Development of a sulfolane plume in an aquifer located in discontinuous permafrost

Abstract

The release of sulfolane from a petroleum refinery to a river flood plain aquifer in a discontinuous permafrost region in North Pole, Alaska has been thoroughly monitored, with the initial site characterizations beginning in 2009. It has been observed that the sulfolane plume advancement is different from typical contaminant plume development in aquifers in the temperate region. This difference relates to the existence of permafrost. Permafrost itself is impermeable but open or lateral taliks provide a connection point of subpermafrost and suprapermafrost groundwater. The redirection of groundwater by these thawed areas in permafrost can produce unpredictable contaminant concentrations at various depths of the aquifers. Groundwater also has the ability to converge and diverge as a result of varying permafrost-table distribution. The contaminant can be channeled and redirected in an area with a deep permafrost-table and be absent or minimal along a shallow permafrost-table. The objective of this study is to examine the relationship between the progression of the sulfolane groundwater plume and the spatial distribution of the discontinuous permafrost and topography in the area between the Tanana and Chena Rivers using the results obtained from 156 monitoring wells, including well logs and sulfolane concentrations. An additional goal of this research is to classify the permafrost features and mechanisms controlling the transport of sulfolane. Spatial maps of the temporal contaminant distribution are produced to aid with the plume delineation, as well as contaminant trend analyses for each monitoring well (shallow/mid/deep) sulfolane concentration over the measured period. A permafrost-table elevation (top of permafrost) map was developed and utilized as a base map under the sulfolane concentration contours to correlate permafrost location and the spatial distribution of sulfolane over a period of six years. This study finds that the variable distribution of permafrost has a great effect on the flow of groundwater, and thus contamination, in the aquifer. The presence of open taliks is the most substantial modifier to the predicted path of the sulfolane groundwater contamination plume. In addition, degradation of permafrost distribution in the future due to thawing would further enhance the preferential movement of the groundwater and sulfolane and continue to move contamination in directions that would not have been predicted by looking at regional groundwater gradients alone. An area thought to be absent of sulfolane contamination may become susceptible, and the well network should be expanded to accommodate extended monitoring of this particular sulfolane plume.