£% United States
Environmental Protection
*'¦¦1 mm. Agency
EPA/600/R-21/272 | November 2021 | www.epa.gov/research
Identifying and Evaluating Vapor
Intrusion through Preferential
Migration Routes and Points of
Entry into Buildings
RESEARCH AND DEVELOPMENT
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Identifying and Evaluating Vapor
Intrusion through Preferential
Migration Routes and Points of Entry
into Buildings
B. Schumacher1, A. Lee2, M. Plate2, L. Abreu2, J. Zimmerman3, and A. Williams3
1U.S. Environmental Protection Agency
Office of Research and Development
Athens, GA
2U.S. Environmental Protection Agency
Region 9
San Francisco, CA
3U.S. Environmental Protection Agency
Office of Research and Development
Research Triangle Park, NC
U.S. Environmental Protection Agency
Office of Research and Development
Washington, DC 20460
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Table of Contents
TABLE OF CONTENTS
Executive Summary 1
1 Background and Objectives 3
1.1 Proj ect Obj ective s 5
1.2 Literature Search 5
1.3 Selection of Research Effort/Study Sites 6
1.3.1 San Fernando Valley - Los Angeles County 6
1.3.2 Moffett Field - Santa Clara County 7
1.3.3 San Gabriel Valley 1 - Los Angeles County 8
1.3.4 San Gabriel Valley 2 - Los Angeles County 8
1.3.5 Central Valley - Fresno County 8
1.4 Field Investigation Methods Applied 8
1.4.1 Forward Looking Infrared (FLIR) Camera 10
1.4.2 Borescope 10
1.4.3 Hot Wire Anemometer 11
1.4.4 Helium Leak Detectors 11
1.4.5 Pressure Differential Meter 11
1.4.6 Radon Detectors 12
1.4.7 Field Portable GC/MS 12
1.4.8 Field Portable Thermal Desorption Cavity Ring-Down Spectroscopy (CRDS) 13
1.4.9 TO-15 Canisters 14
1.4.10 Passive VOC Samplers 14
1.5 Field Mitigation Methods Tested 15
2 Site-Specific Results and Case Studies 17
2.1 San Fernando Valley - Los Angeles County 18
2.1.1 SFV Building 1 18
2.1.2 SFV Building 2 26
2.1.3 SFV Building 3 29
2.1.4 SFV Building 4 35
2.2 Moffett Field 40
2.2.1 MF Building 3 40
2.2.2 MF Building 45 50
2.2.3 MF Building 126 54
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Table of Contents
2.3 SGV Building 1 61
2.4 SGV Building 2 65
2.5 CV Building 1 68
2.6 Effectiveness of the Screening Method and Tools Tested 72
3 Conclusions and Recommendations for Future Work 75
3.1 Potential Migration Routes and Vapor Entry Point Identification 75
3.2 Pathway Dynamics 76
3.3 Mitigation Effectiveness 76
3.4 Recommendation for Future Study 77
4 References 79
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Table of Contents
List of Tables
Table 1-1. San Fernando Valley Buildings 7
Table 1-2. Moffett Field Buildings 7
Table 1-3. Technologies Applied at Each Building 9
Table 2-1. Sample ID Codes 18
Table 2-2. Summary of Techniques Used at SFV1 26
Table 2-3. Summary of Techniques Used at SFV 2 29
Table 2-4. Summary of Techniques Used at SFV 3 35
Table 2-5. Summary of Techniques Used at SFV 4 40
Table 2-6. Moffett Building 3 Indoor Air Radon Data Measured by Consumer Grade Radon
Detectors 48
Table 2-7. Summary of Techniques Used at MF 3 50
Table 2-8. TCE concentrations (in jig/m3), during, and after sealing in Building 45 using the field
portable GC/MS 53
Table 2-9. Summary of Techniques Used at MF 45 54
Table 2-10. Summary of Techniques Used at MF 126 61
Table 2-11. Summary of Techniques Used at SGV 1 65
Table 2-12. Summary of Techniques Used at SGV 2 68
Table 2-13. Summary of Techniques Used at CV 1 72
Table 2-14. Summary of Techniques Used 74
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Table of Contents
List of Figures
Figure 1-1. Slab-on-Grade Preferential Migration Routes and Points of Entry Driven by 4
Figure 1-2. Slab-on-Grade Preferential Migration Routes and Points of Vapor Entry Driven 5
Figure 1-3. FLIR Camera (left) and Mobile Phone with FLIR Camera Attachment 10
Figure 1-4. Borescope 10
Figure 1-5. Hot Wire Anemometer 11
Figure 1-6. Helium Leak Detector Probe in Use in Conduit Trench 11
Figure 1-7. Pressure Differential Meter 12
Figure 1-8. Radon Detectors (professional detector on the left and consumer grade on the right).. 12
Figure 1-9. Field Portable GC/MS with Probe in Potential Preferential Migration Route Conduit. 13
Figure 1-10. Cavity Ring-Down Spectroscope (CRDS) 13
Figure 1-11. 6 L TO-15 Canisters (left) and 400 mL TO-15 Canister (right) 14
Figure 1-12. Passive VOC Sampler 15
Figure 1-13. Retrofit floor drain valves 16
Figure 2-1. Preferential Migration Routes and Points of Vapor Entry Testing using Field Portable
GC/MS, Differential Pressure, and Professional Radon Detector 17
Figure 2-2. SFV Building 1 Sampling Locations 19
Figure 2-3. SFV Building 1 Follow-up Study Locations 20
Figure 2-4. Small Conference Room Differential Pressure 21
Figure 2-5. Map Room/Library Differential Pressure 21
Figure 2-6. Small Conference Room Pathway TCE/PCE Concentration November 2-3, 2019 22
Figure 2-7. Picture of Pathway in Communication Conduit of Small Conference Room 22
Figure 2-8. Small Conference Room Pathway TCE and PCE Concentration November 4, 2019 23
Figure 2-9. Indoor Source of PCE 24
Figure 2-10. Helium Air Exchange Rate Small Conference Room 25
Figure 2-11. SFV Building 2 Sampling Locations 27
Figure 2-12. Building SFV 3 Sampling Locations 30
Figure 2-13. Crack Sealing, Building SFV 3 32
Figure 2-14. Differential Pressure SS to IA SFV 3, November 5, 2021 32
Figure 2-15. SFV 3 Air Exchange Rate 34
Figure 2-16. Building SFV 4 Sampling Locations 36
Figure 2-17. Differential Pressure Pathway to IA SFV 4, February 2021 37
Figure 2-18. Building SFV 4 Overnight Data, February 2021 38
Figure 2-19. Differential SS to IA SFV 4, November 2019 39
Figure 2-20. Moffett Building 3 Sampling Locations 41
Figure 2-21. Differential Pressure Moffett Building 3 Restroom, May 2019 42
Figure 2-22. Differential Pressure Moffett Building 3 Locker room, September 2019 43
Figure 2-23 Discrete Pressure Testing in May 2019 44
Figure 2-24. Differential Pressure Moffett Building 3 Cafe, March 2019 44
Figure 2-25. Helium Injection into Cleanout in Moffett Building 3 47
Figure 2-26. FLIR Picture of Temperature Gradient Cafe Wall 49
Figure 2-27. Moffett Building 45 Sampling Locations 51
Figure 2-28. Picture Building 45 Pathways 52
Figure 2-29. Moffett Building 126 Sampling Locations 55
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Table of Contents
Figure 2-30. Moffett Building 126 Study Area Sampling Locations 56
Figure 2-31. Moffett Building 126 West Restroom (105) Pressure, May 2019 57
Figure 2-32. Moffett Building 126 East Restroom (104) Pressure, May 2019 58
Figure 2-33. Moffett Building 126 West Restroom (105) Continuous TCE/PCE, May 2019 59
Figure 2-34. Moffett Building 126 East Restroom (104) Continuous TCE/PCE, May 2019 59
Figure 2-35. Moffett Building 126 East Restroom (104) Air Exchange Rate, September 2019 60
Figure 2-36. SGV Building 1 Sampling Locations 62
Figure 2-37. SGV 1 FLIR Potential Vapor Entry Point, August 2018 63
Figure 2-38. PCE/Chloroform Ratios in SGV1 by Suite 64
Figure 2-39. SGV 2 Sampling Locations 66
Figure 2-40. SGV 2 West Restroom Air Exchange Rate, November 2019 67
Figure 2-41. CV Building 1 Sampling Locations 69
Figure 2-42. CV 1 FLIR Potential Vapor Entry Point, November 2018 69
Figure 2-43. CV 1 Continuous VOC Data, November 17-18, 2018 70
Figure 2-44. CV 1 Floor Drain Trap 71
Figure 2-45. CV 1 Floor Drain Slab Gap 71
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Notice
The information in this document has been funded wholly by the United States Environmental
Protection Agency under contract number EP-C-11-036 to the Research Triangle Institute. It has
been subjected to external peer review as well as the Agency's peer and administrative review
and has been approved for publication as an EPA document. Mention of trade names or
commercial products does not constitute endorsement or recommendation for use.
Acknowledgments
This project was conceived, directed, and managed by Brian Schumacher (EPA ORD CEMM
EPD) and Alana Lee (EPA Region 9). Mathew Plate and Lilian Abreu, EPA Region 9, were
instrumental in field sampling support, testing of the various techniques to determine preferential
pathways, and review of this report. John Zimmerman and Alan Williams, EPA ORD CEMM
WECD, provided valuable technical reviews and field sampling support. The EPA Region 9
Laboratory provided volatile organic chemical analysis of the air, pathway, and subslab soil gas
samples, Bob Hopeman (EPA Region 9 Field Analytical Support Program) and contractor
support from the Environmental Services Assistance Team provided the field portable GC/MS
analysis. The R9 Technology and Data Solutions Center provided valuable GIS and data
management support. RTI International and Jacobs prepared initial draft versions of this report
through the STREAMS III contract (EP-C-16-016).
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Executive Summary
Executive Summary
The U.S. Environmental Protection Agency (EPA) Region 9 (R9) vapor intrusion (VI) team has
observed preferential migration routes and points of vapor entry into many buildings and
recognized the need to research pathway entry investigation techniques, and potential mitigation
strategies and their effectiveness. EPA R9 partnered with the EPA Office to Research and
Development (ORD) through the Regional Applied Research Effort (RARE) program.
The objective of this research effort was to identify methods to evaluate potential preferential
migration routes and points of entry into building space and assess the effectiveness of easily
implementable field mitigation measures. Where possible, the team attempted to quantify the
contribution to the indoor air concentrations of volatile organic compounds (VOCs) from an
identified preferential migration route or point of vapor entry. To meet this goal, the vapor
intrusion team identified and used screening methods and tools (e.g., low cost testing of tracers
and field portable sensors or meters) to rapidly identify points of entry to the indoor environment
in 10 buildings located at 4 field sites. For a selected set of potential pathways, the research
effort identified and tested the effectiveness of simple, easily implementable mitigation measures
taken to minimize or prevent potential exposure from preferential migration routes and vapor
intrusion points of entry.
The R9 vapor intrusion team identified 12 buildings within California that had known vapor
intrusion with high possibilities of having vapor intrusion preferential migration routes and
points of vapor entry. Discrete vapor entry points were identified in 10 of the buildings. A more
in-depth research effort was then conducted in six buildings over a two-year period.
Technologies used for testing and identification of points of entry included: forward looking
infrared (FLIR) camera (intrusion detection using temperature gradients), borescope (conduit
pathway assessment), hot wire anemometer (pathway and zone flow), micromanometer
(continuous and discrete differential pressure monitoring), trace helium detector (tracer and air
exchange testing), radon detection with both research and consumer grade meters (potential
tracer/surrogate), field portable gas chromatograph-mass spectrometer (GC/MS), field portable
cavity ring down spectrometer (CRDS), evacuated canister analysis by method TO-15, and
passive VOC samplers analysis via method TO-17.
Two mitigation techniques employed were (a) sealing of visible cracks and open conduits and (b)
retrofitting floor drain valves with a simple mechanical device designed to allow water to pass
down through a floor drain while preventing soil gas and sewer gas from moving upward into the
indoor space. Changes in ventilation patterns within a building were also observed to have a
marked influence on vapor intrusion and; thus, making ventilation changes could be used as a
mitigation technique.
Using these techniques EPA was able to:
identify preferential migration routes and vapor entry points into the building,
make recommendations to optimize ventilation conditions to minimize vapor intrusion,
test the effectiveness of simple, easily implementable mitigation measures, and
better understand short term, diurnal, and seasonal conditions that promote preferential
migration routes and points of vapor entry into buildings.
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Executive Summary
In buildings where vapor intrusion may be dominated by preferential migration routes, it is
recommended that multiple techniques be used together to understand pathway flow in real time
and under different ventilation and weather conditions.
Real-time VOC analysis (e.g., field portable GC/MS), discrete sampling (e.g., TO-15 canisters
and passive VOC samplers) under variable conditions, and differential pressure monitoring, were
the most useful technologies in identifying preferential migration routes and points of entry into
a building. Alternative, real-time analysis technologies, such as the portable cavity ring down
spectrometer, can be equally as useful as the field portable GC/MS. Selection of the real-time
VOC analyzer technology for use in the field is based on the target chemicals, data quality needs,
and the other considerations. Tracer testing (e.g., radon and/or helium), may provide some useful
data at some buildings.
Vapor intrusion points of entry are most significant when they contain not only high
concentrations of VOCs but deliver significant air flow and, thus, mass. It is useful to
supplement observations of chemical concentrations with other instruments, such as manometers
and anemometers, to observe the driving forces for and the directionality of advective gas flow
through the building envelope. Measurements that define how many vapor entry points are
present and measure the cross-sectional area of vapor entry points can also be useful. Finally,
since indoor air concentrations are controlled by the balance between soil gas entry and
dilution/ventilation in indoor air, air exchange rate measurements provide helpful context to
determine the importance of a particular entry point.
In some cases, results in this project suggested substantial short-term effectiveness for sealing
approaches. However, as noted in EPA's Technical Guide for Assessing and Mitigating the
Vapor Intrusion Pathway from Subsurface Vapor Sources to Indoor Air (EPA, 2015), verifying
the effectiveness of sealing requires monitoring over time and sealing approaches are generally
most effective when paired with a depressurization technology.
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Background and Objective
1 Background and Objectives
The U.S. Environmental Protection Agency (EPA) Region 9 (R9) vapor intrusion team and the
EPA Office of Research and Development (ORD) worked cooperatively on a Regional Applied
Research Effort (RARE) to: (a) study contaminant flow from preferential migration and vapor
entry points into buildings, (b) evaluate screening methods and tools to detect the preferential
migration routes and vapor entry points, and (c) test the effectiveness of several simple
mitigation techniques. The role of preferential pathways during vapor intrusion is poorly
understood and the complexity and variability of the pathways has only recently come to light.
EPA (2015) defines the term "preferential migration route" as a:
Naturally occurring subsurface feature (e.g., gravel lens, fractured rock) or
anthropogenic (human-made) subsurface conduit (e.g., utility corridor or vault,
subsurface drain) that is expected to exhibit little resistance to vapor flow in the
vadose zone (i.e., exhibits a relatively high gas permeability) or groundwater flow
(i.e., effectively exhibits a relatively high hydraulic conductivity), depending upon
its location and orientation relative to the water table and ground surface, thereby
facilitating the migration of vapor-forming chemicals in the subsurface and
towards or into buildings.
Anthropogenic examples include sewer lines and manholes, utility vaults and
corridors, elevator shafts, subsurface drains, permeable fill, and underground mine
workings that intersect subsurface vapor sources or vapor migration routes. In
highly developed residential areas, extensive networks of subsurface utility
corridors may be present, which can significantly influence the migration of
contaminants. A preferential migration route can be a "significant" influence on
vapor intrusion when it is of sufficient volume and proximity to a building that it
may be reasonably anticipated to influence vapor migration towards or vapor
intrusion into the building.
EPA's Technical Vapor Intrusion Guide, distinguishes "preferential migration routes from
adventitious and intentional openings in a building that may also facilitate vapor entry from the
subsurface (see Section 2.3), but which are expected to typically be present in all buildings (e.g.,
cracks, seams, interstices, and gaps in basement floors and walls or foundations; perforations due
to utility conduits)." For this study, preferential migration routes are defined similarly to
"conduit" vapor intrusion as defined by Kapuscinski (2021) in which intentional openings in
walls and floors were placed in the building such as those needed to carry water, utility,
communication, and sewage to and from the building. Vapor points of entry are defined as the
cracks, seams, interstices, and gaps in floors, walls, and foundations (i.e., predominantly
unintentional openings between the subslab and indoor air) where active vapor intrusion is
occurring into the building.
Examples of preferential migration routes include sewer lines (broken or whole), plumbing and
power lines/conduits that are open ended or poorly sealed, sumps, floor drains, utility tunnels,
and elevator shafts. A depiction of preferential migration routes and vapor entry points observed
by EPA Region 9 is presented in Figure 1-1 and Figure 1-2. This research effort focused
primarily on techniques for identifying the types of preferential migration routes and points of
vapor entry across the building envelope (i.e., the separation of the interior and exterior of a
3
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Background and Objective
building) depicted in these figures. Vapor migration pathways can be dependent or independent
of building depressurization (driving force). Pathways that are dependent on building
depressurization, as shown in Figure 1-1, are foundation gaps, poorly installed subslab ports,
data and power conduits, abandoned utilities, and gaps around utilities. Pathways that are
independent on building depressurization, as shown in Figure 1-2, are elevator shafts and
associated appurtenances, sewer pipes, and HVAC systems.
EPA's goal was to identify: (a) sites that represent different environmental conditions within
Region 9, (b) different types of preferential migration routes and vapor entry points, and (c)
different building construction and use. Five sites in California with known vapor intrusion were
evaluated. Sites selected for this RARE study were in the San Francisco Bay area, the Los
Angeles basin, and the California Central Valley. The site locations represent the different
weather and groundwater conditions present in much of EPA Region 9.
