oEPA
United States
Environmental Protection
Agency
EPA/540/SR-92/010
August 1995
SUPERFUND INNOVATIVE
TECHNOLOGY EVALUATION
Technology Demonstration
Summary
Silicate Technology Corporation,
Solidification/Stabilization of PCP
and Inorganic Contaminants in
Soils; Selma, CA
A Superfund Innovative Technology
Evaluation (SITE) demonstration was
conducted to evaluate the ability of the
solidification/stabilization treatment
process developed by Silicate Tech-
nology Corporation (STC) to reduce the
mobility and leaching potential of or-
ganic and inorganic contaminants in
soils. The treatment process is based
on STC's proprietary alumino-silicate
product, FMS Silicate.
The demonstration was held at the
Selma Pressure Treating site in Selma,
CA, in November 1990. The STC tech-
nology was demonstrated using con-
taminated soils from an unlined waste
disposal pond at this site that con-
tained significant levels of pentachlo-
rophenol (PCP), arsenic, copper, and
chromium.
The evaluation of STC's treatment
process was based on (1) contaminant
mobility, as measured by several leach-
ing tests and total waste analysis; (2)
structural integrity of the solidified ma-
terial, as measured by physical, engi-
neering, and morphological tests; and
(3) economic factors based on cost in-
formation from STC supplemented by
information from the demonstration.
Treated soil from the demonstration
was monitored for a period of 32 mo,
ending in July 1993.
The STC process reduced the mobil-
ity of PCP, arsenic, and copper. (Ef-
fects on chromium mobility were
difficult to interpret because of the low
teachable concentrations of chromium
in the raw waste). Physical properties
of the product indicated good struc-
tural stability, and microstructural
analyses of the product showed that
the treatment process produced a
dense, homogeneous, rock-like mate-
rial with low porosity. The treatment
resulted in an increase in volume and
a slight increase in bulk density.
The remediation cost, using the STC
solidification/stabilization treatment
process, is approximately $190 to $3307
yd3 when used to treat large amounts
(15,000 yd3) of waste similar to that
found at the Selma Pressure Treating
site.
This Summary was developed by
EPA's National Risk Management Re-
search Laboratory, Cincinnati, OH, to
announce key findings of the SITE pro-
Printed on Recycled Paper
-------
gram demonstration that is fully docu-
mented in two separate reports (see
ordering information at back).
Introduction
In response to the Superfund Amend-
ments and Reauthorization Act of 1986
(SARA), the U.S. Environmental Protec-
tion Agency's (EPA) Office of Research
and Development (ORD) and the Office of
Solid Waste and Emergency Response
(OSWER) established a formal program to
accelerate the development, demonstra-
tion, and use of new and innovative tech-
nologies as alternatives to traditional
containment systems for hazardous
wastes. This program is called the SITE
Demonstration Program. The major ob-
jective of the SITE Demonstration Pro-
gram is to develop reliable performance
and cost information for these technolo-
gies.
In November 1990, a demonstration test
of STC's solidification/stabilization process
was conducted at the Selma Pressure
Treating wood-preserving site in Selma,
CA. STC's solidification/stabilization tech-
nology is designed to reduce the mobility
and leaching potential of organic and inor-
ganic constituents in contaminated soils.
The Selma Pressure Treating site, a wood
preserving facility, contains soils contami-
nated with organics, predominantly PGP;
and inorganics, primarily arsenic, chro-
mium, and copper.
The objectives of the STC SITE dem-
onstration were:
To determine whether the STC tech-
nology could reduce the mobility and
leachability of organic and inorganic
contaminants, as measured by vari-
ous leaching procedures.
To assess the structural characteris-
tics of the solidified waste and the
effectiveness of stabilization over a
3-yr period.
To determine volume and density in-
creases resulting from the treatment
process.
To develop information required to
estimate the capital and operating
costs for the treatment system.
Description of Technology
(provided by STC)
STC has developed two groups of re-
agents: SOILSORB HM, for treating
wastes having inorganic constituents, and
SOILSORB HC, for wastes having organic
constituents. These two groups of reagents
can be combined to treat wastes that have
both organic and inorganic contaminants.
