Unravelling groundwater and surface water sources in the Esteros del Iberá Wetland Area: An isotopic approach.

In the Esteros del Iberá Wetland Area (EIWA, NE Argentina), the southern sector of the transboundary Guarani Aquifer System (SAG) is overlain by the Ramsar listed Iberá Wetlands and several rivers, that combined extend across 37,930 km2 and represent one of the largest freshwater systems on the South American continent. Previous hydrogeological studies encompassing the entire SAG proposed preferential discharge of groundwater of various origins and ages to the EIWA. In this study, a multi-tracer study using major ionic species, δ18O, δ2H and 222Rn was conducted in lagoons, rivers, wells, and boreholes in the EIWA to confirm if discharge from the transboundary SAG is contributing to the surface water system. End-member Mixing Analysis (EMMA) determined the existence of four main end-members: groundwater from the SAG, more saline groundwater from the deeper Pre-SAG, and two poorly mineralised end-members from shallow, Post-SAG. EMMA calculations clearly illustrated complex binary and ternary mixing patterns involving the four end-members and highlighted the role of geological structures, specifically regional steep faults, in controlling the mixing patterns. 222Rn activities allowed in-situ identification of preferential deep groundwater discharge into both surface waters and shallow groundwaters. These findings provide strong evidence for the widespread existence of upward flows along major faults in this sector of the SAG, inducing complex mixing flow patterns and explaining the presence of old groundwater in shallow aquifers. Mapping the sources of water and the hydrological interactions are relevant for improving water balance estimates and develop management policies towards the preservation of these wetlands.

Using isotope data to characterize and date groundwater in the southern sector of the Guaraní Aquifer System.

The Guaraní Aquifer System (SAG) is the largest transboundary aquifer in Latin America, extending beneath parts of Brazil, Paraguay, Argentina, and Uruguay. This paper presents the results of recent hydrogeological studies in the southern portion of the SAG. Locally, the abundance of surface water bodies precluded the use of conventional hydrological tools to characterize groundwater flows. Geological, hydrochemical and environmental isotope investigations were integrated to postulate a revised hydrogeological conceptual model. The revised geological model has provided a better definition of the geometry of the aquifer units and outlined the relevance of regional faults in controlling flow patterns. The new potentiometric map is consistent with groundwater flow from the SAG outcrops to the centre of the Corrientes Province, where upwards flows were identified. Hydrochemical and isotope data confirmed the widespread occurrence of mixing. Noble gas isotopes dissolved in groundwater (4He and 81Kr/Kr) provided residence times ranging from recent recharge up to 770 ± 130 ka. Groundwater age modelling confirmed the role of the geological structures in controlling groundwater flow. The southern sector of the SAG is a multilayer aquifer system with vertical flows and deep regional discharge near the Esteros del Iberá wetland area and along the Paraná and Uruguay rivers.

Persistent impacts of an abandoned non-sanitary landfill in its surroundings.

The inadequate disposal of solid waste, a common practice in developing countries, can represent an important pollution source since the closure of these deposits typically does not include the adoption of monitoring, isolation, or remediation techniques. Even so, several disposal areas are abandoned, without performing long-term monitoring in order to evaluate the depletion of contaminants' concentrations. This research aimed at comparing current and historical physicochemical data of water resources surrounding a non-sanitary landfill situated in a Guarani Aquifer recharge zone. The primary objective was to recognize whether significant changes in contaminants concentrations occurred, as well as if the area still poses a significant threat to the environment, 20 years after ending disposing activities. Samples from eight monitoring wells and three surface water points (upstream and downstream to the deposit) were evaluated in the periods of 1996-1997 and 2016-2019. The parameters pH, electrical conductivity (EC), alkalinity, chemical oxygen demand (COD), oxidation-reduction potential (ORP), chloride, nitrate, iron, manganese, calcium, and magnesium were investigated. Contamination has been detected in the landfill surroundings since the ending of the waste disposal (1996-1997), even though its intensity reduced within short distances from the waste mass. Nevertheless, no statistical variation occurred in 20 years' time considering COD, chloride, calcium, magnesium, and ORP. Moreover, increases of EC, pH, alkalinity, iron, and manganese concentrations were observed for the years of 2016-2019. The results indicate that the evaluated contaminants do not suffer depletion in the surroundings of non-sanitary landfills in sandy aquifers, considering a time span of 20 years. This study also suggests that those areas need to be adequately remediated to permit other future land uses.

