Constraining Aquifer Architecture with Electrical Resistivity Imaging in a Fractured Hydrogeological Setting

Abstract

Two-dimensional and three-dimensional electrical resistivity imaging (ERI) surveys were conducted on the southern part of Saturna Island, British Columbia, and interpreted using a lithology- and structure-based hydrogeological conceptual model. Highly resistive sections of the images are interpreted as lightly fractured sandstone units of the Protection Formation. More conductive regions of the images are interpreted as the mudstones of the Cedar District Formation. The two-dimensional (2-D) cross sections contain sub-vertical zones of decreased resistivity that cut across the sub-horizontal formations. The three-dimensional (3-D) image displays a resistive formation on the western side of the image that is separated from a more conductive region by a sub-vertical contact. The sub-vertical contact in the 3-D image and the sub-vertical low resitivity zones in the 2-D images are aligned, and the low resistivity zones are interpreted as the intensely fractured Harris Fault zone. By interpreting the 2-D and 3-D ERI results using a hydrogeological conceptual model, and verifying the results against outcrop observations and previously-collected borehole video and geophysical data, the aquifer architecture can be accurately constrained at a sub-regional scale.