These facilities start out by scooping away the earth to a footage depending on how far down the rock cap is. They then line the entire site with a thick mat to prevent any 'juicy stuff' from filtering into the water table. Most landfills have an upper end of 15 to 30 year service date. Management of these facilities also includes use after the site has been filled. Interestingly enough, trees are discouraged from growing because of their root system.
Car tires pose a hazard when they end up in the landfill because they trap gases.
When an airway in the compacted landfill trash is created, these gases can travel great distances through a gravel bed, or just under the surface. Any nearby flame is a potential time bomb with a gaseous condition nearby. Tire retailers now charge a fee for disposal, and facilities have been created to grind and reuse them in such things as soaker hoses and barrier fencing. Used batteries, spent motor oil, old paint and other household products are other things that should never end up in a community landfill. Paper generally breaks down rapidly, but not when dumped in a huge anaerobic mass into the landfill.