Exxon spokeswoman Claire Hassett told the Billings (Mont.) Gazette the company was drilling holes for replacement sections of the Silvertip oil pipeline that are, in some parts, 50 feet below the bottom of the river.
"We expect to complete the work by March 2012," she said.
Around 1,200 barrels of oil spilled from Exxon Mobil's Silvertip pipeline into the Yellowstone River near Billings in early July. Flooding slowed cleanup efforts and teams were sent in to remove debris soaked with oil after water levels dropped.
State environmental directors said they want Exxon to pull any remaining sections of Silvertip out of the river as they fear it could become a danger as waters erode the river bed. The original section was about 5 feet under the river bottom.
Exxon said it expected to pay $135 million in cleanup operations for the July spill. A regional director for the Pipeline and Hazardous Materials Safety Administration told the newspaper Exxon was "doing a good job" on direction drilling for the pipeline.