Monitoring Dnapl Pumping Using Integrated Geophysical Techniques

The removal of DNAPL during pumping has been monitored using integrated in situ<br>geophysical techniques. At Hill Air Force Base in Utah, a free-product DNAPL plume<br>(consisting predominantly of TCE) is pooled in water-wet soil on a thick clay aquitard.<br>Groundwater pumping at Operable Unit 2 (OU 2) began in 1994; to date, nearly 30,000<br>gallons of DNAPL have been recovered from the site. From September, 1994 through<br>September, 1995, changes in the basin during DNAPL pumping were monitored using an<br>integrated geophysical system. Fiber optic sensors and neutron logs verify the presence of<br>DNAPL in the vicinity of three boreholes which form a cross section from the perimeter of<br>the basin to its center. Cross borehole electrical resistance tomography (ERT) images the<br>changes in formation electrical properties due to the removal of DNAPL, extending the<br>understanding of DNAPL removal between the boreholes. During pumping, electrical<br>resistivities decreased; we suggest that these decreases are directly caused by the reduction<br>in DNAPL. During ground water pumping, water with relatively low resistivity replaces<br>some of the DNAPL pockets as the highly insulating DNAPL is removed. The results<br>suggest that, as DNAPL is pumped from a nearby well, product slowly drains along the<br>top of an aquitard and into the pump well, where it collects.