DERR-2024-005966

195 North 1950 West
Mailing Address: P.O. Box 144840 Salt Lake City, UT 84114-4840
Telephone [phone] ) 359-8853 [phone]
www.deq.utah.gov
Printed on 100% recycled paper
State of Utah

SPENCER J. COX
Governor

DEIDRE HENDERSON
Lieutenant Governor
Department of
Environmental Quality

Kimberly D. Shelley
Executive Director

DIVISION OF ENVIRONMENTAL
RESPONSE AND REMEDIATION

Brent H. Everett
Director
ERRC-051-24

April 15, 2024

Adam Plonsky
Manager, BU Environmental Compliance
Dominion Energy
2221 Westgate Drive
Rock Springs, Wyoming 82901

RE: Response to Comments to Questar Gas Company Salt Lake Operations Facility
Revised Remedial Action Plan

Dear Mr. Plonsky:

The Utah Department of Environmental Quality (UDEQ), Division of Environmental
Response and Remediation (DERR) has reviewed the Questar Gas Company Salt Lake North
Operations Facility Revised Remedial Action Plan following the response to comments received on
April 2, 2024. The DERR has no additional comments and concurs with finalizing the document.

ency of groundwater
sampling at the site from semi-annual sampling to annual sampling. The DERR agrees with the
proposed change; however, this will be contingent on the results of future sampling activities, and
if deemed necessary (i.e. there is a noticeable fluctuation in contaminant levels between events),
may revert to a semi-annual sampling frequency.

If you have any questions, please contact me at [phone].

Sincerely,

Kelsey Robinson, Project Manager
Division of Environmental Response and Remediation

KS/lg

April 2, 2024

BY EMAIL

Kelsey Robinson
Utah Division of Environmental Response and Remediation
195 North 1950 West
P.O. Box 144880
Salt Lake City, Utah 84114-4880

RE: Comments to Questar Gas Company Salt Lake Operations Facility Revised
Remedial Action Plan

Dear Ms. Robinson:

Questar Gas Company (dba Dominion Energy Utah) is pleased to provide these responses to Utah
Division of Environmental Response and Remediation (Division) comments regarding the Questar
Gas Company Salt Lake Operations Facility Revised Remedial Action Plan that were received in
an e-mail dated January 16, 2024. For ease of review, Division comments have been copied below,
with Questar Gas Company responses below each comment in italicized text.

Comment 1. Table of Contents: This section does not include page references to ‘Table of
Contents’ or ‘Acronyms and Abbreviations’. The DERR recommends adding these sections to the
Table of Contents.

Response 1: Agreed. “Table of Contents” and “Acronyms and Abbreviations” have been added
as pages i and ii, respectively, in the Table of Contents.

Comment 2. Page 1, Section 1.0 Introduction & Regulatory Status, Paragraph 2, Sentence 3: The
Environmental Covenant document is described in this sentence. However, it is not listed in the
‘References’ section of the report. The DERR recommends adding this to the ‘References’ list.

Response 2: Agreed. The Environmental Covenant is referenced in two locations in the text as
“(UDEQ, 2012)”, and a corresponding entry has been added to the References section.

Comment 3. Page 2, Section 1.1 Site Information: Location, History, & Background, Paragraph
3, Last Sentence: This sentence refers to ‘O&M’. However, this acronym has not been previously
Utah Department of Environmental Quality
April 2, 2024
Page 2
defined in the report. Please define this acronym and also include it with in the ‘Acronyms and
Abbreviations’ section of the report.

Response 3: Agreed. The acronym “O&M” has been defined on first use in the text and added to
the “Acronyms and Abbreviations” section of the report.

Comment 4. Figure 2 Site Map: This figure outlines a ‘New Building Dimension’ at the Site. This
building appears to have already been expanded based on recent aerial photographs. The DERR
recommends updating the figure with current areal imagery and also confirming if this expansion
had any effect on the integrity of SWP-1.

Response 4: Agreed. The figure has been updated with current aerial imagery. The expansion did
not have any effect on the integrity of SWP-1.

Please contact me at [e-mail] or 307-371-0966 with any additional
questions or comments.

Thank You,

Adam Plonsky
Manager, BU Environmental Compliance

CC: Lawrence Cannon, AECOM
Kris Benson, Questar Gas Company

Enclosure: Questar Gas Company Salt Lake North Operations Facility Revised Remedial Action
Plan

QUESTAR GAS COMPANY
S ALT LAKE NORTH OPERATIONS FACILITY
R evised Remedial Action Plan
Prepared by
September 2023
Revised March 2024
Revised Remedial Action Plan
Questar Gas Company
March 2024 Page i
TABLE OF CONTENTS

