Mobilization and rupture of LNAPL ganglia during freeze-thaw: two-dimensional cell experiments.

Experiments were conducted on dodecane at residual saturation (21-26%) in a two-dimensional water-saturated glass bead cell (0.5 mm diameter)--to simulate light nonaqueous phase liquid (LNAPL) trapped below the water table--subject to controlled freeze-thaw cycles. The experiments reveal substantial remobilization and rupture of LNAPL ganglia during freeze-thaw, especially during the first few cycles. This includes the detachment and upward mobilization of LNAPL from larger ganglia during upward propagation of the freezing front; the formation of numerous subsinglet ganglia during this transport process, and their entrapment in ice; and the coalescence of such small ganglia during thawing, to form larger singlets. Theoretical calculations suggest that the LNAPL redistribution is caused by large freezing-induced pressure gradients, of up to 6 orders of magnitude higher than the water-LNAPL interfacial (capillary) pressure. The findings have important implications for the understanding and remediation of LNAPLs in cold climate regions.