1

Sorption and Leaching of Trace-Level

Metals by Polymeric Well Casings

Thomas A. Ranney and Louise V. Parker April 1996

SPECIAL REPORT 96-8
2

Abstract

The most commonly used well casing materials (polyvinyl chloride [PVC],

polytetrafluoroethylene [PTFE] and stainless steel) cannot be used for all

monitoring applications. Therefore, a series of experiments was conducted to

compare three alternative polymeric well casing materials (fluorinated ethylene

propylene [FEP], fiberglass-reinforced epoxy [FRE] and fiberglass-reinforced

plastic [FRP]) with PVC and PTFE. These studies were conducted to determine

the overall suitability of these materials for use in groundwater monitoring

wells. Previous studies compared these materials for sorption of dilute organic

solutes, leaching of organic constituents, and resistance to degradation by

chemicals, especially organic solvents. This particular study focuses on

sorption and leaching of metals. This study shows that the fiberglass materials

were more apt to leach metal contaminants than PVC, FEP, and PTFE. Leached

concentrations, with one exception (Pb leaching from FRP), were below

maximum allowable limits set by the US EPA for drinking water. With respect

to sorption, none of the polymers sorbed the anions tested, but all of them

sorbed the cations tested. FEP and PTFE were much less sorptive than the other

materials. These results and those from our previous studies can be used,

along with other considerations, to select a casing material that is best suited

for the intended monitoring application and conditions in the well.

For conversion of SI units to non-SI units of measurement consult ASTM

Standard E380-93, Standard Practice for Use of the International System

of Units, published by the American Society for Testing and Materials,

1916 Race St., Philadelphia, Pa. 19103.

This report is printed on paper that contains a minimum of 50% recycled

material.
Special Report 96-8

Sorption and Leaching of Trace-Level

Metals by Polymeric Well Casings

Thomas A. Ranney and Louise V. Parker April 1996

Prepared for

U.S. ARMY ENVIRONMENTAL CENTER

SFIM-AEC-ET-CR-95085

Approved for public release; distribution is unlimited.

US Army Corps


of Engineers

Cold Regions Research &


Engineering Laboratory
PREFACE

This report was prepared by Thomas A. Ranney, Staff Scientist, Science and Technology

Corporation, Hanover, New Hampshire, and Louise V. Parker, Research Physical Scientist, Applied Research Division, Research and Engineering Directorate, U.S. Army Cold

Regions Research and Engineering Laboratory (CRREL). Funding for this work was

provided by the U.S. Army Environmental Center (USAEC), Aberdeen Proving Ground,

Maryland, Martin H. Stutz, Project Monitor.

The authors thank Martin Stutz and USAEC for their support of this work; Robert

Forest, CRREL, for carefully cutting the well casing pieces; and Alan Hewitt, Research

Physical Scientist, CRREL, and Dr. C.L. Grant, Professor Emeritus, Department of Chemistry, University of New Hampshire, for their technical reviews of this manuscript.

This publication reflects the personal views of the authors and does not suggest or

reflect the policy, practices, programs, or doctrine of the U.S. Army or Government of the

United States. The contents of this report are not to be used for advertising or promotion

purposes. Citation of brand names does not constitute an official endorsement or approval

of the use of such commercial products.
CONTENTS

Page

Preface ................................................................................................................................. ii

Introduction ........................................................................................................................ 1

Materials and methods ..................................................................................................... 3

Materials ......................................................................................................................... 3

Procedure for the leaching study................................................................................ 3

Procedure for the sorption study ................................................................................ 3

Analyses ......................................................................................................................... 3

Results and discussion ...................................................................................................... 4

Leaching study .............................................................................................................. 4

Barium ............................................................................................................................ 4

Cadmium ....................................................................................................................... 5

Chromium ...................................................................................................................... 6

Copper ............................................................................................................................ 7

Lead ................................................................................................................................ 7

Nickel .............................................................................................................................. 8

Zinc ................................................................................................................................. 9

Arsenic, beryllium, selenium, and silver ................................................................... 9

Sorption study .................................................................................................................... 9

Anions ............................................................................................................................ 9

Cations ............................................................................................................................ 10

Conclusions and recommendations ................................................................................ 10

Literature cited ................................................................................................................... 12

Appendix A: Concentrations of anions and cations sorbed by well casings ............ 14

Abstract ............................................................................................................................... 16

ILLUSTRATIONS

Figure

1. Sorption of lead by well casings .......................................................................... 10

TABLES

Table

1. Performance ranking of polymeric well casing materials ............................... 1

2. Method detection limits and EPA primary drinking water

quality standards ............................................................................................ 2

3. Concentration of metals found leaching from well casings ............................ 4

4. Mean normalized concentrations of metals leaching from well casings ....... 8

5. Mean normalized concentrations of As, Cd, Cr, and Pb sorbed by

well casings ..................................................................................................... 9

6. Other factors affecting well casing selection for monitoring wells ................ 11
INTRODUCTION

Ideally, any material that is used as either a

well casing or screen in a groundwater monitoring well should be strong enough to remain intact

once installed in the well, should resist degradation by the environment, and should not affect

analyte concentrations in samples by leaching or

sorbing organic or metal contaminants. Recent

draft RCRA guidance by the U.S. Environmental

Protection Agency (US EPA 1992) acknowledges

that none of the most commonly used casing materials in groundwater monitoring wells (polytetrafluoroethylene [PTFE], polyvinyl chloride

[PVC], or stainless steel [SS]) can be used for all

monitoring applications. Therefore, we undertook

a series of studies to assess the suitability of several other candidate materials for use in well casings. The four materials we initially considered

were acrylonitrile butadiene styrene (ABS), fluorinated ethylene propylene (FEP), fiberglass-reinforced epoxy (FRE), and fiberglass-reinforced plastic (FRP).

For anyone not familiar with these materials,

ABS is a thermoplastic material like PVC and is a

terpolymer of acrylonitrile, butadiene, and styrene. A wide range of properties can be achieved

by varying the ratio of these monomers and by

using additives (Sax and Lewis 1987). FEP is a

fluoropolymer and is a copolymer of tetrafluoroethylene and hexafluoropropylene. It is similar to

PTFE in its chemical and physical properties, although it has a slightly higher coefficient of friction (Sax and Lewis 1987). According to the manufacturer, FRE well casing is constructed of 75%

high silica glass and 25% high purity, closed molecular epoxy. The epoxy is manufactured from

bisphenol A-type epoxy resins cured with methyl

tetrahydrophthalic anhydride (Cowgill 1988). According to the manufacturer’s literature, the FRP

used in this study consisted of 70% fiberglass and

30% polyester resin (by weight).

A literature review found only a few studies

that dealt with sorption of organic solutes and

leaching of organic constituents by these four materials. Gillham and O’Hannesin (1990) rated several polymeric materials with respect to sorption

of organic solutes (Table 1). With respect to leaching of organic contaminants from FRE casing,

Cowgill (1988) found that two organic contaminants leached from ground casings (diethyl

phthalate and bisphenol A), but nothing leached

from intact casings after three weeks’ contact.

To assess the overall suitability of these four

materials for use in groundwater monitoring wells,

we conducted a series of studies to examine the

chemical resistance of these materials (Ranney and

Parker 1995), sorption of organic solutes by these

materials (Ranney and Parker 1994), and leaching

Sorption and Leaching of

Trace-Level Metals by Polymeric Well Casings

THOMAS A. RANNEY AND LOUISE V. PARKER

Table 1. Performance ranking of polymeric

well casing materials (from least affected to

most affected).

Degradation by Chemicals

FEP, PTFE < FRE < FRP < PVC < ABS

Taken from Ranney and Parker (1995)

Sorption of Organic Solutes

FRE, PVC < FEP, PTFE, FRP << ABS

Taken from Ranney and Parker (1994)

Rigid PVC < FG < PF < PTFE < PE < flexible PVC

where: FG = epoxy-impregnated fiberglass

PE = polyethylene

PF = polyvinylidene fluoride

Taken from Gillham and O’Hannesin (1990)

Leaching of Organic Constituents

PVC, FEP, PTFE < FRE < FRP << ABS

Taken from Ranney and Parker (1994)
of organic constituents from these

materials (Ranney and Parker 1994).

