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i! Research EPA 600 7 7B /. .-
November 19/H
Research c*e) L»evelopfi«r.t
Pollution Control
Guidelines for Coal
Refuse Piles and
Slurry Ponds
Interagency
Energy/Environment
R&D Program
Report
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the INTERAGENCY ENERGY-ENVIRONMENT
RESEARCH AND DEVELOPMENT series. Reports in this series result from the
effort funded under the 17-agency Federal Energy/Environment Research and
Development Program. These studies relate to EPA's mission to protect the public
health and welfare from adverse effects of pollutants associated with energy sys-
tems. The goal of the Program is to assure the rapid development of domestic
energy supplies in an environmentally-compatible manner by providing the nec-
essary environmental data and control technology. Investigations include analy-
ses of the transport of energy-related pollutants and their health and ecological
effects; assessments of, and development of. control technologies for energy
systems; and integrated assessments of a wide range of energy-related environ-
mental issues.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/7-78-222
November 1978
POLLUTION CONTROL GUIDELINES
FOR COAL REFUSE PILES AND SLURRY PONDS
by
W. A. Wahler and Associates
Palo Alto, California 94303
Contract Nos. 68-03-2344 and 68-03-2431
Project Officer
Edward R. Bates
Extraction Technology Branch
Industrial Environmental Research Laboratory
Cincinnati, Ohio 45268
INDUSTRIAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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DISCLAIMER
This report has been reviewed by the Industrial Environmental Research
Laboratory, U.S. Environmental Protection Agency, and approved for publica-
tion. Approval does not signify that the contents necessarily reflect the
views and policies of the U.S. Environmental Protection Agency, nor does men-
tion of trade names or commercial products constitute endorsement or recom-
mendation for use.
ii
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FOREWORD
When energy and material resources are extracted, processed, converted,
and used, the related pollutional impacts on our environment and even on our
health often require that new and increasingly more efficient pollution con-
trol methods be used. The Industrial Environmental Research Laboratory-Cin-
cinnati (lERL-Ci) assists in developing and demonstrating new and improved
methodologies that will meet these needs both efficiently and economically.
Reported here are the results of a study to investigate acid and heavy
metal ion concentrations in water passing through refuse piles, suspended
solids in waters from refuse areas and slurry ponds, noxious gases from ox-
idation and fires in refuse piles, and airborne particulates from dry, exposed
refuse surfaces. The report compiles information on construction practices
applicable to pollution control from local refuse disposal sites and concludes
that with proper planning coal refuse disposal sites can be put to useful
purposes and become an asset rather than a liability. For further information
contact the Extraction Technology Branch of the Resource Extraction and Han-
dling Division.
David G. Stephan
Director
Industrial Environmental Research.Laboratory
Cincinnati
iii
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ABSTRACT
The objective of this study was to develop pollution control guidelines
for construction, operation, and reclamation of coal refuse disposal piles
and slurry ponds. Eight active refuse pile sites and six slurry pond sites
in the eastern coal-mining region, selected as representative of the best
technology and operating procedures now in use for reducing water and air
pollution hazards, were evaluated. Detailed air and water quality sampling
programs were carried out in conjunction with in-depth studies of disposal
facility construction, operation, and reclamation methods.
It was concluded that environmentally acceptable refuse piles and slurry
ponds can be developed and operated using current technology (most of which
is available now in the mining and construction industries). For refuse piles,
proper layering and compaction techniques, drainage control (particularly of
acid drainage), diversion of surface and ground waters around refuse piles,
and ongoing reclamation of finished surfaces by covering them with selected
materials and promoting vegetative growth will combine to reduce both air
and water pollution. For slurry ponds, acid water drainage through dams or
abutments, as well as suspended solids in waters from the ponds, constitute
the major pollution control concerns. These problems can be minimi zed by:
(1) properly discharging slurry into ponds and maximizing slurry travel dis-
tance through the ponds to obtain maximum settling of suspended solids; (2)
proper design of slurry retention dams; (3) avoiding large flowthroughs of
runoff from upstream drainage areas; (4) returning clarified pond waters to
preparation plants for reuse; (5) isolating contaminated seepage waters from
ground and surface waters; and (6) collecting seepage below retention dams,
treating it (if necessary), and releasing it or pumping it back to the slurry
ponds.
This report was submitted in fulfillment of Contracts 68-03-2344 and
68-03-2431 by W. W. Wahler & Associates under the sponsorship of the U.S.
Environmental Protection Agency. The report covers the period December 3,
1975 to December 16, 1977, and work was completed as of June 30, 1978.
iv
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CONTENTS
Foreword ill
Abstract iv
Figures vii
Tables viii
Abbreviations ix
Acknowledgments x
Section
1 Introduction 1
Statement of the Problem 1
Purpose of the Study 2
Scope of Work 2
Method of Approach 3
Report Organization 5
2 Summary of Findings and Pollution Control Guidelines .... 7
Findings 7
General Conclusions 10
Summary of Guidelines 11
Suggestions for Future Research 14
3 Coal Refuse Properties 16
Pollution Mechanisms 16
Properties of Coarse Refuse 20
Properties of Fine Refuse 38
4 Preparation Plant Procedures 44
Refuse Recovery Circuits 44
Process Quantities 45
Material Sizing 45
Summary of Principal Guidelines 47
5 Site Selection 48
Environmental Considerations 48
Coal Refuse Deposit Classification System 50
Pollution Control 53
Summary of Principal Guidelines 56
6 Conveyance Systems 57
Coarse Refuse Conveyance 57
Slurry Transport Systems 58
Summary of Principal Guidelines 59
7 Guidelines for Refuse Pile Construction and Operation .... 60
Site Preparation 60
Site Development 64
Site Operation 69
Summary of Principal Guidelines 78
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8 Guidelines for Slurry Pond Construction and Operation .... 80
Slurry Pond Water Circuits 80
Pond Operation 84
Temporary Slurry Ponds 87
Slurry Retention Dams and Dikes 87
Pond Inspection and Maintenance 91
Summary of Principal Guidelines 91
9 Guidelines for Reclamation and Abandonment 93
Refuse Piles 93
Slurry Ponds 96
10 Alternative Disposal and Pollution Control Methods 98
Burial of Refuse In Surface Mine Spoil Piles 98
Underground Disposal 99
Use of Refuse as Construction Material 99
Dry Disposal of Fine Coal Refuse 100
References 102
Appendix A Results of Site Investigations and Sampling Programs . . . 104
Appendix B Field and Laboratory Tests Used to Determine
Refuse Properties 194
Glossary of Geotechnlcal Terms ... 205
Glossary of Coal Preparation Terms 211
vl
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FIGURES
Number Page
1 Gradation Summary, Coarse Coal Refuse 22
2 Gradation Summary, Fresh Coarse Coal Refuse 23
3 Atterberg Limits, Coarse Coal Refuse 25
4 In-Place Dry Density, Coarse Coal Refuse 28
5 Natural Moisture Content, Coarse Coal Refuse . 29
6 Effects of Grain Size on Permeability of Coarse Materials . . 31
7 Effects of Fines on Permeability of Coarse Materials .... 32
8 Gradation Summary, Fine Coal Refuse 39
9 Natural Moisture Content, Fine Coal Refuse 41
10 In-Place Dry Density, Fine Coal Refuse 42
11 Simple Refuse Pile Forms 51
12 Simple Slurry Pond Forms 51
13 Example of Subdraln 62
14 Site Development: Valley-Fill Refuse Pile 65
15 Site Development: Side-Hill Refuse Pile 66
16 Cell Development Plan for Waste Heap 67
17 Alternative Development Plan for Waste Heap 68
18 Improper Refuse Placement by Truck Dumping 71
19 Improper Refuse Placement by Aerial Tramcar Dumping 71
20 Slurry Pond with Fine Refuse Delta 82
21 Flood-Water Storage for Prevention of Downstream Pollution. . 83
22 Upstream Slurry Discharge System 83
23 Methods for Raising Slurry Pond Embankments 89
24 Zoned Dam Section 90
vll
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TABLES
Number Page
1 Average Changes in Water Pollutant Concentrations
between Water Inlet and Outlet Points 9
2 Averaged Air Quality Data for All Sites Sampled 11
3 Effects of Weathering on Coarse Refuse 27
4 Compaction Characteristics of Coarse Coal Refuse 30
5 Selected Chemical Characteristics of Underground Mine
Refuse Samples 34
6 Analyses of Effluents from Refuse from Mines in Five
Eastern U.S. States 35
7 Coal Refuse Production at Study Site Plants 46
viii
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ABBREVIATIONS
cm centimeter t
cu yd cubic yards Ib
ft foot/feet m
2 9
ft square feet ra*
ft3 cubic feet m3
A
ft-lb/ft* foot-pounds per square foot mg
gal
gpm
gm
ha
In.
kg
km
gallon(s)
gallons per minute
gram(s)
hectare
inch(es)
kilogram(s)
kilometer(s)
mg/£
mgd
Mt
Mt/d
Pa
tpd
yr
liter(s)
pound(s)
meter(s)
square meter(s)
cubic meter(s)
milligram(s)
mllligram(s) per liter
million gallons per day
metric tons
metric tons per day
Pascal(s)
ton(a) per day
year
ix
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ACKNOWLEDGMENTS
Many individuals in government agencies (particularly in the U.S. Bureau
of Mines and the Mine Safety and Health Administration) offered valuable ad-
vice and assistance in the site selection phase of this study, as did members
of the staff of the American Mining Congress. During final site selection,
officials and operating personnel of many disposal sites materially assisted
the study team with the site examinations. The cooperation of all these peo-
ple is gratefully acknowledged'.
The participation and wholehearted cooperation of the mine company man-
agements and the operating personnel of the nine selected sites was invalu-
able to the project team in carrying out the field work. Despite extremely
adverse winter weather conditions, and despite their own busy schedules, the
personnel at all nine sites were always ready to assist the field crews in
completing each site visit with a minimum of difficulties. This generous re-
sponse was in the great tradition of the mining industry to freely share op-
erating experience and successful technological innovations. This study is
truly the result of outstanding cooperation among government research and
regulatory groups, industry management, and site operating staffs.
The subcontractor for the water quality field and laboratory testing was
Environmental Control and Technology Corporation of Ann Arbor, Michigan. USC
Incorporated, of Pittsburgh, Pennsylvania, carried out the air quality field
sampling and laboratory testing programs.
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SECTION 1
INTRODUCTION
STATEMENT OF THE PROBLEM
With renewed interest in and demand for coal as a source of energy has
come a growing emphasis on pollution control in coal mining and utilization
activities. Much of the coal mined in the eastern United States today is
washed and processed to remove impurities and enhance quality, and the refuse
created during processing must be disposed of in an environmentally acceptable
manner. Coarse refuse, composed of chunks of soft shale or sandstone rocks
that range in size from sand to coarse gravel or cobbles, is generally dis-
posed of in dry landfills (called "refuse piles"). Fine refuse, a silt-sized
material, is usually transported from the processing plant in slurry form and
disposed of in settling ("slurry") ponds.
Four general types of pollutants—two affecting water quality and two
affecting air quality—are created by coal refuse disposal operations:
• Acids and heavy metals — these go into solution and create "acid
drainage problems when waters come into contact with refuse piles that contain
soluble pyritic materials.
• Sediments — suspended solids in waters from refuse areas, created
by surface erosion of refuse piles and/or solids carryover from slurry ponds.
• Gases — noxious gases released to downwind areas by refuse pile
oxidation and fires.
• Particulates — fine-grained refuse that, upon drying, may be carried
off from exposed piles as silt-sized, airborne particles.
Acid drainage (from active or abandoned disposal sites) is perhaps the
most serious of these types of environmental pollution. Numerous small
streams in the nation's eastern coal belts have been contaminated with acids,
dissolved salts, and heavy metals and are now incapable of supporting aquatic
life. In some mountainous areas of eastern Kentucky and southern West
Virginia, however, the major water pollution concern is sedimentation. Here,
as a result of heavy rainfall and storms, streambeds and adjacent land sur-
faces have become covered with inert, dark-colored coal refuse sediment which
inhibits aquatic life, adversely affects vegetation, and renders the environ-
ment unattractive.
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Gaseous emissions create significant air pollution problems. In the
past, coal refuse fires were sometimes purposely started to produce a hard
clinker residue ("red dog") used in road building. However, most coal refuse
fires started as a result of heat generated by the chemical oxidation of car-
bonaceous material in the refuse piles. Again historically, such fires were
often allowed to smolder for many years, releasing high-sulfur gases and smoke
to the atmosphere. Modern refuse piles seldom have ignition problems, because
of present practices which result in less combustible material within the pile
and because air permeabilities within the refuse mass are lower.
Airborne particulates from coal refuse disposal areas have sometimes been
a concern. The principal dust problems occur with abandoned slurry ponds which
have dried out and have not been properly protected from winds. Dust from haul
roads near populated areas may also be a concern.
In the past, disposal of coal refuse tended to be an end-of-the-line,
least-cost process, and many disposal areas were essentially unplanned and
unmanaged. Now, however, for environmental and safety reasons, disposal
practices are being significantly improved, as are disposal site reclamation
techniques, and careful preplanning for disposal facilities and operations is
increasingly being recognized as an essential in the development and utiliza-
tion of coal resources.
PURPOSE OF THE STUDY
The Industrial Environmental Research Laboratory-Cincinnati (lERL-Ci) of
the U.S. Environmental Protection Agency (EPA) assists in the development and
demonstration of new and better ways to control pollution caused by the ex-
traction, processing, and utilization of our nation's energy and materials
resources. As part of this responsibility, lEKL-Ci sponsored this study,
which had as its ultimate objective the development of guidelines for con-
struction, operation, and reclamation of coal refuse piles and slurry ponds,
with emphasis on environmental (water and air quality) protection and safety.
Included in the guidelines are considerations of refuse haulage, compaction,
layering, drainage, soil covering, preparation plant processes, and site
reclamation. To secure vital input for the development of the guidelines and
other purposes, the study also included extensive air and water quality
sampling and analysis programs, so that any detrimental effects caused by the
disposal of coal wastes could be identified and evaluated.
SCOPE OF WORK
The scope of work for the study included the following major items:
1. A review of current literature and interviews with key federal, state,
and industry personnel to obtain information concerning proper disposal
facility design for environmental protection, construction and maintenance
methods, and final close-down and reclamation procedures for coal refuse
piles and slurry ponds.
2. Selection and field evaluation of eight refuse pile and six slurry
pond sites, chosen to be representative of the best technology and construc-
tion procedures now in use in terms of reducing water and air pollution
-------
hazards. These sites, all in the eastern United States and in both flat and
mountainous terrain, were each visited and evaluated four times, to determine
operational procedures and problems and to carry out detailed water and air
quality sampling and evaluation programs.
3. Sampling programs at each site to determine flow, acidity, pH, con-
ductivity, alkalinity, sulfate ion, ferric and ferrous iron, aluminum, magne-
sium, manganese, copper, zinc, lead, cadmium, nickel, and mercury concentra-
tions in waters emanating from the site.
4. Sampling programs at each site to determine air pollution parameters
for sulfur and nitrogen dioxide, hydrogen sulfide, carbon monoxide, and
methane, and to measure and evaluate particulate emissions and concentrations.
5. Development of the construction and operation guidelines.
6. Preparation of this report, which contains case studies of the sites
visited, the data gathered in connection with the study, and the guidelines.
The stability of coal refuse retention embankments is an important con-
sideration in the development and utilization of disposal facilities. Since
the Buffalo Creek disaster of February 1972, when a coal refuse dam failure
caused 125 deaths and extensive damage in the downstream drainage basin, this
aspect of refuse disposal has received considerable national attention. In
this connection, the reader is directed to numerous recent studies and govern-
ment regulations concerning the safe disposal of coal refuse (see, for exam-
ple, References 1 through 4). Although the scope of work for this study did
not include specific evaluations of embankment stability, the study team has
drawn on its considerable experience with such problems in developing these
guidelines, and where pollution control and stability considerations interact
or affect each other, appropriate note has been made throughout the report.
METHOD OF APPROACH
Site Selection and Field Investigations
Selection of the field study sites involved the following steps:
• Development, from the information obtained through the literature
search and interviews, of a master list of more than 30 candidate sites.
• Aerial surveys of each site.
• Identification of 18 particularly promising sites, and after owner
approval and clearance had been obtained, a more detailed ground inspection
of each site.
• Final comparisons and evaluations of sites.
• Final selection of nine sites, which include eight refuse piles and
six slurry ponds. These sites, identified throughout the report as Sites A
-------
through I, are located in the states of Illinois, Indiana, Pennsylvania, and
West Virginia.
The detailed field studies involved making four visits to each site to
obtain and develop data on refuse pile and slurry pond construction,methods
and to conduct air and water quality sampling programs. These visits, carried
out over a 12-month period, were arranged so that each site was investigated
during both wet and dry weather conditions. For maximum efficiency, and to
minimize interference with normal site operations, the construction, water
quality, and air quality subteams visited each site together whenever this was
possible. However, because the air quality data collection required longer
sampling periods than did the water quality program or the construction
studies, the air quality team could not always maintain the same schedule as
the other groups.
At each site the study team reported to a site staff member who usually
accompanied the team during the field investigation. Site conditions were
reviewed to identify current and recent refuse disposal areas and to determine
if there had been any changes in operating procedures since the last visit.
Water quality sample selection points had been determined during the site
selection phase of the study; in the study field visits, after wind directions
had been determined, the same general locales were also used for the air
quality sampling, wherever possible.
Water Quality Sampling
Clean containers, rinsed with distilled water, were used for collection
of representative water samples. Samples to be analyzed later in the labora-
tory were refrigerated to preserve them until the tests could be run. Anal-
yses for properties susceptible to time deterioration were either performed
in the field immediately after the samples were taken, or later the same day
in the study team's mobile van.
Air Quality Sampling
A four-wheel-drive vehicle was used to transport the air sampling equip-
ment to the selected sampling location. The gasoline-powered generator for
the sampler was always operated at least 30 meters (100 feet) downwind of the
sampling point. A RAG 5-fias Sampler was operated for mea.9uremp.nt runs of
4, 6, or 8 hours. The sampler was inspected visually every half-hour, to
ensure that proper bubbling action and vacuum conditions were present. Wind
direction and speed, as well as temperature, were measured at least once an
hour.
A battery-powered RAC Midget Impinger, charged with a tared filter paper
disc which had been transported in a sealed cassette, was operated for 1 hour
at 15 liters per minute. At the end of the sampling period, the disc was
replaced in the cassette and resealed.
On the first site visits to all sampling locations, an AID portable gas
chromatograph and a recorder (both battery-powered) were taken* to the samp-
pling points. Samples of 10 cc of air were collected in a syringe and
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injected into the chromatograph. However, successful use of this equipment
demands a steady base and no air drafts, and attempting to operate the unit
in the four-wheel-drive vehicle resulted in unsteady baselines. Therefore,
for the second site visits the chromatograph was set up where steady work sur-
faces were available—for example in an office building, superintendent's
office, or bathhouse. Air samples were collected in syringes and taken to the
gas chromatograph for injection. This procedure yielded satisfactory results.
For the third and fourth visits, the gas chromatograph remained in the air
quality subcontractor's offices and the air samples were returned in sealed
syringes. Previous tests for CO and Clfy, with analyses performed as much as
two weeks after sample collection, had yielded valid results, and the proce-
dure proved satisfactory in this case also.
Development of Guidelines
Information obtained from the literature search, discussions with key
personnel, and site visits was compiled and evaluated. To this body of
material was added much valuable information drawn from the past experience
of the study team members regarding disposal practices and problems in other
types of mining operations and in other industries. Although the guidelines
are intended primarily for those responsible for the everyday tasks of con-
structing, operating and reclaiming disposal facilities, considerable informa-
tion has been included that can be valuable in the planning and engineering
phases of facility development. Recommendations and suggestions are provided
to indicate how technology used in other fields can be successfully adapted
to coal refuse disposal, and examples of acceptable practice are given to
illustrate solutions to specific problems.
As far as possible, the guidelines were prepared to conform to current
federal and state safety regulations, as well as to environmental protection
regulations. Any conflicts that appear to exist between safety and environ-
mental considerations as they relate to construction procedures are noted in
the guidelines, for attention and resolution by others, as appropriate.
REPORT ORGANIZATION
Section 2 summarizes the study findings and the guidelines for disposal
site development, operation, and reclamation. Also included in Section 2 are
some suggestions for possible future research into factors that may have
important bearing on pollution control and disposal site development and
utilization. Section 3 discusses pollution mechanisms and the physical and
chemical properties of coal refuse. Section A deals with coal preparation
plant processes and procedure, Section 5 with site selection, and Section 6
with conveyance systems for transporting refuse from plant to disposal area.
Sections 7 and 8 present construction and operation guidelines for refuse
piles and slurry ponds, respectively, and Section 9 provides guidelines for
site abandonment and reclamation. Section 10 describes a number of alterna-
tive techniques for refuse disposal and pollution control that may be appli-
cable in specific situations.
Detailed descriptions of the study sites, together with the air and
water quality data obtained and analyzed in the study, are included in
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Appendix A. Appendix B discusses and describes certain standard field and
laboratory tests, used to determine the properties of soils, that can be
usefully applied to the determination of coal refuse properties. Finally,
glossaries of geotechnical terms and coal preparation and relevant water and
air pollution terms are provided.
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SECTION 2
SUMMARY OF FINDINGS AND POLLUTION CONTROL GUIDELINES
FINDINGS
Construction and Operation of Slurry Ponds and Refuse Piles
Slurry Ponds—
Prior to 1972, coal refuse slurry ponds were often formed by dumping
coarse refuse across narrow valleys to create embankments behind which fine
refuse was placed hydraulically.^ Some of these embankments (dams or dikes)
were built haphazardly, without adequate concern for embankment stability or
the possibility of overtopping. Also, when an embankment was constructed by
dumping refuse down steep slopes from aerial tramways, trucks, or mine cars,
the base of the embankment was highly permeable and heavy seepage at the down-
stream toe was common. If acid-producing refuse was used, the seepage water
was acidic and had high concentrations of heavy metal ions.
In addition to acid water drainage through dams or abutment formations,
a major slurry pond pollution control concern today is the removal of sus-
pended solids from the pond. Usually, the most troublesome ponds are large,
crossvalley impoundments in narrow, steep valleys which lie below large drain-
age basins. During heavy rains, concentrated, high-velocity runoff waters
enter such ponds, reducing pond efficiency and disturbing previously settled
solids. Special control provisions are usually required for such situations.
In the construction and operation of slurry ponds, the following general
guidelines are of major importance in controlling pollution:
• The minimum practical velocity should be used in discharging slurry
into a pond.
• Travel distance of slurry through the pond surface should be maximized,
to achieve maximum settling of suspended solids.
• Wherever possible, clarified pond waters should be returned to the
preparation plant for reuse.
• Clarified water for return to the plant or for discharge to streams
should be removed from points as close as possible to the top water surface
of the pond.
*For numbered references, see list at end of report.
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Seepage appearing at the downstream toe of the pond retention dam
should be collected, treated (if necessary), and released or pumped back to
the retention pond.
Refuse Piles—
Drainage from old, acid-producing refuse piles and from erosion of exposed
refuse banks is generally a serious water pollution control problem, as
is the problem posed by suspended solids from slurry ponds. In the past, coal
refuse was usually dumped from trucks or rail cars over steep slopes, or from
aerial tramways across narrow, steep valleys. Coarse refuse particles there-
fore collected near the toes of the slopes, and finer constituents remained
near the top of the pile. These loose piles often became unstable if they
were used to impound water, or if they were saturated by moisture from heavy
rains or from springs within foundation areas. Ground or surface waters pass-
ing through the permeable base of an acid-producing refuse pile became highly
acidic. The acid waters, in turn, dissolved heavy metals in the refuse,
further degrading downstream water systems. Also, surface waters from adja-
cent areas and from the pile itself would often (especially after heavy storms)
erode large gullies in the pile and deposit the sediment downstream.
Another type of pollution problem—one of air pollution—was created by
the fact that many old refuse piles that contained large amounts of coal
either caught fire or were purposely ignited. Such fires were allowed to
smolder, sometimes for years, steadily releasing noxious gases and particulate
matter into the surrounding atmosphere.
Today, fortunately, these disposal practices have been largely abandoned,
and in the construction and operation of new refuse piles it is relatively
simple to guard against these causes of air and water pollution.
In the construction and operation of refuse piles, the following general
guidelines are of major importance in controlling pollution:
• Layering and compaction. Proper layering and compaction techniques
and operations will help significantly in eliminating particle segregation
and in reducing the air and water permeability of the refuse mass.
• Drainage control. Both surface and ground water should be diverted,
by means of ditches or subdrains, around refuse piles in order to minimize
acid runoff and/or surface erosion. Runoff water from pile surfaces should
be directed away from slope faces into ditches or sedimentation ponds. Drain-
age appearing from beneath piles should be collected and treated, if necessary,
before release to the environment.
Water Quality Sampling Program
As indicated in the tabulation below, at the five sites (A through E)
where unique inlet and outlet points could be identified it was found that,
except at Site A, the pH was lower in the outlet (discharge) waters than in
the inlet waters, although, on the average, most differences were relatively
small. The tabulation represents averages of the measurements taken on all
visits to the sites:
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Site
B
Inlet point
Outlet point
Change
+0.1
-0.3
-0.6
-0.8
7.6
4.7
-2.9
The sampling program also indicated that if oxidation of pyritic material
in a disposal area had occurred or was occurring, there were generally
increases in pollutant concentrations in the discharge waters as compared with
concentrations in inlet waters. Where acidic water was in contact with the
refuse, there were increased concentrations of ferrous iron, total iron, sul-
fates, dissolved heavy metals (copper, manganese, nickel, and zinc), and,
depending on the mineral content of the refuse, there were increased concen-
trations of chloride and the lighter metals such as aluminum and magnesium.
Table 1 indicates average changes in pollutant concentrations based on
measurements taken at inlet versus outlet points at Sites A through E. As for
the changes in pH values given above, these figures represent averages of all
measurements taken on all visits to the sites. Detailed findings for each
visit to each site are given in Appendix A, together with details for other
sites which did not have both an identifiable inlet point and an identifiable
outlet point. Study of Appendix A reveals that the actual concentrations
measured varied widely, depending on the site being studied, the time of year
for each visit to each site, sampling locations, etc. However the data given
in Table 1 appear to give a reasonably valid general picture of the changes in
quality caused by the passage of water through coal refuse disposal facilities.
TABLE 1.
Pollutant
Ferrous iron
Total iron
Aluminum
Chloride
Copper
Lead
Magnesium
Manganese
Nickel
Sulfate
Zinc
AVERAGE CHANGES IN WATER POLLUTANT CONCENTRATIONS
BETWEEN WATER INLET AND OUTLET POINTS
(mg/liter)
Increase or Decrease (-) as Measured at Outlet Point
ABC D E
0.03
0.44
0.32
-8
0.001
-0.007
4
0.07
0.001
75
0.01
0.47
15.84
1.14
139
0.005
0.024
26
2.50
0.022
925
0.05
0.93
5.10
0.93
15
0.012
0.009
63
5.44
0.017
,426
0.012
6.83
9.13
3.10
None
0.011
0.006
9
1.96
0.021
203
0.06
299.9
351.5
42.51
205
0.031
-0.001
104
29.31
0.408
3,037
2.67
-------
Air Quality Sampling Program
All of the sites visited were exercising operating control over airborne
particulates; that is, roads were being sprinkled when conditions required,
and exposed refuse surfaces were being covered and seeded to prevent wind
erosion. Although no samples were taken after a long, hot, dry spell when
dust might be at its worst, the particulate measurements were in general quite
low. This may have been due in part to the use of watering trucks, but the
wet, fine-grained nature of the waste, the layering of material, and the low
level of traffic in the refuse areas (four to six trips an hour were usual)
are also significant factors.
Table 2, a summary of the data gathered in the air sampling program, pre-
sents figures on air pollutant concentrations that represent a composite aver-
age for all the sites visited. Detailed measurements for each site are given
in Appendix A. Gaseous emissions were well within the normal backgrounds
expected for the geographic areas. While four single-day samplings at one
specific point cannot be considered ultimate scientific proof, the data
obtained suggest that these coal refuse piles and slurry ponds do not contrib-
ute significant levels of nitrogen dioxide (N02), sulfur dioxide (S02), hydro-
gen sulfide (H2S),. carbon monoxide (CO), or methane (CH2) to the atmosphere.
There was some evidence that the extremely cold weather during the second site
visits (in January 1977) caused a lowering of gaseous emissions. However,
this may have been a result of decreased industrial activity during this cold
period, since much of the mining and associated industrial traffic had almost
ceased.
It is obvious from the data collected during this study that proper con-
struction practices, routinely applied, can lead to development of coal refuse
piles that produce little or no gaseous emissions. The permeability that led
to pyritic decomposition and eventual burning of old, randomly dumped piles
does not exist to a significant extent in today's properly layered, compacted
sites.
GENERAL CONCLUSIONS
The overall conclusion reached by the study team, from the literature
search, interviews, and field study program, is that environmentally accept-
able coal refuse disposal facilities can be constructed, operated, and
reclaimed using current technology. The potential for pollution of air and/or
water can be reduced sufficiently that both fine and coarse refuse disposal
sites can be operated during the life of a coal processing plant without
deleterious effects on the environment, and the site can later be returned to
a productive use. However, the accomplishment of such operation and reclama-
tion is not a simple hit-or-miss proposition. Well-planned utilization of
10
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TABLE 2. AVERAGED AIR QUALITY DATA FOR ALL SITES SAMPLED
Visit 1 Visit 2 Visit 3 Visit 4 Average
Temperature (°C) -5 -24 16 24
Weather Conditions
Wind Speed (mps) 3.0 2.7 2.0 1.1
Wind Speed (mph) 6.5 6 4.5 2.5
Wind Direction
Dust/Particulates (mg/liter) 0.03 0.01 0.03 0.02 0.02
Gases (mg/liter)
Nitrogen dioxide 0.047 <0.01 0.036 0.028 0.029
Sulfur dioxide 0.078 <0.01 0.036 0.028 0.037
Hydrogen sulfide 0.046 <0.03 0.014 0.012 0.024
Carbon monoxide 1.5 1.3 1.7 1.5 1.5
Methane 3.1 3.0 3.3 3.3 3.2
modern materials and equipment technology, primarily from the construction
industry, is necessary in order to achieve pollution-free refuse disposal.
The guidelines presented in this report and summarized in the following para-
graphs were developed in the context of this general conclusion.
Throughout the guidelines, a continual emphasis on air and water control
is obvious. If the introduction of air into the refuse material is controlled,
extensive oxidation of pyrites will not occur and significant amounts of gas-
eous and acidic pollutants will not form. If ground and surface waters are
isolated from the refuse material, little or no alteration of these waters
will take place.
SUMMARY OF GUIDELINES
This discussion briefly summarizes the guidelines we believe embody the
most important considerations associated with proper development, operation,
and reclamation of refuse piles and slurry ponds to achieve satisfactory
environmental (air and water quality) protection. For more comprehensive
discussions of the guidelines, and for details of all the guidelines, the
reader is referred to the subsequent sections of this report.
The guidelines follow the sequence of (1) site development, (2) site
operation, and (3) site reclamation. There is inevitably some redundancy in
using this chronological approach, but since the guidelines are intended for
day-to-day use by persons concerned with specific aspects of these three
principal life stages of disposal sites, it is believed that this redundancy
is acceptable.
Site Selection
• Refuse piles and slurry ponds should be isolated from surface and
ground waters.
11
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If possible, the disposal facility should be so sited that drainage
from the refuse pile is diverted into the slurry pond.
Sites with large drainage areas above the disposal facility should be
avoided.
Cross-valley refuse piles should be avoided.
Preparation Plant Procedures
• Coarse acid-producing refuse from rotary breakers should be mixed
with screened refuse or placed in noncritical (central) areas of a refuse
pile.
Preparation plant procedures should be directed at increasing the
percentage of fines to reduce air and water permeability of placed and com-
pacted refuse material.
Conveyance Systems
• Acid-producing refuse should not be used as haul-road building
material.
Conveyor belts should be provided with a belt reversal mechanism to
avoid spillage on the belt return run.
• Aerial tramway systems should include provisions to preclude uninten-
tional dumping of refuse along tramway routes.
• Slurry pipelines for fine refuse should be located away from land-
slide areas, and structural sleeves should be provided where the pipeline
passes under roadways.
Site Development
• Debris from clearing and grubbing operations should not be disposed
of in refuse piles or slurry ponds.
• Where feasible, topsoil from stripping operations should be stock-
piled for later use in reclamation.
• At refuse pile sites where there are springs, foundation subdrains to
control groundwater should be incorporated.
Surface waters should be diverted around refuse piles and slurry ponds.
• Where appropriate, sedimentation basins should be planned for and
developed downstream from refuse piles.
• A valley-fill refuse pile operation should start at the head of the
valley and progress in the downstream direction.
12
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• Cell-type construction methods should be used to dispose of acid-
producing refuse on flat or gentle terrain.
Refuse Pile Operations
• Exposed working surfaces of refuse piles, particularly acid-producing
refuse, should be kept to the minimum consistent with safe and effective
operations.
• Finished refuse surfaces should be reclaimed soon after completion,
and in any case during the operational life of the facility.
• Permanent side slopes should be no steeper than 2 horizontal to 1
vertical.
• Top surfaces should be sloped to drain away from side slopes.
• Top surfaces should be graded on an approximately 1-1/2 percent slope.
The degree of dust control required on haul roads should be determined
on the basis of conditions at the specific site.
• Coarse refuse should be placed using methods that will not result in
segregation of materials. Refuse should not be dumped or pushed over the
faces of steep slopes.
• Truck-placed piles of potentially acid-producing refuse should be
leveled and compacted at least once every working shift.
• Lift thickness should be the minimum practical, and in any case should
be no more than 60 centimeters (2 feet).
Nonstructural refuse embankments may be compacted satisfactorily by
controlled routing of construction equipment over thin lifts. Loaded scrapers
are usually more effective than bulldozers or on-highway trucks for this
operation.
• Special, noncritical areas on the site should be designated or
reserved for placement operations during inclement weather.
• Operations that cause an increase in the percentage of fines (to a
maximum of approximately 15 percent) in acid-producing refuse, and thereby
reduce the permeability of the compacted mass, are considered desirable.
Slurry Pond Operations
• If possible, slurry ponds should have "closed" water circuits.
• Slurry ponds with "open" water circuits should have sufficient
settling area to meet point source discharge requirements.
13
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• The use of acid-producing refuse in slurry pond retention embankments
should be avoided unless seepage waters can be isolated.
• Sites should be inspected at least once a week in order to observe
operating conditions and to make any necessary adjustments in pond operations.
Reclamation
• Drainage should be directed away from side slopes except in lined
channel sections.
• Refuse pile surfaces should be graded to a minimum slope which will
not result in ponding of waters.
• A cover layer of nontoxic clay soils sufficiently thick to promote
acceptable vegetative growth should be provided.
• Piles that may contain acid-producing refuse should have an imperme-
able upper zone of natural soil or refuse extending from the surface to at
least 60 cm (2 feet) below the depth of frost penetration, to exhibit perco-
lation of surface water.
Alternative Disposal and Pollution Control Techniques
Coarse refuse from surface mine operations should, if possible, be
buried in the mine spoil piles.
Refuse disposal in underground mine workings should be undertaken only
after detailed evaluations of potential groundwater degradation have been made.
• Slurry ponds should not be constructed in surface mine spoil banks
unless groundwater and embankment stability studies indicate it is safe to
do so.
SUGGESTIONS FOR FUTURE RESEARCH
At some future date, consideration should be given to selecting a few
(two or three) sites where round-the-clock measurements can be made over an
extended period of time, using sophisticated recording instruments to deter-
mine any significant changes in air or water quality. Attempts might be made
to correlate variations in these measurements with dumping practices and other
operations. For comparison purposes, simultaneous measurements should be made
upwind or upstream from the sites.
Also, although it might prove difficult to secure operator cooperation,
investigations of other disposal facilities (including some "hot" or acid
piles) that are not utilizing good construction practice might be considered.
It must be emphasized that the sites investigated in this project were con-
sidered to be following good practices. Comparisons with poorly operated
sites might indicate the amount of environmental benefit that could be real-
ized by proper operations at all sites.
14
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Information has been developed by the Illinois State Geological Survey
and others on groundwater contamination by trace elements from municipal land-
fills. Included in this information are some assessments of the effectiveness
of various types and thicknesses of clay pond liners in trapping trace ele-
ments. With existing knowledge of trace elements in coals and coal cleaning
wastes, it may be worthwhile to initiate some research and prototype studies
to evaluate the physical effectiveness, comparative environmental impacts, and
economics of using clay liners to reduce groundwater contamination from coal
refuse piles and slurry ponds.
15
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SECTION 3
COAL REFUSE PROPERTIES
In order to evaluate the effect of a coal refuse disposal area on water
and air quality and to suggest effective pollution control guidelines for such
facilities, it is necessary to understand the properties of the refuse mate-
rial, the pollution-forming mechanisms, and the factors which significantly
influence these mechanisms. It is not possible to use identical pollution
control guidelines for all refuse sites. Some types of refuse have a high
pollution potential, so that extensive control measures must be employed.
Other types have a lower pollution potential and therefore require less in the
way of pollution control. For example, refuse capable of producing acid
requires more extensive controls than does nonacid-producing refuse. The
properties of both coarse and fine refuse significantly affect construction
and operations from the standpoint of pollution control.
An understanding of water and air pollution formation mechanisms and the
factors which significantly influence these mechanisms is of paramount impor-
tance. Without this understanding, pollution control guidelines would have to
be formulated on a trial-and-error basis. This type of approach is extremely
risky when dealing with variable material properties and site capabilities and
can result in unnecessary cost and unacceptable levels of pollution.
POLLUTION MECHANISMS
There are four principal forms of pollutants associated with coal refuse
piles and/or slurry ponds:
Water Pollutants
1. Acid drainage from refuse piles
2. High suspended solids concentrations in drainage water from refuse
piles and slurry ponds
Air Pollutants
1. Release of noxious gases from burning refuse piles
2. Dust from active refuse piles and exposed slurry pond deltas
Water Pollution
Acid Drainage—
Acid drainage requires the presence of water, oxygen, and sulfur compounds
capable of oxidizing. By far the most common acid-producing sulfide mineral is
iron sulfide, but others (copper, zinc, or lead sulfides) may also be associ-
ated with the refuse.
16
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The chemical reactions in acid production are believed to be as follows.
First, the pyrite is oxidized by oxygen to produce ferrous sulfate and, when
water is added to the system, sulfuric acid is produced r^1
2FeS
2
2H20
(pyrite) (ferrous sulfate + sulfuric acid)
Subsequent oxidation of ferrous sulfate produces ferric sulfate:
4FeS0 + 2HS0 + 0 - >
The reaction may then proceed to form a ferric hydroxide or basic ferric sul-
fate and more acid:
2Fe(OH)3
3 + 2H20 - > 2Fe(OH)
A low pH water is produced (pH 2 to 4.5). At these pH levels, the heavy
metals such as iron, calcium, magnesium, manganese, copper, and zinc which are
also associated with the refuse are more soluble and enter into the solution
to further pollute the water.
Not all pyritic material is readily oxidizable. Caruccio^ has shown that
finer-grained pyrites (2 - 15 microns) rapidly decompose when exposed to the
atmosphere, while coarse pyrite particles (larger than 50 microns) remain
relatively stable. In addition, there may be other chemical constituents
(e.g., lime) in the refuse which tend to neutralize the acid produced.
Several other variables can influence the amount of acid produced:
1. The amount of soluble impurities in the refuse pile
2. The distance water travels through the pile
3. The oxidation rate of the pyrite material
4. The time water is in contact with the soluble materials
5. Temperature (the lower the temperature the lower oxidation rate)
Suspended Solids —
Suspended solids in waters leaving a refuse area are caused principally
by surface erosion of refuse piles and insufficient settling of solids in
slurry ponds. Erosion is caused by water moving over a material at a velocity
sufficient to carry off particles of material.
The principal variables that affect the settling of suspended solids in a
slurry pond are the particle size and specific gravity of solids, the kinematic
viscosity of the fluid, velocity of slurry movement through the pond, and
length of free-water surface between the slurry discharge point and the clear
17
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water decant structure. The settling velocity of a suspended solid, which
varies approximately with the square of the particle diameter, is the most
significant variable with respect to efficiency of settling basins. Most fine
refuse is silt-sized, with varying amounts of sand. The specific gravity of
fine coal refuse normally ranges from 1.6 to greater than 2.4, depending on
the composition of the materials. This is substantially less than most soils,
which have specific gravities near 2.6 to 2.7.
The primary variable that affects the kinematic viscosity of water is
temperature. The viscosity of water at 1°C is about twice the viscosity
at 30°C. Ponds are therefore much less efficient in the winter than in the
summer. The velocity of the fluids through a settling pond affects the time
available for particle sedimentation and the drag forces, or resistance to
downward movement, on the settling particle. The lower the velocity, the less
the turbulence and the greater the efficiency of the pond. The greater the
length of the slurry path over clear water, the more time there is avilable
for the particles to settle.
