HomeMy WebLinkAboutDERR-2025-005258Stantec Consulting Services Inc.
2890 East Cottonwood Parkway Suite 300
Salt Lake City UT 84121-7283
Tel: (801) 703-1927
Fax: (801) 266-1671
April 30, 2025
Mr. Joseph Katz
Utah Department of Environmental Quality
Division of Environmental Response and Remediation
195 North 1950 West
Box 144840
Salt Lake City, UT 84114-4840
Subject: Site Center’s Proposed Work Plan for Installation of One Sub-Slab Soil Gas
Monitoring Probe and
Supplemental Sampling of Indoor Air and Sub-Slab Soil Gas Monitoring Probes
Former Ft. Union Dry Cleaners (VCP Site #C079)
The Shops at Ft. Union
Midvale, Salt Lake County, Utah
Dear Mr. Katz:
Stantec Consulting Services Inc. (Stantec) has prepared this letter-report on behalf of Site Centers
to provide the Utah Department of Environmental Quality, Division of Environmental Response and
Remediation (DERR), Voluntary Cleanup Program (VCP) with a proposed plan for installing one
additional sub-slab soil gas monitoring probe and collecting sub-slab soil gas and indoor air
samples at The Shops at Ft. Union shopping mall in Midvale, Utah (the Property; VCP Site # C079).
The actions proposed herein were discussed on March 13, 2025 between representatives of the
DERR, Site Centers, Stantec, and Property co-owners (CDRE Properties and Woodbury
Corporation). Reference Figures 1, 2, and 3 for site- and suite-specific location maps.
This Proposed Work Plan (PWP) includes a proposed VCP project closure approach, as discussed
with the DERR, recently. Site Centers/Stantec’s December 2016 Amended Proposed Remedial
Action Plan (RAP) proposed sampling of 12 original sub-slab soil gas sampling probes and indoor
air samples within each of the eleven (11) tenant suites, as part of one final VCP site sampling
program. However, in consideration of the fact that we have observed significant decreases and
‘non-detections’ of contaminant constituents of potential concern in numerous tenant suites,
subsequent to 2016, this PWP proposes an amended closure sampling approach for sub-slab soil
gas and indoor air sampling/analysis that might serve to help close the VCP project. It is requested
that this PWP and actions proposed herein be considered as an amendment to the 2016 RAP.
A historical tenant within Suite #34 included a former dry cleaning facility that used Volatile
Organic Compound (VOC) tetrachloroethylene (PCE) as part of its operations. Historically, PCE
was detected in groundwater, subsurface soil gas, and indoor air. PCE and degradative by-
product trichloroethylene (TCE) were not quantified in groundwater when last sampled in
November 2020. PCE and by-products including TCE were detected within sub-slab soil gas and
localized indoor air during past VCP investigations; however, VOC concentrations in soil gas and
indoor air have decreased significantly over time. Only TCE was detected during the most recent
April 30, 2025
Mr. Joseph Katz
Page 2 of 2
V//203706007/05-delivs/2025/PWPSuppAirSampling
August 2024 sampling of Suite #38 in excess of its respective Commercial Indoor Air Vapor Intrusion
Screening Level (VISL).
The actions proposed herein are intended to investigate whether TCE within indoor air might be
associated with possible VOCs in subsurface soil gas or a possible interior source of VOCs. In
summary, the following tasks will be implemented in accordance with measures outlined in this
letter-report PWP:
1) Install a new sub-slab soil gas monitoring/sampling probe inside the hallway that is located
immediately west of/adjacent to Suite #34 (the former dry cleaning tenant suite) to
investigate subsurface soil gas conditions in an inferred downgradient (hydraulically)
direction in close proximity to the former dry cleaner operations.
2) Collect sub-slab soil gas samples from the newly-installed probe and the four existing sub-
slab soil gas monitoring probes (in Suites: #38 [It’s About Time], #46 [Sally Beauty]; and two
inside #50 [Office Max]. Soil gas samples will be analyzed for VOCs by Method TO-15.
3) Collect indoor air samples from the following tenant suites, since these were the only suites
within which VOCs were detected during recent sampling events: Suite #s 32, 34, 36, 38,
40, 46, and 50, as noted on attached Figure 3. Indoor air samples will be analyzed for PCE;
TCE; 1,2-DCA; cis/trans-DCE; and vinyl chloride by Method TO-15, Single Ion Monitoring
(SIM).
This PWP includes proposed sampling, analysis, and DERR reporting protocol to be used for any
future sampling deemed warranted at the site, in the event that supplemental sub-slab soil gas
and/or indoor air sampling/analysis is needed at the VCP site. If you have any questions or needs
for clarification, please contact me at (801) 703-1927.
