DERR-2024-011019

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Enbridge Gas
1140 West 200 South
Salt Lake City, Utah 84104
United States
VIA EMAIL
September 19, 2024
Kelsey Robinson
Environmental Scientist
Utah Department of Environmental Quality
Division of Environmental Response and Remediation
168 North 1950 West
Salt Lake City, Utah 84116
RE: Environmental Covenant Questar Gas Salt Lake Operations Center – 2024
Monitoring Well Installation
Dear Ms. Robinson:
Questar Gas Company (Questar), d/b/a as Enbridge Gas Utah (EGU), is providing notification to
the Division of Environmental Response and Remediation (DERR) to conduct ground disturbance
activities within the Salt Lake Operations Center Environmental Covenant boundaries. The ground
disturbance activities will take place as part of implementation of the Updated Operations and
Maintenance Manual – Salt Lake Operational Center North. An overview of the Environmental
Covenant boundaries is provided in Figure 1, and planned ground disturbance areas are shown in
Figure 2. Project details are provided herein.
EGU intends to install monitoring wells and piezometers in alignment with its Remedial Action
Plan and Operations and Maintenance Plan, approved by DERR on April 15th, 2024 and April 23rd,
2024, respectively. Monitoring well and piezometer installations will be completed by a 3rd party,
State of Utah licensed well drilling company between October 7th and October 14th, 2024. A total
of three new monitoring wells and three new piezometers are proposed with one monitoring well
and three piezometers being installed within the Environmental Covenant boundaries. Wells and
piezometers will be installed via direct-push using 3.75-inch direct-push rods. The total depth of
wells will be based on the depth to the confining layer at each location as interpreted by the field
geologist but is not anticipated to be deeper than approximately 20 feet. Wells will be screened
from approximately 5-15 feet using 10-20 silica sand, sealed to the surface with bentonite hydrated
with fresh water, and completed with flush mount well covers installed in concrete. Following
installation wells and piezometers will be developed until water is visually clear or until 5 well
volumes of water are removed. Proposed monitoring well locations are included as Figure 2. A
proposal with scope of work details are included as Attachment A. Soil cuttings, development
water, and related wastes will be containerized for characterization and off-site disposal at a
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permitted facility.

An EGU Environmental Compliance Coordinator (ECC) will lead a Health Hazard Advisory
(HHA) meeting with all involved personnel to review the property’s history and potential health
hazards for the day’s tasks prior to any work requiring ground disturbance. All project personnel
will be required to attend the HHA meeting and verify that they understand the information
provided. The ECC will remain onsite for the duration of the ground disturbing work to perform
continuous environmental monitoring. The ECC will visually inspect excavated soils for signs of
contamination (odor, staining, discoloration, indication of free product or residuals) and conduct
atmospheric monitoring with a field-calibrated photoionization detector (PID), as necessary. If
any contaminated soils are encountered, they will be isolated, characterized, and managed for
appropriate off-site disposal.

The ECC will stop work if Action Levels specified in the Environmental, Health, Safety and Site
Management Plan (2.50 parts per million-volt) are exceeded. Work will re-commence following
the implementation of exposure controls and reduction in exposure to contaminants in the
breathing zone to below prescribed Action Levels. Upon completion of the work, EGU will submit
a report to UDEQ to provide information related to any impacted materials encountered, laboratory
analytical results, and waste generation and disposal.

If you have any questions or concerns related to this notice, please contact Kris Benson at 801-
349-6950 or [e-mail].

Sincerely,

Adam Plonsky
Manager, Environmental

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Figure 1 – Questar Gas Co. Salt Lake Operations Center Overview

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Figure 2 – Monitoring Well/Piezometer Locations (New Installation Locations in Red)

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Attachment A – Proposal to implement the Updated Operations and Maintenance Manual – Salt
Lake Operational Center North, Salt Lake City, Utah

AECOM
756 E Winchester, Suite 400
Salt Lake City UT, 84107
w ww.aecom.com
801 904 4000 t el
August 9, 2024

Mr. Adam Plonsky
Enbridge Gas Utah
1140 W 200 S
P.O. Box 45360
Salt Lake City, UT 84145-0360

Re: Proposal to I mplement the Updated Operations and Maintenance Manual – Salt Lake
Operational Center North, Salt Lake City, Utah

Mr. Plonsky:

AECOM Technical Services, Inc. (AECOM) is pleased to offer this proposal to Enbridge Gas Utah
(EGU) for the Salt Lake Operational Center North project to implement the updated Operations and
Maintenance Manual (OMM) based on approval by the Utah Department of Environmental Quality
(UDEQ). This proposal is being prepared in response to your recent verbal request.

AECOM ADDITIONAL SCOPE OF WORK

Annual Slurry Wall and Cap Inspection
AECOM will inspect the slurry wall and cap during the annual groundwater sampling event according
to the OMM. Inspection forms will be completed (Slurry Wall Inspection Form and Surface Cap
Inspection Form) and included in the annual report .

