DRC-2015-002246 - 0901a06880524034

Energy Fuels Resources
(USA) Inc.
DRC-2015-002246 WHITE MESA MILL
Tailings Data Analysis Report
MafGh-April2015
© MWH
BUILDING A BETTER WORLD
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MWH Tailings Data Analysis Report
TABLE OF CONTENTS
1.0 INTRODUCTION 1
1.1 Project Background 1
1.2 Historical Tailings Data 2
1.3 Objectives of Tailings Investigation 3
1.4 Objective of Tailings Data Analysis Report 3
2.0 TAILINGS INVESTIGATION 5
2.1 CPT Soundings 5
2.2 Direct Push Sampling 9
3.0 LABORATORY INVESTIGATION 10
4.0 TAILINGS CHARACTERIZATION 14
4.1 Tailings Classification 14
4.2 Pore Pressures 16
4.3 Tailings Density 18
4.4 Hydraulic Conductivity 19
4.5 Consolidation Properties 21
5.0 SUMMARY 23
6.0 REFERENCES 24
LIST OF TABLES
Table 2-1 CPT Testing Summary
Table 3-1 Geotechnical Laboratory Testing Schedule
Table 3-2 Summary of Laboratory Testing Results
Table 4-1 Estimated Elevation of Top of Saturated Tailings
Table 4-2 Summary of In-Situ Tailings Density from Laboratory Testing and
Estimated from CPT Soundings
Table 4-3 Average Measured Tailings Density Values
Table 4-4 Summary of Laboratory Measured Vertical Hydraulic Conductivity
Table 4-5 Summary of Estimated Horizontal Hydraulic Conductivity from CPT Data
Table 4-6 Estimation of Hydraulic Conductivity for Sand Tailings Samples
Table 4-7 Summary of Laboratory Measured Consolidation Parameters
Table 4-8 Summary of Estimated Horizontal Coefficient of Consolidation from CPT
Soundings
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LIST OF FIGURES
Figure 1-1 Regional Location Map
Figure 2-1 CPT Sounding and Sampling Locations
Figure 2-2 Thickness Contours of Interim Cover and Tailings
Figure 4-1 Estimated Elevation of Top of Saturated Tailings, October 2013
Figure 4-2 Thickness of Saturated Tailings, October 2013
Figure 4-3 Tailings CPT Sounding and Sampling Location - Cross Section A
Figure 4-4 Tailings CPT Sounding and Sampling Location - Cross Section B
Figure 4-5 Tailings CPT Sounding and Sampling Location - Cross Section C
Figure 4-6 Pore Pressure vs. Elevation from CPT Soundings, CPT-2W3 and CPT 2W3A
LIST OF APPENDICES
Appendix A Cone Penetration Testing Results
Appendix B Subsurface Exploration Logs
Appendix C Direct Push Sampling Photographs
Appendix D Geotechnical Laboratory Test Results
Appendix E Interpretation Graphs of CPT and Laboratory Data
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1.0 INTRODUCTION
This report presents the results of the tailings investigation of Cells 2 and 3 at the White Mesa
site. This report has been prepared for Energy Fuels Resources (USA), Inc. (EFRI) by MWH
Americas, Inc. (MWH) for submittal to the Utah Division of Radiation Control (DRC). The
objectives and background for this report and supporting data are summarized below.
The DRC requested that EFRI collect site-specific tailings data to supplement existing data used
for technical analyses in the White Mesa Reclamation Plan, Version 5.0 (Denison, 2011) and
the Infiltration and Contaminant Transport Modeling (ICTM) Report (MWH, 2010). This request
was part of DRC's February 2013 review comments (DRC, 2013a, b) on EFRI's August and
September 2012 responses to DRC's Round 1 interrogatories for the White Mesa Reclamation
Plan Rev. 5.0 and the ICTM Report (EFRI, 2012a, b).
1.1 Project Background
The White Mesa Uranium Mill (Mill) is located in San Juan County in southeastern Utah,
approximately 6 miles south of Blanding, Utah. The site is located on White Mesa, a flat area
bounded on the east by Corral Canyon, to the west by Westwater Creek, and to the south by
Cottonwood Canyon. A site location map is shown in Figure 1-1. The Mill is located at an
elevation of 5,600 ft above mean sea level. EFRI facilities consist of a uranium processing mill
and five lined tailings/process solution storage cells located within an approximately 686-acre
restricted area. The tailings cells are located south of the Mill and comprise the following:
• Cell 1 - 55 acres, used for the evaporation of process solutions
• Cell 2-65 acres, used for storage of barren tailings sands (which has been filled
with tailings sands and covered with a minimum of approximately 3 feet of interim
cover across the cell)
• Cell 3-70 acres, used for storage of barren tailings sands (which has been
partially covered with a minimum of approximately 3 feet interim cover across the
majority of the cell, except the center of the cell which is currently receiving mill
waste)
• Cell 4A - 40 acres, used for storage of barren tailings sands and evaporation of
process solutions
• Cell 4B - 40 acres, currently being used for evaporation of process solutions
The Mill was initially licensed by the United States Nuclear Regulatory Commission (NRC) in
August 1979, and the tailings system was licensed in May 1980 under NRC Source Material
License No. SUA-1358. After the State of Utah became an Agreement State for uranium mills
in August 2004, the NRC license was replaced with the current State of Utah License (License)
and the Ground Water Discharge Permit (GWDP).
EFRI (formerly Denison Mines (USA) Corp.) submitted an application to DRC for License
renewal on February 27, 2007 and for renewal of the GWDP on September 2, 2009. Updated
GWDP renewal applications were submitted in 2012 and 2014. Among the documents
submitted to DRC in support of the license and permit renewals, the most recent EFRI
documents reviewed by DRC for the license renewal include the Reclamation Plan, Revision 5.0
(Denison, 2011) and the ICTM Report (MWH, 2010). The ICTM Report was originally submitted
in support of the GWDP renewal. DRC provided interrogatories for these documents in March
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2012 (DRC, 2012a, b) in regards to the license renewal. EFRI provided responses to these
interrogatories for the Reclamation Plan, Revision 5.0 in May and August 2012 (Denison,
2012a; EFRI, 2012a) and for the Revised ICTM Report in May and September 2012 (Denison,
2012b; EFRI, 2012b). DRC provided review comments on EFRI's responses in February 2013
(DRC, 2013a, b).
On April 30, 2013, EFRI, DRC, MWH, and URS Corporation (URS) met at URS' office in
Denver, CO to discuss specific issues identified in DRC's February 2013 review comments,
including DRC's request for site-specific tailings data. EFRI proposed a tailings investigation to
address the request for additional information and committed to provide DRC with a work plan
for the investigation. The initial work plan for the proposed tailings investigation (MWH, 2013a)
was provided to DRC on June 24, 2013. DRC provided comments on the work plan in a letter
dated July 2, 2013 (DRC, 2013c). A revised work plan (MWH, 2013b) and responses to DRC
comments (MWH, 2013c) were provided to DRC on August 1, 2013. DRC provided approval of
the work plan verbally to EFRI on September 12, 2013 (documented in EFRI, 2013).
