United States
Environmental Protection
Agency
Office of
Research and
Development
Office of Solid
Waste
and Emergency
Response
EPA/540/4-91/005
Revised August
1992
&ER& Ground-Water Issue
SURVEY OF LABORATORY STUDIES RELATING TO
THE SORPTION/DESORPTION OF CONTAMINANTS
ON SELECTED WELL CASING MATERIALS
Jose L. Llopis1
INTRODUCTION
The Regional Superfund Ground Water Fo-
rum is a group of ground-water scientists
representing U.S. Environmental Protection
Agency's (U.S. EPA's2) Regional Offices, or-
ganized to exchange up-to-date information
related to ground-water remediation at haz-
ardous waste sites. Well casing materials
used at hazardous waste sites is an issue
identified by the forum as a concern of
CERCLA decision makers.
To address this issue, this paper was pre-
pared through support from the Environmen-
tal Monitoring Systems Laboratory-Las Vegas
(EMSL-LV), under the direction of J. Lary
Jack, with the support of the Superfund Tech-
nical Support Project. For further information,
contact Ken Brown, EMSL-LV Center Direc-
tor, at FTS (702) 798-2270 or J. Lary Jack at
FTS (702) 798-2270.
All aspects of a ground-water sampling pro-
gram have the potential to affect the composi-
tion of a ground-water sample. The potential
for the introduction of sample error exists from
the time drilling commences and continues to
the time water samples are analyzed in the
laboratory. The high degree of accuracy
(parts per billion (ppb) range) required of some
chemical analysis dictates that all potential
sources of error of a ground-water sampling
program be identified and sources of error in
such aspects be minimized. One potential
source of error is the interaction of the ground-
water sample with material used in well casings
for monitoring wells. Well casing materials may
introduce error in a sample by interacting with
water while it is still in the well and altering the
water composition. Proper selection of casing
materials used for ground-water monitoring
wells is critical in minimizing errors introduced
by this interaction. This paper is a survey of
scientific studies related to a specific process
which potentially affects materials used to pro-
duce monitoring well casings and screens.
This paper should not be exclusively used to
select the proper well casing/screen material
for a site specific situation. Other factors must
be considered into the selection process, in-
cluding: site specific water chemistry, sub-
strate physical bearing properties, formation
conductivity, design life of monitoring well,
presence of NAPL's, etc.
Selection of the proper casing material for
monitoring wells has been a subject of much
controversy since the publication of the U.S.
EPA's Resource Conservation and Recovery
Act (RCRA) Ground-Water Monitoring Techni-
cal Enforcement Guidance Document (TEGD)
(U.S. EPA 1986). The TEGD suggests the use
of polytetrafluoroethylene (PTFE, Teflon®) or
stainless steel (SS) for sampling volatile organ-
ics in the saturated zone and further states
"National Sanitation Foundation (NSF) or
American Society for Testing and Materials
(ASTM) approved polyvinylchloride (PVC) well
casing and screens may be appropriate if only
Geotechnical Laboratory, Department of the Army Waterways Experiment Station, Corps of Engineers, 3909 Halls Ferry
Road, Vicksburg, MS 39180-6199
For a list of abbreviations, see page 15.
/T \
£ I echnology ~Z-
O
-------
trace metals or nonvolatile organics are the contaminants antici-
pated".
SOURCES OF ERROR
Error can be introduced into the ground-water sample by casing
materials with several processes including:
a. Chemical attack of the casing material.
b. Sorption and desorption.
c. Leaching of the casing material.
d. Microbial colonization and attack (Barcelona et al., 1985)
Before proceeding further, it is necessary to define the terminol-
ogy used in this report. The terms "sorbed" or "sorption" are used
many times in the literature to refer to the processes of adsorp-
tion and absorption especially when the exact mechanism is not
known. Adsorption is defined as the adherence of atoms, ions,
or molecules of a gas or liquid called the adsorbate onto the
surface of another substance, called the adsorbent; whereas,
absorption is the penetration of one substance (absorbate) into
the inner structure of another called the absorbent. In this report,
rather than distinguishing between the processes of adsorption
and absorption, the term sorbed will be used synonymously with
both processes, unless otherwise noted. Desorption refers to
the process of removing a sorbed material from the solid on
which it is sorbed. Leaching refers to the removal or extraction
of soluble components of a material (i.e., casing material) by a
solvent (Sax and Lewis, 1987).
Casing material in contact with a liquid has the potential to allow
either leaching and/or sorption. Factors influencing sorption of
organics and metals are discussed by Jones and Miller (1988)
and Massee et al., (1981), respectively. These factors include:
1. The surface area of the casing. The greater the ratio of
casing material surface area to the volume of adsorbate the
greater the sorption potential.
2. Nature of the analyte (chemical form and concentration).
3. Characteristics of the solution. This includes factors such
as pH, dissolved material (e.g., salinity, hardness),
complexing agents, dissolved gasses (especially oxygen,
which may influence the oxidation state), suspended matter
(competitor in the sorption process), and microorganisms
(e.g., trace element take-up by algae).
4. Nature of the casing material (adsorbent). This includes
factors such as the chemical and physical properties of the
casing material.
5. External factors. These factors include temperature, con-
tact time, access of light, and occurrence of agitation.
According to Barcelona et al., (1988) considerations for select-
ing casing material should also include the subsurface geo-
chemistry and the nature and concentration of the contaminants
of interest. Tney also state that strength, durability, and inert-
ness of the casing material should be balanced with cost
considerations. Ford (1979) summarized factors related to the
analyte that can affect adsorption (Table 1).
TABLE 1. FACTORS AFFECTING ADSORPTION
1. An increasing solubility of the solute in the liquid carrier decreases its
adsorbability.
2. Branched chains are usually more adsorbable than straight chains. An
increasing length of the chain decreases solubility.
3. Substituent groups affect adsorbability.
Substituent Group
Hydroxyl
Amino
Carbonyl
Double Bonds
Halogens
Sulfonic
Nitro
Aromatic Rings
Nature of Influence
Generally reduces absorbability; extent of decrease
depends on structure of host molecule.
Effect similar to that of hydroxyl but somewhat
greater. Many amino acids are not adsorbed to any
appreciable extent.
Effect varies according to host molecule; glyoxylic
are more adsorbable than acetic but similar increase
does not occur when introduced into higher fatty
acids.
Variable effect as with carbonyl.
Variable effect.
Usually decreases adsorbability.
Often increases adsorbability.
Greatly increases adsorbability.
4. Generally, strong ionized solutions are not as adsorbable as weakly
ionized ones; i.e., undissociated molecules are in general preferentially
adsorbed.
5. The amount of hydrolytic adsorption depends on the ability of the
hydrolysis to form an adsorbable acid or base.
6. Unless the screening action of the adsorbent pores intervene, large
molecules are more sorbable than small molecules of similar chemical
nature. This is attributed to more solute-adsorbent chemical bonds
being formed, making desorption more difficult.
7. Molecules with low polarity are more sorbable than highly polar ones.
(Source: Ford, 1979)
Berens and Hopfenberg (1981) conducted an investigation to
determine a correlation between diffusivity and size and shape
of the penetrant molecules. Their study indicated that as the
diameter of "spherical" penetrant molecules increased, the
diffusivity decreased exponentially. Another finding of the study
was that flattened or elongated penetrant molecules such as n-
alkanes had greater diffusivities than spherical molecules of
similar volume or molecular weight. This may indicate that
elongated molecules can move along their long axis when
diffusing through a polymer.
Reynolds and Gillham (1985) used a mathematical model to
predict the absorption of organic compounds by the different
-------
polymer materials. Curves based on their model were fit to
experimental data and showed reasonable agreement. This
agreement supports their concept that uptake is the result of
absorption. They also determined that no relationship was
found between the order of absorption and readily available
parameters such as aqueous solubility or octanol/water parti-
tioning coefficient. They concluded that predicting the amount
of absorption for a particular organic compound was not pos-
sible at that time.
