Directory UMM :Data Elmu:jurnal:E:Environmental Management and Health:Vol10.Issue1.1999:

Air flow optimization and surfactant enhancement to
remediate toluene-contaminated saturated soils
using air sparging
Krishna R. Reddy
Department of Civil and Materials Engineering, University of Illinois, Chic ago, USA
Robin Semer
Department of Civil and Materials Engineering, University of Illinois, Chic ago, USA
Jeffrey A. Adams
Department of Civil and Materials Engineering, University of Illinois, Chic ago, USA

Keywords
Airflo w, Expe rime nt, Gro undwate r

Abstract
This pape r pre se nts the re sults o f
labo rato ry e xpe rime nts that
inve stigate the re mo val o f vo latile
o rganic c o mpo unds fro m saturate d so ils thro ugh the use o f air
sparging. Thre e se rie s o f e xpe rime nts we re pe rfo rme d in a c o lumn te st apparatus using two
diffe re nt so ils to re pre se nt ac tual
fie ld c o nditio ns, name ly, a fine

grave l and a me dium to fine
Ottawa sand (bo th o btaine d fro m
so urc e s ne ar Chic ago , Illino is,
USA) c o ntaminate d with to lue ne ,
a majo r c o nstitue nt o f pe tro le um
pro duc ts. The re sults sho we d that
to lue ne was re mo ve d fro m grave l
ve ry e ffic ie ntly using air sparging;
c o mple te re mo val was ac hie ve d
using a varie ty o f air flo w rate s.
Ho we ve r the to lue ne re mo val
rate s in te sts using sand we re
signific antly le ss. Eve n at the
highe st air flo w rate use d during
te sting, c o mple te to lue ne re mo val
to o k e ight time s lo nge r than in
c o mparable te sts using grave l.
With lo w air flo w rate s this was
no t ac hie ve d e ve n afte r 1 7 ho urs
o f te sting. It was furthe r fo und

that the inje c tio n o f fo ams ge ne rate d with surfac tants, SDS and
witc o no l SN7 0 , at lo w air flo w
rate s during the use o f air sparging was fo und to ac c e le rate the
bulk re mo val o f to lue ne in sand,
but the use o f surfac tants did no t
fac ilitate the re mo val o f re sidual
le ve ls o f c o ntaminatio n.

This study was partially
funded by the University of
Illinois at Chicago (UIC). The
authors are thankful to John
Gramsas for fabricating the
column test setup.
Enviro nme ntal Manage me nt
and He alth
1 0 / 1 [ 1999] 5 2 –6 3
© MCB Unive rsity Pre ss
[ ISSN 0956-6163]

[ 52 ]

Introduction
Su bsu r fa ce con ta m in a tion ca u sed by th e
in filtr a tion of h ydr oca r bon s, in clu din g petr oleu m pr odu cts, poses ser iou s envir on m en ta l
pr oblem s. Hydr oca r bon r elea ses often occu r
in itia lly w ith in th e va dose zon e a n d th en
m igr a te dow n w a r d th r ou gh th e soil, even tu a lly r ea ch in g th e w a ter ta ble. Ligh t n on -a qu eou s ph a se liqu id (LNAP L) con stitu en ts of
petr oleu m pr odu cts ten d to floa t on top of th e
w a ter ta ble a n d a s a r esu lt m ay be tr a n spor ted
ver tica lly a n d h or izon ta lly du e to w a ter ta ble
flu ctu a tion s. Su ch flu ctu a tion s m ay be th e
r esu lt of sea son a l va r ia tion s, well pu m pin g, or
gr ou n dw a ter flow con dition s. Th ese LNAP Ls
w ill per sist for deca des w ith in th e su bsu r fa ce
u n less r em edia l a ction is ta ken .
A n u m ber of r em edia l tech n ologies, in clu din g pu m p-a n d-tr ea t, bior em edia tion a n d soil
w a sh in g/ flu sh in g h ave been u sed to tr ea t
con ta m in a ted gr ou n dw a ter. However, in m a n y
ca ses, th ese m eth ods h ave pr oven to be in effective, expen sive, u n r elia ble, a n d often r equ ir e

