5-EPA
United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S7-81-155 Oct. 1981
Project Summary
Pilot Field Studies of FGD
Waste Disposal at Louisville
Gas and Electric
R. VanNess, A. Plumley, N. Mohn, C. Ullrich, and D. Hagerty
Properly prepared landfill from FGD
sludge/fly ash mixtures can prevent
trace element contamination of under-
lying groundwater. Analyses of leach-
ates from the series of landfill im-
poundments in this study show that
trace elements on the RCRA list of
contaminants were found in concen-
trations below those proposed to
characterize hazardous or toxic wastes.
Decreasing concentrations, with
time, of trace contaminants were
observed in both leachate and runoff
samples obtained from the stabilized
sludge mixtures. Small, synthetically
lined, above-ground impoundments
provided higher concentrations of
trace contaminants than the subsur-
face impoundments since no attenua-
tion by local soil was provided and
vegetation that might minimize runoff
was not established on these sites.
Most sites developed compressive
strengths significantly greater than
the minimum required for recreational
or light structural landfill. Water
samples from beneath larger subsur-
face impoundments indicated that the
filtering action of soil aids in decreasing
the concentration of contaminants
reaching the ground water supply.
Certain mixtures have undergone a
fixation reaction, reducing the per-
meability and minimizing the release
of moisture and/or contaminants to
the surrounding soil.
This Project Summary was devel-
oped by EPA's Industrial Environ-
mental Research Laboratory. Research
Triangle Park, NC. to announce key
findings of the research project that is
fully documented in a separate report
of the same title (see Project Report
ordering information at back).
Introduction
The most extensive commercial
experience in flue gas desulfurization
(FGD) to date has been with lime/lime-
stone wet scrubbers. It is anticipated
that these systems will account for most
sulfur or SOa removal at electric power
stations for the next 10 to 15 years. A
major challenge associated with the
commercial development of these
systems is the disposal of large amou nts
of by-product sludge within the con-
straints of land and water quality
regulations. It has been estimated that,
by 1985, air quality control regulations
will require the installation of FGD
systems on plants representing 60
million kW of electric generating
capacity per year. If this estimate is
realized, over 27.2 Mg (30 million tons)
of ash-free by-product sludge (50
percent solids) will be produced per
year.111
Over the past 11 years, more than 50
different procedures for direct disposal
or process utilization of this sludge have
been evaluated.12'31 Most investigators
have concluded that utilization will not
be able to provide viable alternatives to
proper disposal of the sludge any more
than utilization of fly ash (10 to 15
-------
percent of annual production) has
solved the problem of fly ash disposal.
Consequently, most waste by-products
from FGD will be disposed of in ponds or
used as landfill. The choice of disposal
methods and amount of treatment
required will depend on the geographical
location, legal and environmental
requirements, economic considerations,
and the preferences of the operating
company.
Prior laboratory work has indicated
the environmental advantages of the
disposal of stabilized FGD by-product
sludges over untreated FGD sludges.
Haas and Ladd141 showed that waste
solids from a limestone scrubbing
system could be stabilized by dewatering
and subsequent mixing with clay soil or
a western type fly ash having a high
alkali content. Further studies'5'61 showed
that the addition of fly ash and/or lime
to FGD sludge solids resulted in the
formation of a number of mineral
compounds of high strength and low
permeability.
These initial studies focused primarily
on treatment of FGD sludges to enhance
structural properties. However, in
addition to being physically unstable,
FGD sludges contain varying concentra-
tions of trace elements and dissolved
salts which have the potential to
contaminate surface and groundwater.
Although some soils will absorb many of
the trace elements in FGD sludge, major
ions (such as calcium, sulfate, and
chloride) may not be readily absorbed.
Therefore, the disposal of sludge must
also address procedures to minimize
runoff and to control or prevent seepage.
Consequently, leachate analyses were
added to the unconfined compressive
strength and permeability tests that
were already a part of sludge-landfill
stabilization studies.
The work described in this report is a
major laboratory/field demonstration of
landfill disposal of FGD by-product
sludges by Louisville Gas and Electric
with Combustion Engineering, Inc. and
the University of Louisville, performed
under contract with the Industrial
Environmental Research Laboratory of
EPA at Research Triangle Park, North
Carolina.
This project was designed to dem-
onstrate the feasibility of landfill
disposal of by-product FGD sludge
treated with various mixtures of fly ash
and stabilizing additives.
Prior to the start of this demonstration,
two criteria were established to define
an acceptable landfill material: (1)
landfill material must have sufficient
structural integrity to meet minimum
standards of: compressive strength
X).1 MPa (1 ton/ft2) and permeability
<5 x 10~5 cm/s
and (2) landfill
material must not contaminate ground-
water by leachate or surface water by
runoff or erosion. The standards used for
leachate evaluation were the levels
which had been proposed for defining
leachates from hazardous wastes under
the Resource Conservation and Recovery
Act (Section 261.24)"" and the U. S.
Public Health Service Drinking Water
Standards. Both of these standards are
shown in Table 1.
Project Objectives
This project was designed to dem-
onstrate the feasibility of environmen-
tally acceptable landfill disposal of
mixtures of FGD by-product sludge a
fly ash. The FGD by-products used
this demonstration were obtained frc
the wet scrubbing of flue gas frc
combustion of 3 percent sulfur Wt
Kentucky coal at the 65 MW statii
generator (No. 6) at the Paddy's Ri
Station of Louisville Gas and Electi
Co., Louisville, Kentucky. Fly ash w.
obtained from the electrostatic precif
tator hoppers of the No. 6 stea
generator during the test period.
The project was part of an oven
program which covered scrubber testir
as well as waste disposal. The was
disposal project consisted of two phas<
each using a different absorbent 1
remove SOa from the flue gas during tr
scrubbing operation.
