A multivariate non-parametric approach for estimating probability of exceeding the local natural background level of arsenic in the aquifers of Calabria region (Southern Italy)

A regional investigation on natural background levels and contamination assessment of shallow groundwater contaminants in a coastal urbanized area

Knowledge on natural background levels (NBLs) is indispensable for evaluating groundwater contamination at regional scales. This study used a combination of modified oxidation capacity method and the box plot method to assess NBLs of common contaminants including iron, nitrite, sodium, total hardness, fluoride, sulfate, and selenium in groundwater of a coastal urbanized area of China (Pearl River Delta [PRD]), discussed geochemical factors controlling NBLs of these related contaminants in various groundwater units via multivariate statistical techniques, and evaluated groundwater comprehensive contamination in the PRD on the basis of groundwater NBLs. Results showed that NBLs of iron, nitrite, sodium, total hardness, fluoride, and sulfate in Groundwater Unit I of the PRD were higher than those in other groundwater units. Conversely, NBLs of selenium in Groundwater Units II and III of the PRD were higher than that in other groundwater units. Both of NBLs of iron and total hardness in Groundwater Unit I were higher than their allowable limits in groundwater quality standards recommended by China, while others were not. The high NBL of iron in Groundwater Unit I was probably attributed to the reductive dissolution of iron minerals in Quaternary sediments induced by the mineralization of organic matters in overlaid marine sediments. By contrast, the irrigation of river water and the leaching of trapped seawater in overlying marine sediment were likely responsible for the high NBL of total hardness in Groundwater Unit I. Using a groundwater contamination evaluation method on the basis of NBLs shows that uncontaminated groundwater accounted for 17.6%, 32.4%, 45.9%, and 53.6% in urban lands, peri-urban lands, agricultural lands, and other lands of the PRD, respectively. Groundwater with moderate to extremely high contamination was mainly distributed in Foshan, Dongguan, southern part of Guangzhou, western part of Shenzhen, northern part of Zhongshan, southern part of Zhuhai, and downstream of these cities. The leakage of industrial wastewater and domestic sewage and the irrigation of contaminated river water were likely main factors controlling groundwater comprehensive contamination in the PRD. PRACTITIONER POINTS: Groundwater natural background levels (NBLs) of seven contaminants in a coastal urbanized area (Pearl River Delta) were assessed. Geochemical factors controlling groundwater NBLs of seven contaminants in the Pearl River Delta were discussed. Groundwater comprehensive contamination in the Pearl River Delta was assessed on the basis of groundwater NBLs.

Natural background levels and driving factors of aluminum in shallow groundwater of an urbanized delta: Insight from eliminating anthropogenic-impacted groundwaters

Knowledge on natural background levels (NBLs) of aluminum (Al) in groundwater can accurately assess groundwater Al contamination at a regional scale. However, it has received little attention. This study used a combination of preselection and statistic methods consisting of the oxidation capacity and the boxplot iteration methods to evaluate the NBL of shallow groundwater Al in four groundwater units of the Pearl River Delta (PRD) via eliminating anthropogenic-impacted groundwaters and to discuss driving factors controlling high NBLs of Al in groundwater in this area. A total of 280 water samples were collected, and 18 physico-chemical parameters including Redox potential, dissolved oxygen, pH, total dissolved solids, HCO3 -, NH4 +, NO3 -, SO4 2-, Cl-, NO2 -, F-, K+, Na+, Ca2+, Mg2+, Fe, Mn, and Al were analyzed. Results showed that groundwater Al NBLs in groundwater units A-D were 0.11, 0.16, 0.15, and 0.08 mg/L, respectively. The used method in this study is acceptable for the assessment of groundwater Al NBLs in the PRD, because groundwater Al concentrations in various groundwater units in residual datasets were independent of land-use types, but they were opposite in the original datasets. The dissolution of Al-rich minerals in sediments/rocks was the major source for groundwater Al NBLs in the PRD, and the interaction with Al-rich river water was secondary one. The high groundwater Al NBL in groundwater unit B was mainly attributed to the acid precipitation and the organic matter mineralization inducing the release of Al in Quaternary sediments. By contrast, the high groundwater Al NBL in groundwater unit C mainly was ascribed to the release of Al complexes such as fluoroaluminate from rocks/soils into groundwater induced by acid precipitation, but it was limited by the dissolution of Mg minerals (e.g., dolomite) in aquifers. This study provides not only useful groundwater Al NBLs for the evaluation of groundwater Al contamination but also a reference for understanding the natural geochemical factors controlling groundwater Al in urbanized deltas such as the PRD. PRACTITIONER POINTS: The natural background level (NBL) of groundwater aluminum in the Pearl River Delta (PRD) was evaluated. The dissolution of aluminum-rich minerals in sediments/rocks was the major source for groundwater aluminum NBLs in the PRD. The acid precipitation and organic matter mineralization contribute to high groundwater Al NBL in the groundwater unit B. The acid precipitation contributes to high groundwater Al NBL in the groundwater unit C, while dissolution of magnesium minerals limits it.

