Around 1,200 barrels of oil were released from Exxon Mobil's Silvertip pipeline into the Yellowstone River near Billings, Mont., in early July. Flood waters slowed cleanup efforts and teams were later sent in to remove debris piles soaked with oil after the water levels declined.
Montana Gov. Brian Schweitzer said there weren't any surprises in samples taken in and around the site of the spill.
"The analysis shows that the petroleum components are consistent with what you would expect to find in crude oil," he said. "One piece of good news is that the crude oil did not contain a lot of heavy metals or toxic additives that persist for long periods in the environment."
The state sampled more than a dozen drinking water wells, six irrigation wells and also took samples from the river.
Schweitzer and state environmental officials said none of the tests came back with levels of petroleum chemicals that exceeded safe drinking water standards.
A spokeswoman for Exxon Mobil told United Press International in response to e-mail questions that Silvertip had carried oil from tar sands in Canada since the 1980s. But "crude in the portion of the pipeline that failed was a mix of Wyoming Asphaltic (80 percent) and Elk Basin crude (20 percent)," the spokeswoman said.