Sand tank experiments have been used to study a surfactant-enhanced aquifer remediation (SEAR) process during which downward migration of dense nonaqueous phase liquid (DNAPL) has been observed in some of these experiments. Through numerical simulation of one particular sand tank experiment conducted at Sandia National Laboratories we show in this paper that this downward migration of DNAPL can be anticipated and controlled even in a very difficult geosystem environment. The results indicate that design simulations play a significant role in the design of either laboratory column experiments or field SEAR application and that surfactant flooding can be accomplished without loss of hydraulic control of DNAPL under typical alluvial aquifer/aquitard conditions and with only minor vertical mobilization within the aquifer (i.e., <1% of the DNAPL present). The design simulations are considered as a sensitivity analysis exercise in which the heterogeneity in the permeability field and DNAPL saturation and other critical variables are varied to produce a robust design. The simulation results indicate that the significant downward mobilization of DNAPL as observed in the Sandia sand tank experiment is a result of the use of high-permeability materials, weak viscous (horizontal) forces, and low surfactant solubilization potential. The downward mobilization of DNAPL is a design issue to be evaluated and controlled rather than an inevitable consequence of the use of surfactants to remove DNAPL.