U.S. Environmental Protection Agency Industrial Environmental Research E PA-600/7-77-051
Office of Research and Development Laboratory
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Research reports of the Office of Research and Development, U.S.
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EPA-600/7-77-051
May 1977
AN EVALUATION OF THE DISPOSAL
OF FLUE GAS DESULFURIZATION WASTES
IN MINES AND THE OCEAN:
Initial Assessment
by
R.R. Lunt, C.B. Cooper, S.L. Johnson,
J.E. Oberholtzer, G.R. Schimke, and W.I. Watson
Arthur D. Little, Inc.
Acorn Park
Cambridge, Massachusetts 02140
Contract No. 68-03-2334
Program Element No. EHE624A
EPA Project Officer: Julian W. Jones
Industrial Environmental Research Laboratory
Office of Energy, Minerals, and Industry
Research Triangle Park, N.C. 27711
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Washington, D.C. 20460
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ABSTRACT
This report presents an initial assessment of the feasibility of the
disposal of flue gas desulfurization wastes in mines and in the ocean.
The study was conducted by Arthur D. Little, Inc. for the Industrial
Environmental Research Laboratory of the U.S. Environmental Protection
Agency under Contract No. 68-03-2334. The purpose of the assessment was
to evaluate the environmental, technical, regulatory, and economic aspects
of the use of such disposal sites. As a part of this study, available
data on the chemical and physical properties of both treated and untreated
sludges generated in ongoing governmental and privately funded sludge
characterization programs were also collected and summarized. The report
is based upon data available through January 1976.
This assessment represents the first phase of a three-phase program.
The second phase of work involves a refinement of the initial assessment
based upon laboratory tests focused on key disposal impact issues. The
third phase will involve a demonstration/simulation testing of viable mine
and ocean disposal alternatives. Future reports will be issued covering
these later phases of the work.
iii
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TABLE OF CONTENTS
PAGE
ABSTRACT ill
LIST OF TABLES vii
LIST OF FIGURES ix
ACKNOWLEDGMENTS xi
CONVERSION FACTORS xii
I. INTRODUCTION 1
A. BACKGROUND 1
B. PURPOSE AND OBJECTIVES OF THE STUDY 4
C. CONTENT OF THE REPORT 6
REFERENCES 7
II. CONCLUSIONS AND RECOMMENDATIONS 9
A. MINE DISPOSAL 9
B. OCEAN DISPOSAL 15
III. EXECUTIVE SUMMARY 21
A. CHEMICAL AND PHYSICAL CHARACTERISTICS OF FGD SLUDGES .... 21
B. MINE DISPOSAL 23
C. OCEAN DISPOSAL 37
D. ECONOMICS OF CONCEPTUAL DISPOSAL SYSTEM DESIGNS 48
REFERENCES 50
IV. CHARACTERISTICS OF FGD SLUDGES 51
A. CHEMICAL CHARACTERISTICS OF UNTREATED FGD SLUDGES 51
B. PHYSICAL AND ENGINEERING PROPERTIES OF UNTREATED FGD
SLUDGES 60
C. EFFECTS OF TREATMENT ON THE PHYSICAL AND ENGINEERING
PROPERTIES OF FGD SLUDGES 69
D. EFFECTS OF TREATMENT ON POLLUTANT MIGRATION FROM FGD
SLUDGES 73
REFERENCES 81
V. MINE DISPOSAL OF FGD SLUDGE 83
A. REVIEW OF THE MINING INDUSTRY 83
B. DISPOSAL OF FGD SLUDGE IN SURFACE COAL MINES 109
C. DISPOSAL OF FGD SLUDGE IN UNDERGROUND MINES 132
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TABLE OF CONTENTS (Continued)
PAGE
D. DISPOSAL OF SLUDGE IN SELECTED UNDERGROUND MINERAL MINES . . 157
E. FGD SLUDGE AS A TAILINGS AMENDMENT 162
F. ASSESSMENT OF THE TECHNOLOGY 171
G. ASSESSMENT OF REGULATORY ENVIRONMENT RELATIVE TO FGD
SLUDGE DISPOSAL , 189
H. CONCLUSIONS AND RECOMMENDATIONS 207
GLOSSARY 213
REFERENCES 216
VI. OCEAN DISPOSAL 219
A. DESCRIPTION OF OCEAN ENVIRONMENT 219
B. DESCRIPTION OF THE REGULATORY ENVIRONMENT 229
C. FATE AND EFFECTS OF FGD SLUDGES ON THE CONTINENTAL SHELF . . 235
D. FATE AND EFFECT OF FGD SLUDGES IN THE DEEP OCEAN 255
E. ASSESSMENT OF TECHNOLOGY 260
F. CONCLUSIONS AND RECOMMENDATIONS 281
GLOSSARY 284
REFERENCES 288
VII. DISPOSAL SYSTEM COSTS 291
A. BASIS FOR DESIGN AND ECONOMICS 291
B. COAL MINE DISPOSAL 291
C. OCEAN DISPOSAL 300
vi
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LIST OF TABLES
TABLE NO. PAGE
1-1 Projected Sludge Production 4
IV-1 Major Components in FGD Sludge Solids 53
IV-2 Concentrations of Trace Elements in FGD Sludges 56
IV-3 Levels of Chemical Species in FGD Sludge Liquors and
Elutriates 58
IV-A True and Bulk Densities of FGD Sludge Solids 63
IV-5 Permeabilities of Untreated FGD Sludges 67
IV-6 Effect of Sludge Treatment on Bulk Density 71
IV-7 Effect of Sludge Treatment on Permeability 72
IV-8 Unconfined Compressive Strengths of Treated FGD Sludges .... 74
IV-9 Comparison of the Chemical Constituents in Sludge Liquors
with Leachate after 50 Pore Volume Displacements 78
IV-10 Comparison of the Chemical Constituents in Eastern Limestone
Sludge Leachate with Chemfix Chemically Treated Sludge
Leachate 79
V-l Land Utilized and Reclaimed by the Mining Industry in the
United States in 1930-71 and 1971, by Selected Commodity ... 84
V-2 Production of Bituminous Coal and Lignite in U.S. by Region
Underground, Strip and Auger Mining (1973) 88
V-3 Number of Coal Mines by States (1973) 89
V-4 Number of Domestic Metal and Nonmetal Mines in 1973, by
Commodity and Magnitude of Crude Ore Production 97
V-5 Production of Ore in the U.S. by Mining Method - 1971
for the Major Mineral Commodities 98
V-6 General Types of Metal and Nonmetal Mines as Related to
Geologic Nature of Deposits 100
V-7 Coal Mines - Screening for Acceptability for FGD Disposal . . . 105
V-8 Metal and Nonmetal Mines - Screening for Acceptability
for FGD Disposal 106
vii
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LIST OF TABLES (Continued)
TABLE NO. . PAGE
V-9 Mine Drainage Classes 149
V-10 Comparative Properties of Potential Tailing Amendments .... 170
V-ll Comparison of Water Quality Criteria and Practical Range
of Measurement Methodology 186
VI-1 Major Constituents of Seawater 222
VI-2 Toxic Heavy Metals of Importance in Marine Pollution Based
on Their Seawater Concentration and Toxicity 223
VI-3 Approved Interim Ocean Dumping Sites, East and Gulf Coasts . . 226
VI-4 Trace Contaminant Concentrations in Reported Sludge Liquors
from Eastern Coals and NAS Minimal Risk Criteria for the
Marine Environment 249
VI-5 Concentrations of Trace Elements in Sludge Solids and
"Minimal Risk Criteria" 252
VII-1 Sludge Basis for Conceptual Design 292
VII-2 Capital Cost Basis (1978 Completion) 293
VII-3 Unit Cost Factors 294
VII-4 Capital and Operating Costs for Mine Disposal Alternatives . . 301
VII-5 Capital and Operating Costs for Ocean Disposal Alternatives
(Bottom-Dump Disposal) 306
viii
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LIST OF FIGURES
FIGURE NO. PAGE
1-1 Power Plants in the U.S. over 100 Mw in Size Having Coal
Burning Capability (1975) 2
IV-1 Particle Size Distribution of FGD Sludges 61
IV-2 Viscosity of Desulfurization Sludge 65
IV-3 Relationship between Compressive Strength and Curing Time
for Sludge Treated with Fly Ash and Quicklime (Ontario Hydro) . 75
IV-4 Relationship between Compressive Strength and Curing Time
for Sludge Treated with Fly Ash and Cement (Ontario Hydro) . . 76
V-l Coal Fields of the United States 85
V-2 Mining Methods Used in U.S. Bituminous Coal Production .... 87
V-3 Area Strip Mining with Concurrent Reclamation 90
V-4 Contour Coal Stripping 92
V-5 Block Methods of Contour Strip Mining 93
V-6 Types of Underground Coal Mines 94
V-7 Area Coal Stripping Ill
V-8 Cross Section - Operating Strip Coal Mine 112
V-9 Cross Section - Western Strip Mine 115
V-10 Contour Backfill 118
V-ll Regional Groundwater Movement in Surface Coal Mines 123
V-12 Conventional Room and Pillar Coal Mining Main Haulage -
Conveyor 134
V-13 Typical Longwall Mining Cross-Sections Showing Caving Action . 135
V-14 Longwall Stowing - Conventional 138
V-15 Plan - Room and Pillar Mine 140
V-16 Seismic Risk Areas and Fault Zones in the United States .... 144
V-17 Regional Groundwater Movement in Sealed Underground Mines . . . 153
ix
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LIST OF FIGURES (Continued)
FIGURE NO. PAGE
V-18 Blind Hydraulic Flushing of Abandoned Lead-Zinc Mine 159
V-19 Longwall Stowing - Lateral 183
VI-1A Atlantic Coastal Waters and Dump Sites 220
VI-1B Gulf Coastal Waters and Dump Sites 221
VI-2 Pathways of Interactions in a Simplified Ocean Dumping
Scenario 227
VI-3 Schematic Diagram Showing Transport Processes - Hinged
Bottom-Dump Barge 236
VI-4 Observed Sulfite Oxidation Rates 246
VI-5 Factors Contributing to the Cumulative Distribution of
Dumped Sludge 256
VII-1 Surface Mine Disposal Operations 295
VII-2 Underground Mine Disposal Operations 298
VII-3 Ocean Disposal Operations 302
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ACKNOWLEDGMENTS
This study was conducted by Arthur D. Little, Inc. (ADL) for the
U. S. Environmental Protection Agency under Contract No. 68-03-2334. The
report reflects the work of many members of the ADL staff, consultants,
and subcontractors. Those participating in the study are listed below.
Principal Investigators (ADL):
Richard R. Lunt, Project Manager
Charles B. Cooper, Ocean Assessment
Sandra L. Johnson, Mine Assessment
James E. Oberholtzer, Sludge Characterization
Gerald R. Schimke, Ocean Technology
William I. Watson, Mine Technology
Contributing Staff (ADL):
John H. Cawley Ralph A. Home
Lawrence N. Davidson Charles R. LaMantia
Paula J. Didricksen Edward G. Pollak
Joan E. Harrison Phillip S. Thayer
Theodore P. Heuchling James R. Valentine
Consultants and Subcontractors:
John T. Gormley, et al. (D'Appolonia Consulting Engineers, Inc.)
D. Joseph Hagerty and C. Robert Ullrich (University of Louisville)
Bostwick H. Ketchum (Woods Hole Oceanographic Institute)
Donald Langmuir (Pennsylvania State University)
Guy C. McLeod (New England Aquarium)
William J. Seevers, et al. (Geraghty and Miller, Inc.)
Many other individuals and organizations have made significant
contributions to this study. In particular, we wish to acknowledge
Julian W. Jones, the EPA Project Officer, for his guidance throughout the
course of this work and his invaluable assistance in the preparation of
this report. We would also like to thank Robert E. Landreth of the
Municipal Environmental Research Laboratory, U. S. Environmental Protection
Agency for his continuing support and advice; and Jerome Rossoff and
Ronald C. Rossi of the Aerospace Corporation and Jerome L. Maloch of the
U. S. Army Engineer Waterways Experiment Station for their cooperation in
providing and interpreting data on sludge characteristics.
xi
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CONVERSION FACTORS
English/American Units
Length:
1 inch
1 foot
1 fathom
1 mile (statute)
1 mile (nautical)
Area:
1 square foot
1 acre
Volume:
1 cubic foot
1 cubic yard
1 gallon
Weight/Mass:
1 pound
1 ton (short)
Pressure:
1 pound per square inch
Concentration:
1 part per million (weight)
Speed:
1 knot
Energy/Power:
1 British Thermal Unit
1 megawatt
Temperature:
1 degree Fahrenheit
Metric Equivalent
2.SAO centimeters
0.3048 meters
1.829 meters
1.609 kilometers
1.852 kilometers
0.0929 square meters
4,047 square meters
28.316 liters
0.7641 cubic meters
3.785 liters
0.4536 kilograms
0.9072 metric tons
0.07031 kilograms per square centimeter
1 milligram per liter
1.853 kilometers per hour
1,054.8 Joules
3.600 x 109 joules per hour
5/9 degree Centrigrade
xii
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I. INTRODUCTION
A. BACKGROUND
There are now more than 1,000 fossil fuel-fired steam electric
plants operating in the United States. Of the total generating capacity
amounting to well over 300,000 megawatts, roughly 200,000 megawatts have
been designed to fire coal either exclusively or as an option with oil
and/or gas. The map in Figure 1-1 shows the distribution of plants over
100 megawatts in the United States as of 1975 that have the capability of
firing coal. The plants shown include all those originally designed to
burn coal, except for those which are known to have been converted to
either oil or gas burning exclusively (primarily plants in eastern
metropolitan areas, such as New York City).
The vast majority of the coal-fired capacity is located in the
eastern section of the country, an area rich in high sulfur coal. For
the most part, eastern plants have burned locally available high sulfur
coal. In recent years low sulfur has accounted for less than 30% of the
total coal burned in eastern power plants. More than half of the eastern
low-sulfur coal has been channeled into metallurgical markets.
A number of studies have been conducted in the last five years to
project the need for flue gas desulfurization (FGD) systems to control
emissions of S02 and determine the capability of equipment suppliers to
meet these needs (1,2,3,4). These studies have generally focused on coal-
fired capacity because of the increasing use of coal, uncertainty in the
oil supply situation, and the greater ease with which oil-fired plants
can switch to low-sulfur oil, if available. In 1975 the U.S. Environmental
Protection Agency (EPA) estimated the cumulative need for FGD systems on
utility boilers to be about 65,000 megawatts of coal-fired generating
capacity (1), and that by the end of 1980 the need would rise to about
90,000 megawatts. Taking into account industrial boilers and oil-fired
plants, the need could easily exceed 100,000 megawatts by 1980.
However, the installation of FGD systems is expected to lag behind
this anticipated need. Presently the capacity of operational FGD systems
totals less than 6,500 megawatts. And, based upon current trends, the
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N)
FIGURE 1-1 POWER PLANTS IN THE U.S. OVER 100 Mw IN SJZE HAVING COAL BURNING CAPABILITY (1975)
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capacity of operational FGD systems may reach only about 35,000
megawatts by 1980. By 1985, the figure could exceed 100,000 megawatts.
Better than 90% of the FGD capacity now in service and under
construction involves non-regenerable (waste producing) FGD technology,
a trend which is expected to continue through 1985. The principal non-
regenerable systems produce solid waste (sludge) and fall into the
following four general categories: direct lime scrubbing, direct
limestone scrubbing, fly ash scrubbing, and dual alkali systems (scrub-
bing with a soluble sodium absorbent followed by regeneration of the
absorbent with lime).
Both the character and quantity of the sludge produced by these
systems vary widely depending upon the operating conditions of the
boiler, the sulfur content of the coal, and the type and design of the
scrubber system. In general, the sludge consists of mixtures of calcium
sulfate (as CaSOi* • 2H20 or CaSCi* • 1/2H20), calcium sulfite (as
CaSOa • 1/2H20), and lesser amounts of unreacted lime or limestone, as
well as small but significant quantities of soluble constituents (e.g.,
calcium and sodium salts). Many also contain fly ash which can be
simultaneously removed with S02 in the scrubbers and/or admixed with
the S02 scrubber sludge.
The amount of dry, ash-free sludge can range from as low as about
40 Ibs/megawatt-hour (<5% by weight of the coal burned) in low-sulfur
coal applications to greater than 160 Ibs/megawatt-hour (<20% by weight
of the coal burned) for high-sulfur coal applications. Table 1-1 shows
projections of sludge production for the years 1980 and 1985, assuming
35,000 megawatts and 100,000 megawatts installed, capacity, respectively.
Assuming an average annual load factor for all plants of 70%, the amount
of wet sludge including fly ash (50% solids) would total about 40 million
short tons in 1980 and about 110 million short tons in 1985. These
figures are based upon a distribution of FGD system by capacity of
roughly 50% limestone, 40% lime and dual alkali, and 10% fly ash scrubbing.
This distribution reflects the increasing use of limestone scrubbing sys-
tems, particularly in medium- and low-sulfur coal applications.
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TABLE 1-1
PROJECTED SLUDGE PRODUCTION
Year 1980 1985
Assumed On-Line Capacity (Mw) 35,000 100,000
Dry FGD Sludge (thousands of short tons/year) 8,500 24,500
Dry Ash (thousands of short tons/year) 10,500 30,000
Total Dry (thousands of short tons/year) 19,000 54,500
Water (@ 50%) (thousands of short tons/year) 19,000 54,500
Total Wet Sludge (thousands of short tons/year) 38,000 109,000
Approximate Total Volume (acre-feet/year) ^20,000 ^60,000
A principal concern with the widespread application of non-regenerable
systems is the disposal of the large quantities of sludge produced.
Most utility installations of nonregenerable FGD systems now in operation
in the United States employ disposal methods involving some form of on-
site ponding or impoundment of the sludge. The earliest systems used
unlined disposal areas. Many recently installed systems use lined areas,
and some include chemical treatment of the wastes to improve structural
properties and reduce the mobility of potential pollutants. Aside from
the possible adverse chemical/biological impacts, the use of ponds, land-
fills', and impoundments may be limited by the large tracts of land required,
land that may not be readily available. Depending upon the sulfur content
of the coal (and ash content), the land requirement for disposal can range
from as low as 0.25 acre-feet/megawatt-year to greater than 1.0 acre-feet/
megawatt-year. In the Northeast such land requirements can pose significant
limitations on the burning of any high-sulfur fuel.
B. PURPOSE AND OBJECTIVES OF THE STUDY
The purpose of this study, therefore, is to evaluate the feasibility
of mines and the ocean as alternative sites to ponds and landfills for the
disposal of FGD sludge. This report presents the results of the initial
assessment of the technical, environmental, regulatory, and economic
aspects of these alternatives.
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Specific objectives of the study were to:
• collect available data on the chemical, physical, and engineering
properties of both treated and untreated sludges and potential for
pollutant mobility in order to provide a data base for the assess-
ment effort;
• evaluate the potential fate of sludges in mine and ocean environ-
ments, including the identification of physical, chemical, and
biological impacts of concern, and, to the extent possible,
determination of realistic disposal criteria;
• review the state-of-the-art of technology related to disposal
operations with emphasis on detection, monitoring, and control,
as appropriate.
• investigate possible benefits that may result from disposal
operations (e.g., subsidence control, use of sludge as a tailings
amendment);
• review and assess federal and stage regulations, focusing on their
adequacy for protecting the environment; and
• develop conceptualized designs and prepare preliminary estimates
of capital and operating costs for representative, feasible disposal
operations.
While the scope of the study is quite broad, the focus is on the
environmental assessment. It serves as the basis for developing disposal
criteria, defining and evaluating relevant technology, formulating con-
ceptual disposal schemes, and assessing the adequacy of existing regulations
for protecting the environment. The overall assessment approach is basically
a three-step process involving: (1) grouping of disposal sites by character-
istic conditions and/or regions (e.g., deep versus shallow ocean, western
versus eastern mines, strip versus deep mines, etc.); (2) evaluation of
the fate (impact) of untreated sludge for an assumed simple disposal
operation; and (3) evaluation of the effects of controlling the disposal
by limiting or altering sludge properties, adjusting the method of place-
ment, or imposing indirect measures to minimize impacts. As appropriate
and to the extent allowed by the available sludge data, the assessment has
taken into account the variability in principal sludge characteristics
according to region (type of coal) and type of FGD system.
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By design, this approach provides a general assessment of the
feasibility of the disposal of FGD sludge in mines and in the ocean, and
the identification of those options which appear to be most promising.
Any decision regarding the viability of a particular disposal operation
should be based upon the pertinent site-specific and sludge-specific
conditions—an assessment which is beyond the intent and scope of this
study.
This initial assessment represents the first phase of a three-phase
program. The second phase will involve laboratory studies related to
certain key impact issues identified in the first phase, and an update
and refinement of the initial assessment. The third phase will involve
additional testing and simulation or demonstration of promising ocean
and mine disposal options.
C. CONTENT OF THE REPORT
The report contains six chapters following this introduction.
• Chapter II presents the conclusions and recommendations of this
initial assessment.
• Chapter III is a topical summary of the report.
• Chapter IV is a review of the available data on FGD sludge
properties, used as a data base for this assessment.
• Chapter V contains the assessment of the disposal of FGD sludges in
mines, including:
physical, chemical, and biological impacts;
- potential benefits;
- status of disposal technology; and
- adequacy of regulations and responsibility of regulatory programs.
• Chapter VI contains the assessment of the disposal of FGD sludges
in the ocean, including:
- physical, chemical, and biological impacts;
- status of disposal technology; and
- adequacy of regulations.
• Chapter VII summarizes capital and operating costs for conceptualized
designs for representative disposal schemes.
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REFERENCES
1. Sulfur Oxide Throwaway Sludge Evaluation Panel (SOTSEP). Final Report -
Technical Discussion (Vol. II). EPA-650/2-75-010b, April 1975.
2. EPA, Report of the Hearing Panel. National Public Hearings on Power
Plant Compliance with Sulfur Oxide Air Pollution Regulations.
Washington, D.C., January 1974
3. Sulfur Oxide Control Technology Assessment Panel (SOCTAP). Final
Report on Projected Utilization of Stack Gas Cleaning Systems by
Steam-Electric Plants. PB221-356, (APT D 1569), April 1973.
4. Stone, R. and D. E. Brown. Forecasts of the Effects of Air and Water
Pollution Controls on Solid Waste Generation. Ralph Stone and Company,
Inc. EPA Contract No. 68-03-0244, August 1974.
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II. CONCLUSIONS AND RECOMMENDATIONS
The conclusions and recommendations are presented in two parts.
The first part gives the conclusions of the environmental, technical,
and regulatory assessments and the need for additional research and
information regarding the use of mines for the disposal of flue gas
desulfurization (FGD) wastes. The second part gives the analogous
conclusions and recommendations for the assessment of the ocean
disposal of FGD wastes.
A. MINE DISPOSAL
1. Technical/Environmental Considerations
The overall conclusion from this assessment of the disposal of
FGD sludges in mines is that while promising from both a technological
and an environmental standpoint, such disposal operations can result
in significant environmental impacts and each proposal for FGD sludge
disposal must be assessed on a case-by-case basis to determine the
magnitude and acceptability of these impacts. The fate of the sludge
and the extent of the environmental impacts will depend primarily on
the geology of the particular disposal site and on the specific
characteristics of the sludge but also on the indigenous quality of
receiving groundwaters and potential pathways to surface waters.
Specific conclusions of the assessment are as follows:
• There is sufficient available space in the United States
being generated annually in active mines for disposal of all
FGD sludge. Individual coal mines in most cases have space
available to dispose of at least the amount of sludge
produced from the coal extracted.
Mines employing surface stripping or underground convention-
al room and pillar operations are the most promising because
of their accessibility and availability of space. Open
pit mines are generally not promising because use of the
space would hinder access to mineral reserves. Underground
mines employing caving (by longwall, pillar robbing, or
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stoping) have limited promise because they lack available
space. By production and available space, the most promising
categories of active mining for accepting sludge are ranked
as follows:
1. surface coal mining;
2. underground room and pillar coal mining;
3. underground room and pillar limestone mining;
4. underground room and pillar lead-zinc mining;
5. underground room and pillar salt mining; and
6. underground longwall coal mining.
Placement and handling techniques for FGD sludge disposal in
both surface and underground mines are available and have been
demonstrated for disposal of other materials in mines (i.e. ,
coal refuse), although the techniques may require modifications
for application to FGD sludge disposal. There is the potential
for significant disruption of ongoing mining operations due to
the volume and physical properties of sludge to be handled.
One potential physical impact of concern is liquefaction of
the sludge either during disposal operations or after disposal
is completed. However, sound engineering design of sludge
placement, proper site selection, and constraints on sludge
properties can control such impacts.
The major potential adverse chemical impact of FGD sludge
disposal in the vicinity of mining is increased constituent
loadings (especially sodium and calcium chlorides and
sulfates) to the mine drainage discharge. In areas removed
from the influence of mine drainage pump-out the principal
potential adverse chemical impact of FGD sludge is leachate
contamination of groundwater. Leachate concentrations
for treated and untreated sludges are generally expected
to be within the ranges of concentrations of the
chemical constituents in FGD sludge liquors for hundreds
10
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of years due to the slow movement of groundwater. How-
ever, the significance of the impact on the groundwater
will depend importantly on the quality of the groundwater
and the total quantity of leachate produced as well as its
concentration. This must be evaluated on a case-by-case
basis relative to potential contaminant contributions to
downgradient water supply wells and surface waters. In some
cases the quality of the leachate would be no worse* and
possibly better, than existing mine drainage, at least with
regard to acidity and total dissolved solids (TDS).
- The generation of sludge leachate will be site-specific,
with the greatest amounts produced when sludge is within a
groundwater regime of high transmissivity (having a steep
hydraulic gradient and high permeability). Attenuation of
FGD sludge leachate is also site-specific, with the least
attenuation in acidic groundwater environments having
soil and rock of limited ion exchange capacity. Integrating
these two factors, ranking of mining categories on a
national perspective (in order of the most promising):
1. underground limestone and coal room and pillar
mines above the water table;
2. coal surface area mines (Interior and Western);
3. coal surface contour mines (Eastern);
4. lead-zinc underground room and pillar mines; and
5. coal underground room and pillar, and longwall
mines within the water table (Eastern and Interior).
Note: Salt mines were not specifically addressed within
the scope of this study, even though they could receive the
highest ranking. Salt mines have generally been assigned
a higher priority with regard to the disposal of wastes,
e.g., hazardous radioactive wastes.
- The generation of sludge leachate is also sludge-specific
with decreasing amounts occurring with decreasing sludge
11
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permeability (especially through compaction or chemical
treatment). The concentrations of constituents in
leachate is also sludge-specific, with concentrations
tending to decrease as alkalinity increases, fly ash
content decreases, and inorganic constituents originally
present in coal decrease, i.e., chloride and trace metals.
Discharge of sludge leachate to surface waters can adversely
affect aquatic life by the addition of biocumulative trace
metals. In the case of sludges containing sulfite, there is
the potential toxicity of dissolved sulfite itself as well
as the potential depletion of dissolved oxygen due to the
sulfite.
In surface mines, control techniques to minimize groundwater
contamination include decrease of sludge permeability through
compaction or chemical treatment and placement of sludge
outside the groundwater reservoir through modified disposal
operations. In underground mines, the primary control
technique is chemical treatment.
The state-of-the-art of site monitoring and analytical
techniques to predict and assess impacts is adequate for
FGD sludge disposal. The general location of monitoring
sites must be based upon geologic field surveys in order
to develop appropriate background and leachate data.
In underground mines, FGD sludge placement results in the
potential benefits of lessening acid drainage formation and
long-term subsidence, primarily by sealing exposed coal
against air exposure which leads to pyritic sulfur oxidation
and also leads to pillar deterioration.
FGD sludge provides little potential as an amendment to mine
tailings for enhancing vegetative growth. In this regard,
FGD sludge generally ranks poorly in comparison to limestone
and sewage sludge.
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2. Regulatory Considerations
Recent shifts in regulatory attitudes show a growing concern for
groundwater protection from seepage or leachate from the disposal
of wastes. Given the recent Resource Conservation and Recovery Act
of 1976, existing laws are legally adequate to insure protection of
the geologic environment from waste disposal. However, because of
the technical difficulties of completely characterizing an underground
environment and of locating monitoring wells, regulation should rely
on guidelines for site selection and waste acceptance and should
allow for case-by-case assessment by professional geologists and
geochemists.
Specific conclusions are as follows:
• The lead authorities for FGD sludge disposal appear to be
the federal and state environmental protection agencies,
• The lead legislation is expected to be the Resource Conserva-
tion and Recovery Act of 1976, involving state resolution
of Federally approved programs and the existing planning
infrastructure established for 208 areawide wastewater
management planning under the Federal Water Pollution Control
Act Amendment of 1972.
• The combination of federal and state legislation is legally
adequate to protect the environment during and after FGD
sludge disposal; however, regulations are needed with site
selection and waste acceptance guidelines based upon the
characteristics of FGD sludge and research on potential
environmental impacts.
• Additional legislation and standards may be required to
protect worker health and safety. Administration of the
health and safety requirements need clarification, especially
between authorities of OSHA and MESA.
• Because of the non-point source nature of air and water
emissions from FGD sludge disposal and the large variations
in FGD sludge character, disposal should be regulated on
a case-by-case basis.
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3. Need for Additional Research and Information
The following research needs are believed most important at this
time.
• Development of additional, more comprehensive physical and
engineering properties data base and corroboration (or
comparison) of results with field data. Of particular
interest are:
- triaxial compression tests for shear strength of untreated
sludges to determine the ability to support loadings
while unconfined;
- dynamic triaxial compression tests for untreated sludges to
simulate resistance to shear under seismic cyclic loadings
applicable to various regions of coal reserves;
- consolidation tests for untreated and soil-like treated
sludges to simulate density and permeability under various
static loadings related to overburden pressures; and
- Atterberg limits for untreated sludges.
Some of this testing is now underway in programs funded by
EPA and other governmental agencies, and will be reviewed
as available as a part of the Phase II effort.
• Development of a data base on key chemical impact issues
relating to mine disposal. Of particular importance are:
- the potential for TOS leaching from sludges and rates of
TOS oxidation;
- the potential for chemical attack of cement/concrete by
sludge liquors and leachate;
- the potential for S02 evolution during the initial stages
of sludge disposal in underground mines with acidic
environments;
- the short-term effects of climate (e.g., freezing,
excessive rainfall, etc.) on the physical properties of
untreated sludges and pollutant mobility.
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These will be addressed in Phase II. Where data are not
available, appropriate laboratory tests will be performed.
• Laboratory or field testing relating to the handling, storage
and placement techniques (including hydraulic and pneumatic
stowing) to determine optimum sludge properties, preview
technical difficulties and assess secondary environmental
effects (e.g., creation of dust during handling, storage
and placement). It is expected that these issues would be
addressed, to the extent possible, during the simulation/
demonstration testing in Phase III.
• Survey of dust, noise, airborne contaminants and other
health and safety criteria affecting waste disposal operations,
and clarification of the respective roles of health and
safety regulatory authorities (e.g., OSHA and MESA).
• Field survey of various mines (especially coal, limestone,
and lead-zinc) to develop a more extensive data base on
the alkalinity/acidity of drainage, the extent of pillar
robbing, the pathways and rate of groundwater flow, and
the potential for long-term subsidence.
B. OCEAN DISPOSAL
1. Technical/Environmental Considerations
Two major overall conclusions emerge from this assessment of
the disposal of FGD sludges in the ocean. First, there is an
overriding need for case-by-case analysis of the environmental
feasibility of ocean disposal of specific FGD sludges. The emphasis
in such analyses should be twofold, focusing both on the type of
sludge and disposal site environmental conditions. Second, control
options involving chemical treatment of sludge, limitations on the
type of sludge disposed of, and control of the method of sludge
placement (either dispersed or concentrated bottom-dump disposal)
all appear to be technically feasible. Economic feasibility,
however, is less clear-cut and would serve to limit the viability of
several of the most promising environmental options.
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Specific conclusions are as follows:
• Unless further work contradicts the anticipated sedimentation
and suspension impacts, the disposal of untreated or treated
FGD sludges with soil-like physical properties by bottom-
dump barge or outfall on the continental shelf must be
considered to be environmentally unacceptable.
• Based upon available information on sulfite toxicity, it
appears that an almost immediate (on the order of minutes)
dilution factor greater than 10,000:1 for sulfite alone is
required in the dispersed disposal of untreated sludges
containing large fractions of sulfite. The technology is
.not currently available for attaining such dilution factors
for untreated sulfite-rich sludges in an economical manner.
Therefore, the dispersed disposal of sulfite-rich sludges,
both on and off the continental shelf, is not considered to
be a promising option at the present time. Further information
on organisms uptake and toxicity of TOS could justify
reevaluation of this conclusion.
• Several disposal options appear promising and are recommended
for further research. These include:
- dispersed disposal of untreated sulfate-rich FGD sludges
on the continental shelf;
- concentrated disposal of treated brick-like FGD sludge on
the continental shelf;
- dispersed disposal of untreated sulfate-rich FGD sludges in
the deep ocean; and
- concentrated disposal of both untreated sulfate-rich FGD
sludges and-treated FGD sludges in the deep ocean.
Recommended additional research is discussed in more detail
below.
2. Regulatory Considerations
In general, given the present vigilance in agency attitudes
towards ocean dumping, the existing regulations appear to be
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adequate to insure protection of the ocean environment. However,
several specific recommendations are considered appropriate at this
time. These are as follows:
• Pending revisions to the existing ocean dumping regulations
that would allow for additional empirical considerations
(e.g., field data and models) in the determination of limiting
permissible concentrations in the ocean at the disposal
site should be adopted.
• Existing absolute limits on permissible concentrations of
mercury and cadmium in solid fractions of wastes should be
reevaluated through consideration of the actual anticipated
long-term availability of the contaminants on a case-by-case
basis.
• Inherent disincentives to deep ocean dumping (e.g., extra
monitoring requirements) should be reevaluated in light of
the apparent desirability of certain deep ocean disposal
options.
There appears to be no need for additional sludge-related legislation
concerning ocean disposal at this time.
3. Need for Additional Research and Information
The following research needs are believed most important at
this time.
• A body of empirical data needs to be developed concerning the
chemical and physical fate of sludge in seawater. Of
particular importance are:
- dissolution rates of various treated and untreated FGD
sludges in the representative types of seawater that would
characterize the disposal area environs; and
- physical transport of both treated and untreated sludges
in the water column during descent and subsequently in the
marine benthos (near the bottom).
These effects will be studied in laboratory-scale testing
with untreated sludges during the Phase II program.
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A body of empirical data needs to be developed regarding
the biological impacts of sludge disposal. Specifically:
- uptake of both liquid and solid constituents of FGD
sludges by various marine organisms need to be
developed;
- in particular, for uptake associated with short-term
exposure of pelagic organisms; and
- lethal and sub-lethal effects thresholds need to be
developed for exposure of a variety of representative
marine organisms to FGD sludges (one of the focal points
of such research should be the dynamics of food web
transfer of potential toxicants).
The investigation of such biological impacts is planned for
the simulation/demonstration testing in Phase III.
Mechanisms for eliminating existing economic disincentives
to deep ocean disposal should be developed. These could
include consideration of such options as a greater federal
role in baseline and disposal area monitoring.
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III. EXECUTIVE SUMMARY
A. CHEMICAL AND PHYSICAL CHARACTERISTICS OF FGD SLUDGES
Both the chemical composition and the physical and engineering
properties of the sludge produced by any given FGD process at any particular
time depend upon a large number of factors including: the composition of
the coal burned, the type of boiler and its operating conditions, the
method of particulate control employed, and the type of FGD system
employed and the way in which it is operated. Sludge characteristics,
therefore, and the chemical composition in particular, can vary over
extremely wide ranges. The most extensive studies characterizing sludges
are being conducted by the Aerospace Corporation (Aerospace) and the United
States Army Corps of Engineers Waterways Experiment Station (WES) for the
U.S. Environmental Protection Agency (EPA). Although these programs are
still underway, the data are sufficient to establish the range of sludge
characteristics that might be encountered. Additional data will be
required, however, to predict the characteristics of sludge produced by
a particular process or process type under a given set of conditions, and
more extensive testing of physical and engineering properties is necessary
to accurately predict the behavior of sludges in actual disposal operations.
1. Chemical Composition of FGD Sludges
The principal substances making up the solid phase of FGD sludges
are calcium-sulfur salts (calcium sulfite and/or calcium sulfate) along
with varying amounts of calcium carbonate and fly ash. The ratio of
calcium sulfite (CaSC-3'1/2 H20) to calcium sulfate (present as CaSO «l/2
H£0 or gypsum, CaSOit*2H20) can vary over an extemely wide range depending
upon the extent to which oxidation occurs within the system. Oxidation is
generally highest in systems installed on boilers burning low sulfur coal
or in systems where oxidation is intentionally promoted. Fly ash will be
present in the sludge if the scrubber also serves as a particulate control
device or if separately collected fly ash is admixed with the sludge.
Varying amounts of unreacted limestone (up to 40%) can be found in sludges
produced from direct limestone scrubbing. In direct lime of dual alkali
process sludges, CaCC>3 is often present in smaller amounts due to
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Impurity in the reagent lime, reaction with small amounts of absorbed
C02 or solution softening with sodium carbonate.
A variety of trace elements find their way into FGD sludges from
a number of sources: from coal where they are present either in mineral
impurities or as organometallic compounds; from lime, limestone, or other
reagents used in the FGD systems; and even from the process makeup water
used. The levels of trace elements found in the sludge depend primarily
upon their level in the coal, the amount, if any, of ash that is collected
or admixed with the sludge, and the efficiency of the scrubber system in
capturing trace metal vapors. The range of concentrations that have been
measured in a variety of sludge samples cover two orders of magnitude
and are similar to the range of concentrations found in coal (1,2,3).
For sludges containing fly ash the concentrations of the most prevalent
trace metals (cadmium, manganese, zinc, etc.) can range as high as a few
hundred parts per million (ppm).
The liquid phases of FGD sludges contain dissolved in them a variety
of substances ranging from traces of a variety of metals to substantial
amounts of commonly occurring ions like sodium, calcium, chloride, and
sulfate. As was the case with the composition of sludge solids, concen-
trations of soluble substances in sludge liquors can vary by two orders
of magnitude or more. The total dissolved solids (TDS) level can vary
from about 2,500 mg/liter to as much as 100,000 mg/liter depending on the
chloride/sulfur ratio in the coal, the type of system, and the extent to
which the solids are dewatered (and washed), if at all (1,2). However,
because of the insolubility of many of the trace metal hydroxides, only
a very small fraction of the total amount of almost every trace metal
present in the sludge is found dissolved in the sludge liquor.
2. Physical and Engineering Properties of Untreated FGD Sludges
The physical and engineering properties used to characterized FGD
sludges have generally been those which have proven useful in character-
izing and predicting the behavior of soils in construction and landfill
operations. The most commonly used tests include particle size distribution,
bulk density, unconfined compressive strength, compaction moisture/density
relationships, viscosity, permeability, and leaching behavior. To date,
there has been little work involving triaxial compression testing,
consolidation behavior, or Atterberg limits.
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Determinations of particle size distribution by sedimentation carried
out at WES indicated that for most sludges the particle size distributions
fell in the range of 5-50 microns, a range corresponding to silty to sandy
soil. However, particles both smaller (less than 1 micron) and larger
(at least 200 microns) have been observed (4). The true densities of the
solid particles themselves range from about 2.1 to about 2.6 g/ml (1,2,5).
But, depending upon the quantity of liquor present and the amount of
entrained air, the specific gravity of the product sludge can range from
about 1.3 to 1.8.
The viscosity of an FGD sludge increases as the solids content
increases, although the exact relationships depend on the particular
material (particle size distribution, crystalline morphology, and the
quantity of ash present) as dictated by process type and operating
conditions. The highest viscosities were observed for agglomerated
sulfite-rich crystals such as those produced by dual alkali systems
(which become difficult to pump at greater than 40% solids), and the
lowest viscosities were observed for sludges containing a high fraction
of gypsum. Increasing amounts of fly ash seemed to reduce the viscosity,
perhaps because the spherical particles act as ball bearings (1).
The extent to which FGD sludges can be dewatered also depends upon
the size and shape of the crystals as well as the dewatering process.
Sulfite-rich sludge can typically be thickened to 20% to 40% solids and
filtered to 35% to 80% solids. Sulfate-rich sludge can usually be thick-
ened to 30% to 60% solids and filtered to 60% to 90% solids.
If the solids content of FGD sludges is increased sufficiently by
filtration, centrifugation, or by other means such as addition of a dry
material, they are amenable to compaction into a material which can be
quite firm and which, if confined, can support considerable weight.
Maximum dry bulk densities of about 70-85 Ibs/cubic foot have been observed
for sludges compacted according to the Proctor method (5,6). While sludges
compacted in this manner are quite firm, they have very little load-bearing
strength when the restraining mold is removed. Measurements of unconfined
compressive strengths have ranged from nil to 20 Ibs/square inch.
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Coefficients of permeability have been measured for both compacted
and uncompacted sulfite- and sulfate-rich sludges. Measured values
generally fall in the range of about 10"1* to 10~5 cm/second.
3. Effects of Treatment on Sludge Properties
A variety of treament processes have been developed for altering the
physical properties of FGD sludges. Depending upon the kind and amount
of reagent added during treatment, the treated material can become
reasonably hard with low permeabilities after it cures, or it can be
a dry, soil-like material which can harden after compaction.
While most processes currently being offered are considered pro-
prietary, the addition of lime and fly ash, or a similar source of silicate,
is believed to be the basis for one or more of the available treatment
technologies. Lime and a silicate-containing material undergo a pozzolanic
reaction in which calcium from the lime reacts with silica to produce
a cementitious calcium-silicate matrix which gives strength to the treated
mass and reduces its permeability. Treatment processes of the sort which
produce a relatively hard material generally exhibit unconfined compres-
sive strengths in the range of 100-400 Ibs/square inch (4,5), although one
treatment process included in the WES program resulted in unconfined
compressive strength of nearly 5,000 Ibs/square inch. Unconfined compres-
sive strengths of soil-like materials, after being remolded and Proctor
compacted, ranged from 20-50 Ibs/square inch (4).
Preliminary data on leaching potential obtained from accelerated
laboratory leach tests and field testing in small ponds (1,2,7) indicate
that treatment can reduce the concentration of total dissolved solids
and the predominant soluble ions which constitute the IDS in leachates.
Whether or not the concentrations of trace substances are reduced has yet
to be established with any degree of certainty. In some cases, reported
concentrations of certain trace elements have actually been higher in
leachates from treated sludge. However, treatment processes still hold
promise for reducing the pollutant potential of sludges. Decreasing the
permeability can, in and of itself, be a significant factor in reducing
pollutant mobility. But there is also the possibility that major soluble
substances are immobilized. And the improved handling properties of
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treated sludges may permit better control of sludge placement and, in the
case of ponds, of surface contours which can result in better control of
surface water runoff.
B. MINE DISPOSAL
1. Screening of Mine Alternatives
There are over 15,000 mines in the United States today which together
produce over one-half billion tons of coal and 2.5 billion tons of metallic
and nonmetallic minerals. About one-third of these mines individually
produce over 100,000 tons/year.
To focus on the most promising alternatives, mines have been broadly
grouped according to region, mineral mined, mine capacity, and method of
mining; and each group has been screened with regard to overall technical
feasibility. The screening process considered the capacity for sludge,
ease of disposal, prevention of future resource recovery and general
proximity to sludge sources. This screening is derived from a national
perspective and does not consider small mines having site-specific
conditions favorable to sludge disposal.
a. Coal Mines
About one-half of the coal currently produced in the United States
is surface mined, and one-half is produced from underground mines. The
vast majority of coal production in the Western region involves surface
mining methods, while in the Eastern and Interior regions, underground
mining accounts for roughly 60% of the total coal production.
In general, inactive coal mines are not considered as technically
promising for disposal as active mines. Unreclaimed inactive and depleted
surface mines usually consist of the final strip pit (which is often
filled with water) and a series of ridges of overburden, leaving little
available capacity for sludge placement. Reclaimed surface mines by
definition do not have any capacity for FGD sludge disposal. Old and
inactive underground coal mines are often caved, with remaining voids
being difficult to locate and utilize for sludge placement.
On the other hand, FGD sludge disposal in active coal mines is tech-
nically promising on several counts. The quantity of sludge produced
generally amounts to less than 50% of the weight of the coal burned; thus,
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there should be sufficient capacity for FGD sludge from a power plant to
be returned to the active coal mine supplying the plant. Also, there is
an existing network of transfer and handling equipment for the transport
of coal from a mine to a power plant, and this network might be modified
and expanded for use in transport of the sludge.
Surface coal mines in the Interior and Western regions appear to be
the most technically promising because of their individual capacity and
the relative ease of sludge placement within the context of the commonly
employed area mining operation. Eastern surface coal mines are considered
less promising because of their lower production capacity and the prevalent
contour mining method which makes sludge placement more difficult. Of the
underground coal mines, Eastern and Interior conventional room and pillar
mines are the most technically promising. There are few underground mines
in the Western regions (and these are of limited capacity). Because of
roof caving, underground longwall mines and room and pillar mines practicing
pillar robbing have limited capacity, and it will be difficult to locate
remaining voids.
b. Metal and Nonmetal Mines
The two principal types of mineral mines are underground and open pit.
Most metallic and nonmetallic mineral mines are open pit (or quarry).
However, there are a significant number of underground mines producing
limestone, gypsum, salt, copper, iron ore, lead, uranium, and zinc. The
principal methods of underground mining are room and pillar, caving, and
cut and fill (and its variation).
While there are countless inactive and abandoned underground mines,
these are not usually promising for sludge disposal. Most of them involved
mining methods employing caving, leaving limited capacity for sludge.
Many are currently inactive for market reasons and may be reopened as
market conditions dictate. Only the significant void left from past
lead-zinc mining operations appears viable for sludge disposal, as high
extraction percentages (^70%) were achieved by room and pillar methods,
and future lead-zinc supplies would not be greatly affected by sludge
disposal.
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Of the active metal and nonmetallic mineral mines, underground room
and pillar, lead-zinc, and limestone mines show the greatest promise for
sludge disposal. Currently, there are more than a dozen active lead-zinc
mines producing over 100,000 tons of ore annually and about 30 underground
room and pillar limestone mines producing over 300,000 tons of limestone
per year. Limestone mines are of particular interest, since all non-
regenerable systems involve the use of limestone either directly or
indirectly and a transportation network may already exist between limestone
mines and FGD systems. However, where a large fraction of a limestone
mine's production is used to supply FGD systems, it may not be able to
dispose of all the sludge produced because the volume of dewatered, ash-
free sludge (at 50% solids) is many times greater than that of the limestone
used.
Other types of active underground mines are considered to be less
promising due either to the value of the remaining unextracted ore that
would be inaccessible after sludge disposal or due to the limited capacity
and difficulty of sludge placement. Active open pit mines would not
provide good disposal sites because the nature of the mining operation
requires maintenance of the entire excavated area for downdip access to
reserves.
2. Environmental Assessment
Based upon the screening of the mining industry, the methods of
disposal available, and the overriding operational constraints in disposal,
the following general mine options were selected for assessment:
Mineral
Coal
Coal
Mining Method
Surface
Underground
Room and Pillar
Region
Disposal Method
Eastern, Interior, Truck Dumping
Sludge Form
Moist Filter Cake
Longwall
Lead-Zinc Underground
Limestone Underground
and Western
Eastern, Interior
Eastern, Interior
Interior
Interior
into Pit
Hydraulic Stowing Thickened Slurry
Pneumatic Stowing Moist Filter Cake
Hydraulic Stowing Thickened Slurry
Truck Dumping Moist Filter Cake
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The impacts of sludge disposal were assessed based upon a range of
average mine conditions and range of untreated sludge characteristics
common to each region. Methods for mitigating impacts were then assessed,
taking into consideration factors such as sludge treatment, modification of
disposal operations, control of site selection, and leachate collection and
treatment.
a. Physical Impacts of Untreated Sludge
In the disposal of untreated sludge in mines the physical impacts of
principal concern are: uncontrolled flow or seepage of sludge during
disposal operations, consolidation of sludge deep-layered in surface mine
pits, and the potential for liquefaction of sludge after disposal has
been completed.
In order not to overly disrupt mining operations it is important in
surface mine disposal that the sludge be relatively dry so that it can
be easily handled and have minimal tendency to flow. However, while
simple dewatering (by thickening and filtration or centrifugation) may
produce a relatively dry sludge, the material may be near enough to its
liquid limit that when rewetted slightly or stressed it may liquefy and
flow. In addition, liquefaction could be caused by dumping overburden on
sludge layered in the pit, by vibrations from nearby mining operations,
or seismic disturbances.
In underground mines, liquefaction would be of principal importance
where bulkheads are not employed to retain the sludge. Bulkheads would
be part of a system employing hydraulic stowing but would not normally be
included where pneumatic or dry stowing is employed.
Consolidation of sludge is of prime importance in surface mines where
deep layers of sludges (greater than 5-10 feet) are created, particularly
where the overburden is relatively shallow. The significance of con-
solidation depends on the time required for most of the settlement to
occur and the ultimate proposed use of reclaimed strip mine land.
Both consolidation and liquefaction potential will importantly
depend upon the properties of the sludge as well as the manner of sludge
placement and loading on the sludge. As of the writing of this report
there is no definitive data available on the properties of sludge relative
to these effects.
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b. Effects of Untreated Sludge on Water Quality
Most mines are wet, and it can be assumed that groundwater overlying
the mined area will eventually flow into the mined area and saturate any
FGD sludge deposit. Sludges disposed in surface mines are subjected to
groundwater flowing through unconsolidated sediment and broken rock over-
burden. Underground mines receive groundwater flowing through cracks,
fissures, and faults in overlying (and underlying) strata into the mined
area. Under most mining conditions, FGD sludge is expected to be saturated
unless measures are taken to isolate the sludge either by diverting ground-
water or placing the sludge above the water table.
Groundwater moving through disposed sludge picks up soluble chemical
species. According to leachate studies of FGD sludge, there is a first
flush of soluble species from the liquor associated with the sludge lasting
one or two pore volumes, with most species dropping to near their equili-
brium concentrations after a displacement of about 10-30 pore volumes.
Because of the extremely long time it takes for sludge to pass one pore
volume of leachate through its matrix, leachate concentrations close to
those of the original sludge liquor would be expected to prevail for
hundreds to thousands of years. Significance of the impact of the leachate
on groundwater will, of course, depend importantly on the total quantity
of the constituents leached as well as its concentration. To some degree,
leachate concentrations will be affected by the composition of the infil-
trating water. In most cases, though, acidity levels per se in mine waters
should have little effect on leachate concentrations, since few mines have
drainage of pH less than A, and accelerated leaching and elutriate tests
at pH's of 4 and 7 show little difference in leachate concentrations (2).
Chlorides and sulfates are the major soluble species in sludge, and
in most cases, IDS in the leachate plume would be expected to exceed
recommended drinking water standards. Other species such as cadmium,
mercury, and zinc would also be expected to be substantially raised in
waters receiving sludge leachate; however, IDS levels should "red flag"
contamination.
Little attenuation of soluble species is expected for most mine
disposal situations. In most cases, the sludge would test on rock strata
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in a layer below (and possibly partially mixed with) broken rock over-
burden, and there would generally be little or no direct contact of sludge
or its leachate with soil. Therefore, adsorption of leachate constituents
will not be significant in the immediate vicinity of the mine, and pre-
cipitation is the only feasible attenuation mechanism in most cases.
Aluminum, beryllium, cadmium, copper, cobalt, iron, lead, manganese,
mercury, molybdenum, nickel, and zinc may be partially precipitated under
neutral to alkaline conditions. If limestone overburden is present,
carbonate salts may form with cadmium, calcium, copper, iron, lead, and
zinc. Insignificant attenuation of arsenic, boron, selenium, and chromium
is expected. No attenuation of sodium, chloride, or sulfate would be
expected.
Leachate from the sludge layer is accessible to surface water by two
pathways: (1) mine sump pump-out, which contains a mixture of groundwater,
sludge leachate, and surface runoff and (2) groundwater recharge of down-
gradient surface waters. The effect is obviously a function of the dilution
factor of the receiving stream and its baseline water quality. In some
cases, sludge leachate would be no worse (and conceivably better) than
existing mine drainage, at least with regard to acidity levels and TDS,
and leachate discharges to rivers polluted upstream by mining operations
may not cause any appreciable impact on instream chemical concentrations.
However, leachate discharges to pristine small streams may show significant
water quality impact. Cadmium, mercury, and zinc in particular may be
increased to above fresh water aquatic life criteria. From a biological
standpoint, TDS in general and these three heavy metals would provide
cause for concern in small pristine receiving streams. In addition to
the direct toxicity problems of the estimated increments in these metals,
the potential problems of accumulation and synergism would also exist in
larger streams. Mercury and cadmium are persistent cumulative toxicants
and the toxicity of the latter can be increased by zinc.
TOS (total oxidizable sulfur = sulfite + bisulfite) in leachate may
also present a toxicity potential of concern, both in terms of the direct
toxicity of the TOS itself and for its COD. Groundwaters tend to be
anaerobic, and TOS could persist to receiving streams. Since little data
are available on TOS in sludge leachates, TOS toxicity can only be identified
at this time as a potential problem.
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c. Control Techniques to Minimize Adverse Impacts
The control techniques available for minimizing adverse impacts
include:
• sludge processing or treatment;
• control of disposal method;
• collection and treatment of sludge leachate or runoffs; and
• control of site selection.
Sludge treatment by chemical fixation techniques should enhance
physical properties and thereby ensure minimal operational and physical
impacts, although well-filtered sludge (possibly admixed with ash) may,
in many cases, be adequate to avoid most adverse operational and physical
impacts. A treated sludge would also reduce mobilization of pollutants
through reduction in the sludge permeability, decreased sludge contact
area, and possibly reduction in the solubility of potential pollutants.
Adjusting the disposal operations to isolate the sludge from the
groundwater would improve environmental impacts. If in surface mines,
part of the rock overburden were deposited in the pit to a depth above
the groundwater table prior to disposal of the sludge, then the rate of
leachage generation would be lessened. However, such an operation may
be technically impractical or economically unattractive. In underground
mines, disposal between strata of low transmissivity (a function of
permeability and hydraulic gradient) would limit the access of groundwater
to the sludge deposit and thereby limit leachate production.
Collection and treatment of sludge leachate does not appear to be
a viable alternative for controlling environmental impacts. Groundwater
collection requires extensive pumping wells or infiltration galleries,
and the chlorides and sulfates collected in the leachate cannot be readily
treated by existing wastewater processes.
The best control technique may be adequate evaluation and selection
of the optimum site based upon the geologic conditions favorable to disposal
and the characteristics of the sludge. Factors to be considered include:
permeabilities of adjacent strata, hydraulic gradient of groundwaters
through the mined area, seasonal location of the water table, type of
pyrite coal and resulting acid drainage formation, buffering capacity of
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background groundwater, distance and pathways to downgradient receiving
surface waters, and potential for attenuation of dissolved species.
d. Potential Benefits from Sludge Disposal
Neutralization of Acid Mine Drainage
All coal mines have potential for the formation of acid mine drainage
as pyrite is exposed to air and water. A surface mine which is reclaimed
concurrent with mining has less potential for acid drainage formation than
one which is not immediately reclaimed. An underground room and pillar
mine has the potential for continuously exposing pyrite to air and
humidity, thereby allowing the worst acid mine drainage conditions to
develop. An underground longwall mine, through controlled caving of the
roof and pillar extraction, minimizes pyrite exposure and acid drainage
formation. Disposal of FGD sludge could limit future acid drainage
formation by sealing pyrite from air exposure.
Where there is presence of limestone in a surface or underground
mine's overburden, neutralization of the acid mine drainage occurs.
Similarly, FGD sludge has some ability to neutralize acid drainage.
Calcium carbonate in the sludge would be expected to be the principal
neutralization agent, since there is usually very little residual calcium
oxide or calcium hydroxide. However, disposing of untreated sludge
containing sulfite in very acidic waters may result in off-gassing of SC^
which could prohibit such operations.
Subsidence Control
Subsidence may occur in underground mines when the seam extraction
panel is large enough to induce the mine roof to fail and collapse into
the mine void. In room and pillar mining, pillars are left in place to
provide roof support. However, after a room and pillar mine is abandoned,
natural deterioration of the pillars may weaken them sufficiently to allow
roof collapse. In longwall mining, controlled roof collapse is a part of
the mining operation, and subsidence is expected to occur within several
days of ore extraction.
Experience with hydraulic and pneumatic stowing of coal refuse and
sandfill in conjunction with longwall mining has indicated lessening of
subsidence from 90% of the seam thickness to 25-55%. FGD sludge is not
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expected to achieve the same degree of subsidence control, especially if
it does not readily consolidate on placement.
In cases of long-term subsidence attributed to pillar deterioration,
deposits of treated or untreated FGD sludge could partially seal the
pillars from air exposure, groundwater seepage, and microorganisms. As
a result, the reaction rates of chemical and biological pillar deteriora-
tion should be significantly lessened. However, the use of treated sludge
in some manner either to line or replace pillars to allow additional coal
extraction is not considered economically attractive.
Untreated Sludge as a Tailings Amendment
Tailings are highly variable in composition, as are FGD sludges.
Tailings have been successfully revegetated for over fifteen years,
usually using "soil amendments" such as limestone, sewage sludge, fly
ash (where available), and, less often, soil itself. Materials used as
soil amendments are chosen on a case-by-case basis to meet particular
needs, but the potential for any material as a soil amendment depends
upon its ability to alleviate any conditions that limit plant growth.
In general, FGD sludge appears somewhat useful in its potential for
reducing acidity (unless it is acidic itself), reducing heat absorption
and increasing moisture retention. It is doubtful if sludge could
alleviate any problems with phytotoxins or salinity and may aggravate
such problems in some cases. To prevent creating new problems, the
sludge to be used must be screened for heavy metals, salinity, and
acidity. But even an alkaline sludge with low salinity and heavy metals
holds less promise as a soil amendment than either limestone or sewage
sludge.
3. Technology Assessment
a. Handling and Transport
There are four basic modes of transport that can be used for moving
sludge: slurry pipeline, barge, truck, and rail. Since all of these
modes are technically feasible, the selection of the most appropriate mode
or combination of modes must be made on the basis of a cost/benefit
analysis, taking into account all operations involved (processing, trans-
fer, transport, and disposal) and institutional constraints that may be
imposed (e.g., regulations governing waste transport inter- and intra-state)
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The overall practicality of pipeline transport of sludge will depend
upon a number of factors relating to the pipeline requirements and the
operation of the FGD process and the disposal system. Of particular
importance are the water balances at the power plant and mine, and the
specific sludge dewatering or treatment requirements, if any, prior to
disposal. Special consideration in the design of pipelines would have to
be given to slurry viscosity, slurry velocity, abrasion/corrosion resistance,
freeze protection, and potential long-term scaling or hardening of sludge
in the pipe. These factors along with the institutional constraints of
long-distance pipelines will act to restrict the practical distance
of slurry pipelines for mine disposal to mine mouth power plants
involving transport distances no more than a few miles.
Hauling sludge by rail is an attractive prospect, since most large
power plants receive coal by rail; however, the sludge would need to be
a moist filter cake or treated material. New facilities would be required
at both the power plant and mine for storing, handling, loading, and
unloading the sludge, all of which can be accomplished using existing,
available technology (for a moist filter cake or processed material).
Truck transport and disposal of sludge is now used by utilities.
Recent experience at a number of power plants indicates that untreated
sludge should be at least the consistency of a moist filter cake with
little tendency to liquefy, particularly if rear-dump trucks are used.
Slurries or partially dewatered materials are difficult to load and dump
and could leak liquor during transport, necessitating special trucks.
