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Cr(VI) is a carcinogen with proven mutagenic and genotoxic effects. The effects of the depositional environment (e.g., paleoweathering, paleoclimate, and paleoredox condition) on Cr enrichment in non-ultramafic aquifer solids are unclear. In this study, we presented the sedimentary characteristics of a borehole from a typical non-ultramafic aquifer with high Cr groundwater in Jingbian, central Ordos Basin, China. Chromium was enriched in the K1h sandstone aquifer, especially at depths of 400–500 m, with the highest value of mass transport coefficient (τAl,Cr) up to 92.13% and τAl,Fe up to 33.5%. The provenance of aquifer Cr was predominantly intermediate and felsic igneous rocks with a mafic rock mixture. This mafic source was inferred from Cr-rich granodiorite and mafic/ultramafic rocks in the Yinshan (Daqingshan–Wulashan) Block, northern Ordos Basin. The Cr-rich aquifer in K1h was developed due to a moderate chemical index of alteration (CIA) (mean, 56.7) under relatively warm and humid paleoclimate, as evidenced by high CIA-temperature (CIA-Temp) (mean, 6.79 °C) and paleoclimatic index values (mean, 0.40). Fe–Mn redox cycling in the oxic to suboxic environments contributed to aquifer Cr accumulation. Using path analysis, we identified that paleoclimate created favorable weathering conditions and enrichment of Fe contributed to the formation of high-Cr aquifers. The study reveals the formation of positive Cr anomalies in non-ultramafic aquifers, which is the potential source of groundwater Cr, and highlights the effects of depositional factors on Cr accumulation during aquifer deposition or early diagenesis. It can provide new insights into the natural processes of high-Cr sediments occurring in non-ultramafic aquifers. [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]

An examination of a few examples of aquifer use shows the importance and fragility of groundwater, with poor management leading to overextraction by individuals and authorities producing subsidence - sinking cities. Freshwater is one of our most precious resources and it is rapidly disappearing, leading to global drying. At the same time, the global and urban populations are increasing, with civil unrest increasing due, in part, to freshwater shortages. The increasing global population and global urbanisation are driving an increase in water use, restriction of aquifer recharge and increased aquifer pollution. It is argued that urban population growth with attendant increased water use, combined with climate change and poor management, is significant in water stress. Particular attention must be paid to the effect of rising populations on local water resources, especially groundwater, and the knock-on effect on urban sustainability. [ABSTRACT FROM AUTHOR]

The Huayingshan coalfield is one of the most important coal districts in Southwest China. Coal mining may have an impact on the hydrochemical characteristics and regional evolution of karst groundwater. This study aims to analyze the hydrogeochemical characteristics, identify the evolution processes, and influencing factors that govern the hydrochemistry in multilayer karst aquifers in the coalfield. Statistical methods and conventional techniques were utilized to gain a thorough understanding of the origin and hydrogeochemical evolution of karst groundwater. The results revealed that the groundwater was fresh water and natural to mildly alkaline. It suggested that the relative abundance of main ions was proposed to be Ca2+ Mg2+ > K+ + Na+ for cations and > Cl– > for anions. A Piper diagram of the investigated water samples demonstrated that most groundwater was of the HCO3-Ca type. The results showed that dissolution of carbonate, gypsum, halite, and silicate minerals highly influenced the formation of , , Ca2+, Mg2+, and Na+. Cation exchange and/or absorption was another important regulatory process. concentrations were excessively high, proving that karst water was affected by agricultural activities in certain aquifers. Moreover, S2– concentrations were high in the borehole and mine tunnel samples, suggesting great acidification potential. Coal mining carries a risk of deteriorating the local water environment. This exposes sulfide minerals to oxygen and water, increases concentration, and reduces groundwater pH. Scientific research must focus on specific recharge area locations, runoff and drainage pathways, and hydrochemical evolution processes of karst water, and the contact of sulfide with water and oxygen must be controlled to protect groundwater quality and reduce pollution. The results suggest it may be helpful for investigation and treatment of water environment pollution, aid the protection of karst groundwater in the Huayingshan coalfield, and serve as a model for other comparable studies. [ABSTRACT FROM AUTHOR]

Southern Tunisia belongs to the Sahara desert, one of the driest regions of the world, where groundwater research is crucial to satisfy the water demand. In this region, the Jurassic aquifer appears as a potential resource. Nevertheless, the related information is too limited to develop a suitable plan for exploitation. The present study aimed for a thorough understanding of the Jurassic series using borehole and seismic reflection data. Well logs from 40 petroleum boreholes were analyzed both qualitatively and quantitatively to define precisely the potential water reservoirs and determine their petrophysical characteristics. Comparison of the various recordings revealed the abundance of sandstone and dolomite deposits in the Sebaia Formation (Dogger–Malm) and the evaporitic composition of the Abreghs Formation (Lias). The Sebaia Formation is enriched in clays toward the south as indicated by well logs correlation and computed shale volumes (Vsh reaching 27.8%). The south-east part of Southern Tunisia contains mostly sandy Jurassic reservoirs, exhibiting the highest estimated porosities (22.8–31%). Lithostratigraphic correlations were established to firstly approach the geometry of the Jurassic aquifer. These correlations highlighted that the Jurassic series have variable depth and thickness along the Dahar structure, which thicken and deepen from the Dahar to the west and disappear in the Jeffara. These findings were further refined by the interpretation of 198 seismic profiles, which display several NW–SE-, E–W- and NE–SW-trending normal faults that influenced the Jurassic reservoirs depth, thickness, facies and petrophysical characteristics as well as groundwater circulation. The present study yielded interesting results that may enormously guide the investigation of the Jurassic aquifer in Southern Tunisia. Furthermore, it may be considered as an example for hydrogeophysical applications in the "Sahara" and other arid zones worldwide. [ABSTRACT FROM AUTHOR]

Groundwater remains the most dependable resource for various essential uses such as drinking, cleansing, agricultural irrigation, and industrial applications. In urban areas, the dependency on groundwater to meet water demands is significant. However, this resource faces threats from overuse and poor management, leading to a degradation in quality primarily due to the unchecked release of industrial and household wastes. The escalation of industrial activities and rapid urban growth have amplified the volume of wastewater, adversely affecting the purity of freshwater sources within aquifers. This investigation focuses on evaluating the impact of industrial and urban effluents on groundwater quality in the city of Faisalabad. The main contributors to groundwater pollution include the indiscriminate disposal of industrial and urban effluents through unlined drains and the extensive application of chemical agents in agriculture, such as fertilizers, and pesticides. To understand the physiochemical properties of both, drain and groundwater, samples were collected at various distances 50 m, 100 m, and 150 m from drain outlets. This study utilized Geographic Information Systems (GIS) to accurately map and analyze the distribution and impact of contaminants. Parameters such as pH, electrical conductivity (EC), total dissolved solids (TDS), total hardness, bicarbonates, calcium and magnesium hardness, and chloride levels were examined. The findings indicated that contaminant levels were highest in drain water and increased in concentration the closer they were to the drainage sources, with the exception of pH levels. All samples exceeded the World Health Organization's (WHO) safe limits, deeming them unfit for use. This finding indicates widespread contamination, posing significant public health risks and highlighting the urgent need for improved waste management and water treatment practices in Faisalabad. It underscores the critical importance of implementing effective pollution control measures to safeguard public health and ensure water security in the region. However, a notable correlation was observed between the concentration of pollutants in drain water and key indicators such as EC, TDS, total hardness, and magnesium hardness, highlighting their role in deteriorating aquifer water quality. Moreover, groundwater samples collected 50 m from drains exhibited the highest pollutant concentrations compared to those taken further away, at 100 m and 150 m distances. [ABSTRACT FROM AUTHOR]

