I would suggest that the evaluation be made based on the 'readily accessible' criteria. Basically determine if the box and associated hardware is one of those items which is required to be readily accessible, and then determine if the surrounding conditions provide the necessary access.
As far as I know, a meter is not required to be readily accessible by the NEC, but may be required to be readily accessible by the power company. On the other hand, the power company may be using some remote meter reading system, and not particularly care where the meter is located...in the greater Boston area I've noticed a number of meters sitting high up on utility poles, supplying things like cable or telephone equipment boxes.
Junction boxes in general are not required to be readily accessible, but they cannot be buried.
Things like breakers and disconnects however do have to be readily accessible in most circumstances.
If the enclosure contains the main breaker or disconnect, then IMHO you should require a flat platform or pad with safety rail sufficient to make the enclosure readily accessible. If, on the other hand this box simply contains the meter, then I don't believe that the electric code would provide a basis for requiring changes.
I do not believe that accessibility for repairs is sufficient basis for requiring better access. It might be that an electrician working on this box would have to set a ladder from the base of the retaining wall rather than being able to stand at grade level, but electricians working on ladders is not extraordinary or inappropriate.
A question along these lines: if code requires readily accessible disconnection means in any given circuit, can you additionally have inaccessible disconnection means? Or does code require that if you add a disconnect it must be readily accessible? If, for example, there is a breaker in the enclosure being discussed _and_ a main breaker in the panel inside the house, then would the breaker inside the house count as the readily accessible disconnect, and the breaker in the enclosure count as some sort of supplementary disconnect?
-Jon