exten ded tim e per iods for a dequ a te clea n -u p
(Ar dito a n d Billin gs, 1990; Leon a r d a n d
Br ow n , 1992; NRC, 1994; Reddy et al., 1995). Th e
soil va por extr a ction (SVE ) m eth od h a s
pr oven to be a n effective a n d less expen sive
tech n iqu e for th e r em edia tion of vola tile
or ga n ic com pou n ds w ith in th e va dose zon e;
h owever, it ca n n ot be u sed to tr ea t sa tu r a ted
soil zon e con ta m in a tion . Th er efor e, a differ en t
r em edia tion tech n iqu e m u st be u sed for sa tu r a ted soils a n d gr ou n dw a ter.
In -situ a ir spa r gin g is becom in g a n in cr ea sin gly popu la r option w ith in th e USA for th e
r em edia tion of sa tu r a ted soils a n d gr ou n dw a ter con ta m in a ted w ith vola tile or ga n ic
com pou n ds (VOCs). P r eviou s field investiga tion s h ave sh ow n a ir spa r gin g to be a n efficien t a n d effective m eth od wh en a pplied to
su ch con ta m in a n t con dition s (J oh n son et a l.,
1993; Reddy et a l., 1995). Air spa r gin g is m ost
effective wh en a pplied to con ta m in a n ts w ith
Hen r y’s Law con sta n ts gr ea ter th a n 10–5 a tm
m 3/ m ol a n d va por pr essu r es gr ea ter th a n

5m m Hg (Leon a r d a n d Br ow n , 1992). It is a

sim ple m eth od to apply; field im plem en ta tion
is per for m ed u sin g r ea dily ava ila ble equ ipm en t. Sin ce n o specia l equ ipm en t is r equ ir ed,
a ir spa r gin g h a s pr oven to be a cost-effective
r em edia l m eth od. In situ a ir spa r gin g is
per for m ed by in jectin g a ir below th e gr ou n dw a ter con ta m in a tion plu m e, a s sh ow n in
F igu r e 1. Th e in jected a ir th en tr avels tow a r ds
th e gr ou n d su r fa ce, cr ea tin g a ir pa ssa gew ays.
Th e con ta m in a n ts a r e pa r tition ed in to th e
va por ph a se th r ou gh th e a ction of differ en t
m ech a n ism s, in clu din g vola tiliza tion , dissolu tion , a n d desor ption , wh ich r esu lt fr om th e
a ction of th e in jected a ir. Th e con ta m in a n tla den a ir con tin u es to tr avel u pw a r d th r ou gh
th e a ir pa ssa gew ays, even tu a lly en ter in g th e
va dose zon e. Th e va por s a r e th en collected
u sin g a soil va por extr a ction system , a s
sh ow n in F igu r e 1. Addition a lly, th e in jected
a ir in cr ea ses su bsu r fa ce oxygen levels, a idin g
in th e a ction of a er obic biodegr a da tion . A
deta iled r eview of th e m ech a n ics of th e a ir
spa r gin g pr ocess is pr ovided by Reddy et a l.
(1995).

Cu r r en t a ir spa r gin g design m eth ods a r e
h eavily ba sed on em pir ica l appr oa ch es a n d
lim ited field exper ien ce r a th er th a n a r a tion a l
design ba sis beca u se ver y little is u n der stood
r ega r din g th e m a ss tr a n sfer / tr a n spor t/ tr a n sfor m a tion m ech a n ism s th a t occu r du r in g th e
u se of a ir spa r gin g. Addition a lly, little is
k n ow n a bou t th e effects of con tr ol va r ia bles,
in clu din g in jection a ir flow r a te a n d pr essu r e.
To pr ovide a better u n der sta n din g of th ese
m ech a n ism s a n d va r ia bles, a com pr eh en sive
a ir spa r gin g r esea r ch pr ogr a m h a s been
u n der w ay a t th e Un iver sity of Illin ois at
Ch ica go (UIC) sin ce 1993. Th e r esea r ch
in clu des th e per for m a n ce of exten sive on edim en sion a l a n d two-dim en sion a l labor a tor y
exper im en ts. Kn ow ledge ga in ed fr om th e
con tr olled la bor a tor y exper im en ts w ill be
u sed to develop a con ceptu a l m odel of th e a ir
spa r gin g pr ocess a s well a s a com pr eh en sive
m a th em a tica l m odel th at ca n ser ve a s a
pr edictive tool for th e optim a l design of a ir