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]

Characterizing the 3D distribution of hydraulic properties in glacial sediments is challenging due to fine‐scale heterogeneity and complexity. Borehole lithological data provide high vertical resolution but low horizontal resolution. Geophysical methods can fill gaps between boreholes, providing improved horizontal resolution but low vertical resolution. Machine learning can combine borehole and geophysical data to overcome these challenges. However, few studies have compared multiple machine learning methods for predicting hydrofacies in glacial aquifer systems. This study uses colocated airborne electromagnetic resistivity and borehole lithology data to train multiple machine learning models and predict the 3D distribution of hydrofacies in glacial deposits of eastern Nebraska, USA. Random Forest, Gradient Boosting Classifier, Extreme Gradient Boosting, Multilayer Perceptron, and Stacking Classifier were used to model 3D probabilistic distributions of hydrofacies (sand and clay) at a grid size of 200 m × 200 m × 3 m. Comparison of the predicted 3D hydrofacies models shows that the probability distributions and the contrasts between hydrofacies vary. The classification metrics show that the Stacking Classifier model performed better than other machine learning models in predicting hydrofacies. Multi‐Layer Perceptron and Stacking Classifier models show sharp vertical transitions between the low and high sand probability while other machine learning models show gradual transitions. K‐means clustering was used to translate the Stacking Classifier model into a 4‐class hydraulic conductivity model. This study shows that machine learning methods advance our understanding of glacial hydrogeology by improving the vertical and horizontal resolution of hydrofacies distribution and resolving aquifer‐aquifer and stream‐aquifer connections. Plain Language Summary: Sediments deposited by glaciers are host to numerous aquifers globally, including the northern USA, providing an important source of groundwater. The size, shape, and physical properties of these aquifers are highly variable, so predicting groundwater flow and resource availability is a challenge. We used machine learning and data from airborne geophysics and boreholes to generate high‐resolution, 3D models of a glacial aquifer in Nebraska, USA. We compare and contrast five different machine learning models, showing that there are differences in the models' performances and abilities to construct geologically plausible results. These models help estimate the aquifer properties, locate aquifer boundaries, and provide a basis for constructing numerical models of groundwater flow. Key Points: A machine learning approach is presented for 3D probabilistic hydrofacies modeling using AEM and borehole dataThis approach generates clustered probabilistic hydrofacies and estimates aquifer and streambed hydraulic conductivity3D probabilistic hydrofacies allow for characterizing the heterogeneity and continuity of aquifer and aquitard units [ABSTRACT FROM AUTHOR]

Water contamination assessment could serve as an effective tool for pollution control and prevention. However, using only standard groundwater pollution assessment techniques is not enough to provide a holistic contamination assessment. In this study, standard hydrogeochemical and microbial techniques, multiple numerical indices (heavy metal evaluation index [HEI], heavy metal pollution index [HPI], water quality index [WQI], pollution index of groundwater [PIG]), and chemometric models (principal component analysis and correlation analysis) were integrated to assess the aquifer intrinsic vulnerability and pollution sources of groundwater within the Adani suburban, southeastern Nigeria. Twenty groundwater samples from drinking wells were collected and subjected to physicochemical and microbiological analysis. The results revealed that the water is moderately acidic (pH 4.8–6.9), fresh (TDS < 1000), and soft (Hardness 5–25 mg/L). All analyzed physicochemical constituents occurred within the WHO acceptable standards except for NO3, PO4, and NH4, due to influx and leaching from poor sanitary conditions, agricultural activities, and solid waste materials. The concentration of heavy metals was in the order of Mn > Zn > Ni > Fe > Cu > Pb > As > Cd, with Ni, Mn, Cu, and As, recording values above the required standards. Microbial analysis revealed the presence of pathogens such as Staphylococcus aureus, Escherichia coli, and Salmonella/Shigella in the water; attributable to poor sanitary conditions. WQI and PIG revealed that 80–85% of the water samples are unfit for drinking. The groundwater flow map shows that the direction of flow of groundwater is majorly from the eastern to western regions of the study area, suggesting that contaminants will be moved mostly from the eastern to western regions. Public waste disposal sites and agricultural activities are therefore recommended to be limited to the western regions. Frequent monitoring and evaluation of the water resources in the region is recommended for the sustainability of public health and water resource management. [ABSTRACT FROM AUTHOR]

Water is at the core for achieving all 17 sustainable development goals (SDGs). The current study was performed for the appraisal and modeling of the vulnerability of regional aquifers to anthropogenic perturbations. Samples of water were examined to determine their physical and chemical properties. pH of groundwater varied from a value of 7.08 to a value of 8.46. Total dissolved solids (TDS) varied from 1048-1580 mg·L-1. Results revealed that 79% of Ca2+, 47.3 % of Mg2+, and 100% of Na+ and Cl- in water samples exceeded the standard permissible limits. The aquifer vulnerability index (AVI) revealed that Neogene aquifer was categorized as high vulnerability to extremely high vulnerability class of risk of contamination. AVI index method was also performed for the other major aquifers demonstrating that Dammam aquifer was categorized in the high vulnerability class, whereas Er Radhuma and Aruma categorized as moderately vulnerable to contamination. This study demonstrated an integrated model to help investigate the vulnerability of regional aquifers and highlighted the need for continuous monitoring campaigns to investigate the effects of anthropogenic activities on aquifers to make timely and effective decisions. [ABSTRACT FROM AUTHOR]

Free aquifers have become an important water supply option for underdeveloped and developing countries, due to the resource quality and relatively low extraction prices. However, overexploitation and the lack of territorial planning guidelines in these areas endanger groundwater availability and quality. In this context, this study aimed to analyze the vulnerability to groundwater contamination and contribute to the conservation of the ecosystem services, provided by the Guarani aquifer in Brotas, Brazil, by applying the PESTICIDE-DRASTIC-LU model. The application of this model allowed the identification of priority conservation areas within the context of ecosystem services that groundwater provides to local inhabitants. To this end, we collected, treated, and analyzed seven different hydrogeological data to understand the environmental dynamics of the system and to identify which areas are most vulnerable to aquifer contamination. The results pointed out that 64% of the study area presents zones of high and very high vulnerability to contamination, due to the local hydrogeological characteristics (sandy soils and rocks) and the various anthropogenic activities, mainly with large plantations of sugar cane and eucalyptus. In addition, the mapping allowed the spatial demonstration of the places that should be considered a priority for the conservation of ecosystem services provided by local groundwater. Thus, our results can serve as a baseline to define public action strategies for the preservation and sustainable management of the Guarani aquifer areas. [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]

