Post-remediation evaluation of a LNAPL site using electrical resistivity imaging

Abstract

Present understanding of the earth's subsurface is most often derived from samples at discrete points (wells) and interpolations or models that interpret the space between these points. Electrical resistivity imaging techniques have produced an improved capability to map contaminants (especially NAPLs--NonAqueous Phase Liquids) away from traditional wells using actual field data. Electrical resistivity image data, confirmed by drilling, have demonstrated that LNAPL (Light NAPL--less dense than water, such as gasoline) contaminants exist outside of a delineated and remediated area in Golden, Oklahoma. The data also demonstrate that LNAPL exists between monitoring and remediation wells which indicate low contaminant levels when sampled. Additionally, the electrical images provided the drilling location with the highest concentration of hydrocarbon ever found on the site, even after two phases of remediation work had been performed, although the sampling protocols varied. The results indicate that current methods of post-remediation site characterization are inadequate for complete site characterization.

Heterogeneity of Infiltration Rates in Alluvial Floodplains as Measured with a Berm Infiltration Technique

“…The profiles typically employed electrode spacings of 1 to 1.5 m with an associated depth of investigation of approximately 13 m, which included the vadose zone, alluvial aquifer, and bedrock. The resistivity sampling with the SuperSting R8/IP and subsequent inversion used a proprietary routine devised by Halihan et al (2005), which produced higher-resolution images than conventional techniques.…”

The hydraulic conductivity structure of gravel-dominated vadose zones within alluvial floodplains

“…The data acquisition and inversion utilized a proprietary Oklahoma State University method (HF, OSU Office of Intellectual Property, 2004;Halihan et al, 2005) to acquire apparent resistivity data and convert them to a model resistivity profile. The HF method has been utilized successfully within a number of applications published in the peer-reviewed literature (Halihan et al, 2005;Ong et al, 2010;Heeren et al, 2010Heeren et al, , 2011Keppel et al, 2011;Halihan et al, 2011Halihan et al, , 2012Halihan et al, , 2013Christenson et al, 2012;Heeren et al, 2014). The method has even been used and accepted by government agencies, such as the Department of Defense and U.S. EPA.…”

“…A collinear array of multiple electrodes produces a dataset consisting of apparent resistivities at depths determined by the geometry of the electrode configuration (Herman, 2001). Mathematical inversion of the "apparent resistivity" creates a two dimensional (distance and depth) model of the resistivity of the earth material (Loke and Dahlin, 2002;Halihan et al, 2005;Slater, 2007). The resistivity of earth materials is non-unique, with many different materials having similar and overlapping resistivities (Zohdy et al, 1974;Burger et al, 2006), and interpreting the geology of subsurface resistivity patterns requires independent evidence, such as site stratigraphy, in situ or laboratory testing, or core samples.…”

High-resolution Electrical Resistivity Tomography monitoring of a tracer test in a confined aquifer

“…As resistivity depends on properties such as saturation, solute concentration and temperature, timelapse ERT can be used to monitor natural and anthropogenic processes that cause changes in these properties, such as infiltration (Daily et al, 1992;Looms et al, 2008), saline intrusion (Slater and Sandberg, 2000;Ogilvy et al, 2007;, leachate recirculation (Guerin et al, 2004), and contaminated land remediation (Daily and Ramirez, 1995;LaBrecque et al, 1996;Slater and Binley, 2003;Halihan et al, 2005.…”