I hope this is a translation problem. My concern is a statement in a report about contamination found in a Tokyo park:
NHK: Radioactive hot spots found in Tokyo parkhttp://www3.nhk.or.jp/daily/english/20120625_29.html
[Excerpt] "According to science ministry guidelines, decontamination is required when radiation is at least one microsievert higher than surrounding areas. Based on these guidelines, 9 of the 14 surveyed places in Mizumoto Park will be decontaminated."
Majia here: I hope this does not mean that extreme hot spots alone will be decontaminated.
Consider a headline from a couple of weeks ago:
Shoji Nomura. Radioactive 'black soil' patches: A scourge or a solution? Asahi Shimbun Weekly Area (2012, June 14), http://ajw.asahi.com/article/0311disaster/fukushima/AJ201206140067
[excerpted] "...There have also been locations in the greater Tokyo area with high radioactivity levels. For example, Kawajima in Saitama Prefecture had a level of about 420,000 becquerels per kilogram. The area in front of the Crafts Gallery of the National Museum of Modern Art, Tokyo, in the Kitanomaru Park of Tokyo's Chiyoda Ward had a reading of about 90,000 becquerels per kilogram while Shinbashi in Minato Ward had a reading of about 70,000 becquerels per kilogram...."
Majia here: The NHK article about the Tokyo park indicates that even highly contaminated areas like these documented in the Asahi Shimbun Weekly would not be de-contaminated unless they measured one microsievert higher than surrounding areas.
I suspect that there must be a base level of contamination in Japan over which everything is de-contaminated. At least, I hope there is....
I know that the exposure level for adults from "external" radiation is 20 millisieverts....at least 19 millisieverts too high!