Mobilization of trichloroethene (TCE) during ethanol flooding in uniform and layered sand packs under confined conditions

Five horizontal flow experiments were conducted in homogeneous and layered sand packs to evaluate the effectiveness of mobilization of trichloroethene (TCE) by ethanol flooding. A small quantity (5-7 mt) of pure TCE was injec ted into the center of each sand pack, and then horizontal ethanol floods w ere conducted at darcy velocities between 4 and 12 m d(-1). Once ethanol co ntacted the region initially affected by TCE in uniform sand packs, rapid d ownward and upgradient flow of TCE occurred along sloping ethanol-water int erfaces. In layered sand packs the bulk mobilization of TCE appeared to be associated more with phenomena resulting from interfacial tension reduction rather than with enhanced dissolution processes. Heterogeneities promoted a variety of bypassing and mixing phenomena that resulted in, but were not limited to, physical displacement of TCE at the edges of discrete fine-grai ned lenses due to localized confined flow conditions; upward migration of e thanol through finer-grained sons due to buoyancy; rapid downward mobilizat ion of TCE; upgradient mobilization of TCE around heterogeneities; and migr ation of TCE into finer-grained soils at locations both upgradient and down gradient of the TCE source zone. Enhanced TCE dissolution was also observed .