Visualization of Residual Non-Aqueous Phase Liquid Subject to Freeze-Thaw

摘要

Experiments were conducted in a two-dimensional cell (containing a monolayer of 0.5mm glass beads held between two glass sheets), to examine the behavior of dodecane (Light Non-Aqueous Phase Liquid - LNAPL) or trichloroethylene (Dense Non-Aqueous Phase Liquid -DNAPL) at residual saturation, subject to various freeze-thaw cycles. The freezing front was propagated vertically upwards through the cell in all experiments. In the LNAPL experiments, a substantial upward remobilization of LNAPL was observed with successive freeze-thaw cycles, due to the detachment of mobile LNAPL from larger ganglia during freezing and transport above or with the freezing front. Significant fragmentation of LNAPL ganglia also occurred, due to the shedding and entrapment of mobile LNAPL in the polycrystalline ice, and subsequent formation of sub-singlet and singlet ganglia on thawing. The cooling rates affected the LNAPL migration to some extent, due to the formation of a uniform nucleation front during slow cooling. The DNAPL behaved in a similar manner, with significant upward mobilization of DNAPL from the lower part of the cell (although not as significant as took place with the LNAPL), and significant horizontal movement in some regions. These experiments have significant implications for the behavior and remediation of residual LNAPL and DNAPL in cold regions.