Search Results (797)

Landfilling remains a widely used method for municipal solid waste disposal but may pose long-term risks to soil and groundwater. To address the fragmented management of landfill-related environmental information, this study developed a geographic information system (GIS)-based “One Map” framework that integrates landfill facilities, hydrogeological information, environmental monitoring data, pollutant indicators, and sensitive receptors into a unified spatial database. The framework links spatial features with attribute information and supports visualization, multi-criteria queries, statistical analysis, groundwater-quality assessment, and the preliminary screening of potentially undetected environmental risks. A municipal solid waste landfill in Xichuan County, Nanyang City, China, was selected as a case study, and groundwater quality was evaluated using the single-factor pollution index and Nemerow comprehensive pollution index. No Class III standard exceedance was identified at the five monitoring wells during the sampling event; however, the available hydrogeological and operational data were insufficient to attribute differences among wells to landfill-derived contaminant transport. The primary contribution is not a new GIS engine, but a landfill-specific data model and workflow that integrate fragmented survey outputs into a spatial decision-support environment. Because the case study comprises five wells and a single monitoring campaign, the findings represent a point-specific workflow demonstration rather than temporal or regional validation. Interpretation followed a source–pathway–receptor framework, but source attribution remained constrained by the absence of contemporaneous hydraulic-head data, a verified operational chronology, and quantitative leachate-management records. Repeated monitoring, an upgradient baseline, and a denser well network are required for stronger environmental inference. Full article

Accurate prediction of dissolved phosphorus (P) transport to groundwater, and especially to drain tiles, is a major challenge, particularly in structured soils where preferential flow dominates subsurface hydrology. Existing vadose zone models rely on advection–dispersion formulations that insufficiently represent macropore-driven transport, leading to underestimation of dissolved P losses. This study develops a simplified convective–preferential (CP) transport equation to describe event-scale movement of dissolved P through the vadose zone to groundwater. The equation conceptualizes the soil profile as a near-surface distribution zone that acts as a linear reservoir with a transmission zone below where preferential flow is activated when imposed fluxes exceed the effective matrix conductivity. Under these conditions, P-rich event water bypasses much of the soil matrix, rapidly reaching the groundwater. The CP equation uses a small set of physical parameters, based on partitioning the flux between the matrix and preferential pathways. Model results were validated against laboratory leaching experiments, published column studies of various soil textures, and tile-drained field soils. The CP equation reproduced observed dissolved P breakthrough patterns and flow-dependent concentration in tile drains. Model results confirm that significant P transport occurs during high-intensity rainfall on saturated soils with restrictive layers on structured soils with a low-permeable hardpan. Full article

Seawater intrusion (SWI) increasingly threatens coastal aquifers that serve growing communities, emphasizing the need for generalizable, process-based diagnostics. We evaluate SWI in a multilayer coastal aquifer system in southern Alabama, USA, by integrating three groundwater sampling campaigns during spring–early summer 2025 (March, April, and June), hydrogeochemical–isotopic analyses, and variable-density SEAWAT modeling. This study couples HFE–Gibbs–isotope diagnostics with hydraulic-head-constrained SEAWAT modeling to characterize seawater intrusion extent and process state in a multilayer coastal setting. Groundwater major ions and δ¹⁸O/δ²H indicate dominantly meteoric, rock-weathering waters (Ca–HCO₃ inland) with localized Na–Cl near the coast; most samples plot in the rock dominance field, and stable isotope values cluster near the meteoric water line. A 3-D SEAWAT model (seven layers, 150 × 150 m cells), calibrated to available groundwater head observations using PEST, indicates that modeled intrusion is concentrated at depth in confined Miocene units, whereas shallow groundwater sampled from the unconfined zone remains largely fresh based on hydrogeochemical and isotopic evidence. Because chloride observations were used primarily for interpretation rather than direct transport calibration, the modeled deep salinity distribution is treated as a process-based estimate rather than a uniquely calibrated chloride field. To quantify exposure and process state, we introduce two indicators: a Depth-Weighted Intrusion Index (DWII) integrating the extent and intensity of the transition zone across layers, and an Ion-Exchange Departure Index (IEDI) capturing normalized Na–Cl departures from conservative mixing due to cation exchange. Predominantly negative IEDI values indicate reverse exchange with weaker intensity during spring freshening and only localized forward exchange episodes. Beyond the site-specific findings, the DWII and IEDI introduced in this study provide practical tools for detecting and quantifying subtle seawater intrusion in low-salinity coastal aquifers and may be applicable to other coastal aquifer systems with similar hydrogeological settings. Full article

