Groundwater plays a pivotal role in mediating nitrogen transfer to aquatic ecosystems, particularly in arid regions. Water scarcity, coupled with intensive agricultural activities, has placed the groundwater systems under significant pressure from non-point source pollution, underscoring the need for targeted investigation. Focusing on the Chinese Loess Plateau (CLP), we combined dual-isotope analysis (δ15N-NO3-, δ18O-NO3-) with water isotopes (δD-H2O, δ18O-H2O) and implemented a dual-framework approach to investigate nitrate dynamics. Specifically, we applied the MixSIAR model to quantify nitrate source contributions and employed the Geographical Detector model to identify spatial and seasonal drivers. The results showed that local piston-flow recharge predominates beneath the thick vadose zone. Nitrate concentrations decreased with increasing well depth (0.04 mg/L/m), accompanied by a convergence of nitrate isotopic signatures toward soil organic nitrogen (SN). Nitrate was derived primarily from SN (43 %) and ammonium NH4+ fertilizer (NHF) (34 %), underscoring the dominance of agriculture-related sources. Seasonal patterns revealed minor denitrification during the wet season. Spatial analysis identified land use, precipitation, and the normalized difference vegetation index (NDVI) as key factors controlling nitrate variability. Notably, nitrate leaching was strongly driven by precipitation in regions with sparse vegetation cover. These findings demonstrate that, although nitrate transport and transformation in the CLP are governed by its uniquely deep vadose zone and arid hydrogeological conditions, the integrated isotope and spatial framework developed here provides a transferable approach for investigating nitrate dynamics in other vulnerable deep groundwater systems worldwide.

Study region: Guozhuang spring area, Shanxi, North China. Study focus: This study proposes a Chaotic Sparrow Search Algorithm-enhanced Weighted Broad Learning System (CSSA-WBLS) for groundwater potential assessment. The framework mitigates data imbalance via instance weighting in WBLS and enhances parameter optimization using chaotic operators within CSSA. New hydrological insights for the region: Groundwater is a critical freshwater resource for sustainable water supply management. However, evaluating its potential faces two key challenges: severe data imbalance (fewer spring occurrence samples than non-spring samples) and suboptimal parameter optimization in existing models. Geospatial data were compiled using GIS analysis and field surveys. Eleven predictive factors spanning geology, hydrology, and anthropogenic influences were identified using the frequency ratio, random forest feature importance, and multicollinearity diagnostics. A dataset exhibiting a 1:10 spring/non-spring ratio was split into training (70 %) and testing (30 %) sets. BLS and WBLS models were hybridized with the Sparrow Search Algorithm (SSA) and CSSA to optimize network architecture and node parameters, addressing SVM limitations with imbalanced data. Model performance under imbalance was evaluated using ROC-AUC, accuracy, sensitivity, specificity, balanced accuracy, F1-score, confusion matrices, and Friedman testing. CSSA-WBLS achieved superior performance across over all metrics (AUC = 0.874) and effectively addressed data imbalance. Spatial mapping identified 18.78 % of the area as high-potential groundwater zones. CSSA-WBLS thus provides an efficient framework for groundwater assessment and has significant potential for regional applications.

Streamwater-groundwater interaction (SGI) plays a critical role in the exchange of water, energy, and contaminants in terrestrial water cycle systems. While shallow groundwater has traditionally been considered the primary contributor to streamflow, recent evidence suggests that deep fossil groundwater, predating the Holocene, also discharges into rivers. However, the mechanisms driving SGI across different geological layers remain largely unknown. Here we examined SGI across five large watersheds (7,636–60,916 km2) in China’s Loess Plateau (CLP), using 651 streamwater and groundwater samples collected during dry and wet seasons and analyzed for isotopic and hydrochemical indicators. Our results revealed clear distinctions in the interactions between river water and shallow loess pore groundwater (LPG) or deep fissure groundwater (DFG). LPG exhibited one-way connectivity to streamwater, with an average groundwater discharge ratio of 24 %, whereas a two-way recharge and discharge system exist between DFG and rivers, with an average discharge ratio of 19 %. Both groundwater systems showed higher discharge ratios during the wet season than the dry season. Spatially, discharge ratios from LPG and DFG were lower in central CLP but increased towards the north and south. Loess thickness and geological formations primarily govern these patterns. While LPG primarily influences localized water exchange dynamics, DFG drives regional hydrological connectivity across multiple watersheds. Our findings provide new insights into the stratigraphic mechanisms controlling SGI, offering targeted strategies for sustainable water resource management in the CLP and similar regions.

