United States
Environmental Protection
Agency
&EPA
Office of Radiation Programs
Las Vegas Facility
P.O. Box 98517
Las Vegas NV 89193-8517
EPA/520/6-90/008
April 1990
Radiation
Idaho Radionuclide
Study
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RADIONUCLIDE EXPOSURE STUDY
POCATELLO AND SODA SPRINGS, IDAHO
April 1990
US ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RADIATION PROGRAMS
LAS VEGAS FACILITY
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FOREWORD
In December 1989 the National Research Council published its
Biological Effects of Ionizing Radiation or BEIR 5 Report which
offers new risk estimates from radiation exposure. These new
risk factors are about twice the risk factors used within this
report. The Environmental Protection Agency has not incorporated
the BEIR 5 risk estimates into its risk calculation procedures.
The risk factor associated with the conclusions in this report is
400 cancer deaths attributable to radiation exposure per one
million person-rem of dose.
The risks expressed in this report are based on calculations
that assume a lifetime (about 70 years) of exposure to the
conditions that were measured.
As the elemental phosphorus industry in southeast Idaho is
about 35 years old, the actual risks to the population as a whole
are less than the estimated risks reported here. However, if the
population and the use of phosphorus slag in building materials
remain or increase in the same proportions as they exist today,
these risk levels will be reached within forty years. At that
time, we estimate the probability of contracting cancer due to
exposure from elemental phosphorus slag to be about one chance in
2,500 in Pocatello and one chance in 700 in Soda Springs.
Wayne ^. Bliss, ^Director
Las Vegas Facility
Office of Radiation Programs
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STATEMENT OF FINDINGS
As committed by EPA in 1985 when it promulgated emission
standards for radionuclides as hazardous air pollutants, a
radionuclide exposure study has been conducted in southeastern
Idaho to estimate the radiation dose resulting from the elemental
phosphorus industry.
From April 1986 through September 1988, the Office of
Radiation Programs' Las Vegas Facility, investigated the
dispersion of radionuclides through the environs of Pocatello and
Soda Springs, Idaho, the relative importance of their sources and
pathways affecting the populations of both towns, and the
magnitude of the attendant risks. One of the most significant
components of risk to the inhabitants was the exposure to gamma
rays originating from elemental phosphorus waste.
The Las Vegas Facility conducted the investigation in
cooperation with EPA's Region 10 office, the State of Idaho, the
Idaho Mining Association, the governments of Bannock and Caribou
counties, and the towns of Pocatello, Chubbuck and Soda Springs,
and with the contracted assistance of EG&G and Battelle's Pacific
Northwest Laboratory.
Gamma ray exposures to the populations of Soda Springs and
Pocatello, with the attendant risks, and the corresponding values
for average and maximally exposed individuals in both
communities, are listed in Tables A through E. Exposure to
outdoor sources is the greatest contributor to the population
dose in Pocatello, due to slag used in street paving, while that
to the residents of Soda Springs is mostly due to indoor (home)
exposure, caused by slag in home foundations. Inclusion of the
airborne components, principally due to airborne polonium-210 and
lead-210, increase both dose and risk estimates, as shown in
Table F and Figure A.
11
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TABLE A. SUMMARY OF ANNUAL NET POPULATION DOSES, BY AGE AND
ACTIVITY GROUP, FOR SODA SPRINGS, FROM ELEMENTAL
PHOSPHORUS WASTES (Person-rem)
Location
Teenage and Total by
Employed non-employed Exposure
Adults Adults Children Infants Elements
Main Floor
Basement
Driveway
Sector*
Community
Workplace
Total by
age group
TABLE B.
35.
13.
3.
4.
5.
18.
81.
SUMMARY
98
22
58
80
09
70
37
OF
27.
10.
5.
9.
15.
0
67.
ANNUAL
36
06
42
21
65
69
11.
4.
2.
6.
3.
0
28.
85
35
35
46
97
99
13
3
0
1
1
0
19
NET POPULATION DOSES BY
ACTIVITY GROUP, FOR POCATELLO,
PHOSPHORUS WASTES (Person-rem)
Location
Main Floor
Basement
Driveway
Sector*
Community
Workplace
Total by
age group
Employed
Adults
83.
13.
40.
41.
49.
89.
318.
94
91
34
17
58
50
44
Teenage and
non-employed
Adults
50.
8.
48.
61.
119.
0
288.
05
29
21
96
74
25
FROM
Children
25.
4.
24.
49.
37.
0
141.
29
19
37
77
59
21
.32
.14
.39
.47
.32
AGE
88.
30.
11.
21.
26.
18.
197.
AND
51
77
35
86
18
70
4
ELEMENTAL
Infants
26
3
0
11
14
0
55
.47
.00
.49
.10
.06
Total by
Exposure
Elements
185.
29.
112.
164.
221.
89.
803.
75
39
92
39
01
50
0
* General vicinity of residence.
111
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TABLE C. YEARLY RISK FOR THE POPULATIONS OF POCATELLO AND SODA
SPRINGS
Annual
Community Population Dose Risk
Pocatello 803 person-rem 0.3 deaths/year among
57,000 people
Soda Springs 197.4 person-rem 0.1 deaths/year among
3,800 people
TABLE D. CALCULATED NET GAMMA-RAY DOSES (mrem/yr) TO AVERAGE
INDIVIDUALS IN POCATELLO AND SODA SPRINGS
Average Annual
Community Individual Dose Lifetime Risk
Pocatello
Soda Springs
14 mrem
52 mrem
0.0004
0.0014
TABLE E. CALCULATED NET GAMMA-RAY DOSES (mrem/yr) TO MAXIMALLY
EXPOSED INDIVIDUALS IN POCATELLO AND SODA SPRINGS
Maximum Annual
Community Individual Dose Lifetime Risk
Pocatello 145 mrem 0.004
Soda Springs 205 mrem 0.006
Lifetime risk values represent the probabilities of contracting a
fatal cancer, i.e. "4 in 1000" for the maximally exposed
individual in Pocatello (Table D) and "6 in 1000" for the
maximally exposed individual in Soda Springs, (Table E) assuming
they remain in their respective communities throughout their
lifetime.
IV
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TABLE F. GAMMA DOSE AND RISK ESTIMATES, INCLUDING AIRBORNE
COMPONENT, TO MAXIMALLY EXPOSED INDIVIDUALS IN
POCATELLO AND SODA SPRINGS
Pocatello Soda Springs
Airborne Dose Contribution 23 mrem 4 mrem
Slag Dose* 145 mrem 205 mrem
Total Effective
Whole Body Dose 168 mrem 209 mrem
Lifetime Risk** 0.005 0.006
* From exposure to gamma rays from slag material. There is no
radon dose component; radon levels, where measured, were
indistinguishable from background.
** "Lifetime Risk" represents the probability of contracting a
fatal cancer caused by radiation exposure above background for
individuals residing in the subject communities during 70 years
(a "lifetime.") The maximally exposed individual in Pocatello
has "5 in 1000" chances of dying of cancer, while the
corresponding individual in Soda Springs incurs a risk of "6 in
1000" of dying due to the same cause.
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ANNUAL DOSES COMPARED TO MAXIMUM ANNUAL DOSES
(mrem/year)
Soda Springs,
Maximally Exposed
Individual
209 -i
Pocatello,
Maximally Exposed
Individual
168 -
Soda Springs,
Average Individual
52 -
Pocatello,
Average Individual
14 -
Natural Background (100-105 mrem) J
-175
- 100
- 25
- 10
Indoor Exposure Limit
from 40 CFR 192 (gamma
radiation)
National Council of
Radiation Protection
(NCRP) Recommendations
on Limits For Exposure
to Ionizing Radiation
(NCRP Report #91)
EPA Dose Limit for
Nuclear Fuel Cycle
Facilities
(40 CFR 190)
EPA Effective Dose
Limit for NRC, DOE
Facilities
(40 CFR 61)
Figure A. Slag and Airborne Doses, as Compared to
Recommended Maximum Annual Doses in Excess
VI
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TABLE OF CONTENTS.
Page
Introduction 1
I. GAMMA DOSE AND RISK ESTIMATES OF ELEMENTAL
PHOSPHORUS WASTES 2
A. Purpose and Scope 2
B. Summary and Analyses of Survey Data 2
1. Aerial Survey 2
2. Ground Survey 3
3. Comparison of Ground and Aerial Survey Data 3
C. Exposure Scenarios 8
1. Selected Exposure Scenarios 8
2. Exposed Population 14
D. Gamma Radiation Exposure Estimates 16
1. Selection of Exposure Rate Data 16
2. Outline of Estimation Methods 17
3. Quality Assurance 18
4. Gamma Radiation Dose Estimates 19
E. Summary and Results 36
II. DOSE AND RISK ASSESSMENT FOR AIRBORNE EMISSIONS ... 40
A. Assessment Methodology 40
1. Environmental Transport 40
2. Estimation of Dose and Risk 40
B. Parameters Used in Assessment 41
1. Population Data 41
2. Agricultural Data 41
3. Meteorological Data 41
4. Plume Rise 42
5. Source Term 42
C. Results of the Dose and Risk Assessment
for Air Pathway 43
References 44
vii
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FIGURES
Figure Page
Pocatello Sector Average Aerial Exposure Rates
(Adjusted to 1 Meter Above Ground Level) in /iR/h. .
