the effect of soils on the permeation of plastic pipes by organic chemicals

8/10/2019 The Effect of Soils on the Permeation of Plastic Pipes by Organic Chemicals

1/8

The Effect of Soils on the Permeation of Plastic Pipes by Organic ChemicalsAuthor(s): Thomas M. Holsen, Jae K. Park, Laurent Bontoux, David Jenkins and Robert E.SelleckSource: Journal (American Water Works Association), Vol. 83, No. 11, Health Effects(NOVEMBER 1991), pp. 85-91Published by: American Water Works AssociationStable URL: http://www.jstor.org/stable/41293557.

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2/8

The Effect of Soils

on the Permeation

of Plastic

Pipes

by Organic

Chemicals

Thomas M.

Holsen,

Jae

K.

Park,

Laurent

Bontoux,

David

Jenkins,

and Robert

E. Selleck

Polybutylene

ipes

0.75 in.)

buried

n both

water-saturatednd unsaturatedoils

contaminated

ith

oluene,

richloroethylene,

,2-dichlorobenzene,

nd

-chlorophenol

were

ermeated

o

detectable

evels

n 1

to 150

days, epending

nthe

rganic

hemical

and ts oncentration.

omparison

f hese esults ith

ipe-bottlexperiments

ontain-

ing

no soil showed hat he oncentration

f

organic

hemical

n

the oil

pore

ontrols

the

rate

f

organic

hemical

ermeation

hrough

uried

lastic ipes.

The

results lso

indicatehat ndertherwisedenticalonditions,lastic ipes uriedna soil ofhigh

organic

arbon ontent ill e

permeated

ore

lowly

han

ipe

uriedn a soil of

ow

organic

arbon

ontent.

ven

o,

soils of

very igh rganic

arbon ontentannot e

relied n

to

protect

lastic

ipe

from

ermeation

y

organic

hemicals.

method

or

predicting

he

quilibrium

oncentrationf

rganic

hemicaln the

oil

pore

wasuseful

in

determining

hether

plasticpipe

buried n

contaminatedoil

is

likely

o be

permeated.

During

he ast

decade,

waternsome

plastic

nd

gasketed iping ystems

as

been

ontaminated

y rganic

hemicals

permeatinghrough

he

pipes.

The rate

and

xtent f

ermeation

s

thought

obe

influenced

y

various oil

constituents,

especially organic

matter,

which can

sorb

organic

hemicals nd reduce heir

soil-pore oncentrations.n thisstudy,

competitive

orption xperiments

f or-

ganic

hemicals

y

oils nd

plastic ipes

were onducted o

nvestigate

heeffect

of oils on

organic

hemical

ermeation

through lasticpipes

and to

develop

method o assess the

potential

f n or-

ganic

hemical ontainedn soil o

per-

meate

plastic ipe.

Compost,

material

with

high rganic

matter

ontent,

as

also used

n

these

xperiments

o deter-

mine

whethert ouldbe

added o

plastic

pipebedding

o

protect

he

pipeby

orb-

ing

organic

hemicals.

Previous

nvestigations

Previousworkhas shownthat oils

sorb

rganic

hemicals,

ecreasing

heir

mobility

nd

activity.1-4

hese studies

have also shown hat he amount f or-

ganic

chemical

hat an be sorbed

by

a

water-saturatedoil can be

predicted

y

using simple

artitioning

odel

with

partition

oefficient,

p)

if

the

organic

carbon ontent f

a

soil,

mass of

soil,

mass of

water,

nd mass

and

type

for-

ganic

chemical re

known. his

simple

model holds

for

hydrophobic

rganic

chemicals f

he

aqueous-phase

quilib-

rium

oncentrations below

10~5

M

or s

NOVEMBER

991

less than alf ts

queous

saturationon-

centration,

hichevers

the

controlling

factor.4 bove these

levels,

the

iso-

therms

sually

ecomeconvexwith

e-

spect

to the

ordinate,

ndicating

n

in-

creased

orption

apacity

t

high rganic

chemical oncentrations.

Kp

anbe calculated

y

multiplying

he

soil organiccarbon-organichemical

partition

oefficient

Koc

by

he

organic

carbon

ontentf he oil

oc)

Hassett t

al3 reduced he

extensive

xperimental

dataofothers o obtain

he

following

e-

lationships

between

Koc

nd

organic

chemical

queous solubility

S,

given

n

milligrams

er

itre)

roctanol

ater

ar-

tition oefficient

Kow):

log

oc

3.950.62

ogS

(1)

log oc0.0880.909og 0 (2)

Hassett t al indicated hat

good ap-

proximation

f

rganic

hemical

orption

by

soils

couldbe made from and

sug-

gested

hat

oc

an be

predicted

rom

q

1

with 95

percent

onfidenceevel hat

the

experimentally

easured

Koc

value

willbe within 0.90

og

units

i.e.,

ess

than ne order f

magnitude)

f he

pre-

dicted

alue.The 95

percent

onfidence

limit or

he

prediction

f

Koc

rom

0

w

s

0.76

og

units.Other imilar

quations

for

redicting

oc

avebeen ummarized

in

reference.

The

organic

matter

ontentf ifferent

soilsvaries reatly: rairie rasslandur-

face soil

contains to 6

percent,

andy

desert oil contains

percent,

nd

peat

soils containmorethan90

percent.6

soil's

organic

arbon ontentan be esti-

TABLE 1

Organic

hemicalssedn

oil-pipe

nteractiontudies

Organic

hemical S

(mg/L

Kow*

Mobility

lass

0-Chlorophenol

28,500

62

Veryigh

Trichloroethylene

1,100

334

Medium

Toluene

515

522 Medium

1,2-Dichlorobenzene

148

2,900

Low

*Octanol-water

artition

oefficients

rom

eference5

f lassifiedn ermsf otentialobilityadaptedromriffinnd oy2)

TABLE 2

Results

f

article-size

nd

rganic

arbon

nalysis

i i

-

Organic

arbon

Classification

y

article-Size

Soil

percent

f

ry eight

Analysis21

CAD

3.9

Clay

oam

RFS

1.6

Clay

oam

CFSL

0.8 Fine

andy

oam

Sand

0.1

Loamy

and

Compost

48

THOMAS

.

