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About radioactive material in tap water

Final update date March 12, 2020

About the safety of tap water

About inspection system of Yokohama-shi

About inspection results

About water purification soil

About the safety of tap water

QQ
1.Is it okay to drink tap water from Yokohama?
A.

Tap water in Yokohama does not interfere with drinking.

The management target value of radioactive materials in tap water is "10 becquerels / kg" (total value of cesium-134 and 137).
Test results of radioactive cesium in tap water and tap water at three water purification plants (Kawai, Nishiya, Kojaku) in Yokohama city are not detected (detection limit value 1 becquerel / kg or less), and are below the management target value. You.

QQ
2.What is the regulation of radioactive substances in tap water?
A.

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

From April 1, 2012, a new standard under the Food Sanitation Law was set for radioactive substances in foods containing drinking water, and radioactive cesium in drinking water was changed from 200 becquerels / kg to 10 becquerels / kg. ".
In response to this change, "10 becquerels / kg" (total value of cesium-134 and 137) was set as a management target for radioactive substances in tap water by notification from the Ministry of Health, Labor and Welfare. For radioactive iodine, no new management target has been set because the half-life is short (about 8 days).

Notification of the Ministry of Health, Labor and Welfare's Health Bureau Water Supply Section Manager dated March 5, 2012 ("Setting of management target values for radioactive substances in tap water (PDF: 172KB)" "Details (PDF: 226KB)")

Index values and management targets for radioactive substances in tap water
Date Indicator value and management target value

Indicator value (target value)
(Unit: Becquerel/kg)
[Radioactive iodine]

Indicator value (target value)
(Unit: Becquerel/kg)
[Radioactive cesium]

March, 2011 Index values for food and beverage intake restrictions
(Provisional figures for baby/infant
300
(100)
200
April, 2012 Tap water management target 10
QQ
3.What happens if radioactive cesium exceeding the management target value is detected?
A.

We will investigate the cause and inform water users.

Even if the concentration of radioactive materials in tap water exceeds the management target value (10 becquerels / kg), it does not mean that it is not suitable for drinking.
However, if radioactive cesium exceeds the target value, we will immediately investigate the cause and notify water users for safety and security.

Notification of the Ministry of Health, Labor and Welfare's Health Bureau Water Supply Section Manager dated March 5, 2012 ("Setting of management target values for radioactive substances in tap water (PDF: 172KB)" "Details (PDF: 226KB)")

About inspection system of Yokohama-shi

QQ
4.What is your inspection system in City of Yokohama, Water Works Bureau inspection system.
A.

We secure a detection limit of 1 becquerel / kg or less and inspect tap water and tap water from three water purification plants in Yokohama city.

In City of Yokohama, Water Works Bureau City has been conducting radiological inspections of tap water at three water purification plants (Kawai, Nishiya, Kojaku) in Yokohama since March 19, 2011.

In June 2012, City of Yokohama, Water Works Bureau germanium semiconductor detector in June 2012.
By using a germanium semiconductor detector, for each of cesium-134 and cesium-137, the detection limit value of 1 becquerel / kg or less is secured, the system is enhanced so that high-precision inspections can be performed, and radioactive materials are inspected precisely. .
Currently, tap water and tap water from three water purification plants (Kawai, Nishiya, Kojaku) in Yokohama are inspected once a month.
In addition, tap water at 15 regular water quality inspection points in the city is also inspected once a month.

Q5 for germanium semiconductor detectors

Radioactive Material Inspection System for City of Yokohama, Water Works Bureau System
Date events Inspection frequency Inspection Agency
March 11, 2011 Great East Japan Earthquake - -
March 19 Inspection of tap water in Yokohama started Every day Yokosuka Water Works Bureau of Yokosuka
August 1
(Until March 31, 2012)
Inspections in City of Yokohama, Water Works Bureau began Every day City of Yokohama, Water Works Bureau
January 4, 2012 Testing using germanium semiconductor detectors began. Once every three weeks at Kawai, Nishitani and Kojaku water purification plants Yokohama Institute of Public Health
April 2 Inspection based on new management target values (10 becquerels / kg) started once a week Kanagawa Prefecture Wide Area Water Supply Corporation
June 5 Introduced a germanium semiconductor detector in City of Yokohama, Water Works Bureau, and began testing. Twice a week City of Yokohama, Water Works Bureau
August 7 - once a week City of Yokohama, Water Works Bureau
after January, 2014 - once a month City of Yokohama, Water Works Bureau
QQ
5.What is a germanium semiconductor detector?
A.

Inspection equipment that can be tested for high sensitivity with a detection limit of 1 becquerel / kg or less.

