SUBSURFACE SITE CHARACTERIZATION USING THE INTEGRATION OF MULTIPLE DATA PLATFORMS: THE WHOLE IS GREATER THAN THE SUM OF THE PARTS

Environmental site characterization efforts can benefit greatly from a “co-interpretation” or integrated-synergistic approach to defining an accurate subsurface model. Where available, historical aerial photography forms the initial data platform for understanding of waste disposal practices and subsequent site layout. These data are then integrated with the results of both geophysical and intrusive subsurface investigations at the site. This type of co-interpretation of data platforms generates a better understanding of site conditions than any one data set alone when portions of the data sets show evidence of agreement regarding the presence of subsurface features.

We present results of application of this method in a Cambro-Ordovician carbonate valley of southwest Virginia. Integration of the data sets begins with comparing and contrasting available boring data from locations with downhole geophysical data. During this assessment, 1) depth to weathered bedrock and 2) depth to competent bedrock and selected from site lithologic and downhole geophysical data and subsequently transferred into a data set for seismic tomography, resulting in selection of the depth to these two horizons across the site. These depth-to-horizon selections are then integrated into data sets for resistivity by plotting depth-to-horizon selections on selected resistivity profiles. By using this integrated method, a more accurate assessment of the sometimes ambiguous meaning of resistivity signatures can be completed. Finally, these data are ground-truthed by comparing and contrasting the results to subsequent borings conducted across the site.

Results of application of this method indicate that any one method alone does not provide an adequate representation of subsurface conditions and may lead to erroneous conclusions. Traditional site characterization based on borehole advancement may over, or under, represent subsurface irregularities. Moreover, attempts to characterize the subsurface using only geophysical methods can lead to erroneous interpretations of zones of high or low resisitivity. This is especially true in areas underlain by carbonate aquifers, where identification of conduit versus diffuse flow regimes is crucial to adequate site characterization.