Air Pollution
Gases from Refuse Pile Fires—
Ignition of combustible material within a refuse pile, and the resulting
release of noxious gases, can be initiated in several ways. These include
spontaneous combustion, careless burning of trash on or near the bank, grass,
brush, or forest fires, camp fires left burning, and intentional ignition to
create residue ("red dog") which may be used for road base or other foundation
purposes.
All these mechanisms except spontaneous ignition are the result of human
activities and must be controlled by education and site security. Spontaneous
ignition occurs when the heat generated by the oxidation of organic material
(including coal) and/or pyrite is sufficient to cause ignition. For this to
occur, sufficient air must enter the refuse dump to oxidize the coal and other
combustible materials, but the air must be insufficient to carry away the heat
generated during the oxidation. In studies by England's National Coal Board^
it was determined that temperature, coal rank, presence of pyrites, moisture,
voids ratio, and specific surface influence spontaneous combustion.
Temperature. The combination of atmospheric oxygen with carbonaceous
material is exothermic (heat is given off). If the generated heat is not
dissipated, the oxidizing and heating effects become cumulative and the
temperature rises rapidly, increasing the rate of oxidation still more. Coal
and carbonaceous materials may oxidize in the presence of air at temperatures
far below their ignition points. Cellulose materials, such as wood, straw,
jute, paper, and cardboard, do not react appreciably with oxygen until they
approach their ignition temperatures, in the range of about 260°C to 300°C.
However, at ambient temperature and in the presence of moisture, these
materials are subject to spontaneous heating through the action of certain
microorganisms. For this reason, and because they ignite easily, materials
containing cellulose should not be deposited in or on coal refuse piles.
18
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Coal Rank. In general, lower rank coals are more reactive and hence
more susceptible to self-heating than higher rank coals.
Presence of Pyrites. Iron pyrite (FeS2) is oxidized at normal tempera-
tures by moist air to form sulfate and sulfuric acid. This reaction is highly
exothermic. Pyrite, if present in sufficient proportion, and particularly
when finely divided and associated with carbonaceous matter, increases the
tendency toward spontaneous combustion in coal refuse piles. When heating
occurs, the oxidation of pyrite and organic sulfur in the coal will form sul-
fur dioxide, and if there is insufficient air for complete oxidation, hydrogen
sulfide will be given off. The characteristic smells of these gases sometimes
provide a means of detecting a burning area or hot spot.
Moisture. At relatively low temperatures, an increase in free moisture
increases the rate of spontaneous heating. High inherent moisture, a feature
of low rank coals, is, paradoxically, indicative of a tendency to spontaneous
heating. The presence of free moisture is essential for the oxidation of
pyrite, and in the presence of pyrite, moisture accelerates oxidation and
contributes to heating.
Voids Ratio and Specific Surface. The ease with which air passes through
refuse containing carbonaceous material determines the rate at which heat
generated by oxidation is carried away. With large-size material and larger
air voids, the movement of air is usually sufficient to carry away any heat
generated by oxidation and to cool the material. With well-graded or fine
material with small air voids, the air remains stagnant and the heat generated
is retained in the mass, but when the available oxygen is consumed, heating
stops. With intermediate gradings and voids the conditions for spontaneous
heating are ideal, and the heated parts may form hot spots and eventually
break into flame. Another important factor in the oxidation process is the
specific surface of the carbonaceous materials exposed to air. The rate of
oxidation generally increases as the specific surface increases, i.e., as the
size of particles decreases.
Burning refuse piles are largely confined to old deposits which contained
considerable combustible material and which were dumped in large, loose piles.
Modern refuse piles seldom have ignition problems, because there is less com-
bustible material in the pile and because air permeabilities in the refuse
mass are lower.
Dust—
Dust is the transport by wind of small particles (less than 1 mm in
diameter). Such particles have a lower falling velocity than the upward
velocity of the turbulent winds and are carried in eddies that move in all
directions. Dust from dry refuse piles and associated haul roads can be a
pollution source because vehicular traffic causes the fine components of the
refuse to be physically lifted up from the surface and carried away by winds.
Dust can also be a problem on slurry ponds which have large deltas of exposed
fine refuse above the pond level.
Winds are usually classified by speed, direction, and turbulence. Sur-
face winds are turbulent for all velocities over approximately 2 to 3 mph.
19
-------
However, wind velocity decreases substantially toward ground level because
of frictional drag. Since soil erosion is strictly a surface phenomenon, the
wind speeds and turbulence to be considered in connection with soil erosion
are those at, or close to, the ground. This turbulence is usually observed
as gusts that cause localized soil disturbance. The minimum threshold veloc-
ity required to start soil movement varies with grain size. The threshold
velocity for grain sizes from 0.1 to 0.15 mm is 8 to 9 mph at 15 cm (6 in.)
above the ground. Above and below these sizes threshold velocity increases.
The range of threshold velocity for all grain sizes is from 13 to 30 mph at a
height of 30 cm (1 ft) above the surface.
Wind separates the soil into two fractions by removing and redepositing
elsewhere the highly erodible grains, leaving wind-stable particle sizes
behind, and wind also provides the energy for saltation—the process of
alternately lifting and dropping particles. The amount of soil eroded by wind
depends on wind velocity, height of protruding nonerodible particles, and dis-
tance between protrusions. The height that slows wind velocity to 9 mph or
lower is called the "critical height," and the ratio of height of projection
to the minimum distance between projections that will prevent the movement
of erodible fractions is called the "critical surface-roughness coefficient."
These are the most important factors to be taken into account when considering
the interactions of winds and soils.
PROPERTIES OF COARSE REFUSE
The physical and chemical properties of coarse refuse have received sub-
stantial attention in the past. Most investigations of physical properties
have been directed at evaluating the suitability of materials for use in
engineered fills or at determining the safety or stability of coarse refuse in
piles or embankments to retain slurry ponds. Work on chemical properties of
coarse refuse has been primarily associated with establishing suitable plant
growth directly on exposed piles and to a lesser extent on pollution control.
As indicated in the list below, physical properties refer to both index
and engineering properties; these reflect the physical makeup of the soil-like
materials. The materials may consist of rock particles, gravel, sand, silt,
or clay, or they may be processed materials such as coal refuse. Regardless
of the type, their physical properties must be determined on the basis of
experience and/or field and laboratory tests, in order to determine the
physical makeup and engineering characteristics of the material.
PHYSICAL PROPERTIES OF COARSE REFUSE
Index Properties Engineering Properties
Grain-size distribution Moisture-density characteristics
Plasticity Relative compaction and density
Specific gravity Permeability
Parent material Compressibility
Soil structure Static and dynamic shear strength
Ignition point tests Moisture-volume changes
20
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Field and laboratory tests used to determine the physical properties of
refuse are described in Appendix B. An important consideration in such test-
ing is degradation of the material during the sampling, transporting, and test-
ing stages. Coal refuse is commonly composed of soft, clay-shale particles
which readily break down into smaller particles when exposed to air and/or
water and when mechanically handled and tested. As a consequence, laboratory
testing of degraded refuse materials may yield results which are not repre-
sentative of the actual physical properties in the field. Such results can
be extremely misleading. For example, if permeability tests are performed on
reconstituted coarse refuse samples compacted in a mold with an impact hammer,
some of the gravel-sized particles may have broken down into finer sizes. As
a result, the laboratory permeability value may be substantially less than the
actual field value. Therefore, the physical properties of refuse materials
which are affected by particle size degradation should be determined by field
rather than laboratory testing, if possible.
The physical properties data presented herein were compiled from test
results obtained by W. A. Wahler & Associates during research work performed
for the U.S. Bureau of Mines and the MLning Enforcement and Safety Administra-
tion, and during investigatory and analytical work for coal mining companies.
Several other technical references were reviewed and, where available, appro-
priate data have been included. Two references in particular, "Tentative
Design Guide for Mine Waste Embankments in Canada," prepared for the Mines
Branch Mining Research Center, and "Spoils Heaps and Lagoons," a technical
handbook prepared by the National Coal Board of England, were useful in this
connection.
Index Properties
Grain-Size Distribution—
The gradation results for 128 samples of coarse coal refuse are presented
on Figure 1 in the form of a range of all samples tested, a range encompassing
70% of all data, and the arithmetic average. These data represent gradation
results from burning and nonburning refuse dumps which were constructed by
aerial tram or random truck dumping methods. While these data have a rather
broad range, elimination of the upper and lower 15 percentiles reveals a rea-
sonably narrow range for the remaining 70%. The heights of the refuse dumps
from which the data were obtained range from tens to several hundreds of feet.
Similar data on grain-size distribution were obtained from the National Coal
Board of England and the Canadian Mining Research Center.
The effects of particle breakdown due to weathering and handling are
shown on Figure 2, which presents the average gradation results for "fresh"
coal refuse from three sites, as well as the average gradation for the 128
samples referenced on Figure 1. These samples were obtained directly from
dump surfaces within one day after being deposited there. Comparing the
average gradation results for all samples with those of the fresh material, it
is observed that the material as originally deposited on the dumps was classi-
fied as a well-graded gravel with more than 60% of the material coarser than
the #4 sieve and less than 10% finer than the #200 sieve. The gradation
results for the average of all samples tested, however, indicate that less
than 40% of the material is coarser than the #4 sieve and approximately 15%
21
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co
N3
25 HR. 7 HR.
45 MIN. 15 MIN.
100
HYDROMETER ANALYSIS
TIME READINGS
80 MIN. 19 MIN. 4 MIN. 1 MIN.
I
200
U.S. STANDARD SERIES
100 50 30 16
SIEVE ANALYSIS
I
CLEAR SQUARE OPENINGS
3/8 3/4 1-1/2
DIAMETER OF PARTI OLE IN MILLIMETERS
CLAY (PLASTIC) TO SILT (NON-PLASTIC)
I
SAND
GRAVEL
FINE
| MEDIUM |
COARSE
FINE
1
COARSE
'i'"!! RANGE ENCOMPASSING 70 PERCENT CONFIDENCE LIMITS kVys] RANGE OF ALL SAMPLES
AVERAGE GRADATION FOR 12B SAMPLES FROM 8 SITES
Figure 1. Gradation summary, coarse coal refuse.
-------
HYDROMETER ANALYSIS
SIEVE ANALYSIS
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FINE
fERAGE GRADATION OF FRESH WASTE FROM 3 SITES
MEDIUM | COARSE
GRAVEL
FINE | COARSE
VERAGE GRADATION FOR 128 SAMPLES TAKEN FROM
VARIOUS LOCATIONS AND DEPTHS OF EXISTING
°F
DUMPS OR IMPOUNDMENTS.
Figure 2. Gradation summary, fresh coarse coal refuse.
-------
of the material is finer than the #200 sieve. The roughly parallel nature of
the two average gradations shown on Figure 2 below the #4 sieve indicates that
the majority of the breakdown is occurring on the plus #4 particle sizes.
The grain-size distribution of coarse refuse can vary significantly
depending on a number of factors, including the nature of the coal seam and
the materials above and below the seam, mining methods, preparation plant pro-
cedures and efficiencies, handling and placement methods, compaction, and age.
Because of the importance of grain-size distribution and the many factors
that affect it, periodic testing of refuse gradation is advisable during the
operational life of the disposal area. It is suggested that samples for test-
ing be obtained after refuse placement, at depths of 90 to 120 cm (3 to 4 ft)
below the surface.
Atterberg Limits—
Atterberg limits are index properties which may be used in evaluating the
fine (smaller than the #40 size sieve) component of coarse refuse. The major-
ity of the coarse refuse material is nonplastic. Seventeen samples out of some
150 samples tested in the laboratory exhibited some plasticity (Figure 3). The
averaged results indicate a liquid limit of 30% and a plasticity index of less
than 10%. It appears, therefore, that the fines in coarse refuse are predom-
inantly silty.
Specific Gravity—
Specific gravity is defined as the ratio of the unit weight of a substance
and the unit weight of water at 4°C. As an index test, specific gravity is
somewhat indicative of the durability of a material. Materials with low
specific gravities are likely to break down and change their physical proper-
ties over time. Materials with high specific gravities normally do not
deteriorate rapidly. Specific gravity also affects the unit weight of a
material. Other factors being equal, a material with a low specific gravity
has a low unit weight. Specific gravity values for coarse coal refuse range
from about 1.6 to greater than 2.4, depending upon the composition of the
materials. The specific gravity results for 37 coarse refuse samples are
presented below.
SPECIFIC GRAVITY OF COARSE COAL REFUSE SAMPLES
No. of Range of
Samples Specific Gravity
3 1.60 - 1.80
9 1.81 - 2.00
13 2.01 - 2.20
4 2.21 - 2.40
8 > 2.40
Average Specific
Gravity 2.14
24
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80
70
60
50
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CO
5 30
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ML
CH
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MH
10 20 30 40
50 60 70 80
LIQUID LIMIT (X)
90 100 110 120
KE Y
RANBE OF ATTERBERG LIMITS FOR 17 SAMPLES
Figure 3. Atterberg limits, coarse coal refuse.
-------
Most soils have specific gravities which range from 2.5 to 2.9, with
an average value of about 2.7. Coarse refuse is therefore considered to have
a low specific gravity.
Parent Material—
Parent material refers to the basic rock type—such as shale, sandstone,
limestone, or coal—from which the refuse was derived. Most coal refuse comes
from soft rock formations, principally shales. Some of these shales break
down partially into smaller particles when exposed to the atmosphere and when
placed and compacted in a fill. The breakdown of coarse particles into finer
particles is important because it affects the engineering properties of the
material.
Investigations by W. A. Wahler & Associates and by the University of
West Virginia^ have confirmed the degradation effect caused by weathering.
Table 3 shows the effect of weathering on shale refuse from four West Virginia
mines. The "fresh" refuse was taken directly from the refuse hopper as it
came from the preparation plant. Old refuse was taken from the refuse pile
where it had been exposed for 18 months to 30 years.
Engineering Properties
Natural Water Content and Dry Density—
The natural water content and dry density of coarse coal refuse depend on
the method of disposal used and on whether the dump is burning. In-place dry
density and water content data obtained from eight sites in West Virginia are
summarized on Figures 4 and 5, respectively. These data were obtained from
both field and laboratory tests. Water content values (Figure 5) ranged from
2% to 28%, with approximately 90% of all the data falling between 4% and 16%.
The arithmetic average of the natural moisture content, based on dry weight,
for the 141 samples tested was 10.4%. In-place dry density values (Figure 4)
had a wide range, from 961 to 1,858 kg/m3 (60 to 116 lb/ft3), with about 84%
of the results greater than 1,281 kg/m3 (80 Ib/ft3). The arithmetic average
for the 134 samples was 1,448 kg/m3 (90.4 lb/ft3).
Compaction—
A number of laboratory compaction tests are used by the industry, and
each one gives appreciably different results. The choice of which test to use
is based principally on the proposed use of the material (i.e., general fill,
highway base, earth dam) and depends also on the personal preference of the
investigator. It is therefore difficult to summarize the compaction data
available in the literature statistically.
In an extensive survey of coal refuse piles in the eastern part of the
nation, W. A. Wahler & Associates performed 38 compaction tests on coarse coal
refuse in accordance with ASTM D1557-70, modified to 768 joules/m3 (20,000 ft-
lb/ft3) compactive energy.1 The results (presented in Table 4) show a broad
range of maximum laboratory densities—from 1,221 to 1,981 kg/m3 (76.2 to
123.7 lb/ft3). A somewhat progressive increase in maximum density can be
seen when the data are grouped according to ranges of specific gravity. The
major factors influencing the scatter of data are the differences in specific
gravity and gradation for the individual samples.
26
-------
TABLE 3. EFFECTS OF WEATHERING ON COARSE REFUSE
Grain Size (%)
Gravel (#4-3")
Sand
Coarse (//10-/M)
Medium (#40-#10)
Fine (//200-//40)
Silt (0.005 mm-#200)
Clay (<0.005 mm)
Atterberg Limits
Liquid limit (%)
Plasticity index
Shrinkage limit (%)
Unified Soil
Classification
Specific Gravity
of Solids (Gs)(gm/cc)
Ignition Loss (% oven
Fresh-
Coarse
64.3%
3.0
4.9
12.2
10.9
4.7
NP
GM
1.68
42.6
57.4
Philippi
Samples
Fresh-
Fine
8.7%
35.0
43.3
10.5
1.1
0.4
NP
SW
1.98
__
Humphrey
Samples
Old
27.1%
20.2
23.7
11.6
6.5
10.6
31.2
5.2
24.8
SW-SM
2.0
49.3
50.7
Fresh
57.0%
25.4
15.8
0.7
0.7
0.4
NP
GP
2.22
29.0
71.0
Old
41.4%
12.6
9.6
16.6
18.9
0.9
36.0
11.0
22.4
SC
2.41
27.2
72.8
Shoemaker
Samples
Fresh
76.0%
16.3
3.3
1.2
1.6
1.6
30.6
10.1
15.2
GP
2.52
17.3
82.7
Old
61.3%
18.4
10.6
3.5
2.9
3.3
34.2
15.9
17.8
GP-GC
2.63
15.0
85.0
McElroy
Samples
Fresh
89.4%
5.2
2.9
1.7
0.8
—
28.4
8.4
19.0
GW
2.45
16.2
83.8
Old
50.6%
20.4
13.8
5.6
4.9
4.7
36.8
13.1
16.3
GP-GC
2.61
18.9
81.1
dry wt)
Ash
42.
57.
6
4
49.
50.
3
7
29.0
71.0
27.2
72.8
17.3
82.7
15.0
85.0
16
83
.2
.8
18.9
81.1
a. 24 hours at 600 C.
Source: Reference 5
-------
60
70
80
DRY DENSITY, pcf
90
100
110
1000
1200
1400
DRY DENSITY, kg/in3
1600
1800
AVERAGE = 1448 kg/m3
NOTE: DATA FROM 134 SAMPLES FROM 8 SITES IN WEST VIRGINIA.
Figure 4. In-place dry density, coarse coal refuse.
Compaction tests are used in evaluating the unit weight and moisture con-
tent of embankments such as dams, roadway bases, and other structural fills.
In construction control of structural fills, it has been traditional to
specify the percent compaction (commonly 95%) by comparing the maximum dry
density determined in the fill with the dry density determined in the labora-
tory. This practice is not in uniform use in refuse disposal.
Quantitative data on the effect of field placement and compaction of
coarse refuse are lacking. Nevertheless, it is reasonable to assume that some
particle breakdown does occur in the placement and compaction of coarse refuse.
Permeability—
The permeability characteristics of coarse coal refuse materials are
evaluated by reviewing field and laboratory test data. Values of the coeffi-
cient of permeability range between 10~2 and 10~6 cm/sec, with a typical value
28
-------
>-
o
NOTE: DATA FROM 141 SAMPLES FROM 8
SITES IN WEST VIRGINIA.
10 12 14 16 18 20
NATURAL MOISTURE CONTENT, %
24 26 28 30
AVERAGE = 10.7*
Figure 5. Natural moisture content, coarse coal refuse.
29
-------
TABLE 4. COMPACTION CHARACTERISTICS OF COARSE COAL REFUSE
U)
o
Laboratory-Compacted Maximum Dry Density
Optimum
No. of
Tests
3
8
13
14
Specific
Gravity Range
1.75 -
1.81 -
2.01 -
2.21 -
1.80
2.00
2.20
2.63
Low
Kg/m3
1,221
1,440
1,451
1,477
Lb/ft3
76.2
89.9
90.6
92.2
High
Kg/m3
1,530
1,672
1,738
1,981
Lb/ft3
95.5
104.4
108.5
123.7
Average
Kg/m3
1,405
1,579
1,642
1,752
Lb/ft3
87.7
98.6
102.5
109.4
Moisture Content (%)
Low
7.5%
7.5
6.5
7.5
High
19.5%
14.0
11.5
15.0
Average
12.6%
10.5
9.7
11.7
Source: Reference 1.
-------
of 10"^ cm/sec. The permeability of refuse is the most important physical
property with respect to air and water pollution control. The significant
variables that influence the permeability of coarse refuse are grain size and
compaction. (Compaction of a well-graded refuse reduces the continuous voids
in the material; this in turn reduces permeability.)
Well-graded refuse with an optimum percentage of fines has a very low
permeability, while uniformly graded coarse refuse with little or no fines has
a high permeability. Figure 6 shows the influence of grain size on permeabil-
ity for clean, coarse-grained materials. The more well-graded the material,
the less the permeability. This is due to the reduction in voids through which
fluids can pass. For example, refuse with a grain size similar to that of
curve 6 on Figure 6 is approximately 200 times more permeable than refuse
similar to curve 11.
CLEAR SQUARE OPENINGS
100
US STANDARD SIEVE NUMBERS
810 16 30405070100 200
100 8 B 43 2
108 8 43 2
1.8.6 .4 .3 .2 .188
GRAIN SIZE MILLIMETERS
COBBLES
COARSE 1 FINE
GRAVEL
COARSE I
MEDIUM 1
SAND
FINE I
1
COEFFICIENT OF PERMEABILITY. K
Figure 6. Effects of grain size on permeability
of clean, coarse-grained materials.
Other grain size characteristics that influence the permeability of
coarse-grained materials are the percentage and type of fines passing the #200
sieve (see Figure 7). A well-graded, coarse-grained material with 15% silt or
clay fines is approximately 100,000 times less permeable than coarse-grained
material with no fines. As the percentage of fines is increased beyond about
15%, the effect on permeability becomes less pronounced.
31
-------
10
10'
,-2,
10
,-4
10'
10
,-7
10
,-8
EFFECT OF FINES ON PERMEABILITY
^
TYPE OF FINES MIXED WITH
COARSE GRAINED MATERIAL:
10'
to-
10"
5 10 15 20 25
PERCENT BY WEIGHT PASSING NO. 200 SIEVE
Figure 7. Effects of fines on permeability of coarse-grained materials.
Compressibility—
The compressibility characteristics of coarse refuse are difficult to
investigate in the laboratory. However, in the W. A. Wahler & Associates'
studies just cited, evaluations were made of data from saturated, isotropic-
ally consolidated triaxial test samples and from one saturated anisotropically
consolidated triaxial sample, whose average initial densities ranged from
1,362 to 1,522 kg/m3 (85 to 95 lb/ft3). A range of volumetric compression of
3% to 6% was observed for the anisotropically consolidated samples as compared
with 9% for the isotropically consolidated samples at 689 x 103 Pa (100 psi)
maximum principal effective stress. Because of the relatively high permeabil-
ity of the coarse material, the time delay associated with the consolidation
process is extremely short. In other words, straining within a saturated
embankment due to a load application would occur very rapidly. Also, the
magnitude of the volumetric compression is considered high compared to an
average value of less than 3% volumetric strain at 689 x 103 Pa (100 psi) for
a well-compacted material with gradation characteristics similar to those of
coarse coal refuse.
Shear Strength—
Shear strength parameters of the coarse refuse material were determined
from laboratory triaxial tests performed under ICU test conditions on 51
laboratory-fabricated and undisturbed tube samples. The parameters, based on
32
-------
effective stresses, ranged from 34° to 41°, with essentially zero cohesion
intercept. It is interesting to note that the dry densities of the triaxial
samples varied considerably, and yet the effective stress friction angles
varied less than 7°. The influence of the scatter in density is more reflected
in the shear strength parameters based on total stresses; friction angle ranged
from a value less than 15° to approximately 20°, with 48.3 x 103 Pa (7 psi)
cohesion intercept.
The relatively high shear strength values of the coarse refuse materials
indicate one very important point. Since these materials are inherently
quite strong compared to other construction materials, if proper construction
techniques are utilized, a dam or dump made with these materials, utilizing
current earth dam design standards, could provide a safe, adequate structure.
Chemical Properties
When the coal was geologically formed, various salts, minerals, and trace
metals were concentrated in the coal seam and in the rocks above and below the
seam. These impurities were, for the most part, locked into the ground due to
the physical condition associated with the coal seam. The air and water per-
meability of the geological environment, was, as a whole, relatively low
except where the coal outcropped. The mining and processing of coal changes
the physical makeup of the environment and in many cases exposes the various
chemical components of the coal seam directly to the atmosphere. The process-
ing of coal tends to concentrate many of these impurities in the refuse. Under
certain conditions, the impurities may be leached from the refuse in sufficient
quantities to cause objectionable environmental effects.
Only limited data are available in the literature concerning the chemical
properties of coarse coal refuse. However, in one survey of 79 refuse piles
in Pennsylvania, Davidson tested the chemical properties of the actual refuse.
The results are summarized in Table 5.
From his study, Davidson concluded that there was no correlation between
the physical or chemical properties of the refuse and the coal seam being
mined or with the depth from which the samples were collected.
While data concerning the chemical properties of coarse refuse are some-
what scarce, there are more data available on the chemical properties of
effluent discharges from refuse piles. Martin** has compiled a substantial
amount of chemical data on seeps and direct runoff from refuse piles in
Pennsylvania, West Virginia, Kentucky, Indiana, and Illinois. The results are
shown in Table 6.Martin concluded that the water pollution load from refuse
piles varied greatly, depending on the coal seam mined, the mining methods,
preparation processes, and pile construction. He found that the central por-
tion of the eastern coal province (southern West Virginia and eastern Kentucky)
apparently produced less acidic runoff than did the other areas of the eastern
and interior provinces.
33
-------
TABLE 5. SELECTED CHEMICAL CHARACTERISTICS OF SAMPLES
OF UNDERGROUND MINE REFUSE
Range
Average
Median
Highest
Lowest
A
3.1
2.9
4.1
2.6
B
3.4
3.2
6.8
2.2
SEA
C
PH
3.0
3.1
3.4
2.4
M
C1 D
3.5 3.8
3.3 3.6
4.4 6.1
2.6 3.0
Exchangeable acidity (meq H+/100
Average
Median
Highest
Lowest
Average
Median
Highest
Lowest
Avearge
Median
Highest
Lowest
Average
Median
Highest
Lowest
Number of
Samples
8.5
5.8
22.2
2.3
0.87
0.75
2.23
0.22
1,209
657
3,227
235
0.2
0.2
1.0
0.0
10
9.8
7.0
113.0
0.6
1.88
0.61
20.20
0.12
3,395
1,087
26,575
62
1.3
0.9
15.5
0.0
88
6.4
4.4
15.6
3.4
Conductance
1.51
0.64
5.06
0.27
Sulphates
12,097
4,688
50,438
362
Phosphorus
0.6
0.7
1.0
0.2
8
5.1 6.4
4.2 6.7
10.5 14.5
2.4 2.4
(mmho/cm)
0.32 0.31
0.21 0.22
1.30 1.71
0.10 0.08
(ppm 804)
873 739
788 520
2,000 3,037
235 37
(ppm P)
1.0 1.8
1.0 0.3
2.2 16.5
0.3 0.0
16 26
E
3.8
3.4
9.4
2.4
gm)
8.0
6.5
39.0
0.4
1.61
0.86
8.57
0.12
4,643
1,050
30,150
62
3.1
1.4
16.5
0.0
50
Pittsburgh
3.6
3.1
7.7
2.4
8.8
9.1
33.4
0.3
2.30
2.48
6.75
0.12
10,953
6,937
30,150
270
6.7
6.1
21.0
0.7
70
Source: Reference 7.
34
-------
TABLE 6. ANALYSES OF EFFLUENTS FROM REFUSE FROM MINES
IN FIVE EASTERN U.S. STATES8
Conduc- Total
Sample pH tivity Acidity Alk. 804 Na Me Al K Ca Mn Fe Ni Cu Zn
PENNSYLVANIA1*
Eastern Pennsylvania (anthracite)
PI
P2
P3
P4a
P4b
3.0
4.1
4.5
5.8
4.3
4,400
3,000
1,300
130
200
689
250
25
6
25
- 3,000
- 1,600
500
5 60
0 75
100
60
4
6
6
250
140
45
2
3.
Western
P5a
P5b
0P6
"P7
P8
P9
P10
Pll
P12
P13
7.5
7.5
3.6
2.1
3.5
2.2
3.1
2.6
2.7
3.7
600
660
925
10,400
3,700
10,000
13,600
5,600
12,400
3,500
0
0
325
23,100
1,300
24,400
34,300
6,100
15,500
1,330
160 106
170 106
420
27,500
1,485
29,750
40,500
5,750
17,750
1,125
16
16
35
35
87 4.8
50 15
10 2.6
0.9 0.5
4 3.0 0.5
Pennsylvania
1.0 2.2
1.0 2.5
28
948
40
668
999
353
1,014
68
340
180
100
13
13
70
70
50
90
4
0.4
0.9
0.01
0.1
4.5
545
9.1
69
63
86
31
15
30 1.7
0.6 1.1
1.2 0.3
0.1 -
0.7 -
0.1 -
0.1 -
5.8
3,758
175
3,732
6,168
1,265
3,197
130
0.14 2.8
0.18 2.4
0.04 0.5
-
0.1
— _
— —
WEST VIRGINIA0
Northern
Wl
Wl
W2
W3
2.9
3.0
4.9
3.4
16,500
9,300
5,000
3,200
4,090
6,940
150
85
10,054
9,560
3,800
- 2,400
780
250
664
680
146
105
Southern
W4
W5
W6
5.2
3.1
4.5
640
5,200
710
11
300
15
310
- 3,300
400
14
600
6
28
230
45
West Virginia
50
220
3.6 22
4.0 8
West Virginia
1 10
20 25
1.8 11
145
380
415
450
30
310
36
67
70
9
10
3.4
25
1.8
2,240
2,940
260
170
45
120 1.0
40
0.2
0.1
0.1
1.5
0.3
-------
TABLE 6 (continued)
Conduc- Total
Sample pH tivity Acidity Alk.
S04 Na Mg
Al
K
Ca
Mn
Fe
Ni
KENTUCKY*1
Kl
K2
K3
K4
K5
3.8
5.0
6.9
2.5
2.4
1,200
840
880
6,800
4,200
210
30
7 135
7,020
2,380
1,066
690
690
9,827
3,629
22
30
115
270
150
Eastern
85
56
26
Western
195
90
Kentucky
70
10
1.8
Kentucky
440
244
42
16
3.1
13
0.7
74
60
50
300
200
8.1
3.1
3.5
72
26
2.5
2.0
6.2
3,400
630
0.25
-
-
3.0
0.45
^ INDIANA6
INI
IN2
IN2
IN3
IN3c
IN4
IN4
INS
IN6
IN6a
IN6b
IN6p
3.2
2.8
2.6
2.4
8.0
2.5
2.2
2.3
2.5
7.9
2.9
2.3
1,480
2,500
2,400
6,400
2,150
9,800
15,000
1,200
150 -
800
760 -
6,500
0 266
10,300
16,400
13,600
7,277
125
5,660 -
8,667 -
850
1,711
1,700
9,512
1,456
10,400
15,200
15,000
14,282
564
10,544
16,103
40
30
18
200
130
42
20
256
4
75
100
100
285
165
185
5.6
52
50
340
10
6.2
-
3.4
3.0
1.4
150
200
160
350
300
342
11
25
24
120
0.6
40
36
56
12
0.03
10
11
25
100
160
2,600
2.5
4,180
5,500
4,500
2,320
0.5
2,233
2,147
-
-
0.40
1.6
0.13
Cu Zn
1.1
0.16
0.
0.
8
2.9
1.7
7.2
(continued)
-------
TABLE 6 (continued)
CO
Total
Sample pH Conductivity Acidity
11 3.6
12 2.9
13 3.3
14 3.1
15 2.8
16 2.4
I7a high 8.8 1,990
median 6.6 1,080
low 4.2 226
I7b high 3.4 19,150
median 2.65 6,370
low 2.05 875
18 high 3.54 24,100
median 2.5 16 , 800
low 2.1 9,400
Source: Reference 8.
a. All values in milligrams per liter except
b.
c.
d.
e.
f.
Acidity to pH 7.3 for samples PI - P5b.
Acidity to pH 7.3 except for sample Wl.
Acidity to pH 7.3.
Acidity to pH 7.3 for samples INI - IN3c.
Acidity by hot hydrogen peroxide method E
ILLINOIS
640
4,600
6,100
5,900
8,700
14,400
190
-20
-550
21,400
6,500
500
25,700
21,430
9,300
conductivity
, ASTM D-1067,
so4
1,200
3,200
2,800
1,950
3,550
3,540
5,760
550
80
23,550
6,100
625
28,600
24,000
4,530
(umhos) and
for samples
Total
Fe Fe
55
1,400
50
1,200
4,600
13,500
89
2.9
0
5,930 5,
1,510 1,
115
7,820 7,
7,090 6,
3,360 2,
pH (standard).
I7a - 18.
53
0
0
370
160
89
560
710
520
Total
Solids
8,570
14,420
16,830
11,060
13,860
35,320
-------
The most serious problem associated with the chemical composition of
refuse is the presence of the pyritic group of minerals (commonly iron sulfide)
in a form which oxidizes readily. In the presence of air and water the chemi-
cal reactions produce sulfuric acid. However, not all pyrite is readily oxi-
dized. Caruccio9 found that finer-grained pyrites (2 to 15 microns) oxidized
rapidly in the presence of air but that coarser pyrites (greater than 50
microns) remained stable.
While acid drainage is accepted as the most serious chemical water pollu-
tion problem associated with refuse piles, other chemical pollutants are a
dominant concern for specific mines. For example, in parts of southern
Illinois there are sufficient alkaline salts in the refuse to neutralize acid
production, but a high concentration of chloride(s) in the refuse is a cause
of concern.
PROPERTIES OF FINE REFUSE
Fine refuse is generated in the preparation plant at various points,
depending on the beneficiation method used. Fine refuse is a sandy, silty
type of material which is commonly mixed with water conveyed hydraulically to
settling basins. The physical properties of fine refuse, particularly its
grain-size distribution and resulting in-place dry density, are significantly
influenced by the natural sedimentation process in the settling basin, which
tends to concentrate the larger, heavier particles near the discharge point
and the finer, lighter particles farther away.
Essentially the same type of physical and chemical properties testing is
used for fine refuse as for coarse refuse. But, although the identifying
properties are the same, the two materials are entirely different in physical
makeup.
Index Properties
Grain-Size Distribution—
The gradation results for 63 samples of fine coal refuse from eight sites
in West Virginia are shown on Figure 8.^ The results, presented in the form
of a range of all samples tested, a range including 70% of all data, and the
arithmetic average, indicate that an average of 45% of these materials pass
the #200 sieve. The range in percent passing this sieve varies from approxi-
mately 18% to 98%, which reflects the influence of the point of discharge and
the settling characteristics of the materials.
Plasticity—
The minus #40 fraction of the fine refuse materials is nonplastic.
Several attempts were made to perform Atterberg limits tests on the fine
refuse, and, although a liquid limit between 30% and 50% was achieved on some
samples, it was not possible to roll threads to 0.32 cm (1/8 in.) diameter in
order to determine the plastic limit; therefore, the material is classified as
nonplastic.
38
-------
VO
25 HR. 7 MR.
45 MJN. 15JIIN_.
100
HYDROMETER ANALYSIS
TIME READINGS
BO HIN. 19 MIN. 4 MIN. 1 MIN.
SIEVE ANALYSIS
U.S. STANDARD SERIES I
CLEAR SQUARE OPENINGS
3/4*' 1-1/2" 3"
DIAMETER OF PARTICLE IN MILLIMETERS
CLAY (PLASTIC) TO SILT (NON-PLASTIC)
SAND
FINE
| MEDIUM |
COARSE
GRAVEL
FINE I
COARSE
RANGE ENCOMPASSING 70 PERCENT CONFIDENCE LIMIT
—— AVERAGE GRADATION FOR 63 SAMPLES FROM 8 SITES
RANGE OF ALL SAMPLES
Figure 8. Gradation summary, fine coal refuse.
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Specific Gravity—
Specific gravity values for the fine refuse range from about 1.3 to 2.2,
depending on the percentage of coal in the material. Specific gravity results
for 30 fine refuse samples are tabulated below.
No. of Samples Specific Gravity Range
8 1.30 - 1.40
15 1.41 - 1.60
4 1.61 - 1.80
2 1.81 - 2.00
1 2.01 - 2.20
Average Specific
Gravity 1.53
Source: Reference 1.
Engineering Properties
Natural Water Content and Dry Density—
The natural water content and dry density of the fine refuse materials
were determined from both field density and undisturbed tube samples. Results
of the natural water content for 87 samples are shown on Figure 9, in the form
of observed water content versus frequency of occurrence. A range in natural
water content from 8% to 56% was observed, with an average value of 30.9%.
Seventy-eight field dry density values were determined for the fine refuse
materials (see Figure 10). These values ranged from 705 to 1,346 kg/m3 (44 to
84 lb/ft3), with 85% of all the values ranging between 769 and 1,089 kg/m3
(48 and 68 lb/ft3). The arithmetic average dry density value was 884 kg/m3
(55.2 lb/ft3). Although these values are exceedingly low for the fine refuse
materials, compared to an average dry density of 1,762 to 1,922 kg/m3 (110 to
120 lb/ft3) for typical soils, the void ratio of the fine refuse indicates a
generally close packing of individual grains. An average void ratio (a com-
parison of the volume of voids with the volume of solids in a given sample)
of 0.5 or less is not uncommon.
Compaction—
The moisture-density characteristics of the fine refuse materials were
determined by testing 15 samples compacted in accordance with ASTM D1557-70,
modified to 768 joules/m3 (20,000 ft-lb/ft3) compactive energy. The results
indicate that a maximum dry density between 921 and 1,065 kg/m3 (57.5 and
66.5 lb/ft3) was achieved for a specific gravity between 1.3 and 1.4, and that
a range of 1,185 to 1,297 kg/m3 (74.0 to 81 lb/ft3) was achieved for specific
gravities between 1.41 and 1.70.
When the range of in-place dry densities previously referenced is com-
pared with maximum laboratory densities, it is observed that the ponding
methods being used to dispose of the fine refuse materials resulted in rela-
tive compactions of approximately 75% to 85%; however, the in-place moisture
40
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o
111
u
u
12
IB
44'
48
20 24 28 32 36 40
NATURAL MOISTURE CONTENT. %
NOTE: DATA FROM 87 SAMPLES FROM 8 SITES IN WEST VIRGINIA.
52 56 60
AVERAGE = 30.8*
Figure 9. Natural moisture content, fine coal refuse.
contents were 10% to 20% higher than the optimum moisture contents. If fine-
grained coal refuse is to be used as a construction material for water-
retaining structures, the material could be compacted, by the use of mechani-
cal compaction equipment. However, regardless of the density to which the ma-
terial is compacted, it must be recognized that the low specific gravity and
resulting in-place dry densities could lead to piping or instability problems
if the fine-grained material is not properly ballasted, or confined, by
heavier materials.
Permeability—
The permeability characteristics of the fine coal refuse materials were
determined by thoroughly reviewing the disposal methods and laboratory test
results. This evaluation indicated that a significant degree of anisotropy is
developed in the flue-grained refuse materials because of their method of dis-
posal. The fine-grained materials in the field are found to be highly lentic-
ular, with stratifications varying from fractions of an inch to several inches
41
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30
40
DRY DENSITY, pcf
50 60
70
BO
800
1000
DRY DENSITY, kg/a3
1200 1400
AVERAGE = 884 kg/m3
NOTE: DATA FROM 78 SAMPLES FROM 8 SITES IN WEST VIRGINIA.
Figure 10. In-place dry density, fine coal refuse.
in thickness. The finest-grained silts usually constitute the thinner part-
ings, and probably reflect variations in inflow of the slurry. These materials
exhibit a coefficient of permeability of about 10" ? cm/sec, whereas the fine-
to medium-grained silty sand which constitutes the coarser fraction of the
fine-grained material has a maximum coefficient of permeability of about 3 x
10~4 cm/sec. The ratio of horizontal to vertical permeability for the fine
refuse material ranged from 15:1 to 100:1, with an average value of approxi-
mately 25:1.
3
The National Coal Board of England study indicates a range in the
coefficient of permeability of 10~* to 5 x 10~7 cm/sec in the horizontal
direction and 10"6 to 7 x 10"^ cm/sec in the vertical direction.
The high degree of anisotropy of permeability values for the fine refuse
materials is extremely important to recognize when considering the stability
characteristics of refuse impoundments, especially if fine-grained materials
42
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form the foundation for an overlying coarse refuse embankment. The reason
for the concern is that the relatively high ratio of horizontal to vertical
permeability causes water to flow preferentially in a horizontal direction
through these materials, thereby possibly transmitting high pore pressures
beyond the toe of the embankment.
