SWRHL-69
ENVIRONMENTAL SURVEY OF URANIUM MILL
TAILINGS PILE, MONUMENT VALLEY. ARIZONA
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
Environmental Control Administration
Bureau of Radiological Health
August 1969
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SWRHL-69
ENVIRONMENTAL SURVEY OF URANIUM MILL
TAILINGS PILE, MONUMENT VALLEY, ARIZONA
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
Environmental Control Administration
Bureau of Radiological Health
US EPA
Headquarters and Chemical Libraries
EPA West Bldg Room 3340
Maiicode 3404T
1301 Constitution Ave NW
August 1969
Washington DC 20004
202-566-0556
Permanent Collection
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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
Vanadium Corporation of America uranium tailings pile,
Monument Valley, Arizona, 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 existing radiation levels 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 mill tailings be stabilized against
wind erosion. Otherwise, periodic monitoring will be
necessary in the future.
1
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ACKNOWLEDGEMENTS
Sincere appreciation is expressed to the Vanadium Corporation
of America for the cooperation and assistance provided during
the survey. Without their cooperation the study could not
have been adequately performed.
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TABLE OF CONTENTS
ABSTRACT .
ACKNOWLEDGEMENTS ....
TABLE OF CONTENTS i
LIST OF TABLES .
LIST OF FIGURES
I. PURPOSE ,
II. LOCATION & DESCRIPTION
III. ENVIRONMENTAL SURVEY
A. Sampling Procedures
1. External radiation exposure „
2. Air sampling
3. Water sampling
4. Tailings sampling
B. Analytical Procedures „
IV. RESULTS
A. External Radiation
1. Natural background
2. Tailings & stockpile area
3. Housing area
4. Perimeter
5. Thermoluminescent dosimeters
B. Air Sampling
1. Long-lived airborne particulate activity . .
2. Radon gas t,
C. Ground Water Sampling
D. Tailings Sampling „
V. DISCUSSION OF RESULTS . '
A. External Radiation Exposure *
1. Tailings and stockpile area ,
2. Housing area
i
ii
ii
v
vi
1
1
3
3
3
3
5
5
7
7
7
7
7
7
10
10
10
10
10
10
17
17
17
19
19
iii
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Table of Contents (Continued)
B. Air Sampling 19
1. Long-lived airborne particulates 19
2. Radon-222 and daughter products 20
C. Ground Water 21
VI. SUMMARY AND RECOMMENDATIONS 21
A. External Radiation 21
B. Airborne Radioactivity 21
1. Airborne particulates 21
2. Radon gas 22
C. Waterborne Radioactivity 22
D. Recommendation 22
REFERENCE 24
DISTRIBUTION
iv
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LIST OF TABLES
Table I. External radiation measurements, Monument Valley 8
Uranium Mill May 1968.
Table II. Comparison of TLD and E-500B data, Monument Valley 11
Uranium Mill.
Table III. Gross alpha particulate radioactivity in air, 12
Monument Valley Uranium Mill.
Table IV. Average Long-lived radioactivity in air, Monument 13
Valley Uranium Mill.
Table V. Atmospheric radon-222, Monument Valley Uranium 14
Mill.
... -fir
Table VI. Radioactivity in ground water, Monument Valley 16
Uranium Mi 11.
Table VII. Tailings sampling, Monument Valley Uranium Mill. 18
v
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LIST OF FIGURES
Figure
1.
Vanadium Corp. of America Uranium Mill,
Monument Valley, Arizona.
2
Figure
2.
Air sampling locations,Monument Valley Uranium Mill.
4
Figure
3.
Tailings sampling locations,Monument Valley
Uranium Mill.
6
Figure
4.
External radiation measurements.Monument Valley
Urani urn Mi 11.
9
Figure
5.
Atmospheric radon-222 pCi/1.Monument Valley
Uranium Mill.
