United States
Environmental Protection
Agency
Office of
Radiation Programs
Washington DC 20460
Technical Note
ORP/TAD-80-1
Radiation
EPA
HEALTH RISKS TO DISTANT POPULATIONS
FROM URANIUM MILL TAILINGS RADON
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TECHNICAL NOTE
ORP/TAD-80-1
Health Risks to Distant Populations
From Uranium Mill Tailings Radon
Jerry J. Swift, Ph.D.
May 1981
Environmental Protection Agency
Office of Radiation Programs
Washington, D.C. 20460
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PREFACE
This document was first drafted in June 1974 as part of a
program to determine which measures to use to control radioactivity
from tailings piles at inactive uranium mills. In the interim more
sophisticated analyses methods have become available; but the basic
conclusions remain valid. This revised and updated version is
published now in support of environmental and public health
protection standards developed by the Environmental Protection Agency
under the Uranium Mill Tailings Radiation Control Act of 1978.
iii
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CONTENTS
Chapter Page
1* Introduction 1
1.1 Purpose of this Report 1
1.2 Background 1
2. Radon Release Rate 4
3. Dispersion of Radon 6
3.1 Within Eighty Kilometers 6
3.2 Nationwide 7
3.3 Worldwide 10
4. Exposure to Radon Decay Products 11
5. Health Risks 20
6. Discussion .24
6.1 Comparison with Other Estimates 24
6.2 Uncertainties 25
References 29
Appendix A—Tailings Coordinates 32
Appendix B—Adjustment for Area Source 33
Table
2-1. Estimated Surface Areas and Radium-226 Concentrations of
Uranium Tailings Located at Inactive Mill Sites 5
3-1. Annual Average Dispersion of Radon-222 from Uranium
Tailings Piles to Distances of 80 Kilometers 8
4-1. Collective Radon-222 Decay Product Exposure to the
Population within 80 km of the Uranium Tailings Pile
at Grand Junction, Colorado 13
4-2. Collective Radon-222 Decay Product Exposure to the
Population within 80 km of the Uranium Tailings Pile
at Gunnlson, Colorado *. 14
iv
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CONTENTS (continued)
Table Page
4-3. Collective Radon-222 Decay Product Exposure to the
Population within 80 km of the Newer Uranium Tailings
Pile at Rifle, Colorado 15
4-4. Collective Radon-222 Decay Product Exposure to the
Population within 80 km of the Uranium Tailings Pile
at Shiprock, New Mexico 16
4-5. Collective Radon-222 Decay Product Exposure to the
Population within 80 km of the Uranium Tailings Pile
at Falls City, Texas 17
4-6. Collective Radon-222 Decay Product Exposure to the
Population within 80 km of the Uranium Tailings Pile
at Mexican Hat, Utah 18
4-7. Collective Radon-222 Decay Product Exposure to the
Population within 80 km of the Uranium Tailings Pile
at Salt Lake City, Utah 19
5-1. Comparison of the Estimated Fatal Lung Cancer Commitment at
Selected Distances Due to Radon-222 from Tailings
at Seven Inactive Uranium Mill Sites 22
5-2. Comparison of the Estimated Fatal Lung Cancer Commitment at
Selected Distances Due to Release of 1000 Curies of
Radon-222 from Tailings at Seven Inactive
Uranium Mill Sites 23
6-1. Summary of the Estimated Risk of Fatal Lung Cancer
Commitment at Selected Distances Due to Radon-222 from
Tailings at Seven Inactive Uranium Mill Sites 38
Figure
3-1. Annual Average Radon-222 Concentrations (Units of 10~20Ci/m3)
Due to a Continuous Release of One Curie Per Year from
the Salt Lake City, Utah, Tailings Location 9
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1: INTRODUCTION
1.1 Purpose of this Report
This paper has several purposes: to illustrate the effects of
tailings piles on a variety of local and regional populations, to
assess the effects of the tailings on distant populations, and to
compare our methods and results with assessments by others.
1.2 Background
Uranium mill tailing piles can expose the population to
radiation by several pathways. We believe the air pathway to be the
most important. Radon-222, which is produced in the pile and
released to the air, is the principal radionuclide.
Uranium-238 undergoes radioactive decay with a long half-life,
4.47 billion years, producing a series of other radionuclides,
including radium-226 (half-life 1600 years) and its decay product,
radon-222 (half-life 3.82 days). Thus, radium-226 and radon-222 are
commonly found with uranium ore and with the waste, i.e. tailings,
from the mills that separate uranium from the ore. Radon is a gas,
but when it is created, it may or may not be trapped inside grains of
tailings. The emanating fraction,-'- i.e., the fraction of the
radon-222 that is released from the grains, is about 0.2 (Fo78). The
radon-222 gas that is released into the spaces between the grains of
tailings material diffuses toward the overlying tailings surface;
some reaches the surface and some undergoes radioactive decay
enroute.
The radioactive products of radon-222 decay are not noble gases,
and they interact with and remain in the tailings. The radon-222
that reaches the surface escapes into the air above, where it is
mixed into the passing airstream by normal local air turbulence. The
wind carries the radon-222 with it and continually decreases the
concentration by further mixing and dilution. The radon-222
concentration is also decreased by its radioactive decay.
1The release of radon into interstitial spaces in the tailings
is called "emanation;" the release of the radon from the tailings
surface into the air is sometimes called "exhalation,"' but we are not
using that term because Inhalation and exhalation are performed by
people at the other end of this pathway.
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Radioactive products of the decay, as free ionized atoms, are
carried along in the air currents where they tend to attach to dust
particles. Thus, persons breathing air downwind of the tailings pile
will be exposed to radon-222 and also to its radioactive decay
products, which may be either free ions or carried by dust particles.
Air entering a building downwind of the tailings pile remains
inside it for a time that depends on the rate at which air enters and
leaves the building. Radon-222 in the air continues its normal rate
of radioactive decay, forming the series of radioactive decay
products that may be inhaled by persons in the building.
Some of the radioactive decay products of radon-222 are retained
in the tracheobronchial region of the lungs, irradiating the fluids
and tissues, and thus increasing the chance that cancer will form
there. In contrast, persons exposed outdoors to the same
concentration of radon-222 from a nearby tailings pile (e.g., within
1 km) , may receive exposure to the lungs from the associated radon
decay products that is appreciably smaller (e.g., a factor of 10)
than that received indoors, because a delay time is lacking for decay
products to accumulate (Sc74, Sw76). At long distances from the
pile, when the decay products have "grown in," exposures resulting
from the released radon will be similar indoors and outdoors.
In March 1974, the U.S. Environmental Protection Agency and the
U.S. Atomic Energy Commission testified at hearings before the Joint
Committee on Atomic Energy on pending bills to provide a remedial
action program for a tailings pile at an Inactive uranium mill site
on the edge of Salt Lake City, Utah. Both Federal agencies
acknowledged that there are other uranium tailings sites that present
public health problems and that legislation to deal with all inactive
mill sites would provide more effective control.
