Acid in situ leaching (ISL) is a common approach to the recovery of uranium in the subsurface. In acid ISL, there are numerous of chemical reactions among the injected sulfuric acid, groundwater, and porous media containing ore layers. A substantial amount of radioactive elements including U, Ra, Rn, as well as conventional elements like K, Na, and Ca, and trace elements such as As, Cd, and Pb, are released into the groundwater. Thus, in acid ISL, understanding the transport and reactions of these substances and managing pollution control is crucial. In this study, a three-dimensional reactive transport modeling (RTM) using TOUGHREACT was built to investigate the dynamic reactive migration process of UO22+, H+, and SO42− at a typical uranium mine of Bayan-Uul. The model considering the partial penetration through wellbore in confined aquifer and complex chemical reactions among main minerals like uranium, K-feldspar, calcite, dolomite, anhydrite, gypsum, iron minerals, clay minerals, and other secondary minerals. The results show that after mining for one year, from the injection well to the extraction well, the spatial distribution of uranium volume fraction does not consistently increase or decrease, but it decreases initially and then increases. After mining for one year, the concentration front of UO22+ is about 20 m outside the mining area, the high concentration zone is mainly inside the mining area. The concentration front of H+ is no more than 50 m. SO42− is the index with the highest concentration among the three indexes, the concentration front of SO42− is no more than 100 m. The concentration breakthrough curve of the observation well 10 m from the mining area indicates that the concentrations of the three indicators began to significantly rise approximately after mining 0.05 years, reached the maximum value after mining 0.08 to 0.1 years, and then stabilized. The parameter sensitivity of absolute permeability and specific surface area of minerals shows that the concentration of H+ and SO42− is positively correlated with absolute permeability. The concentration of H+ is negatively correlated with the specific surface area of calcite, anhydrite, K-feldspar, gypsum, hematite, and dolomite. The concentration of SO42− is positively correlated with the specific surface area of K-feldspar and Hematite, and negatively correlated with the specific surface area of calcite, anhydrite, gypsum, and dolomite. The influence analysis of pumping ratio and non-uniform injection ratio shows that the non-uniform injection scheme has a more significant impact on pollution control. The water table, streamline, capture envelope, and the concentration breakthrough curve of five schemes with different pumping ratios and non-uniform injection ratio were obtained. The water table characteristics of five schemes shown that increase in the pumping ratio and the non-uniform injection ratio, the water table convex near the outer injection well is weakened and the groundwater depression cone near the pumping well is strengthened. This characteristic of water table exerts a notable retarding influence on the migration of pollutants from the mining area to the outside. For the scheme with a pumping ratio is 0 (the total pumping flow rate is equal to the total injection flow rate) and a non-uniform injection ratio is 0 (the flow rate of inner injection well Q1,Q2,Q3 is equal to the flow rate of outer injection well Q4,Q5,Q6), the streamline characteristics shown that a segment of the streamline of is diverging from inner region to the outer region. For other schemes, the streamline exhibits a convergent feature. It is indicated that by increasing the pumping ratio and non-uniform injection ratio, a closure flow field can be established, confining the groundwater pollutants resulting from mining within the capture envelope. Hence, the best scheme for preventing pollution migration is the scheme with a pumping ratio is 0 (the total pumping flow rate is equal to the total injection flow rate) and a non-uniform injection ratio is 0.1 (the flow rate of inner injection well Q1,Q2,Q3 is 10% more than the flow rate of outer injection well Q4,Q5,Q6). In this scheme, the optimal stable concentration of UO22+, H+, and SO42− at the observation well obtained by RTM is lower than other schemes, and the values are 0.00316 mol/kg, 2.792 (pH), and 0.0952 mol/kg. The inner well injection rate is 194.09 m3/d, the outer well injection rate is 158.89 m3/d, and the pumping rate is 264.00 m3/d. Numerical simulation analysis suggests that a scheme with a larger non-uniform injection ratio is more conducive to the formation of a strong hydraulic capture zone, thereby controlling the migration of pollutants in the acid ISL. A reasonable suggestion is to adopt non-uniform injection mining mode in acid ISL.

