahal hills on the west and the Garo hills on the east. Groundwater occurs under unconfined condition in a thick zone of saturation within the Quaternary alluvial sediments. Three hydrochemical facies with distinct characteristics have been identified which are dominated in general by alkaline earths and weak acids. The major‐ion chemistry of the area is controlled by weathering of silicate minerals, rainfall recharge, ion‐exchange processes and anthropogenic activities such as irrigation return flow and the application of inorganic fertilizers and pesticides. A stoichiometric approach suggests that mineral dissolution and anthropogenic activities contribute 79% and 21% of the total cations dissolved in groundwater. Principal component analysis (PCA) of 42 groundwater samples using 13 chemical parameters indicates that the combined processes of recharge of groundwater from rainfall, sediment water interaction, groundwater flow, infiltration of irrigation return water (which is arsenic rich due to the use of arsenic‐bearing pesticides, wood preservatives, etc. and the pumping of arsenic‐rich groundwater for agriculture purpose), oxidation of natural or anthropogenic organic matter and the reductive dissolution of ferric iron and manganese oxides play a key role in the evolution of groundwater in the study area. Factor 2 scores, associated with the infiltration of irrigation return water and spatial distribution of arsenic concentration reveal that the groundwater of the municipal area will not be affected by arsenic in the future in spite of heavy groundwater abstraction. Another PCA with geologic, geomorphic, anthropogenic, geochemical and landuse factors indicates that arsenic concentration in groundwater increases with increasing area of mango orchards, sand lithofacies and nitrate and decreases with increasing distance of paleochannel from the monitored well and depth of bore wells. High loading on nitrate may be attributed to the use of fertilizer, pesticides, etc. in mango orchards and agricultural land. High loadings on log pCO₂, mango orchards (with negative sign) and phosphate (with positive sign) indicate that mango orchards provide the organic waste material which is decomposed to form organic carbon. The organic carbon undergoes oxidative carbon degeneration by different oxidants and increases the concentration of CO₂ in the aquifer. The reducing condition thus developed in the aquifer helps to dissolve the arsenic adsorbed on iron hydroxide or oxy‐hydroxide coated margins of sand, iron rich heavy mineral grain margins, clay minerals and Fe–Mn concretions present in the aquifer matrix. Copyright © 2007 John Wiley & Sons, Ltd.     

Groundwater quality in some Voltaian and Birimian aquifers in northern Ghana—application of mulitvariate statistical methods and geographic information systems

Abstract

Groundwater is a priceless resource in the economies of the rural populations in northern Ghana. A combination of multivariate statistical and spatial analytical techniques was applied to groundwater data from the Voltaian and Birimian aquifers in parts of northern Ghana. The objective was to classify the groundwater quality control parameters and determine whether the aquifers deliver groundwater of acceptable quality for domestic and commercial irrigation purposes. It was found that groundwater quality is dominated by the weathering of accessory minerals that are predominant in the Obosum and Oti beds of the Middle Voltaian in the north, and incongruent silicate mineral weathering ranks second among the major causes of variation. The two processes account for over 70% of the total variance in the hydrochemistry and interpolation maps generated for these two major factors are discussed. The mineral weathering and dissolution processes are less apparent within the Birimian aquifers. Four spatial groundwater types were distinguished by differences in EC and pH, which are high among the water types within the Obosum and Oti beds, and generally low within the Birimian aquifers. Mineral stability diagrams suggest that montmorillonite is the most stable clay mineral phase in the system, a significant finding in terms of cation exchange processes. This, in turn, has affected the irrigation quality of groundwater from the aquifers in the area. Our findings suggest that the Birimian aquifers are more suitable for irrigation, due to generally low salinities and sodicities, and those associated with the Obosum and Oti beds of the Middle Voltaian are less suitable.

Editor D. Koutsoyiannis; Associate editor Y. Guttman

Citation Yidana, S.M., Banoeng-Yakubo, B., Aliou, A.-S., and Akabzaa, T., 2012. Groundwater quality in some Voltaian and Birimian aquifers in northern Ghana—application of mulitvariate statistical methods and geographic information systems. Hydrological Sciences Journal, 57 (6), 1168–1183.     