STC's treatment of wastes involves sili-
cate-forming reactions, which bind and
microencapsulate the contaminants. Heavy
metal ions are incorporated into the crys-
tal lattice structure of a highly insoluble
calcium-alumino-silicate compound. Treat-
ment of organic wastes involves seques-
tering the organic compounds into a
surface-modified, layered, alumino-silicate
mineral. The organic layers of the sur-
face-modified alumino-silicate can adsorb
as much as 20 times their own weight of
organic constituents. Microencapsulation
of the alumino-silicate compound forms
an additional physical barrier to leachates.
The result is a very stable compound
analogous to common rock-forming sili-
cate minerals.
Waste characteristics that may affect
the performance of the STC technology
include: clay content, coal and lignite con-
tent, moisture content, oil and grease con-
tent, pH of the waste, concentrations of
volatile organics, and aggregate size of
the waste. These factors may affect the
quality of the solidified waste mixture or
may affect the amount of reagent required
for solidification. The amount of reagent
required for stabilization can be adjusted
according to variations in organic and in-
organic contaminant concentrations deter-
mined during treatability testing. The STC
process is not recommended for wastes
contaminated with low-molecular-weight
organic contaminants such as alcohols,
ketones, and glycols.
Demonstration Procedures
The STC solidification/stabilization pro-
cess was used to treat approximately 16
tons of contaminated soil from an unlined
waste disposal pond. Wastes from the
wood treatment plant had been disposed
of through placement into an unlined pond
and a nearby sludge pit. Previous investi-
gations had shown that soils from this
area contained elevated levels of PCP
(1,900 to 8,400 parts per million [ppm]),
arsenic (375 to 1,900 ppm), chromium
(1,900 ppm), and copper (1,500 ppm). In
addition, oil and grease levels ranged from
10,000 to 20,000 ppm.
Site investigations and treatability stud-
ies were first conducted to characterize
the waste and establish the appropriate
type and amount of reagents. A startup
and test batch was made, using clean
sand instead of the waste material to check
operating and sampling procedures. This
batch served as a treatment process blank.
Contaminated soil from the unlined
waste disposal pond was excavated and
placed on a plastic-lined pad. Pretreat-
ment consisted of mixing raw waste mate-
rial in the treatment mixer to reduce the
waste aggregate size to 3/8-in. diameter
or less. Due to insufficient size reduction
of agglomerated waste, the waste aggre-
gate size was further reduced to approxi-
mately 1 to 2 mm by manual screening.
The screened waste was loaded into a 5-
yd3 high-intensity batch mixer, where pre-
determined amounts of the silicate
reagents and water were added. The mix-
ture was blended thoroughly, poured into
cardboard molds, and placed in a storage
area onsite for long-term testing and evalu-
ation. Five 2.5 yd3 batches of raw waste
were treated during the demonstration.
Sampling and Analyses
Samples of raw and treated waste were
submitted for chemical and physical char-
acterization. Raw waste samples were col-
lected directly from the batch mixer and
placed in sample containers prior to the
addition of the treatment reagents. After
mixing, the treated wastes were poured
into three, 1 yd3 cardboard molds. Treated
waste samples were collected from the
cardboard forms immediately after the
treated waste was poured from the mixer,
and allowed to cure for 28 days prior to
analysis.
The contaminants of regulatory concern
at the Selma Pressure Treating site were
arsenic and PCP; however, other target
analytes were the metals chromium, cop-
per, nickel, and lead as well as volatile
and semivolatile organic compounds such
as phenanthrene, tetrachlorophenol, phe-
nol, and naphthalene. The corresponding
critical measurements for the demonstra-
tion were the toxicity characteristic leach-
ing procedure (TCLP) for arsenic (and
other inorganic analytes) and total waste
analysis (TWA; SW 846 Method 8270) for
PCP (and other organic analytes). Non-
critical measurements included TCLP-Dis-
tilled Water and California Waste
Extraction Test (CALWET) leach proce-
dures. Additional noncritical measurements
for the demonstration included the TCLP-
Cage, a modified American Nuclear Soci-
ety (ANS 16.1) leach test, and analysis
for polychlorinated dibenzo-p-dioxins
(PCDD) and polychlorinated dibenzofurans
(PCDF). In addition, chemical character-
ization of the raw and treated waste in-
cluded pH, Eh, loss on ignition, and
neutralization potential analysis. Engineer-
ing and geotechnical tests included par-
ticle size analysis, bulk density,
permeability, and unconfined compressive
strength, as well as petrographic analysis,
scanning electron microscopy, and Fou-
rier transform infrared spectroscopy.
