Mixing depth is an important quantity in the determination of air pollution concentrations. Fire-weather forecasts depend strongly on estimates of the mixing depth as a means of determining the altitude and dilution (ventilation rates) of smoke plumes. The United States Forest Service (USFS-Savannah River) routinely conducts prescribed fires at the Savannah River Site (SRS), a heavily wooded Department of Energy (DOE) facility located in southwest South Carolina. For many years, the Savannah River National Laboratory (SRNL) has provided forecasts of weather conditions in support of the burn program, including an estimated mixing depth using potential temperature change with height at a given location. This paper examines trends in the average estimated mixing depth daily maximum at the SRS over an extended period of time (>3 years) derived from numerical atmospheric simulations using two versions of the Regional Atmospheric Modeling System (RAMS). This allows for differences to be seen between the model versions, as well as trends on a multi-year time frame. On a monthly basis, seasonal trends are as expected with the highest mixing depth predictions occurring during the summer months, although lower maximum summer values are predicted to occur in the earliest year (2003). The variation in average mixing depth during the summer months agrees with annual variability in local observations (i.e. average temperature, precipitation, and heat stress). In addition, comparisons of predicted mixing depth for individual days in which special balloon soundings were released are also discussed.