Soda Springs Sector Average Aerial Exposure Rates
(Adjusted to 1 Meter Above Ground Level) in /iR/h. ,
Average Outdoor Ground Survey Exposure Rates in
MR/h, by Sector, in Pocatello, Including the
Number of Properties Surveyed and the Number of
Measurements
4. Average Outdoor Ground Survey Exposure Rates in
juR/h, by Sector, in Soda Springs, Including the
Number of Properties Surveyed and the Number of
Measurements 10
5. Ratio of Average Aerial to Ground-Based Exposure
Rates in Selected Sectors of Pocatello 11
6. Estimated Pocatello Population Distribution 12
7. Estimated Soda Springs Population Distribution... 13
Vlll
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TABLES
Number Page
1. An Example Comparison of Ground (1 meter) and Aerial
(corrected to 1 meter) Gamma-Ray Exposure Rate Ranges.. 6
2. Comparison of Aerial (corrected to 1 meter) and Ground
(1 meter) Gamma-Ray Exposure Rates for Pocatello and
Soda Springs, Idaho 7
3. Assumed Exposure Conditions for Individuals in
Pocatello and Soda Springs 15
4. Population Distribution by Net Exposure Rate and Age
Groups in Home Environs (First Floor, Basement,
Driveway) for Soda Springs 20
5. Annual Population Exposure, in Person-rein, by Age Groups
in Home Environs (First Floor, Basement, Driveway) for
Soda Springs 21
6. Composition of Population in Sectors by Age Groups for
Soda Springs 22
7. Net Exposure Rates in Each Sector and in Community for
Soda Springs (p.R/h) 23
8. Annual Outdoor Exposure, in Person-rem, by Age Group for
Soda Springs 25
9. Workplace Exposures for Adults Employed 2000 Hours in
Outdoor Occupations, in Soda Springs 26
10. Workplace Exposures for Adults Employed 2000 Hours in
Indoor Occupations, in Soda Springs 27
11. Population Distribution by Net Exposure Rate and Age
Groups in Home Environs (First Floor, Basement,
Driveway) for Pocatello 28
12. Annual Population Exposure, in Person-rem, by
Age Groups in Home Environs (First Floor, Basement,
Driveway) for Pocatello 29
13. Composition of Population in Sectors by Age Groups for
Pocatello Area 30
IX
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14. Net Exposure Rates in Each Sector and in Community for
Pocatello Area (/iR/h) 31
15. Annual Outdoor Exposure, in Person-rem, by Age Group for
Pocatello 32
16. Workplace Exposures for Adults Employed 2000 Hours in
Outdoor Occupations, in Pocatello 34
17. Workplace Exposures for Adults Employed 2000 Hours in
Indoor Occupations, in Pocatello 35
18. Summary of Net Exposures, in Person-rem, Per Age and
Activity Group, for Soda Springs 37
19. Summary of Net Exposures, in Person-rem, Per Age and
Activity Group, for Pocatello 38
20. Yearly Risk for the Population of Pocatello and
Soda Springs 38
21. Calculated Net Gamma-Ray Doses (mrem/yr) to Average
Individuals in Pocatello and Soda Springs 39
22. Calculated Net Gamm-Ray Doses (mrem/yr) to Maximum
Individuals in Pocatello and Soda Springs 39
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INTRODUCTION
In 1979, the U.S. Environmental Protection Agency (EPA)
listed radionuclides as hazardous air pollutants and was
required by the Clean Air Act to issue emission standards for
radionuclides. In October 1984, EPA was ordered by the U.S.
District Court, Northern District of California, to issue
standards for elemental phosphorus plants and other source
categories under Section 112 of the Clean Air Act.
Phosphorus ores contain approximately 60 times the levels of
natural radioactivity normally found in the Earth's crust. Some
of the radioactivity is released to air and water during
processing of the ores, and some is distributed in the
environment through the use of solid byproduct wastes. The EPA
has established a radionuclide standard limiting polonium-210
(Po-210) air emissions per elemental phosphorus plant to 2 curies
per year (Ci/y).
At the issuance of the standard in 1985, EPA stated:
"The areas surrounding two plants, the FMC plant
in Pocatello, Idaho and the Monsanto plant in Soda
Springs, Idaho are characterized by high total levels
of radiation from a variety of sources. The storage
and widespread use of slag, and possibly other waste
products from these plants, have significantly
increased the natural background radiation levels in
parts of the communities. In particular, phosphate
slag from these plants has been widely used in
aggregate in road and house construction in these
areas. EPA and the State of Idaho will initiate a
total assessment of the various sources and will
investigate ways to reduce or prevent risks from
growing."
In 1987, the U.S. Environmental Protection Agency's (EPA)
Office of Radiation Programs' Las Vegas Facility (ORP/LVF)
contracted with Battelle's Pacific Northwest Laboratory (PNL) to
conduct a study to determine the radiation exposure to Pocatello
and Soda Springs residents from the local phosphorus industry
that had been operating for several decades.
The objective of the study was to determine the magnitude
and relative importance of the various industrial sources of
radiation and to estimate the dose to the affected populations.
Following a review of pertinent literature, two components were
considered to be most significant: gamma dose and risk estimates
from using elemental phosphorus wastes, and the dose and risk
estimates due to air emissions from the phosphorus plants.
Conspicuously absent were the elevated radon concentrations
expected to originate from phosphogypsum; radon levels were found
to be indistinguishable from background.
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I. GAMMA DOSE AND RISK ESTIMATES OF ELEMENTAL PHOSPHORUS WASTES
This section of the report is devoted to: (A) the purpose
and scope of the gamma radiation study; (B) a summary and
analysis of the survey data; (C) a description of exposure
scenarios; (D) the computation and compilation of gamma radiation
exposure estimates; and (E) summary and discussion of results.
A. Purpose and Scope
The purpose was to estimate annual radiation doses from
local sources of gamma radiation to maximally exposed individuals
and to the collective population of the cities of Pocatello and
Soda Springs, Idaho. The estimation of radiation doses was based
on ambient radiation measurements made in the respective
communities.
B. Summary and Analysis of Survey Data
A brief summary of the data collection methods used for both
aerial and ground surveys, as well as figures, follow.
1. Aerial Survey
Aerial surveys of the Pocatello and Soda Springs communities
were performed in June and July 1986 by the Remote Sensing
Laboratory of EG&G, Inc., Las Vegas, Nevada. Selection of the
area to be surveyed was based on the presence of elemental
phosphorus plants, the long-term, widespread use of phosphorus
slag material from the plants throughout the area, and the local
population distribution. Fort Hall was also surveyed to measure
background radiation levels in the same geographic area.
The aerial survey of Pocatello included the FMC elemental
phosphorus plant, the Simplot phosphate fertilizer plant, and the
municipal airport. The survey covered an area of over 200 square
kilometers.
The Soda Springs site aerial survey covered over 40 square
kilometers, and included the Monsanto elemental phosphorous plant
and the Kerr-McGee vanadium plant.
The aerial measurement system consisted of twenty sodium
iodide scintillation detectors and data acquisition equipment
mounted on a helicopter. Each area was surveyed along
predetermined parallel lines spaced 76 meters apart at a mean
altitude of 46 meters above ground. More detailed discussions of
the systems and procedures used can be found in the EPA report
documenting these surveys (Berry 1987), as well as in separate
publications (Jobst 1979, Clary 1981, and Boyns 1976).
-------
The aerial survey exposure rate contours were projected and
enlarged so that the areas contained within the contours could be
planimetered by sector prior to use in calculating population
exposures. For ease of data processing, the "sectors" used in
calculation were the result of partitioning both communities into
radial grids along 16 compass directions, with circular
subdivisions every 1.6 kilometers (1 mile) from the grid centers.
The grid centers were elemental phosphorus plants in each
community. The average aerial exposure rates by sector,
resulting from this survey, are provided in Figure 1 for
Pocatello and Figure 2 for Soda Springs.
2. Ground Survey
Ground surveys of specific residential properties in Soda
Springs and Pocatello were performed in the summer and fall of
1987. Properties surveyed were obtained through a request for
volunteers within the communities.