Loading of a relatively dry material can be readily accomplished using
a combination of conveyors and hoppers, front-end loaders, or bucket cranes.
Special provisions may be required to prevent freezing of the sludge or
excessive rewetting due to rainfall. It may also be necessary to provide
for rail car washing at the mine site (including a system to collect and
treat the runoff).
Where utiliites receive coal by barge, barging of wastes would be
a logical alternative to overland transport. While use of coal barges is
possible, a barging system dedicated to sludge transport would provide
greater flexibility, eliminate tying up coal deliveries, and minimize
intermediate sludge storage. While barges could conceivably be used to
handle thickener underflow, dry filter cake or treated material would
result in fewer unloading problems.
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b. Disposal Methods
Strip Mines
Disposal of filter cake or treated sludge in a surface mine would be
most easily accomplished with rear-dump trucks, whether the sludge were
returned to the pit prior to or along with overburden or were dumped
between mounds of replaced overburden. Unless truck haulback methods
were used for returning overburden, any operation other than simply
dumping the sludge in the mined-out pit prior to the return of overburden
would require additional road construction and a corresponding increase
in disposal costs.
It would probably not be possible to use coal haulage vehicles, since
sludge loading and dumping would increase truck cycle times and reduce
productivity. Also, many newer trucks are large (80-100 tons) bottom-dump,
aluminum-bodied trucks not amenable to maneuvering in coal mine pits,
particularly on sludge layers.
Underground Mines
There are three approaches for disposal of wastes in underground
mines: pneumatic backfilling, hydraulic backfilling (or flushing), and
mechanical stowing.
There has only been limited experience with pneumatic backfilling of
materials in U.S. mines, although there has been considerable work done
in European coal mines, primarily with fly ash. In room and pillar mines,
pneumatic backfilling would be acomplished by blind injection. In longwall
mines it could be used to place sludge in the gob area as a part of the
normal operation prior to roof collapse. However, if the sludge is too
moist, it may clog conventional equipment, even when admixed with ash or
tailings; and the presence of fly ash may cause excessive abrasion. On
the other hand, the very fine fraction of the sludge, when sufficiently
dried, may create dust problems not uncommon in pneumatic stowing opera-
tions.
There has been considerably more experience with hydraulic backfill-
ing of ash and coarse tailings. Hydraulic backfilling could be accomplished
either by controlled or blind injection. Unless sufficient slope exists,
bulkheading will be required, particularly where sludge is introduced
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through boreholes in the mine roof. Depending upon viscosity, slurries
up to 50-60% solids may be hydraulically stowed; however, 40% solids
probably represents a reasonable upper limit. Hydraulic backfill of some
treated sludges may require underground piping rather than introduction
through roof boreholes. With hydraulic backfilling it may be necessary
to collect any drainage or pump out decanted liquor for controlled dis-
charge or treatment. Where dry sludge is reslurried at the mine, collected
drainage may be recycled for slurrying the sludge.
Mechanical stowing can be used in any underground room and pillar
mine using existing types of equipment and conveyance systems. In most
mines, mechanical stowing would involve a labor-intensive, rather ineffi-
cient operation. In hillside limestone mines, though, mechanical stowing
by truck dumping would be the preferred method of disposal, since these mines
are readily accessible. However, this type of operation would limit the
space utilization.
c. Monitoring
The measurement of physical, chemical, and biological changes that
occur in the region of a disposal site is required to determine the fate
and effects of the sludge. Monitoring of the site will be required prior
to, during, and after disposal. It is particularly important that back-
ground data on site conditions (e.g., surface water, groundwater, geology,
climate) be gathered for a period of at least one year prior to disposal
to establish seasonal fluctuations and that a control site be monitored,
if possible, during and after disposal. The particular chemical species
to be followed will depend upon background groundwater levels and sludge
characteristics, but general parameters that may be useful in detecting
influx of leachate into groundwaters would be sodium, chloride, sulfate,
and TOS. These are least attenuated by soil or rock.
Because continuous monitoring is not required and such monitoring
devices are of limited availability, the monitoring program should be
based on grab samples from groundwater wells. These need to be located
within the disposal area as well as up and downgradient. Core samples
will also be needed to assess physical and chemical changes in the sludge.
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The frequency of sampling will vary for different disposal operations
and will undoubtedly need to be adjusted according to observed effects.
The initial sampling frequency should be based upon expected permeability
and groundwater flow rates.
4. Regulatory Environment
a. Federal
Four areas of federal laws and statutes have been evaluated with
regard to their adequacy for protecting the environment: waste disposal,
transportation, water quality, and health and safety. Selected regulations
issued by agencies in order to implement and enforce provisions of the
relevant statutes were examined; however, regulations pursuant to the
major transportation acts and the Occupational Safety and Health Act of
1970 were not included due to their extensive technical detail and numbers.
The regulatory assessment was conducted from a legal perspective only,
focusing on identification and characterization of relevant federal
legislation, coverage provided by related laws and regulations, and
characterization of administrative authority.
The following eighteen current federal statutes and regulations were
reviewed:
• Waste Disposal
Solid Waste Disposal Act of 1965
EPA Guidelines for the Land Disposal of Solid Wastes
Resource Conservation and Recovery Act of 1976
• Transportation
Hazardous Materials Transportation Act
Transportation of Explosives Act
Hazardous Cargo Act
Ports and Waterways Safety Act of 1972
• Water
Federal Water Pollution Control Act Amendments of 1972
Safe Drinking Water Act
Dam Safety Act of 1972
• Health and Safety
Federal Metal and Nonmetallic Mine Safety Act
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Health and Safety Standards for Metal and Nonmetallic Underground
Mines and Proposed Amendments
Federal Coal Mine Health and Safety Act of 1969
Health Standards for Underground Coal Mines
Safety Standards for Underground Coal Mines
Health Standards for Coal Mine Surface Work Areas
Safety Standards for Surface Coal Mines and Surface Work Areas
of Underground Coal Mines
Occupational Safety and Health Act of 1970
With the passage of the Resource Conservation and Recovery Act (RCRA)
in October 1976, coverage provided by federal legislation should be
extended to encompass all aspects of the disposal of FGD waste solids.
Although regulations specifically addressing the disposal of FGD sludge
have not yet been issued under the RCRA, it is expected to be the lead
legislation regulating FGD sludge disposal.
In terms of overall solid and hazardous waste management, the RCRA
provides for comprehensive regulatory authority at the federal level and
an institutional framework for planning and regulatory implementation at
the state level. Together with the Federal Water Pollution Control Act
Amendments (FWPCA) and the Safe Drinking Water Act (SDWA), which now
provide authority to regulate some aspects of underground discharges from
wastes, the RCRA should provide adequate legal protection for both ground-
water and surface.waters. Under the RCRA, the FWPCA, and several of the
health and safety statutes, FGD wastes will be subject to specific federal
standards and criteria including:
• characterization of wastes (as hazardous or nonhazardous);
• point-source effluent guideline limitations (as influenced by
the water quality of receiving streams);
• health standards pertaining to dust and airborne contaminants; and
• safety standards pertaining to refuse piles and impounding struc-
tures, roof support, and ventilation.
However, existing health and safety standards do not specifically address
FGD sludge, and new legislation and/or modifications of existing standards
may be required. Furthermore, appropriate administrative authority for
regulatory promulgation and enforcement of health and safety standards
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need study and clarification. Any changes should be determined following
a thorough technical assessment of the adequacy and applicability of
existing standards to FGD waste disposal operations.
Existing laws and regulations, though, do appear adequate to cover
transportation of FGD sludge. Transport of similar materials by modes of
transportation under consideration for FGD sludge is a frequent and
familiar practice of commerce, and existing transportation regulations
in combination with the other legislation discussed above should provide
adequate legal protection for the environment.
b. State
At the state level there are laws and regulations which either enhance
existing federal laws and regulations or fill gaps in these regulations.
Laws governing mining activities (i.e., reclamation, sealing, subsidence
control, and acid mine drainage) and permit regulations for wastewater
effluent, mine drainage, and solid waste disposal sites are generally
covered at the state level.
In assessing state regulations, Pennsylvania was selected as a model
state. Pennsylvania is an industrialized state with extensive mining
operations and a number of utilities planning (or operating) FGD systems.
The Department of Environmental Resources (DER) currently has lead
responsibility for regulating sludge disposal in mines. The primary
regulating statutes are administered by the Bureau of Land Protection and
Reclamation, the Bureau of Water Quality Management, and the Bureau of Mine
and Occupational Safety. The regulating statutes do not specifically
address FGD disposal in mines; however, collectively the statutes can be
interpreted as providing coverage for all aspects of sludge disposal.
In order to ensure orderly and environmentally sound disposal of FGD
sludge, the DER is considering regulatory amendments to existing statutes.
Some amendments regarding mine disposal may be clarified by a pilot field
program recently undertaken under an EPA grant to evaluate sludge disposal
in underground mines.
C. OCEAN DISPOSAL
1. Environmental Assessment
There is a basic distinction between shallow ocean (continental shelf)
and deep ocean (off-shelf) environments. The upper levels of the water
column in both these environments are contiguous and are treated as a
unified environment. However, the lower water columns and sea bed of the
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continental shelf and deep ocean are distinct. The former is biologically
productive and changeable, affording habitat for resources of importance
to man, while the latter is stable, diverse, and of limited value in terms
of living resource exploitation.
The "baseline" ocean dumping scenario chosen for analysis involves the
use of conventipnal-bottom-dump barges.,on the continental shelf. This
would be the quickest, cheapest, preferred method in the absence of regula-
tory constraints. Thus, impacts are discussed below in terms of this mode
of operation. Subsequent-,discussion focuses on major alternatives to
this mode, including:
• dispersed dumping on the continental shelf;
• conventional dumping off the continental shelf (deep ocean);
• dispersed dumping off the continental shelf; and
• concentrated dumping of treated sludges.
a. Physical Transport
The physical fates of sludge of three different consistencies have
been evaluated. These types are: dewatered (untreated), slurry (dispersed),
and treated (brick-like).
At some solid content (perhaps on the order of 50% for some materials)
dewatered, untreated sludge probably hangs together and falls through the
water as a cohesive mass. Simple lab experiments and preliminary modeling
results indicate that more than 95% of the dumped material will reach the
bottom intact after rapid descent and remain as a heap on the bottom.
Continuous utilization of the same site would result in the accumulation
of significant amounts of dumped material.
Sludge slurries which have been considerably diluted or which simply
have a low solids content will very likely disperse widely and sink slowly.
Within a few minutes, FGD sludge slurries would be expected to be distributed
throughout a water column several hundred feet in depth. The initial dilution
achievable by available equipment is expected to range between 5 x 10 and
1 x 101*.
Preliminary findings indicate that treated, brick-like sludge would
sink quickly and remain intact on the bottom for an indeterminate period
of time. Uncertainty surrounding the dissolution rate of such material
needs to be resolved.
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b. Environmental Impact Potential
Four principal categories of potential impacts for FGD sludge disposal
in the ocean environment are discussed below. These are:
• impacts of benthic sedimentation;
• impacts of sludge suspended in the water column;
• impacts of sulfite-rich sludge; and
• trace contaminant impacts.
The chosen order of presentation does not necessarily reflect the relative
significance of these several impact potentials.
Benthic Sedimentation
The benthic environment in the vicinity of dump sites would be
characterized by substrates substantially or entirely composed of sludge.
Such conditions would have serious impact potential. Benthic ecologists
generally regard the coarse-grained substrate (e.g., coarse sand) as most
conducive to the establishment of rich, diverse marine benthic macrofaunal
assemblages. Sediments of finer composition, especially if relatively
uncornpacted, provide the least stable and most limiting type of habitat.
In addition to the physical character of the sludge, its relative lack of
nutrient content may serve as a further limitation upon benthic faunal
community establishment.
Sludge Suspended in the Water Column
Many of the dominant finfish of the continental shelf dump sites may
be expected to exhibit intermediate sensitivity to suspended sediments.
In quantitative terms this sensitivity may be defined as experiencing 10%
mortality during 24-hour exposure to suspended sediment concentrations
between 1,000 and 10,000 mg/liter. Such concentrations would be expected
upon initial dilution throughout the dump site water column, but duration
of organism exposure is expected to be brief in the upper and mesopelagic
zones.
The extent to which other contaminants (including sulfite and heavy
metal residues) are part of the dumped sludge is another important aspect
of impact potential. Once within the stomach of a fish, particles are
exposed to acidic conditions capable of stripping absorbed contaminants
and making those contaminants available for damage or concentration within
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the organism or elsewhere in the food web. Thus, certain major contaminant
impact potentials may be relatively independent of the extent to which
water column concentrations of sulfite or trace metals might be increased
by dumping activities. These types of impacts could be important over the
long term at dump sites to such benthic finfish as cod and flounder, whose
feeding habits involve sediment suspension and ingestion.
Sulfite-Rich Sludge
The impact of the introduction of sulfite into the ocean environment
as consequence of FGD sludge disposal is of interest for two reasons.
First, sulfite has a measurable toxicity; and second, it will react with
dissolved oxygen, leading to a depletion of dissolved oxygen.
If the sludge is diluted by a factor of 500 in the course of being
dumped, the resultant concentration of sulfite in the stomach of disposal
area fish might be on the order of 0.006 M. This concentration is roughly
six times the median 50% lethal concentration for fish at pH 6 (0.001 M)
observed under laboratory conditions (8). Sulfite toxicity has been
demonstrated to be pH dependent, increasing with decreasing pH. Thus,
a concentration of 0.006 M sulfite in the stomach of finfish, where pH
levels would be 1 or 2, may have especially serious impacts. However,
more data needs to be obtained concerning organism uptake of suspended
particles of FGD sludge during the short-term exposures that would be
characteristic of ocean dumping conditions before the real impact potential
of sulfite-rich sludges regarding toxicity can be accurately quantified.
If the FGD sludge solids would dissolve instantaneously upon being
diluted and dumped, and if the oxidation in real seawater would proceed
as rapidly as uncatalyzed laboratory experiments proceeded, one would
expect to find severe reductions in dissolved oxygen in the vicinity of
the dump. However, calcium sulfite is very insoluble and it is unlikely
that complete dissolution would occur in one or a few minutes. It is
likely that solids dissolution rather than oxidation would be the limiting
step in the dissolution/oxidation sequence.
Trace Contaminant
The anticipated initial dilution of sludge liquor by a factor of 500
could result in concentrations of five trace metals approaching or in
excess of the "minimum risk" levels recommended by the National Academy
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of Sciences (NAS) (9). In decreasing order of apparent impact potential,
these metals are: mercury, zinc, selenium, cadmium, and nickel. Four of
these five (excepting selenium) are included in the elements of principal
concern identified by Ketchum et al. (10).
The reported range of trace contaminant levels in the solid phase of
FGD sludges encompasses considerably higher concentrations than found in
the sample sludge liquors. As with the liquors, values in the high range
have been obtained from sludges containing fly ash. As in the case of
sulfite, the impact potential of trace contaminants bound or adsorbed to
solid fractions of the sludge will be dependent upon critical variables
such as dissolution rate and particle uptake by free-swimming organisms.
Too little is known of these types of interactions over the short term to
allow for a feasible prediction of quantitative impacts.
c. Environmental Impact of Applicable Control Options
Restrictions on Sludge Composition
The impacts of benthic sedimentation, as discussed above, would not
be affected to any significant degree by restricting types of untreated
sludges disposed of on the continental shelf by bottom-dump barges.
Likewise, the impacts of suspended sludge in the water column would not
be affected from the gross standpoint of organisms' sensitivity to sediments
in general. However, two subsets of the suspended sediment impacts, the
impacts of sulfite and associated^ trace contaminants, could be significantly
mitigated by restricting the types of sludges disposed of at sea.
Disposal by Dispersion
If FGD sludge slurries were pumped overboard in a manner sufficient
to achieve instantaneous dilution on the order of 5,000 to 10,000, three
of the four impact potentials discussed above would be substantially
mitigated. Sulfite impacts would remain of potential significance in the
dispersed disposal option.
Concentrated Bottom Disposal
For purposes of this discussion, concentrated bottom disposal is
presumed to include chemical treatment of FGD sludge resulting in a cement-
or brick-like waste product. It appears that all four of the principal
impact potentials discussed above would be substantially mitigated by this
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control option. Of course, overriding this and all other considerations
of this control option is the question of dissolution. If the lifetime
of the material in concentrated form is relatively brief, two of the
advantages of this option would be removed. The trace contaminants
within the treated sludge would become available upon dissolution and
still might be problematic. Provided that questions concerning the
dissolution of concentrated, treated sludge can be resolved, this option
appears to offer considerable promise.
Chemical Treatment
With the exception of concentrated disposal of brick-like treated
material, chemical treatment appears to offer few, if any, advantages
over the traditional bottom-dump disposal of untreated FGD sludge. The
sulfite impacts discussed above might be mitigated to considerable degree
by chemical treatment, but the impacts of benthic sedimentation and
suspended sludge in the water column would be comparable to those associated
with typical untreated material. Trace contaminant impact potential could
be equal to, or possibly greater with soil-like chemically treated sludge
containing fly ash, than with untreated material. The potential impacts
from brick-like treated material are expected to be less but remain
unquantified.
Deep Ocean Dumping
In general, the short-term effects of conventional dumping of FGD
sludge in the upper water column (pelagic zones) of the deep ocean would
be similar to effects described above for the continental shelf. The
major differences between deep ocean and on-shelf disposal emerge in
consideration of long-term benthic and food web impacts.
The wider dispersion that would be achieved by disposal in depths of
several thousand feet would preclude many of the adverse impacts of benthic
sedimentation associated with shallower on-shelf disposal. The differences
between deep ocean and on-shelf disposal regarding suspended sediment and
sulfite impacts appear relatively minor.
The impacts of dissolved trace contaminants in sludge liquors would
be similar to those discussed above in conjunction with on-shelf disposal.
However, two characteristics of the deep ocean dumping environment tend to
mitigate trace contaminant impact potential. First, deep ocean sediments
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appear to be a natural sink, exhibiting considerably higher concentrations
of potential contaminants than near-shore areas. Second, and more important,
the lack of_flpDp£tunrty tojTjEontact between contaminants residing in the
deep ocean benthos and food webs of importance to man would largely elim-
inate the ris^~o^~pollution^episodes affecting human populations. The
trade-oTfbetween impacting the relatlverly -stabJ.e_bu.t-ar-ea-Hy extensive
deep ocean communities would have to be weighed against these advantages.
Disposing of only sulfate-rich sludges in the deep ocean would serve
to mitigate one of the remaining principal impact potentials, i.e., sulfite
toxicity. Overall, deep ocean disposal of sulfate-based wastes by conven-
tional means appear to be a relatively viable option on environmental
grounds.
Disposal by dispersion sufficient to achieve instantaneous dilution
on the order of 5,000 to 10,000 also appears to be a relatively viable
option from an environmental standpoint. These levels of initial dilution
would mitigate suspended sediment and trace contaminant impacts, probably
reducing them to insignificant levels. Potential problems of sulfite
toxicity and/or oxygen demand in the upper water column would be mitigated
but perhaps not resolved by deep ocean dispersal.
Disposing of treated brick-like FGD sludge in the deep ocean is
probably the most desirable of all options considered from an environmental
standpoint. All of the major impacts discussed above would be substantially
mitigated by this combination of controls. The disposal of chemically
treated, soil-like FGD sludges in the deep ocean could also mitigate
sulfite impact potentials. Combined with dispersion, this would probably
be a relatively attractive environmental alternative. However, the
combination of treatment and deep ocean disposal may not be economically
attractive.
2. Technology Assessment
Assessment of the technology available for the dumping of FGD sludge
in the ocean focuses on three areas: transportation, navigation, and
surveillance and monitoring. For this assessment, investigation in each
area determined whether technological means for successful dumping exists
or could be developed within the present state-of-the-art.
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a. Transportation
Transportation from the shoreline to offshore dump sites (either on
the continental shelf or off) could be accomplished using either surface
vessels (self-propelled or tug/barge combination) or pipeline.
The technology for appropriate underwater pipeline construction
falls into three categories: bottom pull, floating pipe, and lay barge
pipeline positioning. Lay barge techniques have been used to install
underwater pipelines of 30-inch diameter for distances over 100 miles.
The costs of offshore pipelines generally vary with length of the
line, depth, pipe size, ocean terrain, and materials to be transported.
The greatest single cost factor in such pipelines is the installation cost,
which generally runs more than 50% of the total investment. Maintenance
is usually the biggest cost factor in the operation of such pipelines.
Surface craft adequate for offshore disposal purposes exist and are
in use today. There are two large-capacity bottom-dump type barges
currently built in the United States (the largest in the world) which
carry American Bureau of Shipping ocean-going classification—a 3,000-cubic
yard (4,050-ton) barge and a 4,000-cubic yard (5,000-ton) barge. Such
barges would have roughly the capacity required for sludge disposal
operations.
Self-propelled hopper-type ships are also currently in use for waste
disposal. The basic configuration of these types of vessels would resemble
the hopper-type dredges owned and operated by the U.S. Army Corps of
Engineers. The capacity of these hopper dredges varies from a low of
720 cubic yards to a high of 8,277 cubic yards; however, European dredges
have now reached 15,000 cubic yards capacity.
Better (specially designed) equipment is feasible. Newer designs may
be required to control the rate of release of sludge, particularly where
high dilution factors are required. However, under almost all conditions,
disposal of slurried sludge would be economically impractical. The cost
of transporting FGD slurries would be unattractive, and reslurry of dry
or thickened sludge on board large disposal vessels would require impractically
large pumping capacities.
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A major cost consideration for surface craft involves the necessity
to employ two or three crew shifts if the dump site is located outside
a round trip range which can be covered in eight hours or less.
b. Navigation and Surveillance
To limit the impacts of sludge disposal, the location of dumping has
to be controlled. There are two aspects to such control. The first deals
with navigational accuracy available (or the ability to find any specified
dump site with precision). The second deals with policing the operation
to make certain that dumping takes place at the specified location (within
the accuracy limits of the available navigation systems).
Adequate means of navigation are currently available to allow fixing
the location of any particular dump to well within one mile with visual
control and within 0.5 to 3.0 miles with Loran-A, an electronic navigation
system currently in use along all coastlines of the United States, the
Great Lakes, the Gulf of Alaska, the Hawaiian Islands, and Puerto Rico.
The Loran-A navigation system is old and relatively expensive to maintain.
It is to be phased out of operation over the next 7-10 year period.
Recently, Loran-C, OMEGA, and NAVSAT have become available for use by
commercial shipping. Loran-C now provides precision accuracies of ±0.25
to ±0.5 nautical miles without degradation at sunrise or sunset. System
improvements now underway are expected to provide a 15-20 fold improvement
in precision accuracies.
Precisional accuracies on the order discussed above are certainly
adequate to the navigational requirements of pumping. However, for the
purposes of surveying and site monitoring, it may be necessary to achieve
even greater accuracies in some instances, e.g., for work with submersible
vehicles. Sonar Transponder systems are available which allow a submersible
to return to its exact previous position.
Surveillance of ocean dumping is currently accomplished by the U.S.
Coast Guard (USCG) through a manned system of ship riders, and waterborne
and airborne observers. Development of an automated Offshore Disposal
Surveillance System (ODSS) is underway. The ODSS system will use a fully
automatic Loran-C receiver, data logger, and recorder with a format on
magnetic tape suitable for computer analysis by the USCG, if required.
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ODSS may also be interlocked with dump release mechanisms, thus assuring
accurate location of dumps. Such equipment could be required before
permits are issued.
c. Monitoring
In this context, monitoring is distinguished from model verification
research, although both activities require work at sea. Model verification
work needs to be performed in order to provide the reliable capability of
predicting plume dispersion in time and space. Once adequately accomplished,
there will be no need for routinely duplicating the original work. Monitor-
ing, on the other hand, requires the definition or establishment of an
environmental baseline and routine resurveys to determine whether changes
have taken place, the nature of the changes, and their trends.
A baseline survey of the magnitude required prior to sludge dumping
could generally be expected to require up to 18 months to complete. One
cruise alone might last one to three weeks. Trend assessments will be
required at the FGD disposal site three to four times per year after
disposal begins. Additional surveys of selected critical parameters may
be necessary during periods of heavy dumping.
Standard oceanographic techniques exist for collection and analysis
of water, sediment, and biotic samples. Special large-volume samplers and
highly sensitive laboratory techniques have been developed to monitor trace
constituents. However, the reliability of these techniques is such as to
require caution to interpreting the results.
Currents can be determined directly and indirectly. Indirect measure-
ments (e.g., drift cards or drift bottles) require long periods of
observation and subjective interpretation but can be relatively inexpensive
for each data point. Moored current meters (and other instruments) can
provide long-term direct observations which are highly useful. However,
reliability is still a problem, and fouling or other failures which degrade
efficiency or render the data useless are issues with which to deal.
Bathymetric surveys can be accomplished with sufficient horizontal
and vertical accuracy and precision to provide effective monitoring of
a concentrated dump site.
46
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Recent experience indicates that offshore ocean dumping site surveys
that require one to two weeks of ship time to complete will require an
additional three to four months for data evaluation, analysis, and reporting.
A typical ocean survey program of this type costs in the range of $200,000
to $250,000 per cruise including preliminary conclusions and a summary data
report.
3. The Regulatory Environment
The regulatory environment is discussed in terms of the current
statutory base, administrative regulations, and agency attitudes.
The discussion of legislation highlights five aspects of the Marine
Protection Research and Sanctuaries Act of 1972 (P.L. 92-532), the basis
for all domestic regulation of ocean dumping. These are:
• statement of policy;
• mandatory considerations in the issuance of permits;
• penalties;
• preemption of other jurisdictions; and
• establishment of regulations.
Substantive revisions to the EPA Ocean Dumping Regulations are still
pending as of this writing. The following four aspects of existing and
pending regulations are focal points in this report:
• consideration of alternatives;
• prohibited materials;
• other factors limiting permissible concentrations; and
• monitoring requirements.
Agency attitudes were sampled by visits with administrative and
technical support staff at EPA headquarters, Marine Water Quality
Laboratories, and regional offices. In summary, the regulatory
environment surrounding ocean dumping is not favorable to new dumping
initiatives at this time. The phasing-out of existing dumping and alter-
natives to future dumping are receiving emphasis. In addition, unless
proposed regulations are modified, Eastern sludges could be precluded from
ocean dumping entirely on the basis of the cadmium content of the solid
phase. Mercury limits are also specified but appear to be somewhat less
of a potential constraint on FGD sludge disposal.
47
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D. ECONOMICS OF CONCEPTUAL DISPOSAL SYSTEM DESIGNS
1. Basis for Design and Economics
Conceptual system designs and general capital and operating costs have
been prepared for five ocean disposal and six mine disposal options. Costs
are based upon 365,000 tons per year of dry sludge (including ash) from a
500-megawatt power plant burning typical Eastern coal (3.0% sulfur, 10.0%
ash, and 0.85 Ibs of coal/kwh). The sludge (with ash) is assumed to be
available either as a dry filter cake (50% solids), a 35% solids slurry
(thickener underflow), or as treated sludge. No costs have been included
for sludge processing such as filtration, drying, fly ash addition, or
treatment; however, where treated, brick-like sludge is handled, an estimate
for excavation of treated sludge from stabilization ponds or impoundments
has been included.
Capital costs are based upon 1978 completion of construction and
include: installed equipment cost for the battery limits disposal system
(transfer/handling/placement), engineering and contractors' fees, working
capital, owner's expense, startup, and interest and escalation during
construction. Not included in capital investment are extensive site
preparation, land cost, auxiliary utilities, fees for permits, or, as
previously indicated, sludge treatment equipment.
2. Coal Mine Disposal Economics
The conceptual systems include the disposal of both filter cake
(admixed with ash) and treated sludge in onsite and offsite surface area
coal mines, and the disposal of slurried, untreated sludge (with ash) in
onsite and offsite underground coal mines. For onsite mines, either truck
transport (filter cake and treated sludge) or pipeline (thickener underflow)
are used for transport of the sludge. For offsite mines, rail haul of
either treated sludge or filter cake is assumed. Preliminary estimates
have shown truck haul and slurry pipeline to be impractical for long-
distance sludge transport.
For untreated sludge (or treated, soil-like sludges) estimated
disposal costs including transfer and intermediate storage range from
$3.00-3.50 per dry ton for onsite disposal to $6.50-8.00 per dry ton
for offsite disposal. Disposal of treated sludges requiring the use of
stablization ponds or impoundments increases costs by about $2.00-2.50 per
ton to account for excavation of the ponds. These estimates do not include
48
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site monitoring costs, which are strongly a function of the hydrology,
sludge characteristics, and parameters (species) measured. Sludge
processing costs must also be added to these transfer/placement costs
to determine overall disposal system economics.
3. Ocean Disposal
Conceptual system designs and associated costs have been developed
for five ocean disposal options—two for on-shelf (25 nmi) and three for
off-shelf (100 nmi) dumping. Estimates include on-shelf disposal of both
untreated and treated, brick-like sludge; and off-shelf disposal of
untreated filter cake, thickener underflow and treated, brick-like sludge.
While disposal of untreated sludge on the shelf is not presently considered
promising due to the potentially adverse environmental impacts, it has been
included for comparative purposes.
It is assumed in preparing the conceptual system designs that the
sludge is produced in an Eastern power plant with ready access to the
ocean, i.e., facilities for berthing barges are available with sufficient
area for installation of a sludge transfer/storage system. Costs have
been developed for operations including tug/barge combinations and self-
propelled ships. In all cases, the system costs utilizing self-propelled
ships are less than for tug/barge combinations due to the lower capital
investment (shorter cycle times for ships and, therefore, fewer ships
required).
In summary, disposal of untreated filter cake (with ash) on the shelf
is estimated to run $4.00-5.00 per dry ton of sludge. For treated sludge
requiring stabilization ponds or impoundments, costs would be approximately
$2.00-2.50 per dry ton to cover the cost of excavation of the sludge.
Deep (off-shelf) ocean disposal of filter cake or treated sludge runs
about $3.00-4.00 per dry ton more than shallow (on-shelf) ocean disposal.
And disposal of thickener underflow in the deep ocean costs approximately
$1.00 more per ton than filter cake disposal. As with mine disposal
costs, these estimates do not include monitoring costs (which are not
a direct function of the sludge quantity) or sludge processing costs.
49
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REFERENCES
1. Leo, P. P. and J. Rossoff. Control of Waste and Water Pollution from
Power Plant Flue Gas Cleaning Systems: First Annual R and D Report.
EPA-600/7-76-018, October 1976.
2. Maloch, J. Chemical Fixation of Hazardous Waste and Air-Pollution-
Abatement Sludges. Interim results of an EPA program conducted by
the Environmental Effects Laboratory, U.S. Army Engineer Waterways
Experiment Station, Vlcksburg, Mississippi, to be published.
3. Esso Research and Engineering Company. Potential Pollutants in Fossil
Fuels. NTIS.
4. Maloch, J. Chemical Fixation of FGD Sludges — Physical and Chemical
Properties. Paper presented at the EPA Symposium on Flue Gas
Desulfurization, New Orleans, March 1976.
5. A Laboratory and Pilot Plant Study of the Dual Alkali Process for S02
Control. Unpublished results obtained under EPA Contract No. 68-02-1071
by Arthur D. Little, Inc., to be published.
6. Klym, T. W. and D. J. Dodd. Landfill Disposal of Scrubber Sludge.
Paper presented at the National ASCE Environmental Engineering Meeting,
Kansas City, October 1974.
7. Fling, R. B. et al. Disposal of Flue Gas Cleaning Wastes - EPA Shawnee
Field Evaluation - Initial Report. EPA-600/2-76-070, March 1976.
8. Sano, H. C. and A. Semizo. pH Dependence of the Toxicity of Sulfite in
Water. Kogyo Gijutsu Shikensho Kiho, 22_ (4):293-298, 1971.
9. National Academy of Sciences, Water Quality Criteria, 1972. A Report
of the Committee on Water Quality Criteria, Washington, D.C., 1972.
10. Ketchum, B. H., V. Zitko, and D. Saward. Aspects of Heavy Metal and
Organohalogen Pollution in Aquatic Ecosystems. In: Ecological
Toxicology Research: Effects of Heavy Metal and Organohalogen
Compounds, A. D. Mclntyre and C. F. Mills, eds. Plenum Press, New
York and London, 1975. pp. 75-81.
50
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IV. CHARACTERISTICS OF FGD SLUDGES
A. CHEMICAL CHARACTERISTICS OF UNTREATED FGD SLUDGES
The chemical composition of the sludge produced by any given FGD
process at any particular time depends upon a number of factors including
the composition of the coal being burned, the type of boiler and its
operating conditions, the method of particulate control employed, and the
type of FGD system employed and the way in which it is operated. Because
of the numerous variables involved, sludge composition can vary over
extremely wide ranges. The following sections review ranges of chemical
composition which might be encountered in FGD sludges. The results of
sludge composition measurements that are presented have been assembled
from a variety of sources and represent those available as of this writing.
Principal sources of data have been the studies conducted by The Aerospace
Corporation (Aerospace) and the United States Army Engineer Waterways
Experiment Station (WES) for the Environmental Protection Agency (EPA).
These programs, and others, are continuing and it is expected that addi-
tional data on sludge characteristics will be available in the near future.
The samples characterized in most studies usually consist of one or
at most a few samples taken from different FGD systems on particular days.
It must be stressed that the compositions of samples taken from any one
of the systems could be quite different on different days. Similarly,
the same type of FGD system installed on another boiler and run under
a different set of operating conditions can produce a sludge with entirely
different properties. Thus, the data cited should be viewed as illustra-
tive of the effects of various phenomena which can influence sludge
composition rather than as defining the composition of sludge produced
by a particular process or process type.
1. Major Components in FGD Sludge Solids
The major solid components comprising FGD sludges include calcium-
sulfur salts (usually calcium sulfite, calcium sulfate, or a mixture of
the two) with varying amounts of calcium carbonate and fly ash. The
ratio of calcium sulfite (CaSOs • 1/2 H20) to calcium sulfate (usually
present as gypsum, CaSOit • 2H20) can vary over an extremely wide range.
51
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Table IV-1 contains examples of sludges which contained only very small
amounts of calcium sulfate (Paddy's Run) and some which contained essen-
tially no calcium sulfite (Mojave and Utah). Oxidation, and consequently
the calcium sulfate-to-calcium sulfite ratio, is usually greater in systems
burning low sulfur western coal. Less oxidation usually takes place in
direct lime than in direct limestone systems. However, it is possible to
promote oxidation in either of those systems to produce sludges with a
high calcium sulfate/calcium sulfite ratio. The same is true for dual
alkali systems. When high sulfur coal is burned and the boiler and FGD
system are operated appropriately, the calcium-sulfur salts can consist
primarily of calcium sulfite. However, if intentional oxidation is
performed, gypsum can be the predominant calcium-sulfur salt.
Fly ash is the other major component which can vary over wide concentra-
tion ranges. In some systems, e.g. Paddy's Run, Mojave, or Scholz, fly ash
is collected separately in electrostatic precipitators or mechanical
collectors ahead of the FGD scrubber. Such fly ash collection is usually
very efficient and little if any fly ash is found in the sludge. In other
systems, the 862 scrubber also functions as a particulate control device
and the collected fly ash can comprise from 20 to 60% of the FGD sludge
solids. Even in installations where fly ash is collected separately,
it can be admixed with ash-free sludge in an attempt to improve the
handling properties of the sludge.
Varying amounts of unreacted limestone (CaCOs) can be found in the
sludges from direct limestone processes. Direct lime and dual alkali
processes utilizing lime for regeneration usually operate with only small
amounts of excess lime over that required for liquor regeneration. However,
lime is often contaminated with some limestone which passes through the
system unreacted and ends up in the sludge, and lime can also react with
C02 for mixing small amounts of CaCOs- Some dual alkali processes employ
sodium carbonate softening to reduce dissolved calcium levels in order to
minimize scrubber scaling. The softening reaction produces calcium
carbonate, which leaves with the sludge.
Other calcium-sulfur salts have been reported, in certain FGD sludges
on the basis of X-ray diffraction measurements. They have been detected
in only isolated cases and their presece needs to be confirmed by other
52
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TABLE IV-1
Plant
Shawnee
Shawnee
Duquesne
Paddy's Run
Cholla
Mo j ave
Parma
Scholz
Utah
Montana
Location
Eastern
Eastern
Eastern
Eastern
Western
Western
Eastern
Eastern
Western
Western
MAJOR
Process
Limestone
Lime
Lime
Lime
Limestone
Limestone
Dual Alkali
Dual Alkali
Dual Alkali
Fly Ash
COMPONENTS IN FGD SLUDGE SOLIDS
CaS03-l/2H20
19-23
50
13
94
11
2
14
65-90
0.2
0-5
Percent by
CaSOir2H20
15-32
6
19
2
17
95
72a
5-25
82b
5-20
Weight
CaC03
4-42
3
0.2
0
2.5
0
8
2-10
11
nil
Flyash
20-43
41
60
4
59
3
7
nil
9
40-70
Source
Other (Ref)
1
1
9.8% CaS3010 1
2
14% CaS203-6H20 1
2
3
4
1
5-30% MgS04 5
Portion (20% of sludge) reportedly CaS04-l/2H20
Portion (18% of sludge) reportedly CaSOi,
-------
chemical tests. However, on the basis of known FGD system chemistry, the
presence of those substances, regardless of what their exact identity is
finally determined to be, should not significantly alter the general
characteristics of FGD sludges as related to their disposal.
2. Trace Elements in FGD Sludges
A variety of trace elements find their way to FGD sludges from a
number of sources. Coal itself contains a large number of trace elements
present either in minerals occluded within the coal or as organometallic
compounds (compounds of arsenic and selenium, in particular) distributed
throughout the coal itself. The lime or limestone generally used as a
reagent in FGD systems also contains mineral impurities which contribute
trace elements to the sludge. And, depending on the quality of the process
water used in the system, measurable amounts of trace elements can enter
with it. However, there are few reported measurements of trace elements
in process water and makeup chemicals.
The level of trace elements in the sludge depends primarily upon
three factors: the level of various trace constituents in the coal
relative to its sulfur content (and in FGD process additives); the amount
of ash, if any, collected with or admixed with the sludge; and the effi-
ciency of the scrubber system in capturing volatile trace constituents.
Many of the elements are not highly volatile and will be retained in the
ash (fly ash and bottom ash) matrix. The extent to which fly ash is a
part of the sludge composition determines the presence of the least
volatile elements in FGD sludge but has little impact on the presence of
highly volatile elements. On the other hand, the concentrations of such
highly volatile elements as arsenic, mercury, and selenium which appear in
the sludge will depend upon the extent to which they are present in and
released from the coal and, more importantly, the efficiency with which
they are captured in the scrubber. Mercury and selenium are likely to
be present in the flue gas as elemental vapors that might not be scrubbed
efficiently.
Assuming that the limestone, lime, and process water makeup to the
system are not contaminated with trace elements and that all highly
volatile species are captured in the scrubber, then the FGD system would
54
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increase the concentration of trace elements proportionate to the coal
weight lost upon combustion. Since the burning of one ton of coal
produces 0.05-0.20 tons of dry scrubber sludge without fly ash (depending
upon the sulfur content and SC>2 removal efficiency) and up to 0.4 tons of
scrubber sludge with fly ash, it could be expected that trace element
levels in the sludge could increase by a factor of 2X to 20X over those
found in coal.
In addition to changes in concentration of trace constituents in
sludge as compared to coal, there is also a change in the form and avail-
ability of these constitutents. Important differences in trace element
chemistry and availability between the original coal material and the FGD
sludge are as follows:
Original Coal FGD Sludge
Trace elements contained in highly Trace elements dispersed in poten-
insoluble mineral matrix and tially soluble CaSOi^ and CaSOs
therefore inaccessible and immobile matrix and therefore eventually
accessible
Undisturbed geological material Sludge composed of fine particles
compact, relatively non-porous with with finite permeability
low leaching rates
Trace elements usually present as On combustion, trace element con-
stable, insoluble organometallics, taining compounds are converted to
sulfides, or carbonates (6) oxides (in certain cases, elemental
forms) which are more soluble and
chemically reactive
A number of the important trace elements which have been found in
FGD sludges containing up to 60% ash are listed in Table IV-2 along with
the range of concentrations at which they have been detected in conjunction
with measurements performed on from 5 to 9 samples. Also included are the
median observed concentrations for the particular sets of samples studied
and a comparative listing of ranges of trace motal levels which have been
measured in a variety of coal samples.
The observed concentrations range over as much as two orders of mag-
nitude which is a result, primarily, of the fact that the levels of trace
elements in coal can vary by that same extent. The measured concentrations
of a given element in the sludge samples studied generally fall within the
same range as do typical concentrations in coal. That the trace element
55
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TABLE IV-2
Element
Arsenic
Beryllium
Cadmium
Chromium
Copper
Lead
Manganese
Mercury
Nickel
Selenium
Zinc
CONCENTRATIONS
OF TRACE ELEMENTS
Concentration Median
Ranges (ppm) Concentration (ppm)
3.4-63
0.62-11
0.7-350
3.5-34
1.5-47
1.0-55
11-120
0.02-6.0
6.7-27
<0.2-19
9.8-118
33
3.2
4.0
16
14
14
63
1
17
7
57
IN FGD SLUDGES
Number of
Observations
9
8
9
8
9
9
5
9
5
9
5
Range of Trace Elements
Measured in Coal (ppm) (8)
3-60
0.08-20
-
2.5-100
1-100
3-35
0.01-30
-
0.5-30
0.9-600
Values as reported.
Source: References (1) and (7).
-------
concentrations in sludge is not observed is not known at the present time.
However, only a few sludge measurements have been made, and in none of the
cases was the coal analyzed for its trace element content.
3. Composition of Liquors Entrained Within FGD Sludges
The liquid phases of FGD sludges contain dissolved in them a wide
variety of substances ranging from trace amounts of a variety of metals,
some of which are toxic at low levels, to substantial amounts of commonly
occurring ions like sodium, calcium, chloride, and sulfate. Because the
substances dissolved in sludge liquors are more available to impact the
environment quickly when the sludge is disposed of than are substances
in sludge solids (and also because liquors are considerably easier to
analyze than solids) the compositions of FGD sludge liquors have been
studied in considerably more detail than have compositions of sludge
solids. Drawing primarily from the studies at Aerospace and WES, the
ranges of concentrations at which a number of substances have been detected
in sludge liquors and elutriates have been tabulated in Table IV-3. Again,
as was the case with the composition of FGD sludge solids, the concentration
at which a substance was detected in the sludge liquor varied by a factor
of 100 or more. The results of direct measurements and elutriate tests
were combined in preparing Table IV-3 because the elutriate tests produced
results which covered about the same range as did the direct measurements.
Dilution accompanying the elutriate test could have been at most a factor
of ten; lower concentrations were probably not observed because of the
relatively large reservoirs of trace elements available for dissolution
from the solids. Because for some substances the set of observed concentra-
tions contains one value which is very much greater or very much less than
the remaining observations which are grouped more closely together, the
median value for each set of measurements is also included in Table IV-3
to provide an indication of what a "likely" concentration might be.
On the basis of both the median and maximum observed concentrations,
antimony and arsenic concentrations seem to be higher in FGD sludge liquors
produced from eastern coals. On the other hand, levels of boron and chloride
appear higher in sludge liquors from western coals. It must be point out,
however, that the variation in concentrations of a particular substance in
57
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Ln
00
TABLE IV-3
LEVELS OF CHEMICAL SPECIES IN FGD SLUDGE LIQUORS AND ELUTRIATES
Eastern Coals
Species
Antimony
Arsenic
Beryllium
Boron
Cadmium
Calcium
Chromium
Cobalt
Copper
Iron
Lead
Manganese
Mercury
Molybdenum
Nickel
Selenium
Sodium
Zinc
Chloride
Fluoride
Sulfate
IDS
PH
Range in
Liquor (ppm)
0.46-1.6
<0. 004-1. 8
<0. 0005-0. 05
41
0.004-0.1
470-2,600
0.001-0.5
<0. 002-0.1
0.002-0.4
0.02-0.1
0.002-0.55
<0. 01-9.0
0.0009-0.07
5.3
0.03-0.91
<0. 005-2. 7
36-20, 000a
0.01-27
470-5,000
1.4-70
720-30, 000a
2, 500-70, 000a
7.1-12.8
Median
(ppm)
1.2
0.020
0.014
41
0.023
700
0.020
0.35
0.015
0.026
0.12
0.17
0.001
5.3
0.13
0.11
118
0.046
2,300
3.2
2,100
7,000
~~
Total No. of
Observations
4
15
16
1
11
15
15
3
15
5
15
8
10
1
11
14
6
15
9
9
13
—
Western Coals
Range in
Liquor (ppm)
0.09-0.22
<0. 004-0. 2
0.0006-0.14
8.0
0.011-0.044
240-(^45, 000)b
0.024-0.4
0.1-0.17
0.002-0.6
0.42-8.1
0.0014-0.37
0.007-2.5
<0. 01-0. 07
0.91
0.005-1.5
<0. 001-2. 2
l,650-(-\>9,000)a
0.028-0.88
1, 700-43, 000b
0.7-3.0
2, 100-18, 500a
5, 000-95, 000b
2.8-10.2
Median
(ppm)
0.16
0.009
0.013
8.0
0.032
720
0.08
0.14
0.20
4.3
0.016
0.74
<0.01
0.91
0.09
0.14
—
0.18
1.5
3,700
12,000
—
Total No. of
Observations
2
7
7
1
7
6
7
2
7
2
7
6
7
1
6
7
2
7
2
3
7
3
levels of soluble sodium salts in dual alkali sludge (filter cake) depend strongly on the degree of cake
wash. The highest levels shown reflect single measurements on an unwashed dual alkali filter cake.
(See text.)
Levels of soluble chloride components in sludges are dependent upon the chloride-to-sulfur ration in the
coal. The highest levels shown are single measurements for a western limestone scrubbing system operating
in a closed-loop using cooling tower blowdown for process makeup water.
Source: References (1) and (7).
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sludge liquors from two plants burning one type of coal can be much greater
than the relatively small difference which appears to be a function of coal
type.
With regard to the trace elements present in FGD sludges, a comparison
of Table IV-3 with Table IV-2 shows quite clearly that only a very small
fraction of the total amount of almost every trace metal present in the
sludge is found dissolved in the sludge liquor. The insolubility of many
of the metal hydroxides is the primary reason for this phenomena.
Solubilities of compounds of the major ions in solution, e.g., sodium,
chloride, and sulfate, do not vary appreciably with pH, and the concentra-
tions of these ions in solution tend to rise to a point where the rate at
which they are collected or formed is in balance with the rate at which
they are rejected from the system in the sludge liquor. In direct lime and
direct limestone slurry systems, sodium concentrations generally do not
exceed a few thousand ppm. In sodium-based dual alkali systems, sodium
concentrations in sludge liquors can range from 4,000 to 8,000 ppm or, if
the filter cake is not washed well, even higher. For example, during
sampling of the Utah and Parma dual alkali systems for the WES and Aerospace
programs, the filter cake was not washed well and sodium levels (primarily
Na2SOi| and NaCl) exceeded 20,000 ppm. In contrast, during periods of
proper cake wash, cake samples from the Scholz dual alkali system showed
less than 8,000 ppm of sodium.
Soluble chloride concentration is primarily a function of the chlorine/
sulfur ratio in the coal being burned and the system water rejection rate.
While chloride concentrations in liquors are generally less than 4,000 or
5,000 ppm, levels as high as 43,000 ppm have been reported for systems
burning low sulfur western coal when a very tight liquor loop is maintained
and when cooling tower blowdown is used for makeup water.
Sulfate concentrations are limited by the solubility product of gypsum.
In direct lime or limestone slurry systems they generally do not rise above
5,000 to 8,000 ppm. However, soluble alkali or alkaline earth compounds
containing magnesium or sodium are sometimes intentionally introduced into
direct limestone systems to improve their performance. Under those circum-
stances sulfate concentrations can rise to 10,000 ppm or more. In well
operated dual alkali systems (in which filter cake is well washed) soluble
sulfate in the filter cake interstitial liquid generally ranges from
5,000 to 10,000 ppm.
59
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B. PHYSICAL AND ENGINEERING PROPERTIES OF UNTREATED FGD SLUDGES
The various physical properties of FGD sludges are important factors
in the feasibility of almost every step of a candidate FGD sludge disposal
scheme. Viscosity determines the feasibility and cost of transporting
sludge slurries through pipelines. The ease and degree to which sludges
can be dewatered affects costs of transportation, chemical treatment (if
applied) and placement. The permeabilities of sludges affect the rate at
which pollutants are leached. These, and the other physical and engineering
properties of importance, all depend primarily on the percent solids in the
sludge and on the morphology and size of the solid particles. Like the
chemical composition of sludges, the morphology and size of sludge particles
depends on, and can vary widely as a function of, the sulfur content of the
coal, the way the boiler is operated, the type of particulate control
employed, and the type of FGD system employed and the mode in which it is
operated.
The results of measurements of physical and engineering properties
that are presented in this section are representative of those available
when this report was prepared. Programs involving the characterization
of physical and engineering properties are still underway and additional
work is anticipated. The physical and engineering properties that have
been measured in the past have generally been those which have proven
useful in predicting the behavior of soils in construction and landfill
operations. As soil mechanics experts continue to examine FGD sludge in
greater detail and apply new and different tests, a more complete under-
standing of the nature of FGD sludge will be possible. At present,
Atterberg Limit Tests (both plastic and liquid) and consolidation tests
are just beginning to be run on a limited number of sludge samples by the
Civil Engineering Department of the University of Louisville. Also, as
yet, no comprehensive triaxial compression tests have been run on FGD
sludges. Data from these types of tests will be invaluable in predicting
the behavior of FGD sludges in different disposal environments (9).
1. Particle Size Distribution
The solid phase of FGD sludges is comprised of particles normally
ranging in effective diameter from about 1 to 200 microns. The family of
particle size distribution curves shown in Figure IV-1 shows the general
60
-------
100
80 -
•5 60
m
0>
i! 40
Range of Typical Data
20 -
0 I i i i i I i i
1.0 0.5
Source: Reference 10.
100
0.1 0.05
0.01 0.005
0.001
Grain Size (mm)
FIGURE IV-1 PARTICLE SIZE DISTRIBUTION OF FGD SLUDGES
-------
distribution of sludge particle sizes as determined by sedimentation tests.
The bimodal particle size distribution curve which is displaced to the left
from the other curves was determined for a sample of sludge produced by an
eastern direct limestone slurry process. About 40% by weight of the
particles in that slurry had equivalent diameters greater than 50 microns;
a second major portion of the solids had particle sizes within a relatively
narrow band centered about ten microns. A bimodal distribution of that
sort would be found if the sludge consisted of a mixture of large calcium
sulfate/calcium sulfite crystals and smaller particles of fly ash or
unreacted limestone.
Two distribution curves obtained on samples of eastern and western
dual alkali sludges show about 10 to 20 weight % of the solids particles
with equivalent diameters of less than a few microns. However, dual alkali
systems do not necessarily produce sludges containing significant amounts
of very fine particles. Other dual alkali systems under different process
operating conditions have produced sludges in which bulk of the particle
diameters ranged from 20 to 50 microns and larger (11).
Q 2. FGD Sludge Densities and Dewatering Characteristics
Sludges produced by FGD systems are composed of two phases—sludge
solids and entrained liquor (as well as entrained air). Depending on the
proportions of each phase, the specific gravity of the product sludge can
range from about 1.3 to 1.8. The true densities of the solid particles
themselves, as shown in Table IV-4, are considerably higher, about 2.45 (1).
Since most unthickened slurries found in FGD processes contain on the
order of 10% by weight suspended solids, they are frequently dewatered by
one means or another prior to being discharged from the process to avoid
the unnecessary discharge of large amounts of process liquor. The wet bulk
densities of eight sludges after being dewatered in laboratory tests designed
to simulate settling, settling followed by draining, filtration, and centri-
fugation are included in Table IV-4. Active dewatering by filtration or
centrifugation generally produced a more dense sludge containing a higher
percent of solids—wet bulk densities ranged from about 1.4 to 1.9 gram per
cubic centimeter, and weight: percent solids ranged from about 43 to 80%.
The highest wet bulk densities and percents solids were observed for a
62
-------
TABLE IV-4
OJ
TRUE AND BULK DENSITIES OF
Plant
Shaunee
Shawnee
Duquesne
Cholla
Mohave
Parma
Utah
Location
Eastern
Eastern
Eastern
Western
Western
Eastern
Western
Process
Limestone
Lime
Lime
Limestone
Limestone
Dual Alkali
Dual Alkali
Date
Sampled
2/1/73
6/15/74
3/19/74
6/17/74
9/1/74
3/30/73
7/18/74
8/9/74
Fly Ash
(%)
20
40
41
60
59
3
7
9
True
Density
(g/cc)
2.48
2.45
2.53
2.50
2.53
2.53
2.45
2.60
FGD SLUDGE SOLIDS
Settled
Density
1.45
1.52
1.34
1.40
1.39
1.65
1.26
1.29
z
Solids
45.0
52.9
43.4
47.6
46.7
66.6
40.0
37.4
Drained
Density
1.51
1.53
1.37
1.47
1.44
1.67
1.39
1.30
%
Solids
51.7
58.3
45.3
54.2
50.9
67.2
43.9
37.8
Filtered
Density
1.65
1.70
1.55
1.52
1.48
1.78
1.57
1.38
%
Solids
65.0
65.9
56.0
47.0
53.4
80.3
57.8
43.1
Cencrifugation
%
Density Solids
1.56
1.56
1.37
1.47
1.60
1.86
1.40
1.54
55.8
63.3
49.9
57.2
60.9
75.0
50.9
62.2
Source: Reference (1).
-------
western limestone sludge containing very little fly ash. That particular
sludge consisted almost entirely of gypsum which dewaters very well because
it exists as rather large regular crystals.
The dewaterability of FGD sludges with actual process equipment tends
to parallel the laboratory studies. Sludges containing primarily calcium
sulfate can be dewatered to a greater extent than high calcium sulfite
sludges. However, in practice, sludges are often not dewatered to the
degree that can be achieved in the laboratory. Typical levels of percent
solids which have been achieved are:
Weight Percent Solids
Sludge Type Thickening/Clarification Filtration
Sulfite-rich CaS03 • 1/2 H20 ' 20-35 35-75
Sulfate-rich CaSOi^ • 2H20 (gypsum) 40-60 60-80
It is important to note that dewatering properties are strongly
dependent upon the type and size of crystals grown. Since large gypsum
crystals can be grown by controlling reaction rate, it is generally believed
that gypsum solids can be more readily dewatered. However, the dewatering
properties of sulfite-rich sludges can also be greatly improved by con-
trolling crystal size and/or causing agglomeration of small crystals. In
general, dual alkali systems have the capability for producing filter cakes
containing up to 65% solids and higher because the calcium sulfite formation
reaction is conducted in a crystallizer/reactor independent from the
scrubber system. However, recent tests with direct lime and limestone
systems have shown that sulfite crystal growth can also be controlled
(resulting in improved dewatering properties) by closer control of system/
boiler operating conditions.
\y 3. Slurry Viscosities
Since slurry pumping is one potential means of FGD sludge transport,
the viscosities of a number of FGD slurries were measured by Aerospace (1).
Viscosities as a function of percent solids in the slurry are shown in
Figure IV-2 for sludges from two western limestone (WLS) processes, an
eastern limestone (ELS) process, two eastern lime (EL) processes, a western
dual alkali (WDA) process, and an eastern dual alkali (EDA) process.
64
-------
Curve System
Source
Date Fly Ash. %
WLS
WLS
ELS
ELS
ELS
EL
EL
WDA
EDA
Arizona Cholla Slurry Tank 4/1/74 58.7
SCE Mohave 3/30/73 3.0
TVAShawnee 7/11/73 40.9
TVAShawnee 6/15/74 40.1
TVA Shawnee 2/1/73 20.0
Duquesne Phillips 6/17/74 59.7
TVA Shawnee 3/19/74 40.5
Utah Gadsby Double Alkali 8/9/74 7.9
GM Parma Filter Cake 7/18/74 7.4
8
'6
0.
120
100
80
60
40
20
70
Source: Reference 1.
60 50
Solids Content, Weight %
40
30
FIGURE IV-2 VISCOSITY OF DESULFURIZATION
SLUDGE
65
-------
A complete explanation of all of the factors underlying the wide range
of viscosities observed is not available at the present time, but both
the amount of fly ash and the morphology of the calcium/sulfur salt
particles seem to play roles.
The two western limestone sludges contain very different amounts of
fly ash. The one containing the greater amount was observed to be less
viscous. However, both exhibit steep viscosity versus % solids curves
characteristic of gypsum and materials of larger and more uniform grains.
The three eastern limestone sludge curves represent the behavior of three
samples taken from the same process at different times. The two samples
containing about 40% fly ash were less viscous than the one containing
20%. The samples from the eastern lime processes seemed to depend in the
same fashion on fly ash content although they were shifted to higher
viscosities from the eastern limestone sludges. The two dual alkali
sludges exhibited the highest viscosities of all of the samples tested.
Particles in the dual alkali and eastern lime sludges that were not fly
ash appeared to be somewhat fluffy agglomerates of very fine crystals
as compared to the considerably larger rectangular plates found in the
direct limestone sludges. The higher viscosities of the dual alkali and
direct lime sludges as a group were attributed to that morphology
difference (1).
In addition to illustrating the wide variation in slurry viscosity
that one will encounter upon going from one process to another, the curves
in Figure IV-2 also illustrate the very important point that day-to-day
changes in boiler/FGD system operation are likely to cause significant
changes in sludge viscosity. A decrease in the amount of fly ash collected
or a change in morphology of the solids as a result of a change in operating
conditions could change the energy required to pump the slurry.
n 4. Permeabilities of FGD Sludges
Shown in Table IV-5 are coefficients of permeability, k, determined
for a number of FGD sludges in two studies. Included in Table IV-5 are
determinations of void ratio, e, the quotient obtained by dividing the
portion of the total sludge volume occupied by liquor and air by the
volume occupied by solid phase. Coefficients of permeability were
66
-------
TABLE IV-5
Location
Eastern
Eastern
Western
Eastern
PERMEABILITIES OF UNTREATED FGD SLUDGES
Settled
Process
Limestone
Sample 1
Sample 2
Lime
Sample 1
Sample 2
Sample 3
Limestone
Sample 1
Sample 2
Sample 3
Dual Alkali
Sample 1
Sample 2
ea
1.53
2.07
1.83
1.65
1.25
0.96
1.20
0.75
5.11
2.19
(cm/secl
1 x
3 x
2 x
6 x
1 x
3 x
2 x
8 x
8 x
2 x
ID-*
10~5
ID-"
ID'5
10-"
10~
10- 5
io-5
10-"
Compacted
ea
1.27
1.56
1.68
1.42
0.97
0.63
1.20
0.50
4.17
1.95
^cm/sec)
8
1
5
1
7
1
1
9
3
8
x 10"5
x 10~5
x 10" 5
x ID' 5
x 10~5
x 10~5
x 10" 5
x ID' 5
x 10~5
x 10"5
Western
Dual Alkali
2.77
1 x 10~3
2.61
1 x 10-"
ae = Void ratio
k - Coefficient of permeability
Source: References (1) and (10).
67
-------
determined for samples which had been allowed to "drain" and for those
which were "compacted". Measurements of the coefficient of permeability
after draining were made by pouring a volume of sludge into a permeameter,
allowing the solids to settle to equilibrium, and then performing the
permeability measurement. Compacted samples were made either by vibrating
the permeameter containing settled solids (10) or by using a plunger to
further compact the settled solids (1).
With the exception of a western limestone and a western dual alkali
sludge, which when drained were very permeable, all coefficients of
permeability for drained samples ranged from about 2 x 10 5 to 2 x 10 ** c.m/
second. All samples showed a reduction in permeability after being
compacted with permeabilities ranging from about 1 x 10 5 to 1 x 10 ** cm/
second.
