soils (desert pavement and desert mound) showed a very different distribution of the plutonium. In the desert pavement of Area 13, the plutonium was concentrated in the greater than 2.90 g/cm* band, whereas in the desert mound it was In the surface samples from Area concentrated in the 2.5 - 2.7 g/cm? band. occurs in the greater than soils both in plutonium 11, the distribution of However, in the smaller size classes, the data suggest that 2.90 g/cm band. plutonium is distributed in the lighter fractions as well as the heaviest fraction. Implications of Findings on Plutonium Distribution Evidence indicates that plutonium is moving downward into deeper horizons in The association of plutonium with the finer particle the desert pavement soils. sizes in the deeper horizons supports this hypothesis of downward movement. Density gradient What is not established is (are) the mechanism(s) of movement. segregation of mineral particles from the different size classes and depths may provide some insight into the mechanism(s). The higher activity associated with the less than 20 wm size particles in the desert mound as compared to the adjacent desert pavement indicates that the finer sizes of plutonium are derived from a source close to GZ. The distribution of mineral particle sizes with depth in the mound suggests considerable mixing of the secondary aeolian material with the original substrate. Important questions are raised about the mode of sampling desert mounds. Further studies are needed to establish the distributional pattern of plutonium in desert mounds. It must be stressed that the results presented in this progress report are preliminary and subject to change with additional information presently being obtained. It is also expected that the results from these studies, compared and collated with those being obtained by other participants in the soils program, will help to evaluate further the situation existing in these NTS test areas. FUTURE PLANS The desert pavement-desert mound samples taken at 102 feet from GZ in Area 11 will be investigated in a manner similar to the sample reported herein. Results of studies on samples previously taken in Area 11 as part of the preliminary mound study (Brady, 1975) will be examined, and samples which show promise of providing further insight into the plutonium distribution in the desert mounds will be investigated. Additional fractionation of the organic material from the inorganic fraction will be made of several desert mound samples. The separated organic fraction will be analyzed for plutonium to obtain the plutonium concentration, and studies will be made to compare differences in characteristics of the organic- versus inorganic-associated plutonium. 12