NGWA Event and Education Recordings Archive

Discontinuous or continuous permafrost underlies the majority of Alaska. In areas impacted by permafrost the presence of infrastructure can create a disturbance in the thermal balance, resulting in thawing of the permafrost. If the permafrost contains excess ice, thawing results in ground subsidence and possible failure of an improperly constructed system. Hence, infrastructure located in these regions must include a means of protecting the underlying permafrost from thawing. A common means of protecting the permafrost is to construct structures on 2- to 4-foot-thick beds of gravel, known as gravel pads. On the North Slope of Alaska, accidental spills of petroleum products have contaminated a number of gravel pads supporting the oil field’s infrastructure. As in any subsurface contamination situation, an understanding of groundwater flow is required prior to assessing the fate and transport of the released contaminants. However, prior to this study we knew very little about the movement of water (known as pad pore water) contained in these unique environments. The study presented here is an ongoing study focused on identifying the factors that influence the flow of pad pore water. We have monitored water levels and ground temperatures over several years in five different Prudhoe Bay, Alaska locations. Results show that four main factors influence the flow of pad pore water: spatially differing rates of thaw in the pad, the spatially different rates of ground freezing in the fall, the location of surface water bodies, and the topography of the original ground surface prior to placement of the gravel.