Almost every gas station eventually pollutes the earth beneath it, experts told Grist. The main culprit: the underground storage tanks that hold tens of thousands of gallons of fuel, one of the most common sources of groundwater pollution. Typically, two or three of these giant, submarine-shaped tanks are buried under a station to store the gasoline and diesel that gets piped to the pump. A large tank might be 55 feet long and hold as many as 30,000 gallons; a typical tank might hold 10,000 gallons. Leaks can occur at any point — in the storage tank itself, in the gas pumps, and in the pipes that connect them. Hazardous chemicals can then spread rapidly through the soil, seeping into groundwater, lakes, or rivers.