DRC-2015-004287 - 0901a0688054fe3e

Department of
Environmental Quality
Amanda Smith
Executive Director
State of Utah DIVISION OF RADIATION CONTROL
GARY R HERBERT
Governor
Rusty Lundberg
Director
SPENCER J COX
Lieutenant Governor
MEMORANDUM
TO: File, Energy Fuels Resources (USA) Inc., White Mesa Mill, Tailings Data Analysis
Report; Project:
THROUGH John Hultquist, Section Manager
FROM: Eric Boone, Enviroi tgineer III
DATE: January 20, 2015
SUBJECT: Geotechnical Review of White Mesa Mill, Tailings Data Analysis Report dated
October 2014, Prepared by MWH Americas, Inc., RML# UT1900479, San Juan
County, Utah
Introduction
This technical memorandum to file presents geotechnical review comments on the subject report
prepared by MWH Americas, Inc. (MWH) for Energy Fuels Resources (USA) Inc., (EFRI). The
subject report presents the results of a work plan dated July 2013 (Revision transmittal dated
August 1, 2013) to collect site-specific tailings data on tailings Cells 2 and 3 at the White Mesa
facility in San Juan County, Utah. The objectives of the referenced work plan have been restated
in Section 1.2 of the report.
Findings
1. Section 2.1 - CPT Soundings
The widely dispersed cone penetration testing (CPT) soundings have provided a significant
improvement in the available data to model the geotechnical properties of the tailings soil
profile within Cells 2 and 3. The referenced 1986 paper by Larson and Mitchell (L&M) for
the U.S. Department of Energy Uranium Mills Tailings Remedial Action (UMTRA) Project
provides early experience interpreting CPT data to characterize uranium tailings piles.
Notwithstanding the variation of tailing soils over small distances causing a soil sample taken
at a given interval to potentially be quite different from the soil penetrated by an adjacent CPT
sounding, the paper is quick to point out that predicted Unified Soil Classification System
(USCS) material classifications within a typical CPT classification zone may vary greatly with
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Geotechnical Review of Tailings Data Analysis
January 8, 2015
site specific classification testing results. This paper highlights the importance of developing
site specific correlations between the CPT record and site specific laboratory classification and
proposes a classification scheme unique to uranium mill tailings. It is inferred that the
characterization scheme developed by Larson and Mitchell was adopted by MWH to reduce
the CPT data into categories which site specific geotechnical properties could be assigned.
The L&M scheme utilizes three traditional brackets to capture and categorize mine tailings:
(1) Sand which is material with 0% to 30% passing the #200 sieve; (2) Sand Slime which is a
mixture that has 30% to 70% passing the #200 sieve; and (3) Slime which is a material with
70% to 100% passing the #200 sieve. MWH has recommended adjustments to the L&M
scheme which is to be discussed later.
The work plan anticipated 7 CPT soundings in each cell for a total of 14 soundings. More
than 14 CPT soundings were completed. Each CPT sounding was to extend into the tailings
profile to at least within 5 feet of the predicted depth to the cell liner. The CPT soundings
within Cell 2 typically reached to within 2 feet of the predicted liner depth, it is unfortunate
though that within Cell 3, soundings CPT-3-8S, CPT-3-4N, and CPT-3-3S were each
terminated without apparent obstruction at depths more than 5 feet from the predicted liner by
approximately 7.5 feet, 8.3 feet, and 9 feet, respectively. In general, the DRC acknowledges
that the CPT field program collected field data as it was intended to undertake. However, the
work plan indicated the CPT soundings would be used to develop profiles that characterize the
tailings stratigraphy and thereby allow for interpretation and modeling of the various tailing
materials both vertically and laterally. Cross-sections through the tailings impoundments are
absent from the Tailings Data Analysis Report and without cross-sections (profiles) depicting
the stratigraphy of the tailings materials at each CPT sounding it is unclear how the tailings
material types are distributed and therefore uncertain how they should be geotechnically
modeled.
The Location Map identified as Figure 2-1 does not consistently call-out the depth penetrated
by each CPT sounding. Please review and update the map with the missing information. Also
note there is a depth called-out on settlement monitoring point 2W6-N without an exploration
at this location. Please review and revise. A note regarding the general purpose of the
additional two locations of CPT-2W6-S(2) and CPT-2W6-S(3) should be added to the plan
sheet notes.
