core liners, can be permeated by many gases.
Table 4. Extruded samples.
This phenomenon has been established for
a. Comparison of samples collected with 3- and 10-cm3
oxygen (Barbeau et al. 1995), and although not
syringes and transferred directly to VOA vials.
yet documented, has been demonstrated us-
ing a vapor fortification process (Hewitt and
3-cm3 syringe
10-cm3 syringe
(g TCE/g)
(g TCE/g)
Grant 1995) to treat a soil with TDCE, Ben,
TCE, Tol, ethyl benzene, and para- and ortho-
3.40.4*
4.00.4
xylene, held in glass ampoules covered with
* Average and standard deviation, n = 5
TFE.
A closer look at the results in both Tables 2
b. Comparison of samples collected with either 3- or
and 3 shows a fairly continuous decreasing
10-cm3 syringes, half of the samples being extruded di-
trend in analyte concentration with time for
rectly into VOA vials, the other half extruded into a plas-
the TFE covered samples, but a more sporadic
tic bag, stored for 1- to 2-minute period and then trans-
trend for aluminum foil. An explanation for
ferred to a VOA vial.
this discrepancy between the coverings: while
3-cm3 syringe
10-cm3 syringe
TFE allows for uniform rate of loss by pen-
etration through the entire covered end of the
VOA vial
plastic bag
VOA vial
Plastic bag
(g TCE/g)
(g TCE/g)
(g TCE/g)
(g TCE/g)
core liner, vaporization losses occur only
around the rim when aluminum foil is used.
1.60.4†
0.140.09
3.10.6
0.720.16
The tightness of the seal between these two
† Average and standard deviation, n = 4
metal surfaces was variable from sample to
sample, resulting in variable rates of loss for
individual samples.
The most important finding of these two experi-
were extruded directly into a vial or were tem-
ments (Table 2 and 3) is that VOC volatilization
porarily stored in a plastic bag. The two sam-
losses are not prevented by covering the open ends
plers used in these experiments were 10- and 3-
cm3 plastic syringes with 1.4- and 0.8-cm i.d., re-
of core liners with either of these two materials.
The rate of VOC losses from intact soils held in a
spectively. A statistical comparison of the mean
core liner thus would be more dependent on the
TCE concentrations estimates for these samplers,
rate of analyte diffusion in a given matrix. There-
when transferred immediately to VOA vials con-
fore, grain size, soil type, moisture content, or-
taining water, found a small but significant dif-
ganic carbon content, transportation conditions,
ference at the 95% confidence level. On the av-
erage the samples collected with the 3-cm3 sy-
etc., would all be variables. Based on the experi-
ringe were 15% lower in estimated TCE concen-
ments performed, unsaturated soils with low or-
tration.
ganic carbon and clay contents would be suspect
The second experiment looked at the effect of
after very short periods of storage, perhaps even
extruding an intact soil core into a plastic bag for
less than a single day. In contrast to the poor per-
temporary storage. When samples passed through
formance of TFE sheets of <0.02 mm thickness,
the formulation and ≥ 0.13 mm thickness of the
this additional step were compared to samples
transferred directly to prepared VOA vials, those
material used to seal VOA vials serves as an ad-
extruded from a 3-cm3 syringe showed a loss of
equate barrier for the prevention of VOC volatil-
greater than 90% in TCE concentration, while those
ization losses over a period of a couple of weeks
transferred with the 10-cm3 syringe showed a loss
(Hewitt 1995c). Indeed, solutions of several VOCs
of 77%. Both of these experiments suggest that
( T D C E , T C E , p e rc h l o ro e t h y l e n e , B e n , To l ,
sample size (i.e., surface area to mass ratio) is an
ethylbenzene, and para- and ortho-xylene) showed
important variable, and that large volatilization
only a 5% to 15% reduction in concentrations when
losses are likely when an extruded soil sample is
held in Teflon-lined gray butyl rubber-capped
exposed for less than 2 minutes, even if placed in-
VOA vials for 28 days under similar conditions as
side a plastic bag. Based on these findings both
the covered core liners.
the diameter of the soil collection device (i.e.,
Geoprobe, Veihmeyer tube, etc.), and the method
Extruded samples
by which an extruded sample is transferred to a
Table 4 presents TCE concentration variations
prepared vial can significantly influence the VOC
for samples collected with different size plastic
concentrations present.
syringes and as a function of whether samples
7
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