Implementation of an image analysis technique to determine LNAPL infiltration and distribution in unsaturated porous media

Light non-aqueous phase liquids (LNAPLs) represent a great category of soil contaminants that can become a persistent, secondary and long-term source of contamination. In order to successfully confront with LNAPL pollution, their infiltration and distribution in the subsurface must be studied. The purpose of this article is to present the investigation results for the flow and distribution of two typical LNAPL (Soltrol 220 and Diesel Fuel) in two different types of unsaturated porous media (sand). Four LNAPL transient spills were simulated in an experimental sand matrix, using two different sand configurations. Photographs were frequently taken under stable conditions and the movement of the liquid was defined by an image analysis technique, producing saturation profiles. As it was proved, LNAPL move slower in the fine sand than in the coarse sand, due to its small coefficient of permeability. LNAPL saturation was estimated to be 80-100% mainly in the interface of the two sand layers, where vertical movement is limited and horizontal dominates, indicating that the interface of fine and coarse layer is able to act as a capillary barrier, which prevents LNAPL infiltration in the coarse layer.