Compressibility—
The compressibility characteristics of the fine refuse materials were
investigated utilizing triaxial test results. (Because of the extremely low
density and nonplastic characteristics of these materials, it is very diffi-
cult to prepare samples for one-dimensional consolidation tests.) A range of
volumetric compression of 2% to 4% was observed for the anisotropically con-
solidated samples, as compared with approximately 6% for the isotropically
consolidated samples at 689 x 103 Pa (100 psi) maximum effective principal
stress. The initial dry densities for the triaxial samples ranged from 833
to 1,025 kg/m3 (52 to 64 pcf). These data indicate that the fine-grained
materials are, in fact, less compressible than the coarse-grained materials
discussed earlier. Again, it should be pointed out that the compressibility
characteristics of the fine-grained materials are not unusually high; there-
fore, these materials can be safely used as construction materials if proper
construction techniques and adequate protection against uplift and piping
potential are incorporated in the design.
Shear Strength—
Shear strength parameters of the fine refuse materials were determined
from laboratory triaxial tests performed on 32 samples, to obtain shear
strength versus normal stress for both effective and total stress. These
undisturbed tube samples were tested under ICU conditions.
The shear strength results indicate that the angle of internal friction,
based on effective stresses, ranges from 37 to 40.5 degrees, with little or no
cohesion indicated, and that the angle of internal friction based on total
stresses is approximately 20 degrees, with a cohesion intercept from 20.7 to
68.9 x 103 Pa (3 to 10 psi). The shear strength results are remarkably con-
sistent, considering the range in dry densities tested, and obviously reflect
the angularity observed in the fine-grained materials. As stated earlier, the
shear strength values for these materials also appear to be consistent with
those for other construction materials.
Chemical Properties
Very little documentation is available on the chemical properties of fine
coal refuse. However, Haynes and .Klirastra* have determined some chemical proper-
ties of such refuse from sites in Illinois.10 Their results indicate that
fine refuse generally has a low pH and a high exchangeable calcium ion
capacity.
The main reason why there are so very few data on fine refuse chemical
properties is that the major pollution concern with respect to slurry ponds
is usually the carryover of suspended solids, rather than chemical pollution.
It would be reasonable, however, to assume that the chemical properties of fine
and coarse refuse from a given preparation plant would not differ significantly.
43
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SECTION 4
PREPARATION PLANT PROCEDURES
The properties of coal refuse are significantly influenced by the proce-
dures used in the preparation plant. The most important physical property of
refuse, grain size, is strongly dependent on the coal preparation process.
Minor changes in the grain-size characteristics of coarse refuse have a dra-
matic influence on its permeability, and the permeability of the emplaced
refuse is the most important physical property in terms of water and air
pollution potential. Although the grain-size distribution of fine refuse also
affects water and ai'r pollution potential, the effects are less pronounced
than for coarse refuse.
REFUSE RECOVERY CIRCUITS
The recovery circuit of a preparation plant has four principal components:
dry solids recovery, coarse refuse slurry concentration and solids disposal,
fine refuse slurry concentration and slurry disposal, and dust collection and
disposal. The dry solids recovery and disposal process is simple and straight-
forward. These solids are generated in the coarse coal circuit as reject
material from the rotary breaker and as dewatered solids from the coarse refuse
screen. They are conveyed directly to the refuse bin for transport to the
solids disposal area.
The water and refuse slurry from the hydrocyclone module and the Deister
table module in the intermediate-size and fine-size coal cleaning circuit is
piped to a screen classifier. The classifier concentrates the larger solids,
commonly the plus 28-mesh Tyler sieve size, and discharges them to a conveyor
system for transport to the refuse bin. The moisture carried out of the
classifier is collected via natural drainage during the conveying process and
is piped to a static thickener.
The fine refuse, including the silt and clay particles generated through-
out the coal-washing system, is collected as a slurry underflow from the screen
classifier or from the froth flotation module. This slurry is usually piped
directly to the static thickener, where it is concentrated with the aid of
various flocculants and piped in concentrated form to the slurry pond. The
clarified water overflow from the static thickener is returned to the plant
water system. This is one of the circuits used in conventional preparation
plants. In a more sophisticated plant, the thickened concentrate underflow
from the static thickener is routed to a refuse recovery vacuum filter and the
filtrate is conveyed to the refuse bin for later transport to the disposal
site. Slurry disposal is thus eliminated.
44
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A dust collection system in the preparation plant usually consists of a
dust collector and a wet scrubber attached to a thermal drying module. The
slurry generated from the wet scrubber is piped to the static thickener.
PROCESS QUANTITIES
Over the past years, the percentage of refuse generated per ton of coal
produced in the eastern United States has increased dramatically, particularly
with respect to coal obtained from underground mines. This increase is largely
due to changes in mining methods, to the demand for cleaner coals, and to the
development of more efficient coal cleaning processes.
Table 7 presents data on refuse production at the sites studied during
this project. At all the sites, substantially greater tonnages of coarse
refuse than of fine refuse are generated. The maximum reported reject percent-
ages at these sites is approximately 30%, but there are other coal preparation
plants that have as much as 50% to 60% reject material.
MATERIAL SIZING
The refuse particle sizes usually generated in various types of recovery
circuits are described below:
Coarse Refuse from Rotary Breaker
The refuse generated by the rotary breaker generally has a gradation
between 10 cm and 30 cm. This material is very coarse and highly permeable.
The percentage of coal included in the material may be relatively high because
layers of coal may adhere to the refuse particles. Because of these charac-
teristics, refuse from the rotary breaker could in certain cases require
special pollution control consideration.
Refuse from the rotary breaker is either handled separately from the
coarse refuse generated in other circuits or it is mixed with the other refuse
prior to loading the material for transport. If the rotary breaker refuse is
handled and disposed of separately, special provisions at the disposal area
may be required to isolate this potentially troublesome product from air and
water, particularly if the refuse is acid producing. If, however, this refuse
is mixed with the other coarse refuse prior to loading for transport, or if
the product is further crushed to smaller sizes, special pollution control
provisions usually are not required.
It should be noted that the amount of reject from the rotary breaker is
usually small (1% to 2% of the total coarse reject) compared to the total
reject produced by the plant. Thus proper disposal of the reject from the
rotary breaker is not considered a major problem.
Coarse Refuse from Screening Circuit
The coarse refuse generated in the screening circuit is usually graded
between the No. 28 Tyler sieve size and a top size of 10 cm to 15 cm. In some
plants the bottom size separation has been lowered from the No. 28 to the
45
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TABLE 7. REFUSE PRODUCTION AT STUDY SITE PLANTS
Clean Coal
Ratio of
Coarse - Fine Percent Solids
.te
A
B
C
D
E
F
6
H
Type of
Mine
Surface
Underground
Underground
Underground
Underground
Underground
Underground
Underground
Production Percent Coarse to Processing
(metric tons/day) Reject Fine Refuse Methods
9,070 19% 2.8:1
5,442* 15b
2,721 25 6:1
4,308 25 2:1
9,070a 17b
6,122-6,694 18-25
8,480 15 2:1
10,884-12,698 30 8:1
Jigs and heavy
media
Froth flotation
and heavy media
Heavy media,
froth flotation
Jigs
Froth flotation,
heavy media
Jigs and heavy
media
Froth flotation,
heavy media
Heavy media,
Refuse Sepa- Concentration
ration Size in Slurry
—
#100 Tyler
#28 Tyler
#10 Tyler
#100 Tyler
#28 Tyler
#28 Tyler
#100 Tyler
—
—
14%
15
—
—
—
35
concentrating
tables, froth
flotation
a. Raw coal production.
b. Coarse reject only; data on fine reject not available.
-------
No. 100 Tyler sieve. In other plants the bottom size separation has been
increased to the No. 10 Tyler sieve. Materials within these ranges are
classified as semipermeable.
A comparison of the gradation of coarse refuse samples from disposal
areas with the gradation limits established in the preparation plants indicates
that there is an increase in the percentage of fines generated between the
plant and the disposal area. This increase is attributed to degradation due
to handling, compaction, and weathering.
Preparation plant procedures determine, to a large degree, the gradation
and therefore the permeability of the refuse. Efforts in the preparation
plant to minimize pollution potential of coarse refuse can most effectly be
directed toward increasing the percentage of fines (percent by dry weight
passing the No. 200 sieve) in the coarse refuse to an optimum value on the
order of 15%.
Fine Refuse
Fine refuse generated in the preparation plant is commonly a cohesionless,
sandy silt with a low specific gravity. This material is usually pumped in
slurry form to settling ponds for disposal. Some of the more sophisticated
preparation plants dewater the fine refuse sufficiently that it can be handled
by conventional haulage equipment and can be placed in the disposal facility
in the same manner as coarse refuse.
The pollution potential of fine refuse in slurry ponds is primarily
related to silt carryover from ponds with open-water circuits and to airborne
participates from exposed pond surfaces. Except for dewatering the fine
refuse, there is little that can be done in the preparation plant to make fine
refuse more environmentally acceptable in the pond. However, in special situa-
tions where there is insufficient settling area in the pond, a chemical floccu-
lant can be added to the slurry to agglomerate the fine refuse particles and
thus to increase the rate of particle settlement.
SUMMARY OF PRINCIPAL GUIDELINES FOR PREPARATION PLANT PROCEDURES
The division between coarse and fine refuse in the preparation plant
should be on the smallest screen opening practical.
• Pollution control efforts in the preparation plant can most effectively
be directed toward increasing the percentage of fines in the coarse refuse
generated.
47
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SECTION 5
SITE SELECTION
Selecting a coal refuse disposal site involves consideration of a number
of interrelated variables. Some of the more important of these are hazard
potential (and/or embankment safety), environmental impact, land availability,
and cost. Land availability and cost are self-explanatory considerations.
Hazard potential involves detailed consideration of the stability of refuse
piles and slurry ponds, and this aspect is regulated by MSHA. The principal
environmental considerations include water quality, air quality, and land use.
The principal site selection variables in terms of environmental factors are
topography, hydrology, surface and subsurface conditions, and proximity of the
site to developed areas.
In some situations the selection of a refuse disposal area is relatively
straightforward. For example, in Indiana, state laws require that coarse
refuse from surface mines be disposed of in the bottom of the mine pit and
covered with the mine spoil. Perhaps the most difficult areas to evaluate are
the mountainous regions of Appalachia, where the steep topography limits the
choice of suitable disposal sites.
ENVIRONMENTAL CONSIDERATIONS
Water Quality
The principal environmental concern with regard to a coal refuse disposal
facility is usually water quality. Water quality concerns are associated with
chemical degradation (such as acid drainage) and suspended solids. The most
critical technical consideration in attempting to control water pollution at
a refuse pile or slurry pond site is isolation of the site from surrounding
surface and ground waters. Sites that have significant amounts of through
drainage are less desirable than sites that have only minimal drainage. Like-
wise, a site where there is underground spring activity is less desirable
than a site which has no spring activity.
Another very important consideration in site selection is the location of
the refuse pile relative to the slurry pond. If at all possible, the refuse
pile should be so sited that drainage from the surface of pile is directed
into the pond. The pond then also functions as a sedimentation basin for any
eroded sediment from the pile. In many situations, the slurry pond waters are
alkaline and may effectively neutralize limited amounts of acid drainage from
the pile.
48
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Other site selection factors related to water quality include the
presence of permeable substrata, which could lead to groundwater degradation,
and the presence of shallow, underground mine workings, limestone solution
caverns, landslides, or unstable ground, which could threaten the integrity of
the refuse pile or slurry pond. Also, water pollution is usually more easily
controlled on sites which have a gentle topography as compared to sites which
are steep.
Air Quality
The principal air pollution concern associated with modern refuse piles
is dust. (Burning refuse piles, which release various gases to the atmosphere,
are largely restricted to older deposits that contain significant amounts of
combustible materials and that were constructed by end dumping off steep
slopes.) As in any construction activity, some dust and machinery noise are
always associated with refuse pile construction. To minimize the adverse
effects of dust and noise, sites should be remote or isolated from public
areas, as far as possible. Specifically, sites where the prevailing winds
would travel over refuse piles in the direction of nearby housing areas should
be avoided.
Other factors to be considered are the length and location of haul roads
between the disposal site and the preparation plant. Long haul roads through
public areas are, of course, less desirable than short haul roads through
isolated areas.
Another consideration in air pollution control is the method of disposal
of trees, shrubs, and similar materials that are cleared from a refuse area.
Often the dried debris from such clearing operations is burned. If a site is
heavily wooded, air pollutants can be created by such burning operations.
Land Use and Reclamation
Land use and reclamation are very important factors which should be care-
fully evaluated in selecting a site. The long-term environmental effects of
the completed refuse disposal facility are a vital part of the pollution con-
trol effort. In some cases it is possible to develop a finished refuse area
so that the land's ultimate use has greater public or private value than was
the case prior to refuse placement. For example, filling and reclamation of
steep valleys in Appalachia can create flat land, which is at a premium in
many localities and which can be used for parks, recreation areas, etc. Fore-
sight, proper planning, and a conscientious effort can result in a refuse area
which is an economic asset to the mine owner rather than a liability, as has
so often been the case in the past.
From a pollution control viewpoint, choosing a refuse disposal site which
minimizes the surface area for the required ultimate storage volume is very
important. Concentrating the refuse in a small area not only optimizes land
use but also reduces the water pollution potential.
49
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COAL REFUSE DEPOSIT CLASSIFICATION SYSTEM
Given a particular disposal site, there are several facility configura-
tions that might be utilized. The configuration with respect to site topog-
raphy can dramatically influence the choice of pollution control methods. Land
forms usually control the configuration of a coal refuse deposit, and particu-
larly of the height and type of embankment. In the steep, mountainous terrain
of Appalachia, cross-valley dumps and impoundments are most common and, because
of the presence of narrow stream valleys or hollows, embankments tend to be
relatively high. In contrast, in the flatter terrain of the Midwest disposal
sites often cover larger areas and embankments are lower. The higher embank-
ments and larger refuse piles usually (but not always) present greater poten-
tial air and water pollution problems.
System Development
A coal refuse classification system was developed by W. A. Wahler &
Associates-'- to classify the numerous types of refuse piles and slurry ponds
found in the coal fields of the eastern part of the United States. The follow-
ing definitions were established:
Dump; A permanent or long-term accumulation of coal mine or coal process-
ing refuse on or in earth; not capable of impounding fluid.
Impoundment; A depression, an excavation, a permanent or long-term accu-
mulation of coal mine or coal processing refuse, or other facility
on or in the earth; capable of impounding fluid.
Except when a disposal facility is constructed specifically for the pur-
pose of impounding liquids, its configuration usually depends on the equipment
used to move the refuse and on the topography of the disposal site. Of these
two factors, the topography most affects the general configuration. Five
classes of refuse pile configurations have been established:
I. Valley-fill
II. Cross-valley
III. Side-hill
IV. Ridge
V. Waste heap
In addition, four slurry pond classifications have been selected:
VII. Cross-valley
VIII. Side-hill
IX. Diked pond
X. Incised pond
These classes are illustrated on Figures 11 and 12.
By dividing complex disposal sites into simple forms, the classification
system adequately defines the type (or types) of sites. However, using these
simple forms for extremely complex sites may make the data collection task
50
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VALLEY-FILL TYPE I
CROSS-VALLEY TYPE II
SIDE-HILL TYPE III
RIDGE TYPE IV
WASTE HEAP TYPE V
Figure 11. Simple refuse pile forms.
CROSS-VALLEY TYPE VII
SIDE-HILL TYPE VIII
DIKED POND TYPE IX
INCISED POND TYPE X
Figure 12. Simple slurry pond forms.
51
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more difficult. When this appears to be the case, the configurations call for
special definition (such as plan, sketches, and diagrams) and are designated
as Type VI for refuse piles and Type XI for slurry ponds.
Each type of site described above has some unique characteristic. The
nine simple types (I through V and VII through X) are discussed in the follow-
ing paragraphs.
Type I; Valley-Fill Refuse Pile
A valley-fill pile completely fills a valley, has an almost flat, hori-
zontal or sloping upper surface, and cannot impound water. The pile is
usually extended downslope by placement of refuse on the "downstream" face of
the pile; however, some have started as cross-valley fills that are later
filled in on the "upstream" side. This type of coarse refuse pile is common
in hilly or mountainous terrain.
Type II; Cross-Valley Pile
A cross-valley pile bridges a valley but does not completely fill it.
The crest of the pile may be reasonably horizontal or it may slope steeply.
So that it will not constitute an impoundment, it must be drained by natural
or man-made means. This type of facility is common in hilly and mountainous
terrain. As discussed later (under Type VII: Cross-Valley Slurry Pond), one
common practice is to use a cross-valley refuse pile as a dam or dike to
retain a fine-refuse slurry pond. Other practices are to construct a cross-
valley pile with culverts running under it to carry stream flows, or to make
the refuse so pervious that water will flow through the voids.
Type III; Side-Hill Pile
A side-hill pile is constructed along one side of a valley. If the pile
becomes large enough to cross the low point (or stream) in the valley, it can
in part or in total be classified as a cross-valley pile. Side-hill piles are
well suited to gently sloping sites where the ground conditions are stable.
Type IV; Ridge Pile
A ridge pile straddles a ridgeline or the nose of a ridge. This type of
refuse disposal facility, although sometimes used in gentle or hilly terrain
where valley slopes are stable, is not in common use.
Type V; Waste Heap
Waste heaps are constructed on relatively flat surfaces and have sloping
surfaces around all sides. This type of coarse refuse pile is very common in
the Midwest, where flatlands predominate.
Type VII; Cross-Valley Slurry Fond
A cross-valley pond often has a retention embankment that resembles a
normal earth dam. The embankment crosses the low point of the valley and has
52
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a crest above the natural drainage elevation. This type of Impoundment facil-
ity is in widespread use wherever the topography permits, because this is
usually the most economical method of creating an adequate slurry pond. The
embankment may or may not be partially or fully composed of coarse mine refuse.
Type VIII; Side-Hill Pond
A side-hill slurry pond is usually a three-sided dike system located on
gently sloping ground. The fourth side is the valley slope. As does the side-
hill refuse pile (Type III), the side-hill pond requires gentle and stable
valley side slopes. This type of construction is commonly found in wide
valleys where slopes are not steep.
Type IX; Diked Pond
A diked pond has a four-sided embankment which completely encircles the
impoundment area. There is no inflowing drainage area outside the crest of
the embankment. Closed dike systems are common in the Midwestern flatlands.
For reasons of economics, the embankments are usually low in height.
Type X; Incised Pond
An incised pond is formed by an excavation and lies completely below the
surrounding ground surface. This type of disposal facility is commonly used
by surface mines, where the last cut in the mining operation can be developed
as the slurry pond.
POLLUTION CONTROL
Each type of refuse pile or slurry pond has particular advantages, dis-
advantages, and/or requirements which are related to pollution control. Some
of the more important considerations are summarized below.
Type I; Valley-Fill Pile
A valley-fill pile can best be developed by starting at the head of the
valley and filling in the downstream direction. Many valleys in Appalachia
are deep and relatively narrow. By filling in such a valley, it is possible
to store large amounts of refuse within a relatively small area. Limiting the
surface area of the pile reduces the total amount of exposed refuse and there-
fore reduces the water pollution potential. Also, filling in a valley and
reclaiming the surface eventually provides valuable flat or gently sloping
land.
Natural springs or water seeps along valley sides are common in certain
locales. Valley-fill piles in such areas must therefore have underdrain
systems. Depending on construction methods, a perimeter ditch around the
sides of the valley may be required to divert drainage away from the pile.
53
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Type II; Cross-Valley Pile
A cross-valley pile, in contrast to a cross-valley pond, is not intended
to impound water. Therefore, rather large culverts in valley bottoms are
generally required, to pass flood waters. This type of arrangement is normally
the least desirable of all the refuse pile types, because water diversion and
long-term reclamation require maintaining the underlying culverts.
If the refuse material particles are of such a size that stream flows
pass freely through large, open voids, this is considered poor pollution con-
trol management, because the water could pick up harmful acidity or suspended
solids. The potential for spontaneous combustion is also increased, because
air can enter the open voids in the refuse.
Type III; Side-Hill Pile
Side-Hill piles are well suited to gently sloping terrain where ground
conditions are stable. For such a facility, however, diversion of uphill
waters is almost always required. With this type of refuse pile the main
valley drainageway is always left open. Therefore, compared to valley-fill or
cross-valley refuse piles, diversion of uphill surface waters around a side-
hill refuse pile can normally be accomplished in a more reliable fashion, thus
reducing the water pollution potential. Care must be taken to limit the
lateral extent of the side-hill refuse pile in the vicinity of the main drain-
ageway in the valley bottom. If the refuse pile unduly restricts the flow
capacity of the main valley stream, floods could erode out substantial amounts
of the pile, causing serious downstream water pollution concerns, a poor
aesthetic appearance, and a potential for major stability problems which, if
not rectified, could lead to temporary damming of the drainageway and subse-
quent downstream flooding.
Type IV: Ridge Pile
A ridge pile requires no special diversion works, because there is no up-
hill drainage basin. However, special erosion-resistant drainage ditches are
needed on the side (or sides) of the pile, in order to drain its upper surface.
A ridge pile should be sited where there are stable valley slopes capable
of withstanding the additional stress imposed by refuse. The top of the ridge
should be relatively wide and the valley slopes should be relatively flat, so
that significant amounts of refuse can be stored satisfactorily.
Because this type of refuse pile normally is highly visible and exposed,
it should be avoided, if possible.
Type V: Waste Heap
Where the topography permits, this type of pile is considered to be the
most favorable with respect to safety and pollution control. The shape of
this type of pile is quite flexible, which permits optimum utilization of the
site. Surface drainage usually can be easily diverted around the pile through
open ditches.
54
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A waste heap can be moderately to highly visible, and slope reclamation
requirements are usually more extensive than for other types of piles.
A waste heap is best developed using cellular construction procedures.
Type VII; Cross-Valley Slurry Pond
This type of disposal facility is most advantageous at sites where the
drainage area is small and where the valley slopes are gentle. It is least
advantageous where there are steep valley slopes and large upstream drainage
basins. Cross-valley slurry ponds in narrow valleys with large upstream drain-
age areas are often major water pollution sources. Because reliable diversion
of upstream waters is difficult to achieve, heavy flood-water runoff can
literally flush out fine refuse previously deposited in the slurry pond, dis-
charging the material to downstream receiving streams and thus creating sedi-
mentation and chemical water pollution problems. Cross-valley slurry ponds
with the adverse characteristics mentioned above should therefore be avoided.
Cross-valley ponds with small drainage basins above the pond often may be
designed to hold flood waters, thus eliminating or reducing the need for down-
stream releases. In such a case the pond's water circuit may be closed and
clarified water may be recycled to the preparation plant for reuse. This
dramatically eliminates or reduces the pollution potential. Also, with this
type of slurry pond it is often possible to develop large fine-refuse storage
capacity and settling areas at a comparatively low cost.
Type VIII; Side-Hill Pond
The pollution control considerations for side-hill slurry ponds are the
same as those mentioned for side-hill refuse piles.
Type IX: Diked Pond
Diked ponds are considered to be the best form of slurry pond from a
water pollution standpoint, because they eliminate the problem of an upstream
drainage basin discharging waters into the pond. Essentially flat or very
gentle sloping terrain is required for a diked pond.
Diked pond embankments are normally not as high as other types of slurry
pond embankments. Also, diked ponds are readily amenable to being divided
into compartments for better management of distribution of settled solids,
decanting of clarified water, and/or reclamation activities.
Type X; Incised Pond
The most significant disadvantage of the incised, or below-grade, pond is
the potential for ground-water degradation. The excavation for the pond (or
spoil banks if the pond is located in an abandoned surface mine) may expose
more permeable subsurface conditions than exist on the natural ground surface.
If pond waters are contaminated, or if seepage through spoil areas picks up
excessive amounts of dissolved salts, ground-water degradation problems could
55
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arise. Pond liners could be used to seal off permeable zones; however, liners
are costly and are subject to damage if the solids are to be reclaimed later.
SUMMARY OF PRINCIPAL SITE SELECTION GUIDELINES
It is important to locate refuse piles and slurry ponds in areas where
the refuse can be isolated from ground and surface waters.
• Whenever feasible, a refuse pile should be sited so that drainage from
the pile is directed into the slurry pond (if any).
Sites with shallow underground mine workings, limestone caverns, or
highly permeable subsurface conditions should be avoided.
• Waste heap piles and diked slurry ponds are usually the most advanta-
geous types of disposal arrangements in terms of pollution control.
• Cross-valley slurry pond sites with steep valley slopes and large
upstream drainage basins should be avoided.
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SECTION 6
CONVEYANCE SYSTEMS
Coarse refuse can be transported from the preparation plant to the dis-
posal area using trucks, scrapers, rail, conveyor belts, or aerial tramways,
alone or in various combinations. Each system (or combination) has different
advantages and disadvantages from the standpoint of pollution control. The
conveyance of fine refuse from preparation plants to slurry ponds is accom-
plished using pumps and one or more pipelines. Properly designed and con-
structed, the pipeline is an excellent transport vehicle with respect to pollu-
tion control.
COARSE REFUSE CONVEYANCE SYSTEMS
Refuse spillage between the preparation plant and disposal area creates
two pollution control problems:
1. Erosion and Siltation - spilled refuse is normally loose and highly
susceptible to erosion. The eroded material may be transported to and depos-
ited in streambeds where it can inhibit aquatic life and vegetative growth.
2. Acid Drainage and Heavy Metals - waters falling on, or passing
through, acid-producing refuse will pick up oxidized sulfur and soluble heavy
metals which could significantly pollute downstream waters.
Each conveyance system has characteristics which require provisions to
minimize potential pollution.
Wheeled Vehicles (Trucks and Scrapers)
To minimize spillage from wheeled vehicles, they should not be overfilled,
and the gates on the vehicles should be carefully maintained to ensure tight
closure. In addition, the haul roads between the preparation plant and the
disposal area should not be constructed of acid-producing refuse unless the
roads are surfaced with a relatively impermeable wearing surface or drainage
from the roads is controlled within acceptable water quality limitations.
Rail Transport
Railroads are seldom used for hauling coarse refuse; when they are, the
spillage control precautions necessary for truck and scrapers also apply to
rail transport. However, railroad track beds are not usually constructed with
coarse refuse as ballast.
57
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Conveyor Belts
The use of a conveyor belt system for refuse transport involves the
removal of refuse via the belt to a storage location adjacent to the disposal
area. From there the refuse is distributed by truck, scraper, or bulldozer
units. An important feature of refuse disposal conveyor belts is a belt
reversal mechanism, so that the belt can be mechanically rotated at the dis-
charge point to prevent the wet, refuse-carry ing side from contacting the
return idlers. This prevents the deposition of carry-back material along the
beltway and the buildup of wet, sticky material on the return idlers, thus
minimizing adverse effects on belt alignment.
Aerial Tramways
Aerial tramways are sometimes used in steep terrain where slopes exceed
allowable grades for wheeled vehicles or conveyor systems. Prior to the 1972
Buffalo Creek disaster, aerial tramway systems were commonly used to gravity-
dump refuse across a valley. In many cases, this led to undesirable materials
segregation, slope instability, refuse pile fires, and water pollution. Modern
practice requires aerial tramways to dump the refuse adjacent to the disposal
area. From this point it is moved by bulldozers or loaded into trucks or
scrapers and placed in controlled layers.
Some of the older tramway systems had severe spillage problems along the
cableways, particularly during freezing weather. Wet refuse would freeze or
stick in the tramcars and fail to dump at the proper unloading point. Tram-
cars would often lose the material somewhere along the tramway alignment while
returning in the upside-down position to the preparation plant. Cleaning up
spillage along the route of an aerial tramway is a rather difficult and awkward
task, because the terrain that aerial tramways traverse is usually steep.
Aerial tramways should incorporate provisions for preventing unintentional
dumping of refuse along the tramway route.
SLURRY TRANSPORT SYSTEMS
For pollution control, a slurry pipeline, which is an enclosed system, is
an excellent means of conveying fine refuse from the preparation plant to the
disposal area. Refuse spillage is limited to potential leaks between pipe
joints or to accidental breaks. Occurrences of this nature are relatively rare
and normally prompt immediate remedial action.
Leaks in pipelines sometimes occur where the lines go under roadways or
where shifting ground disturbs the original alignment. These problems can be
minimized in several ways, for example by installing structural sleeves between
the roadbed and pipe. Pipeline alignments that cross unstable ground should be
avoided, unless problem areas have been stabilized.
Slurry pipelines are constructed of a variety of materials including
steel, concrete/asbestos/cement, plastic, and other synthetic resins. The
pipelines may or may not be buried. Buried lines are less susceptible to
damage from surface activities and normally are not exposed to the extreme
temperature variations that cause expansion and contraction of surface
58
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pipelines. Surface pipelines, on the other hand, are easily inspected and can
be readily repaired in the event leaks do occur. Slurry pipelines normally
have a drain valve and a sump at each low point along the alignment. These
valves and sumps are required to avoid plugging of the line in the event of a
pump shutdown when the line is full of slurry. For proper pollution control
management, the sumps should be adequately sized to accommodate the drained-
off slurry and the sumps should be cleaned and solids properly disposed of
after each use. Prior to any planned pump shutdown, the pipeline should, of
course, be flushed with clear water to avoid plugging the line.
SUMMARY OF PRINCIPAL CONVEYANCE SYSTEM GUIDELINES
• Acid-producing refuse should not be used as a construction material
for haul roads.
• Conveyor belts should be equipped with a belt reversal mechanism on
the return circuit.
• Aerial tramway systems should include provisions to preclude spillage
of refuse along tramway routes.
• Structural sleeves should be installed in pipeline systems where such
lines pass under roadbeds.
• Pipeline alignments should not pass through unstable ground areas
unless provisions have been made to stabilize problem areas.
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SECTION 7
GUIDELINES FOR REFUSE PILE CONSTRUCTION AND OPERATION
Pollution control during coal refuse pile construction and operation
involves the following principal considerations: site preparation and develop-
ment; drainage and erosion control; refuse haulage, placement, and compaction;
and dust control. The construction and operation of a coal refuse pile are
similar to these activities for other major earthwork construction projects
such as dams, roads, and structural fills. Many construction and engineering
techniques used in construction work can be utilized for coal refuse disposal,
if proper recognition is given to the unique character of refuse material it-
self and to the logistics associated with its production and transport. For
example, in a major earthwork project some control is normally exercised over
the type of materials placed in a fill, but the coal refuse disposal operator
has little control over the type, quantity, or quality of reject material.
Also, coal preparation plants operate under all weather conditions, and often
during both daylight and dark hours. The refuse disposal operations must be
able to adapt to the changing conditions without hampering preparation plant
procedures. Refuse disposal requires handling a fairly steady stream of
reject material on a relatively continuous basis, under varying weather condi-
tions, over the life of the mine or plant.
SITE PREPARATION
Site preparation for refuse piles involves:
• Clearing, grubbing, stripping, and disposal of trees and heavy brush.
• Installation of a subdrain system (if required).
• Diversion of natural runoff water around the refuse site.
• Provision of a siltation basin downslope of the refuse pile (if
required).
Clearing, Grubbing, and Stripping
Trees and heavy brush must be cleared in order to provide suitable access
to the site and to remove organic material which could later decompose and
cause environmental or structural problems. Grubbing of large, closely spaced
tree stumps is normally required to prevent tire damage to the haulage equip-
ment. Stripping of topsoil from under the pile area is done to establish a
more stable foundation for the refuse pile and to provide a source of material
for future reclamation activities.
60
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The principal pollution concern with respect to clearing and grubbing is
disposal of the debris. Trees of commercial value can, of course, be salvaged
and sold. However, many disposal sites contain large amounts of trees and
brush which have little or no commercial value. Options for disposal of this
debris generally include chipping, burial, burning, and stockpiling.
Trees, tree limbs, and heavy brush can be reduced to wood chips using
portable mechanical devices. The wood chips are hauled from the site and sold
to chemical and industrial plants. This option represents the best environ-
mental alternative for disposal of debris from heavily wooded sites that are
within economic haul distances from wood chip users.
Cleared materials are sometimes buried, if the terrain is suitable and if
the quantity of material is not too great. Cleared debris must not be buried
in or under the refuse pile, because this would jeopardize the structural
integrity and permeability characteristics of the pile. Instead, burial must
be done outside the limits of the pile and in conformance with sanitary land-
fill regulations.
Burning of stacked or piled trees and brush, a traditional means of dis-
posal, has come under increasing criticism and regulation for obvious safety
and environmental reasons. If burning is permitted, only small fires should
be used, and only under controlled conditions. Ashes should be quenched and
properly buried or covered outside the refuse disposal pile. In some cases,
the use of an air curtain jet may be desirable to increase the temperature of
the burning material and thus reduce the air pollution potential.
In stockpiling cleared debris, large bulldozers are usually employed to
push the material to the edge of the work area, where it is allowed to remain.
Often the debris is simply left aboveground to decay. After a few years, the
trees and brush dry out and can then constitute a substantial fire hazard.
For this reason, stockpile materials from clearing operations should be covered
with earth as specified in sanitary landfill regulations.
It is considered good practice to limit clearing and grubbing operations
to immediate work areas, instead of clearing an entire refuse disposal area at
the start of operations. This is to avoid unnecessary erosion and siltation
problems. Also, In many parts of Appalachia the hillsides are unstable, and
clearing the natural ground cover tends to increase the amount of water perco-
lation into the soil, which in turn could lead to landsliding.
Stripping, or topsoil removal, is done to provide a firm foundation for
the refuse pile and to develop a source of material for future site reclama-
tion activities. This may reduce or eliminate the need for opening additional
borrow areas for reclamation soils. However, some latitude is required when
the refuse pile is located on steep terrain and it is not practical to stock-
pile and rehandle the topsoil.
Installation of Subdrains
The purpose of a subdrain system is to drain away subsurface waters before
they can reach the base of the refuse pile. Subdrains are required wherever
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springs or water seeps occur under a proposed pile. Subdrains are necessary
for embankment stability and water pollution control reasons. By reducing the
water in the pile's foundation, they also facilitate the initial placement of
refuse. Subdrains are commonly required in the hilly terrain of Appalachia
but are seldom needed at the flatter sites found in the Midwest.
As shown on Figure 13, subdrains normally consist of one or more layers
of granular material surrounding a pipe. The gradation of this material is
very important in terms of satisfactory performance of the system, and improper
design and/or construction techniques have led to numerous problems in the
past. The interested reader should refer to Reference 2 for a discussion of
and recommendations for appropriate subdrain designs.
ROCK FILL
SEWER PIPE LAID
WITH OPEN JOINTS
GRADED GRAVEL
OR CRUSHED ROCK
vw-:.v.Sv- •.••;: •••:-:Y----.:£:-'-&
//$VWfi3$l^$SV:$&*^
S— SOIL FOUNDATION—5
SELECTED
FINE ROCK
GRADED SAND
a. OPEN JOINT PIPE
IMPERVIOUS EMBANKMENT
PERFORATED
BONDED C.M.P.
SAND AND GRAVEL
GRADED GRAVEL
OR CRUSHED ROCK
GRADED SAND
S SOIL FOUNDATION-
b. PERFORATED PIPE
Figure 13. Example of subdrain.
62
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It is often hard to locate all the springs or water seeps in a proposed
disposal site until the site has been cleared. Therefore, subdrain layout is
usually not undertaken until construction activities expose spring and seep
locations.
If the overlying refuse is acid-producing, the permeable portion of a sub-
drain system should be covered with at least 60 cm (about 2 feet) of clay soil
or other suitable low-permeability material. This is to prevent contamination
of the collected spring waters by waters which may be seeping through the
refuse pile.
Diversion of Natural Runoff
Diversion of runoff waters around a refuse pile is an essential pollution
control requirement. Normally, diversion ditches are excavated around the
perimeter of the site, to control surface drainage. In flat or gentle terrain,
construction of such ditches is relatively straightforward, but in steep,
heavily wooded terrain, where valley-fill disposal operations are common,
ditch construction is more difficult. The design and construction of diver-
sion ditches is further complicated in many parts of Appalachia by the exis-
tence of active landslides along valley slopes, because drainage ditches that
run parallel to the ground contours increase slope instability. However,
ridgetop disposal sites, or sites where the drainage is consistently away from
the refuse pile, do not require diversion facilities.
Diversion ditches must be protected with riprap, drop structures, or
other suitable materials or devices in cases where the water velocity would
cause erosion of the natural materials.
Siltation Basins
Siltation and debris basins are often constructed downslope from refuse
piles as a means of minimizing the discharge of waters containing suspended
solids. In most cases, such basins also serve other purposes. For example,
five of the nine study sites have Siltation basins incorporated in their lay-
outs, and these basins may have one or more functions, including serving as a
recirculating pond, a receiving basin for slurry pond waters, a makeup water
and Siltation collection basin, and/or an emergency slurry pond.
The most common function of a siltation basin is to act as a slurry pond
for fine refuse. Directing surface drainage from a coal refuse pile into a
proper slurry pond is an excellent means of pollution control. Such an arrange-
ment can substantially promote the removal of suspended solids and the partial
or complete neutralization of acid drainage.
In the steep, narrow valleys of Appalachia it is very difficult to pro-
vide permanent siltation basins, because major embankments and associated
spillway structures would be needed in order to develop adequate settling areas
and to prevent overtopping. In these circumstances, special arrangements
would be required, which might include:
63
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Construction of a major downstream slurry pond and appropriate
spillway.
• Development of small, temporary siltation basins immediately below the
toe of the refuse pile, with appropriate diversions around the basin. These
basins would have to be abandoned periodically and new ones would have to be
constructed downstream as the refuse pile expanded in the downslope direction.
Installation of special retention structures (for example sheet piles)
that would permit overtopping without breaching.
SITE DEVELOPMENT
Prior to starting disposal operations, it is essential to have a site
development plan that includes pollution control measures. Appropriate start-
ing and ending points must be established, as well as detailed plans for drain-
age and reclamation works. The plan should include the sequential construction
operations associated with full development of the site. The scope and detail
required for site development and pollution control planning will, of course,
vary according to the nature of the individual site and the properties of the
refuse to be disposed of.
Site development planning is greatly influenced by the type of refuse
pile (valley-fill, side-hill, waste-heap, etc.) selected. For each type there
are preferred construction schemes that will aid in pollution control.
Figure 14 is a plan and section of a valley-fill refuse pile with a down-
stream slurry pond. For pollution control, it is important to start filling
at the head of the valley and to develop the site in the downslope direction.
Ideally, the pile should be brought up to a finished surface elevation that is
slightly above the elevation of the drainage basin, so that drainage from the
finished surface can be readily directed into adjacent drainage basins. This
avoids the need to construct and maintain ditches along the side of the valley,
and pollution risks associated with ditch failures during heavy rains are thus
eliminated.
The refuse area in Figure 14 is constructed in benches (or strips) per-
pendicular to the valley line. After each bench reaches its ultimate level,
the finished surface is sloped to drain away from the working slope and is
covered with earth as required for reclamation procedures.
The arrangement shown in Figure 14 minimizes the exposed refuse surface
area, provides a reliable system for diverting surface and subsurface waters,
and allows reclamation activities to take place during the operating life of
the site. The downstream slurry impoundment also serves as a sedimentation
basin for any coarse refuse eroded off the slopes of the active refuse pile.
64
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LIMITS OF
DRAINAGE BASI
-ACTIVE REFUSE
PLACEMENT AREA
C-HEAD OF VALLEY -
FINISHED REFUSE
AREA
SPILLWAY
PLAN OF DISPOSAL AREA
ACTIVE
REFUSE AREA
RECLAMATION
EARTH COVER
FINISHED
REFUSE SURFACE
FUTURE REFUSE
DEVELOPMENT •
SUBDRAIN SYSTEM
IF REQUIRED
SECTION M
Figure 14. Site development: valley-fill refuse pile.
Figure 15 is a site development example for a side-hill refuse pile. The
development is very similar to that for a valley-fill pile, except that a
permanent ditch is constructed immediately above the upper limit of the pile.
Both the uphill natural drainage and the drainage off the covered refuse pile
are directed into this ditch. From a pollution control standpoint, a side-
hill pile can most advantageously be constructed in perimeter strips, starting
from the uphill diversion ditch. Topsoil removed for a new perimeter strip
foundation is placed on the top finished refuse surface as part of the ongoing
reclamation of the facility.
65
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r T
r
r
T
FINISHED AND RECLAIMED REFUSE AREA
WORKING REFUSE STRIP
FUTURE REFUSE STRIPS
MAIN DRAINAGEWAV
PLAN OF SIDE-HILL REFUSE PILE
•DIVERSION DITCH
WORKING REFUSE STRIP
FUTURE REFUSE STRIPS
MAIN DRAINAGEfAY-
WHERE REQ'D
SECTION A-A
Figure 15. Site development: side-hill refuse pile.
66
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Figures 16 and 17 illustrate two types of site development arrangements
for waste heap refuse piles. Figure 16 shows a cellular system which is
similar to the way many sanitary landfills are developed. The object here is
to build and reclaim individual cells, in order to minimize exposed surfaces
and thus reduce the water pollution potential. Cell dimensions should be the
minimum consistent with safe, effective construction. The cells are usually
rectangular, to facilitate refuse placement operations. In this example the
DIVERSION DITCH
PROPERTY LIMITS
PLAN OF REFUSE PILE
ACTIVE REFUSE CELL
FUTURE CELL
FINISHED CELL COVERED WITH
CLAYEY MATERIAL AND
ESTABLISHED PLANT GROWTH
SECTION A-A
Figure 16. Cell development plan for waste heap refuse pile.
