There are two factors there really, the nuclear stuff, and the material that was swept out to sea from the surrounding area which would have happened whether or not the reactor was there.
I wish there was a way to know what the actual condition of Fukushima is. News reports have been so conflicting, it seems the only way to know what's going on would be to go and measure things yourself.
The Bay Area is not Northern California. It is Central California. Examples of places in Northern California include Yreka, Eureka, Redding, and Klamath Falls.
I have found that (Bay Area subset of N. CA) is a very common misconception of people who have recently moved to the area.
"SF isn't north enough to be Northern California" is a common view of people who live in Eureka, Redding, etc., but in my experience people who live in SF think of it as northern California. California basically has two big centers of population: SoCal is LA and friends, and NorCal is SF and friends. Above that are remote regions heard of in legends (either old legends about the gold rush, or newer legends about pot farming).
The Bay Area is definitely not within Central California, taken as a sociogeographic term. The Central California Coast is the coastal region between roughly Santa Barbara and Point Lobos, centered on SLO. There is also another inland definition of Central California: https://en.wikipedia.org/wiki/Central_California
I would make the comparison to "Upstate New York" [0]. I like this Wikipedia article more than the one for Northern California because it admits that "there is no clear or official boundary between Upstate New York and Downstate New York".
The same is true for Northern and Southern California. There's no official distinction. Calling the Bay Area part of Northern California places too much emphasis on the Los Angeles area. By analogy, saying that "North" begins at the Transverse Ranges is like saying that "Upstate" begins at Yonkers. Ridiculous.
"Northern California is the northern portion of the U.S. state of California. The San Francisco Bay Area (which includes the cities of San Francisco, Oakland, and San Jose), and Sacramento (the state capital) as well as its metropolitan area are the main population centers."
It's relative. For example, most of the people in what is called "Northern Ontario" really live in almost-southernmost Ontario. That probably drives the people who really do live in the north crazy, but since there are almost none of them, almost nobody cares.
http://en.wikipedia.org/wiki/Holocene_extinction