5. Compactability of FGD Sludges
Although FGD sludges are often characterized as being "gooey" or, at
best, thixotropic (which is a misnomer), that behavior is due to the fact
that many sludges are often only dewatered to solids contents ranging from
less than 40 to perhaps 60%. If they are dewatered further by very effi-
cient filtration or centrifugation, or by other means such as the simple
addition of dry fly ash, they can be compacted in a manner not unlike that
in which soil is compacted during the course of building roads or dams to
produce a material which is quite firm and which will support considerable
weight. For soils and soil-like materials there exists an optimum moisture
content at which the material can be compacted to the greatest extent as
evidenced by a maximum dry bulk density, for a given compactive effort.
At least two studies have been carried out in which the compactability
of untreated FGD sludges was studied. Klym and Dodd (12) compacted a
sludge composed of about equal amounts of calcium sulfite and calcium
sulfate according to the standard Proctor method described in ASTM D698-70.
A maximum dry bulk density of 84 Ibs/cubic foot could be achieved if the
sludge was dried to contain 77 weight % solids. However, even at 72%
solids the sludge could be compacted, but a dry bulk density of only
about 79 Ibs/cubic foot could be achieved. In another study (11),
a calcium sulfite sludge produced' by a dual alkali process was compacted
68
-------
by the same standard Proctor method which was used for the direct limestone
sludge. The dual alkali sludge could be compacted to a maximum dry density
of about 72 Ibs/cubic foot at 75% solids.
When confined in a mold, sludge_samples have exhibited significant
resistance to the action of compaction hammers. This resistance disappears
when samples are removed from the mold. A few measurements of the uncon-
fined compressive strengths of untreated dual alkali FGD sludges have been
made, and as expected, unconfined compressive strengths were quite low,
ranging from nil to 20 Ibs/square inch (11). In essence, sludges
exhibit only slight "apparent" cohesion, produced by capillary action
(surface tension); this behavior is characteristic of fine granular soils.
Such materials are very susceptible to disturbance such as vibration.
Tests on sludge samples have shown that untreated sludges can '"liquefy"
under vibration (personal communication, J. Hagerty).
C. EFFECTS OF TREATMENT ON THE PHYSICAL AND ENGINEERING PROPERTIES OF FGD
SLUDGES
Since the sludges produced by many FGD systems are, in fact, slurries
or liquefiable sludges, they are usually disposed of in sludge ponds. Even
after being allowed to settle in the pond for extended periods of time, the
settled material is often still incapable of supporting sufficient weight
to permit reclamation of the pond for productive use. To make sludge
disposal areas more amenable to future productive use and to improve
handling properties of sludges during disposal operations, a variety of
treatment procedures for altering the physical properties of sludges have
been proposed.
Most of the processes currently in use are often by private companies
who consider the details of treatment to be proprietary. One general class
of process which was studied by Ontario Hydro and reported in detail (12)
involves the addition of lime or portland cement along with fly ash to the
FGD sludge. Lime and fly ash undergo the well known pozzolanic reaction
in which calcium from the lime reacts with silica in the fly ash to produce
a cementitious calcium silicate matrix which tends to increase the struc-
tural strength and reduce the permeability of the sludge. Portland cement,
which contains both calcium and silica, becomes cementitious itself when
69
-------
wetted and allowed to cure, and presumably the additional silica in any
fly ash which is added can also participate in the cementing reaction.
One company, IU Conversion Systems (IUCS) is generally known to offer
a treatment procedure based on lime/fly ash addition to process a reason-
ably hard material with low permeability. Other commercial vendors offer
proprietary treatments which also produce relatively hard materials; e.g.,
Dravo Corporation which offers chemical treatment through use of an additive
called Calcilox . Another vendor, Chemfix, a division of the Carborundum
Company, offers a procedure which can produce a treated material which has
soil-like qualities instead of being a hard, concrete-like material.
Studies of the effects of a number of commercially available treat-
ment procedures on the physical and engineering properties of FGD sludges
have been conducted at WES. The treated materials were poured without
compaction into cylindrical molds for curing. With the exception of a
soil-like treated material which was remolded and compacted according to
the standard Proctor method prior to measurement of permeability and
unconfined compressive strengths, the other treated materials were simply
removed from the cylindrical molds in which they were cured and then
tested.
1. Effect of Treatment on Sludge Density
Shown in Table IV-6 are the bulk densities of the untreated and treated
sludges studied in the WES program (10). Since at least some of the vendors
wished to remain anonymous, the procesors and the materials treated by them
are identified only by letter codes. Bulk densities of treated materials
were generally observed to range from about 50-110 Ibs/cubic foot. In most
cases Processes A, B, and E produced treated materials which were consid-
erably more dense than the untreated sludge. In several cases, one process,
G, produced a material that was less dense than the untreated sludge.
2. Effect of Treatment Process on Permeability
Shown in Table IV-7 are the measured coefficients of permeability for
sludges treated by each of the five commercial processors (10). Process A
generally reduced the coefficient of permeability by about two orders of
magnitude. Treatment by Process B, which produced a soil-like material,
resulted in permeabilities that were within an order of magnitude of those
70
-------
TABLE IV-6
Location
Eastern
Eastern
Eastern
Western
Western
Process
Lime
Limestone
Dual Alkali
Limestone
Dual Alkali
EFFECT OF
Untreated
52
63
52
89
47
SLUDGE TREATMENT ON BULK DENSITY
Bulk Density (lb/ft3)
Process "A" Process "B" Process "E" Process "F" Process "G"
100 77 101
108 89 83 — 63
96 91 99 — 53
109 80 111 81 57
97 82 83 — 68
Source: Reference (10)-
-------
TABLE IV-7
EFFECT
OF SLUDGE TREATMENT ON PERMEABILITY
Coefficient of Permeability (cm/sec)
Location
Eastern
Eastern
Eastern
Western
Western
Process
Lime
Limestone
Dual Alkali
Limestone
Dual Alkali
Compacted
Untreated
1 x 10~5
8 x 10~5
3 x 1(T5
1 x 1(T5
7 x 1
-------
of untreated sludges. Process E produced a wide range of changes in
permeability. The permeability of an eastern lime sludge was increased
by treatment while that of the others was decreased, in one case by more
than six orders of magnitude.
3. Unconfined Compressive Strengths of Treated Sludges
Relatively little information is presently available on the strength
of materials treated by processes in which the treatment formulae are
known. Ontario Hydro did report on the development of strength in sludges
treated with fly ash and either lime or Portland cement. Their treated
materials were sufficiently dry after treatment that they could be
compacted by the Proctor procedure prior to curing. Compressive strengths
after 1, 2, and 4 weeks of curing for samples treated with fly ash and
lime are shown in Figures IV-3 and IV-4. With only two exceptions, all
samples showed Compressive strengths of about 100 Ibs/square inch;
more fly ash resulted in a higher strength. However, upon adding 15%
Portland cement, final strengths in the range of 600 to 800 Ibs/
square inch were achieved.
The results of unconfined Compressive strength tests performed at
WES on a number of treated sludges are shown in Table IV-8 (10). Processes
A, F, and G all produced materials with Compressive strengths in the range
of 100-400 Ibs/square inch. Process E materials had strengths of nearly
5,000 Ibs/square inch.
The unconfined compressive strengths of the soil-like materials
produced by Process B were measured after remolding test cylinders by
Proctor compaction at the optimum moisture content. The observed strengths,
ranging from about 20 to 50 Ibs/square inch, were slightly greater than
those discussed previously for untreated materials.
D. EFFECTS OF TREATMENT ON POLLUTANT MIGRATION FROM FGD SLUDGES
The impact of the pollutants contained in a mass of FGD sludge on the
environment into which it is disposed does not depend solely on the amounts
of pollutants in the liquid and solid phases of the sludge, but it also
depends upon the rate at which interstitial liquor containing dissolved
pollutants is flushed from the sludge and the rate at which pollutants
in the solid phase of the sludge dissolve into the water permeating through
73
-------
TABLE IV-8
UNCONFINED COMPRESS IVE STRENGTHS OF TREATED FGD SLUDGES
Unconfined Compressive Strength (psi)
Location
Eastern
Eastern
Eastern
Western
Western
Process
Lime
Limestone
Dual Alkali
Limestone
Dual Alkali
Process "A"
100
—
188
403
337
Process "B"
24
45
43
35
23
Process "E"
2,570
720
2,220
4,486
1,374
Process "F" Process "G"
—
243
86
396 126
144
Source: Reference (10).
-------
400
Ln
U
V
1_
to
3
CT
CO
i_
0)
a.
c
CO
a)
8
£
a.
E
o
O
300
200
100
-• 65% Fly Ash + 5% Lime
I 1 39% Fly Ash + 5% Lime
is fr 65% Fly Ash + 15% Lime
«• * 39% Fly Ash + 15% Lime
14
Curing Time In Days
28
Source: Reference 12.
FIGURE IV-3
RELATIONSHIP BETWEEN COMPRESSIVE STRENGTH AND CURING
TIME FOR SLUDGE TREATED WITH FLY ASH AND QUICKLIME
(ONTARIO HYDRO)
-------
1,000
800 -
U
c
CT
V)
i_
IV
CL
TJ
3
O
Q.
01
600 -
400 -
CO
IB
•2 200
in
O>
Q.
E
o
o
65% Fly Ash + 5% Cement
I 39% Fly Ash + 5% Cement
65% Fly Ash + 15% Cement
39% F ly Ash + 15% Cement
Curing Time In Days
Source: Reference 12.
FIGURE IV-4
RELATIONSHIP BETWEEN COMPRESSIVE STRENGTH AND
CURING TIME FOR SLUDGE TREATED WITH FLY ASH
AND CEMENT(ONTARIO HYDRO)
-------
it. In addition to enhancing the disposability of sludges by improving
their dimensional stability, sludge treatment processes can reduce
pollutant migration by decreasing the permeability of the sludge mass,
decreasing the solubility of potential pollutants, or both.
Little information is presently available concerning the leaching
of potential pollutants from treated and untreated sludges, although a
considerable amount of work on leaching properties is now underway.
Concentrations of a number of pollutants in leachate samples taken at the
beginning and end of accelerated leaching tests which were performed on
four different sludges are shown in Table IV-9. Concentrations of sulfate
and chloride as well as total dissolved solids (IDS), the concentration
in the leachate after 50 pore volumes of leach liquor, had passed through
the sludge and reached similar levels even though the initial concentrations
in the sludge liquors were significantly different. In all cases IDS had
fallen to about 1,500-2,500 ppm and sulfate had fallen to about 1200 ppm;
these levels probably reflect the equilibrium solubility of the calcium
sulfate component of the sludge solids. The other chemical species showed
the same tendency to level off to similar concentrations after 50 pore
volumes of leaching had taken place.
One attempt to evaluate the effect of sludge treatment on pollutant
leaching conducted by Aerospace (1) involved a comparison of the accelerated
leaching behavior of samples of untreated sludges with the behavior of the
same materials after treatment. The effect of treatment on the concentra-
tion of a number of pollutants in the first pore volume and 50th pore volume
of leachate collected from treated and untreated eastern limestone sludge
is shown in Table IV-10. In most cases, the concentrations of substances
in the first pore volume were somewhat lower for the treated material.
Concentrations of major soluble species such as chloride and sulfate as well
as TDS were reduced by about a factor of 2 to 3. Concentrations of arsenic,
chromium and selenium were also substantially lower. Cadmium levels in the
first pore volume of leachate were essentially the same, but levels of copper,
lead and zinc in the first pore volume were slightly higher for the treated
material than for the untreated material.
Initial results obtained from the Shawnee Field Test Program (13)
indicate that treatment can produce similar reductions in the concentrations
77
-------
TABLE IV-9
c»
COMPARISON OF THE CHEMICAL CONSTITUENTS IN SLUDGE LIQUORS
WITH
LEACHATE AFTER 50 PORE VOLUME DISPLACEMENTS
(Concentrations in
Eastern
Limestone
Western
Shawnee
As
Be
Cd
Cr
Cu
Pb
Hg
Se
Zn
Cl
F
S03
SOi,
PH
TDS
(Clarifier
Liquor3
0.14
0.054
0.003
0.09
0.01
0.25
<0.05
0.08
0.20
2,300
6.2
80
10,000
8.3
15,000
Underflow)
Leachate
0.01
0.004
<0.001
0.003
0.010
0.01
<0. 00005
0.006
0.045
120
<0.2
25
1,200
5.0
2,400
(FDS
Limestone
Cholla
Tank
Liquora
<0.004
0.
0.
0.
0.
0.
0.
2.
0.
1,
0.
0.
4,
3.
8,
14
Oil
14
20
01
07
2
11
700
7
9
000
04
700
Discharge)
Leachate
<0
0
0
0
0
0
0
0
0
.0004
.004
.001
.002
.01
.001
. 00005
.05
.04
110
6
9
1
5
1
.1
.0
,150
.9
,900
mg/liter)
Eastern
Dual Alkali
Parma
(Unwashed
Liquor5
<0.004
<0.005
<0.02
<0.02
0.06
0.55
0.0009
0.087
0.63
4,400
60
160
30,000
12.76
72,000
Filter Cake)
Leachate
<0.
0.
<0.
<0.
<0.
<0.
<0.
0.
0.
95
0.
30
1,
6.
1,
002
004
001
001
001
001
00005
010
04
2
100
1
650
Western
Limestone
Mohave
(Centrifuge Cake)
Liquor3 Leachate
0.012
0.02
0.05
0.4
0.6
0.04
<0.05
0.120
0.18
43,000
30
1.5
8,000
6.7
95,000
<0.004
0.004
<0.001
0.003
0.010
<0.001
<0. 00005
0.004
0.045
120
<0.2
0.3
1,250
4.45
2,100
Liquor analysis for liquor occluded with sludge solids as disposed.
Source: Reference (1).
-------
TABLE IV-10
COMPARISON OF THE CHEMICAL CONSTITUENTS IN EASTERN
LIMESTONE SLUDGE LEACHATE WITH CHEMFIX
CHEMICALLY TREATED SLUDGE
As
Cd
Cr
Cu
Pb
Hg
Se
Zn
Cl
F
S04
TDS
pH
Source:
Sludge
1st Pore Vol.
0.14
0.003
0.09
0.01
0.25
<0.05
0.08
0.20
2300
6.2
10,000
15,000
8.3
Reference (1).
- Aerobic
50th Pore Vol.
0.01
<0.001
0.003
0.010
0.01
<0. 00005
0.006
0.045
120
<0.2
1200
2400
5.0
LEACHATE
Chemfix
1st Pore Vol.
0.04
0.003
0.04
0.05
0.35
<0.005
0.01
0.5
1400
0.9
3000
7000
4.70
- Aerobic
50th Pore Vol.
0.006
<0.001
<0.001
0.005
<0.001
<0.0005
0.002
0.065
60
0.2
650
1500
6.01
79
-------
of major soluble species in actual test pond leachates. Whether or not
the concentrations of trace substances are reduced has not yet been
established with any degree of certainty.
In the WES program to evaluate the chemical treatment of sludges,
five different FGD sludges were each treated by a number of commercial
processors, and both the treated and untreated materials are being
subjected to long-term leaching experiments to assess the effects of
treatment on sludge pollution potential. A large number of substances,
both trace and major constituents, are being measured in the leachate
collected from the leaching columns. At the present time only preliminary
data are available and results are inconclusive. In some cases there is
evidence that treatment may not have reduced the concentration of dissolved
solids in the leachate over the first few pore volume displacements, while
in other cases there is a definite improvement in the leachate quality.
In summary, it is apparent, based upon the information available at
the present time, that treatment processes, in general, improve the
handling properties and in most cases increase the strength and reduce
the permeability of FGD sludges. However, no definitive conclusions can
be drawn as yet concerning the ability of treatment processes to reduce
the concentrations of contaminants in leachate (leachate quality) from
treated sludges.
80
-------
REFERENCES
1. Leo, P. P. and J. Rossoff. Control of Waste and Water Pollution from
Power Plant Flue Gas Cleaning Systems: First Annual R and D Report.
EPA-600/7-76-018, October 1976.
2. Ifeadi, C. N. and H. S. Rosenberg. Lime/Limestone Sludges -- Trends
in the Utility Industry. Proceedings, Symposium on Flue Gas
Desulfurization, Atlanta, November 1974.
3. Interess, E. Evaluation of the General Motors' Double Alkali SO-
Control System. EPA-600/7-77-005, January 1977.
4. Lunt, R. R. et al. Evaluation of the Dual Alkali S02 Control System
at Gulf Power Company's Scholz Station — Interim Results. Paper
presented at the EPA Symposium on Flue Gas Desulfurization, New Orlears,
March 1976.
5. Montana Fly Ash S02 Scrubbing Test Program.
6. Gluskoter, H. J. Mineral Matter and Trace Elements in Coal. In:
Trace Elements in Fuel, S. P. Babu, ed. Advanced Chemistry, Serial 141,
American Chemical Society, Washington, D. C., 1975. pp. 1-22.
7. Maloch, J. Chemical Fixation of Hazardous Waste and Air-Pollution-
Abatement Sludges. Interim results of an EPA program conducted by
the Environmental Effects Laboratory, U.S. Army Engineer Waterways
Experiment Station, Vicksburg, Mississippi, to be published.
8. Esso Research and Engineering Company. Potential Pollutants in Fossil
Fuels. NTIS.
9. Hagerty, D. J. and C. R. Ullrich. Land Disposal of FGD Sludges. Paper
presented at the 82nd National AIChE Meeting, Atlantic City, New Jersey,
August 1976.
10. Maloch, J. Chemical Fixation of FGD Sludges — Physical and Chemical
Properties. Paper presented at the EPA Symposium on Flue Gas
Desulfurization, New Orleans, March 1976.
11. A Laboratory and Pilot Plant Study of the Dual Alkali Process for S02
Control. Unpublished results obtained under EPA Contract No. 68-02-1071
by Arthur D. Little, Inc., to be published.
12. Klym, T. W. and D. J. Dodd. Landfill Disposal of Scrubber Sludge.
Paper presented at the National ASCE Environmental Engineering Meeting,
Kansas City, October 1974.
13. Fling, R. B. et al. Disposal of Flue Gas Cleaning Wastes - EPA Shawnee
Field Evaluation - Initial Report. EPA-600/2-76-070, March 1976.
81
-------
V. MINE DISPOSAL OF FGD SLUDGE
In this study, mines are evaluated for their feasibility as disposal
alternatives for flue gas desulfurization (FGD) sludges. Metallic, non-
metallic, and coal mines are initially screened for their available
capacity, location, and ease of sludge placement. Those which appear most
technically promising are subsequently reviewed for environmental impacts,
regulatory constraints, operation, and monitoring. Because of the overview
nature of this report, mines are reviewed in terms of the conditions
believed most typical for a given mineral, mining method, and region.
However, mines of any method and region may actually be a promising local
disposal alternative with regard to site-specific hydrogeologic and
environmental factors.
A. REVIEW OF THE MINING INDUSTRY
In 1971 there were about 0.6 billion tons of surface and underground
coal produced, 0.2 billion tons of underground metal and nonmetal minerals
produced, and about 2.5 billion tons of open pit metal and nonmetal
minerals produced. Of the many commodities mined, bituminous coal accounted
for the largest percentage of lands used for mining. In 1971 there were
about 73,200 acres used for bituminous coal mining operations, of which
about 48,000 acres were active mining areas. The total of all metallic
and nonmetallic mineral operations (excluding coal) used about 130,000
acres. Of these, sand, gravel, and stone accounted for the greatest amount
of land use—together about 71,400 acres. Table V-l summarizes the land
utilization and reclamation by mining industry in the United States through
1971.
The greatest amount of land reclamation occurs in coal mining, and the
least for metal mines. Because surface mining of coal usually allows full
seam extraction, reclamation does not inhibit future resource recovery.
Reclamation of most lands used for metallic and nonmetallic mineral mines
would, however, often unfavorably affect future resource extraction.
1. Coal Mining
a. Coal Production
The coal fields of the continental United States are shown in Figure V-l
(there are reserves in Alaska not shown) broken down by region—Eastern,
83
-------
TABLE V-l
LAND UTILIZED AND RECLAIMED BY THE MINING INDUSTRY
IN THE UNITED STATES IN 1930-71 and 1971.
BY SELECTED COMMODITY
Commodity
Land utilized,
acres'
Land reclaimed,
acres3
Metals :
Copper
Iron ore
Uranium
Otherb
Totalc
Nonmetals :
Clays
Phosphate rock
Sand and gravel
Stone
Otherd
Total0
Solid Fuels:
Bituminous coal
Other6
Totalc
Grand Total0
1930-71
166,000
108,000
12,800
237,000
524,000
167,000
77,300
660,000
516,000
138,000
1,560,000
1,470,000
105,000
1,570,000
3'65°'°00
1971
19,100
8,620
1,950
6,740
36,400
7,460
10,200
46,400
25,000
6,030
95,100
73,200
1,710
74,900
206 '°°°
Percent
reclaimed,
1930-71
4,810
4,630
810
33,000
43,300
58,700
12,300
197,000
124,000
14,100
406,000
1,000,000
14,100
1.010.000
1,460,000
1971
1,410
2,330
440
8,400
12,600
1930-71
2.9
4.3
6.3
13.9
8.3
4,330
2,070
34,300
9,480
3,070
35.1
15.9
29.8
24.0
10.2
53,200 26.0
94,600
2.230
96,900
68.0
13.4
64.3
Includes area of surface mine excavation, area used for disposal of surface
mine waste, surface area subsided or disturbed as a result of underground
workings, surface area used for disposal of underground waste, and surface
area used for disposal of mill or processing waste.
Bauxite, beryllium, gold, lead, manganese, mercury, molybdenum, nickel,
platinum-group metals, silver, titanium (ilmenite), tungsten, vanadium,
and zinc.
c
Data may not add to totals shown because of independent rounding.
Aplite, asbestos, barite, boron minerals, diatomite, emery, feldspar,
fluorspar, garnet, graphite, greens and marl, gypsum, kyanite, lithium
minerals, magnesite, mica, millstones, olivine, perlite, potassium salts,
pumice, pyrites, salt, sodium carbonate, talc, tripoli, vermiculite, and
zeolite.
eAnthracite and peat.
Source; Land Utilization and Reclamation in the Mining Industry, 1930-1971,
United States Department of the Interior, Bureau of Mines, 1974.
84
-------
00
FIGURE V-1
COAL FIELDS OF THE UNITED STATES
-------
Interior, Western, and Pacific Coast. There are large reserves of coal
occurring principally in about 25 states, but the major production is
currently from nine states (Alabama, Illinois, Indiana, Kentucky, Ohio,
Pennsylvania, Virginia, West Virginia, and Wyoming). The future production
is expected to shift as greater volumes are produced from Western states.
As shown in Figure V-l, states in the Western regions are rich in low-
sulfur coal, while coal reserves in the Eastern and Interior regions are
predominantly medium- and high-sulfur coal.
About half of the coal currently produced in the United States is
surface mined; the other half is produced from underground coal mines.
Production by mining method is shown in Figure V-2. The majority of coal
production in the Western region involves surface mining methods, while
in the Eastern and Interior regions, underground mining accounts for
roughly 60% of the total coal production (1973). Tables V-2 and V-3 show
the number of mines and distribution of coal production by mining method
and state.
b. Coal Mining Methods
Strip Coal Mining
Mining practice in strip coal mines mostly involves the use of drag-
lines and shovels for overburden removal, smaller shovels and front-end
loaders for coal digging, and trucks for hauling. In a few cases, scrapers
and bucket wheel excavators are used in soft overburdens. In strip coal
mining where the overburden is relatively soft or can be loosened somewhat
by gentle blasting, the dragline is the preferred machine to use for
digging and casting. If the formations over the coal seam are hard and
compact and tend to break into blocky or hard-to-handle aggregates of
blocky chunks, then large shovels are preferred. Roughly half of the
surface mining involves draglines, while the other half involves shovels.
The conventional strip mining method for relatively flat or level
areas is known as "area stripping." A typical area strip mining operation
is shown in Figure V-3. Area stripping is common in the Western and
Interior coal mining regions.
When coal is open-surface mined on steep slopes, the system is called
"contour stripping." These steep slope conditions prevail in the Eastern
86
-------
100
en
CONVENTIONAL MINING - Hand Loading
Y//V//Y//VS sYSSlK / / X s / / / /
CONVENTIONAL MINING - Mechanical, Loading
g Continuous Mining
?S<^^^^^^I<^S«^>^>CXP<^S^^^^^ 5
10
0
1940 1942 1944 1946 1948 1950 1952 1954 1956 1958 1960 1962 1964 1966 1968 1970 1972 1974
Source: U.S. Bureau of Mines.
FIGURE V-2
MINING METHODS USED IN U.S. BITUMINOUS COAL PRODUCTION
-------
TABLE V-2
PRODUCTION OF BITUMINOUS COAL AND LIGNITE IN U.S. BY REGION
UNDERGROUND,
STRIP AND
AUGER MINING (1973)
(thousands of short tons)
Underground Strip and Auger
Eastern Province
Alabama
Kentucky (Eastern)
Maryland
Ohio
Pennsylvania
Tennessee
Virginia
West Virginia
Interior Province
Arkansas
Illinois
Indiana
Iowa
Kansas
Kentucky (Western)
Missouri
Oklahoma
Texas (lignite)
Western Province
Arizona
Colorado
Montana:
Bituminous
Lignite
New Mexico
North Dakota (lignite)
Utah
Wyoming
Pacific Coast Province
Alaska
Washington
Total
7,892
41,500
64
16,205
46,255
4,785
23,339
95,448
235,488
3
32,578
782
385
21,900
85
55,733
3,377
20
1,062
5,105
680
10,244
35
35
301,500
11,901
32,500
1,690
29,140
30,391
4,208
10,530
19,791
140,151
455
28,971
24,485
470
1,145
31,100
4,980
2,540
6,945
101,091
2,965
2,855
9,530
400
8,278
7,400
35
12,920
44,383
700
3.175
3,875
289,500
Total
19,793
74,000
1,754
45,345
76,646
8,993
33,869
115,239
375,639
458
61,549
25,267
855
1,145
53,000
4,980
2,625
6,945
156,824
2,965
6,232
9,550
400
9,340
7,400
5,140
13,600
54,627
700
3.210
3,910
591,000
88
-------
TABLE V-3
NUMBER OF COAL MINES BY STATES
(1973)
Eastern Province
Alabama
Kentucky
Maryland
Ohio
Pennsylvania
Tennessee
Virginia
West Virginia
Interior Province
Arkansas
Illinois
Indiana
Iowa
Kansas
Missouri
Oklahoma
Texas (Lignite)
Western Province
Arizona
Colorado
Montana
New Mexico
North Dakota (Lignite)
Utah
Wyoming
Pacific Coast Province
Alaska
Washington
Total
29
76
3
75
62
16
9
62
332
1
21
13
2
3
7
4
_2
53
1
4
4
2
8
_9
28
1
I
2
451
Underground
8
51
15
44
3
34
93
248
20
2
1
23
3
1
5
_1
10
281
Producing over 100,000 tons/year.
Producing over 200,000 tons/year.
89
-------
Jj!j Undisturbed ^
w2jl£: I and i'^'-vij";
^^ Original Surface
v ^;..
Stripping Bench =
FIGURE V-3 AREA STRIP MINING WITH CONCURRENT RECLAMATION
-------
coal region. In conventional contour stripping, spoil or waste is stripped
and dumped downhill from the cut, as shown in Figure V-4. A variation of
contour stripping is known as "haulback" or "block stripping" (Figure V-5),
where spoil is removed horizontally into the mined-out cut rather than
dumped downhill.
Underground Coal Mining
There are two basic underground coal mining methods: room and pillar,
and longwall. Underground coal mines are often classified as slope, drift,
or shaft mines, depending upon the method of access rather than the mining
method used. Figure V-6 shows sketches of these three possibilities.
Room and pillar mines remove the coal in "rooms" and leave "pillars"
to support the roof. If the pillars are not robbed, the coal extraction
in this procedure is on the order of 50%. If geologic and roof conditions
permit and if surface caving can be allowed, the pillars can be robbed
(removed) as one retreats back to the access opening. This can increase
extraction to 70-80%. Complete extraction through pillar robbing is not
technically feasible, as roof collapse following robbing limits access to
nearby pillars.
Room and pillar coal extraction can be "conventional" or "continuous."
Conventional means that the coal is extracted in a series of steps which
are: undercutting the coal, drilling, blasting, loading, and shuttle car
haulage to main haulage belts or rails. Continuous methods use a continuous
mining machine which cuts the coal, loads it, and delivers it to shuttle
cars (which really makes the system only semi-continuous) or to conveyor
belts for removal from the mine. In most room and pillar systems another
important step is to place roof bolts for supports as the mining proceeds.
Longwall mining systems rely on the controlled caving of the roof.
The system consists of a coal cutting machine, chain conveyor system, and
hydraulic movable roof support. Most U.S. coal mines using longwall
techniques also produce coal by room and pillar methods. Hence, coal
production from any mine is rarely all from the longwall mining operation
itself.
The operation of longwall coal systems is more nearly continuous
(when they operate successfully) than room and pillar mining, with coal
91
-------
Elev 1400'
Elev 1000'
Cropline
Elev 600'
Typical section showing coal seam outcrop in steep terrain suitable only for
contour mining.
'"tour
\ — .
\
\
\
\ 4th Cut
\
\
\
\
\
\3rd
\
\
K^^S^5SSSS^^^S5SSSS5Ax
Cut
Outcrop
Cross section (end view) of conventional surface mining showing sequence
of operation.
Economic Limit
of Operations
, 2nd Cut
_!/__
Cross section of a contour mining operation. Seldom can more than two cuts
be taken in steep terrain. Some coal along the outcrop is invariably lost
as it is soft, weathered, and oxidized, thereby losing its heat value. The
width of the weathered portion is highly variable.
Source: Cassidy, S.M., Elements of Practical Coal Mining, Society of Mining Engineers,
New York, 1973.
FIGURE V-4 CONTOUR COAL STRIPPING
92
-------
The Truck Haulback Method
1. Overburden 2. Acid Material 3. Coal Seam 4. Haul Road 5. Acid Backfill 6. Overburden Backfill
.••
The Scraper Haulback Method
1. Overburden 2. Acid Material 3. Coal Seam 4. Haul Road 5. Acid Backfill 6. Overburden Backfill
FIGURE V-5 BLOCK METHODS OF CONTOUR STRIP MINING
93
-------
Preparation Plant
i Surface
Coal Seam
X
Slope Mine
Surface
Main Conveyor Belt
Transfer House
Preparation
Plant
Drift Mine
Headframe
Preparation
Plant
Surface
M.MM..M.
V^WU^-SW^
Coal Seam
.Storage Bin
Shaft Mine
Source: Cassidy, S.M., Elements of Practical Coal Mining, Society of Mining Engineers,
New York, 1973.
FIGURE V-6 TYPES OF UNDERGROUND COAL MINES
94
-------
cutting, removal, and prop advance going on steadily. When the props are
advanced, the unsupported roof caves and leaves what is known as gob area.
A recent development in longwall mining has been the adaptation of the
method of what is known as "shortwall mining." Shortwall mining involves
use of heavy-duty advancing props just as in conventional longwall mining;
but instead of a coal cutting machine and conveyor removal system, a con-
tinuous mining machine is used.
Longwall mining methods (including shortwall mining) cannot be used in
all underground coal mines in the United States. Application of longwall
operations are limited to areas where the surface above can be disturbed
and where the coal to be mined occurs in configurations amenable to the
longwall layout. It is generally not applicable in areas where there is
massive or difficult-to-cave roof. Also, in some circumstances, the high
dust levels created may be difficult to control to the low limits specified
by Federal Government safety regulations. As a result, longwall mining
currently accounts for only about 3% of the total underground coal production.
This amount is slowly, but steadily, increasing.
c. Capacity for Sludge Disposal in Coal Mines
The weight of dry sludge produced can vary from 5% (not including ash)
of the weight of coal burned for low-sulfur coal to as much as 35% (includ-
ing ash) for high-sulfur coal. Taking into account the water occluded with
solids, these weights would increase by as much as 50% to 100%. Based upon
current projection of FGD sludge production (see Table 1-1), FGD sludge with
ash may require as much as 20,000 acre-feet of disposal space in 1980 (less
than 10% of the volume of coal mined) and that by 1985 the annual volume
could reach 60,000 acre-feet (about 20% of the volume of coal mined).
By comparing the amount of sludge from stack gas scrubbing with the
amount of coal burned, it is apparent that the annual volume of FGD sludge
produced is considerably less than the volume of coal mined (mined coal
includes production for power plants as well as for industrial raw material
requirements). However, the volume of coal mined is not necessarily the
volume of the available void for sludge disposal. In surface mines, for
example, sludge disposal would have to be scheduled to keep up with the
continuous extraction-reclamation process to utilize the entire volume of
95
-------
the extracted seam. In addition, in surface mines, sludge could not be
placed at the coal seam outcrop due to potential slope stability and sludge
erosion problems. In underground mines, increased use of pillar robbing
and longwall mining techniques allows roof collapse to significantly fill
the void left from seam extraction and to render some remaining voids
inaccessible. There is no data on the total amount of coal produced from
a combination of longwall and pillar robbing practices. However, as the
current national coal recovery estimate is about 60% from all underground
mines, nearly one-half of the mine space must be devoted to operations
allowing caving.
2. Metal and Nonmetal Mining
a. Metal and Nonmetal Mineral Production
Tables V-4 and V-5 show the number and distribution of mines by size
and general mining method that are annually producing substantial quantities
of metallic and nonmetallic minerals. By far, the greatest number of mines
involve the production of sand, gravel, and stone (including limestone).
Most of these mines are open pit or quarry. However, there is significant
underground mining of limestone. Significant underground mining of copper,
lead, zinc, iron, and salt also occurs.
b. Metal and Nonmetal Mining Methods
Underground Metal and Nonmetal Mining
In underground metal and nonmetal mining (excluding coal), access to
the ore can be through vertical or sharply inclined shafts, or through
horizontal or slightly dipping passageways. These passageways are called
adits in metal mines.
Once underground, passages are driven to get to and develop the actual
area where the ore is extracted. These passages are usually horizontal
and are called drifts. Passages that cut across the drifts are crosscuts.
To get to the ore body from the openings, one drives raises (upward) or
winzes (downward). The drifts and crosscuts are used as haulage ways to
get ore out of the mine. Haulage equipment can be tracked (rail) , track-
less (truck), conveyor belt, or in a few cases, hydraulic, where mined ore
is pumped through pipelines.
96
-------
TABLE V-A
NUMBER OF DOMESTIC METAL AND NONMETAL MINES IN 1973.
BY COMMODITY AND MAGNITUDE OF CRUDE ORE PRODUCTION3
Commodity
Total Number
of Mines
100,000
to
1,000,000
Tons
1,000,000
to
10,000,000
Tons
More Than
10,000,000
Tons
Metals
Bauxite
Copper
Gold:
Lode
Placer
Iron Ore
Lead
Mercury
Silver
Titanium:
Tungstea
Uraniumb
Zinc
Other0
Total
Ilmenite
Metals
Nonmetals
Abrasives'1
Asbestos
Barite
Boron minerals
Clays
Diatomite
Feldspar
Fluorspar
Gypsum
Mica (scrap)
Perlite
Phosphate rock
Potassium rock
Pumice
Salt
Sand and gravel
Sodium carbonate (natural)
Stone:8
Crushed and broken
Dimension
Talc, soapstone, pyrophillite
Vermiculite
Otherf
Total Nonmetals
16
64
29
50
69
36
21
41
7
25
75
28
12
473
9
6
41
2
1,420
13
21
16
75
15
12
42
7
158
18
6,995
3
4,623
405
51
3
29
Grand Total
13,964
14,437
5
15
2
2
22
11
1
16
20
_2
98
2
16
152
2
8
3
42
7
2
13
1
6
9
2,240
1,717
3
1
9
4,233
4,331
17
2
25
3
7
1
_4
59
2
1
11
18
6
6
118
3
205
1
360
419
16
5
21
aExcludes wells, ponds, or pumping operations.
Data incomplete.
cAntimony, beryllium, manganiferrous ore, molybdenum, nickel, platinum-group metals,
tin, and vanadium.
''Emery, garnet, and tripoli.
elncludes limestone (see text).
^Abrasive stone, aplite, graphite, greensand marl, iron oxide pigments (crude),
kyanite, lithium minerals, magnesite, mica (sheet)., millstones, olivine, and
wollastonite.
97
-------
TABLE V-5
PRODUCTION
FOR
OF ORE IN
THE MAJOR
(Thousands
Material Open Pit
Bauxite
Copper
Gold
Iron Ore
Lead
Mercury
Silver
Titanium-Ilmenite
Tungsten
Uranium
Zinc
Total Metals
Asbestos
Barite
Clays
Diatomite
Fluorspar
Gypsum
Phosphate Rock
Salt
Sand & Gravel
Stone (inc. Limestone)
Total Nonmetals 1,
2,709
222,450
3,477
206,412
<1
156
29
21,525
22
2,929
156
459,865
2,373
3,785
53,871
551
59
8,022
132,911
720
919,608
844,953
966,853
THE U.S. BY MINING
MINERAL COMMODITIES
of Short Tons)
Underground
Wa
26,002
1,985
12,678
9,962
120
710
—
641
3,127
9,007
64,232
wa
114
1,114
—
691
2,298
322
14,661
—
31,930
51,130
METHOD-1971
Total
2,709
248,453
5,461
219,091
9,962
276
739
21,525
663
6,056
9,163
524,098
2,373
3,899
54,985
551
749
10,319
133,233
15,381
919,608
876,883
2,017,981
7.
Underground
—
10.5
36.3
5.8
100
43.5
96.0
—
96.7
51.6
98.3
12.3
—
2.9
2.0
—
92.3
22.3
0.2
95.3
—
3.6
2.5
alnformation withheld to avoid identification of a sole producer.
98
-------
The actual area in the mine where ore is removed is called a "stope."
There are a wide variety of stoping methods with the principal ones being
room and pillar, caving, and cut and fill. The method of stoping and
access used depends upon the type of ore being mined and the geologic
nature of deposit. Table V-6 shows the various underground mining tech-
niques used for metal and nonmetallic minerals.
• Room and Pillar
This system is similar to that used in conventional room and
pillar coal mines. Typical extraction efficiencies for ore deposits
are about 50%, but in many cases ore extraction can be increased
to 70-80% by robbing pillars as is done in coal mining.
• Caving
This method is used for large disseminated deposits. Access
to the ore body is from below, and large blocks (hundreds of square
feet) are undercut and induced to cave. Ore is then extracted
through ore passes into haulage equipment below.
• Cut and Fill, Square Set, Open Stopes, Long Hole, Shrinkage
These methods (and a number of others, as well as various
combinations) are used for vein-type deposits where there is
vertical or steeply dipping ore structure of limited width (3 feet
to 30 feet wide).
Cut and fill involves mining the ore and filling the empty
spaces with broken waste rock or tailings from the milling opera-
tion. Square set stoping involves supporting the open spaces with
timber. This method is no longer extensively used because of the
high cost of timber and the labor to install it. Open stopes merely
refers to mines left open where there is no need to fill.
Long hole stopes are those where drilling is accomplished by
a series of long (50-100 feet) holes from a series of access
openings rather than drilling shorter (5-6 feet) holes every shift.
These stopes can be filled or not as needed.
Shrinkage stopes involve breaking the ore and mining upward
in a stope working from the surface of the broken ore. Enough
broken ore is withdrawn to provide working space. When mining is
finished, the stope is full of broken ore, which is then drawn out.
The final space open can be filled but is often left open.
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TABLE V-6
GENERAL TYPES OF METAL AND NONMETAL MINES AS
RELATED TO GEOLOGIC NATURE OF DEPOSITS
A. Underground Mines
1. Bedded - Flat Lying or Slightly Dipping - Sedimentary-Type Deposits:
Examples: Copper - Michigan
Lead, Zinc - Missouri, Tri-State District
Zinc - Tennessee, Washington
Uranium3 - Colorado, New Mexico, Utah, Wyoming
Salt - Kansas, Louisiana, Michigan, Ohio, New York
Limestone - Iowa, Illinois
Gypsum - New York
Trona - Wyoming
Potash - New Mexico, Utah
Iron Ore - Missouri, Michigan, New York, Pennsylvania, Wyoming
Phosphate - Montana, Idaho
General Mining Procedure:
Access - Shafts, Inclines and Ramps, and Adits - On Level Mining
Haulage - Rail, Truck, Belt, Combinations of These
Stoping - Room and Pillar
2. Large Disseminated Ore Bodies:
Examples: Copper - Arizona
Molybdenum - Colorado
Iron Ore - Pennsylvania, Michigan, Missouri
General Mining Procedure:
Access - Shafts or Adits - Approach below Ore Bodies
Haulage - Usually Rail (Ore-thru-Ore Passes)
Stoping - Block or Panel Caving
3. Vein-Type Deposits - Wide and Narrow - Usually Dipping:
Examples: Gold - South Dakota
Silver, Copper - Idaho
Copper - Montana, Arizona, Tennessee, New Mexico
Lead, Zinc - Idaho, Utah, Colorado, New York
Silver, Copper - New Jersey, New Mexico, Montana
Fluorspar - Nevada, Kentucky, Illinois, Colorado, Montana
Mercury - California, Oregon, Nevada
Uranium - Colorado
General Mining Procedure:
Access - Shafts, Adits, Inclines - Both Hanging and Footwall Approaches
Haulage - Rail and Trackless
Stoping - Cut and Fill, Square Set, Open Stopes, Long Hole, Shrinkage
B. Open Pit and Surface Mines
Examples: Copper - Arizona, Nevada, New Mexico, Utah
Iron Ore - Michigan, Minnesota, California
Uranium - New Mexico, Wyoming
Phosphate Rock - Florida, Tennessee
Gold - Nevada
General Mining Procedure:
Access - Benches after Removal of Overburden
Haulage - Truck, Rail, Belts
Mining - Shovels, Front-End Loaders
1Uranium - Special case in this group with sub-level and on-level mines, random pillars,
small scattered deposits, radon problem, etc.
Source: Arthur D. Little, Inc.
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The major method of gaining access to underground ore bodies uses
vertical shafts, which in the United States vary from about 200 feet in
depth to nearly 5,000 feet. These shafts are usually rectangular or
circular and are normally lined with timber, concrete, or steel.
These shafts usually have compartments or arrangements for communica-
tion cables, water power, and compressed air lines. Most shafts in metal
mines service a number of levels where there are shaft stations. In flat-
bedded sedimentary type deposits, only one horizon is generally mined so
that the shaft services only one level.
Where the topography permits, horizontal or slightly dipping openings
(adits) also are used as a means of access to ore bodies. Many mines in
mountainous regions have combinations of shafts and adits for developing
and working the ore body. Adits are of any reasonable size that allows
space for the required vehicles and accessory items such as cables, pipe,
and ventilation tubes. Adits can be several miles long.
Haulage ways are sized to allow adequate movement of men, materials,
and ore haulage vehicles. Distances from the shaft can vary from about
400 feet to about 5 miles, depending on the type of mine and on how much
it has been developed. Rail haulage is currently the most common mode of
transportation in all underground mines, and it is not uncommon to have
three or four trains operating at one time. In such situations, traffic
control lights and systems are used. Increased use of trackless vehicles
is replacing rail haulage in some new mines.
In vein-type mines the haulage distances are often less than those for
caving mines. Usually, the shafts will be centrally located with respect
to the ore body, and haulage will be on a number of levels going both ways
from a shaft or shafts for several thousands of feet.
Some recent mining systems have gone to a trackless haulage system
using LHD (load, haul, dump) equipment. Ramps are driven from the surface
to connect all levels for easy access and flexibility of equipment usage.
Ore is moved to ore passes and hoisted.
Open Pit Metal and Nonmetal Mining
The typical open pit metal or nonmetal mine or quarry is an operation
that first removes overburden to reach the ore, then mines the ore and
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delivers it to a processing plant where processing takes place, resulting
in a finished salable product and a waste for disposal.
Open pit mining is carried out by the major operations of drilling,
blasting, loading, and hauling. Earth-moving equipment is used, such as
shovels, draglines, front-end loaders, bulldozers, scrapers, and trucks.
Conveyor belts are often used, as well, for haulage. A wide variety of
sizes and makes of equipment are used. Much of the equipment is very large,
that is, shovels up to 25-cubic yard capacity, draglines with up to 200-cubic
yard buckets, and off-highway trucks up to 200-ton capacity. Overburden is
moved out of the mine area and dumped in waste piles.
c. Capacity for Sludge Disposal in Metal and Nonmetal Mines
Since a 500-megawatt power plant can produce between 400,000 and
1 million short tons of wet sludge annually, a significant number of
the mines shown on Table V-4 would easily have adequate ore extraction
to provide capacity for sludge from one or more plants (assuming all the
voids created were remaining and accessible). As Table V-5 indicates,
few of the commodities listed could fully accommodate the estimated
annual production of the nation's sludge. Most of the metal and non-
metal ore production is from open pit mines unsuitable technically for
waste disposal. None of the commodities listed as employing underground
mining techniques could individually accommodate all of the nation's FGD
sludge in their active underground cavities.
Limestone mines are of particular interest, since all throw-away
systems involve the use of limestone either directly or indirectly (through
the use of limestone to manufacture lime). For this reason there is often
a transportation network (rail and/or truck) that is in service or readily
available for delivery of the limestone.
There are presently about 30 underground room and pillar limestone
mines in 12 states with each mine producing over 300,000 tons of limestone
per year. The total limestone production from these mines amounts to over
20 million tons annually. With the exception of one mine located in
California, all of these mines are located in the Interior and Eastern
regions (Oklahoma, Illinois, Kentucky, Ohio, Tennessee, Virginia, Kansas,
Iowa, Missouri, and Pennsylvania). About half of this underground limestone
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stone production is spread across the midsection of the country in four
states—Kentucky, Illinois, Missouri, and Kansas.
A mine dedicated to providing limestone for use in FGD systems will
not be able to handle all of the sludge produced from those systems. As
a rule-of-thumb, roughly 1.2-1.4 tons of dry FGD sludge (without ash) are
generated for every ton of limestone used. Including water, this sludge
will require a volume for disposal more than three times that created by
the limestone removal. Where only a fraction of the limestone produced in
any mine is used in FGD systems, that mine could serve as a disposal site
for all of the FGD sludge generated from the limestone.
3. Screening of Mine Disposal Options
The purpose of this report is to assess the feasibility of FGD sludge
disposal in mines, but clearly not all the different mine environments can
be addressed. There are thousands of mines throughout the United States,
and each one is different in some respect. However, they can be grouped
by region, mineral mined, mining method, and size; impacts can be assessed
for conditions deemed average for the various mine groupings. Therefore,
in order to focus on the most promising alternatives, we have grouped mines
according to region and mineral mined and have ranked these groups of mines
for their technical feasibility. Those mine options selected as most
promising technically are described and assessed for environmental impacts
in the following sections of this report.
Technical criteria were used to screen mines because of ease of
grouping mines by technical factors (location, mining method, disposal
method, and capacity) versus grouping by environmental factors (hydro-
geology, water resources, biota) and because the inclusion of environment
criteria in the mine selection would impose predictive value judgments on
the outcome of the environmental assessment. The mining methods included
were: surface area and contour strip mining, underground room and pillar,
underground longwall, underground cut and fill, open pit, and quarry mining.
Sludge placement methods included hydraulic slurry pumping, pneumatic stow-
ing, and truck dumping.
A ranking system to choose the most promising types of mines inherently
involves value judgment based on professional experience and literature
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review. We expect there will be individual mines, within the mine groups
considered least promising, which will provide a worthy local disposal site.
However, our ranking is derived from a national perspective and does not
consider small mines having site-specific favorable conditions.
For categories of mining commodities and mining methods, disposal
feasibility is ranked according to the limitations below:
• probably limited capacity;
• difficult handling or placement of sludge; and
• prevention of future resource utilization due to sludge placement.
A category of mining is not considered a promising solution to the nation's
projected sludge disposal needs if it typically has one or more of the
above limitations. Tables V-7 and V-8 rank the mine options. Rating of
the mine options is as follows:
1. promising for FGD sludge disposal;
2. may be promising for FGD sludge disposal;
3. of doubtful promise for FGD sludge disposal; and
4. not promising for FGD sludge disposal.
a. Coal Mine Screening
From Table V-7 it is apparent that active coal mines are generally
favored as more technically promising than inactive coal mines. The
opportunity for sludge disposal in inactive coal mines depends on site-
specific local situations.
Unreclaimed inactive and depleted surface mines usually consist of
the final strip pit (which is often filled with water) and a series of
ridges of overburden. Sludge placement would require extensive earth
movement. Ownership and responsibility for the mine may be dubious, and
sludge placement costs would probably require governmental sponsorship.
Reclaimed surface mines by definition do not have any capacity for FGD
sludge disposal.
Old and inactive underground coal mines are often caved and filled
with groundwater of unknown flow patterns caused by the hydrogeologic
changes created by mining. The voids are difficult to find because of prior
roof collapse as pillars deteriorated and failed; even the initial open
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Lignite:
Eastern
Interior
Mountain
Bituminous :
Eastern
Interior
Mountain
Anthracite :
Eastern
Interior
Mountain
TABLE V-7
COAL MINES
SCREENING FOR ACCEPTABILITY FOR FGD DISPOSAL
Underground Surface Mines
Inactive Active Inactive Active
R&P L.W. R&P L.W. Contour Area Contour Area
____ _ _ _ _
____ _ 4 _ 2
4-4- - 4 - 2
3422 4 4 3 3
3-2- - 4 - 1
3432 - 4 - 1
3-4- 3 - 3
4 _ _ _
R&P = Room and Pillar
L.W. = Longwall
Note: Numbers refer to ratings described in text.
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Ore Type
Metal Ores
Bauxite
Copper
Gold
Iron Ore
Lead
Mercury
Silver
Titanium
Tungsten
Uranium
Zinc
All Others3
Nonmetallics
Sand and Gravel
Stone:
Limestone
Others (Granite,
Traprock, etc.)
Phosphate Rock
Salts
All Othersb
TABLE V-8
METAL AND NONMETAL MINES
SCREENING FOR ACCEPTABILITY
Underground
Inactive
or Abandoned
Portions-Active
4
4
4
3
2
4
4
4
4
4
2
4
Active
4
4
4
4
3
4
4
4
4
4
3
4
FOR FGD DISPOSAL
Open
Inactive
4
3
4
3
4
4
4
4
4
4
4
4
Pits
Active
4
4
4
4
4
4
4
4
4
4
4
4
4
4
2
4
4
4
4
4
Pits & Quarries
Inactive
Active
4
3
3
4
4
4
Antimony, beryllium, moly, nickel, Pt. group, tin, vanadium, rare earths.
DAsbestos, abrasives, barite, boron, clays, diatomite, feldspar, fluorspar, gypsum, mica,
perlite, potash, pumice, talc, soapstone, vermiculite, pigments, kyanite.
-------
cavities (before roof collapse) are difficult to delineate, as underground
mining plans were generally not submitted. Only under local conditions,
such as those prevalent in the anthracite region of Pennsylvania, might
sludge placement in abandoned underground mines be justified to limit acid
drainage formation and surface subsidence damages.
Active surface area coal mines in the Interior and Western regions
receive the highest ranking as technically promising for sludge disposal
because of their individual capacity (assuming sludge disposal occurs
simultaneously with extraction and reclamation) and the ease of sludge
placement within existing operations. The Eastern surface mines are
generally considered less promising because they individually are much
smaller mines. Also, the Eastern contour mining allows less ease of sludge
placement than area stripping.
While the active underground coal mines show technical promise for
accepting FGD sludge, they are not considered as promising as the active
surface mines. Sludge placement would add complication and additional
maneuvering to the already difficult working conditions. Also, many of
the underground mines mix techniques of conventional room and pillar with
pillar robbing and/or longwall mining within one mine and would therefore
require more than one method of sludge placement and range of sludge
properties.
b. Metal and Nonmetal Mine Screening
Of the active metal and nonmetal underground mines, only the room and
pillar operations on relatively horizontal seams are viable (see Table V-6).
Copper, iron ore, lead, zinc, salt, and limestone are mined in substantial
quantities by underground room and pillar methods. Other methods of under-
ground mining, such as caving and cut and fill, leave little available
void for sludge disposal. A small amount of sludge might be mixed with
sandfill and introduced into stopes of mines employing fill; however, these
amounts are not considered substantial enough to rank these mine categories
as promising to provide solutions to the pending national sludge disposal
needs. Underground mining of precious metal, such as gold and silver,
which often occurs in steeply dipping deposits, may not employ fill;
however, FGD sludge disposal would discourage the future mining of the
deeper vein segments left in place.
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Of the active underground metal mines, only lead-zinc mines show
promise for sludge disposal by our ranking system. These lead-zinc mines
have about 70% of the ore extracted after room and pillar mining and pillar
robbing (called slabbing); the void space after ore extraction generally
remains open and accessible. Also, because of the high extraction per-
centage, it is doubtful that these mines would be reopened for further
exploitation.
Of the active underground nonmetal mines, limestone and salt room
and pillar mines show promise. There are about 30 active underground room
and pillar limestone mines with substantial capacity for sludge placement.
Some of these are dry hillside mines with thick mine seams (averaging 40 feet
thick). And there is easy access for dry FGD sludge dumping. About 60% of
the ore is removed by the room and pillar method, with the remainder left
as pillars for roof support. Because of the thickness of the seam (up to
100 feet thick), roof collapse could create substantial subsidence at the
surface. Therefore, it is doubtful that future pillar robbing would occur
and that FGD sludge disposal would be significant to future resource recovery.
There are about 16 active room and pillar salt mines annually producing
about 18 million tons per year in total. Room and pillar salt mines are
dry. Even though below the water table, their shafts are carefully sealed
to prevent water entry. Extraction of 60-70% of the salt is normal, with
the remainder left as pillars. Since these mines are not caved and are
accessible, placing moist to dry sludge would be feasible. Placement of
wet sludge would generally not be practical because it could dissolve salt
in the pillars, allowing them to weaken and possibly result in roof collapse.
Site-specific assessment would be required to determine the viability of
placing wet sludge. The published literature contains an assessment of
waste disposal in underground salt mines (1).
Active open pit metal and nonmetal mines, while abundant and indi-
ually large voids, are not considered viable FGD sludge disposal sites
because of the nature of mining. Generally, overburden is removed from
the mine area and the mineral mined downwards from the surfaces in benches.
For example, small amounts of copper are deposited in porous strata about
1,000 feet thick, and the ore is mined in concentric circular benches from
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the surface. Because of the nature of mining, neither overburden nor
tailings are returned to the pit during the life of the mine. These open
pits are not normally reclaimed, as shown in Table V-l. In the case of
some active iron ore open pit mines, mining advances down-dip along the
ore seam. It may be possible to construct impoundments to isolate the
mined-out portion for FGD sludge disposal; however, such impoundments would
block access from the surface to the working faces. Therefore, the category
of open pits is considered generally unpromising.
There is no readily available information on the location and condition
of inactive or depleted mines, either open pit or underground. In some
cases, these are closed for economic reasons linked to market demand and
many be reopened for additional recovery of valuable material. It is
believed that most of the abandoned mines are closed for economic reasons
and that few are fully depleted. There are probably three or four finished
open pit metal mines in Arizona, several in Nevada, Utah, and Montana, and
six or seven in the iron ore regions of Minnesota and Michigan. These
often form manmade lakes where water sport recreation develops. Most
abandoned underground mines have been stripped of all timber and equipment
and are not easily accessible. These underground mines might be large in
total tonnage but individually are expected to have limited capacity. Only
the old lead-zinc underground mines of southeast Missouri and the limestone
underground of the Midwest appear to provide a large capacity for sludge
and to have remained largely intact (not caved).
On the basis of the above discussion, mine cases selected for impact
assessment because of technical feasibility are:
• surface coal mines - active;
• underground coal mines - active;
• underground lead-zinc mines - abandoned or mined-out portions of
active; and
• underground limestone mines - abandoned or mined-out portions of
active.
B. DISPOSAL OF FGD SLUDGE IN SURFACE COAL MINES
1. Range of Conditions Possible
There are three types of active surface coal mines showing promise for
the disposal of flue gas desulfurization sludge. Based on the technical
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considerations previously discussed, Interior and Western surface area coal
mines show the greatest promise; Eastern surface contour coal mines show
less promise due to their lower indiviudal capacity and the greater diffi-
culty of sludge placement.
Each coal mine is unique. Its operation, hydrology, geology, ground-
water, and soils characteristics are necessarily different from those of
any other mine. However, in order to assess impacts of FGD sludge disposal
in mines, general conditions have been chosen that are believed to be
average for a given type of mine and region of the United States. By com-
paring a site-specific mine with the conditions we define as average,
site-specific impacts may be extrapolated from this report.
a. Interior Surface Area Coal Mine
Coal production from an Interior surface area coal mine ranges between
0.1 and 6.5 million short tons annually. Coal is mined from seams varying
in thickness between 2.5 feet to 7 feet. Depth of overburden material to
be stripped before the seam is extracted varies from a feather edge at
the seam outcrop to about 120 feet. The dip of the coal seam ranges from
horizontal to about 5 degrees.
The average Interior surface mine produces about 1.5 million short
tons of coal annually as a washed product (1.9 million short tons are
removed from the mine, and washing wastes are returned). The principal
coal seam mined is 6 feet thick and covered with about 85 feet of overburden
bedrock and soil. The coal seam is bounded by relatively impervious under-
clay or shale, with most of the overburden rock being limestone. The soils
in the Interior region vary widely; often they are clayey (resulting in
little natural leaching) and therefore high in bases. Overburden, which
is moved and later placed on the sludge, will be a mixture of soil and
broken rock materials as well as some coal particles.
An Interior surface area mine averages reserves of 30 million tons and
has a life of 20 years. This allows the coal seam to be stripped in six
90-foot wide cuts each year. A typical pit length is two miles. Mining
operations begin where the coal outcrops or is closest to the ground
surface and continues with pits running perpendicular to the seam dip.
Figures V-7 and V-8 illustrate mining operations and cross-sectional
dimensions of a mine.
110
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Overburden Isopach
Coal Contour
Surface Contour
Projection of cuts in a surface mine. In this case both the coal seam and surface are
relatively level.
3rd
2nd Initial
Spoil Spoil spoil
Overburden
Typical cross section of an "area" surface mining operation with relatively level coal
and surface.
Source: Cassidy, S.M., Elements of Practical Coal Mining, Society of Mining Engineers,
New York. 1973.
FIGURE V-7 AREA COAL STRIPPING
111
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High Wall
Strata In
Place
Water Level in Finished/I
Probable Water Level
Active Pit
Topsoil Replaced Thin Layer T — 2'
Sump
Scale 1" = 80'
1 /
4th /
Pass /
/
3rd
Pass
I /
! /
-'
! 2nd
| Pass
1 • i
[
1st
Pass
> —
Shale Basement
:V
Sludge in Place
90'
Water Seeps
In
Coal In Place
6' Thick
Broken and Placed
Overburden — Leveled
(Limestone, Shales, Etc.)
FIGURE V-8 CROSS SECTION - OPERATING STRIP COAL MINE
-------
In the Interior coal region, power plants are in relatively close
proximity to coal mines. A large mine could conceivably handle FGD sludge
from more than one power plant. For high-sulfur coal, roughly twice the
quantity of sludge (including ash) produced from the coal mined could be
returned to the pit (assuming coal refuse tailings comprising about 25% of
the quantity of coal removed were also being returned to the pit). A small
mine, which supplies only part of a utility's coal requirements, therefore,
might be contracted to handle all or part of the FGD sludge from one power
plant. For the above example of an Interior mine producing 1.5 million
short tons of coal yearly (after separating the coal refuse) approximately
an equal volume of sludge could be returned, up to 2.0 million tons of
compacted sludge.