67
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cell construction sequence was developed in such a way as to maintain site
drainage. Other equally satisfactory sequences could be utilized. As for a
side-hill pile, topsoil removed from beneath the foundation of a new cell is
placed directly on the surface of a finished cell, as part of the ongoing
reclamation work.
Figure 17 shows a waste heap pile developed in conjunction with a slurry
pond. The pile is developed in a manner similar to that for the side-hill
DIVERSION DITCH
r
PROPERTY LIMITS-
1
/
-<
_
<
X
"i A A
A A A
^-SLURRY DISCHARGE SLURRY POND
>_ PIPE
DECANT PIPE
I A A A
FINISHED REFUSE SECTION
^ r T r r
ACTIVE REFUSE SECTION
^^
FUTURE REFUSE SECTION
^•M
'
4
^
\
N
^
^
x. A
"iry"
o
Ul
u.
— IE
« t—
f
O.A
/
/
-<
_,/
-^
=i =
_J
^>
PUMP
RETURN LINE TO
PREPARATION
PLANT
PUN OF ALTERNATIVE REFUSE PILE
-DIVERSION OITCH
r
DRAINAGE INTO SLURRY POND
EARTH COVER LAYER
FINISHED^,.
REFUSERS-
FUTURE
REFUSE
SECTION
SECTION A-A
Figure 17. Alternative development plan for waste heap refuse pile.
68
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pile (Figure 15). This type of arrangement may be satisfactory for nonacid-
producing refuse, but for acid-producing refuse the cellular type of system
(Figure 16) is preferable.
These examples reflect some of the major pollution control considerations
associated with relatively simple types of refuse piles. When slurry ponds
are used in conjunction with piles, adherence to the basic principle of emplac-
ing the coarse refuse above the slurry pond will improve pollution control and
may eliminate the need for separate siltation basins.
The severity and type of water pollution problems vary with the chemical
characteristics of the refuse and with specific site conditions. However, acid
drainage from the pile and drainage waters containing excessive amounts of sus-
pended or dissolved solids are always a concern. Therefore, site development
plans should be directed at isolating the refuse from the surrounding environ-
ment during the operating life of the pile as well as during abandonment
activities.
DRAINAGE AND EROSION CONTROL
Throughout the preceding discussions, the critical importance of drainage
and erosion vis-a-vis refuse disposal has been emphasized. Proper control of
drainage and erosion from refuse piles is a vital part of pollution control.
Coarse refuse is usually highly susceptible to erosion—extremely deep and
extensive erosion gullies can develop in a refuse pile if drainage provisions
are inadequate. Outside surface waters should be diverted away from the pile,
and drainage systems must be developed for water that falls directly on the
disposal area.
The diversion of outside water is almost always accomplished with simple
ditches. Because definitive criteria are lacking, sizing of diversion ditches
has been determined somewhat arbitrarily in actual practice. Present EPA
regulations regarding point source discharges from refuse storage areas,
although not specifically directed at diversion ditches, permit waiving the
effluent limitations for runoff that results from a 10-year, 24-hour precipi-
tation event. We believe this is a reasonable criterion for sizing diversion
ditches for sites where there is no downstream impoundment. For waste heaps,
the failure, or overflow, of a diversion ditch is normally not a critical con-
cern. In gently sloping terrain, where heavy runoffs may result in ditch
overflows and perhaps in saturation of the toe of the refuse pile, ditch main-
tenance is usually restricted to periodic cleaning of sediments and erosion
control. On the other hand, the failure of a diversion ditch above a refuse
pile can result in heavy erosion and downstream water pollution. In this case
large, concentrated flows of water are directed over the pile. Experience at
study site E indicates that substantial maintenance is required for ditches
excavated along steep, unstable, wooded hillsides, even if the ditches are
designed and built in accordance with present MSHA regulations.
Surface drainage off the refuse pile itself is another important factor.
The surface of the pile should always be sloped away from the side slopes, to
avoid erosion problems. Where collected surface drainage must be brought down
the face of a refuse pile, as is the case with a waste heap, special erosion
69
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resistant ditches should be provided. These ditches might be lined with rip-
rap or other suitable material to control erosion. Also, the working refuse
surface should be as flat as possible in order to minimize erosion, but should
still have sufficient grade to ensure positive runoff without shallow ponding
of waters. This is particularly important if the refuse is acid-producing.
For example, at site E, surface grades were initially specified at 0.5 percent.
However, controlling grades to this flat a slope was not practical, and minor
ponding of waters resulted. Site operating personnel therefore selected a
1.5-percent surface slope, which was found to be satisfactory with respect to
removing the water without ponding or serious erosion.
Although the primary control on erosion is proper drainage, it is also
important to cover finished refuse surfaces immediately with earth and to
establish a vegetative growth. This is really a part of reclamation activi-
ties, and is therefore addressed in Section 9 of this report.
DUST CONTROL
In Section 6, we discussed the various means used to transport coal refuse
from the preparation plant to the disposal area. Once the coarse refuse
reaches the disposal area, rubber-tired wheeled vehicles are used almost exclu-
sively to haul and* place the refuse. (This is principally because of MSHA
regulations that require the refuse to be placed in layers not more than 60 cm
(2 ft) thick.) Haulage equipment is usually used to compact the refuse.
The principal pollution control consideration associated with haulage in
the refuse disposal area is dust control on the haul roads. Large dust clouds
from haul roads are objectionable for reasons of operator health and safety
and air and water pollution. Disposal areas where several pieces of equipment
operate in set traffic patterns usually have one or more water trucks available
to wet down the roads and reduce the dust problem.
The degree of haul roads dust control required is almost entirely depen-
dent on the size and location of the refuse disposal operation. Haul road
dust control requirements should be established on a site-by-site basis. At
some sites (for instance study site C) haul road dust control is not necessary
because of short haul distances, the use of only one piece of hauling machin-
ery, and the remoteness of the site from heavily populated areas. Other sites
(for example study sites B, E, and H) require haul road dust control proce-
dures principally for reasons of operator safety and health.
Control procedures usually involve the use of water trucks to wet down
the surface of the haul road. Other procedures include utilization of film
or hygroscopic chemicals, sprinkler systems, or paving. In freezing weather,
dust control requires special attention to avoid icing.
REFUSE PLACEMENT
Refuse placement procedures should be planned to prevent materials segre-
gation and to minimize the seepage of moisture into the pile. In the past,
materials segregation has been a chief cause of water and air pollution from
coal refuse piles. Placement procedures that have caused serious material
70
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segregation have involved the use of trucks or aerial tramcars to push or dump
refuse over the edges of steep slopes (see Figures 18 and 19).
NOXIOUS GASES
FROM SMOLDERING
REFUSE PILE
SPRING ACTIVITY
Figure 18. Improper refuse placement by truck dumping.
COARSE PARTICLES
NEAR BASE
AERIAL
TRAMCAR
FINE PARTICLES
NEAR TOP OF PILE
Figure 19. Improper refuse placement by aerial tramcar dumping.
71
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When refuse falls down a steep slope, the coarse particles roll toward
the bottom and the fine particles tend to remain near the top. The result is
a loose, highly segregated refuse pile whose base is much more permeable than
the top. It is not uncommon to find large water flows passing through the
bases of old piles of this type. If the refuse is acid-producing, clean waters
entering the pile become acidic and develop high concentrations of dissolved
solids. Also, because the air permeability in such piles grades from high near
the bottom to low near the top, smoldering fires within the mass of the refuse
pile are common. The end result can be a combination of acid drainage that
releases water pollutants to the downstream drainage basin and pollution from
the smoldering fires that release sulfurous or other noxious gases to the
surrounding atmosphere.
It is important to minimize the infiltration of water into acid-
producing refuse before the materials are compacted. This particularly applies
to disposal operations that use dump trucks for hauling refuse. It is common
practice for the trucks to dump refuse in loose piles which are periodically
leveled and compacted with a bulldozer. The refuse as dumped from trucks is
loose and highly permeable and rain or snowmelt easily percolates through the
material, which greatly increases the pollution load of seepage water. A case
in point was described by one of the operating personnel at study site D.
This disposal operation involves a wide, cross-valley refuse embankment which
retains a slurry pond. Coarse refuse is truck-hauled and dumped in piles on
the embankment. The working surface of the refuse is sloped into the slurry
pond for sediment control purposes. Operating data indicate that drainage
from the acid-producing refuse into the pond did not seriously affect the
water quality of the pond and that the water level in the reservoir could be
controlled by periodically pumping water which met the EPA point source dis-
charge regulations into the public stream. During one winter period, several
loose piles of refuse had been dumped on the working surface. Operational
procedures called for periodic leveling and compacting of the piles; however,
in this instance the piles were allowed to stand for a longer than normal
period. A heavy snowfall occurred which prohibited work on the piles. Later,
the snow melted and percolated slowly through the loose refuse. The resulting
drainage into the slurry pond carried such high pollution loads that the entire
pond required lime treatment before the water could be safely discharged into
the public stream. Fast experience indicated that, if the piles had been
leveled and compacted, the snowmelt would not have resulted in this high
pollution load.
Leveling and compacting dumped refuse do not normally constitute a full-
time operation for a bulldozer. As a consequence, this work is done on an "as
required" or "when convenient" basis rather than on an established schedule.
The basic requirement is that acid-producing piles be leveled and compacted
prior to a precipitation event which results in runoff. It is not always
possible to meet this requirement, because of weather uncertainties. Never-
theless, some reasonable guidelines are necessary for limiting the amount of
loose, truck-dumped, acid-producing refuse that can be placed prior to level-
ing and compaction. Two suggested methods, which may be used separately or
in combination with each other, are;
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1. To require leveling of piles on an established periodic basis, for
example at least once every working shift. Also, when rain or snow is pre-
dicted, leveling and compacting equipment should be active on the working
surface.
2. To limit the exposed working area where refuse is being placed so
that an excessive pollution load will not be released to downstream waters
during and after a precipitation event.
The second method is the most desirable, because it would minimize not
only pollution loads from water seeping through the refuse but also the loads
from water running off the surface of leveled and compacted refuse. Although
there are no quantitative data available from which to develop guidelines for
limiting exposed acid-producing refuse surfaces, it is best to keep such sur-
faces to the minimum consistent with efficient and safe construction practices.
LIFT THICKNESS
MSHA regulations specify that the lift thickness of coarse refuse be not
more than 60 cm (2 ft). As indicated in the tabulation below, the study sites
use lift thicknesses substantially less than this.
Owner-Specified
Lift Thickness
Site Centimeters
B 20-30
C 60 (max.)
D 60 (max.)
E 20-30
F 45-60
G 45 (max.)
H 60 (max.)
Inches
8-12
24 (max.)
24 (max.)
8-12
18 - 24
18 (max.)
24 (max.)
Actual Lift
Thickness
Centimeters
10
15
30
10
30
30
15
30
30
45
30
45
45
30
Inches
4
6
12
4
12
12
6
12
12
24
12
18
18
12
Haulage Equipment
Used
Scrapers
Scrapers
Trucks
Scrapers
Trucks
Trucks
Scrapers
The principal reason given by site operators for using lift thicknesses
thinner than required is improved trafficability. They have learned through
experience that the thinner the lift, the easier it is for vehicles to travel
over the material without creating excessive tire rutting. Having a firm,
unyielding surface for the haul units improves productivity and decreases
operating and maintenance costs.
The tabulation above also shows that when scrapers are used to haul and
place refuse, the lift thickness is usually substantially less than when
trucks are used. Scrapers are designed to place materials in thin lifts, and
they are also expected to operate fairly independently of bulldozers. When
trucks are used for refuse hauling, the material is dumped in piles which are
periodically leveled and compacted with a bulldozer, which has no traffica-
bility problems and thus can spread the refuse in thicker lifts than a scraper
can.
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COMPACTION
Lift thickness should be determined in relation to the required compactive
effort—the thinner the lift, the less the compactive effort required. In gen-
eral, the cleaner or more permeable the material, the easier it is to compact
and the greater the allowable lift thickness. Compaction has a significant ef-
fect on the permeability of the emplaced refuse, and this in turn affects the
pollution load in waters discharged from the pile.
Compaction is required, in most engineering applications, primarily to
increase refuse strength and decrease compressibility. For pollution control,
compaction is required primarily to reduce the air and water permeability of
the material. Reducing air permeability reduces the potential for spontaneous
combustion, which leads to refuse pile fires and thus to air pollution. Re-
ducing water permeability reduces moisture infiltration into the refuse and
thus reduces the pollution potential for waters leaving the pile.
Only limited data are available about the effects of compaction on refuse
permeability. Most of the reported work has been done in the laboratory,
using rammer-type hammers to compact reconstituted samples. Unfortunately,
the sampling and testing processes tend to degrade the shale refuse, so that
the percentage of fines in laboratory-test samples is often greater than that
in in-situ materials. Thus, laboratory data may not accurately represent
field conditions.
13
In a laboratory study of retorted oil shales, which have properties
similar to those of coal refuse, the effects of different compactive efforts
on permeability were investigated. The results of this program indicate that,
at a low compactive effort, permeability (K) = 480 - 2,088 x 10"^ cm/sec; at
a medium compactive effort K = 41 - 157 x 10~° cm/sec; and at a high compac-
tive effort K = 16 - 51 x 10"^ cm/sec.
The earth-dam engineering permeabilities of soil can be classified as
shown below:
Permeability (cm/sec) Classification
Greater than 10~4 Pervious
10~4 to 10~6 Semipervious
Less than 10~" Impervious
Accordingly, material tested at low, medium, and high compactive efforts can
be classified as pervious, pervious to semipervious, and semipervious, respec-
tively. Also, refuse material placed with a high compactive effort can be as
much as 100 times less permeable than refuse placed with a low compactive
effort.
Compaction of refuse reduces the permeability of the mass by pushing the
refuse particles closer together and breaking down some of the large particles
into smaller particles, thus increasing the percentage of fines. Both of
these mechanisms reduce the void ratio and porosity of the refuse mass. The
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reduction of voids by pushing the particles closer together is more pronounced
with well-graded materials. The greater the range of particle sizes, the
greater the reduction in voids for a given compactive effort. The more poorly
graded the refuse, the less will be the effect of compaction on reduction of
voids. For example, refuse from the rotary breaker in the preparation plant
is very poorly graded. Compaction of this material, assuming no particle
breakdown and resultant increase in fines, has only a minor effect on perme-
ability.
Refuse breakdown into smaller particles for a given compactive effort is
primarily a function of type of equipment used and angularity and hardness of
the particles. Fortunately, from a permeability or water infiltration stand-
point, the vast majority of coal refuse is a soft shale or clay shale, which
is degradable with exposure to weather and mechanical handling or compaction.
The anticipated effects of various types of compaction equipment on breakdown
or degradation of refuse particles may be summarized as follows:
Type of Compaction Anticipated Effect on
Equipment Refuse Degradation Remarks
Rubber-tired trucks Low —
scrapers, rollers
Bulldozers and grid Low to moderate Fines generated pri-
compactors marily at surface
Smooth drum static and Low to moderate "
vibratory rollers
Sheepsfoot rollers Moderate to high Approximates rammer-
type laboratory
compaction test effects
Vibratory sheepsfoot High "
For acid-producing refuse or refuse utilized in constructing the core of
a water and/or slurry retention dam, the percentage of fines is a critical
factor in minimizing infiltration. For these situations it is advisable to
use equipment which will maximize degradation and produce an optimum percent-
age of fines. Alternatively, fines (such as fine coal refuse or selected
borrow) can be mixed with the coarse refuse. In several earth-dam technology
applications a material with insufficient fines has been modified so that the
end result had sufficient fines.14-18 in these cases physical means were used
to increase fines and reduce the permeability of soil-rock materials. Also,
Sherard^-^ suggests that wetting the material and allowing it to weather is
another method of increasing fines. Other possible methods include using
heavy industrial-type disks on thin refuse lifts to crush some of the soft
shale particles and thus create additional fines, or adding fines from the
fine coal refuse circuit in the preparation plant.
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In earth-rock dam technology, one of the main concerns in using soft rock
materials such as coarse coal refuse is that the materials may soften appre-
ciably with time and with exposure to air and water. However, if there are
enough fines to fill the voids, and if the fines are reasonably well compacted
at the proper water content, no significant embankment softening will occur.19
Therefore, increasing the proportion of fines to reduce permeability (and thus
to make the material more acceptable environmentally) also adds to the integ-
rity of the structure.
Most pile compaction uses hauling and/or spreading equipment. When the
refuse is used as structural fill, special compactors are used. (For example,
at site I, where the downstream portion of the dam is being*constructed of
refuse, an 11-ton, smooth drum, vibratory roller is used for compaction.)
When the refuse is used as a nonstructural fill, only random travel of the
hauling equipment is usually specified (this requirement is sufficient to meet
present MSHA regulations). Among the study sites, only site G has a more de-
finitive criterion for compacting with hauling equipment. Here the drivers
are instructed to change their truck paths so that each refuse layer is com-
pacted by at least four to six coverages of the truck wheels. When rubber-
tired equipment is used for compaction, it is vitally important to maintain
proper tire pressures.
Sawyer and Fredland found that, given equal lift thicknesses and an
equal number of compaction passes, the coal waste compaction achieved using
a scraper is substantially greater than that obtained using a bulldozer.
These findings have been substantiated by field observations and by the ex-
pressed opinions of the construction and mining industries. Although de-
finitive field data are not yet available, it is also the general opinion
that scrapers are superior to conventional on-highway trucks in the degree
of compaction achieved by random routing of equipment.
In the last 20 years or so the use of thin lifts and heavy rubber-tired
equipment has also been adopted by the electric power industry for compaction
of large coal storage piles adjacent to power plants. Most coal-fired utility
plants keep a 60- to 90-day supply of coal on hand to help ensure uninterrupted
power generating capability. As the size of the generating plants has
increased, so has the size of the coal storage piles. Prior to the 1960s,
many of these coal piles ignited basically for the same reasons as did some
older coal refuse piles. Such fires presented an economic loss to the util-
ities, and immediate action was usually taken to extinguish the fires or hot
spots by digging them out and wetting down the exposed hot coals. However, as
coal preparation plant processes changed so that coal received at the plants
had a greater proportion of fines, and as large, rubber-tired bulldozers that
operate most effectively on thin lifts became more widely available, the prob-
lem of coal storage pile fires was practically eliminated. This is because
it became possible to reduce the air permeability of the pile mass so much
that there would no longer be sufficient oxygen to support the ignition
mechanism.
Another adverse environmental feature of older coal storage piles that
has largely disappeared today was the underdrain system. Formerly, many
storage piles were constructed on a permeable base of sand, to facilitate
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drainage and supposedly to reduce the moisture content of the coal. These
underdrain systems probably added to the amount of air available to the
interior of the pile and thus increased the potential for pile ignition.
Because today's storage piles are tight and relatively impermeable, they do
not require underdrain systems. Not only has the air pollution potential been
reduced, but also, because water infiltration into the pile has been mini-
mized, the potential for water pollution has been reduced.
Certain factors should be considered with regard to compaction equipment
type and operation. The following factors are particularly important. In
choosing bulldozers, crawler types with conventional tracks are generally best.
Bulldozers with wide tracks are used for work on soft ground where low contact
pressures are critical. Low contact pressure, or flotation track, bulldozers
are unsuitable for use as compaction equipment. When using on-highway trucks
for compaction, special attention and control are required to obtain reliable
routing of the trucks over the pile. Because on-highway trucks are particu-
larly sensitive to surface irregularities, they tend to follow one relatively
smooth path over the pile, except in the immediate dumping area.
PILE OPERATION IN ADVERSE WEATHER
During prolonged periods of heavy rain or snow, or when temperatures are
well below freezing, special or modified disposal operations are sometimes
required, depending on site conditions, types of equipment used, and severity
of the weather. In conventional earthworks construction, operations are
stopped when weather conditions are poor. In contrast, coal preparation plants
must operate in all weather conditions, in order to maintain efficiency.
Therefore there must either be temporary refuse storage provisions or proce-
dures must be adopted to permit refuse placement during adverse weather.
For inclement weather operations, the working area should be kept to an
absolute minimum. At some sites (particularly at sites in Great Britain),
special areas are designated for use in bad weather. These areas are usually
readily accessible and are located in noncritical sections of the site, and
remote or critical sections are used only in favorable weather.
In periods of prolonged rainfall, trafficability is reduced, equipment
may be mired down, and ruts that collect water are created in the refuse sur-
face, which adds to the water pollution potential and to site accessibility
problems. These difficulties are particularly acute at sites that have long,
steep haul roads and that use on-highway trucks for refuse hauling. To mini-
mize rainfall effects, refuse area surfaces should be sloped to drain and
compacted to a hard, tight surface. The object is to drain away the rainfall
as rapidly as possible, so that it does not excessively soften the surface or
infiltrate the refuse mass.
Snowfall can also affect operations and pollution control procedures,
especially with respect to water pollution loads. The amount of pollutants
picked up by water is related to contact time. When small amounts of water
trickle over refuse, the pollution load picked up is substantially greater
than that to be expected from an equal amount of water from a sudden rainfall.
Therefore, acid-producing refuse piles should be leveled and compacted prior
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to a snowfall, to minimize moisture infiltration during the snowmelt. Also,
refuse should not be placed without first clearing snow from the working sur-
face. Placing refuse on a snow blanket not only increases the pollution poten-
tial but can seriously affect the stability of the pile when the snow melts.
If possible, cleared snow should be piled at a location away from the refuse
surface. Care should be taken to keep the piled snow out of diversion ditches,
so as not to obstruct snowmelt drainage.
Another weather-related event that can affect pile operations is a period
of freezing weather. Most refuse comes out of the preparation plant quite
wet. Refuse particles may then freeze together in large lumps, creating han-
dling problems for trucks, conveyors, and storage bins. A principal concern
with placing refuse in freezing weather is the inability to achieve satisfac-
tory compaction. In summary, and as a general guideline, it can be said that
refuse placed during freezing weather should be disposed of only in special,
noncritical areas.
SUMMARY OF PRINCIPAL PILE CONSTRUCTION AND OPERATION GUIDELINES
• Only immediate work areas should be cleared and grubbed.
• Burning of-cleared and grubbed debris should not be permitted unless
approved by regulatory agencies.
• No debris or organic material should be disposed of in the refuse pile.
• Topsoil from under the proposed pile should be removed, and should be
stockpiled for future use in reclamation unless steep terrain or other con-
siderations make this impractical.
Foundation subdrains should be provided in areas where there are
springs.
Surface waters should be diverted around all refuse piles.
Drainage from piles should be directed into siltation basins until the
piles become inactive and have been covered and adequately protected against
erosion.
• A valley-fill pile should be developed starting at the head of the
valley.
• Waste heaps are best developed using cellular construction methods.
Side-hill piles should be developed in perimeter strips.
Cross-valley piles should be avoided wherever possible.
Exposed pile surfaces should be minimized and finished surfaces
should be reclaimed.
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• Refuse surfaces should be sloped to drain away from side slopes.
• Active surfaces should be as flat as possible, to minimize erosion,
but should be steep enough to permit positive drainage without shallow ponding
of waters.
• Haul road dust control requirements should be established on a site-
by-site basis.
• Refuse should be placed using methods that minimize material segrega-
tion. Dumping refuse over steep slopes is specifically not recommended.
• Truck-placed piles of refuse that are. potentially acidrproducing should
be leveled and compacted at least once during every working shift.
• Lift thicknesses of placed refuse should be 60 cm (2 ft) or less.
• Nonstructural refuse embankments may be compacted satisfactorily by
planned routing of construction equipment over thin lifts.
• Loaded scrapers are more effective for compacting refuse than are
bulldozers or on-highway trucks.
• Specially designated noncritical portions of a disposal site should be
reserved for refuse placement during inclement weather.
• When rubber-tired equipment is used for compaction, it is very impor-
tant to maintain appropriate tire pressures.
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SECTION 8
GUIDELINES FOR SLURRY POND CONSTRUCTION AND OPERATION
Disposing of fine waste in slurry ponds is generally the most efficient
and economical disposal method. The basic process of pumping a mixture of
water and solids into one end of a pond, allowing the solids to settle out in
the calm water, and discharging the clarified water at the other end of the
pond is simple and effective.
The most critical concern with respect to slurry ponds is the safety of
the retaining dam. In the past, many slurry retention dams were constructed
without adequate provisions for embankment stability or for safe handling of
flood waters. Today, with the advent of strict MSHA regulations and mine
owners' greater awareness of safety considerations, such problems are gradu-
ally being resolved.
From a pollution control standpoint a well sited, designed, and operated
slurry pond has several important features that make it superior to a refuse
pile. First, the vast majority of the refuse in a slurry pond is submerged
during the operating life of the facility. Oxidation of pyritic materials
and the resulting production of acid are thereby effectively eliminated. In
contrast, acid-producing refuse in a dry landfill cannot be totally isolated
to avoid acid drainage.
Except for the retaining dam or dike system, the detailed and careful
provisions for erosion control and refuse placement and compaction required
for a refuse pile are not required for a slurry pond. Also, dust control
from active slurry ponds does not usually present a significant problem. And
finally, a properly operated slurry pond with all of the refuse under water
can be much more aesthetically pleasing than an active refuse pile.
Although slurry ponds do have these advantages, they can nevertheless
contribute significantly to water pollution. The most common pollution con-
trol concern is the carryover of suspended solids from the ponds into public
streams. Chemical pollution of slurry pond waters which are not recirculated
can also be of concern, particularly if significant amounts of soluble salts
or lime are associated with the refuse.
SLURRY POND WATER CIRCUITS
Ponds that discharge clarified sluicing waters into public streams are
classified as "open" systems, and ponds that return clarified sluicing water
back to the preparation plant for reuse are termed '"closed" systems. There is
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considerable debate concerning classifying pond systems as "closed," since
there are always some water losses out of ponds from seepage or storm over-
flows. However, because of increasing environmental concerns and the scarcity
of adequate water supplies in certain parts of the country, many slurry pond
water circuits are being closed as far as possible. Of the seven slurry pond
systems investigated in this study, for example, three are closed systems.
Closed Circuits
A closed water circuit, as used here, is defined as a circuit that re-
cycles slurry water back to the preparation plant for reuse; also, in this
circuit the seepage losses out of the pond are minimal. The principal operat-
ing problem is buildup of dissolved solids in the water as it is constantly
reused. At two of the study sites, the plant operators mentioned that their
principal objection to the closed circuit was the buildup of dissolved salts
in the reclrculated waters. These salts were adversely affecting some prepara-
tion plant operations and the integrity of some of the structural components
in the plants.
A closed circuit usually includes rather large, separate clarified water
ponds. Separation of these ponds allows operation of the return water pumps
without having to be concerned about drawing slurry water with high concentra-
tions of suspended solids.
It should be noted that a closed circuit still requires a source of make-
up water. In coal cleaning, the preparation plant uses substantial quantities
of water that is not returned to the circuit. Coal as shipped generally has a
higher moisture content than its natural moisture content. Evaporation and
seepage cause additional water losses.
For a slurry pond to operate effectively with a closed water circuit,
outside drainage waters should be diverted around the pond to avoid overload-
ing the retention capacity of the pond and spilling excess waters into public
streams. Also, slurry pond sites with pervious substrata should be avoided
or properly sealed off.
Open Circuits
In an open water circuit, free water is not recycled but is discharged
from the pond to the public streams on a continuous or regular basis. Sus-
pended solids are of considerable concern in open water circuit ponds that
discharge fairly regularly to public streams.
The amount of suspended solids discharged depends on pond efficiency and
operating procedures. Most ponds have a single point discharge opposite a
decant pipe. At the study sites, the refuse solids are allowed to build up
above the water line near the discharge point, and form a delta extending
toward the overflow decant structure. The farther the delta extends toward
the decant structure, the greater the amount of suspended solids discharged,
because settling time in free water is reduced. Discharge water is sampled
periodically and, when the concentration of suspended solids approaches the
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maximum permitted by the regulatory agencies, operations are modified to
increase the free-water path between the discharge and decant points.
In an open water circuit system it is difficult to minimize suspended
solids during storms. This is especially true at sites which have large
drainage areas above pond level from which runoff flows directly into the
pond. Pond efficiency is drastically reduced because of the greater quanti-
ties and higher velocities of water passing through the pond. Even more sig-
nificant is the scouring action of fast-moving, turbulent streams entering the
ponds and the physical erosion and resuspension of solids previously deposited.
These solids are literally flushed out of ponds into downstream receiving
streams. A typical situation of this sort is shown on Figure 20.
LIMITS OF
DRAINAGE BASIN
SLURRY PIPELINE
INTERMITTENT STREAM ^--
-DECANT STRUCTURE
FINE REFUSE DELTA FORMED DURING LOW
FLOWS AND ERODED DURING HEAVY RUNOFF
Figure 20. Slurry pond with fine refuse delta eroded
by large stream flows.
Several measures can be employed to control the effects of storm waters
on slurry ponds. For example, the retention dam and spillway can be con-
structed to a height sufficiently above operation pool elevation to retain the
flood waters, as illustrated schematically on Figure 21. Routine clear-water
decanting would then be accomplished by pumping over the dam rather than dis-
charging through a gravity-flow decant structure. (This method is in use at
Sites B and D.) Most preparation plants operate only two shifts, so pumping
of excess water is usually done prior to the start of sluicing operations in
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SPILLWAY ELEV.
-FREEBOARD BETWEEN OPERATING WATER POOL
AND SPILLWAY ELEVATIONS SUFFICIENT TO
EXPOSED FINE
REFUSE DELTA-
K7 OPERATING POOL ELEV.
SUBMERGED FINE REFUSE
NOTES: t. OPERATING POOL ELEVATION MAINTAINED BY PERIODIC PUMPING EXCEPT DURING
HEAVY STREAM FLOWS. EXCESS WATERS ARE USUALLY PUMPED IN EVENINGS.
AFTER SLURRY SLUICING OPERATIONS HAVE STOPPED AND SUSPENDED SOLIDS
HAVE SETTLED.
2. SPILLWAY SHOULD BE DESIGNED TO PASS MAXIMUM PROBABLE FLOOD. AS REQUIRED
BY MSHA.
Figure 21. Flood-water storage in slurry ponds to minimize
downstream water pollution.
the morning. This allows the maximum time to permit suspended solids to settle
out before the water is discharged downstream.
Another flood-water control method involves constructing a decant system
that is aligned up a primary hollow (see Figure 22). This can reduce the
adverse effects created by an incoming stream that scours away previously
SLURRY PIPELINE WITH
MULTIPLE DISCHARGE POINTS
CLEAR-WATER OVERFLOW
STREAM FLOW
ENTERING PON3
CLEAR-WATER DECANT PIPE-
NOTE: RETENTION DAM IS RAISED AND CLEAR-WATER DECANT PIPE IS EXTENDED AS REQUIRED
TO DEVELOP ADDITIONAL STORAGE CAPACITY.
Figure 22. Upstream slurry discharge system. Note clear-water decant
pipe in upper reaches of settling pool.
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deposited refuse. Still another type of control can be achieved by providing
a sufficient depth of water in the pond to prevent scouring by incoming waters
and to allow settlement of suspended solids during storms.
Finally, it is theoretically an acceptable approach to construct diver-
sion ditches around a slurry pond, designed so that the ditches discharge
waters below the slurry pond dike or dam. In practice, however, this approach
is not always reliable, particularly for use in steep terrain where landslides
and debris can cause diversion system failures just when the ditches are needed
most during heavy storms. A diversion ditch collects water from uphill areas
and concentrates it on one large stream; if the ditch is breached, overflowing
waters can create concentrated flow paths and thus lead to highly erosive
action across the pond.
The measures mentioned above are applicable to slurry ponds where there
are large drainage areas above pool elevation. For ponds with no significant
drainage area above pool elevation (for instance diked ponds), the storm-water
problem is usually not so severe. The primary effect in these cases is a loss
of pond efficiency, due to a greater discharge velocity. Scouring action is
not pertinent because there are no large, concentrated, incoming flows. During
severe storms, incoming waters may exceed the storage capacity of a pond and
the mixed slurry and storm waters may pass over the spillway.
To summarize, it is usually not reasonable or necessary to design slurry
impoundments with major outside drainage areas to retain the water from a
probable maximum precipitation event. Some overflow from such impoundments
should always be expected. Present EPA guidelines permit effluent discharges
during, and four hours after, an event larger than a 10-year, 24-hour-frequency
storm. A slurry pond with an open-water circuit should therefore be designed
to retain the water generated by a storm up to this magnitude.
POND OPERATION
Control of Chemical Pollutants
The types of chemical pollutants in slurry pond waters depend in large
part on the chemistry of the refuse and source water. Pollutant concentra-
tions depend on the total water balance and on whether the water is recircu-
lated (closed circuit) or whether it is used once and discharged from the
system (open circuit). The tabulation below shows the results of chemical
tests of slurry pond waters at the study sites. It is interesting to note
that all the pond waters sampled had a pH near neutral or on the alkaline side.
Indeed, most slurry ponds have a pH near or above 7. This fact suggests that
a certain amount of untreated acid drainage water could be injected into a
pond. If properly done, the water chemistry of the resultant mix might be
improved over that of the original constitutents.
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Site
A
F
G
H
PH
7.65
7.4 - 8.3
8.15
8.34
Acidity
(mg/& as
0 - 2.0
Alkalinity
CaCO)
Remarks
341
54 - 240
163
208
Closed circuit
Closed circuit
Closed circuit
(seep sample)
Open circuit
Control of Dissolved Solids
Control of the water chemistry or the dissolved solids in a slurry pond
is a difficult and complicated matter that normally requires special chemical
and physical treatment. Sluicing coal refuse almost always increases the con-
centration of dissolved solids in water. Fortunately, these concentrations in
most open-circuit slurry ponds are relatively low and fall within present
regulatory requirements for point source discharges.
Control of Suspended Solids
The principal variables that affect settlement of suspended solids in a
slurry pond are particle size and specific gravity of solids, kinematic vis-
cosity of the fluid, velocity of slurry through the pond, and length of free-
water surface between the slurry discharge point and the clear-water decant
structure.
The tabulation below shows the effects on settling of particle size, the
most significant variable with respect to efficiency of settling basins. The
settling velocity of the suspended solid varies with the square of the particle
diameter.
TIME AT WHICH PARTICLES WILL SETTLE
IN STILL WATER AT 10°C
(Specific Gravity = 2.65)
Particle Diameter
(mm)
10.0
1.0
0.1
0.01
0.001
0.0001
0.00001
Material
Gravel
Coarse sand
Fine sand
Silt
Bacterial
Clay
Colloids
Time Required to
Settle 30 Centimeters (1 Foot)
0.3 seconds
3 seconds
38 seconds
33 minutes
35 hours
230 days
63 years
Source: Reference 4.
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The specific gravity of fine coal refuse normally ranges from 1.6 to
greater than 2.4, depending on the composition of the materials. This is
substantially less than the specific gravity of most soils, which ranges from
about 2.6 to 2.7.
o The kinematic viscosity of water at 1°C is about twice its viscosity at
30 C. Slurry ponds are therefore much less efficient in the winter than in
the summer.
The velocity of slurry through a settling pond affects the time available
for particle sedimentation and the drag forces, or resistance to downward
movement, on the settling particles. The lower the velocity, the less the
turbulence and the greater the efficiency of the pond. Also, the greater the
length of the slurry path over free water, the more time there is available
for solids to settle out of suspension.
Some sites use single point slurry discharge arrangements. After a period
of time a delta of solids builds up in front of the discharge point; as this
delta grows in the direction of the clear-water decant structure the amount of
suspended solids increases because the slurry path over free water is being
shortened. At some time the amount of suspended solids will exceed allowable
limits for discharging to public streams or for use in the preparation plant.
Before this occurs, operations should be modified to avoid exceeding the
limitations. Traditionally, this has been done in one or more of a number of
ways. For example, a diversion dike can be built out into the pond to direct
the flow path of the slurry into dead areas of the pond. (This was done at
sites A and D.) Also, the slurry discharge point can be moved to free-water
areas around the edge of the pond, as is done at site H. Another method
involves raising the pond water elevation by placing stoplogs or plugs in an
appropriately designed decant structure. This is also done at site H.
Control of Other Pollutants
At many sites (for example at sites C and D), pollutants other than fine
coal waste are deposited in slurry ponds for pollution control. The most
common of these pollutants are acid mine drainage and/or precipitates from the
chemical treatment of acid mine drainage. Another interesting example of
accommodating additional pollution loads in a slurry pond is at site F, where
the fresh-water lake used for makeup water purposes is contaminated with
detergents from domestic sources upstream. Although this makeup water is
acceptable for use in the jig water circuit in the preparation plant, it fouls
the heavy media separation process. Therefore, the water with the detergent
load is put into the slurry pond, so that the detergents are degraded by the
dirty pond waters. By the end of the slurry pond water cycle the detergents
are no longer active and the water can be cycled through the heavy media
process.
Dust Control
At some sites where large, exposed refuse deltas lie appreciably above
the operating pool elevation, dust problems have arisen from fines blowing off
the surface. If the ponds are located near populated areas or highways, the
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dust clouds can be a hazard. However, this situation is not common in the
eastern U.S. coal fields, because of the generally humid climate and because
of the drawing up of water by capillarity through the fine, silty refuse. More
serious problems of this nature are encountered during abandonment activities
after the pool level is dropped and prior to covering the pond with soil.
Where fines blowing off the delta of a slurry pond do create problems, the most
positive remedy is to raise the operating pool level and discharge the slurry
at lower points in the pond.
TEMPORARY SLURRY PONDS
If suitable property of sufficient size is not available, coal operators
sometimes resort to the use of small, temporary ponds. It should be noted that
many temporary ponds are so small that chemical coagulants must be added to
increase the effective particle size and facilitate settling. These ponds are
cleaned out periodically and solids are placed in dry storage. Because of the
necessity of maintaining operations during the cleanout or reclaim period,
most such systems are composed of more than one pond. Thus one pond can be
cleaned while another is still in operation.
Cleaning slurry ponds is normally done with a dragline positioned along
the edge of the pond, and the solids are stockpiled to facilitate drainage.
A front-end loader then picks up the solids and puts them on trucks to be
taken to a dry refuse disposal area—usually a coarse refuse pile.
Cleaning out the solids in a temporary slurry pond is somewhat difficult.
The fine coal refuse is usually waterlogged and hard to handle with conven-
tional earthmoving equipment. Unless physically confined, the wet solids tend
to flow when stockpiled along the edge of the retaining dike. This is particu-
larly true of the very fine solids at the lower end of a pond opposite the
slurry discharge point.
In this type of operation, certain pollution control precautions are
especially important. First, the refuse stockpiled from the dragline should
be drained toward a sump or small retention basin to retain suspended solids
and contaminated waters. Also, the trucks that haul fine refuse should be
equipped with tight tailgates to minimize loss of solids along the haul road.
Sometimes the fine refuse is in a semiliquid state and tends to slosh around
in a moving truck. Special retention provisions are required for this situa-
tion. In final disposal activities, the fine refuse from the pond should be
placed only in nonstructural fill areas, since compaction of this material is
usually not practical. The fine material should be kept near the center of
the coarse refuse pile, where it can be readily confined by the coarse refuse.
SLURRY RETENTION DAMS AND DIKES
The safety of embankments that retain slurry ponds is of paramount concern
to coal operators and to those who live downstream of such impoundments. It is
not the intent of this report to provide dam safety guidelines for water-
retention embankments. Nevertheless it is appropriate to include some general
comments with respect to impoundment structures from the standpoints of safety
and pollution control.
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Safety Considerations
An impounding embankment may fail for one or more of three principal
reasons: (1) the embankment and/or its foundation have insufficient strength
to resist the applied loads and a slope failure results; (2) there is insuffi-
cient spillway capacity to pass flood flows and the dam fails by overtopping;
and (3) materials in the embankment or its foundation are eroded away by
excessive seepage velocities (piping). Slope failures are generally the
result of (1) high internal water levels caused by improperly controlled
seepage through the retaining embankment and/or foundation, or (2) steep
embankment slopes constructed on weak foundations. Flood-flow overtopping of
a retaining embankment due to the lack or inadequacy of a spillway is the most
common cause of failures of earth-type dams. Piping occurs most commonly
along conduits that pass through an embankment below the water line.
Many slurry impoundment dams or dikes are constructed in stages to mini-
mize initial capital expenditures. When a mine starts up, a low starter
embankment constructed of natural materials is usually built. As the impound-
ment is filled with fine refuse, additional storage capacity is developed by
raising the height of the retaining embankment, or by extending the embankment
to adjacent areas, or by abandoning the pond and constructing a new pond else-
where. For economic and land use reasons, the trend today is to raise impound-
ments to greater heights to develop the necessary storage capacity.
