Multivariate statistical analysis of chemical and stable isotopic data as indicative of groundwater evolution with reduced exploitation

Groundwater resources in the North China Plain (NCP) are undergoing tremendous changes in response to the operation of groundwater exploitation reduction (GWER) project. To identify groundwater evolution in this complex context, hierarchical cluster analysis (HCA) and principal component analysis (PCA) were combined to interpret an integrated dataset of stable isotopes and chemical data from four sampling campaigns in a pilot area of groundwater control. We proposed a novel HCA approach integrating stable isotopes and chemical signals, which successfully partitioned the groundwater samples into the unconfined and the confined water samples. Stable isotopic evidence showed that the lateral inflow and the surface water may contribute more to groundwater recharge in this region than local modern precipitation. The unconfined water’s main hydrochemical types were Na type with mixed anions, and Na–Cl–SO₄ type, while the confined water was mainly Na–Cl and Na–SO₄ types. Geochemical processes mainly involved the dissolution/precipitation of halite, gypsum, Glauber's salt, feldspar, calcite and dolomite, as well as the cation exchange. PCA results showed that water–rock interaction (i.e., salinity-based and alkalinity-based processes) predominated the hydrochemical evolution, along with local nitrate contamination resulting from fertilizers and domestic sewage. The GWER project regulated the natural evolution of unconfined water chemistry, and significantly reduced the unconfined water’s salinity (mainly Na⁺, Mg²⁺, SO₄^2?). This may be attributed to upward leakage from low-salinity confined water at some parts of the aquifer. Additionally, insignificant changes in the confined water’s salinity reflected that the impact of GWER on the confined aquifer was negligible. This study facilitates the groundwater classification effectively in the areas lack of geological data, and enhances the knowledge of groundwater chemical evolution in such a region where groundwater restoration is in progress, with important implications for groundwater sustainable management in similar basins worldwide.     

Assessment of natural and anthropogenic influences on regional groundwater chemistry in a highly industrialized and urbanized region: a case study of the Vaal River Basin,South Africa

The Vaal River Basin is an economically significant area situated in the interior of South Africa (SA), where mining, industrial, domestic and agricultural activities are very intense. The purpose of the study was to assess the influence of geology and anthropogenic activities on groundwater chemistry, and identify the predominant hydrochemical processes in the basin. Data from seventy groundwater sites were retrieved from the national database, and attention was paid to fifteen water quality parameters. Groundwater samples were clustered into seven hydrochemically distinct groups using Hierarchical Cluster Analysis (HCA), and three samples treated independently. A Piper plot revealed two major water types, Ca–Mg–HCO₃ and Ca–Mg–SO₄-Cl, which were linked to dissolution of the underlying geology and mine pollution. The Ca?+?Mg vs HCO₃?+?SO₄ plot indicated that reverse ion exchange is an active process than cation exchange in the area. Principal component analysis (PCA) was used to identify the main natural and anthropogenic processes causing variation in groundwater chemistry. Four principal components were extracted using PCA that explains 82% of the total variance in the chemical parameters. The PCA results can be categorized by four components: (1) evaporites and silicates weathering enrichment of Na, K, Cl, SO₄ and F, and anthropogenic Cl; (2) dissolution of dolomite, limestone and gypsum; (3) agricultural fertilizers (4) wastewater treatment. This study reveals that both natural and anthropogenic activities are the cause of groundwater variation in the basin.     

Multivariate analysis and geochemical investigations of groundwater in a semi-arid region,case of superficial aquifer in Ghriss Basin,Northwest Algeria