The reaction between the lixiviant and the minerals in the aquifer of In-situ uranium leaching (ISL) will result mineral dissolution and precipitation. ISL will cause changes in the chemical composition of groundwater and the porosity and permeability of aquifer, as well as groundwater pollution. Previous studies lack three-dimension numerical simulation that includes a variety of minerals and considers changes in porosity and permeability properties simultaneously. To solve these problems, a three-dimensional reactive transport model (RTM) which considered minerals, main water components and changes in porosity and permeability properties in Bayanwula mine has been established. The results revealed that: (1) Uranium elements were mainly distributed inside the mining area and had a weak trend of migration to the outside. The strong acidity liquid is mainly in the mining area, and the acidity liquid dissolved the minerals during migrating to the outside of the mining area. The concentration front of major metal cations such as K+, Na+, Ca2+ and Mg2+ is about 150m away from the boundary. (2) The main dissolved minerals include feldspar, pyrite, calcite, sodium montmorillonite and calcium montmorillonite. Calcite is the most soluble mineral and one of the sources of gypsum precipitation. Other minerals will dissolve significantly after calcite is dissolved. (3) ISL will cause changes in porosity and permeability of the mining area. Mineral dissolution raises porosity and permeability near the injection well. Mineral precipitation reduced porosity and permeability near the pumping well, which can plugging the pore throat and affect recovery efficiency negatively.

Uranium extraction through the in situ leaching method stands as a pivotal approach in uranium mining. In an effort to comprehensively assess the repercussions of in situ uranium leaching on groundwater quality, this study collected 12 representative groundwater samples within the Bayan-Uul mining area. The basic statistical characteristics of the water samples showed that the concentrations of SO42− and total dissolved solids (TDS) were relatively high. Through the use of cluster analysis, the water samples were categorized into two distinct clusters. Seven samples from wells W-d, W-u, N01, W10-2, W08-1, W10-1, and W13-1, situated at a considerable distance from the mining area, were grouped together. Conversely, five samples from wells W08-2, W13-2, W01-1, W02-2, and the pumping well located in closer proximity to the mining area, formed a separate cluster. A decision tree-based machine learning approach was employed to discern the influence of various hydrochemical indicators in forming these clusters, with results indicating that SO42− exerts the most substantial influence, followed by Ca2+. The mineral saturation indices from geochemical modeling indicated that, as the distance from the mining area increased, the trend of calcium minerals changed from dissolution to precipitation; iron minerals were in a precipitation state, and the precipitation trend was gradually weakening. In light of these findings, it is clear that in situ uranium leaching significantly impacted the groundwater in the vicinity of the mining area. The prolonged consumption of groundwater sourced near the study area, or its use for animal husbandry, poses potential health risks that demand heightened attention.

Groundwater holds an important role in the water supply in Linyi city, China. Investigating the hydrochemical characteristics of groundwater, and revealing the factors governing groundwater geochemistry, is a primary step for ensuring the safe and rational exploitation of groundwater resources. This study used a self-organizing map (SOM) and multivariate statistical methods to assess groundwater quality in the urban area of Linyi city. Based on the hydrochemical dataset consisting of nine parameters (i.e., pH, Ca2+, Mg2+, Na+, K+, HCO3−, Cl−, SO42−, and NO3−) from 89 groundwater samples, the SOM was first applied to obtain the weight vectors of the output nodes. Hierarchical cluster analysis (HCA) was used for organizing the nodes into four clusters. The node cluster indices were then remapped to the groundwater samples according to the winner node for each sample. The hydrochemical characteristics and factors controlling the groundwater geochemistry of the four clusters were analyzed using principal component analysis (PCA) and graphical methods including Piper and Gibbs diagrams, as well as binary plots of the major ions in groundwater. Results indicated that groundwater geochemistry in this area is primarily governed by water–rock interactions, such as the dissolution of halite, calcite, and gypsum, along with the influence of municipal sewage and the degradation of organic matter. This study demonstrates that the integration of an SOM and multivariate statistical methods improves the understanding of groundwater geochemistry and hydrochemical evolution in complex groundwater flow systems impacted by utilization.

