Skyline Abandoned Uranium Mine
Waste Pile Site
Removal Action Report
Navajo Nation, San Juan County,
Utah
TDD No.: TO-02-09-11-01-0006
PAN No.: 002693.2132.01 RF
March 2012
Prepared for:
U.S. ENVIRONMENTAL PROTECTION AGENCY
Region 9
Prepared by:
ECOLOGY AND ENVIRONMENT, INC.
1940 Webster Street, Suite 100
Oakland, California 94612
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able of (ontents
Section Page
1 Introduction 1-1
2 Site Information 2-1
2.1 Site Location 2-1
2.2 Site Description 2-1
2.3 Site Background 2-1
2.4 Previous Investigations 2-2
3 Summary of START Activities, March 2010 Through
October 2011 3-1
3.1 Preconstruction Planning 3-1
3.1.1 Biological and Botanical Surveys 3-1
3.1.2 Cultural Resources Survey 3-1
3.1.3 Drawings and Specifications 3-2
3.1.4 Sampling and Analysis Plan 3-2
3.2 Air Sampling 3-2
3.3 Excavation W ork 3-5
3.3.1 Borrow Area 3-7
3.3.2 Repository Construction 3-7
3.3.3 Arroyo Excavati on 3-11
3.3.4 TSDA Excavation 3-14
3.3.5 TLDA Excavation 3-14
3.3.6 AML Repository Excavation 3-17
3.3.5 Mesa Slope Excavation 3-17
4 Laboratory Results and Gamma Activity Scan Data 4-1
4.1 Background Sampling 4-1
4.1.1 Soil Sampling 4-1
4.2 Correlation Study Between Ra-226 Activity Concentrations in Surface
Soils and Co-located One-Minute Gamma Activity Counts 4-1
4.2.1 Detection Limit Study 4-3
4.3 Unnamed Arroyo Confirmation Surface Soil Sampling and Gamma
Activity Measurements 4-4
4.3.1 Lower Portion of Unnamed Arroyo - UA1 4-4
4.3.2 Upper Portion of Unnamed Arroyo-UA2 4-8
4.4 TSDA Surface Soil Sampling and Gamma Activity Measurements 4-12
4.5 TLDA Surface Soil Sampling and Gamma Activity Measurements 4-16
4.6 AML Surface Soil Sampling and Gamma Activity Measurements 4-20
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Table of Contents (cont.)
Section Page
5 Discussion 5-1
6 References 6-1
Appendix A
Site Photographs A-1
Appendix B
Biological Survey Report B-1
Appendix C
Cultural Resources Report C-1
Appendix D
Drawings and Specifications D-1
Appendix E
Sampling and Analysis Plan, Skyline AUM Waste Pile Site
Removal Action, April 2011 E-1
Appendix F
Air Sampling Data F-1
Appendix G
Geotechnical Testing Data G-1
Appendix H
Liner Testing Documents H-1
Appendix I
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Table of Contents (cont.)
Section Page
Laboratory Analytical Reports and Data Validation Reports for
July through October 2011 Soil Sampling Data 1-1
Appendix J
Histograms of Correlated Ra-226 and Gamma Activity Scan Data.... J-1
Appendix K
Gamma Activity Scan Data and Correlated Ra-226
Concentrations for UA1, UA2, TLDA, and TSDA K-1
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t
ist of l a hies
Table Page
Table 1 Estimated Excavation Volumes, Skyline Mine Waste Pile Site Removal
Action, San Juan County, Utah 3-5
Table 2 Restoration Seed Mix, Skyline Mine Waste Pile Site Removal Action, San
Juan County, Utah 3-11
Table 3 Correlated Radium 226 Concentrations in Surface Soil and Gamma Activity
Measurement Data, UA1, UA2, TLDA, and TSDA, Skyline Mine Waste Pile
Site Removal Action, San Juan County, Utah1 4-2
Table 4 Statistics for Post-Excavation Radium 226 Concentrations Based on
Correlated Gamma Scan Data for UA1, UA2, TSDA, and TLDA, Skyline
Mine Waste Pile Site Removal Action, San Juan County, Utah 4-4
Table 5 Summary of Surface Soil Sample Results for Radium 226 and Associated
Gamma Activity Counts, Lower Arroyo (UA1) Decision Area, Skyline Mine
Waste Pile Site Removal Action, San Juan County, Utah 4-5
Table 6 Summary of Surface Soil Sample Results for Radium 226 and Associated
Gamma Activity Counts, Upper Arroyo (UA2) Decision Area, Skyline Mine
Waste Pile Site Removal Action, San Juan County, Utah 4-11
Table 7 Summary of Surface Soil Sample Results for Radium 226 and Associated
Gamma Activity Counts, Talus Slope Decision Area (TSDA), Skyline Mine
Waste Pile Site Removal Action, San Juan County, Utah 4-14
Table 8 Summary of Surface Soil Sample Results for Radium 226 and Associated
Gamma Activity Counts, Transloading Decision Area (TLDA), Skyline Mine
Waste Pile Site Removal Action, San Juan County, Utah 4-17
Table 9 Summary of Surface Soil Sample Results for Radium 226 and Associated
Gamma Activity Counts, Existing Repository Area (AML), Skyline Mine
Waste Pile Site Removal Action, San Juan County, Utah 4-20
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ist of Figures
Figure Page
Figure 1 Site Location Map 1-2
Figure 2 Site Features Map 1-3
Figure 3 Air Sampling Locations 3-3
Figure 4 Graph of Detected Final DAC Alpha Activity Values at Skyline AUM Waste
Pile Site Removal Project, May through September 2011, Skyline AUM
Waste Pile Site Removal, San Juan County, Utah 3-6
Figure 5 Repository Surface Gamma Activity and Site Features 3-9
Figure 6 Lower Unnamed Arroyo (UA1) Confirmation Sample Locations, RA-226 in
Surface Soils and Associated Gamma Activity Count 3-12
Figure 7 Upper Unnamed Arroyo (UA2) Confirmation Sample Locations, RA-226 in
Surface Soils and Associated Gamma Activity Count 3-13
Figure 8 Talus Slope Decision Area Confirmation Sample Locations, Ra-226 in
Surface Soils and Associated Gamma Activity Count Figure 9 Transloading
Decision Area Confirmation Sample Locations, Ra-226 in Surface Soils and
Associated Gamma Activity Count 3-15
Figure 9 Transloading Decision Area Confirmation Sample Locations, Ra-226 in
Surface Soils and Associated Gamma Activity Count 3-16
Figure 10 Former Navajo AML Repository Surface Gamma Activity and Mesa Slope
Excavation Boundary 3-18
Figure 11 Graph of Selected Ra-226 Activity Concentration and Gamma Activity Count
Correlation Data, Skyline AUM Waste Pile Site Removal Action, San Juan
County, Utah 4-3
Figure 12 Graph of Surface Soil Ra-226 Activity Concentration and Associated One-
Minute Gamma Activity Count, Lower Arroyo (UA1) Decision Area, Skyline
AUM Waste Pile Site Removal Action, San Juan County, Utah 4-7
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List of Figures (cont.)
Figure Page
Figure 13 Graph of Surface Soil Ra-226 Activity Concentration and Associated One-
Minute Gamma Activity Count, Upper Arroyo (UA2) Decision Area, Skyline
AUM Waste Pile Site Removal Action, San Juan County, Utah 4-12
Figure 14 Graph of Surface Soil Ra-226 Activity Concentration and Associated
One-Minute Gamma Activity Count, Talus Slope Decision Area (TSDA),
Skyline AUM Waste Pile Site Removal Action, San Juan County, Utah 4-15
Figure 15 Graph of Surface Soil Ra-226 Activity Concentration and Associated One-
Minute Gamma Activity Count, Transloading Decision Area (TLDA), Skyline
AUM Waste Pile Site Removal Action, San Juan County, Utah 4-19
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t
ist of Abbreviations and Acronyms
AML
AML Repository
AOC
ASTM
AUM
bgs
cpm
Cs-137
DAC
DCGLw
E&E
ERRS
ERS
ft2
GPS
HASL
HDPE
kcpm
mil
MDCR
MSDA
Nal
NNAML
NNEPA
oz
pCi/g
psi
Navajo Nation Abandoned Mine Lands Program
Existing repository area constructed by the AML program in the late 1990s
area of concern
American Society for Testing and Materials
Abandoned Uranium Mine
below ground surface
counts per minute
Cesium-137
derived air concentration
derived concentration guideline level over a wide area
Ecology and Environment, Inc.
Emergency and Rapid Response Services
Emergency Response Section
square feet
Global Positioning System
US Department of Energy Health and Safety Laboratory
high density polyethylene
kilo-counts per minute
thousands of an inch
Minimum Detectable Count Rate
Mesa Slope Decision Area
Sodium Iodide
Navajo Nation Abandoned Mine Land Program
Navajo Nation Environmental Protection Agency
ounce
picocuries per gram
pounds per square inch
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List of Abbreviations and Acronyms (cont.)
QC
quality control
R
Correlation Coefficient
R2
Sum of Square Residuals
Ra-226
Radium-226
Ra-228
Radium-228
RAT
Rapid Assessment Tool
SAP
sampling and analysis plan
SMWP
Skyline AUM Waste Pile
START
Superfund Technical Assessment and Response Team
TDD
Technical Directive Document
Th-230
Thorium-230
TLDA
Transloading Decision Area
TRI
Texas Research International
TSDA
Talus Slope Decision Area
UA1
lower portion of unnamed arroyo
UA2
upper portion of unnamed arroyo
UI
laboratory data rejected due to low abundance
U.S. EPA
United States Environmental Protection Agency
yd3
cubic yards
|iCi
microcuries
|iCi/cc
microcuries per cubic centimeter
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1 Introduction
The United States Environmental Protection Agency (U.S. EPA) tasked Ecology and
Environment, Inc.'s (E & E's) Superfund Technical Assessment and Response Team (START)
to support a U.S. EPA-funded removal action at the former Skyline Abandoned Uranium Mine
(AUM) Waste Pile Site (SMWP) located in the Oljato Chapter of the Navajo Nation (Navajo),
Monument Valley, San Juan County, Utah. The location of the Skyline Mine is shown on Figure
1. Site features are depicted on Figure 2.
In July 2005, the Navajo Nation Environmental Protection Agency (NNEPA) identified multiple
locations at the SMWP site with gamma radiation activity (gamma activity) counts more than
two times above the background level. At the request of the NNEPA, the U.S. EPA and the
START conducted several removal assessments from 2008 to 2011 at the SMWP. The soil
sampling and gamma activity scans conducted during the removal assessments defined several
areas at the SMWP where a removal action would be required to mitigate elevated contaminant
concentrations in soil. Removal assessment work conducted prior to March 2010 is summarized
in the Skyline A UM Waste Pile Removal Assessment Report, Navajo Nation, San Juan County,
Utah (E & E 2010).
The purpose of this document is to summarize the soil removal action and the confirmation soil
sampling conducted in the removal areas. This report also includes a description of assessment
work performed between March 2010 and the start of the removal activities in March 2011.
Removal assessment work described herein was performed by START under technical directive
document (TDD) No. TO-02-09-08-11-0001.
The purpose of the removal work performed by START, the U.S. EPA, and the Emergency and
Rapid Response Services (ERRS) contractor was to reduce elevated contaminant concentrations
in soil; to confirm that residual Ra-226 concentrations in soils remaining after the removal action
were below the site action levels; and to ensure that no off-site migration of airborne
contaminants at unacceptable activity concentration levels occurred during the removal
activities.
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2 Site Information
2.1 Site Location
The former Skyline AUM is located on top of Oljato Mesa (the mesa), approximately 1.5 miles
northwest of Gouldings in Monument Valley, San Juan County, Utah. The SMWP site is located
approximately 700 feet below and east of the former mine at the eastern base of the mesa at 37°
01' 13.99" north latitude, 110° 13' 50.97" west longitude.
2.2 Site Description
The areas of concern with regard to this report are the Skyline AUM, the SMWP site, and
associated residential and pastoral areas east and downgradient from the foot of the mesa. Site
features are depicted on Figure 2. Photographs of the Skyline AUM, the SMWP site, and related
START assessment activities are included in Appendix A.
Approximately five homesites with residential structures are located between 600 feet and 1,800
feet east and northeast of the SMWP site. These residential properties are cross gradient to the
waste piles, and runoff from the portions of the SMWP site that are impacted by mine waste does
not flow through them. Land use in the project area is characterized by a low density of single-
family residences surrounded by open grazing land. Areas near the foot of the mesa are
characterized by talus slopes covered with waste rock and/or waste ore that was pushed over, or
fell from, the top of the mesa where the operating mine was located. Portions of the cliff directly
below the mine are visibly stained a grey-green color from this activity.
The road to the top of the mesa is in poor condition, and therefore access to the top of the mesa is
generally limited to 4-wheel drive vehicles, all-terrain vehicles, or foot traffic. Other than several
former uranium mine sites, miscellaneous barbed-wire fences, and one abandoned hogan, there is
no known permanent infrastructure on the top of the mesa.
