Inverse Geochemical Modeling Research Articles

Distribution and Enrichment Factors of High-Arsenic Groundwater in Inland Arid Area of P. R. China: A Case Study of the Shihezi Area, Xinjiang

To study the distribution, sources and enrichment factors of groundwater As in the Shihezi area in Xinjiang, China, 19 indexes in 23 groundwater samples were tested and analyzed with a control area of 1611 km2. Results showed that As concentrations ranged between non-detected and 49.1 μg/L with an average of 11.0 μg/L. Among all the samples, 34.8% of which had As concentrations greater than 10 μg/L, according to “Standards for Drinking Water Quality (GB5749-2006)”. Groundwater As showed a significant spatial distribution. High-As groundwaters (>10 μg/L) were mainly distributed in the confined groundwater in the northern part of the study area. Arsenic concentrations in the deep confined groundwater were higher than that in the shallow confined groundwater due to mixed exploitation of groundwater in confined groundwater region and overexploitation of deep groundwater in the Shihezi area. The hydrogeochemical type of groundwater changed from HCO3·SO4–Ca·Na in the southern piedmont zone to HCO3·SO4–Na in the northern fine soil plain. High-As groundwater generally occurred under weakly alkaline and reducing conditions with dominant hydrogeochemical type of groundwater of HCO3·SO4–Na. Groundwater As mainly derived from As-containing minerals in the coal seam of the southern mountain and the extensive use of As-containing pesticides in agricultural areas. Enrichment of groundwater As was mainly influenced by climate, geological settings and hydrogeochemical characteristic. In the transition zone of oasis and desert in the north of study area, intensive evaporation of groundwater promoted the enrichment of As in shallow groundwater. In the confined groundwater area in the northern part of the study area, relatively weak groundwater runoff and reducing environment may contribute to groundwater As enrichment in confined aquifers. In addition, high pH values and high F− concentrations in the groundwater may contribute to the enrichment of groundwater As, while TDS, total Fe and Mn concentrations of groundwater had little effect on As enrichment in the study area. Two confined groundwater flow paths were selected in the study area. Inverse geochemical modeling was performed using PHREEQC. The results showed that As-containing realgar dissolved in groundwater, indicating that realgar was the major mineral source of groundwater As. The dissolved amount of realgar along deep confined groundwater flow path was higher than that along shallow confined groundwater flow path, indicating that the concentrations of As dissolved in deep confined groundwater were higher than that in shallow confined groundwater. Meanwhile, dissolution of fluorite in groundwater caused the increase in groundwater F−, which further confirmed that groundwater As and F− had a positive correlation.

Application of Environmental Tracers in the Memphis Aquifer and Implication for Sustainability of Groundwater Resources in the Memphis Metropolitan Area, Tennessee

AbstractFourteen years of results from environmental tracer sampling for 3H, He isotopes, noble gases, and SF6 in production wells screened in the Memphis aquifer in Memphis, Tennessee, are presented and used to determine the age and mass proportion of modern water (<60 years old) pumped from this regionally important public supply aquifer. The results indicate persistent presence of modern water in water pumped from one or more production wells in most of the well fields sampled. The percentage of modern water is quantified by three methods: tritium‐loading history, inverse geochemical modeling, and lumped parameter modeling. The mixing percentages and ages determined from each technique are generally in agreement, but also emphasize the unique information provided by each tracer and associated modeling approaches. The implications of the tracer data for sustainability and vulnerability are also considered, especially in regard to potential water quality threats to the water supply in the Memphis, Tennessee, metropolitan area.

Geochemical behavior of an acid drainage system: the case of the Amarillo River, Famatina (La Rioja, Argentina).

