EPA-440/9-75-007
INACTIVE & ABANDONED
UNDERGROUND MINES
Water Pollution Prevention & Control
U.S. ENVIRONMENTAL PROTECTION AGENCY
Washington, D.C. 20460
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This report is issued under Section 304(e)(2)(B) of Public Law 92-500. This
Section provides:
"The Administrator, after consultation with appropriate Federal and State
agencies and other interested persons, shall issue to appropriate Federal
agencies, the States, water pollution control agencies, and agencies
designated under Section 208 of this Act, within one year after the
effective date of this subsection (and from time to time thereafter)
information including. . . (2) processes, procedures, and methods to
control pollution resulting from —
(B) mining activities, including runoff and siltation from new, currently
operating, and abandoned surface and underground mines;..."
This publication is the second in a series issued under Section 304(e)(2)(B) of
Public Law 92-500 concerning the control of water pollution from mining activities.
The first report, "Processes, Procedures and Methods to Control Pollution from
Mining Activities", was issued in October 1973 (Publication
No. EPA-430/9-73-011).
This report provides technical and cost information on alternative
control measures. Sufficient descriptive information is provided to guide the
reader in the tentative selection of alternative measures to be applied in specific
cases. The details of application and methods of construction of each measure
must be ascertained on a case-by-case basis by qualified professionals in the
mining and water pollution control fields.
Mark A. Pisano, Director
Water Planning Division
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INACTIVE AND ABANDONED UNDERGROUND MINES
Water Pollution Prevention and Control
Preparded for
Office of Water and Hazardous Materials
United States Environmental Protection Agency
Washington, D.C. 20460
JUNE, 1975
*
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ACKNOWLEDGMENTS
This report was prepared by Michael Baker, Jr., Inc., Beaver, Pennsylvania, for
the Nonpoint Sources Branch, Water Planning Division, Office of Water and
Hazardous Materials (Contract No. 68012907).The Project Officers for EPA were
Edgar A. Pash and Charles P. Vanderlyn. Principal investigators in this study were
R. Lennie Scott and Ronald M. Hays.
The assistance and cooperation received from representatives of Federal, State
and local agencies, and industry, is gratefully acknowledged.
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ABSTRACT
Underground mining operations across the United States produce a number of
environmental problems. The foremost of these environmental concerns is acid
discharges from inactive and abandoned underground mines that deteriorate streams,
lakes and impoundments. Waters affected by mine drainage are altered both
chemically and physically.
This report discusses in Part I the chemistry and geographic extent of mine
drainage pollution in the United States from inactive and abandoned underground
mines; underground mining methods; and the classification of mine drainage control
techniques. Control technology was developed mainly in the coal fields of the
Eastern United States and may not be always applicable to other regions and other
mineral mining.
Available at-source mine drainage pollution prevention and control techniques
are described and evaluated in Part II of the report and consist of five major
categories: (1) Water Infiltration Control; (2) Mine Sealing; (3) Mining Techniques;
(4) Water Handling; and (5) Discharge Quality Control. This existing technology is
related to appropriate cost data and practical implementation by means of examples.
A summary of the mineral commodities mined in the United States follows
Part II and relates to type, locale and environmental effects.
A list of minerals, mineral formulas, glossary and extensive bibliography are
included to add to the usefulness of this report.
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CONTENTS
Acknowledgments i
Abstract ii
Figures vii
Tables ix
Abbreviations and Symbols x
I Underground Mines and Water Pollution 1
1.0 Mine Drainage Pollution in the United States 3
2.0 Chemistry of Mine Drainage Pollution 9
3.0 Environmental Effects of Pollution 21
4.0 Methods of Underground Mining 25
5.0 Control of Mine Drainage 35
H Manual of At-Source Pollution Control Techniques 39
1.0 Water Infiltration Control 43
1.1 General Discussion 45
1.2 Subsidence Sealing and Grading 46
1.3 Borehole Sealing 54
1.4 Surface Regrading 59
1.5 Surface Sealing 70
1.6 Surface Water Diversion 73
1.7 Channel Reconstruction 77
2.0 Mine Sealing 81
2.1 General Discussion 83
2.2 Dry Seals 87
2.3 Air Seals 93
2.4 Hydraulic Seals 106
2.4-1 Double Bulkhead Seal 109
2.4-2 Single Bulkhead Seal 119
2.4-3 Permeable Limestone Seal 132
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CONTENTS (Cont.)
2.4-4 Gunite Seal 145
2.4-5 Clay Seal 151
2.4-6 Grout Bag Seal 159
2.4-7 Shaft Seal 164
2.4-8 Gel Material Seal 169
2.4-9 Regulated Flow Seal 173
2.5 Curtain Grouting ]75
3.0 Mining Methods 181
3.1 General Discussion 183
3.2 Downdip Mining 184
3.3 Longwall Mining 188
3.4 Daylighting 191
4.0 Water Handling 195
4.1 General Discussion 197
4.2 Evaporation Ponds 198
4.3 Slurry Trenching 200
4.4 Alkaline Regrading 211
4.5 Controlled Release Reservoirs 216
4.6 Connector Wells 219
5.0 Discharge Quality Control 223
5.1 General Discussion 225
5.2 Mine Backfilling 226
5.3 Pressurizing With Inert Gas 231
5.4 Underground Precipitation 234
III Mineral Commodities Mined 239
1.0 Ferrous Metals 243
1.1 Chromium 245
1.2 Cobalt ' ' 245
1.3 Columbium 246
IV
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CONTENTS (Cont)
"'age
1.4 Iron 246
l.S Manganese 249
1.6 Molybdenum 249
1.7 Nickel 250
1.8 Rhenium 251
1.9 Silicon 251
1.10 Tantalum 252
1.11 Tungsten 252
1.12 Vanadium 254
2.0 Nonferrous Metals 255
2.1 Aluminum 257
2.2 Antimony 257
2.3 Arsenic 258
2.4 Beryllium 258
2.5 Bismuth 259
2.6 Cadmium 259
2.7 Cesium 260
2.8 Copper 260
2.9 Gallium 263
2.10 Germanium 264
2.11 Gold 264
2.12 Hafnium 265
2.13 Indium 266
2.14 Lead 266
2.15 Magnesium 268
2.16 Mercury 269
2.17 Platinum-Group Metals 270
2.18 Radium 270
2.19 Rare-Earth Elements 271
2.20 Rubidium 271
2.21 Scandium 272
2.22 Selenium 272
2.23 Silver 272
2.24 Tellurium 274
2.25 Thallium 275
2.26 Tin 275
2.27 Titanium 275
2.28 Zinc 276
2.29 Zirconium 278
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CONTENTS (Cont.)
3.0 Nonmetals .................... 279
3.1 Asbestos .................. 281
3.2 Barium ................... 282
3.3 Boron ................... 282
3.4 Clays ................... 283
3.5 Corundum and Emery ............. 284
3.6 Diamond .................. 284
3.7 Diatomite .................. 284
3.8 Feldspar .................. 285
3.9 Fluorine .................. 285
3.10 Garnet ................... 286
3.11 Gem Stones ................. 286
3.12 Graphite .................. 287
3.13 Gypsum .................. 287
3.14 Kyanite and Related Minerals .......... 287
3.15 Lithium .................. 288
3.16 Mica .................... 288
3.17 Perlite ................... 288
3.18 Phosphorous ................. 288
3.19 Potassium .................. 290
3.20 Pumice ................... 290
3.21 Salt .................... 291
3.22 Sand and Gravel ............... 291
3.23 Soda Ash .................. 291
3.24 Stone ................... 292
3.25 Strontium .................. 292
3.26 Sulfur ................... 293
3.27 Talc .................... 293
3.28 Vermiculite ................. 294
4.0 Energy Sources ................... 295
4.1 Coal .................... 297
4.2 Thorium ................. 290
4.3 Uranium .................. 299
IV Glossary of Terms
V List of Minerals ..................... ~ , ~
VI Bibliography
v
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FIGURES
:ure Page
I Underground Mines and Water Pollution
4.0-1 Methods of Entry to Underground Coal Mines 28
4.0-2 Room and Pillar Method of Mining 29
4.0-3 Method of Shrinkage Sloping 30
4.0-4 Method of Cut and Fill Sloping 31
4.0-5 Method of Square-Set Sloping 33
II Manual of At-Source Pollution Control Techniques
1.2-1 Infiltration of Water Through Subsided Area 47
1.2-2 Subsidence Hole Backfill, Blacklegs Watershed 52
1.3-1 Typical Method of Borehole Sealing with Cement Grout . . . . .55
1.3-2 Typical Method of Borehole Sealing with Rock and Concrete . . . 56
1.4-1 Cross Section of Typical Contour Regrading 60
1.4-2 Cross Section of Typical Terrace Regrading 61
1.4-3 Typical Regrading Methods Elkins, W. Va. 62
1.4-4 Typical Regrading Underground Mine Dents Run, W. Va 66
1.4-5 Typical Regrading Auger Hole Dents Run, W. Va 67
1.6-1 Proposed Water Diversion Ditch Cherry Creek, Maryland 75
1.7-1 Reconstructed Channel, Blacklegs Creek 79
2.2-1 Typical Dry Seals, 1930's Sealing Project 88
2.2-2 U.S. Bureau of Mines Dry Seal 90
2.3-1 Typical Air Seals, 193 O's Sealing Project 94
2.3-2 U.S. Bureau of Mines Air Seal 98
2.3-3 Typical Air Seal Shavers Fork, West Virginia 102
2.4-1-1 Quick Setting Double Bulkhead Seal Clarksburg, W. Va Ill
2.4-1-2 Construction Drawing of Deep Mine Seal 113
2.4-2-1 Secondary Concrete Block Bulkhead, Saxton Mine . . . .. . . .121
2.4-2-2 Design of Primary Bulkhead Used at Saxton 122
2.4-2-3 Design of Primary Bulkhead Used at Saxton Mine 123
2.4-2-4 Single Bulkhead Concrete Seal-Butte, Montana 124
2.4-2-5 Grouted Aggregate Bulkhead, Mine No. 40-016 126
2.4-2-6 Quick Setting Bulkhead Seal, Clarksburg, W. Va 128
2.4-3-1 Typical Cross Section of Permeable Aggregate Seal 133
2.4-3-2 Permeable Limestone Seal - Mine RT5-2, Opening No. 2 .... 135
2.4-3-3 Permeable Limestone Seals - Stewartstown, W. Va 137
2.4-4-1 Typical Gunite Seal 146
2.4-4-2 Proposed Gunite Seal, Cherry Creek Watershed 147
2.4-5-1 Cross Section Typical Clay Seal 152
2.4-5-2 Clay Seal, Shaw Mine Complex 154
2.4-5-3 Proposed Clay Seal, Cherry Creek Watershed 157
Vll
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FIGURES (Cont.)
;ure Page
2.4-6-1 Cross Section of Expendable Grout Retainer Underground
Mine Seal 160
2.4-6-2 Grout Bag Seal Mine No. 14-042A Clarksburg, W. Va 161
2.4-7-1 Cross Section Typical Shaft Seal 165
2.4-7-2 Shaft Seal with Concrete Slab 166
2.4-8-1 Arrangement of Proposed Gel Material Seal 170
2.4-8-2 Injection Procedure for Gel Material 171
3.3-1 Typical Longwall Plan 189
3.4-1 Daylighting of Abandoned Underground Mines 192
4.3-1 Typical Slurry Trench Detail 201
4.3-2 Slurry Trench Construction Rattlesnake Watershed, Pa 202
4.3-3 Typical Slurry Trench Profile Elk Creek, W. Va 206
4.3-4 Typical Slurry Trench Cross Sections Elk Creek, W. Va 207
4.4-1 Typical Alkaline Regrading 212
4.4-2 Typical Alkaline Regrading, Elk Creek, W. Va 214
4.6-1 Interception of Aquifers by Connector Wells 220
5.2-1 Backfilling Abandoned Underground Mines with Coal Refuse . . .227
5.4-1 ' Plan of Bulkheads Piping, Weirs and Portal Driscoll No. 4
Mine Vintondale, Pennsylvania 235
vm
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TABLES
Table Page
I Underground Mines and Water Pollution
1.0-1 Abandoned and Inactive Underground Mines in the
United States as of 1966 6
2.0-1 Mine Drainage Classes 12
2.0-2 Sulfides and Sulfosalts ... 14
II Manual of At-Source Pollution Control Techniques
1.4-1 Direct Cost of Surface Reclamation by Various
Methods on Selected Work Areas Elkins, W. Va. 64
1.4-2 Regrading Costs Dents Run Watershed 68
2.3-1 Expenditures October 1, 1937 to September 1, 1967,
1930's Mine Sealing Project 96
2.3-2 Analysis of Mine Water Samples Mine RT 9-11 104
2.4-1-1 Contract Estimates Mine Sealing — Stone
House Area Bulter County, Pennsylvania 115
2.4-3-1 Labor Costs Permeable Limestone Seals
Stewartstown, W. Va 139
2.4-3-2 Equipment Costs Permeable Limestone Seals
Stewartstown, West Virginia 140
2.4-3-3 Incorporated Materials Permeable Limestone
Seals Stewartstown, West Virginia . 141
2.4-3-4 Miscellaneous Costs Permeable Limestone
Seals Stewartstown, West Virginia 142
5.2-1 Costs of Hydraulic Backfilling Rock
Springs, Wyoming 229
III Mineral Commodities Mined
2.8-1 Minerals of Copper 261
IX
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ABBREVIATIONS AND SYMBOLS
AASHO - American Association of State Highway Officials
ac — acre(s)
cfm — cubic foot (feet) per minute
cu m — cubic meter(s)
cu m/hr — cubic meter(s) per hour
cu yd — cubic yard(s)
EPA — Environmental Protection Agency
gal/acre/day — gallon(s) per acre per day
gal/hour — gallon(s) per hour
gpm — gallon(s) per minute
ha — hectare(s)
hr — hour(s)
I.D. — inside diameter
kg — kilogram(s)
kg/day — kilogram(s) per day
Ib/acre — pound(s) per acre
Ib/day — pound(s) per day
LF — linear foot (feet)
LM — linear meter(s)
MGD — million gallons per day
mg/1 — milligram(s) per liter
O.D. — outside diameter
psi — pound(s) per square inch
SCFH — standard cubic feet per hour
sq ft — square foot (feet)
sq m — square meter(s)
sq yd — square yard(s)
tons/day — tons per day
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I
UNDERGROUND MINES
AND WATER POLLUTION
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1.0
MINE DRAINAGE POLLUTION
IN THE UNITED STATES
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In the United States water pollution resulting from mining activities has long
been recognized as a major environmental problem. Mine drainage pollution results
from many types of mining activities and includes both physical (i.e., sedimentation)
and chemical (i.e., acidification, metal contamination, etc.) pollutants. Active and
abandoned surface and underground mines, mineral processing plants, mine and
processing plant waste disposal areas, haulage roads, and tailing ponds are typical
sources of mine related water pollution (130).
One of the most serious pollution problems arising from mining activities is
acid mine drainage resulting from the chemical reaction of sulfide minerals
(commonly iron sulfides) and air in the presence of water. Acid mine drainage is
commonly associated with coal and hard rock mining areas in the United States. In
general the more serious and extensive acid mine drainage problems exist in the
more humid coal regions east of the Mississippi River (11). In 1964 the U.S.
Department of the Interior, Fish and Wildlife Service, reported that acid mine
drainage adversely affected fish and wildlife habitat in 9,477 kilometers
(5,890 miles) of streams and 6,062 hectares (14,967 acres) of impoundments in
20 states in the United States (64). Of the total affected waters, coal mining
operations accounted for 97 percent of the acid mine drainage pollution reported
for streams and 93 percent of that reported for impoundments.
In 1970 more than 19,308 kilometers (12,000 miles) of streams in the United
States were reportedly significantly degraded by mining related pollution (130). Of
the total affected kilometers, 16,920 kilometers (10,516 miles) or approximately
88 percent were located in the Appalachian coal region (Pennsylvania, West Virginia,
Ohio, eastern Kentucky, Tennessee, Maryland, and Alabama). In addition, more
than 965 kilometers (600 miles) of streams reportedly were degraded by coal mining
in states in the Illinois, Western Interior, and Rocky Mountain coal regions. The
remaining portion of the stream pollution resulted from the mining of: (1) copper
(California, Montana, Nevada, New Hampshire, Tennessee, Virginia, and Wyoming);
(2) lead and zinc (Colorado, Idaho, Kansas, Missouri, Montana, Oklahoma, and
Tennessee); (3) uranium (Rocky Mountain States); (4) iron (Lake Superior iron
region); (5) sand and gravel (all states); (6) phosphate (Florida and other states);
(7) gold (Alaska); (8) bauxite and barite (Arkansas); and (9) molybdenum, gold, and
other metals (Colorado).
Abandoned mines and abandoned mine waste disposal areas contribute a large
portion of the total pollution resulting from mining activities. Numerous abandoned
underground mines are located throughout the United States and many are
discharging mine drainage pollutants. In 1966 the U.S. Bureau of Mines estimated
that more than 88,000 inactive and abandoned underground mines were in
existance (126). A listing of these mines by state is presented in Table 1.0-1. More
recent estimates indicate that this list is incomplete. In Colorado alone there is
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Table 1.0-1
Abandoned and Inactive Underground Mines
In The United States as of 1966
State
Alabama
Alaska
Arizona
Arkansas
California
Colorado
Connecticut
Delaware
Florida
Georgia
Hawaii
Idaho
Illinois
Indiana
Iowa
Kansas
Kentucky
Louisiana
Maine
Maryland
Massachusetts
Michigan
Minnesota
Mississippi
Missouri
Montana
Nebraska
Nevada
New Hampshire
New Jersey
New Mexico
New York
North Carolina
North Dakota
Ohio
Oklahoma
Oregon
Pennsylvania
Rhode Island
South Carolina
Coal
310
6
269
32
565
115
11
1,605
960
1,138
528
12,045
564
1
466
334
48
5
2,187
251
61
7,824
Metal
64
773
186
3,045
1,699
6
62
1,749
39
60
681
4
7
7
7
278
87
1,520
1,691
1,346
24
26
277
61
78
12
35
283
1,140
160
2
30
Nonmetal
27
6
82
7
3
28
208
124
2
13
120
1
1
6
1
36
146
10
3
23
17
1,129
53
3
55
4
17
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Table 1.0-1 (cont.)
State Coal Metal Nonmetal
South Dakota 1 172
Tennessee 2,931 42 11
Texas 21 31
Utah 44 1,348 8
Vermont — 17 3
Virginia 14,397 14 6
Washington 247 907 52
West Virginia 20,616 — 9
Wisconsin ~ 389 1
Wyoming 2£ 295 —
Total 67,613 18,654 2,215
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reportedly more than 10,000 abandoned prospector pits. Recent studies estimate
that in excess of 200,000 inactive and abandoned underground mines exist in the
United States.
All abandoned underground mines do not discharge mine drainage pollutants.
The extent and distribution of pollution discharging from abandoned underground
mines will depend upon such factors as: hydrology, geology, topography, and
climatology of the mine site; extent and method of mining; availability of air and
water; and the distribution of sulfide minerals.
For many years abandoned underground coal mines have been recognized as
major sources of mine drainage pollution. Of the sources of mine drainage pollution
located and described in Appalachia during 1964 to 1968 by the Federal Water
Pollution Control Administration, abandoned underground mines were found to
contribute 52 percent of the acid discharged to streams (130). In 1973 acid
production from abandoned eastern underground mines totaled more than
2.3 million kilograms per day (5 million Ib/day), which was the largest single source
of acid mine drainage pollution in the United States.
Acid mine discharges from abandoned non-coal mines do occur in the United
States, but reportedly are not as severe or extensive as coal mine drainage. Many
non-coal underground mines are developed below drainage, and therefore naturally
flood when they are abandoned. Mines located in arid or semi-arid areas of the West
are less likely to discharge, since water is not readily available to transport
pollutants. However, adverse environmental effects resulting from the discharge of
pollutants from abandoned, underground non-coal mines have been documented in
the Rocky Mountain States and other mining areas of the United States.
REFERENCES
1,5, 11,23,34,50,63,64,80,93,94,96,120, 120, 126, 128, 129, 130, 131
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2.0
CHEMISTRY OF MINE
DRAINAGE POLLUTION
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Mine drainage may be defined as ground or surface water draining or flowing
from, or having drained or flowed from, a mine or area affected by mining activities.
The type and characteristics of drainage produced by a particular mine or mined
area will depend upon the mineral commodity mined and the nature of the
surrounding geologic formations. Waters affected by mine drainage typically are
altered chemically by the addition of iron, sulfate, acidity (or alkalinity), hardness,
dissolved solids, and various metals and altered physically by the addition of
suspended solids such as silt and sediment (1, 54).
The characteristics of mine drainage range from acid to neutral to alkaline.
Acid mine drainage is generally defined as having a low pH, net acidity, high iron,
high sulfates, and significant concentrations of aluminum, calcium, magnesium, and
manganese. Alkaline mine drainage is generally defined as having a pH near or
greater than neutrality, net alkalinity, high sulfates, low aluminum, and significant
concentrations of calcium, magnesium and manganese (54). Based upon studies
performed by the Federal Water Pollution Control Administration, a classification of
mine drainage has been developed. These four classes are presented in Table 2.0-1.
Alkaline mine drainage usually does not have as severe adverse effects upon the
environment as does acid mine drainage. Alkaline drainage may result where no acid
producing minerals are associated with a mineral body or where neutralization of
acid drainage has occurred. In underground mine situations, alkaline drainage may
become acid as the result of the oxidation and hydrolysis of ferrous iron. The
potential for alkaline drainage exists in many mining areas of the West where
overburden material is highly alkaline and sometimes saline. However,
documentation of alkaline and saline drainage problems is almost nonexistent (59).
Acid mine drainage results from the oxidation or decomposition of sulfides and
sulfosalts which are commonly associated with mineral bodies. The general formula
for sulfides is AmXn where A consists of the metallic elements or sometimes arsenic,
antimony, and bismuth. Elements of sulfides are (49, 51):
Ag
Cu
Tl*
Au*
Fe
Co
Ni
Zn
Pb
Hg
Mn*
Ca*
Cd
As
Sb*
Bi*
Pt*
Ru*
Sn*
Mo*
W*
S As
Se Sb*
Te Bi*
*Rare or uncommon
11
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Table 2.0-1
Mine Drainage Classes
pH
Acidity, mg/1 (CaCO3)
Ferrous Iron, rag/1
Ferric Iron, mg/1
Aluminum, mg/1
Sulfate, mg/1
Class 1
Acid Discharges
2 - 4.5
1,000 - 15,000
500 - 10,000
0
0 - 2,000
1,000 - 20,000
Class 2
Partially Oxidized
ard/or
Neutralized
3.5 - 6.6
0 - 1,000
0 - 500
0 - 1,000
0-20
500 - 10,000
Class 3
Oxidized and
Alkaline
6.5 - 8.5
0
0
0
0
500 - 10,000
Class 4
Neutralized
and
Not Oxidized
6.5 - 3.5
0
50 - 1,000
0
0
500 - 10,000
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The general formula for sulfosalts is AmBnXp. The major elements of the
sulfosalts are:
A JL 2L
Cu As S
Ag Sb
Pb Bi
Sn Sn
Due to the number of chemical elements and the complexity of composition,
the diversity of chemical combinations is great. More than 125 sulfides and sulfosalts
are known to occur naturally. Thus, the potential for trace metals in discharges from
mines is also present. A list of naturally occurring sulfides and sulfosalts is presented
in Table 2.0-2.
The most common sulfides are the sulfides of iron (pyrite, marcasite, and
pyrrhotite). Pyrite (FeS2) is the most common and abundant of sulfide minerals
known. Marcasite is found in surface or near surface deposits and is more frequently
associated with limestone, clays and lignite. Pyrrhotite is commonly associated with
pentlandite ((Fe,Ni)9Ss) and other sulfides. It is given the formula Fei-xS where x
varies from 0 to 0.2 (49).
The oxidation of these iron sulfides in the presence of air water is responsible
for the formation of acid drainage from mines. In recent years much research
regarding the oxidation of FeS2 has been conducted in the Appalachian coal region
of the United States. The following equations represent the basic chemical reactions
which describe an acid drainage situation:
FeS2(s) + 7/2 O2 + H2O = Fe+2 + 2SO4'2 + 2H+ (1)
Fe+2 + 1 /4 02 + H+ = Fe+3 + 1 /2 H2O (2)
Fe+3 + 3H2O = FeOHs(s) +3H+ (3)
FeS2(s) + 14Fe+3 + 8 H2O = 15Fe+2 + 2SO4'2 + 16H+ (4)
Equation 1 represents a heterogenous reaction involving crystalline pyrite with
gaseous or dissolved oxygen and liquid or vapor water. As can been seen from the
equation, oxygen oxidizes the sulfide in pyrite to sulfate. The basic function of the
water is to transport the oxidized material from the surface as accumulation of these
products will affect the oxidation rate.
13
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Table 2.0-2
Sulfides and Sulfosalts
Aquilarite — Ag4SeS
Alkalinite - PbCuBiSs
Alabandite — MnS
Alaskaite - Pb(Ag,Cu)2Bi4S8 possibly
Andorite - PbAgSbsSe
Aramayoite - Ag(Sb,Bi)S2
Argentite - Ag2S
Argyrodite - AggGeS6
Arsenopyrite - FeAsS
Baumhauerite — Pb4AsgS ] 3
Beegerite - Pb6Bi2S9
Benjaminite — Pb(Cu,Ag)Bi2S4 possibly
Berthierite - FeSb2S4
Berthonite -
Bismuthinite —
Bornite - CusFeS4
Boulangerite - PbsSb4Sl i
Bournonite - PbCuSbSs
Braggite - (Pt,Pd,Ni)S
Bravoite - (Ni,Fe)S2
Canfieldite - AggSnS6
Chalcocite - Cu2S
Chalcopyrite - CuFeS2
Chalcostibite - CuSbS2
Chiviatite - PbsBigSjs possibly
Cobaltite - CoAsS
Colusite - Cu3(As,Sn,V,Fe,Te)S4
Cooperite - PtS
Cosalite -
Covellite - CuS
Cubanite -
Cylindrite -
Daubreelite - Cr2FeS4
Diaphorite -
Digenite - Cu2-x§
Dimorphite —
Dufrenoysite -
Emplectite - CuBiS2
Enargite -
14
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Table 2.0-2 (cont.)
Famatinite - CusSbS4
Fizelyite - PbsAg2Sb8Si8 possibly
Franckeite -
Freieslebenite -
Fuloppite -
Galena - PbS
Galenobismutite — PbBi2S4
Geocronite - Pbs(Sb,As)2S8
Germanite - (Cu,Ge)(S,As)
Gersdorffite - NiAsS
Gladite - PbCuBisSg
Glaucodot - (Co,Fe)AsS
Gratonite - Pb9As4Sis
Greenockite — CdS
Gruenlingite - Bi4TeSs or near Bi2(Te,Bi)S2
Gudmundite - FeSbS
Guitermanite — Pb i QAs6S 19
Hammarite -
Hauerite — MnS2
Heteromorphite -
Hutchinsonite - (Pb,Tl)2(Cu,Ag)AssSio
Jamesonite -
Jordanite -
Joseite - Bi3Te(Se,S)
Kermesite -
Klaprothite -
Kobellite - Pb2(Bi,Sb)2Ss
Laurite - RuS2
Lautite - CuAsS
Lengenbachite - Pbg(Ag,Cu)2As4S 13
Lillianite - Pb3Bi2S6
Linstromite — PbCuBi3S6
Linnaeite Series - (Co,Ni)2(Co,Ni,Fe,Cu)S4
Livingstonite - HgSb4S7
Loellingite - FeAsS2
Lorandite - TiAsS2
Marcasite — FeS2
Matildite - AgBiS2
Meneghinite -
Metacinnabar — HgS
Miargyrite — AgSbS2
15
-------
Table 2.0-2 (cont.)
Millerite - NiS
Molybdenite - MoS2
Nagyagite - Pb5Au(Te,Sb)S5-g
Oldhamite - GaS
Orpiment —
Owheeite -
Pearceite - AgJ6As2Si1
Pentlandite - (Fe,Ni)9Sg
Plagionite - (PbsSbgSn)
Platynite - PbBi2(Se,S)3
Polybasite -
Proustite -
Pyrargyrite -
Pyrite - FeS2
Pyrostilpnite -
Pyrrhotite - Fei-xS (x lies between 0 and 0.2)
Ramdohrite -
Rathite - Pb 13As 18 840
Realgar — AsS
Rezbanyite -
Samsonite —
Sartorite - PbAs2S4
Schirmerite -
Seligmannite — PbCuAsSs
Semseyite - Pb9Sb8S21
Smithite - AgAsS2
Sphalerite — ZnS
Stannite - Cu2FeSnS4
Stephananite — AgsSbS4
Sternbergite - AgFe2Ss
Stibnite - Sb2Ss
Stromeyerite — AgCuS
Sulvanite - CusVS4
Teallite - PbSnS2
Tennantite - (Cu,Fe)i2As4Si3
Tetradymite - Bi2Te2S
Tetrahedrite - (Cu,Fe)i2Sb4Si3
Tungstenite — WS2
Ullmannite - NiSbS
Voltzite - ZnsS4O
Wehrlite - BigTesS possibly
16
-------
Table 2.0-2 (cont.)
Weibullite - PbBi2(S,Se)4
Wittichenite - CuaBiSa
Wittite - Pb5Bi6(S,Se)i4
Wurtzite - ZnS
Xanthoconite —
Zinkenite -
17
-------
The products of pyrite oxidation undergo additional reactions as shown in
Equations 2 thru 4. Ferrous iron produced by pyrite oxidation is oxidized to ferric
iron (Equation 2). The ferric iron hydrolyzes to form insoluble ferric hydroxide
(Equation 3). The ferric iron may be reduced by pyrite to form ferrous iron
(Equation 4) which is then available for oxidation via Equation 2..Four equivalents
of acidity are produced during this cycle. Two equivalents are produced during the
oxidation of sulfide and the remaining two with the resulting hydrolysis of ferric
iron.
The acid produced by the oxidation of iron sulfides lowers the pH of water
draining from the material. The iron sulfides are seldom pure and are commonly
associated with other sulfides or sulfosalts. As the iron sulfides oxidize, associated
sulfides and sulfosalts are oxidized or exposed to extreme chemical conditions which
result in their breakdown. This breakdown results in the release of metallic,
non-metallic, and sulfate ions to the environment (49, 51).
In addition to the chemical reactions involved in acid mine drainage formation,
certain bacteria are capable of oxidizing sulfide minerals. These bacteria are:
(1) Thiobacillus ferrooxidans
(2) Ferrobacillus ferrooxidans
(3) Thiobacillus sulfooxidans
These bacteria rely solely upon the oxidation of inorganic materials such as iron and
sulfur for their energy source. Presently, at least nineteen metallic sulfides and
sulfosalts are known to be oxidized by this bacteria group (49).
The concentration and number of different metal ions in acid mine drainage
will depend upon the sulfides and sulfosalts present, and the chemical characteristics
of the metal ion and water. Iron is the most common metal found in acid mine
drainage. The principal species are ferrous iron (Fe+2), ferric iron (Fe+3), ferrous
hydroxide (Fe(OH)2), and ferric hydroxide (Fe(OH)s). Metallic and non-metallic
ions may precipitate on may be carried away in solution. It is known that ions such
as copper, cobalt, manganese, zinc, and nickel all form soluble salts under acid mine
drainage conditions. However, lead forms relatively insoluble salts under similar
conditions and is rarely found in high concentrations in mine drainage
discharges (49). Analysis of mine drainage samples collected in the Appalachian coal
region by the Federal Water Pollution Control Administration revealed that zinc
18
-------
cadmium, beryllium, copper, silver, nickel, cobalt, lead, chromium, vanadium,
barium, and strontium were commonly found in concentrations less than one
milligram per liter (54).
REFERENCES
1, 21, 30, 34, 48, 49, 50, 51, 54, 59, 79, 102, 130
19
-------
3.0
ENVIRONMENTAL EFFECTS
OF POLLUTION
21
-------
The discharge of pollutants from inactive and abandoned underground mines
adversely affects the potential use of affected streams and impoundments in all
forms: domestic, industrial, recreational, navigational, municipal, and agricultural.
Acid production resulting from the oxidation and decomposition of sulfide minerals
is one of the most, if not the most, serious environmental problem resulting from
underground mining activities. Acid drainage results in the deterioration of receiving
waters by lowering pH, reducing alkalinity, increasing hardness, and adding
undesirable amounts of suspended material, and metallic and non-metallic ions.
Acid mine drainage can be extremely damaging to aquatic life. Acid waters
support only limited water flora, such as acid-tolerant molds and algae, and usually
will not support fish life. The coating of stream bottoms with precipitated metal
salts smothers invertebrate life, decreases oxygen content, and reduces the breeding
area for aquatic species. Metallic and non-metallic ions found in acid drainage are
often in concentrations sufficient to be harmful or even toxic to aquatic life. As
previously discussed (see Section 1.0), a 1964 report estimated that fish and wildlife
habitat were adversely affected by acid mine drainage in 9,477 kilometers
(5,890 miles) of streams and 6,062 hectares (14,967 acres) of impoundments in the
United States.
Physical mine drainage pollution (i.e., sedimentation and siltation) adversely
affects the environment by filling stream beds with sediment, destroying fish
habitat, and increasing treatment costs for industrial, municipal and domestic
supplies. Physical pollution problems commonly result from surface mining
activities. Underground mining results in little surface disturbance and subsequently
produces only minor physical pollution problems. However, mine waste piles usually
associated with underground mines are common sources of siltation and acid mine
drainage.
Some damages resulting from mine drainage pollution may be evaluated in
monetary terms. Treatment costs for municipal, industrial and other water uses will
increase as a result of additional treatment required and the replacement of
equipment damaged by polluted waters. Additional expenditures will also be
required for the inspection, maintenance, and early replacement of water structures
and equipment such as bridges, culverts, locks, boat hulls, pumps, and possibly
concrete structures. Water affected by mine drainage pollution may also be limited
for such recreational uses as fishing, boating, swimming, camping, and picnicking.
REFERENCES
1, 5, 48, 49, 64, 80, 120, 126, 128, 129, 130, 131
23
-------
4.0
METHODS OF
UNDERGROUND MINING
25
-------
Underground mining methods are those in which access to a mineral body is
made via shaft, slope, or drift entries. A shaft is a vertical entry employed when the
mineral is located a substantial distance under the ground surface, A slope entry is
an inclined shaft commonly developed when the mineral body is located at a
distance beyond the outcrop. A drift entry is a horizontal or near horizontal opening
driven into the outcrop of a mineral body (21). These methods of entry as used in .a
typical underground coal mine are depicted in Figure 4.0-1.
The particular underground method of mining employed will generally depend
upon the size and shape of the mineral body. In coal mining the two principal
underground methods are room and pillar, and longwall. In room and pillar mining,
main entries, cross entries, panel entries, and rooms are driven into the coal
seam (130). This method divides the underground mine into a series of mined out
rooms with pillars left for roof support. Although room and pillar mining is
primarily applied to coal mining, it may be utilized in the mining of any mineral that
occurs as a bedded deposit. Figure 4.0-2 shows a plan view of a typical room and
pillar system.
Longwall mining is a method of removing a mineral seam by means of a
longwall or working face which may exceed 305 meters (1,000 feet) in length. The
primary advantages of longwall mining are increased production and efficient
mineral recovery. Longwall mining is discussed in this manual (in conjunction with
downdip mining and daylighting) as a method of mining that may be implemented
to prevent or control the formation of mine drainage pollutants (See Part II,
Section 3.0 - Mining Methods).
Due to the irregular shape of ore bodies, metal, and non-metallic minerals are
generally mined by stoping methods. Sloping is a method of excavation in which a
mineral body is drilled, blasted, and removed by gravity through chutes to a haulage
level below (49). Three common stoping methods are: (1) shrinkage stope; (2) cut
and fill stope; and (3) square set stope.
The shrinkage stope is most used in steeply dipping vein deposits where the
walls and mineral body require little or no support. As the mineral is blasted
down,sufficient mineral is removed through the chutes, to allow miners to drill and
blast the next section (46,49). An example of the shrinkage stope is shown in
Figure 4.0-3.
The cut and fill stope is used in wider irregular mineral bodies. The mineral is
blasted down and removed from the stope. Prior to removal of the next section of
mineral, waste material is placed in the stope for wall support. This method of
mining is shown in Figure 4.0-4.
27
-------
=-
1—f—rr 0 . T~V. ; . .' ". Sandstone" °
Coal
SHAFT ENTRY
DRIFT ENTRY
SLOPE ENTRY
Coal
FIGURE 4.0-1
METHODS OF ENTRY TO UNDERGROUND COAL MINES
(Adapted from Ref. 129)
-------
Outcrop
FIGURE 4.0-2
ROOM and PILLAR METHOD OF MINING
29
-------
H
H
H
H
H
H
H
H
H
FIGURE 4.0-3
METHOD OF SHRINKAGE STORING
(Adapted from Ref. 130)
30
-------
S*A
1
II II II
Haulage Way
n n n
4««*N
•••«••;•.
• o B o o
0 0 « 9 <> _° ,°
FIGURE 4.0-4
METHOD OF CUT AND FILL STORING
(Adapted from Ref. 130)
31
-------
In a square-set stope, square-set timbers are used to support the walls as the
mineral is removed. After each blast, the square-set timbers are erected, chutes, and
man way are raised, and waste material is backfilled (49). The square-set stoping
method is shown in Figure 4.0-5.
REFERENCES
21, 46, 48, 49, 126, 128, 129, 130
32
-------
Flooring
Unbroken Mineral
Backfilled
Waste
Material
Standard
Timber Sets
FIGURE 4.0-5
METHOD OF SQUARE-SET STORING
33
-------
5.0
CONTROL OF MINE DRAINAGE
35
-------
Mine drainage control techniques may be divided into two major categories:
(1) at-source and (2) treatment. At-source techniques are those which are designed
to prevent or control the formation and/or discharge of mine drainage pollutants.
Treatment involves the collection and processing of mine drainage to produce a
water of quality suitable for discharge to the environment. In general, at-source
techniques appear to be more feasible than treatment for controlling pollution
discharges from abandoned underground mines. At-source techniques may be
permanent and not require continuous expenditures for maintenance and operation
as do treatment techniques. The various at-source techniques applicable to
abandoned underground mine situations are described in this manual.
Although the effects of mine drainage pollution have been recognized since the
1800's, little research and demonstration of methods for controlling this pollution
was performed prior to the 1930's. At this time various methods of mine sealing to
control pollution were investigated by the U.S. Bureau of Mines and other Federal
agencies. Beginning in the early 1960's an intense research and demonstration effort
was begun in the United States. As a result of this effort many at-source control
techniques applicable to active and abandoned surface and underground mines were
demonstrated with varying degrees of success.
Many of the at-source control techniques that have been developed to date are
applicable to abandoned underground mines. The demonstration of a majority of
these techniques has been limited to underground coal mines in the Appalachian
coal region. Therefore, the discussion of the various techniques in this manual in
general will be related to coal mines. However, in most instances the techniques
discussed are applicable to underground mines of all types.
REFERENCES
1,5,23,51,96,97,128,129,130
37
-------
II
MANUAL OF
AT-SOURCE POLLUTION
CONTROL TECHNIQUES
39
-------
This section will identify at-source pollution prevention and control techniques
applicable to inactive or abandoned underground mines, whose practicability or
feasibility have been successfully demonstrated or strongly indicated by research
results. These control measures have been classified under five major headings:
(1) Water Infiltration Control; (2) Mine Sealing; (3) Mining Techniques; (4) Water
Handling; and (5) Discharge Quality Control. Information on these pollution control
techniques includes a general description of each technique, a description and
evaluation of various applications, detailed cost information, an evaluation of the
effectiveness and practicability of each technique, and when applicable,
recommended procedures for selection and implementation.
41
-------
1.0
WATER INFILTRATION CONTROL
43
-------
1.1 GENERAL DISCUSSION
Water infiltration control techniques are designed to reduce the total volume of
water entering an underground mine, and thus, reduce the volume of mine water
discharge. During the development of underground mines, water may be
encountered in various quantities. This water must be pumped from the mine during
active mining, and in many situations, the weight of water removed will be more
than the total weight of mineral extracted. After abandonment of the mine,
infiltrating water either floods the mine workings or discharges from the
mine (27,127).
Infiltrating water may enter underground mines from above, below, or laterally
through adjacent rock strata. Earth fractures such as faults, joints, and roof fractures
resulting from surface subsidence are commonly primary causes of water entrance
into abandoned underground mines. Factors affecting the quantity of water entering
a mine will be the depth of the mine, location of water bearing strata, and ground
water flow patterns. Investigations of the quantity of water entering underground
coal mines have found the average rate of infiltration to range from approximately
6,262 to 10,280 liters per hectare per day (670 to 1,100 gal/acre/day) (27).
Water flowing through underground mines flushes pollutants from the mine
and may result in their discharge to the environment. A reduction in the amount of
flow usually results in a reduction in total pollution load discharging from the mine.
The techniques discussed in this section can be used to reduce the volume of surface
and groundwater available to enter the mine system and transport pollutants. The
selection of a control technique will depend upon the characteristics of the mine
system and the expected cost effectiveness of the technique. In order for water
infiltration control to be effective in controlling mine drainage pollution, the
reduction in mine water flow must not be accompanied by an increase in
concentration of pollutants (127).
REFERENCES
2,27,51,58, 127, 132
45
-------
1.2 SUBSIDENCE SEALING AND GRADING
DESCRIPTION
Before or after abandonment of underground mines, fracturing or general
subsidence of overlying strata often occurs. This increases the vertical permeability
of the strata, and can result in the flow of large volumes of water into the mine. The
volume of water diverted into the underground mine will depend upon the structure
of the overlying rock, and the surface topography and hydrology of the
area (21,27). A drawing depicting the vertical infiltration of water through a
subsided area is shown in Figure 1.2-1.
Water infiltration can be effectively controlled by increasing surface water
runoff. Grading subsidence areas will eliminate surface depressions and increase
surface water velocity. During the 1930's U.S. Public Health Service sealing program,
subsidence areas were either filled with earth or ditched on the downhill side to
prevent the accumulation of water.
Vertical permeability may be decreased by placing impermeable materials in
the subsided area. These materials may be compacted on the surface and graded, or
placed in a suitable sealing strata below groun level. Materials which have been
successfully utilized for subsidence sealing are rubber, clay, concrete, and cement
grout.
IMPLEMENTATION
Roaring Creek — Grassy Run Watershed
In 1964, a mine sealing demonstration program was initiated in the Roaring
Creek - Grassy Run Watershed near Elkins, West Virginia. The program was a
cooperative effort between Federal agencies and the state of West Virginia. Sealing
was to involve construction of dry and air seals, water diversion from mines,
backfilling strip mines, and sealing subsidence areas and boreholes (57, 101).
During a six month survey, a total of 1,563 subsidence areas, holes, and surface
cracks were located in the watershed. Of these 1,128 were located within 91 meters
(300 feet) of strip mine highwalls. In an effort to seal these openings, the U.S.
Bureau of Mines negotiated a cooperative agreement with the Dowell Division of the
Dowell Chemical Company, to experiment with chemical grouting of the subsidence
areas (37).
Five sites with cover ranging from 18.3 to 27.4 meters (60 to 90 feet) were
selected for the experimental program. At each site holes were drilled and a
cement-bentonite grout was pressure injected. The grout proved to be ineffective in
46
-------
FIGURE 1.2-1
INFILTRATION OF WATER
THROUGH SUBSIDED AREA
(Adapted from Ref. 21)
-------
sealing the areas. Extensive fracturing of underlying rock permitted the grout to
flow into abandoned workings in the Lower Kittanning coal seam. A total of
2,000 bags of cement and 200 bags of bentonite were used during grouting. Drilling
and grouting costs were $4,342 and $8,411, respectively, for a total cost of $12,753.
Successful sealing of subsidence areas may be achieved in areas where rock
fracturing is less severe. In such instances the grout will move laterally from the
injection holes and form a horizontal grout curtain. Grout injection has been
successful in sealing discharges from subsided areas and abandoned mine shafts.
Backfilling of subsidence areas was also demonstrated at the Elkins site. Within
individual subsidence areas, vegetation was cleared and weathered material was
removed by dozer down to bedrock. The weathered material, plus suitable material
from other areas, was backfilled in 31 to 61 centimeter (12 to 24 inch) layers and
compacted. The areas were graded to the approximate original contour to increase
surface runoff. This backfilling technique successfully curbed the infiltrating water
problem and most probably prevented the entrance of air into the mine (8, 27). The
costs of backfilling and grading individual subsidence areas are not available.
A single sheet of 0.24 centimeter (3/32 inch) butyl compound was placed over
a subsidence area located in a wooded area with rocky terrain. In preparation for
applying the butyl sheet, all trees, stumps, and other vegetation, and approximately
0.3 meters (1 foot) of topsoil were removed from the area. A ditch 15.2 centimeters
(6 inches) deep was dug around the subsided area and the sides of the 6.1 by
12.2 meter (20 by 40 foot) butyl sheet were tucked into it. The sheet was sealed by
compacting clay in the ditch and covering the sheet with soil originally removed
from the area (8, 27). The cost of the butyl compound was approximately $10.76
per square meter ($1.00/sq ft). Initial indications were that the butyl sheet
successfully sealed the area.
Chemical surface sealants were experimentally applied to two subsidence areas
in the watershed (117). On one area, Dowell applied a chemical powder that was to
form a self-sealing gelatinous coating upon being wetted. The material proved not to
be self-sealing, and after a heavy rain washed to the center of the area. Consequently
this method was considered an unsatisfactory approach. Costs of applying the
chemical were not available.
Diamond Alkali Company sprayed a mixture of Siroc Nos. 1 and 2 and cement
over a small cleared subsidence area. The Siroc accelerated the drying time, but the
material cracked. Bentonite was spread over the surface and wetted to fill the cracks.
The technique was considered unsatisfactory, since bentonite could not be mixed
and applied with the other ingredients. Costs for this technique were not available.
48
-------
Pennsylvania Operation Scarlift Projects
Backfilling and grading of subsidence areas, to control water infiltration has
been performed under several of Pennsylvania's Operation Scarlift projects. Specific
projects which have involved sealing subsidence areas are: SL 102-1-1 Mohawk
Valley, South Fayette Township, Allegheny County; SL 118-1 Shaw Mine Complex,
Elk Lick Township, Somerset County; and SL 182-1 Blacklegs Creek Watershed,
Young and Conemaugh Townships, Indiana County.
Project SL 102-1-1 involved filling and grading of subsidence holes, and
excavating and lining of approximately 1,280 linear meters (4,200 LF) of drainage
channel to prevent the loss of natural surface water to an underground mine. The
project work was performed by Richard Construction Company, Inc. and completed
in September, 1970 (84).
Drainage channels were excavated and the bottoms lined with a
15.2 centimeter (6 inch) loose layer of a bentonite and sand mixture (5 parts sand to
1 part bentonite). Subsidence holes, were filled to one-half depth with 0.6 meter
(2 foot) maximum size rock. The top layer of rock was of smaller size. Soil was
placed in 20.3 centimeter (8 inch) layers and compacted to 90 percent of maximum
density. The backfilled area was graded to 0.3 meters (1 foot) above natural ground
level.
If the subsidence hole extended into the underground mine, porous rock was
placed from the bottom of the mine to one-half the depth of overburden above the
mine roof. The remainder of the fill and grading were performed as described above.
The total cost of the project, which included lump sum bids and contingent
items, was $65,136.50. Itemized costs were as follows (84):
Lump Sum Bid
Clearing and Grubbing 5.3 ha (13 ac) $ 11,700
Drainage Channel 8,411 cu m
(ll,000cuyd) 16,500
Grading Subsidence Holes 3,823 cu m 3,750
(5,000 cu yd)
Soil Treatment and Planting • 5.3 ha (1 Sac) 5,850
49
-------
Contingent Items
Clearing and Grubbing 0.6 ha@ $l,750/ha $ 1,050
(1.5ac)($700/ac)
Drainage Channel 1,392 cu m @ $3.92/cu m 5,461.50
(1,820.5 cu yd)($3.00/cu yd)
Grading Subsidence Holes 114.7 cu m @ $ 1.31/cu m 150
(150cuyd)($1.00/cuyd)
Bentonite Clay 90.7 metric tons @ 20,000
$220.51/metric ton
(100tons)($200/ton)
Planting 0.6 ha @ $l,125/ha 675
(1.5ac)($450/ac)
Project SL 118-1 involved backfilling and grading of a subsidence area, and
placing a flume to conduct surface water across the work area. Work on the project
was performed by the Sanner Brothers Coal Company and was completed in
September, 1971 (84).
The scope of work performed under the contract included: clearing and
grubbing of the subsided area; dismantling and removal of structures from the work
area; spreading and compacting mine spoil piles; filling subsidence areas and mine
drifts; regrading the entire work area; fertilizing and seeding; and furnishing and
installing 1.2 meter (48 inch) bituminized fibre flume.
The total cost of the project was $21,090. Itemized costs were as follows (84):
Clearing and Grubbing 3.24 ha @ $617/ha $2,000
(8 ac)($250/ac)
Dismantle Existing Structures Lump Sum 100
Spread and Compact Mine Spoil 229 cu m Lump Sum 3,000
(300 cu yd)
Furnish and Install Flume 274 m @ $ 19.68/m 5,400
(900 ft)($6.00/ft)
Fertilizing and Seeding 3.24 ha @ $740/ha 2,400
(8 ac)($300/ac)
50
-------
Foreman 120hr@ $6.00/hr $ 720
Laborer 500 hr@ $5.00/hr 2,500
D-8 Angledozer and Operator 120 hr @ $28/hr 3,360
3 cu yd Hi-lift and Operator 40 hr @ $22/hr 880
Dump truck and Operator 40 hr @ $ 12/hr 480
Field Officer Lump Sum 250
In the Blacklegs Creek watershed, two subsidence areas were backfilled and
sealed with bentonite to prevent the flow of surface water into an abandoned
underground mine in the Pittsburgh coal seam. This work was performed under
Project SL 182-1 in conjunction with stream channel reconstruction and lining.
Work was completed in March, 1974 by the project contractor, B.R. Loughry (84).
Both subsidence areas were located in areas where cover over the mine was less
than 7.6 meters (25 feet). Caving of the mine roof and overlying strata had created
subsidence holes on the surface. Prior to backfilling with rock, all loose, pervious
material was removed from the holes and the sides of the excavation were cleaned.
At both locations a porous rock ranging in size from 7.6 centimeters to
0.3 meters (3 inches to 1 foot) was placed from the mine floor to 1.2 meters (4 feet)
above the mine roof. A 0.9 meter (3 foot) layer of No. 4 stone and a 0.3 meter
(1 foot) layer of No. 2B stone were successively placed and compacted on top of the
rock fill. To provide a water tight seal, a 0.3 meter (1 foot) layer of a bentonite and
sand mixture was placed and compacted on the No. 2B stone. The remainder of the
subsidence hole was backfilled with compacted soil. A section view of the backfill
and bentonite seal placed at Location 1 in Young Township is shown in Figure 1.2-2.
Sealing of the subsidence holes, and reconstructing and lining of stream
channels successfully reduced the infiltration of surface water into the underground
mine. As a result of the project, flow in tributaries to Blacklegs Creek was increased.
Costs of backfilling and sealing the subsidence holes were not available. Lump
sum bids for subsidence sealing and channel construction for Locations 1 and 6 were
$8,000 and $4,000, respectively. At Location 1, 46 linear meters (150LF) of
channel with bentonite seal were constructed. At Location 6, channel construction
included 61 linear meters (200 LF) with bentonite seal and 145 linear meters
(475 LF) without bentonite seal.