Prior to starting the investigation, MWH provided a final update to the work plan to EFRI on
October 10, 2013 (MWH, 2013d). The final update included the following procedural revisions:
1) improved sample handling and shipping procedures, 2) replacement of the recommended
geotechnical laboratory with two alternative certified laboratories (due to the previously listed
laboratory no longer having a valid radioactive materials license), 3) added text to note that
settlement had been checked prior to the investigation, and 4) updated schedule for the field
investigation.
At the request of DRC, EFRI submitted draft tailings investigation data on August 22, 2014 to
DRC. DRC provided review comments on the draft data to EFRI on September 24, 2014. EFRI
submitted a Tailings Data Analysis Report on October 17, 2014. The report addressed DRC's
September 24, 2014 data review comments. DRC provided review comments on the October
2014 report on January 22, 2015. EFRI submitted a revised report on March 9, 2015 to address
these comments. DRC provided review comments on the March 2014 report on March 31,
2015. This report includes revisions to the October 2014March 2015 Tailings Data Analysis
Report to address DRC's January 2015March 2015 review comments.
1.2 Historical Tailings Data
Previous geotechnical data collected on tailings at the White Mesa site was provided in Denison
(2009). The testing was limited to testing on samples collected from ore grinding prior to mill
operation and a few bulk tailings samples collected after operations commenced. CSM (1978)
conducted gradation testing on 9 tailings samples from grinding tests. The results for percent
passing the No. 200 sieve ranged from 30 to 47 percent. Chen and Associates (1987)
conducted specific gravity, Atterberg limits, standard Proctor, and percent passing the No. 200
sieve tests on one bulk tailings sample. Western Colorado Testing (1999) performed testing on
6 tailings samples (2 samples from Cell 2 and 4 samples from Cell 3). Testing included specific
gravity, Atterberg limits, standard Proctor, and percent passing the No. 200 sieve. The range of
percent passing the No. 200 sieve for the 1987 and 1999 testing was 23 to 83 percent, with an
average of 43 percent. This historic data will be considered for future technical analyses as a
| subset of the tailings data in this report.
Water level data is available at the sump location in Cell 2. Surface water levels were
measured for Cell 3. There is no additional water level instrumentation (i.e. piezometers) in the
remaining areas of the cells.
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Water levels in the Cell 2 sump have been measured since January 2009, and have been
decreasing by an average of 0.8 feet/year since the start of dewatering. The water level
elevation for the Cell 2 sump during time period of the tailings investigation (October 2013) was
5596.4 feet. This compares with the top of saturation levels in Cell 2 at CPT locations near the
Cell 2 sump ranging from elevation 5603 to 5604 feet.
Surface water levels were measured for Cell 3 from January 2001 through the spring of 2011.
Additional mill waste has been added to Cell 3, but additional tailings process solutions have not
been added since the beginning of 2009. Interim cover was placed over the majority of Cell 3.
Surface water level elevations after 2009 ranged from 5600 to 5605 feet. Since dewatering in
Cell 3 has not yet been started, 2010-2011 surface water level readings would be similar to the
water level in the tailings during the tailings investigation. This is consistent with top of
saturation levels in Cell 3 CPT testing ranging from approximate elevation 5600 to 5605 feet.
1.3 Objectives of Tailings Investigation
The objectives of the tailings investigation (outlined in the October 2013 work plan) are listed
below:
• Address the DRC request for site-specific tailings data
• Characterize the tailings to clarify the tailings stratigraphy and measure the physical
properties associated with tailings consolidation, settlement, and pore water drainage
• Conduct tailings characterization with Cone Penetration Test (CPT) soundings, direct
push sampling, and geotechnical laboratory testing on selected representative
tailings samples
• Conduct the CPT soundings and sampling in areas of Cells 2 and 3 that are
accessible for exploration, and in a manner that does not damage the underlying
drainage and liner system in the cells
The tailings objectives of the tailings investigation focused on obtaining information on the
tailings from the CPT soundings and direct push sampling. Evaluation of the interim cover
material was not included as part of the tailings investigation. The intent of the tailings
investigation was to provide site-specific tailings data as requested by the DRC. The interim
cover material has been evaluated extensively as documented in Denison (2011) and EFRI
(2012a). The installation of monitoring instrumentation was also not included as part of this
tailings investigation.
1.4 Objective of Tailings Data Analysis Report
The objective of this report is to present the results of the tailings investigation. The October
2013 work plan listed the following items to be included in this report:
• A site plan showing the CPT soundings and direct push sampling locations
• Presentation of field results including raw data outputs from the CPT measurements
(i.e. tip resistance, friction ratio, dynamic pore pressures, and pore pressure
dissipation readings)
• Presentation of laboratory testing results
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• Interpretation of results including correlation of CPT and direct push samples,
estimation of water levels, and development of subsurface profiles
• A summary of estimated soil properties based upon CPT soundings using
established correlations and direct push sampling information
The results of this investigation will be used to update technical analyses to address DRC
review comments on the Reclamation Plan Revision 5.0 and the revised ICTM Report.
Although the data presented in this report will be used for these future technical analyses, it is
not the intent of this report to provide specific recommendations on how tailings properties will
be selected for each type of analysis.
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2.0 TAILINGS INVESTIGATION
The tailings investigation within Cells 2 and 3 was conducted between October 15 and 23, 2013
and included CPT soundings followed by direct push sampling to calibrate the CPT results and
collect samples for geotechnical laboratory testing. The remaining cells (Cells 1, 4A and 4B)
could not be accessed with the CPT rig. Cell 1 and 4B contain process solutions only. Cell 4A
is partially filled with tailings and process solutions, with a small portion of the tailings beach
above the process water level. In addition, there is a small area in the center of Cell 3 that
could not be accessed with a CPT rig. This inaccessible area was receiving mill waste and was
not covered with interim cover.
The health and safety practices and procedures to minimize exposure of radioactive materials
outlined in the work plan were followed during the tailings investigation.
2.1 CPT Soundings
Seven CPT soundings at locations adjacent to selected settlement monuments in both Cell 2
and Cell 3 were proposed in the approved work plan (MWH, 2013b). Figure 2-1 shows
locations where the CPT soundings were conducted for the field investigation. The locations
shown on Figure 2-1 include the same locations proposed in the work plan, as well as locations
added during the investigation. Two additional CPT soundings were conducted in Cell 2
between settlement monument 2W6-S and the Cell 2 sump location. These locations were
added during the investigation at the request of EFRI to collect additional information on water
levels near the sump. In addition, two CPT soundings, CPT-2W3A and CPT-2W4-CA, were
added for Cell 2 adjacent to settlement monuments 2W3 and 2W4-C to conduct additional pore
pressure dissipation tests at these locations. CPT-3-7S was proposed in the work plan,
however debris was encountered and refusal occurred during the CPT probe advancement, as
well as at an adjacent location where a second attempt was made (CPT-3-7SA). CPT-3-8S was
added during the investigation to replace CPT-3-7S.
ConeTec, Inc. (ConeTec) of Salt Lake City, Utah conducted the CPT soundings under
supervision by MWH personnel. The CPT soundings were performed in accordance with ASTM
D5778-12 and industry standard practices. A compression model electronic piezocone
penetrometer, with a 15-cm2 tip and a 225-cm2 friction sleeve was used for the testing.
