Here's a better source from the Guardian: http://www.theguardian.com/world/2013/aug/09/fukushima-fallo...

Quote:

But the US Nuclear Regulatory Commission and other experts have said the seepage will not affect areas beyond the sea directly off the coast of Fukushima Daiichi. "Even 300 tonnes [a day] — that's still going to be diluted to an almost undetectable level before it would get to any US territory," said the commission's information officer Scott Burnell.

You have to remember that this water isn't pure radioactivity, it's itself already a dilution.