After the March 1974 hearings, these agencies began a
cooperative study, involving the concerned States and Federal
agencies, to determine the current situation at the inactive uranium
mill sites and to evaluate remedial measures for each site. The
results of the study were published in a series of reports by the
main contractor, Ford, Bacon & Davis Utah, Inc. (References
Fo76-Fo77g are from this series, which includes reports numbered
GJT-1 through GJT-20.) Shortly thereafter, the Uranium Mill Tailings
Radiation Control Act of 1978 (PL 95-604) created a joint
Federal/State remedial action program for most inactive mill sites.
In the early stages of the cooperative study of the inactive
sites and as a contribution to determining which aspects of the
tailings piles should be investigated, a report—"Potential
Radiological Impact of Airborne Releases and Direct Gamma Radiation
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to Individuals Living Near Inactive Uranium Mill Tailings Piles"—
(Sw76) was published. This report (Sw76) addressed certain radiatio'n
exposure pathways for people within a few kilometers of the tailings
piles, including inhaling airborne short-lived radon decay products.
During this same period, the first draft of this present document was
prepared. It provided a preliminary estimate of the comparative
potential radiation exposures of populations at various distances due
to inhaled short-lived radioactive decay products of radon-222
released by the tailings piles to the air.
The most significant change here from that early draft is
presenting the results in terms of health risk rather than dose
equivalent.
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2: RADON RELEASE RATE
For the air pathway, in which the lung is exposed to inhaled,
short-lived radioactive products of the decay of radon-222 released
from the piles, the long-term average radiation exposure is assumed
to be proportional to the total amount of radon released to the air.
We take the amount released by each pile to be a constant (see
below) times the product of the concentration of radon-226 (the
precursor of radon-222) in the pile and of the surface area of the
pile.
Table 2-1 lists inactive uranium mill sites and estimates the
surface area and radium-226 concentration for the tailings piles at
each site (En80). Changes in these data may occur as piles may be
reworked to extract more uranium or vanadium, or perhaps reshaped.
For the estimate of radon release in Table 2-1, we assume that
radon-222 is released to the air at an average rate of 1.0 pCi/m^
each second for each pCi of radium-226 per gram of tailings. Our
estimate comes from treating the tailings as if they are homogeneous
and are not covered by much other material, such as soil or water.
The release rate is assumed to be uniform and continuous throughout
the year. Measurements of the radon release rate from any of these
piles taken over short periods have differed appreciably from the
estimates used here, e.g., from one-fourth to two times as great
(Fo76, Fo77a-Fo77g). We consider these measurements to be no more
reliable representations of the average releases than our estimates
(see Section 6.2).
Ford, Bacon & Davis Utah, Inc. (Fo76, Fo77a-Fo77g) report that
the tailings at some sites are in more than one pile and that
different portions of the tailings at a site can have different
characteristics. Such nonuniformities may make the local radon
release rate greater or smaller than we estimate.
A number of the piles have soil, covering the tailings, and some
are quite wet (e.g., at Falls City, Fo77a), conditions that tend to
reduce radon release rates. Some of the tailings at inactive mill
sites also have been subjected to a variety of treatments that might
(at least temporarily) change their release rates. In the present
work, we make no attempt to account for the effects of the treatments.
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Table 2-1. Estimated Surface Areas and Radium-226 Concentrations
of Uranium Tailings Located at Inactive Mill Sites
Tailings
Site
Monument Valley, Ariz.
Tuba City, Ariz.
Durango, Colo.
Grand Junction, Colo.
Gunnison, Colo.
Maybell, Colo.
Naturita, Colo.
Rifle, Colo, (new)
Rifle, Colo, (old)
Slick Rock, Colo. (1)
Slick Rock, Colo. (2)
Lowman, Idaho
Ambrosia Lake, N.M.
Shiprock, N.M.
Lake view, Ore.
Canons burg, Pa.
Falls City, Texas
Ray Point, Texas
Green River, Utah
Mexican Hat, Utah
Monticello, Utah
Salt Lake City, Utah
Converse County, Wyo.
River ton, Wyo.
Average Ra-226
Concentration3
(pci/g)
50
924
700
784
420
274
800
868
1008
784
686
532
644
700
420
unknown
448
518
812
784
910
896
336
560
Tailings
Areaa
(105m2)
1.21
0.89
0.85
2.39
1.58
3.24
0.93
1.30
0.53
0.77
0.24
0.20
4.25
2.91
1.21
0.73
5.91
1.90
0.36
2.75
1.62
4.05
0.20
2.91
Estimated Annual
Rn-222 Release
(Ci)
200
2600
1900
5900
2100
2800
2300
3600
1700
1900
500
300
8600
6400
1600
«~ —
8400
3100
900
6800
4700
11500
200
5100
a(En80).
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3: DISPERSION OF RADON
We have treated the dispersion of radon-222 from its release at
a tailings pile until the exposure of populations to its decay
products in several phases.
The first phase estimates dispersion within 80 km of the
tailings pile; the second estimates dispersion while the radon is
windborne over the North American continent until it departs eastward
over the North Atlantic Ocean; and the final phase considers the
worldwide dispersion.
For all distances greater than 12 km, the dispersion was
estimated using techniques adapted from Machta, Ferber, and Heffter
(Ma73). We assume that once it is released to the atmosphere, radon
is dispersed by the wind and is removed only by its intrinsic
radioactive decay and not by any other process (e.g., sorption).
3.1 Within Eighty Kilometers
Dispersion to 12 km from a pile was calculated with the AIREM
code (Ma74), using a standard sector-averaged equation
(equation 3.144 in Slade (S168)). For locations within a few
kilometers of a pile, an adjustment was made for the size of the pile
(see Appendix B). As in (Sw76), meteorological data from the Fort
St. Vrain reactor site in Colorado (Re70) was used for exposures out
to 12 km, because accurate site-specific data for the individual
tailings piles are lacking (see Section 6.2).
From 12 km to 80 km, the dispersion model of Machta et al.
(Ma73) (for a source located at Morris, Illinois) was used, averaged
over all directions. Machta's data for exposures in the 12 to 80 km
range were approximately one-fourth those of the AIREM calculation,
but were used in order to be consistent with the exposures at greater
distances. Table 3-1 gives the annual average dispersion in seconds
per cubic meter, averaged over all compass directions, for distances
ranging out to 80 km from the tailings center.
We used the annual average dispersion, averaged over all
directions, for simplicity and because of insufficient data to
justify greater sophistication. Long-term measurements of radon
concentrations near tailings piles (He69) show large variations with
the direction from the pile.