A methodology for evaluating the relative pollution level of metal pollution in surface sediments of rivers based on the statistical results of relevant literatures covering world-wide rivers

Due to the intervention of human activities, the background values of riverbed sediment exhibit spatiotemporal variability, which can affect the accuracy of risk assessment results. Using risk assessment that do not rely on background values is an executable alternative to avoid such problems. In this study, a relative pollution level assessment (RPLA) method which was based on the statistical results of relevant literatures was proposed. This method includes a four-step data processing procedure to extract the evaluation indexes of relative pollution degree of pollutants in environment and a series of relative pollution status assessment methods to evaluate the overall relative pollution level and regional difference of world-wide rivers. To demonstrate how to use RPLA method, 310 relevant literatures covering world-wide rivers were selected. And the ambient background value (x̅), the world-wide threshold values (WWTV) and the relative pollution grades (LEVEL I ∼ IV) of 9 target metals (Cr, Ni, Cu, Zn, As, Cd, Pb, Sb and Tl) in riverbed surface sediments of world-wide rivers were extracted and used for evaluation. Moreover, the stability and applicability of RPLA method were evaluated. Results show that the evaluation results of RPLA method are robust and comparable with traditional evaluation method.

Hydrogeochemical characterization, quality assessment, and potential nitrate health risk of shallow groundwater in Dongwen River Basin, North China

Assessing groundwater geochemical formation processes and pollution circumstances is significant for sustainable watershed management. In the present study, 58 shallow groundwater samples were taken from the Dongwen River Basin (DRB) to comprehensively assess the hydrochemical sources, groundwater quality status, and potential risks of NO3- to human health. Based on the Box and Whisker plot, the cation's concentration followed the order of Ca2+  > Mg2+  > Na+  > K+, while anions' mean levels were HCO3-  > SO42-  > NO3-  > Cl-. The NO3- level in groundwater samples fluctuated between 4.2 and 301.3 mg/L, with 67.2% of samples beyond the World Health Organization (WHO) criteria (50 mg/L) for drinking. The Piper diagram indicated the hydrochemical type of groundwater and surface water were characterized as Ca·Mg-HCO3 type. Combining ionic ratio analysis with principal component analysis (PCA) results, agricultural activities contributed a significant effect on groundwater NO3-, with soil nitrogen input and manure/sewage inputs also potential sources. However, geogenic processes (e.g., carbonates and evaporite dissolution/precipitation) controlled other ion compositions in the study area. The groundwater samples with higher NO3- values were mainly found in river valley regions with intense anthropogenic activities. The entropy weight water quality index (EWQI) model identified that the groundwater quality rank ranged from excellent (70.7%) and good (25.9%) to medium (3.4%). However, the hazard quotient (HQ) used in the human health risk assessment (HHRA) model showed that above 91.38% of groundwater samples have a NO3- non-carcinogenic health risk for infants, 84.48% for children, 82.76% for females, and 72.41% for males. The findings of this study could provide a scientific basis for the rational development and usage of groundwater resources as well as for the preservation of the inhabitants' health in DRB.

Evaluating natural background levels of heavy metals in shallow groundwater of the Pearl River Delta via removal of contaminated groundwaters: Comparison of three preselection related methods

Assessing natural background levels (NBLs) in groundwater is a global concern. Knowledge on groundwater NBLs in urbanized areas is challenging due to the impact of complex human activities. Preselection related methods are common ones for assessing groundwater NBLs. The present study used three preselection related methods to assess groundwater heavy metals (lead, zinc, barium) NBLs in four groundwater units of the Pearl River Delta (PRD) where urbanization continues, and to identify the best one for assessing groundwater NBLs in urbanized areas. Here, methods include a preselection method (method-P), a preselection dominated method (method-PD), and a statistic dominated method (method-SD). Results showed that the method-PD was better than other two methods for assessing groundwater NBLs of heavy metals in the PRD. This is supported by the evidence that differences among heavy metals concentrations in various land-use types in residual datasets formed by the method-PD were insignificant. NBLs of lead in groundwater units I to IV assessed by the method-PD were 2.8 μg/L, 5.9 μg/L, 5.8 μg/L, and 2.6 μg/L, respectively. NBLs of zinc in groundwater units I to IV assessed by the method-PD were 30 μg/L, 180 μg/L, 160 μg/L, and 100 μg/L, respectively. NBLs of barium in groundwater units I to IV assessed by the method-PD were 120 μg/L, 120 μg/L, 90 μg/L, and 50 μg/L, respectively. Compared to the method-PD, the method-SD often underestimates groundwater NBLs of heavy metals because of using the experiential evaluation for residual datasets. The method-P also has an inaccurate evaluation of groundwater NBLs of heavy metals in comparison with the method-PD, owing to both of using the experiential evaluation and the absence of a function for outliers test. The method-P combining with an outliers test would be better than itself for assessing groundwater NBLs. Therefore, the method-PD is the first choice to be recommended for assessing groundwater NBLs in urbanized areas such the PRD. However, this method should not be taken into account for assessing groundwater NBLs in areas where groundwater Cl/Br mass ratios are invalid. Instead, the method-SD and the method-P combining with one outliers test may be choices, because no constraint for these two methods.

