Technical Note
ORP/LV-77-2
RADIOLOGICAL SURVEY AT THE
INACTIVE URANIUM MILL SITE
NEAR RIVERTON, WYOMING
JUNE 1977
o
LU
O
U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RADIATION PROGRAMS
LAS VEGAS FACILITY
LAS VEGAS, NEVADA 89114
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Technical Note
ORP/LV-77-2
RADIOLOGICAL SURVEY AT THE
INACTIVE URANIUM MILL SITE
NEAR RIVERTON, WYOMING
Richard L. Douglas
June 1977
OFFICE OF RADIATION PROGRAMS LAS VEGAS FACILITY
U.S. ENVIRONMENTAL PROTECTION AGENCY
LAS VEGAS, NEVADA 89114
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This report has been reviewed by the Office of Radiation
Programs Las Vegas Facility, Environmental Protection Agency,
and approved for publication. Mention of trade names or
commercial products does not constitute endorsement or recommenda
tion for use.
11
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PREFACE
Uranium mills are designed to extract uranium from ore which
contains radioactive isotopes of the naturally-occurring uranium
series decay chain. These isotopes, some of which are extremely
long-lived, are discarded as mill wastes into large ponds and
piles. Wind and water erosion have scattered the mill wastes
over large areas of these sites' local environs, resulting in
land contamination and increased population radiation exposure.
This survey was made at the request of the Wyoming
Department of Health and Social Services to evaluate existing
radiological conditions at the inactive uranium mill site at
Riverton, Wyoming.
Donald W- Hendricks
Director, Office of
Radiation Programs, LVF
111
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CONTENTS
Page
LIST OF FIGURES vi
LIST OF TABLES vi
ACKNOWLEDGMENTS vii
INTRODUCTION 1
History of the Riverton Uranium Mill Site 1
Previous Surveys 2
Study Participants 4
SURVEY METHODS 5
Gamma Survey 5
Water Sampling 7
Radon Progeny (Working Level) Sampling 8
Miscellaneous Soil and Tailings Sampling 8
RESULTS AND DISCUSSION 9
Gamma Survey 9
Water Sampling 16
Radon Progeny (Working Level) Sampling 18
Miscellaneous Soil and Tailings Sampling 20
SUMMARY AND CONCLUSIONS 21
REFERENCES 22
v
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LIST OF FIGURES
Number Pa§e
1 Results of Gamma Radiation Survey 11
2 Radiological Parameters as a Function of Distance
from the Tailings Pile 15
3 Location of Water and Radon Progeny
(Working Level) Samples 17
LIST OF TABLES
Number Page
1 Depth Test in Plowed Field East of Tailings Pile 10
2 Radiological Parameters as a Function of Distance
from the Tailings Pile 14
3 Radium-226 Concentrations in Water 19
4 Indoor Radon Progeny (Working Level) Results 19
5 Radium-226 Concentration in Tailings and
Miscellaneous Soil Samples 20
VI
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ACKNOWLEDGMENTS
The perseverance of Messrs. Jon Yeagley, Edd Johnson,
Tom Fife, Joe Stano, and John Myers in making the gamma survey
measurements are gratefully acknowledged. Mr. Myers also
contributed to the study by contacting local residents and
obtaining permission for water and radon progeny sampling,
and by collecting the samples. His assistance in these areas
is especially appreciated.
Vll
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INTRODUCTION
In September, 1975 the State of Wyoming* (Johnson, 1975)
requested, through the Nuclear Regulatory Commission (NRG), that
the Environmental Protection Agency's (EPA) Office of Radiation
Programs-Las Vegas Facility (ORP-LVF) conduct a survey to evalu-
ate the radiological environmental status of the inactive uranium
mill site near Riverton, Wyoming. Of particular interest was the
extent of windblown tailings from the site. The State also
requested that the Riverton site be included in the evaluation of
inactive uranium mill sites which is being conducted jointly by
EPA and the Energy Research and Development Administration (ERDA)
The objectives of this evaluation program are described in the
"Summary Report, Phase I Study of Inactive Uranium Mill Sites and
Tailings Piles" (ERDA, 1974).
