HomeMy WebLinkAboutDERR-2024-012267
Summary Report of January 2024
PlumeStop® Injections in Groundwater
VCP-C049
Cottonwood Heights, Utah
Salt Lake County, Utah
Prepared for:
Linde Gas & Equipment Inc.
(formerly Praxair Distribution, Inc.)
6880 South 2300 East
Cottonwood Heights, Utah
Prepared by:
Stantec Consulting Services Inc.
2890 East Cottonwood Parkway, Suite 300
Salt Lake City, UT 84121
Project No.: 203708160
May 16, 2024
Remedial Task associated with Implementation
of October 2023 Proposed Remedial Action Plan
for TCE in Groundwater
Sign-off Sheet and Signatures of Environmental Professionals
Project No.: 203708160/05-delivs/delivs/2024/SumRept PlumeStop Injects 1
This document was prepared by Stantec Consulting Services, Inc. (“Stantec”) for Linde Gas &
Equipment Inc. (the “Client”). The conclusions in this Report are Stantec’s professional opinion, as of
the time of the Report, and concerning the scope described in the Report. The opinions in the
document are based on conditions and information existing at the time the scope of work was
conducted and do not take into account any subsequent changes. The Report relates solely to the
specific project for which Stantec was retained and the stated purpose for which the Report was
prepared. The Report is not to be used or relied on for any variation or extension of the project, or for
any other project or purpose, and any unauthorized use or reliance is at the recipient’s own risk.
Stantec has assumed all information received from the Client and third parties in the preparation of
the Report to be correct. While Stantec has exercised a customary level of judgment or due
diligence in the use of such information, Stantec assumes no responsibility for the consequences of
any error or omission contained therein.
This Report is intended solely for use by the Client in accordance with Stantec’s contract with the
Client. While the Report may be provided by the Client to applicable authorities having jurisdiction
and to other third parties in connection with the project, Stantec disclaims any legal duty based
upon warranty, reliance or any other theory to any third party, and will not be liable to such third
party for any damages or losses of any kind that may result.
Prepared by:
John G. Russell, III, CPG
Utah PG #5216074-2250
Sr. Hydrogeologist, Environmental Risk Manager
Reviewed by:
Cody Fauth
Geology
SUMMARY REPORT OF JANUARY 2024 PLUMESTOP® INJECTIONS IN GROUNDWATER
Project No.: 203708160/05-delivs/delivs/2024/SumRept PlumeStop Injects ii
Table of Contents
1.0 EXECUTIVE SUMMARY .................................................................................................1.1
1.1 INTRODUCTION ........................................................................................................... 1.1
1.2 BACKGROUND............................................................................................................ 1.1
2.0 JANUARY 2024 GROUNDWATER TREATMENT PROGRAM ..........................................2.1
2.1 PLUMESTOP CARBON PRODUCT ............................................................................... 2.1
2.2 PLUMESTOP INJECTION PROGRAM ........................................................................... 2.1
2.2.1 Preparation in Advance of Injection Program ....................................... 2.1
2.2.2 January 2024 Microbial Injection Locations and Process ...................... 2.2
2.2.3 Monitoring for Satisfactory Distribution of Injected PlumeStop ............. 2.5
3.0 REMEDIAL PROGRESS MONITORING PROGRAM .......................................................3.1
3.1 POST-REMEDIAL, GROUNDWATER QUALITY MONITORING PROGRAM ................... 3.1
3.1.1 Monitoring Schedule ................................................................................ 3.1
3.2 ONGOING SEMI-ANNUAL, INDOOR AIR AND SUB-SLAB DEPRESSURIZATION
SYSTEM (SSDS) MONITORING PROGRAM .................................................................. 3.2
LIST OF FIGURES
IN TEXT:
Figures A and B REGENESIS Summary Report Figures
FOLLOWING TEXT:
Figure 1 Monitoring Well Location Map
Figure 2 Groundwater Monitoring Wells and Abandoned Groundwater
Sampling Borings
SUMMARY REPORT OF JANUARY 2024 PLUMESTOP® INJECTIONS IN GROUNDWATER
Project No.: 203708160/05-delivs/delivs/2024/SumRept PlumeStop Injects iii
Abbreviations
ft Feet
LGE Linde Gas & Equipment Inc.
