g/L. Currently, the EPA has not set an MCL for
tions of samples exposed to PVC, PTFE, or FEP
casings. However, after 40 days' exposure, con-
silver in drinking water. However, a previous MCL
centrations of samples exposed to FEP casings
value given in the EPA's Interim Primary Drink-
were significantly higher than the controls. Gen-
ing Water Standards (Federal Register 1975) was
50 g/L, and the values observed in this study
erally, concentrations of Ni in samples exposed to
the two fiberglass materials were significantly
are well below this value. Again, there are no data
greater than the other three materials. Mean nor-
available for these four analytes that would allow
malized concentrations for samples exposed to
comparisons to be made with SS casings.
these two materials ranged from approximately 2
to 3.5 times the control values (Table 4). However,
SORPTION STUDY
these elevated Ni levels may be the result of an
experimental artifact rather than constituents
Initial concentrations were 51 g/L for As, Cr,
leaching from the casing material. Nickel electro-
and Pb and 20 g/L for Cd.
plate was used to bind the diamonds to the steel
band that was used to cut these two materials.
Anions
The other materials were cut with a steel slotting
saw, which did not have diamonds bonded to it.
Arsenic
Even for the samples with the highest concen-
There was no significant loss of As in any of
trations of Ni, leached concentrations were less
the samples exposed to the casing materials
than 3 g/L, well below the MCL of 100 g/L set
(Table 5, Table A1). Since arsenic exists as nega-
by the EPA for drinking water (US EPA 1994).
tively charged arsenates or arsenites under the
No comparison can be made with the SS cas-
oxidizing to slightly reducing conditions found
ings, because Hewitt's (1989) study, which was
in natural waters (Fowler et al. 1979), these re-
conducted under similar conditions, did not test
sults agree with several previous studies (Masse
for Ni. Under anoxic conditions, however, Hewitt
et al. 1981, Parker et al. 1990, Hewitt 1992) that
(1992) found that SS 304 and 316 casings leached
have shown that anions do not strongly associate
consistently higher concentrations of Ni than any
with polymeric surfaces. In comparison, data from
of the casings we tested in this study. Means for
samples exposed to SS 316 were the highest and
Table 5. Mean normalized concentrations of As,
were 4 to 5 times higher than the concentrations
Cd, Cr, and Pb sorbed by well casings.
of samples exposed to the fiberglass casings.
Contact time, hours
Zinc
Treatment
1
8
24
72
After one day of exposure, all the samples ex-
ARSENIC
posed to the well casings had significantly higher
PVC
1.02
1.01
1.01
1.00
PTFE
0.99
1.01
1.00
0.99
concentrations of Zn than the control samples
FEP
0.99
1.00
1.01
1.00
(Table 3g, Table 4). Concentrations in samples ex-
FRE
0.99
0.99
0.99
0.99
posed to the FRP casings were significantly high-
FRP
1.01
1.00
1.00
1.00
er than those in samples exposed to the other cas-
CADMIUM
ings; mean normalized concentrations were
PVC
0.93
0.87
0.83
0.79
approximately 7 to 12 times control values.
PTFE
0.97
0.95
0.93
0.99
FEP
0.98
0.96
0.95
0.98
Leached concentrations cannot be compared with
FRE
0.95
0.91
0.89
0.94
any MCL standard for Zn because the US EPA
FRP
0.96
0.96
0.90
0.94
has not set one. Also, no comparisons can be made
with the SS casings because there are no data avail-
PVC
1.01
1.01
1.00
0.99
able.
PTFE
1.00
1.00
1.00
0.99
FEP
1.00
1.00
1.01
1.00
FRE
0.95
0.98
0.99
0.98
Arsenic, beryllium,
FRP
1.01
1.03
1.00
1.00
selenium, and silver
LEAD
Concentrations of As, Be, and Se were all be-
PVC
0.90
0.70
0.61
0.56
low the MDL. The majority of the values for Ag
PTFE
0.98
0.95
0.94
0.93
were also below the MDL, and do not show any
FEP
0.97
0.95
0.93
0.93
apparent pattern or trend (Table 3h). In all cases,
FRE
0.89
0.65
0.55
0.45
FRP
0.91
0.71
0.59
0.52
leached concentrations of Ag were less than 0.80
9
Previous Page