Three basic methods of raising slurry pond embankments are shown on
Figure 23. From the dam safety viewpoint, the upstream method is the least
desirable, and is commonly the cause of numerous stability problems. This is
principally because of the weak slurry foundation and the potential for devel-
oping adverse water pressures at the junctions of the successive raises. This
type of embankment is particularly susceptible to failure during earthquakes.
The downstream method is normally the safest of the three, but is also is the
most expensive, because larger embankment volumes are required. Regardless
of the method of construction used, qualified engineers who are experienced in
this field should be consulted.
Retention embankments constructed by the upstream and centerline methods
usually have wide crests in order to reduce the risk of an embankment slope
failure extending to the free-water pool and causing a major breach, and to
create additional disposal capacity for coarse refuse.
A major economic concern in staged construction of cross-valley dams
with large drainage basins is the necessity for abandoning and reconstructing
spillways with each successive raise in embankment height. Such spillways
may represent a major portion of the construction cost in slurry pond develop-
ment.
Coarse Refuse as an Embankment Construction Material
A major pollution control consideration in constructing slurry pond
embankments is whether coarse refuse is a suitable construction material. The
principal concern here is with seepage through acid-producing refuse. An
example is the condition at site D, where approximately 7.9 liters/sec (125
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SLURRY DISCHARGED AT EMBANKMENT
UPSTREAM CONSTRUCTION
DOWNSTREAM CONSTRUCTION
SLURRY DISCHARGED AT EMBANKMENT
•SETTLING POOL
1 DAM
CENTERLINE CONSTRUCTION
Figure 23. Methods for raising slurry pond embankments,
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gal/min) of relatively chemically pure water seep through the refuse embank-
ment, producing highly contaminated water which requires expensive treatment
in order to meet present water discharge requirements. Once a leak through an
embankment occurs, it is generally difficult to stop. Provisions are normally
made to protect the structural integrity of the embankment by the use of drains
and stability beams. The amount of leakage, however, usually is not stopped—
it is just controlled. If this situation develops during the operating life
of the pond and is remedied by treating the seepage waters, the question then
arises as to what happens when the facility is abandoned. It is reasonable to
expect the seepage quantity to be reduced but not necessarily eliminated. The
chemical quality of these seepage waters may even deteriorate further, and the
care or treatment of these seepage waters after abandonment would then become
a semipermanent concern, in the same manner as acid mine drainage. At sites
which do not have acid-producing refuse, seepage water through the refuse
dumps normally meets present water quality standards and may safely be dis-
charged to public streams.
All water-retention embankments leak. At a few sites the embankments are
so tight and the seepage is so minor that the seeping water evaporates when it
reaches the outer slope. At other sites seepage through the retention embank-
ment may represent a significant portion of the water that is injected into
the pond.
The risk of leakage through acid-producing refuse embankments is a con-
tinuing concern. However, there are several methods for building slurry
impounding embankments of acid-producing coarse refuse. These include using
a zoned embankment such as that shown on Figure 24. Here the thin, upstream,
nonacid-producing clay zone forms a water barrier. Any water that seeps
through this zone is safely drained away through the permeable chimney, hori-
zontal, and abutment drain zones. The acid-producing refuse, which comprises
the majority of the dam, is completely isolated from seeping waters from the
pond. Another method is to control the gradation of soft shale refuse so that
it has a very low permeability. This could be accomplished by mixing fines
with the coarse refuse or by mechanically degrading the refuse with special
compaction equipment or industrial-type disks to create additional fines.
ULTIMATE DAM ELEV.
INITIAL DAM ELEV.-
V
COMPACTED COARSE REFUSE
&&£$&\
-CHIMNEY DRAIN
-PREPARED FOUNDATION
CONTINUOUS FOUNDATION
ND ABUTMENT DRAIN
Figure 24. Zoned dam section, showing water barrier formed by clay zone.
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The first method is the most reliable for embankment stability and pollu-
tion control. However, it may be very costly in parts of Appalachia because
of the scarcity of suitable drain material. The second method will help reduce
the amount of seepage through the refuse. Fresh refuse from the preparation
plant is normally a permeable material. It is only through degradation by
exposure to air and water and by mechanical handling that sufficient fines are
created to significantly reduce permeability. The amount of fines created
varies with material exposure time, weather conditions, handling equipment,
etc. More positive controls on permeability are required if the material is
to be used as a water barrier.
Perhaps the most environmentally reliable method of constructing slurry
pond embankments is to avoid the use of acid-producing refuse in the embank-
ment. Then, if a leak does occur, it can be controlled with suitable graded
filters and allowed to drain to receiving streams without significant adverse
water pollution.
POND INSPECTION AND MAINTENANCE
Under present MSHA regulations, slurry ponds must be inspected weekly for
safety reasons. As a part of this inspection, or in a separate inspection,
pollution control observations should also be made. Activities which are
required include:
a. Observation and control of the delta formed below the slurry discharge
point.
b. Observation of clear-water decant or water return facilities. Partic-
ular attention should be given to detecting and repairing any leaks
in the slurry pipeline.
c. Observation and control of the operating pool elevation
d. Observation and maintenance of ditches
e. Water sampling and testing of any waters leaving the site
f. Determination of the quantity and quality of seepage waters
(seepage survey)
g. Observation and repair of erosion gullies on retaining embankments.
PRINCIPAL GUIDELINES FOR SLURRY POND CONSTRUCTION AND OPERATION
• Whenever possible, slurry pond waters should be recycled to the
preparation plant. Open-water circuits should be avoided.
• Sites where there are large drainage areas above the slurry pond
should be avoided or should have special provisions to control the
effects of incoming storm waters.
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Slurry pond operations should maximize the free-water distance between
the slurry discharge point and the clear-water decant structure.
Fine refuse reclaimed periodically from temporary ponds should be
placed in confined, nonstructural areas of the refuse pile.
The use of acid-producing coarse refuse in impounding embankments
should be avoided unless special precautions are taken to minimize
or eliminate acidic seepage.
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SECTION 9
GUIDELINES FOR RECLAMATION AND ABANDONMENT
Slurry pond or refuse pile abandonment and reclamation activities deter-
mine in large part how much pollution will be released to the environment on a
permanent or long-term basis. Specific requirements and procedures for aban-
donment and pollution control depend on federal and local regulations, indi-
vidual site and material conditions, and the end use planned for the facility.
The most common abandonment and reclamation requirements are drainage and
erosion control, covering the exposed refuse surfaces with a layer of natural
soil, and establishing a vegetative growth. The object of these activities is
to return the land to productive use and to eliminate potential environmental
pollution.
REFUSE PILES
Reclamation of refuse piles should be an integral part of the ongoing
development of the facility. It should not be started only after refuse place-
ment has stopped. Section 7 contains a discussion of various schemes which
allow reclamation to proceed simultaneously with development of refuse piles.
Earth Cover^ Layer
Refuse pile reclamation almost invariably involves covering the finished
refuse surface with a layer of nontoxic soil in order to establish plant
growth and control erosion. Also, the earth cover layer can effectively elim-
inate chemical contamination of surface waters moving over acid-producing
refuse and can reduce infiltration of surface water into the interior of the
refuse mass. Because of the harsh chemical character of refuse and its low
plant nutrient value, and because its dark color leads to high surface temper-
atures, it is very difficult to establish a vegetative growth directly on
coarse refuse.
The thickness of the soil cover required for abandoned refuse piles
varies with state regulations. The following list indicates some of the many
state regulations on soil covering for abandoned acid-producing refuse areas
at surface mines.
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Minimum Cover over Acid-
Producing Refuse Areas
State
Arkanasas
Colorado
Illinois
Indiana
Iowa
Kansas
Kentucky
Maryland
Missouri
Montana
New Mexico
North Dakota
Ohio
Oklahoma
Pennsylvania
Tennessee
Texas
Virginia
Washington
West Virginia
Wyoming
Centimeters
91
61
122
61
61
61
61
122
Feet
3
2
2
2
2
4
91 3
305 cm (10 ft) clean
fill +30 cm (1 ft)
topsoil
122
122
61
122
4
2
4
Remarks
Or 122 cm (4 ft) of water at all
times
May be soil or water. Slurry to
be confined in depressions and
allowed to revegetate naturally.
Soil or water
Coal wastes buried in pits and
stabilized. May also be covered
with water.
All refuse to be buried
Not specific
Or permanent water impoundment
Not specific
Not specific
Not specific
Not specific
Or covered with permanent water
Alternate 76 cm (30 in.) acid
layers with 61 cm (24 in.) clean
fill in refuse pile. Bottom of
pile to have 91 cm (3 ft) of
clean fill.
Cover with spoil
Not specific
Not specific
Source: Reference 23.
The amount of soil cover required for abandoning a refuse area has a
significant effect on reclamation costs. If too little cover is specified,
long-term pollution problems could result, but if too thick a cover is speci-
fied, the costs are unnecessarily high. In many cases the thickness of the
covering layer is determined by the type of vegetation the land is to support.
For example, reclaimed land to support row crops requires a thicker soil cover
than land to be used for pasture. For pollution control, we believe, the
thickness of a cover layer should be based on whether the refuse is acid-
producing and on the permeability of the underlying refuse material. If the
refuse is nonacid-producing, the quality of runoff or seepage waters is
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usually within present water quality regulations for point source discharges,
and the cover layer need only be thick enough to support the desired vegeta-
tion. Increasing cover layer thickness beyond this point will not necessarily
increase erosion resistance.
If the refuse is acid-producing, infiltration of surface water into the
refuse mass becomes a major consideration. If a clay-type cover layer is
perfectly intact and properly sloped, it can be relatively thin and little
infiltration will occur. The problem is that thin soil cover layers never
form perfect seals. They are constantly exposed to weather changes (freeze-
thaw, wet-dry), mechanical demage (plowing, vehicular traffic, animal tracks,
minor erosion), and plant root activity. All these factors tend to reduce the
effectiveness of thin cover layers in minimizing surface water infiltration.
If the underlying refuse material is acid-producing and permeable, the long-
term water pollution potential can be significant. If the refuse is relatively
impermeable for a reasonable distance below the zone of natural or man-made
disturbance, infiltration into the refuse material is minimized. (Methods
for making coarse refuse less permeable were discussed in Section 7.)
For abandoned refuse piles that support conventional pasture-type vege-
tation, the controlling surface disturbance factor is often maximum frost
penetration. Eastern U.S. coal-producing regions have recorded frost pene-
trations ranging from 25 cm (10 in.) to 127 cm (50 in.). The relatively
impermeable material should extend about 61 cm (2 ft) below the zone of maxi-
mum disturbance.
In summary, abandoned refuse piles should be covered with a layer of non-
toxic clay soil of sufficient thickness to promote acceptable vegetative
growth. Also, there should be a relatively impermeable zone of natural soil
or refuse material under flat-lying areas, extending 61 cm (2 ft) below the
maximum depth of frost penetration. The first requirement is directed at pre-
venting pollution of runoff waters and the second requirement at preventing
pollution of ground or seepage waters. For nonacid-producing refuse piles,
the second requirement would not apply.
Erosion Control
The control of erosion from refuse piles is a major concern. Erosion
control requirements are generally more stringent for reclamation and aban-
donment than for active pile operation. The reason for this is that, during
active operations, ditches and related facilities can readily be maintained,
but after abandonment, maintenance of erosion control facilities is usually
more difficult to initiate because equipment is not immediately available.
Consequently, erosion control measures undertaken during abandonment must be
of a permanent nature and must call for a minimum of maintenance. For example,
perimeter ditches on steep, unstable hillsides around a valley-fill deposit
may be acceptable during the operating life of the pile, but they should not
be relied on after abandonment, because they normally require considerable
maintenance. Whenever possible, permanent diversion ditches above a refuse
area should be avoided. If this is not possible, as for example with a side-
hill refuse pile, the diversion and drainage ditch should be designed and
constructed to achieve minimum long-term maintenance. On waste-heap piles,
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surface waters must be collected and at some point brought down the side
slopes. The ditch leading down the slopes of the pile should be kept on a
minimum grade and should have an erosion-resistant facing such as riprap, con-
crete, or commercially available half-pipes.
Finished surface slopes on top of the pile should always be directed away
from the side slopes; otherwise serious erosion could result. The surface
slopes should be graded as flat as possible to minimize erosion, but with
sufficient grade to drain the runoff without shallow ponding of water.
Providing erosion protection for the finished side slopes of a refuse
pile is another important consideration. As mentioned previously, surface
drainage should always be directed away from side slopes. The type of vegeta-
tive cover established on side slopes is also important, because a higher
degree of erosion resistance is required on these steep slopes. The use of a
grass mixture which includes crown vetch is becoming quite popular. This type
of grass develops a thick mat of spreading, intertwining stems and roots which
is highly resistant to erosion. Because crown vetch takes some time to become
established, other, more rapidly developing grasses are commonly included in
the mix to provide short-term erosion control and protection. Care should be
taken in selecting the final grade of side slopes. If the slope is too steep,
it may prove difficult or impractical to work on it to cover it with earth,
establish plant growth, and provide maintenance. Therefore slopes steeper
than about 2 horizontal to 1 vertical should be avoided, as this is about the
steepest slope on which tracked bulldozers can operate effectively. Flatter
slopes may be required for stability reasons, depending on conditions at the
site.
SLURRY PONDS
Slurry pond reclamation normally is not undertaken until the site is
abandoned. Prior to abandonment of a slurry pond, it is important to sluice
the fine refuse in a manner that will result in a reasonably flat surface
with a gentle gradient toward the overflow structure which protects the reten-
tion dam. Low areas or dead spots within the pond must be filled so that when
the pool is removed the surface of the settled solids will have positive
drainage. This is usually accomplished by periodically relocating the slurry
discharge point around the perimeter pond.
When the slurry pond is to be abandoned the free water is treated, if
necessary, and discharged to downstream receiving streams. If conditions
permit, the free water may be allowed to evaporate or may be disposed of by
other acceptable means. After the free water is removed the surface of the
refuse must be allowed to dry out enough that it may be covered with earth.
During the drying period the surface of the silty, fine refuse develops an
upper crust which is highly susceptible to wind erosion. In high winds,
large, thick, dust clouds may then blow off unprotected, abandoned slurry
ponds. If a thick, permanent plant growth can be established directly on the
refuse this condition can be alleviated, but in most cases this cannot readily
be accomplished and a layer of vegetation-supporting soil is required.
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Covering a recently abandoned slurry pond may call for special construc-
tion techniques. Beneath the thin surface crust of dried refuse the material
can be saturated and highly unstable. This is particularly true of areas near
clear-water decant or pump return structures where the finer portions of solids
have settled out. Hauling equipment usually cannot travel directly over the
surface of these areas because the ground is too soft. Conventional practice
calls for the use of light equipment, and for pushing a fill out ahead of the
equipment to serve as a working pad. The thickness of this pad can be quite
large in the lower portions of the pond area.
The thickness of the earth cover layer should be the minimum necessary
to support the desired vegetation. Providing a reliable and impermeable cover
of clay, as suggested for acid-producing refuse piles, would not normally be
required for slurry ponds, since the refuse lies in a closed basin. Also,
the permeability of fine refuse is generally much lower than that of coarse
refuse.
The reclamation plan should include provisions for plugging with concrete
any decant or overflow pipes that are located beneath retaining dams or dikes.
Permanent drainage out of the abandoned pond should be provided for by an
erosion-resistant open spillway designed to pass the flood flows specified in
the regulations.
MSHA regulations require that slurry ponds be abandoned according to a
plan which ensures slope stability and which precludes any future water
impoundment. ^ This rule applies to slurry impoundments that are more than
152 cm (5 ft) deep and that provide more than 24,672 cubic meters (20 acre-
feet) of water storage or to impoundments that are more than 6 meters (20 ft)
deep. An impoundment such as a slurry pond can serve as an effective pollu-
tion control device by reducing the amount of suspended solids released to
downstream waters. Therefore, consideration should be given to leaving a small
sedimentation basin in the pond area provided the water quality of such a pond
is acceptable, the basin does not exceed regulation size, and there are no
acidic leaks downstream.
For slurry ponds other than diked or incised ponds, permanent drainage or
diversion ditches are required. These ditches should be planned with consider-
ation given to the same factors as those mentioned for refuse piles.
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SECTION 10
ALTERNATIVE DISPOSAL AND POLLUTION CONTROL METHODS
So far we have discussed primarily the methods for controlling pollution
from conventional refuse piles and slurry ponds. There are other disposal
methods which are used, however, depending on individual site conditions.
These methods include burial in spoil piles of surface mines, underground
disposal in mined-out areas of subsurface mines, utilization of refuse as a
construction material, and dry disposal of fine coal refuse.
In this section, the general features and relevant pollution control
aspects of some of these alternative disposal techniques are discussed.
BURIAL OF REFUSE IN SURFACE MINE SPOIL PILES
Coarse Refuse
Burial of coarse refuse in active surface mine spoil piles is common in
the Midwest. Normal procedures include trucking the coarse refuse back to the
bottom of the active mine pit and dumping it at the toe of the spoil bank.
Special layering or compaction is usually not required. As stripping opera-
tions progress, the refuse is covered with relatively great thicknesses of
spoil material, thus minimizing the release of pollutants to the environment.
If the bottom of the mine pit is below the water table, as is the case at many
Midwestern surface mines, the potential for acid production from the refuse is
essentially eliminated. Other advantages of this type of arrangement are that
the spoil pile eyesore is eliminated, there are no refuse slope stability
problems, and land use is more effective.
The only potential pollution concern with this method is the possibility
that air and water may infiltrate through the loose spoil and into acid-
producing refuse above the water table, releasing chemical pollutants into
the ground-water regime. However, this concern is thought to be minor com-
pared to those resulting from some other disposal methods. The thickness of
the spoil cover and its generally low permeability indicate that any release
of chemical pollutants to the ground water would be relatively small.
Slurry Ponds
At some Midwestern surface mines, slurry ponds have been developed between
successive rows of old spoil banks or in the last furrow of a surface mine
cycle. The principal pollution control concern in these cases is that large
amounts of water could seep from the pond into the loose, semipermeable spoil
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banks and thus pollute ground water. Seepage waters not only contain dissolved
solids from the slurry pond but may also pick up large concentrations of salts
from the spoil material. At one active surface mine where a slurry pond was
constructed in contact with mine spoil, seepage waters entering the active
mine pit created slope stability problems along the spoil side of the pit and
also created difficulties in attempting to dewater the pit. The water enter-
ing the pit had a high concentration of dissolved solids, mainly due to leach-
ing in the spoil banks, and would not meet discharge water quality requirements.
Placing of slurry ponds or any type of water impoundment on mine spoil
should be avoided. If this is not economically feasible—and at many large
surface mines it is not—the use of sealed ponds should be considered, and
special ground-water investigations may be desirable to identify potential
pollution problems and to develop solutions.
UNDERGROUND DISPOSAL
Disposing of coal refuse underground, in mined-out coal seams, is an
environmentally attractive disposal method in certain circumstances, and such
systems have received considerable attention in the United States and Europe.
The principal advantages of this method are that hazardous and unattractive
surface refuse piles and ponds are eliminated, ground subsidence over mined
areas is reduced, and less surface pollution is created. The principal dis-
advantages are cost, the potential for ground-water pollution, and health and
safety problems for mine workers engaged in backfilling operations in active
mines.
In the United States, underground disposal of coal refuse is used pri-
marily to control subsidence in abandoned mine workings under developed resi-
dential and commercial areas. In a report to the National Science Foundation,
a study commission concluded:
In general the economic costs of underground disposal exceed by far
the normal costs of surface disposal. Only if the physical condi-
tions at a mine site for enviornmentally acceptable surface disposal
were so adverse or the social benefits of underground disposal so
great would underground disposal become economically competitive
with surface disposal for modern, high production rate coal mines.24
In pollution control, the principal concern in using underground refuse
disposal is its effect on ground water. Storage of acid-producing refuse in
mines where both air and water are available can lead to increased acid mine
drainage. Coarse refuse injected in a mine usually has significantly greater
air and water permeability than coarse refuse deposited in a properly con-
structed surface facility. Detailed ground-water studies and expert opinion
are recommended in cases where underground disposal above the water table is
contemplated.
USE OF REFUSE AS CONSTRUCTION MATERIAL
Various ways of using coarse refuse have been tried in past years in
attempts to turn an economic liability into an economic asset. Some of these
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uses include refuse as a construction fill, as a lightweight aggregate, as
roadbase and antiskid materials, or as a brickmaking material. Of these, only
its use as construction fill has had a significant success. Fills constructed
of refuse have been used for paved roads, dams, and area fills. The most
promising construction use is as an area fill in the steep, mountainous
regions of Appalachia where flat, usable land is at a premium. Properly con-
structed and reclaimed, a disposal area can be utilized for residential or
light commercial buildings, playgrounds, cemeteries, etc. The potential or
refuse as a structural fill is dependent on embankment quality and on operators'
ingenuity and local needs. Several new refuse operations have been started
with specific end uses, other than agricultural, in mind. The trend toward
constructing usable refuse fills is likely to continue.
Pollution control concerns with respect to utilization of refuse for
construction fills depends in large part on the end use. If acid-producing
refuse is used, a major consideration is the potential for acid drainage. Each
situation should be evaluated on an individual basis. For example, a recrea-
tional lake on an unsealed acid-producing refuse pile would not be considered
a good end use unless the entire refuse pile could be submerged. On the other
hand, a large, flat refuse pile, properly covered with natural soil and vege-
tation, would probably be an excellent location, for a football field, a base-
ball diamond, or similar type of recreational facility.
DRY DISPOSAL OF FINE COAL REFUSE
Instead of disposing of fine coal refuse in slurry form behind a reten-
tion dam, it is possible to dewater the slurry at the preparation plant and to
dispose of the fine refuse in a dry landfill in a manner similar to coarse
refuse disposal. As outlined by Nunenkamp,^^ the operation involves the
following steps:
1. Clarif ication - slurry with a low percentage of solids is put through
a thickener tank to concentrate the solids into a thickener underflow.
2. Mechanical Dewatering - thickener underflow containing about 30%
solids is mechanically dewatered using filters, centrifuges, high-speed
screens, or similar devices. In most cases the resulting solids contain a
high percentage of moisture and are hard to handle. Because the solids are
in a semifluid state there may be spillage problems on haul roads in the
disposal area. Heavy equipment is unable to maneuver over the material and
an attempt to mix coarse refuse with this material can render the entire
refuse pile unstable. Segregated disposal is also awkward because the area
containing the fine refuse material must be allowed -to air-dry sufficiently
to support hauling and placing equipment. Because of this problem, further
dewatering may be necessary.
3. Thermal Drying - the numerous approaches to dewatering refuse tail-
ings by thermal methods all require technical and economic assessment on a
case-by-case basis. Both direct heat and indirect heat contact systems have
been studied experimentally. It is generally considered that neither the
direct nor the indirect drying system has a strong potential for dewatering
fine refuse slurry, as both processes give a product that, though dry, still
100
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lacks desirable characteristics for subsequent handling and final disposal.
Such systems also add a large capital and operating cost for a secondary ther-
mal dryer and partlculate recovery system. However, some thermal dewatering
systems are available that do not merely dry the material. These systems are
the fluid-bed calcining agglomerator and the multiple-hearth incinerator.
Pilot-plant tests have indicated that when a mechanically dewatered refuse
slurry of 35% to 45% moisture is placed in a multiple-hearth incinerator and
ignited, it can consume itself and generate enough heat to preheat and ignite
the incoming feed.
The major deterrent to the widespread use of slurry dewatering is cost.
From a pollution control standpoint, the methods used for slurry dewatering
may in fact result in greater air and water pollution than does the use of
slurry ponds, because of stack gas emissions from thermal dryers and erosion
and sedimentation from storm waters passing over the exposed, highly erodable,
fine refuse placed in the disposal area, or because additional acid-producing
refuse is exposed to air and water in the disposal area.
Pollution control guidelines for constructing refuse piles that have fine
refuse as the principal waste component are different from guidelines for
refuse piles constructed of coarse refuse, because the physical properties of
the two types of refuse are significantly different. The major pollution
concerns are:
1. Erosion - fine refuse is highly erodable and exposed slopes must be
protected with a resistant covering.
2. Dust - exposed refuse dries on the surface to a powderlike consistency.
Winds and equipment traffic raise the' material from the pile in large, thick
clouds of airborne particulates.
3. Refuse Strength - under many conditions where water is present, fine
refuse has less strength than coarse refuse. It must be compacted in thin
lifts (less than 30 cm) and at carefully controlled moisture contents (compac-
tion of fine refuse depends very strongly on moisture content). As a fill,
fine refuse (sandy silt) is one of the most difficult of all materials to
manage.
In conclusion, it appears that presently available methods for effectively
dewatering and disposing of fine refuse in dry disposal areas are very costly,
and possibly are more environmentally harmful than properly constructed and
operated slurry ponds. Where dewatering and dry disposal of fine refuse are
required because no suitable slurry pond site is available, special pollution
control measures are needed. These measures should be defined on a site-
specific basis.
101
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REFERENCES
1. W. A. Wahler & Associates. "Coal Mine Refuse Disposal Practices and
Technology," USBM Contract S0122084, Mining Enforcement and Safety Admin-
istration, U.S. Department of the Interior, February 1974.
2. D'Appolonia Consulting Engineers, Inc. "Engineering and Design Manual,
Coal Refuse Disposal Facilities," for Mining Enforcement and Safety
Administration, U.S. Department of the Interior, undated.
3. National Coal Board of England. "Spoil Heaps and Lagoons," 1970.
4. U.S. Mining Enforcement and Safety Administration. "Design Guidelines
for Coal Refuse Piles and Water, Sediment, or Slurry Impoundments and
Impounding Structures," April 16, 1976.
5. Moulton, L. K. et al. "Coal Mine Refuse: An Engineered Material," in:
Proceedings of the First Symposium on Mine and Preparation Plant Refuse
Disposal, National Coal Association, October 1974. pp. 1-25.
6. U.S. Department of the Navy. "Design Manual: Soil Mechanics, Founda-
tions, and Earth Structures," NAVFAC DM-7, March 1971.
7. Davidson, W. H. "Reclaiming Refuse Banks from Underground Bituminous
Mines in Pennsylvania," in: Proceedings of the First Symposium on Mine
and Preparation Plant Refuse Disposal, National Coal Association, October
1974. pp. 186 - 199.
8. Martin, J. F. "Quality of Effluents from Coal Refuse Piles," in: Pro-
ceedings of the First Symposium on Mine and Preparation Plant Refuse
Disposal, National Coal Association, October 1974. pp. 26 - 37.
9. Caruccio, F. T. "The Quantification of Reactive Pyrite by Grain Size
Distribution," in: Proceedings of the Third Symposium on Coal Mine
Drainage Research, May 1970. pp. 123 - 131.
10. Haynes, R. J. and W. D. Klimstra. "Some Properties of Coal Spoilbank
and Refuse Materials Resulting from Surface Mining Coal in Illinois,"
Institute for Environmental Quality, State of Illinois, October 1975.
11. Hill, R. D. "Water Pollution from Coal Mines," presented at: Forty-
Fifth Annual Conference of the Water Pollution Control Association of
Pennsylvania, 1973.
102
-------
12. Nunenkamp, D. C. "Coal Preparation Environmental Engineering Manual,"
U.S. Environmental Protection Agency, May 1976.
13. Woodward-Clyde Consultants. "Research and Development Program on the
Disposal of Retorted Oil Shale: Paraho Oil Shale Project," PB-253-598,
U.S. Bureau of Mines, July 1975.
14. . "Belt Drives Fill for Earth Dam," Engineering News-
Record, December 3, 1942.
15. . "Conveyor Moves Fill down a Mountain," Construction
Methods and Equipment, November 1958. p. 84.
16. Bennett, P. T. "Materials and Compaction Methods: Missouri Basin Dams,"
Report 95, Question 22, Sixth Congress on Large Dams, New York, 1958.
17. Lane, K. S. and R. 6. Fehrman. "Tuttie Creek: A Dam of Rolled Shale and
Dredged Sand," presented at: Convention of the American Society of Civil
Engineers, Reno, Nevada, June 1960.
18. . "Triple-Threat Rigs at Briones Dam," Western Construc-
tion, February 1963. p. 58.
19. Sherard, J. L. et al. Earth and Earth-Rock Dams, John Wiley and Sons,
New York, 1963.
20. Sawyer, S. G. and J. W. Fredland. "Experience in Field and Laboratory
Compaction Testing of Coarse Coal Mine Waste," presented at: Second
Symposium on Coal Preparation, October 1976.
21. . "Million-Dollar Refuse Disposal System," Coal Mining
and Processing, December 1976. pp. 80-82.
22. Hill, R. D. "Sedimentation Ponds: A Critical Review," in: Proceedings
of the Sixth Symposium on Coal Mine Drainage Research, October 1976.
pp. 190 - 199.
23. U.S. Department of the Interior. "Laws and Regulations Affecting Coal,"
June 1976.
24. National Academy of Sciences. "Underground Disposal of Coal Mine Wastes,"
Washington, D.C., 1975.
103
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APPENDIX A
RESULTS OF SITE INVESTIGATIONS AND SAMPLING PROGRAMS
This appendix presents the detailed results of the site investigations and
water and air quality sampling programs. For each site, pertinent hydrologic
data and descriptions of site features and operations are given, together with
tables presenting the measurement data obtained in the sampling programs.
Averaged data showing increases or decreases in water pollutant concen-
trations are presented only for Sites A through E, because these were the
only sites sampled where unique points could be identified both for water
entering a disposal area and for water leaving the disposal area. No air
quality measurements were made at Site A, because it consists only of a slurry
impoundment with no dry-land refuse pile and the air quality sampling program
was concerned only with emissions from refuse piles.
No water or air quality sampling was carried out at Site I, which is not
exclusively a coal refuse disposal site. Instead, it is an impoundment de-
signed, developed, and operated by an electric utility company primarily for
disposal of flyash from nearby generating plants. The utility is permitting
a coal mining company to dispose of refuse at this site in order to raise the
main embankment of the impoundment dam. Site I was included in the visits
primarily to investigate the special pollution control methods required in
this unusual disposal situation, and also to document an outstanding example
of cooperation between two types of enterprises to achieve environmentally
acceptable refuse disposal in a manner that has benefits for both companies.
104
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SITE A
SLURRY
POND
v
t r >• .,,2"
i T ^ _, -/ ^
HYDROLOGIC DATA
Drainage Area: 32 ha (78 acres)
Precipitation (mean annual): 107 cm (42 in.)
Fond Evaporation (average annual): 89 cm (35 in.)
Temperature Extremes (Jan-July): Mean max. 6°C(43°F) to 32°C (89°F)
Mean min. -3°C (26°F) to 26°C (78°F)
Rainfall Design Frequencies: (24-hour storms)
5-yr
Depth, cm (in.)
Max. Storm Water Volume,
m3xl()3 (acre-ft)
10.7(4.2)
33(27)
10-yr
11.9(4.7)
38(31)
50-yr
15.2(6.0)
48(39)
IQO-yr
16.51(6.5)
52(42)
105
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SITE A: FEATURES AND OPERATIONS
Site A is in typically Midwestern flatlands. The impoundment is a cross-
valley facility constructed across a small, unnamed tributary of a nearby creek.
The topography to the immediate west of the site has been modified by surface
mining and land reclamation activities. The modified drainage area above the
pond is very small—less than 2.023 ha (5 acres)—and is composed of reclaimed
mine spoils. A creek approximately 152.4 m (500 ft) downstream of the impound-
ment generally flows year around and during heavy rains has been reported to
back up water to or near the toe of the embankment.
The embankment retaining the slurry pond was constructed in 1971 using
natural clayey soils placed in thin lifts and compacted with sheepsfoot
rollers. The downstream slopes were aerially seeded with fescue, alfalfa,
clover, and bluegrass. The upstream slope, above the water line, was later
riprapped with limestone in those areas where wave action was causing erosion
problems. The crest of the embankment is used as a coal haulage road and is
traversed by 164 Mt (180-ton) trucks.
Slurry is pumped into the upper portion of the impoundment at approxi-
mately 13.25 m^pm (3,500 gpm). At the lower end of the pond clear water is
decanted by gravity into a 32.4 ha (80-acre) freshwater lake located 0.805 km
(one-half mile) to the south. Pumps at the lake recirculate the water back to
the coal preparation plant. This site has an NPDES discharge point (#001) at
a vertical drop outlet in the lake. This is monitored weekly and water samples
are analyzed when discharge occurs. Any makeup water requirements are obtained
from the creek.
DIMENSIONAL DATA
Retaining Embankment
Crest width
U/S slope
D/S slope
Max. vert, distance to foundation
Spillway
22.56 m
12.19 m
2-24"
(74 ft)
(2:1)
(3:1)
(40 ft)
C.M.P.s
Retention Area
Maximum storage pond area 29.5 ha (73 acres)
Normal storage pond area 29.5 ha (73 acres)
Ultimate storage volume 2,159,000 m3 (1,750 acre-ft)
Freeboard 1.52 m (5 ft)
Total drainage area 31.6 ha (78 acres)
106
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TYPE OF REFUSE AND PRIOR PROCESSING
The two coal seams surface-mined at the site are vertically separated by
an interbed of shale and/or limestone that varies between 1 m (3 ft) and 1.3 m
(4 ft) in thickness. The shale/limestone refuse is returned to the mine cut
during the mining process. All other run-of-the-mine material is brought to
the preparation plant, separated on a 15 cm (6-in.) screen, and processed
using jig wash boxes. Of the 11,350 Mt/d (12,500 tpd) thus processed, approxi-
mately 19% is rejected: 5 % in fine refuse, which is routed to the slurry
pond, and 14% in coarse refuse, which is returned to the active surface mine
pit for use as deep fill. Thus, the average production of the mine is 9,100
Mt/d (10,000 tpd) of clean steam coal. The reported average chemical quality
of the washed coal is as follows:
Moisture 13.12%
Volatiles 33.35%
Ash 9.63%
Fixed Carbon 43.90%
Sulfur 3.34%
Heat Content 11,020 Btu
POLLUTION CONTROL CONSIDERATIONS
The preparation plant recirculates slurry pond waters.
The minor seepage from the toe of the dikes, which is typical of a well-
designed and -constructed embankment, is nonacid and reports to the fresh-
water reservoir.
A creek, located immediately downstream and approximately parallel to the
dikes, provides an excellent water sampling station for determining the
influence of the slurry pond on public streams.
The dikes are covered first with native clayey soils, and soon become
vegetated. The upstream surfaces are riprapped with coarse rock to
minimize wave action erosion.
107
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CREST OF DAM (74 FT. WIDE AT THIS POINT). WITH
SLURRY POND TO RIGHT. IN THE BACKGROUND ARE
THE PREPARATION PLANT AND STORAGE SILOS
GENERAL VIEW OF SLURRY POND. WITH iso cu. YD.
DRAGLINE IN THE BACKGROUND.
108
-------
EXPOSED FINE REFUSE IN UPPER PORTION OF SLURRY POND. EARTH
MOUND AT RIGHT CENTER WAS BUILT TO REDIRECT SLURRY INTO
DEAD SECTIONS OF THE POND AND THUS INCREASE POND SETTLING
EFFICIENCY.
NORTHERN DOWNSTREAM SLOPE OF EARTH RETAINING EMBANKMENT (LEFT).
EXCELLENT GRASS COVERING PROVIDES EROSION CONTROL THE LIGHT
COLORED SLOPES (UPPER RIGHT) ARE UNRECLAIMED MINE SPOIL.
109
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TABLE A-l. SUMMARY OF WATER QUALITY DATA: SITE A
(Averages for four site visits)
Sampling Point
Parameter
Flow (liters/min)
PH
Dissolved 02 (ing/liter)
Acidity (mg/liter as
Alkalinity (mg/liter as
Conductivity (umhos/cm)
Pollutant (me/liter)
Aluminum
Cadmium
Chloride
Copper
Ferrous iron
Total iron
Lead
Magnesium
Manganese
Mercury
Nickel
Sulfate
Zinc
1
(Inlet) a
17-33
2,
1,
7
7
201
433
0
0
80
0
0
1
0
155
1
<0
0
275
0
.88
.15
.84
.003
.005
.08
.04
.016
.16
.0001
.012
.02
2b
17-
8.
7.
211
2,488
1.
0.
76
0.
0.
1.
0.
156
1.
<0.
0.
1,415
0.
33
08
50
20
004
004
08
30
009
21
0001
015
02
3 (Outlet)0
17-
8.
7.
204
2,423
1.
0.
72
0.
0.
1.
0.
159
1.
<0.
0.
1,350
0.
33
00
0
16
003
004
11
48
009
23
0001
013
03
Increase (+) or
Decrease (-) between
Inlet and Outlet Points
+0.12
-0.15
+3
-10
+0.32
-8
-0.001
+0.03
+0.44
-0.007
+4
+0.07
+0.001
+75
+0.01
a. Upstream from slurry pond.
b. Approximate midpoint on perimeter of site.
c. Near edge of property, where creek exits site.
-------
TABLE A-2. WATER QUALITY DATA: SITE A, SAMPLING POINT 1
a
Sampling Date
Parameter
Flow (liters/min)
pH
Dissolved 02 (mg/liter)
Acidity (mg/liter as CaC03)
Alkalinity (mg/liter as
Conductivity (umhos/cm)
Pollutant (mg/liter)
Aluminum
Cadmium
Chloride
Copper
Ferrous iron
Total iron
Lead
Magnesium
Manganese
Mercury
Nickel
Sulfate
Zinc
July 1976
13.5
7.45
7.15
166
2,160
1.3
<0.001
39
0.002
0.1
1.45
0.012
112
0.83
<0.0001
<0.001
1,000
0.01
Sept 1976
17-29
8.15
—
215
2,270
0.67
—
149
—
0.1
0.98
—
137
0.49
<0.0001
__
1,200
0.02
Jan 1977
Frozen
7.80
—
262
3,200
0.38
0.001
52
0.011
0.03
0.34
0.001
240
2.6
<0.0001
0.027
1,700
0.04
June 1977
20-37
8.10
—
162
2,100
1.0
0.006
78
0.002
0.08
1.7
0.034
130
0.72
<0.0001
0.009
1,200
0.02
a. Upstream from slurry pond.
-------
TABLE A-3. WATER QUALITY DATA: SITE A, SAMPLING POINT 2
a
Sampling Date
Parameter
Flow (liters/rain) .
pH
Dissolved Oo (mg/liter)
Acidity (mg/liter as CaC03)
Alkalinity (mg/liter as CaC03)
Conductivity (umhos/cm)
Pollutant (mg/liter)
Aluminum
Cadmium
Chloride
Copper
Ferrous iron
Total iron
Lead
Magnesium
Manganese
Mercury
Nickel
Sulfate
Zinc
July 1976
13.5
8.20
7.50
190
2,160
2.0
<0.001
45
0.001
0.1
1.83
0.005
113
0.96
<0.0001
0.005
960
0.01
Sept 1976
17-29
8.30
—
210
2,390
0.77
—
148
—
0.10
1.24
—
132
0.49
<0.0001
__
1,300
0.02
Jan 1977
Frozen
7.70
—
262
3,200
0.94
0.006
56
0.008
0.04
0.33
0.003
240
2.6
<0.0001
0.030
2,000
0.04
June 1977
20-37
8.10
—
180
2,200
1.1
0.006
55
0.002
0.06
1.80
0.018
140
0.80
<0.0001
0.009
1,400
0.02
a. Sampling point at approximate midpoint on perimeter of site.
-------
TABLE A.A WATER QUALITY DATA: SITE A, SAMPLING POINT
Sampling Date
CO
Parameter
Flow (.liter/min)
pH
Dissolved 02 (rag/liter)
Acidity (mg/liter as CaCO$)
Alkalinity (mg/liter as CaCQ$)
Conductivity (umhos/cm)
Pollutant (mg/liter)
Aluminum
Cadmium
Chloride
Copper
Ferrous iron
Total iron
Lead
Magnesium
Manganese
Mercury
Nickel
Sulfate
Zinc
July 1976
13.5
8.00
7.00
185
2,190
1.4
<0.001
35
0.001
0.1
1.78
0.006
119
0.83
<0.0001
<0.001
1,000
0.02
Sept 1976
17-29
B.10
—
200
2,400
1.2
—
141
—
0.26
2.02
—
135
0.70
<0.0001
w —
1,200
0.02
Jan 1977
Frozen
7.75
—
249
2,900
0.94
0.006
57
0.008
0.01
0.33
0.003
240
2.60
<0.0001
0.030
1,800
0.04
June 1977
20-37
8.10
—
180
2,200
1.1
0.006
55
0.002
0.06
1.8
0.018
140
0.80
<0.0001
0.009
1,400
0.02
a. Near edge of property, where creek exits site.
-------
SITE B
REFUSE PILE
(ULTIMATE)
HYDROLOGIC DATA
Drainage Area 220 ha (540 acres)
Precipitation (mean annual): 102 cm (40 in.)
Pond Evaporation (average annual): 76 cm (30 in.)
Temperature Extremes (Jan-July): Mean max. 6°C (42°F) to 31°C (88°F)
Mean min. -4°C (24°F) to 17°C (62°F)
Rainfall Design Frequencies: (24-hour storms)
5-yr
Depth, cm (in.)
