ENVIRONMENTAL SURVEY OF URANIUM MILL
TAILINGS PILE, MEXICAN HAT, UTAH
by
Robert N. Spelling
Technical Services Program
Southwestern Radiological Health Laboratory
Department of Health, Education, and Welfare
Public Health Service
Consumer Protection and Environmental Health Service
SWRHL-68
October 1969
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SWRHL-68
ENVIRONMENTAL SURVEY OF URANIUM MILL
TAILINGS PILE, MEXICAN HAT, UTAH
by
Robert N. Snelling
Technical Services Program
Southwestern Radiological Health Laboratory
Department of Health, Education, and Welfare
Public Health Service
Consumer Protection and Environmental Health Service
October 1969
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ABSTRACT
At the request of the Navajo Tribal Council through the PHS
Division of Indian Health at Window Rock, Arizona, an environmental
radiological survey was conducted on the A-Z Minerals Corporation
uranium tailings pile, Mexican Hat, Utah, in May 1968. The purpose
of the survey was to identify any radiation hazards which might
exist and recommend methods for their control. The survey included
evaluation of external gamma radiation, airborne radioactivity, and
waterborne radioactivity. The results of the survey indicate that
the external radiation levels on the tailings area exceed recommended
exposure limits for individuals in the general population. Therefore,
the area should not be released for public use in its present state.
Action which would permit the release of the area would involve
covering the tailings with uncontaminated dirt to an extent that
would diminish the external radiation to an acceptable level and
to stabilize the covering against wind erosion.
Radiation levels in air and water do not exceed recommended
exposure limits. However, to minimize the possibility of increased
activity from weather conditions different from those existing
during the survey, it is recommended that the tailings be stabilized
against wind erosion. Otherwise, periodic monitoring will be
necessary in the future.
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ACKNOWLEDGEMENTS
Sincere appreciation is expressed to the A-Z Minerals
Corporation for the cooperation and assistance provided
during the survey. Without its cooperation, the study could
not have been adequately performed.
11
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TABLE OF CONTENTS
ABSTRACT i
ACKNOWLEDGEMENTS i i
TABLE OF CONTENTS i i i
LIST OF TABLES iv
LIST OF FIGURES v
PURPOSE I
LOCATION AND DESCRIPTION I
ENVIRONMENTAL SURVEY 3
A. Sampling Procedures 3
I. External Radiation Exposure 3
2. Air Samp I ing 3
3. Water Samp I ing 8
4. Tailings Material 8
B. Analytical Procedures 8
IV. RESULTS II
A. External Radiation II
B. Ai r Samp I ing 15
I. Long-lived Airborne Particulate Radioactivity 15
2. Radon Gas 15
3. Radon Daughter Products 22
C. Water Samp I ing 22
D. Tailings Sampling 22
V. DISCUSSION OF RESULTS 27
A. External Radiation Exposure 27
B. Ai r Samp I ing 28
I. Long-lived Airborne Particulates 28
2. Radon-222 and Daughter Products 30
C. Water Samp I ing 31
VI. SUMMARY AND RECOMMENDATIONS 31
REFERENCES ,4
DISTRIBUTION
iii
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LIST OF TABLES
Table I. External radiation measurements, Mexican Hat 12
Uranium Mi I I, May 1968.
Table II. Comparison of TLD and E500B data. 16
Table III. Gross alpha particulate radioactivity in air, 17
Mexican Hat Uranium Mi I I, May 1968.
Table IV. Long-lived airborne particulate radioactivity, 18
Mexican Hat Uranium Mill.
Table V. Atmospheric radon-222, Mexican Hat Uranium Mill, 19
May 1968.
Table VI. Particulate radon daughter products in air, 23
Mexican Hat Uranium Mill.
Table VII. Long-lived radioactivity in water,Mexican Hat 24
Urani urn Mill.
Table VIM. Tai I ings anal ys is, Mexi can Hat Uranium Mi I 1. 25
iv
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LIST OF FIGURES
Figure I. Mill site, Mexican Hat, Utah. 2
Figure 2. Mill property, A-Z Minerals Corp. Mexican Hat, 4
Utah.
Figure 3. Air sampling locations.Mexican Hat Uranium Mill. 5
Figure 4. Radon sampling locations,Mexican Hat Uranium Mill. 7
Figure 5. Water sampling locations,Mexican Hat Uranium Mill. 9
Figure 6. Tailings material sampling locations,Mexican Hat 10
Uranium Mill.
