DRC-2024-005579

State of Utah

SPENCER J. COX
Governor

DEIDRE HENDERSON
Lieutenant Governor
Department of
Environmental Quality

Kimberly D. Shelley
Executive Director

DIVISION OF WASTE MANAGEMENT
AND RADIATION CONTROL

Douglas J. Hansen
Director

MEMORANDUM

TO: File

THROUGH: Adam Wingate, Manager

FROM: Chris Leahy, P.G.

DATE: May 7, 2024

SUBJECT: Review of the Energy Fuels Resources (USA) Inc. (EFR), White Mesa Uranium
Mill, Blanding, Utah March 4, 2024, Source Assessment Report for Selenium in
Monitoring Well MW-03A
Ground Water Discharge Permit No. UGW370004 (GWDP)

Introduction

A Source Assessment Report (SAR) for Selenium in Monitoring Well MW-03A at the White
Mesa Uranium Mill (Mill) was submitted by Energy Fuels Resources (USA) Inc. (EFR) to the
Utah Division of Waste Management and Radiation Control (Division) on March 4, 2024.

Selenium in MW-03A exhibited consecutive exceedances of the applicable Ground Water
Compliance Limit (GWCL) and EFR is required under the GWDP Part I.G.4 relating to violations
of Part I.G.2 of the GWDP to perform an assessment of the sources, extent, and potential
dispersion of Selenium at MW-03A. The SAR was submitted for review and approval of source
assessment investigation findings including a proposed revised Ground Water Compliance Limit
(GWCL) for Selenium in MW-03A.

Monitoring well MW-03A is located approximately 2,000 feet hydraulically downgradient from
Mill Tailings Cells 4A and 4B. MW-03A has been evaluated in recent EFR reports, studies, and
other SAR’s including a 2008 Revised Background Groundwater Quality Report for New Wells, a
2008 University of Utah groundwater isotopic study, a 2012 Sitewide SAR, a 2012 Sitewide pH
Report, and a 2014 SAR. It is noted that the above investigations indicated that exceedances in
MW-03A are likely due to natural background influences that impact the geochemical conditions
at MW-03A, and not associated with Mill activities.

EFR March 4, 2024 MW-03A Source Assessment Report
DWMRC Review Memo
Page 2

SAR Review

The SAR is broken up into five primary sections:
1. Introduction (Section 1.0).
2. Categories and Approaches for analysis (Section 2.0).
3. Results of the analysis (Section 3.0).
4. Statistical evaluation and calculation of revised GWCL’s (Section 4.0).
5. Conclusions and recommendations (Section 5.0).

The following Division summarized review findings focus on the results, statistical evaluation,
and conclusions and recommendations discussed in the SAR. Figure 1 below depicts the
time/concentration plot for Selenium in monitoring well MW-03A (data through the 4th Quarter
2023).

Figure 1 – Time Series Plot of Historical Selenium Concentration at MW-03A

EFR Results of Investigations of Potential Sources of Increasing Trends at MW-03A

1. Site-Wide Groundwater pH Changes

Division review of Section 3.1 of the SAR notes that field pH in nearly all MW-series monitoring
wells, including MW-03A, was decreasing prior to about 2016 (Figure 2). This has resulted in
mobilization of pH sensitive metals and increases in concentrations of these metals in
groundwater. However, since about 2016, the site-wide decreasing pH trend has reversed in
nearly all MW-series monitoring wells (including MW-03A), and pH is now generally stable to
increasing (Figure 3). This includes upgradient and far cross- and downgradient monitoring wells.
The SAR states that the post-2016 increase in pH is inconsistent with a TMS source, as TMS
solutions have a low pH, and mixing of potential seepage of TMS solution with groundwater
would cause a decrease (rather than increase) in pH. The post-2016 increasing pH shows that
MW-03A is unimpacted by the TMS.

EFR March 4, 2024 MW-03A Source Assessment Report
DWMRC Review Memo
Page 3

Figure 2 – Time Series Plot of Historical pH Data at MW-03A

Figure 3 – Time Series Plot of Post-2016 pH Data at MW-03A

EFR March 4, 2024 MW-03A Source Assessment Report
DWMRC Review Memo
Page 4

2. Changes in Groundwater Levels and Groundwater Chemistry at MW-03A

Division review of the SAR notes that substantial changes in water levels have occurred in the last
12 years due to cessation of water delivery to the wildlife ponds. “Currently, although water
levels have declined substantially in the center of the perched groundwater mound associated with
the northern wildlife ponds, water levels have not returned to pre-pond seepage conditions, and
the groundwater mound is still expanding.” Figure 4 below shows historical water levels at MW-
03A.