MCL Maximum Contaminant Level
MDL Method Detection Limit
µg/m3 Micrograms per cubic meter
µg/kg Micrograms per kilogram (aka, parts per billion-ppb; soil)
µg/L Micrograms per liter (aka, parts per billion-ppb; groundwater)
mg/kg milligrams per kilogram (aka, parts per million-ppm)
PRB Permeable Reactive Barrier
PCE Tetrachloroethylene (aka, perchloroethylene or perc)
PVC Polyvinyl Chloride
PDI Praxair Distribution, Inc.
PRAP Proposed Remedial Action Plan
QA/QC Quality Assurance/Quality Control
RL Reporting Limit
RSL Risk-Based Screening Level
SSDS Subsurface Soil Gas Depressurization System
TCE Trichloroethylene
UDEQ
(UDAQ/UDERR)
Utah Department of Environmental Quality
(Division of Air Quality/Division of Environmental Response and Remediation)
US EPA United States Environmental Protection Agency
VISL Vapor Intrusion Screening Level
VOC Volatile Organic Compound
VCP Voluntary Cleanup Program
SUMMARY REPORT OF JANUARY 2024 PLUMESTOP® INJECTIONS IN GROUNDWATER
EXECUTIVE SUMMARY
May 16, 2024
Project No.: 203708160/05-delivs/delivs/2024/SumRept PlumeStop Injects 1.1
1.0 EXECUTIVE SUMMARY
1.1 INTRODUCTION
On behalf of Linde Gas & Equipment Inc. (LGE, formerly Praxair Distribution, Inc. [PDI]), Stantec
Consulting Services Inc. (Stantec) has prepared this report to document groundwater treatment
activities conducted during January 2024 at and near the LGE facility located at 6880 South
2300 East in Salt Lake City, Utah. Reference Figures 1 and 2 for regional and site-specific location
maps. The remedial program was administered in accordance with the protocol proposed
within LGE’s October 2023 Proposed Remedial Action Plan (PRAP), which was approved by the
Utah Department of Environmental Quality, Voluntary Cleanup Program (UDEQ, VCP) in early
January 2024.
REGENESIS® Remediation Services’ (REGENESIS) injected proprietary permeable reactive barriers
(PRBs) including PlumeStop® Liquid Activated CarbonTM (collectively, “PlumeStop”) into
trichloroethylene- (TCE) impacted groundwater located beneath localized portions of the LGE
property and downgradient (northwest/west) of the LGE property. The injected carbon product
is intended to capture TCE within the aquifer for supplemental natural reduction in TCE
concentrations in groundwater located downgradient of the carbon injection-points. In turn, it is
anticipated that the reduction in TCE concentrations in groundwater will result in a reduction of
gaseous-phase TCE in the unsaturated vadose zone, thereby reducing or eliminating the
potential for intrusion of gaseous-phase TCE into subsurface soil gas and overlying buildings.
This report provides a summary of the field activities and resources associated with the January
2024 injection program and future-planned environment monitoring to investigate the progress
and effectiveness of the injections in pursuit of VCP site closure. As detailed in the PRAP, the next
report that will be submitted to the UDEQ will summarize the first quarter of routine monthly
groundwater quality monitoring, sampling, and analytical laboratory result reports following the
January 2024 injections. Thereafter, three sequential quarterly (July, October, and January)
summary reports will be submitted to the UDEQ, reporting the results of quarterly
monitoring/sampling of groundwater for a timeframe of one year subsequent to the January
2024 injections.
1.2 BACKGROUND
Of the 15 groundwater monitoring wells that are part of the VCP site, TCE has been detected in
groundwater at concentrations above either the Method Detection Limit (MDL) or Reporting
Limit (RL) in wells MW-2, MW-3, MW-6, HP-2, HP-3, HP-5, and HP-9 (reference Figure 2). The last
sampling date during which a TCE concentration in any of the monitoring wells was at or
exceeded the UDEQ Cleanup Level of 5 micrograms per liter (aka, parts per billion-ppb) was at
well MW-2 in October 2014 (5.0 ppb in both the MW-2 normal and duplicate samples,
respectively). TCE concentrations in groundwater have declined in all monitoring wells since
SUMMARY REPORT OF JANUARY 2024 PLUMESTOP® INJECTIONS IN GROUNDWATER
EXECUTIVE SUMMARY
May 16, 2024
Project No.: 203708160/05-delivs/delivs/2024/SumRept PlumeStop Injects 1.2
monitoring began in 2005, with the highest concentrations detected during the most recent
sampling event of April 2023 being 1.5 ppb at well HP-9 and 1.1 ppb at HP-5.
