Groundwater Utilization Research Articles

Co-occurrence of arsenic and fluoride in groundwater of Guide basin in China: Genesis, mobility and enrichment mechanism

Endemic arsenic poisoning and fluorosis caused by primary high arsenic (As) and high fluoride (F−) groundwater have become one of the most serious environmental geological problems faced by the international society. High As and high F− groundwater exists in Neogene confined aquifers in Guide basin, with concentrations of 355 μg/L and 5.67 mg/L, respectively, and showing a co-occurrence phenomenon of As and F− in the groundwater. This poses a double threat to the health of tens of thousands of local residents. In this study, based on the systematic collection of groundwater and borehole sediment samples, analysis of hydrochemistry and isotope indexes, combined with laboratory tests, purpose of this study is to reveal the migration rule and co-enrichment mechanism of As and F− in aquifers, and finally establish a hydrogeochemical conceptual model of the enrichment process of As and F−. The main conclusions are as follows: hydrochemical type of unconfined and confined groundwater in Guide basin is Ca–Na–HCO3 and Na–Cl–HCO3 type, respectively. Main minerals in sediments are quartz and plagioclase. Concentrations of As and F− are lower in unconfined groundwater, but higher in confined groundwater, and which show a gradual increasing trend along the groundwater flow path. The mineralization of natural organic matter in confined aquifer causes iron and manganese oxide minerals containing As to dissolve gradually, which leads to the gradual release of As into groundwater. Large amount of HCO3− produced by mineralization of organic matter precipitate with Ca2+ in groundwater, resulting in reduction of Ca2+ content, promoting the dissolution of fluoride-containing minerals such as fluorite (CaF2), and continuously releasing F− into groundwater. Meanwhile, competitive adsorption reactions in confined aquifers causes more As and F− to be released from mineral surface into groundwater, which gradually migrate and accumulate along groundwater flow. Finally, it is established that a conceptual model for the formation of high As and F− groundwater in the confined aquifer of Guide basin. The research results not only help to improve our understanding of the formation and evolution of groundwater with high As and F− with similar geological background, but also provide scientific basis for rational development and utilization of groundwater, and prevention and control of chronic As and F− poisoning in local and similar areas.

DEEP AND MACHINE LEARNING FOR MONITORING GROUNDWATER STORAGE BASINS AND HYDROLOGICAL CHANGES USING THE GRAVITY RECOVERY AND CLIMATE EXPERIMENT (GRACE) SATELLITE MISSION AND SENTINEL-1 DATA FOR THE GANGA RIVER BASIN IN THE INDIAN REGION

Abstract. Accurate estimation of groundwater levels in river basins is paramount for hydro-geological research and sustainable water resource management. In this paper, we introduce a deep learning framework explicitly developed for precise groundwater level estimation in the Ganga River Basin. Leveraging the combined band information of Sentinel-1 synthetic aperture radar (SAR) and GRACE satellite data, our approach capitalizes on the trans-formative capabilities of Vision Transformers (ViT) and their variants, with a particular focus on Swin-Transformer variant enriched with Normalization Attention Modules (NAMs).To address the unique challenges of the Ganga River Basin, we curated a comprehensive dataset, forming a robust foundation for training computer vision models tailored to this distinct geographical region. Through rigorous experiments, our state-of-the-art Vision Transformers demonstrated significant potential in groundwater level estimation, with the Swin-Transformer NAM-based model achieving an outstanding Mean Absolute Error (MAE) of 1.2. These remarkable results surpass conventional methodologies and underscore the substantial advancements achieved through advanced transformer-based architectures in this domain. Moreover, this research contributes a robust dataset for future endeavours, fostering further advancements in groundwater estimation and related fields. This study represents a substantial step towards advancing sustainable groundwater utilization practices in the Ganga River Basin and beyond.

