However, two approximate methods may
"under quiescent conditions, or after
be used — the resuspension factor ap-
administrative control has been established
proach and an argument based upon
in the case of an accident. "
ambient air particulate concentrations,
10°°/m is suggested under conditions of
with the assumption that the particulates
moderate activity.
are derived from the contaminated sur-
ever, that exceptionally higher values
face.
(mean of 10° °/m) were observed during
The former method has been fre-~
A value of
Stewart states, how-
quently used, but almost always in the
the Hurricane Trial (Monte Bello Islands)
context of a fresh surface deposit.
and credited this to the nature of the
The
latter method is inappropriate to the
small islands exposed to sea breezes,
fresh deposit situation, but should be
Values approaching 10° 3/m when dust is
reasonably valid after enough time has
raised by pedestrians and vehicles are
elapsed for the surface-deposited mater-
also reported by Stewart.
Kathren® has also considered the re-
ial to become fairly well mixed with a
suspension factor approach and has
few centimeters of the soil surface.
recommended the use of 10 7/m asa
as
Resuspension Factor Approach
conservative but appropriate value for
The resuspension factor, K, is defined
setting standards for PuO, surface contamination,
3
K = Air concentration (Ci/m”™)
,
Surface deposition (Ci/m?)
and thus has units of m},
Langham 4,5 has suggested that a
value of 10° °/m is a reasonable average
It is almost -
value to use in estimating the potential
always implied that both measurements
are made at the same location.
The diffi-
culties with this approach are fairly
to 10° ‘jm and reports that his own
the particle-size distributions of the con-
measurements in 1956 produced a value
taminant and the soil surface, vegetation
of 7X10 °/m,
Stewart! and Mishima”
These recommended values, however,
have tabulated values of K from many
are all intended for application during the
experiments including those involving
time period immediately following deposi-
laboratory floors as well as native soils.
tion.
As would be expected, the tabulated
values cover an enormous range and vary
Most of the high
values, however, are derived trom experiments with laboratory floor surfaces and/
or with artificial disturbance,
.
.
For outdoor situations, Stewart”
1
Numerous studies
1, 5-8 have shown
that air concentrations of resuspended
materials decrease with time,
With the
assumption that this decrease can be
represented hy a singic exponential function, half-times of 35 to 70 days have
been reported”? 7,8
sug-
At the same time,
‘measured values lie in the range of 107°
geometrical configuration of the source,
from 107° to 10° 3/m,
contaminated area.
however, Langham notes that many
obvious — no allowance is made for the
cover, etc.
hazard of occupancy of a plutonium-
This decrease in
air activity is not explainable by the
gests as a guide for planning purposes
relatively minor luss of material from
that a value for K of 10° °/m be used
the initial site of deposition’ 6 but is
>
TY_tA
at