Using Multi‐Electrode Resistivity to Reconcile Inherent Velocity‐Depth Ambiguities of Refraction Traveltime Inversion for a Petroleum Waste Site

Abstract

In order to solve the ambiguity that results from estimating the velocities and depths of discontinuities using refraction traveltime methods that assume a vertically and laterally homogeneous and isotropic media, a second geophysical method is suggested that allows an independent estimation of depth, that second method being multi‐electrode resistivity. This multi‐method example is among many that can be demonstrated as potential game‐changers for assessment plans of a site for which little is known at the beginning of the investigation. This is due to the fact that with one method alone, one should place significant error bars on all results, a fact that is not popular with engineering clients who are accustomed to greater precision. For this multi‐method example, the site was used for many years as a repository of petroleum wastes. The client's interest was an assessment of the waste volume and location. Thus, two critical variables need to be determined, the waste location, on the basis of its presumed electrically resistive nature, and the volume, for which the depths estimated to waste boundaries by two independent methods give sufficient corroboration to allow accurate volumetric calculations.