DRC-2020-017140 - 0901a06880d56f4e

October 19, 2020
ENERGYFUELS
Div of Waste Management
and Radiation Control
OCT 2 0 2020
Energy Fuels Resources (USA) Inc. 225 Union Blvd. Suite 600 Lakewood, CO, US, 80228 303 974 2140
C -2ozo- 01 711-1-0 www.ener • yfuels.cson
Sent VIA E-MAIL AND OVERNIGHT DELIVERY
Mr. Ty L. Howard
Director
Division of Waste Management and Radiation Control
Utah Department of Environmental Quality
195 North 1950 West
P.O. Box 144880
Salt Lake City, UT 84114-4880
Re: Transmittal of Source Assessment Report for MW-28 White Mesa Miff Groundwater Discharge
Permit UGW370004
Dear Mr. Howard:
Enclosed are two copies of Energy Fuels Resource (USA) Inc.'s ("EFRI's") Source Assessment Report
("SAR") for MW-28 at the White Mesa Mill. This SAR addresses the constituents that were identified as
exceeding the GWCL in the 1st Quarter 2020 as described in the Division of Waste Management and Radiation
Control ("DWMRC")-approved Q1 2020 Plan and Time Schedule. EFRI submitted the Plan and Time Schedule
for MW-28 on May 21, 2020. DWMRC approval of the Plan and Time Schedule was received by EFRI on
June 22, 2020. An extension request for the SAR due date was submitted on September 2, 2020 and approved
by DWMRC on September 3, 2020. Pursuant to the Plan and Time Schedule EFRI has prepared this SAR.
This transmittal also includes two CDs each containing a word searchable electronic copy of the report.
If you should have any questions regarding this report please contact me.
Yours very truly,
ENERGY FUELS RESOURCES (USA) INC.
Kathy Weinel
Quality Assurance Manager
CC: David C. Frydenlund
Terry Slade
Logan Shumway
Scott Bakken
Stewart Smith (HGC)
Angie Persico (Intent)
White Mesa Uranium Mill
State of Utah Groundwater Discharge Permit No. UGW370004
Source Assessment Report Under Part I.G.4
For Exceedances in MW-28 in the First Quarter of 2020
Prepared by:
Energy Fuels Resources (USA) Inc.
225 Union Boulevard, Suite 600
Lakewood, CO 80228
October 19, 2020
EXECUTIVE SUMMARY
This Source Assessment Report ("SAR") is an assessment of the sources, extent, and potential
dispersion of uranium and selenium in MW-28 at the White Mesa Mill ("the Mill") as required
under State of Utah Groundwater Discharge Permit UGW370004 (the "GWDP") Part I.G.4,
resulting from out-of-compliance status under Part I.G.2 of the GWDP relating to those
constituents in MW-28. Each of those constituents occurs naturally at the Mill (INTERA, 2008)
and has exhibited exceedances of the applicable Groundwater Compliance Limits ("GWCLs") in
various other wells at the site over time and from time-to-time. As will be demonstrated in this
SAR, the increased concentrations of uranium and selenium in MW-28 are the result of
implications from the existing nitrate/chloride plume, which is currently being remediated under
a Corrective Action Plan ("CAP") for nitrate + nitrite and chloride in groundwater, and are not the
result of any potential seepage from the Mill's tailings management system ("TMS").
Groundwater at the Mill site has been evaluated in multiple recent investigations and reports,
including the Revised Background Groundwater Quality Report (INTERA, 2007a) and the New
Wells Background Report (INTERA, 2008) (collectively with INTERA, 2007b, the "Background
Reports"), the pH Report (INTERA, 2012), an isotopic investigation (Hurst and Solomon, 2008), a
report discussing the occurrence and likely impact of naturally-occurring pyrite on perched
(shallow) groundwater (the Pyrite Report [HGC, 2012a]), and multiple SARs.
At the time of the Background Reports, MW-28 had a limited data set comprised of 11 data
points per GWDP parameter. Significantly more data points are now available, providing a more
robust understanding of the water quality and behavior of MW-28. In general, the behavior of the
key indicator parameters, chloride, fluoride and sulfate, in MW-28 has not changed significantly
since the time of the Background Reports. Chloride concentrations in MW-28 were increasing at
the time of the Background Reports, although not significantly. The increasing concentrations of
chloride, which currently have a statistically significant increasing trend, have continued as a
result of MW-28's location within the downgradient toe of the nitrate/chloride plume (which pre-
dates the Mill and originates upgradient of the Mill and TMS). Fluoride concentrations were
decreasing at the time of the Background Reports, and continue to exhibit a decreasing trend that
is not currently significant. Sulfate concentrations were increasing (not significantly) at the time
of the Background Reports and currently exhibit no trend. Uranium concentrations were
exhibiting no trend at the time of the Background Reports. Although concentrations of uranium
remain relatively low for the Mill site, the concentrations began to increase more recently and
now exhibit a statistically significant increasing trend.
As demonstrated herein, mass balance analysis and geochemical considerations indicate that
potential TMS seepage is not contributing to the groundwater chemistry at MW-28. Migration of
the nitrate/chloride plume; oxidation of pyrite by nitrate; and mobilization of uranium and
selenium by nitrate are the most likely causes of the increases in chloride, selenium, and uranium
measured in MW-28. In addition, uranium may also be mobilized by increased bicarbonate in the
perched groundwater from natural background influences; and selenium may be generally
elevated within the nitrate/chloride plume due to its primary source (the historical pond, which
pre-dates the Mill and is located upgradient of the Mill and TMS) having seeped through Mancos
Shale, a known source of selenium contamination. Increased chloride, uranium, and selenium
concentrations that are unrelated to potential TMS impacts is consistent with previous mass
balance analyses performed on the nitrate/chloride plume that were based on nitrate
concentrations within the plume as described in the December 2009 Contamination Investigation
Report (INTERA, 2009).
In sum, the increasing trends in uranium and selenium in MW-28 are the result of implications
from the nitrate/chloride plume, which is already being remediated under the CAP, and from
natural background influences, and is not the result of any potential seepage from the Mill's
TMS or other activities at the Mill. As a result, it is appropriate to adjust the GWCLs for uranium
and selenium in MW-28 to account for these influences. In accordance with the DWMRC-
approved Flowsheet (from INTERA [2007a], included as Appendix E), increasing trends of this
nature (i.e., resulting from implications from an existing plume being remediated by an existing
Corrective Action Plan or from background influences) necessitate a modified approach for
calculation of GWCLs. The modification in this approach considers a more recent dataset and
the greater of (1) mean + 2cr, (2) highest historical value, (3) background x 1.5, or (4) the
fractional approach (i.e., the prescribed fraction of the Utah Groundwater Quality Standards
applicable to the class of water in the well) , to determine representative and appropriate GWCLs
for trending constituents. Regular revisions to GWCLs for constituents in wells with
significantly increasing trends over time due to background is consistent with the United States
Environmental Protection Agency's ("USEPA's") Unified Guidance (USEPA, 2009). Such
revisions account for the trends and minimize unwarranted out-of-compliance status in such
wells in the future.
TABLE OF CONTENTS
1.0 INTRODUCTION ............................................................................................................... 1
1.1 Previous Plan and Time Schedule .................................................................................... 2
1.2 Source Assessment Report Organization ......................................................................... 3
2.0 CATEGORIES AND APPROACHES FOR ANALYSIS .................................................. 4
2.1 Approach for Analysis ..................................................................................................... 4
2.2 Approach for Setting Revised GWCLs ............................................................................ 5
2.3 University of Utah Study .................................................................................................. 5
3.0 RESULTS OF ANALYSIS ................................................................................................. 6
3 .1 Site-Wide pH Changes ..................................................................................................... 7
3.2 Changes in Groundwater in MW-28 ................................................................................ 8
3.3 Indicator Parameter Analysis ........................................................................................... 9
3.4 Mass Balance Analyses .................................................................................................. 10
3.5 Summary of Results ....................................................................................................... 13
3.5.1 Uranium .................................................................................................................. 13
3.5.2 Selenium ................................................................................................................. 14
4.0 CALCULATIONS OF GROUNDWATER COMPLIANCE LIMITS ............................. 14
4.1 Evaluation of Modified Approaches to Calculation of GWCLs for Trending
Constituents ............................................................................................................................... 15
4.2 Proposed Revised GWCLs ............................................................................................. 16
5.0 CONCLUSIONS AND RECOMMENDATIONS ............................................................ 17
6.0 REFERENCES .................................................................................................................. 19
Table 1
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
Figure 7
Figure 8
Figure 9
LIST OF TABLES
Proposed GWCLs
LIST OF FIGURES
White Mesa Site Plan Showing Locations of Perched Wells and Piezometers
Kriged 2nd Quarter Nitrate (mg/L) (Nitrate+ Nitrite as N) White Mesa Site
Kriged 2nd Quarter Chloride (mg/L) White Mesa Site
Kriged 2nd Quarter 2020 Water Levels White Mesa Site
Groundwater Elevation for MW-28
pH and Bicarbonate at MW-28 Since 2015
Ratio of Chloride to Fluoride Concentrations in MW-28
Uranium and Nitrate at MW-28 Since Q2 2015
Selenium and Nitrate at MW-28 Since Q2 2015
LIST OF APPENDICES
Appendix A GWCL Exceedances for First Quarter 2020 under the March 19, 2019
GWDP
Appendix B Statistical Analysis for MW-28 SAR Constituents
B-1 Statistical Analysis Summary Table
B-2 Comparison of Calculated and Measured TDS for Samples with Complete
Major Ions
B-3 Charge Balance Calculations
B-4 Descriptive Statistics
B-5 Data Used for Statistical Analysis
B-6 Extreme Outlier Status for Use in Analysis
B-7 Box Plots
B-8 Box Plots for MW-28 and in Upgradient and Downgradient Wells
B-9 Box Plots for SAR Parameters in Groundwater Monitoring Wells
B-10 Histograms
B-11 Time Series Plots
B-12 Time Series Plots with Events
Appendix C Statistical Analysis for Indicator Parameters in MW-28
C-1 Indicator Parameter Analysis Summary Table
C-2 Descriptive Statistics of Indicator Parameters
C-3 Data Used for Statistical Analysis
C-4 Data Omitted from Statistical Analysis
C-5 Box Plots for Indicator Parameters
C-6 Piper Diagram for Cell 1, MW-28, and Upgradient and Downgradient Wells
C-7 Histograms for Indicator Parameters
C-8 Time Series Plots and Linear Regressions for Indicator Parameters
C-9 Time Series with Events
Appendix D Mass Balance Calculations
Appendix E Flowsheet (Groundwater Data Preparation and Statistical Process Flow for
Calculating Groundwater Protection Standards, White Mesa Mill Site
[INTERA, 2007a])
Appendix F Flowsheet Analysis for Post-Inflection Data (Modified Approach) for
Purposes of Calculating GWCLs
F-1 Descriptive Statistics for Modified GWCL Data Set and All Data
F-2 Data Used
F-3 Box Plots
F-4 Histograms
F-5 Linear Regression Analysis
Appendix G Input and Output Files (Electronic Only)
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ACRONYM LIST
Background Reports collectively refers to relevant background reports for this well and site:
the Existing Wells Background Report (INTERA, 2007a), the Regional
Background Report (INTERA, 2007b), and the New Wells Background
Report (INTERA, 2008)
CAP Corrective Action Plan
CFCs chlorofluorocarbons
CIR Contaminant Investigation Report
DF Dilution Factor
DO Dissolved Oxygen
Director Director of the Division of Waste Management and Radiation Control
DWMRC State of Utah Division of Waste Management and Radiation Control
EFRI Energy Fuels Resources (USA) Inc.
GWCL Groundwater Compliance Limit
GWDP State of Utah Ground Water Discharge Permit UGW370004
GWQS Groundwater Quality Standard
µg/L micrograms per liter
mg/L milligrams per liter
Mill White. Mesa Uranium Mill
OOC out of compliance
pH Report INTERA (2012b)
P&TS Plan and Time Schedule
PVC Polyvinyl Chloride
Pyrite Report HGC (2012a)
QAM Quality Assurance Manager
SAR Source Assessment Report
TDS Total Dissolved Solids
TMS Tailings Management System
University of Utah Study Hurst and Solomon, (2008)
USEPA United States Environmental Protection Agency
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1.0 INTRODUCTION
Energy Fuels Resources (USA) Inc. ("EFRI") operates the White Mesa Uranium Mill (the
"Mill"), located near Blanding, Utah (Figure 1). Groundwater is regulated under the State of
Utah Groundwater Discharge Permit UGW370004 (the "GWDP"). This is the Source
Assessment Report ("SAR") required under Part I.G.4 of the GWDP, relating to Part I.G.2 of the
GWDP with respect to uranium and selenium in groundwater compliance monitoring well MW-
28. Uranium in MW-28 has had dual exceedances reported prior to the first quarter of 2020 and
was the subject of a Plan and Time Schedule ("P&TS") dated December 4, 2014. The December
4, 2014 P&TS was submitted after dual exceedances of uranium in MW-28, that were reported
after physical damage to the well and casing in May 2014. Details of the December 4, 2014
P&TS are included in Section 1.1 below.
