Federal investigators are probing last week’s massive natural gas line explosion that killed as many as seven people and engulfed dozens of homes in San Bruno, California. The pipeline was owned and operated by Pacific Gas and Electric Company. Residents of San Bruno have told the media they had smelled gas odors in the neighborhood before the blast. Internal documents from PG&E show that the company knew there could be problems with the pipeline at the heart of the blaze. One document obtained by CNN said the line had a “relatively high risk and likelihood of failure.” The document recommended the line be replaced, warning that its location in a populated area “makes the risk of a failure at this location unacceptably high.” On Sunday, a state regulator in California ordered PG&E to check for leaks in all of its thousands of miles of natural gas pipelines.