As a result of the State's request, a study was conducted at
the Riverton site during the period September 30 to October 2,
1975. The organizations participating in the study included the
State of Wyoming, EPA (ORP-LVF and Region VIII), NRC, Indian
Health Service, and Solution Engineering, Inc. The individuals
who conducted the survey are listed below.
HISTORY OF THE RIVERTON URANIUM MILL SITE
The Riverton mill site is about two and one-half miles
southwest of the center of the town of Riverton, and is located
on fee land within the Wind River Indian Reservation. Fremont
Minerals, Inc. began operations at the site in 1958. The mill
was later purchased by Susquehanna-Western, Inc., and milling
* Division of Health and Medical Services, Department of Health
and Social Services
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operations ended in June, 1963. The nominal capacity of the mill
was 550 tons per day, and about 910,000 tons of tailings were
generated. Based on the average grade of the ore processed, the
tailings have a calculated average radium-226 concentration of
about 660 pCi/gram, and the total radium content of the pile is
estimated at about 500 Curies (PHS, 1970; radium data from USAEC
Division of Occupational Safety).
The main mill building was partially dismantled in the early
1970's and most of the equipment was salvaged. Western Nuclear,
Inc. is currently using some of the remaining facilities at the
site to produce sulfuric acid which is used at operating uranium
mills in the Gas Hills area. At the time of this survey,
Solution Engineering, Inc. held an option to recover uranium from
the tailings by means of a leaching process.
The original tailings pond and pile covered about 40 acres.
In 1972, Susquehanna-Western stabilized the tailings pile. The
*
pile was rearranged to cover about 80 acres, fenced, and covered
with a layer of clean material. The cover material was obtained
from the immediate vicinity of the pile, and ranges from coarse
gravel to the local topsoil. Clean fill was also placed on a
portion of the ore storage yard northeast of the mill buildings.
The covered pile was apparently seeded, but at the time of this
survey, there was very little established vegetation on the pile.
Bare tailings were visible at a few spots on the pile, and along
most of the fence around the perimeter of the pile.
PREVIOUS SURVEYS
Previous radiological surveys were conducted at the Riverton
site by the U.S. Public Health Service (PHS) in June 1970 (PHS,
1970), and by the U.S. Atomic Energy Commission (AEC) in March
1973 (AEC, 1973) .
* The nominal area inside the fence (See Figure 1). The actual
pile covers 72 acres, according to the Phase II Engineering
Assessment made by Ford, Bacon $ Davis Utah Inc.
2
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During the AEC survey on March 13, 1973, water samples were
collected at three locations and soil samples were collected at
20 locations. The water samples were analyzed for natural
uranium, thorium-230, and radium-226. Radium and thorium con-
centrations were below the detection limit (0.09 and 0.4 pCi/1,
respectively) in all three samples. Uranium concentrations in
water were 3.7 pCi/1 at a residence 600 feet south of the
tailings pile, 10 pCi/1 in Riverton, and less than the detection
limit of 1.8 pCi/1 at a residence 3200 feet northeast of the
pile.
Nineteen of the 20 soil samples were analyzed for thorium-
230 and radium-226, and 4 of the 19 were also analyzed for
natural uranium. Three samples, collected on or immediately
adjacent to the pile, had high levels of all three nuclides.
Levels of radium and thorium were slightly elevated (up to about
five times background levels) at locations 125 feet, 500 feet,
and 1500 feet northeast of the pile at 30U azimuth; at a resi
dence 1000 feet northeast of the pile at 60°; and at a residence
600 feet south of the pile.
Measurements of the direct (gamma) radiation level were made
at each of the sampling locations. The type of instrument used
and its sensitivity were not reported. The only report of these
results was the statement that "These measurements did not
reveal the presence of radioactivity deposits other than those
also shown through soil sampling."