Four of the five batches treated during
the demonstration were analyzed. Batch
-------
2 was excluded from complete analytical
evaluation because the contaminated soils
had not been well mixed after the treat-
ment, resulting in large (up to 1 in.) pock-
ets of untreated waste. In subsequent
batches, the problem was solved by
screening the raw waste to reduce the
aggregate size to approximately 1 to 2
mm. Batch 1 and batches 3 through 5
appeared to be homogenous mixtures.
Tables 1 to 3 give average concentra-
tions of critical analytes for TCLP, TWA
and TCLP-Distilled Water analyses for both
raw and treated wastes, as well as the
associated contaminant percent reduction
(corrected for dilution caused by addition
of treatment reagents and water of hydra-
tion). Unless otherwise noted, the results
are reported as the mean and sample
standard deviation of six samples. Tables
4 and 5 present results for unconfined
compressive strength and permeability.
Table 6 lists the federal regulatory thresh-
old limit concentrations for the critical
analytes.
Results and Discussion
The following conclusions about the ef-
fectiveness and cost of STC's solidifica-
tion/stabilization treatment process are
based on analytical results and general
observations from the SITE demonstra-
tion.
PCP was successfully treated using
the STC process. Initial raw waste
concentrations of PCP as high as
10,000 ppm in a single sample were
reduced 91% to 98% to values as
low as 19 ppm, as measured by TWA
(EPA SW 846 Method 8270;
semivolatile organic compound extrac-
tion performed on ground samples
passing 100 mesh using methylene
chloride). This complies with EPA's
draft policy guidance on stabilization
of organics, which states that total
waste analyses should be used to
assess the effectiveness of stabiliza-
tion processes for treating semivolatile
and nonvolatile organics (OSWER Di-
rective No. 9200.5-220). Leaching
tests for PCP, using the TCLP, but
using distilled water instead of acetic
acid, indicated reductions up to 97%
(from as high as 110.0 ppm in a single
sample to as low as 0.47 ppm). Treat-
ment of other toxic organic com-
pounds could not be evaluated
because of the very low concentra-
tions of such compounds.
Arsenic was successfully immobilized.
Standard TCLP tests using acetic acid
produced reductions in leachable con-
centrations of up to 92% (from as
high as 3.8 ppm in a single sample to
as low as 0.044 ppm). TCLP proce-
dures, using distilled water in place of
acetic acid, produced reductions of
98% or greater (from as high as 1.4
ppm in a single sample to not de-
tected). Arsenic analyses were con-
ducted by EPA Method 7060.
Chromium was not successfully im-
mobilized; however, chromium was
not targeted for treatment because of
low leachable concentrations in the
raw waste. Although leachable con-
centrations of chromium increased fol-
lowing treatment, they were still well
below the federal regulatory thresh-
old limit concentration for chromium.
Chromium analyses Were conducted
by EPA Method 3010.
Copper also was not targeted for treat-
ment. However, copper was success-
fully immobilized. Reductions of
leachable concentrations of copper
ranged from 81% to 99%. Copper
analyses were conducted by EPA
Method 3010.
After a 28-day curing period (open air
and ambient site temperature), the
treated wastes exhibited high physi-
cal stability. Testing at 6, 18, and 32
mo following the demonstration was
conducted to determine long-term sta-
bility. Unconfined compressive
strength (UCS) of the treated wastes
was moderately high after 28 days,
averaging 260 to 350 Ib/in2, as deter-
mined by the American Society for
Testing and Materials (ASTM) method
D1633-84.
