Interpreting DNAPL saturations in a laboratory‐scale injection using one‐ and two‐dimensional modeling of GPR data

Abstract

Ground‐penetrating radar (GPR) is used to track a dense non–aqueous phase liquid (DNAPL) injection in a laboratory sand tank. Before modeling, the GPR data provide a qualitative image of DNAPL saturation and movement. One‐dimensional (1D) GPR modeling provides a quantitative interpretation of DNAPL volume within a given thickness during and after the injection. DNAPL saturation in sublayers of a specified thickness could not be quantified because calibration of the 1D GPR model is nonunique when both permittivity and depth of multiple layers are unknown. One‐dimensional GPR modeling of the sand tank indicates geometric interferences in a small portion of the tank. These influences are removed from the interpretation using an alternate matching target. Two‐dimensional (2D) GPR modeling provides a qualitative interpretation of the DNAPL distribution through pattern matching and tests for possible 2D influences that are not accounted for in the 1D GPR modeling. Accurate quantitative interpretation of DNAPL volumes using GPR modeling requires (1) identification of a suitable target that produces a strong reflection and is not subject to any geometric interference; (2) knowledge of the exact depth of that target; and (3) use of two‐way radar‐wave travel times through the medium to the target to determine the permittivity of the intervening material, which eliminates reliance on signal amplitude. With geologic conditions that are suitable for GPR surveys (i.e., shallow depths, low electrical conductivities, and a known reflective target), the procedures in this laboratory study can be adapted to a field site to delineate shallow DNAPL source zones.

Time‐lapse monitoring of DNAPL in a controlled cell

“…Several studies (Brewster and Annan ; Brewster et al . ; Johnson and Poeter ; Hwang et al . ; Bano et al .…”

“…Both phases can be present in the same areas with different amounts and the extension of the transition zone, between the contaminated and uncontaminated area, depends on the physical properties of the soil and the fluids.The DNAPL source, the plume extent and the saturation in relation to the depth of the DNAPL are generally determined by using monitoring wells, soil cores and vertical profiling such as push technology, etc. These kinds of technologies lead to higher costs and considerable effort in the field, as DNAPLs migrate through the soil in an extensive way.Several studies (Brewster and Annan 1994;Brewster et al 1995;Johnson and Poeter 2005;Hwang et al 2008;Bano et al 2009) have demonstrated the effectiveness of a georadar for detection and monitoring of widely contaminated areas by DNAPLs,…”

“…Several studies (Brewster and Annan 1994;Brewster et al 1995;Johnson and Poeter 2005;Hwang et al 2008;Bano et al 2009) have demonstrated the effectiveness of a georadar for detection and monitoring of widely contaminated areas by DNAPLs,…”

Electrical permittivity and resistivity time lapses of multiphase DNAPLs in a lab test

“…In recent years, geophysical methods in the detection and monitoring of contaminants commonly known as Dense Non‐Aqueous Phase Liquids (DNAPLs) have become very important in the remediation of contaminated sites. Several studies [ Cardarelli and Di Filippo , ; Hwang et al ., ; Johnson and Poeter , ; Goes and Meekes , ; US EPA (Environmental Protection Agency) , ; Newmark et al ., ; Daily and Ramirez , , Brewster and Annan , ] have shown the effectiveness of geophysical methods in the location and remediation of sites contaminated by DNAPLs. The combination of geophysical data and conventional intrusive data from soil and water sampling [ Chambers et al ., ] has the advantage of producing information concerning the entire contaminated area at low cost and in a relatively short time.…”

DNAPL mapping by ground penetrating radar examined via numerical simulation

“…Johnson (2003) carried out a number of laboratory experiments using GPR in simple geometries such as homogenous and layered sand boxes. Johnson and Poeter (2005) used GPR to track the temporal and spatial distribution of DNAPL injected into a laboratory sand tank. DNAPL saturations were determined by using the two-way travel time of radar waves reflected from a steel sheet placed below the tank, where decreased travel times indicated increased DNAPL volumes.…”