The PHS survey was conducted on June 29, 1970. In addition
to the environmental radiological aspects of this survey, other
objectives were to answer questions which had been raised regard-
ing selenium toxicity to livestock in adjacent pastures, and
regarding possible contamination of salvage materials which were
being removed from the site.
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External gamma exposure rate measurements were taken on and
around the pile and mill using an Eberline E-500B geiger survey
meter. Elevated gamma levels (greater than a background rate of
0.03-0.04 mR/hr) were not found further than about 60 feet from
the pile.
Lumber which had been removed from the site was located and
monitored for alpha contamination with an Eberline PAC-1SA.
Isolated spots of surface contamination were found, with the
maximum reading being 6800 dpm/100 cm2 (instrument background was
500 dpm/100 cm2). The report concluded that the surface con-
tamination levels observed represented no health problems.
Other conclusions of the report were that the mill and
tailings areas should be fenced to control access, and that the
pile should be stabilized to prevent wind erosion of the tailings
material.
STUDY PARTICIPANTS
The following individuals participated in the 1975 survey of
the Riverton mill site:
Jon Yeagley, U.S. EPA, Region VIII
Richard Douglas, U.S. EPA, ORP-LVF
William Moore, U.S. EPA, ORP-LVF
Michael O'Connell, U.S. EPA, ORP-LVF
Edd Johnson, Wyoming Department of Health § Social Services
J. B. Baird, U.S. NRC, Region IV
Herman Paas, U.S. NRC, Region IV
John Myers, U.S. PHS, Indian Health Service
Tom Fife, Solution Engineering, Inc.
Joe Stano, Solution Engineering, Inc.
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SURVEY METHODS
GAMMA SURVEY
The primary objective of this study was to determine the
extent of windblown tailings around the site. The technique used
to meet this objective was that developed for use in the gamma
radiation surveys which were conducted at other inactive uranium
mill sites as part of the joint ERDA/EPA evaluation of these
sites. Basically, the survey technique consists of taking
ground-level gamma measurements with a modified Baird-Atomic NE-
148A scintillometer.
The theory and methods used in this survey technique are
described by Douglas and Hans (1975), and summarized by the
following excerpt from that report:
"The NE-148A contains a one inch by one
and one-half inch Nal crystal detector
calibrated with radium-226. The output is in
microroentgens per hour (yR/h), with a range
of 0 to 3,000 yR/h. The time constant of the
scintillometers was increased to ten seconds
in order to lessen the rapid meter fluctua
tion, thereby reducing the need for subjec-
tive averaging of readings by the operator.
In addition, the instruments used in this
study have a sliding lead shield attached
which can be interposed between the detector
and the ground. At a given location, two
readings were taken with the scintillometer
placed on the ground. One reading was taken
5
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with the shield between the detector and the
ground ("closed" reading} and one with the
shield removed ("open" reading). The effect
of the shield on a "closed" reading is to
significantly shield the detector from any
gamma photons originating from the ground
beneath the sci'ntillometer, while having
essentially no effect on gamma shine from a
distant source, such as the pile. Therefore,
if tailings are present at the location of
the reading, there will be a significant
difference between the "open" and "closed"
readings. This differential gamma reading,
referred to as "delta" (A), indicates the
presence or absence of tailings at that
particular location. It also provides an
empirical estimate of the quantity of surface
tailings present. While the units of the
delta value are yR/h, it should be kept in
mind that the delta value is not numerically
equal to exposure rate."
Two-hundred-foot intervals were measured and flagged along
the fence around the pile. At each measured point, perpendicula
lines were extended out from the fence, and delta readings were
taken at paced 200-foot intervals along these lines until back-
ground delta readings were obtained. This resulted in a
200-x 200-foot grid of readings around the pile. Background
readings taken in the Riverton area established a background
delta value of A4.