Performance analysis of groundwater quality index models for predicting water district in Tamil Nadu using regression techniques

The widespread utilization of groundwater in various sectors, including households for drinking purposes and the agricultural and industrial domains, has elevated its status as an indispensable and crucial natural resource. Groundwater has seen significant changes in both quantity and quality factors. Water Quality Index (WQI), which is dependent on a number of factors, is still a crucial gauge of water quality (WQ) and a key component of efficient water management. If there is an automated method for forecasting WQ, the administration will benefit. The main goal of this project is to develop a machine learning (ML) model to forecast the quality of groundwater in several areas of Tamil Nadu (TN), India. The available dataset encompasses comprehensive data groundwater attributes, encompassing parameters such as pH, electrical conductivity (EC), total hardness (TH), calcium (Ca[Formula: see text], magnesium (Mg[Formula: see text], sodium (Na[Formula: see text], bicarbonate (HCO[Formula: see text], nitrate (NO[Formula: see text], sulfate (SO[Formula: see text], and chloride (Cl[Formula: see text]. In this study, various ML regression algorithms such as linear, least angle, random forest and support vector regressor models and their comparison with the ensemble model (EM) were depicted to predict WQI, and the results were evaluated using performance metrics. It is found that the EM has a lower RMSE in the order of [Formula: see text]. Further, the predicted WQI values are used to classify the districts of TN.

Hydrochemical Characteristics and Controlling Factors of Shallow and Deep Groundwater in the Heilongdong Spring Basin, Northern China

Heilongdong Spring Basin (HSB) is located in a semi-arid region in northern China. In the past few decades, it has been influenced by anthropogenic activities. Currently, there is a lack of information about the impact on the hydrogeochemistry and groundwater quality of different aquifers. To address this concern, the present study used conventional hydrochemical diagrams, stable isotope analysis and multivariate statistical techniques to analyze hydrochemical characteristics and controlling factors of shallow and deep groundwater in the study area. The results showed that all groundwater samples were weakly alkaline. The shallow groundwater (SGW) was mainly composed of SO4-Ca and SO4·HCO3-Ca·Mg water types with high TDS values. However, the predominant water types of deep groundwater (DGW) were HCO3-Ca·Mg and HCO3·SO4-Ca·Mg types with relatively low TDS. The large majority of shallow groundwater had poor water quality, which was influenced by natural factors and anthropogenic activities, characterized by high concentrations of SO42−, NO3−, and Cl−. In contrast, the overall water quality of deep groundwater was good, mainly controlled by the natural background. Nonetheless, a few karst groundwater samples of DGW in runoff areas exhibited close hydraulic connections with SGW samples and presented contamination to a certain degree. Our research results provide a scientific basis for the utilization and protection of groundwater in different aquifers in northern China.

Penilaian Kerentanan Air Tanah terhadap Pencemaran dengan Menggunakan Metode DRASTIC di Daerah Imbuhan Cekungan Air Tanah Jakarta

The CAT Jakarta is a critical water resource that extends across several provinces in Indonesia, covering DKI Jakarta, Banten, and West Java. This basin comprises both recharge and discharge areas that support human settlements and various economic activities. The recharge area in CAT Jakarta covers 321.4 km2 and is densely populated, raising concerns about groundwater contamination. The study used the DRASTIC method to assess groundwater vulnerability, with seven parameters: Depth to Water Table (D), Net Recharge (R), Aquifer Media (A), Soil Media (S), Topography (T), Impact of the Vadose Zone (I), and Hydraulic Conductivity of the Aquifer (C). The vulnerability index obtained that 36.51% of the research area has a low vulnerability level, with values ranging from 101 to 119. The remaining 63.49% has a medium level of vulnerability, with values ranging from 120 to 157. These results suggest that the CAT Jakarta recharge area is at risk of contamination from pollutants with low to moderate intensity. Therefore, it is crucial to monitor and regulate activities that involve the use of groundwater in the area to prevent contamination. This study can guide policymakers and stakeholders in implementing effective management strategies for sustainable groundwater utilization in the CAT Jakarta basin.