Respectfully,
Stantec Consulting Services Inc.
________________________
John G. Russell, III, CPG
Utah Licensed PG #5216074-2250
Sr. Hydrogeologist, Environmental Risk Manager
CC: C. Reddersen/Site Centers
A. Usdan/CDRE and K. Johanos/Woodbury
R. Pratt and C. Hooton/Stantec
PROPOSED WORK PLAN FOR SUPPLEMENTAL AIR SAMPLING
1
1.0 PROPOSED SUB-SLAB SOIL GAS PROBE INSTALLATION PROTOCOL
Figure 4 identifies locations of four existing sub-slab soil gas monitoring probes, as well as the
generalized location of a proposed probe to be installed near the northwest corner of Suite #34.
In accordance with procedures detailed within Site Centers/Stantec’s July 2019 Amended
Proposed Work Plan for Sub-Slab Soil Gas and Indoor Air Sampling report, which was approved by
the DERR previously, Stantec will install one sub-slab soil gas monitoring probe within the eastern
drywall of the hallway that is located west of, and contiguous to, the former dry cleaner Suite #34.
The approximate four foot (4-ft.) wide hallway provides access from Suite #36 to a bathroom
located west of the southwest corner of Suite #34, as may be noted by review of the following
photograph:
View toward the North, generally
One (1) airtight, sub-slab soil gas monitoring probe will be constructed through the concrete floor
within the eastern wall of the hallway. In general, the following methodology will be employed to
construct and install the sub-slab, soil gas monitoring probe, in accordance with standardized
United States Environmental Protection Agency (US EPA) protocol:
1. A portable, rotary hammer drill will be used to advance an approximate 1-inch and 0.5-
inch diameter, masonry drill bits through the approximate 4-inch thick, concrete slab floor
of the building (as may be noted by review of the above cross-sectional figure entitled
'Vapor Pin set in concrete').
2. Upon drilling the hole through the concrete slab, a Vapor Pin Enterprises, Inc. 0.5-inch
diameter by 3.5-inch long, steel ‘vapor pin’ (aka, probe) will be installed within the 0.5-inch
diameter borehole. The top of the pin will be completed just above the concrete floor
surface (inside the wall) to provide easy access for sampling. Prior to installation, the outer
surface of the vapor pin will be covered with a thick layer of quick-setting, cement patch
that will ensure an air-tight seal of the annular space between the outer probe surface
and the concrete borehole. The cement patch material will be a non-volatile/non-
petroleum-based, grout material, such as the commercial-named product Quick-FixTM
produced by Custom Building Products (or similar).
Proposed sub-slab soil gas probe/vapor pin to be installed
inside the drywall in the general location behind the
cardboard box that is leaning temporarily against the wall (a
few feet south of the northern divider-wall between Suites
#36 and #34).
Vapor Pin set in concrete Typical Vapor Pin Vapor Pin Cap
The drywall will be cut to allow access for drilling/installing the
new soil gas probe through the 4-inch diameter, concrete
floor underlying the wall. Following installation of the air-tight,
soil gas monitoring probe, the cut in the drywall will be
covered by a flush-mounted cover-plate to provide future
access to the probe.
Suite
#50
Suite
#34
Suite
#36
PROPOSED WORK PLAN FOR SUPPLEMENTAL AIR SAMPLING
2
3. Then, a Vapor Pin Enterprises, Inc. 1-inch diameter, steel, female-threaded vapor pin cap
will be secured to the 1-inch diameter, steel, male-threaded adaptor section of the vapor
pin. As may be noted by review of the above photographs, the vapor pin will actually
have two different air-tight caps, including a small, 0.25-inch diameter, plastic cap that
covers the compression fitting top of the 0.5-inch diameter probe and a 1-inch diameter,
steel, screw-tight cover that also secures to the vapor pin and keeps the plastic cap atop
the air-tight vapor pin.
4. Following installation of the sub-slab soil gas monitoring probe, the hole in the drywall will
be covered by an aesthetic cover-plate that will be secured flush to the drywall so that it
may be removed easily to provide access to the soil gas probe, if and when needed.
2.0 PROPOSED SUB-SLAB SOIL GAS PROBE SAMPLING PROTOCOL
Figure 4 identifies the locations of the newly-proposed, sub-slab, soil gas probe and the four
existing, accessible probes. Stantec will coordinate with the DERR, property owner, and tenants for
collection of sub-slab soil gas samples from the five accessible probes identified on Figure 4 herein.
The sub-slab probe sampling program will occur on the same day as (or within one day of when)
the indoor air samples are collected, as detailed in following report section 3.0 Proposed Indoor Air
Sampling Program.