Material requirements for backfilling and sealing the two subsidence holes
were:
51
-------
Restored Surface
Ground Surface
LOCATION OF SEAL AS
DETERMINED BY
ENGINEER
(In Rock Strata)
/•BENTONlTE;;:SEAL-:;:
0.3m (I ft.)
0.3m (I ft.)
MIXTURE OF BENTONITE
AND SAND
PITTSBURGH COAL SEAM
MINE VOID
2.7m (9ft.)
FIGURE 1.2-2
SUBSIDENCE HOLE BACKFILL, BLACKLEGS WATERSHED
(Adapted from Ref. 84)
-------
Location 1 Location 6
cu m (cu yd) cu m (cu yd)
Rock Fill 101(132) 75(98)
No. 4 Stone 11 (15) 7 (7)
No. 2B Stone 4 (5) 2 (3)
Soil Backfill 53 (70) 6 (8)
Bentonite and Sand 4 (5) 2 (3)
Excavation -- 15(20)
EVALUATION AND RECOMMENDATIONS
Sealing and grading of subsidence areas has been successful in reducing the
volume of water entering abandoned underground mines. The effectiveness of this
water infiltration control technique will depend upon the size of the area, extent of
surface fracturing, materials utilized, and the method of construction. Concrete and
clay type seals placed in subsidence holes should prove to be the most effective
sealing method. These seals should also prove to be effective in controlling
discharges from the underground mine water pool.
A compacted clay backfill may be placed in shallow surface depressions to
prevent collection and diversion of surface waters into the mine. These areas should
be either graded to increase the surface velocity of water or filled to above existing
ground contours to divert water around the area. Diversion ditches may also be
utilized to collect and convey water around the subsided area. The cost of
backfilling will include clearing and grubbing, placing clay material, grading, and
planting. The cost of clay will normally range from $2.62 to $5.23 per cubic meter
($2.00 to $4.00/cu yd) depending upon availability and transportation costs.
Grout materials may be applied to areas where vertical fracturing is not
extensive. In severely fractured areas the grout will be unable to fill the voids and
may flow directly to the mine void. Grouting costs will depend upon the size of the
area being treated, drilling required, and the total amount of grout injected.
Estimates for horizontal grout curtains range from $29,630 to $98,765 per hectare
($12,000 to $40,000/acre). The cost of grouting work performed at the mine sealing
demonstration project near Elkins, West Virginia was approximately $2,600 per
subsidence area.
The construction of concrete or clay seals will require excavation of the
subsidence area, cleaning of the hole, backfilling with suitable rock fill, placement of
the seal, grading, and revegetation of the affected area. Construction costs for these
seals must be developed on an individual basis.
REFERENCES
8,21,27,37,52,57,75,84,100, 101, 117, 127, 129
53
-------
1.3 BOREHOLE SEALING
DESCRIPTION
Underground mines are commonly intercepted by boreholes extending from
the ground surface. These holes are often drilled during mineral exploration, but
may be utilized for supplying power to underground equipment or discharging water
pumped from active sections. Upon abandonment of an underground mine these
boreholes may collect and transport surface and ground waters into the mine, or
may discharge mine drainage from a flooded mine having a water level above
borehole elevation.
These vertical, or near vertical, boreholes can be successfully sealed by placing
packers and injecting a cement grout. Often abandoned holes will be blocked with
debris and will require cleaning prior to sealing. The packers should be placed below
aquifiers overlying the mine to prevent entry of sub-surface waters, but should be
well above the roof to prevent damage to the seal from roof collapse. A typical
method of borehole sealing with cement grout is shown in Figure 1.3-1.
A borehole may also be sealed by filling the hole with rock until the mine void
directly below the hole is filled to the roof. Successive layers of increasingly smaller
stone should be placed above the rock. A clay and/or concrete plug is then placed.
The remainder of the borehole may be filled with rock or capped. This method of
borehole sealing is shown in Figure 1.3-2.
IMPLEMENTATION
Tanoma Complex, Indiana County, Pennsylvania
A borehole was successfully sealed at the Tanoma Complex, Upper Crooked
Creek, Indiana County, Pennsylvania under Pennsylvania project SL 107-6-1. Work
was performed in September, 1973 by Pennsylvania Drilling Company. The seal was
placed to eliminate the flow of highly acid water from the Lower Freeport coal seam
to the Lower Kittanning coal seam (84).
The existing 26 centimeter (10.25 inch) diameter borehole was cleaned from
top to bottom. A packer was connected to 17.8 centimeter (7 inch) O.D. steel casing
and placed at 98.5 meters (323 feet). The packer was hydraulically set by pumping
water through the 17.8 centimeter (7 inch) casing at pressures up to 703 thousand
kilograms per square meter (l,000psi). Cement grout was pumped through
cementing ports to the outside of the casing until the cement rose to the Lower
Freeport opening. The installation was completed by pumping a top cementing plug
into place.
54
-------
GROUND SURFACE
/ / / /
::•*
x / / /
CEMENT'
ABANDONED MINE VOID
FIGURE 1.3-1
TYPICAL METHOD OF BOREHOLE SEALING
WITH CEMENT GROUT
55
-------
•BOREHOLE
GROUND SURFACE
•''•'• 0- '°: °'. 'Q-' ' ••/• ' '•'•'• ''9:-'. "''.
/ / /
/ / /
/ / /
/ /
•'•':'• '• :•••'•' • "'•'.' : •;.•-•::•'•':•'•'
— — — — — — — — — — — —
zi~ — — i~z_~z_~n_r~mr
" • ' *•
•.;'>;;.
k--'.' t
•;';;;: -. •.' P.'.' .'.'.;:. ;:o;: ' '•'•'.'•.9-v.'.v.°.'. • • '.• ••°': ••''.-'•'.
/ / / /
/ / /
/ / /
/ / /
'.' • " .:'•• ' •'•'.'.'.:. •. • ••'•'•';•' :''.'.'•' •-'.';'•'' •.'.'•
.••••••• • ••.••.'...••-. • • ' . . . • . • . . •.
— — CONCRETE PLUG
— — — — • — • —
•^BENTONITE LAYER -^^^^r^^^^^T
ROCK FILL
STONE LAYERS -=-=--=-=•= =.— =_-
ABANDONED MINE VOID
FIGURE 1.3-2
TYPICAL METHOD OF BOREHOLE SEALING
WITH ROCK AND CONCRETE
56
-------
A threaded cap was placed on top of the casing and a 0.6 centimeter
(0.25 inch) thick plate was tack welded between the existing 26 centimeter
(10.25 inch) casing and the 17.8 centimeter (7 inch) casing. The completed seal
successfully stopped leakage between the two coal seams. Costs of constructing the
seal were as follows:
Mobilization and Demobilization Lump Sum $ 1,000
Ream 26 Centimeter 99 LM @ S26.25/LM 2,600
hole (10.25 inch) (325 LF)($8.00/LF)
Seal 26 centimeter Lump Sum
hole (10.25 inch)
TOTAL
Wildwood Mine, Allegheny County, Pennsylvania
In June, 1973 a discharge of approximately 5,678 cubic meters per day
(1.5 MGD) with 300 mg/1 iron occurred from an old diamond drill hole at the
Wildwood Mine near Pine Creek, Hampton Township, Allegheny County,
Pennsylvania. The mine is in the Upper Freeport coal seam and had been in
operation until December, 1968. Subsequent sealing of shafts and boreholes resulted
in a flooding of the mine to an elevation above the drill hole. The drill hole discharge
was successfully sealed in October, 1973 by Pennsylvania Drilling Company, under
Pennsylvania Project SL 198-1.
Sealing the hole involved exposing the 7.6 centimeter (3 inch) hole and
cleaning it to a depth of approximately 54.9 meters (180 feet). A packer was placed
and the hole was cemented to the top. Costs of construction were as follows (84):
Exploration, Cleaning and Plugging $6,500.00
Cement in Place 262.50
TOTAL $6,762.50
EVALUATION AND RECOMMENDATIONS
Boreholes act as conduits and are capable of transmitting large volumes of
water to underground mines. They may also discharge mine water pollutants to the
environment if the abandoned mine floods to a level above the borehole elevation.
Boreholes may be successfully sealed by placing concrete plugs or other
impermeable materials in the hole. The seals must be capable of withstanding the
expected water pressure, but should be located well enough above the mine roof to
prevent roof collapse. Borehole sealing should be performed in conjunction with
mine closure and sealing programs.
57
-------
The total cost of sealing a borehole will depend upon such factors as the depth
and diameter of the hole, exploration and cleaning required, and the method of
sealing. Prior to sealing the borehole should be cleaned for its entire length. Cleaning
costs will normally range from $33 to $66 per linear meter ($10 to $20/LF). Sealing
by injecting cement grout will normally range in cost from $49 to $66 per linear
meter ($15 to $20/LF). The total cost of borehole sealing including exploration,
mobilization and demobilization, labor, and materials should range from $66 to
$132 per linear meter ($20 to $40/LF).
REFERENCES
70,84, 127, 129
58
-------
1.4 SURFACE MINE REGRADING
DESCRIPTION
Water discharging from underground mines often originates as surface water on
non-regraded surface mines. This commonly occurs in the eastern United States
where coal outcrops are contour stripped. These strip mines will often intercept
underground workings or have underground mine entries and auger holes along the
highwall. When these openings occur on the updip side of an underground mine,
large volumes of surface water may be conveyed to underground workings. Surface
mines may collect water and allow it to enter a permeable coal seam. This water can
flow along the seam to adjacent underground mines (127).
Various methods of surface mine regrading have been practiced in the eastern
coal fields. The selection of a regrading method will depend upon such factors as:
the amount of backfill material available, the degree of pollution control desired,
future land use, funds available, and topography of the area (29). Section views of
contour and terrace regrading methods are shown in Figures 1.4-1 and 1.4-2. In both
of these regrading methods, surface runoff is diverted away from the highwall. Prior
to backfilling, impervious materials may be compacted against the highwall to
prevent the flow of water to adjacent underground mines.
IMPLEMENTATION
Roaring Creek — Grassy Run Watershed
Surface mine regrading, to control water infiltration, was performed as part of
an acid mine drainage demonstration project conducted in the Roaring
Creek — Grassy Run watersheds near Elkins, West Virginia. The project was a
cooperative effort between Federal agencies and the state of West Virginia. Strip
mines along coal outcrops were collecting and diverting water into abandoned
underground mines. Since the coal dipped from the Roaring Creek watershed to the
Grassy Run watershed, water was diverted from one watershed to another through
the underground workings, resulting in a flushout of acid mine drainage (57, 101).
Three methods of regrading were used on the surface mines — contour, pasture,
and swallow-tail. Contour regrading was performed when the highwall was fractured
and unstable. The top of the highwall was usually pushed down to complete the
backfill. Pasture and swallow-tail regrading are variations of terrace regrading. They
were performed when the highwall was stable. Cross sections of these two regrading
methods are shown in Figure 1.4-3.
59
-------
-Original Ground Surface
Diversion Ditch
Regroded Ground Surface
FIGURE 1.4-1
CROSS SECTION OF TYPICAL CONTOUR REGRADING
(Adapted from Ret. 127)
60
-------
Original Ground
Diversion Ditch
^Mineral ^r —-
Regraded Ground Surface
•Slope Away From Highwall
_......... N^ ^-ope way rom
^:':.V.\''^'P)^|i^^;NV:-Xv.:V::;':;;:;^
%;•/••'••:::.:::-:-:i;.::\ of
^-"••••:::••• ••;.•• .-.A Fill
FIGURE 1.4-2
CROSS SECTION OF TYPICAL TERRACE REGRADIN6
(Adapttd from Rtf. 127)
61
-------
Original Ground Surface
1 1 1
I.I 1
1 1 1
1 1 1
1 1 1
1 1 1
__^ _^_ „_ ,
ZZH~ Z-ILZ."!"
Underground Mine
^
.;
'•\
• • • ' \ tg~ R6orod6d Ground Surface
^•••-••^^^
^Coqi .Seam ::•; ''.;/;'.-V;' :•:•••'•;•: /.' .'-.•' '•^••'•'•'•'•'•'•\:'-'-\'.'- '• '.'• '•• .'•'•'
Out slope-
PASTURE REGRAOIN6
T^T
Original Ground Surface
II
I.I.I
•'••S
'
Regraded Ground Surface
-Waterway For Drainage
i':\:^':\'^':^:^^ Outslope
SWALLOW TAIL RE6RAOIN6
FIGURE 1.4-3
TYPICAL REGRADING METHODS
ELKINS, W.VA.
(Adapted from Rtf. 32)
62
-------
The effectiveness of the surface mine regrading was difficult to evaluate. Due to
cost overruns, reclamation and sealing of a large 1,215 hectare (3,000 acre)
underground mine was not completed. Therefore, the effectiveness of water
infiltration control in reducing the mine discharge could not be evaluated. A
preliminary evaulation of runoff from regraded areas indicated that flow in adjacent
streams was increasing, and thus, less water was entering the underground mine.
The discharge from a smaller un erground me was reduced by eliminating the
infiltration of water through an opening in a strip mine highwall. The pit floor was
approximately 6.1 meters (20 feet) below an adjacent stream bed. The initial
stripping operation had diverted stream flow toward the highwall. Instead of the
water flooding the pit, flow was diverted through the highwall opening to an
adjacent underground mine.
The infiltration was elminated by compacting clay against the highwall to
above the base level of the stream, and regrading with available spoil to expedite
surface runoff away from the highwall. The pre-stripping stream bed was also
re-established by backfilling (8).
Surface mine regrading and revegetating were begun in the summer of 1966 and
completed in the spring of 1968(101). In total, 264 hectares (651 acres) were
regraded at an average cost of $4,094 per hectare ($l,658/acre). During regrading a
total of 2,339,676 cubic meters (3,060,000 cu yd) of material was moved at an
average cost of $0.46 per cubic meter ($0.35/cu yd). The average costs of clearing
and grubbing, and revegetating the 264 hectares (651 acres) were respectively
$815 per hectare ($330/acre) and $612 per hectare ($248/acre) (101). Considering
the average costs per hectare for clearing and grubbing, regrading, and revegetating,
the overall surface mine regrading cost at Elkins was $5,221 per hectare
($2,236/acre).
The average direct cost (materials, equipment, and labor) for selected work
areas ranged from a low of $1,165 per hectare ($472/acre) for contour regrading to
a high of $2,793 per hectare ($1,13I/acre) for combination pasture-contour
regrading. Direct costs of surface mine regrading by various methods on selected
work areas are presented in Table 1.4-1.
Dents Run Watershed
A demonstration project to control mine water pollution by water infiltration
control is being conducted in the Dents Run watershed in Monongalia County,
West Virginia. The project is a cooperative effort between the U.S. Environmental
Protection Agency and the state of West Virginia. The program was established to
fulfill the requirements of Section 14 of the Federal Water Pollution Control Act, as
amended.
63
-------
ON
TABLE 1.4-1
Direct Cost of Surface Reclamation
by Various Methods on Selected Work Areas
Elkins, West Virginia
Area No.
3
4
5
8
9
37
MEAN
23 & 24
28
27
29 & 30
44
MEAN
1
2
MEAN
10
11
MEAN
Hectares
(Acres)
4.8
1.9
1.7
3.2
4.7
5.3
21.6
31.5
4.5
27.5
15.3
10.8
89.6
7.6
16.3
23.9
56.8
19.0
75.8
(11.9)
(4.7)
(4.3)
(7.9)
(11.7)
(13.0)
(53.5)
(77.9)
(11.0)
(68.0)
(37.7)
(26.7)
(221.3)
(18.7)
(40.3)
(55.0)
(140.3)
(47.0)
(187.3)
Type Of
Backfill
Pasture
Pasture
Pasture
Pasture
Pasture
Pasture
Contour
Contour
Contour
Contour
Contour
S wallow-
Tail
Swallow-
Tail
Pasture/
Contour
Cost/Hectare
(Cost/Acre)
Reclamation
$ 946
138
2,457
1,827
1,067
1,970
$1,402
$1,059
654
1,333
1,338
1,012
$1,165
$ 778
1,743
iL'4_3Z
$2,617
3,311
IP-jJL9!
(383)
(56)
(995)
(740)
(432)
(798)
(no8)
(429)
(265)
(540)
(542)
(410)
(472)
(315)
(706)
(582)
(1,060)
(1,341)
(1,131)
Type
Seeding
C & H
C
C
C
C
C 6 H
C, H, T
C, H, T
C & H
C, H, T
C, H, T
C, H, T
C, H, T
C, H, T
C
Cost/Hectare
v^ost/Acre)
Reclamation
+ Seeding
$1,316
346
2,780
2,074
1,291
2,252
$1,684
$1,652
1,511
2,240
1,837
1,689
$1,862
$1,348
2,012
"
$1,802
$3,052
3,699
$3,215.
(533)
(140)
(1,126)
(840)
(543)
(912)
(682)
(669)
(612)
(907)
(744)
(684)
(754)
(546)
(815)
J730)
(1,236)
(1,498)
(1,302)
Cost/Hectare
(Cost Acre)
Reclamation + Seeding
+ Clearing & Grubbing
$1,422
430
2,807
2,556
1,380
2,538
$1,877
$1,738
2,178
3,148
1,985
2,005
$2,267
$1,398
2,081
$1,864
$3,519
3,822
$3,595
(576)
(174)
(1,137)
(1,035)
(559)
(1,028)
(760)
(704)
(882)
(1.-275)
(804)
(812)
(918)
(566)
(843)
(755)
(1,425)
(1,548)
(1,456)
Type Seeding: C = Conventional, H = Hydroseeding, and T = Trees
-------
Within the watershed the Pittsburgh, Redstone, Sewickley, and Waynesburg
coal seams have been surface and drift mined. Water infiltration into underground
mines is occurring through intersected underground workings, drift entries, and
auger holes along strip mine highwalls. A feasibility study (132) identified four strip
mines which diverted significant amounts of surface water to underground mine
workings. Sealing of highwall openings and regrading of surface mines were proposed
to control water infiltration. The effectiveness of the project was to be evaluated by
monitoring stream flows and mine discharges within the watershed.
During 1972, three strip mines in the watershed were regraded — Section G,
Strip Area R; Section G, Strip Area A; and Section C, Strip Area C. Work on the
areas included: placing a diversion ditch above the highwall, compacting clay soil in
auger holes and drift entries, contour or pasture regrading, soil treatment and
seeding. Typical methods of regrading are shown in Figures 1.4-4 and 1.4-5. The
costs of regrading and seeding the three areas ranged from $9,351 to $10,800 per
hectare ($3,787 to $4,374/acre) (100). Itemized costs of regrading the three areas are
presented in Table 1.4-2.
A final report evaluating the effectiveness of the water infiltration control
project is to be completed in June, 1975. Based on data that has been collected, it
appears that there may not be sufficient information to properly evaluate this
technique in Dents Run. Since implementation of the project, borehole discharges
have been affected by active underground mining. The failure to install continuous
stream flow monitoring systems in the watershed may make it very difficult to
analyze the effect of infiltration control.
EVALUATION AND RECOMMENDATIONS
Water infiltration resulting from surface mining operations can be effectively
controlled by regrading. A hydrogeologic study should be performed to determine
the nature and extent of infiltration and to assist in the development of a regrading
plan. The regrading method must be designed to divert surface water away from the
surface mine highwall and increase surface runoff. Impervious materials should be
compacted into hydraulic openings between surface and underground mines. The
regraded area should be revegetated to prevent erosion of the graded fill material and
increase surface runoff.
The selection of a regrading method will depend upon such factors as the
height and condition of highwall, original slope of ground, volume and condition of
available spoil material, and available regrading equipment. Sufficient grading must
be performed to conduct flow around the surface mine. The regrading method may
include ditching and fluming of the mine area to facilitate surface runoff.
65
-------
Surface Water Diversion Ditch
Regraded Ground Surface
H ~ ~ ~ TLILTSm"
(5ft.)
Min.
Underground Mine
1.8m
,6ft.)
in.
i.v.
(6
M
Compacted Clay Soil
FIGURE 1.4-4
TYPICAL REGRADING UNDERGROUND MINE
DENTS RUN, W. VA.
(Adapted from Ref. 132)
-------
Surface Water Diversion Ditch
Regraded Ground Surface
ON
Auger Hole
i.-. ;v>..->.. ^^ ^- rtegraaea i?rouna ourrace
^3^':::;::'• '•'•';'; '•: • i^f7"; -TT?.^-M .77^. _X^
1.5 m l~Wk;: ••• ••'•'••• •: •'••••• •'••.'.•.'.•'•'•'•••'•'•'•'•^vn-TTrr-Tr*..T-T-
(5ft) _L\-•'•'•• •••'••'• ••'•'• '.'•"•'.'.•'• '.'.'•'• '.'•'•'•'•'.•'•'.••.'•'•:.-:'.::'-:'-:::^^-:'f:^f-T^f.
X]1P\/' ^\S NX" ~\f \X^ \S "N^kto * w .» ^ ^ M .& ^^^^^1*-^^
>!\AAAAAA-.-+*<*»-*.*••-*. *"-*.«-
V
-—- ^-Compacted Clay Soil
i.8m
(6ft.)
Min.
FIGURE 1.4-5
TYPICAL REGRADING AUGER HOLE
DENTS RUN, W.VA.
(Adapted from Ref. 132)
-------
Table 1.4-2
Regrading Costs Dents Run Watershed
Job 1
Section G
Strip R
Hectares (Acres)
Description of
Work
!•
oo
2.
3.
4.
5.
Grading $ 8
Lime
Fertilizer
Seeding & Planting
Mulch
Total Hectare & Acre $ 9
TOTAL COST $60
6.5
(16)
Cost/Hectare
(Cost/Acre)
,148 (3,300)
62
119
595
427
,351
,592
(25)*
(48)
(241)
(173)
(3,787)
Job 2
Section G
Strip A
4.1
(10)
Cost/Hectare
(Cost/Acre)
$ 6,963
210
126
541
474
$ 8,314
$33,670
(2,820)
(85)
(51)
(219)
(192)
(3,367)
Job 3
Section C
Strin C
9.2
(22.8)
Cost/Hectare
(Cost/Acre)
$ 9,444 (3,825)
227
121
533
474
$10,800
$99,727
(92)*
(49)
(261)
(192)
(4,374)
*Cost includes treatment of impounded water
All jobs consisted of diversion ditches, rip rap outslope, and compacted backfill in auger
holes. Modified contour regrading was performed on Job 1. Jobs 2 and 3 were pasture
regraded.
-------
The cost of regrading will include backfilling and grading of the open cuts, and
revegetation of the affected area. When old abandoned surface mines are re graded,
additional expenditures for clearing and grubbing, and establishing mine access may
be required. Regrading of these mines will normally be more difficult than regrading
of active operations, since spoil material was placed without considering future
regrading requirements. The construction of diversion ditches and sealing of highwall
openings will further increase regrading costs.
Based on previous surface mine regrading costs, backfilling and grading using
contour and terrace techniques should average respectively $4,938 per hectare
($2,000/acre) and $4,445 per hectare ($ 1,800/acre). Clearing and grubbing costs will
be approximately $1,235 per hectare ($500/acre). Revegetation costs, including
lime, fertilizer, seeding, and mulch will range from $1,235 to $1,3 5 8 per hectare
($500 to $550/acre). The range in total cost of regrading, including clearing and
grubbing, backfilling, grading, and revegetation will generally be as follows: Contour
Regrading - $4,445 to $9,383 per hectare ($1,800 to $3,800/acre) and Terrace
Regrading - $3,704 to $8,395 per hectare ($1,500 to $3,400/acre).
REFERENCES
8, 29, 32, 47, 69, 75, 100, 101, 106, 127, 127, 132
69
-------
1.5 SURFACE SEALING
DESCRIPTION
Water infiltration into underground mines can be controlled by reducing
surface permeability. This may be accomplished by placement of impervious
materials, such as concrete, soil cement, asphalt, rubber, plastic, latex, clay, etc., on
the ground surface. Surface permeability may also be decreased by compaction;
however, the degree of success will depend upon soil properties and compaction
equipment utilized (127).
A seal below the surface would have several advantages over surface seals: it
would be less affected by mechanical and chemical actions; land use would not be
restricted; and the seal would be located in an area of lower natural
permeability (115). The seal would be formed by injecting an impermeable material
into the substrata. Asphalt, cement and gel materials have been used to control
water movement below the surface. The effectiveness of various latexes, water
soluble polymers, and water soluble inorganics has been demonstrated in laboratory
and field tests. However, large scale applications of sub-surface sealants to control
acid mine drainage have not been demonstrated.
IMPLEMENTATION
Impermeable Surface Seals
Several sealants have been used to reduce water infiltration into underground
mines through subsided areas. Backfilling and compacting with clay to reduce
vertical permeability in these areas is commonly practiced in the eastern coal fields.
Other materials which have been demonstrated are sheets of butyl (rubber)
compound, various chemical compounds, and cement grout.
Clay is one of the least expensive sealing materials. Costs for clay including
installation may range from $2.62 to $7.85 per cubic meter ($2.00 to $6.00/cu yd).
Costs for rubber range from $5.38 to $10.75 per square meter ($0.50 to $1.00/sq ft)
installed. Costs of cement grout will depend upon the volume and mixture of
materials placed and the amount of drilling required. The following unit prices have
been used in preparing job bids: drilling - $6.56 to $9.84 per linear meter ($2.00 to
$3.00/LF); cement - $3.00 to $4.50 per bag; cement admixture - $4.41 to
$8.82 per kilogram ($2.00 to $4.00/lb); and fly ash - $8.82 to $22.00 per metric
ton ($8.00 to $20.00/ton).
70
-------
Asphalt and concrete prove to be excellent surface sealants but they are
expensive. The only present economically feasible method of utilizing these
materials as surface sealants is multi-purpose use. The surface could be sealed by
constructing roads, parking lots, runways, etc. Concrete costs will normally range
from $39 to $78 per cubic meter ($30 to $60/cu yd). Asphalt installation may range
from $2.00 to $6.00 per square meter ($0.19 to $0.56/sq ft) (127).
Latex Soil Sealant
Uniroyal, Inc. conducted laboratory and field tests to determine the feasibility
of using latex as a sub-surface sealant. Field experiments were conducted in 1972 at
two sites in Clearfield County, Pennsylvania (115). Various latexes, water soluble
polymers, clays, and water soluble inorganics were investigated in the laboratory.
Field investigations were limited to ammonium hydroxide, sodium carbonate, and
Naugatex J-3471 latex.
In laboratory tests good sealing efficiency was obtained when latex was applied
at a rate equivalent to 4,484 to 5,605 kilograms per hectare (4,000 to
5,000 Ib/acre). Application of a 5 percent rubber latex to a saturated core of soil
reduced the seepage rate from 15 to 2 milliliters per minute (0.24 to 0.03 gal/hour).
During field tests, dilute solutions of sealants were sprinkled on test plots and
flushed into the soil with water. The effectiveness of sealing was determined by
comparing soil moisture and permeability of treated and untreated test plots.
Field testing of latex indicated that the latex was deposited progressively as it
passed through the soil. The ideal situation would be for the latex to coagulate in a
narrow zone 0.6 to 0.9 meters (2 to 3 feet) below the surface. Application of latex
to field test plots resulted in a decrease in permeability in the top 25.4 centimeters
(10 inches) of soil. An effective sub-surface seal was not demonstrated in the field.
Based on application rates used in the field, raw material costs of latex would be
approximately $2,469 per hectare ($ 1,000/acre). Equipment and operating costs
would vrange from $494 to $1,235 per hectare ($200 to $500/acre), depending
upon the size of area treated and availability of suitable water (115).
Effective seals were formed in both laboratory and field tests by applying
dilute solutions of ammonium hydroxide or sodium carbonate. This seal is only
temporary, however, since the two chemicals are water soluble. Very dilute clay
dispersions were applied to laboratory soil columns. Pore blockage occurred at the
surface, but in no case was penetration greater than 5.1 centimeters (2 inches).
Field test plots were located over abandoned underground coal mine workings.
Since the size of the plots was small compared to the size of the mine, no change in
mine effluent quality or quantity was expected. Therefore, the evaluation of sealing
effectiveness did not involve monitoring of mine effluent.
71
-------
EVALUATION AND RECOMMENDATIONS
The effectiveness of surface sealing will depend upon the type of material
applied, the method of application, and the degree of maintenance performed.
Surface sealants will be subjected to mechanical forces (traffic, weather, ground
movement, vegetation, etc.) and chemical action (oxidation, etc.). In areas where
surface sealing is utilized, the use of land for agriculture, industry, and recreation
may be limited. Such factors may limit surface sealing to relatively small and remote
areas.
The injection of grouting materials below the surface can be an effective
method of surface sealing. However, in severely fractured areas, the grout will be
unable to completely fill the void space and sealing efficiency will be reduced.
Grouting costs will depend upon the size of the area being treated, drilling required,
and the total volume of grout material injected. Estimates for horizontal grout
curtains range from $29,630 to $98,765 per hectare ($12,000 to $40,000/acre).
Clay materials appear to be a practical sealing material. The clay should be
compacted in layers and covered with soil to protect against weathering. The clay
sealant will severely limit the use of land for agriculture and industrial purposes, but
would be applicable to relatively small surface areas. The feasibility of clay sealants
will normally depend upon the availability of suitable materials.
Asphalt, concrete, rubber, and plastic do not appear to be acceptable sealing
materials. Asphalt and concrete are not economically feasible. Rubber and plastic
are easily damaged and would require an extensive maintenance program. Attempts
to cover these materials with soil have been unsuccessful. A soil cover proved to be
unstable and any vegetative cover established would result in root damage to the
seal.
REFERENCES
29, 57, 115, 127, 129
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1.6 SURFACE WATER DIVERSION
DESCRIPTION
Surface cracks, subsidence areas, non-regraded surface mines, and shaft, drift
and slope openings are often the source of surface water infiltration. Water diversion
involves the interception and conveyance of water around these underground mine
openings. This procedure controls water infiltration and decreases the volume of
mine water discharge.
Ditches, trench drains, flumes, pipes, and dikes are commonly used for surface
water diversion. Ditches are often used to divert water around surface mines. Flumes
and pipe can be used to carry water across surface cracks and subsidence areas. To
ensure effective diversion, the conveyance system must be capable of handling
maximum expected flows. Riprap may be required to reduce water velocities in
ditch type conveyance systems.
IMPLEMENTATION
Surface Mines
Diversion ditches are often placed on the uphill side of a highwall or an open
pit. These ditches significantly reduce the volume of water entering both active and
abandoned surface mines. The diversion ditch is the most commonly used method of
water diversion in surface mining and, in fact, is required by law in some states.
Surface water flowing into abandoned surface mines is often diverted to
adjacent underground workings, either through highwall openings or along a
permeable mineral bed. The diversion of water around such areas will significantly
reduce water infiltration.
Diversion ditches are often constructed above the highwall of a regraded
surface mine. Surface water flowing over the highwall can percolate to the base of
the highwall and flow to adjacent underground workings. The diversion ditch
reduces the volume of percolating water and also prevents erosion of the regraded
area.
Plans and specifications for surface mine regrading performed under
Pennsylvania's Operation Scarlift Program frequently require the diversion of surface
water around the mine. Project SL 132-2-101.1, Rattlesnake Creek watershed,
required a diversion ditch and drainage flume to collect surface water above the
highwall. The diversion ditch was constructed at a cost of $3.28 per linear meter
(Sl.OO/LF). Unit costs for water diversion were as follows (84):
73
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Diversion Ditch 56.4 LM @ $3.28/LM $ 185
(195LF)($1.00/LF)
Riprap 50.2 sq m @ $23.92/sq m 1,200
(60 sq yd)($20.00 sq yd)
Drainage Flume 96 LM @ S65.62/LM 6,300
(315LF)($20.00/LF)
Concrete Endwall Lump Sum
TOTAL
Plans and specifications for pollution abatement in the Cherry Creek
watershed, Maryland, require the construction of a diversion ditch above surface
mine highwalls (106). The ditch is to have side slopes of 2:1 and a minimum depth
of 0.6 meters (2 feet). Excavated material is to be placed between the ditch and
existing high wall. Dumped riprap is to be placed in specified areas to control water
velocity and prevent ditch erosion. Cost estimates for constructing the diversion
ditch and placing riprap were $1.31 per cubic meter ($1.00/cuyd) and $6.54 per
cubic meter ($5.00/cu yd) respectively. Views of the diversion ditch and method of
placing riprap are presented in Figure 1.6-1.
Underground Mines
Surface water flowing directly to underground mines through surface cracks,
subsidence areas, and slope, drift or shaft mine entries can be a major source of
water infiltration. Water diversion around such areas will significantly reduce the
volume of water entering underground mines.
A diversion ditch or dike will often effectively divert water around surface
openings. Stream channels are often reconstructed and lined with an impervious
material to carry water across fractured ground surface (See Section 1.7). If
construction of a diversion ditch is infeasible, pipe, flumes or similar structures may
be used to convey water around or over surface openings.
A 122 centimeter (48 inch) bituminized fibre flume was placed over a regraded
subsidence area at the Shaw Mine Complex, Somerset County, Pennsylvania (84).
This work was performed under Project SL 118-1. A total of 274 meters (900 feet)
of flume was furnished and installed at a cost of $ 19.69 per linear meter ($6.00/LF).
Regrading and fluming of the area reduced the flow of surface water to the
underground mine.
74
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)riginal Ground
• ^t Proposed Diversion Ditch
0.6m(2ft.) ^Original Ground
.Place Ditch Excavated
Material
•Existing Highwall
DIVERSION DITCH DETAIL
^Original Ground
Original Ground-
/0.3m(lft.)min.
Riprap
SECTION
/Flow Line of Riprap Orjgina, Ground
^W*^
0.9m
V0.3m(lft.)min.
PROFILE
(3ft.) min.
0.9m (3ft.) min.
DUMPED RIPRAP DETAIL
FIGURE 1.6-1
PROPOSED WATER DIVERSION DITCH
CHERRY CREEK, MARYLAND
(Adapted from Ref. 106)
75
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EVALUATION AND RECOMMENDATIONS
Surface water diversion reduces the volume of water flowing into an
underground mine, and thus, reduces the volume of water available to flush out
mine drainage pollutants. The factors which will affect -the selection and
implementation of a diversion technique will be topography, availability of
equipment, condition and type of soil, and the quantity of water expected. Any
diversion technique when properly designed and utilized can greatly reduce the flow
of surface water to underground mines. Although the costs of diversion may be high,
this is an effective method of controlling mine drainage pollution from both active
and abandoned mines. In most instances the cost of diversion will be significantly
less than that required to treat an equal volume of mine water.
Diversion ditches are a relatively inexpensive, but effective method of
collecting and conveying surface water. Lining of these ditches with concrete,
asphalt or other material may be required to control water velocity and reduce
erosion. Dumped riprap will prove to be an effective method of reducing water
velocities in the ditch.
The range in costs for constructing diversion ditches will depend upon the
width and depth of the ditch and the type of construction equipment utilized.
Estimated costs range from $1.64 to $6.56 per linear meter ($0.50 to S2.00/LF) of
ditch, with perhaps the average being approximately $3.29 per linear meter
($1.00/LF). Dumped riprap will normally cost between $6.54 and $26.16 per cubic
meter ($5.00 and $20.00/cu yd).
The cost of flumes and pipe will depend upon their size, and labor and
equipment required for installation. The estimated cost for placing a 92 centimeter
(36 inch) half section of bituminized fibre pipe is $32.80 per linear meter
($10.00/LF). The cost of constructing dikes will usually be based upon the volume
of material moved. The average cost of construction will normally range from $0.52
to $1.04 per cubic meter ($0.40 to $0.80/cu yd).
REFERENCES
8, 27, 29, 32, 57, 62, 69, 84, 106, 107, 127, 129
76
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1.7 CHANNEL RECONSTRUCTION
DESCRIPTION
Vertical fracturing and subsidence of strata overlying underground mines often
create openings on the ground surface. Streams flowing across these openings may
have a complete or partial loss of flow to the underground workings. During active
operations pumping of this infiltrating water places a physical and financial burden
upon the mining company. Water infiltrating into abandoned underground mines is
available to flush out mine drainage pollutants. In both active and abandoned
underground mines the problems of infiltrating stream flow can be effectively
controlled by reconstructing and/or lining the stream channel (127).
When practical, water infiltration will best be controlled by diverting the
stream channel around underground mine openings. The reconstructed channel
bottom may be lined with an impervious material to prevent seepage or flow to the
underground mine. To ensure complete and effective diversion, the reconstructed
channel must be capable of handling stream flow during peak flow periods.
In instances when stream flow cannot be diverted to a new channel, flow into
underground mines can be controlled by plugging the mine openings with clay or
other impervious material. The feasibility of sealing the channel bottom will depend
upon the ability to locate fractures in the stream bed and successfully place the
impervious material.
IMPLEMENTATION
Pennsylvania Operation Scarlift Projects
A 1974 report (32) prepared for the U.S. Environmental Protection Agency
estimated the cost of channel reconstruction in the Monongahela River basin to be
$65.62 per linear meter (S20.00/LF). The estimate included an allowance for
increased tonstruction costs, channel slope grading, soil treatment and seeding. This
estimate was based on actual costs incurred in three Pennsylvania Operation Scarlift
Projects: SL 102-1-1, Chartiers Creek, Allegheny County; SL 135-1, Catawissa
Creek, Luzerne County; and SL 143-1, Alder Run, Clearfield County.
A total of 3,024 linear meters (9,920 LF) of stream channel was reconstructed
under the three projects. The costs per linear meter of reconstructed channel were:
Project SL 102-1-1 - $50.85 ($15.50/LF), Project SL 135-1 - $39.37 ($12.00/LF),
and Project SL 143-1 - $88.58 ($27.00/LF). Unit costs for excavation ranged from
$0.80 to $3.40 pef cubic meter ($0.61 to $2.60/cu yd).
77
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In total, 800 linear meters (2,625 LF) of stream channel were reconstructed at
five different locations along tributaries of Big Run, Harpers Run, Sulphur Run, and
Whiskey Run in Blacklegs Creek watershed, Young and Conemaugh Townships,
Indiana County, Pennsylvania. Work was completed by B. R. Loughry in
March, 1974 under Pennsylvania Project SL 182-1. Water in the tributaries was
flowing into abandoned underground mine workings through subsidence holes, and
cracks and crevices in the stream beds. At two locations channels were reconstructed
around subsidence holes. Other sections of channel bottom were sealed with
bentonite to ensure continuous flow of water across mine openings (84).
A bentonite seal was placed along the bottom of 412 linear meters (1,350 LF)
of reconstructed channel. The channel was excavated to 0.6 meters (2 feet) below
finished grade with a bottom width of 2.1 meters (7 feet). The bottom was graded
and compacted in preparation for placing the bentonite seal. A 15.2 centimeter
(6 inch) layer of 5 parts sand to 1 part granulated bentonite was placed and well
compacted on the channel bottom. Two 23 centimeter (9 inch) layers of best
available impervious material were placed and compacted over the bentonite. The
width of the channel bottom at finished grade was 1.8 meters (6 feet).The channel
sides were graded to a slope of 2:1 for a minimum of 0.9 meters (3 feet) from the
channel bottom, then graded to existing terrain. Typical channel sections with and
without the bentonite seal are shown in Figure 1.7-1.
Reconstruction and sealing of the channels resulted in increased flow in the
Blacklegs Creek tributaries. At Locations 2, 3 and 4 a total of 549 linear meters
(1,800LF) of channel was reconstructed at an average cost of $20.04 per linear
meter (S6.11/LF) Construction costs for the complete project, which included
backfilling two subsidence holes, totaled $23,000 (84).
EVALUATION AND RECOMMENDATIONS
The reconstruction of stream channels is an effective method of reducing
surface water infiltration to abandoned underground mines. The costs of stream
diversion will normally be much less than treatment costs of an equal volume of
mine water. There is not much documentation of the use of this diversion technique
in mine related projects. However, there is considerable experience available in
stream channel construction in conjunction with highway projects.
The feasibility of reconstructing a channel will depend upon channel size,
topography, and extent of surface fracturing. If flow cannot be diverted to a new
channel, the existing channel should be graded and lined to improve flow efficiency.
Channel excavation costs will normally range from $1.31 to $3.92 per cubic meter
($1.00 to $3.00/cu yd). Lining of the channel bottom with clay will cost between
$1.20 to $2.40 per square meter ($1.00 to $2.00/sq yd). The total cost of channel
reconstruction may also include protection of channel slopes with riprap or
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'Grodt to Existing Terrain
0.9m(3tt)min.
Grads to Existing Terrain.
2.1m (7ft.)
43.7cm (18 in.)
COMPACTED FILL
2-23cm(9in.) Layers
I5.2cm(6in.)
BENTONITE SEAL
CHANNEL SECTION WITH BENTONITE SEAL
Srods to Existing Twain
0.9m(3ft.) min. L_ 1.8m (6 ft.)
Grade to Existing Terrain-
Q.9m(3ft.)min.,
FINISHED GRADE
CHANNEL SECTION WITHOUT BENTONITE SEAL
FIGURE 1.7-1
RECONSTRUCTED CHANNEL, BLACKLEGS CREEK
(Adapted from Rtf. 84)
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vegetative cover. The total cost per linear meter of reconstructed channel will
normally range from $32.81 to $82.02 ($10.00 to $25.00/LF).
REFERENCES
8, 27, 29, 32, 38, 57, 62, 69, 84, 107, 127, 129
80
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2.0
MINE SEALING
81
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2.1 GENERAL DISCUSSION
Mine sealing is defined as the closure of mine entries, drifts, slopes, shafts,
subsidence holes, fractures, and other openings in underground mines with clay,
earth, rock, timber, concrete blocks, brick, steel, concrete, fly ash, grout, and other
suitable materials. The purpose of mine sealing is to control or abate the discharge of
mine drainage from active and abandoned mines.
Mine seals have been classified into three types based on method of
construction and function (32, 39). The three seal types are:
1. Dry Seal — The dry seal is constructed by placing suitable material in mine
openings to prevent the entrance of air and water into the mine. This seal
is suitable for openings where there is little or no flow and little danger of
a hydrostatic head developing.
2. Air Seal — An air seal prevents the entrance of air into a mine while
allowing the normal mine discharge to flow through the seal. This seal is
constructed with a water trap similar to traps in sinks and drains.
3. Hydraulic Seal — Construction of a hydraulic seal involves placing a plug
in a mine entrance discharging water. The plug prevents the discharge and
the mine is flooded. Flooding excludes air from the mine and retards the
oxidation of sulfide minerals.
Mine sealing performed in the early 1900's was for safety reasons and not mine
drainage control. Seals were constructed to confine water in certain sections of the
mine, to extinguish mine fires and to hold back gases.
The possibility of utilizing mine seals to control drainage from mines was
discussed in several technical reports in the 1920's and early 1930's. Observation of
mines where entries had been sealed by caving revealed a better quality discharge
than mines where entries were open and water discharged freely. A mine sealing
project sponsored by the Bureau of Mines in 1932 indicated that the air sealing of
mines reduced the acidity of mine drainage.
The Federal Government started an extensive mine sealing program in 1933 as
Works Progress Administration and Civil Works Administration projects (39, 69, 74).
This program was continued for several years in Ohio, Pennsylvania, West Virginia,
Indiana, Illinois, Kentucky, Tennessee, Maryland, and Alabama. Several
investigations were made into the effectiveness of this sealing program, but no
definite conclusions were drawn and the subject is still open to debate.
83
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Mine sealing research was conducted in the 1940's, 1950's and 1960's by
Bituminous Coal Research, Inc., Mellon Institute, U.S. Bureau of Mines, and various
states and universities. Research and demonstration projects relative to mine sealing
have been conducted in the past decade by the U.S. Environmental Protection
Agency, and the U.S. Bureau of Mines assisted by both the U.S. Geological Survey
and U.S. Corps of Engineers. As a result of this research, new sealing methods have
been developed and many are presently being demonstrated.
The feasibility of sealing mines to control or abate pollution discharges will
depend upon more than the ability to close existing mine openings. The
characteristics and conditions of the underground mine system must be considered
in the planning and implementation of any sealing program. Therefore, the first step
in mine sealing is the collection and analysis of available site data which should
include, but not be limited to the following (39, 112, 127):
Geology
The local structure will determine whether a mine will have a discharge and
whether a mine can be effectively sealed. Since the geologic structure varies for
different mineral seams it is important that geologic information be collected for
each mine.
The geologic structure of the mine should be determined by drilling boreholes
or examination of outcrops. From the borehole information a structure map is
constructed which will show the strike and dip of the strata, folding, anticlines,
synclines, fractures, and faults. The location and direction of joints should be
plotted. The composition of the mineral seam and associated strata, mineral
structure, contours, and outcrop lines are factors which also deserve consideration
before mine sealing.
Hydrology
The elevation of the ground water table and the flow of ground water through
rock strata are important factors in the design of mine seals. Ground water levels will
determine the head expected against a seal. The flow of water in the mine will
determine the location and type of seal placed in the mine. Some factors affecting
ground water flow are rock type, dip of beds, joints, faults, and fracturing.
A water table map may be prepared by determining the elevation of all springs
and swamps found above the outcrop line and water levels in boreholes and wells.
These elevations should be plotted on a map and contoured. It should be assumed
that any water located above the mineral seam will eventually flow into the mine
and result in an increase of hydrostatic head on mine seals.
84
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Mining Considerations
The method by which a mine is developed is important in determining sealing
methods to be used. If a mine is developed updip then seals will be placed at the
lowest elevation of the mine and there will be a maximum head created against these
seals. In mines where mining is developed downdip the head against mine seals will
be greatly reduced or completely eliminated. When the head against seals is kept to a
minimum the seals will be safer and much more likely to abate pollution. Other
mining factors affecting the success of sealing will be: the relationship of the sealed
mine to other mines, both active and abandoned; the condition and width of mineral
barriers along outcrops and between adjacent mines; and the location of seals with
respect to solid strata and subsidence areas.
The construction of mine seals in abandoned or inactive underground mine
may be generally classified as either accessible or inaccessible (32, 39). These two
classifications may be defined as:
Accessible — The mine is open from the portal or shaft to the construction area
or may be opened with minor effort. Seals are constructed from within the
mine and may be visually inspected during construction.
Inaccessible — The mine is caved or flooded at the portal or shaft and would
require major effort and expenditure to re-open. Mine seals would be placed
from above ground through boreholes. There is no opportunity for visual
inspection during construction other than borehole cameras.
The cost of constructing mine seals will depend upon various cost factors such
as materials, labor, equipment, drilling, and grouting (29). The significance of each
factor will depend upon the type of seal being constructed, the size and location of
the seal, and the method of construction.
Materials which may be required during seal construction are aggregate,
concrete, masonry block, mortar, clay or soil, mine timbers, pipe, and grouting
materials. Labor costs will greatly depend upon the size of the job, the method of
construction and the amount of site preparation required. The cost of equipment
will depend upon such factors as equipment required for the particular method of
construction, job size, and equipment availability.
Drilling costs will include drilling required to determine the location and
alignment of mine entries and for placing materials in inaccessible mine seals.
Drilling may also be required for inspection of the finished seal or preparing grout
curtain drill holes in areas of permeable strata.
85
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Often the seal and adjacent strata are grouted to reduce water percolation. The
costs of grouting will include drilling, materials, labor, geologic testing, and
equipment. If grouting is to be performed the cost will usually be listed separately
from the price quoted per seal (29).
REFERENCES
8,27,29,32, 34,39,40,51,69,71,74, 111, 112, 127
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2.2 DRY SEAL
DESCRIPTION
Since the 1930's air sealing program of the U.S. Bureau of Mines (See
Section 2.3), dry seals have been utilized in conjunction with various air sealing
projects. Common practice has been to place dry seals in openings where there is
'little or no danger of a buildup of hydrostatic head. The main objective of this seal is
to prevent the entrance of air and water into underground mines.
Dry sealing involves the placement of impermeable materials or structures in
mine drifts, slopes, shafts, subsidence areas, fractures, and other openings. The seals
may be constructed of masonry block, clay, soil, or other suitable materials. This
type of sealing is generally confined to openings on the high side of a mine where
the mine workings lie to the dip (32).
IMPLEMENTATION
1930's Sealing Program
During the period from 1933 to 1939 and from 1947 to 1949 a $5.4 million
mine sealing program was administered by the U.S. Public Health Service in several
states east of the Mississippi River (69). As a result of this program an estimated
8,000 seals were placed in the openings of several hundred mines (73). The mines
were sealed by placing dry seals in all entries except for one where an air seal was
placed to allow water to discharge.
Often mine openings could be effectively dry sealed by blasting and caving
mine portals. When this method was impractical stone and earth were used to fill the
opening or a rock wall was constructed across the entry and backfilled with earth
and rock. Sketches of such sealing methods are shown in Figure 2.2-1.
An actual evaluation of the effectiveness of the dry seals in preventing the
entrance of air and water into mines was never made. Often the problem of air and
water entry into sealed mines is due to cracks and fissures in overburden and along
the outcrop, and not to leakage at sealed entries.
During the period from October 1, 1935 to September 1, 1937 a total of
84,844 openings were sealed in seven states under the Federal mine sealing
program (9). The total cost of constructing these seals including technical
supervision, labor, materials, equipment, and miscellaneous expenses was
$3,327,799.01. No information was available on the cost of individual air and dry
seals. However, the average cost per mine and opening sealed was $1,049.45 and
$39.22, respectively.
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NOTE: To be used in dry openings
where it is impractical to
blast in portal.
Thick Stratum of Stone
Earth at top of seal to be
tamped in such manner
that a permanent air seal
will be obtained
EARTH SEAL FOR DRY OPENING
NOTE: Rock and Earth Fill
In Dry Openings Only
ELEVATION
PLAN
ROCK AND EARTH FILL SEAL
FIGURE 2.2-1
TYPICAL DRY SEALS, 1930s SEALING PROJECT
(Adapted from Ref. 36)
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Bureau of Mines Sealing
Dry seals were constructed during a U.S. Bureau of Mines project to evaluate
the effectiveness of air sealing on a 31 hectare (77 acre), abandoned, highly acid
drift mine 64.4 kilometers (40 miles) northeast of Pittsburgh, Pennsylvania (73, 75).
Sealing was started under contract in November, 1965 and completed in May, 1966.
Seven dry seals were constructed on concrete footers, hitched into the roof and ribs,
and coated with urethane foam. Timbering was also performed on either side of each
seal for roof support. This type of dry seal is shown in Figure 2.2-2.
Additional work on the sealing project involved placing an air seal; constructing
two concrete dams in the main drift and air course; backfilling, compacting, grading,
and seeding of two strip mines on the outcrop; clay sealing and grouting of a badly
caved drift. As a result of the sealing, oxygen content in the mine was reduced from
20.9 percent to about 17.0 percent. During a 32 month period after sealing, effluent
volume was reduced a total of 26.5 million liters (7 million gallons) (75).
The average cost of each of the seven dry seals placed in the mine was
$5,089 (75). Material costs and quantities per seal were as follows:
Materials Quantity Cost
Urethane Foam 100 kg (222 Ib)
Timbering 7.2 cu m (3,060 bd ft)
Masonry Blocks 222
Concrete Footers 2.1 cu m (2.8 cu yd)
TOTAL $838
Labor requirements for constructing the seals (including the air seal) averaged
625 hours per seal at an average cost of $3,750 per seal. Average equipment costs,
including operator, were $1,120 per seal. Equipment costs were chiefly related to
clean-up of entries and grading for drainage and stability around the portals.
Roaring Creek — Grassy Run. West Virginia Seals
In 1964, a demonstration project site to evaluate mine sealing was selected in
the Roaring Creek —Grassy Run watershed near Elkins, West Virginia (57, 101).