In these studies, we compared these

four materials with two other commonly used polymeric well casing

materials, PVC and PTFE. The results

from these two studies are summarized in Table 1. The results for sorption of organic solutes agree fairly

well with Gillham and O’Hannesin’s

(1990) findings, except that they

found FRE to be more sorptive of organic solutes than rigid PVC, and we

did not (Ranney and Parker 1994).

We believe the reason their findings

differed slightly from ours is because

they tested FRE tubing and PVC pipe

while we tested well casings made for monitoring

wells. It was decided to eliminate ABS from further consideration since our studies (Ranney and

Parker 1994, 1995) had shown the ABS tested

(waste and vent pipe) was not a good material for

monitoring organic contaminants and because

ABS well casing was no longer available.

To determine the overall suitability of FEP, FRE,

and FRP for groundwater monitoring wells, it is

also important to assess whether these materials

sorb or leach metals. A review of the literature on

sorption and leaching of metals by these products

produced relatively little information.

According to Masse et al. (1981) anions do not

strongly associate with polymer surfaces such as

polyethylene (PE) and PTFE. Hewitt (Parker et al.

1990, Hewitt 1992) observed that PTFE and rigid

PVC did not sorb the anionic forms of As and Cr.

However, sorption of cations by these polymers

does appear to occur (Masse et al. 1981, Parker et

al. 1990, Hewitt 1992). Only one laboratory study

(Raber et al. 1983) was found that specifically addressed sorption of metals by any of these three

materials. Raber et al. (1983) tested twelve different polymers for sorption of three radionuclides

( SeO3

2-, Sr2+, and Cs+) and found that FEP and

PTFE were among the least sorptive materials.

Several studies (Hewitt 1989, Parker et al. 1990,

Hewitt 1992, 1994) have assessed sorption of metals by PTFE. Since FEP and PTFE are both fluoropolymers, data for PTFE may indicate how FEP

will perform. These studies show that under static conditions there was relatively little sorption of

several cations (Pb, Cd, Cu, Fe) by PTFE when

compared with rigid PVC and especially SS casings (Parker et al. 1990, Hewitt 1992). However,

under dynamic conditions, significant losses of

several cations (Cd, Pb, and Fe) occurred in some

samples exposed to PTFE (and PVC) screen, although these losses were substantially less than

those observed for SS screens (Hewitt 1994).

With respect to the literature on leaching of metals from FEP, FRE, or FRP, only one relevant laboratory study (Cowgill 1988) was found. Cowgill

searched for 30 elements in water samples that

had been exposed to a ground powder of FRE

well casings. Apparently, no elements leached after 72 hours’ exposure, but after three weeks, mg/

L levels of B and Cl and μg/L levels of P, Mg, and

Zn were found in the leachate. These concentrations were all below the EPA’s drinking water standards or else were not regulated.

Although no other studies were found for FEP

and FRP, we expect that FEP may behave similarly to PTFE. Hewitt (Hewitt 1989, 1992) reported

that under static conditions PTFE leached substantially less of some metals than rigid PVC and

especially SS well casings. Under dynamic conditions, concentrations of several metals (Cd, Cr,

Cu, Fe, Ni, Pb) in samples exposed to PTFE (and

PVC) well screens did not differ from the controls

(Hewitt 1994).

In this report, we will compare sorption and

leaching of metal species by FEP, FRE, FRP, PTFE,

and PVC. In the leaching study 11 metals (Ag, As,

Ba, Be, Cd, Cr, Cu, Pb, Ni, Se, and Zn) will be

sought. With the exception of Ba, all these metals

are on the EPA’s priority pollutant list. Also, the

US EPA has established maximum contaminant

levels (MCLs) in drinking water (US EPA 1994)

for all these metals except Ag and Zn (Table 2). In

the sorption study, these five casing materials were

exposed to a solution containing a mixture of μg/

L concentrations of As, Cd, Cr, and Pb.

Table 2. Method detection limits and EPA primary drinking water

quality standards (Maximum Contaminant Levels [MCLs]).

MDL MDL EPA primary drinking water std.

leaching study sorption study 1975 Interim std1 1994 Std2

Metal μg/L μg/L μg/L μg/L

Ag 0.010 — 50 —

As 0.41 1.5 50 50

Ba 5.1 — 1000 2000

Be 0.084 — — 4

Cd 0.059 0.064 10 5

Cr 0.12 0.7 50 100

Cu 0.37 — 1000 1300

Ni 0.66 — — 100

Pb 0.35 0.89 50 15

Se 8.5 — 10 50

Zn 0.19 — — —

1

 Given in the Federal Register (1975).

2

 Given in US EPA (1994).

2
MATERIALS AND METHODS

Materials

Five types of 5-cm-diameter (2-in.) well casings or pipes were used in this study. For PTFE,

FRP, FRE, and PVC, we used well casings manufactured specifically for groundwater monitoring.

We were unable to find a manufacturer that made

FEP well casings, but did find one that made “pipe

for sampling groundwater.” We will refer to all of

these materials as casings throughout this report.

Because the thickness of the walls of the five

casing materials differed, we cut rings of the casings to varying lengths (~2 cm long) so that the

surface area would be constant (80 cm2). The material surface-area-to-aqueous-solution-volume

ratio was 0.82 cm2/cm3. Special care was taken to

prevent any contamination from grease, oil, dirt,

solvent, etc. during the cutting process. The PTFE,

FEP, and PVC casings were cut with a high-speed

steel slotting saw (VASCO M-2). The two fiberglass materials, FRE and FRP, were cut with a

high-speed steel (1076) diamond band saw. The

ratio of cut surface area to total surface area was

approximately 18% for PTFE and PVC, 17% for

FRP, 15% for FEP, and 7% for FRE.

The ring sections were rinsed with several volumes of deionized (Millipore) water and allowed

to air dry in a Class 100 clean room where all

subsequent cleaning and prep work was done.

Plastic gloves and nylon tweezers were used to

handle the ring sections.

Polypropylene (PP) jars (125 mL) with PP screw

caps were used as the sample containers. The jars,

PP Eppendorf pipet tips, PP volumetric flasks with

PP screw caps, nylon tweezers, PE autosampler

cups, and two 4-L brown glass bottles used to

hold the groundwater were acid cleaned prior to

being used. The equipment was acid cleaned by

soaking in a 10% v/v of redistilled nitric acid and

deionized water for several days, rinsing with

deionized water, soaking in deionized water for

several more days, rinsing with deionized water,

and air drying. A Brinkman dispensette was

flushed with several volumes of 2% v/v nitric

acid solution and rinsed with several volumes of

deionized water. The groundwater (pH 5.7) used

in this study was from a well (45 m deep) located

in Hartland, Vermont.

Procedure for the

leaching study

One of the ring sections was placed in a PP jar,

98 mL of groundwater was added using a calibrated Brinkman dispensette, and the jar was tightly capped. The sample jars were filled randomly

from one of two 4-L bottles of groundwater and

were stored in the dark at room temperature. There

were three replicate samples for each treatment

and time, including the controls. Contact times

were 1, 5, 20, and 40 days. Controls consisted of

jars filled only with groundwater.

On the sampling day, the jars were opened, the

ring section was removed, and 2 mL of concentrated nitric acid was added to the sample jar (giving a final pH of <1 and an acid concentration of

2% v/v). This was done because acidification to a

pH of less than 1.5 has been shown to be effective

in preventing losses of trace metals from natural

waters and aids in recovery of sorbed metals from

the vessel walls (Subramanian et al. 1978, Hewitt

1989). The jars were then recapped, swirled for 10

seconds, and left until the analyses were conducted at the end of the study.

