The Colorado Oil and Gas Conservation Commission is investigating four large releases of wastes from oil-and-gas reserve pits near Rifle, acting commission director Dave Neslin said Thursday.
The spills took place between November 2007 and last month and drained into Garden Gulch, west of the Roan Plateau.
One release of about 30,000 barrels of drilling mud was promptly reported to the state, Neslin said in a statement.
A second release by a different operator was also reported, but that operator failed to report two other releases of still undetermined volumes.
The releases appear to have been caused by failures in the liners in the pits, said Deborah Frazier, a commission spokeswoman.
The commission is withholding the names of the two operators and approval on 80 drilling permits pending the completion of the investigation.
