[en] Decommissioning is an emerging international issue in the nuclear industry. Termination of the decommissioning authorization involves releasing the facility from the regulatory control for restricted or unrestricted use in the future. Prior to releasing the facility from regulatory control, it must be shown that the site has been sufficiently cleaned up to meet either restricted or unrestricted use in the future. To meet the required standards the site owner has to show that the soil at the facility has been sufficiently cleaned up. To do this one must know the contamination of the soil at the site prior to clean up. This involves sampling that soil to identify the degree of contamination. Regulatory guidelines for site reuse after decommissioning are commonly challenged because the majority of the activity in the soil at or below the limit of detection. RESRAD is a computer model designed to estimate radiation doses and risks from RESidual RADioactive materials. Using additional statistical analyses of contaminated soil after decommissioning is expected to have the following advantages: a better and more reliable probabilistic exposure assessment, better economics (lower project costs) and improved communication with the public. This research will develop an approach that defines an acceptable method for demonstrating compliance of decommissioned NPP sites and validates that compliance. Summary statistic and confidence intervals were compared to conventional methods. Proposed methods were performed using the soil samples from the monazite powder manufacturing plant. The preliminary evaluation shows that the proposed method can be effectively used to provide: the best estimate radioactivity levels at decommissioned NPP site and estimates of uncertainty in the mean value