ITRC Vapor intrusion intro -
continued
CONTINUED ON P. 17
![Text Box: COCs and their concentrations in soil and groundwater—the future use of the data and the regulatory requirements that will be applied to the data are used to determine the appropriate laboratory analytical methods
Potential sources and source areas of vapors (e.g., soil; groundwater; nonaqueous-phase liquid [NAPL])
Geology and hydrogeology in the area of the site
Approximate location of vapor sources in the subsurface and the distances (lateral and vertical) between the sources and the building
Current subsurface soil gas–to–indoor air migration routes (e.g., utility conduits, sewers, diffusion through vadose zone soils,…)
Construction features of existing buildings (e.g., size, age, presence of foundation cracks, entry points for utilities, and number of distinct enclosed units)
Potential future uses for undeveloped lands based on municipal zoning laws”
On Page 25…
“When an acute or emergency hazard resulting from vapor intrusion is suspected, the initial priority should be the immediate safety of the building occupants. Unless the indicators are unambiguous in nature (odors, physiological symptoms, etc.), it is unlikely that a significant decision such as evacuation could be made without interior measurements (subslab soil gas and/or](image113.gif)
![Text Box: indoor air samples). The judgment to conduct an interior investigation should be made on a site-specific basis. Each regulatory agency has its own preferences as to when subslab soil gas and indoor air sampling is warranted.
If the prompt collection of interior samples is warranted, several sampling techniques may be employed to make an acute/emergency decision. An investigator may choose to use a photoionization detector (PID), combustible gas indicator (CGI), or similar field screening device to determine whether volatile gases are present at substantial levels that could indicate an immediate hazard. Other investigative methods may be preferable to obtain more accurate determinations of VOC concentrations.
Conversely, it may be determined an interim remedial measure (IRM) would either remove the receptors from acute exposure (e.g., evacuation of the affected buildings) or disrupt the migration route (e.g., subslab depressurization or similar remedial systems).
Whichever option is selected, it must be made on a case-by-case basis, using the agencies’ best judgment, and must be done rapidly. In general, vapor concentrations of this magnitude are not common”.
On Page 26…
“… some volatile chemicals may naturally degrade into other compounds (e.g., trichloroethene[TCE] can break down to vinyl chloride), so the suite of](image114.gif)