This study aims to investigate the hydrochemical characteristics of shallow aquifer in a semi-arid region situated in northwest Algeria, and to understand the major factors governing groundwater quality. The study area is suffering from recurring droughts, groundwater resource over-exploitation and groundwater quality degradation. The approach used is a combination of traditional hydrochemical analysis methods of multivariate statistical techniques, principal component analysis (PCA), and ratios of major ions, based on the data derived from 33 groundwater samples collected in February 2014. Results show that groundwater in the study area are highly mineralized and collectively has a high concentration of chloride (as Cl^?). The dominant water types are Na-Cl (27%), Mg-HCO₃ (24%) and Mg-Cl (24%). According to the (PCA) approach, salinization is the main process that controls the hydrochemical variability. The PCA analysis reveal the impact of anthropogenic factor especially the agricultural activities on the groundwater quality. The PCA highlighted two types of recharge: Superficial recharge from effective rainfall and excess irrigation water distinguished by the presence of nitrate and lateral recharge or vertical leakage from carbonate formations marked by the omnipresence of HCO₃^?. Additionally, three categories of samples were identified: (1) samples characterized by good water quality and receiving notable recharge from carbonate formations; (2) samples impacted by the natural salinization process; and (3) samples contaminated by anthropogenic activities. The major natural processes influencing water chemistry are the weathering of carbonate and silicate rocks, dissolution of evaporite as halite, evaporation and cation exchange. The study results can provide the basis for local decision makers to ensure the sustainable management of groundwater and the safety of drinking water.     

Isotopic and hydrochemical studies of groundwater flow and salinity in the Southern Upper Rhine Graben

In order to determine the origin and the propagation mechanisms of highly concentrated chloride brines within the Quaternary aquifer system in the southern part of the Upper Rhine Graben, a combined isotope (H, O, C) and hydrochemical analysis was carried out. Groundwater recharge in this area is a complex system, consisting of local precipitation, river bank filtration, lateral flow from the Graben borders and, to a minor extent, an old Pleistocene component. In some areas, groundwater consists of up to 90% of recent bank filtrate, reaching depths down to at least 100 m. The isotopic and hydrochemical results show, that the elevated chloride concentrations in the Quaternary aquifer mainly result from leaky settling basins charged by the French potash mines until the mid 1970s. Input of natural brines coming from tertiary salt diapirs is of only minor importance. While infiltrating, the anthropogenic brines were strongly diluted by local river bank filtrate of the Rhine. Nevertheless, maximum chloride concentrations nowadays still reach some 10,000 mg/l at the base of the aquifer at a depth of more than 100 m below surface. The main volume of the brines is stored in the less permeable lower part of the quaternary sediments (Breisgau-Formation) whereas only a minor part is transported northwards with the rapid convective groundwater flow. Brines undergoing only dilution preserve their hydrochemical characteristics (NaCl-type). In contrast, brines recirculated from the Breisgau-Formation show a northwards increasing alteration through ion exchange processes. Potassium and sodium may be fixed in the fine grained aquifer material while calcium is set free into the groundwater. After a flow distance of about 12 km, complex hydraulic interactions between groundwater and surface waters lead to the rise of strongly diluted and hydrochemically altered brines with chloride contents up to maximum 700 mg/l. The presented case study is an example for a detailed analysis of a multi-component groundwater mixing system using combined isotope and hydrochemical methods. Furthermore, cation exchange is shown as a major process affecting the hydrochemical evolution of the young groundwater in the southern Upper Rhine Graben which is locally strongly polluted by chloride as a consequence of former potash mining.     

The hydrochemical facies and anomalous fluoride content in the Serra Geral aquifer system,southern Brazil: a GIS approach with tectonic and principal component analysis

Groundwater with high fluoride content and water mixture patterns were studied in Serra Geral aquifer system (SGAS) using three aspects, principal component analysis (PCA), tectonic scenery and hydrochemical interpretation from 309 groundwater chemical data information from deep wells. A four-component model is suggested and explains 81% of total variance in the PCA. Six hydrochemical facies were identified. These facies suggest two different fluoride sources. Tectonic approach shows the relationship between defined hydrochemical facies and regional fracture control. The applied methodology reveals a minimum level to understand hydrochemical mixtures. The fluoride enrichment mechanisms into the groundwater are comprised in advance to guide the future uses of SGAS to the public supply.     