2.3 Site Background
Portions of the Navajo Nation are on geologic formations rich in radioactive uranium ores.
Beginning in the 1940s, widespread mining and milling of uranium ore for national defense and
energy purposes on Navajo tribal lands led to a legacy of abandoned uranium mines. The Skyline
AUM is one of approximately 520 AUMs located on the Navajo Nation. During the late 1990s,
portions of the Skyline AUM on top of the mesa were closed by the Navajo Nation Abandoned
Mine Land (AML) program. This work focused on removing immediate physical hazards
including sealing the mine portals, consolidating loose accessible mine waste, and capping it
with uncontaminated fill material. However, due to the steep terrain, residual mine waste at the
eastern edge of the mesa and the bottom of the mesa were not removed during mine closure
activities.
As part of regular mining operations, a gondola was used to transport ore from the Skyline AUM
to the foot of the mesa where it was loaded into trucks for transport to the mill. One area of
documented elevated gamma activity was located approximately 500 feet southeast of the base
of the stained areas of the cliff. This area may have been the transloading area where ore was
transferred from ore cars to trucks for transport to a uranium mill.
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2. Site Information
According to NNEPA personnel, the top of the mesa and the SMWP area are used seasonally
during the spring, summer, and fall by local residents as pastureland for grazing sheep, horses,
and cattle and gathering traditional herbs and plants. Nearby residents have expressed concern to
the NNEPA regarding the potential for wind-blown and water-borne radioactive particles to
migrate from the site and impact their livestock and/or properties.
2.4 Previous Investigations
In 2001, the U.S. EPA Region 9 Emergency Response Section (ERS) demolished one structure
constructed of radioactive stone and located in the residential area east of the SMWP site (E & E
2001).
During a site inspection performed by the NNEPA in July 2005, gamma radiation activity
(gamma activity) counts greater than two times the background level were detected in
approximately 80 locations at the SMWP site. The NNEPA requested assistance from the U.S.
EPA in performing an investigation of the SMWP site and surrounding area to determine the
nature and extent of the contamination and to mitigate any potential impacts to human health
and/or the environment.
Because the uranium present in the mine waste is naturally occurring, it is expected to be in
secular equilibrium with its daughter decay products. The radioisotope radium-226 (Ra-226) was
selected for use as a proxy indicator for all radioisotopes in the uranium decay chain because it is
the only radioisotope in the decay chain with well-established risk versus dose data.
In November 2008, START collected 28 surface soil samples for Ra-226 analysis from two areas
of concern (AOCs) within the SMWP site and performed surface gamma activity scans at the
SMWP site using the Rapid Assessment Tool (RAT) developed by the U.S. EPA. Each RAT unit
was equipped with a Ludlum Model 2241-2 Digital Survey Ratemeter (2241) with a Ludlum
Model 44-10 2-inch diameter sodium iodide (Nal) gamma scintillation detector (2x2), a
Panasonic Toughbook® laptop computer, and a Trimble® Model GeoXT™ Global Positioning
System (GPS) unit. The RAT software developed by the U.S. EPA allows the user to
simultaneously collect and record gamma activity counts and their associated GPS locations and
display this information in real time on the laptop computer.
As part of the removal assessment performed at the site in November 2008, a background area
with similar geology and no known or suspected impacts from mining was also selected. Surface
soil samples and gamma activity scan data were collected at 14 locations within the background
area to allow for a comparison of Ra-226 concentrations and gamma activity counts in soils from
the Skyline AUM. The average background area Ra-226 soil concentration for the 14 samples
was 0.16 picocuries per gram (pCi/g).
The 28 soil samples collected in the two AOCs within the SMWP site during the November 2008
removal assessment activities documented the presence of mine waste that contained Ra-226
above background concentrations at both areas (E & E 2009). These locations were the suspected
former transloading area, designated the transloading decision area (TLDA), and the top of the
talus slope immediately below the mine, designated the talus slope decision area (TSDA).
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2. Site Information
START performed additional removal assessments in July 2009, August 2009, October 2009,
and March 2010, collecting surface and subsurface soil samples for Ra-226 analysis and using
the RAT to collect surface gamma activity measurements at various AOCs of the SMWP site
(E & E 2010). Analysis of the 2008 through 2010 removal assessment data sets indicated that
one-minute surface scans of gamma activity correlated strongly to Ra-226 concentrations in
surface soil samples where Ra-226 concentrations and gamma activity counts were significantly
above background levels. Based on the results of the previous removal assessments at the SMWP
site, the following AOCs (Figure 2) were identified for a removal action: an unnamed arroyo
flowing east and away from Oljato Mesa (Lower and Upper Portions of Unnamed Arroyo- UA1
and UA2); the TSDA and the TLDA at the base of the mesa; an existing mine waste repository
at the top of the mesa (Existing Repository Area or AML Repository); and the slope of the mesa
immediately below the mine and leading to the TSDA (Mesa Slope Area).
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3 Summary of START Activities, March
2010 Through October 2011
The following sections describe field activities performed by the U.S. EPA, the ERRS
contractor, and the START between March 2010 and October 2011. During the soil removal
actions, confirmation soil sampling, associated one-minute gamma activity scans at the
confirmation soil sample locations, and roving surface gamma activity scans of each excavated
AOC were conducted to document that soils impacted with Ra-226 above the action levels had
been effectively removed within the boundaries of the AOCs. Perimeter and work zone air
monitoring were used to document that off-site migration of contaminants at unacceptable
activity concentrations did not occur, and therefore, that there was no unacceptable exposure to
nearby residents, workers, or the general public. Prior to each mobilization, the START updated
the site-specific health and safety plan as needed.
3.1 Preconstruction Planning
3.1.1 Biological and Botanical Surveys
Biologists from E & E and Dodge Environmental LLC (Dodge) conducted biological surveys for
special status species at five areas of the Skyline AUM site on February 24 and 25, 2011. The
results of the survey were included in E & E's March 24, 2011, report titled, Summary of Results
of Biological Surveys for the Skyline Abandoned Uranium Mine Waste Pile Site Removal, Navajo
Nation, San Juan County, Utah (E & E 201 la). A copy of the report is included in Appendix B.
The five areas that were surveyed were identified as Borrow Areas 1 and 2, Repository Area,
Southwest Staging Area, Water Tank Area, and Northeast Area. The biologists verified the
current land use for each area, mapped habitat and vegetation cover types, and recorded locations
of potential special status species resources. No special status plant or animal species were
observed during the field surveys; however, potential signs of two special status wildlife
species, kit fox and banner-tailed kangaroo rat, were found during surveys. The potential kit
fox signs that were found were a large burrow on the western side and potential kit fox tracks
on the eastern side of the Borrow Areas 1 and 2. A potential burrow for banner-tailed kangaroo
rats was found at the northern base of the talus slope in the Northeast Area. Additionally, potential
habitat for Cronquist milkvetch was identified in the Northeast Area (E & E 201 la).
The report concluded that there was little evidence of sensitive plant and wildlife species within
the project area and therefore limited expected impacts on individuals of any sensitive species.
Limited impacts to sensitive wildlife species include temporary loss or disturbance of nesting and
foraging habitat, although many species would be able to move into surrounding areas of the same
habitat where activities are not occurring (E & E 201 la).
3.1.2 Cultural Resources Survey
On November 8 and 9, 2010; December 4, 6, and 29, 2010; and February 21 and 22, 2011,
CSWTA, Inc. conducted a cultural resources inventory survey on approximately 142 acres of
land for the Skyline AUM removal project. The results of the survey are in CSWTA Inc.'s May
12, 2011 report titled, "A Cultural Resources Inventory Survey for the Existing Skyline AUM Site
for Uranium Clean-Up in the Vicinity of Oljato, San Juan County, Utah" (CSWTA, Inc. 2011). A
copy of the report is included in Appendix C.
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3. Summary of START Activities, March 2010 Through October 2011
CSWTA, Inc. carefully examined all exposed ground surfaces and paid special attention to areas
of erosion and deflation. The area was surveyed by sub-parallel pedestrian transects spaced 10-
12 meters apart. No cultural resources, traditional cultural properties, or sacred places were
inventoried during the survey. No collections were made during the survey (CSWTA, Inc. 2011).
3.1.3 Drawings and Specifications
E & E prepared construction drawings and specifications for each of the proposed excavation
work areas and the repository construction at the Skyline AUM. As-built construction drawings
of the repository and the specifications are included in Appendix D.
3.1.4 Sampling and Analysis Plan
Prior to and during mobilization activities, the START prepared the June 2011 Sampling and
Analysis Plan (SAP) titled, "Sampling and Analysis Plan, Skyline Abandoned Uranium Mine
Waste Pile Site Removal Action, Navajo Nation, San Juan County, I //ah" (E & E 201 lb). A copy
of the SAP is included in Appendix E. The SAP described methods and procedures for
collecting, analyzing, and evaluating air samples at the perimeter of work zones and
confirmation soil samples in excavated areas.
3.2 Air Sampling
Prior to commencing dust-generating activities in the contaminated excavation areas, two air
sampling pumps were set up at the perimeter of the work zone and run for approximately 8 to 10
hours (i.e., a standard work day) to establish background alpha and beta activity concentrations
in ambient air. The background air samples were used to establish the COPC activity
concentrations that are naturally occurring in the air unrelated to the removal activities occurring
at the site.
Air sampling was performed during all activities that had the potential to generate dust containing
radioisotopes. In general, three or four air sampling pumps were set up on the perimeter of each
work zone that had the potential to generate contaminated dust. Pumps were located such that at
least one pump was located in a downwind direction. Pumps were set up between the work zone
and the homesites whenever contaminated soils were disturbed on the valley floor. In order to
collect more representative data, the air sampling locations nearest the work zones were moved as
the work area boundaries changed. The locations of various air monitoring stations are depicted on
Figure 3. The dates indicated on Figure 3 correspond to when the sample assembly was put into
service at that location.
In general, immediately prior to the start of work each day, a new 47-millimeter diameter
borosilicate glass-fiber filter was installed in the sample pump. A calibrated flow measurement
device was connected to the filter head. The pump was started and the initial flow rate and start time
were recorded on the field log. After recording the flow, the flow-measurement device was removed
and the sample head was set up to run normally. The sample pump and generator were periodically
checked to ensure that the systems were operating and that loose dust was not accumulating on the
surface of the filter. If dust was observed, the final flow rate was measured and recorded, the filter
was collected for analysis, and a new filter was placed into service. If no loose dust was observed,
the final flow rates were measured and the filters were collected daily at the completion of dust-
generating activities.
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TDD: 09-11-01-0006
Source: ESRI 2010; E&E 2011; Microsoft Virtual Earth 2011
Path: M:\Oakland\Skyline\Maps\MXD\Report\Dec2011\Figure3_Air_Sampling_Locations.mxd
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Figure 3
Air Sampling Locations
Skyline AUM Waste Pile
Site Removal
San Juan County, Utah
rcolugy and environment, Inc.
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3. Summary of START Activities, March 2010 Through October 2011
Air samples were analyzed in the field by counting the gross alpha and beta activity on each
sample filter using a Ludlum Model 3030 Alpha/Beta Counter. The initial and final flow rates
and the run time were used to calculate the total flow and subsequently, the estimated activity
concentrations.
Alpha and beta activity concentrations were compared to the Nuclear Regulatory Commission's
Derived Air Concentration (DAC) Annual Limits on Intake values as listed in Appendix B to 10
Code of Federal Regulations, Part 20. The DAC value is the allowable intake limit for a worker
at a nuclear facility in a typical 2,000-hour work year. Depending on the amount of time that had
elapsed between sample collection and sample analysis, alpha activity concentrations were
variously compared to the values for Ra-226 and thorium-230 (Th-230). Each air sample was
generally counted three times. The first count was typically performed immediately after sample
collection, and the associated DAC from this measurement was compared to the DAC for Ra-
226. Subsequent counts were respectively performed on the next two working days. The final
count of alpha activity for each sample was compared to 10 percent of the DAC value for Th-230
of 3 x 10"12 microcuries per cubic centimeter (|iCi/cc). The DAC for Th-230 was selected
because it was the most conservative DAC value for any radioisotope expected to occur at
detectable levels within the project site. Alpha activity concentrations did not exceed 10 percent
of the DAC value, and no worker exceeded 2,000 hours on site. Final activity concentrations for
beta radiation were within the range of background concentrations for all samples collected. The
data indicated that no unacceptable exposures occurred either within or at the perimeter of the
site, for either alpha or beta radiation. A graph of the estimated DAC based on the final alpha
activity concentration for each sample is shown on Figure 4. Note that not all samples contained
a detectable amount of alpha activity.
Air sampling was generally conducted in accordance with the SAP. One exception was that the
initial sample count was occasionally delayed for up to 24 hours due to rain. The delay was
necessary because the presence of moisture typically attenuates alpha activity on the air filters,
which would bias the results low. Daily air sampling data (i.e., field data sheets) including flow
rate and run time, estimated alpha activity concentrations in ambient air, and other pertinent data
are included as Appendix F.