Gillham and O'Hannesin (1990) attempted to predict the rate of
uptake of benzene, toluene, ethylbenzene, and p-, m-, and o-
xylene onto samples SS316, PTFE, rigid PVC, flexible PVC,
polyvinylidene fluoride (PVDF), flexible PE,and FRE employing
the same model as that used by Reynolds and Gillham (1985).
Their results showed the diffusion model data fitted their experi-
mental data quite well, suggesting the sorption mechanism was
absorption into the polymer materials agreeing with the results
of Reynolds and Gillham (1985). They also determined, that for
the organic compounds used in this study, the rate of uptake
increased with increasing hydrophobicity of the organic com-
pound and varied with the physical characteristics of the poly-
mer casing material.
TYPES OF CASING MATERIALS
A variety of materials may be used for casing and screening
ground-water monitoring wells. These materials include glass
and metallic and synthetic materials. Rigid glass has the least
potential for affecting a sample and is the material of choice for
sampling organics (Pettyjohn et al., 1981). However, because
the use of glass as a casing material is impractical for field
applications because of its brittleness, it will not be further
considered in this report. Instead, this report will focus on the
metallic and synthetic materials most commonly used for
monitoring well construction.
Metals
Metals are often chosen as casing materials because of their
strength. Metals used for casing include SS, carbon steel,
galvanized steel, cast iron, aluminum, and copper. The various
metals used for well casings may react differently to different
compounds. Reynolds et al., (1990) conducted a study using
SS, aluminum, and galvanized steel to determine their potential
to cause problems in samples collected for analysis for haloge-
nated hydrocarbons. The metals were subjected to aqueous
solutions of 1,1,1-trichloroethane (1,1,1-TCA), 1,1,2,2-
tetrachloroethane (1,1,2,2,-TET), hexachloroethane (HCE),
bromoform (BRO), and tetrachloroethylene (PCE) for periods
up to 5 weeks. The study indicated that, of the metals used, SS
was the least reactive followed by aluminum and galvanized
steel. Stainless steel caused a 70 percent reduction of BRO and
HCE after 5 weeks. Aluminum caused over a 90 percent
reduction for all but one of the compounds while galvanized steel
showed over a 99 percent reduction for all of the compounds.
Many investigations have shown that errors may be introduced
into the water sample as a result of using metal casings. For
instance, Marsh and Lloyd (1980) determined steel-cased wells
modified the chemistry of the formation water. They state that
trace element concentrations of the ground water collected from
the wells were not representative of the aquifer conditions and
did not recommend the use of steel casing for constructing
monitoring wells. They suspected that reactions between the
ground water and the steel casing raise the pH of the water
which causes the release of metal ions into solution. Pettyjohn
etal., (1981) found metals strongly adsorb organic compounds.
For example, they claim that DDT is strongly adsorbed even by
SS. Hunkin et al., (1984) maintain that steel-cased wells are
known to add anomalously high iron and alloy levels as well as
byproducts of bacterial growth and corrosion to a sample.
Houghton and Berger (1984) discovered that samples from
steel-cased wells were enriched in cadmium (Cd), chromium
(Cr), copper (Cu), iron, manganese, and zinc (Zn) relative to
samples obtained from plastic-cased wells.
Stainless steel is one type of metal used for casing and that
appears to have a high resistance to corrosion. In fact, the U.S.
EPA (1987) states that SS is the most chemically resistant of the
ferrous materials. Two types of SS extensively used for ground-
water monitoring are stainless steel 304 (SS304) and stainless
steel 316 (SS316). These are classified as austenitic type SS
and contain approximately 18 percent chromium and 8 percent
nickel. The chemical composition of SS304 and SS316 is
identical with the exception being SS316 which contains 2-3
percent molybdenum. Brainard-Kilman (1990) indicate SS316
has improved resistance to sulfuric and saline conditions and
better resistance to stress-corrosion.
The corrosion resistance of SS is due to a passive oxide layer
which forms on the surface in oxidizing environments. This
protective layer is only a few molecules thick. It recovers quickly
even if removed by abrasion (Fletcher 1990). However, several
investigators note that SS is still susceptible to corrosion. Under
corrosive conditions, SS may release iron, chromium, or nickel
(Barcelona et al., 1988). Hewitt (1989a) found in a laboratory
study that samples of SS316 and SS304 were susceptible to
oxidation at locations near cuts and welds. When these cuts and
welds are immersed in ground water, this surface oxidation
provides active sites for sorption and also releases impurities
and major constituents. SS may be sensitive to the chloride ion,
which can cause pitting corrosion, especially over long term
exposures under acidic conditions (U.S. EPA, 1987).
Parker et al., (1989) evaluated samples of SS304 and SS316 for
their potential to affect aqueous solutions of 10 organic com-
pounds. The 10 organics used in the study were RDX,
trinitrobenzene (TNB), c-1,2-DCE, t-1,2-DCE, m-nitrotoluene
(MNT), TCE, MCB, o-dichlorobenzene (ODCB),
p-dichlorobenzene (PDCB), and m-dichlorobenzene (MDCB) at
concentrations of 2 mg/L Their study indicated the SS well
casings did not affect the concentration of any of the analytes in
solution.
Synthetic Materials
Synthetic materials used for casing evaluation include PTFE,
PVC, polypropylene (PP), polyethylene (PE), nylon, fiberglass
reinforced epoxy (FRE), and acrylonitrile butadiene styrene
(ABS). The two most commonly used synthetic casing materials
are PVC and PTFE. Very little information regarding the
suitability of FRE as a casing material is presently available in
-------
the literature; however, a 3-week dwell-time study conducted by
Cowgill (1988) indicated that FTFE revealed no detectable
quantities of the substances used in its manufacture. Hewitt
(1989a and 1989b) determined that PTFE was the material of
choice for sampling inorganic compounds whereas, Barcelona
(1985) recommends PTFE for most all monitoring applications.
PTFE is a man-made material composed of very long chains of
linked fluorocarbon units. PTFE is considered as a thermoplas-
tic with unique properties. It is very inert chemically and no
substance has been found that will dissolve this polymer (The
Merck Co. Inc. 1984). The Merck Co. Inc. (1984) reports that
nothing sticks to this polymer. This antistick property may
prevent grouts from adhering to PTFE casing and prevent the
development of an effective seal around a PTFE casing. PTFE
also has a very wide useful temperature range, -100° to
+480° F; however, for most ground-water monitoring applica-
tions these extremes of temperature would rarely be
encountered.
PTFE has a low modulus of elasticity making the screened
portion PTFE casing prone to slot compression under the weight
of the well casing above. PTFE is also very flexible and the
casing sometimes has the tendency to become "crooked" or
"snake" especially in deep boreholes. Special procedures are
then required to install the casing. Morrison (1986) and Dablow
et al., (1988) discuss different techniques used to overcome
installation problems inherent to PTFE wells. PTFE also has the
tendency to stretch thus, making PTFE cased wells susceptible
to leaks around threaded joints.
PVC casing is an attractive alternative to PTFE and SS because
it is inexpensive, durable, lightweight, has better modulus and
strength properties than PTFE, and is easy to install. However,
these characteristics alone do not justify its use as a monitoring
well casing material. The casing material must not react
significantly with the surrounding ground water, leach, sorb, or
desorb any substances that might introduce error into the
sample. Many studies have been conducted comparing PVC to
other casing materials to determine its suitability for use in
monitoring wells.
