Landfills are sites for dumping waste, buried and covered by soil. According to the waste management hierarchy, landfilling is the least preferable option. There are numerous environmental impacts associated with landfilling. For example, the sites contribute to air pollution and global warming: as organic material decomposes, it releases methane (a potent greenhouse gas), They also contribute to groundwater pollution by leaching toxic chemicals. In most countries, landfilling is still the waste management technique of choice, with 40% of all plastic waste being sent to landfills.