At each residence, indoor measurements were made on the main
floor and in the basement using a Reuter-Stokes pressurized ion
chamber (PIC). The corresponding outdoor measurements were
obtained with a Ludlum Scintillometer Model 19, in the front
yard, back yard, garden, driveway, sidewalk, and street in front
of the residences surveyed. The average outdoor exposure rates
from the ground surveys are provided by sector in Figure 3 for
Pocatello and Figure 4 for Soda Springs. The ground survey
covered 100 homes in Pocatello and 19 homes in Soda Springs.
3. Comparison of Ground and Aerial Survey Data
The comparative data shown in Table 1 suggest the validity
of using the aerial survey data for areas not included in the
ground survey. Although the table compares aerial and ground
data obtained in Pocatello, similar considerations apply to Soda
Springs. For some sectors of both communities, the ground survey
data indicated higher exposure rate ranges than indicated for the
same districts by the aerial data (adjusted to 1 meter above the
ground surface). This is because the aerial data measurements
average the exposure rate over much larger areas than the ground
survey data, thereby showing a lower average exposure rate range
for what could be rather small, isolated areas contaminated with
phosphorus slag (Berry 1987). On the other hand, those areas
within the city known to include larger pockets of phosphorus
slag showed the highest exposure rate ranges in the aerial
survey.
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NNW
NW
WNW
W
WSW
SW
SSW
NE
SE
Figure 1. Pocatello Sector Average Aerial Exposure Rates
(Adjusted To 1 Meter Above Ground Level) in jiR/h.
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N
NW
WNW
W
WSW
SW
NNW
NNE
NE
ESE
SE
Figure 2. Soda Springs Sector Average Aerial Exposure Rates
(Adjusted to 1 meter Above Ground Level) in
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TABLE 1. An Example Comparison of Ground (1 Meter) and Aerial
(corrected to 1 Meter) Gamma-Ray Exposure Rate
Ranges1
Exposure Rate Percent of Measurements
Category Range at Given Exposure Rates
(MR/h)
Aerial Ground
A <9 0 0
B 9-11 0 5
C 11.1-14.5 36 41
D 14.6-17 36 29
E 18-22 23 12
F 23-30 5 4
G 31-50 0 3
H 51-100 0 6
Due to the greater field of vision of airborne detectors,
aerial exposure rate measurements may average readings from large
areas, thus misrepresenting small zones of high exposure rates
detectable by ground surveys. Accordingly, the results of the
aerial surveys of both communities were adjusted to represent
ground level exposure rates by the use of aerial/ground ratios,
intended to account for possible bias in aerial survey data.
For the community as a whole, aerial/ground ratios, shown in
Table 2, were based on average aerial survey data and the average
of ground survey measurements. These aerial/ground ratios were
applied to aerial survey averages obtained for individual
sectors, except for those for which enough ground survey data
were present to justify an independently calculated aerial/ground
ratio.
1As noted in Figure 5 of Berry 1987
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TABLE 2 . Comparison of Average Outdoor Gamma Ray Exposure Rates
in Pocatello and Soda Springs, Based on Aerial Surveys
and Modified by Aerial/Ground Ratios
Pocatello Soda Springs
Community Average Aerial Exposure 18.6 20.7
Rates, (corrected to 1 meter
above ground) in /iR/h
Average Aerial/Ground Ratios 0.93 0.81
(based on empirical data, with
ground survey values obtained
with a Ludlum Scintillometer
Model 19 , at 1 meter above ground)
Community Average Exposure Rates, 20.0 25.6
in ^R/h (corrected by aerial/ground
ratios to correspond to Ludlum
Model 19 Scintillometer values
at 1 meter)
Community Average Exposure Rates, 16.6 19.8
in /LiR/h Adjusted to Pressurized
Ion Chamber (PIC) Values (a standard
for human exposure determination)
Net Community Average Exposure 4.6 7.8
Rates, Adjusted to PIC Values in
(minus background of 12
The general procedure for estimating outdoor exposure rates
follows:
1. Exposure rates observed for each sector during the
aerial survey were divided by the appropriate aerial/ground
ratios. The resultant gross community average exposure rates
correspond to Scintillometer ground level measurements, since
these were the instruments predominantly used during the ground
survey, and thus for obtaining aerial/ground ratios.
2. The results were then adjusted to PIC exposure rates by
the following regression equation:
E(PIC) = 0.582 E(L-19) +4.9
where E(PIC) = exposure rate, MR/h, as measured by a
Pressurized Ion Chamber (PIC)
E(L-19) = exposure rate, juR/h/ as measured by a Ludlum
Scintillometer Model 19 (L-19)
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The regression equation was generated by a comparison of PIC
and corresponding scintillometer values on the main floors and
basements of Pocatello and Soda Springs residences.
The adjustment was needed since exposure rates obtained by
PIC are standard for establishing human exposure.
3. The environmental background, as determined by previous
PIC measurements was then subtracted.
When fewer than 20 outdoor measurements were available in a
sector, as shown in Figures 3 and 4, the aerial/ground ratio was
based on community averages rather than on sector data. If more
than 20 outdoor measurements were available in a sector, as was
the case in Pocatello, individually determined sector
aerial/ground ratios were used to correct sector exposures, as
shown in Figure 5.
Sector averages were then multiplied by the number of
individuals, in Figures 6 and 7, and exposure scenario hours to
obtain the average population exposure in that sector. The
exposures were then summed to provide a total population
exposure, for future risk estimates.
C. Exposure Scenarios
1. Selected Exposure Scenarios
One single, basic set of exposure scenarios was developed
for Pocatello and Soda Springs, to estimate time spent by
individuals of different age groups in different exposure
environments, such as the main floors and basements of their
homes, adjacent driveways, sidewalks and streets, the general
vicinity (sector), and the community as a whole. In addition,
employed adults were divided into those subjected to indoor and
outdoor exposures at their places of work.
Population exposures utilized these scenarios by
distributing the residents in various zones in each community
among the age groups mentioned above, applying the
findings of the aerial and ground surveys to determine exposure
rates applicable to each group in each zone and finally summing
the results.
Maximum exposure rates observed at locations included in the
scenario were multiplied by the corresponding time intervals and
the results were combined to generate total exposures for
maximally exposed individuals, in each of the groups addressed in
the scenario. Such combinations of maximum exposures, though
hypothetical, were considered to be possible. When conditions
8
-------
NNW
N
NE
NW
WNW
W
\N8\N
SW
SSW
Number of residential
properties monitored
Number of outdoor
ground measurements
SE
Average of all outdoor
ground measurements
Figure 3. Average Outdoor Ground Survey Exposure Rates in
by Sector, in Pocatello, Including the Number of
Properties Surveyed and the Number of Measurements
-------
NNW
NNE
NW
NE
WNW
ENE
W
WSW
SW
SSW
Number of residential
properties monitored
Number of outdoor
ground measurements
Average of all outdoor
ground measurements
Figure 4. Average Outdoor Ground Survey Exposure Rates in /xR/h by
Sector, in Soda Springs, Including the Number of
Properties Surveyed and the Number of Measurements.
10
-------
NNW
NW
WNW
W
WSW
SW
SSW
N
NE
[72) Value used to calculate
the sector average
SE
Figure 5. Ratio of Average Aerial to Ground-Based Exposure Rates
in Selected Sectors of Pocatello
11
-------
N
NNW
NE
NW
WNW
28S2 3052 3531 2323
WSW
SW
SSW
SE
Figure 6. Estimated Pocatello Population Distribution
12
-------
NW
WNW
W
WSW
SW
NNW
NNE
NE
ENE
SE
Figure 7. Estimated Soda Springs Population Distribution
13
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observed during the survey diverged from those postulated by the
scenario, and produced higher maximum individual exposures, the
scenario was modified to accommodate these conditions. For
example, the maximally exposed individual in Soda Springs was a
teenager residing in the basement of his parent's home, which
necessitated a change of scenario.
A summary of the scenarios used to determine potential
radiation doses to individuals and the general population is
provided in Table 3.
All residents (including those subjected to maximum
exposures) were exposed 8000 h/yr in their respective
communities. During the remaining 760 h/yr, the residents were
assumed to be away from the communities and exposed only to
background radiation.
2. Exposed Population
In general, the residents of Pocatello and Soda Springs were
found to be exposed to gamma radiation, to varying degrees,
during their daily activities; at their places of business; in
and around their homes and property; and in the streets and
sidewalks making up their neighborhood and the community.
The communities were divided into radial grids centered on
the main stacks at the elemental phosphorus plants within each of
the communities. The grids were composed of radial sectors in the
16 primary compass directions further subdivided at 1.6 kilometer
(one mile) intervals.