The sealing was to involve sealing subsidence areas and boreholes, backfilling strip
mines, water diversion from mines, and the construction of dry and air seals.
During the project 43 dry masonry seals were constructed in mine openings.
The dry seals were constructed from two courses of fly ash blocks and coated with
urethane foam on both sides to protect the blocks from acid attack. The mine was
timbered on both sides of the seal to keep the weight of the roof off the seal.
89
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-filled hitch
Voids between blocks
filled w/urethane foam
Faces of seal coated
w/ urethane foam
1.3cm (1/2 in.) Joint
20.3x20.3x4O.6cm
(8x8x16 in.)
concrete block
JL2.5
\ nr i»,
._ _ to 5cm
(Ito2in.)cavityfilled
w/urethane foam
TOP VIEW
2.5 to 5 cm
(Ito2in) Spacefilled
•— w/urethane foam
20.3x20.3x406 cm
x8xl6in)
concrete block
containing fly ash
Faces of seal coated
w/urethane foam
CROSS-SECTION
FIGURE 2.2-2
U.S. BUREAU OF MINES DRY SEAL
(Adapted from Ref. 75)
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The effectiveness of the dry seals could not be evaluated as air sealing of a large
1,215 hectare (3,000 acre) mine was not completed due to cost overruns. However,
dry seals such as the ones constructed at Elkins should effectively prevent the
entrance of air and water through mine entries.
An analysis of construction costs of 25 dry seals at the Elkins job showed a
maximum cost of $6,376 per seal and a minimum cost of $1,358 per seal. The
average cost per seal was $2,212 (101).
A breakdown of the seal construction was:
Work Area Number Direct Cost
Number of Seals Cost per Seal
2 2 $ 4,000 $2,000
7 3 5,298 2,766
8 1 6,376 6,376
14 1 1,358 1,358
27 12 23,706 1,975
30 6 14,574 2,429
The considerably higher cost of the dry seal on Work Area No. 8 was due to
high labor cost involved in opening and timbering the portal prior to seal
construction.
EVALUATION AND RECOMMENDATIONS
Dry seals are used only as a method of preventing the entrance of air and water
into underground mines. These seals are not designed to withstand water pressure;
therefore, their use must be limited to areas where little or no hydrostatic head is
expected. Dry seals are commonly used to close shaft, slope and drift entries,
subsidence areas, fractures, and other openings to underground mines.
The use of masonry block seals will be limited to horizontal or near horizontal
accessible entries. These seals should be placed on a concrete footer and hitched into
the roof and sides of the opening. Timbering of the mine roof may be required to
keep the weight of overlying strata off of the seal. The cost of constructing this type
seal will depend upon the size and condition of the mine opening and the amount of
materials, equipment, and labor required. Masonry block seal costs will range from
$2,500 to $5,000 per seal.
Often an effective dry seal can be constructed by compacting clay or other
suitable materials into the mine opening. The cost of constructing these seals will
include materials, labor, equipment, and any grading and revegetation required. The
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cost of this work can be measured on a cubic meter (cubic yard) basis or a lump sum
fee. The unit price for placing clay seals will range from $2.62 to $5.23 per cubic
meter ($2.00 to $4.00/cu yd). The costs of constructing clay bulkheads in mine
openings will range from $2,500 to $4,500 per seal.
Masonry block walls and clay plug seals may also be used to hydraulically seal
underground mines. These seals must be designed and constructed to withstand the
maximum expected water pressure. The implementation of these seals is further
discussed in Sections 2.4-2 and 2.4-5.
REFERENCES
5,9, 21, 32,36,39,42,52,56,57,60,61,62,69,71,73,75,99, 101, 111, 127
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2.3 AIR SEALS
DESCRIPTION
Air sealing of mines in the eastern coal fields has been practiced since the early
1920's. Several evaluations of various sealing projects have been made; however, the
effectiveness of air seals remains a controversial issue.
Air sealing of underground mines involves the sealing with impermeable
materials of all openings into the mine through which air may enter. One entry,
usually the lowest entry to the mine, is provided with an air trap which allows water
to discharge from the mine but prevents the entrance of air. In a successfully air
sealed mine the oxidation of sulfide minerals will be retarded, and thus, the
formation of mine drainage pollutants controlled.
Results of previous air sealing projects indicate that the success of sealing will
depend upon the ability to locate and seal all air passages to the mine. Underground
mines have numerous air passages such as surface mines, boreholes, joints, fissures,
and subsidence cracks. Even if all passages are located and sealed, porous overburden
and fractured outcrops may allow breathing of the mine with each change in
barometric pressure.
IMPLEMENTATION
1930's Sealing Project
During the early 1920's, researchers for the U.S. Bureau of Mines observed that
mines having caved or otherwise sealed entries were discharging water containing
little or no acidity. It was concluded that caving and/or sealing of the entries
excluded oxygen from the mine and prevented the formation of mine drainage. In
order to evaluate air sealing, three mines were experimentally sealed by the Bureau
in 1932 and discharges were analyzed. A reduction in acidity demonstrated that air
sealing reduced or prevented the formation of mine drainage. As a result of this
program, the Federal Government began an extensive mine sealing program in 1933
under Work Progress Administration and Civil Works Administration projects (69).
During the periods from 1933 to 1939 and from 1947 to 1949, the
$5.4 million sealing program was administered by the U.S. Public Health Service in
the states of Ohio, Pennsylvania, West Virginia, Indiana, Illinois, Kentucky,
Tennessee, Maryland, and Alabama (69). As a result of this program, air and dry
seals were placed in the openings of several hundred mines (73). The mines were
sealed by placing dry seals in all entries except for one where an air seal was placed
to allow water to discharge. Sketches of the types of seals used are shown in
Figure 2.3-1.
93
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Concrttt masonary air-trap seal
15.2cm.to 25.4cm. (6in.to 10in.)thick
Field Stone
.--Water Level 30.5 cm. {I ft.) deep
ELEVATION
Basin locattd at
point of lowest
elevation
LOOM field stone to be used as
a filter and trash rack
PLAN
CONCRETE OR MASONRY AIR-TRAP SEAL
Clay a Rock Seal
Blind Ditch
Rocks set in cement mortar
30.5cm (I ft.)
Section Through Blind Ditch
Use Tile Pipe For Small Flow
CLAY 8 ROCK WATER SEAL FOR CAVED PIT MOUTH
FIGURE 2.3-1
TYPICAL AIR SEALS, I930's SEALING PROJECT
(Adopted from Ref. 36)
Rock
94
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An overall evaluation was never made as to the effectiveness of the program in
reducing mine drainage pollution. The U.S. Public Health Service estimated a
28 percent reduction in the acid load of the Ohio River. The Pennsylvania Sanitary
Water Board partially attributed a decrease in acidity in the Monongahela River to
the sealing program (73). It was also claimed that the program so reduced the mine
drainage problem in Pennsylvania that in various streams fish life returned and water
was used for industrial and domestic purposes (71). A West Virginia report (61)
claimed that as of February 1, 1936, a reduction of 77.8 percent occurred in the
acid load discharging from 345 sealed mines.
During the period from October 1, 1935 to September 1, 1937, a total of
3,171 mines and 84,844 openings were sealed in seven states under the Federal mine
sealing program (9). Mines were sealed in the seven states as follows:
Openings Sealed
State Mines Sealed and In Progress
Alabama 31 660
Indiana 60 910
Kentucky 488 2,625
Maryland 19 45
Ohio 1,769 18,111
Pennsylvania 468 58,212
West Virginia 336 4,281
A listing of the expenditures for these seals is shown in Table 2.3-1. An analysis
of these costs reveals that the average cost per mine sealed and per opening sealed
was $1,049.45 and $39.22, respectively. The average labor cost per hour was
$0.496 (9).
Pennsylvania Sealing Program
After the completion of the Federal sealing program, most areas failed to
continue sealing abandoned mines. The Pennsylvania Department of Mines had been
sealing mines since passage in 1935 of the Bituminous Mining Law, Act No. 55. In
1947, a Pennsylvania law created a Mine Sealing Bureau within the State
Department of Mines and appropriated $1,090,000 to continue work on mine
sealing.
An evaluation of the Pennsylvania sealing work reported that (71): the
Borough of Barnesboro began taking its water supply from the discharge of a sealed
mine; between 1937 and 1950 the Youghiogheny River showed a decrease in acid
load from 789 to 168 metric tons per day (870 to 185 tons/day); the Casselman
River which had once been heavily polluted with mine drainage became alkaline and
95
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Table 2.3-1
ON
Expenditures October 1, 1937 to September 1, 1967
1930's Mine Sealing Project
State
Alabama
Indiana
Kentucky
Maryland
Ohio
Pennsylvania
West Virginia
USPHS
Technical
Supervision
$ 8,060.16
20,819.35
61,217.03
11,304.39
66,610.89
130,905.70
73,174.38
Labor
$ 35,124.24
99,800.63
141,619.73
24,606.06
647,932.89
1,467,661.79
395,589.86
Materials
Equipment
& Other
$ 2,211.97
3,638.87
7,210.14
2,440.98
29,146.79
38,882.63
59,840.53
Total
Expended
$ 45,396.37
124,258.85
210.046.90
38,351.43
743,690.57
1,637,450.12
528,604.77
Region
$372,091.90
$2,812,335.20
$143,371.91 $3,327,799.01
-------
fish appeared; and in several areas in the central part of the state, water discharging
from sealed mines was being piped directly to homes and used for domestic
purposes. As indicated, some remarkable results of sealing were claimed; however,
no technical information was supplied to substantiate these results.
An investigation was begun in 1947 under the auspices of the Sanitary Water
Board of the Department of Health of Pennsylvania to study the effectiveness of air
sealing of coal mines to decrease the discharge of pollutants (18). Seven individual
mines in Westmoreland and Fayette Counties in Pennsylvania were air sealed during
1949 and 1950. Water samples were periodically collected and analyzed between
1947 and 1960. The oxygen content of the mine atmosphere was also monitored
after sealing.
From the data collected during this study it was concluded that air sealing did
not result in a significant reduction in acid load or oxygen content. Therefore, it was
determined that although correct in theory air sealing was ineffective in practice.
Bureau of Mines Sealing
To further evaluate the effectiveness of air sealing the U.S. Bureau of Mines
sealed a 31 hectare (77 acre), abandoned, highly acid, drift mine 64.4 kilometers
(40 miles) northeast of Pittsburgh, Pennsylvania (73, 75). Sealing was started under
contract in November, 1965 and completed in May, 1966. Eight separate seals (one
air and seven dry) were constructed. As shown in Figure 2.3-2 the seals were
constructed on concrete footers, hitched into the roof and ribs, and coated with
urethane foam.
Additional work in the sealing project involved constructing two concrete dams
in the main drift and air course; backfilling, compacting, grading, and seeding of two
strip mines on the outcrop; clay sealing of a 9.1 meter (30 foot) diameter subsidence
hole; and clay sealing and grouting of a badly caved drift. Construction of the seals
also involved timbering on either side of each seal for roof support.
Results of the chemical analysis of samples taken before and after sealing were
as follows (75):
97
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1111 vi i"v
./• S s ->i J S S S\ S .xV S\ S S s A I
Hitch
ELEVATION A
oo
Roof Rock
Facts of Seal Coated w/ Urethane Fbam«f
Asbestos-cement pipe
30.5cm(l2in.)id
Concrete Footer
FIGURE 2.3-2
U.S. BUREAU OF MINES AIR SEAL
(Adapted from Ref. 75)
-------
Before Sealing After Sealing
Parameter
pH
Total Acidity
(mg/1)
Sulfate
(asS04)(mg/l)
Calcium
(as CaCX)3)(mg/l)
Range
2.9-3.2
75-
655-
203-
1,290
2,260
1,242
Mean
3.1
514
1,403
505
Range
3.0-5.5
45 - 490
356- 1,180
36 - 625
Mean
3.4
211
874
405
Magnesium
(asMgCO3)(mg/l) 109-520 285 76-336 185
Total Iron
(as Fe2O3)(mg/l) 13-508 160 5-160 62
Their results show an increase in the mean value of pH from 3.1 to 3.4 and a
decrease in the mean concentrations of acidity, sulfate, calcium, mangnesium, and
total iron. After sealing the oxygen content in the mine was lowered from
20.9 percent to about 17.0 percent.
After sealing a reduction of 26.5 million liters (7 million gallons) in effluent
volume and a reduction of 150 mg/1 in effluent acidity were attributed to the air
sealing (75). The reduction in oxygen concentration seemed to stabilize the mine,
and thus, decreased the variance in total acidity of the effluent.
The total cost for sealing, reclamation and related work at the mine was
$57,420. A breakdown of the costs follows (75):
Timber treated - 56.9 cu m (24,390 bd ft) $ 5,146
Urethane Foam - 908 kg (2,000 Ib) 3,510
. Masonry blocks - 2,002 5 24
Pipe-51m (167 ft) 528
Concrete - 21 cu m (28 cu yd) 504
Miscellaneous 288
TOTAL MATERIAL $ 10,500
99
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Equipment and operator
Labor (5,000 man-hours)
TOTAL EQUIPMENT AND LABOR
Sealing 2 strip pits 1.2 hectares
(3 acres), 1 surface subsidence
depression, and 1 caved entry
Grading access roads and
portal areas
GRAND TOTAL
$ 8,960
30,000
$49,460
7,000
960
$57,420
The cost of the air seal including mucking, timbering, hitches, footers, masonry
blocks, and foam was $14,800. This cost was high due to the size of the entry,
6.7 meters (22 feet) wide and 1.5 meters (5 feet) high. The average cost of each dry
seal was $5,089.
Shavers Fork, West Virginia Seals
In the spring of 1966 a fish kill was reported at the U.S. Bureau of Sport
Fisheries and Wildlife Fish Hatchery at Bowden, West Virginia. This kill was
reportedly due to the discharge of acid mine drainage into Shavers Fork. In an
attempt to improve the water quality of Shavers Fork, the West Virginia Department
of Mines air sealed several small mines which were discharging into Taylor Run, Red
Run, and Fishing Hawk, all tributaries to Shavers Fork (99).
A total of twelve air seals and four dry seals were placed in five different
abandoned coal mines. A breakdown of the seal placement follows:
Area 1 Big Knob Mine
Savage Mine
Summerset-
Cambria Mine
Area 2 Red Run Mine
Seals
Placed
6 Air Seals
1 Air Seal
1 Dry Seal
1 Air Seal
1 Dry Seal
2 Air Seals
2 Dry Seals
Date
Constructed
October, 1967 Sewell
November, 1967 Sewell
September, 1967 Sewell
August, 1967 Sewell
Area 3 Fishing Hawk Mine 2 Air Seals August, 1968 Sewell
100
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All seals were constructed by prison labor under direction of the West Virginia
Department of Mines. The mines were sealed by timbering the mine entries, placing
solid concrete block seals, and backfilling against the block seal. A diagram of the air
seal is shown in Figure 2.3-3.
Beginning in November, 1967, seasonal samples were collected at the seals and
analyzed by the U.S. Environmental Protection Agency, A review of four years of
data indicates that ion concentration and pollution loads discharging into Shavers
Fork did not change to a great extent. Discharges at Big Knob and Savage Mines
showed a reduction in mean acid loads of 60 to 80 percent, iron 25 percent, and
sulfur 45 to 51 percent (99). This decrease in loads was due to a decrease in
discharge and not an improvement in water quality. The results of the effectiveness
of these seals was questionable as sufficient background data was not collected, and
experienced technicians were not always available to collect samples and measure
flows.
Roaring Creek — Grassy Run, West Virginia Seals
The Committee of Public Works of the U.S. House of Representatives issued a
report, "Acid Mine Drainage," in 1962 which called for a demonstration program to
evaluate mine sealing procedures. In 1964, the first demonstration project site was
selected in the Roaring Creek — Grassy Run watershed near Elkins, West Virginia.
The project was a cooperative effort between Federal agencies and the state of
West Virginia (57, 101).
Work was begun on the air sealing of a large 1,215 hectare (3,000 acre)
underground mine. Sealing was to involve sealing subsidence areas and boreholes,
backfilling strip mines, water diversion from mines, and the construction of dry and
air seals. Due to cost overruns sealing of this mine was never completed and only the
south side of the mine was sealed. Eleven air seals were placed in the mine.
Subsidence areas over much of the area were not corrected and several entries were
not sealed. As a result of the incomplete sealing no reduction in oxygen
concentration behind the seals was observed and there was little if any reduction in
pollution load discharging from the mine (60).
A small (several acres) isolated mine, RT 9-11, was completely sealed during
the Elkins project. Sealing work involved the placement of an air seal, the sealing of
one portal with clay, and the regrading of 31.6 hectares (78 acres) of surface mined
area.
Within two months after sealing the oxygen content in the mine dropped to
9.1 percent. The oxygen content varied between 7.0 and 10.8 percent until the
fourth quarter of 1969 when the level raised to near 15 percent. It has remained
near that level since (57, 60).
101
-------
[FOOTER]
FIGURE 2.3-3
TYPICAL AIR SEAL
SHAVERS FORK, WEST VIRGINIA
(Adapted from Ref. 99)
102
-------
Analysis of samples collected at mine RT 9-11 are shown in Table 2.3-2. A
reduction in the concentration of acidity, iron, and sulfate has been observed.
However, due to an increase in flow, there has been little reduction in pollution load
discharging from the mine.
A total of 55 masonry seals (43 dry and 12 air) were constructed during the
Roaring Creek - Grassy Run Project. A cost breakdown of the 55 seals
follows (101):
Total Direct Labor $65,949
Total Equipment 50,729
Total Indirect Cost 110,913
TOTAL $227,591
Direct and indirect costs included clean-up of mine entrance, temporary and
permanent timbering, concrete footers, concrete block walls, urethane foam coating,
75 percent overhead and 6 percent general and administrative.
The average cost per seal for the construction of the 55 seals was $4,138.
Direct labor and equipment costs per seal averaged $1,199 and $922, respectively.
An analysis of three air seals constructed shows that direct costs ranged between
$3,128 and $5,032 and the average cost per air seal was $4,076.
EVALUATIONS AND RECOMMENDATIONS
Although air sealing has been performed since the early 1930's, there has not
been much documentation of the effectiveness of this sealing technique. The
evaluation of many air sealing projects has been based upon limited or insufficient
data collected before and after sealing. The long term effectiveness of air sealing in
controlling mine drainage pollution from abandoned underground mines has not
been documented.
The most extensive air sealing project was the 1930's sealing program
administered by the U.S. Public Health Service. However, no funds were provided
for an evaluation of the project effectiveness or for routine inspection and
maintenance of the seals. Many of these seals have been destroyed and many of the
sealed openings are now discharging large quantities of pollution. A review of the
more recent sealing projects reveals that there is a general disagreement among the
various investigators as to the effectiveness of air sealing in controlling pollution
discharged from abandoned underground mines.
103
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Table 2.3-2
Analysis of Mine Water Samples
Mine RT 9-11
Oxygen
Within
Mine
Percent
Before
Mean
Sealing3
21
Minimum
After
Year -
1967
1968
1968
1968
1968
1969
1969
1969
1969
1970
1970
1970
1970
1971
1971
1971
1971
1974d
Sealing
Quarter
4
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
-
9.1
8.3
10.8
7.0
7.4
—
—
7.0
14.8
15.0
12.0
—
13.3
15.0
15.3
14.0
—
—
Acidity
CaC03
mg/1
591
438
359
325
334
344
265
350
339
376
327
263
310
297
294
249
248
276
326
370
PH»
2.8
3. 1C
3.2
3.2
3.2
3.2
3.2
3.2
3.2
2.9
3.1
3.1
2.9
3.1
3.3
3.2
3.2
3.0
2.9
3.1
Iron
mg/1
93
48
85
74
68
72
72
63
91
62
71
74
49
72
83
56
47
56
73
10
Sulfate
mg/1
1,035
710
797
686
702
708
627
645
656
717
678
603
628
845
606
488
508
460
535
410
aMarch 1964 - August 1967
bMedian Value
cMaximum Value
Samples collected August, 1974 by EPA Personnel
104
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A majority of the air sealing projects have been performed in the eastern coal
fields. The success of these projects has depended upon the ability to locate and
effectively seal all air and water passages to the underground mine system. After
completion of the sealing operation, new air passages may develop as a result of roof
collapse and fracturing of overlying strata. Air sealing may also produce a pressure
gradient between the mine and outside atmosphere which results in air flow into and
out of the underground mine.
Although air sealing does not appear to be a suitable method of controlling
mine drainage pollution in the eastern coal fields, this technique may be applicable
to mines having thick, unfractured overburden and tight outcrops. Under such
conditions a reduction in the oxygen concentration of the mine atmosphere and an
improvement of water quality could be expected. However, the long term
effectiveness of air sealing will depend Upon the method of seal construction and the
condition of the natural mine system.
The costs of constructing air seals will range from $4,000 to $6,000 per seal.
The seals should be placed on concrete footers, hitched into the side and roof of the
openings, and coated to protect against acid attack. Timbering of the opening should
be performed to keep the weight of the roof off of the seal. Factors affecting the
cost of construction will include the size and condition of the mine opening, method
of construction, and the amount of equipment, materials, and labor required.
REFERENCES
2, 4, 5, 9, 18, 20, 21, 27, 32, 36, 39, 42, 52, 56, 57, 60, 61, 62, 69, 71, 73, 74, 75,
99, 101, 111, 118, 127
105
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2.4 HYDRAULIC SEALS
Hydraulic sealing of abandoned underground mines creates an impoundment in
which mine seals and the mine perimeter serve as an underground dam. The success
of sealing will depend upon the ability of the entire dam structure to withstand
water pressure and control mine water seepage. Properly designed and constructed
hydraulic seals are capable of withstanding pressures in excess of 300 meters
(1,000 feet) (39). However, mine seals form only a small portion of the underground
dam. The mine perimeter which forms most of the impoundment determines the
feasibility and practical limits of inundation.
Mineral barriers along the mine perimeters are often the weakest link in the
underground impoundment. During active mining, barriers are left along mineral
outcrops and between adjacent mines. These mineral barriers are of non-uniform
thickness and frequently are unable to withstand water pressure. Physical failure of
these barriers can occur; however, more often, seepage resulting from increased
water pressure prevents significant increases in water level.
The first step in hydraulic sealing is to determine the ability of the natural mine
system to impound water. This will require the collection and evaluation of available
pertinent mine site data including (127):
1. Mine Maps
2. Hydrogeologic Data
3. Borehole Logs
4. Outcrop Lines
5. Mineral Structure Contours
6. Aerial Photogrammetric Mapping
This data will assist in identifying hydraulically unsound areas such as surface
mined outcrops, subsidence holes, boreholes, fractured mineral barriers, and other
highly permeable zones that may allow water to discharge.
The feasibility of inundating the mine is determined by plotting the expected
limits of the mine pool on a mine map. All areas where water pressure will be
exerted are identified and hydraulically evaluated to determine their ability to
withstand the maximum expected pressure. The ability of hydraulically unsound
areas to impound water may be improved by sealing or grouting. However, such
106
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remedial measures may be technologically or economically impractical. If the
natural mine system severely limits the feasibility of mine inundation, the desired
mine pool elevation will have to be lowered or the sealing project abandoned.
Mine seals can be constructed in a variety of ways, using many different types
of materials. Seals can be placed to plug shaft, drift and slope entries, boreholes,
subsidence areas, and similar discharging openings. The seals must have sufficient
internal strength to withstand water pressure and should be anchored into the mine
opening. Leakage often occurs around seals due to the fractured and unstable
condition of the strata surrounding the seal. As previously mentioned, sufficient
internal strength is easily obtained. Anchoring of the seal and controlling leakage
will be much more difficult.
Mine sealing is a dangerous operation requiring the knowledge and judgment of
persons having expertise in mining, engineering, and hydrogeology. Sudden
discharges resulting from the failure of a seal or the natural mine system can have
devastating downstream effects upon human life, property, and aquatic organisms.
Mine sealing decisions related to seal design and construction, therefore, require
technical evaluation by competent individuals.
The build up of excessive water pressure within a sealed mine can be controlled
by drilling an emergency discharge borehole into the mine. The borehole would be
drilled from a surface elevation equal to the maximum allowable mine pool
elevation. As the mine pool approaches the maximum level, gravity discharge
through the borehole prevents further water level increase. The borehole must be
capable of discharging water at a rate equal to the maximum expected inflow to the
mine pool. This emergency discharge system requires little maintenance and
supervision. The borehole should be cased its entire length and protected at the
surface to insure that it remains open and operational.
A mine pool drawdown system should also be included in the mine sealing
plan. Theis system would allow the mine to be completely drained in emergency
situations, or in the event that the mine is reopened. During mine sealing, a pipe
should be constructed through a mine seal, preferably at the lowest mine entry. The
pipe is equipped with a manual valve on the outby side of the seal. When the valve is
opened water discharges from the mine and the mine pool can be lowered to its
pre-sealing level.
Various types of hydraulic seals have been recently demonstrated in the United
States. A majority of this sealing work has been performed on abandoned
underground coal mines in the East, as part of Federal and state acid mine drainage
research and demonstration programs. Few of these sealing techniques have been
completely successful in controlling mine drainage discharges. In some instances, the
lack of success has been due to failure of the seal, but in most cases is attributable to
the condition of the natural mine system.
107
-------
A major problem encountered during the various sealing efforts has been the
inability to anchor the seal into the roof, ribs and floor of the mine. Leakage around
the seal and through adjacent strata has often prevented significant increase of the
mine pool. Curtain grouting adjacent to the mine seal has been partially successful in
controlling seepage through highly permeable zones. The installation of grout
curtains is presently required in many mine sealing projects.
The hydraulic sealing techniques described in this section include: double
bulkhead, single bulkhead, permeable limestone, gunite, clay, grout bag, shaft, gel
material, and regulated flow.
REFERENCES
2, 19, 27,39,42,45,46,47,58,62,72,81, 111, 112, 127
108
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2.4-1 DOUBLE BULKHEAD SEAL
DESCRIPTION
This seal is constructed by placing two retaining bulkheads in the mine entry
and then placing an impermeable seal in the space between the bulkheads. These
seals have been successfully demonstrated in both accessible and inaccessible mine
entries (32, 127).
The front and rear bulkheads are placed to provide a form for the center seal.
This seal is formed by injecting concrete or grout through the front bulkhead, if
accessible, or through vertical pipes from above the mine. Bulkheads have been
constructed with quick setting cement and grouted coarse aggregate.
Grouting of the bulkheads and center seal may be required to prevent leakage
along the top, bottom, and sides of the seal. Curtain grouting of adjacent strata is
often performed to increase strength and reduce permeability.
IMPLEMENTATION
Quick Setting Bulkheads
The Halliburton Company under contract to the Federal Water Quality
Administration (now Environmental Protection Agency) developed a method for
constructing double bulkhead seals in accessible mine openings. The front and rear
bulkheads were constructed by preparing two separate slurries and mixing them
together as they were pumped into the mine. The slurries react to give a viscous
quick setting material which is able to support its own weight as it builds (47). The
composition of the slurries was as follows:
Slurry No. 1 Slurry No. 2
Water - 3,293 liters (870 gal) Water - 3,974 liters
Cement-180 sacks (1,050 gal)
Bentonite - 318 kilograms
(700 Ib)
Sodium Silicate - 1,949 liters
(515 gal)
In February, 1969 a quick setting double bulkhead seal was constructed in
Opening No. 5 of Mine 62-008 near Clarksburg, West Virginia. This is a small,
8.1 hectare (20 acre), abandoned drift mine in the Pittsburgh coal seam. Prior to
109
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sealing, water was discharging at a rate of 0.16 liters per second (2.5 gpm). Analysis
of the water indicated that the discharge had a pH of 2.8, acidity of 2,260 mg/1, and
total iron of 600 mg/1 (98).
Front and rear bulkheads were constructed by hydraulically injecting the quick
setting slurry. The void between the bulkheads was filled by pumping Halliburton
Light Cement through grout pipes in the front bulkhead. A section view of the
completed seal is shown in Figure 2.4-1-1.
Leakage from this seal did not occur until September, 1970. Samples of this
discharge were collected and analyzed between September, 1970 and June, 1971.
The mean flow rate during this period was 0.01 liters per second (0.22 gpm). With
the exception of acidity which decreased, ion concentrations in the discharge were
about the same as before sealing. The minimum flow through the seal did reduce the
pollution load for all parameters by better than 90 percent. The maximum
hydrostatic head established behind the seal was 170 centimeters (67 inches) (98).
The total cost of constructing this seal was $9,499. This included $894 for site
preparation, $3,872 for materials, and $4,683 for equipment and operators.
A similar double bulkhead seal was constructed in the drift entry of an
abandoned deep mine in the Kittanning coal seam (Mine RT 5-2) near Coalton,
West Virginia. Prior to sealing in September, 1969, the mine was discharging at an
average rate of 4.7 liters per second (74 gpm) (47, 98).
The rear bulkhead was constructed with quick setting cement material just in
front of an existing air seal. Grout pipes and AASHO No. 67 limestone were placed
in front of the rear bulkhead. The front bulkhead was then constructed of the same
material as the rear bulkhead. The limestone aggregate was stablized and made
impermeable by grouting with Halliburton Light Cement.
The completed seal successfully eliminated flow from the mine entry. Seven
days after work completion the head behind the seal was 0.98 meters (3.22 feet).
However, leakage was observed coming through an unknown opening to the right of
the seal. Remedial work involved placing a permeable aggregate seal in this opening.
As of October, 1969 the head behind the double bulkhead seal appeared to be
stabilizing at approximately 1.2 meters (3.78 feet) (47).
A physical inspection was made of this seal in September, 1971. There was
some flaking off of the front bulkhead, but no seepage was observed. The mine
entry was in good condition as the portal had been timbered prior to sealing.
The total cost of constructing this seal was $9,463. This included materials,
equipment, and $ 1,079 for site preparation.
110
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1.6m
(52ft.)
'*:::' •'••V:'cr-.:V-'.v- v>:
6. :
O' '
"."..'
o" • •. '•
.-•o '.'•:
-."•.'•• ••?.•'
.-•:-p-.-.o
. " -
•••":
-------
Grouted Aggregate Seals
The grouted aggregate double bulkhead seal was developed for sealing
inaccessible mine entries in Moraine State Park, Butler County, Pennsylvania. This
area has been extensively surface and underground mined for the Middle Kittanning
coal seam. In May, 1967, the Pennsylvania Department of Mines and Mineral
Industries engaged Gwin Engineers, Inc. to perform extensive engineering and
geologic investigations and recommend a mine drainage abatement program. The
rehabilitation project was to restore the aesthetic appearance of the area and prevent
mine drainage pollution of the proposed 1,306 hectare (3,225 acre) Lake
Arthur (95).
The engineering report recommended the construction of 60 mine seals at an
estimated cost of $15,000 per seal. A contract for sealing was awarded in 1969 and a
total of 65 double bulkhead seals was constructed between February, 1969 and
August, 1971. This work, Pennsylvania Project SL 105-3, was performed by
B. H. Mott and Sons, Inc.
Front and rear bulkheads were constructed by placing coarse, dry aggregate
through vertical drill holes. The bulkheads were then grouted to form solid front and
rear seals. Water was pumped from the void between the bulkheads and concrete was
poured to form a center plug. At each mine entry, curtain grouting of adjacent strata
was performed for a minimum of 15 meters (50 feet) on both sides of the
seal (32, 127). A construction drawing of this type of deep mine seal is shown in
Figure 2.4-1-2.
The mine sealing program was successful in reducing pollution discharges from
abandoned mines in the park. The hydraulic seals were constructed in the openings
of 19 mines. After sealing, the discharges from these mines were as follows (43):
eight mines had no flow; one mine had an average flow less than 0.06 liters per
second (1 gpm); eight mines have reduced flow rates; one mine has the same flow
rate; and one mine increased from 0.06 to 0.13 liters per second (1 to 2 gpm). As a
result, flow rates have been reduced from 9.2 to 3.6 liters per second (146 to
57 gpm).
Water levels within the mines are fluctuating within a range of 0.3 to 1.5 meters
(1 to 5 feet) which varies with precipitation and infiltration. The head behind the
seals has ranged from less than 0.3 meters (1 foot) to a maximum of 11.6 meters
(38 feet).
The total cost of constructing the seals and performing related grouting work
was $1,266,213 (43). The costs per seal ranged from $8,308 to $58,437, with an
average cost of $19,480 per seal. An average of 155 kilograms per day (341 Ib/day)
of acid was abated by the sealing program. This equals a cost effectiveness of
$8,169 per kilogram per day ($3,713 per Ib/day) of acid abated.
112
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-T—f
Bulkhead Drill Holes 15.2cm(6in.)dia on
0.9m(3ftTCenters w/Alignment Across
the Main Entry. Drill Holes to be Extended
Into Coal Ribs as Shown.
Observation ft/or
Pump Drill Hole
15.2cm (6in.)dia.
-f
Core Drill Holes-
As Directed By
The Engineer
E
10.
PLAN
.Observation
4 ft/or Pump
/Drill Hole
Location to be
Determined
In Field
Injection Holes For Center Plug Area.Location
and No. of Holes Dependent on Conditions,This
Drawing Shows the Minimum No.of Holes
Additional Holes May Be Required.
Grout Curtain Holes 7.6cm (3 in.) dia. on 3m
(10ft.) Centers on Alignment Parallel to ft
Approx. Halfway Between Front ft Rear
Bulkhead Drill Holes 15m (50ft.) on Both
Sides of the Mine Entry.
Distance Between Front ft Rear
Bulkhead Alignment 6.1 to 7.6m
(20 to 25ft.) as Directed by the
Engineer.
,Core Drill Hole
'and Injection
Hole Alignment
>xFfont BulkheoK 1°.
XlCourse Aqqregoterv
Portal
PROFILE
FIGURE 2.4-1-2
CONSTRUCTION DRAWING OF DEEP MINE SEAL
(Adapted from Ref. 43)
-------
Curtain grouting of adjacent strata represented 60.6, percent of the total cost
of the Moraine State Park project. Due to the inability to determine subsurface
conditions, the quantities required for curtain grouting were difficult to estimate.
Estimated contract costs and the actual costs for grouting were as follows (32):
Estimated
Contract Costs Actual Costs
Total Curtain Grouting $517,750.00 $819,745.60
% Total Project Cost 46.50 60.60
Cost/LM Drilled 24.05 26.80
(LF Drilled) (7.33) (8.17)
Cost/LM Curtain 169.82 262.47
(LF Curtain) (51.76) (80.00)
The double bulkhead grouted aggregate seal has been used in various main
drainage abatement projects performed in Pennsylvania as a part of that State's
Operation Scarlift Program. Nine of these seals were recently constructed under
Project SL 110-1C, Stone House Area, Brady Township, Butler County (84). Work
on this project was completed by the contractor, Allied Asphalt Company, Inc. in
September, 1974. The estimated cost of construction including grouting the center
concrete plug and curtain grouting adjacent strata was $11,740 per seal. The actual
costs of construction were $17,881 per seal. A listing of the contract estimates is
presented in Table 2.4-1-1.
EVALUATION AND RECOMMENDATIONS
The double bulkhead method of sealing mine entries has been successful in
flooding abandoned underground mines and withstanding relatively large amounts of
hydrostatic pressure. A majority of grouted aggregate seals constructed since 1969
have been placed in abandoned underground coal mines in Pennsylvania. These
sealing projects are funded as a part of Operation Scarlift, Pennsylvania's
$500 million bond issue for a Land and Water Conservation and Reclamation Fund.
Demonstration of the quick setting bulkhead seals has been limited to projects
performed by the Halliburton Company in West Virginia. Implementation of double
bulkhead seals in abandoned underground mines outside the eastern coal fields has
not been documented.
The maximum hydrostatic head established behind this seal type has been
approximately 12.2 meters (40 feet). Properly designed and constructed seals should
114
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Table 2.4-1-1
Contract Estimates
Mine Sealing - Stone House Area
Butler County, Pennsylvania
Estimated
Description Quantity Cost
Mine Sealing Bulkhead Construction
a. Drilling 15.2 cm 2,438 LM 6 $9.84/LM $ 24,000
(6 in) Holes (8,000 LF)(53.00/LF)
b. Concrete Aggregate 544 metric tons @ 6,000
$11.03/metrie ton
(600 tons)($10.00/ton)
c. Concrete 268 cu m @ $39.24/cu m 10,500
(350 cu yd)($30.00/cu yd)
d. Borehole Camera 15 days @ $300/day 4,500
Survey
Observation Drill Holes
a. Drilling 15.2 cm 91 LM @ $9.84/LM 900
(6 in) Holes (300 LF)($3.00/LF)
b. Casing Left 46 LM @ $6.56/LM 300
in Hole (150 LF)($2.00/LF)
Pressure Grouting & Exploratory Drilling
a. Drilling 2,134 LM @ $9.84/LM 21,000
(7,000 LF)($3.00/LF)
b. Cement for 5,000 sacks @ $4.00/sacks 20,000
Grouting
c. Fly Ash for 522 metric tons @ 11,500
Grouting $22.05/metric ton
(575 tons)($20.00/ton)
115
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Table 2.4-1-1 (cont.)
Description
Quantity
Estimated
Cost
d. Sand for Grouting
e. Admixture for
Grouting
Grout #1
Grout #2
Grout #3
f. Grout Pressure
Testing
1.8 metric tons @
$33.08/metric ton
(2 tons)($30.00/ton)
45.4 kg @ $6.61/kg
(100 Ib)($3.00/lb)
379 liters @ $0.79/liter
(100 gal)($3.00/gal)
379 liters @ $0.79/liter
(100 gal)($3.00/gal)
50 hours @ $30.00/hour
g. Grout Connection 150 @ $10.00 each
h. Core Drilling
Center Plug
152 LM @ $19.69/LM
(500 LF)($6.00/LF)
60
300
300
300
1,500
1,500
3,000
TOTAL CONTRACT ESTIMATE $105,660
February, 1973
Actual Costs as
Completed
September, 1974
$160,930
116
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be capable of withstanding greater pressures. The feasibility of sealing most often
will be limited by the ability of the natural mine system to withstand water pressure
and prevent water seepage (See Section 2.4).
• Technical specifications for the construction of grouted aggregate bulkheads
frequently require curtain grouting of adjacent strata to decrease permeability.
Grout holes are usually drilled on 3 meter (10 foot) centers on both sides of the seal.
Massive leakage, however, can occur along the perimeter of the seal. Due to the
settling of concrete and aggregate materials, it is difficult to form a good seal at the
mine roof. The sides, top, and bottom of the seal should be well grouted to insure an
effective seal around the bulkhead perimeter. Curtain grout holes should then be
spaced to insure that the entire space between holes is grouted.
Seals placed in accessible openings may be anchored by chipping a keyway in
the perimeter of the mine entry prior to injecting grout or concrete for the center
plug. Quick setting bulkheads may be constructed so that they fit tighter in the mine
as water pressure increases. The roof, sides, and floor should be cut to form a wedge
shape prior to pneumatic placement of the quick setting cement slurry. Sufficient
anchoring will allow the seals to withstand a greater hydrostatic head and will
decrease leakage around the seal perimeter. Grouting of the seal perimeter and
adjacent strata should also be performed.
An emergency discharge borehole should be drilled into the mine to allow
gravity discharge when the mine pool approaches its maximum allowable level. A
pipe with valve should be constructed through a seal near the lowest elevation of the
mine to allow drawdown of the mine pool (See Section 2.4).
The cost of constructing double bulkhead seals will depend upon the size of the
opening, the amount of material placed, the expected hydrostatic head, grouting
requirements around the seal perimeter, and the amount of site preparation
required. Inaccessible seal costs will include drilling required to locate the mine
opening and place the sealing materials.
Grouted aggregate seals including curtain grouting will normally range in cost
from $10,000 to $30,000 per seal. The amount of curtain grouting required will
depend upon subsurface conditions at each individual work site. In some instances
the average .costs for bulkhead construction and related grouting work may exceed
$50,000 per seal. Bids were opened on December 10, 1974 for the construction of
two double bulkhead seals under Operation Scarlift Project SL 108-3-1, East Branch
Clarion River, Sergeant Township, McKean County, Pennsylvania. The engineer's
estimate of unit prices for bulkhead construction, excluding grouting were:
117
-------
Unit Price
Approximate Engineers
Description Quantities Estimate
Drilling 15.2 cm (6 in) Holes 640 LM $13.12
(2,100LF)
Coarse Aggregate 190 metric tons $49.61
for Bulkheads (210 tons) 45.00
Class "C" Concrete 38.2 cu m $71.93
for Center Plug (50.0 cu yd) 55.00
Quick setting double bulkhead seals in accessible entries should range between
$15,000 and $18,000 per seal excluding grouting. Grouting around the seal
perimeter and curtain grouting of adjacent strata may result in construction costs
exceeding $20,000 per seal.
REFERENCES
32, 38, 40, 41, 43, 44, 47, 77, 84, 95, 98, 100, 127
118
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2.4-2 SINGLE BULKHEAD SEAL
DESCRIPTION
Single bulkhead seals are generally constructed of poured concrete, quick
setting cement material, or grouted aggregate. They can be constructed of other
materials, such as masonry block or brick. This type of seal has been demonstrated
in both accessible and inaccessible mine entries (45, 127).
Single bulkheads constructed of poured concrete were used to flood abandoned
sections of underground coal mines as early as 1926 (45). Such seals were capable of
withstanding water pressures as great as 49,217 kilograms per square meter (70 psi),
or 49.2 meters (161.5 feet) of water.
Grouted aggregate bulkheads are constructed by placing coarse, dry aggregate
in the mine either directly from within the mine opening or through vertical
boreholes. The aggregate is then grouted with a quick setting cement slurry to form
a solid aggregate plug (127).
Single bulkhead seals have also been constructed in accessible entries by
preparing two slurries and blending them together as they are pumped into the mine.
The slurries react to give a viscous quick setting cement material which is able to
support its own weight as it builds. The completed seal forms a solid plug in the
mine opening (47).
The effectiveness of single bulkhead seals most often will depend upon the
ability to control leakage around the seal perimeter. Grouting along the top, bottom,
and sides of the bulkhead may be required. Curtain grouting of adjacent strata is
often performed to increase strength and reduce permeability.
IMPLEMENTATION
Concrete Bulkheads
A 1937 report (45) described the successful and extensive water sealing
program at three mines in the midwest coal fields of the United States. These three
mines were the Saxton and Dresser, near Terre Haute, Indiana, and the Hegler, near
Danville, Illinois. All three of the mines had water conditions that required sealing of
abandoned sections. Each of these mines reportedly had over a hundred single
bulkhead seals.
119
-------
Two types of seals, primary and secondary, were constructed in these mines.
Primary seals were designed to withstand hydrostatic heads in excess of 49.2 meters
(161.5 feet). Secondary bulkheads were designed as temporary, low pressure seals
for a safeguard against the sudden break of other seals. Secondary bulkheads were
constructed in several different ways of concrete, blocks, and brick, in both straight
and curved shapes against the pressure side. The design of a secondary concrete
block bulkhead used at the Saxton Mine is shown in Figure 2.4-2-1.
Primary bulkheads were normally constructed of poured or quick setting
concrete. These bulkheads were hitched into the ribs and roof to solid unfractured
coal. When the floor was of clay, the bulkhead hitching was sunk through to solid
stratum. The top of the entry was timbered for a distance of 6 to 12 meters (20 to
40 feet) to prevent roof falls.
Grout pipes were often constructed in the bulkhead for pressure grouting of
the seal perimeter. A small diameter pipe for gas testing and water pressure
measurements, and a larger pipe 7.6 to 15.2 centimeters (3 to 6 inches) with a strain
inside and a gate valve outside were also placed through the seal. The larger pipe was
used for draining the flooded section. The design of two primary concrete bulkheads
placed in the Saxton mine are shown in Figures 2.4-2-2 and 2.4-2-3.
The costs of constructing these seals will, of course, vary with each installation.
At the Dresser Mine, the cost of constructing secondary or low pressure seals in
1937 ranged from $149 to $162 per seal. Based on values of the Engineering News
Record Construction Cost Index, the costs of these seals as of January, 1975 would
range from $1,300 to $1,500. In 1935, total labor and material costs for
constructing two primary bulkheads (Figure 2.4-2-2) in the Saxton Mine were
$589.90. The total volume of material placed in the two seals was 55.3 cubic meters
(72.3 cuyd). The cost of constructing these seals as of January, 1975 would be
approximately $3,200 per seal.
A single bulkhead concrete seal placed in a copper mine near Butte, Montana
reportedly withstood a head of 853 meters (2,800 feet) of water. This seal was
placed in a 2.7 by 2.1 meter (9 by 7 foot) crosscut to prevent the flow of mine
water from an abandoned mine to the active Anselmo Mine, operated by the
Anaconda Company. The sides, top, and bottom of the seal were hitched into
rhyolite. Information on the costs of constructing this seal was not available. Plan
and section views of the completed seal are shown in Figure 2.4-2-4.
Grouted Aggregate Bulkheads
In December, 1967, grouted limestone aggregate seals were placed in two
openings of Mine No. 40-016 near Clarksburg, West Virginia. This mine was a small,
120
-------
Precast Concrete Blocks
20.3x20.3x40.6 cm
(8x8x16 in.)
/
PLAN VIEW
FIGURE 2.4-2-1
SECONDARY CONCRETE BLOCK BULKHEAD, SAXTON MINE
(Adapted from Ref. 45)
'«•*
-------
Maximum Water Pressure
49217 kg/sq. in. (70psi)
Entry Approximatley
3m (10 ft.)
PLAN VIEW
Grout Pipe
5.1 cm (2 in.)
Slate
~^7
:.'.»•.'•'.•'•iA.-.•*:'•• .'•-i;
f.o-/-'o-.::-o-:•;«:.';':o.]
-xjj; t :..*.-.••.;•:*•&
AMo: •:<.;.:..»-:o^V.i
Sandy Shale
5.1 cm (2 in.) Cone. Blocks-
Grout Pipe
Test .Pipe
• '•'.'•'.'. • o •• •' .0 :: • 9.
S S S s S
o ° Drain Pipe< ?•
'••'•.• o- .'"
ll •
0 . •
Sandy Shale-
3m (10 ft.)
V/, Fireplay
FRONT VIEW
SIDE VIEW
FIGURE 2.4-2-2
DESIGN OF PRIMARY BULKHEAD USED AT SAXTON MINE
(Adapted from Ref. 45) ,
-------
tJ
c
1 r= -
1
1 • — -
| ^
1 =~
1 &==
V
•
IT
_JL_
JL
~T
Hi
"JL
n
|(
JL.
lit
— "~7T
II*
— li— =1
II
XI
1
— —^
,
>
<
A
t?
1
b>
3
m
rv>
•*
r*
1.2 to 1.5m r 0.5m (1.75 ft.)
Water
Pressure
II r
" P
n v.
li
li
II
Jroy Shale Roof
Test Pipe
in.) Drain Pipe
FRONT VIEW
SIDE VIEW
FIGURE 2.4-2-3
DESIGN OF PRIMARY BULKHEAD USED AT SAXTON MINE
(Adapted from Ref.45)
-------
SECTION A-A
33.5m (110 ft.)
•^'-^IvA'^l^
.4W 4T- VT* lU"1, *4 *J*fl.
s::::xfc:s£<''
• / V « A A
,* * " > r
^1
_ V
y'»~*1
' b •
' t>
Poured
>
PLAN VIEW
FIGURE 2.4-2-4
SINGLE BULKHEAD CONCRETE SEAL-BUTTE, MONTANA
124
-------
abandoned drift mine in the Pittsburgh coal seam. Construction of the seals and
remedial grouting work were performed by the Halliburton Company (47, 98).
The bulkhead seals were constructed by pneumatically placing 1.9 to
3.8 centimeter (3/4 to 1-1/2 inch) graded limestone in the mine. Each of the openings
was about 3.7 meters (12 feet) wide and 2.1 meters (7 feet) high. The aggregate was
then grouted by injecting a cement slurry through pipes placed in the mine prior to
placing the aggregate. Sealing reduced the discharge from the two openings to about
0.44 liters per minute (7 gpm), a reduction of 85 percent. A typical cross section of
the seals placed at the mine is shown in Figure 2.4-2-5.
The perimeter of the seals were grouted in an attempt to further reduce the
mine discharge. Holes were drilled on each side of the mine entries at an angle
extending through the coal outcrop to a point about midway in the grouted
aggregate. Various grout mixtures were then pumped through these holes. The
remedial grouting reduced the flow rate from the mine to 0.27 liters per second
(4.2 gpm).
After sealing, samples of the mine discharge were periodically collected and
analyzed between September, 1968 and June, 1971. During this period, flow from
the mine varied between 0.08 and 1.1 liters per second (1.3 to 18 gpm). The
hydrostatic head behind the seal ranged from 236 to 290 centimeters (93 to
114 inches). Data collected in 1970 and 1971 showed increased pollution loads over
previous years because of increased flow, resulting from massive leakage around the
seals (98).
The total cost of the sealing project was estimated to be $17,696, or
$8,848 per seal. Itemized costs for constructing the two seals were as follows (32):
Cleaning and Site Preparation $ 387
Aggregate Placement
Equipment Rental 3,060
Material - 272 metric tons @ $3.64/metric ton 990
(300 tons) ($3.30/ton)
Labor 640
Aggregate Grouting
Equipment Rental 1,322
Material 3,260
Labor 720
125
-------
1.9 to 3.6cm
(3/4 to 1-1/2 in.)
Aggregate >
0.95cm
(3/8 in.)
Minus
Aggregote
1.9 to 3.8cm
(3/4 to l-l/2in.)
Aggregate
Grouted Section
0.95cm
.(3/8 in.)
Minus
Aggregate
o o & v o o
fto • o »
A n 0 fr p D
2.54cm
(I in.)
Grout Pipes
1.9 to 3.8cm
(3/4 to I-1/2in.)
Aggregate
.54cmi (I in.)
rout Pipes
ON
76m (25ft.)
TYPICAL SECTION
5.1 cm (2 in.)
Drain Line
2.54 cm (I in.) Grout Pipes
OPENING NO. 2
OPENING NO. I
FIGURE 2.4-2-5
GROUTED AGGREGATE BULKHEAD, MINE NO. 40-016
(Adapted from R«*. 47)
-------
Remedial Grouting
Site Preparation and Restoration $ 1,310
Equipment, Material and Labor 6,007
TOTAL $17,696
Quick Setting Bulkheads
In November, 1968, the Halliburton Company under contract to the Federal
Water Quality Administration (now Environmental Protection Agency) constructed
a quick setting single bulkhead seal in an abandoned mine near Clarksburg,
West Virginia. The mine, No. 62-008, was a small drift mine located in the
Pittsburgh coal seam. The bulkhead was placed in the main portal, Opening No. 4,
which was approximately 3.6 meters (12 feet) wide and 1.5 meters (5 feet)
high (47, 98).
The bulkhead was constructed by preparing two slurries and mixing them
together as they were pumped into the mine opening. The slurries react to give a
viscous quick setting material which is able to support its own weight as it builds.
The composition of the slurry was as follows:
Slurry No. 1 Slurry No. 2
Water - 3,293 liters Water - 3,974 liters
(870 gal) (1,050 gal)
Cement — 180 sacks Bentonite — 318 kilograms
(700 Ib)
Sodium Silicate - 1,949 liters
(515 gal)
A section of the completed bulkhead seal is shown in Figure 2.4-2-6.
Only limited records were kept on the quality of the water discharging from
the mine prior to sealing. Water samples collected and analyzed during September
and October, 1968 showed the following (98): average discharge - 0.17 liters per
minute (2.7 gpm), acidity — 17.7 kilograms per day (39 Ib/day), and total
iron — 3.7 kilograms per day (8.1 Ib/day).