15
vi
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ENVIRONMENTAL SURVEY OF URANIUM MILL
TAILINGS, MONUMENT VALLEY, ARIZONA
I. PURPOSE
On April 24, 1968, the Division of Indian Health requested the National
Center for Radiological Health to conduct a study of the Vanadium Corp. of
America tailings pile located at Monument Valley, Arizona. It was requested
that the study identify any radiation hazards which might exis^ and recom-
mend 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 site is located on the Navajo Indian reservation approximately
seventeen miles from Mexican Hat, Utah. The property is leased to the millint
company by the Navajo Tribal Council. The surrounding land is arid and
sparsely populated, although there are several private dwellings within one-
half mile of the tailings area. The land is utilized primarily for cattle
and sheep grazing with some limited farming.
The mill was designed and operated for the upgrading of lpw grade
uranium ore and is at present inactive.
B. Description.
For purposes of description, the mill property is divided into two
areas: the tailings and stockpile area, and the housing area.
1. Tailings and stockpile area
The original tailings pile was reprocessed for recovery of uranium
and disposed in a new location. The old tailings area and ore stockpile
area and the present tailings pile are shown in Figure 1. The present
tailings pile covers approximately 25 acres and contains an estimated
1
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*
1.5 x 105 tons of tailings material. The radium content estimated from the
average uranium assay of mill feed material (assuming radium iij, equilibrium
*
with uranium) is approximately 90 pCi/g or 122 :total curies.
2. Housing Area
There are several dwellings located in the vicinity of the old mill and
tailings area. One dwelling was occupied by the mill superintendent during
the period of the survey.
III. ENVIRONMENTAL SURVEY
A. Sampling Procedures
1. External radiation exposure
External radiation measurements were obtained using a portable geiger
survey meter. Gamma (closed window) readings were obtained at the surface
and at the three-foot level. A grid was established over the area and
readings obtained at 250-foot intervals. A total of 82 pairs of readings
was recorded.
In addition to the portable instrument readings, three thermoluminescent
dosimeters (TLD's) were placed at the three-foot level at each pf the air
sampling stations and inside the mill superintendent's house (see Figure 2).
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 a
0.8-micr.on pore size filter. A high volume air sampler was used at a flow
rate of about five cubic fe»t per minute. Four sampling stations were
established on and about the tailings area (Figure 2). Continuous twenty-
four hour samples were obtained at stations 1, 2 and 3 on each of ten
consecutive days.
~
Division of Raw Materials, USAEC, 1967
Model E-500B, Eberline Instrument Corp., Santa Fe, New Mexico
wwW
Gelman Acropore Filter, Gelman Instrument Co., Ann Arbor, Michigan
3
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Electric power was available only between the hours of 4:30 PM flnd 8:30 AM
at station 4. At this station the air was sampled only during tphis 16-hour
period. Each individual filter was analyzed for gross alpha activity. In
addition, all filters from each station were composited for analysis of
radium-226, thorium-230, and natural uranium.
b) Radon gas
Atmospheric samples were obtained by grab sampling with a two-liter
flask. The stopcocks of the flask were opened and air was pulled through
the flask for five minutes at a rate of ten liters per minute ajfter first
passing through a 0.8-micron pore size membrane filter. At the end of the
sampling interval, the flask was allowed to come to atmospheric pressure
and the stopcocks were closed. The samples were picked up by the PHS
aircraft and flown to Las Vegas, Nevada, for immediate analysis of radon-222.
Samples were collected at six locations on one or more occasions for
a total of eleven samples (Figure 2).
c) Meteorology
Wind direction and speed were estimated by visual observation. The
predominant wind direction at the mill site for the ten-day sampling period
was from the south. According to V.C.A. personnel, this is the predominant
wind direction throughout the year. During the first six days <>f sampling
the wind was light (0-5 mph). During the last four days, however, winds
estimated at 10-20 mph were encountered. In general, lapse conditions were
encountered during daylight hours with slight inversions at n1g|[»t,
3. Water sampling
Ground water samples were obtained from five wells in the ^rea (Table
VI, page 16). One-gallon grab samples were obtained and analyzed for radium-
226 and natural uranium activity.
, 4. Tailings sampling
Samples of tailings material were collected at the locations indicated
in Figure 3. Approximately 400cc of surface material was taken from each
location. The samples were analyzed for thorium-230, radium-226, and
natural uranium.
5
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B. Analytical Procedures
All laboratory analyses were performed at the Southwestern Radiological
Health Laboratory.
