WIPP Environmental Monitoring Project Radionuclides in Ambient Aerosols Introduction CEMRC collects and analyzes samples of particulate matter from the atmosphere ("aerosols") as part of its WIPP Environmental Monitoring (EM) project. These atmospheric studies are an important part of the WIPP EM because if radioactive contaminants were released from the WIPP, those materials could be rapidly dispersed through the atmosphere and spread throughout the environment. In addition, the inhalation of aerosol contaminants from the WIPP represents a potential route of exposure to radionuclides for the local citizenry. The WIPP EM aerosol studies began prior to March 26, 1999, which is when the first radioactive waste shipment was received at the facility. Baseline samples collected before the receipt of the waste have been used for the first objective of these studies, which is to characterize the background concentrations of selected radionuclides in the atmosphere of the WIPP/Carlsbad area. The data also are being used in statistical comparisons to determine whether the concentrations of any of these substances changed after the WIPP became operational, that is, after shipments of nuclear waste began arriving at the facility. A final objective for the studies is to investigate the relationships between the concentrations of radioactive and non-radioactive substances in aerosol particles. Sample collection and analysis Detailed information regarding the sampling design for the WIPP EM ambient aerosol studies was presented in the CEMRC 1998, 1999 and 2000 reports. Briefly, for the radionuclide studies, high-volume aerosol samples are collected from four sites, On Site, Near Field, Cactus Flats, and Hobbs. These samples are collected on 20 x 25 cm Gelman A/E® glass fiber filters over time intervals of several weeks. At Cactus Flats and Near Field, high-volume samples for the radiochemistry studies are collected for both total suspended particles (TSP) and PM10 particles less than 10 mm, aerodynamic equivalent diameter). At On Site and Hobbs, only TSP samples are collected. The activities of selected radionuclides, including 238Pu and 239,240Pu, are determined following multiple separation and purification steps. The volumes of air sampled and gravimetric data are used to determine activity concentrations (nBq m-3) and activity densities (mBq g-1), respectively. Beginning with samples collected during January - March, 2001, only TSP Samples are being analyzed and reported, and PM10 samples are being archived. Preliminary analyses show that the activity concentrations of 239,240Pu exhibit pronounced seasonal cycles, with peak activities generally occurring between March and May of each year. Some evidence for interannual variability also can be seen in the data. Measurements of 239,240Pu during the operational monitoring phase through January 2001 are consistent with baseline data. Although individual aerosol samples collected in March to April 1999 and April to May 2000 were higher in 239,240Pu activity per cubic meter of air than in any baseline samples, similar patterns were measured for certain naturally occurring elements that are not components of the TRU waste deposted at the WIPP. This indicates that those higher air concentrations of 239,240Pu were associated with periods when the material in the air was dominated by greater concentrations of resuspended dust, which is known to contain fallout plutonium (see CEMRC data and summaries on studies of plutonium in local soils). Based upon analyses of these patterns, it is concluded that the observed variations in 239,240Pu are not related to releases from the WIPP. Table RD-3.  239,240Plutonium in Ambient Aerosols (February 1998 - January 2001)