organic liquids are common polluters of the subsurface environment 
 . once released , these nonaqueous phase liquids ( napls ) tend to become entrapped within soils and geologic formations where they may serve as long - term contaminant reservoirs . 
 the interphase mass transfer from such entrapped residuals will ultimately control environmental exposure levels as well as the persistence and/or remedial recovery of these contaminants in the subsurface . 
 this paper summarizes national institute of environmental health sciences - sponsored research designed to investigate and quantify napl entrapment and interphase mass transfer in natural porous media . 
 results of soil column and batch experiments are presented that highlight research findings over the past several years . 
 these experiments explore dissolution and volatilization of hydrocarbons and chlorinated solvents in sandy porous media . 
 initial concentration levels and long - term recovery rates are shown to depend on fluid flow rate , soil structure , napl composition , and soil wetting characteristics . 
 these observations are explained in the context of conceptual models that describe entrapped napl morphology and boundary layer transport . 
 the implications of these laboratory findings on the subsurface persistence and recovery of entrapped napls are discussed.imagesfigure 1figure 3figure 9