1. Gross alpha and gross beta determinations were performed,
after sample preparation, by counting directly in an end window, gas flow,
proportional counter.
2. Radon-222 analysis was performed by cryogenic separation and
subsequent alpha scintillation counting.
3. Radium-226 was determined after sampling 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 gamma measurements obtained at the surface and
at three feet for the various areas. Figure 4 indicates the location and
magnitude of individual measurements.
1. Natural background
The background radiation level in the surrounding area was found to
average 0.04 mR/hr both at the surface and at three feet.
2. Tailings and stockpile area
The radiation exposure at the three-foot level was found to range from
a minimum of 0.03 mR/hr to a maximum of 0.2 mR/hr with an average of 0.08
mR/hr. There was no significant difference between the readings at three
feet and those at the surface.
3. Housing area
The radiation exposure at three feet in the housing area was found to
average 0.04 mR/hr. This exposure represents background levels of radiation.
7
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TABLE I
EXTERNAL RADIATION MEASUREMENTS
Monument Valley Uranium Mill
May 1968
Number of
mR/hr @ Surface
mR/hr @ 3'
Area
Measurements
Ave.
Range
Ave.
Range
Background
6
.04
.03-.06
.04
.02-.06
Housing Area
8
,04
.02-.07
.04
.01-.05
Tailings and
Stockpile
Area
50
.09
.02-0.3
.08
.03-0.2
Perimeter
18
.03
.02-.04
.03
.01-.04
8
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4. Perimeter
Measurements made along the perimeter of the property (approximately
200 ft. from the fence) averaged 0.03 mR/hr. This represents background
levels of exposure.
5. Thermoluminescent dosimeters
A comparison of the results obtained from the TLD's and the portable
instrument measurements is shown in Table II. The results are in good
agreement.
B. Air Sampling
1.. Long-lived airborne particulate activity
The long-lived gross alpha activity found on individual filters is
shown in Table III. The upwind station (#3) averaged 1.6 x I0"5 pCi/1
gross alpha activity over the first six days. No valid samples were
obtained from station #3 during the last four days because of recurrent
sampler failure. The downwind stations showed no significant difference
from station #3 during the first six days. During the last four .days,
when strong, winds.were encountered, a significant increase in alpha
activity was noted for all three downwind stations. The average gross
alpha activity for the total collection period for downwind stations
ranged from 7.0 x 10"5 pCi/1 at station 2 to 10,3 x 10"5 pCi/1 at stations
1 and 4.
Table IV shows the average gross alpha activity along with radium-226,
thorium-230, and natural uranium activity for each station for the entire
sampling period.
2. Radon gas
Table V summarizes the radon-222 activity concentrations found at
specified sampling times and locations. Figure 5 shows the average radon
concentrations at each sampling location.
C. • Ground Water Sampling
Table VI summarizes the average radium-226 and natural uranium results
for each sampling location. Stations 3 and 5 can be considered as background
stations because of their distance from the tailings area. Th^re is no sig-
nificant difference between the samples taken in the vicinity
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TABLE II
COMPARISON OF TLD AND E-500B DATA
Monument Valley Uranium Mill
STATION
TLD
E-500B
#
mR/hr
.mR/hr
1
0.07
0.07
2
0.02
0.02
3
0.05
0.06
4
0.09
0.07
Inside
Super.
House
0.05
0.12
11
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TABLE III
GROSS ALPHA PARTICULATE RADIOACTIVITY IN AIR
Monument Valley Uranium Mill
STA
Gross Alpha Activity pCi/1 x 10~5
5 day
Total
#
May
28 29 30 31
June
12 3 4 5 6 7
Ave
Ave
1
2.1
LT 1
LT 1
1.2
5.2
42.4
1.8
10.3
2
LT 1
2.2
7.9
LT 1
LT 1
LT 1
39.5
5.5
1.4
*
7.0
3
3.6
LT 1
LT 1
7.1
LT 1
LT 1
1.6
1.6
4*
1.0
7.9
3.3
LT 1
LT 1
2.1
49.9
3.5
33.8
4.0
2.3
10.3
LT 1 » less than 1 x 10~5 pCi/1 (assumed equal to zero for averaging)
= sampler failure
* Samples collected between 1630 hrs and 0830 hrs
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TABLE IV
AVERAGE
LONG-LIVED RADIOACTIVITY IN AIR
Monument Valley Uranium Mill
STA
#
Gross a
10"5 pCi/1
226Ra
10"5 pCi/1
230Th
10"5 pC1/l
U Natural
10"5 vg/1
1
10.3
2.3
4.5
6.2
2
7.0
0.5
0.7
1.2
3
1.6
0.1
0.6
1.4
4*
10.3
0.6
1.1
4.0
Sample collected between 1630 hrs and 0830 hrs
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TABLE V
ATMOSPHERIC RADON-222.
