| Contamination of soil and groundwater are major environmental concerns. There are several techniques to reconstruct a non-aqueous phase liquid (NAPL) contamination zone in bench-scale geo-environmental studies that apply transparent soils. Using optical imaging techniques, the most crucial issues are to determine the optimum concentration and the best color of dye as a tracer to correlate the spatial concentration of contamination with color pixel information. Most bench scale flow studies employ monochromatic grayscale imaging to analyze the concentration of mostly red-dyed tracers in porous media. However, use of grayscale utilizes a third of the available information in color images, which typically contain three color space components. In this research, a novel methodology for optical imaging of three-dimensional (3-D) multiphase liquid flow is proposed. The natural aquifer is simulated using a transparent soil surrogate that represents the macroscopic behavior of natural sand. To achieve transparency, transparent fused quartz grains were saturated with a matched refractive index mineral oil solution that represents the natural aquifer and injected with a color-dyed sucrose solution to simulate dense NAPL (DNAPL) contamination. Several calibration models were first conducted to determine the best color dye with its optimum concentration and ideal color space components for rendering DNAPL concentration. Having calibration models, the spatial volume of DNAPL zone was then estimated. In addition, a novel iterative reconstruction algorithm named 3D carving was developed to resolve three two-dimensional (2-D) projections into a 3-D model. At the end, an experimental model was conducted to evaluate the performance of the new methodology. The results show that the proposed methodology provides better efficacy for NAPL zone reconstruction in comparison with conventional image analysis routines. The technology presented in this reaserch is a sustainable, fast, accurate, non-intrusive, and inexpensive method for spatial mapping of contamination zones using transparent soil models. |