Part I.G.2 of the GWDP provides that an out-of-compliance ("OOC") status exists when the
concentration of a constituent in two consecutive samples from a compliance monitoring point
exceeds a Groundwater Compliance Limit ("GWCL") in Table 2 of the GWDP. The GWDP was
originally issued in March 2005, at which time GWCLs were set on an interim basis, based on
fractions of State of Utah Ground Water Quality Standards ("GWQSs") or the equivalent,
without reference to natural background at the Mill. The GWDP also required that EFRI prepare
a background groundwater quality report to evaluate all historical data for the purposes of
establishing background groundwater quality at the Mill site and developing GWCLs under the
GWDP. As required by then Part I.H.3 of the GWDP, EFRI submitted three "Background
Groundwater Quality Reports" (INTERA 2007a, 2007b, 2008) (collectively, the "Background
Reports") to the Director (the "Director") of the State of Utah Division of Waste Management
and Radiation Control ("DWMRC") (the Director was formerly the Executive Secretary of the
Utah Radiation Control Board and the Co-Executive Secretary of the Utah Water Quality Board).
Based on a review of the Background Reports and other information and analyses, the Director re-
opened the GWDP and modified the GWCLs to be equal to the mean concentration plus two
standard deviations ("mean + 2o") or the equivalent for each constituent in each well, based on an
"intra-well" approach. That is, the compliance status for each constituent in a well is determined
based on current concentrations of that constituent in that well compared to the historic
concentrations for that constituent in that well, rather than compared to the concentrations of the
same constituent in other monitoring wells. The modified GWCLs became effective on January 20,
2010. On January 19, 2018, and March 19, 2019, revised GWDPs were issued, which set revised
GWCLs for certain constituents in certain monitoring wells as approved by the Director through
previously approved SARs relating to those constituents in those wells. GWCLs apply to
groundwater monitoring wells located in the perched aquifer at the Mill.
While consecutive exceedances of chloride have been noted in MW-28 and other wells at the
Mill, a P&TS and an associated SAR for chloride in MW-28 have not been required or
appropriate considering the other actions currently undertaken by EFRI as determined by
DWMRC Staff relating to the existing nitrate/chloride plume at the site. Nitrate + nitrite (referred
to as nitrate hereinafter) and chloride in monitoring wells at the site have been the subject of
ongoing investigations at the Mill. The shallow groundwater nitrate/chloride plume, which
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consists of the commingled nitrate (nitrate plume) and chloride (chloride plume) components
shown in Figures 2 and 3, likely originated primarily from a former stock pond (the historical
pond shown on Figure 1)) located upgradient of the Tailings Management System ("TMS"), but
may have received a contribution from a chemical spill also located some distance upgradient
from the TMS. The nitrate plume is defined by groundwater concentrations exceeding 10
milligrams per liter ("mg/L") nitrate as nitrogen; and the commingled chloride plume is defined by
groundwater concentrations exceeding 100 mg/L chloride. The nitrate plume boundary is based on
the OWQS for nitrate, whereas the chloride plume boundary is defined by a threshold
concentration that appears to exceed the background chloride concentrations within the perched
groundwater.
EFRI submitted a Corrective Action Plan ("CAP") in February 2012 for nitrate + nitrite and
chloride in groundwater. The CAP was approved on December 12, 2012, and the activities
associated with the CAP are on-going. These activities include active remediation by pumping
since the first quarter of 2013. Although active remediation by pumping removes nitrate mass and
accelerates plume remediation, the nitrate plume is also naturally degrading through reaction with
naturally-occurring pyrite in the formation. As discussed in HOC (2017), natural degradation
provides a significant proportion of total nitrate mass removal.
The nitrate/ chloride plume is located downgradient of the northern wildlife ponds. Prior to the first
quarter of 2012, these unlined ponds provided a source of recharge that created a perched
groundwater mound and a source of dilution. Although wildlife pond recharge is substantially
diminished since 2012, as shown in Figure 4, a remnant of the former groundwater mound still
exists upgradient of the TMS. The groundwater mound increased hydraulic gradients that acted to
increase plume migration rates while dilution acted to limit dissolved constituent concentrations
within the plumes. Since water delivery to the northern ponds ceased in March 2012, the
groundwater mounds have declined, hydraulic gradients have diminished, and reduced dilution has
caused increases in constituent concentrations in portions of the plumes (HOC, 2018).
Figure 5 is a plot of groundwater elevation over time at MW-28. As shown, groundwater levels
increased prior to about 2017 before levelling off. The increase was the result of former wildlife
pond recharge and the levelling off due to reduced recharge from the ponds since 2012.
1.1 Previous Plan and Time Schedule
On May 28, 2014, EFRI Environmental Staff identified damage to MW-28 during routine,
quarterly sampling activities. Upon arrival at MW-28, EFRI Environmental Staff noticed that
there was evidence that a vehicle had struck the outer protective metal casing of MW-28 and it
was slightly bent and leaning to the west. Inspection of the inner, 10-inch polyvinyl chloride
("PVC") protective casing and the 4-inch well casing also showed signs of damage. The concrete
seal between the 10-inch outer casing and the 4-inch casing was cracked, and EFRI
Environmental Staff noted that the inner PVC casing was likely cracked and/or broken. Upon
discovery of the damage on May 28, 2014, EFRI Environmental Staff contacted the EFRI
Quality Assurance Manager ("QAM"). The EFRI QAM notified DWMRC in person, while at
the DWMRC offices in Salt Lake City. On June 2, and June 5, 2014 Environmental Staff and
Bayles Exploration repaired the well and removed the debris in the bottom of the well resulting
2
from the damage. The Environmental Staff then over pumped the well and removed over 4
casing volumes to redevelop the well. The well was sampled and the routine, second quarter
2014 sample was collected on June 18, 2014.
Three constituents in MW-28, uranium, vanadium and cadmium, were reported above their
respective GWCLs in the second quarter 2014. Per the GWDP, EFRI began accelerated
monitoring for these three constituents in the third quarter 2014. The fourth quarter 2014 results
for vanadium and cadmium were below the GWCLs. The uranium concentrations remained
above the GWCL in the third quarter 2014. Part I.G.4 c) of the GWDP requires a P&TS for
constituents exceeding their GWCL over two consecutive monitoring periods. The P&TS
specified that an assessment of the uranium concentrations would be completed after the first
quarter 2015 sampling event. If the uranium concentrations continued to exceed the GWCL,
EFRI would perform a video inspection of the interior of MW-28 to investigate the possibility of
additional physical damage to the well structure that may be causing the elevated uranium
results. The uranium concentrations in MW-28 fluctuated above and below the GWCL between
2014 and 2018. Beginning in 2019, the uranium concentrations have been consistently above the
GWCL. As a result of these uranium results and the consecutive selenium exceedances in Q4
2019 and Ql 2020, a P&TS for uranium and selenium concentrations in MW-28 was submitted
to DWMRC on May 21, 2020. The P&TS was approved by DWMRC by letter dated June 22,
2020.
1.2 Source Assessment Report Organization
A description of the approach used for analysis is provided in Section 2.0; the results of the
analyses are presented in Section 3.0; the calculation of GWCLs is provided in Section 4.0; and
conclusions and recommendations are presented in Section 5.0. Section 6.0 lists references cited.
The analyses performed for this Report are organized in Appendices A through G. Appendix A
contains a table showing exceedances; Appendix B contains the statistical analysis performed on
uranium and selenium; Appendix C contains the indicator parameter analysis; Appendix D
contains the mass balance analysis; and Appendix E contains the Groundwater Data Preparation
and Statistical Process Flow for Calculating Groundwater Protection Standards, White Mesa Mill
Site, San Juan County, Utah ("Flowsheet") that was developed based on the United States
Environmental Protection Agency's ("US EPA") Statistical Analysis of Groundwater Monitoring
Data at RCRA Facilities, Unified Guidance (USEPA, 1989, 1992). This Flowsheet was approved
by DWMRC prior to completion of the Background Reports. Appendix F contains the flowsheet
analysis to address revising GWCLs for constituents with increasing trends. Appendix G is
included on the compact disc that accompanies this SAR and contains the electronic input and
output files used for statistical analysis.
Statistical analysis was performed using the software package "R." Risa free statistical package
that allows the analyst to perform statistical analysis and format and output graphs more
effectively than the Statistica software package used in the past. Input and output files included
in Appendix G can be imported into either R or Statistica to replicate the results presented in
this SAR.
3
2.0 CATEGORIES AND APPROACHES FOR ANALYSIS
Previously EFRI has categorized wells and constituents in five categories as follows:
• Constituents Potentially Impacted by Decreasing pH Trends Across the Site
• Newly Installed Wells with Interim GWCLs
• Constituents in Wells with Previously Identified Rising Trends
• Pumping Wells
• Other Constituents
This SAR addresses two constituents (selenium and uranium) in one well (MW-28). These
constituents fall into the fifth category: other constituents. It is important to note that selenium
and uranium can fall within the first category when downward pH trends are noted; however pH
in MW-28 is near-neutral and does not exhibit a decreasing trend.
It is also important to note that the current GWCLs for selenium and uranium were calculated at
the time of the Background Reports using 11 data points. The natural variability of groundwater
chemistry across the site is well documented, and that variability is expected to increase within
the proximity of the commingled nitrate and chloride plume (collectively the nitrate/chloride
plume).
Additional factors that may have contributed to a change in behavior of groundwater conditions
in MW-28 are discussed in Section 3.2.
2.1 Approach for Analysis
The first step in the analysis is to perform an assessment of the potential sources for the
exceedances to determine whether they are due to background influences or Mill activities. If the
exceedances are determined to be caused by background influences, then it is not necessary to
perform any further evaluations on the extent and potential dispersion of the contamination or to
perform an evaluation of potential remedial actions. Monitoring will continue; and, where
appropriate, a revised GWCL is proposed to reflect changes in background conditions at the Mill
site.
The analysis performed in this SAR considers all available data to date to help determine if there
have been any changes in potential TMS seepage indicator parameters (e.g., chloride, sulfate,
fluoride, and uranium) since the date of the New Wells Background Report and the influences of
the nitrate/chloride plume that may suggest a change in the behavior of the groundwater in the
well.
As discussed in the Background Reports (INTERA, 2007a, 2007b, 2008), indicator parameters of
potential TMS seepage include chloride, sulfate, fluoride, and uranium. Chloride is the best
indicator of potential TMS seepage; however, chloride is problematic as an indicator parameter
for those groundwater monitoring wells impacted by the chloride plume (EFRI, 2020). Sulfate
4
and fluoride are useful indicator parameters under geochemical conditions allowing conservative
(i.e., non-reactive) behavior. Uranium behavior may range from conservative to non-
conservative depending on the geochemical conditions.
Groundwater impacted by any potential seepage from the TMS is expected to exhibit increasing
concentrations of chloride, sulfate, fluoride, and uranium, among other constituents. While
uranium can be the most mobile of trace metals under certain conditions, it is typically retarded
behind chloride, fluoride, and sulfate due to possible sorption and precipitation and would likely
not show increasing concentrations in groundwater until sometime after chloride, fluoride, and
sulfate concentrations had begun to increase (INTERA, 2007a). Based on data provided in
USEPA (2008) uranium is generally expected to sorb and have comparatively poor mobility at
the near-neutral pH conditions encountered at MW-28. Regardless, although the absence of a
rising trend in constituent concentrations would indicate that there has been no impact from the
TMS, a rising trend in concentrations could also result from natural influences (INTERA, 2007a,
Section 12.0).
The evaluation of SAR parameters and indicator parameters in MW-28 was supported by a
statistical analysis that followed the process outlined in the Flowsheet (INTERA, 2007a)
attached as Appendix E. As discussed in Section 1.2, the Flowsheet was designed based on
USEPA's Statistical Analysis of Groundwater Monitoring Data at RCRA Facilities, Unified
Guidance (USEPA, 1989, 1992, 2009), and was approved by DWMRC prior to completion of
the Background Reports (INTERA, 2007a, 2007b, 2008).
2.2 Approach for Setting Revised GWCLs
If the preceding approach indicates that the previous analysis in the Background Reports has not
changed, or that the OOC status of selenium or uranium in MW-28 is due to natural or other site-
wide influences that are already being addressed by corrective action, then new GWCLs may be
proposed for the constituents. The revised GWCLs use the DWMRC-approved Flowsheet,
including the last decision of the process that directs the analyst to consider a modified approach
to determining a GWCL if an increasing trend is present.
2.3 University of Utah Study
At the request of the DWMRC, T. Grant Hurst and D. Kip Solomon of the Department of
Geology and Geophysics of the University of Utah performed a groundwater study (the
"University of Utah Study") at the Mill site in July 2007 (Hurst and Solomon, 2008). The
purpose of this study was to characterize groundwater flow, chemical composition, noble gas
composition, and water age to evaluate whether the increasing and elevated trace metal
concentrations in monitoring wells at the Mill, all of which were identified in the Background
Reports (INTERA, 2007 a, 2007b, 2008), may indicate that potential seepage from the TMS is
occurring.