ConeTec used a track-mounted CPT rig to advance the CPT probe into the tailings. The CPT
probe was advanced into the subsurface vertically at a constant rate to obtain a continuous
profile of the tailings at each location. Upon completion of the sounding, the CPT probe was
retracted. The holes partially caved upon retraction, and were then backfilled from the ground
surface with bentonite pellets, which were subsequently hydrated. The actual CPT probe
depths for the soundings were less than the maximum allowable probe depths provided in the
approved work plan (MWH, 2013b) for all the locations except CPT-3-8S, CPT-2W6-S(2), and
CPT-2W6-S(3). For these CPT locations added during the field investigation, the maximum
allowable probe depths were estimated using the same procedure provided in the work plan and
the depths were provided to field personnel prior to conducting the soundings. The intention of
recommending a maximum allowable probe depth was to provide a buffer zone to minimize the
potential for puncture of the tailings liner system in Cells 2 and 3 during the investigation. The
total depth of each sounding is shown on Figure 2-1 and in Table 2-1. For comparison
purposes, total thickness contours of interim cover and tailings are provided in Figure 2-2. The
total thickness of interim cover and tailings at each CPT location, as well as each settlement
monument, are also shown on Figure 2-2. The estimated thickness of interim cover and tailings
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at each CPT location is greater than the total depth of the CPT sounding at each location,
indicating that no CPT probes came close to the liner.
Cone tip resistance, sleeve friction, and dynamic pore pressures were measured at 2-inch
intervals for each sounding location. Shear wave velocity was measured at designated
locations, and the weighted average velocity over the profile is listed in Table 2-1. Pore
pressure dissipation tests were conducted at select depths based on review of CPT sounding
measurements and to assist with estimating static phreatic levels or pore pressures. 28 pore
pressure dissipation tests were conducted, and the results are summarized in Table 2-1.
The ConeTec field report with CPT data and field logs for the CPT soundings is provided as
Appendix A. Field logs of CPT soundings were obtained electronically in real time during
soundings. The log recorded an approximate location and depth (0.2 foot accuracy) of each
sounding. The log includes tip and sleeve resistances, pore pressures, and other measured
parameters. In addition, the logs contain interpretations of CPT measurements using published
correlations (e.g. for soil behavior type).
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Table 2-1 CPT Testing Summary
Tailings
Cell
CPT
Sounding Elevation (ft) Latitude/
Longitude
CPT
Depth
(ft)
PPD1 Testing
PPD
Depth
(ft)
Pore
Pressure
at PPD
Depth (ft)
Water Table
Calculated
from PPD
Test (ft)
Shear Wave
Velocity2
(ft/s)
Cell 2
CPT-2W2
CPT-2W3
CPT-2W3A
CPT-2W4-C
CPT-2W4-CA
CPT-2W5-C
CPT-2W6-S
CPT-2W6-S(2)
CPT-2W6-S(3)
CPT-2VV7-C
CPT-2E1
5615.86 37.533317/
-109.512367 20.34 13.94 11.2
5615.72 37.533617/
-109.511300 21.65
18.54 18.4
21.65 24.1
3.12
5615.72 37.533617/
-109.511283 4.43 3.94
4.43 4.2
5616.24 37.533100/
-109.509967 26.57 17.39 12.1
5616.24 37.533100/
-109.509950 9.35
6.07 0.6
9.35 5.2
5615.86 37.532917/
-109.508467 30.18 12.63 11.0
5615.85 37.532183/
-109.507033 29.20
15.09 4.5
29.20 16.9
5614.93 37.532133/
-109.507417 25.59 19.85
5614.66 37.532050/
-109.507700 25.10 21.65 12.9
5619.60 37.532533/
-109.505300 28.05 15.09 8.5
5619.95 37.532800/
-109.503700 28.05 20.51 11.3
2.8
0.2
3.2
3.9
0.2
5.3
5.5
4.2
1.7
10.6
12.3
12.0
6.5
9.2
459
457
510
606
485
539
530
Notes
1. PPD = pore pressure dissipation
2. Shear wave velocities were measured for the CPT soundings indicated. The velocity values listed are the weighted average over the profile.
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Table 2-1 CPT Testing Summary (continued)
Tailings
Cell
CPT
Sounding Elevation (ft) Latitude/
Longitude
PPD Testing
CPT
Depth
(ft)
PPD
Depth
(ft)
Pore
Pressure
at PPD
Depth (ft)
Water Table
Calculated
from PPD
Test (ft)
Seismic
Velocity
(ft/s)
Cell 3
CPT-3-1S
CPT-3-2C
CPT-3-3S
CPT-3-4N
CPT-3-6N
CPT-3-7SJ
CPT-3-7SAJ
CPT3-8N
CPT-3-8S
5612.56 37.530767/
-109.515350 17.88 12.80 8.2 4.6
5610.82 37.532400/
-109.513783 20.34 12.47 6.9 5.5
5609.63 37.530600/
-109.514433 23.79 18.86 14.9 4.0
5608.70 37.530600/
-109.514467 21.16 13.12 13.8
21.16 18.5 2.7
5607.44 37.531933/
-109.511650 18.54
8.86 5.6 3.2
18.54 15.3 3.2
5607.63 37.531330/
-109.508800 8.04 No PPD Test
5607.63 37.529600/
-109.508067 10.01 9.02
5608.37 37.529783/
-109.505833 15.26 10.01
3.94
5608.70 37.529050/
-109.504883 15.26 6.07
15.26
9.4
6.5
4.6
0.8
10.2
3.5
5.3
5.1
488
463
549
369
418
518
494
Notes
1. PPD = pore pressure dissipation
2. Shear wave velocities were measured for the CPT soundings indicated. The velocity values listed are the weighted average over the profile.
3. Refusal at 8 and 10 feet for CPT-3-7S and CPT-3-7SA, respectively. CPT-3-8S added to replace this location.
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2.2 Direct Push Sampling
Direct push sampling was completed after the CPT soundings. ConeTec performed the direct
push sampling under the direction of MWH personnel. The approved work plan listed two direct
push sampling locations per tailings cell (four total), which were to be selected during the field
program based on the results of the CPT soundings. Direct push sampling was actually
conducted at the Ftme-eight sampling locations shown on Figure 2-2. The locations were
selected to span the range of material responses (e.g. pore pressures, soil behavior types)
measured during CPT testing, as well as to provide sufficient tailings samples for laboratory
testing. Samples depths were selected based on review of the CPT results. In the work plan,
approximately 30 6-inch long samples were to be collected based on the direct push sampling
frequency and laboratory testing program. A total of 49 samples were collected. 46 samples
were selected for testing, and 38 of the samples had lengths of 6 inches or greater.
Piston-type samplers were used to collect relatively undisturbed samples without generating soil
cuttings. The direct push samplers were deployed from the CPT rig. The samplers have 1.5-
inch inner diameters and are 24 or 36 inches in length. The soil sampler was initially pushed in
a "closed" position to the desired sampling interval. The inner cone tip portion of the sampler
was then retracted leaving a hollow sampler with an inner liner containing soil sample tubes (1.5
inches in diameter). The hollow sampler was then pushed in a locked "open" position to collect
a soil sample. The filled sampler and push rods were then raised to the ground surface. Upon
completion of direct push sampling, the sampler was retracted. The holes partially caved upon
retraction, and were then backfilled from the ground surface with bentonite pellets, which were
subsequently hydrated.