Long-term geophysical monitoring of an abandoned dumpsite area in a Guarani Aquifer recharge zone.

Even though attenuation processes in the subsurface are known to reduce the impacts of contaminant plumes, their importance is significantly dependent on geological and climatic characteristics, as well as on the leachate quality. The knowledge of attenuation processes linked to different geological formations is therefore fundamental in predicting the impacts of waste disposal areas. Geophysical methods are useful tools for assessing and delineating contaminant plumes, as well as their changes with time, which enables their lower-cost monitoring and association with geological and environmental properties. This paper shows the results of geophysical surveys conducted in the years of 1996, 2005 and 2018 in a waste disposal area located at a Guarani Aquifer recharge zone in Brazil. The objective of this study was to show the evolution of the contamination plume, as well as discuss some possible transport and attenuation processes that the contaminants may undergo in similar areas. Five geophysical sections surveyed within a time span of 20 years were compared, and the information was integrated with physicochemical data from monitoring wells. The results show a horizontal plume spreading, reaching about 200 m from the deposit and about 60 m of depth, 20 years after the ending of disposal activities. The measured resistivities in 2018 are similar to the ones found in 1996 and 2005 in the same surveyed areas, showing that a significant temporal attenuation did not occur. Moreover, samples collected close to anomaly zones and within a distance of 200 m from the deposit presented concentrations of some heavy metals above the screening values according to the Brazilian legislation, showing a metals mobility higher than previously expected, which can be possibly explained by the aquifer's acidic conditions. The estimated plume velocity was about 7 m/yr, a plume deepening was observed until about 50 m and changes in water flow direction and/or diffusion processes made the plume spread to areas previously regarded as upgradient. Therefore, the present paper shows that the rehabilitation of sites neighboring waste disposal sites (less than 200 m from it) did not seem to be feasible through natural attenuation in sandy soils and that the plume spreading is significant in this geological formation. Thus, abandoned disposal areas, constantly considered to be closed after the ending of disposal activities in developing countries, generate plumes which move silently and may reach areas of concern in the future.

Metals risk assessment for children's health in water and particulate matter in a southeastern Brazilian city.

Ribeirão Preto City is supplied by the Guarani Aquifer System and suffers with intense environmental degradation due to growth of the vehicle fleet, burning of cane fields and also with water contamination by agricultural products, such as pesticides and fertilizers. The aim of the present study was to assess the human health risk derived from the exposure to metals through water and air (PM10) for two population groups (adults and children) of the municipality of Ribeirão Preto during the dry and wet seasons. Seasonal and spatial assessments of the metal concentrations in supply wells and household waters and the concentrations of PM10 and its metals were also performed. Element concentrations were determined by inductively coupled plasma spectrometry. Environmental exposure to metals were assessed under a residential scenario and estimated considering the three main routes of exposure: ingestion, dermal contact and inhalation. The results showed a higher concentration of PM10 during the dry season, which may be due to the lower precipitation and higher number of burns in this period. Copper in household waters presented a great increase when compared with the concentrations of the supply wells, probably related to the contamination during the route from its source until the residences supply. Although presenting levels in accordance with the national legislation, household waters in the municipality of Ribeirão Preto may be a concern for human exposure to metals for children during the wet season as well as the levels found for the carcinogenic risk (ELCR).

Combining lead isotopes and cluster analysis to distinguish the Guarani and Serra Geral Aquifer Systems and contaminated waters in a highly industrialized area in Southern Brazil.

