Techfiical Note
ORP/LV-75-5
GAMMA RADIATION SURVEYS
AT
INACTIVE URANIUM MILL SITES
AUGUST 1975
OFFICE OF RADIATION PROGRAMS - LAS VEGAS FACILITY
U.S. ENVIRONMENTAL PROTECTION AGENCY
LAS VEGAS, NEVADA 89114
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Technical Note
ORP/LV-75-5
GAMMA RADIATION SURVEYS
AT
INACTIVE URANIUM MILL SITES
Richard L. Douglas
Joseph M. Hans, Jr.
AUGUST 1975
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 recommendation for
their use.
ii
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PREFACE
Uranium mills, a part of the nuclear fuel cycle, 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 parts of
the mill site's local environs, resulting in land contamination
and increased population radiation exposure.
This study was made in cooperation with the Energy Research
and Development Administration to evaluate existing conditions at
inactive uranium mill sites in order that appropriate remedial
actions can be taken to decontaminate the site environs, minimize
erosion, and reduce population exposures.
u)
Donald W. Hendricks
Director, Office of
Radiations Programs, LVF
iii
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TABLE OF CONTENTS
LIST OF FIGURES vi
LIST OF TABLES vii
ACKNOWLEDGMENT viii
SUMMARY AND CONCLUSIONS 1
INTRODUCTION 2
Nature of the Problem 2
Historical Background 2
Sites Surveyed 4
SURVEY METHODS 7
Radiological Measurements 7
Interpretation of Measurements 8
Physical Location of Radiological
Measurement Points 9
SUMMARY OF SURVEY RESULTS AT INDIVIDUAL SITES 11
Monument Valley, Arizona 13
Tuba City, Arizona 14
Grand Junction, Colorado 15
Gunnison, Colorado 17
Slick Rock-North Continent, Colorado 18
Slick Rock-Union Carbide, Colorado 20
Rifle (Old), Colorado 21
Rifle (New), Colorado 22
Durango, Colorado 23
Maybell, Colorado 25
Naturita, Colorado 26
Lowman, Idaho 2 7
Ambrosia Lake (United Nuclear), New Mexico 28
Shiprock, New Mexico 29
Falls City, Texas 30
Ray Point, Texas 31
Salt Lake City, Utah 32
Green River, Utah 35
Mexican Hat,-Utah 36
Converse County, Wyoming 37
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APPENDICES Page
A - Calibration of Scintillometer 79
B - Technical Basis of Interpretation of Field
Measurements 82
C - EPA Radiological Criteria for Decontamination
of Inactive Uranium Mill Sites 85
LIST OF FIGURES
Figure Page
1. Inactive Uranium Mill Sites Included in
Phase I Evaluation 5
2. Gamma Radiation Survey - Monument Valley, Arizona 39
3. Gamma Radiation Survey - Tuba City, Arizona 41
4. Gamma Radiation Survey - Grand Junction, Colorado 43
5. Gamma Radiation Survey - Gunnison, Colorado 45
6. Gamma Radiation Survey - Slick Rock - North
Continent, Colorado 47
7. Gamma Radiation Survey --Slick Rock - Union Carbide,
Colorado 49
8. Gamma Radiation Survey - Rifle (Old), Colorado 51
9. Gamma Radiation Survey - Rifle (New), Colorado 53
10. Gamma Radiation Survey - Durango, Colorado 55
11. Gamma Radiation Survey - Maybell, Colorado 57
12. Gamma Radiation Survey - Naturita, Colorado 59
13. Gamma Radiation Survey - Lowman, Idaho 61
14. Gamma Radiation Survey - Ambrosia Lake (United
Nuclear), New Mexico 63
vi
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Figure Page
15. Gamma Radiation Survey - Shiprock, New Mexico °5
16. Gamma Radiation Survey - Falls City, Texas 67
17- Gamma Radiation Survey - Ray Point, Texas 69
18. Gamma Radiation Survey - Salt Lake City, Utah 71
19. Gamma Radiation Survey - Green River, Utah 73
20. Gamma Radiation Survey - Mexican Hat, Utah 75
21. Gamma Radiation Survey - Converse County, Wyoming 77
A-l Differential Gamma Reading (A) vs. Surface
Contamination Level (u>) 81
A-2 Absorbed Dose Rate (3 Feet Above Disc) vs. Radius
of Disc for a Surface Contamination Level (to) of
1 pCi/cm2 of 226Ra 81
LIST OF TABLES
Table Page
1. Inactive Uranium Mill Sites Included in Phase 1
Evaluation °
2. Approximate Areas Enclosed by the Iso-Exposure
Rate Lines at Inactive Mill Sites 12
vii
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ACKNOWLEDGMENT
Funding for this study was provided in part by the Office
of Energy, Minerals, and Industry, U.S. Environmental Protection
Agency, Office of Research and Development.
viii
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SUMMARY AND CONCLUSIONS
[This report presents the results of gamma radiation
surveysjconducted by the Office of Radiation Programs--Las
Vegas Facility (ORP-LVF) of the U. S. Environmental Protec-
tion Agency (EPA) fat twenty inactive uranium mill sites in
the Western United States_.J The purpose of these surveys was
to measure the extent to which radioactive material had been
spread into the environment from the sites by the action of
wind and/or water erosion, and by milling activities. 1lhe
results indicate that hundreds of acres of land exclusive of
the tailings piles have been contaminated to above-background
levels. Some of the contaminated land is private, off-site
property.]
Survey techniques were developed to locate the spread
radioactive materials and to estimate the gamma exposure
rates resulting from them. These measurements were com-
plicated by the presence of direct gamma radiation from the
tailings piles. Iso-exposure rate lines were located
around each site and plotted on site maps to facilitate site
decontamination decisions. These lines, corresponding to
post-cleanup exposure rates of background, 10 microroentgens
per hour and 40 microroentgens per hour, were selected to
correspond to current ORP criteria for decontamination of
inactive uranium mill sites.
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INTRODUCTION
NATURE OF THE PROBLEM
The uranium-bearing ore, as delivered to the mill or
upgrader, contains both uranium-238 and uranium-235. Both
of these isotopes are radioactive parents of long chains of
radioactive daughter products. These radioactive daughter
products are discharged from the mill as waste or tailings.
The principal environmental implications and associated
health hazards appear to be related to radionuclides of the
uranium-238 decay chain, primarily thorium-230, radium-226,
radon-222 ( a noble gas), and radon-222 progeny. Although
these radionuclides appear in nature, their concentrations
in tailings material are several orders of magnitude greater
than their average terrestrial concentrations.
Since large quantities of the mill wastes have been
piled at mill site locations in a relatively mobile physical
form, they pose potential sources of exposure to man.
These potential sources are:
1. Inhalation of wind-blown particulate tailings
material from the piles.
2. Inhalation of the progeny of radon-222 which
diffuses from the tailings piles.
3. External whole body gamma exposure from the
tailings piles and the tailings scattered into the
local environment.
4. Internal exposure from ground and surface water
contaminated by materials leached or eroded from
the tailings piles.
HISTORICAL BACKGROUND
Following hearings conducted in Washington, D. C., on
March 12, 1974, by the Subcommittee on Raw Materials of the
Joint Committee on Atomic Energy (JCAE), the Environmental
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Protection Agency (EPA) and the Atomic Energy Commission*
(AEC) agreed to conduct a joint study of inactive uranium
mill tailings piles in the Western United States.
The purpose of this joint effort is to perform a com-
prehensive study of all inactive mill sites rather than to
to continue to treat the problem on a case-by-case basis as
evidenced by the remedial action program in Grand Junction,
Colorado, and proposed legislation relating to the Vitro
site in Salt Lake City, Utah. The study will be conducted
as a cooperative, two-phase undertaking by the AEC, EPA, and
concerned states.
Phase I of the study, which was conducted during the
period April - October 1974, was intended to provide a
summary of conditions at each of the inactive sites and rec-
ommendations for further studies which were considered nec-
essary to fully evaluate the need for remedial actions.
Twenty-one inactive mill sites, located in eight states,
were selected for study. Three study teams were selected
and each was assigned a list of sites. The team for each
site was composed of representatives from the following
organizations:
-EPA, Office of Radiation Programs, Las Vegas Facility
-EPA Regional radiation representative for the region
in which the site was located.
-Lucius Pitkin, Inc. (contractor to the AEC)
-Radiation Program representative from the state
involved.
The available records for each site were reviewed by
the study team in order to assemble all pertinent informa-
tion regarding the history and operation of that site.
Each site was then visited to determine the physical condi-
tion of the site, the need for corrective action, proximity
to populated areas and prospect for increased population,
approximate area of tailings, and availability of suitable
cover for stabilization. An interpretation of hydrological
conditions at most sites was provided by ORP-LVF, and mete-
orological data were provided by the Las Vegas Air Resources
* Now the Energy Research and Development Administration
(ERDA)
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Laboratory of the National Oceanic and Atmospheric Adminis-
tration. Specific area population data were obtained by
ORP-LVF and ORP-Hq.
A detailed Phase I report was then prepared for each
site. A draft report was prepared by the Lucius Pitkin,
Inc. (LPI) representative of the site evaluation team, and
the draft was reviewed by the other team members and by
other ORP-LVF staff. Comments were sent back to the AEC's
Grand Junction office and a final report prepared by Atomic
Energy Commission staff. These final reports, comprising
all together three large loose-leaf binders, were issued and
given limited distribution, in September 1974. In October, a
17-page Summary Report was issued by the AEG.
The second phase of the study will include evaluation
of the problem, detailed examination of alternative solu-
tions, and the preparation of cost estimates and detailed
plans and specifications for appropriate remedial action.
This part of the study will require gamma radiation surveys
to determine the extent of spread of wind-eroded and/or
water-eroded tailings materials from the tailings pile.
Estimated remedial action costs for all sites will be pre-
pared for presentation to the JCAE during Phase II.
The ORP-LVF agreed to conduct the gamma radiation sur-
veys at each site. In order to obtain optimum weather
conditions for the field work, the surveys were started in
the spring of 1974.
SITES SURVEYED
Twenty-one inactive uranium mill sites were selected
for Phase I study. Their locations are listed in Table 1
and shown in Figure 1.
