This development was revealed today by Rep. Ed Markey (D-Mass.), who posted correspondence between his office, ExxonMobil and the Pipeline and Hazardous Materials Safety Administration (PHMSA) on his website.
According to the documents, PHMSA approved an Emergency Response Plan that included a "Worst Case Discharge" scenario that requires ExxonMobil to detect and shut down the pipeline in 12 minutes in 2009. On March 14, ExxonMobil submitted a revised plan to PHMSA that would extend the detection and shutdown time to a total of 18 minutes. In correspondence with Markey, ExxonMobil maintained that this revised plan was in effect on March 29, but when asked by Markey to verify that, PHMSA said the revised plan has yet to be approved.