Fukushima 2011-Rainwater

The following is archived information that was originally published on this website in 2011.

Important information about this page.

The Department of Health posted daily results of environmental monitoring in March and April 2011 in response to the nuclear events following the earthquake and tsunami in Japan. All detections of radioactive material were far below any public health risk. The data posted online included monitoring conducted by the state health department in addition to the federal monitoring that is always taking place. In May, when amounts of radioactive material were lower than detection levels with standard monitoring, the additional state sampling and daily data posting were stopped. Daily federal monitoring has concluded, but the historical data for that period is available on the Environmental Protection Agency's RadNet website.

Rainwater samples
(testing for Iodine-131)


in pCi/L*
4/29/2011 1.0
4/26/2011 2.6
4/19/2011 3.4
4/16/2011 3.5
4/11/2011 1.8
4/7/2011 8.9
4/4/2011 15.4
4/1/2011 5.9
3/31/2011 25.4
3/28/2011 58.2
3/25/2011 161

*Measures are in picocuries
per liter (pCi/L).

Rainwater samples are
collected in the Seattle area.

Radiation monitoring in rainwater

The Washington State Department of Health is collecting and testing rainwater for the presence of radioactive materials after the nuclear power plant emergency in Japan. The earthquake and tsunami on March 11 damaged the reactors and caused radioactive iodine (iodine 131) to be released to the air.

State health department testing showed very low levels of I-131 in rainwater, as expected. The amounts detected are far below any public health concern. Iodine levels have decreased sharply and are expected to drop below detection limits in the next few weeks. Sampling will continue until the iodine is no longer detected in rainwater. This data table shows iodine levels measured in picocuries per liter (pCi/L) of rainwater.

To verify the rainwater detection, several samples from cistern drinking water supplies in the state were tested. Cistern systems collect rainwater for drinking. Our test results showed even lower traces of radioactive iodine in the cistern than in our rainwater samples — 12, 11, 10, and 7 picocuries per liter — confirming radioactive iodine from Japan is not a health threat in the water.