The selection, characterisation and monitoring of suitable waste-disposal sites is critically important decision for local and regional community authorities within the EU. This decision must be based upon detailed near-surface geological data including the depth and location of permeable strata and structures, and the identification of potential leakage sites. In addition, the sites must be monitored for possible sub-surface leakage of contaminated waters. This project aimed to transfer existing controlled source audio magnetotellurics (CSAMIT) technology from the natural resource sector to the environmental sector.
CSAMT together with passive magnetotellurics (MT) has been successfully developed for exploration of oil and natural gas resources. The frequency range used up to 10 Khz providing an upper penetration depth of about 30 m when a typical 50 Ohmm layer is assumed. The technique can therefore provide important data on geological structure and stratigraphy to depths of 30 to 4000m.
This penetration depth is not shallow enough for environmental engineering purposes, and an extension to higher frequencies is therefore necessary. This was implemented by using the signals from radio transmitters in the VLF and long wave range. The ENVIRO-M.T. system was adapted from CSAMT to a frequency range of 200 Khz, which would mean an upper penetration depth of about 7 m when a 50 Ohmm overburden is assumed. The ENVIRO-M.T. system will consist of a battery powered laptop computer which contains a plug-in high speed broadband spectrum analyser.
The technique was demonstrated on waste depository sites selected by end-users, who consisted of environmental engineering contractors and consultants as well as environmental regulatory authorities.