Various compounds are added to the basic PVC polymer during
the manufacturing process of rigid PVC. These compounds
include thermal stabilizers, lubricants, fungicides, fillers, and
pigments (Boettner et al., 1981; Packham, 1971). It is pre-
sumed that the additional compounds have the potential to leach
into the ground water. Tin, found in some thermal stabilizers, is
one of the compounds suspected of leaching from PVC.
Boettner et al., (1981) found that as much as 35 ppb dimethyltin
could be leached from PVC in a 24-hour period. Other com-
pounds used as thermal stabilizers, and potential sources of
contaminants, are calcium, Zn, and antimony.
Another compound suspected of leaching from PVC casing is
residual vinyl chloride monomer (RVCM). According to Jones
and Miller (1988), 1-inch diameter Schedule 40 PVC pipe
containing 10-ppm RVCM leaches undetectable quantities (at
the 2.0-ppb sensitivity level) of vinyl chloride into stagnant water
retained in the pipe. They also report that 98 percent of the PVC
casing currently manufactured in North America contains less
than 10-ppm RVCM and most casing contains less than 1 ppm
RVCM. This implies that a 1-inch diameter pipe should leach
2.0-ppb or less RVCM. The amount of RVCM leached would
also decrease as the casing diameter increased because of the
lower specific surface. Specific surface (R) is defined as the
ratio of the surface area of the casing material in contact with the
solution, to the volume of the solution. Thus, as casing diameter
increases, the specific area decreases.
The NSF (1989) has established maximum permissible levels
(MPL) for many chemical substances used in the manufacturing
of PVC casing (Table 2). These levels are for substances found
in low pH extractant water following extraction procedures
described by the NSF (1989). Sara (1986) recommends the use
of NSF-tested and approved PVC formulations to reduce the
possibility of leaching RVCM, fillers, stabilizers, and plasticizers.
TABLE 2. MAXIMUM PERMISSIBLE LEVELS FOR CHEMICAL
SUBSTANCES
Substances
Antimony
Arsenic
Cadmium
Copper
Lead
Mercury
Phenolic Substances
Tin
Total Organic Carbon
Total Trihalomethanes
Residual Vinyl Chloride Monomer*
MPL mg/L Action levels mg/L
0.05
0.050
0.005
1.3
0.020
0.002
0.05'
0.05
5.0'
0.10
3.2 2.02
* In the finished product ppm (mg/kg).
1 This is an action level. If the level is exceeded, further review and/or
testing shall be initiated to identify the specific substance(s), and
acceptance or rejection shall be based on the level of specific
substances in the water.
2 Additional samples shall be selected from inventory and tested to
monitor for conformance to the MPL.
(Source: NSF Standard Number 14)
Common practice was to use cleaner-primers and solvent
cements to join PVC casing sections used in monitoring wells.
Cements used for joining casing sections dissolve some of the
polymer and "weld" the casing sections together. Past studies
showed a correlation between certain organic compounds
found in ground-water samples and the use of PVC solvent
cement (Boettner et al., 1981; Pettyjohn et al., 1981; Sosebee
etal., 1983; CurranandTomson, 1983). Sosebeeetal., (1983)
found high levels of tetrahydrofuran, methylethyiketone,
methylisobutylketone, and cyclohexanone, the major constitu-
ents of PVC primer and adhesive, in water surrounding ce-
mented casing joints months after installation. Sosebee et al.,
(1983) determined that besides contaminating the ground-
water sample these contaminants have the potential to mask
-------
other compounds found in the ground water during laboratory
analysis. Boettneretal., (1981) found, in an experiment in which
solvent cement was used for joining PVC casing,
methylethylketone, tetrahydrofuran, and cyclohexanone leach-
ing into water supplies after more than 2 weeks of testing.
Houghton and Berger (1984) conducted a study to determine the
effects of well casing composition and sampling method on
water-sample quality. Three wells were drilled on 20-ft centers
to a depth of 60 feet and cased with PVC, ABS, and steel.
Samples collected from the wells indicated ABS-cased wells
were enriched in dissolved organic carbon by 67 percent and in
total organ ic carbon (TOC) by 44 percent relative to samples from
the steel-cased well. The PVC-cased well was enriched in
dissolved organic carbon and TOC by approximately 10 percent
relative to the steel-cased well. The high TOC concentrations
found in the ABS and PVC casings are suspected to have been
derived from the cement used to connect the casing sections.
Other compounds suspected of leaching from PVC and into
ground water are chloroform (CHCL) and carbon tetrachloride
(CCL). Desrosiers and Dunnigan (1983) determined that PVC
pipe did not leach CHCI3 or CCL4 into deionized, demineralized,
organic-free water, or tap water in the absence of solvent cement
even after a 2-week dwell time.
PVC primers and adhesives should not be used for joining PVC
monitoring well casing sections. The recommended means for
joining PVC casing is to use flush-joint threaded pipe casing.
Foster (1989) provides a review of ASTM guideline F480-88A
which describes in detail the standard PVC flush-joint thread.
Junketal., (1974) passed "organic free" water through PE, PP,
latex, and PVC tubings, and a plastic garden hose. They found
o-creosol, naphthalene, butyloctylfumarate, and butyl-
chloroacetate leaching from the PVC tubing. These contami-
nants are related to plasticizers which are added to PVC during
the manufacturing process to make it more flexible. Rigid PVC
well casing contains a much smaller quantity of plasticizer and
should be less prone to leaching contaminants (Jones and Miller,
1988).
LEACHING AND SORPTION STUDIES
Many studies have been undertaken to determine the interaction
of different casing materials with volatile organic compounds
(VOCs) and trace metals. Much of the research has been aimed
at determining whether PVC can be used as a substitute for more
expensive materials such as PTFE, FRE, and SS. A review of the
literature investigating the potential effects of assorted well
casing materials on ground-water samples is presented below.
Organic Studies
Lawrence and Tosine (1976) found that PVC was effective for
adsorbing polychlorinated biphenyls (PCB) from aqueous sew-
age solutions. They reported that the low solubility and hydro-
phobic nature of the PCBs makes them relatively easy to adsorb
from aqueous solution. Parker et al., (1989) suggest the PVC
appears to be effective only in sorbing PCBs at concentrations
close to their solubility limits.
Pettyjohn et al., (1981) discuss materials used for sampling
organic compounds. They provide a list of preferred materials for
use in sampling organic compounds in water. Their choice in
order of preference is glass, PTFE, SS, PP, polyethylene, other
plastics and metals, and rubber. They do not indicate whether
the materials in the list were sections of rigid or flexible tubing or
what testing procedures were followed. They note that experi-
mental data on the sorption and desorbtion potential of casing
materials using varied organic compounds were not available.
Miller (1982) conducted a laboratory study in which one of the
objectives was to quantify adsorption of selected organic pollut-
ants on Schedule 40 PVC 1120, low density PE, and PP well
casing materials. These materials were exposed to six organic
pollutants and monitored for adsorption over a 6-week period.
The VOCs used, along with their initial concentrations, were BRO
(4 ppb), PCE (2 ppb), trichloroethylene (TCE) (3 ppb),
trichlorofluoromethane (2 ppb), 1,1,1-TCA (2 ppb), and 1,1,2-
trichloroethane (14 ppb). The results showed that PVC adsorbed
only PCE. The PVC adsorbed approximately 25 to 50 percent of
the PCE present. The PP and PE samples adsorbed all six of the
organics in amounts ranging from 25 to 100 percent of the
amount present.
Curran and Tomson (1983) compared the sorption potential of
PTFE, PE, PP, rigid PVC (glued and unglued), and Tygon
(flexible PVC). The procedures used in this investigation con-
sisted of pumping 20 L of organic-free water with a 0.5-ppb
naphthalene spike through each tubing at a rate of 30 mL/min.
The tests showed that 80 to 100 percent of the naphthalene was
recovered from the water for all materials except Tygon tubing.