Figure 1-1. Slab-on-Grade Preferential Migration Routes and Points of Entry Driven by
Building Depressurization.
Pathways Dependent on Indoor Pressure
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Background and Objective
Figure 1-2. Slab-on-Grade Preferential Migration Routes and Points of Vapor Entry Driven
by Independent Forces.
Pathways with Independent Driving Forces
I HVAC driven do»
5L
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1.1 Project Objectives
Project objectives reviewed in this report included to:
1. Identify and use screening methods and tools (e.g., low cost testing of tracers and field
portable sensors or meters) to rapidly identify if the vapor intrusion pathway exists and if
it is complete;
2. Account for the incidence/frequency of occurrence and significance of the potential
preferential migration routes and vapor entry points to focus vapor intrusion pathway
investigations,
3. Quantify and compare indoor air contamination that can be attributed to each identified
preferential migration route or vapor entry point into the building; and
4. Identify and test the effectiveness of mitigation measures taken to minimize or prevent
potential exposure from preferential migration routes and vapor intrusion points of entry
into the building.
The first objective was completed primarily via field experience and a literature search to
identify sites and investigation methods viable for the project. The second, third, and fourth
objectives were accomplished in the field with real-time data analyses and afterward, utilizing
the analytical data produced and supplemented with literature search results.
1.2 Literature Search
A literature search was conducted to define the characteristics of the situations where preferential
migration routes for vapor intrusion have been shown to occur. Cases were found both by
conventional computerized literature searching methods and through an informal survey of
practitioners.
The literature search was expanded from the work previously reported by Kastanek et al. (2016)
which summarized preferential migration routes and points of vapor entry with an emphasis on
subsurface utilities (e.g., within pipes, backfill around pipes or wires). A database was built
detailing 18 preferential migration route cases identified from investigations conducted at 15
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Background and Objective
different project sites at both military and civilian industrial, commercial, and residential
structures in nine U.S. states and Denmark. Data collected during the evaluation (where
available) included utility characteristics (e.g., depth below ground surface, backfill type,
materials of construction), release characteristics (e.g., historical release straight to sewer line,
shallow groundwater, high concentration in soil gas close to utility line), and building
characteristics (e.g., empty or abandoned traps, intentional open connections for drainage). This
allowed the cases studied in the field during the project to be compared to the characteristics of
those previously reported in the literature. The expanded database contains many cases beyond
sewers including those in which the vapor entry points involved floor cracks, utility conduits,
malfunctioning heating, ventilation, and air conditioning (HVAC) systems, and elevators.
1.3 Selection of Research Effort/Study Sites
Based on the team's collective project and research experience, the following preferential
migration routes, points of entry, and building-specific operations have contributed to measured
vapor intrusion:
Sewer lines with dry traps, compromised integrity, and poorly sealed cleanouts,
Conduits for electrical, phone, and data wires,
Gaps between piping and concrete slabs,
Gaps between structural footers and concrete slabs,
Exposed soil areas inside walls and under plumbing (e.g., unlined crawl spaces, earthen
floors),
Unsealed or improperly sealed elevator pits and pistons,
Sumps and floor drains, and
Ventilation and heating systems with air supply or return at slab or crawlspace level.
The team identified buildings with multiple potential preferential migration routes and points of
entry based on this understanding. Sites and buildings studied are summarized in the following
subsections.
1.3.1 San Fernando Valley - Los Angeles County
The study site is a former metal plating facility located in the southeastern San Fernando Valley
(SFV) - Los Angeles County, California with known chlorinated volatile organic compound
releases to soil and groundwater and VOC vapor intrusion impacts in surrounding buildings.
Located in a dense, mixed-use, urban area with bordering residential neighborhoods, this former
industrial facility is comprised of two adjacent properties (the North Property and South
Property) separated by an alley.
The solvents trichloroethene (TCE) and tetrachloroethene (PCE) were released into the
subsurface, with PCE being the predominant solvent, at both the North and South Properties at
various times during facility operation. Most releases occurred on the South Property. The area is
predominantly covered by buildings and pavement. Subsurface utilities may play a significant
role in VOC distribution, transport, and loss through small open areas and cracks.
The site is underlain by alluvial valley fill deposits comprised of unconsolidated sands and
gravels with localized discontinuous fine-grained intervals of silt and clay. Groundwater flow is
to the southeast and depth to water measured at the site is approximately 54 to 62 feet below
ground surface (ft bgs).
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Background and Objective
The buildings studied at the SFV site are summarized in Table 1-1.
Table 1-1. San Fernando Valley Buildings.
Building
Building Use
Square feet
Approx. Dimensions (ft)
Mechanical
Ventilation
1
Office Space / Lab Space
/ Storage Space
6600
42 x 20 (geotech lab)
50 x 90 (offices)
30x40 (storage)
HVAC / exhaust
on demand in
main suite
2
Meeting Space
3200
50 x 38 (upper)
48 x 26 (lower)
HVAC when
occupied
3
Former Northern Facility
/ Storage Space
1800
80 x 23 (front, storage)
None
4
Office space
3200
51 x 58 (1st floor)
HVAC
A long-term demonstration scale ORD research project (2016 - 2020) testing soil vapor
extraction (SVE) for vapor intrusion mitigation was being conducted at the SFV site
simultaneously with this study's field sampling. The SVE project has acquired long-term records
of indoor air, subslab soil gas, external soil gas, and groundwater data, with the SVE system
being both on and off (RTI, 2020; Stewart et al., 2020).
1.3.2 Moffett Field - Santa Clara County
This Moffett Field (MF) study site is located in Santa Clara County, California, near the southern
tip of San Francisco Bay. The 1,500-acre Naval Air Station Moffett Field site was commissioned
in 1933 as a naval air station to support a "lighter-than-air" (LTA) program. The LTA program
involved training pilots to fly blimps and servicing the aircraft. Moffett Field is underlain with
deep alluvial fill of interbedded gravels, sands, and clays. Regional shallow groundwater
contamination, primarily with TCE and PCE, from historical releases is encountered at
approximately 5 to 10 ft below ground surface (bgs).
Three buildings at Moffett Field were studied and are summarized in Table 1-2.
Table 1-2. Moffett Field Buildings.
Building
Building Use
Square feet
Approx. Dimensions (ft)
Mechanical
Ventilation
3
Meeting Space /
Cafe and
Kitchen
30000
150 x 60 (cafe / kitchen)
200 x 75 (meeting space)
50 x 100 (storage)
HVAC/
Exhaust
45
Workspace
8600
25 x 45 (restrooms and
storage)
75 x 100 (main)
None
126
Museum
13000
15 x 55 (addition)
100 x 122 (main)
HVAC
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Background and Objective
1.3.3 San Gabriel Valley 1 - Los Angeles County
At the San Gabriel Valley location 1 (SGV1) in Los Angeles County, California, a single multi-
unit commercial building adjacent to a former industrial site was selected. The building was
identified as having low level vapor intrusion, primarily into the units closest to the former
industrial site. The building is approximately 3,600 square feet and was originally designed to
have six 600 square foot units. At the time of the first site visit, there were 4 separate units.
Subsequently, additional units were combined to accommodate the primary tenant. The building
utilizes HVAC systems in occupied units.
1.3.4 San Gabriel Valley 2 - Los Angeles County
The San Gabriel Valley location 2 (SGV2) investigation focused on a 600 square foot residential
support building adjacent to a dry cleaner in Los Angeles County, California. A leaking
underground storage tank associated with the dry cleaner released PCE to the vadose zone
approximately 50 feet from the selected test building. The dry cleaner is still operational, but no
longer uses PCE. However, significant concentrations of PCE remain in the vadose zone. The
building consists of two abandoned restrooms with toilet and shower fixtures, an active laundry
room, and a storage room. All rooms have only one external door and window and there are no
internal doors connecting the rooms. There was no active ventilation at the time of testing.
1.3.5 Central Valley - Fresno County
The Central Valley (CV) location in Fresno County, California, is a single commercial
office/warehouse building. The parcel was the site of a former chemical distribution and
handling facility. Contamination was present in the surface soils and did not impact deep
groundwater at the site. In approximately the year 2000, a soil removal remedial effort was
conducted, and the lot was regraded with new fill. Subsequently, the lot was redeveloped, and an
office/warehouse was constructed. Residual TCE and PCE are present in the vadose zone.
The current building is divided into approximately 1,000 square feet of office space, 1,500
square feet of workshop space, and 5,500 square feet of warehouse space. Historic TCE
contamination was located near the front of the current office space and historic PCE
contamination was located under the warehouse and workshop areas. EPA had previously
identified the office floor drain as a preferential migration route into the office space with TCE
as the primary contaminant detected.
1.4 Field Investigation Methods Applied
Multiple techniques were tested to identify screening methods and tools (e.g., low cost testing of
tracers and field portable sensors or meters,) to rapidly identify if the vapor intrusion pathway is
complete. Preferential migration of soil vapors can be highly temporally variable. Thus,
preferential migration routes and points of vapor entry that are only active some of the time can
result in significant indoor air concentration spikes or persistence, depending on indoor air
exchange and pathway irregular flow patterns. There is no guarantee that all preferential
migration routes and points of entry can be easily observed or identified. Repeated visits under
varying conditions (e.g., ventilation changes and wind loadings) may be needed to observe a
preferential pathway in operation (McHugh et al., 2018; Schuver et al., 2018).
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Background and Objective
The field study at each site primarily consisted of operational testing of various technologies
used for detecting vapor intrusion at the point of entry. The technologies were evaluated based
on:
Objective evidence of locating vapor intrusion points of entry in one or more buildings,
often in conjunction with evidence provided by complementary technologies, and
Subjective assessments of the ease of use and utility of the tools under realistic field
operational constraints of schedule and access.
Since vapor intrusion can occur from multiple locations and is temporally variable, figures of
merit for these technologies, such as sensitivity, false positive rates, and false negative rates, are
difficult to measure under realistic field operational conditions. For example, clear evidence that
vapor intrusion via a preferential migration route or point of vapor entry is occurring at a specific
location in the building does not rule out other vapor entry points elsewhere in the same building.
An inability to locate discrete vapor intrusion points of entry in a given building might occur
where advective vapor intrusion entry points are numerous, diffusional entry is dominant, and/or
the advective entry points are physically inaccessible.
The specific technique tested at each site for indoor versus outdoor air, subslab soil gas, and
preferential migration route and vapor entry point determinations are summarized in Table 1-3.
A brief discussion of each of the technologies follows.
Table 1-3. Technologies Applied at Each Building.
Bldg
FLIR Camera"
Borescope
Hot wire anemometer
Helium Tracer
Pressure differential (AP)
Consumer Grade Radon Detector
Professional Radon Detector
Field Portable GC/MS
Field Portable CRDS
TO-15 Canisters / Method TO-15
Passive VOC / Method TO-17
SFV 1*
X
X
X
X
X
X
X
X
X
SFV 2
X
X
X
X
X
X
X
SFV 3
X
X
X
X
X
X
X
SFV 4
X
X
X
X
X
X
X
MF 3
X
X
X
X
X
X
X
X
X
X
MF 45
X
X
X
X
X
X
MF 126
X
X
X
X
X
X
SGV 1
X
X
X
X
X
SGV 2
X
X
X
X
X
X
X
CV 1
X
X
X
X
X
X
X
X
*SFV - San Fernando Valley; MF - Moffett Field; SGV - San Gabriel Valley;
9
-------
Background and Objective
CV - Central Valley.
"FLIR - Forward Looking Infrared Camera; GC/MS - Gas chromatography/Mass
Spectrometry; CRDS - Cavity Ring-Down Spectroscope; VOC - Volatile Organic Compound.
1.4.1 Forward Looking Infrared (FLIR) Camera
The FLIR camera is a thermal imaging camera that detects temperature differences (Figure 1-3).
FLIR cameras can either be a handheld camera or as an attachment to your mobile phone.
Typically, reds and oranges represent areas or items of higher temperatures while blues and
green represent lower temperatures.
Figure 1-3. FLIR Camera (left) and Mobile Phone with FLIR Camera Attachment.
1.4.2 Borescope
A borescope is an instrument used to inspect the inside of a structure through an opening (Figure
1-4). The borescope consists of a camera/viewing screen and a flexible optical hose with a
lighted end. The borescope optical hose is pushed through an opening, such as a floor drain, and
provides visible evidence of the integrity of the conduit being examined.
Figure 1-4. Borescope.
10
-------
Background and Objective
1.4.3 Hot Wire Anemometer
The hot wire anemometer is used to measure the direction and velocity of air flow (Figure 1-5).
The hot wire anemometer consists of a probe containing the hot wire which is cooled when air
flows over it. The cooling changes the resistance in the hot wire which is then converted into air
flow velocity.
Figure 1-5. Hot Wire Anemometer.
1.4.4 Helium Leak Detectors
Helium leak detectors are units used to detect tracer gases (Figure 1-6). The helium leak detector
was used to detect helium injected into the subslab that was "leaking" through cracks or
incomplete seals in buildings. The helium leak detector was also used to measure the helium
decay rate in a room that can then be related to the room's air exchange rate.
Figure 1-6. Helium Leak Detector Probe in Use in Conduit Trench.
1.4.5 Pressure Differential Meter
The pressure differential meter monitors the pressure differences between two locations. A dual
pressure differential meter is seen in Figure 1-7 which is measuring difference between the
ambient air at its location (the two brass nipples with no hosing attached) and two separate
locations in the building as indicated by the red and green hoses. Depending upon the setup of
the tubes, the values may either be negative of positive. A negative reading indicates a vacuum
while a positive reading indicates an over pressurization in the room.
11
-------
Background and Objective
Figure 1-7. Pressure Differential Meter.
1.4.6 Radon Detectors
Radon detectors use alpha spectrometry to measure the natural decay of radium, thorium, or
uranium (typically) that are naturally occuring in the soil and rock. Radon is an odorless,
colorless, tasteless gas known to cause lung cancer. There are two types of radon detectors used
in this study which are consumer grade detectors and professional grade detectors (Figure 1-8).
The consumer grade radon detectors are small units readily available at a local hardware store or
on-line. These units continuously monitor radon gas and provide time-integrated 2-day and 7-day
radon concentrations. The professional grade radon detectors are highly sensitive and accurate
radon detectors that provide concentration reading about every 15 minutes.
Figure 1-8. Radon Detectors (professional detector on the left and consumer grade on the right).
1.4.7 Field Portable GC/MS
Field portable gas chromatograph/mass spectrometer (GC/MS) systems are smaller versions of
the laboratory based GC/MS units. Field portable GC/MS systems (Figure 1-9) are used in the
field for the analysis of volatile organic compounds (VOCs). These units allow for the
12
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Background and Objective
quantitative identification of VOCs, even when these substances are present at trace levels in
complex matrices.
Figure 1-9. Field Portable GC/MS with Probe in Potential Preferential Migration Route Conduit.
1.4.8 Field Portable Thermal Desorption Cavity Ring-Down Spectroscopy (CRDS)
The field portable thermal desorption cavity ring-down spectroscopy (CRDS) is a highly
sensitive optical spectroscopic technique that allows for the quantification of VOCs through light
absorbance of a beam emi tted by a laser. A ramped thermal desorption unit provides temporal
separation of molecules.
Figure 1-10. Cavity Ring-Down Spectroscope (CRDS).
13
-------
Background and Objective
1.4.9 TO-15 Canisters
A TO-15 canister is a stainless steel container that has had the internal surfaces specially
passivated/chemically deactivated to not absorb anything from the atmosphere inside the vessel
(Figure 1-11). TO-15 canisters have special valve system (restrictors) that allow air to be
collected over a time-integrated duration (8 to 24 hours typically). The TO-15 canisters are
clean-certified prior to usage. Once the sampling has been completed; the canister is shipped to
an analytical laboratory for VOC analysis by EPA method TO-15 (EPA, 1999). All TO-15
canisters used during this study were analyzed by the EPA Region 9 Laboratory.
Figure 1-11. 6 L TO-15 Canisters (left) and 400 mL TO-15 Canister (right).
1.4.10 Passive VOC Samplers
Passive VOC samplers are comprised of an adsorbent material contained within a protective
shield that will allow air to enter the adsorbent but prevent ingress of soil particles and water.
These passive devices are used to sample VOCs over time (typically days and weeks) and have
been tested out to one year after deployment (EPA, 2012). Once the sampling period is complete,
the passive VOC samplers are sent to an analytical laboratory for analysis by EPA method TO-
17 (EPA, 1999). All the passive samples collected as part of this study were analyzed by the
EPA Region 9 Laboratory.
The passive VOC sampler used in this study was of the radial variety (Figure 1-12).
14
-------
Background and Objective
Figure 1-12. Passive VOC Sampler.
1.5 Field Mitigation Methods Tested
The suite of tools employed identified preferential migration routes and vapor intrusion points of
entry. Field efforts were undertaken to seal pathway entry points and assess the effectiveness and
reduction in the number of entry points and indoor air VOC concentrations. Sealing of entry
points can be taken as evidence for of identifying preferential migration routes and vapor
intrusion points of entry and the effectiveness of easily implementable mitigation technologies.
Follow-on studies could employ approaches, such as long duration continuous VOC monitoring
or controlled pressure testing, to better understand the efficacy of point of entry detection and
mitigation technologies.
Crack sealing with caulk, foam or epoxy is generally viewed as a part but not the totality of a
complete vapor intrusion mitigation strategy (EPA, 2008, 2015).
To block vapor intrusion migration through floor drains, easily implementable, low cost retrofit
floor drain valves were used. The retrofit floor drain valves are a simple mechanical device
designed to allow water to pass down through a floor drain while preventing sewer and soil gas
from moving upward.1 The retrofit floor drain valves were installed at Moffett Field (Figure 1-
13)
1 More information about Dranjer valves can be found at https J/www.dranier.com/products/. Note that the product
line includes devices designed to be used with and without active subslab depressurization.
