The migration of petroleum through soil that comprises the active layer (the zone above permafrost zone that experiences season freezing and thawing) is a function of the season in which the petroleum is released. Migration of released petroleum during periods when the active layer is unfrozen or thawing will be influenced by high soil-water contents in poorly drained soils, and by the shallow nature of the active layer in many permafrost regions. During periods when the active layer is frozen, migration of released petroleum will be greatly influenced by the presence of ice in the soil. Freezing and thawing cycles will impact the distribution of petroleum in the subsurface, independent of the season the petroleum was released.
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