These variations may be caused by topography, diurnal wind pat-
terns, diurnal variations in radon release rate, or other factors,
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and are strongly site-specific within a few kilometers of the
tailings. Data from the tailings location itself are required for a
better estimate, but are not available (see Section 6.2).
3.2 Nationwide
Over periods of a year or more, winds will carry radon in all
directions from a tailings site. The four-day half-life of radon-222
is sufficiently long that exposure to this radon source is national
(and even hemispherical) in extent. Prevailing winds generally carry
the radon to the east, so that annual exposures from a tailings pile
diminish more rapidly in other directions from the pile.
Machta, Ferber, and Heffter have estimated regional, national,
and worldwide pollutant concentrations from continuous releases
(Ma73). There had been several earlier calculations of national
exposure levels following release of gaseous effluents from a single
site. For example, Knox and Peterson (Kn72) had estimated population
exposures over large areas of the United States and worldwide,
following releases of krypton-85 from nuclear power plants and
nuclear fuel processing plants.
The data from (Ma73) were adapted for the estimate presented
here. We adjusted the concentration isopleths from (Ma73) for North
America for radon-222 decay during its travel time, using mean wind
speeds. The resulting isopleth pattern was superimposed on the map
of the United States at each tailings pile location, providing annual
average concentrations for the 48 contiguous States.
A similar approach was used for Canada and Mexico, although the
population data (Ne74) were not as detailed as that for the United
States. Figure 3-1 shows the isopleth pattern using the Salt Lake
City tailings pile as the source. The source strength from which the
isopleths were developed is a continuous release rate of one curie
per year. If the concentration varied greatly within a State near
the tailings pile, concentration isopleths were fitted to a map of
the State so that county-by-county exposures could be estimated.
After we performed this relatively simple estimation process,
more accurate methods were developed and applied (Tr79). We will
compare the methods and results in Chapter 6.
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Table 3-1. Annual Average Dispersion of Radon-222 from
Uranium Tailings Piles to Distances of 80 kilometers
(averaged over all compass directions)
Average Distance from
Pile Center
(km)
0.25
0.5
0.6
0.75
1.25
1.5
1.75
2.0
2.25
2.5
2.75
3.25
3.5
3.75
4.5
7.5
9.6
15
24
30
40
50
60
70
80
Annual ,
Average Dispersion '
(s/m3)
2.4xlO~5
6.9xlO~6
4.7xlO~6
2.9xlO~6
8.2xlO~7
6.3xlO~7
5.0xlO~7
4.1xlO~7
3.5xlO~7
3.0xlO~7
2.6xlO~7
2 .IxlO"7
1.8xlO~7
1.6xlO~7
1.2xlO~7
4.9xlO~8
3.5xlO~8
1.3xlO~8
3.9xlO~9
2.3xlO-9
1.4xlO~9
l.OxlO"9
8.2xlO-10
6.6xlO-10
5.7xlO-10
a(s/nr) = seconds per cubic meter. If the annual
average release rate to the air is given in picocurles per
second, the product of it and the annual average dispersion
will be an annual average concentration in the air in units of
picocuries per cubic meter.
^An average over all directions, of the annual averages
for 16 compass directions.
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Figure 3-1. Annual Average Radon-222 Concentrations
(Units of 10~20 Ci/m3) Due to a Continuous
Release of One Curie per Year from the
Salt Lake City, Utah, Tailings Location
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3.3 Worldwide
Worldwide exposure estimates were based on data from Machta et
al. (Ma73), where the source term Is a continuous release of one
curie per year of krypton-85. When adjustments are made for the more
rapid decay of radon-222, only the earlier phases of worldwide
dispersion are of interest. In a manipulation similar to that
applied to the regional and national isopleths, we shifted the
isopleth pattern for the early worldwide dispersion phase to the west
(about 20 degrees of longitude for the tailings pile at Salt Lake
City). The concentration over each individual country was multiplied
by the population of that country, and the product was corrected for
the radioactive decay of radon-222 while it travels to that location.
Windborne radon circles the world in about 30 days. After
30 days, about 0.004 times the original amount of radon remains,
which is insignificant when compared to the uncertainty in the
estimate of worldwide exposures. Therefore, there is no need for
longer-term assessment of worldwide dispersion of radon-222, as
Machta et al. (Ma73) did for krypton-85. We made only one estimate
of collective exposures in Europe and Asia because the dispersion
would be virtually the same for any pile located in the western
United States.
Machta1s work (Ma73), from which we derived the dispersion
beyond 12 km, represents an initial effort at calculating nationwide
and worldwide dispersion. Their computer program was not available
for general use at the time this document was drafted. The approxi-
mation we used, of translating the isopleths from the source location
at Morris, Illinois (used by Machta, et al.) to the various tailings
pile locations, does not incorporate differences from site to site in
regional wind patterns.
Therefore, our results show a smaller variation in collective
exposures per 1,000 curies released than recent site-specific
calculations (Tr79). Because we use the same isopleth pattern at
each tailings location, our estimates reflect primarily differences
in population distributions. In Chapter 6 we compare the results of
this simple procedure with the recent, more accurate calculations
(Tr79).
10
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4: EXPOSURE TO RADON DECAY PRODUCTS
Population data from the 1970 census are shown in Tables 4-1
through 4-7 for various distant sectors around uranium mill tailings
pile locations (See Appendix A). We use the population data combined
with radon concentration levels to estimate annual average population
exposures as a function of their distances from a tailings pile.
Census Bureau data indicate no one is living in the immediate
vicinity of certain tailings piles. Because the census data were
compiled by adding small groups of people together and assigning them
a collective location, this is not the actual case. There are
occupied dwellings and even small population groups where none are
shown by the census. However, people are unlikely to be mislocated
by more than a. few kilometers. Other sources (e.g., Fo77a-Fo77g)
have provided estimates of nearby populations which we have added to
the Census Bureau data where the latter showed zero population.
For the populations exposed at distances greater than 80 km, we
used 1970 census data for cities, counties, and States (Ne74).
We estimate the population exposure to radon and its decay
products similarly as in (Sw76). When radon is first released from
the tailings pile, it may be regarded as unaccompanied by its decay
products. Because it does not react chemically, radon is retained in
the body only in negligible amounts when inhaled, and causes only a
small radiation exposure of the lungs* Thus, the radon from a
tailings pile may add little to outdoor background radiation
exposures immediately downwind. However, when radon enters a
building and is given time to decay by the slow rate at which indoor
air is exchanged for outside air, a buildup of decay products of
radon-222 will occur in the air.
We assume that delay in the building air exchange provides time
for the buildup of short-lived radon decay products to about 70
percent of the radioactive decay equilibrium value (Un77). We also
assume that in outdoor air, far from the pile, approximately the same
70 percent equilibrium ratio of decay products is eventually obtained
(Un77).
