For fast-degraded chemicals such as 1，3. dichloropropene(1，3-D)，their long persistent time in topsoils cannot be explained bv the ordinary first. order kinetics of biOdegradatiOn that iS commonly used in the simulation of chemical transport in soils. The Monod kinetics of biodegradatiOn，which iS usually defined as the mathematical relationship between the residual concentration of the growth. 1imiting substrate and the specific growth of degraders in laboratory reactors，was found to be responsible for the phenomenon of "decelerated biodegradatiOn". To take advantage of both the simplicity Of first. order kinetics in transport modeling and the realistic description Of Monod kinetics for a physical situation. a simplified method was used to represent Monod kinetics with the corresponding pseudo first. order kinetics. Pseudo first. order constants fitted with Monod kinetics were later substituted into the transport model. A satisfactory agreement between field measurement and simulated results using these constants was achieved.