About radioactive material in tap water

As for the tap water of Yokohama-shi, drinking does not have trouble.

Management target value of radioactive material in tap water is "10 becquerels/kg" (total value of cesium 134 and 137).
It is the non-detection (detection limit level 1 becquerel/kg or less), and test result of tap water of three water purification plant (Kawai, Nishiya, willow tit) in Yokohama-shi and radioactive cesium of water supply Haramizu is less than management target value.

From April 1, 2012, new management target value "10 becquerels/kg" (total value of cesium 134 and 137) is set.

From April 1, 2012, new standard in the food hygiene law was set about radioactive material in food including drinking water and was changed to "10 becquerels/kg" from past 200 becquerels/kg about radioactive cesium in drinking water.
We received this change, and, about tap water, "10 becquerels/kg" (total value of cesium 134 and 137) was set as management target value of radioactive material in tap water by notice of Ministry of Health, Labour and Welfare. In addition, about radioactive iodine, new management target value is not set because half-life is short (about eight days).

※Notice of Ministry of Health, Labour and Welfare health station Channel section manager dated March 5, 2012 (": 172KB) (PDF about setting of management target value to affect radioactive material in tap water" "in detail: 226KB) (PDF")

We are the cause and study and will tell water supply user.

Even if the density of radioactive material in tap water is beyond management target value (10 becquerels/kg), it is not meaning not to be suitable for drinking.
But when radioactive cesium is beyond target value, we are the cause promptly and study and will tell water supply user for relief, security.

※Notice of Ministry of Health, Labour and Welfare health station Channel section manager dated March 5, 2012 (": 172KB) (PDF about setting of management target value to affect radioactive material in tap water" "in detail: 226KB) (PDF")

We secure detection limit level 1 becquerel/kg or less and inspect tap water of three water purification plant in Yokohama-shi and water supply natural water.

In City of Yokohama, Water Works Bureau, we carry out inspection of radioactive material about tap water of three water purification plant (Kawai, Nishiya, willow tit) in Yokohama-shi from March 19, 2011.

In City of Yokohama, Water Works Bureau, we introduced germanium semiconductor detector newly in June, 2012.
We secure detection limit level 1 becquerel/kg or less and expand the system to be able to give a test with high precision and inspect radioactive material for each cesium 134 and cesium-137 precisely by using germanium semiconductor detector.
We are inspecting tap water of three water purification plant (Kawai, Nishiya, willow tit) in Yokohama-shi and water supply natural water at monthly frequency now.
In addition, we inspect tap water of periodical examination of water point of 15 city at monthly frequency.

※It is Q5 about germanium semiconductor detector

Inspection of high sensitivity that is with detection limit level 1 becquerel/kg or less of is possible inspection equipment.

About each cesium 134 and cesium-137, we secure detection limit level 1 becquerel/kg or less by using germanium semiconductor detector, and sensitive inspection is possible.

State of inspection with germanium semiconductor detector

It looks like we set sample in the detector inside

"As a general rule, it is said more than once a month" by notice from Ministry of Health, Labour and Welfare.

Inspection frequency is notified by Ministry of Health, Labour and Welfare saying, "as a general rule, but we inspect by the above depending on the inspection systems such as water supply companies more than once a month once a week till enough information in high turbidity such as the rain, thaw is collected".

※Notice of Ministry of Health, Labour and Welfare health station Channel section manager dated March 5, 2012 (": 172KB) (PDF about setting of management target value to affect radioactive material in tap water" "in detail: 226KB) (PDF")

We think that we can secure safety for radioactive cesium by turbidity management and periodical inspection.

We received accident of Fukushima Daiichi Nuclear Power Station of 2011 and carried out inspection at the above-mentioned frequency in City of Yokohama, Water Works Bureau once a week until December, 2013. As a result of past inspection, we are never detected about radioactive cesium including time when turbidity of water supply Haramizu rose in typhoons by tap water of Yokohama-shi and water supply natural water. Because enough information about the tendency was collected about tap water and radioactive cesium of water supply Haramizu, we did inspection frequency more than once a month from January, 2014.
In addition, we can remove radioactive cesium with cloudiness in process of clean water processing of water purification plant because ingredient of cloudiness includes the most in water supply Haramizu.
We will carry out turbidity management thoroughly in future and think that by confirming by periodical inspection, can secure safety for radioactive cesium.

We increase inspection frequency and, depending on the situation, strengthen monitoring of radioactive material.

