A SIMPLIFIED IMAGE ANALYSIS METHOD TO STUDY LNAPL MIGRATION IN POROUS MEDIA

Abstract

A novel Simplified Image Analysis Method was developed and tested to assess the saturation distribution values for water and LNAPLs (Light Non-Aqueous Phase Liquids) in granular soils subjected to fluctuating groundwater conditions. This method, based on the Beer-Lambert Law of transmissivity, determines the saturation of water (Sw) and LNAPLs (So) by comparing the average optical densities (Di) for each matrix element of the tested domain to the corresponding average optical densities for three base pictures of the same domain taken with two digital cameras attached to two different band-pass filters (λ=450 nm and 640 nm). Two equations with two unknowns (Sw and So) are defined for each mesh element, which enables the saturation distribution to be calculated under dynamic conditions. The three base conditions for the domain are: (i) fully saturated with water (Di10), (ii) fully saturated with LNAPL (Di01), and (iii) completely dry (Di00). The Simplified Image Analysis Method was then applied to analyze the behavior of two fluctuating groundwater systems, namely, two-phase air-water and three-phase air-water-LNAPL, in a one-dimensional column, 3.5×3.5×50 cm, filled with Toyoura sand. The mass balance of the drainage-imbibition three-phase air-water-LNAPL system showed a difference of just 4.7% in LNAPL, demonstrating that this non-intrusive and non-destructive method is reliable for providing water and LNAPL saturation distributions throughout the domain when studying the effects of porous soil contamination by LNAPLs subjected to dynamic conditions.