HOLSENTAL

85

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3/8

mated

y

multiplying

he

organic

matter

content

y

0.59.7

Recent

work on the fate of

organic

chemical

apors

n

soil has shown hat

water nd

organic

hemicals

ompete

or

sorption

ites nmineralurfaces.

hese

results

greed

with

hose

f

arlier ork-

ers8"12 hofound hat s the

relative u-

miditiesn the soil

pores

ncreased,

he

amount f rganichemical apororbed

decreased. t

elative umidities

reater

than50

percent,

he sotherms ecame

practically

inear

as

they

o in

aqueous

solutions),

ndicating

hat

partitioning

into he oil

organic

matter ecamemore

important

han

dsorption

nto hemin-

eral urfaces. t

bout 0

percent

umid-

ity,

the

amount

of

organic

chemical

sorbed

y

oilswas

found o be

equal

to

the mount orbed nder

aturatedon-

ditions. hese resultsndicate hat

qs

1

and 2

can be used under nsaturateds

well as saturated

onditions

f

the soil-

pore

relative

umidity

s

high,

s is

typi-

cal below hefirst

ew entimetresf he

soilsurface.13'14

Material nd methods

The

organic

hemicals sed inthese

experiments

re listed

n

Table 1. Care

was

taken o ensure

overage

f wide

range

of soil

sorption

haracteristics.

Chemicalswere all

pesticide-grade

nd

wereused as received.

The four

oils electedwereCalifornia

alluvial

eposit

CAD),

Richmond ield

Station

op

soil

(RFS),

Columbiafine

sandy

oam

CFSL),

and

sand.

Compost

was obtained rom heEast

Bay

Munici-

pal Utility

istrict,

akland,

Calif. oil

organic

arbon ontents ndclassifica-

tion yparticle-sizenalysisre hownn

Table 2.

15

The

compost article-size

is-

tribution as not determined

ecause

the wide

range

of

particle

izes

(some

were

up

to2 cm

ong)

ndthe

density

f

the

compost

less

than

water)

made he

sedimentation

echniquenapplicable.

The 1.9-cm-

0.75-in.-)

D

polybutylene

(PB)

pipe

was

bought

rom local

sup-

plier

ndwas used

as received.

Competitiveorptionxperiments

Saturated onditions.

ll

experiments

were onducted t 20-22C. ix 20.3-cm-

(8-in.-) iameter,

5.4-cm-

10-in.-)

ong

polyvinyl

hloride

PVC)

columnswere

fitted ith learPVCcovers tboth nds,

and two

PB

pipes

were

placed through

the column nd

its

covers.The

covers

and

pipes

were ealed n

place

with ili-

cone

caulking.

he ends of the

pipes

were ealed with n aluminum

lug

nd

silicone

caulking.

he aluminum

lug

had

a

sampling ort ontaining

PTFE-

coated

eptum hrough

hich

7.6-cm-

(3-in.-)

ong

hypodermic

eedle ouldbe

introducedo

sample

he

pipe

water.

The columns

were

filled

with

oil

and

saturated

ithwater. he

PB

pipes

were

filled ith istilled ater.

rganic

hem-

86 RESEARCHND ECHNOLOGY

TABLE

3

Quantities

f

materials

dded

o

otating

estolumns

saturatedoil ests

Chemicalolume

SoilMass Water

olume

Soil

ype

Organic

hemical mL

kg

L

CAD

Toluene 3.6

5.3 3.0

RFS Toluene 3.6 5.8 2.9

CFSL Toluene

3.6 5.4

3.2

Sand

Toluene

1.2 7.3

2.7

Sand

lusompost

Toluene 1.2

5.6 0.5 2.9

RFS

1,2-Dichlorobenzene

2.2

4.8 3.3

Sand

1,2-Dichlorobenzene

2.2

6.8 2.8

Sand

lusompost

1,2-Dichlorobenzene

2.2 5.5 0.5 2.8

RFS

Trichloroethylene

5.0 4.9 3.1

Sand

Trichloroethylene

5.0 7.0

2.8

Sand

lus

ompost Trichloroethylene

5.0 5.7 0.6

2.8

RFS

0-Chlorophenol

50 5.2 2.8

Sand

0-Chloro

henol

50 7.1 2.8

Sand

lus

ompost 0-Chlorophenol

50 6.0

0.6 2.5

TABLE 4

Comparisonf redicted

ndmeasurednitial

oil-pore-water

oncentration

in

he aturatedoil olumns

Concentration

From From

From

Measured Isotherm

Eq

1

Eq

2

Organic

hemical Soil

mg/L mg/L mg/L mg/L

Toluene CAD 75

55 74 38

Toluene CFSL 210

210 182 94

Toluene RFS 230 300 197 100

Toluene Sand 135

250 260 140

Toluene

Sand

lusompost

62 50 18 9.4

1,2-Dichlorobenzene

FS 48

50 45 5.6

1,2-Dichlorobenzene

and 90 110 47 11

1,2-Dichlorobenzene

and

lusompost

37 27 35 8.1

Trichloroethylene

RFS 250 650 540 260

Trichloroethylene

Sand 350

850

1,100

750

Trichloroethylene

Sand

lusompost

325 380 200 96

0-Chlorophenol

RFS

11,300 12,000 24,500 7,200

0-Chlorophenol

Sand

22,200 21,500 28,500 9,100

0-Chlorohenol Sandlusompost 9,600 8,300 9,040 2,700

300

Toluene

-

3.5

L

dded

n

ay

A-A

CAD

ore

ater

_

0.5

L

oluenedded

RFS

ore

ater

250

I

CFSL

ore

ater

W 0.5mLoluenedded

c

o

O

c

50-

A

A

A

Temperature

0 C

H

-

1

i

'