Procedure for the

sorption study

The procedure for the sorption study was similar to the leaching study except that one mL of a

mixed metal spike solution containing 5 mg/L

As, Cr, Pb, and 2 mg/L Cd was added to 97 mL of

groundwater in a PP jar. The mixed metal spike

solution was prepared from serial dilutions in

deionized water of certified (Fisher Scientific Co.)

metal standards (1,000 mg/L). Cd and Pb were in

solution as cations, while Cr (as dichromate) and

As (as arsenite or arsenate) were anions. After adding the metal spike, each jar was swirled to mix

the solution, the section of casing was placed in

the jar, and the jar was then tightly capped. Controls consisted of jars filled with the test solution

but no casing material. Final concentrations were

approximately 51 μg/L for As, Cr, and Pb and 20

μg/L for Cd. The samples were stored in the dark

at room temperature. There were three replicate

samples for each casing material and time, including the controls. Contact times were 1, 8, 24, and

72 hours. When a sample was taken, the jar was

opened, the ring section was removed, and the

remaining solution was acidified as described previously.

Analyses

Analyses were performed by Graphite Furnace

Atomic Absorption (GFAA) using a Perkin-Elmer

Model 5100 Atomic Absorption Spectrophotometer, with a Perkin-Elmer model 5100 Zeeman background correction module, a Perkin-Elmer model

600 graphite furnace, and a Perkin-Elmer model

3
AS-60 autosampler. Instrument operating procedures followed the general recommendations

found in the manufacturer’s analytical methods

manual (Perkin-Elmer 1981). Working standards

were serial dilutions prepared from a certified (Environmental Resource Associates) primary mixed

metal standard (1 mg/L). A range of four standard concentrations, analyzed in duplicate, was

used to calibrate the instrument for each metal. A

calibration check standard for each metal was prepared from serial dilutions of a certified (Fisher

Scientific Co.) metal standard (1,000 mg/L). The

check standard was analyzed every ten samples.

If analyses indicated that drifting from the standard curve was occurring, the instrument was

recalibrated and any samples analyzed since the

last check were reanalyzed. All dilutions of standards were in deionized water containing nitric

acid (2% v/v).

Method Detection Limits (MDLs) (Table 2) were

determined following the procedure outlined in

the Federal Register (1984). All the samples were

analyzed twice and means were taken. Analysis

of Variance (ANOVA) tests were performed on

samples that showed metal concentrations consistently higher than the established MDL. If a

significant difference was detected by the ANOVA, then Fisher’s Least Significant Difference

(LSD) test was performed to determine which

materials differed from the controls and from each

other. A 95% confidence level was used in these

statistical tests.

RESULTS AND DISCUSSION

Leaching study

The results for those analytes where detectable

levels were observed (Ba, Cd, Cr, Cu, Pb, Ni, Zn,

and Ag) are given in Tables 3a–h. In instances

where one or more of the three replicate values

for a given metal, material, and time were below

the MDL, the MDL was used in estimating a mean

value. Mean normalized concentrations were determined by dividing the mean concentration for

a particular material, analyte, and time by the

mean concentration of the control samples for the

same analyte and time. A normalized mean concentration of 1.0 meant no sorption or leaching

occurred. Table 4 shows the mean normalized concentrations for these same analytes, except for Ag.

Because the concentration of Ag was often less

than the detection limit, mean normalized concentrations were not determined for this metal.

Table 3. Concentration (μg/L) of metals found

leaching from well casings.

a. Barium

Contact time, days

Treatment 1 5 20 40

CONTROL 27.6 56.9 18.8 38.7

CONTROL 25.6 71.5 19.0 37.9

CONTROL 29.4 28.0 21.5 31.4

 

X 27.5a 52.2a 19.8a 36.0a

% RSD 7.05 42.4 7.50 11.1

PVC 49.8 73.7 17.9 35.3

PVC 55.0 75.0 10.5 29.4

PVC 48.1 94.1 48.1 51.3

 

X 51.0e 81.0b 25.5a 38.7a

% RSD 7.05 14.1 78.0 29.3

PTFE 39.1 76.3 13.7 42.2

PTFE 40.1 68.3 13.9 30.5

PTFE 39.2 102 18.9 56.5

 

X 39.5c 82.2b 15.5a 43.0a

% RSD 1.31 21.4 18.9 30.3

FEP 37.1 60.2 21.6 28.6

FEP 38.1 77.7 17.7 26.5

FEP 34.9 92.0 311 101

 

X 36.7b,c 76.6a,b 117a 52.0a

% RSD 4.48 20.8 144 81.4

FRE 41.3 65.6 13.5 25.4

FRE 47.6 58.6 12.6 38.2

FRE 49.4 86.1 36.4 109

 

X 46.1d 70.1a,b 20.8a 57.6a

% RSD 9.27 20.4 64.6 78.5

FRP 28.8 70.8 21.7 45.7

FRP 33.8 68.5 27.7 28.9

FRP 33.0 74.2 33.9 74.7

 

X 31.9a,b 71.1a,b 27.8a 49.8a

% RSD 8.35 4.0 21.9 46.5

Values with the same letter for the same time were not significantly different.

Barium

All the samples, including the control samples,

showed considerable variability from day to day

and among the replicates (Table 3a). Throughout

the study, the samples exposed to the casings all

had slightly elevated mean normalized concentrations, although usually less than 2.0 (Table 4).

After one day of exposure, concentrations in samples exposed to the PVC, PTFE, FEP, and FRE casings were significantly greater than the controls

(Table 3a), with leaching greatest from the PVC

and FRE casings and least from the FRP casings.

Because of the sizable variability among replicates,

most of the samples were not significantly different from the controls on the subsequent days (Table 3a), even though the concentrations remained

consistently higher than the controls.

4
b. Cadmium

Contact time, days

Treatment 1 5 20 40

CONTROL LD LD LD LD

CONTROL LD LD LD LD

CONTROL LD LD LD LD

 

X <0.059 <0.059 <0.059 <0.059

% RSD — — — —

PVC LD 0.088 0.19 0.12

PVC LD 0.084 0.10 0.29

PVC LD 0.088 0.14 0.36

 

X <0.059 0.087a 0.15a,b 0.26b

% RSD — 2.3 30 48

PTFE 0.064 0.083 0.090 0.084

PTFE LD 0.092 0.063 0.10

PTFE LD 0.069 0.091 0.088

 

X <0.061 0.081a 0.081a 0.092a

% RSD — 15 20 12

FEP 0.061 0.089 0.15 0.13

FEP LD 0.15 0.091 0.15

FEP 0.098 0.18 0.079 0.26

 

X <0.073 0.14a 0.11a 0.18a,b

% RSD — 34 34 38

FRE 0.23 0.28 0.16 0.21

FRE 0.15 0.18 0.31 0.28

FRE 0.24 0.23 0.37 0.20

 

X 0.21a 0.23b 0.28b 0.23b

% RSD 24 23 39 18

FRP 0.48 0.62 0.76 0.91

FRP 0.30 0.62 0.63 0.75

FRP 0.81 0.68 0.97 0.80

 

X 0.53a 0.64c 0.78c 0.82c

% RSD 48 4.8 22 9.7

LD Values less than MDL.

Values with the same letter for the same time were not significantly different.

c. Chromium

Contact time, days

Treatment 1 5 20 40

CONTROL LD LD LD LD

CONTROL LD LD LD LD

CONTROL LD LD LD LD

 

X <0.12 <0.12 <0.12 <0.12

% RSD — — — —

PVC 0.18 LD LD LD

PVC 0.20 LD 0.13 0.13

PVC LD LD 0.28 LD

 

X <0.17 <0.12 <0.18 <0.12

% RSD — — — —

PTFE 0.26 LD LD LD

PTFE 0.26 LD LD LD

PTFE LD LD LD LD

 

X <0.21 <0.12 <0.12 <0.12

% RSD — — — —

FEP LD LD LD 0.23

FEP 0.13 LD LD LD

FEP 0.21 LD 0.18 0.26

 

X <0.15 <0.12 <0.14 <0.20

% RSD — — — —

FRE 0.70 0.55 0.25 0.91

FRE 0.46 0.17 0.15 0.41

FRE 0.89 0.28 0.46 0.20

 

X 0.68a 0.33a 0.29a 0.51a

% RSD 9.0 59 54 72

FRP 1.44 0.30 0.32 0.19

FRP 0.29 0.24 0.24 0.13

FRP 0.44 0.34 0.16 0.18

 

X 0.72a 0.29a 0.24a 0.17a

% RSD 87 17 33 19

LD Values less than MDL.

