Crews finished the effort on Friday and patrolled the 35-acre perimeter daily to ensure it was out, Lockwood said. It was during Monday's patrol that a state forest service crew spotted the wildfire — also on Denver Water property — alerted authorities, and began fighting it, Lockwood said. It wasn't clear if the wildfire was inside the controlled burn zone.
The Jefferson County sheriff's office will determine the cause of the blaze, while the Colorado State Forest Service was conducting its own review, Lockwood said.
Stacy Chesney, a spokeswoman for Denver Water, said the agency was "trying to be proactive" to protect water supplies from soil runoff caused by deforestation.
The area has several watersheds that feed metropolitan Denver and is several miles from the location of the 2002 Hayman fire, one of Colorado's worst, which destroyed 133 homes and 466 outbuildings over 215 square miles.
Protocols for controlled fires include monitoring them until they are determined to be cold — meaning nothing is at risk for reigniting, said Roberta D'Amico, spokeswoman for the National Interagency Fire Center in Boise, Idaho.
Fire officials normally check weather, terrain and other factors to create a burn plan and alert municipal authorities, D'Amico said.
Carole Walker, director of the Rocky Mountain Insurance Information Association, said state agencies have limited immunity for performing regular duties.