Not a water purification plant or at a waste water treatment plant, but a plant that burns regular, household garbage in eastern Tokyo was found with a high level of radioactive cesium in the fly ashes caught in the incinerator filter.
Edogawa-ku is located at the eastern end of Tokyo. Along with its northern neighbor Katsushika-ku, Edogawa-ku seems to have been in denial of the elevated radiation levels throughout the ward, and has only recently (June 18) started to measure the radiation at multiple locations within the ward.
The Edogawa waste disposal plant is located by the Edogawa River that separates Edogawa-ku and Chiba Prefecture. The plant can burn 600 tonnes of garbage per day with 24-hour operation, with 2 incinerators. It's in a mixed residential/commercial neighborhood, with 2 elementary schools nearby, and a nursery school right next to the plant, according to the Google Map.
From Sankei Shinbun (6/27/2011):
東京都と東京２３区清掃一部事務組合は２７日、一般家庭ゴミなどを処理する２３区内の清掃工場のうち、江戸川清掃工場で発生した焼却灰から、１キロ グラムあたり８千ベクレルを超える放射性セシウムが検出されたと発表した。同組合によると、灰はフィルターで集められ、運搬時などは密閉しているほか、施 設周辺の空間放射線量の測定結果からも、外部環境への影響はないとみている。
The Tokyo Metropolitan government and the "Clean Association Tokyo 23" (organization of waste disposal facilities in Tokyo's 23 "ku" or wards) announced on June 27 that radioactive cesium in excess of 8,000 becquerels/kilogram was detected from the fine ashes from the waste disposal plant in Edogawa-ku. The plant burns regular garbage collected from households in Edogawa-ku. According to the Association, the ashes are collected by the filter, and the filter is in a sealed container during transport. The air radiation levels have been measured around the plant, and there appears to be no effect on the environment.
According to the Tokyo Metropolitan government, it was the first time that any municipal government measured the ashes from the regular waste disposal.
There are two types of ashes as the result of incineration at the waste disposal plants: "main ashes" that collect inside the incinerator, and "fly ashes" that are collected by the filter.
Rradioactive cesium of over 8,000 becquerels/kilogram was detected from the fly ashes produced at the Edogawa Waste Disposal Plant. Cesium from the main ashes from the plant, or the fly ashes and main ashes from the other waste disposal plants was less than 8,000 becquerels/kilogram.
The fly ashes at the Edogawa plant will be stored temporarily at a facility at the plant that can shield radiation. The main ashes will be buried in the final waste processing facility.都では、今後も灰を継続して調査するとともに、多摩地域の市町村にも調査を要請する。
The Tokyo Metropolitan government will continue the survey of the ashes, and will ask municipalities in Tama region [western part of Tokyo] to conduct the survey.
There is no safety standard for radioactive materials in wastes OUTSIDE Fukushima Prefecture. So, the Tokyo Metropolitan government is using the standard that the national government has set for Fukushima Prefecture, and it will bury the main ashes and fly ashes as long as the radioactive materials detected are less than 8,000 becquerels per kilogram.
Now, here's the actual survey result, dated June 27. The amount of cesium detected from the fly ashes at the Edogawa plant is 9,740 becquerels/kilogram.
Other high but below 8000 numbers (page 3):
Katsushika: 6,610 becquerels/kg
Ota: 6,030 becquerels/kg
Koto: 4,850 becquerels/kg
Meguro: 4,180 becquerels/kg
Looking at the numbers for the air radiation in the surrounding areas (page 5), contrary to what Sankei reports, the areas do seem to have elevated levels of air radiation.
For the Edogawa Plant, the air radiation level inside the plant is between 0.07 to 0.16 microsievert/hour. Outside the plant, the level is much higher, between 0.21 to 0.24 microsievert/hour.
As I said above, a nursery school is right next to the plant, and there are 2 elementary schools nearby.
Ashes, ashes, we all fall down...