Figure 7. External radiation measurements.Mexican Hat 13
Urani urn MiI I tai |jngs pi Ies.
Figure 8. External radiation measurements.Mexican Hat 14
Uraniurn Mill.
*
Figure 9. Long-lived alpha activity in air, Mexican Hat 20
Uranium Mill.
Figure 10. Atmospheric radon-222, Mexican Hat Uranium Mill. 21
Figure II. Natural uranium in water, Mexican Hat Uranium Mill. 26
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ENVIRONMENTAL SURVEY OF URANIUM MILL
TAILINGS PILE, MEXICAN HAT, UTAH
I. PURPOSE
On December 21, 1967, the Director, Division of Indian Health,
requested the National Center for Radiological Health to conduct a
study of the A-Z Minerals Corporation's tailings pile located at
Mexican Hat, Utah. It was requested that the study identify any
radiation hazards which might exist and recommend methods for their
control.
- In response to this request, the tailings area was surveyed in
May 1968. The results and conclusions of the survey are presented
herein.
II. LOCATION AND DESCRIPTION
A. Location:
The mill was originally operated by the Texas-Zinc Minerals
Corporation and transferred to A-Z Minerals Corporation in 1963.
Uranium production was discontinued in February 1965.
The mill property is located approximately one mile southwest of
the community of Mexican Hat, Utah (Figure 1). The site is situated
on the Navajo Indian Reservation; the property being leased to the
company by the Navajo Tribal Council.
The San Juan River flows from east to west approximately one mile
north of the mill property. Gypsum Creek (actually a dry wash) is
located approximately one-half mile east of the tailings pile. The
surrounding land is unpopulated and at present is not used for either
farming or grazing.
B. Description:
For purposes of description, the mill property is divided into
three main areas: the tailings area, the mill area, and the housing
I
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Scale : 1" = 1OOO ft.
Figure 1. Mill site, Mexican Hat, Utah.
2
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area (Figure 2).
1. Tailings Area. The tailings area covers approximately 35 acres
and contains an estimated 2.2 x 106 tons of tailings material.*
The radium content estimated from the average uranium assay of
mill feed material (assuming radium in equilibrium with uranium)
is approximately 1000 pCi/g, or 6500 total curies.*
2. Mill Area. The mill area includes the mill buildings and former
stock pile areas. It is located adjacent to and west of the
tailings area.
3. Housing Area. The housing area is located approximately 0.5 miles
southwest of the tailings area and consists of approximately 60
dwellings, a school, and various community buildings.
III. ENVIRONMENTAL SURVEY
A. Sampling procedures:
1. External Radiation Exposure. External radiation measurements were
obtained using portable geiger survey meters.** Gamma (closed
window) readings were obtained at the surface and at the three-
foot level. A grid was established over the area of interest and
readings obtained at 240-foot intervals. A total of 212 pairs of
readings were recorded.
In addition to the portable instrument readings, thermoluminescent
dosimeters (TLD's) were placed in triplicate at the three-foot
level at each of the air sampling stations (see Figure 3). The
TLD's respond only to gamma radiation.
2. Air Sampling.
a. Long-lived Airborne Particulate Radioactivity:
Airborne particulate radioactivity was sampled by drawing air through
* Division of Raw Materials, USAEC, 1967.
** Model E-500B, Eberline Instrument Corp., Santa Fe, New Mexico
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HOUSING
r= AREA
Scale : 1" = 1OOO ft.
Figure 2. Mill property, A-Z Minerals Corp. , Mexican Hat, Utah.
4
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-AREA TAILINGS
Scale : 1" = 1OOO ft.
Figure 3. Air sampling locations Mexican Hat Uranium Mill.
5
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a 0.8u pore size filter.* A high volume air sampler was used
at a flow rate of about five cubic feet per minute. Nine
sampling stations were established on and about the tailings
area (Figure 3). Continuous 24-hour samples were obtained at
each station on each of eleven consecutive days. Each indi-
vidual filter was analyzed for gross alpha activity. In addi-
tion, all filters from each station were composited for analysis
of natural uranium, radium-226 and thorium-230.