Hydrogeochemical and isotopic characterization of the Gioia Tauro coastal Plain (Calabria - southern Italy): A multidisciplinary approach for a focused management of vulnerable strategic systems

This work pursues the hydro-geochemical and isotopic characterization of the complex groundwater system of the Gioia Tauro Plain, one of the most important industrialized and agricultural coastal areas of southern Italy. The anthropic pressure exposes the water resources at risk of depletion and quality degradation making the plain groundwater a system of high scientific and social interest. The plain is characterized by a shallow aquifer, mostly recharged by local rains and a deep aquifer apparently less influenced by local precipitation. Both aquifers are mainly Ca-HCO₃ waters except for localized sectors where Na-HCO₃, Na-Cl and Ca-SO₄ waters are present. In deep aquifer, both prolonged interaction with sedimentary rocks, mainly deriving from the erosion of crystalline rocks, and direct cation exchange represent the primary factors controlling the formation of Na-HCO₃ waters. Mixing processes between these waters and either connate brine and/or deep thermal waters contribute to the formation of isolated high salinity Na-Cl-rich waters. In shallow aquifer, inputs of N-rich sewage and agriculture-related contaminants, and SOx emissions in proximity of the harbor are responsible of the increasing nitrate and sulphate concentrations, respectively. The Cl/Br and NO₃/Cl ratios highlight contamination mainly linked to agricultural activities and contribution of wastewater. Along the northern boundary, the warmest groundwater (Na-Cl[SO₄]) were found close to a bend of the main strike-slip fault system, locally favouring the rising of B- and Li-rich deep waters, testifying the influence of geological-structural features on deep water circulation. Despite the high-water demand, a direct marine intrusion is localized in a very restricted area, where we observed an incipient groundwater-seawater mixing (seawater contribution ≤7 %). The qualitative and quantitative conditions of the shallow aquifer still have acceptable levels because of the relatively high recharge inflow. A reliable hydrogeochemical conceptual model, able to explain the compositional variability of the studied waters, is proposed.

Identifying the geochemical evolution and controlling factors of the shallow groundwater in a high fluoride area, Feng County, China

Understanding how groundwater is formed and evolves is critical for water resource exploitation and utilization. In this study, hydrochemistry and stable isotope tracing techniques were adopted to determine the key factors influencing groundwater chemical evolution in Feng County. A total of fourteen wells and five surface water samples were investigated in November 2021. The δD and δ¹⁸O compositions show that both surface water and groundwater are recharged from atmospheric precipitation. The dominating order of cations and anions in groundwater appears to be Na⁺ > Mg²⁺ > Ca²⁺ > K⁺ and HCO₃^- > SO₄^2- > Cl^- > NO₃^- > F^-, respectively. The groundwater hydrochemical facies are mainly characterized by HCO₃-Ca-Mg and SO₄-Cl-Na types. The chemical evolution of groundwater is dominated by water-rock interaction and cation exchange reactions. The major ions in groundwater are mainly controlled by various geogenic processes including halite, gypsum, calcite, dolomite, Glauber's salt, feldspar, and fluorite dissolution/precipitation. Furthermore, the abundant fluoride-bearing sediments, together with low Ca²⁺, promote the formation of high F^- groundwater. Approximately 85.7% and 28.6% of groundwater samples exceeded the permissible limit for F^- and NO₃^- respectively. Apart from geogenic F^-, human interventions (i.e., industrial fluoride-containing wastewater discharge and agricultural phosphate fertilizer uses) also regulate the F^- enrichment in the shallow groundwater. Nitrate pollution of the groundwater may be attributed to domestic waste and animal feces. Our findings could provide valuable information for the sustainable exploitation of groundwater in the study area and the development of effective management strategies by the authorities.

