U.S. Environmental Protection Agency clean-up coordinators today said the black goo leaking from the Sand Creek shoreline north of downtown Denver is a “a gasoline-like material” that contains cancer-causing benzene.

Highly-toxic, benzene has been linked to leukemia and federal authorities have determined that even minute amounts are harmful.

EPA lab test results released Thursday evening indicate benzene concentrations ranging from 2,000 parts per billion where liquid enters Sand Creek to 480 ppb where the creek enters the South Platte River — well above the 5 ppb national drinking water standard.

“We don’t want anybody drinking water in Sand Creek,” EPA emergency response manager Curtis Kimbel said, adding that significant dilution occurs in the Platte.

No public health warnings have been issued.

Since Monday, the federal agency has been managing work to keep the black liquid leaking from the banks of Sand Creek from fouling the South Platte River, a major source of drinking and agricultural water for northeastern Colorado.

No public health warnings have been issued.

On Wednesday, Kimbel said a plume migrating from Suncor Energy’s refinery and under property owned by Metro Wastewater was daylighting at the creek.

“We believe its source is from our refinery,” Suncor Energy refining vice president John Gallagher said this morning.

Gallagher said Suncor has developed a plan to mitigate the plume and is working with state and federal agencies.

Thursday afternoon, the Colorado Department of Public Health and Environment issued a written order specifying actions the company must take to address on- and offsite contamination.

The order requires Suncor to: conduct daily inspections along Sand Creek; sample water along Sand Creek; monitor indoor air at the Metro Wastewater plant and install ventilation systems if necessary within seven days; investigate groundwater contamination under the wastewater plant, and clean up any oil on banks of Sand Creek and the South Platte by March.

Suncor processes 93,000 barrels per day of gasoline, diesel fuel and paving-grade asphalt. About 85 percent of the crude oil processed in Commerce City comes from Colorado and Wyoming, Gallagher said. Suncor also refines oil sand crude from Canada.

Kimbel said he still is awaiting the complete results from lab tests of samples collected this week, but said so far there does not appear to be any signature chemicals from processing of oil sand crude in the underground plume.

About a half dozen workers meanwhile are reinforcing the sandbags and dams adjacent to Sand Creek that are designed to stop the black liquid from further contaminating the creek and the river.

“We have secured any material from entering the creek. We’re pretty happy with the process,” Gallagher said. “Our job, No. 1, is still to make sure we keep the waterways protected.”

Kimbel said EPA will conduct “an extensive investigation to determine the source” of the pollution.

Wednesday, a state health department official said a pipe had broken under a storage tank at the refinery. However, today Kimbel said the break “happened quite some time ago” and “is a long ways away” from the creek and so it remains unclear whether it is the source of the plume.

Emergency response coordinators have discussed a strategy for following the plume back from the creek shoreline toward the refinery, but the focus is on containing the mess in the creek as snow falls over the Denver area.

Round-the-clock work since Monday “has significantly reduced the amount of material that has gone into the river,” Kimbel said. “We have not seen dead fish or birds.”

It remains unclear how long the pollution has been leaking into the water. A fisherman reported a murky sheen on the water and a foul odor on Sunday morning.

Several cities, including Aurora, rely on the South Platte for drinking-water supplies.

Aurora Water is not drawing water from the river, utility spokesman Greg Baker said.

“CDPHE did notify us of the situation so we can monitor it,” Baker said. “If contamination were to occur at a time when we were using our river supply, we have numerous protocols in place to ensure that any impact on the river will not affect our drinking-water supply.”

The area has the been site of refining operations since 1938 and has a long history of environmental problems, some inherited by Suncor from the previous owner, Conoco.

Owners for 25 years have been working to clean up pollution on the site. Earlier this year, samples collected from monitoring wells indicated new contamination, a health department spokesman said Thursday. The contamination also was detected under the Metro Wastewater property to the north of the refinery.

On Oct. 26, a letter from the health department to Suncor’s senior remediation officer said “recent releases of hazardous waste and hazardous constituents onsite are now migrating offsite in excess of applicable standards.” The letter ordered Suncor to figure out how to keep the contamination from entering groundwater.

The confluence of the creek and river is a focal point of the Sand Creek Regional Greenway, which includes a recreational path along the creek that draws runners, cyclists and other recreational users.

Bruce Finley: 303-954-1700

or bfinley@denverpost.com