WASHINGTON It will take several months to investigate the cause of the leak on ExxonMobil's Silvertip oil pipeline crossing the Yellowstone River, the U.S. pipeline safety regulator told Congress on Thursday.
"We will also ensure that the Silvertip pipeline is free of safety and environmental risks before Exxon Mobil is granted permission to restart the line," Cynthia Quarterman, head of the Pipeline and Hazardous Materials Safety Administration, told lawmakers at a House hearing looking into the leak.
Any violations of federal pipeline safety regulations by Exxon will be "swiftly addressed," she said.
Quarterman said the Yellowstone River was still too high to examine the section of the pipe that leaked, and it "may take weeks if not months" before the pipeline can be brought up from the river bed.
On Wednesday, Exxon said it had begun preliminary work to replace the pipeline that ruptured and spilled an estimated 1,000 barrels of oil into the Yellowstone River in Montana two weeks ago.
PHMSA said oil from the spill have been found at least 240 miles downstream from the site where the pipeline burst.
The company does not yet know what caused the leak, and is focused on cleaning up the oil, said Gary Pruessing, president of Exxon Mobil Pipeline Co.
"We have not put any end date on a clean-up," Pruessing told lawmakers, noting the company has been challenged by high water levels.
Exxon plans to replace the damaged pipeline by laying a new section of pipe 30 feet below the river bed, Pruessing said -- going beyond federal regulations that require pipelines to have at least 4 feet of ground cover in a river bed that is more than 100 feet wide.
Exxon and the Environmental Protection Agency have said there is no danger to public health from the oil spill, but the National Wildlife Federation disagreed.
"The spill has directly impacted the health and livelihoods of landowners along the river. People have become sick due to exposure of the oil fumes," said Douglas Inkley, a senior scientist with the environmental group.
(Additional reporting by Anna Driver in Houston; Editing by David Gregorio and Lisa Shumaker)