As a result of the disruption in the supply of fuel from Gulf-area refineries following Hurricane Isaac, and at the request of Governors, EPA has exercised its authority under the Clean Air Act to temporarily waive certain federal clean gasoline requirements for gasoline sold and distributed in Louisiana, Mississippi, Alabama, Georgia, Florida, Tennessee, South Carolina and North Carolina. The disruption and delays in production and delivery of gasoline resulted from effects of Hurricane Isaac. 

This waiver was granted by EPA in coordination with the Department of Energy (DOE). EPA Administrator Lisa P. Jackson determined that extreme and unusual supply circumstances exist, which may result in a temporary shortage of gasoline compliant with federal regulations. The federal waiver will help ensure an adequate supply of gasoline in the impacted states until normal supply to the region can be restored.

The waiver applies to the use of low Reid Vapor Pressure (RVP) "summertime" gasoline for the remainder of the "high ozone" period, which ends on Sept 15. Due to a number of continuing refinery outages caused by Hurricane Isaac, and the slower-than-expected-pace of restarts of other Gulf-area refineries, EPA determined that there would not be an adequate supply of summertime gasoline for these states through Sept 15. The waiver allows available supplies of higher RVP "wintertime" gasoline to be used prior to the end of the high ozone period, in order to prevent a gasoline supply shortfall in these states. 

States bordering on this area are projected to have sufficient supplies of compliant summertime fuel through the end of the high ozone period in two weeks, and no shortages are expected to develop. However, EPA will continue to actively monitor fuel supplies in these areas, and will act expeditiously if needed to prevent a shortfall.

More information: http://epa.gov/enforcement/air/fuel-waivers.html