Surfactant-enhanced aquifer remediation (SEAR) offers proven techniques for overcoming the effects of geological heterogeneities, such as low permeability silty sands in an otherwise coarse sand aquifer. First used for enhanced oil recovery (EOR), these techniques involve changing the viscosity of the fluids in situ to raise pore pressures and divert injected surfactant solutions away from the high permeability zones. The viscosity of the DNAPL determines the choice of viscosifier: polymers for high-viscosity DNAPLs such as coal tar and creosote, and surfactant foams for low-viscosity DNAPLs such as chlorinated solvents. George Hirasaki of Rice University, who developed the concept as an EOR tool while with Shell Oil, pioneered the use of surfactant-foam flooding with INTERA at Hill AFB, UT. The DNAPL source zone at Hill originally contained 50,000 gallons of waste chlorinated degreasing solvent from aircraft maintenance operations. This DNAPL is approximately 75% TCE. Contrary to conventional wisdom, this DNAPL wets the sand and gravel aquifer. Because the aquifer at Hill is highly heterogeneous, surfactant flooding could result in removal of DNAPL preferentially from the coarse zones without removing the DNAPL from the finer-grained zones just above the stratigraphic trap formed by the underlying clays. Injecting air into the surfactant stream at periodic intervals so that viscous foam forms in the permeable zones of the aquifer already cleaned of DNAPL can prevent this preferential removal, because the foam is of sufficient viscosity to divert subsequently injected surfactant into lower permeability sands at the base of the aquifer. During 2001-2002, Hirasaki and INTERA undertook the removal of the remaining residual DNAPL from the Hill AFB aquifer using large-scale foam floods that appear to have removed all remaining DNAPL.