Hydrogeophysical Characterization of the Marizal–São Sebastião Aquifer System in the Surroundings of the Limpec Sanitary Landfill, Camaçari, Bahia, Brazil

ABSTRACT. A detailed hydrogeophysical survey was conducted using the geoelectrical method in the surroundings of the LIMPEC sanitary landfill, municipality of Camaçari, Bahia, Brazil. Twenty-six vertical electrical soundings (VESs) were done, configured according to the Schlumberger electrode array and spaced up to 400 m between current electrodes. Hydrogeological quali-quantitative information was obtained by integrating geoelectrical results to data from wells and local geology information, namely: (i) an apparent resistivity map showed the occurrence of a conductivity anomaly, possibly attributed to the contamination plume, dispersed within the saturated zone, and presenting a SSE convection direction; (ii) one-dimensional inversions allowed to interpret the stratigraphic pattern, identify static level depth and the occurrence of possible contamination plumes, and indicate the direction of groundwater flow, which was also towards SSE; (iii) two-dimensional inversions produced inverted geoelectrical profiles, with a mean error below 2%, and confirmed the occurrence of possible contamination plumes disseminated within the unsaturated zone and dispersed within the saturated one. The geoelectrical facies with the highest resistivity values (> 600 ohm.m) were related to the São Sebastião Formation. Facies with intermediate values (100 to 800 ohm.m) regarded the Marizal Formation. In turn, those with the lowest values (< 100 ohm.m) were related to contamination plumes and/or eventual occurrences of silt/clay; (iv) the parameters of porosity, hydraulic conductivity, and transmissivity were estimated between 19.2 and 34.2%, 0.11 and 3.37 x10-3 cm/s, and 4.7 and 145.6 m²/d, respectively; and (v) local free aquifer vulnerability was classified as high, according to the evaluation using the GOD method.Keywords: geoelectrical method, urban solid waste, hydrodynamic parameters. Caracterização Hidrogeofísica do Sistema Aquífero Marizal – São Sebastião, no Entorno do Aterro Sanitário Limpec, Camaçari, Bahia, BrasilRESUMO. Um estudo hidrogeofísico de detalhe, utilizando o método geoelétrico, foi conduzido no entorno do aterro sanitário LIMPEC, município de Camaçari, Bahia, Brasil. Vinte e seis sondagens elétricas verticais (SEVs), sob configuração do arranjo Schlumberger de eletrodos, com espaçamento de até 400 m entre os eletrodos de corrente foram executadas. Informações quali-quantitativas de âmbito hidrogeológico foram alcançadas a partir da integração dos resultados geoelétricos a dados de poços e informações da geologia local, a saber: (i) o mapa de resistividade aparente revelou a ocorrência de uma anomalia condutiva, possivelmente atribuída à pluma de contaminação, dispersa na zona saturada, apresentando sentido de convecção na direção SSE; (ii) as inversões unidimensionais possibilitaram interpretar o padrão estratigráfico, identificar a profundidade do nível estático, a ocorrência de possíveis plumas de contaminação e apontar o sentido do fluxo hídrico subterrâneo também para SSE; (iii) as inversões bidimensionais geraram perfis geoelétricos invertidos, com erro médio inferior a 2%, e confirmaram a ocorrência de possíveis plumas de contaminação disseminadas na zona não saturada e dispersas na zona saturada. Os fácies geoelétricos de maiores valores de resitividade (>600 Ohm.m) estão atribuídos à Formação São Sebastião. Os fácies de valores intermediários (100 a 800 Ohm.m), referem-se à Formação Marizal. Já os de menores valores (<100 Ohm.m), a plumas de contaminação e/ou eventuais ocorrências de silte/argila; (iv) os parâmetros porosidade, condutividade hidráulica e transmissividade foram estimados serem entre 19,2 a 34,2%, 0,11 a 3,37 x10-3 cm/s e 4,7 a 145,6 m²/d, respectivamente; e (v) a vulnerabilidade do aquífero livre local foi classificada como alta, segundo avaliação realizada utilizando o método GOD. Palavras-chave: método geoelétrico, resíduos sólidos urbanos, parâmetros hidrodinâmicos.