The US EPA Vapor Intrusion Screening Level (VISL) “target groundwater concentration” for TCE in
groundwater with risk for possible vapor intrusion into overlying buildings is 1.19 ppb. It is
anticipated that reducing and/or eliminating TCE concentrations in groundwater (e.g., TCE
liquid-phase mass) should result in a corollary reduction in TCE concentrations in overlying
subsurface soil gas (TCE gaseous-phase mass). In turn, the reduction in TCE mass within
subsurface soil gas should reduce the potential for subsequent migration of gaseous-phase TCE
into overlying buildings.
REGENESIS’ PlumeStop product was injected into the upper 10 feet of the aquifer in injection-
points located at and downgradient of the LGE property. As groundwater flows/attenuates
naturally through the PlumeStop treatment/injection areas, the injected carbon will intercept
and capture TCE in groundwater, thereby reducing the total mass of TCE attenuating farther
downgradient (toward the northwest/west) from the PRB injection areas. With time, the injected
PlumeStop will reduce TCE concentrations in groundwater located in the vicinity and
downgradient of injection-points to below the US EPA VISL groundwater target concentration
deemed protective of overlying indoor air quality. This report presents a summary of the January
2024 injections of PlumeStop at the project site.
SUMMARY REPORT OF JANUARY 2024 PLUMESTOP® INJECTIONS IN GROUNDWATER
JANUARY 2024 GROUNDWATER TREATMENT PROGRAM
May 16, 2024
Project No.: 203708160/05-delivs/delivs/2024/SumRept PlumeStop Injects 2.1
2.0 JANUARY 2024 GROUNDWATER TREATMENT PROGRAM
2.1 PLUMESTOP CARBON PRODUCT
REGENESIS’ PlumeStop consists of carbon particles milled to 1 to 2 micrometers in size. The
particle size and the proprietary surface chemistry allow the carbon particles to be suspended
as a colloid in the subsurface. The material was formulated to not only flow as a colloidal liquid,
but also allow the PlumeStop carbon to attach to soil particles within the aquifer. The physical
appearance of PlumeStop is similar to that of black to dark-gray ink. PlumeStop is designed to
work quickly by allowing sorption of contaminants from the dissolved liquid-phase to the carbon,
resulting in rapid reductions of contaminant concentrations within groundwater.
2.2 PLUMESTOP INJECTION PROGRAM
2.2.1 Preparation in Advance of Injection Program
In advance of the project, Stantec subcontracted GPRS, Inc., a nationally recognized Ground
Penetrating Radar (GPR) consulting firm, to conduct a local GPR buried utility-locate throughout
the proposed injection areas. Stantec also coordinated a formal Blue Stakes of Utah Utility
Locators’ utility-locate. Likewise, Stantec communicated with on-site LGE staff regarding
potential buried utilities at the LGE property. No buried utilities were identified within the
proposed injection areas and none were encountered during the project.
REGENESIS’ subcontracted drilling firm, Interphase Drilling, and all REGENESIS injection
equipment, products, and field staff, mobilized to the LGE site during January 2 and 3, 2024.
Stantec helped coordinate mobilization efforts between all parties and on-site LGE
representatives. Before initiating field work activities on January 4th, Stantec and LGE
orchestrated an on-site health and safety ‘Kick-off Meeting.’
Site access, proposed project details, and health and safety related concerns were discussed
with on-site LGE, REGENESIS, Interphase Drill, and Stantec representatives, with all field activities
coordinated through LGE’s on-site Operations Manager, Mr. Dusty Wadsworth. Prior to starting
the project, a jobsite safety inspection was completed and documented, with introductory
communications related to on-site, potential hazards, directions to the closest hospital, and
emergency contacts discussed and documented. Additional activities conducted prior to and
during field work included use of a LGE snow blower to help clear land surfaces of thick snow
cover for drill rig access and provide a safe working environment. No health and safety-related
issues were encountered during implementation and completion of field activities.
