The operator of the plant collected samples from 4 locations at the compound of the plant on March 25th and 28th for analysis by an outside organization.
The utility says the radioactive substance was detected on the soil about 500 meters west-northwest of the No.1 reactor and a site near a solid waste storage facility 500 meters north of the reactor.
The first sample measured 0.26 becquerels of plutonium-238 per 1 kilogram of soil, down about 50 percent from the volume found earlier.
http://www3.nhk.or.jp/daily/english/06_40.html Not really fair to say that the levels are "down about 50%" since Plutonium isn't exactly going to dissapear in a week. Better to say that the levels around the plant are somewhat variable (as you would expect) and these levels at least don't show an ongoing deposition of new PU.
One piece of encouraging news was "This level is almost the same as the amount usually in the Japanese soil and also about the same the level of fallout from nuclear tests in the atmosphere outside Japan."