The challenges connected with constructing and maintaining a landfill are related to protecting the surrounding environment from contamination caused by the wastes being deposited in the landfill. This contamination may be odor, solid materials blown out of the landfill, or - the most serious concern - may be pollution of ground water caused by liquids seeping from the waste deposits into soil and water below the landfill. Construction of a landfill is highly regulated and inspections are conducted to insure that safeguards are implemented to prevent such contamination.
Far below the ground level where waste materials are deposited, landfills are built upon a base level of very dense clay. It will hold in place any contaminants that may wash down through protective layers above it, preventing any pollution from reaching water acquifers or other sources below the landfill.
On top of the clay is a sloped layer of barrier material to prevent any liquids from reaching the clay. Collection pipes at the bottom of the slopes collect the liquid and pipe it to collection tanks where it can be treated and purified. A layer of sand covers the barrier and pipes, and another barrier layer and series of collection pipes is on top of the sand.
Dirt covers the sand, and the waste products are left on top of the dirt. Most landfills use earthmoving equipment to bury each day's additional materials to prevent odor, inhibit insects and vermin, and to minimize movement of materials within the landfill cavity.
When one area of a landfill is deemed at capacity, the entire area will be covered with clay, a barrier membrane to prevent penetration by precipitation, a layer of sand, and soil that will be planted to prevent erosion and absorb precipitation from the ground covering the waste.
See Figure 1 below for a cross-section diagram of a landfill.