DRC-2025-002415

299 South Main Street, Suite 1700 ▪ Salt Lake City, Utah 84111
[phone] ▪ Fax: [phone] ▪ www.energysolutions.com

July 30, 2025 CD-2025-153

Mr. Doug Hansen, Director
Division of Waste Management and Radiation Control
P.O. Box 144880
Salt Lake City, UT 84114-4880

Subject: Groundwater Quality Discharge Permit No. UGW450005 – First Semi-Annual
2025 Accelerated Groundwater Monitoring Report

Dear Mr. Hansen:
In accordance with Part I.H.1.b of Groundwater Quality Discharge Permit Number
UGW450005 (Permit), this report summarizes the groundwater analytical data collected
from monitoring wells under accelerated monitoring from January 1 through June 30,
2025. The report includes a data summary table (Table 1) that lists sampling dates,
analytes, analytical results, and the compliance status for each well monitored during the
first half of 2025. Additionally, the report provides a detailed discussion of each analyte
and corresponding well.

P3-95 SWC
Compliance monitoring well P3-95 SWC has been in out-of-compliance (OOC) status for
total uranium, uranium-234 (U-234), and uranium-238 (U-238) since September 2013.
The most recent exceedances of Groundwater Protection Levels (GWPLs) at this well
occurred from February through May 2025 (Table 1). EnergySolutions attributes these
exceedances to stormwater infiltration caused by precipitation events. During this period,
the Clive Facility experienced 51% of the 31-year average precipitation, as reported in
the 2024 annual meteorological summary (Trinity Consultants, 2024).
On March 15, 2024, the Director of the Division of Waste Management and Radiation
Control granted conditional approval (DRC-2024-004377) for EnergySolutions’ plan to
restore well P3-95 SWC to compliant status (CD-2023-204; October 9, 2023). This plan
included tracer dye testing to evaluate transport pathways. Details of the planned actions
were outlined to the Division on February 20, 2025 (CD-2025-035). EnergySolutions
submitted a variance request to extend the deadline to begin the tracer dye test from April
25, 2025 to April 25, 2026 (CD-2025-081) due to the lack of precipitation needed to
begin the test. The variance request was approved by the Division on May 19, 2025
(DRC-2025-001463).
Groundwater extraction has been a demonstrated effective method of maintaining below-
GWPL uranium concentrations in P3-95 SWC groundwater. To address remediation of
groundwater containing elevated uranium concentrations, submittal CD-2023-204
proposes to perform groundwater extraction at well P3-95 SWC. The schedule for
groundwater extraction will be coordinated with the tracer dye test, to optimize test

Mr. Doug Hansen
July 30, 2025
CD-2025-153
Page 2 of 9

results, i.e., groundwater extraction will not occur during the tracer dye testing to prevent
possible dilution of the dye in well P3-95 SWC groundwater.
To eliminate the potential source of surface water infiltration in the vicinity of well P3-95
SWC, EnergySolutions has managed storm water in the north-south, road-side ditch near
the well as Priority 1 under a temporary variance from DWMRC. On September 22,
2023 (DRC-2023-071888), DWMRC approved an extension of the temporary variance
until September 22, 2026.
Additional information for well P3-95 SWC is available in status reports for the first
quarter (May 14, 2025; CD-2025-102) and second quarter (July 17, 2025; CD-2025-150)
of 2025.

