EPA 821-R-00-007

COAL REMINING 

BEST MANAGEMENT PRACTICES 

GUIDANCE MANUAL

MARCH 2000

Office of Water

Office of Science and Technology

Engineering and Analysis Division

U.S. Environmental Protection Agency

Washington DC, 20460
 
 Coal Remining BMP Guidance Manual

Acknowledgements

Acknowledgments

This manual was developed under the direction of William A. Telliard of the Engineering and

Analysis Division (EAD) within the U.S. Environmental Protection Agency’s (EPA’s) Office of

Science and Technology (OST). The manual was made possible through a cooperative team

effort. EPA gratefully acknowledges the contribution of the team members involved in this effort

(Jay W. Hawkins of the Office of Surface Mining Reclamation and Enforcement and Keith B.C.

Brady of Pennsylvania’s Department of Environmental Protection) for the countless hours spent

and determination in bringing this effort to completion. Their commitment and dedication to this

product was key to the Office of Water’s mission of providing guidance and technical support to

its stakeholders. EPA also wishes to thank DynCorp Information and Enterprise Technology for

its contributions and invaluable support, and the Interstate Mining Compact Commission and its

member states for extensive information and data collection activities in support of this effort.

Disclaimer

The statements in this document are intended solely as guidance. This document is not intended,

nor can it be relied upon, to create any rights enforceable by any party in litigation with the United

States. EPA may decide to follow the draft guidance provided in this document, or to act at

variance with the guidance, based on its analysis of the specific facts presented. This draft

guidance is being issued in connection with the proposed amendments to the Coal Mining Point

Source Category. EPA has solicited public comment on the information contained in the

proposal. This guidance may be revised to reflect changes in EPA’s approach. The changes in

EPA’s approach will be presented in a future public notice.

The primary contact regarding questions or comments to this manual is:

William A. Telliard

Engineering and Analysis Division (4303)

U.S. Environmental Protection Agency

Ariel Rios Building, 1200 Pennsylvania Avenue, N.W.

Washington, DC 20460

Phone: 202/260-7134

Fax: 202/260-7185

email: telliard.william@epamail.epa.gov
 Coal Remining BMP Guidance Manual

Acknowledgments
Coal Remining BMP Guidance Manual

Table of Contents

TABLE OF CONTENTS

Page

SECTION OUTLINE ....................................................... i

LIST OF TABLES ........................................................ ix

LIST OF FIGURES ....................................................... xiii

GLOSSARY AND ACRONYMS ............................................ xvii

EXECUTIVE SUMMARY ................................................ xxvii

INTRODUCTION .......................................................... 1

INTRODUCTION TO BEST MANAGEMENT PRACTICES ..................... 21

Section 1.0 Hydrologic and Sediment Control BMPs .......................... 1-1

1.1 Control of Infiltrating Surface Water ............................... 1-3

1.2 Control of Infiltrating Groundwater ............................... 1-31

1.3 Sediment Control and Revegetation ............................... 1-69

Section 2.0 Geochemical Best Management Practices .......................... 2-1

2.1 Sampling .................................................... 2-5

2.2 Alkaline Addition ............................................. 2-29

2.3 Induced Alkaline Recharge ...................................... 2-63

2.4 Special Handling .............................................. 2-79

2.5 Bactericides ................................................ 2-127

Section 3.0 Operational Best Management Practices .......................... 3-1

Section 4.0 Passive Treatment ............................................ 4-1

Section 5.0 Integration of Best Management Practices ......................... 5-1

Section 6.0 Efficiencies of Best Management Practices ......................... 6-1

Section 7.0 Best Management Practices - Costs ............................... 7-1

APPENDICES

Appendix A: EPA Coal Remining Database - 61 State Data Packages .............. A-1

Appendix B: Pennsylvania Remining Site Study ............................... B-1

Appendix C: Interstate Mining Compact Commission Solicitation Sheet Response

Summary ................................................... C-1
Coal Remining BMP Guidance Manual

Table of Contents
Coal Remining BMP Guidance Manual

Table of Contents i

Section Outline

Introduction ............................................................... 1

Environmental Conditions ............................................... 1

Waters Impacted by Pre-SMCRA Mining .............................. 1

303(d) List ..................................................... 3

Abandoned Mine Land Program and AMLIS ........................... 4

Industry Profile ....................................................... 7

Regulatory History ..................................................... 7

Remining ............................................................ 9

Existing State Remining Programs ........................................ 15

Introduction to Best Management Practices .................................... 21