The air data were reviewed daily by START as part of the data validation process. Seven of the
daily background quality control (QC) samples were slightly below the acceptable range for
background beta activity. The lower limit on background beta concentrations for a minimum 4-
hour sample run time was approximately 41 counts per minute (cpm) and was based on
measurements of background beta activity at the site made prior to the start of contaminated soil
excavation. Background values as low as 39 cpm were occasionally observed during daily
instrument quality control checks. Because the background activity concentrations are subtracted
from the sample beta activity concentrations as part of the estimate of airborne beta activity, the
calculated sample results for beta activity may have been biased high. Thus, the air sample
results are considered to be conservative estimates of alpha and beta activity at these locations.
In addition to the daily review by START personnel, personnel from the U.S. EPA's
Environmental Response Team (ERT) in Las Vegas, Nevada, mobilized to the site from May 16
through May 19, 2011. ERT personnel inspected sampling equipment and procedures and
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3. Summary of START Activities, March 2010 Through October 2011
collected co-located duplicate samples as part of a quality assurance and quality control program
intended to validate methods and procedures. No major exceptions to the SAP or problems with
the air sampling program were noted. Two relatively minor suggestions were made and
immediately implemented. The first recommendation was to not analyze wet samples, because
the presence of moisture on the sample filter can attenuate alpha activity. The second
recommendation was to determine the activity count per unit time (e.g., alpha count rates above
500 counts per minute for an eight-hour sampling period) that would indicate an actual or
potential exceedance of the DAC for radon-222, Ra-226, or Th-230 and post the information in a
prominent location near the samplers. It was also suggested that the contact information for the
START and ERRS project managers and health and safety officers be posted on the same form
with instructions to immediately notify those personnel if an exceedance occurred. The
information was posted in the field laboratory.
3.3 Excavation Work
Excavation work began on March 28, 2011, and continued in various phases until September 20,
2011. Repository construction, final grading and capping, and restoration and stabilization
activities continued until approximately October 15, 2011. Approximately 27,148 cubic yards
(yd3) of contaminated soil were excavated from the various decision areas and placed in the
constructed repository. The estimated volume excavated from each decision area is included on
Table 1. Approximately 20,000 yd3 of the contaminated material was moved from the valley
floor to the top of the mesa using a "skyline" system. The skyline system utilized a top-loading,
bottom-dumping, pneumatically-activated, 4 yd3-capacity hopper bucket suspended on steel
cables (see photos in Appendix A). The skyline hopper bucket was able to move an average of
approximately 380 yd3 per day from the stockpile at the base of the mesa to trucks waiting at the
top of the mesa.
Table 1 Estimated Excavation Volumes, Skyline Mine Waste Pile Site Removal Action,
San Juan County, Utah
E & E Project No. 002693.2132.01 RF
TDD No. TO-02-09-11-01-0006
Excavation Source
Dates Material Transported
to Repository
Estimated Excavation Volume
(yd3)
AML
6/1/11-6/9/11
4540
TLDA
7/25/11-9/20/11*
1800
TSDA
7/25/11-9/20/11*
4000
UA1 and UA2
7/25/11-9/20/11*
14612
Mesa Slope
6/20/11-7/21/11
2196
TOTAL
27148
Notes:
*Soil excavated from the TLDA, TSDA, UA1, and UA2 was stockpiled in the North Stockpile before being
transported to the repository on the indicated dates.
yd3 = cubic yards
AML = existing repository area
TLDA = transloading decision area
TSDA = talus slope decision area
UA1 = lower unnamed arroyo decision area
UA2 = upper unnamed arroyo decision area
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5.00E-13
Figure 4: Graph of Detected Final DAC Alpha Activity Values at Skyline AUM Waste Pile Site Removal Project, May through
September 2011, Skyline AUM Waste Pile Site Removal, San Juan County, Utah
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TDD No: TO-02-09-11-01-0006
PAN No: 002693.2132.01RF
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ecology and environment, inc.
3. Summary of START Activities, March 2010 Through October 2011
3.3.1 Borrow Area
Clean fill soil and rock used to construct and repair roads and the repository were excavated from
a borrow area located approximately '/2-mile north of the former mine site on top of Oljato Mesa
(Figure 2). Approximately 35,000 yd3 of material were excavated from the borrow area for use
as bedding material, general fill, or rock armoring. A mechanical power-screen was used to
segregate the appropriate gradation of rock or soil. Although originally proposed for use and
included in the cultural resource and biological surveys, the potential borrow area located on the
north side of the access road was not used or disturbed.
3.3.2 Repository Construction
Soils contaminated above the applicable action level were excavated and placed in a repository
constructed on top of Oljato Mesa approximately 400 feet south of the former mine. As-built
construction drawings for the repository, including survey drawings of the foundation's surface
and the final surface, are included in Appendix D. Excavation for the repository foundation
occurred from about April 4, 2011, until approximately May 19, 2011. Not all locations were
excavated to the proposed depth due to the presence of hard rock in the bottom of the repository.
Upon reaching final excavation depths, an 18-inch-thick layer of screened soil (bedding material)
was placed on the bottom of the excavation. The material was compacted using a vibrating
sheep's-foot compactor (grid-roller). In-place soil density and moisture testing using American
Society for Testing and Materials (ASTM) D6938 was performed by Geomat Inc., Farmington,
New Mexico, to ensure a minimum of 90 percent relative compaction was achieved. The density
and moisture testing were also used to develop a method specification for watering and
compaction that was subsequently used during placement of compactable fill materials (i.e.,
bedding material and general fill material). Copies of the geotechnical test data are included as
Appendix G.
After installing the bedding material, Northwest Linings and Geotextile Products Inc., of Kent,
Washington (Northwest Linings), mobilized to the site and began installing the lower geotextile
membrane. The lower geotextile membrane (geomembrane) consisted of: 1) a bottom layer of
16-ounce (oz) per square yard geotextile fabric; 2) a middle layer of 60-thousandths of an inch
(mil) thick high density polyethylene (HDPE) membrane textured on both sides; and 3) and an
upper layer of 200-mil thick drainage layer. The drainage layer consisted of a plastic mesh
covered on both sides with by an 8-oz per square yard geotextile fabric.
During the installation of the HDPE liner, trial seams were made and test coupons were cut from
them. Destructive seam-strength testing was performed on at least four trial double-wedge
welded seams prior to each shift and after lunch each day.
After installing the HDPE layer and prior to installing the drainage layer, all double-wedge
welded seams were tested by sealing the seam, then pressurizing the interstitial space with air to
a minimum of 40 pounds per square inch (psi) for at least five minutes in accordance with the
construction specifications. Upon achieving a passing test result (i.e., less than 3 psi drop in five
minutes), the opposite end of the seam was cut in the presence of the engineer. An immediate
drop in pressure at the gauge end indicated the air channel in the seam was continuous. Extrusion
welded seams were tested for leaks by brushing them with soapy water and then applying a
vacuum using a standard vacuum box apparatus. After verifying that the seam was under a
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3. Summary of START Activities, March 2010 Through October 2011
minimum of 5 inches of mercury vacuum, Northwest Linings and START inspected the area for
bubbles that would indicate leaks. In both of the above cases, small leaks were occasionally
found, repaired, and retested until a passing result was achieved. Copies of the field testing forms
and panel layout diagrams are included in Appendix H.
Destructive testing of the installed double-wedge welded seams was also performed. Northwest
Linings cut 10 sections of seams selected at random and submitted them under chain-of-custody
control to Texas Research International (TRI) for material and seam testing. Tests performed
included: tensile strength by ASTM D638, thickness by ASTM D5994, puncture strength by
ASTM D 4883, tear resistance by ASTM D 1004, and weld strength in peal and shear by ASTM
D6932. All seams and materials exceeded the minimum construction specifications. Liner test
data are included in Appendix H.
To prevent storm water runoff from eroding cover material and potentially exposing
contaminated soils, an HDPE-lined drainage channel was constructed along the eastern and
northeastern edge of the repository. The lined portion of the channel was approximately 450 feet
long. The channel's location is depicted on Figure 5. Down gradient from the repository, the
channel was excavated into native soil and rock in order to route runoff to an existing arroyo on
the northwest side of the repository.
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Project#: 002693.2132.01 RF
TDD: 09-11-01-0006
¦ t • . * .*>,•- ** • r-* '
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Source: E&E 2011; Microsoft Virtual Earth 2011
Path: M:\Oakland\Skyline\Maps\MXD\Report\Dec2011\Figure5_Repository_Surface.mxd
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• 14846-19960
• >19961
Ra-226 Concentration
pCi/g-Picocuries per gram
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(Counts per Minute)
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>5.0
>19961
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Figure 5
Repository Surface Gamma
Activity and Site Features
Skyline AUM Waste Pile
Site Removal
San Juan County, Utah
ecology and environment, inc.
Citrtal Erhronmerra Sp«oa*Hr
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ecology and environment, inc.
3. Summary of START Activities, March 2010 Through October 2011
After installing and testing the lower geomembrane layer, 4-inch-diameter 0.020-inch slotted
Schedule 40 polyvinyl chloride pipe was installed parallel to the berm in the lowest
(southwestern) portions of the repository. The slotted pipe was wrapped in a semi-permeable
pipe-sleeve then connected to a solid pipe that penetrated the berm. All pipe connections were
solvent-welded. A pipe-boot was manufactured from the 60-mil HDPE then installed and sealed
around the pipe using butyl mastic, neoprene gaskets, and pipe clamps. The pipe-boot was
subsequently extrusion-welded to the interior surface of the HDPE liner to form an integral,
water-tight system. The extrusion welds were tested using the vacuum box method. Upon
completion of the repository, a riser pipe, 4-inch diameter ball-valve, and threaded cap were
installed on the pipe. An American Association of State and Highway Transportation Officials
HS-20-rated utility vault was installed around the riser and valve assembly. Vaults that receive
the HS-20 certification are rated to withstand loads up to 16,000 pounds with a tire contact area
of 8 inches by 20 inches. The location of the utility vault and riser pipe are shown on Figure 5.
After completing the lower geomembrane layer and piping, a minimum of 18 inches of bedding
material was placed and compacted onto the membrane. The thickness of the bedding layer was
temporarily increased to 30 inches of cover in areas where haul trucks were operating. Once the
bedding material was moisture-conditioned, graded, and compacted, approximately 27,000 yd3
of impacted soils were placed and compacted into the repository in 12-inch to 18-inch-thick lifts.
Upon completion of contaminated soil excavation and disposal activities, an 18-inch-thick layer
of bedding material was placed and compacted onto the repository surface. Northwest Linings
then remobilized and installed the upper geomembrane layer. The upper geomembrane layer
consisted of 16-oz-per-square-yard (16 oz) filter fabric, overlain by 60-mil textured HDPE,
which was overlaid with 12 oz or 16 oz filter fabric.
The upper geomembrane layer was subjected to the same testing requirements used to assess the
lower geomembrane layer. During the HDPE installation, trial seams were made at the beginning
of each day and immediately after breaking for lunch. The seams were tested on site using a
portable tensiometer. All installed seams were pressure or vacuum tested until there were no
apparent leaks. Destructive seam tests were performed on 10 test patches submitted to TRI. Test
results indicated all seams exceeded the minimum requirements. Copies of the test data and
panel layout diagrams are included in Appendix H.
After completion of the liner testing, an 18-inch-thick layer of bedding material was placed,
moisture-conditioned, and compacted into the surface. To prevent burrowing animals from
potentially damaging the liner, a 1-foot-thick layer of 2-inch median diameter to 8-inch median
diameter rock was placed on the bedding material. To limit gamma emissions from the impacted
material and promote evapotranspiration, approximately 30 inches of general fill material was
placed in lifts, moisture-conditioned, and compacted. To limit potential erosion, the drainage
channel and the steeper exterior slopes on the west and northwest sides of the repository were
armored with 4-inch-diameter to 8-inch-diameter rock.
A roving gamma activity scan was performed over the final repository surface using a Ludlum
2241 coupled with a 2-inch diameter Nal gamma-scintillation detector (2x2). The meter and
detector were connected to a Trimble GPS unit and a Panasonic Toughbook® computer using
the U.S. EPA's RAT software. Except for isolated areas in the southern portion of the repository
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3. Summary of START Activities, March 2010 Through October 2011
where liner repairs were in progress, elevated gamma activity greater than about two times
background was not detected.
At the completion of site activities, all new roads constructed at the site were decommissioned,
ripped, and seeded. The seed mix used for re-seeding the decommissioned roadways and the
excavation and borrow areas is listed in Table 2.
Table 2 Restoration Seed Mix, Skyline Mine Waste Pile Site
Removal Action, San Juan County, Utah
E & E Project No. 002693.2132.01 RF
TDD No. TO-02-09-11-01-0006
Seed
Percent
Berber or Palestine Orchard Grass
16
Slender Wheatgrass
28
Rose Clover
14
Sub Clover
14
Zorro Fescue
8
Ettlin's Wildflower Mix
20
3.3.3 Arroyo Excavation
The excavation area in the unnamed arroyo UA1 and UA2 decision areas extended for
approximately 1,600 feet of the channel and varied from about 20 to 100 feet in width.
