Radioactive Microparticles Related to the Woolsey Fire in Simi Valley, CA
/Author(s) Marco Kaltofen, Maggie Gundersen, and Arnie Gundersen
Received 25 May 2021, Revised 13 August 2021, Accepted 27 September 2021, Available online 8 October 2021
Journal of Environmental Radioactivity
Volume 240 / December 2021
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Highlights
Wildfire in radiologically contaminated zones is a global concern; contaminated areas around Chernobyl, Fukushima, Los Alamos, and the Nevada Nuclear Test Site have all experienced wildfires.
Three hundred sixty samples of soil, dust and ash were collected in the immediate aftermath of the Los Angeles (CA, USA) Woolsey fire in 2018.
Radioactive contamination from the partially-burned former Santa Susana nuclear research facility was found in the fire zone.
A limited number of widely scattered locations had evidence of radioactive microparticles originating at the research facility.
X-ray data showed that ashes from the fire could spread site contaminants to distant, but widely spaced, locations.
Abstract
In November 2018, the Woolsey Fire burned north of Los Angeles, CA, USA, potentially remobilizing radioactive contaminants at the former Santa Susana Field Laboratory, a shuttered nuclear research facility contaminated by chemical and radiochemical releases. Wildfire in radiologically contaminated zones is a global concern; contaminated areas around Chernobyl, Fukushima, Los Alamos, and the Nevada Nuclear Test Site have all experienced wildfires. Three weeks after the Woolsey Fire was controlled, sampling of dusts, ashes, and surface soils (n = 360) began and were analyzed by alpha- and beta-radiation counting. Samples were collected up to a 16 km radius from the perimeter of the laboratory. Controls and samples with activities 1σ greater than background were also examined by alpha and/or gamma spectroscopy or Scanning Electron Microscopy with Energy Dispersive X-ray analysis. Of the 360 samples collected, 97% showed activities at or close to site-specific background levels. However, offsite samples collected in publicly-accessible areas nearest to the SSFL site perimeter had the highest alpha-emitting radionuclides radium, thorium, and uranium activities, indicating site-related radioactive material has escaped the confines of the laboratory. In two geographically-separated locations, one as far away as 15 km, radioactive microparticles containing percent-concentrations of thorium were detected in ashes and dusts that were likely related to deposition from the Woolsey fire. These offsite radioactive microparticles were colocated with alpha and beta activity maxima. Data did not support a finding of widespread deposition of radioactive particles. However, two radioactive deposition hotspots and significant offsite contamination were detected near the site perimeter.
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