TABLE OF CONTENTS .......................................................................................................... i
ACRONYMS AND ABBREVIATIONS.................................................................................. ii
1.0 INTRODUCTION & REGULATORY STATUS ............................................................. 1
1.1 Site Information: Location, History, & Background ................................................. 1
1.2 Site Description ...................................................................................................... 3
1.3 Summary of Site Risks ........................................................................................... 4
1.4 Summary of Site Screening Levels .......................................................................... 4
2.0 REVISED REMEDIAL ACTION PLAN......................................................................... 5
2.1 Proposed Remedy................................................................................................... 5
2.1.1 Slurry Wall................................................................................................... 5
2.1.2 Surface Cap .................................................................................................. 5
2.1.3 Groundwater Monitoring ................................................................................ 5
2.2 Groundwater Extraction System Decommissioning.................................................. 6
2.3 Soils Handling Plan ................................................................................................ 6
2.4 Environmental and Public Health Impacts ............................................................... 6
2.5 Institutional Requirements ...................................................................................... 6
3.0 REMEDY IMPLEMENTATION .................................................................................... 7
4.0 REFERENCES ............................................................................................................... 7

FIGURES
Figure 1 Project Location Map
Figure 2 Site Map

APPENDICES

Appendix A Civil Order No. C-84-7118 (Department of Health, 1991)
Revised Remedial Action Plan
Questar Gas Company
March 2024 Page ii
ACRONYMS AND ABBREVIATIONS

bgs below ground surface
BTEXN benzene, toluene, ethylbenzene, xylene, and naphthalene
CGR coal gasification residuals
CWA Clean Water Act
DERR Division of Environmental Response and Remediation
Dominion Dominion Energy Services, Inc.
DWMRC Utah Division of Waste Management and Radiation Control
EPA U.S. Environmental Protection Agency
gpm gallons per minute
MCL Maximum Contaminant Levels
mg/L milligrams per liter
O&M Operations and Maintenance
OSHA Occupational Safety and Health Administration
PAH polycyclic aromatic hydrocarbon
QGC Questar Gas Company
RAP Remedial Action Plan
RCRA Resource Conservation and Recovery Act
RSL Regional Screening Levels
UDEQ Utah Division of Environmental Quality
USEPA United States Environmental Protection Agency
VISL vapor intrusion screening level
VOC volatile organic compound