Tygon tubing sorbed over 50 percent of the naphthalene. PTFE
showed the least contaminant leaching of the synthetic materials
tested. They concluded that PVC can be used as a substitute for
PTFE in monitoring wells if the casing is properly washed and
rinsed with room temperature water before installation. They
also conclude that PE and PP could suitably be used as well
casings.
Barcelona et al., (1985) presented a ranking of the preferred rigid
materials based on a review of manufacturers' literature and a
poll of the scientific community. The list presented by Barcelona
et al., (1965) recommended the following casing materials in
order of decreasing preference: PTFE, SS316, SS304, PVC,
galvanized steel, and low carbon steel. Table 3 presents
recommended casing materials tabulated in Barcelona et al.,
(1985) along with specific monitoring situations.
Reynolds and Gillham (1985) conducted a laboratory study to
determine the effects of five halogenated compounds on six
polymer materials. The five compounds used in this study were
1,1,1-TCA, 1,1,2,2-TET, HCE, BRO, and PCE. The polymer
materials studied were PVC rod, PTFE tubing, nylon plate, low
density PP tubing, low density PE tubing, and latex rubbertubing.
The authors evaluated nylon plate because nylon mesh is often
used as a filter material around screened portions of wells. Latex
rubber tubing was evaluated as a material that represented
maximum absorption. The materials were tested under static
conditions to simulate water standing in the borehole. Measure-
ments were made over contact times that ran from 5 minutes to
5 weeks.
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TABLE 3. RECOMMENDATIONS FOR RIGID MATERIALS IN
SAMPLING APPLICATIONS
(In decreasing order of preference)
Material Recommendations
PTFE (Teflon<^ Recommended for most monitoring situations
with detailed organic analytical needs, particularly
for aggressive, organic leachate impacted
hydrogeologic conditions. Virtually an ideal
material for corrosive situations where inorganic
contaminants are of interest.
Stainless Steel 316 Recommended for most monitoring (flush
(flush threaded) threaded) situations with detailed organic
analytical needs, particularly for aggressive,
organic leachate impacted by hydrogeologic
conditions.
Stainless Steel 304
(flush threaded)
PVC (flush threaded)
other noncemented
connections, only NSF-
approved materials
for casing or potable
water applications.
May be prone to slow pitting corrosion in contact
with acidic high total dissolved solids aqueous
solutions. Corrosion products limited mainly to
Fe and possibly Cr and Ni.
Recommended for limited monitoring situations
where inorganic contaminants are of interest and
it is known that aggressive organic leachate
mixtures will not be contacted. Cemented
installations have caused documented
interferences. The potential for interaction and
interferences from PVC well casing in contact
with aggressive aqueous organic mixtures is
difficult to predict. PVC is not recommended for
detailed organic analytical schemes.
Recommended for monitoring inorganic
contaminants in corrosive, acidic inorganic
situations. May release Sn or Sb compounds
from the original heat stabilizers in the
formulation after long exposure.
Low Carbon Steel May be superior to PVC for exposures to
Galvanized Steel aggressive aqueous organic mixtures. These
Carbon Steel materials must be very carefully cleaned to
remove oily manufacturing residues. Corrosion is
likely in high dissolved solids acidic environment,
particularly when sulfides are present. Products
of corrosion are mainly Fe and Mn, except for
galvanized steel which may release Zn and Cd.
Weathered steel surfaces present very active
sites for trace organic and inorganic chemical
species.
(Source: Barcelona et al., 1985)
Results of the study are presented in Table 4. The results show
that PVC absorbed four of the five compounds; however, the
rate of absorption was relatively slow (periods of days to weeks).
Given this slow absorption rate, they do not consider there would
be significant absorption by PVC if wells were purged and
sampled the same day. The one organic compound that was not
absorbed significantly by the PVC during the 5-week test period
was 1,1,1-TCA. The loss of BRO to PVC in this study was
approximately 43 percent after 6 weeks; whereas, Miller (1982),
in a similar experiment, indicated no losses from solution over
the same time period.
TABLE 4. TIME AT WHICH ABSORPTION REDUCED THE RELATIVE
CONCENTRATION IN SOLUTION TO 0.9
PVC
PTFE
Nylon
PP
PE
Latex
Rubber
1,1,1-TCA
>5 weeks
BRO
>5 weeks
1,1,1-TCA
-6 hours
1,1,2,2-TET
-4 hours
1,1,2,2-TET
-15 minutes
1,1,2,2-TET
<5 minutes
1,1,2,2-TET
-2 weeks
1,1,2,2-TET
-2 weeks
1,1,2,2-TET
-1 hour
BRO
-1 hour
BRO
<5 minutes
1,1,1-TCA
<5 minutes
BRO
-3 days
1,1,1-TCA
-1day
BRO
-30 minutes
1,1,1-TCA
-1 hour
1,1,1-TCA
<5 minutes
BRO
<5 minutes
HCE
-1day
HCE
-1 day
PCE
-30 minutes
HCE
<5 minutes
HCE
<5 minutes
PCE
<5 minutes
PCE
-1day
PCE
<5 minutes
HCE
<5 minutes
PCE
<5 minutes
PCE
<5 minutes
HCE
<5 minutes
(Source: Reynolds and Gillham, 1985)
PTFE showed absorption of four of the five compounds tested.
There was no significant absorption of BRO over the 5-week test
period. It is noted that approximately 50 percent of the original
concentration of PCE was absorbed within an 8-hour period.
The concentration of this compound may be affected even when
the time between purging and sampling is short.
The other casing materials demonstrated significant absorption
losses within minutes to a few hours after exposure to the
organic compounds. The use of nylon, latex rubber, PP, and PE
as a well casing material will cause a significant reduction in the
concentration of the organic compounds even when the time
between purging and sampling is short. They state that agree-
ment between the model study and experimental results support
the concept that absorption of the organic compounds by the
polymers occur by sorption/dissoluiion of the compounds into
the polymer surface followed by diffusion into the polymer
matrix.
-------
Parker and Jenkins (1986) conducted a laboratory study to
determine if PVC casing was a suitable material for monitoring
low levels of the explosives 2,4,6-trinitrotoluene (TNT),
hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), octahydro-
1,3,5,7-tetranitro 1,3,5,7-tetrzocine (HMX), and 2,4-
dinitrotoluene (DNT). Samples of PVC casing were placed in
glass jars containing an aqueous solution of TNT, RDX, HMX,
and DNT. After 80 days, the solution was tested to determinethe
concentration of TNT, RDX, HMX, and DNT left in solution. After
the 80 days, the solutions containing RDX, HMX, and DNT
showed little loss, whereas TNT showed a significant loss. PVC
casing was tested under sterile and nonsterile conditions in a 25-
day experiment to determine whether microbial degradation or
sorption by PVC was the cause for losses of TNT, RDX, HMX,
and DNT. ResuJts indicated that the loss of TNT in the test was
caused by microbial activity rather than to adsorption. The
increased microbial activity may be caused by bacteria initially
present on the unsterilized PVC casing, increased surface area
for colonization provided by the PVC surface, leaching of
nutrients from the casing increasing the growth of bacteria, and
the rate of biodegradation.
Parker and Jenkins (1986) do not consider PVC casing to
significantly affect ground-water samples when monitoring for
TNT, RDX, DNT, and HMX if the time between purging of the well
and sampling is short. They concluded PVC is an acceptable
casing material for ground-water monitoring of TNT, RDX, DNT,
and HMX.