Since the FGD system at Paddy's Ru
was placed in operation in 1971
carbide lime, a locally available b\
Table 1. Criteria for Evaluation of Leachate Environmental Impact
U. S. Public Health
Service
Drinking Water Standards
Characteristics
Physical
Color, units
Taste
Threshold odor number
Turbidity, units
Chemical
Alkyl benzene sulfonate
Arsenic
Barium
Cadmium
Chloride
Chromium (hexavalent)
Copper
Carbon chloroform extract'*'
Cyanide
fluoride™
Iron
Lead
Nitrate
Phenols
Selenium
Silver
Sulfate
Zinc
Mercury
Total dissolved solids
Suggested Limit
That Should
Not Be Exceeded
15
Unobjectionable
3
5
mg/l
0.5
0.01
250
1
0.2
0.01
0.7-1.2
0.3
45
0.001
250
5
500
Cause for
Rejection
mg/l
O.05
1.0
0.01
0.05
0.2
1.4-2.4
0.05
0.01
0.05
Proposed
Toxicity
Criteria for
Hazardous
Waste
under RCRA
mg/l
5.0
100
1.0
5.0
5.0
1.0
5.0
0.2
(al Organic contaminants.
-------
product from acetylene manufacture,
consisting primarily of Ca(OH>2, has
been used as the absorbent. Phase I of
the waste disposal project was designed
to provide a demonstration of impound-
ment of mixtures of fly ash and chemi-
cally treated sludge from carbide lime
scrubbing.
From the standpoint of general usage,
commercial lime is more likely to be
utilized as the SOa absorbent. Phase II
was conducted, therefore, using sludge
obtained from scrubber operation with
commercial lime absorbent.
Conclusions
1. FGD waste sludges can be stabilized
to give compressive strengths greater
than the minimum required for
acceptable landfill disposal. In this
study, stabilized sludge samples
developed compressive strengths
ranging from 0.29 to 2.39 MPa (3.0
to 25 tons/ft2) when cured and
tested under controlled laboratory
conditions. Subsequent field testing
of selected stabilized sludge mixtures
showed strength from 0.01 to 0.50
MPa (0.13 to 5.4 tons/ft2), measured
on core samples removed from the
field sites and tested in the laboratory.
2. The correlation between strengths
measured on laboratory samples and
on core samples from field testing of
a particular sludge was poor. It was
felt this was due primarily to the
unavoidable disturbance of the core
samples during collection. The use of
a concentric drill/Shelby tubes
(Dennison sampler) should prove
more satisfactory for this application.
In-situ plate load tests on several
field sites showed strengths devel-
oped in stabilized sludges which
were significantly higher than indi-
cated by core sample measurements.
3. Stabilization reduces the permeabil-
ity of sludges, thus minimizing
leachate generation. In this study,
both laboratory and core samples
from field test sites showed an
inverse relationship between strength
and permeability.
4. Properly prepared landfill from FGD
sludge/fly ash mixtures can prevent
trace element contamination of the
underlying groundwater. All leachates
collected from stabilized sludges in
this study contained trace elements
in concentrations below those
proposed to define a hazardous
waste under RCRA (Table 1).
5. Process II mixtures (containing
rotary drum vacuum filter cake, fly
ash, and fixative) had the optimum
combination of compressive strength
and permeability for landfilling both
carbide lime and commercial lime
sludges. Process I, utilizing thickener
underflow, had low bearing capacity
and relatively high permeability.
Process III, which compounded
mixtures with filter press high solids
cake, was too brittle. Process I and III
mixtures gained little compressive
strength with time and thus are
considered unacceptable.
Project Description
The project was divided into two
phases: laboratory testing and field
demonstration. The laboratory tests
provided baseline values for the strength,
permeability, and leachate quality of
each mixture evaluated. The field
demonstration provided similar infor-
mation on the behavior of stabilized
materials under natural environmental
conditions including precipitation and
freeze/thaw. Included in the field phase
was evaluation of the handling, trans-
portation, and placement of the various
sludge mixtures.
In this project, the stabilization of
sludge from three dewatering processes
was evaluated in the laboratory and
under field conditions. Process I involved
mixing fly ash and a fixative (stabilizing
additive) with thickener underflow to
form a pumpable mixture that was self-
hardening upon standing. Process II
consisted of mixing fly ash, partially
dewatered sludge, and a fixative to form
a compactable stable landfill. Process III
used a maximum dewatered sludge,
fixative, and/or fly ash to form a
compactable stable landfill.
The laboratory tests screened a large
number of stabilized sludge/fly ash
mixtures for consideration in the field
demonstration phase. The sludges were
mixed with fly ash in ratios ranging from
0:1 to 1.5:1 parts by weight fly ash to dry
scrubber solids. Varying percentages of
fixative (lime, hydrated lime, carbide
lime, or Portland cement) were added to
determine the quantity necessary to
achieve optimum results.
To predict the landfill behavior of
stabilized sludges, the following tests
were performed.
1. Unconfined compressive strength.
2. Permeability.
3. Leachate analysis.
The results of the laboratory testing
are discussed in depth.
Briefly, on the basis of the laboratory
test results, 10 mixtures were chosen
for field evaluation. The mixtures were
chosen to allow comparison between
sludges with different degrees of
dewatering and/or fixation additives.'91
A quantity of each mixture was
prepared in the field with a process train
designed for this purpose. The sludge/
flyash/treated mixtures were impounded
in specially prepared sites to facilitate
collection of leachate. Ten commercial
above-ground swimming pools and five
larger subsurface impoundments were
used as monitored disposal sites for the
mixtures
(9,10)
Laboratory Testing
The laboratory testing phase served
as a screening effort in which many
stabilized sludge mixtures could be
evaluated. The data provided the basis
for selecting a smaller group of mixtures
for further field evaluation.
