Groundwater pollution risk assessment based on groundwater vulnerability and pollution load on an isolated island

Identification of groundwater pollution sources and health risk assessment in the Fengshui mining area of Central Shandong, China

The crux of groundwater protection lies in a profound understanding of the sources of pollutants and their impacts on human health. This study selected 47 groundwater samples from the Fengshui mining area in central Shandong Province, China, employing advanced hydrogeochemical techniques, positive matrix factorization (PMF), and Monte Carlo analysis methods, aimed at unveiling the characteristics, origins, and health risks of water pollutants. The results indicated that the majority of samples exhibited a slightly alkaline nature. Notably, the concentrations of fluoride (F-) and nitrate (NO3-) exceeded China's safety standards in 40.43% and 23.40% of the samples, respectively. Moreover, a water quality index (WQI) below 50 was observed in approximately 68.09% of the sites, suggesting that the water quality in these areas generally met acceptable levels. However, regions with higher WQI values were predominantly located in the northern and southern parts of the mining area. PMF analysis revealed that regional geological and industrial activities were the primary factors affecting water quality, followed by mining discharges, fundamental geological and agricultural processes, and leachate enrichment activities. The health risk assessment highlighted the heightened sensitivity of the youth demographic to fluoride, with a more pronounced non-carcinogenic risk compared to nitrate, affecting about 31.89% of the youth population. Hence, it is imperative for local authorities and relevant departments to take prompt actions to remediate groundwater contamination to minimize public health risks.

Groundwater heavy metal(loid)s risk prediction based on topsoil contamination and aquifer vulnerability at a zinc smelting site

Groundwater pollution is a recurrent problem in abandoned non-ferrous metal smelting sites, and its severity is influenced by topsoil contamination, hydrogeological characteristics, and hydrogeochemical conditions. In such unique areas, traditional methods for evaluating groundwater pollution risk are biased, as the long production history of these sites have led to highly polluted and heterogeneous soil and groundwater. Herein, based on a typical lead-zinc smelting site, As, Pb, Zn, Cd, Mn, and Ni were found to be the predominant heavy metal (loid)s in groundwater, with respective exceedance rates of 44.4%, 50.0%, 72.2%, 88.9%, 88.9%, and 61.1%. Combined with the groundwater pollution characteristics, the representative hydrogeochemical factors were screened out to optimize the following aquifer vulnerability evaluation using the AHP-DRASTICH method. A comprehensive evaluation model (DI-NCPI) for groundwater pollution risk was established by combining the DRASTICH index (DI) obtained after optimization and the Nemerow comprehensive contamination index (NCPI) of topsoil. The fit between DI-NCPI and groundwater heavy metal (loid) pollution index reached 0.956, which laterally confirms that the model has some reference value. In terms of distribution, the high-risk and very high-risk zones were mainly concentrated in the zinc smelting system, located in the southeastern and central-western parts of the site. These areas have relatively high levels of topsoil contamination and aquifer vulnerability and require focused attention in site remediation. This research highlights the importance of combining topsoil contamination and aquifer vulnerability to evaluate groundwater pollution risk in smelting areas. It provides a more targeted reference for groundwater remediation strategies in abandoned smelting sites, as well as severely polluted industrial areas.

Hydrodynamic Groundwater Modeling and Hydrochemical Conceptualization of the Closure Mining Area of the WuMa River Watershed of China