To evaluate sources of solute concentrations at the Mill, low-flow groundwater sampling was
used as a method for collecting groundwater quality samples from 15 monitoring wells. In
addition, surface water samples were collected from TMS Cells 1, 3, and 4A, and two wildlife
5
ponds. Passive diffusion samplers were also deployed and collected to characterize the dissolved
gas composition of groundwater at different depths within the wells. Samples were collected and
analyzed for the following constituents: tritium, nitrate, sulfate, deuterium and oxygen-18 of
water, sulfur-34 and oxygen-18 of sulfate, trace metals (uranium, manganese, and selenium), and
chlorofluorocarbons ("CFCs").
Hurst and Solomon (2008, page iii) concluded generally that,
[t]he data show that groundwater at the Mill is largely older than 50 years, based
on apparent recharge dates from chlorofluorocarbons and tritium concentrations.
Wells exhibiting groundwater that has recharged within the last 50 years appears
to be a result of recharge from wildlife ponds near the site. Stable isotope
fingerprints do not suggest contamination of groundwater by tailings cell leakage,
evidence that is corroborated by trace metal concentrations similar to
historically-observed observations.
Hurst and Solomon (2008) also concluded that,
[i]n general, the data collected in this study do not provide evidence that tailings
cell leakage is leading to contamination of groundwater in the area around the
White Mesa Mill. Evidence of old water in the majority of wells, and significantly
different isotopic fingerprints between wells with the highest concentrations of
trace metals and surface water sites, supports this conclusion.
It should be further noted that subsequent to the University of Utah Study EFRI submitted the
Contaminant Investigation Report ["CIR"}, White Mesa Uranium Mill Site, Blanding Utah,
dated December 30, 2009 (INTERA, 2009), in connection with the nitrate/chloride plume at the
Mill site.
3.0 RESULTS OF ANALYSIS
This section describes the potential geochemical influences on groundwater in MW-28 and
results of the analysis, summaries of which are presented in Appendices B and C. Supporting
analyses are presented in Appendices D and F.
As shown in Appendix B, and as will be discussed below, both uranium and selenium
concentrations are relatively low for the site. Prior to 2012 selenium concentrations are variable.
Notable changes in both uranium and selenium occur in 2014 (at the time of the wellhead impact
and repair) as well as post 2017. For purposes of evaluating the increasing concentrations of
uranium and selenium post 2017, and for calculating appropriate compliance limits, subsets of
post 2017 data are analyzed along with the complete data sets as presented in Appendix F. For
uranium analysis, extreme outliers relating to the wellhead impact were removed from the
dataset prior to analysis; however extreme outliers identified as part of the recent increasing
trend were retained. For selenium analysis, one extreme outlier was identified as part of the
6
recent (post 2017) increasing trend but was retained for analysis. Post 2017 data for both
uranium and selenium are normally distributed and exhibit statistically significant increasing
trends.
3.1 Site-Wide pH Changes
As has been documented in INTERA (2012), a decreasing trend in pH has been observed in
almost every groundwater monitoring well across the site, including upgradient and far
downgradient monitoring wells; and decreasing pH is one of the most important contributors to
increasing concentrations of many naturally-occurring parameters.
Hydro Geo Chem, Inc. (["HGC"]), 2012a) ("The Pyrite Report") attributed the decline in pH
across the Mill site to the site-wide existence and oxidation of pyrite in the perched groundwater
monitored at the site. Based on HGC (2012a) pyrite has been noted in approximately 2h of the
lithologic logs for wells installed at the site since 1999, and verified by laboratory analysis in
core and cuttings from at least 25 monitoring wells, including MW-28, as well as MW-27, which
is located upgradient of MW-28 (Figure 4).
Pyrite may oxidize according to the following reaction (Williamson and Rimstidt, 1994):
(reaction 1)
Reaction 1 will increase hydrogen ion (acid) concentrations, which results in decreasing pH.
Oxidation of pyrite and the resulting decrease in pH enables subsequent pH-dependent reactions
to occur, including the mobilization of naturally-occurring metals and metalloids (such as
selenium) in the formation (McClean and Bledsoe, 1992). In addition, pyrite typically contains
many contaminants including selenium (Deditius, 2011) that are expected to be released upon
pyrite oxidation.
The likely causes for site-wide oxidation of pyrite include processes that increase oxygen
transport to groundwater such as the following: (1) infiltration of oxidized water from the
wildlife ponds upgradient of the Mill site; (2) changing water levels and incorporation of oxygen
in air-filled pore spaces into groundwater; (3) the introduction of oxygen during pumping related
treatment of the nitrate/chloride plume; and (4) the introduction of oxygen during increased
sampling of monitoring wells (INTERA, 2012). Many of these mechanisms, in particular
changing water levels, are expected to impact MW-28. Water levels at many site wells increased
due to former seepage from the northern wildlife ponds located upgradient of the TMS. As
shown in Figure 5, as a result of former wildlife pond seepage, water levels at MW-28 increased
by nearly 5 feet between 2006 and 2017 before levelling off.
However, pyrite may also oxidize in the absence of oxygen by reacting with nitrate within the
nitrate/chloride plume. Because of its location at the leading edge of the nitrate/chloride plume,
MW-28 is expected to be impacted by this process (Figure 2 and 3).
As discussed in HGC (2017) nitrate consumption through pyrite oxidation is consistent with the
stability of nitrate concentrations in MW-30 and MW-31, which are located at the downgradient
southern toe of the nitrate plume (Figure 2). As will be discussed below, pyrite oxidation by
7
nitrate may occur by two potential pathways; one which releases acid, and one which consumes
acid.
Based on Hayakawa et al (2013), the acid-producing reaction resulting in the oxidation of pyrite
in the presence of bacteria and nitrate is as follows:
(reaction 2)
Based on Spitieri et al (2008), the acid-consuming reaction resulting in the oxidation of pyrite in
the presence of nitrate is as follows:
(reaction 3)
The relative dominance of pyrite oxidation by dissolved oxygen (producing acid and sulfate by
reaction 1) and/or by nitrate (producing acid and sulfate by reaction 2; or producing sulfate but
consuming acid by reaction 3) may result in sulfate production with or without a decrease in pH.
Because pH is generally increasing at MW-28 since early to mid-2016 (Figure 6), it appears that
reaction 3, at least at the present time, is likely dominating the geochemistry of MW-28 and
causing pyrite to oxidize while consuming acid. Prior to 2016, the pH at MW-28 was generally
decreasing and was likely dominated by reaction 1 or 2.
The general increase in pH in MW-28 since early to mid-2016 appears to correlate with a general
increase in bicarbonate (Figure 6) over the same period. MW-28, although located immediately
downgradient of Cell 1, is also located downgradient of the Mill site. Increasing bicarbonate
likely originates from enhanced infiltration of precipitation within relatively flat graded areas
within the Mill site and surrounding areas that leaches carbonate from alkaline soils overlying
the bedrock hosting the perched groundwater. Because negligible bicarbonate concentrations
occur within the TMS solutions, the TMS is an unlikely contributor to the bicarbonate in MW-
28.
3.2 Changes in Groundwater in MW -28
At the time of the Background Rep011s, MW-28 had a limited data set composed of 11 data
points per GWDP parameter. At the time of this SAR, 40-62 data points are available, providing
a more robust understanding of the water quality and behavior of MW-28. Other factors that may
also contribute to the behavior of constituents in this well are discussed below.
Increasing concentrations of various analytes in wells located within and marginal to the
nitrate/chloride plume are due to the continued downgradient migration of the plume. MW-28 is
located within the leading edge of the nitrate/chloride plume and is generally downgradient of
the historical pond, the most likely contributor to the nitrate/chloride plume. As discussed in
Section 1.0, the historical pond was located upgradient of the Mill and TMS (HGC, 2018).
Chloride at MW-28 has been generally increasing since the well was installed (Appendix C-8);
however nitrate is lagging chloride due to likely degradation by pyrite, and has not yet exceeded
10 mg/L. However, nitrate began increasing in late 2014, reaching 5 mg/Lin late 2019.
8
The increase in nitrate since late 2014 correlates to increases in selenium and uranium
concentrations that have resulted in exceedances of the GWCLs (Figure 8 and Figure 9). The
increases in selenium concentrations may result from one or more of the following: nitrate
oxidizing and mobilizing naturally-occurring selenium (Wright [1999]; Bailey et al [2012];
Shultz et al [2018]); selenium that may be generally elevated in the nitrate/chloride plume due to
the historical pond having seeped through the Mancos Shale ( a source of selenium [US
Department of Energy, 2011]) is now migrating past MW-28; and/or selenium may be released
from pyrite oxidized by nitrate or by elevated dissolved oxygen ("DO") in the plume. Pyrite
commonly contains selenium and other trace metals as contaminants (Deditius et al [2011]).
Since 2016, concentrations of bicarbonate (and calcium) at MW-28 appear to be generally
increasing (Figure 6). The recently elevated concentrations of calcium and bicarbonate are
consistent with mobilization of naturally-occurring uranium in the formation. As discussed in
Desbarats et al (2017), and Drage and Kennedy (2013), high mobility and elevated
concentrations of uranium are frequently associated with relatively high calcium and carbonate
species concentrations; and Burow et al (2017) note the correlation between increases in
groundwater uranium and bicarbonate concentrations in the arid west.
There is also abundant evidence in the literature of the association between increased nitrate and
increased uranium in groundwater, which has been documented in many aquifers. Mechanisms
for mobilization of uranium by nitrate are discussed in Senko et al (2005); Wu et al (2010);
Westrop et al (2018); and Asta et al (2020).
3.3 Indicator Parameter Analysis
As discussed in the Background Reports (INTERA, 2007a, 2007b, 2008), indicator parameters of
potential TMS seepage include chloride, sulfate, fluoride, and uranium. Chloride is the best
indicator of potential TMS seepage; however, chloride is problematic as an indicator parameter
for those groundwater monitoring wells impacted by the chloride plume (EFRI, 2020). Sulfate
and fluoride are useful indicator parameters under geochemical conditions allowing conservative
(i.e., non-reactive) behavior. Uranium behavior may range from conservative to non-
conservative depending on the geochemical conditions.
Groundwater impacted by any potential seepage from the TMS is expected to exhibit increasing
concentrations of chloride, sulfate, fluoride, and uranium, among other constituents. While
uranium can be the most mobile of trace metals under certain conditions, it is typically retarded
behind chloride, fluoride, and sulfate due to possible sorption and precipitation and would likely
not show increasing concentrations in groundwater until sometime after chloride, fluoride, and
sulfate concentrations had begun to increase (INTERA, 2007a). Based on data provided in
USEPA (2008) uranium is generally expected to sorb and have comparatively poor mobility at
the near-neutral to slightly acidic pH conditions encountered at MW-28. Regardless, although the
absence of a rising trend in constituent concentrations would indicate that there has been no
impact from the TMS, a rising trend in concentrations could also result from natural influences
(INTERA, 2007a, Section 12.0).
9
In general, the behavior of indicator parameters in MW-28 has not changed significantly since
the time of the Background Reports. A summary of statistical analysis of indicator parameters is
included in Appendix C-1. Appendix C-2 presents a comparison of descriptive statistics for
indicator parameters from the Background Reports and this 2020 SAR. Data used in the analysis
and data removed prior to analysis are presented in Appendices C-3 and C-4, respectively. The
distribution and identification of outliers and extreme outliers in indicator parameter
concentration data sets are demonstrated in the box plots included in Appendix C-5. A Piper
diagram, which can be used to distinguish between different waters, is presented in Appendix C-
6.
Chloride concentrations in MW-28 were increasing at the time of the Background Reports,
although not significantly. The increasing concentrations of chloride have continued and the
trend is currently statistically significant (see Appendix C-8 for a time series). Fluoride
concentrations were decreasing at the time of the Background Report, and continue to exhibit a
decreasing trend that is not significant at the time of this SAR. Uranium concentrations were
exhibiting no trend at the time of the Background Report. Although concentrations of uranium
remain relatively low compared to the Mill site generally (Appendix B-10), the concentrations
began to increase more recently (post 2017) and now exhibit a statistically significant increasing
trend. Time series plots with vertical lines to indicate events that may have contributed to
observed changes in indicator parameters are included in Appendix B-12 and Appendix C-9.
Sulfate concentrations were increasing (not significantly) at the time of the Background Reports.
Currently, sulfate concentrations in MW-28 exhibit no trend.
3.4 Mass Balance Analyses
The 2020 SAR for MW-31 (INTERA, 2020), another well impacted by the nitrate/chloride
plume, included a mass balance analysis to predict fluoride concentrations assuming a
hypothetical situation under which potential TMS seepage has entered the groundwater and has
become diluted during transport before reaching MW-31. Predicted fluoride concentrations were
based on dilution factors ("DFs") calculated for other indicator parameters (uranium, chloride,
and sulfate) using average TMS Cell 1 concentrations and current MW-31 concentrations. A
similar mass balance analysis has been performed for MW-28.