Values with the same letter for the same time were not significantly different.

All the values were well below the MCL of

2000 μg/L set by the US EPA for drinking water

(US EPA 1994). The highest concentration found

was 311 μg/L for a sample exposed to FEP; all the

other samples had concentrations that were less

than 110 μg/L.

Cadmium

For the control samples, concentrations of Cd

were below the MDL (Table 3b). After one day of

contact, only samples exposed to the two fiberglass casings had Cd concentrations above the

MDL. Subsequently, samples exposed to all five

casing materials had concentrations above the

MDL. Generally, samples exposed to the PVC,

PTFE, and FEP casings had the lowest concentrations and there was no significant difference between these materials. Concentrations in samples

exposed to the FRP and FRE casings were significantly greater than the other three casings (days

5, 20, 40). However, concentrations in samples exposed to FRE casings were always significantly

less than those in samples exposed to FRP. Mean

concentrations for samples exposed to FRP ranged

from 9 to 14 times control values, while for FRE

they ranged from 3.6 to 4.8 times control values

(Table 4).

In all cases, leached Cd concentrations remained

well below the EPA’s drinking water standards

(US EPA 1994) of 5 μg/L. Samples exposed to FRP

casings were the highest and yet these were still

below 1.0 μg/L. For samples exposed to the other

four casings, concentrations remained less than

0.4 μg/L.

Table 3 (cont’d).

5
Contact time, days

Treatment 1 5 20 40

CONTROL 17.3 18.6 18.7 17.9

CONTROL 17.8 18.4 18.9 17.8

CONTROL 17.5 18.1 19.0 18.3

 

X 17.5a 18.4a 18.9a 18.0a

% RSD 1.48 1.31 1.01 1.28

PVC 16.3 14.1 9.24 12.0

PVC 15.2 14.5 14.0 9.34

PVC 14.6 13.5 12.2 15.2

 

X 15.4b 14.0c 11.8c 12.2b

% RSD 5.86 3.49 20.5 24.0

PTFE 16.6 17.7 17.8 18.0

PTFE 19.6 17.2 17.3 16.1

PTFE 15.7 17.5 20.1 19.1

 

X 17.3a 17.5a 18.4a 17.7a

% RSD 11.6 1.32 8.26 8.52

FEP 15.8 15.7 16.9 14.6

FEP 15.9 15.1 16.1 14.4

FEP 16.0 15.1 14.7 13.9

 

X 15.9a,b 15.3b 15.9b 14.3b

% RSD 0.50 2.09 7.23 2.37

FRE 8.58 9.62 8.42 5.12

FRE 10.7 11.2 9.76 8.03

FRE 10.4 10.1 8.12 9.52

 

X 9.90d 10.3d 8.77d 7.56c

% RSD 11.6 7.95 9.92 29.6

FRP 13.5 11.1 11.4 8.92

FRP 12.3 10.4 9.38 8.48

FRP 13.2 12.5 10.1 8.82

 

X 13.0c 11.3d 10.3c,d 8.74c

% RSD 5.08 9.44 10.1 2.63

Values with the same letter for the same time were not significantly different.

Contact time, days

Treatment 1 5 20 40

CONTROL LD LD LD LD

CONTROL LD LD LD LD

CONTROL LD LD LD LD

 

X <0.35 <0.35 <0.35 <0.35

% RSD — — — —

PVC 0.39 LD 0.36 LD

PVC LD LD 0.74 0.44

PVC LD LD LD 0.48

 

X <0.36 <0.35 <0.48 <0.42

% RSD — — — —

PTFE 1.6 LD 0.59 LD

PTFE 0.50 0.37 0.41 0.39

PTFE LD LD 0.62 LD

 

X <0.82 <0.36 0.54a <0.36

% RSD — — 20 —

FEP 1.8 LD 0.46 LD

FEP 0.41 LD 0.52 LD

FEP 0.36 0.46 0.87 0.37

 

X 0.85a <0.39 0.62a <0.36

% RSD 95 — 35 —

FRE LD LD LD LD

FRE LD LD 0.35 0.38

FRE 0.57 LD LD LD

 

X <0.43 <0.35 <0.35 <0.36

% RSD — — — —

FRP 20 9.4 8.5 11

FRP 8.7 15 7.1 5.5

FRP 6.0 6.7 7.8 13

 

X 12b 10 7.8b 9.8

% RSD 66 39.4 8.8 40

LD Values less than MDL.

Values with the same letter for the same time were not significantly different.

Chromium

For the control samples, concentrations of Cr

were all below the MDL (Table 3c). Concentrations of Cr in samples exposed to PVC, PTFE, and

FEP were also generally below the MDL. Only

samples exposed to FRE and FRP casings leached

concentrations of Cr that were consistently above

the MDL. However, there was no significant difference between the Cr concentrations of samples

exposed to these two materials.

The highest concentration observed in any one

sample was 1.44 μg/L (for a sample exposed to

FRP); the remainder of the samples had concentrations that were less than 1.0 μg/L. These concentrations were all well below the MCL (100 μg/

L) set by the US EPA (1994) for drinking water.

The results from this study can be compared

with the results from a similar study (Hewitt 1989)

that was concerned with metals leaching from

PVC, PTFE, and SS 304 and 316 casings. In that

study, Cd levels were highest in samples exposed

to the 316 SS. At the beginning of the study (days

1 and 5), the mean concentration of Cd in the samples that were exposed to FRP casings was approximately half the mean concentration Hewitt

observed leaching from samples exposed to the

316 SS. However, these high mean values for the

316 SS were primarily due to the presence of one

high value among the replicates. Later in the study

(days 20 and 40), concentrations of samples exposed to the 316 SS were consistently lower than

the mean concentration of samples exposed to FRP.

Table 3 (cont’d). Concentration (μg/L) of metals found leaching from well casings.

d. Copper e. Lead

6
Even though leached concentrations were highest in samples exposed to FRE and FRP, these concentrations were generally well below levels

Hewitt (1989) observed leaching from SS 304 and

316 casings and screens under similar conditions.

Copper

The initial Cu concentration of the groundwater used in this study was approximately 18 μg/L

(Table 3d). Table 4 clearly shows that none of the

materials leached Cu but rather, with the exception of PTFE, sorbed significant quantities. It was

surprising that FEP sorbed 10 to 20% of the copper while PTFE did not, since we expected the

two fluoropolymers to perform similarly. The two

fiberglass materials showed the greatest sorption

of Cu, with ~50% loss by the end of the study. In

comparison, losses by the end of the study were

32% for PVC and 20% for FEP.

In a similar study, Hewitt (1989) found SS 316

casings leached significant quantities of copper;

mean concentrations of leached Cu were 3 to 8

times background values.

Lead

For the control samples, lead concentrations

were all less than the MDL (Table 3e). Only samples exposed to the FRP casings consistently had

Pb concentrations above the MDL. Normalized

concentrations for samples exposed to FRP ranged

from 22 to 34 times control values (Table 4). In

several samples, concentrations approached or exContact time, days

Treatment 1 5 20 40

CONTROL LD 0.72 LD 0.99

CONTROL LD LD LD 1.14

CONTROL LD 0.87 LD 0.97

 

X <0.66 <0.75 <0.66 1.03a

% RSD — — — 8.74

PVC 0.71 0.93 0.91 1.16

PVC LD 0.77 0.69 1.69

PVC 0.83 0.99 0.96 1.33

 

X <0.73 0.90a 0.85a 1.39a,b

% RSD — 12.2 16.5 19.4

PTFE 0.78 0.90 0.82 1.17

PTFE 1.08 1.13 0.67 1.14

PTFE 0.71 1.08 0.96 1.13

 

X 0.86a 1.04a 0.82a 1.15a

% RSD 23.3 11.5 18.3 1.74

FEP 0.86 1.01 0.56 1.38

FEP 1.61 1.05 1.03 1.45

FEP 1.12 1.34 1.05 2.32

 

X 1.20a,b 1.13a 0.88a 1.72b,c

% RSD 31.7 15.9 31.8 30.2

FRE 1.32 1.62 1.24 2.31

FRE 2.23 1.58 1.17 2.27

FRE 2.36 1.75 2.09 1.81

 

X 1.97b,c 1.65b 1.50b 2.13c

% RSD 28.9 5.45 34.0 13.2

FRP 2.83 2.29 2.12 1.92

FRP 1.62 1.72 1.67 2.49

FRP 2.38 2.29 1.74 2.13

 

X 2.28c 2.10c 1.84b 2.18c

% RSD 26.8 15.7 13.0 13.3

LD Values less than MDL.

