only 10 to 15% over a week when the concentra-
analyte of concern has properties that favor a gas-
tions were around 3 mg/kg, while losses of be-
eous state even more so than TDCE (i.e., vinyl chlo-
tween 35 to 60% occurred in five days when con-
ride) it would be prudent to use even more strin-
centrations were some two orders of magnitude
gent protocols, i.e., a shorter holding period
lower. This observation suggests that it may be
between collection and analysis.
more critical to preserve samples with low levels
(less than 0.2 mg/kg) of VOC contamination as
compared to those with moderate and high con-
SUMMARY
centrations. Additional supporting evidence for
this observation is that experiments performed
Within the last few years, new guidance has
under similar conditions with this same soil type
come from the U.S. EPA and ASTM with regard to
showed even slower losses when concentrations
how soil samples acquired for VOC characteriza-
were around 8 mg/kg (Fig. 2), and were negligible
tion should be collected and handled in prepara-
when the total VOC concentrations exceeded 200
tion for instrumental analysis. The features of this
mg/kg (Hewitt 1995b).
new guidance that will have the greatest impact
The results in Table 8 suggest that a slurry com-
on improving data quality are the use of less dis-
posed of 5 mL of water and 5 g of soil held in a 22-
ruptive and fewer transfer steps, and the use of
mL or larger VOA vial could be frozen as a means
vessels with hermetically sealable closures for
to prevent the biological degradation of VOCs. Al-
transportation and storage. The new measures for
though vessels filled to less than a third of their
sample preservation will also help improve the
total volume did not break when frozen, they were
data quality. To assist with the implementation of
susceptible to breakage under these conditions
this new guidance, two very different protocols
when vessels were filled to around half full.
have been developed. In one case, all steps lead-
The last observation is that once a septum has
ing up to those associated with the analysis pro-
been punctured, regardless of the presence of
cess are performed in the field, while the other
MeOH, analytes may diffuse through this breach
more traditional approach has all steps associated
in the protective layer. Although not shown here,
with sample preparation and analysis occur in a
additional studies has shown that this loss mecha-
laboratory.
nism is more prevalent when soil is present. To
The focus of this report was to evaluate three
limit this potential source of error, the needle used
methods for secure transporting and storing
to introduce a solution into a sealed VOA vial
samples so that the laboratory protocol could be
should be small in diameter, and sample analysis
used. This study showed core barrel liners
should occur soon (one or two days) thereafter.
wrapped with sheets of Teflon or aluminum foil
Furthermore, if these samples are archived, an ali-
failed to comply with the intent of this new guid-
quot of MeOH should either be transferred to an
ance, i.e., a hermetic seal was not created with re-
appropriate-sized vessel or the punctured septum
spect to the analytes of concern. In contrast, the
should be replaced with one that is intact.
storage of samples in the En Core sampler or an
Project data quality objectives should be con-
empty VOA vial was found to be consistent with
sulted in addition to experimental findings, such
the intent of the new guidance, and in general 80%
as those presented here, when developing stan-
or greater of the analyte concentrations were re-
tained over a two-day storage period at 4 2C.
dard operating procedures. The collection, trans-
portation, and storage of samples to be prepared
Moreover, after this initial two-day storage period,
and analyzed for VOCs presents numerous chal-
which corresponds to the length of time currently
lenges that are seldom rivaled by the other classes
recommended before samples need to be pre-
served, samples transferred to a freezer (12 3C)
of hazardous constituents. Even under the con-
trolled conditions afforded by laboratory experi-
often showed no significant change in concentra-
ments the results associated with those VOCs that
tions over an additional 12 days of storage. For
have high vapor pressures are often less precise
several reasons, this method of sample preserva-
and accurate as compared to less volatile analytes.
tion appears to be better suited for VOCs in soil
Inspection of the variance in the TDCE concentra-
matrices than acidification. For instance, acidifi-
tions and the values established for this analyte
cation is incompatible with carbonates, causes the
as compared to the spike concentration, shown in
decomposition of styrene and perhaps other tar-
Tables 5 and 7, respectively, are examples of this
get analytes, and has the potential to cause the
phenomena. For this reason, when the principal
formation of acetone. These findings and obser-
19
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