To include all of the urban residential population in the
Pocatello area, the one-mile sectors extended to 12 miles in the
SE direction and to 9 miles in other directions. However, in
Soda Springs none of the sectors had to be extended beyond five
miles from the central point to include essentially all of the
population.
The populations of individual sectors were calculated on the
basis of the number of dwellings in each sector, as determined
from 1986 aerial photographs, the 1980 census, and the County
and City Data Book, 1988, U.S. Department of Commerce, Bureau of
the Census. The total number of residents, according to these
sources, was approximately 57,000 for Pocatello (including
Chubbuck) and 3800 for Soda Springs.
In calculating maximum individual exposures the scenario
included personnel employed by the phosphorus industry, as well
as other non-phosphorus industry occupations.
14
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TABLE 3. Assumed Exposure Conditions for Individuals
in Pocatello and Soda Springs
Exposure Location Exposure Period fh/vr)
Exposure Location Adult1 Teen2 Child3 Infant
Home
main floor
basement
Driveway*
Sector
Community
Work Place
4300
700
200
4300
700
400
4300
700
400
6300
700
400 1000 1600
400 1600 1000
2000
500
500
Exposure Conditions
(net exposure rate
based on)
ground survey
ground survey
ground survey
average**
sector aerial
survey avg+
community
aerial survey
avg++
aerial survey
average++
1 Adult: Employed adults, for purposes of scenario.
2 Teen: Individuals aged 13-19 years. For scenario purposes
this group also includes adults in home occupations.
3 Child: Individuals of 5-12 years of age.
* Includes observed measurements for driveway, sidewalk, and
street for each individual property surveyed at ground
level.
**
Average of driveway, sidewalk, and street readings for each
individual property.
Modified by ratio of average ground survey data within the
sector (if greater than 20 outdoor measurements were
available in that sector) to average aerial survey data
within the sector. If fewer than 20 outdoor measurements
were available in a sector, the modifier was the ratio of
the average ground data for the community to the average
aerial data for the community. The results were corrected
further to correspond to PIC exposure rates, a standard for
human exposure calculations.
Modified by ratio of average ground survey data (outdoor
measurements only) for community to average aerial survey
data within community. Adjustments to PIC exposure rates
were made.
15
-------
D. Gamma Radiation Exposure Estimates
This section provides a summary of the methods used and a
listing of the steps taken to estimate the gamma radiation doses
that could potentially be received by individual residents and
the general population of Pocatello and Soda Springs.
External radiation doses have been estimated from the
results of aerial and ground-based gamma radiation surveys. The
measured exposure rates were reported in units of juR/h (0.001
mR/h), and the resulting exposure estimates were expressed in mR
(milliroentgen). Although the exposure estimates were in mR, the
calculated doses reported here are in dose equivalent units
(mrem) to allow comparison with dose equivalents reported
elsewhere in this document. Although the radiation exposure
conditions in the environment (multi-energy radiation field) may
differ considerably from the calibration conditions (gamma ray
photons from a single or perhaps a few radioisotopes in air), the
conversion factor relating mrem to mR is assumed to be "1.0"
throughout this report. In this way it is possible to compare
doses from other sources and from internal exposure (such as from
inhalation or ingestion of radionuclides).
1. Selection of Exposure Rate Data
Aerial measurements generally were used to estimate outdoor
gamma radiation exposures. That is, the aerial survey data,
averaged for each sector, were multiplied by the ratio of ground-
to-aerial survey data averaged within each sector, if greater
than 20 outdoor measurements were available in a sector.
Otherwise, aerial survey data for each sector was multiplied by
the ratio of ground-to-aerial survey data averaged for the
community as a whole. In either case, the resultant outdoor
exposure rates for each sector were adjusted to correspond to PIC
measurements, as previously explained.
Ground survey measurements were used to characterize
exposure rates in the home environs (main floors, basements, and
driveways) throughout the communities at large. No adjustment to
PIC values were required for main floors and basements, since the
values obtained during the survey were PIC readings. For
driveways, sidewalks and streets surveyed with scintillometers,
appropriate adjustments were made using the regression equation
following Table 2.
Workplace exposures in Pocatello and Soda Springs were
estimated by using both methods described above. Aerial survey
data and aerial/ground ratios were employed for adult employees
16
-------
in outdoor occupations*, distributed by sectors throughout both
communities proportionately to the general population. For indoor
occupations, employed adults were assumed to be exposed to the
same distribution of exposure rates that were encountered in
homes (main floors) during the ground survey.
2. Outline of Estimation Methods
The following assumptions were made in calculating indoor
exposures to the residents of the various sectors:
The ground surveys of main floor and basement exposure
rates in both Pocatello and Soda Springs were representative
of the conditions in these communities. The numbers of main
floors and basements within specific exposure rate ranges,
in the survey samples, correspond to similar distributions
in the communities at large.
Workers employed in indoor occupations were subjected to
exposure rates following the same distribution as estimated
for the communities at large, based on the ground survey, as
above.
For maximally exposed individuals, the "worst case"
combinations of maximum exposure rates in the basement, main
floor, and work place were projected, based on the ground
survey. Conditions uncovered during the survey that would
lead to higher individual exposures were also included in
the estimate, even if only single instances of such somewhat
unusual conditions were recorded, such as the case of a
college student living in the basement of his parents' home,
with exposure rates substantially in excess of background
levels. Accordingly, an alternate scenario to that of Table
3 was developed, for a teenager spending 4300 hours in the
basement and 700 hours on the main floor.
Background exposure rates for Soda Springs residences were
12 MR/h; for Pocatello basements, 11 ^R/h; and for Pocatello
main floors, 10.5 pR/h, based on ground survey data.
Each residence surveyed included an adult employed outside
the home, an adult or teen not employed outside the home, a
child of elementary school age, and a pre-school infant, for
purposes of maximum individual exposure estimates.
* Farming and outdoor manufacturing, with number of
workers estimated on the basis of the 1988 County and City
Data Book, U.S. Department of Commerce.
17
-------
Similar assumptions were made in calculating outdoor exposures:
The ground survey "driveways" (the average of driveways,
sidewalks, and streets) in both communities were
representative of the conditions in the communities at
large. The numbers of "driveways" within specific exposure
rate ranges correspond to similar distributions in Pocatello
and Soda Springs.
Workers employed in outdoor occupations were apportioned
among the various sectors proportionately to the population
distribution in both communities, and assumed to be subject
to the same exposure rates as previously calculated for
those sectors.
Maximum individual exposures from the driveway, the sector,
the community and an outdoor occupation were estimated on
the basis of a "worst case" combination of the corresponding
exposure rates, and projected to occur to individuals
subject to maximum rates in the basements and main floors of
their homes. Conditions that would lead to higher
individual exposures were also included in the estimate,
even if the number of individuals subjected to such exposure
rates could not be determined. Exposure rates up to 65 ^R/h
were expected (based on survey data) for phosphorus industry
workers, railroad yard workers, and airline service/
maintenance crews.
Background outdoor exposure rates for Pocatello and Soda
Springs were 12 fj,R/h.
3. Quality Assurance
The following steps were taken to assure quality and
continuity in deriving the gamma radiation dose estimates as part
of the overall study effort:
Contractor and EPA personnel evaluated reasonableness of
EG&G aerial survey results by comparing them to ground
survey data.
The PNL Project Manager, and EPA staff from the Office of
Radiation Programs in Washington, DC, and the Las Vegas
Facility developed exposure scenarios.
Staff reviewed the field survey (ground-level) data to
assure consistency between instruments.
The ground and aerial survey data were converted to the same
radial grids as the population data.
18
-------
The survey instruments used were calibrated with NIST
(formerly National Bureau of Standards) traceable standards.
4. Gamma Radiation Dose Estimates
Table 4 divides the various age groups in Soda Springs into
subgroups, based on the net gamma radiation levels to which they
are exposed in their home environs. These exposure levels
correspond to the distribution of gamma rates measured on main
floors, basements and "driveways" during the Soda Springs home
survey. It should be noted that "driveway" exposure rates
average gamma measurements made on the driveway, the sidewalk and
the street adjoining each residence included in the survey.
The durations of exposure for the various population
groupings at the locations of interest were postulated in
Table 3. The products of these time intervals and the net
exposure rates in Table 4 result in Table 5, a tabulation of
annual exposures, in excess of natural background, to which the
groups under discussion were subjected. To facilitate future
risk projections, the exposure borne by each group was expressed
as a "population dose", i.e. by multiplying said exposure, in
terms of "equivalent dose" (in rem) by the number of people in
the group. The last column in Table 5 represents the sum of
population doses for members of all age groups subjected to
specific exposure levels, in a given location in or around the
home. The sum of the entries in this column, 131 person-rem,
represents the total population dose borne by the inhabitants of
Soda Springs solely due to residing in their homes.