Sykes et al., (1986) performed a laboratory study to determine
if there was a significant difference in the sorption potential
between PVC, PTFE, and SS316 when exposed to methylene
chloride (dichloromethane or DCM), 1,2-dichloroethane (1,2-
DCA), trans-1,2-dichloroethylene (t-1,2-DCE), toluene, and
chlorobenzene (MCB). Samples of the various well casing
materials were placed in jars containing aqueous solutions of
the solvents at concentrations of approximately 100 ppb. The
concentration of each solvent was determined after 24 hours
and again after 7 days. The study concluded that there were no
statistically different chemical changes in the solutions exposed
to PVC, PTFE, and SS316 casing. Thus, it could be presumed
that PVC, PTFE, or SS316 are suitable casing materials for
monitoring DCM, 1,2-DCA, t-1,2-DCE, toluene, and MCB when
the period between well purging and sampling is less than 24
hours.
Barcelona and Helfrich (1986) conducted a field study at two
landfills to determine the effects of different casing materials on
sample quality. Wells were constructed upgradient and
downgradient of each of the two landfill sites. The wells at
Landfill 1 were constructed of PTFE, PVC, and SS304; whereas,
the wells at Landfill 2 were constructed of PVC and SS.
They observed that the downgradient SS and PTFE wells at
Landfill 1 showed higher levels of TOC than did the PVC wells.
The upgradient wells at Landfill 1 showed no significant differ-
ence among casing material type. TOC sampling at Landfill 2
showed similar results; however, no significant differences
among material types were determined either upgradient or
downgradient of the landfill.
Levels of 1,1-dichloroethane (1,1-DCA) and cis-1,2-
dichloroethylene (c-1,2-DCE) were significantly higher for the
downgradient SS wells than for PTFE and PVC cased wells at
Landfill 1. They suspect that PTFE and PVC tend to have a
greater affinity for these organic compounds than does SS.
At Landfill 2 they noted greater levels of 1,1-DCA and total
volatile halocarbons in the PVC wells than in the SS wells. They
hypothesize that the higher levels of the organic compounds
found in the water samples from the PVC cased well may be
caused by the sorptive and leaching properties of PVC which
tend to maintain a higher background level of organic com-
pounds in the ground water relative to SS. They did not suspect
the SS and PVC wells at Landfill 2 are intercepting ground water
of different quality since the wells are approximately 4 feet apart.
The authors conclude that well casing materials exert signifi-
cant, though unpredictable effects on TOC and specific VOC
determinations. Parker et al., (1989) suspect that a larger
statistical base is needed before such conclusions can be
drawn. Parker et al., (1989) also suggest the possibility that
differences in well construction methods may have had an effect
on the quality of these water samples.
Gossett and Hegg (1987) conducted a laboratory test to deter-
mine the effects of using a PVC bailer, a PTFE bailer, and an
ISCO Model 2600 portable pump on the recovery of CHCI3,
benzene, and 1,2-DCA. The effect on recovery of VOCs was
studied by varying the lift height and the casing material. The
casing materials consisted of either PVC or SS. In their
conclusion they state that either PVC or SS would be suitable for
collecting VOC samples.
Parker et al., (1989) performed a laboratory study to compare
the performance of PVC, SS304, SS316, and PTFE subjected
to aqueous solutions of RDX, trinitrobenzene (TNB),
c-1,2-DCE, t-1,2-DCE, m-nitrotoluene (MNT), TCE, MCB,
o-dichlorobenzene (ODCB), p-dichlorobenzene (PDCB), and
m-dichlorobenzene (MDCB) at concentrations of 2 mg/L. A
biocide was added to the samples to eliminate possible losses
due to biodegradation.
Prior to the experiment, they conducted a test to determine if the
casing materials were capable of leaching any compounds into
water. Samples of casing material were placed in vials contain-
ing well water and allowed to stand for 1 week. No evidence of
materials leaching from any of the casing materials was noted.
Casing samples were placed in sample jars containing an
aqueous solution of the organic compounds and sampled ini-
tially and at intervals between 1 hour and 6 weeks. Table 5
presents results after a 1 -hour, 24-hour, and 6-week dwell time.
The test results indicated that after 6 weeks PTFE had sorbed
significant amounts of all the compounds with the exception of
RDX and TNB. In the same time period, PVC showed significant
sorption of TCE, MCB, ODCB, PDCB and MDCB. In each one
of the cases where the PVC and PTFE both sorbed significant
amounts of analytes, PTFE always had the greatest sorption
rate. After 6 weeks, the SS samples exhibited no significant
sorption of the tested compounds.
At the 24-hour mark, PTFE and PVC had experienced signifi-
cant sorption of all the compounds with the exception of RDX,
TNB, and MNT. For the compounds sorbed by PTFE and PVC,
PTFE had the higher rate of uptake with the exception of c-1,2-
DCE. SS showed no significant sorption of any of the com-
-------
TABLE 5. NORMALIZED* CONCENTRATION OF ANALYTES FOR
FOUR WELL CASINGS WITH TIME
Analyte
RDX
TNB
C-1.2-DCE
t-1,2-DCE
MNT
TCE
MCB
ODCB
PDCB
MDCB
Treatment
PTFE
PVC
SS304
SS316
PTFE
PVC
SS304
SS316
PTFE
PVC
SS304
SS316
PTFE
PVC
SS304
SS316
PTFE
PVC
SS304
SS316
PTFE
PVC
SS304
SS316
PTFE
PVC
SS304
SS316
PTFE
PVC
SS304
SS316
PTFE
PVC
SS304
SS316
PTFE
PVC
SS304
SS316
1 hour
1.03
1.01
0.99
1.01
1.01
1.01
0.99
1.02
1.01
1.00
0.97
0.95
1.00
1.00
0.95t
1.00
1.03
1.02
1.00
1.02
1.00
1.01
0.96
1.00
1.01
1.01
0.98
0.99
1.01
1.02
0.98
1.01
0.92t
0.95
0.91 1
0.94
1.00
1.02
0.99
1.03
24 hours
1.00
0.98
1.01
1.01
1.00
0.98
1.00
1.01
0.96t
0.95t
1.00
1.00
0.88t
0.93t
1.00
1.00
0.99
0.98
1.01
1.02
0.85t
0.94t
1.01
1.00
0.90t
0.95t
1.00
1.01
0.88t
0.94t
1.00
1.01
0.77t
0.92|
1.00
1.00
0.78t
0.92t
1.00
1.00
6 weeks
0.99
1.00
0.98
1.00
1.01
1.02
1.00
1.02
0.79f
0.90
0.98
0,99
0.56t
0.83
1.00
1.00
0.90t
0.94
1.07
0.99
0.40f
0.88t
0.99
1.00
0.51 1
0.86t
0.99
0.99
0.43t
0.86t
1.00
1.00
0.26t
o.sot
1.02
1.02
0.26t
o.sot
1.02
1.01
* The values given here are determined by dividing the mean
concentration of a given analyte at a given time and for a particular well
casing by the mean concentration (for the same analyte) of the control
samples taken at the same time.
^Values significantly different from control values.
(Source: Parker etal., 1989)
pounds tested. It appears that PTFE cased wells will introduce
a greater bias into ground-water samples than those cased with
PVC if the time between sampling and purging is 24 hours.
They also conducted a desorption experiment on the samples
that had sorbed organics for 6 weeks. After 3 days of testing, the
PVC and PTFE samples showed desorption of analytes sorbed
in the previous experiment. The desorption study showed that
PTFE, in general, showed a greater loss of analytes than PVC.
Jones and Miller (1988) conducted laboratory experiments to
evaluate the adsorption and leaching potential of Schedule 40
PVC (PVC-40), Schedule 80 PVC (PVC-80), ABS, SS, Teflon-
PFA, Teflon-FEP, PTFE, and Kynar-PVDF. Organic com-
pounds used in this experiment were 2,4,6-trichlorophenol
(2,4,6-TCP), 4-nitrophenol, diethyl pthalate, acenaphthene,
naphthalene, MDCB, 1,2,4-trichlorobenzene, and
hexachlorobenzene. Samples of casing material were placed
into glass vials each containing an organic compound having an
approximate initial concentration of 250 ppb.