The WuMa River (WMR) watershed is located in Renhuai City, Guizhou Province of China, which is a first-class tributary of the Chishui River. The geochemical investigation mainly included the determination of groundwater pH, total hardness, total dissolution solid, major cationic and anionic, and the geochemical groundwater modeling. The principal component analysis (PCA) and Gibbs model were used to analyze the pollution type and geochemical composition. The geochemical investigation results show that the cations of groundwater are dominated by Ca2+ and the anions are dominated by HCO3-; therefore, two main hydrochemical types in the study area are identified as Ca2+-Mg2+-HCO3- and Ca2+-Mg2+-SO42-. The chemical composition of groundwater in this area is mainly controlled by weathering of the carbonate rocks. The ion concentration of groundwater in the study area exhibited significant spatial variability between dry and wet seasons, while temporal changes of cationic and anionic concentrations exhibited irregularities. In PCA and FA analysis, PC1, PC2, and PC3 were extracted, which could explain 51.92, 26.98, and 12.61% of the total information, respectively. F1 explained 67.44% of the total variance, among which Ca2+, Mg2+, K+, SO42-, and Cl- contributed the most among the factors and were the main factors controlling the chemical composition of groundwater. The relative error between the measured water level and the simulated water level is less than 2%, which meets the requirements of simulation accuracy. During the simulation period of the model, a total recharge of 339.05 × 104 m3 was observed in the simulated area, primarily attributed to infiltration from rainfall. The total excretion amounted to 330.78 × 104 m3, primarily through evaporation, with a minor amount of lateral outflow. The migration pathway of pollutants in groundwater primarily follows the direction of groundwater flow while diffusing vertically. The migration range of the pollutant is in accordance with the direction of groundwater flow and extends along the larger hydraulic gradient, demonstrating consistency. The findings of this study serve as a reminder that the closure of coal mines can constitute a significant source of water pollution. Simultaneously, they offer empirical data and theoretical references for the simulation and prediction of groundwater contamination in enclosed coal mines.

Groundwater nitrate pollution risk assessment based on the potential impact of land use, nitrogen balance, and vulnerability

The predicting groundwater nitrate pollution risk, especially in terms of changes in fertilizing, has not been fully investigated so far. In particular, there is no comprehensive method to assess this risk in areas of different land use type, and not only in agricultural areas. The aim of this study was to develop a novel multicriteria methodology for groundwater nitrate pollution risk assessment, which meets these issues. A further aim was to determine how much this risk would change if the amount of organic and synthetic fertilization was reduced. An assumption was that groundwater pollution risk is a combination of the potential adverse impacts of land use, fertilization, and intrinsic groundwater vulnerability to pollution. The impact of fertilization was holistically evaluated by balancing nitrogen from spatially differentiated the size of the breeding, species of livestock, manure and synthetic fertilizers input, and spatially differentiated topsoil, with nitrogen uptake by different crops. The nitrate concentration in the leachate was used as a measure of the impact of fertilization. This concentration was compared to the natural baseline nitrate concentration in groundwater. Three fertilization scenarios for groundwater pollution risk assessment in two study areas were discussed. Under typical agricultural, climatic, soil, and geological conditions in Europe for the current total fertilization level of 95-120 kg N ha-1 groundwater nitrate pollution risk is low and moderate, but for fertilization of 150-180 kg N ha-1, a reduction in the total fertilization (synthetic and manure) by 40 to 50% may be required to achieve low risk of degradation of natural groundwater quality. Predictive simulations of groundwater nitrate pollution risk confirmed that reducing synthetic and organic fertilization has an effect, especially in areas with intensive fertilization. This method may allow for a holistic and scenario-based assessment of groundwater pollution risk and may help decision-makers introduce solutions to manage this risk under conditions of climate change, preservation of groundwater quality, and food security.

A comparative study of DNAPL migration and transformation in confined and unconfined groundwater systems

To explore the migration and transformation process of dense non-aqueous liquid (DNAPL) pollutants' multiphase flow, specifically nitrobenzene (NB), in confined groundwater (CG) versus unconfined groundwater (UG), a two-dimensional sandbox experimental device was designed and constructed. This involved constructing a vadose zone-UG- aquitard-CG structure, which was then subjected to different scenarios. Real-time analysis and numerical simulation methods were established and employed, with a particular focus on the detailed investigation results of actual contaminated site. The study found that when the same amount of NB was injected, the special structure of the CG layer resulted in a more pronounced reverse diffusion of NB in both the dissolved and NAPL phases. This was especially true for the dissolved phase, which was more likely to diffuse reversely. Meanwhile, CG did not directly interact with the vadose zone, and there was no loss of gas phase NB after the leakage in CG. As a result, higher concentrations of dissolved phase NB were generated, leading to the emergence of a larger area of NB contaminant plumes with CG flow. Importantly, the simulation study of the actual site and the laboratory experimental results were found to be validated, further validating the conclusion that direct leakage of NB into CG results in a higher concentration and larger area of dissolved phase contaminant plume, causing more serious pollution to the groundwater environment.

