HR: 08:00h
AN: H51A-01    [Abstracts]
TI: Radon Content in Ground Waters Drawn From the Metamorphic Basement, Eastern Sao Paulo State, Brazil.
AU: Lucas, F d
EM: lucas@iag.usp.br
AF: Department of Geophysics, University of Sao Paulo, Rua do Matao, 1226, Cidade Universitaria, Butantan, Sao Paulo, BRA 05508-090, Brazil
AU: * Brenha Ribeiro, F
EM: brenha@iag.usp.br
AF: Department of Geophysics, University of Sao Paulo, Rua do Matao, 1226, Cidade Universitaria, Butantan, Sao Paulo, BRA 05508-090, Brazil
AB: Ground water drawn from granitic and metamorphic rocks frequently presents relatively high radioactivity, mostly due to the presence of uranium, radium and radon isotopes. In particular, the radon isotope 222Rn seems to have particular significance since it is normally much enriched in ground water in relation to other uranium series isotopes and is in large disequilibrium with its 226Ra mother isotope. Furthermore, radon is one of the main agents of radioactivity transfer from crust uppermost layers to lower atmosphere. At the eastern part of Sao Paulo State, southeastern Brazil, it outcrops a metamorphic terrain with a large number water bearing fractures that composes a set of fractured aquifers. Ground water is drawn from these aquifers through a large number of relatively shallow drilled wells, mostly less than 200 m deep. The radioactivity, and in particular the radon activity concentration, of the ground waters drawn from this metamorphic terrain has not yet been investigated in detail. The 222Rn activity concentration was measured in ground waters drawn from three wells drilled in different rocks of this metamorphic basement. The first well cuts a K-feldspar bearing granite, the second well cuts a granite- gneiss and the third well cuts a gneiss. The ground water samples were collected between July, 2005 and August, 2006 with a time interval of about one month between sampling campaigns. The year long mean activity concentrations were, (76 +/- 7) Bq/L for the first well, (26 +/- 3) Bq/L for the second well and (39 +/- 4) Bq/L for the third one. The activity concentrations show a time dependent variability that is interpreted as consequence of rain fall seasonal variations.
DE: 0478 Pollution: urban, regional and global (0345, 4251)
DE: 0496 Water quality
DE: 1040 Radiogenic isotope geochemistry
DE: 1831 Groundwater quality
DE: 1880 Water management (6334)
SC: Hydrology [H]
MN: 2007 Joint Assembly