Workshop 6: Looking Beyond Natural Variation in Vapor Intrusion: Understanding, Controlling, and
Addressing Site Variables for Improved Practices and Effective Protection Strategies. (The 23rd Annual
International Conference on Soil, Water, Energy, and Air—March 19, 2013, San Diego, CA)
ABSTRACTS (in order of presentation)
Indoor Air and Soil Gas Temporal Variability Effects on Sampling Strategies: Evidence from Controlled
and Uncontrolled Conditions in an Indianapolis Duplex.
Brian Schumacher*, John Zimmerman, Chris Lutes, Brian Cosky, Robert Norberg, Blayne Hartman, and
Robert Truesdale
Management of vapor intrusion (VI) sites can be complicated by temporal variability in indoor air,
subslab, and soil gas contaminant concentrations. At an intensively monitored but unoccupied pre-1920
duplex, thousands of volatile organic compound (VOC) and radon measurements in soil gas and indoor
and outdoor air have been collected over two years (three winter seasons) along with ancillary data
(meteorological, differential pressure, and other related variables). The primary indoor air VOC dataset
was collected with 7-day integrated passive samples. A complimentary data set of VOC concentrations
was also collected over several time periods using a field-portable GC collecting and analyzing samples
from 14 indoor, outdoor, and subsurface locations every 150 minutes. Radon was analyzed continuously
indoors and out, with periodic radon grab samples taken from soil gas as well. Groundwater data were
also collected and analyzed for VOCs.
We will use these data to assess the causes and amount of temporal variability in VOC and radon vapor
intrusion into the duplex. For example, continuous monitoring of indoor air with 7-day integrated
passive samplers shows that while the expected pattern of higher vapor intrusion during winter is
observed, there is substantial variation within a given winter and between successive winters. We are
also evaluating temporal variability time scales and how they might affect site sampling strategies and
management decisions, including how to best characterize the upper tail of the temporal distribution for
short term exposure and risk estimates.
The house was recently fitted with a typical subslab depressurization (SSD) mitigation system, which has
been cycled on and off for several multiweek periods this winter to see how temporal variability in VOC
concentrations may be controlled by SSD. Preliminary results show that the SSD system has a significant
and rapid effect on soil gas VOC distributions at depths up to 13 ft below ground (which is 7 ft below the
SSD system), and that radon and VOCs behave differently under the influence of a SSD mitigation
system.
Brian Schumacher and John Zimmerman, US EPA/ORD/NERL, , Las Vegas, NV 944 East Harmon Ave., Las
Vegas, NV 89119 Phone: (702) 798-2242 FAX: (702) 798-2107 schumacher.brian@epa.gov
Christopher C. Lutes and Brian Cosky, ARCADIS, 4915 Prospectus Drive, Suite F, Durham, NC 27705,
Phone 919-544-4535 Clutes@arcadis-us.com
Robert Truesdale and Robert Norberg, RTI International, 3040 East Cornwallis Road, Research Triangle
Park, NC 27709 Phone 919-541-6152 rst@rti.org
Blayne Hartman, Hartman Environmental Geoscience, 717 Seabright Lane, Solana Beach, CA 92075
blayne@hartmaneg.com
*Presenting Author: Brian Schumacher
AEHS 2013 Workshop 6 Abstracts
1
Multi-Year Monitoring of a House Overlying a Dilute Chlorinated Hydrocarbon Plume: Implications for
Pathway Assessment using Indoor Air Sampling and Forced Under-Pressurization Tests
C. Holton, H. Luo, Y. Guo, P. Dahlen, and P. C. Johnson*
Ira A. Fulton Schools of Engineering, Arizona State University
K. Gorder and E. Dettenmaier
Hill Air Force Base
Real-time monitoring of a home overlying a dilute chlorinated hydrocarbon (CHC) plume has been
underway since about February 2010, including indoor air concentrations (CHCs and radon), building
parameters (e.g., exchange rate, under-pressurization, HVAC operation), and environmental factors
(e.g., precipitation, temperature, wind speed and direction). Phase I, from February 2010 through
August 2012, focused on monitoring under natural conditions. Phase II, currently in progress, involves
monitoring under constant forced building under-pressurization.
