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In this study, major ions, isotopes and rare earth elements (REEs) were tested in groundwater from the coal-bearing sandstone aquifer of the Wolonghu coal mine in northern Anhui Province, and the elemental geochemical behavior and controlling factors in groundwater were discussed. The results indicate that the overall sandstone water is weakly alkaline, and the hydrochemical type is SO4-Na. The relationship between δD and δ18O suggests a hydraulic connection between the sandstone aquifer and the limestone aquifer. The composition characteristics of δ34SSO4 a nd δ18OSO4 indicate that the high concentration of SO42- in groundwater mainly comes from the dissolution of sulfate minerals. The content of rare earth elements (ΣREEs) in groundwater is controlled by pH value and carbonate complexation reaction, and it shows a relative enrichment feature of heavy rare earth elements (HREEs) after standardization with Post-Archean Australian Shales. Ce shows a slight negative anomaly and is mainly influenced by the redox environment, while the Eu anomaly is attributed to the dissolution of silicate minerals. Compared to groundwater quality before the mine closure, the weakening of hydraulic conditions led to an increase in ΣREEs, Ca2+, Mg2+, SO42-, and TDS concentrations accompanied by a significant decrease in HCO3- concentration. In addition, the difference between light rare earth elements (LREEs) decreased, whereas the differentiation between LREEs and HREEs gradually increased. Our findings provide valuable insights into the evolution of groundwater quality in abandoned mines and its genesis mechanism. The results could guide the utilization of groundwater resources in abandoned mines. [ABSTRACT FROM AUTHOR]

The migration of a groundwater contaminant plume consisting of light nonaqueous phase liquids (LNAPLs) along the Ionian coastline of Sicily, Italy, has been reported to follow a trajectory that is inconsistent with the regional hydraulic gradient. The influence of several faults affecting the fractured carbonate bedrock aquifer, and groundwater abstraction from a well, were hypothesized to be responsible for the anomalous trajectory of the contaminant plume. A conceptual hydrogeological model was developed for the study area that incorporated structural information derived from geophysical surveys and the mapping of fractures in bedrock outcrops. This conceptual model was incorporated into numerical groundwater flow and solute transport models to simulate the groundwater transport of the light nonaqueous phase liquids. Four model scenarios representing different levels of complexity were tested to assess the relative influence of geological heterogeneity and groundwater abstraction on the migration of the contaminant plume. Results show that underground major discontinuity systems, invoking the presence of the faults in the model domain accounted for the observed migration of the contaminant plume, act as conduits for groundwater flow. Conversely, groundwater abstraction from a well was found to result in relatively minor, localized impacts to the migration of the contamination plume. This study demonstrates the importance of incorporating geological heterogeneity into groundwater modelling and environmental risk assessments associated with the storage of LNAPLs. [ABSTRACT FROM AUTHOR]

Hydrochemical and geophysical methods were used to assess saline paleo-water mass transfer induced by piston flow in the alluvial aquifer of the Oltrepò Pavese plain (northern Italy). The surface aquifer shows salinity contamination from a Tertiary substrate of marine origin, due to mixing of the shallower fresh groundwater with the Po Plain's deep brines. The study also used continuous monitoring of groundwater electrical conductivity, temperature and piezometric levels. Well logging and geophysical imaging, conducted at different times, revealed that the contamination varies over time, and that the water salinity and the depth of the transition zone (between the surface freshwaters and the deep saline waters) are subject to modifications. This is due to a pressure transfer—and, subsequently, mass transfer−from the groundwater circuits of the nearby Apennine mountains. It suggests that a hydraulic connection exists between the fractured Apennine water circuits and the deeper Mio-Pliocene and Tertiary saline-water circuits found below the plain's alluvial aquifer. Coinciding with significant recharge episodes that affect Apennine water circuits (prolonged rainfall and snow melt at mid-high altitudes), there is a pressure transfer transmitted along the water circuits in which saline water resides, providing an impulse to rise along the discontinuities and reach the alluvial aquifer. The conceptual model is supported by evidence that wells constructed in correspondence to hydraulically active tectonic discontinuities are affected by the arrival of saline waters with variable delays, while wells sited in sectors not affected by tectonic discontinuities are diluted by 'fresh' waters connected to alluvial aquifer recharge. [ABSTRACT FROM AUTHOR]

In Chad, hard-rock aquifers are the main source of drinking water for the population located on basement areas. In these basement aquifers, and in particular those of the Guéra region, water drilling failure rates remain high despite research on one- and two-dimensional electrical resistivity techniques and lineaments as a means to improve access to the resource, mainly because these techniques are only used on an observational and structural basis to locate fractures. This study combines electrical resistivity tomography (ERT) with geology, hydrogeology and geomorphology, in order to characterise the structure and geometry of the aquifer system, assess borehole productivity and determine the factors controlling it. After validating the large dataset and its representativeness, 315 high- and low-yield wells, of which 41 have complete geophysical datasets, were selected. This large dataset allows a multi-parameter approach to (1) better characterise each facies according to its electrical resistivity and (2) clearly identify the main formations constituting the local conceptual hydrogeological model. The most suitable areas for productive boreholes are characterised by the presence of an overburden of <20 m depth, well-developed weathered and fractured horizons of granites and biotite granites (preferably) containing little or no clay, and a nearby drainage network. The most substantial flow rates are found in the first 30 m of the fissured horizon, below the base of the alterites. The experience gained from the present study will guide future analysis of ERT sections in order to reduce the probability of drilling dry wells. [ABSTRACT FROM AUTHOR]

The Middle Western Cheliff plain hosts an important alluvial aquifer that is exploited for various uses including drinking water supply, irrigation and industry. This study aims to provide a hydrogeochemical characterisation of groundwater by using statistical methods and binary diagrams, as well as to evaluate the physico-chemical quality of groundwater by using the water quality index (WQI). Moreover, parametric indices such as SAR and %Na were used to evaluate the suitability of groundwater for irrigation. The hydrochemical approach based on results of 45 analyses of groundwater samples for the dry period 2019 enabled the determination of the most dominant chemical facies, which was chloride, sulphate, calcic and magnesium. The binary diagrams used indicated that the water-rock interaction and the evaporitic phenomenon are major geochemical processes that control the mineralisation of groundwater. The evaluation of groundwater quality for drinking water supply using WQI provided results with values ranging from 45.95 to 194.78, and above 60% of samples were classified into the category of excellent to good quality (WQI < 100), while the remaining 40% of water samples were classified in the category of poor quality for drinking (WQI > 100). However, the quality of groundwater is mostly acceptable for irrigation, mostly for plants with salinity-tolerant in drained soils. [ABSTRACT FROM AUTHOR]

This study assessed the vulnerability of groundwater resources to the failure of the urban fuel distribution network under an earthquake. A case study of the Tehran, Iran, gas distribution network and the Tehran–Karaj Plain aquifer was conducted. To assess the seismic vulnerability of buried fuel pipelines in Tehran based on the fuel distribution network components, three possible earthquake scenarios were studied. To assess damage to the pipeline, a comprehensive model was developed using machine learning (ML). This model can assess and predict damage to a fuel pipeline and its type (i.e., leakage or full breakage). Moreover, aquifer contamination was assessed using the DRASTIC model. It was found that the ML-based pipeline seismic vulnerability assessment model had good performance in predicting seismic damage to the fuel distribution network, with a RMS error (RMSE) and a correlation coefficient (R) of 0.004 and 0.99, respectively. The results showed that the presented model had an acceptable efficiency in assessing the probability of seismic vulnerability of the buried pipeline and analyzing the pollution of the aquifer based on different earthquake scenarios. The developed groundwater seismic vulnerability assessment model can be used for further analysis in future research. Practical Applications: Earthquakes are one of the most important natural disasters, and have caused widespread financial, human, and environmental losses in different regions of the world, especially in seismic areas. The existence of faults and the possible deterioration of buried pipes makes earthquake crisis and its serious damage to humans and the environment more severe. One of the most important threats in this situation is the contamination of underground water with hydrocarbon substances due to leakage from the fuel transmission network. In this research, to evaluate the pollution of the aquifer due to the damage to the fuel transmission network, we developed a model using the machine learning method to analyze the vulnerability of the buried pipeline. The DRASTIC model also was used to evaluate aquifer pollution. To evaluate the presented model, the fuel transmission network and aquifer of Tehran, Iran, were studied. The results indicated acceptable performance of the proposed model for assessing the seismic vulnerability of groundwater. The presented model can be used for other areas. [ABSTRACT FROM AUTHOR]

The valorization of Lake Maga for agricultural purposes has not only contributed to the socio-economic development of the study area, but has also modified the surface water (SW) and groundwater (GW) flow regimes. Understanding the interaction between the SW and the shallow Quaternary aquifer, under land use change and soil structure modification, is still a challenge, especially in the semi-arid area. In this study, GW level, hydrogeochemical characterization, and geological features are used to understand, locally, the influence of Lake Maga, its associated hydraulic components, and the other SW bodies on the GW behaviour. GW levels were measured in 51 wells in December 2012 and monitored in February 2013, and in 15 wells (beyond the 51) in June 2017 and December 2018. Physicochemical parameters of SWs and GWs were measured in the field, and 15 water samples were collected for major ion characterization. The GW levels were close (mean value ≈5 m) to the land surface, with zero to very low (< 1 m) water level fluctuations near SW bodies. The GW levels (< 2 m) are influenced more by their proximity to irrigation canals, ponds, and streams than Lake Maga (mean ≈3.5 m). The analysis of electrical conductivity (EC) values and GW levels showed that the weakly mineralized (< 200 µS.cm−1) GW were associated with the shallower GW table level. The moderate GW mineralization (200 < EC < 700 µS.cm−1) were more influenced by the geological texture of the shallow aquifer. The analysis of the geological characteristics of the sub-shallow aquifer structure in the locality of Pouss is mainly sandy, while in the localities of Maga and Guirvidig, clay, clayey-sand and sandy-clay materials dominate. There are no trends in GW chemical evolution from Lake Maga waters towards the shallow groundwater table (SGWT). The mixing-ratios values showed that the SW contributed for more than 65% (mean) to the sub-shallow aquifer in the study area, and the highest SWs (80%) contribution occurred in the locality of Pouss, close to Lake Maga, pond, Logone River, irrigation canal, and seasonal stream, associated with the shallowest GW levels (< 1.5 m). The proximity to SW bodies and the texture of the fluvio-lacustrine deposit of the shallow aquifer strongly influenced GW table levels and their hydrogeochemical characteristics. This work could be a prerequisite to understand how the physicochemical and chemical properties of GW in the shallow aquifer evolve and respond under the influence of SW bodies. [ABSTRACT FROM AUTHOR]