The mass balance model is based on current concentrations of fluoride, uranium, chloride, sulfate
and selenium in MW-28 and mean concentrations of the same constituents in Cell 1 water. The
mean concentrations in Cell 1 were based on data collected between 2003 and 2019 (EFRI
2019). Samples of Cell 1 water have produced variable results between 2003 and 2019, so
average concentrations were used to describe the Cell 1 water. The model calculates estimated
fluoride contributions to MW-28 groundwater from hypothetical TMS seepage based on
measured concentrations of chloride, sulfate, uranium and selenium. The model assumes
potential TMS seepage has entered the groundwater and has become diluted during transport
before reaching MW-28 and that this occurred far enough in the past to potentially reach MW-28
at the present time. Therefore, the most recent analyses of MW-28 groundwater were selected to
represent modern MW-28 water.
10
For this mass balance calculation, indicator parameters are assumed to be conservative tracers
(INTERA, 2007a) and not subject to attenuation during transport. Therefore, if the TMS is a
source of contamination at MW-28, the concentration of fluoride in MW-28 is expected to be
proportional to the concentrations of uranium, chloride, sulfate, and selenium in the TMS
solutions. Although this model assumes only hypothetical TMS seepage and dilution by natural
groundwater at MW-28, the most likely causes of increasing constituent concentrations in this
well include the nitrate/chloride plume and oxidization of naturally occurring pyrite, as discussed
in Section 3.2, and as will be discussed in more detail below.
Model calculations are presented in Appendix D. The mass balance calculations are based on
DFs computed as the ratio of a particular constituent's current (Q2 2020) concentration in MW-
28 to its average concentration in TMS Cell 1 solutions since 2003. The DFs calculated for all
indicator parameters based on the ratio of Cell 1 and MW-28 constituent concentrations vary by
four orders of magnitude.
Based on the computed DFs for uranium, chloride, sulfate, and selenium, the predicted MW-28
fluoride concentrations are 0.033, 11.9, 30.1 and 0.0028 mg/L, respectively; yet the most recent
observed concentration of fluoride in MW-28 is 0.687 mg/L. The dissimilarity between predicted
and measured fluoride concentrations and the large range in calculated DFs for the four indicator
parameters indicate that potential TMS seepage is not a contributor to the groundwater chemistry
of MW-28. Instead, fluoride concentrations in MW-28 are similar to most natural waters (< 1
mg/L; Hem 1985) and are more consistent with natural processes.
If the same mass balance methodology is applied to uranium, the predicted MW-28 uranium
concentrations range from 0.5 micrograms per liter ("µg/L") (based on the fluoride DF) to 5,349
µg/L (based on the sulfate DF); yet the most recent observed concentration of uranium in MW-
28 is 5.91 ug/L. As with fluoride, the dissimilarity between predicted and observed uranium
concentrations and the large range in calculated DFs for the four indicator parameters indicate
that potential TMS seepage is not a contributor to the groundwater chemistry at MW-28.
In addition, if the same mass balance methodology is applied to selenium, the predicted MW-28
selenium concentrations range from 120 µg/L (based on the uranium DF) to 108,892 µg/L (based
on the sulfate DF). All of the predicted concentrations of selenium substantially exceed the most
recent observed selenium concentration of approximately 10.2 µg/L, an even more compelling
indication that potential TMS seepage is not a contributor to the groundwater chemistry at MW-
28.
Both fluoride and sulfate concentrations at MW-28 are stable (Appendix C), which is
inconsistent with potential TMS seepage. Because chloride and fluoride are the most
conservative and mobile parameters, and because concentrations of chloride are increasing and
fluoride is stable, the ratio of chloride to fluoride concentrations is increasing (Figure 7). If the
chloride in MW-28 resulted from a potential TMS impact, the MW-28 chloride to fluoride ratio
should be decreasing (rather than increasing) because the chloride to fluoride ratio in Cell 1
(approximately 11 based on average concentrations) is much lower than the ratio at MW-28 (188
as of Q2 2020, Figure 7). Based on the ratio of the most conservative parameters (chloride to
fluoride), the MW-28 'geochemical signature' is becoming more and more unlike the signature
11
of TMS solution. The increase in the chloride to fluoride ratio at MW-28 is, however, consistent
with the position of MW-28 in the downgradient toe of the nitrate/chloride plume and the
ongoing downgradient migration of the plume. As discussed in Section 3.2 and INTERA (2009),
the nitrate/chloride plume originated primarily from an upgradient pre-Mill source. This source
(the historical pond) was located approximately 500 feet upgradient (northeast) of TMS Cell 1
(INTERA, 2009).
Furthermore, the ratios of other indicator parameters in MW-28 differ substantially from ratios of
the same constituents in Cell 1 solutions. The average chloride to average sulfate ratio in Cell 1
is approximately 0.14 while the Q2 2020 ratio in MW-28 is approximately 0.06; the ratio of
average chloride to average uranium in Cell 1 is approximately 61 while the Q2 2020 ratio in
MW-28 is approximately 21,827; and the ratio of average chloride to average selenium in Cell 1
is approximately 3 while the Q2 2020 ratio in MW-28 is approximately 12,647. None of these
ratios are reflective of a TMS impact.
Finally, nitrate, a component of the nitrate/chloride plume which originates upgradient of the
Mill and TMS, is an anion with a mobility in soils and groundwater that is expected to be
comparable to chloride and fluoride, which generally migrate at about the same velocity as the
groundwater; whereas uranium and selenium are expected to be significantly retarded with
respect to these conservative parameters and to migrate substantially more slowly than
groundwater. However, beginning in 2015, there is a strong correlation between increases in
uranium and nitrate (Figure 8), and between increases in selenium and nitrate (Figure 9).
Because 1) nitrate is an anion with a mobility comparable to chloride; 2) uranium and selenium
are expected to be retarded with respect to nitrate; and 3) uranium and nitrate, and selenium and
nitrate, are increasing nearly simultaneously; the behavior of these parameters at MW-28 is
consistent with geochemical changes in the immediate vicinity of the well and not to a relatively
remote potential source such as TMS seepage.
Based on the correlations between uranium and nitrate, and between selenium and nitrate, the
most likely mechanisms for increases in uranium and selenium are 1) mobilization of naturally
occurring uranium and selenium in the formation by nitrate; and 2) release of selenium from
selenium-bearing pyrite via oxidation by nitrate as discussed in Section 3.2. The lack of decrease
in pH at MW-28 suggests that pyrite oxidation by nitrate occurs through the pathway (reaction 3
described above and in HGC, 2017) that consumes rather than produces acid. In addition, as
discussed in Sections 3.1 and 3.2, increased bicarbonate from background influences may
mobilize naturally-occurring uranium; and selenium may be generally elevated within the
nitrate/chloride plume due to its potential primary source (the historical pond) having seeped
through Mancos Shale.
Overall, the mass balance analysis and geochemical considerations indicate that potential TMS
seepage is not a contributor to the groundwater chemistry at MW-28. Migration of the
nitrate/chloride plume; oxidation of pyrite by nitrate; and mobilization of uranium and selenium
by nitrate are the most likely causes of the increases in chloride, selenium, and uranium
measured in MW-28, which is located in the downgradient toe of the plume where such increases
would be expected (as indicated above). In addition, uranium may be mobilized by increased
bicarbonate from background influences in the perched groundwater; and selenium may be
12
generally elevated within the nitrate/chloride plume due to its primary source (the historical
pond) having seeped through Mancos Shale. That increased chloride, uranium and selenium are
unrelated to potential TMS impacts is consistent with previous mass balance analyses performed
on the nitrate/chloride plume that were based on nitrate concentrations within the plume as
described in the December 2009 CIR (INTERA, 2009) .
The nitrate mass balance calculation presented in INTERA (2009) suggested that groundwater
mounding would occur underneath the TMS if the nitrate/chloride plume was caused by
hypothetical TMS seepage. The results of this calculation predicted that a 5-foot groundwater
mound would be expected if the nitrate/chloride plume was caused by TMS seepage. This nitrate
mass balance calculation was updated in the 2015 SAR (INTERA, 2015, Appendix F-2).
Although a substantial groundwater mound was predicted, such a mound has not been identified
beneath the TMS cells (Figure 4).
3.5 Summary of Results
As discussed in the Background Reports (INTERA, 2007a, 2007b, 2008), indicator parameters of
potential tailings system seepage include chloride, sulfate, fluoride, and uranium. Chloride is the
best indicator of potential TMS seepage; however, chloride is problematic as an indicator
parameter for those groundwater monitoring wells at the Mill impacted by the chloride plume
(EFRI, 2020). MW-28 is located within the leading edge of the nitrate/chloride plume, which
originates upgradient of the Mill and TMS. Analysis of the next most conservative constituents
fluoride and sulfate demonstrate that changes in chemistry at MW-28 are inconsistent with a
TMS impact. Fluoride and sulfate concentrations at MW-28 are decreasing or stable,
respectively; the ratios of chloride to fluoride and of chloride to sulfate at MW-28 differ
substantially from average ratios of these constituents within Cell 1; and the ratios of chloride to
fluoride at MW-28 and of average chloride to average fluoride in Cell 1 are becoming more
different over time; all of which are inconsistent with potential TMS impact. The increasing ratio
of chloride to fluoride at MW-28 is, however, consistent with continued downgradient migration
of the nitrate/chloride plume past MW-28.
3.5.1 Uranium
As noted in Section 3.3 above, uranium concentrations are relatively low for the site, and as
shown in Appendix B are exhibiting a statistically significant increasing trend. Notable changes
in uranium concentration trends occur in 2014 at the time of the wellhead impact and repair, and
again in 2017. The subset of data post 2017 that were analyzed alongside the complete data set
and presented in Appendix F are normally distributed and exhibit a significantly increasing
trend.
However, in addition to the behavior of indicator parameters discussed above in Section 3.5,
which are inconsistent with a potential TMS impact, the ratio of average chloride to average
uranium in Cell 1 is approximately 61 while the Q2 2020 ratio in MW-28 is approximately
21,827, also not reflective of a potential TMS impact. Furthermore, in performing the mass
balance analysis discussed in Section 3.4, the inability of any of the calculated DPs for chloride,
13
fluoride, sulfate or selenium to predict the concentration of uranium at MW-28 to within even an
order of magnitude, is also inconsistent with a potential TMS impact.
As discussed above in Section 3.4, the most likely mechanisms for increased uranium at MW-28
are 1) mobilization of naturally occurring uranium in the formation by nitrate supplied by the
nitrate/chloride plume; and 2) increased mobility of naturally-occurring uranium resulting from
generally increased bicarbonate from natural background influences. The nearly simultaneous
increases in highly mobile nitrate and relatively immobile uranium at MW-28 are reflective of
geochemical changes in the immediate vicinity of the well and not of any potential seepage from
the TMS.
3.5.2 Selenium
Selenium concentrations are relatively low for the site. The time series plot provided in
Appendix B shows the variability in selenium concentrations prior to 2012, as well as an
increase in concentration following the 2014 wellhead impact and repair. As with uranium,
concentrations of selenium begin to increase more steeply in 2017. The subset of data post 2017
analyzed alongside the complete data set as presented in Appendix F are normally distributed
and exhibit a significantly increasing trend.
However, in addition to the behavior of indicator parameters discussed above in Section 3.5,
which are inconsistent with a potential TMS impact, the ratio of average chloride to average
selenium in Cell 1 is approximately 3 while the Q2 2020 ratio in MW-28 is approximately
12,647, also inconsistent with a potential TMS impact. Furthermore, in performing the mass
balance analysis discussed in Section 3.4, the inability of any of the calculated DFs for chloride,
fluoride, sulfate or uranium to predict the concentration of selenium at MW-28 to within even an
order of magnitude; and the one to more than four order of magnitude overprediction of selenium
concentrations based on DFs; are also inconsistent with a potential TMS impact.
As discussed above in Section 3.4, the most likely mechanisms for increased selenium at MW-28
are 1) mobilization of naturally occurring selenium in the formation by nitrate supplied by the
nitrate/chloride plume; 2) oxidation of selenium-bearing pyrite by nitrate; and 3) generally
elevated selenium concentrations within the nitrate/chloride plume now migrating past MW-28.
As discussed above, the likely source of the potentially elevated selenium in the nitrate/chloride
plume is the Mancos Shale. The nearly simultaneous increases in highly mobile nitrate and
relatively immobile selenium at MW-28 are reflective of geochemical changes in the immediate
vicinity of the well and not of any potential seepage from the TMS.
4.0 CALCULATIONS OF GROUNDWATER COMPLIANCE LIMITS
The findings of analyses discussed above support the conclusions that (1) MW-28 is not being
impacted by any potential TMS seepage, and (2) increasing concentrations of constituents in
MW-28 are the result of background and/or influences such as the nitrate/chloride plume, which
are already being addressed under the CAP. Furthermore, the existing GWCLs for MW-28 were
developed at the time of the Background Reports using 11 data points that are no longer
14
representative of current conditions at that location. Therefore, revision of GWCLs for SAR
parameters in MW -28 is proposed.
4.1 Evaluation of Modified Approaches to Calculation of GWCLs for Trending
Constituents
According to the DWMRC-approved Flowsheet (Appendix E), if an increasing trend is present,
a modified approach should be considered for determining GWCLs. The constituents included in
this SAR, uranium and selenium in MW-28 are exhibiting significantly increasing trends that can
be attributed to one or more of the following: (1) natural background conditions; (2) pyrite
oxidation in the aquifer, which can release metals and/or increase the mobility of metals, (3) the
location of this well within the nitrate/chloride plume, which is actively being remediated
according to the CAP (HGC, 2012b); and/or (4) effects of recent events on groundwater in MW-
28, such as the wellhead impact and repair.