SUMMARY REPORT OF JANUARY 2024 PLUMESTOP® INJECTIONS IN GROUNDWATER
JANUARY 2024 GROUNDWATER TREATMENT PROGRAM
May 16, 2024
Project No.: 203708160/05-delivs/delivs/2024/SumRept PlumeStop Injects 2.2
2.2.2 January 2024 Microbial Injection Locations and Process
During January 4 through 19, 2024, Stantec geologist, Mr. Cody Fauth, observed REGENESIS and
Interphase Drilling implement PlumeStop injections at the LGE and Residence B properties.
Injection-points are identified in the below aerial image (Figure A) from REGENESES’. Each
injection borehole was advanced by the direct-push boring process, whereby product was then
pressure-injected, utilizing downhole, steel rods, from the ground surface into the upper 10 feet
of the aquifer (approximately 9 to 19 feet beneath the Residence B property and 14 to 24 feet
below the LGE property).
FIGURE A. Injection-point map
LGE
Property
SUMMARY REPORT OF JANUARY 2024 PLUMESTOP® INJECTIONS IN GROUNDWATER
JANUARY 2024 GROUNDWATER TREATMENT PROGRAM
May 16, 2024
Project No.: 203708160/05-delivs/delivs/2024/SumRept PlumeStop Injects 2.3
On-site, potable water sources were used for slurry-mixing REGENESIS products within a
REGENESIS portable trailer located near the injection-points. As depicted below, the portable
trailer was equipped with two interior 350-gallon mixing tanks, pumps, and delivery systems
manifolded for direct connection to each of the injection-points. Mixed REGENESIS product was
pressure-slurried into each injection-point assembly for injection into the subsurface.
FIGURE B. General schematic of portable trailer
In summary, the PlumeStop product was injected at the following volumes and rates, which
differed between the two properties as explained in more detail below:
• LGE Property: A total of 15,400 gallons of PlumeStop at an average injection rate
approximating 4.44 gallons per minute (gpm) and an average injection pressure of 25
pounds per square inch (psi).
• Residence B: A total of 1,357 gallons of PlumeStop at an average injection rate
approximating 2.34 gpm and an average injection pressure of 39 psi.
Before starting field work, REGENESIS advised that there is usually a rise in the local water table
when injecting PlumeStop product into the upper 10 feet of an aquifer. The rise in elevation of
the water table varies between sites and depends on site-specific, subsurface aquifer lithologic
and hydrogeologic characteristics.
The water table beneath the western portion of the LGE property was measured in monitoring
wells at a subsurface depth of approximately 14 feet below grade, as of January 2024. Since
there were no significant concerns for affecting a rise in the water table beneath western
portions of the LGE property, REGENESIS utilized an average PlumeStop product injection rate
approximating 4.44 gpm and an injection pressure of 25 psi, similar to other REGENESIS product
injection sites. No issues were encountered with the injection program.
SUMMARY REPORT OF JANUARY 2024 PLUMESTOP® INJECTIONS IN GROUNDWATER
JANUARY 2024 GROUNDWATER TREATMENT PROGRAM
May 16, 2024
Project No.: 203708160/05-delivs/delivs/2024/SumRept PlumeStop Injects 2.4
Historically, the depth to the water table beneath and in close proximity to Residence B was
approximated between 10 to 11 feet below natural grade. The elevation of the Residence B
basement floor is approximately nine feet below natural grade (i.e., one to two feet above the
historical water table).
In consideration of the shallow water table beneath the Residence B property, and the potential
for possible water intrusion risk to the basement, Stantec and REGENESIS observed the installation
of two shallow, 1.5-inch diameter groundwater monitoring piezometers located adjacent to the
eastern-most side of the Residence B home, namely PZ-1 and PZ-2 (reference Figure A). Stantec
monitored water levels in the wells prior to and during the product injection program,
investigating for possible rise/fluctuations in the water table as extrapolated by the water levels
within the wells. The drilling firm was prepared to reduce the volume and rate of injection of
product, if deemed necessary to prevent potential risk of water intrusion.
