| Three-dimensional numerical simulations were conducted to examine the effectiveness of hydraulic displacement as a primary remediation technique for the removal of DNAPL from the subsurface. Simulations were performed using a two-phase flow model and a spatially correlated, random hydraulic conductivity field. Various release volumes (500, 2000, and 5000 gallons; equivalent to 1.893 m3, 7.571 m3 and 18.927 m3), various types of DNAPL (PCE, TCE, 1,1,1-TCA), and various hydraulic conductivity distributions were investigated while the volume recovered, the number of nodes invaded by DNAPL, and the saturation distribution before and after hydraulic displacement were monitored. DNAPL volume recovery ranged from 30%-45% for all simulations illustrating that hydraulic displacement is capable of recovering significant volumes of DNAPL from the source zone. 1,1,1-TCA, a small average hydraulic conductivity field and a large variance permeability field exhibited the highest recoveries, attributed to the large number of pools present. Saturation distributions showed a general increase in the number of nodes containing residual DNAPL, demonstrating that hydraulic displacement is effective at reducing DNAPL saturations and therefore producing a stable source zone.;In addition to two-phase flow simulation, a solute transport model was utilized to simulate the aqueous phase concentration and mass flux distributions both before and after hydraulic displacement. An increase in the concentration exiting the domain was observed in all dissolution simulations performed after hydraulic displacement in comparison to dissolution simulations performed before hydraulic displacement. An increase in the total aqueous phase mass flux was also observed for dissolution simulations after hydraulic displacement compared to those prior to hydraulic displacement. The increase in concentration and total mass flux show that hydraulic displacement increases the overall rate of mass transfer from DNAPL to flowing groundwater due to an increase in DNAPL-water surface area associated with shifting pooled saturations to residual levels. |