DRASTIC is a model that is commonly used to assess vulnerability to groundwater contamination at the landscape scale. When sparse data are available to populate the layers of the model, it can be difficult to ascertain the true usefulness of the model produced map. In this research, an alluvial aquifer in Kermanshah province of western Iran was mapped using the generic DRASTIC model. The data available for populating the model layers were generally sparse. The model was validated using a nitrate concentration map constructed from well water measurements within the DRASTIC map area. Based on the data collected and analyzed, a range of values from 107 to 177 was found. Therefore, the final vulnerability map was divided into only two classifications, moderate and high, instead of the normal five classifications typically used. The results showed that there was no significant relationship with nitrate concentration by statistical methods. However, the field conditions and the method used have good accuracy. Field evaluations showed that karst water recharge acts as a factor in diluting nitrate concentrations. Evaluation of all final map classification methods (generic DRASTIC, natural breaks (Jenks), equal intervals, quantile, geometrical interval, and fuzzy classifiers) showed that based on cross-validation, the most consistent classifier is the generic DRASTIC based one with 62% and the quantile method is in second place with 36%. Changing the weights and rates of layers to justify the model within the measured nitrate concentrations does not show the inherent nature of the aquifer to contamination. The results of this model emphasize the use of generic DRASTIC with correct data and field study before any optimization. In addition, if optimization is to be performed, it is necessary to add a layer or layers that relate to those factors having the greatest impact on aquifer pollution or dilution of the ionic content of groundwater in the study area. Based on the results obtained from this research, it is concluded that the DRASTIC model can be used to produce a reliable result, useful for planning to reduce groundwater contamination potential, particularly in vulnerable areas. [ABSTRACT FROM AUTHOR]

Investigating the repercussions of climate change and irrigation timing on groundwater contamination necessitates thorough examination of the fluctuations in seawater and groundwater recharge temperature. This study introduces an innovative numerical approach to analyze groundwater salinity and temperature dynamics across three distinct scenarios using the SEAWAT code based on Henry's problem. The first scenario delves into the impact of seawater temperature, the second focuses on the consequences of aquifer freshwater recharge temperature, and the third amalgamates the effects of both scenarios. Remarkably, the study reveals that saltwater intrusion (SWI) experiences a decline attributable to the aquifer's heightened seawater temperature and the diminished inland freshwater temperature. Furthermore, combining these two scenarios has a more pronounced effect on aquifer pollution; the temperature-induced changes in SWI for this third scanrio reach + 8.10%, + 12.70%, + 16.20%, + 24.90%, + 28.30%, and + 31.80% compared to the case without considering the temperature effect. Notably, our results propose a potential strategy to mitigate SWI by introducing cold freshwater recharge into aquifers, such as irrigation at night time when water temperature is low. This innovative approach underscores the interconnectedness of various environmental factors. It provides a practical avenue for proactive intervention in safeguarding groundwater quality against the adverse impacts of climate change and irrigation practices. [ABSTRACT FROM AUTHOR]

This paper analyses the effects of environmental flows on water quality within a highly regulated basin, focusing on the Turia River basin in the eastern Iberian Peninsula. Through water management and water quality models, a series of simulations were conducted, introducing variations in the outflows of the Loriguilla reservoir to evaluate the effects of different environmental flow scenarios on water quality, particularly at the location of the intake for the water supply to Valencia. Three environmental flow scenarios were analyzed, alongside an alternative management scenario, considering their implications on water quality and reliability of water demand. The findings of this paper, particularly the nitrate (NO3−) concentration evolution, highlight the influence of minimum e-flow and e-flow regimes on water quality within the basin. These results suggest that while modifying the current flow regime can lead to some improvements in nitrate concentrations at the Valencia supply intake point, the primary cause of high nitrate concentrations is attributed to irrigation return flow and the pre-existing contamination of the aquifer. This analysis offers valuable insights into the complexities of water quality management in regulated basins, emphasizing the need for a multi-faceted approach to address the diverse factors influencing water quality and demand supply reliability. [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]

This study presents a meticulously edited article that assesses the uncertainty associated with contamination dispersion in a porous aquifer environment. The article employs a conceptual model incorporating finite difference flow modeling and particle tracking methods grounded in particle movement theory within groundwater flow. The groundwater flow model utilizes an automatic calibration technique, PES, and independent verification, to minimize statistical discrepancies in the optimized parameters. The statistical summary of the model output reveals the average pollution concentration in the study area, specifically the landfill aquifer in northern Iran. The results indicate that the initial contamination value at the boundaries is zero, whereas 91,802 units are discharged into the sea. Moreover, approximately 3,317,290,003 pollution units have been extracted from pumping wells along the contamination plume over 10 years. Furthermore, the drainage network releases 1,778,680,001 pollution units, resulting in a net outflow of 5,082,740,007 units from the same drainage network. Additionally, 9,912,180,003 units were discharged from the leaky boundaries. It should be noted that these statistics can be reversed depending on the specified period. The difference between the input and output pollution values in the study area indicates a net accumulation of 8192 units. To analyze the sensitivity of contamination dispersion in the porous aquifer environment and the variations in coastal drainage patterns obtained from the finite difference simulation, the explicit and implicit methods, as well as the random walk particle tracking method, were investigated in a portion of the basin area using the South Side Implicit method. One of the main objectives of this sensitivity analysis is to evaluate the results of the uncalibrated qualitative model and examine the particle dispersion in the adjacent area of the contaminated landfill region to assess the error of the proposed model by developing a limited test. The calculated error or computational difference between the explicit and implicit methods and the applet model is considered negligible. For example, the calculated error between the explicit and backward methods and the applet model ranges from 0.086 to 0.372 units for a concentration interval of 0.512 units and 0.680 units for a time interval 0.537. Therefore, the computational differences are not significant. Furthermore, based on theoretical sensitivity analysis of contamination dispersion, the laboratory model demonstrates that the flow direction in this modeling is from west to east, as expected. [ABSTRACT FROM AUTHOR]

