Vapor Intrusion Exposure:
Long-Term Evidence-Based Protection & Sustainability in
Residential, Commercial, and Industrial Buildings
The 25th Annual AEHS International Conference on Soil, Water, Energy, and
Air—March 23-24, 2015, San Diego, CA
Abstracts (in order of presentation)
Monday Afternoon, March 23, 2015 – 1:00–5:00 PM PDT
Introduction, Welcome, Overview, and Overarching Context
Dr. Henry Schuver, U.S. EPA ORCR; Doug Grosse, U.S. EPA NRRML (ret.); John Zimmerman, U.S. EPA NERL
Since 2004, the USEPA has sponsored annual Vapor Intrusion (VI) Workshops at the AEHS Foundation’s Annual
International West Coast Conference in San Diego, CA. This years’ technical workshop, which will be held over
two successive half-day sessions, is focused on the latest scientific observations and evidence regarding the
efficacy of various management approaches for providing long-term (sustainable) evidence-based protection.
Commonly VI risks are presented by contaminated groundwater sources, and the long-term evidence-based
approaches and degree of certainty expected for groundwater ingestion exposures (e.g., NRC 20121) will be
compared with those currently typical for the VI pathway’s inhalation exposures. The evidence and scenarios
considered will range from the simplest pre-construction and existing (single family) residential settings, to more
complicated residential scenarios and the typically even-more variable non-residential “large building”
scenarios.
Residential scenarios will include the latest data from two of the world’s most thoroughly studied VI-research
houses (and consideration of their representativeness) along with studies that illustrate the building-specific
complexities that are often only observable after applying physical intrusion controls/ diagnostics to a given
building. Finally, because “there are two choices for dealing with a possible vapor intrusion pathway at a given
site: (1) invest in sampling and analyses to confirm whether or not the potential exposure is of concern, or (2)
install a vapor mitigation system,”* this workshop will continue the discussion from our 2014 workshop by
presenting the latest scientific and economic evidence for informing such a decision, likely made more efficient
by an earlier awareness of the long-term stewardship obligations that can become more obvious with time. Also
note that in response to numerous ‘too much information in too little time to discuss’ comments from our
previous workshops, this split-day format will allow an optional informal evening discussion session that is being
planned for all technical topics, including impacted-community stakeholder groups’ comments and perspectives.
1
Alternatives for Managing the Nation’s Complex Contaminated Groundwater Sites, NRC 2012.
http://www.nap.edu/catalog/14668/alternatives-for-managing-the-nations-complexcontaminated-groundwater-sites
EPA/AEHS 2015 Vapor Intrusion Workshop Abstracts
1
Passive Samplers for the Investigations of Air Quality
Heidi Hayes, Eurofins Air Toxics; Dr. Helen Dawson, Geosyntec Consultants; Robert Truesdale, RTI International;
Chris Lutes, CH2MHill; Dr. Todd McAlary, Geosyntec Consultants
Passive air samplers are gaining increased interest as a means to investigate subsurface vapor intrusion to
indoor air. In response to this interest, the U.S. EPA Engineering Technical Support Center has developed an
Engineering Issue Paper (EIP) that compiles and summarizes the available information on the advantages and
proper use of passive samplers in indoor air investigations of volatile organic compounds (VOCs) at vapor
intrusion and other sites where VOCs are of concern. The EIP covers passive sampler basics (theory, design and
operation), sampling program design and implementation, data quality objectives, how to interpret results, and
current challenges, limitations, and research needs.
As compared to conventional indoor air sampling techniques using evacuated canisters or pumped tubes,
passive samplers are simple to deploy, require no mechanical equipment to operate, and can be used to obtain
long-term integrated VOC measurements. A successful passive sampling program requires careful planning to
ensure reliable results are achieved and data quality objectives are met. The available passive sampler
configurations and considerations for sampler selection are discussed, including targeted compound list,
reporting limit requirements, and desired sampling duration. Field and laboratory protocols relevant to passive
air samplers are presented along with approaches to verify passive sampler field performance. Additional
research is needed to evaluate the performance of passive samplers over longer-term sample durations and to
determine the applicability of passive samplers for a wide range of VOCs including challenging compounds such
as low molecular weight chemicals and those with relatively low risk-based screening levels.
EPA/AEHS 2015 Vapor Intrusion Workshop Abstracts
2
Vapor Intrusion Pathway Screening for Soil Excavation Remedies
Dr. Helen Dawson, Geosyntec Consultants; Chris Lutes, CH2MHill; Dan Carr Sanborn|Head Associates; Dr. Todd
McAlary, Geosyntec Consultants; Robert Truesdale, RTI International
Soil excavation often is a component of site remedies for subsurface volatile organic compound (VOC)
contamination. Bulk soil sampling and analysis is a conventional method for assessing the completeness of soil
excavation remedies, but information is lacking on how to use soil sampling and analysis results to determine
whether a soil excavation remedy for VOC contamination has been completed to a degree that is protective of
the vapor intrusion (VI) pathway. To address this issue, the U.S. EPA Engineering Technical Support Center has
developed an Engineering Issue Paper (EIP) that discusses the benefits and limitations of bulk soil sampling for
assessing VI risks from contaminated soil and describes alternatives for monitoring and enhancing soil remedies
at sites where soil excavation is being considered or used as a remedy for VOC-contaminated soils.