At this level of decay product buildup, one pCi of radon-222 per
cubic meter of air is accompanied by approximately 7 x 10"^ Working
11
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Levels (WL) of the principal short-lived decay products, polonium-
218, lead-214, and bismuth-214. (The Working Level is defined (32 FR
11183) as any combination of the short-lived radon decay products in
one liter of air that will result in the ultimate emission of
1.3 x lO"^ MeV of potential alpha energy.)
In Tables 4-1 to 4-7, we present the collective exposures in
person Working-Level years (person-WL-years). We consider this a
more appropriate unit than the rem for estimating risks due to radon
decay products because the WL has been related to the incidence of
lung cancers observed in uranium miners exposed to those decay
products. Yearly exposure is more appropriate for the exposure
circumstances considered here than the Working Level Month (WLM) used
for uranium miners. Continuous exposure to one WL for a year is
roughly equivalent to 27 WLM, for a member of the general population
(Gu79).
We assume that, on the average, the exposed population spends
75 percent of the time indoors. Therefore, for exposures within
40 km of the tailings, we assumed that 75 percent of the exposure was
at 7 x 10~6 WL per pCi/m3 (indoors) and 25 percent at 5 x 10~6
WL per pCi/m3 (outdoors). At greater distances, we assume that
decay products have accumulated so that exposures are about the same
indoors and outdoors, at 7 x 10~*> WL per pCi/m3.
Tables 4-1 through 4-7 show the 'estimated collective exposures
at various distances from the tailings piles, covering the local and
regional populations. The estimated collective exposure to the
national population for a long-term (to average over fluctuations)
release of 1000 curies is 0.7 person-WL-year, averaged over the seven
locations.
The estimated collective exposure to the adjacent countries of
Canada and Mexico is about 0.1 person-WL-year for a long-term release
of 1000 curies, and to the rest of the world also about 0.1
person-WL-year. About 60 percent of this latter amount is
experienced in western Europe, and radioactive decay makes the
collective exposure smaller in India and eastward.
12
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Table 4-1. Collective Radon-222 Decay Product Exposure to the
Population within 80 km of the Uranium Tailings Pile
at Grand Junction, Colorado
Distance from
center of pilea
(km)
Population in
increments of
distance
Annual collective
exposure^
(person-WL-years)
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
5.0
10
20
40
80
166
1,022
5,024
3,611
6,224
7,001
3,697
800
4,022
8,401
8,684
3,851
18,084
1
4
5
2
3
2
0.9
0.2
0.6
0.5
0.1
0.01
0.02
Total
70,421
19
aOuter radius of an annulus whose inner radius is the next
smaller distance.
bFor an annual release of 5,900 Ci radon-222.
13
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Table 4-2. Collective Radon-222 Decay Product Exposure to the
Population within 80 km of the Uranium Tailings Pile
at Gunnison, Colorado
Distance from Population in Annual collective
center of pile3 increments of exposure
(km) distance (person-WL-years)
1
2
3
4
5
10
20
40
60
80
738
2,237
1,738
0
0
345
938
1,529
318
14,379
2
0.6
0.2
0
0
0.007
0.005
0.002
0.0001
0.004
Total 22,122 2.8
aOuter radius of an annulus whose inner radius is the next
smaller distance.
bFor an annual release of 2,100 Ci radon-222.
14
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Table 4-3. Collective Radon-222 Decay Product Exposure to the
Population within 80 km of the Newer Uranium Tailings Pile
at Rifle, Colorado
Distance from Population in Annual collective
center of pile3 increments of exposure"
(km) distance (person-WL-years)
1
2
3
4
5
10
20
40
60
80
42
2,108
0
0
548
0
1,397
2,621
11,939
19,976
Total 38,631
0.1
1
0
0
0.05
0
0.01
0.004
0.01
0.01 '
1.2
aOuter radius of an annulus whose inner radius is the next
smaller distance.
"For an annual release of 3,600 Ci radon-222 from the newer
tailings location at Rifle, Colorado.
15
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Table 4-4. Collective Radon-222 Decay Product Exposure to the
Population within 80 km of the Uranium Tailings Pile
at Shiprock, New Mexico
Distance from Population in Annual collective
center of pile3 increments of exposure0
(km) distance" (person-WL-years)
0.8
1.6
2.4
3.2
16
32
40
48
64
80
0
2,550
0
0
4,671
4,625
dl 1,822
A
a!4,449
15,857
16,794
Total 70,768
0.0
3
0
0
0.2
0.02
0.02
0.02
0.02
0.02
3.3
aOuter radius of an annulus whose inner radius is the next
smaller distance.
''Population data out to 1.6 km from Ford, Bacon & Davis Utah,
Inc. (Fo78).
cFor an annual release of 6,400 Ci Radon-222.
dPopulation count between 32 and 48 km divided into 32 to 40 km
and 40 to 48 km according to the ratio of the areas of the annuli.
16
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Table 4-5. Collective Radon-222 Decay Product Exposure to the
Population within 80 km of the Uranium Tailings Pile
at Falls City, Texas
Distance from Population in Annual collective
center of pilea increments of exposure"3
(km) distance (person-WL-years)
1
2
3
3.5
4
5
10
20
40
60
80
C50
50
90
160
200
200
600
4,196
28,448
67,876
821,665
0.3
0.04
0.04
0.04
0.04
0.04
0.05
0.09
0.1
0.1
1
Total 923,535 1.8
aOuter radius of an annulus whose inner radius is the next
smaller distance.
^For an annual release of 8,400 Ci radon-222.
cPopulation data to 10 km from Ford, Bacon & Davis Utah, Inc.
(Fo78).
17
-------
Table 4-6. Collective Radon-222 Decay Product Exposure to the
Population within 80 km of the Uranium Tailings Pile
at Mexican Hat, Utah
Distance from Population in Annual collective
center of pilea increments of exposure
(km) . distance (person-WL-years)
0.5
1.0
1.5
1.8
2.0
10
20
40
80
C2
10
47
143
115
0
2,681
1,235
10,212
0.02
0.04
0.05
0.1
0.08
0
0.05
0.004
0.01
Total 14,445 0.4
aOuter radius of an annulus whose inner radius is the next
smaller distance.
bFor an annual release of 6,800 Ci of radon-222.
cPopulation data out to 2 km from Ford, Bacon & Davis Utah, Inc,
(Fo78).
