Did Tokyo Metropolitan Government "Create" the Hot Spots in Mizumoto Park in Katsushika, Tokyo?

That's what it seems like, if the tweet by Ms. Ayako Ishikawa, the head of the citizens' group "Protect children in Koto-ku", is correct. She tweeted:

水元公園局所汚染の件、なぜ１ｍ高１μSv/hを超えたか、都建設局と環境局にヒアリング。今回のケースは施設側の管理が原因。側溝を清掃する際に集めた泥を集積させたため、高線量になった。

About the hot spots in Mizumoto Park, we asked the Metropolitan Bureau of Environment and of Construction why the radiation levels at 1 meter off the ground exceeded 1 microsievert/hour. It was the case of mismanagement of the facility. They piled up the sludge from the side drains after cleaning the drains [on to the particular areas], resulting in high radiation.

According to Ms. Ishikawa, it seems the park routinely removes the sludge from the side drains as part of the park maintenance and dump the sludge onto the ground nearby, usually in shrubs and under the trees. The practice is to prevent the parking lot from being flooded in heavy rains from clogged-up side drains.

If that's the case, the Tokyo Metropolitan government has spread the radiation contamination and created new hot spots in the park.

Either it didn't occur to the park facility management that the sludge from the side drains in a park located in the high-radiation area in Tokyo may be highly radioactive after 15 months of concentration of radioactive materials, or it did occur to them but they self-censored and continued their pre-Fukushima routine, as the Tokyo Metropolitan government stance has always been that there is no radioactive contamination in Tokyo to worry about and to do something about.

The Tokyo Metropolitan Bureau of Construction released the result of their June 25 survey, here. The survey result shows the radiation levels where the park dumped the side drain sludge are between 0.98 and 1.22 microsievert/hour, at 1 meter off the ground. The areas just outside these locations, which are now fenced off, have rather elevated radiation levels, between 0.24 to 0.55 microsievert/hour, also at 1 meter off the ground. The general radiation level in the park is stated in the report at 0.16 microsievert/hour at 1 meter off the ground.

The radioactivity (in becquerels) could be quite high if the radiation level at 1 meter off the ground exceeds 1 microsievert/hour. It is very likely that it will easily exceed the 8,000 becquerels/kg (radioactive cesium) standard set by the Ministry of the Environment for "safe" regular disposal in a landfill. I wonder if they are testing the radioactivity.

For more on the topic, see my previous post.

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