The information and analysis presented in the EIP indicates that bulk soil sampling is useful for identifying and
delineating source areas with high concentrations of VOCs, such as where NAPL is present, and for estimating
the total VOC mass that may be present in soils at a site. However, available analysis methods are not
sufficiently sensitive to detect VOCs in bulk soil concentrations corresponding to typical VI screening levels and,
consequently, bulk soil sampling alone may not to provide adequate information to fully assess potential VI
exposures after a soil excavation. Other technical challenges with bulk soil sampling and analysis include the
potential for low bias (underestimation) of VOC levels from VOC loss during sampling and analysis, and the
difficulty in characterizing the heterogeneity in VOC concentration distributions in the bulk soil mass of interest.
Soil excavation can be an appropriate part of a VOC contamination remedy if focused on shallow accessible
source materials with relatively high concentrations of VOCs, which are readily measured with bulk soil samples.
However, because of the limitations described above, other polishing remedies are likely to be needed to
augment soil excavation. Polishing options include SVE, bioventing, and natural attenuation (for PHCs);
enhanced/accelerated bioattenuation (for chlorinated hydrocarbons); building structure mitigation; institutional
controls; and/or backfilling of the excavated areas with low-permeability barrier materials that will reduce the
concentrations reaching the surface. The time frame other remedies would need to be applied depends on the
total mass of VOCs remaining in the soil after excavation and the rate of mass depletion through either natural
or engineered means.
EPA/AEHS 2015 Vapor Intrusion Workshop Abstracts
3
Soil Vapor Extraction: Mitigation of Vapor Intrusion from Subsurface Sources over Large Areas
Dr. Lloyd “Bo” Stewart, P.E., Praxis Environmental Technologies, Inc.
Decades of soil vapor extraction to remediate sources of contamination in the vadose zone illustrate the
dominance of soil heterogeneity and mass transfer limitations on the migration of volatile contaminants in the
subsurface. Almost all applications of SVE experience an exponential-like decay in the initial extracted vapor
concentration followed by a slow, asymptotic decay that can persist for many years. The initial decay represents
the sweep of a permeable soil volume and generally indicates an area of influence that largely exceeds that
indicated by traditional vacuum responses. The subsequent slow, persistent decay is associated with the mass
transfer limited migration of contaminants from low permeability soils (e.g., clay), soils with high water
contents, and contaminated groundwater. These mass transfer limitations can be quantified by well-established
techniques (e.g., concentration rebound during a suspension of extraction). The site-specific mass transfer rates
are then applied to other site concerns such as groundwater impact and vapor intrusion into buildings. Two
example sites are presented where SVE data are utilized to characterize the mass transfer of contaminants in
the subsurface and the results used to predict the impact on underlying groundwater and overlying vapor
intrusion. The results also illustrate the large area over which SVE can be protective against vapor intrusion,
dependent upon the depth of application, subsurface geology, surface conditions, etc. In one example site, a
single SVE well below a fine-grained soil interval is shown to capture vapors volatilizing from contaminated
groundwater over an area of approximately five acres.
EPA/AEHS 2015 Vapor Intrusion Workshop Abstracts
4
A Case for Profiling of Soil and Rock at VI Sites: Total Mass and Mass Flux as Metrics
Daniel B. Carr, P.E., P.G., and David Shea, P.E., Sanborn, Head & Associates, Inc.; Dr. Helen Dawson, Geosyntec
Consultants
Based on field experience over the last decade it is increasing evident that the total mass of VOCs in the
subsurface coupled with the rate of mass depletion or transfer through either natural or engineered means are
important metrics for assessing the potential risks posed by vapor intrusion. These parameters are relevant
both to assessing the potential risk under present conditions and assessing the length of time the pathway may
pose a risk. This presentation makes the case that detailed profiling of relevant soil or rock properties and VOC
mass distribution at a few locations can dramatically improve site conceptual models and better inform risk
management decisions about the vapor intrusion pathway.
We will introduce approaches for estimating VOC mass flux and total mass from soil data and demonstrate how
these estimates can be used to evaluate the vapor intrusion pathway. We will present examples illustrating the
application of these approaches and discuss considerations and methodologies for developing and executing
this characterization work. Finally, we will discuss potential applications of these concepts in the context of the
life cycle of a vapor intrusion site from assessing future building scenarios to development of criteria for
shutdown/termination of mitigation system operation.
EPA/AEHS 2015 Vapor Intrusion Workshop Abstracts
5
Mass Transfer Concepts in Predicting VI: Large Building Examples
David Shea, P.E., Brad Green, P.G., and Daniel Carr, P.E., P.G., Sanborn, Head & Associates, Inc.
Recent experience with vapor intrusion (VI) characterization and mitigation of large buildings supports that data
collection oriented toward estimating mass transfer rates can be particularly useful for predicting long-term VI
exposures, establishing mitigation performance goals, and criteria for termination/exit of VI mitigation. A site
conceptual model for VI prediction built on mass balance and mass flux principles is more robust than the
conventional approach that relies mainly on concentration data from short-term, relatively small volume
samples, which are typically subject to a high degree of variability that makes assessing long-term chronic
exposure problematic. Since structures act as macro-scale flux chambers, certain types of data collection in
support of assessing VI data in terms of mass flux can be used to estimate potential short- and long-term indoor
air exposure conditions. We will present and discuss how data such as VOC gross mass estimates in
groundwater and the soil column, mass transfer mechanisms including volatilization, partitioning, and diffusion
rates, and building air exchange rates may influence mass loading to a building. Performance data from subslab
depressurization mitigation of large buildings suggests that long-term VI potential is diffusion-limited and may
be readily predictable based on subsurface profiling. In the short term, VI potential may be greater due to
advective transfer of mass from storage in the vadose zone. By investing in data collection that will support mass
transfer estimates, better predictions of long-term VI potential and mitigation performance are achievable.