Understanding the extent of interactions between groundwater and surface water through major ion chemistry and multivariate statistical techniques

The present work examines the possible use of major ion chemistry and multivariate statistical techniques as a rapid and relatively cost‐effective method of identifying the extent of groundwater and surface water (GW–SW) interaction in an urban setting. The original hydrogeochemical dataset consists of groundwater (n = 114), stream water (n = 42) and drain water (n = 24) samples, collected twice in a year for the pre‐ and post‐monsoon seasons, for three successive years along an 8 km reach of the Delhi segment of River Yamuna, India. The dynamic and similar seasonal changes of hydro‐geochemical facies and major ion trends of river, drain and groundwater samples indicate the existence of an empirical relationship between GW and SW. Results of both R‐ and Q‐mode factor and cluster analyses highlight multi‐scale control of the fluid exchange distributions, with distinct seasonal alteration in mode and extent of GW–SW interaction, namely, the influence of the mixing zones between urban river and groundwater and the pattern of groundwater flow through the river bed. Hierarchical cluster analysis (HCA) of sampling locations efficiently illustrates different groups that comprise samples severely influenced by contaminated surface water downstream and the upstream fresh water samples. These results substantiate the strong exchange processes between GW and SW all along the stretch. The study shows that the combination of an empirical and statistical relationship between different ionic species and sampling locations can provide greater confidence in identifying the extent of GW–SW interaction/exchange processes. Copyright © 2008 John Wiley & Sons, Ltd.     

Hydrochemical characteristics and groundwater evolution modeling in sedimentary rocks of the Tono mine,Japan

Based on geochemical data collected by Japan Nuclear Cycle Development Institute (JNC) in the Tono uranium mine, a conceptual groundwater evolution model developed by JNC is tested to evaluate whether equilibrium-based concepts of water–rock interaction are consistent with observed variations in the mineralogy and hydrochemistry of the Tono mine area. The chemical evolution of the groundwaters is modeled assuming local equilibrium for selected mineral–fluid reactions, taking into account the rainwater origin of these solutions. Results suggest that it is possible to interpret approximately the actual groundwater chemistry (i.e., pH, Eh, total dissolved concentrations of Si, Na, Ca, K, Al, carbonate and sulfate) if the following assumptions are adopted (a) CO₂ concentration in the gas phase contacting pore solutions in the overlying soil zone=10⁻¹ atm, and (b) minerals in the rock zone that control the solubility of respective elements in the groundwater include: chalcedony (Si), albite (Na), kaolinite (Al), calcite (Ca and carbonate), muscovite (K) and pyrite (Eh and sulfate). This result helps to build confidence in the use of simplified geochemical modeling techniques to develop an understanding of dominant geochemical reactions controlling groundwater chemistry in rocks similar to those that could be used for the geological disposal of radioactive wastes. It is noted, however, that the available field data may not be sufficient to adequately constrain parameters in the groundwater evolution model. In particular, more detailed information characterizing certain site properties are needed to improve the model. For this reason, a model that accounts for ion-exchange reactions among clay minerals, and which is based on the results of laboratory experiments, has also been evaluated in the present study. Further improvement of model considering ion-exchange reactions are needed in future, however.     

Water-rock interactions drive chemostasis

The western U.S. is experiencing shifts in recharge due to climate change, and it is currently unclear how hydrologic shifts will impact geochemical weathering and stream concentration–discharge (C–Q) patterns. Hydrologists often use C–Q analyses to assess feedbacks between stream discharge and geochemistry, given abundant stream discharge and chemistry data. Chemostasis is commonly observed, indicating that geochemical controls, rather than changes in discharge, are shaping stream C–Q patterns. However, few C–Q studies investigate how geochemical reactions evolve along groundwater flowpaths before groundwater contributes to streamflow, resulting in potential omission of important C–Q controls such as coupled mineral dissolution and clay precipitation and subsequent cation exchange. Here, we use field observations—including groundwater age, stream discharge, and stream and groundwater chemistry—to analyse C–Q relations in the Manitou Experimental Forest in the Colorado Front Range, USA, a site where chemostasis is observed. We combine field data with laboratory analyses of whole rock and clay x-ray diffraction and soil cation-extraction experiments to investigate the role that clays play in influencing stream chemistry. We use Geochemist's Workbench to identify geochemical reactions driving stream chemistry and subsequently suggest how climate change will impact stream C–Q trends. We show that as groundwater age increases, C–Q slope and stream solute response are not impacted. Instead, primary mineral dissolution and subsequent clay precipitation drive strong chemostasis for silica and aluminium and enable cation exchange that buffers calcium and magnesium concentrations, leading to weak chemostatic behaviour for divalent cations. The influence of clays on stream C–Q highlights the importance of delineating geochemical controls along flowpaths, as upgradient mineral dissolution and clay precipitation enable downgradient cation exchange. Our results suggest that geochemical reactions will not be impacted by future decreasing flows, and thus where chemostasis currently exists, it will continue to persist despite changes in recharge.     

