Ninth International Conference on Permafrost ... - IARC Research

Ni n t h In t e r n at i o n a l Co n f e r e n c e o n Pe r m a f r o s tvelocities. Several regions of the project site have similargroundwater contours during each sampling event. Bycomparing the permafrost distribution with the convergingand diverging groundwater flow-paths, the variances ingroundwater flow can be attributed to areas of discontinuouspermafrost.Vertical gradient measurements in the nested wells alsoindicate that masses of discontinuous permafrost likelyaffect the hydraulic gradient in those areas.ConclusionsThe permafrost distribution map shows a high degree oflateral and vertical variability between frozen and unfrozensoils at the site. The groundwater elevation maps demonstratethat the heterogeneity of subsurface hydraulic conductivities,attributable to areas of discontinuous permafrost, affectlateral and vertical groundwater flow. Vertical gradientswere measured in the aquifer and are likely a result of thedistribution of frozen soils.Figure 1. Permafrost distribution map showing contours of theelevation of the top of permafrost below the ground surface; thepermafrost contour interval is 5 feet. The dark areas represent areaswhere the top of permafrost is at a greater depth below the groundsurface; light areas represent where the top of permafrost is closerto the ground surface.DiscussionPermafrost distributionThe permafrost distribution map illustrates that the topof the permafrost is highly variable within short horizontaldistances across the study site. The southeastern portion of themap has a larger number of sample points, and discontinuitiesare better represented. The central area of the site showsan area where permafrost was not encountered during thewell installations. The wells were installed to 50 feet in thislocation, which represents a “hole” in the permafrost. Inthe northwestern area of the site, shallow permafrost wasencountered at 20 feet to 25 feet below the ground surface.The thickness of the permafrost masses is unknown; andnone of the wells in the area extend through permafrost.There are very few sample points in the northeast section ofthe map, as this area is outside the delineated contaminantplume boundary; it is likely discontinuities exist on the samescale as in the other portions of the site.Groundwater elevationsA general groundwater trend towards the northwest isevident in the groundwater elevation maps (not shown).In addition to the regional trends, each of the groundwaterelevation configurations exhibit patterns with varyinggradients that show changing groundwater directions andFurther WorkThe permafrost distribution and groundwater elevationmaps served as a starting point for further research toinvestigate the relationship between contaminant movementand areas of discontinuous permafrost. Thematic maps ofcontaminant concentrations were also created and overlain onthe permafrost distribution and groundwater gradient mapsto assess spatial and temporal trends in the concentration datathat may be correlated to areas of discontinuous permafrost.AcknowledgmentsThe authors would like to acknowledge input and supportprovided by project managers at Shannon & Wilson Inc, andthe Alaska Department of Environmental Conservation.ReferencesAnderson, G.S. 1970. Hydrological Reconnaissance of theTanana Basin, Central Alaska: U.S. Geological SurveyHydrologic Investigations Atlas HA-319.Hinzman, L.D., Kane, D.L. & Woo, M.K. 2005. Permafrosthydrology. In: M.G. Anderson (ed.), Encyclopediaof Hydrological Sciences. John Wiley & Sons, Ltd.,2679-2693.Prowse, T.D. & Ommanney, C.S.L. 1990. Northern Hydrology:Canadian Perspectives. National Hydrology ResearchInstitute. Science Report No. 1, 308 pp.Shannon & Wilson, Inc. 2002–2007. Groundwater QualityAssessments ADOT & PF Peger Road Operationsand Maintenance Facility, Fairbanks, Alaska.40