Krishna R. Reddy, Robin Semer
and Jeffrey A. Adams
Air flo w o ptimizatio n and
surfac tant e nhanc e me nt
to re me diate to lue ne c o ntaminate d saturate d so ils
using air sparging
Enviro nme ntal Manage me nt
and He alth
1 0 / 1 [1 9 9 9 ] 5 2 –6 3

spa r gin g field system s ba sed on site-specific
da ta (Reddy a n d Zh ou , 1996). Addition a lly,
da ta fr om a ir spa r gin g field system s cu r r en tly
in oper a tion w ill be u sed to va lida te a n d
im pr ove th e m odel.
Du r in g th e u se of a ir spa r gin g, con ta m in a tion eith er in con ta ct w ith or in th e vicin ity
of a n a ir pa ssa gew ay is vola tilized a n d
r em oved wh ile con ta m in a tion dista n t fr om
th e pa ssin g a ir m oves tow a r d th e a ir ch a n n els

th r ou gh diffu sion . Diffu sion is often a r a telim itin g pr ocess; r em edia tion of con ta m in a n t
tr a pped in soil por es or in th e in ter stices of
clay occu r s ver y slow ly. Wh ile th e m a jor ity of
th e con ta m in a n t m a ss is r em oved r ela tively
qu ick ly th r ou gh vola tiliza tion , a sym ptotic
levels a r e r ea ch ed wh en r esidu a l con ta m in a n t r em ova l becom es diffu sion -depen den t.
Th e r em ova l of r esidu a l con ta m in a tion often
ta k es sign ifica n tly lon ger th a n th e r em ova l of
th e in itia l bu lk con ta m in a tion . In cr ea sed
dissolu tion of th e r esidu a l or ga n ic com pou n d
wou ld a cceler a te th e r em edia tion pr ocess
con sider a bly by m obilizin g th e con ta m in a n t
a n d a llow in g it to in ter a ct w ith th e flow in g
a ir m or e qu ick ly. Th e u se of su r fa cta n t foa m s
a s a n a ir spa r gin g en h a n cem en t tech n iqu e

m ay sign ifi ca n tly in cr ea se th e m obility of
r esidu a l con ta m in a n ts, a llow in g for m or e
efficien t r em ova l.
Th is pa per pr esen ts th e r esu lts of la bor a tor y

exper im en ts wh ich investiga ted th e effectiven ess of a ir spa r gin g in r em ovin g tolu en e fr om
differ en t types of sa tu r a ted soils. On e-dim en sion a l colu m n exper im en ts wer e con du cted
u sin g two differ en t types of soil, a fin e gr avel
a n d a m ediu m to fin e sa n d, u n der differ en t
in jected a ir flow con dition s. Th e effect of
su r fa cta n t foa m in jection cou pled w ith a ir
spa r gin g on con ta m in a n t r em ova l efficien cy
h a s a lso been eva lu a ted in th is pa per.

Experimental program
M aterials
Two differ en t soil types wer e u sed in th is
r esea r ch : a fin e gr avel, a n d a m ediu m to fin e
Ottaw a sa n d. La bor a tor y tests wer e fi r st
per for m ed on th ese soils to deter m in e th eir
in dex a n d en gin eer in g pr oper ties. Th ese tests
in clu ded gr a in size a n a lysis, specifi c gr avity,
m in im u m a n d m a xim u m den sities, a n d
h ydr a u lic con du ctivity. Th e test r esu lts for

Figure 1
Sc he matic o f In Situ Air Sparging Syste m

[ 53 ]

Krishna R. Reddy, Robin Semer
and Jeffrey A. Adams
Air flo w o ptimizatio n and
surfac tant e nhanc e me nt
to re me diate to lue ne c o ntaminate d saturate d so ils
using air sparging
Enviro nme ntal Manage me nt
and He alth
1 0 / 1 [1 9 9 9 ] 5 2 –6 3

th ese two soils a r e su m m a r ized in Ta ble I.
Th e gr a in size distr ibu tion for th e two soils is
sh ow n in F igu r e 2. Tolu en e, a m a jor
con stitu en t of ga solin e a n d oth er petr oleu m
pr odu cts, w a s selected a s th e r epr esen ta tive

VOC for th is in vestiga tion a n d is r ou tin ely
u sed a s a n in dica tor of or ga n ic con ta m in a tion in gr ou n dw a ter a t field sites. Th e pr oper ties of tolu en e a r e sh ow n in Ta ble II.
Two differ en t su r fa cta n ts wer e u sed to gen er ate foa m s in th is stu dy, sodiu m dodecyl su lfate (SDS) a n d w itcon ol SN70. Ea ch of th ese
Table I
Charac te ristic s o f so ils use d in e xpe rime nts
Property
Unified soil classification,
ASTM D 2487
Effective particle size, D10 ,
ASTM D 422
Coefficient of uniformity,
Cc* , ASTM D 422
Coefficient of curvature,
Cu* , ASTM D 422
Specfic gravity, Gs ASTM D 854
M inimum dry density (g/ cm3 ),
ASTM D 4254
M aximum dry density (g/ cm3 ),
ASTM D 4253
Hydraulic conductivity (cm/ s),
ASTM D 2434

