Crosswell Radar Tomography Investigation Of The Eastern Snake River Plain Basalt Flows At The Ineel

A radar tomography investigation was conducted to delineate the hydro-stratigraphy of<br>the unsaturated zone in the area of the Radioactive Waste Management Complex (RWMC),<br>Idaho National Engineering and Environmental Laboratory (INEEL), Idaho. The RWMC lies on<br>the eastern Snake River Plain Basalt flows. These flows are typically less than 10 m thick and<br>are controlled by the underlying topography. The basalt flows are commonly interbedded and<br>overlain with alluvial, lacustrine, and eolian sediments. These interbedded sedimentary units,<br>with the complex basalt flow structures, create an area where the hydrology is controlled by the<br>complex assemblage of interbeds and basalt fractures. To better understand the potential<br>contaminant transport processes in the interbedded basalts and sediments, crosswell radar was<br>employed to delineate the complex basalt flow and volcaniclastic environment. The US<br>Geological Survey's (USGS) borehole tomography radar system was employed in a well pair at<br>the RWMC in a wet year, 1999, and in a relative dry year, 2001. Tomograms were constructed<br>from the crosswell data and compared. Results indicate that the radar system can detect the<br>electromagnetic structure of the basalt flows at the study site. The radar data indicate that the<br>structure of the basalt can vary significantly in a lateral distance of 4 m. Comparisons between<br>the wet year and the dry year tomograms indicate that the radar data show changes in water<br>saturation.