João Carlos Dourado

Resistity (DC) method applied to aquifer protection studies

Ensaios pelo metodo da eletrorresistividade, tecnica de campo da sondagem eletrica vertical (Schlumberger array) foram executados no municipio de Canoas/RS. Esses ensaios tiveram como objetivo principal obter um diagnostico do lencol freatico em areas de Refinaria - REFAP/PETROBRAS. Este trabalho apresenta uma identificacao geoeletrica da litologia e uma estimativa da relacao entre a resistividade e parâmetros de Dar Zarrouk (resistencia transversal unitaria e condutância longitudinal unitaria) com as propriedades transmissividade e protecao frente a contaminantes dos aquiferos. Nos sedimentos saturados, os valores de resistividade definiram a seguinte litologia: camadas argilosas (resistividade 40 ohm-m). Foram identificadas duas camadas arenosas; uma correspondendo ao aquifero livre e outra ao confinado, limitado entre duas camadas de argila. No mapa da resistencia transversal do aquifero livre, as tendencias de valores altos foram associadas com as zonas de transmissividades altas; as quais sao sugeridas para a instalacao pocos de monitoramento. O mapa de condutância longitudinal ilustra a impermeabilidade da camada argilosa sobreposta ao aquifero confinado. Valores de S > 1,0 siemens indicariam zonas nas quais esse aquifero estaria mais protegido frente a contaminantes; em compensacao, valores de S < 1,0 siemens indicariam zonas de riscos provaveis de contaminacao.

Correlation of Electrical Resistivity and Induced Polarization Data with Geotechnical Survey Standard Penetration Test Measurements

Resistivity (DC) and time domain induced polarization (IP) soundings were made in the Rio Claro and Corumbatai Formations within the Sedimentary Basin of Parana in the state of Sao Paulo, Brazil. The Rio Claro Formation is composed of sand-clay sediments and sandstones. The Corumxad batai Formation consists of claystones, sandy siltstones and clay siltstones. The present paper shows a geoelectrical identification of the lithology and an estimate the relationship between the geoelectrical parameters (resistivity and chargeability from IP) and Dar Zarrouk parameters (transverse resisxad tance T and longitudinal conductance S) with the geotechnical survey results using the Standard Penetration Test (SPT). Resistivity and chargeability values for the soils (layer above the water table) of the Rio Claro and Corumbatai Formations varied considerably, 131 to 26,646 ohm-m and 0.4 to 23.4 mV/V rexad spectively, which is characteristic for unsaturated sediments. The contrast in chargeability between sandstones (Rio Claro Formation) and sandy siltstones (Corumbatai Formation) was small (0.1 to 5.8 mV/V). Fortunately, the contrast in resistivity identified these lithology (200 to 516 ohm-m and

Monitoramento da atenuação natural de pluma de contaminação pelo método de radar de penetração no solo (GPR)

The monitoring of the natural attenuation in contaminated areas has shown an alternative technique of low cost for the remediation of contaminated areas. The microorganisms degradation is one of the most important processes in the natural attenuation of contaminants, especially composites of Non-Aqueous Phase Liquid (NAPL). In many cases, the action effective of this process results in generation of organic acid, under high concentrations causes the mineral dissolution presents in the subsurface where if it finds the contamination, with release of ions. The increase on the amount of ions collaborates for the increase of the electric conductivity of the environment. The physical principle of the Ground Penetrating Radar (GPR) is the emission of electromagnetic waves of high frequency. The propagation of the electromagnetic wave depends on the frequency of emitted signal and the electric properties of the subsurface. The increase of electrical conductivity in the subsurface results in the attenuation of the signal and, for consequence, in the reduction of the of penetration depth of electromagnetic wave. This factor allows the monitoring of contaminated areas with natural attenuation from temporal analyses with the GPR. This paper presents a comparative study between profiles of GPR acquired in 1998 and 2003 in an area contaminated for composites of Light Non-Aqueous Phase Liquid (LNAPL), in processes of the natural attenuation. The results indicate an increase of the conductivity in the subsurface, from the accented attenuation it signal GPR observe in the 2003 sections. This increase can be associated to the release of ions for mineral dissolution, for the attack of organic acid resultants of the biodegradation process.

