Through laboratory and field studies we are beginning to gain a better understanding of how petroleum migrates through Arctic and Antarctic terrestrial environments. The presence of ice in soils found in these environments greatly influences petroleum migration at the time of release and during subsequent freezing and thawing cycles. Possibly the most predominant effect ice contained in the pore space has on the migration of released petroleum is the formation of preferential pathways, resulting in wider lateral petroleum distributions than would be expected in soils not impacted by extreme cold temperatures. Moreover, freeze and thaw cycles tend to increase the downward migration of petroleum and influence the distribution of disconnected petroleum blobs.
In addition to ice influencing petroleum migration and distribution, the typically shallow nature of the active layer and the resulting thin layer of suprapermafrost ground water impacts the vertical distribution of petroleum in the subsurface. In temperate climates with thick saturated zones, petroleum (as a free phase liquid) does not penetrate past the top few tens of centimeters of saturated soil. Given the thin nature of the saturated zone above permafrost, petroleum will distribute throughout the entire suprapermafrost saturated zone, resulting in dissolved phase plumes distributed throughout the entire depth of the saturated zone, and minimal dilution of the dissolved phase plume by uncontaminated ground water.
An understanding of these processes is necessary as petroleum-impacted areas of the Arctic and Antarctic are cleaned up over the next several decades. More study is needed, however. One of the main topics that require further attention is the validation of what is being measured in laboratory studies and described in theoretical studies against what is occurring in the field. Mackay et al. (1974a, b, 1975) as well as Johnson et al. (1980) provide well-described results from controlled field studies; however, these studies took place over 30 years ago. Laboratory and theoretical studies have focused our attention on influences that these past researchers may have not been aware of and thus not looked for during their studies. Additional field studies will greatly improve our understanding of petroleum migration in these environments and improve our response methods.
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