To begin at the bottom, the soil underneath the landfill is prepared (called a “subgrade"). A bottom liner is fitted in made of compacted clay, which kind of acts like a bathtub. A thick plastic layer—polyethylene or HDPE—is next, it’s called a geomembrane and protects against leaking and gas escaping. Leaking of liquids from soluble material as it breaks down is called leachate. Even benign things such as mothballs can break down the plastic as well as your everyday margarine, vinegar, ethyl alcohol, shoe polish and peppermint oil.
Leachate collection is next and is accomplished with a series of pipes. Pipes with holes in them are buried between layers of gravel. The pipes are attached to sumps, which have pumps inside (often referred to sump-pumps). When the wastewater is driven to the low area sumps, it is then transported by pumping action thorough the pipes to another facility for treatment or disposal. (Sometimes it goes into special ponds where bacteria render it useful again.)
Geotextile is a fabric that comes in several types such as mailbag sacking, felt or felt with holes. It is normally placed on top of the collection pipe system because it separates solids; the liquid goes through the holes in the weave and prevents the pipes from clogging.
This fabric then has a layer of sand over it, gravel if available, or even a plastic mesh called “geonet." It is just another way to drain the leaching fluids that will eventually be sent to the pipe system.
There will be trucks, huge bulldozers and giant graders continually covering the waste with six to twelve inches of soil. Referred to as the “daily cover"—it is reducing odors and keeping litter in place. (Not to mention, it deters the birds, rodents and other scavengers who are nearby looking for food.)
On top of the whole shebang will be cover vegetation in areas that are full. Generally, this means native grasses and growing shrubs, plants that to help maintain the soil coverage. Just as a farmer plants “cover" crops to give the soil nutrients and keep the land from blowing away, so is cover vegetation in a landfill.