Detecção de cavidades em arenitos utilizando gravimetria, eletrorresistividade e GPR

This paper shows the results of geophysical research in areas of sand exploration near the city of Descalvado, SP, Brazil. The main objective of this research is to detect cavities inside sandstones belonging to the Piramboia and Botucatu Formations in the Parana sedimentary basin. These cavities were indirectly caused by human activity, i.e., the lowering of the water table for the purpose of sand extraction. The geophysical techniques employed were: gravity, resistivity (dipole-dipole electrical profiling) and ground penetrating radar (GPR). In the first stage of the work gravity and resistivity surveys were used to indicate where exists voids due to the collapse of the roof of a cavity. The results obtained with these two techniques were coherent because the gravity showed a mass absence in the area of influence of the cavity and the dipole-dipole electrical profiling detected an increase of electric resistivity in this same area. In the second stage, the GPR survey detected the same cavities by means of the hyperbolic features that appear in the radargrams.

Análise de contaminantes de fase líquida não aquosa (NAPLs) por aplicação do método eletromagnético indutivo (EM)

The improper discarding of industrial residues in the soil has caused damages to the environment and to the human health. The identification and diagnosis of contaminated areas are necessary procedure of that it is possible to take measured by containment of the polluting source and posterior remediation. The geophysical techniques can assist the characterization of the ground subsurface, definition of the contamination plumesize, selection of sampling points and pumping wells. This work presents some results from the application of the Inductive Electromagnetic method in an industrial area contaminated by benzene, toluene, xylene (BTX) and dichloroethene. The results indicate two migrations of the patterns for the subsurface contaminants. A horizontal trend of migration extends up to 15m depth and a vertical trend of migration in the vertical plan enters 15 to 60 m depth. The divergent trends of migration are conditioned by density of the composites that constitute the plume of contamination, or either, a floating interval LNAPL (BTX), overlapped to an interval DNAPL (1,2 dichloroethene).

Feições crustais determinadas pela análize azimutal da função do receptor, na região da estação sismológica de Rio Claro (RCLB)

This paper presents an analysis of receiver functions to estimate crustal structure beneath the Rio Claro Seismological Station, which has been in operation since October 2002. The depths obtained for the Moho discontinuity range from 36 to 44 km. A systematic variation of Moho depths with azimuth was observed. Larger values were obtained with events arriving from the North and the values of 36 km were observed with teleseisms arriving from the SW. This result shows that in the region there is an elevation of the Moho discontinuity near the Domo de Pitanga structural high. This result probably indicates a tectonic origin for this structure caused by deep deformation processes involving the whole lithosphere.

Aplicação do método eletromagnético indutivo (EM) no monitoramento de contaminantes em subsuperfície

The combined use of monitoring wells and geophysical techniques constitutes the form most adequate for identification and the monitoring contaminated areas. This procedure allows the location of wells and monitoring in strategically points, optimizing the results and minimizing costs. The Electromagnetic Inductive Method (EMI) presents ample possibilities of application in environmental studies due the facility in the acquisition of data, versatility of the equipment in field and the possibility of scanning in the ample areas in short time. This paper realizes a comparative analysis of EMI data collected in 1992 and 2003. The studied place is an industrial area that presents contamination the soil and groundwater for Benzene, Toluene, Xylene, 1,2 dichloroethene, Sodium and Chloride, product of the infiltration of effluent chemistries directly of the ground. The results indicate accented attenuation of the contaminant plume, with probable reduction in the contamination degree. The composites of light non-aqueous phase liquids (LNAPLs) had presented superior trend of horizontal, concomitant migration to the movement of the groundwater. The composites of dense non-aqueous phase liquids (DNAPLs) had more presented an accented trend of migration in the vertical direction, possibly due to absence of impermeable surfaces. The inorganics composites had followed the flow of composites of non-aqueous phase liquids (NAPLs), what in turn it allowed the characterization of the contamination plume as a conductive body in relation to the adjacent areas.