Values with the same letter for the same time were not significantly different.

Contact time, days

Treatment 1 5 20 40

CONTROL 3.33 3.40 5.38 5.00

CONTROL 3.41 3.42 5.45 5.23

CONTROL 3.42 3.49 5.22 5.33

 

X 3.39a 3.44a 5.35a 5.18a

% RSD 1.47 1.45 2.24 3.28

PVC 8.41 14.0 18.0 11.0

PVC 6.51 11.2 11.0 21.0

PVC 7.48 10.7 16.6 18.1

 

X 7.46b 12.0c 15.2c 16.7b

% RSD 12.7 15.0 24.2 31.1

PTFE 6.30 5.36 12.1 10.0

PTFE 8.51 7.02 8.48 9.73

PTFE 5.07 5.59 14.2 10.5

 

X 6.63b 5.99b 11.6b,c 10.1a

% RSD 26.2 15.0 24.9 3.67

FEP 5.65 7.86 9.03 7.84

FEP 5.26 5.49 10.5 8.79

FEP 7.20 7.41 7.39 8.79

 

X 6.03b 6.92b 8.98a,b 8.48a

% RSD 17.1 18.2 17.5 6.49

FRE 8.57 10.7 11.4 17.8

FRE 7.38 12.2 12.6 19.7

FRE 7.89 10.6 12.6 10.5

 

X 7.94b 11.2c 12.2b,c 16.0b

% RSD 7.56 7.80 5.50 30.5

FRP 22.3 39.5 36.1 44.7

FRP 25.2 38.4 37.0 44.1

FRP 22.2 40.9 44.7 43.3

 

X 23.2c 39.6d 39.3d 44.0c

% RSD 7.32 3.21 12.1 1.23

Values with the same letter for the same time were not significantly different.

Table 3 (cont’d).

f. Nickel g. Zinc

7
ceeded the MCL of 15 μg/L set by the US EPA

(1994) for drinking water, although the mean values for each day and material were below this

limit. For samples exposed to the other materials,

concentrations were well below the MCL. Concentrations were always less than 2 μg/L and generally were less than 1 μg/L.

Lead concentrations in the samples exposed to

FRP were much higher than Hewitt (1989) observed for samples exposed to SS 304 and 316

under similar conditions. The other materials

(PVC, PTFE, FEP, and FRP) appear to leach less

lead than SS 304 and 316 casings did under similar conditions.

Nickel

Concentrations of Ni in the control samples

were below the MDL, except for the 40-day samTable 4. Mean normalized concentrations of metals leaching from well casings.*

Contact time, days

Treatment 1 5 20 40

BARIUM

PVC 1.85 1.55 1.29 1.08

PTFE 1.44 1.57 0.78 1.20

FEP 1.33 1.47 5.90 1.44

FRE 1.68 1.34 1.05 1.60

FRP 1.16 1.36 1.41 1.38

CADMIUM

PVC ≈1.0 >1.5 >2.5 >4.4

PTFE ≈1.0 >1.4 >1.4 >1.6

FEP ≈1.2 >2.4 >1.9 >3.0

FRE >3.6 >3.9 >4.8 >3.9

FRP >9.0 >11 >13 >14

CHROMIUM

PVC ≈1.4 ≈1.0 ≈1.5 ≈1.0

PTFE ≈1.8 ≈1.0 ≈1.0 ≈1.0

FEP ≈1.2 ≈1.0 ≈1.2 ≈1.7

FRE >5.7 >2.8 >2.4 >4.3

FRP >6.0 >2.4 >2.0 >1.4

COPPER

PVC 0.88 0.76 0.63 0.68

PTFE 0.99 0.95 0.97 0.98

FEP 0.91 0.83 0.84 0.80

FRE 0.56 0.56 0.46 0.42

FRP 0.74 0.62 0.55 0.49

LEAD

PVC ≈1.0 ≈1.0 ≈1.4 ≈1.2

PTFE ≈2.3 ≈1.0 >1.5 ≈1.0

FEP >2.4 ≈1.1 >1.8 ≈1.0

FRE ≈1.2 ≈1.0 ≈1.0 ≈1.0

FRP >34 >29 >22 >28

NICKEL

PVC ≈1.1 >1.2 >1.3 1.4

PTFE >1.3 >1.4 >1.2 1.1

FEP >1.8 >1.5 >1.3 1.7

FRE >3.0 >2.2 >2.3 2.1

FRP >3.4 >2.8 >2.7 2.1

ZINC

PVC 2.2 3.48 2.84 3.22

PTFE 1.96 1.74 2.17 1.94

FEP 1.78 2.01 1.68 1.63

FRE 2.35 3.24 2.28 3.08

FRP 6.86 11.5 7.34 8.48

* The mean normalized concentration was determined by

dividing the mean concentration of a given analyte at a given

time and for a particular casing material by the mean concentration (for the same analyte) of the control sample taken

at the same time.

The mean normalized concentrations for samples where

one or more values for the controls were less than the MDL

are marked with >.

In cases where one or more values for the sample are also

less than the MDL, the mean normalized concentration is

marked with ≈.

Table 3 (cont’d). Concentration (μg/L) of metals

found leaching from well casings.

h. Silver

Contact time, days

Treatment 1 5 20 40

CONTROL LD 0.047 0.019 LD

CONTROL 0.011 LD 0.064 LD

CONTROL LD LD LD LD

 

X <0.010 <0.022 <0.031 <0.010

% RSD — — — —

PVC 0.015 LD LD

PVC 0.028 0.019 LD 0.048

PVC LD LD 0.028 0.021

 

X <0.018 <0.013 <0.016 <0.026

% RSD — — — —

PTFE LD LD LD 0.043

PTFE LD 0.010 LD LD

PTFE LD LD 0.059 LD

 

X <0.010 <0.010 <0.026 <0.021

% RSD — — — —

FEP 0.040 LD 0.014 0.033

FEP LD LD LD 0.079

FEP 0.051 LD LD LD

 

X <0.034 <0.010 <0.011 <0.041

% RSD — — — —

FRE 0.040 0.031 LD LD

FRE LD LD LD 0.025

FRE 0.037 LD 0.060 LD

 

X <0.029 <0.017 <0.027 <0.015

% RSD — — — —

FRP LD LD LD LD

FRP LD 0.050 0.018 LD

FRP LD LD LD LD

 

X <0.010 <0.023 <0.013 <0.010

% RSD — — — —

LD Values less than MDL.

ples (Table 3f). Thus, statistical comparisons with

the control samples could be made only for the

40-day samples. Throughout the study, there was

no significant difference between the concentra8
tions of samples exposed to PVC, PTFE, or FEP

casings. However, after 40 days’ exposure, concentrations of samples exposed to FEP casings

were significantly higher than the controls. Generally, concentrations of Ni in samples exposed to

the two fiberglass materials were significantly

greater than the other three materials. Mean normalized concentrations for samples exposed to

these two materials ranged from approximately 2

to 3.5 times the control values (Table 4). However,

these elevated Ni levels may be the result of an

experimental artifact rather than constituents

leaching from the casing material. Nickel electroplate was used to bind the diamonds to the steel

band that was used to cut these two materials.

The other materials were cut with a steel slotting

saw, which did not have diamonds bonded to it.

Even for the samples with the highest concentrations of Ni, leached concentrations were less

than 3 μg/L, well below the MCL of 100 μg/L set

by the EPA for drinking water (US EPA 1994).

No comparison can be made with the SS casings, because Hewitt’s (1989) study, which was

conducted under similar conditions, did not test

for Ni. Under anoxic conditions, however, Hewitt

(1992) found that SS 304 and 316 casings leached

consistently higher concentrations of Ni than any

of the casings we tested in this study. Means for

samples exposed to SS 316 were the highest and

were 4 to 5 times higher than the concentrations

of samples exposed to the fiberglass casings.