Managed aquifer recharge has become a standard water resources management practice to promote the development of locally sustainable water supplies and combat water scarcity. However, installation of injection wells for replenishment purposes in urban areas with complex hydrogeology faces many challenges, such as limited land availability, potential impacts on municipal production wells and known subsurface contamination plumes, and complex spatially variable hydraulic connections between aquifer units. To assess the feasibility and cost‐effectiveness of injecting advanced treated water (ATW) into a complex urban aquifer system, a Simulation‐Optimization (SO) model was developed to automate a systematic search for the most cost‐effective locations to install new wells for injecting various quantities of ATW, if feasible. The generalized workflow presented here uses an existing MODFLOW groundwater model—along with advanced optimization routines that are publicly available—to flexibly accommodate a multiobjective function, complex constraints, and specific project requirements. The model successfully placed wells for injection of 1 to 4 MGD of ATW in aquifers underlying the study area. The injection well placement was primarily constrained by avoiding excessive impact on environmental sites with underlying groundwater plumes. The largest costs were for well installation and piping to the wells from the existing ATW pipes. This workflow is readily adaptable to other sites with different complexities, decision variables, or constraints. [ABSTRACT FROM AUTHOR]

The Maggiore Valley well field plays a fundamental role in supplying drinking water to a large territory of the Piedmont Region (northwestern Italy) and has been intensively exploited since the early twentieth century. This water resource is hosted in a deep, multilayered aquifer system. The main purpose of this study was to characterize the recharge processes of the deep aquifer through hydrochemical and isotopic assessments, as well as the water quality in the recharge and drainage areas. For this purpose, 128 physical–chemical analyses (major ions) and 50 isotopic analyses (δ18O and δ2H) were carried out on samples collected in shallow and deep aquifer complexes in two sampling campaigns in 2021. From the results, a hydrogeological conceptual model of recharge processes was developed. The chemical data confirm the presence of bicarbonate–calcium facies in most samples of the shallow and deep aquifer complexes. Clear hydrochemical differences were observed among the investigated sectors. The recharge areas were identified as (1) far zones, namely the shallow aquifer complex of the Cuneo Plain, and (2) the shallow and deep aquifer complexes with groundwater mixing in the riverside sector of Po Plain in the Turin area. The mixing of waters from the Cuneo Plain and Turin Plain was verified in the well field area. The isotopic values of the artesian well water also confirmed contributions from the Turin and Cuneo Alps. This study clarified the recharge processes, thereby defining potential pollutant pathways, and the results provide additional support for groundwater resource management and protection. [ABSTRACT FROM AUTHOR]

Contamination due to rapid urban development, industrialization, and agricultural sources is increasingly threatening the groundwater resources of the plioquaternary phreatic aquifer of the Middle Western Cheliff. An intrinsic vulnerability assessment was carried out based on the DRASTIC method on parameters involved in the vertical transfer of pollution from the soil surface. The vulnerability maps obtained showed a high extension of areas of medium vulnerability (54%). On the other hand, areas of low vulnerability occupied about 36%. The high and very high vulnerability was mainly related to low water depth values (8% and 2%, respectively). The results of a sensitivity analysis using the two tests--the single parameter sensitivity analysis and the map removal sensitivity analysis--show that every parameter is, without fail, required for the computation of the vulnerability index. The validation of the vulnerability map produced by the DRASTIC method confirmed the evolution of this sensitivity which decreases towards the S.W. of the plain with nitrate concentrations between 30 and 120 mg/L. Planners can use the produced risk maps as tools to make a preliminary choice of priority locations for various forms of environmental sustainability. [ABSTRACT FROM AUTHOR]

Existing aquifer water abundance evaluation methods employ fixed and constant index weights and overlook variations within major influencing factors as well as interactions among multiple factors. We propose a water abundance index method based on a variable weight model that considers various water abundance influencing factors and their respective weights, and quantitatively determines the weights of the same factor across different state values. This paper establishes a comprehensive system of four categories and 16 subcategories of main influencing factors that describe the distribution pattern of water abundance, considering lithological characters, hydraulic characteristics, structural factors, and geophysical parameters that influence aquifer water abundance. The variable weight model is used along with the K-means clustering method in dynamic clustering to determine the variable weight interval thresholds for each index of the main influencing factor. Additionally, we investigated the construction of the state variable weight vector, determination of weight adjustment parameters, quantitative assessment of the interaction relationship, and relative importance of each main influencing factor in relation to aquifer water abundance. Finally, an evaluation method and mathematical model for the water abundance index based on the variable weight model are developed. This study provides a detailed description of the specific implementation steps of the water abundance index method based on the variable weight model, using the direct water-filled J2z–#2 coal seam roof fissured aquifer in the Xiaojihan coal mine as a case study. The evaluation results were then verified using drainage data from the working face. The findings indicate that a comparison with the traditional constant weight evaluation results demonstrates that the variable weight model better reflects the characteristics of aquifer heterogeneity and achieves higher prediction accuracy. [ABSTRACT FROM AUTHOR]

In arid regions characterized by large variations in groundwater salinity, the data derived from irrigation and domestic water supply wells may exhibit bias, reflecting an overall lower salinity than the true aquifer distribution. This bias stems from the decommissioning, non-use, or disrepair of wells that are frequently sources of higher salinity readings, rendering them unavailable for sampling. Baseflow-fed streams, agricultural drains, seeps, springs issuing into agricultural drains, and randomly located test hole samples tend to manifest higher averages and ranges of salinity when compared to supply wells. Agricultural drain flows, springs, and test holes, if sampled following recommended guidelines, are less susceptible to such bias. This study presents a case of groundwater bias identified through an initial water well sampling program in El Paso (Texas, USA). Subsequent rounds of sampling, incorporating drain samples, spring samples, and test hole samples, revealed a more comprehensive understanding of the salinity dynamics. The dataset not only highlights the existence of bias but also provides evidence for a combined geological and agricultural origin of salinity. Additionally, it demonstrates that drain sampling in an earlier study did not accurately depict a primary salinity source due to incomplete analysis of the data. Recommendations are outlined to mitigate bias, emphasizing the importance of sample control from baseflow-fed drains, springs, water wells, and test hole samples. The study also infers the upwelling of saline groundwater from deeper formations in the study area, contributing to a more comprehensive understanding of groundwater salinity dynamics. [ABSTRACT FROM AUTHOR]

In recent years groundwater contamination through nitrate contamination has increased rapidly in the managementof water research. In our study, fourteen nitrate conditioning factors were used, and multi-collinearity analysis is done. Among all variables, pH is crucial and ranked one, with a value of 0.77, which controls the nitrate concentration in the coastal aquifer in South 24 Parganas. The second important factor is Cl−, the value of which is 0.71. Other factors like—As, F−, EC and Mg2+ ranked third, fourth and fifth position, and their value are 0.69, 0.69, 0.67 and 0.55, respectively. Due to contaminated water, people of this district are suffering from several diseases like kidney damage (around 60%), liver (about 40%), low pressure due to salinity, fever, and headache. The applied method is for other regions to determine the nitrate concentration predictions and for the justifiable alterationof some management strategies. [ABSTRACT FROM AUTHOR]

The main objective of this research paper was to find out the major governing factors controlling fluoride enrichment in groundwater resources in the Jaipur region of India. Chemical analysis of collected water samples revealed that 36% of the collected groundwater samples exhibit fluoride concentration of more than 1.5 mg/L as per BIS, 10,500 and WHO, 2017. An attempt has been made to discuss occurrence of fluoride alongside its spatial distribution in the study area with respect to geology and groundwater flow direction. Chloroalkaline indices, Gibb's plot, Piper diagram and various inter-ionic bivariant plots have been applied to recognize hydrochemical processes and dissolution trends resulting in high concentration of fluoride in groundwater. There exist five water types in the study area: Ca-HCO3, Na-HCO3, Na-Cl, Ca-Mg-Cl and Ca-Na-HCO3. Due to ion association of excess Cl− emanating from wastewater, Na-HCO3 type water finally gets changed as Na-Cl type in aquifer. In the study area, 82% of water samples enriched in F− concentration (>1 ppm) pertain to Na-Cl type. Geochemical modelling confirms that reduced Ca2+ ion activity due to oversaturation of calcite with respect to fluorite might have triggered the favourable condition for dissolution of fluoride bearing minerals leading to fluoride enrichment in groundwater. To further assess the extent of natural and anthropogenic processes, the data was subjected to multivariate statistical analysis by performing correlation analysis, principal component analysis and hierarchical cluster analysis. [ABSTRACT FROM AUTHOR]

