Vibratory Mobilization of Immiscible Liquid Ganglia in Sands

Abstract

It is well known that residual NAPL (nonaqueous phase liquid) ganglia remain trapped in the saturated domain after pump‐and‐treat operations and create a long‐term source of contamination. Mobilization and extraction of these ganglia is a problem of paramount importance in ground‐water remediation. The present study consists of laboratory and theoretical investigations on the effect of vibrations on mobilization of these ganglia. Laboratory tests were conducted using a variable‐amplitude vibrating table on two sandy soils contaminated with hexadecane. Vibrations augmented by viscous forces due to flowing water yielded better recovery of ganglia than under buoyancy conditions alone. The mobilization of ganglia was found to depend on initial soil density and water flow rate under which the ganglia were trapped. In general, higher vibration amplitudes resulted in higher removal of NAPL ganglia. The existing mobilization criteria were modified to take into account the cyclic pore pressures and relative density changes observed during vibrations. The modified mobilization criteria when applied to the laboratory test conditions yielded information about stable lengths of ganglia in the two sands at each vibration amplitude. The percentages of trapped volume occupied by ganglia of various ranges of lengths in the two sand samples were deduced. The results indicate that localized vibrations in a saturated domain, when augmented by suitable flow conditions, can effectively mobilize and extract NAPL ganglia.