Protecting Cape Town’s Groundwater from Fuel Stations: An In-Depth Analysis of Regulatory Requirements

In the face of mounting water supply challenges, Cape Town has increasingly turned to alternative sources, like groundwater. However, the utilisation of groundwater carries inherent risks, particularly the contamination stemming from land-based activities, such as fuel stations. Leaks from underground tanks at these stations represent a major global cause of groundwater pollution, and Cape Town is no exception. To safeguard public health and mitigate potential harm, it is imperative to examine the legal regulations governing fuel station development, assess measures for controlling their environmental impacts and evaluate strategies for managing the associated risks. This study aims to provide an exhaustive review of the regulatory framework concerning the environmental impacts of fuel stations, focusing on groundwater protection in Cape Town. A combination of desk research and interviews was employed to gather and analyse data. The findings show a deficiency in precautionary measures for safeguarding groundwater near fuel stations. Consequently, through this study, the existing legal framework’s effectiveness is called into question, with this study suggesting actions to address these identified shortcomings.

A Review of the Status, Effects, Prevention, and Remediation of Groundwater Contamination for Sustainable Environment

Most water systems that support ecosystems and feed humans are depleted or stressed. Aquifer characteristics, topography, subsurface activities, climate, and geochemical processes regulate groundwater availability, a reliable source of fresh water. Globally, agriculture, industries, and the domestic sector are the three major sectors that consume vast quantities of freshwater resources. Further anthropogenic activities, such as soil leaching, acid rain, fertilizer, pesticides, mining, and other industrial activities, resulted in the release of organic and inorganic pollutants that affected global water resources. In India, groundwater is used in huge quantities, resulting in groundwater depletion of 1 to 2 m a year. Low-income countries face many issues related to water pollution, and the availability of safe water is minimal. In 2019, deaths due to unsafe sanitation accounted for 2.2% of the total global deaths, amounting to 1.2 million people’s deaths. India recorded 6.6% of deaths due to unsafe sanitation in 2019. India and China accounted for around 90.41% and 60.4% of the groundwater utilization for agricultural purposes, respectively. In 2020, China and India utilized vast quantities of nutrients (nitrate and phosphate) for crop growth to enhance crop yield, resulting in the highest nitrate and phosphate concentrations in groundwater. Remediating contaminants from different sources requires knowledge of their concentration, behavior, cycling, and degradation pathways. According to safety guidelines, limiting and optimizing crop organic and inorganic fertilizer, pesticide waste disposal, and empty container disposal can reduce groundwater contamination. The present study summarized groundwater utilization in various sectors, potential sources of groundwater contamination impacts on human health and the environment, preventive measures, and mitigation methods to overcome groundwater pollution.

Unlocking the hidden potential: groundwater zone mapping using AHP, remote sensing and GIS techniques

Groundwater resource problems are increasing development and planning challenges due to climate change and overexploitation, necessitating assessments of their potential and productivity. The study area has been facing a groundwater level decline problem for many years, and these results can help increase the groundwater level in the basaltic rock area. In this research, we have worked on the demarcation and suitability of groundwater potential zones using GIS and Analytical Hierarchical Process (AHP) methods for the Urmodi River Basin. This research prepared eight thematic maps, that is, geomorphology, geology, drainage density, land use/land cover, elevation, lineament density and slope from satellite data and GIS methods, which play a primary factor in determining the proper groundwater potential zones. In this study, every thematic map was allocated weights depending on its specific characteristics and contribution to the groundwater potential capacity. The weights were determined using the AHP method, which considers the comparative significance of every layer about others. This weighting procedure allowed for a comprehensive assessment of the factors influencing groundwater potential in the Urmodi River basin. The resulting groundwater potential map was divided into four classes, that is, good, excellent, moderate, and poor. The study revealed that approximately 22.69% of the basin had excellent groundwater potential, 28.96% had good potential, 25.32% had moderate potential, and 22.92% had poor potential. These study findings suggest that a significant portion of the Urmodi River Basin exhibits good to moderate groundwater potential, indicating promising opportunities for sustainable groundwater utilization in the region. The groundwater potential zone map accuracy is 84% based on the Receiver Operating Characteristic (ROC) method. These results can have implications for sustainable groundwater resources and provide a framework for conducting similar assessments in other regions. The results can be more important for sustainable development goals and helpful in increasing groundwater levels in the area.