Sixty mixtures were prepared for the
initial laboratory screening. Sludges
from two FGD scrubbing processes
were used in this study. One sludge was
generated at LG&E's Paddy's Run Unit
No. 6 using carbide lime as the scrubber
absorbent. This carbide lime sludge
contains mainly calcium sulfite (Table
2). Less than 10 percent of the sulfur
products are oxidized to calcium sulfate.
Because of the high sulfite content, the
carbide lime sludge is very difficult to
dewater. Previous field observations
had indicated that the thickener under-
flows contained 18 to 24 percent solids
and the vacuum filter cake contained 35
to 40 percent solids. Tests at vendor
laboratories had shown that 50 to 55
percent solids could be obtained with a
filter press operating at 1035 KPa (150
psig). The other sludge evaluated in the
laboratory program resulted from the
operation of Combustion Engineering's
12.340 NmVhr (12,000 scf m) prototype
scrubber using commercial lime as the
scrubber absorbent. The commercial
lime sludge contains a greater amount
of calcium sulfate, with 10 to 20 percent
of the sulfur products oxidized to the
sulfate form (Table 2). As a result, the
material dewatered considerably better
than the carbide lime sludge. Thickener
underflow was expected to contain 26
to 30 percent solids which field vacuum
filtration had been shown to dewater
the material to 50 percent solids.
-------
Table 2. Carbide and Commercial Lime Typical Analysis
(in % by weight unless noted otherwise)
Analysis
CaO
S02""
S03'c)
MgO
Alz03
FezOa
SiOz
NazO
KZ0
TiO2
COZ
cr
Cu (ppm)
Pb (ppml
Cd(ppm)
Hg (ppm)
As (ppm)
Se (ppm)
Commercial Lime Sludge
As Rec'd
40.53
8.63
36.42
0.17
2
<0.03
10
1
Mg Added
38.07
5.26
39.20
1.87
0.87
1.74
4.17
0.12
0.05
0.01
7.3
0.22
10
40
Carbide
Lime
Sludge
30.10
5.43
38.13
0.19
3.48
4.03
10.8
0.19
0.38
0.10
9.0
0.19
130
80
3
<0.03
3
1
Fly
Ash
1.71
0.75""
—
0.56
14.8
35.8
43.0
0.33
1.16
0.62
0.12
0.19
70
100
6
0.06
34
1
-------
define toxicity. These substances are
also regulated under EPA's National
Primary Drinking Water Standards
(Table 1).
Leachate analyses for all laboratory
samples are appended to the report. The
fixation reaction minimizes the release
of contaminants to the leachate as can
be seen by comparing the stabilized
sludge leachate analysis to a sludge and
sludge/fly ash mixture containing no
fixative (Table 5). In addition, the quality
of the leachates improved with time in
the stabilized mixtures, indicating that
the fixation reaction continues for some
period after initial placement. Several
mixtures had very low permeabilities,
and the necessary pore volumes were
never collected.
Based on the laboratory tests, 12
mixtures were chosen for further
evaluation under field conditions. The
field mixtures were chosen from labora-
tory samples which developed strengths
greater than 0.1 MPa(1 ton/ft2) and had
low permeabilities. Field mixtures are
identified by number in Table 3.
Field Demonstration
Scrubber and Pilot Waste
Handling System
Process Configurations
The FGD system at Paddy's Run Unit
No. 6 consists of two scrubber modules
which operate in parallel at full load.
Figure 2 shows the overall arrangement
of the scrubbing system during the
collection of the by-product used during
this study. Inlet SOa concentrations
were about 2000 ppm at a gas flow rate
of 180,000 NmVhr (175,000 acfm) with
the boiler at half load. A liquid/gas ratio
(L/G) of 7.5 l/Nm3 (28 gal./1000 cfm)
was maintained during the test program.
For Phase I (carbide lime), S02 removal
ranged between 75 and 83 percent. A
slurry inlet pH of 8 was controlled over
the 6-week period required to collect
and process sufficient by-product to fill
six impoundments.
During Phase II (commercial lime),
about 2000 ppm magnesium was added
to allow assessment of its effect on
system operation. The slurry inlet pH of
8 was maintained and S02 removal
exceeded 90 percent. The sludge by-
product was processed and all 10
remaining impoundments were filled
within a month.
A schematic flow diagram of the
waste material handling system used to
process the sludge during the field
demonstration phase is shown in Figure
3.
The entire thickener underflow was
pumped around a 244 m (800 ft)
circulation loop. A slip stream taken
Table 3. Laboratory Program Sludge Test Sample Identification
Field
Mix
1
2
3
5
6
4
7
8
9
10
11
12
Sample
No.
PI
P2
P3
P4
P5
P6
P7
P8
P9
P10
P11
P12
P13
P14
P15
P16
P17
P18
P19
P20
P21
P22
P23
P24
P25
Sludge
Composition
24% C.L
24% C.L.
42% C.L.
42% C.L
42% C.L
55% C.L.
55% C.L.
55% C.L
55% C.L
65% CaO
50% CaO
50% CaO
50% CaO
50% CaO
50% CaO
50% CaO
50% CaO
50% CaO
50% CaO
50% CaO
50% CaO
50% CaO
50% CaO
50% CaO
50% CaO
Fly
Ash
Sludge
Ratio
1:1
1:1
1:1
1:1
1:1
1:1
1:1
0:1
0:1
1:1
0.5:1
0.5:1
1.5:1
0.5:1
0.5:1
1.5:1
0.5:1
1:1
1:1
0.5:1
1:1
1:1
1:1
0.5:1
1.5:1
Fixative
5%C.L(a>
25% C.L.
5% C.L
15% C.L
% CaOlcl
None
3% C.L
None
5% CaO
None
3% P.C.""