In the area of the Interior region where most of the surface area
mining occurs the climate is moderately wet. Precipitation ranges from
32 to 42 inches annually, with annual runoff ranging from 7 to 12 inches.
While it is not possible to specify the geology which may be encoun-
ered in a specific mine, the following generalizations prevail in the most
actively mined portion of the Interior coal region (especially southwest
Illinois). The area consists of plains underlain by gently dipping con-
solidated bedrock formations. The overburden consists of a thick layer of
clayey soil of low groundwater yield; only river valley alluvium yields
significant groundwater. The soil portion of overburden is typically
underlain by limestone which provides low to moderate groundwater yields
for local water supplies. Below the coal seam and its abutting underclay
or shale, limestone and sandstone strata commonly provide moderate yield
of public water supply. The bedrock dips gently, while the surface plains
undulate with a prevailing dip to where the coal seam outcrops. The
regional groundwater flows in the direction of surface drainage; however,
in the active portions of a mine, groundwater flow may be controlled by
other factors, i.e., impervious strata underlying the extracted coal seam.
Mine drainage in this region is usually neutral to alkaline. This
may be attributed to one or more factors. For example, the coal seam may
be low in the types of pyrite (especially framboidal pyrite) believed to
cause acid drainage upon exposure to air and water. The prevalence of
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limestone in the overburden causes a very alkaline background groundwater
which may neutralize acid drainage if and when it forms.
b. Western Surface Area Coal Mine
The production of coal from Western mines ranges from 0.6 to 6.8 million
short tons annually. As methods Improve to extract the wide seams prevalent
and to mitigate environmental degradation, this production will increase.
Seam thicknesses in the Western region range from 4 feet to 100 feet thick.
Overburden depth ranges from a feather edge at the seam outcrop to about
125 feet at the point where surface stripping is currently halted. The
seam dip varies from horizontal to as much as 10 degrees. Most of the seams
dip downward from the outcrop and into an underground basin.
The most prevalent Western surface area mining conditions include
large production from the outcrop of thick, moderately to steeply dipping
seams, such as the Hannah seam in Wyoming. Therefore, for the average
mining scenario a Western surface coal mine produces about 6.0 million
short tons of coal per year from a 70-foot thick coal seam overlain with
30 feet of overburden. The rock overlying the coal seam includes a sequence
of sandstone, siltstone, shale, and limestone. The soil mantle is thin.
Soils are sandy, with some clay and silt, and low in organic matter. The
soil layer ranges from 5 to 15 feet deep and usually is basic.
The subbituminous coal reserves in the State of Wyoming exceed
13.0 billion tons. The reserves of each mine depend upon the acreage
owned by the mining company and the economic limits set by overburden
depth. Typically, a mine operates on two benches with shovels and trucks.
About 100,000 tons of coal are mined per acre, and 44 acres are mined
yearly. Figure V-9 shows a cross-section of average conditions for a mine.
A Western mine may be producing for a mine-mouth plant or for one or
more remote plants linked by unit train. If all of the sludge (including
ash) produced from the subbituminous coal is returned to the mine, there
would be about 0.25 tons of FGD sludge with fly ash (50% moisture) returned
for every ton of coal removed. Therefore, for a mine producing 6.0 million
short tons of coal per year about 1.5 million short tons of sludge would be
returned for disposal. This sludge would fill roughly 20-30% of the void
created by coal extraction.
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Original Surface
Reclaimed
± 45'
L
Overburden & Sludge
Dumped Over Brow
Hard Sandy Shale
Bottom
Sludge Mixed in With
Overburden
/ oa eam
r / S / .
Some Water in Pit
Pumped Out
Scale 1" = 80'
FIGURE V-9 CROSS SECTION - WESTERN STRIP MINE
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The geology of each mine varies. However, for the area within the
Western coal region where most of the surface mining currently occurs
(namely, Wyoming) some generalized conditions prevail. The area is water
poor. Precipitation ranges from 8 to 24 inches annually, and runoff ranges
from less than 1 inch to as much as 20 inches. The high runoffs are
indicative of the flash flooding characteristic of semi-arid areas.
Groundwater recharge is low, as low precipitation and high runoff couple
with significant evapotranspiration loss to result in little percolation.
Within the coal mining areas, groundwater is found mostly in the bedrock
units of sandstone and coal.
There is little acid drainage in the area. The environment does not
provide the optimum acid formation conditions of oxygen coupled with high
humidity. Also, while there is not an abundance of limestone in this
region, the soils are basic (because the dry conditions have allowed
limited leaching of the salts) and resulting groundwaters have significant
buffering capacity. Finally, there may be a limited amount of reactive
pyrite.
c. Eastern Contour Strip Mine
Contour strip mines occur where coal seams outcrop on hillsides.
These mines are principally located in the Eastern coal region. Collect-
ively, their production compares with Interior and Western mines. However,
the production of coal from individual Eastern contour strip mines is
generally less than from individual Interior or Western strip mines
(compare Tables V-2 and V-3). The production of an Eastern surface contour
mine varies from about 0.01 to 1.5 million short tons. The coal seam thick-
ness ranges from about 2.5 feet to 7 feet. Overburden depth ranges from
nil at the hillside outcrop to 100 feet at the final pit. Most of the seams
are nearly horizontal; however, there are slight dips or undulations that
slope as much as 10 degrees. An average surface contour mine produces
about 0.4 million short tons of coal annually. The coal seam is about
6 feet thick, with overburden up to 120 feet thick. In a contour mine
with a finished pit it is common practice to recover more coal by augering
into the seam.
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In the average contour strip mine case, the approximate dimensions
mined annually are 565 feet by 2,840 feet (37 acres). If the hillside
slope is about 12 degrees or less, a "contour" backfill, as illustrated in
Figure V-10, can be used. In this case, the highwall is completely covered
and the area is reclaimed to the approximate original topography. Where
surface slopes are steeper than 12 degrees, a "terrace backfill" is often
used; the highwall is cut back and pushed into the pit and a terrace is
left on the hillside. Backfilled overburden consists mostly of broken rock
from hillside sandstone and shale outcroppings.
Many power plants in the Eastern coal region are in close proximity to
the coal mines. Since most of the Eastern surface coal mines are small
producers, they would probably accept sludge from only one power plant.
An Eastern mine producing about 0.4 million short tons of coal annually
(after coal preparation) could accept an approximately equivalent volume of
sludge, weighing up to 0.5 million short tons.
In the Eastern coal region most of the surface contour mining occurs
in western Pennsylvania and eastern Ohio. From west to east the area
becomes increasingly wet. Precipitation ranges from 30 to 48 inches, and
runoff ranges from 10 to 30 inches. The geology of this region is very
complex. Aquifers are difficult to locate. Coal seams and other rock
strata at high elevations in the Appalachian plateaus are nearly horizontal
and unaltered. Groundwater recharge and availability in the plateaus are
limited, while groundwater yields are plentiful in the valley alluvium.
In the plateaus, small to moderate yields come from limestone and sandstone
aquifers.
Soils in this area are low in bases, largely because the humid environ-
ment has led to excessive leaching of salts from the soil mantle. This,
coupled with the limited existence of limestone strata, leads to groundwater
with little or no buffering capacity. Acid mine drainage in the area is
substantial for a number of reasons; the pyrite in the coal is often of the
acid-forming variety, the coal exposure to air and high humidity encourages
acid formation, and the low buffering capacity of background groundwater
cannot neutralize the drainage once it has formed. As the acidity of the
drainage increases, microorganisms which thrive in low pH environs markedly
catalyze the reactions.
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Diversion Ditch
00
Backfilled Slope
\
Dike
(as Needed)
570'
Sludge Layer
FIGURE V-10 CONTOUR BACKFILL
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2. Impact Assessment
As a basis for the assessment of sludge impact, we assume that in all
three surface mine cases, disposal would involve placing the sludge by rear-
dump trucks in the mined-out portion of the strip before returning overburden
(or as overburden is returned to the pit in mines whereas haulback mining
is practiced). Placing the sludge in the pit before overburden is returned
is the easiest mode of disposal and will have the least disruptive effects
on existing mining operations. Other methods of disposal are considered
control techniques which mitigate adverse technical or environmental impacts.
a. Technical/Physical Impacts
Sludge Physical Constraints
In operating strip coal mines, overburden is moved with draglines,
shovels, or bucketwheels and then the coal is mined with front end loaders,
shovels, and trucks. The coal mining and hauling equipment and maintenance
and supply vehicles all operated on the floor of the pit and on roads down
into the pits. For efficient operation, pit bottoms and roads must be in
reasonably good condition and are maintained with road graders, etc.
Mining operations could not continue effectively if the sludge flowed
or acted like a mud when placed in the pit. The sludge has to be such that
it can be placed by a rear-dump truck and covered with overburden without
it spreading or squeezing out and flowing. It should also have some
stability when rewetted (by precipitation) and should not flow under such
conditions. It does not need to be of such strength that it will support
mobile equipment, since it can be placed and covered without equipment
running directly on it. In order for untreated FGD sludge to meet the
above conditions for strip mine placement, it should be filtered or
centrifuged and possibly admixed with fly ash. It should be immediately
placed in the pit and covered with overburden or inventoried in stockpiles
protected from rain. If left in open stockpiles, there is some potential
for the material to erode when it rains.
Laboratory studies indicate that FGD sludges vary in compacted dry
density from about 80-100 Ibs/cubic foot after Standard Proctor compaction.
If left uncovered or unmixed with overburden, sludge of these densities
would be a poor foundation material and would not support traffic.
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Furthermore, it is doubtful that truck dumping of loose FGD sludge and
consolidation under the static loading of replace overburden would allow
optimum compacted densities to be achieved in the field.
Groundwater returning to its original water table elevation in the
reclaimed land areas of the mine may saturate the sludge. Even when placed
in a loose state and saturated, the fine grained sludge is not expected to
be liquefiable because of the overlying confining pressures of the replaced
overburden. At the outcrop (especially of an Eastern contour mine) where
the overburden depth is small, a dike should be designed and constructed to
retain the sludge under applicable seismic loadings.
The amount of sludge handled in any surface mine should not exceed the
amount of coal removed (by volume) for several reasons. First, the objectives
of strip mine reclamation include returning the mined terrain to topographic
configurations similar to the initial terrains. Second, the overburden and
sludge are unconsolidated upon return, and even addition of the same weights
will result in a thicker mass. Third, returning significantly more sludge
to a mine than the coal extracted could slow down the simultaneous mining
and reclamation activities.
Sludge dumping can be adapted to allow mixing of the overburden and
sludge. In contour strip mines where haulback methods are used, there will
be some mixing of sludge and overburden. In such mines, mixing may be
accomplished with minimal impact on the operation of the mine. However,
in most strip mines, mixing requires more handling (such as by the dragline
or shovel) than may be readily acceptable to mining management. Since
mixing with overburden may result in some soil attenuation of solute
contaminants in the sludge, it is addressed in the discussion of control
techniques.
Handling and Placement
Sludge would be most easily placed in the mined-out pit by truck
dumping, but it is not recommended that coal haulage vehicles be used for
sludge transport and placement. In some mines where rear-dump type trucks
are used, sludge could possibly be transported by the existing coal haulage
trucks on their return trip from the coal washing plant to the pit.
However, such an operation may not be cost-effective, since the turn-around
time for coal transport would undoubtedly increase due to the time required
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for loading and dumping sludge. Some sludge would also get mixed in with
the coal, unless the sludge releases easily from the trucks. Since the
coal is washed, a small amount of contamination can be tolerated, but any
significant amount of contamination would necessitate cleaning the trucks,
creating a delay.
Furthermore, most mines are now using large, bottom-dump trucks for
coal haulage. While many trucks are designed to carry up to 100 tons of
coal, they are lightweight with bodies usually constructed of aluminum.
Not only could the sludge corrode the aluminum, but the bottom dumping of
sludge would also be technically impractical. These types of trucks are
not designed for ease of maneuvering in mine pits, and operating these
trucks on a layer of sludge would be practically impossible.
Congestion in the working pit may result from the use of two-truck
transport systems—one for sludge and one for coal haulage. Careful
consideration needs to be given to general scheduling of coal/sludge
transport as well as mining and reclamation activities in order to minimize
inefficiency and lost productivity.
Additional technical impacts which may result from sludge disposal
include potential dust problems if the fine grained sludge is allowed to
dry when stockpiled, slide potential if the sludge is saturated when
stockpiled, and erosion potential from storm runoff. These impacts can be
minimized by disposing sludge in the same continuous manner in which coal
is mined, thereby lessening the need for large sludge stockpiles. Chemical
treatment of sludge would also lessen the potential for structural insta-
bility.
Although equipment exists at power plants for emptying coal cars,
storing coal, and sometimes heating unit trains under freezing conditions,
no such equipment exists at the mining end of the train operation to
handle sludge. Sludge disposal would likely require a capital expenditure
for sludge handling and transfer. Special handling may also include
washing of the unit trains which might transfer sludge from the power plant
to the mine before these cars could be filled with coal for their return
trip. Delays due to increased handling and transfer procedures at the mine
are expected to increase the overall costs at the mine.
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FGD sludge disposal is not expected to impact on mine reclamation
operations. In fact, partial filling of the mine void will help to allow
reclamation to original topographic conditions. Coarse coal refuse from
processing operations is already returned to the pit in most modern
operations. FGD sludge disposal would parallel the coal refuse disposal
operation.
b. Environmental Impacts
Sludge Leachate
FGD sludge disposal is expected to contaminate contacted groundwater for
hundreds to thousands of years in any surface coal mine disposal case. The ex-
tent of the effect and its acceptability can only be determined on a site-specific
basis. The following discussion provides an overview assessment of relative
impacts among Eastern, Interior, and Western surface coal mines as well as
some basis for future assessments of specific FGD sludge disposal proposals.
Leachate production is equivalent to the amount of percolation and
groundwater underflow passing through the disposed sludge. During mining
and disposal the groundwater table is depressed, as needed, by pumping to
keep the working area dry. Therefore, percolation is the dominant cause
of leachate production in the vicinity of the working area. Once the
working area is sufficiently removed from sludge disposal so that the
initial water table is reestablished, groundwater underflow (saturated zone
below the water table) becomes the dominant cause of leachate production,
provided sludge disposal is below the water table.
Locally, underground hydrology may vary widely. Regionally, certain
generalizations about the underground hydrology can be developed for the
regional water balance (including factors of precipitation, evapotrans-
piration, and runoff) and the surface topography. Figure V-ll depicts the
generalized movement of regional groundwater during and after surface mining
of coal seams in the Eastern, Interior, and Western regions. As shown,
pumping during mining alters the groundwater regime and may remove underflow
from the sludge disposal. Once mining is completed in the sludge disposal
area, the groundwater underflow essentially resumes its former flow con-
figuration. The percolation rate is locally increased due to the disturbance
and haphazard replacement of the overburden; however, the regional underflow
rate is relatively unaltered.
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Depressed / '
Water Table
During Eastern Contour Mining
After Eastern Contour Mine Reclamation
Depressed Water
Table -,
Sludge
Coal
During Interior Area Mining
Water Table
VVOlCl I uUIC -^
Sludge
Coal
After Interior Area Mine Reclamation
Depressed Water
Table
Sludge in Overburden
L
During Western Area Mining
Water
Table
After Western Area Mine Reclamation
FIGURE V-11 REGIONAL GROUNDWATER MOVEMENT IN
SURFACE COAL MINES
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Since groundwater is derived almost entirely from precipitation,
seasonal variations occur. The water that does not become runoff, or
escape through evaporation and transpiration, percolates into the reservoir
of groundwater. Typically, water levels are highest in. the spring and
lowest in the late fall. Snow melt and spring rains recharge groundwater.
And since plants draw heavily on soil water during the summer, percolating
water is removed before it reaches the groundwater underflow, and the water
table lowers. As a result, the coal seam may be within the groundwater
regime for only a portion of the year.
In Figure V-ll the mine cases are shown under the worst case condition,
where the undisturbed water table is largely above the initial coal seam
and subsequent sludge layer. This may not be the typical condition for
the Eastern mine because the steep surface stopes and thin soil overlying
the bedrock result in high runoffs and little percolation. This may also
not be the case in the Western mine, where there is almost no groundwater
recharge. The Interior mine, on the other hand, occurs in a moderately wet
climate having gently sloping plains allowing time for percolation into the
thick soil mantle.
Most surface mining advances downdip or horizontally from the outcrop
or the lowest depth of overburden. As the mining continues, the water table
is depressed more with each successive working pit. Sludge placed in the
initial pits may therefore remain above the water table during mining.
And, as mentioned, the primary means of leachate generation is percolation
of rainfall through the overburden and sludge layers (or sludge/overburden
mixture in the Western case). Most of the leachate would probably flow
locally to a collection sump in the active mining pit. Minor amounts would
flow into the regional groundwater underflow.
Leachate collected in the working pit with the background mine drainage
would add to the contaminant level of the discharge. Since mine drainage
collected and pumped from the working pit must meet EPA recommended effluent
guidelines, wastewater treatment of the drainage may be required before
discharge. Parameters limited by effluent guidelines for coal mine dis-
charge are iron, aluminum, manganese, nickel, zinc, and total dissolved
solids.
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During Eastern Contour Mining
After Eastern Contour Mine Reclamation'
Depressed Water
Table
\
Sludge
Coal
During Interior Area Mining
Water Table -,
rtrrnr—. JL^HT
Sludge
Coal
After Interior Area Mine Reclamation
Depressed Water
Table
Sludge in Overburden
1
During Western Area Mining
After Western Area Mine Reclamation
FIGURE V-11 REGIONAL GROUNDWATER MOVEMENT IN
SURFACE COAL MINES
123
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Since groundwater is derived almost entirely from precipitation,
seasonal variations occur. The water that does not become runoff, or
escape through evaporation and transpiration, percolates into the reservoir
of groundwater. Typically, water levels are highest in. the spring and
lowest in the late fall. Snow melt and spring rains recharge groundwater.
And since plants draw heavily on soil water during the summer, percolating
water is removed before it reaches the groundwater underflow, and the water
table lowers. As a result, the coal seam may be within the groundwater
regime for only a portion of the year.
In Figure V-ll the mine cases are shown under the worst case condition,
where the undisturbed water table is largely above the initial coal seam
and subsequent sludge layer. This may not be the typical condition for
the Eastern mine because the steep surface stopes and thin soil overlying
the bedrock result in high runoffs and little percolation. This may also
not be the case in the Western mine, where there is almost no groundwater
recharge. The Interior mine, on the other hand, occurs in a moderately wet
climate having gently sloping plains allowing time for percolation into the
thick soil mantle.
Most surface mining advances downdip or horizontally from the outcrop
or the lowest depth of overburden. As the mining continues, the water table
is depressed more with each successive working pit. Sludge placed in the
initial pits may therefore remain above the water table during mining.
And, as mentioned, the primary means of leachate generation is percolation
of rainfall through the overburden and sludge layers (or sludge/overburden
mixture in the Western case). Most of the leachate would probably flow
locally to a collection sump in the active mining pit. Minor amounts would
flow into the regional groundwater underflow.
Leachate collected in the working pit with the background mine drainage
would add to the contaminant level of the discharge. Since mine drainage
collected and pumped from the working pit must meet EPA recommended effluent
guidelines, wastewater treatment of the drainage may be required before
discharge. Parameters limited by effluent guidelines for coal mine dis-
charge are iron, aluminum, manganese, nickel, zinc, and total dissolved
solids.
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During mining, relative impacts for each of the surface coal mine
cases would vary according to:
• the amount of leachate due to percolation;
• the dilution of leachate due to surface runoff and collected
groundwater in the mine water drainage; and
• the leachate contaminant level as affected by the composition of
the replaced overburden and background quality of the mine drainage.
For the Eastern case where precipitation is the greatest, leachate
generation from percolation through overburden will be significant. Surface
runoff from the steep slope above mining will provide substantial dilution.
Since the overburden has minor buffering capacity and the mine drainage is
typically acidic, potential for dissolution of chemical species in the FGD
sludge will be great.
For the Interior case where precipitation is moderately high, leachate
generation through the overburden will be significant. The runoff in this
region is less because gentle slopes encourage percolation, while the
groundwater pumped from the mine will provide dilution. The overburden
has significant buffering capacity attributed to the limestone present,
resulting in alkaline mine drainage which should discourage dissolution of
a number of FGD sludge chemical species.
There is very little precipitation in the Western case, and the amount
of leachate generated will be limited. Similarly, there will be little
mine drainage collected in the active mining area to provide dilution. As
soils in this region are basic and mine drainage is normally neutral to
alkaline, dissolution of FGD sludge constituents will not be encouraged.
However, the leachate will undoubtedly add to the already high concentrations
of dissolved solids naturally prevalent in these waters.
Based on the above discussion, contamination of mine drainage discharge
would result from placing sludge in nearly all Eastern, Interior, and Western
mines. The acid conditions prevalent in Eastern mines would probably result
in the greatest concentrations of FGD sludge constituents contaminating the
discharge. Because the major pollutant loadings would be from chloride,
sulfate, sulfite, and sodium sludge constituents, treatment (if required
to meet effluent guidelines) of the discharge would be costly. None of
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these chemical species are readily removed by practical wastewater treatment
processes, including biological treatment, sedimentation, and precipitation.
As the active mining area advances from the outcrop or lowest depth
of overburden, the areas initially receiving FGD sludge are reclaimed and
the water table is restored. The sludge, deposited in a loose state,
densifies as the overlying static loading from overburden causes consoli-
dation. Permeabilities of the sludge are expected to range from about 10"1*
to 10~^ cm/second, with the lower level attained as the sludge consolidates.
The maximum rate of leachate generated from the groundwater underflow
passing through the sludge will be a function of the sludge permeability,
the hydraulic gradient of the groundwater regime, and the cross-sectional
area of the sludge perpendicular to the direction of groundwater flow.
The leachate generated will not be collected as part of mine drainage,
but it will exhibit plug flow within the regional groundwater underflow.
Leachate flows through the interconnection of voids in both the sludge and
the overburden and subsequently through the fractures and discontinuities
in the bedrock. Little dilution of the leachate is experienced, although
there is slight diffusion at the edge of the leachate plume (or slug).
After mining, relative impacts for each mine case would vary for:
• the amount of leachate produced by the transmission of groundwater
underflow; and
• the leachate contaminant level as affected by the background
groundwater quality.
For the Eastern case, groundwater underflow is limited by the lack of
recharge. However, the water present flows quickly because: (1) the steep
surface topography leads to a steep hydraulic gradient, and (2) water often
moves through fractured rock faster than through alluvium intergranular
openings. Because the background groundwater has little buffering capacity,
chemical species prone toward dissolution will contaminate the leachate.
There is moderate underflow of groundwater available for leachate
production in the Interior case, but the hydraulic gradient of groundwater
underflow is small. As a result, leachate generates slowly and moves
slowly from the disposal area. The alkaline background quality of the
groundwater underflow encourages precipitation of a number of chemical
species, thereby lessening the pollutant potential.
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There is very little underflow of groundwater available in most
Western mines. Coupled with the small hydraulic gradient of the underflow,
leachate production is very limited, and spread of the leachate plume is
extremely slow. The basic condition of the soil overburden leads to an
alkaline background groundwater which inhibits dissolution of many chemical
species in the sludge.
In summary, after mine reclamation a unit of sludge generally produces
leachate most quickly in the Eastern surface coal mine and least quickly in
the Western surface coal mine. However, the total amount of leachate
possible is related to the amount of sludge, and Eastern mines generally
have the least capacity for sludge disposal. Western mines have the
greatest capacity for sludge disposal, although amounts are limited by the
feasibility of long-distance transport. For the estimated average mining
scenarios the Eastern mine case annually receives 0.5 million short tons
of sludge, the Western mine case receives 1.5 million short tons of sludge,
and the Interior mine case receives 2.0 million short tons of sludge.
In general, leachate concentrations will tend to be greatest for the
Eastern and Western cases. The Eastern case results in high sludge species
dissolution rates because of the nonalkaline background groundwaters most
often prevalent. Loadings for the Western case are substantial because of
the generally higher concentrations of soluble constituents in FGD sludge
produced from Western coals (see Table IV-3).
As mentioned, leachate from sludge will move in a plume (or slug) and
dilution will be minimal, although some diffusion of concentrations occurs
at the edge of the plume. In addition, concentrations released from the
sludge are not expected to noticeably decrease for many years. In accel-
erated laboratory leaching studies, sludge leachate constituents decreased
with increasing pore volumes of water passing through the sludge (until
equilibrium solubility constants were reached). Since groundwater moves
very slowly, taking tens to hundreds of years for one pore volume of
leachate to pass through a layer of sludge, contamination of groundwater
in the vicinity of the disposal site could therefore be noticeable for
hundreds to thousands of years. However, the impact of the leachate on
groundwater will depend importantly on the total quantity of the constituents
leached as well as its concentration.
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The significance of contaminant levels in the leachate plume will
depend on several factors. First, contamination is more significant if
it occurs in naturally high quality groundwaters than in highly mineralized
groundwaters. Second, the solute transport of most chemical species is
lessened by attenuation mechanisms in the aquifer medium. Therefore, the
significance of leachate depends on the .distance of medium providing
attenuation before reaching downgradient wells which provide potable or
irrigation water supplies. Significance is also related to the impact of
leachate to surface waters according to their prevalence of aquatic
organisms and/or use for water supplies.
According to laboratory testing, most of the total dissolved solids
in sludge leachate are calcium and sodium chlorides and sulfates, which
are not attenuated or precipitated to any measurable degree. A small amount
of total dissolved solids is attributed to trace elements such as aresenic,
boron, cadmium, chromium, copper, lead, mercury, and zinc. These trace
elements are affected by attenuation on clay or organic soils and by pre-
cipitation by iron oxides or hydroxides; however, in the assumed surface
mine disposal cases, the sludge layer is not mixed with soil matrix to
provide attentuation through cation exchange capacity, and iron present in
mine drainage may not be in a form which encourages precipitation.
Selenium and chromium are expected to be especially troublesome
solubles in the leachate because they dominantly appear in the anionic
form in sludge and are therefore not affected by cation exchange and cation
oxide precipitation mechanisms. Arsenic and boron are expected to leach
because they are not readily precipitated, adsorption being their primary
mechanism of attenuation. Aluminum, beryllium, cadmium, copper, cobalt,
iron, lead, manganese, mercury, molybdenum, nickel, and zinc are expected
to be partially attenuated by precipitation mechanisms under the neutral
to alkaline pH conditions prevalent in the Interior and Western surface
mine cases. In the Interior case where limestone is present, carbonate
salts may form with cadmium, calcium, copper, iron, lead, and zinc. With
the acid background groundwater prevalent in the Appalachian plateau
contour mines, potential for precipitation of metals is limited.
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The quantities of sludge allowable in a particular mine can be
estimated for the site-specific geologic and hydrologic features of the
mine and surrounding environs, for the composition of sludge placed, and
for the relative quality and uses of indigenous groundwaters and surface
waters. The maxiumum leachate produced will depend on the hydraulic
gradient of the percolation and/or underflow passing through the sludge
layer, the in-situ permeability of the sludge, and the cross-sectional area
of sludge perpendicular to the gradients of percolation and/or underflow
and can be estimated according to Darcy's Law for flow of fluids through
porous media. The leachate concentrations leaving the sludge layer will
most likely approximate the liquor concentrations of FGD sludge to be
disposed. Solute transport modeling, while still in the infant stages of
research and development, may be employed to provide some indication of
attenuation of the leachate constituents. And finally, the water use
criteria and assimilative flow capacity of downgradient surface waters can
be used in a steady-state stream model to indicate the amount of leachate
discharge allowable.
Biological Considerations
From a biological standpoint, total dissolved solids in general and
the high concentrations of heavy metals (especially mercury, cadmium, and
zinc) would provide cause for concern if leachate discharges to a small
pristine receiving stream. In addition to direct toxicity problems of
the estimated increment in mercury, cadmium, and zinc, potential problems
of accumulation and synergism would exist, especially in small streams.
Mercury and cadmium are persistent, cumulative toxicants, and the toxicity
of the latter can be increased by zinc. The high concentrations could
provide a source of chronic accumulation and ultimate hazard to man via
recreationally valued finfish (e.g., trout) harvested in the receiving
stream.
Total oxidizable sulfur (TOS) in leachates may also present a toxicity
potential of concern—both in terms of the toxicity of sulfite itself and
for the possibility of decreasing dissolved oxygen levels in surface waters
(groundwaters for the most part tend to be anaerobic or at least very low
in oxygen). Unfortunately, almost no leachate data exist for TOS, and
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such data would be invaluable in estimating TOS impacts. Based upon the
estimated solubility product of calcium sulfite alone in low ionic strength
solutions (5 x 10~7), the equilibrium concentration of sulfite would be
expected to be on the order of 5-10 ppm. The actual level of sulfite
present will depend upon the concentration of calcium and ionic strength
of the leachate. Large quantities of calcium sulfate in the sludge will
decrease soluble sulfite levels, since calcium sulfate dissolves more
readily and increases calcium concentrations. In addition, sulfite may be
present in the liquor occluded with the solids; however, it is uncertain
how much of this soluble sulfite will persist after handling and disposal
of the sludge or how microorganisms in mine water may interact with TOS
catalyzed reactions. Therefore, the question of TOS impact cannot be
evaluated until further data are available on the presence and persistence
of TOS in sludge leachate and in the company of indigenous microorganisms
in mine water.
3. Control Techniques to Minimize Adverse Impacts
All control techniques to minimize impacts add to either the cost
of disposal or the cost of producing coal. The rationale for control
techniques to minimize adverse impacts of technical and environmental
significance are discussed within the impact assessment. Possible measures
that can be used to mitigate the impacts of the disposal of untreated
sludge include: sludge processing or treatment, control of site selection
and method of disposal, collection and treatment of sludge leachate or
runoff, and restrictions on allowable sludge properties.
Untreated sludge disposed of in surface mines should be filtered or
otherwise dewatered to eliminate extra moisture in order to reduce the
potential for sludge slide or liquefaction, difficulties in sludge trans-
port and handling, and accelerated leachate production. Sludge treatment
by chemical fixation techniques would enhance handling properties and
thereby minimize technical impacts, although a well-filtered sludge
(possibly admixed with ash) may in many cases be adequate to avoid most
adverse technical impacts. A treated sludge should also physically reduce
mobilization of pollutants through reduction in the sludge permeability
and decreased sludge contact area. The improved physical and handling
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properties of treated sludges may also provide greater flexibility in
sludge placement, which in conjunction with proper site selection may
reduce adverse impacts.
Mixing the sludge with clay may provide cation exchange attentuation
and with organics may provide adsorption. The soils of the Interior case
are characterized by high clay content, organics, and bases. As a result,
the soil overburden is an optimum media for mixing with the sludge to
provide attenuation. Western soils, on the other hand, tend to be sandy,
low in organics, and have little clay. Their attenuation abilities would
not be very good, and importation of foreign clay would be economically
unfeasible. There is very little soil in the overburden of Eastern contour
coal mines; it is doubtful that any mixing of overburden with the sludge
would enhance attenuation of solute chemical species.
In the Interior case, where soil overburden may be mixed with sludge,
copper and lead would be attenuated readily, while the following species
would be to a lesser degree: arsenic, boron, cadmium, fluoride, iron,
manganese, mercury, molybdenum, nickel, and zinc. Selenium, chromium, and
sulfate would not be attenuated because soil conditions are basic. Calcium
and sodium are not likely to participate extensively in exchange due to
large concentrations commonly found already adsorbed on clay crystals.
Chloride is not attenuated under any circumstances.
In predicting soil attenuation of a particular chemical species, there
are several considerations. The quantity and mineral content (e.g. , aluminum
hydrous oxides) of clay, the pH, the organic matter, and the relative con-
centrations of other species are all important. One must be aware of the
possibility of forming metal chelates with organics, which will act against
attenuation. There is also the chance of leaching additional components
from a soil in contact with the sludge. Including the mechanism of pre-
cipitation, the prediction of attenuation in soil becomes a complicated and
individual problem.
Another control technique is simply to limit the disposal of FGD
sludges based upon sludge characteristics and site properties. For
example, it may be appropriate in certain cases to limit disposal of
sludges having high TDS levels and that are not alkaline in nature. The
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alkalinity is affected by scrubber operation and the type and level of
fly ash present. Generally, alkalinity increases with an increase in fly
ash (however, most trace elements are concentrated in fly ash). If the
sludge layer is kept alkaline, conditions for precipitation of most trace
elements are enhanced. For this reason, co-disposal of FGD sludge with
coal refuse should be Investigated for potential adverse effects on pH and
trace element solubility. Since not all coal refuse causes significant
acid drainage formation, this issue is site-specific.
Collection and treatment of sludge leachate does not appear to be
a viable control technique. Groundwater collection requires expensive
pumping wells or infiltration galleries. Also, the principal leachate
parameters creating adverse impacts are chlorides and sulfates. Neither
of these can be readily treated by existing wastewater treatment processes.
Only certain metals are amenable to treatment through oxidation and pre-
cipitation techniques.
Operations other than the assumed disposal operation, described as
being the least troublesome to mining operations, may improve the impacts.
This could include both the method of sludge placement and the form of the
sludge deposits created. For example, if part of the rock overburden were
deposited in the pit until a depth above groundwater was attained and then
part of the soil overburden were deposited above the rock overburden, the
sludge layer could then be deposited and covered with remaining overburden.
This alteration of the disposal operation would isolate the sludge layer
from the groundwater aquifer and provide a clay adsorption media for down-
ward precipitating leachate. However, since the process of digging by
shovel or dragline in one pit occurs in a continuous motion by the same
machine with overburden replacement in the worked-out pit, this technique
would seriously hamper mining productivity.
C. DISPOSAL OF FGD SLUDGE IN UNDERGROUND MINES
1. Range of Conditions Possible
There are two types of underground coal mines showing promise for
disposing of FGD sludge. According to the technical ranking order, active
underground room and pillar mines and active underground longwall mines
show the most promise. Both types of mines are predominantly in the
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Eastern and Interior coal regions, with most production from the Eastern
region (see Table V-2). Figure V-12 shows a planar view of a conventional
room and pillar mine. Figure V-13 shows a cross-sectional view of a long-
wall mine working face.
Each underground mine is unique in its depth, hydrogeology, and
operation. For example, there are some that are essentially dry because
of thick, unfaulted shale comprising the floor and roof. There are also
many that are wet because of water access through natural cracks, fissures,
and joints in the adjoining strata or through induced discontinuities
caused by roof caving and mining operations.
a. Room and Pillar Mines
The production of coal from underground room and pillar coal mines
in the Eastern region varies from 0.01 to 4.1 million short tons annually
mined from seam thicknesses that vary from 2.5 to 12 feet thick. Over-
burden depths range from 200 feet to 2,500 feet, with some seams outcropping
at a hillside and others buried far below the river valleys. Dips range
from horizontal to 10 degrees, with most seams dipping only slightly down-
ward from the outcrop.
An average Appalachian underground room and pillar mine produces about
0.5 million short tons of coal annually. The coal seam mined is about
7 feet thick and located about 400 feet below the ground surface. About
40-50% of the coal is left in place as pillars to support the mine roof
from caving. If roof geologic conditions permit and either the mine is
deep enough to allow overlying strata to absorb strain deformation or the
surface land use can permit subsidence, pillars can be robbed as one retreats
back to the access openings. This increases extraction to as high as 80%.
The annual volume of FGD sludge which can be placed in a conventional
room and pillar mine is roughly equivalent to the amount of coal removed,
considering that sludge cannot be placed in entries. In a room and pillar
mine where pillar robbing is practiced, no sludge can be placed in the areas
designated for caving.
The coal seams in this region are gently sloping, averaging a 3% slope.
Sludge placement could be designed so that sludge decant water and mine
drainage is collected upgradient of the disposal area, with sludge settling
133
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Loading Machine Coal Shot
and Shuttle Car Down
Loading Machine
and Shuttle Car
75 ft
20 ft
20ft
*—»
s
Curtain
Shuttle
Car
^•0
50
ft *r[—50 ft—,
«-50
0)
QC
c
LLJ
Permanent Stopping
ft-^»J50ft_J
Source: Woodruff, S.W., Methods of Working Coal and Metal Mines, Vol. 3,
Pergamon Press, New York (1966).
FIGURE V-12 CONVENTIONAL ROOM AND PILLAR COAL MINING
MAIN HAULAGE - CONVEYOR
134
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As roof supports are
advanced, the roof
immediately behind the
supports is allowed to cave
Ideal Caving Conditions
Gob swell supports upper beds and yields
under their weight, permitting them to slowly bend
without breaking.
Immediate roof
subjected to pressure
from upper roof
bending action
Immediate roof supported
by face supports & bed
separation removes loading
of upper beds
Immediate roof
caves — material
fills voids
Compression from
upper strata
consol dates caved
material
Upper beds slowly
squeeze the broken
immediate roof
material to the limit without
themselves breaking
9A
Static conditions
restored
Source: Weir, J.P., & Kachik, O.J., "Outlook for Long Wall Mining in North America,"
Mining Congress Journal, 55 (7). 1969.
FIGURE V-13
TYPICAL LONGWALL MINING CROSS-SECTIONS SHOWING
CAVING ACTION
135
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and filling the downgradient area. The sludge could be placed as a slurry
of 20-40% solids, which would be typical of thickener underflow from most
of the scrubbing systems. Bureau of Mines experience in backfilling mines
with coal refuse reports pumping slurries of 10-50% solids (5). If addi-
tional water is needed to maintain an optimum water to solids pumping ratio,
mine water drainage can be used.
In the Appalachian coal region of the Eastern region most of the under-
ground coal mining production occurs in West Virginia; second in production
is Pennsylvania. The region is humid, with precipitation ranging from about
40 to 60 inches annually and runoff ranging from 12 to 30 inches annually.
The coal seams are nearly horizontal and are bordered above and below by
other nearly horizontal strata. In the Appalachian plateaus, small to
moderate yields of groundwater are derived from the sandstone and limestone
aquifers. Most of the high yields in the region come from the river valley
alluvium. Some moderate yields are available from the folded and faulted
deep rock strata; however, these waters tend to be highly mineralized due
to the lack of circulation. Extensive underground mining in this region
has complicated the hydrogeology. Groundwater eventually fills abandoned
mine voids present below the water table. This groundwater often flows
slowly through a series of interconnected.mines until finally discharging
at a surface outcrop or into the alluvium.
b. Longwall Mines
Most of the longwall mining in the United States occurs within room
and pillar mines. Longwall sections are developed when geologic conditions
and surface land use allow roof collapse; in deep underground mines under-
lying hard rock strata, longwall mining may result in no surface deformation.
Longwall production in a single mine varies from 0.2 to 1.2 million short
tons, with the larger production value occurring in a mine which is almost
entirely longwall. The seam thicknesses mined by longwall vary from 2.5
to 12 feet thick, with overburden depths ranging from 200 to 2,500 feet.
Most of the seams are horizontal or slightly dipping. However, slopes
range up to 10 degrees.
There are about 50 longwall mines operating today. Based on current
experience, most U.S. longwall coal mine management believe longwall mining
136
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is best suited for 3.5 to 5 foot seam thicknesses overlain by overburden
depths of 1,200 feet or more. Average production from longwall mining
within a coal mine would be 0.2 million short tons annually.
The amount of FGD sludge which could be placed in a longwall section
before controlled roof collapse depends mostly on the speed of the place-
ment operation. Sludge placement must keep pace with mining and roof
collapse operations, since the distance allowable between the working face
and caved section is kept small to prevent uncontrolled roof collapse.
Probably no more than 50% of the volume of coal removed by longwall can
be filled by sludge placement prior to roof collapse.
Since the longwall mining case occurs in the same region as the room
and pillar case, hydrogeology described above applies. Groundwater seepage
from overlying strata may be more severe in longwall cases because roof
collapse induces cracks, fissures, and joints in the overlying strata
which allow groundwater infiltration to the mine area. However, strata
below the coal seams remains undisturbed and maintains its natural
permeability for water leaving the mine.
2. Impact Assessment
Disposal in the mined-out portions of an active room and pillar mine
where pillars have not been robbed would involve hydraulic backfill using
a pumped slurry technique. The sludge could be either thickener underflow
from the scrubbing system or a slurry of treated sludge which would set
up in the mine. While placement of treated sludge blocks is possible, as
is construction of support pillars with treated, concrete-like sludge,
these procedures are not considered technically and economically promising.
In order to contain the sludge, bulkheads between pillars would be
constructed and sludge then introduced through boreholes from the surface.
The concept is sketched in Figure V-14, which gives a plan and cross-
section view. Pneumatic placement of sludge is also technically feasible.
However, because of the additional sludge processing required to obtain
the low sludge water content necessary for pneumatic stowing, hydraulic
placement appears more promising.
In a longwall mining operation, hydraulic placement would not be
acceptable because of potential hazard to miners as the roof caves upon
137
-------
Conveyor-
-650 Feet
Dip
Plow
Coal Face
Brattice Cloth
Positioned Face Pipe
Pack
Waif
Slower
Conventional Pneumatic Stowing Layout
for a Longwall Face
Source: Courtney, W.J., and Singh, Madan M., "Pneumatic Stowing: It Must be Looked
At Now," Coal Mining and Processing, H (2), 1974.
FIGURE V-14 LONGWALL STOWING - CONVENTIONAL
138
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a slurried material. Therefore, disposal in the working face of an active
longwall mine involves pneumatic stowing of relatively dry sludge, as
indicated in Figure V-15. The dry sludge could be either a filtered,
untreated sludge or a soil-like, chemically treated sludge. A water spray
would be used to keep the dust under control.
a. Technical/Physical Impacts
The first reported backfilling of mine workings was for hydraulic
placement of crushed coal mine waste underground at Shenandoah, Pennsylvania
in 1864 (6). Since then, hydraulic backfilling has been mostly applied in
Europe and India. Many European coal mines underlie highly developed
industrial areas or commercial waterways requiring protection from sub-
sidence. The backfilling contributes to roof control and permits a greater
percentage of coal recovery from the mine. Recently, hydraulic backfilling
in Germany and Great Britain has been replaced by pneumatic backfilling.
Coal mine refuse has been placed in the abandoned mines of eastern
Pennsylvania. The old coal washing waste bank material was crushed and
pumped down holes into abandoned and flooded anthracite mines. Also, dry
fly ash has been blown down holes into an abandoned Pennsylvania mine.
Although the above backfilling projects have been accomplished, there is
little information which resulted from placement of a fine grained material
in mines. It would appear that filling the voids of these abandoned mines
has sealed pyrite from oxidation to acid drainage, lessened subsidence
attributed to pillar deterioration, displaced stagnant underground mine
pools, and decreased connecting underground channels for groundwater flow
and methane gas.
Subsidence Control
The following discussion explains the cause of subsidence, the need
for subsidence lessening, and the properties of FGD sludge that might help
to lessen subsidence. Removing underground minerals through mining can
result in the roof of the mine collapsing and the overburden falling into
the mine void, subsequently causing a subsidence trough at the earth
surface. Factors affecting the degree of subsidence are the height,
length, and width of the mine void; the depth and character of the over-
burden; the size, character, and distribution of pillar supports; backfill
139
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Pillar
Pipe from
Surface as Required
25'
Place Bulkhead
Active Mining
Area
(All Same Room & Pillar
System)
C/21
uirc
X—Section
Pillar
FIGURE V-15 PLAN - ROOM AND PILLAR MINE
140
Seam Thickness Varies
From 24" •- 120"
-------
amounts and character; movements of underlying strata; and groundwater
movement. Generally, the differential ground movements (strain, slope,
and curvature) of the surface decrease with increasing depth of mining,
and a critical depth based on allowable strain of surface structures can
be estimated (10).
Near-term subsidence occurs over active longwall or pillar robbing
sections after a critical volume has been extracted. Observations taken
at numerous British underground coal mines show that 94% of final subsidence
occurs immediately after complete critical extraction (11 and 12). Near-
term subsidence does not occur during active room and pillar mining by
conventional means (where pillars are left in place). However, long-term
subsidence may occur over conventional room and pillar mines where the
pillars have deteriorated by groundwater dissolution of the solubles.
The maximum depth of subsidence possible is about 90% of the seam
thickness. The total U.S. land area undermined for production of coals,
metals, and nonmetals has been estimated as about 7-1/2 million acres (5).
Nearly one-third of this acreage exhibits some subsidence. Of this sub-
sidence, 85-95% was believed related to coal mining, 3-10% was attributed
to hard rock mining, and 2-5% was attributed to nonmetal mining. About
2 million acres have been reportedly affected by coal mine subsidence (9).
Less than 5% of the 2 million acres show significant subsidence affecting
existing land use (7 and 8).
Backfilling FGD sludge into underground mines has limited potential
to lessen short-term subsidence (i.e., pneumatic stowing into a longwall
section before roof collapse) and to lessen long-term subsidence
(i.e., hydraulic stowing into a mined-out room and pillar section where
pillar robbing is not permitted). Placing sludge in the void left from
extraction may lessen the depth of the subsidence trough. While the back-
fill material would not have the bearing capacity of the original ore
seam, it would provide some support upon consolidation. Hydraulic stowing
with coal refuse in British and French coal fields has lessened the
maximum subsidence factor of 90% to ranges of 25-45%. Pneumatic stowing
has lessened factors to ranges of 45-55%.
141
-------
The ability of FGD sludge to lessen subsidence depends upon the
compression index of the placed sludge. The compression index, obtained
from soil mechanics consolidation tests, measures the amount of settlement
the sludge will experience under varying loadings (i.e., the weight of the
overburden). Each sludge will have different compression indices for a
range of loadings, and each mine will vary in the loadings applied.
Therefore, the subsidence lessening potential of sludge can only be
estimated on a site-specific basis. However, since longwall mining and
pillar robbing are currently allowed only under rural areas, without
buildings or roads susceptible to damage caused by earth settlement, the
importance of reducing short-term subsidence is minor.
The positive benefits to subsidence control accrued from FGD sludge
backfilling are related to long-term subsidence in room and pillar mines.
In these mines, sludge placement would limit the long-term deterioration
of support pillars by partially sealing them from air exposure and ground-
water dissolution. The sludge would also apply some lateral pressure to
support the pillars.
Liquefaction of FGD Sludge
Certain FGD sludges have the potential to liquefy under certain
conditions. Even so, the following discussion explains why sound engineer-
ing prevents any hazard from this sludge property. Liquefaction is a
deformation due to buildup of high pore water pressures created by either
cyclic or static stress applications. Earthquakes result in dynamic shear
stresses and shear strains which cause dislocation of grain-to-grain
contact. This causes volumetric compaction in dry materials; however,
saturated materials retard compaction until the pore water can drain.
Pore water pressures increase as the intergranular stresses decrease.
If the intergranular stresses are eliminated, the material has no shear
resistance and flows like a liquid (14).
FGD sludge which has been hydraulically placed in a conventional
room and pillar mine has the potential to liquefy for the following
reasons.
142
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• Hydraulically placed sludge will have a low relative density, lower
than coarser hydraulic fills typically employed. Typical sandfills
in mines have a relative density averaging 55% (6). Hydraulic fills
for foundation support having less than 10% fines typically achieve
densities of 50-60% without compaction (13). Liquefaction potential
of a material increases with decreasing relative density (14).
• FGD sludge is uniformly graded with most particles in the silt
size, and liquefaction occurs most easily in uniformly graded
soils of the fine sand and silt sizes (14).
• Most sludges appear to be relatively cohesionless, although there
has been little testing of engineering properties to confirm this.
Despite the variance of particle shape from needles to platelets,
the surface appears unreactive and intergranular attractive forces
appear limited. Tests for Atterberg limits indicate some sludges
have little or no plasticity.
• Sludges hydraulically placed in underground mines would most likely
remain saturated. FGD sludge does not drain readily,-and the flow
of water from the disposal area would be restricted by the per-
meability and discontinuities of confining strata. Continuous
recharge from overlying groundwaters is expected.
• Sludges have a low specific gravity which limits their ability to
maintain intergranular contact under cyclic loading. Sludges have
specific gravities from 2.3 to 2.6, while soils typically range
from 2.6 to 2.8.
While surmising that sludge is susceptible to liquefaction, the impact
is probably not significant. The significance of liquefaction potential
is directly related to the seismicity of a site and the confining strengths
of the surrounding materials or structures. Most underground coal mining
occurs in seismically inactive areas of minor risk (compare Figure V-l and
Figure V-16). The sludge would be confined by the unmined strata, the
pillars left in place, and the bulkheads between pillars. The bulkheads
can be readily designed to withstand both cyclic earthquake loading and
the sudden loading from liquefied sludge.
143
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»T-*l»^» --- »-—- :*--*-*V
-------
Corrosion Potential
There is some potential that the long-term exposure of the bulkhead
to FGD sludge may somewhat weaken its strength. Sulfates are corrosive
to concrete under acidic conditions. The stronger the concentration of
the sulfate salts, the more active the corrosion. The sulfates react
chemically with the hydrated lime and hydrated calcium aluminate to form
calcium sulfate and calcium sulfoaluminate, respectively. These reactions
are accompanied by considerable expansion and disruption of the concrete.
The relative degrees of attack on concrete by sulfates are given below.
ATTACK ON CONCRETE BY SOILS AND WATERS CONTAINING
VARIOUS SULFATE CONCENTRATIONS
Relative Degree Water-Soluble Sulfate ppm Sulfate (as SOit)
Sulfate Attack (as 50^) in Soil Samples in Water Samples
Negligible 0.00 to 0.010 0 to 150
Positive3 0.10 to 0.20 150 to 1,000
Considerable 0.20 to 0.50 1,000 to 2,000
Severeb Over 0.50 Over 2,000
Use type II cement.
Use type V cement.
Source; "Concrete Manual," A Water Resources Technical Publication,
United States Department of the Interior, Bureau of Reclamation,
7th edition.
Sulfate in sludge is often in the range of 2,000 to 4,000 ppm. From
the above table, sludge falls into the third category, where the degree
of sulfur attack is severe. In this case, the concrete which should
be used for bulkhead construction is portland cement, type V. This
concrete has low tricalcium aluminate content and therefore is the least
susceptible to sulfate corrosive action. The Ferrari grade of portland
cement, with virtually no tricalcium aluminate content, was found to have
the optimum sulfate resistance, with concretes resisting 15,500 ppm sulfate
for over 25 years without any sign of corrosion (15); however, the Ferrari
grade is not readily available in the United States.
145
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Sulfite content in sludge may be as serious a corrosive as sulfate.
However, there is no information to indicate the level of corrosion which
might be expected for given sulfite concentrations. In addition, there is
no information for determining the synergistic effect on corrosion that the
combination of chemical species in FGD sludge might create. Corrosion test-
ing should be done using concrete with type V cement. Because this concrete
takes three months, instead of one month, to cure, lead time for adequate
sample preparation is significant. In addition, use of the type V cement
for bulkhead construction requires early construction to ensure complete
curing before sludge placement.
In general, massive structures are more resistant than thin structures,
and stagnant conditions result in less corrosion than flowing conditions.
Corrosion resistance is affected by the porosity of the concrete as well
as by chemical factors. Where chlorides are present, they may or may not
attack the concrete. However, if they penetrate a porous concrete, they
can cause corrosion of the reinforcing steel and spalling. Lowering the
water-cement ratio when building the bulkhead will help lower the perme-
ability to chlorides and help protect embedded steel. Also, coating the
steel with epoxy will help mitigate corrosion.
Effects on Productivity
Conventional underground room and pillar coal mining results in 50-60%
ore extraction. The remainder is left in place as pillars. Longwall
mining allows for about 80% ore extraction. Stowing of FGD sludge would
impact upon the potential recovery of coal resources from a conventional
room and pillar mine, but no impact upon future recovery would occur in
the longwall mine.
Pneumatic stowing of sludge into a caving face of a longwall mine is
not a simple job. There are potential safety hazards to operators located
in the vicinity of the caving. In addition, noise from the pneumatic
systems and dust from the blowing of dry FGD sludge fines into the caving
face would impact upon working conditions of the longwall operation.
FGD sludge disposal underground would impact upon room and pillar
mine productivity because of the increased labor and equipment involved.
Increased handling involves creating adequate drainage for sludge leachate
and decant collection and pump-out. The sludge would be slurry backfilled
at a higher water to solids ratio than desired for the final settled sludge
146
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mass. Of necessity, there would be an excess of water requiring removal
and potential treatment before discharge. Drainage would have to be
appropriately designed so that water would not seep into the active
portions of the mine. Borehole drilling, bulkhead construction, piping,
pump-out water storage, and pump-out water treatment employed as part of
the disposal operations will increase the handling requirements and use of
the surface land above the mine. Congestion on the surface may result and
hinder the movement of coal from the mine.
In the case of longwall mining productivity as affected by FGD sludge
disposal, the impacts are expected to be less. The sludge would have to
be dry and therefore would require no special drainage or mine water pump-
out treatment. Also, no bulkhead construction would be required. In
Germany, stowing machines which allow lateral discharge by pneumatic
backfill equipment are currently in use. Continuous miners often have to
slow down to allow the backfilling to keep up, thus maintaining a short
distance between the cutting wall and the caving. Stowing takes place
during the same shift as ore excavation, and productivity loss is exper-
ienced.
Potential Beneficial Effects (AMD Control)
Sludge placement in underground room and pillar mines may allow
improved ventilation control because of the filling of the mine void.
Similarly, filling the mined-out portion of the mine may prevent some
migration of methane into the mine. Explosion and fire hazard would be
reduced. Another potential benefit to the mine atmosphere may be attrib-
uted to the usually alkaline nature of FGD sludge.
FGD sludge may, upon disposal in underground coal mines, partially
neutralize existing acid mine drainage. Acid drainage is probably the
most familiar and widespread water quality problem associated with certain
coal seams mined. The oxidation of reactive forms of iron pyrite (FeS2)
in the presence of moisture leads to acidity, according to the following
reactions:
2FeS2 + 702 + 2H20^-2FeSOit -I- 2H2SOit (Eq. 1)
+ 02 + 10H20 -> AFe(OH)3 + H2SOit (Eq. 2)
147
-------
The neutralization of acid mine drainage Involves oxidizing ferrous
iron to ferric iron and raising pH by addition of an alkaline. Table V-9
shows the potential for limestone treatment of acid mine drainage having
different ferrous concentrations.
There are many alkaline reagents being used to neutralize acid
drainage. The five most common compounds are (17):
Reagent Chemical Formula Relative Efficiency Relative Cost
Limestone CaCO$ .8 1
Quick Lime CaO .9 4.5
Hydrated Lime Ca(OH)2 .95 5
Caustic Soda NaOH .99 18
Soda Ash Na2C03 .99 16
Limestone is the lowest cost neutralization reagent. The relative
efficiency for lime Ca(OH)2 and caustic soda (NaOH) is high but relative
cost is.high as well. Overtreatment of acidic water with NaOH or Ca(OH)2
can make it too alkaline. On the other hand, it is impossible to overtreat
water with limestone. In this case, pH of 8 is seldom exceeded (16).
Since FGD sludge contains some of the above reagents, there is a
possibility it can be used instead. Its neutralizing capacity is due to
calcium carbonate (CaC03) and hydroxyl (OH~). Typical compositions of
different sludges are as follows:
Moles of CaCOs/liter pH Moles of OH~/liter
Limestone Sludge 1.75 7 10~7
Lime Sludge 0.30 11 10~3
Dual Alkali 0.30 11 10"3
(caustic soda)
Since the limestone sludge usually contains significant concentrations
of unreacted calcium carbonate, it is probably the best FGD sludge for
neutralization purposes. The hydroxide levels shown for each of the sludges
are low and not expected to provide much neutralization.
148
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TABLE V-9
Chemical
Parameter
PH
Ac id itya
Ferrous Iron (mg/1)
Ferric Iron (mg/1)
Aluminum (mg/1)
Sulfate (mg/1)
Class I
Very Acid
Not Oxidized
Not Neutralized
2 - 4.5
1,000 - 15,000
500 - 10,000
0
0 - 2,000
1,000 - 20,000
MINE DRAINAGE CLASSES
Class II
Slightly Acid
Partially Oxidized
and /or Neutral
3.6 - 6.6
0 - 1,000
0 - 500
0 - 1,000
0 - 20
500 - 10,000
Class III
Neutral to Alkal.
Totally Oxidized
and Neutralized
6.5 - 6.8
0
0
0
0
500 - 10,000
Class IV
Neutral to Alkal,
Not Oxidized
But Neutralized
6.5 - 8.5
0
50 - 1,000
0
0
500 - 10,000
Expressed as approximate number of milligrams of CaCO» required to neutralize a liter of mine drainage of
each class.
Source; Reference (17).
-------
In a room and pillar mine with very acidic drainage (1,000-15,000
expressed as milligrams of CaCOa required for neutralization) , up to 143
grams of a settled limestone sludge (50% solids having 30% CaC03) would
be needed to neutralize 1 liter of acid drainage. The degree of neutral-
ization achievable in a specific mine will depend on the acidity of the
drainage and the ratio of sludge to drainage available in the disposal
operation.
Acid mine drainage in underground mines also contains unoxidized
sulfide which can be released into the atmosphere as follows:
S= + 2H+-»- H2St (Eq. 3)
The alkaline substances in the sludge would raise the pH of the mine
drainage and convert H2S to HS~, thereby decreasing the amount of hydrogen
sulfide evolved as a gas. Since FGD sludges contain no sulfide, addition
of nonalkaline sludge to the mine would not be expected to increase the
evolution of hydrogen sulfide.
Calcium sulfite in many FGD sludges will react with sulfuric acid
in acid mine drainage of pH less than 4. The reaction product is sulfur
dioxide, as shown in the following equation:
CaS03(S) + H2SOif — R <4 > CaSOit + H20 + S02t (Eq. 4)
The above reaction may occur in mines having the worst type of acid mine
drainage (pH 2.5-4). S02 evolution should occur only in the initial period
of disposal because the buffering capacity of the sludge would eventually
raise the pH of mine drainage.
For totally oxidized sludge (all CaS(\) no reaction occurs. Only at
pH levels less than about 2.5 would there by any appreciable dissolution
of calcium sulfate to form soluble bisulfate:
CaSO^(S) + H2S04 „ ^, , > Ca(HSOi,)2 (Eq. 5)
pn
-------
b. Environmental Impacts
Sludge Leachate
All underground coal mines have some infiltrating water. Water enters
the mine from rock strata above, below, and adjacent to the mine void.
The amount of water depends on several factors. One factor, shown on
Figure V-16, involves the location of the mine either above or below the
groundwater table. Since the regional water table varies with the seasons
as precipitation, evapotranspiration, and percolation fluctuate, a mine
may be within the groundwater reservoir for only a portion of the year.
Essentially, any water present above the mine will eventually infiltrate
into the mine. Waters entering from below are dominated by artesian
pressures and will rise into the mine relative to their hydrostatic head.
Although mines within the groundwater reservoir have the greatest potential
for receiving infiltrating waters that can generate leachate (especially
as the depth of the mine increases and the hydrostatic head of water
respectively increases), even mines above the water table receive percola-
tion as it passes through to replenish the underlying groundwater reservoir.
Underground water travelling through rock moves through faults, joints,
fractures, and solution cavities which occur naturally, and through bore-
holes collapsed roof and mined-out sections created by mining. Some
interaggregate flow through rock pores may also participate in the ground-
water movement, especially in porous limestone or sandstone strata which
serve as aquifers. The overall movement of the regional groundwater flow
relates to the surface topography and is essentially laminar. However,
locally the groundwater follows the paths of the multiple discontinuities.
As a result, the leachate does not move in a plume as in unconsolidated
sediment but in series of channelized slugs. Regionally, the rate of flow
is controlled by overall strata permeability, even though locally, ground-
water flows more quickly through individual fractures than through porous
medium. There is some possibility that the fine grained sludge particles
would fill the fractures of strata underlying the sludge, thereby decreasing
its ability to transmit leachate.