15
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Background and Objective
Uninstalled Installed Schematic
In some instances, ventilation changes (e.g., shutting and opening doors and fans turned on or
off) and other adjustments to reduce the degree of depressurization in a space can be beneficial in
mitigating the vapor intrusion. Increasing air exchange rates within the building or room is also a
mitigation technique that can be utilized to reduce or minimize vapor intrusion.
Details of the pros and cons of these techniques are provided in EPA literature (2008, 2015).
Figure 1-13. Retrofit floor drain valves.
Flettftfo Rub&er Rang*!
-------
Section 2 Site-Specific Results and Case Studies
2 Site-Specific Results and Case Studies
The following subsections detail the data collected and the results of each individual field test
(Figure 2-1). Ten case studies are highlighted to help readers conceptualize general findings.
Results reported include investigation tools used to locate preferential migration routes and
points of entry; chemical concentrations; and the mitigation techniques employed and their
effectiveness. Table 2-1 presents the sample identifier codes used along with sampling location
in this section. Note: All building room configuration figures are oriented North-South
throughout this document.
Figure 2-1. Preferential Migration Routes and Points of Vapor Entry Testing using Field Portable
GC/MS, Differential Pressure, and Professional Radon Detector.
17
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Section 2 - Site-Specific Results and Case Studies
Table 2-1. Sample ID Codes.
MATRIX
CODE
MATRIX CODE
DEFINED
BZ
BREATHING ZONE
OA
OUTDOOR AIR
PP
POTENTIAL
PATHWAY
IS
INDOOR SOURCE
RR
RESTROOM
MH
MANHOLE
SC
SEWER CLEANOUT
SG
SOIL GAS
ss
SUB SLAB
2.1 San Fenian do Valley - Los Angeles County
The San Fernando Valley - Los Angeles County (SFV) study sampling began in 2019 with the
SVE research project's SVE system turned off and near the end of a year-long third rebound
period.
2.1.1 SFV Building 1
SFV Building 1 is a one-story office building with offices and storage rooms occupied by two
different tenants (Figure 2-2). The building is divided into a larger commercial office space and
a small geophysical laboratory. The remaining approximately one-third of the building is used
for storage and is occupied only periodically. The building has a long-term history of monitoring
during all phases of the SVE research project (RTI, 2020; Stewart et al., 2020) in the map
room/library.
Field activities under this EPA study were completed in February and November 2019.
18
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Section 2 Site-Specific Results and Case Studies
Figure 2-2. SFV Building 1 Sampling Locations.
Small Conference
Room SFV Building 1
Map Room/
Library
Phone Closet
DLB8PP
III
Men's Women's RR
February 2019
Data collected in February 2019 were from the use of a field portable GC/MS, passive VOC
samplers, and TO-15 canisters. Radon concentrations were also collected using a consumer grade
radon detector over a two-day sample duration.
Subslab soil gas concentrations, up to 44,000 (ig/m3 of PCE, were detected at location DL43SS
in the map room/library with the field portable GC/MS (validated by TO-15 canister analysis
with a concentration of 36,000 jag/m3). Indoor air results were non-detect or detected at less than
10 (.ig/m3 PCE in indoor air throughout the building. The indoor air results varied:
8.8 |ig/m3 PCE in the storage room using field portable GC/MS
o 7.5 jig/'ni3 PCE confirmed by TO-15 canister analysis
o 6.4 jig/m3 confirmed using a 2-day passive VOC sampler (DL15BZ)
5.2 iig/m3 PCE in the phone closet (southwest corner of Figure 2-2) using field
portable GC/MS
o 7.2 |ag/m3 PCE confirmed using a 2-day passive VOC sampler (DL41PP)
1.4 ug/m3 in the map room/library using the field portable GC/MS (DL37BZ).
The heterogeneity of the indoor air results suggested the indoor air concentrations may have been
influenced by unknown indoor air sources or differences in ventilation rates within portions of
the building.
Measurement with the consumer grade radon detector over 2 days resulted in a radon
concentration of 0.3 picocuries per liter (pCi/L) from the storage room. This concentration is
19
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Section 2 Site-Specific Results and Case Studies
typical of background ambient air radon concentrations nationally. This result combined with the
variable PCE concentrations throughout the building led to a preliminary hypothesis that the
PCE in the storage room area was influenced by an indoor source and was not related to
ventilation differences throughout the building.
Figure 2-3. SFV Building 1 Follow-up Study Locations.
DL82PP
DL86PP
DL60PP
DL83PP
DL8.1BZ
Small Conference Room
Cubicle Area
SFV Building 1
DL43SS
DLB4PP
OL37BZ
Map Room/Library
DL86PP
November 2019
Elevated PCE concentrations identified during the February 2019 sampling led to further
investigation in November 2019 using the discrete and continuous pressure differential meter,
field portable GC/MS, passive VOC samplers, TO-15 canisters, radon determination using the
professional radon detector, borescope, hot wire anemometer, and helium air exchange tracer
testing. Follow-up testing was conducted over the weekend November 2-3, 2019 in the
unoccupied building followed by some additional sampling on Monday, November 4, 2019 when
the building was occupied. Testing was performed in the map room/library, small conference
room, and cubicle areas in the central part of the building (Figure 2-3). The testing over the
weekend and following workday was performed to examine differences between the weekend
and weekday building FIVAC operation conditions.
Approximately 9 hours of differential pressure data were acquired overnight at several locations
wi thin the building. On the evening of November 2, the differential pressure measured in the
small conference room (DL81BZ) indicated that the small conference room was generally
positively pressurized in comparison to the subslab (DL43SS) and that the small conference
room was slightly negatively pressurized with regard to the outdoor air (Figure 2-4).
20
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Section 2 - Site-Specific Results and Case Studies
Figure 2-4. Small Conference Room Differential Pressure.
where IA = Indoor Air, SS = Subslab Gas, and OA = Outdoor Air.
Approximately 12 hours of differential pressure data was acquired on November 3 and 4 which
indicated that the map room/library was at times negatively pressurized and at times positively
pressurized with respect to the subslab (DL43SS) (Figure 2-5).
Figure 2-5. Map Room/Library Differential Pressure.
Differential Pressure in Pascals in 10 Minute Intervals
9:30:04 AM 12:30:27 PM 3:30:49 PM 6:31:11PM 9:31:32 PM 12:32:11AM 3:32:31AM 6:32:56 AM
^lACRtoSS ^^lACRtoMR
The pressure differential between the small conference room (DL81BZ) and the subslab
(DL43SS) indicated the presence of a cyclic event. The cyclic event appeared to be influenced by
HVAC usage and changes in the weather. The pressure differential fluctuations are believed to
be directly connected to a preferential migration route and points of entry for vapor intrusion (to
be discussed) measured in the small conference room floor communication conduit pathway
(DL80PP).
21
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Section 2 Site-Specific Results and Case Studies
Figure 2-6. Small Conference Room Pathway TCE/PCE Concentration November 2-3, 2019.
Preferential Pathway (DL80PP) -11/2/19-11/3/19
Non-detect results
represented with open
symbols at 14 the reporting
limit concentration
TCE
aPCE
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o
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O
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CO
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o
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Figure 2-7. Picture of Pathway in Communication Conduit of Small Conference Room.
22
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Section 2 - Site-Specific Results and Case Studies
Figure 2-8. Small Conference Room Pathway TCE and PCE Concentration November 4, 2019.
Preferential Pathway (DL80PP) -11/4/19
160
140
120
~100
E
O)
3 80
c
o
| 60
20
TCE
i PCE
Non-detect results
represented with open
symbols at H the reporting
limit concentration
t i .
i A
Field portable GC/MS data, Figure 2-6, showed elevated PCE and TCE concentrations at the
potential pathway (DL80PP) in the small conference room with a mid-floor communication
conduit vapor entry point (Figure 2-7; probe placed inside communication box with lid closed).
PCE and TCE concentrations declined steadily from 92 and 16 |ig/m3 to 7.2 |ig/m3and non-
detect, respectively, from the afternoon hours on November 2, 2019 (17:14) to early the next
morning (06:37). The concentrations then rebounded during the day around noon time. A sharp
decline in PCE and TCE concentrations after noon on November 4, 2019, was also observed
(Figure 2-8).
The cover on the communication conduit is normally closed (Figure 2-7) but may be open when
the small conference room is in use which would result in elevated PCE vapor intrusion via this
preferential migration route and point of entry. Three grab samples were taken inside the
communication conduit with the field portable GC/MS:
32 |ig/m3PCE on 11/2/2019 at 13:05 with the conduit cover open
39 |ig/m3 PCE on 11/2/2019 at 15:08 with the conduit cover open
ND PCE on 11/4/2019 at 16:07 with the conduit cover closed.
The distinctly higher concentrations of PCE when the conduit cover was open versus closed
indicates that PCE is entering the small conference room via a preferential migration route
associated with the conduit when the conduit is exposed directly to the driving forces associated
with the building's ventilation system operation.
Radon data supports the hypothesis that the communication conduit in the small conference
room is a preferential migration route and vapor entry point. Continuous data were acquired with
23
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Section 2 Site-Specific Results and Case Studies
28-minute duration samples from November 2, 2019 at 18:02 to November 3, 2019 at 09:32
using the professional radon detector. During this time frame, the radon concentrations ranged
from non-detect (<0.1 pCi/L) to 3.79 pCi/L, with a mean of 1.29 pCi/L. No clear temporal
pattern of radon concentrations was discernible.
Field portable GC/MS data showed high PCE concentrations in the storage room with
concentrations of 480 (.ig/m3 in the plenum above the drop ceiling (DL96PP) and 67 ug/m3 in the
janitor closet (DL98PP) connected to the storage room. The TCE concentrations in these samples
were very low (1.1 |ig/m3 above the ceiling jig/nr and <1.1 (ig/m3 in the closet). The TCE:PCE
ratio at DL43SS ranged from 0.18 to 0.38 using field portable GC/MS and TO-15 canister data.
These ratios were similar to the ratios observed in previous years at that same location (RTI,
2020). Therefore, it is suspected that the source of PCE in the storage area was an indoor air
source and not a result of vapor intrusion due to the markedly different TCE:PCE ratio when
compared to the indoor air TCE:PCE ratio of around 0.002. After careful searching, a PCE
indoor air source was located in a small janitor closet off the main storage room. The PCE
containing consumer product was identified as "Sheila Shine" and was removed at
approximately 11:00 on November 3, 2019 (Figure 2-9). It is suspected that this PCE source was
present for several years and may have influenced indoor air PCE concentrations at this building.
Figure 2-9. Indoor Source of PCE.
The overall distribution of PCE and TCE in the building in the time integrated samples (most
TO-15 canisters collected air samples for 8 hours while the passive VOC samplers were
deployed for 2 to 4 days) varied depending on location within the building. The highest
concentrations of PCE were found near the storage room and connected janitor closet (assumed
to be due to the indoor air source) while the highest TCE concentrations were found in the small
conference room. This distributional pattern is indicative of vapor intrusion of TCE in the main
office areas (i.e., conference rooms, cubicle area, offices, break room, and restrooms) and the
indoor source, Sheila Shine, being the dominating PCE source in the storage room and
connecting rooms and hallways of the building.
guarantee
^onornically
24
-------
Section 2 - Site-Specific Results and Case Studies
Figure 2-10. Helium Air Exchange Rate Small Conference Room.
Helium air exchange tracer measurements, via the tracer gas decay method of NBS (1988), were
made on November 3, 2019 yielding an estimated air exchange rate of about 6 exchanges per
hour for the small conference room (Figure 2-10) with the ventilation system operating. Helium
was injected into the room and measurements were taken every 5 minutes over a 25 minute time
period. The result indicated that the ventilation system was working and; thus, capable of
distributing any PCE or TCE entering the building through this preferential migration route and
point of entry to the rest of the building. The possible interaction between the preferential
migration route and ventilation system would need further investigation to test this hypothesis.
The borescope and hot wire anemometer were tested in this building but provided no useful or
supporting evidence of preferential migration routes or points of entry.
Building Summary
Overall, results from seven of the nine techniques employed in this building indicated a
preferential migration route and point of entry in the small conference room via the
communication conduit (Table 2-2). Other preferential migration routes and points of entry may
be present but may have been masked due to the presence of the PCE indoor air source (Sheila
Shine), found in the janitorial closet associated with the storage room, and its potential
distribution throughout the building through the HVAC system. The use of multiple methods and
techniques to assess preferential migration routes of entry allowed vapor intrusion to be properly
identified and not mistakenly dismissed as an indoor source in this building.
25
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Section 2 - Site-Specific Results and Case Studies
Table 2-2. Summary of Techniques Used at SFV1.
Method
Beneficial in
identifying
preferential
migration routes
and points of
entry
Borescope
*
Hot Wire Anemometer
*
Helium Tracer Testing
* * *
Differential Pressure - Discrete or Continuous Mode
**
Consumer Grade Radon Detector
**
Professional Radon Detector
**
Field Portable GC/MS
* * *
TO-15 Canister
**
Passive VOC Sampler
**
* - not used to identify preferential migration route/vapor point of entry, ** - preferential migration route/vapor point of entry indicated and
identified if used in conjunction with other techniques, *** - preferential migration route/vapor point of entry clearly identified.
2.1.2 SFV Building 2
Building Background
This building houses an organizational meeting space and that is normally only occupied a few
hours per week (Figure 2-11). Spaces within the building include: a kitchen, a pool (billiards)
room, restrooms, and a large meeting room. The building was constructed in 2 parts built
adjacent to each other on an approximately 3-foot grade with an internal ramp connecting the
interior spaces. Three rounds of indoor air samples were acquired in 2014 and 2015 prior to the
initiation of the SVE research project. PCE concentrations ranged from 1 to 47 |ig/m3 and TCE
concentrations ranged from less than 1 to 13 |ig/m3.
26
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Section 2 Site-Specific Results and Case Studies
Figure 2-11. SFV Building 2 Sampling Locations.
Meeting Room
SFV Building 2
ULI,rr DL59RR
I * IcfcAflPP
~L12PP Upper Men's
RR
Upper Women's Restroom
DL21PP
Small RR
DL22PP
Lower Men'|
Storage
DL208Z
Kitchen
Initial investigations in 2016 suggested that a complete vapor intrusion pathway was present in
the building but had been substantially reduced by SVE operation (RTI, 2020). Based on results
from late within the SVE research project, indoor air concentrations were expected to be less
than 10 |ag/m3 PCE and less than 1 ug/m3 TCE. Subslab soil gas concentrations were expected to
be approximately 1,000 |ig/m3 PCE and 500 ug/m3 TCE. Field activities at SFV Building 2 were
completed in February and November 2019.
February 2019
Techniques employed at SFV Building 2 in February 2019 included the use of the field portable
GC/MS, passive VOC samplers, and consumer grade radon detectors for a 2-day sample
duration. The field portable GC/MS survey locations throughout the building included: a
restroom sink, electrical panels, coaxial cable outlets/conduits, sewer cleanout, and a restroom
floor drain. At most survey locations, the PCE and TCE concentrations were non-detects.
However, PCE was detected at 0.84 |ig/m3 beneath the kitchen sink and at 12 jig/m3 in the sewer
cleanout. The PCE average concentration of two passive VOC samplers left for 2 days in the
breathing zone of the pool hall and the kitchen was 1.2 fig/in3. Subslab concentrations of TCE
27
-------
Section 2 - Site-Specific Results and Case Studies
were not detected by the field portable GC/MS but elevated PCE concentrations were detected at
a concentration of 2,300 |ig/m3,
November 2019
The elevated PCE concentrations (up to 2,300 |ig/m3 in the subslab) led to further investigation
in November 2019. The additional testing included the use of the field portable GC/MS, TO-15
canisters, helium tracer, borescope, and professional radon detector.
Indoor air concentrations determined by field portable GC/MS were not detected inside the
building for either PCE or TCE. In contrast, PCE and TCE were detected in the subslab using the
field portable GC/MS with concentrations of 830 and 150 |ig/m3, respectively. The subslab
concentration was further tested using the TO-15 canisters with resultant concentrations of 500
|ig/m3 PCE and 90 |ig/m3 TCE supporting the results from the field portable GC/MS. These
subslab concentrations are consistent with the observed dramatic reductions in soil gas
concentrations during the SVE research project and; thus, indicate that only a moderate strength
vapor intrusion source was present during the time of this study.
Employing the professional radon detector, a higher radon concentration (1.7 pCi/L) in an upper
level men's restroom was found when compared to the kitchen on the lower level (0.14 pCi/L).
This result suggests a possible entry point for vapors in the men's restroom. (Note: the upper
level is not a true second floor but rather a 3-ft higher level to the north end of the building.)
Subslab radon concentration was measured at 132 pCi/L.
A helium tracer test was conducted by injecting helium into the subslab port and monitoring for
its entry into the building at suspected vapor entry point locations. The only significant entry
point was detected along the adjoining wall between the upper and lower portions of the
building. However, no PCE or TCE concentrations were detected at the same location so a
preferential migration route is not indicated.
The borescope was tested in this building but provided no useful or supporting evidence of a
preferential migration route or vapor point of entry.
Building Summary
Overall, results from the five of the six techniques employed in this building indicated the
potential for a weak or incomplete pathway (Table 2-3). While concentrations of PCE and TCE
were clearly detected in the subslab gas, their entry into the building along suspected preferential
migration routes was suspect. The use of the potential pathway techniques provided strong
indications that limited vapor intrusion was, if at all, occurring at this time in this building.
28
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Section 2 - Site-Specific Results and Case Studies
Table 2-3. Summary of Techniques Used at SFV 2.
