INFLUENCE OF VISCOUS, GRAVITATIONAL, AND CAPILLARY FORCES ON DNAPL SATURATION

Four dense nonaqueous phase liquids (DNAPLs)-bromoform, chlorobenzene, tetrachloroethylene, and trichloroethylene-were used to investigate t he influence of viscous, gravitational, and capillary forces on DNAPL saturation in a natural aquifer sand. The relative magnitudes of these forces are expressed in terms of two dimensionless groups, the Capill ary Number (N-Ca), defined as the ratio of the viscous force to capill ary force, and the Bond Number (N-Bo), defined as the ratio of the gra vitational force to capillary force. Nondimensionalization of the equa tions governing two-phase flow suggests that DNAPL saturation should b e a function of a linear combination of the Capillary and Bond Numbers (N-Ca/k(IV) - N-Bo), provided the permeability to water (k(IV)) in th e presence of discontinuous DNAPL is considered. Experimental studies in which DNAPL saturations were measured over a range of Capillary and Bond Numbers for upward, horizontal, and downward displacement of DNA PL by water corroborate the results of the nondimensionlization. DNAPL saturations generally decreased with increasing Capillary Number and with decreasing Bond Number until N-Ca/k(IV) - N-Bo was greater than a pproximately 1 x 10(-5), at which point residual saturation was attain ed. For the DNAPLs used in this study, with adhesion tensions on the o rder of 26 dynes/cm and Bond Numbers ranging from 1.3 x 10(-7) to 2.4 x 10(-6), residual saturation was attained at Capillary Numbers greate r than approximately 5 x 10(-5). These results provide a means of esti mating the system conditions under which the DNAPLs studied achieve re sidual saturation in aquifer material.