Review the interpretation of the static Pore Pressure Dissipation (PPD) tests results reported in
Table 2.1 for CPT-2W3A. These two PPD's appear to have been done in essentially dry
conditions and the interpretation of the results appears to indicate a water surface that is
present within inches of the ground surface. This would be incorrect for dry conditions.
Please review and revise the interpretation and any other report component that relied on this
data or interpretation.
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2. Section 2.2 - Direct Push Explorations
The DRC acknowledges that additional direct push explorations were added over the work
plan amount of 2 explorations per cell. Sample data collected from the field direct push
sampling program will be invaluable to understanding the degree of variability of geotechnical
physical properties within the material placed in Cells 2 and 3. This data goes to the primary
goal of calibrating the abundant CPT soundings. However, before acknowledging the Direct
Push field program achieved the objectives of the work plan the following review comments
need to be addressed.
The eight representative logs in Appendix B need to be internally consistent with respect to
grammatical technique and symbol usage. Please indicate in a suitable place the standard
ASTM practice (2487 or 2488; or both) used to classify the soil encountered. The elevation
information is absent from each log, please revise each log to include this information.
Symbols within the "Run" column appear to indicate on a few logs that there are sample runs
over 24 inches in length up to 36 inches in length, however most sample runs were 24 inches
in length. Is this a correct representation of what occurred in the field? The work plan
described the sampler as being 12 to 18 inches in length and Section 2.2 of the report indicates
the sampler was 24 inches in length with an internal diameter of 1.5 inches. If it was possible
to achieve sampling runs over 24 inches in length please describe in further detail the
longitudinal dimensions of available sampling jars, rig tooling, as well as the length of the
sample sleeves or rings. Provide details of the alternate sampler set-up to assure that the
sampler could accommodate accidental over driving without disturbing (compressing) the
sample. Please clarify/revise instances where the push sample symbol is absent from the
"Push Samples" column on the following logs: CPT-2W3; CPT-2W4-C; CPT-2W6-S(3); and
CPT-2E1. Explain the apparent fixed-size graphical symbol with the adjacent value of inches
recovered.
Please describe the rationale that was used to determine what portion of the tailings profile is
represented by a typical 24 inch sample run that recovered less than 50% of the penetration
length attempted, especially for the longer sample attempts. For example explain how 2 to 6
inches of recovered material from a 24 inch sample run was accurately positioned on the log.
Discuss if it was possible for a sequence of sandy material at the beginning of a sample run,
overlying a softer cohesive sequence of material could develop internal sleeve friction,
sufficient enough to plug the sampler tip and thus preventing any further sample collection.
On initial review there seems to be a bias to placing the recovered sample as representative of
the bottom of a 24 inch sample run and then scheduling and developing lab results to establish
a correlation to the CPT data from this designated "bottom depth". This procedure could
incorrectly place material that was captured at the initial penetration to the bottom of the
sample interval.
Difficulties with achieving decent (> than 67%) sample recovery is a factor with every
successful exploration program. It is noted that based on current information on the Direct
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Push logs, sample recovery achieved an overall success rate of approximately 40% recovered
of the sample run attempted. Furthermore of the nearly 160 lineal feet of Direct Push
explorations the total sample length recovered represents less than 20% of the lineal feet
explored by the Direct Push explorations. Additionally it is also noted that Direct Push
explorations CPT-2W2, CPT-2W6-S(3), and CPT-3-6N experienced good sample recovery, as
compared to explorations CPT-2W3, CPT-2W4-C, CPT-2W6-S(2), CPT-2E1, and CPT-3-4N
which experienced sequences over 8 feet to as much as 28 feet (see CPT-2E1) in length where
sampling was attempted but limited data was collected. Ideal recovery rates of more than 67%
would minimize introducing error and uncertainty, below 50% recovery might be considered
too uncertain given the narrative on sampling procedures discussed above. MWH needs to
clearly indicate what criteria would be appropriate for correlation and why.
