The commission said it will improve leachate capacity at informal landfills. Leachate is any liquid that, in passing through matter, extracts solutes, suspended solids or any other component of the material it has passed through. "Informal landfills pose a serious environmental threat and health damage to the country if left unregulated," said Mao Da, an expert in solid-waste management at Beijing Normal University. Mao said the standard of landfills in the capital varies, and some without proper management are posing a serious threat to the environment. Without a proper landfill procedure, some buried waste will seriously pollute underground water and soil. Some waste even pollutes air quality, Mao said.