6.30. The design of the geological disposal facility for safety in the post-closure period should make optimal use of the intrinsic features of the host geological environment and includes engineered barriers that complement the natural barrier system. Disposal facilities for both high level and intermediate level waste are expected to perform over much longer time periods than those usually considered in industrial applications. Investigation of the ways in which analogous natural materials have behaved in geological settings in nature, or how ancient artefacts and anthropogenic constructions have behaved over time, may contribute to confidence in the assessment of long term performance of the facility. It is important to demonstrate that both the fabrication of waste containers and the construction of engineered barriers are feasible (e.g. in underground laboratories) in order to gain confidence that an adequate level of performance can be achieved.