All disposals, at whatever depth, are susceptible to human intrusion but in the case of deep disposal it is widely accepted that this is confined to exploratory drilling, the probability of which is reduced by avoiding sites with mineral resources. In contrast, human intrusion into a near-surface disposal can take many forms such as construction of buildings and roads, pipeline burial and archaeological excavations. A 1987 NEA study25 indicated that excavations for domestic buildings rarely go deeper than 3 m while the maximum depth for a road construction was taken as 10 m. These figures may be compared with recent proposals for intermediate depth disposal in Japan26 and France27 where the specified target depths are 50-100 m and 15-200 m respectively. In general, it may be reasonably assumed that, with a few exceptions, disposal below a few tens of metres will avoid the potential for large-scale inadvertent excavation. The exceptions are largely site specific: the possibility that deep road or railway cuttings or tunnels might be constructed will be determined by the hilliness of the terrain; in places where high-rise buildings could be placed, the foundation depth (normally a few tens of metres) will be dependent on soil strength.

It is tempting and sometimes even useful to equate low-, intermediate — and high-level wastes with near-surface, intermediate-depth and deep disposal, respectively. There is a difficulty, however, because containment and isolation do not inevitably increase monotonically with depth. It is possible, for instance, that a bedded salt formation lying between 200 and 300 m would provide superior containment to a fractured basement rock at 600 m. Similarly, a formation that does not lie close to a mineral resource will provide better isolation than one that does, even if the latter is at the greater depth. The important point is that when deciding on an appropriate facility depth, there are no fixed rules: each case must be addressed individually.