The Phase I data set of 8000+ CHC indoor air samples includes instantaneous samples collected on 2hour intervals and time-averaged samples collected over 4-hour periods. Those data show long periods
of relative vapor intrusion (VI) inactivity with sporadic VI activity in combination with long periods of
relative VI activity and sporadic VI inactivity. CHC impacts to indoor air vary over two to three orders of
magnitude, while radon concentration variations are typically within 5X of the baseline signal. The data
also include 16 soil gas snapshots at three depths between the foundation and groundwater. Phase I
data are currently being used to test different strategies for indoor air monitoring as a basis for pathway
assessment under natural conditions. The majority of CHC exposure is attributable to infrequent events
that are difficult to anticipate and are unlikely to be adequately characterized by conventional pathway
sampling frequencies and durations. With respect to other pathway assessment indicators under
discussion, the data show that: a) radon (soil gas vs. indoor air) is not a good quantitative predictor of
the CHC indoor air impacts, although there are increases in radon concentrations with increases in CHC
concentrations for the highest magnitude CHC concentration events, and b) indoor air sources can
create sub-slab soil gas plumes, thereby confounding use of sub-slab data as a VI indicator.
In Phase II the home is being maintained at a building under-pressurization of about 5 Pa relative to the
central sub-slab region through use of exhaust blowers venting to the attic. The objective is to use the
home as a large-scale flux chamber to assess temporal variability in CHC emissions from groundwater,
and the sensitivity of forced under-pressurization pathway assessment tests to time of testing. The
Phase II data set includes about 3400 air samples across 6 months at 40-min, 2-hour, and 4-hour
intervals. Through monitoring of exhaust CHC and tracer gas concentrations, subsurface emission rates
are being calculated. Emission rates during Phase II are being compared with those observed under
natural conditions in Phase I.
*Presenting Author: Paul Johnson
AEHS 2013 Workshop 6 Abstracts
2
Spatial and temporal variability: order statistics for indoor air concentrations from 2 sites with large
data sets
Todd McAlary*, Hester Groenevelt, Jamey Rosen, and Donna Kuntz
Geosyntec Consultants, Inc.
This presentation presents a simple statistical analysis of spatial and temporal variability of data
collected from 2 sites with large data sets. The purpose of this analysis is to improve understanding of
the range of variability in indoor air concentrations from house-to-house and from time-to-time, in
order to make more informed decisions regarding data adequacy and margins of uncertainty in risk
management decisions and response actions. The two sites have very different conditions, which makes
for an interesting comparison:
Characteristic
Depth to Groundwater (ft)
Geologic Materials
Typical Foundation Design
Compound of concern
Sample Duration / Type
# Buildings Analyzed
# Rounds of Samples
Site 1
10-20
Clayey Till
Basements
Trichloroethene
24-hr / passive
470
Up to 25 (n=2631)
Site 2
~200
Loose Quarry Rubble Backfill
Crawl-spaces
Hexachlorobutadiene
24-hr / pumped ATD tubes
35 (some in many rooms)
4 (each in duplicate) (n=862)
The analysis focuses on the magnitude of the difference in concentration from one sample to the next.
The spatial variability is characterized by the ratio of the VOC vapor concentration in one house
compared to the next house. The temporal variability is the ratio of the concentration in one sample to
the next sample in the same house. The order statistics for spatial and temporal variability at the two
sites were as follows:
Spatial Variability
50th %-ile
90th %-ile
98th %-ile
Site 1 (TCE)
2
10
100
Site 2 (HCBD)
2-3
8-12
16-160
Temporal Variability
50th %-ile
90th %-ile
98th %-ile
Site 1 (TCE)
2
7
12
Site 2 (HCBD)
2
5
8
These order statistics show that the degree of variability was very similar for the two sites, despite
significantly different site conditions. Furthermore, it shows that in most cases, the results of two
successive samples in time or two adjacent buildings are within about one order of magnitude. This is
potentially useful information for risk management decision-making and policy-making. Considering
there are a number of other sites with large data sets, further analysis of this kind is recommended.
*Presenting Author: Todd McAlary
AEHS 2013 Workshop 6 Abstracts
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Analysis of long-term unmitigated data for apartment buildings at CDOT MTL site and for single family
homes at the Redfield site.
Jeff Kurtz* and David Folkes,
EnviroGroup - Geosyntec, Denver, CO
The vapor intrusion impacts associated with the presence of chlorinated volatile organic contaminant
plumes in the groundwater beneath two residential areas in Colorado have been the subject of
extensive site investigations and indoor air sampling efforts. Large data sets of indoor air data collected
over decade long monitoring programs at the Redfield and CDOT MTL, Colorado sites are analyzed to
illustrate the temporal distributions in the concentration of volatile organic compounds that one may
encounter when evaluating the potential for exposures due to vapor intrusion.