The long-term release of heavy metals from inactive tailing ponds poses a persistent threat to groundwater quality, yet the effectiveness of commonly employed risk control measures—such as anti-seepage liners and chemical stabilization—remains insufficiently evaluated under realistic field conditions. This study aims to assess the effectiveness of risk control strategies at a Pb Zn mine tailing pond in Yunnan Province, China. A dynamic 2D numerical pollutant transport model was developed, calibrated, and validated against observed hydraulic heads and metal concentrations from monitoring wells within the study aquifer. The calibrated model showed good agreement with field measurements. Simulation results indicate that anti-seepage liners alone are insufficient to ensure compliance with the Class III standards of the Chinese Groundwater Quality Standards, even under ideal conditions where all leaching from the tailing pond is prevented. In contrast, a combined strategy—chemical stabilization reducing Pb leaching from historically contaminated soils (initial Pb: 183 µg L⁻¹) by at least 70%, together with anti-seepage systems reducing infiltration flux by over 94.4%—would be sufficient to restore groundwater quality to within regulatory limits. Full article

Groundwater quality assessment during well drilling could be biased by transient contamination from drilling equipment and fluids. To address this issue, batch leaching tests, sequential filtration experiments, and field validation were combined. Batch leaching experiments were performed on painted and unpainted drilling rods. Unpainted carbon-steel rods promoted marked Fe and Mn release through oxidative corrosion, whereas painted rods released Zn through progressive dissolution of the zinc coating and As under transiently reducing conditions. Leaching tests performed on fresh and exhausted drilling muds revealed elevated concentrations of SO₄²⁻, Cl⁻ and Na⁺, attributable to the drilling additives rather than the drilling muds. Meanwhile, exhausted drilling muds showed a limited enrichment in trace elements, likely due to sorption onto the aquifer matrix. Stepwise filtration showed that 0.15 µm membranes effectively removed colloid-associated trace elements, while major ions remained unaffected by filters’ pore size. Field data from two wells confirmed that Fe, Mn, Zn, and Al anomalies detected during drilling-phase sampling were consistent with release by drilling equipment and muds. The coupled laboratory–field approach provides a practical framework for identifying and minimizing drilling-induced artifacts, supporting the use of in situ 0.15 µm filtration and extended purging to obtain representative groundwater quality data. Full article

The objective of this study was to propose a simple, low-cost in-situ remediation method for NO₃⁻-N that effectively utilizes natural denitrification processes. We verified the inflow of surrounding groundwater containing high concentrations of NO₃⁻-N when groundwater at the denitrification depth was pumped, as well as the denitrification effect at that depth, under two pumping flow-rate conditions (low and high) at a site where denitrification had been confirmed. The results suggest that pumping groundwater at the denitrification depth enables the inflow of surrounding groundwater, thereby enabling denitrification of high-concentration NO₃⁻-N in the surrounding groundwater under oxidizing conditions. The denitrification amounts were 72 mg-N/h for the high-flow Pumped Denitrification Test (PDT) and 3.3 mg-N/h for the low-flow PDT. Additionally, the nitrate removal efficiency of the high-flow PDT was higher than the results obtained in previous studies at the same site and season under natural groundwater flow. It was also comparable to that of artificially created denitrification environments at other sites when assuming conditions with high NO₃⁻-N concentrations in shallow groundwater. This study demonstrated that the pumping of reductive groundwater transports high concentrations of NO₃⁻-N along with the surrounding groundwater, and that denitrification occurs without impairing denitrification capacity. Full article

The Cau river basin in northern Vietnam is experiencing increasing pressures on water resources due to rapid urbanization, industrial development, agricultural expansion, and inadequate wastewater management. Understanding the interactions between surface water, groundwater, and water quality is essential for developing effective and sustainable water management strategies. This study developed and applied a coupled MIKE SHE–MIKE 11 framework to simulate surface–groundwater connectivity and its influence on water quality dynamics in the Cau river basin. Hydrometeorological and water quality datasets collected during 2023–2024 were used to calibrate and test the integrated model at key monitoring locations, including Cha, Phuc Loc Phuong, and Dap Cau stations. The hydrological component demonstrated satisfactory performance, with Nash–Sutcliffe Efficiency (NSE) values ranging from 0.55 to 0.79 for water level simulations, indicating a reliable representation of surface and subsurface flow processes. Simulated river–aquifer exchange fluxes revealed pronounced spatial variability across the basin. Upstream reaches predominantly functioned as groundwater recharge zones, whereas the middle and downstream sections exhibited dynamic bidirectional exchanges governed by river stage fluctuations, hydraulic gradients, and local hydrogeological conditions. Water quality simulations for BOD₅, COD, NH₄⁺, total nitrogen (TN), and total phosphorus (TP) showed good agreement with observations, with calibration and testing errors generally remaining below 25%. Incorporating surface–groundwater interactions improved the representation of pollutant transport, residence time, and nutrient accumulation processes compared with conventional river-only simulations. The results demonstrate that river–aquifer connectivity plays a critical role in regulating both hydrological processes and water quality conditions in the basin. The coupled modeling framework provides a robust scientific basis for identifying critical interaction zones, assessing pollution risks, optimizing monitoring programs, and supporting integrated water resource planning. By explicitly linking hydrological connectivity with water quality dynamics, the proposed framework serves as a practical decision-support tool for sustainable water resource management in the Cau river basin and other river–aquifer systems facing increasing environmental pressures and progressive water quality degradation. Full article