The four sites located on the Navajo Reservation
(Shiprock, Mexican Hat, Tuba City, and Monument Valley) were
handled somewhat differently from the other sites. In the
fall of 1973, the Indian Health Service (IHS) approached
both the EPA and the AEC for technical assistance and advice
regarding these sites. They were particularly concerned
about the site at Shiprock, since the Navajo Engineering and
Construction Authority (NECA), an enterprise of the Navajo
Tribe, was headquartered at this site and was conducting a
school there to train Navajos as heavy equipment operators.
In addition, the State of Utah was conducting a trade school
in the buildings on the Mexican Hat site, and various uses
were being proposed for the buildings at the Tuba City site.
In November 1973, the Navajo Tribe formally requested EPA's
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CONVERSE COUNTY*
(SPOOK)
SALT LAKE CITY
GREEN RIVER
0GUNNISON
SLICK ROCK (2)
MEXICAN HAT
• AMBROSIA LAKE
(UNITED NUCLEAR)
INACTIVE
URANIUM MILL SITES
INCLUDED IN
PHASE I EVALUATION
Figure 1
5
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assistance in evaluating the radiological situation at all
four sites. As a result of this request, ORP-LVF, in coop-
eration with the IHS, had initiated surveys of these sites
before the organization of the Phase I/Phase II studies had
been formalized. The gamma survey work at these four sites
was completed by the end of April 1974.
A gamma survey was not done at the Lakeview, Oregon,
site because Atlantic Richfield Company (ARCO), the owner of
the site, in agreement with the Oregon Department of Human
Resources, stabilized the pile during the summer of 1974.
The State considered ARCO's stabilization effort to have
effectively eliminated any radiological problems associated
with the site, and therefore requested that the Lakeview
site not be included in the Phase II gamma survey program.
•u
As a result of the Lakeview exception, ORP-LVF made
Phase II gamma surveys at only 20 of the 21 sites listed in
Table 1.
TABLE 1. INACTIVE URANIUM MILL SITES
INCLUDED IN PHASE I EVALUATION
Arizona: New Mexico:
Monument Valley* Ambrosia Lake (United Nuclear)
Tuba City* Shiprock*
Colorado: Oregon:
Grand Junction Lakeview
Gunnison
Slick Rock-North Continent Texas:
Slick Rock-Union Carbide Falls City
Rifle (Old) Ray Point
Rifle (New)
Durango Utah:
Maybell Salt Lake City
Naturita Green River
Mexican Hat*
Idaho:
Lowman Wyoming:
Converse County (Spook)
* Indicates site located on Navajo Reservation
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SURVEY METHODS
RADIOLOGICAL MEASUREMENTS
The purpose of the gamma radiation surveys was to
locate "off-pile" areas contaminated with wind-eroded and
water-eroded tailings. This required measuring gamma radia-
tion originating from the tailings on the ground in the
presence of gamma radiation originating from the pile itself.
In order to separate these two components, a modified Baird-
Atomic scintillometer (Model NE-148A) was used.
The NE-148A contains a 1 inch by 1% inch Nal crystal
detector calibrated with 226Ra. The output is in micro-
roentgens 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 fluctuation,
thereby reducing the need for subjective averaging of read-
ings 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 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 scintillometer, 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.
Because of energy response and efficiency factors
associated with the small Nal crystal, meter readings ob-
tained with the scintillometer must be corrected to obtain
the true exposure rate. The readings obtained during these
surveys were not corrected; hence, the delta values are
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designated in the legend of each map as "uncorrected" dif-
ferential gamma readings. However, since the delta values
are the difference between two readings, the fact that the
readings were not corrected does not affect the numerical
value of the delta.
Because of ambient background radiation, a small delta
value will be obtained even in the absence of tailings.
Through experience, this "background delta" has been found
to be in the range of Al to A4, with values at most locations
of about A2 or A3.
Since the basic purpose of this project was to deter-
mine the extent of the spread of tailings, the pile itself
and the former (or existing) mill site area were generally
not surveyed in detail. These areas are known to be con-
taminated, and we did not consider a detailed survey of
these areas to be within the scope of this project.
It should also be noted that these surveys do not pro-
vide information on the depth of the contamination. The
delta measurement only provides information regarding tail-
lings on the surface at that location, and does not define
the depth to which the tailings may occur. In practice,
however, windblown tailings were found to be located on or
near the ground surface. This is not always true of con-
tamination in such areas as drainage washes, mill yards, ore
storage areas, and areas in close proximity to the tailings
piles. In these areas, such factors as soil erosion, ground-
water leaching, vehicular traffic, and earth work have often
tended to move the radioactive material into the soil or
partially bury it, often in a very erratic manner.
INTERPRETATION OF MEASUREMENTS
Delta values can be correlated with tailings surface
contamination levels, and consequently with the above-ground
exposure rate resulting from a given contamination level.
The scintillometers were calibrated using mill tailings with
a known radionuclide content in a surface contamination con-
figuration. If the windblown tailings are on the ground
surface (the most general case), delta can be related to
activity per unit area, designated as 01. The units of w are
picocuries (pCi) of 22bRa per square centimeter (cm^). The
details of this calibration are given in Appendix A.
Once A has been determined, the above-ground g
exposure rate can be calculated, assuming that the
progeny are in equilibrium with the 226Ra. In practice the
calibration and the exposure rate calculation were combined
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so that .delta is related directly to exposure rate without
going through the separate step of determining w . The
relationship between delta and the above-ground exposure
rate from surface tailings contamination is given in Appen-
dix B.
The basic purpose of the gamma surveys was to delineate
contaminated land areas to be considered for decontamination
by earth removal. In order to facilitate decisions on
outlining these areas, iso-exposure rate contour lines were
located around each site. In keeping with current Environ-
mental Protection Agency guidance (Appendix C), lines corres-
ponding to 40 yR/h, 10 yR/h, and background were located.
The significance of these lines is as follows:
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 desig-
nation.
Several assumptions, as listed on page 82 of Appendix B,
were involved in the construction of these residual iso-
exposure rates lines. It was also necessary to average the
delta values on each radial. Because the real-life situation
is different from the "average", it should be expected that,
at any site, certain points may be found after cleanup where
the exposure rate and/or the radium-226 concentration in
soil might vary significantly from the average value. Such
areas could only be found by exposure rate measurements
taken during or after the cleanup operation. A monitoring
program should, therefore, be designed and conducted as an
integral part of the cleanup operation at each site.
PHYSICAL LOCATION OF RADIOLOGICAL MEASUREMENT POINTS
The gamma surveys for the four sites on Navajo lands
were performed by locating points of predetermined delta
value around the mill site. The points were physically
located by working back and forth until the desired delta
value was found. This point was then marked with a stake,
and the stake was located by conventional land surveying
methods performed by engineers of the Indian Health Service.
The points were then plotted on a map and connected to form
"iso-delta" lines around the site.
This technique was used at Green River which was the
first site surveyed on the Phase II list. However, as more
experience was accumulated, a variety of techniques were
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employed depending upon terrain features, visibility, and the
availability of physical landmarks such as roads, fences, etc.
Frequently, radial lines were extended out from one or more
control points located on the pile. Delta measurements were made
(usually at approximately 200-foot intervals) along the radial
lines, and the measurement points were located by using a theodo-
lite and stadia rod. In some cases, a base line was chained or
paced around the pile perimeter, and radial lines were extended
out at right angles from the base line, with the measurement
points usually being located by pacing. In areas where consid-
erable residential or commercial development existed, and maps
were available, measurement points were located by pacing along
streets and roads. The4specific technique of point location used
at each site is described in the individual site summaries.
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SUMMARY OF SURVEY RESULTS AT INDIVIDUAL SITES
This section presents the detailed results of the gamma
surveys. For each site, a map shows the locations of the radi-
ation measurements and the delta values at each location. Based
on the delta values, the background, lO/^R/h and 40^/tR/h lines
have been constructed where possible, as described in the pre-
vious section and in Appendix B. These lines are also shown on
the site map.
A short writeup has also been prepared for each site which
provides:
A brief summary of the operating history of the mill
(obtained from the Phase I report).
A brief description of the survey methods used at
the site.
A descriptive summary of the iso-exposure rate lines
and the areas which they encompass.
Comments on any unique features or problems associ-
ated with the site.
Table 2 summarizes the areas of the tailings piles and the
areas within the iso-exposure rate lines at the various sites.
At some sites, one or more of the lines were either not construc-
ted or were not closed, thereby making an area measurement impos-
sible. The areas were measured on the maps using a planimeter.
Since a precise engineering survey was not made at each site,
slight errors may have occurred in the construction of the maps.
Therefore, the areas are listed as being approximate areas.
For some sites, the tailings pile areas listed in Table 2 -'
vary somewhat from the nominal areas given in the corresponding
site writeup. The latter areas were extracted from the Phase I
reports, and variations may be due to such factors as changes in
pile configuration due to stabilization efforts and difficulty in
locating the precise pile boundaries.
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TABLE 2. APPROXIMATE AREAS ENCLOSED BY
THE ISO-EXPOSURE RATE LINES AT INACTIVE MILL SITES
Approximate area
(acres)
Tailings
Site Pile(s)
Monument Valley 15
Tuba City 27
Grand Junction 47
Gunnison 30
Slick Rock (NC) 7
Slick Rock (UC) 19
Rifle (Old) 20
Rifle (New) 21
Durango 10
Maybell 81
Naturita 15
Lowman 7 2
Ambrosia Lake 104
Shiprock 118
Falls City 142
Ray Point 48
Salt Lake City 94
Green River 9
Mexican Hat 77
Converse County 42 3
Within lines, but excluding tailings
40 yR/hr 10 yR/hr Background
N.C. (A6) 1 52
(A15)1 128 (A7) 1 169
N.C. N.C.
12 26
N.C. 12
3 41
17 44
114 169
N.C. N.C.
322 452
N.C. N.C.
N.C. 11
210 390
N.C. (A7)1 126
139 256
'19 39
114 198
N.C. (A8)1 44
N.C. (A7)1 127
N.C. 88
N.C.
(A3)1 202
314
68
33
81
243
312
N.C.
745
N.C.
