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DEVELOPMENT OF A SUB-SLAB AIR SAMPLING PROTOCOL TO SUPPORT ASSESSMENT OF VAPOR INTRUSION
Citation:
DiGiulio*, D C. DEVELOPMENT OF A SUB-SLAB AIR SAMPLING PROTOCOL TO SUPPORT ASSESSMENT OF VAPOR INTRUSION. Presented at Super-Quad Univ./Region 9 Conf, Berkeley, CA, 10/8-10/2003.
Description:
The primary purpose of this research effort is to develop a methodology for sub-slab sampling to support the EPA guidance and vapor intrusion investigations after vapor intrusion has been established at a site. Methodologies for sub-slab air sampling are currently lacking in referred literature. EPA's guidance on vapor intrusion lists five key questions in assessing the quality of sub-slab data. (1) Do analytical results meet the required detection thresholds? (2) Have ambient (outdoor) air or other sources of vapors been considered? (3) Does the data account for temporal variability? (4) Does the data account for spatial variability? (5) Is there any reason to suspect systematic error in sampling and analysis?
Sub-slab sampling was conducted at homes near the Raymark Superfund in Stratford, Connecticut to assess these questions in detail and used to assist in protocol development. At least three sub-slab vapor probes were installed in each house. Indoor, outdoor, and sub-slab samples were collected in 100% certified 6-L Summa canisters and analyzed for a list of halogenated and non-halogenated compounds by EPA's New England Regional Laboratory using EPA Method TO-15. Sub-slab samples were also collected in 1-L Tedlar bags using a peristaltic pump and dedicated tubing and analyzed for a list of target compounds on-site by EPA's New England Regional Laboratory.
Sub-slab sampling effectively differentiated sources of indoor air contamination. Comparison of outdoor, indoor, and sub-slab air concentrations revealed that elevated levels of 1,1-dichloroethene and trichloroethene in indoor air were attributable to ground-water contamination while other VOCs detected in indoor air such as benzene, toluene, and xylene were attributable to indoor VOC sources. Detection limits achieved through the use of EPA Method TO-15 (typically 0.5 ppbv) for outdoor and indoor air sampling were adequate for direct assessment of risk. Detection limits achieved through the use of Tedlar bags and on-site analysis by gas chromatography (typically 10 ppbv) were adequate for indirect assessment of risk by sub-slab sampling. Sub-slab VOC concentrations exhibited substantial temporal and spatial variability (coefficient of variation exceeding 100%). Systematic sources of error (e.g., loss of VOCs through Tedlar bags, vapor probes as source of VOCs) were insignificant.