1

i

i

1

i

i

i

0 10 20 30 40 50

60 70

Day

f

xperiment

Figure

. Concentrations

f oluene

n

oil

pore

water

n

hree olumns

uring

aturated

competitive

orptionxperiments

JOURNAL

WWA



4/8

250

Toluene

A A

CAD

ore

ater

T

RFS

ore

ater

^

200

CFSL

ore

ater

f

"

O

100

Temperature

0 C

0

I

*

i

*

1

*

i

*

'

*1

*

1

0 10 20 30 40 50 60 70

Day

f

xperiment

Figure

.

Concentrationsf oluene

nPB

pipe

water

nthree olumns

uring

at-

urated

ompetitive

orption

xperiments

200

0.5

mL

oluenedded

Toluene

175 w X 1 2mLolueneddedn ay"

_

^

and

ore

ater

7Y

J

T

0.5mLoluenedded

A-

A

and

ompost

ore

ater

150

/' / I X

and

ipe

ater

/ '

/

1

y

/

A-

A

and

ompostipe

ater

25

JOT

Temperature

0 C

o Dm

|

Dq

Din

- f-

|

a-,

1

0 10 20 30 40 50 60 70

Day

f

xperiment

Figure

. Concentrationsf oluene

n

pore

water nd

PB

pipe

water

n

a

sand

and and

plus ompost

olumn

uring

aturated

ompetitiveorptionxperiments

3001

Toluene

O O

CAD

ore

ater

^

~

A A

CFSL

ore

ater

E

50

RFS

ore

ater

"

A___.

2.

00

0-93

C

1/

0.98

o II

150

I

Temperature

0 C

0

I

I100"

1

0'50

1

so-

P

^

o-

Decimalsndicatenitialelativeoncentration

0-cjM==

1

1

,rT

-

1

1

1

1

1

1

1

0

10

20 30

40 50

Day

f

xperiment

Figure

.

Comparison

f oncentrationsf oluene

n

the

PB

pipe

water f

CAD,

RFS,

nd

CFSL

unsaturatedsoil olumns

I

NOVEMBER991

icalswere

njected

nto

he aturatedoil

to

start

he

experiments

Table 3)

The

columnswere rotated

ontinuously

nd

organic

chemical

concentrationwas

monitored

n

the oil

pore

water ndthe

pipe

water.

Unsaturatedonditions.oil

was

placed

into 15-L

glass

bottles,

nd waterwas

added to

bring

hewater ontent f

he

soil to approximately0 percent well

above hewater ontentf he oils

quil-

ibratedwith relative

umidity

98

per-

cent.15he

organic

hemicalwas

added,

the

tops

of the bottles ealed with

PTFE-coated

rubber

topper,

nd the

bottle otated n a

roller able

or

8

h

to

equilibrate

he oil nd he

rganic

hem-

ical

vapor.

The

soil was thenremoved rom he

glass

bottles nd

packed

ntoPVC col-

umns

through

hich wo

1.9-cm

0.75-

in.)

PB

pipes

had been

placed.

The

amount f

organic

hemical orbedon

the oil

was determinedtthe tart f he

experiments

yplacing

oil

amples

nto

centrifugeubes and extractinghem

with5 mL of

a mixture f 50

percent

reagent-grade

exane nd 50

percent

e-

agent-grade

cetone. The vials

were

mixed

yrotating

hem or minimumf

4 h

and thenwere

centrifuged.

he

or-

ganic

chemical

mixture as then ana-

lyzed y gas

chromatograph

GC).

At the end of the

experiment,

he

amount f

organic

hemical n thesoil

was

again

determined

sing

he

proce-

dure

ust

described.

The

experiments

were

onductedt 20

2C.

Organic

hemical

nalysis. GC,*

a

sample

concentrator

quipped

with n

autosampler

purge

nd

trap),f

nd

a

headspacegas analyzerwereusedfor

all

required

nalyses.

Liquid samples

were

analyzed

y

di-

rect

njection

hen heir oncentrations

were

greater

than

approximately

.5

mg/L,

epending

n the

organic

hemi-

cal involved.

amples

were

ntroduced

into

2-m-long,

-mm-ID

acked

glass

column.

Liquid amples

with

concen-

tration f less than

approximately

.5

mg/L

were

analyzed sing

the

sample

concentratorn

conjunction

ith he

GC.

Operation

nd calibrationf he

sample

concentratorollowed S

Environmental

Protection

gency

methods 01 or

602,

depending

n

the

organic

hemical.16,17

Vapor sampleswereanalyzedusing

the

headspace

analyzer

n

conjunction

with heGC. The entire

ystem

as

cali-

brated

y analyzing

he

headspace

gas

abovewater

ontaining

known

oncen-

trationf

rganic

hemical.

The

concentrationf

rganic

hemical

insoil

pores

was

determined

yplacing

saturatedoil

samples

nto -mL

eactor

*Model

880,ewlett-Packard,

vondale,

a.

fModel

460,

.I.

orp.,ollege

tation,

exas

JModel9395A,ewlett-Packard,vondale,

a.

80/120arbopack

/3%

P-1000,

upelco

nc.,

Bellafonte,

a.