Because the hydraulic gradient of regional groundwater flow is
dependent on the surface topography, coal seams located in hills are
subject to a steep hydraulic gradient. Deeper seams are affected by the
changing gradient as groundwater recharges river valley alluvium. Very
151
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deep seams may experience little or no flow, as strata are essentially
impermeable (see Figure V-17).
During mining, groundwater is removed from the active area. If the
coal seam is bound by aquiludes or relatively unfaulted strata which do
not transmit much groundwater flow, only small amounts of groundwater must
be pumped from the mine as it slowly infiltrates and collects in a sump.
If the coal seam is bound by one or more aquifers, it may be necessary to
pump a lot of water and depress the water table. In either situation,
sludge placed in a mined-out section near the active working area would
probably receive little groundwater infiltration.
Sludge placed hydraulically in a mined-out section of an active room
and pillar mine will probably be obtained from the thickener underflow of
the scrubber. No addition of water to the thickener underflow would be
needed to allow slurry pumping. During disposal the suspended sludge
particles would settle, and the sludge decant water would be continuously
removed to make room for more sludge. This decant water essentially would
have the concentration of sludge liquor, so collection and treatment of
the decant water would be a necessary part of the disposal operation and
a troublesome one. The most concentrated species in the sludge liquor are
dissolved solids of chloride, sulfate, sulfite, and sodium (see Table IV-5)
which are not readily removed by ordinary wastewater treatment processing.
Biological, sedimentation, and precipitation processes do not remove these
constituents, and the more sophisticated processes which do remove them are
very costly.
As mining proceeds away from the sludge disposal area or as the mining
is completed and the mine sealed, the area becomes removed from the influence
of pumping. Groundwater will infiltrate the sludge disposal area until the
voids are filled and then will develop a steady-state movement into and out
of the area. If the adjoining strata are relatively undisturbed by mining,
which is the case in active conventional room and pillar mines, the ground-
water flow will resume its original flow patterns. If, however, the
adjoining strata is disturbed, the groundwater flow into the mine will be
substantially altered. In a longwall mining area, overburden fracture
induced by roof collapse allows substantial infiltration of overlying
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Fractured Permeable
Rock
Negligible Permeability
(a) Underground mine containing sludge lies above groundwater table, and results
in no significant leachate generation
(b) Underground mine containing sludge lies below groundwater table; leachate is
produced and moves with regional groundwater flow toward discharge in
a surface water.
(c) Underground mine containing sludge lies well below (over 500') major
river valley, therefore leachate is confined by limited groundwater move-
ment within dense strata.
FIGURE V-17 REGIONAL GROUNDWATER MOVEMENT IN SEALED
UNDERGROUND MINES
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waters Into the mine. Also, deterioration of pillars in abandoned under-
ground mines has led to long-term subsidence and extensive infiltration
of overlying waters. In Appalachian plateaus where extensive mining has
occurred, interconnection of abandoned underground mining coupled with
augered holes that connect underground mines to surface contour, mines
encourage substantial underground channeling and also discharge of ground-
water to the surface and into the alluvium.
As noted, leachate generated from sludge disposal is a direct function
of infiltration waters. The amount of water infiltrating varies for local
conditions of strata and sludge in the disposal area. This variation is
very site-specific and cannot be covered in detail in this report. Placed
sludge for the room and pillar mine will probably be slightly more permeable
than in the longwall mine after caving. On the other hand, room and pillar
mining results in little disturbance to adjoining strata and therefore does
not result in an increased flow of groundwater into the mine; longwall
mining results in substantial fracturing of adjoining strata and subsequent
increasing of infiltration.
In addition to the amount of water infiltrating the sludge disposal
according to the type of mining, infiltration varies for regional conditions
of water balance, depth of seams mined, and surface topography. Most of
the underground mining occurs in the Eastern coal province and principally
within the Appalachian plateaus of West Virginia, Pennsylvania, and
eastern Kentucky. Underground mining also occurs to a lesser degree in
the Interior coal region within Illinois and western Kentucky. The
principal difference between these coal regions is the hydraulic gradient
of groundwaters within the mining area. For Eastern mines located in the
plateaus the hydraulic gradient is steep. And for Eastern mines located
below the river valleys the hydraulic gradient is small. In conclusion,
the greatest potential for leachate generation occurs in the Eastern
plateaus due to the steep hydraulic gradient.
The leachate concentrations emanating from FGD sludge are related to
the initial chemical composition of the sludge and the background quality
of infiltrating groundwater. Fewer chemical species will leach under
alkaline conditions, especially metals which form precipitates. Some
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species are not affected, though, by the differences in alkalinity of
infiltration water. Chloride, sulfate, sulfite, and sodium are not
expected to be appreciably attenuated under any pH condition, and resulting
leachate concentrations will directly relate to the initial chemistry of
the sludge. Outside of precipitation, the attenuation mechanisms which
occur in soil (such as ion exchange and adsorption) do not appreciably
occur in rock.
In general, the groundwaters in the Eastern plateau mines have less
buffering capacity than the groundwaters in the Interior mines. The
buffering capacity of the groundwater is principally related to the
existence of limestone in strata above the coal seam. Also, the buffering
capacity is related to the generation of acid mine drainage in mined seams
above the one being considered for sludge disposal. As a result of
alkalinity differences between the regions, Eastern mines may result in
more concentrated leachate from sludge than Interior mines.
Placing FGD sludge in underground mines within the groundwater regime
could result in significant groundwater contamination which could continue
for hundreds to thousands of years. Therefore, the site-specific nature
of proposed mine disposal alternatives must be carefully investigated.
The following discussion explains the issues most significant to assessing
groundwater contamination potential.
The amount of leachate produced from FGD sludge disposed in an under-
ground cavity depends on the passage of waters through the sludge. The
limiting factor in leachate generation may be either the amount of water
the sludge will transmit or the amount of influent waters infiltrating the
mine and its driving force (hydraulic gradient as a function of hydrostatic
head).
In situ permeability of the sludge varies for the type of sludge, the
method of placement, and the chemical treatment of the sludge, if any.
Untreated sludge hydraulically placed in an underground room and pillar
mine will initially be in a slurry with about 20-30% solids, then will
deposit into a layer or series of cone shapes having decreasing permeability
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with time. Settled sludges tested in a laboratory averaged lO"1* cm/second
permeability. Untreated sludge pneumatically stowed in a longwall section
will be placed in a loose dry state, but the caved roof will consolidate
the sludge with time under its static loading. There is no data simulating
sludge permeability under these conditions.
In addition to the above aspects of FGD sludge permeability, there is
some possibility that some sludges of high alkalinity may self-seal, with
precipitates from the infiltrating waters filling void spaces between the
sludge particles. If the sludge were to self-seal, even if only on its
exposed surface, waters would channel around the sludge deposit.
Biological Considerations
Groundwater which has flowed through the sludge and become contaminated
can reach surface water by two pathways: (1) mine sump pump-out may be
discharged to a receiving stream after some treatment to effluent guidelines
limitations, and (2) mine water flow within the groundwater reservoir to
its discharge into a spring or river valley alluvium.
Once leachate reaches a surface water, the significance of impact
depends on the assimilative flow capacity of the receiving water, its
current and indigenous water quality, and its existing and desired uses.
Total oxidizable sulfur (i.e., sulfite) present in the sludge leachate will
pass through the anaerobic groundwater environment without being appre-
ciably oxidized and will exert an oxygen demand on the receiving water.
Depletion of dissolved oxygen, if substantial, will adversely affect
aquatic organisms. Also, some of the trace metals, if not significantly
attenuated in the groundwater regime, can bioaccumulate through the food
chain and ultimately affect human health.
3. Control Techniques to Minimize Adverse Impacts
Control techniques are discussed within the impact assessment.
A summary of techniques for underground coal mines is presented below.
In underground room and pillar coal mines, FGD sludge placement
raises technical issues of minimal subsidence control and potential
spontaneous liquefaction. These issues would be limited if FGD sludge
were treated prior to disposal. The treatment method preferred would
result in a concrete-like sludge matrix, taking only a short time to set
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up underwater. Care would have to be taken so that treated sludges do
not "set up" in pipes or boreholes.
In the underground room and pillar case, highly acid drainage coupled
with sludge disposal results in possible concrete and steel corrosion
(used in bulkheads) and a potential for sulfur dioxide gas formation.
These impacts may be minimized by restricting sludge disposal to nonacidic
mine water environments.
Impacts of leachate on groundwater are not readily mitigated. Sludge
drainage and decant water collected during disposal operations may be
processed for pollutant removal of some heavy metals. However, leachate
over the long term can be lessened by two procedures. First, the mine
selected for disposal can be located above the groundwater table. Second,
sludge chemical treatment can be employed to decrease the exposed surface
area of the sludge and decrease sludge permeability, thereby decreasing
leachate production. While some treatment processes involve setting up
underwater, there is very little data regarding the physical/chemical
stability of treated sludge under long-term saturated conditions.
The impacts of the longwall mining case do not require mitigation by
sludge treatment. The disposed sludge is dry and consolidated by caved
overburden. The amount of longwall mining is limited and the resulting
sludge and subsequent leachate is limited.
D. DISPOSAL OF SLUDGE IN SELECTED UNDERGROUND MINERAL MINES
1. Lead-Zinc Mines
a. Range of Conditions Possible
FGD sludge disposal in abandoned or mined-out portions of active room
and pillar lead-zinc mines appears promising. These primarily occur in
Southeast Missouri, which we refer to as the Interior region.
Lead-zinc ores occur within a limestone matrix, which accounts for
the alkaline conditions of the mine drainage. The mines are generally
deep, with overburden depths ranging from 1,000 to 1,600 feet. The ore
body thickness ranges from 10 to 100 feet. The ore body is horizontal,
with slight dips and undulations up to about 2 degrees. Production of an
active room and pillar lead-zinc mine varies from 0.4 to 2.5 million short
tons annually, with most mines being at the lower production level (see
Table V-4).
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There are about seven active mines operating in the Southeast Missouri
lead-zinc ore region. An average ore body thickness of 30 feet is mined,
with panel widths of about 40 feet. As much as 80% of the ore is extracted
if the pillars are "slabbed" (robbed). Because of the very large average
panel openings, bulkhead construction along a line of pillars would be
costly to implement.
No bulkhead construction would be necessary in abandoned lead-zinc
mines, and blind flushing from boreholes drilled from the surface could
be accomplished (as shown in Figure V-18). From some fifteen abandoned
lead-zinc mines in the Southeast Missouri region about 400 million short
tons of ore have been removed. The voids created are still believed to
be largely intact, although filled with groundwater, and the space for
sludge disposal is substantial.
Sludge would be pumped as a slurry, with solids content similar to
that coming from a thickener underflow (about 20-40% solids by weight).
b. Impact Assessment
In both the active and abandoned lead-zinc mines the sludge would be
hydraulically placed as a pumped slurry. In the active mines, sludge
would be hydraulically placed by controlled flushing from within the mine
or by blind flushing from boreholes. In the abandoned mines, sludge would
be hydraulically placed by blind flushing from boreholes drilled from the
surface. Mine water and decant water must be continuously pumped from the
abandoned mines as sludge settles.
All of the lead-zinc mines experience wet conditions. The abandoned
mines are typically filled with water, while the active mines are contin-
uously pumped to permit mining. The water is alkaline because the rock
environment is largely dolomitic; pH is generally about 8. While the
lead-zinc occurs within a limestone matrix which serves as a high yield
aquifer, artesian groundwater supplies in the region are generally derived
from the water-bearing sandstones above and separate from the lead-zinc
ore seam.
Technical Impacts
We will not attempt to duplicate in this section the background
material on subsidence, sulfur dioxide gas formation, concrete corrosion,
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Old Shaft
Pump-Out
-', Water Level
171 (50' - 100'
>x Below Surface)
' -.>; >
'I I J '•
^-O - \'
''N ''
X Decant Water
Pillars of Lead-_
Zinc ore in Limestone,
Left in Place
FIGURE V-18
BLIND HYDRAULIC FLUSHING OF
ABANDONED LEAD-ZINC MINE
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and spontaneous liquefaction previously discussed. However, relative to
this discussion and to the specific mining conditions typical of lead-zinc
underground room and pillar mines, the following impacts are projected.
• Lead-zinc mines are deep and generally underlie hard rock strata.
Subsidence is not a significant impact issue for these mines.
• The mine drainage from the lead-zinc region of Southeast Missouri
is alkaline. As a consequence, no impact of sulfur dioxide gas
formation in these mines is expected. Likewise, if bulkheads are
constructed to enable sludge disposal in active mines, corrosion
potential will be lessened because of the groundwater's high pH.
• The region of the lead-zinc belt tends to exhibit moderate to major
seismic risk potential. Saturated FGD sludge in abandoned mines
or mined-out portions of active mines could liquefy upon deep earth
vibration. However, the liquefaction potential is not considered
significant in this case. If the mine is abandoned, liquefied
sludge would flow freely within the confines of the mine. Because
of the deep shaft's length, no sludge would discharge to the
surface. In an active mine the bulkhead design would incorporate
the potential for sudden loading from liquefied sludge as well as
from earthquake cyclic loadings.
The U.S. Environmental Protection Agency (EPA) has proposed effluent
guidelines for the lead-zinc mining industry. In active mines, FGD sludge
disposal would probably result in an increased pollutant loading in the
mine drainage as sludge interstitial waters leach. This may impair the
mine's ability to meet effluent guidelines and discourage the mine owner's
acceptance of sludge disposal in mines. In abandoned mines, pumping of
mine water displaced by backfilling could create a new discharge subject
to effluent guidelines. Parameters of concern include total suspended
solids because of the fine grained particles prevalent in sludge and
include dissolved inorganics such as copper, mercury, cadmium, and zinc,
which in sludge liquor reach concentrations exceeding effluent limitations
by more than an order of magnitude.
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b. Environmental Impacts
The movement of groundwater through the disposed sludge mass will
cause production of leachate contaminated by soluble sludge chemicals.
Each year of sludge disposed in the mine would increase the total leachate
flow. Because the mine is deep, strata is dense and impermeable due to con-
fining pressures and the groundwater movement through the sludge layer is
expected to be slow. As a result, leachate is likely to remain in the
deep, unused portions of the groundwater regime. Thus, water/liquor
displaced during disposal may present a much more serious problem than
straight leachate.
c. Control Techniques to Minimize Adverse Impacts
Control techniques are the same as those discussed for underground
room and pillar coal mines.
2. Limestone Mines
a. Range of Conditions Possible
Production of an active underground limestone mine ranges from 0.2
to 3.5 million short tons annually. The ore body thickness varies from
20 to 100 feet thick, with little or no overburden at an outcrop to as much
as 1,000 feet of overburden for deeper seams. The ore bodies are generally
horizontal, although some might slightly dip to 2 degrees.
Of all the underground room and pillar limestone mines in the United
States, the seven in the Kansas City area are the most promising by the
technical ranking system used. These mines are dry, located in hillsides
above the water table (1). Deep wet limestone mines are not considered
to be promising because limestone strata are the principal water supply
aquifers in the Interior region, where most of these mines occur.
A typical mine in the Kansas City area produces about 0.9 million
tons of limestone annually. The seam has an average thickness of 40 feet
and has virtually no slope. About 70% of the limestone deposit is
excavated, leaving pillars for roof support. The seam is accessible from
the side of a hill, and FGD sludge could be placed by trucks driving
directly into the mine workings. In addition to the 210 million cubic
feet of mine void being created each year, these mines are reputed to
have about 4,800 million cubic feet of space from past operations.
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b. Impact Assessment
Technical Impacts
The technical impacts of placing sludge in worked-out portions of
active or abandoned limestone room and pillar mines are minimal. The
sludge would be a moist or dry solid, and the mine would be dry. Therefore,
there would be no drainage requirement or involvement with effluent guide-
lines limitations. Generally, trucks are able to drive in and out of these
mines, and subsidence is not considered an issue. Outside of the direct
transfer and placement of the FGD sludge, no special handling requirements
or constructions would be required.
There may be some competition for use of these mines for more profit-
able activities. As a result, waste disposal would receive a lower priority
from the owner's viewpoint. Some of these mines are already being used for
warehouse space. They are also good candidates for office space and
agribusiness (e.g., chicken raising). In addition, the dry isolated nature
of these mines adds to their suitability for more hazardous waste disposal
than FGD sludge disposal.
Environmental Impacts
With dry sludge dispossed under dry mine conditions, no leachate
production or sludge drainage is expected to result from disposal in hill-
side room and pillar limestone mines. Therefore, no environmental impacts
are projected for this case. Also, because the sludge is expected to
remain dry, slide potential (which normally occurs under saturated conditions)
will be minimal.
E. FGD SLUDGE AS A TAILINGS AMENDMENT
The purpose of this investigation is to determine if FGD sludge can
be added to the surface of tailings from mineral processing wastes (e.g.,
coal refuse, mineral tailings) to enable those tailings to support vegetation.
The findings indicate FGD sludge is a rather poor tailings amendment.
1. Evaluation of FGD Sludge as a Tailings Amendment
Support of vegetation is usually provided by soil, which is a mixture
of a mineral substrate, air, water, and organic matter. Nutrients, macro-
as well as secondary and micro-nutrients, must be present to greater or
lesser degree, and the substrate must be free from toxic conditions.
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Beyond these basic requirements, however, it is not possible to merely
define the conditions necessary for vegetational growth (soil conditions)
and then determine whether the FGD sludge and tailing combination can meet
those conditions. "Soil conditions" range from the conditions of desert
sand to peat bogs to bedrock outcroppings. Also, the phrase "free from
toxic conditions" varies with plant species and includes, in a sense, any
environmental condition which is outside of the particular niche require-
ments of the plant.
Tailings are highly variable. Coal refuse can contain coal, rock,
bonded coal and rock, carbonaceous shale, pyrite, broken and decaying
timbers, discarded machine parts and cable, paper containers, decayed
brattice cloth, and grease- and oil-soaked rags. Particle sizes range
from below 0.002 ppm to boulders (18). Zinc tailings in England range
from very coarse to very fine with corresponding differences in water
retention capabilities. Zinc residues in those tailings range from 1,370
ppm to 35,940 ppm. These same sights contained calcium levels ranging
from 5 ppm to 310,500 ppm. Iron (taconite) tailings also range consider-
ably in particle size, while pH remains about 7-8 (19). Coal refuse
ranges in pH from extremely acidic (pH 2-3) to neutral or slightly
alkaline (pH 7-9) (20).
Tailings have been successfully revegetated for over fifteen years.
Various hardy grasses are chosen as "target" plants, and the conditions
which are phytotoxic to these plants are alleviated by the addition of
"soil amendments." Usually, the material added is limestone, sewage sludge,
or less often, soil itself. Fly ash has been used where available because
of its ability to neutralize acidic conditions, reduce bulk density,
increasing moisture retention capacity, and allow greater root penetra-
tion (18).
As shown in Table IV-1, FGD sludge contains variable but significant
amounts of fly ash. It also contains significant amounts of gypsum used
as a soil amendment in agricultural soils to increase alkalinity and improve
soil substrate (21). Gypsum is also used to decrease sodium and boron
toxicity, but the gypsum must be free of toxins for any significant reduction
in toxicity to occur (a condition which is not met by the gypsum in the FGD
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sludge) (22). The presence of fly ash and gypsum in FGD sludge has led to
its consideration as a soil amendment for tailings. The following dis-
cussion presents the results of a brief investigation of this possibility.
Materials to be used as "soil amendments" are chosen on a case-by-case
basis to meet the particular needs of the tailings under consideration.
The potential for any material to be used as an amendment depends on its
capabilities to meet these needs, i.e., to alleviate the conditions which
limit plant growth. Although these conditions are highly variable, they
usually involve a subset of the following:
• lack of nutrients;
• incapacity to retain moisture;
• surface instabilitiy or compacted surface;
• excess absorption or reflection of sunlight causing heat injury
to plants;
• heavy metal contamination;
• excess salinity; and
• excess acidity.
The discussion below briefly assesses the potential of FGD sludge to
alleviate these problems.
Lack of Nutrients
The major nutrients required by plants are phosphorus, potassium, and
nitrogen. Calcium, sulfur, and magnesium are the secondary nutrients
necessary for growth along with numerous micro-nutrients.
FGD sludge appears to have little or no phosphorus and a small,
variable amount of nitrogen (0-50 ppm NOa in sludge). FGD sludge would
provide calcium (8,400-120,000 ppm in sludge) and sulfur (8,300-50,000 ppm
SOl; and 60-380 ppm 803 in sludge). This sulfur level may be phytotoxic,
considering the amounts often present in tailings from the oxidation of
pyrites. For example, the addition of gypsum to agricultural soil sometimes
causes a decrease in plant growth due to excess sulfates. In citrus groves
1 ton/acre gypsum caused sulfur levels to increase to 1.43% in leaves
(recommended range 0.2 to 0.3%), decreasing tree growth. The rate of
application of gypsum may have been unusually high, however.
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Lack of nutrients in the FGD sludge is not, however, a limiting
problem in its use on tailings because of the ready availability of
fertilizers which are usually applied as supplements to most tailings
amendments anyway.
Incapacity to Retain Moisture
Vegetational growth is supported by soil which is 40% to 70% solid
and about 20-25% water by volume in agricultural soil (although plants
can be supported in widely different soil compositions). The remaining
volume is air which is usually 99-100% saturated with water. The texture
of the soil or the size of the soil particles determines the soil's
moisture retention capacity. Because FGD sludge appears to be consistently
fine in texture (e.g., 0.001-0.05 mm), it is likely to significantly
increase the moisture retention capacity of those tailings which are sandy
or coarse in texture (> 2 mm). Tailings which are finely textured would not
be benefited from the addition of sludge; these tailings tend to form
compacted and easily eroded surfaces which also create moisture retention
problems.
Surface Instability
Wind erosion can be a problem for vegetational growth because of the
instability of the surface during seed germination and the potential for
sandblasting of young plants (23). The potential for agglomeration of the
tailing-sludge mixture should be investigated.
Compacted Surface
Fine tailings have a tendency to form a compacted surface which retards
moisture penetration and root penetration. No information is presently
available on the tendency or lack of tendency of the tailing-sludge mixture
to form a crust or compacted surface once spread on the land.
Excess Surface Reflection or Absorption of Heat
Tailings tend to concentrate heat so that surface temperatures are
high and the topmost soil layer loses all available moisture (23). Because
the sludge seems to be consistently light in color (except when the fly
ash component is particularly high), the sludge could reduce the absorption
of heat by the tailings, increasing the chance of successful seedling
germination.
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Excess Salinity
The availability of water for plant consumption can be decreased by
the development of high osmotic conditions in the plant substrate. Plants
wilt, morphological changes occur (leaf curling, yellowing), and growth
rate decreases. The mechanism which would account for these detrimental
effects of salinity is not known; it is generally believed that the soluble
salts increase the solute suction of the soil water, decreasing the uptake
of water by the plants (24).
Salinity is a problem in most tailings. Tailings may become excess-
ively saline in the recycling of processings waters. The salinity of copper
mill tailings, for example, is equivalent to 2.4 atmospheres osmotic con-
centration ('vS.OOO mg/liter TDS). The U.S. Bureau of Mines found that
this concentration would limit initial growth of plants, although it would
not significantly hinder initial germination (25). Deep mine coal wastes
have been found to be "extremely salty due to the oxidation of pyrites;"
for copper, zinc, lead, and uranium ores, "salinity is a common problem"
(no salinity values reported) (26). Salinity has also been a problem in
vegetating pulverized fuel ash (26).
Unfortunately, the salinity of the sludge also appears to be high
(2,600-95,000 mg/liter TDS in FGD sludge liquors from eastern and western
coals). The criteria generally assumed for irrigation water is 500 mg/
liter. Water with TDS concentrations of 2,000-5,000 mg/liter is recommended
only for tolerant plants on permeable soils where particular management
practices are observed. Water with above 5,000 mg/liter TDS is not suitable
for irrigation. Irrigation criteria are not directly applicable to the one-
time application of sludge on land. They do, however, give an indication
of the magnitude TDS which would be added to the already saline salts.
The ability of the sludge alkalinity to cause precipitation of soluble
salts does not appear to be significant enough to decrease the salinity of
the sludge-tailing mixture. Furthermore, the capability of gypsum to
precipitate salts is not clear. Tests in India show that gypsum replaced
exchangeable Na in sodic soils and removed soluble salts (22). Other tests,
however, have not substantiated these results (27).
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Acidity
While iron tailings are usually fairly neutral (7.5-8.4), most other
tailings are acidic. Uranium tailings from Wyoming and Colorado had pH
values of 2.3 to 4.5. Bituminous coal surface mine spoils in Pennsylvania
had pH values of 2.5-4.7.
The effect of acidity is indirect. Apparently, the phytotoxicity
occurring at low pH's is caused by increased availability of toxic
substances. (In agricultural soils, elements necessary for plant growth
can become toxic at low pH conditions.) Tailing reclamation work has
generally sought to raise pH values to 6.5 or above as a. prerequisite to
vegetating the tailings (23). The ability of sludge to neutralize the
acidic conditions of the tailings depends on the frequency of high pH
conditions in the sludge. Ranges of pH for FGD sludge are 7.1-12.8 for
eastern coals (fifteen observations) and 2.8-10.2 for western coals (seven
observations). Although we expect that sludge is most often neutral to
alkaline, the potential for eliminating acidic conditions in tailings is
difficult to assess with this limited information. It would seem that two
of the constituents of FGD sludge, fly ash and CaCQ$, would indicate a
higher potential for eliminating acidic conditions than the pH ranges above
indicate.
Excess Heavy Metals and Other Toxins
Tailings are usually high in metal and other toxins resulting from
mineral processing (25,28, and 29). Particular toxins vary with the
minerals involved. In copper tailings, for instance, copper, nickel,
and zinc are high. Sulfides and sulfates are common to many types of
tailings (29).
The effects of the chemical species found in tailings vary widely
among plants. Zinc, copper, and nickel are usually toxic to most plants,
although there are several tolerant grass species. A zinc "tolerance"
based on 1:2:8 ratio for the relative toxicity interaction of Zn:Cu:Ni in
soil has been suggested to be 250 ppm zinc (equivalent). This is based on
an average of relative tolerance for many crops and varies according to
levels of organic matter, phosphate, and pH. Similar tolerance levels
have not been established for other metals and toxins. Irrigation water
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criteria have been established based on information on levels known to be
nontoxic (not necessarily the maximum nontoxic levels).
The ability of the FGD sludge to precipitate heavy metals and other
toxins does not appear to be significant. The FGD sludge itself appears
to be high in heavy metals and other toxins; in some cases it may be toxic
enough to create problems where none exist in the tailings. Even under a
high pH condition (7.1-12.8), the FGD sludge liquor can contain relatively
high levels of some metallic species. For many of the following elements,
levels ranged from obviously safe to obviously toxic:
Range in Sludge Liquor (ppm) Irrigation Standard (ppm)
Boron 8-41 0.75
Cadmium 0.004-0.1 0.01
Manganese <0.01-9.0 0.20
Molybdenum 0.9-5.3 0.01
Nickel 0.03-1.5 0.02
Selenium <0.005-2.7 0.02
Many factors influence the availability of toxins to plants (adsorption,
chelation, leaching). In order to assess the effect of the toxins, it would
be necessary to have a particular species in mind. It would be necessary
to test the particular FGD sludge to be used, the level of toxins currently
found in tailings, the tolerance of the particular plants involved, and
other factors such as organic matter, pH, etc. It seems safe to assume,
however, that FGD sludge will not be able to alleviate existing phytotoxins
problems in tailings.
In summary, the potential for use of FGD as a tailing amendment is
highly variable. The particular requirements of the tailings involved
must be established first, then the FGD sludge would have to be carefully
tested to see if it met those requirements. To prevent creating new
problems, the sludge would have to be screened for high heavy metals and
other toxins, salinity, and acidity. From the information available, it
seems doubtful that sludge could alleviate any problems with phytotoxins
or salinity. Neither, probably, could it alleviate nutrient deficiency
problems, although this is a much less serious limitation.
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Acidic conditions could be neutralized if the sludge pH were high
enough. The sludge could alleviate moisture retention problems and excess
heat absorption by tailings. Alleviating surface instability and compaction
problems by the addition of sludge needs further investigation. Further
investigation, in fact, is needed in all areas which involve chemical and
physical interactions of tailings and sludge.
2. Comparison of FGD Sludge to Other Amendment Alternatives
Table V-10 shows the tailing problems discussed above and the
alleviating capabilities of FGD sludge, limestone, and sewage sludge.
Nutrient Deficiency
Sewage sludge usually contains significant amounts of macro-nutrients.
Dried sewage sludge, for example, contains 19,900 ppm P and 4,200 ppm K
(information on N not available) (30). The nutrient content of limestone
is negligible.
Moisture Retention Problems
Although no specific data is available, both dried sewage sludge and
crushed limestone are known to be comprised of a wide range of particle
sizes. It is likely that both would increase moisture retention.
Surface Problems
Liquid sludge has been shown to increase surface stability but does
little for a compacted surface (30). Limestone probably would have no
effect on surface problems.
Heat Injury to Plants
The dark color of dried sewage sludge would decrease reflection of
light tailings and increase absorption of dark tailings. Limestone, being
light in color, would do the opposite.
Excess Salinity, Acidity, and Toxins
Limestone has been shown to precipitate salts, increase pH, and lower
the availability of toxins (29). Sewage sludge has been shown to increase
pH, although large amounts of sludge are needed. Sewage sludge also has
been reported to decrease availability of metals by chelation.
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TABLE V-10
COMPARATIVE PROPERTIES OF POTENTIAL TAILING AMENDMENTS
Sewage
FGD Sludge Limestone Sludge
Lack of nutrients 0 0 +
Moisture Retention Problems + + +
Surface Instability ? 0 +
Compacted Surface ? 0 0
Excess Absorbtion of Heat + + 0
Excess Reflection of Heat 00+
Excess Salinity + ?
Excess Acidity + + +
Heavy Metal Contamination - + +
0 neither helps nor hurts significantly
+ alleviates problems to some degree
aggrevates problem
? indicates no information available
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F. ASSESSMENT OF THE TECHNOLOGY
1. Handling and Transport
There are four basic modes of tranportation that could be used in
moving sludge between a power plant and mine: slurry pipeline, barge,
truck, and rail. Since all of these modes are technically feasible, the
selection of the most appropriate mode or combination of modes should be
made on the basis of a cost/benefit analysis, taking into account all
operations (transfer, transport, and processing) in the transportation
system.
Undoubtedly, though, certain institutional considerations will become
factors in the decision process, e.g., the political and regulatory problems
associated with transporting wastes across state boundaries. In many cases,
institutional considerations may be the deciding factors. Such institu-
tional factors will not be directly addressed in assessing technical or
economic feasibility.
The following discussion briefly reviews the state of the technology
for these four modes of transport and their applicability to FGD sludge.
Various means of handling sludge in support of these transportation systems
will also be discussed.
a. Slurry Pipeline
The pipeline transportation of slurry products and industrial waste
materials is a proven technology, at least over short distances and for
liquids of relatively low viscosity (<20 cp). However, there are very
few long-distance (> 20 miles), forced-main pipelines now in service for
transporting slurries.
The most common uses for slurry pipelines is for transporting coal
or mineral process tailings. These slurries have low viscosities at solids
contents up to 50-60%. There are numerous pipelines throughout the world
now handling tailing and coal slurries for distances up to 10-15 miles.
Examples of long-distance slurry pipelines include the following.
• The 108-mile coal slurry pipeline in Ohio—This 10-inch line which
handled 1,050 ppm of 50% slurry is no longer in service.
• The 53-mile iron concentrate pipeline in Tasmania—This 9-inch line
currently handles a water/iron concentrate slurry containing up to
55-60% solids.
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• The Black Mesa pipeline in Arizona—This 273-mile coal slurry
pipeline handles 600 tons of coal per hour at concentrations up
to 50% solids. The line is 18 inches in diameter, and the flow
averages about 4,500 gpm.
Installed costs for overland pipelines of this type assuming a level,
open terrain typically run $50,000-100,000 per mile for a 6- to 8-inch
diameter line. Power requirements for operating such lines generally run
30-70 hp per ton-mile per day for 35-50% solids.
Application to Sludge Transport
There has been little experience in transporting slurries of FGD
sludge or FGD sludge-like materials over very long distances. However,
some FGD system installations are now using pipeline transport (up to
7 miles long) for moving thickened sludge (thickener underflow at 15-40%
solids) to disposal/treatment areas. Such runs are typically on the order
of a few hundred to a few thousand feet. Open-impeller, rubber-lined
centrifugal pumps are usually used.
There has also been experience piping dredged materials over short
distances, materials which are similar to FGD sludge in physical properties
and consistency (silt and fine sand). For example, in beach nourishment
projects it is common to transport dredged materials up to five miles.
One of the new hydraulic cutterhead pipeline dredges claims a capability
of pumping fine dredged materials for distances of almost ten miles.
In assessing the feasibility of slurry pipelines for long-distance
transport of FGD sludge, consideration must be given to both technical
design factors and overall system practicality. Technical design factors
include slurry viscosity, slurry velocity, abrasion/corrosion resistance,
and freeze protection.
Viscosity. The viscosity of FGD slurries depends upon the level of
suspended solids, the type and size of crystals generated, and the quantity
of fly ash occluded with the sludge. As shown in Figure IV-2, sludges with
high levels of gypsum, fly ash, and/or residual limestone tend to have
lower viscosities at a given solids concentration than sludges that are
predominantly sulfite, with little or no fly ash. In order to ensure an
operable pipeline, either the type of solids to be generated must be known
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a priori (based upon projected process operating conditions) or the pipeline
must be designed for a low, safe level of suspended solids that would ensure
a reasonable slurry viscosity. It is reasonable to assume that, unless the
sludge to be transported is almost entirely fly ash, long-distance slurry
pipelines for sludge would be designed to handle no more than 25-30% solids.
With large quantites of fly ash, up to 45-50% solids may be possible.
Velocity. Many of the existing coal and tailings slurry pipelines
are designed for a velocity of 3-6 feet/second. Velocities on the order
of 5-8 feet/second for FGD sludges would probably be required to prevent
settling and pluggage of the line.
Abrasion/Corrosion. The presence of fly ash, high chloride concentra-
tions, and frequently, low liquor pH requires the use of abrasion/corrosion
resistant materials in the pipeline construction. The length of the pipe-
line, the level of fly ash and chloride, the slurry pH, the terrain to be
covered, and the pipeline configuration will determine the most appropriate
materials. In most cases, carbon steel piping is not adequate. Fiberglass,
fiberglass-lined carbon steel, and rubber-lined carbon steel are all
possibilities, although rubber-lined piping over long distances would
probably be prohibitively expensive and may be very difficult to maintain
if rubber lining failures occur.
Freeze Protection. Consideration must be given to protection against
freezing of the slurry. Simple methods would include insulation and
location of the pipeline underground below the freeze line. Heat tracing
would be economically prohibitive. In areas where extremely cold climates
exist, the cost of freeze protection may limit the length of pipelines.
The overall practicality of pipelining slurries of FGD sludge will
depend not only on the cost and feasibility of the pipeline itself but
also the effects of pipelining on the operation of FGD system and the
disposal system. Of particular importance may be the power plant/FGD
system water balance. In cases where water conservation is of concern
and closed-loop operation is desirable, long pipelines may not be practical.
Also, the dewatering or treatment of the sludge prior to disposal, if
required, may present problems. For example, it may be desirable or
necessary to admix ash with dewatered sludge either to increase the solids
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content or adjust the ash/sludge ratio to provide a better mix for treatment
(fixation). Dewatering sludge at the mine may also create disposal problems
for the filtrate, unless it is recycled to the power plant.
These factors, as well as costs for long-distance pipelines (that
could run more than 25% of the installed FGD system cost), will limit the
applicability of long-distance piping for sludge transport. Short-distance
pipelines (<20 miles), on the other hand, may be a much more practical
option.
b. Rail Haul
The hauling of FGD sludge by rail is an attractive prospect, since
most large-scale industrial and utility power plants maintain in-plant
rail sidings and car unloading facilities for receiving coal shipments.
Where coal is delivered by unit trains and empty cars are returned directly
to the coal mine, the entire roundtrip cost is already borne by the utility.
Also, the amount of sludge to be returned to the mine from one power plant
is always considerably less than the amount of coal delivered.
The type of rail car most amenable to sludge transport would be the
bottom dump hopper cars, particularly the newer "rapid discharge, self-
clearing" type. Bottom dump cars are in widespread use for coal delivery
to utilities and ought to be applicable to FGD sludge transport with little
or no modifications. Such cars could handle untreated FGD sludge in the
form of a moist cake or treated FGD sludge either as a brick-like or soil-
like material. FGD sludge as a slurry or partially dewatered (semi-liquid)
material could not be handled in such cars. It would have to be either
further processed by dewatering, drying, or treatment, or a rail car of
different design would have to be used. In most cases, further processing
either by dewatering and/or partial drying would be economically more
attractive than the use of specially designed rail cars.
There would be need, of course, to add new transfer/storage facilities
at both the power plant and the mine for loading and unloading the sludge.
The transfer facility at the power plant for handling and loading the sludge
into the rail cars would be conceptually quite simple. The sludge would
be .conveyed from the dewatering site to a loading dock or area above the
tracks. The cars would then move below a set of feed hoppers which would
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direct the sludge into the cars. The sludge could be moved by front-end
loaders, bulldozers, hydraulic ramps, or overhead crane. There would be
need for some storage capacity at the transfer station and a number of
feed hoppers in order to ensure that the unit trains would not be slowed
by the sludge loading process.
Depending upon the type of sludge generated and the climatological
conditions, it might be necessary to cover the storage and handling areas
at the transfer station in order to prevent excessive rewetting of the
sludge, which could impair sludge handling operations. In very cold
climates it might also be necessary to provide for an enclosed, partially
heated storage/transfer building to prevent freezing of the sludge during
winter months. The problems of freezing and rewetting are primarily ones
associated with the handling of untreated material. Unless the solids con-
tent of the material is marginally low, there would probably be no need for
protection against rewetting of the sludge due to rainfall while in transit.
Even a number of heavy rainfalls would not increase the moisture level of
sludge by more than a few percent. Of more concern is the possibility of
runoff or leakage of leachate from the cars due to rain. This would be
unlikely unless the sludge were already too wet to absorb the additional
water, in which case the simple movement and vibration of the car alone
would probably cause leakage of mother liquor. Provisions would have to
be made to ensure that the sludge were dry enough or that the cars would
not drain. If rainfall alone could cause leakage, then the cars could be
covered with removable plastic tops or tarps.
A transfer storage area analogous to that at the power plant would
also have to be installed at the mine site for unloading and storing the
sludge. An unloading system similar to that used for coal would probably
be applicable to FGD sludge. There should be few problems encountered in
unloading by either rotating car dumpers or rapid discharge, bottom dump
hopper cars. With the bottom dump hopper cars, vibration of the car
similar to that used for coal discharge will undoubtedly be required,
particularly for discharging untreated FGD sludge. The sludge would be
discharged onto a conveyor belt, which would then carry the sludge to
a storage/handling facility for interfacing with the disposal operation.
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As with the loading facilities, there may be need for special pro-
visions, particularly for untreated sludges, to protect against sludge
freezing or excessive rewetting prior to disposal. In fact, it may be
necessary to provide for a warming house similar to that used in handling
coal should the sludge freeze during shipment. In handling untreated
sludges, it will probably also be necessary to provide for car washing
after disposal to clean the cars prior to loading them with coal.
The facilities and equipment described above are all technically
feasible and applicable to the handling and transport of both moist,
untreated and treated FGD sludges. There would be no need for the development
of new technology, although there may be need for some small modifications
of existing equipment. It is doubtful whether a fully automated transfer
facility would be practical, or even desirable, at the present time.
The cost for installing and operating such a system would obviously
depend upon the quantity and type of sludge generated, the climatological
conditions within which the system must operate, and the length of the rail
haul. There are no existing freight rates which rail companies can apply
directly to the transport of sludge, and estimates that could be prepared
by rail companies even for site-specific situations could be quite
speculative. A good starting point for estimating rates would be the rates
for hauling sand and gravel or gypsum. However, based upon the fact that
trains now in use return to the coal mines empty and that the commodity
value of sludge is nil, lower rates may be negotiated. A reasonable rate
over distances greater than 100 miles ought to be in the range of l-3c/
ton-mile.
c. Truck Transport
Transport of sludge via truck is one approach now being used by
utilities and is widely considered for future use where off-site disposal
is required. The trucking of sludge necessitates dewatering prior to
transport or the use of specially designed trucks, which would minimize
the spill of contaminated or occluded liquor along public highways. Such
specially designed trucks and the costs associated with transporting liquid
make slurry transport economically unattractive.
176
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One study conducted by Combustion Engineering on truck haulage of
sludge involved the transport of 75 tons of settled, drained FGD sludge
(50% calcium-sulfur salts, 50% ash) from the limestone scrubber system at
Kansas Power and Light's Lawrence facility to Dulles Airport in Washington,
B.C. (1,300 miles). Two types of trucks were used, one with a flat bottom
trailer and one with a round bottom trailer. No leakage of sludge was
observed, although there was drainage of excess water (liquor) through the
tailgate during transport. At Dulles some difficulties were encountered
with the discharge of sludge from the flat bottom trailer. Manipulation
with a backhoe was required to remove all sludge from the flat bottom
trailer. No difficulties were encountered in readily discharging all of
the sludge from the round bottom trailer.
Similar difficulties have been experienced by some other utilities in
handling and transporting semi-dewatered sludges using standard flat bottom
dump trucks. In cases where the sludge has been dewatered to a moist filter
cake, no such difficulties have been encountered with flat bottom dump
trucks. Both dual alkali filter cake and centrifuged gypsum wastes have
been easily handled using front-end loaders and dump trucks at Gulf Power
Company's Scholz Plant in Sneads, Florida. These solids have been readily
discharged from the dump trucks without need for additional manipulation.
Therefore, in using trucks for transporting sludge either over short
or long distances, it would be advantageous to produce as dry a material
as possible with minimal tendency for liquefaction. For untreated materials
a moist filter cake or sludge admixed with ash would be most easily handled.
There should be no difficulty handling treated sludge. Loading of the
trucks could be accomplished either by a hopper feed system similar to
that described in conjunction with rail haul or by using front loaders or
bucket crane.
Trucking of sludge would be most attractive in cases where the trucks
are used for local handling of the sludge or where use can be made of coal
trucks that deliver coal to the power plant. Long-distance transport of
sludge by truck is generally more costly than rail and probably pipeline.
Long-distance haulage rates (>50 miles) typically run between 4c and 6c per
ton-mile for similar materials (e.g., sand, gypsum). Short haul rates are
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considerably higher but vary sharply with region and distance. More
favorable rates may be negotiable for specific point-to-point local runs
using dedicated trucks or empty coal trucks.
d. Barging
Barges are frequently used on the nation's rivers and intercoastal
waterways for transporting both waste materials (e.g. , dredge spoils) and
commodities (e.g., sand, coal, lime/limestone). Where utilities receive
coal by barge, barging of wastes back to the coal mine (or other mines)
would be a logical alternative to overland transport. Use of empty coal
barges would be preferable; however, the ability to quickly empty and clean
the barges prior to reuse for coal would be a concern. Loading and unload-
ing of standard hopper barges with dry or moist solids usually involves
overhead cranes with clamshell scoops or buckets. Since this can be a
time-consuming operation, it may be necessary to add barges to the fleet.
Dedicated barges and tug(s) for waste transport would provide a more
flexible operation, particularly for handling thickener underflow which
could be pumped directly into the barge and from the barge to the disposal
site.
Barges for use on inland waterways generally carry 1,000-2,000 tons of
cargo. A typical 500-Mw power plant operating on high-sulfur coal with a
70% load factor would utilize one or two barges per day. Barges could be
filled (and stored) for a week at a time and towed using one tug to the
disposal site.
Barges purchased for dedicated waste transport service would cost
$150,000 to $200,000. Barging rates could run anywhere from 0.5c to 1.5c
per ton-mile depending upon location of service, tonnage handled, and
transport distance. However, transfer costs could be considerably higher
than those of other transport modes, particularly if solids have to be
handled with overhead cranes.
2. Disposal Methods
a. Surface Coal Mines
Disposal of FGD sludge in active surface coal mines, while certainly
technically feasible, does require some limitations on the physical con-
dition of the sludge and/or disposal operation. The most practical means
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of disposing of the sludge would be as a slightly moist or dry solid. The
sludge could then be dumped into the mined-out strip either along with or
prior to replacing overburden. To handle a sludge as a slurry or as a
material that exhibits a strong tendency to liquefy could present signifi-
cant operational problems. The sludge could flow after being dumped either
on its own or due to replacement of the overburden. In such a case, unless
special precautions are taken to prevent flow (e.g., trenching of the
disposal area or creation of small retainer walls with overburden), then
the sludge could complicate coal removal in the following strip. Such
operational considerations and potential problems are discussed in more
detail in the evaluation of surface mine disposal alternative(s).
Sludge is most easily placed in a mined-out pit by truck dumping,
but it is not recommended that coal haulage vehicles be used for sludge
transport and placement. In some mines where rear-dump trucks are used,
sludge could possibly be handled by the coal trucks on their return trip
from the coal washing plant to the pit. However, such a system could lead
to unacceptable delays in the coal mining operation due to the additional
time for sludge loading and unloading as well as the possible need to rinse
out the trucks following sludge transport to prevent contamination of the
coal.
Furthermore, many mines are now using large bottom dump trucks for
coal haulage. While many trucks are designed to carry up to 100 tons of
coal, they have lightweight bodies, usually constructed of aluminum. Not
only could the sludge corrode the aluminum, but also bottom dumping of
sludge would be technically impractical. These trucks are difficult to
back up and are not designed for ease of maneuvering in mine pits, and
operating these trucks on a layer of sludge would be extremely difficult.
In fact, operating any type of disposal truck on a sludge layer would
probably be impractical, Thus, the amount of sludge that can be disposed
of by truck dumping in the pit will, in most cases, be limited by the type
of truck used.
Alternatively, in some mines the sludge could be dumped in the pit by
the dragline or shovel returning overburden. However, this approach could
seriously hamper the mining operation, since the process of digging in one
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pit occurs in a continuous motion using the same machine with overburden
replacement in the worked-out section.
b. Underground Mines
Room and Pillar Mines
Disposal (backfilling) of waste or fill material in underground room
and pillar mines has been demonstrated or practiced in both the United
States and Europe. There are basically three approaches that can or have
been employed: pneumatic backfilling, hydraulic backfilling (or flushing),
and mechanical stowing.
Pneumatic Backfilling. Pneumatic backfilling of mine voids simply
would involve blowing material through a pipeline from the surface into the
vacant rooms of the mine. The pipeline could be set either in boreholes
through the roof of the mine or could be mounted at an underground station,
entering the mine through an existing shaft. Practically speaking,
pneumatic backfilling would be done by blind injection, that is, without
the aid of men underground during the backfill operation to direct the flow
of material and control the distribution.
There has only been limited experience with pneumatic backfilling
materials in mine voids in the United States, but considerable work has
been done in European coal mines. Pneumatic backfilling has been used for
the disposal of fly ash. This experience indicated that with fly ash
fairly good roof contact could be achieved. Although the properties of FGD
sludge are, in most cases, considerably different from those of fly ash, it
is reasonable to assume that a pneumatic backfilling system could be readily
designed. Of course, the backfill efficiency would differ from that
attained with fly ash.
One obvious factor limiting the pneumatic conveyance of FGD sludge is
that the sludge must be dry or, at worst, a moist powder. In backfilling
a mined-out section of an active mine, dust control would be a major
ccmcern with such a material, as it is with any such dry stowing operation.
Traditionally, "brattice cloth" (a heavy sacking material) is erected to
control dust generated in pneumatic stowing of waste materials in mines.
However, the wastes have generally been grainy, coarse mine tailings that
may not have had the same potential for dust. Other measures may be
required for dry sludge.
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Consideration must be given to the type of equipment and piping used.
If the sludge is slightly moist, it may tend to clog conventional equipment.
If so, equipment design must be modified or the sludge pre-dried. Admixing
of relatively dry, untreated sludge with fly ash may produce a sufficiently
free-flowing material for pneumatic stowing. The fly ash may also impart
a scouring action to keep piping and equipment relatively clean. The
pressurized sludge tank and piping system, though, would have to fabricated
out of abrasion-resistant material appropriate for use when fly ash con-
taining sludges are stowed.
Hydraulic Backfilling. There has been considerably more experience
with hydraulic backfilling both in the United States and Europe than with
pneumatic backfilling. This method of disposal has been used to return
coarse tailings from metal mines as well as coal wastes to mine voids.
In contrast to pneumatic backfilling, hydraulic backfilling can be
practically accomplished either by controlled or blind injection. The
distribution of material achieved depends upon the pressure head in the
pipeline, the solids content of the slurry, the arrangement of the discharge
piping, and the characteristics of the mine void (mine layout, coal bed
slope, etc.). In some cases where there is sufficient slope of the area
being filled, it may not be necessary to install bulkheads to block out
the disposal area. However, in most operations utilizing mined-out portions
of active mines it would have to be assumed that bulkheading would be
required, particularly where the sludge is introduced through the boreholes
in the mine roof.
In hydraulically backfilling FGD sludge, it is reasonable to assume
that a slurry containing a minimum of 25-30% solids could be piped into the
mine void. With this slurry concentration, settling in the mine void can
be expected, and provisions may need to be made to pump out water/liquor
runoff. If dry sludge is being slurried for hydraulic backfilling (rather
than straight thickener underflow), then the collected drainage can be
recycled for slurrying the sludge.
If the piping used in the backfill operation involves anything but
straight vertical sections, it will have to be designed to maintain a
minimum velocity of about 7 feet/second. For sludges containing fly ash,
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the piping and slurry handling equipment will have to be fabricated out
of abrasion-resistant material.
Mechanical Stowing. Mechanical stowing of sludge can be accomplished
in active mines using existing transport/conveyance equipment or equipment
that can be readily adapted for use in the mine. Such an operation would
generally not be economically attractive in comparison to hydraulic back-
filling. However, it may be an appropriate method in certain mines such
as underground limestone mines where there is ready access to mining areas.
In some limestone mines it would be possible to place a moist sludge
relatively easily, since a truckload could be driven into the placement
area, dumped into a hopper, and stowed in the rooms.
Longwall Mines
Although both hydraulic and pneumatic backfilling of waste have been
used in conjunction with longwall mining, pneumatic stowing would be the
preferred and perhaps only method of introducing sludge into longwall
cavities. Unlike wastes that have been hydraulically backfilled in longwall
mines in Europe (such as mine tailings), untreated FGD sludge does not drain
to a relatively dry material even when mixed with relatively large quantities
of fly ash. Thus, slurries pumped into longwall cavities could be readily
forced out when the roof collapses and could cause severe problems in the
coal mining operation.
Pneumatic stowing of sludge does appear to be feasible, although there
may be some equipment redesign required to achieve a viable operation.
Efficient, continuous lateral discharge pneumatic stowing equipment, such
as that shown in Figure V-19, have been developed in Europe for handling
dry materials. This equipment, though, may not be directly applicable to
FGD sludge disposal unless the sludge is in the form of a dry, free-flowing
solid. And such a material may result in significant dust problems, as
with any such pneumatic stowing operation. However, it is reasonable to
assume that appropriate handling and disposal equipment could be developed
to implement an acceptable disposal system.
3. Monitoring Methods
a. Background
For the land disposal of FGD sludges it will be necessary to measure
any physical, chemical, or biological changes that occur in the region
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Conveyor-
a
n
npTp
•u
« Dip
C
Plow
//Self Advancing
ill —r
r
o ° o ri:;'''!!'-".'::',-'".'-''.'1^''' "',<''••.': ^'^rV.c'v/S'"'-:-
. o »'-..*^ :<.-'?^---'*- ••:••>•--:', •- 1. -A, -•'/vj^M
650 feet
Coal Face
Flow
Stowed Gob
Mine Layout — Longwall Mining
With Lateral Stowing
: I Telescopic Sections
Supply
Railroad
Stowagl*
Supply Conveyor
Self Advancing Jacks
Plow
Hydraulic Deflectors
Source:
Jacks
Discharge Wall
Cross Section Through Longwall Face With
Lateral Pneumatic Stowing
Courtney, W.J., and Singh, Madan M., "Pneumatic Stowing: It Must be Looked
At Now," Coal Mining and Processing, H (2), 1974.
FIGURE V-19 LONGWALL STOWING - LATERAL
183
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surrounding the disposal site. In particular, the groundwater which will
receive any substances leached from the sludge and which may transport these
substances away from the site must be checked periodically for evidence of
contamination from sludge leachate. Indication of such contamination will
stem from an appropriately planned program of measurements during and after
disposal coupled with a thorough knowledge of the condition of the ground-
water prior to disposal. Factors such as the climate and hydrology of the
area and normal effect of the physical disposal operation (such as backfill-
ing of overburden) in the absence of the sludge must also be considered.
To correlate the seasonal variations of groundwater flow and quality with
climate and precipitation, it may be desirable to locate a rain gauge and
record temperature near the disposal site.
For each land disposal option there are four major questions to be
answered, all of which are interrelated via the hydrology and geochemistry
of the disposal site:
• what species or substances to monitor;
• how to monitor these species, including sampling and measurement;
• where to monitor them, particularly with respect to placement of
sampling sites; and
• frequency of monitoring.
Each of the above questions will be discussed in general in the following
paragraphs and in specific terms for the individual disposal cases.
b. Species and/or Substances to be Monitored
In considering which of the many possible species to monitor as an
indication of contamination of groundwater by sludge leachate, it is
necessary to consider three points.
• What species are already present in the groundwater?
• What species are present in the sludge and at what concentrations
relative to the groundwater?
• How are these species likely to behave during the leaching
process?
Implicit in the question of what species are present in the grounwater is
the question of concentration level.
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For mining operations it has been recommended that background
groundwater quality data should be obtained for a period of two years
prior to initiating mine activities (31). For each disposal site it is
imperative that measurements of groundwater quality be obtained prior to
the start of any disposal operation.
Background data in the mined area would incorporate geochemical
changes in groundwater attributed to disturbance and replacement of the
overburden. Therefore, simultaneous measurement of groundwater upgradient
of the mining area may be needed. It is also recommended that groundwater
be monitored during disposal from wells upgradient of the disposal site
(both within and removed from the mined area). Quarterly or bimonthly
measurements should be obtained to ascertain the seasonal variation in
water quality at the site.
Table V-ll gives a list of various species which are of importance to
the acceptability of water for diverse uses. This listing, together with
a list of the various species present or expected in the sludge (see
Tables IV-1, IV-2, and IV-3) form the basis for assessing the predisposal
water quality. At the very least, measuremnt of the unperturbed groundwater
should be made for all the species listed in Table V-ll.
In those cases where feasible, additional groundwater samples should
be taken from an analogous operation as, for example, in an operating
surface coal mine. Analysis of these samples can aid in understanding
what, if any, effect the disposal operation itself has on the concentrations
of the various species in the groundwater.
Because of the high degree of variability in composition, each specific
sludge requires characterization and identification of significant trace
metal levels. From a comparison of Table IV-3 with Table V-ll, there are
a number of elements likely to be of concern (e.g., Mn, Hg, Se, etc.).
It is necessary to know the initial groundwater concentrations for these
species. If the groundwater already has a high concentration of a specific
species, the value of that parameter as an indicator of contamination is
lessened.
The expected leaching behaviors of various species present in sludge
have been discussed in Chapter IV. In general, sulfate, chloride, and
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TABLE V-ll
COMPARISON OF WATER QUALITY CRITERIA AND
PRACTICAL RANGE OF MEASUREMENT METHODOLOGY
Parameter
Biostimulants
Dissolved Oxygen
Ammonium
Nitrate
Nitrite
Water Quality Criteria
Levels (mg/1)
Public Water Freshwater
Supply Aquatic Life
Cd
Cr
Cu
Fe
Hg
Mn
Ni
Pb
Zn
0.5
10
1.0
0.001
0.01
0.05
I5)b
0.1
0.01
0.05
1.0
0.3
0.002
0.05
[0.2]b
0.05
5.0
6.8
•w0.02a
Q
•x.0.005"
Measurement
Practical Range
(nm/1)
0-20, ± 0.1
0.01-2
0.05-10
0.05-1
0.005 up
0.001-1
Methodology
Polarographic
sensor
Automated
colorimetry
Colorlmetry
Colorimetry
Colorimetry
Colorimetry
~
—
—
0.004°
0.05
•^.006"
—
0.002 Max
Ceiling
0.00005 Avg. Max
—
•vfl.03a
0.03
M).03a
0.05-20
5-1000
0.002 up
0.001-2
0.05-100
0.05-10
0.1-20
0.002 up
0.01-2
0.01-10
0.01-10
0.05-2
AA
AA
AA (hydride
evolution)
AA (extraction)
AA
AA
AA
AA (cold vapor)
AA
AA (extraction)
AA (extraction)
AA
Inorganic Nonmetals
B
Cl"
SO,-
Physical Properties
Total Dissolved
Solids
Total Suspended
Solids
PH
1.0
250
250
5-9
Minimize
80
5-9
0.1-1
20-400
5-35.000
10-400
20-20,000
Colorimetry
Tit rimetry
Ion-selective
electrode
Nephlometric
Evaporation &
weighing
Filtration &
weighing
Approximate concentration only; criteria Involve response of most sensitive
biological species.
bCriteria for Irrigation water; no public water supply criteria.
'Criteria for soft water (0.03 mg/1 in hard water).
dAnalysis methods listed in "Manual of Methods for Chemical Analysis of
Water and Wastes", EPA MDQARL, Cincinnati, Ohio, 1974; and In "Proposed
Criteria for Water Quality," Vol. II, EPA, Washington, October 1973.
^ater quality criteria taken from "Proposed Criteria for Water Quality",
U.S. EPA, October 1973.
AA
Atomic absorption spectrophotometry, utilizing auxiliary techniques
such as extraction (for preconcentration) where noted
186
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sodium are less attenuated than others, and chemical oxygen demand (COD)
and total dissolved solids also are not particularly attenuated (32).
The latter often is related to sodium salts of the anions. Changes in the
concentrations of these species (and parameters) which are least attenuated
during the leaching process are the most useful indicators of the influx
of sludge leachate into the groundwater. Once it is established through
monitoring of some or all of these indicators that sludge leachate is
present in the groundwater, then a more extensive monitoring program for
other constituents previously found in the sludge liquors can be instituted.
c. Sampling and Measurement of Contaminant Species
The two major alternative approaches to the sampling and measurement of
groundwater constituents are real-time, in situ measurement of components of
the sample stream and removal of discrete grab (or integrated) portions of
the sample stream for subsequent measurement.
The in situ measurement approach eliminates the need for sample
handling (with the attendant possiblity of contamination); however, the
number of different monitoring devices (or "probes") is extremely limited
at this time (conductivity, pH, Cl, Na, and dissolved oxygen) and the long-
term accuracy (drift) of those is generally poor. Only conductivity
represents a real possibility for such monitoring and has been used
frequently in similar monitoring programs. In the present study the
predicted leaching behavior (transients) for all species is sufficiently
slow so that continuous monitoring would not be required in order to
observe the concentration changes taking place.
The general approach to be taken for the monitoring sludge disposal
tests would be to obtain uncontaminated, representative samples from the
aquifer or surface water and to transport these samples to an appropriately
equipped laboratory for measurement. The value of accurate analysis
outweighs any time savings which might be gained by in situ measurement.
A listing of measurement methods and range of application for a number
of important water quality parameters is given in Table V-ll. These methods
are the ones which are generally used and recommended by the U.S. EPA for
monitoring drinking water and wastewater. As recommended by EPA, samples
should be taken into acid-washed plastic containers and filtered (except
for suspended solids samples) and stabilized where necessary.
