many of the factors that are involved in movement of transuranics in the
environment and the deposition and retention of transuranics in human beings
are not well established.
"The Advisory Group is of the opinion that the recommended cleanup criteria
as discussed in Item 2 below will result in average transuranic radiation doses
to subsequently exposed populations that will be commensurate with proposed
EPA guidelines. The EPA considers its guidance levels to be equivalent to a
lifetime risk of about 14 premature cancer deaths per 100,000 persons exposed
and to perhaps an equal number of genetic effects, although these estimates
are based on many uncertain assumptions and are generally considered to be
quite conservative. An estimate of 14 cancers per 106,000 people would
correspond to a 3% chance of one cancer appearing in a population of 200
people exposed to EPA guidance levels for their lifetime; or expressed
differently, to a probability of one cancer in every 2,100 years (assuming a
constant population size).
"2.
Considering the physical and ecological limitations to removal of transuranics
from the Enewetak Atoll, the Advisory Group recommends the following:
All one-quarter or one-half* hectare areas on village islands should be cleaned
unless (with 70% confidence) the average concentration in surface (0-3 em) soil
does not exceed 40 pCi/g. That is, each one-quarter or one-half hectare area
should be cleaned if the average concentration plus one-half sigma (for the unit
area) exceeds 40 pCi/g. From the information currently available and used for
dose assessment, we believe this procedure will provide a reasonable
expectation that doses in the bone and lung will be commensurate with the
EPA guidance. In terms of radiation dose-sparing benefit to future inhabitants,
cleanup of a standard area on a village island is worth about 4 times as much as
eleanup to a given level on an agricultural island and 12 times as much as
cleanup of the same area to the same level on a picnic island. However, in the
light of existing contamination levels and available cleanup resources, it would
appear that cleanup of all one-quarter or one-half hectare areas on village
islands according to the above criteria should receive first priority. Because
the other islands may have increased use over that currently assumed, a second
priority should be the cleanup of agricultural island half-hectare areas unless
(with 70% confidence) the average concentration for the unit does not exceed
80 pCi/g. A third priority should be the cleanup of picnic island half-hectare
areas unless (with 70% confidence) the average concentration for the unit does
not exceed 160 pCi/g. If resources are exhausted, some islands may not be
cleaned up; final dose assessment may indicate that these islands will have to
be permanently quarantined. We note that the soil profile on Pearl is
anomalous since the concentration of transuranics appears to be uniform with
depth, We believe that the possibility of effective cleanup for use as a village
or agriculture island is remote. However, the possibility of covering Pearl with
the less contaminated soil from the village islands and, perhaps, from the
agricultural islands should be considered for lowering the average surface
contamination levels and reducing the logistics problems of transporting the
soil from the other islands to Runit.
*1/4 heetare if IMP readings are taken on a 25 meter grid; 1/2 hectare if a
30-meter grid is used." (Bair, 4/1978.)
Information and data provided to the Advisory Group for review included a draft dose assessment by
LLL as agreed in the 6 January meeting. The new assessment indicated that the controlling dose
may be ingested through the food chain rather than through inhalation of transuranics as had earlier
been believed.
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