some depth (Fig. 3, trace D); these profiles generally correlated with
areas which had been subjected to testing, construction, or earthmoving activities.
Several of the profiles indicated that 239 py
may have migrated beyond the depth sampled,
Penetration of
(1976)
Pu remained unknown.
of radionuclide concentrations
thus
the total depth of
A 1974 study by Noshkin et al,
in the ground water reservoir of
one of the islands revealed that 739?" %py had migrated to a depth of
80 m below the island surface
(Fig.
4).
Plutonium-239,240 was detected
environments.
As was shown in the soil profiles presented by Lynch
and Gudiksen (1973), Noshkin (1976) also observed that the vertical
distributions of 779-?"°pu at any one test weil were unrelated to the
distributions found on other islands or at different test wells on
the same island.
Nevissi et al, (1976) discussed the distribution of 739'?"°pu in soils
of Bikini Atoll.
Plutonium-239,240 was detected as deep as 100 cm in
soil profile samples with the distribution shown in Fig.
5.
Trace A
ts a profile characteristic of a disturbed soil, possibly due to earth
movement, construction, or clean up efforts, Traces B and C are two
additional plutonium profiles from Bikini Atoll.
It was noted that
all the profiles exhibited 7°*'?**pu distributions similar to those of
3%r measured on the same samples.
.
According to Nevissi (1976) there are three possible transport mechanisms
for plutonium in Bikini soils:
solution transport, biological transport, and suspension transport.
Based on the soil and biological conditions at Bikini, it was concluded that solution transport and bioclogical
transport were not the major methods by which plutonium migrated
downward.
The suspension and resuspension of plutonium and plutoniumbearing particles was the principal mode of plutonium transport in these
soils.
Nevissi (1976) noted the cbservation of Held et al. {1965} that
the algal crust of the atoll soils tend to retain a greater portion of
@11
radionuclides.
Although it was not possible to predict the mechanism
Depth Below Ground Surface (m)
at all intermediate depths sampled, suggesting that a portion of the
233,2495) was very mobile throughout the water-saturated coral-sand
Fig. 4.
239,240 by (FCI /1)
0
,
:
20h
4
40F
;
60 be
a
0
Vertical
a
2
2
(Adapted
239¢240R, and their dis-
tribution at Bikini, are not likely to change significantly in the
immediate future unless mechanical disruption of the soil occurs.
Safety Shot Sites
A program is in progress under the auspices of NAEG to determine the inventory, distribution, and biological fate of transuranics and other
Prevalent radionuclides at the Safety Shot Sites of NTS.
To date,
this program has generated data on soil plutonium, americium, and
uranium distributions for areas where safety tests of nuclear weapons
have occurred.
52
A
4
Distribution of
Enewetak Atoll
Of plutonium retention by the organic crust, the properties of the algal layers and the large adsorptive surface area may be one explanation.
It was concluded that the present Isvels of
.
53
2
6
239,240.
8
Pu in a Test Well,
from Noshkin et al.,
1976).