Zinc

After one day of exposure, all the samples exposed to the well casings had significantly higher

concentrations of Zn than the control samples

(Table 3g, Table 4). Concentrations in samples exposed to the FRP casings were significantly higher than those in samples exposed to the other casings; mean normalized concentrations were

approximately 7 to 12 times control values.

Leached concentrations cannot be compared with

any MCL standard for Zn because the US EPA

has not set one. Also, no comparisons can be made

with the SS casings because there are no data available.

Arsenic, beryllium,

selenium, and silver

Concentrations of As, Be, and Se were all below the MDL. The majority of the values for Ag

were also below the MDL, and do not show any

apparent pattern or trend (Table 3h). In all cases,

leached concentrations of Ag were less than 0.80

Table 5. Mean normalized concentrations of As,

Cd, Cr, and Pb sorbed by well casings.

Contact time, hours

Treatment 1 8 24 72

ARSENIC

PVC 1.02 1.01 1.01 1.00

PTFE 0.99 1.01 1.00 0.99

FEP 0.99 1.00 1.01 1.00

FRE 0.99 0.99 0.99 0.99

FRP 1.01 1.00 1.00 1.00

CADMIUM

PVC 0.93 0.87 0.83 0.79

PTFE 0.97 0.95 0.93 0.99

FEP 0.98 0.96 0.95 0.98

FRE 0.95 0.91 0.89 0.94

FRP 0.96 0.96 0.90 0.94

CHROMIUM

PVC 1.01 1.01 1.00 0.99

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

FRP 1.01 1.03 1.00 1.00

LEAD

PVC 0.90 0.70 0.61 0.56

PTFE 0.98 0.95 0.94 0.93

FEP 0.97 0.95 0.93 0.93

FRE 0.89 0.65 0.55 0.45

FRP 0.91 0.71 0.59 0.52

μg/L. Currently, the EPA has not set an MCL for

silver in drinking water. However, a previous MCL

value given in the EPA’s Interim Primary Drinking Water Standards (Federal Register 1975) was

50 μg/L, and the values observed in this study

are well below this value. Again, there are no data

available for these four analytes that would allow

comparisons to be made with SS casings.

SORPTION STUDY

Initial concentrations were 51 μg/L for As, Cr,

and Pb and 20 μg/L for Cd.

Anions

Arsenic

There was no significant loss of As in any of

the samples exposed to the casing materials

(Table 5, Table A1). Since arsenic exists as negatively charged arsenates or arsenites under the

oxidizing to slightly reducing conditions found

in natural waters (Fowler et al. 1979), these results agree with several previous studies (Masse

et al. 1981, Parker et al. 1990, Hewitt 1992) that

have shown that anions do not strongly associate

with polymeric surfaces. In comparison, data from

9
a study that tested types 304 and 316 SS casings showed that these casings were slightly sorptive (e.g., 10% loss in 24 hours) under

similar conditions (Parker et al. 1990).

Chromium

Because Cr was added to the groundwater as dichromate, a negatively charged species, we would expect the results for this

anion to be similar to those for As. Statistical analyses of these data indicated that losses due to sorption were not significant for

any of the casing materials, except for a few

of the samples exposed to the FRE casings

(Table A2). However, these losses were slight:

less than 5% (Table 5).

In similar studies that examined sorption

of Cr by SS 304 and 316 casings, there was some

slow sorption by SS 316 casings (e.g., 13% in eight

hours) (Parker et al. 1990).

Cations

Cadmium

While the polymeric casings did not tend to

sorb anions, this was not the case for cations.

FEP was the only polymeric material of the five

tested that had no significant effect on Cd concentrations. PVC was the most sorptive material

tested—losses ranged from 7 to 21% (Table 5), and

these losses were significant for all four sampling

times (Table A3). Also, losses of Cd became significant after eight hours for samples exposed to

FRE (9% loss) and after 24 hours for samples exposed to FRP (10% loss). Cd concentrations were

also significantly lower in samples that were exposed to the PTFE casings after eight and 24 hours

(~5 to 7% loss), but not by the end of the study.

There was less sorption of Cd by the PTFE, FRE,

and FRP casings as the study progressed. This

may be because, as the leaching study showed,

these materials leach low levels of this analyte.

In a similar study, both types of SS casings (304

and 316) leached Cd and therefore no sorption

was observed (Parker et al. 1990). However, under low DO conditions, SS 304 was very sorptive

of Cd (losses ranged from 18% at eight hours to

60% at 72 hours) (Hewitt 1992).

Lead

Since lead also exists as a cation in solution, we

would expect that some of the casing materials

would sorb Pb in a fashion similar to Cd. Previous studies (Parker et al. 1990, Hewitt 1992) have

shown that this analyte is readily sorbed by SS,

PVC, and PTFE well casings. Table 5 and Figure 1

show that there was substantial sorption of Pb in

the samples exposed to the PVC, FRE, and FRP

casings. These losses were significant after one

hour of exposure (Table A4). Sorption tended to

be significantly greater for FRE than FRP or PVC.

By the end of the study (72 hours), mean losses

for these materials were 57% for FRE, 48% for

FRP, and 44% for PVC. After 24 hours, concentrations of samples exposed to the fluoropolymers

(FEP and PTFE) were also significantly lower than

the controls, indicating that sorption had occurred.

However, these losses were small (2 to 7%).

Sorption by the most sorptive material, FRE,

appears to be equivalent to what has been observed under similar conditions for SS 304 and

less than what has been observed for SS 316 (Parker et al. 1990). Although we do not have any explanation, sorption of Pb by PVC appears to be

considerably greater in this study than what was

observed in a previous study (Parker et al. 1990).

CONCLUSIONS AND

RECOMMENDATIONS

These studies show that, with respect to leaching, the fiberglass materials were more apt to leach

higher concentrations of contaminants than the

other three materials. However, in at least one

case (Ni), we suspect that this may be the result of

an experimental artifact. With the exception of Cd,

the performance of PVC was almost as good as

the fluoropolymers. The concentrations of leached

contaminants were relatively low and did not approach limits set by the US EPA for drinking waConcentration Relative to Control

Contact Time (hr)

1.0

0.8

0.6

0.4

0.2

0 16 32 48 64 80

PVC

PTFE

FEP

FRE

FRP

Figure 1. Sorption of lead by well casings.

10
ter, except for the FRP casings that leached Pb.

Comparisons of these data with a similar study

conducted by our laboratory (Hewitt 1989) indicated that FRE, PVC, PTFE, and FEP tended to

leach less than SS 304 and 316 casings, while this

was not always the case for FRP, especially for

Cd and Pb.

It is possible that FRE and FRP casings would

leach less under dynamic conditions. Previous

studies by Hewitt (1989, 1992, 1994) have shown

that PVC leached Cr and Pb under static conditions, but did not do so under dynamic conditions. In addition, several older studies (Packham

1971a,b; Gross et al. 1974; Dietz et al. 1977) have

shown the leaching of metal stabilizers from PVC

pipe appears to be due to a surface phenomenon,

i.e., concentrations of leached metal stabilizers are

highest initially, drop off with additional flushing

with water, and then level off.

With respect to sorption, none of the five materials sorbed the anions tested, As and Cr. However, all five materials sorbed the cations tested

(Cu, Cd, Pb), although the two fluoropolymers

were the least active. With respect to sorption of

Cd, PVC was the most active while FRE and FRP

were more sorptive of Pb and Cu (with FRE being

slightly more sorptive). Again, we might expect

that these effects would be mitigated in a well

where the water is replenished and sites for sorption become less available with time. However,

Hewitt (1994) found that PVC and PTFE well

screens continued to sorb cations under dynamic

conditions. A comparison of our results with a

similar study of sorption of metals by SS casings

(Parker et al. 1990) also indicates that SS materials

are much more sorptive than the polymeric materials we tested.

Based on our findings in this study, we would

tentatively rank these materials’ impact on metal

concentrations as follows:

FEP, PTFE < PVC < FRE < FRP.

