Each year, as part of its ongoing commitment to safe operating practices Lawrence Livermore National Laboratory (LLNL) conducts prescribed burns at its Site 300 complex. LLNL consistently adheres to stringent, self-imposed safety standards in all of its activities, and the annual prescribed burning at Site 300 is done to prevent an accumulation of vegetative fuels (primarily grasses) that could cause an unacceptable risk of wildfire ignition. The LLNL prescribed burn procedure (Burklin, 2001) calls for the sequential, controlled burning individual small land plots by the LLNL Fire Department. Essentially the same burning procedure is repeated on a yearly basis. The burns usually are conducted in May and June; however, on rare occasions the burning has been done as late in the year as July. To the best of our knowledge there has never been an environmental problem caused by the smoke from these prescribed burns. Indeed, the avoidance of undesirable environmental impacts is inherent in the very concept of prescription burning. In order to better understand, in a quantitative sense, the atmospheric dispersion of smoke from prescribed burns at Site 300, and to examine how smoke behavior might differ for different burn months and burn-plot terrain, the National Atmospheric Release Advisory Center (NARAC) at LLNL has simulated the smoke dispersion from eight prescribed burns. Four of these bums were conducted on two days in June 1999, and the other four bums were conducted on two days in July 2000. This report describes the atmospheric models, fuel data, and atmospheric data used in the case studies. It also describes the GIS-based analysis of the simulations, and summarizes the simulation results.