THOMAS

.HOLSENETAL7



5/8

TABLE 5

Comparison

f

redicted

ndmeasurednitialelativeoncentrations

inunsaturated-soil-column

xperiments

mg

orbed

per

,000

From

From From

Organic

hemical Soil

g

soil

Measured

sotherm

q

1

Eq

2

Toluene CAD

3,040

0.50 0.5 0.82 0.42

Toluene CFSL

3,560

0.93

1.0 1.0 1.0

Toluene RFS 4,000 0.98 1.0 1.0 1.0

Toluene Sand

950 0.92 1.0 1.0 1.0

Toluene

Sand

lus

ompost

2,400

0.70

0.7 0.63 0.32

Trichloroethylene

FS

1,000

0.68

0.64 0.51 0.24

Trichloroethylene

and

725 0.83

0.78 1.0 1.0

Trichloroethylene

and

lusompost

1,400

0.81 0.85 0.23 0.11

0-Chlorophenol

RFS

7,300

0.50

0.58 1.0 0.32

o-Chlorophenol

Sand

3,160

0.93 1.0

1.0 1.0

o-Chlorophenol

Sand

lusompost

5,100

0.44 0.53 0.26 0.1

300

|

^

-

Toluene

f

250-

O-OSand

jj

A A

and

lusompost

|

O^o

.92

g.200

/a. /

c

/

0)

/

g

150

/

" I 0.70*5 / Temperature0 C5

100-

/

/

50-

/

A

/

Decimalsndicatenitialelativeoncentration

A|A

*i

1

1

1

1

1

1

1

1

1

1

1

0 10

20

30 40

50 60

Day

f

xperiment

Figure

.

Comparison

f oluene oncentrations

nPB

pipe

water

rom sand nd

sand

plus ompost

nsaturated-soil

olumn

vessels

sealed withPTFE-coated

epta

and screw

aps

and then

entrifuged

t

5,000

rpm

for 0

min.The

supernatant

was then

nalyzed

n he amemanners

thepipe- ater amples.

Results

Competitiveorption

f

organic

hemi-

cals

by

soils and

plastic

pipes.

Results

from

duplicate

xperiment

nwhich wo

identicalcolumnswere contaminated

with

oluene

howed hat

oil-pore

olu-

ene concentrations

ere imilar

hrough-

out the

45-day xperiment.

ipe-water

toluene oncentrations

n both olumns

and n two

pipes

containednthe same

columnwere lmost dentical.hese re-

sults ndicate hat he

experiments

re

reproducible

nd that he toluene on-

centrations

were uniform

hroughout

each column.

PB

pipes

[1.9-cm

0.75-in.)]

were ex-

posed

to toluene

n

separate

olumns

containing

AD,

RFS,

and CFSL soils.

Soils were added to the

columns,

nd

after aturation ith

water,

.6

mL

tolu-

ene was added. On

days

8

and

19,

ddi-

tional oluene

0.5mL)

wasadded o ach

column o maintain

he

soil-pore-water

toluene oncentration

Figure

1).

With

the amemass

f

oluene

n

ach

olumn,

the

oil-pore-water

oluene oncentration

was lowestin the CAD soil

column,

which

had

the

highest rganic

arbon

88

RESEARCHND ECHNOLOGY

content

3.9

percent),

nd

highest

nthe

CFSL soil

column,

hich ad the owest

organic

arbon ontent

0.8

percent).

Figure

shows hat he

oil-pore-water

toluene oncentrationad a marked f-

fect nthe

oluene

reakthrough

nto he

pipe

water.

n

the

CFSL

soil,

which ad

the

highest

oncentrationftoluene

n

the

soil-pore

water,

breakthrough

c-

curred

fter

pproximately

4

days;

n

theRFS

soil,

which

ad

an ntermediate

concentration

f oluene

n the

oil-pore

water,

reakthrough

ccurred fter

p-

proximately

6

days;

n

the

CAD

soil,

whichhad the

owest oncentration

f

toluene

n

the

soil-pore

water,

break-

through

idnot ccur ntil

fter 0

days.

A

similar

xperiment

as carried

ut

with 1.9-cm

0.75-in.)

B

pipe

nwater-

saturated and

(a

popular ipe-bedding

material) nd water-saturatedand to

which

approximately

0

percent by

weight ompost

had

been added.

The

goal

of his

xperiment

as to

determine

whether

ompost

ould

be added to

in-

crease

the amount

f

organic

hemical

sorbed,

herebyffording

ome

degree

of

protection gainst

permeation.

ni-

tially,

.2

mL

oluene

was

added;

n

addi-

tional

aliquot

of 0.5

mL

toluene

was

addedon

days

, 8,

and19.

In the column

ontaining

and

only,

the

concentration

ftoluene

n the soil-

pore

water as

nitially

uch

igher

han

that n the column

ontaining

and and

compostFigure

)

This

llowed much

faster oluene

breakthrough

about

25

versus

0

days).

The

greater

oluene

p-

take

s

a result f

pipepermeation

n

he

sand column aused a

more

rapid

de-

crease

n

he oluene

oncentration

n

he

soil-pore

ater n this olumn

ollowing

thefinal

ddition

f oluene

n

day

19.

Experimentssimilar to those de-

scribed

were

arried

ut

using

olumns

containing

.9-cm

0.75-in)

B

pipes

nd

RFS

soil,

CFSL

soil, and,

nd mixture

of sand and

compost

nd the

organic

chemicals

1,2-dichlorobenzene,

richlo-

roethylene,

nd 0-chloro

henol.

Results

were imilar

o those

eported

the on-

centrationf

organic

hemicals

n

the

soil-pore

aterdecreasedwith ncreas-

ing rganic

arbon ontentn he oil nd

apparent

reakthrough

imes ncreased.

The

predicted

nitial oncentration

f

organic

hemicals

n

the

oil-pore

ater

for ach soil

was

compared

ith heex-

perimentally

easured alue

using

he

experimentallyeterminedartitiono-

efficients15etween

he oil ndwater

or

a

particular

rganic

hemical

ndvalues

predicted

rom

olubility

Eq

1)

and

K0w

(Eq

2),

the nitial oil

mass,

the

nitial

water

mass,

nd

the nitial mount

for-

ganic

hemical

njected

y

massbalance.

