Groundwater Sampling Devices
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CONCLUSIONS AND RECOMMENDATIONS
The PDB samplers were the easiest to use of the samplers we tested. How-
ever, they should not be used to sample the larger, more hydrophobic explosive
and pesticide compounds or metals. These findings support USGS guidance
(Vroblesky 2001). Although we were not able to recover comparable concen-
trations of all of the VOCs in these studies, these differences were generally
less than 15%. We believe that most of these differences occurred because this
sampler yielded a time-averaged concentration rather than the concentration at
the time of sampling.
The HydraSleeve samplers were also easy to operate but the up-and-down
motion used to fill them apparently elevated the turbidity in our well. Although
our standpipe studies indicated that this device generally yielded representative
samples of pesticides, explosives, and metals, we would recommend using this
device only in wells where the turbidity is not affected by its use. In some wells,
this may mean redeveloping the well prior to using this device. The results from
these studies indicate that there may be some small loss of volatiles when this
device is used; loss of TCE in the field study was 11%. Leaving the sampler in
the well overnight prior to sampling may reduce these losses.
The Kabis Sampler was relatively easy to deploy but the larger-sized device
was heavy to recover. We observed bubbling in the standpipe and heard it bang
against the wall of the standpipe and well, which apparently raised the turbidity
in the well. This device recovered representative concentrations of explosives,
pesticides, and metals in the lab studies. However, again, we would caution
against using this device to sample for metals or hydrophobic organics such as
pesticides in wells where the turbidity is affected by its use. Because there are
concerns about the surging action within the well with large-diameter devices, we
would recommend using a device that is considerably smaller in diameter than
the well. In the standpipe studies, there were small, statistically significant
differences between the concentrations of VOCs in the controls and samples
taken with this device but the differences were both positive and negative, which
indicates that there is not a strong bias in either direction. The exception to this
was loss of TCE (one of the more volatile analytes) in the low-level study where
loss was substantial, 18%. We also observed a relatively small (7.5%) loss of this
analyte in the field study but this loss was not statistically significant. Einfield
and Koglin (2000) also observed losses of the more volatile analytes, TCE and
PCE, in a similar standpipe study.
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