Feasibility Study of Using Centrifuge for Investigating LNAPL Migration in Unsaturated Soils

Abstract

Centrifuge modeling appears potentially useful for studying geo-environmental problems such as pollutant migration in subsurface systems. In this study, the “modeling of models” technique was used to validate the feasibility of using a geotechnical centrifuge to model the transport behavior of light non-aqueous phase liquids (LNAPLs) in unsaturated soils. All the experiments were conducted to simulate a gasoline spill from a leaking underground storage tank (UST) and the subsequent subsurface migration of the gasoline. When the gravity in the centrifuge reached the desired g-level, the gasoline was released from the UST and then it migrated in the unsaturated soil corresponding to a prototype time equivalent of one year. After the centrifuge tests, soil samples were collected using sampling tubes and the concentrations of individual constituent in the LNAPL were directly measured by means of gas chromatograph analysis. Results obtained from the centrifuge tests at different g-levels show that similar migration patterns are found for LNAPL transport in unsaturated porous media. The location of the peak concentration and the behavior of lateral spreading can be adequately described. In addition, centrifuge test data show that the migration pattern of LNAPLs is related to the soil type and the physical properties of individual constituents in the LNAPLs.

Keywords:

• Centrifuge modeling
• contaminant transport
• geo-environmental engineering
• light non-aqueous phase liquids
• leaking underground storage tanks
• modeling of models.

The authors thank Mr. Yin Kunting for his tremendous assistance throughout the centrifuge tests. The research work reported in this paper was financially supported by Hong Kong RGC Competitive Earmarked Research Grant (Project No. HKUST 6112/99E) and the National Science Foundation of China (Project No. 50209006).