These coexisting areas show morphologic and topographic differences; and in the plutonium-contaminated areas, the plutonium-activity levels, as measured by field survey instruments (FIDLER), are higher in the desert mound than in the contiguous desert pavement. Since these mounds serve not only as the "host" soil for the desert shrubbery but as sites for other biological activity, it is important that the character and behavior of the plutonium in these two related soil systems be investigated and understood. The objective of this study is to define the differences in Included characteristics of the plutonium in these two related soil systems. in this report are data on plutonium concentration as a function of depth, particle size, and particle density on two soil samples from a desert mound in Area 11 and a desert pavement sample 5 ft from the mound. MATERIALS AND METHODS The samples were collected by personnel of the Reynolds Electrical and Engineering Company (REECo) in June 1975. Two samples were taken in Area 11; both samples were in a northwesterly direction from ground zero (GZ) of "C" site. One desert pavement~-desert mound. sample was located 102.4 ft (31.2 meters) from GZ, and the other was 30.7 ft (9.4 meters) from GZ. This report covers results obtained to date on the sample located 30.7 ft from GZ. The samples were taken in slices representing 2.5-cm depth increments, and four vertical depth samples were taken down to 10 cm. The samples were placed in double plastic bags without further treatment and placed in l-gal aluminum cans which were sealed for shipment. Upon arrival, the samples were placed in glove boxes, opened, air-dried, and the samples passed through a 2-mm sieve to determine the gravel content. Aliquots of the less than 2-mm size fraction were taken for total plutonium analysis as well as for particle size segregation. Plutonium was analyzed by the HASL-LASL technique using HF-HNO3 digestion, with 236pu as internal tracer for recovery efficiency correction (Tamura, 1975a). Sample size for analysis was 10 g for the unsegregated soil; for segregated size fractions, 10 g were used where sample size permitted; otherwise, one-half of the sample was used for plutonium analysis. Particle size segregation to obtain sand, silt, and clay fractions was performed as described earlier (Tamura, 1975a)}. No dispersing agent or mechanical dispersive technique was applied prior to segregation; hence, the reported particle size reflects "existing" sizes rather than ultimate particle sizes as normally determined. Density gradient segregation, when performed on selected size fractions, utilized gradient solutions ranging from 1.8 to 2.90 g/cm? Tetrabromoethane (TBE) was the heavy density solution; ethanol containing 10% polyvinylpyrrolidone (PVP) was the dispersant, and mixed with appropriate amount of TBE was the light solution. The samples were treated for 2 minutes with ultrasonic vibration to induce mineral disaggregation. For more detailed description of the technique, readers are referred to papers by Francis et al., 1972a, and Francis and Tamura, 1972b.