Teams tallying damage from an Exxon Mobil Corp. oil spill into the Yellowstone River have found contamination along roughly 60 percent of shoreline that's been inspected downstream from the pipeline break, Montana's chief environmental regulator said.
The tally released Tuesday by Montana Department of Environmental Quality director Richard Opper offers one the first clear gauges of the scope of the spill after weeks of high water slowed access to fouled areas.
Just over 40 percent of shoreline inspected to date had light to very light oil. Seventeen percent had moderate oil. Just 1 percent was heavily contaminated.
The state says the July 1 spill, which came amid flooding from mountain snowmelt, dumped up to 1,200 barrels of oil, or 54,000 gallons, into the Yellowstone near Laurel. Exxon Mobil says it lost 1,000 barrels.
The investigation into what caused the pipeline to break could take months. Meanwhile, more than 800 cleanup workers and support personnel are involved in mopping up the spill.
Opper says teams of federal, state and Exxon Mobil workers have now inspected about half of the riverbank and islands between Laurel and Lockwood, where most of the damage occurred.
"That is the area of the greatest impact we're looking at, and so it gives you an idea of the degree of impact we're seeing," Opper said. "I'm glad it wasn't worse. But it's still a huge problem for landowners, both private and public, and we'll do what we can to address this as efficiently as we can."
Exxon Mobil last week finished initial work on the first four of dozens of cleanup sites scattered along the riverbank and stretching across fields that were flooding when the pipeline broke.
The Environmental Protection Agency set an early September deadline for Exxon Mobil to finish the cleanup, but agency officials have said that's not a hard date and the company will continue working as long as it takes for the job to meet Montana's stringent cleanup standards.
State officials said they checked a site where oil was reported 240 miles downstream near the town of Terry and no oil was found. Discoloration in the water apparently was caused by a side stream entering the river.
The EPA has said the farthest downstream that oil has been confirmed was near Custer, 72 miles from the spill site in Laurel.