Saudi Arabia struggles to supply its population with enough clean water as being one of the biggest and fastest-growing nations outside its own continent. For this study 49 groundwater samples were collected between June and December of 2021. Different analytical techniques were used for determinations of anions and cations concentration. Using World Health Organization's recommended safe limits to compare results that were collected. Groundwater is affected by aquifer matrix disintegration, water infiltration from irrigation systems, and water–rock interactions, according to the results of the hydrogeochemical study. The anions HCO3−, CO32−, Cl−, NO32−, and F−, as well as the cations Na+, K+, Ca2+, and Mg2+, were also presented in the collected groundwater samples in acceptable concentrations. Using physical characteristics and hydrochemical characterizations is also a commendable approach to regulating the quality of groundwater samples collected for crop agriculture and irrigation. Most of the collected groundwater samples are desired and fit for human and industrial consumption. In addition, application of the statistical analysis concluded that in some locations contaminated surface water may recharge the groundwater. A variety of physical characteristics, including as EC, SAR, RSC, KR, MH, CR, PI, and PS, are widely used to regulate the quality of groundwater samples collected for crops agriculture and irrigation. Piper and Gibbs diagrams for groundwater hydrochemical characterizations were used. The obtained results indicated that the collected groundwater samples are acceptable for crops drinking, agriculture and irrigation. [ABSTRACT FROM AUTHOR]

Groundwater pollution is a current issue that may result in considerable negative effects on human health and the ecological balance. In the present study, the authors evaluated pollutants in groundwater in Maricá Municipality, located on the east side of Rio de Janeiro state in Brazil. The evaluated parameters were temperature, pH, electrical conductivity, Eh, dissolved oxygen, chlorides, nitrates, dissolved organic carbon, total inorganic carbon, phosphates, and total and thermotolerant coliforms. Due to the large number of evaluated points, they were divided into zones according to the respective hydrographic basin. The local accelerated urbanization accompanying income from oil production has led to uncontrolled population growth and associated groundwater pollution. The results of the present study suggest that sewage pollution of Maricá groundwater is already a significant issue. The lack of investment in basic sanitation has led to an imbalance in the local groundwater reservoir. In certain locations of the municipality, dissolved organic carbon (DOC), nutrient, and bacteria concentrations increase and spread in the aquifers because of domestic waste disposal. As aquifers are the main source of freshwater for the residents, contamination of them represents a potential threat to local public health. [ABSTRACT FROM AUTHOR]

A common challenge in many cities in Europe is endangerment of natural resources due to soil and water pollution. Despite extensive investigation and remediation measures over decades and current practices of environmental management, residues of pollutants persist in soil and groundwater, reducing the functionality of many urban areas. In complex hydrogeological systems, where contaminated plumes are overlapping and/or diffuse contamination is present, technical and administrative activities have to be thoroughly planned and executed in the long term to secure the recovery of groundwater quality. Communities need a management strategy (MS) to manage soil and groundwater contamination in urban areas, especially where contamination exceeds local scales but does not reach the national level. A MS drives administrations to understand hydrogeological system properties, define new, reachable target values and give practical guidance for the implementation of necessary measures. Implementation of a MS fosters the early involvement of key stakeholders and their contribution to the development of MS itself. The strategy has proven to be an appropriate and flexible tool for the transfer of scientific knowledge to the planning, coordination and implementation necessary for the remediation of large-scale groundwater contamination. [ABSTRACT FROM AUTHOR]

Developing an accurate map to control groundwater pollution is becoming increasingly important to fulfill requirements of the Algerian water directives. Evaluating groundwater vulnerability to nitrate contamination in the eastern Mitidja aquifer has become crucial for water resource control and preservation. In this research, some of the commonly used ensemble methods namely Categorical Boosting, Adaptive Boosting and Random Forest were employed to model the spatial groundwater vulnerability to nitrate concentration based on the maximum acceptable concentration in drinking water according to the Algerian directives (50 mg/L). The study were carried out on the evaluation of different possible influencing parameters including depth to groundwater, permeability, rainfall, vadose zone, distance to river, drainage density, land use land cover, Normalized Difference Vegetation Index, slope, topographic wetness index and elevation. The proposed approach aims to understand and control the vulnerability and pollution process of the groundwater aquifers with the smallest available dataset to assess vulnerability predictive mapping. The best results based on the receiver operating characteristic and area under the curve (ROC-AUC) showed that the Categorical boosting indicated the highest accuracy of 94% then the adaptive boosting algorithm with 92%, and the Random forest algorithm with 89%. It revealed that climatic and hydrogeological factors are the key factors determining groundwater vulnerability to NO3 concentration in the eastern Mitidja. It is concluded that the risk of groundwater pollution covers a large area of the groundwater resources in the city of Algiers, Blida, and Boumerdas in northern Algeria. [ABSTRACT FROM AUTHOR]

Agricultural activities can generate contaminants that enter underlying granular aquifers and become transported within the groundwater to adjacent streams. This paper reports on estimation of the transit time of groundwater through a saturated granular unconfined aquifer in an agricultural region of Saguenay-Lac-Saint-Jean, Quebec (Canada). A multi-technique approach is applied, integrating analytical, hydrogeochemical, and numerical methods—to determine groundwater flow from a recharge (wetland) to discharge zone (groundwater seep). Fieldwork observations, including borehole drilling, soil/groundwater sampling, and piezometers, were combined with laboratory measurements of soil hydrogeological properties and stable (δ18OH2O and δ2HH2O)/radioactive (3H) isotopes in the collected groundwater. The Dupuit–Forchheimer-based analytical method used here estimated a groundwater transit time of 7.75 years, whereas the hydrogeochemical-based and three-dimensional FEFLOW numerical method produced estimates of 7.34 and 7.27 years, respectively. The similarity of the three estimates highlights the robustness of the approach, which integrates field data to produce accurate assessments of groundwater transit time. This multi-technique approach will help in the sustainable management of groundwater resources and for preparing effective environmental plans for agricultural practices in areas underlain by aquifers. [ABSTRACT FROM AUTHOR]

The study is aimed at evaluating the groundwater accumulations present in Alice using magnetic and electrical resistivity measurements to examine the trends of structural elements and characterize the groundwater resource for borehole drilling. The magnetic maps show a low magnetic linear structure moving northwest to southeast direction, which may be caused by fractures. The linear high intensities were probably caused by dolerite dykes, while dolerite sills caused broader high-intensity areas. The depth slices show that the near-surface magnetic structures are visible to a depth of about 19 m, and the deep-seated structures are found at a depth of about 31 m, possibly deeper. Twenty-five vertical electrical soundings (VES) of the Schlumberger array were measured with AB/2 varying between 1.5 m and 250 m across the study area. The VES interpretation showed four geoelectric layers composed of HK and HA curve types. The geoelectric layer's thicknesses are (1) topsoil from 0.4 to 1.8 m, (2) weathered layer from 0.8 to 17.5 m, and (3) weathered/fractured layer from 9.9 to 143.9 m; the third layer could be the productive water-bearing zones, and (4) bedrock layer has an infinite thickness. The layers have resistivity values of 20-5752 Ωm, 3-51 Ωm, 136-352 Ωm, and 44-60428 Ωm, respectively. A correlation of the VES with the borehole log indicated a well-matched result. The magnetic and electrical resistivity surveys provided a detailed subsurface structure and helped identify possible fractures that could act as a passage for groundwater. [ABSTRACT FROM AUTHOR]

The city of Gagal suffers from insufficient drinking water, and the population turns to surface water, wells and drillings without guarantee of quality. In order to characterize the hydrogeochemical and bacteriological properties of the waters of the aquifer system in the city of Gagal, to contribute to improving its knowledge, field campaigns were undertaken to sample the groundwater. The present study focuses on the hydrogeochemical and bacteriological characterization of drinking water in Gagal, southwestern Chad. The methodology consisted of acquiring existing data, a field campaign, and a chemical and bacteriological analysis of the water in the laboratory. The results of the physicochemical analyses revealed that the values of the parameters such as conductivity, pH (5.23), Ca² (26.11 mg/L), Mg²(5.14 mg/L), Na(3.54 mg/L), K(1.34 mg/L), HCO3 -(81.74 mg/L), Cl-(11.77 mg/L), SO4 -(1.94 mg/L), and NO3 - (8.70 mg/L) conformed to the WHO potability standards. Piper's diagram showed calcic and magnesian bicarbonate facies represented by 75%; and calcic and magnesian sulfate chloride facies in 25% of the analyzed waters. The bacteriological (Total coliforms (0 to more than 135,200 CFU/100 ml), Escherichia coli (0 and 14,400 CFU/100 ml), faecal enterococci (0 and 4600 CFU/100 ml)) study confirmed that the water from the wells and boreholes showed pollution of bacterial origin. Using these waters may endanger the populations with the risks of hydric diseases. [ABSTRACT FROM AUTHOR]

Quaternary glacial aquifers are important water sources for irrigation in many agricultural regions, including eastern Nebraska, USA. Quaternary glacial aquifers are heterogeneous, with juxtaposed low-permeability and high-permeability hydrofacies. Managing groundwater in such aquifers requires a realistic groundwater-flow model parameterization, and characterization of the aquifer geometry, spatial distribution of aquifer properties, and local aquifer interconnectedness. Despite its importance in considering uncertainty during decision-making, hydrofacies probabilities generated from multiple-point statistics (MPS) are not widely applied for groundwater model parameterization and groundwater management zone delineation. This study used a combination of soft data, a cognitive training image, and hard data to generate 100 three-dimensional (3D) conditional aquifer heterogeneity realizations. The most probable model (probability of hydrofacies) was then computed at node spacing of 200 × 200 × 3 m and validated using groundwater-level hydrographs. The resulting hydrofacies probability grids revealed variations in aquifer geometry, locally disconnected aquifer systems, recharge pathways, and hydrologic barriers. The profiles from hydrofacies probability at various locations show spatial variability of the streambed and aquifer connectivity. Groundwater-level hydrographs show evidence of these aquifer characteristics, verifying the general structure of the model. Using the MPS-generated 3D hydrofacies probability and hydrologic data, a novel workflow was developed in order to better define high-resolution groundwater management zones and strategies. In general, the conditional probability of hydrofacies helps improve the understanding of glacial aquifer heterogeneity, the characterization of aquifer-to-aquifer and streambed-aquifer connections, and the delineation of groundwater management zones. This MPS workflow can be adapted to other areas for modeling 3D aquifer heterogeneity using multisource data. [ABSTRACT FROM AUTHOR]