The Amarillo River (Famatina range, Argentina, ~29° S and ~67° W) is unusual because acid mine drainage (AMD) is superimposed on the previously existing acid rock drainage (ARD) scenario, as a Holocene paleolake sedimentary sequence shows. In a markedly oxidizing environment, its water is currently ferrous and of the sulfate-magnesium type with high electrical conductivity (>10mScm-1 in uppermost catchments). At the time of sampling, the interaction of the mineralized zone with the remnants of mining labors determined an increase in some elements (e.g., Cu ~3 to ~45mgL-1; As ~0.2 to ~0.5mgL-1). Dissolved concentrations were controlled by pH, decreasing significantly by precipitation of neoformed minerals (jarosite and schwertmannite) and subsequent metal sorption (~700mgkg-1 As, 320mgkg-1 Zn). Dilution also played a significant role (i.e., by the mixing with circumneutral waters which reduces the dissolved concentration and also enhances mineral precipitation). Downstream, most metals exhibited a significant attenuation (As 100%, Fe 100%, Zn 99%). PHREEQC-calculated saturation indices (SI) indicated that Fe-bearing minerals, especially schwertmannite, were supersaturated throughout the basin. All positive SI increased through the input of circumneutral water. PHREEQC inverse geochemical models showed throughout the upper and middle basin, that about 1.5mmolL-1 of Fe-bearing minerals were precipitated. The modeling exercise of mixing different waters yielded results with a >99% of correlation between observed and modeled data.

Acid-Generating and Leaching Potential of Soils in a Coal Waste Rock Pile in Northeastern China

ABSTRACTThe present study involved the assessment of potential generation of acid drainage and also metal leaching from an abandoned large (175 m) low sulfur waste rock pile—the dominant mine waste at the site—at the Haizhou coal mine. Laboratory-based static and column leaching tests on waste rock samples were conducted. The static tests were done for 8 composite samples collected from different parts of pile. A column study was performed using mixture of waste rock soil samples to assess metals attenuation process of background soils in vicinity of pile when rainwater reacts with low-sulfide waste rocks. Total concentration of major elements in solid samples was determined using dispersive X-ray fluorescence spectrometry (XRF) and chemical analysis of leachate were measured by inductively coupled plasma optical emission spectrometry (ICP-OES), ion chromatography and titration methods. The inverse geochemical modeling using PHREEQC was applied to explain possible mass transfer processes between column leachates of waste pile and background soils. Static tests (including acid–base accounting (ABA) and net acid generation (NAG)) and mineralogical information suggest that the waste rock is non-acid generating. The large amount of aluminosilicate minerals and probably trace amounts of carbonates with respect to low sulfur content of waste rock pile represents a potentially large source of neutralization potential according to static test results. It was also found that presence of inherent neutralizing materials in waste rock and also in surrounding background soils provide sufficient neutrality and possibly immobilize the trace and heavy metal contents of waste rocks and potentially protects water resources.

Characteristics of change in water quality along reclaimed water intake area of the Chaobai River in Beijing, China

To reveal the basic characteristics and controlling factors of water quality change in the project Wenyu to Chaobai reclaimed water diversion, the water quality in the study area was monitored for one year at seven monitoring sites. Inverse geochemical models of the statistical groups were developed using PHREEQC to elucidate the hydrochemistry characteristics of reclaimed water and the factors. The monitoring results indicated that nitrogen and phosphorus contents were significantly reduced along the river mainly caused by seasonal and location variation. The pH ranged from 7.44 to 9.81. Photosynthesis of algae and denitrification in anaerobic microenvironment ultimately led to a sudden pH increase after the Jian River and the Chaobai River confluence. Mg2+ and SO42− levels dropped obviously in the summer and increased in winter seasons after intersection. Na+ and Cl− are relatively stable, and marked drop in the concentration only after the two rivers meet. And there is a decrease of Ca2+ and HCO3− and increase in CO32− during monitoring period. As a whole, the primary ions and nutrient components, including nitrogen and phosphorus, had high levels in winter. Algae's photosynthesis and respiration were observed to have an impact on the river water quality; there was precipitation–dissolution of minerals and denitrification from upstream to downstream. Inverse geochemical PHREEQC modeling confirmed that there was precipitation of aragonite or calcite, and gypsum or anhydrite in summer, and dissolution in winter; as well as precipitation of dolomite in winter, and cationic exchange and denitrification along the river.

