Development of an Interfacial Tracer Test for DNAPL Entrapped in Discrete Fractured Rock

Abstract

<p>Denser-than-water, non-aqueous phase liquids (DNAPLs) are contaminants that pose a serious threat to groundwater quality because of their high toxicity and ease of mobility once released into the groundwater system. In order to effectively assess the risk to human and ecological health, and to select an appropriate remediation strategy, the DNAPL source zone must be accurately characterized. The area of the DNAPL-water interface is one feature commonly used to characterize the DNAPL source zone; it is significant as it measures the surface area available for DNAPL mass transfer into the groundwater causing contamination. Additionally, many remediation strategies depend on the inter-phase mass transfer. At present, interfacial tracer tests have been successful for determining the DNAPL-water interfacial area in unconsolidated porous media, yet no study has applied this technique to fractured rock systems. The purpose of this study was to develop an interfacial tracer technique for determining the DNAPL-water interfacial area, anw in fractured rock environments. The experimental design involved four phases (1) characterizing two fracture planes using hydraulic and tracer studies, (2) trapping a known mass of a DNAPL, hydrofluoroether 7100 (HFE7I00) in the fractured rock systems, (3) performing interfacial tracer tests with sodium dodecyl benzene sulphate, sodium dodecylbenzene sulphonate (SDBS) as the reactive tracer and acid yellow 17 as the non-reactive tracer to derive an anw measurement, and (4) verifying the anw value through visualization using digital image analysis. While the interfacial tracer technique was only applied to two unique fractures in this study, it demonstrates the ability to obtain a measure of the DNAPL-water contact area, and offers an additional tool for the characterization of DNAPL source zones at the lab-scale; further work is required to evaluate the tracer test methodology for field applications.</p>