Table 4. Comparison of average and standard deviation of concentrations (mg/kg)

Table 3. Average and standard deviations (n = 2) of analyte concentrations (mg/kg)

DISCUSSION - SR99_050019

SR99_05
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12

prior to preparing for analysis. The results of these

Table 4. Comparison of average and standard de-

experiments involving field-contaminated soils

viation of concentrations (mg/kg) for samples re-

were very consistent with the laboratory findings

moved from core barrel liners in the field (D0) vs.

those stored for two and four days at 4 2C in

for this analyte (Table 5), e.g., no statistically sig-

nificant change in concentration over a short two-

core barrel liners covered with a thin metal disk

day holding period, and frequently no significant

lid, then wrapped with a sheet of translucent, non-

change over extended holding periods.

elastic Teflon.

The first laboratory experiment using empty

Storage period

VOA vials as containers for transporting and stor-

ing soil samples evaluated the effect of storage

Compound

D0*

D2**

temperature. The results in Table 7 show the same

trends in analyte concentration relative to room

1st Coring

temperature and refrigerated storage, as seen in

TDCE

ND†

CDCE

experiments performed using sealed glass am-

0.620.08

0.400.07

0.110.04

TCE

poules as storage chambers (Fig. 2, Hewitt 1995a).

65%††

18%

At room temperature there was rapid degradation

2nd Coring

of the aromatic compounds. Indeed, after seven

TDCE

days of storage at 21 2C, Ben, Tol, E-Ben, and p-

0.250.04

0.150.01

0.120.01

CDCE

Xyl were not detected. When stored at 4 2C for

60%

48%

0.420.07

0.240.02

0.110.11

14 days, these same four aromatic compounds

TCE

57%

26%

were reduced in concentration by more than 60%

from the D0 values. With the exception of CDCE,

3rd Coring

0.0950.038

0.0640.004

the chlorinated compounds showed much smaller

TDCE

67%

losses for these storage periods and conditions.

0.470.09

0.350.01

0.100.03

CDCE

When these samples were stored at 12 3C, the

74%

21%

concentrations established after 14 days of stor-

0.240.06

0.140.01

0.0240.011

TCE

age in freezer were within 5% of the values estab-

58%

10%

lished on D0. This table also shows that there was

*n = 4.

good agreement between the spike and D0 analyte

**n = 2.

concentrations.

†ND = Not detected.

In the second experiment, we compared intro-

††Percentage found relative to the D0 analyte concentration.

ducing spiked samples to a VOA vials that already

contained a solution vs. introducing them to empty

VOA vials and then adding solution through the

first two days of storage at 4 2C. Furthermore,

septum after various storage periods and condi-

this slow rate of loss appears to have continued

tions. Direct headspace analysis vs. MeOH extrac-

for Ben and TDCE after the samples in the En Core

tion was also compared. Table 8, which shows the

samplers were moved to the freezer. The remain-

results of these comparisons, indicates (1) there is

ing analytes (TCE, PCE, E-Ben, p-Xyl, and o-Xyl)

no apparent effect caused by introducing the wa-

showed no statistically significant changes in

ter through septa, (2) analyte recoveries relative

analyte concentrations relative to D0, while CDCE,

to the spike concentration were not as accurate for

and Tol showed no statistically significant reduc-

samples dispersed in water and analyzed directly

tion in concentration after being placed in the

as opposed to those extracted with MeOH, and

freezer (e.g., relative to D2).

(3) losses of aromatic compounds decreased when

Each of the 10 field trials (Table 6) involving the

frozen. The first observation suggests that adding

5-g En Core sampler was initially evaluated using

an aqueous solution through septum, as would

the Students' t-test at a 95% confidence interval.

be necessary for either headspace or purge-and-

This statistical analysis showed that in only one

trap analysis, is comparable to having the aque-

case was there a difference between the mean TCE

ous solution present in the VOA vial at the time of

concentrations. The trial (trial 6) that had signifi-

sample collection. The discrepancy in analyte re-

cant difference between the mean values showed

covery relative to these two methods of sample

that a slightly lower (12%) TCE concentration ex-

preparation, i.e., vapor partitioning vs. MeOH

isted for the soil samples obtained and stored in

extraction, is consistent with that of earlier stud-

the En Core sampler for seven days at 4 2C,

ies (Askari et al. 1996, Minnich et al. 1996, Hewitt

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