8.11. As stated in para. 8.9, the operational safety case is often built on a set of conservative assumptions in order to manage the uncertainties at that stage of development of the facility. Monitoring and surveillance undertaken to confirm performance are therefore expected to provide data that may be different from those used for the safety case, and are generally expected to be more realistic. Similarly, because of the conservatisms in the safety assessment, environmental monitoring data may be expected to remain within those levels forecast in the safety case. However, monitoring results may also provide apparent or actual contradictions, such as variations in parameters or the occurrence of events not anticipated in the safety assessment. Such results could be labelled as ‘unexpected’, as they do not appear to confirm prior expectations. Communication of monitoring results and their related uncertainties to the regulatory body and other interested parties should be started early in the process, as it is generally easier to explain uncertainties before beginning a monitoring programme than to try to provide an explanation after monitoring has started.