Uncontrolled urbanization and industrial growth are increasing the vulnerability of groundwater to pollution. Vulnerability assessment has become a key element for the areas which are more susceptible to anthropogenic pollution. This study focuses on evaluating the vulnerability of the Rachna Doab aquifer to pollution through the comparison of five GIS based models i.e., DRASTIC, Pesticide DRASTIC, Modified DRASTIC, Modified Pesticide DRASTIC, and DRASTICA. Models were calibrated using measured values of electrical conductivity (EC), total dissolved solids (TDS), and nitrate concentration. The DRASTICA model exhibited the highest coefficient of determination ( R 2 ) values of 0.72 and 0.75 for nitrate concentration and EC, respectively. Among the pesticide-based models, the Modified Pesticide DRASTIC model demonstrated high ( R 2 ) values of 0.64 and 0.67 for EC and TDS, respectively. Map removal sensitivity analysis indicated that parameters such as hydraulic conductivity, impact of vadose zone and aquifer media have less significance in the DRASTICA model. The study also incorporated an improved weight-based approach by using single parameter sensitivity analyses to enhance the correlations between water quality parameters and the DRASTICA index, which improved to 0.76 for nitrate concentration and 0.80 for EC. DRASTICA identified high and very highly vulnerable zones, covering 46.6% and 12.3% of total area, respectively. The Modified Pesticide DRASTIC model identified 75.5% of the area as falling within the high to very high vulnerability zones. The identified vulnerable zones should be prioritized in future groundwater pollution control and preservation efforts to safeguard water resources in the Rachna Doab region. [ABSTRACT FROM AUTHOR]

This research paper presents an investigation of an aquifer structure using a combination of gravity and seismic analyses, calibrated by hydrogeological data. This work illustrates how crucial it is to study geological structures and fault networks as preliminary work to understand water- and pollutant-flow systems and aquifer vulnerability, especially with the increased frequency of drought events and climate change pressures. A Plio-Quaternary coastal northeastern aquifer in Tunisia was chosen as the study case. First, a hydrogeological approach was performed using water wells, and piezometer data showed an important fluctuation in the piezometric level and a notable depression in the piezometric surface observed in the southern part of the study area. Secondly, gravity data were analysed and calibrated using a seismic profile. The results demonstrated the presence of shallow NE–SW faults less than 300 m below the region's principal wadis, as well as deeper faults of varying depths (from 400 to 2600 m) that influence the basin structure, aquifer geometry and resulting water flow. The combination of these approaches revealed that the variations in the aquifer thickness, piezometric surface depression zones and groundwater flow are mainly controlled by shallow and deep geological structures and their tectonic reactivation. [ABSTRACT FROM AUTHOR]

This paper investigates the optimal remediation process in an aquifer using Modflow 6 software and genetic algorithms. A theoretical confined aquifer has been polluted over a long period of time by unnoticed leakage in a pipeline conveying leachate from an adjacent landfill to a wastewater treatment plant. When the extended leakage and groundwater pollution are discovered, the optimal planning of the remediation strategy is investigated using the pump-and-treat method or/and hydrodynamic control of the pollution. The practical goal is to find the optimal locations and flow rates of two additional pumping wells, which will pump the polluted water or/and control pollution, protecting an existing drinking water pumping well, securing its fully operational mode even during the remediation process with the minimum possible cost, simply represented by the pumped water volume of the additional wells. The remediation process is considered complete when the maximum concentration in the aquifer drops below a certain limit. The Modflow software (handled by the Flopy Python package) simulates the flow field and advective–dispersive mass transport, and a genetic algorithm is used as the optimization tool. The coupled simulation–optimization model, Modflow-GA, complemented by a sophisticated post-processing results analysis, provides optimal and alternate sub-optimal remediation strategies for the decision makers to select from. [ABSTRACT FROM AUTHOR]

This study aims to present a comparative assessment of hydrochemical characterization and groundwater quality in karst aquifers with the support of GIS which is essential to correlate the source of water with climate and geology, and to evaluate suitability of water for various uses. The study area is the Altinova region in Turkey where intensive agricultural activities prevail and travertine covers 85% of the study area. A total of 25 groundwater wells were monitored by seasonal field measurements and extensive water quality analyses for a period of one year to establish correlation between groundwater quality, its source, regional climate, and geology. A comprehensive analysis was conducted to assess the groundwater's suitability for irrigation based on electrical conductivity, sodium adsorption ratio, sodium percentage, magnesium hazard, permeability index, residual sodium bicarbonate, Kelly's ratio, and an irrigation water quality (IWQ) index. This multi-parameter evaluation was further integrated with geospatial analysis using ArcGIS, providing a detailed spatial understanding of hydrochemical variations across the area. Major cations and anions dominance were identified as Ca2+ > Na+ > Mg2+ > K+ and HCO3− > Cl− > SO42−, respectively. Spatial mapping identified high concentrations of Ca2+, TDS, TH, and SO42− in non-karstic areas, occasionally exceeding WHO guidelines. Nitrate concentrations displayed varied spatial distribution. The SAR values generally matched C2-S1 and C3-S1 classes, suggesting medium to high salinity risks and low sodium presence. Based on the IWQ index and observed correlations with total dissolved solids, the groundwater in Altinova's karstic aquifer is considered suitable for irrigation, with salinization largely due to ionic interactions and geology. The presented comparative assessment provides a holistic approach for understanding hydrochemical characteristics of karst aquifers, and analyzing the impacts of natural factors and anthropogenic pollution sources on groundwater quality. [ABSTRACT FROM AUTHOR]

A remediation approach which uses pump and treatment (PAT) to enhance the biodegradation of organic contaminants by increasing dispersive mixing between plumes and groundwater was evaluated for a phenol-contaminated aquifer, using a reactive transport model which simulates kinetic reactions between an electron donor (ED) in the plume and electron acceptor (EA) in the groundwater. The influence of system design and operation was examined in six modelling scenarios. Injection or extraction of groundwater increases biodegradation above no action and the location, pumping rate, and distance between well(s) are important variables which influence biodegradation. An increase in pumping rate, distance of the wells from the plume centreline, and changing the flow direction increase dispersive mixing between the plume and groundwater. This increases plume spreading and the plume fringe interface, providing a greater flux of dissolved EAs for biodegradation. In general, injection of groundwater containing natural EAs enhances biodegradation more than extraction. The enhancement of biodegradation is sensitive to the relative fluxes of ED and EA, as controlled by the arrangement of the wells. In the best performing scenario, biodegradation was enhanced by 128%, compared with no action. [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]

Groundwater stands as a crucial lifeline in numerous regions across the globe, a significance magnified in water-scarce locales like the Middle East. With depleting water resources exacerbated by global climate change, the imperative for sustainable groundwater management becomes increasingly urgent. This research employs a groundwater flow modeling approach, utilizing Visual MODFLOW (version 4.6.0.166), to scrutinize the present state and future security risks of groundwater resources in the Erbil basin. A distinct aspect of this study involves investigating the interaction between the groundwater aquifers of Greater Zab and Lesser Zab Rivers, along with an exploration of the Erbil aquifers, rivers interaction and recharge zones as a second novelty in this research. The model, calibrated for heterogenous anisotropic unconfined aquifer transient conditions, exhibits a high correlation coefficient (CC) of 0.997 during calibration and 0.985 in the validation process respectively. Findings indicate a general groundwater flow direction from northeast to southwest in the Erbil basin, aligning with surface observations. Despite groundwater aquifers supplying only 55% of the current water demand from the existing wells, the computed balance reveals river leakages of 33,432 m3/day into the aquifers. The study forecasts a substantial increase in the dry area of the groundwater aquifer under climate change scenarios, especially when recharge rates diminish. To mitigate these impacts, the study recommends preventing illegal well drilling and implementing continuous monitoring using distributed sensors. The insights gleaned from this research are anticipated to furnish essential information for sustainable planning and effective management of groundwater resources in the Erbil basin and its environs. [ABSTRACT FROM AUTHOR]

