CONTAMINANT MASS-TRANSFER DURING GAS-PHASE TRANSPORT IN UNSATURATED POROUS-MEDIA

This study was conducted to investigate the relative effects of physic al heterogeneity, gas-liquid mass transfer, and rate-limited sorption on the gas-phase transport of contaminants in idealized unsaturated ho mogeneous and heterogeneous porous media. The transport of methane in the unsaturated homogeneous porous medium was ideal, whereas that of t richloroethene and benzene was nonideal, governed by rate-limited diff usive mass transfer in immobile water and by rate-limited sorption/des orption. Transport of both methane and trichloroethene through the uns aturated heterogeneous porous medium was nonideal. Gas-phase mass tran sfer between unsaturated advective and nonadvective domains caused non ideal transport of methane. Trichloroethene nonideality was due to a c ombination of gas-phase mass transfer between advective and nonadvecti ve domains, diffusion within immobile water, and rate-limited sorption /desorption. The transport of trichloroethene through the heterogeneou s porous medium was predicted by use of a multiprocess mass transfer m odel, wherein all parameters were estimated independently.