Objective The Dupuit model of well flow is a classical steady-state well flow model for a homogeneous unconfined aquifer in a round island. However, it does not consider the widely existing infiltration recharge from precipitation, and is also inapplicable for stratified heterogeneous aquifer systems. Therefore, it must be modified to address these issues. Methods On the basis of the revised Dupuit well flow model which incorporates infiltration recharge, this study further extended its application to a stratified heterogeneous unconfined aquifer. The Girinskii's potential function was used to construct the differential equations for the radial groundwater flow according to the water balance principle, and the analytical solutions satisfying the boundary conditions are then obtained as formulas of the flow rate, water table and groundwater divide. Taking the bilayer structure as an example, typical groundwater level curves with respect to 30 scenarios of different parameter values were investigated. A special phenomenon was found in which the curves of different hydraulic conductivities intersect at a single point, which could also be proven in theory. This analytical model still adopted the Dupuit assumption and did not consider the "hydraulic jump" phenomenon on the wall of the pumping well. To check the impact of these constraints on the applicability of the analytical formulas, a two-dimensional numerical model for axially symmetric seepage was built for comparison. Results As indicated by the results, the relative error of the groundwater level estimated from the analytical solution is generally less than 4%, except for the zone near the pumping well. On the groundwater divide, where the Dupuit assumption is mostly invalid, the relative errors of the analytical solution to both the distance and height of the divide are smaller than 0.1%. Conclusion The Dupuit assumption does not significantly influence applicability of the analytical model.

Acid in-situ leaching (ISL) is a common approach to the recovery of uranium in the subsurface. As some toxic and harmful substances might be produced by the chemical reactions among the injected sulphuric acid, the groundwater, and the porous media during leaching processes, the pollution control of the mining plan for ISL is important. In this study, a three-dimensional reactive transport modeling (3DRTM) was applied to decide the pollution control mining plan, considering the partial penetration through wellbore in confined aquifer and complex chemical reactions between main minerals. Based on the 3DRTM, different pumping ratio and non-uniform injection schemes were compared. The results show that the preferential pollution control mining plan is non-uniform injection ratio equal 0.1. By analyzing the characteristics of water table and streamline, it is concluded that the scheme has a strong hydraulic capture effect. In this scheme, the concentration of UO22+, H+, SO42- obtained by 3DRTM is lower. The inner well injection rate is 194.09 m3/d, the outer well injection rate is 158.89 m3/d, and the pumping rate is 264.00 m3/d. A reasonable suggestion is to adopt non-uniform injection mining mode in ISL.

Graphical methods have been widely used for visualization, classification, and interpretation of aqueous geochemical data to obtain a better understanding of surface and subsurface hydrologic systems. This method note presents WQChartPy, an open-source Python package developed to plot a total of 12 diagrams for analysis of aqueous geochemical data. WQChartPy can handle various data formats including Microsoft Excel, comma-separated values (CSV), and general delimited text. The 12 diagrams include eight traditional diagrams (trilinear Piper, Durov, Stiff, Chernoff face, Schoeller, Gibbs, Chadha, and Gaillardet) and four recently proposed diagrams (rectangle Piper, color-coded Piper, contour-filled Piper, and HFE-D) that have not been implemented in existing graphing software. The diagrams generated by WQChartPy can be saved as portable network graphics (PNG), scalable vector graphics (SVG), or portable document format (PDF) files for scientific publications. Jupyter and Google Colab notebooks are available online to illustrate how to use WQChartPy with example datasets. The geochemical diagrams can be generated with several lines of Python codes. Source codes of WQChartPy are publicly available at GitHub (https://github.com/jyangfsu/WQChartPy) and PyPI (https://pypi.org/project/wqchartpy/).