Revised Remedial Action Plan
Questar Gas Company
March 2024 Page 1
1.0 INTRODUCTION & REGULATORY STATUS
In 1991, Civil Order No. C-84-7118 was issued by Utah Department of Health, Division of Environmental
Health which amended and replaced a 1987 Consent Decree for the subject facility. A copy of the Civil
Order is provided in Appendix A. The Order incorporated the 1988 site Investigation and Proposed
Remedial Action Plan (1988 RAP) (Dames & Moore, 1988). The order states that Mountain Fuel Supply
Company will comply with the 1988 RAP as it shall be amended, modified, or terminated by the parties.
This revised remedial action plan (RAP) is an update to the 1988 RAP to amend the remedy for the site to
hydraulic containment (slurry wall) without groundwater extraction. The site is currently regulated under
the Utah Department of Environmental Quality (UDEQ), Division of Environmental Response and
Remediation (DERR). An Environmental Covenant (UDEQ, 2012) prevents future residential use of the property and assures that any future owners of the property or any portion of the property will implement,
administer, and maintain all activity and use restrictions as detailed in the Covenant.
1.1 Site Information: Location, History, & Background
The Questar Gas Company (QGC) Salt Lake Operations Center is located at 1140 West 200 South in Salt
Lake City, Utah. The former Utah Gas & Coke Company property which produced synthetic gas by coal
gasification between 1908 and 1929 (Dames & Moore, 1988) was located in the northeast portion of the
operations center , near 1000 West 100 South, and is referred to as the North Operations Facility (the site)
in the historical documents related to this project. The project location is shown on Figure 1.
In 1983, coal gasification residuals (CGR) were discovered during the construction of an underground
utility corridor at the site. A subsequent Phase I Preliminary Investigation conducted in 1985 identified polycyclic aromatic hydrocarbons (PAHs) and volatile organic compounds (VOCs) in site soils and PAHs,
VOCs, and phenolic compounds in site groundwater (Dames & Moore, 1986).
A Phase II Confirmatory Investigation was conducted to define the extent and migration pathways of CGR. During the investigation, CGR was found on site, both above and within the water table. Off-site, CGR was
found within the water table and contaminant migration was noted to be primarily toward the south (Dames
& Moore, 1988). Based upon the Phase I and II results, a slurry wall, groundwater extraction remedy, and
repairs to the asphalt/concrete surface cover of the site to function as a surface cap, were proposed in the
1988 RAP and approved by the Department of Health in a letter dated July 29, 1988. CGR encountered
during the assessments appears to be weathered and thought to be on the order of 100 years old.
In 1989, the slurry wall was constructed around an approximately nine-acre area encompassing the site and
surrounding areas (Figure 2). The total length of the slurry wall is approximately 2,400 feet. The slurry wall extends into the underlying clay layer a minimum depth of three feet. The clay layer is typically
encountered at a depth of approximately 18-23 feet below ground surface (bgs), thus, the slurry wall was
installed to a total depth of approximately 21-26 feet bgs. The slurry wall has a minimum width of
approximately two feet (Dames and Moore, 1988). The slurry wall design and installation is consistent with
the industry standard “keyed-in” slurry wall containment approach. The intent of the slurry wall was to isolate the primary source of CGR within the slurry wall. During the slurry wall construction, the
asphalt/concrete surface cap was inspected and confirmed to be free of significant cracks or voids which
would allow surface water to permeate the cap. The intent of the surface cap was to minimize surface water
infiltration.
A groundwater extraction system was installed after construction of the slurry wall. The extraction system
consists of four groundwater extraction wells interior to the slurry wall, within the contaminant containment
area, and seven off-site extraction wells exterior to the slurry wall (Dames and Moore, 1986). Five of the
seven off-site extraction wells were installed south of the site in the Euclid Avenue residential area. The other two extraction wells were installed north of the Operations Center on the railroad right-of -way as an
interim measure until construction of a remedy for the site known as the "Barber Tar Products site"
Revised Remedial Action Plan
Questar Gas Company
March 2024 Page 2
commenced. The system was designed to maintain an inward hydraulic gradient within the slurry wall and
to limit further migration of impacted groundwater off-site.
In a letter to Mountain Fuel dated November 14, 1989, the State expressed concern for the integrity of the
slurry wall and specifically the outward hydraulic gradient that existed across the slurry wall measured by
groundwater levels at SWP-5 and SWP-6 (Figure 2). These piezometers are located inside and outside of
the slurry wall to the southeast, respectively. To address the State’s concerns, Dames & Moore conducted
site investigations and a performance review of the extraction well system and slurry wall was conducted
between November 9, 1989, and January 1990 (Dames and Moore, 1990).
The site investigations identified several extraction wells which were inefficient in 1990. These wells were
redeveloped, and efficiency was improved. The system flow rate increased from approximately 5 to 70 gallons per minute (gpm). Preliminary results noted that groundwater levels, inside and outside of the slurry