Per the SAR: “Changes in saturated thicknesses and rates of groundwater flow can result in
changes in concentrations of dissolved constituents (or pH) for many reasons. For example, as
discussed in HGC (2012), groundwater rising into a vadose zone having a different chemistry than
the saturated zone will result in changes in pH and groundwater constituent concentrations. If the
rise in groundwater represents a long-term trend, long term changes in groundwater constituent
concentrations (or pH) result.”

Figure 4 –Time Series Plot of Historical Groundwater Levals at MW-03A

The SAR and literature cited in the SAR also discuss mobilization of naturally-occurring selenium
in groundwater from pyrite in the formation and mobilization under increasingly oxidizing
conditions such as at MW-03A. Per the SAR, “oxygen concentrations (and oxidizing conditions)
have been generally increasing at MW-03A, consistent with the generally decreasing manganese
concentrations at the well. Manganese is a redox sensitive metal that is relatively mobile in the
absence of oxygen and relatively immobile when oxygen is present.”

EFR March 4, 2024 MW-03A Source Assessment Report
DWMRC Review Memo
Page 5

3. Tailings Solution Groundwater Indicator Parameter Trends

The SAR Section 3.3 discusses four primary indicator parameters (Chloride, Fluoride, Sulfate and
Uranium) which would be detected in ground water in the event of a discharge from the Mill
tailings cells. Per the SAR, “Complete data sets for MW-03A indicator parameters demonstrate
that chloride, sulfate, and pH are stable and uranium and fluoride have significantly decreasing
trends. Trend analysis of the post-November 2019 indicator parameter subsets show decreasing
trends for chloride, sulfate, and uranium, and no trend for either fluoride or pH, further
demonstrating stable to decreasing concentrations in indicator parameters during this time period.
The stable to decreasing behavior of indicator parameters indicates that MW-03A is unimpacted
by any potential seepage from the TMS.” The Division completed time series plots from 2005-
2023 to confirm trends for the four indicator parameters at MW-03A (Figure 5, Figure 6, Figure 7,
and Figure 8).

Figure 5 –Time Series Plot of Historical Chloride Concentration at MW-03A

Figure 6 – Time Series Plot of Historical Fluoride Concentration at MW-03A

EFR March 4, 2024 MW-03A Source Assessment Report
DWMRC Review Memo
Page 6

Figure 7 –Time Series Plot of Historical Uranium Concentration at MW-03A

Figure 8 –Time Series Plot of Historical Sulfate Concentration at MW-03A

4. Mass Balance Analysis

Section 3.4 of the SAR discusses mass balance analysis at MW-03A noting that: since 2008,
“water levels at MW-03A have risen by approximately 1.5 feet, causing the saturated thickness to
increase by approximately 13%.” If the water level increase were the result of TMS seepage
containing approximately 13% TMS solution, the chloride concentration (4th quarter 2023 value of
62 mg/L) would be approximately 3,600 mg/L; the fluoride concentration (4th quarter 2023 value
of 0.7 mg/L) would be approximately 420 mg/L; the sulfate concentration (4th quarter 2023 value
of 3,370 mg/L) would be approximately 25,300 mg/L; and the uranium concentration (4th quarter
2023 value of 18.9 μg/L) would be approximately 48,500 μg/L. The concentration of Selenium in
MW-03A would exceed 1,270 µg/L rather than the 4th quarter 2023 value of 132 µg/L.

EFR March 4, 2024 MW-03A Source Assessment Report
DWMRC Review Memo
Page 7

5. Source Assessment Conclusions

Per the 3.5.1 of the SAR, EFR finds that MW-03A has not been impacted by seepage from the
tailings cells, and that current changes in groundwater chemistry and Selenium OOC at
monitoring well MW-03A are due to changing groundwater background conditions. The SAR
includes discussion of the assessment and Section 3.5.1.1 lists the 4 factors supporting that EFR
conclusion. Specifically, per the SAR:

1. “Indicator parameters chloride, and sulfate are stable and uranium and fluoride have
significantly decreasing trends.
2. pH has been generally stable to increasing since 2016.
3. Increasing water levels related to former wildlife pond recharge are expected to impact
the MW-03A groundwater chemistry and contribute to trends in dissolved constituents.
4. Mass balance analysis indicates that water level increases at MW-03A do not result from
potential TMS seepage.”

Per Division review of the SAR and historical data for MW-03A, the out-of-compliance status for
selenium in does not appear to be associated with contamination from a tailings wastewater
source. Based on these findings it is appropriate to adjust the GWDP groundwater compliance
limits consistent with the currently Division approved groundwater data statistical process flow
chart for the Mill and associated guidance.