Assessing natural background levels of geogenic contaminants in groundwater of an urbanized delta through removal of groundwaters impacted by anthropogenic inputs: New insights into driving factors

Knowledge on driving forces controlling natural background levels (NBLs) of geogenic contaminants (GCs) in groundwater of coastal urbanized areas are still limited because of complex hydrogeological conditions and anthropogenic activities. This study assesses NBLs of two GCs including arsenic (As) and manganese (Mn) in four groundwater units of the Pearl River Delta (PRD) with large scale urbanization by using a preselection method composed of the chloride/bromide mass ratio versus chloride concentration and the oxidation capacity with the combination of Grubbs' test. More importantly, driving factors controlling NBLs of As/Mn in groundwater of the PRD are discussed. Results showed that groundwater As/Mn concentrations in residual datasets were independent of land-use types, while those in original datasets in different land-use types were distinct because of various human activities, indicating that the used preselection method in this study is valid for NBLs-As/Mn assessment in groundwater of the PRD. NBL-As in coastal-alluvial aquifers was >6 times that in other groundwater units. NBL-Mn in coastal-alluvial aquifers was 1.4 times that in alluvial-proluvial aquifers, and both were >4 times that in other two groundwater units. High NBLs-As/Mn in coastal-alluvial aquifers is mainly attributed to reduction of FeMn oxyhydr(oxides) induced by mineralization of organic matter in Quaternary sediments. Elevated pH also contributes higher NBL-As in coastal-alluvial aquifers. By contrast, higher NBL-Mn in alluvial-proluvial aquifers than in other two groundwater units mainly ascribes to reduction of FeMn oxyhydr(oxides) in Quaternary sediments triggered by irrigation of reducing river waters. In addition, more occurrence of As/Mn-rich sediments and the infiltration of As/Mn-rich river water are also important factors for high NBLs-As/Mn in coastal-alluvial aquifers. This study shows that revealing natural driving factors of GCs-rich groundwater in coastal urbanized areas on the basis of identification of contaminated groundwaters via the used preselection methods is acceptable.

A New Scenario-Based Approach for Water Quality and Environmental Impact Assessment Due to Mining Activities

Water quality assessment and its monitoring are necessary for areas of mining activities. In Malaysia, the mining industry is the backbone of the manufacturing and construction sectors. This study used spatio-temporal water quality modeling along a reach with mining activities during high and low discharges at Sungai (river) Lebir and Sungai Aring, situated in Gua Musang, Kelantan, Peninsular Malaysia. The objective was to assess the spatio-temporal environmental impact of mining activities during the wet and dry seasons. Data were collected at different locations along the reach. Point and non-point sources were near the mining site. Overland flow calculation at the mining site was found with the widely used SCS (Soil Conservation Service) curve number method. Several scenarios were analyzed, such as baseline, worst-case, and with-mitigation. The study revealed that baseline values of all parameters were either in a natural condition or slightly polluted, except for aluminum. All parameters were estimated at a high concentration from the mining site to downstream during the worst case of the wet season. Whereas, during the worst case of the dry season, no significant differences were observed compared to baseline values. In the with-mitigation scenario, parameter concentrations were improved and similar to baseline values. Overall, the scenario selection was helpful in the environmental impact assessment. Furthermore, this study will be significant in pre- and post-mining assessment and environmental clearance.

Hydrochemical Characteristics and Formation Mechanism of Strontium-Rich Groundwater in Tianjiazhai, Fugu, China

Strontium-rich groundwater exists in the underlying carbonate rocks of the Tianjiazhai Shimachuan River basin, Fugu, China. In this study, the hydrochemical characteristics and formation mechanisms of Sr-rich groundwater were assessed using mathematical statistics and traditional water chemistry, combining geological and hydrogeological conditions, as well as hydrogeochemical theory. The results showed that the Sr2+ content range in Sr-rich groundwater was 0.85~2.99 mg·L−1, which is weakly alkaline fresh water. HCO3− Ca·Mg·Na was the main facies type of Sr-rich groundwater. Sr-rich groundwater has relatively stable contents of chemical elements. The water–rock interaction was the main factor controlling the hydrochemical characteristics of Sr-rich groundwater, particularly carbonate dissolution, influenced by some degree of cation exchange. The Sr element in groundwater mainly comes from the dissolution of the sandstone of the Yanchang Formation. The higher the degree of weathering and the longer the water–rock reaction time, the more favorable the dissolution and enrichment of Sr in groundwater. Moreover, the large weathering thickness and fracture development of the rocks in the Tianjiazhai area provide favorable conditions for the formation of Sr-rich groundwater. The results of this study provide a scientific basis for developing effective policies to protect Sr-rich groundwater resources.

Geochemical Background for Potentially Toxic Elements in Forested Soils of the State of Pará, Brazilian Amazon

The objectives of this study were to establish geochemical background values of aluminum (Al), iron (Fe), arsenic (As), barium (Ba), cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), manganese (Mn), nickel (Ni), lead (Pb), vanadium (V), and zinc (Zn) for eastern Amazon soils and to assess the relationship between soil chemical and granulometric attributes using univariate and multivariate procedures. Samples from the topsoil (0–0.2 m) were collected in several areas with minimal or no human intervention. Pseudo total concentrations of potentially toxic elements were extracted via acid digestion and quantified via inductively coupled plasma optical emission spectrometry (ICP-OES). The results revealed that the soils present high acidity, low levels of cations and organic carbon, and highly heterogeneous geomorphological characteristics. The elements Fe (9300 mg kg−1) and Al (8200 mg kg−1) showed the highest mean concentrations in the study, while As (0.8 mg kg−1) and Cd (0.1 mg kg−1) presented the lowest levels. The results of this study indicate that the 90th percentile can be used to formalize quality reference values for the State of Pará and that the 98th percentile can be considered for areas rich in mineral deposits.

