Effects of Areal Orientation on DNAPL Recovery by Neutral Buoyant Co-solvent Flooding

INTRODUCTION Dense non-aqueous phase liquids (DNAPLs) are organic contaminants in ground water characterized by low solubility and density greater than water [1]. DNAPL-contaminated aquifers frequently are treated using the remediation technique known as pump-and-treat [2]. The process can reduce the mass of DNAPL contamination to residual saturations by injecting water though injection wells and removing water and contaminant through recovery wells. Residual DNAPL saturations following in-situ water flooding can be as much as 15% of the pore space [1]. Co-solvent flooding is a ground water remediation technology that can be used to enhance the performance of pump-and-treat. Laboratory and field studies have demonstrated the effectiveness of using alcohol solutions to remove residual non-aqueous phase liquids [3, 4]. Commonly used co-solvents are hydrophobic alcohol solutions that can modify DNAPL density to neutral buoyancy and control the risk of downward mobilization of DNAPL globules. The objective of this investigation was to study the efficiency of residual DNAPL removal from porous media by neutral buoyant cosolvent flooding as a function of planar inclination. A two-dimensional (2D) laboratory model was designed, assembled and used to investigate effects of direction of groundwater gradient flow on residual DNAPL recovery using a double-triangle well pattern in the horizontal (x-z) plane. Additional experiments are being conducted with the 2D model oriented at planar inclinations of 30, 60 and 90 degrees. Results of experiments completed in the horizontal plane are shown below. Additional results of experiments conducted at planar inclinations will be included in the final presentation.