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)