Each sample was assigned a designation based on the tailings cell number, site location, and
the depth interval. The sample designation and date was recorded on the sample tube. Each
sample tube had the end caps secured with wax. The original field logs recorded the depths of
samples from the bottom of the sample run. The sample depths have been revised on the logs
to represent depth from the top of the sample run. This revisions is documented in the notes on
the logs. In addition, the sample designations provided to the laboratory have been revised in
the laboratory report. A sampling log was recorded for each direct push location. The logs are
provided in Appendix B. Photographs of the collected samples are provided as Appendix C.
The primary objective of the direct push sampling was to provide site-specific correlation of CPT
results. Samples collected were shipped via UPS to S&ME, Inc. (S&ME) in Knoxville,
Tennessee. Handling and shipping of samples was conducted in accordance with EFRI White
Mesa standard procedures. Samples were wrapped in multiple layers of bubble wrap and
placed in a vertical axial orientation (i.e. upright) in 5-gallon buckets. Packing materials were
added to the buckets to limit the potential for shifting of the samples while in transit to the
laboratory. This was consistent with the sample handling procedure in the work plan. Due to the
radioactive classification of the tailings samples, no other shipment method (such as shipment
by air) was possible. Geotechnical laboratory testing was conducted on selected samples and
the results are summarized in Section 3.
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3.0 LABORATORY INVESTIGATION
Geotechnical laboratory testing was conducted on selected samples collected during the tailings
investigation by S&ME in Knoxville, Tennessee. S&ME was selected for the testing at that time
because: (1) they had an active radioactive materials license for geotechnical testing of
materials with low levels of radionuclides, and (2) had the capabilities to provide the required
geotechnical tests.
S&ME was listed as a potential geotechnical laboratory for the tailings samples in the October
2013 work plan. This laboratory, as well as CB&I Federal Services, LLC, were added to the
work plan to replace Advanced Terra Testing, Inc. as potential testing laboratories after
Advanced Terra Testing, Inc. informed MWH that their radioactive materials license was
currently in the process of being renewed and would not be valid at the time of the investigation.
At the time of the field investigation, further discussions with CB&I Federal Services indicated
they would not be able to provide consolidation testing for the project and were removed from
consideration.
Samples were shipped to S&ME in mid-November 2013 after their receipt and review of the
radiological survey data on the adjacent tailings samples collected by EFRI during the October
2013 field investigation. Review of the radiological survey data is a requirement for S&ME's
radioactive materials license.
Initial geotechnical testing consisted of index testing for use in classifying the tailings. Samples
were then selected for permeability and consolidation testing based on tailings classification.
Laboratory testing was conducted over several months, due to the limited number of available
consolidation and permeability test cells.
Laboratory tests included natural water content, in-situ dry density, grain-size analysis (sieve
and hydrometer), Atterberg limits, specific gravity, hydraulic conductivity, and consolidation
testing, as summarized in Table 3-1. The actual testing schedule is similar to the anticipated
testing schedule in the approved work plan. The actual testing schedule was updated from the
schedule listed in the approved work plan based on review of actual samples collected. The
tested samples were selected to characterize the range of tailings encountered and to provide a
site-specific correlation of CPT sounding results. All laboratory testing was conducted according
to applicable ASTM standards. A detailed summary of the results (Table D-1) and the S&ME
laboratory testing report are provided in Appendix D. The test results are summarized in Table
3-2 by tailings type (i.e. sand, sand-slime, and slime). Evaluation of tailings type is discussed in
Section 4.1.
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Table 3-1 Geotechnical Laboratory Testing Schedule
Geotechnical Laboratory Test No. of Tests ASTM Standard
Natural Moisture Content and Density 34 ASTM D2216 and D2937
Particle Size (sieve and hydrometer) ASTM D422
Particle Size (sieve and No. 200 wash) 11 ASTM D6913
Particle Size (No. 200 wash) ASTM D6913
Specific Gravity ASTM D854
Atterberg Limits 13 ASTM D4318
Permeability Test ASTM D5084
Consolidation Test ASTM D2435
Previous tailings laboratory testing data (Chen and Associates, 1987; Western Colorado Testing,
1999) were within the range of laboratory testing results for the October 2013 tailings
investigation. The average percent passing the No. 200 sieve from the limited amount of
previous testing is 43 percent. The average percent passing the No. 200 sieve from the
October 2013 investigation is 50 percent.
The collected tailings sample diameters (1.4 inches) were within the expected sample diameter
range listed in the work plan (1.0 to 1.5 inches). For the consolidation testing, this sample
diameter is smaller than the minimum diameter recommended per ASTM D2435 (2.0 inches)
and therefore the testing results are considered non-standard. The sample disturbance zone
can be greater relative to the overall sample size for a 1.4 inch versus 2.0 inch sample. This
can potentially cause an increase or decrease in compressibility if breakdown of cementation of
gypsum occurs or density increases, respectively. The measured consolidation parameters for
the tailings samples tested were within the expected range for uranium tailings as discussed in
Section 4.5. However, someSome studies indicate that a reduction in diameter from 2.4 to 1.2
or 1.4 inches for fine-grained soils (clays) has an insignificant impact on measured consolidation
parameters (Kongkitkul et al, 2014; Shogaki, 2006). The studies indicate that the consolidation
parameters measured for the tailings slimes samples may not have been impacted bv the
smaller sample diameter. These studies are not applicable to the coarser sand and sand-slime
tailings. In addition, the measured consolidation parameters for the tailings samples tested
were within the expected range for uranium tailings as discussed in Section 4.5.It is
recommended that the laboratory testing results be interpreted conservatively and assume the
impact of using a smaller diameter sample causes decreased compressibility.
It is likely that gypsum is present in the tailings at White Mesa, based on the ore geology and
the acid leach process used in the mill. However, the laboratory testing procedures were not
modified to account for gypsum. This is consistent with tailings characterization testing
conducted at other uranium tailings facilities under Uranium Mill Tailings Remedial Action
(UMTRA) work for the U.S. Department of Energy (DOE).
The hydroscopic nature of gypsum in the tailings can result in erroneously high measured water
contents using standard test methods. ASTM D2216 suggests drying soil samples containing
gypsum at a lower oven temperature (60 degrees Celsius) than using the standard oven
temperature (110 degrees Celsius).
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For a recent example, uranium tailings samples collected from the Church Rock Uranium Mill
site were tested for water content using both oven temperatures. Water contents measured at
60 degrees Celsius were about 0.5 to 3.0 percent lower than water contents measured at 110
degrees Celsius (MWH, 2014). The resulting specific gravity showed an insignificant (less than
0.01 percent) difference between samples tested using the lower oven temperature versus the
standard oven temperature (MWH, 2014). Since the acid leach process at the Church Rock Mill
site was similar to the White Mesa Mill, similar variations in water content and specific gravity
would be measured on the White Mesa tailings between the two oven temperatures.
Saturated tailings thicknesses were estimated using CPT testing results, and natural moisture
contents were only measured as a check for estimating the saturated tailings thicknesses. It is
| not expected that natural moisture contents will fhet-be used in any future technical analyses for
the Reclamation Plan and ICTM Report.