Permeability of the treated waste was
low (<1.7 x 10'7 cm/sec by Test
Method for Solidified Waste Charac-
terization, TMSWC-13). The relative,
cumulative weight loss after 12 wet/
dry (ASTM D4843-88) and 12 freeze/
thaw (ASTM D4842-90) cycles was
negligible (less than 1%).
Treatment of the wastes resulted in
volume increases ranging from 59%
to 75% (68% average), with slight
increases in bulk density.
The STC process successfully solidi-
fied contaminated soils that contained
less than 2% oil and grease (EPA
Method 413.2) and initial moisture
contents of up to 6%.
Petrographic (ASTM 856) analyses,
including microscopical, X-ray diffrac-
tion, scanning electron microscopic,
and Fourier transform infrared analy-
ses, indicated good binder-to-aggre-
gate bonding. Metal containment was
good.
TCLP extracts for metals and TWA
for PCP of the 6-mo cured samples
showed increased concentrations of
contaminants released from the
treated waste.
Analyses for the 18-mo cured samples
showed improved percent reductions
relative to the 6-mo cured sample test
results, averaging 88% reduction for
arsenic, and 96% reduction for PCP.
Chromium and copper concentrations
showed slight to moderate increases
in the TCLP-extracts over the 18-mo
period.
Analyses for the 32-mo cured samples
showed TWA extract concentrations
of PCP to be comparable to 18-mo
results. TCLP extract concentrations
of arsenic at 32 mo were comparable
to 6-mo results. Chromium concen-
trations continued to exhibit increases
in TCLP extracts, whereas copper
concentrations more closely re-
sembled 28-day results than extracts
at either 6 mo or 18 mo.
UCS of the 18-mo treated wastes in-
creased an average of 245% over
values obtained after a 28-day curing
period before subsequently decreas-
ing 27% between 18 and 32 mo.
The process equipment used during
the technology evaluation was ob-
served to be mechanically reliable.
No equipment-related problems oc-
curred during the six-day demonstra-
tion.
The process equipment used during
the demonstration produced a homog-
enous, solidified product, after pre-
treatment screening and size
reduction of surface hardpan material
down to 1 to 2mm.
The STC process has been estimated
to cost approximately $190 to $330
per yd3, when used to treat large
quantities (15,000 yd3) of waste, simi-
lar to that found at the site.
-------
Table
1. Summary of TCLP Results
Arsenic
Concentrations (mg/L)
Treated Waste
Batch
1
3
4
5
Average
% Reduction*.*
Average
% Reduction a.b
Average
% Reduction a.b
Average
% Reduction a.b
Raw Waste
1.8 ±0.47
1.1 ±0.23
2.4 ±0.60
3.3 ±0.33
28-day
0.086 ±0.055
92
0.10 + 0.030
83
0.875 + 0.15
35
0.55 ±0.10
71
Chromium
6-month
0.24 ±0.071
77
0.26 ±0.033
56
0.61 ±0.17
55
0.465 ±0.1 4
75
Concentrations (mg/L)
18-monthc
0.071 ±0.011
93
0.11+0.089
82
0.1 85 ±0.040
86
0.1 7 ±0.020
91
32-month
0.40 + 0.19
61
0.17 + 0.033
72
0.47+ 0.30
65
0.52 ±0.1 9
73
Treated Waste