16
617
(A3)1 229
411
94
510
(A4)1 153
(A3)1 457
187
N.C. - Line was not constructed or was not closed (see site
summary text for explanation)
(1) Delta line corresponding to appropriate iso-exposure
line (see Appendix B)
(2) Mill residue stockpile areas
i.3) - Includes tailings, overburden piles, and waste dumps
(tailings only approximately 2-1/2 acres)
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MONUMENT VALLEY, ARIZONA
The former Monument Valley uranium ore upgrading plant
is located in Cane Valley on the Navajo Reservation approxi-
mately 17 miles southwest of Mexican Hat, Utah. The site
was used for upgrading ore, batch leaching, and finally heap
leaching. Most of the 1.1 million tons of tailings sands
form a pile of approximately 20 acres in size and is estimated
to contain 50 curies of radium-226. The remaining sands are
scattered about an adjacent wash west of the pile.
The iso-exposure rate lines were constructed from
staked points locating pre-determined delta values. Al-
though wind and water erosion of the tailings are evident,
the background and 10 yR/hr lines are located relatively
close to the site. This may be attributed to the low radio-
nuclide content of the tailings. Both lines extended further
away from the pile on the north and east sides due to wind
erosion and prior activities in the diked area on the east
side.
The background line was terminated on both sides of the
west end of the site because it became very irregular and
difficult to locate because of rock outcroppings and scattered
ore. The 10 yR/hr line beginning west of the points where
the background line was terminated is not related to an
above ground exposure rate for the same reasons the back-
ground line was terminated. It does, however, outline the
ore scattered over that area.
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TUBA CITY, ARIZONA
The Tuba City uranium mill site is located on the
Navajo Reservation approximately six miles east of Tuba
City, Arizona adjacent to the south side of U. S. Highway
164. The surrounding area is sparsely occupied except for
the former mill housing area which is approximately 1000
feet away and uphill in a northerly direction from the
tailings piles.
Approximately 0.8 million tons of ore were processed at
this mill from 1956 until 1966, and the resulting tailings
piles cover approximately 34.5 acres. In addition, lightly
used evaporation ponds lie adjacent and south of the tailings
piles. The radium-226 activity in the tailings piles is
estimated to be 670 curies. Although the tailings piles
were chemically stabilized in 1968, the stabilization has
failed and extensive wind erosion has occurred in the
northeasterly direction from the piles.
The iso-exposure rate lines were constructed from
staked points locating pre-determined delta values. The
background line is relatively close to the evaporation ponds
to the south and extends approximately 500 feet away from
the site on the west side. It crosses U. S. Highway 164 on
the north side and runs approximately 3600 feet from the
piles in the downwind northeasterly direction. Both the 10
and 40 pR/hr lines parallel the background line and exhibit
a sharp departure from the site in the northeast direction.
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GRAND JUNCTION, COLORADO
The Climax Uranium Company (now AMAX Uranium Corporation)
processed approximately 2.2 million tons of uranium-vanadium
ore at the Grand Junction mill between 1951 and 1970. An
estimated 1.9 million tons of tailings remain in the 55-acre
pile. The total estimated Ra-226 inventory is 1350 curies.
The pile is located on the north bank of the Colorado River
at the southeast edge of the city of Grand Junction.
A formal land survey to locate the gamma measurement
points was not made because of the large area involved, and
because of the considerable line-of-site interference due to
buildings and trees. Instead, the measurement points were
located by pacing along streets, and in reference to existing
landmarks. The points were transferred to maps obtained
from the city engineering department, and the final map was
prepared by tracing from a mosaic of these maps.
AMAX property north of the mill and pile was purchased
by Industrial Development, Incorporated (now Colorado West
Improvement, Inc.)- This area was not included in this
survey because it had recently been surveyed and decontamin-
ated for development as an industrial park. Several indus-
trial buildings were in existence and others were under
construction at the time of this survey.
The background delta value for the Grand Junction area
was A3. Therefore, the background line was constructed at
A4. The 10 and 40 yR/hr lines were not constructed at this
site because sufficient survey points could not be obtained
due to the extensive development surrounding the site.
In the residential and commercially developed area west
and northwest of the site, the survey was conducted by
taking readings on lawn or unpaved areas adjacent to the
streets and sidewalks. No attempt was made to conduct a
detailed survey in this area because of the extensive degree
of development, and because the area had previously been
surveyed on a house-to-house basis by the Public Health
Service. In this area, the background line was located
approximately one-half mile, or slightly more, from the
center of the pile. This verifies the extent of windblown
tailings reported in the Phase I report on Grand Junction.
Some unusually high readings were found in this area (e.g.,
the A70 on Winters Avenue between 8th and 9th Streets) which
are probably due to use of tailings.
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Some indication of windblown tailings was found around
the feedlot immediately west of the pile. Definitely elevated
levels (A20-A50) were found below the corrals on the river
bank. No other readings were obtained between Struthers
Ave. and the river, so the background is shown as a dashed
line in this area. If decontamination is to be undertaken,
the area should be surveyed in more detail.
North of the site, the background line parallels the
D & RGW tracks. Relatively low levels of windblown tailings
were found between D Road and the tracks. Higher, but
erratic, levels were found on the west side of 12th Street
in open areas where readings could be made.
Northeast of the site, the area along 27% Road and in
the southwest corner of 27% and D Roads consists largely of
residential development. Readings were taken primarily
along the roads. The open fields owned by the State and by
AMAX immediately northeast of the site were surveyed on a
grid basis. The tailings repository area was not surveyed.
Based on the readings obtained in this area, the back-
ground line crosses D Road at the intersection with 27%
Road, and proceeds south along the east side of 27% Road.
It makes a slight jog to the east at C% Road, and then
proceeds south to the river. As mentioned previously, if
decontamination were to be undertaken in this area, the few
open areas east of 27% Road should be surveyed in more
detail.
The state-owned areas north and east of the tailings
repository were originally effluent ponds for the mill.
This is reflected by the relatively high and randomly-
distributed delta values which were obtained in these areas.
The values obtained in the tract owned by AMAX fronting on
27% Road are more indicative of windblown tailings.
On the south side of the river, readings were taken on
top of the bluff at the Mesa County school property and in
adjoining privately-owned areas. Most of the readings
obtained were background. In view of the prevailing wind
direction, and the results reported in the Phase I report on
Grand Junction, no further readings were taken on this side
of the river.
16
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GUNNISON, COLORADO
The mill site and tailings are located near the south
edge of Gunnison, adjacent to the Gunnison County airport.
The tailings were impounded by a rectangular shaped dike 950
x 1440 feet approximately 12 feet high. The mill site
encompassed approximately 62 acres, of which 30 acres is
occupied by the tailings pile. The site has been covered
with gravel and vegetated with grasses. Records indicate
that 540,000 tons of ore, averaging 0.1570 U^Os was proc-
essed. The tailings are estimated to contain approximately
420 pCi/gm of radium-226.
Survey points for the Gunnison site were located using
a theodolite and stadia rod. One instrument setup was made
on the pile, and 17 radial lines were extended out from the
pile. Readings were taken at approximately 200-foot inter-
vals along the radials until approximate background delta
values were obtained.
Tailings spread, as indicated by the background line,
extend approximately 900 feet north of the pile. The back-
ground line in the northeast and southeast sections were
approximated by extrapolation. The 10 yR/h line extends
northward about 500 to 700 feet from the pile, closing to
160 to 200 feet on the east and west sides. The ore stock-
pile area almost completely lies within the 10 yR/h line.
The 40 yR/h line encompasses the north sides of the
pile and lies approximately 100 feet inside the 10 yR/h
line. It also merges with the pile midsection on the east
and west sides. A 40 yR/h line was approximated on the ore
storage area. However, previous studies indicate that ore
storage areas are highly variable, probably due to location
of the stockpiles.
17
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SLICK ROCK (NORTH CONTINENT), COLORADO
The North Continent site is located on the Dolores
River about one-half mile from Slick Rock in San Miguel
County, Colorado. Approximately 37,000 tons of ore were fed
to the mill for the extraction of uranium, vanadium, and
radium. The estimated inventory of Ra-226 in the pile is
about 30 curies. In 1971, the pile was contoured, covered
with six inches of tbpsoil, and seeded and fertilized in
accordance with State of Colorado regulations.
A preliminary survey of the site was conducted using
the theodolite and stadia rod. These points are shown on
the map as a dot enclosed by a square. A more detailed
survey was then made by pacing lines off the fence which
bounds the pile on the east and southeast sides. Readings
were taken at approximately 50-foot intervals along these
lines. These lines were extended out until background delta
values were reached or until the terrain prevented further
extension of the line. The background delta value for the
area was found to be A2.
Since the pile had been covered with topsoil, it was
difficult to determine its boundaries visually. Radiation
readings on the pile area were erratic, ranging from A450 to
background. This indicates, as is implied in the Phase I
report, that the "pile" is not uniformly distributed. As a
result, the entire area designated as the tailings pile on
the map probably includes somewhat more area than the tail-
ings actually occupy. In addition, some tailings material
was found off the pile in the river flood plain to the
northwest of the pile. This is apparently the result of
water erosion, which possibly occurred before the pile was
covered.
Some elevated readings were found along the road north
of the site. These appeared to be due to ore haulage and/or
operations of the Burro Mine across the road to the north-
east of the site. Therefore, these areas were not included
within the background line.
The background line was established at A3, with some
minor adjustments made for terrain considerations. The
entire bench within the curve of the Dolores River was
included within the background line. This includes the area
where the original residential and mill support buildings
18
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were located. Although some of this area is at or near
background, numerous hot spots (apparently due to mill
operations) and some evidence of windblown tailings were
found in this area. West of the pile, the background line
was established on the east bank of the river. Additional
readings, not shown on the map, were taken on the mesa west
of the river and downstream along the river. These readings
were at background.
The 10 yR/hr line lies within about 100 feet of the
fence on the east side of the pile. It was joined with the
background line at the bridge north of the site and at the
end of the fence southwest of the site. West of the pile,
the two lines run concurrently along the river.
A 40 yR/hr line was not located at this site because an
insufficient number of elevated delta values were found off
the pile area to allow construction of the line.