Testing results for particle size distribution using the hydrometer and for the No. 200 sieve wash
can show higher values of fines content using standard testing methods than sample
preparation and testing procedures modified to account for gypsum. The measured percent
fines for the tailings samples were used with the CPT test results to classify the tailings (see
Section 4.1). The tailings were classified using the method from Larson and Mitchell (1986)
based on measured laboratory and CPT data for uranium tailings from numerous sites. The
measured laboratory data used for the Larson and Mitchell (1986) study did not account for
gypsum in the tailings (Ned Larson, personal communication, February 9, 2015). Therefore, the
tailings classification for the White Mesa tailings would not change if the hydrometer testing
were modified to account for gypsum. The measured percent fines of the tailings will be used
for liquefaction analyses, but is not planned to be used for any other technical analyses for the
Reclamation Plan and ICTM Report. A reduction in the percent fines to account for gypsum in
the tailings would not significantly affect the tailings liquefaction analysis results.
| DRC (20442015) requested review of the results of the percent passing the No. 200 test using
ASTM D1140 prior to using ASTM D422 for the 11 samples tested with both procedures. The
results showed a higher percent passing the No. 200 sieve with the subsequent sieve analysis
(ASTM D422). This is expected with additional interaction with the deflocculant and mechanical
shaking for the sieve analysis. An average increase of 5 percent for percent passing the No.
200 sieve was measured between the initial No., 200 wash test (ASTM D1140) and the
subsequent sieve analysis (ASTM D422). The standard deflocculant (sodium
hexametaphosphate) at the standard ASTM recommended concentration (4 percent) was used
for the recommended ASTM standard duration (2 to 16 hours). Because no additional or
different deflocculant was added to account for the presence of gypsum, gypsum in the solution
would flocculate resulting in a higher measured percentage of larger particles for the initial No.
| 200 wash. The subsequent testing using ASTM D422 would allow for breakdown of the-a
portion of the remaining gypsum during shaking. The test results from the subsequent sieve
analysis (ASTM D422) were reported for the percent passing No. 200 sieve results and were
used for tailings classification. Future geotechnical analysis will consider the uncertainty in the
laboratory measured percent passing the No. 200 sieve for these eleven samples.
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Table 3-2 Summary of Laboratory Testing Results3
Tailings
Tyffe
% Finer
than No.
200 Sieve
Natural
Water
Content (%)
In-Situ Dry
Density (pcf)
Atterberg Limits (%)°
LL PL PI Specific
Gravity
Hydraulic
Conductivity
(cm/s)
Consolidation Properties'
cv
9 (cm2/s)
Sand
18
(11.2-29.2)
27
(25.5-29.2)
97
(93.5-98.3) Not Tested Not Tested Not Tested Not Tested
Sand-
Slime
47
(34.2-58.1)
35
(13.2-71.6)
88
(56.2-114.4)
34
(26 - 54)
23
(19-30)
10
(6-24)
2.80
(2.77-2.84)
9.0E-076
(1.6E-07-3.3E-06)
0.32
(0.11 -0.66)
0.001
(0.0005-
0.002)
Slime
71
(60.2-97.0)
41
(29.3-63.8)
78
(61.0-94.6)
41
(31 -68)
26
(23 - 36)
16
(7-32)
2.86°
(2.85-2.86)
1.3E-06ae
(1.7E-07-9.8E-06)
0.28a
(0.27-0.28)
0.002"
(0.0005 -
0.003)
Notes:
a. Average laboratory values shown in table with ranges shown in parentheses
b. Sand tailings (0 - 30% fines); Sand-slime tailings (30 - 60% fines); Slime tailings (60 - 100% fines) (adjusted from ranges defined in Larson and
Mitchell, 1986)
c. NP = non-plastic; LL = liquid limit (%); PL = plastic limit (%); PI = plasticity index (%)
d. Two samples tested.
e. Geometric mean
f. Cc = compression index; cv = coefficient of consolidation
g. cv value estimated from linear portion of consolidation curve
cm/s =| cubic meterscentimeters per second, cm2/s = square centimeters per second, pcf = pounds per cubic foot
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4.0 TAILINGS CHARACTERIZATION
CPT field data and laboratory testing results were used to characterize the tailings at the White
Mesa site. Material properties estimated based on this data will be used in technical analyses to
address DRC review comments on the Reclamation Plan Revision 5.0 and the revised ICTM
Report. Appendix E includes figures used to assist with interpreting the CPT and laboratory
data.
4.1 Tailings Classification
A number of criteria have been used for classifying soil types from CPT measurements,
including the method by Lunne, Robertson, and Powell (1997). This method is based on soil
behavior type zones, and is used-provided as a default soil classification method by the CPT
contractor, ConeTec, used for the tailings characterization. The soil behavior types used by
Lunne, Robertson, and Powell (1997) include a range of types including sensitive fine-grained
material, organic material, gravelly sand, sand, silty sand, sandy silt, clayey silt, silty clay, clay,
and overconsolided or cemented material. The criteria used to categorize the tailings for this
investigation were based upon criteria used by the DOE for interpreting CPT tests specifically in
uranium tailings (Larson and Mitchell, 1986). As noted in Larson and Mitchell (1986),
classification of tailings using soil behavior type zones similar to the method by Lunne,
Robertson, and Powell (1997) result in a higher level of uncertainty than the classification
method presented in Larson and Mitchell (1986). Therefore, the DOE criteria, and not the soil
behavior types method was used to classify the tailings. Soil behavior type listed in the CPT
results report provided by ConeTec (Appendix A) was not used for tailings classification.
The DOE criteria as outlined in Larson and Mitchell (1986) divide uranium tailings into the three
general categories based upon the percentage of material finer than the No. 200 sieve (% fines)
by weight as follows:
• Sand Tailings (0 to 30 percent passing the No. 200 sieve)
• Sand-Slime Tailings (30 to 70 percent passing the No. 200 sieve)
• Slime Tailings (70 to 100 percent passing the No. 200 sieve)
The use of other index parameters, such as Atterberg limits and density, are not included in
defining these categories.
The DOE criteria provide a correlation between CPT results, specifically the cone tip resistance
and the side-friction/tip-resistance ratio, and these three tailings classifications. This correlation
from Larson and Mitchell (1986) is shown on Figure E.1-1 in Appendix E. This correlation is
based on 87 tailings samples analyzed for 5 uranium mill tailings sites. CPT data from the
White Mesa tailings investigation are shown on the graph for locations where laboratory data is
also available. The data points are designated as sand, sand-slime, or slime tailings based on
their respective laboratory-measured percent passing the No. 200 sieve results (on 20
samples). The measured percent passing the No. 200 sieve value is shown adjacent to each
data point.
