One person was killed in June's explosion 15 miles east of Durango. Halliburton and other contractors were doing maintenance work on the BP pipeline at the time.
Colorado Public Radio reported Thursday that federal regulators found that a valve on the pipeline was left closed. That caused pressure to build up quickly, rupturing the pipeline.
An Occupational Safety and Health Administration citation obtained by the station faults BP and the contractors for not having safety procedures in place before the work began. BP, Halliburton and the other contractors were each fined $7,000, the maximum allowed under the law.