GW-23
In accordance with Part I.G.2 of the Permit, on August 9, 2023, EnergySolutions
provided notice that well GW-23 entered probable out-of-compliance (POOC) status for
total uranium (CD-2023-159). The total uranium concentration of the 2023 annual
monitoring sample, collected in May 2023, exceeded the GWPL.
EnergySolutions believes the total uranium exceedance at well GW-23 was caused by
variability of the natural concentration of uranium, possibly related to infiltration and
groundwater mounding occurring west of the well location. Depth-to-water
measurements collected during the first half of 2023 indicated mounding had occurred
west of well GW-23 in response to drainage of non-contact water from the offset on the
south side of the Class A West embankment. Despite the concentration increase, the
U-234 to U-238 isotopic ratio of the 2023 annual sample remained consistent with the
Clive Facility background ratio.
Subsequent to the May 2023 exceedance, the total uranium concentrations of eight
consecutive quarterly samples collected from well GW-23 have been less than the
GWPL. This includes the samples collected during first and second quarters of 2025
(Table 1). Review of field parameters, radiological analytical data, U-234/U-238 ratios,
and non-radiological analytical data provide no evidence of contamination in well GW-
23 groundwater. Based on data collected since the May 2023 exceedance,
EnergySolutions submitted a request to return GW-23 to in-compliance status on June 24,
2025 (CD-2025-132) and the Division approved the request on July 23, 2025 (DRC-
2025-002209).

GW-26
In accordance with Part I.G.2 of the Permit, on December 17, 2024, EnergySolutions
provided notice that well GW-26 entered POOC status for total uranium (CD-2024-255).
The total uranium concentration of the 2024 annual monitoring sample, collected in May
2024 (0.0377 milligrams per liter [mg/L]), exceeded the GWPL (0.037 mg/L).

Mr. Doug Hansen
July 30, 2025
CD-2025-153
Page 3 of 9

EnergySolutions believes the total uranium exceedance at well GW-26 was caused by
variability of the natural concentration of uranium, possibly related to infiltration and
groundwater mounding occurring south of the well location. Depth-to-water
measurements collected during the first half of 2024 indicated mounding had occurred in
vicinity of well GW-26 in response to drainage of non-contact water from the offset on
the south side of the Class A West embankment. Despite the concentration increase, the
U-234/U-238 isotopic ratio of the 2024 annual sample remained consistent with the Clive
Facility background ratio.
Subsequent to the May 2024 exceedance, the total uranium concentrations of two
consecutive quarterly samples collected from well GW-26 have been less than the
GWPL. This includes the samples collected during first and second quarters of 2025
(Table 1). Review of field parameters, radiological analytical data, U-234/U-238 ratios,
and non-radiological analytical data provide no evidence of contamination in well GW-
26 groundwater.

GW-58
In accordance with Part I.G.2 of the Permit, on September 5, 2024, EnergySolutions
provided notice that well GW-58 entered POOC status for total uranium (CD-2024-184).
The total uranium concentration of the 2024 annual monitoring sample, collected in May
2024 (0.047 mg/L), exceeded the GWPL (0.046 mg/L). On January 22, 2025,
EnergySolutions provided notice that well GW-58 entered POOC status for U-234 (CD-
2025-013). The U-234 concentration of the October 2024 4th quarter POOC sample (31.7
picoCuries per liter [pCi/L]) exceeded the GWPL (31.2 pCi/L).
EnergySolutions believes the total uranium and U-234 exceedance at well GW-58 were
caused by variability of the natural concentration of uranium, possibly related to
infiltration and groundwater mounding occurring near the well location. Depth-to-water
measurements collected during the first half of 2024 indicated mounding had occurred
around GW-58 in response to drainage of non-contact water to the Southwest Corner
Pond and infiltration from Pond spillway overflow. Despite the concentration increase,
the U-234 to U-238 isotopic ratio of the 2024 annual sample and the 2024 4th quarter
sample remained consistent with the Clive Facility background ratio.
Subsequent to the May 2024 total uranium exceedance, samples from two consecutive
quarters have been below the total uranium GWPL; however, the 2025 annual sample
(0.048 mg/L) exceeded the GWPL (Table 1). Subsequent to the October 2024
exceedance for U-234, samples from two consecutive quarters have been below the U-
234 GWPL . This includes the samples collected during first and second quarters of 2025
(Table 1). Review of field parameters, radiological analytical data, U-234/U238 ratios,
and non-radiological analytical data provide no evidence of contamination in well GW-
58 groundwater.