As shown in Figure.1-1, the tailings classifications based on percent passing the No. 200 sieve
do not fit with the general CPT result categories in Larson and Mitchell (1986). The samples
classified as sand tailings based on percent fines fall within the sand-slime tailings category,
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except for the sample with 29% passing the No. 200 sieve which falls on the sand-slime/slime
cutoff line. The samples classified as sand-slime tailings based on percent fines fall within both
the sand-slime and slime tailings categories on the graph. The samples classified as slime
tailings based on percent fines fall within the slime tailings category on the graph. Correlation
with the laboratory results for percent fines and the Larson and Mitchell (1986) graph indicate
that better site-specific correlation would be obtained if the material definitions based on percent
fines were modified and the curves adjusted so that the sand and sand-slime tailings are
combined and the sand-slime/slime cutoff is shifted. This adjustment is consistent with ASTM
D5778 for CPT of soils, which recommends the collection of samples from adjacent borings to
CPT soundings be used to provide site specific correlations to CPT data. It is understood that
there should be a division between the sand and sand-slime tailings, however the selection of a
division line is not clear based on comparison of laboratory testing data with the CPT test
results. To address DRC's concern with combining the sand and sand-slime tailings within one
division on Figure E.1-2 (DRC, 2015), the sand/sand-slime division line from Larson and
Mitchell (1986) has been added to this figure and associated figures. It will be considered for
future technical analyses that this division is not correlated to the site-specific laboratory testing
results for the sand tailings and conservative adjustment of parameters to address uncertainty
will be evaluated. The recommended modifications to the classifications for the White Mesa
tailings are listed below and Figure E.1-2 shows the data points classified using this criteria on
the adjusted graph.
• Sand Tailings (0 to 30 percent passing the No. 200 sieve)
• Sand-Slime Tailings (30 to 60 percent passing the No. 200 sieve)
• Slime Tailings (60 to 100 percent passing the No. 200 sieve)
Figure E.1-3 and Figure E.1-4 show all the CPT data (cone resistance versus friction ratio) for
Cells 2 and 3, respectively, along with the adjusted graph for denoting the division between
sand and^ sand-slime/-, and slime tailings. Using these figures, approximately 10, 65, and 25
percent of the tailings are categorized as sand, sand-slime, and slime tailings, respectively, for
Cells 2 and 3. and the remainder are categorized as sand and sand slime tailings for both Cell
2 and Cell 3. Figure E.1-5 through Figure E.1-20 show the CPT data (cone resistance versus
friction ratio) for each CPT location and the recommended sand-aftd-. sand-slime/-, and slime
tailings division. These figures indicate a-ranges of approximately 0 to 30 percent, 35 to 80
percent, and 5 to 60 percent of sand, sand-slime, and slime tailings, respectively, from CPT
soundings in Cells 2 and 3. tailings slimes from the CPT soundings in both Cell 2 and Cell 3.
Using the tailings classification provided in Figure E.1-2, the tailings profiles were developed for
each CPT location and are shown in Figures E.1-21 through Figure E.1-37. A layer of interim
cover is shown at the top of each profile. The CPT soundings show evidence of this interim
cover, which has higher tip resistance than the underlying tailings. A minimum of 3 feet of
interim cover has already been placed in covered areas and this is consistent with the estimated
thickness shown on the profiles. Profiles showing the tailings layers classified based on
laboratory testing are shown for locations where direct push sampling was conducted. The
tailings samples were classified according to the percent passing the No. 200 sieve as sand
tailings (0 to 30 percent fines), sand-slime tailings (30 to 60 percent fines), and slimes (60 to
100 percent fines).
Figure 4-3 through Figure 4-5 show sections through Cells 2 and 3 and include tailings profiles
developed from the CPT results. Review of these figures, as well as the boring logs and
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laboratory results indicate there is significant interbedding and minimal segregation of tailings
within each cell. This is expected, since the tailings discharge points in Cells 2 and 3 were
located throughout the cells and not just along the perimeter. The tailings in Cells 2 and 3 also
appear to be similar in particle size distribution and other geotechnical characteristics. The
tailings within Cells 2 and 3 were processed from similar ores and using the same crushing,
grinding and processing procedures.
4.2 Pore Pressures
Both CPT pore pressure dissipation tests and dynamic pore pressure measurements were
evaluated to conservatively estimate the top of the saturated tailings zone. Equilibrium pore
pressures measured during pore pressure dissipation tests often yield values that are higher
than actual steady-state pore pressure at the specific location and depth. Figure E.2-1 through
Figure E.2-16 show pore pressure versus elevation results from the CPT soundings. Dynamic
pore pressures and the results from the pore pressure dissipation tests are shown on the
figures. The estimated elevation of the top of the saturated tailings shown on the figures was
selected as—the—depth—where—continuous—elevated—dynamic—pefe—pressures—were
encounteredbased on pore pressured dissipation tests. -Hydrostatic pore pressures with depth
are shown on the figures and were used to assist with estimating the top of the saturated
tailings by evaluating tho trend of pore pressures below this depthestimated using pore pressure
dissipation test results. The estimated maximum elevations of the top of the saturated tailings
at the CPT locations are listed in Table 4-1 and shown in Figure 4-1. Figure 4-2 shows the
estimated maximum saturated tailings thicknesses.
Previous versions of this report used both dynamic pore pressure measurements and pore
pressure dissipation test results to estimate the elevation of the top of the saturated tailings.
This approach was revised to address DRC comments (DRC, 2015) regarding the use of
dynamic pore pressures. Dynamic pore pressures typically represent the upper bound of the
actual equilibrium pore pressures since they are the sum of the equilibrium pore pressure and
excess pore pressures due to shearing. The pore pressures due to shearing are usually
positive unless the tailings are heavily overconsolidated (i.e. overconsolidation ratio, OCR,
greater than 4). There are some thin zones within the saturated tailings where dynamic pore
pressures are less than hydrostatic pressures, indicating potential heavily overconsolidated
zones. Overall, the dynamic pore pressure results indicate the tailings are primarily normally
consolidated to slightly overconsolidated. Laboratory results for tailings samples tested for
consolidation show all samples have OCRs less than 4. It should be noted that the values for
preconsolidation pressure listed in the laboratory reports were incorrectly determined and
should not be used. Using the traditional Casagrande method to estimate preconsolidation
pressures, OCRs range from less to 1 to approximately 3, which indicates the tailings are not
dilative. There are also some lenses of elevated pore pressures at shallow depths, but these
are considered perched zones in the interim cover and/or tailings due to seasonal infiltration
influences. No data is available, but considering the climate at the White Mesa site, it is likely
these perched zones are seasonal versus perennial in nature.
Figure 4-6 is provided as an example of how the elevation of the top of saturated tailings was
estimated for a CPT location with more than one pore pressure dissipation test conducted.
Figure 4-6 also presents a comparison of the dynamic and static pore pressures measured for
CPT-2W3 and CPT-2W3A. As shown in the figure, upper bound and lower bound hydrostatic
pore pressures were estimated based on 5 pore pressure dissipation tests. The upper bound
hydrostatic line (with a water level at the ground surface elevation) does not represent field
conditions. The ground surface in Cell 2 was visually dry during the tailings investigation. In
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addition, thick zones within the tailings with negative pore pressures is not expected. The lower
bound hydrostatic line corresponds fairly well with the trend of the dynamic pore pressures with
depth. T-h4s-An average hydrostatic line between the upper and lower bound was conservatively
selected to estimate the maximum elevation of top of saturated tailings, lower bound line, along
with the trend in dynamic pore pressures, were used to estimate the selected elevation of the
top of saturated tailings.