EPA/AEHS 2015 Vapor Intrusion Workshop Abstracts
6
ORD VI-Research Duplex and Wheeler Building, Indianapolis- Summary of Evidence to Date: Temporal
Variability in Long-term Mitigation Performance and Before Mitigation: What Causes It?
Dr. Brian Schumacher and John Zimmerman, U.S. EPA/ORD/NERL; Christopher C. Lutes, CH2M HILL; Brian Cosky,
ARCADIS U.S., Inc. (ARCADIS); Robert Truesdale and Robert Norberg, RTI International
We will present observations and statistical analysis on indoor air and soil gas data, collected over four years
(including parts of five winter seasons) along with data on meteorological and hydrological variations at an
unoccupied pre-1920 duplex. The monitoring program has now included a set of mitigation on/off tests as well
as a year-long period of continuous post mitigation monitoring. Extensive time series statistical analyses were
completed to examine the causes of temporal variability with and without the mitigation system operation. This
presentation will address some of the frequently asked questions about this study, such as:
 What is the role of preferential pathways, including sewer lines, in this data set?
 To what extent are the features of this duplex and other well studied cases “typical” of the US housing
inventory?
 Is the VOC mass observed entering the duplex primarily from groundwater or vadose zone sources?
 Why do chloroform and PCE differ at this site, in terms of sources and VI behavior?
 What is the spatial and temporal variability of the observed attenuation factors?
Additionally, new data will be presented from the 100,000 square-foot Wheeler Arts Building, which was an
industrial facility from 1911 until 1995. Subsequent renovations converted the building into live-work lofts,
office space and a theater. In this presentation we will present temporal variability data collected pre and post
installation of a mitigation system was installed in 2010. Indoor VOCs include a mix of constituents dominated
by vapor intrusion sources and those dominated by indoor sources. This presentation will focus on the
performance of the mitigation system during a 6 month VOC monitoring period over the winter of 2013-2014.
This case study will demonstrate relatively low post mitigation variability in a commercial building.
EPA/AEHS 2015 Vapor Intrusion Workshop Abstracts
7
Diagnosing Vapor Intrusion Occurrence, Impact, and Contributing Pathways
Dr. Paul C. Johnson, Ira A. Fulton Schools of Engineering, Arizona State University, with contributions from: C.
Holton, Y. Guo, P. Dahlen, H. Luo, K. Gorder, E. Dettenmaier, and R. Hinchee, Arizona State University, Hill AFB
ERB, Chevron Energy Technology Company, IST
Regulatory guidance for assessing the vapor intrusion (VI) pathway varies from the federal to the state and local
levels, but most utilize sparse point-in-time multiple-lines-of-evidence data sets. When interpreting the data
and making decisions, indoor air data are weighted heavily and data interpretation, decision-making, and
mitigation schemes are founded on a simplistic conceptual model of the vapor intrusion pathway.
Recent publications from focused VI studies suggest that the conventional approach is neither robust nor timely,
and that we need to develop assessment approaches that are practicable and reliable, provide timely answers,
and that work in a range of scenarios (e.g., multi-zone residences, office and industrial buildings).
This presentation will summarize key lessons-learned from five years of study at a house overlying a dilute
chlorinated solvent plume and implications of these results for more rapid and robust VI pathway assessment.
Particular emphasis will be placed on recently published results from long-term controlled pressure tests and
the combined use of controlled pressure testing, soil gas monitoring, and screening-level modeling to identify
pathways contributing to vapor intrusion impacts. The need to re-conceptual the vapor intrusion pathway will
also be discussed as well as future plans for a new study recently funded by the Environmental Security
Technology Certification Program (ESTCP).
EPA/AEHS 2015 Vapor Intrusion Workshop Abstracts
8
Tuesday Morning, March 24, 2015 – 8:30 AM–12:00 PM PDT
The value of proper diagnostics and pathway identification for radon mitigation systems—commercial and
residential examples
Tony McDonald, A-Z Systems
Choosing the correct SSD System technology based on complete diagnostic data ensures a successful mitigation
system. Scenarios discussed include identifying multiple or disconnected preferential VI/RN pathways,
overcoming temperature driven radon spikes in homes, the limitations of horizontal remediation wells, and
utilizing suction trenches as a force multiplier
EPA/AEHS 2015 Vapor Intrusion Workshop Abstracts
9
Soil Vapor Extraction and Subslab Depressurization Work Together for Successful Mitigation of a
Series of Commercial Buildings
Dr. Loren Lund, Christopher Lutes, Kim Stokes, Michael Niemet, and Scott McKinley, CH2M HILL; Michael Torres,
USEPA – Region 6, Dallas, Texas
The McGaffey and Main Ground Water Plume Superfund Site in Roswell, New Mexico has been the focus of
remediation efforts as a result of historical releases of tetrachloroethylene (PCE) from multiple dry cleaner
facilities. PCE concentrations up to 11,900,000 μg/m3 have been detected in shallow soil vapor samples, which
have contributed to vapor intrusion to indoor air at several buildings. The site’s source area setting consists of
mixed residential and commercial buildings. The Record of Decision for the site specified that a vapor intrusion
mitigation system (VIMS) be installed and operated to protect indoor air until remediation of vadose zone soil is
completed using an enhanced soil vapor extraction (SVE) system. The USEPA implemented a vadose zone
remedy for the site’s source area that utilizes a holistic approach with centralized blowers, underground piping,
and a vapor phase treatment system that services several sub-slab depressurization (SSD) systems and SVE wells
and trenches. After the first several months of operation, the combined VIMS and SVE remedies have removed
over 450 pounds of PCE from the subsurface.