Mr. Doug Hansen
July 30, 2025
CD-2025-153
Page 4 of 9

GW-77
In accordance with Part I.G.2 of the Permit, on November 20, 2019, EnergySolutions
notified DWMRC that compliance monitoring well GW-77 entered POOC status for the
sum of radiums (CD19-0234). The sum of radiums concentrations in the 2019 annual
sample exceeded the background-based GWPL (5.46 pCi/L) established for this well.
Radium-226 (Ra-226) and radium-228 (Ra-228) are naturally occurring radionuclides in
Clive Facility groundwater. EnergySolutions believes the observed radium exceedance
was caused by fluctuations in background concentrations that may be related to increased
infiltration in the vicinity of the well due to above-average precipitation rates at the Clive
Facility that occurred in the first half of 2019. Accelerated quarterly sampling of well
GW-77 for Ra-226 and Ra-228 began in fourth quarter 2019.
Sum of radiums with a GWPL equal to or near 5 pCi/L is a less than optimal metric for
efficient groundwater compliance monitoring at the Clive Facility:
• Background concentrations of the sum of radiums in Clive Facility groundwater
commonly exceed the Permit universal GWPL of 5 pCi/L as documented by
DRC/DWMRC approval of background-based GWPL exceptions for 20
compliance monitoring wells, including GW-77.
• The universal GWPL of 5 pCi/L is a Maximum Contaminant Level (MCL)
established for protection of drinking water due to the carcinogenic effects of
radium (alpha/beta decay) when ingested. Clive Facility groundwater is naturally
non-potable with high concentrations of dissolved solids due to its occurrence in
saline lake-bed sediments.
• Technical analytical factors, such as matrix interference, related to analysis of
isotopic radium in saline groundwater may influence reported results.
For the first half of 2025, the sum of radiums concentration in groundwater at well
GW-77 did not exceed the GWPL (Table 1). Since the initial 2019 exceedance, well
GW-77 has been sampled for 19 consecutive quarters. Only one subsequent exceedance
of the sum of radiums GWPL has occurred during the 19-quarter period, the first quarter
2022 sample duplicate. Apparent concentration trends and seasonality patterns are not
observed in the radium concentration data from the well. Linear regression of the entire
well GW-77 sum of radiums data set, with duplicate results removed, provided a slope of
1.03-05 pCi/L per day. From the first sample collected on November 24, 1998, to the
most recent sample, collected on May 16, 2024, regression estimates the sum of radiums
concentration has increased by 0.10 pCi/L, which is less than the typical counting
uncertainty reported for isotopic radium analyses. In addition, during the 19-month
accelerated monitoring period, there have been no observed changes in the general
chemistry, field parameter data, or U-234/U-238 ratio; and indication of contamination is
not observed in the other radiological data from the annual samples collected from well
GW-77. Any suggestion that contamination is causing a slow increase in the radium

Mr. Doug Hansen
July 30, 2025
CD-2025-153
Page 5 of 9

concentration at well GW-77, or more broadly, slow increases in radium or uranium
concentrations at other Clive Facility wells, with the exception of well P3-95 SWC, is not
supported by groundwater chemistry data collected to date.
Based on eight consecutive quarterly POOC samples with sum of radiums concentrations
below the GWPL, on May 17, 2024 (CD-2024-110), EnergySolutions submitted a request
to return well GW-77 to in-compliance status. EnergySolutions again requested a return
to in-compliance status for GW-77 on February 5, 2025 (CD-2025-022). This request was
approved by DWMRC on April 11, 2025 (DRC-2024-007488).

GW-126
In accordance with Part I.G.2 of the Permit, on November 30, 2022, EnergySolutions
notified DWMRC that compliance monitoring well GW-126 entered POOC status for the
sum of radiums (CD-2023-198). The sum of radiums concentration of the 2022 annual
monitoring sample exceeded the GWPL. The first quarterly sample was collected in
December 2022.
For the first half of 2025, the sum of radiums concentration of the annual sample
collected in May 2025 (5.21 pCi/L) exceeded the GWPL (5 pCi/L) (Table 1). Since the
initial 2022 exceedance, well GW-126 has been sampled for eleven consecutive quarters.
Other subsequent GWPL exceedances occurred in the quarterly sample collected on
August 17, 2023 and August 20, 2024.
EnergySolutions believes the observed radium exceedances are caused by natural
fluctuations in background concentrations possibly related to infiltration occurring in the
vicinity of the well due to precipitation events at the Clive Facility. Laboratory analytical
factors may also contribute to the sum of radium exceedances observed at well GW-126.
Refer to submittals CD-2022-198, CD-2023-047, CD-2024-036 for additional discussion
of analytical factors.