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

ABSTRACTA 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

Rock–water interactions and pollution processes in the volcanic aquifer system of Guadalajara, Mexico, using inverse geochemical modeling

In order to understand and mitigate the deterioration of water quality in the aquifer system underlying Guadalajara metropolitan area, an investigation was performed developing geochemical evolution models for assessment of groundwater chemical processes. The models helped not only to conceptualize the groundwater geochemistry, but also to evaluate the relative influence of anthropogenic inputs and natural sources of salinity to the groundwater. Mixing processes, ion exchange, water–rock–water interactions and nitrate pollution and denitrification were identified and confirmed using mass-balance models constraint by information on hydrogeology, groundwater chemistry, lithology and stability of geochemical phases. The water–rock interactions in the volcanic setting produced a dominant NaHCO3 water type, followed by NaMgCaHCO3 and NaCaHCO3. For geochemical evolution modeling, flow sections were selected representing recharge and non-recharge processes and a variety of mixing conditions. Recharge processes are dominated by dissolution of soil CO2 gas, calcite, gypsum, albite and biotite, and Ca/Na exchange. Non-recharge processes show that the production of carbonic acid and Ca/Na exchange are decreasing, while other minerals such as halite and amorphous SiO2 are precipitated. The origin of nitrate pollution in groundwater are fertilizers in rural plots and wastewater and waste disposal in the urban area. This investigation may help water authorities to adequately address and manage groundwater contamination.

Hydrochemical investigation of shallow groundwater in northwest margin of Lop Nur, northwest China

A hydrochemical investigation was conducted in northwest margin of Lop Nur to evaluate the groundwater chemical patterns and the main hydrological processes occurring in the groundwater system. Fourteen representative groundwater samples were collected from different springs and boreholes. Hydrochemical data of the groundwater showed that SO4, Cl-Na and Cl, SO4-Na water types were dominant in this area, and the total dissolved solid (TDS) content rose along the flow path of the groundwater. Ionic relation analysis was used in conjunction with geochemical modeling to investigate the evolution of the chemical composition of groundwater. PHREEQC was used for inverse geochemical modeling. It is demonstrated that the groundwater, recharged mainly in the northern low mountains, acquired its mineralization properties principally from water–rock interactions, i.e., dissolution of evaporates and reverse cation exchange. The dissolution of halite, Glauber’s salt, dolomite and calcite determined the Na+, Cl−, Mg2+, Ca2+, SO4 2− and HCO3 − chemistry, but evaporation and precipitation also influenced the water composition. The shallow groundwater of Lop Nur was characterized by high salinity and slow circulation.

Geothermometric evaluation of geothermal resources in southeastern Idaho

<p><strong>Abstract.</strong> Southeastern Idaho exhibits numerous warm springs, warm water from shallow wells, and hot water from oil and gas test wells that indicate a potential for geothermal development in the area. We have estimated reservoir temperatures from chemical composition of thermal waters in southeastern Idaho using an inverse geochemical modeling technique (Reservoir Temperature Estimator, RTEst) that calculates the temperature at which multiple minerals are simultaneously at equilibrium while explicitly accounting for the possible loss of volatile constituents (e.g., CO<sub>2</sub>), boiling and/or water mixing. The temperature estimates in the region varied from moderately warm (59<span class="thinspace"></span>°C) to over 175<span class="thinspace"></span>°C. Specifically, hot springs near Preston, Idaho, resulted in the highest reservoir temperature estimates in the region.</p>

Occurrence and distribution of arsenic in the sediments of a carbonate-rich unsaturated zone

Three combined approaches were used to study the arsenic (As) occurrence in carbonate-rich unsaturated zone from a large plain environment (Pampean plain, Argentina). A sequential extraction procedure (SEP) was used to identify the As-bearing phases and distribution along a 2-m-long unsaturated zone profile, whereas XRD and SEM/EDS were used to determine the mineralogical features of the sediments. In this hydrogeologic environment, groundwater levels tend to be close to the surface (<5 m) and hydrogeochemical processes that develop during infiltration and recharge through the unsaturated zone may release the As hosted in the sediments to shallow aquifers. According to SEP results, the unsaturated zone was divided in an upper and a lower zones. Disregarding the As contained in the silicates, low crystalline Fe(III) oxyhydroxides were the main As-bearing minerals in the upper zone. Its presence was confirmed by SEM/EDS analysis. In the lower zone, carbonates were the main As-bearing minerals, also supported by XRD analysis. The chemical composition from the resulting water-extractable step of the SEP was constrained using geochemical inverse modeling (PHREEQC) to elucidate those potential geochemical processes that may control the As release or retention during, for instance, an infiltration event. They showed that Na/Ca exchange promoted the calcite dissolution which, in turn, raised the pH as a result of proton consumption. High pH and HCO3 − contents favored the As desorption from low crystalline Fe(III) oxyhydroxides in the upper zone, where they were present in higher proportion.