These aspects of the sampling procedures as discussed in the preceding two paragraphs are
especially important to understand as based on the adjacent CPT soundings the tailings profile
frequently changes classification vertically within several inches and certainly within a 24
inch sample run. Given the inherent frequent profile changes the tailings characterization
report needs to explain clearly how any proposed correlation scheme accounted for 1) an
apparent overall low sample recovery; 2) an often limited amount of material being recovered
for testing; and 3) the apparent uncertainty of sample location within the 24 inch interval,
along with the associated biased to assign samples to the bottom of a sample run.
It is reported by L&M that the credibility of their classification scheme was high because the
correlations were established with continuous sampling data because they recognized that
tailings material changes occur within a relatively short distance vertically and laterally.
Several examples of how this sample variability was encountered during the laboratory testing
program and the correlation effort are described later in this memo.
It is noted that sampling within the upper sand section (working platform) of each tailings cell
is nearly absent, there are 2 possible representative samples collected at the interface with the
tailings soil, please indicate if this omission was intentional and describe how this absence of
data will be filled. To be complete the Tailings Data Analysis Report needs to include
interpretation, past or present, on this sequence of material. The DRC is curious how
geotechnical properties of this variable thickness sequence (sometimes up to 10 feet thick with
occasional scattered debris) throughout both of the tailings profiles will be modeled during
engineering analysis. Another material identified by the CPT soundings that was not sampled
and tested consists of sequences of Sensitive Fine Grained soil. See CPT plots for SP2W3;
SP3-3S; and SP3-6N. This material falls within Zone 1 of typical soil behavior classification
charts. The L&M plot of data did not have to account for this zone as they didn't have data to
plot within this zone. Please review the CPT data within this zone and clearly justify within
the report that the geotechnical properties of the Sensitive Fine Grained soil are similar to
those for slimes. As indicated above the DRC is curious how geotechnical properties of this
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randomly positioned sequence of material in both of the tailings profiles will be modeled
during engineering analysis.
Please explain or clarify the presentation on the logs of the instances where the upper value of
two moisture content and two dry density results are values from deeper in the sample run.
Standard convention would present data on the deeper sample material below data from a
shallower portion of the sample run. With the profile changes why introduce a possible
misunderstanding? However, finding credit for consistency this same convention was
repeated in Table D-l. Within the log for CPT-2W4-C please clarify the length of sample
recovered from sample interval 7 to 9 feet. Additionally the moisture content and dry density
for the sample from CPT-2W4-C @ 8.9 feet have been incorrectly posted to the log of CPT-
2W3. The moisture content and dry density for the sample identified as CPT-3-6N @ 10.5
feet have been omitted from the log. The logs do not utilize an abundant number of symbols
but is there a symbol legend describing a typical attempted / recovered sample, as well as
other typical log details? A legend could help resolve several of the above questions in one
place. The columns for % Gravel - % Sand - % Passing No. 200 sieve would be expected to
add up to 100%. While minor there are a few instance were the % Sand is off by 0.1% and
appears to be associated with a rounding error. A bigger deviation from the lab sheet result to
the data placed on the log is noted for sample CPT-3-6N @ 6.5 feet with the % Sand entered
on the log. Please review these comments and revise the logs and report as appropriate. The
photo logs are very helpful and appreciated. Please consider adding a running head and/or
page numbering to the pages of photos in Appendix C.
3. Section 3.0 - Laboratory Testing
The following four paragraphs describe procedural aspects of the laboratory program that
were identified during the DRC review but were not thoroughly acknowledged within the
body of the Tailing Data Analysis Report. With the intent to develop a site specific
correlation to CPT soundings review these items and expand the narrative of the
characterization report to account for them and how they might or might not affect the
correlation. The subsequent reviews comments are based on technical or editorial items.
Delayed Testing
The DRC notes that with the delay in testing of often over 2 months, ordinary expectations for
timely geotechnical testing conditions were not observed. This comment is based on the
following history inferred from the report. Samples were collected from the White Mesa
tailings during 4 days of exploration between October 17th and October 23rd, 2013. Samples
collected during the field exploration program were presumably delivered to the MWH
Colorado offices and then shipped to S&ME's laboratory in late November to early December
2013. S&ME completed the gradation testing program between December 17th and 19th, 2
months following the field program. With an exception of one consolidation test completed
within approximately 1.5 months the remaining four consolidation tests where started more
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than 3 months after they were recovered from the tailings. The moisture contents and moist
unit weights presented within S&ME's Materials Test Report (pg. 45) need to be updated with
the date of testing. Ideally laboratory testing would commence directly upon returning from
the field with the samples.
