HP 6890 series autosampler-injector, all
Table 1. Summary of TCE studies using a bailer.
under the control of HP-Chemstation soft-
Mean initial conc.
Mean desorbed conc.
ware, was used. The GC was operated in
(mg/L)† (S.D.)
TCE study
(mg/L)* (S.D.)
Treatment
direct injection mode with 1-L injections.
Hydrogen was used as the carrier gas (151 First
119 (0.6)
wash
0.0032 (0.0001)
cm/sec) and nitrogen as the makeup gas Second
132 (0.0)
wash
0.0044 (0.0005)
(60 mL/minute). The instrument was set
wash + oven dry
LD
with the following operating parameters:
* Concentration of the well water
an injector temperature of 270C; and a
†
Concentration found in DI water from the "decontaminated"
detector temperature of 300C. The oven
device
was programmed with an initial tempera-
LD = Less than method detection limit (0.0024 mg/L)
ture of 150C and a hold time of one
S.D. = Standard deviation
minute, then ramp at 20C/minute to
250C and hold five minutes. The column was a
ture was well below the materials' reported deg-
Restek Rtx-200, 6-m 0.53-mm i.d., 1.50-m film.
radation temperature. Clearly, if this method is to
The estimated detection limits were determined
be used, the hottest temperature the materials in
according to the EPA protocol described in the
the device can withstand needs to be determined.
Federal Register (1984).
Pump studies
Third TCE study--Effect of a wash procedure on
a pump exposed to high concentrations. We see
RESULTS AND DISCUSSION
that when the pump and tubing received no
cleaning treatment other than pumping three
TCE studies
The experimental data showing the results for
system volumes of DI water through the system,
all the replicates in the TCE studies can be found
substantial concentrations of TCE were released
in Tables A1A6.
into the DI water as it was pumped through the
system (Table 2).
Bailer studies
Following a hot detergent wash and rinse, there
First TCE study--Effect of a hot detergent wash on
were still detectable concentrations of TCE in the
bailer exposed to high concentrations. In this study,
DI water when it was pumped through the sys-
the bailer was washed with hot detergent and
tem. However, these concentrations were more
rinsed with hot water after it was used to sample
than an order of magnitude lower than before the
a well with relatively high concentrations of TCE.
wash treatment. We observed that the desorbed
Table 1 shows that this treatment still leaves re-
concentration actually increased after more water
sidual contamination on the bailer; the contami-
was pumped through the system. We believe this
nation is then desorbed back into the DI water at
is because outer portions of the sampling tubing
detectable levels when a sample is taken.
and the compressed-air tubing were made of poly-
Second TCE study--Effect of an additional hot air
ethylene. Polyethylene tubing has been shown to
drying step on bailer exposed to high concentrations.
be more sorptive of TCE than the rigid fluoro-
Because the previous study showed that washing
polymers (FEP, PTFE, etc.) (Parker and Ranney
alone was not sufficient to completely remove the
1996, 1997a) and also desorbs higher concentra-
contamination, the bailer was dried in an oven at
tions of TCE back into solution (Parker and Ranney
105C for 24 hours after using the same wash
1997a). Thus, we believe that TCE sorbed by the
procedure on the bailer as in the previous study.
outer PE tubing was desorbed into the DI water
The hot air treatment appears to have been ef-
in the upper portions of the standpipe (above the
fective as we were unable to detect any TCE
pump) and was then drawn down into the pump
when the bailer was used to sample fresh DI
with additional pumping.
water (Table 1).
Following this treatment, the tubing and blad-
However, there was one problem with this de-
der pump were left to air dry for one week. This
contamination protocol: the bailer was warped by
was done to allow for slow desorption of the
the oven drying step. We are at a loss to explain
sorbed TCE. However, even after one week, sig-
this because information supplied by the manu-
nificant levels of TCE were released into the DI
facturer of FEP and PTFE tubing (the same mate-
water by both the bladder pump and the tubing.
rials used in the bailer) claimed that this tempera-
Thus, air drying at room temperature for one
9
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