Radon Gas:
Eight locations were selected for the collection of radon gas
samples (Figure 4). The sampling technique consisted of
pulling filtered air through a small low-volume pump (10 ml/min)
into a 30-liter Mylar bag. r A continuous 24-hour sample was
collected at each location. The collected samples were picked
up by PHS aircraft and flown to Las Vegas for immediate analysis
for radon-222.
Short-lived Particulate Radon Progeny:
The short-lived particulate radon daughter products were sampled
by pulling air through a glass fiber filter using a high volume
air sampler. Each sample was collected for 15 minutes at a flow
rate of about 10 cfm. Samples were collected at the radon
sampling locations (Figure 4). The filters were alpha counted
immediately in the field utilizing a specially designed alpha
scintillation counter. Activity was calculated using the
Tsivoglou technique.2
*Gelman Acropore Filter, Gelraan Instrument Company,
Ann Arbor, Michigan.
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M|LL TAILINGS
AREA
Scale : 1" = 1OOO ft.
Figure 4. Radon sampling locations Mexican Hat Uranium Mill.
7
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d. Meteorology:
Wind direction and speed were estimated by visual observation. The
predominant wind direction at the mill site for the 11-day sampling
period was from the southwest. According to A-Z Minerals Corp.
personnel, this is the predominant wind direction throughout the
year. During the first seven days of sampling, the wind was light
(0-5 mph). During the last four days, however, winds estimated at
10-20 mph were encountered during the daylight hours. In general,
lapse conditions were encountered during daylight hours with light
inversions at night.
3. Water Sampling.
Two springs were located in the vicinity of the tailings area at
which ground water samples were taken (Figure 5). The first was
located about 1000 feet northeast of the tailings area in the
wash running from the tailings area (Sta. 1). The wash was dry
between the spring and Gypsum Creek. The second spring was just
south of the junction of Gypsum Creek and the wash from the tailings
area (Stations 2 and 3). Gypsum Creek was dry upstream from the
spring. In addition to the ground water samples, the drainage
from the acid blowdown operation at the mill was sampled. One-
gallon grab samples were obtained at each location, some stations
being sampled on several occasions. The samples were analyzed for
radium-226 and natural uranium activity.
4. Tailings Material.
Samples of tailings material were collected at the locations indi-
cated in Figure 6. Approximately 400cc of surface material was
taken from each location. The samples were analyzed for thorium-230,
radium-226 and natural uranium.
B. Analytical Procedures:
All laboratory analyses were performed at the Southwestern Radio-
logical Health Laboratory.
1. Gross alpha and gross beta determinations were performed, after sample
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MEXICAN HAT
MILL
I PROPERTY
f
N'
R/VER
Scale : 1" = 1OOO ft.
Figure 5. Water sampling locations Mexican Hat Uranium Mill.
9
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TO
e
H
ft)
TO
3
ft)
rh
n>
0
TO
I—1
O
n
ft)
c-h
M«
^ O
o ts
CO
cl
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preparation, by counting directly in an end window,gas flow, pro-
portional counter,
2. Radon analysis was performed by cryogenic separation and subsequent
alpha scintillation counting.
3. Radium-226 was determined after sample preparation by the radon
emanation technique.
4. Uranium analysis was accomplished by fluorometric technique.
5. Thorium-230 analysis was performed by means of solvent extraction
and subsequent alpha counting.
IV. RESULTS
A. External Radiation:
Table I summarizes the results of the portable instrument survey on
each of the unique areas. Figures 7 and 8 indicate the location and
magnitude of the individual measurements at the surface level and at
three feet.
1. Natural Background. The natural background radiation was found to
average 0.03 mR/hr both at the surface and the three-foot level.
2. Tailings Area. The radiation exposure at the three-foot level on
the tailings area ranged from a minimum of .02 mR/hr on the extremi-
ties of the pile to a maximum of 3 mR/hr on the pile. The average
was 0.5 mR/hr. No significant difference was noted between the
surface and three-foot level.
3. Mill Area. The average exposure at the three-foot level within the
mill area was 0.1 mR/hr with a range of 0.02 mR/hr to 0.5 mR/hr.
Again, there was no significant difference between readings at the
surface and at three feet.
4. Housing Area. The average exposure at the three-foot level in the
housing area was found to average 0.03 mR/hr. This exposure repre-
sents background radiation.