A VIMS pilot study, conducted at one of the buildings, indicated that traditional SSD systems were not
appropriate at the site because high PCE concentrations in the untreated exhaust vapors were ultimately reentrained into the building. As a result, centralized blowers and a granular activated carbon based treatment
system were designed to treat exhaust vapors from both the VIMS and SVE system. The full-scale VIMS remedy
consists of SSD systems in six buildings with a combined flow of approximately 1,000 standard cubic feet per
minute (scfm). The SVE remedy consists of nine relatively deep SVE extraction wells and two shallow SVE
trenches with a combined flow of approximately 250 scfm. A HAPSITE portable gas chromatograph/mass
spectrometer (GC/MS) was used to assess real-time changes in PCE concentrations in the indoor air and sub-slab
exhaust vapors during VIMS startup.
PCE concentrations in the VIMS exhaust averaged approximately 72,400 μg/m³ immediately following startup.
Within 24 hours, indoor air PCE concentrations were reduced by approximately one order of magnitude at most
buildings as measured by the HAPSITE. After one month of operation, indoor air PCE concentrations had
dropped by up to 99 percent, while the extracted sub-slab vapor PCE concentrations were virtually unchanged.
The SVE system was brought online two months after VIMS startup. During SVE startup, PCE concentrations in
the SVE exhaust averaged 210,000 μg/m³. The average PCE concentration in the SVE exhaust declined to
8,900 μg/m³ after 5 months of SVE operation. After 7 months of VIMS operation, both indoor air and sub-slab
vapor PCE concentrations were reduced to near or below the USEPA regional screening level. The results suggest
that the SVE system is remediating deep vadose zone soil while limiting transport of the high concentration PCE
vapors to shallow soil underlying the building slabs. Rebound pilot testing at one building after taking the VIMS
offline showed a small increase in PCE indoor concentrations after 30 days with subslab levels remaining below
detection limits, which indicated SVE is likely sufficient to mitigate vapor intrusion while remediating the vadose
zone source. Additional long-term monitoring and system optimization are planned as part of future operations
and maintenance activities.
EPA/AEHS 2015 Vapor Intrusion Workshop Abstracts
10
ESTCP Research on Optimization of Vapor Intrusion Mitigation Systems in Large Military Buildings
Todd McAlary, Geosyntec Consultants; Dr. Paul Johnson, Arizona State University; Bill Angell, University
of Minnesota; Bill Brodhead, WPB Enterprises, Inc.; Bill Wertz, NYSDEC; Henry Schuver, U.S. EPA ORCR;
Robert Ettinger, Paul Nicholson, Geosyntec Consultants
Mitigation systems for radon and VOC vapor intrusion mitigation have traditionally been designed to induce a
vacuum below the floor (sub-slab depressurization). There are challenges with this concept: 1) the range of
pressure differential across the floor depends on the building design, wind and weather conditions, floor slab
integrity and operation of mechanical fans, 2) measuring an induced vacuum that is clearly resolved from
ambient cross-floor pressure fluctuations requires a certain “signal to noise” ratio that is not consistent from
building to building, 3) the permeability of materials below the floor and leakage of air across the floor have a
significant influence, but are not typically quantified. New methods for measuring design parameters and
monitoring the performance of mitigation systems are being tested to assess whether mitigation can be
achieved more cost-effectively, especially for large buildings.
Results of testing at a 64,000 ft2 building will be presented, including mass flux monitoring, transient and
steady-state pneumatic testing, sub-floor helium testing (inter-well and flood designs), radon monitoring and
mathematical modeling to quantify the permeability of the materials below the floor and the leakance across
the floor slab. These new lines of evidence provide insight into the performance of the system, and provide
strong scientific evidence for system optimization. The study shows the system can be operated with about 10fold reduction in cost and may result in a reduction in health risks with minimal modification.