The Flowsheet contemplates GWCLs being set in various circumstances based on (1) the
fractional approach; (2) the highest historical value; and (3) the mean + 2cr, and states that for
rising trends a modified approach can be considered. In proposing a modified approach for the
GWCLs for uranium and selenium in MW-28, the following alternative approaches to
calculating GWCLs have been considered, in addition to the fractional approach, highest
historical value, and mean + 2cr:
1. 1.5 times background concentration as defined in Utah Administrative Code ("UAC")
R317-6-4.3.
The U AC R317-6-4.3 recognizes that "contaminants" may be present as part of naturally
occurring background conditions:
When a contaminant is present in a detectable amount as a background
concentration, the concentration of the pollutant may not exceed the greater of
1.5 times the background concentration or 0.5 times the ground water quality
standard or background plus two standard deviations ...
In this rule, background concentration is defined as the "concentration of a pollutant in ground
water upgradient or lateral hydraulically equivalent point from a facility, practice or activity
which has not been affected by that facility, practice or activity." Background at the Mill has
been determined on an intrawell basis, as defined in the Background Reports. Therefore, to be
conservative, the mean concentration is proposed to be used as background for the purposes of
this calculation. The mean concentration would assume all data to date ( or a data subset as
described below), after following the data quality steps of the Flowsheet.
2. Using recent data to calculate GWCLs.
This approach follows the DWMRC-approved Flowsheet (Appendix E) by taking into account
increasing trends and processing the data consistently with previously determined GWCLs. In
this approach, the complete data set, which exhibits an increasing trend for uranium and
15
selenium over the history of the well record, is divided into a subset of data based on
identification of a point of inflection where the results have shifted. This approach is appropriate
in wells, such as MW-28, that have been thoroughly investigated and where the causes of
increasing trends are not due to any potential TMS seepage or other Mill-related impacts that are
not already being addressed. For purposes of this modified approach and to be consistent with
previous SARs, a point of inflection was identified in the uranium and selenium data sets, and
data from post-April 2017 were evaluated (Appendix F) in addition to the full data sets. Both of
the uranium and selenium post-April 2017 data sets are normally distributed, and exhibit
significantly increasing trends.
These two modified approaches, in addition to (1) the fractional approach; (2) the highest
historical value; and (3) the mean+ 2cr, have been considered for developing revised GWCLs for
uranium and selenium in MW-28, which are increasing in concentration for reasons other than
any potential TMS impact. Based on this analysis, the most appropriate GWCL for uranium and
selenium in MW-28, considering increasing trends, is proposed as the highest of the following:
(1) fractional approach; (2) highest historical value; (3) mean + 2cr, calculated using either the
full data set or the post April-2017 data set; or (4) 1.5 times background, calculated using either
the full data set or the post April-2017 data set. This modified approach of choosing the highest
of these values combines elements from the Flowsheet and from previously approved GWCLs
(DWMRC, 2016).
4.2 Proposed Revised G W CLs
In accordance with the Flowsheet, the increasing trends identified for selenium and uranium warrant
a modified approach to the calculation of GWCLs. For both of these SAR parameters,
concentrations are significantly increasing with a non-parametric distribution. Post inflection
data are significantly increasing with a normal distribution. Considering the increasing trends, a
modified approach of choosing the highest of the following: (1) fractional approach; (2) highest
historical value; (3) mean + 2cr, calculated using either the full data set or the post April-2017
data set; or (4) 1.5 times background, calculated using either the full data set or the post April-
2017 data set, would be appropriate. Flowsheet analysis has been performed for these data
subsets and the complete datasets and is summarized in Appendix B-1 and Appendix F-1.
GWCLs determined according to the Flowsheet using all data to date and the post April-2017
data are presented in Appendix B-1. In both the Flowsheet and the modified approach, the
fractional approach to GWCL is selected as the most appropriate GWCL (Table 1), because it is
the greater of: (1) the fractional approach; (2) he highest historical value, (3) the mean + 2a,
calculated using either the full data set or the post April-2017 data set; and (4) 1.5 times
background, calculated using either the full data set or the post April-2017 data set.
As a result of this analysis, the proposed revised GWCLs are set out on Table 1 below.
16
Table 1 Proposed GWCLs
Parameter GWCL" Flowsheet Revised Rationale GWCL
Selenium (ug/L) 11.1 25 Fractional Approach
Uranium (ug/L) 4.9 15 Fractional Approach
Notes:
a= 2019 GWDP No.UGW370004.
5.0 CONCLUSIONS AND RECOMMENDATIONS
Background groundwater quality at the Mill site was thoroughly studied as described in the
Background Reports (INTERA, 2007a, 2007b, 2008) and in the University of Utah Study (Hurst
and Solomon, 2008). The Background Reports and the University of Utah Study concluded that
groundwater at the Mill site has not been impacted by Mill operations. These studies also
acknowledged that there are natural influences operating at the Mill site that have caused
increasing trends and general variability in background groundwater quality.
Consistent with the conclusions of the Background Reports and the University of Utah Study, the
conclusion of this SAR is that groundwater in MW-28 is not impacted by potential TMS
seepage. Mass balance calculations have demonstrated that concentrations of SAR parameters,
and indicator parameters are consistent with background groundwater concentrations, and not the
result of potential TMS seepage. Increasing chloride at MW-28 is attributed to its location within
the downgradient toe of the nitrate/chloride plume that was identified in 2009, and that is
currently addressed under a separate corrective action (HGC, 2012b).
One goal of this SAR was to identify any changes in circumstances identified in previous studies.
Accordingly the change in MW-28 parameter concentrations is attributed to migration of the
nitrate/chloride plume and oxidation of pyrite by nitrate contained within the nitrate/chloride
plume. As discussed in Section 3.2, nitrate mobilizes naturally occurring uranium and selenium
in the formation and pyrite oxidation releases selenium from selenium-bearing pyrite. The lack
of decrease in pH at MW-28 suggests that pyrite oxidation by nitrate occurs through the pathway
(reaction 3 described in Section 3.1 above and in HGC, 2017) that consumes rather than
produces acid. In addition, as discussed in Sections 3.1 and 3.2, increased bicarbonate at MW-28
from natural background influences may mobilize naturally-occurring uranium; and selenium
may be generally elevated within the nitrate/chloride plume due to its primary source (the
historical pond) having seeped through Mancos Shale, a known source of selenium
contamination. Furthermore, increases in water levels at MW-28 related to former wildlife pond
recharge, and increased sampling frequency, may influence constituent concentrations.
Therefore, increasing constituent concentrations result from background influences and/or
changes in sampling frequency that are unrelated to the TMS.
In addition to the above factors, a site-wide comparison of constituent concentrations in MW-28
shows that even though many constituents have significant increasing long-term trends, their
17
concentrations are less than or within the range of site-wide background concentrations. This
constitutes further evidence that increasing chloride, selenium, and uranium concentrations in
MW-28 are likely due to background influences and the location of this well at the leading edge
of the existing nitrate/chloride plume, and not to potential TMS seepage.
Finally, the nitrate/chloride plume originates upgradient from the Mill and TMS demonstrating
that the TMS is not contributing to the increases in concentrations observed in MW-28. The
nitrate/chloride plume likely originated primarily from a former stock pond upgradient of the
TMS, although it may have received a contribution from a chemical spill some di tance also
upgradient from the TMS.
18
6.0 REFERENCES
Asta, M., Beller, H., & O'Day, P. (2020). Anaerobic Dissolution Rates of U(IV)-Oxide by
Abiotic and Nitrate-Dependent Bacterial Pathways. Environmental Science and
Technology 54, 13, 8010-8021.
Bailey, Ryan T.; William J. Hunter; and Timothy K. Gates, 2012. The Influence of Nitrate and
Selenium in Irrigated Agricultural Groundwater Systems. Journal of Environmental
Quality, vol. 41 (3), pp 783-792.
Burow, KR; K Belitz; NM Dubrovsky; and BC Jurgens, 2017. Large-Scale Decadal Changes in
Uranium and Bicarbonate in Groundwater of the Irrigated Western US. Sci. Total Env.
586: 87-95. May 15, 2017.
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19
---, 2012b. Corrective Action Plan for Nitrate White Mesa Uranium Mill, Near Blanding,
Utah.
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Environmental Science and Technology 44, 5104-5111.
21
FIGURES
APPENDIX A
GWCL Exceedances for First Quarter 2020 under the March 19, 2019 GWDP
M_onitor1' Well
(Water lass) Constituent Exceeding G-WCL
Chloride (mg/L)
MW-11 (Class II) Sulfate (mg/L)
Manganese (ug/L)
MW-14 (Class Ill) Fluoride ( mg/L)
Sulfate (mg/L)
MW-25 (Class II]) Cadmium (ug/L)
Nitrate+ Nitrite (as N) (mg/L)
Chloroform (ug/L)
MW-26 (Class Ill) Chloride (mg/L)
Methvlene Chloride (u!Y/1)
Nitrogen, Ammonia as N
Nitrate+ Nitrite (as N) (mg/L)
Chloride (mg/L)
MW-30 (Class I]) Selenium (ug/L)
Uranium (ug/L)
Field pH (S.U.)
Nitrate+ Nitrite (as N) (mg/L)
MW-31 (Class Ill) Sulfate (mg/L)
TDS (mg/L)
Chloride (mg/L)
MW-36 (Class Ill) Sulfate (mg/L)
Field pH (S.U.)
MW-12 (Class l[I) Uranium (ug/L)
Beryllium (ug/L)
Cadmium (ug/L)
Fluoride (mg/L)
MW-24 (Class Ill) Nickel (mg/L)
Manganese (ug/L)
Thallium (ug/L)
Sulfate (mg/L)
Field pH (S.U.)
MW-27 (Class Ill) Nitrate+ Nitrite (as N) (mg/L)
Chloride (mg/L)
Selenium (ug/J)
MW-28 (Class JU) Nitrate+ Nitrite (as N) (mg/L)
Gross Alpha (pCi/L)
Uranium (ug/L)
MW-32 (Class II]) Chloride (mg/L)
MW-35 (Class II) Nitrogen. Ammonia as N
Notes:
NS= Not Required and Not Sampled
NA= Not Applicable
Exceedances are shown in yellow
C:l.i 20201Results
February Feb~
GWCL in March Ql 2020 QJ 2020 10-20 2020
19, 2019 GWDP SamphiDate Result Monlhly Monthly
Sample Dare Result
Required Quarterly Sampling Wells
39.16 38.9 42.1 1/15/2020 2/4/2020 1309 l/28/2020 1180 1260
164.67 169 227
0.22 l/15/2020 0.128 2/4/2020 0.145
2330 2250 2190
1.5 1/15/2020 1.35 2/5/2020 1.52
0.62 0.873 0.978
70 1260 1640
58.31 l/15/2020 78.8 2/4/2020 66.9
5 2.79 2.76
0.92 0.578 0.602
2.5 16.4 17.8
128 182 187
47.2 1/15/2020 49.7 2/5/2020 49.9
8.32 8.88 9.06
6.47 -8.5 7.31 7.30
5 17.5 18.0
993 1/14/2020 1120 2/4/2020 1150
2132 2220 2240
143 381 370
3146.21 l/14/2020 2660 2/5/2020 2540
6.49 -8.5 7.01 7.18
Required Semi-Annual Sampling Wells,
23.5 1/16/2020 21.9 NS NA
2 2.07 NA
6.43 7.30 NA
0.47 0.805 NA
50 1/22/2020 68.1 NS NA
7507 7010 NA
2.01 l.92 NA
2903 2960 NA
5.03 -8.5 6.01 NA
5.6 1/16/2020 6.18 NS NA
105 151 NA
11.l 13.4 NA
5 1/16/2020 NA NS NA
2.42 l.79 NA
4.9 7.56 NA
35.39 l/14/2020 38.0 NS NA
0.14 1/16/2020 0.0919 NS NA
-
March.2!)20 March
Monthly 2020
Sample Dato Mo.nthly
R~ult
-
41.0
3/10/2020 1120
183
<0.100 3/10/2020 2150
3/11/2020 1.41
1.60
1720
3/10/2020 76.9
4.44
0.387
19.0
182
3/11/2020 48.1
9.50
7.18
19.2
3/10/2020 1080
2380
368
3/10/2020 2890
7.24
NS NA
NA
NA
NA
NS NA
NA
NA
NA
NA
NS NA
NA
NA
NS NA
NA
NA
NS NA
NS NA
Pursuant to the DWMRC letter of February 24, 2020, these constituents will no longer be monitored on an accelerated schedule. These constituents will be
dropped from this report after this quarter.