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Surface water samples are usually taken using appropriate "grab"
sampling procedures. Samples from subsurface aquifers are taken using
air-lift or mechanical pumps made from inert materials. Samples intended
for measurement of dissolved oxygen or oxidizable species (such as sulfite)
are taken by mechanical pump.
d. Location of Sampling Points
The location of sampling points in the receiving waters is a function
of the disposal mode being employed and the hydrology of the area. In
cases such as the surface area mines, the receiving water may be a surface
stream or river which can be sampled in a relatively straightforward manner.
If uncertainty exists regarding the path of leachate flow from the sludge,
it may be necessary to establish one or more monitoring wells across the
presumed downgradient, both to establish the true flow pattern and to make
certain that sufficient area coverage is provided to intercept the leachate
plume. The relative merits of utilizing pumped and unpumped wells for
monitoring has been discussed in published literature (31). Continuously
pumped wells are useful for monitoring wider areas, but the interpretation
of the resulting data is somewhat more complicated.
An extensive discussion of well placement for monitoring solid waste
landfills is also available in published literature (33). Location of
wells to monitor leachate plumes in unconsolidated sediment is less difficult
than location of monitoring wells in bedrock. For disposal cases where
sludge is used on the surface as a tailings amendment or is placed within
the working pit of an active surface mine, wells may be placed in the broken
up overburden, consisting of broken rock and soil which has been replaced
after mining has been completed. This overburden material should initially
have a fair amount of permeability to transmit water, although with time
the overburden may consolidate and decrease in permeability. For disposal
cases where sludge is placed in underground room and pillar or longwall
mines, location of the monitoring wells will be more complex. Groundwater
flow through rock with fractures and solutions must be intercepted through
trial and error. A well may fail to intercept any fractures or solution
cavities, thereby resulting in no groundwater yield, or it may bypass the
leachate and intercept groundwater which has not been contaminated.
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Mathematical modeling of the groundwater flow patterns of the individual
test sites has been shown to be useful in designing the array of monitoring
locations (31), but the utility of this approach obviously varies with the
extent of geological and hydrological data available for each site.
e. Frequency of Monitoring
The frequency with which monitoring measurements must be made is a
function of the velocity of groundwater movement and the degree to which
the leachate species are attenuated or retarded during passage through the
geological strata. The model of the transport of leachate species in
groundwater is one which indicates a rapid increase in concentration of
less attenuated species during the leaching or elution of the first pore
volume of sludge, and then a gradual decrease. Some laboratory studies
(Chapter IV) have shown some increase in concentration of species which
are somewhat attenuated later in elution; however, the concentration change
was small. Thus, during and immediately after the disposal operation, it
would be necessary to monitor the concentrations of less attenuated
"indicator" species rather frequently in order to obtain initial data on
attenuation in "uncontaminated" soil. Because of the great uncertainties
in the permeability data and calculations regarding the times required to
elute "pore volumes" of sludge, the initial monitoring frequency would be
at a rather high rate, possibly as little as 0.05 times the estimated pore
volume transit time. The actual timing must be worked out for each case
as a function of projected pore volume transit time, actual amount of
sludge disposed, and desired location (distance) of monitor sites.
G. ASSESSMENT OF REGULATORY ENVIRONMENT RELATIVE TO FGD SLUDGE DISPOSAL
1. Review of Federal Legislation
a. Waste Disposal Legislation
Relevant federal legislation pertaining to waste disposal includes
the Solid Waste Disposal Act of 1965, as amended, the EPA Guidelines for
the Land Disposal of Solid Waste, and the recently passed Resource
Conservation and Recovery Act (RCRA). The RCRA amends both the Disposal
Act and the Guidelines; however, regulations and programs which it
authorizes will not be promulgated or implemented until at least 18 months
after enactment. Hence, this section will discuss the Disposal Act and
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the Guidelines, as well as the RCRA, and will describe current waste
disposal practices which likely will remain unchanged until the new
regulations are implemented.
The Solid Waste Disposal Act and the Guidelines for the Land Disposal
of Solid Wastes
Prior to passage of the RCRA, all direct regulation of waste disposal
remained at the state and local levels. The Solid Waste Disposal Act gave
EPA only promotional and advisory power, while the Guidelines only recom-
mended to local authorities procedures for waste disposal.
The Disposal Act provided for research, training, and demonstration
activities related to waste disposal and authorized planning and construction
grants to state and local agencies for development of solid waste disposal
plants, and construction of new or improved solid waste disposal facilities.
The only regulatory mandate in the Act occurred in Section 211. This
section required federal agencies to comply with the solid waste Guidelines
authorized under Section 209 (see below). (No comparable requirement was
made of the private sector or of state and local agencies.)
The Guidelines recommended procedures for regulating the design,
construction, and operation of land disposal sites. They defined solid
wastes, sludges, and hazardous wastes, and recommended that hazardous wastes
and sludges containing free moisture be treated as special wastes requiring
case-by-case approval of the responsible agency for acceptance at disposal
sites.
Neither the Disposal Act nor the Guidelines relate in any direct
regulatory way to the disposal of desulfurization wastes. Because both
are advisory in nature and do not provide regulatory authority, there has
been and currently remains considerable variation among states and local-
ities in the type, extensiveness, and enforcement of regulations pertaining
to solid and hazardous waste disposal. The Guidelines could have promoted
more uniform practices, but EPA reports that a relatively small percentage
of state and local authorities appear to have utilized the Guidelines in
formulating their procedures and regulations. The studies and grants
provided under the Disposal Act heightened the awareness of many states
of solid and hazardous waste problems and in some states resulted in
190
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departmental reorganization and improved regulations and enforcement, but
in many other states there was little change.
Desulfurization waste may be determined to be hazardous due to the
heavy metals present in its leachate, although this determination has not
yet been made. The disposal and management of hazardous wastes under the
Disposal Act and the Guidelines has remained a problem for almost all
states, including most of the states which have established laudable
systems for managing and disposing of nonhazardous solid waste. State
needs for effective hazardous waste management include an enforceable
definition of hazardous waste, a comprehensive approach to groundwater
protection including procedures for analyzing leachate and attenuation
effects, and a system for regulating the transport of wastes from the point
of generation to the disposal site.
The Resource Conservation and Recovery Act (RCRA)
The Resource Conservation and Recovery Act was signed into law in
4
October 1976. The Act creates federal and state regulatory authority for
both solid and hazardous wastes. Federally approved solid waste management
plans are mandatory for each state, while federally authorized state
hazardous waste programs are optional. In all states without such programs
the federal government will regulate hazardous wastes.
!EPA's Office of Solid Waste Management has indicated that desulfur-
ization sludge likely will be considered hazardous waste under the Act.
'In contrast, solid waste personnel in Pennsylvania, Illinois, and Kentucky
indicate that based on leachate constitutents they would not classify
desulfurization sludge as hazardous. Resolution of this difference must
await promulgation of regulations authorized in Section 3001 which will
identify the characteristics of hazardous waste and list particular
^hazardous wastes."\ Large quantities of FGD sludge will be generated and
will require disposal. Because there is question regarding the nature of
desulfurization sludge, the following discussion covers provisions of the
Act which pertain to both hazardous and nonhazardous wastes.
Key definitions in the Act which pertain to desulfurization waste
disposal include hazardous waste, sludge, and solid waste. Relevant
sections of these definitions follow:
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• hazardous waste—"a solid waste, or combination of solid wastes,
which because of its quantity, concentration, or physical,
chemical, or infectious characteristics may...pose a substantial
present or potential hazard to human health or the environment
when improperly treated, stored, transported, or disposed of, or
otherwise managed."
• sludge—"any solid, semi-solid, or liquid waste generated from an
...air pollution control facility..."
• solid waste—"any garbage, refuse, sludge from an...air pollution
control facility...including solid, liquid, semi-solid, or contained
gaseous material..."
Section C, Hazardous Waste Management, authorizes the Administrator of
the EPA to establish a hazardous waste management system and provides for
authorization of state hazardous waste programs in states where programs
meet the requirements of the Act. Sections 3001 through 3006 require that
within 18 months after enactment the Administrator shall:
• develop and promulgate criteria for identifying characteristics
of hazardous wastes;
• promulgate regulations identifying characteristics of hazardous
waste and listing various hazardous wastes;
• promulgate regulations which establish standards for generators
and transporters of hazardous waste and performance standards for
owners and operators of waste facilities;
• promulgate regulations which require that each owner/operator
obtain a permit;
• promulgate guidelines to assist states in the development of state
hazardous waste programs.
These requirements are discussed in the following paragraphs.
Development of specific and/or quantitative criteria and regulations
which identify characteristics of hazardous waste should provide federal
and local authorities with long needed guidance in the management of
hazardous wastes. Although EPA personnel have not yet determined a com-
prehensive approach to development of such criteria and regulations, they
have initiated work on two relevant, related procedures, a Standard
Leaching Test and a Standard Attenuation Procedure.
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The regulations which establish standards for generators and
transporters of hazardous waste must include requirements respecting
recordkeeping, labeling, and reporting practices and use of a manifest
system. Regulations which establish performance standards for owners and
operators of facilities must include requirements respecting: (1) treatment,
storage, or disposal of waste by methods satisfactory to the Administrator;
(2) the location, design, and construction of hazardous waste facilities;
and (3) contingency plans for effective action to minimize unanticipated
damage from treatment, storage, or disposal of hazardous waste.
The regulations regarding permits to operate waste facilities must
require that permit applications provide estimates of quantities and con-
centrations of hazardous wastes to be disposed of and technical descriptions
of the disposal site.
Guidelines developed by EPA will assist states in developing hazardous
waste programs. States will be "authorized to carry out such program(s)
in lieu of the Federal program when such programs are equivalent." In
accord with this, EPA has indicated that these guidelines will include
requirements that state programs, as a minimum, must comply with all the
federal criteria, regulations, and standards promulgated under the Act.
The Act does not require promulgation of uniform groundwater criteria
for monitoring and site selection. Although such criteria would be
desirable from the perspective of enforcement, they cannot be readily
established due to seasonal variations and other variations in groundwater
composition upgradient of disposal operations which therefore affect down-
gradient compositions. Hence, monitoring and site suitability judgments
must be made on a site-specific basis.
Finally, regarding hazards waste, Section 3006 discusses the procedures
and timing for implementation of state hazardous waste programs. Guidelines
to assist states in the development of such programs must be promulgated by
the Administrator within 18 months of enactment. States may then submit
an application for program authorization which must be approved or dis-
approved by the Administrator within 180 days of submittal. Alternatively,
states which have in existence hazardous waste programs pursuant to state
law within 21 months after enactment may be granted "interim authorization"
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to carry out such programs in lieu of the federal program for 24 months,
if the state program is substantially equivalent to the federal program.
Subtitle D, State or Regional Solid Waste Plans, requires that each
state establish and implement a solid waste management plan which has
received approval of the Administrator as meeting the requirements of the
Act. The governor of each state is authorized to identify regions for
solid waste management, identify an agency to develop and implement the
State Plan, and identify which solid waste functions will be the responsi-
bility of the state and which will be the responsibility of regional or
local authorities.
The following are areas which the guidelines must address and which
are important for effective planning for and regulation of desulfurization
waste disposal:
"the varying regional, geologic, hydrologic, climatic, and other
circumstances under which different solid waste practices are required
in order to insure the reasonable protection of the quality of the
ground and surface waters from leachate contamination, the reasonable
protection of the quality of the suface waters from surface runoff
contamination, and the reasonable protection of ambient air quality;"
"characteristics and conditions of collection, storage, process-
ing, and disposal operating methods, techniques and practices, and
location of facilities where such operating methods, techniques, and
practices are conducted, taking into account the nature of the
material to be disposed;" and
"the constituents and generation rates of waste."
In summary, the RCRA provides comprehensive regulatory authority at
the federal level in the area of hazardous and solid waste management where
previously there was none. Under the Solid Waste Disposal Act, the federal
government had advisory and promotional powers in waste disposal matters
but no regulatory power. Under the RCRA the federal government is
authorized to provide direction and continuity in waste management. To
this end, the Act provides for the establishment of criteria for identifying
hazardous waste, creates an institutional framework for federal and state
planning, authorizes the federal government to provide the states with
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guidelines and requirements for development of state programs, and author-
izes comprehensive regulatory promulgation at both the federal and state
level with regard to hazardous and solid waste.
Further, the Act provides unquestionable coverage for desulfurization
waste disposal through very specific definitions of sludge and solid waste
and through a broad definition of hazardous waste. The definition of
"sludge" specifically includes solid, semi-solid, or liquid waste generated
from an air pollution control facility, while "solid waste" is defined to
include sludge from such a facility. "Hazardous waste" is defined as a
solid waste which poses hazards to human health or the environement when
improperly treated, stored, transported, or disposed of. EPA currently
believes that desulfurization waste will be considered hazardous waste,
although the final determination has not been made. However, should the
regulations authorized under Section 3001 for identifying characteristics
of hazardous waste and the listing of hazardous wastes ultimately indicate
such wastes to be considered solid but nonhazardous, the definitions of
"sludge" and "solid waste" insure that coverage will still be provided by
the Act.
Of particular importance to desulfurization waste disposal operations
are the sections providing for protection of groundwater quality. With
regard to hazardous waste, Section 3004 requires performance standards
applicable to disposal site owners and operators as may be necessary to
protect human health and the environment. Such standards must include
requirements for "disposal by practices...satisfactory to the Administrator.
With regard to solid waste, Section 4002 requires that the guidelines for
state plans which the Administrator promulgates shall consider the hydro-
logic, geologic, and other circumstances required to insure "protection of
the quality of the ground and surface waters from leachate contamination."
Based on these sections, it can be assumed that the performance standards
and the state solid waste plans will require groundwater protection.
Finally, although the Act provides adequate legal protection of the
environment by addressing groundwater degradation and by providing an
institutional framework for planning, regulatory implementation and
enforcement, the technical aspects of providing protection can only be
handled on a site-specific basis.
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b. Water Legislation
The Dam Safety Act, the Federal Water Pollution Control Act Amendments
(FWPCA), and the Safe Drinking Water Act have been included for assessment
in the area of water legislation. Focus of concern with the Dam Safety Act
is the anticipated safety and environmental regulation of all dam structures,
including the impoundments likely to be part of certain desulfurization
waste disposal operations. The primary concern with the FWPCA and the Safe
Drinking Water Act is their approach to protection of the nation's waters,
particularly groundwater, from pollution.
The Dam Safety Act required initial inspection and inventory of all
dams of specified size and a subsequent report to Congress recommending
legislation and regulatory structures to assure public safety from dam
disasters. To date, the inventory has been completed, and all federal dams
have been inspected. (No appropriation of funds for inspection of non-
federal dams was made.) The report will be submitted to Congress within
a few weeks. Although details of the report have not been disclosed, the
Corps has indicated that the report will recommend a comprehensive national
Dam Safety Program (which includes regular dam inspection) and will provide
a model state law and model inspection guidelines for use by the states in
establishing state programs. The report also will recommend appropriate
roles for the states and the federal government. The Corps has indicated
further that the laws and regulations which eventually will be promulgated
with respect to dam specifications and inspections likely will apply to
most mine site impoundments.
Both the FWPCA and the Safe Drinking Water Act authorize protection of
the nation's waters. Together, they employ a variety of approaches to
pollution control. Interpretations to date have produced even further
variations. Thus, assessing the adequacy of these laws in protecting the
environment is a complex task, and this discussion focuses on standards
and criteria which protect surface waters through regulation of discharges
from point sources and protection of ground and surface waters through
regulation of seepage (nonpoint source). Point source regulation presents
a simpler problem, as the FWPCA provides authorization for effluent
standards as influenced by the water quality of the receiving stream under
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several sections, including 301, 302, and 402. Regulation of seepage
discharges (excepting seepage from deep well injection, discussed below)
is not directly authorized in either act, nor are standards or criteria
applicable to such discharges provided for. However, EPA has indicated
that sections 208 and 402 of the FWPCA and Sections 1424 and 1431 of the
Safe Drinking Water Act may be interpreted to regulate such discharges.
Following is a summary of the potential relevance of each of the
above sections to FGD sludge disposal operations.
Federal Water Pollution Control Act Amendments (FWPCA), PL92-500
• Section 301—"There shall be achieved...effluent limitation of
point sources other than public-owned treatment works." Point
source effluent limitations for mines have been prepared and are
currently under review. The limitations regulate all point sources
on mine property. They would apply to desulfurization waste dis-
posal operations, as most operations will discharge into existing
mine pits or create new point sources such as discharges from
pumping out of abandoned underground mines or from pumping
collected groundwater, seepage, precipitation, and surface runoff
from surface mine pits.
• Section 302—"authorizes effluent limitation to enable attainment
or maintenance of that water quality in a specific portion of the
navigable waters which shall assure protection of public water
supplies..." Although protection of public water supplies could
be interpreted to include protection of groundwater to date,
development of effluent limitations has considered only the quality
of receiving surface waters. When the water quality of the
receiving stream meets the. standards for its designated use, the
federal effluent guideline limitations are applied. When the water
quality of the receiving stream does not meet standards for its
designated use, effluent limitations more stringent than the
federal guideline limitations are applied.
• Section 402—authorizes under the National Pollutant Discharge
Elimination System (NPDES) permits "for discharge of any pollutant"
which meets all applicable requirements of the Act. To date, EPA
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focus largely has been limited to protection of surface water
quality, and.permits have been issued for discharge to surface
water only. However, EPA has indicated that future interpretations
may require NPDES permits for discharges to groundwaters as
"discharge of any pollutant" can be interpreted to include as
receivers both surface and groundwater.
• Section 208—Subsection (b)(2)(K) requires that any areawide waste
treatment management plan shall include "a process to control the
disposal of pollutants on land or in subsurface excavations within
such area to protect ground and surface water quality." Most area-
wide plans currently are being prepared. EPA has" indicated that,
although the Act has been interpreted primarily as a surface water
law to date, future interpretations of Section 208 likely will
broaden to include groundwater protection. Seepage resulting from
mine disposal of desulfurization waste could be regulated through
the areawide plans under Subsection (b)(2)(K), although the primary
vehicle for regulation is expected to be the RCRA discussed pre-
viously.
Safe Drinking Water Act, PL93-523
This Act authorizes national primary and secondary drinking water
regulations applicable to public water systems to protect the public health
and welfare. The regulations must specify contaminants, maximum contaminant
levels, and critera and procedures to assure a supply of drinking water
which complies with such levels. To date, procedures for the assurance of
such a supply have not directly included protection of groundwater from
seepage except in land application of municipal wastewaters.
Based on discussion with the EPA Office of Water Supply, only Sections
1424 and 1431 of the Act may be interpreted as applicable to desulfurization
waste disposal in mines. Section 1424, "Interim Regulation of Underground
Injections," (Subpart (e)) states:
"If the Adminstrator determines...that an area has an aquifer
which is the sole or principal drinking water source for the area and
which, if contaminated, would create a significant hazard to public
health...no commitment for Federal financial assistance...may be
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entered into for any project which the Administrator determines may
contaminate such aquifer through a recharge zone so as to create
a significant hazard to public health..."
This section could be used to prohibit disposal in specific mines when
federal funding is involved, if leaching and site analyses indicate probable
groundwater contamination.
Section 1431, "Emergency Powers," authorizes the Administrator to "take
such actions as he may deem necessary" to protect the health of the public
upon receipt of information that a contaminant is present or is likely to
enter a public water system which may present an imminent and substantial
endangerment of the public's health. Actions which the Administrator may
take include: "(1) issuing such orders as may be necessary to protect the
health of persons who are or may be users of such system...and (2) commencing
a civil action for appropriate relief, including a restraining order or
permanent or temporary injunction." This section provides broader coverage
than Section 1424 in that the Administrator's authority is not limited to
situations involving federal funds but extends to all situations where
contaminants may endanger public water systems. Regulation of existing FGD
sludge disposal may be covered under this section, although new disposal
operations are expected to be covered under the RCRA, discussed previously.
The Office of Water Supply has indicated that no other sections of
the Safe Drinking Water Act are being interpreted to apply directly to
desulfurization waste disposal. Until relatively recently, some questions
remained regarding applicability of Part C, Protection of Underground Sources
of Drinking Water, which addresses underground injection control programs.
EPA has recently completed the regulations for state control programs
(authorized in Part C, Section 1421) and indicates they are not intended
to include mines of any type. The regulations are limited to deep wells
which are defined as openings with "depth greater than surface diameter."
In summary, both the FWPCA and the Safe Drinking Water Act contain
authority to protect groundwater from seepage, but such authority has been
rarely exercised to date. EPA's regulatory efforts under the FWPCA have
been limited primarily to discharges to surface waters due to the cost-
effectiveness of regulating the point sources first and the technical
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complexities inherent in regulating underground discharges. Only recently
has attention been focused on regulating groundwater pollution.
Interpretation of the FWPCA as a groundwater law (as well as a surface
water law) results in comprehensive legal coverage for all aspects of
desulfurization disposal operations relevant to water pollution. However,
truly effective regulation of seepage under the Act requires improved
technical capability, as discussed in the section of Waste Disposal
Legislation.
In the Safe Drinking Water Act, authority to regulate seepage in
emergency situations or when federal funds are involved exists under
Sections 1424 and 1430. In the FWPCA, authority to regulate seepage
exists under Section 208, which provides for areawide waste treatment
management plans, and Section 204, which provides for NPDES permits.
Based on discussion with EPA, it appears that future regulation of seepage
from waste disposal in mines will occur primarily under Section 208 through
the areawide plans.
c. Health and Safety Legislation
Federal regulation of health and safety is shared by two agencies,
the Mining Enforcement and Safety Administration (MESA) and the Occupational
Safety and Health Administration (OSHA). The specific authority of each
agency with regard to mines was clarified in 1974 in a jointly issued
Memorandum of Understanding. The Memorandum defines mining and milling
activities, and states:
"MESA has enforcement authority for employee safety and health
in mines and mills. OSHA has safety and health enforcement authority
in processes beyond mines and mills."
Despite the Memorandum, MESA officials indicate that there continued to be
specific cases where the authorities of MESA and OSHA need clarification.
In resolving these cases, MESA authority frequently is considered limited
to the "health and safety of miners working on mine property."
In addition to federal regulation, many states maintain a substantial
regulatory role in mining operations and mine health and safety. States
frequently enforce federal standards and complementary state standards,
and promulgate and enforce additional standards and regulations in areas
not addressed by the federal government, such as subsidence, mine drainage,
and reclamation.
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Included in this assessment are three acts which provide for health
and safety regulations by MESA and OSHA, namely the Metal and Nonmetal Mine
Safety Act, the Federal Coal Mine Health and Safety Act, and the Occupational
Safety and Health Act, and the health and safety standards and proposed
amendments issued by MESA pursuant to these acts. (OSHA standards and
regulations have not been included due to their extensive detail and
questionable relevance to this study.)
The MESA health and safety standards regulate many activities and
conditions of both underground and surface mine areas, including general
air quality and ventilation; dust and noise levels; sampling methods and
procedures; material handling and storage; use of equipment; and loading,
hauling, and dumping. The Safety Standards for Surface Coal Mines and
Surface Work Areas of Underground Coal Mines include new adopted amendments
pertaining to refuse piles and impoundments. Disposal of desulfurization
wastes in mines will likely necessitate creation of stockpiles and impound-
ments similar in material and engineering properties to those addressed
in the amendments.
A detailed assessment of the adequacy of the existing federal health
and safety legislation to protect miners and the public from any ill effects
of mine disposal of desulfurization wastes is not presented here. Use of
mines for disposal of desulfurization wastes would present regulatory bodies
with a new situation not anticipated when current regulations and standards
were established. Although there are areas of regulation which can be
interpreted to apply to desulfurization waste disposal should such disposal
near implementation, the entire spectrum of health and safety regulations
would require thorough assessment. Considerable additions and modifications
likely would be required. MESA officials have stated that clarification of
authority regarding regulation of mine disposal would need considerable
study. Consideration would minimally include the respective roles of MESA,
OSHA, and other existing or new federal authorities, and the role of the
various state governments.
In summary, the current health standards and regulations of particular
importance to disposal of FGD wastes include those pertaining to dust
(standards), airborne contaminants (threshold limit values), noise, and
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sampling and measurement procedures. Standards for surface and underground
coal mines are currently as follows:
• dust—average concentration of respirable dust of 2 mg/cubic meter
of air or less;
• airborne contaminants—the threshold limit values adopted by the
American Conference of Governmental Industrial Hygienists in 1970;
and
• noise—maintenance of noise level during each shift at or below
the following permissible noise exposures.
Duration per Day Noise Level
(hours) (dBa)
8 90
6 92
4 95
3 97
2 100
1-1/2 102
1 105
3/4 107
1/2 110
1/4 or less 115
Additional health regulations will likely be required in certain other
areas, and some of the above standards would probably be modified.
Current safety standards and regulations of particular interest
include those in the area of surface installations (including equipment,
materials storage, stockpiling, reclaiming, refuse piles, and impounding
structures), ground control, loading and haulage, roof support, and
ventilation. Existing safety regulations cover the primary areas of
operation of desulfurization waste disposal. Thus, safety standard
changes would be primarily adaptions rather than additions.
e. Transportation Legislation
Relevant federal legislation in the area of transportation includes
the new Hazardous Materials Transportation Act, the Transportation of
Explosives Act, the Hazardous Cargo Act, and the Ports and Waterways
202
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Safety Act. These acts authorize numerous regulations governing all modes
of transport—motor carriage, rail, water, pipelines, and air.
Although each act is addressed to materials of a hazardous or dangerous
nature, the acts vary in their definition of hazardous and dangerous mater-
ials. In certain cases, particularly the Explosives and Cargo Act, the
definitions create doubt as to applicability to desulfurization wastes.
Additional questions of applicability stem from the remaining chemical and
physical questions regarding the hazardous nature of desulfurization wastes.
However, the Hazardous Materials Transportation Act, which will
effectively replace these two acts in time, appears to possibly be appli-
cable to desulfurization wastes. The Act regulates hazardous materials
defined as follows: "substances or materials in a quantity and form which
may pose an unreasonable risk to health and safety or property when trans-
ported in commerce." Further, the Act defines commerce to include the
transport of desulfurization waste under consideration. Commerce is defined
as "trade, traffic commerce or transportation, within the jurisdiction of
the United States, (A) between a place in a state and any place outside of
such state, or (B) which affects trade, traffic, commerce, or transportation
described in clause (A)."
An assessment of the adequacy of the regulations pursuant to these
acts is beyond the scope of this effort due to their extensive numbers and
technical detail. However, in summary, the four acts provide for regulation
of all modes of transportation under consideration; desulfurization wastes
are a type of material covered by the acts; and the transport of similar
materials in slurry, solid, and semi-solid form is a common longstanding
activity of commerce. Hence, transportation of desulfurization wastes
likely will not require new regulations or modification of the existing
administrative structure. The effectiveness and adequacy of the existing
structures and regulations can be further assessed, as needed, by review
of their historical adequacy with similar materials in the various modes
of transportation.
2. Review of State Regulations
At the state level there are a number of statutes which might affect
the disposal of FGD sludge in mines. The extent to which the laws and
203
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regulations of the various states might affect FGD sludge disposal will
depend on the interpretations of the various enforcement agencies. As
mentioned previously, no states have been identified that have statutes
specifically directed toward regulating the disposal of FGD sludge in mines.
The existing statutes differ for each state. It is impossible within
the scope of this report to cover for each state the laws and regulations
which might impinge on FGD sludge disposal in mines. Therefore, the laws
of one state, Pennsylvania, have been examined. Pennsylvania is considered
to be representative of states with potential for FGD sludge disposal.
• It is an industrialized state and is confronted with disposing
large amounts of FGD sludge.
• In certain areas, land suitable for surface disposal of sludge
is limited.
• It has many active and abandoned surface and underground mines
which might be used for sludge disposal.
• Stowing of materials in abandoned mines has occurred to limit
subsidence and acid drainage formation.
• Its mining laws and regulations are comprehensive and deal with
mining conditions similar to these found in other mining states.
In Pennsylvania, statutes in three areas, mining, water, and solid
waste, may apply to FGD sludge disposal in mines. The specific statutes,
as amended, are as follows.
Mining
Pennsylvania Bituminous Coal Mine Act, Act 339, July 17, 1961
Act 346 (relating to anthracite coal mines), November 10, 1965
The Coal Mine Sealing Act of 1947, Act 490, June 30, 1947
Sealing Abandoned Bituminous Coal Mines, Act 55, May 7, 1935
Surface Mining Conservation and Reclamation Act, Act 418, May 31, 1945
Water
The Clean Streams Law, Act 394, June 22, 1937
Pennsylvania Industrial Wastes Regulations, Title 25, Chapter 97,
September 2, 1971
\
Pennsylvania Mine Drainage Permits Regulations, Title 25, Chapter 99,
September 2, 1971
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Pennsylvania NPDES Permit Regulations, Title 25, Chapter 92,
September 28, 1973
Solid Waste
Pennsylvania Solid Waste Management Act, Act 241, July 31, 1968
Pennsylvania Solid Waste Regulations, Title 25, August 2, 1971
Some of the mining statutes are concerned with protecting the mine
workers, while others are concerned with protecting the environment.
Worker-oriented acts include the Bituminous Coal Mine Act and Act 346
(relating to anthracite coal mines) which focus on maintenance of mine
conditions that insure miner health and safety. Environment-oriented acts
include the Coal Mine Sealing Act of 1947 and the Sealing Abandoned Bituminous
Coal Mines Act, both of which require the sealing of abandoned mines in order
to control acid mine drainge. Also, the Surface Mining Conservation and
Reclamation Act seeks to guarantee appropriate reclamation of surface mining
areas by requiring detailed reclamation plans and posting of bonds.
The water laws and regulations focus on protection of both surface
and groundwaters by requiring permits for any discharges or activities
which may affect those waters. The Clean Streams Law and the NPDES Permit
Regulations provide for control of industrial waste discharges, related
seepage, and discharge from mines. The Mine Drainage Permit Regulations
provide additional control of mine discharges by setting discharge limita-
tions on acid, iron, pH, and other constituents of drainage such as aluminum,
sulfates, and manganese. Finally, the Industrial Wastes Regulations pro-
hibit the disposal of inadequately treated wastes in mines.
The Solid Waste Management Act and subsequent regulations focus on
protecting land and water resources by requiring permits for all land
disposal, including disposal in mines, of solid and hazardous wastes.
The Solid Waste Management Act requires a permit for transport of wastes
to mines, approval of the Department of Environmental Resources, the
Department of Commerce, and the county commissioners for waste disposal
in mines, and a plan and bond for landscape restoration following such
disposal. The Solid Waste Regulations require that a permit be obtained
from the Department of Environmental Resources before any land can be used
for either solid or hazardous disposal. In issuing a permit for either
solid or hazardous wastes, the Department will consider factors related
to site selection, storage, operations, reclamation, and transportation.
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The assessment of the Pennsylvania statutes has been performed in
much the same way as that of the federal statutes. The following is a
summary of the assessment.
• The Department of Environmental Resources will have lead responsi-
bility for regulating FGD sludge disposal in mines. The primary
regulating statutes are administered by the Bureau of Mine and
Occupational Safety, the Bureau of Water Quality Management, and
the Bureau of Land Protection and Reclamation.
• The regulating statutes do not specifically address FGD sludge and
sludge disposal operations, thus requiring individual interpretation.
However, regardless of interpretation, collectively the statutes
appear to provide coverage for all aspects of FGD disposal. On-
land FGD sludge disposal is already being regulated in Pennsylvania.
• Specific areas of the regulating statutes which might be interpreted
as covering sludge disposal include those which:
- prohibit the dumping of offensive material into coal mines;
- prohibit the disposal of inadequately treated wastes into
underground mines;
require that a permit be issued before any land can be used for
solid waste disposal;
require a reclamation plan be approved by the state before any
surface mining operation is permitted; to assure that the
reclamation is carried out according to the approved plan, a
bond must be deposited with the state (such a reclamation plan
and bond could be required for disposal of FGD sludge in surface
mines; alternatively, disposal of FGD sludge could be integrated
into surface mine reclamation plans);
- require the sealing of mines in order to prevent acid mine
drainage once mining operations have ceased; and
- regulate and protect water quality (these not only include
regulations related to point and nonpoint source mine discharges
but also regulations which prevent unauthorized continuous or
intermittent contact of a solid waste with groundwater).
206
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Pennsylvania has become aware of certain problems in using its existing
regulations to control FGD sludge disposal. Consequently, the Department of
Environmental Resources is considering regulatory amendments needed in order
to permit an orderly and environmentally sound disposal of FGD sludge. For
example, mine sealing requirements may need modification to accommodate FGD
disposal. Additional required amendments may be clarified by a pilot field
program currently being conducted under an EPA grant which would evaluate
the disposal of FGD sludge in underground mines. The proposed program would
Pennsylvania and placing them in a deep inactive mine within a reasonable
distance of the source power plants.
H. CONCLUSIONS AND RECOMMENDATIONS
1. Technical/Environmental Considerations
The overall conclusion from this assessment of the disposal of
FGD sludges in mines is that while promising from both a technological
and an environmental standpoint, such disposal operations can result
in significant environmental impacts and each proposal for FGD sludge
disposal must be assessed on a case-by-case basis to determine the
magnitude and acceptability of these impacts. The fate of the sludge
and the extent of the environmental impacts will depend primarily on
the geology of the particular disposal site and on the specific
characteristics of the sludge but also on the indigenous quality of
receiving groundwaters and potential pathways to surface waters.
Specific conclusions of the assessment are as follows:
• There is sufficient available space in the United States
being generated annually in active mines for disposal of all
FGD sludge. Individual coal mines in most cases have space
available to dispose of at least the amount of sludge
produced from the coal extracted.
Mines employing surface stripping or underground convention-
al room and pillar operations are the most promising because
of their accessibility and availability of space. Open
pit mines are generally not promising because use of the
apace would hinder access to mineral reserves. Underground
mines employing caving (by longwall, pillar robbing, or
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stoping) have limited promise because they lack available
space. By production and available space, the most promising
categories of active mining for accepting sludge are ranked
as follows:
1. surface coal mining;
2. underground room and pillar coal mining;
3. underground room and pillar limestone mining;
4. underground room and pillar lead-zinc mining;
5. underground room and pillar salt mining; and
6. underground longwall coal mining.
Placement and handling techniques for FGD sludge disposal in
both surface and underground mines are available and have been
demonstrated for disposal of other materials in mines (i.e.,
coal refuse), although the techniques may require modifications
for application to FGD sludge disposal. There is the potential
for significant disruption of ongoing mining operations due to
the volume and physical properties of sludge to be handled.
One potential physical impact of concern is liquefaction of
the sludge either during disposal operations or after disposal
is completed. However, sound engineering design of sludge
placement, proper site selection, and constraints on sludge
properties can control such impacts.
The major potential adverse chemical Impact of FGD sludge
disposal in the vicinity of mining is increased constituent
loadings (especially sodium and calcium chlorides and
sulfates) to the mine drainage discharge. In areas removed
from the influence of mine drainage pump-out the principal
potential adverse chemical impact of FGD sludge is leachate
contamination of groundwater. Leachate concentrations
for treated and untreated sludges are generally expected
to be within the ranges of concentrations of the
chemical constituents in FGD sludge liquors for hundreds
208
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of years due to the slow movement of groundwater. How-
ever, the significance of the impact on the groundwater
will depend importantly on the quality of the groundwater
and the total quantity of leachate produced as well as its
concentration. This must be evaluated on a case-by-case
basis relative to potential contaminant contributions to
downgradient water supply wells and surface waters. In some
cases the quality of the leachate would be no worse, and
possibly better, than existing mine drainage, at least with
regard to acidity and total dissolved solids (IDS).
- The generation of sludge leachate will be site-specific,
with the greatest amounts produced when sludge is within a
groundwater regime of high transmissivity (having a steep
hydraulic gradient and high permeability). Attenuation of
FGD sludge leachate is also site-specific, with the least
attenuation in acidic groundwater environments having
soil and rock of limited ion exchange capacity. Integrating
these two factors, ranking of mining categories on a
national perspective (in order of the most promising):
1. underground limestone and coal room and pillar
mines above the water table;
2. coal surface area mines (Interior and Western);
3. coal surface contour mines (Eastern);
A. lead-zinc underground room and pillar mines; and
5. coal underground room and pillar, and longwall
mines within the water table (Eastern and Interior).
Note: Salt mines were not specifically addressed within
the scope of this study, even though they could receive the
highest ranking. Salt mines have generally been assigned
a higher priority with regard to the disposal of wastes,
e.g., hazardous radioactive wastes.
- The generation of sludge leachate is also sludge-specific
with decreasing amounts occurring with decreasing sludge
209
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permeability (especially through compaction or chemical
treatment). The concentrations of constituents in
leachate is also sludge-specific, with concentrations
tending to decrease as. alkalinity increases, fly ash
content decreases, and inorganic constituents originally
present -in coal decrease, i.e., chloride and trace metals.
Discharge of sludge leachate to surface waters can adversely
affect aquatic life by the addition of biocumulative trace
metals. In the case of sludges containing sulfite, there is
the potential toxicity of dissolved sulfite itself as well
as the potential depletion of dissolved oxygen due to the
sulfite.
In surface mines, control techniques to minimize groundwater
contamination include decrease of sludge permeability through
compaction or chemical treatment and placement of sludge
outside the groundwater reservoir through modified disposal
operations. In underground mines, the primary control
technique is chemical t^ctment.
The state-of-the-art of site monitoring and analytical
techniques to predict and assess impacts is adequate for
FGD sludge disposal. The general location of monitoring
sites must be based upon geologic field surveys in order
to develop appropriate background and leachate data.
In underground mines, FGD sludge placement results in the
potential benefits of lessening acid drainage formation and
long-term subsidence, primarily by sealing exposed coal
against air exposure which leads to pyritic sulfur oxidation
and also leads to pillar deterioration.
FGD sludge provides little potential as an amendment to mine
tailings for enhancing vegetative growth. In this regard,
FGD sludge generally ranks poorly in comparison to limestone
and sewage sludge.
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2. Regulatory Considerations
Recent shifts in regulatory attitudes show a growing concern for
groundwater protection from seepage or leachate from the disposal
of wastes. Given the recent Resource Conservation and Recovery Act
of 1976, existing laws are legally adequate to insure protection of
the geologic environment from waste disposal. However, because of
the technical difficulties of completely characterizing an underground
environment and of locating monitoring wells, regulation should rely
on guidelines for site selection and waste acceptance and should
allow for case-by-case assessment by professional geologists and
geochemists.
Specific conclusions are as follows:
• The lead authorities for FGD sludge disposal appear to be
the federal and state environmental protection agencies.
• The lead legislation is expected to be the Resource Conserva-
tion and Recovery Act of 1976, involving state resolution
of Federally approved programs and the existing planning
infrastructure established for 208 areawide wastewater
management planning under the Federal Water Pollution Control
Act Amendment of 1972.
• The combination of federal and st^.e legislation is legally
adequate to protect the environment during and after FGD
sludge disposal; however, regulations are needed with site
selection and waste acceptance guidelines based upon the
characteristics of FGD sludge and research on potential
environmental impacts.
• Additional legislation and standards may be required to
protect worker health and safety. Administration of the
health and safety requirements need clarification, especially
between authorities of OSHA and MESA.
• Because of the non-point source nature of air and water
emissions from FGD sludge disposal and the large variations
in FGD sludge character, disposal should be regulated on
a case-by-case basis.
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3. Need for Additional Research and Information
The following research needs are believed most important at this
time.
• Development of additional, more comprehensive physical and
engineering properties data base and corroboration (or
comparison) of results with field data. Of particular
interest are:
- triaxial compression tests for shear strength of untreated
sludges to determine the ability to support loadings
while unconfined;
- dynamic triaxial compression tests for untreated sludges to
simulate resistance to shear under seismic cyclic loadings
applicable to various regions of coal reserves;
- consolidation tests for untreated and soil-like treated
sludges to simulate density and permeability under various
static loadings related to overburden pressures; and
- Atterberg limits for untreated sludges.
Some of this testing is now underway in programs funded by
EPA and other governmental agencies, and will be reviewed
as available as a part of the Phase II effort.
• Development of a data base on. key Chemical impact issues
relating to mine disposal. Of particular importance are:
- the potential for TOS leaching from sludges and rates of
TOS oxidation;
- the potential for chemical attack of cement/concrete by
sludge liquors and leachate;
- the potential for SO2 evolution during the initial stages
of sludge disposal in underground mines with acidic
environments;
- the short-term effects of climate (e.g., freezing,
excessive rainfall, etc.) on the physical properties of
untreated sludges and pollutant mobility.
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GLOSSARY
acid — A substance containing hydrogen which may be replaced by metals
with the formation of salts.
acre-foot — A unit for measuring the volume of water, is equal to the
quantity required to cover 1 acre to a depth of 1 foot and is equal
to 43,560 cubic feet. The term is commonly used in measuring volumes
of water used or stored.
alkaline — Having the qualities of a base.
alluvial — Describes earth materials that have recently (geologic time
scale) been deposited by moving water.
aquilude — stratum that does not transmit groundwater and has no storage
capacity.
aquifer — A formation, or a group of formations, that is water-bearing and
water-transmitting.
Atterberg Limits — Indicate the boundaries as a soil proceeds from a solid
to liquid state, including shrinkage limit, plastic limit, and liquid
limit.
borehole — A hole made with a drill, auger, or other tools.
bulkhead — A construction for containment of a gas, liquid, or solid
within a section of a mine.
confined aquifers — Formations bound above and below by aquiludes, which
transport groundwater under pressure.
Darcy's Law — Relation of flow between hydraulic gradient and velocity
applicable to laminar groundwater flow within a porous medium:
V = Ki, where V = velocity, K = coefficient of permeability, and
i = hydraulic gradient.
dip — The angle at which a bed, stratum, or vein is inclined from the
horizontal.
dragline — A type of excavating equipment which casts a rope-hung bucket
a considerable distance, collects the dug material by pulling the
bucket toward itself on the ground with a second rope, elevates the
bucket, and dumps the material on a spoil bank, in a hopper, or on
a pile.
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evapotranspiration — Water withdrawn from land area by evaporation from
water surfaces and moist soil and plant transpiration.
highwall — The exposed vertical or near vertical wall associated with
strip or area surface mines.
liquefaction — Deformation due to buildup of high porewater pressures
created by either cyclic or static stress applications.
outcrop — The part of a rock formation that appears at the surface of the
ground. It includes those deposits that are so near to the surface as
to be found easily by digging.
overburden — Material of any nature, consolidated or unconsolidated, that
overlies a deposit of useful materials, ores, or coal.
precipitation — The discharge of water, in liquid or solid state, out of
the atmosphere, generally upon a land or water surface. The term
precipitation is also commonly used to designate the quantity of water
that is precipitated, measured in inches of depth, and includes rain-
fall, snow, hail, and sleet.
pyrite — Iron disulfide, FeS2; contains 46.7% iron, 53.3% sulfur.
e - e
relative density — Dr = - - x 100%
- •*- e - e .
max min
where e = in-place void ratio
e . = void ratio of soil in densest state
min
e = void ratio of soil in loosest state
max
room and pillar — A system of mining in which the coal or ore is mined in
rooms separated by narrow ribs or pillars.
runoff — The part of. the precipitation that appears in surface streams.
It is the same as stream flow unaffected by artificial diversions,
storage, or other works of man in or on the stream channels.
strike — The direction or bearing of a horizontal line in the plane of an
inclined stratum that is perpendicular to the direction of the dip.
subsidence — The lowering of the strata, including the surface, due to
underground excavations.
tailings — Mineral refuse from a milling operation usually deposited from
a water medium.
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unconfined aquifers — Formations that allow groundwater to flow freely
and seek its own level, with hydraulic gradients equal to the free
surface and invariant with depth.
water table — The upper surface of the zone of saturation.
215
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REFERENCES
1. Wiles, Carlton. Evaluation of Hazardous Wastes Emplacement In Mined
Openings, prepared by Fennix & Slsson for Solid and Hazardous Waste-
Research Laboratory, National Environmental Research Center, Cincinnati,
Ohio 45268.
2. Water Quality Criteria 1972, National Academy of Sciences, National
Academy of Engineering, Washington, D. C., 1972.
3. Gray, Donald H. and Lin Yen-Kuang. Engineering Properties of Compacted
Fly Ash, Journal of Soil Mechanics and Foundations Divisions, ASCE
No. SM4, April 1972.
4. Livingston, Daniel A. Data of Geochemistry, Chapter G. Chemical
Composition of Rivers and Lakes, Geological Survey Professional Paper
440-G, U. S. Government Printing Office, 1963.
5. Whaite, Ralph H. and Alice S. Allen. Pumped-Slurry Backfilling of
Inaccessible Mine Workings for Subsidence Control, IC-8667, Bureau of
Mines Information Circular, 1975.
6. McNay, Lewis M. and Donald R. Corson. Hydraulic Sandfill in Deep Metal
Mines, IC-8663, Bureau of Mines Information Circular, 1975.
7. Cochran, William. Mine Subsidence-Extent and Cost of Control in a
Selected Area, IC-8507, Bureau of Mines Information Circular, 1971.
8. Paone, James, et al. Land Utilization and Reclamation in the Mining
Industry, 1930-71, IC-8642, Bureau of Mines Information Circular, 1974.
9. Underground Disposal of Coal Mine Wastes, Study Committee to Assess the
Feasibility of Returning Underground Coal Mine Wastes to the Mined-Out
Areas, National Academy of Sciences/National Academy of Engineering, 1975.
10. Brauner, Gerhard. Subsidence Due to Underground Mining (In Two Parts)
2. Ground Movements and Mining Damage, IC-8572, Bureau of Mines
Information Circular, 1973.
11. Brauner, Gerhard. Subsidence Due to Underground Mining (In Two Parts)
1. Theory and Practices in Predicting Surface Deformation, IC-8571,
Bureau of Mines Information Circular, 1973.
12. Voight, Barry, and William Pariseau. Soil Mechanics and Foundations
Division - State of Predictive Art in Subsidence Engineering.
13. Turnbull, Willard J. and Charles I. Mansur. Compaction of Hydraullcally
Placed Fills, Journal of Soil Mechanics and Foundations Division, ASCE
SM11, November 1973.
216
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REFERENCES
(Cont.)
14. Liquefaction Problems in Geotechnical Engineering, American Society of
Civil Engineers Annual Convention, Preprint 2752, September 27 -
October 1976.
15. "Corrosion of Concrete by Sulfate Ions," Materials Performance, Volume
12, July 1973.
16. An Appraisal of Neutralization Processes to Treat Coal Mine Drainage,
Environmental Protection Technology Series EPA-670/2-73-093, November
1973.
17. Coal Refuse Disposal Facilities, E. D'Appolonia Consulting Engineers,
Inc., Engineering and Design Manual, U.S. Department of the Interior,
Mining Enforcement & Safety Administration, 1975.
18. Coalgate, Jerry L, et al. GOB Pile Stabilization, Reclamation, and
Utilization, Contract No. 14-32-001-1218, Office of Coal Research and
Development Report No. 75.
19. Dickinson, Sam Experiments in Propagating Plant Cover at Tailing Basins,
Mining Congress Journal, October 1972.
20. Staff, Bureau of Mines, Methods and Costs of Coal Refuse Disposal and
Reclamation, IC-8576, Bureau of Mines Information Circular, 1973.
21. Poonia, S. R. and D. R. Bhumbla. Effect of Gypsum and Calcium Carbonate
on Plant Yield and Chemical Composition and Calcium Availability in
a Non-Saline Sodic Soil, Department of Soil Science, Haryana Agriculture
University, Hissar, Haryana, India.
22. Sahota, N. S. and D. R. Rhumbla. Effect of Leaching Saline-Alkali Soils
with and without Gypsum on the Soluble Salts, Boron and Exchangeable
Calcium and Sodium of the Soils, Punjab Agricultural University,
Ludhiana, Punjab, India, September 1970.
23. Smith, R. A. H. and A. D. Bradshaw, Stabilization of Toxic Mine Wastes
by the Use of Tolerant Plant Populations, Department of Botany,
University of Liverpool.
24. Black, C. H. Soil-Plant Relationships, (2nd ed.), John Wiley & Sons,
New York, 1968.
25. Dean, K. C. et al. Methods and Costs for Stabilizing Fine-Sized Mineral
Wastes, RI-7896, Bureau of Mines Report of Investigations, 1974.
26. Berg, William A. How to Promote Plants in Mine Wastes, Mining Engineering,
November 1970.
217
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REFERENCES
(Cont.)
27. Gupta, I. C. and Harish Chandra, Effect of Gypsum in Reducing Boron
Hazard of Saline Waters and Soils, Central Soil Salinity Research
Institute, Karnal Annals of Arid Zone, Vol. II, Nos. 3 and 4,
September and December 1972.
28. Driver, Charles et al, Assessment of the Effectiveness and Effects of
Land Disposal Methodologies of Waste Water Management, Department of
the Army, Corps of Engineers, Wastewater Management Report 72-1,
January 1972.
29. Dean, Karl C. and Richard Havens, Stabilizing Mineral Wastes, U. S.
Bureau of Mines, E/MJ, April 1971.
30. Sopper, William E. et al, Using Sewage Effluent and Liquid Digested
Sludge to Establish Grasses and Legumes on Bituminous Strip-Mine
Spoils, Department of the Interior, Pennsylvania State University,
March 1974.
31. Warner, Don. L.., Rationale and Methodology for Monitoring Groundwater
by Mining Activities, National Environmental Research Center, Office
of Research and Development, U. S. Environmental Protection Agency,
Las Vegas, Nevada 89114.
32. Mahlock, J. L., Chemical Fixation of Hazardous Waste and Air Pollution-
Abatement Sludges, U.S. Army, Engineer Waterways Experiment Station,
Corps of Engineers, January 1975.
33. Procedures Manual for Monitoring Solid Waste Disposal Sites, Wehran
Engineering Corp. (Middletown, New York) and Geraghty and Miller, Inc.
(Port Washington, New York), OSWAMP, US EPA, Contract No. 68-01-3210,
1976. Draft report.
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VI. OCEAN DISPOSAL
A. DESCRIPTION OF OCEAN ENVIRONMENT
1. Continental Shelf Environment
a. Physical Characterization
Figure VI-1 shows East and Gulf coastal waters, and the relationship
of the coastline to the shelf break and lower limit of the continental
slope.
The continental shelf extends from the shore to the shelf break
which is generally defined by the 200-meter or 100-fathom contour. It
is relatively broad off the Atlantic and the Gulf Coasts (approximately
60 miles wide off the New York and New Jersey coasts where most of the
ocean dumping has taken place). It is characterized by topography of low
relief, and because of its relatively shallow depth, sediments on the
shelf are within the range of influence of storm waves and currents.
Currents on the shelf generally have identifiable to strong tidal
components superimposed on mean current parallel to the shore. The mean
drift may oscillate under influence of the wind. Recent studies by Lavelle,
et al. (1) have shown that sediments in 20 meters of water can be quite
readily transported by winter currents on the shelf. Within two weeks of
injection at a point, radioactive sand could be traced a distance of
200 meters from the injection site. Within six weeks the radioactive
pattern extended approximately 1500 meters.
Water characteristics over the shelf generally reflect the waters'
proximity to land. Effects of rivers with their dose of sediments and
nutrients (and very often contaminants as well) are observed in the water
properties. In the vicinity of river discharges the waters are less
saline than in the open ocean.
The oceanographic environment of the shelf can be characterized as
one where physical processes are active. It is a border area between the
land and the sea, and continuously changes under the influences of physical
forces. Materials introduced into this environment will be subject to
active physical attack. Although they may become seasonally stratified,
the shelf waters are subject to extensive mixing due to natural tidal
and wind-driven forces.
219
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NEW YORK
9
10
WASHINGTON
CHARLESTON
38
JACKSONVILLI
41
100 FATHOMS 1000 FATHOMS
SO -100 150 ZOO
c
SCALE NAUTICAL MILES
ENVIRONMENTAL REPORTER
FEDERAL REGULATIONS
SEC. 227.8 p94-95 AS OF
2-7-75
30°-
28°-
26°
28°
- 26°
24°
24°
82°
76°
68°
66°
64°
62° 60P
FIGURE VI - 1A. ATLANTIC COASTAL WATERS AND DUMP SITES.
220
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80°
ro
r-o
30°
18°
28°
CONTINENTAL
100 FATHOMS 1000 FATHOMS
0 50 IOO 150 ZOO
SCftLE NauTlCfiL MILES
ENVIRONMENTAL REPORTER
FEDERAL REGULATIONS
SEC. 227.8 p94-95 AS OF
2-7-75
96C
94
88°
86°
84°
82°
80°
18°
FIGURE VI - 1B. GULF COASTAL WATERS AND DUMP SITES.
-------
b. Ocean Chemistry
The major constituents of seawater are relatively uniform and well
known. Some of them, notably calcium and sulfate, can also be important
constituents of FGD sludge. Table VI-1 lists seawater constituents
reported to be present in excess of 100 mg/liter.
TABLE VI-1
MAJOR CONSTITUENTS OF SEAWATER
Concentration
Constituent
Chloride
Sodium
Magnesium
Sulfate
Calcium
Potassium
mg/1
18,980
10,561
1,272
884 (as S)
400
380
moles /I
0.548
0.470
0.054
0.028
0.0102
0.0100
Source; Reference (2).
Considerably less definitive information is available concerning
typical concentrations of trace elements in seawater. In particular,
it appears that considerable variation exists in the results of different
analytical efforts to detect heavy metals in seawater. One of the more
recent reviews of the subject concluded, "It is clear that we need to
know much more about concentrations, distributions, speciation, and
toxicity of these elements before final conclusions can be reached about
the hazards they represent to the marine ecosystem" (3).
Table VI-2 lists toxic heavy meatals of importance in marine pollution
based upon their seawater concentrations and concentrations considered by
the National Academy of Sciences (NAS) (4) to pose minimal risk of
deleterious effects.
222
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TABLE VI-2
TOXIC HEAVY METALS OF IMPORTANCE IN MARINE POLLUTION BASED
ON THEIR SEAWATER CONCENTRATION AND TOXICITY
Element
Mercury
Cadmium
Silver
Nickel
Selenium
Lead
Copper
Chromium
Arsenic
Zinc
Manganese
Seawater Concentration
(yg/liter)
A
0.23
0.1
0.3a
7a
0.09a
0.033
3a
0.5
2.6
ioa
2a
B
0.053
0.05
1 0.1
2
0.45
0.033
3a
0.6a
2.3
5
2a
Toxicity
(yg/liter)
C
0.1
0.2
1
2
5
10
10
10
10
20
20
Ratios
A/C
2
0.5
0.3
3.5
0.018
0.003
0.3
0.05
0.26
0.5
0.1
B/C
0.5
0.25
0.1
1
0.09
0.003
0.3
0.06
0.23
0.25
0.1
A: (5)
B: (6)
C: Water quality criteria: concentration considered to pose minimal risk
of deleterious effect (4).
Variations occur; some not related to salinity, depth, or ocean basin.
Source: Reference (3).
Four elements which emerge from such considerations as being of high
potential hazard are mercury, cadmium, nickel, and zinc. The impact
potential of these and other trace metals in the quantities found in FGD
sludges are discussed below.
Trace element levels in unpolluted marine sediments are highly
variable and ranges covering factors greater than 10X appear to be the
rule rather than the exception. These levels are probably somewhat more
reliably known than the corresponding values for seawater. In all cases,
the range of concentrations extends above the levels reported for seawater.
223
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c. Biological Regimes
The dominant aspect of the continental shelf ecosystem Is the high
degree of interrelationship therein. Shelf organisms frequently range
between the upper layers of the water column (i.e., pelagic environments)
and the bottom (benthic areas). Bluefish and mackerel are examples of
such wide-ranging feeders of commercial and recreational importance.
The continental shelf and associated estuaries constitute the majority
of critical habitat for organisms valued by man. With few exceptions
(e.g., pelagic fisheries for tuna and some deep dragging for lobsters)
commercial fisheries' harvests are conducted on the shelf. The constant
interaction among both biotic and abiotic aspects of the shelf ecosystems,
and the importance of these ecosystems to man imply that emphasis be
placed upon the impact potentials of FGD sludge disposal in continental
shelf waters.
d. Effects of Ocean Dumping Activities on the Continental Shelf
The areas used most extensively for ocean dumping on the continental
shelf (e.g., the New York Bight dump sites in Environmental Protection
Agency (EPA) Region II) exhibit conditions representative of significant
deterioration and/or radical alteration from uncontaminated areas. How-
ever, the location of such dump sites in the immediate area of influence
of major independent sources of contamination, such as the Hudson River
estuary in the New York Bight, makes discrimination of ocean dumping
effects extremely difficult. There are exceptions. For example, the
dumping of large volumes of dredged material in the New York Bight over
the last 30 years has caused an elevation in bottom contours near the
dump site of about 30 feet. Recently, EPA administrative hearings on the
future of ocean dumping of Philadelphia's municipal sewage sludge con-
cluded that short-term (about six months) utilization of a new dump site
off the Delaware Bay produced a discernible and unacceptable pattern of
increased heavy metal uptake and concentration in area biota, especially
shellfish. The resultant decision was to continue the implementation of
a near-term phase-out of the city's dumping activity. Recent studies in
the New York Bight have also indicated that there appears to be rather
rapid flux of introduced trace contaminants from the dumped material into
224
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the surrounding environment. Table VI-3 lists approved interim ocean
dumping sites as of February 1975 (shown in Figure VI-1), and indicates
their principal use. Most of these sites are for dredged materials, for
which regulatory responsibility is shared between the Corps of Engineers
and EPA. This list is subject to revision.
Figure VI-2 shows the pathways of ecological interaction in a
simplified continental shelf ocean dumping scenario. It is intended as
a reference point for the text discussions of potential impacts in subse-
quent sections of the report. As illustrated in Figure VI-2, the exten-
sive interface between ocean organisms and man becomes a major factor in
ocean dumping considerations.
2. Deep Ocean Environment
a. Physical Characterization
Deep ocean in this context means beyond the shelf break. Typically,
it would refer to an area either part way down the continental slope or
well beyond. The important differences as compared to the shelf are that
it is a greater distance from land and is deeper. The greater distance
from land is reflected in water properties which often do not receive
the land's influence as directly as the shelf waters. The water off the
shelf is more likely to be directly influenced by major ocean circulation
features such as the Gulf Stream. The greater depth serves to isolate
the bottom from wave forces and contributes to a more quiescent bottom
environment in which sediments are less mobile than on the shelf.
The greater distance from land also has economic ramifications when
transportation systems for sludge disposal operations are considered.
b. Deep Ocean Chemistry
There is some evidence that the deep ocean, particularly off the
Atlantic and Gulf Coast shelves serves as a relatively stable sink for
deposition of various materials. Systematic trends in trace element
concentrations are evident, with concentrations of such elements in deep
sea clays ranging from 2 to 12 times higher than in near-shore sedi-
ments (7). A principal difference between the deep ocean and shelf
environments from a chemical standpoint is that the relative stability
225
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TABLE VI-3
APPROVED INTERIM OCEAN DUMPING SITES, EAST AND GULF COASTS
NUMBER ON MAP
(Fig. VI-1)
to
to
I
2
3
4
5
6
7
B
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
DEPTH (feet)
EPA REGION I
120
100
180
174
108
126
60
312
EPA REGION II
88
103
90
80
200
20
20
20
6.000
6,000
6,000
6,000
EPA REGION III
40
120
150
6,000
38
63
6,600
EPA REGION IV
45
50
28
20
21
29-36
PRIMARY USE
NUMBER ON MAP
(Fig. VI-1)
Dredged Materials
Toxic Waste
Mud
Cellar Dirt
Sewage Sludge
Waste Acid
Wreck Dumping
Sand (Hopper Dredge)
Toxic Chemical Waste
Chemical Waste
H M
Dredged Materials
H M
Conventional Munitions
Sewage Sludge
Neutralized Acid Wastes
Industrial Salt Waste
Arsenic Solutions
Sand
Silt and Sand
Conventional Munitions
Sand and Silt (Hopper Dredge)
ii » »
Mostly Sand and Shell
II M
" II
Sand with some Shell'and Silt
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
DEPTH (feet)
20-36
31
37
33
39
31
41-68
26-57
24
36
11
29
28
32
24
44-48
23-32
23-32
36-42
30-40
40
36-42
36-42
EPA REGION VI
6+
6+
18+
18+
45+
2,400
2,400+
24
30
6
36
30
36
12
Unspecified
PRIMARY USE
Sand with some Shell and
Sand and Silt Silt
Sand, Shell, and Mud
Sand and Shell
Fine Sand
Sand and Shell
Sllty Sand and Shell
Poorly Graded Sand and Silt
Dredged Materials (Hopper
" " Dredge)
Dredged Materials
Chemical Wastes
Dredged Materials
Unspecified
Source; Environmental Reporter; Federal Regulations Sec. 227.8, pp. 94-95, February, 1975.
