Transparent Aquabeads to Model LNAPL Ganglia Migration Through Surfactant Flushing

Light nonaqueous phase liquids (LNAPLs) represent potential long-term sources for continuing groundwater contamination. Their movement in the subsurface is controlled by several complex multiphase conditions because of soil heterogeneity and fluid saturations. The first part of this paper reviews previous experimental studies on LNAPL transport. For developing numerical models and remediation technologies, these studies reproduce the transport parameters, such as density, viscosity, capillary pressure, saturation and residual saturation, and relative permeability found in the subsurface environment. The second part presents 2D tank experiments of LNAPL ganglia migration using transparent synthetic soils. The main contribution of this part is to demonstrate the possibility for the transparent Aquabeads model for better simulation of macroscopic flow properties of natural soils. Transparent synthetic soil can visualize flow problems in the subsurface environment by an optical system and digital image processing. A water-based transparent material called Aquabeads is suitable for modeling flow properties of natural soils. Advantages of Aquabeads over available transparent synthetic soils include such features as their being a water-based material, having similar macroscopic hydraulic characteristics to natural soils, and compatibility with water- and oil-selected surfactants/alcohols used for simulating multiphase flow. Therefore, this transparent material is suitable for visualizing 2D flow and soil-contamination problems. Surfactant-flushing tests were conducted to model LNAPL ganglia transport through a multilayer Aquabeads model. This model visualized the concentration profile and upward migration of motor oil ganglia during surfactant flushing. The results showed the feasibility of surfactant flushing on multilayer soils using the Aquabeads model.