STOCHASTIC-ANALYSIS OF TRANSPORT AND DECAY OF A SOLUTE IN HETEROGENEOUS AQUIFERS

A stochastic analysis of transport and first-order decay for a solute plume in a three-dimensionally heterogenous aquifer shows that a spati ally variable decay rate produces effects both in the transient and st eady state characteristics of the effective decay rate, effective solu te velocity, and longitudinal macrodispersivity. The effective decay r ate is found to be less than the mean, which implies that decay predic tions that employ spatial averages of observations will tend to overes timate the rates of mass transformation due to decay. The effective so lute velocity is found to be the only field scale coefficient dependen t on the correlation between decay and log hydraulic conductivity. The longitudinal macrodispersivity is found to be reduced relative to tha t of a conservative/nondecaying solute. The characteristic timescale o f the transient development of all field-scale coefficients is reduced by the presence of a heterogeneous decay rate. All of these trends ar e accentuated with increasing decay rate variability. Increased peak c oncentrations, earlier arrival times, and decreased plume spreading ar e practical consequences of the derived results. The stochastic analys is presented here provides a vehicle to link laboratory-scale measurem ents with these field-scale predictions.