10%P.C.
3%P.C.
3% CaO
10% CaO
3% CaO
5% P.C.
3%P.C.
5% P.C.
5% CaO
3% CaO
3% Ca(OHh(*
5% CaO
10% Ca(OH)2
3% Ca(OH)z
Permeability
cm/s
7.6 x 10's
8.5 x 10's
2.9 x 1Q-6
7.7 x 10~7
1.1 x 10'6
5.7 x 10'7
2. 1 x 10'7
3.9 x 1Q-*
4.5 x 1Q-7
7.0 x W6
1.4 x 10~5
2.9 x 10~*
2.5 x 1O'6
4.1 x ;o~6
2.3 x W*
5.7 x 10~7
3.5 x 10'5
5 x ;cr5
1.1 4 x 10~5
1.5x 10'5
2.94 x 10'B
9.2 x /O"6
1.05 x 10~*
1.8x W'5
3.8 x 1Q-*
60-Day
Unconfined
Compressive
Strength
MPa
0.78
0.50
0.86
1.40
2.40
Not
0.88
0.29
0.14
0.56
O.64
0.70
0.87
1.20
0.15
0.52
0.27
0.82
0.81
0.68
1.90
0.66
1.31
t/ft*
b
b
8.2
5.2
9.0
14.6
25.1
Tested
9.2
3.0
1.5
5.9
6.7
7.3
9.1
12.5
1.6
5.4
2.8
8.6
8.5
7.1
19.8
6.9
13.7
(a>Carbide lime.
""Too weak (soft) to test.
^Commercial lime.
'"'Portland cement.
^Commercial quicklime.
-------
Table 4. Leachate Analyses - Limits and Methods
(Determined on Both Laboratory and Field Samples
Detection Limit Method of
ppm Test
Calcium
Magnesium
Carbonate
Sulfite
Su/fate
Chloride
Copper
*Lead
*Cadmium
*Mercury
* Arsenic
*Selenium
Ca
Mg
C02
S03
S04
Cl
Cu
Pb
Cd
Hg
As
Se
0.05
0.01
1.0
1.0
1.0
0.05
0.02
0.001
0.01
0.001
0.001
0.001
Atomic Absorb.
Atomic Absorb.
COz Absorption Train
lodine-lodate Titration
Barium Perch/orate Titration
Mercuric Nitrate Titration
AA (flame)
AA (furnace)
AA (flame)
AA (flameless)
AA (furnace)
AA (furnace)
(Determined on Field Samples Only)
Iron
Zinc
*Chromium
Aluminum
Manganese
Sodium
Nickel
*Barium
"Silver
Fluoride
Boron
Beryllium
Vanadium
Nitrate
Fe
Zn
Cr
Al
Mn
Na
Ni
Ba
Ag
F
B
Be
V
NO3
0.03
0.004
0.01
0.1
0.01
0.002
0.04
0.1
0.01
0.01
0.1
0.01
1.0
1.0
AA (flame)
AA (flame)
AA (flame)
AA (flame)
AA (flame)
Emission
AA (flame)
AA (flame)
AA (flame)
Spec. Ion Elec.
Carminic Acid Color i metric
AA (flame)
AA (flame)
Brucine Sulfate Colorimetric
*ln RCRA list of contaminants.
from the loop was used to fill a 25.4
(10-in.) dia. x 3 m (10 ft) high sli
surge tank. The remaining slurry \
then returned to the vacuum fi
which is normally used to dewater
bulk solids prior to disposal. Th
processes were used to prepare
mixtures for disposal.
For Process I, the slurry was pum|
from the surge tank through a 3.8-
(1.5-in.) magnetic flowmeter directly
the mixer into which additive and f lye
were being metered.
In Process II, the sludge was <
watered in the filter press to produo
filter cake of the same solids content
the filter cake from the commerc
rotary vacuum filter. When remov
from the filter press, the filter cake 1
into a surge bin from which it w
metered into the mixer by a 15.2-cm |
in.) variable speed screw (VSS) convey
Fly ash and additive were simultaneous
metered into the mixer.
Process III was used to evaluate tl
use of a filter press operating at hii
pressure to dewater the sludge. T
filter press provides a means of obtainii
a much drier cake than can be obtaim
with a vacuum filter.
The filter cake was stabilized with 1
ash. All mixtures were discharged in
trucks, transported 11.2 km (7 mi.) tot!
Cane Run Plant, and placed in the te
impoundments.
Table 5. Laboratory Leachate Analyses
Sludge Only
55% Carbide Lime
0:1 Fly Ash to Sludge
No Fixative
Mix 7
65% Comm. Lime
1:1 Fly Ash to Sludge
3% P. C.
Mix W
50% Comm. Lime
1:1 Fly Ash to Sludge
No Fixative
Mix 9
50% Comm. Lime
1:1 Fly Ash to Sludge
3%CaO
Pore Volume #
Cont.
/jmhos/cm
pH
TDS (ppm)
Cl' (ppm)
SOs (ppm)
Cd (ppm)
Cu (ppm)
Pb (ppm)
Hg (ppm)
As (ppm)
SO; (ppm)
Ca (ppm)
Se (ppm)
Mg (ppm)
1 & 2
6850
7.8
4100
345
30
0.02
0.06
0.2
0.001
0.05
5390
260
0.023
—
5 &6
2500
7.5
1500
<5
—
<0.01
0.02
0.1
0.002
0.01
1960
300
0.002
—
/ & 2
2850
7.8
1700
10
40
0.02
0.02
0.1
0.018
0.03
1580
320
—
0.18
5 &6
2000
7.7
1200
15
—
<0.01
0.02
0.1
0.001
0.03
1470
300
0.003
0.16
1 &2
2550
9.2
1400
20
30
0.0 1
<0.02
—
0.002
0.007
1320
650
0.010
0.10
5 &6
575
8.0
345
<5
20
0.01
<0.02
—
0.002
0.003
218
110
<0.001
0.04
1 & 2 5 &6*
1800
9.3
1100
15
230
<0.01
<0.02
<0.1
0.001
0.01
440
6.7
0.008
0.02
(*}Due to low permeability of samples, pore volumes 5 & 6 were not available for 60 days of collection.