In theirfirst experiment, the organic compounds were mixed with
neutral pH ground water. The batches were sampled immedi-
ately and then at intervals of 1 -, 3-, and 6-weeks. The results
showed that there was no appreciable change in adsorption of
the compounds after 1 week except for 2,4,6-TCP, which totally
adsorbed after 3 weeks. The results also indicate that PTFE
might be less likely to adsorb these compounds. Jones and
Miller (1988) also point out that at the concentrations used in this
study, PTFE, PVC-40, and PVC-80 exhibited very little differ-
ence in the amounts of adsorption.
In their second experiment, Jones and Miller (1988) attempted
to determine the amount of the adsorbed compounds that would
be released back into uncontaminated ground water after a 6-
week exposure time. After a 2-week period, very little release of
organic contaminants was observed. They state that only zero
to trace amounts of the sorbed contaminants were desorbed into
the noncontaminated ground water. Only PVC-80 and Teflon-
PFA desorbed naphthalene.
They repeated their adsorption and leaching experiments using
polluted ground water with a pH of 3.0. The adsorption experi-
ment showed that, with the exception of ABS casing, the casing
materials showed less adsorption at the contaminated low pH
level than at the noncontaminated neutral pH level. One
possible explanation is there could be stronger binding and
more preferential complexing of the experimental pollutants with
other pollutants in the contaminated ground water. Another,
more likely explanation, is that there is a relationship between
the extent of adsorption, pH, and pK, with a maximum adsorp-
tion occurring when the pH is approximately equal to pK. They
explain that as the pH decreases, the hydrogen ion concentra-
tion increases and the adsorption tends to decrease, suggesting
a replacement of the adsorbed compound by the more preferen-
tially adsorbed hydrogen ions.
Jones and Miller (1988) concluded there is no clear advantage
to the use of one particular well casing material over the others
for the organics used in the study. Well purging procedures,
sampling device selection and composition, and sample storage
are probably of greater influence to sample integrity and repre-
sentativeness than well casing material selection. They found
8
-------
the amount of adsorption generally correlates with the solubility
of the chemical independent of the well casing material.
Gillham and O'Hannesin (1990) conducted a laboratory study to
investigate the sorption of six monoaromatic hydrocarbons
onto/into seven casing materials. The six organic compounds
used were benzene, toluene, ethylbenzene, and p-, m-, and o-
xylene. The seven casing materials used in the evaluation were
SS316, PTFE, rigid PVC, flexible PVC, polyvinylidene fluoride
(PVDF), flexible PE, and FRE. The materials were placed in
vials containing an aqueous solution of all six organic materials.
Concentrations of the organics in the solution ranged between
1.0 and 1.4 mg/L Sodium azide (0.05 percent), a biocide, was
added to the solution to prevent biodegradation of the organics.
The solutions were sampled 14 times from 5 minutes to 8 weeks.
Results of the study are presented in Table 6 and indicate that
SS is the most favorable casing material for sampling organics.
Stainless steel showed no significant uptake after an 8-week
exposure period; whereas, all the polymer materials adsorbed
all the organic compounds to some degree. The order of
magnitude of adsorption for the various polymer materials
tested was flexible PVC > PE > PTFE > PVDF > FRE > rigid PVC
(from greatest to least sorption). Flexible tubing materials
showed substantial uptake after 5 minutes of exposure. Rigid
PVC showed the lowest rate of uptake of the polymer materials.
TABLE 6. TIME INTERVAL WITHIN WHICH THE CONCENTRATION
PHASE FOR THE COMPOUND AND CASING MATERIAL BECAME
SIGNIFICANTLY DIFFERENT FROM 1.0
Time, hours
Ethyl-
Material Benzene Toluene benzene m-Xylene o-Xylene p-Xylene
SS316 >1344
PVC (rigid) 48-96 24-48 12-24 12-24 12-24 12-24
FRE 24-48 3-6 0.1-1.0 3-6 3-6 3-6
PVDF 24-48 3-6 1-3 1-3 0.1-1.0 1-3
PTFE 24-48 3-6 1-3 3-6 6-12 1-3
PE 0-0.1 0-0.1 0-0.1 0-0.1 0-0.1 0-0.1
PVC (flexible) 0 - 0.1 0-0.1 0-0.1 0-0.1 0-0.1 0-0.1
(Source: Gillham and O'Hannesin, 1990)
Gillham and O'Hannesin (1990) conclude all of the polymer
materials tested, except flexible PVC and PE, are suitable
casing materials in monitoring wells. This is based on selection
of an appropriate casing diameter and an appropriate interval
between purging and sampling. They state rigid PVC is the most
favorable polymer material for casing in monitoring wells.
Reynolds et al., (1990) conducted laboratory tests to evaluate
the effects of five halogenated hydrocarbons on several casing
materials. The halogenated hydrocarbons and casing materials
used in the experiment were identical to those used by Reynolds
and Gillham (1985) with the addition of glass, SS316, aluminum,
and galvanized sheet metal to the casing materials.
The results indicated borosilicate glass was the least likely of the
10 materials to affect the samples. The results also showed that
all of the metals had the potential to sort compounds from
solution. The order of the compound sorption rate for the metals
was galvanized steel > aluminum > SS (greatest to least
sorption).
Results of the sorption experiments indicated rigid PVC was
preferable to PTFE for sampling low concentrations of haloge-
nated hydrocarbons. The compound sorption rates, from great-
est to least sorption, are latex > low density PE > PP > nylon >
PTFE > rigid PVC. The rates of compound loss, from greatest
to least loss, are PCE > HCE > 11,1,1 -TCA > BRO > 1,1,2,2-TET.
It should be noted the inequalities shown above are not neces-
sarily significant. For example, the rates between PTFE and
rigid PVC are not significant and the same is true for nylon and
PP. Their study showed flexible polymer tubing is likely to have
greater sorption rates than rigid polymers which is in agreement
with Barcelona et al., (1985). They also found evidence that
there is a correlation between compound solubility and sorption,
substantiating earlier studies. Reynolds et al., (1990) found
diffusivity decreased as mean molecular diameter increased
which agrees with a study performed by Berensand Hopfenberg
(1982), based on polymeric diffusivity tests.
They suggest the use of PTFE in monitoring wells in areas where
higher concentrations might be encountered, for instance near
a solvent spill. Their study showed a polymer exposed to high
concentrations of an organic compound that is agood solvent for
the polymer, that the polymer will absorb large quantities of the
solvent and swell. However, it is difficult to predict the swelling
power of various solvents. As an example, rigid PVC can absorb
over 800 percent of its weight in DCM but only 1 percent of CCL4.
Schmidt (1987), however, found no swelling or distortion of rigid
PVC casing or screen when exposed to various gasolines for 6.5
months.
Taylor and Parker (1990) visually examined PVC, PTFE,
SS304, and SS316 with a scanning electron microscope (SEM)
to determine how they were affected by long-term exposures (1
week to 6 months) to organic compounds. Organics used in this
test were PDCB, ODCB, toluene, and PCE at concentrations of
17.3,33.5,138, and 35.0 mg/L, respectively (approximately 25
percent of their solubilities in water).
SEM examinations showed no obvious surface structure
changes for any of the materials exposed to the different
concentrated organic aqueous solutions. They caution, how-
ever, that this study cannot be extended to instances where
casing materials are exposed to pure organic solvents. They did
not report the amount of compound sorbed by the different
casing materials.