Arsenic pollution of groundwater is a serious concern in the developing world. Over the last decade, significant progress has been made in arsenic remediation in India, where millions of households are exposed to arsenic poisoning through drinking water drawn from contaminated aquifers. Arsenic-treatment units (ATUs) have been effective in helping regions where piped-water supply of surface water is unachievable due to logistic constraints. However, no policy measure exists on environmental and economic management of the voluminous wastewater produced by ATUs. The waste is highly toxic in terms of its arsenic content and leachability and therefore can readily re-contaminate local environments if suitable stabilisation methods are not implemented. This paper presents an investigation of the recent developments in arsenic-wastewater-management practices of a severely affected state called West Bengal. Commercial fixation of the waste by incorporation into building materials is often seen as a potent method for ultimate encapsulation of arsenic toxicity. By analysing the practical efficacy of such a prospective project, the author has made an attempt to model scenarios involving non-hazardous and financially beneficial arsenic waste management for sustainable arsenic mitigation in the region. [ABSTRACT FROM AUTHOR]

This investigation is aimed at exploring the mobilization and sources of Fe, Mn, and As in aquifers through geochemical characterization, spatial analysis, and statistical approaches. Analytical results showed that the average concentrations of Fe (10.17 mg/L) and Mn (3.6 mg/L) crossed the guideline value but not As in all samples. In this study, the elevated levels of dissolved organic carbon, salinity, total hardness, and log10 pCO2; the lower value of dissolved oxygen; and some oxidizing groups of samples influence the reductive environment of Fe and Mn weathering. The investigation illustrated that the source of both metals on the upper platform is consolidated silty soil and aquifer sediment, whereas, in the river valley, they originate from Fe and Mn-bearing nodules in the rich clay layer and tidal mud. In addition, the frequent fluctuation of river flow, excess water mining, and an unbalanced recharge/discharge ratio are the causes of higher concentrations of both metals. The correlation matrix and factor analysis of Fe and Mn with redox-sensitive water variables confirmed that a favourable reductive situation fosters the Fe and Mn release process. Studies have also shown the significant possibility of forming a metal complex with organic and inorganic substances. The higher dissolution of Fe and Mn minerals causes As to be adsorbed on them, leading to less release of As into groundwater. This investigation provides a basis for the rational use of groundwater and the defense of public health in zones with high Fe and Mn contents. [ABSTRACT FROM AUTHOR]

Geochemical and mathematical methods are presented, which include NETPATH model and the Moore-Penrose pseudo-inverse (MPPI) to quantify the contributions of water from distinct recharge areas and aquifers to public supply wells in the city of Madison, Wisconsin. Previous studies investigated the hydraulic connectivity between different aquifers in the study area and proved the impact of the shallower aquifers as well as the surface water on some of the deep wells, but did not address the percentages of the contributions of such sources. The MPPI, executed by MATLAB code, in conjunction with the inverse-based NETPATH model was used to estimate the mixing proportions of four end members ("initials") in some of the deep groundwater wells. The quantitative estimation of the contribution of the different water resources (reference waters) on the water extracted from the deep municipal wells is considered as the main ultimate goal of this manuscript. Therefore, in this paper, many tools including WATEQ program, NETPATH and MPPI codes, were applied to verify the influence of such reference waters as well as to assess their ratios in the deep municipal wells. Datasets including major ion chemistry and stable isotopes (such as δ18O and δD) data were manipulated to determine similarities and differences between the samples and reference waters. These data provided a basis for selecting and grouping of the samples that are believed to be affected by mixing. The results showed that there are two groups of wells; one group was mainly affected by the deeper Mount Simon water (about 70%), while the second group showed a slight increase in the shallower Tunnel City water (up to 15%) and a significant increase in the Wonewoc Formation water (up to 40%) with a decrease in the ratio of the deeper Mount Simon water. The contribution of lake waters was almost around 20% in all of the studied groundwater wells. It is worth mentioning that it is not easy to choose the most appropriate models that express the mixing ratios if the necessary data are not available, as well as the appropriate programs used to adapt these data correctly. Therefore, the MPPI mathematical program was adapted along with other geochemical programs in order to constrain the models computed by such programs as well as to verify that the outputs of these programs will be as close to reality as possible. Generally, quantification of the contribution of different sources of recharge to ground-water sheds light on the vulnerability of a certain aquifer or well to pollution. Such analysis may also highlight the need for additional characterization of aquifer heterogeneity at a given location. [ABSTRACT FROM AUTHOR]

Groundwater is one of the major sources of exploitation in arid and semiarid regions. Spatial and temporal quality distribution is an important factor in groundwater management. Thus for protecting groundwater quality, data production on spatial and temporal distribution is essential. The present study has applied multiple linear regression (MLR) techniques to predict the fitness of groundwater quality in Kermanshah province, west of Iran. The parameters examined were Total dissolved solids (TDS), Total hardness (TH), Sodium adsorption ratio (SAR). the quality variables were modelled by MLR. Finally, the performance of the models was assessed using the coefficient of determination (R2). The relationship between parameters by MLR showed that TDS and water quality parameters in semi-deep wells and aquifers had a strong positive correlation (r = 0.94, r = 0.98) and there was a strong positive significant correlation between SAR and water quality parameters in deep wells and aquifers (r = 0.98, r = 0.99). Also, TH and water quality parameters in all water sources had a strong positive correlation (r = 1). The MLR model could serve as an alternative and cost-effective tool for groundwater quality prediction where there is limitation in laboratory facilities, trained expertise or time. Consequently, the usefulness of these linear regression equations in predicting the groundwater quality is an approach, which can be applied in any other locations. [ABSTRACT FROM AUTHOR]

High-cost remediation of groundwater pollution makes it important to obtain exact information about the source. This is quite difficult to achieve in naturally ill-posed inverse problems of this kind. If the aquifer parameters are also unknown, the problem becomes even more challenging. To address this difficulty, we propose the alternating direction genetic algorithm (ADGA) approach, together with modification of the order of magnitude of the decision variables, to increase the accuracy of the results and computational efficiency. Seven scenarios were designed to test the accuracy of the proposed approach in aquifer with different properties, number of pollution sources, parameters and measurement errors. The results show that combining the ADGA approach with modification of the order of magnitude of the decision variables for identifying both groundwater pollution source and aquifer parameters significantly increases the accuracy of estimated results. The NE value for the estimated results decreased from 9.81% to 58.44% for different cases, and computation time is about half decreased. In addition, the approach is applicable in situations where concentrations of observational data with measurement error, and for multiple source locations and non-uniform media. [ABSTRACT FROM AUTHOR]

Groundwater assets are the foremost imperative assets of freshwater accessible to people especially in arid and semi-arid regions. For the investigation of temporal changes in groundwater nitrate pollution and the role of agriculture and other sources in the pollution of groundwater, the information on 42 drinking water wells with suitable distribution in the plain in Bouin-Daran Plain in the center of Iran was used. The results showed that the amount of hydraulic conductivity in the plain for different areas after calibration in steady state was calculated between 0.8 and 34 m/day. After calibrating the model in permanent conditions, the model was calibrated in non-permanent conditions for 2 years. The results showed that in a wide area of the region, the nitrate ion concentration has values of more than 25 mg/L. This shows that the average concentration of this ion in the region is generally high. The highest level of pollution in the aquifer of the plain is related to the southern and southeastern parts of the plain. Due to the agricultural activities with the use of large amounts of fertilizers in this plain, there is a potential for pollution in all of the places, and it requires codified and executive planning for agricultural operations as well as the use of groundwater sources. The DRASTIC vulnerability estimation method is only useful for estimating the areas that have a high potential for contamination and according to the validation tests, it has also provided a suitable estimate. [ABSTRACT FROM AUTHOR]

There is an urgent need to explore and analyze new aquifer recharge potential zones (ARPZ) in arid regions exposed mainlyto hard rock local aquifers, whether fractured or non-fractured, for investment and fulfillment of the Saudi Vision 2030. Over-pumping, seawater intrusion, climatological changes, population growth, lack of traditional water supplies, expensive desalinized water, and excessive evaporation have characterized the Duba region of Tabuk province of Saudi Arabia (SA). Aquifer productivity and potentiality are affected by surface geology, rainfall, lineament density, drainage density, slope, elevation, soil, and normalized difference vegetation index (NDVI). This study aims to demarcate the ARPZ using integrated remote sensing and geographic information system (GIS) and (RS) approaches. The relative importance of each parameter was determined based on its impact on the aquifer's potential through the analytical hierarchical process (AHP). The ARPZ zones are categorized into five classes starting from very low to very high potentiality. Southern, western, and northern areas have high to very high aquifer potentiality and recharge. They made up roughly 43% of the area that was examined. About 41.8% of the research area is comprised of low to very low groundwater potentiality, and this potentiality is dispersed over the western and central regions of the region. The medium aquifer potentiality level reflects about 15.2%. The high to very high aquifer potentiality areas coincide with low concentrations of total dissolved solids (TDS), electrical conductivity (EC), and nitrate (NO3). The outcomes emphasized the decisiveness of the entire study and its applicability to any place with similar groundwater aspirations and management. [ABSTRACT FROM AUTHOR]