Excavation depths in the UA1 decision area ranged between 1 foot and 4 feet below ground
surface (bgs), but generally averaged 1 foot to 2 feet bgs. The excavation depth in the UA2
decision area was estimated to be approximately 2.5 feet to 4 feet bgs. Actual excavation depths
exceeded 8 feet bgs in isolated locations in UA2 near the base of the talus slope, but generally
averaged about 3 feet to 4 feet bgs at the upstream end and 1 foot to 3 feet bgs at the downstream
end. A total of approximately 14,612 yd3 of contaminated material was removed from the UA1
and UA2 decision areas and subsequently disposed of in the repository. The estimated volume
excavated from each decision area is included on Table 1. After soil excavation was completed
in the arroyo areas, confirmation soil samples were collected and the RAT unit was used to scan
the final surface for elevated gamma activity. The approximate extents of the excavations in each
decision area are respectively shown on Figure 6 and Figure 7.
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IUA1-001-070811 13.04 110746]
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• 0-13140
O 13141-14845
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Excavation Boundary
N
100 200
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Ra-226 Activity
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UA1-003-070811
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Ra-226 Concentration
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0-3.0
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3.5-5.0
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>5.0
>19961
Figure 6
Lower Unnamed Arroyo (UAi)
Confirmation Sample Locations
RA-226 in Surface Soils and
Associated Gamma Activity Count
Skyline AUM Waste Pile
Site Removal
San Juan County, Utah
1 ecology and environment, inc.
Project#: 002693.2132.01 RF
TDD: 09-11-01-0006
Source: E&E 2011; Microsoft Virtual Earth 2011
Path: M:\Oakland\Skyline\Maps\MXD\Report\Dec2011\Figure6_UAI_Decision_Area.mxd
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Legend
/'. Soil Sample Location
Gamma Activity (Counts per Minute)
• 0-13140
O 13141-14845
• 14846-19960
•' >19961
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Excavation Boundary
N
100
Feet
Soil Sample ID
Ra-226 Activity
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Correlated Gamma
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UA2-71211-005
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Ra-226 Concentration
pCi/g-Picocuries per gram
Correlated Gamma Activity
(Counts per Minute)
0-3.0
0-13140
3.0-3.5
13141-14845
3.5-5.0
14846-19960
>5.0
>19961
Figure 7
Upper Unnamed Arroyo (UA2)
Confirmation Sample Locations
RA-226 in Surface Soils and
Associated Gamma Activity Count
Skyline AUM Waste Pile
Site Removal
San Juan County, Utah
ecology and environment, inc.
Project#: 002693.2132.01 RF Source: E&E 2011; Microsoft Virtual Earth 2011
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ecology and environment, inc.
3. Summary of START Activities, March 2010 Through October 2011
3.3.4 TSDA Excavation
The excavation area for the TSDA was originally estimated to be approximately 16,000 square
feet (ft2) with an excavation depth of approximately 1.25 feet. During removal work, the TSDA
was expanded both laterally and vertically due to the presence of residual mine waste. Final
excavation depths at the top of the talus slope exceeded 8 feet below the original ground surface.
The lateral boundaries were extended to include the upper 200 to 300 feet of the arroyos that
drained the north and south side of the talus slope. The final excavation area was estimated to be
34,123 ft2. The approximate extent of the TSDA excavation area is shown on Figure 8.
Excavation depths within the TSDA typically did not exceed 6 to 8 feet before encountering
bedrock or very large boulders. Some of the large boulders, competent native rock, and/or
bedrock ore bodies in the uppermost portion of the Unnamed Arroyo (UA2) and on top of the
talus slope exhibited relatively high gamma activity readings (up to approximately 145,000
cpm). Whenever possible, loose material was excavated and rock areas that appeared to be native
material but still exhibited elevated gamma activity were covered with clean fill. Due to the steep
terrain and the relative inaccessibility, portions of the elevated areas within the channels and at
the top of the talus slope could not be completely covered. A total of approximately 4,000 yd3 of
contaminated material was removed from the TSDA and subsequently disposed of in the
repository. The estimated volume excavated from each decision area is included on Table 1.
After the initial soil removal action was completed, confirmation soil samples were collected and
the RAT unit was used to perform roving and static gamma activity scans.
3.3.5 TLDA Excavation
The excavation area for the TLDA was originally estimated to be approximately 21,000 ft2 with
an excavation depth of approximately 1.25 feet. During removal work, the TLDA was expanded
to adjacent areas on the north and northwest sides to include areas where contaminated material
was stored and handled prior to being loaded into the skyline. The approximate extent of the
TLDA excavation area is shown on Figure 9. A total of approximately 1,800 yd3 of contaminated
material was removed from the TLDA and subsequently disposed of in the repository. The
estimated volume excavated from each decision area is included on Table 1. Upon completion of
soil disposal activities and demobilization of the skyline system, additional surface soil sampling
and gamma activity scans were performed in the newly included areas to confirm that material-
handling operations had not adversely impacted them. After the soil removal action was
completed, confirmation soil samples were collected and the RAT unit was used to perform
roving and static gamma activity scans.
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|tSDA-072111-003 | 0.65115603
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TDD: 09-11-01-0006
7
| Jsource: E&E 2011; Microsoft Virtual Earth 2011
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l V'i 3 TSDA-072111-012 I 8.6
v :
\ " -T
1 ? ' • r
: > \ I V" ^ '\r
jfc A: « _ * VqajS
.846 ] 12365L
•*—*
d
TSDA-072111-018 ] 0.977 ] 11098
r-
r O «v *
* .
TSDA-072111-01610.651110163H
1 % '
:
Legend
A Soil Sample Location Approximate Talus Slope
_ . , , ... x • 2* Decision Area
Gamma Activity (Counts per Minute) -—¦ D ,
/ v r ' Excavation Boundary
• 0-13140
© 13141-14845
• 14846-19960
• >19961
Feet
Soil Sample ID
Ra-226 Activity
Concentration
(pCi/g)
Correlated Gamma
Activity
(Counts Per Minute)
TSDA-072111-007
3-2
13695
Ra-226 Concentration
pCi/g-Picocuries per gram
Correlated Gamma Activity
(Counts per Minute)
0-3.0
0-13140
3.0-3.5
13141-14845
3.5-5.0
14846-19960
>5.0
>19961
Figure 8
Talus Slope Decision Area
Confirmation Sample Locations
RA-226 in Surface Soils and
Associated Gamma Activity Count
Skyline AUM Waste Pile
Site Removal
San Juan County, Utah
ecology and environment, inc.
-------
¦-«* ~ -
TLDA-101311-016 | 0.334 | 6867I
TLDA-081511-001 11.91 | 7303I
ITLDA-081511-012 11,
lTLDA-081511-005 | 2.14
Project#: 002693.2132.01 RF
TDD: 09-11-01-0006
s. * # • /
_ 'v V. • —— , t • " ¦
[ ' \T ':^L * • -y' - - ^TLDA-i^-022 10.293 I 647s]
' x | TLDA-10J311-0201 ^1416974}—A _ /\
Source: E&E 2011; Microsoft Virtual Earth 2011
Path: M:\Oakland\Skyline\Maps\MXD\Report\Dec2011\Figure9_TLDA_Decision_Area.mxd
B
• yjTLDA-™3H^^]0349] 6959^
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• ^V
^SjSTLDA-081511-013 ] 0.598 ] 7962IHC I
I^BTLDA-081511-014 ] 0.489 ] 7519
b ' «*7#v- '
TLDA-0S1511-002 | 0.268 | 7155I
• *. *
^PJtLDA-081 511-009 | O.334 | 6817^;
¦ ^ ' f—-— —
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' v • HTLDA-101311-019 I 0.362 I 6615 ¦ •
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• I 1 —|
•^Jg|TLDA-101311-018 ] O.355 ] 6653H
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r8 l r>-»
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lTLDA-081511-003 | 0.917 | 8430I
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2 ! • *
Pii-nS'ic-ii-nn-j l r\ l Smfil
ITLDA-O8I5II-OIO | O.464 | 8786
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: &
1
0810.458181741
~ • •• • »
' ¦ . v *;„•'. -V '
: : :
Legend
/'. Soil Sample Location
Gamma Activity (Counts per Minute)
• 0-11435
o 11436-13140
• 13141-19960
• >19961
r-> Transloading Decision Area
Excavation Boundary
• # 9 « Material Stockpile Area
Soil Sample ID
Ra-226 Activity
Concentration
(pci/g)
Correlated Gamma
Activity
(Counts Per Minute)
TLDA-081511-002
0.268
7155
N
100
Feet
Ra-226 Concentration
pCi/g-Picocuries per gram
Correlated Gamma Activity
(Counts per Minute)
0-2.5
0-11435
2.5-3.0
11436-13140
3.0-5.0
13141-19960
>5.0
>19961
Figure 9
Transloading Decision Area
Confirmation Sample Locations
RA-226 in Surface Soils and
Associated Gamma Activity Count
Skyline AUM Waste Pile
Site Removal
San Juan County, Utah
ecology and environment, inc.
Citrtal Erhronmerra Sp«oa*Hr
-------
E
ecology and environment, inc.
3. Summary of START Activities, March 2010 Through October 2011
3.3.6 AML Repository Excavation
Excavation activities within the AML Repository initially proceeded in 1-foot lifts. After each
foot of soil was excavated or when visible mine waste appeared to have been removed, the
excavated areas that could be safely accessed on foot were traversed by a START carrying the
RAT in order to collect surface gamma activity measurements. Based on the results of the
gamma activity scan, additional soils were excavated as necessary in 0.5- to 1-foot-thick
increments. During excavation work, it became apparent that the amount of loose accessible
mine waste buried in the AML Repository was less than the originally estimated 9,000 yd3.
Excavation depths within the AML Repository decision area typically did not exceed 4 to 5 feet
before encountering bedrock. Portions of the bedrock appeared to be the topographical low end
of the ore body and exhibited relatively high gamma activity readings (up to approximately
700,000 cpm). No attempt was made to remove the native bedrock/ore material. Instead, ERRS
staff removed the remainder of the loose impacted material and then covered the ore bodies to
the extent possible with a minimum of 3 feet of clean fill material. Due to the terrain (i.e., an
overhanging rock shelf and nearly vertical slopes), some portions of the ore body were not able
to be completely covered. A total of approximately 4,540 yd3 of contaminated material was
removed from the existing AML Repository and subsequently disposed of in the newly
constructed repository. The estimated volume excavated from each decision area is included on
Table 1. After soil excavation was concluded, confirmation soil samples were collected and the
RAT unit was used to scan the final surface for elevated gamma activity. The approximate extent
of the AML excavation and other site features are shown on Figure 10.
3.3.5 Mesa Slope Excavation
The Mesa Slope Decision Area (MSDA) included the steeply sloped areas with residual mine
waste located east and northeast of and below the former mine area and AML repository. Soils
were removed from this area using either a long-reach excavator or a l-yd3-capacity drag bucket
that was operated using a skyline system. The skyline system was used to scrape ore from the
Mesa Slope area from about June 20 through July 23, 2011. After July 23, 2011, the bucket on
the skyline system was replaced with a large 4-yd3-capacity bottom-dump (hopper) bucket, and
the skyline system was used to haul soil from the valley floor to the AML repository.
Approximately 2,196 yd3 of impacted material were removed from the slope and hauled to the
repository for disposal. The estimated volume excavated from each decision area is included on
Table 1. The approximate lateral extent of the excavated area is depicted on Figure 10. Due to
the extremely steep slopes (approximately 50 to 60 degrees), uneven terrain, and adjacent
vertical cliff face, not all visible mine waste was removed from this area. Due to concerns for
worker safety, no attempt was made to scan or sample the MSDA; however, based on visual
evidence, an estimated 85 to 90 percent of the original volume of mine waste was removed.
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TDD No. TO-02-09-11-01-0006
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|aML-100211-01 | 0.582113210I
|AML-100211-02 I 0.688 11571 o|
|AML-100211-06 I 0.648 112396]
|AML-100211-03 11-54 115795BJ
Project#: 002693.2132.01 RF
TDD: 09-11-01-0006
Source: E&E 2011; Microsoft Virtual Earth 2011
Path: M:\Oakland\Skyline\Maps\MXD\Report\Dec2011\Figure10_Navajo_AML_Repository.mxd
;.v
^^AML-100211-051 0.591126516
AML-100211-04 ] 0-753 115921
v
Legend
/\ Soil Sample Location
Approximate Perimeter of the
Navajo Nation Abandoned Mine
Lands Program Repository Excavation
Gamma Activity (Counts per Minute)
• 0 -19960 /T*\. MeSa Sl°pe Decision Area (MSDA)
© 19961-30000
• 30001-100000
• >100000
' Approximate Excavation Boundary
Soil Sample ID
Ra-226 Activity Concentration
pCi/g- Picocuries per gram
Correlated Gamma
Activity
(Counts Per Minute)
AML-100211-02
0.688
15710
N
50
Feet
Figure 10
Former Navajo AML Repository
Surface Gamma Activity and
Mesa Slope Excavation Boundary
Skyline AUM Waste Pile
Site Removal
San Juan County, Utah
ecology and environment, inc.
