Groundwater chemical baseline values to assess the Recovery Plan in the Matanza-Riachuelo River basin, Argentina

The human health risk assessment and countermeasures study of groundwater quality

Due to various geological, hydrogeological conditions and human activities, groundwater of different regions has distinct hydrochemical characteristics. The harmful chemical components of groundwater affect human health, and thus, the groundwater quality health risk assessment (GQHR) is important to local residents. It is vital to select GQHR factors combined with hydrochemical features, and to explore their formation, concentration characteristics and the prominent controlling role of influencing risk distribution from natural and human reasons. The factors of NO₃^-, NO₂^-, NH₄⁺ and F^- were extracted as assessment factors to evaluate the GQHR. The factors NO₃^-, NO₂^- and NH₄⁺ are derived by human activities and F^- stems from irrigation of geogenic high-fluoride groundwater and fertilizer use. The results of GQHR showed the risk order as children > adult females > adult males. The low- and medium-risk regions correspond to high groundwater levels, which are mainly controlled by natural factors. The high-risk regions located in eastern part of the study area, which were affected by both natural and human reasons. The targeted measures to prevent the increase of groundwater health risk caused by different dominant controlling effects were put forward. The research provides a scientific basis for the safety of groundwater supply and environmental exposure in this area. The research ideas and methods can be a reference for similar studies.

Intra- and inter-annual variations in metal concentrations in the superficial water of a highly polluted urban basin of Argentina

To protect ecosystems impacted by human activities and prevent their degradation, it is imperative to evaluate variations in the concentration of environmental pollutants over time. Here, we evaluated the intra- and inter-annual variations of several metals from 15 sites in the Matanza Riachuelo River basin (one of the most polluted in the world) and determined the physicochemical and meteorological parameters associated with these changes from 2008 to 2015. For this, in each site, we used Asymmetric Eigenvector Maps and Redundancy Analysis. The results highlighted temporal patterns of metal concentrations and several factors associated with them, perhaps related to the actions performed in the area since 2008. Additionally, we found that the effects of physicochemical and meteorological factors on metal concentrations were site-dependent, possibly related to the presence of different local sources of pollution or characteristics of the river in each site, such as its sediments. This approach could be applied to different scenarios (aquatic and terrestrial) and could provide a tool to help decision-makers address the harmful consequences of the continuous advance of human activities on human and ecosystem health.

Coupling of multi-hydrochemical and statistical methods for identifying apparent background levels of major components and anthropogenic anomalous activities in shallow groundwater of the Liujiang Basin, China

Natural background levels (NBLs) is a prerequisite for distinguishing anthropogenic groundwater pollution and judging the evolution of groundwater quality. However, due to regional differences of hydrogeochemitry and water-rock interaction, coupled with long-term anthropogenic activities, it is no longer accurate to assess NBLs with only statistical methods or without considering human impact. Herein, multi-hydrochemical and statistical methods were examined to identify apparent background levels and anthropogenic anomalous activities of shallow groundwater by selecting Liujiang Basin as a study area. The results showed that the differences in hydrochemical characteristics among each hydrogeological unit (HU) fully illustrated the necessity of rationally dividing HU for background value identification. The application of the concept of apparent background levels (ABLs), that is, incorporating normal human activities into the background levels, efficiently solved the problem of being unable to obtain pristine NBLs due to long-term human activities. The coupling of Hydrochemistry and Grubbs' test (Hydro-Grubbs) was confirmed as the optimal method in identifying and eliminating anthropogenic groundwater anomalies, performing sufficiently superiority when compared with purely statistical methods. It is mainly because the Hydro-Grubbs method not only considers the discreteness of the data itself, but also considers the internal connection and evolution process of the hydrochemical compositions. For the eliminated abnormal points, 91.0-93.6% of which have been effectively explained by pollution percentage index and the impact of coal mining, industrial activities, residents, agricultural activities, and septic tanks leakage, proving the rationality and reliability of Hydro-Grubbs method and ABLs evaluation result. This finding will assist in accurately identifying anthropogenic pollution on a regional scale and guiding future efforts to protect groundwater resources.