By using a germanium semiconductor detector, for each of cesium-134 and cesium-137, a detection limit of 1 becquerel / kg or less is secured, and high-sensitivity inspection is possible.

sushi-20120601-Geruma1.jpg
Testing with a germanium semiconductor detector

sushi-20120601-Geruma2.jpg
Setting a sample inside the detector

QQ
6.Is there a standard for inspection frequency?
A.

The notification from the Ministry of Health, Labor and Welfare states that "in principle, at least once a month".

According to the Ministry of Health, Labor and Welfare, the inspection frequency is as follows: "In principle, at least once a month, but until sufficient information is collected during high turbidity such as rainfall and thaw, depending on the inspection system of water utilities, etc. In addition, we will inspect at least once a week. "

Notification of the Ministry of Health, Labor and Welfare's Health Bureau Water Supply Section Manager dated March 5, 2012 ("Setting of management target values for radioactive substances in tap water (PDF: 172KB)" "Details (PDF: 226KB)")

QQ
7.Is it all right if I don't check it every day?
A.

We believe that turbidity management and periodic inspections can ensure safety against radioactive cesium.

Following an accident at Fukushima Daiichi Nuclear Power Station in 2011, City of Yokohama, Water Works Bureau 2013 following the accident at the Fukushima Daiichi Nuclear Power Station in 2011. As a result of previous inspections, radioactive cesium has never been detected in tap water and tap water in Yokohama City, including when the turbidity of tap water increased due to a typhoon. Since sufficient information on the tendency of tap water and radioactive cesium in tap water and tap water was collected, the inspection frequency was set at least once a month from January 2014.
Most of the radioactive cesium is found in tap water as a component of turbidity, so it can be removed along with turbidity during the water purification process at the water purification plant.
We believe that thorough turbidity management and periodic inspections will ensure safety against radioactive cesium.

QQ
8.Do you change the inspection frequency in the future?
A.

Depending on the situation, we will increase the frequency of inspections and strengthen the monitoring of radioactive materials.

In City of Yokohama, Water Works Bureau conducts inspections according to the inspection frequency indicated in the notification of the Ministry of Health, Labor and Welfare.
However, if a large-scale release of radioactive materials occurs in the future, or if any abnormality occurs in the water purification process at the water purification plant, the frequency of inspection will be increased to strengthen monitoring of radioactive materials.

QQ
9.Do you inspect radioactive materials other than radioactive cesium?
A.

Inspection of radioactive cesium can confirm the safety of all regulated radioactive substances, so no inspection of substances other than radioactive cesium is performed.

A survey by the Ministry of Education, Culture, Sports, Science and Technology has found that radioactive substances subject to regulation other than radioactive cesium have a very low concentration compared to radioactive cesium.
The management target value (10 becquerels / kg) for radioactive cesium set by the Ministry of Health, Labor and Welfare is set after considering other radioactive materials. Inspection of radioactive cesium can confirm the safety of all regulated radioactive substances, so there is no need to re-examine substances other than radioactive cesium.

Notification of the Ministry of Health, Labor and Welfare's Health Bureau Water Supply Section Manager dated March 5, 2012 ("Setting of management target values for radioactive substances in tap water (PDF: 172KB)" "Details (PDF: 226KB)")

About inspection results

QQ
10.What are the results of radiological tests so far?
A.

Since March 25, 2011, no radioactive material has been detected in tap water.

The City of Yokohama, Water Works Bureau City has been conducting radiological inspections of tap water at three water purification plants in Yokohama since March 19, 2011.
According to the results so far, all radioactive cesium is below the detection limit and has never been detected.
In addition, radioactive iodine was detected in tap water at some water purification plants that supply water to Yokohama City for three days from March 22 to 24, 2011 immediately after the earthquake, but March 25 Not detected after that.

Summary of results of radioactive material inspection in tap water (unit: becquerel / kg)
Date events Test samples Test results Detection limit
March 11, 2011 Great East Japan Earthquake
March 19 Inspection of tap water in Yokohama All water purification plants supplying water to Yokohama city Non-detection About 10
March 22 Detection of radioactive iodine from tap water Kojaku Water Purification Plant 55.3 About 10
March 22 Detection of radioactive iodine from tap water Ayase Water Purification Plant (Kanagawa Prefecture Wide Area Water Supply Corporation) 13.7 About 10
March 23 Detection of radioactive iodine from tap water Kojaku Water Purification Plant 56.8 About 10
March 23 Detection of radioactive iodine from tap water Kawai Water Purification Plant 11.91 About 10
March 23 Detection of radioactive iodine from tap water Ayase Water Purification Plant (Kanagawa Prefecture Wide Area Water Supply Corporation) 55.7 About 10
March 23 Detection of radioactive iodine from tap water Sagamihara Water Purification Plant (Kanagawa Prefecture Wide Area Water Supply Corporation) 18.4 About 10
March 23 Detection of radioactive iodine from tap water Nishi-Nagasawa Water Purification Plant (Kanagawa Prefecture Wide Area Water Supply Corporation) 9.2 About 10
March 24 Detection of radioactive iodine from tap water Kojaku Water Purification Plant 23.5 About 10
March 24 Detection of radioactive iodine from tap water Kawai Water Purification Plant 8.8. About 10
March 24 Detection of radioactive iodine from tap water Ayase Water Purification Plant (Kanagawa Prefecture Wide Area Water Supply Corporation) 21.4 About 10
March 24 Detection of radioactive iodine from tap water Sagamihara Water Purification Plant (Kanagawa Prefecture Wide Area Water Supply Corporation) 12.5 About 10
after March 25 Not detected in any tap water All water purification plants supplying water to Yokohama city Non-detection About 10
January 4, 2012 Testing started using germanium semiconductor detectors Three water purification plants in Yokohama Non-detection About 1
after April 2 Testing started using germanium semiconductor detectors All water purification plants supplying water to Yokohama city Non-detection About 1