Several miscellaneous measurements of external radiation
levels were made:
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1. Three traverses were made on the pile to measure the
approximate delta values and external gamma exposure
rates on the covered pile. Spot measurements were made
where visible patches of bare tailings were observed.
2. In the plowed field west of the pile, delta measure-
ments were made at successive depth increments of five
centimeters to determine the extent to which windblown
tailings had been mixed into the soil profile.
3. Some special measurements were made to correlate gamma
exposure rate, delta measurements, and radium concen-
tration in the soil as a function of distance from the
pile. These parameters were measured at 200-foot
intervals along a line extending 1200 feet out from the
fence along the north side of the pile. The starting
point for this line was 1000 feet west of the northeast
corner of the pile fence. The gamma exposure rate was
measured with a Reuter-Stokes pressurized ionization
chamber (PIC Model RSS-111) with a digital readout.
Readings were taken at the ground surface and at a
height of one meter. The gamma exposure rate at the
ground surface and at one-meter height, as well as the
delta measurement, was also measured with the scintil
lometer. Soil samples were collected at each measure-
ment point using a metal scoop which collects a sample
100 centimeters square and five centimeters deep.
WATER SAMPLING
At the request of the Indian Health Service, water samples
were collected from 12 private wells and at the St. Stephens
School in the vicinity of the site. These wells averaged 250
feet in depth, with a maximum depth of 300 feet (personal commu-
nication, John T. Myers, IHS). A background well water sample
was also collected in Riverton, and a surface water and a shallow
7
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well water sample were collected on the site. All well samples
were collected by filling a one-gallon container from the tap.
The water samples were analyzed for dissolved radium-226 using
the methods described by Johns (1975) .
RADON PROGENY (WORKING LEVEL) SAMPLING
Air samples were collected at three locations to measure the
indoor working level, using the Radon Progeny Integrating Sampling
Unit (RPISU). This sampler collects radon progeny on a filter
which is in close proximity to a thermoluminescent dosimeter
(TLD) chip. A portion of the alpha particle energy released
during decay of the radon progeny is deposited in the TLD. The
TLD then is read out in the laboratory, and the reading related,
by a calibration factor, to the working level in the air sampled.
A background sample was collected in Riverton, and other
samples were collected at two houses (one unoccupied at the time)
near the mill site. The houses were in the predominant downwind
direction from the site, in an area which appeared to have the
highest level of contamination by windblown tailings. An attempt
was made to collect a 24-hour sample at each location in order to
average the diurnal variations, but such a sample was obtained at
only one of the locations.
MISCELLANEOUS SOIL AND TAILINGS SAMPLING
In addition to the soil samples discussed under the Gamma
Survey (above), three additional soil samples were collected in
the plowed field east of the pile. A grab sample of tailings
material was collected from a bare spot on the pile. All these
samples were analyzed for radium-226 using the methods described
by Johns (1975).
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RESULTS AND DISCUSSION
GAMMA SURVEY
The results of the gamma survey are shown in Figure 1. The
delta value is shown at each measurement point. Iso-exposure
rate lines were constructed on the basis of these delta values by
the method of Douglas and Hans (1975) . In keeping with current
Environmental Protection Agency guidance (EPA, 1974) iso-lines
corresponding to residual gamma exposure rates of 40 yR/hr,
10 yR/hr, and background were located. The significance of these
lines is as follows (Douglas and Hans, 1975):
"If scattered tailings and ore are removed
from inside a given line (toward the pile), and if
the pile is removed or covered to provide essentially
complete gamma shielding, then the remaining tailings
outside the line (away from the pile) would produce a
net gamma exposure rate, three feet above ground,
approximately equal to that of the line designation."
As can be seen in Figure 1, the most extensive area of
contamination lies in a sector southeast of the pile. The maximum
distance from the pile fence to the background line was about
2500 feet east of the southeast corner of the pile. The land in
this sector is mostly undisturbed range land. The land immedi
ately east and northeast of the pile is cultivated. This cultiva
tion quite likely has reduced the level of surface contamination
(as measured by the delta method) by mixing windblown tailings
material into the soil. Therefore, more tailings have probably
been deposited on the east and northeast sectors than the results
of this survey indicate.
