The State of California adopted the Low-Threat Underground Storage Tank Case Closure Policy (Low-Threat Policy), and it became effective on August 17, 2012. The Low-Threat Policy specifically applies to petroleum Underground Storage Tank (UST) sites. Through a process of scientific evaluation and public participation, the California State Water Resources Control Board (SWRCB) promulgated an “updated and enlightened view” of “how clean is clean” for petroleum products (primarily gasoline) in soils and groundwater. The policy takes into account the protection of California’s precious groundwater resources and the current science of health risk exposures to humans. In effect, the Low-Threat Policy increases the threshold of gasoline allowed to remain in the soils and groundwater and provides clearer criteria for case evaluation and closure.