GW-141
In accordance with Part I.G.2 of the Permit, on September 6, 2024, EnergySolutions
notified DWMRC that compliance monitoring well GW-141 entered POOC status for
selenium (CD-2024-185). The selenium concentration of the 2024 annual monitoring
sample exceeded the GWPL. The first quarterly sample was collected in October 2024.
Subsequent to the August 2024 exceedance, the selenium concentrations of POOC
samples have not exceeded the GWPL (Table 1).
EnergySolutions believes the observed selenium exceedances are caused by natural
fluctuations in background concentrations possibly related to infiltration occurring in the
vicinity of the well due to precipitation events at the Clive Facility. Laboratory analytical
factors may also be the reason for the selenium exceedances observed at well GW-141.

Mr. Doug Hansen
July 30, 2025
CD-2025-153
Page 6 of 9

CONCLUSIONS
During the first half of 2025:
• Well P3-95 SWC remained in OOC status for total uranium, U-234, and U-238.
• Wells GW-23, GW-26 and GW-58 remained in POOC status for total uranium. A
request to return to well GW-23 to in-compliance status was submitted on June
24, 2025 (CD-2025-132) based on the collection of eight consecutive quarterly
samples with total uranium concentrations below the GWPL. This request was
approved by the Division on July 23, 2025 (DRC-2025-002209).
• Wells GW-77 and GW-126 were in POOC status for sum of radiums. GW-77 was
returned to in-compliance status on April 11, 2025 (DRC-2024-007488).
• Well GW-141 remained in POOC status for selenium.
All accelerated monitoring samples collected at well P3-95 SWC during the first half of
2025 were less than the GWPLs for U-234 and U-238. Total uranium concentrations
exceeded the GWPL in March and May of 2025.
Total uranium, U-234, and U-238 exceedances at well P3-95 SWC reflect shallow
subsurface contamination in the vicinity of the well. Correlation of periods of
precipitation and infiltration with GWPL exceedances, and rapid concentration declines
in response to groundwater extraction indicate the contamination source is located in the
vadose zone. In response to observed exceedances during the first half of 2023, on
October 9, 2023, EnergySolutions submitted a plan to return well P3-95 SWC to in-
compliance status. DWMRC provided conditional approval of the plan on March 15,
2024. Details of the planned actions were further outlined to the Division on February
20, 2025 (CD-2025-035) and April 25, 2026 (CD-2025-081). Monthly OOC sampling for
isotopic uranium continues at the well.
The total uranium exceedances at wells GW-23, GW-26 and GW-58 reflect variations in
the natural concentration of uranium in groundwater related to mounding and/or
infiltration in the vicinity of these wells. Mounding to the west of well GW-23 may have
affected groundwater conditions at the well. Since only one exceedance was observed at
well GW-23, it is also possible the exceedance is related to analytical factors. GW-23
