Geophysical Monitoring Of A Controlled Kerosene Spill

In order to minimize groundwater contamination from a hydrocarbon fuel spill, it is<br>necessary to locate and then remediate zones in the subsurface where the fuel has pooled.<br>Electrical property based geophysical surveys have met with mixed success in delineating<br>these contaminated zones. The objectives of our research were to provide a basis for<br>improved survey design and interpretation for accidental spill sites by testing several<br>geophysical methods on a controlled hydrocarbon fuel spill in a relatively simple<br>environment.<br>Monitoring instrumentation was installed in a 3.6 m diameter by 1.7 m deep polyethylene<br>tank. A system of well screens was placed on the bottom of the tank in a gravel layer and<br>the test cell was then packed with sand. The monitoring instrumentation included a vertical<br>geophysical access tube, glass observation wells, peizometers, soil gas access tubes,<br>dielectric permittivity, and resistivity monitoring probes.<br>Kerosene was injected near the centre of the test cell in five separate injections of varying<br>I quantities. A total of 343 litres of kerosene was injected. Ground penetrating radar, in situ<br>dielectric permittivity and resistivity, neutron logging, and radon soil gas surveys were<br>performed throughout the experiment. Surface EM, surface resistivity, EM induction<br>logging, and borehole television surveys were also performed, but the results of these<br>surveys are not be discussed in this paper as these were less definitive in understanding pool<br>development.<br>Following each kerosene injection, we observed changes in the responses of most of the<br>geophysical techniques which we attribute principally to the reduction in water content due to<br>the movement of kerosene into the capillary fringe and unsaturated zone.