Method
Beneficial in
identifying
preferential
migration routes
and points of
entry
Borescope
*
Helium Tracer Testing
* * *
Professional Radon Detector
**
Field Portable GC/MS
* * *
TO-15 Canister
**
Passive VOC Sampler
**
* - not used to identify preferential migration route/vapor point of entry, ** - preferential migration route/vapor point of entry indicated and
identified if used in conjunction with other techniques, *** - preferential migration route/vapor point of entry clearly identified.
2.1.3 SFV Building 3
Building Background
This building includes a business office and open storage space in part of the former northern
facility (Figure 2-12). The adjacent building that shares a common wall with this building had a
dirt floor only at the time of this study. Three rounds of indoor samples were collected in 2014
and 2015, prior to the initiation of the SVE research project, with resultant PCE concentrations
ranging from 19 to 64 |ig/m3 and TCE ranging from 2 to 15 |ig/m3.
Under this EPA study, investigation activities were completed in February and November 2019.
Crack sealing with fast drying epoxy was tested at this building as a mitigation technique.
29
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Section 2 Site-Specific Results and Case Studies
Figure 2-12. Building SFV 3 Sampling Locations.
i a
1
Office
Restroom 1
DU30RR
Restroom 2
DLB1SS
DL30BZ
Storage Area
I
DLAOSS
DL31PP
DLB2PP
DLB5PP U
DL86PP
DLB3PP
|
|
February 2019
Techniques employed during the research project in February 2019 for the determination of
VQCs included the use of field portable GC/MS, passive VOC samplers, and TO-15 canisters.
Radon concentrations were determined using the consumer grade radon detector for a 2-day
sample duration.
In the open storage space, a concentration of 6.1 ug/nr' PCE was measured in the indoor air by
the field portable GC/MS. At a floor crack in the open storage space (DL31PP), the field portable
GC/MS detected 6,800 |.ig/m3 PCE and 220 (ig/m3TCE. A 2-day passive VOC sampler placed at
the same location (DL31PP) resulted in PCE and TCE concentrations of 21 jag/m3 and 1.3
ug/m3, respectively. An 8-hr TO-15 canister at location DL31PP resulted in concentrations of
1,000 jig/m3 PCE and 50 |ig/m3 TCE. Thus, while these three methods yielded significantly
different results quantitatively, yet higher than the indoor air, all three methods (i.e., field
30
-------
Section 2 - Site-Specific Results and Case Studies
portable GC-MS, passive VOC sampler, and TO-15 canister) clearly indicated that the floor
crack was likely a preferential migration route and point of vapor entry. The differing results
from the three methods may be attributed to the difficulty in perfectly collocating the sampling
inlets, starvation of source concentration, and temporal variability. Peak observed crack
concentrations from both the field portable GC/MS and TO-15 canister were somewhat higher
than had been previously observed (RTI, 2020) or found in this project in November 2019 (to be
discussed). This finding could suggest considerable spatial subslab variability under this building
near the cracks.
Indoor air concentrations of 11 |ig/m3 PCE and 0.8 |ig/m3 TCE were observed with passive VOC
samplers in the restroom indoor air. These values were consistent with the PCE concentration in
the open storage room and from the previous observations in this building.
A consumer grade radon detector result of 1.1 pCi/L was found in the restroom. This value is
consistent with previous readings taken at this building throughout the month. Ambient air radon
concentrations (as determined using the professional radon detector) in this study ranged from
0.15 to 0.44 pCi/L. The elevated radon concentrations in this building may indicate radon gas
intrusion is occurring.
November 2019
In November 2019, in addition to the use of the field portable GC/MS, passive VOC samplers,
and TO-15 canister, discrete and continuous pressure differential testing and helium tracer
testing were conducted. Radon data was collected using the professional radon detector.
To estimate the size and extent of floor slab cracking, in an uncarpeted back portion of the open
storage room, cracks were measured for length and width. The largest observable crack was 14
meters in length, running the observable width of the building, and ranged from 1 to 3
millimeters wide. An estimated total of 220 square centimeters of crack area were observed. To
determine if these cracks were a preferential migration route vapor entry point, EPA staff sealed
them on November 5, 2019 with a quick drying epoxy (Figure 2-13).
31
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Section 2 Site-Specific Results and Case Studies
Figure 2-14. Differential Pressure SS to IA SFV 3, November 5, 2021.
Indoor Main (DL30BZ)
Date: 11/5/2019
Indoor main / South SS
Figure 2-13. Crack Sealing, Building SFV 3.
Differential pressures between the indoor air and subslab were observed (Figure 2-14), with high
time resolution (i.e., one reading every second), for a period of just over an hour on November 5,
2019 at the same time that the crack sealing was being performed. The data indicates periods of
both positive and negative pressurization. Differential pressure data collected under the SVE
research project indicated daily average differential pressures fluctuating around the 0.0 value
which is consistent with these results.
-6.0 >
10:04
10:19 10:33 10:48 11:02 11:16 11:31 11:45
32
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Section 2 - Site-Specific Results and Case Studies
Field portable GC/MS subslab concentrations of PCE were 44 |ig/m3 and 780 |ig/m3. These PCE
concentrations are within the range of concentrations identified during the SVE research project
when the SVE system was turned off in 2018 and 2019 (RTI, 2020). The results of two TO-15
canister samples were 50 |ig/m3 and 600 |ig/m3 PCE indicating similar PCE concentrations.
Field portable GC/MS measurements taken in the indoor air in the open storage area and in the
adjacent bathroom immediately before crack sealing commenced resulted in PCE concentrations
of 1.8 |ig/m3. A five-hour indoor air TO-15 canister sample in the open storage area had a similar
PCE concentration of 2.5 |ig/m3 on the same day.
Multiple field portable GC/MS observations were made by placing the vapor sampling probe on
the floor cracks. Most of the concentrations were similar to those made in the indoor air, but one
of value measured at 11:33 at the major crack (as identified above) sampling location in the open
storage room yielded a value of 110 |ig/m3 PCE. This value is indicative of a vapor point of
entry. A second measurement at the same location taken at 15:09 the same day had a
concentration of 3.1 |ig/m3 PCE suggesting that the sealing had a beneficial effect in reducing
PCE vapor intrusion. A TO-15 canister measurement from the same crack location result of 2.6
|ig/m3 PCE corroborates the field portable GC/MS result.
Testing at a different crack location had similar results to those found from the major crack in the
open storage room crack. At a tri-junction, y-shaped crack, the field portable GC/MS
measurement decreased from 16 |ig/m3PCE at 11:42 to 3.3 |ig/m3 at 15:58. Similarly, at a crack
location at the far west side of the building had PCE concentrations decrease from 6.1 |ig/m3
PCE at 12:01 to <1.4 |ig/m3 at 15:46. A TO-15 canister grab sample (i.e., valve opened with no
flow controller) taken post sealing at an eastern side of the building floor crack had a PCE
concentration of 4.9 |ig/m3.
A short series of indoor air PCE and TCE field portable GC/MS measurements were made at the
same locations on November 5, 2019 just after the completion of the crack sealing. The results
showed a modest degree of temporal variability and somewhat lower PCE concentrations than
had been previously observed. The field portable GC/MS data would not be expected to reflect
the full benefit of the sealing operation since the air at the crack was collected only hours after
the sealant was applied and the building had not had time to come to a new equilibrium
reflecting a new, lower vapor intrusion rate.
The radon data collected between 12:09 and 13:09 on November 5, 2019 with the professional
radon detector suggested a fairly weak (in comparison to other sites nationally) subslab radon
concentration of between 49.8 and 55.6 pCi/L and an indoor air concentration between 0.73 and
0.87 pCi/L.
A helium air exchange tracer test was conducted at this location on November 5, 2019. Helium
was introduced for 13 minutes at 20 L/min, after which the flow rate was increased to 75 L/min
for 7 minutes. The team moved the sampling inlet on the helium detector around the room and
used a fan to circulate air. Samples were taken from two locations (Loci, Loc2) to evaluate the
mixing of the helium. Based on the observed decay after mixing, an air exchange rate of 1.5 per
hour was estimated (Figure 2-15).
33
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Section 2 - Site-Specific Results and Case Studies
Figure 2-15. SFV 3 Air Exchange Rate.
AER by DECAY
7000 |
£ ' l\
1 *
4000
loc2
loci
Time(min)
Building Summary
Overall, results from the techniques tested indicated vapor intrusion was occurring within the
building (Table 2-4). The field portable GC/MS data clearly identified floor cracks as vapor
points of entry. The passive VOC samplers and TO-15 canister data support this identification.
Radon values from either the consumer grade instrument or the professional grade radon detector
indicated that vapor intrusion via preferential migration routes may have been occurring but was
inconclusive.
The identification of the floor slab cracks as vapor entry points was further supported by
examination of the results after the floor cracks were sealed. Post mitigation samples were
collected shortly after sealing and indoor air concentrations had considerable reductions in PCE
concentrations. However, complete confirmation would ideally require post mitigation testing
after the building had time to come to a new equilibrium, the epoxy sealant had fully cured, and
under a variety of different differential pressure conditions.
34
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Section 2 - Site-Specific Results and Case Studies
Table 2-4. Summary of Techniques Used at SFV 3.
Method
Beneficial in
identifying
preferential
migration routes
and points of
entry
Helium Tracer Testing
* * *
Differential Pressure - Discrete or Continuous Mode
**
Consumer Grade Radon Detector
**
Professional Radon Detector
**
Field Portable GC/MS
* * *
TO-15 Canister
**
Passive VOC Sampler
**
* - not used to identify preferential migration route/vapor point of entry, ** - preferential migration route/vapor point of entry indicated and
identified if used in conjunction with other techniques, *** - preferential migration route/vapor point of entry clearly identified.
2.1.4 SFV Building 4
Building Background
SFV 4 is a one-story office building with an interior partial second floor. Spaces investigated
included a cubicle area, supply room, electrical room, and utility closet. Prior to the initiation of
the SVE research project, samples collected of indoor air in January 2014 showed little evidence
of vapor intrusion. In contrast, indoor air samples collected in January 2015 had concentrations
of PCE between 6.9 and 7.3 |ig/m3. A long-term dataset had been acquired in this building in the
second phase of the SVE research project with monitoring at multiple subslab and indoor air
locations. Field study activities were completed in February and November 2019 focusing on the
same two general areas of the building (i.e., the utility closet and the cubicle area). Sampling
locations for SFV 4 are presented in Figure 2-16.
35
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Section 2 Site-Specific Results and Case Studies
Figure 2-16. Building SFV 4 Sampling Locations.
North Offices
SFV Building 4
Cubicle Area
Breakroom
DL08PP
Rest room B
DLA2PP
Restroom A
DLA6SS
OL3QPP Supply Closet d^vspp
~~DL09PP^ DL32SS
DL27PP
Utility
Closet DL64B2
DL33S5
South Offices
Reception
DL07PP
Electrical
Room
DLA3PP
February 2019
Techniques employed during the research project in February 2019 for the determination of
VOCs included the use of field portable GC/MS, passive VOC samplers, and TO-15 canisters.
Radon concentrations were determined using the consumer grade radon detector for a 2-day
sample duration. Differential pressure measurements were made between the indoor air and
within two open pipes in the utility closet and the indoor air in the cubicle area just outside the
utility closet.
Differential pressures measured between the two open pipes and utility closet open space, and
the indoor air in the cubicle area (Figure 2-17) had small pressure differences (i.e., low driving
forces) with spikes swinging between positive and negative pressures which could indicate the
influence of opening and closing exterior building doors.
36
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Section 2 - Site-Specific Results and Case Studies
Figure 2-17. Differential Pressure Pathway to IA SFV 4, February 2021.
Under Stairs (DL26PP, DL27PRDL09PP)
Small Pipe Under Stairs to Indoor
Large Pipe Under Stairs to Indoor
Under Stairs to Indoor
2/12/19 12:00
2/13/19 0:00
2/13/19 12:00
2/14/19 0:00
2/14/19 12:00
A PCE concentration of 1,700 |ig/m3 was found with the field portable GC/MS at subslab
(DL32SS) location in the utility closet This concentration is consistent with the concentration
range observed in the previous sampling period (RTI 2020). Two potentially significant
preferential migration routes and vapor entry points were identified with the field portable
GC/MS in the utility closet. The utility closet had two open pipes (presumed to be electrical or
communication conduits) that penetrated the slab and had visible cracks in the concrete near and
around a subslab vapor port. A maximum PCE concentration in the indoor air of the utility closet
was observed with field portable GC/MS of 53 |ig/m3.
To further investigate the potential vapor entry points in the utility closet, an approximately 12
hours of continuous field portable GC/MS data were acquired from the utility closet location
overnight from February 13 to February 14, 2019 (Figure 2-18).
37
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Section 2 - Site-Specific Results and Case Studies
Figure 2-18. Building SFV 4 Overnight Data, February 2021.
30
25
20
o>
C
o
TO
¦£ 15
o
c
o
O
10
5
0
2/13/19 12:00 2/13/19 18:00 2/14/19 0:00 2/14/196:00
The dataset showed a substantial increase in PCE concentrations that began around 22:00 hours
on February 13, 2019, which is potentially an indication that concentrations are elevated after
business hours and that a preferential migration route existed. Passive 2-day VOC sampler
results had PCE concentrations of 7.6 |ig/m3 in the utility closet.
With the identification of elevated PCE concentrations in the utility closet, mitigation was
performed in August 2019. The subslab vapor port, installed during the SVE research project,
had become loose and was replaced. Additionally, backer rods and caulking were used to seal the
visible floor cracks on the concrete floor and the two open pipes were sealed with an expanding
sealant foam.
November 2019
Further investigation at SFV 4 in November 2019 consisted of continuous pressure differential
testing; field portable GC/MS measurements; passive VOC samplers; TO-15 canister sampling;
radon measurement using both the consumer grade radon and the professional radon detectors;
and helium air exchange tracer testing.
Differential pressure data shows that the cubicle area indoor air was negatively pressurized in
November 2019 by between 1.5 and 4.6 Pa in comparison to the subslab in the utility closet
(Figure 2-19). The supply room was also negatively pressurized relative to the subslab
(DLA6SS); typically, by one to three pascals. Negative pressure differentials in relation to the
subslab were also identified in the electrical room. Near neutral pressure differentials were
identified between the cubicle area, supply room, and electrical room. The negative differential
pressures in relation to the subslab at all tested locations and the near neutral differential
pressures in relation from the same locations to the cubicle indoor air indicate that a driving force
was present from subslab to interior of the building during the November 2019 testing period.
Preferential Pathway Understair Closet (DL09PP)
Non-detect results represented
with open symbols at the reporting
limit concentration
A PCE
~
~ A A
~
A A
A A
A
A
~
~
A
~ ~
k A
A
38
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Section 2 - Site-Specific Results and Case Studies
Figure 2-19. Differential SS to IA SFV 4, November 2019.
Under Stairs (DL64BZ)
03
Q_
<1)
:5
to
V)
a)
£
c
it
6.0
3.0
0.0
-3.0
-6.0
Date: 11/4/2019
-Wilson Indoor to Under stairs Subslab
^ j.
I
11
1
10:59 11:02 11:05 11:08 11:11 11:13 11:16 11:19
Two-day passive VOC samples were collected in the utility closet, supply room, and electrical
closet, as well as the cubicle area. Results showed all concentrations were similar to the outdoor
air samples indicating that vapor intrusion was not significant during the November 2019
sampling period. This result also suggests the effectiveness of the August 2019 sealing work in
the utility room, although temporal variability cannot be ruled out without multiple rounds of
testing.
In conjunction with sampling the passive VOC samplers, indoor air samples were measured with
the field portable GC/MS. Results for PCE and TCE concentrations were non-detect at the floor
gap, water heater seam, and at sealed crack and pipe locations in the utility closet indicating no
vapor intrusion was occurring at these locations, in contrast to the February 2019 results. In the
electrical room, PCE and TCE concentrations at or below the analytical reporting limit were
observed at a wall conduit and around a subslab port indicating a lack of vapor entry points in
this room. The field portable GC/MS data coupled with the differential pressure measurements
observed suggests a beneficial impact from the sealing effort. For example, the maximum PCE
concentration in the utility closet (DL09PP) in February 2019 was 53 |ig/m3 yet in November
2019, no PCE was detected.
Subslab soil gas PCE concentrations ranged from 70 to 500 |ig/m3 using TO-15 canister samples.
This concentration range is consistent with previous data collected during the SVE research
project. This finding suggests residual PCE subslab gas concentrations still remain.
Two-day radon concentrations using the consumer radon detector in the utility closet were
identical (1.2 pCi/L) in both February 2019 and November 2019, suggesting that the sealing
activities had little to no effect on radon concentrations or that the source of the radon in this
room is from the bricks or aggregate used in the floors or water heater platform's concrete.
A helium air exchange rate of approximately six exchanges per hour was estimated in November
2019; however, air mixing was incomplete, so this value has considerable uncertainty.
39
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Section 2 - Site-Specific Results and Case Studies
Building Summary
Overall, results from the techniques tested indicated vapor intrusion was occurring in the
building in February 2019, especially in the utility closet (Table 2-5). The field portable GC/MS,
passive VOC sampler, and TO-15 canister data support this conclusion. Radon detection and
performing helium air exchange tracer testing did not provide a definitive answer on the
existence of a preferential migration route or vapor entry point, in general. Post mitigation
sample results from the utility closet demonstrated effective reductions in PCE concentrations.
The combined evidence of persistent PCE and TCE subslab soil gas concentrations; an advective
driving force; and low to non-detect indoor air concentrations in November 2019 suggests that
the sealing performed was effective in reducing and minimizing vapor entry into SFV 4.
Table 2-5. Summary of Techniques Used at SFV 4.
Method
Beneficial in
identifying
preferential
migration routes
and points of
entry
Helium Tracer Testing
* * *
Differential Pressure - Discrete or Continuous Mode
**
Consumer Grade Radon Detector
**
Professional Radon Detector
**
Field Portable GC/MS
* * *
TO-15 Canister
**
Passive VOC Sampler
**
* - not used to identify preferential migration route/vapor point of entry, ** - preferential migration route/vapor point of entry indicated and
identified if used in conjunction with other techniques, *** - preferential migration route/vapor point of entry clearly identified.