Est. Storm Water Volume,
m3x 103 (acre-ft)
8.4(3.3)
185(150)
10-yr
9.9(3.9)
222(180)
50-yr
12.2(4.8)
274(220)
100-yr
13.2(5.2)
296(240)
114
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SITE B: FEATURES AND OPERATIONS
Site B is located in a steep, narrow hollow which has occasional springs
along the valley slopes. The site is in mountainous terrain and has a maximum
relief of 137 m (450 ft). The refuse area is a valley-fill type disposal
facility which was started in 1969. Immediately below the present refuse area
is a slurry pond which eventually will be covered with refuse.
A perimeter ditch, excavated into the hillside above the refuse, com-
pletely surrounds the refuse and discharges the collected waters below the
disposal area. The perimeter ditches are continuously maintained to keep them
clear of debris and to repair any local landslide conditions. Rainfall on the
refuse pile in the immediate vicinity of the impoundment is directed into the
slurry impoundment, where it is either allowed to evaporate or is pumped over
the dam into the streambed. The slurry impoundment is fitted with a large,
concrete spillway to prevent overtopping. Slurry is presently being pumped
into the impoundment.
Refuse is taken by conveyor from the preparation plant to a storage bin
adjacent to the slurry impoundment. Two Terex scrapers, Model TS24, with a
capacity of 18 vr (24 yd-*), haul the refuse from the bin to the head of the
hollow, where the material is placed in the downstream direction. The speci-
fied maximum lift thickness is 31 cm (12 in.); however, the scraper operators
prefer to lay the refuse in lifts 15 to 20 cm (6 to 8 in.) thick. The surface
of the refuse Is to be crowned with a minimum slope of 1 to 1-1/2%. Side slopes
are a maximum of 2 (horizontal) to 1 (vertical). A water truck and a D-9 bull-
dozer are used to maintain the haul roads. The bulldozer is also used to
dress the refuse area. A D-8 bulldozer was used for the initial construction
of the channels. Restoration of the refuse is primarily accomplished during
downtime periods such as when the mine or preparation plant is temporarily out
of production; however, this is an ongoing activity and is not limited to down-
time. Restoration includes covering all finished refuse surfaces with 30 to
60 cm (1 to 2 ft) of clay soils, and seeding.
DIMENSIONAL DATA
Refuse Area
Surface area 24-32 ha (60-80 acres)
Drainage area 220 ha (540 acres)
Maximum height 76 m (250 ft)
Finished surface slope 1 to 1^%
Finished side slope Maximum 2:1
TYPE OF REFUSE AND PRIOR PROCESSING
The coal is mined from a seam located at an average depth of 91 m (300 ft)
below ground surface. The coal is high-sulfur steam coal approximately 1.5m
(5 ft) thick. In this area, the coal seam has a shale parting up to 46 cm
(18 in.) in thickness. Mining operations remove the coal and shale parting,
115
-------
along with the materials later separated in the preparation plant. Continuous
and longwall miners are presently used to extract the coal.
The preparation plant uses a combination of froth flotation and heavy
media circuits to clean the coal. The coarse refuse is separated with a series
of screens at 0.8 cm (0.3 in.). The minus 0.8 cm (0.3 in.) material is mixed
with the washed coarse size to obtain a plant product. The run-tof-the-mine
coal production is approximately 6,370 Mt/d (7,000 tpd), with 15% being coarse
reject. The chemistry for the coal produced has been reported as follows:
Moisture 6.08%
Ash 14.21%
Sulfur 4.14%
Heat content 11,780 Btu
POLLUTION CONTROL CONSIDERATIONS
When the slurry pond is in operation, excess clarified water is decanted
into the public streams (open-water circuit).
Drainage off the acid-producing refuse pile in the upper reaches of the
hollow is directed into the slurry pond.
An interceptor ditch has been cut into the sides of the valley to divert
the major portion of incoming waters around the refuse pile.
The site is in difficult mountainous terrain with numerous springs.
Landsliding occurs along the steep, heavily wooded valley slopes.
Restoration (i.e., covering with earth and seeding) is proceeding on
finished surfaces of the refuse pile. While restoration goes on at the
head of the hollow, refuse placement continues in the downstream direction.
Stream flows above and below the refuse disposal area allow for water
sampling and testing to evaluate pollution control at the refuse area.
116
-------
LOWER END OF REFUSE PILE (FOREGROUND) SLOPES INTO SLURRY
POND (CENTER). WHITE NOTCH CUT IN CENTER OF RETAINING
DAM IS SPILLWAY STRUCTURE. ALONG THE RIGHT ABUTMENT OF
THE VALLEY A PERIMETER DITCH DIVERTS DRAINAGE AND RUN-
OFF WATERS AWAY FROM CLEARED AREA.
CLOSEUP OF PERIMETER DITCH. THESE DITCHES REQUIRE CONTIN-
UAL MAINTENANCE TO KEEP THEM CLEAR OF DEBRIS AND SILT.
PERIODIC REPAIR OF SLOPE FAILURES is ALSO COMMON.
117
-------
UPPER END OF REFUSE PILE. NOTE DUST CLOUD TRAILING SCRAPER
AT CENTER. To MINIMIZE EROSION AND POTENTIAL FOR LAND-
SLIDES. CLEARING OF VEGETATION ON ABUTMENTS IS LIMITED TO
THAT REQUIRED FOR IMMEDIATE WORKING NEEDS.
VIEW FROM LOWER END OF SLURRY POND LOOKING TOWARDS THE REFUSE
PILE. NOTE THAT DRAINAGE OFF THE REFUSE PILE IS DIRECTED
INTO THE SLURRY POND.
118
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FINISHED REFUSE SURFACE AT HEAD OF RUN. THE SURFACE HERE is
BEING COVERED WITH SOIL AND RECLAIMED. TOPSOIL HAS BEEN
PLACED OVER AREA TO THE RIGHT. WHILE LEFT SURFACE IS EXPOSED
REFUSE IN FINAL PROCESS OF GRADING
119
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TABLE A-5. SUMMARY OF WATER QUALITY DATA: SITE B
(Averages for four site visits)
N>
O
Parameter
Flow (liter/min)
PH
Dissolved Qy (rag/liter)
Acidity (rag/liter as €3003)
Alkalinity (mg/liter as CaC03)
Conductivity (umhos/cm)
Pollutant (mg/liter)
Aluminum
Cadmium
Chloride
Copper
Ferrous iron
Total iron
Lead
Magnesium
Manganese
Mercury
Nickel
Sulfate
Zinc
Sampling Point
1 (Inlet)8
7.0
7.9
10.6
139
522
0.53
0.002
48
0.002
0.06
0.77
0.004
13
0.14
<0.0001
0.004
98
0.03
2b
321 - 875
7.9
10.5
163
1,153
0.69
0.002
112
0.007
0.07
1.51
0.003
22
0.99
<0.0001
0.013
590
0.02
3C
88
7.5
9.3
333
2,885
2.33
0.031
206
0.120
0.66
27.88
0.034
67
5.05
<0.0001
0.028
1,500
0.13
3AC
8.0
9.3
354
2,840
4.40
—
377
—
1.90
40.00
—
65
5.20
<0.0001
«•»
1,600
0.24
4 (outlet)d
545
7.6
9.3
242
2,110
1.67
0.004
187
0.007
0.53
16.61
0.028
39
2.64
<0.0001
0.026
1,023
0.08
Increase (+) or
Decrease (-) between
Inlet and Outlet Points
+538
-0.3
-1.3
+103
+1,588
+1.14
+0.002
+139
+0.005
+0.47
+15.84
+0.024
+26
+2.50
+0.022
+925
+0.05
a. Hillside stream above refuse pile.
b. Lower end of diversion ditch along site perimeter.
c. Combined slurry pond seepage and refuse pile drainage.
d. Downstream from confluence of diversion ditch and Sampling Point 3 flow.
-------
TABLE A-6. WATER QUALITY DATA: SITE B, SAMPLING POINT T
Sampling Date
Parameter
Flow (liter/mln)
pH
Dissolved 02 (mg/liter)
Acidity (mg/liter as CaC03)
Alkalinity (mg/liter as CaCO$)
Conductivity (umhos/cm)
Pollutant (mg/liter)
Aluminum
Cadmium
Chloride
Copper
Ferrous iron
Total iron
Lead
Magnesium
Manganese
Mercury
Nickel
Sulfate
Zinc
July 1976
12
7.90
—
124
470
0.25
<0.001
—
0.001
0.1
0.18
0.005
11.6
0.04
0.0003
0.001
91
<0.01
Sept 1976
2
8.05
10.6
145
497
0.21
—
65
—
0.07
0.31
__
13
0.14
<0.0001
__
90
0.01
Jan 1977
10
7.85
—
129
440
1.1
0.001
34
0.004
0.03
1.6
0.002
14
0.23
<0.0001
0.006
100
0.08
June 1977
4
7.9
—
157
680
0.57
0.003
44
0.001
0.04
1.0
0.006
14
0.13
<0.0001
0.006
110
0.01
a. Hillside stream above refuse pile.
-------
TABLE A-7. WATER QUALITY DATA: SITE B, SAMPLING POINT 24
Samp1ing Date
(O
Parameter
Flow (liter/lain)
PH
Dissolved 0;> (mg/liter)
Acidity (mg/liter as €3003)
Alkalinity (mg/liter as CaC03)
Conductivity (umhos/cm)
Pollutant (mg/liter)
Aluminum
Cadmium
Chloride
Copper
Ferrous iron
total iron
Lead
Magnesium
Manganese
Mercury
Nickel
Sulfate
Zinc
July 1976
750 - 950
6.50
141
1,900
0.26
<0,001
—
0.004
0.1
0.1
0.001
23.5
1.11
<0.0001
0.013
760
0.01
Sept 1976
120
8.50
10.5
152
141
0.28
—
127
_-.
0.01
0.21
—
22
0.86
<0.0001
„._
630
0.01
Jan 1977
800
8.15
—
205
970
1.9
0.001
100
0.010
0.05
5.0
0.001
22
1.9
<0.0001
0.014
370
0.03
June 1977
93
8.30
—_
154
1,600
0.32
0.004
110
0.007
0.03
0.72
0.006
21
0.07
<0.0001
0.011
600
0.01
a. Lower end of diversion ditch along site perimeter.
-------
TABLE A"8. WATER QUALITY DATA: SITE B, SAMPLING POINT 3*
Sampling Date
to
Parameter
Plow (liter/min)
PH
Dissolved Oo (mg/liter)
Acidity (mg/liter as CaC03>
Alkalinity (mg/liter as CaC03)
Conductivity (umhos/cm)
Pollutant (mg/liter)
Aluminum
Cadmium
Chloride
Copper
Ferrous iron
Total iron
Lead
Magnesium
Manganese
Mercury
Nickel
Sulfate
Zinc
July 1976
190
6.70
—
275
2,800
4.4
0.001
—
0,012
0.4
3.5
0.065
74
5,9
0.0003
<0.001
1,500
0.21
Sept 1976
50
7.95
9.3
354
2,840
4.4
—
377
—
1.9
40,0
—
65
6.2
<0,0001
__
1,600
0.24
Jan 1977
20
7.45
--
340
2,600
0,43
0.002
110
0.011
0.20
37.0
0.010
64
4.3
<0,0001
0.031
1,400
0.05
June 1977
92
7.90
•"-
362
3,300
0,09
o.oio
130
0.012
0.14
31.0
0.027
64
3.8
<0.0001
0.053
1,500
0.03
a. Combined slurry pond seepage and refuse pile drainage.
-------
TABLE A-9. WATER QUALITY DATA: SITE B, SAMPLING POINT 3AC
to
Parameter
Flow (liter/min)
pH
Dissolved Oo (mg/liter)
Acidity (mg/liter as
Alkalinity (mg/liter as CaC03)
Conductivity (umhos/cm)
Pollutant (mg/liter)
Aluminum
Cadmium
Chloride
Copper
Ferrous iron
Total iron
Lead
Magnesium
Manganese
Mercury
Nickel
Sulfate
Zinc
Sampling Date
Sept 1976
7.95
9.3
354
2,840
4.4
377
1.9
40
65
5.2
<0.0001
1,600
0.24
a. Combined slurry pond seepage and
refuse pile drainage.
-------
TABLE A-10. WATER QUALITY DATA: SITE B, SAMPLING POINT 4*
Sampling Date
to
Parameter
Flow (liter/min)
pH
Dissolved Oo (ing/liter)
Acidity (mg/liter as CaC03)
Alkalinity (mg/liter as CaC03)
Conductivity (umhos/cm)
Pollutant (mg/liter)
Aluminum
Cadmium
Chloride
Copper
Ferrous iron
Total iron
Lead
Magnesium
Manganese
Mercury
Nickel
Sulfate
Zinc
July 1976
1,140
6.45
—
158
2,000
0.94
<0.001
—
0.003
0.1
3.53
0.076
29
1.58
0.011
0.0004
850
0.03
Sept 1976
50
7.95
9.3
354
2,840
4.4
—
377
—
1.9
40
—
65
5.2
<0.0001
__
1,600
0.24
Jan 1977
800
7.90
—
226
1,300
1.8
0.003
75
0.008
0.04
13
0.006
28
2.3
<0.0001
0.041
540
0.04
June 1977
190
8.15
—
230
2,300
0.32
0.007
110
0.009
0.08
9.9
0.002
34
1.5
<0.0001
0.038
1,100
0.03
a. Downstream from confluence of diversion ditch and Sampling Point 3 flow.
-------
TABLE A-ll. AIR QUALITY DATA: SITE B
Sampling Date
Temperature (°C)
Weather Conditions
Wind Speed (mps)
Wind Speed (mph)
Wind Direction
Dust/Particulates (mg/liter)
Gases (mg/liter)
Nitrogen dioxide
Sulfur dioxide
Hydrogen sulfide
Carbon monoxide
Methane
12/21/76
-5
Snow flurries,
3"-4" of snow
3.7
8.5
NW
0.017
0.044
<0.110
<0.09
1.7
3.0
1/19/77
-26
Ground frozen,
snow-covered
2.2
5
W
0.010
-------
SITE C
HYDROLOGIC DATA
Drainage Area:
19 ha (47 acres). No tributary drainage
to disposal site.
107 cm (42 in.)
76 cm (30 in.)
Mean max. 6*C (42°F) to 29°C (84°F)
Mean min. -4°C (24°F) to 17°C (62°F)
Rainfall Design Frequencies: (24-hour storms)
Precipitation (mean annual);
Fond Evaporation (average annual):
Temperature Extremes (Jan-July):
5-yr
Depth,, cm (in.) 8.4(3.3)
Max. Storm Water Volume, 5(4)
m3x!03 (acre-ft)
10-yr 50-yr IQQ-yr
.9(3.9) 12.2(4.8) 13.2(5.2)
6(5) 7(6) 9(7)
127
-------
SITE C: FEATURES AND OPERATIONS
The topography at this site is a sloping transition between flat river-
bottom lands and rolling upland hills. The disposal area consists of a refuse
pile and adjacent slurry ponds. The closed dike system retaining the ponds is
built from coarse refuse.
The disposal area is divided into three basic compartments. The north-
west area is an inactive slurry pond, the southeast area is an active slurry
and mine drainage pond, and the central area is the dry disposal site for
coarse refuse. Surface drainage from the uplands is diverted around the dike
system by means of a ditch. Since water percolates through the permeable base
of the impoundments, there are no outlet or spillway facilities.
Presently, coarse refuse is brought by conveyor from the preparation
plant to a bin at the refuse area. From the bin, the refuse is loaded into a
Model 631C Caterpillar scraper and spread in approximately 15 cm (6 in.) lifts.
Compaction is achieved by systematic routing of the haulage equipment. Haul
roads are maintained with two D-7 bulldozers. The dikes are continually being
raised with coarse refuse. Approximately 774 Mt/d (850 tpd) of coarse refuse
is placed in the disposal area. The gradation of the material is between the
No. 28 and the 10 cm (4 in.) Tyler sieve sizes.
Slurry containing approximately 14% solids by weight is discharged from
the wash plant to the active pond at a typical rate of 636 var/d (168,000 gpd).
Mine drainage underflow is discharged at a variable rate into the same pond.
The fine refuse in the slurry is smaller than the No. 28 Tyler sieve size.
DIMENSIONAL DATA
Slurry Pond Embankments
Crest width 9-31 m (30-100 ft)
U/S slope 1.4:1
D/S slope 1.4:la
Max. vert, distance to foundation 38 m (125 ft)
Slurry Ponds (Nos. 1, 2, 3)
Total normal storage area 34 ha (84 acres)
Freeboard 2 - 5 m (7 - 15 ft)
Total existing storage volume 408,000 m (533,000 yd3)
Coarse Refuse Area
Area 4.25 ha (10.5 acres)/yr
Surface slopes ±5%
Side slopes 1.4:la
Max. depth (projected) 27 m (90 ft)
Storage volume 1,440,000 m3 (1,880,000 yd3)
a. To be flattened to 2:1 in near future.
128
-------
TYPE OF REFUSE AND PRIOR PROCESSING
The coal mined at this facility is from a seam approximately 2 m (7 ft)
thick which is located at a depth of 76 m (250 ft) below the valley bottom.
It is a low-sulfur metallurgical coal, mined using conventional room and
pillar techniques. Whenever possible, the pillars are recovered when retreat-
ing. Coal brought to the preparation plant is processed using heavy media,
froth flotation, and water table circuits. Approximately 3,640 Mt (4,000 tons)
of raw coal are mined per day. Twenty-five percent or approximately 910 Mt
(1,000 tons) per day of the total extraction is rejected. Coarse refuse
accounts for 85% of the total reject, and fine refuse for 15%.
POLLUTION CONTROL CONSIDERATIONS
The major part of the drainage from the refuse pile is directed into the
slurry pond.
The major portion of liquids entering the slurry ponds seeps out of the
previous pond bottom. There is no water return from the ponds to the
preparation plant.
Sampling and testing of minor seepage through the coarse refuse dikes
into drainage ditches provide the bases for evaluating pollution control.
129
-------
AERIAL VIEW OF ACTIVE REFUSE PILE AND SLURRY POND
PREPARATION PLANT is IN THE FOREGROUND WITH THE
REFUSE CONVEYOR RUNNING FROM THE PLANT TO THE
REFUSE PILE.
NORTHERN SLURRY PONDS NOTE PERIMETER DITCH VISIBLE
TO THE RIGHT OF THE ENCLOSING DIKE SYSTEM PREPA-
RATION PLANT THICKENER IS AT UPPER LEFT.
130
-------
GENERAL VIE* OF SLURRY PONDS. THE POND TO THE RIGHT is
THE ACTIVE AREA. AND THE POND TO THE LEFT IS INACTIVE
SEPARATING THE TWO PONDS is THE REFUSE CONVEYOR ALIGN-
MENT (RIGHT CENTER).
CREST OF THE COARSE REFUSE DUE SYSTEM ENCLOSING THE SLUR-
RY PONDS. THE CREST 1IDTH IN THIS AREA IS APPROXIMATELY
50 FT. NOTE THAT THE CREST IS SLOPED TO DRAIN INTO THE
SLURRY POND (RIGHT) AND NOT TOWARDS THE EMBANKMENT'S OUT-
SIDE SLOPE. TO THE LEFT OF THE EMBANKMENT. THE PREPARA-
TION PLANT CAN BE SEEN.
131
-------
TABLE A-12. SUMMARY OF WATER QUALITY DATA: SITE C
(Averages for four site visits)
Sampling Point
Co
to
Parameter
Flow (liter/min)
pH
Dissolved 0? (ing/liter)
Acidity (mg/liter as CaC03)
Alkalinity (mg/liter as CaCOj)
Conductivity (umhos/cm)
Pollutant (mg/liter)
Aluminum
Cadmium
Chloride
Copper
Ferrous iron
Total iron
Lead
Magnesium
Manganese
Mercury
Nickel
Sulfate
Zinc
1 (Inlet)8
17
8.0
8.8
287
594
0.48
<0.001
13
0.002
0.07
0.47
0.009
16
0.08
<0.0001
0.017
274
0.01
2 (outlet)6
96 - 380
7.4
9.9
146
2,368
1.41
0.005
28
0.014
1.00
5.57
0.018
79
5.52
<0.0001
0.028
1,700
0.05
3C
30 - 88
8.0
11.4
205
2,608
2.38
0.004
61
0.026
0.11
8.63
0.035
86
8.40
<0.0001
0.075
1,575
0.20
4d
20
7.3
—
202
2,920
1.70
0.001
—
0.001
0.10
4.90
0.014
118
4.8
0.0002
0.037
2,600
0.04
Increase (+) or
Decrease (-) between
Inlet and Outlet Points
+79 - +313
-0.6
+1.1
+1,774
+0.93
+0.004
+15
+0.012
+0.93
+5.10
+0.009
+63
+5.44
Hone
+0.017
+1,426
+0.04
a. Diversion ditch uphill from slurry pond area.
b. Downstream from confluence of diversion ditch and slurry pond seepage.
c. Diversion ditch parallel to and between the two slurry ponds.
d. Small seepage area at right side of impoundment.
-------
TABLE A-13. WATER QUALITY DATA: SITE C, SAMPLING POINT 1
Sampling Date
Parameter
Flow (liter/tain)
pH
Dissolved Q£ (mg/liter)
Acidity (mg/liter as CaC03)
Alkalinity (mg/liter as
Conductivity (umhos/cm)
Pollutant (mg/liter)
Aluminum
Cadmium
Chloride
Copper
Ferrous iron
Total iron
Lead
Magnesium
Manganese
Mercury
Nickel
Sulfate
Zinc
July 1976
16
8.10
—
296
445
0.87
<0.001
__
0.003
0.2
1.07
0.017
13.1
0.15
0.0002
<0.001
60
0.01
Sept 1976
Standing
- 7.90
8.8
311
660
0.49
—
15
__
0.05
0.10
—
12
0.03
<0.0001
„-,-
84
0.01
Jan 1977
3
8.00
—
268
540
0.45
<0.001
12
0.002
0.01
0.41
0.003
17
0.08
<0.0001
0.044
71
0.01
June 1977
48
7.90
—
272
730
0.11
0.001
12
<0.001
0.01
0.31
0.006
20
0.05
<0.0001
0.005
880
0.02
a. Diversion ditch uphill from slurry pond area.
-------
TABLE A-14. WATER QUALITY DATA: SITE C, SAMPLING POINT 2
a
Sampling Date
Parameter
Flow (liter /rain)
pH
Dissolved Oo (mg/llter)
Acidity (mg/liter as
Alkalinity (mg/liter as CaCC>3)
Conductivity (umhos/cm)
Pollutant (mg/liter)
Aluminum
Cadmium
Chloride
Copper
Ferrous iron
Total iron
Lead
Magnesium
Manganese
Mercury
Nickel
Sulfate
Zinc
July 1976
280 - 380
7.50
129
1,750
4.6
<0.001
—
0.012
0.1
7.9
0.040
63
2.9
0.0005
0.054
1,400
0.07
Sept 1976
90
7.70
9.9
149
2,420
0.20
—
26
~
0.16
2.09
__
64
2.8
<0.0001
__
1,600
0.03
Jan 1977
13
7.40
—
152
1,900
0.38
0.001
31
0.007
3.6
9.9
0.006
60
4.4
<0.0001
0.032
1,200
0,07
June 1977
1
7.20
—
153
3,400
0.45
0.013
28
0.023
0.15
2.4
0.008
130
12
<0.0001
0.028
2,600
0.017
a. Downstream from confluence of diversion ditch and slurry pond seepage.
-------
TABLE A-15. WATER QUALITY DATA: SITE C, SAMPLING POINT 3
Sampling Date
CO
Ul
Parameter
Flow (liter/mln)
pH
Dissolved Oo (rag/liter)
Acidity (mg/liter as
Alkalinity (mg/liter as 03003)
Conductivity (umhos/cm)
Pollutant (mg/liter)
Aluminum
Cadmium
Chloride
Copper
Ferrous iron
Total iron
Lead
Magnesium
Manganese
Mercury
Nickel
Sulfate
Zinc
July 1976
50 - 100
7.85
—
217
2,020
1.9
<0.001
—
0.017
0.2
5.7
0.012
79
9.1
<0.0001
0.082
1,500
0.13
Sept 1976
30
7.85
11.4
201
2,810
1.9
—
75
—
0.19
2.93
—
88
8.8
<0.0001
__
1,900
0.49
Jan 1977
10
8.20
—
218
2,600
4.9
0.001
51
0.028
0.03
22
0.032
85
6.7
<0.0001
0.059
1,100
0.11
June 1977
76
8.25
—
184
3,000
0.82
0.011
58
0.032
0.10
3.9
0.06
93
9.0
<0.0001
0.085
1,800
0.09
a. Diversion ditch parallel to and between the two slurry ponds.
-------
TABLE A-16. WATER QUALITY DATA: SITE C, SAMPLING POINT 4*
Sampling Date
July 1976
Parameter
Flow (liter/mln) 20
PH 7.30
Dissolved Oo (mg/liter)
Acidity (mg/liter as CaCQ$)
Alkalinity (mg/liter as CaCX^) 202
Conductivity (umhos/cm) 2,920
Pollutant (mg/liter)
Aluminum 1.7
Cadmium 0.001
^ Chloride
u> Copper 0.001
Ferrous iron 0.1
Total iron 4.9
Lead 0.014
Magnesium 118
Manganese 4.8
Mercury 0.0002
Nickel 0.037
Sulfate 2,600
Zinc 0.04
a. Small seepage area at right side of impoundment.
-------
TABLE A-17. AIR QUALITY DATA: SITE C°
Sampling Date
\
Temperature (°C)
Weather Conditions
Wind Speed (mps)
Wind Speed (mph)
Wind Direction
Dust/Particulates (mg/liter)
Gases (mg/liter)
Nitrogen dioxide
Sulfur dioxide
Hydrogen sulf ide
Carbon monoxide
Methane
12/15/76
-1
Clear ,
1/2" snow
2.0
4.5
S
0.066
0.067
0.120
<0.07
1.5
3.4
1/27/77
-23 - -17
Cold,
ground frozen
2.2
5
W
0.010
<0.01
<0.01
<0.03
1.1
3.0
5/18/77
4-10
Wet , rained
last hour
of test
2.6
6
N
0.020
0.044
0.082
0.002
1.5
3.8
6/23/77
27 - 32
Clear,
dry
0.5-0.9
1-2
SW
0.030
0.040
0.078
0.002
1.5
3.7
Averag
0.03
0.04
0.07
0.02
1.4
3.5
a. Sampling point east and south of east pond.
-------
SITE D
HYDROLOGIC DATA
Drainage Area:
Precipitation (mean annual):
44 ha (109 acres)
114 cm (45 in.)
Fond Evaporation (average annual): 64 cm (25 in.)
Temperature Extremes (Jan-July): Mean max. 6.7°C (44°P) to 30°C (86°F)
Mean min. -4.4°C (24°F) to 15.6°C (60°F)
Rainfall Design Frequencies: (24-hour storms)
5-yr
Depth, cm (in.)
Est. Storm Water Volume,
m3x!03 (acre-ft)
8.6(3.4)
37(30)
10-yr
9.9(3.9)
43(35)
50-yr
12.4(4.9)
54(44)
100-yr
13.5(5.3)
59(48)
138
-------
SITE D: FEATURES AND OPERATIONS
This coal waste disposal site is in mountainous terrain with a maximum
relief of approximately 122 m (400 ft). Coarse refuse is used to construct a
cross-valley dam which retains the slurry impoundment. Immediately downstream
of the dam are two catch basins, each 3.05 m (10 ft) high, that extend over
0.4 ha (1 acre). These catch basins collect any seepage waters that exit at
the downstream toe of the dam. From the catch basins the seepage water is
pumped to a water treatment facility, treated, and then returned to the slurry
impoundment.
The dam is constantly raised with coarse refuse brought in 18.2 Mt (20-
ton) Euclid dump trucks to the top of the dam, where it is dumped into piles.
A D-7 tractor then levels the piles into lifts approximately 30 to 46 cm (12
to 18 in.) thick. Compaction is achieved by routing of the equipment on each
lift. The crest of the embankment is sloped toward the impoundment to prevent
ponding and to minimize erosion of the downstream slope. An open-cut spillway,
founded in rock, is located on the right abutment.
Additional refuse storage is located upstream of the impoundment. This
supplementary area is a valley-fill type of refuse pile which was not in
operation during our site visits.
The slurry pipe from the preparation plant discharges, at an average rate
of 1,090 m3pd (288,000 gpd) with 15% solids by weight, into the northern end
of the impoundment near the dam. A diversion dike, built of refuse, has been
constructed into the pond to direct the slurry toward the upstream portion of
the retention area. The water level in the impoundment is controlled by a
system of pumps, located near the spillway, which discharge excess water into
a nearby creek. Very heavy storm waters would pass over the spillway.
DIMENSIONAL DATA
Retention Dam/Refuse Area
Crest length 346 m (1,135 ft)
Crest width 128 m (420 ft)
D/S slope 2*s :1
Max. vert, distance to foundation 43 m (140 ft)
Approximate volume 3.825(106) m3 (5,000,000 yd3)
Slurry Pond
Maximum storage pond area 5.7 ha (14 acres)
Normal storage pond area 5.7 ha (14 acres)
Freeboard 3.05 m (10+ ft)
139
-------
TYPE OF REFUSE AND PRIOR PROCESSING
The coal mined at this site is from a seam which is 2.1 to 2.4 m (6.9 to
7.8 ft) thick, located at a depth of 91 to 244 m (300 to 800 ft) below the
ground surface. It is a steam coal with approximately 3% sulfur. The prepara-
tion plant uses a Baum jig to clean the coal. Separation of the coarse refuse
is at approximately the No. 10 Tyler sieve size. Mining is done using conven-
tional room and pillar techniques with continuous miners. The raw coal produc-
tion at the mine is approximately 4,550 Mt/d (5,000 tpd), with roughly 25%
reject. Seventeen percent of the total production is coarse reject and 8 per-
cent fine reject. Slurry disposal was started in 1951. It is not known when
refuse disposal was first started.
POLLUTION CONTROL CONSIDERATIONS
o Significant volumes of polluted seepage water come out of the toe of the
refuse dam that retains the slurry pond. These waters, collected in
small, downstream catch basins, are chemically treated and returned to
the pond.
o Drainage from the refuse areas is directed into the slurry pond. In
accordance with regulatory requirements, excess pond waters are pumped
over the dam into a nearby creek (open-water circuit).
o Water sampling and testing of a nearby creek upstream and downstream of
the refuse area allow pollution control to be evaluated.
o The older surface of the embankment has been regraded and seeded to
reduce erosion.
o The toe area of the embankment above the catch basin is being regraded to
control all seepage into the basin. Seeding will be done upon completion
of grading.
140
-------
GENERAL VIEW OF SLURRY POND. THE REFUSE PILE EXTENDS OUT INTO
THE POND TO DIVERT THE SLURRY TOWARDS THE UPPER PORTION OF
THE POND AREA. THUS GRAVITY DRAINAGE INCREASES THE POND'S
EFFICIENCY IN SETTLING SOLIDS.
141
-------
TOE OF REFUSE DAM, WITH CATCH BASINS IN
THE BACKGROUND. NOTE HEAVY SEEPAGE
(APPROXIMATELY 125 GPM) FROM NEAR THE
BASE OF THE DAM. MAIN STREAM CHANNEL
IS IMMEDIATELY BEYOND CATCH BASINS.
142
-------
to
TABLE A-18. SUMMARY OF WATER QUALITY DATA: SITE D
(Averages for four site visits)
Sampling Point
Parameter
•Flow (llter/min)
PH
Dissolved 0? (rag/liter)
Acidity (ng/liter as CaC03)
Alkalinity (mg/llter as CaC03)
Conductivity (umhos/cm)
Pollutant Cms/liter)
Aluminum
Cadmium
Chloride
Copper
Ferrous iron
Total iron
Lead
Magnesium
Manganese
Mercury
Nickel
Sulfate
Zinc
la
265
5.9
—
—
50
4,060
4.8
<0.001
—
0.003
600
175
0.001
105
10
<0.0001
0.009
2,700
0.12
2 (Inlet)b
1,700
7.4
10.8
—
75
665
1.0
0.002
16
0.002
0.12
2.67
0.006
15
0.74
<0.0001
0.008
262
0.04
3 (Outlet)0
1,552
6.6
11.0
24
35
990
4.1
0.002
16
0.013
6.95
11.80
0.012
24
2.70
<0.0001
0.029
565
0.10
Seepage Point
Standing
5.3
__
—
5
— —
42.0
0.001
—
0.007
430
236
0.052
125
15
<0.0001
0.160
2,900
0.35
Increase (+) or
Decrease (-) between
Inlet and Outlet Points
-148
-0.8
+0.2
+24
-40
+325
+3.1
None
None
+0.011
+6.83
+9.13
+0.006
+9
+1.96
None
+0.021
+203
+0.06
a. Embankment seepage entering catch basin.
b. Stream sample, upstream from site.
c. Stream sample, downstream from site.
d. Small seepage area on left abutment of embankment.
-------
TABLE A-19. WATER QUALITY DATA: SITE D, SAMPLING POINT 1
Sampling Date
July 1976
Parameter
Flow (liter/min) 265
pH 5.90
Dissolved Oo (mg/liter)
Acidity (mg/liter as CaCC^)
Alkalinity (mg/liter as CaC03) 50
Conductivity (umhos/cm) 4,060
Pollutant (mg/liter)
Aluminum 4.8
Cadmium <0.001
Chloride
Copper 0.003
Ferrous iron 600
Total iron 175
Lead 0.001
Magnesium 105
Manganese 10
Mercury <0.0001
Nickel 0.009
Sulfate 2,700
Zinc 0.12
a. Embankment seepage entering catch basin.
-------
TABLE A-20. WATER QUALITY DATA: SITE D, SAMPLING POINT 2e
Sampling Date
Ut
Parameter
Flow (liter/min)
pH
Dissolved 02 (mg/liter)
Acidity (mg/liter as
Alkalinity (mg/liter as
Conductivity (umhos/cm)
Pollutant (me/liter)
Aluminum
Cadmium
Chloride
Copper
Ferrous iron
Total iron
Lead
Magnesium
Manganese
Mercury
Nickel
Sulfate
Zinc
July 1976
7.20
—
67
700
0.58
<0.001
—
0.002
0.1
0.23
0.006
16.9
0.66
0.0001
0.011
280
0.02
Sept 1976
2,200
7.50
10.8
88
750
2.2
—
14
—
0.26
9.0
—
18
0.99
<0.0001
—
370
0.06
Jan 1977
1,700
7.25
—
58
460
0.91
0.002
15
0.003
0.20
0.98
0.010
14
0.76
<0.0001
0.007
190
0.06
June 1977
1,200
7.80
—
86
750
0.29
0.004
19
0.001
0.01
0.47
0.002
13
0.55
<0.0001
0.006
210
0.02
a. Upstream from site.
-------
TABLE A-21. WATER QUALITY DATA: SITE D, SAMPLING POINT 3
Sampling Date
Parameter
Flow (liter/min)
PH
Dissolved Oo (mg/liter)
Acidity (mg/liter as CaC03)
Alkalinity (mg/liter as CaC03)
Conductivity (umhos/cm)
Pollutant (me/liter)
Aluminum
Cadmium
Chloride
Copper
Ferrous iron
Total iron
Lead
Magnesium
Manganese
Mercury
Nickel
Sulfate
Zinc
July 1976
610
6.15
—
—
22
1,030
4.5
<0.001
—
0.008
15
14
0.008
25.3
4
0.0007
0.038
490
0.09
Sept 1976
2,700
6.95
11.0
— —
52
1,010
3.5
—
14
—
3.5
6.9
—
26
2.4
<0.0001
_ _
590
0.06
Jan 1977
1,700
7.00
—
—
45
720
2.1
0.003
16
0.009
3.6
7.3
0.009
21
2.0
<0.0001
0.012
420
0.08
June 1977
1,200
6.30
—
24
21
1,200
6.4
0.002
18
0.022
5.69
19
0.020
24
2.4
<0.0001
0.038
760
0.18
&. Downstream from site.
-------
TABLE A-22. WATER QUALITY DATA: SITE D, SAMPLING POINT1
Sampling Date
July 1976
Parameter
Flow (liter/min) Standing
pH 5.30
Dissolved Oo (mg/liter)
Acidity (mg/liter as CaC03)
Alkalinity (mg/liter as CaC03) 5
Conductivity (umhos/cm)
Pollutant (mg/liter)
Aluminum 42
Cadmium 0.001
Chloride
Copper 0.007
Ferrous iron 430
Total iron 236
Lead 0.052
Magnesium 125
Manganese 15
Mercury <0.0001
Nickel 0.16
Sulfate 2,900
Zinc 0.35
a
a. Left abutment of embankment.
-------
TABLE A-23. AIR QUALITY DATA: SITE D
a
Sampling Date
00
Temperature (°C)
Weather Conditions
Wind Speed (mps)
Wind Speed (mph)
Wind Direction
Dust/Particulates (mg/liter)
Gases (mg/liter)
Nitrogen dioxide
Sulfur dioxide
Hydrogen sulfide
Carbon monoxide
Methane
12/20/76
-1 - 0.5
Rain, sleet,
water in ruts
1.5 - 2.0
4-5
SSW-SW
0.033
0.077
0.07
<0.07
1.2
3.0
1/20/77
-26
Ground frozen,
18" snow
2.2
5
WNW
0.010
<0.01
<0.01
<0.03
1.2
3.0
5/17/77
27
Hot, hazy
1.4
3
SW
0.033
0.077
0.07
<0.07
1.2
3.0
6/23/77
27
Clean ,
dry
0.5 - 0.9
1-2
S
0.04
0.040
0.074
0.004
1.6
3.3
Averaj
0.03
0.05
0.05
0.03
1.3
3.1
a. Sampling point 100 yards south of pond.
-------
SITE E
ACTIVE REFUSE
DISPOSAL AREA
I?;—M-^t-r:
INACTIVE REFUSE
DISPOSAL AREA
HYDROLOGIC DATA
Drainage Area: Bl ha (200 acres)
Precipitation (mean annual): 102 cm (40 in.)
Pond Evaporation (average annual): 76 cm (30 in.)
Temperature Extremes (Jan-July): Mean max. 6°C (42°F) to 31°C (88°F)
Mean min. -4°C (24°F) to 17°C (62°F)
Rainfall Design Frequencies: (24-hour storms)
5-yr
10-yr
50-yr
100-yr
Depth, cm (in.)
Est. Storm Water Volume
(acre-ft)
8.4(3.3) 9.9(3.9) 12.2(4.8) 13.2(5.2)
40(32) 46(37) 57(46) 62(50)
149
-------
SITE E: FEATURES AND OPERATIONS
Site E is in mountainous terrain typical of Appalachia and has a maximum
relief of 122 m (400 ft). Disposal was started at this site in 1958 and dis-
plays a combination of valley-fill, sidehill, ridgetop, and heaped-pile dis-
posal practices. In 1974, the mine operator concentrated disposal operations
in an area where valley-fill practices are used exclusively. Site visits were
restricted to this area, because it is the active sector of the larger disposal
area. There is an emergency disposal area at the top western portion of the
refuse pile adjacent to the storage bin.
The selected disposal area is a steep, narrow hollow which has numerous
springs along the valley slopes. These springs, and accompanying landslide
problems, are quite common to the area. Prior to placing refuse in this loca-
tion, the area was cleared and grubbed. Most of the trees and heavy brush
were put through a wood chipper and the chips were marketed by a forestry group
assigned to the improvement of woodlands owned by the coal company.
After clearing and grubbing, a trial underdrain system was installed in
one area to intercept spring water and carry it under the refuse. The under-
drain system is composed of perforated pipes and a permeable blanket of boiler
slag. The boiler slag is a waste product from one of the nearby steam-electric
generating stations.
To intercept surface drainage, a perimeter ditch has been excavated into
the hillside above the refuse. This ditch generally surrounds the refuse area
and discharges the collected water downstream of the disposal area. The
perimeter ditch is continually maintained to keep it clear of debris and to
repair any local landslide conditions.
Refuse is taken by conveyor from the preparation plant to a storage bin
adjacent to the disposal area. From the bin, the refuse is loaded into a Terex
Model TS24 scraper with a capacity of 18 m3 (24 yd3), and is hauled to the head
of the hollow, where it is placed in the downstream direction. The specified
maximum lift thickness is 31 cm (12 in.); however, the scraper operators pre-
fer to lay the refuse in lifts 15 to 20 cm (6 to 8 in.) thick. The surface
of the active refuse area is projected to be crowned with a minimum slope of
1%%. Side slopes are a maximum of 2 (horizontal) to 1 (vertical). A water
truck and D-7 bulldozer are used to maintain the haul roads. The bulldozer is
also used in dressing the refuse area. An emergency refuse storage area at
the downstream portion of the disposal area is used when the conveyor from the
preparation plant is down. A 46 Mt (50-ton) dump truck hauls refuse directly
from the preparation plant during conveyor shutdown periods. Restoration of
the refuse is primarily accomplished during downtime periods, such as when the
mine or preparation plant is temporarily out of production; however, it is an
ongoing activity and is not totally limited to downtime periods. Restoration
includes covering all finished refuse surfaces with 30 to 60 cm (1 to 2 ft) of
clay soils, and seeding.