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SLICK ROCK (UNION CARBIDE), COLORADO
This site is located at the community of Slick Rock in
San Miguel County, Colorado. Approximately 350,000 tons of
tailings remain from the operation of a uranium-vanadium
upgrader which was operated here from 1957 through 1961.
The tailings pile is located adjacent to the Dolores River.
The estimated Ra-226 inventory of the pile is 70 curies.
Five control points were established on the pile and
mill site. Radial lines were extended from these control
points using a theodolite and stadia rod. Differential
gamma readings were taken at approximately 100-foot inter-
vals along the radials. The background delta value for the
area was found to be A2.
The background line encloses most of the flood plain of
the Dolores River east of the pile, lies along the base of
the cliff northeast of the pile, and takes in the flood
plain of the river north of the site. On the west and south
sides, it closely follows the road which circumscribes the
site, and includes a small portion of the housing area
southwest of the site. The maximum distance of this line
from the pile is about 1350 feet in the southwest direction.
The 10 yR/hr line roughly parallels the background
line, but lies within an average of about 200 feet of the
pile on the east, north, and northwest sides. It bisects
the Rocky Mountain Natural Gas property, and includes the
entire mill site area southwest of the pile.
The 40 yR/hr line is unique at this site in that it
does not encircle the pile. It encloses an area of about
three acres near the road south of the site. This is appar-
ently the former location of the settling ponds shown in the
Phase I report.
20
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RIFLE (OLD), COLORADO
The old Rifle mill site and pile are located approxi-
mately 1/8 of a mile southeast of the town of Rifle in
Garfield County, Colorado. The tailings pile covers an area
of about 10 acres, and has been stabilized with a minimum
depth of six inches of top soil. The pile contains about
350,000 tons of tailings material with an estimated Ra-226
inventory of 320 curies.
Survey points for the Rifle site were located using a
stadia rod and theodolite. A control point was located on
the pile and 16 radials were traversed. Measurements along
each radial were taken at 200-foot intervals.
Tailings spread as indicated by the background line
(A4) extends approximately 2700 feet northeast of the pile,
2200 feet northwest, and 1300 feet south.
The 10 yR/hr line remains within 700 feet of the pile
and intersects the west end of the pile. The 40 uR/hr line
parallels and lies approximately 200 feet inside the
10 yR/hr line. It intersects the pile at several locations
including the west end.
All iso-exposure rate lines intercepted the Colorado
River. Construction of the lines within the river area was
based on readings taken on each side of the river.
21
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RIFLE (NEW), COLORADO
The new Rifle pile is located about one mile southwest
of the town of Rifle, Colorado. The mill on the site is
presently being operated by Union Carbide Corporation for
processing vanadium. The tailings are deposited in two ad-
jacent piles that appear as one pile with two different
levels. The older pile is 55 feet high and the newer pile is
40 feet high. Both piles have been seeded without soil
cover. The piles are watered and presently show some grass
cover. The pile complex is 21 acres in area and contains
2.7 million tons of tailings material with an estimated
content of 2,130 curies of Ra-226.
The survey was carried out using theodolite and stadia
techniques. Two setups were required on the pile and radials
were constructed from these two base points. Readings were
taken at approximately 200-foot intervals until background
delta values were obtained.
The background line encompasses a rather large area,
completely enclosing the mill site, a portion of the rail-
road, and the Colorado River to the east and south. The
broken portion of the background line to the south indicates
that the line location was estimated in this area due to the
inaccessibility of the area.
The 10 jaR/hr line enclosed the mill and tailings area
to the west, north and east, and crosses the southern por-
tion of the site, property.
The 40 yR/hr line generally parallels the 10 yR/hr
line. It also encompasses the tailings and mill site except
on the south.
It should be noted that during the survey, Interstate
70 was under construction south of the site. This may
affect the final location of the three lines once construc-
tion is completed.
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DURANGO, COLORADO
This mill site and tailings pile is located at the base
of Smelter Mountain immediately adjacent to the Animas River
on the southern edge of the town of Durango. An estimated
1.627 million tons of ore were processed, and 1.555 million
tons of tailings are estimated to remain, having a theoreti-
cal Ra-226 inventory of 1200 curies.
Survey points at the Durango site were located by
pacing and by orientation relative to physical landmarks.
The points were then transferred directly to a base map
showing the site property and physical features, thereby
eliminating the need for an engineering survey. The back-
ground delta value for the area was A2.
Remnants of the old diversion ditch are still apparent
on the slope of Smelter Mountain, beginning about at the
west property line, running southeasterly above the piles
and mill site, and paralleling the Animas River to the old
raffinate pond area. This ditch was arbitrarily selected as
the approximate upper edge of the survey area because it was
felt that decontamination above this point would be imprac-
tical due to the steepness of the slope.
Little contamination was found going up the canyon
(Lightner Creek and U. S. 160-550) to the northwest of the
site, nor upstream along the Animas River. Varying con-
tamination levels were found along the Animas River down-
stream of the site, presumably due to erosion and/or dis-
charges of mill effluents or tailings to the river in the
past.
Generally, significant delta values were found below
the millsite, down to and throughout the old raffinate pond
area. Since the mill was shut down, the ponds have been
leveled, covered with topsoil, and seeded. As a result, no
particular contamination pattern appears from the surface
readings obtained in this area. If measurements were
made to some depth, it might be possible to better define
the specific contaminated areas.
Only the background and 10 yR/hr lines were constructed
at this site. Although several elevated delta values were
23
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found, they occurred randomly and no general pattern which
would allow construction of a 40 yR/hr line could be dis-
cerned.
North of the site, the background line begins at the
base of the mountain about 1600 feet northwest of the small
pile. It proceeds east to the D & RGW yards, then angles to
the southeast through several blocks of the city of Durango.
It crosses the river below the new bridge and proceeds
generally south between the river and the county road,
crossing this road slightly below the road to the city dump.
fe
The 10 yR/hr line closely parallels the background
line, but lies an average of 200 to 400 feet inside it. It
terminates approximately at the industrial park which is
being developed south of the site, but does not include the
buildings currently located there. Another small area of
elevated readings further south was included in a separate
10 yR/hr area.
The pattern of slightly elevated readings along the
county road in this area is an apparently anomalous finding.
It seems unlikely that this is due to windblown tailings,
since areas much closer to the pile do not show similiar
contamination levels. The cause for these readings is at
present unexplained. Insufficient readings were obtained to
the west of this area to allow closure of the background and
10 yR/hr lines. Therefore, they were terminated in this
area on the basis of available data.
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MAYBELL, COLORADO
The mill site and tailings pile are located 4 miles
northeast of Maybell, Colorado, in Moffat County. The 70
acres of tailings have been contoured and covered to a depth
of six inches with soil from the nearby area. Records in-
dicate that 2.6 million tons of tailings material are depos-
ited in the pile containing an estimated 640 curies of
Ra-226. Open pit mines and their associated waste are
located adjacent to the pile on all sides except to the
east.
Using a theodolite and tape, a control traverse was
established along the fence enclosing the pile. Radials
were run from the traverse and measurements were taken at
200-foot intervals until background readings were encoun-
tered. Mine waste was not differentiated from blown tail-
ings because of the close proximity of the mine wastes to
the tailings pile. Therefore, it should be noted that, at
this site, much of the area enclosed by the background and
10 and 40 yR/hr lines is due to the mining activities rather
than to windblown tailings.
The background line (A4) extends 5000 feet west of the
pile enclosing most of the mine area to the west. It returns
to within 3000 feet north of the pile, and averages a dis-
tance of 2000 feet east of the pile. South of the pile, the
background line goes around a small open pit mine and then
returns to within 200 feet of the pile at the southwest
corner.
The 10 yR/hr line lies an average of 700 feet inside
the background line. It also encloses the open pit area to
the west and encounters the small open pit mine to the
south. The 10 yR/hr line intersects the pile on the south-
west corner and emerges at the west side of the pile.
The 40 yR/hr line parallels the 10 yR/hr line on the
west and north sides of the pile and lies approximately 50
to 100 feet within the 10 yR/hr line in these directions.
On the east and south sides of the pile, the 40 yR/hr line
stays within 700 feet of the pile and intersects it simi-
larly to the 10 yR/hr line in the southwest corner of the
pile. It then emerges from the pile on the west side.
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NATURITA, COLORADO
The millsite and tailings are located two miles west of
Naturita, Colorado in the narrow San Miguel Canyon. The
tailings were impounded in a 20-acre area adjacent to the
San Miguel River. After the mill shut down in 1963, it was
partially dismantled and the tailings were stabilized in
accordance with Colorado regulations. During the period that
the present tailings pile was accumulated, 704,000 tons of
ore were processed at the Naturita mill. The total estimated
Ra-226 content in the pile is 490 curies.
The majority of the survey points for the Naturita site
were located using a theodolite and stadia rod. Extensive
contamination of the canyon caused by the plume from the old
roaster stack was found in the down-valley direction, so it
was necessary to place survey locations across the canyon
for several miles downstream. The theodolite was set up at
five different locations in order to cover the millsite
area. The instrument locations were tied to one another
using the instrument and the stadia rod. Instrument read-
ings were taken at about 200-foot intervals along radials
from the instrument locations.
The extent of contamination from the windblown tailings
and/or the plume from the old roaster stack is indicated by
the background line. In the area of the mill and tailings
pile, the whole canyon from cliff to cliff has been con-
taminated. The contamination from the plume extends for
several miles down the valley.
The 10 yR/hr line is within 200 feet of the pile to the
southwest and 400 feet to the -northeast. Due to extensive
contamination both up-valley and down-valley, the 10 yR/hr
line was not closed in these directions.
The 40 yR/hr line is- within 100 feet of the pile to the
southwest and 300 feet to the northeast. It extends 2200
feet from the pile up-valley and could not be closed down-
valley due to the extensive contamination from the plume.
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LOWMAN, IDAHO
This mill site is located near Lowman in Boise County,
Idaho and is presently owned by Michigan Chemical Corp. of
Chicago, Illinois. The 35-acre site is located in a steep-
sided mountain valley, bordered on the west by Clear Creek
and on the south by State Highway 21.
