1 hour, we moved the Microtip to each location
secured, the VOA vial was hand shaken for 5 to 10
and allowed it to sit for 15 minutes prior to turn-
seconds to disperse the soil. After visually check-
ing it on and randomly measuring the eight
ing the foil liner for adhering clumps of soil
working standards.
(knocked off when present), we analyzed the
sample by forcing the sampling line through the
In addition to evaluating working standards,
foil liner and 3 cm beyond, into the VOA vial. The
we did two separate field trials using field-
highest reading displayed by the digital meter
contaminated soils. One involved near-surface
(< 0.3 m deep) soil samples. The other was done
within a couple of seconds of the puncturing of
the foil liner was the value recorded. The total
when two vapor extraction systems were in-
amount of time between exposing a fresh soil sur-
stalled. The boreholes for these remediation sys-
face and completing this analysis was less than 1
tems were made with a roto-sonic drill. Samples
minute.
obtained during this drilling operation extended
to depths beyond 30 m. Both of the field trials
took place on a site where TCE is the principal
Working standards
Separate weighed stock standards of 0.53 mg
contaminant (Hewitt 1994, Hewitt and Shoop
TCE/mL and 1.1 mg gasoline/mL were prepared
1994, Hewitt et al. 1995).
by transferring approximately 10 and 40 L of
In the trial involving near-surface sampling
these constituents, respectively, to 25 mL of
locations, the results obtained from the on-site,
MeOH. Working standards were prepared by
rapid total soil vapor analysis procedure were
transferring 4 L of these stock standards to VOA
compared to results from collocated grab sam-
vials containing 10 or 20 g of the loam from our
ples, collected using an in-vial procedure that
site, so as to achieve the desired 0.2-mg VOC/kg
et al. 1992). The sampling locations were flat 20-
concentration. Aliquots of the stock standard
were transferred with a 10-L syringe to a clean
20-cm surfaces, dug with a spade to depths of 10
surface on the inside of the VOA vial. Once
to 30 cm. At each location, a site-specific working
capped, with the foil liner and with the hole-
standard was analyzed just prior to the digging of
punched septum in place, the vials were hand
the hole. Immediately after exposing a fresh soil
shaken and allowed to sit for at least 2 hours be-
surface, we used two 10-mL syringes to collect
fore analysis. The working standards were ana-
the soil for the total VOC vapor analysis. Once the
lyzed using the same procedure as described for
soil vapor analysis was completed, a single
soil samples.
syringe was used to collect a collocated sample
for HS/GC analysis. The grab samples taken for
HS analysis were transferred with a modified
EXPERIMENTS
syringe directly to 44-mL VOA vials containing 20
Experiments were performed to determine the
mL of Type 1 water (Hewitt et al. 1995). All three
response of the Microtip HL-2000 to working
collocated soil subsamples were obtained within
standards of various moisture contents under dif-
5 cm of one another, and on-site analysis and
ferent meteorological conditions. Initially, we ex-
sample collection was completed within 2 min-
perimented with a native soil. We did a second
utes of a fresh surface being exposed. At some
experiment using the same soil after air drying it
locations, the same hole was dug deeper for addi-
and passing it through a 30-mesh sieve, then cre-
tional sets of samples, without a second (or third)
ating 10 and 20% moisture by weight and water-
working standard being measured.
saturated conditions. These moisture levels were
Soils taken from the boreholes during the sec-
selected for assessing the robustness of the instru-
ond field trial were either transferred from the
mental response for a 0.2-mg TCE/kg working
drilling auger to a plastic bag or were obtained
standard. For this robustness evaluation, six rep-
down-hole in a rigid plastic core liner (1.5 to 3 m
licate 10-g quantities of each soil moisture condi-
length). Samples retrieved after first being trans-
tion were transferred to VOA vials and spiked
ferred to a plastic bag were highly disturbed (dis-
with 4 L of the TCE stock standard. In addition,
aggregated), while those obtained immediately
six VOA vials with no soil were spiked. Dupli-
after the core liners (10-cm diameter) were cut
cates of each sample condition (empty, 10%, 20%,
maintained the native soil structure to a much
and water-saturated) were left at room tempera-
greater degree. Along with the site-specific work-
ture (23C), placed outdoors in direct sunlight
ing standards and VOA vials prepared for the on-
(35C), or put in a coldroom (1C). After waiting
site, rapid total VOC vapor analysis, 22-mL VOA
4
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