Did the Army Corps know Exxon pipeline vulnerable?

The corps has been tinkering with the upper Yellowstone River as the Billings Gazette's Clair Johnson tells us:

The plan, called the Upper Yellowstone River Special Area Management Plan, directs the Corps to evaluate how a project may affect the entire watershed, flood plain and valley before approving a permit. “The road map is here,” said Todd Tillinger, program manager for Corps’ Montana Regulatory Branch in Helena. “Our goal is to keep it (the river) as intact as we can.” The Corps study began after two consecutive years of record flooding in the late 1990s triggered a rash of bank stabilization permits to prevent further erosion or property damage.

Talli Nauman at Native Sun News told us back in May that the Pipeline and Hazardous Materials Safety Administration is the Department of Transportation's regulatory body:

“We will hold pipeline operators accountable when they put the public or the environment at risk,” said U.S. Transportation Secretary Ray LaHood. “Pipeline operators must be vigilant about following safety regulations to prevent accidents and keep our communities safe without disrupting energy supplies.”

Reuters brings this:

After inspecting the pipeline in July 2009, PHMSA issued a warning letter to Exxon a year later about oil leaking from some of the valves on the pipeline. Exxon resolved all the concerns raised by the agency and no fine was issued.

The Button Valley Bugle has superlative coverage of the Silvertip Pipeline saga:

You would think that a company with record profits of $11 billion in the first quarter of this year and $45 billion in 2008, a company that can afford to pay its CEO $29 million last year, could afford to put a few million into its aging infrastructure. ExxonMobil Corporation has a problem keeping it’s products out of our waterways.

From a post in Switchboard, the blog of the Natural Resources Defense Council, Anthony Swift says:

An accident that should have been prevented is not really an accident. Tragedies like the Yellowstone River spill can be prevented by strong safety regulations and the proactive action of regulators. Today we are in desperate need of both.

The corps has been very quiet about a breach under its purview. Wouldn't Exxon have had to consult with the corps before restarting the now-burst pipeline and how could they not have known the potential for scouring on a flooding Yellowstone River?