Similar considerations apply to the calculation of exposure
and doses in the outdoor environment, here described in terms of
"sector" and community average values. Given the exposure
durations postulated by Table 3, varying for each age group,
population exposures and doses in individual Soda Springs sectors
would depend on the composition of the population of each sector,
as summarized in Table 6. The corresponding sector exposure
rates are based on the aerial survey values in Figure 2, modified
by the aerial/ground ratios in Table 2, adjusted to PIC values by
the subsequent regression equation, and reduced to net exposure
rates by subtracting the environmental background (12 /iR/h) . Net
community average exposure rates for Soda Springs are those
calculated previously for Table 2, or 7.8 /iR/h. Table 7 lists
the net exposure rates, per sector, for the population of
Soda Springs, and the corresponding net community exposure rates,
to which all Soda Springs inhabitants are subjected equally,
regardless of the sector in which they reside.
The durations of exposure to sector and community net gamma
levels were given, by age group, in Table 3. The products of
these time intervals, the population groups in Table 6, and net
sector and community rates in Table 7 yield the annual exposures,
19
-------
TABLE 4. POPULATION DISTRIBUTION BY NET EXPOSURE RATE1
AND AGE GROUPS2 IN HOME ENVIRONS (FIRST FLOOR,
BASEMENT, DRIVEWAY) FOR SODA SPRINGS
Net
Exposure
Rate
(MR/h)
Number of
Employed
Adults
Number
of
Teens
Number
of
Children
Number
of
Infants
FIRST FLOOR
0 440
3.2 425
6.8 343
11.0 425
335
323
261
323
146
140
113
140
105
101
81
101
BASEMENT
0
2.4
8.4
25.6
38.0
293
572
196
474
98
223
435
149
360
75
97
189
65
156
32
69
136
47
113
23
DRIVEWAY
0
2.3
7.1
13.8
17.9
22.5
163
245
408
245
408
163
124
186
311
186
311
124
54
81
135
81
135
54
0
0
0
0
0
0
1 Tabulated exposure rates represent range averages.
2 The number of individuals in each age group is based on Bureau
of Census data. Their further distribution among exposure
rate ranges is based on the ground survey.
20
-------
TABLE
ANNUAL POPULATION EXPOSURE, IN PERSON-REM, BY AGE
GROUPS IN HOME ENVIRONS (FIRST FLOOR, BASEMENT,
DRIVEWAY) FOR SODA SPRINGS
Exposure (Dose)
Net
Exposure
Rate
Employed
Adults
Teens
Children
Infants
Sum of
Exposure
FIRST FLOOR
0
3.2
6.8
11.0
0
5.86
10.02
20.10
0
4.46
7.62
15.28
0
1.93
3.30
6.62
0
2.04
4.27
7.00
0
14.29
25.21
49.00
BASEMENT
0
2.4
8.4
25.6
38.0
0
0.97
1.16
8.48
2.61
0
0.74
0.88
6.44
2.00
0
0.32
0.38
2.79
0.85
0
0.23
0.28
2.03
0.60
0
2.26
2.70
19.74
6.06
DRIVEWAY
0
2.3
7.1
13.8
17.9
22.5
0
0.12
0.57
0.69
1.47
0.73
0
0.17
0.87
1.02
2.24
1.12
0
0.07
0.38
0.44
0.97
0.49
0
0
0
0
0
0
Grand Total
0
0.36
1.82
2.15
4.68
2.34
130.61
21
-------
TABLE 6. COMPOSITION OF POPULATION IN SECTORS BY AGE GROUPS FOR
SODA SPRINGS
Population of
Sector
NE2
ENE2
E2
SSE2
SSE3
SSE4
SI
S2
S3
S4
SSW1
SSW2
SSW3
SSW4
SSW5
SW2
SW3
WSW1
WSW3
NW2
Population
in
Sector
36
3
12
203
52
3
3
548
760
9
3
545
1391
33
6
15
118
9
42
6
Employed
Adults In
Sector
15
1
5
87
22
1
1
236
327
4
1
234
598
14
3
6
51
4
18
3
Teens
in
Sector
12
1
4
67
17
1
1
181
251
3
1
180
459
11
2
5
39
3
14
2
Children
in
Sector
5
1
2
28
7
1
1
77
106
1
1
76
195
5
1
2
17
1
6
1
Infants
in
Sector
4
0
1
21
6
0
0
54
76
1
0
55
139
3
0
2
11
1
4
0
22
-------
TABLE 7. NET EXPOSURE RATES IN EACH SECTOR AND IN COMMUNITY
FOR SODA SPRINGS
Net Exposure Net Exposure Rate
Rate in Each in Community
Sector Sector (jiR/h) (/xR/h)
NE2 5.1 7.8
ENE2 4.4 7.8
E2 4.4 7.8
SSE2 9.1 7.8
SSE3 3.8 7.8
SSE4 4.4 7.8
SI 11.6 7.8
S2 6.5 7.8
S3 10.4 7.8
S4 3.7 7.8
SSW1 4.4 7.8
SSW2 5.5 7.8
SSW3 7.2 7.8
SSW4 2.6 " 7.8
SSW5 2.6 7.8
SW2 2.6 7.8
SW3 5.4 7.8
WSW1 3.7 7.8
WSW3 4.7 7.8
NW2 4.4 7.8
23
-------
by age group and sector, for the residents of Soda Springs.
Table 8 expresses the resultant values in terms of population
dose, i.e. in "person-rem" for direct application in risk
estimates. The Soda Springs population dose from outdoor
activities beyond the home environs is calculated by summing the
values in the last columns in Table 8, which total 48 person-
rem.
Table 9 describes the workplace exposures for Soda Springs
adults engaged in outdoor occupations. The basic assumption
implicit in the tabulated values is that outdoor exposures
incurred during work hours do not differ from exposures during
other outdoor activities. Thus Table 9 follows the format of
Table 7, in terms of net exposure rates, per sector, borne by 28%
of the employed adults in the corresponding sector. The
resulting exposures are expressed in terms of equivalent dose
times the number of exposed adults, per sector, yielding a total
of 6.6 person-rem.
Table 10 describes workplace exposures for Soda Springs
adults in indoor occupations. Indoor workplace exposure rates
are assumed not to differ from the main floor rates observed
during the Soda Springs survey. Thus Table 10 employs the same
exposure rate distributions as originally listed for Table 4
"First Floor" values, with the corresponding number of exposed
employed adults reduced to 72%. The total population dose for
indoor workers in Soda Springs amounts to 12.1 person-rem.
The sum of population doses for the various environments and
age groups covered in Tables 5,8,9, and 10 results in a total
population dose of 197 person-rem, incurred annually by the
approximately 3800 residents of Soda Springs. This represents an
average dose, per resident, of 52 mrem/yr above background.
Tables 11 through 17 provide the corresponding population
and exposure (dose) data for Pocatello. The population dose due
to exposures in the Pocatello area home environs is 328 person-
rem, as shown in Table 12, and that from outdoor activities is
385 person-rem, in Table 15. Workplace exposures due to outdoor
occupations add a total of 62 person-rem to the population dose,
as seen in Table 16, and indoor occupations contribute an
additional dose of 27 person-rem, in Table 17.
The sum of population doses for the various environments and
age groups covered in tables 12,15,16 and 17 results in a total
population dose of 803 person-rem, incurred annually by the
approximately 57,000 residents of Pocatello. This represents an
average dose, per resident, of 14 mrem/year above background.
