Characterization of LNAPL distribution in whole domains subject to precipitation by the simplified image analysis method

The Simplified Image Analysis Method (SIAM) is a laboratory technique devised to assess the three-phase dynamic saturation ofwater and Non-Aqueous Phase Liquids (NAPLs) in granular soils. This method is based on an extension of the Beer-Lambert Law ofTransmittance that establishes a linear relationship between the saturation of water (S_w), NAPL (S_o), and their corresponding average optical densities (D_i), for pictures taken using two consumer-grade digital cameras attached to two band-pass filters (wavelengths λ=450 and 640 nm). In this study, we use SIAM to characterize the migration of diesel (density ρ=0.865 g/cm³, viscosity ν=7mm²/s), a Light NAPL (LNAPL), when subject to different precipitation conditions (precipitation intensity i=6.6 and 63.2 mm/h) in a one-dimensional column (3.5×3.5×50 cm) filled with Toyoura sand (particle density ρS =2.65 g/cm³, equivalent grain size D₆₀ =0.196).