Temporal and Spatial Groundwater Contamination Assessment Using Geophysical and Hydrochemical Methods: The Industrial Chemical Complex of Estarreja (Portugal) Case Study

With more than a half-century in operation, the industrial chemical complex of Estarreja (ICCE) in northern Portugal has left serious environmental liabilities in the region. Although protective measures were implemented, soils, surface, and groundwater contamination caused by persistent pollutants are still prevalent. This study presents data from several geophysical and hydrochemical campaigns carried out to monitor groundwater contamination in the Estarreja region over a period of 30 years. Both geophysical and hydrochemical data showed a good agreement and revealed an important anomaly caused by groundwater contamination (high levels of Na, Cl, SO4, and Fe, among others) in 2006–2007, likely caused by the remobilization of waste pollutants (roasted pyrites, soils, and sludge) during their deposition in a sealed landfill (operating between 2003 and 2005). More recently, in 2016, this impact persists, but was more attenuated and showed a general migration pattern from E to SW according to one of the main groundwater flow paths. Groundwater flow in this region has a local radial behaviour. Drainage effluent systems, such as ditches and buried pipes formerly used by ICCE, are also likely to contribute to some contamination “hotspots”. Finally, the results obtained by the combined use of these two approaches allowed for the delineation of the contamination plume for future monitoring.

Environmental Factors and Metal Mobilisation in Alluvial Sediments—Minas Gerais, Brazil

In areas contaminated by potentially toxic elements (PTEs), knowledge of processes of metal mobilisation is the basis for the choice of appropriate remediation methodologies. The mobilisation of metals is a function of several factors, and the response to these factors must be well known during the planning of remediation strategies. The activity of an ore metallurgical plant in South-East Brazil resulted in major contamination by several heavy metals. Reversing the contamination’s negative impact required geochemical assessment of the area, including the physicochemical characterisation, quantification, and delimitation of PTEs, and the rating of the solubilisation/mobilisation capacity of these elements. The definition of spatial patterns for PTEs’ distribution allowed the construction of contamination risk maps which work as a tool for the mitigation and control of the contamination plume. The chemical analysis of interstitial water and selective and sequential extraction methodologies showed that elements that occur in the environment in critical concentrations (Zn, Cd, Pb, As) are mostly associated with easily mobilised forms (soluble, exchangeable cations, associated with Mn oxides). Given the great mobility of the contamination plume, any process of removal of contaminated material becomes unfeasible, thus the strategy of remediation for the stream and associated alluvial deposits must be based on methods of in situ decontamination.

Temporal and spatial variation of hydrochemical contamination in a former radium-uranium tailing dam as a result of environmental remediation field works

The main objective of this work was to understand the evolution of water quality within a tailings dam of a former radium-uranium mining site as a response to environmental remediation works. For this, results of numerical groundwater modeling were combined with multivariate hydrochemical trend analysis derived multivariate Principal Component Analysis and K-means clustering analysis. Numerical groundwater models were developed with the aim of detecting the main flow paths inside the tailings dam and across its bordering. These models allowed the identification of the hydrodynamic flows in the area that are most likely to be directly responsible for relevant hydrochemical exchanges in time. The spatial evolution of the contamination plume in time was mapped considering a cumulative interpretation that integrates all the hydrochemical indicators simultaneously through multivariate and clustering analysis. Resulting hydrochemical maps were superposed with the flow paths identified from modelling allowing to conclude that the contamination plume migrates within the tailings in the dependence of the main water flow paths that percolates within the tailings dam due to the existence of old shafts and old pre-existing streamlines located underneath the tailings dam. The methodology adopted allowed the verification of a general improvement in groundwater quality with a spatial reduction of the contamination plume within the tailings dam.