GtWaJli
-------
4 Laboratory Results and Gamma
Activity Scan Data
Soil samples collected were analyzed by General Engineering Laboratories (GEL), Charleston
South Carolina, for Ra-226 by gamma spectroscopy with ingrowth by U.S. Department of
Energy Health and Safety Laboratory (HASL) Method 300.4.5.2.3, a modification of EPA
Method 901.1. Surface soil gamma activity was measured in the field using a RAT equipped
with a Ludlum Model 2241 or 2221 meter and a Ludlum Model 44-10 2x2 detector.
Soil samples were collected and analyzed in accordance with the SAP. Disposable soil sampling
equipment was used to collect the samples; therefore, equipment rinse blanks were not collected.
All data were validated by a qualified chemist and, except where noted in the specific cases
discussed herein, found to be suitable for the uses intended. Excluding duplicates, a total of 102
surface soil samples were collected and analyzed. The chemist noted the presence of relatively
low concentrations of radium-228 (Ra-228) in approximately 54 soil samples and cesium-137
(Cs-137) in approximately 10 samples. The presence of Ra-228 is likely a decay product of
naturally occurring thorium-232 and attributable to natural sources. Detected concentrations of
Ra-228 ranged from 0.016 pCi/g to a maximum of 1.5 pCi/g and were greatest in the samples
collected from the former AML Repository area. Detected concentrations of Cs-137 ranged from
0.016 to 0.11 pCi/g. The presence of Cs-137 in surface soils is most likely attributable to historic
fallout from above-ground atomic weapons testing conducted by the United States Military at
either the Nevada Test Site or in New Mexico.
4.1 Background Sampling
4.1.1 Soil Sampling
During the November 2008 and August 2009 removal assessment activities, the START
performed one-minute gamma activity counts and collected co-located soil samples from the
surface and at 1 foot bgs at 14 locations within a background area with similar geology to the
Skyline AUM site and no known or suspected impacts from mining. A summary of the Ra-226
concentrations in surface soil and associated surface gamma activities from November 2008 and
August 2009 are summarized in the Skyline A UM Waste Pile Removal Assessment Report,
Navajo Nation, San Juan County, Utah, dated May 25, 2010, and prepared by Ecology and
Environment, Inc. (E & E 2010). The average concentration of Ra-226 in surface soil samples
from the background area was 0.16 pCi/g during the 2008 surface soil sampling event and 0.260
pCi/g during the 2009 subsurface soil sampling event (E & E 2010).
4.2 Correlation Study Between Ra-226 Activity Concentrations in
Surface Soils and Co-located One-Minute Gamma Activity
Counts
As part of the data evaluation process, detected Ra-226 soil activity concentrations between 2
pCi/g and 5.35 pCi/g and their associated one-minute gamma activity counts were selected for
use in a correlation study. Except where field notes suggested an obvious bias due to sample
geometry, all samples in the selected range were used in the study. The purpose of the study was
to develop an equation that allows the user to predict the surface soil Ra-226 activity
concentration based on roving gamma activity scan data. The range of sample concentrations
was selected because it bounds the applicable range of project-specific action levels (i.e., action
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4. Laboratory Results and Gamma Activity Scan Data
levels ranged from 2.5 to 5.0 pCi/g). The purpose of selecting this range is to promote a higher
degree of confidence in the correlation between observed gamma activity and Ra-226 at
concentrations near the action levels. It was not considered necessary or useful to have strong
correlations between data sets for observed gamma activity levels or activity concentrations that
are obviously well below or well above the action level. The selected samples and the associated
gamma count data are listed in Table 3. A graph of the correlation between data sets is shown on
Figure 11. As shown on the table, the correlation coefficient (R) between data sets was 0.913,
suggesting a strong positive correlation between data sets at activity concentrations near the
action levels. Similarly, the sum of the squared residuals (R2) was calculated from the trend-line
equation in Figure 11. The calculated R2 value of 0.833 also suggests good correlation between
the data sets and is above the typical U.S. EPA acceptance criteria of 0.70. The trend-line
equation shown on Figure 11 was subsequently used to develop the relationship between gamma
activity and Ra-226 activity concentrations in surface soil that is shown on figures depicting
RAT data for the UA1, UA2, TSDA, and TLDA Decision Areas (Figures 6 - 9). Although no
surface soil samples were collected from the newly constructed repository, this relationship was
also used to estimate Ra-226 concentrations in surface soils in that area (Figure 5).
Table 3 Correlated Radium 226 Concentrations in Surface Soil and Gamma
Activity Measurement Data, UA1, UA2, TLDA, and TSDA, Skyline
Mine Waste Pile Site Removal Action, San Juan County, Utah1
E & E Project No. 002693.2132.01 RF
TDD No. TO-02-09-11-01-0006
Radium 226
Associated Gamma Activity
Sample ID
(PCi/g)
Count (one-minute count)
UA2-71211-002
2.08
11998
UA2-71211-005
2.13
11007
TLDA-081511-005
2.14
8803
TSDA-072111-001
2.51
13826
UA2-71211-003
2.72
11995
UA1-018-070811
2.80
10392
UA1-001-070811
3.04
10746
UA2-71511-013
3.14
12047
TSDA-072111-007
3.20
13695
TSDA-072111-002
3.22
15707
UA2-71211-006
3.22
12582
TSDA-072111-010
4.00
18828
TSDA-072111-006
5.20
19882
TSDA-072111-906
5.35
19758
TSDA-072111-008
5.39
23363
R-Correlation Coefficient
0.913
R2-Sum of Squared Residuals
0.834
Notes:pCi/g - picocuries per gram
1. Correlation data includes one-minute gamma activity measurements and corresponding surface soil
concentrations (by HASL method 300.4.5.2.3) for samples with detected activity concentrations
between 2 and 5.35 pCi/g.
Bold -Indicates the detected concentration was above the respective action level
UA1-Lower Unnamed Arroyo Decision Area; UA2-Upper Unnamed Arroyo Decision Area
TLDA-Transloading Decision Area; TSDA-Talus Slope Decision Area
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4. Laboratory Results and Gamma Activity Scan Data
Ra-226 Activity Concentration (pCi/g)
Figure 11 Graph of Selected Ra-226 Activity Concentration and Gamma Activity
Count Correlation Data, Skyline AUM Waste Pile Site Removal Action, San
Juan County, Utah
Notes: Ra-226 - radium 226
pCi/g - picocuries per gram
TDD No. TQ-02-09-11-01-0006 E & E Project No. 002693.2132.01RF
4.2.1 Detection Limit Study
To determine the approximate effective area of detection of the 2x2 gamma detector used to
perform the confirmation surveys, START performed one-minute gamma activity counts using
Cs-137 gamma radiation check sources with stated activities of 1 microcurie (|iCi) and 5 |iCi.
One-minute gamma activity counts were performed at 1-foot incremental distances (0 to 10 feet)
from the check source in each cardinal direction until observed gamma activity levels could not
be distinguished from measured background activity. Background gamma radiation levels were
measured in the same fashion at 2-foot intervals. Based on observed data, the effective range of
detection for gamma radiation in the 1 to 5 |iCi range was between 3 and 5 feet. In order to be
conservative, START used 3 feet as the estimated radius of detection (i.e., 6-foot diameter).
Based on this study, all figures depicting RAT gamma scan data show a 6-foot diameter colored
circle to depict the measured gamma activity.
Roving gamma activity scan data were used in conjunction with the correlation equation to
estimate the Ra-226 concentrations in surface soils in each decision area after excavation.
Statistics for the UA1, UA2, TSDA, and TLDA decision areas are shown below in Table 4.
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4. Laboratory Results and Gamma Activity Scan Data
Table 4 Statistics for Post-Excavation Radium 226 Concentrations Based on
Correlated Gamma Scan Data for UA1, UA2, TSDA, and TLDA, Skyline Mine
Waste Pile Site Removal Action,
San Juan County, Utah
E & E Project No. 002693.2132.01 RF
TDD No.
TO-02-09-11 -01 -0006
Statistics
UA1
UA2
TSDA
TLDA
Number of Measurements
8068
20950
19030
8036
Mean Correlated Residual Ra-226
Concentration (pCi/g)
1.96
1.90
2.31
1.46
Standard Deviation (pCi/g)
0.36
0.54
1.63
0.28
Mean plus 3x
Standard Deviation
3.03
3.51
7.2
2.29
DCGLw (pCi/g)
3.0
3.0
3
2.5
No of Measurements
Above DCGLw
30
446
4042
23
Estimated Excavation Area
(Square Feet)
103788
61957
34123
47017
Minimum (pCi/g)
0.94
0.48
0.73
0.73
Maximum (pCi/g)
3.87
5.83
41.7
4.31
Median (pCi/g)
1.96
1.87
1.9
1.43
Range (pCi/g)
2.93
5.35
40.9
3.58
Quartile 25% (pCi/g)
1.70
1.55
1.46
1.26
Quartile 50% (pCi/g)
1.96
1.87
1.9
1.43
Quartile 75% (pCi/g)
2.20
2.26
2.78
1.62
Quartile 100% (pCi/g)
3.87
5.83
41.7
4.31
pCi/g = picocuries per gram
DCGLw = derived concentration guideline level for a wide area
UA1-Lower Unnamed Arroyo Decision Area; UA2 -Upper Unnamed Arroyo Decision Area
TLDA-Transloading Decision Area; TSDA-Talus Slope Decision Area
4.3 Unnamed Arroyo Confirmation Surface Soil Sampling and
Gamma Activity Measurements
4.3.1 Lower Portion of Unnamed Arroyo - UA1
On July 8, 2011, the START collected confirmation surface soil samples from the lower portion
(UA1) of the unnamed arroyo that receives runoff from the Skyline AUM. Locations for surface
soil samples collected from the UA1 are shown on Figure 6. A summary of the analytical data
for surface soil samples collected from the UA1 is included on Table 5.
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4. Laboratory Results and Gamma Activity Scan Data
Table 5 Summary of Surface Soil Sample Results for Radium 226 and Associated Gamma
Activity Counts, Lower Arroyo (UA1) Decision Area, Skyline Mine Waste Pile Site
Removal Action, San Juan County, Utah
E & E Project No. 002693.2132.01 RF
TDD No. TO-02-09-11-01-01
Associated One-Minute
Radium 226
Method
Gamma Activity Count
Sample ID
(pCi/g)
Detection Limit
(cpm)
UAl-001-070811
3.04
0.164
10746
UA1-002-070811
0.840
0.144
8120
UAl-003-070811
1.87
0.126
9532
UAl-004-070811
1.50
0.114
9834
UAl-005-070811
1.05
0.172
7438
UAl-905-070811
0.810
0.0907
7438
UAl-006-070811
1.80
0.133
9513
UAl-007-070811
1.27
0.0869
8754
UAl-008-070811
0.827
0.0929
7973
UAl-009-070811
1.64
0.108
10347
UA1-010-070811
1.49
0.0818
10055
UAl-011-070811
1.17
0.104
9609
UA1-012-070811
1.27
0.147
8743
UAl-013-070811
1.88
0.133
10260
UA1-014-070811
1.81
0.102
11036
UAl-015-070811
0.813 UJ
0.274
8192
UAl-915-070811
0.714
0.109
7059
UA1-016-070811
1.96
0.178
11103
UA1-017-070811
0.923
0.0829
9118
UA1-018-070811
2.80
0.155
10392
UA1-019-070811
1.16
0.0958
9635
UAl-020-070811
1.87
0.120
11215
UAl-021-070811
0.347
0.0958
7644
UAl-022-070811
0.657
0.101
8008
UAl-023-070811
1.63
0.114
11391
UAl-923-070811
1.77
0.152
11565
UAl-024-070811
1.03 UJ
0.377
11020
MINIMUM (Ra-226)
0.347
7,644
MAXIMUM (Ra-226)
3.04
10,746
AVERAGE
1.41
pCi/g
9,472
STANDARD DEVIATION
0.6
pCi/g
1,379
R-Correlation coefficient
0.721
R2 Sum of squared Residual
0.524
Notes:
Radium 226 concentrations by EML HASL 300, 4.5.2.3
Gamma activity counts by Ludlum Measurements Inc. Model 2241 Ratemeter and Detector Model 44-10 2"x2" Nal
Gamma Scintillator
pCi/g = picocuries per gram cpm = counts per minute
UJ= data value qualified due to low abundance (i.e not detected at the indicated method detection limit)
Results above the area-specific action levels are indicated in bold.
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ecology and environment, inc.
