For many years I have come to feel that as we run out of natural resources it will be inevitable that we start to see our landfills as resources. A web search on "landfill mining" turned up some interesting information, there is even a Wikipedia entry on the subject. This article: "Landfill Mining - Goldmine or Minefield" in Waste Management World provides a substantial overview of the current thinking.
Aside from extracting useful material such as steel, energy can be extracted from less useful waste. Soil used as filler can be recovered and reused, either on-site or in carefully selected areas. The economics of recovering recyclable materials has not yet been proven so buried plastics and glass are not a primary concern due to the highly contaminated nature of these materials. Of course the health and safety issues of extracting potentially toxic materials is a serious consideration when attempting a project like this. Processes for recovering high-value rare-earth metals have not been fully developed yet, but it is a serious consideration if these materials can be extracted in a viable manner. Think about the hundreds of millions of rechargeable batteries from phones and power tools that have entered the waste stream that contain valuable - but toxic lithium and other rare earth metals.
Incidentally, very little material from lead-acid batteries enters the waste stream because automobile batteries have historically been one of the most recycled items in history. The typical new lead-acid battery contains 60 to 80 percent recycled lead and plastic. If you happen to have an old lead-acid battery laying around, you can take it to a recycling center. Other rechargeable batteries can be taken to battery recycling centers nearby.
Reasons for mining landfills include land reclamation and opening up easements for roadways and other public use. Landfill owners are very interested in turning their assets into cash flow rather than costing them money. The third annual Global Landfill Mining Conference & Exhibition will be held this November. To quote their webpage "If 'waste to energy' and metal prices are today's hot topics, then you can view a landfill as being a gold mine and a coal mine rolled into one."
That this topic is generating significant interest sufficient to support a major conference is very encouraging.
A Belgian company Group Machiels is actively mining a landfill about 50 miles east of Brussels that dates back to the 1960s and expect that 45% of its contents can be fully recycled, while the rest can be converted to electricity. The group has formed a joint venture with Advanced Plasma Power, a U.K. based waste-to-energy company. Advanced Plasma Power converts non-recyclable material into clean-burning natural gas. This is used to generate electricity sufficient for 100,000 homes and the residue is converted into a building material called Plasmarok. This project is considered the first of its kind and clearly, both companies expect to make a profit from this venture. If this model proves out landfills may well become future gold mines!
I also found a March, 2014 news article about a landfill in Richfield, Michigan in which the town is seriously considering opening up mining rights to their landfill.