Table 3. Holding time concentration (g/g)
septum. This aqueous solution was then analyzed
results for soil subsamples treated at three
by HS/GC.
different analyte levels and prepared for HS/
GC analysis.
Analysis
Both the HS/GC and PT/GC/MS analyses of
Analyte
Day 0
Day 8
Day 14
subsamples were performed following procedures
Treatment A
that have been described in more detail elsewhere
0.71 0.01
0.66 0
0.64 0.03
TDCE
(Hewitt et al. 1992). Briefly, HS/GC analysis was
1.0 0
0.59 0
Ben
ND*
0.88 0
0.78 0.02
0.84 0.03
performed at room temperature after shaking the
TCE
2.6 0
1.4 0
Tol
ND
VOA vials for two minutes to obtain a headspace
equilibrium. Headspace vapors were removed
Total
5.19
3.43
1.48
from the sealed VOA vial using a gas-tight syringe
Treatment B
to penetrate the Teflon-faced silicon septum. These
32 0
32 1
30 1
TDCE
50 1
8.8 4.2
headspace vapors were then injected into a Photo-
Ben
ND
41 1
36 0
28 2
TCE
Vac gas chromatograph (model 10S10, PhotoVac,
40 1
24 2
3.6 1.6
Tol
Inc.) equipped with a packed column containing
Total
163
100.8
61.6
10% Se-30 on Chromsorb 80/100 mesh. Sample
analyte concentrations were established relative to
Treatment C
aqueous headspace standards. For those samples
33 1
35 0
34 1
TDCE
65 0
65 4
58 1
treated by adding 0.25 g of NaHSO4, this same
Ben
53 1
55 2
48 1
TCE
amount of acid was added to the standards to com-
92 3
88 4
82 5
Tol
pensate for the small (approximately 5%) salting-
Total
243
243
222
out effect.
Subsamples analyzed by PT/GC/MS followed
*ND--not detected
the general SW-846 Method 8240 guidelines for
soils containing VOCs at less than 1 g/g (U.S.
C, which had the highest cumulative VOC con-
Environmental Protection Agency 1986). These
centration, showed no reductions in concentration
subsamples were held in VOA vials equipped with
greater than 13% for any of the four analytes. In
a special adapter so that they could be quickly at-
contrast, the concentrations Ben and Tol decreased
tached to a purge-and-trap system. By design, this
by more than 90% over the 14-day holding period
special adapter attaches to the purge-and-trap
in the A and B treatment batches.
manifold after a Teflon ball is pushed out of an
air-tight seat, which momentarily (<1 s) creates a
Effect of acidification
circular opening (<1 mm in diameter) in the lid of
Tables 4 and 5 show the results obtained for the
the 44-cm3 vial. Since the low-level PT/GC/MS
two holding time experiments involving sub-
subsample already contained 3 mL of water, only
samples chemically preserved by acidification. The
an additional 3 mL was used to introduce the in-
subsamples prepared for HS/GC analysis showed
ternal standard.
no losses that exceeded 10% for any of the com-
Table 4. Analyte concentrations (g/g) for soil
RESULTS
subsamples prepared for HS/GC with 0.25 g of
NaHSO4 and stored refrigerated and at room tem-
peratures.
Effect of analyte concentration
The initial (day 0) cumulative VOC concentra-
Analyte
Day 0
Day 4
Day 8
Day 14
tions for the treatment batches A, B and C were
NaHSO4/22C
approximately 5.2, 160 and 240 g/g, respectively
4.50.1
4.40.1
4.30.1
4.30.2
TDCE
(Table 3). After storage for 14 days at room tem-
8.60.2
8.40.1
8.70.3
8.70.1
Ben
perature, the cumulative concentrations had de-
9.10.3
8.50.3
8.70.2
8.60.3
TCE
130
120
130
130
creased for these three treatment batches by 71, 61
Tol
and 8%. With the exception of one TCE value,
NaHSO4/4C
which is perhaps aberrant, the variations in con-
4.10.2
4.60.2
4.30.2
TDCE
centrations between holding times were no greater
7.90.3
9.10.4
8.50.5
Ben
8.10.3
9.00.4
8.40.4
than 13% for the two chlorinated compounds, in-
TCE
120.6
130.6
130.6
Tol
dependent of treatment level. Similarly, treatment
4
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