Risk reduction during chemical flooding: Preconditioning DNAPL density in situ prior to recovery by miscible displacement

Dense, nonaqueous phase liquids (DNAPLs) are separate phase compounds that commonly contaminate groundwater supplies. Miscible displacement methods us ing surfactants and alcohols to recover the DNAPLs have been proposed, but concerns have been raised about mobilizing the DNAPLs deeper into previousl y uncontaminated media. In this paper, the concerns are addressed by reduci ng DNAPL density prior to elimination of interfacial tension. Laboratory-me asured equilibrium phase behavior demonstrates the ability of 2-butanol to reverse the density contrast between tetrachloroethene (PCE) and water prio r to miscibility, resulting in a DNAPL phase less dense than the aqueous ph ase. Laboratory experiments using an upward gradient flow cell demonstrate that 2-butanol, introduced as an aqueous solution to a PCE pool suspended w ithin a water-saturated sandpack, partitions strongly into the PCE. Pools o f PCE exposed to 1 pore volume of water saturated with 2-butanol and subseq uently recovered by miscible displacements with 1-propanol showed that betw een 56.6% and 97.6% of the DNAPL mass was recovered for total alcohol compl ements of between 0.24 and 1.0 pore volume. In all two-phase samples produc ed, the NAPL phase was less dense than the aqueous phase. Analysis of a sta tic DNAPL pool shows that the use of a 2-butanol preflood may prevent the d ownward mobilization predicted to occur for more conventional alcohol flood s.