2.2 Moffett Field
Three buildings were studied at Moffett Field (MF), namely, buildings 3, 45, and 126.
2.2.1 MF Building 3
Building Background
This building consists of a conference center; meeting rooms; cafe dining room/bar; kitchen;
several smaller offices/storage rooms; public and kitchen employee restrooms; and a locker
room. The building is approximately 25,000 square feet (CES, 2020). The kitchen is large with
several areas with grill surfaces and large vent hoods overhead. The building has an unoccupied
crawlspace with a raised wooden floor and wooden walls in the northeastern part of the structure
The western portion of the building is slab on-grade construction. In previous studies, indoor air
concentrations above EPA commercial indoor air cleanup level for Moffett Field of 5 |ig/m3 for
TCE were identified in the room 130; indoor air at several potential pathway locations in 2012
and 2016; and in the indoor air of room 108 in 2018. An exceedance of EPA commercial indoor
air screening level of 2 |ig/m3 for PCE was identified in room 130 in 2019 (NAVFAC, 2019).
40
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Section 2 Site-Specific Results and Case Studies
Previous studies identified potential preferential migration routes and points of entry including
floor drains in rooms 126 and 110 (kitchen); restrooms and the janitor closets; electrical conduits
in the northeastern corner of room 110 and 112; and phone line conduits that penetrate the floor
in room 130 (communication room) (NAVFAC, 2019). Figure 2-20 depicts the portion of
Building 3 evaluated in this research effort.
Retrofitting of a floor drain was tested at Building 3 as a simple, easily implementable mitigation
technique. Mitigation including closing preferential migration route and vapor entry points with
seals and plugs, submembrane depressurization in the crawlspace areas on the eastern half of the
building and subslab depressurization in the western half of the building are planned but have not
yet been performed as of August 2021.
Figure 2-20. Moffett Building 3 Sampling Locations.
Field Activities Summary
Field activities and the techniques used to identify preferential migration routes and vapor entry
points were as follows:
February 24, 2019 to March 12, 2019: TO-15 canisters, passive VOC samplers; field
portable cavity ring down spectrometer; discrete and continuous pressure; hot wire
anemometer; consumer grade radon detector; and professional radon detector.
May 6 to May 9, 2019: TO-15 canisters, passive VOC samplers; field portable GC/MS
analysis, discrete and continuous pressure, and hot wire anemometer
41
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Section 2 - Site-Specific Results and Case Studies
July 2019: consumer grade radon detector
Sept 17 to Sept 26, 2019: passive VOC samplers, field portable GC/MS; discrete and
continuous pressure measurements; FLIR camera; helium tracer air exchange tracer
testing; consumer grade radon detector; and professional radon detector
December 2019: consumer grade radon detector
January 2020: consumer grade radon detector.
After preliminary screening and testing at Building 3, the project team focused on the kitchen
and associated employee restroom areas. The kitchen employee restroom area consisted of a
locker room and restroom separated by a door.
Pressure Differential and Flow Measurements
Continuous pressure measurements in May and September 2019 indicated that the restroom was
approximately 60 pascals negatively pressurized relative to the locker room (Figure 2-21) when
the restroom door was closed. The restroom was strongly negatively pressured (approximately -
80 pascals) in comparison to the subslab port indicating a strong driving force for vapor intrusion
into the restroom existed.
Figure 2-21. Differential Pressure Moffett Building 3 Restroom, May 2019.
20
0
aT
-20
CD
03
C
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Section 2 - Site-Specific Results and Case Studies
Figure 2-22. Differential Pressure Moffett Building 3 Locker room, September 2019.
80
60
nT
i 40
0)
3
(/>
ffl
£ 20
(TJ
C
-------
Section 2 Site-Specific Results and Case Studies
Figure 2-23 Discrete Pressure Testing in May 2019.
Subslab Flow Velocity into Locker Room m/s
Hall door open RR door closed
3 Both doors open
Hall door closed
Pressure indoor/subslab Pa
RR door open
Both doors closed i
-0.4 -0.2 0
0.2 0.4 0.6 0.8
Simultaneous with differential pressure monitoring, consistent air velocities of outdoor air
flowing into the cafe of 2 to 2.7 m/s were measured with the hot wire anemometer. For
comparison, typical velocity values in indoor air are below 0.3 m/s (Aswegan and Pich, 2014).
Airflows below 0.75 m/s are often specified for fire protection (Gai and Cancelliere, 2017).
Airflow was also measured from an electrical outlet into the cafe with the detectable velocities
ranging between 0.35 and 2.7 m/s.
The air flow rate into the building and the differential pressure measured between the subslab
and the locker room indoor air were found to be sensitive to the opening and closing of the doors
between the locker room and bathroom and between the locker room and hallway. Similarly,
sensitivity to flow path alteration was also found in the cafe where the opening of the roll-up
food service window between the cafe and the kitchen and the opening of the cafe doors for
business hours significantly impacted the vapor intrusion driving forces (Figure 2-24). When the
cafe opened its doors for business around 09:30, marked changes in pressure differential were
seen with a greater driving force moving outdoor air into the cafe.
Figure 2-24. Differential Pressure Moffett Building 3 Cafe, March 2019.
Cafe (MF07OA, MF13PP)
30
MF B3 Outdoor air to Indoor Cafe
-MF B3 Electrical Outlet Path to Indoor Cafe
Date: 3/8/2019
8:09
8:38
9:07
9:36
10:04
10:33
44
-------
Section 2 - Site-Specific Results and Case Studies
VOC Analysis with Field Portable GC/MS
Field portable GC/MS measurements showed substantial temporal variability in the cafe patio
subslab (MF16SS) with TCE concentrations ranging from 350 |ig/m3 TCE in May 2019 to
10,000 |ig/m3 TCE in September 2019. A May TO-15 canister sample at the same location
reported 1,400 |ig/m3 TCE; well within the range of concentrations determined by the field
portable GC/MS.
"Subslab" concentrations, in this case drawing air from the crawlspace air, were much lower in
the space bar2 (MF18SS) with values ranging from 17 to 19 |ig/m3 TCE, as measured by field
portable GC/MS, in May 2019 and September 2019. A TO-15 canister result from May 2019 had
30 |ig/m3 TCE.
TCE concentrations measured by the field portable GC/MS were more significant in the subslab
air under the locker room (MF17SS) with concentrations ranging from 1,400 |ig/m3 in May 2019
to 3,400 |ig/m3 in September 2019. A May 2019 TO-15 canister sample from the same subslab
port (MF17SS) in the locker room had a TCE concentration of 1,200 |ig/m3 which is consistent
with the field portable GC/MS results.
Three discrete measurements were made with the field portable GC/MS in the restroom indoor
air on May 6, 2019 and resulted in PCE not being detected while TCE concentrations ranged
between 15 and 22 |ig/m3. A long-term continuous record (i.e., the field portable GC/MS set to
continuously take measurements with air sampling probe left in one location) of TCE and PCE
concentrations was acquired using the field portable GC/MS in the restroom on September 23
and 24, 2019. TCE was detected at concentrations up to 5 |ig/m3 in the indoor air and PCE was
not detected. A September 2019 seven-day passive VOC sample from the restroom indoor air
had concentrations of 5.6 |ig/m3 TCE and <0.18 |ig/m3 PCE. A September 2019 six hour TO-15
canister sample from the restroom had concentrations of 3.9 |ig/m3 TCE and <0.17 |ig/m3 PCE.
Thus, the three techniques used in September 2019 had broadly consistent concentrations despite
significantly different sample durations.
TCE concentrations were similar in the indoor air of the adjacent locker room. A TO-15 canister
sample had a TCE concentration of 3.2 |ig/m3 in May 2019 while the three-day passive VOC
sample had a concentration of 0.97 |ig/m3. At the same location, a seven-day and three-day
passive VOC sample collected in September 2019 had TCE concentrations of 2.6 and 4.3 |ig/m3,
respectively.
VOC data was significantly impacted by the change in driving forces in the kitchen and cafe
area. The field portable GC/MS detected high TCE concentrations in some vapor points of entry.
For example, high TCE concentrations ranging between 3,100 and 3,300 |ig/m3 at the restroom
floor drain face plate in May 2019; however, other samples taken at the same location in the
same month a few days later had no detectable TCE. Similar concentrations of 2,200 |ig/m3 were
observed a few days later after the non-detects when the restroom door was closed essentially
maximizing the pressure differential between the subsurface and indoor air.
Distinctly lower concentrations (26 |ig/m3) were observed in September 2019 with the floor
drain temporarily sealed off with duct tape, a concentration of 70 |ig/m3 TCE was obtained near
the room 120 restroom floor drain in February 2019 in a TO-15 canister sample. Lower TCE
2 The term space bar was used to describe an area for eating/drinking with a decorative theme related to space travel.
45
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Section 2 - Site-Specific Results and Case Studies
concentrations at this floor drain were also observable using passive VOC samplers set up near
the floor drain which had 34 |ig/m3 in both a 5-day and 11-day duration samples collected in
March 2019. When TCE concentrations were measured after installation of the retrofit floor
drain valve using the field portable GC/MS, concentrations dropped from 2100 |ig/m3 to 26
|ig/m3 clearly indicating that the floor drain was a vapor entry point at this location.
Other nearby potential preferential migration routes and points of entry were observed in May
2019 with the field portable GC/MS. A restroom wall opening where the drainpipe went through
the tiled wall and plumbing chase had TCE concentrations of 57 and 39 |ig/m3, respectively.
TCE concentrations in the indoor air were generally lower further away from the restroom within
the building. Across the hall from the restroom area, field portable GC/MS concentrations in
September 2019 were <1.1 |ig/m3 TCE in room 115 and 0.35 |ig/m3 in room 115E. Additionally,
a TO-15 canister sample in the kitchen and cafe room 108 had 0.55 |ig/m3 TCE in May 2019 and
a TO-15 canister sample in the cafe room 108 had 0.4 |ig/m3 TCE in September 2019. However,
a second vapor point of entry was evident in the space bar indoor air as indicated by a
measurement of 5.1 |ig/m3 TCE by the field portable GC/MS in September 2019 and 71 |ig/m3
TCE at an electrical outlet in the space bar on the same day. Two additional outlets in the space
bar area had elevated TCE concentrations of 6.7 to 9.6 |ig/m3. Interestingly, when continuous
monitoring at the space bar outlet (i.e., a potential preferential migration route location MF13PP)
on September 26, 2019, TCE and PCE concentrations were consistently below detection limits.
Field Portable Thermal Desorption Cavity Ring Down Spectrometer
Building 3 was also the only building in the study where a field portable cavity ring down
spectrometer (CRDS) instrument was used to determine TCE in February 2019. The restroom
floor drain concentrations observed ranged from 99 to 139 |ig/m3 TCE. While these
concentrations were lower than concentrations observed with other instruments, these results
would have been sufficient to highlight the drain as a potential preferential migration route. Only
two indoor air samples were collected with results of 1.4 |ig/m3 in the cafe and 14 |ig/m3 TCE in
the space bar. These concentrations were broadly consistent with those observed using the field
portable GC/MS. A concentration of 12 |ig/m3 TCE was found at one of the space bar electrical
outlets indicating the same potential point of vapor entry as indicated by the field portable
GC/MS. A 11.4 |ig/m3 TCE concentration was found in a kitchen floor drain and was found to be
comparable to a 3.9 |ig/m3 TCE concentration found with the field portable GC/MS at the same
location in September 2019. These results illustrate the utility of this instrument in identifying
potential preferential migration routes and points of vapor entry. Broadly, although the work was
done in different months and noting the field portable CRDS data set is considerably smaller
than that of the field portable GC/MS, it appears that both instruments have identified the same
preferential migration routes and vapor entry points.
Helium Air Exchange Rate Determination
Air exchange rates were estimated using constant supply helium with the following results:
20 air exchanges per hour for the restroom with the hall and restroom doors closed
15 air exchanges per hour for the locker room/restroom (room 120) with the locker room
to restroom door open but the locker room to hall door closed.
46
-------
Section 2 Site-Specific Results and Case Studies
Figure 2-25. Helium Injection into Cleanout in Moffett Building 3.
Helium Tracer Testing
Helium was used to trace a potential preferential vapor migration route in the kitchen (Figure 2-
25). Helium was injected at the sewer cleanout outside the building and searched for with the
helium leak detector inside the kitchen. As a result of the helium tracer testing, leaking pipes
were clearly identified below the kitchen sink. Further helium tracer testing was conducted by
injecting helium into the subslab port in the locker room in an attempt to determine other
potential points of entry and if the preferential migration route near the kitchen sink was
continuous throughout other areas of the building. Upon helium injection, a potential preferential
migration route to the old cold room (115E) wall was also identified.
The restroom floor drain after mitigation by retrofitting with a drain plug showed no helium
detections, qualitatively indicating a good seal.
Radon Measurements
Radon indoor concentrations were measured using the consumer grade radon detector for one or
more seven-day periods at four locations in Building 3: cafe room 108, restroom, space bar, and
kitchen locker room (room 120). All results were less than 1 pCi/L. Since site-specific
comparison ambient air data were not acquired and these concentrations are within the range of
47
-------
Section 2 - Site-Specific Results and Case Studies
typical ambient concentrations in the United States, the use of consumer grade radon detectors is
questionable for the identification of potential preferential migration routes at this building.
However, for contemporaneous samples, the space bar location is consistently lower than cafe
room and the locker room. Due to these differences within Building 3, it may be interpolated that
the cafe room and locker room are probably experiencing some level of vapor intrusion as the
average radon concentrations were above the highest ambient air radon concentration of 0.44
pCi/L found in the study area. Though there are limited contemporaneous data collection rounds,
the restroom had the higher average radon concentration than the spacebar although lower than
the locker room. The two and seven-day radon data are summarized in Table 2-2.
Table 2-6. Moffett Building 3 Indoor Air Radon Data Measured by Consumer Grade Radon
Detectors.
Location
Sample
Duration
(Days)
Number of
Samples
Average
Result
(pCi/L)
Maximum
Result
(pCi/L)
Building 3 Kitchen
2
2
0.45
0.5
Building 3 Locker Room
2
9
0.62
1
7
9
0.8
0.9
Building 3 Restroom
2
8
0.46
0.7
7
7
0.54
0.6
Building 3 Cafe room
2
1
0.4
0.4
7
1
0.7
0.7
Building 3 Space Bar
2
4
0.2
0.4
7
3
0.3
0.4
Subslab radon data acquired with the professional radon detector were relatively consistent
across all three buildings at Moffett Field, showing radon concentrations in subslab soil gas
between 100 and 200 pCi/L). The subslab radon soil source strength that should produce clearly
discernable elevated indoor aid radon concentrations if vapor intrusion was occurring.
FLIR Camera
The consumer grade FLIR camera was used to observe various potential vapor entry points in
Building 3 over several visits. Most vapor entry points could not be identified with the FLIR
camera. However, some locations, such as the baseboard of the cafe/space bar wall where TCE
entry had been previously observed (Figure 2-26), did show temperature gradients consistent
with vapor entry.
48
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Section 2 Site-Specific Results and Case Studies
Figure 2-26. FLIR Picture of Temperature Gradient Cafe Wall.
Building Summary
Overall, results from the techniques tested indicated vapor intrusion was occurring in Building 3,
with vapor points of entry identified in the restroom, locker room, and space bar (Table 2-7).
The field portable GC/MS, passive VOC sampler, TO-15 canister, and CRDS data support this
conclusion. Pressure differential monitoring clearly showed that strong driving forces were
present in the restroom and locker room between the subslab and indoor air. Helium tracer
testing identified several preferential migration routes and the use of the FLIR camera
occasionally identified a possible vapor point of entiy. Radon detectors did not identify potential
preferential migration routes or points of entry but did provide some indication of where vapor
intrusion was more likely to occur in the building.
Building 3 demonstrated that exhaust ventilation conditions, as found in the kitchen and
restroom, can cause driving forces that can significantly impact vapor intrusion via preferential
migration routes and points of entry. The opening and closing of doors, depending upon location,
had marked effects on pressure differentials and TCE concentrations between the restroom,
locker room, and adjoining hallway.
The vapor intrusion mitigation effectiveness of retrofitting the restroom floor drain was
demonstrated through TO-15 canister and passive TO-17 sampler analysis, and helium tracer
testing.
49
-------
Section 2 - Site-Specific Results and Case Studies
Table 2-7. Summary of Techniques Used at MF 3.
Method
Beneficial in
identifying
preferential
migration routes
and points of
entry
FLIR Camera
*
Hot Wire Anemometer
*
Helium Tracer Testing
* * *
Differential Pressure - Discrete or Continuous Mode
**
Consumer Grade Radon Detector
**
Professional Radon Detector
**
Field Portable GC/MS
* * *
Field Portable CRDS
* * *
TO-15 Canister
**
Passive VOC Sampler
**
* - not used to identify preferential migration route/vapor point of entry, ** - preferential migration route/vapor point of entry indicated and
identified if used in conjunction with other techniques, *** - preferential migration route/vapor point of entry clearly identified.
2.2.2 MF Building 45
Building Background
Building 45 is an approximately 9,000 square foot (SF), structure used primarily for technology
testing. The main portion of the building, approximately 7,500 SF, is a large, open area with over
20-foot high ceilings (Figure 2-27). The remainder of the building consists of a one-story
support section with restrooms and storage areas. At the time of the research effort, building 45
was used several days per month for short durations (2 to 4 hours). The building does not have a
working ventilation system and there is limited passive and exhaust ventilation, such as through
open windows and restroom fans. However, the interior height of the building allows for
significant vertical mixing. Potential preferential migration routes and vapor entry points in the
forms of visible cracks and seams in the concrete floor slab, electrical conduits, a utility corridor
trench, and a sump were identified (NAVFAC, 2019). The sump was reported as 6 feet deep
(CES, 2020). The corridor trench traverses the building from east to west with an estimated
depth of 2 feet (Figure 2-28). Indoor air field screening results conducted prior to the initiation
of the research project had PCE detections >2 |ig/m3 in 2016 and 2017 and TCE >5 |ig/m3 in
2016 (CES, 2020).