4. Laboratory Results and Gamma Activity Scan Data
The START collected confirmation soil samples, including three duplicate samples, at 24
discrete locations in the UA1. The sample locations were distributed in a series of linear transects
oriented perpendicular to the arroyo channel, with the exception of soil sample location UA1-
024, which was situated in undisturbed soils downgradient of the channel excavation. One-
minute gamma activity measurements were performed at each surface soil sampling location.
The results are included in Table 5.
Ra-226 concentrations in surface samples collected in the UA1 ranged from 0.347 pCi/g to 3.04
pCi/g. A graph of these data is shown on Figure 12. The average concentration for the sample set
was 1.41 pCi/g. One sample (UA1-001-070811) exceeded the site-specific action level of 3
pCi/g with a concentration of 3.04 pCi/g.. Surface one-minute gamma activity counts at the 24
surface soil sample locations ranged from 7.059 kilo-counts per minute (kcpm) to 11.565 kcpm,
with an average of 9.472 kcpm. The correlation coefficient for the Ra-226 laboratory analytical
data for the soil samples and the field-measured gamma activity counts was 0.724 and the R2
value was 0.524, indicating a relatively weak positive correlation between the measurements.
The exact reason for the relatively weak correlation was not evaluated, but previous correlation
studies performed at the site indicate that correlation between Ra-226 concentration and
associated gamma activity data sets is poor when detected activity concentrations of Ra-226 are
less than about 1.5 pCi/g (E&E 2010). At UA1, 15 of the 24 surface soil samples used in the
decision area correlation had measured concentrations of less than 1.5 pCi/g. Although a
qualitative study was not performed, it is hypothesized that the effects of small changes in
topography, solar radiation, and detector geometry have an influence on measured gamma
activity, and thus introduce an unknown amount of error to each measurement. While these
errors occur at both high and low concentrations/gamma activities, their influence is much
greater at low concentrations; the magnitude of the error becomes negligible in comparison to the
stronger gamma field produced by soils with higher (i.e., greater than about 1.5 pCi/g) Ra-226
concentrations.
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4. Laboratory Results and Gamma Activity Scan Data
Figure 12 Graph of Surface Soil Ra-226 Activity Concentration and Associated One-
Minute Gamma Activity Count, Lower Arroyo (UA1) Decision Area, Skyline
AUM Waste Pile Site Removal Action, San Juan County, Utah
Notes: Ra-226 - radium 226
—¦—Radium 226
—«— 1 -Minute Gamma Count
(pCi/g)
12000
K\ .\ '\ ,\ .\ .N K\ ,\ K\ K\ .\ K\ kN kN '\ -N '\ J\ kN .\ .\ K\ \ \ K\
Sample Location
c
10000o
>
"XI
O
8000 ^
E
E
ro
O
6000 |
4000
pCi/g - picocuries per gram
TDD No. TQ-02-09-11-01-0006 E & E Project No. 002693.2132.01RF
The laboratory data were reviewed by qualified chemists as part of the data validation process.
Samples UA1-015-070811 and UA1-024-070811 were qualified due to low abundance and
therefore labeled with the data qualifier UJ. According to GEL's acceptance criteria, all data
except for one sample met their data quality objectives and were considered to be acceptable for
use according to their criteria. Sample LA 1-003-070811 and its laboratory duplicate were
outside the laboratory's range of the acceptable relative percent difference (RPD) requirement of
0 to 20 percent, with a value of 21.9 percent; however, the samples did meet the laboratory's 0 to
3 relative error ratio requirement with a value of 2.04, and the project SAP criteria of within 35
percent RPD. Data were also validated by a qualified START chemist. All data met the
acceptance criteria stated in the project SAP. Laboratory analytical reports and data validation
reports are included in Appendix I.
After excavation work was completed, the START also traversed the entire area on
approximately 4-foot-wide transects carrying the RAT in order to measure and record surface
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4. Laboratory Results and Gamma Activity Scan Data
gamma activity at one-second intervals. The correlation equation shown on Figure 11 was used
to estimate the post-excavation residual concentration of Ra-226 in surface soils based on the
roving gamma activity scan data. Based on the observed gamma activity in UA1, the estimated
median and mean values of Ra-226 were both 1.96 pCi/g and the standard deviation was 0.36
pCi/g. The mean and the median values were approximately equal, suggesting the data are not
skewed. Statistical data for gamma activity results and correlated Ra-226 values are shown in
Table 4. The histogram of the gamma data and the associated estimated Ra-226 concentrations
are included in Appendix J. Gamma activity data collected using the RAT system are included in
tabular form in Appendix K. The histogram supports the conclusion that the data are not skewed
and are approximately normally distributed. Based on the histogram, the minimum detectable
count rate (MDCR) above background is approximately 6.90 kcpm, which corresponds to a Ra-
226 concentration of 1.17 pCi/g. Of the 8,068 sample measurements collected, 30 correspond to
Ra-226 concentrations above 3.0 pCi/g, with a predicted maximum of 3.87 pCi/g. Of the 30
measurements above the action level, 19 of them correspond to concentrations between 3.0 and
3.3 pCi/g.
Based on Figure 6, there was no obvious pattern of elevated activity distribution, although
elevated readings occurred with greater frequency in the southern portion of the decision area.
During the scan work, operators were directed to try to laterally define areas of elevated gamma
activity. In practice this meant that scanning measurements in more contaminated areas were
more tightly spaced and occurred at a higher density and frequency than scanning measurements
made in non-impacted areas with the typical scanning frequency. A preliminary review of the
gamma scan data indicated that measurements tended to be grouped around elevated areas with
greater frequency, suggesting the tabular data, including the mean and median values, and the
total number of elevated measurements for each data set, were likely biased high. START notes
that although it is appropriate for the situation, the practice of defining the lateral extent of the
elevated areas will generally bias the gamma scan statistical data slightly higher, since more
points are collected from contaminated areas. Additionally, due to the steep uneven terrain, it
was not always possible to perform evenly spaced transects when conducting gamma scans,
especially in the TSDA and the upper portion of the UA2 decision area. It is possible that
repeatedly traversing a small contaminated area because accessibility to other areas was not
possible may also have biased measurements. Because of these potential biases, the actual size of
the elevated measurement area is not considered equivalent to the product of the detector area
and the number of elevated measurements, as Multi-Agency Radiation Survey and Site
Investigation Manual (MARSSIM) guidance suggests (MARSSIM 2000). No attempts were
made to estimate or otherwise account for the suspected biases.
4.3.2 Upper Portion of Unnamed Arroyo-UA2
On July 15, 2011, the START collected confirmation surface soil samples from the upper portion
(UA2) of the Unnamed Arroyo that receives runoff from the Skyline AUM. Locations for
surface soil samples collected from the UA2 are shown on Figure 7. A summary of the analytical
data for surface soil samples collected from the UA2 is included on Table 6.
The START collected confirmation soil samples, including four duplicate samples, at 23 discrete
locations in the UA2 distributed in a series of linear transects perpendicular to the arroyo
channel. One-minute gamma activity scans were collected at each of the surface soil sampling
locations.
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4. Laboratory Results and Gamma Activity Scan Data
Ra-226 concentrations in surface samples collected in the UA2 ranged from 0.27 pCi/g to 3.22
pCi/g. The average concentration for the sample set was 1.26 pCi/g. Two samples (UA2-071211-
006 and UA2-71211-013) exceeded the site-specific action level of 3 pCi/g at concentrations of
3.22 and 3.14 pCi/g, respectively. Surface one-minute gamma activity counts at the 23 surface
soil sample locations ranged from 7.641 kcpm to 12.582 kcpm, with an average of 10.558 kcpm.
The correlation coefficient for the Ra-226 laboratory analytical data for the soil samples and the
field-measured gamma activity counts was 0.793 and the R2 value was 0.629, indicating a
relatively weak positive correlation between the measurements. The reason for the poor
correlation is likely attributable to the large proportion of detected sample concentrations that
were less than 1.5 pCi/g. A graph of these data is shown on Figure 13.
The data were reviewed by a qualified chemist at GEL as part of the data validation process.
Except for three samples, all data met the laboratory's data quality objectives. Samples UA2-
071211-904, UA2-071211-011, and UA2-071511-016 were qualified as estimated due to low
abundance and were labeled with the data qualifier UJ. All QC samples met laboratory
acceptance criteria. Data were also validated by a qualified START chemist. All data met the
acceptance criteria stated in the SAP and were considered to be acceptable for the intended use.
Laboratory analytical reports and data validation reports are included in Appendix I.
After excavation work was completed, the START also traversed the entire area on
approximately 4-foot-wide transects carrying the RAT to measure and record surface gamma
activity at one-second intervals. The gamma activity measurements were used to estimate Ra-
226 concentrations using the correlation equation shown on Figure 11. A histogram of the
gamma activity and estimated Ra-226 concentration data is included in Appendix J. A tabular
summary of the gamma activity scan data from the UA2 is included in Appendix K.
The median (1.87 pCi/g) and mean (1.90 pCi/g) estimated Ra-226 concentrations calculated from
the gamma scan data were less than the removal action level of 3.0 pCi/g. The mean and the
median values were approximately equal, indicating the data were not skewed. Statistical data
for estimated Ra-226 values are shown in Table 4. The histogram of the gamma activity and
associated estimated Ra-226 concentration data (Appendix J) supports the conclusion that the
data are not skewed and are approximately normally distributed. Based on the histogram, the
MDCR above background is approximately 6.90 kcpm, which corresponds to a Ra-226
concentration of approximately 1.17 pCi/g. Of the 20,950 sample measurements collected, 446
corresponded to Ra-226 concentrations above 3.0 pCi/g, with a predicted maximum of 5.83
pCi/g. Of the 446 elevated measurements, 68 were greater than 3.5 pCi/g.
Similar to the data for UA1, an informal observation of the coordinates of the elevated
measurements suggested they tended to be grouped around contaminated areas, supporting the
hypothesis that the gamma data may be biased slightly high. As an example, the 14 highest
gamma activity readings corresponded to Ra-226 concentrations ranging from 4.40 pCi/g to the
maximum of 5.83 pCi/g. Of those 14 measurements, 13 were collected within 1 foot of each
other, suggesting the operator was attempting to bound an isolated occurrence of elevated
material (e.g., a chunk of ore). Because of this bias, the actual size of the elevated measurement
area is not considered equivalent to the product of the detector area and the number of elevated
measurements. No attempt was made to estimate or otherwise account for the suspected bias.
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4. Laboratory Results and Gamma Activity Scan Data
Based on Figure 7, there was no obvious pattern of distribution, although elevated readings
occurred with slightly greater frequency in the northern and eastern portions of the UA2 decision
area.
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4. Laboratory Results and Gamma Activity Scan Data
Table 6 Summary of Surface Soil Sample Results for Radium 226 and Associated
Gamma Activity Counts, Upper Arroyo (UA2) Decision Area, Skyline Mine Waste
Pile Site Removal Action, San Juan County, Utah
E & E Project No. 002693.2132.01 RF
TDD No. TO-02-09-11-01-0006
Sample ID
Radium 226
(PCi/g)
Method
Detection Limit
Associated One-Minute
Gamma Activity Count (cpm)
UA2-71211-001
0.908
0.102
10228
UA2-71211-002
2.08
0.160
11998
UA2-71211-003
2.72
0.0952
11995
UA2-71211-004
0.270
0.0906
7641
UA2-71211-904
0.397 UJ
0.242
7851
UA2-71211-005
2.13
0.109
11007
UA2-71211-006
3.22
0.104
12582
UA2-71211-007
0.678
0.103
9778
UA2-71211-008
1.32
0.166
10861
UA2-71211-009
0.853
0.113
9827
UA2-71211-010
1.73
0.133
12477
UA2-71211-011
0.739 UJ
0.320
9191
UA2-71211-012
0.742
0.0965
10582
UA2-71211-912
0.818
0.0813
10454
UA2-71511-013
3.14
0.134
12047
UA2-71511-014
1.85
0.125
10187
UA2-71511-015
1.17
0.0909
11155
UA2-71511-915
1.38
0.116
11343
UA2-71511-016
0.423 UJ
0.123
9513
UA2-71511-017
0.586
0.0827
9234
UA2-71511-018
1.50
0.103
11240
UA2-71511-019
0.505
0.155
9570
UA2-71511-020
1.40
0.141
11848
UA2-71511-920
1.46
0.0961
11928
UA2-71511-021
0.624
0.136
9441
UA2-71511-022
0.703
0.0998
10441
UA2-71511-023
0.745
0.102
10638
MINIMUM
0.27
7,641
MAXIMUM
3.22
12,582
AVERAGE
1.26
pCi/g
10,558
STANDARD DEVIATION
0.82
PCi/g
1,295
R-CORRELATION
COEFFICIENT
0.793
R2-SUM OF SQUARED
RESIDUALS
0.629
Notes:
Radium 226 concentrations by EML HASL 300, 4.5.2.3
Gamma activity counts by Ludlum Measurements Inc. Model 2241 Ratemeter and Detector Model 44-10 2"x2" Nal
Gamma Scintillator
pCi/g = picocuries per gram cpm = counts per minute
UJ = qualified as estimated due to low abundance (i.e. not detected at the method detection limit)
Results above the area-specific action levels are indicated in bold.