Monument Valley Uranium Mill
STATION
#
Radon-222 pCi/1
5/28, 1445'hrs
6/3, 1000 hrs
6/6, 1000 hrs
J
1
0.5
0.4
1.5
0.8
2
0.1
0.1
3
' 0.3
0.4
0.4
4
0.5
0.5
5
(i nside
house)
0.7
0.4
0.2
0.4
6
(backgroui
,d> °-2
0.2
14
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TABLE VI
RADIOACTIVITY IN GROUND WATER
Monument Valley Uranium Mill
# LOCATION
Number
of
Samples
226Ra
pCi/1
U nat,
vg/1
1 Supt.'s House, well
1
0.1
18
Luke Yazze's well
^ 1/4 mile south
1
0.2
6
Tom Adaci's well
3 6 miles south
1
0.1
4
. Tony Yazze's well
4 1/2 mile east
1
1.5
ND
Cain Valley Spring, well
® 4 miles north
1
0.5
2
16
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background samples.
D. Tailings Sampling
Table VII summarizes the results of the thorium-230, radium-226, and
natural uranium analysis on tailings material. The radium content on the
tailings samples averaged 59 pCi/g. This average is somewhat below that
predicted from the average assay of mill feed material (90 pCi/g). The
thorium-230 averaged 46 pCi/g and natural uranium averaged 33 ug/g (.003%).
A soil sample taken 100 feet northeast of the pile displayed results of
the same order of magnitude.
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 un-
restricted 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."1 The Council further recommends, hjPwever, 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 residence on the area is
calculated and compared to the recommended RPG of 0.5.rem/yr. The net gamma
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TABLE VII
TAILINGS SAMPLING
Monument Valley Uranium Mill
AREA
Number
of
Samples
U
X
wg/g
Range
230T
X
i pCi/g
Range
226Ra
X
PCi/g
Range
Tailings Pile
3
33
17-49
46
28-56
59
48-77
100' NE of Pile
1
18
27
31
18
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radiation (i.e., minus background) at 3 feet is used for this computation.
1. Tailings and stockpile area
The average exposure at the three-foot level on the tailings and stock-
pile area was found to be 0.08 mR/hr. Subtracting background (0.04 mR/hr)
yields an average net exposure of 0.04 mR/hr. The whole body average yearly
dose for an individual having 24-hour/day residence on the tailings would
be approximately 0.35 rem/yr. This dose is less than the RP6 of 0.5 rem/yr.
The highest single measured exposure of 0.2 mR/hr (0.16 mR/hr net) at three
feet would result in a yearly dose of 1.1 rem for continuous exposure. This
is two times the RP6 of 0.5 rem/yr but represents the 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.
2. Housing area
The housing area showed background levels of exposure.
B. 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 concen-
trations 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 guide (RCG) for unidentified natural radionuclides in air of 8 x 10"®
pCi/1 (when protactinium-231 is assumed absent). If gross alpha activity
is above this guide, identification of the speci'fic radionuclides contrib-
uting to the total alpha activity is necessary 1n order to evaluate the
potential long-range hazard associated with the Inhalation of the airborne
particles.
