Graduation Year

2008

Document Type

Dissertation

Degree

Ph.D.

Degree Granting Department

Environmental and Occupational Health

Major Professor

Raymond D. Harbison, Ph.D.

Keywords

Soil vapor intrusion, Risk assessment, Benzene, Inhalation unit risk, Cancer

Abstract

Regulatory agencies have recently focused on assessing the potential for soil vapor intrusion (SVI) and risk posed to occupants of residential and commercial properties overlying and surrounding former Manufactured Gas Plants (MGPs). This study evaluated the potential for SVI at 10 commercial buildings and 26 single family and multi-family residential properties overlying and/or adjacent to three former MGPs. The potential for SVI exposure was categorized into three groupings according to thickness of the vadose zones: no vadose zone; 0 - 6 feet thick, and 6 to 25 feet thick. Indoor and outdoor air and soil vapor samples were collected and analyzed for VOCs by the USEPA Method TO-15. These findings were compared to federal and state regulatory background data sets. The results did not identify evidence of MGP-related soil vapor intrusion from any of the 36 sites regardless of depth to water table or proximity to MGP source tar or dissolved phase plumes.

In addition, comparative risks were calculated based on maximum and mean concentrations for benzene, toluene, ethylbenzene, and xylenes measured in ambient air samples, soil vapor, and indoor air. These chemicals were selected based on frequency of detection within the data sets. Hazard Indexes were calculated using the study results and the mean, maximum and 95th percentile concentrations from regulatory data bases. Carcinogenic risks associated with benzene were calculated using both the measured mean and maximum study results and the mean, maximum and 95th percentile concentrations from state and federal data bases. The calculated Hazard Indexes were less than 1 or were comparable to the regulatory mean and maximum background levels. Calculated cancer risks for residential and occupational exposures ranged from 9.75x10?6 to 4.52x10?4. However background benzene exposure not related to former MGP sites ranged from 9.9x10?6 to 3.59x10?³.

Cancer risk and exposures to indoor air, soil vapor or ambient air concentrations were equivalent or less than a normal resident in the northeast United States. No increased public health risks were associated with occupied residential or commercial properties overlying or surrounding MGPs.

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