A contaminated site investigation: comparison of information gained from geophysical measurements and hydrogeological modeling

The investigation of contaminated sites is usually a long and expensive pro cess. It is therefore desirable to use a combination of methodologies in an integrative approach that can reduce redundant information gathering. The objective of this study was to examine the usefulness of 2 non-intrusive ex ploration techniques in a contaminated site investigation. Borehole positio ning based on geophysical measurements was compared to positioning based on the Bayesian expert system for flow-field modeling. The goal set at the fi eld site was the assessment of the type and load of contaminants transporte d from the landfill site to the adjacent aquifer and the extent of leachate plumes within the groundwater. The two methods made different demands on i nformation gathering and were found to be complementary. The geophysical ap proach focused attention on the waste compartments at the site and on mixin g plumes in the adjacent aquifer but could not, without prior information, provided information on the flow field. The Bayesian approach to flow-field modeling determined areas of greatest model uncertainty at the model bound aries. The model highlighted areas of greatest uncertainty that might other wise have been overlooked and provided information on the most likely mean direction of the leachate plumes, it was concluded that both methods contri bute to a site investigation and should be used before additional drilling is carried out. (C) 2000 Elsevier Science B.V. All rights reserved.