24
-------
ro
en
TABLE 8. ANNUAL OUTDOOR EXPOSURE, IN PERSON-REM, BY AGE GROUP FOR
SODA SPRINGS
Exposure (Dose) in Sector and Community
Sector
NE2
ENE2
E2
SSE2
SSE3
SSE4
SI
S2
S3
S4
SSW1
SSW2
SSW3
SSW4
SSW5
SW2
SW3
WSW1
WSW2
NW2
Employed
Adults
0.08
0
0.02
0.59
0.10
0
0.01
1.35
2.38
0.02
0
1.24
3.59
0.06
0.01
0.02
0.27
0.02
0.09
0.01
Teens
0.21
0.02
0.07
1.45
0.28
0.02
0.02
3.44
5.74
0.05
0.02
3.24
9.03
0.17
0.03
0.08
0.70
0.05
0.24
0.03
Children
0.08
0.02
0.03
0.63
0.10
0.02
0.03
1.40
2.59
0.01
0.02
1.26
3.77
0.06
0.01
0.02
0.28
0.01
0.09
0.02
Infants
0.02
0
0.01
0.17
0.03
0
0
0.38
0.70
0.01
0
0.37
1.04
0.01
0
0.01
0.07
0.01
0.03
0
Sum of
Outdoor
Exposure
0.39
0.04
0.13
2.84
0.51
0.04
0.06
6.57
11.41
0.09
0.04
6.11
17.43
0.30
0.05
0.13
1.32
0.09
0.45
0.06
Grand Total
48.06
-------
TABLE
Sector
WORKPLACE EXPOSURES FOR ADULTS EMPLOYED 2000*
HOURS IN OUTDOOR OCCUPATIONS, IN SODA SPRINGS
Net Exposure Rate No. of Employed Employed Adult
Workplace, Outdoors Adults Exposed Exposure
(person-rem)
NE2
ENE2
E2
SSE2
SSE3
SSE4
SI
S2
S3
S4
SSW1
SSW2
SSW3
SSW4
SSW5
SW2
SW3
WSW1
WSW3
NW2
5.1
4.4
4.4
9.1
3.8
4.4
11.6
6.5
10.4
3.7
4.4
5.5
7.2
2.6
2.6
2.6
5.4
3.7
4.7
4.4
4
1
1
24
6
1
1
65
90
1
1
65
165
4
1
2
14
1
5
1
0.041
0.009
0.009
0.437
0.046
0.009
0.002 "
0.845
1.872
0.007
0.009
0.715
2.376
0.021
0.005
0.010
0.151
0.007
0.019
0.009
40 hours per week, 50 weeks per year, totaling
2000 hours per year.
6.599
26
-------
TABLE 10. WORKPLACE EXPOSURES FOR ADULTS EMPLOYED 2000
HOURS IN INDOOR OCCUPATIONS, IN SODA SPRINGS
Net Exposure Rate No. of Employed Employed Adult
Workplace, Indoors Adults Exposed Exposure
(/iR/h) (person-rent)
0 319 0
3.2 307 1.96
6.8 248 3.37
11.0 307 6.75
Grand Total 12.08
27
-------
TABLE 11. POPULATION DISTRIBUTION BY NET EXPOSURE RATE AND AGE
GROUPS IN HOME ENVIRONS (FIRST FLOOR, BASEMENT,
DRIVEWAY) FOR POCATELLO
Net
Exposure
Rate
(MR/h)
Number of
Employed
Adults
Number
of
Teens
Number
of
Children
Number
of
Infants
FIRST FLOOR
0 9802 5841 2946 2113
0.5 10074 6003 3031 2170
1.5 5173 3082 1557 1115
2.6 1361 812 410 293
3.2 545 325 164 117
5.3 272 163 83 58
BASEMENT
0 10890 6490 3277 2347
0.5 9802 5841 2949 2112
1.5 3811 2272 1147 822
2.4 2178 1298 655 470
7.4 545 325 164 117
DRIVEWAY
0 2454 1458 734 0
0.6 4356 2596 1311 0
2.1 5989 3570 1802 0
4.0 2178 1298 655 0
7.7 1633 974 ' 491 0
10.1 2178 1298 655 0
13.5 3811 2272 1147 0
16.4 1361 812 410 0
19.1 2450 1460 738 0
24.9 272 163 83 0
27.8 272 163 83 0
36.6 272 163 83 0
28
-------
TABLE 12. ANNUAL POPULATION EXPOSURE, IN PERSON-REM, BY AGE
GROUPS IN HOME ENVIRONS (FIRST FLOOR, BASEMENT,
DRIVEWAY) POCATELLO
Exposure (Dose)
Net
Exposure
Rate
/uR/Hr
Employed
Adults
Teens
Children
Infants
Sum of
Exposure
FIRST FLOOR
0
0.5
1.5
2.6
3.2
5.3
0
21.66
33.36
15.22
7.50
6.20
0
12.91
19.88
9.08
4.43
3.71
0
6.52
10.04
4.58
2.26
1.89
0
6.83
10.54
4.80
2.36
1.94
0
47.92
73.82
33.68
16.55
13.74
BASEMENT
0
0.5
1.5
2.4
7.4
0
3.43
4.00
3.66
2.82
0
2.04
2.39
2.18
1.68
0
1.03
1.20
1.10
0.85
0
0.74
0.86
0.79
0.61
0
7.24
8.45
7.73
5.96
DRIVEWAY
0
0.6
2.1
4.0
7.7
10.1
13.5
16.4
19.1
24.9
27.8
36.6
0
0.44
2.39
1.74
2.45
4.36
10.29
4.49
9.31
1.36
1.52
1.99
0
0.52
2.86
2.08
3.02
5.19
12.27
5.36
11.10
1.63
1.81
2.38
0
0.26
1.44
1.05
1.52
2.62
6.19
2.71
5.60
0.83
0.92
1.21
0
0
0
0
0
0
0
0
0
0
0
0
Grand Total
0
1.22
6.69
4.87
6.99
12.17
28.75
12.56
26.01
3.82
4.25
5.58
328.00
29
-------
TABLE 13.
COMPOSITION OF POPULATION IN SECTORS BY AGE GROUPS
FOR POCATELLO AREA
Population
Sector
N4
N5
NNE3
NNE4
NNE5
NE2
NE3
NE4
NE5
NE6
NE7
ENE2
ENE3
ENE4
ENE5
ENE6
E3
E4
E5
E6
E7
E8
ESE3
ESE4
ESE5
ESE6
ESE7
ESE8
ESE9
SE4
SE5
SE6
SE7
SE8
SE9
SE10
SE11
SE12
SW3
SW4
WSW4
WSW5
Population
in
Sector
69
61
184
206
116
184
94
43
417
569
116
18
199
2950
2031
102
1814
2852
3052
3531
2323
4
65
1317
5516
10100
8461
345
70
29
2027
2780
1212
1305
2445
489
175
32
11
33
18
11
Employed
Adults In
Sector
33
29
88
98
55
88
44
20
197
55
9
9
94
1396
960
48
857
1349
1444
1670
1099
3
30
622
2609
4778
4002
164
33
14
959
1314
573
617
1157
231
83
15
5
15
9
5
Teens
in
Sector
17
17
51
57
33
51
25
13
118
160
33
5
57
834
575
29
513
808
864
998
657
1
19
373
1560
2859
2394
97
19
9
573
787
344
370
692
138
50
8
4
9
5
4
Children
in
Sector
10
9
27
29
17
27
14
6
60
81
17
3
28
419
288
14
258
405
433
502
330
0
9
187
784
1434
1201
50
10
4
288
395
171
185
347
70
25
5
1
5
3
1
Infants
in
Sector
9
6
18
22
11
18
11
4
42
273
57
1
20
301
208
11
186
290 -
311
361
237
0
7
135
563
1029
864
34
8
2
207
284
124
133
249
50
17
4
1
4
1
1
30
-------
TABLE 14
NET EXPOSURE RATES IN EACH SECTOR AND IN COMMUNITY
FOR POCATELLO AREA
Sector
Net Exposure
Rate in Each
Sector (/iR/h)
Net Exposure Rate
in Community
N4
N5
NNE3
NNE4
NNE5
NE2
NE3
NE4
NE5
NE6
NE7
ENE2
ENE3
ENE4
ENE5
ENE6
E3
E4
E5
E6
E7
E8
ESE3
ESE4
ESE5
ESE6
ESE7
ESE8
ESE9
SE4
SE5
SE6
SET
SE8
SE9
SE10
SE11
SE12
SW3
SW4
WSW4
WSW5
NW3
NNW3
1.5
1.3
2.1
0.8
1.5
3.2
1.7
1.3
2.2
2.6
1.8
3.7
3.5
6.9
5.0
1.9
5.7
4.9
2.9
3.3
5.6
2.8
3.6
3.9
1.4
2.3
4.2
3.5
2.9
2.0
2.3
6.1
3.4
4.2
7.4
4.1
2.1
1.6
2.8
1.0
1.6
1.3
1.3
1.4
4.6
4.6
4.6
4.6
4.6
4.6
4.6
4.6
4.6
4.6
4.6
4.6
4.6
4.6
4.6
4.6
4.6
4.6
4.6
4.6
4.6
4.6
4.6
4.6
4.6
4.6
4.6
4.6
4.6
4.6
4.6
4.6
4.6
4.6
4.6
4.6
4.6
4.6
4.6
4.6
4.6
4.6
4.6
4.6
31
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OJ
ro
TABLE 15. ANNUAL OUTDOOR EXPOSURE, IN PERSON-REM, BY AGE
GROUP FOR POCATELLO AREA
Exposure (Dose) in Sector and Community
Sector
N4
N5
NNE3
NNE4
NNE5
NE2
NE3
NE4
NE5
NE6
NE7
ENE2
ENE3
ENE4
ENE5
ENE6
E3
E4
E5
E6
E7
E8
ESE3
ESE4
ESE5
ESE6
ESE7
Employed
Adults
0.08
0.07
0.24
0.21
0.13
0.27
0.11
0.05
0.54
0.16
0.02
0.03
0.30
6.42
3.69
0.12
3.53
5.13
4.33
5.28
4.48
0.01
0.10
2.11
6.26
13.19
14.09
Teens
0.15
0.15
0.48
0.47
0.29
0.54
0.23
0.11
1.13
1.59
0.30
0.06
0.62
11.89
7.11
0.27
6.70
9.91
8.86
10.64
8.51
0.01
0.21
4.20
13.67
27.62
27.67
Children
0.07
0.06
0.21
0.17
0.12
0.26
0.10
0.04
0.49
0.71
0.13
0.03
0.29
6.55
3.63
0.11
3.54
5.04
4.00
4.96
4.47
0
0.09
2.03
5.36
11.87
13.60
Infants
0.03
0.02
0.06
0.06
0.03
0.07
0.03
0.01
0.14
0.98
0.18
0.00
0.08
1.73
0.99
0.04
0.96
1.38
1.17
1.42
1.21
0
0.03
0.57
1.69
3.55
3.80
Sum of
Outdoor
Exposure
0.33
0.30
0.99
0.91
0.57
1.14
0.47
0.21
2.30
3.44
0.63
0.12
1.29
26.59
15.42
0.54
14.73
21.46
18.36
22.30
18.67
0.02
0.43
8.91
26.98
56.23
59.16
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TABLE 15.