Groundwater nitrate (NO3-) and sulfate (SO42-) pollution in semi-arid regions has attracted widespread attention. However, unveiling the dynamics and sources of NO3- and SO42- in regional groundwater is challenging because of complex anthropogenic activities and hydrogeological conditions. This study combined physicochemistry and multiple stable isotopes (δ2H-H2O, δ18O-H2O, δ15N-NO3-, δ18O-NO3-, δ34S-SO42-, and δ18O-SO42-) to explore the spatiotemporal patterns, driving factors, sources, and potential health hazards of NO3- and SO42- in groundwater on the Loess Plateau, China. Results showed that NO3- and SO42- concentrations exhibited significant spatiotemporal variations between the wet and dry seasons. The primary factors controlling the NO3- spatial difference were NDVI, land use type, and distance to mining area and precipitation, distance to mining area, and NDVI in the wet and dry seasons, respectively. Distance to river, precipitation, and evaporation in the wet season and NDVI, precipitation, and elevation in the dry season were the dominant drivers of spatial heterogeneity in SO42-. The explanatory power of the interaction between the two factors was greater than that of any individual factor. Soil organic nitrogen, ammonium fertilizer, and manure and sewage attributed to agricultural activities contributed the most to NO3- in groundwater. Sulfide oxidation and evaporite dissolution were the most prominent SO42- sources. Denitrification and sulfate reduction were prevalent in the wet season, while nitrification was dominant in the dry season. Health risk assessment suggested that children faced higher non-carcinogenic risks than adults in both wet and dry seasons. This study provides valuable insights into regional scale groundwater pollution in semi-arid regions.

Streamwater-groundwater interaction (SGI) plays a critical role in the exchange of water, energy, and contaminants in the terrestrial water cycle system. While shallow groundwater has traditionally been considered the primary contributor to streamflow, recent evidence suggests that deep fossil groundwater, which predates the Holocene, also discharges into rivers. However, the mechanisms driving SGI across different geological layers remain largely unknown. Here we examined SGI across five large watersheds (7,636-60,916 km2) in China's Loess Plateau (CLP), using 651 streamwater and groundwater samples collected during dry and wet seasons and analyzed for isotopic and hydrochemical indicators. Our results revealed clear distinctions in the interactions between river water and shallow loess pore groundwater (LPG) or deep fissure groundwater (DFG). LPG exhibited one-way connectivity to streamwater, with an average groundwater discharge ratio of 24 %, whereas a two-way recharge and discharge system exist between DFG and rivers, with an average discharge ratio of 19 %. Both groundwater systems showed higher discharge ratios during the wet season than the dry season. Spatially, discharge ratios from LPG and DFG were lower in central CLP but increased towards the north and south. Loess thickness and geological formations primarily govern these patterns. While LPG primarily influences localized water exchange dynamics, DFG drives regional hydrological connectivity across multiple watersheds. Our findings provide new insights into the stratigraphic mechanisms controlling SGI, offering targeted strategies for sustainable water resource management in the CLP and similar regions.