EPA/AEHS 2015 Vapor Intrusion Workshop Abstracts
11
Survey of LTS programs (State & Federal)
David Gillay, Barnes & Thornburg LLP
This presentation will highlight the results of a survey of representative state and federal Long Term Stewardship
(LTS) programs. The highlights will focus on key benchmarks that are essential for a viable LTS program,
including but not limited to regulatory, legal, and practical mechanisms used to track, enforce, maintain, and
manage LTS obligations. The federal LTS program springs from US EPA’s new IC policy which is set forth in two
guides: Institutional Controls: A Guide to Planning, Implementing, Maintaining, and Enforcing Institutional
Controls at Contaminated Sites, EPA-540-R-09-001 (Dec. 2012) [referred to as “IC Guidance”] and Institutional
Control: A Guide to Preparing Institutional Control Implementation and Assurance Plans at Contaminated Sites,
EPA-540-R-09-002 (Dec. 2012) [referred to as “ICIAP Guidance”]. The IC Guides are relevant to cleanup actions
taken at Comprehensive Environmental Response, Compensation and Liability Act (CERCLA, or Superfund),
Brownfields, federal facility, underground storage tank (UST), and/or Resource Conservation and Recovery Act
(RCRA) sites. EPA’s IC Guidance clarifies how to plan, implement, maintain, and enforce ICs at contaminated
sites. The IC Guidance was designed to help promote consistent national policy on these prevalent issues. The
ICIAP Guidance is the companion document to the IC Guidance and offers a template to develop IC plans at
contaminated sites where the response action includes ICs. EPA describes an ICIAP as a “document designed to
systematically: (a) establish and document the activities associated with implementing and ensuring the longterm stewardship of ICs: and (b) specify the persons and/or entities that will be responsible for conducting these
activities.” If a responsible party plans to leave residual contamination in place as part of a remedial action, then
these IC Guides will help identify the long-term care, stewardship obligations, and costs for such risk-based
remedies.
EPA/AEHS 2015 Vapor Intrusion Workshop Abstracts
12
Example application of LTS for the CVI pathway (and VOC sources)
Megan Hamilton, Environmental Forensic Investigations, Inc. (EnviroForensics)
Long Term Stewardship (LTS) is a topic that is currently at the forefront of the Environmental Field, as it is a
pivotal component of site closure. In 2014, U.S. EPA and the Indiana Department of Environmental Management
(IDEM) clarified and refined guidance that significantly affects how contaminated sites are investigated,
remediated, and closed. Some of these clarifications involve the potential LTS obligations related to residual
contamination remaining after remedial activities have been completed. Long-term management is necessary in
these situations to protect human health and the environment. This presentation will outline an example
application of how the emerging concepts of LTS can be practically applied to a site with chlorinated volatile
organic compounds (VOCs) and a completed chlorinated vapor intrusion (CVI) pathway. The presentation will
outline three site remediation strategies with LTS components included, along with associated conceptual costs
for each.
EPA/AEHS 2015 Vapor Intrusion Workshop Abstracts
13
Residential Building Vapor Intrusion Lifecycle Cost Evaluation for Natural and Controlled Conditions
Dr. Ian Hers, Golder Associates Ltd.; Robert Truesdale, RTI International; Dr. Henry Schuver, U.S. EPA ORCR; Chris
Lutes, CH2MHill; David Folkes, Geosyntec Consultants
The long-term evidence-based protection and sustainability of approaches to evaluate and mitigate pathway
completeness and potential risk is an emerging topic of interest to vapor intrusion practitioners. This
presentation develops a lifecycle cost evaluation for residential buildings by comparing a strategy involving
monitoring only to one where a building is mitigated early in the process followed by a limited monitoring
program to verify that mitigation is effective. For monitoring programs, the concept of equivalent protection is
introduced to enable the efficacy of different monitoring frequencies to be compared in the context of both
acute and chronic toxicological concerns. Indoor concentration variability plays a role in the design of
monitoring programs and data interpretation. Data from four case studies are summarized to provide insight on
this issue.
A comprehensive monitoring and mitigation design basis is established to support the lifecycle cost analysis and
a detailed cost breakdown is provided for monitoring only and mitigation scenarios based on typical cost ranges
for residential houses. Preliminary results of the lifecycle analysis indicate that for an acute concern with a
monitoring frequency that is equally protective to mitigation (i.e., sampling on a monthly or bi-monthly basis),
lower costs are associated with the mitigation option when compared to the monitoring only scenario, with a
breakeven point of less than 2 years. For monitoring appropriate to characterize a chronic concern, the lifecycle
analysis does not indicate a clear difference with respect to costs for monitoring only versus mitigation,
assuming that less frequent monitoring is appropriate for the mitigation scenario.
EPA/AEHS 2015 Vapor Intrusion Workshop Abstracts
14
Non-residential Building Vapor Intrusion Lifecycle Cost
Chris Lutes, CH2MHILL; Dr. Ian Hers, Golder Associates Ltd.; David Folkes, Geosyntec Consultants; Dr. Henry
Schuver, U.S. EPA ORCR; Robert Truesdale, RTI International
In this presentation we will compare the economics for two basic scenarios that could be chosen at a building
with one round of indoor air data already in hand:
1) mitigation early vs.
2) extensive investigation
The context for the analysis will be a hypothetical industrial/commercial building with conditions that make this
decision “in the grey area”. The goal will be to compare costs to deliver an equivalent level of protectiveness
with either approach. Cumulative cost curves over 30 years will be presented. A sensitivity analysis will explore
the impact of:
 Building size
 Building Complexity
 Mitigation difficulty (soil type)
 Sampling frequency requirements and
 Reporting requirements
 Remediation that reduces the operational time
on these costs.