As shown n Table

4,

measured

on-

centrationsf

trichloroethylene

n

the

soil-pore

water were lower

than

pre-

dicted

rom he sotherms

or ll

soils,

particularly

and and

RFS

soil,

probably

as a result f he

rapid ptake

f richlo-

roethylene

y

the

PB

pipes

the

values

determined

xperimentally

ere ob-

tained ne

day

fter

rganic

hemical d-

dition)Even o, heresafairgreement

between

redicted

nd

measured nitial

concentrations

f

toluene, ,2-dichloro-

benzene,

nd

0-chlorophenol

n

the

oil-

pore

water. Differences etween

pre-

dicted and

experimental

alues were

probably

lso because

of differences

n

soil

preparation

etween

he sotherm

studies

and the

column

xperiments.

Soils used

in

the

sotherms ere care-

fully

ieved

o removemost f he

roots,

debris,

nd

pebbles,

whereas

the soil

used

n

he

olumn

xperiments

as

only

roughly

leaned

of

larger

rocks and

clumps

f oots.

Predictions

singEqs

1

and

2 are in

fairlyood greementithmeasuredal-

ues

except

when and

nd

compost

ere

involved.his

discrepancy

s not

urpris-

ing

because

the

predictive

quations

were

developed

or

oil,

not

ompost.

n

general,

redictions

rom

olubilityEq

1)

appear

o be better

han hose from

ifow

Eq

2)

however,

oth

quations ive

good

first

stimates

f the

equilibrium

concentrations

n the

oil-pore

ater.

Unsaturated

ompetitive

orption

xperi-

ments. n unsaturated-soil-column

x-

periment

as conducted

o determine

whether

uniform

istribution

f

rganic

JOURNAL

WWA



6/8

chemical

n the

oilwas

being

chieved.

Concentrations

f

toluene

n

the

pipe

water ere

monitored

n

wo

ipes laced

in

RFS

soil.The toluene

oncentration

n

water

in

the

two

pipes

was

similar

throughout

he

xperiment.

Unsaturated

oil-column

xperimental

results

on

CAD, RFS,

and

CFSL soils

(Figure

)

show hat

or ll

of hese oils

(which orbed pproximatelyhe same

amountof

toluene,

Table

5)

toluene

breakthrough

as much

faster

n the

RFS and

CFSL

soils han

n heCAD

soil.

These differences

n

breakthrough

ime

were a

result f

the different

oil-pore-

vapor

oluene

oncentrations.

he

rela-

tive

oncentrationf

toluene

n

the soil

pore

in

equilibrium

ith

he soil

was

found o

be 0.53

for he

CAD

soil,

.98for

the

RFS

soil,

nd 0.93

for he

CFSL soil

(Table5)

These results

re reflected

n

Figure

4,

which hows

that

he fastest

breakthrough

nd

highest

oncentration

of oluene

n

the

pipe

water re

foundn

the

oilwith

he

highest

ore-vapor

on-

centration.hese results re consistent

with he act

hat heCAD soilhas

a much

higher

rganic

arbon ontent han

i-

ther

he

RFS or CFSLsoils.

The results

f nsaturated-soil-column

experiments

n toluene

nd sand

and

sand

plus

ompost

ndicated

hat oluene

breakthrough

as

much faster

n the

sand han

n

the and

plus

ompost

ven

though

he

and

plus

ompost

ontained

approximately

.5 times more toluene

than he

sand

Figure

).

Again,

his e-

sult an

be

explained y

comparing

he

relative oluene

oncentration

n

the

oil

pores

measured

y

headspace nalysis.

For he

and

plus ompost,

his alue

was

0.7;for he and lone, twas 0.92.

The results

f nsaturated-soil-column

experiments

n

trichloroethylene

nd

o-

chlorophenol

nd RFS

soil, sand,

and

sand

plus

compost

were

very

imilar

o

those

escribed arlier.

he soil

with he

highestpore-gas

oncentration

sand)

permeated

he

PB

pipes

most

rapidly,

and he oil

with he owest

ore-gas

on-

centration

RFS)

yielded

he owest

er-

meation ate

rrespective

f the actual

mass of

organic

hemical

resent

n the

column.

Unsaturated-soil-column

xperiments

were unsuccessful

with

1,2-dichloro-

benzene because

(1)

the

1,2-dichloro-

benzene reakthroughimewasgreater

than 0

days

trelative

oncentration

.8,

(2)

the mass of

1,2-dichlorobenzene

sorbed

by

soils was

only pproximately

1,250

mg/l,000g

or

FS

oil,

nd

3)

the

1,2-dichlorobenzene

artition

oefficient

with

PB was

very

high approximately

25,000

t

activity

.70).

8

For these

rea-

sons,

the concentrationf

1,2-dichloro-

benzene

n

the

soil-pore as

in the col-

umns

dropped

rapidly

during

the

experiment,

nd

the

PB

pipes

werenot

permeated

o a detectable

egree

even

after 0

days.

NOVEMBER991

S

100

|

Toluene

>

"

O

Bottle

xperiments

8.

A

aturated-soil-column

xperiments

2

75


xperiments

2

c

-

cJ

A

1

f

50-

AO

o

*-

&o

m

g

u

Temperature

0 C

o

=

5

A

A

I o

0-|

i

1

1

1

1

1

1

1

1

1

0.0

0.2

0.4 0.6

0.8

1.0

Relativeoncentration

Figure

.

Comparison

f he

ime eeded

o reach

tolueneoncentration

f

1

mg/L

n

the

pipe

water

or he

bottle,

aturated-soil,

ndtheunsaturated-soil

x-

periments

75 1

o

c

0

1

60-

g

Trichloroethylene

g

2

O

Bottle

xperiments

0

A


xperiments

o.