CO
co
ANNUAL OUTDOOR EXPOSURE, IN PERSON-REM,
GROUP FOR POCATELLO AREA (continued)
BY AGE
Exposure (Dose) in Sector and Community
Sector
SE4
SE5
SE6
SE7
SE8
SE9
SE10
SE11
SE12
SW3
SW4
WSW4
WSW5
NW3
NNW3
Grand
Employed
Adults
0.04
2.65
5.62
1.83
2.17
5.55
0.80
0.22
0.04
0.01
0.03
0.02
0.01
0.11
0.05
Total
Teens
0.08
5.54
10.59
3.70
4.28
10.21
1.58
0.47
0.07
0.04
0.08
0.05
0.03
0.24
0.10
Children
0.03
2.38
5.67
1.72
2.09
5.70
0.78
0.20
0.04
0.01
0.03
0.02
0.01
0.09
0.03
Infants
0.01
0.71
1.52
0.50
0.59
1.4-9
0.22
0.06
0.01
0.00
0.01
0.00
0.00
0.03
0.01
Sum of
Outdoor
Exposure
0.16
11.28
23.40
7.75
9.13
22.95
3.38
0.95
0.16
0.06
0.15
0.09
0.05
0.47
0.19
385.31
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TABLE 16. WORKPLACE EXPOSURES FOR ADULTS EMPLOYED 2000 HOURS
IN OUTDOOR OCCUPATIONS, IN POCATELLO
Sector
Net Exposure Rate
Workplace, Outdoors
(MR/h)
No. of Employed
Adults Exposed
Employed Adult
Exposure
(person-rem)
N4
N5
NNE3
NNE4
NNE5
NE2
NE3
NE4
NE5
NE6
NE7
ENE2
ENE3
ENE4
ENE5
ENE6
E3
E4
E5
E6
E7
E8
ESE3
ESE4
ESE5
ESE6
ESE7
ESE8
ESE9
SE4
SE5
SE6
SE7
SE8
SE9
SE10
SE11
SE12
SW3
SW4
WSW4
WSW5
W3
NW3
1.5
1.3
2.1
0.8
1.5
3.2
1.7
1.3
2.2
2.6
1.8
3.7
3.5
6.9
5.0
1.9
5.7
4.9
2.9
3.3
5.6
2.8
3.6
3.9
1.4
2.3
4.2
3.5
2.9
2.0
2.3
6.1
3.4
4.2
7.4
4.1
2.1
1.6
2.8
1.0
1.6
1.3
1.3
1.4
10
9
26
29
16
26
13
7
59
81
16
2
29
419
288
15
257
405
434
502
330
1
9
187
783
1434
1202
49
10
4
288
395
172
185
347
69
24
5
2
5
2
2
14
6
0.030
0.023
0.109
0.046
0.048
0.166
0.044
0.018
0.260
0.421
0.058
0.015
0.023
5.782
2.880
0.057
2.930
3.969
2.517
3.313
3.696
0.006
0.065
1.459
2.192
6.596
10.097
0.343
0.058
0.016
1.325
4.819
1.170
1.554
5.136
0.566
0.101
0.016
0.011
0.010
0.006
0.005
0.036
0.014
34
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TABLE 17. WORKPLACE EXPOSURES FOR ADULTS EMPLOYED 2000
HOURS IN INDOOR OCCUPATIONS, IN POCATELLO
Net Exposure Rate
Workplace, Indoors
(MR/h)
No. of Employed
Adults Exposed
Employed Adult
Exposure
(person-rem)
0
0.5
1.5
2.6
3.2
5.3
Grand Total
6862
7052
3621
952
381
190
0
7.05
10.86
4.95
2.44
2.01
27.31
35
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E. Summary and Results
Table 18 is a summary of net population doses in Soda
Springs by age group and exposure scenario. The most significant
dose is that received by employed adults and the dominant
exposure environment is the home (main floor and basement).
Table 19 is a similar summary of net population doses in the
Pocatello area. The most significant dose is again that received
by employed adults, with workplace exposure being the leading
contributor. The dominant exposure environment is no longer the
home, but the sector (immediate vicinity beyond the home
environs) and the community at large.
The primary source of gamma radiation in both Pocatello and
Soda Spring is radioactive slag, a residue from phosphate
industry processes. The observations summarized in Tables 18 and
19 are compatible with the different uses found for this residual
slag, in the two communities. In Soda Springs, radioactive slag
was used in some home foundations, while in Pocatello it was
repeatedly used in paving"streets.
Table 20 relates the total population doses of Tables 18 and
19 and eguates them to annual risk rates, in terms of cancer
deaths per year in each community. These risk rates were based
on the expectation that a population dose of 1,000,000 person-
rem would result in roughly 400 cancer deaths per year, as
derived from Hiroshima - Nagasaki data and other sources.
Tables 21 and 22 summarize the net gamma dose calculations
for average and maximally exposed individuals in Pocatello and
Soda Springs, respectively. The calculations for Pocatello are
based on a hypothetical combination of maximum exposures in home
environs, sector, community, and workplace. The resultant annual
dose of 145 mrem corresponds to a fatal cancer risk of 0.00006
per year for the hypothetical maximally exposed individual, an
employed adult. Based on the commonly accepted projection of 70
years under these conditions, this yearly risk represents a
potential 0.004 lifetime risk to the individual in question.
This yearly dose to the maximally exposed individual in Soda
Springs is based on a scenario noted during the home survey. A
teenager having a basement bedroom who also spends time studying
and watching television in the basement recreation room would
occupy the basement 4300 hours annually, and spend only 700 hours
on the first floor. His yearly dose is 205 mrem, corresponding
to a fatal cancer risk of 0.00008 per year. If the subject
individual were to maintain this lifestyle for 70 years, his
lifetime risk would amount to 0.006 (Table 21).
36
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A more likely scenario for potential lifetime exposure is
that of the employed adult in Soda Springs, subjected to a
hypothetical combination of maximum exposures in home environs,
sector, community, and workplace. The resultant annual dose of
191 mrem corresponds to a lifetime risk of 0.005.
TABLE 18. SUMMARY NET POPULATION DOSES, IN PERSON-REM, BY AGE
AND ACTIVITY GROUP, FOR SODA SPRINGS
Location
Teenagers and Total by
Employed non-employed Exposure
Adults Adults Children Infants Elements
Main Floor
Basement
Driveway
Sector
Community
Workplace
Total by
age group
35
13
3
4
5
18
81
.98
.22
.58
.80
.09
.70
.37
27.
10.
5.
9.
15.
0
67.
36
06
42
21
65
69
11
4
2
6
3
0
28
.85
.35
.35
.46
.97
.99
13.
3.
0
1.
1.
0
19.
32
14
39
47
32
88
30
11
21
26
18
.51
.77
.35
.86
.18
.70
Grand Total
197.4
Propagated sampling error estimates for exposure rates,
population and time intervals allocated to each location included
in the scenario yielded an equivalent standard deviation of ± 25
person-rem, a coefficient of variance of 13%.