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4. Laboratory Results and Gamma Activity Scan Data
Figure 13 Graph of Surface Soil Ra-226 Activity Concentration and Associated One-
Minute Gamma Activity Count, Upper Arroyo (UA2) Decision Area, Skyline
AUM Waste Pile Site Removal Action, San Juan County, Utah
Notes: Ra-226 - radium 226
aH
-Radium 226
(pCi/g)
¦1-Minute Gamma
cv* dp c?*1 c?* ^ 'O' 'O' n*' ^ ^ ^ ^ ^ ^ <0" n'*'
14000
120qg
c
3
O
o
ioog|
o
<
800CE
E
ro
0
o
600C£
4000
pCi/g - picocuries per gram
TDD No. TQ-02-09-11-01-0006 E & E Project No. 002693.2132.01RF
4.4 TSDA Surface Soil Sampling and Gamma Activity Measurements
On July 21, 2011, the START collected confirmation surface soil samples from the TSDA.
Locations for surface soil samples collected from the TSDA are shown on Figure 8. A summary
of the analytical data for surface soil samples collected from the TSDA is included on Table 7.
The START collected confirmation soil samples, including three duplicate samples, at 23
discrete locations distributed in a grid pattern within the TSDA. One-minute gamma activity
scans were collected at each of the surface soil sampling locations. Radium-226 concentrations
in surface samples collected in the TSDA ranged from 0.224 pCi/g to 8.65 pCi/g. The average
concentration for the sample set was 2.43 pCi/g. Eight sample locations (including one duplicate
sample) exceeded the site-specific action level of 3 pCi/g, with exceedances ranging from 3.22
pCi/g to 8.65 pCi/g. Surface one-minute gamma activity counts at the 23 surface soil sample
locations ranged from 8.798 kcpm to 25.255 kcpm, with an average of 14.075 kcpm. The
correlation coefficient between the Ra-226 laboratory analytical data for the soil samples and the
field-measured gamma activity counts was 0.789, and the R value was 0.62, indicating a
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4. Laboratory Results and Gamma Activity Scan Data
relatively weak positive correlation between the measurements. The reason for the poor
correlation is likely attributable to the large proportion of detected sample concentrations that
were less than 1.5 pCi/g. As discussed previously, the observed correlation is poor at low
concentrations and gamma activity levels. A graph of these data is shown on Figure 14.
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4. Laboratory Results and Gamma Activity Scan Data
Table 7 Summary of Surface Soil Sample Results for Radium 226 and Associated Gamma
Activity Counts, Talus Slope Decision Area (TSDA), Skyline Mine Waste Pile Site
Removal Action, San Juan County, Utah
E & E Project No. 002693.2132.01 RF
TDD No. TO-02-09-11-01-0006
Sample ID
Radium 226
(PCi/g)
Method
Detection Limit
Associated One-Minute Gamma
Activity Count (cpm)
TSDA-072111-001
2.51
0.105
13826
TSDA-072111-002
3.22
0.134
15707
TSDA-072111-003
0.650
0.0948
15603
TSDA-072111-004
0.458
0.0977
16825
TSDA-072111-005
7.43
0.158
16556
TSDA-072111-006
5.20
0.160
19882
TSDA-072111-906
5.35
0.153
19758
TSDA-072111-007
3.20
0.120
13695
TSDA-072111-008
5.39
0.166
23363
TSDA-072111-009
7.55
0.185
25255
TSDA-072111-010
4.00
0.130
18828
TSDA-072111-011
0.504
0.162
10357
TSDA-072111-012
8.65
0.156
16831
TSDA-072111-013
2.12
0.126
17849
TSDA-072111-014
0.730
0.106
12022
TSDA-072111-015
0.571
0.107
10045
TSDA-072111-016
0.651
0.0908
10163
TSDA-072111-916
0.623
0.126
10191
TSDA-072111-017
0.606
0.103
9683
TSDA-072111-018
0.977
0.105
11098
TSDA-072111-019
0.429
0.179
9495
TSDA-072111-020
0.425 UJ
0.246
9364
TSDA-072111-021
0.413 UJ
0.219
9139
TSDA-072111-921
0.418 UJ
0.103
9250
TSDA-072111-022
0.224
0.213
8798
TSDA-072111-023
0.846
0.105
12365
MINIMUM
0.224
8,798
MAXIMUM
8.65
16,831
AVERAGE
2.429
pCi/g
14,075
STANDARD
DEVIATION
2.616
pCi/g
4,712
R-CORRELATION
COEFFICIENT
0.789
r2-sum OF SQUARED
RESIDUALS
0.623
Notes:
Radium 226 concentrations by EML HASL 300, 4.5.2.3
Gamma activity counts by Ludlum Measurements Inc. Model 2241 Ratemeter and Detector Model 44-10 2"x2" Nal
Gamma Scintillator
pCi/g = picocuries per gram cpm = counts per minute
UJ = qualified as estimated due to low abundance (i.e. not detected at the method detection limit)
Results above the area-specific action levels are indicated in bold.
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4. Laboratory Results and Gamma Activity Scan Data
Figure 14 Graph of Surface Soil Ra-226 Activity Concentration and Associated
One-Minute Gamma Activity Count, Talus Slope Decision Area (TSDA),
Skyline AUM Waste Pile Site Removal Action, San Juan County, Utah
Notes: Ra-226 - radium 226
^ c?5 cl* ^ c?' c?> hip ^ ^ o? rD' tt> 9^ 6> >• ^ >
rOVOVOvOVOvOVOVOVOVOrOVOVOvOvOVOVOVOrOVOVOVOVOVOVOV'O^
(b
25000
2200C§
o
o
1900C&
'5
1600^
4000
pCi/g - picocuries per gram
TDD No. TQ-02-09-11-01-0006 E & E Project No. 002693.2132.01RF
The laboratory soil sampling data were reviewed by a qualified START chemist as part of the
data validation process. All sample results and procedures met data quality objectives and were
considered to be acceptable for use as stated in the SAP. Samples TSDA-0721-020, TSDA-0721-
021, and TSDA-0721-022 were qualified as estimated due to low abundance and were labeled
with the data qualifier UJ. All QC samples met laboratory acceptance criteria. Laboratory
analytical reports and data validation reports are included in Appendix I.
After excavation work was completed, the START traversed the area on approximately 4-foot-
wide transects carrying the RAT in order to collect surface gamma activity measurements. Due
to the steep, rocky uneven terrain in the TSDA, not all areas could be sampled or scanned.
Additionally, poor geometry between the GPS unit and the associated satellites prevented the
collection of spatial data (coordinates) at some locations close to the mesa. However, because the
sampler was within the boundary of the decision area at the time, these data were collected and
included in the data set. Gamma activity scan data from the TSDA are depicted on Figure 8. The
gamma activity measurements were used to estimate Ra-226 concentrations using the correlation
equation shown on Figure 11. A histogram of the gamma activity and associated Ra-226
concentration data is included in Appendix J. A tabular summary of the gamma activity scan data
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4. Laboratory Results and Gamma Activity Scan Data
from the TSDA is included in Appendix K. Statistical data for estimated Ra-226 values are
shown in Table 4.
As discussed in Section 3.3.4, the ERRS contractor was unable to excavate all impacted material
above the 3.0 pCi/g action level for Ra-226 due to the presence of large, competent, native ore-
bearing rock or bedrock and/or steep topography. In general, although concentrations decreased
by approximately 80 percent, surface Ra-226 concentrations remain above the action level in the
western and northern portions of the TSDA, including the uppermost reaches of UA2 (Figure 9).
The size of this post-excavation residual elevated area was estimated at 18,750 ft2. Smaller
isolated areas of elevated activity were also present in the arroyo that drains the south side of the
talus slope.
Of the 19,030 gamma activity sample measurements collected, 4,042 corresponded to Ra-226
concentrations above 3.0 pCi/g, with an estimated maximum of 41.67 pCi/g. Of the 4,042
samples that corresponded to values above 3 pCi/g, 2,511 were less than 4.0 pCi/g and 3,527
were less than 5.0 pCi/g, suggesting that most of the values were only slightly above the action
level and, based on previous modeling data, unlikely to significantly increase risks to human
health or the environment (E & E, 2010). The median (1.90 pCi/g) and mean (2.31 pCi/g) Ra-
226 concentrations calculated from the gamma scan data were less than the removal action level
of 3.0 pCi/g. The mean value was slightly greater than the median value, suggesting a possible
bias or skew. The histogram of the gamma activity and associated Ra-226 concentration data
(Appendix J) supports the hypothesis that the data are slightly skewed towards the higher
concentrations. There are several potential reasons for the observed skew. The most likely reason
is the bias in the measurement method that was previously discussed. As discussed, once sample
collection personnel observed elevated gamma activity, they spent more time in the elevated
areas relative to other areas in order to define the boundaries of the elevated gamma activity. For
example in the TSDA, 48 of the 53 highest gamma readings were all collected within 1-foot of
each other. These measurements included every estimated Ra-226 activity concentration value
between 14 pCi/g and 41.67 pCi/g. This suggests that one isolated location in the western portion
of the TSDA had material with residual Ra-226 concentrations in the 40 pCi/g range, while all
other areas were less than 14 pCi/g. Based on the histogram, the MDCR was approximately 6.90
kcpm, which corresponds to a Ra-226 concentration of approximately 1.17 pCi/g.
4.5 TLDA Surface Soil Sampling and Gamma Activity Measurements
On August 15, 2011, and October 13, 2011, the START collected confirmation surface soil
samples from the TLDA, located at the foot of the mesa. Locations for surface soil samples
collected from the TLDA are shown on Figure 10. Note that the soil sampling decision area was
expanded to include portions of the material stockpile area located north of the TLDA. This area
was graded and used to stockpile contaminated soil during the removal effort; therefore, it was
included in final confirmation sampling and gamma scanning activities. A summary of the
analytical data for surface soil samples collected from the TLDA is included on Table 8.
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4. Laboratory Results and Gamma Activity Scan Data
Table 8 Summary of Surface Soil Sample Results for Radium 226 and Associated Gamma
Activity Counts, Transloading Decision Area (TLDA), Skyline Mine Waste Pile Site
Removal Action, San Juan County, Utah
E & E Project No. 002693.2132.01 RF
TDD No. TO-02-09-11-01-0006
Sample ID
Radium 226
August 2010
(pCi/g)
Radium 226-
November 2008
& August 20091
(pCi/g)
Method
Detection
Limit
Associated One-Minute
Gamma Activity Count
(cpm)
TLDA-081511-001
1.91
0.562
0.116
7303
TLDA-081511-002
0.268
21.0
0.060
7155
TLDA-081511-003
0.917
24.8
0.0806
8430
TLDA-081511-004
0.487
3.43
0.0616
8073
TLDA-081511-005
2.14
28.1
0.122
8803
TLDA-081511-006
0.833
0.782
0.0782
8409
TLDA-081511-9062
1.04
N/A
0.101
8333
TLDA-081511-007
0.684
1.7
0.103
8026
TLDA-081511-008
0.458
1.6
0.0797
8174
TLDA-081511-009
0.334
2.66
0.075
6817
TLDA-081511-010
0.464
0.974
0.0794
8786
TLDA-081511-011
1.19
8.56
0.0723
9150
TLDA-081511-012
1.58
2.19
0.0947
9286
TLDA-081511-013
0.598
1.05
0.113
7962
TLDA-081511-014
0.489
2.67
0.0652
7519
TLDA-101311-015
0.466
N/A
0.115
7729
TLDA-101311-016
0.334
N/A
0.0983
6867
TLDA-101311-017
0.431 UJ
N/A
0.135
8812
TLDA-101311-018
0.355
N/A
0.0903
6653
TLDA-101311-9182
0.389
N/A
0.0785
6595
TLDA-101311-019
0.362
N/A
0.0757
6615
TLDA-101311-020
0.314 UJ
N/A
0.187
6974
TLDA-101311-021
0.349
N/A
0.0802
6959
TLDA-101311-022
0.293
N/A
0.102
6478
TLDA-101311-023
0.321
N/A
0.0695
6643
MINIMUM
0.268
0.562
pCi/g
6,478
MAXIMUM
2.14
28.1
pCi/g
9,286
AVERAGE
0.68
7.15
pCi/g
7,702
STANDARD
DEVIATION
0.5
9.8
pCi/g
898
R-CORRELATION
COEFFICIENT
0.565
R2- SUM OF SQUARED
RESIDUALS
0.319
Notes: UJ = qualified as estimated due to low abundance (i.e. not detected at the method detection limit)
Radium 226 concentrations by EML HASL 300, 4.5.2.3
Gamma activity counts by Ludlum Measurements Inc. Model 2241 Ratemeter and Detector Model 44-10 2"x2" Nal
Gamma Scintillator
pCi/g = picocuries per gram cpm = counts per minute N/A = not applicable
Results above the area-specific action levels are indicated in bold.
