DNAPL FLOW BEHAVIOR IN A CONTAMINATED AQUIFER - EVALUATION OF FIELD DATA

A pool of dense nonaqueous phase liquid (DNAPL) containing TCE and other-chlorinated solvents has been removed from the subsurface at Hill Air Force Base, Utah, as part of an interim remdial action. The removal of the DNAPL pool means that future off-site migration of dissolved contaminants:in the ground water is minimized, and costs for final remedial actions are reduced. A pump-and-treat system recovered more than 23,000 gallons of DNAPL and one million gallons of contaminated ground water from the aquifer. The efficiency of this remedial action was evaluated on the basis of extensive field and laboratory data. The behavior of DNAPL flown the aquifer sands was characterized by collecting core samples from two borings in the DNAPL pool and measuring relative permeabilities and DNAPL saturation. Core flooding results show that approximately on-third of the DNAPL originally in the pool is not recovered by water displacement, but remains as a residual saturation held in place by capillary pressure. However, subsequent flooding with two pore volumes of surfactant solution reduced the residual DNAPL saturation in the sand by one order of magnitude. Analytical and numerical models for the DNAPL flow behavior at the site were developed. This is the first time that such models have been developed and applied to an actual DNAPL pumping test conducted in the field. Because measured permeabilities and residual saturations were used to calibrate the models, the model predictions could be used to provide valuable insights into the controlling mechanisms for DNAPL recovery. The data collection and modeling procedures outlined in this paper can be used to enhance the efficiency and minimize the cost to clean up this and other DNAPL-contaminated sites.