150
-------
DIMENSIONAL DATA
Refuse Area
Surface area 24.3 ha (60 acres)
Drainage area 81 ha approx. (200 acres)
Maximum height of refuse 76 m (250 ft)
Finished surface slope 1 to 1%%
Finished side slopes Maximum 2:1
TYPE OF REFUSE AND PRIOR PROCESSING
Coal is mined at Site E from a seam located at an average depth of 120 to
180 m (400 to 600 ft) below ground surface. The coal is a high-sulfur steam
coal approximately 1.5 m (5 ft) thick. In this area, the coat. seam has a shale
parting up to 46 cm (18 in.) thick. Mining operations remove both the coal
and shale parting along with the materials later separated in the preparation
plant. Continuous miners are presently used to extract the coal, but it is
planned to use longwall operations in the near future.
The preparation plant uses a combination of froth flotation and heavy
media circuits to clean the coal. In the heavy media circuit, the Chance cones
use sand as their media. The coarse refuse is separated with screens at 1.1 cm
(0.4 in.). Minus 1.1 cm (0.4 in.) material is mixed with the wash coarse size
to obtain plant product.
Fine refuse (smaller than the No. 100 sieve) is pumped in slurry form
behind a dam located on a nearby drainage channel. The dam is operated by a
large utility company primarily as a retention basin for flyash. The run-of-
the-mine coal production is approximately 9,100 Mt/d (10,000 tpd). Of this,
approximately 17% is coarse reject. The reported coal chemistry is as follows:
Moisture 5.34%
Ash 14.63%
Sulfur 4.30%
Heat content 11,834 Btu
POLLUTION CONTROL CONSIDERATIONS
o There is no slurry pond associated with the refuse pile at this site.
o Some acid drainage enters the basin above the disposal area from inactive
or abandoned refuse areas to the east of the active disposal area. As
the active refuse area expands, much of the acid drainage from the inac-
tive area should be blocked off to reduce the pollution potential.
o An interceptor ditch has been cut into the sides of the valley to diveit
a major .part of incoming water around the refuse pile.
151
-------
The site is in difficult mountainous terrain with numerous springs; land-
sliding problems occur along the steep, heavily-wooded valley slopes.
Stream flows above and below the refuse disposal area allow for water
sampling and testing to evaluate pollution control at the refuse area.
Any erosion of the refuse is contained on site.
152
-------
REFUSE DISPOSAL AREA VIEWED FROM NEAR MIDPOINT. DARK
MATERIALS IN FOREGROUND COMPRISE ACTIVE DISPOSAL AREA.
LIGHT COLORED MATERIALS IN BACKGROUND ARE AN OLDER.
INACTIVE SECTION DRAINAGE IS MAINTAINED BY THE CHANNEL
ALONG THE RIGHT SIDE OF THE VALLEY.
SURFACE OF ACTIVE REFUSE AREA. HEAVY SCRAPERS ARE ABLE TO
PASS OVER THE REFUSE WITH A MINIMUM OF SURFACE YIELDING.
RELATIVE FIRMNESS OF SURFACE is DUE TO PLACEMENT OF FILL
IN THIN LIFTS.
153
-------
DIVERSION DITCH AROUND ONE OF THE VALLEY'S ABUTMENTS.
VALLEY SLOPES AT THIS SITE ARE LANDSLIDE PRONE. NOTE
THAT THE CLEARING OF VEGETATION IS LIMITED TO MINIMUM.
11VERSION DITCH DIRECTING DRAINAGE WATER ALONG THE RIGHT
SIDE OF THE VALLEY ABOVE THE REFUSE.
L54
-------
LOAD-OUT REFUSE BIN. THE CONVEYOR BELT HAS A TURN-OVER
FEATURE ON THE RETURN LINE. THE TURN CLEANS THE BELT
OF STICKING REFUSE PARTICLES AND THUS PREVENTS RANDOM
DROPPING OF REFUSE MATERIAL ALONG THE CONVEYOR ALIGN-
MENT.
155
-------
TABLE A-24. SUMMARY OF WATER QUALITY DATA: SITE E
(Averages for four sice visits)
Sampling Point
Ui
Parameter
Flow (liter/min)
PH
Dissolved 02 (mg/liter)
Acidity (mg/liter as
Alkalinity (mg/liter as CaC03)
Conductivity (umhos/cm)
Pollutant (mg/liter)
Aluminum
Cadmium
Chloride
Copper
Ferrous iron
Total iron
Lead
Magnesium
Manganese
Mercury
Nickel
Sulfate
Zinc
1 (Inlet)8
38 - 75
7.6
10.2
—
59
623
0.24
0.001
4.3
0.002
0.10
0.24
0.004
7.4
0.19
<0.0001
0.002
63
0.01
2b
139 - 280
7.3
5.4
—
528
3,460
0.35
0.003
311
0.002
3.04
6.88
0.006
22
6.3
<0.0001
0.004
1,233
0.03
3C
19
3.5
—
4,020
—
8,900
380
0.027
—
0.230
510
1,210
0.003
350
36
0.0008
0.320
6,400
8
4 (Outlet)d
347 - 950
4.7
10.8
822
18
4,493
42.75
0.007
209
0.033
300
351.75
0.003
111.8
29.5
<0.0001
0.410
3,100
2.70
Increase (+) or
Decrease (-) between
Inlet and Outlet Points
309 - 875
-2.9
+0.6
+822
-41
+3,870
+42.51
+0.006
+204.7
+0.031
+299.9
+351.54
-0.001
+104.4
+29.31
None
+0.408
+3,037
+2.69
a. Control sample from drainage above site.
b. Drainage from new fill area.
c. Drainage from new and old fill areas.
d. Composite of old and new fill areas, surface runoff, and adjacent spring water.
Point is confluence of all water leaving site before going to treatment plant.
-------
TABLE A-25. WATER QUALITY DATA: SITE E, SAMPLING POINT 1°
Sampling Date
Parameter
Flow (liter/min)
PH
Dissolved 02 (ing/liter)
Acidity (rag/liter as
Alkalinity (mg/liter as
Conductivity (umhos/cm)
Pollutant (mg/liter)
Aluminum
Cadmium
Chloride
Copper
Ferrous iron
Total iron
Lead
Magnesium
Manganese
Mercury
Nickel
Sulfate
Zinc
July 1976
75 - 150
7.60
—
45
1,800
0.28
<0.001
—
0.001
0.3
0.3
<0.001
6.1
0.12
<0.0001
<0.001
38
0.01
Sept 1976
Standing
7.95
10.2
70
202
0.33
—
1
—
0.04
0.23
—
7
0.31
<0.0001
__
42
0.01
Jan 1977
Standing
7.30
—
65
250
0.27
0.002
8
0.003
0.01
0.35
0.002
9.8
0.18
<0.0001
0.004
110
0.03
June 1977
Standing
7.60
—
56
240
0.09
0.001
4
<0.001
0.04
0.08
0.008
6.8
0.13
<0.0001
0.001
61
<0.001
a. Drainage point above site.
-------
TABLE A-26. WATER QUALITY DATA: SITE E, SAMPLING POINT 2C
Sampling Date
oo
Parameter
Flow (iiter/min)
PH
Dissolved 02 (mg/liter)
Acidity (mg/liter as
Alkalinity (mg/liter as
Conductivity (umhos/cm)
Pollutant (me/liter)
Aluminum
Cadmium
Chloride
Copper
Ferrous iron
Total iron
Lead
Magnesium
Manganese
Mercury
Nickel
Sulfate
Zinc
July 1976
190 - 280
7.20
—
543
5,100
0.39
0.002
—
0.005
0.1
2.13
<0.001
23.3
0.76
<0.0001
0.004
1,700
0.02
Sept 1976
170
7.50
5.4
567
4,740
0.60
—
694
—
11
15.2
—
39
2.3
<0.0001
__
2,100
0.07
Jan 1977
280
7.40
—
531
1,500
0.22
0.002
58
<0.001
0.03
3.0
0.002
7.8
0.52
0.0005
0.008
390
0.03
June 1977
57
7.00
—
472
2,500
0.]7
0.006
180
<0.001
1.01
7.2
0.014
18
1.8
<0.0001
0.002
740
0.01
a. New fill area.
-------
TABLE A-27. WATER QUALITY DATA: SITE E, SAMPLING POINT 3*
Sampling Date
July 1976
Parameter
Flow (liter/min) 19
pH 3.50
Dissolved Q£ (mg/liter)
Acidity (mg/liter as CaC03) 4,020
Alkalinity (mg/liter as CaC03>
Conductivity (umhos/cm) 8,900
Pollutant (mg/liter)
Aluminum 380
Cadmium 0.027
Chloride
Copper 0.23
Ferrous iron 510
Total iron 1,210
Lead 0.003
Magnesium 305
Manganese 36
Mercury 0.0008
Nickel 0.32
Sulfate 6,400
Zinc 8.0
a. Confluence of drainage from new and old fill areas.
-------
TABLE A-28. WATER QUALITY DATA: SITE E, SAMPLING POINT 4
a
Sampling Date
Parameter
Flow (liter/min)
PH
Dissolved 02 (mg/liter)
Acidity (mg/liter as
Alkalinity (mg/liter as
Conductivity (umhos/cm)
Pollutant (mg/liter)
Aluminum
Cadmium
Chloride
Copper
Ferrous iron
Total iron
Lead
Magnesium
Manganese
Mercury
Nickel
Sulfate
Zinc
July 1976
750 - 950
3.80
—
1,570
—
6,300
85
0.007
—
0.058
440
560
0.001
166
43
< 0.0001
0.31
4,200
5.2
Sept 1976
150
5.00
10.8
522
—
4,670
29
—
422
—
220
267
—
113
32
< 0.0001
__
3,400
2.1
Jan 1977
Frozen
6.15
—
436
18
2,800
29
0.001
86
0.015
220
260
0.008
75
21
< 0.0001
0.69
2,100
1.7
June 1977
140
3.80
—
760
—
4,200
28
0.014
120
0.025
318
320
0.001
93
22
< 0.0001
0.23
2,700
1.8
a. Confluence of waters leaving site.
-------
TABLE A-29. AIR QUALITY DATA: SITE Ee
Sampling Date
Temperature (°C)
Weather Conditions
Wind Speed (mps)
Wind Speed (mph)
Wind Direction
Dust/Particulates (mg/liter)
Gases (mg/liter)
Nitrogen dioxide
Sulfur dioxide
Hydrogen sulfide
Carbon monoxide
Methane
12/21/76
-12 - -10
Snow flurries,
3"-4" of snow
3.7 - 8.9
8-20
NW-NNW
0.015
0.048
0.22
<0.09
1.7
3.1
1/19/77
-26
Ground frozen,
12"-18" snow
2.2
5
W
0.020
<0.01
<0.01
<0.03
1.2
3.3
4/28/77
27 - 28
Fair
0 - 0.2
0 - 0.5
W
0.040
0.025
0.010
0.002
2.3
2.8
6/20/77
15 - 27
Hazy,
ground damp
0 - 0.9
0-2
W+E
0.004
0.023
0.002
0.006
1.8
3.7
Avera
0.02
0.02
0.06
0.02
1.8
3.2
a. Sampling point far eastern corner of area.
-------
SITE F
;-v\f UNO : £
• -*./*• 447 ••:.->.
V1TER POND\
WATER
-!- RESEUWilR
H->^.
^-^T'l) v.
HYDROLOGIC DATA
Drainage Area: 81 ha (200 acres)
Precipitation (mean annual): 107 cm (42 in.)
Pond Evaporation (average annual): 89 cm (35 in.)
Temperature Extremes (Jan-July): Mean max. 7°C (44°F) to 26°C (90°F)
Mean min. -3°C (26°F) to 19°C (67°F)
Rainfall Design Frequencies: (24-hour storms)
5-yr
10-yr
50-yr 100-yr
Depth, cm (in.)
Est. Storm Water Volume,
m3x!03 (acre-ft)
— _,___- a_ff_ - •" — J —_ ~_~ •" J ~
10.7(4.2) 12.2(4.8) 15.7(6.2) 20-23(8-9)
49(40) 62(50) 74(60) 82(65)
162
-------
SITE F: FEATURES AND OPERATIONS
Site F, a combined slurry impoundment and refuse disposal area, is located
in typical Midwestern flatlands. The impoundment and disposal areas are
totally retained by a perimeter dike system constructed of native clay soils.
The original slurry impoundment area is now used to dispose of the coarse
refuse. There is a 24.4 m (80 ft) high mound of refuse in this area which was
placed many years ago, before present-day disposal practices and regulations
were put into effect. It is understood that this mound is to be graded to
acceptable slopes in the future. Presently, coarse refuse from the preparation
plant is being hauled to the disposal area in 20 Mt (22 ton) dump trucks and
deposited in piles. A bulldozer periodically levels the piles in lifts 46 cm
to 61 cm (18 in. to 24 in.) thick, and the equipment is routed over each lift
to facilitate limited compaction. The surface of the refuse is sloped toward
the clear-water pond to minimize drainage out of the dike system and to prevent
ponding of water. There is no history of fires with this refuse pile.
The diked area north of the refuse area is used as the slurry impoundment.
The slurry is pumped at approximately 2.27 m^pm (600 gpm) into the southeast
corner of this area and the solids allowed to settle. Clear water is then
decanted into the clarified water pond through a divider dike constructed
across the southwestern end of the impoundment. Water from the clarified
water pond-is returned to the coal preparation plant for reuse. There is no
point source discharge into the natural streams. Makeup water is obtained at
approximately 2.27 m^pm (600 gpm) from a freshwater reservoir west and south
of the preparation plant.
The perimeter dike has a heavy, volunteer growth of grasses and bushes on
the downstream slope. The upstream slope is also protected with grasses,
except where wave action has caused erosion problems. Plans are being devel-
oped by the mine owner to rehabilitate the portions of the dike system which
have been damaged by wave action.
The slurry retention dikes were constructed in a sequential pattern,
starting in 1959, near the southeast corner of the present site. As the stor-
age area filled, new dikes were constructed until the entire system reached
its present configuration.
DIMENSIONAL DATA
Refuse Area
Surface Area 28.3 ha (70 acres)
Average depth 8.84 m (29± ft)
Storage volume 140,000 Mt (154,000 tons)
Average surface' slope (2%±)
Average side slopes (2:1)
163
-------
Slurry Impoundment
Crest length 2,134 m (7,000 ft)
Crest width 0.91-3.05 m (3-10 ft)
U/S slope (2:1)
D/S slope (1.5:1)
Max. vert, distance to foundation 10.7 m (35 ft)
Surface area 32 ha (79 acres)
Storage volume 1.224(106) Mt (1,345,000 tons)
Clear Water Impoundment
Maximum storage pond area 15.4 ha (38 acres)
Normal storage pond area 15.4 ha (38 acres)
Max. vert, distance to found. (6.10 m (20 ft)
Freeboard 3.05 m (10+ ft)
Spillway None
TYPE OF REFUSE AND PRIOR PROCESSING!
A low-sulfur metallurgical coal is mined at this facility. The seam
averages 2.3 m (7.5 ft) thick and is located at an approximate depth of 200 m
(660 ft). The coal is mined using continuous miners and room and pillar
techniques developed by the mine operators. Coal brought to the preparation
plant is processed using Baum jigs and a heavy media circuit. Approximately
8,190 Mt (9,000 tons) of raw coal are mined per day. Of this total, between
18% and 25% is rejected. The raw coal, as mined, has a reported typical
analysis (dry basis) of approximately 1.5% sulfur and 15% to 20% ash.
POLLUTION CONTROL CONSIDERATIONS
o The preparation plant recirculates slurry pond waters; makeup water comes
from a lake with a high domestic detergent load.
o The coarse refuse pile is located within the retention dike system.
o Drainage from the refuse pile is retained within the slurry pond and
used in the plant water circuit.
o Any seepage from the clarified water pond is routed into the makeup water
reservoir.
164
-------
PARTIAL VIEW OF THE ACTIVE COARSE REFUSE AREA NOTE THAT
THE REFUSE AREA IS SLOPED INTO THE CLARIFIED WATER POND
REFUSE PILES (LEFT CENTER AND BOTTOM CENTER) HAVE BEEN
RECENTLY DUMPED BY TRUCKS. A BULLDOZER FROM THE PREPA-
RATION PLANT PERIODICALLY LEVELS AND COMPACTS THE PILES
INACTIVE REFUSE PILE PLACED IN PAST YEARS. THIS PILE is
COMPLETELY CONTAINED BY EARTH DIKES. THE STRUCTURE WILL
BE RE6RADEO AND RECLAIMED TO CONFORM TO REGULATORY RE-
QUIREMENTS.
165
-------
SLURRY LINE DECANTING INTO THE SOUTHEAST CORNER OF THE
SLURRY POND THE VERY GENTLE TERRAIN SURROUNDING THE
REFUSE AREA IS CHARACTERISTIC OF THIS REGION
WATER QUALITY SAMPLING POINT. LOCATED IMMEDIATELY OUTSIDE THE
SOUTHWEST CORNER OF THE CLARIFIED WATER POND. DURING RUNOFF
EVENTS THIS CHANNEL IS OCCUPIED BY A MOVING STREAM. AT OTHER
TIMES ANY WATER IN THIS PORTION OF THE CHANNEL REMAINS STAGNANT
(AS SHOWN HERE).
166
-------
TABLE A-30. SUMMARY OF WATER QUALITY DATA: SITE F, SAMPLING POINT 2*
(Averages for two site visits)
Sampling Point 2
Parameter
Flow (liter/min) Standing
pH 7.8
Dissolved Q£ (mg/liter) 9.0
Acidity (mg/liter as 63003)
Alkalinity (mg/liter as CaCOs) 96
Conductivity (umhos/cm) 2,315
Pollutant (mg/liter)
Aluminum 3.2
Cadmium 0.002
Chloride 548
Copper 0.009
Ferrous iron 0.30
Total iron 5.18
Lead 0.019
Magnesium 36
Manganese 10.3
Mercury <0.0001
Nickel 0.015
Sulfate 625
Zinc 0.04
a. At sampling point 1, the upstream control point, no water
was found during either of the site visits.
b. Downstream from lower right abutment of dike.
-------
TABLE A-31. WATER QUALITY DATA: SITE F, SAMPLING POINT 2'
Sampling Date
00
Parameter
Flow (liter/min)
pH
Dissolved Oo (mg/liter)
Acidity (rag/liter as CaC03)
Alkalinity (mg/liter as CaC03)
Conductivity (umhos/cm)
Pollutant (mg/liter)
Aluminum
Cadmium
Chloride
Copper
Ferrous iron
Total iron
Lead
Magnesium
Manganese
Mercury
Nickel
Sulfate
Zinc
July 1976
Standing
8.85
167
3,050
4.0
0.002
630
0.009
6.7
0.019
46
5.6
<0.0001
0.015
630
0.04
Sept 1976
Standing
6.8
9.0
24
1,580
2.3
465
0.30
3.65
27
15
<0.0001
620
0.05
a. Downstream from lower right abutment of dike.
-------
TABLE A-32. AIR QUALITY DATA: SITE
Sampling Date
ON
vo
Temperature (°C)
Weather Conditions
Wind Speed (mps)
Wind Speed (mph)
Wind Direction
Dust/Particulates (mg/liter)
Gases (mg/liter)
Nitrogen dioxide
Sulfur dioxide
Hydrogen sulfide
Carbon monoxide
Methane
1/6/77
-2
Light snow on
ground, 2 "-3"
1.6
4
SSW
0.022
<0.01
<0.01
<0.03
1.2
3.3
1/17/77
-27
Ground frozen,
snow- covered
4.5
10
NW
0.010
<0.01
<0.01
<0.03
1.3
2.7
3/23/77
-1-4
Wet
3.2
7
W+NW
0.020
0.02
0.04
0.01
1.5
3.5
6/16/77
18 - 24
Fair,
ground damp
1.1
2.5
SW
0.020
0.02
0.02
0.03
1.2
2.8
Averag
0.018
0.01
0.01
0.01
1.3
3.1
a. Sampling point off haulage road, 100 feet downwind of dumping area.
-------
SITE 6
HYDROLOGIC DATA
Drainage Area: 53 ha (130 acres)
Precipitation (mean annual): 107 cm (42 in.)
Pond Evaporation (average annual): 89 cm (35 in.)
Temperature Extremes (Jan-July): Mean max. 7°C (44°F) to 32°C (90°F)
Mean min. .-3°C (26°F) to 19°C (67°F)
Rainfall Design Frequencies: (24-hour storms)
Depth, cm (in.)
Est. Storm Water Volume,
m3x!03 (acre-ft)
5-yr 10-yr 50-yr 100-yr
10.7(4.2) 12.2(4.8) 15.7(6.2) 17.0(6.7)
57(46) 62(50) 80(65) 86(70)
170
-------
SITE G: FEATURES AND OPERATIONS
Site G is in typical Midwestern flatlands. The disposal area is a com-
bined slurry impoundment and refuse dump; coarse refuse is used to build the
dikes that retain the slurry pond. Surface drainage is directed around the
outside perimeter of the dike system and collected in a small reservoir imme-
diately downstream of the impoundment. Water collected in this reservoir is
pumped back into the clarified water pond. Below this collection reservoir is
a large, multipurpose reservoir constructed by the Corps of Engineers. North
of the site is a fresh-water reservoir which was constructed and is being
operated by the company as a source of makeup water for the preparation plant.
The pond area is divided into two compartments by a center divider dike.
The southern compartment contains the slurry settling basin, and the northern
compartment is used as a clarified water pond. The differential water head
across the compartments is 3.05 m (10 ft) and is maintained by a decant pipe
through the divider dike. Water in the clarified water pond is recycled back
to the preparation plant. Makeup water is obtained from the clarified water
pond and from the fresh-water reservoir. There is no point source discharge
out of the ponds.
When the dike system was begun in 1967, native clay soils were used to
construct a low starter embankment. Since then, coarse refuse has been used
to raise the dikes. The refuse is hauled to the dikes with a 46 Mt (50 ton)
dump truck and spread into 46 cm (18 in.) thick lifts with a D-8 Caterpillar.
As a part of the truck hauling operations, the drivers are instructed to change
the paths of their trucks so that each refuse layer is compacted with at least
four to six coverages of the truck wheels. Additional compaction is achieved
through the operation of the bulldozer in leveling the dumped refuse piles.
During the site survey, safety berms were being constructed on the top inside
and outside edges of the embankments to prevent vehicles from accidentally
slipping off the dike crest.
DIMENSIONAL DATA
Embankment
Crest length 3,048 m (10,000 ft)
Crest width 12-30 m (40-100 ft)
U.S slope 1.25:1
D/S slope 1.25:1
Max. vert, distance to foundation 10.7 m (35 ft)
Slurry Pond
Maximum storage pond area 30.8 ha (76 acres)
Normal storage pond area 30.8 ha (76 acres)
Existing storage volume 1.13(106) m3 (920 acre ft)a
Existing freeboard 3.05 m (10 ft)a
171
-------
Clear Water Pond
Maximum storage pond area 20.6 ha (51 acres)
Normal storage pond area 20.6 ha (51 acres)
Existing storage volume 1.0(106) m3 (800 acre ft)a
Existing freeboard 3.05 m (10 ft)a
a. These values will change as refuse is added to
impoundment structures.
TYPE OF REFUSE AND PRIOR PROCESSING
Coal is mined from a seam approximately 229 m (750 ft) below the ground
surface. Raw coal is processed in the preparation plant using a combination
of froth flotation and heavy media procedures. The mine production rate
averages 10,000 Mt/d (11,000 tpd) of raw coal. Approximately 15% of this is
rejected. It is estimated that about 66% of the reject is coarse refuse and
about 34% is fine. The reported coal chemistry at this facility is shown
below.
Met. Coal (%) Steam Coal (%)
Total moisture 11.5 12.0
Volatile matter 36.1 35.0
Dry Fixed carbon 58.1 53.0
Basis Ash 5.8 12.0
Sulfur 0.7 0.75
Heat content 13,500 Btu 12,700 Btu
The reported water balance for the preparation plant is listed below:
Cubic Meters/ Gallons/
To Plant Minute Minute
Fresh water to all pump glands 0.29 78
Fresh water to all magnetic separators 1.67 440
Fresh water for makeup3 3.43 905
5.39 1,423
From Plant
With 1% in. x 0 met. coal 0.23
With 3/4 in. x 1/2 mm steam coal 0.14
With 3 in. x 1/2 mm refuse 0.18
With 1/2 mm x 0 refuse 4.00
Evaporation 0.84
5.39 1,423
a. Makeup water is estimated at 60% from "C" pond and 40% from fresh-
water reservoir.
172
-------
POLLUTION CONTROL CONSIDERATIONS
o The preparation plant recirculates slurry pond waters.
o Seepage out of the pond is retained by the small dam downstream from the
dikes, and then is pumped back into the plant's water circuit.
o The dikes retaining the slurry pond are largely constructed of nonacid-
producing coarse refuse.
o Due to the flat terrain, there is no runoff onto the site. Consequently,
minimal dike erosion occurs.
173
-------
IN THIS AERIAL VIEW. THE PREPARATION PLANT IS
AT LEFT CENTER PONDS EXTEND FROM THE PREPA-
RATION PLANT TOWARDS THE UPPER RIGHT
LOWER PORTION OF REFUSE DISPOSAL AREA. WITH
ACTIVE SLURRY PONO TO THE RIGHT NOTE THE
GENERAL FLATNESS OF THE TERRAIN.
174
-------
SLURRY POND LIES TO LEFT OF THE EMBANKMENT AND
CLEARWATER POND TO THE RIGHT. PREPARATION
PLANT IS IN THE BACKGROUND.
CREST OF REFUSE DIKE RETAINING SLURRY POND. CREST
WIDTH AT THIS POINT IS APPROXIMATELY 60 FT. REFUSE
MOUNDS ALONG THE EDGES OF THE CREST ARE SAFETY
BERMS INTENDED TO PREVENT TRUCKS FROM SLIPPING OFF.
175
-------
TABLE A-33.
SUMMARY OF WATER QUALITY DATA: SITE G
(Averages for four site visits)
Sampling Point
Parameter
Flow (liter/min)
pH
Dissolved Oo (mg/liter)
Acidity (mg/liter as CaC03)
Alkalinity (mg/liter as
Conductivity (umhos/cm)
Pollutant (mg/liter)
Aluminum
Cadmium
Chloride
Copper
Ferrous iron
Total iron
Lead
Magnesium
Manganese
Mercury
Nickel
Sulfate
Zinc
la
Standing
8.21
8.8
184
1,433
2.0
0.002
320
0.010
0.18
2.21
0.007
4.6
0.75
<0.0001
0.013
313
0.02
l-l/2b
6
7.85
8.2
190
2,310
8.2
—
798
—
4
7.40
—
9
0.28
<0.0001
__
440
0.11
2C
4.4
8.1
9.1
382
5,908
1.9
0.007
1,270
0.009
0.58
2
0.013
20.8
0.94
<0.0001
0.023
450
0.05
a. Small pond on northwest corner of site.
b. Small seepage area near downstream toe of embankment.
c. Ditch parallel to one pond, upstream from point where it
drains into pond for return to plant.
-------
TABLE A-34. WATER QUALITY DATA: SITE G, SAMPLING POINT 1
Sampling Date
Parameter
Flow (liter/min)
pH
Dissolved Q£ (mg/liter)
Acidity (mg/liter as CaCO$)
Alkalinity (mg/liter as
Conductivity (umhos/cm)
Pollutant (me/liter)
Aluminum
Cadmium
Chloride
Copper
Ferrous iron
Total iron
Lead
Magnesium
Manganese
Mercury
Nickel
Sulfate
Zinc
July 1976
Standing
8.15
163
1,200
2.2
0.001
160
0.010
0.4
2.36
0.015
3.5
0.45
<0.0001
0.002
200
0.01
Sept 1976
None
8.6
8.8
190
1,330
1.2
390
0.09
1.35
4.5
1.3
<0.0001
240
0.01
Jan 1977
Standing
7.90
193
1,400
0.53
0.002
280
0.006
0.08
0.22
0.004
5.3
0.33
<0.0001
0.006
300
0.02
June 1977
Standing
8.20
190
1,800
4.1
0.004
450
0.015
0.16
4.90
0.003
4.9
0.91
<0.0001
0.032
510
0.03
a. Small pond on northwest corner of site.
-------
TABLE A-35. WATER QUALITY DATA: SITE G, SAMPLING POINT 1%
Sampling Date
Sept 1976
Parameter
Flow (liter/min) 6
pH 7.85
Dissolved Oo (rag/liter) 8.2
Acidity (mg/liter as CaC03)
Alkalinity (mg/liter as CaCOa) 190
Conductivity (umhos/cm) 2,310
Pollutant (mg/liter)
Aluminum 8.2
Cadmium —
Chloride 798
Copper
Ferrous iron 4.0
Total iron 7.4
Lead
Magnesium 9
Manganese 0.28
Mercury <0.0001
Nickel
Sulfate 440
Zinc 0.11
a. Small seepage area near downstream
toe of embankment
-------
TABLE A-36. WATER QUALITY DATA: SITE G, SAMPLING POINT 2
Sampling Date
VD
Parameter
Flow (liter/min)
pH
Dissolved 0? (mg/liter)
Acidity (mg/liter as CaC03)
Alkalinity (mg/liter as CaC03)
Conductivity (umhos/cm)
Pollutant (mg/liter)
Aluminum
Cadmium
Chloride
Copper
Ferrous iron
Total iron
Lead
Magnesium
Manganese
Mercury
Nickel
Sulfate
Zinc
July 1976
2.5
8.20
—
508
7,200
1.6
0.008
900
0.007
0.3
1.33
0.031
15.3
0.26
<0.0001
<0.001
510
0.02
Sept 1976
10
8.20
9.1
314
3,830
4.0
—
1,540
—
1.9
3.91
—
14
0.19
<0.0001
•*•*
520
0.05
Jan 1977
1
7.90
—
284
5,600
0.41
0.002
440
0.009
0.04
0.36
0.002
30
1.1
<0.0001
0.056
300
0.08
June 1977
4
8.10
—
420
7,000
1.5
0.010
2,200
0.011
0.08
2.4
0.007
24
2.2
<0.0004
0.011
470
0.04
a. Ditch parallel to one pond, upstream from point where it drains
into pond for return to plant.
-------
TABLE A-37. AIR QUALITY DATA: SITE G
Sampling Date
Temperature (°C)
Weather Conditions
Wind Speed (nips)
Wind Speed (mph)
Wind Direction
•- Dust/Part iculates (me/liter)
00 **
o
Gases (mg/liter)
Nitrogen dioxide
Sulfur dioxide
Hydrogen sulfide
Carbon monoxide
Methane
1/6/77
-4
Light snow
(3"-5"), ground
frozen
1.7
4
SSW
0.017
0.015
0.020
0.030
1.5
3.0
1/17/77
-26 - -29
Ground frozen,
snow-covered
2.2 - 4.5
5-10
N+NW
0.010
<0.01
<0.01
<0.03
1.3
2.9
3/23/77
-1-4
Ground wet,
raining
3.2
7
W+NW
0.023
0.020
0.040
<0.01
1.5
3.5
6/16/77
15 - 18
Fair,
ground damp
0.9 - 1.3
2-3
sw
0.017
0.015
0.020
0.030
1.5
3.0
Avera;
0.016
0.012
0.020
0.015
1.5
3.1
a. Sampling point corner of haulage road, far eastern corner of area.
-------
HYDROLOGIC DATA
Drainage Area: 43 ha (105 acres)
Precipitation (mean annual): 102 cm (40 in.)
Pond Evaporation (average annual): 76 cm (30 in.)
Temperature Extremes (Jan-July): Mean max. 6°C (42°F) to 29°C (85°F)
Mean min. -4°C (24°F) to 17°C (62°F)
Rainfall Design Frequencies: (24-hour storms)
5-yr
10-yr
50-yr
100-yr
Depth, cm (in.)
Est. Storm Water Volume,
m3x!03 (acre-ft)
8.4(3.3) 9.9(3.9) 12.2(4.8) 13.2(5.2)
35(28) 40(32) 49(40) 53(43)
181
-------
SITE H: FEATURES AND OPERATIONS
Site H is in undulating terrain that has a maximum relief of approximately
76 m (250 ft). The refuse pile, located immediately upstream of the slurry
pond, combines features of both valley-fill and ridge-type structures. The
slurry pond is a cross-valley impoundment.
When the refuse pile was started in 1959, the area was cleared, grubbed,
and stripped, and topsoil was stockpiled for future use in reclamation. Refuse
is taken from the preparation plant by underground rail haulage, through non-
productive coal workings, to a point under the disposal area. From here it is
skip-hoisted 107 m (350 ft) through a vertical shaft, at approximately 5.46
Mt/m (6 tpm), to a temporary storage bin. Two 32 Mt (35 ton) WABCO scrapers
take the refuse from the bin to the disposal area, where it is placed in
approximately 31 cm (12 in.) lifts and compacted by random routing of haulage
equipment. Haul roads are maintained with a water truck and D-7 bulldozers.
The surface of the refuse is sloped at approximately 2% to 3% into the slurry
pond or into specially provided siltation basins. Side slopes are covered with
clay soil and hydroseeded as the pile is raised. There is no history of fires
in the refuse pile.
The slurry pond dam, constructed in 1959, has a central clay core with
coarse refuse shells. The slopes were covered with soil and seeded. A con-
crete spillway is located on the left abutment and an outlet works near the
right abutment. Slurry with an average of 35% solids is pumped from the pre-
paration plant through a 13 cm (5 in.) pipeline at 1.04 - 1.13 m3pm (275 - 300
gpm). The pipeline follows essentially the same route as the underground rail
system which hauls the refuse. Near the pond the pipeline is brought to the
surface through a vertical borehole, and the slurry is discharged into the
southern portion of the impoundment. The solids settle in this portion of the
pond and the clear water is decanted through the northern outlet works into a
nearby tributary of a river.
DIMENSIONAL DATA
Refuse Area
Surface area 40± ha (100± acres)
Maximum depth 30 m (100± ft)
Average surface slopes 2% to 3%
Average side slopes 2:1
Slurry Pond Embankment
Crest length 610 m (2,000 ft)
Crest width 21 m (70 ft)
U/S slope 1:1
D/S slope 2:1
Max. vert, distance to foundation 30.5 m (100 ft)
Approximate volume 9.95(105) m3 (1,300,000 yd3)
182
-------
Slurry Pond
Drainage area 43 ha (105 acres)
Normal storage 27 ha (66 acres)
Freeboard 3.7 m (12 ft)
Spillway Concrete Chute
Outlet works 25-cm (10 in.) pipe
TYPE OF REFUSE AND PRIOR PROCESSING
The coal mined at Site H is from a seam which has an average thickness of
2 m (7 ft) and is located at a depth of 90 - 120 m (300 - 400 ft) below ground
surface. This low-sulfur, high-volatile, metallurgical coal is mined by con-
ventional room and pillar techniques, with full recovery in the retreat phase.
Raw coal brought to the preparation plant is processed in three beneficiation
systems: heavy media sand cone, concentrating table, and froth flotation.
Approximately 10,900-12,700 Mt (12,000-14,000 tons) of raw coal are processed
daily in the plant. Approximately 30% of this is reject. The ratio of coarse
refuse to fine refuse is 8:1.
POLLUTION CONTROL CONSIDERATIONS
A major portion of the drainage from the refuse pile is directed into the
slurry pond.
The pond has a flow-through water circuit; clarified waters are discharged
into a nearby drainage area.
Refuse from the preparation plant is brought to the disposal area through
nonproductive, underground coal workings. This procedure eliminates the
need for off-site, above-ground haul roads or conveyance systems.
The completed embankment surface has been seeded to reduce erosion.
183
-------
TABLE A-38.
SUMMARY OF WATER QUALITY DATA: SITE H
(Averages for four site visits)
Sampling Point
oo
Parameter
Flow (liter/min)
pH
Dissolved Q£ (mg/liter)
Acidity (mg/liter as CaC03)
Alkalinity (mg/liter as CaC03)
Conductivity (umhos/cm)
Pollutant (mg/liter)
Aluminum
Cadmium
Chloride
Copper
Ferrous iron
Total iron
Lead
Magnesium
Manganese
Mercury
Nickel
Sulfate
Zinc
la
0.62
7.8
10.4
285
1,188
0.05
<0.001
169
0.001
0.03
1.44
0.003
35
0.50
<0.0001
0.002
280
0.02
l-l/2b
533
8.1
10
300
1,737
0.20
<0.001
73
0.001
0.03
1.09
0.002
24
0.76
<0.0001
0.008
923
0.02
2C
2,538
8.2
10.2
198
1,732
0.52
0.001
136
0.002
0.07
0.84
0.009
13
0.36
<0.0001
0.001
718
0.02
a. Small stream adjacent to site perimeter.
b. Overflow from main settling pond.
c. Downstream from confluence of main pond overflow and
discharge of embankment drain system.
-------
TABLE A-39. WATER QUALITY DATA: SITE H, SAMPLING POINT le
Sampling Date
Ui
Parameter
Flow (liter/min)
PH
Dissolved 02 (mg/liter
Acidity (rag/liter as
Alkalinity (mg/liter as CaC03)
Conductivity (umhos/cm)
Pollutant (mg/liter)
Aluminum
Cadmium
Chloride
Copper
Ferrous iron
Total iron
Lead
Magnesium
Manganese
Mercury
Nickel
Sulfate
Zinc
July 1976
0.5
8.34
—
208
1,280
<0.01
<0.001
—
0.001
0.1
5.24
0.005
32.9
1.9
<0.0001
0.001
640
0.05
Sept 1976
0.5
7.31
10.4
314
1,170
0.02
<0.001
248
0.001
0.02
0.02
0.001
35
0.04
<0.0001
0.002
170
0.01
Jan 1977
0.5
7.83
—
307
1,100
0.09
0.001
120
0.001
0.01
0.05
<0.001
38
v 0.02
<0.0001
0.002
150
0.01
June 1977
1
7.60
—
311
1,200
0.06
<0.001
140
<0.001
0.01
0.47
0.006
36
0.02
<0.0001
0.002
160
0.02
a. Small stream adjacent to site perimeter.
-------
TABLE A-40. WATER QUALITY DATA: SITE H, SAMPLING POINT
Sampling Date
00
ON
Parameter
Flow (liter/min)
PH
Dissolved Oo (mg/liter)
Acidity (mg/liter as
Alkalinity (mg/liter as CaCC>3)
Conductivity (umhos/cm)
Pollutant (mg/liter)
Aluminum
Cadmium
Chloride
Copper
Ferrous iron
Total iron
Lead
Magnesium
Manganese
Mercury
Nickel
Sulfate
Zinc
Sept 1976
910
7.88
10.0
237
1,810
0.29
<0.001
76
<0.001
0.07
1.76
0.002
26
1.0
<0.0001
<0.001
940
0.02
Jan 1977
50
8.22
—
385
1,100
0.16
0.002
71
0.007
0.01
0.31
0.003
26
0.65
<0.0001
0.004
730
0.02
June 1977
640
8.10
—
280
2,300
0.14
<0.001
73
<0.001
0.02
1.2
0.001
20
0.62
<0.0001
0.018
1,100
0.03
a. Overflow from main settling pond.
-------
TABLE A-41. WATER QUALITY DATA: SITE H, SAMPLING POINT 2
Sampling Date
oo
Parameter
Flow (liter/mln)
pH
Dissolved Q£ (tng/liter)
Acidity (mg/liter as CaCO$)
Alkalinity (mg/liter as CaC03)
Conductivity (umhos/cm)
Pollutant (mg/liter)
Aluminum
Cadmium
Chloride
Copper
Ferrous iron
Total iron
Lead
Magnesium
Manganese
Mercury
Nickel
Sulfate
Zinc
July 1976
3,400
8.38
-—
176
1,580
0.31
<0.001
—
0.003
0.1
0.68
0.008
13.6
0.3
<0.0001
<0.001
700
0.03
Sept 1976
3,100
7.96
10.2
182
1,750
0.42
0.001
139
<0.001
0.14
1.21
0.008
16
0.54
<0.0001
<0.001
840
0.01
Jan 1977
850
8.17
—
270
1,800
0.80
0.003
130
0.004
0.01
0.62
0.011
13
0.33
<0.0001
0.003
550
0.02
June 1977
2,800
8.10
—
165
1,800
0.53
0.001
140
0.002
0.03
0.83
0.009
9.5
0.26
<0.0001
0.008
780
0.02
a. Downstream from confluence of main pond overflow and
discharge of embankment drain system.