Hydrogeochemical Characteristics of Bottled Waters Sourced from Bedrock Aquifers in South Korea: Evaluation of Water Type and Natural Background Levels

The hydrogeochemical properties of bottled waters (n = 37) were examined to evaluate the factors governing their quality and to suggest the natural background levels (NBLs) of groundwater. The bottled waters were sourced from bedrock aquifers of various geological types and analyzed for 14 physicochemical parameters and 48 trace elements. The bottled waters mainly consisted of the Ca-HCO3 type with low TDS (mean = 158.4 mg/L; n = 33) regardless of geological type, indicating low degrees of water–rock interaction. The results of principal component analysis (PCA) showed that these waters were characterized by the dissolution of calcite and Ca-plagioclase (PC1) and the weathering of Na-plagioclase and cation exchange (PC2). The PCA results with low concentrations of TDS and F (mean = 0.4 mg/L) revealed that the waters represent slightly mineralized groundwater, probably because the boreholes were installed in fractured aquifers, avoiding high F concentrations (>1.5 mg/L). The 90th percentiles for the Ca-HCO3 type bottled waters were proposed as the NBLs for Korean groundwater for 11 major elements and 20 trace elements. The NBLs of NO3 (7.9 mg/L) and F (0.9 mg/L) were similar to the 90th percentiles of EU bottled waters (n = 1785), implying the suggested NBLs are acceptable for groundwater quality management.

Spatial Distribution and Source Identification of Water Quality Parameters of an Industrial Seaport Riverbank Area in Bangladesh

The Pasur River is a vital reservoir of surface water in the Sundarbon area in Bangladesh. Mongla seaport is located on the bank of this river. Many industries and other commercial sectors situated in this port area are discharging waste into the river without proper treatment. For this reason, geospatial analysis and mapping of water pollutant distribution were performed to assess the physicochemical and toxicological situation in the study area. We used different water quality indices such as Metal Index (MI), Comprehensive Pollution Index (CPI), and Weighted Arithmetic Water Quality Index Method (WQI) to improve the understanding of pollution distribution and processes determining the quality of river water. Multivariate statistical methods were used to evaluate loads and sources of pollutants in the Pasur River system. The results indicate that the sources of contaminants are both geogenic and anthropogenic, including untreated or poorly treated wastewater from industries and urban domestic waste discharge. The concentration range of total suspended solid (TSS), chloride, iron (Fe), and manganese (Mn) were from 363.2 to 1482.7, 108.2 to 708.93, 1.13 to 2.75, and 0.19 to 1.41 mg/L, respectively, significantly exceeding the health-based guideline of WHO and Bangladeshi standards. The high Fe and Mn contents are contributions from geogenic and anthropogenic sources such as industrial waste and construction activities. The average pH value was 8.73, higher than the WHO and Bangladeshi standard limit. WQI (ranging from 391 to 1336), CPI (6.71 to 23.1), and MI (7.23 to 23.3) were very high and greatly exceeded standard limits indicating that the Pasur River water is highly polluted. The results of this study can be used as a first reference work for developing a surface water quality monitoring system and guide decisionmakers for priorities regarding wastewater treatment.

Assessment of Concentration Levels of Contaminants in Groundwater of the Soutpansberg Region, Limpopo Province, South Africa

Groundwater contributions towards improved food security and human health depend on the level of contaminants in groundwater resources. Many people in rural areas use groundwater for drinking purposes without treatment and knowledge of contaminant levels in such waters, owing to parachute research in which research outputs are not shared with communities. This study argues that parachute research exposes groundwater users to health hazards and threatens the food security of communities. Concentration levels of contaminants were measured to ascertain suitability of groundwater for drinking and irrigation purposes. A total of 124 groundwater quality samples from 12 boreholes and 2 springs with physiochemical data from 1995 to 2017 were assessed. This study found high concentration levels of contaminants, such as F−, NO3−, Cl−, and total dissolved solids, in certain parts of the studied area. In general, groundwater was deemed suitable for drinking purposes in most parts of the studied area. Combined calculated values of sodium adsorption ratios, Na%, magnesium hazards, the permeability index, residual sodium carbonate, and total dissolved solids determined that groundwater was suitable for irrigation purposes. The discussion in this paper shows that scientific knowledge generated on groundwater quality is not aimed at developing skills and outputs for improved human health and food security but rather for scientific publication and record keeping, leaving communities where such data has been gathered devoid of knowledge about groundwater quality. In this study, it is recommended that research outputs on groundwater quality should be shared with groundwater users through various initiatives.