为计算洞庭湖平原水资源并分析未来气候变化对研究区水资源量的影响,基于2010-2013年洞庭湖平原实测水文气象数据以及DEM、土地利用、土壤类型等数据,利用ArcSWAT构建了洞庭湖平原分布式水文模型进行径流模拟,对土壤水、河道径流和地下水分别进行了水均衡分析,并通过设置5种不同的未来气候变化情景,研究了气候变化对水资源量的影响.结果表明:①洞庭湖平原年均降雨量为254.27×108 m3,实际蒸散发量占总补给量的59.96％,土壤对地下水的补给量占总补给量的30.93％,地表径流量和侧向流量占总补给量的20.37％,因此大气降雨的主要排泄方式是蒸散发,在降雨量变化幅度较大时研究区内土壤对地下水的补给比地表径流受降雨的影响更大,土壤水呈负均衡;②均衡期内地表水年均资源量为120.84×108 m3,基流量对河道径流的补给量(57.13％)大于地表径流对河道径流的补给量(41.12％);该流域地下水补给的主要来源是土壤对地下水的补给,模拟期内年均地下水资源量为78.64×108 m3,地下水呈正均衡;③地表径流量、河道径流总量、基流量与气温呈负相关关系,与降雨量呈正相关关系,不同气候变化情景下,降雨量、地表水资源量和地下水资源量的变化明显,当降雨量减少10％(年均降雨量减少118.62 mm)、温度升高1℃时,年均地表水资源量减少19.18×108 m3,地下水资源量减少2.7×108 m3,而当降雨量增加10％(年均降雨量增加118.62 mm)、温度下降1℃时,年均地表水资源量增加23.77×108 m3,地下水资源量增加4.2×108 m3.

Due to high toxicity, arsenic is regarded as a major global environmental pollutant. The present study is investigated the potential factors influencing to elevate concentration of arsenic in groundwater, surface water, and soil of the Dongting basin. The arsenic contamination potential prediction map and categories were developed using various GIS techniques such as Ordinary Kriging and the Quantile method. Then the “Raster calculator” tool was applied to verify the impact of the factors on arsenic. Eighty-four single-factor, bi-factor, and multi-factor models were established to investigate effective combinations among factors of each phase. Additionally, statistical tests were computed to evaluate arsenic between classes and factors. The arsenic value varies in groundwater from 0.0001 to 0.1582 mg/l, while in surface water between 0.0001–0.0287 mg/l and soil sediments range from 1.8–45.69 mg/kg. JunShan and GongAn groundwater resources have been identified as posing a high risk to human health. The single factors showed the best match frequency of arsenic with a population density of 66.86% in water and land use depicted match frequency of arsenic 73.19% in soil. The statistical calculations with percentage frequency factors also depicted positive trends. The correlation of the factors with arsenic in soil and water showed slow oxidation and reduction in the groundwater system. Treated portable water could be the best option to reduce the health risk of the local community.

Carbon dioxide (CO 2 ) storage capacity is the main criterion for assessing CO 2 geological storage. Based on actual data from the Shiqianfeng formation in the Ordos Basin, three-dimensional (3D) models were built using the TOUGHVISUAL visualization software and simulated using the TOUGH2 integral finite difference modeling code with the ECO2N fluid property module to explore the impact of formation attributes (formation slope) and controllable factors (injection temperature) on CO 2 storage capacity. A total of 16 schemes were designed, with four injection temperatures (24 ℃, 31 ℃, 38 ℃, and 45 ℃) and four formation slopes (0°, 5°, 10°, and 15°). Simulation results showed that the injection temperature and formation slope both had a significant influence on CO 2 storage capacity. The impact of injection temperature on the total storage amount was more obvious than that of the impact of formation slope. A higher injection temperature resulted in a greater total storage amount. Increasing the formation slope and injection temperature increased the gas-phase, dissolved-phase, and total CO 2 storage amounts in the upper left section of the injection well, but decreased them in the lower right part of the injection well. The impact of formation slope on the conversion rate from gas-phase CO 2 to dissolved-phase CO 2 was more obvious than the impact of injection temperature. A steeper formation slope resulted in a higher conversion rate. A smaller formation slope and a higher injection temperature should be selected to store CO 2 .

