Sorption and Leaching of
Trace-Level Metals by Polymeric Well Casings
THOMAS A. RANNEY AND LOUISE V. PARKER
cording to the manufacturer 's literature, the FRP
INTRODUCTION
used in this study consisted of 70% fiberglass and
Ideally, any material that is used as either a
30% polyester resin (by weight).
well casing or screen in a groundwater monitor-
A literature review found only a few studies
ing well should be strong enough to remain intact
that dealt with sorption of organic solutes and
once installed in the well, should resist degrada-
leaching of organic constituents by these four ma-
tion by the environment, and should not affect
terials. Gillham and O'Hannesin (1990) rated sev-
analyte concentrations in samples by leaching or
eral polymeric materials with respect to sorption
sorbing organic or metal contaminants. Recent
of organic solutes (Table 1). With respect to leach-
draft RCRA guidance by the U.S. Environmental
ing of organic contaminants from FRE casing,
Protection Agency (US EPA 1992) acknowledges
Cowgill (1988) found that two organic contam-
that none of the most commonly used casing ma-
inants leached from ground casings (diethyl
terials in groundwater monitoring wells (polytet-
phthalate and bisphenol A), but nothing leached
rafluoroethylene [PTFE], polyvinyl chloride
from intact casings after three weeks' contact.
[PVC], or stainless steel [SS]) can be used for all
To assess the overall suitability of these four
monitoring applications. Therefore, we undertook
materials for use in groundwater monitoring wells,
a series of studies to assess the suitability of sev-
we conducted a series of studies to examine the
eral other candidate materials for use in well cas-
chemical resistance of these materials (Ranney and
ings. The four materials we initially considered
Parker 1995), sorption of organic solutes by these
were acrylonitrile butadiene styrene (ABS), fluor-
materials (Ranney and Parker 1994), and leaching
inated ethylene propylene (FEP), fiberglass-rein-
forced epoxy (FRE), and fiberglass-reinforced plas-
Table 1. Performance ranking of polymeric
tic (FRP).
well casing materials (from least affected to
For anyone not familiar with these materials,
most affected).
ABS is a thermoplastic material like PVC and is a
terpolymer of acrylonitrile, butadiene, and sty-
Degradation by Chemicals
rene. A wide range of properties can be achieved
FEP, PTFE < FRE < FRP < PVC < ABS
by varying the ratio of these monomers and by
Taken from Ranney and Parker (1995)
using additives (Sax and Lewis 1987). FEP is a
Sorption of Organic Solutes
fluoropolymer and is a copolymer of tetrafluoro-
FRE, PVC < FEP, PTFE, FRP << ABS
ethylene and hexafluoropropylene. It is similar to
Taken from Ranney and Parker (1994)
PTFE in its chemical and physical properties, al-
Rigid PVC < FG < PF < PTFE < PE < flexible PVC
though it has a slightly higher coefficient of fric-
where: FG = epoxy-impregnated fiberglass
tion (Sax and Lewis 1987). According to the man-
PE = polyethylene
ufacturer, FRE well casing is constructed of 75%
PF = polyvinylidene fluoride
Taken from Gillham and O'Hannesin (1990)
high silica glass and 25% high purity, closed mo-
lecular epoxy. The epoxy is manufactured from
Leaching of Organic Constituents
bisphenol A-type epoxy resins cured with methyl
PVC, FEP, PTFE < FRE < FRP << ABS
Taken from Ranney and Parker (1994)
tetrahydrophthalic anhydride (Cowgill 1988). Ac-
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