The two piezometers, each of which was constructed of 15 feet of 1.5-inch diameter, 0.01-
slotted, Schedule 40 PVC well screen, were drilled and installed as close as practicable to (within
several feet of) the side of the home. Each wellhead has an approximate 12-inch stick-up above
the ground surface and is equipped with a dedicated PVC slip-on cap. Water levels in the
monitoring wells were monitored by means of a hand-held, electronic water level indicator
capable of measuring to an approximate 0.01-foot accuracy. The static water levels in PZ-1,
PZ-2, and nearby monitoring well HP-5 approximated 10.5 feet below grade, before the injection
program began.
The initial injection-point in the residence backyard was drilled approximately 6 feet west of
injection-point IP-45 identified on Figure A. The initial injection-point was used as a preliminary
pilot-test borehole, whereby REGENESIS and Stantec monitored water levels in monitoring wells
PZ-1, PZ-2, and HP-5, while the drilling firm injected the PlumeStop/water slurried product at the
same injection rate and pressure as implemented while injecting at the LGE property.
Immediately upon initiating injection of product within the pilot-test boring, Stantec observed
rises in water levels in nearby monitoring wells PZ-1 and HP-5 to an approximate height of
between 9- to 9.5-feet below grade, and halted the injection process. The near-instantaneous
rise in the localized water table indicated a potential risk to the basement if the injection
program continued at the same rate.
Another pilot-test injection-point was drilled in the southeastern corner of the residence
backyard in the vicinity of injection-point P-74 on Figure A, to investigate the impacts of
injecting PlumeStop/water product at similar rates and pressures in an injection-point located as
far away from the house as practicable. Injecting at an approximately 4 gpm and a pressure of
25 psi (as implemented at the LGE property) resulted in similar rises in water levels measured in
monitoring wells PZ-1, PZ-2, and HP-5 to approximate depth of 9 to 9.5 feet below grade. Stantec
stopped the injection program to discuss how the driller might adjust the injection process.
SUMMARY REPORT OF JANUARY 2024 PLUMESTOP® INJECTIONS IN GROUNDWATER
JANUARY 2024 GROUNDWATER TREATMENT PROGRAM
May 16, 2024
Project No.: 203708160/05-delivs/delivs/2024/SumRept PlumeStop Injects 2.5
REGENESIS recommended that we inject a more concentrated PlumeStop product with a
smaller volume of intermixed water and at a reduced injection rate at injection-point IP-45, as
they had observed success with this approach at other similar sites. REGENESIS claimed that use
of a more concentrated PlumeStop product would allow injection of a smaller volume of
product at a reduced injection rate, which in turn might affect smaller rises in the local water in
the vicinity of the injection-points. The concentrated product would still be injected within the
upper 10 feet of the aquifer and would provide more concentrated treatment of local water, as
groundwater migrated through the permeable reactive barrier. Likewise, injections of the
concentrated PlumeStop product only required one north-south oriented line of injection-points
at the residence, as opposed to the two herringbone-oriented, injection rows implemented at
the LGE property.
Sequentially, injection rates and pressures were adjusted at IP-45, until an injection of
concentrated PlumeStop product at a rate of 2.34 gpm and injection pressure of 39 psi resulted
in the water levels in monitoring wells PZ-1 and HP-5 stabilizing at a subsurface depth
approximating 9.5 feet below grade. Thereafter, the amended injection program was
implemented, progressing from IP-45 toward the south and the final injection-point IP-74 (see
Figure A). While monitoring water levels in the PZ-1, PZ-2, and HP-5 continually throughout the
duration of the injection program, Stantec did not observe water levels in monitoring wells rising
to a subsurface elevation that might intersect the basement floor elevation.
2.2.3 Monitoring for Satisfactory Distribution of Injected PlumeStop
Stantec and REGENESIS field staff implemented a subsurface soil and groundwater monitoring
program located in close proximity to injection-points and designed to investigate local impacts
to the subsurface during and following localized PlumeStop injections. The intent of the
subsurface investigative activities was to verify that the injected PlumeStop product was
emplaced satisfactorily within the upper 10 feet of the aquifer along the permeable reactive
barriers.