Implementation and evaluation of different techniques to modify DRASTIC method for groundwater vulnerability assessment: a case study from Bouficha aquifer, Tunisia

Groundwater vulnerability assessment has nowadays evolved into an essential tool towards proper groundwater protection and management, while the DRASTIC method is included among the most widely applied vulnerability assessment methods. However, the high uncertainty of the DRASTIC method mainly associated with the subjectivity in assigning parameters ratings and weights has driven many researchers to apply various methods for improving its efficiency. In this context, in the present study, different techniques were implemented with the aim of modifying the DRASTIC framework and thus enhancing its performance for groundwater vulnerability assessment in the Bouficha aquifer, Tunisia. In a first stage, the land use type (L) was incorporated as an additional parameter in the typical DRASTIC framework, thus taking into consideration the impact of anthropogenic activities on groundwater vulnerability. Subsequently, the rating and weighting systems of the developed DRASTIC-L framework were modified through the application of statistical methods (DRASTIC-L-SA) and genetic algorithms (GA) (DRASTIC-L-GA) in an attempt to investigate and compare both linear and nonlinear modifications. To evaluate the various vulnerability frameworks, correlation between vulnerability values and nitrate concentrations, expressed as Spearman's rank correlation coefficient (ρ) and Correlation Index (CI), was examined. The results revealed that the DRASTIC-L-GA framework developed by applying a fully GA-based optimization procedure provided the highest values in terms of the performance metrics used, making it the most suitable for the study area. In addition, the aquifer under study was found to be less vulnerable to pollution when employing the typical DRASTIC framework instead of the modified ones, leading to the conclusion that the former substantially underestimates pollution potential in the study area.

Potential toxic element contamination and non-carcinogenic risk assessment of groundwater from rapidly growing urban areas in Telangana, India

Groundwater is a critical resource for drinking purposes that is under pressure and polluted with multiple inorganic contaminants. Among various contaminants, potentially toxic element contamination in groundwater has significant public health concerns due to their toxicity at a low level of exposure. This investigation aimed to assess the toxic element contamination and associated non-carcinogenic human health risk at rapidly growing urban centers in Telangana to ensure potable water and to generate baseline data in the study province. Thirteen potential toxic trace elements (Al, As, B, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Se, and Zn) were determined in 35 groundwater samples collected from the Karimnagar and Siddipet smart cities in lower Manair River basin using inductively coupled plasma mass spectrometry (ICP-MS). The trace element concentration is found in the range for Al (1-112 µg/L), As (2-8 µg/L), B (34-438 µg/L), Cd (bdl-2 µg/L), Co (bdl-17 µg/L), Cr (bdl-4 µg/L), Cu (bdl-216 µg/L), Fe (4-420 µg/L), Mn (bdl-3311 µg/L), Ni (5-31 µg/L), Pb (bdl-62 µg/L), Se (1-18 µg/L), and Zn (3-1858 µg/L). Analytical data of groundwater revealed the occurrence of toxic elements observed as above the acceptable limits of Bureau of Indian Standards for drinking purposes found in the order of Al > Ni ≥ Mn > Se ≥ Cu ≥ Pb > Fe with 26% > 14% ≥ 14% > 9% ≥ 9% ≥ 9% > 6% of samples, respectively. The non-carcinogenic health risk to humans upon groundwater ingestion has been evaluated and found to be non-hazardous for all the individual elements studied except for aresenic. However, cumulative hazard quotient observed as > 1 in the category of infants and children might be a major potential health concern. This study provided baseline data and suggested implementing preventive measures to protect human health around the urban areas of lower Manair river basin, Telangana, India.