The mill was used for the recovery of concentrates of
columbite-euxenite and monazite plus by-products of magne-
tite, ilmenite, zircon and garnet. Source material for the
mill came from an area 20 miles north of Lowman. The major-
ity of the material at this site consists of dense sand
residues containing varying amounts of uranium and thorium
and their radioactive progeny. This material is placed in
a number of discrete piles largely south of the abandoned
mill building foundation. The remainder of the material im-
mediately adjacent to the foundation consists of ore pile
residues, a small tailings pile, and pond dike.
Observations contained in the Phase I report indicate
that erosion was minimal around the site and this was con-
firmed by the radiation survey. Delta measurement points
were located with a theodolite and stadia rod. The back-
ground line is located close to the piles and mill yard.
This line is estimated to bound the east side of the site at
Clear Creek. Measurements, not shown on the map, were made
approximately 1/4 mile to the north and the east to confirm
that the background delta value was eight. Therefore, the
background line was placed at a delta nine. The 10 yR/hr
line encompasses the mill yard and joins the piles on the
east and northwest sides of the site. It is assumed to be
located on the bank of Clear Creek on the west side of the
site.
A portion of the 40 yR/hr line was constructed through
the mill-site area and terminated at the junction of the
line and tailings piles. The northeast section of this line
was approximated due to lack of additional data.
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AMBROSIA LAKE (UNITED NUCLEAR), NEW MEXICO
The site of United Nuclear Corporation's mill and
tailings pile is located about 25 miles north of Grants, New
Mexico, in Section 28, Township 14 North, Range 9 West, New
Mexico Principal Meridian. The tailings pile is west of the
mill site, covers 100 acres, and has an average depth of 20
feet. The pile consists of approximately 2.6 million tons
of tailings with an estimated Ra-226 content of 1,520 curies.
The pile has not been stabilized, but the surface slimes
have dried and have formed a fairly durable crust that
resists wind erosion well.
Survey points at this site were located using a theodo-
lite and stadia rod. An initial traverse was laid out
around the pile. This traverse was a square 2500 feet per
side. Perpendiculars were run from the traverse at 500-foot
intervals and an additonal diagonal was run at each corner.
Measurements were taken at 200-foot intervals along the
perpendicular and diagonal lines, except on the east side of
the pile where various mill buildings were encountered.
The background line (A4) encompasses the entire complex,
including pile and mill. The west end of the site adjoins a
mine and ore-storage location, and, during the survey, it
became quite evident that background closure would not occur
on the west side due to the deposition of ore in that area.
This also applies to the 10 yR/hr line which also encounters
the ore activity at the west" end of the property.
The 40 yR/hr line encloses the pile as well as a major
portion of the mill site. At the south end of the pile,
this line encounters the main roadway into the mill site.
This road is used for ore haulage and has generally elevated
levels, represented by the 40 yR/hr line. This activity is
the reason for the discontinuity in the 40 pR/hr line where
it crosses the road at the southwest corner of the pile.
Several minor hot spots were encountered during the
survey. These locations are evident from the readings shown
on the map.
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SHIPROCK, NEW MEXICO
This uranium mill site is located on the Navajo Reserv-
ation on the south side of the town of Shiprock, New Mexico
adjacent to the south bank of the San Juan River. It was
built by Kerr-McGee Oil Industries and operated from 1954
until 1963. Vanadium Corporation of America operated the
mill until 1968. Tailings produced by the latter operator
were stored in the northeast section of the site and sta-
bilized with soil and river gravel. The remaining tailings
were not stabilized.
The iso-exposure rate lines were constructed from
staked points locating pre-determined delta values. The
background line was located approximately 1400 feet from the
piles on the southeast side of the site and about 800 feet
on the southwest side. It closely follows the fence line of
the ore-storage yard in the northeast and turns to the
north on the north side of the site. The line was terminated
on the north side and the southeast side at the river bluff,
although some tailings are at the base of the bluff. The
10 yR/hr line follows the general shape of the background
line and remains outside the site fence line except for a
small portion in the north. It does not terminate at the
river bluff, but follows the bluff down the entire length of
the site.
Neither the background or 10 pR/hr lines could be
established in the river bottom or across the river, al-
though the strongest winds blow in this direction (north-
east) . The absence of a long downwind tail is probably due
to greater dispersion of the windblown tailings as they are
lifted over the combined height of the stabilized pile and
river bluff.
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FALLS CITY, TEXAS
The mill site is located in Karnes County, Texas, ten
miles southwest of Falls City. Tailings have been impounded
on the site at six different locations and solutions have
been collected in an open pit mine known as Pond #6. Most
of the tailings piles have been covered and seeded as de-
scribed in the Phase 1 report. Records indicate that
2,500,000 tons of ore were processed averaging 0.16 percent
11303. Tailings are estimated to contain 1,020 curies of
Ra-226.
Survey points for the Falls City site were located by
establishing base lines around both the major site and
minor site (pile #3). The base lines were located along
established landmarks and fences. Where necessary, the base
lines were accurately measured to maintain the accuracy of
the survey. Perpendicular traverses were paced from the
base lines and delta measurements were made at specified
intervals (usually 200 feet) until the background delta was
found. Background delta values varied between 3 and 5
because of ore body locations close to the ground surface
throughout the site area.
At the major site, which includes the mill, the back-
ground line encompasses the entire pile, pond and mill area.
The 10 yR/hr line follows the pile contours quite closely at
the north end of the site. On the west and east portions of
the site, the 10 yR/hr line extends 1000 feet from the pile
area and is indicative .of drainage from the piles known to
have occurred in both of these directions. The 40 yR/hr
line gives further definition of these two drainage areas.
The 40 yR/hr line west of pile #5 and east of pile #5 and
the mill area extends away from the pile areas and is di-
rectly related to drainage from the piles in these two
directions.
At the minor site (pile #3), the background line encom-
passes the pile and a stock pond to the east of the pile.
The 10 yR/hr line essentially encompasses the pile but not
the stock pond. The 40 yR/hr line intersects the pile on
the north and south ends and routes around the west side of
the pile. This would be indicative of wind-blown tailings
in the predominant wind direction.
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RAY POINT, TEXAS
The mill site and tailings pile are located in Live Oak
County, Texas, one mile west of Ray Point and 7% miles
northeast of Three Rivers. The tailings disposal area
consists of approximately 50 acres surrounded by a dike 5 to
6 feet high on the north end and 35 feet high on the south
end. The dike consists of compacted native soil and is well
covered with vegetation. The northern portion of the pile
has been stabilized with asphalt and seeded. There is good
plant growth at the present time. The pile consists of
490,000 tons of tailings estimated to contain 230 curies of
Ra-226.
Survey points for the Ray Point site were located by
measuring base lines along portions of the fences and dikes
comprising the site and tailings pile. Perpendicular lines
were paced off from these base lines. Accuracy was main-
tained because of the relatively short distances that were
paced on the perpendiculars.
The background delta value was determined from measure-
ments on site and varies from A3 to A4, which appears to be
a normal variation for the site vicinity. The background
line lies within 400 feet of the pile except in the northeast
sector. The predominant wind direction is from the southeast,
and the survey results indicate windblown tailings reside
close to the pile. The northeast sector background boundary
is probably related to mill operations and ore haulage and
storage rather than to windblown tailings.
The 10 yR/hr line emerges from the pile on the northwest
side, encompasses the mill and ore-storage areas and returns
to the pile on the east side.
The 40 yR/hr line encloses the ore-storage area and a
portion of the mill site. This line intersects a small
portion of the pile on the northeast corner. There is a
small emergence of the 40 yR/hr line on the northwest side
of the pile due to blown tailings. This portion of the line
remains within 75 feet of the pile, traverses approximately
600 feet and then returns to the pile.
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SALT LAKE CITY, UTAH
The Vitro mill site and tailings piles are located near
the intersection of Interstate 15 and 3300 South in Salt
Lake City. Thfe piles cover about 110 acres and contain
approximately 1.7 million tons of tailings with an estimated
Ra-226 inventory of 1380 curies.
The shaded areas on the map represent the general
boundaries of areas which have been developed or which had,
at the time of the survey, obviously been recently disturbed.
In general, gamma measurements were not made in these areas
due to the fact that much of these areas were paved, occupied
by buildings or railroad tracks, or were otherwise considered
unrepresentative. A formal land survey to locate the gamma
measurement points was not made because of the large area
involved and because of the considerable line-of-sight
interference due to buildings and trees. Instead, the
measurement points were located by pacing along and from
streets and railroads, and the locations were transferred to
copies of large-scale aerial photographs obtained from the
county engineering office. The final map was prepared by
tracing from a mosaic of these copies.
Although a few background delta values of one were
obtained, the most consistent background delta for the area
was found to be A2. Therefore, the background line was
established at A3 (See Appendix B).
BACKGROUND LINE
East of the site, the background line parallels the
west side of 1-15. Its maximum easterly distance from the
site is about 800 feet, at 3300 S. South of this street, it
angles to the southwest, and reaches a maximum southerly
distance of about 1200 feet from the site at, and immedi-
ately west of, 700 W. From this point, the line angles
generally northwest, intersects 3300 S at 1000 W, and paral-
lels 3300 S to 1100 W. Much of the area enclosed by this
line south of 3300 S consists of residential, commercial, or
industrial development. As a result, sufficient readings
were not obtained in most of this area to be able to con-
struct the line accurately. In such cases, the inferred
location of the line between available points is indicated
by a dashed line.
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From the 3300 S and 1100 W intersection, the background
line goes north along the east side of 1100 W to the point
where the street ends at the Jordan River. Readings on the
east side of the street were taken in the relatively undis-
turbed field, and were consistently A5. However, on the
west side of the street, which is largely residential devel-
opment, readings were Al and A2. Presumably, factors associ-
ated with the residential use, such as traffic and establish-
ment of lawns, have dispersed and/or incorporated tailings
material into the soil, thus accounting for the abrupt
change in the delta values. The maximum westerly distance
of the line from the site is about 1600 feet.
At the end of 1100 W, the line proceeds north along the
east bank of the Jordan River. This is shown as a dashed
line, since some of the readings are greater than A3, but
readings were not taken west of the river. The grid was
stopped approximately 800 feet north of the confluence of
Mill Creek and the Jordan River. The area from this point
north was not thoroughly surveyed on a grid basis. There-
fore, the background line was constructed due east of this
point, although it might lie somewhat further north had more
readings been taken.
