Studying contaminant transport and chem ical reduction in subsurface sediment by modeling flow in porous media

This paper presents imaging and modeling aspects of an interdisciplinary study of subsurface pollution and environmental remediation. F18 - FDG PET and Tc99m - NaTcO₄ SPECT studies were performed to follow dynamic changes in the radiotracer distribution in model systems. Radioisotope solution was pumped through the test columns filled with sand or sediment in order to reproduce subsurface conditions of groundwater flow through saturated sediment layers. Dynamic sequences of the radiotracer distribution were acquired and analyzed. The ultimate goal was to measure porosity and parameters of the sediment and, in the future, to study radiotracer immobilization in the column through reductive precipitation. In order to extract the relevant information from the dynamic images, computational fluid dynamics model of the liquid flow in porous medium were designed and implemented. Qualitative similarities between the imaged and simulated radio tracer distributions were achieved with appropriate values of the computational mesh, the local medium permeability, and other model parameters.