Note) All water purification plants that supply water to Yokohama city
Kawai Water Purification Plant, Nishitani Water Purification Plant, Kojaku Water Purification Plant (City of Yokohama, Water Works Bureau
Ayase Water Purification Plant, Sagamihara Water Purification Plant, Nishi-Nagasawa Water Purification Plant (Kanagawa Prefectural Wide Area Water Supply Corporation)

The existing inspection system (frequency and measurement organization) is Q4

QQ
11.What does "non-detection (detection limit value *)" in the test result mean?
A.

This means that the radioactive material inspection equipment is below the minimum concentration that can be detected.

"Not detected (detection limit value *)" means that the concentration of radioactive material in the inspected tap water is lower than the detection limit (the lowest concentration that can detect a device that tests radioactive material). You.
If the test result is "Not detected (detection limit value *)", the radioactive substance concentration is "less than 0".

QQ
12.Why is the detection limit slightly different?
A.

It differs slightly each time depending on the condition of the inspection equipment and the surrounding environment.

Inspections are conducted strictly, but since they are very precise inspections, the detection limit varies slightly depending on the condition of the inspection equipment and the surrounding environment. The detection limit at that time (the lowest concentration that can be detected) is calculated for each inspection.

About water purification soil

QQ
13.What is the water purification soil?
A.

It is a collection of impurities such as earth and sand and turbidity in tap water.

Tap water is made based on lakes and river water. This lake and river water contains earth and sand and turbidity.
Water purification soil is impurities such as earth and sand and turbidity that purify tap water (water from lakes and rivers) and remove when tap water is made.

QQ
14.Why is radioactive cesium detected in purified water generated soil?
A.

This is because impurities such as turbidity in tap water are concentrated at high concentrations.

Most of the radioactive cesium is found in tap water as a component of turbidity, and is removed along with turbidity during the water purification process at the water purification plant.
Until 1 kg of water purification soil is generated, 20,000 to 26,000 liters of tap water is treated (the average amount of water used by ordinary households per month is 15,000 liters). In other words, impurities such as turbidity in tap water are concentrated from 20,000 to 26,000 times.
No radioactive material has been detected in tap water since March 25, 2011.

QQ
15.How do you dispose of water-purified soil in City of Yokohama, Water Works Bureau generated soil?
A.

Since September 2011, it has been reused as a raw material for cement.

The City of Yokohama, Water Works Bureau Nishitani Water Purification Plant has reused earth and sand generated by water purification treatment at Kawai Water Purification Plant and Nishiya Water Purification Plant as horticultural soil materials, but in response to the accident at the Fukushima Daiichi Nuclear Power Station, it has been used as horticultural soil. I am refraining from using it.
Since August 2011, the concentration of radioactive cesium contained in the water purification soil has continued to be lower than the national standard (100 becquerels / kg), so it has been reused as a cement raw material since September 2011. .
The sediment generated before September was temporarily stored in a sludge treatment facility at the Nishitani Water Purification Plant, but was disposed of by the end of 2011.
In addition, earth and sand generated at Kojaku Water Purification Plant are properly treated at City of Yokohama, Environmental Planning Bureau Water Purification Plant.

QQ
16.What are the regulations on water purification soil?
A.

If the total radioactive cesium is less than 8,000 becquerels / kg, landfill disposal is possible.

According to the notification of the Ministry of Health, Labor and Welfare, if the total radioactive cesium is less than 8,000 becquerels / kg, landfill can be disposed of at a managed disposal site.
In addition, items that are below the standard before distribution to the market (100 becquerels / kg for reuse in concrete, etc.) can be reused.
Regarding the use of horticultural soil, it is appropriate to refrain from shipping products.

Notification of the Ministry of Health, Labor and Welfare's Health Bureau dated June 16, 2011, "Consideration on the Immediate Handling of Water Purification Occurrence Soil with Radioactive Substances (External Site)"

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