The dynamics of methane (CH₄), nitrous oxide (N₂O) and carbon dioxide (CO₂) in groundwater have rarely been investigated. As dissolved gases they may be transported to distant sites and, hence, to the atmosphere. Crumps Cave (CC) is located on a perched aquifer in south-central Kentucky. Water was sampled at a waterfall within the cave located 15 m below the surface, at two adjacent surface wells 15 m and 50 m deep, providing samples from the epikarst and regional aquifer, respectively. Dissolved gases and geochemistry parameters were analyzed for seasonal changes across three years of weekly monitoring (2015–2017) using Kruskal–Wallis H tests and Bonferroni-corrected pairwise comparisons. Dissolved CO₂ concentrations are mainly controlled by percolation through the epikarst, influenced by soil respiration, and vary with rainfall and seasonal temperature fluctuations. CH₄ showed a site-dependent pattern: concentrations were significantly elevated in warm seasons at the shallow and deep wells, where anaerobic conditions and agriculturally derived organic matter promote methanogenesis; no seasonal variation was detected at the cave site, where oxic conditions limit CH₄ year-round. N₂O was significantly elevated in cold seasons at all three sites, driven by cold-season denitrification of agriculturally derived nitrates. N₂O did not differ between sites, indicating seasonal temperature-driven denitrification as the primary control rather than site hydrology, with cold-season denitrification of agriculturally derived nitrates from fertilizer application. Indirect gas emissions are characteristic of karst systems and may be transported or stored in aquifers through complex interactions of groundwater recharge, microbial activity, and seasonal land-use variability. Full article

Landfill leachate represents a long-term source of contamination that may significantly affect groundwater and receiving water bodies through the migration of organic, inorganic, and toxic pollutants. This study evaluated the long-term migration of landfill leachate and its potential environmental impacts using the LandSim Release 2 probabilistic software model applied to two municipal waste landfills in the Republic of Serbia: the regional sanitary landfill “Gigoš” in Jagodina and the sanitary landfill “Meteris” in Vranje. The modelling framework integrated laboratory leachate analyses, hydrogeological conditions, engineered barrier system characteristics, and receptor-oriented contaminant transport assessment. Model validation was performed through comparison of simulated and laboratory-measured concentrations. Two scenarios were analyzed for each site: an engineered sanitary landfill scenario with a functional containment system and a conservative barrier-failure scenario representing complete loss of engineered barrier functionality. Ten representative leachate parameters were included, covering nitrogen compounds, inorganic ions, toxic substances, and heavy metals/metalloids. The results showed that engineered protection systems significantly delay contaminant migration and reduce receptor concentrations, while barrier-failure conditions lead to earlier pollutant breakthrough and higher environmental risk. The simulations demonstrated that under the engineered sanitary landfill scenario, receptor concentrations of all analyzed contaminants remained below the corresponding maximum allowable concentrations, with contaminant migration occurring only after several centuries. In contrast, the conservative barrier-failure scenario resulted in substantially earlier contaminant breakthrough, with nitrogen compounds and phenols representing the greatest environmental concern due to their rapid migration and exceedance of regulatory thresholds, while the “Meteris” landfill generally exhibited higher receptor concentrations than the “Gigoš” landfill. These findings highlight the importance of predictive modelling and long-term monitoring for sustainable landfill management and groundwater protection. Full article