Inorganic Studies
Massee et al., (1981) studied the sorption of silver (Ag), arsenic
(As), Cd, selenium (Se), and Zn from distilled water and artificial
sea water by borosilicate glass, high-pressure PE, and PTFE
containers. The effect of specific surface (R in crrr1), i.e., the
ratio of the surface area of the material in contact with the
solution, to the volume of the solution, was also studied. Metals
were added to the distilled and artificial sea water. The pH levels
of the aqueous solutions used were 1, 2, 4, and 8.5. Water
-------
samples were tested at intervals ranging between 1 minute and
28 days. Losses of As and Se were insignificant for all the
treatments. At pH levels of 1 and 2, no significant sorption from
either distilled water or artificial sea water was observed for any
of the containers or metals used in this study. Test results of the
sorption of Ag, Cd, and Zn from distilled water and sea water are
presented in Tables 7 and 8, respectively.
The results showed PTFE sorbed substantial amounts of Ag,
Cd, Zn, and the amounts sorbed were dependent on the pH and
salinity of the solutions. Specific surface was found to have a
significant effect on the sorption of metals by PTFE. For
example, at the end of 28 days the loss of Ag to PTFE with R =
5.5 cnr1 was almost 4 times higher than for R = 1.0 cm-1.
Massee et al., (1981) concluded that sorption losses are difficult
to predict because the behavior of trace elements depends on
a variety of factors such as trace element concentration, mate-
rial, pH, and salinity. They noted that a reduction in contact time,
specific surface, and acidification may reduce sorption losses.
Miller (1982) conducted a study to determine the potential of
PVC, PE, and PP to sorb and release Cr(VI) and lead (Pb) when
in a Cr(VI)-Pb solution and in a solution of these two metals
along with the following organics; BRO, PCE, TCE,
trichlorofluromethane, 1,1,1-TCA, and 1,1,2-trichloroethane.
Tables 9 and 10, respectively, present the results for the Cr(VI)
and Pb adsorption and leaching studies. The results showed
that none of the materials tested adsorbed Cr(VI) to any signifi-
cant extent when in a solution with Pb. When in a solution with
Pb and 6 other organics, 25 percent of Cr(VI) was adsorbed by
the 3 casing materials. No leaching of Cr(VI) was observed from
any of the materials either in the metals only or metals and
organics solutions. Seventy-five percent of the Pb was
adsorbed by PVC when in a solution with Cr(VI) and also when
in a solution of Cr(VI) and the six organics. PE and PP showed
about 50 percent adsorption of Pb when in a solution with Cr(VI).
The casing materials did not leach any Pb when in a solution with
Cr(VI); however, when in a solution with Cr(VI) and 6 organics,
the 3 casing materials leached approximately 50 percent of the
Pb initially adsorbed. In his study, Miller found that PVC
TABLE 7. SORPTION BEHAVIOR OF SILVER, CADMIUM, AND ZINC IN TABLE 8. SORPTION BEHAVIOR OF SILVER, CADMIUM, AND ZINC IN
DISTILLED WATER ARTIFICIAL SEA WATER
Metal
Ag
Cd
Zn
Material
PH
Rfcrrr1)
Contract
Time
1 hour
1 day
28 days
1 hour
1 day
28 days
1 hour
1day
28 days
Borosilicate
PE Glass
4 8.5 4
1.4 3.4 1.0 3-4 1.0 4.2
Sorption (%)
fO 15 25 36 * 4
25 66 72 49 32 18
96 100 59 100 82 80
* * 7 69 * *
* * * 47 * *
* * * 31 * *
* * * $5 * *
* * 8 56 * *
* * 12 56 * *
8.5
1.0 4.2
9 21
26 48
72 63
6 26
10 32
* *
23 22
26 22
PTFE
4 8.5
14 5.5 10 5,5
* * * 10
4 6 5 25
15 55 22 28
* * 7 38
* * 10 48
* * 15 46
* * 3 16
* * 5 27
* * 6 20
'Denotes a loss smaller than 3 percent.
Borosilicate
Material PE Glass PTFE
pH 4 8.5 4
R(cnv1) 1,4 3.4 1,0 3.4 1.0 4.2
Contract
Metal Time Sorption (%)
Ag 1hour * * 6 5 * *
1day * * 24 28 4 4
28 days * * 46 78 82 71
1 day »**»**
28days * * * * 14 36
Zn 1hour »**.«**
1day ******
28days * * * * 20 19
8.5 4 8J
1.0 4.2 1,4 5,5 1,0 5.5
3 3 * * * 4
6 9 * * 6 12
40 67 * * 2? 37
9 31 * * * *
5 26 4 * * *
4 9 5 * * *
'Denotes a loss smaller than 3 percent.
(Source: Massee era/., 1981)
(Source: Massee era/., 1981)
10
-------
TABLE 9. TRENDS OF CHROMIUM (VI) EXPOSED TO SYNTHETIC
WELL CASING (COMPARED TO CONTROLS)
Adsorption/Leaching
Casing
Material
PVC
PE
PP
(Source:
Metals
Only
No adsorption
No adsorption
No adsorption
Miller, 1982)
Metals and
Organics
Slight (25%)
adsorption
Slight (25%)
adsorption
Slight (25%)
adsorption
Metals
Only
No leaching
No leaching
No leaching
Metals and
Organics
No leaching
No leaching
No leaching
TABLE 10. TRENDS OF LEAD EXPOSED TO SYNTHETIC WELL
CASING (COMPARED TO CONTROL)
Adsorption
Adsorption/Leaching
Casing
Material
PVC
PE
PP
Metals
Only
Mostly {75%}
adsorbed
Moderate (50%)
adsorption
(defayed)
Moderate (50%)
adsorption
(delayed)
Metals and
Organics
Mostly (75%)
absorbed .
Moderate (50%)
adsorption
Slight (25%)
adsorption
Metals
Only
No leaching
No leaching
No leaching
Metals and
Organics
Mostly (75%)
absorbed
Mostly (75%)
adsorbed
Mostly (75%)
adsorbed
(Source: Miller, 1982)
generally causes fewer monitoring interferences with VOCs
than PE and PP and that PVC adsorbed and released organic
pollutants at a slower rate relative to PE and PP.
Hewitt (1989a) examined the potential of PVC, PTFE, SS304,
and 8S316 to sorb and leach As, Cd, Cr, and Pb when exposed
to ground water. The pH, TOC, and metal concentrations of the
solution were varied and samples taken between 0.5 and 72
hours. The study showed that PTFE had the least-active
surface and showed an affinity only to Pb (10 percent sorption
after 72 hours). PVC and SS leached and sorbed some of the
metals tested. PVC was a source for Cd and sorbed Pb (26
percent sorption after 72 hours). The SSs were the most active
of the materials tested. SS304 was a source of Cd and sorbed
As and Pb. SS316 was also a source of Cd and sorbed As, Cd,
and Pb. The study showed results were affected by the solution
variables (i.e., pH, TOC, and concentration). SS304 and SS316
showed evidence of corrosion near cuts and welds which may
provide active sites for sorption and release of contaminants.
Hewitt (1989a) concludes PTFE is the best material for monitor-
ing the metals used in this study whereas, SSs are not suitable.
He states that although PVC was affected by Cd and Pb it should
still be considered as a useful casing material based on econom-
ics, and that when the time between purging and sampling is less
than 24 hours, the effects of Cd and Pb on PVC may be of less
concern.
Hewitt (1989b) conducted a study to determine the amounts of
barium, Cd, Cr, Pb, Cu, As, Hg, Se, and Ag leached from PTFE,
PVC, SS304, and SS316 in ground water. Table 11 summarizes
the results of the investigation. Results indicate that PTFE was
the only material tested not to leach any metals into the ground-
water solution. PTFE, however, did show atrend to sorb Cu with
time. PVC and SS316 showed a tendency to leach Cd; in
addition, these two materials, along with SS304, sorbed Pb.
