GRA's eighth symposium in the Groundwater Contaminant Series
drew a total of 419 attendees at two locations (260 in San
Jose and 159 in Long Beach) during back-to-back days on
September 30 and October 1, 2003. Cooperating agencies assisting
with the symposium were Cal/EPA Department of Toxic Substances
Control (DTSC), San Francisco Bay Regional Water Quality
Control Board (RWQCB), and U.S. EPA, Region 9. Attendees
included regulators, industry professionals, consultants,
lawyers, students, and interested citizens. The exhibit
hall had 10 booths with companies offering various services
pertaining to soil gas collection, analysis and consultation.
Prior to the symposium in San Jose, GRA's San Francisco
Bay Area Branch held a dinner meeting featuring Roger Brewer
of the San Francisco Bay RWQCB. His talk, entitled "RWQCB'S
Newly Issued Environmental Screening Levels: New Indoor
Air and Soil Gas Screening Levels and Other Updates", provided
a perfect introduction for the September 30 symposium.
GRA Directors Brian Lewis, Symposium Chair/ Moderator and
Tom Mohr, GRA Seminar Chair, opened the symposium by welcoming
the attendees and thanking the cooperating agencies, speakers,
co-sponsors, and exhibitors. Brian provided an overview
of the relevance of indoor air issues on a statewide basis.
The goal of the symposium was to provide all parties with
DTSC's and the RWQCB's perspective, and, in turn, solicit
feedback from the attendees on this evolving subject. The
symposium was organized into eight presentations, followed
by a panel discussion.
The first presentation, with the theme of "Overview of Why
Indoor Air is an Issue: The California Perspective", was
given by two speakers: Roger Brewer, Ph.D., San Francisco
Bay RWQCB; and David Berry, Ph.D., DTSC. In his presentation,
Indoor Air Vapor Intrusion: SF Bay RWQCB Perspective (Is
the Fog Lifting?), Dr. Brewer provided an overview of the
magnitude of the potential problem in the San Francisco
Bay Area. Heating systems, basements, and strong winds can
exacerbate vapor intrusion by reducing the internal air
pressure and creating a vacuum effect that enhances advective
flow from underlying soils into buildings. Direct collection
and analysis of indoor air samples is complicated by the
presence of the same chemicals in many household goods (e.g.,
aerosol sprays, dry-cleaned clothing, cleaners, etc). Indoor
air sampling is sometimes impractical due to the intrusive
nature of the sampling in individual residences as well
as the size of the plumes and number of structures potentially
affected. As an alternative, the San Francisco Bay RWQCB
has developed conservative screening levels for the evaluation
of potential vapor intrusion and indoor air impact concerns.
Screening levels for soil gas, soil and groundwater based
on the use of the Johnson and Ettinger Model (JEM), are
provided in the document Screening For Environmental
Concerns at Sites With Contaminated Soil and Groundwater
(July 2003, www.swrcb.ca.gov/rwqcb2/esl.htm).
Screening levels are based on a target excess cancer risk
of one-in-a-million and a target hazard quotient of 0.2
for noncancer effects.
Dr. Berry provided an overview of DTSC's rationale for developing
guidance that differs from both the USEPA and the San Francisco
Bay RWQCB. DTSC is developing guidance for the evaluation
of the vapor intrusion pathway with an expected release
in January 2004. Both DTSC and the RWQCB will follow the
new guidance. DTSC's approach differs from USEPA and the
RWQCB in several areas. For example, DTSC will not include
screening values for soil gas, soil and groundwater in the
guidance. Rather, DTSC provides for generic conservative
modeling for sites with limited data. If such modeling fails,
additional site data, including soil gas sampling and site-specific
modeling would be required. Indoor air monitoring would
be the last step in the evaluation process.
The next presentation, given by John Moody, USEPA, Region
9, provided a case study of the former GTE Government Systems
site in Mountain View, California where TCE has impacted
a residential community. Due to the sensitive nature of
the situation, Mr. Moody did not disclose street locations.
The former GTE site was re-developed for residential use
in 1996 - 1998 following soil and groundwater remedial activities.
Indoor air samples were initially collected in 2000. Samples
collected throughout the homes yielded consistent results.
Certain homes have been retrofitted with active ventilation
systems with positive results. Additional soil gas and groundwater
investigations are planned as well as additional indoor
air monitoring.
Next, Paul Johnson, Ph.D., Professor and Associate Dean
of the Ira A. Fulton School of Engineering, Arizona State
University, presented a talk entitled, "Confusion? Delusion?
What Do We Really Know About Vapor Intrusion?" Dr. Johnson,
one of the authors of the original JEM, discussed the debate
concerning current regulatory guidance and the practical
implications associated with such guidance. His talk focused
on reviewing basic technical concepts, empirical evidence
and lessons-learned from empirical analyses, the current
understanding and conceptualization of the pathway, and
the translation of that understanding to mathematical algorithms.
Lastly, he presented recent results from three-dimensional
numerical visualization studies and offered recommendations
for the future.
Following a lunch break, Dan Gallagher, DTSC, provided the
audience with a more in-depth overview of DTSC's forthcoming
guidance for the evaluation of the vapor intrusion to indoor
air exposure pathway for sites in California. DTSC's guidance
will emphasize the importance of collecting high quality
contaminant data when characterizing subsurface plumes.
Mr. Gallagher discussed the approaches for collecting high
quality soil gas, soil matrix, groundwater, and flux chamber
data. However, the DTSC guidance document will specify that
soil gas samples are the preferred contaminant data for
evaluating vapor intrusion to indoor air. Additionally,
Mr. Gallagher provided the conceptual approach for the use
of the JEM within California. DTSC is proposing a two-step
approach, generic evaluations and site-specific evaluations.