Gravel-bed river floodplains occur in river corridors around the globe. One key habitat of these floodplains are alluvial aquifers that provide habitat for a wide range of obligate groundwater species. Multiple species of the amphipod genus Stygobromus commonly occur in alluvial aquifers, as well as in karstic phreatic systems, but few studies have investigated the population structure and its relevance to the biogeography of the genus. Using reduced representation genome sequencing, RAD-seq, we investigated the population structure and genetic connectivity of an undescribed Stygobromus species in several alluvial aquifers on floodplains of the Flathead River, Montana (USA). Amphipods were genetically similar (pairwise FST ranging from 0.0061 to 0.0092) at multiple sites within floodplains but three genetic clusters were segregated among floodplains (pairwise FST ranging from 0.0303 to 0.0547), suggesting some geographic isolation of populations. These floodplain aquifers are separated by bedrock canyons that could be migration barriers resulting in the observed spatial segregation of populations. [ABSTRACT FROM AUTHOR]

The instability of colloidal gas aphrons (CGAs) in aquifers is one of the major obstacles influencing the remediation efficiency of CGAs-flushing. In this study, hydrophobic nano-SiO2 (HN-SiO2) was utilized to enhance the stability of CGAs. The batch experiments were carried out to investigate the effect of hydrogeochemical conditions on the stability of HN-SiO2 stabilized CGAs in aquifers, such as ions, pH, and nitrobenzene (NB); 2-D tank experiments designed with various injection velocities and medium particle sizes were conducted to determine the factors influencing the migration of CGAs in the aquifer; and 1-D column experiments were established to evaluate the remediation efficiency of HN-SiO2 stabilized CGAs flushing for NB removal. The results indicated that HN-SiO2 had a favorable effect on the stability of CGAs, which enhanced the half-life of CGAs from 328 to 1,050 s. HN-SiO2 particles formed a shell film on the gas-liquid interface of CGAs to slow down the gas escape and drainage velocity. The stability of CGAs decreased while pH<6 or pH>8 , whereas this was enhanced with the addition of 0.1 wt.% NaCl. The 2-D tank experiments demonstrated that the HN-SiO2 stabilized CGAs had better stability when they flowed in aquifers compared to sodium dodecyl sulfate (SDS) CGAs. The fine medium and high injection velocity facilitated CGAs forming the larger radius remediation area. The injection pressure was inversely proportional to the medium grain sizes, whereas directly proportional to the injection velocities. In addition, column experiments demonstrated the remediation efficiency of HN-SiO2 stabilized CGAs (81.7%) flushing for NB removal was higher than that of SDS CGAs (61.4%) flushing. Therefore, in comparison with SDS CGAs, HN-SiO2 stabilized CGAs were more efficient reagents for NB removal. CGAs-flushing technique using HN-SiO2 stabilized CGAs is feasible to remedy the contaminated aquifers. The contamination caused by dense nonaqueous phase liquids in aquifers has a great threat to ecosystems and human health. Colloidal gas aphron (CGA) flushing has been proposed as an effective remediation technology for dense nonaqueous liquids contaminated aquifers. However, the instability of colloidal gas aphrons in aquifers is one of the major obstacles influencing remediation efficiency. In this work, the hydrophobic nano-SiO2 was used to improve its stability. Besides, the migration of colloidal gas aphron generated with sodium dodecyl sulfate (SDS) and SDS/SiO2 was investigated, and the remediation efficiency for nitrobenzene removal of SDS/SiO2 colloidal gas aphrons flushing was evaluated. SiO2 had a favorable effect on the stability of colloidal gas aphrons, enhancing the half-life of colloidal gas aphrons from 328 to 1,050 s, and the enhancement effect was more evident with the increasing SiO2 concentration. The tank experiment results indicated that SDS/SiO2 colloidal gas aphron had fine migration performance and wide applicability in aquifer environments. In addition, column experiments demonstrated the remediation efficiency of hydrophobic nano-SiO2 stabilized colloidal gas aphrons flushing for nitrobenzene removal was higher than that of SDS colloidal gas aphrons flushing. Therefore, the colloidal gas aphron flushing technique using SDS/SiO2 colloidal gas aphrons is feasible to remedy the contaminated aquifers. [ABSTRACT FROM AUTHOR]

The largest confined aquifers hydraulically continuous from the Algeria Atlas Mountains as a recharge area to the Tunisian Chotts were discharge area. Is being largely used in the valley of Oued Souf, southeastern of Algeria and part of the northeastern Sahara, composed with sedimentary series ranging from the lower Cretaceous to the Quaternary. These formations have favored several aquifer layers with variable hydrodynamic behavior depending on their facies . The high expansion of the agricultural field needs irrigation from groundwater aquifers in this area. The overexploitation of the shallow aquifer causes severe deterioration of groundwater quality and soil suffusion at arid areas. The high salinity (electrical conductivity exceeds 3600 mS.cm-¹) coupled with groundwater level decline pose serious problems for current irrigation and domestic water supplies. Although, the multi-layers of complex terminal (CT) and continental intercalary (CI) aquifers is used to approve the water supplies. In aim to corroborate the hydrochemical process, and to investigate the water potentialities and mineralization of CT and CI groundwater aquifers, chemical tools namely major elements and trace elements are studied. The isotopic (δ 18O, δ 2H) hydrogeochemical study helps to identify and classify this deep underground water aquifers relationship. The samples isotopic signal shown a current recharge of the CT, according to the regional rainfall signal. [ABSTRACT FROM AUTHOR]