Evaluation of natural background levels of high mountain karst aquifers in complex hydrogeological settings. A Gaussian mixture model approach in the Port del Comte (SE, Pyrenees) case study

The hydrogeological processes driving the hydrochemical composition of groundwater in the alpine pristine aquifer system of the Port del Comte Massif (PCM) are characterized through the multivariate statistical techniques Principal Component Analysis (PCA) and Gaussian Mixture Models (GMM) in the framework of Compositional Data (CoDa) analysis. Also, the groundwater Natural Background Levels (NBLs) for NO₃ and SO₄ and Cl are evaluated, which are specially important for indicating the occurrence of groundwater contamination derived from the anthropic activities conducted in the PCM. The different hydrogeochemical facies found in the aquifer system of the PCM comprises low mineralized Ca-HCO₃ water for the main Eocene karst aquifer, and Ca-SO₄ and highly mineralized NaCl water types in the minor aquifers discharging from the PCM. The NBL values of SO₄, Cl and NO₃ obtained for the main karst aquifer are 14.33, 4.06 and 6.55 mg/L, respectively. These values are 35, 3 and 1.2 times lower than the respective official NBLs values that were determined by the water administration to be compared with in the case of conducting a pollution assessment characterization in the main karst aquifer. Official overestimation of NBLs can put important groundwater resources in the PCM at risk.

Spatial Assessment of Groundwater Quality and Health Risk of Nitrogen Pollution for Shallow Groundwater Aquifer around Fuyang City, China

Prolonged exposure to intensive and extensive agricultural and industrial activities is leading to an increased deterioration of groundwater quality, especially nitrogen pollution in shallow groundwater aquifers. This study was carried out using the fuzzy comprehensive method to assess the overall groundwater quality, and the noncarcinogenic risks were estimated using the human health risk assessment method recommended by the United States Environmental Protection Agency (USEPA) via drinking water intake pathways around Fuyang City, China. A total of 34 samples were collected from shallow groundwater private wells, and 16 parameters were analyzed for each groundwater sample. The evaluation results of groundwater quality show 14.7% of groundwater samples classified as poor and very poor quality, and NO3-N, TH, TDS, Fe3+, and Mn are of high potential to affect the quality of potable drinking water. These are mainly derived from anthropogenic pollutants, predominantly due to uncontrolled agricultural and industrial activities, as well as some natural processes. The noncarcinogenic risk of nitrate indicates that 8.82% of groundwater samples surpass the permissible limit recommended by the USEPA for both adults and children. This study may provide the local authority with insights into making scientific decisions for exploiting groundwater in a sustainable manner so as to protect public health.

Assessment of the impact of natural and anthropogenic activities on the groundwater chemistry in Baotou City (North China) using geochemical equilibrium and multivariate statistical techniques

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.

Characterisation of the natural attenuation of chromium contamination in the presence of nitrate using isotopic methods. A case study from the Matanza-Riachuelo River basin, Argentina

The groundwater contamination by hexavalent chromium (Cr(VI)) in a site of the Matanza-Riachuelo River basin (MRB), Argentina, has been evaluated by determining the processes that control the natural mobility and attenuation of Cr(VI) in the presence of high nitrate (NO₃^-) contents. The groundwater Cr(VI) concentrations ranged between 1.9E-5 mM and 0.04 mM, while the NO₃^- concentrations ranged between 0.5 mM and 3.9 mM. In order to evaluate the natural attenuation of Cr(VI) and NO₃^- in the MRB groundwater, Cr and N isotopes were measured in these contaminants. In addition, laboratory batch experiments were performed to determine the isotope fractionation (ε) during the reduction of Cr(VI) under denitrifying conditions. While the Cr(VI) reduction rate is not affected by the presence of NO₃^-, the NO₃^- attenuation is slower in the presence of Cr(VI). Nevertheless, no significant differences on ε values were observed when testing the absence or presence of each contaminant. The ε⁵³Cr determined in the batch experiments describe a two- stage trend, in which Stage I is characterized by ε⁵³Cr ~-1.8‰ and Stage II by ε⁵³Cr ~-0.9‰. The respective ε¹⁵N_NO3 obtained is -23.9‰ whereas ε¹⁸O_NO3 amount to -25.7‰. Using these ε values and a Rayleigh fractionation model we estimate that an average of 60% of the original Cr(VI) is removed from the groundwater of the contaminated site. Moreover, the average degree of NO₃^- attenuation by denitrification is found to be about 20%. This study provides valuable information about the dynamics of a complex system that can serve as a basis for efficient management of contaminated groundwater in the most populated and industrialized basin of Argentina.

