Hydrogeochemical Characteristics and Groundwater Quality Evaluation Based on Multivariate Statistical Analysis

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.

Drinking water quality evaluation in supply systems in Wuhan, China: application of entropy weight water quality index and multivariate statistical analysis

In this study, source water, finished water, and tap water were sampled monthly from two large drinking water treatment plants in Wuhan city, China for 12 months where physicochemical and microbiological parameters were measured, and the complex monitoring data was analyzed using single-factor assessment method, entropy weight water quality index (EWQI), and multivariate statistical techniques (i.e., cluster analysis (CA), discriminant analysis, and correlation analysis). The results of the single-factor assessment method showed that the total nitrogen pollution was the main problem in the source water quality, and the finished and tap water met the required quality standards. The EWQI values indicated that the overall quality of the source, finished, and tap water samples was "Excellent." In addition, strengthening monitoring of parameters with high entropy weights, including Pb, Hg, sulfide, Cr in surface water and Hg, aerobic bateria count, and As in drinking water, were suggested, as they were prone to drastic changes. Spatial CA grouped the finished and tap water samples from the same plant into a cluster. Temporal CA grouped 12 sampling times of source water into Cluster 1 (June), Cluster 2 (April-May, and July-November), and Cluster 3 (December-March). Concerning finished and tap water, except the October was regrouped, the result of temporal CA was consistent to that of the source water. Based on similar characteristics of water samples, monitoring sites and frequency can be optimized. Moreover, stepwise discriminant analysis indicated that the spatiotemporal variations in water quality among CA-groups were enough to be explained by four or five parameters, which provided a basis for the selection of monitoring parameters. The results of correlation analysis showed that few pairwise correlations were both significant (P < 0.05) and stable across sampling sites, suggesting that the number of monitoring parameters was difficult to reduce through substitution. In summary, this study illustrates the usefulness of EWQI and the multivariate statistical techniques in the water quality assessment and monitoring strategy optimization.

Assessment of hydrogeochemistry in groundwater using water quality index model and indices approaches

Groundwater resources around the world required periodic monitoring in order to ensure the safe and sustainable utilization for humans by keeping the good status of water quality. However, this could be a daunting task for developing countries due to the insufficient data in spatiotemporal resolution. Therefore, this research work aimed to assess groundwater quality in terms of drinking and irrigation purposes at the adjacent part of the Rooppur Nuclear Power Plant (RNPP) in Bangladesh. For the purposes of achieving the aim of this study, nine groundwater samples were collected seasonally (dry and wet season) and seventeen hydro-geochemical indicators were analyzed, including Temperature (Temp.), pH, electrical conductivity (EC), total dissolved solids (TDS), total alkalinity (TA), total hardness (TH), total organic carbon (TOC), bicarbonate (HCO3-), chloride (Cl-), phosphate (PO43-), sulfate (SO42-), nitrite (NO2-), nitrate (NO3-), sodium (Na+), potassium (K+), calcium (Ca2+) and magnesium (Mg2+). The present study utilized the Canadian Council of Ministers of the Environment water quality index (CCME-WQI) model to assess water quality for drinking purposes. In addition, nine indices including EC, TDS, TH, sodium adsorption ratio (SAR), percent sodium (Na%), permeability index (PI), Kelley's ratio (KR), magnesium hazard ratio (MHR), soluble sodium percentage (SSP), and Residual sodium carbonate (RSC) were used in this research for assessing the water quality for irrigation purposes. The computed mean CCME-WQI score found higher during the dry season (ranges 48 to 74) than the wet season (ranges 40 to 65). Moreover, CCME-WQI model ranked groundwater quality between the "poor" and "marginal" categories during the wet season implying unsuitable water for human consumption. Like CCME-WQI model, majority of the irrigation index also demonstrated suitable water for crop cultivation during dry season. The findings of this research indicate that it requires additional care to improve the monitoring programme for protecting groundwater quality in the RNPP area. Insightful information from this study might be useful as baseline for national strategic planners in order to protect groundwater resources during the any emergencies associated with RNPP.

Groundwater Quality Assessment in the Northern Part of Changchun City, Northeast China, Using PIG and Two Improved PIG Methods

As a numerical indicator, the pollution index of groundwater (PIG) has gained a great deal of popularity in quantifying groundwater quality for drinking purposes. However, its weight-determination procedure is rather subjective due to the absolute dependence on experts’ experience. To make the evaluation results more accurate and convincing, two improved PIG models (CRITIC-PIG and Entropy-PIG) that integrate subjective weights and objective weights were designed, and they were employed to appraise groundwater suitability for drinking purposes in the northern part of Changchun City. A total of 48 water samples (34 unconfined water samples and 14 confined water samples) with abundances of Ca²⁺ and HCO₃⁻ were collected and tested to obtain the data for the analyses. The results showed that 60.4%, 47.9% and 60.4% of the water samples manifested insignificant pollution and were marginally potable based on the values of the PIG, CRITIC-PIG and Entropy-PIG, respectively. Though 48% of the water samples had different evaluation results, their level difference was mostly 1, which is relatively acceptable. The distribution maps of the three sets of PIG values demonstrated that the quality of groundwater was the best in Dehui City and the worst in Nongan County. Groundwater contamination in the study area was mainly caused by the high concentrations of TDS, TH, Fe³⁺, F⁻ and NO₃⁻, which not only came from geogenic sources but also anthropogenic sources.