EPA/AEHS 2015 Vapor Intrusion Workshop Abstracts
15
Community perspective on non-quantitative aspects of assessment/mitigation decisions, including a recent
school case and the need for early risk communication
Lenny Siegel, Center for Public Environmental Oversight (CPEO); Nate Burden, FICS (Fidelity Inspections)
Public stakeholders at vapor intrusion study sites, if properly informed about investigations in a timely fashion,
can be constructive partners in developing suitable, protective environmental responses. Using recent
experience at Moffett Military Housing (California), former Ft. Gillem (Georgia), and above all the HanesLowrance Middle School Complex in Winston-Salem, North Carolina, Lenny Siegel will describe how trust
remains the key foundation of any community engagement strategy. If people feel they have been denied
information, or if agencies fail to work with community-based organizations, then community members may
assume the worse.
EPA/AEHS 2015 Vapor Intrusion Workshop Abstracts
16
Update on Soil Gas Mitigator’s Standard and Credential
Kyle Hoylman, Protech Environmental; Tony McDonald, AZ Solutions, Inc.
A review of the progress toward finalizing the AARST/ ANSI Standard for Residential Radon/ VI Mitigation
Systems will be presented. Current committee discussions include decision making based on site specific
contamination levels, the relationship between sub-slab contaminate strength and discharge requirements, and
designing low maintenance systems. A preview of how to get involved in the upcoming public comment period
on the standard and credential will also be discussed.
EPA/AEHS 2015 Vapor Intrusion Workshop Abstracts
17
Poster Abstracts
Monday Evening, March 23, 2015 – 7:00–9:00 PM PDT
Estimating Mass Flux to Groundwater & Vapor Intrusion from SVE Data and High Resolution Measures of
Permeability and Concentration
Dr. Lloyd Stewart, Praxis Environmental Technologies, Inc., Burlingame, California, USA
Background/Objectives. Techniques to estimate accurately the long-term contaminant mass loading to
underlying ground water or overlying buildings from persistent contaminant sources in the vadose zone have
been studied for more than two decades. The results are commonly used for assessing closure of SVE systems.
Guidance is provided by EPA, Army Corps of Engineers, and Department of Energy. Benchmarks for ceasing soil
vapor extraction (SVE) are usually based on mass flux predictions from simplistic transport models such as
VLEACH that assume one-dimensional vertical transport through uniform soil with a constant infiltration rate.
The boundary condition at the water table ignores any interaction with the ground water. The results from such
modeling are very often unrealistic as dominant transport features are marginalized or lost. The presented work
describes a robust framework for predicting the impact to vapor intrusion or ground water of residual vadose
zone contamination. The approach overcomes the deficiencies of assuming a uniform vadose zone while
maintaining a simplicity of calculation and a connection to actual conditions. An example site in Southern
California with a highly stratified, TCE-contaminated vadose zone where SVE had operated for five years
illustrates the approach.
Approach/Activities. The evaluation of the residual TCE mass in the vadose zone of the example site was
initiated by reviewing the extraction and rebound data measured during SVE. The SVE data yielded estimates of
diffusion-limited mass transfer constraints calculated as described in USACE (2002). The mass transfer
constraints observed during SVE are often ignored but are the same as those that dominate post-SVE transport.
The SVE values provide a basis for estimating contaminant diffusion rates. Concurrent with the SVE data
evaluation, a field effort employed pneumatic logging to provide high resolution measures (i.e., 2-cm vertical
intervals) of vapor permeability and TCE concentration along SVE well screens located among the centroid of the
residual mass. With these profiles, a layered model of the vadose zone with variable diffusion coefficients was
readily constructed and the high resolution vapor concentration profile provided the initial condition for
modeling. The modeling was performed with a modified VLEACH code that included variable soil properties and
more realistic boundary conditions at the water table and ground surface. A boundary condition representing
the resistance of ground water to the entry of contaminants was employed and is described.
Results/Lessons Learned. The model diffusion coefficients based on the logged profiles were found to be
consistent with those estimated from the SVE data, providing independent support for the model validity. The
calculation of mass flux into groundwater and its mixing were consistent with historical ground water
concentrations measured in monitoring wells adjacent to the site. The initial rate of TCE mass entering ground
water was almost an order-of-magnitude less than the end of SVE, as expected. A comparison calculation with
VLEACH and a uniform vadose zone revealed that property averaging eliminated the dominant transport process
at the site yielding unrealistic results.
EPA/AEHS 2015 Vapor Intrusion Workshop Abstracts
18
Remote monitoring and management of vapor intrusion systems supporting structured OM&M and efficient
long term stewardship
Tom Hatton and Daniel Nuzzetti, Clean Vapor, LLC
For the past 25 years technical advancements in soil depressurization systems and the application of allied
technologies to better manage vapor intrusion sites have been at a virtual standstill. Post mitigation Operations
and Maintenance programs are typically proposed as part of commissioning reports but only occasionally do
they advance to the next stage of field application. Advancements in telemetry and an increased awareness in
the importance of delivering an extended standard of care have ushered in a new era of vapor intrusion
Operations Maintenance, Monitoring and Management.
With a greater need for continued care, consultants have been able to integrate telemetric monitoring and
active management into the sites long term stewardship agreement. The poster will graphically illustrate how
integrating dynamic controls and telemetric surveillance at a subject site has facilitated real time active offsite
management and yielded significant energy savings. The poster will also illustrate how the application of
telematics can achieve a component of regulatory compliance; provide a greater level of care through real time
performance monitoring, fault notification and active management. Telemetrically managed systems can deliver
automated regulatory and client reports all within the umbrella of energy savings, reducing operational costs
and limiting liability.
