shaking, causing only the glass ampoule to break.
purge-and-trap gas chromatography mass spec-
For this study three separate secondary standards
trometry (PT/GC/MS) Method 8260 (U.S. EPA
were supplied to W.L. Gore & Associates. To test
1986) were initially compared using vapor forti-
the VOC affinity of the Tenax-TA sorbent pack
fied soil samples. These secondary quality assur-
with these QA samples, one was allowed to equili-
ance (QA) standards were fortified with 14
brate for 1 day, while the other two were allowed
VOCs, ranging in concentration from 5 to 100
g/g (Table 1). Briefly, vapor fortification in-
to equilibrate for 9 and 15 days.
volves exposing a desiccated soil held in small
(1-mL) glass ampoule to vapors emanating from
Field samples
Discrete grab and passive soil vapor samples
an organic solution, inside of a sealed chamber
were collected at 18 separate locations, at the
(Hewitt 1994b). This method of producing per-
CRREL (Fig. 1). This site has previously been char-
formance evaluation samples is precise, mimics
acterized as having TCE contamination in both
an environmental pollution pathway, and uses a
the vadose zone and groundwater, ranging in
1-week or longer exposure period. Furthermore,
concentration from <0.001 to >100 ppm (g/g or
once fortification has been completed and the
mg/L, Hewitt 1994b, Hewitt and Shoop 1994).
ampoules heat sealed, analyte concentration re-
Consequently, the locations chosen for this com-
main stable for up to 6 months.
parison study took full advantage of this feature.
To analyze the VOCs present in one of these
In general, the soils typical of this site are silty-
vapor-fortified samples, the entire ampoule is
sands with a moisture content of around 10% and
placed inside of a container (usually a volatile
an organic carbon content of <1.0%. However,
organic analysis [VOA] vial or equivalent vessel)
with the appropriate solvent or sorbent for the
the substrate was dominated by either silty-clays
chosen method of analysis. For this study Type 1
or sand at a couple of the sampling locations.
water was used for HS/GC, methanol for Method
The near-surface holes, from which grab
8260 (U.S. EPA 1986), and a single Tenax-TA sor-
samples were collected and then the Gore-Sorber
bent pack for the Gore-Sorber module. Once the
modules were placed, were made using a Veih-
VOA vial or vessel has been capped, the soil is
meyer tube. A Veihmeyer tube uses a sliding bar
dispersed for extraction/equilibration, by hand
hammer to push its hollow stem into the soil
subsurface, and, once removed, a
10
3.2-cm-i.d. open channel remains
from the ground surface to the
9
depth of interest. Grab samples
6
were collected and the Gore-Sorber
8
5
modules were initially exposed
4
1
3
(installed) on 4 December 1995. For
7
2
the purpose of this report, all of the
samples taken from a single loca-
tion (Fig. 1) will be referred to as
colocated. These sampling loca-
11
tions were created, 42 grab samples
collected, and 18 Gore-Sorber mod-
12
ules installed in approximately 4
13
hours by two people.
For in-vial sample handling and
Laboratory Building
HS/GC analysis, two grab samples
14
(≈3 g each) were taken from each
15
location (hole), one at 76 cm and a
second at 91 cm. In addition, at six
16
locations grab samples from a
depth of 84 cm were collected and
17
placed directly into jars with a
Gore-Sorber module. The vessels,
used for shipping and storage of
Figure 1. Map of sampling locations.
the sorber modules, were 125-mL
18
3
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