45-

nsaturated-soil-column

xperiments

a

22

2

c

30-

1

E

O

. Temperature0 C15- A

A

o

S

A

H

1

'

1

1

1

1

1

o.o

0.2

0.4

0.6

0.8

1.0

Relative

oncentration

Figure

.

Comparison

f

he ime

eeded

o

reach

trichloroethylene

oncentra-

tion

f

1

mg/L

n the

pipe

water

or he

bottle,

aturated-soil,

nd

the

unsatu-

rated-soil

xperiments

00-

1,2-Dichlorobenzene

a

>

^

O

Bottle

xperiments

8.

A


xperiments

8

E

150

a>

cc

o

c

J|100-

A

|i

-

o

iE

Temperature

0 C

5 50- A

Q

C

8

"

O

3

o-|

1

1

1

1

1

1

i

|

i

|

0.0

0.2

0.4

0.6

0.8

1.0

Relative

oncentration

Figure

.

Comparison

f

hetime

needed

oreach

1,2-dichlorobenzene

on-

centration

f 1

mg/L

n the

pipe

water

or

he

bottle

nd

saturated-soil

xperi-

ments

300-1

o-Chlorophenol

2g0

O

Bottle

xperiments

.2 A aturated-soil-column

xperiments

2


xperiments

0 0

g

200

o

o

If

{'" A a O

o

EE

A

O

|l00-

E

8.^

a

-

1

50-

A

Temperature

0 C

o-|

.

1

i

1

1

1

1

1

.

1

0.0

0.2 0.4

0.6 0.8

1.0

Relativeoncentration

Figure

.

Comparison

f he ime

eeded o reach

n

0-chlorophenol

oncentra-

tion f 10

mg/L

n the

pipe

water or

he

bottle,

aturated-soil,

nd the

unsatu-

rated-soil

xperiments

THOMAS

.HOLSENETAL9



7/8

Measured nd

predicted

elative on-

centrationsortheentire

ange

of or-

ganic

hemicals

nd oils

Table5)

show

excellent

greement

xcept

for

xperi-

ments

n

which

ompost

was

used. The

predicted

oncentrationf

rganic

hem-

ical nthe

vaporphase

was obtained

y

dividing

he

mount f

organic

hemical

sorbed

mg/

,000

g

soil)

by

ts

experi-

mentallyeterminedartitionoefficient

or

partition

oefficients

btained rom

Eqs

1

and 2.

These resultsmust hen e

divided

y

the

aqueous

solubility

f he

organic

hemical

in

milligrams

er

itre)

to

obtain relative

oncentration.

The times

equired

oreach

oncentra-

tions f

1

mg/L,

mg/L, mg/L,

nd

10

mg/L,

espectively,

or

oluene,

richlo-

roethylene,,2-dichlorobenzene,

nd o-

chlorophenol

n

the

pipe

water

or nsat-

urated oils re

compared

ith he

imes

required

or

aturated

oil and

pipe-bot-

tle

experiments18

n

Figures

-9.

The

graphs

re

plotted

nterms

f he

day

f he

xperiment

oreach

pipe-wa-

ter oncentrationf1or 10mg/L ersus

external

ater r

soil-pore

ater

elative

concentration

o that

he

experimental

results an

be

compared

ven

though

they

were not

run t

exactly

he

same

externalelative

oncentrations.

he re-

sults of thetwo

types

of

experiments

agree

very

well

ven

though

he

experi-

ments

differeds

follows:

1)

organic

chemicals

were dded

to the

pipe-bottle

experiments

everal imes

ach week

o

keep

the external

oncentration

airly

constant,

o the

xternal

rganic

hemi-

cal

concentrationn

the

pipe-bottle

x-

periments

luctuated

great

dealmore

than n

he

oil-column

xperiments,

nd

(2) the emperaturef hepipe-bottlex-

periments

as

more

closely

ontrolled

than

n

the oil-column

xperiments.

For

1,2-dichlorobenzene,

oluene,

nd

trichloroethylene,

hetime hatwas

re-

quired

o

reach

1

mg/L

n

he

pipe

water,

at

the same

external

elative

oncentra-

tion,

was the ame

regardless

f

heex-

ternal

hase.

A

comparison

f the

time thatwas

needed in

order o reach a

pipe-water

concentrationf

0

mg/L

-chloro

henol

for

he

pipe-bottle

xperiments

nd soil-

column

experiments

onducted with

0.75-in.

B

pipe Figure

)

shows

hat he

saturated oilresults o

not

gree

with

theunsaturatedoilresults r thepipe-

bottle

esults,

articularly

trelativeon-

centrations

bove0.2.

This ackof

gree-

ment

may

have been

caused

by poor

mixing

nthe

saturated-soil-columnx-

periments.

en times

s much

organic

chemicalwas

addedto the

0-chlorophe-

nol

olumns

50

mL)

s to

ny

f he

ther

soil

columns.This

may

have

allowed

small

pockets

f

ssentially ure

0-chlo-

rophenol

o be in

contact ith he

pipes

during

he

nitial

tages

of the

experi-

ment,

esulting

n

much aster

-chloro-

phenol

reakthrough.

90

RESEARCHND

ECHNOLOGY

The

results f

hese

xperiments

ndi-

cate that

he

concentrationf

organic

chemical

n

the

soil

pore

controls

he

permeation

ate and

that he

soil-pore

concentrationan

be

predicted

rom x-

perimentally

eterminedr

empirically

predicted artition

oefficients

etween

the

oil ndwater

or

particular

rganic

chemical

f

he

nitialoil

mass,

he

nitial

watermass, ndtheamount forganic

chemical

re

known. he

experimental

results lso

ndicate hat

ipes

buried n

soils

high

n

organic

arbon

ontent r

that heuse of

ompost

o

ncrease soil

organic

carbon

content

ncreased he

time

equired

o

organic

hemical reak-

throughompared

with

ipes

buried

n

soils ow n

organic

arbon

ontent;

ow-

ever,

n

none f

he

xperiments

as

per-

meation

liminated.