APPENDIXB
Appendix B-3: Charge Balance Calculations for Major Cations and Anions in MW-28
Well Date
MW-28 6/21/2005
MW-28 9/22/2005
MW-28 12/14/2005
MW-28 3/22/2006
MW-28 6/23/2006
MW-28 9/12/2006
MW-28 10/24/2006
MW-28 3/15/2007
MW-28 6/20/2007
MW-28 8/28/2007
MW-28 10/23/2007
MW-28 3/12/2008
MW-28 6/3/2008
MW-28 8/6/2008
MW-28 11/5/2008
MW-28 2/4/2009
MW-28 5/12/2009
MW-28 8/17/2009
MW-28 10/12/2009
MW-28 1/19/2010
MW-28 4/19/2010
MW-28 11/12/2010
MW-28 4/11/2011
MW-28 10/5/2011
MW-28 5/8/2012
MW-28 11/14/2012
MW-28 5/15/2013
MW-28 12/4/2013
MW-28 6/18/2014
MW-28 11/5/2014
MW-28 4/21/2015
MW-28 11/10/2015
MW-28 04/20/2016
MW-28 11/1/2016
MW-28 4/19/2017
MW-28 10/18/2017
MW-28 4/19/2018
MW-28 10/30/2018
MW-28 4/24/2019
MW-28 10/22/2019
MW-28 4/15/2020
meq/L= mllliequivalent per liter
HC03 = Bicarbonate
so, = Sulfate
Appendix B
Calcium Sodium
(meq/L) (meq/L)
22.55 13.14
25.65 12.44
26.55 13.18
25.70 12.79
24.50 12.01
26.00 13.01
25.85 12.79
25.90 14.44
26.00 12.66
26.45 11 .57
26.85 12.27
24.45 12.70
25.65 13.18
27.25 13.53
27.25 13.57
23.90 12.44
24.10 12.57
26.25 13.14
25.55 13.40
25.80 0.03
24.95 13.18
24.55 12.53
25.60 13.48
25.20 11 .74
26.05 12.96
25.30 13.44
24.30 14.70
23.70 12.48
27.64 13.61
23.85 12.05
26.50 14.31
26.50 13.40
25.25 12.88
24.30 12.88
24.20 13.40
24.15 13.53
26.55 13.61
28.94 15.88
28.64 16.53
28.39 15.27
26.85 14.96
Source Assessment Report for MW-28
White Mesa Uranium Mill
'Magnesmm Potassmm
(meq/L) (meqll)
' 12.18 0.30
13.66 0.27
16.70 0.32
15.47 0.30
13.74 0.30
15.63 0.31
15.14 0.31
15.80 0.37
15.47 0.32
14.81 0.28
15.14 0.29
13.16 0.29
13.74 0.28
14.73 0.29
14.48 0.31
12.92 0.28
13.33 0.26
13.90 0.30
13.82 0.29
13.82 0.30
13.41 0.29
13.33 0.30
13.74 0.30
13.74 0.28
14.56 0.33
14.40 0.35
13.41 0.29
13.33 0.27
14.81 0.32
13.33 0.30
15.30 0.31
14.89 0.28
14.40 0.29
13.82 0.33
13.82 0.32
15.14 0.33
14.81 0.33
16.70 0.34
16.29 0.33
17.19 0.30
15.63 0.33
" I Total Cation HC03 Chloride so. Total Amon Charge Balance I
Charge ' Charge '
(meq/L) (meq/L) ; (meqll) (meq/L) 1 (meqll) Error . j I
48.16 -2.54 -2.26 -41.85 -46.65 1.60%
52.02 -2.49 -2.71 -48.09 -53.29 -1 .21%
56.75 -2.70 -2.43 -49.55 -54.68 1.85%
54.26 -2.49 -2.34 -48.30 -53.14 1.04%
50.55 -2.85 -2.57 -45.60 -51.02 -0.46%
54.95 -1 .56 -2.06 -49.55 -53.17 1.65%
54.08 -2.56 -2.43 -52.47 -57.45 -3.02%
56.50 -2.28 -2.74 -48.72 -53.73 2.51%
54.44 -2.47 -2.65 -49.14 -54.26 0.16%
53.11 -2 .64 -2.68 -50.80 -56.12 -2.76%
54.54 -2.65 -2.79 -49.34 -54.79 -0.23%
50.61 -2.61 -2.79 -48.09 -53.49 -2.77%
52.85 -2.44 -2.91 -49.14 -54.48 -1.52%
55.79 -2.62 -2.79 -48.72 -54.13 1.51%
55.60 -2.52 -2.79 -48.72 -54.04 1.43%
49.54 -2.52 -2.57 -48.72 -53.81 -4.13%
50.26 -2.56 -2.28 -50.18 -55.02 -4.52%
53.59 -2.51 -2.82 -49.14 -54.46 -0.81%
53.06 -2.59 -2.93 -49.55 -55.08 -1.86%
39.94 -2.70 -2.88 -48.72 -54.30 -15.24%
51.83 -2.59 -3.05 -48.09 -53.73 -1.80%
50.71 -2.57 -3.02 -47.68 -53.27 -2.47%
53.13 -2.54 -3.07 -43.51 -49.13 3.91%
50.97 -2.39 -4.03 -48,72 -55.15 -3.94%
53.90 -2.62 -3.22 -47.68 -53.52 0.36%
53.49 -2.48 -3.24 -35.60 -41.33 12.83%
52.71 -2 .56 -2.88 -42.27 -47.70 4.98%
49.79 -2 .88 -3.07 -47.26 -53.22 -3.33%
56.39 -4.80 -3.22 -50.18 -58.19 -1.57%
49.53 -2.88 -3.30 -46.85 -53.03 -3.40%
56.42 -3.00 -3.53 -51.84 -58.37 -1 .70%
55.07 -2.64 -3.27 -50.80 -56.71 -1.47%
52.81 -2.48 -3.41 -48.93 -54.82 -1.87%
51.33 -2.50 -3.55 -47.47 -53.52 -2.10%
51.74 -2.48 -3.39 -41 .02 -46.88 4.93%
53.15 -2.86 -3.47 -40.81 -47.14 6.00%
55.30 -2.50 -3.89 -47.47 -53.86 1.32%
61.86 -2.60 -3.36 -42.47 -48.43 12.18%
61.79 -2.96 -4.65 -49.76 -57.37 3.71%
61.16 -4.68 -4.20 -50.39 -59.27 1.57%
57.77 -2.96 -3.64 -47.47 -54.07 3.31%
~¥nlNTERA
Appendix B-5: MW-28 Data Used for Analysis
Well Date Sampled
MW-28 6/21/2005
MW-28 9/22/2005
MW-28 12/14/2005
MW-28 3/22/2006
MW-28 6/23/2006
MW-28 9/12/2006
MW-28 10/24/2006
MW-28 3/15/2007
MW-28 6/20/2007
MW-28 8/28/2007
MW-28 10/23/2007
MW-28 3/12/2008
MW-28 6/3/2008
MW-28 8/6/2008
MW-28 11/5/2008
MW-28 2/4/2009
MW-28 5/12/2009
MW-28 8/17/2009
MW-28 10/12/2009
MW-28 1/19/2010
MW-28 4/19/2010
MW-28 11/12/2010
MW-28 4/11/2011
MW-28 10/5/2011
MW-28 5/8/2012
MW-28 11/14/2012
MW-28 5/15/2013
MW-28 12/4/2013
MW-28 6/18/2014
MW-28 11/5/2014
MW-28 4/21/2015
MW-28 11/10/2015
MW-28 4/20/2016
MW-28 11/1/2016
MW-28 4/19/2017
MW-28 10/18/2017
MW-28 4/19/2018
MW-28 10/30/2018
MW-28 4/24/2019
MW-28 7/12/2019
MW-28 10/22/2019
MW-28 1/16/2020
MW-28 4/15/2020
MW-28 7/8/2020
MW-28 6/21/2005
Appendix B
Source Assessment Report for MW-28
White Mesa Uranium Mill
Parameter Name
Selenium
Selenium
Selenium
Selenium
Selenium
Selenium
Selenium
Selenium
Selenium
Selenium
Selenium
Selenium
Selenium
Selenium
Selenium
Selenium
Selenium
Selenium
Selenium
Selenium
Selenium
Selenium
Selenium
Selenium
Selenium
Selenium
Selenium
Selenium
Selenium
Selenium
Selenium
Selenium
Selenium
Selenium
Selenium
Selenium
Selenium
Selenium
Selenium
Selenium
Selenium
Selenium
Selenium
Selenium
Uranium
Page 5 of 14
Report Report Units Qualifier 1
Result I
6 ug/1
5 ug/1 u
8 ug/1
8 ug/1
5 ug/1 u
8 ug/1
7 ug/1
5 ug/1 u
6 ug/1
5 ug/1
5 ug/1
5 ug/1 u
5 ug/1 u
5 ug/1 u
5 ug/1 u
11 ug/1
6 ug/1
5 ug/1 u
5 ug/1 u
5 ug/1 u
7 ug/1
5 ug/1 u
7 uq/1
5 ug/1 u
5 ug/1 u
5 ug/1 u
5 ug/1 u
5 uq/1 u
6 ug/1
5 ug/1 u
9 ug/1
6 ug/1
5 ug/1 u
5 ug/1 u
6 uq/1
7 ug/1
8 ug/1
9 ug/1
12 ug/1
11 ug/1
17 ug/1
13 ug/1
10 ug/1
16 uq/1
3 ug/1
~¥.INTERA
Appendix B-5: MW-28 Data Used for Analysis
Well Date Sampled
MW-28 9/22/2005
MW-28 12/14/2005
MW-28 3/22/2006
MW-28 6/23/2006
MW-28 9/12/2006
MW-28 10/24/2006
MW-28 3/15/2007
MW-28 6/20/2007
MW-28 8/28/2007
MW-28 10/23/2007
MW-28 3/12/2008
MW-28 6/3/2008
MW-28 8/6/2008
MW-28 11/5/2008
MW-28 2/4/2009
MW-28 5/12/2009
MW-28 8/17/2009
MW-28 10/12/2009
MW-28 1/19/2010
MW-28 4/19/2010
MW-28 11/12/2010
MW-28 4/11/2011
MW-28 10/5/2011
MW-28 5/8/2012
MW-28 11/14/2012
MW-28 5/15/2013
MW-28 12/4/2013
MW-28 9/16/2014
MW-28 2/9/2015
MW-28 4/21/2015
MW-28 7/21/2015
MW-28 11/10/2015
MW-28 2/2/2016
MW-28 4/20/2016
MW-28 9/1/2016
MW-28 11/1/2016
MW-28 1/25/2017
MW-28 4/19/2017
MW-28 8/22/2017
MW-28 10/18/2017
MW-28 2/21/2018
MW-28 4/19/2018
MW-28 9/12/2018
MW-28 10/30/2018
MW-28 1/22/2019
Appendix B
Source Assessment Report for MW-28
White Mesa Uranium Mill
Parameter Name I
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Page 6 of 14
Report 1 Report Units Qualifier Result
4 ug/1
3 ug/1
4 uq/1
5 ug/1
3 ug/1
3 ug/1
3 ug/1
5 uq/1
4 ug/1
3 ug/1
3 ug/1
3 ug/1
3 ug/1
4 ug/1
3 uq/1
3 ug/1
3 ug/1
3 uq/1
4 ug/1
3 uq/1
3 ug/1
3 ug/1
3 ug/1
3 ug/1
3 uq/1
4 ug/1
3 uq/1
11 ug/1
4 ug/1
6 uq/1
5 ug/1
5 ug/1
5 ug/1
4 ug/1
5 ug/1
4 ug/1
6 uq/1
5 ug/1
6 uq/1
5 ug/1
4 ug/1
5 ug/1
7 ug/1
6 ug/1
7 ug/1
---SslNTERA
Appendix B-5: MW-28 Data Used for Analysis
Well Date Sampled
MW-28 4/24/2019
MW-28 7/12/2019
MW-28 10/22/2019
MW-28 1/16/2020
MW-28 4/15/2020
MW-28 7/8/2020
Appendix 8
Source Assessment Report for MW-28
White Mesa Uranium Mill
I
Parameter Name 1
i
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Page 7 of 14
---' -
Report Report Units Qualifier Result
10 ug/1
8 ug/1
12 ug/1
8 ug/1
6 ug/1
12 ug/1
l!!INTERA
Appendix B-6: Extreme Outlier Status for Use in Analysis
----·--
Reason , Location ID Date Sampled , Parameter Name Report Result Report Units
Extreme
Extreme
Extreme (Hi h , Identified as part of an inc
Extreme (Hi h , Identified as part of an inc
Appendix B
Source Assesment Report for MW-28
White Mesa Uranium Mill
Removed
MW-28 6/18/2014
MW-28 11/5/2014
Included in Analysis
MW-28 10/22/2019
MW-28 10/22/2019
Uranium 61 .3
Uranium 21 .2
Uranium 12.4
Selenium 16.5
~4.INTERA
Appendix 8-7: Box Plots
16
-14 :::::: C) ::, 12 -E ::, 10 ·c
(l) a> 8 U)
6
60
50 -:::::: C) 40 ::, -E 30 .2
C (ti
I-20 ::,
10
Appendix B
Selenium in MW-28
• 0
0
0
Percent nondetect: 43%
Min: 5, Mean: 6.98, Max: 16.5, Std Dev: 2.93
Upper extreme threshold (Q75 + 3xH): 16.1
Lower extreme threshold (Q25 -3xH): -3.325
Uranium in MW-28 ..