The bulkhead seal successfully eliminated the mine discharge until
September, 1969. At this time massive leaks began to occur between the bulkhead
and the surrounding coal strata. Water quality records maintained between
September, 1969 and June, 1971 showed the mine discharge varied between 0.03 to
2.8 liters per second (0.45 to 44.9 gpm). Due to the increased flow, acid and iron
loads (kg/day) increased significantly. During the period after sealing, the
hydrostatic head behind the seal remained constant at 251 centimeters (99 inches).
127
-------
oo
1.8m
(5.8ft.)
/
\
• '•'.'•••'.'.'•' • • ' • • / ' • ' •
•.••.•'-' • '.' •'. • •' '• - • ' •
•.'-.'• . . ••' . . 'o-'-. -.'-.. ' '.!-.'•
3m (10ft.)
AV6.
HIGH WALL
1.6m (5.2ft.) i 0.8m
0.3m
(Iff.)
(2.5ft.)
FRONT VIEW
SIDE VIEW
FIGURE 2.4-2-6
QUICK SETTING BULKHEAD SEAL, CLARKSBURG, W.VA.
(Adapted from Ref. 47)
-------
The total cost of constructing the single bulkhead seal in Opening No. 4 was
$3,564. This included $647 for site preparation, $1,165 for materials, and $1,752
for equipment and operators (32).
EVALUATION AND RECOMMENDATIONS
The grouted aggregate single bulkhead seal has been demonstrated in both
accessible and inaccessible mine entries. Generally, this type seal has been ineffective
in controlling mine water discharges. Massive leakage has often occurred due to
incomplete grouting of the aggregate or poor anchoring in the mine entry. The
maximum head reportedly held by the grouted aggregate bulkhead is approximately
3 meters (10 feet).
Highly permeable zones are often located around the perimeter of the
bulkhead. The effectiveness of the seal will depend upon the ability to form a water
tight seal along the top, sides, and bottom of the aggregate. Therefore, these areas
should be grouted along the total length of the bulkhead. Curtain grouting on both
sides of the seal will be required when the adjacent strata is hydraulically unsound.
The use of the grouted aggregate single bulkhead seal should be limited to areas
where low pressure is expected. The double bulkhead seal would be better suited for
high pressure application (See Section 2.4-1).
The cost of constructing a grouted seal will depend upon the type of opening
(accessible or inaccessible), the volume of aggregate placed, and the amount of
grouting work required. The cost of a single bulkhead grouted aggregate seal
(including curtain grouting 15.2 meters (50 feet) on both sides of the seal) in a
3.7 meter (12 foot) wide by 1.5 meter (5 foot) high mine void at a depth of
15.2 meters (50 feet) would be approximatel $ 11,000 as follows:
Drill Holes (8) 129 LM @ $13.15/LM $ 1,696
(424 LF)(4.00/LF)
Cement for Grouting 35 sacks @ $4.70/sack 165
Fly Ash for Grouting 35.4 metric tons® 696
$22.03/metric ton
(39 tons)($20.00/ton)
Bentonite for 90.8 kg @ $22.03/kg 2,000
Grouting (200 lb)($ 10.00/lb)
No. 2B Stone 27.2 metric tons @ 1,350
$49.63/metric ton
(30 tons)($45.00/ton)
129
-------
Curtain Grouting 30.5 LM @ S163.93/LM 5,000
(100LF)($50.00/LF)
TOTAL $10,991
Unit prices for this estimate were based upon the December, 1974 engineer's
estimate for constructing two deep mine seals in Pennsylvania under Operation
Scarlift Project SL 108-3-1. Total costs of constructing single bulkhead aggregate
seals will normally range between $10,000 and $20,000 per seal.
Concrete bulkhead seals have been constructed in underground mines since the
early 1900's. These seals were used to confine water in abandoned sections of mines,
extinguish mine fires, or hold back mine gases. The concept of utilizing these seals to
control acid mine discharges from abandoned underground mines has developed in
recent years. The hydrostatic head behind a majority of these seals has been less
than 61 meters (200 feet). Bulkheads can be designed to withstand water pressures
in excess of 305 meters (1,000 feet); however, the maximum hydrostatic head will
be limited by the condition of the natural mine system (See Section 2.4).
Bulkheads constructed of poured or quick setting concrete should be anchored
by hitching into the roof, sides, and floor of the mine opening. The perimeter of the
opening may also be cut to form a wedge shape prior to placement of the concrete.
This shape allows the seal to fit tighter in the mine opening as water pressure
increases. Sufficient anchoring will allow the bulkheads to withstand a greater
hydrostatic head and will decrease leakage around the seal perimeter. Grouting of
the seal perimeter and adjacent strata should also be performed.
The total cost of constructing single bulkhead seals will depend upon such
factors as size and condition of the opening, expected hydrostatic head, and
materials, equipment, and labor required. At $78.47 per cubic meter ($60/cu yd)
the cost of concrete alone for the seal constructed near Butte, Montana (See
Figure 2.4-2-4) would exceed $15,000. However, the average costs of seal
construction including grouting will normally range between $5,000 and
$10,000 per seal.
Single bulkheads constructed of concrete block are highly susceptible to
damage and should not be used where high water pressure is expected. The mine
opening should be timbered on both sides of the seal to keep the weight of the roof
off the seal. Concrete block wall seals will cost in the range of $1,500 to $5,000
each.
130
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Plans and specifications for sealing abandoned underground mines should
include provisions for an emergency discharge borehole to allow gravity discharge
when the mine pool approaches its maximum allowable level. A pipe should be
constructed through at least one bulkhead to allow drawdown of the mine pool (See
Section 2.4).
REFERENCES
27,32,45,47,77,98,100, 127
131
-------
2.4-3 PERMEABLE LIMESTONE SEAL
DESCRIPTION
Sealing of underground mines with permeable seals involves the placement of
permeable alkaline aggregate in mine openings where acid water may pass through it.
As the acid water passes through the alkaline material, neutralization occurs and
precipitates are formed. These precipitates fill the void space in the aggregate and in
time the seal actually becomes a solid single bulkhead seal and floods the mine. A
section of a permeable seal is shown in Figure 2.4-3-1.
An example of a permeable seal would be the use of limestone as the alkaline
aggregate material. Seals of this type have been constructed and successfully
demonstrated by the U.S. Environmental Protection Agency and Halliburton
Company at sites in West Virginia (47, 98).
IMPLEMENTATION
Laboratory Studies
NUS Corporation, Cyrus William Rice Division and E. D'Appolonia Consulting
Engineers, Inc. (87) conducted laboratory studies of self-sealing limestone plugs for
mine openings. The purpose of these studies was to determine the optimum
limestone material for such a treatment and sealant technique.
Based on previous research by Bituminous Coal Research, Inc., (13) three
limestones, Types A, B and C, were selected for the limestone plug study. The
limestones were classified according to effective neutralization with Type A — the
most effective neutralizing agent; Type B — intermediate; and Type C — the least
effective neutralizing agent.
Laboratory studies were performed on six size ranges of each of the three
limestones using ferric, ferrous, and ferric/ferrous synthetic mine waters. A summary
of the results of these studies follows (86, 87):
1. A 0.95 centimeter (3/8 inch) to dust size Type A aggregate placed at
60 percent relative density was the most satisfactory material tested.
2. Aggregate volume losses can occur due to settling of the stone upon being
wetted, erosion, and chemical reactions.
3. Limestone permeable seals will perform best on ferric mine waters.
132
-------
Ground Surface
Aggregate
. .
u
' . . \
/ •; • : °.'';\
Mine Entry
Aggregate Seal, Variable Width
FIGURE 2.4-3-1
TYPICAL CROSS SECTION OF PERMEABLE AGGREGATE SEAL
(Adapted from Ref. 127)
133
-------
4. Bentonite and fly ash additives improve water flow and treatment
properties.
5. Iron is precipitated and trapped in the aggregate but calcuim sulfate is not.
Clarksburg, West Virginia Seal
A permeable limestone aggregate seal was placed in Mine No. 62-008 near
Clarksburg, West Virginia by Halliburton Company in June, 1969 (47, 98). A total
of 61 metric tons (67 tons) of Harrold No. 12 limestone was pneumatically placed in
the 1.3 meter (4.3 foot) by 3.7 meter (12 foot) drift. The finished seal was
11 meters (36 feet) in length at the base and had 7.6 meters (25 feet) of roof
contact. Some settling later occurred which left a gap between the roof and
aggregate.
Prior to sealing, water was discharging from the mine at a rate of 0.19 liters per
second (3 gpm) and had a pH of 3.0 and mean acidity of 200 mg/1. After sealing, pH
increased (6.3 to 6.9) and acidity averaged 150 mg/1, but there was no reduction in
flow from the mine. Iron loads were 70 percent higher while sulfate loads did not
change appreciably. The evaluation of the effectiveness of this seal was affected by
the limited data collected prior to sealing.
The total cost for placing the permeable limestone aggregate seal in Mine
No. 62-008 was $3,048. This cost included $756 for site preparation, $237 for
materials, and $2,055 for equipment and operators (32).
Coalton, West Virginia Seal
In September, 1969, Halliburton Company placed a permeable limestone seal
in Opening No. 2 of Mine RT 5-2 near Coalton, West Virginia (47, 98). A total of
150 metric tons (165 tons) of AASHO No. 8 aggregate and agriculture lime were
pneumatically placed in the drift. The void space between the roof and aggregate
was grouted by pumping 2.8 cubic meters (100 cubic feet) of grout slurry into the
upper portion of the aggregate. Plan and section views of the seal are presented in
Figure 2.4-3-2.
After sealing mean flow rates decreased better than half and water discharging
through the seal was of better quality. Mean acid, total iron, and sulfate
concentrations were reduced 99 percent, 98 percent and 94 percent, respectively.
Hydrostatic head behind the seal stabilized above 1.8 meters (6 feet) after
January, 1970.
134
-------
3m(IOft)
Grout Plaetd In
^— Space BftwMn
C_ Roof and Aggregate
Highwall
AASHP No. 8 Aggr>gatfi 8V
;. • Agricultural- Lfrn« •/."-.'•.
7m (23.3 ft.)
Roof
SECTION VIEW
9m (30ft.) ova
LimcstdM •: Aggrcgat*
Highwall
PLAN VIEW
FIGURE 2.4-3-2
PERMEABLE LIMESTONE SEAL-MINE RT5-2,Opening No.2
(Adopttd from Rtf. 47)
135
-------
A physical inspection of this seal was made in September, 1971 and the seal
was determined to be in excellent condition (98). At that time water was still
seeping through the seal, indicating that all voids in the seal had not been filled by
the chemical reaction between the mine water and the limestone.
Construction costs for the permeable seal placed in opening No. 2 of Mine
RT 5-2 totaled $8,463. The cost included $3,447 for site preparation, $1,690 for
materials and $3,320 for equipment and operators. This cost was higher than the
Clarksburg seal due to excessive excavation required to prepare the opening, extra
grouting materials required for grouting the upper section of the seal, and the
corresponding extra equipment required (32).
Stewartstown, West Virginia Seals
In August, 1974, ECI-Soletanche, Inc., under contract with the Environmental
Protection Agency, installed four permeable limestone seals and grout curtains in
four deep mine entries near Stewartstown, West Virginia (100).
Each mine seal was constructed by pneumatically injecting AASHO No. 8
limestone aggregate and additives into the mine entries (10). The voids between the
roof and seal were grouted with a cement, fly ash, bentonite grout mixture. Strata
adjacent to the mine seals were pressure grouted for a minimum distance of
9.1 meters (30 feet) on both sides of the mine entries. A plan view of the seals is
shown in Figure 2.4-3-3.
An estimate of material requirements for the four seals made by EPA personnel
follows (10):
Mine Seals 1A and IB
AASHO No. 8 limestone - 0.95 cm to 245 metric tons
0 (3/8 inch to 0) (270 tons)
5 weight percent of rock dust 13 metric tons
(14 tons)
Bentonite (5 weight percent 13 metric tons
of final mixture) (14 tons)
Mine Seal No. 2
AASHO No. 8 limestone - 0.95 cm to 118 metric tons
0 (3/8 inch to 0) (130 tons)
136
-------
• Entry No. 2
Entry No. I
Entry No. I
Entry No. 3
I0.2cm(4in)l0 Drain
w/Valvt
LIMESTONE SEAL
3m (10ft) Center Spacing
Grout Holts
LIMESTONE SEAL
Observation Well
Sch 40 Pip*Casing,20.3cm(8ia)
FIGURE 2.4-3-3
PLAN VIEW
PERMEABLE LIMESTONE SEALS-STEWARTSTOWN, W.VA.
(Adapted from Rcf. 47)
-------
5 weight percent of rock dust fines 6.3 metric tons
(7 tons)
Mine Seal No. 3
AASHO No. 8 limestone - 0.95 cm to 136 metric tons
0 (3/8 inch to 0) (150 tons)
5 weight percent of rock dust fines 7.3 metric tons
(8 tons)
10 weight percent of fly ash 13.6 metric tons
(15 tons)
Actual material requirements for these seals varied approximately + 5 percent
from the estimate. Grout requirements were 8.7 cubic meters (310 cubic feet) for
the pressurized grout curtains and 26.8 cubic meters (958 cubic feet) for grouting of
void space between aggregate and roof (100).
EPA personnel are collecting water samples from the mine discharges and will
evaluate seal performance. The final evaluation will contain information on the
effectiveness of the bentonite and fly ash additives.
An estimated breakdown of anticipated costs for the Stewartstown seals
showed the total cost of construction to be $88,500 (33). The cost breakdown is as
follows:
Labor Costs $29,086
Equipment 20,142
Incorporated Materials 14,640
Miscellaneous Cost 5,724
Total Direct Cost $69,592
Overhead & Profit 18,908
TOTAL BID PRICE $88,500
Based upon the estimated total bid price, the average cost for placing each seal
would be $22,125. The high cost of constructing these seals is partially attributed to
equipment utilization. A further breakdown of labor, equipment, incorporated
materials, and miscellaneous costs is presented in Tables 2.4-3-1 through 2.4-3-4.
138
-------
Table 2.4-3-1
Labor Costs
Permeable Limestone Seals
Stewartstown, West Virginia
Classification No.
Laborers
Drill Operator
Drill Helper
Equipment Operator
Truck Driver
Foreman
Engineering
4
1
1
2
1
1
1
Rate/Hour
$ 5.38
6.08
5.89
6.02
5.70
70 . 00/day
150. 00/day
HEW and
Pension
$ .53
.64
.53
.64
.46
6. 00/day
6. 00/day
Payroll
Taxes 15%
$ .81
.90
.89
.90
.86
i0.50/day
22. 50/day
Living
Expenses
$ 1.50/hr.
1.50
1.50
1.50
1.50
15. 00/day
25 . 00/day
Total/Hour
$ 8.22
9.12
8.81
9.06
8.52
111.50
203.50
No. of
Hours
320
220
220
320
320
40
10
Total
$10,521.60
2,006.40
1,938.20
5,798.40
2,726.40
4,460.00
2,035.00
$29,086.00
-------
Table 2.4-3-2
Equipment Costs
Permeable Limestone Seals
Stewartstown, West Virginia
Truck Tractors
Bulk Trailers
Hi Lift Crawler MTD
Back Hoe
Dozer
Dewatering Pump
Grout Plant With Pump
Stake Bed Truck
Rotary Drill
Core Drill
Air Compressor
Auxiliary Pneumatic Blower
Dump Truck
Winch Truck
Pick-Up Truck
Pneumatic Packers, Pipes
Site and Accessories
No.
2
4
1
1
1
1
1
1
1
1
1
1
1
1
1
1
Complement
Days at Job
50
50
60
60
40
60
50
10
10
10
50
50
50
50
60
50
Value
$ 20,000
30,000
8,000
6,000
10,000
4,000
10,000
£. 000
100,000
6,000
8,000
8,000
6,000
4,000
4,000
6,000
Rental/Day
$ 54.00
81.00
21.60
16.20
27.00
10.80
27.00
21.60
270.00
16.20
21.60
21.60
16.20
10.80
10.80
16.20
Total
$ 2,700.00
4,050.00
1,296.00
972.00
1,080.00
648.00
1,350.00
216.00
2,700.00
162.00
1,080.00
1,080.00
810.00
540.00
648.00
810.00
TOTAL
$20,142.00
-------
Table 2.4-3-3
Incorporated Materials
Permeable Limestone Seals
Stewartstown, West Virginia
Material
§8 Limestone 0.95 cm to 0
(3/8 inches to 0)
Bentonite
Rock Dust
Fly Ash
Cement
15.2 cm (6 in.) Pipe
10.2 cm (4 in.) Pipe
20.3 cm (8 in.) Sched Pipe
5.1 cm (2 in.) Perforated
Timber 10.2 cm x 10.2 urn
(4 in. x 4 in.)
Planking 5.1 cm x 25.4 cm
(2 in. x 10 in.)
Posts
Fertilizer and Seeds
Shut Off Valve
Quantity
499 metric tons
(550 tons)
12.7 metric tons
( 14 tons)
36.3 metric tons
( 40 _ons)
90.7 metric tons
(100 tons)
1,500 bags
76.2 m (250 ft)
18.3 m ( 60 ft)
15.2 m ( 50 ft)
91.4 m (300 ft)
91.4 m (300 ft)
61.0 m (200 ft)
20
1
Unit Price
$12.13/metric tons
($11.00/ton)
$75.08/metric ton
($68.10/ton)
F. OBB. Pgh. plus
$ 5.40/metric ton
($ 4.90/ton)
delivery
$16.54/metric ton
($15.00/ton)
$17.64/metric ton
($16.00/ton)
$ 2.30/bag
6.89/m (2.10/ft)
6.23/m (1.90/ft)
19.69/m (6.00/ft)
3.61/m (1.10/ft)
0.82/m (0.25/ft)
0.82/m (0.25/ft)
1.00/each
150.00
TOTAL
Total
$ 6,050.00
1,022.00
600.00
1,600.00
3,450.00
525.00
114.00
300.00
330.00
75.00
50.00
20.00
300.00
150.00
$14,640.00
141
-------
to
Table 2.4-3-4
Miscellaneous Costs
Permeable Limestone Seals
Stewartstown, West Virginia
Jonds 1%
Insurance 1%
^uel and Lube $42.50/day 40 Workdays
Jtilities & Phone $20.00/day 40 Workdays
Small Tools
$ 885.00
885.00
1,700.00
800.00
1,454.00
TOTAL
$5,724.00
-------
EVALUATION AND RECOMMENDATIONS
Implementation of permeable limestone seals has been limited to
demonstration programs sponsored by the Environmental Protection Agency in
West Virginia. The long term effectiveness of this type seal has not been
demonstrated. The seal has been effective in improving water quality and reducing
the volume of mine discharge. Increases in pH and alkalinity, and decreases in acid,
iron, and sulfate loads have demonstrated the neutralizing ability of the seal. This
neutralization effect, however, is expected to decrease as the limestone aggregate
becomes coated with precipitate.
The theoretical end result of the permeable seal is a hydraulic seal. Neither the
Clarksburg nor the Coalton seals have been successful in eliminating flow from the
mine opening. The seals have attained various levels of mine inundation. Leakage
through the seal indicates that precipitates are not plugging the aggregate void or the
precipitates are unable to withstand water pressure. The addition of fly ash and
bentonite to the Stewartstown seals is expected to further improve sealing
effectiveness.
The use of the permeable type seal is limited to accessible mine entries. The
limestone aggregate (or other suitable alkaline material) must be properly graded and
placed to ensure that the mine water flowing through the seal has sufficient
retention time to be neutralized. The completed seal must be capable of
withstanding the maximum expected hydrostatic head. To allow drawdown of the
mine pool, a pipe should be constructed through the aggregate, and an emergency
discharge borehole should be drilled into the mine to allow gravity discharge when
the mine pool approaches its maximum allowable level (See Section 2.4).
During construction of the demonstration seals, settling of the limestone
aggregate has created a gap between the mine roof and the top of the seal. Atv
Clarksburg, water flowing over the top of the seal resulted in significant increases in
iron and acid loads in the mine discharge. Grouting of this void space at the Coalton
mine successfully eliminated leakage through this area. To ensure that a watertight
seal is formed around the seal perimeter, grouting of the sides and bottom of the seal
should also be performed. When strata adjacent to the seal are fractured or
hydraulically unsound, curtain grouting will be required.
The costs of constructing permeable seals will depend upon such factors as: size
of opening, materials, grouting requirements, site preparation, and proper selection
and utilization of equipment. It is difficult to estimate average costs of constructing
these seals since only six have been constructed as part of demonstration projects.
143
-------
Construction costs have ranged from $3,048 to $22,125 per seal. As improved
methods of construction are developed, costs should generally range from $5,000 to
$10,000 per seal.
REFERENCES
10, 13, 32, 33, 47, 53, 86, 87, 98, 100, 127
144
-------
2.4-4 GUNITESEAL
DESCRIPTION
This seal is constructed by placing successive layers of gunite, a pneumatically
placed low slump concrete, in a mine opening until the opening is completely filled.
The roof, sides, and floor of the mine opening are cut so that a tapered seal will be
formed. This seal must be placed in an accessible entry in areas of sound to
reasonably sound adjacent strata. A wood bulkhead is constructed on the inby side
to support the initial placement of gunite. Proper adjustment of mix and injection
nozzles allows the gunite to stand vertically, thus, eliminating the need for
forms (127). Plan and section views of a typical gunite seal are shown in
Figure 2.4-4-1.
IMPLEMENTATION
Cherry Creek Watershed, Maryland
Installation of three gunite seals has been proposedfor abatement of acid mine
drainage from Mine 902 in the Cherry Creek watershed, Maryland (106). The seals
will be placed in entries of an abandoned underground mine in the Upper Freeport
coal seam. The mine discharges an average of 15.4 kilograms per day (34 Ib/day)
acid. Complete flooding of this mine will require that the seals be capable of
withstanding 10.7 meters (35 feet) of head. Plans and specifications for these seals
were prepared for the Appalachian Regional Commission by Skelly and Loy, and
Zollman Associates, Inc. in July, 1973.
The seals will be constructed by excavating the mine opening, shaping the
entries, and placing concrete (gunite) pneumatically in layers until the entries are
sealed. A 15.2 centimeter (6 inch) borehole will be drilled into the mine for
observation and pumping of water from the mine during construction. This hole will
also act as an emergency discharge, should the mine pool ever exceed maximum
design level.
A 20.3 centimeter (8 inch) drain pipe with manual gate valve will be
incorporated in one of the seals to allow for mine pool drawdown in the event of
failure or emergency. Grout curtains will be placed adjacent to the seals to prevent
mine water leakage through the disturbed area. A section view of one slope entry
showing the proposed location of the gunite seal, borehole, and drain pipe is shown
in Figure 2.4-4-2.
The gunite mix is to consist of one part expansive type cement, four parts sand,
and no more water than is required to maintain satisfactory control over rebound
145
-------
Limits of Seal
. .-sent Floor
•'•.•*:•.• • j/'•'* /n?nd Cejling v..
Floor, ceiling and walls cut to
form wedge shaped seal.
\Wood
Barrier
Clay Floor
SECTION "A-A"
FIGURE 2.4-4-1
TYPICAL GUNITE SEAL
(Adapted from Ref. 127)
146
-------
{Proposed 15.2cm(6in.)Mine Pool Pumpdown
I Monitoring and Safety Release Bore Hole
Curtain
Top of Slope Entry
_!—*=
- — Bottom of
V
,Limit of Excavation for Deep Mine Seal
JBackf ill to Approximate Existing Contour
las Approved by Enqineer
10cm (8 iru Plastic Pipe
/Limit of Excavation for Deep Mine Seal
_ Ground
Dumped Riprap
nhole with 20cm (Sin.) Gate Valve
Grout Drill Holes to Extend to the
Existing Underclay
Drilled to Bottom of the Existing Coal Seam
Bottom of Upper Freeport Coal
FIGURE 2.4-4-2
PROPOSED GUNITE SEAL, CHERRY CREEK WATERSHED
(Adapted from Ref. 106)
-------
and to obtain proper hydration of the cement. Prior to application of the gunite any
unsound material will be removed from the roof, walls, and floor of the entry. The
floor is to be maintained in a dry condition during placement of the gunite. The
completed seals are to be backfilled and the work area graded and revegetated.
Construction of the gunite seals should begin in the near future. Approximate
quantities of material and unit prices have been estimated, and are as follows (106):
15.2 cm (6 in)
Borehole
Grout Drilling
and Inserting
Clearing and Grubbing
Excavation for Deep
Mine Seals
One Concrete Endwall
Diversion Ditch
Dumped Riprap
20.3 cm (8 in)
Plastic Pipe
One 20.3 cm (8 in)
Plastic Gate Valve
One Manhole, Frame
and Cover
Revegetation with
Ground
Concrete Deep
Mine Seal
15.2LM@$164/LM
(50 LF)($50/LF)
518LM@$13.94/LM
(1,700LF)($4.25/LF)
Lump Sum
3,823 cu m @ $0.99/cu m
(5,000 cu yd)($0.75/cu yd)
Lump Sum
61 cu m@$1.31/cum
(80cuyd)($1.00/cuyd)
49.9 cu m @ 56.54/cu m
(60 cu yd)($5.00/cu yd)
61 LM@$49.21/LM
(200LF)($15.00/LF)
0.4 ha @ $877/ha
(1 ac)($355/ac)
103cum@$285/cum
(135cuyd)($218/cuyd)
$ 2,500
7,200
400
3,800
100
100
300
3,000
800
500
400
29,400
148
-------
Curtain Grouting
Materials
a. Cement 175 bags® $5.00/bag $ 900
b. Aggregate 45.4metric tons® 300
$5.51/metric ton
(50 tons)($5.00/ton)
c. Fly Ash 650 bags @$1.50/bag 1,000
d. Sand 16 metric tons @ 600
$36.38/metric ton
(18tons)($33.00/ton)
e. Admixtures 227 kg@ $1.10/kg 300
(500 lb)($0.50/lb)
Mobilization and Included in Individual
Demobilization Estimates
TOTAL $51,600
EVALUATION AND RECOMMENDATIONS
The gunite seal shows promise of being an effective hydraulic seal for accessible
mine entries. The wedge shape allows the seal to become tighter in the mine opening
as water pressure increases. Since the gunite is pneumatically placed in the opening,
a watertight seal should be formed between the mine and the seal perimeter. This
seal is expected to be particularly effective in sealing against higher hydrostatic
heads. Similarly shaped seals constructed of poured concrete were placed in Indiana
coal mines as early as 1925. (See Section 2.4-2). These seals reportedly withstood
water pressures as high as 49,217 kilograms per square meter (70 psi).
This seal will be most effective when located in relatively sound strata.
Preparation of the mine opening will include cleaning and shaping of the roof, sides,
and floor. When unstable roof conditions are encountered timbering of the entry
may be required. The use of an expansive type cement in the gunite mix should
create a tight fitting plug in the mine opening.
When seals are located in areas of fractured or hydraulically unsound strata,
curtain grouting will be required. In such instances grouting of the seal perimeter
may also be deemed necessary. Grout pipes should be placed along the perimeter of
the seal prior to injection of the gunite mix.
149
-------
Since this type seal has not yet been demonstrated, it is difficult to estimate
construction costs. The cost of placing gunite seals at Cherry Creek, West Virginia
was estimated at $285 per cubic meter ($218/cuyd). Additional expenses will
include excavation, cleaning, timbering and shaping of the mine opening, and curtain
grouting of adjacent strata. The estimated average cost of the Cherry Creek seals,
including grouting, is approximately $13,000 per seal.
REFERENCES
70, 106, 127
150
-------
2.4-5 CLAY SEAL
DESCRIPTION
Clay may be placed in openings of underground mines to form a hydraulic seal
or to control infiltrating water. A good quality plastic clay should be used to ensure
impermeability. The seal is constructed by first cleaning the mine opening of debris
or any other material that would make the clay seal ineffective. The clay material is
placed in layers and compacted to enable the clay to flow into cracks and voids
along the walls and roof of the seal area. Earth should be backfilled over the seal to
hold it in place and prevent erosion. Under ideal conditions a clay seal constructed
in this manner may withstand up to 10 meters (30 feet) of hydrostatic head (127).
A cross section of a typical clay seal is shown in Figure 2.4-5-1.
IMPLEMENTATION
Roaring Creek — Grassy Run Watershed
Clay seals were constructed during a demonstration project to evaluate mine
sealing in the Roaring Creek — Grassy Run watershed near Elkins, West Virginia.
This project was a cooperative effort between Federal agencies and the state of
West Virginia. Sealing operations were conducted in an effort to evaluate air sealing
of abandoned underground coal mines (101).
A total of 41 openings were sealed with clay during the project. These seals
were placed in areas where surface mine highwalls were badly fractured and the
stripping operations had intercepted deep mine workings. The seals were constructed
by placing 0.6 meter (2 foot) layers of clay against the highwall and compacting
with a vibrator sheeps foot roller. In most instances the seals were placed on the
updip side of underground mines to prevent the entry of air and water.
During air sealing of a small abandoned underground mine, two clay seals were
placed along the outcrop on the downdip side of the mine. Later, as the water level
in the mine rose, water near the seal flowed up through the overburden and over the
top of the seal. Erosion of the clay seal allowed the mine pool to drain.
The average cost per seal for 10 clay seals placed in Work Areas 1 through 9
was $950. A total of 8,020 cubic meters (10,490 cu yd) of clay was placed at a cost
of $1.19 per cubic meter ($0.91/cu yd). At Work Area 10, costs were higher due to
greater haulage distance from the borrow pit to the work area. Six seals were
constructed at an average cost of $2,360 per seal. The cost per cubic meter of clay
was$.1.58($1.21/cuyd)(101).
151
-------
•Ground Surface
Underground Mine
Earth Backfill
Compacted Clay Seal
In Mine Opening
FIGURE 2.4-5-1
CROSS SECTION TYPICAL CLAY SEAL
152
-------
Shaw Mine Complex. Somerset County, Pennsylvania
Clay seals were installed along the highwall of box cuts excavated at the Shaw
Mine Complex, Elklick township, Somerset County, Pennsylvania (84). In an
attempt to hydrologically isolate sections of the Shaw Mine, overburden above the
abandoned mine was excavated and the Redstone and Pittsburgh coals removed.
After the mining operation was completed, clay barrier seals were constructed in the
cut to flood portions of the underground mine. Pennsylvania Projects SL 118-2B
and SL 118-3-2 involved reclamation of the excavated cuts which included
installation of clay seals, contour backfilling, and planting and seeding. A sketch of
the clay seal installed at the Shaw Mine Complex is shown in Figure 2.4-5-2.
Project SL 118-2B involved installing approximately 22,938 cubic meters
(30,000 cu yd) of clay along the cut for approximately 274 linear meters (900 LF).
The clay was installed in 30.5 centimeter (12 inch) layers and compacted by a dozer
running over the clay and/or trucks running over the clay as they traveled to and
from the clay pits. The seal was held to a width of not more than 6 meters (20 feet)
at the bottom and not more than 4.6 meters (15 feet) at the top'.
Approximately 512,282 cubic meters (670,000 cu yd) of spoil were moved
during backfilling. Rocks larger than 15.2 centimeters (6 inches) were covered with a
minimum of 1 meter (3 feet) of soil. In areas where reclaimed land would be used
for farming a minimum of 30.5 centimeters (12 inches) of best soil available was
placed over all rocks 15.2 centimeters (6 inches) in size. Backfilling was done
coincident with the clay seal installation to keep the seal from becoming too wide.
All areas planted were worked with a disc and/or harrow wherever practical and
fortified with 4.5 metric tons of pulverized limestone per hectare (2 tons/acre).
Trees were planted on 2.4 meter by 2.4 meter (8 feet by 8 feet) centers for
approximately 1,728 trees per hectare (700 trees/acre).
Work under this project was completed in June, 1972 by M.F. Fetterolf Coal
Company, Inc. Costs of reclamation were as follows:
Installing Clay Seal - 22,938 cu m Lump Sum $ 54,000
(30,000 cu yd)
Backfilling, Planting - 512,282 cu m Lump Sum 127,300
(670,000 cu yd)
Liming, Planting Trees - 20.3 ha Lump Sum 2.500
(50 ac)
TOTAL $183,800
153
-------
AREA TO BE CONTOUR BACKFILLED
AND PLANTED
[—3.7 to 4.6m
02tol5ftJ
PITTSBURGH COALl\
4.6 to 6m
(15 to 20ft.)
FIGURE 2.4-5-2
CLAY SEAL, SHAW MINE COMPLEX
(Adapted from Ret. 84)
154
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Based on the lump sum values, unit costs of individual work items woud be:
Installing Clay Seal $2.35/cu m ($ 1.80/cu yd)
Backfilling $0.25/cu m ($0.19/cuyd)
Liming, Planting Trees $123/ha ($50/ac)
Under project SL 118-3-2 approximately 42,053 cubic meters (55,000 cu yd)
of clay were installed along 792 linear meters (2,600 LF) of the cut. Backfilling the
cut involved moving 856,352 cubic meters (1,120,000 cu yd) of spoil material. The
method of seal installation and backfilling was the same as for project SL 118-2B.
All areas to be seeded were fortified with 4.5 metric tons of pulverized limestone per
hectare (2 tons/acre) and 5 60 kilograms of 10-20-20 fertilizer to the hectare
(500 Ib/acre). A mixture of alfalfa, timothy and clover was applied at 22 kilograms
per hectare (20 Ib/acre).
Work on this project was completed in May, 1973 by Sanner Brothers Coal
Company. Costs of reclamation were as follows:
Install Clay Seal 42,053 cu m @ $2.75/cu m $115,500
(55,000 cu yd)($2.10/cu yd)
Contour Backfill 856,352 cu m @ $0.24/cu m 201,600
(1,120,000 cu yd)($0.18 cu yd)
Liming, Fertilizing, 24.3 ha @ $309/ha 7.500
Seeding (60 ac)($ 125/ac)
TOTAL $324,600
Cherry Creek Watershed, Maryland
Installation of a clay seal has been proposed for abatement of acid mine
drainage from Mine 904 in the Cherry Creek watershed, Maryland. The clay seal will
be placed in an abandoned slope entry to the Upper Freeport coal seam. This
pollution source discharges an average of 2.3 kilograms per day (5 Ib/day) acid. Plans
and specifications for the seal were prepared for the Appalachian Regional
Commission by Skelly and Loy, and Zollman Associates, Inc. in July, 1973 (106).
The discharge from Mine 904 is through an existing subsurface drain.
Placement of the clay seal will require excavation of overburden to uncover the mine
entry and intercept the subsurface drain. A 15.2 centimeter (6 inch) borehole will be
constructed (complete with case and cap) behind the seal for the purpose of
155
-------
monitoring water level and quality in the mine. The clay seal is expected to
eliminate the discharge and completely inundate the mine. Plan and section views of
the proposed seal are shown in Figure 2.4-5-3.
The seal shall be constructed by placing clay in 30.5 centimeter (12 inch)
layers, and compacting with available hauling and spreading equipment or other
suitable, approved means. The seal is to extend a minimum of 7.6 meters (25 feet)
on either side of the slope entry and extend below the mine floor far enough to
intercept the existing drainway. Upon completion of seal construction the work area
is to be backfilled, graded, and revegetated.
Construction of the clay seal should begin in the near future. Approximate
quantities of material and unit prices have been estimated and are as follows (106):
Monitoring Well 7.6 LM @ 27.89/LM $ . 200
(25 LF)($8.50/LF)
Clearing and Grubbing Lump Sum 200
Excavation 2,294 cu m @ $0.98/cu m 2,300
(3,000 cu yd)($0.75/cu yd)
Clay Seal 229 cu m @ $4.71/cu m 1,100
(300 cu yd)($3.60/cu yd)
Revegetation with 0.2 ha @ $877/ha 200
Ground Agriculture (0.5 ac)($355/ac)
Limestone
Mobilization and Included in Individual
Demobilization Estimates
TOTAL $4,000
EVALUATION AND RECOMMENDATIONS
Implementation of clay seals should be limited to accessible mine entries where
low water pressure is expected. The effectiveness of these seals in controlling mine
discharges will depend upon such factors as the quality of clay, method of
construction, and type and condition of the mine opening. Clay seals have
successfully been placed in mine openings to prevent the entry of air and water into
air sealed mines. However, when these seals are properly compacted and backfilled,
they are capable of eliminating mine discharges and inundating abandoned
underground mines.
156
-------
2.4m (8ft.) Min.
\
1N
|:|
7.6m (25ft.) Min.
^JMine Opening
^-Varies
7.6m (25 ft.) Mia
PLAN
Subsurface Drain
I5.2cm(6in.) Observation Hole Drilled-
Behind Clay Seal
2.4m(8ft.)Min.
Slope as Approved
By the Engineer ~"\ Existing Ground-
Mine Opening
_________
.5m (5ft.) Min
Limit of Excavation S
for Deep Mine Seal
SECTION A-A
FIGURE 2.4-5-3
PROPOSED CLAY SEAL, CHERRY CREEK WATERSHED
(Adapted from Ret 106)
157
-------
Clay seals must be constructed with sufficient internal strength to withstand
the maximum expected water pressure. Seals placed in drifts, slopes, highwall
fractures, or similar openings should extend beyond the perimeter of the opening.
Construction specifications for Cherry Creek require that the clay seal extend a
minimum of 7.6 meters (25 feet) on either side of the slope entry, a minimum of
3 meters (10 feet) above the bottom on the entry, and a minimum of 1.5 meters
(5 feet) below the entry. Shafts, subsidence holes, and similar vertical openings
should be sealed in areas of relatively sound and impermeable strata. Completed
seals should be backfilled, graded, and revegetated.
Costs of constructing clay seals will depend upon the type and size of opening;
site preparation required; the availiability of suitable clay material; and the amount
of backfilling, grading, and revegetation required. The cost of installing clay seals
will normally range between $2.62 and $5.23 per cubic meter ($2.00 and
$4.00/cu yd). Total construction costs will range from $2,000 to $4,500 per seal.
REFERENCES
32,38,70,84, 100, 101, 106, 127
158
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2.4-6 GROUT BAG SEAL
DESCRIPTION
Construction of a grout bag seal involves the placement of successive layers of
expendable grout containers in an accessible mine opening. Nylon or cotton cloth
grout retainers are placed on the floor of the mine and inflated with cement slurry
to conform to the shape of the mine entry. After the cement slurry sufficiently
hardens and is capable of withstanding a load of about 2,109 kilograms per square
meter (3 psi) a second row of shorter retainers is placed above it and inflated with
cement slurry. This process is repeated until the entire area between the floor and
roof of the mine entry is filled by the retainers. A cross section of an expendable
grout retainer seal is shown in Figure 2.4-6-1.
IMPLEMENTATION
Clarksburg, West Virginia Seal
In May, 1967, Halliburton Company constructed a grout bag seal in an isolated
2 hectare (5 acre) mine (Mine No. 14-042A) in the Pittsburgh coal seam south of
Clarksburg, West Virginia. Prior to sealing a flow of 1.1 liters per second (18 gpm)
was discharging from the mine. Analysis of the mine water showed a pH of 2.6,
iron — 558 mg/1, acidity — 2,750 mg/1, and acid load 280 kilograms per day
(616 Ib/day). The floor of the mine was shale and the roof and walls were of coal.
The coal was irregular in shape and contained many fractures (47).
The seal constructed in the mine consisted of four expendable grout retainers
forming four successive layers. The seal was constructed by placing a
6.1 x 3 x 0.9 meter (20 x 10 x 3 foot) retainer on the floor and inflating it with
cement slurry to conform to the shape of the mine. When the first retainer had
hardened sufficiently to withstand a load, a second nylon retainer,
4.9 x 3 x 0.9 meters (16 x 10x3 feet), was placed on the first. The process was
repeated to place a third nylon retainer 4.3 x 3 x 0.9 meters (14 x 10x3 feet), and
a fourth cotton retainer 3 x 3 x 0.9 meters (10 x 10x3 feet), to completely fill and
seal the opening. The completed mine seal is shown in Figure 2.4-6-2.
After sealing, leakage around the bag seal was measured at 0.09 liters per
second (1.5 gpm), a reduction of 92 percent from flow measured prior to sealing.
This leakage was later reduced to 6.02 liters per second (0.33 gpm) by injecting a
tota^of 189 liters (50 gallons) of Halliburton PWG grout fluid around the first and
second grout retainers. No further grouting was performed, as the remaining leakage
appeared to be coming frprn coal fractures to the left.of the seal (32, 47).
159
-------
Ground Surface
Expendable
Grout
Retainers
MjneEntry
FIGURE 2.4-6-1
CROSS SECTION OF EXPENDABLE GROUT RETAINER
UNDERGROUND MINE SEAL
(Adopted from Ret. 127) 16Q
-------
ApproK.2.4mtBfft,
2.5cm(l iiOGreut
7.6crn(3 in J Drain Pip*
2.5cm (I In) Grout Pip*
2.5 cm (I In.) Grout Pipe
2.5cm Qin) Roof Sampling
1 1.5m (5ft.)
Appro*. 2.4m(8ft.)
PLAN VIEW
2.4m (8ft.)
26cm(K>25in)
50.8cm(2OiiO|
508cm (20ia)
76.2cm(30in)
-2.5cm (I in.) Dia. Fill Tube
-7.6cm (3in.) Dia Fill Tubes
-Middle Sample Tube
Top Sample Tube
2.5cm(lia)Dia
Plastic Grout Pipe
irODia.—I V^-25cm(l in.) Grout Pipe NykxiRetai
stic Grout Pipe ^ 7.6cm(3in.)Draina Sampling Tube
Mine Floor
FRONT VIEW
FIGURE 2.4-6-2
GROUT BAG SEAL
ELEVATION
Mine No. I4-042A Clarksburg, W.Va.
(Adapted from Ref. 47)
-------
Later an unsuccessful attempt to further reduce flow was made by pumping a
gel material of bentonite and shredded cane fiber into the void space behind the
mine seal. A total of 156 thousand liters (41,200 gallons) of gel material, utilizing
13,620 kilograms (30,000 pounds) of Wyoming bentonite and 134 kilograms
(295 pounds) of shredded cane fiber, were pumped into the mine. After completion
of pumping, the flow rate from the mine had increased to 0.03 liters per second
(0.55 gpm).
Water quality analyses performed by the U.S. Environmental Protection
Agency indicate that ion concentrations of iron, acidity, and sulfates have not
changed significantly since sealing. Mean values of samples collected between
August, 1970 and June, 1971 were: total iron - 497 mg/1, hot acidity - 1,750 mg/1,
and sulfates - 3,210 mg/1. Pollution loads, however, have decreased better than
90 percent due to reduced flow. The mean flow and acid load during the same
sampling period were 0.07 liters per second (1.08 gpm) and 10.4 kilograms per day
(23 Ib/day), respectively (98).
An inspection made four years after seal construction revealed that there was
no leakage between the bag layers. The bond between the bags and coal surface had
been broken due to deterioration of the coal, and massive leakage was occurring.
Costs for constructing the grout retainer seal and Halliburton PWG grout fluid
treatment at Mine No. 14-042A were reported to be $5,000(130). Materials and
equipment used in placing the gel material of bentonite and shredded cane fiber cost
$2,771. Access rights and site restoration required additional expenditures of
$579 (47). The total cost of construction and remedial work would therefore be
$8,350.
A 1967 estimate of the costs of sealing an open drift using 9.1 meter (30 foot)
expendable grout retainers was as follows (29):
Site Preparation $
Entrance Preparation
Four (4) Expendable Grout Retainers
Piping, Valves, Labor
Incidental Expenses
Water Hauling and Storage
Filling Material
Mixing and Placement Equipment
TOTAL ESTIMATED COST $6,800
162
-------
If filling material can be economically processed on site, slurry price for filling
the retainers could be reduced by as much as SO percent. The total estimated cost
would then be $5,400.
EVALUATION AND RECOMMENDATIONS
Demonstration of this seal type has reportedly been limited to the work
performed at the Clarksburg mine. This seal successfully reduced the mine discharge
from 1.1 liters per second (18 gpm) to a mean discharge of approximately 0.09 liters
per second (1.5 gpm). Although pollution loads decreased, water quality showed
little improvement. The hydrostatic head behind the seal was estimated to be
1.8 meters (6 feet).
This seal has limited application in controlling mine drainage pollution from
abandoned underground mines. The retainer bags do not form a good bond with the
surface of the mine opening. Leakage around the seal perimeter will be difficult to
control. Grouting and other remedial work at Clarksburg failed to eliminate the
mine discharge. Concrete type bulkheads would appear to be more suitable sealing
techniques.
Based upon previous demonstration work and cost estimates the cost of
constructing a grout bag seal in an average drift entry would range from $10,000 to
$15,000. Grouting of the seal perimeter and curtain grouting of adjacent strata
would result in additional expenditures.
REFERENCES
27,29,32,47,98, 127, 130
163
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2.4-7 SHAFT SEAL
DESCRIPTION
A shaft is a vertical or near vertical entry into an underground mine. Upon
abandonment of a mine, shaft entries are commonly filled with miscellaneous
materials, covered, or fenced off for public safety. In instances where the shaft has
the potential to discharge mine water or to divert water into the mine, an
impermeable type seal should be constructed. Discharges of acid mine water from
abandoned mine shafts is common in the eastern coal fields.
The placement of shaft seals involves opening the shaft and removing all debris.
A suitable sealing zone in the strata is then located. Any water discharging from the
shaft is controlled by pumping the mine pool. The shaft is backfilled to the sealing
zone with miscellaneous fill and the impermeable seal is placed. A key may be
chipped in the adjacent strata to help anchor the seal. The sealing operation is
completed by backfilling the shaft to ground level. A cross section of a typical shaft
seal is shown in Figure 2.4-7-1.
IMPLEMENTATION
Pennsylvania Sealing Program
Shaft entries were sealed during the Federal Works Progress Administration and
Civil Works Administration air sealing projects which began in 1933 (36). When
practical the shafts were filled with earth and rock. When this method was
impractical or objectional a concrete slab was placed over the shaft and backfilled
with earth.
After completion of the Federal sealing program, Pennsylvania continued to
seal mines under the State Department of Mines sealing program which initiated
with passage of the 1935 Bituminous Mining Law, Act No. 55. Mine entries were
sealed in an effort to prevent mine fires and reduce the flow of acid mine water (71).
Abandoned shafts were initially sealed by placing a concrete slab over the shaft
opening. It was later discovered that decay of timber in the shaft allowed the shaft
to collapse, thereby causing the concrete slab seal to become ineffective. This
method of sealing was terminated and shafts were sealed by filling from bottom to
top with earth and clay. As of 1952, approximately 150 shafts ranging in depth
from 6.1 to 183 meters (20 to 600 feet) in depth had been sealed (71). A sketch of
the concrete slab type seal is shown in Figure 2.4-7-2.
164
-------
ORIGINAL GROUND
SEALED MINE SHAFT
}-l-^;i^^-;^.
• •'. • :'. • 'o.'; •' •:' • •.'••'.•! • • •
••.••.:.•:•.:::•.::••.•••.••>•.:::
/
/ / 7
/ / /
. KEY CHIPPEC
-IN SRATA
..
.--.-.--O---.--.-
A ;:.-.•;. '•'<• .;
- .MISC.'.'- . •'.
/ /
/ / / /
; M is'c.:: :•.'•'•'.
CONCRETE AND/OR
PLUQ-. • .' - ••
'
UNDERGROUND MINE
FIGURE 2.4-7-1
CROSS SECTION TYPICAL SHAFT SEAL
165
-------
Earth Backfill
Ground Level
Concrete Slab Placed
Over Shaft Opening
ELEVATION
•o
o
• o
0
. 0- • 0 • • -Q-
^^^U^^^VjV
, • * I* * . .* A , . . • • *."•••• "*.
f|jS^;l
6 . ° .0. : °: •
SECTION A-A
o . :
. o
' • . .
o
0
00
Note: Old Rails May Be Used
To Reinforce Concrete Slab
FIGURE 2.4-7-2
SHAFT SEAL WITH CONCRETE SLAB
(Adapted from Ref. 36)
166
-------
Wildwood Mine. Allegheny County. Pennsylvania
In March, 1971, a discharge of approximately 8,706 cubic meters per day
(2.3 MGD) containing 244 mg/1 iron occurred from an abandoned air shaft at the
Wildwood Mine near Pine Creek, Hampton Township, Allegheny County,
Pennsylvania. The mine is in the Upper Freeport coal seam and had been in
operation until December, 1968. Upon closure of the mine all boreholes were sealed
with concrete, and slope and shaft entries were filled with incombustible materials.
As the mine flooded discharges occurred from the air shaft, a slope entry, and a
hillside breakout.
Remedial work performed at the mine included placing a concrete seal in the
air shaft and grouting the slope and hillside discharges. The sealing operation was
performed in the fall of 1972 by Allied Asphalt Company, Inc. under Pennsylvania
Project SL198(84). Although all funds were expended, the mine was not
completely sealed. Two small diameter pipes connecting the mine to the surface
were overlooked while sealing the shaft. However, the iron concentration in the air
shaft discharge decreased to 70 mg/1.
Work involved in sealing the air shaft included the following:
1. Diversion of drainage from the shaft by pumping.
2. Excavation of the shaft fill and cleaning of the shaft 3 to 4.6 meters (10
to 15 feet) below ground level.
3. Chipping a key in the shaft liner and coating with an expansion agent.
4. Installation of reinforcing rods and pouring a minimum 0.6 meters (2 feet)
of concrete.
5. Grouting of any leaks that occurred after the seal cured.
6. Backfilling of the shaft to ground level.
The estimated costs of performing the specified work were:
Excavation and 765 cu m @ $2.62/cu m $ 2,000
Backfill (1,000 cu yd)($2.00/cu yd)
Pumping and Cleanout 40 hours @ $60/hour 2,400
Labor and Equipment
167
-------
Reinforced Concrete 76.5 cu m @ $ 196/cu m 15,000
(Includes Key) (100 cu yd)($150/cu yd)
Cement Grout 100 bags @ $4.50/bag 450
TOTAL $19,850
EVALUATION AND RECOMMENDATIONS
Hydraulic sealing of shafts is generally more successful than sealing horizontal
or near horizontal entries along outcrops. The extent of leakage around a shaft will
be dependent upon the hydrostatic head and the vertical permeability of adjacent
strata. In general, very deep underground mines can be successfully sealed. Leakage
is likely to occur in shallow underground mines where there is the possibility of the
mine flooding to a level above the seal elevation. A complete hydrogeologic
evaluation should be made prior to shaft sealing.
In instances where it is determined that shaft discharges will not occur, rock
and earth, or concrete cap type seals may be sufficient. However, concrete and/or
clay plugs placed in a suitable sealing zone, such as a sandstone bed, are
recommended for discharging shafts. The 1969 Health and Safety Act presently
requires that all shaft openings in inactive or abandoned coal mines be either capped
with concrete or filled for the entire depth of the shaft.
The cost of constructing shaft seals will be highly variable and will depend
upon such factors as size and depth of the shaft; excavation, cleaning and backfilling
required; type of seal placed; and grouting work required. The cost of backfilling
abandoned shafts will generally range from $7,000 to $35,000 for shafts from 30.5
to 152 meters (100 to 500 feet) in depth. Concrete seals will generally range in price
from $20,000 to $25,000 per seal.
REFERENCES
36,71,84, 127
168
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2.4-8 GEL MATERIAL SEAL
DESCRIPTION
The construction of a gel material seal involves the injection of a chemical
grout and filler into a mine cavity through a vertical borehole. The chemical grout
has a controllable setting time which allows a stiff, gel-like plug to be formed in the
mine cavity without the benefit of retaining bulkheads. The gel material produced
must be strong, chemically resistant, impermeable, and capable of withstanding
expected water pressure.
