Three Enbridge Corp. crude oil pipelines crossing Minnesota's Tamarac River were exposed by floodwater erosion years ago, and were still exposed in mid-2014. None of the pipes had failed at that point, but one was being propped up by steel legs, according to an MPR News account.
Federal regulations aren't much help. The only rule that addresses pipe burial at major river crossings requires petroleum pipelines to be laid at least four feet below the riverbed at the time of construction. Once a pipeline's installed, there are no requirements regarding burial depth. There is no rule requiring exposed pipelines to be reburied, though a spill under those conditions would invite regulatory penalties for leaving the line exposed to hazards.
What's more, federal rules put the pipeline companies in charge of identifying all threats that could cause a spill in highly populated or environmentally sensitive areas, and the companies get wide latitude in deciding what to do about them, according to Rebecca Craven, program manager at the Pipeline Safety Trust, a nonprofit group that tracks pipeline risks and regulations.