[Brief Introduction of Pollution Sites Remediation and Risk Assessment and Its Policy Making in United States].

Site remediation has become an imperative part of environmental protection in China due to recent economic development, urban spreading, new industries replacing old ones, relocation of old industrial sites, and increased environmental conscience. This paper mainly introduced the concept, method, calculation, risk assessment and management for polluted sites remediation based on experience from California, USA. Further, the paper presented the concept of vapor intrusion and how to use vapor intrusion methodology to determine site remediation standard. Mathematical modeling approaches were also discussed in terms of how to determine the residual pollutant concentrations in soil and how to calculate indoor vapor concentrations. Based on risk assessment, California Environmental Protection Agency, Water Resources Control Board issued a 'Low Threat Underground Storage Tank Case Closure Policy' for impacted underground storage tank sites. The numerical criteria in the Policy were based on calculations of human health risk assessment. Finally, a real case study in California, USA, was presented to demonstrate how the risk assessment calculations were applied in polluted site remediation, which helps to answer the question of 'how clean is clean'.