IMPLEMENTATION
Laboratory and Field Testing
Laboratory testing of commercially available grouts and filler materials was
performed by Dravo Corporation to select materials suitable for constructing a gel
material seal (25). Five different chemical grouts with various combinations of fly
ash, mine refuse, sand, and gravel as fillers were tested. Of the five chemical grouts
tested only AM-9, a vinyl polymer grout, was found to meet the requirements of
adequate strength, good gel time control, and resistance to mine acid. A grout slurry
of 6.8 kilograms (15 pounds) fly ash to 3.8 liters (1 gallon) of 15 percent AM-9
solution was selected for use in an experimental mine sealing project.
An abandoned deep mine located in Deny Township, Westmoreland County,
Pennsylvania, approximately 56 kilometers (35 miles) east of Pittsburgh, was
selected for demonstration of the gel material seal. The mine, which was known as
the Salem No. 2 mine, is located in Keystone State Park. Of the three openings into
the mine only one was discharging acid water. The two non-discharging entries were
sealed with double bulkhead aggregate seals with concrete pressure grouted center
plugs. The discharging entry was selected for injection of the gel material.
The seal was to be placed through a vertical borehole from the surface. After
placement fly ash was to be pumped into the mine side of the seal. The fly ash was
to neutralize any leakage that escaped the seal and to help plug any leaks that did
develop. A sketch of the proposed seal is shown in Figures 2.4-8-1 and 2.4-8-2. The
safety bulkhead is for protection during development and testing of the seal.
Actual injection of the grout material was begun on March 1, 1972. The grout
slurry was directed upward and toward the walls through an injection nozzle. The
anticipated result of this injection method was the formation of wedges on each side
of the corridor which started at the walls and sloped toward the middle where mine
drainage was flowing. As the wedges met the flow of mine drainage would be
blocked and an effective hydraulic seal would be formed.
169
-------
1 JLJLJLJLJLJLJLJ1.JLJ
JLJljLjLJLjLJWjLJLJLjLj
JL JL JL JL JlVA JL JL -L Ji
U.J1JLJLJ1JLJ1JLJIJJ.J.J
jLjLjLjLjLJLjLjiJLjLjt
JLJIJIJIJLJL
Jl JL 1L4J.J1
PLAN
-------
Ground Ltvtl
Mint Void
Injtction Equipmtnt
Stotiontd Htrt'
Injtetion Holt
-Injtction Nozzlt
ELEVATION
FIGURE 2.4-8-2
Injtetion Holt-
1 '#&/*&&
SECTION
INJECTION PROCEDURE FOR GEL MATERIAL
(Adapttd from Rtf. 25)
-------
The formation of the seal was never completed as the slurry was diluted by the
mine drainage before a gel was formed. However, a satisfactory gel was apparently
formed on both sides of the entry. The flow from the mine during slurry injection
was approximately 9.5 liters per second (150 gpm).
Cost information for a completed gel material is not available. Dravo
Corporation did, however, estimate that the cost of grouting materials for a mine
seal 3.7 meters (12 feet) wide by 8.5 meters (28 feet) long would be $9,000. This
estimate was based upon the use of AM-9 chemical grout.
EVALUATION AND RECOMMENDATIONS
Failure of the demonstration seal was attributed to dilution and erosion of the
gel material in the high flow mine. The possible application of this sealing technique
in low flow or dry mine entries has not been tested. Based on the estimated cost for
the AM-9 grouting materials, this seal type is not competitive with other hydraulic
sealing techniques.
Further research and demonstration efforts should be directed to reducing the
cost of materials and injection procedures. Reductions in material costs may be
achieved by investigating the application of various grout slurry mixtures.
Modification of the grout mix with cement as an admixture may produce an
acceptable sealing material. Quick setting bulkheads constructed with cement,
bentonite, and sodium silicate slurries have been successfully demonstrated in
accessible mine openings (See Sections 2.4-1 and 2.4-2). Material costs for these seals
have been less than one-third the estimate for the AM-9 grout mix.
RFERENCES
25, 127
172
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2.4-9 REGULATED FLOW SEAL
DESCRIPTION
Underground mine discharge rates are variable and depend upon the response
of individual mines to seasonal variations in precipitation. Mines near the surface
usually have a short response time. In underground mines having thick cover,
precipitation may not affect the volume of mine water discharge for several weeks.
Consequently, a mine may discharge maximum pollution loads to a receiving stream
during periods of low stream flow. If the receiving stream is unable to assimilate the
pollution load, adverse environmental effects can result. The regulated flow seal is
designed to release mine water in amounts that the receiving stream is capable of
assimilating at any given time (127).
This sealing technique may be used when complete inundation of a mine is
impractical. All mine entries must be hydraulically sealed and capable of
withstanding the maximum hydrostatic head expected during periods of maximum
precipitation. The regulated flow seal is constructed with a pipe drain to maintain an
acceptable discharge to the receiving stream.
IMPLEMENTATION
This is a theoretical mine drainage control technique; its use has not been
documented.
EVALUATION
The implementation of regulated flow seals should be limited to abandoned
underground mine discharges that are major sources of stream pollution. The
economic feasibility of this technique can be determined by comparing the cost of
treatment plant construction and operation, and mine seal installation.
The technical feasibility of implementing this technique will depend upon the
ability to seal the individual mine. The maximum pool elevation that can be safely
held by the mine seals and adjacent strata should be determined by performing a
complete hydrogeologic study of the mine. A borehole should be drilled into the
mine from a surface elevation equal to the maximum allowable mine pool elevation.
This borehole would be used for mine pool monitoring and also function as an
emergency overflow when the mine pool approaches its maximum safe level (See
Section 2.4).
173
-------
The drain pipe from the regulated flow seal should be equipped with either a
manual or mechanical valve to regulate the mine discharge. The pipe and valve
system should be capable of completely draining the mine pool in case of emergency
or reopening of the mine.
Mechanical valves would be controlled by continuous monitors located in the
receiving stream. These monitors would measure various properties of the stream
(i.e., pH, flow, etc.) and regulate the mine discharge to maintain acceptable stream
water quality. This system could also be operated in conjunction with a treatment
plant. The stream monitoring equipment would be programmed to divert the mine
discharge to the treatment plant only during periods when the stream was unable to
assimilate the pollution load.
The costs of implementing this mine drainage control technique must be
developed on an individual application basis. The total cost of hydraulically sealing
the mine will depend upon the methods and extent of sealing required.
Implementation of the regulated flow seal in conjunction with treatment facilities is
expected to result in substantial savings in treatment plant capital and operating
expenses.
REFERENCES
127
174
-------
2.5 CURTAIN GROUTING
DESCRIPTION
Grouting is the process of injecting fluid materials into permeable rock and/or
soil formations to fill pore spaces and reduce permeability. Curtain grouting is
commonly performed in conjunction with hydraulic sealing of underground mines
to control leakage around seals and stabilize outcrop areas. The grout mixtures are
pressure injected through vertical boreholes. The injected material sets to form a
stiff gel or hardened cement-type material that creates an impermeable barrier in the
grouted medium (29).
Grouting mixtures are generally divided into two main categories, true
solutions and slurries. True solutions are a mixture of soluble monomeric materials
in water or other solvent. These solutions have low viscosity and may be injected
into permeable zones without fracturing the treated medium. Slurries are
suspensions of finely divided cementing materials in a fluid medium. These fluid
materials are more viscous than true solutions and cannot be pumped into pores
smaller than the grout particles. Slurries which are a combination of true solutions
and finely divided solids have also been developed.
IMPLEMENTATION
Grout curtains are commonly utilized to control leakage around bulkhead seals.
The grout is normally placed through boreholes drilled from above on 3 meter
(10 foot) centers and extending away from the seal for a minimum 15.2 meters
(50 feet) on both sides of the mine entry. This method of grouting is presently
required as part of many of the mine sealing projects performed under
Pennsylvania's Operation Scarlift program. Contract bids for Project SL 108-3-1,
East Branch Clarion River, McKean County, Pennsylvania, which included
construction of bulkhead seals and curtain grouting, were opened in
December, 1974 (84). The engineer's estimate for pressure grouting was as follows:
Quantity Unit Price
Drilling 7.5 cm 1,067 LM $ 10.66
(3 in) holes (3,500 LF) (3.25)
Drilling 15.2 cm 76.2 LM 13.12
(6 in) holes (250LF) (4.00)
Cement for Grouting 907 metric tons 110.25
(1,000 tons) (100.00)
175
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Quantity Unit Price
Fly Ash for Grouting 1,678 metric tons 22.05
(1,850 tons) (20.00)
Sand for Grouting 18 metric tons 44.10
(20 tons) (40.00)
Grout Admixtures
Grout No. 1 45.4kg 22.03
(lOOlb) (10.00)
Grout No. 2 379 liters 3.96
(100 gal) (15.00)
Grout No. 3 379 Liters 3.96
(100 gal) (15.00)
Pressure Testing 20 hours 35.00
Grout Connections 100 5.00
Core Drilling 61 LM 47.57
(200 LF) (14.50)
Based on this estimate, the total cost for pressure grouting would be $158,275.
The bid prices of six contractors for this grouting work ranged from $117,425 to
$321,500.
Horizontal grout curtains have also been placed to reduce water infiltration
through subsidence areas and other fractured zones. The effectiveness of these seals
has depended upon the method of grout injection and the condition of the medium
being treated. Minimum and maximum costs per hectare of horizontal grout curtain
were estimated by Halliburton Company in 1967 and are as follows (29):
176
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Minimum Estimate
Site Preparation
Four holes — 15.2 meters
(SO feet) Deep — Including
Moving
Grout Packers
Piping, Valves, Labor
Incidental Expenses
Grouting Material
Water Storage and Hauling
Mixing and Placement
Equipment
Engineering Service
TOTAL
Site Preparation
100holes- 15.2 meters
(50 feet) deep — Including
Moving
Packers
Piping, Valves, Labor
Incidental Expense
Hectare
$ 1,975
1,358
988
988
494
6,173
1,235
1,556
1,235
$16,002
Maximum Estimate
Hectare
$ 2,469
2,716
12,346
7,407
1,235
Acre
$ 800
550
400
400
200
2,500
500
630
500
$ 6,480
Acre
$ 1,000
1,100
5,000
3,000
500
177
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Hectare Acre
Grouting Material 6,173 2,500
Water Storage and Hauling 1,852 750
Mixing and Placement
Equipment 4,691 1,900
Engineering Service 2,716 1,100
TOTAL $41,605 $16,850
The effectiveness of grouting operations will be difficult to assess. During
injection of the grout material there is no way to determine where the grout is going
or how effectively it is sealing permeable areas. The effectiveness of curtain grouting
has not been documented by monitoring of seepage rates through permeable zones.
However, grouting of bulkhead perimeters, subsidence fractures, shaft seals, and
aggregate bulkheads has successfully reduced mine water discharges from
underground mines.
EVALUATION AND RECOMMENDATIONS
Curtain grouting is a convenient and generally effective method of reducing the
flow of water through fissures, fractures, and permeable strata. The placement of
grout curtains simply requires the drilling of holes and pressure injection of the
grouting material. However, grouting operations require skilled personnel having
knowledge of the available grout materials, the equipment used, and the various
grouting techniques.
The effectiveness of grout curtains will depend upon the method of injection,
the grout material applied, and the type and condition of the geological formation
being treated. Grout packers may be utilized to plug the grout hole and allow
grouting of individual zones. Alteration of the grout mixture and viscosity will
further improve the efficiency of grout injection. A limited subsurface investigation
should be performed to obtain information on the character of the strata to be
grouted and assist in the estimate of grouting requirements. Grout holes must then
be properly spaced to ensure that the total area between holes receives grout
treatment.
The following factors must be considered when estimating the cost of placing
grout curtains: grout materials and admixtures, drilling and injection equipment, site
preparation, labor requirements, water storage and handling, grout packers, and
178
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engineering service. The major factors affecting the total cost of placing the grout
curtain will be the amount of drilling required and the total volume of grout
injected. Vertical grout curtains will normally range in cost from $115 to $262 per
linear meter ($35 to $80/LF) of curtain. The cost of horizontal grout curtains will
range from $29,630 to $49,400 per hectare ($ 12,000 to $20,000/acre).
REFERENCES
27,29,32,46,84,89, 127
179
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3.0
MINING METHODS
181
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3.1 GENERAL DISCUSSION
This section will discuss mining methods that may be implemented to prevent
or control the formation of mine drainage pollutants after underground mining is
completed. Mining methods discussed will include downdip, longwall and
daylighting. Downdip and longwall mining may be incorporated in active
underground mines. Daylighting is not a method of underground mining, but is a
means of controlling water pollution from abandoned underground mines. These
methods will not be universally applicable. Their feasibility will be determined by
the characteristics of individual mine sites.
183
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3.2 DOWNDIP MINING
DESCRIPTION
Many of the presently inactive and abandoned underground mines were
devloped to the rise. Mine openings were located at a low elevation in the mineral
seam and active mining proceeded updip. This method of mining allows easy haulage
of loaded mine cars downdip to the mine entrance. It also allows gravity discharge of
most water infiltrating into the active workings. However, mines developed to the
rise are potential sources of mine drainage pollution. Water entering the mine often
becomes polluted and will be free to flow from the mine both during active mining
and after abandonment. Sealing of many of these abandoned mines will be
extremely difficult due to excessive hydrostatic heads that will develop as the mine
floods.
A significant amount of the mine drainage problem we now face would not
have occurred if the mine had been developed downdip. This mining method
involves the location of mine openings at a high elevation in the mineral seam and
development of the mine in a downward direction. After the mine is abandoned
flooding will be automatic and the hydrostatic head developed at sealed entries will
be minimized (70, 127).
The implementation of the downdip mining method will result in additional
costs during active mining. Water collecting in active sections of the mine must be
pumped to the surface. These costs will be highly variable and may be prohibitive at
times. Hydraulically sound mineral barriers must be left in place around the mine
perimeter, so that flooding will occur naturally. Since these barriers consist of in
place minerals, they result in a loss of an appreciable amount of potentially
recoverable mineral.
IMPLEMENTATION
The downdip method of mining was recently investigated by Skelly and Loy,
Engineers and Consultants under contract to the United States Environmental
Protection Agency. The project included physical and economic evaluation of updip
and downdip mining on both active and abandoned mine sites. A draft report (104)
was submitted to EPA in February, 1975.
The pollution control effectiveness of downdip mining was evaluated by
comparing two abandoned underground coal mines. These mines were the Shoff and
Yorkshire No. 1 Mines which lie in Bigler Township, Clearfield County,
Pennsylvania, on opposite banks of Clearfield Creek. These two mines had the
following similarities (104): coal seam mined (Clarion coal or "A" seam), coal
184
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quality, mine size, mining method, time period of operation, availability of mine
history and mapping, geologic controls, hydrologic controls, topographic regime,
and measurable discharges. The major dissimilarity was the method of mine
development. The Shoff Mine was developed updip while the Yorkshire No. 1 Mine
was developed downdip.
To evaluate the effectiveness of mine flooding in controlling or eliminating the
production of acid mine drainage, monitoring stations were established at all
discharge points of both mines. Five discharge points at the Shoff Mine and two at
the Yorkshire No. 1 Mine were sampled eight times between July 30, 1974 and
December 2, 1974.
A comparison of the quality of water discharging from the two mines indicates
that the Yorkshire No. 1 Mine discharges were of better quality than those of the
Shoff Mine. The range in concentrations of various mine drainage indicators during
the sampling period was as follows:
Shoff Mine Yorkshire Mine
Field pH 2.1- 5.1 4.4- 5.8
Acidity (mg/1) 340-4,600 16- 116
Total Iron (mg/1) 12.7-1,335 0.3- 59.4
Sulfates (mg/1) 475 - 3,750 300 - 575
Manganese (mg/1) 3.7- 18.4 1.5- 3.4
Aluminum (mg/1) 0.4- 95.5 0- 7.2
Specific Conductance 1,025 - 4,550 600 - 1,010
(micromhos)
Water quality data clearly shows that the unflooded Shoff Mine is a major
source of mine drainage pollution, while discharge quality from the flooded
Yorkshire No. 1 mine ranged from marginal to slightly acid. Since the
abandoned mines were similar in all other respects, the report concluded
that the primary factor controlling water quality was the direction
of mine development.
An active mine having both updip and downdip sections was evaluated to
determine major advantages and disadvantages of each method of mine
development. This mine, the Stott No. 1 Mine is located in Huston Township,
Clearfield County, Pennsylvania and operated by Lady Jane Collieries, Inc. The mine
is operated in the Lower Kittanning coal seam. Conventional room and pillar mining
methods are used and coal is transported from the mine by a conveyor belt system.
The major factors expected to be affected by the method of mine development
were production, coal haulage, and pumping. An evaluation of these factors at the
Stott No.l revealed the following (104):
185
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1. During 1973, production from updip and downdip sections was
approximately equal, and mining downdip was no more or less
advantageous than mining updip.
2. The direction of belt haulage in any mining situation, including downdip
mining, does not appear to be a significant economic factor.
3. Pumping costs may be substantially increased by downdip mine
development, but they most likely will not reach the point of adversely
affecting production economics.
EVALUATION AND RECOMMENDATIONS
The downdip mining method should be considered as an alternative to mine
sealing or treatment to maintain acceptable water quality from abandoned
underground mines. Since mine entries are located at an elevation above the
underground workings, flooding of the mine can occur naturally when mining is
completed. Flooding will isolate sulfide minerals in the mine, and thus, control the
formation of acid mine drainage pollutants. Since oxidation will be minimized,
water discharging from flooded downdip mines should normally be of better quality
than discharges from unflooded updip mines.
Mining downdip will also improve the feasibility of sealing mine entries to
control mine drainage pollution. The ability to effectively hydraulically seal a mine
depends not only upon the strength of the seal, but also on the condition of the
natural mine system (See Section 2.4). When mines are developed updip, mine seals
and adjacent strata (which is often fractured and unsound) will be subjected to
maximum hydrostatic heads. When downdip mining is implemented these
hydraulically unsound areas will be subjected to little or no water pressure.
Initial evaluations indicate that there are no technological limitations to the
implementation of this mining technique. At the active mine site in Pennsylvania,
neither mine production nor haulage and pumping costs were significantly affected.
However, due to the variable nature of individual mines, production economics must
be evaluated at each potential mine site.
Downdip mining should be implemented wherever significant reduction in
pollution discharges will result. This mining technique is expected to be of major
economic importance to coal mine operators who will be required to comply with
186
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the recently proposed effluent limitation guidelines for the coal industry. These
guidlines will require an operator to meet certain effluent standards both during
mining and after abandonment, regardless of the mining method employed.
REFERENCES
27,31,70,72,81, 104, 127,129
187
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3.3 LONGWALL MINING
DESCRIPTION
Longwall mining is a method of removing a mineral seam in one operation by
means of a longwall or working face. The workings advance in a continuous line
which is usually 61 to 183 meters (200 to 600 feet) in length, but reportedly, may
exceed 305 meters (1,000 feet). Self-advancing powered supports are commonly
utilized to keep the longwall face open and prevent roof falls. As mining progresses,
the supports are advanced and the roof is allowed to break and cave immediately
behind the support line (46, 113). A plan of the longwall mining system is shown in
Figure 3.3-1.
At the present time the longwall method is employed primarily for the mining
of coal. However, its use may be extended to other sedimentary deposits such as
clay, gypsum and salt. The thickness of the longwall cut will be limited by the height
of available roof supports. Flat to moderately dipping coal seams may be
successfully mined with the longwall system.
IMPLEMENTATION
Longwall mining has reportedly been practiced in at least the following
countries: China, England, France, Germany, India, Poland, Russia and the United
States. As of 1970, the United States had longwall units operating in 18 coal mines
in the states of Pennsylvania, Utah, Virginia, and West Virginia. In these mines seam
thickness and length of longwall face ranged from 97 to 213 centimeters (38 to
84 inches and 91 to 182 meters (300 to 600 feet) respectively. The U.S. Bureau of
Mines has proposed that longwall methods be used to mine thick seam coal reserves
of the western United States.
EVALUATION AND RECOMMENDATIONS
Longwall mining is employed primarily for the advantages achieved during
active mining (i.e., increased production and efficient mineral recovery). However,
longwalling should also be an effective method of preventing mine drainage
pollution after mining is complete. Fracturing and caving of the roof behind the
advancing face will reduce void space within the mine. This may result in reduced
oxygen-sulfide contact, and thus, the oxidation of sulfides will be inhibited.
Although caving may prevent the production of mine drainage pollution in an
abandoned mine, the volume of water infiltrating during active mining may be
significantly increased. This water must be pumped from the mine and may require
188
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i
;";••"
yv
Face length
' take-off conveyor
_ Mt
varies
Wm
V'fi/t'tt'
Mineral
SK Self-advarK5ing;$*$
^ powered supports' %;
FIGURE 3.3-1
TYPICAL LON6WALL PLAN
189
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treatment prior to discharge on the surface. Increases in pumping and treatment
costs will place a financial burden upon the operator during mining. However, since
the production of mine drainage pollutants in abandoned sections will be retarded, a
reduction in pollution loads discharging from the mine will result.
The implementation of this mining technique should be of major economic
importance, especially to coal operators who will soon be required to comply with
the recently proposed effluent limitation guidelines for active and abandoned mines
in the coal industry.
REFERENCES
46, 113
190
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3.4 DAYLIGHTING
DESCRIPTION
Daylighting is the term applied to the stripping of recoverable mineral reserves
'in abandoned underground mines. The technique is performed in the same manner
asstrip mining. Overburden is removed, mineral reserves are recovered, and the area
is backfilled, graded, and revegetated. This technique abates mine drainage
discharges by removing pollution forming material and replacing the abandoned
mine void with a regraded surface mine.
Two major factors which will determine the feasibility of daylighting a
particular area are the thickness and type of overburden material, and the quality
and amount of recoverable mineral. The total value of the recovered mineral must
offset the cost of the daylighting operation, including mineral and surface rights
acquisition. Other factors affecting feasibility are access to the site, topography of
the area, and the ability to control erosion and water pollution during
operation (31, 127).
As shown in Figure 3.4-1 excavation and mining proceeds in a cut sequence. As
each new cut is made, spoil material is placed in the previously mined area to the
rear of excavation. Excavating and mining equipment are located on the.bench
between the highwall and spoil. When topography allows, spoil material from the
initial cut may be placed along the outcrop. If this is not feasible, the spoil may be
stockpiled in an adjacent area and later returned for backfilling of the mined area.
After completion of the final cut the entire mined area is reclaimed by grading and
revegetating.
IMPLEMENTATION
Daylighting as a mine drainage abatement technique is presently in the research
and development stage. A study was performed to determine the technical and
economic feasibility of daylighting an abandoned underground mine in the Lostland
Run watershed of the Upper Potomac River basin near Deer Park, Garret County,
Maryland (31). The study concluded that daylighting at the project site was feasible
and that reclamation would produce usable land and improve present water quality.
The completed project should eliminate 227 kilograms per day (500 Ib/day) of acid
discharging from the 30 hectare (75 acre) site into the North Branch of the Potomac
River via Lostland Run. ,.
The coal seam selected for the project demonstration is the 1.3 meter (51 inch)
Lower Bakerstown which has a maximum overburden thickness of approximately
16.8 meters (55 feet) at the project site. This coal has been previously surface and
191
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Mine Drainage
Abandoned
Underground Entri
Overburden Placed
on Previous Cuts
Direction of Cut
^o
(•o
Overburden Material
Abandoned. Underground Workings^
\x\\\\\\ \ x \
1060
1040
1020
1000
980
FIGURE 3.4-1
DAYLIGHTING OF ABANDONED UNDERGROUND MINES
-------
deep mined. An estimated 30 to 35 percent of the Lower Bakerstown coal remains
in-place, underlying the unstripped areas of the site.
The proposed sequence of operation at the demonstration site is as
follows (31):
1. Clearing and grubbing of 12 hectares (30 acres) of one growth timber and
evergreens.
2. Stockpiling of upper 0.6 meters (2 feet) of topsoil material.
3. Constructing drainage ditches around the site to divert drainage to two
siltation ponds.
4. Excavation of overburden material and mining of coal in a cut sequence.
5. Regrading of mined area.
6. Soil preparation, seeding, and mulching of regraded area.
7. Monitoring of site discharges to evaluate effectiveness of project.,
Although the feasibility study concluded that daylighting was technically and
economically feasible, the project has been delayed by land easement problems since
September, 1973. The demonstration project at Deer Park is now expected to begin
in the late spring or early summer of 1975.
In September, 1973, the cost of this demonstration project was estimated at
$482,735. Credit for the sale of coal was estimated at $191,000. This estimate was
based upon a sale price for coal of $4.69 per metric ton ($4.25/ton). Recent
increases in coal prices will improve the economic feasibility of the project. An
additional $4,500 was credited to the project for reclamation of the 6.1 hectare
(15 acre) Buffalo Coal Company strip mine. The total estimate of project costs was
as follows (31):
Estimated Cost $476,760
Credit for Coal -191,000
Credit for Reclamation - 4,500
Estimated Net Cost $281,260
Water Analysis 6,450
193
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Additional Soil Nutrient
Analysis Phase II, III 3,800
Engineering plus Fees (Includes
Stream Gauging and Sediment
Monitoring Stations) 191,225
TOTAL $482,735
EVALUATION AND RECOMMENDATIONS
Daylighting is a method of mining that can be utilized to eliminate pollution
from abandoned underground mines. This method is similar to the mountain top
removal method of surface mining which is presently used to remove coal seams that
lie high on a mountain and cannot be mined by underground methods. The major
difference between these two techniques is the condition of the seam being mined.
Virgin seams would be mined by the mountain top removal method, while
daylighting would be performed to completely strip out abandoned underground
workings.
The feasibility of daylighting will depend upon the total value of mineral
reserves that will be recovered during mining. Therefore, a complete resource
evaluation will be required to determine the quality and amount of remaining
mineral. Mining costs including land acquisition, overburden removal, and
reclamation must then be developed. The total cost of mining may exceed the
market value of the mineral reserves. In such instances the daylighting operation
may be subsidized and the subsidy cost could be partially or completely balanced in
terms of pollution abatement benefits.
REFERENCES
31,38, 108, 125, 127
194
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4.0
WATER HANDLING
195
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4.1 GENERAL DISCUSSION
This section will discuss various methods of reducing the environmental impact
of mine drainage pollutants discharging from abandoned underground mines. These
techniques may be applied in conjunction with at-source abatement and control
techniques (i.e., water infiltration control, mine sealing) or implemented as an
alternative to treatment when at-source techniques are technically infeasible or
economically unattractive.
Water handling may include methods for conveying water from the mine,
regulating mine discharge to the environment, or reducing the pollution load of the
discharge. These techniques will not be applicable to all mine drainage situations.
The selection and implementation of water handling techniques will depend upon
such factors as geology, hydrology, topography, and climatology of the mine area.
The techniques discussed in this section will include: evaporation ponds, slurry
trenching, alkaline regrading, controlled release holding ponds, and connector wells.
197
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4.2 EVAPORATION PONDS
DESCRIPTION
Holding ponds may be constructed to collect and impound discharges from
abandoned underground mines, thus, preventing discharge to the environment. This
system is designed to allow evaporation of the mine water to the atmosphere.
Therefore, its use will be limited to arid or semiarid areas having high evaporation
rates. The impoundment or series of impoundments must be capable of handling
peak discharge rates during periods when precipitation exceeds evaporation rates.
The impoundment structure must be constructed of materials that will prevent
leakage of the impounded water.
IMPLEMENTATION
In the Republic of South Africa, shallow lakes and evaporation areas have been
established for the disposal and storage of mine water from underground coal and
gold mines (107). These waters may be utilized as cooling water or process water for
selected industries requiring low quality water, or for large scale desalination should
this process become economically feasible. In the Orange Free State, various shallow
lakes are presently being utilized for recreational purposes. Evaporation areas are
also designed to collect storm water runoff and mineral pollution from slime dams.
The implementation of these waste water control techniques is expected to
reduce effluent volumes from mining activities to manageable proportions. The
establishment of large scale projects throughout the Republic of South Africa,
however, will require thecooperation and assistance of government, local, and
regional authorities.
The impounding of mine drainage has been considered in the United States as a
preventative measure in controlling stream pollution from acid mine water (69).
Ponds are commonly used for settling of insoluble compounds in mine and
treatment plant discharges, regulating the rate of discharge to streams, and
impoundment of mine refuse and preparation plant wastes. Documented cases of the
utilization of evaporation ponds as a sole water pollution control device were not
available in the literature.
EVALUATION AND RECOMMENDATIONS
Evaporation ponds would appear to be an efficient method of controlling
discharges from underground mines in semiarid mining regions of the West and
Southwest. This system must have the capacity to collect and impound the mine
198
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discharge during winter months when evaporationrates will be low and during
periods of peak discharge rates. Periodic inspection and maintenance of the
impoundment will be required to ensure that the system functions properly. To
maintain sufficient storage capacity, settled solids must be periodically removed
from the pond.
The planning and construction of evaporation pond systems will require an
investigation of the hydraulic and meteorological characteristics of the abandoned
mine site. The impoundment must be constructed of materials capable of
withstanding the maximum expected water pressure. Lining of the bottom of the
pond with clay or other suitable material may be required to control leakage and
prevent pollution of ground water. An overflow device should be constructed to
"prevent erosion or rupturing of the impoundment structure during peak flow
periods. If the impoundment is to be utilized for recreational activities, the
construction plan should provide access to the area.
The cost of constructing the impoundment structure including materials,
compacting, and grading will generally range from $1.31 to $2.62 per cubic meter
($ 1.00 to $2.00/cu yd). Lining costs will depend upon the material used and the
area covered. Clay liners will range in cost from $1.20 to $2.40 per square meter
($1.00 to $2.00/sqyd). Riprap and vegetative cover for slope protection may be
required and will result in increased expenditures.
REFERENCES
69,70,96,107, 127
199
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4.3 SLURRY TRENCHING
DESCRIPTION
A slurry trench is a narrow, vertical excavation in unconsolidated material with
the sides maintained by a water, clay slurry (usually bentonite). The trench may be
excavated with a backhoe, clam shell, dragline or connecting drill holes. The clay
slurry is backfilled, when possible, with the previously excavated material or
material with suitable grain size distribution. As the slurry dries an impermeable clay
is formed in the trench, thus, in effect, forming a ground water dam. The technique
has been primarily used for dewatering building foundations and for ground water
cut-off trenches below dams placed on unconsolidated material (70, 84, 105, 127).
A slurry trench may be used to control mine drainage discharges from
underground mines in areas where discharges are occurring from mine openings,
outcrop areas, highwalls, intersected underground workings, etc. In such situations,
the placement of a slurry trench with a top level above that of the discharge will
result in an increase in water level at the discharge point, and in the underground
mine. Acid production will be reduced as the result of inundating oxidizable sulfide
minerals. Figure 4.3-1 illustrates the utilization of a slurry trench to control mine
drainage from underground mine workings intersected by surface mine operations.
IMPLEMENTATION
Rattlesnake Creek Watershed, Pennsylvania
The final inspection of construction of approximately 412 meters (1,350 feet)
of slurry trench in the Rattlesnake Creek watershed, Jefferson County, Pennsylvania
was completed in November, 1974. Construction was performed under Pennsylvania
Project SL 132-2-101.1 by Trans-Continental Construction Company, Inc. (84).
Two trenches were constructed along the highwall of an abandoned surface mine.
Trench I begins on the east end of the surface mine and runs along the highwall for
approximately 351 meters (1,150 feet). Trench II joins Trench I and continues
around the hillside for approximately 61 meters (200 feet) to enclose an abandoned
underground coal mine entry. Plan and elevation views of the two slurry trenches are
shown in Figure 4.3-2.
The surface mine and underground entry had previously been backfilled. The
backfilling of the underground entry resulted in a partial flooding of the mine and a
subsequent leakage of mine drainage through the coal seam along the surface mine
highwall. The slurry trench was placed in an attempt to increase the water level in
the underground mine and control leakage from the highwall. Field investigations of
200
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•Original Ground Surface
Backfilled Ground Surface
Slurry Trench
•Inundated Mine Void
FIGURE 4.3-1
TYPICAL SLURRY TRENCH DETAIL
(Adapted from Ref. 105)
201
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De«p Mine Sea
Not*; Total length of Trenches I 8 H
approximately 412m (1350ft.)
O
to
Approximate rock line
/of Highwall
Trench I
Slurry wall rides up over
rock at Highwall
Trench
± 1.5m (5ft.)
PLAN
Approx. 23 to 27m
Top of Trench 1--^
HfsSm (1492 ft.) 3.7 ml
Bottom of Trench I— ^ ^
75 to 90 ft.
456m(l496ft.)^
_^___^^
L e v
^^--^Vj-t 451 m (1480ft.)
•^^ s^ Approximately
/Top of Trench H
^451 m( 1480ft.)
Drift Opening^
446m (1464 ft.) D
-t447m(!465ft.)
Bottom of Trench H —
SECTION
FIGURE 4.3-2
SLURRY TRENCH CONSTRUCTION
RATTLESNAKE WATERSHED , PA.
-------
the completed project indicate that an increase in water level in the underground
mine has occurred and water is discharging over the slurry trench.
Work performed in placing the slurry trench, as outlined in the technical
specifications, included the following:
1. Clearing and grubbing within the limits of grading.
2. Dewatering of the underground mine so that a reinforced concrete seal
could be constructed.
3. Removal and burial of bony and acid forming material on the work area.
4. Grading of the work area.
5. Constructing a diversion ditch above the highwall to divert water away
from the graded area.
6. Placing riprap to control erosion.
7. Placing drainage flume and constructing concrete endwall.
8. Placing approximately 2,787 square meters (30,000 sq ft) of slurry trench
as measured on a vertical plane through centerline of trench (maximum
depth 8.5 meters (28 feet) - Minimum width 0.6 meters (2 feet)).
9. Placing reinforced concrete deep mine seal in the mine opening.
10. Timbering on each side of the mine seal.
11. Revegetation — Liming, treating with soil supplement, seeding, and
mulching.
Total costs incurred in constructing the two slurry trenches were $190,835.
The cost of placing the estimated 2,787 square meters (30,000 sq ft) of slurry trench
was $123,000 which equals a cost per square meter of $44.13 ($4.10/sq ft).
Itemized construction costs were as follows:
Clearing and Grubbing Lump Sum $ 6,075
Dewatering Deep Mine Lump Sum 7,500
Removal and Burial Lump Sum 7,650
of Bony Material
203
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Grading Lump Sum 15,000
Diversion Ditch 56.4 m @ $3.28/m 185
(Above Highwall) (185 ft)($ 1.00/ft)
Riprap 50 sq m @ $24/sq m 1,200
(60 sq yd)($20/sq yd)
Drainage. Flume 96 m @ $65.62/m 6,300
(315ft)($20/ft)
Concrete Endwall Lump Sum 1,000
Reinforced Concrete 9.6 cu m @ $ 130.79/cu m 1,250
Mine Seal (12.5 cu yd)( $ 100/cu yd)
Timber Sets 10 @ $ 200 e ach 2,000
Revegetation Lump Sum 14,625
Treatment of Mine 101 hours® $50/hr 5,050
Drainage
Placing Slurry Trench Lump Sum 123,000
Elk Creek Watershed, West Virginia
Skelly and Loy, Engineers and Consultants has completed pre-design
engineering for the demonstration of slurry trenching within the Elk Creek
watershed, West Virginia (105). Five sites were evaluated to determine the feasibility
of demonstrating slurry trenching in conjunction with alkaline regrading (See
Alkaline Regrading, Section 4.4). Each of the demonstration sites lies in an area of
past extensive underground and surface mining of the Pittsburgh and Redstone coal
seams. The sites are characterized by pollution discharges resulting from breached
crop barriers during subsequent strip and auger mining.
The slurry trenches will be constructed into the underclay of the Pittsburgh
seam. Limestone and soft claystone above this seam provide large volumes of
alkaline rich spoil material. Prior to slurry trench construction this spoil will be
regraded to a modified contour or terrace backfill. After regrading the slurry trench
will be excavated through the spoil to the Pittsburgh underclay. The completed
slurry trench will cause a rise of mine water within the spoil material prior to
discharge over the trench. The depth of the constructed slurry trench will be 4.6 to
204
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7.6 meters (15 to 25 feet). The proposed project will demonstrate the neutralization
of mine water within the spoil and the decrease in acid production due to deep mine
inundation. A profile and cross sections of slurry trench construction proposed for
the Elk Creek project are presented in Figures 4.3-3 and 4.3-4.
An estimate of construction costs has been made for each of the five
demonstration sites within the watershed. The estimated costs for Site No. 1
including aerial photography, mapping, regrading, revegetation, and constructing
610 linear meters (2,000 LF) of slurry trench are $189,700. Approximately
477 kilograms per day (1,051 Ib/day) of acid will be neutralized which equals an
estimated cost effectiveness of $398 per kilogram per day ($180 per Ib/day) of acid
abated. Estimated costs are as follows:
Grading 22,938 cu m @ $0.65/cu m $ 15,000
(30,000 cu yd)($0.50/cu yd)
Slurry Wall 3,716 sq m @ $43.06/sq m 160,000
0.6 m thick (40,000 sq ft)($4.00/sq ft)
(2ft)
Revegetation 2.43 ha @ $ 1,235/ha 3,000
(6 ac)($500/ac)
Contingency 5 percent 8,900
Aerial Photography Lump Sum 2,800
and Mapping
TOTAL $189,700
Estimated construction costs at Site No. 2 are $173,000, which includes roof
collapse in conjunction with constructing the slurry trench. Elimination of the
$10,000 lump sum estimate for mine roof collapse and adjustment of contingency,
results in an adjusted estimated cost of slurry trench construction of $162,500.
Estimated construction costs excluding mine roof collapse would be:
Grading 45,876 cum @ $0.65/cu m $ 30,000
(60,000 cu yd)($0.50/cu yd)
Slurry Wall 2,787 sq m @ $43.06/sq m 120,000
0.6 m thick (30,000 sq ft)($4.00/sq ft)
(2ft)
205
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Existing Ground
. ^-TOP OF SLURRV TRENCH,,
*** —• — —* —— —— •""" 1.5%
o
OS
1.5%
UNDERCLAY (PITTSBURGH COAL)
390m (1280ft.)
378m (1240ft.)
1500
I 366m (1200ft.)
400
FIGURE 4.3-3
TYPICAL SLURRY TRENCH PROFILE
Elk Creek, W. Va.
(Adapted from Ref. 105)
-------
PropoMd
Slurry
Trtnch
Uiiderciay^
MODIFIED CONTOUR BACKFILL
Proposed Grade
Existing Ground-^
Nott: Slurry Trench Placed
Back From Outcrop •
For Best Utilization
Of Alkaline Spoil
Pittsburgh Coal
!Sj!!;pp£^^
Proposed
Slurry
Trench
Underclay-
TERRACE BACKFILL
FIGURE 4.3-4
TYPICAL SLURRY TRENCH CROSS SECTIONS
ELK CREEK , W.VA.
(Adapted from Ref. 105)
207
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Revegetation 2.03 ha @ $ 125/ha 2,500
(5 ac)($500/ac)
Contingency 5 percent 7,600
Aerial Photography Lump Sum 2,400
and Mapping
TOTAL $162,500
Samples collected at Site No. 3 show that an average of 26 kilograms per day
(57 Ib/day) of acid are discharging into Elk Creek. Approximately 100 percent
effectiveness is expected for eliminating pollution from this site. Total estimated
construction costs are $171,300 for a cost effectiveness of $6,590 per kilogram per
day ($3,005 per Ib/day). Estimated construction costs are as follows:
Grading 44,437 cu m @ $0.65/cu m $ 29,000
Slurry Wall 3,047 sq m @ $43.06/sq m 131,200
0.6 m thick (32,800 sq ft)($4.00/sq ft)
(2ft)
Revegetation 2.43 ha @ $ 1,235/ha 3,000
(6 ac)($500/ac)
Contingency 5 percent 8,100
TOTAL $171,300
The total estimated construction costs at Site No. 4 are $62,100.
Neutralization of approximately 139 kilograms per day (306 Ib/day) of acid equals a
cost effectiveness of $450 per kilogram per day ($203 per Ib/day) of acid abated.
Estimated construction costs are as follows:
Grading 13,304 cu m @ $0.65/cu m $8,700
(17,400 cu yd)($0.50/cu yd)
Slurry Wall 1,124 sq m @ $43.06/sq m 48,400
0.6 m thick (12,100 sq ft)($4.00/sq ft)
(2ft)
Revegetation 1.62 ha @ $ 1,235/ha 2,000
(4 ac)($500/ac)
Contingency 5 percent 3.000
TOTAL $62,100
208
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Initial chemical analyses of samples collected from Site No. 5 indicated that the
flow was acid. However, all analyses following the third sampling round showed net
alkalinity and a decrease of acidity concentrations to zero. Subsequently, the site is
not deemed feasible for demonstrating acid mine drainage abatement techniques.
Estimates of construction costs at the site are as follows:
Grading 12,081 cu m@ $0.65/cu m $7,900
(15,800 cu yd)($0.50/cu yd)
Slurry Wall 1,895 sq m @ $43.05/sq m 81,600
0.6 m thick (20,400 sq ft)($4.00/sq ft)
(2ft)
Revegetation 1.62 ha @ $ 1,235/ha 2,000
(4 ac)($500/ac)
Contingency 5 percent 4,600
TOTAL $96,100
EVALUATION AND RECOMMENDATIONS
The preliminary results of research investigations and demonstration projects
indicate that slurry trenching is an effective method of partially inundating
abandoned underground mines. The extent of inundation will depend upon the top
elevation of the slurry trench and the rise of the mine workings. This technique may
be applied to underground mines where the downdip outcrop has been stripped
mined or intersected by auger holes and drift mine openings.
Designs for external seals, in which a dam was constructed around a drift mine
opening, have been found in records of coal mine sealing projects of the 1930's. The
slurry trench is an external ground water dam constructed in unconsolidated
material. Various construction projects have demonstrated its effectiveness as an
impermeable barrier. Applicable experience related to mine drainage pollution
control has reportedly been limited to the work performed in Pennsylvania under
Project SL 132-2-101.1. The ability of this water handling technique to control acid
production will be further evaluated in the Elk Creek demonstration project.
Construction of the slurry trench will require backfilling, grading, and
compacting of suitable material on the work site. The cost of this work will depend
upon the availability of material and total volume moved. The costs of placing the
slurry wall will range between $32.30 and $53.82 per square meter ($3.00 to
$5.00/sq ft). The estimated cost of constructing 0.6 meter (2 foot) thick slurry
trench is approximately $43.60 per square meter ($4.05/sq ft). Additional expenses
209
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will include clearing and grubbing, and revegetation of the work area. The
construction of diversion ditches around the work site may be required to prevent
erosion of the graded backfill and slurry trench wall.
REFERENCES
70, 84, 105, 127
210
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4.4 ALKALINE REGRADING
DESCRIPTION
Alkaline regrading is a specialized surface mine reclamation technique for the
control of underground mine discharges. Utilization of this technique is limited to
areas where alkaline materials lie above a mineral seam and have been intermixed
with spoil material during surface mining operations. Regrading of the surface mine
with alkaline spoil allows mine discharges along the mineral seam to come into
contact with previously inaccessible alkaline material (70, 127). In areas where
conditions are favorable, alkaline regrading may be used as a method of neutralizing
underground acid mine discharges. A method of alkaline regrading is shown in
Figure 4.4-1.
IMPLEMENTATION
Elk Creek Watershed. West Virginia
Alkaline regrading has been practiced in the Elk Creek watershed in
West Virginia. The Pittsburgh and Redstone coal seams in this area have been
extensively surface and deep mined. The Redstone seam is usually 9 to 12 meters
(30 to 40 feet) above the Pittsburgh. The material between the two seams consists of
a soft claystone with a thin lense (maximum thickness — 1 meter (3 feet)) of
limestone. Discharges are normally acid since mine water does not have access to the
alkaline material. Alkaline discharges were observed after the outcrop of an
underground mine was surface mined and terrace regraded with spoil material. Prior
to surface mining, water discharging from the underground mine was highly acid.
Similar conditions have been observed at several strip mines in the area.
This technique will be demonstrated, in the near future, in conjunction with
slurry trenching in the Elk Creek watershed (See Slurry Trenching, Section 4.3).
Pre-engineering design was completed in November, 1974 by Skelly and Loy,
Engineers and Consultants. The slurry trench will increase the water level within the
spoil material, thus, more alkaline material will be exposed to acid discharges,
retention time in the spoil will be increased, and neutralization will be enhanced.
Effectiveness of the demonstration program will be documented by a water quality
sampling program (105).
Five sites within the watershed have been evaluated to determine the feasibility
of demonstrating alkaline regrading. Each of the sites lies in an area of past extensive
underground and surface mining of the Pittsburgh and Redstone coal seams. The
211
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•Original Ground Surface
Inplace Alkaline Material
•Highwall
Spoil with Intermixed
Alkaline Material
Acid Discharge from
Mineral Seam
Mine Void
OPEN SURFACE MINE
Spoil with Intermixed
Alkaline Material
Backfilled Ground
Surface
REGRADED SURFACE MINE
FIGURE 4.4-1
TYPICAL ALKALINE REGRADING
(Adapted from Ref. 70)
212
-------
sites are characterized by pollution discharges resulting from breached crop barriers
during subsequent strip and auger mining. Each of the demonstration sites will be
regraded with alkaline spoil to a modified contour or terrace backfill. After
regrading a slurry trench will be excavated to the Pittsburgh underclay. The method
of alkaline regrading at the Elk Creek sites is shown in Figure 4.4-2.
Alkaline regrading at the five demonstration sites is expected to result in an
overall reduction in acidity, iron, manganese, and aluminum concentration in the
discharges, with a subsequent increase in alkalinity (therefore, pH). It is estimated
that a 25 percent utilization of alkaline material at Site No. 3 will effectively abate
acid pollution for 600 years.
Estimates of construction costs for alkaline regrading and slurry trench
excavation have been made by Skelly and Loy (105). The unit cost estimates for
alkaline regrading are: Grading - $0.65 per cubic meter ($0.50/cu yd),
Revegetation - $1,235 per hectare ($500/acre). Estimated grading and revegetation
requirements, and associated costs at the individual sites are:
Site No. 1
Grading 22,938 cu m (30,000 cu yd) $ 15,000
Revegetation 2.43 ha (6 ac) 3,000
TOTAL $18,000
Site No. 2
Grading 45,876 cu m (60,000 cu yd) $30,000
Revegetation 2.03 ha (5 ac) 2,500
TOTAL $32,500
Site No. 3
Grading 44,347 cu m (58,000 cu yd) $29,000
Revegetation 2.43 ha (6 ac) 3.000
TOTAL $31,000
213
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HIGH WALL
>0
-------
Site No. 4
Grading 13,304 cu m( 17,400 cu yd) $ 8,700
Revegetation 1.62 ha (4 ac) 2.000
TOTAL $10,700
Site No. 5
Grading 12,081 cu m (15,800 cu yd) $ 7,900
Revegetation 1.62ha(4ac) 2,000
TOTAL $ 9,900
EVALUATION AND RECOMMENDATIONS
Alkaline regrading is classified as a water handling technique because of its
ability to neutralize underground mine discharges. The implementation of the
specialized surface mine regrading method will be limited to areas where alkaline
spoil material is available for neutralization. Regrading with alkaline spoil associated
with the Pittsburgh coal seam has effectively neutralized underground mine
discharges occurring along surface mined outcrops. This technique would
undoubtedly be applicable to other mining areas having similar conditions.
The effectiveness of alkaline regrading will depend upon the volume and
characteristics of the available alkaline spoil material. Alkaline materials will be best
utilized when they are thoroughly mixed and evenly distributed throughout the
surface mine spoil. The construction of a slurry trench in the regraded spoil is
expected to result in increased retention time of acid water and more efficient
utilization of alkaline material. The ability of the slurry trench to restrict ground
water flow and increase water level in regraded spoil has been demonstrated in the
Rattlesnake watershed in Pennsylvania (See Section 4.3).
The costs for alkaline regrading will be the same as contour and terrace
regrading. The total cost of regrading, including clearing and grubbing, backfilling,
grading, and revegetation will normally range from $4,445 to $9,383 per hectare
($1,800 to $3,800/acre) for contour regrading, and $3,704 to $8,395 per hectare
($1,500 to $3,400/acre) for terrace regrading. The selection of the regrading method
will depend upon such factors as height and condition of highwall, original slope of
ground, volume of available spoil, and available regrading equipment.
REFERENCES
70, 105, 127
215
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4.5 CONTROLLED RELEASE RESERVOIRS
DESCRIPTION
Abandoned underground mines commonly discharge pollutants throughout the
year. The rate of discharge will depend upon the response of the individual mine to
seasonal variations in precipitation. Therefore, it is possible that a mine may
discharge maximum pollution loads during periods when the receiving stream is
unable to assimilate large quantities of pollution. This water handling technique
involves the construction of large holding ponds or reservoirs to collect mine water
discharges. The mine water is released only during periods when the receiving stream
will be capable of accepting the water (70, 127).
Controlled release reservoirs may be utilized to regulate abandoned
underground mine discharges, effluent flows from treatment facilities, or flows of
extensively polluted streams to downstream river systems. The implementation of
this technique will require monitoring of various characteristics (i.e., pH, flow, etc.)
of the receiving stream. Discharge from the reservoir must be continuously regulated
to maintain acceptable stream water quality.
IMPLEMENTATION
A 1942 report (5) advocated the application of flow regulation as a method to
control mine drainage pollution of streams of the Ohio River basin. This program
was to be implemented, in conjunction with mine sealing, to reduce the
environmental effects of various wastes (including mine drainage) during periods of
low stream flow. The construction of reservoirs on the Allegheny River having a
total capacity of 259 million cubic meters (210,000 acre-feet) was expected to
reduce the maximum monthly acidity by 14 parts per million. The implementation
of a similar program on the Monongahela River was expected to reduce maximum
monthly acidity by 10 parts per million.
Numerous reservoirs have been constructed within the Ohio River basin by the
U.S. Army Corps of Engineers for flood control, navigational purposes, and
regulation of stream flow volume. The Tygart River reservoir near Grafton,
West Virginia is operated primarily for flood control, but, has been successful in
reducing down stream acidity. During the period 1930-34 the average monthly
stream hardness resulting from mine drainage pollution was reduced 11 parts per
million (5, 69).
Controlled release holding ponds have been recommended as a method of
control discharges from underground coal mines (2). The mine discharge would be
diverted to a holding pond equipped with a constant head, floating outlet which
216
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rises and falls with water level. The outlet would be anchored in the pond and
connected with a flexible hose to the discharge pipe. This system would provide a
constant rate of discharge from the holding pond.
A controlled release holding pond has been utilized to control the discharge of
Spring Creek into Keswick Reservoir, Shasta County, California. Pollution of Spring
Creek has resulted from the mining of silver, gold, copper, and pyrite in the vast Iron
Mountain mining complex. A summary of water quality in Spring Creek
follows (125):
pH 2.0 - 3.0
Specific Conductance (micromhos) 440 - 2,810
Acidity (mg/1) 28-1,800
Copper (mg/1) 0.5- 18
Zinc (mg/1) 0.6- 136
Iron (mg/1) 27 - 438
Hardness (mg/1) 89- 100
Sodium (mg/1) 3.9 - 4.4
Sulfates (mg/1) 119- 401
Chlorine (mg/1) 2 (one value)
Nitrates (mg/1) 1.1 (one value)
Aluminum (mg/1) 20- 133
Arsenic (mg/1) 0- 0.32
Chromium (mg/1) 0- 0.04
Lead (mg/1) 0- 0.20
Manganese (mg/1) 0.24- 1.10
The discharge of Spring Creek to Keswick Reservoir had a history of creating
fish kills. The controlled release holding pond was constructed in 1963 by the
Bureau of Reclamation. This pond was to serve two purposes: (1) store water which
was to be discharged at a controlled rate to Keswick Reservoir; and (2) collect metal
precipitates and sediment so that they would not enter the reservoir. The system
worked well until a 30.5 centimeter (12 inch) rain in 1968 caused an overflow and
fish kill. Later studies concluded that the fish kill would not have occurred if the
pond discharge had been properly regulated. The cost of constructing this pond was
estimated at from $ 1 to $2 million.