BACKGROUND: Groundwater is closely related to surface water. Groundwater over-extraction has triggered a series of negative ecological effects in the Daqing River basin. The evolution of groundwater chemical characteristics is influenced by both natural and anthropogenic factors. The analysis of groundwater chemical characteristics can indicate the meteorological-hydrological and water-rock interaction during groundwater runoff, thus reflecting the groundwater circulation path, groundwater system characteristics and evolution laws, etc. It also helps to monitor groundwater dynamics and prevent the occurrence of groundwater pollution. OBJECTIVES: To clarify the chemical characteristics and evolution of groundwater in the plain area of the Daqing River basin, which will be important for the rational development and utilization of water resources in the basin. METHODS: 47 water samples from the shallow aquifer groups and 32 water samples from the deep aquifer groups were collected to analyze the main anions (Cl -, SO 2- 4, NO - 3 ) and cations (K +, Na +, Ca 2+, Mg 2+ ). The water chemistry characteristics and evolution laws were studied by using the water chemistry type, Gibbs model and ion ratio relationship. On - site portable water quality analyzer ( HACH - HQ40d) was used to test pH ( accuracy 0. 01), total dissolved solids ( TDS, accuracy 0. 01 ) and other parameters, and groundwater samples were collected after the indicators were stabilized. All samples were sent to the laboratory at low temperature and stored in a refrigerator at 4℃, and groundwater alkalinity was determined by titration on the same day. Seven days later, the samples were sent to the Institute of Hydrogeology and Environmental Geology, Chinese Academy of Geological Sciences for testing of major anions ( Cl -, SO 2- 4, NO - 3 ) and major cations ( K +, Na +, Ca 2+, Mg 2+ ) using inductively coupled plasma-optical emission spectrometry (iCAP6300). The anion and cation charge balance error was less than 5%, and the anion and cation test accuracy was 0. 01mg / L. The test results showed that the largest deviation was in the water sample from Hanbao Village, Liu Lizhuang Town, Anxin County, Baoding City, Hebei Province, which was from the shallow aquifer groups, and the maximum TDS reached 6015. 00mg / L. The TDS of the shallow aquifer groups ranged from 254. 10 to 6015. 00 mg / L, with an average of 664. 14mg / L, a large coefficient of variation and a large variation in TDS, indicating that the shallow aquifer groups were affected by meteorological and human factors. The TDS of the deep aquifer groups ranged from 197. 10 to 691. 40mg / L, with an average of 278. 58mg / L, and the coefficient of variation was small, indicating that the groundwater of the deep aquifer groups was less affected by meteorological and human activities than that of the shallow aquifer groups. A small portion of the sampling points of the shallow aquifer groups in the area were brackish water and salt water. The TDS of the deep aquifer groups was generally less than 1000mg / L, which was suitable for use as a mining layer. The pH values of the shallow and deep aquifer groupss in the study area were not very different ( 7. 35 - 8. 92) and were alkaline. The NO - 3 maximum value of 298. 40mg / L and SO 2- 4 maximum value of 3091. 00mg / L in the shallow aquifer groups, but the average value was not significant, indicating that the shallow aquifer groups have caused nitrate and sulfate pollution in local areas due to agricultural activities and other effects In the shallow layer of the study area, except for the difference in hydraulic conditions in the northern piedmont plain where flaky or spotty HCO3 -Cl-SO4 and HCO3 -Cl type water occurred, the anions in most of the piedmont plain were mainly HCO3 type, and the cations were mainly Ca and Ca -Mg and Mg -Ca. During the discharge of groundwater along the piedmont plain to the mouth of the alluvial fan, the cations changed from Ca-Mg type to Na type in order through Ca-Mg-Na, Na -Ca-Mg, Na-Mg-Ca, Na-Ca to Na type, and anions from HCO3 type to SO4 and Cl type via HCO3 -SO4, HCO3 -SO4 -Cl, HCO3 -Cl-SO4, SO4 -Cl. The deep groundwater cations were relatively more complex, and the zonation was more obvious: from the piedmont plain to the bottom of the alluvial fan, the cations transition from Ca, Ca-Mg, Mg-Ca, Na-Mg-Ca (Mg-Ca-Na) type to Na-Ca and Na type water. The shallow aquifer groups were basically located in the area of water-rock interaction, and individual points showed some influence of evaporation concentration. The deep aquifer groups were subjected to water - rock interaction and less affected by evaporation and atmospheric precipitation. The analysis results showed that the milligram equivalent concentration ratio of ( Ca 2+ + Mg 2+ ) + ( HCO - 3 + SO 2- 4 ) to Na + + K + - Cl - was close to - 1, indicating a more significant cation exchange effect. The groundwater samples in this study area were mostly distributed near the end elements of silicate minerals, indicating that weathering of silicate minerals ( such as feldspar) was the main hydrogeochemical control factor in the study area, which was consistent with the lithological characteristics of aquifers in the groundwater of the Daqing River basin plain, and the test results also showed that HCO - 3 was the dominant ion in both shallow and deep aquifer groups. The SI values of calcite in the shallow aquifer groups in this study area ranged from -0. 46 to 1. 35, dolomite SI values from -0. 88 to 3. 02, gypsum SI values from -3. 1 to -0. 68, and rock salt SI values from -8. 53 to -4. 75, indicating that calcite and dolomite were partially saturated and partially unsaturated, and both gypsum and rock salt were unsaturated. Cl - / ( Na+ +K+ ) could determine whether the groundwater was influenced by the dissolution of silicate rock. Most of the groundwater samples in this study area exhibited Cl - / (Na+ +K+ ) < 1, indicating that, in addition to rock salt in dissolved state, silicate mineral dissolution ( e. g., potassium feldspar and sodium feldspar) was the main source of excess Na+ and K + . The Na + content may also originate from cation exchange, and the high Cl -, the higher concentration may be the input of foreign contamination. The HCO - 3 / (Ca 2+ +Mg 2+ ) of the samples from the shallow aquifer groups was basically less than 1, showing excess Ca 2+ and Mg 2+, suggesting other sources of Ca 2+ or Mg 2+, while the (HCO - 3 +SO 2- 4 ) / (Ca 2+ +Mg 2+ ) of the shallow aquifer groups was distributed above and below the 1 ∶ 1 line on both sides, suggesting that evaporite minerals (e. g. gypsum) may also be an important source of Ca 2+ for the shallow aquifer groups, as evidenced by the unsaturated state of gypsum in groundwater, in addition to the increase in SO 2- 4 due to human activities. Both HCO - 3 / (Ca 2+ +Mg 2+ ) and (HCO - 3 +SO 2- 4 ) / (Ca 2+ +Mg 2+ ) of the deep aquifer groups lay above the 1 ∶ 1 line, and the excess HCO - 3 implied silicate dissolution dominance, or the presence of cation exchange, leading to a lower Ca 2+ content. (Cl - +SO 2- 4 ) / (HCO - 3 ) could indicate the dissolution status of evaporites and carbonates, and water samples from shallow and deep aquifer groups were mainly distributed in the (Cl - +SO 2- 4 ) / (HCO - 3 )= 1 ∶ 1 line below, which indicated that its chemical components were more dissolved by carbonate rocks. In the influence zone of the Caohe River in the northern part of Mancheng District, the water chemistry changed from HCO3 - Ca - Mg water to Cl - HCO3 - Ca -Na water; at the alluvial fan margin of Jiehe River in Shunping County and at the alluvial fan margin of Rejected Horse River in Zhuozhou City, the proportion of Na content in groundwater gradually exceeded that of Mg as the cation content second only to Ca, and the water chemistry changed from HCO3 -Ca-Mg water to HCO3 -Ca-Na-Mg type water. The groundwater in the central plain changed from Cl-HCO3 -Ca-Na and HCO3 -Cl-Ca-Na type water with island and strip distribution of SO4 - HCO3 -Na-Mg, SO4 -HCO3 -Na, SO4 -Na-Mg and HCO3 -Na-Mg type water to Cl-HCO3 -Ca-Na, SO4 -Cl -NaMg type water dominated and mingled with HCO3 -Cl-Ca-Mg, Cl-SO4 -Na-Mg, HCO3 -Cl-SO4 -Na, HCO3 -SO4 -Na, HCO3 -SO4 -Na, HCO3 -SO4 -Na-Mg, and Cl-SO4 -Na-Mg type water. The average NO - 3 content of the shallow aquifer was 28. 78mg / L, and the average NO - 3 content of the deep aquifer was 4. 55mg / L, indicating that nitrate pollution was serious in the shallow groundwater local area of the study area. Referring to the groundwater quality standard (GB / T 14848—2017) for ClassⅢ water, there were 17 sampling points in the shallow aquifer groups with NO - 3 content over 20mg / L and 5 sampling points in the shallow aquifer groups with SO 2- 4 greater than 250g / L, indicating that these sampling sites were affected by anthropogenic activities, resulting in nitrate and sulfate pollution. A ratio of SO 2- 4 / Ca 2+ to NO - 3 / Ca 2+ greater than 1 indicated that industrial and mining activities had a greater impact on groundwater, and a ratio less than 1 was more disturbed by agricultural activities and residential sewage. The results showed that the ratio of the deep aquifer groups was greater than 1, and only the 240m well in the north of Erlangmiao Village, Dingzhou City, Baoding City, Hebei Province, was less than 1. This indicated that the deep aquifer groups were basically affected by industrial and mining activities, but not by agricultural activities and residential sewage. In the shallow aquifer groups, there were 27 water samples with SO 2- 4 -Ca 2+ to NO3 -Ca 2+ ratio greater than 1, and 20 water samples with SO 2- 4 -Ca 2+ to NO - 3 - Ca 2+ ratio less than 1, indicating that the shallow aquifer groups were partly influenced by industrial and mining activities, and partly influenced by agricultural activities and domestic sewage of residents. CONCLUSIONS: The characteristics and evolution of groundwater chemistry in the plain area of the Daqing River basin was investigated by using the water chemistry method, clarifying the characteristics of the water chemistry and the evolution of water chemistry types in the plain area of the Daqing River Basin. Reasons for the evolution trend were also investigated, indicating that the evolution of groundwater chemistry is increasingly influenced by human activities. Relevant research will be conducted on the prediction of the future evolution of water chemistry. [ABSTRACT FROM AUTHOR]

Estimation of groundwater travel time distribution (TTD) is critical to environmental assessment and successful urban water management. This paper presents a novel analytical approach to account for the groundwater TTD in an unconfined aquifer, considering the impervious urban structure and the modified aquifer hydraulic properties due to consolidation processes. The analytical solution follows the Dupuit-Forchheimer assumption and is verified through comparisons with numerical results. Sensitivity study reveals a potential increase in the mean travel time when the aquifer intersects with an impervious underground structure, while the degree of change depends on the interplay of two mechanisms (i.e., the increase in upgradient groundwater storage and the decrease in pore space of the consolidated zone). Global sensitivity analysis suggests that urban groundwater TTD systems are strongly dependent on both construction-related parameters and aquifer compressibility, indicating that adaptive strategies of groundwater management should be taken for different aquifer types. The proposed analytical model has great implications for the management of water resources in urban areas, the utilization of urban groundwater for human consumption, and the quality of urban aquifers. [ABSTRACT FROM AUTHOR]

Mine-influenced groundwater (MIW) at a former copper mine site has affected an alluvial aquifer that also contains groundwater with solutes characteristic of natural mineralization and agricultural activities. Many of the solutes are common to at least two of three potential sources, and some solutes (e.g., sulfate and uranium) are common to all three. This precludes the conventional use of one, or several, characteristic solutes to identify the extent of MIW. So, we used five independent lines of evidence (LOE) to define the extent of MIW in the alluvial aquifer. The five LOE are multivariate statistical analysis of an extensive groundwater analyte suite, groundwater sulfur isotope (δ34SSO4) data, probabilistic calculations of groundwater velocity and flow distance, isotopic (3H/3He) estimates of groundwater age, and extent of nitrate in groundwater originating from agricultural activities. [ABSTRACT FROM AUTHOR]

Although chalk aquifers are not too often associated with conduit flow, they are highly productive groundwater systems and, like limestone aquifers, they can be vulnerable to contamination when exposed to land use activities. The Danish carbonate rocks are generally recognized to be highly fractured and covered by thick Quaternary sediments. Fissure flow is pronounced, occurring in the upper 50–100 m due to Pleistocene glaciations. According to recently published maps of the distribution of karst in Europe, Denmark has no karst. However, this study concludes that karstified chalk and limestone aquifers are an important source of freshwater in Denmark. Four national datasets on karst features, groundwater flow, groundwater chemistry, and fish ecological quality ratio (EQR) data now indicate more heterogeneous structures and preferential flow pathways in the chalk and limestone aquifers than had been conceptualized and modelled with a national water resources groundwater/surface-water model in the recent past. This study provides new qualitative evidence that rapid and preferential flow of water and agrochemicals from the surface through thinner parts of the Quaternary cover layers, sinkholes and solution-enlarged fractures may likely impact the vulnerability of chalk and limestone aquifers. Additionally, due to the preferential flow system, some gaining streams discharged by karstified chalk and limestone aquifers show increased fish EQR values when using observed river daily discharge data instead of simulated daily discharge. [ABSTRACT FROM AUTHOR]

One of the biggest challenges in characterizing clandestine groundwater pollution sources is correctly estimating the number of such sources and their physical locations. Indiscreet underground disposal of toxic waste leading to groundwater pollution is widespread, and it is extremely difficult to detect the number of such sources and their locations. In this study, a real-life scenario of groundwater pollution in suburban New South Wales, Australia, is solved using a simulated annealing (SA)–based linked simulation optimization (LSO) technique with Benzene, Toluene, Ethylbenzene and Xylene (BTEX). The developed LSO considers the number of pollutant sources and their locations as explicit unknowns. This overcomes a crucial limitation in the earlier methods that limited the search to a few known potential source locations. The results show the applicability of the developed methodology to real-life groundwater pollution problems without making limiting assumptions about the number of sources or potential source locations being known, which has not been addressed to date. The developed methodology can potentially improve the process of remediation of polluted groundwater aquifers by simultaneously identifying the number of pollution source locations and release flux histories. The results of the study can be used to assist remediation engineers in developing an appropriate reclamation approach for a polluted aquifer, where knowledge of groundwater pollutant source characteristics is vital. The suggested method will aid in holding polluters accountable, contributing to predictions about the fate and movement of pollution, and developing a strategy for monitoring compliance. When implementing the results from the modeling technique to real-life scenarios of groundwater pollution, the equifinality of the solution cannot be entirely ruled out. The accuracy of the results is governed by assumptions and simplifications made in the model to simulate the aquifer response. Even the model calibration is dependent on the availability of data, which may be noisy and erroneous, resulting in nonunique solutions. [ABSTRACT FROM AUTHOR]

