Effects of Groundwater Fluctuation on Geoenvironmental Contamination

Abstract

The alteration of weather patterns due to climate change is affecting not only the historical levels of the oceans, but also of groundwater tables. Therefore, the importance of a correct understanding of the behavior of contaminants in the subsurface due to fluctuating groundwater conditions is not only evident, but urgent. In this paper we describe a new Simplified Image Analysis Method developed to assess the behavior of Non-Aqueous Phase Liquids (NAPLs) in granular soils when subject to fluctuating groundwater conditions. This new method, based on a derivation from the Beer-Lambert Law of Transmissivity, is used to determine the saturation distribution of water (Sw) and NAPL (So) in three-phase (air-water-NAPL) two-dimensional domains, by replacing the average optical density values calculated at two different wavelengths (λ = 450 nm and 640 nm) in the linear regression equations obtained for each matrix element of the tested domain, and solving for Sw and So. The two regression equations are obtained after the analysis of photographs of the domain taken at the two aforementioned wavelengths under each of the following three limit conditions: a) Sw = 100%, So = 0%; b) Sw = 0%, So = 100%; and c) Sw = So = 0%. The Simplified Image Analysis Method was then used to analyze the behavior of three different fluctuating groundwater systems, a two-phase air-water column system, a three-phase air-water-NAPL column system, and a three-phase air-water-NAPL tank. Results show that this non-intrusive and non-destructive method is reliable in providing water and NAPL saturation distributions throughout the domain when studying the effects of porous soil contamination by NAPLs subject to dynamic conditions.