Batch
1
3
4
5
Average
% Reduction a.b
Average
% Reduction a.b
Average
% Reduction a,b
Average
% Reduction a,b
Copper
Raw Waste
0.1 3 ±0.087
<0.05
0.10 ±0.062
0.27 ±0.053
28-day
0.245 + 0.005
-230
0.19 ±0.012
NC
0.28 ±0.010
-390
0.32 + 0.033
-110
6-month
0.28 ±0.008
-280
0.25 + 0.012
NC
0.51 ±0.078
-810
0.63 ±0.04
-310
Concentrations (mg/L)
18-monthc
0.355 + 0.075
-380
0.295 ±0.040
NC
1.2 ±0.091
-2,000
1.1 ±0.16
-610
32-month
0.77 ±0.31
-940
0.47 ± 0.052
NC
1.45 ±0.1 8
-2,500
1.2 + 0.082
-680
Treated Waste
Batch
1
3
4
5
Average
% Reduction***
Average
% Reduction a.b
Average
% Reduction a.b
Average
% Reduction a.b
PCP
Raw Waste
3.4 ± 1.2
1.4 ±0.1 5
6.5 ± 1.1
9.4 ± 1.4
28-day
0.090 + 0.005
95
0.075 ±0.007
91
0.10 + 0.005
97
0.062 ±0.01 2
99
6-month
0.1 2 ±0.008
94
0.14 ±0.017
82
0.25 ±0.008
93
0.17 ±0.052
97
18-monthc
0.36 + 0.17
81
0.1 4 ±0.036
82
0.90 ±0.29
75
1.44 ± 0.36
74
Concentrations (mg/L)
Treated Waste
Batch
1
3
a = Per
Average
% Reduction*-**
Average
% Reduction a.b
cent Redtjntinn - \ 1 - (1
Raw Waste
1.5 ±0.1 3
2.3 ±0.33
+ Additives Ratio) x
28-day
3.4 ± 1.5
-300
<0.25
>81
Batch
Raw Waste
4 A verage 1.75 + 0.57
% Reduction a.b
5 Average 2.3 ± 1.4
% Reduction a.b
32-month
0.15 ±0.1 3
92
0.098 + 0.029
88
0.15 + 0.046
96
0.10 ±0.008
98
Treated Waste
28-day
5.5 + 0.32
-460
0.9+ 1.25
31
Concentration of Treated Waste inn 1
b = The additives ratio is the weight of additives, including water of hydration, divided by the weight of raw wastes. Values are 0761 0764 0 776 and
0.746 for Batches 1,3,4, and 5, respectively.
c = Results reported as mean and standard deviation of four samples. (Other results refer to six samples )
NC = Not calculated
-------
Table 2. Summary of TWA Results8
POP
Concentrations (mg/kg)
Treated Waste1*
Batch
1
3
4
5
Average
% Reduction0 -d
Average
% Reduction c>d
Average
% Reduction c>d
Average
% Reduction c-d
Raw Waste
2,350 ±660
2,000 ±270
7,700 ±1,1 00
8,300+ 1,400
28-day
120 ± 42
91
85 ±33
92
120 ± 38
97
220 ± 150
95
6-month
100 ±29
92
99 ±17
91
370 ±85
91
800 ± 440
83
18-month
27+ 12
98
30 ±16
97
99 ±3
98
410 + 530
91
32-month
190± 170
86
49 ±36
96
105 ±47
98
415+110
91
a = Total concentrations of metals not expected to change for solidification/stabilization after correction for additives. Results for metals are reported in
the Applications Analysis Report and the Technology Evaluation Report.
b = Nondetected concentrations assigned a value of 106 (twice the method detection limit) for the 28-day and 6-month samples. Use of nonstandard
dilutions in subsequent analyses resulted in no nondetected concentrations.
c = Percent Reduction = \ 1 - (1 + Additives Ratio} x
Concentration of Treated Waste
Concentration of Raw Waste
x 100
d= The additives ratio is the weight of additives, including water of hydration, divided by the weight of raw wastes. Values are 0.761, 0.764, 0.776, and
0.746 for Batches 1, 3, 4, and 5, respectively.