Groundwater is an important freshwater resource and hosts specialized microbial assemblages providing fundamental ecosystem services. The current knowledge on the role of aquatic microorganisms in subsurface ecosystems is still limited. This work aimed to explore the links between groundwater hydrogeochemical properties and microbial community traits in a volcanic unconfined aquifer, moderately impacted by anthropic activities. The main physical and chemical parameters of groundwater samples were analyzed, along with microbial biomass (total cell counts, ATP-active biomass concentration), potential metabolic activity, and physiological profiles at the microbial community level (Biolog ™ EcoPlates). The results showed the coexistence of oxidizing and reducing groundwater conditions across the study area. We discriminated two groups of oxidizing/reducing groundwater samples (Ox and Red), each including two subgroups with different chemical conditions attributed to contrasting levels of anthropogenic impact for non-intensive agricultural practices and waste disposal activities (Ox − and Ox + ; Red − and Red +). Although the microbial biomass was likely not affected by changing redox, the microbial metabolic potential and functional diversity changed significantly. In the Ox samples, the community-level physiological profiles were different, mainly owing to the utilization of carboxylic acids (Ox − > Ox +) and carbohydrates (Ox + > Ox −). In the Red samples, a wider set of organic substrates were consumed by the microbial communities, including those less bioavailable (e.g., phenols). Significant differences were also found between Red − and Red + , mainly owing to the relative increase in the utilization of amino acids in Red − , polymers and amines in Red + , along with the active biomass. By reflecting the local redox conditions and moderate levels of anthropogenic impact, the applied approach highlighted changes of microbial metabolic potential and physiological profiles that imply direct repercussions on biogeochemical cycling and the ecosystem services provided by groundwater microorganisms. [ABSTRACT FROM AUTHOR]

Rogério Tadeu de Souza, Luiz Eduardo Panisset Travassos, Olga Susana Heredia, Mariana Alicia Paparas, Silvia Alejandra Sicilia, Franco Urbani Patat, Rosa María Valcarce Ortega, Moraima Fernández Rodríguez, Francisco Bautista, Liane Gamboa Corrales, Nathalia Vanessa Uasapud Enríquez & Yameli Aguilar Duarte: First Steps to understanding Intrinsic Vulnerability to Contamination of Karst Aquifers in Various South American and Caribbean Countries Protecting groundwater in karst aquifers is extremely important. Vulnerability maps can greatly help proper decision making based on physical environmental attributes that influence how easily a contaminant applied to the land surface can reach groundwater due to anthropogenic activities, and the properties of the contaminants. Methods for determining vulnerability based on the COST Action 620 Approach, when applied in the study area, may lead to contradictory results. The main purpose of this study is to provide an overview of academic research on intrinsic karst aquifer vulnerability methodologies applied in South American and Caribbean countries. Secondly, it describes studies related to karst aquifers that, in some cases, lack specific information on intrinsic vulnerability. The objective is to encourage and to help develop specific methods for determining karst vulnerability in these regions. To achieve these purposes, a systematic literature review was conducted including studies conducted at institutions such as universities, national water institutes, and by geological services. Several methods have been used in the region such as COP, DRASTIC, RISK, EPIK, PI, PaPRIka, and the Slovene Approach. And some attempts have been made to develop a specific methodology that best suits the specificities of the region's karst aquifers. South America and the Caribbean have almost 5 % of the world's carbonate rocks. Some countries have large extensions of their territory covered by karst rocks, such as Peru, 15.4 %; Cuba, 67 %; and Mexico 25.29 %. Estimates indicate that more than 10 million people use water from karst systems in Mexico. In Cuba, 33 % of all available water volume originates from groundwater, and 91.51 % from karst aquifers. In Mexico, 13 studies have been conducted on the importance of karst aquifers, which mostly address the Yucatan Peninsula, followed by Brazil (9 studies), Cuba (5), Colombia (1) and Peru (1). Information about the theme is scarce in most of the other countries in the region. Some studies have incongruent results given the regional characteristics of tropical karst. [ABSTRACT FROM AUTHOR]

DRASTIC is a model used to reliably assess the pollution potential of aquifers at global location. Despite various criticisms of this model or its optimization, sometimes the territorial or geological conditions still must rely on this model approach based on its simplicity. The existence of sinkholes in the alluvial aquifer with an underlying karst aquifer is a clear example of the need to change or optimize the DRASTIC model to improve accuracy of prediction. In this study, the DRASTIC model was changed by adding two factors, the distance to a sinkhole and the sinkhole catchment factors. The modified DRASTIC model was then used to evaluate the pollution potential of Abarkouh aquifer in Yazd province, Central Iran. The intrinsic vulnerability index of Abarkouh aquifer was calculated by the weighted sum method in GIS. The resulting numerical values ranged between 62 and 176 for full study area. Without adding the two layers related to Sin-DRASTIC, the generic DRASTIC Index map showed summed values ranging between 54 and 130. The final Sin-DRASTIC map was divided it into 4 orders very low (<106; 722 km2, 78%), low (107-133; 186 km2, 20%), low to moderate (133-160; 15.3 km2, 1.7%), and moderate vulnerability (161-176; 1.7 km2, 0.3%) vulnerability. Both of the created maps showed high Area Under the Curve values at 76% and 78% for the generic DRASTIC and Sin-DRASTIC respectively. However, the area of the aquifer containing the sinkholes showed low and very low zones of contamination vulnerability on the generic DRASTIC map. The sensitivity analysis showed that the aquifer vulnerability to pollution is mainly controlled by the vadose zone impacts and the sinkhole catchment factor. Therefore, it is concluded that for geologic settings containing sinkholes that are open or contain higher vertical hydraulic conductivity sediment compared to the general matrix of the unconfined aquifer, the Sin-DRASTIC model method yields a superior prediction. Sin-DRASTIC is a modified version of the generic DRASTIC method that used in regions wherein sinkholes occur The Sin-DRASTIC models was applied to intrinsic vulnerability of Abarkouh aquifer, Central Iran. The high AUC values at 76% and 78% for the generic DRASTIC and Sin-DRASTIC respectively, show the accuracy of the results. In the Sin-DRASTIC map the sinkhole areas showed a high potential for groundwater contamination [ABSTRACT FROM AUTHOR]

The present research aims to determine the sources and concentration of uranium in the groundwater of the hard rock aquifer. Two hundred and fifty-four groundwater samples were collected, and the analysis shows the uranium concentrations range from 0.5 to 113 ppb (pre-monsoon) and 0.5 to 120 ppb (post-monsoon). Factor analysis illustrates that the lower concentrations of uranium in the study region may be due to the poor dissolution of minerals in the subsurface. Saturation Index values confirm that the Uraninite mineral is undersaturated, and the U4O9 has dominant distribution during both seasons. During both seasons, four samples have a uranium concentration of more than 60 ppb, which might be due to the fertilizer usage in the agricultural activities in the study area. The GIS technique highlights the uranium-contaminated location and polluted water quality parameters using the Inverse Distance Weighted spatial interpolation plots. [ABSTRACT FROM AUTHOR]

Underground natural gas storage is a promising solution to lowering greenhouse gas emissions and attaining sustainable development goals. However, several issues prevent the application of storage projects on a global scale. An accurate estimation of the delivered amount of natural gas from each storage site might be used for supply and demand. Due to this fact, this study proposed hybrid intelligent models integrating the least square support vector machine (LSSVM), differential evolution (DE), imperialist competitive algorithm (ICA), cultural algorithm (CA) , teaching learning-based optimization (TLBO), genetic algorithm (GA), and particle swarm optimization (PSO) for approximating the deliverability of underground natural gas storage in different geological formations. We have employed vast data sets of 782 reservoirs from depleted fields to train and validate the proposed intelligent models to predict underground natural gas storage deliverability in the USA. The visual and analytical assessments were used to investigate the performance of the developed intelligent systems. The predicted results showed that all of the intelligent models agreed with the recorded data. Moreover, the statistical indicators revealed that the LSSVM coupling TLBO model shows the highest accuracy in predicting the deliverability of natural gas storage in the depleted field among three intelligent models. Also, the optimal intelligent model accurately predicts 880 and 600 data measurements of saline aquifers and salt domes, respectively. The optimal intelligent model yields a root mean square error (RMSE) value of less than 0.022. The correlation factor (R2) is over 0.998, 0.999, and 0.906 for the depleted field, saline aquifers, and salt domes, respectively. The results highlight the importance of combining smart approaches with nature-inspired strategies in forecasting storage site deliverability. In light of these findings, researchers are better equipped to reduce petroleum energy usage and increase community acceptability of natural gas as part of the transition to green energy. [ABSTRACT FROM AUTHOR]