Shipping Disturbance
Sample disturbance is something geotechnical engineers always try to minimize so that
laboratory testing can closely represent field conditions. There is no mention in the report
how the specimens were physically handled during the 1300 mile journey between Colorado
and Tennessee. The DRC believes there would be considerable opportunity for sample
disturbance caused by the shipping of the samples to Tennessee in lieu of the proposed
laboratory (understood to be subsequently disqualified) situated roughly 70 miles south of
MWH's Fort Collins office in Lakewood, Colorado. Unit weights of predominately sandy
samples would likely have experienced densification and loss of interstitial water during
transport. Clearly the consolidation samples from CPT-2W2@7.5 feet, CPT-2W3@7.0 feet
and CPT-2W6-S(2)@13.0 feet display characteristics of sample disturbance with the subdued
transition to the virgin compression curve. The permeability specimens would also be
expected to have been affected by the shipping process.
Sample Tool Disturbance
Please research and interpret published studies on the potential disturbance of Direct Push
samples with inner diameters equal to or less than 1.5 inches that are used for geotechnical
testing. Section 6.2.2 of ASTM D2435 (Consolidation test method) states that the minimum
specimen diameter or inside diameter of the specimen ring shall be 2 inches. The samples
obtained are 1.4 inches in diameter or approximately 70% of the specified minimum diameter.
To further understand the impact of a smaller sample consider if the outer 1/8-inch perimeter
of the 1.4-inch diameter specimen is disturbed by internal wall friction, this results in 33% of
the specimen area being disturbed. Furthermore ASTM D2435 Section 6.2.3 specifies that the
minimum specimen diameter-to-height ratio shall be 2.5. The specimens were 1 inch in
height resulting in a 1.4 ratio which is approximately 56% of the specified ratio. It is
unfortunate the data is subject to these uncertainties. The results from 5 consolidation tests
have been published with the report based on these sample conditions. A subjective re-
plotting of the subdued curve could result in lower over-consolidation ratios (OCR) consistent
with normally consolidated behavior. The two consolidation samples identified as CPT-
2W2@7.5 feet and CPT-2W3@7.0 feet appear to have overestimated the preconsolidation
value with OCR values of 1.9 and 2.9, respectively.
Gypsum Presence
There has risen the concern of the influence of gypsum (CaSO^FhO) being present in the
tailings samples and thus affecting the accuracy of several laboratory test methods. The 2nd
paragraph of report Section 3.0 acknowledges the potential for high moisture contents and
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high fines contents. The method to determine moisture content of soil, ASTM D2216,
specifically points out that standard lab procedure may dehydrate the crystalline water
contained in gypsum and suggests that a lower drying temperature of 60° C be utilized in lieu
of the standard 110° C. As acknowledged the higher drying temperature burns off the
hydrated water resulting in erroneous higher moisture contents and the creation of anhydrite
particles not normally present in the natural tailings material. The potential error enters in the
results of ASTM Dl 140 (#200 Sieve wash) run at the higher temperature in that dry weights
are increased thus altering the outcome of the gradation distribution potentially with higher
fines contents; the results of ASTM D4318 (Atterberg limits) which are entirely based on
moisture contents, which would be suspect, and therefore the outcome could be
misrepresentative. The results of ASTM D422 would be affected similarly and apparently the
hydrometer testing as indicated by the abrupt curvature behavior of the hydrometer gradation
curves.
MWH states in the second paragraph of Section 3.0 "The measured laboratory data used in
Larson and Mitchell (1986) study did not account for gypsum in the tailings. " This
conclusion may not be correct in as much as the L&M paper is silent on whether their test data
accounted for gypsum. The reviewer concurs that this concern will affect certain input
parameters for liquefaction hazard analysis which benefit from fines content. Possibly the
correction for fines content will need to be conservatively reduced.
General Laboratory Review Comments
The following review comments are based on technical or editorial items noted during DRC's
review of the Laboratory Investigation section of the report.
Figure E.4-1 Summary of Atterberg Limits Tests Results has incorrectly plotted division
lines at the lower left corner of the standard plasticity chart. The "A"-line has been extended
diagonally to the X-axis instead horizontally at PI = 4 from an LL = 0 to 25.5. The "U"-line
has also been extended diagonally to the X-axis instead of vertically at LL = 16 to a PI = 7.
