What problem is caused by waste in landfills?

There is a risk of contamination of surrounding watercourses and ground water. Flammable methane gas has to be vented into the atmosphere, or burnt off. The land needs many years after landfill has ceased before it can be built on. Landfill sites are becoming scarce, which is why recycling is encouraged nowadays. The more that is recycled, the less waste has to be dumped in a landfill.