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The results of the "depth test" conducted in the plowed
field immediately east of the pile lend some credence to the
above hypothesis. This test was made 50 feet east of a point
along the fence which was 400 feet north of the southeast corner
of the pile fence. A surface delta reading was taken, and
successive five-centimeter depth increments of soil were removed,
with a delta reading taken at each five-centimeter interval. The
results of this test are shown in Table 1.
TABLE 1. DEPTH TEST IN PLOWED FIELD EAST OF TAILINGS PILE
Depth Increment
(Centimeters)
Surface
5
10
15
20
25
30
Delta Reading
(yR/hr)
9
10
9
7
5
5
4
Since the background delta reading was A4, the results of
this test indicate that tailings have been mixed into the soil
profile, at this particular location, to a depth of 20 to 30
centimeters. It should also be noted that slight increases in
the delta readings occur along the survey lines, extending east
from the pile, as they cross Highway 789 and the north-south road
about 1500 feet east of the pile. This is undoubtedly due to
increased surface contamination, relative to the plowed field,
since these areas have not been cultivated.
In view of these results, the location of the 10 yR/hr line
in the field east of the pile, and of both the 10 yR/hr and
background lines in the field northeast of pile, should be
considered only approximate, since they only represent current
levels of surface contamination.
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GAMMA RADIATION SURVEY
INACTIVE URANIUM MILL SITE
RIVERTON.WYOMING
UNCORRECTED DIFFERENTIAL GAMMA READING - pR/h
SURVEY DATE OCTOBER 1975
Figure 1. Results of gamma radiation survey
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The 40 yR/hr line encompasses an area of about 30 acres,
exclusive of the tailings pile. This includes a strip averaging
about 200 feet in width along most of the north side of the pile,
and former ore storage area northeast of the mill yard. The mill
yard itself was arbitrarily included within the 40 yR/hr line, as
indicated by the dashed line. The delta readings in the mill
yard were too erratic to allow construction of the 40 yR/hr line,
due to the spotty nature of contamination in the yard. However,
it is apparent that the entire mill yard is sufficiently contami
nated to warrant decontamination.
The 10 yR/hr line encompasses about 99 acres, exclusive of
the tailings pile. As discussed above, the mill yard was included
within this line. The dashed portion of this line along the west
side of the mill yard and along the county road north of the mill
indicate that the delta readings were not sufficiently uniform in
these areas to allow the theoretical construction of the line.
Therefore^ the location of this portion of the line is somewhat
subjective, and is based on adjacent readings and practical
considerations for decontamination. Two houses south of the pile
are within the 10 yR/hr line.
The background line encompasses about 460 acres, exclusive
of the tailings pile. Except for the two cultivated fields
discussed above, this is largely range or pasture land. About
six houses are within the background line.
The results of the special measurements to correlate gamma
exposure rate, delta readings, and radium-226 concentration in
the soil are shown in Table 2. Figure 2 shows the one-meter
gamma exposure rate (PIC), delta readings, and radium-226 con-
centrations as a function of distance from the pile. In a
relatively undisturbed area, such as the one chosen for this
test, these parameters are shown to correlate very well. An
unexplained source of activity (probably ore spillage) was
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TABLE 2. RADIOLOGICAL PARAMETERS AS A FUNCTION OF DISTANCE FROM THE TAILINGS PILE
Gamma Exposure Rate (yR/hr) Radium-226 Concentration
Distance from
Fence (Feet) l
6
100
200
400
600
800
1000
1200
Delta Reading
(uR/hr)
30
13*
20
12*
12
7*
9
5*
6
5*
6
5*
8
9*
5**
8
5*
S u r
PIC2
128
75
51
34
26
24
21
21
face
Scint?