Spatial distribution of hydrochemical facies and its impact on groundwater utilization

Spatial distribution of hydrochemical facies and its impact on groundwater utilization

Study of Ground Water Behaviour in the Tons Pump Canal Command Area of Karchhana Tehsil, Prayagaraj

The study of groundwater behaviour in the Tons Pump canal command area of Karchhana Tehsil was carried out by utilizing ground water table data from 1997 to 2021 (25 years). During the study period, the pre-monsoon water table depth ranged from 3.25 m to 19.55 m, whereas the post-monsoon depth ranged from 1.71 m to 17.70 m. The water table trend in the study area during the pre-monsoon season revealed that at 83.55% of the locations having falling trend, while the remaining 16.45% experienced neither rising nor falling trend in the water table. During post-monsoon season, the water table was falling at 89.99% locations, with the rest 10.10% having neither rising nor falling trend. Therefore, the study found that the majority of the study area was experiencing water table fall due to over-exploitation of ground water in the both pre and post-monsoon season. Development stages of the groundwater utilization study from 1997 to 2021 showed that during the year 1997, all block of the study area was found under safe category.The overall utilisation of groundwater development stage was determined to be 44.93%. In 2021, the overall development stage of groundwater utilization was found to be 64.11% and the entire study area comes under safe category of groundwater utilization. It was found that groundwater levels in the study area were progressively rising. Therefore, it was necessary to enhance the surface water supply through canal systems to reduce the draft of groundwater as well as artificial groundwater recharge is necessary to arrest the groundwater at the desired level in the study area.

Quantitative prediction of the impact of deep extremely thick coal seam mining on groundwater

Reasonable exploitation and utilization of groundwater near coal mines in arid areas are of great significance to regional ecological and geological environment protection and sustainable mining of coal resources. It is a challenge to accurately predict the impact of deep coal mining on groundwater resources before mining. Adopting a coal mine in Inner Mongolia, China, as a case study, first, a well-fitted GA-BP neural network model was established to predict the height of the water-conducting fracture zone (WCFZ). The prediction results of WCFZ were verified by in-situ measured data of optical fiber and cable sensing systems. In Chinese coal mines, hydrogeological research generally lags behind geological exploration. Therefore, in the context of limited hydrogeological data, a variable weight model (VWM) for evaluating the potential groundwater yield of the objective aquifer (OAPGY) was established considering geological survey data before mining. Then, drilling pumping test data was used to verify the OAPGY predictions. Finally, groundwater resource protection measures were proposed according to the zoning results. The research results could provide a reference and basis for sustainable utilization of groundwater and reducing the impact of coal mining on groundwater resources.

Identification of Groundwater Potential Zones Using Remote Sensing and GIS Technique: A Case Study of the Ketungau Basin in Sintang, West Kalimantan

Groundwater is one of the most valuable natural resources in Sintang, but essential basic information regarding its properties and characteristics is presently unavailable. Currently, systemic and uniform investigations, as well as groundwater potential zones mapping are yet to be conducted within the framework of basin area units to support development activities. Therefore, this study aims to identify and map groundwater potential zones using remote sensing and GIS. The employed data were obtained from drainage density, slope steepness, straightness density, total rainfall, lithology, soil type, and land use land cover. The method applied was an interpretation of secondary data, which included a) identification and evaluation of criteria, b) data collection, c) preprocessing, and e) reclassification, while the analysis technique used was a weighted overlay. The results showed that the study location has five classes of groundwater potential zones, namely highly potential, potential, moderate, non-potential, and highly non-potential with areas of 120,754.08 ha (20.62%), 220,693.71 ha (37.69%), 109,668.44 ha ( 18.73), 93,404.38 ha (15.95%), and 41,068.31 ha (7.01%), respectively. Highly potential and groundwater potential zones were identified in the central, eastern, and western parts of the Ketungau basin. In contrast, the dominant non-potential and highly non-potential zones were found along the northern basin boundary. Based on the results, remote sensing and GIS approaches are practical tools for identifying groundwater potential zones, which can be used to determine policies related to groundwater utilization.

