United States
Environmental Protection
Agency
Air and Radiation
(ANR-459)
EPA 520/1-90-016
June 1990
rm
^
EPA
Transuranium Elements
Volume 2
Technical Basis For
Remedial Actions
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TRANSURANIUM ELEMENT
VOLUME n
TECHNICAL BASIS FOR REMEDIAL ACTIONS
BY
GORDON BURLEY
OFFICE OF mDlATION PROGRAMS
U.S, ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, DC 20460
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CONTENTS
CHAPTER
!- ' . - - .
1 INTRODUCTION
2 IMPLEMENTATION OF RECOMMENDATIONS
3 ECONOMIC ANALYSIS OF REMEDIAL ACTIONS
4 INCIDENTS OF NEW CONTAMINATION
5 "SCREENING LEVEL" FOR STABILIZED CONTAMINATION
AND AN "ACTION LEVEL" FOR NEW SOIL CONTAMINATION
6 RADIOLOGICAL ASSESSMENT - ROCKY FLATS PLANT
7 PLANNING AND CONDUCT OF CLEANUP OF ENEWETAK ATOLL
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1. INTRODUCTION
1.1 BACKGROUND
The transuranium elements have an atomic number greater than
92 and are radioactive. The principal transuranium element of
concern is plutonium, which is produced in nuclear reactors and
used in nuclear weapons and as fuel for fast-breeder reactors.
Plutonium-239 is a very long-lived material with a radiological
half-life of about 24,000 years. Other transuranium elements of
importance include neptunium, americium, curium, and californium.
The transuranium elements, especially plutonium, have been
recognized as potentially hazardous even in very small amounts.
Mathematical models, based on an extensive data base, have been
developed to predict the movement of the transuranium nuclides
through the environment to man. The principal modes of intake
are inhalation of resuspended materials previously deposited on
soil surfaces and ingestion through drinking water and other
parts of the food chain. Most of these radionuclides are alpha
emitters and may cause lung, bone, or liver cancer when inhaled
or ingested.
Present levels of the transuranium elements in the
environment have resulted from several sources - regional and
worldwide fallout from the testing of nuclear weapons in the
atmosphere, accidents involving military and related operations,
and local releases from nuclear facilities. The major portion of
the transuranium elements in the environment is the result of
surface and atmospheric nuclear weapons tests during the period
1945-1963. Atmospheric tests injected radioactivity into the
stratosphere which has since then been slowly deposited more or
less uniformly over the lands and oceans of the earth. As a
result of these earlier weapons tests, the existing level of
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FIGURE 1-1
1
H
3
Li
11
Na
IV
.."*"
3/
Rb
=55
Cs
87 :
Fr
4
Be
12
Mg
20
Ca
38
Sr.
56
Ba
88
Ra
. 21
Sc
39
Y
5/-/1
La'
Series
8V-1U3
Act
Series
a
Ti
40
Zr
72
Hf
(104)
23
V
41
Nb
73
,Ta
(105)
24
Cr
42
Mo
74
W
(106)
25
Mn
43
Tc
75
Re
(107)
26
Fe
44
Ru
76
Os
(108)
27
Co
45
Rh
77
Ir
28
Ni
46
Pd
78
Pt
29
Cu
47
Af,
79
Au
30
Zn
43
Cd
80
tig
s
5
B
13
Al
31
Ga
49
In
8i
Tl
6
C
14
Si
32
Re
50
Sn
82
Pb
7
N
15
P
33
As
51
Sb
83
^Bi
8
0
16
S
34
Se-
52
Te
84
Po
9"
F
17
n
35
P.r
53
1
85
At
2
He
10
Ne
18
Ar
36
Kr
54
Xe
86
Rn
Lanthanide
Series
tActinide :
Series
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TABLE 1-1
INVENTORY OF PLUTONIUM FOR SELECTED SITES IN THE UNITED STATES
LOCATION
APPROX INVENTORY
REMARKS
H
I
U)
U.S. (Fallout) 20,000 Ci
Nevada Test Site >155 Ci
(near Las Vegas, NV)
Rocky Flats Plant 8-10 CI
(near Denver, CO)
Mound Laboratory 5-6 Ci
(Miamisburg, OH)
Savannah River Plant 3-5 Ci
(SWareaofSC)
Hanford Site *
(central WA)
Los Alamos Laboratory *
(NW of Santa Fe, MM)
Oak Ridge Laboratory *
(east TN near Knoxville)
Idaho National Engineering Lab *
(central ID)
Trinity Site >45 Ci
(near Alamogordo, NM)
Worldwide Pu-238 = 17,000 Ci
Pu-239 = 440,000 Ci
U.S. Average = 1.5 mCi/km2
Nuclear Test Site
Surface and Subsurface Tests
Weapons Fabrication Facility
Pu-238 Processing Facility
Pu Production Facility
(Pu and higher isotopes)
Pu Production-Research Facility
(high levels of Pu on site)
Weapons Development
(Pu-239 in remote canyons)
Research and Development Facility
Separation, Test, and Research Facility
(Pu-239 in soil/groundwater)
Site of first atomic bomb test
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transuranium element contamination in soils of the United States
is about 0.002 uCi/m2. More recent weapon tests have not added
significant amounts to this level.
Areas where there is substantial localized contamination
above the general background level are well documented and
extensive environmental analyses have been carried out at all
these sites. The sites of highest contamination are, for the
most part, on Federally owned property and access may be
restricted.; Table l-l shows estimates of the amount of plutonium
in the environment at the major United States locations. More
detailed information on the sources and current levels of the
transuranium elements in the general environment is given in
Volume I.
Plutonium and other transuranium elements can move through
the environment by a variety of transport mechanisms and
pathways. These are determined by the chemical and physical form
of the deposited material, the characteristics of the surface,
local land use patterns, and other factors such as wind or
rainfall. Principal environmental pathways to humans are shown
in Fig. l-l..
Transuranium elements released to the environment may exist
as discrete particles or they may become attached to other
materials. The principal modes of transport of these elements
from a source to man are by direct airborne movement from the
source or by resuspension of previously deposited small particles
by the action of wind or other disturbance. Resuspension is a
complex phenomenon affected by a number of factors, including the
characteristics of the surface, type of vegetative cover,
meteorological conditions, and age of the deposit. In general,
resuspension will be relatively high immediately after initial
deposition, gradually decrease with time, and approach a long-
term constant within about one year after deposition.
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PRINCIPAL PATHWAYS OF THE TRANSURANIUM ELEMENTS
i THROUGH THE ENVIRONMENT TO MAN
FIGURE 1-2
1..- 5
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Transport of plutonium and other transuranium elements
through the food chain and subsequent ingestion is generally of
lesser importance than the air pathway. Transuranium elements
may be deposited on plant surfaces or assimilated through the
plant root system. The uptake by plants is relatively small and
most animals, including humans, have a high discrimination factor
against transfer of these elements into body tissues. The
solubility of plutonium in water is very low and nearly ail
Plutonium released into lakes and streams is ultimately deposited
and sorbed onto sediments. Other possible routes of entry into
humans include direct ingestion of contaminated soils and
contamination of wounds, but are generally of minor importance
relative to the inhalation and ingestion pathways.
Potential health effects caused by the transuranium elements
are a function of several biological and physical parameters
including the biological retention time in tissue, the type of
radioactive emission, and the half-life of the nuclide. For the
more important transuranium nuclides, such as Pu-238 or Pu-^239,
biological retention times are very long and radioactive decay
occurs at such a slow rate that uptake of these materials in the
human body will result in prolonged exposure of body organs.
Many of the transuranium nuclides decay by emission of an alpha
particle (ionized helium atom), in a manner similar to radium and
other naturally occurring alpha emitting nuclides. Alpha
particles are highly ionizing and damaging, but their penetration
in tissue is very small (about 40 /iin) . Thus, biological damage
is limited to tissue in the immediate vicinity of the radioactive
material, and a potential health hazard from transuranium
elements in the environment can only result when these materials
are inhaled or ingested into the body.
1-6
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Inhaled particles are initially deposited in various regions
of the respiratory tract, where they remain until either cleared
or .translocated to other body organs. Much of the material
deposited in the lung is cleared within a few days,, but some of
the smaller particles which diffuse into the pulmonary regions of
the lung are removed much more slowly and have a biological half-
life of a year or more. This may lead to an increase in the risk
of lung cancer in exposed individuals. Inhaled transuranium
elements may also transfer and be retained in.other body organs,
and pause cancers of the bone and liver. For the less soluble
transuranium compounds, such as plutonium oxide, this will
contribute only marginally to the tptal risk for the inhalation
pathway. ,;. v
Ingestion of transuranium elements generally represents
a smaller environmental risk to humans than inhalation. A
relatively small fraction of any ingested .transuranium element
may be transferred to the bloodstream from the digestive tract
and deposited ^n bone, liver, gpnadal tissue, and other organs.
In most cases, less than one part in .ten thousand of the ingested
material is absorbed by the body, with the remainder excreted.
The risk to individuals as a result of ingestion of transuranium
elements, is.mainly due to potential bone and liver cancers.
A potential risk of genetic damage to the progeny of exposed
individuals^exists because of possible accumulation of ;the
transuranium elements in gonadal tissues. ,At the dose,rates
.generally deemed acceptable for long-term exposure for persons in
the general population, this risk is small compared to the
.natural incidence of genetic damage.
1 - 7
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1.2
OTHER PUBLICATIONS
The Environmental Protection Agency published the basis and
text of proposed Federal Radiation Protection Guidance in the
Federal Register, Vol. 42, pp. 60956-9, on November 30, 1977.
It also published a technical summary document explaining the
proposed recommendations (EPA 520/4-77-016), and provided
responses to comments (Technical Report, EPA 520/4-78-010).
The Environmental Protection Agency has also published
additional related documents entitled "The Ecological Impact of
Land Restoration and Cleanup" (Technical Report, EPA 520/3-78-
006), "Selected Topics: Transuranium Elements in the General
Environment" (EPA/ORP Technical Note CSDr-78-1) , "Plutonium Air
Inhalation Dose (PAID)" (EPA/ORP Technical Note CSD-77-4), and
"A Computer Code for Cohort Analysis of Increased Risk of Death
(CAIRO)" (Technical Report EPA 520/4-78-012).
A summary of environmental research on transuranium
elements, funded by the Department of Energy through calendar
year 1979, was published recently as Transuranic Elements in the
Environment. Wayne C. Hanson, Editor. It is available as
Document DOE/TIC-22800 from the National Technical Information
Service, U.S.Department of Commerce, Springfield, VA 22161.
The book contains an extensive summary of available information,
prepared by a number of technical experts, on all aspects of the
inventory, distribution in terrestrial and aquatic ecosystems,
environmental transport mechanisms and models, and biological
effects of the transuranium elements.
Comprehensive reports on plutonium and other transuranium
elements prepared by multinational groups of experts have
recently been published by the World Health Organization in
Nuclear PowerHealth Implications of Transuranium Elements
(1982), and by the Nuclear Energy Agency (NEA) of the
1-8
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Organization for Economic Cooperation and Development in The
Environmental and Biological Behavior of Plutonium and Some Other
Transuranium Elements (1982). These reports are intended
primarily for use by Government officials of member countries,
and offer a useful summary of available information in language
intended for a nontechnical audience.
1.3 RISK COMPARISONS
National and international radiation protection
organizations have suggested that the annual average effective
dose equivalent to persons in the general population not exceed
100 mrem per year for all sources except background radiation and
medical exposures. This corresponds to an added risk of about
10"5 per year. Appropriate dose rate limits for specific body
organs may be derived to correspond with these risk limits, and
should consider both the different modes of intake into the body
and the cumulative risks from translocation and retention in more
than one organ. Further recommendations suggest that doses be
kept as-low-as-reasonably-achievable and that there be a
justification for the exposure.
A comparison with other risks is useful in providing a
perspective Understandable to most people. However, such a
comparison can provide only a descriptive basis for individual
judgments and does not provide an analytical decision method.
The major categories of risks leading to premature death (in
order of decreasing probability) include: disease, accidents,
and natural catastrophes. A tabulation of commonly encountered
risks and their probability of occurrence (averaged over the U.S.
population) is shown in Table 1-2. It should be noted that the
risk to a specified critical group (e.g., persons living in an
area/subject to hurricanes) may be much greater than that shown
/
here.
1-9
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TABLE 1-2
PROBABILITY OF DEATH BY VARIOUS CAUSES
(U.S. Population Average for 1978)
H
.1
Cause
Accidents
Motor Vehicle
Air Transport
Railway
Falls
Fire
Drowning
Industrial
Electrocution
Explosion
Firearms
Diseases
Cardiovascular
Malignancies
Influenza/Pneumonia
Diabetes
Natural Events
Lightning
S Tornadoes
Hurricanes
Total Number
of Deaths
52,411
1,880 ..;
602
13,690
6,163
5,784
5,168
984
562
1,806
964,000
396,720
58,230
33,800
* 160
118k
; 9°c
.-: " '-. ;-
Individual Risk
(Pnobability/yr)a
2.4x10-4
8.6x10-6
2.8x10-6
6.3x10-5
2.8x10-5
2.7x10-5
2.4x10-6
4.5x10^6 +
2.6x10-6
8.3x10-6
4.4x10-3
1.8x10-3
2.7x10-4
1.6x10-4
.- " ' : '!-'-.
7.3x10-7 ?
5.4x10-7 ,
4.1xfO-7 'I
- - ' * » - ?
(a) Based on total U.S. Population
(b) 1953-75 "average
(c) 1901-71 average
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For the same reason, it is useful to view an objective for
radiation protection by comparison with the unavoidable exposure
received from natural background radiation. All persons are
exposed to radiation which consists of cosmic rays and the
radiation from naturally occurring radionuclides (such as
uranium) which exist in the general environment. The annual dose
from this background radiation varies by location, with an
average of about 100 millirem per year to persons in the
continental United States. The average risk from natural
background radiation is of the order of 10"5 per year.
, . \ ' ' - ,
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The long radioactive half-lives of some of the transuranium
elements make the evaluation of the total detriment over the
entire.time of persistence in the environment, to the extent
practicable, a question of considerable importance. While such a
procedure is useful in decisions on risk management, it is not
the only consideration and risk management must involve a
balanced judgment of all appropriate factors.
1.4 COSTS OF REMEDIAL ACTIONS
Dispersion of plutonium and other transuranium elements
in the environment may result in a number of different types of
problems, ranging from contamination of soils and other surfaces
to the contamination of structures and persons. The objectives
of remedial actions should be protection of persons and
limitation of long-term environmental contamination. Each
situation will need to be evaluated on a site-specific basis, and
different remedial action options chosen as applicable.
The costs of remedial actions are determined by a number
of factors: (1) the size of the contaminated area, (2) the type
of structures and/or surface(s) that are contaminated, (3) the
population density and distribution, (4) the type of terrain and
other ecological factors, the type of land use, and (5) the .
associated level of contamination. In general, a contaminated
area may be divided into sectors, and appropriate cleanup actions
developed for each sector. The total cost for remedial actions
is the sum of costs for all sectors.
Two categories of situations must be addressed by a review
of economic impacts: (l) existing plutonium and, other-
transuranium element contamination at a few sites where the
contamination is stabilized and the distribution and soil
concentration are well characterized, and (2) possible future
releases (from operating facilities, nuclear weapons accidents,
and other possible sources), where neither the magnitude of
1-12
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release nor its location can be known in advance of the
occurrence.
'A final consideration applicable to any remedial action
program is the possibility that"disturbance of the enyironm^nfc
might do long-term harm. The Environmental Protection Agency
has examined this aspect, and published an extensive analysis
entitled "The Ecological Impact of Land Restoration and Cleanup,"
EPA Technical Report 520/3-78-006. This report examined in
detail the consequences of disturbing some of the more
significant ecosystems and their recovery rates. Such an
evaluation is essential ,prior to the initiation of any major
remedial action program. It can therefore be concluded that .
consideration of all factors involved in deciding on the
feasibility, type, and extent of cleanup is needed prior to
initiation of such actions, and that such decisions must be made
in the context of an overall balancing of the costs and benefits.
1.5
IMPLEMENTATION
Implementation of criteria is the responsibility of the
Federal or State authority under whose jurisdiction the facility
which caused the environmental contamination operates, or which
Otherwise has jurisdiction and/or control of the materials which
are released. Implementation includes determining both the
actual or potential hazard to people and instituting remedial,
actions where required.
The principles of justification, limitation, and
optimization recommended by the International Commission on
Radiological Protection should be applied to the development of
applicable criteria. The full range of options for remedial
actions should be considered and both the effective risk.,
reduction and incremental costs determined relative to a .base
case. An evaluation of "the feasibility and costs for such.'a
range of options should be included as part of the documentation
1-13
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of the decision process. The determination of the appropriate
risk limits for each incident of contamination should be carried
out on a site-specific basis, and decisions on the focus and
extent of remedial actions should be made on the basis of long-
term public health protection.
Specific implementation directives for remedial actions, in
a report entitled "Nuclear Weapon Accident Response Procedures
(NARP) Manual," have previously been provided by the Defense
Nuclear Agency of the Department of Defense (Report DNA 5100.1,
January 1984). This manual provides valuable information on
administrative procedures and technical data applicable to an
emergency response situation* In addition, the United States
undertook a large-scale remedial action operation on the Enewetak
Atoll during the 1970's, with the objective of resettling the
native population of a former weapons test site. Although the
situation was unique, the operation provided valuable experience
applicable to future remedial actions. The Department of Energy
provided cleanup objectives for the transuranium elements, and
applied these to islands categorized by use and occupancy. The
Environmental Protection Agency has also published detailed
general procedures for remedial actions in the "National Oil and
Hazardous Substances Pollution Contingency Plan". Other criteria
and recommendations developed for specific cleanup operations
have been published elsewhere and should be reviewed prior to
initiation of any remedial actions.
Implementation of criteria may be facilitated by direct
measurement of ambient environmental concentrations. ICRP
Publication 26 states (Paragraph 82) that "In many practical
situations it will be convenient to make use of a derived limit,
calculated with the aid of a model, which provides a quantitative
link between a particular measurement and the recommended dose-
equivalent limit or intake limit. In deriving, such a limit the
intention should be to establish a figure such that adherence to
it will provide virtual certainty of compliance with the
1 - 14
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[International] Commission [on Radiological Protection]
recommended dose-equivalent limits. However, failure to adhere
to the derived limit will not necessarily imply failure to
achieve compliance with the Commission's recommendations and'may
require only a more careful study of the circumstances."
It can generally be expected that a variety of techniques
could be used to achieve reductions in risk to exposed persons.
An economic evaluation can be used to identify the- technique or
combination of techniques which will achieve a specified
objective at least total cost. Monetary costs, environmental
costs, and other non-quantifiable costs should all be considered
in the evaluation of each alternative combination of possible
remedial actions.