Hydrochemical Characteristics and Controlling Factors of Surface Water in Upper Nujiang River, Qinghai-Tibet Plateau

Rivers play an essential role in the global matter transport and hydrogeochemical cycle. Hydrogeochemical research is significant to developing and protecting water resources in the Qinghai-Tibet Plateau and its lower reaches. This study aimed to identify the hydrochemical characteristics and controlling factors of Daqu River and Gaqu River in Dingqing County, two tributaries of the upper Nujiang River. This study used spatial analysis, trilinear diagram analysis, and ion ratio analysis of hydrochemical indexes to investigate the hydrochemical characteristics and controlling factors. Results show that Ca2+ and Mg2+, and HCO3− and SO42− are the main cations and anions of these two rivers. HCO3·SO4-Mg·Ca and HCO3·SO4-Ca·Mg are the primary hydrochemical types for the surface water of Daqu and Gaqu Rivers, respectively. The influence of atmospheric precipitation and anthropogenic activities is weak. The carbonated water–rock reaction is the main Ca2+, Mg2+, and HCO3− source, and hot springs act as the primary source of SO42− and supplements Ca2+, Mg2+, and HCO3−. Mg2+ from magnesite dissolution exists in the Daqu River basin. Weak reverse cation exchange occurs in both rivers. Daqu River receives more low-mineralized glacier meltwater along the flow, whereas Gaqu River receives more high-mineralized hot spring water.

Assessment of Contamination along the Tigris River from Tharthar-Tigris Canal to Azizziyah, Middle of Iraq

The Tigris River is the second-longest river in Western Asia and runs through heavily populated areas, especially in Baghdad city with nearly 8 million inhabitants. The water demand is at its highest levels, nevertheless the Tigris discharge has severely declined in the last decades; combined with the fact that the wastewater quantities are increasing, and the wastewater treatment plants are experiencing a deficiency. Four sites were chosen: the Tharthar-Tigris Canal which is located in the north part of Baghdad city, Baghdad city, the Diyala River conjunction with the Tigris River site, and Al-Azizziyah site in the south of Baghdad city near Kut government, to determine the effect of the decreasing Tigris River flow on the water quality and to identify the sources of pollution. In this research, the used method evaluates the concentration of the contaminants along the course of the Tigris River to determine the source of the contaminants as the novelty of this research. The data include the discharge of The Tigris River, a hydrochemical analysis, such as major ions and trace elements, and biological parameters (BOD5, COD, E. coli bacteria, and coliform bacteria MPN/100 mL) as contamination indicators. Multivariate statistical techniques (factor analysis) were applied to evaluate spatial variations, for the years 2005 to 2020, and Phreeqc software was used to assess the saturation indices determine the dominant geochemical processes source responsible for surface water quality. The dominant minerals of the Tigris River were gypsum, anhydrite, and halite. The Tigris River is within the permissible limits for drinking, except at the Tharthar-Tigris Canal and Diyala River, and the main water quality deterioration factors of the Tigris River were recognized as: total dissolved solids, E. coli bacteria, fecal coliform bacteria, BOD5, and COD. By applying the SPSS program, two factors were identified. The first anthropogenic factor discharged into the river represents 71.27% of the variance and is comprised of agricultural land wastewater and sewage water. While the second factor represents 17.02%, indicated by the variables Ca2+, K+, Mg2+, and SO42−. This factor accounts for the chemical weathering of rocky components. It is recommended that a periodic monitoring system is needed to. follow up on pollution levels and water quality for the Tigris River, by conducting seasonal surveys.

Spatial and Temporal Evolution of Groundwater Chemistry of Baotu Karst Water System at Northern China

Karst water quality degradation has been a challenge for domestic and industrial water supplies worldwide. To reveal the possible factors response for karst water quality degradation, Baotu karst spring system is studied as an representative example. In this study, a hydrogeochemical investigation and mathematical, statistical, and geochemical modeling was conducted together to identify the major hydrochemical processes involved in the degradation process. It is found that the karst water is normally fresh, neutral-to-slightly alkaline, with calcium and magnesium as the predominant cations, and bicarbonate and sulfate as the predominant anions. The abnormally high chloride (95.05 mg/L) and nitrate concentrations (148.4 mg/L) give clues to the potential source of contamination in some karst water. The main hydrochemical facies of karst water are HCO3-Ca and HCO3 × SO4-Ca, accounting for 76% of water samples. The water hydrochemistry is controlled mainly by the dissolution of carbonate minerals (calcite, dolomite), followed by the dissolution of silicate and gypsum. The dissolution of calcite and dolomite mostly happens in the recharge area. In the discharge area, the karst water is basically in equilibrium with calcite. The negative SI value of gypsum represents that the water–gypsum interaction is dominated by dissolution along the whole flow path. Cation exchange is observed in the karst water in the indirect recharge area. Along the flow path, the contents of chloride, sulfate, nitrate, and TDS (Total dissolved solids, abbreviated TDS, indicates how many milligrams of dissolved solids are dissolved in one liter of water) vary significantly, which is mostly affected by pollution from human industrial and agricultural activities. The concentrations of major ions were maintained at a low level (<20 mg/L) in the 1960s in karst water. The fast elevation of the parameter values has occurred in the past two decades. The temporal elevation of some pollutants in karst water suggest that global changes (acid rain) and human activity (such as overusing fertilizer) are main factors resulting in the degradation of karst water quality in the study area. The results of this paper provide invaluable information for the management and protection of karst water resources in the urban and rural areas.