Cl/Br ratios and chlorine isotope evidences for groundwater salinization and its impact on groundwater arsenic, fluoride and iodine enrichment in the Datong basin, China

In order to identify the salinization processes and its impact on arsenic, fluoride and iodine enrichment in groundwater, hydrogeochemical and environmental isotope studies have been conducted on groundwater from the Datong basin, China. The total dissolved solid (TDS) concentrations in groundwater ranged from 451 to 8250mg/L, and 41% of all samples were identified as moderately saline groundwater with TDS of 3000–10,000mg/L. The results of groundwater Cl concentrations, Cl/Br molar ratio and Cl isotope composition suggest that three processes including water-rock interaction, surface saline soil flushing, and evapotranspiration result in the groundwater salinization in the study area. The relatively higher Cl/Br molar ratio in groundwater from multiple screening wells indicates the contribution of halite dissolution from saline soil flushed by vertical infiltration to the groundwater salinization. However, the results of groundwater Cl/Br molar ratio model indicate that the effect of saline soil flushing practice is limited to account for the observed salinity variation in groundwater. The plots of groundwater Cl vs. Cl/Br molar ratio, and Cl vs δ37Cl perform the dominant effects of evapotranspiration on groundwater salinization. Inverse geochemical modeling results show that evapotranspiration may cause approximately 66% loss of shallow groundwater to account for the observed hydrochemical pattern. Due to the redox condition fluctuation induced by irrigation activities and evapotranspiration, groundwater salinization processes have negative effects on groundwater arsenic enrichment. For groundwater iodine and fluoride enrichment, evapotranspiration partly accounts for their elevation in slightly saline water. However, too strong evapotranspiration would restrict groundwater fluoride concentration due to the limitation of fluorite solubility.

Hydrogeochemical characteristics and origin of salinity in Ajabshir aquifer, East Azerbaijan, Iran

Inverse geochemical modelling with PHREEQC and multivariate statistical methods were used to determine the origin of groundwater chemical constituents and identify the source of salinity in parts of Ajabshir alluvial aquifer, East Azerbaijan, Iran. Q mode hierarchical cluster analysis (HCA) was used to partition groundwater in the study area into hydrochemical facies. Three major water groups were identified by HCA. Groundwater samples collected from the study area were classified as recharge area waters (Group 1: Na–Ca–HCO 3 water; Group 2: Ca–Na–HCO 3 water) in the northern, central and northeastern areas. Discharge area waters were identified in the vicinity of Urmia Lake and in southern parts of the study area (Group 3: Na–Cl water). Principal components analysis (PCA) with varimax rotation using the Kaiser criterion identified three principal sources of variation in the hydrochemistry. Factor 1 accounts for the salinity of the water, factor 2 represents silicate mineral weathering, and factor 3 represents calcite dissolution and incongruent silicate mineral weathering. Inverse modelling for major ions and the results of HCA confirmed the results obtained with PCA. The results of this study showed that water–rock interaction is an important mechanism in the evolution of water chemistry. The results also identified the following phenomena as important mechanisms in the composition of Group 3 waters: saline water upconing, mixing between freshwater and saline water, reverse flow from the salt flats toward the aquifer, flatness of the ground surface and very low velocity of the groundwater, shallow depth of the groundwater and evaporation from it, a silt–clay boundary at the outlet of groundwater flow from the aquifer, and airborne transport of salt particles from the salt flats.

