glass jars with Teflon-faced cushioned lids, which
used to locate each sampling hole. During the
formed a hermetic seal upon capping. Prior to
sampling period there was a continuous snow
cover (≈30 cm at installation, ≈76 cm at retrieval)
adding the grab samples to these jars, the ePTFE
cord was shortened to eliminate unnecessary
and a frost zone that penetrated 5 to 10 cm below
weight.
the ground surface. The same day the sorbent
Grab samples were collected from the bottom
modules were retrieved from the field, these
of the open channel (hole) using a 116-cm-long,
sample jars and the ones into which grab samples
1.9-cm-i.d. Plexiglas subcorer equipped with a
had been place were packed in a cooler with blue
plunger. This sampling device works in the same
ice and shipped to W.L. Gore & Associates for
manner as a plastic syringe with its tip removed
analysis.
(Griffith et al. 1988). Discrete plugs of undisturbed
soil were obtained immediately after removing
the Veihmeyer tube, by inserting the open barrel
ANALYSIS
of the Plexiglas subcorer approximately 2.5 cm
beyond the hole's present depth. The plug of soil
Grab samples placed in VOA vials containing
was then quickly transferred directly to either a
water were analyzed the day after collection us-
prepared VOA vial or jar containing a Gore-Sorber
ing a HS autosampler (Tekmar 7000) coupled to a
module. These plugs of soil, transferred to jars
GC (SRI, model 8610-0058) equipped with a 15-
containing sorbent modules, remained intact
m, 0.53-mm diam. MXT-1 capillary column (Restex
throughout the study (maintained the cylindrical
Corp.), and photo-ionization/flame ionization se-
shape created by the subcorer).
quential detectors. This same system was also
Soil samples taken for the in-vial collection and
used to determine the VOCs in the vapor-forti-
HS/GC analysis protocol were placed into pre-
fied samples. Before placing the VOA vials that
weighed 22-mL VOA vials containing 10 mL of
either contained field grab samples or vapor-for-
Type 1 water. Before inserting a soil plug, a sheet
tified samples onto the HS auto sampler, they
of Parafilm "M," which had covered the vial to
were shaken for 2 minutes to assist in attaining an
prevent spilling or evaporation, was removed.
equilibrium partition of VOCs among the phases
Immediately after the sample had been extruded
present. In accordance with in-vial analysis pro-
directly into the VOA vial, it was sealed with a
tocols, a portion of the headspace VOC vapors
Teflon-faced septum and aluminum crimp top.
were removed from these VOA vials by punctur-
Using this protocol, grab samples from the depth
ing the septum with a needle.
of interest were collected, transferred, and en-
Analyte concentrations were established rela-
closed in a vessel with hermetic seals, within a
tive to aqueous headspace standards prepared by
adding small (<10 L) quantities of a methanol
minute of exposing a fresh surface.
The moist weight of each soil sample was ob-
(MeOH) stock solution to autosampler vials con-
tained by weighing the collection/analysis VOA
taining 10 mL of Type 1 water. This HS/GC meth-
vial before and after sampling. Likewise the jars
od of analysis has a detection limit of approxi-
mately 0.001 g TCE/g. Instrumental settings for
with Gore-Sorber modules, into which grab
sample were placed, were also weighed before
the autosampler and gas chromatograph, and in-
and after the sampling event to obtain the samples'
formation concerning the performance of this
moist weight. These jars were allowed to sit at
method for establishing VOC concentrations in
room temperature (22C) for 16 days after sample
soil, have been previously documented (Hewitt
collection.
et al. 1992, Hewitt 1995).
The Gore-Sorber modules were quickly posi-
The vapor-fortified soil samples were also ana-
tioned at the bottom of the 3.2-cm-i.d., 91-cm-
lyzed by PT/GC/MS following Method 8260 (U.S.
deep hole by using an insertion tool to push the
EPA 1986). Due the high concentrations of VOC
present (5100 g/g) this sample was first ex-
sorbent end of the cord into the exposed sub-
strate. These modules that were left in the field
tracted with MeOH. Once immersed in MeOH,
were retrieved after 16 days, and placed into their
VOCs associated with a soil matrix become dis-
individual shipping and storage jars. During the
solved in this solvent. Completeness and the rate
16-day exposure period (4 to 20 December 1995)
of extraction is a function of both organic carbon
the holes into which the sorber had been placed
content and macro/micropore structure inherent
were sealed with a cork stopper that was covered
to the matrix (Pignatello and Xing 1996). After
with a Styrofoam dish. Wooden stakes were also
extraction into MeOH, VOC concentrations re-
4
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