ExxonMobil Pipeline Co. is re-burying its Silvertip Pipeline, which broke last summer and spilled crude oil into the Yellowstone River, deeper at two other river crossings to improve safety as required by a federal agency.

Chris Hoidal, regional director of the Pipeline and Hazardous Materials Safety Administration in Denver, said ExxonMobil had completed directional drilling for the pipeline under Rock Creek and under the Clarks Fork of the Yellowstone. Both crossings are in Carbon County.

"They're doing a good job on it," Hoidal said.

The Rock Creek crossing is in the Rockvale area, while the Clarks Fork crossing is about seven miles south of Bridger, according to Montana Department of Environmental Quality maps.

The Rock Creek crossing was pressure-tested last week under the observation of the pipeline agency, said spokesman Damon Hill.

Claire Hassett, an ExxonMobil spokeswoman, said Monday that the pipeline is back in service at the Rock Creek crossing while work is continuing at the Clarks Fork crossing. Work at the Yellowstone River crossing by Laurel is done, she said.

ExxonMobil began directional drilling at the crossings in late November, Hassett said. The pipeline will be about 30 feet or more below the river bottom near the shore and 50 feet or more below the river near the center of the river, she said.

"We expect to complete the work by March 2012," Hassett said.

Hassett declined to provide further information about the project.

The Silvertip Pipeline is a 12-inch diameter pipeline that runs about 69 miles to deliver crude oil from a pump station near Elk Basin, Wyo., to the ExxonMobil Billings refinery.

The waterway crossings are the last two that the pipeline safety agency ordered ExxonMobil to redo after the Silvertip pipeline broke on July 1 and dumped an estimated 42,000 gallons of crude oil into the Yellowstone River near Laurel.

After the pipeline break, the pipeline safety administration ordered ExxonMobil to re-bury the pipeline under the Yellowstone River and to conduct a risk assessment of the line where it crossed any waterway.

The risk assessment found that there was shallow cover on the pipeline at the Rock Creek and the Clarks Fork crossings and a risk for future erosion, Hoidal said. The cover was less that a couple of feet, he said.

Richard Opper, director of the state Department of Environmental Quality, said the state wants ExxonMobil to remove the old pipeline. As rivers move and erode, the pipeline could become a hazard for boaters and fishermen, he said.

State officials have met with ExxonMobil on the Rock Creek crossing and "held the line about the need for removal," Opper said. ExxonMobil is to propose how to remove the pipeline with minimal stream disturbance but has not yet submitted a plan, he said.

DEQ and ExxonMobil have not yet discussed the Clarks Fork crossing, Opper said.

Contact Clair Johnson at cjohnson@billingsgazette.com or 657-1282.