United States
Environmental Protection
Agency
Risk Reduction
Engineering Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/SR-93/051 May 1993
«rEPA Project Summary
Onsite Engineering Report for
Solidification/Stabilization
Treatment Testing of
Contaminated Soils
Judy Hessling, Michael L. Smith, Steve Giti-Pour, John Miller, and Jerry Isenburg
The mechanism of lead fixation by
Portland cement, quicklime/fly ash, and
cement kiln dust/fly ash on a Super-
fund soil was evaluated. Elevated lev-
els of lead (-25,800 ppm) at the site
indicated lead was the primary con-
taminant of concern and solidification/
stabilization (SIS) was chosen as the
best demonstrated available technol-
ogy (BOAT) for treating the soil.
The study was performed in two
phases on all samples: analyzing for
toxicity characteristic leaching proce-
dure (TCLP) extractable lead and evalu-
ating the effectiveness of the treatment
technology with various physical and
chemical tests. Each binder was evalu-
ated at three different binder-to-soil (B/
S) ratios. In addition, one aliquot of
soil was pretreated by heating to re-
move organic carbon from the soil and
then treated with portland cement. The
binder-to-soil ratios were determined
by the generalized acid neutralization
capacity (GANG) test, developed at the
U.S. Environmental Protection Agency's
(EPA) Center Hill Facility (CHF), to stan-
dardize data collection and interpreta-
tion in S/S testing.
Concentrations of lead in the TCLP
extracts from Phase I exceeded lead's
5 mg/L TCLP regulatory limit estab-
lished to classify wastes as character-
istically toxic. These results indicate
the original binders failed to stabilize
lead present in the soil. Results from
Phase II indicate that higher B/S ratios
were able to stabilize lead and reduce
the concentration of teachable lead to
below the TCLP regulatory limit of 5
mg/L. The test wherein soil was pre-
treated by heating to remove organic
carbon indicated the organic carbon
content of the soil may have affected
the ability of the binders to stabilize
lead. A lower B/S ratio was needed to
stabilize lead in the heated soil than in
the unheated soil.
This Project Summary was developed
by EPA's Risk Reduction Engineering
Laboratory, Cincinnati, OH, to announce
key findings of the treatment evalua-
tion study that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
This study was done for the EPA to
supply information to the BOAT data base
for soil remediation. The data base will be
used to develop soil standards for Land
Disposal Restrictions.
S/S refers to treatment processes that
are designed to accomplish one or more
of the following objectives:
• to improve handling and physical
characteristics of the waste by
producing a solid from liquid or semi-
liquid wastes,
• to reduce contaminant solubility in the
treated waste, and/or
• to decrease the exposed surface area
across which transfer or loss of
contaminants may occur.
The objective of this S/S study was to
obtain (1) six sets of pre- and posttreat-
ment sample data on the leachability of
lead and (2) experimental design and op-
erating data that could be used to evalu-
Printed on Recycled Paper
-------
ate the performance of the S/S treatment
system. Three binders, at two B/S ratios
each, were evaluated in this study: port-
land cement, quicklime/fly ash, and ce-
ment kiln dust/fly ash (Phase I). Additional
studies (Phase II) were done because of
the failure of the six original binder mixes
to effectively stabilize lead. Phase II stud-
ies used three new binder mixtures, and
in addition, one portion of soil was first
heated to reduce the organic carbon con-
tent of the soil and then treated with a
binder to stabilize lead. This was done to
determine if the soil's high organic carbon
content (17%) adversely affected the origi-
nal binder mixtures' ability to stabilize the
lead present in the soil.
Procedure
During the remedial investigation of the
site, samples of soil, groundwater, surface
water, and sediments were collected and
analyzed, primarily for total lead. Low con-
centrations of other metals and target com-
pound list (TCL) organic contaminants
were also detected, but they were of mi-
nor significance and did not pose signifi-
cant environmental hazards. Low concen-
trations of polychlorinated biphenyls
(PCBs) were detected in two samples in
the parts-per-billion range.
The soil tested consisted of a dark
brown, sandy, silty clay with a high or-
ganic content (17% total organic carbon
[TOG]) and an average permeability of
1.57 x 10"6 cm/s. Four buckets of raw soil
were collected for the treatability tests.
The soil was homogenized by blending
the four buckets of soil in a 55-gal steel
drum then quartering the soil according to
ASTM Method C702-87 (Method B). The
study was conducted in two phases. The
three binder systems used during the pilot
scale S/S testing consisted of (1) 100%
Type I portland cement, (2) 40% quick-
lime and 60% fly ash, and (3) 67% ce-
ment kiln dust and 33% fly ash. The GANG
test, used to determine the optimum B/S
ratios, generated graphs that indicate pH
versus equivalents of acid/alkali. These
graphs were then used to predict the acid
and alkaline response that would occur
with various B/S ratios. These data were
then used to select the ratios that fall in
the pH range that has been shown to
immobilize lead (pH 8.0 to 11.0 for port-
land cement, pH 8.5 to 10 for quicklime/fly
ash, and pH 8.5 to 10 for the cement kiln
dust/fly ash) at the number of acid equiva-
lents (i.e., 2 eq/kg) used in the TCLP
leach tests. The soil/binder mixes were
prepared in a planetary rotary mixer in
accordance with the protocols in ASTM
Method C305. The order of soil, binder,
and water addition for preparation of the
solidified samples was as follows:
1. Raw soil was sieved to less than 3/8
in. mesh size to crush the 2- to 3-cm
spheres formed by the soil mixing/
homogenization step and to make the
soil more amenable to the treatment
process.
