VLF-R used for waste-site assessment

摘要

The applicability of the electromagnetic VLF-R (Resistivity) method for waste-site assessment is examined here. The frequencies used in conventional VLF (15 to 30 kHz) provide the deepest penetrations of the multi-frequency, extended method of RadioMT. Both methods are considered. VLF data, being effectively single frequency, are insufficient to resolve 1-D (vertical) structure in any detail. At the site investigation scale, however, it is the departures from the background (vertically uniform) structure that are of interest. The purpose of the present paper is to demonstrate the degree to which quantitative resistivity information can be obtained from VLF-R data in the context of waste-site assessment when highly-conductive leachates are encountered. Improved methodologies for the quantitative assessment of VLF data derive from advances in regularised inversion techniques. VLF-R survey data at a former industrial waste site, aided by wide-band (VLF/RadioMT) synthetic modelling and inversion studies, are used to illustrate their shallow (0 to 20 m) resolution capabilities in conductive environments. The application of 2-D regularised (smooth-model) inversion to single-frequency VLF-R survey data is found to be effective provided the noise (non-2-D) components of profile data are understood.