Hazardous materials teams are working to stop an oily messy muck from spreading on Sand Creek and reaching the South Platte River.
The oil seep is located near Interstate 270 and Vasquez Boulevard, about one mile west of the Suncor Energy Refinery in Commerce City.
Video from Airtracker 7 over the scene showed three absorbent booms in the creek, placed there to contain and catch the mess.
Suncor Energy emergency response crews found the seep Monday afternoon after responding to a complaint from a citizen, who called around 11:30 a.m. to report a visible sheen on Sand Creek.
The slick stretched about 200 yards on Monday, said John Gallagher, vice president of refining for Suncor.
"We believe, from what we've seen, it's some form of hydrocarbon. We don't know the source of the material, and we don't know what the material is exactly," Gallagher said.
Gallagher said crews believe the hydrocarbon may have been leaking from a spot along the banks of the creek. Gallagher said about 30 to 40 people worked on the issue overnight.
"As a precaution we're keeping people out of the area. And our response teams are respiratory equipment, just as a precautionary item," Gallagher said.
U.S. Environmental Protection Agency officials said they believe the booms are preventing the oily muck from spreading to the South Platte River.
"We do believe it to be contained and not a huge health threat," EPA spokesman Karen Edson told 7NEWS.
State health department spokesman Warren Smith said it is likely the spill came from the Suncor refinery, but there is no laboratory confirmation of the source yet.
"Well, we're assuming the material is ours," Suncor's Gallagher said. "We haven't confirmed that it's ours. But we're acting like it is. We're responding in what we believe is a responsible way to treat the environment."
"Our priorities really are ensuring the environment is OK," he added. "We have worked since yesterday afternoon, continuously, and we'll continue to work until we're convinced that we've completely isolated the source from the creek."
Suncor produces crude oil and refines it for the production of gasoline, diesel, jet fuel, and asphalt.
The refinery has a history of pollution problems and fines.
The EPA has fined the refinery $364,000 for pollution violations during the past five years.
In the mid-1980s, when Conoco owned the refinery, tests showed that fuel was seeping into the surrounding ground water. Suncor has been under a state order to clean up the pollution, state health officials said.
While state officials say Suncor has diligently worked to remove the underground fuel plume, ground water testing a year ago found the contamination was spreading, said Walter Avramenko, a state health department supervisor overseeing the cleanup. The state has ordered Suncor to develop new plans for cleaning up the fuel seepage.
In 1998, the state fined the plant $72,500 after benzene was discharged into Sand Creek. The refinery was required to pay an additional $290,000 to reduce sulfur emissions in the air.
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