Generic evaluations would use minimal site information.
Sites would be evaluated using the maximum soil gas concentration,
along with the depth to the contamination. Soil type would
be selected from lithologies encountered during site characterization.
For sites that are coarse-grained, the characteristics of
sand, as determined by the United States Soil Conservation
Service (USSCS) classification, would be used in the model.
For sites that are fine-grained, the characteristics of
USSCS loam would be used. A default of 5 liters per minute
for the soil gas advection rate would also be used for generic
evaluations. The other input parameters for the model would
be default values characteristic of California. For site-specific
evaluations, input parameters into the model would be determined
through laboratory and field measurements. Dry bulk density,
grain density (total porosity determination), moisture content
(water-filled porosity determination), and fraction organic
carbon would be determined from laboratory measurements.
Soil air permeability would be determined from field measurements.
Other parameters would be default values, such as the building
indoor-outdoor pressure differential (4 pascals), the residential
indoor air exchange rate (0.5 exchanges per hour), and the
foundation crack-to-total area ratio (0.005).
Todd McAlary, GeoSyntec Consultants, Inc. presented "Empirical
Experience Gathering Data to Assess Vapor Intrusion." Mr.
McAlary noted that the conservative nature of generic screening
criteria and risk evaluations would necessitate the collection
of site-specific soil gas samples. Based on an evaluation
of empirical experience, vapor transport can be evaluated
with confidence, providing rigorous protocols are followed.
Mr. McAlary discussed sampling protocol, and noted that
high purge volume sampling provides an integrated average
approach that may provide additional valuable insights.
He also indicated that groundwater data do not correlate
well with soil gas data, and to use groundwater data to
predict indoor air quality is very difficult without supporting
lines of evidence. Mr. McAlary noted that mathematical modeling
of vapor diffusion is relatively simple whereas advective
gas flow into buildings is much more challenging and requires
further research.
Next, Robbie Ettinger, Shell Global Solutions (US) Inc.,
presented "Background Contamination and its Impact on the
Assessment of Vapor Intrusion." Mr. Ettinger, also one of
the authors of the original JEM, highlighted the difficulties
associated with the use of indoor air sampling results in
evaluating risk due to intrusion of subsurface soil gas.
Interfering background sources can include household activities,
consumer products, building materials and ambient air. Mr.
Ettinger provided information on a number of common environmental
contaminants that are present in common household products
as well as ambient air, as monitored by the California Air
Resources Board. He noted, however, that other researchers
have not found 1,1-Dichloroethene (1,1-DCE) associated with
non-subsurface sources in studies performed to date, suggesting
that its presence in indoor air is indicative of subsurface
soil gas intrusion. Mr. Ettinger highlighted a number of
factors that should be considered to assess the impact of
background on vapor intrusion pathway evaluations, with
emphasis on indoor air sampling considerations.
In a presentation entitled, "Engineering Controls for Reducing
the Levels of Volatile Contaminants in the Indoor Air that
Originated in the Soil Gas", Ron Mosely, USEPA Office of
Research and Development, shared his radon experience with
the audience. He stressed that entry of contaminants into
buildings from soil requires a source, an entry pathway
and driving forces. The exposure pathway would be rendered
incomplete if one of these three entities is successfully
removed. Experience with radon and VOCs has shown that it
is usually simpler and more cost-effective to prevent the
entry of soil gas contaminants, usually with sub-slab ventilation
or depressurization (i.e., engineering controls). Mr. Mosely's
presentation also identified intrusion pathways, driving
forces, and diagnostic criteria for selecting and designing
an appropriate control system.
In an effort to pull together the information presented
thus far in the Symposium, Eric Nichols, LFR Levine-Fricke,
Inc., presented a "Hypothetical Case Study: A Site Road
Map for Vapor Intrusion," demonstrating many of the concepts
previously discussed, to illustrate and guide decisions
at a hypothetical site from initial concern through ultimate
resolution. The hypothetical site was impacted with chlorinated
solvents and petroleum hydrocarbons, resulting in the following
chemicals of potential concern: TCE, 1,1-DCE, vinyl chloride
and benzene. Site soils were previously excavated; a groundwater
pump-and-treat system is in operation. The site was sold
with plans for residential development. The presentation
followed a four-step road map to evaluate soil gas concerns
and potential indoor air risks, ending with the need for
site-specific decisions.
The day was concluded with a Panel Discussion featuring
all of the speakers. Members of the audience raised a number
of issues, including questions raised by a non-technical
member of a community directly impacted by indoor air issues
related to a former industrial/commercial property. Other
issues discussed were DTSC's stated preference for JEM input
based on data collected pursuant to the following hierarchy:
soil gas, groundwater, soil, and flux chamber measurements;
and the degree to which modeling should be relied upon for
decision making. Three-dimensional models have been routinely
used for indoor air assessments for radon but indoor air
samples are always collected prior to decision-making.
The indoor air symposium was co-sponsored by CH2M HILL,
Envirogroup Limited, GeoSyntec Consultants, Inc., LFR Levine-Fricke,
and Malcolm Pirnie. Additional information on the symposium,
including binders with speaker contact information, slides,
abstracts, and supplemental information, can be purchased
from GRA at (916) 446-3626.
By Jim Strandberg, Malcolm Pirnie
Related Links:
> Symposium
Resource Binders Available for Purchase
> Symposium
Program Agenda