Geochemical mechanisms controlling the isotopic and chemical composition of groundwater and surface water in a sector of the Pampean plain (Argentina)

The Samborombón River basin, which has eminently rural characteristics, develops within the Pampean plain along with other basins with serious contamination problems due to the growth of the industrial activities and the absence of a proper groundwater management. Considering that the knowledge of the natural baseline quality is important to measure an imposed environmental change, the aim of this work was to study the mechanisms that control the natural composition of groundwater and superficial water in the Samborombón River basin. In order to achieve this, detailed analysis of the minerals forming the aquifer matrix along with the data obtained from isotopes, major and trace elements were performed. Geochemical processes that define the chemical characteristics and contribute to the evolution of both surface and groundwater are associated with rainwater infiltration, carbonate dissolution, cation exchange and evaporation. Additionally, the low concentration of heavy metals may respond to natural background levels. Comprehending the hydrochemical processes governing groundwater and superficial water quality, particularly in a rural area where water supply is vital for the development of human activities, is essential to prevent environmental deterioration and thus, enhance socio-economic growth.

Hydrogeochemical Characterization and Irrigation Quality Assessment of Shallow Groundwater in the Central-Western Guanzhong Basin, China

Groundwater is the major water resource for the agricultural development of the Guanzhong Basin, China. In this study, a total of 97 groundwater samples (51 from the North Bank of the Wei River (NBWR) and 46 from the South Bank of the Wei River (SBWR)) were collected from the central-western Guanzhong Basin. The aim of this study was to investigate the hydrogeochemical characteristics of the basin and to determine the suitability of shallow groundwater for irrigation. The groundwater of the entire study area is alkaline. The groundwater of the SBWR is fresh water, and the NBWR groundwater is either freshwater or brackish water. The average concentration of ions (except for Ca²⁺) in SBWR samples is lower than in NBWR samples. HCO₃^- is dominant in the groundwater of the study area. Ca²⁺ is dominant in the SBWR while Na⁺ is dominant in the NBWR. The SBWR groundwater is mainly of the HCO₃-Ca·Mg type, and has undergone the main hydrogeochemical processes of rock weathering-leaching. The hydrochemical facies of the majority of the NBWR groundwater samples are the HCO₃-Na type with several minor hydrochemical facies of the HCO₃-Ca·Mg, SO₄·Cl-Na, and SO₄·Cl-Ca·Mg types. Its chemistry is mainly controlled by rock weathering, cation exchange, and evaporation. Salinity hazard, sodium percentage, sodium adsorption ratio, residual sodium carbonate, magnesium hazard, permeability index, Kelley's ratio, potential salinity, synthetic harmful coefficient, and irrigation coefficient were assessed to evaluate the irrigation quality of groundwater. The results of the comprehensive consideration of these indicators indicate that the percentage of NBWR water samples suitable for irrigation purposes ranges between 15.7% and 100% at an average level of 56.7%. Of the SBWR water samples suitable for irrigation, the percentage ranges from 78.3% to 100% with an average of 91.8%. Land irrigated with such water will not be exposed to any alkali hazard, but will suffer from a salinity hazard, which is more severe in the NBWR. Thus, most of the water in the NBWR can be used for soils with good drainage conditions which control salinity.