地下水是雷州半岛的重要供水水源.以雷州半岛地下水为研究对象,采集并测试了47个地下水样品中的常规水化学组分,综合运用Gibbs图解法、Piper三线图、离子比例法等分析方法,研究该区域地下水中主要离子的来源及其控制因素.结果 表明:研究区地下水中主要阳离子和阴离子分别为Na+和HCO3-;浅层孔隙水水化学类型以Cl· SO4混合阳离子型水为主,HCO3·Cl-Na·Ca型水次之,中、深层孔隙水水化学类型主要为HCO3-Na型水,HCO3-Na· Mg型水和HCO3-Na·Ca型水次之,孔洞裂隙水水化学类型为Cl· HCO3-Mg· Na型水和Cl· HCO3-Na型水;影响研究区内地下水的主要水文地球化学过程是水-岩相互作用,地下水中离子比值进一步说明硅酸盐矿物的溶解作用是影响研究区地下水水化学组分的主要控制因素,同时浅层孔隙水水化学组分受到一定程度蒸发浓缩作用的影响,离子交换也是影响中、深层孔隙水的重要水文地球化学过程;硝酸盐在浅层水中普遍存在,37.5％的浅层孔隙水样品中出现NOa污染.该研究结果可为地下水资源合理开发与利用提供一定的借鉴.

Arsenic is considered a poison because of its seriously toxic effects on the human body; elevated concentrations of arsenic in drinking water have been reported in different parts of the world. Investigating the arsenic distributions in soil, surface water (SW), and groundwater (GW) is an interesting topic of research, along with probing its correlations with local factors of the ecosystem and other hydrogeochemical parameters. This study mainly aims to investigate the impacts of various factors on elevated arsenic concentrations in water and soil. The following factors are assessed for their relationship to the propagation of arsenic in Jianghan Plain, which is the study area: population density, pumping rate, rain, land use, surface elevation, water level, and heavy metal contamination. The arsenic contamination potential prediction map and categories were developed using GIS-based techniques, such as ordinary kriging and quantile methods. Then, the “raster calculator” tool was applied to verify the impacts of the abovementioned factors on arsenic concentration. Eighty-four single-factor, bi-factor, and multi-factor models were established to investigate the effective combinations among the factors. Land use and pumping rate were identified from the soil through an equal frequency tool, whereas water population density and pumping rate were obtained with high matching percentages. The arsenic concentrations varied in the ranges of 0.0001–0.1582 mg/L in GW, 0.0003–0.05926 mg/L in SW, and 1.820–46.620 mg/kg in soil sediment. The single factors showed the best equal frequency of arsenic concentration in water for population density (68.62%) and in soil for land use (65.57%) and pumping (63.66%). Statistical calculations with percentage frequency factors also depicted a positive trend. Arsenic was reported to have high correlations with Fe in GW (r2 = 0.4193), with EC in SW (r2 = 0.4817), and with Cu in soil (r2 = 0.623). It is observed that the alkaline behaviors of water bodies are associated with arsenic mobility. Elevated arsenic values were observed in grids along surface flows with high anthropogenic activities and urbanization. Additionally, low concentrations of Fe depicted reduced activities in aquifer systems. Filtering drinking water as well as controlling the suspected sources and factors affecting concentrations of arsenic in the three phases are options for reducing the health risks of the local populations.

