I've absolutely no knowledge on the twists and turns of how procedures work....
But, doesn't Secretary Chertoff implementing Incidence of National Significance make the federal govt in charge?
http://www.dhs.gov/dhspublic/display?content=4773
Excerpt:
The Department of Homeland Security has declared this an Incident of National Significance, the first ever use of this designation under the new National Response Plan. The National Response Plan, which was stood up earlier this year, gives the Department of Homeland Security the lead responsibility to coordinate federal response and recovery efforts. The plan is designed to bring together all federal resources to increase our ability to quickly get relief to those who need it most.
I don't really know about the Incidence of National Significance, Calpernia. Sounds almost more about who has tactical and logistical control, rather than when the federal gov. can act. (But I admit I am probably reading it wrong.) I would imagine that the feds would give the state every opportunity to request assistance before implementing this.
Also, because this is a multi-state problem, it is more effective to deal with it all from a central location and strategic position; rather than try to accomodate three separate response plans. Maybe that has something to do with it?