The line angles northwest from a point just west of the
developed area, crosses 900 W, and continues northwest to
the railroad spur. It is shown as a dashed line along a
section of the railroad, because two A6 readings were ob-
tained along the tracks. It is then shown as a dashed line
proceeding east through the developed area and the D & RGW
switchyard, where it connects with the grid points in the
field northeast of the site. The maximum northerly distance
from the site is about 2100 feet.
The construction of the background line (and 10 and
40 yR/h lines, discussed below) was difficult in the northern
sector due to the extensive development in this area. The
few readings which were obtained are considered the least
reliable of all those taken around the Vitro site, because,
even in the undeveloped areas, the ground in many cases had
obviously been disturbed since the mill operations began.
The lines as shown are considered the best estimate of the
situation existing at the time of the survey, although they
are probably not representative of the situation before the
extensive development took place. Undoubtedly, much of the
windblown tailings material in this area has been covered,
rearranged, or removed in the interim.
33
-------
10 yR/HR LINE
On the east side of the site, the 10 yR/hr line roughly
parallels the main D & RGW track, intersecting the D & RGW
switchyard about 400 feet north of Mill Creek. It is then
shown as a dashed line proceeding southwest through the
switchyard. It parallels Mill Creek, then swings north into
the field east of 900 W, and crosses 900 W just north of
Mill Creek. The maximum northerly distance from the site is
about 1000 feet. The same general difficulties discussed
above were encountered in locating the 10 yR/hr line in this
area.
From 900 W, the line angles to the southwest and crosses
Mill Creek about 1300 feet west of the pile. It then angles
to the southeast, crosses at the intersection of 3300 S and
900 W, and obtains a maximum southerly distance of about 900
feet below the center of the tailings pile. The few read-
ings obtained in the developed area (automobile wrecking
yards) south of 3300 S between 700 W and 500 W indicate that
the 10 yR/hr line essentially parallels 3300 S all the way
to the D & RGW overpass, where it connects with the grid
points in the field east of the site.
40 yR/HR LINE
This line closely parallels the 10 yR/hr line all the
way around the site. The same difficulties discussed pre-
viously were encountered in constructing the line in the
northern and southeastern sectors. The maximum distances of
this line from the site are approximately 700 feet to the
north, 500 feet to the east, 600 feet to the south, and 500
feet to the west. The entire mill site and the sewage
treatment plant are included within the 40 yR/hr line.
Although no readings were taken on the property occupied by
the concrete block plant immediately east of the mill site,
readings around it indicate that it is probably not within
the 40 yR/hr line.
34
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GREEN RIVER, UTAH
The mill site and tailings are one-half mile east of
the Green River and one mile east of the town of Green
River, Utah. The tailings cover an area of about eight
acres on a lower bench, 200 feet north of the mill site.
Records indicate the pile contains 123,000 tons of tailings
material containing approximately 20 curies of Ra-226. The
pile has been covered, and diked on the eastern and northern
sides. Some vegetation is beginning to grow on the cover
material.
The survey of the Green River site consisted of locating
the A4 and A8 lines around the pile using a survey instru-
ment. Once a point on the A4 or A8 line was located by
survey, the location was documented by use of a stadia rod
and theodolite. The map was constructed from the survey
data and shows both the A4 and A8 lines with respect to the
pile.
The A4 line on the map is the background line and the
A8 line is the 10 uR/hr line. A 40 yR/hr line was not
determined for this site.
The background line encompasses the entire pile and
mill complex. It extends 1800 feet to the south of the pile
and 1600 feet to the northeast, which is indicative of
extensive migration of windblown tailings.
The 10 yR/hr line encompasses the pile and intersects
the mill site, enclosing process buildings but excluding the
office building and water tank.
35
-------
MEXICAN HAT, UTAH
The Mexican Hat uranium mill site is located approxi-
mately 1.5 miles southwest from the town of Mexican Hat,
Utah on the Navajo Reservation. Texas-Zinc Minerals built
the mill in 1957 and operated it until 1963, and Atlas
Corporation operated it until 1965. During the eight years
of operation, 2.2 million tons of ore was processed, result-
ing in approximately the same tonnage of tailings. These
tailings were impounded in two adjoining piles, covering 18
and 32 acres. The total radium-226 content of the two piles
is approximately 1560 Ci.
The iso-exposure rate lines were constructed from
staked points locating pre-determined delta values. Wind
and water erosion of the tailings has been extensive at this
site. The background line was located 3600 feet away from
the pile on the downwind or northeast side, and closed in to
approximately 900 feet on the northwest side. It extends
out to 1200 feet on the east and southeast side and encom-
passes the mill and ore-storage yards to the south.
The 10 yR/hr line lies approximately 300 feet away from
the pile, except for the north and northeast directions
where it ranges out to 900 feet. It closely follows the
boundaries of the ore-storage and mill yards to the south.
A 40 uR/hr line was established around the northeast
pile and remained close to its east side and ranged out to
800 feet in a northerly direction. It closed to the west
side of the pile and was generally erratic. This is prob-
ably due to previous scraping operations from repairing or
building a base dike on this side of the pile.
36
-------
CONVERSE COUNTY, WYOMING
The Spook upgrader millsite and tailings are located in
a remote area of Converse County about 23 miles north of
Glenrock, Wyoming. The tailings were dumped over the lip of
the open pit mine forming a V-shaped talus slope. The
tailings have not been stabilized in any way. Several
overburden and mine waste piles are also located in the area
and these are stabilized only very sparsely with natural
vegetation. The records indicate 187,000 tons of ore aver-
aging 0.12 percent l^Og were fed to the upgrader. The total
estimated Ra-226 content in the pile is 60 curies.
The majority of the survey points for the Spook site
were located using a theodolite and stadia rod. A few
points were paced where it was not possible to see the
stadia rod because of ridges. The instrument was set up at
four different locations in order to cover the entire area.
The instrument locations were tied to one another using the
instrument and the stadia rod. Instrument readings were
taken at about 200-foot intervals along radials from the
instrument locations.
Tailings and/or mine waste spread, as indicated by the
background line, varies from 600 feet north of the pile to
2200 feet east of the pile and 2400 feet south of the pile.
A small area of hauled tailings was located near the trailer
about 3000 feet south of the pile. An area about 2000 feet
southeast of the pile had slightly elevated readings which
were probably caused by low-grade ore close to the surface.
The 10 yR/hr line varies from 400 feet north of the
pile to 1800 feet east of the pile and 2000 feet south of
the pile. All but one of the overburden and mine waste
piles lie within the 10 yR/hr line. Two small areas of
elevated readings 1100 and 1700 feet south of the pile were
probably caused by low-grade ore close to the surface. The
10 yR/hr line could not be closed in the area of the open
pit, since no readings were taken in the pit.
The 40 yR/hr line varied from 300 feet southwest to
1500 to 1600 feet east of the pile. This location of the
40 yR/hr line was estimated south of the pile because an
insufficient number of readings were taken to properly
37
-------
establish the location of this line around the small mine
waste pile. The 40 yR/hr line could not be closed in the
area of the open pit, since no readings were taken in the
pit.
Extensive tailings spread to the east was caused by the
frequent high winds from the west. The lower level contamin-
ation to the south of the pile is probably the result of the
general spread of the low-level mine waste that was dumped
in that area.
38
-------
INACTIVE URANIUM MILL SITE
MONUMENT VALLEY , ARIZONA
U. S. ENVIRONMENTAL PROTECTION AGENCY
OFRCE OF RADIATION WOG1AWS - 1*5 «G»! f ACUJTT
4 2 UNCORRECTED DIFFERENTIAL GAMMA READING - trft
SURVEY DATE - APRIL 1974
SCALE IN FEET
0 100 ZOO 300 400
DRAWN BY ANA 1-17-75
-------
GAMMA RADIATION SURVEY
INACTIVE URANIUM MILL SITE
TUBA CITY , ARIZONA
U. S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE Of RADIATION riOOKAMS . IAS VEOAS FAdUTT
A 7 UNCORRECTED DIFFERENTIAL GAMMA HEADING - |iR/h
SURVEY DATE - APRIL 1774
SCALE IN FEET
0 200 400 600 800
DRAWN BY ANB 1-17-75
Figure 3
41
-------
GAMMA RADIATION SURVEY
INACTIVE URANIUM MILL SITE
GRAND JUNCTION , COLORADO
U- 5. ENVIRONMENTAL PROTECTION AGENCY
UNCOMECTED DIFFERENTIAL GAMMA READING -
SURVEY DATE - AUGUST 197 1
DRAWN BY
ANB 1-31-75
CITY OF GRAND JUNCTION
Figure 4
43
s i'J INDUSTRIAL DEVELOPMENT INCORPORATED
-------
GUNNISON COUNTY AIRPORT "7
GUNNISON
GAMMA RADIATION SURVEY
INACTIVE URANIUM MILL
GUNNISON , COLORADO
U.S.ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RADIATION PROGRAMS - LAS VEGAS FACILITY
8- UNCORRECTED DIFFERENTIAL
GAMMA READING - pR/h
SURVEY DATE - AUGUST 1974
SCALE IN FEET
0 200 400 600 800
DRAWN BY
ANB 1 10-75
Figure 5
45
-------
! f
GAMMA RADIATION SUKVEY
INACTIVE URANIUM MILL SITE
(NORTH CONTINENT)
SLICK ROCK , COLORADO
U. S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RADIATION PtOOIAMS . LAS VEOAS FACIUTV
• i UNCORRECTED DIFFERENTIAL GAMMA READING - pR/
(• 3 INDICATES POINT LOCATED BY SURVEY - SEE TEXT )
SURVEY DATE . JUNE 1974
SCALE IN FEET
100 200 300 400
DRAWN BY AN8 1 - 24 - 75
-------
GAMMA RADIATION SURVEY
INACTIVE URANIUM MILL SITE
(UNION CARBIDE)
SLICK ROCK , COLORADO
U.S.ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RADIATION PROGRAMS - US VEGAS FACILITY
'• UNCORRECTED DIFFERENTIAL GAMMA READING - pR/h
SURVEY DATE - JUNE 1974
SCALE IN FEET
0 200 400 600 800
DRAWN BY
ANB 1-7 73
Figure 7
49
•;-'-' ;F<5v-3 f
'
-------
, \
03
Ul C
!-• K
0)
00
TOWN OF
RIFLE, COLORADO
U.S.