-------
Terrestrial Consumers
(Birds, Man)
Pelagic Zones \
Benthic Zone
^wvwCwS. ucean
«« Pel
Dun
l
agic
\
\
( ~^ Benthic
1 » 1
Biota ^~
' Biota
•****+***
Surface
Mixing Zone
_ Thermocline
(Seasonal)
............... Bottom
Sediments
FIGURE VI-2 PATHWAYS OF INTERACTIONS IN A SIMPLIFIED
OCEAN DUMPING SCENARIO
227
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of the deep ocean affords little opportunity for materials accumulated in
the deep ocean to be made available to shelf environments,
c. Deep Ocean Biological Regime
The relative physical stability of the deep ocean is reflected in
corresponding stability of deep ocean benthic communities. In general,
far less is known about the ecosystem dynamics of such communities than
their equivalents on the shelf. It appears that deep ocean benthic sys*-
tems are less productive than shelf communities in terms of biomass, but
far more stable and diverse. Community turnover time, that is, the time
required for a stable community to evolve, is seasonal and perhaps involves
a few years on the shelf. Corresponding values are unknown for the deep
ocean, but estimates on the order of 30 years or more have been reported.
Likewise, the sensitivity of the deep ocean communities to various types
of stress is relatively unknown. It is believed that significant ecolog-
ical stress is typically absent from the deep ocean benthos.
In contrast, it is important to remember that the upper layers of the
deep ocean water column, particularly around the shelf margins, experience
variations similar to those of on-shelf waters. In fact, because of
exchanges of water mass in such areas and the mobility of many planktonic
(free-floating) and nektonic (free-swimming) organisms, it is not appro-
priate to separate the pelagic communities of the upper and middle levels
of the water column in the deep ocean and shelf environments. There is,
however, reason to believe that events in the deep ocean benthos have
little opportunity to influence continental shelf ecosystems in the western
Atlantic and Gulf of Mexico, where up-wellings are not a major character-
istic of the environment.
d. Effects of Previous Deep Ocean Dumping Activities
The deep ocean dumping off the Atlantic and Gulf Coasts has been
confined to materials largely unrelated to FGD sludges, making analogies
difficult. Off-shelf dump sites have been used for disposal of potentially
toxic solutions from industrial waste streams. Comprehensive monitoring has
not been performed; and deep ocean benthic communities have experienced
limited exposure potential to date.
228
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3. Introduction to Disposal Options
This assessment emphasizes ocean dumping from vessels as opposed to
outfalls. Outfalls are not considered in depth for several reasons. First,
it is believed that gross ecological impact potentials (i.e., suspended
sediment concentrations) would pose a significant obstacle to outfall dis-
posal in near-shore waters. Second, the construction of outfalls to extend
over the shelf margin is believed economically infeasible on the Atlantic
and Gulf Coasts. Finally, the regulatory situation concerning outfalls is
in a state of flux.
The "baseline" ocean dumping scenario chosen for analysis involves
the use of conventional bottom dump barges on the continental shelf. This
would be the quickest, cheapest, preferred method in the absence of
regulatory constraints. Thus, impacts are discussed below in terms of
this mode of operation. Subsequent discussion focuses on major alternatives
to this mode, including:
• dispersed dumping on the continental shelf;
• conventional dumping off the continental shelf (deep ocean);
• dispersed dumping off the continental shelf; and
• concentrated dumping of treated sludges on the continental shelf.
B. DESCRIPTION OF THE REGULATORY ENVIRONMENT
1. Statutory Base
The Marine Protection Research and Sanctuaries Act of 1972 (PL92-532)
is the basis for all domestic regulation of ocean dumping. Several major
provisions of this legislation are discussed below.
Policy
Section 2(b) of the Act states,
"The Congress declares that it is the policy of the United States
to regulate the dumping of all types of materials into ocean
waters and to prevent or strictly limit the dumping into ocean
waters of any material that would adversely affect human health,
welfare, or amenities, or the marine environment, ecological
systems, or economic potentialities."
Mandatory Considerations in the Issuance of Permits
The Act states that no dumping may take place without a permit from
the Administrator of the EPA. Section 102(a) conditions the issuance
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of such permits upon determination by the Administrator that,
"... such dumping will not unreasonably degrade or endanger human
health, welfare, or amenities, or the marine environment, ecological
systems, or economic potentialities." The specific review criteria
to be used in reaching these determinations are prescribed as follows:
"(A) The need for the proposed dumping.
(B) The effect of such dumping on human health and welfare,
including economic, aesthetic, and recreational values.
(C) The effect of such dumping on fisheries resources, plankton,
fish, shellfish, wildlife, shore lines and beaches.
(D) The effect of such dumping on marine ecosystems, particularly
with respect to -
(i) the transfer, concentration, and dispersion of such
material and its byproducts through biological, physical
and chemical processes,
(ii) potential changes in marine ecosystem diversity,
productivity, and stability, and
(iii) species and community population dynamics.
(E) The persistence and permanence of the effects of the dumping.
(F) The effect of dumping particular volumes and concentrations
of such materials.
(G) Appropriate locations and methods of disposal or recycling,
including land-based alternatives and the probable impact of
requiring use of such alternative locations or methods upon
considerations affecting the public interest.
(H) The effect on alternate uses of oceans, such as scientific
study, fishing, and other living resource exploitation, and
nonliving resource exploitation.
(I) In designating recommended sites, the Administrator shall
utilize wherever feasible locations beyond the edge of the
Continental Shelf."
230
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Penalties
Section 105 of the Act provides for civil penalties of up to $50,000
for each violation of the Act. It further provides for criminal
penalties of not more than one year imprisonment, $50,000 fine, or
both. Both the Government and private citizens are provided the
opportunity to obtain injunctive relief by Section 105 of the Act.
Preemption of Other Jurisdictions
Section 106(d) of the Act precludes state, interstate, or regional
authorities from adopting or enforcing any rules or regulations
relating to ocean dumping. States may propose ocean dumping criteria
to the EPA Administrator who may adopt them if he wishes. Thus,
unlike the regulatory climate surrounding mine disposal alternatives,
ocean disposal of FGD sludges by barge is the direct responsibility
of only one agency, the Federal EPA.
Establishment of Regulations
Section 108 of the Act gives the Administrator the authority to
establish such regulations as he deems appropriate. The existing
and possible future regulations are discussed below.
2. Administrative Regulations
Ocean dumping regulations were first promulgated by the EPA
Administrator in October of 1973 to become 40CFR 220-227. Subsequent
amendments were adopted during 1974. On June 28, 1976 proposed revisions
to the existing regulations were published in the Federal Register.
A number of substantial changes are included in this proposal, and the
existing regulations are discussed below in light of the changes proposed
on June 28.
In general, Sections 220 through 226 of the regulations prescribe
permit procedures to be followed by applicants and regional administrators.
Adjudicatory hearing and enforcement procedures are also discussed. The
sections of most concern with respect to potential ocean dumping of FGD
sludges are parts 227 and pending part 228, which focus on criteria for
the evaluation of permit applications and monitoring requirements.
Relevant highlights of parts 227 and 228 are discussed below.
231
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a. Consideration of Alternatives
The current ocean dumping regulations provide for consideration of
a wide variety of alternative disposal options. The proposed regulations
appear likely to go a major step further, to the extent of precluding
ocean dumping in favor of any feasible alternative. The following factors
will probably be included in determinations of the need for ocean dumping
versus available options:
• degree of available treatment of the waste;
• available raw material and process changes;
• relative environmental impact and cost of ocean dumping and other
alternatives, including but not limited to landfill, well injection,
recycling, additional treatment, and storage; and
• irreversible or irretrievable consequences of the use of alterna-
tives to ocean disposal.
Determinations of the cost feasibility of available alternatives to ocean
disposal would not require that costs be competitive and would take into
account environmental benefits as well.
b. Prohibited Materials
Under the existing regulations, absolute limits have been set
concerning permissible levels in ocean-dumped wastes for mercury and
cadmium, two constituents of importance in many FGD sludges. Existing
mercury limits are 1.5 ppm in the liquid phase of a waste and 0.75 ppm in
the solid phase. Based on available analyses, sludge liquors could be
disposed of, but many of the sludges themselves would exceed this mercury
limit. For cadmium, the existing limit on concentration in the liquid
phase is 3.0 ppm, and 0.6 ppm in the solid phase. Again, eastern coal
sludge liquors would appear to pass this test, but the range of cadmium
in eastern FGD sludges (0.7 to 15 ppm) would in all cases exceed the
existing EPA limit. Thus, unless these regulations are modified, eastern
sludges could be precluded from ocean disposal entirely on the basis of
the cadmium content of the solid phase.
Proposed revisions to the current regulations retain the existing
limits for mercury and cadmiums but there are indications that these may
change.
232
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c. Other Factors Limiting Permissible Concentrations
In addition to the absolute limits on mercury and cadmium, FGD sludges
would have to meet general criteria for dispersion under the existing
regulations. This criteria requires that the concentration of material
in the "mixing zone" (area swept out by the locus of points constantly
100 meters from the perimeter of the conveyance engaged in dumping, and
20 meters deep or less, depending upon the depth to the thermocline,
halocline, or ocean floor) within four hours is not to exceed 0.01 of
a concentration shown to be toxic to appropriate sensitive marine
organisms.
In the proposed regulations, a "release zone" (100-meter locus as
above, but no depth limit) is prescribed, but no formal "mixing zone."
The existing toxicity limits (0.01 and 4 hours) are retained but apply to
all of the marine environment subject to the influence of the dumped
material. The following alternative techniques would be available to
applicants for determining that area within which toxicity limits would
apply:
• combination of field data and prediction by mathematical modeling;
• theoretical turbulent diffusion relationships, applied to known
characteristics of the waste; and
• when no other means are feasible, it may be assumed that the
waste is evenly distributed throughout the release zone to a
depth of 20 meters.
This last option is effectively the same as use of the "mixing zone"
defined in the present regulations. Overall, the proposed revisions would
add considerable flexibility to this aspect of the permit review process.
d. Monitoring Requirements
Currently, in the absence of specific prescribed requirements the
monitoring of various ocean dumping activities is developed somewhat
ad hoc on a. case-by-case basis. It is considered likely that a Section 228
will be added to the existing regulations, prescribing monitoring require-
ments in considerably more detail. These potential requirements are
discussed below in the assessment of technology.
233
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3. Agency Attitudes and Strategies
The following discussion is based on information and impressions
gained from discussions with EPA personnel in The Office of Marine
Protection and The Office of General Counsel in Washington; the EPA
Environmental Research Laboratory in Narragansett, Rhode Island, EPA
Region II; and the EPA Environmental Research Laboratories at Corvallis
and Newport, Oregon. In general, the prevailing attitude towards ocean
dumping is that it is a highly undesirable method of waste disposal. In
some instances, this attitude is further reflected in a desire to phase
out all ocean dumping activities. In all cases, regulators expressed
a strong desire to utilize any available alternatives in preference to
ocean dumping.
At the regional level there seems to be a general tendency to rely
on the administrative means of control provided by ocean dumping regulations.
Technical analyses as required are developed on a case-by-case basis. The
burden of proof on technical matters clearly resides with prospective
applicants for dumping permits. Agency inclinations toward reductions in
ocean dumping have been boosted by a series of recent successes in efforts
to phase out major dumping activities in Regions II and III. In Region II
more than 25 industrial concerns previously disposing of waste at sea have
found economically feasible landside alternatives and ceased ocean dumping.
The EPA Administrator supported earlier agency recommendations to continue
a tight phase-out of the ocean dumping of Philadelphia's municipal sewage
sludge. This latter decision was characterized by agency personnel as
a potential turning point. Some states, such as Maryland, have also taken
action. In December 1975 the State of Maryland sued the EPA in an attempt
to curtail the ocean dumping of raw sewage sludge by the City of Camden,
New Jersey. In summary, the present trend is decidedly against the
encouragement of ocean disposal.
In addition to the general trend towards phase-out of dumping, there
has been a particular lack of encouragement to deep ocean disposal.
In spite of the high priority given this type of disposal in the enabling
legislation and regulations, the magnitude of deep ocean monitoring
requirements, independent of other major cost factors, has indirectly
discouraged potential deep ocean dumping permit applicants. Cost estimates
for this type of monitoring activity range on the order of $1,000,000 per
year per applicant.
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C. FATE AND EFFECTS OF FGD SLUDGES ON THE CONTINENTAL SHELF
1. Disposal by Bottom-Dump Barge
As discussed in Chapter IV, work on sludge characterization has
progressed to a point where the range of gross physical properties of the
material (i.e., particle size distribution and density) has been determined.
Some insight into the physical behavior of sludge after its introduction
into a water environment has been gained, and areas where fruitful
research could be accomplished have been identified. The major unanswered
question which is critical to assessing the fate of sludges in the marine
environment relates to their solubility in seawater.
If they are relatively insoluble, then there is the potential for
considerably increasing the turbidity in a large region around the dump
site. The small particle size assures that the material will stay in
suspension for a long time if dispersed dumping takes place. The
Massachusetts Institute of Technology (MIT) did related model studies
on material in the vicinity of Boston outer harbor and Massachusetts
Bay (8). The studies showed that suspended sediments with sinking rates
similar to sludge would be transported for 45 miles or more. This may
be typical of the distribution of sludge particles if dumped on the shelf
and if they are relatively insoluble.
If FGD sludges are highly soluble in seawater, then dispersed dumping
could lead to conditions where dissolution takes place before the particles
reach the bottom, and any increase in ocean turbidity would be strictly
temporary. Under these conditions the time frame of interest for assessing
chemical and biological effects would be considerably shorter than for
less soluble material.
a. Physical Transport
The effects of different transport processes on sludge disposal
depend to a large extent on the form and properties of the material.
In the most generalized terms, material dumped into the ocean will
go through one or more of the following phases: 1) convective descent,
2) collapse, and 3) long-term spreading. These phases are illustrated
in Figure VI-3.
235
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N>
CO
Barge —
Sludge -
Loaded, Dumping, barge
underway in hinge-open
position
Convective
Empty, underway
Collapse phase
Long-term spreading phase
FIGURE VI-3 SCHEMATIC DIAGRAM SHOWING TRANSPORT PROCESSES -
HINGED BOTTOM-DUMP BARGE
-------
Convective descent is characterized by waste falling through the
water under the influence of gravity and the momentum associated with its
release. Initial mixing with and entrainment of ambient water occurs
during the descent. This phase ends and the collapse phase begins either
when the dumped material hits the bottom or reaches water of equal or
greater density. At this point the waste material cloud collapses into a
relatively thin layer (either on the bottom or at an intermediate depth) ,
and the long-term spreading and redistribution forces of erosion and
turbulent diffusion predominate.
If the material is solid, impermeable, and insoluble, the collapse
and long-term spreading phases may be insignificant and the principal
transport phenomenon will be rapid vertical descent. If the material is
highly liquid and has a density near that of the receiving water, then
all three phases may be significant in terms of physical transport.
Experiments using dredged material of various consistencies have
demonstrated these phenomena and it is considered likely that a similarity
in behavior will be noted between dredged material and FGD sludge. The
following paragraphs further expand these concepts by focusing on three
likely physical forms of the sludge.
Treated, Brick-Like Sludge
If the sludge is treated, resulting in a brick- or rock-like form, the
sinking rate will be rapid and horizontal displacements from the release
point due to ocean currents will be small, both during descent and after
the material reaches the bottom. Water quality will be affected only to
the extent that leaching of contaminants from the rock-like material takes
place. Although the specific leaching rates of any material proposed for
ocean disposal should be determined prior to the issuing of a dump permit,
preliminary calculations based on available data indicate that leaching
from rock-like fixed sludge in place on the ocean floor will not be environ-
mentally significant. Dilution on the order of 1:1012 is indicated,
assuming a bottom current of 15 cm/second, dilution into the bottom one
meter of water, and a permeability of 10~6 cm/second.
237
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Dewatered, Untreated Sludge
At some solids content (perhaps on the order of 50% for some materials)
the material tends to hang together and fall through the water as a cohesive
mass. Little quantitative information is available about this phenomena,
but it is believed that under such conditions there is very little
opportunity for release of included liquor from the main mass of sludge.
As the body of waste falls through the water at relatively high speeds,
some surface wasting occurs due to turbulent erosion. However, simple
laboratory experiments and preliminary modeling results indicate that more
than 95% of the dumped material would reach the bottom intact after rapid
descent and remain as a heap on the bottom. Continuous utilization of the
same site would result in the accumulation of significant amounts of dumped
material. A heavily used mud dump site in New York Bight has measurably
affected the bottom topography over an area of more than ten square
nautical miles.
The FGD sludge which reaches the bottom would be subjected to the
eroslonal forces of bottom currents at the depositional site. The grain
size of the material in typical sludges is such that one might expect that
unidirectional mean bottom current velocities in excess of 25 cm/second
would be required to sustain erosion. However, oscillatory, rather than
unidirectional currents prevail on the shelf, along with periodic wave
distubances of large magnitude. All of these factors, combined with the
apparent wide range of cohesiveness (and lack of coheslveness) among
different sludges, leave considerable uncertainty about the potential for
sludge erosion and redistribution along the sea bed.
If 5% of the cohesive, untreated sludge is released into the water
column as the main mass descends 200 meters to the bottom, then an Initial
(nearly instantaneous) volume dilution in the range of 1:500 to 1:2,500
is achieved for the released material. This material will be transported
from the dump site by ambient currents.
Slurry-Dispersed Sludge
The Important transport processes for diluted and dispersed sludge
are turbulent mixing and the mean currents. Sludge which has been
considerably diluted or which simply has a low solids content will very
likely disperse widely and sink slowly.
238
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Theoretical models exist for prediction of concentration versus time
and space. However, the assumptions relative to the magnitude of dispersion
coefficients used, and ambient density and velocity fields are critical.
The range of initial dispersion which may be achieved covers several orders
of magnitude. In general, if density stratification exists at the dump
site, it is possible that sludge particles could be trapped above the
thermocline and transported long distances before either dissolving or
settling out.
Empirical data presented in Callaway, et al. (9) show that depth
penetration of low density sewage sludge to the thermocline (11.5 meters)
was achieved in less than 16 minutes after a quasi-instantaneous (6 minutes)
release of 2,380 cubic meters from a stationary barge. The highest
concentration after 16 minutes was observed at the surface and at a depth
of 6 meters, and a dilution of 1:640 within 16 minutes was implied. If
the barge had been moving at a typical 6 knots speed during the dump, it
would have traveled 3,650 feet or some 15 barge lengths and would have
increased both the turbulent mixing energy available and the volume of
the receiving water above the thermocline. It is reasonable to assume
that under such conditions a volume dilution of 1:9,600 would be achieved
within 15 minutes. In the absence of a thermocline the depth of penetration
would likely have been greater than observed.
FGD sludge differs from sewage sludge in two important respects. It
is more dense than seawater and has a higher solids content. The higher
density would tend to minimize the depth-limiting effect of any thermocline
on mixing volume. If dispersion is desired in a bottom dump, special
measures (e.g., stirring) may be required to assure particle suspension
in the sludge because of its high solids content. Within very few minutes
slurry-dispersed FGD sludge would be expected to be distributed throughout
the available water column. This would of course add considerably to the
mixing volume available in Callaway's case. An order of magnitude increase
in the 15-minute dilution rate would be expected in waters 350-feet deep
(i.e., 1:6,400 dilution for the stationary barge and 1:96,000 for the
barge moving at 6 knots).
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b^. Environmental Impact Potential
Four principal categories of potential impacts for FGD sludge
disposal in the ocean environment are discussed below. These are:
• impacts of benthic sedimentation;
• impacts of sludge suspended in the water column;
• impacts of sulfite-rich sludge; and
• trace contaminant impacts.
The chosen order of presentation does not necessarily reflect the
relative significance of these several impact potentials.
Impacts of Benthic Sedimentation
In general, it is expected that disposal of FGD sludges on the
continental shelf by bottom-dump barges would result in physical distribu-
tion of sludge in the benthic environment not unlike that experienced in
conjunction with dredge spoil disposal. This would mean that the benthic
environment in the vicinity of dump sites would be characterized by sub-
strate substantially or entirely composed of sludge. Such conditions
would have serious impact potential. Benthic ecologists generally regard
the coarse-grained substrate (e.g., coarse sand) as most conducive to the
establishment of rich, diverse marine benthic tnacrofaunal assemblages.
Sediments of finer composition, especially if relatively uniform and uncom-
pacted, provide the least stable and most limiting type of habitat (personal
communication, Dr. Dale Calder, South Carolina Division of Marine
Resources, 1975.) Field observations of a shallow bay which received an
indeterminate amount of inadvertent overflow of FGD sludge tended to
provide strong confirmation of the liability of sludge as a benthic
substrate, although quantitative sampling was not initiated. It was
apparent that the benthic macrofloral and macrofaunal communities in areas
seemingly comprised largely of sludge were impoverished compared to other-
wise similar control locations.
In areas of disposal of marine dredge materials the resultant benthic
faunal assemblages have generally developed along recognizable patterns
corresponding to sediment type. Where deposited dredged materials have
been of a relatively fine, silty-clay nature and the ambient environment
has been coarse sand, limited communities dominated by polychaete worms
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and certain pelecypod mollusks have become established on the dredge
spoil areas. Different, often more diverse, communities exist on adjacent
substrate. This type, and perhaps more severe limitations, would also be
expected in FGD sludge disposal areas.
In addition to the physical character of the sludge, its relative
lack of nutrient content may serve as a further limitation upon benthic
faunal community establishment. The extent of this impact potential would
be influenced by the availability of nutrients fluxed into the disposal
site area from other sources, including estuarine detrital export and
deposition from the upper portions of the overlying water column. Thus,
although the lack of nutrients in sludge could prove to be a limiting
factor, it is believed of secondary importance to the physical unsuitability
of the material as a faunal substrate.
Impacts of Sludge Suspended in the Water Column
Elevated levels of suspended sediment have a number of well-documented
effects on marine organisms under laboratory conditions. Considerable
uncertainty is added to analysis of these impacts under field conditions
because of the large variance in duration of organism exposure. In
particular, it is extremely difficult to determine whether free-swimming
nekton (such as finfish) would choose to avoid elevated concentrations of
suspended sediment or would be attracted to such concentrations by the
expected availabilty of food. The latter effect has been observed numerous
times in the field, particularly among marine finfish. However, the
observations related to suspension of natural benthic sediments which
contain food organisms, rather than inorganic waste sediments dumped from
a barge.
Receptor sensitivity is a second major variable. In general, the
available information shows that relatively inactive species characteristic
of the lower levels of the water column (such as flounders) have extra-
ordinary resistance to lethal effects of suspended sediments. These
species (as adults) compensate for potential clogging and mechanical
damage to gills by such techniques as through-gut transport of sediments ,
and would in all likelihood survive the maximum levels of suspended
sediment generated by ocean dumping (10).
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Many of the dominant finfish of the continental shelf dump sites may
be expected to exhibit intermediate sensitivity to suspended sediments.
In quantitative terms this sensitivity may be defined as experiencing
10% mortality during 24-hour exposure to suspended sediment concentrations
between 1,000 and 10,000 mg/liter. Such concentrations would be expected
upon initial dilution throughout the dump site water column, but duration
of organism exposure is expected to be brief in the upper and meso-pelagic
zones. Species of importance in this category include striped bass
(Morone saxatilis), croaker (Micropogon undulatus), bay anchovy (Anchoa
mitchelli), and weakfish (Cynoscion regalis) (10).
In general, the free-swimming estuarine organisms most sensitive to
suspended sediments are sub-adult or younger forms. It is reasonable to
expect the same in marine waters. Forms which have been shown to experience
10% mortality during 24 hours exposure to sediment concentrations less than
900 mg/liter include juvenile bluefish (Pomatomus saltatrix) and adult
silversides (Menidia menidia). Juvenile menhaden (Brevoortia sp.), a
commercially valued species, falls somewhere between this and the preceding
category in sensitivity (10).
In addition to the potential for mortality to commercially or
recreationally valued organisms associated with prolonged exposure to
elevated concentrations of suspended sediments, a variety of adverse
sub-lethal impact potentials exist at these and lesser exposure values.
Many of these sub-lethal effects may be classified as examples of reduced
ecological efficiency. The hogchoker (Trinectes maculatus), a flounder
seemingly insensitive to extended exposure to sediment concentrations in
excess of 100,000 mg/liter, nevertheless was shown to expend significantly
more energy at concentrations of 1,240 mg/liter than under control
conditions (10). Eighty to ninety percent reductions in carbon uptake
by low-salinity estuarine phytoplankton occurred over the course of one
hour's exposure to suspended sediment concentrations between 1,000-2,250 mg/
liter, and 100-150 mg/liter produced reductions on the order of 15-50% (10).
Acartia tonsa, a calanoid copepod typical of seasonally dominant zooplankton
of dump site areas, exhibited reductions in feeding efficiency (measured as
carbon uptake) of 20-100% when exposed for short (5-10 minute) and somewhat
longer (125-minute) periods to suspended, sediment concentrations of
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50-1,000 ing/liter. A somewhat nonselective feeder, this copepod apparently
eats a lot of "junk" instead of its normal food when in the presence of
elevated concentrations of suspended sediment (10).
A third major variable affecting the magnitude of suspended sediment
impacts is the type of sediment involved. All available data indicates
that the finer particles (in the silt/clay and finer range) have greater
impact (than coarser particles) by each of the mechanisms discussed above
(11). Untreated FGD sludge would be in this silt/clay range. The extent
to which other contaminants (including sulfite and heavy metal residues)
are part of the dumped sludge is another important aspect of impact
potential. Through their use of such compensatory mechanisms as through-
gut transport, fish and other organisms pass varying concentrations of
suspended sediment into their digestive tracts. While the extent to which
this occurs may vary with time of exposure, concentrations of previously
suspended sediment in the stomachs of estuarine fishes in the range of
2,000 mg/liter have been recorded (10). Once within the stomach of a fish,
particles are exposed to acidic conditions (pH of 1 or 2) capable of
stripping adsorbed contaminants and making those contaminants available
for damage or concentration within the organism or elsewhere in the food
web (11). Thus, certain major contaminant impact potentials may be
relatively independent of the extent to which water column concentrations
of sulfite or trace metals might be increased by dumping activities. These
types of impacts could be important over the long term at dump sites to
such benthic finfish as cod and flounder, whose feeding habits involve
sediment suspension and ingestion.
Impacts of Sulfite-Rich Sludge
The impact of the introduction of sulfite into the ocean environment
as consequence of FGD sludge disposal is of interest for two reasons.
First, sulfite has a measurable toxicity; and second, it will react with
dissolved oxygen, leading to a depletion of dissolved oxygen (DO). Sulfite
is present in FGD sludges both as soluble sulfite salts in the interstitial
liquid and as solid calcium sulfite. Soluble sulfite concentrations in
the interstitial liquid can range from about 4 x 10~2 M (about 3,000 ppm)
in washed dual alkali filter cakes down to about 1 x 10~3 M (less than
100 ppm) in sludges from direct slurry scrubbing systems. If one were
to dispose of FGD sludges in a manner that insured an instantaneous
243
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dilution by a factor of 101*, the soluble sulfite component would be
diluted to a concentration in the range of A x 10~6 to 1 x 10~7 M. At
those concentrations there should be little or no impact from that component.
A more important consideration is the possible impact of sulfite
present as the insoluble calcium salt. If one considers a one-liter sample
of a typical FGD sludge containing 50 weight % solids, it will contain
about 765 grams of solids. Assuming that all of the solid materials
are CaSO$ - 1/2 H20 (MW = 129.2), a liter of sludge will contain
about 5.9 gram moles of sulfite as calcium sulfite. If the sludge is
diluted by a factor of 500 in the course of being dumped, a total sulfite
concentration of about 0.012 M will result. That concentration is in the
range where there could be impacts from sulfite itself or from reductions
in dissolved oxygen which would accompany any sulfite oxidation which
occurred.
If it is further assumed that the uptake of sulfite-rich suspended
particles by fish in the water column is about the same as observed using
other sediments in laboratory studies, the resultant concentration of
sulfite in the stomach of disposal area fish might be on the order of
0.006 M. This concentration is roughly six times the median 50% lethal
concentration for fish at pH 6 (0.001 M) observed under laboratory
conditions (11). Sulfite toxicity has been demonstrated to be pH dependent,
increasing with decreasing pH. Thus, a concentration of 0.006 M sulfite
in the stomach of finfish, where pH levels would be 1 or 2, may have
serious impacts compared to those reported from previous studies at pH 6.
However, more data needs to be obtained concerning organism uptake of
suspended particles of FGD sludge during the short-term exposures that
would be characteristic of ocean dumping conditions before the real impact
potential of sulfite-rich sludges regarding toxicity can be accurately
quantified.
The solubility of calcium sulfite depends on the ionic strength of
the solution in which it is to be dissolved. Seawater has an ionic
strength, u, of about 0.7. At that ionic strength the apparent solubility
product of CaSOa • 1/2 H20, "K ," has been calculated to be about 8 x 10~6.
Since the apparent solubility product is equal to the product of the
244
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concentrations of calcium and sulfite in solution, a solution of seawater
saturated in calcium sulfite should be about 8 x 10"1* M in sulfite (the
calcium concentration in seawater is approximately 0.01 M). That concentra-
tion is about 50% greater than the total amount of sulfite which would
actually be present if FGD sludge were diluted by a factor of I0k upon
disposal. Thus, in the absence of oxidation one would predict that at
equilibrium all of the sludge would dissolve and a concentration of about
6 x 10"1* M sulfite would be present.
However, even at concentrations less than 10~3 M, sulfite will react
rather rapidly with any dissolved oxygen in the solution (12). The oxida-
tion of sulfite by dissolved oxygen is a very complicated chain reaction
which is catalyzed both positively and negatively by other chemical species
present in the solution—many catalysts are effective at parts per million
levels. Cations like copper and cobalt accelerate the oxidation reaction,
while organic substances tend to inhibit it. Thus, an accurate estimate
of the rate at which sulfite would be oxidized by dissolved oxygen in
seawater is difficult unless one conducts laboratory measurements utilizing
actual samples of the seawater in question. However, Rand and Gale (13)
have studied the uncatalyzed reaction at concentrations of sulfite and
dissolved oxygen similar to those of interest here. They studied the
depletion of dissolved oxygen from a solution which initially contained
7.7 mg/liter DO; dissolved oxygen levels in the upper water column in the
ocean tend to be in the range of 7-10 mg/liter. Into that oxygenated
solution they introduced sodium sulfite to produce an initial concentration
of 9 x I0~k M which is within a factor of two of the 6 x I0~k M sulfite
concentrations which would be present after a 101* dilution of FGD sludge.
The data from one typical run, illustrated in Figure VI-4, show the
concentration of dissolved oxygen after slightly over one minute of
reaction.
Thus, if the FGD sludge solids would dissolve instantaneously upon
being diluted and dumped and if the oxidation in real seawater would
proceed as rapidly as the above uncatalyzed experiment proceeded, one
would expect to find severe reductions in dissolved oxygen in the vicinity
of the dump. Oxygen depletion would probably be a more severe impact than
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0
0.2 0.4
0.6 0.8 1.0 1.2 1.4
Reaction Time (Minutes)
1.6
Source: Reference (12).
FIGURE VI-4 OBSERVED SULFITE OXIDATION RATES
2.0
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the residual sulfite because, as the data above indicate, the total sulfite
concentration was reduced by 4 x lO"1* M in conjunction with the reduction
of DO from 7.7 mg/liter to 0.8 mg/liter. Thus, the 6 x 10"1* M sulfite
concentration present in a volume of diluted FGD sludge should be reduced
to approximately 1.5 x 10"^ M by oxidation.
The above discussion presupposes that the dissolution of FGD sludge
solids is instantaneous. Calcium sulfite is very insoluble and it is
unlikely that complete dissolution would occur in one or a few minutes.
We are not aware of detailed studies of calcium dissolution rates at such
low concentrations of calcium sulfite in seawater; however, we have made
qualitative observations in the laboratory in which 10 mg of FGD sludge was
suspended in 100 ml of 0.6 M NaCl. Only after 10 minutes of stirring was
there a discernable decrease in the amount of suspended solids. More than
30 minutes was required for essentially complete dissolution. Thus, it is
likely that solids dissolution rather than oxidation would be the limiting
step in the dissolution/oxidation sequence. If dissolution is very slow,
the impact that will need to be considered is that of the presence of about
6 x 10"1* M calcium sulfite in solid form and the accompanying impact of the
presence of about 76 ppm of suspended solids which is equivalent to that
concentration of solid calcium sulfite.
Trace Contaminant Impacts
As noted above, proposed EPA regulatory requirements could preclude
the disposal of FGD sludges at sea based solely on the reported range of
cadmium concentrations in the solid phase of sampled sludge. In spite of
the prescribed limits on mercury and cadmium, a thorough investigation
of the impact potentials of these and other sludge-related trace contaminants
was conducted. The principal base for the discussion below comes from the
extensive review and development of recommendations for water quality
criteria adequate to safeguard all marine and estuarine aquatic life per-
formed by a special team under the auspices of the NAS in 1972. The results
of this effort were published by the EPA as part of its comprehensive
recommendations for water quality criteria (4). However, these, too, are
being revised. To supplement this information, a retrieval and analysis
of recent scientific literature on selected contaminants (mercury, cadmium,
and selenium) was undertaken. The results of this effort provided no basis
for revising (either upward or downward) the minimum 'risk thresholds
identified by the NAS team.
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The problems created by trace contaminants in marine systems are
extraordinarily complex. In addition to the traditional considerations
of direct toxicity, potentials for biological accumulation and magnification
of trace contaminants to levels hazardous to consumer organisms in the food
web have been receiving increasing attention. Recent research has also
uncovered an increasing body of knowledge on the complex series of syner-
gistic and antagonistic relationships among the various trace contaminants,
which can become controlling factors of toxicity. Perhaps the single
greatest problem in evaluating the trace contaminant impacts potential of
FGD sludge in the ocean is the lack of definitive empirical data concerning
the short-term and ultimate availability of trace contaminants in the
solid fraction of the material. In particular, critical information is
lacking on sludge dissolution rates, ionic speciation, and typical uptake
and concentration patterns of marine organisms exposed to both dissolved
and solid fractions of sludge trace contaminants.
Liquid Phase Trace Contaminants. If, as anticipated, initial dilution
by a factor of about 500 is achieved upon disposal at sea and the limited
available data reflects "worst case" ranges of trace contaminants in sludge
liquor, the resultant release of most trace contaminants into the marine
environments from sludge liquor would be expected to pose minimal risk to
marine life. Table VI-4 shows the range and median concentrations of
twelve trace contaminants of interest in FGD sludge liquors derived from
the burning of eastern coal, as compared to the criteria considered by
NAS to pose minimal risk to the marine environment. It is important to
note that the high values represent sludges containing fly ash believed
to be a reservoir for heavy metals in sludge.
Based upon the concentrations reported in Table VI-4, the anticipated
initial dilution of sludge liquor by a factor of 500 could result in
concentrations of five trace metals approaching or in excess of the
"minimum risk" levels recommended by NAS. In decreasing order of apparent
impact potential, these metals are: mercury, zinc, selenium, cadmium, and
nickel. Four of these five (excepting selenium) correspond to four of the
five toxic elements of principal concern identified by Ketchum et al. (3).
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TABLE VI-4
TRACE CONTAMINANT CONCENTRATIONS IN REPORTED SLUDGE LIQUORS FROM
EASTERN COALS AND NAS MINIMAL RISK CRITERIA FOR THE
MARINE ENVIRONMENT
Antimony
Arsenic
Cadmium
Chromium
Copper
Fluoride
Iron
Lead
Mercury
Nickel
Selenium
Zinc
NAS Minimal Risk
Criteria (ppm)
0.2*
Q.01
0.0002
o.oib
0.01
0.50
0.05
0.01
o.oooia
0.002
0.005
0.02
Median Range
in Liquor^ (ppm) in Liquorc (ppm)
1.2
0.020
0.023
0.020
0.015
3.2
0.026
0.12
0.001
0.13
0.11
0.046
0.46-1.6
<0.004-1.8
0.004-0.1
0.001-0.5
<0.002-0.4
1.4-70
0.02-0.1
0.002-0.55
0.0009-0.07
0.03-0.91
<0.005-2.7
0.01-27
Concentrations considered to pose hazard; minimal risk levels not
recommended.
Concentration recommended for oyster-producing areas.
Results of 4 to 15 observations (see Table IV-3).
Source: Reference (4).
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A 500-fold dilution of the maximum reported concentration of mercury
in sludge liquor would result in a concentration of 0.0014 ppm. This would
exceed the 0.0001 ppm threshold identified as a hazard to the marine
environment. Mercury can be biologically concentrated several thousand
times and has been implicated as a toxic agent in both acute and long-term
pollution episodes.
The anticipated initial dilution of zinc would result in a water
column concentration of 0.054 ppm, which would exceed the minimum risk
threshold of 0.02 ppm. However, it would be below the hazard threshold
of 0.1 ppm. Another potentially troublesome aspect of zinc levels in FGD
sludge is the tendency of zinc to interact synergistically with cadmium
and copper, thereby increasing the toxic potential of all three elements (4)
Initial dilution of the maximum reported concentration of selenium
in FGD sludge would result in water column concentrations of 0.0054 ppm.
This concentration would slightly exceed the minimum risk criteria of
0.005 ppm. Unlike zinc, selenium appears to have a tendency to act
antagonistically with mercury and cadmium to reduce their toxicities.
However, it also appears that the mechanism of interaction might be
conducive to long-term retention of the otherwise toxic mercury and cadmium
within an organism. This could create further opportunities for higher
levels of food web contamination than might otherwise occur if traditional
toxicity mechanisms were operative. In general, the impact potential of
selenium in marine systems is poorly understood.
Initial dilution of the maximum reported concentrations of cadmium
and nickel in sludge liquors would be expected to result in water column
levels roughly equivalent to the NAS minimal risk criteria. The extent
to which these concentrations might present a problem in the disposal area
environment would in part depend upon the background concentrations of
these and other elements which could react synergistically with the
incrementally added waste. Such factors are highly variable and would
need to be evaluated on a case-by-case basis. The resultant concentrations
of the other seven trace contaminants considered in Table VI-4 would be
expected to present minimal risk to the marine environment. The extent to
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which typical rather than worst case sludges would present differing risks
in trace contaminant impact potential is discussed below in conjunction
with control options.
Solid Phase Trace Contaminants. The reported range of trace
contaminant levels in FGD sludge solids encompasses considerably higher
concentrations than found in the sample sludge liquors. Table VI-5 shows
these concentrations in comparison to the NAS recommended minimal risk
criteria for nine trace elements in sludge solids. As in the case of sulfite,
the impact potential of trace contaminants bound or adsorbed to solid fractions
of the sludge will be dependent upon critical variables such as dissolution
rate and particle uptake by free-swimming organisms. Too little is known
of these types of interactions over the short-term to allow for a feasible
prediction of quantitative impacts.
Trace Contaminants in Organically-Enriched Environments. A special
set of impact potentials may be associated with the deposition of FGD
sludges in organically-enriched enviroments, such as the sewage sludge and
dredge spoil dump sites in the New York Bight. Recent evidence indicates
that heavy metal contamination of the Bight and other dump sites is avail-
able to and being fluxed into local biotic populations. It is believed
that the introduction of organic wastes in these areas provides a means of
concentrating halogenated hydrocarbons (including pesticides) and heavy
metals (as organic-metallic complexes) in lipid tissues of local organisms.
While the heavy metal concentrations in FGD sludge are typically much less
than those in the contaminated dredge spoil and sewer sludge, the overall
effect of dumping these materials into a common area would be to increase
the total amount of toxic metals available for complexing and incorporation
into the food web. On the other hand, burying dredge spoil and sewer
sludge with FGD sludge might dilute the amount of available metals in the
surficial sediment in grossly contaminated areas. Overall, this strategy
appears to have substantial liabilities and would require thorough investi-
gation prior to implementation.
2. Environmental Impact of Applicable Control Options
a. Restricting Types of Sludge Disposed of on the Continental Shelf
Assuming that the sludge to be disposed of is untreated prior to
disposal and therefore remains in the same consistency and particle size
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TABLE VI-5
CONCENTRATIONS OF TRACE ELEMENTS IN SLUDGE SOLIDS
AND "MINIMAL RISK CRITERIA"
NAS Minimal
Risk Criteria (ppm)
Median
in Sludge0 (ppm)
Range
in Sludge0 (ppm)
Arsenic
Cadmium
Chromium
Copper
Lead
Mercury
Nickel
Selenium
Zinc
0.01
0.0002
o.oia
0.01
0.01
o.oooib
0.002
0.005
0.02
33
4.0
16
14
14
1
17
7
57
3.4-63
0.7-350
3.5-34
1.5-47
1.0-55
0.02-6.0
6.7-27
0.2-19
9.8-118
Concentration recommended for oyster-producing areas.
Concentration considered to pose hazard; minimal risk levels not
recommended.
°Results of 5 to 9 observations (see Table IV-2).
Source; Reference (4).
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range, the restriction of sludge type could significantly impact two of
the four principal impact potentials discussed above. The impacts of
benthic sedimentation, as discussed above, would not be affected to any
significant degree by restricting types of untreated sludges disposed of
on the continental shelf by bottom dump-barges. Likewise, the impacts of
suspended sludge in the water column would not be affected from the gross
standpoint of organisms' sensitivity to sediments in general. However,
two subsets of the suspended sediment impacts, the impacts of sulfite and
associated trace contaminants, could be significantly mitigated by restrict-
ing the types of sludges disposed of at sea. As noted above, the range of
trace contaminant concentrations in sludges from eastern coals is such that
in a few instances (i.e., where fly ash is present) even the lowest values
in that range would still present disposal problems under existing EPA
criteria. Likewise, preempting disposal of sulfite-rich sludges might
foreclose ocean disposal as an option for a significant percentage of
potential applicants in East Coast locations. Nonetheless, disposing of
only sulfate-based sludges with trace contaminant concentrations at or below
the median values thus far reported would substantially mitigate the sulfite
and trace contaminant impact potentials discussed above.
b. Disposal by Dispersion
If FGD sludge slurries were pumped overboard in a manner sufficient
to achieve instantaneous dilution on the order of 5,000 to 10,000, three
of the four impact potentials discussed above would be substantially
mitigated. The impacts of benthic sedimentation and of suspended sludge
in the water column could be mitigated by dispersion. There would be
a trade-off in trace contaminant impacts. Such contaminants would be
given wider distribution by dispersion, but the local concentrations
associated with dispersed disposal would bring all trace contaminant levels
into the range of minimal risk criteria. Sulfite impacts would remain of
potential significance in the dispersed disposal option. As noted above,
the assumption of initial dilution on the order of 101* would still result
in potential problems of sulfite oxygen demand. The potential toxicity
of concentrations on the order of 0.00012 M is still substantial, since
this is roughly equivalent to the reported median lethal concentration
at pH 6.
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c. Concentrated Bottom Disposal
For purposes of this discussion, concentrated bottom disposal is
presumed to include chemical treatment of FGD sludge resulting in a cement-
or brick-like waste product. It appears that all four of the principal
impact potentials discussed above (sedimentation, suspension, sulfite, and
trace contaminants) would be substantially mitigated by this control option.
Not only would the problem of benthic sedimentation be avoided, but the
presence of brick-like chunks on the ocean floor could serve as the basis
for creation of attractive new marine benthic habitat. Of course, over-
riding this and all other considerations of this control option is the
question of dissolution. If the lifetime of the material in concentrated
form is relatively brief, two of the advantages of this option would be
removed. The trace contaminants within the treated sludge would become
available upon dissolution and still might be problematic. In fact, they
might be more so over the long term with this option because of the lack
of initial dilution. If dissolution also results in loss of structural
integrity prior to total dissolution, the opportunity for some benthic
sedimentation impacts may be present, dependent upon the frequency and
strength of mechanisms of benthic disturbance, such as storm waves.
Provided that questions concerning the dissolution of concentrated, treated
sludge can be resolved, this option appears to offer considerable promise.
d. Chemical Treatment of Sludge
With the exception of the above mentioned option of concentrated
disposal of brick-like treated material, chemical treatment appears to
offer few, if any, advantages over the traditional bottom-dump disposal
of untreated FGD sludge. The sulfite impacts discussed above might be
mitigated to considerable degree by chemical treatment, but the impacts of
benthic sedimentation and suspended sludge in the water column would be
comparable to those associated with typical untreated material. Trace
contaminant impact potential could be equal to or possibly greater with
chemically-treated sludge than with untreated material. This is principally
because it appears that trace contaminants may be added by certain treatment
processes, such as through the addition of ash. In counterbalance the rate
of availability of trace contaminants could be slowed somewhat by chemical
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treatment. Overall, chemical treatment, other than that which would result
in a brick-like material, appears to offer little promise as an ocean
disposal control option.
D. FATE AND EFFECT OF FGD SLUDGES IN THE DEEP OCEAN
1. Disposal by Bottom-Dump Barge
a. Physical Transport
The same principles of physical transport on the continental shelf
apply to the deep ocean environment, with some modifications due to
increased water depth. There are two main factors which differentiate
these two segments of the ocean environment. One is the relative isolation
and quiescence of the deeper parts of the ocean compared to the continental
shelf. Storm effects which readily stir the continental shelf sediments
may not be in evidence at all off the shelf.
The other factor relates to the greater distance dumped material falls
through the water column. More water is available for dilution, and more
time is available for dissolution. It is not known whether FGD sludge
would dissolve before it reached the bottom in the deep ocean.
No off-shelf dump site has been used for disposal of sludge-like
materials in circumstances that would permit measurement of material
accumulation. Validated models which could predict sludge accumulation
do not exist, and the models which do exist generally are data limited in
that unverified estimates of many input parameters must be used to make
the models function. In this situation it is useful to examine long-term
shallow water (on-shelf) dump sites and to make reasonable extrapolation
to deep water. In this way, at least some insight might be gained as to
the area of the bottom which could be expected to experience sludge
accumulation. (See Figure VI-5.)
The mud dump site in New York Bight has been studied by comparing
present-day bathymetry with that existing prior to the period when dumping
commenced. The water was originally 90 feet deep. In the 33 years since
dumping started, sediments have accumulated to a maximum depth of 30 feet.
In excess of five feet of mud has accumulated over an area 3.2 nautical
miles (nmi) across. Isopach mapping indicates that the major accumulation
has occurred within 1.8 nmi of the designated dump site (two square miles).
It is likely that more than 10 square nautical miles of bottom have been
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D|\is =1 — 1.2 nmi
90 Feet
= 2-3nmi
Dj = 0.25 - 0.37 nmi
Mud Dump Site on Continental
Shelf
1000 Feet
DL = 0.2-0.1
D = 4.1 nmi
Hypothetical Site, Off-Shelf
Notation: Dj = Initial displacement during disposal process
DNS = Displacement due to navigation errors and short dumps
D|_ = Displacement due to long-term bottom transport processes
FIGURE VI-5 FACTORS CONTRIBUTING TO THE CUMULATIVE
DISTRIBUTION OF DUMPED SLUDGE
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covered. Thus, cumulative distribution includes contributions from
navigational errors, short dumps, transport processes, and dispersion
during disposal and bottom transport after disposal, all averaged over the
33 years of dumping at the site.
Short dumps may be of two varieties, those due to heavy weather or
emergency which may be located several miles from the dump site, and those
due to over-anxiousness of the dump crew. Lumping navigation error and
over-anxiousness, we estimate that 1-1.2 nmi of the 1.8 nmi distribution
could be accounted for by short dumping.
Studies conducted by the National Oceanic and Atmospheric Administration
(NOAA) with radioactive sand in 60 feet of water indicate that transport
processes and dispersion during disposal might cause displacement of up
to 500 feet. Sludge has very small amounts of material as large as sand
size and might be expected to sink more slowly and disperse more widely
than the NOAA sand. Based upon preliminary laboratory experiments performed
at Arthur D. Little, Inc. (ADL), it is believed that much of the sludge
will not descend as individual particles. Assuming an average fall rate
of 1/2 to 1/3 that of the NOAA sand, about 1,500-2,250 feet (0.25-0.37 nmi)
of displacement might occur prior to deposit on the bottom in 90 feet of
water. At the mud dump site, then, about 0.37 nmi could be accounted for
in this manner. Bottom transport after disposal and initial deposition
can be considered to account for the remaining displacement of 0.2-0.5 nmi.
Off the shelf navigational errors would be expected to account for
±2-3 nmi of scatter, unless special navigation equipment were required. If
Loran-C, or equivalent, were required, navigational errors would be reduced
to about ±0.25-0.5 nmi. Bottom transport processes would be expected to be
less active, so the dispersion once deposition has occurred should be less
than 0.2-0.5 nmi, perhaps 0.1-0.2 nmi. Transport processes and dispersion
are assumed to be proportional to depth, so that in 1,000 feet of water they
could account for 4.1 nmi as opposed to the 0.37 nmi estimated at the mud
dump site in 90 feet of water. Adding these contributions, it is estimated
that at an off-shelf dump site in 1,000 feet of water a high percentage of
dumped sludge might accumulate within 6.2-7.3 nmi of the designated site
(4.4-4.8 nmi if Loran-C navigation were required). Thus, the bottom area
which might be affected by an off-shelf dump could range from 60 to nearly
170 square nautical miles.
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In order to put these figures in some sort of perspective, assume
that a maximum of 10-15 million short tons of dewatered sludge is produced
annually along the Atlantic coast and it is deposited at a single deep
dump site as a material containing 50% solids weighing 100 Ibs/cubic foot.
Some 11 million curbic yards per year would thus be distributed over at
least 100 square nautical miles. This would amount to an estimated average
annual accumulation of about one inch of sludge throughout the area.
b. Environmental Impact Potential
In general, the short-term effects of conventional dumping of FGD
sludge in the upper water column (pelagic zones) of the deep ocean would
be similar to effects described above for the continental shelf. The major
differences between deep ocean and on-shelf disposal emerge in consideration
of long-term benthic and food web impacts.
The wider dispersion that would be achieved by disposal in depths of
several thousand feet would preclude many of the adverse impacts of benthic
sedimentation associated with shallower on-shelf disposal. However, it is
still possible that, given the lack of subsequent redistribution by storm
waves in the deep ocean, sludge would comprise a substantial portion of the
substrate in a deep ocean dump site. The advisability of deep ocean
disposal from a benthic standpoint would then involve consideration of the
trade-offs inherent in the preemption of the more diverse, more stable deep
ocean benthic communities as opposed to the shelf communities. The latter
are an integral part of the marine food web in which man is a high trophic
level consumer. The deep ocean communities do not play such a role and,
while unique, occupy a considerably greater percentage of the ocean floor
than shelf communities.
The differences between deep ocean and on-shelf disposal regarding
suspended sediment and sulfite impacts appear relatively minor. This is
particularly true of the short-term impacts on the water column. Over the
long term, sulfite would not be available to benthic finfish of direct
commercial and/or recreational importance in the deep ocean.
Trace contaminant impacts would likely be less over the long term in
the deep ocean. The impacts of dissolved trace contaminants in sludge
liquors would be similar to those discussed above in conjunction with
on-shelf disposal. However, two characteristics of the deep ocean dumping
environment tend to mitigate trace contaminant impact potential. First,
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as noted above, deep ocean sediments appear to be a natural sink, exhibiting
considerably higher concentrations of potential contaminants than near-shore
areas. It may be that deep ocean benthic communities are tolerant of
higher ambient concentrations of various contaminants but this is a hypoth-
esis unsupported by empirical evidence at this time. Second, and more
important, the lack of opportunity for contact between contaminants residing
in the deep ocean benthos and food webs of importance to man would largely
eliminate the risk of pollution episodes affecting human populations. Once
again, the trade-off between impacting the relatively stable but areally
extensive deep ocean communities would have to be weighed against these
advantages.
2. Environmental Impact of Applicable Control Options
Disposing of only sulfate-based sludges in the deep ocean would serve
to mitigate one of the remaining principal impact potentials, i.e., sulfite
toxicity. Restricting the allowable sludges for deep ocean disposal on the
basis of trace contaminant content is of lesser importance than for on-shelf
dumping because of the considerable difference in long-term availability of
such contaminants in the deep ocean. Overall, deep ocean disposal of
sulfate-based wastes by conventional means appears to be a relatively
viable option on environmental grounds.
Disposal by dispersion sufficient to achieve instantaneous dilution on
the order of 5,000 to 10,000 also appears to be a relatively viable option
from an environmental standpoint. These levels of initial dilution would
mitigate suspended sediment and trace contaminant impacts, probably reducing
them to insignificant levels. Potential problems of sulfite toxicity and/or
oxygen demand in the upper water column would be mitigated but perhaps not
resolved by deep ocean dispersal.
Disposing of chemically-treated, brick-like FGD sludge in the deep
ocean is probably the most desirable of all options considered from an
environmental standpoint. All of the major impacts discussed above would
be substantially mitigated by this combination of controls. Economic
considerations involved in this type of control scenario would be substan-
tial and are discussed below.
The disposal of chemically treated soil-like FGD sludges in the deep
ocean could mitigate sulfite impact potentials. Combined with dispersion,
this would probably be a relatively attractive environmental alternative.
However, as for the previous control option, economic feasibility is
questionable and further discussed below.
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E. ASSESSMENT OF TECHNOLOGY
1. Introduction
Three areas of technology related to ocean disposal of FGD sludge are
discussed in this section: transportation, surveillance and navigation,
and monitoring. The transportation section deals with pipeline and surface
craft (barge and special vessel) transportation modes. The surveillance
and navigation section addresses the accuracy and adequacy of methods
available for monitoring the location and timing of dumping activities.
Monitoring deals with the assessment of environmental baselines and trends
in the ocean.
2. Marine Transportation and Disposal
a. Background
The vehicles and methods for ocean dumping are determined principally
by the nature and form of the material to be disposed of and by the disposal
site in relation to the site of receipt. Conversely, the nature and form
of the material frequently may be changed to make it acceptable for use
with a given transport system.
There are a number of viable techniques that would permit the bulk
transportation of slurried mixtures to offshore disposal sites. The
existing practical technologies allow controlled dispersal of the sludge
over a great expanse of water, or a "sudden" total dump, or a continuous
pipeline discharge of the material. The techniques would fall into the
following categories:
• submarine pipeline transportation and dispersal at a preselected
offshore disposal site;
• self-propelled hopper ship with throttled discharged disposal or
with a sudden bottom dump capability; and
• tow-barge transportation and controlled dispersal over a great
expanse of water or a sudden total bottom dump.
These varied approaches all are technically feasible systems which
have been utilized full-scale. Selection among them depends upon the
characteristics of the material to be dumped as well as upon the environ-
mental conditions and constraints. In the case where the form and nature
of the material—a deliverable for dumping—is predetermined or fixed,
only the economics of the sea transport and disposal need to be examined.
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In the case where a variety of forms of the material are possible, earlier
elements of the system must be included in economic comparisons. For
example, the total costs of bringing the material to the loading point,
as well as loading costs, must be included in the comparison. That is to
say, possible transport/handling processes must be compared through all
alternative transport/interface branches from a common starting point.
b. Pipeline Transport
For liquids of limited viscosity and for solids which can be particu-
lated sufficiently to form a slurry the continuous-flow pipeline is
mechanically the simplest and usually the most economic. Motive power,
or flow energy, is provided by pumps. However, for large distances or in
rapidly deepening water the capital cost of such a pipe installation may
become predominant and the economics rapidly reach a cross-over point with
other types of systems. The ecological effects of distributing the material
must be considered in the light of the relative importance of benthic and
nektonic biota, and in the light of the behavior of the material discharged
from a single point, i.e., at the end of the outfall. For very heavy
materials, insufficient velocity may be developed at the pipeline exit
to produce sufficient dispersion; material buildups can occur at this
point to make such a scheme impractical. In practice, physical model
examinations may be required to determine critical velocities or appropriate
dilutions of the material.
The U.S. Department of Interior, Bureau of Mines has conducted
extensive research into pumping slurried coal through horizontal pipelines;
however, the comparison between slurried coal and slurried flue gas solid/
liquid waste is such that the developed data may not be compatible with
the present need. It is likely that less than 50% solid to water ratio
would be necessary for long distance FGD sludge transporting by pipeline.
The technology for underwater pipeline construction suitable to
present needs falls into three categories: bottom pull, floating pipe, and
lay barge pipeline positioning. Using the lay barge technique, the various
oil companies have installed underwater pipelines of 30-inch diameter for
distances as great as 108 miles. Other lines have been installed to sizes
as great as 56-inch diameter. Once in position, it is normal engineering
practice to protect the pipe from any vulnerable disruption. A pipe bury
barge or jet barge is used to develop a trench.
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The costs of offshore pipelines generally vary with length of the
line, depth, pipe size, ocean terrain, and material to be transported.
Typical complete installation costs for a 50-mile pipeline run about
$550,000 per mile for a 30-inch diameter line and about $350,000 per mile
for a 12-inch diameter line (in 1975 dollars). These estimates are based
upon a 1974 study by the Oil and Gas Journal (13) and recent experience
in pipeline transportation systems.
The greatest single cost factor in such pipelines is the installation
cost which generally runs more than 50% of the total investment. Although
right-of-way, material, and labor costs have risen significantly over the
past few years, newer and faster construction/installation techniqes have
to a great extent tended to stabilize the cost per mile of pipeline.
Maintenance is a high cost factor in pipeline operation that is
variable by location. Normally, the line is exposed to internal and
external corrosion and internal clogging. External corrosion is combated
with a bitumen, asphaltic, or coal tar material coating over which is
installed a weight coating or concrete sheath. These coatings are used
in conjunction with a cathodic protection system.
c. Transport by Surface Craft
The generalized alternative to pipelines lies in carriage of the
material in batches by surface craft to a selected dump site and its
release there. A prerequisite for surface release is that the material
have a density greater than water—or in the case of inert or harmless
materials, that it be soluble with a rapid natural rate of dispersion.
The vehicle, i.e., the container for this transport of the material, may
be a barge or a self-propelled craft. The material itself may be in any
one of many forms. In general, economics demand that the material be
carried in as concentrated form as possible and that the transport of
large tonnages of water be avoided.
For materials heavier than water, direct release into the water
column under gravitational force is possible. The discharge openings of
the vehicle must be suited to particle size and desired discharge rate,
and the process can be accomplished with a dry material which avoids
carriage of large weights of water.
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This type of dumping through openings in the bottom of the cargo
enclosure of the craft brings about several practical considerations. The
bottom of the cargo compartments, when the craft is empty, must lie above
the light waterline of the craft. Otherwise, the compartment, open to the
sea during the dumping, will partially fill with water. Even if a dewater-
ing system (drains and pumps and overboard discharge) is fitted, large
bottom doors or valves are difficult to maintain watertight. Thus, dump
vehicles frequently are fitted with wing tanks and double bottoms to retain
the cargo space above the light waterline. The openings themselves may
be hinged doors, sliding doors, or conical valves moved axially in round
seats. All three types have been used in self-dumping barges and scows
and dredges.