Geospatial Assessment of Groundwater Quality with the Distinctive Portrayal of Heavy Metals in the United Arab Emirates

Groundwater is a valuable resource, and its quality is critical to human survival. Optimal farming and urbanization degraded groundwater reserves. This research investigates and reports the spatial variability of selected heavy metals developed in the Liwa area of the United Arab Emirates. Forty water samples were collected from existing wells and analyzed for different elements. Principal components analysis was applied to a subgroup of the data set in terms of their usefulness for determining the variability of groundwater quality variables. Geographic information systems were used to produce contour maps to analyze the distribution of heavy metals. Ordinary kriging was used with Circular, Spherical, Tetraspherical, Pentaspherical-Bessel, K-Bessel, Hole effect, and Stable models for better representation. The water quality index was constructed using heavy metal concentrations and other variables. This yielded a value of 900 beyond the limit stated by WHO and US EPA. Nugget analysis showed that Cd (0), K (7.38%), and SO4 (1.81%) variables exhibited strong spatial dependence. Al (27%), Ba (40.87%), Cr (63%), Cu (34%), EC (27%), HCO3 (56%), NO3(36%), Pb (64%), and TDS (53%) represented moderate spatial dependence. As (76%), Mn (79%), Ni (100%), pH (100%), Temp (93%), and Zn (100%) exhibited weak spatial dependence.

Identification of Water Contamination Sources Using Hydrochemical and Isotopic Studies—The Kozłowa Góra Reservoir Catchment Area (Southern Poland)

The application of combined research methods, such as hydrochemical and isotopic analyses, facilitates understanding of the origin of water constituents and migration of contaminants in the aquatic environment. The presented study attempts to identify contamination sources affecting water quality within the Kozłowa Góra reservoir catchment area (southern Poland). A total of 100 water samples were collected from surface water (the Brynica river, streams, and the reservoir) and groundwater (a Quarternary aquifer) in four time periods. During fieldwork, the physicochemical parameters were measured (temperature, pH, electrical conductivity, redox potential, and dissolved oxygen). The chemical analysis included the determination of major ions (HCO3−, SO42−, Cl−, Ca2+, Mg2+, Na+, and K+), nutrients (NO3−, NO2−, NH4+, and PO43−), and total organic carbon. The study was complemented by isotopic analysis of sulphur and oxygen in sulphate, which enabled a more precise identification of stressors affecting water quality in different parts of the catchment area. Chemical and isotopic results (δ34S = 4.38–13.99‰; δ18O 3.59–13.30‰) revealed that wastewater discharges and agricultural activities have a significant influence on the chemistry of the Brynica River and other streams. At some sampling points, a lower quality of water was manifested by elevated concentrations of NO3− (up to 22.6 mg/L) and several other ions (e.g., up to 114 mg/L for Cl−, up to 51.52 mg/L for NH4+, and 12.5 mg/L for PO43−). The quality of groundwater was deteriorated mainly by infiltration of sewage from leaky septic tanks. The level of groundwater contamination varied depending on the location, as higher concentrations of major ions and values of electrical conductivity were observed in residential areas. The Brynica river, streams, and groundwater recharge the drinking water reservoir, and thus its quality depends on these sources. A dilution of water and the presence of biochemical processes led to a reduction of contaminant concentrations in the Kozłowa Góra reservoir (down to 3.5 mg/L for NO3−, 32 mg/L for Cl−, 0.21 mg/L for NH4+, and <0.05 mg/L for PO43−) compared to water in the river and streams supplying the reservoir. The study revealed the role of wastewater discharge and agricultural activities in the evolution of surface water chemistry. The results will be used in further research on the origin and migration of other substances in water, including microcontaminants.