This is clearly depicted in Figure 4 of ASTM D2487. Please review the details of the standard
figure and make corrections as appropriate.
The consolidation test identified as CPT-2W6-S(2)@13 feet has been classified to be
representative of tailings slimes, however the total weight of the specimen used in the
consolidation test set-up is indicative of a sand - slime specimen. Similarly, the consolidation
test identified as CPT-2W6-S(3)@15 feet has been classified to be representative of tailings
sand - slimes, however the total weight of the specimen used in the consolidation test set-up is
indicative of a slime specimen. Please research and review the laboratory testing data as well
as the groupings and graphs that included these results to be sure it is being included with the
appropriate soil grouping. These are examples of the variability of the tailings profile within a
short distance. If appropriate please review and revise any other report component (such as
Table 3-2 or Figure E.l-1) that relied on this data or interpretation.
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The eleven ASTM D422 lab test sheets report an increase in the percent passing the #200
sieve from the result of the ASTM Dl 140 test to the subsequent D422 test result. The amount
of increase ranges from 2.2% to 11.8% with an average increase of 4.9%. While an increase
in the % passing the #200 sieve from the initial wash (Dl 140) to the after dry sieve wash is
common it is typically small. ASTM D6913 indirectly indicates that an increase greater than
2% could be indicative of a problem such as degradation during mechanical shaking; loss of
sample during testing, or other issues such as the influence of the dehydrating the gypsum
crystal and thus appearing to pass the crystalline water as wash water. Please research and
review the laboratory testing data and procedures for the eleven gradations with S&ME to be
sure the tests were performed correctly. If needed please review and revise any other report
component that relied on this data or interpretation.
A note should be added to Table D-l and Figure E.4-1 indicating that the Atterberg Limit
testing on the sample CPT-2E1 @ 27.8 feet is for the portion only passing the #40 sieve;
therefore the coarser fraction of the sample needs to have a gradation analysis in order to fully
use this information.
4. Section 4.0 - Tailing Classification - Correlation
As indicated earlier a characterization scheme developed by L&M has been adopted by MWH
to capture site specific field and lab data with adjacent CPT sounding data and thereby making
it possible to classify material catalogued in the remaining CPT soundings. MWH has
interpreted their data and concluded an adjustment to the L&M brackets is necessary. MWH
has recommended a uniform lateral shift in the curve between the sand-slime and slimes; a
revision in the criteria for % fines content between the sand-slime and slimes from 70% to
60%; and finally the removal of the curve dividing sand from sand-slime material, resulting in
two material types sand-slime and slime. As discussed in the following paragraphs the
adjustments appear to be without merit based on laboratory and field data.
The classification curves by Larson and Mitchell are reported to be based on continuous data
which is neither the case for data presented in the report nor anticipated with the work plan.
The interpretation to adjust the L&M curves is based on 20 specimens from approximately
160 lineal feet of exploration, that were selected for correlation purposes and subjects of
gradation testing. Of the 20 specimens, 8 specimens were from sample runs with recovery
rates less than 50%. Therefore nearly half of the specimens are subject to the uncertainty
discussed previously with regards to sample location within a 24 inch sample run.
There also appears to be several plotting errors in the main interpretation graph, Figure E.l-1
Friction Ratio vs. Cone Resistance Tailings Classification. The graph appears to have
incorrectly plotted or transposed gradation and Cc data for the sandier sample from CPT-2W3
@ 7.0 feet with the more fine grained sample from CPT 3-6N @ 5 feet. Please review and
revise this figure and any other report component that relied on this data or interpretation.
While the plot of data from the sample at CPT-3-4N @ 9' was excluded it emphasizes the
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complex nature of the tailings. The specimen consisted of 9 inches of soil from a 30 inch
sample run. The gradation result of 19.6% fines content classifies the specimen as sand. The
adjacent CPT log SP-34N appears to interpret the following 4 soil behavior transitions
between the 9 to 11.5 feet interval: Silt / Sensitive Fines / Clay / Sandy Silt. The work plan
was not developed with a robust field sampling and laboratory testing program that would
likely provide a sufficient quantity of data to overcome the uncertainties associated with a
tailings soil profile and the potential difficulties in sample recovery.