EVALUATION AND RECOMMENDATIONS
This method of handling mine water pollution may be applied to areas where
other control and abatement techniques are technically infeasible or economically
unattractive. The implementation of this technique should be limited to
217
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underground mine discharges or extensively polluted streams that are major sources
of pollution in the downstream river system. The reservoir must be designed with
sufficient capacity to impound the largest volume of water expected. Efficient and
effective operation of the regulated discharge system will require continuous
monitoring of water quality and flow in the receiving stream.
Controlled release reservoirs will normally require a greater pool capacity than
reservoirs designed solely for flood control. The design of the reservoirs will require
a complete hydrologic evaluation of the area, including field sampling and
monitoring. Variations in stream acid content and flow volumes must be
documented to determine allowable reservoir discharge rates that will maintain
acceptable water quality during periods of high, low, and average stream flows.
The costs of constructing a controlled discharge reservoir will be similar to
reservoirs constructed for flood control and navigational purposes. This information
may be obtained in various forms including cost versus storage area, cost versus
volume, and cost versus drainage area. The major factors affecting the total cost of
construction will be land acquisition costs and the cost of constructing the
impoundment structure and discharge outlet. Initial construction costs will be high;
however, benefits such as flood control, recreational use, and decreased treatment
costs downstream must be considered.
REFERENCES
2, 5, 8, 29, 69, 70, 96, 107, 125, 127
218
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4.6 CONNECTOR WELLS
DESCRIPTION
This mine water handling technique employs hydrogeologic features of an
underground mine to prevent the inflow and contamination of ground water. Wells
are drilled from the land surface to the underground mine. These wells tap overlying
aquifers and convey water downward to the underground mine. This water may be
passed through the mine zone for discharge into underlying aquifers, or conveyed
from the mine through a pipe system (81). This method of intercepting aquifers is
shown in Figure 4.6-1.
IMPLEMENTATION
This technique is theoretical and will require development and demonstration
to determine feasibility. Projects funded by the U.S. Environmental Protection
Agency will demonstrate connector wells on both active and abandoned
underground mines in the near future.
EVALUATION AND RECOMMENDATIONS
The connector well system appears to be suitable for both active and
abandoned underground mines. However, its implementation will not always be
technologically or economically feasible. A complete hydrogeological evaluation will
be required to determine characteristics of the underground mine and associated
aquifers. The connector well system of dewatering aquifers is more complicated than
methods of surface water diversion. Therefore, an experienced hydrogeologist will
be required to analyze hydrogeologic settings, determine feasibility, and design the
system.
The utilization of a pipe system to convey water from underground mines may
be limited to active mine sites. In many abandoned mines it will be dangerous or
impossible'to enter and place pipe systems. In such situations the connector wells
may be cased through the mine zone to allow the discharge of water to underlying
aquifers. The underlying aquifers, however, must be capable of accepting the
expected flow.
Since this technique has not been implemented, cost data is not readily
available. The total cost of implementation will include hydrogeologic evaluations,
drilling, casing, piping, and possibly grouting to control leakage through the mine
219
-------
-Connector Wells
Ground Water Level
Ground Surface
I*- Cosing
-Casing—-
:Spurce;JBed.::
• Confining':••• Bedj
Underground Mine
••-Confining Bed..
tl Deep 11 Aquifer t-J
Sp^-^:^i^.!^.-r-.-^.fi|^ ^
Free Water
Surface
-Connector Wells
Free Water
Surfaces
.Ground
Surface
Mine Drainage
Seepage Face
FIGURE 4.6-1
INTERCEPTION OF AQUIFERS BY CONNECTOR WELLS
(Adapted from Ref. 27)
220
-------
roof. These costs will be variable, and therefore, cost estimates should be developed
on an individual application basis.
REFERENCES
27,68,81, 125, 127, 129
221
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5.0
DISCHARGE QUALITY CONTROL
223
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5.1 GENERAL DISCUSSION
Sulfide minerals responsible for the formation of mine drainage pollution are
commonly associated with ore and mineral bodies. Underground mining exposes
these sulfides to sufficient oxygen and water to allow oxidation and flushing of
pollutants from the mine. Various methods of sealing abandoned mines to prevent
the influx of air and water, and control the quantity of mine water discharge have
been described in previous sections of this manual (See Sections 1.0 and 2.0).
However, such abatement and control techniques are not universally applicable, and
their use will be limited by the technical and economical feasibility of
implementation.
The techniques described in this section are designed to control the quality of
water discharging from an abandoned mine. Two of these control methods, mine
backfilling and pressurizing with inert gas, inhibit the formation of acid mine water
by reducing oxygen-sulfide contact. Underground precipitation is an in situ
treatment technique that produces a neutralized mine effluent. With the exception
of mine backfilling, the demonstration of these techniques has been limited to
research and development programs. Further field evaluation will be required to
demonstrate their feasibility and practicability.
225
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5.2 MINE BACKFILLING
DESCRIPTION
Underground mine backfilling is a method of disposing of mine and milling
wastes. This process had its origin over a century ago in the anthracite coal region of
northeastern Pennsylvania. Underground mines were backfilled to control mine fires,
arrest the spread of squeezes in coal beds, and protect the overlying ground surface.
Backfilling with mine and/or mill waste has been practiced in both active and
abandoned underground mines (35).
Abandoned underground mines underlying populated areas have been
backfilled to prevent surface damage from subsidence. The degree of mine drainage
pollution control resulting from backfilling of abandoned mines has not been
demonstrated. However, control of mine roof collapse and subsidence will restrict
infiltration of air and water through vertical fractures.
Three methods of hydraulic injection commonly used in underground mine
backfilling are: controlled flushing, blind flushing, and pumped-slurry technique. In
both controlled and blind flushing, solids are gravity fed from the surface through
cased boreholes. Controlled flushing is used in mines that are accessible for the safe
entry of workmen. Solids injected through the boreholes are diverted to horizontal
pipes and placed by workmen in various sections of the mine. Blind flushing is used
in flooded or inaccessible mines. Material is sluiced into a borehole until the mine is
filled to the roof. Blind flushing requires more boreholes than controlled flushing
and complete filling between boreholes is not achieved (12, 82). The methods of
controlled flushing and blind flushing are depicted in Figure 5.2-1.
The pumped-slurry technique is a more effective method of backfilling
inaccessible mines. Solids are placed in suspension in a mixing tank and injected as a
slurry through a slurry pump into the mine workings via injection boreholes. This
technique has resulted in the injection of as much as 144,753 cubic meters
(189,319cu yd) of refuse through one borehole. Quantities injected via blind
flushing normally range from 15 to 765 cubic meters (20 to l,000cu yd) per
borehole.
IMPLEMENTATION
Backfilling By Hydraulic Methods
A majority of mine waste disposal in abandoned mines in the United States has
been performed throughout the Appalachian region. Since 1962, twelve projects
226
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Coal Mine Refuse
Crusher^ .stockpile
Rock Stroto ^ ^r * _^. ™"^
Wooden Battery (Dam
Water Pool
CONTROLLED FLUSHING
Soil a Gravel -7
Completed Hole
Flush Hopper
TT Rock Strata ~=~j=^
: : :•••: •.:*:•.••-.•
• •-•.'. •.•.•/.''• .'-.'* '
Coal Seam
BLIND FLUSHING
FIGURE 5.2-1
BACKFILLING ABANDONED UNDERGROUND MINES
WITH COAL REFUSE
(Adapted from Ref. 35)
227
-------
have been completed, three are presently in progress, and more projects are being
planned (35). These projects are conducted to control subsidence damage from
abandoned anthracite and bituminous coal mines.
The costs of underground disposal of mining wastes are difficult to evaluate.
Average costs of various recent abandoned coal mine backfilling projects in the
United States are (35):
Method Cost Per Unit of Fill Injected
Controlled Flushing $2.41 - 3.11/cu m
(1963-1968) ($1.84-2.38/cu yd)
Blind Flushing $3.22/cu m
(1965-1967) ($2.46/cuyd)
Combined Controlled $4.76 - 8.84/cu m
an d Blind Flushing ($ 3.64 - 6.76/cu yd)
(1966-1969)
Pumped-Slurry Techniques $6.28/cu m
(1971-1972) ($4.80/cuyd)
Rock Springs, Wyoming Demonstration Project
The pumped-slurry technique was developed and first demonstrated by the
Dowell Division of Dow Chemical Company at Rock Springs, Wyoming in 1970. The
Dowell process (closed system hydraulic backfilling) works on the Venturi tube
principle. High volumes of material are injected into the mine by maintaining
sufficient particle velocities to transport material to areas beyond the injection
point (82).
Three closed system hydraulic backfilling projects have been completed in
Rock Springs. In all three projects, underground sub-bituminous coal mines
underlying the city were backfilled with sand. Costs for the projects, which include
materials, equipment, pumping, and mobilization are shown in Table 5.2-1.
Green Ridge Demonstration Project
Coal mine refuse was used to backfill two anthracite coal seams underlying
Scranton, Pennsylvania. Work on this project, the Green Ridge Demonstration
Project, was performed in 1972 by Dowell. A total of 12.2 hectares (30 acres) was
backfilled with 408,150 metric tons (450,000 tons) of crushed mine refuse. The
costs per unit weight of material and unit area backfilled were $5.27 per metric ton
($4.78/ton) and $178,267 per hectare ($72,198/acre) respectively (116).
228
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TABLE 5.2-1
Costs of Hydraulic Backfilling
Rock Springs, Wyoming
Proj ect/Contractor
Area Backfilled
Cost Per Unit
Area Backfilled
Material Cost
Per Unit Weight
Project I (Demon-
stration) /Dowel1
Project II/Dowell
Project III/WHAN
Engineering &
Construction
1.1 ha
(2.8 ac)
13.4 ha
(33.1 ac)
22.0 ha
(54.2 ac)
$ 158,025/ha
(64,000/ac)
$ 54,331/ha
(22,004/ac)
$ 52,425/ha
(21,232/ac)
$ 7.89/metric ton
(7.16/ton)
$ 5.27/metric ton
(4.78/ton)
$ 3.83/metric ton
(3.47/ton)
-------
EVALUATION AND RECOMMENDATIONS
Mine backfilling is an effective method of controlling subsidence damage over
abandoned mines and reducing water pollution resulting from the disposal of mine
wastes on land. Although this technique has not been utilized exclusively as a mine
drainage control technique, it is expected that the oxidation of sulfides within a
backfilled mine will be inhibited. The reduction of void space within the mine will
result in reduced oxygen-sulfide contact and an increase in the level of water flowing
through the mine. The implementation of this technique will be limited by the
mining method and characteristics of the mine waste material.
The costs of backfilling abandoned underground coal mines, using the closed
system hydraulic backfill method, have ranged from approximately $49,400 to
$172,800 per hectare ($20,000 to $70,000/acre). The backfilling of abandoned
mines for the sole purpose of controlling mine drainage pollution would be unduly
expensive. However, this technique may be economically feasible when performed
for the dual purpose of mine drainage control and the prevention of subsidence
damage to surface structures. Such a program may be justified when urban areas are
involved.
Documentation of the effectiveness of mine backfilling in controlling
discharges from abandoned mines will require further research and demonstration.
Improved methods of material injection and equipment utilization could result in
decreased costs. The mixture of cementing or gelling agents with the backfill
material to form hydraulic seals in the mine should be investigated. Controlled
flushing methods are less expensive than blind flushing and may be performed
during or immediately following active mining operations. Backfilling in this manner
would be more efficient and less costly in the long run.
REFERENCES
7, 12, 24, 35,82,83, 116, 127
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5.3 PRESSURIZING WITH INERT GAS
DESCRIPTION
The pressurizing of abandoned underground mines with inert gas is a mine
drainage abatement technique similar to mine inundation. Pollution production is
reduced through the reduction of free air oxygen. Experimental laboratory work has
shown that a reduction in oxygen content to 0.4 percent or lower will decrease acid
production 97 percent over that in air.
Maintaining an inert gas atmosphere in an abandoned mine requires that the
pressure within the mine be slightly greater than outside barometric pressure. This
positive pressure will result in continuous exhaling from the mine, thus, eliminating
the entrance of air during mine breathing, commonly associated with barometric
changes in the atmosphere. Inert gas required for pressurization could be obtained
from the exhaust of an internal combustion engine driving an electric generator.
Power credit would cover operating costs and amortization (90, 92).
IMPLEMENTATION
An experimental program to determine the feasibility of pressurizing with inert
gas was initiated in the summer of 1968 by NUS Corporation, Cyrus William Rice
Division under contract to the Pennsylvania Department of Mines and Mineral
Industries. The objective of Phase I of this program was to determine air injection
rates required to pressurize abandoned mines and to develop methods for locating
leaks in abandoned mines where the known entries have been sealed (92).
The mine originally selected for Phase I study was the Whipkey Mine located in
Stewart Township, Fayette County, Pennsylvania. The calculated minimum air
injection rate required to satisfy breathing requirements during rising barometric
pressure was 5 cubic meters per minute (180 cfm). Air was injected at the rate of
14 cubic meters per minute (500 cfm); however, a differential pressure could be
produced only during periods of falling atmospheric pressure. Attempts to
determine the reason for the inability to produce a differential pressure revealed that
three original mine entries which had been backfilled with spoil were the sources'of
leakage.
Operations were switched to an adjacent mine, King Mine No. 2. During an air
injection rate of 16 cubic meters per minute (575 cfm) a positive differential
pressure was developed which varied from 0.51 to 0.71 centimeters (0.20 to
0.28 inches) of water. After closure of a leak occurring from a subsidence hole,
differential pressures up to 2.5 centimeters (1 inch) of water were developed at an
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air injection rate of 56 cubic meters per minute (2,000 cfm). Although positive
differential pressures were successfully developed, a discontinuation of air injection
resulted in a rapid fall of pressure within the mine.
Based on results of air pressurization of the King Mine, capital and operating
costs were developed for treatment of drainage from the mine and application of
inert gas. Calculations were made for lime neutralization of the acid mine drainge,
application of inert gas from a simple inert gas generator, and application of inert gas
from the exhaust of a natural gas engine driving an electric generator. Power credit
from the generator was assumed to be 7 mills per kilowatt hour. Results of the
calculations were as follows (90).
Capital Operation^
Lime Neutralization 1 $ 10,000 $ 5,100/yr
Inert Gas Generator2 18,000 7,900/yr
Natural Gas Engine2 19,000 3,200/yr
1 Basis 136 cu m/day (36,000 gpd), 500 mg/1 acidity mine drainage
2 Basis 546 standard cu m/hr (19,500 SCFH) 50 percent of time
3 Includes 10 year amortization, at 7 percent interest
EVALUATION AND RECOMMENDATIONS
The results of the experimental program conducted in Pennsylvania indicate
that positive differential pressures may be established in abandoned underground
mines. However, the effectiveness of an inert gas atmosphere in controlling the
formation of mine drainage pollution has not been documented. Field
demonstrations of this technique will be required to determine practicability of
implementation. A major disadvantage will be the periodic inspection and
maintenance required during the total period of operation.
The factors that will affect the technical and economic feasibility of
implementing this technique will include: volume of the mine, permeability of
confining strata, rate of change of barometric pressure, fuel costs for operating inert
gas generators, electric power credit, maintenance required, and capital costs of
installation. Preliminary economic evaluations have concluded that capital and
operating costs for an inert gas installation will be considerably less than
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neutralization with hydrated lime. The economic advantage realized will greatly
depend upon the ability to sell bi-product electric power.
REFERENCES
27,29,90,92, 127
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5.4 UNDERGROUND PRECIPITATION
DESCRIPTION
Underground precipitation is accomplished by injecting alkaline water slurries
into abandoned underground mines. The alkaline slurry neutralizes mine water
within the mine resulting in the precipitation of sludge which fills the mine void.
The advantage of filling with sludge is that the sludge is a bulking type precipitate,
taking up more volume than that occupied by the unreacted materials.
The technique may be utilized as either a method of sealing drainage openings,
or for continuous neutralization of effluent mine water. Sealing drainage openings
may be accomplished by injecting slurry behind a rubble barrier and allowing
precipitates to flow into the barrier and plug the openings. Continuous
neutralization produces a treated effluent while filling the mine voids with sludge,
thus, eliminating sludge disposal problems associated with surface treatment
operations.
IMPLEMENTATION
The Parsons-Jurden Corporation conducted a study to evaluate underground
precipitation in abandoned mines, resulting from the reaction of mine water with
hydrated lime and limestone (63, 110). Initial laboratory investigations indicated
that underground precipitation would be a feasible mine drainage abatement
technique. Laboratory tests revealed that under proper flow conditions, the
precipitates formed in the mine would settle in the mine while alkaline water
drained from the mine. A sand barrier placed across a simulated mine adit was
completely sealed off by precipitates which formed in acid water and flowed to the
barrier.
A field demonstration of the technique was conducted during the months of
November and December, 1970 at the Driscoll No. 4 Mine, an abandoned mine, near
Vintondale, Pennsylvania. Field tests were conducted to: (1) demonstrate the sealing
of a rubble barrier by injecting lime slurries on the inby side; and (2) neutralize acid
mine drainage behind a bulkhead so that precipitates settle in the mine and
neutralized water discharges through a drain pipe. Preliminary work involved placing
three bulkheads, a rubble barrier, injection and drainage lines, and weirs in the mine
entries. A plan of the mine portal is shown in Figure 5.4-1.
The rubble barrier placed in the No. 1 west entry was 7.6 (25 feet) long and
consisted of broken slate, shale, and glacial till. The attempt to seal outflow through
the barrier involved alternate injection of hydrated lime and pulverized limestone
behind the rubble pile. At the end of 62 hours of slurry injection the flow of water
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No. I Injection line extends 24.4m(80ft)fromNo.2 Bulkhead-
No. 2 Injection line extends l9.8m(65ft)fromNa2 Bulkheac
No. 3 Injection line extends 15.2 m(50ft)fromNo. 2 Bulkhead -
Supported Plastic
Injection Lines \
36.6m (120ft.):
OJ
~ No. 2 Bulkhead
Coal Pillar
Rubble Pile Sealing
Test Area
NalBulkhead
582.1m (1909.7ft.)
FIGURE 5.4-1
PLAN OF BULKHEADS, PIPING, WEIRS AND PORTAL
DRISCOLL NO. 4 MINE
Vintondale, Pennsylvania
(Adapted from Ref. 110)
low
Flow
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through the barrier stopped, indicating that a plug had been formed. A few hours
later a small flow of approximately 0.06 liters per second (1 gpm) began. Slurry was
again injected but problems with plugging lines resulted in termination of the test
after 345 hours. A total of 18,047 kilograms (39,750 pounds) of hydrated lime and
9,775 kilograms (21,530 pounds) of pulverized limestone were injected during this
phase of the test.
An attempt was made to re-establish the seal during a second test which lasted
251 hours. During this period 27,422 kilograms (60,400 pounds) of hydrated lime
and 8,608 kilograms (18,960 pounds) of pulverized limestone were injected behind
the rubble barrier. The flow of water was never stopped; however, the pH of the
outflowing mine water increased to the 11 to 12 range during slurry injection.
Although the exact reasons for the failure of the precipitates to seal the rubble
barrier are not known, several explanations have been postulated:
1. Shrinkage of gels as they aged may have loosened the plug.
2. Diffusion of mine water into the seal may have caused re-solution of the
precipitates.
3. Once the seal was formed there was no flowing force to carry or hold the
slurry and precipitates against the rubble barrier.
4. The bulk of the precipitates settled to the floor and were unable to seal
areas near the roof and top of the rubble barrier.
The failure to establish and maintain a seal was probably the result of a combination
of factors.
Testing of the continuous neutralization of outflowing water was conducted
behind the No. 2 bulkhead in the mine. During the first test period of 39 hours
4,249 kilograms (9,360 pounds) of hydrated lime were injected into the mine.
Theoretically the slurry should have raised the pH of the effluent mine water to
11.1. Actual pH readings were 3.6 to 4.6. During a second 26 hour test,
7,082 kilograms (15,600 pounds) of hydrated lime were injected. Again the effluent
water failed to reach the theoretical pH of 12, having only a pH of 4.4 to 4.8.
Although the injection of slurry behind the No. 2 bulkhead failed to neutralize
the effluent mine water, feasibility of the technique was demonstrated during the
attempt to reestablish the rubble barrier seal. As previously mentioned the pH of the
outflowing water increased to 11 to 12 during slurry injection. When injection was
stopped, pH dropped to the normal 3 or 4 range. Presumably, the sludge formed
during slurry injection was settling in the mine.
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Cost figures for the individual phases of the project are not available. Total
project cost estimates have been in excess of $250,000 (32).
EVALUATION AND RECOMMENDATIONS
The major advantages of underground precipitation are the filling of mine voids
with sludge, thus, eliminating the need for sludge handling, and the production of a
neutralized mine water discharge. This technique appears to be an effective method
of controlling polluted discharges from abandoned underground mines when other
techniques are infeasible. This in situ treatment technique should be less costly than
standard treatment facilities since mixing tanks, settling basins, and sludge storage
and handling facilities will not be required. As precipitated sludge fills the mine void,
less free air oxygen will be available to further oxidize sulfide minerals and the rate
of pollution formation will be retarded.
The cost of implementing the underground treatment technique will include
alkaline materials utilized for neutralization, and capital and operating costs for
equipment required to inject the alkaline slurry. The slurry may be injected from
above the mine through vertical boreholes or through a pipe system within the mine.
The construction and maintenance of the injection system will result in additional
expenditures. The total cost per unit volume of water treated should approximate
costs of conventional treatment methods; however, capital costs should be
considerably lower.
REFERENCES
32,63,110
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Ill
MINERAL COMMODITIES MINED
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This section is divided into: (1) Ferrous Metals; (2) Nonferrous Metals;
(3) Nonmetals; and (4) Energy Sources. The information includes principal minerals,
types of deposits, location of deposits, location of underground mines, and
environmental problems related to underground mining. Included are all mineral
commodities for which the United States has mineral resources that are mined
currently or may be mined in the future by underground methods.
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1.0
FERROUS METALS
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1.1 CHROMIUM
The mineral chromite is the sole current source of commercial chromium.
Chromite varies compositionally within limits permitted by the formula
((Mg,Fe,Zn,Mn)(Al,Cr)2O4). No chromite has been mined in the United States since
1961. In the past, almost all the chromite mined in the United States came from
Alaska, California, Maryland, Montana, Oregon, and Pennsylvania, with about
one-half of all production coming from Montana.
Primary chromite deposits occur only in certain kinds of ultramafic or closely
related anorthositic rocks. The two major types are stratiform (layered) and
pod-shaped. The Stillwater Complex of Montana is the largest known United States
resource. It is a stratiform deposit where several exposed zones of high-iron
chromiferous material extend in length. Since there is no commercial chromite
mining in the United States, there are no environmental problems related to
underground mining.
1.2 COBALT
Cobalt is a major constituent of approximately seventy minerals and a minor
constituent of several hundred more minerals. The principal sulfide-arsenide minerals
are carrollite (CuCo2S4), smaltite (CoAs3-x), skutterudite (CoAss), and cobaltite
(CoAsS). Cobalt formerly produced in the United States was contained in a pyrite
concentrate which was a byproduct from beneficiating the magnetite-bearing ore
mined at the Cornwall and Grace Mines in Pennsylvania. Both of these mines used a
block caving mining method. These deposits are contact metamorphic deposits
containing magnetite, chalcopyrite, and cobaltiferous pyrite. United States deposits
containing cobalt can be classified geologically as: (1) hypogene deposits associated
with mafic intrusive igneous rocks (Pennsylvania, Maine, Connecticut,
Massachusetts, New York, Washington, Oregon, California, Minnesota, and
Montana); (2) contact metamorphic (Pennsylvania); (3) laterite (California, Oregon,
Washington, and North Carolina); (4) massive sulfide (Tennessee, Maryland, Virginia,
and Alabama); and (5) hydrothermal (Idaho, Nevada, New Mexico, Connecticut,
Virginia, Missouri, Wisconsin, Illinois, and Iowa). Except for the laterite deposits,
the cobalt alw,ays is associated with iron sulfides and often copper and nickel
sulfides. Since cobalt is not produced in the United States, there are no
environmental problems related to underground cobalt mining. If cobalt production
was resumed as a byproduct or coproduct, the environmental problems related to
underground mining of cobalt would be nearly identical to those for iron, copper,
and nickel.
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1.3 COLUMBIUM
Columbium minerals are chiefly oxides and hydroxides, but include a few
silicates. Columbium minerals are not known pollutants and drainage waters from
mines should not degrade the environment, except for sedimentation. The United
States relies on imports for its primary supply of columbium and domestic mine
production is negligible.
1.4 IRON
The iron ore minerals are magnetite (Fe3O4), hematite (Fe2O3), geothite
(Fe2O3-H2O), siderite (FeCOs), pyrite (FeS2), and pyrrhotite (Fei-xS). The iron
oxide minerals are the principal iron ore minerals in the United States. Iron ore
deposits can be classified as: (1) bedded sedimentary deposits; (2) deposits related
directly to igneous activity; (3) deposits formed by hodrothermal solutions; and
(4) deposits produced by surface or near-surface enrichment.
Banded iron formations occur as sedimentary deposits in Precambrian rocks.
The most distinctive and economically significant banded iron formations consist of
iron oxides (magnetite and hematite) and chert (or its recrystallized equivalent) in
alternating thin layers. In some iron formations, siderite occurs with appreciable
amounts of manganese, magnesium, and calcium. Iron silicates, such as greenalite,
minnesotaite, and stilpnomelane occur in some formations. The occurrance of pyrite
and pyrrhotite are rare in banded iron formations. Metamorphism has altered many
iron formations and changed pre-existing minerals to silicates, such as
cummingtonite-grunerite, pyroxene, and olivine. Silicates in the
cummingtonite-grunerite series may contain asbestos-like fibers which represent a
possible health hazard when inhaled and/or ingested. Prominent examples of banded
iron formations in the United States are the Mesabi, Cuyuna, Gogebic, Marquette,
and Menominee Ranges in Minnesota, Wisconsin, and Michigan.
Ironstones, mostly post-Precambrian, occur as bedded sedimentary deposits.
Ironstone deposits vary considerably, but commonly are thick bedded rocks
containing small pellets (ooliths) of limonite, hematite, or chamosite in a matrix of
chamosite, siderite, or calcite. Ironstones may be divided into oxide, carbonate,
silicate, and sulfide facies, depending upon the dominant iron mineral. A prominent
example of the ironstones is the Clinton Formation, extending from Alabama to
New York.
Iron in deposits related directly to igneous activity is believed to be
concentrated during recrystallization as a constituent of early formed minerals that
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may have settled to the base of the magma chamber (magmatic segregations) or as a
constituent of fluids (gases and aqueous liquids) which escape the magma chamber
and deposit iron minerals in surrounding rocks (pyrometasomatic deposits).
Magmatic segregations either can be titaniferous or non-titaniferous. Titaniferous
ores occur as layers and segregations in gabbro, pyroxenite, and anorthosite. The
gabbro and pyroxenite deposits commonly are layered lenses of magnetite, ilmenite,
and silicates, such as pyroxene. Anorthosite deposits are irregular masses and dikes
of coarse-grained ilmenite, magnetite or specularite, feldspar, ulvospinel (Fe2TiO4),
and rutile (TiO2), such as the anorthosite bodies of upper New York State.
Non-titaniferous ores are composed of magnetite and minor amounts of hematite,
such as the Pea Ridge and Pilot Knob deposits of Precambrian age in Missouri.
Pyrometasomatic deposits encompass a wide variety of igneous deposits. Typical
deposits are replacements, usually in limestone, at or near a contact with the parent
igneous rock. At Cornwall, Pennsylvania, the ore contains magnetite associated with
sulfides, such as pyrite and chalcopyrite. Actinolite and chlorite are the predominant
gangue minerals. At the Iron Springs district, Utah, the ore contains magnetite and
the gangue minerals include phlogopite and fine-grained calcsilicates, and significant
amounts of apatite.
Deposits formed by hydrothermal solutions include replacement deposits in
nonferruginous rocks and enrichment of pre-existing non-ferruginous rocks. Small
and medium size replacement deposits occurring as pods, veins, and lenses in
volcanic rocks, breccia ted igneous rocks, and limestone are common in the western
United States. Magnetite and hematite are the typical ore minerals and occur mainly
in association with pyrite and chalcopyrite. Some veins and bedding replacements
consist wholly or largely of siderite. The Benson Mine, New York, is a replacement
deposit consisting of magnetite and hematite as ore minerals and quartz, potassium
feldspar, sillimanite, garnet, and ferromagnesian minerals as gangue minerals. The
enrichment deposits are very high grade deposits approaching 70 percent iron with
the ore consisting of crystalline hematite (specularite) as in the Vermilion district of
Minnesota.
Deposits produced by surface or near-surface enrichment include laterites and
enrichments of low-grade ores. The direct shipping, wash, and semitaconite ores of
the Lake Superior region consisting of soft limonite and hematite are products of
deep residual enrichment of the primary iron formation, in which oxidation of
ferrous minerals was accomplished by partial to complete leaching and replacement
of chert. The brown ores of Texas and the southeastern United States were formed
by oxidation and enrichment of Tertiary strata containing siderite and glauconite.
The hard ores of the Marquette district, Michigan, probably represent in part a
former enrichment and in part a clastic accumulation, now modified by
metamorphism.
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Most United States iron ore is produced in the Lake Superior district in
Minnesota and Michigan. There are relatively small but significant mines producing
iron ore in Alabama, California, Missouri, New York, Pennsylvania, Texas, Utah,
Wisconsin, and Wyoming. In the United States, iron ore is mined principally by open
pit methods with only 4 percent of the iron ore mined by underground methods.
Underground room and pillar methods are used to mine flat-lying or gently dipping,
thin bedded deposits. Caving methods, supplemented by shrinkage and sub-level
sloping, are used to mine massive and vein-type deposits.
There are seven underground iron ore mines in the United States. These are
located in Michigan, Pennsylvania, Missouri, Wyoming, and North Carolina. The
North Carolina mine produces a small amount of high quality magnetite for special
uses.
It is estimated that 30 percent of the total iron in the crude ore is lost in the
conversion of the crude ore to a usable iron ore concentrate or pellet. This loss
occurs because of the inefficiency of benefication processes in recovering fines and
different minerals. As examples, fines are lost during gravity processing of hematite
ores and nonmagnetic iron (hematite, iron silicates, etc.) is lost during magnetic
separation of essentially magnetite ores.
The environmental problems related to underground mining of iron ore are
waste water from mines and dumps and subsidence from underground open stopes.
Surface and groundwater seepage into operating underground mines require
continuous pumping of considerable waste water to maintain dry working areas.
Mine waters may be high in suspended solids and either acidic or alkaline. Surface
run-off and erosion of mine dumps at abandoned and operating mines are a major
source of waste water. These waters usually are turbid and bright red-orange in
color. The red-orange color is related to the suspended solids and indicative of the
red iron oxide or hematite prevalent in the ore or waste rock. These suspended solids
usually can be removed by sedimentation. The suspended solids or silt usually are
high in iron content and alkaline, and occasionally contain manganese and silica.
These waste waters create an unfavorable environment for fish and wildlife. These
waste waters seriously affect the use of swimming beaches, recreational areas, and
lakeshore property because they are an aesthetic nuisance. Red silt deposited in
shallow lake areas may be resuspended by wind-induced currents and be a source of
nuisance for many years. Subsidence is a major environmental problem for
underground mines. Surface land will be altered drastically, often causing damage to
public and private property. Low subsided areas may collect surface water run-off,
which may enter underground workings and then be pumped from underground as
waste water.
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1.5 MANGANESE
The principal ore-mineral forms for manganese are oxides, carbonates, and
silicates. The most important ore minerals are pyrolusite (MnO2), manganite
(MnO(OH)), cryptomelane ((K,H2O)2MnsO 10)), and psilomelane
((Ba,H2O)2MnsOio)). In the recent past, almost all the manganese mined in the
United States came from Minnesota, Montana, and New Mexico, with the Cuyuna
district of Minnesota being the largest producer. Primary manganese deposits can be
classifed into four geologic types: (1) sedimentary (including sea floor nodules);
(2) hydrochemical; (3) residuals; and (4) metamorphic.
Currently, the United States is dependent completely upon foreign sources for
manganese. Domestic resources include deposits in the Chamberlain district of South
Dakota, the Cuyuna district of Minnesota, and the manganese nodules in Lake
Michigan. Large resources of manganese nodules are known to occur on the deep
floor of the Pacific Ocean. There are no environmental problems in the United
States related to underground mining of manganese because of the lack of mining.
Except for increased sediment loads and siltation, manganese mining is not known
to cause water pollution.
1.6 MOLYBDENUM
The ore minerals of molybdenum are molybdenite (MoS2); ferrimolybdite
(FeMoO3-H2O); and jordesite (amorphous molybdenum disulfide). In the past,
molybdenum also was recovered from wulfenite (PbMoO4) bearing ores.
Molybdenum deposits are of five genetic types: (1) porphyry deposits;
(2) contact-metamorphic deposits; (3) quartz veins; (4) pegmatites; and (5) bedded
deposits in sedimentary rocks. In the United States, molybdenum is mined from
porphyry deposits both as a primary product and a by-product. In the porphyry
deposits, copper sulfides and/or molybdenite occur as disseminated grains and in
stockworks of quartz veins and veinlets in fractured or brecciated, hydrochemically
altered granitic intrusive rocks and in the intruded igneous or sedimentary country
rocks. Host intrusive rocks range from intermediate to acidic and include diorite,
quartz monzonite, and granite, and the porphyritic equivalents. In porphyry
molybdenum deposits, molybdenite usually is the only ore mineral, but it is
commonly accompanied by pyrite, fluorite, and small amounts of tungsten, tin,
lead, and zinc minerals. Porphyry copper or copper-molybdenum deposits usually
contain chalcopyrite intimately associated with pyrite and only small amounts of
molybdenum which is recovered as a byproduct.
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In the United States about 58 percent of the molybdenum produced is
recovered as a primary product. About 42 percent is obtained as a byproduct from
mining molybdenum-bearing copper, tungsten, and uranium ores with copper ores
providing most of this production. The United States primary molybdenum
production has come recently from three mines, the Climax and Urad Mines in
Colorado and the Questa Mine in New Mexico. The Climax Mine which is the largest
United States molybdenum mine uses a block caving mining system. The Urad Mine
was closed in 1974 and $5 to $6 million has been allocated for reclamation work.
The Questa Mine is an open pit mine which started production in 1966 and produces
about 10 percent of the United States molybdenum production. The Henderson
Mine near Empire, Colorado, is under development and production is expected to
begin in 1976. Development work also is being conducted at the large Thompson
Creek deposit near Clayton, Idaho. Molybdenum is recovered as a byproduct from
open pit and underground mines in Utah, New Mexico, Nevada, California, and
Arizona. Most known United States reserves of molybdenum are associated with
currently producing porphyry molybdenum and copper-molybdenum deposits.
The environmental problems related to underground molybdenum mining are
mine drainage and subsidence. Pollution of waters by mine drainage can occur
because of acidification and heavy metals resulting from sulfides, principally pyrite
accompanying the ore. Subsidence occurs when using the block caving underground
mining method. Thus, the environmental problems related to United States
molybdenum mining are the same as for other large underground mines mining
sulfide ores.
1.7 NICKEL
Nickel is mined from both sulfide and nickeliferous laterite deposits. For the
sulfide deposits, the principal nickel mineral is pentlandite ((Fe,Ni)9Sg)). Besides
pentlandite, nickel may replace iron in pyrrhotite and pyrite. For the laterite
deposits, the principal nickel source is garnierite, a nickel-magnesium hydrosilicate.
The nickel sulfide deposits typically consist predominately of pyrrhotite and
associated pentlandite and chalcopyrite. The deposits may contain minor amounts
of precious metals, cobalt, and selenium. The sulfides occur as disseminations,
massive bodies, or veins and stringers in the igneous rocks. The deposits occur in or
near peridotite or norite intrusions. The nickeliferous laterite deposits were formed
by the weathering of peridotite, dunite, pyroxenite, or serpentinite. Laterites
formed from the weathering of serpentinite are rich in iron and are called
nickeliferous iron laterites. The nickel most likely is included in the goethite,
limonite, and serpentine minerals. Laterites formed from the weathering of
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peridotite, dunite, and, to a lesser degree, pyroxenite are lower in iron content and
are called nickel-silicate laterites. In these laterites, the nickel occurs either as the
hydrosilicate garnierite or as nickel-bearing talc or antigorite.
The United States relies on imports for most of its nickel. The only United
States primary nickel mine is at Riddle, Oregon, where nickel-silicate laterites are
mined. This is an open pit mine which supplies about 8 percent of the United States
nickel demand. There are no underground primary nickel producing mines in the
United States. A small amount of nickel is produced in the United States as a
byproduct of copper mining.
United States nickel reserves consist of: (1) nickel sulfides in the Duluth
Gabbro of Minnesota and the Stillwater district of Montana; (2) nickel laterites in
California, Oregon, and Washington; and (3) manganese nodules on the deep floor of
the Pacific Ocean (large nodule deposits contain 0.8 percent to 1.1 percent nickel).
Underground mining could occur in both the Duluth Gabbro and the Stillwater
district, resulting in environmental problems similar to those of other nickel sulfide
mining districts (Sudbury, etc.).
1.8 RHENIUM
Rhenium is produced in the United States only as a byproduct from the
wasting of molybdenite concentrates from porphyry copper-molybdenite ores.
Principal rhenium resources are trace amounts occurring in: (1) porphyry
copper-molybdenite deposits; (2) porphyry molybdenite deposits; (3) contact
metamorphic tungsten-molybdenum deposits; (4) molybdenum-bearing pegmatites;
and (5) molybdenite-bearing quartz veins.
1.9 SILICON
Although silica occurs in many minerals, quartz and quartzite are the only
minerals adequate in purity and quantity to be mined for silicon. Silica deposits are
of three types: (1) primary; (2) secondary; and (3) replacement. Primary deposits
result from hydrothermal actions and occur as veins in granite or massive cores in
pegmatites. Secondary deposits result from weathering of primary rock.
Subsequently, wind, water, and ice action concentrated the silica particles into
sandstone beds which then were consolidated and cemented. Some sandstone beds
underwent metamorphic changes, resulting in relatively pure quartzite. Replacement
deposits result from replacement of the country rock by siliceous solutions.
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Silica sand and sandstone are among the more common sedimentary formations
in the United States with resources of silica sand being virtually inexhaustable. All
mining of silica raw materials for conversion to silicon or its alloys is by open pit
methods. Thus, there are no environmental problems related to underground mining
of silica.
1.10 TANTALUM
The principal mineralogical source of tantalum is an isomorphous mineral series
containing tantalum, columbium, iron, and manganese oxides, often called tantalite.
A potential source of tantalum is the microlite-pyrochlore mineral series consisting
of complex oxides of tantalum, columbium, sodium, and calcium combined with
hydroxyl ions of fluorine. Tantalite and microlite occur principally as primary
accessory minerals in granitic rocks. Weathering of these granitic rocks result in
tantalite and microlite being concentrated in alluvial or eluvial deposits. Tantalum
minerals are not known pollutants and drainage waters from mines should not
degrade the environment, except for sedimentation. Past United States production
of tantalum minerals has been small. The United States currently relies on imports
for its primary supplies of tantalum.
1.11 TUNGSTEN
The principal ore minerals of tungsten are the wolframite series consisting of
huebnerite (MnWO4), wolframite ((Fe,Mn)WO4), ferberite (FeWO4), and scheelite
(CaWO4).
Other ore minerals commonly occurring with tungsten minerals are
molybdenite, cassiterite, chalcopyrite, bismuthinite, native bismuth, fluorite,
tetrahedrite, and sphalerite. The principal types of tungsten deposits are:
(1) contact-metamorphic deposits (tactites); (2) tungsten-bearing vein deposits; and
(3) stockworks and related porphyry-molybdenum deposits. Other types of tungsten
deposits are: (1) pegmatites; (2) hot springs; and (3) placers. Tactile deposits result
from high temperature replacement and recrystallization of limestone or dolomite at
or near the contact of intrusive igneous rocks. These deposits contain calc-silicate
minerals, such as garnet, epidote, hedenbergite, and hornblende along with
magnetite, quartz, and calcite. Tungsten in tactites occurs only as scheelite or
molybdenum-bearing scheelite. Pyrite, pyrrhotite, molybdenite, sphalerite,
chalcopyrite, tetrahedrite, stibnite, bornite, and fluorite usually are present. Major
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tungsten production from tactile deposits comes from: (1) Inyo County, California;
(2) Humboldt and Pershing Counties, Nevada; and (3) Beaverhend County, Montana.
In addition to these, known tungsten tactite resources are located in Utah, Arizona,
Washington, and Idaho.
Tungsten-bearing quartz veins consist of quartz or sometimes quartz-calcite
with sheelite and/or one of the wolframite series and minor amounts of other
minerals. Other minerals occurring in recoverable quantities in some deposits are
sphalerite, galena, chalcopyrite, tetrahedrite, arsenopyrite, and gold. Gangue
minerals often are pyrite, pyrrhotite, molybdenite, fluorite, rhodocrosite, and
feldspar. Major productive vein deposits are at: (l)Boriana, Arizona; (2) Atolia,
California; (3) Boulder district, Colorado; (4) Ima, Idaho; and (5) Hamme, North
Carolina. In addition to these, smaller vein deposits are scattered in Arizona, Nevada,
Colorado, Washington, Idaho, and Montana.
In deposits of tungsten minerals as fracture fillings and replacements in
stockworks and breccia zones, sheelite is the only tungsten mineral, except for the
related porphyry-molybdenum occurrences. Deposits of this type occur in Montana,
Nevada, and California. In the prophyry-molybdenum ore body at Climax,
Colorado, small amounts of huebnerite are disseminated in the ore.
In the United States, tungsten is produced as a coproduct or byproduct of
molybdenum and copper mining. About 75 percent of the United States production
comes from tact;te deposits with the Pine Creek Mine, Inyo County, California,
being the largest producer. The Climax ore body, Climax, Colorado, is second in
United States tungsten production. Virtually all United States tungsten ore is
extracted by underground mining methods. Most known United States resources
occur as scheelite in tactite deposits located in California, Nevada, and Montana.
Other tactite deposits are located in Utah, Arizona, Washington, and Idaho. Other
known United States resources occur as ferberite, wolframite, and huebnerite in
quartz veins in Arizona, Idaho, Colorado, and North Carolina and as huebnerite in
the Climax porphyry-molybdenum deposit of Colorado.
The environmental problems related to United States tungsten mining are
similar to those for other large underground mines mining sulfide ores. A water
clarifying chemical system, in which a flocculant-coagulant causes settlement of
solid materials in mine water effluent to Pine Creek is in operation at the Pine Creek
Mine.
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1.12 VANADIUM
The important ore minerals of vanadium are carnotite
(K2(UO2)2(VO4)2-3H2O), coulsonite ((Fe,V)3O4), descloizite-mottramite series
(PbZn(VO4)OH-PbCu(VO4)OH), montroseite (V,Fe)O-OH), patronite (¥84),
roscoelite (K(V,AL)3SisOio(OH)2), and vanadinite (Pb5(VO4)sCl). Most vanadium
currently produced is recovered from ores with no specific vanadium mineral
identifiable.
The five types of vanadium deposits are: (1) deposits of magmatic origin,
including both titaniferous and nontitaniferous magnetite deposits;
(2) hydrothermal vein deposits; (3) epigenetic deposits, including both vanadate and
sandstone deposits; (4) asphaltite deposits; and (5) deposits associated with alkalic
igneous complexes. In the past, the uranium-vanadium deposits in the sandstones of
the Colorado Plateau have been the most productive vanadium source. Various
amounts of uranium and copper are associated with vanadium in these deposits. The
principal ore minerals are silicates and oxides of both vanadium (roscoelite and
montroseite) and uranium, common copper sulfides, and carnotite as a secondary
uranium-vanadium mineral. Vanadium also has been recovered from deposits of
phosphatic shales and phosphate rock in Idaho as a coproduct or elemental
phosphorous. Vanadium also is mined from the alkalic instrusive complex at Wilson
Springs, Arkansas.
The principal United States source of vanadium is the Colorado Plateau
uranium-vanadium ores. For these deep, lenslike sandstone deposits, mining is by
underground open stope and room and pillar methods. Both Arkansas vanadium ore
and Idaho ferro-phosphorous ores were important sources.
Most United States vanadium resources are in deposits that are or will be mined
for vanadium as a coproduct or byproduct. Large titaniferous deposits are located in
Alaska, Wyoming, and New York. Nontitaniferous magnetite containing vanadium is
mined at Buena Vista Hills, Nevada. Uranium ores of the Colorado Plateau and
Idaho phosphate rock are expected to produce substantial vanadium. Certain
carbonaceous shales, oil shales, phosphatic shales, and graphic schists, such as occur
in Idaho and adjoining states, represent large resources of vanadium.
The environmental problems related to underground mining of the
uranium-vanadium sandstones are similar to those for uranium mining, including
radiation hazards.
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2.0
NONFERROUS METALS
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2.1 ALUMINUM
The principal minerals in bauxite ore, the principal source of aluminum, are
gibbsite (Al(OH)s), boehmite (AIO(OH)), and diaspore (AIO(OH)). Bauxite is
formed by the weathering of aluminous rocks, such as feldspars and clays. During
weathering, the bauxite becomes enriched in aluminum by removal of most of the
other elements in the parent rock mainly by solution by subsurface water.
Conditions favorable for the formation of bauxite are: (l)warm tropical climate;
(2) abundant rainfall; (3) aluminous parent rocks of high permeability and good
subsurface drainage; and (4) long periods of tectonic stability to permit deep
weathering. Since bauxite is formed by weathering, deposits usually lie nearly
horizontal close to the surface.
Several types of bauxite deposits occur in the United States. Most of these
deposits are composed primarily of gibbsite with the principal impurity being
kaolinite. The major deposits, located in Arkansas, were formed by the weathering
of nepheline syenite. Other minor lower grade bauxite deposits are located in the
southeastern Appalachian region and the states of Washington, Oregon, and Hawaii.
United States resources of metallurgical-grade bauxite are limited. Other potential
sources of aluminum comprise a variety of rocks and minerals, including alunite,
aluminous shale and slate, aluminum phosphate rock, dawsonite, high-alumina clays,
nepheline syenite, anorthosite, saprolite, coal, ash, and aluminum-bearing
copper-leach solutions.
The United States mines less than 12 percent of its bauxite requirements.
Arkansas produces about 90 percent of the United States bauxite and minor
amounts are mined in Alabama and Georgia. About 10 percent of the United States
production is mined by an underground room and pillar method at the Hurricane
Creek Mine in Arkansas. The two major environmental problems related to
underground bauxite mining are contamination of streams by sedimentation, and
subsidence.
2.2 ANTIMONY
The principal antimony minerals are stibnite (Sb2Ss), valentinite (Sb2Os),
senarmontite (Sb2O3), stibiconite (Sb2O4.H2O), bindheimite (Pb2Sb2O7-nH2O),
kermesite (2Sb2S3-Sb2Os), tetrahedrite ((Cu,Fe,Zn,Ag)i2Sb4Si3), and jamesonite
(Pb4FeSb6Si4). Antimony occurs in epithermal veins, pegmatites, and replacement
and hot spring deposits. Virtually all United States antimony production comes
from complex deposits as a byproduct of silver, lead, copper, and zinc ores.
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Lead-silver mines of the Coeur d'Alene district account for the bulk of the United
States antimony production. Antimony also was produced from complex
antimony-gold-tungsten ores of the Yellow Pine district, Idaho. Mines in Alaska,
Nevada, and Montana also produced minor amounts of antimony. Thus, antimony is
a byproduct or coproduct of mining other ores containing relatively small quantities
of antimony.
The underground mines of the Coeur d'Alene district are mined by horizontal
cut and fill sloping using hydraulic fill. The environmental problems related to
underground mining of these lead-silver ores are principally related to mine drainage
and include siltation, acidification, and heavy metal contamination.
2.3 ARSENIC
The primary arsenic minerals are arsenopyrite (FeAsS), lollingite (FeAs2),
smaltite (CoAs3-x), chloanthite (NiAs2), niccolite (NiAs), tennantite
((Cu,Fe,Zn,Ag)i2As4Si3), enargite (Cu3AsS4), and proustite (AgsAsSs). Arsenic is
found primarily in the following types of metalliferous deposits: (1) enargite-bearing
copper-zinc-lead deposits; (2) arsenical pyrite-copper deposits; (3) native silver and
nickel-cobalt arsenide deposits; (4) arsenical gold deposits; (5) arsenic sulfide and
arsenic sulfide gold deposits; and (6) arsenical tin deposits. United States demand for
arsenic is met mainly by imports with all United States arsenic production as a
byproduct from complex arsenical base-metal ores.
Environmental problems related to underground mining of arsenic-bearing ores
are similar to those normally related to base metal mining. In addition, arsenic in
sulfide minerals exposed to the atmosphere may form soluble arsenates which can
cause surface and ground water pollution.
2.4 BERYLLIUM
The principal beryllium minerals are beryl (Be3Al2(SiC«3)6), bertrandite
(Be4Si2O7(OH)2), phenakite (Be2SiO4), barylite (BaBe2Si2O?), and chrysolberyl
(Al2BeO4), with beryl and sole commercial source of beryllium. Beryllium deposits
can be classified into two general types: (1) pegmatitic and (2) nonpegmatitic or
hydrothermal. The pegmatitic deposits can be divided into fine-grained unzoned and
coarse-grained zoned deposits. The nonpegmatitic deposits can be divided into
hydrothermal, mesothermal, and epithermal deposits. The principal commercial
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sources of beryl are the coarse-grained zoned pegmatites. The pegmatitic deposits are
composed of major amounts of quartz, sodic plagioclase, and microcline, with or
without spodumene, muscovite, or lepidolite.
The United States imports about 20 percent of its beryllium consumption.
Beryl production is essentially a byproduct from mining of feldspar, mica, lithium
minerals, columbite, tantalite, and cassiterite. Pegmatitic deposits occur along much
of the Appalachian Mountains and in South Dakota, Colorado, New Mexico, and
Wyoming, but none of these deposits currently are mined for beryl. Beryllium is
mined as bertrandite from a nonpegmatitic deposit at Spor Mountain, Utah. Other
non-pegmatitic deposits occur in Utah, Colorado, Alaska, Arizona, Nevada, New
Mexico, and New Hampshire, but these are not mined.
Some small pegmatitic deposits are mined principally for beryl by simple open
cut methods. The nonpegmatitic deposit at Spor Mountain, Utah, is mined by
surface mining methods. There are no environmental problems related to
underground mining of beryllium since there are no underground mines.
2.5 BISMUTH
The principal bismuth minerals are bismite (Bi2O3) and bismuthinite (61283).
Hypogene deposits in the western United States account for most United States
bismuth production. Most of the bismuth occurs as a minor constituent in silver,
lead, zinc, copper, gold, tungsten, cobalt, and molybdenum ores. Lead-zinc-silver
replacement deposits in limestone have been an important bismuth source. Small
amounts of bismuth ore have been mined from pegmatite dikes, quartz veins, and
contact-metamorphic zones. Because of the low concentration of bismuth, no
deposits in the United States are mined for the bismuth content alone. All United
States bismuth production is a byproduct of complex base metal ores. Bismuth
resources essentially are associated with copper, lead, and zinc ores located in
Arizona, California, Colorado, Idaho, Montana, Nevada, New Mexico, and Utah.