U. S.
GAMMA RADIATION SURVEY
ABANDONED MILL SITE
RIFLE.COLORADO
ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RADIATION PROGRAMS
LAS VEGAS FACILITY
9 UNCORRECTED DIFFERENTIAL
GAMMA READING - uR/h
SURVEY DATE - AUGUST 1974
SCALE IN FEET
1200 1600
DRAWN BY ANB 11-27-74
-------
CLIFF
CONSTRUCTION AREA
RIFLE.COLORADO 1 MILE
GAMMA RADIATION SURVEY
ACTIVE MILL SITE
RIFLE.COLORADO
.5 UNCORRECTED DIFFERENTIAL
GAMMA READING - li«/h
U. S. ENVIRONMENTAL
PROTECTION AGENCY
OFFICE OF RADIATION PROGRAMS
US VEGAS FACILITY
SURVEY DATE - AUGUST 1974
SCALE IN FEET
300 600 900 1200
DRAWN BY ANB 12-J-74
-------
GAMMA RADIATION SURVEY
INACTIVE URANIUM MILL SITE
FOOTE MINERAL COMPANY
DURANGO , COLORADO
US. ENVIRONMENTAL PROTECTION AGENCY
OFFICt OF RADIATION PROGRAMS - LAS VEGAS FACILITY
UNCOIWECTED DIFFERENTIA! GAMMA READING - ||R/I>
SURVEY DATE - JUNE 1974
-------
RESERVOIR
D
GAMMA RADIATION SURVEY
ABANDONED MILL SITE
MAYBELL , COLORADO
U. S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RADIAHON PROGRAMS - IAS VEGAS FACIUIV
•6 UNCORRECTED DIFFERENTIAL GAMMA READING - nR/h
SURVEY DATE - JULY 1974
SCALE IN FEET
0 500 1000 1500 2000
DRAWN BY ANB 12-2-74
TO HIGHWAY
4
CRAIG 19 MILES
U. S. HIGHWAY 40
R. 94 W 6 tt> P. M. OF COLORADO
\
\
\
\
-------
GAMMA RADIATION SURVEY
INACTIVE URANIUM MILL SITE
NATURITA , COLORADO
U. 5. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF • A NATION FIOOkAMS - IAS VEGAS FACILITY
9 UNCORRECTED DIFFERENTIAL GAMMA HEADING - pR/h
SURVEY DATE - JULY 1974
f 25 M iiiMKl . XX 20
( s .!.5... mm. " ,\\ • . ,;
Figure 12
59
-------
GAMMA RADIATION SURVEY
INACTIVE URANIUM MILL SITE
LOWMAN , IDAHO
U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RADIATION PROGRAMS - LAS VEGAS FACILITY
9- UNCORRECTED DIFFERENTIAL
GAMMA READING - uR/h
SURVEY DATE - AUGUST 1974
SCALE IN FEET
200
400 600
800
DRAWN BY ANB 1-7-75
'WATER TANK
,0
Figure 13
61
TO LOWMAN 'A MILE
^
-------
GAMMA RADIATION SURVEY
INACTIVE URANIUM MILL SITE
(PHILLIPS - UNITED NUCLEAR)
AMBROSIA LAKE , NEW MEXICO
U. S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RADIATION PROGRAMS - LAS VEGAS FACILITY
• 7 UNCORRECTED DIFFERENTIAL
GAMMA READING - pR/h
SURVEY DATE - JUNE 1974
SCALE IN FEET
600
1200
1800
2400
DRAWN BY ANB 1 - 31 - 75
iop|i5oroi>\*ioo
I 'il^'^/MILL
I :''- */
V!Sv"v
\l '" '*"'
5 |4\3 5 7 6 7 82070, fe^O 105^" ^SO {s+T^it *> 8 T'| 7^
^^^^A \ I rL'60 I11 ^f-* DRY-PC^D 'V
302222 4 5 12 5 \7 9 5 8/1^37 ^| -nr^ . -_-r^ , --*^L—, . JL^,^Oi V,°.3.°- ?.2- ^i^^^.- I3 -1?-1?- -6- I1- •?-§-!
-"- - "-"-"- -"=-- - -,- - -<^- -. ^: - ^.-- - - - = =^^. - ------te.- - -r.c------
X
2 9,;K28
32tf/33
Figure 14
63
-------
TOWN OF
I
GAMMA RADIATION SURVEY
INACTIVE URANIUM MILL SITE
SHIPROCK , NEW MEXICO
U. S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RADIATION PROGRAMS - LAS VEGAS FACILITY
7 . UNCORRECTED DIFFERENTIAL GAMMA READING - pR/h
SURVEY DATE - APRIL 1974
SCALE IN FEET
0 500 1000 1500
DRAWN BY ANB 1-11-75
Figure 15
65
-------
GAMMA RADIATION SURVEY
INACTIVE URANIUM MILL SITE
FALLS CITY , TEXAS
• 8 UNCORRECTED DIFFERENTIAL GAMMA READING - |iR/h
U. 5. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RADIATION PROGRAMS - US VEOAS FACILITY
SURVEY DATE - SEPTEMBER 1974
SCALE IN FEET
1000
DRAWN BY ANB 12 -30- 74
-------
GAMMA RADIATION SURVEY
INACTIVE URANIUM MILL SITE
RAY POINT , TEXAS
U. S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RADIATION PROGRAMS - LAS VEGAS FACILITY
UNCORRECTED DIFFERENTIAL
GAMMA READING - pR/h
SURVEY DATE - SEPTEMBER 1974
SCALE IN FEET
0 500 1000
DRAWN BY ANB 11 - 28 - 74
-------
INACTIVE URANIUM MILL SITE
[VITRO)
SALT LAKE CITY , UTAH
US ENVIRONMENTAL FROItCTION AGBJCV
o oo
i SEWAGE TREATMENT PLANT ^ \ \
' '
-------
Figure 19
73
INACTIVE URANIUM MILL SITE
GREEN RIVER,UTAH
-------
MEXICAN HAT , UTAH I MILE
GAMMA RADIATION SURVEY
INACTIVE URANIUM MILL SITE
MEXICAN HAT , UTAH
U. S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RADIATION PROGRAMS - LAS VEOAS FACILITY
3 UNCORRECTED DIFFERENTIAL GAMMA READING
SURVEY DATE - APRIL 1974
0 300 600 900 1200
DRAWN BY ANB 1 - 15 - 75
-------
/ -
i/X1: T°' ' w
»,«» ;-M '3 \
SPOOK MINE
CONVERSE COUNTY,WYOMING
U. S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RADIATION PROGRAMS - LAS VEOAS FACILITY
-------
APPENDIX A
CALIBRATION OF SCINTILLOMETER
The assessment of above-ground exposure rates from
wind-and water-eroded tailings around the tailings pile is
complicated because of interfering radiation from the pile.
In order to compensate for the interfering components,
indirect measurements were made. The measurements were made
by taking two instrument readings at ground level. One
reading was made with a shield interposed between the detec-
tor and the ground surface (closed measurement). The other
reading was made with the shield removed (open measurement).
The difference between the two readings (open minus closed,
or delta (A)) can be related to surface contamination pre-
sent under the instrument.
After the surface contamination has been evaluated over
an area, the above-ground exposure rate can be computed
using conventional calculations and simplifying assumptions.
The relationship between the delta reading and the surface
contamination level, to (pCi 226Ra/cm2) was established by
plotting delta values vs. to under a controlled calibration
procedure. For the calibration, a disc having a radius of
22 inches and depth of one-half inch was filled with assayed
mill tailings. Delta measurements were then made in the
center of the disc. The tailings were then diluted twice
with clean sand, with delta measurements made after each
dilution. This procedure established three points on a
curve relating A to to (Figure A-l) .
Absorbed dose rates were calculated for a point three
feet above the center of a disc with various radii and a
uniform surface contamination of 1 pCi 226Ra/cm2 (with its
progeny in equilibrium) using the following equation:
Dy = 0.254 to Ey ya [E1(yQX) -E1(yQ/ R2+X2 )]
where:
Dy = absorbed dose rate (rads/sec)
to = Ci/m2
Ey = average gamma ray energy per disintegration
(MeV/dis)
79
-------
y = linear energy absorption coefficient for air
a (m-1)
E,(X) = exponential integral
R = disc radius (m)
X = distance above disc center (m)
U = total absorption coefficient for air (m-1)
Absorbed dose rates vs. disc radius are shown in Figure A-2
Delta values corresponding to an above-ground exposure rate
can be obtained from Figures A-l and A-2.
80
-------
100'
I10'
<
1'
10 100 1000
cu (pCi of 226Ra with Its Progeny in Equilibrium)
Figure A-l
Differential Gamma Reading (A) vs Surface Contamination Level (u)
.01
10 100
RADIUS OF DISC (Feet)
1000
Figure A-2
Gamma Absorbed Dose Rate on the Axis (3 feet above disc)
of a Plane Disc from a Uniform Surface Contamination (co)
of 1 pCi/cm2 of 226Ra with its Progeny in Equilibrium
vs Radius of Disc.
81
-------
APPENDIX B
TECHNICAL BASIS OF INTERPRETATION
OF FIELD MEASUREMENTS
NAVAJO NATION AND GREEN RIVER SITES
The background lines around the sites were located by
determining a delta value caused by natural background and
fallout. These values were obtained as close to the site as
possible without adding in a component from tailings on the
ground. Since the Background delta will occur at an infinite
number of places around the sites, one delta unit was added
to it in order to define an inflection point where background
ended and tailings deposition began. For example, if the
highest ambient background delta value was two, tailings
were assumed to be present when a delta three was measured.
The latter was arbitrarily defined as background delta for
a particular site.
The 10 yR/h line was located using the following assump-
tions :
Delta values decreased linearly with increasing
distance near the proximity of the background line.