6
-------
To Stack
mu x
Makeup Water-
Scrubber Bottom
Upper Downcomer
Spray Water
Lower Downcomer
Spray Water
Flow Arrangement
for Carbide Lime and Commerical Lime Testing
Additive
Bottomless
Annulus
Filter Liquid
Filter Solids
Figure 2. Flow arrangement FGD system.
Field Impoundments
General Description
Two general criteria characterize
acceptable landfill disposal practice.
The landfill must (1) not cause contami-
nation of groundwater by leaching, or
surface water by runoff or erosion, and
(2) must provide a material with
minimum structural integrity.
Ten commercial above-ground swim-
ming pools and five large impoundments
(Figure 4) were used as monitored
disposal sites for sludge/fly ash mixtures.
Leachate samples were collected for
analysis 1 week after filling each
impoundment. Thereafter, leachate
was collected at 2- or 3-month intervals.
The leachate collection containers were
emptied and cleaned after each sampling
period. These leachates were analyzed
for dissolved ions including major and
trace constituents. In some instances,
either no leachate sample was produced
or insufficient sample was available to
allow complete analysis. In the latter
case, an analytical priority was estab-
lished to provide maximum information
from the available sample.
Using National Weather Service
precipitation data, the maximum water
which was available to percolate
through the test sites was calculated.
This amount of liquid available was
translated into pore volumes for each
test impoundment. Analysis of the
rainfall data indicates that the large
impoundments were exposed to 2.0 to
2.3 pore volumes of precipitation, while
the small impoundments had seen 3.0
to 3.7 pore volumes, after 600 days.
Thus, the laboratory leachate data
previously discussed would represent 4
to 6 years of comparable field impound-
ment leachate analysis. (Of course, in
many instances, runoff and surface
evaporation at the field sites reduced
the quantity of liquid prior to its passage
through the sludge; therefore, the pore
volume estimates for the field are high.)
Small Scale Impoundments
One type of disposal site consisted
of small scale impoundments (Figure 5).
The primary purpose of these test sites
was to provide a means of determining
the quality of the leachate and runoff
from the test mixtures under field
conditions. The small scale impound-
-------
ments were 10 lined above-ground
swimming pools with a capacity of
about 19 m3 (24 yd3). Four of these were
used for sludge mixtures from a
scrubbing system using carbide lime as
an absorbent and six for sludge from a
system using commercial lime.
The bottom 15.2 cm (6 in.) of each
pool contained non-reactive graded
gravel to facilitate collection of the
leachate. The leachate drained by
gravity to a collection tank.
Runoff was collected from the surface
of the small scale impoundments
through a gravel filter held in place by a
coarse screen. This procedure ensured
drainage regardless of the level to
which the sludge consolidated. The
runoff was analyzed for dissolved
species at the same intervals as
indicated for the leachate.
Large Scale Impoundments
The small scale impoundments
provided a convenient means of deter-
mining maximum leaching rates and
leachate quality without any interference
from local surroundings. In the actual
field site, the landfill will either absorb
or release moisture to the surrounding
soil. The large scale impoundment
areas provided a means of assessing the
impact of the disposal material in terms
of its effect on local soil moisture and
the quality (dissolved ions) of the
moisture in the soil and of the water in
the aquifer beneath the disposal sites.
Five large scale impoundment areas
were excavated, each with a capacity of
about 38 m3 (50 yd3). The disposal sites,
located in natural soil, are of two styles:
approximately 4.9 x 4.9 x 2.4 m (16 x 16
x 8 ft) tapers and 9.1 x 2.4x1.2m (30x8
x 4 ft) pits (Figure 6). Two contained
carbide sludge mixtures while the
remainder contained mixtures of com-
mercial lime sludge (Figure 4). Soil
moisture was monitored by suction
lysimeters located 15.2, 61.0, and
182.8 cm (6, 24, and 72 in.) beneath the
bottom of the test site.
Field Test Results
Strength
Table 6 lists the maximum compres-
sive strengths measured in the labora-
tory and field mixtures. Of the carbide
lime sludge mixtures, only Mix 2
(vacuum filtered sludge, fly ash, and
fixative) developed a compressive
strength >0.10 MPa (1.0 tons/ft2) at all
depths to provide an acceptable landfill
material. Mix 1 (thickener underflow, fly
ash, and fixative) developed a hard
surface crust, but the underlying
mixture could not support any signifi-
cant load. Mix 4 (sludge and fixative, but
no fly ash) did not develop sufficient
strength to provide an acceptable
landfill; in fact, the initial strength of this
mixture, 0.15 MPa (1.5 tons/ft2), was
significantly reduced during the test
program, probably due to freeze/thaw
effects.
All but Mix 7 of the commercial lime
sludge mixtures developed compressive
strengths greater than the 0.28 MPa (3
tons/ft2) capacity of the in-situ vane
shear device. After less than 6 weeks of
placement, Mix 7, the only commercial
lime-sludge/fly-ash mixture which did
not contain a fixative, exhibited little
tendency toward cementitious properties.