18
-------
Table 4-7. Collective Radon-222 Decay Product Exposure to the
Population within 80 km of the Uranium Tailings Pile
at Salt Lake City, Utah
Distance from
center of pilea
(km)
Population in
increments of
distance
Annual collective
exposure**
(person-WL-years)
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
5.0
10
20
40
80
7
156
397
735
8,986
4,228
11,594
12,050
42,679
280,000
106,000
80,000
308,000
o.ic
lc
0.8
0.9
7
3
6
5
.10
30
3
0.4
0.06
Total
854,832
68C
aOuter radius of an annulus whose inner radius is the next
smaller distance.
bFor an annual release of 11,500 Ci radon-222.
cTable C.2 in reference Fo78 indicates a greater population near
the tailings; it includes, within 0.5 miles of the pile's edge, 1400
residents and 3200 employed persons whose exposure would increase
these values by about 13 person-WL-years.
19
-------
5: HEALTH RISKS
The principal radiological health risk from exposure to
radon-222 is lung cancer from irradiation of the bronchial epithelium
of the lung by the short-lived radon decay products. From more
extensive assessments (Tr79, McD79) we have concluded that the
effects of the longer-lived decay products are less significant than
the incidence of lung cancer caused by inhaling short-lived decay
products. The following comparison of health risks does not consider
the risks from long-lived decay products, such as lead-210, or any
other radiation risk associated with tailings piles.
We have estimated risks based only on radon released directly
from tailings piles and have not included radon from tailings that
have blown off a pile or been used in construction. Windblown
tailings are secondary radon sources that could be significant, but
are difficult to assess. Tailings used in building construction, as
in building foundations, can expose people occupying the buildings to
increased indoor radon and radon decay product concentrations
(En79). The effects of tailings used in construction are beyond the
scope of this paper, however.
We estimated the risk by assuming an increased incidence of lung
cancer proportional to the level and duration of increased exposure
to short-lived radon decay products, and proportional to the natural
incidence of lung cancer (a so-called "relative risk" assessment).
Our risk estimates are based primarily on studies of underground
miners. Although there is considerable agreement on the risks from
radon to underground miners, there- is some uncertainty on how to
apply these risk estimates to the general public. The relative risk
estimate we used (En79) gives the same result as the most recent
estimate by the National Academy of Sciences (Na80), which is
calculated on the basis of age-dependent absolute risk. Neverthe-
less, these remain estimates on which there still exists disagreement
in the scientific community (Ra80).
The value we use, 2.3 committed fatal lung cancers per 100
person-WL-years, depends on the lung cancer incidence in the United
States as a whole. For certain States, the local lung cancer rate is
smaller than the national average. The health risks to the local,
regional, and total populations of these States are estimated by
multiplying 2.3 by a corresponding reduction factor. This reduction
factor is, for Texas, 0.967; for New Mexico, 0.537; for Colorado,
0.657; and for Utah, 0.392 (E179). (Some minor inconsistency results
where a site is less than 80 km from a site in another State.)
20
-------
The risk estimates for the rest of the United States, for Canada
and Mexico, and for the rest of the world are based on 2.3 committed
fatal lung cancers per 100 person-WL-years. This probably
overestimates the very small health risks calculated for most other
countries, because their lung cancer rates are generally somewhat
below that in the United States.
Table 5-1 shows the estimated fatal lung cancer commitment in
the populations at various distances from the the seven tailings
piles addressed in this document. Table 5-2 shows the corresponding
estimates with the source strength at each pile normalized to 1,000
curies of radon-222 released per year. We have assumed that for
fairly constant releases over periods of a year or longer, the
exposure in person-WL-years will be approximately directly
proportional to the quantity of radon released.
21
-------
Table 5-1. Comparison of the Estimated Fatal Lung Cancer
Commitment3 at Selected Distances Due to Radon-222 from
Tailings at Seven Inactive Uranium Mill Sites
N>
to
Distance Grand Junction
increment Colo.
0.0 to 5 km
5 to 10
10 to 20
20 to 40
40 to 80
Subtotal
Rest of USA
Total USA
Canada &
Mexico
Rest of V/orld
Total
0.3
0.008
0.002
2xlO~4
3xlO~4
0.3
0.09
0.4
0.02
0.02
0.4
Gunnlson
Colo.
0.04
Ixlfl"4
8xlO"5
3xlO~5
7xlO~5
0.04
0.03
0.07
0.007
0.006
0.08
Rifle
Colo.
0.02
0.0
2x10-4
6xlO"5
1 3xlO~4
0.02
0.06
0.08
0.01
0,01
0.1,
Shlprock Falls City Mexican Hat Salt Lake City
N.M.b Texas Utah Utah
0.03
0.0
— _
6xlO~4
7xlO~5
0.03
0.1
0.1
0.02
0.02
0.1
0.01
0.001
0.002
0.002
0.02
0.04
0.1
0.1
0.03
0.02
0.2
0.003
0.0
4xlO~4
4xlO~5
9xlO~5
0.003
0.1
0.1
0.02
0.02
0.1
0.3
0.3
0.03
0.004
0.005
0.6
0.2
0.8
0.04
0.03
0.9
aAnnual commitment of fatal lung cancers due to inhalation of radioactive short-lived decay
products of radon-222.
^Distance increments for Shiprock are: 0T0 to 3.2 km; 3.2 to 16 km; 16 to 40 km; and 40 to
80 km; instead of the respective Increments given in the left column.
-------
Table 5-2. Comparison of the Estimated Fatal Lung Cancer Commitment
at Selected Distances Due to Release of 1000 Curies of Radon-222 from
Tailings at Seven Inactive Uranium Mill Sites
N>
LO
Distance Grand
Increment
0.0 to 5 km
5 to 10
10 to 20
20 to 40
40 to 80
Subtotal
Rest of USA
Total USA
Canada &
Mexico
Rest of World
Total
Junction
Colo.
0.05
0.001
3xlO~4
3xlO~5
4xlO~5
0.05
0.01
0.06
0.003
0.003
0.07
Gunnison
Colo.
0.02
4xlO~5
3xlO~5
2xlO~5
3xlO~5
0.02
0.02
0.04
-• '
0.003
0.003
0.05
Rifle
Colo.
0.005
0.0
6xlO~5
2xlO"5
9xlO~5
o.bos
0.02
0.02
0.003
0.003
0.03
Shiprock
N.M.a
0.005
0.0
9xlO~5
IxlO"4
0.005
0.02
0.03
0.003
0.003
0.04
Falls City
Texas
0.001
IxlO"4
2xlO~4
2xlO~4
0.003
0.004
0.02
0.02
0.003
0.003
0.03
Mexican Hat
Utah
-4
4x10 *
0.0
5xlO~5
5xlO~6
2xlO~5
5xlO~4
0.02
0.02
0.003
0.003
0.03
Salt Lake City
Utah
0.03
0.02
0.003
3xlO~4
-4
4x10
0.05
0.01
0.06
0.003
0.003
0.07
aDIstance increments for Shiprock are: 0.0 to 3.2 km; 3.2 to 16 km; 16 to 40 km; and 40 to
80 km; instead of the respective increments given In the left column.