The single family residential units in the vicinity of the Redfield groundwater plume are single story
homes ranging from 800 to 1,750 square feet in area, constructed predominately between 1950 and
1965. Approximately 67% have basements, 33% have crawl spaces and less than 1.0% have slab-ongrade construction. Most are heated by natural gas heated air with the remainder being heated by gas
heated hot water. Approximately half of the units have one or more fireplaces. Slightly more than half
of the homes have swamp coolers or air conditioners.
The buildings in the vicinity of the CDOT MTL groundwater plume are largely slab-on-grade, multi-story
apartment buildings, with footprints of 6,000 to 54,000 square feet, built in the 1960’s. On the
periphery of the groundwater plume these are surrounded by single story homes with a mixture of crawl
spaces and slab-on-grade construction.
Indoor air samples were collected over a 24 hour period in 6-liter Summa® canisters at hundreds of
homes overlying the groundwater plume at the Redfield site and 19 apartment buildings and dozens of
single family homes at the CDOT MTL site to determine the extent of vapor intrusion impacts due to 1,1DCE. The canisters were dedicated to the projects and batch certified clean to the detection limits.
Samples were collected from the lowest potential living space within the house, away from vents and
windows. Apartment buildings were sampled in multiple units on all floors. The samples were analyzed
by EPA Method TO-15 in the selective ion monitoring (SIM) Mode with 1,1-DCE reported down to the
Method Detection Limit (varying from 0.011 to 0.04 µg/m3).
We selected 45 un-mitigated homes at the Redfield site where indoor samples have typically been
collected on a quarterly or semiannual basis for a period of approximately 2 to 10 years (average of 7.8
years per property), and where 1,1-DCE was detected above the reporting limit at least 50% of the time.
These homes are generally located along the outside edge of the groundwater plume, adjacent to areas
with mitigated homes. The individual 1,1-DCE concentrations ranged from below reporting limits to 1.4
µg/m3 for the 715 samples collected at these homes. Average annual 1,1-DCE concentration in each of
the 45 homes ranged from 0.023 to 0.27 µg/m3. The data set is limited to this general concentration
range because homes with significantly higher 1,1-DCE concentrations were typically mitigated.
The CDOT MTL data set includes selected biweekly pre-mitigation data from a few apartment buildings
and long-term (up to eight years) seasonal data from several apartment buildings and single family
AEHS 2013 Workshop 6 Abstracts
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homes. 1,1-DCE concentrations for the mitigated apartments ranged up to 100 µg/m3, while those for
the unmitigated buildings were generally less than 0.5 µg/m3. The Redfield and CDOT 1,1-DCE data have
a log-linear distribution. The values range from about 10% of the annual average to about ten times the
annual average concentration of the home or apartment being tested. However, most of the time (e.g.,
plus or minus one standard deviation, or 68% of the data), individual test results are within a factor of 2
or 3 of the average annual concentration.
For the Redfield data, a clear difference among seasons is observed, with median winter concentrations
that were 15% higher than the annual average, and median summer concentrations that were 52%
lower than the annual average. Spring and fall median concentrations were 23% and 17% lower than
the annual average, respectively. Similar results were found for the CDOT apartments and single family
homes. More muted seasonal variability was noted in post-mitigation homes. While seasonal trends
are observed, it is also important to note that nearly the full range of concentrations is observed in any
given season, so that short term variability can overwhelm any seasonal trend. Results from long-term
biweekly sampling at selected locations on the CDOT site show similar variability. Typical variability
between sequentially collected samples was less than a factor of ten.
*Presenting Author: Jeff Kurtz
Quantifying spatio-temporal variability of one site (San Antonio, TX)
Jill Johnston* and Jacqueline MacDonald Gibson,
Dept of Environmental Sciences and Engineering, University of North Carolina-Chapel Hill,
(p) 919-843-5786
(email) jillj@unc.edu
This study examined short-term fluctuations in concentrations of tetrachloroethylene (PCE) in the
indoor air of residential homes due to vapor intrusion in a community in San Antonio, Texas, that sits
atop an extensive, shallow plume of contaminated groundwater. Using a community-based design, we
removed potential indoor sources of PCE and then collected twelve 3-day passive indoor air samples in
each of 20 homes. Results demonstrated a one-order-of-magnitude variability in concentration across
both space and time among the study homes, although all measured concentrations were below riskbased screening levels. We found that within any given home, indoor concentrations increase with the
magnitude of the barometric pressure drop (p=0.048) and humidity (p<0.001), while concentrations
decrease as wind speed increases (p<0.001) and also during winter (p=0.001). In a second analysis to
examine sources of spatial variability, we found that indoor air PCE concentrations between homes
increase with groundwater concentration (p=0.030) and a slab-on-grade (as compared to a crawl space)
foundation (p=0.028), while concentrations decrease in homes without air conditioners (p=0.015). This
study offers insights into the drivers of temporal and spatial variability in vapor intrusion that can inform
decisions regarding monitoring and exposure assessment at affected sites.