The core samples collected for laboratory
strength tests on this mix were extremely
sensitive to disturbance and the samples
were very friable and brittle. Although
core samples collected from the other
commercial lime mixtures all showed
some degree of disturbance due to
sampling, the compressive strength
tests in the University of Louisville
laboratory indicated that cementitious
reactions had occurred to some extent
\
y Circulation Loop
/
in all the commercial lime-sludge/f
ash/fixative mixtures (Mixes 8-12). T
highest strengths measured on cc
samples were from Mix 10 which us
Portland cement as the fixative. Tf
mixture formed a hard surface crust ai
appeared to be very resistant
weathering.
Because of the large degree
disturbance which occurred in the co
samples from the high strength mixture
additional in-situ plate load streng
tests were run on two commercial lirt
mixtures (11 and 12), to better defir
actual in-place strength. In the test c
Mix 12, in large impoundment 4, a tot
load of 1.34 MPa (14 tons/ft2) caused
settlement of 3 cm (1.2 in.), indicatir
that this material would be capable <
bearing significant foundation load
Mix 11, in large impoundment 5, als
showed significant load bearing capacit
Several cycles of loading were applie
with loads up to 1.32 MPa (13.
tons/ft2); the net settlement after th
loads were removed was 2.8 cm (1.
in.). The behavior of Mix 11 under th
plate load tests indicated that thi
material would be able to bear very hig
foundation loads.
Mix 6, in small impoundment 4, wa
transported to the field site in a cemer
To Vacuum Filter
'Filtrate to Drain
Process 1 Only
Vibrator Lime Bin
Bin
f\
Fly
A si-
Bin
High Volume
Pumps
High Pressure Variable Speed
Pump Screw Conveyor
U Variable Spee<
Mixer Screw Conveyc
T Trucks to Disposal
Figure 3. Waste material handling system.
-------
36 -50 56 - 65 49 - 60
40% 56% 60%
In Place Actual Percent Mix Solids
Range
Actual Batch Mix Rec Range
56 -59 45 - 70 55 - 78
Theor.
71% 72% 61% 67%
60 - 80 64 -68 58 - 65
67% 67% 79%
% Solids 24%
F.-S -1:1
Fixative - 5%
- C.L
Batches Cont.
(26)
(Continuous Mix)
C.L = carbide lime
P. C. = port/and cement
Pit 2
Mix No. 2
(85)
(71)
Pit 4
Mix No. 12
Pit 5
Mix No. 11
(110)
(99)
Pit 6
(Empty)
Filter
Batches
Pool Capacity 25 yds.3
Pit Capacity 50 yds.3
Figure 4. Sludge impoundment sites.
mix truck. This experiment was unsuc-
cessful, resulting in the need to add
large quantities of fly ash in order for the
sludge material to discharge from the
truck. The resulting large "snowballs"
froze and disintegrated upon thawing.
Consequently, physical tests were not
performed on Mix 6.
In summary. Process II mixtures
(containing rotary drum vacuum filter
cake, fly ash, and fixative) provided the
optimum combination of maximum
compressive strength and low perme-
ability for the environmentally safe
impoundment of both carbide lime and
commercial lime sludges as landfill. On
the other hand. Process I, utilizing
thickener sludge at 24 percent solids,
was too soft for acceptable landfill. In
addition, mixtures compounded with
filter press (high solids) sludge (Process
III) were brittle, gained little in com-
pressive strength with time, and thus
Vinyl Liner
Screen and Gravel
Filter for Run Off
Collection
Non-Reactive Gravel
Figure 5.
Primary
Leachate
Collection
Reservoir
Small scale impoundments (pools).
9
Ik
'•""•*>"* •••«*•"
Secondary
Leachate
Collection
Reservoir
Run Off
Collection
Reservoir
-------
are not considered acceptable as
landfill.
Permeability
The severe disturbance which
occurred in the core samples made it
difficult to obtain a valid sample for
permeability testing from the field
mixtures. However, for the core samples
tested, it appears that the permeability
of the field mixtures is within an order of
magnitude of that measured on corre-
sponding mixtures during the laboratory
phase. Proper compaction during place-
ment of the field mixtures is a strong
8 feet
(2.4 m)
factor in the reduction of permeability.
In some mixtures (particularly those in
the above-ground pools) where com-
paction was not adequate, the in-situ
mass permeability may be higher than
measured on the core samples. In an
actual full scale landfill operation,
conventional compaction equipment
would be used to ensure that a specified
density is obtained.
As with the laboratory test samples,
an inverse relationship between per-
meability and unconfined compressive
strength was noted for the core samples
(Figure 7).
Pits 1 - 3
Lysimeter
Locations
Side View
16 feet
~(4.9 m)'
o oo I
16 feet
(4.9 m)
Plan View
Pits 4 & 5
8ft
(2.3 m)
Plan View
Lysimeter Locations
Side View
Figure 6. Schematic-large scale impoundments (pits).
10
Leachate Analysis
Major Constituents—
Mix 1 (consisting of carbide Mr
sludge thickener underflow, fly ash, a
lime— Process I mixture) produced t
poorest quality leachates throughc
the field study. This mixture was plac
at «=35-50 percent solids. The leachat
collected from the small above-groui
impoundments contained 1000-5CK
ppm dissolved solids, with an average
approximately 3000 ppm. The sc
moisture samples collected beneath tl
large in-ground impoundments co
taining Mix 1 showed that son
contaminants were leaching from tf
sludge mixture into the underlying so
Initial soil moisture samples collect*
15.2 cm (6 in.)belowthe large impouni
ment contained approximately 40C
ppm of dissolved solids, similar to th
leachates from the small impoundmen
A gradual decrease in dissolved solic
concentration occurred in the so
moisture samples with time and deptl
indicating that some attentuation <
contaminant impact on groundwatt
was provided by the underlying soil.
7x70
1x10
0 0.10.20.30.40.50.60.70.80.91.
UCC - MPa
Figure 7. Permeability vs uncon-
fined compressive strength.