Hydrochemical characterization of groundwater using multivariate statistical analysis: the Maritime Djeffara shallow aquifer (Southeastern Tunisia)

Worldwide, groundwater resources have been considered as the main sources of drinking, domestic uses, industrial and agriculture water demands, especially in arid and semiarid regions. Accordingly, the monitoring of the groundwater quality based on different tools and methods becomes a necessity. The aim of this study was to apply several approaches to assess the water quality and to define the main hydrochemical process which affect groundwater of the Maritime Djeffara shallow aquifer. In addition to the hydrochemical approach, two multivariate statistical analyses, hierarchical clusters analysis (HCA) and principal component analysis (PCA), were carried out to identify the natural and the anthropogenic processes affecting groundwater chemistry. Hydrochemical approach, based on 47 analyzed groundwater samples, shows that most of samples present a sulfate to mixed chloride, with sodi-potassic tendency facies. According to their chemically composition, the HCA revealed three different groups (C1, C2 and C3) according to their electrical conductivity (EC) values: C1 (average EC = 4500 µS/cm), C2 (average EC = 7040 µS/cm) and C3 (average EC = 9767 µS/cm). Furthermore, PCA results show two principal factors account 84.05% of the total variance: (1) F1 represents the natural component, and (2) F2 symbolizes the anthropic component. Moreover, the groundwater quality map of the Maritime Djeffara shows three categories: suitable, doubtful and unsuitable water for irrigation. These different results should be taken to protect water resources in arid and semiarid regions, especially at the alluvial coastal regions. Also, they help to make a suitable planning to manage and protect the groundwater resources.     

山东柴汶河下游古近系朱家沟组含水岩组水文地质特征及地下水富集模式

鲁中南地区古近系朱家沟组是一套具“磨拉石建造”特征的沉积地层,岩性以灰质角砾岩为主,受断裂构造影响,其富水性差异明显。在区域水文地质调查的基础之上,利用柴汶河下游古近系朱家沟组地层调查点与钻孔资料,分析其含水层特征、地下水水化学特征及富水性。结果表明:古近系朱家沟组含水层岩性为钙质胶结灰质砾岩,在90 m以浅裂隙岩溶发育,单井涌水量100~300 m³/d,局部>300 m³/d;裂隙水与汶口盆地南侧岩溶水化学特征相似,表明两者水力联系密切;Gibbs图显示区域地下水呈现岩石风化型,趋向蒸发浓缩型;地下水离子成分主要源于岩盐溶解,并受到人类污染活动影响。依据钻孔资料分析区内地下水富集模式为断裂型灰质砾岩岩溶裂隙蓄水构造模式,认为碎屑岩断裂发育段可作为应急找水靶区。     

广西北海市地下水系统水化学特征的分析

对广西北海市近20年的地下水水质监测资料和2002-2003年野外实地取样的测试资料进行分析,并采用Piper图和Q型群分析进行水化学分类,结果表明该地区北部地下水以Ca·Na-HCO₃型为主,水化学特征显示地下水化学成分受降雨入渗和溶滤的影响,而南部地下水以Na-Cl或Na·Ca-Cl型为主。北海市天然条件下地下水的矿化度低,pH值低,呈偏酸性。低矿化度的雨水、可溶盐含量极低的含水介质、迅速的水循环以及长期的淋滤作用,导致了北海地区地下水低矿化度的特点。     

Groundwater resources of the middle and upper Odra River basin, southwestern Poland

 The total amount of groundwater resources in the middle and upper Odra River basin is 5200×10³ m³/d, or about 7.7% of the disposable groundwater resources of Poland. The average modulus of groundwater resources is about 1.4 L/s/km². Of the 180 'Major Groundwater Basins' (MGWB) in Poland, 43 are partly or totally located within the study area. The MGWB in southwestern Poland have an average modulus of groundwater resources about 2.28 L/s/km² and thus have abundant water resources in comparison to MGWB from other parts of the country. Several types of mineral waters occur in the middle and upper Odra River basin. These waters are concentrated especially in the Sudety Mountains. Carbon-dioxide waters, with yields of 414 m³/h, are the most widespread of Sudetic mineral waters. The fresh waters of the crystalline basement have a low mineralization, commonly less than 100 mg/L; they are a HCO₃–Ca–Mg or SO₄–Ca–Mg type of water. Various hydrochemical compositions characterize the groundwater in sedimentary rocks. The shallow aquifers are under risk of atmospheric pollution and anthropogenic effects. To prevent the degradation of groundwater resources in the middle and upper Odra River basin, Critical Protection Areas have been designated within the MGWB. Received, January 1995 Revised, May 1996, August 1997 Accepted, August 1997     