Building a Vapor Intrusion Case: Use of Multiple Lines of Evidence to Support a Site Conceptual Model for TCE
Migration Under a Residential Neighborhood
Nadine Weinberg, Katherine Eyre, Darren Scillieri, ARCADIS U.S., Inc. (ARCADIS)
Draft guidance released by U.S. Environmental Protection Agency (USEPA) has the potential to extend vapor
intrusion (VI) investigations indefinitely due to perceived uncertainties in the data sets generated to evaluate
this exposure pathway. At this site, a multiple lines of evidence (MLE) approach was used to evaluate VI from a
large trichloroethylene (TCE) plume. TCE concentrations were historically up to 15 milligrams per liter (mg/L) in
groundwater on the source property and determined to be present under several residential and commercial
buildings. An initial, local Agency investigation of VI did not identify any immediate concern.
TCE concentrations in shallow groundwater were later determined to be significantly lower (< 0.050 mg/L but
still exceeding USEPA VI screening levels) than concentrations at deeper depths. Thus, additional VI
investigation was requested, in part due to vadose zone lithology of well-sorted fine to medium grained sand. A
MLE was developed to focus the data collection and analysis, and obtain USEPA approval on the scope. The MLE
started with nested soil gas samples from 17 locations downgradient from the source area. These data
confirmed that TCE was not present in the vadose zone above reporting limits, providing clear evidence that TCE
was not migrating into residential homes.
Per the MLE and agreement with USEPA, direct measurements (i.e., sub-slab soil gas and indoor air) were
required because the Agency continued to express concern that the VI pathway was complete for residences
overlying the TCE plume. With regulatory concurrence on the MLE work plan, data were collected from 21
residences and a commercial building that demonstrated that TCE was not present in sub-slab soil gas or indoor
air above conservative screening levels. Thus, the data confirmed the findings of the comprehensive soil gas
study in which data were collected over and close to the TCE groundwater plume.
EPA/AEHS 2015 Vapor Intrusion Workshop Abstracts
19
A Life Cycle and Cost Analysis of Preemptive Mitigation, Site Characterization, and/or Vapor Source Reduction
Strategies at Industrial VI Sites with Multiple Buildings
Dr. Loren Lund, Christopher Lutes, and John Lowe, CH2M HILL
Preemptive vapor intrusion (VI) mitigation is the phrase used for implementing controls to prevent potential VI
from occurring prior to having fully demonstrated the pathway is complete and significant in a building.
Preemptive VI mitigation has been proposed in the U.S. Environmental Protection Agency (EPA) 2013 External
Review Draft VI guidance as a management strategy that is more timely, more cost effective, less disruptive, and
that is preferable to communities and building occupants. However, it is important to consider the practical
aspects of its implementation and whether this is the case at all buildings/sites. A decision analysis approach is
presented in this poster that allows multiple factors to be considered, such as human health protection,
occupant disruption, time to protection and time to closure. The performance of each mitigation alternative is
scored based on expert judgment and weighted to reflect the priorities of stakeholders in order to calculate an
overall value. These overall values can then be compared with cost.
This poster summarizes several of the above issues and risk management factors, including the basis of design
for preemptive VI mitigation systems, performance monitoring, long-term stewardship, demonstration of risk
reduction, and VI site exit strategies/closure. Examination of different VI site conditions using scenario analysis,
alternatives analysis, and lifecycle assessment indicates that preemptive VI mitigation may only be preferable
for a limited subset of buildings/sites. This is particularly true when considering preemptive VI mitigation at a
large group of non-residential structures. These analyses were also used to systematically evaluate the other
proposed benefits of preemptive mitigation, particularly cost-effectiveness and health risk reduction. A
particular concern identified in these analyses is that preemptive mitigation has the potential to adversely
impact closure of VI sites by averting or deferring the characterization of the nature and extent of subsurface
VOC impacts, as is required under the (National Contingency Plan) NCP. The pros and cons of preemptive VI
mitigation under different scenarios and site/building conditions will be summarized in order to facilitate datadriven risk management decisions.
A Survey of Vapor Intrusion Characteristics of Nonresidential Buildings—are Industrial Buildings Different?
Christopher Lutes, Keri Hallberg, John Lowe, Dr. Loren Lund, Mike Novak, CH2MHill; Patricia Venable, Tanwir
Chaudhry, and Tara Meyers, EXWC; Ignacio Rivera, SPARWAR; Donna Caldwell, NAVFAC-LANT
Background/Objectives: Most vapor intrusion (VI) policy in the US is informed primarily by studies conducted in
residential structures of volatile organic compounds (VOCs) in groundwater, located away from the primary
contaminant release. For example the default attenuation factors used routinely are derived from the EPA
database analysis of residential structures. It has been frequently suggested that nonresidential buildings vary
significantly in their resistance to VI due to foundation and ventilation characteristics, but few datasets are
available to support that hypothesis. In addition, when faced with large populations of buildings within
screening distances of volatile subsurface contaminants, innovative methods are needed to:1) prioritize those
buildings in an area most likely to be effected by VI, and 2) make decisions concerning investigation and
mitigation strategies based on subslab and groundwater data sets.