-------
Table 6. Comparison of Field and Laboratory Results of Physical Testing
Process
Sample
Maximum Compressive Strength
MPa
(tons/ft2)
Minimum Permeability
cm/s
1
II
III
III
III
II
II
II
II
II
Identification
Location
Mix 1
Pit 1
Mix 2
Pit 2
Mix 4
Pool 2
Mix 6
Pool 4
Mix 7
Pool TO
Mix 8
Pit 3
Mix 9
PoolS
Mix 10
Pool 9
Mix 11
PitS
Mix 12
Pit 4
Lab
60 days
too soft
(too soft)
0.78
18.2)
0.88
(9.2)
2.4
(25. 1)
0.29
(3.0)
0.69
(7.2)
1.10
(11.6)
0.52
(5.5)
0.81
(8.5)
0.68
(7.1)
Field
(In-Situ)
Initial
<0.01
0.12
(1.2)
0.24lcl
(2.2)
0.06
(0.6)
>O.2S'bl
(3.2)(c}
0.22'c)
(2.0)
0.26
(2.7)
Final
0.15
(1.6)
>0.28
(>3.0)
0.12
(1.2)
lal
la)
0.27
(2.8)
>0.2S(bl
(>3.0)
>0.2Slbl
(>3.0)
XJ.2S""
(>3.0)
X>.2S'bl
(>3.0)
>0.2S(bl
03.0)
Field
(Core)
Initial
too soft
(too soft)
0.02
(0.2)
0.01
(0.1)
la)
la)
0.07
(0.1)
0.09
(0.9)
0.03
10.3)
0.31
(3.3)
0.10
(1.D
0.10
(1.1)
Final
0.04
(0.4)
0.10
(1.1)
0.03
(0.3)
la)
la)
0.07
(0.8)
(Brittle)
0.14
0.26
(2.8)
0.48
(5.0)
0.15
(1.6)
0.20
(2.1)
Lab
60 days
7.6x10's
2.9x10'6
4.5x10'7
2.1 x10'7
7.0x1 Q-*
4.1 xW6
5.7 xlQ-7
5x1 0'5
2.9x1 0'6
9.2x10'*
Field
(Core)
3x1 Q-5 (724 days)
3.8x10^(661 days)
5.2x10'6 (664 days)
(al
too brittle
0.9x1 0~* (464 days)
4,5x1 0~* (59 days)
1.5x10'* (41 7 days)
1. 2x1 O'6 (466 days)
1. 8x1 0~* (452 days)
Ial/Vof tested in field-spheres from "cement mixing" truck at start.
^Strength exceeded capacity of vane shear test device.
(c)
No initial test (Measured at 48 days).
Process II mixtures consisted of a
sludge dewatered to a solids content
obtainable by rotary drum vacuum
filtration with fly ash and fixative in
various proportions. Due to the superior
filtration properties of commercial lime
sludges, these mixtures were placed at
higher solids contents than the Process
II carbide-lime/sludge mixture. Com-
mercial-lime/sludge mixtures varied
from 58 to 70 percent solids, depending
on fly ash addition, while the single
carbide-lime/sludge Process II mixture
was placed at approximately 54 percent
solids. Solids content at placement had
a strong impact on the ability to compact
the mixtures; and subsequently, on the
permeability of the test site.
The quantity of leachate collected
from the small impoundments contain-
ing Process II mixtures was significantly
lower than from the Process I mix. In
general, no leachate samples were
available from the small above-ground
impoundments containing Process II
mixtures until 2 - 3 months after place-
ment; and, in several cases, no leachate
was produced during the test period.
Leachate quality varied among the
Process II mixtures due to the ratio of fly
ash: sludge, type of fixative, and the
degree of compaction achieved during
initial placement. In many cases, it is
difficult to differentiate these effects.
However, a comparison between Mixes
8, 9, and 11 indicates the trend. All
three mixtures were made with com-
mercial lime sludge, fly ash, and lime as
a fixative: Mix 8 contained a fly
ash/sludge ratio of 0.5:1.0; Mix 11,
1.0:1.0; and Mix 9, 1.5:1.0. The addi-
tional fly ash in Mix 11 allowed greater
compaction than Mix 8, enhanced
fixation, and resulted in a mixture with
lower quantities of leachate generation.
In Mix 9, however, concentrations of
dissolved solids and other contaminants
were higher than those measured in
either Mix 8 or 11. Thus, there appears
to be an optimum proportion of fly ash
(1:1 fly ash/sludge in this case) beyond
which leachate quality begins to degrade.
Process II carbide-lime/sludge mixture
2 contained vacuum filter sludge cake,
fly ash, and carbide lime fixative.
Leachates were available from the
small above-ground impoundment 180
days after placement. The initial
leachate samples contained «=5000
ppm dissolved solids; subsequent
leachate samples contained less than
1000 ppm. Soil moisture samples from
beneath the in-ground impoundment
containing Mix 2 showed a release of
dissolved solids to the groundwater
slightly lower than from Process I
carbide-lime/sludge Mix 1.
Two Process III mixtures were pre-
pared with carbide-lime/sludge and
one with commercial-lime/sludge.
Unfortunately, problems with the sam-
pling equipment prevented the collection
of leachate from the commercial lime
sludge Process III mixture.
Trace Elements—
Trends in trace element concentra-
tions between various sludge mixtures
were more difficult to discern than
those of major constituents due to the
lower accuracy inherent in the analysis
of these elements in the parts per billion
range. In many cases, trace element
concentrations were below detectable
-------
limits or below background levels (as
determined by rainwater and ground-
water analysis).
Mix 1, the Process I carbide-lime/
sludge mixture, produced the leachates
with the highest levels of trace con-
taminants during the study. For example.
