tions (14 g/L) (Appendix Table B4). After 8 hr,
containing compounds (Johnson and Stevenson
1978). These results agree reasonably well with
the TCE concentration in water that was pumped
the findings from our static study (Parker and
through the PVDF tubing was below the detection
level (< 2.6 g/L). In contrast, both the LDPE and
Ranney 1996) where we did not find any spurious
PP1 tubings continued to release high g/L con-
peaks in any of the test solutions exposed to the
PVDF, LDPE, and PP2 tubings, and found only
centrations of TCE into the DI water for 824 hr
and low g/L concentrations for the remainder of
one spurious peak in the test solutions exposed to
the PP1 and P(VDF-HFP) tubings.
the experiment (four days or 96 hr).
These results and those of Devlin (1987) show
Desorption/leaching study
polymer tubing much more readily than from
other types of tubing, simply rinsing fluoropoly-
Another concern in the monitoring industry is
mer tubing with organic-free water is not ade-
whether there is carryover when a tubing is used
to sample more than one well. It is not known
The relationship between the pumping time
how long a tubing would continue to desorb
and the concentration desorbed for each of the
sorbed contaminants. This study looked at the
three tubings is given in Table 7. In this instance, a
dynamics of this process for three tubings that
negative log function adequately describes des-
ranged from relatively nonsorptive to highly
orption from the more sorptive polymers (LDPE,
sorptive (PVDF, PP1, and LDPE). These tubings
PP1).
were contaminated by pumping TCE-contami-
Table 7. Relationship between the pumping
nated well water through them at a flow rate of 1
time (t) and the concentration, mg/L (Cd), of
L/min for seven days. Figure 11 shows the mean
TCE desorbed into water pumped through
concentration (mg/L) of TCE that was released
100 ft of contaminated tubing at 100 mL/min.
into the DI water pumped through these three
tubings at a flow rate of 100 mL/min. (Appendix
Contact
Table B4 gives all the data.) After 30 min, which
time
r†
Material
(min.)*
Relationship
corresponds to rinsing the tubing with three tub-
ing volumes of water, DI water pumped through
PVDF
10
Cd = 0.971 0.0696 log(t)
0.625
the PP1 and LDPE tubings contained high g/L
LDPE
10
Cd = 0.419 0.248 log(t)
0.925
concentrations of TCE (776 and 396 g/L, respec-
PP1
10
Cd = 0.647 0.343 log(t)
0.992
tively), while water that was pumped through the
*Time for water to pass through tubing.
PVDF tubing contained only low g/L concentra-
† Correlation coefficient.
1.0
PVDF
PE
0.8
P1
0.6
0.4
0.2
0
25
50
75
100
Time (h)
Figure 11. Desorbed concentration of TCE in organic-free water pumped
through 100 ft of contaminated tubing.
13