-------
6: DISCUSSION
6.1 Comparison with Other Estimates
Our evaluation was performed primarily to assess the relative
effects of radon from tailings piles on local, regional, and national
populations, rather than to make accurate estimates of the health
risk around individual tailings locations.
However, we will compare here our results with those of Ford,
Bacon & Davis Utah, Inc. (FBDU), which has compiled such data (Fo78)
from its series of reports on most of the inactive uranium mill
sites, including the seven sites we selected.
FBDU's radon-222 annual average concentration exposures compared
to ours are: at Grand Junction, Colorado, 1870 vs.
3000 person-pCi/liter-year; at Gunnison, Colorado, 325 vs. 400
person-pCi/liter-year; at the newer Rifle, Colorado location, 289.6
vs. 200 person-pCi/liter-year; at Shiprock, New Mexico, 2550 vs. 400
person-pCi/liter-year; at Falls City, Texas, 120.7 vs.
80 person-pCi/liter-year; at Mexican Hat, Utah, 127.2 vs. 40 person-
pCi/liter-year; and at Salt Lake City, Utah, 13,200 vs. 10,000
person-pCi/liter-year. (FBDU's values are as given in (Fo78); our
values are to one significant figure).
Most of these pairs of values match within the uncertainties.
At Shiprock, Falls City, and Mexican Hat, we have used the Ford,
Bacon & Davis Utah population data, so the comparison mainly reflects
differences in estimating radon concentrations. These comparisons
are for exposures to the local populations, within a few miles, as
treated in (Fo78).
The procedures used by Ford, Bacon & Davis Utah, Inc. appear to
differ appreciably in thoroughness and sophistication from site to
site, perhaps due in part to the paucity of data for some sites. For
most sites, we believe their results and ours are of comparable
accuracy.
Travis et al. (Tr79) estimated population exposures from four
uranium mill sites using theoretical atmospheric concentration
gradients for North America (provided by the National Oceanic and
Atmospheric Administration) for a unit release from each tailings
location. Of the four sites, only one (Falls City, Texas) coincides
with our selection. At Falls City, Travis et al. estimated, for a
nominal release of 1,000 Ci radon-222 per year, collective exposures
24
-------
of 108 person-pCi/liter-year to the national population, 1.2
person-pCi/llter-year to the Canadian population, and 5.2
person-pCi/liter-year to the population of Mexico. They did not
include the population within 50 miles (about 80 km) in this
calculation. Our estimates for the same areas are: 100
person-pCi/liter-year to the national population, 1 person-
pCi/liter-year to the Canadian population, and 20 person-pd/liter-
year to the population of Mexico. We consider the methods of Travis
et al. more accurate, but the results are very similar.
The differences in (Tr79) among collective national exposures
for the four sites they examined is greater than differences over the
seven we examined, most likely because Travis et al. used more
site-specific data; their smallest value is about 56 percent of their
largest (Falls City), whereas our smallest value is about 82 percent
of our largest (Gunnison). In view of the overall uncertainties in
such estimates (see below), however, our simpler methods appear
adequate.
6.2 Uncertainties
All segments of the radiation exposure pathway have appreciable
uncertainties. The quantities of radon-222 released each year from
the tailings locations are estimated from data derived from the
uranium production records of the now-inactive mills.
Although measurements of the radon release rate have been made,
for most piles only a few scattered measurements were made and those
only over short time periods (Fo76, Fo77a-Fo77g); such measurements
give broad indications of the radon release rates from tailings
piles. We believe our method of estimating radon release rates based
on the tailings composition is as reliable as any when data from
comprehensive, long-term sampling is lacking. The relatively sparse
direct measurements of radon-222 release rates of tailings piles
(e.g., Fo76, Fo77a-Fo77g) show a few samples indicating slightly
higher release rates, and a greater number indicating lower release
rates than our estimates.
The annual release from a tailings pile could be firmly
established only by a long-term monitoring program, sampling fairly
continuously the radon release rate per unit area at a number of
points on the pile. This expensive program is not likely to be
carried out because no specific need for such accurate data has been
determined.
The dispersion of the radon-222 in air has many sources of
uncertainty. Little and Miller (Li79) estimate uncertainties of one
or two orders of magnitude for complex terrain or meterorology using
25
-------
a Gaussian-plume model like that employed here. Furthermore, our use
of uniform dispersion in all directions, with one set of
meteorological data for all sites, ignores differences between
site-specific data and data from a distant location, and differences
in meteorology among regions of the country.
Although the climate at Fort St. Vrain, in central Colorado, is
similar to other locations in western United States, there are
regional differences in large scale weather movements. When the
specific directions are removed from consideration, the differences
may not be as significant. If dispersion calculations are made using
the Fort St. Vrain meteorological data (Re70) and again, using the
Farmington data (Ha79), the ratio of the calculated concentrations
(Fort St. Vrain to Farmington) ranges from 0.76 to 0.28 within 12 km
and is 0.13 at 40 km.
The Farmington data indicate that the concentrations in
individual compass sectors deviate from the directional average by
factors of 0.2 to 3 at 10.8 km; the Fort St. Vrain data indicate
deviations by factors of 0.3 to 2 at 12 km.
These values do not include any consideration of the effects of
complex terrain, a characteristic of most of these tailings
locations. Dispersion, particularly within a few kilometers, is
influenced by local factors such as topography. This is especially
true for low wind-speed inversion conditions which produce peak
concentrations of radon per unit released. Of the tailings sites we
considered, it is likely that only Gunnison, Colorado, would have
site-specific meteorological data available because the tailings are
adjacent to the airport.
It is our view that for most of these tailings locations, data
from a more distant location, even one as close as 5 km, has little
directional significance. Therefore, we believe that our use of
generalized meteorological data is appropriate, and using data from
the nearest weather station generally would not appreciably improve
the accuracy of the results.
The path airborne pollution travels over the northern hemisphere
after leaving the east coast is uncertain. An article in Science
suggests that some pollution may travel north across the polar
regions rather than east across Asia (Ke79). There is also
uncertainty in the amounts of radioactive decay products accompanying
the radon-222, both outdoors and indoors (En80, Gu79, and Un77).
Another source of uncertainty is the relation between the
exposure, in person-WL-years, and health risk. The more we
extrapolate risk data for underground miners to other groups (e.g.,
26
-------
the general population), the greater the uncertainties. A primary
example is converting the same way for the United States, Great
Britain, Europe, and all of Asia. We doubt, however, that using more
representative values for Great Britain, Europe, and Asia would
significantly alter the values in Tables 5-1 and 5-2 for "Rest of
World."
In our estimate, about six-tenths of the collective exposure to
the world outside North America occurs in western Europe and
relatively negligible amounts in Asia. Therefore, much of the
collective exposure occurs in Europe where the lung cancer incidence
is not greatly different from that in the United States.