1.6
ENVIRONMENTAL ASSESSMENTS
Under the provisions of the National Environmental Policy
Act of 1969, it is intended that every major Federal action be
examined in terms of projected impacts and that all available
alternatives be considered. The purpose of such an analysis is
to compare the options in terms of the broad range of projected
health, sociological, economic, and environmental impacts.
Under Section 102(2)D of the National Environmental Policy
Act of 1969, agencies are required to study, develop, and
describe appropriate alternatives to the proposed or recommended
courses of action. The purpose is to analyze the environmental
effects, benefits, costs, risks, and related issues, so as not to
limit options which might better advance environmental, quality or
have less detrimental effect. Examples of such alternatives are
those of taking no action, of postponing action pending further
study, or of taking actions of significantly different nature
which could provide similar benefits with less severe
environmental impacts.
1 - 15
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The possible impacts of a remedial action will vary
according to the nature and scale of the method used for cleanup
and restoration of a contaminated area, and may be particularly
sensitive to the location. The primary impacts of most remedial
actions will generally be some temporary disruption of normal
activities on and near the site, temporary impairment of air and
water quality, and possibly significant effects on flora and
fauna.
.1 - 16
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2, IMPLEMENTATION OF RECOMMENDATIONS (REVISED)
(Reprinted with minor changes from "Response to Comments"
EPA Technical Report 520/4-78-010)
2.1 INTRODUCTION
Implementation of recommendations concerning transuranium
element environmental contamination involves consideration of all
the pathways that could result in radiation doses to persons in
the general population. Such a consideration includes a
determination of the levels and extent of existing contamination
and the projections of actual or potential doses to a critical
segment of the exposed population. This requires an evaluation
of the site, a projection of the radiation dose rates via all
applicable pathways to determine whether recommended dose rates
are exceeded, and initiation of remedial actions where indicated.
A reasonable evaluation of a contaminated site should
include a description of the site and environmental measurements
of contamination levels in environmental media, in sufficient
detail to convey adequate information to the general public.
Environmental pathway and dosimetry models used to estimate
radiation doses to persons should be described to permit
evaluation of the procedures used.
The objective of environmental sampling and analysis is to
derive information for the purpose of estimating dose rates to
pulmonary lung and to bone of exposed individuals. These dose
estimates are derived on the basis of models which consider the
various pathways by which transuranium elements in the
environment may interact with people and produce exposure to
radiation. Such models describe the characteristics of
transuranium elements in the environment, the manner in which
2-1
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they may be transported through the air or through food pathways,
modes of interaction with man (including inhalation or ingestion)
and, finally, factors related to the radiation energy deposition
in organs and tissues. In general, dose estimates are best
derived from data acquired from measurements in the dose pathway
as close as possible to the point where transuranium elements
interact with people. '
Three general procedures can be used to judge compliance
with specific recommendations. These procedures, which are
described in more detail in the following sections, may be used
for the entire site or for portions of the site as appropriate:
a. dose rates can be calculated, using the appropriate
dosimetry models, from measurements of the concentration of the
transuranium elements in air, food, and water at the point o;f
inhalation and/or ingestion by persons. This is the most direct
method. , ,
b. soil concentration levels of the transuranium elements
can be compared to a "screening level" for soil, defined as that
level below which the concentration of the transuranium elements
is not likely to lead to dose rates in excess of the
recommendations. .
c. dose rates can be calculated from the soil contamination
levels of the transuranium elements using site-specific
parameters for transport models and the appropriate dosimetry
models.
2.2 IMPLEMENTATION BY ESTIMATING DOSE RATES TO LUNG AND BONE
The objective of implementing actions is to demonstrate .that
dose rates to members of the critical segment of the exposed
population are not exceeded. The most direct method of showing
compliance for a specific site, or for subareas of a specific
2-2
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site, is to measure transuranium element concentrations in
environmental media such as air, food, and water at the point of
interaction with people and then to calculate the potential
radiation dose rates using the appropriate dose conversion
factors and dose model parameters. When this procedure is used,
adequate documentation should be provided to demonstrate how dose
rates are calculated. It is most appropriate to use realistic
environmental measurements and realistic model input parameters;
conservative parameters should only be used to the extent
necessary to compensate for uncertainties.
Iri certain cases, compliance may be achieved by restricted
occupancy of a site, or portions of a site. Time restrictions
for occupancy, or other use limitations, may be established to
limit the exposure of a critical segment of the population. In
general, such occupancy or use restrictions should be applied
only if remedial actions sufficient to permit unrestricted access
are either impossible or economically prohibitive.
2.2.1 DOSE RATE TO THE LUNG :
Lung dose rates are calculated using appropriate dosimetry
models, which require knowledge of the annual average
transuranium element concentration in air, aerosol partidle size
distribution, and solubility class of the specific radionuclides
present. Apparatus arid procedures for the sampling and analysis
of particulates in air are available, but the accuracy and
precision of measurements must be verified prior to
implementation of the recommendations.
Judgment should be exercised in the design of an air
sampling program to ensure that air concentration levels are
representative of actual exposure conditions. Environmental
measurements of airborne particulates which bias the dose
estimates by the collection of only certain particle size ranges
should be avoided, or a suitable correction should be made.
2 - 3
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It is preferable that the particle size distribution be
experimentally measured for a specific site. Reasonable values
can be assumed based on analogies with similar sites when
projected lung dose rates are small compared to the guidance
level. The solubility class of an aerosol can usually be
determined from the history of the contaminating event and the
subsequent environmental weathering mechanisms.
A derived air concentration "screening level", which
indicates with high probability that a given dose rate will not
be exceeded, may be substituted for a site-specific air
concentration limit. Such a derived air concentration "screening
level" should be based on an activity median aerodynamic particle
diameter (AMAD) not to exceed 0.1 um, which is substantially
smaller than observed values at all sites where transuranium
element contamination presently exists. For an assumed objective
of a committed effective dose equivalent of 10 millirem, the
calculated limiting concentration for this procedure would be
about 1 fCi/m3 of alpha emitting transuranium nuclides, for air
samples averaged over a period of one year or more. Air
concentrations above this value do not necessarily mean that the
objective would be exceeded, but rather indicate that a more
thorough evaluation of existing conditions should be made.
Elevated levels of transuranium elements in air indicate
that these elements may be found in nearby soils. When these
levels approach some limiting value, implementation should
include a characterization of the environmental source term to
provide a means of judgment with respect to the potential for
future exposure levels and the practicality of remedial measures.
2.2.2 DOSE RATE TO THE BONE
Bone dose rates are calculated with appropriate dosimetry
models using a knowledge of the average amounts of transuranium
2-4
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elements that are ingested in a year, their chemical state at the
time of ingestion, and the proper dose conversion, factor.
Inhalation of transuranium elements, especially in soluble forms,
can also lead to radiation doses to bone and should be considered
where appropriate.
Sampling and measurements of transuranium elements in food
and water at the point of human consumption is the most direct
and preferred procedure for determining the annual average
ingested amount of these elements. Alternatively, the amounts of
ingested radionuclides may be estimated using environmental
pathways models. The chemical state at the time of ingestion is
inferred from the medium in which the transuranium elements are
incorporated. In particular, transuranium elements which are
incorporated into biological tissue should be considered as
"organically complexed'? and require a special dose conversion
factor.
Suitable sampling and analytical procedures are available
for the analysis of the transuranium elements in food and water.
As with the inhalation pathway, elevated levels of plutonium and
the transuranium elements in food or water indicate that these
elements may be found in nearby soil or in sediments. Under such
conditions, implementation should include a characterization of
the environmental source term,, to provide a means of judgment
with respect to the potential for future exposure levels and the
practicality of remedial measures.
j ' '
2.3 IMPLEMENTATION BY USE OF A SOIL "SCREENING LEVEL"
Compliance with recommendations may be shown for the total
area of a site, or for subareas of a site, by certifying that
such areas have transuranium element soil concentration levels
less than a derived "screening level". The "screening level"
is a total transuranium element soil concentration level in the
top 1 cm of soil such that dose rates will not exceed the
2-5
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recommendations under the vast majority of land use conditions.
When this implementation mechanism is used, all lands subject to
unrestricted use must meet the screening level criteria. Because
of present uncertainties in the amount of plant uptake for the
more soluble transuranium nuclides, such as americium and curium,
and the resultant possibility of larger doses via the ingestion
pathway than calculated, the "screening level" concept may not be
applicable when the soils of a contaminated area contain these
nuclides in amounts greater than 20-25% of the total activity.
Lands with concentration levels less than the "screening level"
may be judged to be suitable for all normal activities including
residential and agricultural uses. The use of this ^'screening
level" is intended to reduce the land areas requiring extensive
evaluation and to minimize the number of measurements needed.
If land areas have transuranium element levels greater than
the "screening level," it should not be presumed that recommended
dose rates are necessarily exceeded, because conservative
assumptions were used in the derivation. Additional site,
specific evaluations of potential dose rates to lung and .bone
should be made before remedial actions are initiated. ;
Inherent in the application of the screening levels-is the
assumption .that soil contamination by the transuranium elements
will cause radiation exposure through pathways such as the :J
inhalation of resuspended soil, the ingestion of foodstuffs grown
on the soil, the ingestion of soil by children, and the ingestion
of drinking water contaminated by soil runoff.
2-6
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2.4 IMPLEMENTATION BY SITE-SPECIFIC PARAMETERS
Implementation may be shown for a specific site, or for sub-
areas of a specific site, by means of soil measurements by using
pathway and dosimetry models with' parameters determined for the
specific site, to certify that the resulting dose rates do not
exceed recommended values. This approach differs from the use of
a soil "screening level" because parameters such as the
resuspension factor are determined for a specific site. It is
expected that use of site-specific parameters will show that soil
contamination levels higher than the suggested "screening level"
may correspond to organ doses well'below guidance levels.
Implementation by site-specific parameters is appropriate"where
'land areas have transuranium element levels greater than the
"screening level" and further evaluation is necessary to
determine whether or not the recommended dose limits are being
exceeded. - '
The air concentration where people are located generally can
be correlated with the adjacent soil concentration by use of a
resuspension factor, and can be used to estimate the inhalation
dose rate. The site-specific resuspension factor may be either
measured directly or calculated from other data. Direct
experimental determinations are often difficult to make and not
always reproducible. Therefore, calculational techniques are
sometimes preferred although their correlation with measured
values is subject to considerable uncertainty. A method has been
developed (described in Volume I), based on the concept of air
mass loading, which may be useful for this purpose. An
"effective" resuspension factor is derived, defined as the
resuspension factor derived from the air mass loading for the
given location and modified by a "distribution factor" which
takes into account the generally observed nonuniform distribution
of the activity with size of particles in calculating the amount
of transuranium element activity in the inhalable fraction of the
resuspended material. The "distribution factor" is a
2 - 7
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theoretically derived parameter, and its correlation to actually
observed situations has not yet been established. The
resuspension factor derived in this manner is applicable only to
extremely large area sources, and must be further corrected for
the dilution by uncontaminated materials when used for small
contaminated areas.
The ingestion pathway must be evaluated separately, using
data applicable to the specific site in terms of type of crops,
plant uptake parameters, and pathway to a critical segment of the
population. The more unusual transfer mechanisms to people, such
as the ingestion of soil by children and the contamination of
drinking water sources, may also need to be examined if shown to
be of importance.
2.5 SAMPLING AND ANALYSIS METHODS
2.5.1 CHOICE OF METHODS
The choice of suitable methods for sampling and analysis is
the responsibility of the implementing organization. It should
demonstrate that the proposed methods have the necessary
sensitivity, accuracy, and precision. A description of the
apparatus and techniques used to collect the samples, the
procedures for preparing the samples for analysis, and the method
used for radiochemical analysis should be included.
2.5.2 AIR SAMPLING
When air sampling is chosen as the principal method of
implementing the Guidance, continuous monitoring should be
performed at locations indicative of potential doses to persons
in the general population. Aerosol collection efficiencies as a
function of particle size and other appropriate parameters must
be reported for the instruments and placements used. Results
2-8
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must be given in terms of an annual average air concentration of
transuranium elements at the specified site.
2.5.3 FOOD SAMPLING
When foods are grown in contaminated soils, and the
ingestion pathway may represent a hazard to persons in a critical
segment of the population, representative samples should be
obtained for analysis and evaluation. Results should be reported
in terms of activity per unit of wet or dry weight, as
appropriate, for specific food products and for typical "market
basket" averages for an individual.
2.5.4 DRINKING WATER SAMPLING
When soil or sediment analyses indicate the potential for
the presence of transuranium element contamination in drinking
water supplies, periodic monitoring should be performed. Results
should be reported in terms of activity per unit volume for both
raw and finished drinking water.
2.5.5 SOIL SAMPLING
When soil sampling is chosen as either the principal or
ancillary method of complying with the criteria, statistically
valid procedures appropriate to the objective should be used to
characterize the entire area known or suspected to be
contaminated. When soil measurements are made to evaluate the
inhalation pathway, emphasis should be on obtaining
representative samples of surface soils subject to resuspension
and transport. In order to achieve a degree of uniformity in
application, it is useful to define specific procedures. it is
suggested that soil samples be taken to a depth of one centimeter
and include all soil particles less than two millimeters in size.
Several individual samples may be composited for a single
measurement. At some sampling points it may not be possible to
2-9
-------
collect samples to a depth of one centimeter e.g., very stony
soil or a thick grassy area. In such cases, other means must be
found to obtain representative samples.
For site-specific evaluations of resuspension parameters, it
may be necessary to determine the fraction of the total activity
associated with ranges of soil particle sizes (distribution
factor). Standard liquid or air sedimentation and separation
techniques may be used for this purpose. In general, soil
characteristics should be altered as little as possible in the
collection and preparation of the soil sample and care should be
taken to choose a method which does not cause the breaking up of
soil aggregates that were present when the sample was taken.
Radiochemical analysis techniques for the determination of
transuranium elements in soils are available and have been
published. These differ primarily in the method used to
solubilize the plutonium in the sample. Acid leaching, acid
dissolution, and fusion are most commonly used. The fusion
method is considered to be applicable to a wider variety of soils
than the other two methods.
Alternative collection, separation, and analysis methods may
be used but must be adequately justified in terms of technical
validity and relationship to results obtained by the recommended
method.
2.6 STATISTICAL CRITERIA
The characterization of any large area in a cost-effective
manner requires that the sample locations be carefully determined
in order to optimize the information obtained. Statistical
methods are available to permit design of sampling programs to
obtain results with the accuracy and precision desired*
2-10
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When planning a soil survey it is advisable to divide the
total area under investigation into units at the very beginning
of the survey rather than to collect samples more or less
haphazardly. Then samples taken to determine the acceptability
of the land by comparison of measured concentration levels to the
screening level may be collected from sampling units in
accordance with a sampling plan. If it is later decided that
more sampling is necessary, no change in the sampling plan is
necessary, and the location for additional samples will have
already been determined.
The number of samples to take within a sampling unit may be
estimated from the specific statistical approach used in the
sampling plan. An important factor affecting the number of
samples to be taken is the risk of making the wrong decision in
deciding whether a sampling unit is acceptable or requires
remedial action. To reduce the risk of making the wrong
decision, larger numbers of samples must be taken. Judgment must
be used to strike a balance between the desirability of making
the right decision and the difficulties and expense involved in
taking large numbers of samples. An additional factor affecting
the number of samples in the variability of the transuranium
element concentration within a sampling unit. I,f detailed
information is not available on the variability, a simple
approach is to take the same number of samples within each unit.
These could be taken on a grid system to ensure that all subareas
of the sampling unit are sampled. A disadvantage of this
approach is that if the variability is substantially different in
units, then the probability of detecting concentration levels
requiring remedial action will vary from unit to unit.
If estimates of variability are available from past studies,
these can be used to help determine the number of samples
required within each unit so that the probability of making a
correct decision will be the same for all units.
2-11
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After soil concentration levels have been determined, it
must be decided if the area under consideration complies with the
recommendations or whether further evaluation will be needed.
The statistical methodology that is used must be such that few
ass
;umptions regarding the form of the soil concentration
distribution will be necessary to ensure the validity of the
statistical test. The methods should also ensure reasonably low
bounds on the risk of making the wrong decision, and the
probability of not accepting an area which meets the criteria, or
of accepting one which does not, should be small. Acceptance
criteria which allow a maximum chance of error of 5-10% are
generally considered appropriate. 1
Considerable variation generally occurs in environmental
samples, taken even in closely adjacent locations. If one or more
samples from any unit exceed the air or soil concentration limits
corresponding to the recommendations," a decision must be made on
whether the sampling unit is acceptable. Such a decision is best
based on statistical tests which consider both the magnitude of
the deviations from the average arid the number of samples which
are involved. A number of statistical methods are available for
performing such an evaluation, and the choice must be made on the
basis of the data available and the results desired.
2-12
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3. ECONOMIC ANALYSIS OF REMEDIAL
3.1 INTRODUCTION
Dispersion of plutonium and other transuranium elements
in the environment may result in a number of different types of
problems, ranging from contamination of soils and other surfaces
to the contamination of structures and persons. The objectives
of remedial actions should be protection of persons and
limitation of long-term environmental contamination. Each
situation will need to be evaluated on a site-specific basis, and
different remedial action options chosen as applicable.
The costs of remedial actions are determined by a number
of factors: (1) the size of the contaminated area, (2) the type
of structures and/or surface(s) that are contaminated, (3) the
population density and distribution, (4) the type of terrain and
other ecological factors, the type of land use, and (5) the
associated level of contamination. In general, a contaminated
area may be divided into sectors, and appropriate cleanup actions
developed for each sector. The total cost for remedial actions
is the sum of costs for all sectors.
Two categories of situations must be addressed by a review
of economic impacts: (1) existing plutonium and other
transuranium element contamination at a few sites where the
contamination is stabilized and the distribution and soil
concentration are well characterized, and (2J possible future
releases (from operating facilities, nuclear weapons accidents,
etc), where neither the magnitude of release nor its location can
be known in advance of the occurrence.
An assessment of economic impacts of an incident of
environmental contamination requires two considerations:
3-1
-------
(1) development of general radiation protection criteria, and
(2) an optimization of costs and benefits for each appropriate
option in the range between the lower and upper bounds defined by
the radiation protection criteria.
3.2 COST ESTIMATION
Most of the transuranium elements are alpha emitters and
must be inhaled or ingested to cause harm. In general, only
contamination on or near the surface is of importance in the
transport to man. Remedial actions may require reduction of
surface contamination for both soils and structures. Food
may need to be embargoed and alternative supplies provided.
The local residents may have to be relocated and temporary
or permanent access restrictions imposed. The monetary or non-
monetary costs of these detriments must be evaluated and balanced
against the dose reduction achieved by different counter-measures.