The construction of the New Galala City besides great mining (e.g., konoozmisr) and Seawater Reverse Osmosis Desalination Plant projects in the semiarid Gulf of Suez region of Egypt increases the demand for groundwater resources. So, the current research provides integrated stratigraphical, hydrogeochemical, and geophysical studies to investigate the shallow groundwater aquifers in Wadi Araba area on the western side of the Gulf of Suez. The stratigraphic column starts with pre-Cambrian basement rocks which are non-conformably overlain by sedimentary succession of Phanerozoic Erathem. A detailed land magnetic profile has been conducted and processed to estimate the aquifer's geometrical parameters. This includes the subsurface spatial extension and thickness to delineate the prevailed subsurface structures in the study area. Lithostratigraphically, these aquifers are represented by the Paleozoic- lower Cretaceous siliciclastic-dominated sediments of the Nubia Group and fractured carbonate-dominated facies of the upper Cretaceous Galala Formation. Lithological characters, sedimentary facies (fluvial to shallow and open marine), microfacies types, and diagenesis processes (e.g., compaction, cementation, dissolution, and fracturing) are the main factors that affect the quality of the shallow aquifers in the study area. The main microfacies of the studied aquifers are quartz arenite, subarkose, sublitharenite, mudstone/wackestone, and packstone/grainstone. These facies are characterized by different primary and secondary porosities. According to the water sampling standard methods, nineteen groundwater samples were collected from the available hand-dug wells and springs from the Nubian sandstone aquifer and the Upper Cretaceous aquifer, respectively. Inductively coupled plasma–mass spectrometry (ICP–MS), titration, spectrophotometer and a flame photometer were used to obtain a complete chemical analysis. The results of hydrochemical analyses indicated that total dissolved solids (TDS) and concentrations of major ions as well in the lower Cretaceous aquifer increase toward the Gulf of Suez and in general higher than that of springs of the Upper Cretaceous Aquifer. The predominant factors influencing groundwater chemistry include seawater intrusion, evaporation, mineral alteration, dissolution of fossils, and ion exchange. Groundwater in the study area is unsuitable for drinking except in one sample and moderately suitable for irrigation with caution for higher salinity in samples located near the Gulf of Suez. [ABSTRACT FROM AUTHOR]

Heilongdong Spring Basin (HSB) is an ecologically and economically important area in northern China, with widespread and intensive anthropogenic activities (industrialization, mining, agriculture). To understand the hydrogeochemical characteristics and water quality status of groundwater in various aquifers, 33 groundwater samples were collected and analyzed by Piper diagram, Gibbs diagram, Entropy-Weighted Quality Index (EWQI) and Hierarchical cluster analysis (HCA) in the area. The results indicated that the groundwater was mainly derived from meteoric water, and rock weathering was the dominant source of ions in the area. The majority of the karst groundwater samples (KGWs) fell in the category of HCO3-Ca·Mg and HCO3·SO4-Ca·Mg, the hydrochemical faces of pore groundwater (PGWs) and fissure groundwater (FGWs) samples were mainly SO4·HCO3-Ca type with a few of the HCO3·SO4-Ca·type. According to the EWQI, all the KGWs were within the EWQI of below 100 and were suitable for drinking, while the central and eastern parts of regions have elevated EWQI values, especially 3 samples of KGWs were within the EWQI value in the range of 83–95, closing to the "poor" bracket. In addition, 66.7% of FGWs and all the PGWs were unsuitable for drinking. The HCA results showed that local groundwater quality was mainly controlled by geogenic processes and anthropogenic factors. Especially, the shallow groundwater was more affected by anthropogenic activities. Moreover, it was worth noticing that a few karst groundwater samples were close to shallow groundwater samples, which might be related to coal mining and agricultural activities. The present results provide a scientific basis for the protection and utilization of groundwater in different aquifers. [ABSTRACT FROM AUTHOR]

Groundwater-resource quality is assumed to be less responsive to drought compared to that of surface water due to relatively long transit times of recharge to drinking-supply wells. Here, we evidence dynamic perturbations in aquifer pressure dynamics during drought and subsequent recovery periods cause dramatic shifts in groundwater quality on a basin scale. We used a novel application of time-series clustering on annual nitrate anomalies at >450 public-supply wells (PSWs) across California's San Joaquin Valley during 2000-22 to group subpopulations of wells with similar water-quality responses to drought. Additionally, we statistically evaluated the direction and magnitude of multi-constituent water-quality changes across the San Joaquin Valley using a broader dataset of >3000 PSWs with data during two select hydrologic stress periods representing an extreme drought (2012-16) and subsequent recovery (2016-19). Results of time-series clustering and stress-period change analyses corroborate a predominant regional response to pumping stress characterized by increased concentrations of anthropogenic constituents (nitrate, total dissolved solids) and decreased concentrations of geogenic constituents (arsenic, fluoride), which largely reversed during recovery. Cluster analysis also identified a secondary, less commonly occurring group of PSWs where nitrate decreased during drought, but explanatory factor analysis was not able to discern hydrogeologic drivers for these two divergent response patterns. Long-term tracer data support the hypothesis that the predominant regional signal of nitrate increase during drought is caused by enhanced capture of modern-aged groundwater by PSWs during periods of pumping stress, which can drive rapid changes in water quality on seasonal and multiannual timescales. Pumping-induced migration of modern, oxic groundwater to depth during drought may affect geochemical conditions in deeper portions of regional aquifers controlling the mobility of geogenic contaminants over the long term. [ABSTRACT FROM AUTHOR]