Determining the factors controlling the chemical composition of groundwater using geochemical methods and groundwater health assessment in Qixing Town, southwest China

Abstract Studies on groundwater quality and possible hazards to human health are important for improved groundwater utilization. This study explored the chemistry of groundwater in Qixing Town and the influencing factors. Statistical evaluation, ion correlation, Entropy-Weighted Water Quality Index (EWQI) assessment, and human health risk evaluation were conducted on data derived from 25 groundwater samples. The main groundwater chemistry types were HCO3–Na and HCO3–Ca. The results of ion and geological modeling analysis indicated that major ion concentrations were mainly determined by cation exchange. The study on the variation of heavy metal concentration in groundwater with depth shows that the heavy metal content in groundwater decreases first and then increases with the increase of depth, and the EWQI suggested that groundwater was suitable for drinking. The total carcinogenic health risks for Cr and As for both adults and children were higher than the highest permissible hazard value suggested by the United States Environmental Protection Agency (USEPA). The categorization of hazardous ingestion (HI) by the USEPA indicated a negligible non-carcinogenic hazard to human health by toxic metals. The results suggest the need to increase Cr and As contamination monitoring in shallow groundwater. This study can facilitate the rational development of groundwater resources.

Hydrogeophysical Investigation in Parts of the Eastern Dahomey Basin, Southwestern Nigeria: Implications for Sustainable Groundwater Resources Development and Management

Geoelectrical resistivity measurements were conducted in five locations within the eastern portion of the Dahomey basin for the purpose of subsurface evaluation and detecting saturated zones. The locations are Covenant University (L1), Bells University (L2), Oju-Ore-Ilogbo Road (L3), Obasanjo-Ijagba Road (L4), and Iyana Iyesi (L5). The study was carried out to avert the common challenges of drilling low-yield groundwater boreholes in the area. A total of 30 Vertical Electrical Soundings (VES) and five two-dimensional Electrical Resistivity Tomography (ERT) data sets have been acquired along the study areas. The geoelectrical resistivity results were integrated with the borehole logs to generate the spatial distribution of the subsurface lithologies in the area. The delineated subsurface lithologies include the topsoil (lateritic clay), clayey sand, sandy clay, fine silty sand, coarse sand, and shale/clay units. The fine silty sand and coarse sand units were identified as the two main aquifer units within the area. The depths to the upper aquifer unit in the area include 31.7–96.7 m, 38.5–94.0 m, 30.7–57.5 m, 39.1–63.4 m, and 46.9–57.5 m for locations L1, L2, L3, L4, and L5, respectively. At the same time, the depths to the lower aquifer unit in the area include 43.4–112.7 m, 52.2–108.0 m, 44.2–72.5 m, 53.7–78.5 m, and 63.5–72.9 m for locations L1, L2, L3, L4, and L5, respectively. The estimated hydraulic parameters for both aquifers show they are highly productive with mean porosity, mean hydraulic conductivity, and mean transmissivity of 20–22%, 12.4–17.0 × 10−2 m/s, 1.56–2.18 m2/s for the upper aquifer, and 48–50%, 371–478 × 10−2 m/s, 50.00–62.14 m2/s for the lower aquifer. By focusing on these aquifer systems during exploration, sustainable groundwater resources can be secured, providing relief to homeowners within the study area who might otherwise face the frustration of drilling unproductive and low-yield boreholes. However, it is crucial to consider the presence of sub-vertical faults in the study area, as these faults can significantly impact groundwater development and management. These sub-vertical structural faults may lead to changes in the permeability, hydraulic conductivity, and transmissivity of the delineated aquifers, affecting their productivity across the divide and ultimately influencing the overall water availability in the area. Careful consideration of these geological factors is essential for effective aquifer management and sustainable groundwater utilisation.