There are two general techniques for lowering the level of
contamination in surface soils: (1) plowing, Which leaves the
contamination in place, but lowers the concentration levels in
the topmost layer of soil, or (2) removal of all surface soils to
a defined depth and transportation to another location for final
disposal. When the surface soils are removed, they may be stored
on-site, or off-site in State or Federal repositories. On-site
storage is an option that could be used Under certain
circumstances where a part of the site can be reserved for
disposal, and defers or avoids the extremely high costs of off-
site storage. The costs of these alternatives must be evaluated
on a site-specific basis and decisions made on'the=basis of both
feasibility and other factors. I
i% . ,-'n
The threshold of remedial action for residual soil
contamination may be established by a derived soil" "screening
level", which gives a conservative approach to'a corresponding
dose rate to the critical segment of the exposed population.
3-2
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Remedial action would generally not be considered for sites with
soil contamination below this level. Cost-minimization is the
appropriate criterion to identify the preferred set of remedial
actions that will bring a site into compliance. The total cost
of each possible set of options that can attain compliance should
be evaluated to determine the least-cost method.. Environmental
costs and other nonmonetary costs not quantifiable in monetary
terms should, if possible, be considered in the evaluation.
Whenever feasible, it is desirable that costs be quantified
monetarily, but if this is not feasible, they should be ,
quantified in nonmonetary terms/Narrative descriptions should
be used when no quantification is possible. A difficulty is that
different combinations of decontamination procedures are expected
to have somewhat different mixes of monetarily quantifiable,
nonmonetarily quantifiable, and nonquantifiable costs. -
Extensive data on available techniques and decontamination
costs for various types of structural surfaces have been
compiled. These serve as the basis for complex optimization
computer programs which will aid in developing a rational basis
for decisions on appropriate remedial actions. , Optimization
procedures must be carried out separately for each specified
countermeasure, or combination of countermeasures, and may result
in different dose constraints in each case.
Estimated costs of remedial actions were discussed in
general terms in Chapter 4 of the "Response to Comments'V document
published by EPA. A detailed evaluation of costs entitled
"Department of Energy Comments on Decontamination
Costs" is reproduced as an annex to that publication. However,
these are appropriate only for ah assessment of cleanup of
contaminated soils and do not include the added costs for
contaminated structures, relocation, or alternative food
supplies. In general, costs (in 1988 dollars) for most simple
soil cleanup methods would range from less than $1,000 to $20,000
per acre if relocation and disposal of soils is not required.
3-3
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Disposal in a near-surface regional facility is estimated to cost
up to $190,000 per acre, and disposal in a geological repository
$500,000 or more per acre. The added costs of cleanup of
buildings and disposal of residual other materials must be added
to obtain the total costs.
A schematic comparison of remedial action methods and costs
appropriate to a range of soil contamination levels is shown
in Table 3-1, and a summary of various applicable cleanup
measures is shown in Table 3-2.
The Department of Energy (DOE) analyzed the cumulative costs
(in 1977 dollars) of remedial action at three real
* o
(but unidentified) sites. Two area sizes of 1 km and
10 km2 were used at each site for a total of six sets of
costs (Table 3-3). These sites are devoted to a number of uses,
including crops, orchards, pasture, woodlots, forests, shoreline,
and residential and commercial areas. The areas analyzed are so
large that the derived decontamination costs may not represent
realistic estimates of the probable cost of remedial actions.
A comparable analysis in 1988 dollars may range up to double the
above.
The Department of Energy analysis is shown here primarily to
illustrate the effect of different assumptions on the cost
estimates. Comparison of the four sets of remedial actions shows
that for similar treatment strategies there is little
difference in the average costs per unit area of treatment for
the six sites. Off-site disposal at Federal repositories would
account for 82 to 98% of the costs for remedial actions at the
six sites when earth removal is the treatment strategy. However,
it should be noted that these comparisons are limited to the
costs of soil cleanup which may reflect only a portion of the
total costs. . '
3-4
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TABLE 3-1
POSSIBLE REMEDIAL ACTION METHODS AND COSTS
FOR A RANGE OF CONTAMINATION LEVELS
Maximum Soil
Contamination Level
(uCi/m )
0.1
1
10
100
1000
10,000
Maximum
Annual Risk
to Individual
-6
10 /yr
10 /yr
-4
10 /yr
10 /yr
10 /yr
10 /yr
Possible Hethod(s)
Stabilization Restoration Cleanup Disposal
x x Plowing
x x Scaping/ on-site
Plowing
x x Soil Removal on-site
x x Soil Removal/ on-site and/or
Decontamination non-retrievable
x x soil removal container storage
x x soil removal geological repository
(high-level waste)
Estimated Costs
($/acre)
$1,600 (range S900-S4800)
$3,600 (range S1600-S6800)
$6,000 (range $2200 -$8800)
.
$25,000 (range $10,000-$100,000)
$100,000 (range $80. 000 -$200,
$500,000 (range S150,000-S600
000)
,000)
CO
I
01
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TABLE 3-2
IN-PIACE OPTIONS
REMOVAL/ON-SriE DISPOSAL
REMOVAL/OFF-SITE DISPOSAL
STABHJZATION
SITE ACTIONS
REM3VAL
OJ
I
PACKAGING
TRANSPORTATION
DISPOSAL r
RESTORATION
ESTIMATED COSTS
Optional
Plowing (shallow)
(deep)
Soil Cover (4-12")
none
none.
none
none,
Fertilizer/Seeding
Shrubs, etc
Optional
Surface Removal
(Scraping or Vacuuming)
Soil
Grass/Crops, etc
Trees
Selected Materials
Decontamination Materials
Optional
On-Site Moving
On-Site Burial
Topsoil Replacement
Fertilizer/Seeding
Shrubs, etc
$10-50I$/acre
Optional
Surface Removal
(Scraping or Vacuuming)
Soil
Grass, Crops, etc
Trees
Structures, etc
Decontamination Materials
Separation/Classification
Transfer to Special Containers
Storage "
Long-Distance Hauling
(Base Cost + Distance)
Disposal at Designated Site(s)
Topsoil Replacement
Fertilizer/Seeding
Shrubs, Trees, etc
$500K-lM/acre
-------
TABLE 3-3
DEPARTMENT OF ENERGY ESTIMATES
OF REMEDIAL COSTS PER UNIT AREA FOR
ASSUMED REFERENCE SITES
Area
.0 km':
Reference Site One
Reference Site Two
Reference Site Three
10.0 km':
Reference Site One
Reference Site Two
Reference Site Three
Treatment
ER
SR
DP
SP
ER
SR
ER
SR
OP
SP
ER
SR
DP
SP
ER
SR
ER
SR
DP
SP
(a)
". Total Cost
($ Million 1977)
115.6
95.2
12.9
11.4
93.3
133.5
121.2
95.4
21.2
19.5
1127.0
1062.
159
145.2
1103.1
1080.7
1213.0
942.7
144.8
128.5
Cost/km2
($ Million 1977)
115.6
95.2
12.9
11.4
93.3
133.5
121.2
95.4
21.2
19.5
112.7
106.2
16.0
14.5
110.3
108.1
121.3
94.3
14.5
12.9
Cost/acre
($ Thousand 1977)
468
385
52
46
378
540
490
386
86
79
456
430
65
59
4416
437
491
382
59
52
* 15 * cfth removal to dePth of 5 o»; DP = Deep (1-m) plowing; SP - Shallow (25-cm) plowing;
SR « Site restriction, Including construction of a blobarrler.
Average Cost
Average Cost
Average Cost
Average Cost
Eartlv Removal = $45A,000/acre
Site Restriction = $427,000/acre
Shallow Plowing = $59,000/acre
Deep Plowing = $66,000/ acre
Source: Enclosure II, Department of Energy Comments on
Decontamination Costs Discussed in the EPA Proposed Guidance
on Dose Limits for Persons Exposed to Transuranium Elements
in the General Environment, Table 13
3-7
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3.3 COST OF IMPLEMENTATION
3.3.1 EXISTING SITES OF CONTAMINATION
A review of costs of implementation for existing sites of
contamination is most useful when viewed in terms of a specific
objective. The following discussion is intended to supply a
perspective of applying recommendations to these sites in terms
of a soil "screening level" which corresponds to an inhalation
dose to an individual not to exceed a committed effective dose
equivalent of 10 millirem. Alternative objectives in terms of
different dose or soil contamination levels might be chosen.
A brief description is given below for each site (Figures 1-4),
indicating the general contamination pattern and population
distribution.
There are four Federal sites in the United States that
presently have transuranium element contamination above ambient
levels beyond their boundaries. These include the Rocky Flats
Plant in Jefferson County, Colorado, Mound Laboratory in
Miamisburg, Ohio, Nevada Test Site in southern Nevada, and
Trinity Test Site near Alamogordo, New Mexico. The majority of
all contamination released is confined within areas under the
direct control of the Federal government, which imposes
restrictions on the access and use of these areas. Relatively
small amounts of transuranium element contamination exist outside
the boundaries of these sites on lands generally accessible to
the public.
The Rocky Flats Plant (RFP) produces components for nuclear
weapons. There have been two fires which released some plutonium
to the environment. In addition, a number of barrels containing
cutting oil and stored in an open unprotected area slowly
corroded and some of the contents eventually leaked and were
dispersed. On the basis of soil concentration data, all
off-site areas at the Rocky Flats Plant probably would result in
maximum dose rates well below current recommendations. However,
3-8
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TABLE 3-4
Comparison of Areas Outside the Boundaries of Existing Sites
Above Various Soil Concentration Levels ,
Relative to the Screening Level*
(in square miles)
Site
Rocky Flats
NTS
Trinity
Mound
2
0.02 uCi/m
1.6
165
300
0.01
Area above:
2
0.2 uCi/m
0
o
small
0.01
2.0 uCi/m2
0
0
0
0.01
*Screening level = 0.2 uCi/m transuranium elements in top 1 cm of soil
3-9
-------
ROCKY FLATS
PLUTONIUM239 CONTOURS mCi/krri2
FIGURE 3-1
3-10
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confirmatory evaluations may be needed to determine the actual
dose rates to the general population, particularly in the most
highly contaminated areas east of the plant. The area is
sparsely inhabited and there are few people living in the
particular area of concern. The off-site area contaminated to a
, . - o
level one-tenth the "screening level" comprises about 1.6 mi ,
with a current population of less than 600. No uncontrolled
areas are contaminated to a level greater than ten times the
"screening level". All local water supplies are expected to
yield ingestion dose rates well below the dose rate
recommendations.
Mound Laboratory is a major research and development site
for fabrication of radioisotopic heat sources used for space and
terrestrial applications. In 1969 ,a pipeline transporting a
Pu-238 waste solution ruptured, spill ing ..the contaminated
solution. The plutonium migrated slowly into nearby waterways.
The majority of the plutonium is now sorbed and fixed on the
sediments of the North and South Canals. . Maximum concentrations
are to 1 to 3 ,ft. below, the s.ediment surface and currently do not
pose any radiation- problem, since very little of the plutonium is
in soluble form and the canal water is not used for drinking
purposes. Banks immediately adjacent to the canal and overflow
creek subject to occasional flooding have maximum plutonium
concentrations exceeding the "screening level." The amount of
land in question is about 6.01 mi2, and there are no people living
on this land. There are no, areas, with transuranium element
contamination greater than ten times the "screening level." The
nature of the contaminating event limited the contamination to
the waterways and adj acent banks. No immediate cleanup is
indicated for this site, but continued surveillance will be
required.
'''". ;...'*
The Nevada Test Site (NTS) covers an area of 1400 mi2 with
an additional exclusion zone extending 16 to 48 miles. Major
programs at NTS have included nuclear weapons tests, testing for
3 - 11
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MOUND LABORATORY
PRELIMINARY ESTIMATE OF PLUTONIUM 238 AIRBORNE DEPOSITION
(m Ci/km2)
FIGURE 3-2
3-12
-------
«1.3±0.4
W I
- /_ .IDAHO
~--J
1.0*0.2 'o
/ z
I*1
2.2*1.0
9 ±0.2
o.0.9±0.2
oQ.9 iO.l
75 ±0.4
5*0.3
0.7±0.4 <
UTAH
1.1*0.2 |
l.U0.1o° I
Ofl
'8
8
ARIZONA
X
UJ
S
,50
I
100
200
Kilometers
CUMULATIVE NTS DEPOSIT OF Pu-239,240
(mCi per km2)
FIGURE 3-3
3 - 13
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peaceful uses of nuclear explosives, and nuclear reactor engine
development. These activities have resulted in plutonium
contamination in certain areas of the test site and exclusion
areas and slight contamination (above background levels) outside
the exclusion areas. There are no known uncontrolled areas which
have transuranium element contamination exceeding the " screening
level." Land contaminated to one-tenth the "screening level" or
less covers approximately 165 mi2 with a resident population of
less than 240 people.
The Trinity Test Site was the location of the first nuclear
explosion. No other nuclear explosion tests were performed at
Trinity. A site survey was performed by EPA during 1973-74 to
determine residual plutonium concentration contours. The highest
plutonium contamination levels in uncontrolled areas ranged from
0.2 to 0.9 uCi/m2. The amount of land contaminated to a level
one-tenth the "screening level" covers less than 300 mi2, with
fewer than 500 people living in the area in small towns, ranches,
and farms. On the basis of the limited available data, no major
remedial actions would appear to be indicated for this site.
The above describes the method of evaluating the feasibility
and cost of applying a reference recommendation to existing sites
of contamination presently involving plutonium and other
transuranium elements in the United States. On the basis of the
available information, it can reasonably be expected that
implementation of recommendations at a reference level of a
committed effective dose equivalent of the order of 10 millirem
would require only some confirmatory evaluations and probably no
off-site cleanup actions. If that is the case, less restrictive
recommendations would not change the situation. Monitoring
activities are already in place at all these sites, and no
appreciable augmentation of efforts should be anticipated.
Therefore, application of such recommendation to the existing
sites of transuranium element contamination should be possible at
minimum cost.
3 - 14
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3.4.2 FUTURE INCIDENTS
The remedial measures available for case of future incidents
of contamination include stabilization, shallow or deep plowing,
and soil removal with disposal in on-site or off-site
repositories. In urban or industrial areas, houses, buildings,
streets, and sidewalks may require decontamination. Prbtection
of ground and/or surface water may be necessary. Temporary
evacuation of the population may also be required. ,
The location, frequency, and magnitude of possible releases
to the environment of transuranium elements that may occur in the
future is indeterminate and cannot be predicted. Recommendations
for cleanup must allow for sufficient flexibility for evaluation
,of feasible alternatives which.would assure adequate long-rterm
protection of the public health and safety. A detailed
evaluation of possible scenarios for remedial actions would be
both speculative and beyond the? scope of this discussion.
There are few precedents for such prospective actions, there
are literally an infinite number of possible scenarios, and a
generalized benefit-cost analysis is not very useful. Therefore,
criteria which recognize the range of existing radiation
protection recommendations and implement these in a graduated
system of levels of residual risk balanced by compensating
protective actions to keep doses to people "as-loW-as-reasonably-
achievable" may,be most appropriate. This would result in a
system where increased risks are compensated for by increasingly
stringent occupancy restrictions, environmental, monitoring and/or
medical surveillance. Optimization would be required for each
site and the implementing agency would have to consider ;a range
of options within the constraints of the recommendations.
3-15
-------
TRINITY SITE
1973-1974 PLUTONIUM
SOIL SAMPLING RESULTS
(nCi/m2)
FIGURE 3-4
3-16
-------
4. INCIDENTS OF NEW CONTAMINATION
Incidents of new contamination require evaluation in terms
of minimizing the impacts on potentially exposed persons and of
restoration of the environment to as near normal as practicable.
The considerations required include the development and
implementation of emergency response criteria, the stabilization
of the contamination as rapidly and effectively as possible, and
the cleanup and restoration of the site.
v - '
Remedial action for newly created 'contamination must
consider both the short-term and long-range objectives. Initial
priority must be given to protective actions designed to minimize
the impact on potentially exposed individuals and to localize
contamination to the maximum extent practicable. Later actions
can then be concerned with decontamination and restoration of the
affected areas to minimize the total environmental impacts. Such
a contamination incident requires consideration of two
factors - the emergency response protective action criteria, and
the guidance applicable to the.maximum permissible residual
concentration limit for the specific site.
An accident can be divided into three sequential
events in terms of time and related actions (Figure 4-1).
The initial phase is the period,,during the emergency,' the second
is the interim period when preventive actions are appropriate,
arid the final phase is the extended time period when the
situation has stabilized and remedial actions commenced.
The initial phase can be considered ,as a one-time event and
protective action criteria formulated on that basis.
Newly created and deposited contamination of the environment
by transuranium elements may represent a potential danger to the
general public that must be dealt with as promptly as possible.
The resuspension rate for newly deposited contamination has been
4 -'. 1-
-------
PLANNING
o Develop Emergency Plan
o State-Local Review
o Preparation - Equipment
Training
Teetlng
| MCIDEHT
EMERGENCY
0 Aaieaa Emergency Statua
o Preliminary Accident Evaluation
o Activate Emergency Responae Plan
PROTECTIVE ACTIONS
o Start Field Monitoring -
Update Doae Eatinatea
o Implement Protective Actlona
REMEDIAL ACTIONS
o Evaluate Long-Ten Doaea and
Public Health Impact!
o Determine Acceptable Re'aldual Contamination Level
o Develop Remedial Action Plan -
Consider Cleanup Options and Alternatives
o Perform Remedial Actlona
o Certify Compliance
I
to
Diagram of Actions During the Emergency Response,
Protective Action., and Remedial Action Phases of an
Accidental Release of Radioactive Materials from a Facility
FIGURE 4-1
-------
estimated to be higher by a factor of 1000 or more than for aged
sources and therefore represents a proportionately greater
hazard. The immediate objectives should, therefore, be to reduce
the mobility of the new source by stabilization or removal and to
temporarily evacuate those persons who might be subject to
unacceptably high doses. Decisions on suitable protective
actions must be made by responsible local officials. The primary
consideration in such instances must be a minimization of the
health and safety impacts on exposed members of the general
population.
Analyses indicate that when a contaminating event occurs,
most of the radiation dose associated with the event is committed
within a short time (a period of a few weeks or months) -unless
protective measures are taken. This is becauserparticulates from
the initial release may be inhaled directly and the resuspension
factor for newly deposited material is much higher before
weathering and movement into soil surfaces occurs.
Intervention criteria are based on a projection of the
ultimate consequence of the event and a judgment of how certain
actions could reduce the impact. Initial remedial actions will,
to some extent, depend on the information available and on the
judgment of knowledgeable individuals. Initiation of
counter-measures does not imply an acceptable dose, but rather is
ah ex-post-facto effort to minimize risk from an event in
progress or from one that has already occurred.
Development of intervention criteria requires advance
planning, so that emergency response plans can be implemented in
a minimum period of time. Therefore, detailed emergency response
plans should be prepared for all facilities, carriers, or
organizations which handle plutonium in quantities sufficiently
large so that a fractional or total release could present a
hazard to man. Criteria should be developed for their use, local
authorities should be involved in their development and
4 - 3
-------
implementation, and possible^alternatives should be considered.
