3.2-cm-i.d. hole to the depth where the soil vapor
day, nine consecutive 0.500-mL soil-vapor sam-
was taken. However, since the disposable tips
ples were taken after the probe equilibrated for 30
were never retrieved, this second channel was
minutes. The first, fifth, and ninth samples taken
most likely offset slightly from the original. A
were analyzed within 2 hours of collection, while
Veihmeyer tube uses a sliding bar hammer to
equal numbers of the remaining samples were
stored for 3 days at 4 and 12C before analysis.
push its hollow stem into the soil subsurface, and
leaves an open hole when removed.
On another day at a new location, triplicate
Discrete soil samples were collected with a 116-
soil-vapor samples were taken 0.083, 0.25, 0.5, 1, 2,
cm-long, 1.9-cm-i.d. Plexiglas corer equipped
4, 7.5, 24, and 26 hours after the probe was in-
with a plunger. This sampling device works in the
stalled. The sampling started at 0700 on a day that
same way as a plastic syringe with its tip removed
cleared up and became sunny (sunlight reached
(Griffith et al. 1988). A discrete plug of undis-
the sampling location at about 0730). The follow-
turbed soil was collected immediately after the
ing day had very similar weather. During this
Veihmeyer tube had been removed from the hole
longer time study, two sets of triplicate samples
by pushing the open barrel of the Plexiglas corer
were obtained during the 2-hour collection peri-
approximately 2.5 cm beyond the hole's current
od. One set was analyzed immediately while the
depth. Each sample was quickly transferred to a
other was held at room temperature for 24 hours
22-mL VOA vial that was prepared for headspace
prior to analysis. When all of the planned soil-
gas chromatography (HS/GC) analysis. More
vapor samples had been collected, a collocated soil
specifically, for these soil matrix samples, each
matrix sample was obtained. At all of the 13 addi-
VOA vial contained 10 mL of organic free water
tional sampling locations, soil-vapor samples
and had been weighed to the nearest 0.01 g in a
were always taken after at least a 30-minute equil-
laboratory prior to being taken to the field. While
ibration period. Furthermore, except where noted,
in the field, a small piece of Parafilm "M" was
all of the samples taken during these experiments
used to cover the top of the VOA vial to prevent
were analyzed within 4 hours of collection.
the loss of water vapor. The sheet of Parafilm was
As mentioned, a final experiment looked at an
removed just before a soil sample was put inside,
alternative method of handling and storing vapor
then the vial was sealed with a Teflon-lined sep-
samples. For this alternative method, 0.5 mL of
tum and aluminum crimp top. This vial was
organic free water, acidified to a pH of 1.9 with
weighed again once it had been returned to the
NaHSO4 (1 g NaHSO4 in 40 mL of water), was
laboratory to establish the moist weight of the soil
placed into the 22-mL VOA vials prior to their
sample.
being sealed with a Teflon-faced butyl rubber sep-
At the beginning of the field trials, samples
tum and aluminum crimp top cap. To each of the
six vials prepared this way, a 2-L volume of a
were collected on two separate occasions to deter-
mine how long the equilibration period should be
MeOH working standard containing TDCE,
after the probe was installed. In addition, samples
CDEC, TCE, tetrachloroethene, benzene, toluene,
taken on these two occasions were used to assess
ethyl-benzene, para-xylene, and ortho-xylene was
added via a 10-L syringe. In each case, the stan-
fluctuations of TCE soil-gas concentrations with
time. Multiple vapor samples were taken at these
dard was added after two holes were punched
two locations, and at least a single set of triplicate
into the septum with a 22-gauge needle. One of
the holes was used when the standard was trans-
soil-vapor samples was taken at 14 other loca-
ferred onto the inner wall of the vessel with a
tions. A collocated sample of the soil matrix was
smaller gauge needle syringe. Once the standard
taken at all 16 locations. In addition, a final exper-
had been added, the vial was inverted so that the
iment assessed an alternative method for han-
aqueous solution covered the two punctures
dling soil vapor to establish a procedure to extend
made in the septum.
holding times for some common aromatic and
Triplicates of these working standards were
chlorinated compounds.
held for 5 and 12 days at room temperature (22
Multiple sets of triplicate soil-vapor samples
1C). The responses of these working standards
were obtained on 2 days from three separate loca-
were compared to those of sets of triplicate work-
tions. On the first day, triplicate soil-vapor sam-
ing standards prepared from the same stock stan-
ples were taken 15, 30, 60, and 120 minutes after
dard on the day of analysis. Two sets of working
the probe was installed. Soil vapor collection
standards were prepared on the day of analysis.
started at 1005 hours on an overcast and sporadi-
One set was made using one of two puncture
cally rainy day. At a second location on the same
4
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