5. Thermo!uminescent Dosimeters. A comparison of the results obtained
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TABLE I
External Radiation Measurements
Mexican Hat Uranium Mill
May 1968
Area
Background
Housing Area
Mill Area
Tailings Area
Number of
Measurements
10
74
31
97
mR/hr @ Surface
Ave.
0.03
0.04
0.17
0.5
Range
0.02-0.06
0.01-0.2
0.02-0.5
.01-3.0
mR/hr @ 3 Feet
Ave.
0.03
0.03
0.15
0.5
Range
0.02-0.06
0.01-0.1
0.02-0.5
.02-3.0
12
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XA/AS!l
All values in mR/hr. /
Upper value = Gamma exposure (cD 3 feet
Lower value = Gamma exposure (5) surface
Values in parentheses = Thermoluminescent
dosimeter data. /
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-.0.2nMII-L 07
AREA 0.8
(.05)
.05
.04 0.1
•Q2
.02 -04
TRAILER
04 CAMP
04
.0.4
.03
COMMUNITY
HALL
i
(.01)
•Q4 ' j06
0_6 .OJ
04 .04
.04 .02
.04 -01
All values in mR/hr.
Upper value = Gamma exposure @ 3 feet
Lower value = Gamma exposure @ surface
Values in parentheses = Thermoluminescent
dosimeter data.
Figure 8. External radiation measurements Mexican Hat Uranium Mill.
14
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from the TLD's and the portable instrument measurements are shown
in Table II. The results are in good agreement.
B. Air Sampling:
1. Long-lived Airborne Particulate Radioactivity.
The gross alpha radioactivity found on individual filters is shown
in Table III. The background station (Sta. 1) averaged less than
1 x 10"5 pd'/l for eleven days of sampling. Stations 2, 7, 8 and 9
also averaged less than 1 x 10"^ pCi/1, indicating background levels
of activity. Stations 3 and 4 averaged slightly above background
(Sta. 3 = 2.2 x 10~5 pCi/1; Sta. 4 = 1.5 x 10"5 pCi/1). Stations 5
and 6 were significantly above background levels. Station 5, located
on the northeast edge of the tailings pile, averaged 10 x 10"^ pCi/1
with a range of 4.6 x 10~5 pCi/1 to 27 x 10"5 pCi/1 for seven days
of sampling. Station 6, located approximately 500 feet northeast
from the tailings, averaged 19 x 10"^ pCi/1 with a range of from less
than 1 x 10~5 pCi/1 to 51 x 10 pCi/1 for eleven days of sampling.
The average station results are shown in Figure 9. It is apparent
that the activity concentrations are higher than background in the
vicinity of the tailings pile and that the values downwind from the
tailings are higher than those upwind.
Table IV shows the average gross alpha activity along with radium-226,
thorium-230, and natural uranium activity for each station. It should
be noted that stations 3-6 (those indicating positive gross alpha
results) display radium concentrations averaging about a factor of
ten higher than the other stations. These same stations show signi-
ficant concentrations of thorium-230, whereas all other stations do not.
Although the natural uranium concentrations average slightly higher
for stations 3-6, the increase does not appear to be significant with
the exception of Station 3.
2. Radon Gas. Table V summarizes the radon-222 activity concentrations
found at various sampling times and locations. Figure 10 represents
the average radon concentrations at each sampling location.
\5
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TABLE II
Comparison of TIP and E500B Data
Station
1
2
3
4
5
6
7
8
9
BG 1
BG 2
mR/hr @ 3 Feet
TLD1
.01
.03
.05
.55
.42
.04
.02
.01
.02
.01
.01
E500B2
.06
.05
.05
.50
.40
.06
.03
.02
.03
.02
.03
1) eleven day exposure period
2) single survey meter reading
16
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TABLE III
Gross Alpha Particulate Radioactivity in Air
Mexican Hat Uranium Mill
May 1968
Sta
f
1
2
3
4
5
6
7'
8
9
Gross Alpha Activity 10"5 pCi/L
May
27 28 29 30 31 ]
1.2
1.9
2.8
—
27
LT 1
LT 1
LT 1
LT 1
LT 1
LT 1
1.1
LT 1
1.5
LT 1
LT 1
LT 1
LT 1
LT 1
1.5
0.9
8.4
LT 1
LT 1
LT 1
LT 1
LT 1
1.9
4.1
7.8
24
2.4
LT 1
LT 1
LT 1
LT 1
1.4
1.2
10
3. "6
LT 1
LT 1
LT 1
June Ave.