The nuclides 1n the natural uranium decay chain most significant as
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„< are the alpha emitters. These nuclides and their
potential health hazards are the
appropriate RCG 8 x 10"5 pCi/1
Thorium-230 (Sol.) MQ x 10-5 pC1/1
Radium-226 (Insol.) 200 x 10"5 PCi/l
Natural Uranium (Insol.) ^ ^ ^ ^.p
Lead-210 (Sol.) 7M x 1Q-5 pC1/1
polonium-210 (Inso ^ ^ ^ ^ ^ none Qf
It is apparent from c™*"*0" individual radionuclides for the san.pl 1™,
the stations exceeded the RCG ^ concentrations was
period. As expected, the sta ^ ^ w tMs station radium-226
station 1 located direct y ^ ^ ^ 3Q> respectiVely, below
and natural uranium average ^ ^ ^ col|Centrat1o„ of these nuclides
their appropriate guide. Be ^ ^ ^ ^ wil1 excee<1
in the tailings materia 1 ^ ^ future
their guides downwind from th P ^ ^ ^ ^ wMch „ 5light1y
Thorium-230 for station 10-5 pCi/1. The oth«r stations
more than half the appropne, . ^ ^ x 1Q-5 pC1/1 at st#t1on
showed thorium-230 concentra , u 1s doubtful that concentrations
3 to 1.1 x ID"5 P"/l »t s' the gu1de of 8 x lO-5 pCi/1 averaged ov«.
downwind from the pile would ^ ^ impossible to predict absolutely
an extended period of t™e ^ 0n n 1t reconw
on the basis of less than 10 * against wind erosion. This wl1V
mended that the tall W* P1 ^ ttloHum.230 in the future. If the
preclude the J goring will be necessary to insure th,t
pile is riot stabilized, pe „ot exceed the recommended guide ov«
concentrations of thorium-230 in
an extended period.
2. Radon-222 and *aug***r ^ part 2Qj indicates a rad1~
The Code of Federal Beg" * "'m ^ ,,r 1n restricted areas of
ation concentration guide f» ^ „f radon.222 are assumed
3 pCi/1 above natural backg . ' M,st in unfiitered air. (TMs 1s
to be present to the <«tcn* conditions.) To evaluate the potent!*!
interpreted as meaning #» . inhalation of radon and ft. progeny,,
iong-range hazard associated
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the atmospheric radon concentrations were compared to this guide.
None of the radon samples collected on or about the tailings area
were above the recommended guide.
C. Ground Water
Ground water samples obtained in the vicinity of the tailings area
showed background levels of radioactivity.
VI. SUMMARY AND RECOMMENDATIONS
A. External Radiation
1. The net external gamma radiation on the tailings and stock-
pile area: averaged 0.04 mR/hr at three feet above the surface. This cal-
culates to a yearly dose of 0.35 rem/yr for continuous exposure and does not
exceed the recommended Radiation Protection Guide (RPG) of 0.5 rem/yr for
continuous whole body exposure to individuals 1n the general population.,
2. The housing area showed background levels of radiation.
B. Airborne Radioactivity
1. Airborne particulates
The stations located downwind from the tailings area showed gross
alpha concentrations approximately equal to or 1n excess of the Radiation
Concentration Guide (RCG) of 8 x 10"^ pCi/1 for unidentified alpha activity.
None of the stations exceeded the RCG's for radium-226, thorium-230 or
natural uranium, however.
a) Radium-226 and natural uranium
Radium-226 and natural uranium averaged a factor of 100 and 30 respectively
below their appropriate guide. Because of the low concentration of these
nuclides in the tailings material it 1s not expected that these nuclides will
exceed their guides downwind from the pile 1n the future.
b) Thorium-230
Thorium-230 concentrations averaged from one-tenth to one-half the RCG
of 8 x 10"5 pC1/l for the downwind stations. Although 1t 1s doubtful that
21
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concentrations downwind from the pile would exceed the RCG averaged over
an extended period of time it is impossible to predict on the basis of
less than ten days of sampling. On this basis it is recommended that
the tailings pile be stabilized against wind erosion. This will preclude
the possibility of exposure to thorium-230 in the future. If the pile
is not stabilized periodic sampling will be necessary to insure that
concentrations of thorium-230 in air do not exceed the RCG over an
extended period.
2. Radon gas
Radon gas concentrations on and about the tailings area averaged
approximately an order of magnitude below the RCG of 3 pCi/1.
C. Waterborne Radioactivity
Ground water samples obtained in the vicinity of the tailings area
showed background levels of activity.
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 carriage of tailings material into the surrounding
environment and would minimize any 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.
22
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REFERENCE
1. FRC Report #1, May 13, 1960
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