Submitted to: International Symposium on Physics Chemistry and Ecology of Seasonally Froz
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/30/1997
Publication Date: N/A
Interpretive Summary: Permafrost has been proposed as a medium for containment of hazardous liquids, since it is considered nearly impermeable to fluid flow. In this project we examined a 20-year old field test of this concept, to see why it had apparently failed. The site, near Fairbanks, AK, was used in 1971-1972 by the US Army to test the feasibility of storing diesel fuel in unlined permafrost cavities. They excavated a small cavity reaching to a depth of 6.7 m. The lower portion, entirely within the permafrost, was filled with diesel fuel, and the remaining shaft was lined with wood and insulated. They monitored the fuel for one year, then concluded the experiment by pouring sawdust into the tank to absorb the fuel, and backfilling the shaft with gravel. Years later, in 1995, diesel was detected on the soil surface near the original shaft. We were asked to determine if it had migrated through frozen soil. The contaminated soil was removed with a backhoe; during this procedure, samples were taken from the soil surrounding the shaft, and a remote video camera was used to inspect the walls of the tank. The walls were still coated with ice, and the samples showed there had been little movement of diesel fuel into the surrounding soil until its level rose above the upper limit of permafrost. We concluded that the fuel had been displaced by water that moved from the active layer through the gravel in the shaft into the tank below, where it sank beneath the lighter diesel, then froze. The results show that a permafrost cavity will not retain a contaminant if there is any pathway for water movement into it from the active layer above. This should be useful to anyone designing permafrost facilities to contain contaminants.
Technical Abstract: In 1974 an experiment was conducted to test the feasibility of strong diesel fuel in an unlined cavity created in permafrost. A test cavity was excavated, and at the conclusion of the experiment the diesel was not removed, but sawdust was added to adsorb the diesel, and the shaft leading from the cavity to the surface was backfilled with gravel. In 1994, diesel fuel was observed on the soil surface in the vicinity of the shaft. The entire gravel shaft was contaminated with diesel; the soil outside the shaft exhibited much lower levels of contamination. A video camera lowered into the cavity showed massive ice on all cavity walls. We tentatively conclude that during the years 1975-1994 water entered the gravel shaft, migrated downward to the cavity, and displaced the diesel fuel which moved upward through the shaft. The permafrost cavity failed to provide and environmentally sound enclosure for the diesel fuel.