During injections, Stantec monitored the color of water within select groundwater monitoring
wells located in close proximity to injection-points, investigating for visible discoloration
(black/gray darkening, etc.) of groundwater attributable to injection of PlumeStop product, and
observed discoloration of groundwater indicating the presence of PlumeStop within monitoring
wells HP-1, HP-2, HP-3, HP-5, HP-8, MW-2 and MW-3. Following local injections of product in the
vicinity of monitoring wells MW-2 and HP-5, REGENESIS collected samples of groundwater from
the two wells and quantified PlumeStop product at 400 milligrams per liter (aka, parts per million-
ppm) in well MW-2 at the LGE property and 50,000 ppm in well HP-5 at the Residence B property.
Stantec and REGENESIS also observed the drilling and soil sampling of three soil test borings
(CC-1, CC-2, and CC-3 on Figure A), located a few to several lateral feet from injection-points,
to investigate to what degree subsurface soils comprising the upper 10 to 15 of the aquifer might
be impacted by the adjacent product injections. Subsurface soil samples were collected
SUMMARY REPORT OF JANUARY 2024 PLUMESTOP® INJECTIONS IN GROUNDWATER
JANUARY 2024 GROUNDWATER TREATMENT PROGRAM
May 16, 2024
Project No.: 203708160/05-delivs/delivs/2024/SumRept PlumeStop Injects 2.6
continuously in each of the three soil test borings for visual inspection of discoloration and
presence of the PlumeStop product.
At each of the three direct-push, soil test borings, soil samples were collected continuously within
5-ft. long, clear acrylic sampling sleeves for visual inspection. Stantec and REGENESIS field staff
inspected each soil sample, looking for visible signs of discoloration, indicating PlumeStop
product presence within at least the upper 10 feet of the aquifer at each respective location.
The field data at borings CC-1, CC-2, and CC-3 indicated successful product injection and
distribution in-between and radially-outward from respective injection-points. Following
monitoring of the CC-1, CC-2, and CC-3 soil test borings, each boring was backfilled flush to
existing grade with hydrolyzed bentonite pellets.
SUMMARY REPORT OF JANUARY 2024 PLUMESTOP® INJECTIONS IN GROUNDWATER
PROPOSED PUBLIC NOTICE
May 16, 2024
Project No.: 203708160/05-delivs/delivs/2024/SumRept PlumeStop Injects 3.1
3.0 REMEDIAL PROGRESS MONITORING PROGRAM
The following report sections provide a summary of planned actions intended to monitor the
effectiveness and remedial progress, following the January 2024 PlumeStop injection activities.
LGE/Stantec’s PRAP should be referenced for more specific details regarding monitoring
procedures, protocol, and QA/QC measures that will be implemented as part of the proposed
activities.
3.1 POST-REMEDIAL, GROUNDWATER QUALITY MONITORING PROGRAM
To monitor the effectiveness and anticipated reduction in TCE concentrations in groundwater
following PlumeStop injections, static groundwater levels will be measured within, and
groundwater samples will be collected from, the following monitoring wells/piezometers on the
schedule that is proposed below.
- PZ-1, PZ-2, MW-2, MW-3, MW-6, MW-7, HP-1, HP-2, HP-3, HP-5, HP-8, and HP-9.
Remedial objectives for groundwater quality include satisfying TCE and other VOCs’ UDEQ
Screening Levels (MCLs and Groundwater Protection Standards), as well as achieving the US EPA
VISL “target groundwater concentration” for TCE of 1.19 ppb in groundwater that poses a
potential risk for vapor intrusion into overlying buildings. Future groundwater monitoring will be
used as a barometer to indicate the degree of success of the PlumeStop injections into the
uppermost aquifer at the project site. Future groundwater sampling schedules may be
amended and/or discontinued, depending on future media sampling, analytical results, and
corollary discussions between the UDEQ and LGE.
3.1.1 Monitoring Schedule
Static water levels will be measured and groundwater samples be collected for general water
quality parameters and VOC laboratory analysis by Method EPA 8260D/5030A on a monthly
basis for three consecutive months, following the PlumeStop injections. The field activities,
qualitative observations, and analytical laboratory results associated with the first three monthly
monitoring/sampling events (February, March, and April 2024) will be detailed within a
forthcoming First Quarter 2024 Groundwater Monitoring Summary Report.