Public Right-of-Way Permit
A public right-of -way permit will be obtained from Salt Lake City by the driller prior to starting the
work. AECOM will produce a traffic control plan to be used in the permit.

Health and Safety
The existing site health and safety plan will be reviewed and updated as needed for the work. A new
plan will not be developed.

Utility Clearance
Potential underground utilities will be assessed at each location through Blue Stakes of Utah and a
private utility contractor, and each well and piezometer location will be daylighted to approximate 5
feet bgs. Enbridge Gas Utah will mark known private utilities on their property. Daylighting may
include air knife, hydrovac, or hand auger with the appropriate barrel diameter.

Piezometer / Well Installation and Development
AECOM will install three (3) shallow 2-inch monitoring wells (MW-101, MW-102, and MW-103) and
three (3) 1-inch piezometers (PZ-1, PZ -2, and PZ-3) to an approximate depth of 15-20 feet below
ground surface (bgs), as shown on Figure 1. These will generally be located within Salt Lake City
Corporation rights -of -way and streets. Wells will be installed using direct -push technologies to
minimize soil disposal costs. Wells and piezometers will be installed using 3.75-inch direct -push rods.
The t otal depth of wells will be based on the depth to the confining layer at each location as
interpreted by the field geologist, but is not anticipated to be deeper than approximately 20 feet . Soil
cores will be field screened with a photo -ionization detector (PID). Wells will be completed to the
below specifications.

2-Inch Monitoring Well Specifications
• 2” PVC blank from 0-5 feet bgs.
• 2” PVC pre-packed screen (0.020 slots) from 5-15 feet bgs.
• Screw on or slip on bottom cap (no cement).
• Pressure top cap.
• 10-20 silica sand, as needed, from 4-15 feet bgs.
• Hydrated bentonite with potable water, from 1-4 feet bgs.
• 12-inch flush mount completion installed in 0.5’ X 3’ X 3’ concrete pad.

1-Inch Piezometer Specifications
• 1” PVC blank from 0-5 feet bgs.
• 1” PVC pre-packed screen (0.020 slots) from 5-15 feet bgs.
• Screw on or slip on bottom cap (no cement).
• Pressure top cap.
• 10-20 silica sand, as needed, from 4-15 feet bgs.
• Hydrated bentonite with potable water, from 1-4 feet bgs.
• 12-inch flush mount completion installed in 0.5’ X 3’ X 3’ concrete pad.

Completion Replacement
Surface completions will be replaced at six (6) locations (SWP-3, SWP -4, SWP -5, SWP -6, M-10 and
MW-12) to the below general specifications .

Completion Specifications
• Saw cut asphalt (3’ X 3’)
• Excavate around existing casing (1-2’ bgs)
• Cut top of casing off such that new lid will not contact cap or lid.
• Add bentonite and hydrate with potable water, as needed to replace bentonite removed.
• Replace pressure cap to ensure watertight seal.
• 12-inch flush mount completion installed in 0.5’ X 3’ X 3’ concrete pad.

Well Development
Develop six (6) wells and nine (9) piezometers associated with the site (MW-101, MW-102, MW-103,
SW-1, M-10, MW-12, PZ-1, PZ -2, PZ -3, SWP-1, SWP-2, SWP-3, SWP-4, SWP -5, and SWP -6). See
Figure 1. Wells and piezometers will be redeveloped using a submersible pump, bailer, or foot valve
pump . Development will continue until the water is visually clear or until a maximum of five wet boring
volumes of water is removed. Purge water from well development will be containerized, profiled, and
disposed of by Enbridge Gas Utah. A well development form will be completed for each location.

Well and Piezometer Survey
The top of casing and ground surface for each well (MW-101, MW-102, MW-103, SW-1, M -10,
MW-12, PZ-1, PZ-2, PZ-3, SWP -1, SWP -2, SWP -3, SWP -4, SWP -5, and SWP -6) will be
topographically surveyed by a Utah Licensed surveyor. The top of casing for each well will be
surveyed to within +0.01 feet using the National Geodetic Vertical Datum of 1988. The ground surface
for each well will be surveyed by a Utah licensed surveyor to within +0.1 feet using the National
Geodetic Vertical Datum of 1988. Horizontal coordinates will be determined to within +0.1 feet and
reported in Utah State Plane coordinates, NAD 83, US survey feet.

Groundwater Level Measurements
During the annual groundwater monitoring event, depth to groundwater will be measured at 6 wells
and 9 piezometers. Locations are listed in Table 1 below. Depth to groundwater measurements will

be used to calculate groundwater elevations and potentiometric surface maps will be generated for
the areas upgradient of the site, inside the slurry wall, and downgradient of the site.