Sand

Gravel

SP

GP

0.18

2.35

2.1

2.0

1.0
2.67

1.1
–

1.56

1.62

1.85

1.90

1.97 x 10 –2

1.60

Note:
* = C =D / D and C =D 2 / (D D )
u
60
10
c
30
10 60

Figure 2
Grain size distributio n o f so ils use d in this study

[ 54 ]

Table II
Physic al and c he mic al parame te rs fo r to lue ne
(Clarke e t al., 1 9 9 3 )
Molec ular Formula
C7 H8
Aromaticity
Yes
M olecular weight
92.13
Color/ form
Colorless liquid
Boiling point, °C
111
M elting point, °C
–95
Density, g/ cm3
0.8661
Aqueous solubility, mg/ L
515
Vapor pressure, mm Hg
40 (at 31.8°C)
Vapor density (air=1)
3.14
Log Kow (Octonol water coefficient)
1.83 – 2.94
Log Koc (Soil/ water distribution
coefficient referenced to soil
organic content)
1.12 – 3.28
KH, Pa·m3 / mol (Henry’s Law Coefficient)
680

su r fa cta n ts is r elatively in expen sive a n d is
com m er cia lly ava ilable. Th ese su r fa cta n ts
wer e selected beca u se th ey possess low su r fa ce
ten sion , low specific gr avity, good deter gen cy
a n d solu bilization , a n d low soil disper sion .
Addition a lly, both su r fa cta n ts a r e biodegr a dable. Th e pr oper ties of th ese su r fa cta n ts a r e
su m m a r ized in Table III. Wh ile SDS is a n ion ic,
w itcon ol SN70 is n on -ion ic; th er efor e, th eir u se
in th e stu dy a llows for th e investigation of th e
su itability of two differ en t gr ou ps of su r fa cta n ts. Cation ic su r fa cta n ts wer e n ot u sed in
th is stu dy beca u se su ch su r fa cta n ts h ave been
sh ow n to r eta r d con ta m in a n t r em ova l (Abdu l,
1990; Cla r ke et al., 1993).

Krishna R. Reddy, Robin Semer
and Jeffrey A. Adams
Air flo w o ptimizatio n and
surfac tant e nhanc e me nt
to re me diate to lue ne c o ntaminate d saturate d so ils
using air sparging
Enviro nme ntal Manage me nt
and He alth
1 0 / 1 [1 9 9 9 ] 5 2 –6 3

Experimental set-up
A on e-dim en sion a l a ir spa r gin g colu m n a ppa r a tu s w a s u tilized du r in g th e in vestiga tion . A
sch em a tic of th e test a ppa r a tu s is sh ow n in
F igu r e 3. Th e plexigla s colu m n , m ea su r in g 93
cm in h eigh t w ith a n in side dia m eter of 8.7
cm , w a s u sed to con ta in th e test soil. Seven
sa m plin g por ts wer e loca ted a t dista n ces of
9cm , 19cm , 29cm , 39cm , 49cm , 45cm , a n d
59cm , r espectively, fr om th e ba se of th e
colu m n . Th ese loca tion s a r e design a ted a s
por ts 1 th r ou gh 7, r espectively. Th e por ts
con sisted of a septa a n d br a ss sleeves h eld in
pla ce w ith Tefl on fi ttin gs. Th e top a n d bottom
of th e colu m n wer e sea led w ith plexigla s
cover s. E a ch cover fea tu r ed a gr oove h oldin g
a r u bber O-r in g in pla ce, pr ovidin g a n a ir tigh t sea l between th e cover a n d th e colu m n .

Table III
Pro pe rtie s o f surfac tants use d
Surfactant
Chemical Name
Ave. molecular weight
Form
Specific gravity
Solubility in water
Vapor pressure (mm Hg at 25°C)
pH of 1 per cent solution
Critical micelle concentration
Biodegradable
Net charge

SDS

Witconol SN70

sodium lauryl sulfate
288
powder
0.40
10 % in water
negligible
8-10
0.231 wt% (2.31 g/ l)
yes
anionic

ethoxylated alc ohol
392
liquid
0.98
moderately at 25°C