We carry out inspection along inspection frequency shown by notice of Ministry of Health, Labour and Welfare in City of Yokohama, Water Works Bureau.
But cases that occurred increase inspection frequency, and some kind of abnormality strengthens monitoring to radioactive material for clean water processing process in water purification plant again when release of newly large-scale radioactive material will occur in future.

We do not inspect material except radioactive cesium because we can confirm safety of all the radioactive materials which by inspecting radioactive cesium, become a target of regulation.

As for the radioactive material becoming a target of regulation other than radioactive cesium, it is revealed that density is low by survey by Ministry of Education, Culture, Sports, Science and Technology very much in comparison with radioactive cesium.
Management target value (10 becquerels/kg) of radioactive cesium which Ministry of Health, Labour and Welfare set is set after having considered other radioactive material. It is not necessary to perform inspection of material except radioactive cesium some other time because we can confirm safety about all the radioactive materials which by inspecting radioactive cesium, become a target of regulation.

※Notice of Ministry of Health, Labour and Welfare health station Channel section manager dated March 5, 2012 (": 172KB) (PDF about setting of management target value to affect radioactive material in tap water" "in detail: 226KB) (PDF")

After March 25, 2011, radioactive material has not been detected by tap water.

In City of Yokohama, Water Works Bureau, we carry out inspection of radioactive material about tap water of three water purification plant in Yokohama-shi from March 19, 2011.
By past result, all radioactive cesium was less than detection limit level and have not been detected.
In addition, radioactive iodine was detected by tap water of some water purification plant supplying with water in Yokohama-shi for three days from March 22, 2011 just after earthquake disaster to 24th, but is not detected on after March 25.

We mean that inspection equipment of radioactive material is less than the detectable minimum density.

"The non-detection" (detection limit level 0 0) means that radioactive material concentration in tap water which we inspected is less than detection limit level (the minimum density that device inspecting radioactive material is detectable).
If test result is "the non-detection" (detection limit level 0 0), radiological density "is less than 0 0".

It is slightly different every time in state or surrounding environment of inspection equipment.

We carry out inspection closely, but detection limit level is slightly different every time in state or surrounding environment of inspection equipment because it is very exact inspection. At every inspection, we calculate detection limit level at that time (the detectable minimum density).

We collected the earth and sand in water supply natural water and impurities such as cloudiness.

Tap water is made from water of lake and river. The earth and sand or cloudiness are included in water of this lake and river.
Clean water outbreak soil is impurities such as the earth and sand or cloudiness to remove when we purify water supply natural water (water of lake and river) and make tap water.

This is because impurities such as cloudiness in water supply Haramizu are concentrated by high density.

Ingredient of cloudiness includes the most in water supply Haramizu, and radioactive cesium is removed with cloudiness in process of clean water processing of water purification plant.
Water supply Haramizu of 20,000-26,000 liters is handled before 1 kg of clean water outbreak soil occurs (as for the mean quantity of water that ordinary household uses for one month 15,000 liters). In other words, impurities such as cloudiness in water supply Haramizu are concentrated to 20,000-26,000 times.
In addition, radioactive material is not detected from tap water after March 25, 2011.

We reuse as cement raw materials from September, 2011.

At City of Yokohama, Water Works Bureau Nishiya water purification plant, we reused the earth and sand occurring by clean water disposal of Kawai water purification plant and Nishiya water purification plant as material on gardening Doyo, but we receive accident of Fukushima Daiichi Nuclear Power Station and restrain ourselves from the use as gardening soil.
Because the situation less than standard (100 becquerels/kg) that the density of radioactive cesium included in clean water outbreak soil established in country continued after August, 2011, we reuse as cement raw materials from September, 2011.
In addition, we put provisionally in sludge disposal of Nishiya water purification plant facility, and the earth and sand generated before September kept, but completed disposal by the end of 2011.
In addition, we treat the earth and sand generated at willow tit water purification plant appropriately in the City of Yokohama, Environmental Planning Bureau southern part sludge exploitation of resources center.

If the radioactive cesium totals are 8,000 becquerels/kg or less, we fill up, and disposal is possible.

If the radioactive cesium totals are 8,000 becquerels/kg or less, according to the notification of Ministry of Health, Labour and Welfare, inning disposal is enabled in management type disposal ground.
In addition, thing which becomes standard or less (as for the reuse to concrete 100 becquerels/kg) before circulating in market becomes reusable.
In addition, about the use to gardening Yodo, it becomes when it is appropriate to restrain from shipment of product.

※Director Ministry of Health, Labour and Welfare health notification "(the outside site) about way of thinking about the present handling of detected clean water generating soil radioactive material" dated June 16, 2011