wall, are different, indicating that the slurry wall disrupts groundwater flow and is functioning as a low
permeability barrier. Additionally, the study indicated that groundwater elevations (on January 26, 1990)
showed that the interior extraction wells had reduced the water table by approximately one-half foot since
January 8, 1990; however, an outward gradient continued to exist to the south and east. Dames and Moore
stated that they do not believe the outward hydraulic gradient is detrimental to the remediation of the site
since groundwater containment is indicated by the groundwater level elevation contours to the south and
east of the slurry wall. The system pumping rate decreased from around 70 gpm in 1990 to approximately
5 gpm in 2008. It is assumed the extraction wells and piping started to foul with sediment prior to 2000.
Additionally, sediment (silt) and potentially CGR have migrated into the sand pack of the extraction wells,
reducing the effective porosity and specific yield of the well field.
The groundwater extraction and treatment system was turned off at the end of 2017 and is currently offline.
In 2018, the oil/water separator, day tank, and air stripper were cleaned and inspected. During the inspection pin size holes and leaks were found in both the oil/water separator and day tank (Kleinfelder, 2019). Several
groundwater extraction pumps were also noted to be non-operational and in need of replacement. In a letter
dated January 5, 2023, the UDEQ and DERR concurred that the groundwater extraction system can remain
shut down and the RAP and Operations and Maintenance (O&M) Manual be updated to reflect the change.
Supplemental quarterly groundwater monitoring events and a 24-hr pumping test were performed in 2019
using a new groundwater extraction well and supplemental piezometers to evaluate the slurry wall
performance and hydraulic gradients across the site. Groundwater monitoring results were reported to show
a small groundwater mound located in the southern portion of the slurry wall (Kleinfelder, 2020). The results of the pump test were reported as showing that exterior monitoring wells (outside slurry wall) were
not influenced by well drawdown throughout the 24-hr test. It was noted that the pump test did not stress
the aquifer enough to make definitive conclusions, however, it was concluded that the slurry wall was likely
acting as an effective low permeability barrier controlling contaminant migration, even without
groundwater extraction.
Groundwater flow direction prior to wall construction was to the southeast and generally followed the slope
of the confining clay layer at depth (Dames and Moore, 1988, Figure B1-2). The approximate average
horizontal gradient prior to wall construction was 0.003 to 0.004 feet per foot and was calculated from the
1987 potentiometric surface maps (Dames and Moore, 1988). This gradient is within the range of known
gradients in the area. Following slurry wall construction, shallow groundwater is diverted around the slurry
wall with an overall flow direction to the southeast. The flow gradient inside the slurry wall is to the north
and northeast (Kleinfelder, 2020, Figure B1-3). Groundwater elevations were reviewed from 1990 to 2020
from paired piezometers installed across the slurry wall to confirm whether the slurry wall was impacting
horizontal hydraulic gradients onsite and determined the average gradient within the slurry wall to be an order of magnitude greater than the 1987 pre-wall gradient. The order of magnitude difference in horizontal
gradient between pre-wall and post-wall suggests that the slurry wall is functioning as a low permeability
barrier, significantly limiting the migration of CGR from the site (AECOM, 2022).
Revised Remedial Action Plan
Questar Gas Company
March 2024 Page 3
1.2 Site Description
Land Use and Zoning
The site is located in an urban commercial/residential use area of Salt Lake City, Utah and is zoned as
commercial, with limited residential zoning located south and east of the site. Historically, the site was used
as a coal gasification facility and is currently a QGC Operations Center. Historical land use in the immediate
vicinity of the site appeared to be commercial and residential land uses. Current land ownership and uses
in the immediate vicinity of the site are as follows:
• North: Rail Property, Union Pacific
• South: Single family residential, located along Euclid Avenue
• East: Single family residential, located along 1000 West Street
• West: Commercial property, QGC
Nature of Sources and Migration Pathways
Evidence of CGR impacts was found during historical investigations, as a result of past gasification
operations. The Phase I and Phase II Investigation reports have delineated the extent CGR impacts within
the Post-Lake Bonneville Sediments to a depth of approximately 20 feet below ground surface (bgs) (Dames & Moore, 1985 and Dames & Moore, 1988). There is no evidence of water quality impacts from past coal
gasification operations within the deeper underlying lacustrine clay stratum (confining clay layer at depth)
below approximately 20 feet bgs. Based on the analyses of soil samples, the CGR principally includes the
following classes of organic compounds: PAHs, alkylbenzenes, and phenols. The bulk of the CGR impacts
are contained inside the boundaries of the slurry wall and capped under onsite pavement, with some exceptions as described herein. The horizontal extent of soil impacts appears to be generally defined and
associated with CGR at depth.
Groundwater beneath the site consists of an unconfined alluvial shallow aquifer and a deep confined aquifer