A comprehensive understanding of the role of natural and anthropogenic factors in groundwater pollution is essential for sustainable groundwater resource management, especially in alluvial plains with intensive anthropogenic activities. Numerous studies have focused on the contribution of individual factors on groundwater pollution in alluvial aquifers, but distinguishing the effects of natural and anthropogenic factors is limited. In this study, 64 wells were sampled in different seasons from the Yellow River alluvial plain in China for hydrochemical and isotopic analysis to investigate the spatiotemporal distribution, sources and health risks of fluoride and nitrate in alluvial aquifers. Results showed that fluoride contamination was widely distributed without significant seasonal variation, and 78.1 % of the dry season samples and 65.6 % of the wet season samples showed fluoride concentrations above the permissible limit (1.5 mg/L). High-F- groundwater was generally accompanied by Na-HCO3 and Na-HCO3·SO4 water types. Fluoride was from a natural origin mainly associated with mineral dissolution, competitive adsorption, cation exchange, and evaporation. Groundwater nitrate contamination was spatially sporadic and showed significant seasonal differences. Only 13.6 % of the dry season samples and 3.2 % of the wet season samples had NO3- concentrations exceeded the permissible limit of 50 mg/L. The hydrochemical phase evolved from bicarbonate or sulfate type to chloride type with increasing nitrate concentration. Manure and sewage attributed to agricultural activities contributed the most nitrogen to groundwater, followed by soil organic nitrogen and chemical fertilizers, revealing the anthropogenic origin of nitrate. Nitrification was the dominant nitrogen transformation process in the wet season, and denitrification was prevalent in the dry season. Oral ingestion of high fluoride groundwater was a major threat to human health, especially for infants. This study provided a significant reference for water resources management in alluvial aquifers.

Accurately identifying the sources of trace elements in groundwater is difficult, especially in the areas with intensive human activities. This study proposes a framework to identify and quantify the contributions of potential sources of trace elements in groundwater. Health risk assessment is first conducted to identify the trace elements with the highest threats to groundwater quality, and then the geographical detector is used to qualitatively investigate the potential sources and processes dominating the pollution from identified trace elements, and the absolute principal component scores-multivariate linear regression (APCS-MLR) is used to quantify the contributions of different sources to the accumulation of trace elements. The proposed approach was applied to China’s Loess Plateau, a typical water-limited area with rapid urbanization and intensive agricultural activities, after conducting two groundwater sampling campaigns in a flood and a dry season. The trace element concentrations in groundwater exhibited significant spatial and seasonal differences. Health risk assessment revealed that Cr and As through oral ingestion were responsible for non-carcinogenic and carcinogenic risks in different seasons. Land use was the primary factor influencing the spatial heterogeneity of Cr in the flood season, while elevation and distance from city were dominant factors in the dry season. Normalized difference vegetation index (NDVI) and distance from city contributed the most to As change in the flood season, but NDVI was the major contributor in the dry season. The average contributions of potential pollution sources to trace elements in groundwater were in the order of natural source (35%) > geogenic process (17%) > industrial source (13%) in the flood season, but mixed sources (47%) > agricultural activities (18%) in the dry season. Distinguished from the traditional source apportionment methods, the newly proposed approach is not limited to identification of pollutant sources, but also can obtain the exact contributions of different sources. The findings provide useful information for groundwater management in the Loess Plateau.

Hundreds of millions of people around the world are currently exposed to excessive amounts of fluoride (F-) in drinking water. Although the factors controlling the spatiotemporal distribution of F- contents have been analyzed, their contributions have rarely been quantified. In this study, 510 water samples were collected in the dry and wet seasons in China's Loess Plateau to investigate the spatial and seasonal distribution, controlling factors, and potential health risks of F- in natural water. High-F- waters were mainly distributed in valley areas of the Loess Plateau, and more severe fluoride pollution of streamwater and groundwater was found in the wet and dry seasons, respectively. Mineral dissolution, competitive adsorption, adsorption/desorption and cation exchange jointly controlled F- enrichment. Spatiotemporal distribution of high-F- levels was mainly determined by climate and streamwater-groundwater connectivity in the dry season, with contribution rates of 41.7% and 37.6%, and by terrain and anthropogenic activities in the wet season, with contribution rates and 49.9-55.6% and 30.7%, respectively. Fluoride in groundwater through oral intake posed the greatest health risks to infants, followed by children, teenagers and adults in the dry and wet seasons. This study provides a scientific basis for the effective management of high-F- water in arid regions.