1. Data reported in Ecology and Environment's Skyline AUM Waste Pile Site Removal Assessment Report dated May 25,
2010.
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The START collected confirmation soil samples, including two duplicate samples, at 23 discrete
locations distributed in a roughly triangular grid pattern within the TLDA. In accordance with
the SAP, 14 of the samples were collected from the same geographic locations as the surface and
subsurface samples that were collected during the November 2008 and August 2009 removal
assessments (E & E 2010). The Ra-226 surface activity concentrations as detected during that
previous assessment work are included in Table 8 for comparison. Ra-226 concentrations in
surface samples collected from the TLDA in 2011 ranged from 0.268 pCi/g to 2.14 pCi/g. The
average concentration for the sample set was 0.68 pCi/g. None of the samples exceeded the site-
specific action level of 2.5 pCi/g. The minimum, maximum, and average concentrations
decreased from 0.562, 28.1, and 7.15 pCi/g, respectively, in 2008/2009 to the 2011
concentrations of 0.268, 2.14, and 0.68 pCi/g, respectively.
The soil data were reviewed by a qualified START chemist as part of the data validation process.
Except for two samples, all data met data quality objectives and were considered to be acceptable
for use as stated in the SAP. Samples TLDA-101311-017 and TLDA-101311-020 were qualified
as estimated due to low abundance and labeled with the data qualifier UJ. All QC samples met
laboratory and START acceptance criteria. Laboratory analytical reports and data validation
reports are included in Appendix I.
One-minute gamma activity scans were collected at each of the surface soil sampling locations.
A summary of the one-minute gamma activity counts from the TLDA is included on Table 8.
Surface one-minute gamma activity counts at the 23 surface soil sample locations ranged from
6.478 kcpm to 9.286 kcpm, with an average of 7.702 kcpm. The correlation coefficient for the
Ra-226 laboratory analytical data for the soil samples and the field-measured gamma activity
counts was 0.57 and the R2 was 0.32, suggesting a poor positive correlation between the
measurements. The reason for the poor correlation between Ra-226 concentrations and surface
gamma activity is unclear but, as previously discussed, most likely due to the frequent detection
of relatively low gamma activity and Ra-226 activity concentrations in soil. A graph of these
data is shown on Figure 15.
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4. Laboratory Results and Gamma Activity Scan Data
2.5
10000
—¦—Radium 226
CO
CM
CM
9000 c
6000 |
5000 i
7000 <
8000 >
3
O
o
0
01
E
o
o;
0 -I—I—I—I—I—I—I—I—I—I—I—I—I—I—I—I—I—I—I—I—I—I—I—I—I— 4000
Sample Location
Figure 15 Graph of Surface Soil Ra-226 Activity Concentration and Associated One-
Minute Gamma Activity Count, Transloading Decision Area (TLDA), Skyline
AUM Waste Pile Site Removal Action, San Juan County, Utah
Notes: Ra-226 - radium 226
pCi/g - picocuries per gram
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After excavation work was completed, the START traversed the entire area on approximately 4-
foot-wide transects carrying the RAT system to measure and record surface gamma activity at
one-second intervals. The gamma activity measurements were used to estimate Ra-226
concentrations using the correlation equation shown on Figure 11. A histogram of the gamma
activity and associated Ra-226 concentration data is included in Appendix J. A tabular summary
of the gamma activity scan data from the TLDA is included in Appendix K.
The median (1.43 pCi/g) and mean (1.46 pCi/g) estimated Ra-226 concentrations calculated from
the gamma scan data were less than the removal action level of 2.5 pCi/g. The mean and the
median values were approximately equal, indicating the data were not skewed. Statistical data
for estimated Ra-226 values are shown in Table 4. The histogram of the gamma activity and
associated Ra-226 concentration data (Appendix J) supports the conclusion that the data are not
skewed and are approximately normally distributed. Based on the histogram, the MDCR above
background is approximately 6.50 kcpm, which corresponds to a Ra-226 concentration of
approximately 1.1 pCi/g. Of the 8,036 sample measurements collected, 23 correspond to Ra-226
concentrations above 2.5 pCi/g, with an estimated maximum of 4.31 pCi/g.
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4. Laboratory Results and Gamma Activity Scan Data
4.6 AML Surface Soil Sampling and Gamma Activity Measurements
On October 2, 2011, the START collected confirmation surface soil samples after excavation
was concluded at the existing repository (AML) at the top of the mesa. Locations for surface soil
samples collected from the AML are shown on Figure 10. A summary of the analytical data for
surface soil samples collected from the AML is included on Table 9.
Table 9 Summary of Surface Soil Sample Results for Radium 226 and Associated Gamma
Activity Counts, Existing Repository Area (AML), Skyline Mine Waste Pile Site
Removal Action, San Juan County, Utah
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Sample ID
Radium 226
(PCi/g)
Method
Detection Limit
Associated One-Minute Gamma
Activity Count (cpm)
AML-100211-01
0.582
0.0965
13210
AML-100211-02
0.688
0.0929
15710
AML-100211-03
1.54
0.110
15795
AML-100211-04
0.753
0.0952
15921
AML-100211-904
0.731
0.138
15663
AML-100211-05
0.591
0.118
26516
AML-100211-06
0.648
0.0877
12396
MINIMUM
0.582
pCi/g
12,396
MAXIMUM
1.54
pCi/g
26,516
AVERAGE
0.79
pCi/g
16,459
STANDARD DEVIATION
0.34
pCi/g
4,657
R-CORRELATION
COEFFICIENT
-0.117
R2- SUM OF SQUARED
RESIDUALS
0.014
Notes:
Radium 226 concentrations by EML HASL 300, 4.5.2.3
Gamma activity counts by Ludlum Measurements Inc. Model 2241 Ratemeter and Detector Model 44-10 2"x2" Nal
Gamma Scintillator
pCi/g = picocuries per gram
cpm = counts per minute
Results above the area-specific action levels are indicated in bold.
The START collected confirmation soil samples, including one duplicate sample, at six discrete
locations distributed in a triangular grid pattern within the AML. This number was reduced from
the 14 samples originally proposed in the SAP. The sample frequency was reduced for two
reasons. First, not all contaminated soils were excavated. Some areas were obviously part of the
ore body and/or were indurated native sandstones that exhibited elevated gamma activity levels.
As previously discussed, whenever possible these areas were covered with clean fill imported
from the borrow area. Based on U.S. EPA guidance in the field, it was not considered necessary
to sample imported materials at the same frequency as was proposed in the SAP. However, it
was determined that some sampling was necessary to show that surface soils are not
contaminated and that elevated gamma readings are related to the material beneath or near them.
This would not have been possible using only gamma activity scan data.
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4. Laboratory Results and Gamma Activity Scan Data
The soil sampling data were reviewed by a qualified START chemist as part of the data
validation process. All data met data quality objectives and were considered to be acceptable for
use as stated in the SAP. No data were qualified and no problems or exceptions were noted. All
QC samples met laboratory acceptance criteria. Laboratory analytical reports and data validation
reports are included in Appendix I.
Radium-226 concentrations in surface samples collected in the AML cover material ranged from
0.582 pCi/g to 1.54 pCi/g. The average concentration for the sample set was 0.79 pCi/g. None of
the samples exceeded the site-specific action level of 5 pCi/g. One-minute gamma activity counts
were performed at each of the surface soil sampling locations. Surface one-minute gamma
activity counts at the six soil sample locations ranged from 12.396 kcpm to 26.516 kcpm, with an
average of 16.459 kcpm. The maximum gamma activity readings occurred in the northern
portion of the decision area, near an exposed outcropping of ore. This ore body was immediately
south of the mine portals and beneath an overhanging rock. Due to the overhanging rock, not all
of the ore was covered with fill material.
The correlation coefficient for the Radium-226 laboratory analytical data for the soil samples and
the field-measured one-minute gamma activity counts was -0.117 with an R2 of 0.014, indicating
a very weak negative correlation between the measurements. This result was expected, because
laboratory analysis of the soil samples collected at the ground surface detects the radioactivity in
the actual soil sample, while surface gamma activity scans are capable of detecting buried
radioactive materials in the repository, and/or exposed outcroppings of ore, thus producing
gamma activity counts that are biased high.
After excavation work was completed, the START also traversed the entire area on
approximately 4-foot-wide transects carrying the RAT in order to collect a 100 percent surface
gamma activity scan. Some areas on steep uneven terrain could not be scanned to concerns about
worker safety. Residual areas of elevated gamma activity corresponding to Ra-226
concentrations above 5.0 pCi/g were present in the northern and northeastern portions of the
AML decision area, near ore bodies adjacent to the mesa slope excavation area and the former
mine portals.
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5 Discussion
Daily perimeter and work zone air sampling performed during the excavation work indicated that
gross alpha and beta radiation activity concentrations in air did not exceed allowable levels and
no unacceptable exposures occurred.
One confirmation surface soil sample collected from the lower portion of the unnamed arroyo
(UA1) exceeded the site-specific action level of 3 pCi/g with a concentration of 3.04 pCi/g. Two
confirmation soil samples collected from the upper portion of the unnamed arroyo (UA2)
exceeded the site-specific action level of 3 pCi/g with concentrations of 3.14 and 3.22 pCi/g,
respectively. Based on gamma activity scan data, the average estimated Ra-226 activity
concentration in UA1 is 1.96 pCi/g, and the average in UA2 is 1.90 pCi/g. Relatively small
isolated areas of higher gamma activity that correspond to Ra-226 concentrations up to 3.87
pCi/g are present in UA1, and similar isolated areas corresponding to Ra-226 concentrations up
to 5.83 pCi/g are present in UA2.
Eight confirmation soil samples collected from the TSDA exceeded the site-specific action level
of 3 pCi/g, with exceedances ranging from 3.22 pCi/g to 8.65 pCi/g. Elevated Ra-226
concentrations are present in the northern and western portions of the TSDA, in the steep rocky
areas near the base of the mesa. In general, the ERRS contractor removed loose accessible
material to the extent possible using conventional excavation techniques. Residual
concentrations above the site-specific action level either represent background concentrations of
radioactive materials at the site or were mine waste that could not be excavated because of the
steep inaccessible terrain.
None of the confirmation surface soil samples collected from the TLDA exceeded the site-
specific action level of 2.5 pCi/g. RAT gamma activity data indicate an average surface Ra-226
activity concentration of 1.46 pCi/g, with an isolated maximum of 4.31 p/Ci/g.
None of the confirmation surface soil samples collected from the existing repository (AML)
exceeded the site-specific action level of 5 pCi/g. Portions of this area were filled with 3 to 8 feet
of clean fill material. However, vertically-oriented native ore bodies remain partially exposed
near the mine portals. Similarly, although the mass of contaminated soils in the mesa slope
Excavation Area was greatly reduced, residual amounts of ore and/or waste rock remain on the
steep slope below the mine portals.
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6 References
CSWTA, Inc. 2011. "A Cultural Resources Inventory Survey for the Existing Skyline AUM Site
for Uranium Clean-Up in the Vicinity of Oljato, San Juan County, Utah". May 12, 2011.
Ecology and Environment, Inc. (E & E) 2001. "Navajo Radioactive Hogans Site - Removal
Report", U.S. EPA Region 9 TDD File No. 09-01-02-0008. April 2001.
E & E. 2009. "Skyline AUM Waste Pile Assessment Report, San Juan County, Utah", U.S. EPA
Region 9 TDD File Number 09-08-11-0001. May 18, 2009.
E & E. 2010. "Skyline AUM Waste Pile Removal Assessment Report, Navajo Nation, San Juan
County, Utah". May 25, 2010.
E & E. 201 la. "Summary of Results of Biological Surveys for the Skyline Abandoned Uranium
Mine Waste Pile Site Removal, Navajo Nation, San Juan County, Utah". March 24, 2011.
E & E. 201 lb. "Sampling and Analysis Plan, Skyline Abandoned Uranium Mine Waste Pile Site
Removal Action, Navajo Nation, San Juan County, Utah. April 2011.
MARRSIM. 2000. Multi-Agency Survey and Site Investigation Manual. Prepared by the U.S.
Environmental Protection Agency, the U.S. Department of Defense, the U.S. Nuclear
Regulatory Commission, and the U.S. Department of Defense. Revision 1, August 2000.
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Appendix A
Site Photographs
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Appendix B
Biological Survey Report
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Appendix C
Cultural Resources Report
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Appendix D
Drawings and Specifications
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Appendix E
Sampling and Analysis Plan, Skyline
AUM Waste Pile Site Removal Action,
April 2011
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Appendix F
Air Sampling Data
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Appendix G
Geotechnical Testing Data
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Appendix H
Liner Testing Documents
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Appendix I
Laboratory Analytical Reports and Data
Validation Reports for July through
October 2011 Soil Sampling Data
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Appendix J
Histograms of Correlated Ra-226 and
Gamma Activity Scan Data
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Appendix K
Gamma Activity Scan Data and
Correlated Ra-226 Concentrations for
UA1, UA2, TLDA, and TSDA
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