A mechanical failure sent fracking fluid and oil into the surrounding soil for more than 30 hours, state natural resources spokesman Todd Hartman told The Denver Post.
Firefighters were testing air every 30 minutes to ensure leaking natural gas was not about to explode while vacuum trucks were used to suck up the liquid, he said.
A Colorado Oil and Gas Conservation Commission inspector and engineer were testing at the scene but have not yet determined whether the spill contaminated groundwater or streams, the Post reported.
Soil from the well pad and other areas will be tested for contamination, Hartman said, but he did not discuss whether enforcement action would be taken.
"We are still reviewing what happened," he said.