beneath a confining clay layer. The existing site wells, including the extraction wells, are installed in the
unconfined shallow aquifer . Three quarterly groundwater sampling events were conducted in 2020
(Kleinfelder, 2020). Groundwater samples were collected within the slurry wall area and south of the slurry
wall in the Euclid residential area. The samples were analyzed for various analytes, including benzene,
toluene, ethylbenzene, xylene, and naphthalene (BTEXN) and benzo(a)pyrene. Benzene was detected in
groundwater south of the slurry wall at monitoring location E -9 ranging from less than 0.0100 milligrams
per liter (mg/L) to 0.0834 mg/L (Kleinfelder, 2020). Dissolved phase concentrations in groundwater near
E-9 decrease towards the ground surface with increased distance from the CGR (located at depth on top of
the confining layer). Th is dissolved groundwater plume is expected to attenuate over time. There are no
natural or permanent surface water bodies onsite. The Jordan River is located approximately 0.25 miles
west of the site and there are no known discharges from the site to the Jordan River.
The subsurface lithology beneath the site consists generally of imported fill from ground surface to two feet
bgs, sandy silt from approximately three to six feet bgs, and sand or sandy gravel varying from
approximately 2 to 20 feet bgs. Shallow unconfined groundwater is present within the upper sand and
gravelly sand units. A layer of clay and silt which is considered the confining layer separates shallow
unconfined groundwater from deeper confined groundwater. A thin layer of CGR can be found overlying
the confining unit in places. The slurry wall is keyed into the low permeability clays associated with the
confining unit.
The approximate area of CGR and dissolved phase plume, and a conceptual cross-section and generalized
stratigraphic column for the southern portion of the site (slurry wall to Euclid Avenue), are shown in the
Soil Gas and Groundwater Investigation Summary Report (AECOM, 2022).
Revised Remedial Action Plan
Questar Gas Company
March 2024 Page 4
1.3 Summary of Site Risks
Pathways for Exposure
An exposure pathway describes a specific route by which a receptor might directly or indirectly come into
contact with related site impacts. The following elements comprise a potentially complete exposure
pathway: (1) a chemical source, (2) a mechanism of chemical release to the environment, (3) an
environmental transport medium, (4) an exposure point where contact between the contaminated medium
and the receptor occurs, and (5) an exposure route at the exposure point (USEPA, 1991). The current
exposure pathways and receptors considered relevant to this site and this evaluation are summarized below.
Human Exposure
Onsite: Based on the current and reasonably likely future use of the site, the potentially complete exposure
pathways for onsite human receptors are through excavation and construction worker direct contact with
shallow impacted soil and groundwater contained within the slurry wall. Onsite residential exposure is not a complete pathway as the Environmental Covenant (UDEQ, 2012) prevents future residential use of the
property and assures that any future owners of the property or any portion of the property will implement,
administer, and maintain all activity and use restrictions as detailed in the Covenant. Impacted soils will
continue to be managed per the Environmental Covenant and Environmental Health and Safety
Management Plan to limit onsite risks.
Off-site: Receptors off-site, including existing residents along Euclid Avenue, could potentially be exposed
to VOC (volatile organic compound) contamination inside existing or future buildings through intrusion of
soil vapor associated with contaminated groundwater, therefore residential exposure to soil vapors is considered as part of the Conceptual Site Model. In November 2021, AECOM conducted a groundwater
and soil gas investigation at the Site. Concentrations of benzene and ethylbenzene in shallow soil gas were
detected slightly above United States Environmental Protection Agency (USEPA) vapor intrusion
screening levels (VISLs) at two locations along Euclid Avenue. Cumulative cancer risk at these locations
was determined to be equal to 1×10-6 with a hazard quotient less than 1 and is considered within the
acceptable risk range to UDEQ. The results of the screening risk assessment confirm that the current
subsurface conditions are within acceptable risk to residential land use along Euclid Avenue and 10th West
(AECOM, 2022). It should be noted that existing residences along Euclid Avenue were constructed prior
to the development of the Utah Gas and Coke Company. Existing data indicates that impacted shallow soil
(surface to 12 feet bgs) is limited to onsite areas, therefore residential or construction worker exposure to
off-site shallow soil can be screened out as a potential exposure pathway.
Ecological Exposure
The site is covered with buildings and asphalt parking lot, and the surrounding properties are fully
developed. No significant ecological habitat was observed at the site and no ecological receptors are
expected at the site.
1.4 Summary of Site Screening Levels
Monitoring, investigation, or remediation activities at the site will consist of environmental sampling and
laboratory analytical testing. Laboratory analytical results reported as part of the monitoring program, as
well as potential future sampling results, will be compared to screening levels established by the US EPA
including National Primary Drinking Water Regulations, i.e., Maximum Contaminant Levels (MCLs) or
Regional Screening Levels (RSLs).