Table 3. Summary of TCLP-Distilled Water Results
Arsenic
Concentrations (mg/L)
Treated Waste
Batch
1
3
4
5
Chromium
Average
% Reduction3'**
Average
% Reduction3- b
Average
% Reduction3' b
Average
% Reduction3-13
Raw Waste
0.80 ±0.21
0.725 ±0.060
1.25 ±0.1 2
1.1 ±0.09
28-day
<0.01
>98
<0.01
>98
<0. 01 1 + 0.001
>98
<0.012±0.001
>98
Concentrations (mg/L)
32-monthc
<0.009
>98
<0.02
>95
0.05 ±0.02
93
<0.015
>98
Treated Waste
Batch
1
3
4
5
Average
% Reduction3'**
Average
% Reduction3'*3
Average
% Reduction3'13
Average
% Reduction3'*3
Raw Waste
0.19 + 0.072
0.17 ±0.054
0.073 ±0.01 5
0.1 05 ±0.040
28-day
<0.05
>54
<0.05
>48
0.056 ±0.006
-36
0.079 ±0.003
-31
32-monthc
0.30 ±0.032
-178
0.29 ±0.07
-201
0.83 + 0.081
-1900
0.69 + 0.037
-100
-------
Tables, (continued)
Copper
Concentrations (mg/L)
Treated Waste
Batch
1
3
4
5
Average
% Reduction3' b
Average
% Reduction3-**
Average
% Reduction9- b
Average
% Reduction3-*)
PCP
Raw Waste
0.45 ±0.1 6
0.37± 0.084
0.99 ±0.060
0.555 ±0.097
28-day
<0.0305 + 0.001
>88
<0.030
>86
0.054 + 0.002
90 84
32-monthc
0.05 + 0.01
>80
0.04+ 0.01
81
0.09 ±0.01
<0. 032 ±0.001 0. 06 ± 0. 006
>90 81
Concentrations (mg/L)
Treated Waste
Batch
1
3
4
5
Average
% Reduction3'13
Average
% Reduction3' b
Average
% Reduction3^
Average
% Reduction3'**
Raw Waste
35+16
40+18
40+ 10
80+18
28-day
4.0+1.8
80
0.58 ±0.083
97
3.9 ±0.46
83
3.05 + 0.85
93
32-month
r Concentration of Treated Waste
a = Percent Reduction
ion = \1 -
(1 + Additives Ratio) x
b = The additives ratio is the weight of additives, including water of hydration, divided by the weight
of raw wastes. Values are 0.761, 0.764, 0.776, and 0.746 for Batches 1, 3, 4, and 5, respec-
tively.
c = Results reported as mean and standard deviation of four samples. (Other results refer to six
samples.)
Table 4. Summary of Unconfined Compressive Strength Results
Unconfined Compressive Strength (psi)
Batch
1
3
4
5
28-daya
301 + 162
278 ± 20
259 + 65
347 ± 65
6-montha
480 ±41
450 ±85
350 ±230
420 ± 190
18-montha
958 ± 63
763 + 19
1,017 + 73
1,375 + 26
32-month
688 + 1 14b
720 + 48°
679±109d
795 ± 136d
a=Results reported as mean and standard deviation of three samples.
b=Results reported as mean and standard deviation of eight samples.
c=Results reported as mean and standard deviation of two samples.
d=Results reported as mean and standard deviation of nine samples.
-------
Table 5. Summary of Permeability Testing Results
Permeability (1O~7 cm/sec)
Batch 28-day3 32-monthb
1 1.7 ±0.40 4.2
3 1.5 ±0.98 2.8
4 0.9 + 0.41 1.2
5 1.5 ±0.27 2.0
a=Results reported as mean and standard deviation of three samples.
b=Results reported are from single samples.
Table 6. Regulatory Thresholds for Critical Analytes
Critical Analytes Federal Regulatory Threshold Limit
(FRTL) (mg/L)
Arsenic 5.0
Chromium (total) 5.0
Copper
POP 100
-------
The EPA Project Manager, Edward R. Bates, is with the National Risk
Management Research Laboratory, Cincinnati, OH 45268 (see below)
The complete report, entitled "Technology Evaluation Report: Silicate Technol-
ogy Corporation, Solidification/Stabilization of PCP and Inorganic Con-
taminants in Soils; Selma, CA," (Order No. PB95-255709; Cost: $27.00,
subject to change); and
A related report, entitled "Silicate Technology Corporation's Solidification/
Stabilization Technology for Organic and Inorganic Contaminants in Soils;
Applications Analysis Report" (EPA/540/AR-92/010) (Order No. PB93-
172948; Cost $27.00, subject to change) are both available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Manager can be contacted at:
National Risk Management Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 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/540/SR-92/010
------- |