Crews have already sucked up more than 60,000 gallons of "hydrocarbon material" and 5,400 gallons of oil near Parachute Creek, outside the small town of Parachute. Federal regulators haven't said precisely what chemicals are being removed.
A local cattle rancher who uses the area as a grazing field said underground oil pipelines leak frequently and go unreported.
State workers have dug two trenches in the hope of stemming the underground flow.
The source of the leak remains unknown though an energy company, Williams, operates a gas processing plant in the area and The Denver Post said the federal Environmental Protection Agency is preparing to issue it a written "notice of alleged violation" and demand a long-term clean-up plan.