Approach/Activities: We assembled a relational database containing information on 150 sampling zones in 49
military structures at 12 different installations where measurements of chlorinated VOCs were available in
indoor air, subslab soil gas and/or groundwater. The relational database contains chemical measurements,
multiple observations characterizing the buildings, and descriptions of specific locations within a building where
EPA/AEHS 2015 Vapor Intrusion Workshop Abstracts
20
the chemical measurements were made. Building characteristics analyzed include dimensions, use, and
construction date, HVAC type, flooring types, subgrade structures and atypical preferential pathways.
Subsurface characteristics analyzed include soil type, depth to groundwater and distance to location of primary
release. Exploratory data analysis was conducted using graphical presentations and descriptive statistics.
Frequency of detection and issues regarding data censoring were assessed. Screening to minimize the impacts
of indoor sources on the analysis was performed. Buildings influenced by atypical preferential pathways were
analyzed separately.
Results/Lessons Learned: PCE and TCE show a correlation between sub-slab soil gas and indoor air
concentrations as expected; however, only very high sub-slab soil gas concentrations (relative to USEPA [2014]
defaults, which are based primarily on residential buildings) result in indoor air concentrations in excess of
conservative indoor air screening levels. For example, PCE concentrations in sub-slab soil gas in excess of
100,000 µg/m3 were necessary before concentrations in indoor air exceeded the USEPA (2014) indoor air
screening level of 47 µg/m3. TCE concentrations in excess of 2,000 µg/m3 were required in sub-slab soil gas
before indoor concentrations exceeded 3.0 µg/m3.
The correlation between groundwater vapor concentration and sub-slab soil gas concentration for PCE appears
approximately linear on a log-log plot, suggesting a power law relationship between the two variables. A similar
but weaker relationship was observed for TCE. Analysis of the relationship between groundwater vapor
concentration (calculated through Henry’s Law) and indoor air suggests that exceedances of indoor air screening
levels should only be expected when the groundwater vapor concentration exceeds 10,000x the indoor air
screening level in DoD buildings.
Increasing sample zone area was significantly associated with decreasing indoor concentration on a log-log plot.
Higher sub-slab soil gas concentrations were associated with fine (i.e., silt or clay) soil types for PCE; TCE; trans1,2-DCE; cis 1,2-DCE; 1,1,1-TCA; and 1,1-DCE. The single strongest predictor variable for high indoor
concentrations, in many of the multiple regressions performed was winter sampling.
A Real-Time VOC Sensor for VI Investigations: Recent Research, Planned Field Tests, and Potential Future
Applications
Robert Truesdale, Li Han, David Ensor, RTI International; Chris Lutes, CH2MHill
RTI has developed an innovative real- time sensor capable of detecting volatile organic compounds (VOCs) at
low levels in indoor and outdoor air. RTI’s patented sensor operates on the principle of conductivity changes of
composite polymer nanofibers (containing carbon nanotubes) when exposed to sub-ppbv levels of VOCs. It was
developed and tuned to target classes of priority VOCs by selecting polymers with appropriate moieties.
Prototype monitors have been constructed for laboratory feasibility tests where proof of concept has been
demonstrated, including sensitivity to common contaminants of concern for the vapor intrusion (VI) pathway
(i.e., trichloroethylene [TCE]; tetrachloroethylene [PCE]). These contaminants are often of concern at VI sites
because they are resistant to biodegradation (leading to long groundwater plumes under many buildings), have
significant cancer risks, and, for TCE, have short term developmental health effects (i.e., birth defects). These
concerns, along with recent studies suggesting that short term concentration spikes can contribute significantly
to long term VI exposure have created a need for cost-effective “real-time” monitoring of VOCs in indoor and
outdoor air at VI sites. Traditional methods (e.g., TO-15 Summa canisters, passive samplers) do not provide the
temporal resolution for short-term monitoring, have relatively high costs, and do not provide real-time signaling
when VOC levels rise indoors or outdoors. Field deployable GCs can give the real-time, short-interval sampling,
EPA/AEHS 2015 Vapor Intrusion Workshop Abstracts
21
but are expensive to buy and require significant maintenance and a trained operator to operate successfully in
the field.
RTI’s sensor device is small and inexpensive even in the prototype stage; the potential for widespread adoption
is great if certain development challenges can be overcome. It has been demonstrated to be sensitive to both
TCE and PCE down to sub-ppb levels (e.g., 0.03 ppbv TCE) and has a fast response time (< 7 minutes) for both
compounds. The relatively low cost of current prototype sensor (<$500 for the parts) and small size of the
device (cell phone size; < 50g) makes it attractive and potentially suitable for large field applications at VI sites or
for other environmental problems where air VOC concentrations are of concern. Because it works through
conductivity changes, it produces an electrical signal that is ready for telemetric networking through smart
phone apps and other wireless communication technologies.
Side by side studies with TO-15 and passive samplers will be described as a next step for testing of this novel
sensor, including tests against long-term Summa canister devices as well as side by side testing against passive
samplers. Although challenges remain (e.g., compound specificity; interferents [moisture]; unknown lifetime),
approaches to solve these problems have been developed and will be underway soon to provide more robust,
second-generation devices for testing in calendar year 2015-2016.
EPA/AEHS 2015 Vapor Intrusion Workshop Abstracts
22