Sequential steps for sample collection at each sub-slab soil gas sampling probe will be similar to
past sampling events and as follows in summary. New, disposable, 0.25-inch diameter, Teflon
tubing will be secured atop the compression fitting of each sub-slab soil gas sampling pin/probe.
The tubing will extend from the soil gas probe to a manifolded, tubing tee-split, comprised of two
different runs of tubing.
Each tubing run will be equipped with an in-line, air stop-cock valve that may be used to isolate
each separate tubing run. One tubing run will be connected directly to a 1-liter, laboratory-
certified, summa canister equipped with a 30-minute, in-line, air-flow regulator and pressure
gauge. The other tubing run will be attached to a hand-held vacuum pump. It is anticipated that
each tubing section will be less than one linear-foot in length. The entire assembly will be air-tight,
such that there should be no leaking of air amongst the assembled parts.
Prior to individual sub-slab soil gas sample collection, the dead-air space within all dedicated,
inter-connected tubing will be purged and off-gassed to the atmosphere utilizing the vacuum
pump and stop-valves (i.e., purge/tubing air will not be collected within the Summa canister).
Each summa canister will be fitted with a laboratory-certified, flow regulator that controls the rate
at which soil gas may be drawn into the canister. Following purging, the canister valve will be
opened slowly to accommodate the regulated flow of soil gas into the canister. Once the sample
is collected, the summa canister valve will be closed and air pressure recorded. Immediately
following sample collection, the compression fitting of the vapor pin/probe will be capped with its
dedicated air-tight, plastic cap and accompanying 1-inch diameter, steel screw-on cover - so
that the sub-slab probe remains air-tight.
Stantec will record within a field notebook the final vacuum pressure and all quality
assurance/quality control (QA/QC) information labeled on each canister (individual SummaTM
canister tags, specifying cleaning and validation dates, etc.). Stantec will also document each
PROPOSED WORK PLAN FOR SUPPLEMENTAL AIR SAMPLING
3
canister according to serial number, date, time, and sample name, before hand-delivery to the
laboratory.
All sub-slab soil gas samples will be analyzed for VOCs by Method TO-15 by ALS Environmental
(ALS) of Salt Lake City, Utah, a Utah-certified analytical laboratory and a subsidiary of the
worldwide analytical laboratory ALS Group. All results and laboratory reports will be presented to
the DERR in a Summary Report, as discussed in following section 5.0.
3.0 PROPOSED INDOOR AIR SAMPLING PROGRAM
Stantec will coordinate with the DERR, property owner, and tenants at the mall to conduct indoor
air sampling within Suite #s 32, 34, 36, 38, 40, 46, and 50, in similar fashion as conducted in the past.
If in response to this PWP, the DERR requests additional suites be sampled as part of this proposed
sampling event, Site Centers/Stantec will be prepared to do so accordingly. Each indoor air
sample will be collected within a 6-liter, stainless-steel, laboratory-certified, Summa canister,
equipped with a lab-certified, 8-hour, flow rate regulator, that will be provided by ALS
Environmental. The laboratory-provided regulator ensures that equal volumes of indoor air are
drawn into the canister, throughout the duration of the sampling timeframe.
The samples will be collected during normal business hours, as practicable. Sampling locations
within each suite will be located at the same sampling locations as historical sampling areas (i.e.,
where tenant employees spend the majority of their work day, such as registers, office desks, work
stations, etc.). Sample canisters will be located atop the floor at each location, thereby
representing a low-elevation sampling point within each suite.
Following sample collection, the Stantec sampling technician will return to each suite to close
each canister valve and retrieve the canisters for delivery to the laboratory. Stantec will record
within a field notebook the final vacuum pressure and all QA/QC information labeled on each
canister (individual SummaTM canister tags, specifying cleaning and validation dates, etc.).
Stantec will also document each canister according to serial number, date, time, and sample
name, before hand-delivery to the laboratory.
Upon sample collection, each air sample will be hand-delivered to ALS for quantitative analysis of
PCE; TCE; 1,2 DCA; cis- and trans-DCE; and vinyl chloride by the TO-15, Single Ion Mode method.
Stantec will employ strict Chain-of-Custody QA/QC protocol during sampling and delivery of
sample canisters to the laboratory. All results and laboratory reports will be presented to the DERR
in a Summary Report, as discussed in following section 5.0.
4.0 QUALITY ASSURANCE AND QUALITY CONTROL
All quality assurance/quality control and sampling protocol will be administered in similar fashion
as previous air sampling surveys, in accordance with provisions presented within Site
Centers/Stantec’s July 2019 Amended Proposed Work Plan for Sub-Slab Soil Gas and Indoor Air
Sampling report. The following sections discuss the QA/QC measures that will be utilized during
sample collection and laboratory analysis. The laboratory will provide a Level III result reporting
package.