Effectively and efficiently protecting groundwater resources requires a better understanding of spatial and temporal patterns of groundwater geochemistry and their controlling factors (natural and anthropogenic). In this study, to reveal the spatial and temporal patterns of groundwater geochemistry, we explored two clustering methods, i.e., the one-way clustering implemented by using the hierarchical cluster analysis (HCA) and the co-clustering implemented by using the Bregman block average co-clustering algorithm with I-divergence (BBAC_I). The one-way clustering identifies the spatial and temporal patterns separately, whereas the co-clustering identifies the spatial and temporal patterns simultaneously. The two clustering methods were applied to 9 geochemical parameters of 329 groundwater samples collected over the period of 2000 - 2017 from 19 monitoring wells located in the unconfined aquifer of the Dagu River Basin, China. As a first attempt of applying BBAC_I co-clustering to groundwater geochemical data, results show that it is feasible to use the BBAC_I co-clustering method for simultaneously identifying location and timestamp clusters. The clusters identified by the HCA one-way clustering and the BBAC_I co-clustering are similar. Based on the clustering results, two geochemical zones and three geochemical periods of groundwater geochemistry were delineated. The controlling factors of the two geochemical zones are residual seawater freshening, elevated NO3- concentrations, and silicate weathering. The temporal changes between the three geochemical periods are caused by a heavy rainfall in July 2011 after a one-year drought and by ceased flow of the Dagu River after 2013 due to drought conditions. The impacts of drought conditions and anthropogenic activities in the Dagu River Basin on groundwater geochemistry should be considered for managing groundwater resources of the basin.

粤港澳大湾区是中国开放程度最高、经济活力最强的区域之一,在国家发展大局中具有重要的战略地位,大湾区未来的发展离不开水资源的支撑和良好的水生态环境.近年来,随着大湾区经济的快速发展,人口激增,需水量上升,水资源环境问题也日益突出,水安全保障程度不足;地下水是水资源的重要组成部分,具有水量稳定、水质较好的特点,可作为重要的应急备用水源.本文从地下水资源着手,系统梳理了大湾区水资源环境条件、地下水资源状况、特征和开发利用潜力,并提出了应急后备水源地建议,得到以下认识:(1)地下水可划分为松散岩类孔隙水、碳酸盐岩岩溶水、基岩裂隙水三大类,其中松散岩类孔隙水和基岩裂隙水分布最广;(2)湾区内地下水水化学类型较为复杂,丘陵山区以HCO3-Na型、HCO3-Ca型及HCO3-Na+Ca型为主,冲积平原及山间盆地以HCO3+Cl-Na型及HCO3+Cl-Na+Ca型为主,三角洲地区以Cl-Na型微咸-咸水为主;(3)西江、北江及东江干流构成湾区内地下水排泄的总渠道,各支流为地下水的局部排泄基准面,地下水动态变化具季节性特征;(4)地下水整体水质较好,I-Ⅲ类水占比高达66.25％,从丘陵山区到三角洲平原,水质呈变差趋势,尤其在广州、江门、中山、东莞等城市周边水质较差,超标因子主要为氨氮、氯化物、氟化物、硫酸盐等,三角洲地区发育大量"铁质水"和"氨氮水",水质性缺水问题突出;(5)地下水开发利用程度很低,东莞及中山等城市基本未开发利用地下水,在各类地下水中,碳酸盐岩岩溶裂隙水具有规模开采的开发利用潜力;(6)综合分析相关资料,提出将广花盆地等10处富水块段作为应急水源地备选,经初步计算每年可为大湾区提供约4.18亿m3的应急水源保障.为应对突发性水质污染及极端干旱气候等大规模供水危机,保障粤港澳大湾区用水安全,促进大湾区高质量发展,建议加强大湾区的基础水文地质调查工作,掌握地下水的水位、水质、水量的动态变化特征,精准计算可用于应急备用开采的地下水储存量.