125
78
54
38
28
28
28
27
One -Meter
PIC2
109
68
50
33
26
23
22
21
Height
Scint?
110
72
55
36
29
30
28
26
(pCi/gram ± two-sigma
counting error)
130 ±
87 ±
32 ±
28 ±
12 ±
8.2 ±
17 ±
8.3 ±
8.6 ±
2.1
1.7
1.0
0.97
0.62
0.53
0.75 (0-5 cm)
0.53 (5-10 cm)
0.54
1 The toe of the stabilized pile is about 80 feet inside the fence. Therefore, 80 feet should be added
to these distances to obtain the distance from the edge of the pile.
2 Pressurized lonization Chamber
3 NE-148A Scintillometer
* Delta reading in 5-cm deep trench
** Delta reading in 10-cm deep trench
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200-
100
90-
80-
70-
60-
50-
40-
30- L
20 —
10 —
9-
8 —
7 —
6-
5-
Gamma Exposure Rate at one-meter height
(measured with PIC),^u,R/hr
Radium-226 concentration, pCi/gm
Delta reading
I I I I \ \
200 400 600 800 1000 1200
Distance From Fence, feet (add 80 feet for distance from edge of pile)
1400
Figure 2. Radiological parameters as a function of distance
from, the tailings pile
detected by both the delta and the radium-in-soil measurements
about 1000 feet from the pile. This contaminated area was not
reflected, however, by the gamma exposure rate measurements.
This may be because the small increase was less than the sensi
tivity of the PIC, or because the one-meter gamma measurements
"average" over a larger area than do the surface measurements.
Whatever the reason, the delta method is shown to be a sensitive
indicator of soil contamination.
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WATER SAMPLING
The water sampling locations and the dissolved radium-226
concentrations are shown in Figure 3 and Table 3, respectively.
Sampling locations #1 through #13 were residential wells in the
vicinity of the pile, while #14 was in Riverton and is presumed
to be a background sample free of any possible influence from the
mill site. The samples were collected primarily to determine any
potential radiation exposure to people drinking water from these
wells. Consequently, no specific hydrologic information regard-
ing the site was obtained. However, some inferences may be drawn
regarding the pile as a possible source of ground-water contamin-
ation.
A cumulative log probability plot of the 14 data points
(including the background) produced a straight line. The
Kolmogorov-Smirnov goodness-of-fit test indicated that the
observed distribution cannot be rejected as not being log-normal
at the 99 percent confidence level, thus inferring that all the
samples are probably from the same population.
From a hydrologic viewpoint, an eastward ground-water flow
direction is assumed likely, regardless of whether the Wind River
or the Little Wind River are line sources or line sinks relative
to the water table. For this reason, samples #1 through #9 are
located in areas likely to be hydraulically downgradient from the
tailings pile, while samples #10 through #13 are located
upgradient from the pile and are least likely to be affected by
it. A t-test indicated no significant difference, at the 95
percent confidence level, between these two groups of samples.
Consequently, there is no reason to believe that ground-water
contamination, as indicated by radium-226 concentrations, is
present in close proximity to the pile or in downgradient areas
to the east and northeast.
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LEGEND
WATER SAMPLING LOCATION
INDOOR RADON PROGENY (A)
SAMPLING LOCATION
N
RIVERTON
0 1000 2000
iS^
SCALE
4000
BE
r-A-r
. MILL BUILDINGS
Figure 3. Location of water and radon progeny (working level) samples
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Another basis for evaluating the water sample results is by
comparing them to current standards. The Environmental Protection
Agency Drinking Water Standards (EPA, 1976) allow a maximum
combined level of radium-226 and radium-228 of 5 pCi/1. Although
radium-228 was not measured in these samples, it has been
reported (EPA, 1976) that it is almost always lower than the
radium-226 concentration in the same water sample. Since the
maximum radium-226 concentration in these samples is less than 20
percent of the 5 pCi/1 standard, it is unlikely that total radium
concentrations in water approaching the EPA standard are present
in the vicinity of the mill site.
