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|Title:||Application of TEM and DC resistivity techniques in groundwater exploration|
|Presented at:||University of Leicester|
|Abstract:||The project aims to assess the usefulness of TEM in hydrogeological investigations by conducting surveys in two different environments where Schlumberger soundings and borehole logs were also available. One was in Cyprus where two aquifers are separated by a thin, clayey confining layer of variable thickness and formations have small resistivity contrasts. The second was in York where the important Sherwood Sandstone is frequently offset by faults. TEM central and coincident loops soundings were carried out at over 170 locations at 100m intervals along 3 profiles in Cyprus, and with the central loop configuration at 11 locations 1.2 - 5.5 km apart in the Vale of York.;In Cyprus, the central loop was shown to be superior, but using both configurations was useful for data quality control. Care had to be taken to recognise the IP effect when affected the interpretations and limited the penetration depth of the coincident loop data. The 1D TEM models agreed better with the borehole data than the Schlumberger models. The confining layer at 40 to 55 m depth was located in most places to 10% accuracy by the central loop TEM soundings. Another conductive layer at depths > 120 m was interpreted as an impermeable formation which prevents water from infiltrating to greater depth. Joint modelling of TEM and DC resistivity was shown not to be useful because of deviations of the substrate from the ideal 1D condition and the effects of cultural noise.;The survey in York was less successful because of the wide station spacing, equipment malfunction and the complicated geology. The unusually high resistivities previously attributed to the Mercia Mudstone and the Sherwood Sandstone are now shown to be due only to the gypsiferous horizons in the mudstone.;These investigations demonstrated the usefulness of TEM sounding as a primary tool for studies in hydrogeologically important areas. The surveys provided information on the geology below the boreholes and between them wherever a close station spacing was used.|
|Rights:||Copyright © the author. All rights reserved.|
|Appears in Collections:||Theses, Dept. of Geology|
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