50
-------
Section 2 Site-Specific Results and Case Studies
Ventilation System Room 107A
Moffett Building 45
MF61PP
MF48PP
MF51SS
Open Area
Room 103
Figure 2-27. Moffett Building 45 Sampling Locations.
Interim vapor mitigation measures to reduce potential vapor pathways at Building 45 were
initiated in September and October 2019. "These interim measures included sealing of accessible
cracks andjoints in the concrete andfilling an open vault on the east side of Room 101 at
Building 45 with CLSM (controlled low strength material). A total of 85 linear feet of cracks or
expansion joints were sealed within the building. SikaFlex 1A sealant was used to seal cracks or
seams larger than % inch and Sikadur ("racklux was used to seal cracks smaller than ' v inch.
Some cracks within the building were not sealed because they were inaccessible due to floor
coverings or other equipment that could not be moved. " (CES, 2020). Crack and joint sealing
was completed around September 26, 2019.
51
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Section 2 Site-Specific Results and Case Studies
Figure 2-28. Picture Building 45 Pathways.
Investigation activities in Building 45 were completed in May and September 2019 and follow-
up radon results were collected using the consumer grade radon detector for two- and seven-day
periods in January 2020.
May 2019
Techniques used in May 2019 consisted of the field portable GC/MS, passive VOC samplers,
consumer grade radon detector for a two-day sample duration, and discrete differential pressure.
Field portable GC/MS measurements indicated TCE concentrations of 1,600 ag/nr' in the
subslab, 150 Lig/nr1 near a fire riser along the east wall, 47 jig/nr' at a sewer vault outside the
building, and 13 ag/nr' at a middle wall electrical conduit. These results suggest that there are
multiple potential vapor migration routes and points of entry.
TCE concentrations in 3-day passive sampling indoor air ranged from 2.0 to 3.1 jig/m3. Ambient
outdoor air had non-detectable TCE concentrations.
The radon detector and differential pressure measurements did not provide discernible
information in identifying preferential migration routes or points of entiy in this building.
September 2019
Elevated TCE concentrations (observed in May) in the trench preferential migration route led to
further investigation in September 2019, consisting of discrete pressure differential testing, field
portable GC/MS, passive VOC samplers, and TO-15 canisters, and radon monitoring using the
professional radon detector.
A field portable GC/MS concentration of 20,000 ug/rrf TCE was found in the subslab which was
significantly higher than the TCE result in May 2019. This finding confirmed that the trench was
a preferential migration route. Field portable GC/MS was used to analyze a number of locations
repeatedly before sealing on September 23, 2019, while sealing was ongoing, and immediately
thereafter on September 26,2019 (Table 2-3). However, the post-sealing mitigation sample data
does not provide consistent evidence of the crack and joint sealing effectiveness.
52
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Section 2 - Site-Specific Results and Case Studies
Table 2-8. TCE concentrations (In jig/nr*), during, and after sealing in Building 45 using the field
portable GC/MS.
Location
May 6, 2019
Before Sealing
Sept 23, 2019
Before Sealing
Sept 26, 2019
After or During Sealing
Trench Center Wall
31
7.9
Floor Grate Center Wall
<11
9.2
2.4-3.2
Trench East
<11
11
Floor hole center
<11
9.2
Storage room NW floor pipe
<11
<1.1
Sealed trench seam
3.3
15
TO-15 canister samples collected September 23, 2019 had indoor air concentrations at three
locations in the building of between 0.7 and 1.1 |ig/m3 TCE. A TO-15 canister sample at the
trench center had no detectable TCE.
Subslab radon concentrations of 201.3 and 196.4 pCi/L were reported in September 2019 from
MF51SS.
The passive VOC sampler and differential pressure results did not provide discernible
information indicative of preferential migration routes or points of entry in this building.
January 2020
Radon concentrations of 0.7 p Ci/L over 7 days and 0.3 pCi/L over 2 days were measured on
January 21, 2020 in southeast portion of the open room. These results were comparable to the
two-day pre-mitigation sample analyzed on May 9, 2019 that had a radon concentration of 0.8
pCi/L. It should be noted that this data set is insufficiently robust to permit a conclusion about
the mitigation sealing's effectiveness.
Building Summary
Overall, the field portable GC/MS results indicated multiple points of vapor intrusion entry were
present in the building (Table 2-9). The TO-15 canister, passive VOC sampler, and differential
pressure, and radon data did not provide conclusive evidence of preferential migration routes and
points of entry.
53
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Section 2 - Site-Specific Results and Case Studies
Table 2-9. Summary of Techniques Used at MF 45.
Method
Beneficial in
identifying
preferential
migration routes
and points of
entry
Differential Pressure - Discrete or Continuous Mode
**
Consumer Grade Radon Detector
**
Professional Radon Detector
**
Field Portable GC/MS
* * *
TO-15 Canister
**
Passive VOC Sampler
**
* - not used to identify preferential migration route/vapor point of entry, ** - preferential migration route/vapor point of entry indicated and
identified if used in conjunction with other techniques, *** - preferential migration route/vapor point of entry clearly identified.
Installation of a subslab depressurization system is planned for this building.
2.2.3 MF Building 126
Building Background
Building 126 is an approximately 13,000 SF, one-story structure. The building consists of three
adjoined hangar buildings with an addition on the north side. The interior of the building consists
of several large open-air rooms with museum displays, a back room with a train display, two
restrooms, and a janitor closet. The back room and restroom addition may have been added after
original building construction and is about six inches above the grade of the original structure. A
narrow utility corridor runs between the addition and the main building. The building has a
concrete slab floor, some exposed and some carpeted, with visible expansion joints. Floor drains
are present in the restrooms (rooms 104 and 105) and there is a sink drain in the janitor closet.
The sampling locations and building layout are depicted in Figures 2-29 and 2-30.
54
-------
Section 2 Site-Specific Results and Case Studies
Figure 2-29. Moffett Building 126 Sampling Locations.
East Utility Corridor
East Utility Corridor
MF38PP
Train Room 106
MF33SS West Utility Corridor
MF71PP
Main Area Room 103
Mf 7-oBZ
Museum Room 102
MF74BZ M
Office (103)
Break Room
Museum and Workshop Room 101
55
-------
Section 2 Site-Specific Results and Case Studies
Figure 2-30. Moffett Building 126 Study Area Sampling Locations.
In spring 2012, a new HVAC system was installed in the building. A radiant heat system is used
in the building for heating purposes with a mechanical dispersion system. Indoor air samples
collected in 2014, had exceedances above the EPA commercial indoor air screening level for
Moffett Field of 2 ug/nr for PCE with the HVAC system both on and off and a TCE exceedance
in one sample with the HVAC system on. PCE exceedances were also observed in 2016 (CES
2020). The HVAC system was modified in 2017 and NAVFAC (2019) noted lower indoor air
concentrations the following year. However, PCE concentrations exceeded the screening level in
February 2019, both with FIVAC system on and off (CES, 2020).
Field Activities Summary
Field investigation studies were completed in May and September 2019. Techniques tested
included: field portable GC/MS, passive VOC samplers, TO-15 canisters, discrete and
continuous pressure differential data, helium tracer testing, and radon monitoring using the
professional radon detector.
The September 2019 field observations for this project were taken during a period when
mitigation measures were being implemented. CES (2020) states that they: "implemented interim
vapor mitigation measures to reduce potential vapor pathways at Building 126 in September and
October 2019. These interim measures included sealing of accessible cracks andjoints in the
concrete, plugging floor drains in Rooms 104 and 105, and filling the sump and vault in the
utility room at the northwest corner of Building 126 with CLSM. A total of475 linear feet of
cracks or seams were sealed within the building. SikaFlex 1A sealant was used to seal cracks or
seams larger than fS inch and Sikadur ("racklux was used to seal cracks smaller than ' v inch.
Some cracks within the building were not sealed because they were inaccessible due to floor
coverings or larger museum exhibits that could not be moved. Floor drains in Rooms 104 and
105 were sealed using Dranjer1'1 retrofit valves which seal vapors yet allow continued flow of
water down through the drain pathway...." Crack sealing was ongoing on September 24 and 29,
2019 coinciding with this research effort's September sampling period.
56
-------
Section 2 - Site-Specific Results and Case Studies
Pressure Differential and Flow Measurements
In May 2019, continuous differential pressure measurements between restrooms 104 and 105 and
the outdoor air and/or subslab indicated that the restroom pressure differentials were impacted by
diurnal changes in weather and ventilation (Figure 2-31). The pressure differential between the
restroom 105 and the outdoor air (i.e., the blue line) indicates a positive differential pressure in
which air will flow from the restroom towards the outdoor air. The pressure differential between
restroom 105 and the subslab (i.e., the red line) is negative indicating movement of air from the
subslab into the restroom. When taken together, the air flow is from the subslab, through the
restroom, to the outdoor air. During the afternoon of testing, the pattern of restroom to outdoor
air differential pressures was quite variable due to a strong wind load on the building that day.
Once the building closed down for the night (estimated at about 19:00) and the HVAC system
shut off, the pressure differentials greatly decreased between the restroom and outdoor air or
sublab.
Figure 2-
20
15
CL
CL
ro
c 5
CD
il
Q
0
-5
12
Continuous differential pressure measurements in May 7-8, 2019 between restroom 104 and the
outdoor air showed similar diurnal patterns with pressure swings from negative to positive
frequently due to wind events (which are more evident in the higher resolution pressure
monitoring presented in Figure 2-32).
31. Moffett Building 126 West Restroom (105) Pressure, May 2019.
West Restroom (MF19RR)
Date: 5/8/2019 to 5/9/2019
MF B126 West RR to Outdoor Air
MF B126 West RR to Subslab
I l
III
II
lilJLi
ll
P
flpl
p
:00 14:24 16:48 19:12 21:36 0:00 2:24 4:48
57
-------
Section 2 - Site-Specific Results and Case Studies
Figure 2-32. Moffett Building 126 East Restroom (104) Pressure, May 2019.
30
20
"ciT
Et 10
a>
ro
c
ID
o -10
fc
b
-20
-30
14
Continuous differential pressure measurements in September between restroom 104 and the
hallway show very small differential pressures <1 Pa. Simultaneous differential pressures
between the bathroom and subslab were even smaller (<0.3 Pa).
Continuous differential pressure measurements overnight from September 24, 2019 to the
morning of September 25, 2019 between restrooms 104 and 105 and the hallway had a small
pressure variation of ± 1 Pa. Continuous differential pressures between the 104 restroom and the
hallway generally showed that the restroom was positively pressurized by several pascals.
VOC Analysis with Field Portable GC/MS
Field portable GC/MS analysis of subslab ports in the utility corridor in May 2019 had PCE
concentrations of 4,700 |ig/m3 in the west utility corridor (MF33SS), 230 to 1800 |ig/m3 in east
utility corridor (MF34SS) and 4,700 |ig/m3 in the far end of the east utility corridor (MF35SS).
Notable PCE concentrations observed in the field portable GC/MS analysis in May 2019
included 290 |ig/m3 in the floor drain of the 104 restroom, 70 |ig/m3 at the floor drain in the 105
restroom, 6.1 |ig/m3 in the janitor closet (between the two restrooms), and 6 |ig/m3 in the indoor
air of the 105 restroom. Field observations suggest that the vapor entry point at the floor drain
was not the inside of the drain but rather the annulus between the drain and the slab. Continuous
field portable GC/MS data from the indoor air in restroom 105 (Figure 2-33) showed a strong
diurnal pattern in PCE and TCE concentrations ranging from 0.24 to 28 |ig/m3, PCE
concentrations peak in the early morning around 05:00 and decreased sharply around 06:00
presumably when the HVAC system turned from nighttime settings to daytime settings.
Overnight field portable GC/MS data from restroom 104 also showed the strong diurnal pattern
(Figure 2-32) with a peak concentration of 140 |ig/m3 PCE observed at 02:00 with markedly
lower concentrations during active building usage during the day.
East Restroom - Wind Event (MF20RR)
1
MF B126 East RR to Outdoor Air (Wind Event)
MF B126 East RR to Subslab (Wind Event)
1
1
1
1
1
Date:
5/7/2019 to
5/8/2019
¦'
1 1 ¦
111 1 -
Uiii.uJij.L4
J. . t
-j
jbUual .
~T
T
1 if
1 ¦
1 '
1
:24 16:48 19:12 21:36 0:00 2:24 4:48 7:12 9:36
58
-------
Section 2 - Site-Specific Results and Case Studies
Figure 2-33. Moffett Building 126 West Restroom (105) Continuous TCE/PCE, May 2019.
30
25
£ 15
c
(D
O
c
o
0
10
5
0
5/8/19 12:00 5/8/19 18:00 5/9/190:00 5/9/196:00 5/9/19 12:00
Figure 2-34. Moffett Building 126 East Restroom (104) Continuous TCE/PCE, May 2019.
Restroom (MF20RR)
160
TCE
140 ~ APCE
120
E
3 100
1 . *
| 80 A
§ A
I 60
.
40 .
A
* *
20 . .
A t4.
*.« i
0 *****
5/7/1912:00 5/7/1918:00 5/8/190:00 5/8/196:00 5/8/1912:00
In May 2019, TO-15 canister and passive VOC sample results had the highest PCE
concentrations in restroom 104 (32 |ig/m3 in a TO-15 canister sample and 11 |ig/m3 in a 19-hour
passive VOC sample) and second highest concentrations in the restroom 105 (6.2 |ig/m3 in a TO-
15 canister sample and 6.1 to 6.8 |ig/m3 in 19-hour passive samples). Thus, these results broadly
confirm the observations of the field portable GC/MS (Figure 2-34).
In September 2019, the potential preferential migration route location samples associated with
restrooms 104 and 105, all had nondetectable PCE. Results were non-detects even in cases where
the temporary mitigation measures were removed leaving the floor drains open. This finding
suggests that the driving force for vapor intrusion may not have been present in September 2019
in those areas. No PCE concentrations were also observed with continuous field portable GC/MS
in September 2019 in the indoor air of restrooms 104 and 105.
Restroom (MF19RR)
~
~
TCE
a PCE
A A
A A
A
k
A
~
A
~
»
~*A
*
»*tt
Hit
Restroom (MF20RR)
TCE
A PCE
**
* 4
A
A
A
A
A
A
A A
aa*
** A A
12:00 5/7/19 18:00 5/8/19 0:00 5/8/19 6:00 5/8/19
59
-------
Section 2 - Site-Specific Results and Case Studies
Field portable GC/MS observations at locations MF39PP, MF40PP and MF71PP in May and
September 2019 do not confirm the CES (2020) statement that "The primary VI pathway for
Building 126 is believed to be a subsurface utility vault. The utility vault enters into the
southwest-facing side of Building 126, within a utility room that is inside the main lobby of the
Museum (just to the left of the main entrance)
In September 2019, PCE concentrations were significantly lower (<1 |ig/m3) in all the TO-15
canister samples collected including samples collected in restrooms 104 and 105 for sampling
durations between 8 and 24 hours.
Helium Tracer Testing
Helium was injected in the sewer cleanout near the sink in restroom 104 to identify if utility lines
are leaking vapors into the indoor air through this potential vapor point of entry. Helium was also
injected into a subslab port in the east utility corridor to identify if visible cracks in that area
could also be preferential migration route. Preferential migration routes were identified through
utility lines (electrical, phone, etc.) and backfill of the drain through restroom 104. Response
from the helium injected in the subslab port in the utility corridor identified cracks in the
concrete in the corridor (later mitigated with sealant) as points of vapor entry. The restroom floor
drains that were mitigated had no helium detections indicating a good seal was obtained. No
helium was observed inside the restrooms when helium was injected in the sewer cleanout,
indicating that the pipes were not leaking and; thus, not a preferential migration route.
Helium Air Exchange Tracer Testing
Air exchange rates were estimated in September for restroom 104 using a helium tracer decay
method with results of about 1.5 air exchanges per hour (AEH) with the door closed and 4 AEH
with the door open (Figure 2-35).
Figure 2-35. Moffett Building 126 East Restroom (104) Air Exchange Rate, September 2019.
AER by DECAY
\ V-_ \V
\ \
\ \ \
. ¦* .
DirRead
-Tedlar
30 40
Time (min)
60
-------
Section 2 - Site-Specific Results and Case Studies
Radon Measurements
Subslab radon data acquired with the professional radon detector was relatively consistent across
all three buildings studied at Moffett Field. Radon concentrations in subslab soil gas at Building
126 were between 100 to 200 pCi/L. This is indicative of a radon soil source strength that will
only produce clearly discernable indoor concentrations (i.e., >0.3 pCi/L above background)
when the AF is relatively high (higher than 0.003).
Building Summary
Vapor entry points through floor drains and slab seams and cracks were observed in Building
126. Vapor intrusion also appeared to be influenced by diurnal and meteorological conditions.
Overnight, continuous field portable GC/MS analysis and differential pressure monitoring
provided key data in understanding vapor intrusion, preferential migration routes and points of
entry (Table 2-10). The TO-15 canister and passive VOC samplers also indicated that vapor
intrusion was occurring due to their elevated concentrations. Helium tracer testing and air
exchange rate determination provided supporting information as to the presence of a vapor entry
point but could not definitively indicate vapor intrusion was occurring by themselves. The
professional radon detector did not provide discernible information in identifying preferential
migration routes or vapor entry in this building.
Table 2-10. Summary of Techniques Used at MF 126.
