Mj. Unsworth et al., CSAMT exploration at Sellafield: Characterization of a potential radioactive waste disposal site, GEOPHYSICS, 65(4), 2000, pp. 1070-1079
The long term disposal of radioactive waste in an underground repository re
quires the detailed geological evaluation of a potential site. Owing to the
ir inherent sensitivity to the presence of fluids in rocks, electromagnetic
(EM) methods have an important role in this assessment. Controlled-source
EM techniques are especially useful in strong anthropogenic noise environme
nts such as industrial locations. However the complexity of modeling and in
version can limit the quantitative interpretation of controlled-source EM d
ata.
A potential radioactive waste disposal site at Sellafield in Great Britain
has been investigated using a variety of EM exploration techniques. Control
led-source audio-frequency magnetotelluric (CSAMT) data have given the best
subsurface information in an environment that has a high level of cultural
noise. One-dimensional inversions of the Sellafield CSAMT data were found
to be inadequate; 2.5-D forward modeling and inversion were used to interpr
et the data. The resulting resistivity models show good agreement with well
log data collected at the site. These resistivity models show the presence
of a large zone of hypersaline groundwater extending 1 km inland towards t
he potential repository and indicate the effect of faults on the hydrogeolo
gy.