Assessment of the sustainability of groundwater utilization and crop production under optimized irrigation strategies in the North China Plain under future climate change

Over-exploitation of groundwater due to intensive irrigation and anticipated climate change pose severe threats to the water and food security worldwide, particularly in the North China Plain (NCP). Limited irrigation has been recognized as an effective way to improve crop water productivity and slow the rapid decline of groundwater levels. Whether optimized limited irrigation strategies could achieve a balance between groundwater pumping and grain production in the NCP under future climate change deserves further study. In this study, an improved Soil and Water Assessment Tool (SWAT) model was used to simulate climate change impacts on shallow groundwater levels and crop production under limited irrigation strategies to suggest optimal irrigation management practices under future climate conditions in the NCP. The simulations of eleven limited irrigation strategies for winter wheat with targeted irrigations at different growth stages and with irrigated or rainfed summer maize were compared with future business-as-usual management. Climate change impacts showed that mean wheat (maize) yield under adequate irrigation was expected to increase by 13.2% (4.9%) during the middle time period (2041–2070) and by 11.2% (4.6%) during the late time period (2071–2100) under three SSPs compared to the historical period (1971–2000). Mean decline rate of shallow groundwater level slowed by approximately 1 m a−1 during the entire future period (2041–2100) under three SSPs with a greater reduction for SSP5–8.5. The average contribution rate of future climate toward the balance of shallow groundwater pumping and replenishment was 62.9%. Based on the simulated crop yields and decline rate of shallow groundwater level under the future climate, the most appropriate limited irrigation was achieved by applying irrigation during the jointing stage of wheat with rainfed maize, which could achieve the groundwater recovery and sustainable food production.

Control of Structural Landform Evolution on Karst Groundwater Cycle in a Large-Scale Anticlinorium.

Structural landform evolution and hydrogeochemical analyses are crucial for understanding the characteristics of karst groundwater systems and the development of deep karst formed by complex aquifers in a tectonic collision zone. Detailed structural landform evolution analysis was carried out along the large-scale anticlinorium to investigate the temporal evolution of karst aquifer systems and karstification. Results showed that the tectonic activity included weak horizontal compression and slow vertical uplift during the Triassic to Middle Jurassic, forming a denuded clastic platform. This period was mainly preserved in the geological record as burial karst. From the Late Jurassic to the Early Cretaceous, the study area was strongly compressed by S-N-trending stress, and developed E-W-trending high-angle imbricate thrust structures, which controlled the formation of folded and fault-blocked mountains. Vertical multilayered strata underwent a strong horizontal extrusion, forming a large-scale anticlinorium with secondary folds and faults. With the exposure of carbonate rocks due to rapid crustal uplift, karst began to develop, forming a vertical multilayer karst aquifer system and controlling the distribution of karst groundwater. The Fangxian faulted basin was formed from the Late Cretaceous to the Paleogene, whereby landforms were dominated by intermountain basins. Slow crustal uplift caused the retreat of the denudation line to the east, leading to an increase in hydrodynamic conditions and karstification, and the initiation of early karst groundwater systems. Since the Neogene, intermittent and rapid crustal uplift has led to the deepening of rivers, resulting in the formation of peak clusters and canyons, the development of deep karst, and the complete formation of karst groundwater systems. Combined with hydrogeochemical and borehole data, local, intermediate, and regional karst groundwater systems were identified. It has vital significance to the geological route selection or construction of deep-buried tunnels and the utilization of karst groundwater.

Spatial-Temporal Patterns of Shallow Groundwater Levels in the Yellow River Delta, China

Analysis of the various hydrologic features responsible for the spatial and temporal variability in large scale subsurface systems is a critical component of water resources engineering and management. Traditionally, modeling large-scale groundwater flow patterns includes simulations with underlying parameter estimations and associated overarching assumptions. More recently, subsurface hydrologists are using empirical orthogonal function analysis to separate and quantify the primary hydrologic components contributing to observed regional and local-scale groundwater hydrodynamics. In this case study, modern spatiotemporal geostatistics plus primary hydrologic component analysis were conducted on spatially and temporally distributed groundwater levels measured in the Yellow River Delta. The results demonstrate the significant interplay between surface water hydrodynamics, overall groundwater quality, and groundwater utilization at the local scale, plus the significant impact of regional-scale aquifer recharge on groundwater level seasonal variation, largely driven by precipitation events. With increased accessibility to remote sensing data, additional research using these or similar statistical approaches to interpolate, compress, and decompose those features driving subsurface fluid-flow variability will prove to be highly beneficial to water resource engineers and managers.

