A landfill is a carefully engineered and managed structure which acts as a final disposal option for waste. Contrary to what some might think, a landfill is not a "dump". A "dump" is any place where trash is thrown on the ground or waterway without following proper recycling or disposal regulations. These "dumps" are illegal in the state of Iowa.
In a landfill, the cell has a clay or synthetic liner to isolate the waste from the environment, and it's covered with daily to keep it from the air, rain, animals, and to prevent litter.
The Cedar Rapids/Linn County Solid Waste Agency's landfill at County Home Road in Marion is a Class D Landfill. This means that extra care had been taken to protect the environment. The Agency landfill uses a compacted clay layer as well as a high-density (HDPE) liner to isolate waste from the environment. It does not accept hazardous or medical wastes.
Landfilling is the last step in a hierarchy of waste management. Before landfilling are the prefered options of reduction, reuse, recovery, and recycling. The video below, borrowed from Rumpke, describes some of the engineering behind landfill construction.