Based on our findings and those of others (Hewitt

1989, 1992, 1994, Parker et al. 1990), we would

also rank the impact on metal concentrations of

four of these materials and SS as

FEP, PTFE < PVC < FRE < SS.

Selecting well casings for a particular well is

highly dependent upon a number of factors including the size and depth of the well (i.e., strength

considerations), the contaminants of interest, and

characteristics of the well water that might cause

degradation of the casing material. Table 1 summarized most of the research studies on degradation of these polymeric materials by chemicals and

the effects these polymeric casings have on organic contaminants. It should be noted that while

several studies (Parker et al. 1990, Gillham and

O’Hannesin 1990, Parker and Ranney 1994a) have

shown that SS is relatively nonsorptive of a fairly

wide range of organic solutes, Reynolds et al.

(1990) have shown that it can react with highly

halogenated hydrocarbons, causing their degradation. Table 6 summarizes some additional information on the strength of these materials, other conditions that cause degradation of casing

materials, and cost.

This series of experiments clearly shows that,

of the three new materials considered in this study

(FEP, FRE, and FRP), FRE may prove quite useful

in monitoring applications where either SS or PVC

cannot be used, especially in deeper wells. FEP

does not appear to offer any clear advantage over

PTFE. When cost is also considered, PVC still reTable 6. Other factors affecting well casing selection for monitoring wells.

Strength Considerations

(Going from shallowest well to deepest well)

PTFE (~FEP) << PVC, FRP < FRE < SS

Based on manufacturer information and information

in Nielsen and Schalla (1991). FEP was assumed to be

fairly equivalent to PTFE because no strength data

were found.

Corrosion of Stainless Steel

pH < 7.0

DO > 2 ppm

H2S ≥ 1 ppm

Total Dissolved Solids > 1000 ppm

CO2 > 50 ppm

Cl– > 500 ppm

Taken from Aller et al. (1989), Driscoll (1986).

Softening of Plastics by Organic Solutes

Most non-fluoropolymers such as PVC, FRP, FRE, and ABS

can also be degraded by very high concentrations of some

organic solvents. In order for this to happen:

the organic solvent must be a good solvent of the polymer and

the solvent must be present in concentrations that exceed

0.1 times the chemical’s aqueous solubility.

As an example, methylene chloride is a good solvent of PVC.

It must be present at a concentration that exceeds (0.1) × (~1900

mg/L), or ~190 mg/L.

References: Berens (1985), Vonk (1985, 1986), Parker et al.

(1992), Parker and Ranney (1994b, 1995).

Cost of Casing Materials

PVC < FRE < FRP < SS 304 < SS 316 < FEP, PTFE

Based on the price paid for the materials used in this

study in 1993.

11
mains the first choice for most monitoring applications. It is our intention that this information

will be used to select a casing material that will

offer the best possible performance at the least

possible cost.

LITERATURE CITED

Aller, L., T.W. Bennett, G. Hackett, R.J. Petty,

J.H. Lehr, H. Sedoris, D.M. Nielsen, and J.E.

Denne (1989) Handbook of Suggested Practices for

the Design and Installation of Ground-Water Monitoring Wells. Dublin, Ohio: National Water Well

Association.

Berens, A.R. (1985) Prediction of organic chemical permeation through PVC pipe. Journal of the

American Water Works Association, p. 57–65.

Cowgill, U.M. (1988) The chemical composition

of leachate from a two-week dwell-time study

of PVC casing and a three-week dwell-time

study of fiberglass reinforced epoxy well casing. In Ground-water Contamination: Field Methods. ASTM STP 963 (A.G. Collins and A.I. Johnson,

Ed.). Philadelphia: American Society for Testing

and Materials, p. 172–184.

Dietz, G.R., J.D. Banzer, and E.M. Miller (1977)

Water extraction of additives from PVC pipe. In

Proceedings of the Safety and Health with Plastics National Technical Conference, p. 25–29.

Driscoll, F.G. (1986) Ground Water and Wells. St.

Paul, Minnesota: Johnson Division.

Federal Register (1975) Maximum allowable limits in drinking water. Federal Register, March 14,

40(51): 11990–11998.

Federal Register (1984) Definition and procedure

for the determination of the method detection limit. Code of Federal Regulations, Part 136, Appendix B,

October 26.

Fowler, B.A., R.S. Braman, K.Y. Chen, P.A. Gilderhus, P.V. Hodson, M. Katz, J.C. Kent, L.L. King,

J.M. McKim, L.W. Nicholson, D.R.M. Passino,

and W.R. Penrose (1979) Arsenic. In A Review of

the EPA Red Book: Quality Criteria for Water (R.V.

Thurston, R.C. Rosso, C.M. Fetteroff, Jr., T.A. Edsall, and Y.M. Baker, Jr., Ed.). Bethesda, Maryland:

Water Quality Section, American Fisheries Society, p. 19–33.

Gillham, R.W. and S.F. O’Hannesin (1990) Sorption of aromatic hydrocarbons by materials used

in construction of ground-water monitoring sampling wells. In Ground Water and Vadose Zone Monitoring. ASTM STP 1053 (D.M. Nielsen and A.I.

Johnson, Ed.). Philadelphia, Pennsylvania: American Society for Testing and Materials, p. 108–122.

Gross, R.C., B. Engelbart, and S. Walter (1974)

Aqueous extraction of lead stabilizers from PVC

compounds. Society of Plastic Engineering, Technical Paper 20, p. 527–531.

Hewitt, A.D. (1989) Leaching of metal pollutants

from four well casings used for groundwater monitoring. USA Cold Regions Research and Engineering Laboratory, Special Report 89-32.

Hewitt, A.D. (1992) Potential of common well casing materials to influence aqueous metal concentrations. Ground Water Monitoring Review, 12(2):

131–135.

Hewitt, A.D. (1994) Dynamic study of common

well screen materials. Ground Water Monitoring and

Remediation, 14(1): 87–94.

Masse, R., F.J.M.J. Maessen, and J.J.M. DeGoeij

(1981) Loss of silver, arsenic, cadmium, selenium

and zinc traces from distilled water and artificial

sea-water by sorption on various container surfaces. Analytica Chimica Acta, 127: 181–193.

Nielsen, D.M. and R. Schalla (1991) Design and

installation of ground-water monitoring wells. In

Practical Handbook of Ground-Water Monitoring

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concentration on sorption of dissolved organics

by PVC, PTFE, and stainless steel well casings.

Ground Water Monitoring and Remediation, 14(3):

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of rigid PVC by aqueous solutions of organic solvents. USA Cold Regions Research and Engineering Laboratory, Special Report 94-27.

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studies on the softening of rigid PVC by aqueous

solutions of organic solvents. USA Cold Regions

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Influence of casing materials on trace-level chemicals in well water. Ground Water Monitoring Review, 10(2): 146–156.

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densed Chemical Dictionary, Eleventh Edition. New

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Sax, N.I. and R.J. Lewis, Sr. (1987) Hawley’s Con13
Table A1. Concentration (μg/L) of arsenic sorbed by

well casings.

Contact time, hours

Treatment 1 8 24 72

CONTROL 48.7 50.0 48.5 49.9

CONTROL 51.1 50.4 50.6 49.4

CONTROL 49.6 48.5 51.2 49.6

 

X 49.8a,b 49.6a 50.1a 49.6a

% RSD 2.47 2.01 2.81 0.46

PVC 50.4 48.8 51.5 49.6

PVC 50.1 49.9 50.1 50.3

PVC 51.3 51.4 49.8 49.3

 

X 50.6b 50.0a 50.5a 49.7a

%RSD 1.28 2.56 1.76 1.05

PTFE 49.4 50.2 49.7 49.3

PTFE 49.6 49.7 50.1 48.7

PTFE 49.1 50.0 50.6 49.3

 

X 49.4a,b 50.0a 50.1a 49.1a

%RSD 0.45 0.58 0.90 0.71

FEP 49.1 49.2 50.8 49.9

FEP 49.6 50.0 52.3 49.5

FEP 49.7 49.6 48.9 49.4

 

X 49.5a,b 50.0a 50.7a 49.6a

% RSD 0.65 0.75 3.40 0.54

FRE 49.3 49.1 50.2 49.4

FRE 49.1 48.7 50.4 47.9

FRE 49.1 49.0 48.1 49.3

 

X 49.2a 48.9a 49.5a 48.9a

% RSD 0.22 0.43 2.60 1.72

FRP 51.7 48.4 49.5 49.5

FRP 49.8 49.9 50.4 50.7

FRP 50.0 50.5 50.7 48.6

 

X 50.5b 49.6a 50.2a 49.6a

% RSD 2.08 2.18 1.22 2.18

Values with the same letter for the same time were not significantly different.