Environmental problems are the same as related to underground base metal mining,
especially lead, which is mined essentially by underground methods.
2.6 CADMIUM
Cadmium occurs primarily as a yellowish earthy film or an oxide coating on
zinc minerals, usually spahlerite. All United States cadmium production is recovered
as a byproduct during the smelting and refining of zinc. Cadmium resources are
closely associated with zinc resources.
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2.7 CESIUM
The principal mineral of cesium is pollucite (H2O-2Cs2O-2Al2O3-9SiO2).
Lepidolite (K2Li3Al3(AlSi3Oio)2(OH,F)4), and beryl (Be3Al2(Si6Os))
occationally contain cesium. Cesium occurs in certain granites and granite
pegmatites. Pollucite is recovered as a coproduct in mining pegmatites for lithium
minerals and beryl. Cesium also occurs with several other minerals, such as
rhodonite, leucite, spodumene, potash feldspar, and related minerals, but cesium is
not recovered from these as a byproduct. Currently, no cesium is mined in the
United States. However, pollucite has been produced from mines in Maine and
South Dakota.
2.8 COPPER
Copper occurs in about twenty common minerals and about 140 less common
minerals. The common copper minerals are listed in Table 2.8-1. Chalcopyrite is the
most abundant copper sulfide, followed by bornite and chalcocite. The
sulfarsenides, enargite and tennantite, and the sulfantimonides, tetrahedrite and
famatinite, are rare, but each is a major ore mineral in at least one large ore body.
Native copper is abundant in certain types of deposits. Malachite, azurite, and
chrysocolla are the common oxidized copper minerals.
Copper deposits can be classified into the five major types: (1) porphyry
copper deposits and veins, pipes, and replacement deposits; (2) sedimentary
deposits; (3) massive sulfide deposits in volcanic rocks; (4) mafic intrusives forming
nickel-copper despoits; and (5) native copper deposits of the Keeweenaw type.
Porphyry copper deposits are deposits of disseminated copper sulfides that are
in or near a felsic intrusive body. Porphyry copper deposits have petrologic
associations that are dependent on their tectonic environment. Deposits formed in a
thin or poorly developed continental crust are associated either with syenite,
monzonite, or fennite. Deposits formed on thick continental crust, such as in
Arizona, usually are associated with quartz monzonite. The characteristic
porphyritic texture of the intrusive occurs because a part of the copper was trapped
in disseminated grains by the rapid crystallization of the magma. Another part of the
copper escaped from the hot rock mass and was deposited in fractures in the
intrusive and wall rocks. Another part may have escaped completely from the
intrusive and formed vein and replacement deposits in nearby host rocks. Sulfide
minerals in descending order of abundance usually are pyrite, chalcopyrite,
molybdenite, and bornite. The Bingham deposit in Utah is the largest United States
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Table 2.8-1
Minerals of Copper
Major Minerals
Native copper Cu
Chalcocite Cu2S
Covellite CuS
Bornite
Chalcopyrite CuFeS2
Enargite Cu3AsS4
Cuprite Cu2O
Malachite Cu2(OH)2(CO3)
Significant Supplementary Minerals
Tetrahedrite (Cu,Fe,Zn,Ag)i2Sb4S13
Tennantite (Cu,Fe,Zn,Ag)12As4S13
Famatinite Cu3SbS4
Stannite Cu2FeSnS4
Atacamite Cu2(OH)3C1
Tenorite (melaconite) CuO
Azurite Cu3(OH)2(CO3)2
Chrysocolla CuSi03•2H20
Brochantite Cu4(SO4)(OH)6
Antlerite Cu3(SO4)(OH)4
Chalcanthite CuSO4-5H2O
Kroehnkite Na2Cu(SO4)2•2H20
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porphyry deposit. Numerous other porphyry copper deposits occur in the
southwestern United States in Arizona, New Mexico, and Nevada. The principal
byproducts of the porphyry coppers are molybdenum, gold, and silver.
Economically important amounts of selenium, tellurium, and rhenium are obtained
from porphyry copper and molybdenum concentrates. The porpyry copper deposits
produce about 90 percent of the United States copper production.
Copper rich veins, pipes, and replacement deposits may be localized: (l)in
felsic plutonic rocks with local porphyry intrusions (Butte, Montana); (2) in
favorable host rocks near porphyry copper deposits (Bingham, Utah, and Bisbee,
Arizona); and (3) near barren felsic intrusive rocks (Magma and Mission, Arizona).
Veins are formed when metal-rich solutions deposit minerals in faults or fractures.
Replacement deposits form near intrusive contacts or along mineral veins in
sedimentary host rocks and may occur in limestone, dolomite, calcareous sandstone,
or even diabase sills. The mineralogy of vein, pipe, and replacement deposits is more
varied than the mineralogy of the porphyry copper deposits. Copper resources in the
vein, pipe, and replacement deposits are small when compared with the related
porphyry copper deposits.
Strata-bound deposits in sedimentary rocks include some of the world's largest
copper resources. Sedimentary Precambrian deposits in the United States include the
White Pine district in Michigan and the Belt Supergroup in western Montana and
adjacent parts of Idaho. At White Pine, copper occurs in the Nonesuch Shale with
chalcocite the principal sulfide ore mineral. In the Belt Supergroup, copper sulfides
occur in beds of quartzite and siltite. Sedimentary red-bed copper deposits are
associated with red sandstone. These deposits occur in the southwestern United
States and southern Kansas and western Oklahoma. Sedimentary copper deposits
also occur where copper dissolved from sulfide-bearing rocks by leaching and then
traveled laterally before being deposited in a secondary zone (Wallapai district,
Globe-Miami district, and Jerome and Ray, Arizona).
Under various conditions, copper in basalt and andesite may be concentrated to
form massive sulfide deposits. Mineralogically, the deposits consist mainly of pyrite
and/or pyrrhotite and varying amounts of chalcopyrite, sphalerite, and galena.
Chalcopyrite-pentlandite ores occur in mafic intrusives, such as in the Sudbury
district, Ontario. In the United States, copper resources occur in mafic intrusives in
Maine and Minnesota.
In the United States, native copper deposits occur in the Portage Lake
Volcanics on the Keweenaw Peninsula, Michigan. Other United States copper
occurrences that resemble the Keweenaw type are the native
copper-cuprite-azurite-malachite ores in the Catoctin Formation of Maryland and
Virginia.
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In addition to the five major types of copper deposits, there are several
miscellaneous types of deposits. These include: (1) small and very high grade
chalcocite deposits at Kennecott, Alaska, and Mountain City, Nevada and
(2) replacement deposits in carbonate rocks at Bornite-Ruby Creek, Alaska, and
Missouri.
The porphyry copper deposits of the southwest are the major copper resources
of the United States. The sedimentary copper deposits in Wyoming, Idaho, Montana,
and Michigan are the next most important United States copper resources.
The leading copper producing state is Arizona with more than 50 percent of
the United States production, followed by Utah, New Mexico, Montana, Nevada,
and Michigan. About 98 percent of the United States mine production of copper is
recovered from ores mined primarily for copper and the remainder is recovered from
complex or base metal ores. In addition to copper, important amounts of gold,
silver, molybdenum, nickel, selenium, tellurium, arsenic, rhenium, iron, lead, zinc,
sulfur, and platinum-group metals are recovered from copper ores as byproducts.
About 20 percent of the copper produced in the United States comes from
underground mines. These mines are located in Arizona, California, Colorado, Idaho,
Michigan, Montana, New Mexico, Tennessee, Utah, and Washington. Underground
copper mining is done by both caving and supported stopes. Caving methods usually
are block caving or sublevel stoping. Examples of block caving are Miami Copper and
San Manuel, Arizona. An example of sublevel stoping is Copper Basin, Tennessee.
Supported methods of underground copper mining include room and pillar such as
at White Pine, Michigan, and cut and fill such as at Superior, Arizona.
The environmental problems related to underground copper mines are
subsidence and water pollution. Subsidence is a major problem in large block caving
mines where there is no ground support. Subsidence also may be a problem in
supported stopes as the support fails or pillars are recovered. Copper and associated
sulfides result in acidification and discharges of heavy metals into ground and
surface waters.
2.9 GALLIUM
Gallium is concentrated in sulfide minerals, especially the zinc sulfide minerals,
sphalerite, and wurtzite. Gallium apparently replaces zinc in the sphalerite and
wurtzite lattice in limited amounts. In addition to zinc ores, gallium is found in
bauxite ores. Gallium is produced only as a byproduct from processing zinc and
aluminum ores.
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2.10 GERMANIUM
Germanium is concentrated in sulfide minerals, especially the zinc sulfide
minerals sphalerite and wurtzite. Germanium apparently replaces zinc in the
sphalerite and wurtzite lattice in limited amounts. Other sulfide minerals that have
major concentrations of germanium are chalcopyrite, bornite, enargite, tennantite,
and cinnabar. Germanium is produced only as a byproduct from processing zinc
ores.
2.11 GOLD
Gold occurs mainly as native metal, always alloyed with variable amounts of
silver and other metals. The only important gold minerals are the tellurides (gold or
gold plus silver, copper, or lead combined with tellurium).
Gold deposits can be classified into seven types: (1) gold-quartz lodes;
(2) epithermal ("Bonanza") deposits; (3) young placers; (4) ancient (fossil) placers;
(5) marine placers; (6) disseminated gold deposits; and (7) gold byproduct deposits.
Gold-quartz lodes comprise a wide variety of deposits that are essentially
hydrothermal veins of quartz and gold that either replace wall rock or fill open
spaces among fractures. Examples of United States gold-quartz lodes are the Mother
Lode-Grass Valley, California; Homestake, South Dakota; Central City, Colorado;
and Juneau-Treadwell, Alaska. This has been the most productive type of deposit in
the United States with Homestake being the most productive gold-quartz lode mine
in the world. Epithermal deposits are hydrothermal veins of quartz, carbonate
minerals, barite, and fluorite containing gold or gold tellurides and silver. Most
epithermal deposits are in highly altered volcanic rocks. Examples of United States
epithermal deposits are Goldfield, Virginia City, and Tonopah, Nevada and Cripple
Creek, Telluride, Silverton, and Ouray, Colorado. Young placers are composed
primarily of unconsolidated or semiconsolidated sand and gravel that contain very
small amounts of native gold and other heavy minerals. Examples of young placers
in the United States are deposits along the American, Feather, and Yuba Rivers in
the Sierra Nevada of California; along Alder Gulch at Virginia City, Montana; on the
Yukon River at Fairbanks, Alaska; on or near the beach at Nome, Alaska; and at
Boise Basin, Idaho. Ancient (fossil) placers were formed in the geologically distant
past and have been lithified to conglomerate and become part of the bedrock. These
conglomerates consist of small quartz pebbles embedded in a matrix of pyrite and
micaceous minerals and contain gold, uraninite, and platinum-group metals. No
fossil placers have been found in the United States. Marine placers consist of ocean
floor sediment. The gold was derived from the land, transported by streams to ocean
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basins, and deposited with clastic sediments on the ocean floor. Marine placers have
not yielded significant gold production. Disseminated gold deposits consist of very
fine grained gold disseminated in silty and carbonaceous dolomitic limestone. The
deposits were formed by hydrothermal replacement of the host rock and the gold is
accompanied by silica, barite, and a little pyrite and other sulfide minerals.
Examples of United States disseminated gold deposits are Carlin, Cortez, Getchell,
and Gold Acres in Nevada. Geologically similar deposits are Mercur, Utah, and Bald
Mountain and Deadwood, South Dakota.
Gold byproduct deposits account for about 47 percent of the United States
gold production. Of the byproduct gold production, about 80 percent is from
copper ores and the remainder is principally from complex ores of lead, zinc, and
copper. An example of a United States gold byproduct deposit is at Bingham, Utah.
Lode, disseminated, and placer gold deposits account for 53 percent of the gold
mined in the United States with lode and disseminated deposits accounting for
almost all of this production. Underground mining produces about 30 percent of
this gold production while surface mining of disseminated deposits and placers
account for the remaining 23 percent. The Homestake Mine in South Dakota is the
major United States gold producer and accounts for almost all of this underground
gold production. However, other small underground gold mines are in Arizona,
Colorado, Idaho, Montana, and Utah. New underground gold mines now are being
opened in the Cripple Creek, Colorado, area. The Homestake Mine uses a cut and fill
mining method with shrinkage and blast hole sloping.
Environmental problems related to underground gold mines are similar to those
related to other underground base metal mining.
2.12 HAFNIUM
Hafnium occurs as a minor constituent in zirconium minerals, but zircon
(ZrSiO4) is the only commercial source for hafnium metal. Hafnium is a byproduct
from the production of reactor grade zirconium for zircon. Zircon is a byproduct
recovered during processing of dredged heavy mineral-bearing sands to recover
titanium minerals.
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2.13 INDIUM
Indium is concentrated in sulfide minerals, especially the zinc sulfide mineral
sphalerite. Indium apparently replaces zinc in the sphalerite lattice in limited
amounts. Some copper-bearing minerals, particularly chalcopyrite and tetrahedrite,
have small amounts of indium. Indium is recovered entirely as a byproduct in
processing zinc-bearing ores.
2.14 LEAD
The principal lead mineral is galena (PbS). The galena commonly has inclusions
of argentite (Ag2S), argentiferous tetrahedrite ((Cu,Fe,Ag)l2Sb4Sl3), and similar
minerals. Many galena ore bodies near the surface are altered to cerussite (PbCOs),
anglesite (PbSO4), pyromorphite (Pb4(PbCl)(Po4)3), and other minerals. The
primary metallic minerals most commonly associated with galena include pyrite,
sphalerite, chalcopyrite, tetrahedrite or tennantite, and other sulfides, and locally,
marcasite and pyrrhotite. Sphalerite almost always is associated with galena. The
primary gangue minerals associated with lead deposits include quartz; calcite,
dolomite, and other carbonates; barite; and fluorite.
Lead deposits can be classified on the basis of geologic occurrances as:
(1) strata-bound deposits of syngenetic origin; (2) strata-bound deposits of
epigenetic origin; (3) volcano-sedimentary deposits; (4) replacement deposits;
(5) veins; and (6) contact pyrometasomatic deposits. World wide, strata-bound
deposits are the largest and most productive lead deposits. These deposits occur
chiefly in limestone, dolomite, or shale. For strata-bound deposits of syngenetic
origin, the ore minerals are disseminated finely. These ore minerals consist
predominantly of bornite, chalcocite, galena, sphalerite, and tetrahedrite. Accessory
elements often include nickel, cobalt, selenium, vanadium, molybdenum, and silver.
An example in the United States is the Belt Supergroup of northern Idaho and
northwestern Montana where thin beds of galena occur in carbonate rich quartzite
and siltite host rocks. The most common host rocks of the epigenetic stratiform
deposits are shallow-water marine carbonate rocks. The minerals of these deposits
consist predominantly of galena, sphalerite, and pyrite or marcasite. Some deposits
may contain chalcopyrite, siegenite, and other sulfides with nickel, cobalt, copper,
cadmium, silver, and germanium possibly recovered as a byproduct. The gangue
minerals commonly are calcite, dolomite, and jasperoid. In some deposits in
Kentucky, Illinois, and Tennessee, barite or fluorite are major coproducts. United
States districts containing strata-deposits of epigenetic form include southeast
Missouri, Tri-State (Kansas, Missouri, and Oklahoma), Upper Mississippi Valley
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(Wisconsin and Illinois), Metaline (Washington), Kentucky-Illinois, central
Kentucky, central Tennessee, and Appalachian Valley (eastern United States).
The second most productive lead deposits are lenticular massive sulfide deposits
in interstratified volcanic, volcano-sedimentary, and sedimentary rocks. These
volcanic-sedimentary deposits and their metamorphic equivalents range from
deposits in unmetamorphic rocks to recrystallized massive deposits in metamorphic
rocks. At Jerome, Arizona, the ore body is associated intimately with
metamorphosed quartz porphyry. The metamorphic deposits commonly consist of
intimate aggregates of pyrite or pyrrhotite, sphalerite, galena, and chalcopyrite with
minor amounts of quartz, sericite, chlorite minerals, ankerite, and other carbonate
minerals. Host rocks include argillite, metavolcanic rocks, schists, shale, and
carbonate rocks. At Duckstown, Tennessee, the deposits may have originated as
volcano-sedimentary deposits.
The third most productive lead source is the hypothermal replacement
deposits. Although commonly occurring in limestone and dolomite, these deposits
also occur in quartzite and shale and in igneous and metamorphic rocks. The
dominant lead mineral is galena associated with sphalerite, chalcopyrite, and pyrite.
Silver, arsenic, antimony, and cadmium occur in many deposits resulting in
arsenides, antimonides, and sulfosalts. Oxidation often occurs at depth, resulting in a
greater mineral variety. Examples of important massive replacement deposits in the
United States include Tintic, Utah; Bingham, Utah; Oilman, Colorado; and Leadville,
Colorado.
Lead vein deposits are found in all types of rocks. These deposits may occur as
filled veins where ore and gangue minerals occupy open spaces along fractures or as
replacement veins, generally in limestone or other reactive rocks. The dominant ore
minerals in vein deposits are galena, sphalerite, and pyrite. Some deposits contain
argentiferous tetrahedrite, chalcopyrite, silver-lead sulfosalts, and rarely, cobalt,
nickel, and uranium minerals. Gangue minerals include quartz, siderite, calcite,
barite, and fluorite. Examples of lead vein deposits are the Coeur d'Alene district,
Idaho; Butte, Montana; Tintic, Utah; Park City, Utah; Leadville, Colorado; Pioche
district, Nevada; and the Kentucky-Illinois district.
Contact pyrometasomatic deposits in the aureoles of granitic plutons are
localized chiefly in limy or dolomitic rocks that have become bleached,
recrystallized, and silicated. Some deposits occur in calcarious shales, tuffs, and
sandstones. The more common metallic minerals are galena, sphalerite, chalcopyrite,
pyrite, pyrrhotite, arsenopyrite, and magnetite. Bismuth, molybdenum, tungsten,
and gold may occur in some deposits. The gangue minerals include diopside,
hedenbergite, garnet, fluorite, epidote, actinolite, ilvaite, tremolite, quartz, and
other silicates. Examples of contact pyromatasomatic and similar deposits in the
United States are the Central district, New Mexico, and the Darwin Mine, Cerro
Gordo, California.
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Lead largely is mined by underground methods, although some deposits
amenable to surface mining occur in the Tri-State district and Washington.
Underground lead ore mines are in California, Colorado, Idaho, Illinois, Missouri,
and Wisconsin. These underground mines vary in ore output from a few metric tons
per day to over 9070 metric tons per day (10,000 tons/day). Underground stoping
includes both open and supported stopes. Underground methods include block
caving, room and pillar with and without rock bolts, shrinkage stoping, cut and fill,
and timbered stoping.
Southeast Missouri is the leading lead producing district in the United States,
followed by Idaho, Colorado, and Utah. Ores mined principally for lead account for
about 65 percent of the United States lead production, with the remainder being
produced from lead-zinc, zinc, and other complex ores. Most United States lead
reserves are located in Missouri with small known reserves principally in Idaho, Utah,
and Colorado.
Environmental problems related to underground lead mining are pollution of
surface and ground water by acidification and heavy metals. Lead is very toxic and
represents a health hazard to humans.
2.15 MAGNESIUM
The principal magnesium minerals are dolomite (CaMg(COs)2), magnesite
(MgCOs), brucite (Mg(OH)2), and olivine (Mg,Fe)2SiO4). Dolomite is a sedimentary
rock commonly interbedded with limestone. It is formed during diagenesis of
limestone by partial replacement of CaCOs by MgCOs. Dolomite deposits extend
over large areas of the United States and are mined in California, Colorado, Illinois,
Louisiana, Mississippi, Missouri, Ohio, Pennsylvania, South Dakota, Texas, Utah, and
West Virginia. Currently, dolomite is not used as a raw material for producing
magnesium metal.
Magnesite occurs mainly in four types of deposits. Crystalline magnesite occurs
as replacement deposits in dolomite or in limestone locally altered to dolomite. The
principal impurities are calcium, iron, silica, and silicate minerals, such as talc,
tremolite, anthophyllite, or enstatite. The two districts in the United States having
large deposits of this type are at Gabbs, Nevada, and Stevens County, Washington.
Impure crystalline magnesite mixed with talc and with or without quartz occurs as
replacement deposits in ultramafic rocks. Bone magnesite deposits are known to
occur in Red Mountain, California, Oregon, and Pennsylvania. Deposits of bone
magnesite replace bedded rhyolitic tuff in eastern Nevada. Sedimentary magnesite
beds and lenses are interbedded with dolomite, clastic rocks, or strata of volcanic
origin. In the United States, these deposits are limited to several states in the
southwest.
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Brucite rarely is found in minable concentrations, however, two minable
deposits are associated with magnesite at Gabbs, Nevada. Olivine is a common
mineral in quartz-free igneous rocks. The magnesium rich variety, forsterite, forms
the rock dunite, which readily alters to serpentine minerals. In the United States,
fresh dunite occurs in large masses east of Bellingham, Washington, and in smaller
masses in North Carolina and Georgia.
A major portion of the United States magnesium production is obtained from
sea water at Freeport, Texas, with well brines in Texas and brines of the Great Salt
Lake in Utah supplying the remainder. Dolomite, sea water, and well and lake brines
are available in unlimited quantities.
Since all United States magnesium metal is produced from sea water or brines,
there are no environmental problems related to underground mining for magnesium.
2.16 MERCURY
The principal mercury minerals are cinnabar (HgS), metacinnabar (HgS), and
livingstonite (HgSb4S7). The common mercury host rocks are limestone, calcareous
shales, sandstone, serpentine, chert, andesite, basalt, and rhyolite. Deposits have
been formed by replacement, open-space filling, both replacement and open-space
filling, and detrital concentration. Mercury deposits usually occur at relatively
shallow depths in formations of younger volcanic and tectonic activity. In mercury
deposits, silica and carbonate minerals are the common gangue minerals and pyrite
and marcasite may be abundant in deposits formed in iron-bearing rocks. Gold,
silver, or base metals generally are present in only trace amounts.
At the New Almaden Mine in California, folded and faulted sedimentary and
volcanic rocks are intruded by serpentine which was altered along its margins to
silica-carbonate rocks. Silica-carbonate rock was replaced by cinnabar along steep
parallel fractures to depths of about 610 meters (2,000 feet). The New Idria Mine in
California is near the margin of a pluglike serpentine mass that arched upward and
pierced through a thick shale-sandstone. Steeply dipping shale near the serpentine
has been rendered brittle through induration, and, subsequently, shattered. Cinnabar
mostly fills the fractures or coats walls with some cinnabar and metacinnabar occurs
in thick carbonate veins.
Mercury is mined by both surface and underground methods with most of the
mercury mined by underground methods. Mercury production in the United States
comes from a relatively large number of small mines with ore production from
underground mines ranging up to 272 metric tons per day (300 tons/day). California
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is the leading producing state, followed by Alaska and Nevada. Most United States
mercury resources are in California. Mercury is recovered as a coproduct from one
United States gold mine. Both the New Almanden and New Idria are underground
mines. These mines use square-set or modified square-set stoping methods. In some
instances, shrinkage and sublevel stoping are used.
The environmental problems related to underground mining of mercury are
poisoning of workers by mercury vapors and pollution of ground and surface waters
by acidification and heavy metals.
2.17 PLATINUM-GROUP METALS
Platinum, palladium, iridium, osmium, rhodium, and ruthenium comprise the
platinum-group metals. Platinum-group metals are found in five major types of
deposits: (1) stratiform complexes in mafic and ultramafic rocks, such as the
Stillwater Complex in Montana; (2) concentrically zoned ultramafic complexes and
associated mafic bodies, such as in southeastern Alaska; (3) alpine complexes in
mafic rocks, such as at Burro Mountain, Red Mountain, and New Idria, California,
and Twin Sisters and Cypress Island, Washington; (4) copper, nickel, and gold in
mafic and ultramafic rocks, such as at the Rambler and Centennial Mines in
Wyoming; and (5) placer deposits, such as in Alaska, California, Oregon, Washington,
Montana, and Idaho. There also are minor occurrences of platinum-group metals
where these metals are associated with syenites (La Plata district, Colorado, and
Cooke City, Montana) and gold-quartz (Boss Mine, Nevada).
United States production of platinum-group metals is principally as a
byproduct of copper smelting. Significant amounts of platinum-group metals have
been produced from placers of the Salmon River of the Goodnews Bay district,
Alaska. United States reserves are almost entirely in copper ores with a very small
amount in placers. Since most United States mine production of platinum-group
metals is recovered as a byproduct of copper mining, environmental problems are
incidental to copper production.
2.18 RADIUM
Radium is present in small amounts in uranium ore and the geology of radium
and uranium are the same. The United States presently does not produce any
radium, but radium has been recovered from high grade uranium (carnotite) deposits
in Colorado.
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2.19 RARE-EARTH ELEMENTS
The rare-earth elements are the elements having atomic number 57 through 71.
These are lanthanum (La), cerium (Ce), praseodymium (Pr), neodyanum (Nd),
promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb),
dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and
totetium (Le). Yttrium (Y), with atomic number 39, also is classified as a rare-earth.
The rare-earths are essential constitutents of more than 100 mineral species. The
three most important are monazite ((Ce,La,Th,Y)PO4), bastnaesite (CeFCOs), and
xenotime (YPO4). Other minerals such as allanite
((Ca,Ce,Th)2(Al,Fe,Mg)3.Si3Oi2-(OH)), gadolinite (Be2FeY2Si2Oio), euxenite
(Y,Ca,Ce,U,Th)(Nb,Ta,Ti)206), and loparite ((Ce,Na,Ca)(Ti,Nb)2O6) also are
commercial sources. Apatite (Ca5F,Cl,OH)(PO4)3), thorgh not a rare-earth mineral,
may contain rare-earth elements because of substitution.
Primary concentrations of rare-earth-bearing minerals occur in a wide variety of
geologic settings, including veins, gneisses, pegmatites, and alkalic rock complexes
and related carbonates. The largest known rare-earth concentration is the bastnaesite
deposit in carbonatite at Mountain Pass, California. The gangue minerals are
principally barite, carbonates, and quartz. Other deposits of primary concentrations
are known to occur in California, Idaho, Montana, Wyoming, Colorado, New
Mexico, and New York. Most minable concentrations of rare-earths are found in
unconsolidated secondary deposits. These deposits include sea-beach placers,
fluviatile placers, and deltaic deposits. Secondary deposits are known in Idaho,
North Carolina, South Carolina, Florida, and Georgia.
Except for the Mountain Pass, California, deposit, rare-earths usually are
recovered as byproducts. All United States production comes from surface mines.
2.20 RUBIDIUM
Rubidium does not occur in distinct minerals. However, it does occur as an
impurity or associate element in various minerals including lepidolite
(K2Li3Al3(AlSi3Oio)2(OH,F)4), pollucite (Ce4Al4Si9O26'H2O), microcline
(KAlSisOg), and biotite (K(Mg,Fe)3(AlSi3Oio(OH)2) from granites and pegmatites,
and carnallite (KMgCl3-6H2O) from saline deposits. The principal united States
supply has come from the processing of an alkali carbonate residue resulting from
processing imported lepidolite into lithium.
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Rubidium also is recovered as a byproduct from pollucite which is recovered as
a byproduct from pegmatites mined for lithium and beryl. There are no United
States mines producing rubidium, but it does occur sporadically in many New
England pegmatites. Rubidium also exists in certain feldspars, brines, and saline
deposits.
2.21 SCANDIUM
The minerals of scandium are thortveitite ((Se,Y)Si2Ov), sterrettite
(ScPo4 2H20), bazzite (Bes( Sc , Al)2Si6O 1 g), and magbasite
(KBa(Al,Sc)(Mg,Fe)6Si6O20F2)- Many other minerals contain minor amounts of
scandium because of substitution. Scandium occurs in four types of geologic
deposits. These are: (1) pegmatites such as the occurence of thortveitite in the
Crystal Mountain fluorite deposit in Montana; (2) greisen and vein deposits;
(3) variscite deposits such as the sparse occurrence of sterrettite in a highly
brecciated zone in limestone at Fairfield, Utah; and (4) enrichments in other
materials. Scandium is produced only as a byproduct from uranium and tungsten.
The United States currently does not produce any scandium.
2.22 SELENIUM
Selenium occurs principally by substitution in sulfide minerals of copper, iron,
and lead and is most common in chalcopyrite, bornite, and pyrite. Selenium is
principally a byproduct of copper refining. Some selenium also is produced as a
byproduct of lead refining.
2.23 SILVER
The principal silver minerals are native silver (Ag), argentite (Ag2S), polybasite
proustite (AgsAsSs), stephanite (Ag5SbS4), pyrargyite (AgsSbSs), and
cerargyrite (AgCl). Other minerals such as argentiferous tetrahedrite
((Cu,Fe,Ag)i2Sb4Si3) and argentiferous galena ((Pb,Ag)S) have part of their crystal
lattice replaced with silver.
Types of silver deposits can be divided into: (1) deposits with byproduct and
coproduct silver and (2) deposits with silver as a major constituent. Silver is an
important byproduct in nine types of deposits: (1) porphyry copper deposits such as
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in Utah and Arizona; (2) copper-zine-lead replacement deposits and vein clusters
such as in the Butte district, Montana, and the Superior district, Arizona; (3) massive
sulfide deposits; (4) lead-zinc replacement deposits such as the Park City and Tintic
districts, Utah; (5) Mississippi-Valley - and Alpine-type lead, zinc, and flourspar
deposits and related deposits; (6) copper deposits in sandstones and shales such as
White Pine, Michigan; (7) native copper deposits such as the Keweenaw Peninsula in
Michigan; (8) gold deposits in veins, conglomerates, and placers such as the
Homestake Mine, South Dakota, the Mother Lode Belt in California, and the
Colorado mineral belt; and (9) nickel and magnetite deposits such as at Cornwall and
Morgantown, Pennsylvania.
The types of deposits with silver as a major constituent are: (1) epithermal
veins, lodes, and pipes; (2) epithermal disseminated and breccia deposits;
(3) epithermal silver-manganese deposits; (4) epithermal silver-lead-zinc replacement
deposits; (5) epithermal silver-copper-barite deposits; (6) mesothermal
silver-lead-zinc-copper deposits; (7) mesothermal cobalt-silver, cobalt-uraninite-silver,
and cobalt-silver-zeilite deposits; (8) sandstone silver deposits; and (9) sea-floor muds
and hot-spring deposits. Epithermal veins, lodes, and pipes were some of the most
productive deposits mined during the 19th century, but these currently result in
little silver production. Deposits of this type in the United States with notable past
silver production are the Com stock Lode in western Nevada; Hornsilver in San
Francisco district of Utah; Tonopah and Austin, Nevada; Randsburg, California; and
San Juan Mountains and Silver Cliffs district in Colorado. Epithermal disseminated
and breccia deposits currently produce little silver. Past districts included the Calico,
in southeastern California; Taylor and Success east of Ely, Nevada; and Vipont in
northwest Utah. The silver rich manganese carbonate, manganiferous calcite, and
manganese oxide deposits also currently produce little silver. The best known
districts of this type are Lake Valley, New Mexico; Pioche, Tybo, and White Pine,
Nevada; Escalante, southwestern Utah; Tombstone and Aquila, Arizona; Silver Cliff,
Colorado; and Modoc, California. Epithermal silver-lead-zinc replacement deposits
are not common, but a few have been very productive, such as at Aspen, Colorado,
and the Red Mountain district of the San Juan Mountains, Colorado. Epithermal
silver-copper-barite deposits are not important in the United States.
The mesothermal silver-base metal veins of the Coeur d'Alene district of Idaho
are the major United States deposits with silver as the major constituent. The ore is
in replacement veins in weakly metamorphosed argillites, siltites, and quartzites. Ore
near the surface occurs in stringers that form wider veins and masses at depth. The
principal ore mineral is argentiferous tetrahedrite associated with lead, iron, and zinc
sulfides. The gangue is quartz and siderite. Ore has been mined to a depth of
2,438 meters (8,000 feet). The major geologic structure is the Osborn fault which
divides the district into a north group and south group of mines. The eastern part of
the south group is known as the "Silver Belt" because the ores have a higher silver
content.
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Mesothermal cobalt-silver, cobalt-uraninite silver, and cobalt-silver-zeolite
deposits are known in North America, but not in the United States. Silver chloride
deposits disseminated in sandstone occur at Silver Reef in southern Utah.
Mineralized sea-floor muds occur near Niland, California, close to the Salton Sea.
Ores mined principally for silver provide about 25 percent of the United States
silver production. Thus, 75 percent of the silver production in the United States is
produced as a byproduct with base metal ores providing almost all of this
production except for about 1 percent coming from gold-silver ores. Almost
99 percent of all the ores mined principally for silver are mined in Idaho's Coeur
d'Alene district. This district also produces about 20 percent of the silver produced
as a byproduct or coproduct of base metal mining. Thus, the Coeur d'Alene district
is the source of almost 40 percent of all silver produced in the United States. Most
United States silver resources are in base metal deposits as byproduct or coproduct
silver. About three-fourths of these resources are in Arizona, Nevada, Idaho,
Montana, and Utah.
All ores mined principally for silver in the Coeur d'Alene district are mined by
underground mining methods. The steep terrain of the district permits access to
orebodies by adits with development in the ore by winzes and raises. Greater
operating depths are achieved by internal or surface shafts. Almost all mining is by
horizontal cut and fill stoping using hydraulic fill. Development drifts are driven on
the vein or parallel to the vein with crosscuts at regular intervals. Level intervals vary
from mine to mine.
The environmental problems related to underground silver mines are principally
associated with mine drainage. In the Coeur d'Alene district, gross pollution of the
Coeur d'Alene River and tributaries has resulted from siltation, acidification, and
heavy metals contamination. These mine drainage problems are similar to the
environmental problems related to base metal mines.
2.24 TELLURIUM
Tellurium is widely distributed in nature as a constituent of at least
40 minerals. Tellurium rarely occurs in the native state and is usually associated with
gold, silver, copper, lead, mercury and bismith ores. Present United States
production is a byproduct of electrolytic copper refining. Tellurium resources of the
United States are related with porphyry deposits. There are no known deposits
which can be mined only for tellurium. Care must be exercised in handling
tellurium, since several tellurium compounds are very toxic.
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2.25 THALLIUM
Thallium is a relatively rare element. Characteristic thallium sulfide, selenide,
and oxide minerals occur in nature, but they are extremely rare. Most thallium
occurs as a trace element in other minerals. All thallium production in the United
States occurs as a byproduct of the base metal smelting industry, especially zinc and
lead smelting. United States resources principally are associated with zinc deposits.
2.26 TIN
The tin mineral of major commercial importance is cassiterite (SnO2);
although, small amounts of other tin sulfide minerals are mined such as stannite
(Cu2FeSnS4), cylindrite (Pb3Sn4Sb2Si4), and teallite (PbSnS2). There are no
major tin mines of commercial significance in the United States. However, a very
small amount of tin is recovered from placer deposits in Alaska and New Mexico and
as a byproduct of molybdenum at the Climax Mine in Colorado. Both the United
States resource base and foreseeable potential production are negligible, and
virtually all primary tin requirements will be met by importing.
2.27 TITANIUM
The principal titanium minerals of commercial importance are ilmenite
(FeTiOs) and rutile (TiC«2). Small quantities of other titanium minerals such as
anatase (TiO2) and brookite (TiO2) often are associated with ilmenite and rutile.
Many other minerals, including sphene (CaTiSiOs), perovskite (CaTiOs), and
pyrophanite (MnTiOs) are abundant locally in some deposits, but these have not
been mined commercially.
Both ilmenite and rutile occur in primary and secondary deposits. Primary
rutile deposits occur in alkalic igneous rocks, in alkalic noritic-anorthositic
complexes, and in granitic and syenitic veins and pegmatites with all economic
deposits in the noritic-anorthositic complexes. Most primary rutile is recovered as a
byproduct of ilmenite mining. Primary ilmenite deposits occur as ilmenite-magnetite
deposits in gabbro and anorthosite at Tahawus, New York. Secondary deposits of
rutile are derived from weathering of primary rutile occurrences. These deposits
consist mainly of marine placer sands, stream sands and gravels, and lag saprolite
deposits. Deposits of this type occur in Virginia and Arkansas. Secondary deposits of
ilmenite occur as branch fossil placer deposits and as residual deposits formed by
lateritic weathering. Important placer deposits in the United States occur in
northern Florida and near Lakehurst, New Jersey.
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Ilmenite forms most of the economic secondary deposits of titanium. Ilmenite
placer deposits commonly contain rutile and leucoxene, along with other heavy
minerals such as zircon and monazite. Some deposits are worked principally for
other minerals and titanium minerals are a byproduct. The known economic
titanium resources of the United States occur as: (1) ilmenite rock deposits in New
York and Virginia; (2) ilmenite beach sands in Florida, New Jersey, and Georgia;
(3) rutile rock deposits in Virginia; and (4) rutile sand deposits in Florida, South
Carolina, Tennessee, and Georgia. Additional uneconomical ilmenite resources are
known to occur in California, Colorado, Minnesota, Montana, New York, Rhode
Island, Wyoming, Oregon, and Oklahoma. Most of the known titanium resources in
the United States are ilmenite deposits.
Ilmenite is produced from seven operations in New York, Florida, Georgia, and
New Jersey. Rutile is produced at one mine in Florida where ilmenite and zircon are
coproducts. All mining for titanium is by dredging or surface mining methods. Thus,
there are no environmental problems related to underground titanium mining.
2.28 ZINC
The principal ore mineral of zinc is sphalerite (ZnS). Occassionally, sphalerite is
intergrown with wurtzite (ZnS). Zinc sulfides oxidize to secondary minerals such as
smithsonite (ZnCOs) and hemimorphite (Zn4(OH)2Si2Ov-H2O). Franklinite
((Fe,Zn,Mn)(Fe,Mn)2O4), willemite (Zn2SiO4), and zincite (ZnO) are the ore
minerals of the unique deposits at Franklin Furnace and Sterling Hill, New Jersey.
Sphalerite commonly is associated with iron, lead, and copper sulfides such as
pyrite, galena, and chalcopyrite, and gold and silver minerals.
Zinc deposits occur in many diverse geologic environments and can be classified
into seven broad categories. These are: (1) contact-metamorphic deposits;
(2) irregular replacement deposits and associated fissure fillings; (3) vein deposits;
(4) stratabound deposits in metamorphic rocks; (5) strata-bound deposits in
carbonate rocks (Mississippi Valley and Alpine-type deposits); (6) stratiform
deposits; and (7) deposits formed by supergene enrichment or laterization. Zinc
deposits also may be classified by the associated metals as: (1) zinc; (2) zinc-lead or
lead-zinc; (3) zinc-copper or copper-zinc; and (4) base metal if zinc, lead, and copper
all are present.
Contact-metamorphic zinc deposits are those contained in metamorphosed
sedimentary rocks adjacent to igneous intrusives. These occur principally in
carbonate rocks that have been altered metasomatically. Common minerals are
chalcopyrite, pyrite, pyrrhotite, sphalerite, and molybdenite. There are many small
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deposits of this type in the United States including the Central district of New
Mexico and the Darwin district of California. Irregular replacement deposits and
associated fissure fillings often replace contact metamorphic deposits. In addition to
lead and zinc, these deposits often contain appreciable quantities of copper, silver,
and gold. Typical deposits of this type in the United States are the silver-lead-zinc
deposits in the Park City, Bingham, and Tin tic districts of Utah; in the Eureka
district of Nevada; and at Leadville and Oilman, Colorado. Zinc bearing vein deposits
commonly occur in igneous rocks or in rocks near igneous contacts. Zinc veins may
have significant amounts of lead, copper, silver, and gold. Important zinc vein
deposits have been mined in the Coeur d'Alene district of Idaho; at Butte, Montana;
and at many locations in Colorado.
The major known deposits of zinc-lead and lead-zinc ores occur in
metamorphic rocks. These consist principally of pyrrhotite and pyrite accompanied
by sphalerite, galena, and chalcopyrite. Significant deposits of this type occur in the
United States in the Ducktown district of Tennessee; Jerome district of Arizona;
Balmat-Edwards district of New York; and Franklin Furnace-Sterling Hill district of
New Jersey. Zinc deposits in carbonate rocks (Mississippi Valley — type deposits)
also are of major importance. Zinc and usually lead sulfide minerals may occur as
open-space fillings in breccias or be formed by replacements. This type of deposit
occurs in the East and Middle districts of Tennessee; Tri-State district of Kansas,
Missouri, and Oklahoma; Upper Mississippi Valley district of Wisconsin and Illinois;
Friedensville district of eastern Pennsylvania; and the Metaline district of
northeastern Washington.
Stratiform deposits, where the zinc-bearing stratum is interbedded with other
strata, are not common in the United States. Supergene enrichment of silver-bearing
base metal deposits occurs because of weathering of primary ore deposits. Most of
these deposits were formed by weathering of sulfides in the bedrock, with the metals
redeposited as secondary carbonate, silicate, oxide, or sulfide minerals. Major
districts with this type of deposit include Friedensville, Pennsylvania; Austinville,
Virginia; Mascot-Jefferson City, Tennessee; Leadville, Colorado; and Tintic and
Ophir, Utah.
The major identified zinc resources of the United States (80 percent) occur in
the Appalachian and Mississippi Valley regions. The Appalachian region includes the
Franklin Furnace — Sterling Hill district of Pennsylvania; Friedensville district of
Pennsylvania; Balmat-Edwards district of New York; Austinville district of Virginia;
and the East Tennessee district. The Mississippi region includes the Tri-State district
of Kansas, Missouri, and Oklahoma; Upper Mississippi Valley districts in Wisconsin
and Illinois; Central and Southeast Missouri lead belts; and the Middle Tennessee
district.
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Zinc ores provide almost 60 percent of the United States zinc production with
the remaining production coming from zinc-lead ores, lead-zinc ores, copper-zinc
and copper-lead-zinc ores, and other sources. Zinc was produced in 18 States with
New York being the leading producer, followed by Missouri, Tennessee, Colorado,
Idaho, and New Jersey. These six States accounted for about 80 percent of the total
zinc production. Almost all zinc ores are mined by underground methods with mines
in New York, Tennessee, Colorado, New Jersey, Pennsylvania, Virginia, Wisconsin,
Maine, and. California. The underground mining is by square-set, room and pillar,
and cut and fill sloping methods. The near flat lying deposits of the Tri-State, Upper
Mississippi Valley, Metaline, Tennessee, and Virginia districts are mined by room and
pillar methods.
The environmental problems related to underground zinc mining are mine
drainage and subsidence.
2.29 ZIRCONIUM
The important zircon minerals are zircon (ZrSiO4), baddeleyite (ZrO2), and
eudialyte (Na4(Ca,Fe)2ZrSi6Oi7(OH,Cl)2), with zircon being the more important
commercial source. Zircon occurs in both primary and secondary deposits, but
primary deposits are rare. In secondary placer deposits, zircon is concentrated with
other heavy minerals, such as rutile, ilmenite, monazite, and garnet. These placer
deposits are in stream terraces, along beaches, and in sand dunes. Phosphatic
sediments and lithified titanium-rich placers in sandstone or metamorphosed
sandstone also form secondary zircon deposits. The United States has the world's
largest known zircon resources with most of this resource located along the Atlantic
Coastal States of Florida, Georgia, South Carolina, and New Jersey.
Zircon currently is recovered from mineral sands by dredging at Starke and
Green Cove Springs, Florida, and near Folkston, Georgia. There are no
environmental problems related to underground mining of zirconium.
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3.0
NONMETALS
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3.1 ASBESTOS
Asbestos is a term applied to naturally fibrous silicate minerals. The principal
asbestos mineral is chrysotile (Mg6(Si4Oio)(OH)8) with other commercial varieties
being amosite ((Fe,Mg)SiO3), crocidolite (NaFe(SiO3)2-FeSiOs-H2O), tremolite
(Ca2Mg5Si8O22(OH)2), and anthophyllite (Mg,Fe)vSi8O22(OH)2).
Chrysotile asbestos occurs in two geologic settings: (1) large stockworks of
veins in serpentinized peridotite, pyroxenite, and dunite of the "Quebec type" and
(2) veins of thin serpentine layers in limestone of the "Arizone type." The Quebec
type deposits occur in ultra-mafic rocks dominated by peridotite where the rocks
have been altered almost completely to form serpentinites. Additional alteration
resulted in the formation of talc schist, steatite, and massive quartz-carbonate in
shear zones and margins. An example of the Quebec type deposit is the Belvidere
Mountain deposits of northern Vermont. Numerous small to large serpentinite
masses occur along the Pacific Coast in Washington, Oregon, and California. The
Arizona type deposits occur where cherty or siliceous magnesian limestones were
metamorphosed adjacent to igneous intrusions. These deposits usually are small but
the asbestos content of the ore usually is high.
Anthophyllite and tremolite asbestos deposits occur in ultramafic intrusions
and in association with greenstones and amphibolites. Many small deposits of
amphibolite asbestos occur in western North Carolina and northeastern Georgia.
Crocidolite and amosite only occur in certain fine grained cherty ferruginous
metasediments and asbestos deposits of these minerals are not known in the United
States.
California is the leading United States producer with 54 percent of the
production followed by Vermont, North Carolina, and Arizona. All asbestos mining
in the United States was by surface mining methods except for one underground
mine north of Globe, Arizona. The known asbestos resources occur principally in
Vermont, California, and Arizona.
There are environmental problems related to underground mining of asbestos.
Asbestos and asbestos type fibers are a known health hazard in air and possibly
water. Fibrous laden mine dust is a health hazard in the mine and fibrous emissions
from mine ventilation would represent an environmental hazard to areas surrounding
the mine. Efforts continued in 1974 to establish an acceptable level of asbestos dust
fibers in the atmosphere of both mines and general environment. Where occurring,
mine drainage waters can contaminate surface and ground waters, resulting in a
possible health hazard due to ingesting fibers in drinking water.
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3.2 BARIUM
The principal barium minerals are barite (BaSO4) and witherite (
Witherite is of minor importance and is produced commercially only in England.
Barite resources are large and widely distributed. Barite is commonly associated with
quartz, calcite, dolomite, siderite, rhodochrosite, celestite, fluorite, and various
sulfide minerals, such as pyrite, chalcopyrite, galena, sphalerite, and their oxidation
products. Barite is a common gangue mineral in lead, zinc, gold, silver, fluorite, and
rare-earth vein deposits.
Barite occurs in sedimentary, igneous, and metamorphic rocks. Commercial
deposits can be classified as: (1) vein and cavity-filling; (2) residual; and (3) bedded.
Vein and cavity-filling barite deposits are not significant commercially. Residual
barite deposits are formed by weathering of primary deposits. Small amounts of
pyrite, galena, and sphalerite may occur with the barite. These residual deposits lie
within the clayey residuum derived from limestone and dolomite, especially in
southeastern Missouri and the Appalachian region. These include deposits in
Washington County, Missouri; Sweetwater district, Tennessee; and Cartersville
district, Georgia. In bedded deposits, barite occurs as a principal mineral or
cementing agent in stratiform deposits of layered rock sequences. Barite beds
commonly are interbedded with chert, siliceous siltstone, and shale. The principal
gangue mineral is fine-grained quartz and small amounts of clay and pyrite are
common. Deposits of the bedded type include Magnet Cove, Arkansas; Toquima and
Shoshone Ranges, Nevada; and New Castella, California.
Approximately 40 mines in eight states produce barite, with 50 percent of the
production coming from Nevada. Other leading states are Arkansas and Missouri.
Most barite is mined by surface mining methods but there is some barite production
from an underground mine in Arkansas. Environmental problems related to
underground mining of barite is pollution of streams by mine drainage such as the
Ouachita River in Arkansas.
3.3 BORON
The principal commercial boron minerals are the sodium borate minerals borax
(Na2B4Ov-10H2O) and kernite (Na2B4Ov-4H2O). Boron minerals currently mined
occur chiefly as deposits in non-marine Cenozoic rocks. The borate deposit at
Boron, California, is a large, bedded, thick, slightly deformed, lacustrine deposit.
Shale beds containing colemanite (Ca2B6O \\ • 5H2O) and kernite
(CaNaBsO9-8H2O) lie directly over and under the borate deposits. Near Death
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Valley, California, colemanite is mined from formed mudstone and sandstone. At
Searles Lakes, California, sodium borate is produced as a byproduct from brines
pumped from the interstices of mineralogically complex salt layers beneath the dry
lake surface. The total United States boron production comes from mines at Boron
and Death Valley and brines from Searles Lake in California. All mining currently is
by surface mining methods; although, there has been underground mining in the
past. Currently, there are no environmental problems related to underground boron
mining.
3.4 CLAYS
The principal clay minerals are kaolinite (Al4Si4Oio(OH)g), halloysite
(Al4Si401 Q(OH)8-4H2O), montmorillonite ((Al,Mg)g(Si4010)3(OH) i Q-12H2O),
palygorskite (Mg5(Si4Oio)2(OH)4.4H2O), and illite (K2(Si6Al2)Al4O20(OH)4).
Kaolinite and halloysite are formed by hydrothermal, weathering, and sedimentary
processes, either alone or in combination. Hydrothermal clay is formed by solutions
dissolving the country rock and precipitating kaolinite. Residual clay is formed by
chemical weathering and the altering of feldspars and muscovites to kaolinite or
halloysite. Unconsolidated and consolidated sedimentary deposits are formed by the
weatherbed debris being eroded, transported by streams, and then deposited in
lakes. After deposition, leaching may remove iron, potassium, and other ions.
Montmorillonite usually is formed by the devitrification and alteration of volcanic
ash or tuff. Palygorskite is believed to be formed as a chemical precipitate from the
reaction of hydrothermal solutions with sea water having a high magnesium and
silica content. Illite can be formed in many ways, but it usually is found in residual
shale deposits.
Clay deposits are classified into six categories: (1) kaolin; (2) ball clay; (3) fire
clay; (4) bentonite; (5) fuller's earth; and (6) miscellaneous clays. Kaolin clays
consist principally of kaolinite. Kaolin is produced in 17 states, with the primary
producers being Georgia and South Carolina, followed by Arkansas, Alabama, and
Texas. Ball clays are composed principally of kaolinite, but have a higher
silica-to-alumina ratio and more impurities and are finer grained than kaolins
Tennessee is the primary ball clay producer, followed by Kentucky, Mississippi,
Texas, California, Maryland, New York, and Indiana. Fire clay also consists
principally of kaolinite, but usually includes other clay minerals and impurities.
Clays are designated fire clays based on their refractory property. Fire clays
commonly occur as underclay below coal seams with the major producing states
being Missouri, Ohio, Pennsylvania, and Alabama. Bentonites are composed
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principally of montmorillonite group minerals with the principal producing states
being Wyoming, Montana, and South Dakota. Fuller's earth is essentially
montmorillonite or palygorskite with Georgia and Florida the principal producing
states. Miscellaneous clays include all clays not included in the other five
classifications. These miscellaneous clays are mined in almost all states.
Most clays are mined by surface mining methods. There are a few underground
mines, principally mining underclays in coal mining areas. These underground mines,
which are located in Colorado, Ohio, Pennsylvania, Utah, and West Virginia, use a
room and pillar mining method. The possible environmental problems related to
underground clay mining are sedimentation and discoloration of surface waters
because of mine drainage.
3.5 CORUNDUM AND EMERY
Corundum (Al2Os) is the second hardest known natural substance. The United
States has no corundum production, no known reserves, and poorly known
resources.
Emery consists of corundum and magnetite with admixed spinel, hematite,
garnet, and other minerals. Emery is produced in West Chester County, New York,
and Linn County, Oregon. All mining is by surface mining methods.