returned to annual sampling on July 23, 2025 (DRC-2025-002209). Quarterly POOC
sampling for isotopic uranium will continue at wells GW-26 and GW-58.
All accelerated monitoring samples collected at wells GW-77 and GW-126 during the
first half of 2025 and analyzed for Ra-226 and Ra-228 were less than respective GWPLs
for the sum of radiums, with the exception of the annual GW-126 sample collected in
May.
Mr. Doug Hansen
July 30, 2025
CD-2025-153
Page 7 of 9
Radium concentrations at wells GW-77 and GW-126 reflect variation in natural levels of
Ra-226 and Ra-228 in groundwater. On May 17, 2024, EnergySolutions submitted a
request to return well GW-77 to in-compliance status and again on February 5, 2025
(CD-2025-022). This request was approved by DWMRC on April 11, 2025 (DRC-2024-
007488) and well GW-77 was returned to annual monitoring. Quarterly POOC sampling
for Ra-226 and Ra-228 continues at well GW-126.
Quarterly POOC sampling of well GW-141 groundwater for selenium also continues.
Groundwater sampling sheets, data validation worksheets, and analytical laboratory
reports for accelerated groundwater samples collected during the first half of 2025 will be
provided in the 2025 Annual Groundwater Monitoring Report, due on or before March 1,
2026.
Should you have any questions regarding this submission please feel free to contact me at
[phone].
Sincerely,
Mathew R. Schon
Manager, Groundwater and Environmental Program
I certify under penalty of law that this document and all attachments were prepared under my direction or supervision in accordance
with a system designed to assure that qualified personnel properly gather and evaluate the information submitted. Based on my inquiry
of the person or persons who manage the system, or those persons directly responsible for gathering the information, the information
submitted is, to the best of my knowledge and belief, true, accurate, and complete. I am aware that there are significant penalties for
submitting false information, including the possibility of fine and imprisonment for knowing violations.
Mr. Doug Hansen
July 30, 2025
CD-2025-153
Page 8 of 9
P3-95 SWC Total Uranium 1/14/2025 0.180 mg/l 0.141 mg/l Monthly OOC
P3-95 SWC Dup. Total Uranium 1/14/2025 0.180 mg/l 0.149 mg/l Monthly OOC
P3-95 SWC Total Uranium 2/11/2025 0.180 mg/l 0.134 mg/l Monthly OOC
P3-95 SWC Dup. Total Uranium 2/11/2025 0.180 mg/l 0.127 mg/l Monthly OOC
P3-95 SWC Total Uranium 3/11/2025 0.180 mg/l 0.187 mg/l Monthly OOC
P3-95 SWC Dup. Total Uranium 3/11/2025 0.180 mg/l 0.167 mg/l Monthly OOC
P3-95 SWC Total Uranium 4/24/2025 0.180 mg/l 0.163 mg/l Annual OOC
P3-95 SWC Total Uranium 5/19/2025 0.180 mg/l 0.195 mg/l Monthly OOC
P3-95 SWC Dup. Total Uranium 5/19/2025 0.180 mg/l 0.182 mg/l Monthly OOC
P3-95 SWC Total Uranium 6/3/2025 0.180 mg/l 0.172 mg/l Monthly OOC
P3-95 SWC Uranium-234 1/14/2025 48 pCi/l 26.0 ± 3.55 pCi/l Monthly OOC
P3-95 SWC Dup. Uranium-234 1/14/2025 48 pCi/l 28.6 ± 2.58 pCi/l Monthly OOC