Solute transport in rock fractures is strongly influenced by hydrodynamic conditions, and clarifying the Péclet-number-controlled transition of transport regimes is important for understanding contaminant migration in fractured aquifers. Based on three-dimensional numerical simulations, this study investigates conservative solute transport in idealized rough fractures with perfectly mated walls and uniform aperture under a wide range of Péclet numbers (Pe). The evolution of concentration fields, breakthrough curves (BTCs), and diffusive and advective fluxes was analyzed to identify the dominant transport regimes. The results show that, as Pe increases, solute transport changes from a diffusion-dominated regime (Pe < 0.1), to a mixed macro-dispersion-dominated regime (0.1 < Pe < 1000), and finally to a high-Pe advection-controlled regime with Taylor-dispersion-like characteristics (Pe > 1000). Correspondingly, the concentration field evolves from rapid diffusion-driven spreading to a sharper advective front, while the BTCs change from early diffusion-breakthrough curves to step-like breakthrough behavior. Fracture aperture promotes solute spreading and broadens the mixing zone, especially under low-to-intermediate Pe conditions. In contrast, under the perfectly mated and uniform-aperture fracture conditions considered here, increasing roughness mainly induces local tortuosity of the concentration front and has limited influence on the overall BTCs. Flux decomposition further confirms that diffusive flux dominates at low Pe, whereas advective flux becomes increasingly dominant as Pe increases. These findings provide a mechanistic basis for interpreting Pe-controlled solute transport in idealized fracture channels and offer fracture-scale insights for classified groundwater contamination risk assessment. The implications should be interpreted within the assumptions of conservative transport without matrix diffusion, adsorption, or reactive processes. Full article

Agricultural karst watersheds are highly vulnerable to nutrient loss because strong surface water–groundwater (SW–GW) connectivity can rapidly transfer nitrogen and sulfur species from soils, agricultural activities, and human settlements into aquatic systems. However, the coupled behavior and contrasting controls of nitrate (NO₃⁻) and sulfate (SO₄²⁻) in such agroecosystems remain insufficiently understood, limiting effective nutrient and groundwater-quality management. In this study, a typical karst agricultural watershed in Southwest China was selected to investigate the sources, transformation processes, and transport pathways of NO₃⁻ and SO₄²⁻ under strong SW–GW interactions. During the rainy season, 44 groundwater and 40 surface water samples were collected for major hydrochemical and nitrate–sulfate stable isotope analyses. An integrated framework combining hydrochemical analysis, self-organizing maps (SOM), positive matrix factorization (PMF), and MixSIAR were used to identify dominant sources, quantify source contributions, and clarify controlling processes. The results showed that groundwater was mainly characterized by carbonate-controlled Ca-HCO₃ facies, whereas surface water exhibited higher mineralization and a shift toward Ca-SO₄ facies, indicating stronger external inputs and rapid hydrological responses. Nitrate was primarily controlled by external nitrogen inputs, with manure and sewage and soil nitrogen contributing 39–62% and 16–33%, respectively. Nitrate was also regulated by nitrification under oxic conditions, while denitrification was negligible. In contrast, sulfate was predominantly governed by geogenic processes, with sulfide oxidation contributing 63–83%, while other sources were minor. These contrasting controls resulted in distinct spatial and process behaviors: nitrate showed source-driven variability associated with agricultural and domestic inputs, whereas sulfate displayed process-driven accumulation mainly controlled by water–rock interactions. Strong SW–GW connectivity enhanced the transfer of anthropogenic nutrient signals, while subsurface mixing and buffering regulated their expression in groundwater and surface water. These findings demonstrate a clear decoupling between nitrate and sulfate controls in agricultural karst systems and provide a scientific basis for nutrient pollution control, groundwater protection, and sustainable agricultural water management in vulnerable karst regions. Full article

In situ leaching (ISL) is the most popular method for uranium mining worldwide, particularly in arid and semi-arid regions. Despite its economic benefits, ISL raises concerns about radioactive migration and groundwater contamination. This review assesses the environmental impacts of ISL uranium mining, focusing on radionuclide transport pathways and key information gaps. This review, focusing on groundwater contamination, radionuclide migration, soil and sediment contamination, atmospheric impacts, vegetation responses, and ecosystem disturbances, summarizes current understanding of the hydrogeochemical, radiological, and environmental impacts of uranium mining. The analysis indicates that groundwater is the environmental component most vulnerable to contamination during ISL operations due to the injection of acidic or alkaline leaching solutions that may mobilize uranium, radium, sulfates, selenium, arsenic, and other potentially hazardous elements. In addition to impacts on groundwater, there have also been reports of soil contamination, airborne dust, radioactive accumulation in flora, and impacts on aquatic and microbiological resources, particularly in arid and semi-arid regions. Although cleanup methods and natural attenuation can minimize contamination to some extent, residual contamination can persist for decades after mine closure. Overall, ISL uranium mining emphasizes the need for effective groundwater management, long-term environmental monitoring, and improved reclamation methods, balancing surface disturbance with long-term hydrogeochemical and environmental concerns. Full article