The underlying assumptions of any protective action plan is that
some real or potential threshold risk must be exceeded before the
plan is implemented. Therefore, a numerical value must be
proposed as the limiting radiation dose to which people may be
exposed before emergency actions are warranted.
For contaminating incidents involving plutonium or other
transuranium nuclides, primary considerations in the development
of intervention criteria should be given to airborne
radioactivity resulting both from the initial plume and from
material resuspended from the ground. The total integrated dose
commitment from an environmental source is the summation of the
exposures resulting from:
a. the initial cloud and its deposition,
b. the inhalation of resuspended material, where the
resuspension factor decreases with time,
c. all other pathways, including food and drinking water.
Intervention criteria should provide a basis for the
development of site-specific recovery criteria following an
accidental release of transuranium elements to the general
environment. Such criteria are necessary for the long-term
protection of the public health. The recovery criteria must focus
on minimizing the cumulative risks of prolonged exposure by persons
in a critical group of the population, and have the objective of
restoring an area for unrestricted occupancy.
4-4
-------
5. "SCREENING LEVEL" FOR STABILIZED CONTAMINATION
AND AN "ACTION LEVEL" FOR NEW SOIL CONTAMINATION
A general method for deriving a "screening level" for
stabilized transuranium element contamination in soils and an
"action level" for newly deposited contamination is presented,
based on data from existing sites, current dosimetry, and models
for environmental transport. These are intended to provide an
adequate margin of safety below the designated radiation
protection guidance for persons in the general population.
5.1 "SCREENING LEVEL" FOR STABILIZED CONTAMINATION
5.1.1 APPLICATION
A "screening level" can be defined as a conservative method
of relating a dose limit for a critical group to a corresponding
soil contamination level. it is intended primarily to define
areas where residual contamination would lead to doses which are
generally accepted to be of little concern and to allow
unrestricted occupancy of an area. A method for deriving such a
screening level for plutonium and other transuranium element
concentration in soil is presented which is intended to provide a
basis for minimizing both the area around a contaminated site
which must be monitored and the number of soil samples which must
be collected and analyzed. When the transuranium activity in.
soil is at or below the concentration derived by this method, it
is highly unlikely that a given exposure level would be exceeded.
Such a screening level is not intended to be interpreted as a
derived intervention level or as a soil cleanup standard to which
all sites of transuranium contamination must be decontaminated;
instead, when properly applied, it would identify land areas
where no additional monitoring is required. A screening level is
5-1
-------
not a substitute for site-specific information, but may be useful
in its absence.
The method for deriving a screening level was developed by
careful consideration of all currently contaminated sites,
placing particular emphasis on areas for which enough site-
specific data are available for such factors as particle size and
soil activity distributions. After examining these data, a
hypothetical site was defined with a combination of parameters
chosen to be conservative, i.e., .to produce an acceptable level
of transuranium activity more restrictive than that which would
be derived for any of the existing sites. This conservative
approach has been taken due to the uncertainties inherent in any
calculational model, and because of the limited experience with
contamination by the transuranium elements. Sites of future
contamination are also likely to have characteristics similar to
the existing sites.
5'> - , '
Of the various models that have been suggested for relating
soil contamination levels to airborne concentrations, the mass
loading approach appears best suited for use in deriving a soil
screening level. The mass loading approach has been shown to
provide a good capability in predicting air concentrations on an
annual basis at several sites with existing soil contamination
and, since the screening level is intended as a generic value
with application at all sites, it is generally not appropriate to
use one of the more sophisticated resuspension models requiring
detailed site-specific parameters such as wind speed, atmospheric
stability class, soil erodibility index, etc. In applying the
mass loading model to calculating a soil screening level, some
modifications have been made, in an effort to overcome
some of the shortcomings which are fundamental to the approach*
5-2
-------
r5.1.2 ENRICHMENT FACTOR
In an effort to take into consideration the non-uniform
distribution of activity with soil particle size as well as the
non-runiform resuspension of particle sizes, an "enrichment
factor" has been derived which is included in the mass loading
calculation. Potential exposure due to contaminated soil depends
largely on the amount of activity associated with particles in
the respirable size range (generally 10 /urn). It has been
.suggested;by several investigators that sampling of only those
.particles in a soil sample which are within the inhalable size
range :would give :the best measure of risk to the public health.
-However, .the weight fraction, of particles in the less than 10 jum
range is small in most soils, and sampling, separation, and
analysis techniques are correspondingly more difficult and
inaccurate. There is.also considerable evidence that some of the
larger particles really consist of aggregates and are relatively
easily broken down into smaller ones, so that an instantaneous
measurement of a.single- size range may not give a good picture of
long-term trends. Another important objection to limited
sampling is that larger particle sizes may make a substantial
contribution to other possible pathways (e.g., ingestibn), and
hence should be measured. ,Tq evaluate the potential hazard of
*the inhalable fraction.of soils, while retaining the advantages
and conveniences of analyzing the entire soil sample/ the mass
loading approach has been modified by use of an "enrichment
.factor". , The proposed method weights the fraction of the
activity contained within the respirable range in terms of its
deviation^from the activity to mass ratio for the entire sample
and, at the same time, addresses- the problem of the nonuniform
resuspension of particle sizes mentioned in the previous section.
The inhalable fraction of the soil Is weighted by considering the
relative distribution of activity and soil mass as a function of
particle size for representative samples of soil. To accomplish
this, the sample of contaminated soil is segregated into size
increments, and the activity and mass contained within each size
-------
increment is determined. The factor gj is then defined as the
ratio of the fraction of the total activity contained within a
size increment i to the fraction of the total mass contained
within that increment. A value greater than 1 for gj implies an
enrichment of activity in relation to mass within that
incremental fraction, while a value less than 1 indicates a
dilution of the activity with respect to mass relative to the
average for the sample.
In order to evaluate the inhalation of resuspended
plutonium, the nonuniform resuspension of particle sizes in each
size increment of the surface soil must also be considered.
Accordingly, the mass loading can be derived as a function of the
measured particle size spectrum. The fraction of the airborne
mass contained within each size increment is calculated and
designated as fj. The factors of fj and gj can then be
incorporated into the mass loading formulation as follows:
Air Activityj = Air Mass Loading x f j x Soil Activity x gj
Summation over all the size increments results in, the total air
concentration: ,t
Air Activity = Air Mass Loading x Soil Activity x
The term Sfjgj gives the contribution of the plutonium from
each soil size fraction to the total resuspended material,
thereby taking into account both the nonuniform resuspension of
particle sizes as well as the nonhomogeneous distribution of
activity. The summation of fjgj will be referred to as the
"enrichment factor", where fj accounts for the distribution of
airborne mass as a function of particle size and gj accounts for
the variability of both soil activity and soil mass as a function
of particle size.
5-4
-------
TABLE 5-1
U1
Ul
SAMPLE
RF 1A
RF IB
RF 1C
RF 2A
SIZE INCREMENT
v.' ',, -' ' "
105-2000 .
10-105
; <10
105-2000
10-105
:<10
105-2000
10-105
<10
105-2000
10-105
<10
.WEIGHT
FRACTION
.62
.18
.20
.63
.17
.20
.64
.16
.20
.46
.43
.20
ACnVTTY
FRACTION
.07
.40
.53
.39
.06
.55
.43
.07
. .49
.13
.37
.50
g. f
0.12
2.21 .7
2.65 .3
0.63 ;
0.34 .7
2.74 .3
0.68 -
0.46 .7
2.47 .3
0.28
1.10 .7
2.48 .3
f-
2.34
1**
. 1.06
1.06
^.51
average = 1.49
-------
30 20
50
ANNUAL MEAN MASS CONCENTRATIONS :(jug/m3) OF AIRBORNE
PARTICLES FROM NON-URBAN STATIONS OF THE U.S. NATIONAL
AIR SAMPLING NETWORK. 1964 - 1965
FIGURE 5-1
5-6
-------
10
20 30 40 50 60 70 80
100
D
I
O
>
10 =5
>
3)
cc
O
O
I-
m
90
95 9(8 99
99.8
PERCENT OF MASS ASSOCIATED WITH PARTICLES OF-LESS THAN EQUIVALENT DIAMETER
PARTICLE SIZE DISTRIBUTION OF RESUSPENDED SOIL
99.99
FIGURE 5-2
5-7
-------
5.1.3 CORRECTION FOR AREA SIZE
Use of the mass loading approach implies that the air
concentration is at equilibrium with the ground surface, i.e., a
steady state situation exists in which the amount of material
coming up from the surface is balanced by the amount of material
depositing back onto the surface. In the strictest sense this
limit can only be achieved for source areas approaching infinite
dimensions. For source areas of finite dimensions, a fraction of
the airborne mass loading can be derived from an uncontaminated
area upwind which contributes no radioactive dust to the
atmosphere. The smaller the size of the contaminated area, the
less it will contribute to the mass loading level and the greater
the uncertainties involved in applying the mass loading model.
Calculations have shown that, for a contaminated area which
extends over 50 meters in one direction, the air concentration
would be approximately a factor of one hundred smaller than from
an area 5000 meters in length (based upon certain assumptions
regarding meteorological conditions). Therefore, a correction
for area size becomes necessary when applying the mass loading
approach to small areas of contamination. In deriving the
screening level for soil, the area contaminated has been assumed
to be sufficiently large that a correction for area size is not
necessary. It should be recognized that this is a conservative
assumption and that areas of actual contamination may require a
correction for area size; however, since one cannot predict a
priori the extent of a contamination incident nor the prevalent
meteorology, the conservative case has been assumed.
5-8
-------
5.1.4 CALCULATION OF A SCREENING LEVEL ' *
FOR STABILIZED CONTAMINATION
The following assumptions were made in deriving the
screening level: 1) the mass loading for the hypothetical site
was taken to be 100 ng/m3 and to have a particle size
distribution similar to that reported for resuspended dust,
2) the soil is enriched with activity in the respirable size
range relative to the soil as a whole, and 3) the contamination
is widely dispersed and a correction for area size is not
applied.
An annual average mass loading of 100 Mg/m3 is higher than
the annual average for any non-urban site reported by the
National Air Sampling Network (NASN) as shown in Figure 5-1 and
is representative of an assumed very high resuspension rate for
the hypothetical site. The particle size distribution of the
resuspended soil, for use in calculating the screening level,
is from data obtained from fields undergoing wind erosion in
Colorado and Kansas and adapted as Figure 5-2. .Comparison with
other studies substantiates the applicability of these results
to other areas. For example, it has been shown that 30% of
the airborne mass is below 10 jum around the Hanford (WA) site
and 33% of the measured airborne mass was below 10 /im
(mass loading = 100 Aig/m3) in the area around Denver (CO).
Soil particle size and activity distribution data are
available for five sites with plutonium contamination: , Mound
Laboratory (OH), Oak Ridge National Laboratory (TN) , the Nevada
Test Site (NV), the Trinity Site (NM) and the Rocky Flats Plant
(CO). Of these sites, the greatest enrichment of activity within
the fine particle size range is found in samples from the Rocky
Flats area. For this reason, the Rocky Flats soil distribution
(see Table 5-1) was used in calculating the screening level.
Since the size of the contaminated area varies greatly from site
to site, and because of the inability to predict the extent of
5-9
-------
future contaminated areas, a reduction for area size is not
incorporated into the model for a generally applicable screening
level.
The following calculation applies the above general method
to the derivation of a model soil contamination screening level.
For an objective of limiting the annual dose rate to less than
ten percent of the recommendations of national and international
radiation protection organizations for a lifetime risk of <10"4,
the corresponding reference committed effective dose equivalent
to the critical group would be 4 mrem/year (He = 0.04 mSv/yr) .
The derived screening level can be scaled to any alternative
limit. For an assumption of a Class Y compound and inhalation
of plutonium as the critical pathway to humans, the 4 mrem/year
(0.04 mSv/yr) reference dose rate can be related to an air
concentration of 2.0xlO"15 Ci/m3 of plutonium-239 with an assumed
activity median aerodynamic diameter of 1 /zm. The corresponding
screening level is: ; ,
Screening Level =
Air Concentration
Mass Loading x Zf\g-, x C.F.
2 fCi/m3
Screening Level =
100 Mg/m3 x 1.5 x 6.6X10'11
Screening Level = 0.2 /iCi/m2 for He < 10 mrem
. = 8.0 KBq/m2 for He < 0.1 mSv
(C.F. is the units correction factor and is equal to 6.6xlO"11
when a soil density of 1.5 g/cm3 is assumed for a 1 cm depth dry
soil sample. The soil sample should be limited to particles .less
than 1 mm diameter)
The resuspension factor for this hypothetical site is:
Resuspension Factor =
2.0xlO"15 Ci/m3
2. OxlO'7 Ci/m2
= l.OxlO'8 m'1
5-10
-------
5.2 "ACTION LEVEL" FOR NEW PLUTONIUM CONTAMINATION IN SOILS
The protection of persons immediately following an accident
requires implementation of actions which limit the dose rate to
the critical segment of the population. Intervention criteria
generally recommend that the dose be limited to l to 5 rem
(10 to 50 msv) during the initial post-accident phase. This
can be achieved by limiting a combination of the exposure rate
and occupancy time.
The principal difference between the initial phase and the
long-term phase is that the newly deposited contamination is
generally much more mobile and more easily resuspended. This
would be even more enhanced by the movement of people and/gr
equipment in the contaminated zone. Resuspension also varies
with the type and smoothness of the surface, wind velocity, and
other factors. It has been estimated that resuspension from
newly deposited materials may be as high as lO^/m, or a factor of
10,000 greater than for stabilized contamination.
It is possible to derive a soil concentration level for
newly deposited transuranium element contamination which, to a
first approximation, would give an indication of whether a dose
of l rem to the exposed population will be exceeded (the current
recommendation for maximum occupational exposure is an average of
2 rem/ year (20 mSv/yr) . For an exposure averaged over one year,
the dose rate to the pulmonary lung is about one-third the
equilibrium value. The corresponding relationship between the
ambient air concentration and dose rate is given approximately by
3x40 fCi/m = 100 mrem first year He, or
1.2 pci/m3 = l rem
5 - 11
-------
For an objective of limiting the dose from new contamination
to one rem for a continuing exposure of one year, the derived
"Action Level" with the assumption of a constant resuspension
factor of R = lO^/m would be:
Action Level = 0.1
< 1 rem (for one year exposure),
or
Action Level = 4.0 KBq/m2 < 10 mSv
The above derivation is generally conservative and is
derived for the current public health protection objectives for
persons in the general population.' The numerical value of the
"Action Level" depends on the specific dose limit, the assumed
reduction factor for various protective actions, and on site-
specific environmental factors. A smaller resuspension factor
would allow for 'a greater ambient level; The derived "Action
Level" is.most useful for short time periods immediately after
initial deposition. An assumed exponential decrease of the
resuspension factor with a one-^year half-life to an asymptotic
value of lO^/m represents a reasonably conservative approximation
for longer time periods. The dose reduction factor for the first
year is approximately 0.65, and the above calculation becomes
progressively more conservative for increasing time increments
after initial deposition.
The "Action Level" has been derived for an exposure of one
full year, and represents only a:single value in a continuum of
functions. Smaller time increments lead to proportionally
smaller doses. Alternatively, a larger soil concentration level
may be allowed for a shorter exposure time. For example, for
three days the ratio is' 72 hours/8760 hours, or about 1/100. ,:
Therefore, the absorbed dose would be decreased by a factor of
100 for the given soil concentration or, conversely, a dose of
one rem would be received in three days for a soil concentration
100 times greater than the above. The variations in radiation
protection criteria - can be related by the matrix shown in-,
Figure 5-3; :
5-12
-------
Ui
I
H
U)
TIME
8 hrs 3 days 1 mo 1 year
o
2
E
|
O ~
0)
10 1
,u
io-1
10~2
1
0.1
0.01
0.001
10
1
0.1
0.01
100
10
1
0.1
1,000
100
10
1
DOSE (In REN!)
'ACTION LEVELS" FOR PLUTONIUM-239
FIGURE 5-3
-------
an
It should be noted that the above derivation assumes
allowable dose rate limit of 1 rem for the first year
following a release and continuing occupancy, and must be
modified in accord with both the appropriate radiation
protection requirements and other factors. One can conclude
that soil concentration levels of the order of 0.1 to 1
(3-30 KBq/m2) for newly deposited contamination, or the
of detection for the FIDLER probe, represent a proper level for
concern and initiation of protective actions and temporary access
restrictions. A realistic assessment would be expected to lead
to less restrictive conclusions. As such, a derived "action
level" can only give preliminary guidance which must be evaluated
by competent personnel on a site-specific basis.
/iCi/m
limit
5-14
-------
6. RADIOLOGICAL ASSESSMENT - ROCKY FLATS PLANT
[Reprinted With Minor Changes from Response to Comments -
EPA 520/4-78-010]
6.1 INTRODUCTION
This chapter presents an analysis of the potential hazards
to individuals in the general population as a result of
transuranium element contamination in the environs of the USDOE
Rocky Flats Plant. It is intended primarily to serve as an
illustrative example of how to carry out a comprehensive
environmental assessment, and does not represent an evaluation
of potential health hazards. Analysis is limited to data for the
period 1970-77, when public concern about possible health hazards
was greatest. The various pathways by which exposures might
occur under present and projected land usages are examined and
interpreted in terms of ambient levels of contamination.
6.2 INHALATION PATHWAY
6.2.1 AMBIENT AIR CONCENTRATIONS
Under normal operating conditions, minute quantities of
Plutonium and other radionuclides have been released to the
atmosphere from the Rocky Flats Plant. These releases originated
from the plant's ventilation and filtration system. Measurements
of airborne radioactivity in the vicinity of Rocky Flats and the
neighboring communities are made on a continuous basis. in
addition to monitoring the effluent air from production and
research facilities, the Rocky Flats facility maintains a system
of high-volume ambient air samplers within the plant boundary, at
off-site locations in the immediate vicinity of the plant, and in
several communities nearby. Altogether the system comprises
21 air samplers operating continuously within and on the
perimeter of the Rocky Flats security area, and another
6-1
-------
25 samplers located at various distances and directions
from the plant. The data from this network are reported on a
monthly basis to the Rocky Flats Area Office of the Department of
Energy (DOE), the Division of Occupational and Radiological
Health of the Colorado Department of Health, the Denver Regional
Office of the EPA, the Health Departments of Boulder and
Jefferson Counties, and city officials in several communities
near the plant.
In addition to the surveillance network maintained by the
Rocky Flats Plant, the Health and Safety Laboratory (HASL) of
DOE conducted a program of continuous air sampling for plutonium
at the Plant since June 1970 in response to the discovery of
elevated levels of plutonium found in soils at location which
were then off-site. The HASL network consisted of four sampling
locations (Figure 6-1), three of which were downwind (east) from
the original location of the oil drum storage site and the fourth
air sampler was located off-site and upwind from the Rocky Flats
Plant. Air concentration data in attocuries of Pu-239 per cubic
meter of air (aCi/m3) , as reported by this network on a monthly
basis from June 1970 to March 1976, are given in Table 6-1.
