Assessing the Public Health Significance of Subsurface-Contaminant Vapors Intruding into Indoor Air
Henry J. Schuver, U.S. EPA – OSW, Washington, DC

Issues Related to Residual Subsurface Petroleum Odors at a Railroad Yard in Central Pennsylvania
Joseph T. McNally, GeoServices, Ltd., Camp Hill, PA

Incorporating Engineered Controls into Vapor Intrusion Evaluations

Amy Goldberg Day, LFR, Inc., 1900 Powell Street, 12th floor, Emeryville, CA 94608, Tel: 510-596-9507, Fax: 510-652-4906
William Carson, P.E., LFR, Inc., 1900 Powell Street, 12th floor, Emeryville, CA 94608, Tel: 510-596-9671, Fax: 510-652-4906

Currently, some of California brownfields are being considered for residential redevelopment.  Based on economic changes within California , commercial redevelopment is often not a viable financial option. These brownfields include former fuel transfer stations, chemical manufacturing facilities, land fills, and manufactured gas plants. Site specific redevelopment exposure assessments pose an interesting challenge. Most property redevelopments can be designed to eliminate direct contact to soil and groundwater. However, the vapor intrusion pathway could potentially still be complete. To assess potential human health risk associated with residential redevelopment, evaluations were performed to estimate indoor air concentrations inside hypothetical buildings. The results of the evaluations were used as a risk management tool to assess whether vapor controls would be a necessary part of the property redevelopments. LFR uses soil gas or groundwater data as the source concentration for the Johnson & Ettinger vapor transport model. Each identified volatile organic compounds detected in the subsurface is considered. If the results of the modeling indicated that the estimated cancer risk would be above the California regulatory target of 10-6, then the model would be modified considering the influence of engineered controls. Engineering controls include vapor barriers, open podium garages, and subterranean garages. Various modeling parameters were adjusted to replicate the influence of the chosen engineered control on vapor intrusion. Where necessary, the result of the modeling evaluations has been incorporated into the building design as a risk mitigation measure.

Assessing the Public Health Significance of Subsurface-Contaminant Vapors Intruding into Indoor Air

Henry J. Schuver, U.S. EPA – OSW, Ariel Rios Bldg (MC-5303W), 1200 Pennsylvania Ave. NW, Washington, DC  20460, Email: 703-308-8656, Fax: 703-308-8609

While an increasing number of individual contaminated sites are being investigated for ‘vapor intrusion’ (VI), the overall frequency and magnitude of subsurface contaminant vapors intruding into indoor air and their significance to public health remains largely unevaluated.  The objective of this risk assessment is to assess VI at a sufficient number of contaminated sites to gain insight into its public health significance.  Specifically, this risk assessment is intended to predict the number of health outcomes that may be observable in an epidemiologic study of VI over a large geographic area.  Central-tendency probabilistic estimates of exposure-point concentrations are made using groundwater samples from 2,381 contaminated sites, involving 11,210 wells and 55,132 samples of the indicator VOC tricholoroethylene (TCE).  The estimated extent of groundwater contamination from sites with the highest potential for volatilization into the indoor air of residential properties is mapped using ESRI GIS IDW software and data from a state’s Hazsite database.  The attenuation of vapors generated from the upper-most groundwater is estimated for 884 hypothetical overlying residential structures using the USEPA’s empirical database of attenuation.  Receptor characteristics based on county-level statistics are used to estimate individual and age-specific exposures. These are combined with central-tendency probabilistic estimates of toxicity to estimate central-tendency risks for the outcomes under study (Central Nervous System effects and Non-Hodgkin’s Lymphoma).  Few individuals are estimated to be subject to significant risks.  However, uncertainty in the groundwater concentration underlying each building dominates the calculated risks.  This data limitation, the lack of site-specific extrapolations of upper-most water concentrations away from monitoring well observation points and under buildings, prevents more accurate risk estimates.  Three policy recommendations could address this data gap: Iso-concentration e-maps for VI; Bldg-specific point estimates; and Site-specific outlines of VI study areas.  These data could be used to inform and allow pre-construction savings for new buildings. 

Issues Related to Residual Subsurface Petroleum Odors at a Railroad Yard in Central Pennsylvania

Joseph T. McNally, P.G., GeoServices, Ltd., 1525 Cedar Cliff Dr., Camp Hill, PA 17011, Tel:  717-303-2660, Fax: 717-303-2666, Email: jmcnally@geoservicesltd.com
Robert Carson, Hope Tower Associates, LLC, P.O. Box 476, East Stroudsburg, PA 18301-0476, Tel: 570-449-1962

The subjective nature of subsurface odors can be a negative factor when considering development of industrial properties. An example is a property located in Central Pennsylvania that was used as a railroad yard between the 1840s and the 1970s. At this site, which is centrally located in a small town, weathered petroleum hydrocarbons and a petroleum odor, were encountered in shallow soils. A detailed site characterization was subsequently completed following a through review of rail yard history and identification of possible source areas. Soil, soil vapor, and ground water samples were collected using conventional methods and analyzed for an extended suite of organic and inorganic parameters. Laboratory testing showed that concentrations met the State cleanup levels and closure of the site was obtained from the State regulatory agency. A caveat to avoid, or manage, those areas where petroleum odors may be encountered was included in the final report. In spite of laboratory results at acceptable concentrations and obtaining closure from the regulatory agency, the issue of residual subsurface odor was sufficient to impede development of the property. At the time of the site  characterization, measurements for odor were not easily obtained and field-testing for odor was not conducted. As a result, it was difficult to dispel the perception that odors might have a negative impact on future development, even if properly controlled. Although evaluation of odors is typically subjective, methodologies to measure odors in the field are developing and some States have published regulatory compliance values. As this technology continues to develop, field measurements for odor may be an option to minimize subjective interpretations and allow for a more objective comparison of alternatives.

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