Almost 495,000 releases of petroleum from federally regulated underground storage tanks (USTs) have been reported to EPA as of September 2010. Of these, over 93,000 UST site cleanups remain. The Association of State and Territorial Solid Waste Management Officials (ASTSWMO) estimates that cleaning up UST system releases costs the states approximately $700 million each year, in addition to federal expenditures under the Leaking Underground Storage Tank (LUST) Trust fund and costs paid by responsible parties. State agencies maintain responsibility to implement and oversee corrective actions at UST sites, with the exception of federal authority for UST site cleanup in Indian country. The majority of these actions involve UST systems for petroleum fuel rather than chemicals containing hazardous substances and most involve retail fueling stations. Common contaminants associated with fuel releases include benzene, toluene, ethylbenzene, and xylenes (BTEX) and sometimes other chemicals of concern such as methyl tert-butyl ether (MTBE), ethanol, or lead scavengers (ethylene dibromide and 1,2 dichloroethane). Releases of petroleum, used oil, or chemicals can result from problems such as corrosion of the tank or attached pipes, structural failure, or faulty installation. In addition to the tank, components of an UST system include connected underground piping, underground ancillary equipment, and the containment system, if any.