June 2007
Concentration of Tetrachloroethylene in Indoor Air at a Former Dry Cleaner Facility as a Function of Subsurface Contamination: A Case Study
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Bart M. Eklund,
URS Corporation, Austin, TX
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Michelle A. Simon,
U.S. Environment Protection Agency, Cincinnati, OH
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AbstractA field study was performed to evaluate indoor air concentrations
and vapor intrusion (VI) of tetrachloroethylene
(PCE) and other chlorinated solvents at a commercial
retail site in Dallas, TX. The building is approximately 40
yr old and once housed a dry cleaning operation. Results
from an initial site characterization were used to select
sampling locations for the VI study. The general approach
for evaluating VI was to collect time-integrated canister
samples for off-site U.S. Environmental Protection Agency
Method TO-15 analyses. PCE and other chlorinated solvents
were measured in shallow soil gas, subslab soil-gas,
indoor air, and ambient air. The subslab soil gas exhibited
relatively high values: PCE 2,600,000 parts per billion
by volume (ppbv) and trichloroethylene 170 ppbv. The
attenuation factor, the ratio of indoor air and subslab
soil-gas concentrations, was unusually low: approximately
5 106 based on the maximum subslab soil-gas
concentration of PCE and 1.4 105 based on average
values.
ImplicationsVI often is the dominant pathway in risk assessments for
sites with petroleum fuels or chlorinated solvents. Dry
cleaning establishments are a common type of VI site, but
no studies at such sites are found in the literature. This
paper presents the results of an unusually comprehensive
site investigation at a former dry cleaning establishment,
and the results offer important insights into two issues of
intense debate among practitioners: whether external soilgas
data are representative of subslab soil gas and what a
lower bound attenuation factor is (a pivotal issue in recent
VI-related litigation).
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