Revised Remedial Action Plan
Questar Gas Company
March 2024 Page 5
2.0 REVISED REMEDIAL ACTION PLAN
2.1 Proposed Remedy
The proposed remedy consists of hydraulic containment without groundwater extraction. The results and
conclusions from the Soil Gas and Groundwater Investigation Summary Report (AECOM, 2022) support
hydraulic containment without operation of the groundwater extraction system. In a letter dated January 5,
2023, the UDEQ DERR concurred that the existing groundwater extraction system can remain shut down.
Onsite CGR impacts are contained by the existing slurry wall, which is functioning as intended as a low
permeability barrier. The existing groundwater extraction system has been determined to be unnecessary to
maintain hydraulic control and inward gradient within the slurry wall to contain CGR. Hydraulic
containment will continue to be achieved via the existing slurry wall and maintenance of the surface cap. Effectiveness of the remedy will be evaluated by scheduled visual inspections, measuring water levels
inside and outside of the slurry wall, and by collection of groundwater samples for laboratory analysis as
detailed in the revised O&M Manual (Dominion, 2023).
2.1.1 Slurry Wall
The slurry wall extends along the perimeter of the site (approximately 2,400 feet) with a minimum width
of approximately two feet, a depth of approximately 21-26 feet bgs, and is keyed into underlying clay a
minimum of 3 feet. In addition to existing monitoring wells, six paired piezometers were installed to
monitor the differential in water elevations between the inside and outside of the slurry wall. The
piezometers are located on either side of the north, west, and south sides of the slurry wall and are identified
as SWP-1 through SWP-6. The locations of the slurry wall and piezometers are shown in Figure 2.
Groundwater elevation data will be collected, and a potentiometric surface will be contoured to understand
potential groundwater elevation trends on an annual basis during groundwater monitoring. The
potentiometric surface will be contoured in three distinct areas (upgradient outside the wall, inside the wall,
and downgradient outside the wall) based on a minimum of three wells or piezometers per area. The
localized groundwater gradients across the slurry wall will continue to be used to demonstrate performance of the slurry wall. In addition, a visual inspection of the slurry wall will be conducted on an annual basis to
look for obvious areas of encroachment, damage, or penetration to ensure continued integrity to the extent
possible as per the O&M Manual. Details of the water level measurement and inspection procedures are
provided in the revised O&M Manual (Dominion, 2023).
2.1.2 Surface Cap
The area within the slurry wall is paved with asphalt or concrete, or covered with buildings, except for some
landscaped areas in the southern part of the site along 100 South Street. The majority of the area outside of
building footprints consists of asphalt parking and roadways. The existing asphalt/concrete surface cap will
be inspected on an annual basis and repaired to limit precipitation from infiltrat ing to the subsurface. Small
areas which are grass-covered, such as parking lot medians and the lawn along 100 South Street, are
anticipated to have an insignificant contribution to infiltration, and as such, these areas will be left undisturbed. Roof drains drain water to the stormwater collections system to the extent possible. Details of
the surface cap inspection procedures are provided in the revised O&M Manual (Dominion, 2023).
2.1.3 Groundwater Monitoring
A network of monitoring wells is used to monitor water quality and long-term groundwater trends.
Groundwater monitoring will be conducted on an annual basis to evaluate natural attenuation of impacts
over time and to confirm that impacts are not migrating off-site. Monitoring wells and piezometers are used
to collect groundwater elevations for potentiometric surface contouring. Groundwater sample locations and
laboratory analytical methods are detailed in the revised O&M Manual (Dominion, 2023).
Revised Remedial Action Plan
Questar Gas Company
March 2024 Page 6
2.2 Groundwater Extraction System Decommissioning
The existing groundwater extraction system will be decommissioned. Pumps and controls will be removed
from extraction wells and properly disposed. Extraction wells outside of the slurry wall will be properly
abandoned as per Utah Administrative Code. Remediation equipment such as the system enclosure,
oil/water separator, air stripper, controls, pumps, and wiring will be demolished or evaluated for recycling.
Subsurface conveyance piping or electrical conduit will be assessed for abandonment. UDEQ will be
notified prior to any specific abandonment or rehabilitation activities in the form of a letter Work Plan.
2.3 Soils Handling Plan
Prior to undertaking any subsurface or excavation activities at the site, the site-specific Environmental,
Health, Safety and Site Management Plan will be followed (Dominion, 2017). The Plan includes notice
requirements to construction and underground utility workers who could come into contact with subsurface
soil and groundwater conditions beneath the site so they are informed of potential dangers and can take appropriate safety measures to address potential health risks associated with environmental conditions. The
Plan also addresses the management and proper disposal of any regulated materials encountered during the
proposed activities, including the testing, stockpiling, manifesting, transporting, and off-site disposal of
such material, as necessary.
2.4 Environmental and Public Health Impacts
Short and long-term potential environmental and public health effects resulting from the implementation of
the revised remedy have been evaluated. No significant adverse impacts are anticipated. The current
exposure pathways and receptors considered relevant to the site are summarized below.
Human Exposure
As discussed in Section 1.3, the potentially complete exposure pathways for onsite human receptors are
through excavation and construction worker direct contact with shallow impacted soils/groundwater
contained within the slurry wall. Worker exposure will be minimized through the continued implementation
of the site-specific Environmental, Health, Safety and Site Management Plan. Off-site risks are considered
within the acceptable risk range to UDEQ.
Ecological Exposure
As discussed in Section 1.3, no ecological receptors are expected at the site.
2.5 Institutional Requirements
This revised remedy will be implemented in accordance with applicable federal, state, and local regulatory
requirements. The primary federal environmental laws and associated regulations which may be applicable
to the revised remedy are the Resource Conservation and Recovery Act (RCRA) and the Clean Water Act
(CWA). Additionally, the federal authority Occupational Safety and Health Administration (OSHA), which
regulates worker safety and health at hazardous waste sites, contains potentially applicable regulations.
The Division of Environmental Response and Remediation is the lead regulatory authority for the Operations Center project. In addition, the U.S. Environmental Protection Agency (EPA) has granted the
state of Utah Division of Waste Management and Radiation Control (DWMRC) the authority to implement
their own hazardous waste program under RCRA.
Local authority is placed with Salt Lake City Corporation. The Operations Center site lies within the city
boundaries, and the city owns and operates the public water and sewer systems.