In spite of many sources of uncertainty and potential
inaccuracy, the principal objective of this evaluation has been
achieved. Evaluating the exposures with the linear, nonthreshold
health risk model indicates that the cumulative health risks for
distant populations are comparable to the risks for populations near
the tailings piles.
The relatively few people who live within a few kilometers of
tailings piles may receive individual exposures as much as a hundred
times the exposures to individuals at greater distances (as indicated
by Table 3-1). However, when collective exposures are estimated, the
larger number of people at greater distances leads to collective
exposures comparable to those within 5 km, in spite of the much
smaller individual exposures. This can be seen in the summary given
in Table 6-1 (taken from Table 5-1), even though the seven cases
include a wide range in population densities and distributions within
80 km.
Thus, moving a tailings pile away from a relatively populous
area to a more remote site will reduce local radiation exposures to
individuals, but the collective exposures to distant populations can
only be appreciably changed by measures that suppress the release of
radon-222.
27 .
-------
Table 6-1. Summary of the Estimated Fatal Lung Cancera
Commitment at Selected Distances Due to Radon-222
from Tailings at Seven Inactive Uranium Mill Sites
(From Table 5-1)
Distance Increment
Site
Grand Junction,
Colo.
Gunnison, Colo.
Rifle, Colo.
Shiprock, N.M.
Falls City,
Texas
0-5 km
0.3
0.04
0.02
0.03
0.01
USA
(From 5 km out)
0.01
0.03
0.06
0.07
0.1
World
Total
0.4
0.08
0.1
0.1
0.2
Mexican Hat,
Utah 0.003
Salt Lake City,
Utah 0.3
0.1
0.5
0.1
0.9
aAnnual commitment of fatal lung cancers due to
inhalation of radioactive short-lived decay products of
radon-222.
28
-------
REFERENCES
E179 Ellett, Wm., Office of Radiation Programs, U.S. Environmental
Protection Agency, Washington, D.C. 20460, Personal
communication, August 1979.
En79 Environmental Protection Agency, "Indoor Radiation Exposure Due
to Radium-226 in Florida Phosphate Lands," EPA 520/4-78-013,
USEPA, Office of Radiation Programs, Washington, D.C., 1979.
En80 U.S. Environmental Protection Agency, Draft Environmental Impact
Statement for Remedial Action Standards for Inactive Uranium
Processing Sites, EPA 520/4-80-011, Washington, D.C. 20460,
December, 1980.
Fo76 Ford, Bacon & Davis Utah, Inc., "Phase II-Title I Engineering
Assessment of Inactive Uranium Mill Tailings, Vitro Site, Salt
Lake City, Utah," April 30, 1976.
Fo77a Ford, Bacon & Davis Utah, Inc., "Phase II-Title I Engineering
Assessment of Inactive Uranium Mill Tailings, Mexican Hat Site,
Mexican Hat, Utah," Report GJT-3, March 31, 1977.
Fo77b Ford, Bacon & Davis Utah, Inc., "Phase II-Title I Engineering-
Assessment of Inactive Uranium Mill Tailings, Shi pro ck Site,
Shiprock, New Mexico," Report GJT-2, March 31, 1977.
Fo77c Ford, Bacon & Davis Utah, Inc., "Phase II-Title I Engineering
Assessment of Inactive Uranium Mill Tailings, Grand Junction
Site, Grand Junction, Colorado," Report GJT-9, October 1977.
Fo77d Ford, Bacon & Davis Utah, Inc., "Phase II-Title I Engineering
Assessment of Inactive Uranium Mill Tailings, New and Old Rifle
Sites, Rifle, Colorado," Report GJT-10, October 1977.
Fo77e Ford, Bacon & Davis Utah, Inc., "Phase II-Title I Engineering
Assessment of Inactive Uranium Mill Tailings, Gunnison Site,
Gunnison, Colorado," Report GJT-12, November 1977.
Fo77f Ford, Bacon & Davis Utah, Inc., "Phase II-Title I Engineering
Assessment of Inactive Uranium Mill Tailings, Falls City site,
Falls City, Texas," .Report GJT-16, December 1977.
Fo77g Ford, Bacon & Davis Utah, Inc., "Phase II-Title I Engineering
Assessment of Inactive Uranium Mill Tailings, Ray Point site, Ray
Point, Texas," Report GJT-20, December 1977.
29
-------
Fo78 Ford, Bacon & Davis Utah, Inc., "Radiation Pathways and Potential
Health Impacts from Inactive Uranium Mill Tailings," Report
GJT-22, July 1978.
Ha79 Haywood, F. F., Goldsmith, W. A., Lantz, P. M., Fox, W. F.,
Shlnpaugh, W. H., and Hubbard, H. M., Jr., "Assessment of the
Radiological Impact of the Inactive Uranium Mill Tailings at
Shiprock, New Mexico," ORNL-5447, Oak Ridge National Laboratory,
Oak Ridge, Tennessee 37830, December 1979.
He79 U.S. Department of Health, Education and Welfare, "Evaluation of
Radon-222 Near Uranium Tailings Piles," DER 69-1, Public Health
Service, U.S. Department of Health, Education, and Welfare,
Rockville, Maryland 20857, March 1969.
Ke79 Kerr, R. A., "Global Pollution: Is the Arctic Haze Actually
Industrial Smog?," Science, Vol. 205, No. 4403, July 20, 1979.
Kn72 Rnox, J. B. and Peterson, K. R., "Estimates of Dose to Northern
Hemisphere Population Groups from 8%r Emitted by a Single
Nuclear Fuel-Reprocessing Plant," Nuclear Safety 13; 130-135,
March-April 1972.
L179 Little, C. A. and Miller, C. W., "The Uncertainty Associated with
Selected Environmental Transport Models," ORNL-5528, Oak Ridge
National Laboratory, Oak Ridge, Tennessee 37380, November 1979.
Ma73 Machta, L., Ferber, G. J., and Heffter, J. L., "Local and
Worldwide Pollutant Concentrations and Population Exposures from
a Continuous Point Source," U.S. National Oceanic and Atmospheric
Administration, Air Resources Laboratories, June 1973.
Ma74 Martin, J. A., Jr., Nelson, C. B., and Cuny, P. A., "AIREM Program
Manual, A Computer Code for Calculating Doses, Population Doses,
and Ground Depositions Due to Atmospheric Emissions of Radionuc-
lides," EPA-520/1-74-004, U.S. Environmental Protection Agency,
Office of Radiation Programs, Washington, D.C. 20460, May 1974.
McD79 McDowell-Boyer, L. M., Watson, A. P. and Travis, C. C., "Review
and Recommendations of Dose Conversion Factors and Environmental
Transport Parameters for Pb-210 and Ra-226," NUREG/CR-0574
(ORNL/NUREG-55), U.S. Nuclear Regulatory Commission,
Washington, D.C. 20555, March 1979.