Plagioclase weathering in the groundwater system of a sandy,silicate aquifer

The weathering rate of plagioclase was estimated in the groundwater system of a sandy, silicate aquifer formed after the Wisconsin Glacial Stage. The study area is an isthmus lying between Crystal and Big Muskellunge Lakes in northern Wisconsin, USA. Plagioclase occupies 3% of the quartz and K‐feldspar dominated sediments. Groundwater in the study area is recharged in part by precipitation through the isthmus soils and in part by seepage from Crystal Lake, which is of low ionic strength and chemically in steady state. Water analysis revealed that the chemistry of groundwater recharged from Crystal Lake is regulated by mineral dissolution reactions. The rate constant for plagioclase was estimated using mass balances for sodium concentrations along a groundwater flowline from Crystal Lake. For this calculation, various kinds of hydrological/mineralogical information were used: groundwater flow path from oxygen isotope analysis, groundwater travel times from flow modelling, mineral composition from microprobe analysis and surface area of minerals from BET (Brunauer–Emmett–Teller) analysis. The overall range of the estimation was less than an order of magnitude (3·5 × 10^?16 to 3·4 × 10^?15 mol/m²/s). The result is up to three orders of magnitude slower than the previous field estimates, which applied geometric methods in measuring mineral surface areas. However, this result is somewhat higher than the estimates reported by other BET area‐based studies, which were undertaken on soil profiles having different hydrological conditions. This rate difference is interpreted as a result of higher mineral reactivity owing to younger sediment age. The rate difference is smaller when this result is compared with the estimates from the soils of similar age, indicating that the differences in hydrological condition are not sufficient to explain the weathering rate discrepancy between the laboratory and field studies, which is up to five orders of magnitude. Copyright © 2002 John Wiley & Sons, Ltd.     

Distribution and assessment of hydrogeochemical processes of F-rich groundwater using PCA model:a case study in the Yuncheng Basin,China

Hydrogeochemistry and factor analysis were conducted together to assess the distribution and the major geochemical processes in fluoride-contaminated shallow groundwater in the Yuncheng Basin.Spatially,fluoride concentration was low(<1.5 mg/L)in the southern piedmont plain,medium(<4 mg/L)in the central basin,and high(up to 14.1 mg/L)in Kaolao lowland areas in shallow aquifers.A three-factor principal component analysis model explained over 75.1%of the total variance.Sediment weathering leaching and evapotranspiration were recognized as the first primary hydrochemical processes response for the groundwater chemistry and explained the largest portion(42.1%)of the total variance.Factor two reflects the negative influence of human activities,with a positive loading of NO3^-and HCO3^-,and negative loading of well depth.Fluoride-bearing mineral dissolution and alkaline condition was ranked as the third factors responding for groundwater chemistry and explained 11.2%of the total variance.     

Spatial and temporal variability of groundwater quality of an Algerian aquifer: the case of Soummam Wadi

ABSTRACT

Five-year monitoring of physicochemical parameters was performed with two campaigns in low and high water periods of the Lower Soummam catchment. Data from 18 wells were processed by multivariate statistical tools in order to identify the principal factors influencing groundwater chemistry. Two matrices of 14 and 8 physicochemical parameters with 18 groundwater samples collected in wells were obtained. The correlation matrix showed strong associations between nine variables: K⁺, Ca²⁺, Na⁺, SO₄^2?, Cl^?, Mg²⁺, NO₂^?, Zn²⁺ and Sr²⁺. Principal component analysis and factor analysis showed that the cumulated variance of high and low water periods was of 83.19% and 78.55%, respectively. The variables assigned to the mineralization effect or to pollution indicators were presented by the factor analysis. The bivariate plots confirmed a mineralization model, ascribed to dissolution of geological materials, and to high levels of saline contamination attributed to leakages from sanitary systems. They also showed an increase “upstream to downstream” of the mineralization, visualization of temporal variations, and a dilution process identification of the natural mineralization during the recharge of the aquifer.

EDITOR D. Koutsoyiannis; ASSOCIATE EDITOR X. Chen     

Significance of isotopic and geochemical methods to determine the evolution of inland brackish and bitter water: An example from the Zuli river in the upper reaches of the Yellow River,China

With the increasing demand for water resources, the utilization of marginal water resources of poor-quality has become a focus of attention. The brackish water developed in the Loess Plateau is not only salty but also famous for its ‘bitterness’. In the present work, multi-isotope analysis (Sr, B) was combined with geochemical analysis to gain insight into the hydrogeochemical evolution and formation mechanisms of brackish water. These results demonstrate that groundwater in the headwater is influenced by carbonate weathering. After the confluence of several tributaries in the headwater, the total dissolved solids (TDS) of water is significantly increased. The dissolution of evaporates is shown to be the main source of salinity in brackish water, which also greatly affects the strontium isotopic composition of water. This includes the dissolution of Mg-rich minerals, which is the main cause of the bitterness. Furthermore, the release of calcium from the dissolution of gypsum may induce calcite precipitation and incongruent dissolution of dolomite, which also contributes to the enrichment of magnesium. The highly fractionated boron isotopic values observed in the upstream groundwater were explained by the absorption with clay minerals. The inflow of brackish groundwater is the source of river water. Then evaporation further aggravates the salinization of river water, with water quality evolving to saline conditions in the lower reach. When the river reaches the valley plain, the ⁸⁷Sr/⁸⁶Sr ratios decreases significantly, which is primarily related to erosion of the riverbanks during runoff. These results indicate that water resource sustainability could be enhanced by directing focus to mitigating salinization in the source area of the catchment.     

