An unidentified substance has killed or injured hundreds of birds so far.
The Richmond City Council is considering Chevron's plans for a $1 billion project at its refinery there. If it's approved, this is one of the last steps before construction on the project would actually begin.
In a letter to the city, Harris says she still has questions about the oil company's $1 billion expansion project.
More and more crude oil is being transported into California by rail lines, and questions about safety are prompting local governments and environmentalists to take action.