One of the main problems is that even the existence of landfills does not guarantee an adequate treatment of waste. Only between 3.9% and 6.7% of the waste that enters into the selection plants is recuperated, and the rest is deposited in landfills. Managing solid waste costs MXN 3 billion yearly (USD 185 million approximately). Mexico City has 13 transfer stations to select, store and concentrate solid waste. It also has two selection plants to separate waste that can be recycled.