PVC was also shown to leach Cr and provide sorption sites for
Cu. SS316 significantly increased the concentration of Ba and
Cu in the ground-water solution. SS304 consistently contrib-
uted Cr with time to the ground-water solution. None of the well
casing materials contributed significant levels of As, Hg, Ag, or
Se to the ground water.
TABLE 11. SUMMARY OF RESULTS
Cd Cr
Pb
Materials that leached
>1%oftheEPA
drinking water quality
level in ground-water
solutions
Materials that showed
the highest average
overall amount of
analyte leached
SS316 SS316 SS304 SS304
PVC PVC SS316 PVC
PVC SS316
Cu
NA*
SS316 SS316 SS304 SS304 SS316
'Does not apply
(Source: Hewitt, 1989b)
Hewitt (1989b) concludes PTFE is the best casing material
when testing for trace metals while SS should be avoided. He
also states PVC is an appropriate second choice because its
influence on metal analytes appears to be predictable and small.
Casing Material Cost Comparison
A consideration when installing monitoring wells is cost. Costs
to be considered in the installation of monitoring wells are cost
of construction materials, drilling costs, and expected life (re-
placement costs) of the casing material. Table 12 presents a
cost comparison among five casing materials: PVC, SS304,
SS316, PTFE, and FRE. The prices shown were obtained from
Brainard-Kilman (1990) with the exception of the FRE casing,
11
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TABLE 12. CASING MATERIAL COST COMPARISON
Prices reflect the cost of ten 10-ft long by 2-in. diameter casing sections, a
5-ft long 0.010-in slotted screen, and a bottom plug.
Casing Material
Price
PVC*
FRE"
SS304
SS316
PTFE
* Schedule 40 PVC
** Low flow screen
$ 179.50
966.00
1,205.00
1,896.00
3,293.50
whose price was provided by ENCO (1989). The cost estimates
are for ten 10-feet sections (100 feet) of 2-inch threaded casing,
5 feet of 0.010-inch slotted screen, and a bottom plug.
The cost of materials for 1 PTFE well is approximately 18 times
greater than 1 constructed on PVC (Table 12). At first glance,
PVC, by far, is the most economical material for constructing
monitoring wells. However, if drilling and material (bentonite,
cement, sand, etc.) costs are considered, the percent difference
in cost between PVC wells and wells constructed of SS, FRE, or
PTFE is reduced.
For example, assume that the cost of installing, materials, and
completing a 100-feet deep monitoring well (exclusive of casing
material costs) in unconsolidated material is $5,000. When the
cost of casing material is added to the drilling and materials
costs, a PVC-cased well costs $5,179.50 and an SS316-cased
well $6,896.00. When drilling and materials costs are consid-
ered, a PVC-cased well costs approximately 25 percent less
than a SS316-cased well. However, when drilling and materials
costs are not taken into account, PVC casing looks especially
attractive since it is approximately 90 percent less expensive
than SS316 casing. In this case, a SS316-cased well may be
considered to be cost effective especially if organics are ex-
pected to be sampled. Thus, the significance of the "cost of
casing materials versus ground water-casing interaction" issue
is reduced.
CONCLUSIONS
All aspects of a ground-water sampling program have the
potential to introduce error to a ground-water sample. Interac-
tion between monitoring well casing materials and ground
water is only one of the ways in which error may be introduced
in a sampling program. Presently, there are a variety of
materials available for fabricating monitoring wells. The poten-
tial for these casing materials to interact with ground water has
found to be affected by many factors, including pH and compo-
sition of the ground water and the casing-ground water contact
time. The complex and varied nature of ground water makes it
very difficult to predict the sorption and leaching potential of the
various casing materials. Consequently, the selection of the
proper casing material for a particular monitoring application is
difficult. This is evidenced by the lack of agreement among
researchers on which is the "best" material, the problem is
compounded by the inconclusive and incomplete results of
laboratory studies on the effects of rigid well casing materials
with inorganic or organic dissolved species.
Many of the experiments examined the effects of time on the
sorption and leaching potential of the various casing materials.
The experiments were usually run under laboratory conditions
in which distilled or "organic free" water was used and casing
materials were subject to contaminants for periods ranging from
minutes to months. These experiments, in general, indicate a
trend for the materials to be more reactive with the aqueous
solutions with time. Experiments showed if the time between
well purging and sampling is relatively short, some of the more
sorptive materials could be used without significantly affecting
sample quality.
The selection of appropriate materials for monitoring well casing
at a particular site must take into account the site hydrogeology
and several general requirements. These general requirements
for the screens and casing of wells that are used for ground-
water monitoring are the following:
1. Depth to zones being monitored and total depth of well must
be considered.
2. The geochemistry of the geologic materials over the entire
interval in which the well is to be cased and screened must
be taken into account.
3. The wells must be chemically resistant to naturally occurring
waters.
4. The well materials must be chemically resistant to any
contaminants that are present in any and all contaminated
zones of the aquifer or aquifers being monitored.
5. The strength of the materials must be physically strong
enough to withstand all compressive and tensile stresses
that are expected during the construction and operation of
the monitoring well over the expected lifetime.
6. Installation and completion into the borehole during
construction of the monitoring well must be relatively easy.
7. The well materials must be chemically resistant to any
anticipated treatments which are strongly corrosive or
oxidizing.
It may be necessary to conduct site-specific, comparative per-
formance studies to justify preference for a particular well casing
or screening material over another.
12
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14
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ABBREVIATIONS
1,1 -DCA 1,1 -Dichloroethane ODCB
1,1,1-TCA 1,1,1-Trichloroethane p-
1,1,2,2-TET 1,2,2,2-Tetrachlorethane Pb
1,2-DCA 1,2-Dichloroethane PCS
2,4,6-TCP 2,4,6-Trichlorophenol PCE
ALS Acrylonitrile butadiene styrene PDCB
Ag Silver PE
As Arsenic pH
ASTM American Society for Testing and Materials pK
BRO Bromoform PP
C-1.2-DCE cis-1,2-Dichloroethylene ppb
CC14 Carbon tetrachloride ppm
Cd Cadmium PTFE
CHCI3 Chloroform PVC
Cr Chromium RCRA
Cu Copper RDX
DCM Methylene chloride (dichloromethane) RVCM
DNT 2,4-Dinitrotoluene Se
EMSL-LV Environmental Monitoring Systems Laboratory- SEM
Las Vegas SS
FRF Fiberglass reinforced epoxy SS304
HCE Hexachloroethane SS316
Hg Mercury t-1,2-DC.E
HMX Octabydro-1,2,5,7-tetranitro 1,3,5,7-tetrazocine TCE
m- Meta TEGD
MCB Chlorobenzene TNB
MDCB m-Dichlorobenzene TNT
MNT m-Nitrotoluene TOC
MPL Maximum permissible levels U.S. EPA
NSF National Sanitation Foundation VOC
o- Ortho Zn
o-Dichlorobenzene
Para
Lead
Polychlorinated biphenyl
Tetrachloroethylene
p-Dichlorobenzene
Polyethylene
Hydrogen ion concentration of the solution
Log dissociation constant
Polypropylene
Parts per billion (by weight)
Parts per million (by weight)
Polytetrafluoroethylene (Teflon®)
Polyvinylchloride
Resource Conservation and Recovery Act
Hexahydro-1,3,5,7-trinitro-1,3,5-triazine
Residual vinyl chloride monomer
Selenium
Scanning electron microscope
Stainless steel
Stainless steel 304
Stainless steel 316
trans-1,2-Dichloroethylene
Trichloroethylene
Technical Enforcement Guidance Document
Trinitrobenzene
2,4,6-Trinitrotoluene
Total organic carbon
U.S. Environmental Protection Agency
Volatile organic compound
Zinc
15
•U.S. Government Printing Office: 1992— 648-080/60052
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