Temporal and Spatial Water Quality Assessment of the Geumho River, Korea, Using Multivariate Statistics and Water Quality Indices

The Geumho River in South Korea passes through a metropolitan area with a high population density and multiple industrial complexes; therefore, the water quality of this river is of significance for human health and economic activities. This study assesses the water quality of the Geumho River to inform river water quality management and improve pollution control using multivariate statistics and the Korean Water Quality Index (KWQI). Principal component and factor analyses identified factors related to organic pollutants and metabolism (principal factor 1) and phosphorus and fecal coliform content (principal factor 2). Based on the results of the cluster analysis, it was classified into four groups in time and three groups in space. Six temporal variables and seven spatial variables were extracted from discriminant analysis results; the most important water quality variables were high during the spring and summer seasons and in the midstream and downstream regions. Temporally, the KWQI was the highest in winter and the lowest in spring; spatially, the KWQI was the highest in the upstream and the lowest in the midstream sections. These results indicate that to improve effectiveness, water management interventions in the Geumho River should focus on the urban midstream section and spring season.

Hydrodynamics, Hydrochemistry, and Stable Isotope Geochemistry to Assess Temporal Behavior of Seawater Intrusion in the La Yarada Aquifer in the Vicinity of Atacama Desert, Tacna, Peru

The La Yarada aquifer is the primary water resource for municipal, irrigation, and industrial uses in the semi-arid Tacna, Peru. Presently, over-pumping has caused severe groundwater management problems, including the abandonment of saline water wells. This study presents multivariate analysis and chemical–isotopic trends in water to investigate seawater intrusion and hydrogeological processes affecting water quality. The chemical and isotopic analysis of water samples, collected in two campaigns in the dry (August 2020) and wet (November 2020) seasons, together with the 1988 data, were evaluated with a mixing model, cluster, and factor analysis. The hydrochemical and isotopic mixing model suggested the formation of a wedge with 20% seawater intrusion. The heterogeneity of piezometric map isolines corroborates the wedge formation associated with the groundwater movement. The spatial distributions of factors, FA1 and FA2, suggest two processes of seawater front movement: dispersion (diffusion) of chemical elements and different types of water mixing, respectively. At the edge of the La Yarada aquifer, the water head was relatively low, permitting seawater and freshwater mixing. On the other hand, along the sea-land boundary, the water head of the La Yarada aquifer was relatively high, avoiding seawater and freshwater mixing; however, the chemical species were migrating from the seawater to the groundwater due to the diffusion processes. The cluster 4 samples are in the region corresponding to the isotopic mixing process represented by the FA2, while cluster 4 describes the chemical diffusion process represented by the FA2. Thus, the integrated approach is helpful to assess the seawater intrusion mechanisms in coastal aquifers in a semi-arid region.

Multivariate Analysis of Water Quality Data for Drinking Water Supply Systems

Vulnerability of drinking water supply systems (DWSSs) depends on different factors such as failures, loss of security, man-made threats, and the change and deterioration of supply-water quality. Currently, the lifespan of several DWSSs worldwide has been exceeded, exasperating these issues. The monitoring activity and the transparency of information on water availability and quality are becoming increasingly important in accordance with the national regulations and standards, and with guidelines of the World Health Organization (WHO). These activities can be considered as support and guidance tools for identifying health-related risks, for building a safe management of drinking water supply systems, and for improved user confidence in the consumption of tap water. In this context, in the present work an analysis of the quality monitoring data of DWSSs was carried out using multivariate techniques. The analysis considered several chemical–physical parameters collected in the period 2013–2020 for some DWSSs in the Emilia-Romagna region, Italy. Principal component analysis (PCA) and cluster analysis (CA) methods were used to process and reduce the dimensionality of the data, to highlight the parameters that have the greatest influence on the qualitative state of the supplied water and to identify clusters.

Hydrogeochemical and Hydrodynamic Assessment of Tirnavos Basin, Central Greece

A combined hydrogeochemical and hydrodynamic characterization for the assessment of key aspects related to groundwater resources management was performed in a highly productive agricultural basin of the Thessaly region in central Greece. A complementary suite of tools and methods—including graphical processing, hydrogeochemical modeling, multivariate statistics and environmental isotopes—have been applied to a comprehensive dataset of physicochemical analyses and water level measurements. Results revealed that the initial hydrogeochemistry of groundwater was progressively impacted by secondary phenomena (e.g., ion exchange and redox reactions) which were clearly delineated into distinct zones according to data processing. The progressive evolution of groundwater was further verified by the variation of the saturation indices of critical minerals. In addition, the combined use of water level measurements delineated the major pathways of groundwater flow. Interestingly, the additional joint assessment of environmental isotopes revealed a new pathway from E–NE (which had never before been validated), thus highlighting the importance of the joint tools/methods application in complex scientific tasks. The application of multivariate statistics identified the dominant processes that control hydrogeochemistry and fit well with identified hydrodynamic mechanisms. These included (as dominant factor) the salinization impact due to the combined use of irrigation water return and evaporitic mineral leaching, as well as the impact of the geogenic calcareous substrate (mainly karstic calcareous formations and dolostones). Secondary factors, acting as processes (e.g., redox and ion exchange), were identified and found to be in line with initial assessment, thus validating the overall characterization. Finally, the outcomes may prove to be valuable in the progression toward sustainable groundwater resources management. The results have provided spatial and temporal information for significant parameters, sources, and processes—which, as a methodological approach, could be adopted in similar cases of other catchments.