In recent years a new dump scow concept has appeared in the form of
the clam-shell barge. A hopper barge is split along a vertical longitudinal
plane and the two symmetrical halves are hinged at deck level. Buoyancy
compartments are arranged so that when the barge is loaded, a moment exists
to open the joint; when the hopper is empty, a moment exists to snap the
two halves shut. Thus, the mere release of a latch on a loaded barge
causes it to open; the material drops through the entire length of the
split in the bottom; and as the barge is lightened, the halves automatically
shut and may be relatched. No power need be applied. Some of these craft
are self-propelled with one "Harbormaster" or "Schottel" type of unit on
each side of the stern.
In cases where the material is unsuitable or where operating conditions
mitigate against the use of large hull openings and joints, the material
must be lifted over the side of the craft and dropped into the sea. If
a deck barge with bulwarks is used, the material can be shoved overboard
through an opening in the bulwarks by some form of small bulldozer. From
a hopper, methods as crude as the use of a crane and bucket are employed.
The latter requires expenditure of considerable power, use of manpower, arid
is unsuitable in any sort of seaway. Less power and less attendance is
required for pumping the material overboard, but in this case the material
must be liquefied to the extent that a slurry is formed. Water can be
introduced before or after loading, but in general this reduces the capacity
of the vehicle for the material to be dumped. The introduction of water
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can be delayed until the time for actual discharge. The patented MARCONA
ore transport system has a dry granulated mineral during sea transit; just
before unloading, high pressure water jets in the bottoms of the cargo
tanks enslurry the ore to a point where it can be pumped off the ship.
Obviously, such a system raises initial costs and the operating cost of
the craft, but its productivity relative to the basic material is greatly
improved.
Tow-Barge Transportation
Open ocean towing requires special purpose equipment not normally
found at many harbor locations where tow boats are usually of inner harbor
design and usage. To make long-distance tows practical, a maximum payload
must be transported and few barge lines can supply barges that have an
American Bureau of Shipping ocean service classification.
The United States Coast Guard (USCG) has limited jurisdiction over tug
boats and the commanding officer of such vessels can operate with a limited
license restricted to tow boat operation, although most tow boat owners
prefer a commanding officer with a captain's license. Tow boats, if under
300 gross tons, are not subjected to USCG inspections even though they may
be capable of operating on an ocean route. The crews, however, cannot work
more than an eight-hour day with the exception that if a trip is under
600 miles, the crew can operate on a two-watch basis, which means that
a double crew is warranted on each tug boat. In such cases, all officers
come under the federal competency requirements.
According to the USCG, a minimum crew would consist of two operators
(navigators), two engineers, and two deckhands. At least one barging
concern, though, indicates that safe and efficient operation calls for
an additional deckhand and one or two cooks.
The speed of the tow is a variable factor, depending on barge size
and weight, tug horsepower, and weather conditions. In general, tows can
travel at average speeds of 3-4 knots to a maximum of 9.2 knots.
There are two large capacity bottom dump barges (the largest in the
world) built in the United States which carry American Bureau of Shipping
ocean-going classification—a 3,000-cubic yard (4,050-ton) barge and a
4,000 cubic yard (5,000-ton) barge. Such barges typically run $290 to
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$350/dead weight ton (DWT), about $50/DWT more than simple hopper or tank
cargo barges. Thus, these large barges would cost in the vicinity of
$1,200,000 and $1,500,000 each, respectively.
Towing speeds (knots) for these barges would be as follows:
Towing Speed (knots)
Tug Horsepower 3,OOP-Cubic Yard 4,000-Cubic Yard
2,000 7.2 6.5
3,000 8.4 7.8
4,000 9.2 8.6
The barges have a longitudinally-divided hull, hinged at each end
near the deck. Hydraulic cylinders provide the mechanism to open the
lower hull and dump the sludge from within the hopper. The hull can be
opened for a distance of 6 inches for slow in-transit dumping to 12 feet
for a quick, sudden dump. The buoyancy force of the water, controlled by
the cylinders, closes the hull after the load has been dumped. The dumping
mechanism can be operated by means of radio remote control having the radio
transmitter on the towing tug, thus providing complete automatic operation
that would be necessary in the open ocean. The radio remote control system
would cost $12,000 for each barge and would entail one transmitter on the
towing vessel and one receiver on the barge that would be shipyard installed.
Self-Propelled Hopper-Type Ship Waste Disposal
The basic configuration of these vessels would resemble the hopper-type
dredges owned and operated by the U.S. Army Corps of Engineers (currently,
there are no industrially-owned hopper dredges in the United States), the
exception being that the vessels would not require a dredging capability
which involves expensive pumping systems and over-the-side dredge drag
heads and suction lines. It must also be considered that the Army's hopper
dredges are outdated and lack advancement in automation and dump hopper
designs that have been developed in Europe and are now operational on many
dredges.
The capacity of the U.S.-owned hopper dredges varies from a low of
720 cubic yards to a high of 8,277 cubic yards; however, European dredges
have now reached 15,000-cubic yard capacity. To meet sludge disposal
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requirements, the capacity needed for each hopper ship should be at least
4,000 cubic yards. This meets the capacity of the largest available dump
barges.
As discussed in Sections C and D above, the environmental impacts of
sludge dumping in both raw or treated forms have implications on the types
of transportation and disposal methods which might be suitable. If dilution
of 1,000:1 to 10,000:1 can be achieved within a few (5-10) minutes, then
dispersed disposal might be an option. If dispersed disposal is an option,
it would more likely be applied over the continental shelf rather than in
the deep ocean. Although the dispersal mechanisms would be very similar,
economics would argue for the shorter haul distance.
The other option is treating sludge to create a hard (rock-like) form
which could be hauled to the shelf and deposited to contribute to artificial
reefs.
Application to Sludge Disposal
A bottom-dump barge (or self-propelled vessel) of the longitudinally-
hinged variety could be used to transport and dump either partially
dewatered, untreated sludge or treated sludge. A barge for handling
untreated sludge would have to be specially constructed with a rubber
seal at the lips of the bottom joint to prevent loss of sludge because of
poor fit. However, this modification of available barges would probably
be relatively inexpensive. In addition, it might be necessary to install
special nozzles or other mechanisms for cleaning purposes. This could
cause a maintenance problem and would be expensive if it were automated.
If it were man-operated (and a barge rather than a self-propelled vessel
were used), problems transferring a man from the tug to the barge at sea
would be encountered. It is assumed that these problems have been overcome
in the section which follows where comparative operating costs are calcu-
lated.
Sludge could be transported with a high water content (30% or less
solids) and pumped directly overboard if it could be adequately dispersed
and diluted in the wake of the vessel. A self-propelled vessel travelling
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at 10 knots covers 16.0 feet per second. For a cross-section of 30 feet
x 12 feet the craft sweeps out 5,760 cubic feet per second. At a dilution
of 10,000:1, an amount equal to about 0.6 cubic feet per second (about
2,000 cubic feet per hour) could be discharged overboard into this "wake."
Assuming there are 21,000 cubic feet of solids onboard, discharge at this
rate would take about 10 hours. This is feasible, provided a discharge
system can be engineered to distribute the solids into the wake.
Alternatively, dry sludge could be transported and reslurried and
diluted onboard. Preliminary calculations based on a 1,000:1 onboard
dilution of dry sludge prior to discharge indicate that pumps capable of
pumping over 300 million gallons per day would be required. Such pumping
capacity is not feasible onboard a disposal vehicle.
3. Surveillance and Navigation
The impacts of ocean dumping of FGD sludges will be some function of
the geographic area touched by the disposal operation. To limit the
impacts, the location of the dumping has to be controlled. There are two
aspects of such control. The first deals with navigational accuracy avail-
able (or the ability to find any specified dump site with precision). The
second deals with policing the operation to make certain that the dumping
takes place at the specified location (within the accuracy limits of the
available navigation systems).
a.. Navigation System Accuracy
Piloting in inland waters using visual sights on fixed navigational
marks has historically been the most accurate position-fixing means for
ship navigators. Using these means, a ship's position could be located
within several tens of feet. At sea the time-honored celestial navigation
with dead reckoning can fix a ship's position within ±3-5 nmi, if done
carefully.
At present, the Loran-A system provides electronic navigation coverage
along all coastlines of the United States, the Great Lakes, Gulf of Alaska,
Hawaiian Islands, and Puerto Rico. The position accuracy (±0.5 to ±3.0 nmi)
is degraded under many nighttime conditions of operation, and the system
is old and expensive to maintain. The Loran-A navigation system is to be
phased out of operation over the next seven- to ten-year period.
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In addition to Loran-A, over the past 25 years OMEGA, NAVSAT, and
recently Loran-C have become available for use by commercial shipping.
Loran-C now provides position accuracies of ±0.25 to ±0.5 nmi without
degradation at sunrise and sunset. System improvements now underway are
expected to provide a 15- to 20-fold improvement in position accuracies.
As of May 16, 1974, Loran-C became the Coast Guard's approved
navigational system for the Coastal Confluence Zone (50 nmi from shore,
or the 600-fathom contour, whichever is further from shore). At present,
four Loran-C stations provide East Coast coverage. A new master station
is now in operation at Caribou, Maine, which upgrades the accuracy of the
East Coast Loran-C chain. Additional chains will be established in the
Gulf of Mexico, on the U.S. and Canadian West Coast, and in the Gulf of
Alaska to provide ±0.01 nmi position accuracy of the time. By the early
1980's it is expected that the upgraded Loran-C net will be operational,
making position fixes within at least ±0.25 to ±0.5 nmi generally available
to the shipping community within the area potentially used as an ocean
dumping site.
Positional accuracies on the order discussed above are certainly
adequate to the navigational requirements of dumpers. However, for the
purposes of surveying and site monitoring, it may be necessary to achieve
even greater accuracies in some instances, e.g., for work with submersible
vehicles. Sonar transponder systems are available which allow a submersible
to return to its exact previous position.
Where the bathymetry and the ocean monitoring stations in the disposal
areas have been established with Loran-C time difference readings, the
system provides an excellent capability to return to the original positions.
Ship positioning tests in Boston Harbor by USCG 1st District Engineering
Department personnel show that the Loran-C system can provide the Time
Difference (TD) information necessary to return to a given position within
about ±25 feet. With this system it can be expected, then, that where
survey track lines and ocean station position information are tied to
fathometer and bathymetric profiles in the usual manner, improved and
repeatable position accuracies to within 50 feet can be achieved in
future offshore ocean environmental monitoring programs using Loran-C.
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b. Policing the Dump
The USCG is responsible for surveillance of ocean dumping under the
Act and has relied upon a number of methods to carry out its responsibilities.
Visual observation from ships and aircraft has been combined with ship
riders and remote detection devices to monitor dumping operations. The
initial USCG policy called for ship riders on about 10% of municipal
waste and 100% of toxic chemicals disposal operations. This is an expensive
procedure, and electronic means are being developed to replace the ship
riders. In order to insure that dumping takes place at the EPA-specified
location, such a system should include the following:
• continuous position information to and from the disposal areas
available to the tug boat master at all times;
• an enabling signal to an interlock system that does not allow
dumping until the barge is within the specified area; and
• a continuous analog or digital position and time record of ship
position to be made availalbe to the USCG for inspection on
completion of each trip.
The USCG is currently developing an Offshore Disposal Surveillance
System (ODSS). The purpose of ODSS is to allow the USCG to determine
whether the dump was actually made in the specified EPA disposal area at
sea. After the tug and barge return to port, the USCG will inspect and
analyze ODSS logs. The logs are to be recorded by ODSS and printed out
automatically while the vessel is underway to show the track to and from
the disposal zone and the ship's position while disposal operations are
underway.
The ODSS system will use a fully automatic Loran-C receiver, data
logger and recorder with a format on magnetic tape suitable for computer
analysis by the USCG, if required. The system includes a dump status
readout and a dump enable and control subsystem. The enable system is
designed to inform the tow boat operator when the tow is in the dump area
and to enable the dump control interlock system at that time. This allows
the operator to commence dumping only when within the designated dump area.
However, tow boat operators will have a manual override in case the system
malfunctions.
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ODSS system costs are projected by the USCG at under $10,000 for pro-
curement and installation, all of which would be borne by the tug and
barge ocean disposal company. Such equipment could be required before
permits are issued.
4. Monitoring
a. Introduction
Monitoring of FGD sludge disposal at sea implies an oceanographic
measurement program of some sort. As related to sludge disposal, there
are two major categories of at-sea measurement programs which could be
envisioned. First are those programs aimed at enabling better prediction
of the behavior of sludge during and shortly after the initial dump. The
second category deals with longer-term environmental baseline definition
and trend monitoring.
The first category of measurements would focus on obtaining information
for model development and validation. These programs might be very inten-
sive in terms of observation platform (ships, buoys, aircraft, etc.) and
personnel utilization. However, the duration of experiments would probably
be relatively short, and they would not become routine or be repeated
frequently. Such programs would require extensive planning and coordination
beforehand, and significant amounts of laboratory and office analysis after
the at-sea measurements. One can envision a great deal of effort being
devoted to the identification, location, and study of the sludge plume
in situ, possibly using tracers, drogues, high altitude photography, water
samplers, turbidimeters, etc.
The second category of measurement program would focus on definition
of the pre-dump and post-dump oceanographic environment in order to
identify possible impacts. It is envisioned that such a program would
be prescribed in detail as a condition on licenses for FGD sludge dumping
in the ocean. It would undoubtedly incorporate a time series of ocean-
ographic observations (probably seasonal), and the measurement program
would become routine and focused on specific indicator organisms and
sludge components.
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b. Baseline and Trend Assessments
There are two principal types of environmental monitoring appropriate
for the assessment of sludge impacts:
• the baseline assessment; and
• the trend assessment.
Baseline assessments are performed before beginning waste disposal
operations and are generally considered to be synoptic surveys. A base-
line assessment should be designed to provide a representative picture of
the temporal and spatial range of existing marine environmental conditions
over the period of measurement. Physical, chemical, and biological
measurements are required.
The trend assessment results from analysis of the periodic and time-
series data that are gathered in the disposal area after the disposal
operation begins. The trend assessment information should be compared
with control station data taken simultaneously at stations outside the
disposal area, as well as with the baseline data taken before disposal
operations began.
Assessments must be planned with the cooperation of federal, state,
local, and private agencies and be documented and approved by EPA. Such
approval will probably include the preparation of one or more Environmental
Impact Statements for virtually all ocean dump sites presently in use or
proposed for use.
c. Status of Instrumentation and Techniques
Some relatively sophisticated equipment has been developed for the
measurement of important physical, chemical, and biological parameters in
the water column and in the sediments of the ocean floor. Most deep ocean
research and measurement activity has characteristically been carried out
from research and survey vessels. Recent programs have utilized aircraft
and even satellites to measure surface water temperature, and multi-
spectral photography techniques have been used to locate and identify
biological activity and pollution products on the ocean surface. Other
programs have used manned submersibles for observations and for obtain-
ing sediment and biological samples from the ocean floor. The NOAA
Data Buoy Office (Bay St. Louis, Mississippi) has emphasized the develop-
ment and placement of ocean buoys with instrument packages attached
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to the mooringllne data line at fixed ocean depths where long-term time
series measurement can be made. Each of these techniques may ultimately
be useful in monitoring sludge dumping at sea. However, most baseline
and trend surveys of ocean disposal areas will be sampling surveys carried
out periodically from onboard ships.
Sensors to monitor meteorological parameters and the necessary
physical oceanographic parameters of temperature, pressure, current
velocity, etc. are in a good state of development and suitable for "base-
line" measurements. Water samples•, bottom grab samples, coring tools,
and similar sampling equipment are readily available. However, sensors
for continuous in situ monitoring of chemical and heavy metal pollutants
for the most part are not available. It is necessary, at present, to
take a sample of water, sediment, or refuse to a well-equipped laboratory
for laboratory analysis using standard analytical techniques approved by
EPA. Analysis of samples by UV (ultraviolet), IR (infrared), n.m.r.
(nuclear magnetic resonance), spectrofluorometry, or gas chromatography
are newer methods coming into very wide use. Such detailed analysis is
time-consuming and expensive if large numbers of samples are evaluated on
a routine basis. The development of simple biological and chemical sensors
with high sensitivity, a broad range of response, and reliable long-term
unattended operation is needed.
Most biological and dissolved-chemical measurements are made after
water and sediment samples are collected using sample bottles of various
kinds, net hauls, and bottom sediment grab and core samples. Samples
generally are analyzed ashore or, in some cases, in a well-equipped'
laboratory area aboard ship.
d. Water Column Measurement
Water quality measurements to be made at various depths in the water
column at each station include the following:
• temperature;
• salinity;
• dissolved oxygen;
• pH;
• light penetration;
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• total organic carbon;
• inorganic nutrients; and
• suspended solids (or turbidity).
Analysis for selected heavy metals may be required at representative
stations within the disposal area. Additional analysis of dissolved
matter and particulates for constituents of FGD sludge may also be
required. Special precautions and care must be taken to properly
package samples for analysis later in the laboratory.
Sampling of the water column should be made at selected depths to
identify changes throughout the water column that could be caused by the
continued disposal of FGD sludge in any of its various forms. Sampling
at depths represented by the following conditions is recommended (14):
• just below surface;
• middle of the surface layer;
• bottom of the surface layer;
• middle of the thermocline and/or halocline;
• just beneath the thermocline (near top of the stable layer);
• middle of the stable layer;
• as near bottom as possible; and
• near the center of any zone showing pronounced biological
activity or lack thereof.
EPA (14) recommends that a minimum of five water quality sampling stations
be made within boundaries of a dump zone. Additional stations would be
required in areas larger than 20 square nautical miles in size. Additional
sampling stations will also be required when local conditions (e.g. , river
outflows or strong ocean currents or occasional winds) cause an exaggerated
distribution of ocean conditions.
Water Samples
Water samples may be collected at various depths using a variety of
specially adapted water samplers. Although many specialized water samples
have been devised for special purposes, the Nansen bottle and the Van Dorn
type water samples are the most used in the United States.
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The 1.25-liter Nansen sampler with the attached reversing thermometers
is the most accepted equipment for obtaining water temperatures at selected
depths and water samples for salinity, oxygen, silicates, alkalinity,
phosphates, and other chemical analysis. The Van Dorn sampler is available
in 1- to 5-liter and larger sizes and is used to provide large volume
samples for trace analysis.
Where only temperature and salinity as a function of depth are
required, more rapid and continuous profiles can be taken with the salinity,
temperature, depth (STD) or conductivity, temperature, depth (CTD) instru-
ments. The best of these equipments have been in wide use and are considered
highly reliable measurement and recording equipments, e.g., Plessey 9040
series STD. These devices are lowered on an electrical cable and data is
recorded in digital and/or analog format in the shipboard laboratory.
Typical operational specifications for these in situ measurement systems
are:
• salinity = 0 to 40 o/oo ±0.02;
• conductivity = 0 to 5 mmho/cm ±0.002;
• temperature = -5 to +45°C ±0.02; and
• depth = 0 to 300 m ±0.5%.
Some newer equipments include additional measurements of water quality:
• pH = 2 to 12 ±0.1;
• dissolved oxygen = 0 to 20 ppm ±0.2; and
• turbidity = 0 to 100% ±3%.
Biological Samples
Biological samples can be collected with vertical and horizontal
net tows as well as with conventional water samplers.
The Clark-Bumpus sampler is one type widely used for plankton net
tows. It is towed at a chosen fixed depth, utilizes a fine mesh net,
a plankton collection bucket, and an impeller and digital counter to
measure the volume of water flowing through the net.
Mid-water and bottom trawls are used to work at depths below the
thermocline to collect samples of larger organisms than those collected
with the Clark-Bumpus sampler.
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Analysis of the various nekton, phytoplankton, and zooplankton includes
separation and cataloging in the laboratory according to dominant as well
as sensitive, or indicator, organisms. Changes in the mix or populations
of the indicator groups need to be carefully tabulated and compared with
baseline and control station data.
Water Transparency
The penetration and absorption of light and the color and transparency
of waters in and around an ocean dump area are measured with a Secchi disc
or photometer.
The Secchi disc is p simple instrument which provides a relative,
average index of the transparency of seawater near the surface.
The simple photometer measures natural light penetration. Some
equipment provides for color filters that can be selectively triggered
into place to determine light penetration as a function of depth.
Alternatively, laboratory spectrophotometers and water samples are used
for the same purpose.
The hydrophotometer or nephalometer measures light transmission over
a fixed path length to determine the transparency of the water. Measure-
ments can be made of the attenuation coefficient (x) or the scattering
coefficient (k) which is a measure of water turbidity. Water turbidity
measurements may be important for sludge monitoring. Color filters may be
used to obtain spectral information.
e. Bottom Sampling
Inorganic waste deposits can modify the sediment structure of the
sea bottom and change the composition of benthic communities. Therefore,
the size distribution, mineral character, chemical quality, and biota of
the sediments in the proposed disposal area must be assessed.
Benthic biota can be collected with a dredge, or bottom grab sampler.
There are a variety of grab samplers (e.g., Orange Peel Bucket Sampler,
the Clamshell snapper and the Van Veen bottom sampler) that are useful for
obtaining samples of surface sediments and benthic biota from a hove-to
survey vessel. None of them provide an undisturbed sample showing structure
and microlayering.
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Coring devices are designed to penetrate the bottom sediments from
1/2 to 10 or more meters to obtain relatively undisturbed core samples.
Generally, for ocean disposal area surveys, core lengths of 1/3 to 1 meter
will be required.
Gravity-type and piston-type corers are available for this purpose.
Each depends on gravity to penetrate the ocean floor after a release
mechanism has been tripped. Several piston-type corers have been developed
to retain nearly undisturbed core samples. Commonly used coring devices
are:
• Phleger gravity corer - core lengths 1/3 to 1 meter;
• Kullenberg piston corer - core lengths 1 to 20 meters; and
• Hydro-Plastic (PVC) Piston corer - core lengths 1 to 6 meters.
The Phleger gravity corer is widely used and provides sample materials
suitable for most baseline programs. The PVC Piston corer type device
is preferred where relatively undisturbed core samples are required.
When the sample materials are retrieved on deck of the survey vessel.
they must be handled and packaged by approved methods for analysis later
in the laboratory. Tissue samples may have to be analyzed for heavy metals.
Where benthic organisms are to be counted and classified, contamination of
the sample must be minimized.
At a station located near the center of the ocean disposal area,
boctom sediment data should be taken and analyzed for selected heavy
metals including: arsenic, beryllium, boron, cadmium, cobalt, copper,
lead, mercury, nickel, selenium and zinc. These samples require precise
analytical techniques and, in some cases, special laboratory analysis
equipment. The samples must be preserved for subsequent analysis.
f. Bathymetric Survey
Bathymetric survey lines are generally run in rectangular grid
patterns to develop bottom topographic coverage sufficient to allow con-
tours to be determined at intervals of 1 fathom (6 feet) or less. Loran-C
navigation control should allow for spacing of tracklines to about ±50 feet
(if required) in most offshore areas.
The requirements and specifications for each bathymetric survey vary
depending on the trackline control available, the bottom topography, water
depth, and on the chart scale required. In most cases, charts of 1:25,000
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to 1:10,000 will be required to show a 1- to 3-meter contour interval
except in very flat areas. Surveying instruments (precision fathometers,
side scanning sonars, etc.) are sufficiently developed to meet the bathy-
metric monitoring needs associated with FGD sludge disposal.
g. Current Measurements
Many types of instruments have been developed over the years to measure
the speed and direction of ocean currents at different depths in the water
column and near the bottom. These devices range from simple drift bottles
and drogues to very sophisticated telemetering electronic systems tethered
from a ship, surface buoy, or buoyed from the bottom on a taut line.
There are, in general, two broad categories of ocean current measure-
ment instruments in wide used:
• free-floating; and
• fixed.
Those in the first category (free-floating) are useful for determining
water mass movement and general surface and near surface current patterns
in coastal areas. Surface floats, dyes, and mid-water parachute drogues
are commonly used for this purpose. The second category (fixed) includes
instruments that are attached to fixed and floating structures such as
piers, towers, tripods, placed on the ocean floor, or more commonly,
tethered from survey vessels and buoys. This second category includes
mechanical devices and sophisticated electronic equipments. In base-
line and trend measurements these instruments are tethered on a line
from a ship or buoy and record the information on strip chart, magnetic or
paper tape, or telemeter the information to a recording station ashore or
to a nearby surface ship.
Free-Floating Current Measurements
Drift bottles (sealed bottles with a return post card inside) or drift
cards and dye markers are commonly used to show the general movement of a
water mass. Visual means are generally used, but color photography from
overflying aircraft or fluorometric measurements are more sensitive means
of following the dispersion of the dye in the water mass.
Parachute-type drogues have been used for many years to track submerged
currents and, in some cases, deep countercurrents. They are effective for
short-term tagging and tracking of a particular water mass.
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Fixed Current Measurements
A variety of current meters have been designed for this purpose over
the years. The Richardson-type or Hydro Products 650 series profiling-type
current meters are examples of newer equipments which utilize a Savonius
rotor to obtain current speed over a wide range from 0.1 to 5 knots. A small
vane orients itself with the ocean current to within ±10°. The speed and
direction information is digitized and recorded on film to be evaluated
after the current meter is retrieved. Other modern ocean current meters
record speed and direction data in situ on strip chart, magnetic tape, or
telemeter the information in digital form over a wire link to a surface
vessel or shore station. Such information may also be transmitted in a
computer comparable digital format for immediate display and analysis.
The major difficulties with current meters of this type are their
inability to completely resist corrosion and fouling, resulting in
degradation of performance. In long-term measurements these factors can
severly reduce accuracy and precision of sophisticated equipment, particu-
larly at low current speeds. Clearly, a careful calibration of equipment
is required both before and after deployment to account for any degradation
in performance during the survey operation.
Other errors besides those of corrosion and fouling are prevalent in
the use of wide range ocean current meters. One of the most common of
these is platform movement which tends to tow the current meter through
the water and indicate false current speed and direction components.
Precision navigation information can help compensate for this error.
h. Survey Time and Cost Estimate
The cost of producing baseline and trend surveys at coastal offshore
waste disposal areas varies with the sampling frequency and duration, size
of the area, its bathymetry, bottom topography, weather conditions, and
the amount of detail required. Ocean areas near fishing areas or known
spawning grounds may require more detailed survey information than areas
located in less valued locations. Also, if the proposed disposal area is
near shore and there is the risk that waste materials might contaminate
beaches, salt marshes, or other recreation areas, a more extensive survey
and data reduction program may be required. The emphasis and time
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spent on the assessment of various aspects of the environment will depend
on the type and quantity of sludges proposed for disposal at the site and
also on the potential for effects on the local and surrounding environment.
Timing and Duration
Baseline and trend surveys must be conducted to account for seasonal
variabilities in environmental conditions at the site (e.g., ocean currents,
wind, and meteorology).
In some disposal locations the initial surveys may show that seasonal
variations cause no significant changes in the environment at the dispoal
site. As a result, surveys at greater than seasonal intervals may be
scheduled, but an effort should be made to conduct the trend surveys in
climatic conditions as near those of the baseline survey as practical.
The time required to complete a field survey will depend mainly on
the complexity and size of the proposed site as well as upon the types and
variety of data to be collected. The bottom topography and hydrography
will in large part determine the number and location of the bottom sampling
stations. EPA (14) recommends that the ratio of bottom stations to water
column stations should be about 3:1, depending upon the site being evaluated.
Additional bottom sampling stations are needed when there are large Hiscon-
tinuities in the bottom topography, and stations should be set to provide
representative bottom samples on each side of a discontinuity. The number
of bottom stations required will also depend on how well the FGD materials
dissolve before reaching the bottom and also whether the sludge is in a treated
form intended to dissolve slowly on the bottom. With consistent bathymetry
devoid of canyons and rifts, the sampling stations can be uniformly dis-
tributed throughout the area. Additional control stations (upstream and
downstream) should be included.
A baseline survey of this magnitude could generally be expected to
require up to 18 months to complete. One cruise might last one to three
weeks. Trend assessments will be required at the FGD disposal site three
to four times per year after FGD disposal begins. Additional surveys of
selected critical parameters may be necessary during periods of heavy
dumping.
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Cost Estimates
The cost of conducting site surveys will vary with many factors,
including the location and proximity of the site to shore, size of the area,
depth of water, bottom topography, and most important, the complexity and
detail required of the analysis. In addition, bad weather conditions, such
as heavy seas, can significantly lengthen the time required to make the
measurements and acquire the necessary samples at sea. Because of these
factors it is difficult to generalize the cost estimates and time required
to perform a survey. Some useful guidelines might be as follows.
Most baseline and trend surveys are made with small survey vessels
90 to 180 feet in length. Average daily costs for a survey vessel com-
pletely fitted out with the required measurement, survey, and deck handling
equipment is in the range of $2,000 to $2,500 per day. One to three weeks
of ship availability is generally required to complete a site survey which
allows for mobilization and demobilization time necessary to make a leased
vessel suitable for the survey work required.
The number of ocean measurement stations varies, as discussed above.
In ocean disposal areas the density of ocean stations may vary from about
one station per two square miles to about one station per five square miles.
In near-shore areas, for example, where river outflow, tidal currents, or
strong localized ocean currents are a significant factor in determining
potential ocean dumping impacts, an even higher density of ocean sampling
may be justified.
Physical data from oceanographic survey stations is, in large part,
tabulated aboard ship before the ship leaves the area. The chemical,
biological, and sediment oceanography is, in large part, evaluated in
analytical laboratories ashore. It is this detailed laboratory analysis
and reporting of all data that is the most costly and time-consuming part
of an ocean dumping site survey operation. The detailed laboratory analy-
sis work may require many times the ocean disposal site survey time to
complete, depending on the complexity, detail, and quantity of data and
samples to be analyzed and evaluated. For example, highly selective
hydrocarbon analytical techniques that use the powerful combination of
gas chromatography and/or mass spectrometry can determine the presence of
chemical groups within the sample and may add an additional $500 to $1,000
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per station. A final report and interpretation of ocean disposal site
environmental data may require nine months to a year before it can be
completed, reviewed, and released.
Recent experience indicates that offshore ocean dumping site surveys
that require one to two weeks of ship time to complete will require an
additional three to four months for data evaluation, analysis, and reporting.
A typical ocean survey program of this type can cost in the range of $200,000
to $250,000 per cruise including preliminary conclusions and a summary data
report.
F. CONCLUSIONS AND RECOMMENDATIONS
1. Technical/Environmental Considerations
Two major overall conclusions emerge from this assessment of
the disposal of FGD sludges in the ocean. First, there is an
overriding need for case-by-case analysis of the environmental
feasibility of ocean disposal of specific FGD sludges. The emphasis
in such analyses should be twofold, focusing both on the type of
sludge and disposal site environmental conditions. Second, control
options involving chemical treatment of sludge, limitations on the
type of sludge disposed of, and control of the method of sludge
placement (either dispersed or concentrated bottom-dump disposal)
all appear to be technically feasible. Economic feasibility,
however, is less clear-cut and would serve to limit the viability of
several of the most promising environmental options.
Specific conclusions are as follows:
• Unless further work contradicts the anticipated sedimentation
and suspension impacts, the disposal of untreated or treated
FGD sludges with soil-like physical properties by bottom-
dump barge or outfall on the continental shelf must be
considered to be environmentally unacceptable.
• Based upon available information on sulfite toxicity, it
appears that an almost immediate (on the order of minutes)
dilution factor greater than 10,000:1 for sulfite alone is
required in the dispersed disposal of untreated sludges
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containing large fractions of sulfite. The technology is
not currently available for attaining such dilution factors
for untreated sulfite-rich sludges in an economical manner.
Therefore, the dispersed disposal of sulfite-rich sludges,
both on and off the continental shelf, is not considered to
be a promising option at the present time. Further information
on organisms uptake and toxicity of TOS could justify
reevaluation of this conclusion.
• Several disposal options appear promising and are recommended
for further research. These include:
- dispersed disposal of untreated sulfate-rich FGD sludges
on the continental shelf;
- concentrated disposal of treated brick-like FGD sludge on
the continental shelf;
- dispersed disposal of untreated sulfate-rich FGD sludges in
the deep ocean; and
- concentrated disposal of both untreated sulfate-rich FGD
sludges and treated FGD sludges in the deep ocean.
Recommended additional research is discussed in more detail
below.
2. Regulatory Considerations
In general, given the present vigilance in agency attitudes
towards ocean dumping, the existing regulations appear to be
adequate to insure protection of the ocean environment. However,
several specific recommendations are considered appropriate at this
time. These are as follows:
• Fending revisions to the existing ocean dumping regulations
that would allow for additional empirical considerations
(e.g., field data and models) in the determination of limiting
permissible concentrations in the ocean at the disposal
site should be adopted.
• Existing absolute limits on permissible concentrations of
mercury and cadmium in solid fractions of wastes should be
reevaluated through consideration of the actual anticipated
long-term availability of the contaminants on a case-by-case
basis.
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• Inherent disincentives to deep ocean dumping (e.g., extra
monitoring requirements) should be reevaluated in light of
the apparent desirability of certain deep ocean disposal
options.
There appears to be no need for additional sludge-related legislation
concerning ocean disposal at this time.
3. Need for Additional Research and Information
The following research needs are believed most important at
this time.
• A body of empirical data needs to be developed concerning the
chemical and physical fate of sludge in seawater. Of
particular importance are:
- dissolution rates of various treated and untreated FGD
sludges in the representative types of seawater that would
characterize the disposal area environs; and
- physical transport of both treated and untreated sludges
in the water column during descent and subsequently in the
marine benthos (near the bottom).
These effects will be studied in laboratory-scale testing
with untreated sludges during the Phase II program.
• A body of empirical data needs to be developed regarding
the biological impacts of sludge disposal. Specifically:
- uptake of both liquid and solid constituents of FGD
sludges by various marine organisms need to be
developed;
- in particular, for uptake associated with short-term
exposure of pelagic organisms; and
- lethal and sub-lethal effects thresholds need to be
developed for exposure of a variety of representative
marine organisms to FGD sludges (one of the focal points
of such research should be the dynamics of food web
transfer of potential toxicants).
The investigation of such biological impacts is planned for
the simulation/demonstration testing in Phase III.
• Mechanisms for eliminating existing economic disincentives
to deep ocean disposal should be developed. These could
include consideration of such options as a greater federal
role in baseline and disposal area monitoring.
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GLOSSARY
antagonism — In a toxicologlcal sense, an interaction between two or more
substances which results in less damage potential than would be
expected based on the hazards posed by the individual substances.
In other words, the combination tends to suppress toxic effects.
attenuation coefficient — A measure of the space rate of diminution (or
attenuation) of transmitted light.
bathymetry — The science of measuring ocean depths in order to determine
the sea floor topography.
benthic (benthos) — As an adjective, used to describe organisms, events, or
other aspects of the environment found near and including the bottom
of a water body. The noun (benthos) is usually used to describe the
organisms residing in this part of the water column. Macrobenthic
refers to the subset of benthic organisms that are large enough to be
examined with the naked eye.
bioassay — A test in which one or more living organisms is subjected
to stress under controlled experimental conditions.
biological concentration — A process whereby living organisms extract
substances from the surrounding environment and incorporate these
substances or forms thereof within their tissues.
biomass — The weight of living organisms in the population or community
under study.
calanoid copepod — Any of the order of microscopic Crustacea which commonly
are among the dominant zooplankton in estuarine and coastal waters.
control — As in "control location;" an adjective used to describe the
location or set of conditions experiencing all aspects of the
situation under study, except the experimental variable. In ocean
dumping situations a control location might be one where no ocean
dumping has taken place*
detritus (detrital) — A term used to describe decaying organic matter,
especially decaying vegetation.
drag heads — The working element of a hydraulic or hopper dredge which sucks
up sediment off the bottom of a waterway.
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drogue — A current measuring assembly used to "catch hold" of a parcel of
water in order that the water may be tracked over a period of time.
Often consists of a weighted parachute or a pair of crossed wooden
or metal planes.
ecosystem diversity — As used in the Marine Protection Research and
Santuaries Act of 1972, a general term to indicate the amount of
variety in types of organisms and communities in the marine environment.
ecosystems dynamics — The processes of interaction between organisms and
their environment.
faunal assemblages — Groups or communities of animals, usually used in
reference to a group of several different species typically found
together.
food web — A term used to describe the network of relationships between
various organism populations and their food supplies.
gravity corer — Any type of corer that achieves bottom penetration solely
as a result of gravitational forces acting on its mass.
halocline — A well-defined, vertical gradient of salinity which is usually
positive.
"Harbormaster" unit - A semi-portable ship propulsion unit resembling a large
outboard motor.
hove-to — The condition in which a ship is kept headed into the wind with
no headway or by working the engines as necessary.
in-situ — A Latin term meaning in place or in the natural or original
position.
indicator organisms — Under experimental or field observation conditions,
indicator organisms or species would be the forms expected to first
react to the experimental stress under study.
isopach — A contour line on a map drawn through points of equal thickness
of a sedimentary layer.
Loran — A long-range electronic navigation system which uses the time
divergence of pulse-type transmission from two or more fixed stations—
Loran-A was the original operational system; Loran-C is a system with
improved reliability and accuracy.
macrofauna — Animals large enough to be readily seen with the naked eye.
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mooring-line-data-line — A specially designed electrically insulated data-
buoy mooring line through which oceanographic sensors transmit data
to the buoy for storage.
multispectral photography — Simultaneous photography of subject matter
through different colored filters to enhance the capture of spectral
information.
Nansen sampler (Nansen bottle) — A device used by oceanographers to obtain
subsurface samples of seawater.
NAVSAT — A Navy-developed satellite navigation system.
nekton — A term used to describe those organisms, such as fish, capable of
extensive voluntary movement in the water column.
OMEGA — A low frequency electronic navigation system.
pelagic — An adjective used when referring to areas or organisms character-
istic of the open ocean, particularly upper layers of the water column
in contrast to "benthic."
pelecypod mollusks — Any of the class of shellfish often referred to as
bivalves, including the commercially valued forms of clams and oysters.
phytoplankton — Floating plants, often microscopic.
piston-type corer — A corer equipped with a piston inside the core tube
that is attached to the lowering cable. When the corer penetrates
the ocean bottom, the piston provides suction to counteract the
friction between the sediment and the wall of the core tube.
plankton — Free-floating organisms, usually microscopic, and incapable of
extensive voluntary movement in the water column.
polychaete — Any member of the class of marine and estuarine worms,
typically among the most abundant organisms in coastal benthic
communities.
Savonius rotor — A current meter rotor responsive to a wide spectrum of
horizontal flow components, built in the shape of two semi-cylindrical
vanes disposed to form an S.
scattering coefficient — A measure of the attenuation due to scattering of
radiation as it traverses a medium containing scattering particles.
"Schottel" unit — See Harbormaster unit.
seaway— A marine highway.
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sonar transponder systems — Navigation aids based on the employment of
underwater sound.
STD — An instrument which measures and records salinity, temperature, and
depth simultaneously.
stress — In ecological terms, any condition which could serve to limit
a biological function.
sublethal — An adjective used to describe a condition, usually a stress,
that has some adverse effect other than death. The term is often
used to describe a concentration of a substance in the environment
at which organisms would survive but experience some measure of
adversity.
thermocline — A vertical negative temperature gradient in a body of water
which is appreciably greater than the gradients above and below it.
tracklines — Lines on a chart depicting the locus of points where scientific
measurements (e.g., depth, gravity, magnetic field) have been made by
a ship underway.
upwellings — The process by which water rises from a lower to a higher
depth, usually as a result of divergence and offshore currents.
Van Porn sampler — A device used by oceanographers to obtain subsurface
samples of seawater. Usually made of plastic and larger in capacity
than Nansen samplers.
zooplankton — Floating animals, usually microscopic.
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Estuarine Organisms, Phase II. Final Report, University of Maryland,
Department of Environmental Research, Chesapeake Biological Laboratory,
1974. 267 pp.
11. Sano, H.C, and A. Semizo. pH Dependence of the Toxicity of Sulfite in
Water. Kogyo Gijutsu Shikensho Kiho, 22^ (4):293-298, 1971.
288
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12. Rand, M.C. and S.B. Gale. Kinetics of the Oxidation of Sulfites by
Dissolved Oxygen. In: Principles and Applications of Water Chemistry,
S.D. Faust and J.V. Hunter, eds. Wylie, New York, 1967. pp. 380-404.
13. Pipeline Economics. Oil and Gas Journal, 72(32), August 12, 1974.
14. Environmental Protection Agency. Proposed Revision of Ocean Dumping
Regulations and Criteria. Federal Register, June 28, 1976.
289
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VII. DISPOSAL SYSTEM COSTS
A. BASIS FOR DESIGN AND ECONOMICS t «
fljl KV,Jl*-
Conceptual- system designs and general capital and operating costs
f? -Ur l~T- ' W)
have been prepared for a number of feasible ocean and mine sludge disposal
options. Table VII-1 summarizes the sludge basis, and Tables VII-2 and
VII-3 show the assumptions and factors used in the cost estimates.
Costs are based upon the disposal of sludge produced at a 500-megawatt
power plant operating at an average annual load factor of 80% and burning
typical eastern high-sulfur coal (3.0% sulfur, 10% ash, and 0.85 Ibs of
coal per kilowatt-hour). The rate of sludge production is estimated for
90% S02 removal using a well-run direct lime scrubbing system with fly ash
removed upstream of the scrubber system by a highly efficient electrostatic
precipitator.
General sludge characteristics, as discussed in Chapter IV, have been
used. In all cases, the sludge is considered to consist of the combined
ash and calcium-sulfur salts from S02 removal. For the purposes of this
study it is assumed that the sludge is available in the form required at
the FGD system battery limits. No costs have been included for any type
of sludge processing, such as filtration, drying, fly ash addition, or
chemical treatment.
B. COAL MINE DISPOSAL
Conceptual designs and costs have been prepared for four basic trans-
port/disposal operations for onsite and offsite mines—two each for surface
area and underground room and pillar mines. Offsite mines have been
assumed to be 200 miles from the power plant; onsite mines, four miles
from the power plant. For offsite mines, rail haul is assumed to be the
basic mode of transport for the sludge. Initial estimates show truck haul
and slurry pipeline to be impractical over such distances. For onsite
mines, truck haul and pipeline transport are used.
1. Description of System Operations
a. Surface Mine Disposal
The two basic transport/disposal systems evaluated for surface area
mine disposal are shown schematically in Figure VII-1. For each system,
291
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TABLE VI1-1
SLUDGE BASIS FOR CONCEPTUAL DESIGN
Boiler:
capacity - 500 Mw
load factor - 80% annual average
Coal;
0.85 Ibs coal/kwh
3.0% sulfur
10% ash
Pollution Control;
90% S02 removal (scrubber)
99+% particulate removal (ESP)
Sludge Production (thousands of short tons per year)
Annual: dry S02 sludge 225
dry ash 140
dry total 365
wet total (@ 50%) 730
Daily Average: 2,000 (wet)
Daily Peak: 3,000 (wet)
292
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TABLE. VII-2
CAPITAL COST BASIS
(1977 Completion, 30-Year Life)
Capital Investment Includes (battery limits - FGD system)
• Installed Equipment Cost (IEC)
• Engineering and Fees
• Startup
• Working Capital
• Owner's Expense (@ 8% of IEC)
• Interest During Construction (@ 15% - two years)
• Escalation During Construction (@ 8% - two years)
Capital Investment Does Not Include:
• Extensive Site Preparations
• Sludge Processing
• Provision for Utilities
• Land
• Mine Fees (if any)
• Permit Associated Costs
293
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TABLE VII-3
COST;FACTORS
Item
Variable:
Power
Diesel Fuel
Labor:
Direct
Overhead (supervision & fringes)
Maintenance
Plant Overhead
Capital Charges (depreciation)
Unit Cost
$0.015/kwh
$0.40/gal.
$8.00/manhour
70% of Direct Labor
2-5% of Installed
Equipment Cost
40% of Direct Labor
& Maintenance
17% of Total Installed
Cost
Interest/Insurance/Taxes/Fees (rolling stock) 10% of Equipment Cost
294
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Rail
Filter Cake & Ash
or
Soil-like, Treated
Convey
Transfer/
Store
Truck
Off site Mine
200 Miles
to
vo
Treated
Sludge
Stabilization
Pond
| fond |
Onsite Mine
Rail
Transfer/
Store
FIGURE VII-1
SURFACE MINE DISPOSAL OPERATIONS
-------
estimates have been prepared for handling both dry filter cake admixed with
ash and stabilized, treated sludge (processing costs not included).
Onsite Mine-Truck Haul
Either well-filtered sludge mixed with fly ash or stabilized, treated
sludge could be disposed of in a surface area mine. The transfer, handling,
and placement systems would be almost identical; except with treated sludges
requiring stabilization ponds, there will be the added cost of excavating
the ponds.
There are many possible system configurations for handling and trans-
ferring filter cake and ash, depending upon the need to control the filter
cake/ash ratio and the manner in which fly ash collection and filtration
systems are operated. It has been assumed as a basis for the conceptual
design that the fly ash/cake mixing system could be run independently of
the disposal operation so there would be need for storage of the mixed
cake and ash. The sludge leaving the cake/ash mixing ar^ea would be trans-
ferred via belt conveyor to a covered transfer/storage area where an
intermediate stockpile would be maintained. The sludge would then be
loaded into rear-dump trucks using front end loaders.
The rear-dump trucks would transport the sludge to the mine (four
miles) and dump the sludge in the mined-out pit prior to replacing over-
burden. In a typical Interior mine the principal coal seam varies from
three to ten feet thick, so the layer of sludge, which amounts to only
about 40% of the coal seam by weight (3.0% S, 10% ash), would be no greater
than a few feet deep. Thus, there would be no need to level and compact
the sludge with earth-moving equipment to provide a base for trucks so
that the layer could be built up. The operation, therefore, would require
six 35-ton trucks (one spare) and two 3-cubic yard front end loaders (one
spare) to handle the sludge on a one-shift per day basis).
Treated sludges could be available either as a soil-like material at
the battery limits of the treatment plant or as a hardened product in a
stabilization pond which would require excavation. For the soil-like
material the cost structure for untreated filter cake mixed with ash is
assumed. For treatment involving ponding a three-pond batch system is
envisioned (one being filled, one stabilizing, and one being excavated).
296
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It Is assumed that a Sauerman-type system could be used for excavation and
that it could operate on a regular one-shift basis (8 hours/day, 5 days/
week, 50 weeks/year). Excavated material would be transported via conveyor
to the transfer/storage area.
Offsite Mine-Rail Haul
For offsite mine disposal the sludge would be conveyed to a transfer/
storage area where it would be stockpiled as previously described. At the
transfer area the sludge would be loaded into feed hoppers via front end
loaders. The hoppers would be located over the existing rail line "down
track" from the coal unloading area and would discharge directly into the
rail cars. We have assumed two feed hoppers and two front end loaders in
order not to unduly delay the train.
The train would transport the sludge in uncovered cars, 200 miles to
the mine. Since rail rates do not exist and are difficult to obtain for
sludge, we have estimated a rate of $2.00/short wet ton (!
-------
Thickener
to
-------
Assuming that the mine has a seven-foot coal seam 800 feet below
ground and that the sludge will settle to 50% solids (with the excess
water pumped out), the mine area required (with 60% coal extraction) will
amount to about 90 acres per year. Bulkheads would be required on three
sides containing a maximum of about four acres, with one 4-inch borehole
(cased) for each disposal cell. Bulkhead and borehole construction is
assumed to proceed continuously.
Onsite Mine-Pipeline Transport
Where the power plant is located at the mine mouth, the scrubber bleed
can be pumped to the mining area where it is then thickened. The underflow
(20-30% solids) would then be pumped down the boreholes and the overflow
combined with mine pump-out and returned to the scrubber system. It would
also be possible to treat the sludge after thickening and prior to disposal,
as long as a "wet" treatment system were used and the resulting unstabilized
sludge could be easily pumped. However, it would probably not be possible
to return mine pump-out to the FGD system, and care would have to be taken
to minimize plugging of lines due to slow setting of the treated slurry on
the pipe walls. Since it is impossible to estimate the cost for handling
treated slurry without more definitive data, it is assumed that the costs
for disposing of thickener underflow or repulped filter cake would apply
in general to treated slurry.
For disposal costs, only the incremental costs to the FGD and treat-
ment systems have been included—that is, the cost of the pipelines between
the thickening system and the FGD system, and the mine disposal piping and .
bulkhead construction. As a cost basis we have assumed a two-mile distance
from the thickening area to the FGD system and an additional variable
distance ranging from a few hundred feet to a mile between the thickener
and the disposal boreholes (with the distance increasing over the 30-year
life of the mine and power plant). No sludge, slurry, or clear liquor
storage is assumed other than that provided by the thickener and the
thickener hold tank.
Offsite Mine-Rail Haul
Since it would not be economically attractive to pipe slurry (either
thickener underflow or scrubber bleed) over great distances, for offsite
299
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mine disposal, rail haul of filter cake (with ash) and reslurry at the
mine for hydraulic backfilling has been assumed. The system would essen-
tially be a combination of that described for offsite surface mine disposal
(between the FGD system and the mine storage area) and the onsite under-
ground mine case. It would involve conveying the sludge to a storage/
transfer area, loading rail cars and hauling to the mine, dumping the
sludge and conveying to a second storage transfer area, conveying to a
repulping tank, and pumping down the boreholes. The mine pump-out could
be used for reslurrying the sludge.
2. Cost of Disposal Operations
Table VII-4 gives a summary of the cost estimates for these six mine
disposal options based upon the cost factors provided in Tables VII-2 and
VII-3. Note that these costs do not include monitoring. Monitoring costs
will depend strongly on the local/regional hydrology and the parameters
(species) monitored, and are not necessarily a direct function of the
quantity of sludge handled. Therefore, it could be misleading to directly
assess monitoring costs on the basis of tons of sludge handled. It would
be anticipated that the cost of monitoring a typical Interior surface area
mine disposal operation could run on the order of $500,000/year, including
sludge characterization, sample well location, analysis of both core and
water samples, and inspection of the disposal operations.
As would be expected, disposal of untreated sludge or treated, soil-
like sludge in onsite mines provides the least expensive system, with cost
estimates of $3.00-3.50/ton of dry sludge. Offsite disposal in mines
increases costs to $6.50 to $8.00/ton of dry sludge. Disposing of treated
sludge from stabilization ponds increases costs roughly an additional $2.20
to cover the cost of excavation. Again, it should be noted that these costs
do not include any processing costs for the sludge other than pond excava-
tion. Filtration and admixing with ash or treatment additives is not
considered.
C. OCEAN DISPOSAL
Conceptual system designs and associated cost estimates have been
prepared for five ocean disposal systems off the East Coast—two for on-
shelf (shallow ocean) and three for off-shelf (deep ocean) dumping. The
five alternatives are shown schematically in Figure VII-3.
300
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TABLE VII-4
U)
o
CAPITAL AND OPERATING COSTS FOR MINE DISPOSAL
Mine Type
Surface
(truck dump)
Underground
(hydraulic fill)
Location Sludge Type
Onsite ( Filter Cake + Ash
\Soil-like or Treated
Treated, from Stabi-
lization Ponds
Offsite (Filter Cake + Ash
(Soil-like or Treated
Treated, from Stabi-
lization Ponds
Onsite Thickener Underflow
Offsite Filter Cake + Ash
Principal
Transport Mode
Truck
Truck
Rail
Rail
Pipeline
Rail
ALTERNATIVES
Capital Cost
($MM)
1.85
5.50
1.95
5.60
1.05
1.75
Operating
($/dry ton) '
3.30
5.55
6.50
8.70
3.20
8.10
Costs3
(mils/kwh)
0.35
0.6
0.7
0.9
0.35
0.85
including costs for monitoring or sludge processing (see text).
-------
Filter Cake & Ash
Convey
Transfer/Store
Barge
Deep/Shallow
Ocean Dump
Site
I 1
j Treated Sludge '
I Stabilization
Pond
'^MB i^BHB 1
Excavate
Barge
I
Load
Deep/Shallow
Ocean Dump
Site
u>
o
NJ
Thickener Underflow
Barge
Deep Ocean
Dump Site
FIGURE VII-3 OCEAN DISPOSAL OPERATIONS
-------
On-shelf disposal sites have been assumed to be 25 nautical miles (nmi)
offshore, and off-shelf disposal sites to be 100 nmi offshore. In all
cases, bottom-dump disposal has been assumed. While slurry dispersal is
possible, it is more expensive both to transport the slurry and pump dis-
charge the sludge. Transport of relatively dry filter cake and reslurry
at sea prior to disposal is not considered practical due to the large
pumping capacities required onboard.
It has been assumed that the sludge is produced in a power plant with
ready access to the ocean. Thus, facilities for berthing barges would be
available; however, a sludge transfer/storage facility would still be
required.
In developing system costs for ocean disposal operations, the same
sludge production rates have been used as in the mine disposal cases.
While no assumptions have been explicitly made concerning the chemical
nature of the sludge, implicit in the quantity and moisture content of the
sludge is the assumption that the sludge is sulfite-rich. Since disposal
of sulfite-rich sludges is not presently considered promising, quantities
based upon sulfate-rich material would be more appropriate. The adjustment
in total quantity handled could amount to as much as a 30% decrease due to
the generally enhanced dewatering properties of sulfate-rich sludges.
This lower total quantity would reduce the disposal cost (although not
by a proportionate amount).
1. Description of Systems
a. On-Shelf Disposal
Two cases are considered for on-shelf disposal—bottom dumping of
treated, brick-like sludge and untreated filter cake with fly ash. While
disposal of untreated sludge on the continental shelf is not presently
considered to be a promising alternative (either for sulfite-rich or
sulfate-rich) it is included for comparative cost purposes.
The disposal operation for on-shelf disposal would be almost identical
for treated and untreated (filtered) sludge, except that treated sludge is
assumed to require excavation of the treated material from stabilization
ponds as previously described (in order to produce the brick-like material).
The excavated sludge or filter cake admixed with fly ash would be conveyed
to a storage/transfer area for intermediate storage and loading of the
barges. A storage/transfer system involving a hopper feeder has been
303
-------
assumed, a system similar to that used for loading rail cars. However,
the transfer system can vary considerably depending upon the distance
between the power plant and the dock and the type of docking facilities
available. In many cases, an overhead crane might be more appropriate for
loading barges.
The sludge could be transported either by a tug/barge combination or
by a self-propelled ship. A 500-megawatt power plant producing 365,000 tons
of dry sludge (filter cake plus ash) would require one tug and two barges
for an on-shelf dump, using a nominal cycle time of 18 hours for each barge
and a 14-hour cycle time for the tug. Only one self-propelled ship would
be required. Due to its greater speed (10 knots versus 5 knots for the
tug/barge), the self-propelled ship would have a total cycle time on the
order of nine hours under normal conditions. In both cases the system
would need to be designed with the capacity to handle short-term peaks in
sludge production and interruptions due to inclemental weather. Hence, both
the self-propelled ship and each barge should be sized to handle about
2,500 tons of sludge, and the storage area would need to be sized for about
a one-week inventory of sludge.
b. Off-Shelf Disposal
The system design and operation for deep ocean disposal of filtered
(or treated) sludge would be basically the same as that for on-shelf
disposal. The principal difference would be in the longer cycle times
owing to the greater transport distance (100 nmi versus 25 nmi). There-
t
fore, the number and/or capacity of the units would be greater. For deep
ocean disposal two tugs and three barges (48-hour cycle time) or two self-
propelled ships (^24-hour cycle time) would be required. These would
have the same capacities (2,500 tons) as in the on-shelf disposal case
for handling filter cake (with ash). Larger units could be built, but
this would decrease system flexibility.
Since disposal of untreated material (particularly sulfate-rich) off
the shelf appears to be more environmentally acceptable, dumping of
partially settled thickener underflow has also been considered. Thickener
underflow (^35-40% solids) would require larger barges and ships (3,500
tons versus 2,500 tons); hence, higher transport costs. There would be
304
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some cost savings in that the transfer system between the FGD system and
the barge or ship could be quite simple (at the extreme, just a pipeline),
and there would be no need of filtration equipment. However, these cost
savings would be offset by higher transport costs and some type of sludge
storage area, such as an additional barge, to supplement the thickener.
2. Disposal System Costs
Table VII-5 summarizes the capital and operating costs for bottom-
dump disposal of sludge. These estimates include only the costs incurred
in handling and disposing the sludge in the form indicated. Processing
costs such as admixing fly ash with filter cake, conversion to sulfate, or
treatment (except excavation) are not included. Monitoring costs also are
not included. Monitoring costs can be highly variable depending upon ocean
depth, environment, species, or parameters monitored and frequency of
dumping. They will, however, be a significant, if not a major, cost
factor. Assuming two to three monitoring cruises per year (not including
baseline monitoring), monitoring costs could run between $500,000 and
$l,000,000/year for on-shelf disposal and twice this amount for off-shelf
disposal. As in the case of mine disposal, monitoring costs would not be
a direct function of the quantity of sludge dumped, and therefore it would
not be appropriate to include these costs directly in the operating cost
estimates. The same costs could be incurred with an order of magnitude
increase in the quantity of sludge dumped.
In all cases the costs for operating a self-propelled ship disposal
system are lower than those for the tug/barge combination due to the lower
capital investment (fewer ships due to shorter cycle times). The cost
difference, as would be expected, is much greater for the deep ocean
disposal where the proportion of travel time to port time increases. For
deep ocean disposal the self-propelled ship is also favored because it is
more seaworthy and hence less affected by climatological conditions.
In general, disposing of filter cake (with ash) on the shelf runs
$4.00-5.00 per dry ton of sludge, and disposal of treated sludge runs
about $2.00-2.50 per dry ton more due to excavation costs. Deep ocean
disposal runs about $3.00-4.00 per dry ton more than shallow ocean disposal
for similar materials.
305
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TABLE VII-5
CAPITAL AND OPERATING COSTS FOR OCEAN DISPOSAL ALTERNATIVES
(Bottom-Dump Disposal)
Capital Cost
Operating Costsc
U)
o
Ocean Locale
Continental Shelf
(25 nmi)
Deep Ocean
(100 nmi)
Sludge Type
Filter Cake + Ash
(50% solids)3
Treated, from Stabi-
lization Ponds
Filter Cake + Ashb
(50% solids)
Thickener Underflow
(35% solids)b
Treated, from Stabi-
lization Ponds
Transport Mode
Tug/Barge
Self-Propelled Ship
Tug/Barge
Self-Propelled Ship
Tug/Barge
Self-Propelled Ship
Tug/Barge
Self-Propelled Ship
Tug/Barge
Self-Propelled Ship
($MM)
3.7
3.2
7.4
6.9
7.25
5.3
7.95
5.80
7.25
5.3
($/dry ton) ( -v
4.90
4.15
7.10
6.35
8.90
6.85
10.05
8.05
11.10
9.05
mils/kwh)
0.5
0.4
0.7
0.6
0.85
0.65
0.95
0.75
1.05
0.85
tJot considered promising.
Only considered promising for sulfate-rich sludge at the present time.
Costs do not include monitoring which can run $500,000-$!,000,000/year for two to three monitoring
cruises per year. Such costs are not a direct function of the quantity of sludge.
-------
Disposing of thickener underflow will be more expensive than disposing
of a dry, untreated material due to the overriding capital costs for the
ocean transport systems. In order to properly compare overall disposal
costs, sludge processing costs (filtration, oxidation, treatment, admixing,
etc.) need to be included. If untreated sludge can only be disposed of as
a sulfate-rich material, then it may also be necessary to include the entire
FGD system, since oxidation may be most practically accomplished as an
integral part of the FGD operation.
307
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/7-77-051
2.
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
AN EVALUATION OF THE DISPOSAL
OF FLUE GAS DESULFURIZATION WASTES IN MINES
AND THE OCEAN: Initial Assessment
5. REPORT DATE
May 1977
6. PERFORMING ORGANIZATION CODE
7.AUTHOR
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