In the second half of the 20th century, the American economy has undergone profound changes. The focus of economy and work has shifted from cities to suburbs, from north to south, and from east to west. Many enterprises have left a lot of "brown land" after relocation, including industrial land, automobile gas stations, abandoned warehouses and abandoned residential buildings that may contain lead or asbestos. These sites are polluted by industrial waste to varying degrees, which pollutes the soil and asbestos in the sites. 1978, taking the Love Canal incident as an opportunity, 1980, the US Congress passed the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA), which is known as the environmental protection superfund, so it is often called the superfund law.