work plan, such as special training for field per-
samplers choose in advance which procedure of
sonnel, while shipping constraints can be mitigat-
sample handling is most appropriate for a given
ed by surface transport and reducing the quantity
site, or samples for both high-level and low-level
procedures must be obtained. Previously, users of
of MeOH contained in a single vessel.
Method 5030, the procedure cited as being inade-
To deal with the regulatory concerns, we rec-
quate for preventing VOC losses, collected a bulk
ommend the incorporation of a rapid procedure
soil sample that was then shipped to a laboratory
for total VOC analysis at the site. An on-site meth-
so that subsamples could be removed. Under
od of estimating the total concentration of VOCs
past circumstances, laboratory personnel often
present vs. a 0.2-mg/kg working standard could
used an olfactory screening method on the bulk
be part of a decision tree, providing guidance for
sample to establish how the sample would be
subsequent sample preparation and handling.
prepared for analysis.
The actual sample preparation and handling
Proposed Methods 5035 and 5021 use different
could then either be done on-site during the col-
Volatile Organic-compound Analysis (VOA) vials
lection or off-site, provided that an adequate
for their respective automated systems and dif-
transfer device, such as the En Core sampler (En
ferent sample preparation procedures. Conse-
Chem, Inc., Green Bay, Wisconsin) was used (Tur-
quently, it will be imperative that the scope of
riff et al. 1995, Hewitt and Lukash 1996). With this
work clearly identify how the samples will be col-
approach, soil samples from locations where
VOCs were anticipated to be less than 0.2 mg/kg
lected and handled, and the specific equipment
would not be placed in MeOH.
necessary for their analysis. The laboratories' an-
Maintaining the representativeness of highly
alytical protocols become an important concern
contaminated (>1 mg/kg) soil samples is impor-
because, if the dispersionextractant solution is
tant because they are often close to the source, i.e.,
not an organic solvent such as MeOH, the vessel
residual or trapped product. Removal or in-situ
can not be opened to change tops, remove ali-
remediation of this separate or residual phase
quots or introduce surrogates without significant
losses of VOCs. This is because, in the absence of a
should receive the highest priority. In contrast,
solvent, VOCs quickly partition into the gas
concentrations less than 1 mg VOC/kg can be far
phase where they can be readily exchanged with
removed from sources, particularly when the site
ambient air when the vessel is opened. For this
has no confining geological features. Moreover,
reason it may be best to add surrogate com-
areas where only low level contamination exists
pounds after sample collection via a needle punc-
will most likely clean up by degradation or diffu-
ture of the septum.
sion over time, or both, once the source region has
When soils are dispersed in a solvent, such as
been cleaned up.
MeOH, the VOCs are retained as solutes, thus al-
This report presents a feasibility study for a to-
lowing the containers to be opened for the inter-
tal VOC decision marker. Our intent is to inform
mittent removal of aliquots without incurring
site investigators and regulators of soil sample
losses (Hewitt 1995). Other advantages of using
collection and handling practices that better meet
MeOH are that it is less susceptible to matrix ef-
the objective of obtaining representative site in-
fects (Hewitt et al. 1992, Hewitt 1996b, Askari et
formation. This will allow effective cleanup strat-
al. 1996, Minnich et al. 1996, Hewitt 1997), it
egies to be implemented. When in-vial proce-
allows for multiple determinations per sample,
dures are coupled with limited disruption and
exposure collection techniques, VOCs present as
and it is an effective chemical preservative
vapor, sorbed, or liquid are included in the mea-
(Hewitt 1995).
surement (Hewitt 1996a).
Although it is well recognized that in-vial or
solvent immersion approaches are necessary for
maintaining site-representative VOC concentra-
OVERVIEW
tions in soil, there continues to be considerable
reluctance among regulators to accept the use of
Field-portable instruments that measure con-
MeOH in the field during sample collection activ-
centrations of VOCs in the vapor phase within
ities. Human toxicity, transportation issues (i.e.,
soil samples can be affected by the grain size, por-
flammability), and regulatory issues have been
osity, cohesiveness, moisture content, and
cited as reasons for discouraging this practice
adsorption capacity of the matrix, and ambient
(Lesnik and Loy 1995). The first reason cited can
meteorological conditions. Therefore, working
be addressed by additional precautions in the
standards used to estimate soil VOC concentra-
2
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