Petroleum products have contaminated groundwater with harmful organic compounds, such as benzene, toluene, ethylbenzene, and xylenes (BTEX). Collecting and analyzing polluted groundwater samples is expensive and undertaken infrequently. However, quick remedial action in case of unexpected events requires continuous monitoring. In‐situ water quality sensors (pH, EC, DO, ORP) may show correlations with the components of dissolved petroleum hydrocarbon (PHC) such as aromatics and non‐volatile mobile fractions. Correlations are prerequisite to ultimately develop real‐time prediction models. Since suitable field data sets are limited, we simulated the fate of hydrocarbons in groundwater under various realistic conditions using a reactive transport model as novel approach to explore when, where, and why correlations occur. A stationary oil source zone continuously dissolved at the top of a heterogeneous and shallow sandy aquifer over a two‐dimensional cross‐section. Our model considered transient conditions (fluctuating water table) and spatially uniform hydrogeochemical composition. We observed a strong correlation between PHCs and water quality sensors (rolling Spearman's correlation > |0.8|) at varying periods. These correlations are strongly affected by the location of observation wells, the aquifer's hydraulic conductivity, and the availability of calcite and oxide minerals, and other electron acceptors. DO and ORP are significant for the early detection of hydrocarbon contamination, whereas pH and EC are important features for the long‐term monitoring of hydrocarbons. Our findings lay the foundation for the subsequent development of a data analysis model to detect and estimate in real time PHC levels in groundwater using in‐situ water quality sensors. Plain Language Summary: Groundwater contamination by petroleum products, including benzene, toluene, ethylbenzene, and xylenes (BTEX), is a serious environmental concern. However, the collection and analysis of polluted groundwater samples are expensive and infrequently conducted. In the event of unexpected contamination, quick remedial action is crucial, which requires continuous monitoring of groundwater quality. We investigated whether in‐situ water quality sensors like pH, electrical conductivity (EC), dissolved oxygen (DO), and oxidation‐reduction potential (ORP) can predict the concentration of dissolved petroleum hydrocarbons (PHC) in groundwater. Understanding the correlations between these sensors and PHC levels is essential for developing real‐time prediction models. Since field data is scarce, we developed a reactive transport model that simulates the movement of PHC in groundwater under different conditions. Our model simulated a scenario where oil continuously dissolves at the top of a sandy aquifer. The correlation between PHC levels and water quality sensors varies depending on the location and timing of measurements. DO and ORP are particularly useful for detecting early signs of contamination, while pH and EC are important for long‐term monitoring. Our findings provide the foundation for developing data analysis models capable of real‐time detection and estimation of PHC levels in groundwater using water quality sensors. Key Points: In‐situ water quality sensors are highly correlated with petroleum hydrocarbons in groundwater when spatiotemporal variability is consideredDO and ORP are important for early detection, while pH and EC for long‐term prediction of hydrocarbon contamination in groundwaterThe aquifer's hydrogeology impacts hydrocarbon‐water quality correlations by influencing buffering capacity and flow velocity, among others [ABSTRACT FROM AUTHOR]

Volcanic aquifers have become valuable resources for providing water to approximately 2.5 million people in the Yogyakarta-Sleman Groundwater Basin, Indonesia. Nevertheless, hydrogeochemical characteristics at the basin scale remain poorly understood due to the complexity of multilayered aquifer systems. This study collected sixty-six groundwater samples during the rainy and dry seasons for physicochemical analysis and geochemical modeling to reveal the hydrogeochemical characteristics and evolution in the Yogyakarta-Sleman Groundwater Basin. The results showed that groundwater in the unconfined and confined aquifers exhibited different hydrogeochemical signatures. The Ca–Mg–HCO3 facies dominated groundwater from the unconfined aquifer. The groundwater facies evolved into a mixed Ca–Mg–Cl type along the flow direction towards the discharge zone. Meanwhile, groundwater from the confined aquifer showed mixed Ca–Na–HCO3, Na–HCO3, and Na–Cl–SO4 facies. The presence of Mg in the confined aquifer was replaced by Na, which was absorbed in the aquifer medium, thus showing the ion exchange process. The main geochemical processes can be inferred from the Gibbs diagram, where most groundwater samples show an intensive water–rock interaction process mainly influenced by the weathering of silicate minerals. Additionally, only groundwater samples from the confined aquifer were saturated with certain minerals (aragonite, calcite, and dolomite), confirming that the groundwater followed the regional flow system until it had sufficient time to reach equilibrium and saturation conditions. This study successfully explained the hydrogeochemical characteristics and evolution of a multilayer volcanic aquifer system that can serve as a basis for groundwater basin conservation. [ABSTRACT FROM AUTHOR]

Groundwater serves as a primary water source for various purposes. Therefore, aquifer pollution poses a critical threat to human health and the environment. Identifying the aquifer's highly vulnerable areas to pollution is necessary to implement appropriate remedial measures, thus ensuring groundwater sustainability. This paper aims to enhance groundwater vulnerability assessment (GWVA) to manage aquifer quality effectively. The study focuses on the El Orjane Aquifer in the Moulouya basin, Morocco, which is facing significant degradation due to olive mill wastewater. Groundwater vulnerability maps (GVMs) were generated using the DRASTIC, Pesticide DRASTIC, SINTACS, and SI methods. To assess the effectiveness of the proposed improvements, 24 piezometers were installed to measure nitrate concentrations, a common indicator of groundwater contamination. This study aimed to enhance GWVA by incorporating new layers, such as land use, and adjusting parameter rates based on a comprehensive sensitivity analysis. The results demonstrate a significant increase in Pearson correlation values (PCV) between the produced GVMs and measured nitrate concentrations. For instance, the PCV for the DRASTIC method improved from 0.42 to 0.75 after adding the land use layer and adjusting parameter rates using the Wilcoxon method. These findings offer valuable insights for accurately assessing groundwater vulnerability in areas with similar hazards and hydrological conditions, particularly in semi-arid and arid regions. They contribute to improving groundwater and environmental management practices, ensuring the long-term sustainability of aquifers. [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]

The exploitation of coal resources has disturbed the equilibrium of the original groundwater system, resulting in a perturbation of the deep groundwater dynamic conditions and hydrochemical properties. Exploring the formation of mine water chemistry under the conditions of deep coal seam mining in the Ordos Basin provides a theoretical basis for the identification of sources of mine water intrusion and the development and utilization of water resources. This paper takes Longwanggou Coal Mine as the research area, collects a total of 106 groups of water samples from the main water-filled aquifers, comprehensively uses Piper trilinear diagram, Gibbs diagram, ion correlation, ion ratio coefficient and mineral saturation index analysis, and carries out inverse geochemical modeling with PHREEQC software, so as to analyze the hydrochemical characteristics and causes of the main water-filled aquifers in deep-buried coal seams in the research area. The results show that the main hydrochemical processes in the study area are leaching and cation exchange, and the groundwater is affected by carbonate (calcite, dolomite), silicate (gypsum) and evaporite. Calculations of mineral saturation indices and PHREEQC simulations have led to the conclusion that the dissolution of rock salt and gypsum in groundwater accounts for most of the ionic action. Na+, Cl− and SO42− are mainly derived from the dissolution of rock salt and gypsum minerals, while Ca2+ and Mg2+ are mostly derived from the dissolution of dolomite and calcite. The results of the inverse geochemical modeling are consistent with the theoretical analysis. [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]