A significant downward trend with time in the level of plutonium
in air at the stations downwind from the plant can be seen.
It has been suggested by HASL that this downward trend is
attributable to the weathering of the contaminated soil in the
on-site vicinity of the original oil drum storage site. This
weathering may be due to the movement of the plutonium from the
surface down into the soil, as well as changes in the
characteristics of the plutonium remaining on the surface.
In addition to showing a decrease with time the data indicate a
decrease in concentration with increasing distance downwind from
the site of the original spill area. Based upon air and soil
sampling1, as well as the direction of the prevailing winds around
Rocky Flats, HASL concluded in 1972 (2) that the original spill
area was the primary source of plutonium in the Rocky Flats
environment.
6-2
-------
I
U)
RT.73
PIANT
EAST GATE
J^>
GD
SMU AREA
1
a
(21
T. WISTEMN
BISIRVOI*
MIIIS
MAP OF ROCKY FLATS PLANT AND VICINITY
INDICATING CONTINUOUS AIR SAMPLING SITES (1).
FIGURE 6-1
-------
TABLE 6-1
MONTHLY AVERAGE AIR CONCENTRATIONS OF Pu-239
AT ROCKY FLATS PLANT
(Attocuries /Cubic Meter)
JAN.
FEB.
MAR.
APR.
MAY
JUNE
JULY
AUG.
SEP.
OCT.
SITE tl
NOV.
DEC.
SITE #2
SITE S3
SITE 14
1970
1971
1972
1973
1974
1975
19-76
1972
1973
1974
1975
1976
1972
1973
1974
1974
1975
1976
1960.00
5430.00
1160.00
402.00
1260.00
680.00
~
37.80
16.80
141.00
12.20
18.40
21.70
288.00
184.00
_--,
1670.00
3640.00
802.00
1360.00
1240.00
57.70
23.20
34.70
23.10
41.703
39.10
399.00
303.00
7140. oa
4610.00
2520.00
891.00
1780.00
864.00
55.80
462.00°
56.80
14.40
24.20
163.00°
1850.00
72.60
9730.00
1460.00
612.00
1810.00
2180.00
716.00°
135.00
39.70
24.00
283.00°
-~
254.00
236.00
4920.00
2080.00
1780.00
3060.00
2190.00
51.80
176.00
40.40
1460.00
139.00
109.00
1990.00
3800.00
6610.00
3040.00
5470.00
1160.00
~
57.70
140.00
42.00
758.00
684:00
319.00
1250.00
2980.00
4720.00
2920.00
2670.00
567.00
98.90
92.10
78.70
27.40
__
25.80
1430.00
118.00
98.20
790.00
3530.00
1380.00
3320.00
3330.00
426.00
__
55.50
65.00
58.10
14.00
_._
25.70
222.00
146.00
63.10
850.00
4046.00
1050.00
1120.00
179.00
__
119.00
152.00
34.20
9.98
-.
38.20
^ ^
199.00
72.20
693.00
5770.00
1620.00
2010.00
407.00
__
609.00
31.50
24.00
21.90
21.50
__
395.00
189.00
2260.00
5770.00
498.00
1810.00
580.00
1220.00
48.50
25.20
29.20
10.60.
18.50
11.00
1240.00
188.00
--
962.00
3160.00
1860.00
1690.00
643.00
655.00
**
45.20
76.30
43.70
16.40
25.60
16.90
710.00
128.00
NO DATA
Errors are less than 20Z except:
a -error between 20X and 100Z
b -error greater than 100Z
c -suspect, omitted from average
-------
The levels of airborne plutonium at the downwind edge of
the buffer zone (Indiana Street) were approximately the same
level as reported at the monitoring station upwind from the
plant. Although these levels were about twice that expected from
background radioactivity in the Rocky Flats area, the effect of
the spill area upon the off-site environment has been much
reduced from earlier levels.
Comparison of the HASL data for 1976 for the Indiana Street
location (site 2) with the 1975 data reported by the Rocky Flats
Plant (Table 6-2) for the same general area shows the two
networks to agree within a factor of about 2. The values
reported by HASL range between 12 to 23 aCi/m3, while Rocky Flats
reported an average of 37 aCi/m3.
6.2.2
INHALATION DOSES DUE TO ON-SITE CONTAMINATION
An assessment can be made of the doses received through
inhalation by individuals residing off-site at the time the
measurements were made, based upon the considerable amount of air
monitoring data available for the Rocky Flats Plant. In carrying
out this assessment, a deliberate effort has been made to choose
assumptions which are most likely to result in an overestimate of
dose. These are:
1) Inhaled plutonium is considered to be in an insoluble
form, (chemical solubility of an aerosol determines its residence
time in the lung with insoluble compounds being retained the
longest.)
2) The plutonium aerosol is assumed to have a lognormal
distribution with an activity median aerodynamic diameter (AMAD)
of 1 micrometer. (According to the ICRP (3) this implies that
approximately 25% of the aerosol will be deposited in the
pulmonary compartment of the lung. HASL (4) has reported 25% of
6-5
-------
TABLE 6-2
PLUTONIUM IN AMBIENT AIR NEAR ROCKY FLATS PLANT (1976)
[Air Concentation in Attocuries/Cubic Meter]
Distances = 3 to 6 Kilometers
Station
S-31
S-32
S-33
S-34
S-35
S-36
S-37
S-38
S-39
S-40
S-41
S-42
S-43
S-44
Summary
Number of
Samples Taken
12
12
12
3
3
2
12
10
12
12
12
12
11
12
137
Less Than
Detectable
1
1
1
1
0
0
0
0
1
0
1
1
1
1
9
Volume-Weighted Average
Volume
(cubic meters)
461,547.0
543,346.0 "
531,886.0
118,243.0
119,322.0
57,286.0
525,181.0
460,089.0
502,129.0
486,876.0
472,698.0
416,244.0
360,818.0
429,709.0
5,485,374.0
Concentration
maximum
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
.144
.134
.097
.176
.116
.012
.198
.097
.102
.198
.136
.137
.185
.094
.198
<0
<0
<0
<0
0
0
0
0
<0
0
<0
<0
<0
<0
C a
average
.032
.035
.034
.037
.027
.012
.056
.027
.026
.054
.033
.037
.056
.029
+
±
±
±
±
+
±
+
±
±
±
±
±
±
^
96%
96%
95%
550%
538%
1734%
93%
108%
97%
92%
99%
96%
105%
103%
<0,037 ± 29%
a. Volume-weighted average.
-------
the airborne activity being in the respirable range around Rocky
Flats, while Sehmel (5) has reported a 20% respirable fraction.
3) The individual is considered to be exposed continuously
for 1O years at the currently observed air concentration. (No
further reduction in airborne activity as a result of weathering
or remedial actions is assumed)
4) All plutonium was assumed to contribute to the dose, with
no correction being made for ambient background levels of
plutonium.
The PAID code developed by EPA (6) was used to calculate the
annual dose rate. Tables 6-3 and 6-4 have been generated by the
PAID code and relate years of exposure to the resultant dose rate
for various organs. Values in the tables are normalized to an
aerosol concentration of l.O femtocurie per cubic meter of air
(fCi/m3) with a 1 jum AMAD.
6.2.3 INDIANA STREET LOCATION
Indiana Street is the nearest location to the Rocky Flats
Plant where an individual in the general population could live
and be exposed as a result of transuranium contamination
originating from the Plant. This location is in the downwind
direction of the prevailing winds that blow across the Rocky
Flats Plant (7) and, therefore, it represents a worst case for
offsite exposure.
From Figure 6-2 it can be seen that stations 5-35, 5-36,
5-37,5-38, and 5-39 are located along Indiana Street. The station
reporting the highest annual average for 1975 was 5-37 with
0.056 fCi/m3 (Table 6-2). Assuming this level to continue for
the next 70 years, the 70th year dose rates to lung and bone can
be calculated.
6-7
-------
TABLE 6-3
ANNUAL DOSE RATE TO VARIOUS LUNG COMPARTMENTS
FROM CHRONIC EXPOSURE TO PLUTONIUM-239 AEROSOLS
Concentration: 1.0 fCi/m3 Particle AMAD.: 0.05, 1.0 and 5.0 Microns
I
oo
Duration of Pulmonary
Exposure
(Years)
-1
mrad/yr. x 10
O.OSu l.Ou 5.0u
3.9 1.5
.7
9.1 3.5 1.7
Tracheobronchial
mrad/yr. x 10
O.OSu l.Ou 5.0u
2.7 1.1 6.1
3.7 1.5 7.9
Nasopharyngeal
mrad/yr. x 10
O.OSu l.Ou 5.0u
.04 11.
30.
04 11. 30,
10
9.8 3.8 1.8
3.8 1.6 8.1
,04 11. 30,
70
9.9 3.8 1.8
3.8 1.6 8.1
,04 11. 30,
-------
TABLE 6-4
ANNUAL DOSE RATES TO VARIOUS ORGANS
FROM CHRONIC INHALATION OF TRANSURANIUM RADIONUCLIDES
(In Millirad/Year)
Aerosol AMAD: 1 um
Concentration: 1 fci/m~
-3
Nuclida: Pu-239
Nuclide: Pu-241/Aa-241*
Duration of
1
5
10
15
20
30
40
50
70
Exoosqra,
year
years
years
years
years
years
years
years
years
Liver
1.0 E-3
1.3
5.2
8.9
1.3
1.9
2.4
2.9
1.6
E-2
E-2
E-2
E-l
E-l
E-l
E-l
E-l
Skeletal
5.0 E-4
6.5
1.9
3.4
4.9
7.8
1.1
1.3
1.7
E-3
E-2
E-2
E-2
E-2
E-l
E-l
E-l
Eon a
Red
4.
6.
1.
3.
4.
7.
1.
1.
1.
M » »- row
a E-4
2
8
2
7
4
1
2
6
E-3
E-2
E-2
E-2
E-2
E-l
E-l
E-l
_ . .
tnuostea I
6.6 E-3
a.
2.
4.
6.
1.
1.
1.
2.
6
5
5
5
0
5
7
3
E-2
E-l
E-l
E-l
E-0
E-0
E-0
E-0
Nuclida: Xa-241
Duration of
1
5
10
15
20
30
40
50
70
year
years
years
years
years
years
years
years
years
1.
1.
5.
9.
1.
2.
2.
3.
3.
5
9
5
5
3
0
6
0
7
E-3
E-2
E-2
E-2
E-l
E-l
E-l
E-l
E-l
5.0
7.0
2.1
3.6
5.2
B. 2
1.1
1.4
1.8
E-4
E-3
E-2
E-2
E-2
E-2
E-l
E-l
E-l
4
6
1
3
4
7
1
1
1
.6
.3
.9
.3
.8
.5
.0
.3
.7
E-4
E-3
E-2
E-2
E-2
E-2
E-l
E-l
E-l
5
a
2
4
6
9
1
1
2
.8 E-3
.1 E-2
.4 E-l
.2 E-l
.0 E-l
.5 E-l
.3 E-0
.6 E-0
.1 E-0
Liver SXeleta\
1.
a.
4.
1.
1.
3.
5.
6.
a.
4
7
6
1
a
4
0
4
0
E-6 5
E-5 3
E-
E-
B-
E-
E-
1
4
7
1
2
E-3 3
E-3 4
.0
.2
.7
.1
.1
.4
.2
.0
.4
E-7
E-5
E-4
E-4
E-4
E-3
E-3
E-3
E-3
Bong
Red Harrow
4
3
1
1
6
1
2
2
4
.6
.0
.6
.6
.6
.3
.0
.8
. 1
E-7
E-5
E-4
E-4
E-4
E-3
E-3
E-3
E-3
Endosteal
5
3
2
2
4
1
2
3
5
.8
.7
.0
.0
.8
.6
.6
. 5
. 1
E-6
E-4
E-3
E-3
E-3
E-2
E-2
E-2
E-2
Nuclida: Ca-244/Pu-240
1.
1.
4.
7.
9;
1.
1.
i.
1.
6
8
7
3
4
2
4
5
6
E-3
E-2
E-2
E-2
E-2
E-l
E-l
E-l
E-l
6
1
\
2
3
4
5
6
6
.0
.6
.7
.8
.7
.9
.7
.3
.8
E-4
E-3
E-2
E-2
E-2
E-2
E-2
E-2
E-2
5.
1.
1.
2.
3.
4.
5.
5.
6.
6
5
6
6
4
5
3
8
3
E-4
E-3
E-2
E-2
E-2
E-3
E-2
E-2
E-2
6
1
1
3
3
5
6
6
7
. 4
.7
.8
.0
.9
.2
. 1
.7
.3
E-3
E-2
E-l
E-l
E-l
E-l
E-l
E-l
E-l
Alpha dose only - 70th year beta dose rates: liver - O.ll urad;
bone - 0.049 urad.
-------
LOCATION OF
OFF-SITE AMBIENT AIR SAMPLERS (8).
LEGEND
O ON-SITE AIR SAMPLERS
A AIR SAMPLERS, 3 TO 6 KILOMETERS I 2 TO 4 MILES) DISTANCE
COMMUNITY AIR SAMPLERS
FIGURE 6-2
6-10
-------
As shown in Table 6-3, an air concentration of l.o fci/m3
for 1 urn AMAD aerosols of Pu^239 would produce a 70th year dose
rate to the pulmonary compartment of 0.38 mrad/yr; therefore,
proportionally, a concentration of 0.056 fci/m2 (5-37) will
produce a 70th yr dose rate of 0.02 mrad/yr. The bone dose rate
associated with this level of Pu-239 according to Table 6-4 will
i>e 0.009 mrad/yr in the 70th year.
Data on the air concentration of Am-24l have been reported
by HASL (7) for the years 1970 through 1974. These data show the
americium levels, measured at the perimeter fence of the Plant,
to be approximately 11% of the Pu-239 levels. HASL projected
that the Am-241 activity level will reach its maximum value
arising from the decay of Pu-24l in the year 2033 at which time
it will amount to 18% of the Pu-239 activity. For the
calculation of the dose rate from Am-241, it is assumed that
Am-241 is at the maximum of 18% of the Pu-239. The 70th year
dose rate corresponding to a concentration of 1 fci/m3 of Am-241
is 0.4 mrad/yr; proportionally, an air concentration
of'0.18 x 0,056 fci/m3 would produce O.OO4 mrad/yr to the
.pulmonary compartment. The associated bone dose would be
approximately 0,002 mrad/yr.
Based upon these calculations, the total pulmonary dose rate
after 70 years of exposure for an individual living along Indiana
Stzree.t would be 0.024 mrad/yr, while the associated bone dose
would be O.pl mrad/yr. Individuals living further away from the
Rocky Flats Plant should receive even lower doses than these due
to the lower air concentrations reported for the nearby
communities.
6.2.4
INHALATION DOSES DUE TO OFF-SITE CONTAMINATION
A complete assessment of the inhalation pathway.for the
Rocky Flats vicinity must consider the potential hazard from the
low levels of contaminated soil which already exist off-site.
6-11
-------
Questions have been raised as to the. effect of this material in
producing localized exposures which are not necessarily reflected
in the data obtained through the air monitoring network around
Rocky Flats. These inhalation exposures can arise through
various mechanisms including: wind resuspension of contaminated
soil, vehicular and mechanical disturbances of soil, accumulation
and resuspension of dust within the home, as well as the
resuspension of contaminated soil attached to clothing.
The following analysis will attempt to investigate these exposure
mechanisms and assess their potential impact.
6.2.5
WIND RESUSPENSION
Figure 6-3 shows the off-site soil contamination contours
reported by HASL in 1970 (2). Soil sampling programs in 1975 (8)
showed that these contours had not changed significantly from the
1970 report. The highest off-site contour shown by the HASL data
was O.05 uCi/m2. These contours were developed based upon an
inventory sample to a depth of 20 centimeters. What is important
in assessing the resuspension of soil, however, is only the
material existing near the surface. Based upon the HASL soil
depth profiles, Anspaugh (9) stated that approximately 20% of the
total activity is contained within the first centimeter.
Therefore, the highest contour value of 0.05 uCi/m2 would
correspond to 0.01 uCi/m2 when corrected for a 1 cm. depth.
On a mass basis, 0.01 uCi/m2 is equivalent to approximately
2 disintegrations per minute per gram of soil, i.e., 2 DPM/gm.
The offsite area bounded by this contour is approximately two
square kilometers and soil within that area would be projected to
be at or above 2 DPM/gm. Beyond this area, off-site soil will
generally be below this value.
This review uses the mass loading approach as an indicator
of the general resuspension by wind over large land areas.
Because of technical shortcomings identified with the mass
6-12
-------
ROCKY FLATS
PLUTONIUM-239 CONTOURS mCi/km2
FIGURE 6-3
6-13
-------
loading approach (10), the concept has been modified by an area
correction factor to correct for small areas of contamination and
with an enrichment factor to reflect a nonuniform distribution of
radioactivity with soil particle size. This latter modification
is particularly important because transuranium activity
associated with soil particles within the respirable range is a
greater hazard than it would be if associated with the larger
particle sizes.
The mass loading approach assumes the loading of th6 air
with particulates to be an index of resuspension and derives the
airborne concentration of a specific radionuclide by a comparison
with its concentration on the adjacent surface (11).
Specifically,
Air Concentration (fCi/m3) = Soil Concentration (uCi/m2)
x Mass Loading (ug/m ) x U.C.
where U.C. is the units conversion factor based upon
the depth of sampling and the soil density.
, ' ;' / "\ .-::*. "I ,.»
Airborne particulate mass loading is one of the criteria for
clean air standards and measurements are widely available for
urban and nonurban locations through the National Air
Surveillance Network (NASN). The data recorded at nonurban
stations are a better indicator of the levels of resuspended
material than are urban measurements. In general, annual mean
mass concentrations of airborne particulate material at the
nonurban stations range from 5-50 micrograms per cubic meter
(Figure 6-4); the mean arithmetic average for 1966 of all
30 nonurban NASN stations was 38 ug/m3 (11) . From Figure 6-4 an
estimate can be made of the average mass loading for the general
area in which Rocky Flats is located. It would appear that
15 ug/m is reasonably representative of this area on an annual
basis.
Simple application of the mass loading approach without
consideration of the activity distribution as a function of
6-14
-------
30 20
ANNUAL MEAN MASS CONCENTRATIONS (jug/m3) OF AIRBORNE
PARTICLES FROM NON-URBAN STATIONS OF THE U.S. NATIONAL
AIR SAMPLING NETWORK. 1964 - 1965
FIGURE 6-4
6-15
-------
particle size is not appropriate, however, since that would imply
a uniform distribution of activity with particle size as well as
a uniform resuspension of all particle sizes. This has not been
found to be the case at Rocky Flats (12) or at other plutonium
contaminated sites (13).
