Geophysics And The Solvents-In-Groundwater Program

The University of Waterloo has an active research program studying the application of geophysical methods<br>to subsurface contaminant detection and delineation. As part of the Solvents-in-Groundwater Program, the<br>focus of our recent research efforts has been on the class of contaminants referred to as dense nonaqueous<br>liquids (DNAPLs).<br>During the past two years, we have perfomed geophysical monitoring of controlled DNAPL spills in a natural<br>sandy aquifer. The aquifer was isolated from the surrounding environment by steel sheet-pile walls driven<br>into an underlying aquitard.<br>The geophysical monitoring of the first injection of 231 litres of DNAPL into a 3m x 3m x 3.5m deep cell<br>consisted of in situ dielectric permittivity monitoring, ground penetrating radar(GPR) and in situ resistivity<br>measurements. All of these techniques detected changes in the measured physical properties during and<br>following the injection. The GPR monitoring was limited in scope and the data quality, as expected, was<br>affected adversely by the small size of the cell and the numerous metallic monitoring devices installed in the cell.<br>The experience gained during this first injection experiment was applied to the methodology used for<br>extensive geophysical monitoring in the much larger 9m x 9m x 3.3m cell. In this cell, 770 litres of DNAPL<br>were injected, and monitoring was performed using neutron, den&y, and induction logging, borehole radar,<br>surface GPR, and in situ resistivity and dielectric permittivii devices. Most of the geophysical methods<br>successfully monitored the migration of the DNAPL during and following the injection.