Air-Assisted thermal injection for LNAPL remediation
Love, D. W., DeMarco, W., Van Der Camp, J. Durand, C, and Whitworth, T. M., 1999, Geological Society of America, Abstracts with Programs, v. 31, no. 7, p. A-99.
We used sand-box visualization experiments to investigate the ability of thermal injection to remediate free-phase LNAPL immobilized in small traps at aquifer/aquitard interfaces. Thermal or steam injection, long successful in enhancing oil production, is being considered for use in remediation of spilled light nonaqueous phase liquids (LNAPLs) such as gasoline or other fuels. Hobson's formula predicts the trap height (or closure) necessary to immobilize NAPL in small traps in sand aquifers ranges from a few centimeters to several meters or more, depending upon grain size and LNAPL properties. Sedimentary and structural features with closure capable of trapping LNAPLs at aquifer/aqutard boundaries are common in fluvial aquifer settings. We made a 4-cm-high by 8-cm-long trap in a glass-faced aluminum box 21 by 10 by 1.9 cm filled with glass beads ranging in size from 0.2 to 1.5 mm (depending on experiment). After saturating the bead aquifer first with water and then with Marvel Mystery Oil TM, we injected boiling water at a flow rate of 27-38 ml/min. The results show that thermal injection remediates residual LNAPL trapped in pores quite well, but the decrease in water permeability due to the presence of free-phase LNAPL in the trap result in water flow essentially bypassing the trap. Consequently, thermal injection fails to empty small traps of free-phase LNAPL. However, simultaneous injection of air with hot water results in significantly greater remediation efficiency. The air percolates upward into the trap and very effectively displaces the free-phase LNAPL downward into the flowing hot water for removal. Horizontal 1-cm layers of smaller beads (0.5 mm) between thicker layers of 1.5-mm beads within and below the trap slow the removal of residual LNAPL but do not affect displacement of LNAPL by air.
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