In addition, an important consideration in assessing the
potential exposure due to contaminated soil is the amount of
activity associated with particles within the respirable size
range. Johnson (14) has suggested that sampling of only those
particles in a soil sample which are within the inhalable size
range (generally < 10 jum) would give the best measure of risk to
the public health around Rocky Flats. However, the weight
fraction of, particles in the less than 1O /Ltm range is small in
most soils, and sampling, separation, and analysis techniques are
correspondingly more difficult and inadcurate. There is also
considerable evidence that some of the larger particles really
consist of aggregates and are relatively easily broken down into
smaller ones, so that an instantaneous measurement of a single
size range may not give a good picture of long-term trends.
Also a substantial contribution to other possible pathways
(e.g. ingestion) may be via larger particle sizes and measurement
of the contribution of only the inhalable fraction would not
provide all the information that is required.
6.2.5.1
ENRICHMENT FACTOR
The "Enrichment Factor" is intended to 1) give a
mathematical view of the different fractions of the total
radioactivity associated with particles of different size ranges,
and 2) address the problem of the nonuniform resuspension of
particle sizes.
The inhalable fraction of the soil is weighted by
considering the relative distribution of activity and soil mass
6-16
-------
as a function of particle size for representative samples of
=j.j..--- - - --
soil. To accomplish this, the sample of contaminated soil is
segregated into "n" size increments and the activity and mass
contained within each size increment is determined. The factor gj
is then defined as the ratio of the fraction of the total
activity contained within an increment "i" to the fraction of the
total mass contained within that increment. A value greater
than 1 for gj implies an enrichment of activity in relation to
mass, while a value less than 1 indicates a dilution of the
activity with respect to mass.
The nonuniform resuspension of particle sizes is also
considered by measuring the mass loading as a function of
particle size. The fraction of the airborne mass contained
within each size increment "i" is then calculated and designated
as f j . The factors of f j and gi are then incorporated into the
mass loading formulation for each size increment as follows:
Air ConCj = Air Mass Loading x f j x Soil Cone x q\-
Summation over all the size increments results in the total air
concentration:
Air Cone = Air Mass Loading x Soil Cone x
The term Sfjgj weights the contribution of plutonium
from each soil size fraction to the total resuspended material,
thereby taking into account both the nonuniform resuspension of
particles sizes as well as the nonhomogeneous distribution of
activity with particle size.
Data on the distribution of plutonium with soil ; particle
size has been obtained (12) for the vicinity around Rocky Flats
(Table 6-5) . The ratio, q\ has been calculated for each size
increment and indicates an enrichment of activity to mass
associated with soil particles within the respirable size range.
To obtain fj, the data obtained by Chepil (15) for fields
6-17
-------
TABLE 6-5
EXPERIMENTAL DATA FOR WEIGHT AND ACTIVITY FRACTIONS
FOR SOILS IN THE ENVIRONS OF THE ROCKY FLATS' PLANT
[Sampling and Analysis by US Environmental Protection Agency]
H
00
Size Increment (pm)
RF IB
RF 1C
RF 2A
Fract
Act Frace
2000-105
105-10
<10
2000^-105
105-10
<10
2000-105
105-10
-------
undergoing wind erosion in Colorado and Kansas were used. The
results of his findings have been conveniently plotted by Slinn
(16) and reproduced as Figure 6-5. Comparison of Chepil's data
with another study substantiates the applicability to the Rocky
Flats situation. Chepil found 30% of the airborne mass to be
below 10 /im versus a study by Willeke (17) in an area outside
Denver where approximately 33% of the measured airborne mass was
below 10 /na. Values for fj used in this analysis are included in
Talxle 6-5.
6.2.5.2 CORRECTION FOR AREA SIZE
Use of the mass loading approach implies that the air
concentration is at equilibrium with the ground surface,
i.e. , a steady state .situation exists in which the amount of
material coming up from the surface is balanced by the rate at
which material is depositing back onto the surface. In the
strictest sense this limit can only be achieved for source areas
approaching infinite dimensions. For sources of finite
dimensions, a correction must be applied for area size.
Although many techniques are presently under development to
calculate the air concentration arising from an area source, no
generally accepted method has yet been identified. Usually,
these approaches make use of a standard diffusion equation,
modified to handle area sources. One such equation is the
.Button-Chamber la in diffusion equation:
X
QA
[exp(-
4 Vd
n/2
Cz n u
exp(-
4 Vd D2
n/2
U
where X is the air concentration, Ci/m
Q is the amount of activity resuspended per unit
area, per unit time, Ci/m2 sec
Vd is the particle deposition velocity, m/sec
D! and D2 are the distances from the receptor to the nearest
and furthermost edges respectively of the source area
u is average wind speed, m/sec
Cz and n are Suttdn parameters for meteorological
conditions.
6-19
-------
-100
-10
D
1
m
z
m
31
3J
CD
O
3J
tn
o
i
m
CO
3
12 5 10 20 30 40 50 60 70 80 90 95 9j399 99.8 99.99
PERCENT OF MASS ASSOCIATED WITH PARTICLES OF LESS THAN EQUIVALENT DIAMETER
PARTICLE SIZE DISTRIBUTION OF RESUSPENDED SOIL
FIGURE 6-5
6-20
-------
For source areas approaching infinite depth, D2
above equation becomes
XI
and the
QA
Vd
Therefore, the correction term to be applied for areas of finite
size is
1 - exp(-
4 Vd
n/2
7T1/2 Cz n U
The area under consideration in this analysis has been
described earlier. It is bounded by Indiana Street and the
0.05 Ci/m2 isopleth (Figure 6-3) with a width in the downwind
direction of approximately 1 kilometer. This is the most highly
contaminated off-site area and includes sites of projected
residential development. The meteorology for the Rocky Flats
area has been described (8) to have neutral stability at least
50% of the time with a mean wind speed of 4.2 m/sec in 1975.
Healy (18) has suggested values for the parameters required for
the situation of neutral stability: Cz = 0.1 and n = 0.25, while
the ratio Vd/u, which depends upon the surface roughness, ranges
between 0.003 and 0.008 for grassland. A value of 0.005 will be
assumed. Therefore, the correction factor for the area under
consideration is 0.66.
6.2.6 AVERAGE AIR CONCENTRATION DUE TO WIND RESUSPENSION
The average soil concentration for the area is not known,
but it would be somewhere between 0.05 uCi/m2 and the next higher
isopleth of 0.5 uCi/m2. For calculational purposes, 0.25 uCi/m2
will be assumed or approximately 10 DPM/g (based upon 20% of the
radioactivity within the first centimeter). By using the
parameters developed in the previous sections for the Rocky Flats
6-21
-------
area, one can estimate the average air concentration due to wind
resuspension:
Air Cone = Mass Loading x Soil Cone x Enrichment Factor
x Area Correction Factor
Air Concentration =
15 ug/m3 x 10 DPM/g x 10"6 g/ug
12
X Ci/2.22X101* DPM
0.066 fCi/m3
This calculated value of 0.066 fCi/m agrees within a factor
of 2 with the data obtained for the sampling stations along
Indiana Street.
Inherent in the above calculation were some conservative
assumptions. First of all, the wind was assumed to be blowing
100% of the time across the contaminated area in the direction ''of
the receptor. In reality, the reported (8) wind rose for Rocky
Flats indicates that the wind blows from the westerly direction
only about 50% of the time; the remaining time it will be blowing
from the direction of less contaminated land and, therefore, less
. " - ';-',*
radioactivity would be available for resuspension. Second, in
deriving the area correction factor the effect of breathing
height was ignored with the ground level concentration being
calculated. This is a conservative assumption since the airborne
concentration will decrease as a function of the height above the
ground. Although such refinements may be incorporated in the
calculation, the results represent a conservative approach to
deriving the dose rates to potentially exposed persons.
6.2.7
RESUSPENSION OF SOIL BY MECHANICAL DISTURBANCES
The use of land contaminated with transuranium elements in
the vicinity of Rocky Flats for agricultural or building purposes
can result in localized resuspension and presents a potential
inhalation hazard to individuals in the immediate vicinity of the
6-22
-------
opteration. In the vicinity of Rocky Flats, there is some farming
of wheat and the raising of corn for livestock feed. Future
development of the land for residential purposes is also being
advocated. Although only a limited amount of experimental data
are currently available to base an assessment of the inhalation
hazard from such activities, some conclusions and recommendations
can be made.
In assessing the agricultural situation, data obtained by
Milham (19) have been utilized. In that study, a field
contaminated with plutonium near the Savannah River Facility was
subjected to various plowing and seeding activities associated
with planting wheat. The increase in the airborne activity above
that from normal wind resuspension was monitored at the location
°f £he traqtor operator and at the downwind edge of the field
during the various activities. An average increase of a factor
,?°Vas observed in the level of resuspended plutonium at the
of the tractor operator and an increase of a factor
°^ 5 ffci the ed^e of the field. Based upon these observations,
.the average air concentration for the year can be calculated
for these two locations, assuming that the field is cultivated
30 days of the year for 8 hours per day. Again the area under
consideration will be that area of highest off-site contamination
described earlier with an average soil contamination level of
10 pPM/g. m the previous discussion of wind resuspension, this
level of soil activity produced an air concentration of
0.066 fCi/m3. From Milham's data, this activity level would
increase to 2.0 fCi/m3 at the location of the tractor operator
and to 0.33 fci/m3 at the edge of the field during the
agrictiltura:1 operations. The annual average concentration at the
tractor location is then:
;2 f,Ci/m3 X 8/24 hr X 30/360 d + Q.33 fCi/m3 x 330/360 d
+ 0.066 fCi/m3, xie/24 hr x 30/360 d = 0.07 fci/m3
6-23
-------
When these annual Pu-239 concentrations are compared to the value
of 2.6 fCi/m3 which was calculated by the PAID code to correspond
with a dose rate of 1 mrad/year to the lung, one can conclude
that agricultural operations in the area of Rocky Flats would
produce activity levels well below levels of concern. In
addition, after the first plowing cycle, the surface
concentration should be diluted by mixing with soil from below
the surface and subsequent plowings would produce air
concentration lower than that of the first year.
One can also make projections for building activities based
upon the agricultural situation examined above. There does not
appear to be any reason why building activities, such as
excavation and grading, should produce higher instantaneous air
concentrations than those observed during agricultural plowing
and, therefore, should not present a more restrictive situation.
6.2.8 RESUSPENSION OF DUST WITHIN THE HOME
The total amount of soil continuously in the home is not
known but an assumption of 10 g/m3 has been made (20). This
amounts to about 3 Ibs of soil in a modest 1500 square foot
house. Because the floors are harder and smoother than outside
surfaces, the resuspension from these surfaces will be higher.
Resuspension factors of lO^/m have been used in the past to
predict exposures in the work place and studies of Pu02 deposited
on indoor surfaces have been consistent with such a value (21).
The following exposure situation is postulated: the
individual is exposed to contaminated dust in the home for 24
hrs/day, 7 days/week, for 70 years. The dust in the home has the
same activity/gram as outside soil and has an areal distribution
within the home of 10 g/m2. The air concentration resulting from
resuspended dust at 10 DPM/g would be:
10 DPM/g x Ci/2.22xl012 DPM x 10 g/m2 x lO^/m = 0.045 fCi/m
6-24
-------
6.2.9 RESUSPENSION OF DUST FROM CONTAMINATED CLOTHING
Healy (18) has assumed that in a desert environment there
will be 1 mg/cm (1O g/m2) of dust on clothing. While it would
certainly be less for nondesert environments, this value will
also be assumed for Rocky Flats. Because of the proximity of the
contamination to the nose and the mouth, a resuspension factor
higher than the normal outdoor resuspension factor will be
assumed. For this calculation, a value of lO^/m will be assumed
to be sufficiently conservative. Therefore, the resultant air
concentration is:
10 g/m2 x 10 DPM/g x Ci/2.22xl012 DPM x lO^/m = 0.045 fCi/m3
6.3
INGESTION PATHWAY
Wastewater discharged from the Rocky Flats Plant as well as
surface runoff from the Plant site is collected in a number of
holding ponds where it is monitored for its radioactivity content
before being discharged into either Walnut or Woman Creek.
Walnut Creek empties into the Great Western Reservoir which
provides part of the drinking water supply for the City of
Broomfield, while Woman Creek eventually empties into Standley
Lake which is a drinking water supply for the City of
Westminster.
The Rocky Flats water monitoring program consists of
1) effluent monitoring of the water being discharged from the
holding ponds into Walnut and Woman Creeks, 2) the monitoring of
groundwater and 3) the monitoring of the regional water supplies.
In monitoring public water supplies, samples are collected and
analyzed from the drinking water reservoirs (Great Western and
Standley Lake) as well as the finished water in several nearby
communities. As with the air monitoring, the results of this
sampling program are reported regularly to the responsible
Federal, State, and local government agencies and published
on a yearly basis. According to the 1975 published data (8)
6-25
-------
the average concentrations of plutonium and americium in
finished water for the region were <0.027xlO"9 uCi/ml and
<0.032xlO"9 uCi/ml, respectively. The concentration levels of
plutonium and americium in the drinking water of the various
communities surrounding Rocky Flats are given in Table 6-6.
Included in this table are results obtained by Poet and Martell
(22) in 1970. Limited comparison of the two sets of data shows
little change in the activity levels in the drinking water during
this five year period.
6.3.1
BONE DOSE DUE TO INGESTION OF WATER
Assuming that the concentrations of Pu-239 and Am-241 in
drinking water are those reported for the city of Broomfield
(the highest concentrations reported for the more immediate
surrounding communities) and that the consumption rate of water-
is 1.2 liters/day (ICRP Committee II) the annual water ingestion
rates are: . ,
Pu-239. Annual Ingestion Rate , .
0.04xlO"9 uCi/ml x 1200 ml/day x 365 days/yr = 18 pCi/yr
Am-241, Annual Inqestion Rate ,
0.029X10'9 uCi/ml x 1200 ml/day x 365 days/yr = 13 pCi/yr
Conversion of the above ingestion rates into dose rates can
be achieved through the use of Tables 6-7 and 6-8. Table 6-8 has
been normalized to an ingestion rate of 100Q pCi/yr of various
transuranium oxides and relates the years of ingestion to the
resulting dose rate. Since plutonium and americium found in tap
water would probably be in a chemical form other than the oxide,
e.g. the hydroxide or some colloidal form, the solubility and,
therefore, the transfer from the GI tract to the blood would be
greater than for the oxide form. The factors for absorption from
the gastro-intestinal tract as suggested in ICRP Publication 48,
enhanced by an increased infant absorption factor of ten, have
been used. Based upon these conversion factors, the bone
26
-------
TABLE 6-6
PLUTONIUM AND AMERICIUM IN PUBLIC WATER SUPPLIES
Reservoirs
Great Western
Great Western3
Standley Lake
Finished Water
Number of
Sample
36
36
Plutonium Concentration fylfT9) uCi/ml
C minimum c maxii
<0.013
.046
<0.013
0.952
0.214
0.142
C average
<0.099 + 58%
<0.036 + 23%
Arvada
Boulder
Broomfield
Broomfield3
Denver
Golden
Lafayette
Louisville
Ihornton
Westminster
11
12
39
11
11
12
11
12
36
<0.005
<0.005
<0.013
<0.005
<0.005
<0.005
<0.005
<0.005
<0.013
0.019
0.014
0.133
0.038
0.016
0.048
0.030
0.012
0.018
0.210
Average
<0.006 + 50%
<0.007 + 17%
<0.041 + 26%
<0.008 + 29%
<0.009 + 107%
<0.007 ± 67%
£0.006 ± 21%
<0.009 ± 32%
<0.041 + 31%
<0.027 ± 49%
Great Western
Standley Lake
Finished Water
Arvada
Boulder
Broomfield
Denver
Golden
Lafayette
Louisville
Ihornton
Westminster
Average
38
37
11
11
37
11
11
12
12
12
39
a
b
Americium Concent-ration fyfn"9-) uCi/iril"'
<0.014
<0.013
Data of Poet and Wartell (1970)
Sample Average
<0.090
<0 090
<0.001 .
<0.001
<0.023
<0.001
<0.001
<0.001
<0.001
<0_001
<0. 013
0.239
0.015
0.150
0.420
0.044
0.030
0.400
0.007
0.079
<0.033 + 20%
<0.027 + 19%
<0.026 +
<0.006 +
<0.029 +
<0.043 ±
<0.009 ±
<0.007 +
<0.039 +
<0.005 +
<0.029 +
180%
180%
31%
196%
80%
67%
185%
30%
18%
<0.032 ± 25%
6 - 27
-------
TABLE 6-7
FACTORS FOR ABSORPTION FROM THE GASTRO-INTESTINAL TRACT
FOR TRANSURANIUM ELEMENTS
Element/Chem Form ~~~~ ICRP-30* ICRP-48**.
N)
CO
Oxide
Pu-238 Nitrate
Other
Oxide
Pu-239 Nitrate
Other
10
i<
A
4
1<
* ICRP-30
** ICRP-48
10
10
10
Am
Cm
Np
5x10
5xl(T4
ID'2
io-3
occupational exposures
general population exposure (via food pathway)
for plutonium = 10~3
for all other transuranium elements = 10~3
children under one year = 10 x value for adults.
-------
TABLE 6-8
ANNUAL DOSE RATE DUE TO CHRONIC INGESTION OF
PLUTONIUM-239 OXIDE, AMERICIUM-241, PLUTONIUM-241, & CURIUM-244
(In Microrad/Year)
Annual Intake = 1000 pCi/Year
£-L = 10
-3
OT
1
K)
^O
Duration of
Ingestion
tYearal
1
5
10
15
20
30
40
50
70
Plutoniua-239 Oxide
Red Marrpu
7.6
36.5
71.2
102
136
204
254
114
407
Endosteql
1.1 E+2
5.0 E+2
9.8 E+2
1.4 E+l
1.9 E+1
2.8 E+1
1.5 E+1
4.1 E+1
5.6 E+1
24
116
220
120
410
560
690
810
980
Duration of
Ingestion
(Yaarsy
1
5
10
15
20
10
40
50
70
Aaericiura-241
Red Harrow
7.7
38
74
110
140
200
260
120
410
Bone
9.8 E+1
4.8 E + 2
9.4 £*2
1.4 E»3
1.8 EO
2.6 E+J
3.1 E+3
5.2 Etl
5.2 E + 1
Livei;
25
120
230
340
430
590
720
830
990
Duration of
Ingastion
(Yearn)
1
5
10
15
20
30
40
50
70
Plutoniu«-241/A»erioiu»-24l.
