Yokohama City, which has been dumping the radioactive ashes with low radioactivity from burning household garbage at its final disposal landfill (Minami Honmoku) on Tokyo Bay since September last year, has said the runoff water is safely treated by the cesium absorption towers with zeolite.
Well they lied. They used the absorption towers for one month and stopped using them, but never bothered to tell they stopped using them.
In one month, they used 5500 kilograms of zeolite, which absorbed 5000 becquerels/kg of radioactive cesium. In other words, 27.5 million becquerels of radioactive cesium was effectively caught. So the city thought "Oh that's good", and stopped using zeolite.
From Sankei Shinbun Kanto local version (3/6/2012):
Yokohama City didn't explain why it stopped using the cesium absorption system
It was revealed on March 6 that Yokohama City had stopped using the system to absorb radioactive cesium using zeolite in November last year at the city's Minami Honmoku Final Disposal Site (in Naka-ku, Yokohama). The city continued to tell residents about the zeolite absorption system in the meetings to explain the ashes from the sewer sludge being buried in the final disposal site, even after they stopped using the system. The official says, "We are sorry if the residents were misled into thinking the system was still used."
The Minami Honmoku Final Disposal Site is on Tokyo Bay, encircled by the seawalls. When the ashes are dumped on the ocean [inside the seawalls], the displaced water go through the absorption system and is discharged into the ocean [outside the seawalls]. The city started to use 5500 kilograms of zeolite in October last year to process the water, and stopped the usage about one month later. 5,000 becquerels/kg of radioactive cesium was found in the zeolite. The city explains that it was only an experiment to see how effective zeolite was in absorbing [radioactive cesium], and that the radioactivity of the exhaust water is very low.
The city will start cesium absorption treatment at the garbage incineration plants in the city. At the Minami Honmoku site, they will conduct the test of a new system using zeolite to absorb radioactive cesium in September.
According to Yokohama City Assemblywoman Sakura Inoue, the city official in charge said he was impressed with zeolite's ability to absorb radioactive cesium, but he stopped the use anyway because the radioactivity of the treated water was below the national safety level.
Here's a hilarious exchange between the official and Assemblywoman Sakura Inoue during the recent Assembly meeting, as Ms. Inoue relates in her blog:
Inoue: Why did you stop treating water with zeolite?
Official: It was to see the effect of zeolite.
Inoue: I am asking you why you stopped treating the water.
Official: No detection of radioactive cesium in water coming in to the absorption system or in water coming out of the system into the ocean.
Inoue: It's not "no detection", but "below detection limit". Since the ashes were dumped into a large amount of seawater, when you look at the density it may be below the detection limit. But it doesn't mean there was no radioactive cesium. In fact, what was the radioactive density of zeolite after 26 days of use?
Official: 5,000 becquerels/kg.
Inoue: What did you think of the number?
Official: I thought zeolite was quite effective.
Oh boy. But wait, it gets worse:
Inoue: Why did you give misleading explanation? Did you tell the residents, fishermen and harbor workers that you stopped using the zeolite absorption system?
Official: We explained to them that radioactive cesium was not detected.
Inoue: It's not the matter of density but the absolute amount. A large amount of radioactive cesium is being dumped into the bay. Treatment with zeolite should be resumed.
Official: There's no problem, as it is below the national safety standard. We are not going to use zeolite.
Inoue: Why then are you building a new embankment as a new countermeasure against radiation?
Official: To be safer...
Inoue: How much does it cost to build the embankment, and how much does zeolite cost?
Officla: It costs 130 million yen to build the embankment, and 1.2 million yen for one zeolite tower. [Kanagawa Shinbun says it is 1.2 million yen for 2 zeolite towers.]
Here's my take, in an effort to make sense:
The city doesn't want to have highly radioactive (over 8,000 becquerels/kg) zeolite after absorbing radioactive cesium, because they cannot dump zeolite in the landfill if the radioactivity exceeds 8,000 becquerels/kg.
Building the embankment costs a lot more money, and the city wants to spend more money as it is able to distribute money and jobs to the well-connected contractors.
What "national safety limit" of exhaust water is this official talking about? It turns out (according to Kanagawa Shinbun 3/7/2012) to be 60 to 90 becquerels/liter.
Well guess what kind of "safety limit" it is.
Those numbers happen to be the allowed density of radioactive cesium in exhaust water of a nuclear power plant. Cesium-134: 60 becquerels/liter, and cesium-137: 90 becquerels/liter.