•
'
Percent nondetect: 0%
Min: 2.69, Mean: 6.18, Max: 61.3, Std Dev: 8.25
Upper extreme threshold (Q75 + 3xH): 12.3925
Lower extreme threshold (Q25 -3xH): -3.27
Source Assessment Report for MW-28
White Mesa Uranium Mill Page 9 of 14 ~¥.INTERA
Appendix 8-8: Box Plots for MW-28 and Upgradient and Downgradient Wells
Selenium
140
120 -100 ..J 0) ::, -80 E ::, ·2 60 Cl)
Q) en 40
20
0
Downgradient MW-28
Uranium
60 •
50 I -~ 40 0) :::, -E 30 :::, ·2
~ 20 • ::::,
10 a
0
Downgradient MW-28
Notes
All available data used in box plots
Downgradient wells: MW-3A, MW-20, and MW-22.
Upgradient wells: MW-1, MW-18, and MW-19
Appendix B
Source Assessment Report for MW-28
White Mesa Uranium Mill Page 10 of 14
o Outlier
• Extreme
• • 0
9
Upgradient
o Outlier • Extreme
i
'
Upgradient
e:!.INTERA
~ en )> l> z
::J'" 0 "C =o )>
-· C: "C ~ i Uranium (ug/L) -.., (l) Selenium (ug/L) "C
(l) 0:::, !!!. s:: (l) a. ii,
"C
)> -· CY
CD
<l> X co [{l ~ CD C.
..... ..... I\) ..... ..... :::I
!!!. (11 0 (11 0
I\) I\) w C.
c~ 0 0 0 0 0
(JI 0 (JI 0 (11 0
D>
0 0 0 0 0 0 0 ><' .., (/) C ~ 3 "' CD
m
-· (l) C.
I
C: :::, s· le-
CD
3 -CY MW-01 MW-01 ~ ... ..
s:: ~ 0 )( MW-02 1-ffl-1 (l]-il 0
m
=""g "O MW-02 0
a tfl.P• ;:i. cii MW-03A • MW-03A • 1---[Il-1 O 0 ><
0 MW-05 ~ .. • MW-05 Go-• "'CJ
.., 0
s:: MW-11 It MW-11 "°" it
~ MW-12 CDI--IJ-1 MW-12 (D-1 o'
rG MW-14 ••~--[Il--io o• MW-14 .. co
""I
MW-15 • o-{l]--1 o MW-15 1----------c:==::::::I]------l • en )>
MW-17 0 1-m--i) MW-17 i()-1 • ;;o
MW-18 oct---ID-1 MW-18 + "'CJ
MW-19 1-0. MW-19 ~,-l A>
""I A>
"O MW-20 0-1 aJ MW-20 t 3
Q)
(JQ MW-22 1--[[]-1 MW-22 +• CD
Cl) -.... MW-23 ffi--1 MW-23 + CD
.... • ""I C/J tn
0 MW-24 l-1 • C MW-24 • <D -• • iil a, .... MW-25 .. :::, MW-25 I :::, :::I
.i::,. c· 2· G)
MW-26 1-----~-------l 0 3 MW-26 .. 3 ""I
MW-27 •-[} MW-27 + 0
C:
MW-28 ... • MW-28 .. :::I C.
MW-29 .., • MW-29 It ::e
t> MW-30 1-!IJ-il A>
MW-30 -CD
MW-31 ti• MW-31 1--ffi-1 ""I
fl MW-32 <P MW-32 + s:
0
MW-34 • MW-34 IU}l :::I
tll]--oo ;::;: -MW-35 + MW-35 0
z MW-36 + MW-36 1--(D--1 0 :::::!. :::I
MW-37 to MW-37 ~ Ul
-I MW-38 I • 0 MW-38 •oto • 0 :E
I mo CD
m MW-39 I> mo MW-39 X C:
~~ ~~ en • MW-40 1-----D--1 <D -·
MW-40 CD -· 3 !!l
i 3 !!l
CD
CD
Appendix B-12: Timeseries Plots with Events
16
14
..-... ::::::: C) ::::, 12 -E ·= 10 C: Q)
Q) en 8
6
12
10 ..-... ::::::: C) ::::, -8 E ::::,
C: <ti .... 6 ::::>
4
Selenium in MW-28
-
-
-
• -
• -• •• • • • -• • •• • • • . ·--· -· • • • • • • • •
I I I
2005 2010 2015
Sample Date
Uranium in MW-28
-
• -
-
-•
• • ••• • -•• •• , .. ' , .••...... • •• • •• • •
I I I
2005 2010 2015
Sample Date
I 2008-03-15 Peak Groundwater Elevation
I 2012-10-01 Lab Change
•
•
•
•
•
• •
• •
·-.
•
I
2020
• •
•
• • ••
• • • •
• • • • •
I
2020
I 2014-06-01 Five new chloroform pumping wells brought online
I 2014-06-05 Surface impact, repair, and overpump
I 2017-04-19 Inflection point used in analysis
Appendix B
Source Assessment Report for MW-28
White Mesa Uranium Mill Page 14 of 14 ~2¥.INTERA
APPENDIX C
Appendix C-2: Descriptive Statistics of Indicator Parameters in MW-28
Appendix C
Data Set
Analyte
Units
% Non-Detects
N
Normally or Lognormallly
Di~tr:i!)uted?
Mean
Min. Cone.
Max. Cone.
Std. Dev.
Range
Geometric Mean
Skewness
25th Quartile
Median
751h Qua_rtile
Source Assesment Report for MW-28
White Mesa Uranium Mill
2008 Background Report 2020 SAR
Chloride Fluoride Sulfate Uranium Chloride Fluoride Sulfate Uranium
mg/L . mg/L . . mg/L ug/L mg/L mg/L . mg/L ug/L ·---------11 I 11 I 11 I 11 I 62 40 41 52
Normal I Normal I Normal I Normal Normal Not Not
Normal Normal I Normal I
89 0.6 2329 3.7 113 0.6 2285 4.8
73 0.6 2010 2.7 73 0.5 1710 2.7
99 0.7 2520 4.9 165 0.7 2520 12.4
8 0.0 134 0.6 19 0.0 163 2.2
26 0.1 510 2.2 92 0.2 810 9.7
0.6 2325 3.6 111 0.6 2279 4.5
-0.7 -0.8 -1.4 0.8 0.4 0.3 -1.7 2.0
83 0.6 2310 3.4 99 0.6 2280 3.4
91 0.6 2360 3.5 111 0.6 2340 3.9
96 0.7 2380 3.9 125 0.6 2380 5.2
....-SslNTERA
Appendix C-3: Data Used for Statistical Analysis
. Ill -~-~ •
MW-28 6/21/2005
MW-28 9/22/2005
MW-28 12/14/2005
MW-28 3/22/2006
MW-28 6/23/2006
MW-28 9/12/2006
MW-28 10/24/2006
MW-28 3/15/2007
MW-28 6/20/2007
MW-28 8/28/2007
MW-28 10/23/2007
MW-28 3/12/2008
MW-28 6/3/2008
MW-28 8/6/2008
MW-28 11/5/2008
MW-28 2/4/2009
MW-28 5/12/2009
MW-28 8/17/2009
MW-28 10/12/2009
MW-28 1/19/2010
MW-28 4/19/2010
MW-28 9/14/2010
MW-28 11/12/2010
MW-28 2/14/2011
MW-28 4/11/2011
MW-28 8/8/2011
MW-28 10/5/2011
MW-28 2/28/2012
MW-28 5/8/2012
MW-28 7/16/2012
MW-28 11/14/2012
MW-28 3/5/2013
MW-28 5/15/2013
MW-28 7/17/2013
MW-28 12/4/2013
MW-28 2/26/2014
MW-28 6/18/2014
MW-28 9/16/2014
MW-28 11/5/2014
MW-28 2/9/2015
MW-28 4/21/2015
MW-28 7/21/2015
MW-28 11/10/2015
MW-28 2/2/2016
MW-28 4/20/2016
Appendix C
Source Assesment Report for MW-28
White Mesa Uranium Mill
1--:, ... . .
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Page 3 of 18
[llllt:11 1•
80 mg/I
96 mg/I
86 mg/I
83 mg/I
91 mg/I
73 mg/I
86 mg/I
97 mg/I
94 mg/I
95 mg/I
99 mg/I
99 mg/I
103 mg/I
99 mg/I
99 mg/I
91 mg/I
81 mg/I
100 mg/I
104 mg/I
102 mg/I
108 mg/I
106 mg/I
107 mg/I
114 mg/I
109 mg/I
105 mg/I
143 mg/I
109 mg/I
114 mg/I
105 mg/I D
115 mg/I
110 mg/I
102 mg/I
107 mg/I
109 mg/I
113 mg/I
114 mg/I
112 mg/I
117 mg/I
130 mg/I
125 mg/I
113 mg/I
116 mg/I
130 mg/I
121 mg/I
~¥.INTERA
Appendix C-3: Data Used for Statistical Analysis
. ,...-.-il .--.1F.rl·
MW-28 9/1/2016
MW-28 11/1/2016
MW-28 1/25/2017
MW-28 4/19/2017
MW-28 8/22/2017
MW-28 10/18/2017
MW-28 2/21/2018
MW-28 4/19/2018
MW-28 9/12/2018
MW-28 10/30/2018
MW-28 1/22/2019
MW-28 4/24/2019
MW-28 8/16/2019
MW-28 10/22/2019
MW-28 1/16/2020
MW-28 4/15/2020
MW-28 7/8/2020
MW-28 6/21/2005
MW-28 9/22/2005
MW-28 12/14/2005
MW-28 3/22/2006
MW-28 6/23/2006
MW-28 9/12/2006
MW-28 10/24/2006
MW-28 3/15/2007
MW-28 6/20/2007
MW-28 8/28/2007
MW-28 10/23/2007
MW-28 3/12/2008
MW-28 6/3/2008
MW-28 8/6/2008
MW-28 11/5/2008
MW-28 2/4/2009
MW-28 5/12/2009
MW-28 8/17/2009
MW-28 10/12/2009
MW-28 1/19/2010
MW-28 4/19/2010
MW-28 11/12/2010
MW-28 4/11/2011
MW-28 10/5/2011
MW-28 5/8/2012
MW-28 11/14/2012
MW-28 5/15/2013
MW-28 12/4/2013
Appendix C
Source Assesment Report for MW-28
White Mesa Uranium Mill
.. . .
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Chloride
Fluoride
Fluoride
Fluoride
Fluoride
Fluoride
Fluoride
Fluoride
Fluoride
Fluoride
Fluoride
Fluoride
Fluoride
Fluoride
Fluoride
Fluoride
Fluoride
Fluoride
Fluoride
Fluoride
Fluoride
Fluoride
Fluoride
Fluoride
Fluoride
Fluoride
Fluoride
Fluoride
Fluoride
Page 4 of 18
•nF:111 •
127 mg/I
126 mg/I
131 mg/I
120 mg/I
125 mg/I
123 mg/I
121 mg/I
138 mg/I
148 mg/I
119 mg/I
127 mg/I
165 mg/I
133 mg/I
149 mg/I
151 mg/I
129 mg/I
140 mg/I
0.69 mg/I
0.67 mg/I
0.55 mg/I
0.65 mg/I
0.64 mg/I
0.66 mg/I
0.57 mg/I
0.63 mg/I
0.64 mg/I
0.67 mg/I
0.57 mg/I
0.59 mg/I
0.63 mg/I
0.57 mg/I
0.59 mg/I
0.60 mg/I
0.61 mg/I
0.60 mg/I
0.67 mg/I
0.60 mg/I
0.60 mg/I
0.58 mg/I
0.59 mg/I
0.60 mg/I
0.52 mg/I
0.58 mg/I
0.61 mg/I
0.66 mg/I
---2¥alNTERA
Appendix C-3: Data Used for Statistical Analysis
-;,,:11•1 ·~IJ::l ...
