EXPERIMENTAL INVESTIGATIONS OF THE ENTRAPMENT AND PERSISTENCE OF ORGANIC LIQUID CONTAMINANTS IN THE SUBSURFACE ENVIRONMENT

Organic liquids are common polluters of the subsurface environment. On ce released, these nonaqueous phase liquids (NAPLs) tend to become ent rapped within soils and geologic formations where they may serve as lo ng-term contaminant reservoirs. The interphase mass transfer from such entrapped residuals will ultimately control environmental exposure le vels as well as the persistence and/or remedial recovery of these cont aminants in the subsurface. This paper summarizes National Institute o f Environmental Health Sciences-sponsored research designed to investi gate and quantify NAPL entrapment and interphase mass transfer in natu ral porous media. Results of soil column and batch experiments are pre sented that highlight research findings over the past several years. T hese experiments explore dissolution and volatilization of hydrocarbon s and chlorinated solvents in sandy porous media. Initial concentratio n levels and long-term recovery rates are shown to depend on fluid flo w rate, soil structure, NAPL composition, and soil wetting characteris tics. These observations are explained in the context of conceptual mo dels that describe entrapped NAPL morphology and boundary layer transp ort. The implications of these laboratory findings on the subsurface p ersistence and recovery of entrapped NAPLs are discussed.