Groundwater is an important source of fresh water worldwide. Jakarta, the capital city of the Republic of Indonesia, is a large city with a population of more than 10 million and the center of the country's economy and urban development. However, Jakarta has many challenges related to groundwater management. Changes in well GWL serve as a direct indicator of the effects of groundwater evolution, and GWL time series usually contain important information about aquifer dynamics. Therefore, water managers and engineers must model and predict GWL, identify and measure groundwater resources, and maintain a balance between supply and demand. Measuring and analyzing the groundwater table (GWL) of an aquifer are an important and valuable activity in the management of groundwater resources, and information on GWL variability can be used to determine groundwater availability. Accurate and reliable groundwater level estimation is very important because it provides important information about the quantitative groundwater status of an aquifer. The main advantage of AI models is their ability to reproduce nonlinear and complex processes without a full understanding of the underlying physics. As a result, the use of AI techniques in GWL modeling continues to grow, attracting the attention of scientists around the world. Using a nonlinear autoregressive network with extrinsic input (NARX) with a timestep of 14 days, this study is aimed at predicting the volatility of Jakarta's GWL. Based on the research results, both JKT-01 and JKT-03 show a linear downward trend. On the other hand, JKT-02 and JKT-04 show a stable linear trend. GWL increases the linear trend of JKT-05. Variable results are generated by model performance. Model performance (R) varied between 0.2 and 0.9 during the training phase and between 0.2 and 0.9 during the validation phase. The overall performance of the model varies from 0.3 to 0.9. The diverse lithology and high pumping capacity in Jakarta are the reasons for the different modeling results. Forecasts for 14 days (14 timesteps) show that GWL remains constant at certain well locations, while GWL decreases at other locations. This is a consideration that stakeholders can consider to reduce the small effect of the daily GWL pattern as a result of NARX modeling. [ABSTRACT FROM AUTHOR]

Simple Summary: During more than 50 years of exploitation of the sludge repositories near Chepetsky Mechanical Plant (Glazov, Udmurtia, Russia) containing solid wastes of uranium and processed polymetallic concentrate, the soluble compounds entered the upper aquifer due to infiltration. Nowadays, this has resulted in a high level of pollution of the groundwater with reduced and oxidized nitrogen compounds. In this work, quartz, kaolin, and bentonite clays from various deposits were shown to induce biofilm formation and enhance nitrogen removal by an indigenous microbial community capable of anaerobic ammonium oxidation with nitrite (anammox) at low temperatures. The addition of a "warm" anammox community was also effective in further improving nitrogen removal and expanding the list of mineral carriers most suitable for creating a permeable reactive barrier. It has been suggested that the anammox activity is determined by the presence of essential trace elements in the carrier, the morphology of its surface, and most importantly, competition from rapidly growing microbial groups. Future work was discussed to adapt the "warm" anammox community to cold and provide the anammox community with nitrite through a partial denitrification route within the scope of sustainable anammox-based bioremediation of a nitrogen-polluted cold aquifer. In this unique habitat, novel species of anammox bacteria that are adapted to cold and heavy nitrogen pollution can be discovered. The complex pollution of aquifers by reduced and oxidized nitrogen compounds is currently considered one of the urgent environmental problems that require non-standard solutions. This work was a laboratory-scale trial to show the feasibility of using various mineral carriers to create a permeable in situ barrier in cold (10 °C) aquifers with extremely high nitrogen pollution and inhabited by the Candidatus Scalindua-dominated indigenous anammox community. It has been established that for the removal of ammonium and nitrite in situ due to the predominant contribution of the anammox process, quartz, kaolin clays of the Kantatsky and Kamalinsky deposits, bentonite clay of the Berezovsky deposit, and zeolite of the Kholinsky deposit can be used as components of the permeable barrier. Biofouling of natural loams from a contaminated aquifer can also occur under favorable conditions. It has been suggested that the anammox activity is determined by a number of factors, including the presence of the essential trace elements in the carrier and the surface morphology. However, one of the most important factors is competition with other microbial groups that can develop on the surface of the carrier at a faster rate. For this reason, carriers with a high specific surface area and containing the necessary microelements were overgrown with the most rapidly growing microorganisms. Bioaugmentation with a "warm" anammox community from a laboratory reactor dominated by Ca. Kuenenia improved nitrogen removal rates and biofilm formation on most of the mineral carriers, including bentonite clay of the Dinozavrovoye deposit, as well as loamy rock and zeolite-containing tripoli, in addition to carriers that perform best with the indigenous anammox community. The feasibility of coupled partial denitrification–anammox and the adaptation of a "warm" anammox community to low temperatures and hazardous components contained in polluted groundwater prior to bioaugmentation should be the scope of future research to enhance the anammox process in cold, nitrate-rich aquifers. [ABSTRACT FROM AUTHOR]

The Mateur multi-aquifer system, consisting of a Quaternary alluvial aquifer and a Campanian limestone aquifer, is one of the most significant aquifer systems in northern Tunisia, providing domestic and agricultural water supply for the entire Mateur region. The present study aims to unveil the various factors and mechanisms controlling the groundwater chemistry of such a system. Indeed, integrated hydrogeochemical and isotopic approaches are used herein to identify the alluvial and limestone aquifer waters mixing and evolution in the Mateur region. Results show that despite the difference in aquifer lithology, there is little difference in the major ion geochemistry and stable isotope ratios of groundwater within the Mateur plain. Waters from the Quaternary alluvial aquifer are classified into two predominant facies: mixed facies (Ca–Na–SO4–Cl and Ca–Na–HCO3–Cl) and Na–Cl facies. Similarly, waters from the limestone aquifer have also mixed facies (Ca–Na–SO4–Cl) and sodium chloride facies (NaCl). Groundwater δ18O and δ²H values show more homogeneous values along the groundwater flow direction, indicating inter-aquifer mixing processes. Tritium contents of the Campanian aquifer are lower than those of the Quaternary aquifer, indicating a relatively older age or mixture with recent waters. This validates a concept of the hydraulic continuity between the Quaternary aquifer and the Campanian aquifer which is consistent with the geochemical analytical results. [ABSTRACT FROM AUTHOR]

Groundwater is an important factor in establishing new urban communities, especially in coastal arid and semi-arid regions. Egypt is one of the world's driest countries, with hyper-arid territory accounting for 86% of the total area and arid and semi-arid terrain accounting for the rest. The present work aims to demonstrate the powerful integration of geophysical techniques to assess groundwater potentiality and suitability in Gara Oasis (GO), which describes a good example of Egypt's strategic southern extension of its arid north-western coast. Geophysical methods, including electrical resistivity and aeromagnetics, were used to evaluate groundwater resources. The study region reduced to pole total magnetic intensity map is subjected to digital filters that include derivatives, analytic signal, and tilt angle. The possible structures controlling the shallow and deep aquifers are delineated and integrated with geoelectric results. Moreover, two magnetic tomography sections are constructed to show the subsurface distribution of magnetic susceptibilities and formation boundaries. Ten vertical electric soundings (VESs) are measured and used in this study to construct four geoelectrical cross-sections. According to the results, Gara's commonly calculated subsurface resistivity model comprises six major resistivity layers. The 5th layer, in particular, is composed of Fractured dolomitic Limestone and represents a possible promising shallow aquifer. Moreover, as evidenced by various magnetic data filters, the shallow (Miocene carbonate) and deep (Nubian sandstone) aquifers are structurally controlled and regulated by a system of faults or contacts. These contacts trends NW-SE, E-W, and NE-SW as common trends emerged from the total derivative and tilt maps. Results suggest that the central part (N-S zone) together with the western side of Gara, have the most notable aquifer possibility demanded future improvement strategies. [ABSTRACT FROM AUTHOR]

The Ganges River delta complex contains a transboundary aquifer system shared between India and Bangladesh. Although it serves as the main freshwater source for the population inhabiting the delta, the aquifer system is severely contaminated with arsenic (As). This study aimed to determine the control of the delta hydrostratigraphy on the regional-scale depth distribution of As within the aquifer system. We developed the first high-resolution, regional-scale, transboundary hydrostratigraphic model of the Ganges River delta and analyzed the patterns of As distribution as a function of the hydrostratigraphy. Model results indicate that, despite the presence of a single aquifer system across the delta, the hydrostratigraphy is spatially variable and can be architecturally divided into three distinct aquifer subsystems from northwest to southeast: a single, thick continuous aquifer (type I); a vertically segregated, semiconfined aquifer subsystem (type II); and a multilayered, nearly confined aquifer subsystem (type III). Results indicate that the spatial distribution of As is characteristically different in each subsystem. In the type I aquifer, As concentrations tend to be homogeneous at all depths, while in type II and type III aquifers, As concentrations sharply decrease with depth. The intervening aquitards in the type II and type III aquifer subsystems appear to act as natural barriers to infiltration of surficial As or organic matter-rich water to the deeper aquifer zones. This delineation of the regional-scale hydrostratigraphic architecture and resulting understanding of its plausible controls on the depth-distribution of As within the delta should significantly aid in the systematic framing of sustainable management plans for the As-safe aquifers within the Ganges River delta aquifer system. [ABSTRACT FROM AUTHOR]

Sporadic rainfall and limited surface water sources have increased dependency on groundwater in semi-arid region of Punjab. The present paper is comprehensive study carried out in an intensive agricultural region of southwest Punjab to examine the quality and extent of contamination due to trace elements and nitrate in the aquifer system. Total 15 toxic elements are analyzed in groundwater samples (N = 129) covering both the shallow (<60 m) and deeper aquifers (>60 m). Elements such as As, B, Cd, Li, Mn, Pb, Sr, and Se exceed the prescribed limits. Overall, 68 and 13% of samples exceed the NO3− permissible limit (45 ppm) in shallow and deep aquifers, respectively. Contaminants concentration increases toward groundwater flow direction, that is, from northeast to southwest possibly due to arid climatic conditions. Relatively, shallow aquifer is more contaminated than deeper aquifer due to fertilizers input and irrigation return flow. Drinking water quality indices (DWQI) reveal that groundwater is unfit for drinking at most locations. Further, health risk indicate that comparatively, children are at higher risk in terms of non-carcinogenic risk posed by nitrate, and higher carcinogenic risk for As, Cr, and Cd is seen in all age groups. Multivariate analysis reveals the influence of anthropogenic activities on NO3−, Mn, Ni, and Zn levels, while geogenic factors control the, As and Mo concentrations. Present findings suggest regular monitoring of wells to lower the public health risk. [ABSTRACT FROM AUTHOR]