Water quality of the Helvetian and Eocene aquifers in Al Zerba catchment and southern parts of Al Qweek Valley, Aleppo basin, Syria

Groundwater is a key factor for sustainable socio-economic development in arid and semi-arid countries. The study area constitutes the south and southwestern parts of Aleppo basin, north of Syria. It is characterized by semi-arid climate and limited water resources. The aims of this study are to evaluate the groundwater quality with concern to drinking and irrigation suitability, water–rock interaction, and potential source rock to assess the main hydrochemical processes controlling chemical composition of groundwater in the Neogene and Paleogene aquifer systems. Hydrochemical data of 29 irrigation and observation wells distributed in the region were used in this study. Concentrations of the dominant ions are following the order Na+ > Ca2+ > Mg2+ > K+ and HCO3 − > Cl− > SO4 2− for major cations and anions, respectively. Ca–Na–HCO3, Na–Ca–SO4, and Ca–Na–Cl are the main groundwater types in the region. The graphical interpretation and cluster analysis of groundwater samples identified three main hydrochemical facies in the region. These groups are differentiated by three levels of total dissolved solids (TDS) value ranges from 390 mg/l for the group A, 742 and 1795 mg/l for the group B and C, respectively. The results also show that most of the groundwater samples are close to saturation or oversaturation with respect to the minerals: aragonite, calcite, and dolomite, while halite and gypsum are always under-saturated. Furthermore, the inverse geochemical modeling of groundwater samples indicates three main processes that are responsible for groundwater evolution in the region: plagioclase weathering (albite, hypersthene), de-dolomitization, and cation exchange. These processes increase in groundwater salinity from the east to the southwestern parts of the study area. The groundwater in the region is partly critical for drinking and irrigation due to the high average TDS (925 mg/l), nitrate (43.78 mg/l), and salinity. However, groundwater samples exhibited low sodium adsorption ratios, moderate magnesium hazard, and low residual sodium carbonate. Despite of that, this type of water can adversely affect the soil and crops yields in the long term and prevent a sustainable development of agriculture in the region of interest.

Salinization mechanisms of a small alluvial aquifer in the semiarid region of northeast Brazil

The objective of this research was to identify and quantify the primary processes responsible for the increase in salinity observed in the alluvial aquifer during the dry season. Multivariate statistical analysis and inverse geochemical modeling were used to simulate possible salinization mechanisms in the alluvial aquifer. For this, by quantifying electrical conductivity and the concentrations of the ions Ca2+, Mg2+, Na+, K+, Cl-, HCO3- and SO42- in waters from the crystalline basement near the study area, water reservoirs near the alluvial aquifer and the studied alluvial aquifer, groups were formed and discriminant analysis was applied. Significance tests showed that direct evaporation has not only an influence on the alluvial aquifer, but also a mean volumetric contribution of 15.8% from waters of the crystalline basement, accompanied by processes of salt dissolution and precipitation, which would also justify the increase in salinity observed in the alluvial aquifer in the dry period.

Hydrochemical evolution within a large alluvial groundwater resource overlying a shallow coal seam gas reservoir

A combination of multivariate statistical techniques, simple hydrochemical mixing models and inverse geochemical modelling was used to investigate the major hydrochemical evolutionary pathways of a large alluvial aquifer, the upper Condamine River alluvium, south-east Queensland, Australia. Hydrochemical similarities between alluvium and sedimentary bedrock groundwater imply some mixing between alluvial and sedimentary bedrock aquifers, but spatial assessment showed that this was localised around outcrops of sedimentary bedrock in upstream areas. Within the alluvium, a distinct shift towards a low salinity Na–HCO3 water type and a brackish Na–HCO3–Cl water type was obvious in two separate locations. Both of these water types are unique to the alluvium, and inverse modelling shows that they can evolve via a combination of in situ alluvial processes, including diffuse recharge of rainfall or river water or the evolution of basalt-derived groundwater via gypsum dissolution plagioclase weathering, cation exchange and some carbonate precipitation/dissolution. The evolution of these water types is potentially influenced by overlying sodic alkaline soils, and often is associated with a source of sulfate. Evapotranspiration is the dominant salinization process in the alluvium and increases in calcium cations during salinization indicate that brackish Na–HCO3–Cl groundwater in the underlying Walloon Coal Measures are unlikely to have a major influence on salinization in the alluvium. The most saline water types observed were endemic to shallow zones of the alluvium where evapotranspiration is likely. Results demonstrate that a combination of multivariate statistics and inverse geochemical modelling can be successfully used to delineate hydrochemical pathways in complex hydrogeological settings where a range of environmental and anthropogenic factors may be influencing the evolution of water types with similar hydrochemical compositions.