P3-95 SWC Uranium-234 2/11/2025 48 pCi/l 24.9 ± 2.94 pCi/l Monthly OOC
P3-95 SWC Dup. Uranium-234 2/11/2025 48 pCi/l 24.7 ± 1.95 pCi/l Monthly OOC
P3-95 SWC Uranium-234 3/11/2025 48 pCi/l 24.5 ± 2.43 pCi/l Monthly OOC
P3-95 SWC Dup. Uranium-234 3/11/2025 48 pCi/l 30.7 ± 2.25 pCi/l Monthly OOC
P3-95 SWC Uranium-234 4/24/2025 48 pCi/l 28.3 ± 2.59 pCi/l Annual OOC
P3-95 SWC Uranium-234 5/19/2025 48 pCi/l 32.8 ± 2.27 pCi/l Monthly OOC
P3-95 SWC Dup. Uranium-234 5/19/2025 48 pCi/l 28.4 ± 2.14 pCi/l Monthly OOC
P3-95 SWC Uranium-234 6/3/2025 48 pCi/l 29.8 ± 2.17 pCi/l Monthly OOC
Table 1. Sampling Results for Wells in Accelerated Monitoring January through June 2025
Compliance StatusWell ID Analyte Sample Date GWPL Result Sampling Event
Mr. Doug Hansen
July 30, 2025
CD-2025-153
Page 9 of 9
P3-95 SWC Uranium-238 1/14/2025 79 pCi/l 46 ± 4.67 pCi/l Monthly OOC
P3-95 SWC Dup. Uranium-238 1/14/2025 79 pCi/l 49.0 ± 3.36 pCi/l Monthly OOC
P3-95 SWC Uranium-238 2/11/2025 79 pCi/l 43.9 ± 2.57 pCi/l Monthly OOC
P3-95 SWC Dup. Uranium-238 2/11/2025 79 pCi/l 41.6 ± 2.52 pCi/l Monthly OOC
P3-95 SWC Uranium-238 3/11/2025 79 pCi/l 61.4 ± 3.24 pCi/l Monthly OOC
P3-95 SWC Dup. Uranium-238 3/11/2025 79 pCi/l 55.0 ± 3.00 pCi/l Monthly OOC
P3-95 SWC Uranium-238 4/24/2025 79 pCi/l 53.6 ± 3.55 pCi/l Annual OOC
P3-95 SWC Uranium-238 5/19/2025 79 pCi/l 63.9 ± 3.16 pCi/l Monthly OOC
P3-95 SWC Dup. Uranium-238 5/19/2025 79 pCi/l 59.8 ± 3.10 pCi/l Monthly OOC
P3-95 SWC Uranium-238 6/3/2025 79 pCi/l 56.6 ± 2.99 pCi/l Monthly OOC
GW-23 Total Uranium 2/6/2025 0.03 mg/l 0.015 mg/l Quarterly POOC
GW-23 Total Uranium 5/15/2025 0.03 mg/l 0.015 mg/l Annual POOC
GW-26 Total Uranium 2/6/2025 0.037 mg/l 0.035 mg/l Quarterly POOC
GW-26 Total Uranium 5/8/2025 0.037 mg/l 0.034 mg/l Annual POOC
GW-58 Total Uranium 2/11/2025 0.046 mg/l 0.044 mg/l Quarterly POOC
GW-58 Total Uranium 4/17/2025 0.046 mg/l 0.048 mg/l Annual POOC
GW-58 Uranium-234 2/11/2025 31.2 pCi/l 27.2 ± 1.89 pCi/l Quarterly POOC
GW-58 Uranium-234 4/17/2025 31.2 pCi/l 27.9 ± 1.905 pCi/l Annual POOC
GW-77 Ra-226+Ra-228 2/6/2025 5.46 pCi/l 4.12 pCi/l Quarterly POOC
GW-77 Ra-226+Ra-228 5/6/2025 5.46 pCi/l 3.87 pCi/l Annual POOC
GW-126 Ra-226+Ra-228 2/6/2025 5 pCi/l 4.33 pCi/l Quarterly POOC
GW-126 Dup. Ra-226+Ra-228 2/6/2025 5 pCi/l 2.65 pCi/l Quarterly POOC
GW-126 Ra-226+Ra-228 5/13/2025 5 pCi/l 5.21 pCi/l Annual POOC
GW-141 Selenium 2/11/2025 0.0705 mg/L 0.0635 mg/l Quarterly POOC
GW-141 Dup. Selenium 2/11/2025 0.0705 mg/L 0.0574 mg/l Quarterly POOC
GW-141 Selenium 4/8/2025 0.0705 mg/L 0.0638 mg/l Annual POOC
Note: Groundwater Protection Level (GWPL) exceedances are listed in bold.
mg/l - milligrams per liter
pCi/l - picoCuries per liter
OOC - Out-of-Compliance status
POOC - Probable Out-of-Compliance status
J - validation qualifier. Result is estimated.
Table 1. Sampling Results for Wells in Accelerated Monitoring January through June 2025 (continued)
Well ID Analyte Sample Date GWPL Result Sampling Event Compliance Status