Vapor Intrusion - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 442

contaminants as light as vinyl chloride can be trapped, using carefully selected com-
binations of adsorbent media, of which there are hundreds available. Combinations
of adsorbents are often used where there is a mixture of contaminants of interest with
a wide range of sorptive properties. Therefore, an experienced analyst is required
to select the appropriate media, considering the suite of contaminants to be ana-
lyzed, target detection limits and expected concentration ranges. The analyses are
destructive, so it is often advisable to sample in duplicate, even if only one sample
is analyzed, in order to allow an opportunity for repeat analysis, if needed. There is
also a possibility that the pump might fail (e.g., battery failure), in which case the
sample would not be representative of the entire planned sampling interval, in which
case the duplicate sample could avoid a repeated mobilization of the sampling crew.

10.5.4 Field Screening Considerations

Field screening using portable instruments is an important part of site-specific
assessment of subsurface vapor intrusion to indoor air. Field screening may be
used for:

• Rapid assessment of potentially explosive conditions, using an explosimeter or

landfill gas meter.

• Confirming that soil gas purging yields reproducible soil gas samples, using a

flame ionization detector (FID) or photoionization detector (PID).

• Rapid assessment of preferential pathways such as floor drains, sumps, foun-

dation cracks or rooms within a house that might potentially be contributing
background vapors using an FID, PID or mobile laboratory.

• Confirming the integrity of samples through the use of tracers (He, SF 6 ).

• Assessing biodegradation by screening oxygen and carbon dioxide concentra-

tions using a landfill gas meter.

A variety of field instruments may be applied in vapor intrusion investigations,
including photoionization detectors (PIDs) and flame ionization detectors (FIDs),
landfill gas meters, tracer (e.g., SF 6 and He) detectors, as well as mobile labora-
tories equipped with GCs. General information about these various instruments is
provided below.

10.5.4.1 Photoionization Detectors (PIDs) and Flame Ionization Detectors
(FIDs) for VOC Screening

PIDs and FIDs are both capable of detecting VOCs, but some care must be used
in the selection of the appropriate instrument for a particular site, depending on
the types of contaminants present, the expected concentration ranges, and the pres-
ence of any potential interferences. PIDs come with lamps of different power levels
(e.g., 10.3 and 11.7 eV), and the lamp must have a power level higher than the
ionization potential of the contaminant(s) of concern to be useful. PIDs can be