Sources of Variation in Soil Plutonium 

 Concentrations 



JOHN E. PINDER III and DONALD PAINE 



Variations in ^^^Pu and 239,240^^^ concentrations in surface soil near a nuclear-fuel 

 reprocessing facility were attributed to distance from the point of aerial release; 

 micro topographical heterogeneity in deposition; and sampling error, which included 

 aliquoting and analytical errors. Distance from the point of release accounted for 

 approximately 75% of the variation in concentrations of both nuclides, whereas sampling 

 error accounted for less than 5% of the variation. Microtopographical heterogeneity 

 accounted for approximately 20% of the variation in 239.240^^^ concentrations but only 

 5% of the variation in '^^^Pu concentrations. This difference may be due to different 

 histories of deposition of the nuclides at the site. Other sources of variation, errors in the 

 statistical models, and the implications for future sampling are discussed. 



Concentrations of radionuclides in soils, plants, and animals are usually highly variable, 

 with coefficients of variation (standard deviation/mean) usually exceeding 1 .0 

 (Eberhardt, 1964; Remmenga and Whicker, 1967; Finder and Smith, 1975; Shanks and 

 De Selm, 1963). This is especially true of the isotopes of plutonium. Large coefficients of 

 variation in soil plutonium concentrations have been reported for plutonium contamina- 

 tion resulting from weapons testing (Nyhan. Miera, and Neher, 1976; Romney et al., 

 1976), ''safety-shots," i.e., chemical explosions of nuclear weapons material (Gilbert 

 et al., 1976). aqueous discharges from industrial faciUties that handle plutonium 

 (Hakonson and Nyhan, this volume), and deposition of aerial releases from reprocessing 

 faciUties (Adriano, Corey, and Dahlman, this volume; Adriano and Finder, 1977; 

 McLendon, 1975; McLendon et al., 1976). A portion of this large variabiUty may be due 

 to the release of plutonium in particulate form and the analytical errors caused by 

 including various amounts of these particles in a sample (Doctor et ah, this volume; 

 Adriano, Wallace, and Romney, this volume); however, there must be a greater 

 understanding of the causes of this variation before the cycling processes of plutonium 

 can be fully understood or efficient sampling programs can be designed to estimate 

 plutonium concentrations or inventories. The purpose of this study was to evaluate the 

 relative importance of several potential sources of variation in soil concentrations of 

 ^^^Pu and 2 3 9,2 4 op^ ^j^^^ ^^^d been released to the atmosphere from a reprocessing 

 facility at the U. S. Department of Energy's Savannah River Plant (SRP) near Aiken, 

 South Carolina. 



We hypothesized three main components of variation in plutonium concentrations. 

 First, we expected the distance from the point of release to be important because soil 

 concentrations have been shown to decrease with increasing distance from the point of 



165 