Method
Beneficial in
identifying
preferential
migration routes
and points of
entry
Helium Tracer
*
Differential Pressure - Discrete or Continuous Mode
**
Professional Radon Detector
**
Field Portable GC/MS
* * *
TO-15 Canister
**
Passive VOC Sampler
**
* - not used to identify preferential migration route/vapor point of entry, ** - preferential migration route/vapor point of entry indicated and
identified if used in conjunction with other techniques, *** - preferential migration route/vapor point of entry clearly identified.
Both restroom floor drains had retrofit floor drain valves inserted to mitigate the vapor intrusion.
The retrofit floor drain valves had no helium tracer testing detections indicating that a good seal
was obtained.
2.3 SGV Building 1
Building Background
SGV building 1 is a one-story commercial office building, which includes five suites or units (A
through E). Units D and E are connected internally (Figure 2-36).
61
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Section 2 Site-Specific Results and Case Studies
Figure 2-36. SGV Building 1 Sampling Locations.
Field Activities Summary
Investigation activities under this project were completed in August 2018 and November 2019.
Techniques tested included: FLIR camera, passive VOC samplers, and a consumer grade radon
detector for a two-day sample duration.
August 2018
In August 2018, the FLIR camera provided little to no evidence of temperature differences along
room corners or seams indicating no preferential vapor migration routes or points of entry
(Figure 2-37).
62
-------
Section 2 Site-Specific Results and Case Studies
Figure 2-37. SGV 1 FLIR Potential Vapor Entry Point, August 2018.
The seven-day passive indoor air VOC sampler indicated the presence of chloroform, PCE, and
TCE in concentrations that were substantially elevated over the outdoor ambient air sample in
suite D/E. The maximum chloroform, PCE, and TCE concentrations of 15, 2.9 and 3.3 ug/m\
respectively, were observed in the suite D restroom with the restroom fan turned on.
Concentrations in the electrical closet (i.e., the utility cabinet) outside the building were 1.6
ug/m3 PCE and 1.5ug/im3 TCE, similar to those in the indoor air TCE concentrations in the
adjacent suite D/E, of 1.8 and 1.9 |.ig/'m3, respectively. This finding suggested that vapor entry in
both spaces may have had a common source and attenuation.
November 2019
November activities included testing with the consumer grade radon detector, field portable
GC/MS, passive VOC samplers, and TO-15 canisters. Confounding the investigation were
remodeling activities that occurred in suites A, B, and C between the two sampling events.
Indoor air PCE and TCE concentrations of 1.0 ug/m3 were elevated in suite D/E relative to the
outdoor ambient air sample during the six-day passive VOC sampling period, but not
substantially in suites A and B. For example, the maximum concentrations of 0.49 |ig/m3 PCE
and 0.30 ug/m3 TCE were found in Suite B. Suites A and B had active tenant and ventilation
systems while suite D/E was vacant and unventilated. Suite D/E is also over higher
concentrations in the subsurface, as measured in a prior vapor intrusion investigation.
Sewer gas concentrations of 200 iig/m3 chloroform, 10 ug/m3 PCE, and 4.3 ug/m3 TCE were
identified in the sewer cleanout collected just outside the southern wall of the building near unit
D/E with grab TO-15 canisters. This finding indicates that the sewer line is a potential
preferential migration route. In suite A, at the restroom floor drain, PCE concentrations were 12
jag/m3 with the restroom fan on and the restroom door closed and 2.2 lag/nr' with the fan off and
the door open.
63
-------
Section 2 - Site-Specific Results and Case Studies
Figure 2-38. PCE/Chloroform Ratios in SGV1 by Suite.
PCE I Chloroform Ratio
Vadose Zone Source
under Unit D/E
O
A
0.05
0.06
o
o
0.14
O
Q
0.50
E
Unit A
Unit
B
Unit C
Unit D/E
0.05
Sewer
Cleanout
PCE:chloroform soil gas ratios were examined as a potential indicator of vapor intrusion via a
sewer pathway. Upon examination of the PCE: chloroform (Figure 2-38) and PCE:TCE ratios
among the suites and sewer cleanout confirmed two potential vapor entry routes, namely, subslab
vapor intrusion and sewer gas vapor intrusion. During each sampling round the PCE:TCE ratios
were lower in suite D/E than Suites A, B and C. Testing in suite A at the restroom floor drain
yielded a PCE:TCE ratio of 4.8 with the door closed and restroom fan on indicating the floor
drain/sewer system was a source for PCE. Performing a quick succession field portable GC/MS
survey of restroom floor drains in suites A, D, and E, had PCE:TCE ratios of 3.1, 1.6, and 1.4,
respectively. Results from TO-15 canister samples, where PCE and chloroform were tested for
indicate that PCExhloroform ratios in Suite A and B restrooms were comparable to the sewer
cleanout while the ratio in suite D/E is significantly different. This further indicates multiple
sources of vapor entry into the building. With TCE in suite D/E being dominated by subslab
intrusion and PCE in the suite A restroom being dominated by sewer vapor intrusion.
Radon data in suite B in November 2019 and in suite D/E in August 2018 had concentrations
ranging 1.6 to 1.8 pCi/L. These values were somewhat elevated versus expected ambient air
values, which ranged from 0.15 to 0.44 pCi/L, suggesting the potential for soil gas entry.
Building Summary
One preferential migration route and one vapor point of entry were found at this building.
Subslab vapor intrusion through the slab and the sewer connections were identified using data
from the field portable GC/MS, TO-15 canisters, and passive VOC samplers (Table 2-11). The
radon detector and FLIR camera were unable to indicate preferential migration routes or points
of entry.
64
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Section 2 - Site-Specific Results and Case Studies
Table 2-11. Summary of Techniques Used at SGV 1.
Method
Beneficial in
identifying
preferential
migration routes
and points of
entry
FLIR Camera
*
Consumer Grade Radon Detector
*
Field Portable GC/MS
* * *
TO-15 Canister
**
Passive VOC Sampler
**
* - not used to identify preferential migration route/vapor point of entry, ** - preferential migration route/vapor point of entry indicated and
identified if used in conjunction with other techniques, *** - preferential migration route/vapor point of entry clearly identified.
2.4 SGV Building 2
Building Background
The SGV2 building is a small residential support building for mobile home/trailer park. The
building includes two restrooms with toilets and showers that are no longer in use, a laundry
room that is actively used, and a storage room (Figure 2-39). The laundry room door and
window are always open, as such concentration in this space are similar to outdoor air.
65
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Section 2
Site-Specific Results and Case Studies
Figure 2-39. SGV 2 Sampling Locations.
Field Activities Summary
Field investigation activities under this study were completed in February and November 2019.
Techniques tested included: continuous and discrete differential pressure measurements; field
portable GC/MS; passive VOC samplers; and TO-15 canisters; helium tracer decay; and radon
collected using both the consumer grade radon detector for a two-day sample duration as well as
the professional radon detector.
Pressure Differential
Slightly negative pressure differentials were identified in the storage room relative to the subslab
and outdoor air. A short period (approximately 20 minutes) of continuous differential pressure
data was recorded on November 6, 2019 in one restroom and suggests that the restroom was
generally mildly depressurized with respect to subslab and alternating from positive to negative
with respect to outdoor air. In the other restroom, a short period (about 25 minutes) of
differential pressure data was acquired on the same day which had the same results that the
restroom indoor air is generally mildly depressurized with respect to subslab.
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Section 2 - Site-Specific Results and Case Studies
VOC Analysis with Field Portable GC/MS
Initial VOC data was collected on February 13, 2019. Breathing zone field portable GC/MS
concentrations of PCE varied from 40 |ig/m3 PCE in the storage room to 200 |ig/m3 PCE in the
west restroom. These concentrations were confirmed with 2-day passive VOC samplers with
values of 160 |ig/m3 PCE in the storage room and 310 |ig/m3 PCE in the west restroom.
In November 2019, subslab sampling ports were installed in the storage room and east restroom.
TO-15 canister grab samples from the subslab ports had concentrations of 270,000 and 220,000
|ig/m3 PCE, respectively. The shower drains were identified as preferential migration routes in
both restrooms. In the west restroom, at the shower drain opening, the PCE concentration using
the field portable GC/MS was 3,700 |ig/m3. In the east restroom, at the shower drain opening, a
concentration of 600 |ig/m3 PCE was found in a TO-15 canister grab sample. Three-day passive
VOC sampler data collected yielded similar results to the February 2019 sampling with
concentrations of PCE of 110 |ig/m3 in the storage room and 210 |ig/m3 in the west restroom.
Radon Measurements
Radon concentrations were too low to use to help evaluate preferential migration routes and
vapor entry. Subslab radon was measured at 140 pCi/L while indoor air radon in the storage
room was measured at 0.6 pCi/L.
Helium Air Exchange Tracer Testing
Air exchange rates were estimated for the west restroom (Figure 2-40) using a helium tracer
decay method. The measured air exchange rate was extremely low with results of approximately
0.1 AEH. Due to a low air exchange rate and poor mixing a much longer measurement time
would be required to accurately determine AER.
Figure 2-40. SGV 2 West Restroom Air Exchange Rate, November 2019.
AER by DECAY
0 10 20 30 40 50 60 70
Time (min)
Building Summary
The primary preferential migration route or vapor points of entry observed in the building were
the restroom shower drains. Indoor air concentrations were elevated in the restrooms relative to
the storage room where no drains existed as measured by the field portable GC/MS, 2-day
67
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Section 2 - Site-Specific Results and Case Studies
passive VOC samplers, and TO-15 canister samples (Table 2-12). Helium air exchange tracer
testing, differential pressure, and radon measurements were not useful as indicators of a
preferential migration routes or vapor entry points; although, the differential pressure
measurements did indicate a pressure differential favorable of moving subslab soil gas into the
building.
Table 2-12. Summary of Techniques Used at SGV 2.
Method
Beneficial in
identifying
preferential
migration routes
and points of
entry
Helium Tracer
*
Pressure Differential - Discrete or Continuous Mode
*
Consumer Grade Radon Detector
*
Professional Radon Detector
*
Field Portable GC/MS
* * *
TO-15 Canister
**
Passive VOC Sampler
**
* - not used to identify preferential migration route/vapor point of entry, ** - preferential migration route/vapor point of entry indicated and
identified if used in conjunction with other techniques, *** - preferential migration route/vapor point of entry clearly identified.
2.5 CV Building 1
Building Background
This building was constructed in 2001 and is approximately 8,000 square feet. The original
buildings on the site were removed during remediation along with surface soil removal. The CV
Building 1 was built on top of property after adding clean fill on the surface. The building
includes 5,300 square feet of warehouse space and 2,700 square feet of offices and large sewing
room space (Figure 2-41). The site was used for chemical storage until the mid-1980s. Two
cleanups were performed in 1988 and 1995. Ultimately, the top 2 feet of soil were removed and
replaced by fill. Residual PCE and TCE remained in the clay "hard pan" below the fill. In 2015,
high PCE and TCE soil gas concentration were still present in the vadose zone and migrated to
beneath the slab of the new building.
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Section 2 Site-Specific Results and Case Studies
Figure 2-41. CV Building 1 Sampling Locations.
Field Activities Summary
Field investigation activities were completed in November 2018. Techniques investigated
included using: a field portable GC/MS, FLIR camera, TO-15 canisters, passive VOC samplers,
consumer grade radon detectors, and the borescope.
Figure 2-42. CV 1 FLIR Potential Vapor Entry Point, November 2018.
69
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Section 2 - Site-Specific Results and Case Studies
November 2018
During initial investigation activities, a spray can containing a PCE product was identified on the
warehouse shelves. This product and several other VOC-containing products were moved
outside and away from indoor and outdoor air sample locations.
The FLIR camera indicated the potential for a preferential vapor entry point (Figure 2-42) at an
empty, open electrical conduit.
Subslab TO-15 canister samples had concentrations that ranged from 5,500 |ig/m3 PCE and 200
|ig/m3 TCE in the main warehouse to 34,000 |ig/m3 PCE and 14,000 |ig/m3 TCE in the sewing
room and 22,000 |ig/m3 PCE and 29,000 |ig/m3 TCE in the rear office. Two-day passive VOC
samples at the corresponding indoor air locations of the warehouse, sewing room, and rear office
measured 1.2, 8.4, and 4.7 |ig/m3 PCE and non-detect, 1.8, and 7.1 |ig/m3 TCE, respectively.
Preferential vapor entry points were identified by the field portable GC/MS from the sewing
room compressing joints with PCE and TCE concentrations of up to 470 |ig/m3 PCE and 66
|ig/m3 TCE. The field portable GC/MS also identified potential vapor entry points at plumbing
connections in the office restroom and adjacent sink/kitchenette area. Within the office restroom
floor drain, concentrations ranged up to 1,400 |ig/m3 PCE and 1,100 |ig/m3 TCE. The other
preferential migration route was discovered by testing vapors coming through a common wall
shared by sink in the bathroom and the kitchenette sink with concentrations of 110 and 18 |ig/m3
PCE and 170 and 17 |ig/m3 TCE, respectively.
Continuous field portable GC/MS monitoring collected over approximately 15 hours (Figure 2-
43) showed a steady decreasing trend of PCE and increasing TCE at the reception desk
demonstrating a separate, independent VOC source at this building.
Figure 2-43. CV 1 Continuous VOC Data, November 17-18, 2018.
7
6
| 5
| 4
I 3
u
2
1
0
11/17/18 12:00 11/17/18 18:00 11/18/18 0:00 11/18/186:00 11/18/18 12:00
Radon data collected with the consumer grade radon detectors found concentrations of 1.8 pCi/L
in the rear office and office restroom, 1.4 pCi/L in the sewing room and 0.7 pCi/L in the
warehouse restroom space. The higher relative radon concentrations in the rear office, office
restroom, and sewing room locations support the findings of the field portable GC/MS that vapor
intrusion is occurring via preferential migration routes and vapor entry points.
Data collected after the research effort was concluded as part of a subslab depressurization pre-
assessment in April 2021, appeared to confirm that the primary vapor entry points were
associated with the pathways identified in the study. Pressure gradients measured favored vapor
Breathing Zone (WP08BZ)
y
m
«
,
M
1
^ A
A A
with open symbols at the
TCE
a PCE
70
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Section 2 Site-Specific Results and Case Studies
entry in the into the office area and eastern portion of the sewing room (near the front office
area).
Subslab radon concentrations were higher in the rear office subslab and the east side of the
sewing room subslab (near the office restroom) with concentrations of 620 pCi/L and 540 pCi/L,
respectively, than in the west side of the sewing room subslab (near the main warehouse) where
the radon concentration was measured at 150 pCi/L.
Differential pressure gradients indicated that the driving force for vapor intrusion was from the
subsurface into indoor air with values of-1 Pa in the rear office, -0.3 to -0.6 Pa in the east side of
the sewing room. In contrast, in the west side of the sewing room where radon concentrations
were lower, the driving force was from the indoor air to the subsurface with differential pressure
gradients of+1 to +2 Pa.
The consumer grade borescope was also used to confirm water in the floor drain trap (Figure 2-
44) and the gap between the floor drain and the slab as a potential vapor entry point (Figure 2-
45).
Figure 2-44. CV 1 Floor Drain Trap.
11/17/2018 11:20:34
Figure 2-45. CV 1 Floor Drain Slab Gap.
-m.
i * 11/17/2018
Building Summary
Multiple potential preferential migration routes were indicated by all the tested field
investigation methods including the FLJR camera, field portable GC/MS, TO-15 canisters,
passive VQC samplers, consumer grade radon detector, differential pressure meter, and the
borescope (Table 2-13).
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Section 2 - Site-Specific Results and Case Studies
Table 2-13. Summary of Techniques Used at CV 1.
Method
Beneficial in
identifying
preferential
migration routes
and points of
entry
FLIR Camera
**
Borescope
**
Differential Pressure - Discrete or Continuous Mode
**
Consumer Grade Radon Detector
**
Professional Radon Detector
**
Field Portable GC/MS
* * *
TO-15 Canister
**
Passive VOC Sampler
**
2.6 Effectiveness of the Screening Method and Tools Tested
Preferential migration routes and vapor entry points could be clearly identified using techniques
that determined VOC concentrations. The field portable GC/MS was the most definitive
technique used as it yielded concentrations of the VOCs present at a given location (Table 2-4).
Further, the field portable GC/MS sample inlet could be placed on, in, or very near to the
suspected preferential migration route and point of entry reducing the possibility of VOCs
coming from the surrounding ambient air. One limitation to the use of the field portable GC/MS
is the initial cost of the unit and the advanced training required to operate the instrument and to
perform data interpretation.
The use of TO-15 canisters and passive VOC samplers were useful in identifying the potential
for vapor intrusion (Table 2-4). Results from these techniques provided the identification and
concentrations of VOCs present in the indoor air or subslab. Sampling durations ranged from 8
to 24 hours for the TO-15 canisters and from 2 to 7 days for the passive VOC samplers.
Concentrations from these two techniques result in time-integrated values which can be
advantageous since the flow of VOCs through preferential migration routes and vapor points of
entry varies with the pressure differential between the subslab and indoor air. Both techniques
are relatively easy to use although TO-15 canisters require more expertise to ensure that they are
deployed and working properly. Passive VOC samplers are relatively inexpensive while the TO-
15 canisters are more costly due to specialized cleaning and preparation prior to usage. One
disadvantage of using the TO-15 canisters and passive VOC samplers is the time it takes from
sampling to receiving the analytical results. Unlike the field portable GC/MS which provides
real-time data in the field, these two techniques require hours to days for sampling followed by
days to weeks to receive the analytical results.
The field portable thermal desorption cavity ring-down spectrometer provided real-time TCE
analysis (Table 2-4). However, it should be noted that the field portable CRDS had very limited
use (i.e., at only 1 building) in this study and, hence, was not sufficiently evaluated in this study.