Mass transfer

imitations

The

possibility

f

mass

ransfer

imita-

tions

etween he

phase

external o the

pipe

nd the

plastic

ipe

wall

tselfmust

be considered efore aturated-soil-col-

umn esults re

applied

o

actual

erme-

ation vents

ecause

hese

olumns

ere

mixed.

Mass

transfer

imitations an

occur

when

rganic

hemical

bsorption

by

the

pipe

wall s

fast

nough

o

de-

crease

the

externaloncentrationf

or-

ganic

chemical

mmediately

djacent

o

the

pipe

wall. his

decrease

n

oncentra-

tionwould

ccur

f

he

organic

hemical

flux

ntothe

pipe

wall s similar

o or

larger

than the

movement f

organic

chemical

p

to the

pipe

wall.The bound-

ary ayer

reated

y

his

decrease n

ex-

ternal

organic

hemical

oncentration

would

ncrease

he amount f

time

re-

quired or norganichemical operme-

ate a

plastic

ipe

because he

pipe

would

be

exposed

o a

concentrationess than

that

een

n

the

bulk

xternal

hase.

The

flux f n

organic

hemicals char-

acterized

y

multiplying

ts

diffusiono-

efficient

y

ts

concentration

radient

n

the media of nterest.

ecause

plastic

pipes

re buried n

soil

n

which he oil

pores

re

filled

with itherwater

r

air,

diffusion

oefficientsf

organic

hemi-

cals

through

oth

aturatednd

unsatu-

rated oilsmust e

considered.oils

gen-

erally

decrease air or

water

diffusion

coefficients

y

one

ortwo

rders f

mag-

nitude,

primarily

ecause of

the de-

creasedarea available ordiffusionnd

the

tortuous

ath

that the

chemicals

must follow.

Diffusion

coefficients

throughtagnant

ater

re on the

order

of 10"

cm2/s,

nd diffusion

oefficients

through

tagnant

ir are

on theorder f

10"1

m2/s.

Thus,

for

aturated

oils,

diffusion

oefficientsill e on the

rder

of 10"6

m2/s

nd for nsaturated

oils,

on

theorder f10"2

m2/s.

iffusiono-

efficients

hrough

B

andPE

pipe

re on

theorder

f10"

cm2/s.18

The diffusion

oefficients

hrough

oil

are several

orders f

magnitudearger

than

the

diffusion

oefficients

hrough

the

plastic

ipe

wall;

however,

ecause

the

concentration

radient

n

the

plastic

may

be

several orders of

magnitude

greater

han n the

soil,18

here s

the

possibility

f

xternal-phase

ass trans-

fer

imitations,

articularly

n

saturated

soil.

However,

oil-pore

ater nd soil-

pore

gases

are

constantlymoving

e-

cause ofpressure radientsndgravity,

whichwill

hinder

he

development

f

boundaryayer.

Analysis

f

potential

ermeation

vents

These

experimental

esults

can be

used

to

develop

method o

assess the

potential

f

soil o

nfluencehe

perme-

ation f

plastic

ipes

by organic

hemi-

cals. t has

been shown

hat he

relative

organic

hemical

oncentrationn

the

soil

pores

controls he rate

of

permea-

tion.

herefore,

he oilmust e

analyzed

in

uch

way

hat he elative

oncentra-

tion

f

rganic

hemicaln

the oil

pores

can be

predicted.

Inorder o ccomplishhis,wo hings

must

e

known: he mount f

hemical

sorbed n the

oil andthe oil's

organic

carbon

ontent. he

amount f

organic

chemical orbed n

the oil

an bedeter-

mined either

by

purge-and-trap

ech-

niques

n

which

known

mount f oil

is

placed

n

glassvessel,

nd he

orbed

organic

hemicals

stripped

rom

he oil

with n

inert

as

and

ntroduced

nto

GC for

quantification.

lternatively,

known

mount f soil

can be

extracted

with

known

mount f

uitable

olvent

(e.g.,

1:1 hexane:

cetone),

he

mixture

centrifuged,

nd the

supernatant

na-

lyzed

hromatographically.

Theorganicarbon ontentf he oils

can be

determined

sing

the

modified

Mebius

procedure.20

nce

the

organic

carbonontentf he

oil nd

he

mount

of

rganic

hemical

orbed

y

he oil s

known,

he

Koc

or ach

chemical an be

calculated rom

q

1

or

2

or

he

quations

in

reference.

The

partition

oefficientetween

he

organic

hemical nd the

soil,

Kp,

can

then e calculated

y

multiplying

oc

y

oc.

The concentration

f the

organic

chemical

n

the

pore pace

Cp)

can then

be

predicted

y dividing

he amount f

organic

chemical sorbed on

the soil

(mg/1,000

soil)

by

Kp.

The

organic

chemical ore pacerelativeoncentra-

tion

an then

e determined

ydividing

Cp

by

he

organic

hemical

queous

sol-

ubility

n

milligrams

er

itre.

For

example,

onsider soil

with n

organic

arbon ontent

f

2

percent

nd

a

sorbedtoluene

oncentrationf 863

mg/1,000

soil.

Because

Koc

or

oluene

is 186

determined

ith

q

1)

Kp

s 186

x

0.02

3.7,

nd

Cp

s

863/3.7

232

mg/L.

The relative

oncentrationftoluenen

the oil

pores

s

232/515

0.45

515

s the

aqueous

solubility

f

toluene

n milli-

gramsper litre).

f t is

assumed that

JOURNAL

WWA



8/8

relative oncentrationnd

activity

re

equivalent,

his alue anthen e used to

make

predictions

bout he ime eeded

to reach detectableevelsof toluene n

the

pipe

using echniques

escribedn

Park t

al18 r

Figures

-9.