The exposure rate measured at three feet above an
infinite plane with a uniform surface contamination
of 22°Ra ancj progeny will come from a disc with a
radius of 100 feet. (Calculations indicate that on
a smooth surface, approximately 6570 of the exposure
rate will come from a disc with a 100 foot radius.
However, surface roughness factors will increase the
effective percentage to above 90%.)
Direct or indirect exposure from the pile is not
considered.
- Approximately 100% of the contamination would be
removed from inside the line (i.e., toward the
pile).
The average above-ground residual exposure rate
after decontamination would result from contamin-
ation remaining outside the line. This exposure
rate is assumed to come from a disc having a radius
of 100 feet and its axis 100 feet behind the line.
82
-------
The average distance between the 10 yR/h and the back-
ground lines for the sites is approximately 400 feet. In
cases where the distances exceed 400 feet, the location of
the 10 yR/h line may be slightly underestimated and vice
versa. Since delta decreases with increasing distance from
the sites, a uniformly contaminated plane condition does'not
exist on the outside of the 10 yR/h line. Assuming a linear
decrease of delta from the 10 yR/h line to the background
line over a distance of 400 feet, the delta value 100 feet
behind the 10 yR/h line will be about three. The surface
contamination corresponding to a net delta of three will
result in an above-ground exposure rate of 11 yR/h on a disc
with a radius of 100 feet.
A 40 yR/h iso-exposure rate line was located at the
Tuba City and Mexican Hat sites in case a relaxation of the
decontamination criteria was necessary because of practical
aspects and rough terrain. The average distance between
this line and the 10 yR/h line is approximately 200 feet.
Using the same assumptions as for the 10 yR/h line, the
exposure rate 100 feet behind this line is approximately
35 yR/h. A more precise location of this line was not
possible because pile shine increased the meter readings and
necessitated using a scale factor that could only be inter-
preted to delta increments of five.
ALL OTHER SITES
Survey techniques were changed for the remaining sites
whereby delta measurements were made at increasing distances
from the pile on straight lines or radials. Each radial or
line (where possible) was analyzed to locate background,
10 yR/h and 40 yR/h points. These points on the radials or
lines were then connected from iso-exposure rate contour
lines around the sites.
Delta values for background were determined by examining
radial end point values or by measurements taken as close to
the site as possible, generally in the upwind direction. If
several values of delta were observed for background, the
highest value was used.as the background delta. Tailings
were assumed to be present when measurements were equal to
the background delta plus one delta unit.
In order to locate the 10 yR/h point on the radial, the
delta values for each radial were plotted as a function of
distance from the pile. Each delta value was connected with
a straight line. A delta value corresponding to an exposure
rate of 10 yR/h at three feet above a uniformly surface
contaminated disc with a radius of 100 feet was determined.
83
-------
A point on the radial was located where the averages of the
delta values 100 feet in front of and behind the point plus
the point value equaled the pre-detennined delta value. The
10 yR/h line point was then established 100 feet in front
(toward the pile) of the point used for averaging. The
40 yR/h point was established in the same manner as the
10 yR/h line.
84
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APPENDIX C
RADIOLOGICAL CRITERIA FOR DECONTAMINATION OF
INACTIVE URANIUM MILL SITES*
GENERAL
Radiological criteria for an engineering assessment of
possible remedial actions applicable to uranium mill tail-
ings piles and for the decontamination of inactive uranium
mill sites are provided herein. These criteria are applic-
able to the sites, to their surrounding areas which have
been contaminated by radioactive materials from the sites,
and to buildings in which the materials have been used.
Critical radiation exposure pathways from inactive
uranium mill sites to members of the general population are:
1. Radon escaping from the tailings pile carried by
the wind into habitable structures where the holdup
time is long enough, resulting in buildup of radon
daughters to levels greater than the ambient air.
2. Tailings material used for construction of habit-
able structures can result in a buildup of radon
daughters and increased gamma levels .
3. Gamma rays from tailings material cause-whole body
radiation exposure. This includes not only the
"gamma shine" from the tailings pile that exposes
people living nearby, but also the radiation ex-
posure from tailings material that has been eroded
off the pile onto surrounding land. The mill sites
always show elevated gamma exposure levels because
of contamination by ore, tailings solids, and
process solutions.
99fi
4. Ra, Th, and other radionuclides from tailings
piles can be leached into ground water and there-
after into public and irrigation water supplies .
5. Windblown particulate material (Ra and Th) from the
tailings pile can be inhaled causing a radiation
dose to the lung.
* Prepared by U. S. Environmental Protection Agency,
Office of Radiation Programs, December 1974.
85
-------
Remedial actions may be required on inactive uranium
mill tailings piles to reduce or prevent excess radiation
exposure from radon progeny, gamma radiation, 226Ra> an(j
radioactive particulate material. If tailing material has
been used as a building material, remedial actions may be
required to reduce radon concentrations and/or gamma acti-
vity levels. Remedial actions performed on tailings piles
and decontamination of mill sites and surrounding contamin-
ated areas should result in residual exposures that are as
low as practicable. There is no single permissible exposure
level applicable to all such cases. An evaluation should be
made on a case-by-case basis of the risk involved, balanced
against (1) the cost of reducing the residual contamination,
and (2) the economic effect on alternatives such as restrict-
ing the use of the, land. The result of such an analysis can
be used by all concerned to define the "as low as practicable"
residual level of contamination that will be acceptable and
determine whether restrictions will be required on the use
of any contaminated land.
TAILINGS PILE OR POND
The operation of uranium mills result in the generation
of waste material which is disposed of in tailings piles and
ponds. Environmental contamination has occurred at those
sites where measures were not taken to control the movement
of the radioactive material. In order to restore the envi-
ronmental quality and provide for protection of the public,
such sites should be decontaminated and result in residual
gamma radiation levels which are as low as practicable. For
most situations this would require decontamination of the
area by (1) removal of radioactive material to a location
where the material would be isolated from the biosphere, or
(2) providing sufficient cover such that the resultant gamma
radiation levels are as low as practicable, preferably at
background. However, under certain topographical conditions
and economic considerations wherein complete removal is not
practicable, the residual levels should not exceed 40 yR/hr
above background. This value is arbitrarily chosen for the
purpose of providing an engineering estimate on cleanup of
contaminated areas. It is considered to be sufficiently low
that any expected exposures occurring after any remedial
action taken at this level would not constitute a public
concern. However, this should not be considered as the
final criterion.* The gamma radiation level is the net,
corrected measurement at 3 feet above the ground.
* When all phase II information is complete and the health
impact of remedial actions identified an overall determina-
tion of as low as practicable protection levels can be as-
sessed appropriately. Therefore, the above numbers are
subject to change. 86
-------
For each site a determination should be made of the
radium concentration in the soil. Cleanup should reduce the
soil concentration to less than two times the radium back-
ground specific for the area.
If the radioactive material remains in place and
stabilized, the area should be designated as a controlled
area. Due to the difficulty of controlling radon diffusion
and the existing state-of-the-art of stabilization, the land
should be restricted as to human occupancy and be properly
fenced to limit access.
The 22^Ra activity contribution from the site in
ground or surface water should meet applicable State or
Federal standards.
OPEN LAND AREAS
This area refers to all land beyond the fence of the
sites where tailings are located. As with the tailings
areas, decontamination of the uranium mill site and other
areas contaminated by wind or water eroded tailings should
result in residual gamma levels which are as low as prac-
ticable. Cleanup of the area would require returning of the
windblown tailings material to the site and establishing a
controlled area, or moving all the material to a location
that will isolate the material from the biosphere.
If the residual gamma levels are less than 10 yR/hr
above background, the land may be released for unrestricted
use. If residual levels are equal to or greater than
10 pR/hr above background at a given site a determination
should be made of the radium concentration in the soil.
Cleanup should reduce the soil concentration to no more than
two times the radium background specific for the area.
Under certain topographical conditions wherein complete
removal of tailings is not possible or practicable, the
residual levels should be as low as practicable but should
not exceed 40 UR/hr above background and access should be
controlled. This value is arbitrarily chosen for the pur-
pose of providing an engineering estimate on cleanup of
contaminated areas. The gamma radiation level is the net,
corrected measurement at 3 feet above the ground.
STRUCTURES
It is possible that there will be several industrial
and residential structures where tailings have been utilized
for construction purposes. When it has been determined that
tailings were used in the construction, the lower limits of
the guidelines established by the Surgeon General for struc-
tures in Grand Junction, Colorado, will be used.
87
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
REPORT NO.
2.
3. RECIPIENT'S ACCESSIONING.
4. TITLE AND SUBTITLE
Gamma Radiation Surveys at Inactive Uranium Mill Sites
5. REPORT DATE
ATTPJTST 10/7*5
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Richard L. Douglas and Joseph M. Hans, Jr.
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORG \NIZATION NAME AND ADDRESS
10. PROGRAM ELEMENT NO.
U.S. Environmental Protection Agency
Office of Radiation Programs-Las Vegas Facility
P. 0. Box 15027
_Las Vegas, Nevada 89114
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
Same as above.
13. TYPE OF REPORT AND PERIOD COVERED
FTMAT.
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
This report presents the results of gamma radiation surveys conducted by the
Office of Radiation Programs—Las Vegas Facility (ORP-LVF) of the U.S. Environmental
Protection Agency (EPA) at twenty inactive uranium mill sites in the Western United
States. The purpose of these surveys was to measure the extent to which radioactive
material had been spread into the environment from the sites by the action of wind
and/or water erosion, and by milling activities. The results indicate that hundreds
of acres of land exclusive of the tailings piles have been contaminated to above-
background levels. Some of the contaminated land is private, off-site property.
Survey techniques were developed to locate the spread radioactive materials and
to estimate the gamma exposure rates resulting from them. These measurements were
complicated by the presence of direct gamma radiation from the tailings piles.
Iso-exposure rate lines were located around each site and plotted on site maps to
facilitate site decontamination decisions. These lines, corresponding to post-
cleanup exposure rates of baclcground, 10 microroentgens per hour and 4-0 microroent-
gens per hour and 40 microroentgens per hour, were selected to correspond to current
ORP criteria for decontamination of inactive uranium mill sites.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/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
21. NO. OF PAGES
_97_
13. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (ThisReport)'
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
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