Figure 8 compares the concentration of
one trace metal, arsenic, in leachates
from Mix 1 and two Process II mixtures,
Mixes 8 and 11. However, it is important
to note that the concentration of trace
elements in all leachates and soil
moisture samples collected in this study
was belowthat established under RCRA
for defining hazardous wastes. Thus, on
the basis of toxicity, all of the sludge
mixtures tested would be designated
non-hazardous.
Summary of Leachate Analysis
Results—
Based on an evaluation of both major
and trace contaminants measured in
the leachate tests, the following results
were evident:
1. Leachate generation decreased
with time for those mixtures which
were designated—Proceses II and
III. Leachate quality improved with
increasing dryness up to an opti-
mum mixture dryness at place-
ment, beyond which the material
became brittle, permeability in-
creased, and (thus) leachate gen-
eration increased.
2. The quantity of leachate from the
low-solids Process I mixture de-
creased initially, then remained
fairly constant during the test
period. This mixture produced the
poorest quality leachates of the
field study.
3. Soil moisture quality beneath the
large impoundments containing
Process II mixtures increased with
time, indicating a reduction in
leachate generation. Also, quality
increased with depth below the
impoundment, indicating some
physical filtering or chemical ion
exchange reaction with the sur-
rounding soil.
4. The concentration of trace ele-
ments found in the collected
leachate and soil moisture samples
was below RCRA limits through-
out the testing.
The complete data base of all leachate
samples collected from the field test
sites is appended to the report.
References
1. Jones, J.L. (EPA/IERL-RTP) letter to
A.L Plumley, January 8, 1979.
2. Taylor, W.C. Experience in Disposal
and Utilization of Sludge from Lime/
Limestone Scrubbing Processes. In
Proceedings, Flue Gas Desulfuri-
zation Symposium, 1973, EPA-
650/2-73-038 (NTIS PB 230901),
December 1973.
3. Taylor, W.C. and Haas, J.C. Potential
Uses of the By-Product from the
Lime/Limestone Scrubbing of SOz
from the Flue Gases. Presented at
the American Institute of Mining,
Metallurgical and Petroleum Engi-
neers 1974 Annual Meeting, Dallas,
Texas, February 23-28, 1974. Com-
bustion Engineering Publication TIS-
3774A.
4. Haas, J. C. and Ladd, K. Environmen-
tally Acceptable Landfill from Air
Quality Control Systems Sludge.
Presented at Frontiers of Power
Technology Conference, Oklahoma
State University, Stillwater, Okla-
homa, October 1974; Combustion
Engineering Publication TIS-4216.
5. Klym, T. W. and Dodd, D. J. Landfill
Disposal of Scrubber Sludge. ASCE
Annual and National Environmental
Engineering Convention, Kansas
City, Missouri, October 1974.
6. Haas, J. C. and Lombardi, W. J.
Landfill Disposal of Flue Gas Desul-
furization Sludge. Presented at
NCA/BCR Coal Conference and
Expo III, Louisville, Kentucky, Octo-
ber 19-21, 1976. Combustion Engi-
neering Publication TIS-4926.
7. Rossoff, J. et al. Disposal of By-
Products from Nonregenerable Flue
Gas Desulfurization Systems: Second
Progress Report, EPA-600/7-77-
052 (NTIS PB 271728), May 1977.
8. Resource Conservation and Recovery
Act of 1976, PL94-580, October 21,
1976. Federal Register, May 19,
1980, Section 261.24.
9. Van Ness, R. P. et al. Field Studies in
Disposal of Air Quality Control
System Wastes. Presented at the
Third Annual Conference on Treat-
ment and Disposal of Industrial
Wastewaters and Residues, Hous-
ton, Texas, April 1978. Combustion
Engineering Publication TIS-5485.
10. Mohn, N. C. et al. Environmental
Effects of FGD Waste Disposal — A
Laboratory/Field Landfill Demon-
stration. In Proceedings: Symposium
on Flue Gas Desulfurization, Las
Vegas, Nevada, March 1979, Volume
II, EPA-600/7-79-167b (NTIS PB I
133176), July 1979.
12
-------
0.05
0.04
0.03
ppm
0.02
0.01
n n
Small Impoundment - 1
3 Mix 1
.
o
n n
\\ NS NS NS
II II
|| | | 1 1
/
t
f
i
t
/
t
t
.
NS
1
NS
n i
i i ii i
30 60 90 180 270 360 450 540 630 720
Days
0.05
0.04
0.03
ppm
0.02
0.01
°-°c
Small Impoundment - 6
Mix 8
NS NS NS NS W NS „ NS NS NS
i n • n i i n i i i i
30 60 90 180 27O 360 450 540 630 720
Days
0.05
0.04
O.O3
ppm
0.02
0.01
0.0 (
Small Impoundment - 7
Mix 1 1
-
-
NS NS NS NS NS NS PI WS NS NS
I 1 1 I i III i i i
30 60 90 180 270 360 450 540 630 720
Days
Key: CZ1 = Runoff
VT7A = Primary Leachate
NS = No Sample in Reservoir
Figure 8. Leachate and runoff samples - Mix 1, 8, & 11, arsenic fRCRA limit 50 ppm).
13
-------
R. VanNess is with Louisville Gas and Electric Co., Louisville, KY 40232;
A. Plumley and N. Mohn are with Combustion Engineering, Inc.. Windsor, CT
06095; C. Ullrich and D. Hagerty are with the University of Louisville,
Louisville, KY 40232.
Julian W. Jones is the EPA Project Officer (see below).
The complete report, entitled "Pilot Field Studies of FGD Waste Disposal at
Louisville Gas and Electric," (Order No. PB 82-105 479; Cost: $23.00, subject
to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at
Industrial Environmental Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
14
U. S. GOVERNMENT PRINTING OFFICE: I98I/559-092/3333
-------
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