L 2 3 4 5 6 7
LT 1
LT 1
2.2
LT 1
4.6
2.4
LT 1
LT 1
LT 1
LT 1
1.0
1.5
4.8
LT 1
LT 1
LT 1
2.7
5.7
LT 1
27
38
LT 1
LT 1
1.0
LT 1
4.0
1.0
51
LT 1
1.2
LT 1
LT 1
4.0
2.0
5.1
25
LT 1
1.1
LT 1
5.0
1.8
6.1
6.6
37
LT 1
1.2
LT 1
LT 1
2.2
1.5
10.0
19.0
LT 1
LT 1
LT 1
LT 1 = Less Than 1 x 10"5 pCi/L (assumed equal to zero for averaging)
= Sampler failure
17
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TABLE IV
Long-lived Airborne Particulate Radioactivity
Mexican Hat Uranium Mill
Sta.
#
1
2
3
4
5
6
7
8
9
Days
Sampled
11
11
11
10
7
11
5
11
11
Gross
Alpha
10"5 pCi/1
LT 1
LT 1
2.2
1.5
10.0
19.0
LT 1
LT 1
LT 1
22*Ra
10"5 pCi/1
0.02
0.02
0.2
0.1
0.5
0.7
0.07
0.02
0.03
230Th
10" 5 pCi/1
ND
ND
0.7
0.3
0.7
1.4
ND
ND
ND
U Nat
10"5 jig/1
0.02
0.1
1.0
0.2
0.3
0.4
0.06
0.1
0.1
LT 1 = less than 1 x 10"5 pCi/1
ND = not detectable on composited sample
Minimum detectable activity for 226Ra = 0.1 pCi/sample
Minimum detectable activity for 230Th = 5.0 pCi/sample
Minimum detectable activity for natural U = 0.1 pg/sample
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TABLE V
Atmospheric Radon-222
Mexican Hat Uranium Mill
May 1968
Station
1
1
2
3
3
4
4
5
5A
5B
6
Midpoint of
Sampl i ng
Date
5/27
5/28
5/29
6/6
5/30
6/4
5/31
6/3
6/2
6/1
Hour
2030
2300
2100
0030
2330
2400
2100
2300
2300
1930
Radon-222
pCi/1
0.3
0.4
1.6
0.6
5.7
0.7
8.4
14.0
13.0
7.5
19
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LT 1 LT 1
1 mile from tailings
Scale : 1" = 1OOO ft.
All values in 1CT5pCi/l
LT 1: less than 1XlO-5pCi/|
Figure 9. Long-lived alpha activity in air Mexican Hat Uranium Mill.
20
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Scale : 1" = 1OOO ft.
V
Figure 10. Atmospheric radon-222 Mexican Hat Uranium Mill.
21
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Station 1, a background station, showed a radon concentration of
0.3 pCi/1. Station 2, 0.4 pCi/1, can also be considered background
level. Those stations on and about the tailings area showed levels
of radon significantly above background. Individual samples ranged
from a minimum of 0.6 pCi/1 at station 3 to a maximum of 14 pCi/1 at
Station 5A.
3. Radon Daughter Products. Table VI summarizes the results of the radon
progeny evaluation. It should be noted that the levels of activity are
several orders of magnitude lower than the radon concentrations given
in Table V. It must be assumed, therefore, that a very low state of
equilibrium existed between the radon and its progeny during the sur-
vey period.
C. Water Sampling:
Table VII shows the average radium-226 and natural uranium results
for each sampling location.
1. Background. Because there were no suitable ground water sources in
the immediate area, ground water samples from the Monument Valley
area (approximately 22 miles distant) are used as background indi-
cators.
2. Ground Water. The uranium levels are significantly above background
averaging between 1090 ug/1 and 1690 yg/1.
3. Acid Slowdown Water. The acid blowdown water showed a natural
uranium concentration of 15 pg/1 which is only slightly above back-
ground.
Figure 11 shows the average natural uranium concentration for each
location.
