RESULTS AND DISCUSSION Plutonium Concentration in the Soils The concentrations of plutonium in the less than 2-mm soil particles are given In the desert pavement, approximately 95% of the activity is in Table 1. The remaining 5% is distributed in the 0 - 2.5 cm surface layer. the found in lower horizons with indications of a higher concentration in the 7.5 - 10 cm By comparison, the 0 - 2.5 cm layer than in the two intermediate layers. surface layer of the desert mound contains about 60% of the activity with 30% and 7% contributions in the 2.5 - 5.0 and 5.0 - 7.5 cm layers, respectively. This distribution would suggest a sizable buildup of the mound subsequent to the detonation event. However, this interpretation regarding buildup should be reviewed with caution since the observed distribution may be a reflection of the sampling technique used. In sampling the mound, the layers were separated at 2.5-cm increments; the 0 level was measured from the higher elevation point of the mound along the sampling slope. This point is illustrated in Figure 1, a schematic representation of a desert mound. The first increment of 2.5 cm then represents the depth measured from the highest point (0 level) on the mound. At lower sections of the mound, the depth of penetration would be less than 2.5 cm, depending on the slope. Sampling in this manner evidently resulted in a lower mass of sample from the surface layer since the gross weight of this sample was 233 grams in the 0 - 2.5 cm layer as compared with a mean weight of 315 + 3.6 grams for the 2.5 increments of the three lower layers. If one assumes that the buildup of the mound was relatively even, then sampling the mound perpendicular to the sloping surface (Fig. 1) rather than perpendicular to the ground level might better reflect the depth distribution. Assuming that 315 grams represent the mass of soil 10 cm x 10 cm x 2.5 cm (sampling dimensions), then 233 grams represent 74% of the mass based on 250 em, Thus, approximately 26% of the 0 - 2.5 cm layer may be present in the 2.5 5.0 cm layer. If this 26% contributed the same activity to the 2.5 - 5.0 cm layer as found in the surface layer, then the calculated activity in the remaining portion or the 2.5 - 5.0 cm layer would be 5250 dpm/g compared to the measured 7492 dpm/g. Similar calculations of the 5.0 - 7.5 cm layer show that the activity of this layer would be 392 dpm/g compared to the measured 1655 dpm/g; and the 7.5 - 10.0 cm layer would be 97 compared to 174 dpm/g. If the distribution occurred in the manner postulated above, then the calculated results of plutonium distribution would suggest that a small amount existed prior to detonation. It appears worthwhile to sample desert mounds by both methods as well as at different locations around the shrubbery to establish the activity distribution and activity buildup beneath the shrubbery.