Revised Remedial Action Plan
Questar Gas Company
March 2024 Page 7
3.0 REMEDY IMPLEMENTATION
The proposed remedy will be implemented upon UDEQ approval. The historical groundwater monitoring
program has been conducted on a semi-annual basis. Due to the amount of historical data, age of the source
material, and acceptable off-site risks, an annual sampling and reporting frequency are proposed. It is
anticipated that the next groundwater monitoring event would be conducted during Spring 2024.

4.0 REFERENCES
Dominion, 2023. Dominion Energy Services, Inc., Salt Lake North Operations Facility, Operations and
Maintenance Manual. August 2023.
AECOM, 2022. Dominion Energy Services, Inc., Salt Lake North Operations Facility, Soil Gas and
Groundwater Investigation Summary Report. December 2022.
Kleinfelder, 2020. Groundwater Sampling and Slurry Wall Evaluation Report, Dominion Energy
Services, INC. Salt Lake North Operations Facility, 1140 West 200 South, Salt Lake City,
Utah 84145. October 9, 2020.
Kleinfelder, 2019. Site Characterization Report, Dominion Energy, Salt Lake North Operations Facility,
1140 West 200 South, Salt Lake City, Utah 84145. February 14, 2019.
Dominion, 2017. Dominion Questar Gas Company Environmental, Health, Safety & Site Management Plan
North Operations Center Salt Lake City, Utah. May, 2017.
Utah Department of Environmental Quality (UDEQ), 2012. Environmental Covenant. Salt Lake County
Document Number 11411209, Recorded June 15, 2012.
Department of Health, 1991. Civil Order No. C-84-7118
USEPA. 1991. Risk Assessment Guidance for Superfund: Volume I Human Health Evaluation Manual.
Part B, Development of Risk-Based Preliminary Remediation Goals. Interim.
Dames and Moore, 1990. Evaluation of the Effectiveness of the Extraction Well System and Integrity of
the Slurry Wall at the Mountain Fuel Supply Company Operations Center. January 26, 1990.
Dames and Moore, 1988. Site Investigation and Proposed Remedial Action Plan (1988 RAP). August 9,
1988.
Dames and Moore, 1986. Mountain Fuels Supply Company Operations Center Remedial Action Strategy
(RAS). April 10, 1986.
Dames and Moore, 1985. Final Phase I redial Investigation Preliminary Characterization of Operations
Centers Mountain Fuel Supply Company. July 8, 1985.
Revised Remedial Action Plan
Questar Gas Company
March 2024