RADON PROGENY (WORKING LEVEL) SAMPLING
Indoor working level (WL) sampling locations and results are
shown in Figure 3 and Table 4, respectively.
The guidelines set forth by the Surgeon General of the
U.S. Public Health Service (PHS, 1970a) serve as a basis for
evaluating these results. This guidance, which was established
for continuous occupancy situations, states that no remedial
action is indicated at levels below 0.01 WL, that remedial action
may be suggested between 0.01 and 0.05 WL, and that remedial
action is indicated above 0.05 WL.
The standard sampling procedure for the RPISU calls for at
least a 24-hour sampling period in order to average the diurnal
variations in radon and progeny concentrations. However, due to
operational problems with the samplers, only one such sample was
obtained. Furthermore, a comprehensive sampling program to
properly evaluate indoor working levels requires several samples
collected over a period of at least one year in order to average
the annual variations. Consequently, these one-time, short-
duration samples were, at best, a screening test to indicate
potential problem areas.
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TABLE 3. DISSOLVED RADIUM-226 CONCENTRATIONS IN WATER
Radium-226 Concentration
Location* (pCi/1 ± two-sigma counting error)
1 0.26 ± 0.083
2 0.47 ± 0.10
3 0.078 ± 0.047
4 0.96 ± 0.15
5 0.44 ± 0.10
6 0.47 ± 0.11
7 0.15 ± 0.093
8 0.43 ± 0.15
9 0.27 ± 0.11
10 0.57 ± 0.17
11 0.16 ± 0.069
12 0.33 ± 0.093
13 0.19 ± 0.068
14 (Background) 0.22 ± 0.079
Ditch at west end of pile 0.32 ± 0.088
Reinjection well at SE
corner of pile 0.41 ± 0.098
Numbered locations correspond to numbers shown in Figure 3,
TABLE 4. INDOOR RADON PROGENY(WORKING LEVEL) RESULTS
Sampling Time
Location* (Hours) Working Level
A-l Background in Riverton 14.8 0.0009
A-2 Residence (unoccupied
at time of sampling) 24.7 0.0029
A-3 Residence 0.9 0.0055
* Numbers correspond to locations shown in Figure 3.
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With these qualifications in mind, it does not appear that
significantly elevated indoor working levels exist in the vicinity
of the mill site.
MISCELLANEOUS SOIL AND TAILINGS SAMPLING
The analytical results for these samples are shown in Table 5.
TABLE 5. RADIUM-226 CONCENTRATIONS IN TAILINGS
AND MISCELLANEOUS SOIL SAMPLES
Radium-226 Concentration
Sample Type and Location (pCi/gram ± two-sigma counting error)
Exposed tailings on pile 660 + 4.7
Soil from field east of pile:
At fence 77 ±1.6
200 feet east of fence 3.3 ± 0.34
400 feet east of fence 3.2 + 0.33
Unfortunately, a background soil sample was not collected
during this survey to serve as a basis for comparison. However,
the soil concentrations of about 3 pCi/gram appear to be elevated
relative to "normal" radium levels in soil. This is to be
expected in view of the elevated delta readings obtained in this
area. The radium concentration measured in the single tailings
sample agrees very well with the values estimated by the USAEC
for the Riverton pile (PHS, 1970).
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SUMMARY AND CONCLUSIONS
A radiological survey was made of the inactive uranium mill
site near Riverton, Wyoming during the period September 30-
October 2, 1975. The primary purpose of the survey was to
delineate areas which are contaminated by windblown material from
the tailings pile. Secondary purposes were to collect water
samples from local wells, and to collect indoor radon progeny
(working level) samples in structures near the site, in order to
identify any major radiation exposures which may be occurring
through these exposure pathways.