Water quality assessment and hydrochemical characteristics of groundwater on the aspect of metals in an old town,Foshan, south China

The present study is aimed at assessing the water quality and discussing the hydrochemical characteristics and seasonal variation of shallow groundwater on the aspect of metals in the eastern Chancheng district of Foshan city, south China. Multivariate analytical methods such as principal components analysis (PCA) and hierarchical cluster analysis (HCA) were used in this study. The results show that 45% of groundwater in the east-central of study area is not suitable for drinking purpose due to high concentrations of Fe, Pb and Mn. The mean concentrations of Fe, Hg, Cu, Pb, and Mn in dry season are higher than that in wet season. On the contrary, the mean concentrations of Cd, Co, Zn, Ba, Cr, Mo, Ni and Al in wet season are higher than that in dry season. PCA results show that four PCs are responsible for the 78.6% of the total hydrochemical variables in groundwater. Three groups were generated from HCA method. Group 1 reflects the characteristic of wet season and the low ion exchange capacity; group 2 is mainly influenced by the dry season. Reducing environment and high ion exchange capacity are responsible for group 3. The results are useful in addressing future measures in groundwater resource management for local government.     

Geochemical evolution of groundwater in southern Bengal Basin: The example of Rajarhat and adjoining areas,West Bengal,India

Detailed geochemical analysis of groundwater beneath 1223 km² area in southern Bengal Basin along with statistical analysis on the chemical data was attempted, to develop a better understanding of the geochemical processes that control the groundwater evolution in the deltaic aquifer of the region. Groundwater is categorized into three types: ‘excellent’, ‘good’ and ‘poor’ and seven hydrochemical facies are assigned to three broad types: ‘fresh’, ‘mixed’ and ‘brackish’ waters. The ‘fresh’ water type dominated with sodium indicates active flushing of the aquifer, whereas chloride-rich ‘brackish’ groundwater represents freshening of modified connate water. The ‘mixed’ type groundwater has possibly evolved due to hydraulic mixing of ‘fresh’ and ‘brackish’ waters. Enrichment of major ions in groundwater is due to weathering of feldspathic and ferro-magnesian minerals by percolating water. The groundwater of Rajarhat New Town (RNT) and adjacent areas in the north and southeast is contaminated with arsenic. Current-pumping may induce more arsenic to flow into the aquifers of RNT and Kolkata cities. Future large-scale pumping of groundwater beneath RNT can modify the hydrological system, which may transport arsenic and low quality water from adjacent aquifers to presently unpolluted aquifer.     

Integrated geostatistics and GIS techniques for assessing groundwater contamination in Al Arish area, Sinai, Egypt

Sustainable development in El Arish area of North Sinai, Egypt, is retarded by serious environmental problems, where the land-use and land cover of the region is changing over present time. The impact of human activities in the study area is accompanied by the destruction and over-exploitation of the environment. This study applies multivariate statistics (factor and cluster analyses) and GIS techniques to identify both anthropogenic and natural processes affecting the groundwater quality in the Quaternary sands aquifer. The aim of this study was to investigate the impacts on groundwater resources, the potential pollution sources, and to identify the main anthropogenic inputs of both nutrients and trace metal. Since the depth to the water table is shallow especially in the northern part (<4?m), and the aquifer was exposed on the ground surface, it has poor buffering capacity and the pollution risk is very high. Groundwater chemistry in this coastal region has complex contaminant sources, where intensive farming activities and untreated wastes put stress on groundwater quality. Several areal distribution maps were constructed for correlating water quality with possible contributing factors such as location, land-use, and aquifer depth. These maps identified both anthropogenic and natural processes affecting groundwater quality of the studied aquifer. Cluster analysis was used to classify water chemistry and determine the hydrochemical groups, Q-mode dendrogram is interpreted and there are three main clusters. Factor analyses identify the potential contamination sources affecting groundwater hydrochemistry such as: nitrate, sulfate, phosphate and potassium fertilizers, pesticides, sewage pond wastes, and salinization due to circulation of dissolved salts in the irrigation water itself.     

