State health officials have warned the operators of a natural gas plant in western Colorado they could face penalties for a spill that has contaminated Parachute Creek with cancer-causing benzene.

The spill from a 4-inch pipeline at the Williams energy plant released 10,122 gallons of natural gas liquids into soil along the creek, according to a Colorado Department of Public Health and Environment document.

A CDPHE compliance advisory, dated April 30, formally notifies Williams, property owner WPX Energy and pipeline operator Bargath LLC that the spill constitutes disposal of hazardous waste without a permit.

Benzene levels in the creek have increased to 4.8 parts per billion at the sampling point closest to the spill, dissipating to 1.8 and 1.4 ppb downstream, Williams said Wednesday. The federal safe drinking water limit is 5 ppb.

But the limit for benzene in Parachute Creek, which flows into the Colorado River, has been set by the state Water Quality Control Commission at 5,300 ppb — because the creek isn’t designated as a water source for people.

Benzene has reached super-concentrated levels in groundwater along the creek.

Williams crews are aerating the creek and injecting air into soil to try to remove benzene from groundwater. A state air pollution permit is required for this “air sparging” because the process emits vapors.

Williams crews also are pumping hydrocarbons from trenches along the creek to try to stop seepage of benzene into the creek. Diesel-range organic chemical, too, have been detected in the creek.

The Colorado Oil and Gas Conservation Commission on March 20 issued notices of alleged violation to Williams and WPX.

The advisory asks Williams to meet with state officials to discuss problems, schedule cleanup activities and show that laws were not broken. If state officials decide they need to order cleanup and remediation, CDPHE spokesman Mark Salley said in an e-mailed update, they can issue “compliance orders on consent” or a “unilateral compliance order.”

Williams spokesman Keith Isbell said the warning “was fully expected.”

“It does not change the cleanup work that Williams has been doing,” he said. “Our next step is to formally present our current work plan to CDPHE and get their official approval as the new lead regulator.”

Bruce Finley: 303-954-1700, twitter.com/finleybruce or bfinley@denverpost.com