The Rio dos Sinos Watershed area is located at the Middle-West region of the Rio Grande do Sul State, Southern Brazil, along thirty two municipalities and affecting 1.5 million inhabitants and many important industrial centers. Three main aquifers are recognized in the study area: the unconfined-fractured Serra Geral Aquifer System, the porous Guarani Aquifer System, and the Permian Aquitard. This study aims to understand groundwater, surface water and human activity interactions in the Rio dos Sinos Watershed, evaluating the application of stable lead isotopic ratios analyzed for this propose. Thirty six groundwater samples, 8 surface water samples and 5 liquid effluents of tanneries and landfills samples were measured using a Thermal Ionization Mass Spectrometer Thermo-Finnigan and a Neptune Multi-Collector Inductively Coupled Plasma Mass Spectrometer. Groundwater isotopic ratios have a wider range compared to the surface water, with less radiogenic averages 208Pb/204Pb = 38.1837 vs 38.4050 (standard deviation = 0.2921 vs 0.1343) and 206Pb/204Pb = 18.2947 vs 18.4766 (standard deviation = 0.2215 vs 0.1059), respectively. Industrial liquid effluents (tanneries and industrial landfill) have averages 208Pb/204Pb = 38.1956 and 206Pb/204Pb = 18.3169, distinct from effluent samples of domestic sanitary landfill (averages 208Pb/204Pb = 38.2353 and 206Pb/204Pb = 18.6607). Hierarchical cluster analysis led to distinguish six groups of groundwater, representing the three aquifers that occur in the area, two clusters suggesting groundwater mixtures and one demonstrating a highly contaminated groundwater. By analyzing the cluster results and wells' stratigraphic profiles it was possible to distinguish the different aquifers in the area. The Serra Geral Aquifer System has 206Pb/204Pb ratios between 18.4718 and 18.7089; 207Pb/204Pb between 15.6692 and 15.6777; 208Pb/204Pb between 38.6826 and 38.7616; 207Pb/206Pb between 0.8372 and 0.8623; 208Pb/206Pb between 2.0671 and 2.0964 and the Guarani Aquifer System has a wider range (208Pb/204Pb ranged from 37.9393 to 38.1279 and 206Pb/204Pb ranged from 18.0892 to 18.3217). Water mixing of these two aquifer systems is reflected by transitional results. The results confirm that the hierarchical cluster analysis of lead isotopes is a useful tool to discriminate different aquifer conditions, reflecting mostly the influence of the natural lead isotopic composition of the aquifers instead of the anthropogenic activities (urban and industrial), except when the groundwater is highly contaminated by human activity.

Shallow aquifer response to climate change scenarios in a small catchment in the Guarani Aquifer outcrop zone

ABSTRACT Water availability restrictions are already a reality in several countries. This issue is likely to worsen due to climate change, predicted for the upcoming decades. This study aims to estimate the impacts of climate change on groundwater system in the Guarani Aquifer outcrop zone. Global Climate Models (GCM) outputs were used as inputs to a water balance model, which produced recharge estimates for the groundwater model. Recharge was estimated across different land use types considering a control period from 2004 to 2014, and a future period from 2081 to 2099. Major changes in monthly rainfall means are expected to take place in dry seasons. Most of the analysed scenarios predict increase of more than 2 ºC in monthly mean temperatures. Comparing the control and future runs, our results showed a mean recharge change among scenarios that ranged from ~-80 to ~+60%, depending on the land use type. As a result of such decrease in recharge rates, the response given by the groundwater model indicates a lowering of the water table under most scenarios.

Pré-oxidação e adsorção em carvão ativado granular para remoção dos herbicidas Diuron e Hexazinona de água subterrânea / Preoxidation and adsorption in granular activated carbon for the removal of Diuron and Hexazinone from groundwater

O cultivo da cana-de-açúcar exige a utilização de herbicidas, destacando-se o Diuron e a Hexazinona. Alguns dos poços de abastecimento de Ribeirão Preto (SP) construídos no Aquífero Guarani estão situados em pontos de recarga, e a presença de solo de textura arenosa nessas áreas aumenta a vulnerabilidade da água subterrânea à contaminação por herbicidas. Neste trabalho foram monitorados alguns poços localizados na área de recarga e estudou-se a remoção de Diuron e Hexazinona por meio da adsorção em carvão ativado granular (CAG) e da pré-oxidação com cloro e dióxido de cloro em uma instalação piloto de escoamento contínuo. Verificou-se que o tempo de saturação do CAG no ensaio com a pré-oxidação foi inferior ao obtido no ensaio sem a pré-oxidação com ambos os oxidantes, possivelmente pela formação de subprodutos que competiram com a adsorção dos herbicidas.

The cultivation of sugarcane demands the use of herbicides such as Diuron and Hexazinone. Some supply wells from Ribeirão Preto, SP, Brazil, built in the Guarani Aquifer are located in recharge points, and the presence of sandy Quartzarenic Neosol in these areas increases the vulnerability of the groundwater to contamination from herbicides This paper reports the water quality monitored in some wells located in the recharge area and the removal of Diuron and Hexazinone by means of adsorption in granular activated carbon (GAC), preceded or not by preoxidation with chlorine and chlorine dioxide in a pilot plant. The results indicated that Diuron was more strongly adsorbed than Hexazinone and that the saturation time of the GAC in the test with preoxidation was shorter than in the test without preoxidation, which may have occurred mainly due to the formation of by-products that competed with the adsorption of the herbicides.