3.6 DIAMOND
Diamond is the hardest known natural substance. Natural diamond normally
occurs only in an unusual type of peridotitic igneous rock known as kimberlite
which was injected into overlying rocks as pipes. Two kimberlite pipes occur in
Arkansas; one containing no diamond and the other uneconomical amounts of
diamond. Thus, the United States has no known commercial deposits of industrial
diamond.
3.7 DIATOMITE
Diatomite is a sedimentary rock consisting mainly of the siliceous remains of
diatoms, single-celled aquatic organisms. All United States production comes from
surface mines in California, Nevada, Washington, and Oregon.
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3.8 FELDSPAR
Feldspar is a general term to designate a group of anhydrous aluminim silicate
minerals that contain various amounts of potassium, sodium, and calcium. The
principal feldspar minerals are orthoclase and microcline (both KAlSisOg), albite
(NaAlSiaOs), and anorthite (CaA^SisOg). Feldspars are important rock-forming
minerals and occur in significant amounts in most igneous and some sedimentary
rocks. Commercial feldspar deposits are widely distributed. Pegmatite deposits are a
source of massive feldspar crystals. However, most United States production is from
feldspar bearing rocks such as alaskite and from beach sands. Feldspar is mined in
eight states: North Carolina, California, Connecticut, Georgia, South Dakota,
Arizona, Wyoming and Colorado. Almost all feldspars are mined by surface mining
methods, but small deposits can be mined by underground methods. There are no
known environmental problems related to underground feldspar mines.
3.9 FLOURINE
The principal flourine minerals are flourite (CaF2), cryolite
fluorapatite (Ca5(PC«4,CO3)F), and topaz (Al2SiO4(F,OH)2)- Flourspor, the ore of
the mineral fluorite, is the principal commercial source of fluorine.
Fluorine occurs in deposits associated with igneous, sedimentary, and
regionally metamorphosed rocks and in hydrothermal deposits. Deposits associated
with igneous rocks include accessory fluorine minerals disseminated through the
igneous rock and fluorine minerals in pegmatites, carbonatites, and contact aureoles
of intrusive rocks. The flourspar deposits at Crystal Mountain, Montana, are mainly
fluorite with minor amounts of biotite, quartz, feldspar, sphene, rare-earth-bearing
apatite, amphibole, fergusonite, thorianite, and thortveitite. Fluorine deposits
associated with sedimentary rocks include deposits in volcaniclastic and lacustrine
sedimentary rocks and in evaporite, marine-carbonate, and marine-phosphorite
rocks.
The principal commercial sources of fluorine are deposits of hydrothermal
origin. These include deposits in veins and mantos, pipes and stockworks, and zones
of alteration. These deposits occur in almost any type of host rock but are most
common in carbonate, silicic igneous, and silicic metamorphic rocks. In addition to
fluorite, other common minerals are quartz, chalcedonic quartz, opal, barite,
manganese oxides, calcite, clay minerals, and lead and zinc sulfides. Hydrothermal
deposits are located in the Illinois-Kentucky district; at Jamestown, Colorado; and
near Spor Mountain, Utah.
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The Illinois fluorspar district accounts for more than 50 percent of the United
States fluorine production. Other producing states are Colorado, Montana, Nevada,
Texas, Utah, Arizona, New Mexico, and Kentucky.
Most fluorspar is mined by underground methods in Illinois, Colorado, Nevada,
Utah, and Kentucky. In New Mexico, underground mines are being developed and
drilling is continuing at other properties. These mines range in size from very small
to large fully mechanized mines. Bedded deposits usually are mined by a room and
pillar system. Other deposits commonly are mined by top slicing, cut and fill,
shrinkage, and open stoping methods. Underground fluorspar mining is not known
to produce any unusual environmental problems. However, some fluoride
compounds are toxic and harmful to both plant and animal life and the
Environmental Protection Agency is proposing stringent water quality standards for
mine water discharges.
3.10 GARNET
Commercial garnet occurs primarily as almandite (Fe3Al2(SiO4)3).
Commercial sources of garnet occur almost exclusively in metamorphic rocks and in
placer deposits derived from these primary rocks. Garnet deposits are reported in
more than half the states. Currently, all United States production comes from two
states, New York and Idaho. In New York, garnet is produced as a primary product
by surface mining at North Creek and as a byproduct of wollastonite underground
mining at Willsboro. In Idaho, garnet is produced from placer deposits by dragline at
Emerald Creek.
3.11 GEM STONES
Gem minerals are rare and occur in most of the major geologic environments.
Gem minerals usually are silicate, alumino-silicate, or oxide minerals. These minerals
are formed principally by precipitation from aqueous solutions, crystallization of
magmas, and metamorphism. Igneous rocks are the source of many gem stones
including diamond, ruby, sapphire, tourmaline, and topaz. Metamorphic rocks are
the source of ruby, sapphire, and emerald. Placer deposits are formed by the
weathering of primary gem stone deposits. Most gems are dense, resistant to
abrasion, and chemically inert.
Gem stone mining in the United States is essentially by amateur "rock
hounds". However, placer deposits are mined commercially by surface mining
methods and a small underground mine is located near Utica, Montana.
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3.12 GRAPHITE
Graphite is pure crystalline carbon. Natural graphite occurs in three geologic
environments. Graphite occurs as (l)vein graphite in igneous and metamorphic
rocks; (2) flake graphite disseminated through layers of metamorphosed
carbonaceous sedimentary rocks; and (3) amorphous graphite in thermally
metamorphosed coal beds. The only active graphite mine in the United States is the
surface mine at Burnet, Texas, which produces flake graphite. Similar graphite
deposits occur in other areas of Texas and in Alabama, Alaska, New York, and
Pennsylvania.
3.13 GYPSUM
Gypsum (CaSo4-2H2O) and its anhydrous form anhydrite (CaSO4) occur
widely and abundantly in virtually all marine evaporate basins. Deposits were
formed as chemical precipitates from marine waters of high salinity. Gypsum usually
predominates over anhydrite at or near the surface and then grades into anhydrite
deeper in the deposit.
Gypsum is mined in 22 states from 5 7 surf ace mines and 12 underground
mines. The states leading in production are California, Michigan, Texas, Iowa, and
Oklahoma. Underground mines are in Indiana, Iowa, Michigan, Montana, New York,
Ohio, and Virginia. Underground mining generally is by room and pillar methods;
although, steep dipping beds may be mined by shrinkage stoping. The environmental
problems related to underground gypsum mining are negligable.
3.14 KYANITE AND RELATED MINERALS
Kyanite and related minerals are known as the kyanite or sillimanite group and
include kyanite, sillimanite, and andalusite, all having the same chemical
composition (Al2O3-SiO2). The kyanite group minerals occur in nearly all large
areas of metamorphic rocks. These minerals are contained principally in micaceous
schists and gneisses, but they also may occur in quartzose rock and in quartz veins
and pegmatites. Almost all United States production comes from three hard rock
surface mines in Virginia (Willis Mountain and Baker Mountain) and Georgia (Graves
Mountain). Some kyanite-sillimanite was obtained as a byproduct from a titanium
and zirconium sand deposit at Trail Ridge, Florida.
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3.15 LITHIUM
Lithium is mined from pegmatites with the principal lithium minerals being
spodumene (LiAlSi2O6), lepidolite (K2Li3Al3(AlSi3Oio)(OH,F)4), and petalite
(LiAlSi4Oio)- Pegmatites containing spodumene are mined by surface mining
methods at Kings Mountain and Bessemer City, North Carolina. Lithium also is
obtained from brines at Silver Peak, Nevada, and Trona, California.
3.16 MICA
Mica is the general name for several complex hydrous aluminum silicate
minerals including muscovite (KAl2(AlSi3Ol o)(OH)2), biotite
(K(Mg,Fe)3(AlSi30io)(OH)2), and phlogpite (KMgs(AlSi3Oio)(OH)2). Mica
occurs in pegmatites, granite, and mica-rich metamorphic rocks. All mica produced
in the United States is flake mica with North Carolina the largest producing state
followed by Alabama, Arizona, Connecticut, Georgia, New Mexico, and South
Carolina. All mica mining is by surface mining methods and mica usually is produced
as a coproduct with other mineral commodities such as feldspar and kaolin.
3.17 PERLITE
Perlite is a metastable amorphous aluminum silicate with minor impurities and
inclusions. It is a form of volcanic glass associated with surface flows or shallow
igneous intrusives. Perlite deposits of the United States are restricted to the western
states where volcanism was more recent, since alteration of the deposit occurs after
formation of the perlite. Crude perlite is produced from 12 mines in seven states
with New Mexico the principal producing state followed by Arizona, California,
Nevada, Colorado, Idaho, and Texas. Mining is by surface mining methods except
for one underground mine in Lincoln County, Nevada. There are no known
environmental problems related to this underground perlite mine.
3.18 PHOSPHOROUS
The principal commercial phosphorus minerals are phosphates in the apatite
group (Ca5(F,Cl,OH)(PO4)3). Minable concentrations of phosphate, called
phosphate rock, occur in igneous rocks, as guano and related deposits, and as
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sedimentary phosphorite. Apatite occurs in igneous rocks as intrusive masses or
sheets, as hydorthermal veins or disseminated replacements, as marginal
differentiations, or as pegmatites. Largest are the intrusive masses commonly
associated with alkaline igneous rocks. Apatite occurring in igenous rocks and guano
and related deposits currently are not mined and United States resources in these
types of deposits are small.
Sedimentary phosphorite deposits are of four different types. Deposits caused
by divergence upwelling of sea water are characterized by black shale, phosphatic
shale, phosphatic sandstone, phosphorite, dolomite, chert or diatomite, and saline
deposits and red or light-colored sandstone or shale. The phosphate is carbonaceous
and consists of pellets, nodules, and phosphatized bone material and shell. Examples
of this type of deposit include the Permian Phosphoria Formation in the western
United States, the Miocene Monterey Formation of California, the Mississippian and
Triassic deposits of northern Alaska, and the Mississippian deposits of Utah.
Deposits formed in warm currents along the eastern coast of the United States in
Florida, Georgia, and North Carolina consist of phosphatic limestone or sandstone.
Deposits formed on stable shelves or in continental interiors are associated with
limestone, dolomite, shale, and glauconitic sandstone. The phosphate occurs as
nodules or grains. Examples of this type of deposit include the Oreskany Sandstone
in New York, Pennsylvania, and Virginia; sandstone in Tennessee and Arkansas;
black shale in Missouri; shale in Arkansas; several beds associated with limestone in
Alabama and Georgia; and beds associated with glauconite in Tennessee, Alabama,
and New Jersey. Marine deposits concentrated and enriched by secondary processes
are the richest phosphate deposits. Deposits in the Bone Valley Formation of
Florida were formed by submarine reworking of phosphate-rich residuum, followed
by leaching and weathering. River pebble deposits occur in the flood plains of
streams that drain phosphate areas of Florida, South Carolina, and Georgia.
Chemical weathering of phosphatic limestone, such as in Tennessee and Kentucky,
results in phosphate enrichment. Phosphate lake beds occur in Wyoming and Utah.
Florida and North Carolina produce over 80 percent of the phosphate in the
United States. The western states (Idaho, Missouri, Montana, Utah, and Wyoming)
and Tennessee produce the remainder. Most of the known phosphate resources of
the United States occur in Florida and North Carolina with lesser reserves in Idaho
and Montana. Surface mining methods are used hi Florida, North Carolina,
Tennessee, and western states. Underground mining is limited to one mine at Warm
Springs, Montana, where phosphate rock is mined by adit. Production from Missouri
is from apatite recovered from Pea Ridge iron ore mine tailings. Underground mining
methods used to recover high-grade phosphate beds are top slicing, sublevel sloping,
and open -sloping. There are no known environmental problems related to
underground phosphate mining. However, the United States Departments of Interior
and Agriculture have called for an environmental impact study covering federal
western phosphate lands in northern Utah, western Wyoming, southern Montana,
and eastern Idaho. No new operations will be approved until this study is completed.
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3.19 POTASSIUM
The principal commercial potassium minerals are sylvite (KC1) and langbeinite
(K2SO4-2MgSO4). Potassium also occurs in large and early pure deposits of
polyhalite (K2MgCa2(SO4)4-2H2O), but these deposits are not mined. Potassium or
"potash" occurs in two main types of deposits: (1) crystalline deposits of saline
rocks containing sylvite, langbeinite, and related potassium minerals and
(2) concentrated brines in relect lakes and lacustrine sediments of continental origin
in arid regions. The crystalline bedded deposits occur as tabular bodies which may
be primary or replacement in origin. The potassium minerals occur within the
sodium-rich (halite) facies of the evaporite. Most United States potash production
(83 percent) comes from these type deposits in southeastern New Mexico and
eastern Utah. The remaining United States production comes from brines in
California and Utah. California production is from alkaline near-surface brines of
Searles Lake. Utah production is from the nearly neutral waters of the Great Salt
Lake.
The deep bedded potash deposits are mined by underground methods with
eight mines in Eddy County, southeastern New Mexico, and one mine near Moab,
Utah. In New Mexico, deep shaft underground mining is by room and pillar
methods, with pillars being robbed after initial mining. Thicker deposits are mined
by large continuous equipment while thinner deposits are mined by smaller
conventional equipment. At the Utah deposit, a conventional room and pillar
underground mine was converted to a solution mine. Potash is recovered by
dissolving the potash in water underground and pumping to the surface for recovery.
The environmental problems related to underground potash mining are
pollution of surface waters by mine dewatering. This problem is of particular
concern at the Utah operation near the Colorado River.
3.20 PUMICE
Pumice is essentially aluminum silicate of igneous origin with a cellular
structure formed by explosive or effusive volcanism. Volcanic action ejects material
into the air, which is then transported horizontally before deposition to form
pumice. Due to metamorphism, only areas with relatively recent volcanism have
commercial pumice deposits. The principal producing states are California, Oregon,
and Arizona with significant production also from Hawaii, Nevada, and New Mexico.
All current mining is by surface mining methods.
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3.21 SALT
The salt mineral is halite (NaCl). Bedded salt deposits are formed by
evaporation of sea water until salts are partially or entirely deposited. These deposits
may be large horizontal beds or large vertical domes. The domes result from
deformation of deeply buried salt beds under great pressure. Dolomite, shale,
anhydrite, and other evaporites usually occur as impurities.
In the United States, salt is produced by: (1) solution mining; (2) underground
mining; and (3) evaporation of natural brines and sea water. Louisanna and Texas
are the leading salt producing states, followed by New York, Michigan, and Ohio.
Solution mining of salt deposits produces almost 60 percent of the salt produced in
the United States. Underground mining accounts for almost 30 percent of the
United States salt production. The room and pillar method is used for underground
mining of bedded and dome deposits. Underground salt mines are located in Kansas,
Louisanna, Michigan, New York, Ohio, and Texas.
There are no known environmental problems related to underground salt
mines. Most mines are at considerable depth and subsidence is negligible.
3.22 SAND AND GRAVEL
Sand and gravel are unconsolidated rocks and minerals ranging in size from silt
to boulders. These deposits consist predominantly of silica, but other minerals
usually are present. Deposits are formed by the breakdown, erosion, and transport
of bedrock by ice, water, and wind. The principal commercial sand and gravel
deposits are along existing or ancient river channels and in glaciated terrains. These
deposits include flood-plain, outwash-plain, stream-terrace, alluvial-fan, esker, kame,
delta, and moraine deposits. Sand and gravel deposits of different types are located
throughout the United States, but the industry tends to be concentrated
geographically in the large, rapidly expanding urban areas. California leads in
production followed by Michigan, Ohio, Illinois, Wisconsin, Texas, and Minnesota.
All known mining is by surface methods.
3.23 SODA ASH
Soda ash (Na2CO3) occurs naturally as evaporite and brine deposits. Soda ash
resources of the United States are immense. Mose soda ash produced in the United
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States is manufactured synthetically from sodium chloride, ammonia, and carbon
dioxide by the Solvay process. Natural soda ash is obtained from brines and trona
(Na2CO3-NaHCO3-2H2O) deposits. Soda ash is mined by deep shaft underground
methods from an immense deposit of bedded trona in southwestern Wyoming. These
three mines are highly mechanized and use a room and pillar mining .system. There
are no known environmental problems related to underground soda ash mining.
3.24 STONE
Stone is a commercial term which includes all consolidated rock used for
construction and roads, in agriculture, in chemical and metallurgical industries,
cement manufacture, etc. Stone may be classified further into dimension and
crushed stone. Terminology for the dimensional stone industry differs from standard
mineralogical rock descriptions. In addition to true granite, the term granite includes
other types of igneous and metamorphic rocks such as quartz diorites, syenites,
quartz porphyries, gabbros, schists, and gneisses. Dimensional marble includes true
marble and any limestone that will take a high polish and sometimes serpentine,
onyx, travertines, and granite. Hard sandstone sometimes is called quartzite. For the
crushed stone industry, all coarser grained igneous rocks usually are called granite.
Traprock is dense, dark, fine-grained igneous rock. Quartzite may be any
siliceous-cemented sandstone.
Stone is produced in almost all the states. Almost all dimensional stone is
quarried with production methods varying from antiquated to modern. Dimensional
stone is produced from one underground mine in Franklin County, Alabama.
Crushed stone is produced primarily by surface mining, but large scale underground
mining also is used in many areas. About 5 percent of the crushed stone production
in the United States is by underground mining, usually a room and pillar system.
Underground stone mines are in California, Illinois, Indiana, Iowa, Kentucky, Ohio,
Pennsylvania, Tennessee, and West Virginia. There are no known environmental
problems related to underground stone mining.
3.25 STRONTIUM
The principal commercial minerals of strontium are celestite (SrSO4) and
strontianite (SrCO3). Small quantities of strontium commonly occur in igneous
rocks and traces may be found in sedimentary rocks. Potentially commercial
strontium deposits occur as beds, veins, veinlets, nodules, or irregular masses in or
near sediments or sedimentary rocks. These deposits are known to occur in Texas,
California, Washington, Arizona, and Ohio. Strontium minerals have not been mined
in the United States since 1959.
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3.26 SULFUR
Sulfur is produced commerically from four major sources. Elemental sulfur is
recovered from deposits in evaporite rocks using the Frasch hot-water process. These
deposits in Texas and Louisianna occur as anhydrite (CaSO4) cap rock lying on salt
domes and as thick bedded anhydrite. Elemental sulfur also is recovered as a
byproduct from natural gas and petroleum refining operations. Sulfur is recovered as
byproduct sulfuric acid at copper, lead, and zinc roasters and smelters. The fourth
source is sulfur recovered from pyrite which is produced as a byproduct of copper
production at three mines in Arizona and Tennessee.
3.27 TALC
Talc refers to rock composed mainly of magnesium-rich silicate minerals and
having the mineral talc (Mg3(Si4Olo)(OH)2) as an important constituent. The
mineral content of industrial talc may range from pure talc to predominantly
tremolite (Ca2Mg5(Si8O22)(OH)2). Talc deposits of commercial importance occur
mainly in metamorphosed dolomite and altered ultramafic igneous rocks. Most of
the major talc deposits in the United States occur in regionally metamorphosed
dolomite. The talc, tremolite and serpentine rocks occur in carbonate and siliceous
sedimentary rocks as in St. Lawrence County, New York. Similar deposits occur in
North Carolina, Montana, and California. Deposits in Georgia and Texas also occur
in metasedimentary rocks, but these are associated with phyllites, schists, and
quartzites and required extensive metasomatism. Talc deposits associated with
serpentinized ultramafic rocks occur in regionally metamorphosed and folded
sedimentary and volcanic rocks. Deposits of this type occur in Vermont, California,
Texas, and Virginia. Talc deposits are formed by contact metamorphism when
granite plutons and diabase dikes intrude favorable dolomitic sedimentary strata
such as in southern California.
The leading talc producing states are Vermont, New York, Texas, Montana,
California, and North Carolina. Talc is mined by both surface and underground
methods. Almost 50 percent of the production comes from underground mines in
California, Georgia, New York, North Carolina, and Vermont. Underground mines
usually require timbering for stope support. Dust is a major environmental problem
related to underground talc mines. Medical research has shown a positive correlation
between incidence of lung disease and working with or near asbestos which is similar
to the asbestiform minerals tremolite and anthophyllite ((Mg,Fe)7(SigO22)(OH)2)
occuring in talc deposits.
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3.28 VERMICULITE
Vermiculite is a micaceous ferromagnesium-aluminum silicate mineral.
Vermiculite deposits generally are associated with ultra-basic igneous host rocks such
as pyroxenite or serpentine. Vermiculite is produced at two mines in South Carolina
and one mine in Montana. All mining currently is by surface mining methods, but
there has been past production from underground mines.
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4.0
ENERGY SOURCES
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4.1 COAL
Coal is ranked according to fixed carbon and heat content, determined on a
mineral-matter-free basis. In ascending order of rank, coals are classified as lignite,
subbituminous, bituminous, and anthracite. Coal also is classified by grade based on
the content of ash, sulfur, and other deleterious constituents.
Coal is formed by the compression and lateration of plant residue in ancient
fresh or brackish water swamps. Accumulated plant residues were first transformed
into peat containing sand, silt, and mud that was washed into the peat swamps. Plant
growth on the peat swamps was then terminated by trangressing seas. The
submerged peat swamps were then overlayed by sand, silt, and mud from eroding
land masses. These sequences of deposition may have been repeated many times,
forming several sedimentary beds. Weight of the overlying sedimentary formations,
heat produced by depth of burial, structural deformation, and time all contribute to
the progressive compaction and devolatization of peat to form the higher ranks of
coal.
Coal contains widely varying amounts of ash, sulfur, and other deleterious
constituents. Ash is from sand, silt, and mud washed into the peat swamps during
deposition. Most of the sulfur occurs in pyrite and marcasite. Sulfur also occurs as
hydrous ferrous sulfate (FeS4-7H2O), gypsum, and organic sulfur. Coal also contains
small quantities of virtually all metallic and nonmetallic elements. When the coal is
burned, most of these elements are in the ash, but a few may be volatilized and
emitted to the atmosphere.
Coal-bearing rocks are found in 37 states, underlying about 13 percent of the
land area of the 50 states. Bituminous coal is the most abundant and widespread
rank of coal in the United States with the largest resources in Illinois, West Virginia,
Kentucky, Colorado, and Pennsylvania. Lignite is the next most abundant rank of
coal with the largest resources in North Dakota and Montana. Subbituminous coal
resources almost are equivalent to lignite resources. Major subbituminous coal
resources are in Montana, Alaska, and Wyoming. Anthracite resources are small and
principally in Pennsylvania.
Bituminous coal and lignite are mined at approximately 4,500 mines in
24 states. The principal producing states are Kentucky, West Virginia, Pennsylvania,
Illinois, Ohio, and Virginia. These states account for almost 80 percent of the
bituminous coal and lignite produced in the United States. Bituminous coal is mined
by both underground and surface mining methods with underground and surface
mining methods accounting for about 50 percent of the bituminous coal and lignite
production. Underground mining has occurred in all of the major bituminous coal
producing states.
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Anthracite coal is mined in northeastern Pennsylvania by both underground
and surface mining methods. Underground mining accounts for 11 percent of the
anthracite coal production.
Underground coal mining is by room and pillar method and longwall method.
In steeply dipping beds, the room and pillar is modified to a breast and pillar
method. Loading in room and pillar mines can be by continuous miners, mechanical
loaders, and hand loading. Longwall mines use longwall cutting units and conveyors.
In the United States, continuous miners and mechanical loaders produce 62 percent,
and 34 percent, respectively, of the coal produced.
The major environmental problem related to the mining of coal is the
production of acid mine drainage resulting from the oxidation of iron sulfides. Acid
production from abandoned eastern underground coal mines is the largest single
source of acid mine drainage in the United States. In Appalachia alone, more than
16,100 kilometers (10,000 miles) of streams have been affected by coal mine
drainage. Of the sources inventoried in Appalachia, abandoned underground mines
accounted for more than 50 percent of the acid production.
Mine drainage pollution resulting from coal mining has also been reported in
the following states: Illinois coal region (Illinois, Indiana, and western Kentucky);
Western Interior coal region (Iowa, Kansas, Missouri, and Oklahoma); and Rocky
Mountain coal region (Colorado and Montana). However, a majority of the coal
mine drainage pollution occurring outside the Appalachian region reportedly results
from surface mining operations.
4.2 THORIUM
The principal thorium minerals are monazite ((Ce,La,Th,Y)PO4), thorite
(ThSiO4), thorianite (ThO2), uranothorite (isomorphous mineral containing
uraninite and thorianite), and brannerite ((U,Ca,Fe,Th,Y)3Ti5Ol6)- Thorium
deposits are of four types: (l)vein deposits; (2) placers and residual deposits;
(3) deposits in sedimentary rocks; and (4) deposits in igneous and metamorphic
rocks. Vein deposits occur in steeply dipping fractures cutting across the structure of
the host rocks. Thorite is the principal ore mineral. Vein deposits occur in the Wet
Mountains, Colorado and at Hall Mountain, Idaho. Beach and stream placers were
formed from the debris of metamorphic and granitic rocks. These placers often
occur on active beaches where monazite and other heavy minerals are concentrated
in a narrow belt along the shoreline. Important deposits in the United States are in
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Florida and North Carolina where monazite is recovered as a byproduct of ilminite.
Deposits in sedimentary rocks consist of indurated placer sediments such as
sandstones and conglomerates. Thorium mineral deposits occur in some igneous and
metamorphic rocks such as potassic igneous rocks (especially granitic and alkalic
complexes) and carbonatites.
Thorium is produced at two mines in the United States, one at Folkston,
Georgia and the other in Green Cove Springs, Florida. Both of these operations
recover monazite from placer deposits. Thus, there are no environmental problems
in the United States related to underground mining of thorium minerals.
4.3 URANIUM
The principal unoxidized uranium ore minerals are uraninite (UO2) and
coffinite (U(SiO4)i-x(OH)4x). The massive form of uraninite is called pitchblende.
The oxides brannerite (oxide of uranium, titanium, thorium, rare earths, and other
elements) and davidite (oxide of titanium, iron, and uranium) occur in some
unoxidized ores. The principal oxidized uranium ore mineral is carnotite
(K20-2U03-V205-nH20).
Uranium occurs in six types of deposits. These are: (1) peneconcordant
deposits; (2) quartz-pebble conglomerate deposits; (3) vein deposits; (4) uraniferous
igneous rocks; (5) uraniferous phosphatic rocks; (6) uraniferous marine black shales.
The principal United States minable uranium resources occur as peneconcordant
masses in continental and marginal marine sandstone and associated rocks. The
uranium minerals mainly occupy pore spaces of the sandstone, but also may replace
sand grains or carbonized plant fossils. Most of the host sandstone beds are
quartzose, but some are arkosic derived mainly from granitic rocks. Peneconcordant
deposits occur in (1) tabular bodies that are nearly concordant with the gross
sedimentary structures of the sandstone and (2) roll bodies that are crescent-shaped
and discordant to bedding in cross section and nearby concordant to bedding on the
long axes. Tabular type deposits occur in the San Juan Basin, New Mexico, and
Uravan Mineral Basin in the Colorado Plateau. Roll type deposits occur in the
Shirley Basin of Wyoming and the Texas Coastal Plain.
Uranium-bearing veins occur in many kinds of rock. Common types of
alteration associated with uranium veins are sericite, argillic, chloritic, and hematitic.
Base metal sulfides may occur with uranium such as the Schwartzwalder mine in
Colorado. Fluorite occurs in the deposits in Marysvale, Utah. Only small amounts of
uranium have been mined from uraniferous igneous rocks such as pegmatites.
Uranium has not been mined in the United States from igneous rocks such as
granite, deposits in quartz-pebble conglomerates, phosphatic rocks, and marine black
shales.
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Uranium is presently mined at 114 operations in seven states. Wyoming and
New Mexico are the leading producers with 75 percent of the United States
production. Underground mining accounts for almost 50 percent of the United
States production. These underground mines are in Wyoming, New Mexico,
Colorado, and Utah. Production of many small underground mines is by adit or
incline. Larger shaft mines use room and pillar or modified room and pillar mining
systems.
Uranium reserves of the United States are primarily in the Colorado Plateau
and Wyoming Basins. New underground uranium mines are being developed at
Mount Taylor near Grants, New Mexico; Paguate mines near Laguna, New Mexico;
and Powder River Basin, Wyoming.
The environmental problems related to underground uranium mines are
radioactive dust and mine water drainage. Ventilation in mines is closely monitored
and must meet standards to prevent excess accumulations of radon-222, a
radioactive gas. Uranium miners may be subject to an increased risk of lung cancer
due to radon-222 and its daughter products. If airborne radioactive dust is
discharged into the environment at ventilation shafts, there may be a health hazard
to the public. Mine water drainage may contain dissolved chemical constitutents
which represent a possible health hazard, and therefore, must be monitored closely.
Uranium is recovered from mine water by ion exchange prior to discharge at several
underground mines.
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REFERENCES FOR PART III - MINERAL COMMODITIES MINED
6, 22, 26, 30, 48, 49, 64, 80, 88, 91, 94, 96, 119, 120, 121, 122, 126, 130
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IV
GLOSSARY OF TERMS
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Abandoned Mine - A mine that is not producing any mineral and will not continue
or resume operation.
Abatement — The lessening of pollution effects.
Acidity - A measure of the extent to which a solution is acid.
Acid Mine Drainage — Any acidic water draining or flowing on, or having drained or
flowed off, any area of land affected by mining.
Acre-Foot — The quantity of water that would cover an area of one acre, one foot
deep.
Adit — A horizontal or nearly horizontal passage driven from the surface for the
working or unwatering of a mine.
Alkaline — Having the qualities of a base (i.e., a pH above 7).
Alkalinity — A measure of the capacity to neutralize acids.
Alluvial, Alluvium — Sedimentary (clay, silt, gravel, sand, or other rock) materials
transported by flowing water and deposited in comparatively recent geologic time as
sorted or semisorted sediments in river beds, estuaries and flood plains, on lakes,
shores, and in fans at base of mountain slopes.
Anorthosite — Igneous origin rock composed almost entirely of plagioclase;
monomineralic equivalent of gabbro, but lacking in essential monoclinic pyroxene.
Anticline - A configuration of folded stratified rocks in which the rocks dip in two
directions away from a crest or fold axis.
Auger Hole — A hole driven into a mineral seam with a power-driven auger for the
purpose of extracting the mineral-bearing material.
Aureole — Zone in country rock surrounding an igneous intrusion and in which zone
contact metamorphism of the country rock has occurred.
Backfilling — The transfer of previously moved material back into an excavation
such as a mine, ditch, or against a constructed object.
Barrier — Portions of the mineral and/or overburden that are left in place during
mining.
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Bench — The ledge, shelf, table, or terraces formed in the contour method of surface
mining.
Bentonite — A montmorillonite-type clay formed by the alteration of volcanic ash.
Borehole - A hole formed with a drill, auger, or other tools for exploring strata in
search of minerals, for water supply, for blasting purposes, for proving the position
of old workings, faults, and for releasing accumulations of gas or water.
Breccia — Rock formation essentially composed of uncemented or loosely
consolidated, small, angular-shaped fragments.
Bulkhead — A tight partition of wood, rock, or concrete in mines for protection
against gas, fire, and water.
Chert — Very hard glassy mineral, chiefly silica.
Clastic — Consisting of rock fragments or of organic structures that have been moved
individually from their places of origin.
Conglomerate — A cemented clastic rock containing rounded fragments of gravel or
pebble size.
Daylighting — A term to define the procedure of exposing an entire underground
mined area to remove all the mineral underlying the surface.
Deep Mine — An underground mine.
Diabasic — Texture of igneous rocks in which discrete crystals or grains of pyroxene
fill the interstices between lath-shaped feldspar crystals.
Diagenesis — Any change occurring within sediments subsequent to deposition and
before complete lithification that alters mineral content and physical properties of
the sediments.
Dike — Discordant tabular body of igneous rock that was injected into a fissure
when molten, cutting across the structure of the adjacent country rocks and usually
having a high angle of dip.
Dip — The amount of inclination in degrees of a mineral seam or rock bedding plane
from the horizontal. True dip is measured perpendicular to the strike of the bed.
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Downdip - Lying down-slope along an inclined mineral seam or rock bedding plane.
Drift - A horizontal or near horizontal passage underground which follows a vein
and may be driven from the surface.
Effluent - Any water flowing out of the ground or from an enclosure to the surface
flow network.
Eluvial - A residual ore deposit almost formed in situ but mostly displaced by
creep.
Epigenetic - Mineral deposits of later origin than enclosing rocks, or deposits of
secondary minerals formed by alteration.
Epithermal — Applied to hydrothermal deposits formed at low temperature and
pressure.
Esker — Long, winding gravel ridge deposited in the bed of a subglacial stream.
Fault — A fracture or a fracture zone along which there has been displacement of
the two sides relative to one another parallel to the fracture.
Felsic — Light-colored rocks containing an abundance of one or all of feldspar,
lelands or feldspathoids, and silica.
Flume — An open channel or conduit on a prepared grade.
Fly Ash — All solids, ash, cinders, dust, soot, or other partially incinerated matter
that is carried in or removed from a gas stream and usually is associated with
coal-fired electric generating plants.
Fracture - A break in a rock formation due to intense folding or faulting.
Gabbro — A fine to coarse, dark colored crystalline igneous rock composed mainly
of calcic plagioclase, clinopyroxene, and sometimes olivine.
Gangue — Undesired minerals associated with ore, mostly nonmetallic.
Glauconitic Sandstone — A quartz sandstone or an arkosic sandstone rich in
glauconite grains.
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Gneiss — A metamorphic rock of coarse grain size, characterized by a mineral
banding in which the light minerals (quartz and feldspar) are separated from the
dark ones (mica, and/or hornblende); the dark mineral layers are foliated and the
light bands are granulitic.
Ground Water — That water of atmospheric origin which saturates rock openings
beneath the water table.
Grout — A fluid mixture of cement, sand (or other additives) and water commonly
forced into a borehole to seal crevices in rock to prevent ground water or mine water
seepage or flow.
Hard Rock Mining — Loosely used to designate mining in igneous and metamorphic
rock.
Highwall — The exposed vertical or near vertical wall associated with a strip or area
surface mine.
Hydrology — The science dealing with water standing or flowing on or beneath the
surface of the earth.
Hydrostatic Head — The pressure exerted by a column of fluid usually expressed in
kilograms per square meter (Ib/sq in).
Hydrothermal — Applied to magmatic emanations high in water content.
Hypogene — Mineral deposits formed by ascending hot waters.
Inactive Mine — A mine that is not producing any mineral but may continue or
resume operation in the future.
Inby — Toward the working face or interior, and away from the entrance of a mine.
Induration — Process of hardening sediments or other rock aggregated through
cementation, pressure, heat, or some other agency.
Infiltration — The act or process of the movement of water into soil.
Intrusive — Body of igneous rock which while molten penetrated into or between
other rocks, but solidified before reaching the surface.
Joint — A divisional plane or surface that divides a rock and along which there has
been no visible movement parallel to the plane of surface.
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Kame - Rounded hill or oblong ridge terminating abruptly in a high mound and
composed of sand and gravel and having its major axis transverse to the drift
movement.
Kimberlite - Highly serpentinized periodite, usually a breccia because of inclusion
of surrounding rock it has penetrated, occurring in vertical pipes, dikes, and sills.
Lacustrine - Produced by or belonging to lakes; deposits which have been
accumulated in freshwater lakes or marshes.
Lateritic — Extreme type of weathering common in tropical climates where iron and
aluminum silicates are decomposed and silica (along with most other elements) are
removed by leaching.
Lattice — Orderly geometric structure in which a crystal's atoms are arranged.
Leaching — The removal in solution of the more soluble minerals by percolating
waters.
Lenticular — A mass of rock thinning out from the center to a thin edge.
Leucoxene — Brown, green, or black variety of sphene or titanite (CaTiSiOs)
occurring as monoclinic crystals.
Lithification — Complex of processes that converts a newly deposited sediment into
an indurated rock.
Mafic — Pertaining to or composed dominantly of ferro-magnesium rock-forming
silicate.
Mantos - Blanketlike replacement of rock by ore.
Mesothermal — Applied to hydrothermal deposits formed at intermediate
temperature and intermediate pressure.
Metamorphic — Characteristics of, pertaining to, produced by, or occurring during
the metamorphism of certain rocks.
Metamorphism - Any process by which consolidated rocks are altered in
composition, texture, or internal structure by conditions and forces such as pressure,
heat, and the introduction of new chemical substances which do not result simply
from burial and the weight of the subsequently accumulated overburden.
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Metasediment — A partly metamorphosed sedimentary rock.
mg/1 — Abbreviation for milligrams per liter which is a weight volume ratio
commonly used in water quality analysis. It expresses the weight in milligrams of a
substance occurring in one liter of liquid.
Micaceous — Occurring in thin plates or scales like mica.
Mineral — An inorganic substance occurring naturally in the earth and having a
consistent and distinctive set of physical properties and a composition that can be
expressed by a chemical formula. A mineral is commonly defined as a substance
obtained by mining.
Mine Spoil — The overburden waste material removed or displaced from a surface
mining operation that is not considered a useful product.
Monzonite — An aluminum silicate of alkalies.
Moraine — An accumulation of earth and stones carried and finally deposited by a
glacier.
Nepheline Syenite — A coarse-grained igneous rock of intermediate composition,
undersaturated with regard to silica, and consisting essentially of elaeolite, a varying
content of alkali feldspar, with soda-amphiboles and/or soda-pyroxenes.
Neutralization — The process of adding an acid or alkaline material to waste water to
adjust its pH to a neutral position.
Noritic — Like a coarse-grained igneous rock of basic composition consisting
essentially of plagioclase and orthopyroxene.
Outby — Away from the face or toward the entrance of a mine.
Outcrop - The part of a rock formation that appears at the surface of the ground.
Packer — A device lowered into a borehole which automatically swells or can be
made to expand at the correct time by manipulation from the surface to produce a
watertight seal against the sides of the borehole or the casing.
Pegmatite — Coarse-grained igneous rock; irregular in texture and composition,
occurring in dikes or veins, sometimes containing valuable minerals.
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Peridotite - General term for essentially non-feldspathic plutonic rocks consisting of
olivine, with or without other mafic minerals.
Permeability - The measure of the ability of a material to transmit underground
water.
pH — The negative logarithm of the hydrogen-ion activity which denotes the degree
of acidity or of basicity of a solution. Acidity increases with decreasing values
below 7 and basicity increases with increasing values above 7.
Phlogopite — Brown magnesium mica, near biotite in composition, but containing
little iron.
Phyllite — An argillaceous rock intermediate in metamorphic grade between slate
and schist.
Pit — Any mine, quarry or excavation area worked by the open-cut method to
obtain material of value.
Placer — Alluvial or glacial deposit of sand or gravel containing particles of valuable
minerals.
Pollution Load — The amount of pollutants that a transporting stream carries during
a given period of time (usually expressed as kg/day).
Porphyry — All rocks containing conspicuous phenocrysts in a fine-grained or
aphanitic groundmass.
Portal — Any entrance to a mine.
Pyrometasomatic - Formed by metasomatic changes in rocks, principally in
limestone, at or near intrusive contacts, under influence of magmatic emanations
and high temperature and pressure.
Pyroxene - Mineral group, ABSi2O6 where A is chiefly Mg,Fe+2,Ca or Na, and B is
chiefly Mg,Fe+2, or Al.
Pyroxenite - Coarse-grained, holocrystalline igneous rock consisting chiefly of
pyroxenes.
Quartzite — Quartz rock derived from sandstone.
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Raise — A vertical or inclined opening driven upward from a level to connect with
the level above, or to explore the ground for a limited distance above one level.
Reclamation — The procedures by which a disturbed area can be reworked to make
it productive, useful, or aesthetically pleasing.
Regrading — The movement of earth over a surface or depression to change the
shape of the land surface.
Riprap — Rough stone of various sizes placed compactly or irregularly to prevent
erosion.
Schist — Crystalline rock that can be readily split or cleaved because of having a
foliated or parallel structure.
Sediment — Solid material settled from suspension in a liquid medium.
Serpentinite — Rock consisting almost wholly of serpentine minerals derived from
the alteration of previously existing olivine and pyroxene.
Shaft — An excavation of limited area compared with its depth made for mineral
exploration, or for lowering or raising men and materials, removal of ore or water,
and for ventilation purposes in underground mining.
Shear Zone — Zone in which shearing has occurred on a large scale so that the rock
is crushed and brecciated.
Sill — Flat bedded strata for sandstone or similar hard rocks.
Slope — An inclined shaft for access to a mineral seam usually developed where the
seam is situated at a distance beyond the outcrop.
Stockwork - Solid mass of one vein or a rock mass so interpenetrated by small veins
of ore that the whole must be mined together.
Stratum — A section of a rock formation that consists of approximately the same
kind of material throughout.
Strike — The direction (course or bearing) of the line of intersection of an inclined
plane (such as a rock unit bedding plane) with an imaginary horizontal plane.
Stringer — Narrow vein or irregular filament of mineral traversing a rock mass of
different material.
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Subsidence - A sinking down of part of the earth's crust.
Supergene - Ores of minerals formed by downward enrichment.
Surface Water - Water from whatever source that is flowing on the surface of the
ground.
Syenite — Any granular igneous rock composed essentially of orthoclase, with or
without microcline, albite, hornblende, biotite, augit, or corundum.
Syncline — A configuration of folded stratified rocks in which the rocks dip
downward from opposite directions to come together in a trough.
Syngenetic — Mineral deposits formed contemporaneously with the enclosing rocks.
Tactite — Rocks of complex mineralogy formed by contact metamorphism of
limestone, dolomite, or other carbonate rocks into which foreign matter form
intruding magma has been introduced by hot solutions.
Tectonic — Pertaining to rock structures and topographic features resulting from
deformation of the earth's crust.
Topography — The physical features (i.e., relief and contour) of a district or region.
Ultramafic — Some igneous rocks containing no less than 45 percent silica.
Underground Mining - Removal of the mineral being mined without the disturbance
of the surface (as distinguished from surface mining).
Updip — Lying up-slope along an inclined mineral seam or rock bedding plane.
Urethane Foam - A rigid, cellular, acid resistant foam that is formed by mixing
isocyanate and a polyether polyol containing a halogenated hydrocarbon agent
which may be used to protect mining and pollution abatement equipment and
structures.
Winze — A vertical or inclined opening, or excavation, connecting two levels in a
mine, differing from a raise only in construction; a winze is sunk underhand and a
raise is put up overhand.
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V
LIST OF MINERALS
315
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actinolite
Ca2(Mg,Pe)
albite
NaAlSi308
allanite
(OH)
> Fe , Mg ) S i
almandite
Pe3A12(Si°4)3
alunite
(OH )
antigorite
Mg6Si4010(OH)8
antlerite
Cu3(S04)(OH)4
apatite
Ca5(F,Cl,OH)(P04)3
argentiferous galena
(Pb,Ag)S
argentiferous tetrahedrite
amosite
(Fe,Mg)SiO
anatase
argentite
Ag2S
arsenopyrite
FeAsS
and alu site
anglesite
PbSO.
atacamite
Cu2(OH) Cl
azurite
anhydrite
CaSO,
4
anker ite
Ca(Mg,Fe)
anorthite
baddeleyite
ZrO~
barite
BaSO.
barylite
anthophyllite
(OH)
bastnaesite
CeFCO,
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bauxite
A1203-2H20
bazzite
Be (Sc,Al) Si 0
3 2 6 18
bertrandite
beryl
Be3fll2Si6°18
bindheimite
biotite
(OH)
brucite
Mg(OH)2
calcite
CaC03
carnallite
KMgCl • 6H 0
32
carnotite
K2(U02)2 (V04
carrollite
CuCo2S .
cassiterite
Sn°
- 3H20
bismite
B12°3
bisirmthinite
celestite
SrS04
cerargyrite
AgCl
boehmite
AID (OH)
cerussite
borax
Na0B.O_-10H00
247 2
bor ni te
Cu5P.eS4
brochantite
) (OH)
brokite
chalcanthite
CuSO -5H 0
T ^
chalcocite
CU2S
chalcopyrite
CuFeS
chamosite
Feg(AlfSi) 401() (OH)
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chloanthite
NiAs2
chlorite
(Mg,Fe,Al)g(Al,Si)40(OH)
chromite
(Mg,Fe,Zn,Mn)(Al,Cr)204
chrysoberyl
crocidolite
•FeSiO-
cryolite
Na3AlFg
cryptomelane
cummingtonite
(OH)
chrysocolla
CuSiO3-2H2O
chrysotile
Mg6(Si4°10)(°H)8
cinnabar
HgS
cobaltite
CoAsS
colemanite
Ca2B6°ll'5H2°
columbite
(Fe,Mn)Nb00
f. b
corundum
A12°3
coulsohite
cuprite
Cu2°
cylindrite
covellite
CuS
dawsonite
NaAl(OH) CO
descloizite-mottramite series
PbZn(VO )OH-PbCu(VO )OH
diaspore
HA102
diatomite
siliceous remains of diatoms
diopside
CaMgSi.O
2 6
dolomite
CaMg(C03)2
enargite
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enstatite
MgSiO
garnet
(Fe,Mg,Mn,Ca)3(Al,Fe)2(Si04)
epidote
Ca2(Al,Fe) 3^3^12 (OH)
garnierite
"(Ni,Mq)SiO 'I1H 0
eudialyte gibbsite
Na (Ca,Fe)ZrSi O (OH,Cl)_ Al(OH)
4 2617 2 J
euxenite
(Y,Ca,Ce,U,Th)(Nb,Ta,Ti) O
glauconite
K(Fe,Mg,Al)
(OH)
famatinite
goethite
ferberite
FeWO
4
fergusonite
(Y,Er,U,Th)(Nb,Ta,Ti) 0
2 6
greenalite
ferrous silicate isomor
phous with serpentine
grunerite
(Fe,Mg) Si 0 (OH)
/ o / / z
ferrimolybdite
FeMoO -H 0
gypsum
CaS04'2H20
fluorapatite
Ca (PO ,CO )F
543
fluorite
CaF0
halite
NaCl
halloysite
franklinite
(Fe,Zn,Mn)
hedenbergite
CaFeSi 0
2 6
gadolin^te
hematite
Fe2°3
galena
~
hemimorphite
'
320
-------
huebnerite
MnW04
illite
ilmenite
FeTiO~
j amesonite
Pb FeSb S
4 6 14
jordesite
amorphous molybdenum disul
fide
kaolinite
Al4Si4°10 (°H) 8
kermesite
kernite
kroehnkite
kyanite
A12Si°5
langbeinite
limonite
FeO(OH)
livingstonite
HgSb4S7
lollingite
FeAs0
^
loparite
(Ce,Na,Ca)(Ti,Nb)2Og
magbasite
KBa(Al,Sc)(Mg,Fe) Si O F
6 6202
magnesite
MgC03
magnetite
Fe3°4
malacite
Cu (CO ) (OH)
23 2
manganite
)«nO (OH)
marcasite
metaeinnabar
HgS
lepidolite
(OH,F)
mi croc line
leucite
microlite
321
-------
minnesotaite
ferrous silicate isomorphous
with talc
molybdenite
2
monazite
(Ce,La,Y,Th)PO,,
montmorillonite
(Al,Mg)8(Si401())3 (OH)
montroseite
(V,Fe)0-OH
phenakite
phlogopite
" KMg3(AlSi3010) (OH)
pollucite
polybasite
Ag9Sbs6
polyhalite
muscovite
(OH)
niccolite
NiAs
olivine
(Mg,Fe)2Si04
palygorskite
(°H)
patronite
"
pentlandite
perovskite
CaTiO
petalite
LiA1Si4°10
proustite
Ag AsS
psilomelane
(Ba,H 0) Mn 0
2 2 5 10
pyrargyite
Ag3SbS3
pyrite
pyrochlore
NaCaNb^O^F
2. 6
pyrolusite
MnO
^
pyromorphite
Pb4(PbCl)
pyrophanite
MnTiO
322
-------
pyrrhotite
Fel-xs
skutterudite
quartz
~sTo
smalt ite
rhodochrosite
MnCO,
smithsonite
ZnCCT
rhodonite
MnSiO,
soda ash
roscoelite
rutile
(OH)
sodic plagioclase
Na(Al,Si)AlSi 0
2 8
sphalerite
ZnS
scheelite
CaWO
4
sphene
CaTiSiO
senarmontite
Sb2°3
sericite
fine grained muscovite
serpentine
spinel
siderite
FeC03
sieqenite
(Co,Ni)3S4
sillimanite
spidumene
LiAlSi00.
2 6
stannite
Cu FeSnS
stephanite
Ag5SbS4
sterrettite
ScPO -2H 0
stibiconite
323
-------
stibnite
Sb2S3
ulexite
CaNaB O -8H 0
strontianite
SrCO.
ulvospinel
Fe TiO
sylvite
KCl
uraninite
talc
Mg Si 0 (OH)
y3 4 10 2
valentinite
Sb2°3
tantalite
(Fe,Mn)Ta 0
2 6
vanadinite
teallite
variscite
A1PO -2H 0
tennantite
(Cu,Fe,Zn,Ag) 0As S
L2. 4 13
tenorite
CuO
willemite
witherite
BaCC)
tetrahedrite
wolframite
thorianite
wulf enite
PbMoO A
thortveitite
(Se,Y)Si 0
2 7
topajz
wurtzite
(Zn,Fe)S
xenotime
YPO.
treraolite
Ca Mg Si 0 (OH)
2 D o ZZ
zincite
ZnO
tremolite^actinolite
Ca (Mg,Fe) Si 0 (OH)
2 5 8 22 2
zircon
ZrSiO,
324
-------
VI
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325
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130. Warner, Don L., "Water Pollution From Mining Activities in the United
States," Prepared for the Federal Water Quality Administration,
(June, 1970)
131. Wentz, Dennis A., "Effect of Mine Drainage on the Quality of Streams in
Colorado, 1971-1972," Colorado Water Resources Circular No. 21, (1974)
132. Zaval, Frank J., and Robins, John D., "Water Infiltration Control to Achieve
Mine Water Pollution Control," U.S. Environmental Protection Agency,
Office of Research and Monitoring, EPA-R2-73-142, (January, 1973)
338
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-440/9-75-007
2.
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
Inactive And Abandoned Underground Mines-
Water Pollution Prevention And Control
5. REPORT DATE
June 1975
6. PERFORMING ORGANIZATION CODE
7. AUTHORtS)
R. Lennie Scott and Ronald M. Hays
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Michael Baker, Jr., Inc.
4301 Dutch Ridge Road - Box 280
Beaver, Pennsylvania 15009
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
68-01-2907
12. SPONSORING AGENCY NAME AND ADDRESS
U.S. Environmental Protection Aqencv
. Office of Water Planning and Standards
Washington, D.C. 20460
13. TYPE OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CODE
IS. SUPPLEMENTARY NOTES
16. ABSTRACT
This report is prepared in response to the requirements of P.L. 92-500, Section
304(e)(2)(B). It was prepared for use by planners, engineers and resource
managers and provides information on the chemistry and geographic extent of
mine drainage pollution in the U.S. from inactive and abandoned underground
mines; underground mining methods and the characterization of mine drainage
control techniques.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS C. COS AT I Field/Group
Mine Surveys
Mineral Economics
Mining Engineering
Mining Research
Mining Geology
0704, 0804,
0807, 0809,
0813, 1302
0503
8. DISTRIBUTION STATEMENT
19. SECURITY CLASS (This Report)
21. NO. OF PAGES
349
20. SECURITY CLASS (This page)
22. PRICE
EPA Form 2220-1 (9-73)
* U. S. GOVERNMENT PRINTING OFFICE : 1975 632-208/1041
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