D. Tailings Sampling:
Table VIII shows the results of the thorium-230, radium-226, and
natural uranium analysis on tailings material. The radium content averaged
370 pCi/g. This average is somewhat below that predicted from the average
assay of mill feed material (1000 pCi/g). Thorium-230 averaged 1900 pCi/g
with individual values ranging from a minimum 220 pCi/g to a maximum of
22
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TABLE VI
Participate Radon Daughter Products in Air
Mexican Hat Uranium Mill
Sta.
#
SB
5B
5A
5
5
4
3
Collection
Date Time
6/2 2000
6/3 1100
6/3 1400
6/3 1900
6/4 1045
6/4 1430
6/5 1400
pCi/1
218
RaA, Po
0.12
0.21
0.01
0
0
0
0.22
21
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TABLE VII
Long-lived Radioactivity in Water
Mexican Hat Uranium Mill
Sta.
#
1
2
3
4
BG
Location
Wash (spring)
Gypsum Creek
Gypsum Crk (spring)
Acid Slowdown
Monument Valley
Number
of
Samples
3
2
1
2
5
226
Ra
pCi/1
1.5
0.2
0.2
0.5
0.5
U Natural*
ug/1
1690
1090
1160
15
2
1 pg/1 of U natural equals 0.7 pCi/1 of alpha activity
24
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TABLE VIII
Tailings Analysis
Mexican Hat Uranium Mill
AREA
Tailings # 1
Tailings # 2
AVE
#
1
2
3
4
5
6
7
8
9
10
X"
U
ug/g
63
350
69
27
40
70
73
470
120
180
150
230
Th
pCi/g
2400
3000
3700
3200
2800
220
220
2400
480
1200
1900
226
Ra
pCi/g
340
130
31
27
860
580
390
550
320
470
370
25
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Scale : 1" = 1OOO ft
Figure 11. Natural uranium in water Mexican Hat Uranium Mill.
Z6
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3700 pCi/g. Natural uranium averaged 150 yg/g (.015%) with individual
values ranging from a minimum of 27 yg/g to a maximum of 470 yg/g.
V. DISCUSSION OF RESULTS
A. External Radiation Exposure:
The code of Federal Regulations, Title 10, Part 20 indicates a
maximum allowable whole body dose to an individual in an unrestricted
area of 0.5 rem in any period of one calendar year. The regulations
further indicate a maximum allowable dose for continuous exposure to
individuals in an unrestricted area of 2 millirems in any one hour or
100 millirems in seven consecutive days.
The Radiation Protection Guide (RPG) adopted by the Federal Radiation
Council recommends that: "The yearly radiation exposure to the whole
body of individuals in the population (exclusive of natural background
and the deliberate exposure of patients by practitioners of the healing
arts) should not exceed 0.5 rem."3 The Council further recommends,
however, that "every reasonable effort should be made to keep exposures
as far below this level as possible."
To evaluate the potential long-range hazard associated with the
external radiation emitted from the tailings material, the average
yearly whole body exposure for an individual having 24 hour/day resi-
dence on the area is calculated and compared to the recommended RPG of
0.5 rem/yr. The net gamma radiation (i.e., minus background) at 3 feet
is used for this computation.
1. Tailings Area.
The average exposure at the three-foot level on the tailings area
was found to be 0.5 mR/hr (background was assumed negligible). The
whole body average yearly dose for an individual having 24 hr/day
residence on the tailings area, on the basis of this exposure rate
is approximately 4.4 rem/yr. This is nine times the recommended
27
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RPG of 0.5 rem/yr. These findings serve to preclude the release
of the tailings area for public use. Action which would permit
release of the area would involve covering the tailings with
uncontaminated dirt to an extent that would diminish the external
radiation to an acceptable level and to stabilize the covering
against wind erosion. Otherwise, the area should be fenced and
controlled as a radiation area.
Z. Mill Area.
The average radiation exposure at the three-foot level around the
mill area was 0.15 mR/hr. Subtracting an average background of
0.03 mR/hr yields an average net exposure of .12 mR/hr. The yearly
average dose to an individual having 24 hr/day residency in this
area, on the basis of the average value of 0.12 mR/hr, is 1 rem/yr.
This dose is twice the RPG of 0.5 rem/yr but represents the highly
unlikely condition of continuous occupancy. With reasonable
occupancy assumptions it would not be expected that a yearly average
dose in excess of 0.5 rem would occur.
3- Housing Area.
The radiation exposure at three feet in the housing area was found
to consist entirely of background radiation.
