4
ERDC/CRREL TR-02-12
The manufacturer recommends that the sampler should be slowly and
steadily lowered into the well. The inlet and exhaust ports are designed so that
the sampler should not fill as it is being lowered into the well. Once the sampler
has remained stationary for a few seconds, it begins to fill under hydrostatic
pressure and the displaced air (or nitrogen if that was used to purge the system)
escapes through the exhaust port. The sampling bottle rinses six times with for-
mation water, which spills into the larger chamber underneath, prior to collecting
the final sample. According to the manufacturer, the sample container is filled
from the bottom up via laminar flow and in the absence of air, effervescence,
splashing, and bubbling, thereby eliminating those sources of volatilization. The
manufacturer also claims that turbidity is reduced by the hydrodynamic shape of
the sampler and that the sample is collected under ambient pressure in the water
column, which reduces or prevents loss of volatiles due to change in pressure or
other analytes affected by atmospheric oxygen. Specially designed Teflon cone
caps that eliminate the air space above the sample can be purchased for VOA
vials. According to the manufacturer, other advantages are that the device is easy
to operate, is readily decontaminated, and that purging is not required in most
cases, thereby reducing the costs associated with using this device.
Disadvantages include that the preservative must be added after filling the
sample container and that the device cannot be used in wells smaller than 2
inches. These devices are relatively expensive (when compared with disposable
samplers), ranging from ~0 (Model 1) to 00 (Model 3).
Although we did not find any journal papers that examined the capabilities
of this device, we did find an EPA report (Einfeld and Koglin 2000) that did so.
They conducted a standpipe study in which they compared the ability of this
device to recover six VOCs from test solutions. They tested this device in test
solutions with both high (~200 g/L) and low concentrations (1020 g/L) of the
VOCs at two depths within the standpipe. Although they reported that there were
no significant differences for 16 of the 24 comparisons they made, there were
significant differences in eight instances. For five tests there was a negative bias,
and for three tests there was a positive bias. Concentrations of 1,2-dichloroethane
were higher than the controls in three tests (differences ranged from 11% to
18%). Concentrations of TCE and PCE were lower than the controls in four tests
(all these losses were at the high concentration; mean losses were 19% and 32%,
respectively). We observed that this loss appeared to correlate with Henry's
constant for the VOCs tested, i.e., losses were greater for the more volatile
compounds. They also reported that analysis of samples taken from a less
contaminated layer that was below a more contaminated layer showed that this
sampler appeared to either entrain contaminants from the dirty layer or collect a
partial sample as it was lowered through the dirty layer. They also felt that this
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