Centrifuge testing of LNAPL migration and soil vapor extraction for soil remediation

Centrifuge modeling appears to be a useful experimental tool to study geoenvironmental problems, such as pollutant migration in subsurface systems. In this paper, the migration process of light nonaqueous phase liquids (LNAPLs) in unsaturated soils and thereafter soil vapor extraction (SVE) was simulated using the geotechnical centrifuge technique. Two series of centrifuge experiments were conducted to simulate a gasoline spill from a leaking underground storage tank (UST) and the subsequent subsurface migration of the gasoline along with soil remediation techniques. When centrifuge gravity reached the desired g level, the gasoline was released from the UST. It migrated into the unsaturated soil corresponding to a prototype time equivalent to 1 year. In soil remediation tests, after the LNAPLs migration occurred for 1 year, compressed air was injected into the soil mass for periods of 2 and 4 months to extract LNAPLs into the air phase from the contaminated soil. After each centrifuge test, the soil samples were collected using sampling tubes and the concentrations of the individual constituents in LNAPLs were measured by means of gas chromatograph analysis. The spatial distributions of contaminant concentrations were obtained to investigate the transport behavior of contaminants. Centrifuge tests results shown that the concentrations of LNAPLs were remarkably reduced by means of SVE. After SVE for 2 months, 47% of benzene, toluene, ethylbenzene, and o-xylene was removed from the soil; after 4 months of SVE, nearly 68% of contaminant was extracted from the contaminated area. It is demonstrated that SVE could be an effective soil remediation technology. Moreover, the vapor pressure of each contaminant component seems to be an important factor affecting the efficiency of SVE remediation technology.