Hydrochemical signatures of deep groundwater circulation in a part of the Himalayan foreland basin

Groundwater samples were analyzed from 71 springs and wells as part of a larger study in a region of compressional tectonic regime. The study site covers the Peshawar basin and surroundings in the Himalayan foreland of Pakistan. The northern portion is mountainous and the water table is discontinuous in different intermontane valleys, with abundant springs (with normal and anomalous temperatures and composition). The southern part is divided into isolated basins with a number of drilled (“deep”) and dug (“shallow”) wells. Hydrochemical signatures of elevated strontium (Sr), SiO₂, boron (B)—and the geothermometric signatures—all indicate a deep circulation of the emerging groundwater. Moreover, for several of the sample sites, water chemical compositions, measured spring and water well temperatures, and reservoir temperatures calculated for spring waters, all point to origin from deep horizons within the basin. Remarkable proximity of all the thermal and hydrochemical anomalies to major faults suggests that the waters ascended along these faults from greater depths. The area is a natural western extension of the Himalayan Geothermal Belt described in earlier literature for the eastern and central Himalayas.     

Fluoride enrichment mechanism and geospatial distribution in the volcanic aquifers of the Middle Awash basin,Northern Main Ethiopian Rift

Considering the anomalous concentration of fluoride in the ground waters of the Middle Awash basin, a comprehensive survey of the enrichment mechanism as well as its association with common hydrochemical variables was conducted using multivariate statistical methods, Hierarchal Cluster Analysis (HCA) and Principal Component Analysis (PCA). The HCA results indicate a marked heterogeneous spatial distribution of the fluoride concentration, the magnitude of which varies more gradually in the SSW–NNE direction along the Wonji Fault Belt (WFB) than it does in the E-W direction away from this belt. This is strongly associated with the geothermal anomaly that is prominent in the basin interior area. Furthermore, the PCA results show that the magnitude of the fluoride concentration is higher in the groundwater derived from non-calcium bearing aquifers, which are widely distributed in the rift floor. Hydrochemical processes involving a cation exchange reaction cause a systematic Ca²⁺ removal from solution from highland towards the rift floor. This geochemical reaction enhances the fluoride enrichment of groundwater along the same flow direction. In this regard, the geothermal belt of the basin interior area is a hydrogeological block marked by high loads of fluoride whereas the plateau areas are low-fluoride zones. The geospatial distribution of fluoride at the basin scale was estimated using the kriging procedure. Appropriate discrimination between local and regional aquifers is important in order to secure low-fluoride water supply for the community in the basin.     

Identifying the Sources of Solutes in Karst Groundwater in Chongqing,China: a Combined Sulfate and Strontium Isotope Approach

Groundwater from karst subterranean streams is among the world’s most important sources of drinking water supplies, and the hydrochemical characteristics of karst water are impacted by both natural environment and people. Therefore, the study of hydrochemistry and its solutes’ sources is very important to ensure the normal function of life support systems. In this paper, thirty?five representative karst groundwater samples were collected from different aquifers (limestone and dolomite) and various land use types in Chongqing to trace the sources of solutes and relative hydrochemical processes. Hydrogeochemical types of karst groundwater in Chongqing were mainly of the Ca?HCO3 type or Ca (Mg)?HCO3 type. However, some hydrochemical types of karst groundwater were the K+Na+Ca?SO4 type (G25 site) or Ca?HCO3+SO4 type (G26 and G14 site), indicating that the hydrochemistry of these sites might be strongly influenced by anthropogenic activities or unique geological characteristics. The dissolved Sr concentrations of the studied groundwater ranged from 0.57 to 15.06 μmmol/L, and the 87Sr/86Sr varied from 0.70751 to 0.71627. The δ34S?SO42? fell into a range of ?6.8‰?21.5‰, with a mean value of 5.6‰. The variations of both 87Sr/86Sr and Sr values of the groundwater samples indicated that the Sr element was controlled by the weathering of limestone, dolomite and silicate rock. However, the figure of 87Sr/86Sr vs. Sr2+/[K++Na+] showed that the anthropogenic inputs also obviously contributed to the Sr contents. For tracing the detailed anthropogenic effects, we traced the sources of solutes collected karst groundwater samples in Chongqing according to the δ34S value of potential sulfate sources. The variations of both δ34S and 1/SO42? values of the groundwater samples indicated that the atmospheric acid deposition (AAD), dissolution of gypsum (GD), oxidation of sul?de mineral (OS) or anthropogenic inputs (SF: sewage or fertilizer) have contributed to solutes in karst groundwater. The influence of oxidation of sul?de mineral, atmospheric acid deposit and anthropogenic inputs to groundwater in Chongqing karst areas was much widespread.     