72
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Section 2 - Site-Specific Results and Case Studies
Helium tracer testing, similar to the field portable GC/MS, provided definitive evidence of
preferential migration routes since the helium leak detector probe could be place directly on or
over the potential vapor point of entry (Table 2-4). The helium leak detector provided real-time
measurement and could be used to establish air exchange rates within a room which, in turn,
provided some evidence of the potential for VOC accumulation (when air exchange rates are
low) and information on a potential mitigation options (i.e., increase the air exchanges per hour).
The helium leak detector was easy to use and had a moderate cost. Three disadvantages with
helium tracer testing included: (a) instrument drift through time and a slow return to "normal"
once the drift or high helium concentrations were detected, (b) the need for a large (and generally
bulky) tank of helium in the field for helium injection into the suspected potential migration
route, and (c) methane interference if present.
The use of differential pressure monitoring, in either discrete or continuous mode, was useful in
identifying the potential for vapor intrusion to occur due to building depressurization (Table 2-
4). Results from differential pressure measurement clearly indicated whether driving forces were
present that would enhance the movement of VOCs from the subslab to the indoor air.
Differential pressure monitoring also provided information on the potential for movement of
VOCs within a building and could be used to trace VOC sources if elevated VOC concentrations
were found in one room versus another. Differential pressure monitoring was easy to perform
due to the simple set up of instrumentation and easy graphical displays of the results. The initial
cost of the differential pressure system was moderate relative to the other techniques tested in
this project.
Radon detection, whether by a consumer grade radon detector or a professional radon detector,
provided some evidence of vapor intrusion preferential migration routes or vapor entry points
(Table 2-4). The consumer grade radon detector provided indoor air radon concentrations
integrated through the length of time employed in the field. Elevated radon values, relative to the
ambient conditions, clearly indicated that radon vapor intrusion was occurring, but the
preferential migration route or vapor entry point could not be identified specifically with the
consumer detector. In contrast, the professional radon detector could provide direct indoor air
readings, subslab radon concentration, and when connected to a sampling hose, could be used to
monitor radon at a vapor entry point. Both systems were relatively easy to use with the consumer
grade radon detector being relatively inexpensive while the professional radon detector was more
costly.
The FLIR camera was only partially useful in the identification of preferential migration routes
or vapor points of entry in this study. In some cases, clear temperature differences were seen
which could indicate the presence of a vapor point of entry. However, temperature differences
did not correlate well with identified vapor entry points in this study. The FLIR camera had low
relative costs and was very easy to use.
The borescope and hot wire anemometer were two instruments that were relatively inexpensive
and easy to use. However, their value in identification of vapor intrusion and preferential
migration routes or vapor entry points was limited. The hot wire anemometer could only identify
if air flow was occurring but provides no information about VOC concentrations in the flowing
air. The borescope, although used sparingly in the study, can provide visual evidence of breaks
or gaps in pipes, drains, and other conduits if present and within range of the lighted probe tip.
However, no breaks were observed during the study. A gap between a floor drain and building
73
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Section 2 - Site-Specific Results and Case Studies
slab was found in one building and indicated the potential to be a preferential migration route
and was identified by direct VOC measurements.
Table 2-14. Summary of Techniques Used.
Method
Cost1^
Ease of
Use
Beneficial in
identifying
preferential
migration routes
and points of
entry
FLIR Camera
$
!!!
*
Borescope
$
!!!
*
Hot Wire Anemometer
$
!!!
*
Helium Tracer Testing
$$$
H
* * *
Differential Pressure - Discrete or Continuous Mode
$$
!!!
**
Consumer Grade Radon Detector
$
!!!
**
Professional Radon Detector
$$$
H
**
Field Portable GC/MS
$$$
I
* * *
Field Portable CRDS
$$$
I
* * *
TO-15 Canister
$*
H
**
Passive VOC Sampler
$*
!!!
**
Key: $ - lowest relative cost (<$1,000), $$ - moderate relative cost ($l,000-$5,000), $$$ highest relative cost ($5000 and $150,000+); ! - advanced
training or technician required, !! - moderate training required, !!! - little to no training required and easiest to use; * - not used to identify preferential
migration route/vapor point of entry, ** - preferential migration route/vapor point of entry indicated and identified if used in conjunction with other
techniques, *** - preferential migration route/vapor point of entry clearly identified. Note: relative costs are general and highly dependent on quality of
instrument selected.
¦f - Costs presented are to purchase the instrument. Some instruments are also available to be rented.
^ - TO-15 canisters and passive VOC samplers are one-time use per day and cost includes unit + analytical costs. In contrast, the other methods can
provide continual analyses throughout the sampling day.
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Section 3 - Conclusions and Recommendations for Future Work
3 Conclusions and Recommendations for Future Work
The preferential migration route and point of entry research effort examined vapor intrusion
contaminant flow from potential preferential pathways into buildings. This project was
conducted at five vapor intrusion sites within the State of California and examined 10 different
buildings within the selected five sites. Different environmental conditions were represented by
the sites selected.
The objective of this research effort was to assess potential vapor intrusion migration routes and
entry points into buildings with known vapor intrusion and to attempt to specifically identify the
preferential migration routes or points of vapor entry. The research effort methodology identified
and used screening techniques and tools (e.g., low cost tracers and field portable sensors or
meters) to rapidly identify points of vapor entry to the indoor environment. The occurrence and
significance of the potential preferential migration routes were evaluated to focus the R9 vapor
intrusion pathway investigations. Once a potential preferential vapor migration route or point of
vapor entry was confirmed, the research effort identified and tested the effectiveness of easily
implemented, low cost mitigation measures to minimize or prevent potential vapor intrusion
exposure.
3.1 Potential Migration Routes and Vapor Entry Point Identification
Techniques used in assessing and identifying potential vapor migration routes and vapor
intrusion points of entry into buildings included: continuous and discrete pressure differential
measurements; real-time VOC analysis using field portable GC/MS; VOC analysis with TO-15
canisters and passive VOC samplers; field portable cavity ring down spectrometry; radon
monitoring via consumer grade and professional radon detectors; helium tracer testing and air
exchange rate determination; air flow monitoring with a hot wire anemometer; and photographic
evidence collected using a borescope and FLIR cameras. Not all investigation techniques were
applied at all sites/buildings; instead, techniques were selected to best evaluate each location. In
some cases, additional techniques were utilized when initial investigation results indicated the
presence of a potential preferential migration route or vapor entry point.
Using these various techniques, EPA was able to:
identify preferential migration routes and vapor entry points into the building,
identify, conduct, and test the effectiveness of easy to implement mitigation measures,
and
better understand short-term, diurnal, and seasonal conditions that promote preferential
migration routes and vapor entry points into a building.
Multiple preferential migration routes and points of entry were identified as: either confirmed
(i.e., clearly identified by multiple techniques) or suspected (i.e., indicated by one or more
technique). The potential preferential migration routes (e.g., floor drains, utility penetrations, and
conduits; items 1, 2, 3, 4, 5, 8, and 9 below) and points of entry (e.g., gaps and cracks; items 1, 6,
7, and 9 below) identified during this research effort included:
1) Floor drains with entry through slab cracks and gaps - confirmed - 5 buildings (MF 3,
MF 126, SGV 1, SGV 2, and CV)
2) Floor drain with entry through sewer lines - suspected - 1 building (SGV 1)
75
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Section 3 - Conclusions and Recommendations for Future Work
3) Utility line penetration through slabs - confirmed - 1 building (SFV 4)
4) Electrical conduits - confirmed - 4 buildings (MF 3, MF 45, SFV1, and SFV 4)
5) Plumbing conduits in walls - suspected - 1 building (CV)
6) Gaps between slabs and walls - suspected and confirmed - 1 building each (SFV 2 and
MF 3, respectively)
7) Damaged slabs with significant cracks - confirmed - 1 building (SFV 3)
8) Subsurface pits - confirmed - 2 buildings (MF 45 and MF 126)
9) Improperly installed subslab ports and floor cracks - confirmed - 1 building (SFV 4)
In buildings where vapor intrusion may be dominated by preferential migration route flow, it is
recommended that multiple techniques be used together to understand preferential migration
route flow in real-time and under the different conditions that a building may experience.
3.2 Pathway Dynamics
Preferential migration routes and points of entry are most significant when they contain both
high concentrations of volatile organic compounds and deliver significant flow resulting in
greater mass into the building space. A variety of techniques applied during this research effort
clearly identified potential preferential migration routes and vapor points of entry. Additionally,
it was useful to supplement the observations of chemical concentrations, such as those made with
the field portable GC/MS, with other techniques (such as the hot wire anemometer and
differential pressure testing) which indicate the driving forces for and directionality of advective
gas flow through the building envelope (such as the hot wire anemometer and differential
pressure testing). Measurements that identify how many points of entry are present (e.g., helium
tracer testing) and the cross-sectional area of points of vapor entry (e.g., borescope) can also be
useful. Since indoor air concentrations are controlled by the balance between soil gas entry and
dilution/ventilation in indoor air, air exchange rate measurements provide helpful context to
determine the dynamics of a particular point of vapor entry.
One interesting observation noted is that the indoor versus outdoor differential pressure
measurements rarely correlated to indoor versus subslab differential pressure measurements.
This observation is important since indoor versus outdoor differential pressure measurements are
often used as a substitute for indoor versus subslab differential pressure when logistical
considerations, such as luxury flooring materials, make installation of subslab ports impractical.
Significant vapor intrusion preferential migration routes and points of vapor entry were identified
frequently in and around floor drains in the buildings studied in this research effort. Utility
penetrations and electrical systems were identified in some cases as preferential migration routes
through the building envelope. Subsurface pits and floor cracks were also observed to serve as
vapor entry points. In at least one building, significant imbalances caused by local exhaust
ventilation systems provided strong driving forces for soil vapor entry into the building (Figure
1-1)
3.3 Mitigation Effectiveness
Mitigation measures that are low cost and easily implementable were used in this research effort.
The interim mitigation measures included sealing of visible cracks in the slab foundation (in
building SFV 3 where PCE concentrations dropped from 110 |ig/m3 to 3.1 |ig/m3) and insertion
of retrofit floor drain valves (in building MF 126 where PCE concentrations dropped from 32
76
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Section 3 - Conclusions and Recommendations for Future Work
|ig/m3 to <1 |ig/m3) that seal out vapors yet allow continued flow of water down through the
drain. In both cases, substantial short-term effectiveness for the mitigation approaches were
identified. However, in other cases, the results from crack sealing attempts were inconclusive,
possibly indicating that other unsealed vapor entry points still exist in the building (e.g., in
building MF 45). As noted in the EPA Vapor Intrusion Technical Guide (2015), verifying the
effectiveness of sealing requires monitoring over time and sealing approaches are generally most
effective when paired with a depressurization technology. Most of the post mitigation
observations reported in this research effort were made within days of the application of the
sealing methods and, hence, cannot be considered a long-term fix.
3.4 Recommendation for Future Study
Vapor intrusion studies have been limited by the uniqueness of each building studied. There are
specific building sources, construction pathways, and ventilation conditions that make the
understanding of vapor intrusion challenging. In addition, preferential migration route vapor
intrusion is temporally variable such that preferential migration routes that are only active some
of the time. This temporal variability can result in significant indoor air VOC concentration
spikes or cause persistent VOC concentrations, depending on indoor ventilation conditions and
preferential migration route periodicity. This research effort reinforced the spatial and temporal
challenges that are encountered in many vapor intrusion investigations. Further research into
cost-effective, easy-to implement investigative techniques to identify significant vapor intrusion
pathways readily and accurately are needed.
It is difficult to identify all potential preferential migration routes and points of vapor entry
during any single field event. Repeated site visits under different conditions (e.g., ventilation
changes and wind loading) may be needed to observe a preferential migration route or vapor
entry point in operation. Resource and access constraints limited this project, in general, to two
field events and only one follow-up visit during or after mitigation measures were applied.
Future studies identifying potential preferential migration routes and points of entry should
incorporate multiple field events over longer monitoring periods to assess vapor conditions
before and after mitigation.
Since vapor intrusion can occur from multiple locations within a given building and is
temporally variable, the merit of the applied technologies, such as sensitivity, false positive, and
false negative rates, are difficult to measure under realistic field operational conditions. For
example, clear evidence that vapor intrusion is occurring for a particular preferential migration
route or vapor entry point does not rule out that other vapor entry points exist elsewhere in the
building. An inability to locate discrete points of entry in a building might occur if advective
entry points were numerous, if the advective points of entry are physically inaccessible, or if
diffusion-driven vapor intrusion (when advective forces are absent) is the dominant source of
VOCs.
This research effort was conducted in a population of buildings selected with knowledge that
preferential migration routes and vapor entry points were likely to exist and that the vapor
intrusion from the preferential migration routes and vapor entry points would overwhelm vapor
intrusion from diffusion-driven vapor intrusion. Follow-up studies to assess the locations and
prevalence of potential preferential migration routes in buildings where vapor intrusion is a
potential risk (i.e., in building where the preferential migration routes or vapor entry points have
77
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Section 3 - Conclusions and Recommendations for Future Work
yet to be identified) would be valuable to further test the vapor entry point detection techniques
and to verify their usefulness for vapor intrusion investigations. Through the further testing of
the detection techniques at buildings where vapor intrusion is only suspected (i.e., not known), a
more robust examination of their effectiveness can be conducted especially for those techniques
that were of variable usefulness (i.e., FLIR camera, borescope, and hot-wire anemometer) in
detecting preferential migration routes or vapor points of entry. The results would provide vapor
intrusion investigators with information on techniques that can quickly and effectively monitor
and detect vapor intrusion.
78
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Section 4 - References
4 References
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ASHRAE 55 and 62.1. Construction Specifier.
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Construction Engineering Services (CES), 2020, Revised Draft Site 28 Vapor Intrusion
Remedial Design / Remedial Action Work Plan for Buildings 3, 10, 45, 126, N239, and N239A
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Charlesworth, P. (1988). Air Exchange Rate and Airtightness Measurement Techniques - An
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Kapuscinski, R. 2021. Two Proposals Regarding Nomenclature About Vapor Intrusion.
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Kastanek, J., M. Radford, Q. Bingham, C. Holton, K. Moffat, and C. Lutes. 2016. A
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Closure Conference. December.
McHugh, T., & Beck ley, L. (2018, November). Sewers and Utility Tunnels as Preferential
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McHugh, T., Beck ley, L., Sullivan, T., Lutes, C., Truesdale, R., Uppencamp, R., Coskv, B.,
Zimmerman, J., & Schumacher, B. (2017). Evidence of a sewer vapor transport pathway at the
USEPA vapor intrusion research duplex. Science of the Total Environment, 598, 772-779.
National Bureau of Standards. 1988. Tracer Gas Techniques for Studying Building Air
Exchange. NBSIR 88-3708, Gaithersburg, MD. 38 pp.
Persily, A. (1988), Tracer Gas Techniques for Studying Building Air Exchange, National Bureau
of Standards Center for Building Technology
RT1 International. (2020, March 30). Draft Letter Report: Soil Vapor Extraction for Vapor
Intrusion Pilot Study STREAMS 3, TO 03.
Schuver, H. J., Lutes, C., Kurtz, J., Holton, C., & Truesdale, R. S. (2018). Chlorinated vapor
intrusion indicators, tracers, and surrogates (ITS): supplemental measurements for minimizing
the number of chemical indoor air samplesPart 1: Vapor intrusion driving forces and related
environmental factors. Remediation Journal, 28(3), 7-3 I.
Stewart, L., Lutes, C., Truesdale, R., Schumacher, B., Zimmerman, J. H., & Connell, R. (2020).
Field Study of soil vapor extraction for reducing off-site vapor intrusion. Groundwater
Monitoring & Remediation, 40(1), 74-85.
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Section 4 - References
U.S. Environmental Protection Agency (EPA). 1999. Compendium Method TO-15
Determination of Volatile Organic Compounds (VOCs) In Air Collected In Specially-Prepared
Canisters And Analyzed By Gas Chromatography/Mass Spectrometry (GC/MS). January.
EPA/625/R-96/01 Ob.
U.S. Environmental Protection Agency (EPA). 1999. Compendium Method TO-17
Determination of Volatile Organic Compounds in Ambient Air Using Active Sampling onto
Sorbent Tubes. January. EPA/625/R-96/01 Ob.
U.S. Environmental Protection Agency (EPA). (2008). Engineering Issue: Indoor Air Vapor
Intrusion Mitigation Approaches. EPA/600/R-08-115.
U.S. Environmental Protection Agency (EPA). (2012). Fluctuation of Indoor Radon and VOC
Concentrations Due to Seasonal Variations. EPA/600/R-12/673.
U.S. Environmental Protection Agency (EPA). (2015). OSWER Technical Guide For Assessing
And Mitigating The Vapor Intrusion Pathway From Subsurface Vapor Sources To Indoor Air.
OSWER Publication 9200.2-154.
U.S. Environmental Protection Agency (EPA). (2020, May). Regional Screening Levels.
https://www.epa.gov/risk/regional-screening-levels-rsls-generic-tables.
Venable, P., Chaundhry, T. Caldwell, D., Rivera-Duarte, I., Lutes, C., Lund, L., and Hallberg, K.
2015. A Quantitative Decision Framework for Assessing Navy Vapor Intrusion Sites. Naval
Facilities Engineering Command (NAVFAC) Engineering and Expeditionary Warfare Center
(EXWC) TR-NAVFAC-EXWC-EV-1603. June. https://clu-in.org/download/issues/vi/TR-
NAVFAC-EXWC-EV-1603 .pdf.
Yao, Y. Fang, M., Shuaishuai, M., Yihong, Y., Suuberg, E., & Tang, X. 2107. Three-
Dimensional Simulation of Land Drains as a Preferential Pathway for Vapor Intrusion into
Buildings. Journal of Environmental Quality. Technical Reports. Environmental Models,
Modules, and Datasets. November 16.
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