Full profile contamination process simulation and risk prediction of synthetic musk from reclaimed water receiving river to groundwater via vadose zone: A case study of Chaobai River

Long-term infiltration from river receiving reclaimed water will pose potential risk to vadose zone and groundwater because of the persistent and highly toxic contaminants. In order to predict the spatio-temporal distribution of ecological and health risk, a coupled model of HYDRUS-GMS combined risk quotient was proposed. The model can accurately predict water flow, solute transport and risk with model due to the acceptable efficiency (E:0.99), mean absolute error (MAE:0.031 m) and root-mean-square error (RMSE:0.039 m). The content of galaxolide (HHCB), a typical pharmaceutical and personal care product with hydrophobicity and refractory in reclaimed water, increased in vadose zone at an accumulative rate of 6.1 ng g^-1 year^-1 with infiltration time extension. The accumulation will pose ecological risk after 53 years infiltration. The potential risk will extent to groundwater once penetrate through vadose zone, and mainly diffuse along groundwater flow direction. The migration rate along horizontal direction of groundwater flow is 0.03396 m d^-1, which is 9.7 and 1.1 times higher than longitudinal and vertical rates due to the variation of driving force in three directions. The migration rate of HHCB was 2.6% of groundwater flow due to hydrophobicity (LogKow = 5.9). The complete biochemical decomposition of HHCB will take approximately 0.38 year through metabolite within 182.65 m distance. The persistence was attributed to the high chronic toxicity and the low bio-availability. The major biochemical metabolism of HHCB was enzymatic hydrolysis, ring opening, decarboxylation, which was decomposed and carbonized within approximately 0.38 year after 182.65 m migration distance. This study provided a new approach to predict the spatio-temporal risk distribution due to reclaimed water reuse.

Identification and Risk Assessment of Priority Control Organic Pollutants in Groundwater in the Junggar Basin in Xinjiang, P.R. China

The Junggar Basin in Xinjiang is located in the hinterland of Eurasia, where the groundwater is a significant resource and has important ecological functions. The introduction of harmful organic pollutants into groundwater from increasing human activities and rapid socioeconomic development may lead to groundwater pollution at various levels. Therefore, to develop an effective regulatory framework, establishing a list of priority control organic pollutants (PCOPs) is in urgent need. In this study, a method of ranking the priority of pollutants based on their prevalence (Pv), occurrence (O) and persistent bioaccumulative toxicity (PBT) has been developed. PvOPBT in the environment was applied in the screening of PCOPs among 34 organic pollutants and the risk assessment of screened PCOPs in groundwater in the Junggar Basin. The results show that the PCOPs in groundwater were benzo[a]pyrene, 1,2-dichloroethane, trichloromethane and DDT. Among the pollutants, benzo[a]pyrene, 1,2-dichloroethane and DDT showed high potential ecological risk, whilst trichloromethane represented low potential ecological risk. With the exception of benzo[a]pyrene, which had high potential health risks, the other screened PCOPs had low potential health risks. Unlike the scatter distribution of groundwater benzo[a]pyrene, the 1,2-dichloroethane and trichloromethane in groundwater were mainly concentrated in the central part of the southern margin and the northern margin of the Junggar Basin, while the DDT in groundwater was only distributed in Jinghe County (in the southwest) and Beitun City (in the north). Industrial and agricultural activities were the main controlling factors that affected the distribution of PCOPs.