Cluster analysis is a valuable tool for understanding spatial and temporal patterns (e.g., spatial zones) of groundwater geochemistry. To determine cluster numbers and cluster memberships that are unknown in real-world problems, a number of methods have been used to assist cluster analysis, among which graphic approaches are popular and intuitive. This study introduced, for the first time, the t-distributed Stochastic Neighbor Embedding (t-SNE) method as a graphic approach to assist cluster analysis for groundwater geochemistry data. The hierarchical cluster analysis (HCA) was applied to original groundwater geochemistry data, and t-SNE was used to help determine the number of cluster and cluster memberships. Afterward, t-SNE was used to help delineate spatial zones of groundwater geochemistry. The t-SNE-based cluster visualization was compared to the visualization based on principal component analysis (PCA). By applying HCA, PCA, and t-SNE to three geochemical datasets (Oslo transect, Taiyuan karst water, and Jianghan Plain groundwater datasets, which are characterized by different number of samples and features collected across different space and time scales), we found that t-SNE outperformed PCA to assist HCA as a promising tool for helping determine the number of HCA clusters and delineate spatial zones of groundwater geochemistry. It should be noted that t-SNE alone cannot be used for cluster analyses, partly because t-SNE visualization depends on a hyperparameter called perplexity that is a priori unknown for real-world problems. The perplexity values used in this study were determined empirically, and a small value of 0.1 was used for the Taiyuan karst water dataset with 14 samples. For the other two datasets with hundreds of samples, the corresponding perplexity values were 20 and 30, within the range of 5 50 commonly used in t-SNE.

The recharge and discharge of groundwater are mainly vertical surface infiltration recharge, evaporation discharge (evaporation can be shown as negative value of infiltration) and lateral surface water recharge and discharge. One of the most basic problems in hydrogeology is the evaluation criteria of sustainable exploitation of groundwater, which involves the increment of recharge and the decrease of discharge. Therefore, the prediction model of groundwater exploitation must include the above two kinds of recharge and discharge factors, otherwise the evaluation of groundwater cannot meet the requirements. However, the classic Theis unsteady well flow model (1935) only involves the recharge and discharge of the side boundary, and does not considers the surface infiltration recharge of the upper boundary, even when groundwater is pumped near the river. In this way, the analytical model cannot be basically used for prediction, and can only be used for well flow test to obtain the aquifer parameters in dry season. Therefore, the goal of this paper is to develop the Theis unsteady well flow model with surface infiltration recharge. For the problem of phreatic flow, the equation of groundwater flow cannot be established by using head as the dependent variable in a confined aquifer. We use the potential function of the second linearization method to establish groundwater flow equation in the phreatic aquifer. For the solution of the generalized mathematical model of the complex hydrogeological problem with rainfall infiltration and a pumping well, we adopt the method of decomposing it into several simple sub-models and synthesizing them into the solution of the original complex mathematical model. Based on the principle of mass conservation and assuming that the seepage obeys the Darcy’s law and satisfies the Dupuit's assumptions, the differential equation of groundwater flow is established. Then, for the well flow problem with uniform and stable infiltration recharge in two parallel rivers and two kinds of strip regions formed by a river parallel to an impermeable boundary, the general equation of groundwater flow and several kinds of water table equations under specific conditions and their flux equations are obtained. In addition, the “boundary to boundary reflection method” is proposed and applied to solve the same problem in a strip of region between a river boundary in parallel to an impermeable boundary, which reduces many derivation processes. Finally, as a preliminary application of the above theoretical results, it is also an important application, that is, there is a pumping well near the river whose water quality cannot meet the requirements, and the critical flux equation of the pumping well is calculated on the premise of not absorbing the river water. The important and concise relation equation is obtained. The equation can also be used to calculate the critical pumping rate of pumping wells in coastal areas without seawater intrusion. In this paper, the groundwater flow network diagram at a certain time in the process of unstable well flow under the above conditions is given. Compared with the flow network of well flow near the river, which is commonly seen in the literature, the flow network has obvious characteristics.

