Minami Soma City in Fukushima Prefecture is one of the cities whose designation as "evacuation-ready zone" have been lifted and where the residents are supposed to return. The city had been urging the residents to return well before the designation was lifted, and as part of the efforts to encourage the residents to return and live in the city as before, the city has been busy "decontaminating" kindergartens and schools and other public places with advice from Professor Tatsuhiko Kodama of Tokyo University Radioisotope Center.
However, if you look at one and only result that the city has published, the decontamination didn't quite decontaminate, i.e. remove the contamination. If the city has better results elsewhere, it is not showing.
That one result is that of Ishigami Daini Kindergarten decontamination, done on July 30 as the kickoff event for Minami Soma's "decontamination month" (which was the month of August).
According to the "Decontamination Work Evaluation Sheet", the city found:
Drainage on the rooftop measured 33 microsieverts/hour (already decontaminated at the time of July 30 work);
As for indoor radiation level, the radiation 2 meters off the floor was higher than the radiation 1 centimeter off the floor;
Locations whose radiation levels got lower after the work: drainage on the rooftop, under the slide in the playground;
Washing the building didn't result in lower radiation;
Washing the asphalt [parking lot] with high-power washer didn't result in lower radiation;
Nearby residents complained of water from the decontamination work splashing on their properties; not enough notification prior to the work [it looks like the city didn't notify the residents at all].
Noticeable difference observed in before and after radiation levels: under the rain gutters, drainage, under the slide
Location where the radiation levels went up after the decontamination: center of the kindergarten playground, parking lot
Locations where the difference was not noticeably big: playground locations, indoors
The survey meter that they used was "POLIMASTER PM1703M" personal survey meter which measures gamma ray with the accuracy of 30%.
But not to worry. The IAEA Decontamination Mission is coming to Japan. They must surely know what they are doing and advise the Japanese government accordingly.
Does anyone care at this point if the "decontamination" actually decontaminate? It sure seems to be making people feel better that they did the work, and it brings money and job to the area's yard cleaning contractors and heavy equipment operators who will do the soil scraping.