Enbridge Energy Partners LLC was formally fined $2.4 million Tuesday by the U.S. Department of Transportation for the 2007 oil pipeline explosion near Clearbrook, Minn., that killed two Superior men.

The fine was proposed in 2008 but didn't become formal until Tuesday. It must be paid within 20 days, federal officials said.

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The afternoon explosion, which occurred on Nov. 28, 2007, created a huge fire and spilled 15,000 gallons of oil.

In addition to the fine, Enbridge also must revise and implement certain pipeline maintenance and repair procedures and upgrade training efforts for employees. But a company official Tuesday said those actions already have occurred.

"We expected this, but are still surprised by the amount of the penalty," said Larry Springer, an Enbridge spokesman. "We have no problems with the corrective actions ordered and in fact all of the measures already have been in place for some time. ... Certainly this is one of the most tragic things to happen to us. ... But it's had us redouble our efforts to pipeline safety and training."

In proposing the fine in 2008, the DOT said Enbridge didn't follow written procedures for welded couplings at high pressure and for anchoring the pipeline.

"Enbridge procedure 06-03-13 was not followed during the installation of the fittings involved in the accident, and interviews conducted with Enbridge personnel across its pipeline system indicated that these procedures had not been followed consistently for a number of years," the DOT investigation found.

Even before the explosion, state officials told federal regulators about their concerns about high pressure in the pipe and serious problems that could result. The federal investigation later found that "Enbridge operated the pipeline in excess of the design pressure of the Welds-Ends couplings as determined by the manufacturer."

According to DOT's Pipeline and Hazardous Materials Safety Administration, its investigation showed that Enbridge failed to safely and adequately maintain and repair the line. A leak occurred during a repair effort, leading to the explosion apparently ignited by a heater in the work area. The report said Enbridge failed to clear the work area of potential sources of ignition.

Earlier this month, the News Tribune documented more than 1.5 million gallons of oil spilled over the past 30 years from pipelines across northern Minnesota now operated by Enbridge. The company currently is working to clean up a nearly 1 million gallon spill in Michigan.

The U.S. House Transportation and Infrastructure Committee has scheduled a hearing on Enbridge pipeline safety for Sept. 15 in Washington.

"I commend the secretary for taking today's action against Enbridge and for holding Enbridge accountable for this tragic incident," U.S. Rep. Jim Oberstar, D-Minn., chairman of the committee, said in a statement. "The T&I Committee is in the process of investigating Enbridge and its most recent hazardous liquid pipeline failure in Marshall, Mich. As we move forward with this investigation and with the reauthorization of DOT's pipeline safety program, we will be reviewing these incidents, Enbridge's failure history, PHMSA's enforcement of existing federal regulations, and any areas in the law which may need strengthening."