Application of geochemical and stable isotopic tracers to investigate groundwater salinity in the Ochi-Narkwa Basin,Ghana

Rainwater, groundwater and soil-water samples were analysed to assess groundwater geochemistry and the origin of salinity in the Ochi-Narkwa basin of the Central Region of Ghana. The samples were measured for major ions and stable isotopes (δ¹⁸O, δ²H and δ¹³C). The Cl^? content in rainwater decreased with distance from the coast. The major hydrochemical facies were Na-Cl for the shallow groundwaters and Ca-Mg-HCO₃, Na-Cl and Ca-Mg-Cl-SO₄ for the deep groundwaters. Groundwater salinization is caused largely by halite dissolution and to a minor extent by silicate weathering and seawater intrusion. Stable isotope composition of the groundwaters followed a slope of 3.44, suggesting a mixing line. Chloride profiles in the soil zone revealed the existence of salt crusts, which support halite dissolution in the study area. A conceptual flow model developed to explain the mechanism of salinization showed principal groundwater flow in the NW–SE direction.

EDITOR D. Koutsoyiannis

ASSOCIATE EDITOR K. Heal     

Imaging geochemical heterogeneities using inverse reactive transport modeling: An example relevant for characterizing arsenic mobilization and distribution

The spatial distribution of reactive minerals in the subsurface is often a primary factor controlling the fate and transport of contaminants in groundwater systems. However, direct measurement and estimation of heterogeneously distributed minerals are often costly and difficult to obtain. While previous studies have shown the utility of using hydrologic measurements combined with inverse modeling techniques for tomography of physical properties including hydraulic conductivity, these methods have seldom been used to image reactive geochemical heterogeneities. In this study, we focus on As-bearing reactive minerals as aquifer contaminants. We use synthetic applications to demonstrate the ability of inverse modeling techniques combined with mechanistic reactive transport models to image reactive mineral lenses in the subsurface and quantify estimation error using indirect, commonly measured groundwater parameters. Specifically, we simulate the mobilization of arsenic via kinetic oxidative dissolution of As-bearing pyrite due to dissolved oxygen in the ambient groundwater, which is an important mechanism for arsenic release in groundwater both under natural conditions and engineering applications such as managed aquifer recharge and recovery operations. The modeling investigation is carried out at various scales and considers different flow-through domains including (i) a 1D lab-scale column (80 cm), (ii) a 2D lab-scale setup (60 cm × 30 cm) and (iii) a 2D field-scale domain (20 m × 4 m). In these setups, synthetic dissolved oxygen data and forward reactive transport simulations are used to image the spatial distribution of As-bearing pyrite using the Principal Component Geostatistical Approach (PCGA) for inverse modeling.     

Recharge and mineralization of groundwater of the Upper Cretaceous aquifer in Orontes basin,Syria

Abstract

Chemical and isotopic data of groundwater of the Upper Cretaceous aquifer in the Orontes basin, Syria, have been used to assess the groundwater geochemistry, the origin of groundwater recharge and groundwater residence time. The chemical data indicate that dissolution of evaporite minerals is the main process controlling groundwater mineralization. The composition of stable isotopes δ¹⁸O and δ²H, together with ¹⁴C activity, reflect the existence of three different groups: (a) groundwater in the Coastal Mountains with δ¹⁸O of –6.65‰, quite similar to modern-day precipitation, and high ¹⁴C (>50 pmC); (b) groundwater in the unconfined aquifer of the Hama Uplift, which has δ¹⁸O of –5.52‰ and ¹⁴C near 20 pmC, and is recharged locally; and (c) groundwater from the confined aquifer of the Homs Depression, which is characterized by more depleted δ¹⁸O,, –8.01‰, and low ¹⁴C (<7 pmC), and might be recharged in the northern piedmont of the Anti-Lebanon Mountains. The distinctive isotope signatures of the latter two groups indicate different recharge elevations and palaeoclimatic effects. The low recharge rate of the groundwater in the Hama Uplift aquifer, and the even slower recharge rate in the Homs Depression aquifer, are reflected by groundwater ¹⁴C residence times of 5 and over 22 Ka BP, respectively.

Editor D. Koutsoyiannis

Citation Al-Charideh, A., 2013. Recharge and mineralization of groundwater of the Upper Cretaceous aquifer in Orontes basin (Syria). Hydrological Sciences Journal, 58 (2), 452–467.