FIGURES
Revised Remedial Action Plan
Questar Gas Company
March 2024

APPENDIX A

Civil Order No. C-84-7118 (Department of Health, 1991)

.pfib'U t
R. PAUL VA}I DAU BAT NO. 3312
Attorney General
FRED G NEI,SON BAT NO. 2382
Assistant AttorneY General
Attorneys for Plaintiff
236 State Capitol
SaLt Lake City, Utah 84114
Telephone: (801-) 538-L017
IN THE THIRD JUDICIAI DISTRICT COI'RT
STATE OF UTAII
F$l. FF S'lf,Trr'fiT l!: F:1-- ElZ
-
i' ;t' t i J "i
i.tlii - r.-ri il'iiii ii::i
' HAY161991
FFCEIVED
iLJi- 1 a 38$7
. DEQ
E nv,.u,rrnErrtal nesponse E RemedlailOn
OF SAIT I,AKE COI'NTY
ffAHtrurn
- iSlQ i : OCrl K"7 ''
UTAII STATE DEPARTMENT OF
HEALTH, by and through the
DIRECTOR OF THE DIVISION
OF ENVIRONMENTAL IIEATJTH'
Plaintiff,
vs.
MOUNTA]N FUEL SUPPLY COMPAIiIY,
Defendant.
ORDER
Civil No, C-84-7I18
Honorable David S. Young
Pursuant to the joint motion of the parties, it is
hereby ordered:
L. Thls Order amends and replaces the Consent Decree'.'
filed February 25, 1987r ds it has been modified and amended
pursuant to five addenda which are inco,rpcrated herein.
2, Defendant completed an investigation of the sj-te,
and proposed to Plaintiff a Remed.ial Action Plan to include'
inter a1ia, construction of a slurry wal} to isolate the
contaminant source(s), with shallow aquifer purnping designed to
remove groundwater contaminants outside of the wall and to
maintain an inward gradient within the walI so that cont'aminants
there cannot migrate. The Remedial Action Plan submitted by
Defendant dated AugusL gr 1988r ds amendedr and as approved by
Plaintiff effective July 29, L988r referred to as the uRAPut is
incorporated herej-n by this ref erence. Def end'ant shall comply
with the RAP as it shalL be amended, modified or terminated by
the parties.
3. The Extraction well Field operations Manual
submitted by Defendant dated December 8, 1988r ds amencied, and
approved by Plaintiff is i-ncorporated herein by this reference'
The Defendant shau mpnitor contaminant conditions pursuant to
the Extraction Well Field Operations Manualr as it shall be
amended, modified or terminated by the parties, until Defendant
can demonstrate that the Site no Longer presents a threat to
pubtic health or the environment. Defendant shall take such
actions as are necessary to protect public heal-th or the
environment in the event of a release of contaminants from the
Site.
4. Defend.ant has paid Plaintiff $501000 to defray
Plaintiff's costs in evaluating, reviewing and monitoring the
implementation of the investigation, the RAP and the Extraction
WeIl Field Operations Manual. In addition;
-2-
(a) Defendant shall pay Plaintiff t'he sum of $2'600
per year on or before July 1 of each year, conmencing
in the year 1994, and continuing each year until
monitoring is no longer reguired.
(b) The payments reguired by subparagraph (a) finally
settle all past and future financial obligations of
Defendant to Plaintiff with regard to this litigation
regardless of Plaintiff's actuaL expensesr past or
future.
5. Defendant shall cause a noticer approved by
Plaintiff, to be recorded with the Salt L,ake County Recorder
against the Operations Center Site indicating the presence of
coal tars and specifying restrictions on use of the property.
Any transfer of any portion of the Site by Defendant shall be
subject to 60-days prior notice to Plaintiff and the requirement
of a binding agreement enforceable by Plaintiff, committing the
buyer to assume the obligations for Defendant wiLh respect to
this Site.
6. Defendant's full compliance with this order will
satisfy Plaintiff's concerns which originally prompted this
Iitigation. Except as provided in paragraph L2 of this Order'
Plaintiff therefore shall not, based upon matters which are
covered by this Order, nominate Defendant's Site for scoring on
the EPA National Priorities List est.ablished pursuant to Sectj-on
-3-
105(b) of the Comprehensive Environmental Response, Compensation
and Liability Act, 42 v.S.C. Section 9605(b) ' or list the site on
the Hazardous Substances Priority List' established pursuant to
the llazardous Substances Mitigation Act, Chapter 14d of Title 26,
U.C.A. In consideration of this covenant, Defendant agrees not
to assert any claims or causes of action against the state of
Utah or its contractors or employees arising out of expenses
incurred, payments made or work performed pursuant to this order,
however this provision shall not be interpreted to prevent a
claim under the Governmental- Irnmunities Act against the State of
Utah for acts or omissions of its ernployees after the date of
this Order. This covenant extends only to Def,endant and does not
extend to any other Person.
7. Plaintiff and Defendant have designated
coordinators who shall be responsible for the administration of
their respective responsibilities pursuant to the RAP and who
shall receive all written materials and notices required by the
RAP.
8. Defendant shall permit Plaintiff's authorized
representative to have access to the Operations Center Site to
monitor (including sampling) any activity conducted pursuant to
the RAP. As a normal course of action consistent with its
responsibility, Plaintiff shalt provide prior notice requesting
access. Plaintiff shall comply with Defend'ant's existing safety
and security requirements previously provided to Plaintiff'
-4-
g.Defendantshall'uponrequest,makeavailableto
the plaintiff in a timely manner, the results of sarnpling and
testing, and other data generated by Defendant' or on its behalf'
in connection with the RAP including raw data and fields notes
which shall be public information'
L0. During the course of the RAP, the Plaintiff shall-
not initiate any civil ad.ministrative or judicial enforcement
proceedings against Defendant regarding matters covered by this
Order, except as provided in paragraph l-2 below'
Ll. The covenant not to nominate Defendant's site for
scoring on the EPA National Priorities List or to list the Site
on the Ilazardous Substances Priority List shall not apply to the
following:
(a)no.rninationorlistingbasedonthefailureto
cornply with this Order;
(b)nominationorlistingarisingfromtheactionsof
Mountain Fuel supply Company after the effective date
of this Order which exacerbate the release or
threatened release of hazardous substances or maLerial-s
at the Site;
(c)nominatj-onorlistingbasedonconditionsatthe
site which were previously unknown to or undetected by
the state of utah indicating that a hazardous substance
or material has been or is being released into the
-5-
environment or that there is a substantial threat of
such a release; or
(d) nonination or listing based on information received
in whole or in part after remedial action has been
completed, that the remedial action taken at the Site
is not protective of human health and the environment.
plaintiff shall provide notice reasonable under the circumstances
(including no notice in the event a condition requires immediate
response) prior to taking any action under this paragraph. This
Order is not intended to allocate coets incurred by Plaintiff
pursuant to this paragraPh,
L2. Any failure by Defendant to comply with the terms
of this Order shall be excused, and the time for Defendant's
performance extended, to the extent such failure is caused by
circumstances beyond its control.
13. plaintiff and Defendant shall inform the other in
ad.vance of any formal press release made relating to this Order
and the work cond.ucted pursuant to the RAP program or the results
thereof. Either party may respond to inquires about this Order
or the RAp without consulting the other when such inguiries are
made in a manner that precludes prior notice. Either party may
promptly release technical data as necessary to protect public
health; provided, however, that , Lf possible, the other party
will be given an opportunity prior to release to review such
-6-
information and provide comments on the information's technical
accuracy. Any release of such information shall ensure that the
public is informed in a responsible manner.
L4. Nothing in this order shall be interpreted as a
waiver of any sovereign immunity the State of Utah may have'
L5. This Order shall be binding on Defendant, its
successors, and assigns.
15. The Court shall retain jurisdiction
purposes of implementation and enforcement of this
DATED IhiS /b rA day of
for the
Order.
, 1991.
District
-11-
CERTIFICATE OF MAILING
Thisistocertifythatatrueandcorrectcopyofthe
foregoing oRDER was mailed., first class, postage prepaid, to the
- I4,rfollowing this \19 daY of MaY, 1991:
Robert H. Lovell
Questar CorPoration
l-80 East 100 South
Salt Lake CitY, Utah 841-39
AttorneY for Defendant
V)!4Al C,,A
-L2-