Date

August 1988

Document Type

Dissertation

Degree Name

Ph.D.

Department

Dept. of Environmental Science and Engineering

Institution

Oregon Graduate Center

Abstract

In this study, experiments were undertaken to examine both the dissolution of residual dense non-aqueous phase liquids (DNAPLs) in saturated porous media and the transport of the immiscible phase which produces these residuals. Dissolution experiments were carried out in a 75x100x100 cm tank containing Ottawa sand. A zone of residual DNAPL was created in the center of the tank and water samples were taken from a grid of needles that penetrated the sand at the downgradient end of the tank. Experimental data were used to determine contaminant concentrations as a function of velocity, the effect of DNAPL residuals on the permeability of the porous medium, and the interaction of two DNAPLs in a zone of mixed residuals. DNAPL flow was investigated by observing the movement of dye-containing DNAPLs in glass columns and in small sand tanks. Sands with different grain sizes and wetting histories were employed to determine the effect of these factors on the flow. The behavior of flow in the tanks was determined by excavating the sand and observing the distribution of the dye at different depths. In this manner, possible wall effects were avoided. Residual DNAPL saturations were also measured. Results of the dissolution experiments showed that concentrations equal to the aqueous solubility of the compound were easily obtained for the velocities used in this study (10 - 100 cm/day). Modeling of the contaminant plume indicated that there may have been a slight narrowing in the streamlines resulting from reduced permeability in the residual zone. The interaction of two different DNAPL residuals produced lower concentrations but was accounted for by treating the DNAPLs as an ideal solution. Observations made during the flow experiments indicated that a slight reduction in permeability can cause a DNAPL to flow laterally until it finds a more permeable spot through which to continue its downward progress. DNAPL residual saturations were found to be in the range of 15-40%. Model studies showed that the combined demands of relatively low concentrations and long source life found at field sites require sources that consist primarily of small horizontal pools rather than permeable zones of residual.

Identifier

doi:10.6083/M4C24TDR

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