Hydrogeochemical effects of a bulkhead in the Dinero mine tunnel, Sugar Loaf mining district, near Leadville, Colorado

The Dinero mine drainage tunnel is an abandoned, draining mine adit near Leadville, Colorado, that has an adverse effect on downstream water quality and aquatic life. In 2009, a bulkhead was constructed (creating a mine pool and increasing water-table elevations behind the tunnel) to limit drainage from the tunnel and improve downstream water quality. The goal of this study was to document changes to hydrology and water quality resulting from bulkhead emplacement, and to understand post-bulkhead changes in source water and geochemical processes that control mine-tunnel discharge and water quality. Comparison of pre-and post-bulkhead hydrology and water quality indicated that tunnel discharge and zinc and manganese loads decreased by up to 97 percent at the portal of Dinero tunnel and at two downstream sites (LF-537 and LF-580). However, some water-quality problems persisted at LF-537 and LF-580 during high-flow events and years, indicating the effects of the remaining mine waste in the area. In contrast, post-bulkhead water quality degraded at three upstream stream sites and a draining mine tunnel (Nelson tunnel). Water-quality degradation in the streams likely occurred from increased contributions of mine-pool groundwater to the streams. In contrast, water-quality degradation in the Nelson tunnel was likely from flow of mine-pool water along a vein that connects the Nelson tunnel to mine workings behind the Dinero tunnel bulkhead. Principal components analysis, mixing analysis, and inverse geochemical modeling using PHREEQC indicated that mixing and geochemical reactions (carbonate dissolution during acid weathering, precipitation of goethite and birnessite, and sorption of zinc) between three end-member water types generally explain the pre-and post-bulkhead water composition at the Dinero and Nelson tunnels. The three end members were (1) a relatively dilute groundwater having low sulfate and trace element concentrations; (2) mine pool water, and (3) water that flowed from a structure in front of the bulkhead after bulkhead emplacement. Both (2) and (3) had high sulfate and trace element concentrations. These results indicate how analysis of monitoring information can be used to understand hydrogeochemical changes resulting from bulkhead emplacement. This understanding, in turn, can help inform future decisions on the disposition of the remaining mine waste and water-quality problems in the area.

Investigation of groundwater chemistry at a dam site during its construction: a case study of Xiangjiaba Dam, China

Water quality can be used to reflect the hydro-geological features and seepage restrictions around grout curtains. Xiangjiaba Dam, a large hydropower station constructed in southwest of China, was investigated as a case study. Groundwater samples were collected and analysed qualitatively using hydrochemistry diagrams, after which the presence of four major water groups was determined by hierarchical cluster analysis and saturation indices of each group were calculated. Finally, inverse geochemical models of the groups were developed using PHREEQC to elucidate the dissolution/precipitation quality of different minerals and the relative contributions of different seepage sources. The hydro-geochemical methods used were found to be useful for revealing seepage behaviour within the domain during construction of a hydropower station.

Effect of irrigation on Fe(III)–SO42− redox cycling and arsenic mobilization in shallow groundwater from the Datong basin, China: Evidence from hydrochemical monitoring and modeling

• Combined hydrochemical monitoring and modeling were performed in this study. • The periodic variation of redox conditions was observed in the groundwater. • Fe(III)–SO 4 2− redox cycling induced by the irrigation controls As mobilization. Seasonal hydrochemical monitoring has been conducted at a well-known arsenic (As) contaminated site to understand the critical controlling processes on As mobilization and enrichment in groundwater. The hydrochemical results indicate that the water chemistry at the studied site is mainly controlled by evaporates dissolution, and redox reactions during irrigation and non-irrigation periods, respectively. The measured redox-sensitive components indicate that the groundwater experienced periodic redox changes from irrigation to non-irrigation periods and that an enhanced reducing environment prevailed during the non-irrigation period. The observed high As concentration and the strong positive correlation between As and Fe support the conclusion that the Fe oxides/hydroxides reduction and Fe sulfide oxidation releases As during the irrigation period. However, the relatively low As concentration and the close inverse correlation between As, Fe and SO 4 2− show that Fe(III) and SO 4 2− reduction accompanied by the formation of Fe sulfide precipitates, retains As during the non-irrigation periods. The geochemical inverse modeling performed for the selected wells confirms that Fe oxide/hydroxide and Fe sulfide dissolution as well as siderite precipitation are the dominant processes related to the mobilization of As during the water evolution from the pre-irrigation to irrigation period, while Fe sulfide precipitation immobilize As during the groundwater evolution from the irrigation to the post-irrigation period. In general, the combined results of the hydrochemical monitoring and the geochemical inverse modeling support the conclusion that the Fe(III)–SO 4 2− redox cycling induced by periodic irrigation practices controls the mobilization of As in groundwater at this site.