Fluoride (F-) enrichment reduces the availability of groundwater resources in the arid region, and it is thus important to investigate the hydrogeochemistry and health hazards of fluoride-enriched groundwater. Seventy-two groundwater samples (20 unconfined samples from the piedmont plain, 22 unconfined samples and 30 shallow confined samples from the alluvial plain) were collected in the Tarim Basin of China to illustrate the geochemical processes driving the F- enrichment and the incidence of dental fluorosis. The patterns of average ions contents in groundwater are Na+ > Ca2+ > Mg2+ > K+ and SO42- > Cl- > HCO3- > NO3- > F-. The highest F- concentration (average 2.16 mg/L) is observed in unconfined groundwater in the alluvial plain, while the lowest (average 0.63 mg/L) is recorded in unconfined groundwater in the piedmont plain. Approximately 5.0% of unconfined groundwater in the piedmont plain, 90.9% of unconfined groundwater and 33.3% of shallow confined groundwater in the alluvial plain contain F- concentrations exceeding 1.0 mg/L (Chinese drinking water standard). Mineral dissolution, cation exchange, and evaporation play a significant role in the formation of solutes in groundwater. High-F- groundwater is mostly associated with SO4·Cl-Na·Ca, SO4·Cl-Na·Mg, and SO4·Cl-Na types water. Thermodynamic simulations reveal that the dissolution of F-bearing minerals (e.g., fluorite) significantly controls the F- contents in groundwater. High concentrations of F- are closely related to high HCO3-, high Na+, high salinity, cation exchange, and evaporation. This demonstrates that high F- concentrations are caused by the increase in fluorite solubility due to high ionic strength, Ca2+ consumption and the desorption of F- from solid surfaces under alkaline conditions. Mixing with the upper unconfined groundwater plays a vital role in the enrichment of F- in shallow confined groundwater in the alluvial plain. The health risk assessment based on Dean's classification indicates that the percentage prevalence of fluorosis for boys aged 6 to 18 is 15.5% for Yecheng (YC), 18.4% for Zepu (ZP), 33.3% for Shache (SC), 29.8% for Maigaiti (MG), and 44.9% for Bachu (BC), while that for girls of the same age is 14.3% for YC, 24.3% for ZP, 42.2% for SC, 41.4% for MG, and 45.3% for BC. For male and female adults aged between 19 and 68, the percentage prevalence of fluorosis is: YC (11.5%, 12.0%), ZP (18.3%, 20.0%), SC (35.4%, 35.0%), MG (32.5%, 39.7%), and BC (42.4%, 44.3%). It is obvious that younger generation, especially girls, suffers from more severe dental fluorosis. This study has implications for the effective management of high-F- groundwater in arid regions.

Fluoride (F-) and nitrate (NO3-) in groundwater have caused serious health problems worldwide. However, in the Chinese Loess Plateau where groundwater is the primary source of drinking water, previous studies have rarely reported the health risks from fluoride and nitrate in groundwater. Therefore, we collected 105 groundwater samples (78 from shallow aquifers and 27 from deep aquifers) from the western district of the Loess Plateau for physicochemical and isotopic analysis to investigate the sources of F- and NO3- in groundwater and associated health risks. Fluoride concentration in 73.1% of shallow groundwater and 22.2% of deep groundwater exceeds 1.5 mg/L, while NO3- content in 76.3% of shallow groundwater and 51.9% of deep groundwater surpasses 50 mg/L. High-F- groundwater is associated with HCO3-Na, SO4-Na center dot Mg and Cl-Na center dot Mg types water. Fluorine bearing minerals dissolution, cation exchange, calcite precipitation, evaporation, and anthropogenic activities contribute significantly F- in groundwater. Mixing with shallow groundwater is an important source of F- in deep groundwater. The NO3- content is highest in Cl type water, followed by SO4 type and HCO3 type water. NO3- mainly originates from soil organic nitrogen (SON), chemical fertilizers (CF), and manure and sewage (M&S). Nitrification is the dominant transformation process of nitrogen nutrients in groundwater. The hazard index (HI) values for shallow groundwater are 0.203-9.232 for adults, 0.253-11.522 for teenagers, 0.359-16.322 for children, and 0.507-23.043 for infants, while those for deep groundwater are 0.713-5.813 for adults, 0.890-7.254 for teenagers, 1.261-10.277 for children, and 1.780-14.508 for infants. Approximately 96.2% of shallow groundwater poses non-carcinogenic risks to infants and children, followed by 92.3% to teenagers, and 89.7% to adults. All deep groundwater poses non-carcinogenic risks to infants and children, followed by 92.6% to teenagers, and 74.1% to adults. This study is helpful to develop strategies for the integrated management of high fluoride or nitrate groundwater in arid areas.