Na80 National Academy of Sciences, National Research Council, "The
Effects on Populations of Exposure to Low Levels of Ionizing
Radiation," Report of the Advisory Committee on the Biological
Effects of Ionizing Radiations, Washington, D.C., 1980.
30
-------
Ne74 Newspaper Enterprise Association, "The 1974 World Almanac and
Book of Facts," Newspaper Enterprise Association, Inc., 230 Park
Ave., New York 10017.
Ra80 Radiation Policy Council, "Report of the Task Force on Radon in
Structures," Report RPC-80-002, U.S. RPC, Washington, D.C., 1980.
/
Re70 Reiter, E. R., "Revised Supplemental Climatological Report on
Meteorological and Climatological Conditions at the Fort
St. Vrain Generating Station," Department of Atmospheric Science,
Colorado State University, Fort Collins, Colorado, November 1970.
Si68 Slade, David H., Ed., "Meteorology and Atomic Energy 1968,"
Division of Technical Information, U.S. Atomic Energy Commission,
Oak Ridge, Tennessee, July 1968.
Sc74 Schiager, K. V., "Analysis of Radiation Exposures on or Near
Uranium Mill Tailings Piles," Radiation Data and Reports,
Vol. 15, No. 7, U.S. Environmental Protection Agency, July 1974.
Sw76 Swift, J. J., Hardin, J. M. and Galley, H. W., "Potential
Radiological Impact of Airborne Releases and Direct Gamma
Radiation to Individuals Living Near Inactive Uranium Mill
Tailings Piles," U.S. Environmental Protection Agency, Office of
Radiation Programs, Technical Report EPA-520/1-76-001.
Tr79 Travis, C. C., Watson, A. P., McDowell-Boyer, L. M., Cotter,
S. J., Randolph, M. L., and Fields, D. W., "A Radiological
Assessment of Radon-222 Released from Uranium Mills and Other
Natural and Technologically Enhanced Sources," NUREG/CR-0573
(ORNL/NUREG-55) Office of Nuclear Material Safety and
Safeguards, U.S. Nuclear Regulatory Commission, Washington, D.C.
20555, February 1979.
Un77 United Nations Scientific Committee on the Effects of Atomic
Radiation, "Sources and Effects of Ionizing Radiation," United
Nations, New York, 1977.
31
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Appendix A: TAILINGS COORDINATES
Records and reports of the seven tailings piles gave the
coordinates of the mill buildings rather than the tailings. We
determined the locations of the tailings from U.S. Geological Survey
maps and the aerial photographs and site maps in the reports of Ford,
Bacon & Davis Utah, Inc.
The locations listed here represent the centers of the tailings
piles and are believed to be accurate to within +2 seconds of
latitude or longitude. In some cases (e.g., at Falls City, Texas,
where there are six tailings locations) selection of a "center"
represents a judgment.
Grand Junction, Colo.
Gunnison, Colo.
Rifle, Colo, (new)
Rifle, Colo, (old)
Shiprock, N.M.
Falls City, Texas
Ray Point, Texas
Mexican Hat, Utah
Salt Lake City, UT
39°
38°
39°
39°
36°
28°
28°
37°
40°
03'
31'
31'
31'
46'
54'
31'
08'
42'
17"N,
48
26
45
09
16
15
04
11
"N,
"N,
"N,
"N,
"N,
"N,
"N,
"N,
108° 32' 59"W
106° 56' 30"W
107° 48' 57"W
107° 46' 20"W
108° 41' 02"W
98° 07' 46"W
98° 06' 12"W
109° 52' 32"W
111° 54' 44"W
32
-------
Appendix B: ADJUSTMENT FOR AREA SOURCE
We used calculations from (Sw76) to determine the dispersion in
the range to 12 km from the tailings location center. An equivalent
line-source perpendicular to the wind direction through the tailings
center is substituted for the point source generally used in the
AIREM code.
When the wind is in a sector adjacent to that of the receptor
and tailings center, if the receptor is sufficiently close to the
tailings it can still be within the sector of the tailings' plume
(i.e., the plume from the equivalent line source). The exposure from
this fractional overlap is added to that of the receptor's sector
according to the fractional area of the overlap and the wind
direction frequency in the adjacent sector.
The equivalent line source was calibrated against a calculation
in which a circular (200 m radius) model tailings pile was subdivided
into a two-dimensional array of point sources whose monodirectional,
single Gaussian plumes were superimposed on a crosswind row of
receptor locations. Use of the equivalent line source with the AIREM
calculation is consistent with the assumptions concerning concen-
trations in adjacent sectors that are intrinsic to the
sector-averaged equation, equation 3.144 in Slade (S168).
For receptors at downwind distances greater than ten times the
diameter of one tailings pile (a few kilometers), we used a
point-source, which is adequate.
33
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TECHNICAL REPORT DATA
trtcase reaa nn.ntcucjns en inz rcierst: uejore cvrnpisiing/ i
1. REPORT -\O |2.
DRp/TAn-an-i
4. TITLE AND SUBTITLE
Health Risks to Distant Populations from
Uranium Mill Tailings Radon
7. AUTHORlSi
Jerry J. Swift, Ph.D.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Office of Radiation Programs
Environmental Protection Agency
401 M St., SW
Washington, D.C. 20460
12. SPONSORING AGENCY NAME AND ADDRESS
3. RECIPIENT'S ACCESSION ."-.'C.
5. REPORT DATE
May 1981
6. PERFORMING ORGANIZATION CODE
EPA/ORP
8. PERFORMING ORGANIZATION REFGR i MO.
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
13. TYPE OF REPORT AND PERIOD COV = REC
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
Uranium mill tailing piles can expose the population to radiation by
several pathways. The author believes the air pathway to be the most
important and radon-222 to be the principal nuclide. The report illustrates
the effects of tailings piles on a variety of local and regional populations,
assesses the effects of the tailings on distant populations, and compares
EPA methods and results with assessments by others.
17. KEY WORDS AND DOCUMENT ANALYSIS
a. DESCRIPTORS b.lDENTIFI
radon-222
uranium mill tailings piles
radioactive decay products of radon-222
ERS/OPEN ENDED TERMS C. COSATI Held/Group
ji£. DiSTR'tL'T'CN •;.~i-rEMS\'T [ 1 9. SEC1- R I T Y CLASS fT'iis Repor;; J21. NO. OF PAGES
i i -Unclassified 37
J Unlimited |2C SECUP
' I Inr 1 3 <:
TY CL/-S3 Tiiispaffi |22. FPICH
Q 1 f 1 P(H :
EPA For-,1 22*0 — 1 ;«e
,"OUS ECIT'CM IS CBSCLETE
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