-------
TABLE A-42. AIR QUALITY DATA: SITE Hc
oo
00
Temperature (°C)
Weather Conditions
Wind Speed (mps)
Wind Speed (mph)
Wind Direction
Dust/Particulates (mg/liter)
Gases (mg/liter)
Nitrogen dioxide
Sulfur dioxide
Hydrogen sulfide
Carbon monoxide
Methane
12/30/76
-18 - -14
Cold, 2"-3"
snow on
ground
2.0 - 2.2
4-5
S-SE
0.01
0.077
0.001
0.003
1.8
3.2
1/21/77
-26
Very cold,
snowing, 18"
on ground
3.6
8
NW
0.002
0.01
<0.01
<0.03
1.4
3.0
5/18/77
27 - 29
Hot, hazy
1.0
2
SW
0.03
0.028
0.002
0.005
1.5
3.5
6/22/77
21 - 28
Clear, dry
0 - 0.8
0-2
SW
0.002
0.028
0.002
0.005
1.1
3.0
Averagi
0.01
0.033
0.001
0.008
1.4
3.2
a. Sampling point 1/2 mile north of shaft.
-------
SITE
-.
•/ Substations, ~>.-.
/ S / "*•> *°,
*—.: 1' • // '/
«^KS^.
189
-------
SITE I: FEATURES AND OPERATIONS
Site I is an engineered embankment designed and developed primarily for
disposal of flyash from nearby power generating plants. However, coarse coal
refuse from neighboring mines is currently being utilized to raise the main
embankment. The refuse is delivered by scrapers to the portion of the embank-
ment being raised, where it is spread, compacted, and leveled by equipment
operated by the utility company. The utility needs large amounts of fill to
raise the flyash retention dam, so that if the coarse coal refuse was not
available an equal amount of native borrow material would be required. This
would create an environmental condition equivalent to that from an open-pit
mining operation.
Fine coal refuse in slurry form is discharged into the upper end of the
pond. The coarse coal refuse is used for bank fill and coarse boiler slag is
used to construct the drain zones of the embankment. The drain material is
placed not only as a vertical drain to intercept seepage through the impervious
upstream face of the dam, but also along the downstream foundation area and the
abutment contacts to intercept natural seepage water. Interception of pond
and underground waters permits a controlled flow of this water and prevents
'its potential contamination by the coal refuse. In addition, from an engineer-
ing viewpoint, control of the seepage waters is necessary for structural
stability.
190
-------
.
ZONING OF RETAINING DAM. COARSE REFUSE is TO THE RIGHT.
AND THE NATURAL SOIL ROCK ABUTMENT TO THE LEFT. THE DARK
LAYER SEPARATING THE TWO ZONES IS A PERMEABLE BOILER SLAG
FROM A NEARBY POWER PLANT.
TWIN-ENGINED SCRAPER PLACING REFUSE NEAR DAM ABUTMENT. NOTE
THAT THE SCRAPER IS PLACING THE REFUSE IN VERY THIN LIFTS.
THE USE OF THIN LIFTS IMPROVES THE TRAFFICABILITY OF THE
REFUSE SURFACE.
191
-------
•v- .'
WEIGHTED LEVELING BOARD WHICH is PULLED BEHIND A
BULLDOZER TO PROVIDE A SMOOTH, LEVEL SURFACE FOR
THE VIBRATORY COMPACTOR
BULLDOZER AND HEAVY VIBRATORY ROLLER USED TO GRADE
AND COMPACT COARSE REFUSE IN 0AM EMBANKMENT
192
-------
CLEARWATER DECANT STRUCTURE IN SLURRY POND. OUTER
FENCE AND LOG BOOM KEEPS OUT FLOATING LARGE BRUSH
AND LOGS. SMALLER FLOATING BOOM NEAR THE STRUC-
TURE PREVENTS THE FINE PORTION OF THE FLYASH WASTE
FROM BEING DECANTED INTO THE DOWNSTREAM RIVERS
193
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APPENDIX B
FIELD AND LABORATORY TESTS USED TO
DETERMINE REFUSE PROPERTIES
It is advantageous to have a standard method of identifying soils and
categorizing them according to their engineering properties. In 1952, the
U.S. Bureau of Reclamation and the U.S. Army Corps of Engineers, with Profes-
sor Arthur Casagrande of Harvard University as consultant, agreed on a modi-
fication of Professor Casagrande*s airfield classification system for soils
which they termed the "Unified Soil Classification System" (USCS). This
system, which is particularly applicable to the design and construction of
dams and impoundments, takes into account the engineering properties of the
soils, is descriptive and easy to associate with actual soils, and is adapta-
ble to both field and laboratory testing programs. Probably its greatest
advantage is that a soil can be classified readily by visual and manual exami-
nation without the need for costly laboratory testing.
The USCS is based on particle size, amount and distribution of the vari-
ous sizes, and material plasticity. Soils are divided into coarse-grained,
fine-grained, and highly organic (peaty) soils.
FIELD TESTS
A number of field tests can be performed in order to determine certain
physical properties of coal refuse materials. The type and number of field
tests and program sequence depends on whether the results are needed for an
assessment of a potential borrow source, for an ongoing program of construc-
tion control, or for an investigation of a completed dam or impoundment to
determine its condition.
Moisture and Density
In-place determinations of moisture and density or unit weight are
usually made using the American Society for Testing and Materials (ASTM) Test
Method D-1556. This method involves excavating a hole from a horizontal sur-
face, weighing the excavated material, and determining the volume of the hole
by filling it with a sand of known density. A water content determination of
the excavated sample makes it possible to calculate the dry density in the
ground. Various devices using balloons and water or soil have been used to
measure hole volume, but the sand method is most common.
Depending on the maximum and average particle sizes of the material being
tested, the size of the test hole and therefore the type of equipment to be
194
-------
used will vary. For example, field density tests of pervious materials con-
taining particles more than 2 inches in size are usually made using the water-
volume method. This method, which requires the use of a 3-foot- or 6-foot-
diameter ring, has not yet been standardized by ASTM, but has been used as a
means of control on important earth dam projects (for example Oroville Dam,
the highest earthfill dam in the United States). The tabulation below shows
the minimum desired test hole volume, depending on the average gradation
characteristics of the material being tested.
Minimum Test Hole Volumes and Minimum Moisture Content Samples
(based on maximum particle size)
Minimum Test Hole
Maximum Particle Size Volume (ft ) Content Sample (gin)
No. 4 sieve (4.75 mm) 0.025 100
1/2 inch (12.5 mm) .050 250
1 inch (25 mm) .075 500
2 inch (50 mm) .100 1,000
Greater than 2 in. 8-15 (water-
displacement method)
Density tests are usually performed in backhoe pits, dozer pits, or other
types of excavations. Care should be taken to test representative areas and,
if the test location has been prepared using motorized equipment, the test
level should be at least 1 foot below the surface of excavation, to minimize
any disturbing influences of the excavating equipment. Extreme care should
be exercised in performing tests in any type of exploratory pit because the
side walls may be subject to instability or collapse. Federal safety stan-
dards should always be observed when people are working in unsupported
trenches.
Shear Strength
There are several methods for conducting in-situ shear strength tests.
The vane shear test, which is the most commonly used method, shows little or
no promise for coal refuse testing because of the grain size and characteris-
tics of these materials. The vane shear has been used in attempts to deter-
mine in-situ shear strength of fine-grained sludge materials, but these
materials have nonplastic characteristics and therefore tend to dilate when
sheared in an undrained condition. Static cone penetrometers, such as the
Dutch Cone device, have been increasingly popular in the United States in
recent years. Much research is needed, however, to correlate penetration
resistance and sleeve friction ratios with variations in density and shear
strength before the Dutch Cone device can be successfully used for coal refuse
testing. Standard penetration (dynamic) tests have been used to determine the
relative density of coarse-grained, nonplastic mateials, with generally ade-
quate results. This method more properly indicates the uniformity or lack of
uniformity of a deposit, rather than directly indicating the shear strength.
195
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Permeability
As used by soils engineers, the coefficient of permeability is the super-
ficial velocity of water as it passes through a soil under a unit gradient.
The value of the coefficient of permeability reflects the ease with which
water will flow through a soil, and this must be known in order to calculate
the quantity of flow. The range of permeability for soils is extremely great—
from more than 1 cm/sec (1,000,000 ft/yr) for clean gravels to 10~8 cm/sec
(0.1 in./yr) or less for clays.
Approximate values of permeability can be obtained by field testing. The
reliability of the values obtained depends on the homogeneity of the stratum
tested and on certain restrictions of the mathematical formulas used. If
reasonable care is exercised in adhering to the recommended procedures (for
example U.S. Bureau of Reclamation Test Method E-18), useful results can be
obtained.
The two methods of determining the coefficient of permeability that are
used most often in the field are the infiltration, or pumping-in, test and the
pumping-out test. In the first method, water is introduced into a drill hole
or test pit of known dimensions, and the rate of seepage under a fixed or
variable head is observed. The second (and less used) method involves drawing
out water at a constant rate from a drill hole and observing the rate of draw-
down of the water table in observation wells placed in a geometric pattern,
usually radial, at various distances from the point of water withdrawal. Test
data must be interpreted on the basis of simplified formulas or flow net
analyses with application of proper judgment regarding geological factors such
as channeling, layering, and the anisotropic characteristics of deposits.
LABORATORY TESTS
Laboratory tests are usually performed on three types of samples.
• Undisturbed tube samples obtained with special sampling equipment
using a drill rig and undisturbed hand-cut block samples.
Disturbed samples, such as standard penetration samples, bulk samples,
or drill cuttings.
• Compacted samples fabricated to represent materials of known
characteristics.
The hand-cut sample is rarely needed unless the material is very sensitive to
standard sampling procedures or has a minor geologic feature which may be
obscured or otherwise destroyed in the sampling process.
Good-quality undisturbed samples are needed if engineering properties of
in-situ materials are to be obtained by laboratory testing. Special field
techniques are needed to obtain undisturbed samples and, once they are
obtained, care should be exercised in transporting them to the laboratory.
Compacted or fabricated samples are prepared to represent soils with known
196
-------
moisture, density, and structural characteristics. These samples can be used
in lieu of undisturbed samples of materials, such as clean sand, which cannot
be sampled and transported without changes in density. Since the in-situ
characteristics can be measured, the loose materials can be fabricated into
samples that represent undisturbed conditions. These types of samples can
also be used to test the characteristics of man-made or compacted materials.
Classification Tests
Tests required for USCS classification in the laboratory include grada-
tion and Atterberg limits tests.
Gradation. The gradation or grain size analysis of soils is performed
in accordance with ASTM D-422 and D-1140, which involve dry sieving for
materials coarser than the #200 sieve and hydrometer analysis for materials
finer than the #200 sieve. The results are presented in the form of percent
of the total sample passing (based on dry weight) a given size sieve.
Atterberg Limits. A typical soil mass has three constituents: soil
grains, air, and water. In soils consisting largely of fine grains, the
amount of water in the voids has a pronounced effect on soil properties.
Three main states of soil consistencies are recognizable:
• Liquid state, in which the soil is either in suspension or behaves
like a viscous fluid
• Plastic state, in which the soil can be rapidly deformed or molded
without rebounding elastically, changing volume, cracking, or crumbling
• Solid state, in which the soil will crack when deformed or will
exhibit elastic rebound
In describing these soil states, it is customary to consider only the
fraction of soil smaller than the #40 sieve (the upper limit of the fine sand
component). For this soil fraction, the water content in percentage of dry
weight at which the soil passes from the liquid state into the plastic state
is called the Liquid Limit (LL). A device which causes the soil to flow under
certain controlled conditions is used in the laboratory to determine the LL.
The water content of the soil at the boundary between the plastic state
and the solid state is called the Plastic Limit (PL). The laboratory test
used to define this limit consists of repeatedly rolling threads of soil to
1/8-inch diameter until they crumble, and then determining the water content.
The difference between the LL and the PL corresponds to the range of water
contents within which the soil behaves plastically. This difference of water
content is called the Plasticity Index (PI). Highly plastic soils have a
high PI value. In a nonplastic soil, the PL and the LL are the same, and the
PI equals 0. These limits of consistency, which are called Atterberg limits,
are used in the USCS as the basis for laboratory differentiation between
materials of appreciable plasticity (clays) and slightly plastic or nonplastic
materials.
197
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Moisture-Density
The natural or in-place density and water content of a sample obtained in
the field are determined in the laboratory by carefully extruding the sample
from its container, measuring its natural weight and dimensions, and placing
the material in an oven at a controlled temperature to evaporate all retained
water. Coal refuse materials present a special problem, because they contain
combustible material (such as minor amounts of coal) that will burn at temper-
atures below the recommended temperature (110°C) of ASTM D-2216, the applica-
ble standard for determining the moisture content of soils. W. A. Wahler &
Associates has found, by trial and error, that a drying temperature of 30°C
± 3° for a period of 48 hours is appropriate for coal refuse materials.
Once the dry weight of the material is determined, the total and dry unit
weight (density) and water content are determined using the following formulas:
W _ W
w = -^ x 100
d
W
w
Y«
t
Wd
where
W = wet weight of total sample in pounds
W
d = dry weight of total sample in pounds
V = volume of total sample in cubic feet
w = water content, based on dry weight, in percent
Y = total unit weight of material, usually expressed in pounds per
cubic foot
Yd = dry unit weight of material, usually expressed in pounds per
cubic foot.
Specific Gravity
Specific gravity is defined as the ratio of the weight in air of a given
volume of a material at a stated temperature to the weight of an equal volume
of distilled water at a stated temperature. The specific gravity for material
finer than the #4 sieve is determined in accordance with ASTM D-854; for
materials predominantly larger than the #4 sieve, it is determined in accor-
dance with ASTM C-127. The specific gravity of a material must be known or
assumed in order to calculate the void ratio and percent of saturation of a
198
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given material. The following formulas relate void ratio, specific gravity,
saturation, water content, and dry unit weight:
where
e = void ratio
G = specific gravity
Yd = dry unit weight of soil
Y = unit weight of water
S = Saturation in percent
w = water content based on dry weight, in percent
Compaction and Relative Density
Soil moisture-density relationships are determined in the laboratory in
accordance with ASTM D-1557. The prescribed method covers the determination
of density when the material is compacted in a mold of a given size using a
10-pound hammer dropped from a height of 18 inches. Four methods are provided:
Method A - a 4-inch-diameter mold with material passing the #4 sieve.
Method B - a 6-inch-diameter mold with material passing a #4 sieve.
Method C - a 4-inch-diameter mold with material passing a 3/4- inch screen.
Method D - a 6-inch-diameter mold with material passing a 3/4-inch screen.
The method to be used should be indicated in the specifications for the
material being tested. If no method is specified, Method A is usually used.
o
The energy imparted using these procedures is equal to 56,250 ft-lb/ft
and was originally established as a means of laboratory control for airfield
construction where heavy compaction equipment was required. The earth dam
field, primarily through the work of the State of California Department of
Water Resources, has adopted a lighter compaction standard to more realistic-
ally reflect the compaction effort likely to be achieved in the field. This
standard, which is used by W. A. Wahler & Associates, is a. compactive energy
equal to 20,000 ft-lb/ft3. The 10-pound hammer falling 18 inches is also
used in this test; therefore, when testing under Method A with a 4-inch-
diameter mold, the number of blows per layer is reduced from 25 to 15 and the
number of compacted layers is reduced from 5 to 3.
For materials with up to about 12% passing the #200 sieve, water will not
act as a lubricant in the compaction process and a well-defined moisture-
density relationship cannot be developed. For these soils, the compaction
199
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standard used is ASTM D-2049, which utilizes vibratory equipment. The results
are in the form of maximum and minimum densities; in general, the maximum
density values obtained using vibratory methods are greater than those using
impact methods.
Relative density is defined as the state of compactness of a soil with
respect to the loosest and densest states at which it can be placed using the
ASTM D-2049 laboratory procedures. It is expressed as the ratio of the differ
ence between the void ratio of a cohesionless soil in the loosest state and
the given void ratio to the difference between its void ratios in the loosest
and densest states. The mathematical expression for this definition is:
= __ x 100
d e - e .
max min
where
D, = relative density of field sample in percent
= the void ratio corresponding to the loosest laboratory density
e . = the void ratio corresponding to the most compact laboratory
density
e = the void ratio corresponding to the field density
Permeability
The fundamental property involved in fluid flow is permeability. Because
soil permeability depends very much on the arrangement of individual particles,
and because of the difficulty associated with obtaining representative samples,
field determinations are often required in order to determine average permea-
bility. However, since laboratory determinations are much easier to make than
field determinations and permit study of the relationship of permeability to
void ratio, laboratory tests are usually performed regardless of whether field
measurements are made.
Among the methods used in the laboratory to determine permeability are
falling (or variable) head permeameter and constant head permeameter tests,
and direct or indirect measurements from consolidation tests. For relatively
free-draining material with less than 10% passing the #200 sieve, the coeffi-
cient of permeability should be determined in accordance with ASTM D-2434,
which uses a constant head method. For materials with more than 10% passing
the #200 sieve, saturation can have a marked effect on the results (some
materials exhibit a coefficient of permeability 100% greater at a saturation
of 100% than at a saturation of 80%), and it is suggested, therefore, that a
testing procedure be used that will ensure that the sample is completely
saturated before the permeability test is performed.
The permeability of fine-grained materials can be determined from the
results of one-dimensional consolidation tests using the following relation-
ships :
200
-------
c a Y
, v v'w
k = —=-r
1 + e
where
c = coefficient of consolidation
a = coefficient of compressibility
Y = unit weight of water
e = void ratio
Consolidation
Applying stress to a material causes strains. In materials such as clays
and silts, or sands and gravels that contain sufficient quantities of clays
and silts, a certain time is required for strain to occur. In such materials,
the stresses, strains, and time bear definite relationships to each other;
these relationships are mechanical properties of the material, and are called
stress-strain-time relationships. The stress-strain-time relationship (or
consolidation characteristics of a soil) are determined in accordance with
ASTM D-2435. Two soil properties are determined from the one-dimensional
consolidation tests: Cc, the compression index, which is used to calculate
the magnitude of the settlement, and cv, the coefficient of consolidation,
which is used to calculate the rate of settlement.
Critical Hydraulic Gradient
The critical hydraulic gradient is defined as the gradient that occurs
with upward flow of water through soils which causes the effective stress to
be reduced to zero. If this persists in the field, the zone within which it
occurs has no ability to resist shearing stresses ("quick" condition), and
this could result in a progressive shear failure.
The theoretical expression for critical gradient is:
cr
where
i f = critical gradient
G = specific gravity of material
e = void ratio
A simple laboratory test to verify this expression can be performed on
fine coal refuse by compacting the material in small (less than 4-inch-
diameter) lucite cylinders to the average dry density observed in the field.
The materials are then saturated and a head of water is imposed in order to
cause water to flow upward through the soil column. The head is gradually
increased until the soil column becomes buoyant or a blowout (water above the
201
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soil column suddenly turns black) occurs. The critical gradient is calculated
as the difference in total head (tailwater-headwater) divided by the height of
the soil column.
Shear Strength
The evaluation of soil shear strength is essential for the determination
of dam or impoundment safety. Shear strength cannot be estimated from the
angle of repose but must be physically measured in the field or laboratory.
Mohr-Coulomb Failure Law* as:
The shear strength of soil and particulate rock materials is given by the
mb Failure Law* ai
s = a tan ' + c'
where
s = shear strength
a = effective normal stress
' = angle of internal friction as determined by effective stress
c' = cohesion as determined by effective stress
Direct Shear Test. The shearing resistance of soils can be determined
using a simple shear box wherein a soil'sample is confined by a normal pressure and
the force developed during shear testing is measured. The advantages of this
method are that it is relatively uncomplicated and the equipment is not expen-
sive. The disadvantages are that failure is forced to occur on a horizontal
plane, the test must be run in a drained condition, and if conventional equip-
ment is used, the maximum particle size should be limited to about 1/4 inch.
Triaxial Test. Determination of shear strength by means of triaxial
testing requires extensive knowledge and experience. Test results can be
influenced by many factors, including size of sample, method of sampling,
degree of saturation, rate of strain, rate and method of load application,
drainage conditions, and method of failure interpretation. Testing procedures
are usually identified with a three-letter designation:
First letter - defines how the stresses are applied to the sample
I - Isotropically consolidated prior to application of
shearing force
A - Anisotropically consolidated prior to application of
shearing force
Conventional shear strength theory is based on work originated by the French
mathematician Coulomb in 1776 and extended by Otto Mohr, who first wrote
about general strength theory in 1882.
202
-------
Second letter - Indicates whether the sample was consolidated or uncon-
solidated prior to application of the shearing force
U - Unconsolidated
C - Consolidated
Third letter - defines the drainage conditions which existed during
application of the shearing force
U - Undrained
D - Drained
The four most commonly used triaxial tests are:
IUU - Isotropically Unconsolidated Undrained
ICU - Isotropically Consolidated Undrained
ICD - Isotropically Consolidated Drained
ACU - Anisotropically Consolidated Undrained
The triaxial test results are interpreted by the use of the Mohr circle
of stress at some point during the progress of the test. Three types of
failure criteria may be used to interpret the test results; the actual method
selected will depend on material type and on the type of analysis the results
are to be used for:
Maximum Obliquity - maximum ratio of major to minor principal
stresses during shear
Maximum Deviator Stress - major and minor principal stresses occurring
at the point of maximum deviator stress
Specific Percent Strain - major and minor principal stresses occurring
at some specific percent axial strain
Dynamic Triaxial Test. The discussion on triaxial testing also applies
to the evaluation of shear strength under static loading conditions. If the
stability of a dam or impoundment is to be evaluated under earthquake loading
conditions, the shear strength under dynamic loading conditions should be
evaluated. The testing procedures described above for the static test are
used in the dynamic test, except that after the sample has been consolidated
by either isotropic or anisotropic means, it is failed by applying cyclic,
rather than static, loads. For a given consolidation stress, tests of several
samples will be required in order to define the influence of cyclic stress
magnitude and the corresponding number of load applications required to cause
failure. Failure may occur, depending upon the type of material, as the
result of liquefaction or excessive axial strain. Whereas only 3 samples are
necessary for an adequate determination of static shear strength, 12 to 24
samples may be required for an adequate determination of dynamic shear strength
characteristics.
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Unusual Testing Problems
Since coal refuse materials differ from those commonly used in embankment
construction in that coal refuse may have a rather high carbon content, the
potential for burning should be determined by means of ignition point tests.
The results may influence disposal facility if there is a major requirement
for ignition prevention. Generally, coarse and fine sludge materials can
be tested using the soil materials tests discussed above. Except for some
sample fabrication difficulties associated with loose or unconsolidated
materials (particularly in the case of the dry, cohesionless "red dog"), no
great difficulties in testing are likely to be encountered.
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GLOSSARY OF RELEVANT GEOTECHNICAL TERMS
Abutment—the point of contact between the ends of an embankment and the
natural ground material.
Acre-foot—a term used in measuring water volume, equal to the quantity
required to cover 1 acre 1 foot deep, or 43,560 ft^.
Angle, flare—the angle between the centerline of a structure and a wall.
Angle, friction—the angle measured from the abscissa which defines the limit-
ing stress equilibrium between normal stress (effective or total) and
shear stress (the ordinate).
Apron—A floor or lining of concrete, timber, or other resistant material at
the toe of a dam, bottom of a spillway, chute, etc., to prevent erosion
from falling water or from turbulent flow.
Area, discharge—The cross-sectional area of a waterway.
Area, drainage—The area tributary to a lake, stream, sewer, or drain. Also
catchment area, watershed, and river basin.
Backfill—The operation of refilling an excavation. Also the material placed
in an excavation in the process of backfilling.
Basin, stilling—(1) A structure or excavation which reduces velocity or
turbulence of flowing or falling water.
(2) A structure at the outlet end of a spillway to partially
dissipate the energy of flowing water and discharge the water into the
downstream channel in such a manner as to prevent damage to the dam or
dangerous scour to the banks of the channel.
Bedrock—Any solid rock underlying soil, sand, clay, silt, etc.
Berm—A horizontal strip or shelf built into an embankment or cut to break the
continuity of an otherwise long slope, usually for the purpose of reduc-
ing erosion, or to increase the thickness or width of cross section of an
embankment. Also the space left between the upper edge of a cut and the
toe of an embankment.
Capacity, flood storage—That portion of the reservoir capacity which is
reserved for the temporary storage of flood waters to reduce downstream
peak flows.
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Coefficient of permeability—The rate of flow of a fluid through a unit cross
section of a porous mass under a unit dydraulic gradient, at a tempera-
ture of 60°F.
Cohesion—The state or process by which the particles of a body or substance
are bound together, due to the force of attraction between the molecules.
Conduit—A general term for an artificial or natural duct, either open or
closed, for conveying water or other fluids.
Core, impervious—The central portion of an embankment designed and constructed
to prevent the passage of water.
Creep—The movement of water under or around a structure built on permeable
foundations.
Creep, soil—The slow movement, usually over relatively short distances, of a
mass of soil acting under the force of gravity. The term is usually
applied to such a phenomenon when it is much smaller in magnitude and
extent than a landslide.
Crest—The top of a dam, dike, spillway, or weir, to which water must rise
before passing over the structure. It is frequently restricted to the
overflow portion.
Culvert—A closed conduit for the free passage of surface drainage water under
a highway, railroad, canal, or other embankment.
Dam—A barrier constructed across a watercourse for the purpose of creating
a reservoir, diverting water therefrom into a conduit or channel,
generating power, or for retention of debris.
Dam, starter—Initial embankment utilized to create a tailings pond and which
becomes the foundation upon which the main dike is raised.
Dam, toe—(1) The downstream edge at the base of a dam.
(2) The line of a fill slope where it intersects the natural ground,
and the lowest edge of a backslope of a cut where it intersects the
roadbed.
Delta—An alluvial deposit formed where a stream drops its debris load on
entering a body of quieter water; the terminal deposit of a river.
Dike—(1) An embankment to confine or control water, especially one built
along the banks of a river to prevent overflow of low lands or to deflect
water away from a bank.
(2) An embankment constructed to retain water in a reservoir. The term
dam is usually used where the structure is constructed across a water-
course or stream channel, and dike where it is constructed solely on dry
ground.
(3) A vertical or steeply inclined wall of igneous rock, which has been
forced into a fissure in a molten condition, and there consolidated.
Dikes usually obstruct the passage of ground water.
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Drainage tile—The removal of surplus ground water by means of buried pipes.
Water enters through the unsealed joints or through perforations in the
pipe.
Drain pipe—Pipe, usually perforated plastic, which discharges water collected
from a drain zone.
Drain zone—An area within a zoned dam which collects and transmits seepage
water. Usually constructed of coarse gravel.
Erodibility—The relative ease with which one soil erodes under specified con-
ditions of slope as compared with other soils under the same conditions.
Erosion—Wearing away of land or structures by running water, glaciers, winds,
and waves.
Fill—(1) Depth to which material is to be placed (filled) to bring the surface
to a predetermined grade; therefore, fill is the difference in elevation
between a surface point and a point vertically above it at the proposed
grade.
(2) The volume of material to be added.
(3) An embankment.
Fill, hydraulic—An adjective applied to an earth structure or grading opera-
tion in which the fill material is transported and deposited in place
by means of water pumped through a pipe line.
Filter—A device or structure for removing solid or colloidal material, usually
of a type that cannot be removed by sedimentation from water, sewage,
or other liquid. The liquid is passed through a filtering medium, which
may consist of a granular material such as sand, infusorial, or dia-
tomaceous earth, anthracite coal, etc., finely woven cloth, unglazed
porcelain, or specially prepared paper.
Flood, maximum possible—The largest flood that theoretically can occur at a
given site during present geologic and climatic era, assuming simultaneous
occurrence of all possible flood producing factors in the area.
Flood, maximum probable—The maximum flood for which there is a reasonable
chance that it will occur on a given stream at a selected site. It is
often assumed to be equal to the maximum flood observed in areas having
the same or similar physiographic and meterological characteristics. Such
a flood would very likely be less than the maximum possible flood.
Flood, 10-year (or other designated period)—The flow of a stream which has
been equaled or exceeded, on the average, once in 10 years (or other
designated period).
Flow net—A graphical representation of second-order differential equations
used to determine quantity of flow and water pressures.
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Freeboard—The vertical distance between the normal maximum level of the sur-
face of the liquid in a conduit, reservoir, tank, canal, etc., and the
top of the sides of an open conduit, the top of a dam or levee, etc.,
which is provided so that waves and other movements of the liquid will
not overtop the confining structure.
Frequency—(1) The time rate of vibration or the number of complete cycles per
unit time.
(2) A term used to denote the number of times a certain phenomenon
occurs in a given time.
(3) The number of occasions that the same numerical measure of a
particular quantity has occurred between definite limits.
Gradation—A term used to describe the series of sizes into which a soil
sample can be divided.
Gradient—(1) The rate of change of any characteristic per unit of length, or
slope. The term is usually applied to such things as elevation, velocity,
pressure, etc.
(2) The change in a variable quantity, as temperature or pressure,
per unit distance; also a curve representing such a rate of change.
Grain size—Physical size of soil particle, usually determined by either sieve
or hydrometer analysis.
Ground water—Subsurface water occupying the saturation zone, from which wells
and springs are fed. In a strict sense the term applies only to water
below the water table.
Intake—(1) The place where water enters a conduit or other structure.
(2) The works or structures at the head of a conduit or canal into
which water is diverted.
(3) The process or operation by which water is absorbed into the
ground and added to the zone of saturation.
Launder—(1) A trough, channel, or gutter, by which water is conveyed.
(2) In mining, a chute or trough for conveying powdered ore, or for
carrying water to or from the crushing apparatus.
Method, rational—a method of estimating flood flows which will occur from
the drainage basin above any point. For each subdivision of the drain-
age area the quantity of rainfall which will probably occur during the
time of concentration, the percentage of rainfall which will appear as
the surface runoff, and the time required for such flow to reach the
point in question are estimated for various subdivisions of the drainage
area, and from these the flow at the point in question is determined.
Outlet—(1) Downstream opening or discharge end of a pipe, culvert, sewer,
or canal.
(2) Opening near the bottom of a dam for draining the reservoir.
(3) Lateral escape which spills over a natural bank into a depression
or basin.
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Permeability—The property of a material which permits appreciable movement
of water through it when saturated and actuated by hydrostatic pressure
of the magnitude normally encountered in natural subsurface water. The
rate of permeability is measured by the quantity of water passing through
a unit cross section in a unit time when the gradient of the energy head
is unity.
Piping—The action of water passing through or under a dam and carrying with
it to the surface at the downstream toe some of the finer material. Such
action may result in excessive leakage or even failure, as with the
increased porosity of the material due to removal of the fines, the
velocity of the water increases and in turn more and larger-sized material
is removed.
Pond—(1) a Body of water of limited size either naturally or artificially
confined and usually smaller than a lake.
(2) To gather together into a pond.
Pore—As applied to stone, soil, etc., any small interstice or open space,
generally one that admits the passage or adsorption of liquid or gas.
Porosity—(1) The state of being porous or containing insterstices.
(2) An index of the void characteristics of a soil or stratum as
pertaining to percolation; degree of perviousness.
Pressure, pore water—Interstitial pressure acting within the water or air
contained in the void space of soil or rock.
Rain, heavy—Rain which is falling at the time of observation with an intensity
in excess of 0.30 in./hr.
Rate, percolation—The rate, usually expressed as a velocity, at which water
moves through saturated granular material. The term is also applied to
quantity per unit of time of such movement, and has been used erroneously
to designate infiltration rate or infiltration capacity.
Red dog—General term applied to ash-like residue remaining after a coal waste
dump has burned.
Riprap—(1) Broken stone or boulders placed compactly or irregularly on dams,
levees, dikes, etc., for protection of earth surfaces against the action
of waves or currents.
(2) Brush or pole mattresses, or brush and stone, or other similar
materials used for protection.
Runoff, storm—That portion of the total runoff from storm rainfall or rapid
snow melt which reaches the point of measurement within a relatively
short period of time subsequent to the occurrence of the rain or thaw.
Safety, factor of—The ratio of the forces tending to resist embankment fail-
ure to the forces tending to cause such failure. Thus any factor of
safety less than 1.0 indicates an unstable condition.
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Saturation—(1) Completely filled; a condition reached by a material, whether
it be in solid, gaseous, or liquid state, which holds another material
within itself in a given state in an amount such that no more of such
material can be held within it in the same state. The material is then
said to be saturated or in a condition of saturation.
(2) The condition of a liquid when it has taken into solution the
maximum possible quantity of a given substance at a given temperature
and pressure.
Scour—The erosive action of running water in streams, in excavating and carry-
ing away material from the bed and banks. Scour may occur in both earth
and solid rock material.
Seepage—(1) The slow movement or percolation of water through small cracks,
pores, interstices, etc., in the surface of unsaturated material into or
out of a body of surface or subsurface water.
(2) The loss of water by infiltration from a canal, reservoir, or
other body of water, or from a field. It is generally expressed as flow
volume per unit time.
Slope—The inclination or gradient from the horizontal of a line or surface.
The degree of inclination is usually expressed as a ratio, such as 1:25,
indicating one unit rise in 25 units of horizontal distance; or in a
decimal fraction (0.04); degree (2°18'); or percent (4 percent).
Slurry—A thin, watery mud, or any substance resembling it.
Spillway—A waterway in or about a dam or other hydraulic structure for the
escape of excess water.
Stability—The ability of an engineering structure, such as a dam, retaining
wall, etc., to resist movement when loads are applied to it.
Storage—The impounding of water, either in surface or in underground reser-
voirs, for future use. The term differs from pondage in that the latter
refers to more or less temporary retention of the water, whereas storage
contemplates retention for much longer periods.
Stripping—The operation of removing topsbil from the site of a structure,
such as a dam or embankment; shallow excavation.
Toe—The point of contact between the base of an embankment and the foundation
surface.
Void ratio—The ratio of volume of voids to the volume of solids of a sample.
Volume, runoff—The total quantity or volume of runoff during a specified time.
It may be expressed in acre-feet, in inches of depth on the drainage area,
or in other units.
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GLOSSARY OF RELEVANT COAL PREPARATION TERMS
Abatement—Reduction of pollution effects of mine drainage.
Abutment—The point of contact between the ends of an embankment and the
natural ground material.
Acid-producing materials—Usually, rock strata containing significant pyrite
which, if exposed by coal mining, and acted upon by air and water, will
cause acids to form.
Acid mine drainage—Any acid water draining or flowing on or having drained
or flowed off, any land affected by mining.
Acid spoil—The spoil or waste material containing sufficient pyrites so that
the weathering produces acid water and where the pH of the soil deter-
mined by standard methods of soil analysis is between 4.0 and 6.9.
Aquifer—A water-bearing formation through which water moves more readily
than it can through an adjacent formation with lower permeability.
Breaker, rotary—A rotating-drum coal-crushing machine with internal lifting
vanes, and with holes in the drum shell which pass the largest size of
coal desired.
Bulk density—Bulk density is the weight per unit volume of aggregates of
materials. The usual units of bulk density are pounds per cubic foot
(PCF). This includes the weight of the moisture in the aggregate. The
solid material must necessarily be in pieces and air fills the voids in
the aggregate volume.
Classification—Classification is a "sizing" process where the effects of
specific gravity of the particles is a factor in the separation. When
a sizing is carried out on screens the particle must pass through a
given hole size and thus particle dimensions are of primary importance.
Classification, in contrast, is usually a solid-particle-in-a-fluid
sizing process where heavy fine particles can join lighter coarse
particles.
Coefficient of permeability—The rate of flow of a fluid through a unit cross
section of a porous mass under a unit hydraulic gradient at a standard
temperature is called the coefficient of permeability.
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Compressive strength—Resistance of material to rupture under compression,
expressed as force per unit area.
Concentration—Concentration is the term applied to the amount of any substance
occurring in a given amount of water—the common unit is parts per million
(ppm) or milligrams per liter (mg/1).
Degradation—The breakage of coal caused by weathering or handling.
Density—A synonym for specific gravity, which might be solid density, liquid
density, or an overall density of a composite of solids and liquids.
Dewatering—Removal of excess surface moisture.
Distribution—The percentages of each density fraction of the raw coal that
reports to the clean coal. Distribution has a different value, as a rule,
for each density fraction and for each size range of the given density
fraction.
Flotation, froth—A mechanical/chemical process based on the selective adhesion
of some solids in suspension to air bubbles while other solids in the
suspension selectively adhere to water. A separation occurs when finely
disseminated air bubbles are passed through a feed-coal slurry. The
clean coal adheres to the bubbles while other solids in the suspension
rise to the surface, where the forming froth is skimmed off and dewatered.
The refuse tends to stay in suspension.
Hardness—A measure of the ease with which a coal may be made into a pulver-
ized fuel. Thus, it is an indirect measure of the energy required to
reduce a coal in size.
Inherent moisture—Bed moisture, as opposed to extraneous moisture. Inherent
moisture is directly related to the rank of the coal.
Mesh size—Mesh size, or "screen mesh size," has several standards. The most
common standard in the coal industry is the "Tyler square-root-of-two
series" and is the standard followed generally in U.S. research. ASTM
specifications D-410, D-431, E-ll, and E-323 include complementary mesh
openings. ASTM standard E-ll contains the U.S.A. Standard Series.
Primary dewatering screen—A screen used in a coal preparation plant to
receive all the coal and water from the washer. It may or may not be
followed by further dewatering screens.
Rank, coal—The degree to which the original coal-forming material has been
changed by metamorphism through successive states from peat to anthracite.
Refuse—Washed or separated waste material from the raw coal which was the
object of the cleaning process. This material is also called "gob,"
"slate," or "hutch."
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Secondary dewatering screen—A secondary dewatering screen follows a primary
dewatering screen and dewaters and classifies the smaller sizes in a coal
preparation plant.
Sieve Bend—A sieve bend is a rigidly spaced and truly fixed screen used for
preliminary sizing and dewatering of coal ahead of vibrating screens and
centrifuges. It is a stationary, curved, wedge bar screen with the bars
oriented at right angles across the line of flow.
Sieve scale—A sieve scale is a list of apertures of successively smaller
screens and step sizing operation. The sieve ratio is the ratio of the
aperture of a given screen and a given sieve scale to the aperture of the
next finer screen.
Slurry—A suspension of solids in water. Coal slurries range between about
3% and 50% solids and are the form in which coal is fed to cyclones,
hydrocyclones, and flotation cells.
Specific gravity—Specific gravity is the weight of a substance as compared
to the weight of an equal volume of water. From the standpoint of coal
preparation, it is the single most important physical property of coal.
Sulfur—Sulfur occurs in coal in four basic forms: native or free sulfur,
sulfate sulfur, pyritic sulfur, or organic sulfur.
Suspended solid—A solid dispersed in a liquid or gas, usually in particles
of larger than colloidal size. The particles are mixed with but undis-
solved in the fluid.
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/7-78-222
3. RECIPIENT'S ACCESSION*NO.
4. TITLE AND SUBTITLE
Pollution Control Guidelines for Coal Refuse Piles
and Slurry Ponds
5. REPORT DATE
November 1978 issuing date
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
W. A. Wahler and Associates
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
W. A Wahler and Associates
1023 Corporation Way
Palo Alto, California 94303
10. PROGRAM ELEMENT NO.
EHE623 EHB-526
11. CONTRACT/GRANT NO.
68-03-2344 & 68-03-2431
12. SPONSORING AGENCY NAME AND ADDRESS
Industrial Environmental Research Lab.
Office of Research & Development
U.S. Environmental Protection Agency
Cincinnati. Ohio 45268
- Cinn, OH
13. TYPE OF REPORT AND PERIOD COVERED
•ESr.a1 19/7"; - 7/77
14. SPONSORING AGENCY CODE
EPA/600/12
15. SUPPLEMENTARY NOTES
Combined-Final Report for Contracts 68-03-2344 and 68-03-2431
16. ABSTRACT
A large percentage of the eastern coal mined today is washed and processed to
remove impurities and increase quality. The wastes from the preparation process pose
a serious disposal problem. The study investigated acid and heavy metal ion concen-
trations in water passing through refuse piles, suspended solids in waters from refuse
areas and slurry ponds, noxious gases from oxidation and fires in refuse piles, and
airborne particulates from dry exposed refuse surfaces.
The report compiles information on construction practices applicable to pollution
control from coal refuse disposal sites. Water pollution from old, acid-producing
refuse piles and erosion of steep refuse banks was found to be a serious concern, as
was pollution caused by suspended solids from slurry ponds. Present placement proce-
dures combined with removal of a higher percentage of coal from refuse have restricted
the burning bank problems to older disposal sites. With proper planning, coal refuse
disposal sites can be put to useful purposes and become an asset rather than a liabil-
ity.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/GlOUp
coal mines
waste disposal
dust control
air pollution
coal dust
ponds
pollution control
acid mine drainage
slurry ponds
refuse piles
Eastern United States
13B
18. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (ThisReport)
Unclassified
21. NO. OF PAGES
224
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
214
«us GovouumnniiiinMiOFrict I979457-060/1542
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