In order to clarify the sources of nitrate in groundwater of the loess area, a typical loess area in northern Shaanxi Province was selected as the study area in this paper. On the basis of sampling and analysis, multiple environmental tracers such as characteristic ions and stable isotopes (δ(D), δ(18O-H2O), δ(15N-NO-3), δ(18O-NO-3)) were combined to study the spatial distribution characteristics, sources and transformation process of nitrate in groundwater, and the proportional contribution of different sources to nitrate in groundwater was quantitatively evaluated by using isotope mixing model (SIAR). The results show that the percentages of samples with NO-3 concentrations exceeding the WHO drinking water standard (50 mg/L) in shallow groundwater and deep groundwater were 73.7% and 51.9%, respectively, and the overall nitrate contamination level in shallow groundwater (average 91.40 mg/L) was higher than that in deep groundwater (average 78.24 mg/L). The spatial distribution of NO-3 content in shallow groundwater and deep groundwater was influenced by land use types as follows: forest>cropland>grassland>orchard>urban land, and urban land>forest>orchard>grassland>cropland, respectivtly. The main sources of NO-3 in groundwater were soil organic nitrogen, chemical fertilizers, and manure and sewage. Nitrification was the dominant transformation process of nitrogen nutrients in groundwater, while the denitrification was not obvious. The analysis results of SIAR model show that nitrate in groundwater was significantly affected by agricultural activities and urbanization. The contribution rates of soil organic nitrogen, chemical fertilizers, manure and sewage, and atmospheric precipitation to nitrate were 46.9%, 27.3%, 22.8%, and 3.0% for shallow groundwater, and 31.1%, 21.8%, 43.8%, and 3.3% for deep groundwater, respectively.

Water quality and quantity should be paid more attention in regions with arid climate and thick vadose zones since the limited groundwater cannot be replenished rapidly once polluted. This study focused on the Loess Plateau of China to investigate the geochemical mechanism affecting groundwater chemistry and to calculate contribution rates of multiple sources to groundwater solutes. We employed multiple methods (diagrams, bivariate analyses, hierarchical cluster analysis (HCA), sodium adsorption ratio (SAR), water quality index (WQI), correlation analysis, and forward model) for the above purposes. We collected 64 groundwater samples in the thick loess deposits in June 2018 (flood season) and April 2019 (dry season). The average concentrations of cation were in the order of Ca2+ > Na+ > Mg2+ > K+ in the flood season, and Na+ > Ca2+ > Mg2+ > K+ in the dry season. The order of anions contents in the flood season and the dry season were HCO3- > SO42- > Cl- > NO3-. The major hydrochemical facies were Ca-HCO3 and Ca·Mg-HCO3 in the flood season and Na·Ca-HCO3·SO4 and Na-HCO3 in the dry season, respectively. Most of the groundwater (95% in the flood season and 96% in the dry season) was suitable for drinking, and the overall water quality was acceptable for irrigation. Mineral dissolution and cation exchange were important natural processes affecting groundwater chemistry. The forward model showed that the contribution of atmospheric input, anthropogenic input, evaporite dissolution, silicate weathering, and carbonate weathering to solutes in groundwater was 2.3±1.5%, 5.0±7.1%, 19.3±21.4%, 42.8±27.3%, and 30.6±27.1% in the flood season, and 9.1±6.4%, 3.4±5.2%, 20.3±15.9, 56.6±23.2%, and 10.7±15.4% in the dry season, respectively. Obviously, silicate and carbonate weathering contribute the most to groundwater chemistry in the flood season, while silicate weathering and evaporite dissolution contribute the most in the dry season. Although the overall contribution of anthropogenic inputs was insignificant, it was the dominant source of solutes for local groundwater. This study provides fundamental information for water management in arid areas.

