Remobilization of Residual Non-Aqueous Phase Liquid in Porous Media by Freeze−Thaw Cycles

• Published in: Environmental science & technology Vol. 45; no. 8; pp. 3473 - 3478
• Main Authors: Singh, Kamaljit, Niven, Robert K, Senden, Timothy J, Turner, Michael L, Sheppard, Adrian P, Middleton, Jill P, Knackstedt, Mark A
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 15.04.2011
• Subjects: Applied sciences; Aqueous solutions; Biological and physicochemical properties of pollutants. Interaction in the soil; Contamination; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Environmental Monitoring; Environmental Processes; Exact sciences and technology; Freezing; Groundwaters; Hydrocarbons; Natural water pollution; Permeability; Phase Transition; Pollution; Pollution, environment geology; Porosity; Soil and sediments pollution; Tomography; Water Pollutants, Chemical - analysis; Water Pollutants, Chemical - chemistry; Water treatment and pollution; X-Ray Microtomography; X-rays; Freeze thaw cycle; Pollutant behavior; Porous medium; Ice; Permafrost; Water pollution; Soil pollution; Sediments; Nonaqueous phase liquid; Computerized tomography; Ground water
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es200151g

The pore-scale behavior of a nonaqueous phase liquid (NAPL) trapped as residual contamination in a porous medium, subject to freeze−thaw cycles, was investigated by X-ray microcomputed tomography. It is shown that freeze−thaw cycles cause significant NAPL remobilization in the direction of the freezing front, due to the rupture and transport of a significant proportion of (supposedly entrapped) larger multipore NAPL ganglia. Significant NAPL remains in place, however, due to substantial ganglion fragmentation into single- and subpore ganglia. The contraction of branched ganglia into more rounded forms, especially near the top surface, is also observed. Three freezing-induced mechanisms are proposed to explain the results. The findings have important implications for NAPL contamination in cold regions, and for the behavior of water−hydrocarbon systems on the Earth and other planets.