However, two approximate methods may
be used — the resuspension factor approach and an argument based upon
ambient air particulate concentrations,
“under quiescent conditions, or after
administrative control has been established
in the case of an accident, " A value of
107°/m is suggested under conditions of
with the assumption that the particulates
moderaie activity.
are derived from the contaminated sur-
ever, that exceptionally higher values
face.
The former method has been fre-
Stewart states, how-
(mean of 10° Ym) were observed during
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 material to become fairly well mixed witha
few centimeters of the soil surface.
also reported by Stewart,
Kathren® has also considered the resuspension factor approach and has
recommendedthe use of 10°4/m asa
ResusSpension Factor Approach
conservative but appropriate value for
The resuspension factor, K, is defined
setting standards for Pu, surface con-
as
*
K = Airconcentration (Ci/m>)
Surface deposition (Ci/m2) ’
ta
ang thus-has units of m
-1
".,
:
Nis almost -
always implied that both measurements
are made at the same location.
The diffi-
culties with this approach are fairly
_,obvious — no allowance is made for the
geometrica! configuration of the source,
the particle-size distributions of the contaminant and the soil surface, vegetation
cover, etc.
Stewart! and Mishima”
have tabulated values of K from many
experiments including those involving
laboratory floors as well as native soils,
As would be expected, the tabulated
values cover an enormous range and vary
from 1077 to i938 /m.
Most of the high
values, however, are derived from exveri-
ments with laboratory floor surfaces and/
or with artificial disturbance.
For outdoor situations, Stewart! sug-
tamination,
Lenghem* 5 has suggested that 2
value of 10°°/m is a reasonable average
value to use in estimating the potential
hazard of occupancy of a piutoniumcontaminated area,
At the same time,
however, Langham notes that many
measured values lie in the range of 10°°
to 10°! /m and reports that his own
measurements in 1956 produced a value
of 7X 10°°/m,
These recommended values, however,
are all intended for application during the
time period immediately following deposition.
Numerous studies!’ 5-8 have shown
that air concentrations of resuspended
materials decrease witn time.
With the
assumption that this decrease can be
represented by a single exponential func-
tion, half-times of 35 to 70 days have
been reported”? 7, 8
This decrease in
air activity is not explainable by the
gests as a guide for planning purposes
relatively minor loss of material from
that a value for K of 1078 /m be used
the initial site of deposition» °, but is
a
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