Métodos e técnicas geoelétricas rasas na delimitação de área afetada por ruptura em teto de túnel urbano

This paper presents a case study where geophysics was successfully applied to solve a complex problem associated with a tunnel excavation accident in an urban area. It presents and describes the results obtained with geoelectrical methods applied in an emergencial task in a risky urban area in Sao Paulo City. It also compares the techniques and field arrays, ways to present and interpret the data. The employed methods were electroresistivity, induced polarization (IP) and self potential (SP). The objective of the survey was to delineate the extension of a roof failure of an urban tunnel under excavation beneath the Ibirapuera Park in order to orientate the volume of tunnel roof should be treated. Only two days (Saturday and Sunday) were available to carry out the survey and its interpretation. The results were considered satisfactory and brought a significant economy to the final cost of the tunnel. This economy was due to the decreasing of the remediation area from the initial 20 x 20 m (estimated by the engineers) to 3 x 5 m (estimated by the geophysical survey).

Aplicação da técnica de caminhamento elétrico em área contaminada por derivados de petróleo

Geophysical methods are useful technics of geological investigation, thoroughly employed to diagnosis and monitoring contaminated areas, in conjunction with direct techniques of investigation such as chemical analyses. Among these, electric resistivity is more usually used in studies of contaminants in soil and groundwater, due to the high contrast of electric properties between the soil and the pollutant types frequently found, essentially constituted of composed organic and inorganic. Geophysical studies in impacted areas by petroleum products may be describe by anomalies of both low resistivity and high resistivities, confirmed as contaminant by chemical analyses. This apparent contradiction can reflect processes of degradation of the contaminants, directly associated with its residence time in the soil, through the generation of by-products that change the physical properties of the soil and groundwater, principally for the mineral dissolution by action of organic acids and by formation of minerals of oxides and hydroxides minerals. Natural attenuation defines a series of physical, chemical and biological processes that allow the degradation, dispersion and dilution of contaminants in a natural form, in other words, free from human intervention. This paper presents the application of electrical profiling technique in a contaminated industrial area for benzene, toluene, xylene, 1,2 dichloroethene and inorganic salts and it discusses the physical alterations of the contaminated soil through the obtained results, under the optics of the Natural Attenuation in course in the area of study.

Gravimetric survey and modeling of the basement morphology in the sedimentary thickness characterization, NE portion of Paraná Sedimentary Basin - Brazil

The northeast portion of the Parana Sedimentary Ba‑ sin is distinguished by structural highs as the known Pitanga Dome, an uplifted structure identified in the last century. It represents a ge‑ ological and evolutionary evidence of the Parana Sedimentary Basin and has undergone inspired studies and intense exploration surveys. This study consists of a gravimetric survey in the Pitanga Dome area, State of Sao Paulo, Brazil. The Bouguer gravity anomalies have been identified and related to the structural high, sedimentary thickness, and the basement morphology. Processing and enhancement tech‑ niques were used for forward modeling based on previous studies. Thexa0 three models from profiles sectioning the dome have a sedi‑ mentary thickness varying from 200 to 1.250xa0meters. The adopted methodology has provided important results determining that the Pitanga Dome can be understood through rational 3D visualization. The area can be interpreted as an undulating basement with thinning of sedimentary rocks related to deep features (structures) in the crust/ mantle limit (Moho uplift). This characteristic is confirmed by the sedimentary layer thickening present throughout the surrounding area. The results also offer important insights and support for further studies concerning the genesis and evolution of this and other uplif‑ ted structures of the Parana Sedimentary Basin.