ANALYTICAL MODEL FOR HETEROGENEOUS REACTIONS IN MIXED POROUS-MEDIA

The ''funnel/gate system'' is a developing technology for passive grou nd-water plume management and treatment. This technology uses sheet pi lings as a funnel to force polluted ground water through a highly perm eable zone of reactive porous media (the gate) where contaminants are degraded by biotic or abiotic heterogeneous reactions. This paper pres ents a new analytical nonequilibrium model for solute transport in sat urated, nonhomogeneous or mixed porous media that could assist efforts to design funnel/gate systems and predict their performance. The mode l incorporates convective/dispersion transport, dissolved constituent decay, surface-mediated degradation, and time-dependent mass transfer between phases. Simulation studies of equilibrium and nonequilibrium t ransport conditions reveal manifestations of rate-limited degradation when mass-transfer times are longer than system hydraulic residence ti mes, or when surface-mediated reaction rates are faster than solute ma ss-transfer processes (i.e., sorption, film diffusion, or intraparticl e diffusion). For example, steady-state contaminant concentrations wil l be higher under a nonequilibrium transport scenario than would other wise be expected when assuming equilibrium conditions. Thus, a funnel/ gate system may fail to achieve desired ground-water treatment if the possibility of mass-transfer-limited degradation is not considered.