2. Soil and binder were dry blended.
3. Water was added until the mixture
passed the flow table test (ASTM
Methods C230 and C109 - Section
103).
For each B/S mix in Phase I, six 2-in.
diameter by 4-in. long cylinders and one
4-in. diameter by 1-in. long cylinder (used
to determine set time) were prepared. All
molded samples were covered with a thin
plastic sheet and placed in a concrete test
cure box for a 28-day curing period. The
cure box was maintained at 75°F, and
water was kept standing in the bottom of
the box to maintain moist storage.
Because of the failure of the six original
binder mixtures in Phase I to meet the
TCLP regulatory limit of 5 mg/L estab-
lished for lead in treated soils and be-
cause the results of further GANG tests
indicated that higher B/S ratios would im-
prove the stabilization capacity of the
treated samples by decreasing lead
leachate levels, additional S/S studies
(Phase II) were done to determine the
optimum binder mixes for the soils. The
same binders were used in this phase.
The soil, however, was solidified with three
new B/S ratios: (1) 45% portland cement;
(2) 31% quicklime with 46.5% fly ash; and
(3) 93% cement kiln dust with 46.5% fly
ash.
In addition, to determine if the specula-
tion that the heavy organic content of the
soil (17%) may have been the reason the
six original mixtures failed to stabilize the
lead in the soil, the soil was heated for 24
hr at 310°C to remove the organic carbon
from the soil. The sample was then treated
with portland cement at a B/S ratio of
20% based on the soil dry weight before
ignition. Molded samples from Phase II of
the treatability study were prepared in a
manner similar to those prepared in Phase
I. Six replicate molds were solidified for
each of the B/S mixes except for the
heated soil mix. Because of the small
volume of soil available, only three molds
were solidified for the heated soil.
Results
Table 1 shows the physical characteris-
tics for the binder mixtures that solidified
during Phase I and Phase II of the study.
Tables 2 and 3 summarize the results of
the lead analysis performed on TCLP
leachate of the pretreatment and post-
treatment samples collected in Phase I.
A comparison of the results in Tables 2
and 3 indicates the inability of the binders
to stabilize lead. It was theorized that the
high organic content of the soil may have
inhibited the ability of binders to stabilize
lead. Based on personal observation, as
well as analytical data, the organic con-
tent was believed to be mainly humus
material containing cellulose molecules.
Alkali present in the binder mixes may
have acted as catalysts for oxidative reac-
tions between atmospheric oxygen and
cellulose molecules. The products of these
reactions are acid groups. Alkali present
in the mixes would neutralize the acid
groups in the humus material rather than
stabilize the lead present in the soil.
Because of the failure of the original
binders, Phase II was done to determine
if the soil could be effectively treated by
the stabilization process and to determine
the effect of the soil's organic content on
the stabilization process. Tables 4 and 5
summarize the results of the lead analysis
performed on the TCLP extracts of the
pretreatment and posttreatment samples
collected in Phase II.
A comparison of results in Tables 4 and
5 indicates the increased B/S ratios em-
ployed in Phase II were able to reduce
the amount of teachable lead to below the
regulatory limit of 5 mg/L. Phase II results
also indicate the removal of organic car-
bon from the soil improves the stabiliza-
tion capacity of the binder mixes. This is
shown with the 20% portland cement
binder mixture; the amount of leachable
lead was reduced from 14 mg/L (Table 3)
in soil containing organic carbon to <0.2
mg/L (Table 5) in soil that had been heated
to remove the organic carbon.
The binders that set during the 28-day
curing period also exceeded the uncon-
fined compressive strength criteria of 50
psi. Portland cement mixtures showed the
greatest strength. In addition, the removal
of organic carbon from the soil improved
the compressive strength of the 20% port-
land cement binder mixture which can be
seen by comparing Mix Nos. 2 and 10
(Table 1).
Conclusions
Results from the study indicate the soil
can be treated to reduce the amount of
leachable lead to below the regulatory limit
of 5 mg/L with the binder mixtures estab-
lished in Phase II. Portland cement mix-
tures appear to provide the best results
for stabilizing lead in the contaminated
soil used in these tests. Furthermore, all
the solidified samples, regardless of their
-------
Table 1. Physical Characteristics of Cast Samples
Mix
No.
1
2
3
4
7
8
9
10*
Binder Recipe*
16%pc
20% pc
8.5%ql/12.75%fa
10.5%ql/15.75%fa
45% pc
31%ql/46.5%fa
93% ckd/46.5% fa
20% pc
U neon fined
Compressive
Strength,
kPa
462
503
241
207
2612
197
178
1618
Moisture
Content,
60
55
58
55
t
—
—
—
Wet Density,
kgM
1480
1510
1460
1490
Dry Density,
kg/m3
590
675
609
665
*pc = Portland cement.
ql/fa = Quicklime/fly ash.
ckd/fa = Cement kiln dust/fly ash.
fData not available for these tests.
