The company is supposed to assess the pipeline every five years, or even up to 68 months, or notify PHMSA for an extension.

However, it “failed to establish a five-year re-assessment interval for the Patoka to Corsicana segment … after the hydrostatic test of 2005 and 2006 identified a susceptibility to seam failures,” PHMSA said.

It did a transverse flux inspection (TFI), which is useful in detecting seam-related problems, in a series of four runs between July 2012 and February 2013, well past the 5-year limit.

ExxonMobil also failed to take immediate action when it learned about problems, PHMSA said.

Two sites “were identified as immediate repairs” in a vendor report on Aug. 9, 2010, but no action was taken until Aug. 28, 2010, at one and Jan. 6, 2011, at the other, the notice said.

PHMSA wants ExxonMobil to make specific changes to its operating processes, including  notifying the agency of all pre-1970 ERW pipe, and cites a timeline for various actions to be taken.

The Mayflower spill and resulting damages are the center of multiple lawsuits filed by Mayflower residents, the U.S. Environmental Protection Agency and the State of Arkansas in federal and state courts.

ExxonMobil says it has spent an estimated $70.5 million on the spill to date, but did not offer any estimates for future compliance costs. The pipeline is still shut down.