Multivariate and spatio-temporal groundwater pollution risk assessment: A new long-time serial groundwater environmental impact assessment system

Groundwater pollution risk assessment is an important part of environmental assessment. Although it has been developed for many years, there has not yet been a multi-dimensional method that takes into account long time series and spatial factors. We proposed a new method combines the advantages of remote sensing cloud computing, long-term groundwater modeling simulation and GIS technology to solve it efficiently. A coastal industrial park in Hainan was used as the study area. The depth of groundwater level, rainfall, topography and geomorphology, soil moisture, pollution source, pollution toxicity and other more than 10 parameters were used as the indexes. A comprehensive model with remote sensing cloud computing, DRASTIC model and Modflow + MT3DMS was established to assess the pollution risk from 2014 to 2021. The multi-year results indicated that the risk assessment of groundwater pollution was usually on the vertical coastal direction, and the risk increased from far away to near coast. With the discharge of pollutants in the industrial park, the pollution risk in the area 5 km away from the centre increased year by year until it became stable in 2019, and the risk in the centre of the park reached 1 level, covered an area of up to 145400 square metres, accounted for 0.012% of the whole study area. The assessment results in 2020 and 2021 fluctuate slightly compared with those in 2019. Therefore, in terms of groundwater resource protection and resource management, it is necessary to focus on the detection of pollution in the coastal zone and the pollution within 5 km of the centre to strictly control pollution discharge. In this study, the comprehensive assessment includes surface indicators, subsurface indicators, and pollutant indicators. Finally, we achieve a multivariate, spatial and long time series groundwater pollution risk assessment system, which is a new groundwater environmental impact assessment (GEIA) system.

The Interference of Pre-Processing Software for the Numerical Simulation of Groundwater on the Cognition of Environmental Students: Model Mesh Construction as an Example

(1) Background: Software for the numerical simulation of groundwater plays an important role in studying environmental problems. However, it is still unclear whether the pre-processing software of the numerical simulation of groundwater has a negative effect on the cognition of undergraduates in the environmental field who only have basic groundwater flow and solute transport knowledge and software operation skills. (2) Methods: To explore this issue, we used software meshing as an example and selected undergraduates in the environmental field to conduct the questionnaire surveys. A total of 345 undergraduate answer sheets were received, and data analysis was carried out. The students were divided into two groups, one with and another without certain basic groundwater flow and solute transport knowledge or software operation skills. (3) Results: For undergraduate students with some basic knowledge or software operation ability, the proportion of students whose cognition was adversely interfered with by the pre-processing software was 64.3%, and the ratio of students not interfered with was 35.7%. For undergraduates without groundwater flow and solute transport knowledge and relevant software operation skills, the ratios were 63.2% and 36.8%, respectively. (4) Conclusions: Pre-processing software numerical simulation of groundwater could negatively interfere with students' cognition. The basic groundwater flow and solute transport knowledge and software operation skills did not observably reduce the interference degree (p = 0.259) but had significant influences on the undergraduates' thinking modes on the numerical simulation problems (p = 0.009). The interference was mainly caused by the significant difference between the level of knowledge possessed by the students and that represented by the pre-processing software. This paper provides basic scientific data for the optimization of students' knowledge structures and the improvement of teaching methods.

Characteristics of Hydro-Geochemistry and Groundwater Pollution in Songnen Plain in Northeastern China

Agricultural production may cause groundwater pollution. This study investigated the characteristics of shallow groundwater pollution in a typical black land agricultural production area in Northeastern China and the geochemical behavior of major pollutants. A total of 27 and 23 shallow groundwater samples were collected for measuring on-site parameters and major components in 2000 and 2014, respectively. The improved integrated approach was used to assess groundwater contamination. The results showed that the groundwater was slightly polluted by agricultural activities. The average concentrations of major ions of shallow groundwater were found to be in the following order: Ca2+ > Na+ > Mg2+ > K+ for cations and HCO3− > SO42− > Cl− > NO3− for anions. Percentages of 7.4% and 34.8% of the total groundwater sample in 2000 and 2014, respectively, indicated that the shallow groundwater quality has gradually worsened in the past few decades. The concentration of NO3− was a major factor that influenced the observed groundwater quality changes. Scientific and effective fertilization of rice cultivation is an effective way to avoid groundwater pollution, and the improved groundwater quality evaluation methods can further improve the standard of groundwater resource management effectively.