The migration of contaminants from the subsurface into the indoor air environment, in a process described as soil vapor intrusion, is gaining attention as a potential pathway for exposure to contaminated soil and water. Indoor, outdoor and soil air samples were collected from forty homes in North Texas to investigate the attenuation of trichloroethylene (TCE) from contaminated groundwater into residential buildings. The mean and standard deviation of the soil and indoor air attenuation factors (ratio of indoor air concentration to soil vapor concentration) were 0.14 and 0.17, respectively. Five of the 40 values were greater than 0.1 which is the suggested upper-bound by the U.S. EPA (2002). Statistical tools were used to draw correlative relationships between contaminant groundwater, soil air and indoor air concentrations. The VolaSoil model described by Waitz et al. (1996), was modified for use as a screening tool for future investigations of indoor TCE concentration. Using measured soil vapor data, the model under predicted indoor air TCE concentrations likely due to heterogeneities in the unsaturated subsurface. Inputting groundwater TCE concentrations, the model was able to capture the contaminant migration processes and produce results consistent with measured indoor TCE concentrations. Therefore, the model described in this paper maybe appropriate to be use as a screening tool in future investigations in the contamination area. / text

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.

Diesel #2 is used to heat nearly 400,000 dwellings in Virginia. Home heating oil released from leaking underground tanks located adjacent to homes and residing in unsaturated soil adjacent to houses poses a potentially serious health risk. Specifically, the migration of hazardous vapors into buildings, known as vapor intrusion, can negatively impact indoor air quality in homes and public buildings (USEPA 2015). In this look-back study, we assessed the potential for petroleum vapor intrusion by sampling soil vapor at 25 previously remediated spill sites. Residual contaminants, in particular total petroleum hydrocarbons (TPH) and naphthalene, were detected in approximately 1/3 of the samples. Concentration levels were correlated to site variables (building type, remediation time, physiographic region) including previous abatement measures. Spill category as assigned by the remediation contractor was investigated in conjunction with these three site variables. Remediation time was the most promising predictive site variable, with visible trends downward in DEQ Category 2 sites with increased remediation time. Higher contaminant concentrations were found near basement-style dwellings, which we hypothesize is due to the wall of the basement blocking horizontal migration of contaminants and the flow of oxygen to the release source zone. We found that many sites exceeded the sub-slab risk target threshold in naphthalene concentration, which has negative implications on previous abatement strategy efficacy. / Master of Science / Diesel is used to heat nearly 400,000 residences in Virginia. Diesel released from leaking underground tanks located adjacent to homes and residing in soil adjacent to houses poses a potentially serious health risk. Specifically, the migration of hazardous vapors into buildings can negatively impact indoor air quality in homes and public buildings (USEPA 2015). In this study, we assessed the potential for vapor migration by sampling soil vapor at 25 previously remediated spill sites. Residual contaminants were detected in approximately 1/3 of the samples. Concentration levels were compared to site variables (building type, time since spill, soil type) including previous remediation activity. Spill category as assigned by the remediation contractor was investigated in conjunction with these three site variables. Remediation time was the most promising as a predictive site variable. Higher contaminant concentrations were found near dwellings with basements, which we hypothesize is due to the wall of the basement blocking horizontal migration of vapors. We found that many sites exceeded the target threshold in naphthalene concentration, which has negative implications on previous remediation effectiveness.