At present, in the vast majority of coal mine production processes in China, the degree of hydrogeological exploration often lags behind geological exploration. The main difficulty in evaluating the water richness of coal seam top and bottom water-bearing beds is that the existing evaluation methods often rely on less hydrogeological investigation data. How to utilize the abundant geological exploration data in the mining area to appraise the water-rich distribution of sandstone aquifers is a feasible and challenging methodology. At present, some experts and scholars have tried to use multivariate factor analysis to solve the problem of water-richness evaluation, and they have achieved certain results, but there are some shortcomings: (1) The prediction results are mostly qualitative estimations of the water-richness grade, and there is a lack of quantitative analysis of the units-inflow; and (2) at present, the more advanced prediction methods, such as the back propagation (BP) neural network model, have the disadvantages of low accuracy, requiring many iterations, and slow convergence speed. Therefore, with geological exploration data of the 1503E working face of the Yili No.1 coal mine as the basis., this paper uses grey correlation analysis to screen out the factor indexes suitable for the evaluation of the water richness of a weakly cemented sandstone aquifer, and it combines principal component analysis (PCA) with a BP neural network. Based on the selected factor indexes, a prediction model of the water richness of a weakly cemented sandstone aquifer is established. The results show that compared with the existing methods, the prediction accuracy is higher and has a certain application value. [ABSTRACT FROM AUTHOR]

Objectively and accurately evaluating and predicting the water abundance of coal seam roof aquifers is of great significance for ensuring the coal mining safety and the groundwater resource protection. However, evaluation methods are difficult to accurately characterize the differences in water abundance of coal seam roof aquifers in the same layer caused by phase change. In response to these issues, this study focuses on the Zhiluo Formation in the Shendong mining area of China and constructs a method for evaluating water abundance based on the characteristics of groundwater circulation. The method includes three indicators: aquifer recharge capacity, groundwater rock interaction strength, and groundwater renewal capacity. Firstly, a parameter B was proposed to describe the recharge capacity of aquifers, quantitatively characterizing the spatial differences in the recharge capacity of the Zhiluo Formation. Then, the intensity of water–rock interaction was characterized by the hydrochemical characteristics of groundwater in the Zhiluo Formation, and the renewal capacity of groundwater was semi-quantitatively characterized by tritium isotopes. Finally, from the perspective of sedimentary history, the genetic mechanism of the differences in water abundance in the Zhiluo Formation was revealed. The results indicate that due to the significantly lower parameter B of the Zhiluo Formation in the northern part of the Shendong mining area compared to the southern part, and the weak groundwater renewal ability, the water abundance of the Zhiluo Formation in the northern part of the Shendong mining area is significantly weaker than that in the southern part. The differences in sedimentary facies, sedimentation, and diagenetic history of the Zhiluo Formation clastic rocks in the Shendong mining area have affected the water abundance. This study provides new methods for predicting the risk of water inrush in coal mines and evaluating water resource protection. [ABSTRACT FROM AUTHOR]

The present study is aimed to formulate a numerical model to simulate hydrogeochemical reactions controlling pyrite oxidation in unsaturated aquifers under non-uniform flow conditions. A coupled flow and multi-component transport model is solved using a finite difference scheme to simulate the concentration distribution of oxygen (O2), ferrous (Fe2+), ferric (Fe3+), sulphate (SO42−) and hydrogen (H+) ions. An attempt is made to quantify the transport characteristics of pyrite oxidation ions by analysing the spatial moments of concentration profiles. The simulation results suggest that the variable flow rate in the vertical direction significantly enhances the pyrite oxidation near the ground surface. Peak concentration of Fe2+, Fe3+, and SO42− near the ground surface is found to be approximately 2–3 times higher in the case of variable flow. The pH level near the ground surface drops considerably when variable flow conditions exist in the unsaturated zone. The variation in flow parameters such as porosity, and water saturation and reaction parameters such as oxygen diffusion rate and the oxygen consumption rate are found to affect the mass and mobility of Fe2+, Fe3+, and SO42− considerably. Although there has been substantial research on hydrogeochemical events associated with pyrite oxidation in the past, there has been very less focus on the transport qualities of the ions produced in groundwater. The mobility assessment of pyrite oxidation ions in aquifer presented in the study is beneficial to understand the groundwater quality risk associated with mining and to plan and implement effective remediation strategies for the restoration of affected aquifers. [ABSTRACT FROM AUTHOR]

Aquifer characterization is essential for groundwater sustainability in the Niger Delta region. The unconsolidated aquifers of the region are sandy and porous, and have the potential to allow the passage of contaminants to the groundwater resource. The first-order geo-electric parameters of the subsurface, procured by injection of a direct current into the ground were applied to evaluate the aquifer vulnerability in the region. The Schlumberger architecture was engaged to acquire vertical electrical sounding (VES) data at different points and processed using Interpex 1D™. Electrical resistivity imaging (ERI) using a multi-electrode Wenner-α array was also applied across the study area and constrained with existing borehole data to establish the accuracy of the VES results. The VES result revealed the occurrence of 5 to 6 geo-electric strata across the region. The rock types identified from the VES result and ERI pseudo-section were mostly sandstone intercalated with shale and clayey sand at some points. The result also revealed that the depth to water-bearing formation within the area is relatively shallow with aquifer depth values ranging from 7.7 to 103 m and thickness of the aquifer varies from 4.7 to 149.7 m, while the aquifer resistivity values ranged from 470.84 to 2697.7 Ωm. The aquifer protective coverage (APC) assessment revealed that the study area has weak and poor protective covers, while the geo-electric layer susceptibility indexing (GLSI) shows that the area is characterized by low and moderate vulnerability status. The GOD index measurement across the area also revealed that the area has low and average vulnerability status at different points. GOD represents an acronym for three hydrogeological factors, and they are confinement of the aquifer (G), overlying lithology of the aquifer (O), and depth to the aquifer (D). The poor and weak protective covers which gave rise to the low and average vulnerability are indicators that the aquifers within the region are prone to contamination from surface sources. This research is vital for groundwater management and contamination assessment in sandy aquifers. [ABSTRACT FROM AUTHOR]

Groundwater pollution is one of the main challenges in our society, especially in semi-arid Mediterranean regions. This issue becomes especially critical in predominantly agricultural areas that lack comprehensive knowledge about the characteristics and functioning of their aquifer system. Vulnerability to groundwater pollution is defined as the sensitivity of the aquifer to being adversely affected by an imposed pollution load. For the Guadalupe aquifer, various indicators including water level depth, level variation, aquifer properties, soil composition, topography, impact on the vadose zone, and hydraulic conductivity were evaluated to establish spatial vulnerability categories ranging from very low to very high. Two pollution vulnerability scenarios (wet and dry) were studied. The results were compared with the analysis of nitrate concentration and distribution (2001, 2020, and 2021) from samples collected in the field. In the Calafia area, which predominantly relies on viticulture, the primary recharge inputs were identified in areas with a high vulnerability to pollution. Surprisingly, these vulnerable areas exhibited lower nitrate concentrations. This scenario underscores the need for effective management measures to safeguard aquifers in agricultural regions. [ABSTRACT FROM AUTHOR]