*Presenting Author: Jill Johnston
AEHS 2013 Workshop 6 Abstracts
5
Statistical evaluation of variability in indoor air sampling data to support development of vapor
intrusion sampling strategies
Helen Dawson*, Linda Gaines and Rich Kapuscinski, U.S. Environmental Protection Agency, Office of
Superfund Remediation and Technology Innovation, Washington, D.C.
Indoor air sampling and analysis provide the most direct approach to estimating concentrations of toxic,
volatile chemicals in indoor air to which building occupants can be exposed. For these purposes, timeintegrated sampling methods (e.g., 8-hr, 24-hr, or longer), rather than grab sampling methods, are
generally recommended for indoor air.
Temporal and spatial variability in indoor air concentrations make it difficult to determine exposure
concentrations from a single or few samples, because sample-integration periods generally are short
relative to the relevant exposure period (e.g., long-term or chronic exposure). Even for short-term –
subchronic or acute – exposures, a single or few samples may not adequately characterize potential
future concentrations, which may be higher or lower. Nevertheless, regulators, building occupants, and
remediating parties may wish to anticipate, based upon limited sampling data, future conditions, if any,
that pose unacceptable health risks, so they can be avoided or mitigated.
Indoor air time-series sampling data were compiled from several sources and used to calculate a
common set of statistical variability measures for purposes of characterizing and comparing temporal
variability at vapor intrusion sites. This preliminary analysis is intended to foster discussion of sampling
strategies that, despite temporal variability, provide adequate characterization of potential future
concentrations. Data sources include EPA’s vapor intrusion database (EPA 2012a), EPA’s test house in
Indianapolis (EPA 2012b), and some Superfund sites. Data collection and compilation are continuing.
Data and statistics were segregated by compound, site, building, sampling method (e.g., evacuated
canister, passive sampler), sample-integration period, sampling frequency, and monitoring time span.
Measures of variability are presented as a function of various monitoring parameters. Statistical analysis
is continuing.
U.S. Environmental Protection Agency (EPA). 2012a. EPA’s Vapor Intrusion Database: Evaluation and
Characterization of Attenuation Factors for Chlorinated Volatile Organic Compounds and Residential
Buildings [EPA 530-R-10-002]. Currently available online at:
http://www.epa.gov/oswer/vaporintrusion/documents/OSWER_2010_Database_Report_03-162012_Final.pdf
U.S. Environmental Protection Agency (EPA). 2012b. Fluctuation of Indoor Radon and VOC
Concentrations Due to Seasonal Variations. EPA/600/R-12/673. National Exposure Research Laboratory.
Las Vegas, Nevada. September. Currently available online at: http://www.epa.gov/esd/cmb/EPA600-R09-073.pdf
*Presenting Author: Helen Dawson
AEHS 2013 Workshop 6 Abstracts
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Temporal variation of soil gas intrusion and retention: examples from radon vapor intrusion
Dr. Daniel J. Steck
St. John’s University, Schaefer Environmental Radiation Laboratory, Collegeville, MN.
To address some of the specific questions posed earlier today by chlorinated VOC VI researchers, the
temporal behavior of indoor radon is examined for insights and answers to:
• Can we use a few indoor air samples to make appropriate decisions about potential health risks
from future exposures given the observed variability in indoor air concentrations arising from
vapor intrusion?
•
What does long-term quarterly 24-hour indoor air sampling tell us about long-term variability in
long-term averages from VI?
•
How can we best characterize the upper tail of the temporal distribution curve for short term
exposure and risk management?
High density temporal data from two houses are analyzed in two ways. Time series spectral analysis
identify the dominant periods of the variation and distribution analysis provide quantitative measures of
the variation of different sampling intervals and frequencies. Then the distribution statistics from these
two houses are compared to larger samples of houses in the Upper Midwest, the US, UK, and Finland.
Finally, a diagnostic technique is described and applied to the Upper Midwest and US studies.
AEHS 2013 Workshop 6 Abstracts
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