MW-28 11/5/2014
MW-28 4/21/2015
MW-28 11/10/2015
MW-28 4/20/2016
MW-28 11/1/2016
MW-28 4/19/2017
MW-28 10/18/2017
MW-28 4/19/2018
MW-28 10/30/2018
MW-28 4/24/2019
MW-28 10/22/2019
MW-28 4/15/2020
MW-28 6/21/2005
MW-28 9/22/2005
MW-28 12/14/2005
MW-28 3/22/2006
MW-28 6/23/2006
MW-28 9/12/2006
MW-28 10/24/2006
MW-28 3/15/2007
MW-28 6/20/2007
MW-28 8/28/2007
MW-28 10/23/2007
MW-28 3/12/2008
MW-28 6/3/2008
MW-28 8/6/2008
MW-28 11/5/2008
MW-28 2/4/2009
MW-28 5/12/2009
MW-28 8/17/2009
MW-28 10/12/2009
MW-28 1/19/2010
MW-28 4/19/2010
MW-28 11/12/2010
MW-28 4/11/2011
MW-28 10/5/2011
MW-28 5/8/2012
MW-28 11/14/2012
MW-28 5/15/2013
MW-28 12/4/2013
MW-28 6/18/2014
MW-28 11/5/2014
MW-28 4/21/2015
MW-28 11/10/2015
MW-28 4/20/2016
Appendix C
Source Assesment Report for MW-28
White Mesa Uranium Mill
1-=·--·· -
Fluoride
Fluoride
Fluoride
Fluoride
Fluoride
Fluoride
Fluoride
Fluoride
Fluoride
Fluoride
Fluoride
Fluoride
Sulfate
Sulfate
Sulfate
Sulfate
Sulfate
Sulfate
Sulfate
Sulfate
Sulfate
Sulfate
Sulfate
Sulfate
Sulfate
Sulfate
Sulfate
Sulfate
Sulfate
Sulfate
Sulfate
Sulfate
Sulfate
Sulfate
Sulfate
Sulfate
Sulfate
Sulfate
Sulfate
Sulfate
Sulfate
Sulfate
Sulfate
Sulfate
Sulfate
Page 5 of 18
-. .. LIP:_IUll:J
0.60 mg/I
0.56 mg/I
0.52 mg/I
0.56 mg/I
0.59 mg/I
0.59 mg/I
0.70 mg/I
0.57 mg/I
0.57 mg/I
0.70 mg/I
0.55 mg/I
0.69 mg/I
2010 mg/I
2310 mg/I D
2380 mg/I D
2320 mg/I D
2190 mg/I D
2380 mg/I D
2520 mg/I D
2340 mg/I D
2360 mg/I D
2440 mg/I D
2370 mg/I D
2310 mg/I D
2360 mg/I D
2340 mg/I D
2340 mg/I D
2340 mg/I D
2410 mg/I D
2360 mg/I D
2380 mg/I D
2340 mg/I D
2310 mg/I D
2290 mg/I D
2090 mg/I D
2340 mg/I D
2290 mg/I D
1710 mg/I
2030 mg/I
2270 mg/I
2410 mg/I
2250 mg/I
2490 mg/I
2440 mg/I
2350 mg/I
....=--c5INTERA
Appendix C-3: Data Used for Statistical Analysis
. ·--·~Iii
MW-28 11/1/2016
MW-28 4/19/2017
MW-28 10/18/2017
MW-28 4/19/2018
MW-28 10/30/2018
MW-28 4/24/2019
MW-28 10/22/2019
MW-28 4/15/2020
MW-28 6/21/2005
MW-28 9/22/2005
MW-28 12/14/2005
MW-28 3/22/2006
MW-28 6/23/2006
MW-28 9/12/2006
MW-28 10/24/2006
MW-28 3/15/2007
MW-28 6/20/2007
MW-28 8/28/2007
MW-28 10/23/2007
MW-28 3/12/2008
MW-28 6/3/2008
MW-28 8/6/2008
MW-28 11/5/2008
MW-28 2/4/2009
MW-28 5/12/2009
MW-28 8/17/2009
MW-28 10/12/2009
MW-28 1/19/2010
MW-28 4/19/2010
MW-28 11/12/2010
MW-28 4/11/2011
MW-28 10/5/2011
MW-28 5/8/2012
MW-28 11/14/2012
MW-28 5/15/2013
MW-28 12/4/2013
MW-28 9/16/2014
MW-28 2/9/2015
MW-28 4/21/2015
MW-28 7/21/2015
MW-28 11/10/2015
MW-28 2/2/2016
MW-28 4/20/2016
MW-28 9/1/2016
MW-28 11/1/2016
Appendix C
Source Assesment Report for MW-28
White Mesa Uranium Mill
. . . .
Sulfate
Sulfate
Sulfate
Sulfate
Sulfate
Sulfate
Sulfate
Sulfate
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Uranium
Page 6 of 18
. It lt:111 ~
2280 mg/I
1970 mg/I
1960 mg/I
2280 mg/I
2040 mg/I
2390 mg/I
2420 mg/I
2280 mg/I
3.22 ug/1
3.75 ug/1
3.46 ug/1
3.89 ug/1
4.89 ug/1
3.36 ug/1
3.49 ug/1
2.69 ug/1
4.56 ug/1
3.67 ug/1
3.40 ug/1
3.17 ug/1
3.46 ug/1
3.15 ug/1
3.55 ug/1
3.42 ug/1
3.34 ug/1
3.24 ug/1
3.46 ug/1
3.51 ug/1
3.36 ug/1
3.45 ug/1
3.29 ug/1
3.19 ug/1
3.44 ug/1
3.45 ug/1
3.58 ug/1
3.34 ug/1
10.60 ug/1
4.48 ug/1
6.13 ug/1
4.87 ug/1
4.84 ug/1
4.61 ug/1
3.95 ug/1
4.71 ug/1
4.09 ug/1
~S;INTERA
Appendix C-4: Indicator Parameter Data Removed from Analysis
Reason Location ID
Extreme (High) MW-28
Extreme (High) MW-28
Extreme (High) MW-28
Appendix C
Source Assesment Report for MW-28
White Mesa Uranium Mill
Date Sampled Parameter Name
6/18/2014 Fluoride
6/18/2014 Uranium
11/5/2014 Uranium
Report Result Report Units
1.0 ma/I
61 .3 ug/1
21 .2 ua/1
.-3s lNT ERA
Appendix C-5: Box Plots for Indicator Parameters in MW-28
160
-140 ::::: C> g
Q) 120 "C ·;::
0
.c 100 u
80
1.0
-0.9 :::::: C> E 0.8 -Q)
"C ·;:: 0.7 0 ::::,
LL
0.6
0.5
Appendix C
Chloride in MW-28
0
Percent nondetect: 0%
o Outlier
• Extreme
Min: 73, Mean: 112.65, Max: 165, Std Dev: 18.84
Upper extreme threshold (075 + 3xH): 202.25
Lower extreme threshold (025 -3xH): 22
Fluoride in MW-28 ..
Percent nondetect: 2%
o Outlier
• Extreme
Min: 0.518, Mean: 0.62, Max: 1, Std Dev: 0.08
Upper extreme threshold (Q75 + 3xH): 0.880556
Lower extreme threshold (Q25 -3xH): 0.342592
Source Assesment Report for MW-28
White Mesa Uranium Mill Page 1 of 2 B INTERA
Appendix C-5: Box Plots for Indicator Parameters in MW-28
2400 -::::: C) 2200 E -(l) -~ 2000 :::, en
1800
60
50 -::::: C) 40 :::, -E 30 :::,
C ca ... 20 :::>
10
Appendix C
Sulfate in MW-28
0
i
•
Percent nondetect: 0%
o Outlier
• Extreme
Min: 1710, Mean: 2285.12, Max: 2520, Std Dev: 163.34
Upper extreme threshold (Q75 + 3xH): 2680
Lower extreme threshold (Q25 -3xH): 1980
Uranium in MW-28
• o Outlier • Extreme
•
!
Percent nondetect: 0%
Min: 2.69, Mean: 6.18, Max: 61 .3, Std Dev: 8.25
Upper extreme threshold (075 + 3xH): 12.3925
Lower extreme threshold (Q25 -3xH): -3.27
Source Assesment Report for MW-28
White Mesa Uranium Mill Page 2 of 2 ~¥-INTERA
Appendix C-9: Time Series with Events
Sulfate in MW-28
• •
2400
-:::::
• • • -• • • • •• • • .... . . • • • • •• • • • • • • • • en 2200 E -• -Q) ..... • J!!
::::, 2000 Cf) • • -• • •
1800 -
• I I I I
2005 2010 2015 2020
Sample Date
Uranium in MW-28
• 12 -•
• 10 --• ::::: en ::::, -6 E -• • . ;2
C ••
ca ~ 6 => -• • • • •
• ••• • • • . ' •
4 -• • •• -•• • ••• ••• • •• • ~ . • ••• • I I I
2005 2010 2015
Sample Date
I 2008-03-15 Peak Groundwater Elevation
I 2012-10-01 Lab Change
• • •
I
2020
I 2014-06-01 Five new chloroform pumping wells brought online
I 2014-06-05 Surface impact, repair, and overpump
I 2017--04-1'9 Inflection point used in analysis
Appendix C
Source Assesment Report for MW-28
White Mesa Uranium Mill Page 17 of 18 .-SslNTERA
Appendix C-9: Time Series with Events
-::::: C)
E -Q)
-0 ·c::
0 .r.
(.)
-::::: C)
E -Q)
-0 ·;::
0 ::,
LL
Chloride in MW-28
160 -
140 • -
• • 120
100
-
• • • • • • • ·-· • • •• • • • • •• • -• • •• • -• • • • 80 -• • •
•
I I I
2005 2010 2015
Sample Date
Fluoride in MW-28
0.70 -•
• • • • • 0.65 -• • • • •
• • 0.60 -. ·-• •
' • • • i-• • • • 0.55 -•
•
I I I
2005 2010 2015
Sample Date
I 2008-03-15 Peak Groundwater Elevation
I 2012-10-01 Lab Change
•
• ••
• •
• • • • ._ •• • • • • •
I
2020
• • •
• •
• • •
•
•
I
2020
I 2014-06-01 Five new chloroform pumping wells brought online
I 2014-06-05 Surface impact, repair, and overpump I 2017-04-19' Inflection point used in analysis
Appendix C
Source Assesment Report for MW-28
White Mesa Uranium Mill Page 18 of 18 ~¥alNTERA
APPENDIXD
APPENDIXE
APPENDIXF
Appendix F-2: MW-28 Data Used for Analysis
Well Date
Sampled
MW-28 4/19/2017
MW-28 10/18/2017
MW-28 4/19/2018
MW-28 10/30/2018
MW-28 4/24/2019
MW-28 7/12/2019
MW-28 10/22/2019
MW-28 1/16/2020
MW-28 4/15/2020
MW-28 7/8/2020
MW-28 4/19/2017
MW-28 8/22/2017
MW-28 10/18/2017
MW-28 2/21/2018
MW-28 4/19/2018
MW-28 9/12/2018
MW-28 10/30/2018
MW-28 1/22/2019
MW-28 4/24/2019
MW-28 7/12/2019
MW-28 10/22/2019
MW-28 1/16/2020
MW-28 4/15/2020
MW-28 7/8/2020
Appendix F
Source Assessment Report for MW-28
White Mesa Uranium Mill
Parameter Name Report Result '. Report Units
Selenium 6.46 ug/1
Selenium 6.66 ug/1
Selenium 8.20 uq/1
Selenium 8.68 ug/1
Selenium 12.40 ug/1
Selenium 10.60 ug/1
Selenium 16.50 ug/1
Selenium 13.40 ug/1
Selenium 10.20 ug/1
Selenium 15.50 ug/1
Uranium 4.68 ug/1
Uranium 5.68 ug/1
Uranium 4.70 ua/1
Uranium 3.94 ug/1
Uranium 5.06 ug/1
Uranium 7.04 ug/1
Uranium 6.18 ug/1
Uranium 7.12 ua/1
Uranium 9.60 ug/1
Uranium 7.83 ug/1
Uranium 12.40 ug/1
Uranium 7.56 ug/1
Uranium 5.91 ua/1
Uranium 11 .80 ug/1
Page 2 of 8 ~SelNTERA
Appendix F-3: Box Plots
-:::::: Cl :::, -E :::, ·2
Q)
Q)
Cl)
-:::::: C> :::, -E .:!
C: Q) a;
Cl)
Appendix F
16
14
12
10
8
6
Selenium in MW-28 for All Data 1
Selenium in MW-28
• 0 0 Outlier
0 • Extreme
0
Percent nondetect: 43%
Min: 5, Mean: 6.98, Max: 16.5, Std Dev: 2.93
Upper extreme threshold (075 + 3xH): 16.1
Lower extreme threshold (025 -3xH): -3.325
Selenium in MW-28 Post April 2017 -i
16
14
12
10
8
Selenium in MW-28
o Outlier
• Extreme
Percent nondetect: 0%
Min: 6.46, Mean: 10.86, Max: 16.5, Std Dev: 3.52
Upper extreme threshold (075 + 3xH): 27.64
Lower extreme threshold (025 -3xH): -6.17
Source Assessment Report for MW-28
White Mesa Uranium Mill Page 3 of 8 ~¥.INTERA
Appendix F-3: Box Plots
60
50 -::::: C) 40 :::::, -E 30 .:2 C ro .... 20 ::::>
10
12
-10 ::::: C)
2.
E 8 .:2
C: ro .... ::::> 6
4
Appendix F
Uranium in MW-28 for All Data I
Uranium in MW-28
•
0 Outlier • Extreme
•
!
Percent nondetect: 0%
Min: 2.69, Mean: 6.18, Max: 61.3, Std Dev: 8.25
Upper extreme threshold (075 + 3xH): 12.3925
Lower extreme threshold (025 -3xH): -3.27
- ---.
Uranium in MW-28 Post April 2017
Uranium in MW-28
0
Percent nondetect: 0%
o Outlier
• Extreme
Min: 3.94, Mean: 7.11, Max: 12.4, Std Dev: 2.59
Upper extreme threshold (075 + 3xH): 15.405
Lower extreme threshold (025 -3xH): -2.4275
Source Assessment Report for MW-28
White Mesa Uranium Mill Page 4 of 8 ...-9£.slNTERA
APPENDIXG
Input and Output Files (Electronic Only)