The rapid development of urbanization and agriculture poses serious impacts on groundwater in arid and semi-arid areas, which typically have high groundwater depletion rates. In this study, chemical and isotopic analyses combined with different data interpretation methods (diagrams, bivariate analyses, principal component analysis (PCA), and hierarchical cluster analysis (HCA)) were used to identify the major factors controlling groundwater chemistry in an arid and semi-arid region of North China. Sixty-four groundwater samples (35 from unconfined aquifer, 29 from confined aquifer) were collected in Baotou City, North China, and 17 chemical variables were detected for each sample. The complex hydrochemical types in unconfined groundwater (e.g., HCO3-Ca·Mg, HCO3·Cl-Na·Mg, SO4-Na·Mg, and Cl·SO4-Na types) may be related to anthropogenic activities, while the main hydrochemical types in confined groundwater are HCO3-Ca·Mg, HCO3-Na·Mg, HCO3·Cl-Na·Ca, SO4·HCO3-Na·Mg, and Cl·SO4-Na types. Three component models for unconfined and confined groundwater were revealed using PCA, which explained approximately 79.69% and 80.68% of the data variance, respectively, providing a deeper insight into groundwater composition controlled by geochemistry and anthropogenic activities. Three clusters were yielded from HCA. The factors and identified clusters were verified with hydrochemical investigations. Among the natural factors, the main hydrochemical processes involve the dissolution of various minerals (halite, gypsum, feldspar, fluorite, mirabilite, biotite, dolomite, and calcite), cation exchange, evaporation, and mixing. The anthropogenic factors include domestic sewage intrusion and agricultural activities, which are most likely to lead to further declines in groundwater quality. These findings may be useful for improving groundwater resource management for sustainable development in arid and semi-arid areas.

Tensile strength plays a crucial role in many engineering activities involving soils and soft rocks. Currently, several methods for tensile strength determination exist, the most common of which include the direct tension method, Brazilian test, ring test, axial fracturing test, bending test, and hydraulic fracturing test. However, outstanding problems associated with these methods, e.g., undesirable eccentric forces and damage of specimen ends, significantly affect obtained tensile strength values. To overcome these problems, we propose an alternative direct tension test method together with the newly developed apparatus. The proposed method uses an annular specimen that is tension-loaded on the inner hole. The method was evaluated through a series of tests on undisturbed soil and remolded gypsum-sand mixture specimens. For validation, comparison of results between the proposed method and the International Society for Rock Mechanics (ISRM)-suggested method was performed. Based on the results of the experimental program, the proposed method is considered more capable of and more suitable for determining the tensile strength of soils and soft rocks than the ISRM-suggested method.

Hydrogeochemistry and isotope hydrology were carried out to investigate the spatial distribution of fluoride (F-) and the mechanisms responsible for its enrichment in the western region of the Ordos basin, northwestern China. Sixty-two groundwater samples from the unconfined aquifer and fifty-six from confined aquifer were collected during the pre-monsoon (June 2016). Over 77% of groundwater samples from the unconfined aquifer (F- concentration up to 13.30 mg/L) and approximately 66% from confined aquifer (with a maximum F- concentration of 3.90 mg/L) exhibit F- concentrations higher than the Chinese safe drinking limit (1.0 mg/L). High-F- groundwater presents a distinctive hydrochemical characteristic: a high pH value and HCO3- concentration with Ca-poor and Na-rich. Mineral dissolution (e.g., feldspar, calcite, dolomite, fluorite), cation exchange and evaporation in the aquifers predominate the formation of groundwater chemistry, which are also important for F- enrichment in groundwater. Mixing with unconfined groundwater is a significant mechanism resulting in the occurrence of high-F- groundwater in confined aquifer. These findings indicate that physicochemical processes play crucial roles in driving F- enrichment and that may be useful for studying F- occurrence in groundwater in arid and semi-arid areas.

Groundwater is a vital source for domestic and irrigation purposes in the loess area of Northwest China where climate is arid. However, the quality of groundwater in this area is deteriorating due to intensive industrial and agricultural activities, and this has a great adverse impact on human health. In order to better understand the pollution status of groundwater and the health risks to local residents, comprehensive water quality index was applied to assess the quality of drinking water in Yulin City, Northwest China, and sodium adsorption ratio, sodium percentage, residual sodium carbonate and permeability index were used to evaluate the quality of irrigation water. Moreover, the health risks caused by ingestion of groundwater were evaluated using the model proposed by the Ministry of Environmental Protection of the PR China. The results show that all groundwater samples for irrigation will not induce soil salinization, but more than half of them are not suitable for drinking, and Fe, Mn, TH, Mg2+ and NO3–N are the common contaminants which are mainly from natural processes, industrial and agricultural activities. The health risk assessment indicates that children face greater non-carcinogenic risk than adults. The order of contribution of contaminants to non-carcinogenic risk is NO3 − > As > F− > Fe > Mn > Ba2+ > Cr6+ > Zn > NO2 −. The average carcinogenic risk of carcinogens (Cr6+ and As) is 1.17 × 10−4 and 1.37 × 10−4 for adults and children, respectively, which surpasses the permissible level (1 × 10−6) stipulated by the Ministry of Environmental Protection of the PR China. Hence, effective measures are highly demanded to manage groundwater pollution and reduce the risks to human health.