Appraising spatial variations of As, Fe, Mn and NO3 contaminations associated health risks of drinking water from Surma basin, Bangladesh

This study aims to appraise the spatial variations and pathways of groundwater contaminations and associated health risks in the Surma basin, Bangladesh using geostatistics, Fuzzy GIS technique and health risk modelbased on ninety groundwater samples. The results show that the mean concentrations of As, Fe, Mn and NO₃ are below the Bangladesh water quality standard, whereas As, Fe and Mn concentrations exceed World Health Organization guideline values in several sampling sites. The compositional study identifies weathering of source rocks, reductive dissolution of Fe and Mn-oxyhydroxide minerals and various anthropogenic inputs as the key sources of groundwater contamination. The kriged maps show the elevated risks of Fe, Mn and NO₃ concentrations from the south to northern parts and As concentration from the north to southwestern parts of the Surma basin. The results of fuzzy GIS maps confirm the outcomes of kriged maps. Cross validation results show better performance of indicator kriging over probability kriging. The results also show a spatial heterogeneity with As, Fe, Mn and NO₃ concentrations, indicating the low to medium risk categories. A health risk assessment is performed using hazard quotient (HQ) and hazard index (HI). The HQ values imply that the risk of contamination through oral ingestion pathway is medium to high levels for both adults and children as the trace elements show HQ values more than one. It is found that drinking water of several upazilas exhibits high contamination and that children are more susceptible to the non-carcinogenic and carcinogenic risks than adults in the study area.

Identifying and quantifying geochemical and mixing processes in the Matanza-Riachuelo Aquifer System, Argentina

The Matanza-Riachuelo River Basin, in the Northeast of the Buenos Aires Province, is one of the most industrialized and populated region in Argentina and it is worldwide known for its alarming environmental degradation. In order to prevent further damages, the aquifer system, which consists of two overlaid aquifers, is being monitored from 2008 by the river basin authority, Autoridad de la Cuenca Matanza-Riachuelo. The groundwater chemical baseline has been established in a previous paper (Zabala et al., 2016), and this one is devoted to the identification of the main physical and hydrogeochemical processes that control groundwater chemistry and its areal distribution. Thirty five representative groundwater samples from the Upper Aquifer and thirty four from the deep Puelche Aquifer have been studied with a multi-tool approach to understand the origin of their chemical and isotopic values. The resulting conceptual model has been validated though hydrogeochemical modeling. Most of the aquifer system has fresh groundwater, but some areas have brackish and salt groundwater. Water recharging the Upper Aquifer is of the Ca-HCO₃ type as a result of soil CO₂ and carbonate dissolution. Evapotranspiration plays a great role concentrating recharge water. After recharge, groundwater becomes Na-HCO₃, mostly due to cation exchange with Na release and Ca uptake, which induces calcite dissolution. Saline groundwaters exist in the lower and upper sectors of the basin as a result of Na-HCO₃ water mixing with marine water of different origins. In the upper reaches, besides mixing with connate sea water other sources of SO₄ exist, most probably gypsum and/or sulfides. This work highlights the relevance of performing detailed studies to understand the processes controlling groundwater chemistry at regional scale. Moreover, it is a step forward in the knowledge of the aquifer system, and provides a sound scientific basis to design effective management programs and recovery plans.

Combining natural background levels (NBLs) assessment with indicator kriging analysis to improve groundwater quality data interpretation and management

The natural background level (NBL) concept is revisited and combined with indicator kriging method to analyze the spatial distribution of groundwater quality within a groundwater body (GWB). The aim is to provide a methodology to easily identify areas with the same probability of exceeding a given threshold (which may be a groundwater quality criteria, standards, or recommended limits for selected properties and constituents). Three case studies with different hydrogeological settings and located in two countries (Portugal and Italy) are used to derive NBL using the preselection method and validate the proposed methodology illustrating its main advantages over conventional statistical water quality analysis. Indicator kriging analysis was used to create probability maps of the three potential groundwater contaminants. The results clearly indicate the areas within a groundwater body that are potentially contaminated because the concentrations exceed the drinking water standards or even the local NBL, and cannot be justified by geogenic origin. The combined methodology developed facilitates the management of groundwater quality because it allows for the spatial interpretation of NBL values.