With regards to removing the curve defining the transition from sand to sand-slime. The
combination plots of CPT Data from Cells 2 and 3 (Figure E.l-3 and Figure E.l-4,
respectively) clearly indicate that there are sands in the tailings profile. And the field program
recovered tailings that classified as sand. However, the field program for this project appears
to have had difficulty recovering high quality samples from the sand sequences. Insufficient
samples on the part of the field investigation are not justification to remove the published
division line. Furthermore, a conclusion that there are no sands and that the tailings are
predominantly made up of the sand slime tailings may be an unsupported conclusion. Without
cross-sections depicting the stratigraphy of the tailings this may be an unconservative
simplification of the tailings profile.
With the examples above as well as the numerous comments presented earlier in this review
memo with regards to uncertainties with the Direct Push exploration program and the
laboratory data it is not clear that the adjustments to the L&M classification scheme are
adequately justified.
Interim Cover Material and Sensitive Fines Grained Material
The CPT soundings revealed two soil behavior types that have not been adequately
characterized in the Tailings Data Analysis Report. The first being the surface sequence of
sandy soil with debris in Cells 2 and 3. The DRC is curious how geotechnical properties of
this sequence (sometimes up to 10 feet thick) throughout both of the tailings profiles will be
modeled during engineering analysis. The second being the sequences of Sensitive Fine
Grained soil (See SP2W3; SP3-3S; and SP3-6N). This material is typically assigned to Zone
1 of typical soil behavior classification charts. The L&M plot of data did not have to account
for this zone as they did not have data to plot within this zone. Without cross-sections
depicting the distribution of these tailings materials at each CPT sounding it is unclear how the
tailings should be geotechnically modeled for these two soil behavior types. Please provide
profiles that depict the stratigraphy within each tailings cell both vertically and laterally
Impacts on Geotechnical Analysis - Outline Only; future work
Liquefaction: Raw data from the CPT has deviated significantly from ordinary soil data
therefore value of Ic, used in liquefaction evaluation no longer valid; lab values for fines
content by hydrometer (% passing 0.05 mm, Seed) will be required. Need reliable data.
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Settlement: samples are too small; has there been sufficient testing to model four soil types.
Need reliable lab data.
References:
ASTM Designation: D2435-11, Standard Test Methods for One-Dimensional Consolidation
Properties of Soils Using Incremental Loading, American Society for Testing and Materials,
Annual Book of ASTM Standards, Section Four, Construction, Vol. 04.08, West
Conshohocken, Pennsylvania. 2013. www.astm.org.
ASTM Designation: D2487-11, Standard Practice for Classification of Soils for Engineering
Purposes (Unified Soil Classification System), American Society for Testing and Materials,
Annual Book of ASTM Standards, Section Four, Construction, Vol. 04.08, West
Conshohocken, Pennsylvania. 2013. www.astm.org.
ASTM Designation: D6913-04, Standard Test Method for Particle-Size Distribution (Gradation)
of Soils Using Sieve Analysis, American Society for Testing and Materials, Annual Book of
ASTM Standards, Section Four, Construction, Vol. 04.09, West Conshohocken, Pennsylvania.
2013. www.astm.org.
Larson, N. B., and Mitchell, B. (1986). Cone Penetrometer Use on Uranium Mill Tailings. In
Samuel P. Clemence, Editor, Use of In Situ Tests in Geotechnical Engineering: Proceedings
on In Situ '86, a Specialty Conference sponsored by the Geotechnical Engineering Division of
the American Society of Civil Engineers, Geotechnical Special Publication No. 6, pgs. 700-
713.
MWH Americas, Inc. (2014). Energy Fuels Resources (USA) Inc.. White Mesa Mill, Tailings
Data Analysis Report, October.
MWH Americas, Inc. (2013). Energy Fuels Resources (USA) Inc., White Mesa Mill Tailings
Characterization and Analysis Work Plan, July.
Utah Department of Environmental Quality, Division of Radiation Control, Review of Energy
Fuels Resources (USA) Inc. White Mesa Mill Tailings Characterization and Analysis Data
[URS Project UDRC 1102.004] UT1900479. September 24, 2014.