Text Box: Text Box: Page # Text Box: Volume 10, issue 2 Text Box: conditions to assist with the investigative strategy and ensure proper use of the data application of an iterative process (i.e., starts with available data and collects additional data only to meet the needs of making informed decisions) allowance for a site-specific evaluation using modeling, soil gas sampling, indoor air sampling, or mitigation at any point in the process evaluation of multiple lines of evidence that result in decisions based on professional judgment consideration of current and future site use use of screening levels based on the appropriate exposure scenario (e.g., residential, nonresidential, occupational) consistent with the regulatory agency” “Attribution of chemicals in indoor air to vapor intrusion can become a relatively complex and difficult task. It is important to use multiple lines of evidence to reach decisions based on professional judgment.” On Pages 15 – 16... “The following are some lines of evidence, listed in no particular order: soil gas spatial concentrations, including subslab and exterior (some distance outside the perimeter of the foundations) soil gas data with some level of vertical profiling, if appropriate … Text Box: groundwater spatial data, with vertical profiling, if appropriate … background, internal and external, sources … building construction and current conditions … subslab (or crawl-space) soil gas data indoor air data … concurrent outdoor air data … constituent ratios” On Page 16... “… there may be multiple sources of chemicals affecting the overall quality of the indoor air that may not be associated with the investigated chemical release, confounding the interpretation of indoor air sample results. These other sources may be from building materials, heating/cooling energy sources, residual volatile components of stored items, household activities (cooking/cleaning), and consumer products used in the building or background contaminants from ambient outdoor air (Locus Technologies 2006). Thus, indoor air sampling is generally recommended only after identifying the buildings most likely to be impacted to limit the difficult task of evaluating the data and avoiding false positive results.” “Indoor air quality often contains measurable concentrations of volatile and semivolatile compounds from household activities, consumer products, building materials, and outdoor air sources.” Text Box: On Page 17… “…obtain outdoor ambient air samples when collecting indoor air samples. In this way, outdoor air quality can act as a baseline, to which interior and subsurface sources are additive. In many cases, the site-specific chemicals of concern (COCs) may be limited to a few chemicals, which may not be present at significant background levels, so it may be possible to conduct indoor air monitoring for a target list of analytes and avoid complications associated with background contributions. Otherwise, a forensic analysis may be required to assess the relative contribution from subsurface and background sources, possibly requiring multiple lines of evidence and multiple methods of interpretation. Several studies (NJDEP, MassDEP, New York State Department of Health [NYSDOH]) of indoor air quality at homes unaffected by subsurface contamination are currently being conducted to provide a statistical basis for assessing background air quality.” “Prior to indoor air sampling, efforts should be made to address sources of background contamination. Some background sources will occur on a fairly constant basis and are difficult to eliminate (e.g., off-gassing from furniture and treated wood surfaces, volatiles released from long-term stored chemicals or fuels). However, other sources are intermittent and have the potential to skew the data (e.g., cigarette smoke,

ITRC Vapor intrusion intro - continued

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