WASHINGTON (Reuters) - The U.S. pipeline regulator on Monday slapped a $3.7 million fine, the largest penalty ever imposed, on Enbridge Inc for a July 2010 crude oil spill which contaminated stretches of the Kalamzoo River in Michigan.
The Transportation Department's Pipeline and Hazardous Materials Safety Administration (PHMSA) said its probe uncovered two dozen regulation violations related to the leak on Enbridge's Line 6B near the town of Marshall, about mid-way between Detroit and Lake Michigan.
"We will hold pipeline operators accountable if they do not follow proper safety procedures to protect the environment and local communities," Transportation Secretary Ray LaHood said in a statement.
Enbridge has 30 days to respond to the order.
PHMSA's order against Enbridge accuses the company of failing to adhere to regulations for maintaining pipeline integrity.
The agency also said the company attempted to bring the pipeline back into service despite receiving multiple leak alarms the night it ruptured, leading to the release of more oil.
Enbridge's 30-inch line ultimately spilled more than 20,000 barrels of heavy crude and contaminated 38 miles of the Kalamazoo River.
The accident shut down the pipeline for more than two months and spawned a massive clean-up that the company has estimated will cost more than $700 million.
Following the Enbridge spill and other major pipeline accidents, the Transportation Department enhanced its oversight last year.
The department is collecting more data on pipelines and in 2011 closed 102 enforcement cases, its highest level for a single year.
Last December, Congress passed a pipeline safety bill that raised maximum fines and authorized an increase in the number of pipeline inspectors.
Enbridge said it was reviewing the PHMSA order.
"We will not comment specifically on the contents of the (Notice of Probable Violation) until that analysis is complete," the company said in a statement.
(Reporting by Ayesha Rascoe; Editing by Tim Dobbyn and Ron Popeski)