Surface And Borehole Radar Monitoring Of A Dnapl Spill In 3D Versus Frequency, Look Angle And Time

As part of the University of Waterloo continuing experiments at Canadian Forces<br>Base Borden (CFB), a controlled spill of perchloroethylene, a dense nonaqueous phase<br>liquid (DNAPL), was monitored by a variety of geophysical methods. Surface ground<br>penetrating radar (GPR) at 300,500, and 900 MHz and hole-to-hole GPR at 160 MHz were<br>periodically measured at the site for 340 hours. This report presents the results of the first<br>66 hours of 500 MHz surface data and an example of the 900 MHz data at 14 hours. The<br>surface data were acquired on a one meter grid in both directions across a nine meter by<br>nine meter experimental cell. The borehole radar data were acquired between 8 wells<br>circling the spill point on a 3 meter radius, using all 28 combinations of non-repeating holeto-<br>hole pairs, each at 14 different depths in the cell at 25 cm intervals. The resulting multidimensional<br>(x, y, z, time, frequency, look angle) dataset clearly outlines the movement of<br>the DNAPL horizontally and vertically, and the interactions of the DNAPL with the<br>heterogeneous sand matrix. Subtle changes in grain size distribution and the resultant<br>capillary forces in the sand caused the DNAPL to spend more time and distance in<br>horizontal travel than vertical travel.