Project 57 Air Monitoring Report: January 1 through September 30, 2020, with a Review of the Period of Record Radionuclide Analyses

Abstract

On April 24, 1957, the Atomic Energy Commission (AEC) (now the Department of Energy [DOE]) conducted the Project 57 safety experiment in western Emigrant Valley northeast of the Nevada National Security Site (NNSS) (formerly the Nevada Test Site) on lands withdrawn by the Department of Defense (DOD) for the Nevada Test and Training Range (NTTR). The test was performed to (1) assess a technique for estimating plutonium distribution resulting from a nonnuclear detonation, (2) develop biomedical evaluation techniques for use in plutonium-laden environments, (3) evaluate methods of surface decontamination, and (4) evaluate instruments and field procedures for the prompt estimation of alpha contamination (Shreve, 1958). Although the test did not result in the fission of nuclear materials, it did disseminate plutonium across the land surface. Following the experiment, the AEC fenced the contaminated area and returned control of the surrounding land to the DOD. Various radiological surveys were performed in the area and the DOE expanded the demarked Contamination Area (CA) in 2007 by posting signs 200 ft to 400 ft (60 m to 120 m) outside of the original fence. Plutonium in soil attaches preferentially to smaller particles (Tamura, 1985; Friesen, 1992; Murarik et al., 1992; Misra et al., 1993). Therefore, redistribution of soil particles by wind and water are the mechanisms most likely to transport plutonium beyond the boundary of the Project 57 CA. At the request of the DOE, Desert Research Institute (DRI) initiated monitoring in 2011 to determine if radionuclide contamination was detectable in samples of airborne dust and to characterize meteorological and environmental parameters that influence dust transport. Initially, two monitoring stations consisting of radiological, meteorological, and dust sampling equipment were installed near the south and north ends of the eastern boundary of the CA. In January 2015, the original monitoring stations were dismantled and moved farther to the west along the CA boundary. This move was made to place the monitoring stations downwind of ground zero and the High Contamination Area (HCA) with respect to the dominant northerly and southerly winds. A cap was installed over ground zero and the surrounding area in October 2020. Monitoring was discontinued and data collection equipment was removed immediately following cap installation. Therefore, it is not possible to assess the effectiveness of the cap. Samples of particles suspended in the air were collected every two weeks during monitoring. Samples were submitted to Eurofins TestAmerica Laboratories, Inc., to assess gross alpha, gross beta, and plutonium isotope concentrations. In calendar year (CY) 2020, the annual mean gross alpha concentration at monitoring station P57-3 was slightly higher than the value at monitoring station P57-4. The standard deviation and the range of gross alpha values observed at station P57-3 were smaller than the standard deviation and range of values observed at station P57-4. The mean gross alpha concentrations at P57-3 and P57-4 were approximately 0.6 to 1.7 times higher than the mean gross alpha concentrations at the surrounding Community Environmental Monitoring Program (CEMP) stations. The minimum gross alpha concentrations reported for the Project 57 stations were slightly lower than the minimum values observed at the CEMP stations. However, the maximum gross alpha concentrations at the Project 57 stations were approximately an order of magnitude higher than the maximum concentrations observed at the surrounding CEMP stations.