Table A2. Concentration (μg/L) of chromium sorbed

by well casings.

Contact time, hours

Treatment 1 8 24 72

CONTROL 48.8 49.5 50.4 49.4

CONTROL 50.0 49.3 49.4 50.3

CONTROL 49.7 49.8 49.3 49.4

 

X 49.5a 49.5a,b 49.7a,b 49.7a

% RSD 1.29 0.59 1.17 1.09

PVC 49.7 49.4 49.9 49.6

PVC 50.1 50.0 49.5 48.9

PVC 49.8 50.2 49.3 49.1

 

X 49.9a 49.9a,b 49.5a,b 49.2a,b

% RSD 0.44 0.84 0.65 0.75

PTFE 49.7 49.1 49.5 49.4

PTFE 49.9 50.0 49.3 49.5

PTFE 49.1 49.6 50.1 49.5

 

X 49.5a 49.6a,b 49.6a,b 49.5a,b

% RSD 0.79 0.99 0.85 0.16

FEP 49.5 48.6 50.9 50.0

FEP 49.2 49.6 50.2 49.5

FEP 50.1 50.4 49.3 50.1

 

X 49.6a 49.6a,b 50.1b 49.9a

% RSD 0.99 1.84 1.60 0.68

FRE 47.9 48.4 49.2 49.1

FRE 46.3 48.2 49.1 48.4

FRE 47.3 49.0 48.6 49.3

 

X 47.2b 48.6a 49.0a 48.9b

% RSD 1.63 0.87 0.63 0.98

FRP 51.0 50.6 50.2 49.3

FRP 49.3 53.1 48.8 50.1

FRP 49.8 49.4 50.3 49.2

 

X 50.1a 51.0b 49.7a,b 49.5a,b

% RSD 1.72 3.70 1.73 0.99

Values with the same letter for the same time were not significantly different.

APPENDIX A: CONCENTRATIONS OF ANIONS AND CATIONS SORBED BY WELL CASINGS

14
Table A3. Concentration (μg/L) of cadmium sorbed

by well casings.

Contact time, hours

Treatment 1 8 24 72

CONTROL 20.4 20.0 20.3 20.4

CONTROL 20.0 19.8 19.7 20.1

CONTROL 20.0 20.1 20.1 20.2

 

X 20.1a 20.0a 20.1a 20.2a

% RSD 0.94 0.85 1.45 0.74

PVC 18.6 17.2 16.3 15.3

PVC 19.5 18.0 17.0 16.5

PVC 18.2 16.8 16.6 15.9

 

X 18.8b 17.3d 16.6c 15.9c

% RSD 3.46 3.29 2.22 3.65

PTFE 20.5 19.1 19.8 20.1

PTFE 19.4 19.6 17.5 19.7

PTFE 18.7 18.3 18.4 20.4

 

X 19.6a,b 19.0b,c 18.6b 20.0a

% RSD 4.60 3.37 6.14 1.90

FEP 20.2 18.8 19.1 20.1

FEP 18.7 19.6 18.0 19.6

FEP 20.5 18.9 20.1 19.7

 

X 19.8a,b 19.1a,b 19.1a,b 19.8a,b

% RSD 4.85 2.15 5.61 1.31

FRE 19.5 18.1 17.0 18.6

FRE 19.2 18.9 17.6 18.8

FRE 18.9 17.5 19.0 19.7

 

X 19.2a,b 18.2a,b 17.9b,c 19.1b

% RSD 1.67 3.91 5.77 2.83

FRP 19.2 18.8 18.1 19.1

FRP 18.3 19.8 18.0 18.2

FRP 20.2 19.2 18.1 19.7

 

X 19.3a,b 19.3a,b 18.1b 19.0b

% RSD 4.93 2.49 0.44 4.01

Values with the same letter for the same time were not significantly different.

Table A4. Concentration (μg/L) of lead sorbed by

well casings.

Contact time, hours

Treatment 1 8 24 72

CONTROL 50.7 48.9 49.9 50.2

CONTROL 48.4 49.5 51.0 51.3

CONTROL 50.1 51.6 50.1 49.2

 

X 49.7a 50.0a 50.3a 50.2a

% RSD 2.43 2.88 1.15 2.05

PVC 43.4 36.3 30.8 26.2

PVC 45.8 33.4 30.0 28.9

PVC 45.1 35.5 30.9 28.7

 

X 44.8b 35.1b,c 30.6c 27.9c

% RSD 2.72 4.25 1.57 5.37

PTFE 48.2 48.1 45.5 46.6

PTFE 49.0 45.4 48.3 45.8

PTFE 49.0 48.8 48.7 47.2

 

X 48.72a 47.5a 47.5b 46.5b

% RSD 1.01 3.81 3.66 1.59

FEP 49.9 47.7 48.0 46.8

FEP 48.2 47.9 46.9 47.2

FEP 47.2 47.5 45.0 46.2

 

X 48.4a 47.7a 46.6b 46.7b

% RSD 2.87 0.36 3.24 1.03

FRE 44.6 31.6 28.6 22.0

FRE 43.8 33.3 27.7 23.4

FRE 44.2 32.9 27.4 21.9

 

X 44.2b 32.6c 27.9d 22.4d

% RSD 0.95 2.70 2.18 3.71

FRP 45.8 33.4 30.1 23.8

FRP 44.4 37.7 27.2 23.8

FRP 45.0 35.1 31.8 30.2

 

X 45.1b 35.4b 29.7c,d 26.0c

% RSD 1.55 6.16 7.85 14.25

Values with the same letter for the same time were not significantly different.

15
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April 1996

Sorption and Leaching of Trace-Level Metals by Polymeric Well Casings

Thomas A. Ranney and Louise V. Parker

U.S. Army Cold Regions Research and Engineering Laboratory

72 Lyme Road Special Report 96-8

Hanover, New Hampshire 03755-1290

U.S. Army Environmental Center

Aberdeen Proving Ground, Maryland 21010-5401 SFIM-AEC-ET-CR-95085

Approved for public release; distribution is unlimited.

Available from NTIS, Springfield, Virginia 22161

24

UNCLASSIFIED UNCLASSIFIED UNCLASSIFIED UL

The most commonly used well casing materials (polyvinyl chloride [PVC], polytetrafluoroethylene [PTFE] and

stainless steel) cannot be used for all monitoring applications. Therefore, a series of experiments was conducted

to compare three alternative polymeric well casing materials (fluorinated ethylene propylene [FEP], fiberglassreinforced epoxy [FRE] and fiberglass-reinforced plastic [FRP]) with PVC and PTFE. These studies were

conducted to determine the overall suitability of these materials for use in groundwater monitoring wells.

Previous studies compared these materials for sorption of dilute organic solutes, leaching of organic constituents,

and resistance to degradation by chemicals, especially organic solvents. This particular study focuses on sorption

and leaching of metals. This study shows that the fiberglass materials were more apt to leach metal contaminants

than PVC, FEP, and PTFE. Leached concentrations, with one exception (Pb leaching from FRP), were below

maximum allowable limits set by the US EPA for drinking water. With respect to sorption, none of the polymers

sorbed the anions tested, but all of them sorbed the cations tested. FEP and PTFE were much less sorptive than

the other materials. These results and those from our previous studies can be used, along with other considerations, to select a casing material that is best suited for the intended monitoring application and conditions in the

well.

Anions, Cations, FEP, FRE, FRP, Fiberglass-reinforced epoxy, Fiberglass-reinforced plastic, Fluorinated ethylene propylene, Inorganic contaminants,

Inorganic constituents, Leaching, Metals, PTFE, PVC, Polytetrafluoroethylene,

Polyvinyl chloride, Sorption, Well casings