&. Air Sampling:
1. Long-lived Airborne Particulates.
In order to assess the potential long-range health hazard associated
with the inhalation of airborne radionuclides, the average activity
concentrations observed for each sampling station are compared to the
recommended radiation concentration guides (RCG's) as indicated in
The Code of Federal Regulations, Title 10, Part 20. Because the RCG's
are applicable to yearly average concentrations, this comparison
assumes that the meteorological conditions imposed during the sampling
period are representative of the yearly average conditions.
The Code of Federal Regulations, Title 10, Part 20, indicates a radia-
tion concentration guide (RCG) for unidentified natural radionuclides
in air of 8 x 10"5 pCi/1 (when protactinium-231 is assumed absent).
28
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If gross alpha activity is above this guide, identification of the
specific radionuclides contributing to the total alpha activity is
necessary in order to evaluate the potential long-range hazard
associated with the inhalation of the airborne particles.
The nuclides in the natural uranium decay chain most significant as
potential health hazards are the alpha emitters. These nuclides and
their appropriate RCG are shown below:
Thorium-230 (Sol.) 8 x 10'5 pCi/1
Radium-226 (Insol.) 200 x 10'5 pCi/1
Natural Uranium (Insol.) 200 x 10'5 pCi/1
Lead-210 (Sol.) 400 x 10"5 pCi/1
Polonium-210 (Insol.) 700 x 10'5 pCi/1
It is apparent from comparison of these values with Table IV that
none of those stations showing elevated gross alpha concentrations
exceeds the RCG's for individual radionuclides.
The following conclusions can be made:
(1) The tailings pile is resulting in elevated concentrations of
radioactivity in air in the downwind direction. At the present
time, however, these concentrations cannot be shown to exceed
the recommended guides for individual isotopes.
(2) It is impossible to predict whether the condition will worsen
in the future. At present, the pile is still quite moist and
displays a clay-like consistency. As the pile dries out, the
condition could very well worsen. On this basis two courses
of action are possible:
a. The tailings area may be stabilized against wind erosion.
This action would preclude further carriage of tailings
material into the surrounding environment in the future
and would eliminate the potential for any long-term
hazard to anyone inhabiting the area downwind from the
mill property.
b. If the tailings area is not stabilized, periodic monitoring
will be necessary to insure that the recommended concentra-
tion guides are not exceeded.
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Radon-222 and Daughter Products.
The Code of Federal Regulations, Title 10, Part 20, indicates a
radiation concentration guide for radon-222 in air in unrestricted
areas of 3 pCi/1 above natural background. The daughters of radon-
222 are assumed to be present to the extent that they exist in
unfiltered air (this is interpreted as meaning equilibrium con-
ditions). To evaluate the potential long-range hazard associated
with the inhalation of radon and its progeny, the atmospheric
radon concentrations are compared to this guide.
(1) Tailings Area
Average radon concentrations in the tailings area ranged
from a minimum of 3.2 pCi/1 at Station 4 to a maximum of
14 pCi/1 at Station 5A. These values are equal to or
greater than the RCG of 3 pCi/1. It was found, however,
that a very low percent equilibrium existed between radon
and radon daughters. Since approximately 95% of the dose
to the lungs due to inhalation of radon and its daughters
is due to the particulate daughters, the elevated radon
levels cannot be considered as representing violation of
the RCG. It should be pointed out however, that if enclosed
structures were to be built on the tailings material a sub-
stantial increase in both radon and daughters could be
expected within the structure, and the RCG may be exceeded.
Therefore, it is recommended that no enclosed structures
be built on the tailings material.
(2) Mill Area
Station 3 indicated an average radon concentration of 1.1 pCi/1.
Subtracting natural background gives a net average concentration
of 0.8 pCi/1. This is well below the appropriate RCG.
(3) Housing Area
The housing area (Stations 1, 2) showed essentially background
levels of radon-222.
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C. Water Sampling
1. Ground Water.
Ground water samples obtained in the vicinity of the tailings area
showed natural uranium concentrations in excess of 1000 pCi/1.
These values are significantly above background. The Code of
Federal Regulations, Title 10, Part 20, indicates a radiation
concentration guide for natural uranium of 2 x 10 pCi/1. It is
apparent that the concentrations observed are a factor of ten
below the recommended guide.
