Soil thermal regime after fuel spill cleanup response in a continuous permafrost zone

Releases of diesel fuel in the Arctic tundra are a common occurrence. Response to such releases in this region typically involves excavating the contaminated soil and backfilling the excavation with clean material. Owing to the lack of clean stockpiled native soils, coarse-grained soil (aggregate) used for the construction of roads and foundation pads may be the only backfill material available. Backfilling the excavated zone with soil that has different characteristics than the surrounding native soil, combined with the removal of natural vegetation, may drastically change the maximum thaw depth reached during the thawing season, altering the underlying permafrost condition. At the extreme, such measures in areas of ground ice can result in the creation of thermokarsting. We measured maximum thaw depths in aggregate backfill at a diesel spill site located in northwestern Alaska. Using an analytic solution, we investigated the reduction in maximum thaw depth by placing a relatively thin layer (0.5 m) of fine-grained native soil over the aggregate backfill. Such a practice reduces the maximum thaw depth by as much as 1.4 m over backfilling with aggregate only.