Ground water potential assessment and sustainable management.

This paper presents the potential groundwater assessment and sustainable management in the selected study area. It is the most preferred water source in all climatic zones for its convenient availability, drought dependability, excellent quality, and low development cost. The rural areas, which account for more than 85% of the country's population, encountered a shortage of potable water supply which can be solved by proper groundwater utilization. For the present study area, the groundwater potential is assessed and analysed. Thus, the study area falls into four potential groundwater zones ranging from poor to high. However, the current groundwater management practices in the study area are poor. Despite the pervasive and devastating challenges, immediate and proper responses have not yet been given to the problem. Thus, such frustrating threats and challenges have initiated the researcher to work in the project area.

Groundwater quality characteristics and health risk assessment in the valley plain area of the western Qinghai–Tibet plateau

Accurate evaluation of groundwater chemistry, quality, and human health risk could provide detailed and robust evidence of groundwater utilization. Gaer County is an important residential area in western Tibet. A total of 52 samples were collected from the Shiquan River Basin in Gaer County in 2021. Principal component analysis, ratiometric analysis of major ions, and geochemical modeling were conducted to clarify the characteristics of hydrogeochemical compositions and the controlling factors. The groundwater chemistry type is dominated by HCO3–Ca, and its ion concentration from high to low is Ca2+ > Na+ > Mg2+ > K+ and HCO3− > SO42− > Cl− > NO3− > F−. The groundwater compositions were determined by calcite and dolomite dissolution with cation exchange reaction. The human activity causes nitrate contamination, while arsenic contamination is attributed to surface water recharge. According to the Water Quality Index, 99% of the samples meet the requirements of drinking water. Groundwater quality is affected by the arsenic, fluoride, and nitrate concentrations. According to the human health risk assessment model, the cumulative noncarcinogenic risk (HITotal) values for children and the CR values of arsenic (CRArsenic) for adults are higher than 1 and 1E-6, respectively, which are unacceptable risk values. Therefore, appropriate remedial measures are recommended to reduce nitrate and arsenic concentrations in groundwater sources for protecting against further health risks. This study can provide theoretical support and effective groundwater management experience for ensuring groundwater safety in Gaer County and other similar regions around the world.

Optimizing Rotation Forest-Based Decision Tree Algorithms for Groundwater Potential Mapping

Groundwater potential mapping is an important prerequisite for evaluating the exploitation, utilization, and recharge of groundwater. The study uses BFT (best-first decision tree classifier), CART (classification and regression tree), FT (functional trees), EBF (evidential belief function) benchmark models, and RF-BFTree, RF-CART, and RF-FT ensemble models to map the groundwater potential of Wuqi County, China. Firstly, select sixteen groundwater spring-related variables, such as altitude, plan curvature, profile curvature, curvature, slope angle, slope aspect, stream power index, topographic wetness index, stream sediment transport index, normalized difference vegetation index, land use, soil, lithology, distance to roads, distance to rivers, and rainfall, and make a correlation analysis of these sixteen groundwater spring-related variables. Secondly, optimize the parameters of the seven models and select the optimal parameters for groundwater modeling in Wuqi County. The predictive performance of each model was evaluated by estimating the area under the receiver operating characteristic (ROC) curve (AUC) and statistical index (accuracy, sensitivity, and specificity). The results show that the seven models have good predictive capabilities, and the ensemble model has a larger AUC value. Among them, the RF-BFT model has the highest success rate (AUC = 0.911), followed by RF-FT (0.898), RF-CART (0.894), FT (0.852), EBF (0.824), CART (0.801), and BFtree (0.784), respectively. Groundwater potential maps of these 7 models were obtained, and four different classification methods (geometric interval, natural breaks, quantile, and equal interval) were used to reclassify the obtained GPM into 5 categories: very low (VLC), low (LC), moderate (MC), high (HC), and very high (VHC). The results show that the natural breaks method has the best classification performance, and the RF-BFT model is the most reliable. The study highlights that the proposed ensemble model has more efficient and accurate performance for groundwater potential mapping.