Red
0.006
0.14
0.51
1.0
1.7
1.2
4.9
6.5
9.4
Bans
Endoa^eflt
0.08
1.8
6.5
11
22
41
62
82
119
Uxsr
0.02
0.45
1.6
3.1
4.9
8.7
12
16
21
Duration of
Ingestion
1
5
10
15
20
10
40
50
70
Red Harrow
7.9
17
65
92
108
131
150
160
175
Curiu«-244/Plutoniu»-240
9.0 E+1
4.2 E+2
7.5 E+2
1.1 E+3
1.2 E+1
1.5 E+1
1.7 B+l
1.8 E+l
2.0 E+l
2.6 E+1
1.2 E+2
2.1 E+2
2.8 E+2
3.1 E+2
3.9 E+2
4.3 E+2
4.6 E+2
4.8 E+2
-------
dose rate after 70 years of ingestion of drinking water would be
8.8X10"3 mrad/yr for Pu-239 and 6.2X10"3 mrad/yr from Am-241.
6.3.2 BONE DOSE DUE TO INGESTION OF FOODSTUFFS
At present limited agricultural production is carried out in
the environs of Rocky Flats. Most of the food consumed locally
is produced at considerable distances from the Rocky Flats Plant.
Other than a few family garden plots, the only crops grown
locally are wheat and alfalfa. A few cattle also are raised in
the Plant vicinity. Since future residential development is
projected for the Rocky Flats area, it would be reasonable to
project a concurrent increase in family gardening. Therefore, an
assessment has been carried out of the possible dose rates
associated with the consumption of foodstuffs which might be
produced locally. Because no food sampling data are presently
available for the Rocky Flats area, estimates of the potential
doses are based upon data developed in other areas contaminated
with transuranium elements and from laboratory experiments of
transuranium uptake by foodstuffs.
It is not expected that conditions at Rocky Flats would be
such that they would invalidate the use of data developed in
these other environments nor.produce higher dose rate estimates.
For purposes of this assessment, the ingestion rate of the
transuranium elements by man is considered to be the product of
the rates at which different contaminated materials are ingested
and the concentration of the transuranium elements in each
material.
To place these calculations into perspective, we have
adopted the formulation of Martin and Bloom (23) which relates
the ingestion rate H for a particular nuclide to the average
6 - 30
-------
concentration of that nuclide in soil Cs through the following
formulation:
H = Cs x Ij x Dj
where I,- is the ingestion rate of a particular item i and Dj is
the discrimination ratio between that substance and soil.
This formulation makes for easy translation of environmental
levels into dose rates and, thereby, direct comparison with
appropriate guidance limits. The soil concentration used
in this assessment is the same as that developed for the
inhalation pathway calculations, i.e., 0.25 uCi/m2 for Pu-239
and 0.045 uCi/m2 for Am-241 (18% of Pu-239 levels at the time of
maximum ingrowth). If as a result of plowing, this activity is
evenly distributed throughout the top 20 cm, the average
concentration, Cs in units of pCi/g would be:
0.25 uCi/m2 x 106 pci/uci x cms/g x 1/20 cm x m2/104cm2
= -1.25 pCi/g Pu-239
and 0.22 pCi/g Am-241.
The materials considered to be produced on this land and
consumed by individuals living in the area are: leafy vegetables,
other food plants, cow milk, and beef. Also the casual and
deliberate ingestion of contaminated soil will be considered.
Leafy Vegetables and Other Food Plants
Plants grown in soil containing the transuranium elements
can become contaminated through uptake by the roots and systemic
incorporation; in addition, the outer surfaces of the plant can
have contaminated soil deposited upon them as a result of
resuspension. Numerous studies have been conducted and several
reviews (24, 25, 26) have been published covering the range of
discrimination factors that have been observed in laboratory and
field studies. Generally, the discrimination ratio for
6 - 31
-------
incorporation of Pu-239 into the plant is between 10"4 and 10 on
a fresh weight basis and 10"1 to 10'2 for deposition on the plant
surface. In the case of americium-241, the internal incorporation
may be as much as 50 times higher than plutonium due to its
greater solubility. Generally, uptake factors for garden
vegetables are at the .upper end of the "range, therefore, :for
calculational purposes a discrimination ratio of 10 will be
assumed for internal deposition and 10"1 for external deposition
-3
when computing the intake of Pu-239, and a ratio of 5x10 for
internal deposition and 10"1 for external deposition in the case
of Am-241. Since the calculations are for food in a table-ready
condition, decontamination of the food during processing must
also be recognized. In doing so, the assumption of Bloom and
Martin (23) will be employed; namely, 90% of the contamination is
washed off leafy vegetables and 99% of the contamination is
removed from other food plants during washing, peeling, etc.
Likewise, the consumption rates of foodstuffs obtained by Martin
and Bloom from the USDA have been utilized after conversion to a
fresh weight basis (on the basis that vegetation is 70% water).
Table 6-9 shows 'the resultant ingestion rates and discrimination
ratios used in this assessment. >, ,
Equation 7 was used to convert the ingestion rates and
discrimination factors of Table 6-9 into annual intakes of
plutonium and americium. In carrying out the food pathway.,...
calculations, the assumption was made that 25% of the entire
intake for an individual arises from foodstuffs produced locally
on land contaminated with transuranium elements.
The resultant ingestion doses,,are given in Table 6-10.
In converting the annual radionuclide intake .to dose, rates, -
Tables 6-7 and 6-8 were used with the following assumptions:
1. the duration of ingestion is 70 years,
2. externally deposited material is in the oxide form,
with an absorption factor of 10 ,
3. material biologically incorporated in plants and
6 - 32
-------
TABLE 6-9
FOOD INGESTION RATES AND RADIONUCLIDE DISCRIMINATION RATIOsI
Leafy Vegetables
Other Vegetables
Cow Milk
Beef Muscle
Beef Liver
Soil (casual)
Soil (deliberate)
stionJRatef
270 a
740
436 D
273
13
0.01
20
Discrimination Ratio
Pu(ext) 10~1xlO%
Pu(int)
Am(ext)
Am(int)
Pu(ext)
Pu(int)
Am(ext)
Am(int)
Pu
Am
Pu
Am
Pu
Am
Pu
Am
Pu
Am
10-4
io-1xio%
5x10-3
10~4
5xlO-3
3.l7xlQ-8
3.17x10-8
3.29x10-5
3.29x10-5
2.0x10-3
2.0X1Q-3
1.0
1.0
1.0
1.0
a. assumes vegetation is 70% water
b. assumes retention and transport within cow is the same for Pu and Am
6-33
-------
TABLE 6-10
ESTIMATED COMMITTED DOSES (70th Year) TO RED BONE MARROW
OF CRITICAL GROUP NEAR THE ROCKY FLATS PLANT
70th Year Bone
Dose Rate
Substance Radionuclide
Drinking Water Pu
Am
Leafy Vegetables Pu (ext. )
Pu (int.)
Am (ext.)
Am (int.)
Other Vegetables Pu (ext. )
Pu (int.)
Am (ext.)
Am (int.)
Cow Milk Pu
Am ',
Beef Moscle Pu
Am
Beef Liver Pu
Am
Soil (casual) Pu
Am
(deliberate) Pu
Am
Inaestion Rates fpCi/vr)
18
13
297
3
53
27
82
9
15
74
i.eoxio"3
.28xlO~3
1.02
1.85X10"1
2.96
5.33X10"1
18.0
3.2
3.24X104
5.84X103
Total (without Pica)
(with Pica)
6-34
fmrad/vr)
0.008
.006
.014
.071
.026
.067
.004
.020
. 007
.018
.40xlO~5
. 67xlO~6
.0025
.0003
. 0071
. 0013
.0009
. 0016
.14
.26
=0.25 mrad/yr
=0.65 mrad/yr
-------
animals is assumed to have a greater fraction transferred
from the G.I. tract to the blood. For plutonium, this
results in an increase by a factor of 5 in the bone dose for
both plutonium and americium.
Ingestion of Cow Milk
Martin and Bloom have developed a discrimination factor for
dairy cows of 3.2X10"8 based upon assumptions of soil and
vegetation consumption by cattle. Using this value and again
assuming that 25% of the diet is locally produced, one can
calculate the ingestion rates of Pu-239 and Am-241 as a result
of milk consumption:
H (Pu-239) = Cs x I x D
= 1.25 pCi/g x 436 g/day x 365 days x 3.2X10"8
- 1.6X10"3 pCi/yr
H (Am-241) = 0.18 H (Pu-239)
= 0.28X10'3 pCi/yr
Since these transuranium elements would be biologically
incorporated, an increased absorption by a factor of five has
been assumed. The resultant bone doses attributable to the
consumption of milk are shown in Table 6-9.
Ingestion of Beef
Martin and Bloom developed discrimination factors for beef
muscle and beef liver and these have been utilized in the
6 - 35
-------
following calculations of ingestion rates:
Beef Muscle
H (PU-239) = C8 X I X D
1.25 pCi/g x 273 g/day x 0.25 x 365 d/yr
x 3.3XKT8
1.02 pCi/yr
H (Am-241) = 0.18 x H (Pu-239)
= 1.85X10'1 pCi/yr
Beef Liver
H (Pu-239) = 1.25 pCi/g x 13 g/day x 0.25 x 365 d/yr x 2xlO'3
=2.96 pGi/yr
-1
H (Am-241) = 5.33X10"1 pCi/yr
Bone Dose due to Soil Ingestion
Casual Ingestion
Bloom and Martin (23) have assumed a casual ingestion rate
for a desert environment to be approximately 3-4 g/year.
Likewise, Rogers (20) has estimated the accidental ingestion rate
of soil as a result of hand to mouth transfer to be 3-4 g/yr.
Based upon these estimates, one can calculate the plutonium and
americium ingestion and resulting dose rates. The ingestion
period is assumed to be 70 years and the surface soil
concentration of Pu-239 is assumed similar to that for unplowed,
6-36
-------
undiluted soil in the vicinity of Indiana Street; i.e., 1O DPM/g
(4.5 pCi/g). The americium concentration is assumed to be at its
maximum contribution of 18% or 0.8 pCi/g. The resulting bone
doses have been calculated assuming the transuranium elements are
in the relatively insoluble oxide form with an absorption factor
of io"5. , '
Deliberate Ingestion (Pica) !
,' ' ' ' ' - *- ' '* - ' ' !
Healy (27) has addressed the problem of deliberate soil
ingestion by children below the age of five. After reviewing the
limited available data on the topic, he concluded that a
deliberate soil ingestion rate of 20 g/day would be a reasonably
severe case. Applying this estimate to the Rocky Flats situation
would produce the following ingestion rates for deliberate soil
ingestion:
H (Pu-239) = Cs x I x D
= 4.5 pCi/g x 20 g/day x 365 days/yr
= 3.24X104 pCi/yr
H (Am-241) = 5.84X103 pCi/yr
Since this condition of excessive soil ingestion would occur over
a relatively few years, the resultant dose rates are calculated
assuming the, peripd of ingestion to be 5 years'. The results are
included in Table 6-10. ; , ..,.-. . ..-,..
6 - 37-
-------
REFERENCES
1. H. Volchok, M. Schonberg, and L. Toonkel, Pu-239
Concentration in Air Near Rockv Flats. Colorado. HASL-315, Health
and Safety Laboratory, USEFDA (1977).
2. P. W. Krey and [. P. Hardy, Plutonium in Soil Around the
Rockv Flats Plant. HASL-235, Health and Safety Laboratory,
USERDA (1970).
3. Task Group on Lung Dynamics, Health Physics. 12.
p!73 (1966).
4. H. Volchok, R. Knuth, and N. Kleinman, "The Respirable
Fraction of Plutonium at Rocky Flats," Health Physics. 23.
p395 (1972).
5.
G. A. Sehmel, Airborne 238Pu and 239Pu Associated with the
Larger than Respirable Resuspended Particles at Rocky Flats
During July 1973. BNWL- 2119, Battelle Pacific Northwest
Laboratories (1976).
6. USEPA PAID Code to be published.
i
7. P. Krey et al., Plutonium and Americium Contamination in
Rockv Flats Soil. 1973. HASL-304, Health and Safety Laboratory,
USERDA (1976).
8. Environmental Monitoring at Major USERDA Contractor Sites
for 1975, ERDA-76-104, Vol. 1, USERDA, Washington, D.C. (1976).
9. L. R. Anspaugh, L. H. Shinn, P. L. Phelps, and N. C.
Kennedy, "Resuspension and Redistribution of Plutonium in Soils,"
Health Phvsics. 29, p571 (1975).
10. Proposed Guidance on Dose Limits for Persons Exposed to
Transuranium Elements in the General Environment, USEPA,
Washington, D.C. (September 1977).
11. L. R. Anspaugh, "The Use of NTS Data and Experience to
Predict Air Concentrations of Plutonium Due to Resuspension on
the Enewetak Atoll," The Dynamics of Plutonium in Desert
Environment. NVO-14.. p299 (1974)
12. D. E. Bernhardt, "Resuspension of Plutonium; Particle Size
Distribution in Soil," in Evaluation of Sampling and Collection
Techniques for Environmental Plutonium. ORP/LV-76-5, LSEPA
(1976).
6-38
-------
13. T. Tamura, "Physical and Chemical Characteristics of
Plutonium inExisting Contaminated Soils and Sediments," in
Proceedings of the International Symposium on Transuranium
Nuclides in the Environment (Nov. 1975), IAEA, Vienna.
14. C. J. Johnson, R. R. Tidball and R. C. Severson, "Plutonium
Hazard in Respirable Dust on the Surface of Soil," Science.
193. p488 (1976).
15. W. S. Chepil, "Sedimentary Chacteristics of Dust Storms: III
Composition of Suspended Dust," Am. J. Sci. , 225. p2O6 (1957)
16. W. G. Slinn, "Dry Deposition and Resuspension of Aerosol
Particles-A New Look at Some Old Problems," in Atmospheric-
Surface Exchange of Particulate and Gaseous Pollutants. CONF 740-
921, ERDA, Washington, D.C. (1974).
17. K. Willeke, R. Whitby, W. Clark, and V. Mayle," Size
Distribution of Denver Aerosols - A Comparison of Two Sites,"
Atm. Env.. 8, p609 (1974).
18. J. W. Healy, A Proposed Interim Standard for Plutonium in
Soil, LA 5483-MS, Los Alamos Scientific Laboratory (1974).
19. R. C. Milham, J. F. Schubert, J. R. Watts, A. L, Boni, and
J. C. Corey, "Measured Plutonium Resuspension and Resulting Dose
from Agricultural Operations ,on an Old Field at the Savannah
River Plant in the Southeastern U.S.," in Proceedings of the
International Symposium on Transuranium Nuclides in the
Environmentf (Nov. 1975), IAEA, Vienna.
20. D. R. Rogers, Mound Laboratory Environmental Plutonium Study
1974. MM2249, Mound Laboratory (1975).
21. J. S. Jones and S. F..Pond, "Some Experiments to Determine
the Resuspension Factor of Plutonium from Various Surfaces/"
Surface Contamination, B. R. Fish (ed.) , Pergamon Press, New
York, NY (1964), p83. ,
22. S. E. Poet and E. A. Martell, "Plutonium-239 and Americium-
241 Contamination in the Denver Area, I I Health Physics, 23.
p537 (1972)
23. W. E. Martin and S. G. Bloom,. "Plutonium Transport and Dose
Estimation Model," in Proceedings of the International Symposium
on Transuranium Nuclides in the Environment. (Nov. 1975), IAEA,
Vienna. ,
6 - 39
-------
24. D. E. Bernhardt, and G. G. Eadie, Parameters for Estimating
the Uptake of Transuranic Elements by Terrestrial Plants. ORP/LV-
76- 2, USEPA (1976).
25. R. L. Thomas and J. W. Healy, An Appraisal of Available
Information on Uptake by Plants of Transplutonium Elements and
Neptunium. LA-6460-MS, Los Alamos Scientific Laboratory (1976).
26. R. A. Bulman, Concentration of Actinides in the Food Chain,
NRPB-R44, Harwell (1976).
27. J. W. Healy, An Examination of the Pathways from Soil to Man
for Plutonium. LA-6741-MS, Los Alamos Scientific Laboratory
(1977).
6 - 40
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7. PLANNING AND CONDUCT OF CLEANUP
OF ENEWETAK ATOLL
(This Chapter was prepared, in part, by the staff of the ;
Department of Energy and is included to provide a historical
perspective on the implementation of a major remedial action)
Enewetak Atoll is located in the Marshall Islands and was
part of the Pacific Proving Ground;. Forty-three nuclear devices
were detonated by the United States at this atoll from 1948 to
1958. The decision in 1972 to return the Enewetak people to
their home atoll necessitated the removal of contaminated debris
and soil from numerous islands. The experience of planning and
conducting the Enewetak Cleanup Project, particularly that part
related to removal and disposal of transuranium element
contaminated soil, provides a valuable lesson in the practical
aspects of developing and applying radiation protection criteria
in a remote and complex environment.
Radiological cleanup and resettlement of Enewetak Atoll was
a cooperative effort by the Department of Defense (DOD), the
former Atomic Energy Commission (AEC) and current Department of
Energy (DOE), and the Department of the Interior (DOI). These
agencies had previously cooperated in cleanup of Bikini Atoll.
Under a Memorandum of Understanding for Bikini Atoll, DOD
performed the cleanup, AEC was responsible for radiological
safety aspects of cleanup, and DOI performed agricultural
rehabilitation and resettlement of people. Responsibilities of
these agencies were essentially the same for Enewetak. The major
difference between these two cleanup projects, a difference which
greatly increased the difficulties in planning and conducting the
Enewetak cleanup, was that at Enewetak there were significant
island areas requiring cleanup of transuranium element .
contamination in soil. The cleanup of Enewetak Atoll represents
the most recent experience in restoring a large area contaminated
by transuranium elements.
7-1
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ENEWETAK
MIKE CRATER-
ENJEBI
SOUTHWEST\
PASSAGE
DEEP
(i) ENTRANCE
162° 20' EAST
FIGURE 7-1
7-2
-------
IRENE
EDNA
DAISY
CLARA
BELLE
ALICE
LEROY
JANET
KATE,
LUCY
PERCY
KEITH
JAMES
IRWIN
HENRY
North Pacific Ocean
,OLIVE
'PEARL
'RUBY
'SALLY
-TILDA
-URSULA
-VERA
-WILMA
Deep entrance
ELMER
WALT
'GLENN
FRED
Wid«
Map of Enewetak Atoll
(U.S. Name Designation)
FIGURE 7-2
7 - 3
-------
A map of the Enewetak Atoll, with designation of the
principal islands, is shown in Figures 7-1 and 7-2. Transuranium
element contamination in soil and other environmental media on
Enewetak prior to cleanup is summarized in Tables 7-1 and 7-2.
A diagram showing the sequence of events related to the important
decisions, judgments, advice, and agreements that were critical
to Enewetak radiological cleanup is given in Figure 7-3. The
diagram shows the major elements of the remedial action program
from the decision in 1972 to return the islands in habitable
condition to completion of field operations in 1980.