Hydrochemical Characteristics of Arsenic in Shallow Groundwater in Various Unconsolided Sediment Aquifers: A Case Study in Hetao Basin in Inner Mongolia, China

This study focused on the entire Hetao Basin, which can fall into four hydrogeological units, the Houtao Plain, Sanhuhe Plain, Hubao Plain, and South Bank Plain of the Yellow River, all of which are under different geological and environmental conditions. To systematically investigate the hydrochemical characteristics and spatial distribution of high-As groundwater (As > 10 μg/L), 974 samples were collected from shallow groundwater. As indicated from the results, high-As groundwater had an extensive distribution, and its spatial distribution in the four hydrogeological units exhibited significant variability. Three concentrated distribution areas were reported with high-As groundwater, which were all in the discharge areas of groundwater, and the arsenic contents in the groundwater were found to exceed 50 μg/L. The hydrochemical types of high-As groundwater in the HT Plain and the SHH Plain consisted of HCO3 SO4·Cl for anions and Na for cations, while those in the other two plains included HCO3 for anions as well as Na·Mg·Ca for cations. According to the pH values, the groundwater was weakly alkaline in the areas with high-As groundwater, and arsenic primarily existed as arsenite. Furthermore, high-As groundwater in the Hetao Basin was characterized by high contents of Fe (mean value of 2.77 mg/L) and HCO3− (mean value of 460 mg/L) and a low relative concentration of SO42− (average value of 310 mg/L). This study did not identify any significant correlation between groundwater arsenic and other ions (e.g., Fe2+, Fe3+, HCO3−, SO42−, NO2− and NO3−) in the entire Hetao Basin over a wide range of hydrogeological units. The results remained unchanged after the four hydrogeological units were analyzed. The special sedimentary environment evolution of the Hetao Basin was found as the prerequisite for the formation of high-arsenic groundwater. Furthermore, groundwater runoff conditions and hydrogeochemical processes in the basin were indicated as the factors controlling the formation of high-arsenic groundwater.

Arsenic Contamination in Groundwater and Potential Health Risk in Western Lampang Basin, Northern Thailand

This research aimed to investigate the spatial distribution of arsenic concentrations in shallow and deep groundwaters which were used as sources for drinking and domestic and agricultural uses. A geochemical modeling software PHREEQC was used to simulate equilibrium geochemical reactions of complex water–rock interactions to identify arsenic speciation and mineral saturation indices based on groundwater quality and hydrogeochemical conditions. In addition, the potential health risk from arsenic-contaminated groundwater consumption was assessed based on the method developed by the U.S. Environmental Protection Agency. The study area is located at the western part of the Lampang Basin, an intermontane aquifer, Northern Thailand. The area is flat and situated in a floodplain in the Cenozoic basin. Most shallow groundwater (£ 10 m depth) samples from dug wells were of Ca-Na-HCO3 and Ca-HCO3 types, whereas deep groundwater from Quaternary terrace deposits (30–150 m depth) samples were of Na-HCO3 and Ca-Na-HCO3 types. High arsenic concentrations were found in the central part of the study area (Shallow groundwater: <2.8–35 mg/L with a mean of 10.7 mg/L; Deep groundwater: <2.8–480 mg/L with a mean of 51.0 mg/L). According to geochemical modeling study, deep groundwater contained toxic As (III), as the dominant species more than shallow groundwater. Arsenic in groundwater of the Lampang Basin may have been derived from leaching of rocks and could have been the primary source of the subsurface arsenic in the study area. Secondary source of arsenic, which is more significant, could be derived from the leaching of sorbed arsenic in aquifer from co-precipitated Fe-oxyhydroxides in sediments. Quantitative risk assessment showed that the average carcinogenic risk values were as high as 2.78 × 10−3 and 7.65 × 10−3 for adult and child, respectively, which were higher than the acceptable level (1 × 10−4). The adverse health impact should be notified or warned with the use of this arsenic-contaminated groundwater without pre-treatment.

Arsenic Mineral in Volcanic Tuff, a Source of Arsenic Anomaly in Groundwater: City of Chihuahua, Mexico

Arsenic is a naturally occurring trace element that causes many health effects when present in drinking water. Elevated arsenic concentrations in water are often attributed to nearby felsic volcanic sequences; however, the specific rock units to which the groundwater anomalies can be accredited are rarely identified. The groundwater from wells around the city of Chihuahua, Mexico, contains high arsenic content. Arsenic in groundwater increases toward the base rock containing Tertiary volcanic rocks. Through detailed scanning electron microscope (SEM) and electron microprobe (EMP) work, arsenic minerals are identified in the cavities of the Tertiary volcanic tuff from the northeast part of the Tabalaopa Basin, city of Chihuahua. Arsenic minerals, the As–Sr–Al phase (a possible arsenogoyazite–arsenoflorencite group mineral) crystallized in the vesicles of the tuff and the As–Y bearing phase included in biotite, prevail in the studied Tertiary volcanic outcrops. Based on the current study, the arsenic anomaly in the Tabalaopa–Aldama aquifer corresponds to these arsenic phases in the Tertiary volcanic rocks.