The contaminated areas were delineated by making a series of
differential gamma exposure rate measurements at the ground
surface. A total of about 460 acres, exclusive of the tailings
pile, was found to be contaminated above background levels. An
area of 30 acres would have to be decontaminated to reduce the
maximum residual exposure rate to 40 yR/hr, and 99 acres would
have to be decontaminated to reduce the maximum residual exposure
rate to 10 uR/hr.
On the basis of the limited water and working level sampling
conducted during this survey, none of the sample results exceeded
the guidance established by the EPA under the Safe Drinking Water
Act or the Surgeon General's guidelines for indoor radon progeny
levels.
21
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REFERENCES
AEG (1973), "Survey Report, Riverton, Wyoming", Unpublished
report, with transmittal letter from Mr. John W. Flora, Director,
Directorate of Regulatory Operations, Region IV, USAEC, to Mr. K.
L. Hudson, Susquehanna-Western, Inc.
Douglas, R. L. and J. M. Hans, Jr. (1975), "Gamma Radiation
Surveys at Inactive Uranium Mill Sites", Technical Note ORP/LV-
75-5, U.S. Environmental Protection Agency, August 1975
EPA (1974), "Radiological Criteria for Decontamination of Inactive
Uranium Mill Sites", USEPA, Office of Radiation Programs, Field
Operations Division, December 1974
EPA (1976), "Drinking Water Regulations, Radionuclides", Federal
Register, Vol. 41, No. 133, July 9, 1976
ERDA (1974), "Summary Report, Phase I Study of Inactive Uranium
Mill Sites and Tailings Piles", October, 1974
Johns, F. B. (1975), "Handbook of Radiochemical Analytical
Methods", EPA-680/4-75 - 001, U.S. Environmental Protection Agency,
February 1975
Johnson, Edd (1975), Letter dated September 11, 1975 to E. Morris
Howard, Director, Region IV Office of Inspection and Enforcement,
U.S. Nuclear Regulatory Commission
PHS (1970), "Susquehanna-Western Mill Property, Riverton, Wyoming,
On-Site Inspection, June 29, 1970", Unpublished report of the
Southwestern Radiological Health Laboratory, U.S. Public Health
Service
22
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PHS (1970a), "Recommendations of Action for Radiation Exposure
Levels in Dwellings Constructed on or with Uranium Mill Tailings,"
Hearings on the Use of Uranium Mill Tailings for Construction
Purposes, Joint Committee on Atomic Energy (1971), p. 51 54
23
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
. REPORT NO.
ORP/LV-77-2
2.
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
Radiological Survey at the Inactive Uranium Mill
Site Near Riverton, Wyoming
5. REPORT DATE
June 1977
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Richard L. Douglas
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Office of Radiation Programs Las Vegas Facility
U.S. Environmental Protection Agency
P.O. Box 15027
Las Vegas, NV 89114
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
Same as above
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
200/03
15. SUPPLEMENTARY NOTES
16. ABSTRACT
A radiological survey was made of the inactive uranium mill site near
Riverton, Wyoming during the period September 30-October 2, 1975. The primary
purpose of the survey was to delineate areas which are contaminated by windblown
material from the tailings pile. Secondary purposes were to collect water
samples from local wells, and to collect indoor radon progeny (working level)
samples in structures near the site, in order to identify any major radiation
exposures which may be occurring through these exposure pathways.
The contaminated areas were delineated by making a series of differential
gamma exposure rate measurements at the ground surface. A total of about 460
acres, exclusive of the tailings pile, was found to be contaminated above
background levels. An area of 30 acres would have to be decontaminated to
reduce the maximum residual exposure rate to 40 UR/hr, and 99 acres would have
to be decontaminated to reduce the maximum residual exposure rate to 10 UR/hr.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Radioactive Wastes
Radium
Environmental Surveys
Uranium milling
Inactive uranium mill
sites
Uranium mill tailings
piles
1807
0702
0510
3. DISTRIBUTION STATEMENT
Release to public
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
32
20. SECURITY CLASS (This page)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
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