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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#Radioactive Japan: Tokyo Metropolitan Government Finally Agrees to "Decontaminate" Mizumoto Park in Katsushika, Tokyo

Why now, after 15 months from the start of the accident? Because the Tokyo Metropolitan government under Governor Shintaro Ishihara is finally forced to do so because 9 spots in Mizumoto Park in Katsushika-ku (one of the eastern Special Wards with higher levels of radiation than the rest of Tokyo) exceeded even their very lax (and near-impossible to be applied) standard of decontamination.

What's that lax standard? They will decontaminate only if the air radiation level at 1 meter off the ground at a particular spot exceeds the air radiation levels of the surrounding area by more than 1 microsievert/hour.

As recently as on June 12, the Tokyo Metropolitan government issued a statement saying they will not decontaminate locations in Mizumoto Park precisely because of the standard just mentioned above. Their June 12 press release says (my summary):

• Japan Communist Party of the Tokyo Metropolitan Assembly announced the result of their measurement in the park on June 11, and one location allegedly measured 1.10 microsievert/hour.

• Japan Communist Party notified the Ministry of Education and Science, and the Ministry asked that we investigate, including the radiation levels in the surrounding area.

• So we did, using Hitachi-Aloka Medical's scintillation survey meter TCS-172B. We sent out someone from the Environment Bureau in the evening. The result was 0.99 microsievert/hour at 1 meter off the ground, and the surrounding areas measured 0.18 microsievert/hour. So, it is below the standard for decontamination set by the Ministry of Education and Science, which specifies the air radiation to be more than 1 microsievert/hour higher than that of the surrounding area.

• So our conclusion is that there is no need for decontamination.

Never mind that Goshi Hosono's Ministry of the Environment sets the decontamination standard at 0.23 microsievert/hour air radiation. Tokyo is sticking by the Ministry of Education. By insisting on the Ministry of Education's standard, Shintaro Ishihara's government may have been hoping to avoid doing any "decontamination" in their city, which is by the way one of the finalists in the selection of the host city for 2020 Olympics.

But on June 25, the Metropolitan government had to measure the park again after citizens armed with survey meters alerted them again, according to ANN (TV Asahi) News. Now, they are grudgingly admitting that for some unknown reason the radiation levels at 9 spots in the park are higher by more than 1 microsievert/hour than the surrounding areas, with the highest at 1.22 microsievert/hour.

That should be the highest official measurement of air radiation in Tokyo, at 1 meter. Before the Fukushima accident, or for that matter, up to 3:59AM on March 15, 2011, the official radiation measurement in Shinjuku was 0.0384 microsievert/hour. (Go to the page at the Tokyo Metropolitan Institute of Public Health for more data.)

Tokyo Metropolitan TV (Tokyo MX) has a more detailed report, though. According to Tokyo MX, the locations were exactly what the Japan Communist Party of Tokyo Metropolitan Assembly had reported on June 11, but on June 25 the measurement was done by the Construction Bureau of the Tokyo Metropolitan government.

(Some very lax reporting by TV Asahi. Not surprising.)

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23,300 Bq/Kg of Radioactive Cesium from a Mix of Wet Soil and Dead Leaves in Mizumoto Park in Tokyo

(Sorry, you can't just multiply the number by 65 and compare it to the Chernobyl evacuation level. Read on to find out why.)

The Mizumoto Metropolitan Park is located in the eastern Tokyo with elevated radiation levels. The Communist Party delegation of Tokyo Metropolitan Assembly, who has done the survey of radiation levels in Tokyo from very early on in the nuclear crisis, released the result of the latest survey in one of the Metropolitan parks in Tokyo.

The survey found 23,300 becquerels/kg of radioactive cesium from a wet mix of dirt and dead leaves in one location in the Mizumoto Park in Katsushika-ku, Tokyo (No. 4 location in the table posted below).

The delegation did three tests at this location with 2 samples taken on February 15. The third test was done on February 18 by combining the two samples taken on February 15 and tested on February 16 and 17.

It may be important to note that the Communist Party delegation tested the top 1 centimeter of the soil, and the top 1 to 2 centimeters of the soil and dead leaves mixture. The measured numbers may therefore be higher than the samples taken from the top 5 centimeters, which is a normal procedure in the government tests.

To derive "becquerel/square meter" from "becquerel/kg", you multiply "becquerel/kg" number by 65, but that only applies if the soil is taken from the top 5 centimeters. (Ibaraki Prefecture's measurement page as reference, here.)

From the Communist Party delegation of Tokyo Metropolitan Assembly website (English translation is mine; the last two rows are the reference):

According to Yomiuri Shinbun article (2/22/2012), "the Ministry of Education and Science sets the standard of radiation that requires decontamination as locations that test "1 microsievert/hour higher than the surrounding areas", and the Tokyo Metropolitan Bureau of Environment says "There is no need for decontamination at this point.""

Never mind that the Ministry of Environment's decon standard is 0.23 microsievert/hour.

The surface radiation levels and the air radiation levels at 1 meter off the ground all exceed 0.23 microsievert/hour. The highest surface radiation level was 1.54 microsievert/hour, and the highest radiation level at 1 meter was 0.74 microsievert/hour.

Before the nuclear accident, the average background radiation level in Tokyo was slightly above 0.03 microsievert/hour. That was the level right before something very radioactive arrived from Fukushima on March 15, 2011 sometime between 4AM and 4:59AM. (See the Tokyo Metropolitan government's own measurement, here, as the radiation in Shinjuku went from 0.0347 microsievert/hour average between 3AM and 3:59AM to 0.1 microsievert/hour average in the next hour. )

What the Tokyo Metropolitan government needs to do is to scrape 1 centimeter of the soil under the trees and shrubs and remove dead leaves to lower the radiation. But they openly say they are not going to do anything.

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(UPDATE from Kontan Bigcat on Twitter: the 65 multiplier applies only to soil taken from 5 centimeters AND with the soil density (dry) of 1.3 gram/cubic centimeter.

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