HR: 09:35h
AN: H41B-07 INVITED     [Abstracts]
TI: Aquifer and Vadose Zone Pollution Determined From Geoelectrical Measurements With Multi- Electrode Wells and Surface Multi-Profiling
AU: * de Lima, O A
EM: olivar@cpgg.ufba.br
AF: Federal University of Bahia, Center for Research in Geophysics and Geology (CPGG/UFBA), Instituto de Geociencias - UFBA, Campus Universitario de Ondina, Salvador, BA 40170-290, Brazil
AU: Pereira, P d
EM: pandrade@ufba.br
AF: Federal University of Bahia, Center for Research in Geophysics and Geology (CPGG/UFBA), Instituto de Geociencias - UFBA, Campus Universitario de Ondina, Salvador, BA 40170-290, Brazil
AB: During the last three years we are developing hydrobiogeological researches to quantitatively describe the underground contamination of a 4.0 km² area, including two landfill deposits and a tannery industry of Alagoinhas city, Bahia state, Brazil. We used electrical geophysics, geological, geochemical and biological analysis to gain a general understanding of the complex interactions between organic and inorganic pollutants and their environmental impacts. A geological reconnaissance work and a geoelectrical survey using vertical electrical soundings were made around the area to detect and to delineate the extent of the underground contamination plume. The results pointed out the presence of a strong conductive anomaly within the aquifer resulting from invasive fluids both from the landfills and from the surface disposal lagoons from the tannery. Water samples collected at available wells and along the Sauipe river, have shown drastic changes in the total dissolved solids, total chromium, inorganic macro-components, biochemical oxygen demand, chemical oxygen demand, nutrients and bacterial content. As a complimentary work, apparent resistivity and chargeability data were measured as a function of depth along three new multi-electrode wells, and as a function of electrode spacing along five double semi-Schlumberger subsurface profiles. A multi-electrode well is a special monitoring well where we externally install copper electrodes as thin metallic rings spaced by 0.50 m, along its entire filter and casing length. Such electrodes are connected through insulated cables to the ground surface and may be combined into different arrays. Two-side semi-Schlumberger soundings expanded up to 200 m AB/2 spacing and with centers spaced by 50 m along special transverse centered at the plume were inverted using 1D and 2D models. Both techniques were used to detail the groundwater contamination around the Alagoinhas landfills. The electrical measurements performed at the earth surface and within wells, were used both to characterize the plume and to estimate changes in water saturation and water chemistry bellow the water table and throughout the upper vadose section of the Marizal- São Sebastião aquifer system. Well data were acquired during three different campaigns of 2004-2006 years, covering a complete seasonal cycle. The results are quantitativelyinterpreted using the volume conductivity approach described by Lima et al. (2005) extended for condiction of partial water saturation.
DE: 1835 Hydrogeophysics
DE: 1859 Rocks: physical properties
DE: 1895 Instruments and techniques: monitoring
SC: Hydrology [H]
MN: 2007 Joint Assembly