The AEG performed the necessary baseline radiological
surveys in early 1973, and developed dose assessments for a
series of assumed resettlement patterns. In July 1973, the AEC
appointed a Task Group to prepare cleanup radiological criteria
and recommendations. The approach adopted by the AEC Task Group,
in development of radiological safety criteria for use in
planning cleanup and rehabilitation, involved a conservative
application of national and international radiation protection
standards for individuals in the population expected to receive
the highest radiation exposures.
For planning purposes, the Task Group recommended that the
annual dose rate of individuals from exposure to fission products
be limited to 50 percent of the then existing Federal Radiation
Council standards for annual exposure of individuals, and
80 percent of the 30-year standard for a population. Of concern
in the implementation of these criteria was the uncertainty
inherent in predicting dose for returning inhabitants. The types
and amounts of locally grown food that would be eaten, and the
degree to which the inhabitants would comply with restrictions on
land and food use, were among the factors contributing to this
uncertainty.
7-4
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TABLE 7-1
PLUTONIUM CONCENTRATIONS IN SOIL ON" ENEWETAK ATOLL
. -... (PRIOR ,TO CLEANUP) r, . ,; --^
Pu-239 in top 15 cm of so.il
Island
Alice
a
Belle dense
light3
Clara
Daisy dense
light
Edna
Irene
Janet :.
Kate dense
light
Lucy
Mary
Nancy
Percy
Olive dense
light
Pearl hot spot
remainder
Ruby
Sally
Tilda -dense
light
Ursula
Vera
Wilma
Yvonne southern
northern beaches
David, Elmer, Fred
Leroy
All others
a. "dense" and "light" refer to
b. 1 pCi/g in the top 15 cm of s
Mean ,
;- ' (pCi/g)
- . ; 12 , .
26
11
22
41
" '''''' '15
- . . :-. 18. -: ,
11
9- '
...-.: .-17
.:,.", 2 . ,
- -' '8 ;'
'.-. ' ;- . ,8
9
' 4
' F8
3
51l
11
7 .
' : 4'-"-'
:-,:.: '3 ' '
3 . ,-
.--,.-.-- - j_
',,:.- .'-.; . ; 3- ;
1
. i :-.- : . -. 3;2 ,
, ,';- 3-- .,'
. . 0A04 .. ,
0:6
"' 0:0? .
vegetation 'cover
soil is aDDrox1mAf-ol \
Range
(pCi/2> '-
7-130
6-26
. . ..*:. : -4-88 '.
, 22-98 .
' "'* 4-33" '"
-, :-. ; 13-24 .
v 2-280
0.08-170
' ; ; - -.'- 9-50 ^ f
,0.2-14.
~':" 2-^22 '"
, ,,J :-.-- 2-5 v ':' '- ^
-.. 2-28; ...... ..
2-23
:. -.- 2-30- - - '
, ; . 2-4
" ' " 15-530
1-100
.3-24..
" " 6.2-130"
. ,;,- ..... i-a;/.:.
; . ... 1-34
0.3-7 ;
-- .--o. '.6-2.5 . - -.
0. 1-5
:>/r" 0^02-50 '! '
..;,-\ , -.o.-3^18-' "' *'
. ,,., ,0,. 004-0,3 ,..;-
"'" '0.02-2
:- 0.004^^ '"
.<,'.-,. ?^-.. ,-. &.X. -. ...
/ On»tTirolorsf- f r\
ey equvaen
0.23 uCi/mz or 0.045 yCi/tn2 if only the top 1 cm of soil is
considered and 20% of the total activity is. assumed to be in the
top 1 cm of soil.
7-5
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TABLE 7-2
PLUTONIUM AND AMERICIUM CONCENTRATIONS
IN VARIOUS ENVIRONMENTAL MEDIA ON ENEWETAK ATOLL
(PRIOR TO CLEANUP)
Media
Sediments
Surface Waters
Coconuts
Birds
Muscle
Liver
Eggs
Coconut Crabs
Location
Lagoon
Lagoon
Ocean "(East)
As Found
As Found
As Found
Radionuclide
Pu-239
Am-241
Pu-239
Pu-239
Pu-239
Pu-239
Pu-239
Activity
460 mCi/km
170 mCi/km2
9-40 fCi/£
0,3
< 0.022 pCi/g'
0.001-0.1 PCi/ga
0.004-0.07 pCi/ga
0.0005-0.02 pCi/g£
0.001-0.01 pCi/ga
(a) dry weight
-------
Table 7-4 shows the cleanup planning criteria recommended by
the Task Group. It was recognized that the levels of fission
products in soil (predominantly Cesium-137 and Strontium-90 with
half-lives of about 30 years) on some of the northern islands at
Enewetak Atoll could preclude their immediate use as village
islands without removal of a significant portion of the soil of
these islands. The levels of fission product contamination would
be reduced through radiological decay by about 50 percent every
30 years. Removal of the top layer of soil, sufficient to make a
significant reduction in fission product concentration, would
remove much of the organic material and destroy the usefulness of
such islands for agriculture. Temporary restrictions on land use
were considered a preferred alternative to soil removal for such
islands. The Task Group also considered the possibility of using
health risk estimates in the development of cleanup criteria.
The position taken on this approach is stated below:
"The Task Group and its technical advisors have reviewed
the available information from ICRP, UNSGEAR, and the
National Academy of Sciences BEIR Committee that could be
used to estimate the health risk that may be associated with
long-term exposures at the level of the radiation dose and
soil removal criteria being recommended. It is clear from
this review that knowledge of the relationship between
radiation dose and effects of that dose on man as
characterized in dose-effect curves is incomplete even for
external radiation exposures. For internal emitters and
particularly for plutonium, the situation is even less
satisfactory. Using a linear dose-effect curve, exposure at
the level of the recommended criterion of 0.25 rem/y would
give 2.2 X 102 cases (of cancer) per year. The Task Group
views this as a pessimistic upper limit of risk. It could
be inferred that there may be between zero and three cases
of cancer in 100 years if the entire Enewetak population
were continuously exposed to 0.25 rem/y over that time
period. A lack of confidence in the statistics and risk
7-7
-------
FIGURE 7-3
ENEWETAK ATOLL CLEANUP
- SEQUENCE OF EVENTS
SCREENING
SURVEY-MAY 72
ENGINEERING
SURVEY -
OCT.-DEC. 72
ANNOUNCEMENT OF
RETURN OF
ENEWETAK APR. 72
AEC TO PROVIDE
RAO SURVEY.
CRITERIA, ft TECH.
SUPPORT SEPT. 72
OFFICIAL COMMITMENT
FOR CLEANUP
RAD SURVEY
OCT. 72-FEB. 73
SURVEY REPORT,
NV-140 OCT. 73
AEC TASK GROUP.
FLEXIBLE
RADIOLOGICAL
CRITERIA CLEANUP
OPTIONS
JULY 73-JUNE 74
ICRP
NCRP
FRC
HEALY
REPORT
LA5483-MS
74
STUDIES. SURVEYS.
ASSESSMENTS.
DEVELOPMENT OF
RADIOLOGICAL
CRITIERA.
RECOMMENDATIONS
ENEWETAK
ATOLL MASTER
PLAN MAR. 76
ENVIRONMENTAL
IMPACT STATEMENT
APR. ,75 CLEANUP
OPTIONS ft
RECOMMENDATION
CONGRESS &
OMB REVIEW
FUNDING JULY 76
DNA OPERATIONS
PLAN APR. 77
CLEANUP FIELD
OPERATIONS 77--80
MEMORANDUM OF
UNDERSTANDING
DNA-ERDA SEPT. 76
BAIR ADVISORY
COMMITTEE
COMMISSION
POLICY PAPER
JULY 74
DEVELOP AND
ISSUE EIS
CONGRESSIONAL
APPROVAL.
INTERAGENCY
AGREEMENTS.
FUNDING
FIELD
OPERATIONS
7-8
-------
TABLE 7-3
1"ASK GROUP CONCLUSIQSMS
Cleanup and Rehabilitation of Enewetak Atoll is Feasible
Doses from Fission Products will Predominate
The Degree of Cleanup of the Atoll Should be Dictated
by the Requirement to Keep Exposure within Acceptable
Standards
National and International Standards Apply
A Fraction of FRC's, RPG's for Individuals Should be
Utilized to Evaluate Cleanup and Land Use Options
Involving Fission Product Doses
A Fraction of ICRP Standards for Lung for Individuals
Should be Utilized to Develop Flexible Soil Cleanup
Criteria Expressed as a Concentration of TRU Elements
in Soil, i.e., pCi/gm*
A Group of Experts Should Support Cleanup Operations
with Advice on Application of Task Group Criteria to
Specific Situations
Land Use Restrictions, as Opposed to Soil Removal, are
the Recommended Method for Controlling Exposure from
Fission Products
Removal and Disposal of Soil, or a Permanent Quarantive,
are the Only Effective Measure Against Soil TRU
Concentrations Exceeding Task Group Criteria
*The Task Group believed that site-specif ic criteria could be developed on a
case-by-case basis using conservative assumptions and a safety factor, but
that biological and environmental information is not adequate to establish
general cleanup guidance.
7-9
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TABLE 7-4
DEVELOPMENT OF CLEANUP CRITERIA
1974 TASK GROUP REPORT
DOSE BASED ON FEDERAL RADIATION COUNCIL LIMITS
TO INDIVIDUALS, 50 PERCENT OF FRC ANNUAL RATE LIMIT
TO POPULATION, 80 PERCENT OF FRC 30-YEAR GENETIC LIMIT
RESULTING GUIDANCE APPLICABLE TO PLUTONIUM CONCENTRATION
IN SOIL:
OVER 400 pCi/g, REMOVE SOIL
UNDER 40 pCI/g, LEAVE IN PLACE
BETWEEN 40 AND 400, CA'SE-BY-CASE DECISION
1977 SERIES OF FALL MEETINGS BETWEEN DOE AND DNA
CRITERIA TO INCLUDE ALL TRANSURANICS, NOT JUST PLUTONIUM
CLEANUP CRITERIA LINKED TO INTENDED ISLAND USE
AGRICULTURAL ISLAND TO MEET CRITERIA OF 100 pCi/g
CRITERIA INTENDED TO COMPLY WITH EPA PROPOSED GUIDELINES
1978 SERIES OF SPRING MEETINGS BETWEEN DOE AND DNA
PRELIMINARY DOSE ESTIMATES BY LLL INDICATED CLEANUP SHOULD BE
ACCOMPLISHED TO THE FOLLOWING LEVELS TO MEET PROPOSED EPA
CRITERIA:
RESIDENCE ISLAND 10 pCi/g
AGRICULTURAL ISLAND 20 pCi/g
FOOD GATHERING ISLAND 40 pCi/g
1978 BAIR COMMITTEE RECOMMENDATIONS:
1st PRIORITY - CLEANUP TRANSURANICS ON RESIDENTIAL ISLANDS TO
AVERAGE LESS THAN 40 pCI/g FOR EACH QUARTER-
HECTARE AREA
2nd PRIORITY - CLEAN TRANSURANICS ON AGRICULTURAL ISLANDS TO
AVERAGE LESS THAN 80 pCi/g FOR EACH HALF-HECTARE
AREA
3rd PRIORITY - CLEAN TRANSURANICS ON FOOD GATHERING ISLANDS TO
AVERAGE LESS THAN 160 pCi/g FOR EACH HALF-HECTARE
AREA
7 - 10
-------
estimate drawn therefrom has led the Task Group to have
serious reservations about their validity. The Task
Group holds the opinion that such estimates cannot be
used in any definitive way to draw conclusions on
whether current radiation standards are too high or too
low or as a basis for decisionmaking relative to
resettlement of Enewetak Atoll."
Soil contamination levels for the transuranium elements at
Enewetak would not be reduced appreciably with time due to the
long half life for Plutonium-239 (about 26,000 years). There
appeared to be only two options for an island with unacceptably
high soil concentrations of transuranium elements, namely,
l)*remove the contaminated soil or 2) place the island off
limits. The Task Group treated transuranium element soil
contamination as a separate problem..
Plutonium contamination in soil and the need for Federal
standards for remedial actions were subject of considerable
interest in the early I970;'s. The Environmental Protection
Agency was evaluating the need for standards or guides. There
was Congressional interest, and the Enewetak people, through
their legal counsel, were supporting "total" cleanup.
The Task Group favored use of conservative criteria for
transuranium element contamination that could be related to a
dose standard but expressed in terms of an environmental
measurement that can be made in the field. The Task Group
recommended a soil concentration below which cleanup was not
required, a soil concentration above which cleanup was mandatory,
and a range of soil concentrations between these two values where
corrective actions should be determined on a case by case basis
by a team of experts assembled for this purpose. The soil
concentration value above which cleanup would be mandatory was
taken from a LASL report which developed a relationship between
soil concentration of a mixture of transuranium elements typical
7-11
-------
of nuclear weapons and dose to lung through resuspension and
inhalation. A soil concentration of 400 pCi/g (the level at ,
which cleanup is mandatory) was estimated to be equivalent to
the ICRP standard for lung dose for individuals, i.e., 1,500
mrem/y. The soil concentration value below which cleanup would
not be required was arbitrarily set at one-tenth of 400 pCi/g,
or 40 pCi/g. ;'
The Task Group recommendations on soil concentrations were
very general and did not specify details such as the degree of
cleanup required for various land use options and the area over
which soil radioactivity concentrations were to be averaged for
each type of island. These issues were addressed later by the
Bair Committee, a group of technical advisors to the cleanup ;
operation, headed by Dr. William J. Bair, of the Pacific
Northwest Laboratory, in the process of providing more detailed
advice on cleanup in the range of soil concentrations between
40 and 400 pCi/g. Other issues, such as monitoring instruments
and soil sampling-techniques, quality control, and statistical
methods were also addressed later. , :
.""**-,
One of the key items in the task group's deliberation was
the consideration of cleanup and rehabilitation options. The
task group evaluated dose for a five by six matrix,? of .cleanup
levels and food production locations versus living patterns,
and five options for cleanup of transuranium contaminated,soil
ranging from no cleanup to extensive soil removal. Six options
for disposal of contaminated soil were also evaluated. The task
group made recommendations on preferred options. The various
options were presented in an Environmental Impact Statement
developed by the Defense Nuclear Agency.
Preparation of an Environmental Impact Statement for Cleanup
of Enewetak was an important part of planning this project, as
were final agreements between agencies on responsibilities,
funding, and staffing of the field organization that would
7 - 12
-------
perform the cleanup. These agreements and final plans were
documented and formally approved in a Memorandum of understanding
and in an Operation Plan. Since the cleanup criteria for soil
and their implementation at Enewetak determined how much soil was
to be removed for disposal, and to some extent the size of the
task group and the time required, these criteria in large measure
determined the cost of soil cleanup, a subject of considerable
interest to those conducting and supporting cleanup. This
relationship to cost generated a continuing requirement to
explain and defend such criteria and to adapt them to unusual
circumstances throughout the cleanup project.
Cleanup of contaminated soil was an iterative process.
A typical sequence of events was as follows:
1. The history of use of the island plus information from
recent radiological surveys, including information on any
subsurface contamination, was reviewed.
2. Heavy vegetation was either removed or access lanes
were cut.
3. A grid was established marked by wooden stakes bearing
geographic coordinates of the locations. Maximum spacing of
grid lines was 100 meters. In many places a closer spacing
was used.
4. An in-situ survey of Am-241 in surface soil was
performed using the grid points described previously.
Measurements were reviewed by statisticians and recorded in
a data base.
5. Soil samples were collected at locations devised by the
statisticians. These samples were analyzed to determined
the ratio of Pu-239 (and other transuranium elements) to
Am-241. The analysis of this soil was performed in a
7-13
-------
chemistry laboratory established for this purpose on
Enewetak Island.
6. Using the in-situ data for Am-241, and the soil
analysis data, the concentrations of transuranium elements
in surface soil were determined. These concentrations,
plotted on a map along with the cleanup criteria, were used
to determined locations where soil removal was needed.
7. Bulldozers and front-end loaders were used to remove
the contaminated soil. A 6-inch layer was usually removed.
Some amount of crosscontamination of the new surface was
unavoidable. The contaminated soil was hauled away for
disposal on Runit Island.
8. After removal of soil, the area of cleanup was again
monitored. If the new surface met the cleanup criteria, no
further soil removal was needed. If the new surface was
still above the criteria, more soil was removed. This
process continued until the criteria were met. The deeper
excavations were filled with clean soil.
9. The contaminated soil was pumped as a soil-cement
slurry through a pipe to the bottom of a water filled bomb
crater on Runit Island, displacing the water. The crater
was filled with the soil-cement mixture plus other
contaminated debris collected throughout the atoll. The
soil-cement was mounded above the surface of the island and
capped with 18 inches of concrete. When cleanup operations
were completed, Runit Island was placed "Off Limits" and is
to remain quarantined indefinitely.
Cleanup operations covered 81 acres on six island and
104,000 cubic yards of contaminated soil were removed. The total
cost of the cleanup and rehabilitation effort was about $100
7-14
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TABLE 7-5
RISK OF RADIATION-INDUCED CANCER
DEATH AT ENEWETAK
NUMBER RESIDENTS, AVERAGE/YEAR, 30 YEARS 500
ADDITIONAL RADIATION-INDUCED CANCER DEATHS, 30 YEARS 0.026
ADDITIONAL CANCER DEATHS PER YEAR, PER 500 RESIDENTS 0.0009
RATE PER 1,000,000 1p7
APPROXIMATE RISK TO FUTURE RESIDENTS 1.7 x IQ-"
-------
million and required an on-atoll task force of about 1,000 people
for 3 years.
The task force was monitored continuously for radiological
contamination. Personnel were exposed to radiation and to
industrial hazards. Monitoring for intake of radioactivity was
done by the collection and analysis of 24-hour urine samples.
For more than 2,000 samples, only 6 had readings above the
minimum detectable level. For external whole body radiation,
where there were more than 12,000 individual records, only four
exceeded 0.050 rem. The highest was 0.070 rem. There were
63 lost-time accidents and 4 work-related fatalities for a
population of approximately 1,000 persons in the atoll at any one
time over a period of 3 years.
The cleanup operation resulted in restoration of islands in
the southern part of the atoll for full and unrestricted use, and
in cleanup of transuranium contaminated soil on the northern
islands. Soil concentrations of radionuclides were determined
and projected doses to individuals were calculated. A range of
living and dietary patterns were considered including the case
of total dependence on the local food supply. Whole body doses
for those resettled in the southern islands range from 4.5 to
8.6 mrem/y depending on the amount of imported food in the diet.
A summary of projected radiation risks to the Enewetak population
after cleanup is shown in Table 7-5. Predictions of whole body
and bone marrow doses for Enjebi residents exceed the Task Group
recommendations. Enjebi Island is not to be resettled until the
fission products in the soil of that island have decayed to
acceptable levels. Runit Island, where CACTUS crater contains
the contaminated debris and soil from cleanup operations, is
quarantined indefinitely.
<>U. S. GOVERNMENT PRINTING OFFICE : 1 990-717-003:28019
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