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.

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 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.

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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

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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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