HR: 0830h
AN: H21D-0847    [PDF]
TI: Natural Remobilization of Multicomponent DNAPL Pools: Laboratory Evidence
AU: * Roy, J W
EM: jwroy@sciborg.uwaterloo.ca
AF: Department of Earth Sciences, University of Waterloo, Waterloo, ON N2L 3G1 Canada
AU: Smith, J E
EM: smithja@mcmaster.ca
AF: School of Geography and Geology, McMaster University, Hamilton, ON L8S 4M1 Canada
AU: Gillham, R W
EM: rwgillha@sciborg.uwaterloo.ca
AF: Department of Earth Sciences, University of Waterloo, Waterloo, ON N2L 3G1 Canada
AB: Dense non-aqueous phase liquids (DNAPLs) trapped in the subsurface can act as long-term sources of contamination by dissolving into flowing groundwater. Many of these DNAPLs are actually mixtures of different chemical components. In general, the components of higher solubility are removed more quickly, thus altering the composition of the remaining DNAPL, and possibly leading to changes in its physical properties. We theorised that a multicomponent DNAPL pool may become mobile due to the natural dissolution process. The potential for natural remobilization depends on two primary mechanisms: the reduction in pool height as mass is lost by dissolution, and the changes in fluid properties with changing molar ratio of the DNAPL. The difference between the rate of change of each determines whether the potential for remobilization increases or decreases. The purpose of the laboratory experiments presented here was to demonstrate and quantify this process of natural remobilization of a multicomponent DNAPL pool. In the four experiments, a DNAPL pool comprised of tetrachloroethene (PCE) and benzene was created as an open pool overlying glass beads within a water-saturated flow box. Experiments included rectangular and triangular pools. In each of the experiments, remobilization (as breakthrough) was observed more than two weeks after formation of the initial pool. During each experiment, the pool height declined as mass was lost by dissolution, while both aqueous and NAPL sampling indicated a decrease in the molar ratio of benzene, the more soluble component. Small protuberances (displacement) formed along the bottom of the pool as its composition changed with time and the displacement pressure was achieved for various pore throats. Eventually one of the protuberances extended further, forming a finger (breakthrough). In general, the pool emptied as the finger proceeded further into the beads.
DE: 1829 Groundwater hydrology
DE: 1831 Groundwater quality
SC: Hydrology [H]
MN: 2003 Fall Meeting