The RCG for soluble radium-226 is 3 pCi/1. None of the samples
collected exceeded this guide. It must be concluded, therefore,
that although ground water samples in the vicinity of the tailings
are significantly above background, they are still well below the
recommended concentration guides.
VI. SUMMARY AND RECOMMENDATIONS
A. External Radiation:
1. External gamma radiation on the tailings area averaged 0.5 mR/hr
at three feet above the surface. This calculates to a yearly dose
of 4.4 rem/yr for continuous exposure and exceeds by a factor of
nine the recommended Radiation Protection Guide (RPG) of 0.5 rem/yr
for continuous whole body exposure to individuals in the general
population. These findings serve to preclude the release of the
tailings area for public use. Action which would permit release
of said area would be to cover the tailings with uncontaminated
dirt to an extent that would diminish the external radiation to
an acceptable level and to stabilize the covering against wind
erosion. Otherwise, the area should be fenced and controlled as
a radiation area.
2. The tailings pile extends approximately 300 ft. to 500 ft. beyond
the present property line in the easterly direction. The size of
the pile precludes the possibility of returning this material to
the property area and therefore this area should be fenced and
controlled as a radiation area.
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3. The mill area exhibited external gamma radiation levels averaging
0.12 mR/hr above background at three feet above the surface. This
calculates to a yearly average dose of 1.0 rem for continuous expo-
sure which is two times the appropriate RPG of 0.5 rem/yr. With
reasonable occupancy assumptions, however, the yearly average
dose would probably not exceed 0.5 rem.
4. The housing area displayed background levels of external radiation.
B. Airborne Radioactivity:
1. Airborne transport of tailings material in the northeast direction
• from the pile is demonstrated by higher than background levels of
radioactivity in air. None of the stations showing elevated gross
alpha concentrations exceeded the RCG's for radium-226, thorium-230,
or natural uranium, however. Since it is impossible to predict
whether the condition will worsen in the future with the drying out
of the tailings pile, it is recommended that the area be stabilized
against wind erosion. If the area is not stabilized, periodic
monitoring will be necessary to insure that the appropriate con-
centration guides are not exceeded.
2. The gross alpha activity as well as the radium-226, thorium-230,
and natural uranium concentrations in the mill and housing areas
were well below the applicable radiation guides.
3. Radon gas concentrations on and about the tailings area averaged
from 3.2 pCi/1 to 14 pCi/1. These levels exceed the RCG of 3 pCi/1.
It should be pointed out, however, that this guide is applicable to
radon-222 and its daughters "as they occur in unfiltered air". This
may be interpreted as meaning radon in equilibrium with its daughter
products in air. Since it was demonstrated that equilibrium did not
exist between radon and its progeny, at least at the time of
daughter product sampling, it does not appear that the RCG has been
exeeded. Levels of radon-222 in the mill area and housing area are
substantially below the recommended guide.
It should be emphasized, however, that if enclosed structures were
to be built on the tailings material a substantial increase in radon
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concentration would occur within the structure and the RCG may
be exceeded.
C. Waterborne Radioactivity:
Ground water samples obtained in the vicinity of the tailings area
showed natural uranium concentrations in excess of 1000 pCi/1.
These values represent concentrations substantially above background
but are well below the appropriate RCG.
D. Recommendation:
On the basis of the data gathered in this survey, it is recommended
that the mill tailings be properly stabilized against wind erosion.
This action would preclude further carriage of tailings material
into the surrounding environment and would minimize the potential
long-term hazard to anyone inhabiting the area downwind from the
mill property. If the tailings area is not stabilized, periodic
surveillance will be necessary to insure that significant wind
carriage does not occur.
As a result of the external radiation levels on the tailings area
itself, this area should not be released for public use in its
present state. Action which would permit release of the area
would be to cover the tailings with uncontaminated dirt to an
extent that would diminish the external radiation to an acceptable
level and to stabilize the covering against wind erosion.
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REFERENCES
I. Sill, Claude, "An Integrating Air Sampler for Determination of
222Rn," presented at Health Physics Soc. Mtg., Denver, 1968.
2. Tsivoglou, E. C., Ayer, H. E., and Holaday, D. A., "Occurrence
of NonequiIibriurn Atmospheric Mixtures of Radon and i1s Daughters,"
Nucleonics, II, 40, September, I953.
3. FRC Report #l, May 13, I960.
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