COMMERCE CITY, Colo. (CBS4) – There’s a new effort to contain toxic chemicals underground in Commerce City.

CBS4 has learned the spill near the Suncor oil refinery may have started a year ago, not in late November as first reported.

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The spill site is near Interstate 270. Now Suncor and the state health department are working on containing the gasoline-like material that once seeped into Sand Creek.

It took some time to get approval for access onto private property where a trench sits. The property is owned by Metro Wastewater. The goal now is to have the trench contain the toxic materials that are underground.

An excavator has been doing the heavy lifting of dirt for the trench that will drop some 30 feet below the ground’s surface.

“It’s designed to intercept the gasoline-like material that’s floating on the water table,” Robert Beierle with the Colorado Department of Health and Environment said.

It’s polluted with benzene, a component of gasoline that contaminated Sand Creek.

The state health department says the initial clean-up — an emergency response that took place at the water’s surface — cleared the oily mess that is visible to the eye.

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“Our focus right now is to try to contain it onto Suncor’s property,” Beierle said.

The health department says they were notified of the problem’s start last February.

“Of the pipeline that failed pressure testing, which was thought to be probably the source or one of the sources of this material we’re migrating off site right now,” Beierle said. “It’s the only source were aware of and it’s certainly in their best interest to stop it on their property.”

Suncor hasn’t confirmed where the gasoline-like leak began but is cooperating with all aspects of the clean-up, according the health department.

Once the trench is complete the Canadian-based energy company will then move back onto their property to install a second trench.

Suncor says they do not believe there is any leak at this time.

Five-hundred employees of Suncor recently had their blood tested for possible exposure to benzene through the in-house drinking water. The results of the medical tests are not being released.

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