Complex factors can affect carbon dioxide (CO2) geological storage efficiency and capacity. In this paper, a three-dimensional (3D) conceptual model of the Shiqianfeng formation in the Ordos basin was established (a total of 16 sets of schemes) to study the influence of injection temperature on CO2 storage efficiency and migration safety in the sloping formation with a fault. In addition, storage capacity is investigated for CO2 storage site selection. The results show that injection temperature and formation slope have a significant effect on CO2 storage efficiency. Faulting provides a possible channel for CO2 leakage. High injection temperature is more likely to cause CO2 leakage in the sloping formation. When the injection temperatures are 11, 31.5, 51 and 71 degrees C in the 15 degrees slope formation, the time points of CO2 leakage are 200,170,150 and 140 years, respectively. The lower injection temperature results in a higher CO2 concentration near the injection well and a closer migration distance of dissolved CO2. The larger the formation slope is, the farther the dissolved CO2 migration distance will be. The higher injection temperature results in a greater gas phase, dissolved phase, and total CO2 storage amount in the whole formation. The larger the formation slope is, the smaller the CO2 storage capacity will be for CO2 injected over 20 years. However, the larger formation slope resulted in a smaller gas phase and larger storage amount of the dissolved phase CO2 for CO2 migration after 140 years. The influence of the formation slope on the dissolved CO2 migration safety is more obvious than that of injection temperature. However, the influence of the injection temperature on CO2 storage capacity is more obvious than that of the formation slope. (C) 2020 Elsevier Ltd. All rights reserved.

Hydrogeochemical processes and quality assessment for shallow groundwater are pivotal issues to be solved in many regions over the world due to the easy access of shallow groundwater. In this study, eighty-six water samples were collected from shallow aquifers of Chongqing, China, during July–September 2019. Multivariate statistical techniques, major ion ratios, and geochemical modeling were integrated to investigate hydrogeochemical characteristics and controlling factors. Afterwards, groundwater quality in spatial was classified by entropy-weighted water quality index and geographic information system (GIS) spatial analysis. Groundwater samples were alkaline and possessed high total dissolved solids (TDS) values. Two-group samples were distinguished as mix cations-HCO3-SO4 (group 1) and Ca-Mg-SO4 (group 2) facies. Hydrogeochemical compositions of group 1 samples were dominated by silicate dissolution and ion exchange, while sulfate and calcite dissolution were the main factors influencing the hydrogeochemical characteristics of group 2. The overall quality of groundwater samples varied greatly from excellent quality to extremely poor quality. Group 1 samples were found with excellent and good quality and suitable for drinking purposes. Group 2 samples were all unsuitable for direct drinking purposes as the quality varied from medium to extremely poor, but were spatially limited. Groundwaters with relatively poor quality were due to dissolution of sulfate that were locally enriched in the aquifers. The new findings of this study are expected to provide the reference for future management and sustainable exploitation of groundwater in Chongqing.

通过水文地质调查并结合采样分析,研究了内蒙古托克托县地区地下水水质随季节变化的特征机理.结果 表明:大气降水的偏酸性导致丰水期地下水pH值降低;季节变化对本区地下水TDS影响主要表现为丰水期的稀释淋溶作用和枯水期的蒸发浓缩作用.丰水季节随降水进入地下水中的CO2促使含水介质中的硅铝酸盐发生水解,使部分区域HCO3-浓度明显升高.雨季溶解氧随降水补给地下水,氧化富含硫化物的矿物或有机质,会使地下水中的硫酸盐浓度升高;在枯水季节,随着溶解氧的消耗,部分硫酸盐参与有机物的氧化分解,本身被还原,导致其浓度降低.在地下水位埋深浅、农牧业活动剧烈的区域,地表的污染物容易随降水进入含水层,使地下水的CODMn浓度分布随季节发生明显的改变.