Following the crash of a USMC CH-53E helicopter on farmland in Higashi Village on 11 October 2017, the US military detected strontium-90 radioactive contamination at more than 5000 times background levels, as well as contamination from PFOS, likely a result of the firefighting foam used by the USMC to extinguish the burning helicopter. It did not make the findings public; the details only came to light in reports obtained from the USMC via the US Freedom of Information Act.
The documents describe radiation tests on the crashed helicopter’s Inflight Blade Inspection System (IBIS) and de-icing system. Checks on the IBIS registered removable strontium contamination of 144,000 counts per minute (5143 times the background level of 28 counts per minute) and the deicer registered 3,400 counts per minute (121 times background levels).
Moreover, two checks on soil removed by the USMC from the crash site contained levels of radioactive contamination at 1.09 pCi/g and 5.27 pCi/g. According to the report, these levels exceeded US disposal guidelines and so the soil had to be disposed as low-level radioactive waste.
Commenting on the contamination, Ban Hideyuki, co-representative of the Citizens' Nuclear Information Center, called it very high. “Strontium-90 has properties similar to calcium. If it enters the human body and accumulates in bone, it can cause myeloma. It cannot be said that the levels (detected by the military) are safe for human health.”
As well as radioactive contamination, PFOS was detected in one of the soil samples at 700 parts per trillion, exceeding the US Environmental Protection Agency’s screening level of 376 parts per trillion. This newspaper has previously revealed that a USMC report into the accident detailed how Aqueous Film Forming Foam (AFFF) had been sprayed at the scene. Use of the foam had previously been denied by the Okinawa Defense Bureau, the regional branch of Japan’s Ministry of Defense.
The FOIA-obtained reports are the first time that the military’s data from the crash site have been divulged – and they show the accident was more harmful to the environment than previously realized. After the crash, the US military removed soil from the site without the permission of the landowner; later the military presented him with a letter of appreciation which he subsequently returned. Responding to the latest findings, the landowner urged the military to be more open with providing information to the public. Okinawa Times gave the landowner copies of the FOIA-obtained reports.
It is not the first time that the USMC has faced accusations of a cover-up following this helicopter crash. In 2018, a whistleblower with many years of experience working at MCAS Futenma’s environmental division, asserted that the USMC had misled the public about the removal of radioactive materials from the site. Following the accident, the USMC had announced that the substances had been removed by 14 October. However, according to the whistleblower, strontium-90, had remained at the scene for at least one week. The source provided Okinawa Times with a photograph from the site dated 18 October showing four lumps of metal – each around 40cm in length – in which strontium-90 had become lodged into the melted airframe. USMC Chemical, Biological, and Radiological personnel dispatched to the scene had used axes to cut the radioactive materials from the melted wreckage.
Although US military regulations require that emergency responders be informed of potential radioactive exposure, Okinawan fire crews had not been notified.