Supplementary ground geophysics for airborne electromagnetic salinity survey over Jemalong-Wyldes Plains area

Abstract

Airborne transient electromagnetic (TEM) methods initially developed for the detection of deep conductive targets are continuously being upgraded to improve near-surface resolution of both vertical and lateral conductivity distributions suitable for salinity mapping. However, since it is a combination of location, proximity to the surface, as well as the mobility of saline groundwater that constitutes the problem, it is important to the hydrogeologist to map the complete subsurface structure responsible for the aquifer framework. A QUESTEM survey was flown over the Jemalong-Wyldes Plains area, New South Wales, by World Geoscience Corporation with the help of funding by the National Soil Conservation Program. The data have been re-evaluated with respect to ground TEM, DC resistivity, GEONICS EM 34-3, shallow drill hole sampling and a comprehensive hydrogeological investigation. Apparent conductance maps were used to guide the location of specific ground surveys, and conductivity-depth sections calculated from the airborne data were used for semi-quantitative comparison with the ground methods. Comparison with TEM and DC resistivity results showed correlation with true conductivity trends down to ~140 m. Comparison with GEONICS EM 34-3 data and electrical conductivity (EC) measurements on drill cutting samples to a depth of 10 m also showed good correlation with the near-surface features of the airborne TEM conductivity-depth section. The significant correlation with both shallow and deep conductivity trends observed in ground surveys suggests that the presentation of complete conductivity-depth sections calculated from airborne TEM, should become routine procedure in hydrogeological investigation.