Arctic GIS Workshop Poster Abstract
Understanding Ground Water Flow in a Permafrost Environment
CRREL has been analyzing ground water flow beneath Fort Wainwright, near Fairbanks, Alaska, where historical releases of hydrocarbons have introduced contaminants into the ground water system. The presence of discontinuous permafrost complicates deciphering ground water movement and contaminant transport in this area because it creates an extremely complex aquifer distribution. As permafrost degrades, distinct channels and unfrozen zones can develop that concentrate flow along discrete pathways with flow potentially responding to permafrost distribution and its effects on recharge of water from the surface. The problem with defining ground water and thus contaminant movement at this site is thus two-fold: define the permafrost and aquifer distribution and decipher ground water flow patterns.
Data from multiple sources are compiled in databases accessed by our environmental GIS (ReMoTe). Using the geospatial database and GIS, various data types are analyzed to develop conceptual and graphical models of the permafrost and aquifer distributions. For example, geophysical techniques (ground penetrating radar and DC resistivity) are used to define the distribution of permafrost. We use these data with borehole logs and aerial photography to create a three-dimensional model of the permafrost and aquifer configuration with Dynamic Graphics software, EarthVision. The resulting spatially referenced model is subsequently incorporated into ground water and contaminant transport models.
Seepage velocity and direction in thawed zones and below the permafrost are measured in situ with the CRREL ground water flow system. This system operates in monitoring wells using a heat pulse technique, called thermal tag and trace, to measure water movement through the well screen. These systems were installed in clusters at three depths to measure horizontal and vertical movement of ground water. The data record seasonal and annual trends in seepage rate and direction and, in conjunction with the permafrost model define the complex flow and contaminant migration patterns at this site. These patterns are often non-intuitive and without the combined model and in situ measurements, contaminant sources, sinks and flow paths would not be known but are readily accessed and compared as well as updated through the use of the GIS.