Identifying key hydrochemical processes in a confined aquifer of an arid basin using multivariate statistical analysis and inverse modeling

Tertiary fractured permeable confined aquifer, which covered about 70 % of the studying area, played an important role in alleviating drinking water shortages. However, about 58 and 79 % of the groundwater samples exceeded the desirable limits for fluoride (1.5 mg/L) and TDS (1,000 mg/L). Two multivariate statistical methods, hierarchical cluster analysis (HCA) and principal components analysis (PCA), were applied to a subgroup of the dataset in terms of their usefulness for groundwater classification, as well as to identify the key processes controlling groundwater geochemistry. In the PCA, two principal factors have been extracted, which could explain 73 % of the total data variability. Among them, factor 1 revealed the source of groundwater salinity and factor 2 explained the elevated fluoride. Two major groups were classified by HCA and Group 1 was near the groundwater recharge zone and Group 2 was mainly distributed over the groundwater discharge zone. Inverse modeling (NETPATH) results indicated that the hydrochemical evolution was primarily controlled by (1) the dissolution of mirabilite, gypsum and halite for the source of groundwater salinity; (2) the release of the adsorbed fluoride through desorption or through competition with HCO₃ ^? under alkalinity condition for the elevated fluoride in the groundwater.     

Geochemical characterization of karst groundwater in the cradle of humankind world heritage site,South Africa

The karst of the Cradle of Humankind World Heritage Site plays a major role in the assimilation or carrying of acid mine drainage, sewage effluent return flow and agricultural run-off. Infiltration of contaminated water has altered the chemical composition of the natural waters of the karst system. A multivariate statistical method in combination with conventional geochemical and spatial analysis was applied on groundwater and surface water quality samples to determine the spatial extent of hydrochemical impacts from different anthropogenic sources. The application of hierarchical cluster analysis of the major ions (148 samples) recognised three distinct hydrochemical regimes. Cluster 1 is moderately mineralized, especially with regard to chloride, nitrate and sulphate, cluster 2 has a low mineralization with all elements well within the recommended drinking water limits of South Africa and cluster 3 represents highly mineralized samples taken in the vicinity of decanting mineshafts. The cluster solution is confirmed by a simple mixing model, indicating varying contributions of three identified end members (acid mine drainage, treated sewage effluents and pristine dolomitic groundwater) to the groundwater quality in the catchment. The combination of statistical, geochemical and spatial methods in conjunction with end-member mixing analysis provides a reliable method to understand the processes responsible for the groundwater quality variations and to assist in the identification of anthropogenic impacts.     