Note that the evaluation of the comprehensive list of monitoring parameters and evaluation of data
by EFR and the Division at monitoring well MW-03A is ongoing. Out-of-compliance status is
being continuously monitored to ensure that a tailings source is not evident.

EFR Proposed Modified GWCL Statistical Evaluation of Data:

Based on Division review of the SAR statistical analysis, it was noted that analysis for MW-03A
was conducted for the complete historic data set and for a post-November 2019 data set. After
November, 2019, a point of inflection is observed where groundwater levels in MW-03A began to
stabilize and an increasing trend in Selenium concentration was observed. Although the complete
data set and the post-November 2019 data set were evaluated, the selected approach for the
proposed GWCL for selenium is based on the post-November 2019 subset.

The Division approved statistical flow chart for the White Mesa Mill groundwater monitoring
wells clarifies that if an upward trend is apparent for a constituent, then a modified approach
should be considered. The modified approach should allow for a GWCL which considers the
increasing concentration. The proposed GWCL was calculated by selecting the greater of the
following: (1) mean + 2σ, (2) highest historical value, or (3) mean x 1.25 for the post-November
2019 data set. The proposed GWCL for selenium is based on the highest historical value of the
post-November 2019 data set.

EFR March 4, 2024 MW-03A Source Assessment Report
DWMRC Review Memo
Page 8

EFR Statistical methods used in the SAR included:
1. Dixon's test, Rosner's test, and Probability Plots to evaluate outliers.
2. Descriptive statistics for the complete data set and post-inflection data set
3. Shapiro-Wilk Test for normality.
4. Mann-Kendall and Linear Trend Analysis.

The calculations and findings are summarized in the SAR in Appendix A.

Table 1 below summarizes the EFR calculations and rationale for the proposed modified
GWCL’s.

Table 1 - EFR Proposed Revised GWCL for Selenium in MW-03A:
Well
Number
Parameter Current
GWCL
EFR
Proposed
GWCL
Revision
Method to
Determine
GWCL
Division Finding – Is Proposed
GWCL in Conformance with
the Statistical Flow Chart?

MW-03A Selenium 109.58
µg/L
171
µg/L
Highest
Historical
Value*
Increasing Trend allows for
modified approach on Flow
Chart. The Highest Historical
Value Background value
appears appropriate based on
review of data.
*Based on the Highest Historical Value of the post November 2019 Selenium background data set

Conclusions:

Based on the Division review of the background statistics and confirmation that the proposed
parameters for a GWCL modification are showing an increasing trend not apparently associated
with contamination from the Mill, it is appropriate to set the GWCL for Selenium in MW-03A as
the Highest Historical Value of the Post-November 2019 data set. This modified approach is
consistent with the Division approved statistical flowchart for parameters showing increasing
trends.

Based on review, a letter will be sent to EFR of initial approval of the modified GWCL. The
letter will include notification that the modifications are subject to public notice and public
participation requirements, and that the modifications will not be effective until formal issuance of
a renewed or modified GWDP.

EFR March 4, 2024 MW-03A Source Assessment Report
DWMRC Review Memo
Page 9

References

1 Energy Fuels Resources (USA) Inc., March 4, 2024, Transmittal of Source Assessment Report
for MW-03A White Mesa Mill Groundwater Discharge Permit UGW370004

2 Intera, 2007, Groundwater Data Preparation and Statistical Process Flow for Calculating
Groundwater Protection Standards, White Mesa Mill Site, San Juan County, Utah

3 Utah Department of Environmental Quality, January 19, 2018, Modified on March 8, 2021, Utah
Division of Radiation Control, Ground Water Discharge Permit, Permit No. UGW370004, Energy
Fuels Resources (USA) Inc.

4 Intera. 2008, Revised Background Groundwater Quality Report: New Wells for Denison Mines
(USA) Corp.’s White Mesa Uranium Mill site, San Juan County, Utah.

5 Hurst, T.G., and Solomon, D.K. University of Utah, 2008, Summary of Work Completed, Data
Results, Interpretations and Recommendations for the July 2007 Sampling Event at the Denison
Mines, USA White Mesa Uranium Mill Near Blanding, Utah, Prepared by Department of Geology
and Geophysics

6 Energy Fuels Resources (USA) Inc., October 12, 2012, Source Assessment Report, Prepared by
Intera

7 Energy Fuels Resources (USA) Inc., March 18, 2014, Source Assessment Report for Sulfate in
MW-01 and Total Dissolved Solids in MW-03A, Prepared by Intera

8 Hydro Geo Chem, December 7, 2012, Pyrite Investigation Report

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