Table 1
Groundwater Level Locations

Well ID Status Well Type
MW-101 Proposed New Well Source Area Well
(Sample and Water Level) MW-102
SW-1 Existing Well
MW-103 Proposed New Well Sentry Well
(Sample and Water Level) MW-12 Existing Well M-10
PZ-1
Proposed New Piezometer
Piezometer
(Water Level)
PZ-2
PZ-3
SWP -1
Existing Wall Piezometer
SWP -2
SWP -3
SWP -4
SWP -5
SWP -6

• The water level in all wells will be measured before any wells are purged and sampled .
• Depth to groundwater will be measured with an electronic dual interface probe or water level
meter, and the measurement will be recorded on the Static Water Level Log form .
• The water level indicator will be lowered into the well until a change in conductivity indicates that
groundwater has been encountered.
• The depth to water will be measured from the reference point at the top of the well casing .
• All measurements will be made to +0.01 foot. Field measurements will be used in conjunction
with the surveyed elevations of the top of each well or piezometer casing to determine the
groundwater surface elevation (above mean sea level).

Groundwater Sampling
Groundwater Sampling will be collected from monitoring wells listed in Table 2 below using low stress
techniques and a peristaltic pump.
Table 2
Monitoring Well Location

Well ID Status Well Type
MW-101 Proposed New Well Source Area Well MW-102
SW-1 Existing Well
MW-103 Proposed New Well
Sentry Well MW-12 Existing Well M-10

• Each monitoring well will be purged at a rate less than or equal to 0.3 liters per minute until field -
measured parameters stabilize before samples are collected. VOC samples will be collected at a
rate less than or equal to 0.1 liters per minute.
•At a minimum, the parameters of potential of hydrogen (pH), conductivity, oxidation reductio n
p otential (ORP), and temperature will be monitored during purging using portable calibrated
meters. Parameters will be measured approximately every three minutes during purging.
•At least two consecutive field measurements made three minutes apart shall fall within the ranges
stated below before well purging will be considered complete:
o p H = ±0.2 units,
o temperature = ±1 degree Centigrade (ºC),
o conductivity = ±10 percent, and
o ORP = ±10 percent.
•If parameters don’t stabilize after five well volumes have been removed, purging will b e
d iscontinued, and the samples will be collected.
•Groundwater samples will be submitted for volatile organic compounds (VOCs) by 8260B and for
semi-organic compounds (SVOCs) by 8270C.
•Groundwater samples will be shipped to Pace National Laboratory located in Mt. Juliet,
Tennessee, a Utah Certified Laboratory.
•Quality Assurance/Quality Control (QA/QC) samples will include one field duplicate, and a trip
blank collected for each cooler containing samples for VOC analysis. Data validation will not b e
p erformed for routine monitoring .
•With the exception of low-yield monitoring wells, groundwater samples will be collected
immediately after field -measured parameters have stabilized.
•Groundwater samples will be collected in containers supplied by the analytical laboratory.
•New or dedicated pump tubing will be used at each monitoring well.
•Samples will be stored in an ice-chilled cooler.
•Depth to groundwater will be measured every three minutes during purging and drawdown will be
limited to one foot.
•The purg ing rate will be reduced if drawdown is greater than one foot. If drawdown cannot b e
limited to one foot, then the well will be purged dry and allowed to recover to 75 percent prior to
sample collection.
•A groundwater sampling form will be completed at each sampling location at the time of sampling.
Investigation Derived Waste
Investigation-Deriv ed Waste (IDW) will c onsist of water us ed to decontaminate sampling equi pment,
purge water from m onit oring well s ampling, and soil cuttings from well installation. IDW will be
c ontainerized by AECOM and profiled and disposed of by Enbridge Gas Utah. Other wastes s uch as
used t u bing, P PE, packaging materials, and general refuse will be disp osed of in an on-site municipal
waste dumpster. No c osts hav e been inclu ded for dis posal of IDW.
Reporting
A n annual monitoring report will be prepared and s u bmitted t o UDEQ after c ompletion of t he well
installation, s lurry wall and c ap i ns pection, and groundwater monit oring ev ent. The report will
summarize field activities, discuss observ ed field anomalies, present analytical results, and include
c onclusions or rec ommen dations. The report will also include site figures, s ummary t a bles, and
c opies of f ield forms, and laboratory anal ytical reports. A dditionally, s urface and slurry wall inspection
forms will be included in the report . AECOM as sumes one round of comments by Enbridge Gas Utah
and eight (8) hours of time have been included to address the comments.
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PZ-2 PZ-1
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Figure 1
Proposed Sampling
Wells and Piezometers
Dominion Energy
Note: Red Symbol Locations are Proposed
Historical Locations from Site Investigation and
Proposed Remedial Action Plan
August 9,1999 (Dames & Moore 1998 b)
Approximate Location of Slurry Wall
Utah Gas and Coke Company Site
Potential area with CGR and groundwater impacts (Kleinfleder, 2020)
Piezometers (water level only)
Monitoring well (water level and sample collection)
Imagery: Nearmap 2023
0 240
1 INCH = 120 FEET
Project Area