I am unsure how much of a problem this is in other countries, but recycling and high temperature incineration is now beginning to reduce the need for land fill. However, there are many existing, now covered and landscaped, old land-fill sites.
What scope is there for use of even early, crude nanotech for cleanly and safely extracting the resources from these sites?
Would the same techniques be used as on slag heaps or mining spoil heaps, which will contain many valuable minerals?
Could the fact that there is a lot of carbon in land-fill be put to use? Some of this is an existing problem in the form of methane.
Would cooling systems need to be installed to handle the heat generated in the clean up operation? Undisturbed land-fill can have over-heating problems.
Would some sort of fuel or other energy source be sensibly needed, assuming you don't want to generate a lot of carbon dioxide, or iron oxide?
Would it be sensible to plan on the underground area ending up as excavated, presumably with a reinforced roof and supports? Conversion of land fill sites into underground amenity areas?
Some areas contain a lot of water in their land-fill, and care is needed to prevent contamination of surface and ground water. How will this affect things?
Land-fill can be very hetrogenous, and might this restrict the use of specialised nanotech?
(c) Rory O. McLean, 1980 - Feb. 2006 Permission granted to use for non-profit making purposes