As shown in Figure 4-1, the top of saturated tailings elevation is lower for locations closer to the
Cell 2 sump, indicating migration of water towards the sump in Cell 2. For Cell 3, the top of
| saturated tailings elevations range from approximately 5603 5604 to 5606 5608 feet. The Cell 3
tailings would have a relatively consistent top of saturated tailings elevation since dewatering
has not been started. EFRI measured water level elevations in the Cell 3 sump through the
spring of 2011.—The-Surface water level elevations measured for Cell 3 during 2010 through
2011 ranged from 5600 to 5605 feet, and were similar to the top of saturated tailings elevation
estimated from the recent tailings investigation. Additional mill waste has been added to Cell 3,
but additional process solutions have not been added; therefore it is reasonable to assume that
the past water level readings are similar to the top of the saturated tailings elevations estimated
from the field investigation.
Table 4-1 Estimated Elevation of Top of Saturated Tailings
Tailings
Cell
CPT
Sounding
CPT Sounding
Ground Surface
Elevation (ft)
Estimated Depth
to Top of
Saturated
Tailings (ft)
Estimated
Elevation at Top
of Saturated
Tailings (ft)
CPT-2W2 5615.86
CPT-2W3/CPT-2W3A 5615.72
CPT-2W4-C/CPT-2W4-CA 5616.24
CPT-2W5-C 5615.86
Cell 2 CPT-2W6-S 5615.85
CPT-2W6-S(2) 5614.93
CPT-2W6-S(3) 5614.66
CPT-2W7-C 5619.60
CPT-2E1 5619.95
3.92.8
4.31.9
8.95.0
10.01.7
11.5
11.012.0
11.58 8
9.26.5
11.29.2
5611.965613.1
5611.425613.8
5607.345611.2
5605.865614.2
5604.354
5602.95603.93
5603.165605.9
5610.405613.1
5608.755610.8
CPT-3-1S 5612.56
CPT-3-2C 5610.82
CPT-3-3S 5609.63
Cell 3 CPT-3-4N 5608.70
CPT-3-6N 5607.44
CPT3-8N 5608.37
CPT-3-8S 5608.70
8.74.6
5.65.5
3.84.0
3.82.7
4.23.2
3.5
5.2
5603.865608.0
5605.225605.3
5605.835605.6
5604.905606.0
5603.245604.2
5604.879
5603.50
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4.3 Tailings Density
Tailings densities were measured on sand, sand-slime and slime tailings samples collected from
the direct push sampling. The testing results were presented in Table 3-2 and are summarized
below in Table 4-2. Figure E.3-1 and Figure E.3-2 show laboratory-measured total and dry
density values versus depth, respectively. The data points are designated as sand, sand-slime,
or slime tailings based on the modified criteria provided in Section 4.1. The range of measured
densities is also shown on the figures. The figures indicate that there is not a relationship for
density with depth. Density values for sand tailings samples are typically higher than for slime
tailings samples. Density values for sand-slime tailings vary across the total range of measured
values for all tailings types. Figure E.3-3 through Figure E.3-10 show laboratory measured total
and dry density versus depth for each CPT location where samples were collected to measure
in-situ densities. These figures also indicate that there is not a clear increase in density of
tailings with depth.
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Table 4-2 Summary of In-Situ Tailings Density from Laboratory Testing
Tailings Type3
Sand
Sand-Slime
Slime
Average
In-Situ Dry
Density13 (pcf)
97
(93.5-98.3)
88
(56.2-114.4)
78
(61.0-83^94.6)
86
In-Situ Total
Densityb (pcf)
123
(120.8-124.9)
114
(96.4- 129.5)
108
(98.4- 122.7)
112
Notes:
a. Sand tailings (0 - 30% fines); Sand-slime tailings (30 - 60% fines); Slime tailings (60 - 100%
fines) (adjusted from Larson and Mitchell, 1986)
b. Average laboratory values with ranges shown in parentheses,
pcf = pounds per cubic foot
Total density was estimated from CPT data using 1) the relationship provided in Robertson and
Cabal (2012) for a correlation with friction ratio and cone resistance, and 2) the relationship
provided in Lunne et al. (1997) for a correlation with the CPT soil behavior type index. The dry
density was calculated using the total unit weight and the average measured specific gravity of
2.82 for locations where the tailings are expected to be saturated. Comparisons of laboratory
measured dry density versus estimated dry density values from the CPT data using Robertson
and Cabal (2012) and Lunne et al. (1997) are shown on Figure E.23-11 and Figure E.23-12,
respectively. The results indicate that neither relationship provides a good correlation with
measured data at the same depths. Laboratory measured dry density values were also plotted
versus CPT measured values for cone resistance and friction ratio in Figure E.23-13 and
Figure E.23-14, respectively. These figures indicate that there is not a direct relationship
between CPT cone resistance or friction ratio with in-situ dry densities for this data. Since a
reliable correlation between the CPT data and in-situ density was not developed, the average
measured tailings densities listed in Table 4-3 should be used with materials classified
according to Figure E.1-2.
Table 4-3 Average Measured Tailings Density Values
Tailings Type Dry Density (pcf) Total Density
(pcf)
Sand 97 123
Safld/Sand-Slime 9088 44€114
Slime 78 108
pcf = pounds per cubic foot
4.4 Hydraulic Conductivity
Hydraulic conductivity testing was performed for sand-slime and slime tailings samples collected
from the direct push sampling. The testing results were presented in Table 3-2 and are
summarized below in Table 4-4. The testing was performed using effective confining pressures
ranging from 5 to 12 psi. The confining pressure used for each test was selected based on the
estimated overburden pressure for the sample. The geometric mean vertical hydraulic
conductivities of the sand-slime and slime tailings are similar at approximately 1 x 10~6 cm/s.
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Table 4-4 Summary of Laboratory Measured Vertical Hydraulic Conductivity
Tailings
Type
Sand-Slime
Slime
Vertical Hydraulic Conductivity8 (cm/s)
9.0E-07
(1.6E-07-3.3E-06)
1.3E-06
(1.7E-07-9.8E-06)
Note: Geometric mean with range of values shown in parentheses,
cm/s = centimeters per second
The horizontal hydraulic conductivities of the sand-slime and slime tailings were estimated using
CPT data and the relationship provided in Robertson and Cabal (2012), based on CPT soil
behavior. The results are shown in Table 4-5 for the depths where vertical hydraulic
conductivities were measured. The estimated geometric mean horizontal hydraulic
conductivities for the sand-slime and slime tailings are similar, with values of 6.4 x 10"6 and 6.6 x
10"6 cm/s, respectively. The calculated anisotropy ratio (hydraulic conductivity to vertical
hydraulic conductivity) of the sand-slime and slime tailings is about 3 and 5, respectively,
excluding the result of 47 for CPT-2W6-S(3).
Table 4-5 Summary of Estimated Horizontal Hydraulic Conductivity from CPT Data
Tailings Type Location and Depth
Estimated
Horizontal
Hydraulic
Conductivity
(cm/s)
Laboratory
Measured
Vertical
Hydraulic
Conductivity
(cm/s)
Calculated Hydraulic
Conductivity
Anisotropy Ratio
(horizontal/vertical)
CPT-2W2at7.5-8' 3.8E-06 1.4E-06
Sand-Slime CPT-2W3at7-7.8' 9.0E-06 3.3E-06
CPT-2W6-S(3) at 14.5-15' 7.6E-06 1.6E-07 47
Geometric mean 6.4E-06 9.0E-07
Slime
CPT-2W6-S(2) at 12.3 - 12.8' 3.2E-06 1.7E-07
CPT-3-6N at 5.3-5.8' 1.3E-07 9.8E-06
19
Geometric mean 6.6E-06 1.3E-06
cm/s = centimeters per second
The sand tailings samples did not have sufficient cohesion to be used for specimens for
hydraulic conductivity testing. Hydraulic conductivity was estimated using 1) CPT data and the
relationship shown in Robertson and Cabal (2012), and 2) measured grain-size analyses and
the empirical relationships from Fair-Hatch and Harlman (McWhorter and Sunada, 1977). The
results are shown in Table 4-6. Assuming a horizontal to vertical conductivity ratio of
approximately 1, the results indicate an isotropic hydraulic conductivity of approximately 3 x 10"5
to 5 x 10"5 cm/s for the sand tailings.
