Nonaqueous phase liquid subsurface

Lenhard RJ, Johnson TG, Parker JC (1993) Experimental observations of nonaqueous phase liquid subsurface movement. J Contam Hydrol 12 79-101... 

The majority of trichloroethylene present on soil surfaces will volatilize to the atmosphere or leach into the subsurface. Once trichloroethylene leaches into the soil, it appears not to become chemically transformed or undergo covalent bonding with soil components. When trichloroethylene was absorbed onto kaolinite and bentonite, the nuclear magnetic resonance (NMR) spectra showed no evidence of chemical reactions (Jurkiewicz and Maciel 1995). Because trichloroethylene is a dense nonaqueous phase liquid, it can move through the imsaturated zone into the saturated zone where it can displace soil pore water (Wershaw et al. 1994). 

Palmer, C.D. and Johnson, R.L., Physical processes controlling the transport of nonaqueous phase liquids in the subsurface, in Transport and Fate of Contaminants in the Subsurface, EPA 625/4-89/019, U.S. EPA, Washington, 1989. 

High airflow rates may result in unintended fracturing leading to nonuniform flow or short-circuiting of injected air in the subsurface, or may result in unintended mobilization of contaminants as nonaqueous phase liquids (NAPL), dissolved in groundwater, or in soil gas. 

Environmental issues associated with the subsurface release of petroleum hydrocarbons and other organics fall into four areas (1) vapors (Figure 1.5), (2) impacted soils, (3) the presence of nonaqueous phase liquids (NAPLs), and (4) dissolved constituents (i.e., benzene, toluene, ethylbenzene, and xylenes (BTEX), and other components) in groundwater. 

Panday, S., Forsyth, R A., Falta, R. W., Wu, Y., and Huyakorn, P. S., 1995, Considerations for Robust Compositional Simulations of Subsurface Nonaqueous Phase Liquid Contamination and Remediation Water Resources Research, Vol. 31, No. 5, pp. 1273-1289. 

Fountain, J. C., 1997, Removal of Nonaqueous Phase Liquids Using Surfactants In Subsurface Restoration (edited by C. H. Ward, J. A. Cherry, and M. R. Scalf), Ann Arbor Press, Chelsea, MI, pp. 199-207. 

A number of different systems have been investigated to treat nonaqueous-phase liquids (NAPLs) in subsurface soils [287, 324]. In these studies, synthetic surfactants were injected directly into soil to mobilize hydrocarbons. 

A system is homogeneous when the intensive properties are not a function of position, while a system is heterogeneous when the composition of a given mixture varies as a function of position. For example, the subsurface liquid phase usually comprises an aqueous solution incorporating a number of solutes in contaminated subsurface environments, nonaqueous phase liquids also may be present. The air phase of the subsurface includes gases with various partial pressures, and the solid phases comprise a mixture of minerals and organic compounds. 

Fig. 4.7 Simplified conceptual model for Light nonaqueous phase liquid (LNAPL) release and migration. Reprinted from Mercer JW, Cohen RM (1990) A review of immiscible fluids in the subsurface Properties, models, characterization, and remediation. J Contam Hydrol 6 107-163. Copyright 1990 with permission of Elsevier...

Nonadsorptive retention of contaminants can also be beneficial. For example, oil droplets in the subsurface are effective in developing a reactive layer or decreasing the permeability of a sandy porous medium. Coulibaly and Borden (2004) describe laboratory and field studies where edible oils were successfully injected into the subsurface, as part of an in-situ permeable reactive barrier. The oil used in the experiment was injected in the subsurface either as a nonaqueous phase liquid (NAPL) or as an oil-in-water emulsion. The oil-in-water emulsion can be distributed through sands without excessive pressure buildup, contrary to NAPL injection, which requires introduction to the subsurface by high pressure. 

The behavior of nonaqueous phase liquids (NAPLs) as they enter the partially saturated subsurface from a land surface source follows two well-defined scenarios in one case, the physical properties of the NAPL remain unchanged, while in the second case, NAPL properties are altered during transport. In the case of dense NAPLs, the contaminant plume reaches the aquifer and is subject to longterm, continuous, slow local redistribution due to groundwater flushing-dissolution processes. These plumes become contamination source zones that evolve over time, often with major negative impacts on groundwater quality. 

Powers SE, Abriola LM, Weber WJ Jr (1992) An experimental investigation of nonaqueous phase liquid dissolution in saturated subsurface systems—steady state mass transfer rates. Water Resour Res 28 2691-2705... 

Fountain, J.C. Waddell-Sheets, C., Lagowski, A., Taylor, C., Frazier, D., and Byrne, M. (1995). Enhanced Removal of Dense Nonaqueous Phase Liquids using Surfactants -Capabilities and Limitations from Field Trials. In Surfactant-Enhanced Subsurface Remediation, ACS Symposium Series Emerging Technologies 594, Sabatini, D.A., Knox, R.D., Harwell, J.H., (ed.), American Chemical Society, 177-190. 

Powers, S.E., Loureiro, C.O., Abriola, L.M., and Weber Jr., W.J. (1991). Theoretical study of the significance of nonequilibrium dissolution of nonaqueous phase liquids in subsurface systems. Water Resour. Res., 27,463 177. 

Nonaqueous Phase Liquid Pool Dissolution in Subsurface Formations... 

Fig. 1 Schematic illustration of slightly soluble in water dense nonaqueous phase liquid migration in the subsurface and plume formation of dissolved hydrocarbons...

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