239-240 Pu in Surface Soils Average Concentrations of (0-5 cm Depth) of NAEG Study Areas* TABLE 1. Strata 34 Clean 1 2 103 Slate 2 1,286 3 411 3 3 4,688 5 1,847 Avg. 485 Strata Area 1 13 (pet /a) 952 4 ss Avg. 1 92 5 2 725 3 4 3 Ave. 1i-B 213 4 4,555 8,596 11-C 2 3 4 5. Avg. 13 175 Double 1 123 Area 2 Track 2 6,422 11-D 3 3 4 Avg. Slate i 1 2 3,440 99,459 305 3) 8,196 AL 2,637 33,224 is the average bulk density of the soil in the study area of reference (g/cm?) . and A, are given by Gilbert et al. (1975, p. 379). Estimates As suggested by Figure 1, plutonium may be transferred from the soil compartment to compartments representing other ecosystem components. It may also be removed from the soil of a given area by water or wind erosion. Percolation into the profile could remove plutonium from the surface where it is most susceptible to resuspension, and could, if the soil were plowed and rainfall plentiful, transport some plutonium below the root zones of crop plants. 786 2,016 31,977 138,568 6,921 Owing to the extreme variability of plutonium concentrations in soil samples taken from the same general area and to the arbitrary nature of soil compartment boundaries, it would be difficult to design field studies to estimate the overall rate of plutonium loss from the soil compartment. In fact, no such studies have been undertaken in the field or in the laboratory and we have no basis for assuming that the average concentrations of plutonium in the soils of contaminated areas will decrease significantly in the next 100 years or so. 895 4,385 19,802 53,018 6,318 Consequently, the soil concentrations given in Tabie constants for the areas indicated, i.e., 1 will be treated as the soil compartment is assumed to be a continuous and constant source for plutonium transfer to other compartments. In the absence of any evidence that the rate of plutonium loss is, in fact, significantly greater than the rate of loss due to radioactive decay, the equation for the soil compartment is: | 511 CS = C(O)exp(-A,t) , i 87 Slate 2 1,559 Total Study Area - 11,379,100 " 3 5,721 >1000 pci/g 393,700 7 4 5,605 >2000 pCi/e 201,000 m Ave. deep (50,000 cm3/m? = 10% cm2/m2 x 5 cm), and Losses From Soil Compartment 7,462 Clean 2 (2) is the area of stratum i (m7), Estimates of 1, 1,405 2,314 1, /(A,o) of soil bulk densities are given in Table 2 for each study area. These data, not previously published, were also provided by Dr. Gilbert (personal communication). The strata averages in Table 1 are reasonably consistent with the data reported by Gilbert ef al. (1975). 339 3 Avg. 4 5 Avg. ~5 2°x 1075 is the reciprocal of the volume of soil in 1 m? x 5 cm 5,323 Avg. Area A, 257 724 Area 14,245 GMX 4 2x 10 where, Cut is the average concentration of plutonium in the soil of stratum fi (pCi/g), 1 is the inventory (total amount) of plutonium in the soil of stratum i (pCi), oil (pei /e) area. aces. Clean Coa 789 where, Cs is the average concentration of plutonium in the surface soil of a contaminated area at time t (pCi/g), C (0) is the initial concentration as given in Table l, and a° is the radioactive decay\rate of 7339pu (7.7829 x 1078 day~!), t is time in days. p. 379), Table 2, and Equation (2). * Based on Gilbert et_al. (1975, 626 627 (3)