So the Tokyo Metropolitan government finally admitted to the high air radiation level in "Nanbu Sludge Plant" in Ota-ku in Tokyo, after, it turns out, a Tokyo Metropolitan Assemblyman from Ota-ku went inside the plant and measured the radiation.
"Tobu" or Eastern, Sludge Plant in Koto-ku in Tokyo has an even higher level of radioactive cesium, and the plant may have been spewing radioactive cesium from the incinerator where the radioactive sewage sludge is burned, and has been contaminating the air and the soil in the areas around the plant and downwind (upstream) areas along the Arakawa River.
So it's a secondary radiation contamination.
The eastern part of Tokyo has been registering higher air radiation levels than the western part of Tokyo. Unchecked cesium dispersion from the sludge plant ever since the start of the Fukushima I Nuke Plant accident may be good part of the reason.
And we wouldn't have known if it were not for the very concerned parents in Koto-ku who decided to organize themselves and ask a researcher from Kobe University to help them measure the radiation.
From Tokyo Shinbun (6/8/2011):
"Koto Association to Protect Children (江東こども守る会)" held a press conference in the Tokyo Metropolitan Government Building on June 7, and announced the result of its own survey showing the high level of radioactive cesium detected from the athletic ground near the sewage sludge processing plant "Tobu (eastern) Sluge Plant".
調査は、同会が神戸大大学院の山内知也教授（放射線計測学）と実施。検出されたセシウムは一平方メートル当たり二三万ベクレルで、放射線障害防止法で、放射線管理区域からの持ち出しが制限される汚染基準の約六倍という。また、プラント周辺と同区の荒川、旧中川沿いでは、放射線量が毎時〇・二マイク ロシーベルトを超える地点が多くあった。山内教授は「値が高い地域の位置と風向きを考慮すると、下水を通じてプラントに集まった放射性物質が処理過程で再 び大気中に放出されている可能性が高い」と主張。同会は同日、プラントの稼働停止と調査などを求め、都に要望書を提出した。
The survey was done by the Association and Professor Tomoya Yamauchi of Kobe University (radiation measurement). Cesium detected was 230,000 becquerels per square meter, 6 times as high as the limit set for the radiation control zone to restrict one from taking an item out of the control zone. Also, in the area around the plant and along the Arakawa river and the old Nakagawa river, there were many locations that registered high air radiation levels exceeding 0.2 microsievert/hour. [The "official" number measured in Shinjuku-ku is about 0.06 microsievert/hour.] Professor Yamauchi says, "Considering the locations with high air radiation levels and the wind direction, it is highly likely that the radioactive materials in the sewage collected at the plant are being released into the atmosphere through the treatment process." The Association submitted the petition to the Tokyo Metropolitan government demanding the halt of sludge processing at the plant and thorough investigation.
If they are demanding the halt, that means it is still in operation. The plant is located near the river mouth of the Arakawa River in eastern Tokyo as it flows into the Tokyo Bay. Prevailing wind is from the south, going upstream from the plant.
Tokyo Disney Land is about 5 kilometers southeast of the plant, by the way.
The Association uploaded the test result of the samples from 2 locations - athletic ground right next to the sludge plant, and a park 5 kilometers north of the plant; the test was done by a French laboratory (Association pour le Contrôle de la Radioactivité dans l’Ouest). It shows the soil in the park upstream (and downwind) from the plant having higher concentration of radioactive tellurium, iodine, and cesium than the soil taken from the athletic ground right next to the plant.