Mobilization and removal of separate phase chlorinated solvents as lnapls using neutrally buoyant alcohol flooding solutions

FALTA, RONALD W, EBERHARD ROEDER, CINDY LEE, SCOTT BRAME, HEATHER SCHWENINGER, JOHN COATES, TAREK LADAA, JIM MYERS, JOHN MARTIN, JENNIFER PACE, and DELPHINE MICOLET, Departments of Geological Sciences and Environmental Engineering and Science, Clemson University, Clemson, South Carolina

Alcohol flooding is a promising new technique for removing DNAPLs trapped below the water table in high permeability formations. Due to concerns about downward mobilization of DNAPL, most current alcohol flooding approaches emphasize the enhanced dissolution mechanism. However, NAPL mobilization is a much more efficient way to remove the contaminants, provided that the issue of possible downward DNAPL migration can be addressed. The downward NAPL mobilization can be minimized or eliminated by selecting an alcohol which partitions very strongly into the NAPL. Due to the low density of alcohols ,this partitioning can lead to swelling of the DNAPL phase until it is an LNAPL.

In addition to the potential downward mobilization problem, another difficulty in recovering DNAPLs by alcohol flooding is that the low density of the alcohol relative to water makes the cosolvent solution tend to override the resident pore water, leading to poor contact with the DNAPL. This issue can be addressed by adding a very dense solute such as sucrose or CaCl2 to the cosolvent mixture. This dense solute does not partition significantly into the NAPL. With this formulation, it is possible to create an aqueous cosolvent flooding solution which is neutrally buoyant or denser than pure water, and which has the property of mobilizing separate phase chlorinated solvents (such as tetrachloroethylene) as an LNAPL. Examples of cosolvent formulations having these properties include tert-butanol, water, and sucrose; n-propanol, water and sucrose; isopropanol, water and sucrose; and isopropanol, water and CaCl2. We have measured the phase and transport properties of these and other mixtures, and have performed several 2-D sandbox experiments as well as compositional multiphase flow numerical simulations of the NAPL displacement process.

We are currently designing a field test of alcohol flooding for removing separate phase PCE from an unconsolidated water table aquifer at Dover Air Force Base, Delaware. This experiment will be performed in a 5m by 3m by 15m deep test cell formed by sheet pile walls. The PCE will be introduced as a controlled release of approximately 100 liters, near the base of the unconfined aquifer, above a confining clay layer. Our goal in this test will be to mobilize the as an LNAPL using the new alcohol flood design.