Due to their extremely toxic properties, 226Ra and it daughters (222Rn, 210Pb, and 210Po) in drinking groundwater require monitoring. Recent studies have reported exceptionally high levels of natural 210Po (up to 10,000 Bq/m3), 226Ra, and 222Rn isotopes in groundwater. This study aims to provide background data on 226Ra and its daughter radionuclides in the typical agricultural-industrial Dongshan Bay (DSB) before the construction of Zhangzhou Nuclear Power Plant (Zhangzhou NPP). The measurement results indicate that no abnormally high activities of 210Po and 210Pb were detected in the investigated wells. Strong positive correlations between 210Pb and 210Po, as well as between 222Rn and 210Pb activities, suggest that the origins of 210Pb and 210Po in groundwater are strongly influenced by the decay of the parent radionuclides 222Rn and 210Pb, respectively. In the DSB coastal zone groundwater, significant deficiencies of 210Po relative to 210Pb and 210Pb relative to 222Rn were observed, providing further evidence that 210Po and 210Pb are also effectively scavenged due to their geochemical properties (specifically particle affinity) within the groundwater-aquifer system. A systematic comparison among all relevant water bodies in the DSB revealed that the activity concentrations of 210Pb and 210Po in groundwater were the highest, except for rainwater. Based on the evaluation of 210Pb sources, the results imply that submarine groundwater discharge (SGD) is an important pathway for transferring radionuclides (such as 210Pb) from land to the nearshore marine environment, even though the study area has a lower 210Pb background groundwater. By considering all the 210Pb's sources in the DSB, we found low 210Pb background groundwater discharge still needs to be taken into account for small-scale bays. This is because SGD was calculated to be one of the most important 210Pb sources in the bay during observation season. Regardless of whether the system is in a normal state or a nuclear accident emergency state, greater attention should be paid to the groundwater discharge of radionuclides into the ocean. [ABSTRACT FROM AUTHOR]

Aquifer pumping tests represent a standard method for estimating hydraulic characteristics, with practitioners often focusing on late period drawdown data because these are less affected by within‐ and near‐borehole effects (e.g., borehole‐storage and skin effects). Alternatively, groundwater responses to natural forcing (e.g., barometric pressure and earth tides) provide a passive method for estimating aquifer parameters at a low cost. However, to the best of our knowledge, no studies have compared parameters calculated from different periods within a pumping test with those from passive methods. Herein, we compare the aquifer transmissivity estimated using both active and passive methods in two wells located in the Beetaloo Region of Northern Australia. The active method estimates aquifer transmissivity during three periods (i.e., the early, middle, and late periods) of an aquifer pumping test, while the passive method employs groundwater responses to barometric‐pressure and earth‐tide fluctuations. We find that the range of best‐fit aquifer transmissivity is 1.18 × 10−5–1.79 × 10−5 m2/s and 1.73 × 10−5–2.14 × 10−5 m2/s for OW1 and OW2, respectively. The transmissivity estimated from the barometric pressure response method is the largest. The aquifer transmissivity using barometric pressure responses are consistent with early‐ and middle‐period estimates. This suggests that barometric pressure responses are more sensitive to within‐ and near‐borehole effects. The scales of the tidal response method are smaller than those of the pumping test method. Plain Language Summary: The accurate estimation of the hydraulic properties of aquifers is important for effective groundwater management. Both active (aquifer pumping tests) and passive (natural forcing such as barometric‐pressure and earth‐tide fluctuations) methods are used to estimate aquifer hydraulic properties. However, the aquifer parameters estimated from aquifer pumping tests are variable as borehole effects (e.g., borehole storage and skin effects) dissipate as the cone‐of‐depression expands over time. This leads to dynamic changes in parameters during the early, middle, and late periods of an active pumping test. By comparing the aquifer transmissivity from these different periods with those estimated from passive (tidal/barometric pressure) responses and combining with scale effect, we find that barometric pressure responses are consistent with early and middle periods (corresponding to within‐ and near‐borehole effects). The scales of the tidal response method are smaller than those of the pumping test method. Key Points: We estimate aquifer transmissivity using groundwater responses to natural disturbances (earth tides, barometric pressure fluctuations)From early to late period pumping, transmissivity changes slightly and decreases while storage coefficient changes in magnitude and increaseThe result of atmospheric response located in early to middle‐period pumping while AQTESOLV method is within late‐period pumping [ABSTRACT FROM AUTHOR]

Elevated and increasing NO3− ${{\text{NO}}_{3}}^{-}$ concentration in groundwater affect groundwater supplies in China and elsewhere. However, how groundwater flow affects NO3− ${{\text{NO}}_{3}}^{-}$ concentration in groundwater has yet to be fully understood. Herein, multi‐isotopes (15N, 11B, 18O, and 2H) and local indicators of spatial association (LISA) were used to elucidate the spatiotemporal variation, sources, and patterns of NO3− ${{\text{NO}}_{3}}^{-}$ and its response to groundwater flow in Poyang Lake Basin where agriculture, industry and urban coexist. The location of NO3− ${{\text{NO}}_{3}}^{-}$ hotspots identified by LISA tended to move from the middle to lower reaches of Ganfu Plain with groundwater flow, and hotspots area expanded in the upper reaches of Xin River Basin and northwest of the study area during the transition from dry season to wet season. Our results revealed that variations of regional NO3− ${{\text{NO}}_{3}}^{-}$ concentration were controlled by groundwater recharge or flow mode (vertical or lateral), biogeochemical processes and sources (sewage and manure). In some areas with the single stratigraphic structure (unconfined aquifer), spatiotemporal variation of NO3− ${{\text{NO}}_{3}}^{-}$ concentration was influenced by local pollution sources and vertical recharge of current precipitation (vertical flow). In some areas with binary structures (confined aquifer), groundwater was mainly recharged by lateral flow and NO3− ${{\text{NO}}_{3}}^{-}$ concentration was mainly affected by mixing effect of upstream groundwater, reflecting human activities in the upper reaches rather than local human activities. In lakeside floodplain, groundwater NO3− ${{\text{NO}}_{3}}^{-}$ was attenuated by the dissimilatory NO3− ${{\text{NO}}_{3}}^{-}$ reduction to NH4+ ${{\text{NH}}_{4}}^{+}$. This study provides a novel insight into groundwater flow controlling on spatiotemporal distribution of NO3− ${{\text{NO}}_{3}}^{-}$ concentration in the regional scale. Key Points: Regional‐seasonal changes of hotspots and cool spots of nitrate concentration were identified by local indicators of spatial associationNitrate hotspots showed a seasonal shift along flow or expansion dominated by groundwater recharge mode linked with aquifer heterogeneityWe developed a conceptual model of spatiotemporal variation in regional nitrate content that describes the crucial role of groundwater flow [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]