*Heated soil.
Table 2. TCLP Lead Concentrations in Pretreatment Soil Samples from Phase I (mg/L)
Portland Cement (100%) Kiln Dust and Fly Ash (2:
Sample Binder/soil' Binder/soil Binder/soil Binder/soil
42%
95
96
84
82
82
81
87
6.9
* Binder-to-soil ratio calculated on a dry weight basis.
ID
A
B
C
D
E
F
Average
Standard
deviation
16%
86
90
85
73
82
84
83
5.7
20%
84
96
112
87
89
89
93
10.2
36%
90
88
88
89
95
91
90
2.6
Fly Ash and Quicklime (3:2)
Binder/soil Binder/soil
21.25%
84
88
86
88
87
86
86
1.6
26.25%
87
87
88
88
89
91
88
1.5
binder type, exhibited lower leaching po-
tential for lead at the higher B/S ratios.
The results from the study also indicate
the organic content of the soil may affect
the ability of binders to stabilize lead in
the soil. The soil that was heated to re-
move organic carbon showed better stabi-
lization properties than did the soil where
the organic carbon was not removed.
Full characterization of the soil being
treated should be performed to determine
what soil characteristics may be present
that may inhibit the stabilization process
and to determine what pretreatment pro-
cedures should be performed on the soil
to improve the stabilization process.
The full report was submitted in fulfill-
ment of Contract No. 68-C9-0036, Work
Assignment No. 2-69, by IT Corporation,
under the sponsorship of the U.S. Envi-
ronmental Protection Agency.
Table 3. TCLP Lead Concentrations in Posttreatment Soil Samples from Phase I (mg/L)
Portland Cement (100%)
Sample Binder/soil *
ID 16%
A
B
C
D
E
F
Average
Standard
deviation
91
83
83
85
82
86
85
3.3
Binder/soil
16
13
16
12
16
11
14
2.3
Kiln Dust and Flv Ash (2: 1 )
Binder/soil
36%
68
62
67
61
61
64
64
3.1
Binder/soil
42%
56
56
53
52
54
55
54
1.7
Fly Ash and
Binder/soil
21.25%^
120
110
140
110
120
120
120
11
' Quicklime (3:2)
Binder/soil
49
46
49
32
36
63
46
11
Binder-to-soil ratio calculated on a dry weight basis.
Table 4. TCLP Lead Concentrations in Pretreatment Soil Samples from Phase II (mg/L)
Portland
Cement
(100%)
Binder/soil,'
Sample No. 45%
A
B
C
D
E
F
Average
Standard
deviation
81
83
85
87
84
85
84
2.0
Kiln Dust
and Fly Ash
(2:1)
Binder/soil,
139.5%
85
84
84
83
84
83
84
0.8
Fly Ash and
Quicklime
__
Binder/soil,
_ 77.5%
81
85
91
88
88
88
87
3.4
Portland
Cement
(100%)*
Binder/soil,
-2Q%_
110
120
120
NA*
NA
NA
117
5.8
'Binder-to-soil ratio calculated on a dry weight basis.
rSoil heated before treatment to remove organic carbon.
*NA = Not applicable; only three samples collected because of the sample volume available.
*U.S. Government Printing Office: 1993 — 750-071/60236
-------
Table 5. TCLP Lead Concentrations in Posttreatment Soil Samples from Phase II (mg/L)
Sample No.
A
B
C
D
E
F
Average
Standard
deviation
Portland
Cement
(100%)
Binder/soil, "
45%
<0.2
<0.2
<0.2
<0.2
<0.2
<0.2
<0.2
0.0
Kiln Dust and
Fly Ash
(2:1)
Binder/soil,
139.5%
1.3
1.5
1.3
1.6
1.6
1.5
1.5
0.1
Fly Ash and
Quicklime
(3:2) _
Binder/soil,
77.5%
0.45
0.58
0.44
0.46
0.53
0.62
0.51
0.08
Portland
Cement
(100%)*
Binder/soil,
20%
<0.2
<0.2
<0.2
NA*
NA
NA
<0.2
0.0
'Binder-to-soil ratio calculated on a dry weight basis.
fSo// heated prior to treatment to remove organic carbon.
*AW = Not applicable; only three samples collected due to small sample volume available.
Judy Hessling, Michael L. Smith, Steve Giti-Pour, and John Miller are with IT
Environmental Programs, Inc., Cincinnati, OH, 45246, and Jerry Isenburg is
with University of Cincinnati, Center Hill Facility, Cincinnati, OH 45224.
Richard P. Lauch is the EPA Project Officer (see below).
The complete report, entitled "Onsite Engineering Report for Solidification/
Stabilization Treatment Testing of Contaminated Soils." (Order No. PB93-
166 965/AS; Cost: $27.00, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Risk Reduction Engineering Laboratory
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
Penalty for Private Use
$300
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
EPA/600/SR-93/051
------- |