Natural attenuation of benzene and dichloroethanes in groundwater contaminated by leachate from the West KL Avenue landfill in Kalamazoo, Michigan, was evaluated in three phases. Existing data from the previous site investigations were used to locate a series of high‐resolution vertical profile samples. By analyzing data from the discrete vertical profile samples, the rates of attenuation of benzene and dichloroethanes in the plume were forecasted. Permanent monitoring wells were installed over the depth intervals associated with high concentrations in the vertical profile sampling. These wells were monitored over time to extract independent estimates of the rates of degradation of benzene and dichloroethanes. Estimates of first‐order attenuation rate constants were obtained using two methods: a method due to Buscheck and Alcantar (1995), which is based on a one‐dimensional steady‐state analytical solution, and the tracer correction method of Wiedemeier et al. (1996). The rates of attenuation predicted from the vertical profile sampling were found to be in good agreement with the rates obtained from the permanent monitoring well data, indicating that the long‐term behavior of the contaminant plumes is consistent with the initial forecast. The results also indicated that the natural attenuation of benzene, 1,1‐dichloroethane (DCA), and 1,2‐DCA was statistically significant (at the 0.05 level).