Detection of Discontinuities in a Discontinuous Permafrost Aquifer Using Stable Isotopes and Groundwater Temperature

Both stable isotopes and temperature have been used as tracers in many hydrogeological studies. In the study we present here we use both tracers to delineate the location of discontinuities in a contaminated aquifer located in a region of discontinuous permafrost in the Interior of Alaska and to understand groundwater flow in the aquifer. In areas impacted by permafrost, frozen ground acts as an impermeable barrier between the suprapermafrost and subpermafrost portions of the aquifer. Discontinuities in permafrost are areas of possible connection between these two main portions of the aquifer. In contaminated aquifers these areas of connection between the two portions of the aquifer influence the transport of contaminants, necessitating the delineation of these discontinuities and the determination of the influence they have on the groundwater flow. To locate possible discontinuities in this study, multiple groundwater samples were obtained in the supra and subpermafrost portions of the aquifer prior to the 2013 spring thawing period and analyzed for ¹⁸O and ²H. During this period the groundwater aquifer is thought to be close to steady state owing to an overall slowing of recharge during the winter months when atmospheric temperatures rarely rise above freezing. Groundwater temperatures with depth were also measured. Results from these measurements show contrasting trends in δ¹⁸O and δ²H as well as temperature between areas known to contain permafrost and areas of no documented permafrost. Moreover, the spatial trend in δ¹⁸O and δ²H indicate areas of possible groundwater interaction with surface water. Additional rounds of sampling occurred during the 2013 summer and fall seasons for further delineation and comparison.