Use of hierarchical cluster analysis to assess the representativeness of a baseline groundwater quality monitoring network: comparison of New Zealand’s national and regional groundwater monitoring programs

Baseline monitoring of groundwater quality aims to characterize the ambient condition of the resource and identify spatial or temporal trends. Sites comprising any baseline monitoring network must be selected to provide a representative perspective of groundwater quality across the aquifer(s) of interest. Hierarchical cluster analysis (HCA) has been used as a means of assessing the representativeness of a groundwater quality monitoring network, using example datasets from New Zealand. HCA allows New Zealand??s national and regional monitoring networks to be compared in terms of the number of water-quality categories identified in each network, the hydrochemistry at the centroids of these water-quality categories, the proportions of monitoring sites assigned to each water-quality category, and the range of concentrations for each analyte within each water-quality category. Through the HCA approach, the National Groundwater Monitoring Programme (117 sites) is shown to provide a highly representative perspective of groundwater quality across New Zealand, relative to the amalgamated regional monitoring networks operated by 15 different regional authorities (680 sites have sufficient data for inclusion in HCA). This methodology can be applied to evaluate the representativeness of any subset of monitoring sites taken from a larger network.     

A geochemical study of the impact of irrigation and aquifer lithology on groundwater in the Upper Yakima River Basin,Washington, USA

The Yakima River, a major tributary of the Columbia River, is currently overallocated in its surface water usage in part because of large agricultural water use. As a result, groundwater availability and surface water/groundwater interactions have become an important issue in this area. In several sub-basins, the Yakima River water is diverted and applied liberally to fields in the summer creating artificial recharge of shallow groundwater. Major ion, trace element, and stable isotope geochemistry of samples from 26 groundwater wells from a transect across the Yakima River and 24 surface waters in the Kittitas sub-basin were used to delineate waters with similar geochemical signatures and to identify surface water influence on groundwater. Major ion chemistry and stable isotope signatures combined with principal component analysis revealed four major hydrochemical groups. One of these groups, collected from shallow wells within the sedimentary basin fill, displays temporal variations in NO₃ and SO₄ along with high δ¹⁸O and δD values, indicating significant contribution from Yakima River and/or irrigation water. Two other major hydrochemical groups reflect interaction with the main aquifer lithologies in the basin: the Columbia River basalts (high-Na groundwaters), and the volcaniclastic rocks of the Ellensburg Formation (Ca–Mg–HCO₃ type waters). The fourth major group has interacted with the volcaniclastic rocks and is influenced to a lesser degree by surface waters. The geochemical groupings constrain a conceptual model for groundwater flow that includes movement of water between underlying Columbia River basalt and deeper sedimentary basin fill and seasonal input of irrigation water.     

Hydrochemical and isotopic study of groundwater in the Yinchuan plain, China

The Yinchuan plain is located in the arid climate zone of NW China. The western margin of the plain is the Helan mountain connecting a series of normal slip faults. The eastern margin of the plain connects with the Yellow River and adjacents with the Ordos platform. The south of the plain is bordered by the EN fault of the Niushou mountain. The bottom of the plain is the Carboniferous, Permian, or Ordovician rocks. Based on the analysis of groundwater hydrochemical and isotopic indicators, this study aims to identify the groundwater recharge and discharge in the Yinchuan plain, China. The hydrochemical types of the groundwater are HCO₃–SO₄ in the west, HCO₃–Cl in the middle, and Cl–SO₄ in the east. The hydrochemical types are HCO₃–SO₄ in the south, HCO₃–Cl and SO₄–HCO₃ in the middle. The hydrochemical types are complex in the north, mainly SO₄–HCO₃ and Cl–SO₄. Deuterium, ¹⁸O, and tritium values of groundwater indicate that groundwater recharge sources include precipitation, bedrock fissure water, and irrigation return water. Groundwater discharges include evaporation, abstraction, and discharge to surface water. According to the EW isotopic profile, the groundwater flow system (GFS) in the Yinchuan plain can be divided into local flow systems (LFS) and regional flow systems (RFS). Groundwater has lower TDS and higher tritium in the southern Yellow River alluvial plain and groundwater age ranges from 6 to 25 years. The range of groundwater renewal rates is from 11 to 15 % a^?1. The depth of the water cycle is small, and groundwater circulates fast and has high renewal rates. Groundwater has higher TDS and lower tritium in the northern Yellow River alluvial plain. The range of groundwater age is from 45 to 57 years, and renewal rate is from 6 to 0.1 % a^?1. The depth of the water cycle is larger. Groundwater circulates slowly and has low renewal rates.