Investigation of the geochemical evolution of groundwater under agricultural land: A case study in northeastern Mexico

• A scheme of statistical methods was developed to define hydrochemical groups. • An inverse modeling approach considered geogenic and anthropogenic processes. • Weathering of evaporitic rocks represents the main contribution to groundwater chemistry. • A process takes place which converts dolomite into calcite (dedolomitization). • It may not be cost-effective to regulate manure application to mitigate groundwater pollution. Zona Citrícola is an important area for Mexico due to its citriculture activity. Situated in a sub-humid to humid climate adjacent to the Sierra Madre Oriental, this valley hosts an aquifer system that represents sequences of shales, marls, conglomerates, and alluvial deposits. Groundwater flows from mountainous recharge areas to the basin-fill deposits and provides base flows to supply drinking water to the adjacent metropolitan area of Monterrey. Recent studies examining the groundwater quality of the study area urge the mitigation of groundwater pollution. The objective of this study was to characterize the physical and chemical properties of the groundwater and to assess the processes controlling the groundwater’s chemistry. Correlation was used to identify associations among various geochemical constituents. Factor analysis was applied to identify the water’s chemical characteristics that were responsible for generating most of the variability within the dataset. Hierarchical cluster analysis was employed in combination with a post-hoc analysis of variance to partition the water samples into hydrochemical water groups: recharge waters (Ca–HCO 3 ), transition zone waters (Ca–HCO 3 –SO 4 to Ca–SO 4 –HCO 3 ) and discharge waters (Ca–SO 4 ). Inverse geochemical models of these groups were developed and constrained using PHREEQC to elucidate the chemical reactions controlling the water’s chemistry between an initial (recharge) and final water. The primary reactions contributing to salinity were the following: (1) water–rock interactions, including the weathering of evaporitic rocks and dedolomitization; (2) dissolution of soil gas carbon dioxide; and (3) input from animal/human wastewater and manure in combination with by denitrification processes. Contributions from silicate weathering to salinity ranged from less important to insignificant. The findings suggest that it may not be cost-effective to regulate manure application to mitigate groundwater pollution.

RETRACTED ARTICLE: Application of multivariate statistical methods and geochemical modeling to evaluate the surface water of Timgad Basin, East Algeria

After careful investigation carried out in accordance with the COPE guidelines the Editor-in-Chief and the Publisher have decided to retract this article. The text shows significant unattributed overlap with the following articles: Tiri, Ammar, Noureddine Lahbari, and Abderrahmane Boudoukha. ‘‘Hydrochemical characterization of surface water in the Timgad watershed, East Algeria’’, Desalination and Water Treatment, 2014. Tiri, Ammar, Noureddine Lahbari, and Abderrahmane Boudoukha. ‘‘Assessment of the quality of water by hierarchical cluster and variance analyses of the Koudiat Medouar Watershed, East Algeria’’, Applied Water Science, 2015. Belkhiri, L.. ‘‘Statistical categorization geochemical modeling of groundwater in Ain Azel plain (Algeria)’’, Journal of African Earth Sciences, 201101. Belkhiri, L.. ‘‘Application of multivariate statistical methods and inverse geochemical modeling for characterization of groundwater A case study: Ain Azel plain (Algeria)’’, Geoderma, 20101115. Vikram Bhardwaj. ‘‘Hydrogeochemistry of groundwater and anthropogenic control over dolomitization reactions in alluvial sediments of the Deoria district: Ganga plain, India’’, Environmental Earth Sciences, 01/2010. Li Peiyue. ‘‘Hydrochemical Formation Mechanisms and Quality Assessment of Groundwater with Improved TOPSIS Method in Pengyang County Northwest China’’, E-Journal of Chemistry, 2011.