On Thursday night, the Environmental Protection Agency said benzene levels in Sand Creek are 400 times the amount for drinking water standards.
The partial results are from five samples taken at various locations along the creek near the Suncor Plant.
The EPA thinks the test results are further proof that the leak is a refined gasoline of some type.
So far, no public health warnings have been issued, but the EPA is urging people not to drink water in Sand Creek.
Benzene is a highly-toxic chemical linked to leukemia.
"The material is flowing underground, it flowed off the Suncor property, under the Metro Wastewater treatment property then into the river," Curtis Kimbel, EPA emergency response manager, said.
EPA lab results released Thursday evening show benzene concentrations ranging from 2,000 parts per billion around the location of the seep and 480 ppb where the creek enters the South Platte.
The national drinking water standard is 5 ppb.
Some of the oil did get into the South Platte River.
Suncor says its 60 person emergency response team was able to get the area contained.
"We believe we have stopped all of the materials from entering the water ways at this point. The progress we've made today, we've started building a trench between the diked area, and we're going to build a trench there for a secondary level of protection," John Gallagher, Suncor Energy refining vice president, said.
Also on Thursday, the Colorado Department of Public Health and Environment issued a written order demanding Suncor follow certain orders.
In a news release sent out on Thursday afternoon, the CDPHE says Suncor must have the oil seep cleaned up by March 1, 2012.
The CDPHE says it also is ordering Suncor to perform daily inspections to look for evidence of the seep and if it finds any, the company has to collect and sample the liquid.
The department of health says Suncor must also start sampling the air inside the nearby Denver Metro Wastewater Treatment Plant to check to see if the air contains benzene, ethylbenzene, toluene and xylenes. Suncor was told to collect air samples in the air around the creek as well.
If the air samples are found to be at unsafe levels and it's determined it's coming from groundwater, the CDPHE wants Suncor to install a mitigation system.
The CDPHE says it is talking to the Attorney General about possible enforcement action against Suncor over the incident.
(KUSA-TV © 2011 Multimedia Holdings Corporation)