37
-------
TABLE 19. SUMMARY OF NET POPULATION DOSES, IN PERSON-REM, BY
AGE AND ACTIVITY GROUP, FOR POCATELLO
Location
Main Floor
Basement
Driveway
Sector
Community
Workplace
Total by
age group
Employed
Adults
83.
13.
40.
41.
49.
89.
318.
94
91
34
17
58
50
44
Teenagers and
non-employed
Adults Children
50
8
48
61
119
0
288
.05
.29
.21
.96
.74
.25
25
4
24
49
37
0
141
.29
.19
.37
.77
.59
.21
Infants
26.47
3.00
0
11.49
14.10
0
55.06
Total by
Exposure
Elements
185.75
29.39
112.92
164.39
221.01
89.50
Grand Total
803.0
Propagated sampling error estimates for exposure rates,
population and time intervals allocated to each location included
in the scenario yielded an equivalent standard deviation of ± 329
person-rem, a coefficient of variance of 41%.
TABLE 20. YEARLY RISK FOR THE POPULATIONS OF POCATELLO AND
SODA SPRINGS
Community
Annual Population
Dose (person-rem)
Annual Population
Risk
Pocatello
Soda Springs
803 ± 329
197 ± 25
0.3 deaths/year among
57,000 people
0.1 deaths/year among
3,800 people
38
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TABLE 21. CALCULATED NET GAMMA-RAY DOSES (mrem/yr) TO AVERAGE
INDIVIDUALS IN POCATELLO AND SODA SPRINGS
Community
Pocatello
Soda Springs
Average Individual Annual
Dose (millirem/year)
14 ± 6
52 ± 7
Lifetime
Risk
0.0004
0.0014
TABLE 22. CALCULATED NET GAMMA-RAY DOSES (mrem/yr) TO MAXIMALLY
EXPOSED INDIVIDUALS IN POCATELLO AND SODA SPRINGS
Community
Maximum Annual
Individual Dose
Lifetime Risk
Pocatello
Soda Springs
145
205
0.004
0.0056
39
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II. DOSE AND RISK ASSESSMENT FOR AIRBORNE EMISSIONS
This section of the report estimates dose and risk from
radionuclides emitted from the elemental phosphorus plants in
Pocatello and Soda Springs. The section discusses the assessment
methodology used, the actual parameters used, and the dose and
risk resulting from airborne exposure.
A. Assessment Methodology
The Clean Air Act Assessment Package - 1988 (CAP-88)
computer model was used to estimate the dose and risk resulting
from radionuclide emissions to air at Pocatello and Soda Springs.
CAP-88 is a set of computer programs, databases and associated
utility programs that models the transport of radionuclides from
the emission point through the environment to exposed human
populations, and estimates the resulting dose and health impact.
1. Environmental Transport
The computer program which models environmental transport in
CAP-88 is AIRDOS-EPA. This program uses a modified Gaussian
plume equation to estimate the average dispersion of radio-
nuclides released from the stack. Plume rises were calculated
assuming a heated, buoyancy-driven plume. Assessments were done
for a circular grid with a radius of 80 kilometers (50 miles)
around each facility.
AIRDOS-EPA was used to compute radionuclide concentrations
in air, rates of deposition on ground surfaces, concentrations in
food and intake rates to people from inhalation of air and
ingestion of food produced in the assessment area. Estimates of
the radionuclide concentrations in produce, leafy vegetables,
milk and meat consumed by humans were made by coupling the output
of the atmospheric transport models .with the U.S. Nuclear
Regulatory Commission Regulatory Guide 1.109 terrestrial food
chain models.
2. Estimation of Dose and Risk
The computer program RADRISK was used to estimate dose and
risk conversion factors. Factors were computed for the pathways
of ingestion and inhalation intake, ground level air immersion
and ground surface irradiation.
Estimation of dose and risk were made by the program DARTAB,
which combines the inhalation and ingestion intake rates, air and
ground surface concentrations output from AIRDOS-EPA with the
dose and risk conversion factors from the RADRISK database.
40
-------
DARTAB computed the dose and risk to the maximum exposed
individual and to the collective population. DARTAB also
tabulated the number of people and number of health effects at
selected levels of risk.
B. Parameters Used in the Assessment
1. Population Data
Population distributions for Pocatello and Soda Springs,
Idaho, were generated with the utility program SECPOP, which uses
a database of 1980 Census data. Since census enumeration
districts vary widely in their size, the census database is not
very precise at estimating population groups close in to the
facility. The distributions were modified with supplemental data
obtained from surveys of the population within 5 km. of each
facility.
Number of People Distance to Maximum
Facility Within 80 km. Exposed Individual
FMC 170,000 1.8 km
Monsanto 100,000 2.4 km
2. Agricultural Data
Distributions of beef cattle, milk cattle and the land area
under cultivation for food crop production in the assessment area
were generated with the utility program FOODJOB, which uses
state-wide average agricultural productivity data reported for
Idaho. Site-specific data was prohibitively expensive to obtain.
3. Meteorological Data
Meteorological data reported from the Pocatello airport was
used for the airborne dose assessment.
41
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4. Plume Rise
The stack effluent from the calciner plants has a
significant heat content that results in a substantial buoyant
plume rise. The stack parameters used were:
Stack Heat Emission
Facility Height (calories/sec)
FMC 31 m 9.5xl05
Monsanto 27 m S.OxlO5
5. Source Term
The total annual emissions were estimated from monitoring
performed by EPA at the calciner plants in Soda Springs and
Pocatello, Idaho during 1988. The radionuclides which are major
contributors to dose and risk are lead-210 (Pb-210) and polonium-
210 (Po-210). The source terms used were:
Facility Source Term. Ci/year
Pb-210 Po-210
FMC Pocatello 0.14 10.
Monsanto Soda Springs 0.35 1.4
42
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C. RESULTS OF THE DOSE AND RISK ASSESSMENT FOR AIR PATHWAY
FMC POCATELLO. IDAHO
Frequency Distribution of Individual Risks
Number of Deaths/Year
RISK People at this Risk
1 to 10"1 0 0
10'1 to 10"2 0 0
10"2 to 10"3 0 0
10"3 to 10"4 5029 0.01
10"4 to 10"5 94823 0.04
10"5 to 10"6 73778 0.009
less than 10"6 0 0
Total Number of Deaths/Year: 0.06
Maximum Exposed Individual
Effective Dose Equivalent '
(mrem/year): 23
Lifetime Risk: 0.0006, or 6 in 10,000
MONSANTO SODA SPRINGS. IDAHO
Frequency Distribution of Individual Risks
Number of Deaths/Year
RISK People at this Risk
1 to 10'1 0 0
10"1 to 10"2 0 0
10"2 to 10"3 0 0
10"3 to 10"4 0 0
10"4 to 10"5 5247 0.002
10"5 to 10"6 32829 0.0008
less than 10"6 62550 0.0006
Total Number of Deaths/Year: 0.003
Maximum Exposed Individual
Effective Dose Equivalent
(mrem/year): 4
Lifetime Risk: 0.00008, or 8 in 100,000
43
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REFERENCES
1. Berry, H.A. 1987. "An Aerial Radiological Survey of
Pocatello and Soda Springs, Idaho and Surrounding
Area." US EPA-8613, February 1987, Contract Report by
EG&G Energy Measurement, Inc., Las Vegas, NV.
2. Boyns, P.K. 1976. "The Aerial Radiological Measuring System
Arms): Systems, Procedures and Sensitivities." Report No.
EG&G-1183-1691. Las Vegas, NV: EG&G/EM.
3. Clary, H.W. 1981. "An Aerial Radiological Survey of the
Federal-American Partners, Pathfinder, and Union Carbide
Mill Sites and Surrounding Area, Gas Hills Mining District,
Wyoming." Report No. NRC-8206. Las Vegas, NV: EG&G/EM.
4. Jobst, J.E. 1979. "The Aerial Measuring System Program."
Nuclear Safety. March/April 1979, 20:136-147.
5. U.S. Environmental Protection Agency, "Elemental Phosphorus
Production - Calciner Off-gases: Final Emission Test
Report, Monsanto Elemental Phosphorus Plant, Soda Springs,
Idaho," EMB Report No. 88-EPA-01, January 1989.
6. U.S. Environmental Protection Agency, "Elemental Phosphorus
Production - Calciner Off-gases: Final Emission Test
Report, FMC Elemental Phosphorus Plant, Pocatello, Idaho,"
EMB Report No. 88-EPA-02, January 1989.
7. U.S. Nuclear Regulatory Commission, Regulatory Guide 1.109,
"Calculation of Annual Doses to Man from Routine Releases of
Reactor Effluents for the Purpose of Evaluating Compliance
with 10 CFR Part 50" Appendix I (Revision 1), Office of
Standards Development, 1977.
44
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