PROPOSED WORK PLAN FOR SUPPLEMENTAL AIR SAMPLING
4
4.1 SAMPLE REQUIREMENTS, CONTAINERS, AND PRESERVATION
All samples will be collected within laboratory-certified SummaTM canisters equipped with
laboratory-provided, air-flow regulators with integral pressure gauges. Analyses for indoor air will
include PCE; TCE; 1,2 DCA; cis- and trans-DCE; and vinyl chloride by the TO-15, Single Ion Mode
method, while analyses for sub-slab soil gas will include VOCs by Method TO-15.
4.2 CHAIN-OF-CUSTODY, HOLDING TIME, AND RECORD KEEPING
Chain-of-Custody, sample labeling, and record keeping procedures will be in accordance with
measures used previously and deemed adequate for the objectives of the project. All samples
will remain in secure custody of the sampler until hand-delivery to the laboratory. All samples will
be analyzed within prescribed Holding Times and by US EPA- and DERR-approved
methodologies.
4.3 CROSS-CONTAMINATION
The potential for cross-contamination among samples will be minimized by using dedicated,
laboratory-certified, SummaTM canisters and regulators for each individual sample, as well as
new, dedicated, disposable, Teflon tubing during individual sample collection. Anticipated
laboratory QA/QC protocol, sample management, and analytical methodologies are
anticipated to protect against potential cross-contamination of all air samples.
4.4 DATA QUALITY INDICATORS AND QA/QC EVALUATION
Stantec’s proposed sampling protocol, in conjunction with ALS’ proposed laboratory
methodologies and Level III laboratory reporting requisites, are anticipated to satisfy precision,
accuracy, representativeness, completeness, and comparability (PARCC) parameters and be
otherwise adequate for their intended use. All actual sampling protocol and analytical results will
be evaluated in terms of PARCC parameters and discussed in the Summary Report.
5.0 PROPOSED SUMMARY REPORT
Following receipt of all laboratory result reports associated with proposed, investigative activities,
a Summary Report will be prepared for submittal to the DERR. The report will provide a summary
of all site investigation field activities, including site-specific figures, tabulated laboratory results,
and copies of all laboratory result reports, Chain-of-Custody, QA/QC, and corollary deliverables
(Level III reporting, etc.).
FIGURES
Site Center’s Proposed Work Plan
2025 Install One Sub-Slab Soil Gas Monitoring Probe; Sample
Five Sub-Slab Probes; and Sample Suites' Indoor Air
Former Ft. Union Dry Cleaners
Midvale, Salt Lake County, Utah
Design by Revised by
Figure 2 – General Site Location Map
LEGEND The Shops at Fort Union
Date Revised JR JR 8/20/13
CH-1
CH-4
CH-3
CH-2
Not to Scale
Generalized, Outer Perimeter of Property Comprising
The Shops at Ft. Union
Generalized, Areal Extent of VCP Subject Site
Design by Revised by
Figure 3 – Tenant Suites
LEGEND The Shops at Fort Union
Date Revised JR JR 8/21/13
CH-1
CH-4
CH-3
CH-2
Not to Scale
Tenant Suite # Tenant Name (Aug. 2013) Square Feet (sq. ft.)
GN
NS
PB
AT
MC
JD
FSSB
OM
US
#34: Nu Spine Chiropractic
#36: Precious Brows
#42: JDawgs
Figure 4
Sub‐Slab Soil Gas Monitoring Probes
Date Drawn: 3‐25
Red or Green Soil Vapor Extraction (SVE) Skid
HISTORICAL/COVERED Sub‐Slab, Soil Gas Monitoring Probes
SVE Extraction Points
ACCESSIBLE Sub‐Slab, Soil Gas Monitoring Probe
Solid PVC Piping
PROPOSED Sub‐Slab, Soil Gas Monitoring Probe
Horizontal SVE, perforated PVC trench to be installed near northwest corner Suite #34
Suite #52
SVE‐1SVE‐2
Drawn by: JR
Suite #50
Suite #34
20‐ft. deep,
SVE Well W‐2
Buried Utility Corridor incl.
Sewer & Water, grades from
South toward North,
generally west of Suites #32
through #44
Suite #40
Suite #38
Suite #36
Suite #32
Su
i
t
e
#4
2Suite
#46
Su
i
t
e
#4
4
Su
i
t
e
#5
6
Black‐encircled probes are the only accessible (not covered/capped) sub‐slab, soil gas probes