The tritium–helium-3 (³H/³He) dating method was applied to quantify groundwater apparent ages and estimate the migration of anthropogenic tritium in the shallow alluvial aquifer surrounding the Paks Nuclear Power Plant (Hungary). Groundwater samples were collected from monitoring wells between 2013 and 2016 and analyzed for tritium and dissolved noble gases. The investigated aquifer consists mainly of highly permeable sand and gravel deposits hydraulically connected to the Danube River. Reference wells indicate apparent groundwater ages between 26 and 43 years, with an average apparent ³H/³He age of approximately 37 years. Wells located within the operational area of the power plant show apparent ³H/³He ages ranging from 1.3 to 14.1 years, reflecting the transport of tritium released during leakage events associated with damaged sewer pipelines between 2005 and 2007. The spatial distribution of apparent ages reveals heterogeneous groundwater flow paths, and highlights the influence of well-screen sampling on age interpretation. The paper demonstrates that anthropogenic tritium released from nuclear infrastructure can serve as an effective age dating method and improve conceptual models of flow dynamics in shallow alluvial aquifers. Full article

The Wadi Al-Ahsaba watershed is an arid to semi-arid catchment situated in southwestern Saudi Arabia, characterized by intermittent surface flow, high evaporation and low rainfall, and a dam reservoir built for flood control. The work aims to assess hydrological and anthropogenic controls on surface and groundwater quality, pollution status, and human health risks using an integrated approach of hydrogeochemical analysis, multivariable statistics, and water quality and contamination indices. A total of 21 water samples (15 surface water, 6 groundwater) were analyzed for general chemistry, major ions, and trace elements. Hydrogeochemical analysis and principal component analysis (PCA) were implemented to differentiate the geogenic from anthropogenic control on water quality. The pollution status and associated risk were evaluated using water quality index (WQI), contamination degree (Cd), Hazard Quotient (HQ), and Hazard Index (HI). Results suggest limited surface–groundwater interaction, with surface water dominated by Ca–Mg–HCO₃ facies, indicating recent recharge and limited water–rock interaction, whereas groundwater exhibits mixed Ca–Mg–Cl and Ca–Na–Cl–SO₄ types, revealing longer residence time and water–rock interaction. Nitrate (9.5–109 mg/L) and TDS (522–1003 mg/L) exceeded drinking water standards in 90% and 95% of tested samples, respectively, and WQI ranged from 43 to 134, reflecting excellent to poor water. High non-carcinogenic risk from nitrate was observed, especially for infants. The study concluded that the geogenic processes (water–rock interaction, evaporation, and mineral dissolution) control the general chemistry of tested water, while anthropogenic input from wastewater and agriculture input are likely contributors to nitrate contamination. The study contributes to the understanding of arid wadi-dam systems by revealing how limited recharge, hydrological connectivity, and episodic flow control contaminant transport and persistence, underscoring the critical role of integrated hydrological analysis and land use management in safeguarding freshwater resources in arid environments. Full article

Saltwater intrusion (SI) threatens groundwater sustainability in nearshore regions, particularly in Bangladesh, where over-extraction and sea-level rise accelerate aquifer salinization. Accurate prediction of SI dynamics is therefore critical for effective groundwater management. This study developed and evaluated several deep learning and hybrid models, including CNN, DNN, LSTM, CNN–DNN, CNN–LSTM, DNN–LSTM, and CNN–DNN–LSTM, to predict SI in a nearshore aquifer system. Predictor–response datasets were generated using the three-dimensional density-dependent flow and solute transport model FEMWATER. This study presents the first comprehensive benchmarking of standalone and hybrid CNN–DNN–LSTM models for SI prediction in a Bangladesh nearshore aquifer, supported by CRITIC–EDAS-based model ranking. Model performance was assessed using RMSE, MAE, MAD, R, IOA, a-20, NRMSE, along with CRITIC weighting and EDAS ranking. Results indicate that hybrid models integrating LSTM outperformed standalone models. The CNN–LSTM model achieved the best performance at OW1 (RMSE = 1.57 mg/L, MAE = 1.26 mg/L, R = 0.99, IOA = 0.99). The DNN–LSTM model performed best at OW2 (RMSE = 2.87 mg/L, IOA = 0.98, R = 0.97) and OW3 (RMSE = 1.95 mg/L, IOA = 0.99, R = 0.99). In contrast, the DNN model showed poor performance, while the CNN model demonstrated moderate performance and the LSTM model underperformed. Overall, the hybrid CNN–LSTM and DNN–LSTM models demonstrated superior accuracy and robustness for reliable SI prediction and sustainable groundwater management. Full article