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Table 4-6 Estimation of Hydraulic Conductivity for Sand Tailings Samples
Tailings
Cell
Sampling
Location
Sample
Depth
Interval
(ft)
% Passing
No. 200
Sieve
Estimated Hydraulic
Conductivity
using Fair-Hatch and
Harlman relationships
(cm/s)
Estimated Horizontal
Hydraulic Conductivity
using CPT data and
relationship from
Robertson and Cabal
(2012) (cm/s)
Cell 2 CPT-2E1 17-17.4' 29.2 1.5.E-05 5.6E-06
6.5-7 13.0 4.9.E-05 3.3E-04
Cell 3 CPT-3-4N 8.5-9 19.6 2.5.E-05 8.5E-05
11 - 11.5 11.2 4.8.E-05 2.9E-05
Geometric mean 3.1E-05 4.6E-05
cm/s = centimeters per second
The permeability test results for the White Mesa sand, sand-slime, and slime tailings are
consistent with other published uranium tailings test results (Keshian and Rager, 1986). The
specific hydraulic conductivity values to use for analyses will be dependent upon the type of
analyses and how the tailings will be modeled. It is expected that the hydraulic conductivitios
used for tho tailings for future analyses will be lower than the estimated hydraulic conductivities
used in previous analyses.
4.5 Consolidation Properties
Results of laboratory consolidation testing on samples obtained from the direct push sampling
were used to estimate consolidation parameters including the compression index (Cc) and the
vertical coefficient of consolidation (cv). Cc provides an indication of the amount of compression
that can be expected under a change in loading, with higher values of Cc indicating greater
compression and larger settlements. The parameter cv provides an indication of the
consolidation rate with vertical pore water pressure dissipation, with higher cv values indicating
more rapid consolidation. Consolidation tests were performed on sand-slime and slime tailings
samples. The sand tailings samples did not have sufficient cohesion to be used for
consolidation testing. The consolidation testing results for the samples tested were presented in
Table 3-2 and are summarized below in Table 4-7. The results for consolidation parameters
are similar for sand-slime and slime tailings, with an average Cc value of approximately 0.3 and
an average cv value of approximately 0.001 to 0.002 cm2/s. The measured C and c„ values for
the sand-slime and slime tailings samples are consistent with published test results for other
uranium tailings samples (Keshian and Rager. 1986).
Table 4-7 Summary of Laboratory Measured Consolidation Parameters
Tailings
Type
Sand-Slime
Slime
0.32
(0.11 -0.66)
0.28
(0.27-0.28)
cv (cm/s)
0.001
(0.0005-0.002)
0.002
(0.0005-0.003)
cm Is = square centimeters per second
Tho moaourod Ce and c„ valuoo for tho oand olimo and climo tailingo oomploo aro oonoiotont
with publiohod toot results for othor uranium tailings samplos (Koohian and Ragor, 1086).
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As noted in Section 3.0, the consolidation test results are considered non-standard since the
diameters of the samples tested were smaller than the minimum diameter recommended per
ASTM D2435. It is recommended that the laboratory testing results be interpreted
conservatively and assume the impact of using a smaller diameter sample causes decreased
compressibility.
Values of Cc from the consolidation testing were compared with Atterberg limits and in-situ
density test results in Figure E.4-1 and Figure E.4-2, respectively. Figure E.4-1 indicates there
is not a relationship between Atterberg limits and Cc values for the samples tested. Figure E.4-
2 indicates a relationship of increasing Cc values with decreasing in-situ dry densities with a
value of Cc of 0.3 representative of the majority of the samples. Figure E.4-3 shows the
consolidation test results for each sample tested and this graph also indicates a relationship of
increasing Cc values with decreasing in-situ dry densities.
The results of CPT pore pressure dissipation tests can be used to estimate the horizontal
coefficient of consolidation for sands using the leading theoretical solution by Teh and Houlsby
(1991) with the rigidity index estimated based on plasticity index (PI) from relationship presented
in Keaveny and Mitchell (1986). The horizontal coefficient of consolidation (ch) provides an
indication as to the rate of consolidation when pore water is dissipated horizontally, with higher
ch values indicating more rapid consolidation. The results are summarized in Table 4-8. Only
locations where laboratory samples were collected and tested at the same depth were
evaluated. The results indicate ch values ranging from 0.3 to 0.8 cm2/s. These results are
unreasonably high and cannot be explained solely by anisotropy. Other factors than can affect
estimates of Ch from CPT pore pressure dissipation tests are the soil stress history, soil
structure, and whether the dissipation is continued to equilibrium (Robertson and Cabal, 2012).
It is recommended that laboratory measured cv values be used in future technical analyses and
that cv values not be calculated from estimated ch values based on the CPT soundings.
Table 4-8 Summary of Estimated Horizontal Coefficient of Consolidation from CPT
Soundings
Tailings
Cell
Cell 2
Cell 3
Sampling
Location
CPT-2W2
CPT-3-4N
CPT-3-6N
Tailings Type
Sand-Slime
Sand
Slime
Slime
cnrVs = square centimeters per second
PPD
Depth (ft)
13.94
13.12
8.86
18.54
Estimated
ch
(cm2/s)
0.62
0.51
0.34
0.84
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© MWH Tailings Data Analysis Report
5.0 SUMMARY
The tailings investigation was conducted to address DRC's request for site-specific tailings
information, and followed the October 2013 work plan reviewed and approved by DRC. The
results of this investigation will be used to update technical analyses to address DRC review
comments on the Reclamation Plan Revision 5.0 and the revised ICTM Report. The tailings
characteristic parameters presented in this document are based on the methods presented and
our experience with similar materials. Any analyses conducted using these parameters will
consider the conditions and assumptions under which the values were developed.
The results of the tailings investigation indicate the tailings withinthat both Cells 2 and 3 are
relatively uniform have with minimal segregation of tailings within each cell. The tailings within
Cells 2 and 3 are also similar in particle size distribution and other geotechnical characteristics.
Therefore, it is reasonable to assume the test results from the investigation are representative
for both cells.
A correlation between tailings classification and CPT results (i.e., cone resistance and friction
ratio) was discussed in Section 4.1 and shown in Figure E.1-3 and Figure E.1-4 for Cell 2 and
Cell 3, respectively. These figures classify the tailings as sand/sand-slime tailings or slime
tailings based on CPT results. This criteria was developed based on calibration of laboratory
data with CPT results. It is recommended that the materials identified in the CPT soundings be
classified according to this criteria as sand/sand-slime tailings or slime tailings, and that the
laboratory values representing these tailings classifications be used for future technical
analyses.
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© MWH Tailings Data Analysis Report
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