Thereafter, the monitoring program will be reduced to quarterly sampling for three consecutive
quarters, the total duration of which will provide one (1) complete year (four seasons) of
groundwater quality and water level monitoring following the January 2024 PlumeStop
injections. Subsequent quarterly sampling events are scheduled tentatively for July and October
2024 and January 2025. LGE/Stantec will prepare a comprehensive “Annual Summary Report”
for submittal to the UDEQ, after receipt of the January 2025 laboratory report.
SUMMARY REPORT OF JANUARY 2024 PLUMESTOP® INJECTIONS IN GROUNDWATER
PROPOSED PUBLIC NOTICE
May 16, 2024
Project No.: 203708160/05-delivs/delivs/2024/SumRept PlumeStop Injects 3.2
Following the first year of post-remedial action monitoring, similar groundwater monitoring will
continue on a semi-annual (twice per year) schedule, as has been practiced historically, until
conditions indicate groundwater quality satisfies UDEQ regulatory requisites and/or as deemed
acceptable to both LGE and the UDEQ.
3.2 ONGOING SEMI-ANNUAL, INDOOR AIR AND SUB-SLAB DEPRESSURIZATION SYSTEM
(SSDS) MONITORING PROGRAM
Routine indoor air (TCE) and SSDS off-gas emission (VOCs) sampling at Residences A and B (see
Figure 1) will continue on an ongoing, semi-annual (every six months) basis. The next semi-annual
sampling events are scheduled tentatively for April (results pending presently) and October
2024.
Samples will be collected while the respective home HVAC systems are operating. As detailed in
LGE’s PRAP, it is anticipated that routine indoor air quality and SSDS off-gas emission monitoring,
in conjunction with groundwater analytical data, will be used to help gauge how long to
continue operating each SSDS.
Following receipt of each semi-annual laboratory result report, Stantec will prepare a SSDS
Mitigation System Off-Gas Emission Sampling Summary Report for submittal to the UDAQ (with
copies to the UDEQ) in accordance with UDAQ Rule R307-401-15. Air Strippers and Soil Venting
Projects. Stantec will also submit to the UDEQ a brief summary letter-report that documents the
indoor air sampling results. Both reports will include copies of laboratory result reports.
As detailed in LGE’s PRAP, starting in the Spring of 2025, the semi-annual SSDS and indoor air
quality monitoring program will also include sampling and analysis of existing sub-slab soil gas
monitoring probes located within the basements of both residences. It is anticipated that
sampling and analysis of sub-slab soil gas, in conjunction with sampling of indoor air and
groundwater quality, will verify the effect of the PlumeStop injections.
SUMMARY REPORT OF JANUARY 2024 PLUMESTOP® INJECTIONS IN GROUNDWATER
FIGURES
May 16, 2024
Project No.: 203708160/05-delivs/delivs/2024/SumRept PlumeStop Injects
Figure 1 Monitoring Well Location Map
Design by: TH Reviewed by: JR & RP Scale: One Inch approxs. 100 feet
Date: 7/11/2023
FIGURE 1. Ground Water Monitoring Well Location Map
Linde Gas & Equipment Inc.
6880 South 2300 East Street -Salt Lake City, Utah
LEGEND
0 100 200
Ground Water
Monitoring Well
Scale (feet)
MW -5
MW -4MW-1
MW -2
MW -3
MW -6
MW -7MW-8
Residence B
Residence A
LGE Facility
MW -9
SUMMARY REPORT OF JANUARY 2024 PLUMESTOP® INJECTIONS IN
GROUNDWATER
FIGURES
May 16, 2024
Project No.: 203708160/05-delivs/delivs/2024/SumRept PlumeStop Injects
Figure 2 Groundwater Monitoring Wells and Abandoned
Groundwater Sampling Borings
Design by Reviewed by
Figure 2 - Groundwater Monitoring Wells and Abandoned Groundwater Sampling Borings
LEGEND
MW-2 /HP-1 Monitoring Well
HP-4 Abandoned Sampling Boring
Praxair Distribution, Inc.
6880 South 2300 East Street -Salt Lake City, Utah
Date RevisedJRRP 2/17/23
0 25
feet
50
Generalized Scale
MW -2
MW-1
MW -3
MW-7
MW-6
HP- 4
HP-5
HP-6
HP-7
HP-8
HP-1
HP-2
HP-3
HP- 10
HP- 9