Intrusion of Trichloroethylene (TCE) Vapors From Groundwater Into Buildings in Northeast MA
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CitationSidorenko, Irina. 2019. Intrusion of Trichloroethylene (TCE) Vapors From Groundwater Into Buildings in Northeast MA. Master's thesis, Harvard Extension School.
AbstractPeople can be exposed to trichloroethylene (TCE) in homes and businesses from vapors that intrude into buildings from subsurface groundwater and soil. Estimation of health risks is based on measured or modeled vapor concentrations in these buildings. The United States Environmental Protection Agency (U.S. EPA) recommends the use of empirically derived vapor attenuation factors for risk-based screening of the vapor intrusion pathway. The use of these recommended attenuation factors is expected to overestimate indoor air TCE concentrations.
This thesis research examined attenuation factors empirically derived from publicly available hazardous waste site data and identified key predictors and uncertainties. The primary objective of this research was to evaluate whether groundwater is an adequate predictor of indoor air exposure, focusing primarily on Trichloroethylene (TCE), a known human carcinogen and developmental toxicant. The primary research question was: Are current recommended U.S. EPA and MassDEP attenuation factors for TCE reliable for predicting indoor air concentrations of TCE? I answered this question by testing the following hypothesis: recommended attenuation factors for TCE are adequate predictors of indoor air concentrations of TCE for the protection of human health.
This study used data from 18 buildings that are hydraulically downgradient properties of TCE-contaminated sites, with distances from the building not exceeding 30 feet, where depth to groundwater was not more than 25 feet, and where there was no reported soil source contamination. Attenuation factors were calculated for 18 buildings with paired indoor air and groundwater data and for 10 buildings with paired indoor air and subsurface soil gas data for TCE.
For five out of 18 buildings, the mean attenuation factor value between groundwater and indoor air was slightly higher, on average by less than one order of magnitude, than the empirically derived values recommended by U.S. EPA. For five out of 18 buildings, the mean attenuation factor value was higher by one order of magnitude than the value used by Massachusetts Department of Environmental Protection (MassDEP) in its calculation of the regulatory GW-2 standard. In both cases, TCE indoor air concentrations in some buildings were under-predicted. For five out of 10 buildings, the mean attenuation factor between subsurface soil gas and indoor air was higher on average by one order of magnitude than the empirically derived values recommended by U.S. EPA. For four out of 10 buildings, the mean attenuation factor was higher on average by half order of magnitude than recommended by MassDEP. In both cases, TCE indoor air concentrations in some buildings were under-predicted.
The results show that reliance on recommended U.S. EPA empirically derived attenuation factors and the vapor attenuation value used by MassDEP in its calculation of the regulatory GW-2 standard for predicting indoor air concentrations of TCE could under-predict vapor intrusion risk and may not protect health in some circumstances.
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