This calculation

ssumes hat he

par-

titionoefficient

p

s inear t ll relative

concentrations,

ut

n

actuality

t

gener-

allyncreases onlinearlyt relativeon-

centrations

0.5. At relative oncentra-

tions

>0.5,

this methodwould tend to

overestimate

he

organic

hemical ela-

tive

oncentration,

aking

t conserva-

tive

pproach.

his

type

f alculations

also

appropriate

or

organic

chemical

mixturest owrelative oncentrations.

Effectsf

backfill

ype

n

permeation

If

properly

esigned,

hebackfill sed

to surround

plastic ipe

can

help

imit

its

susceptibility

o

permeationy

sorb-

ing

contaminants,

hereby ecreasing

their

oncentrations,

nd/or

physically

limiting

ontaminantccess to the

pipe

bycreatingn impermeablearrier. s

shownnthis

work,

oilsof

high rganic

carbon ontentr theaddition f a soil

with

igh rganic

arbon ontento soil

of ow

organic

arbon ontent ould be

used to

significantly

ncrease he time

needed o

permeate pipe

nd

thus

ig-

nificantly

ecrease the final oncentra-

tion f he ontaminant

n

he

pipe

water.

Alternatively,ine-grainedompressible

soils such as

clay

ouldbe used to imit

themovementf contaminantnd

phys-

ically rotect

buried

ipe

from

ermea-

tion.

Unfortunately,laysgenerally

ave

a

very

ow

organic

arbon ontent nd

therefore ow

sorptive apacity.

The

types f and ommonlysed as backfill

material ffordittle

protection

o the

pipe

because

they

ave

very

ow

organic

carbon ontent nd therefore

ery

ow

sorptive apacity

nd

very

highperme-

ability

ecauseof heir

arge article

ize.

For these

reasons,

and shouldnotbe

used as backfill

xcept

where

bsolutely

necessary,

nd,

at a

minimum,

ative

soils shouldbe used in

their

lace

be-

cause

they enerally

ave

higher rganic

carbon contents

nd lower

permeabil-

itiesthan and. t must

be

noted,

how-

ever,

hat he

use of soils with

igh

or-

ganic

carbon content

and/or

low

permeability

annotbe used

to assure

protectionfplastic ipesfrom ermea-

tion

y rganic

hemicals

they

an

only

be

used to decrease he

number f

per-

meationncidents.

Conclusions

The results

eported

erehave hown

that .75-in.

olybutyleneipes

buried

n

both

water-saturatednd

unsaturated

soils contaminated

ith

oluene,

richlo-

roethylene,

,2-dichlorobenzene,

nd o-

chlorophenol

ere

permeated

o detect-

able evels n 1

to 150

days, epending

n

the

organic

hemical nd ts

concentra-

NOVEMBER991

tion. At

equivalent

relative concen-

tration,

he

pipes

were

permeated

he

fastest

y

trichloro

thylene,

ollowed

y

toluene,

,2-dichlorobenzene,

nd0-chlo-

rophenol. omparison

f these soil-col-

umn esults ith

ipe-bottlexperiments

containing

o soil ndicate hat he con-

centrationf

rganic

hemical

n

he oil

pore space

controls oth the rate and

extent forganic hemical ermeation

through

uried

lastic ipes.

The

results

also ndicate hat

nder therwisedenti-

cal

conditions,

lastic ipes

buried

n

oil

of

high organic

arbon ontent

will

be

permeated

more

lowly

han

pipe

bur-

ied in a soil of ow

organic

arbon on-

tent. ven

o,

soils of

very igh rganic

carbon

content

annotbe reliedon to

protect lastic ipe

from

ermeation

y

organic

hemicals.

The

types

of

sand

commonly

sed as backfillmaterial hat

have both

very

ow

organic

arbon on-

tent nd

veryhigh permeability

fford

little

rotectiongainst ipepermeation.

Thus,

and hould ot e used s backfill

for lastic ipes xceptwhere bsolutely

necessary,

nd,

at a

minimum,

ative

soils shouldbe used intheir

lace

be-

cause of heir

igher rganic

arbon on-

tent nd

ower

ermeability.

Acknowledgment

Thisresearchwas funded

y

theCali-

fornia

Department

f HealthServices

andwas conducted

y

he

Department

f

Civil

Engineering

nd

the

Sanitary

nd

EnvironmentalealthResearch abora-

tory, niversity

fCaliforniat

Berkeley.

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THOMAS.HOLSENTAL

91

t

About

Engineering

an

of

State

ment,

60616.

in

Thomas

Technology,

the

assistant

St.,

Illinois

Environmental

A

the

M.

graduate

Chicago,

Holsen

authors:

professor

Institute

Depart-

3200

IL

S.

of

ishomasM. Holsen s

an assistant

rofessor

in theEnvironmental

Engineering

epart-

ment,

llinois nstitute

of

Technology,

200 S.

State

St.,

Chicago,

L

60616. A

graduate

f

the

University

fCalifornia,

erkeley,

ith

BS, MS, and PhD degrees, olsen s a

member

flAWPRC,CS,

nd

AEEP. His

work asbeen

ublished

reviously

ryour-

nal AWWA nd

Journal

WPCF.

Jae

K.

Park s n assistant

rofessor

t the

Univer-

sity

f

Wisconsin

Madison),

415

Johnson

Dr.,

Madison,

WI 3706.Laurent ontoux

is a

researchcientist ith rocter

Gam-

ble,

uropean

echnical

enter,

emselan

100

B-1820

Strombeekbever,

elgium.

David

Jenkins

s a

professor

nd Robert.

Selleck

s

professor

meritusn

the

epart-

ment

f

Civil

Engineering,niversity

f

California,

erkeley,

A 94720.

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the effect of soils on the permeation of plastic pipes by organic chemicals

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