In order to determine the groundwater quality status and health risks caused by target pollutants in the oil and gas field of Dingbian County, 30 groundwater samples were collected and quantitative analyses of 20 parameters. Hydrogeochemical characteristics of groundwater was analysed using Durov diagram, statistical analysis, Gibbs diagram and correlation analysis. Entropy weighted water quality index evaluated groundwater quality. Health risk assessment model was used to evaluate the health risk to adults and children caused by target pollutants (NO3 −, NH4 +, NO2 −, F−, Mn, Zn, Ba2+, As and Cr6+) through direct ingestion and dermal absorption. The results show that the groundwater is alkaline in the study area and the abundance of cations is Na+ > Mg2+ > Ca2+ > K+ and anions is SO4 2− > Cl− > HCO3 −. All evaluation indicators except K+, NH4 +, Zn and Ba2+ in groundwater exceed the permissible limits of drinking water. Gibbs diagrams display that evaporation crystallisation and rock weathering control the groundwater hydrochemical components. The study shows 53.4% of groundwater samples are not suitable for drinking in the study area. Total dissolved solids (TDS), Mg2+, Na+, SO4 2−, Cl− and total hardness are the main contaminants which mainly come from industrial activities. The health risk assessment shows that the total risks of carcinogens (As and Cr6+) to adults and children are 4.20 × 10−4 and 1.14 × 10−3 per year, respectively, which are far higher than the International Commission on Radiologic Protection recommended maximum acceptable annual level (5.0 × 10−6 per year).

The purpose of this study was to evaluate groundwater quality and health risks of nitrogen pollution in the Shenfu mining area of northwest China. Statistical analysis, Durov diagrams, Gibbs diagrams and correlation analysis were applied to analyse the groundwater chemistry. Entropy weighted water quality index was applied for groundwater quality assessment. The non-carcinogenic risks to adults and children due to drinking nitrogen-contaminated groundwater were assessed using the models recommended by US Environmental Protection Agency. The study shows that the abundances of anions and cations are in the order of HCO3 − > SO4 2− > Cl− and Ca2+ > Na+ > Mg2+, respectively. Gibbs diagrams reveal that groundwater chemistry is mainly controlled by rock weathering. Cation exchange and the dissolution of aluminate minerals, carbonate minerals and halite are the main sources of major ions in the groundwater. More than half of the groundwater in the study area is medium quality, marginally suitable for multiple purposes. NH4–N, NO2–N and organic matter are the main pollutants which mainly derived from agricultural and industrial activities. The mean total hazard index (THI) value of nitrogen for adults and children is 1.563 and 3.126, respectively, which surpasses the permissible limit (THI = 1) recommended by USEPA. Moreover, the NO3–N level in some medium quality water, which is considered suitable for drinking purposes according to Chinese drinking water quality standards, poses high non-carcinogenic risks to adults and children. Therefore, the Chinese government should revise the concentration limit of NO3–N (20 mg/L) in medium quality water so as to ensure the safety of drinking water.

Hydrodynamics dispersion test mainly studies the change in temporal dimension and spatial dimension and dispersion law of groundwater solvent, and then the forecasting development tendency of groundwater contamination. Through the measured data tested by spot dispersion test in one factory in Bao Tou, dispersity can be acquired in the way of a standard curve. The specific results show that longitudinal dispersity (aL) of shallow aquifers is 1.19 similar to 1.28 cm, experience value of transverse dispersity (aT) is 0.24 similar to 0.26 cm. The results can provide a scientific basis for establishing effective prophylaxis and treatment of groundwater contamination in a factory.