Site Characteristics and BMP Selection .................................... 24

Regional Differences .................................................. 26

BMP Implementation .................................................. 36

Verification ......................................................... 37

References .......................................................... 39

Section 1.0 Hydrologic and Sediment Control BMPs .......................... 1-1

Introduction ........................................................ 1-1

1.1 Control of Infiltrating Surface Water ............................... 1-3

Theory ...................................................... 1-3

Site Assessment – Backfill Testing ................................. 1-6

1.1.1 Implementation Guidelines ................................. 1-6

Regrading Abandoned Mine Spoil ............................ 1-7

Installation of Surface Water Diversion Ditches .................. 1-9

Low-Permeability Caps or Seals ............................ 1-11

Revegetation ........................................... 1-14

Stream Sealing ......................................... 1-15

Design Criteria ......................................... 1-17

1.1.2 Verification of Success or Failure ........................... 1-18

Implementation Checklist ................................. 1-20

1.1.3 Case Studies ........................................... 1-21

Case Study 1 ........................................... 1-22

Case Study 2 ........................................... 1-23

Case Study 3 ........................................... 1-26

1.1.4 Discussion ............................................ 1-29

Benefits .............................................. 1-29

Limitations ............................................ 1-29

Efficiency ............................................. 1-29

1.1.5 Summary ............................................. 1-30

1.2 Control of Infiltrating Groundwater ............................... 1-31

Theory ..................................................... 1-31
Coal Remining BMP Guidance Manual

ii Table of Contents

Site Assessment .............................................. 1-33

1.2.1 Implementation Guidelines ................................ 1-34

Daylighting of Underground Mines .......................... 1-34

Sealing and Rerouting of Mine Water from Abandoned Workings ... 1-39

Highwall Drains ........................................ 1-44

Pit Floor Drains ........................................ 1-47

Grout Curtains ......................................... 1-50

Ground Water Diversion Wells ............................. 1-53

Design Criteria ......................................... 1-55

1.2.2 Verification of the Degree of Success or Failure ................ 1-56

Daylighting ............................................ 1-57

Sealing ............................................... 1-57

Drains ................................................ 1-57

Grout Curtains ......................................... 1-58

Diversion Wells ......................................... 1-58

Implementation Checklist ................................. 1-59

1.2.3 Case Studies ........................................... 1-60

Case Study 1 ........................................... 1-60

Case Study 2 ........................................... 1-64

1.2.4 Discussion ............................................ 1-65

Benefits .............................................. 1-65

Limitations ............................................ 1-65

Efficiency ............................................. 1-66

1.2.5 Summary ............................................. 1-67

1.3 Sediment Control and Revegetation ............................... 1-69

Theory ..................................................... 1-69

Site Assessment .............................................. 1-70

1.3.1 Implementation Guidelines ................................ 1-72

Site Stabilization ........................................ 1-75

Revegetation ........................................... 1-75

Direct Revegetation ................................ 1-78

Channel, Ditch, and Gully Stabilization ....................... 1-79

Channel Linings ................................... 1-80

Check Dams ........................................... 1-81

Silt Fences ............................................ 1-83

Gradient Terraces ....................................... 1-84

Design Criteria ......................................... 1-84

1.3.2 Verification of Success or Failure ........................... 1-86

Implementation Checklist ................................. 1-86

1.3.3 Literature Review/Case Studies ............................. 1-88

Case Study 1 ........................................... 1-88

Case Study 2 ........................................... 1-89

1.3.4 Discussion ............................................ 1-92

Benefits .............................................. 1-92

Limitations ............................................ 1-93
Coal Remining BMP Guidance Manual

Table of Contents iii

1.3.5 Summary ............................................. 1-93

References ............................................ 1-94

Section 2.0 Geochemical Best Management Practices .......................... 2-1

Introduction ........................................................ 2-1

2.1 Sampling .................................................... 2-5

Introduction .................................................. 2-5

Acid-Base Accounting .......................................... 2-6

Components of ABA ...................................... 2-6

Paste pH ......................................... 2-7

Percent Sulfur ..................................... 2-7

Fizz Rating ...................................... 2-10

Neutralization Potential ............................. 2-11

Net Neutralization Potential .......................... 2-11

Information Needed to Conduct an Overburden Analysis ............... 2-12

Preparing for Overburden Analysis Sampling ........................ 2-14

Areal Sampling – A Survey of State Practices .................. 2-14

Operational Considerations ................................ 2-18

Stratigraphic Variation ................................... 2-18

Representative Samples ................................... 2-18

Sample Collection and Handling .................................. 2-20

Sample Collection ....................................... 2-20

Air Rotary (Normal Circulation) ...................... 2-20

Air Rotary (Reverse Circulation) ...................... 2-21

Diamond Core .................................... 2-21

Augering ........................................ 2-23

Highwall Sampling ................................ 2-23

Sample Description (Log) ................................. 2-23

Sample Preparation and Compositing ........................ 2-24

2.2 Alkaline Addition ............................................. 2-29

Theory ..................................................... 2-29

2.2.1 Implementation Guidelines ................................ 2-33

Alkaline Materials ....................................... 2-35

Limestone and Limestone-Based Products ............... 2-36

Coal Ash ........................................ 2-37

Other Alkaline Additives ............................ 2-39

Application Rates ....................................... 2-40

Materials Handling and Placement ........................... 2-43

Alkaline Redistribution ................................... 2-45

Alkaline Addition as a Best Management Practice on Shallow

Overburden ..................................... 2-46

2.2.2 Verification of Success or Failure ........................... 2-47

Implementation Checklist ................................. 2-47

2.2.3 Literature Review and Case Studies ......................... 2-48

Case Study 1 ........................................... 2-51
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iv Table of Contents

Case Study 2 ........................................... 2-54

Case Study 3 ........................................... 2-55

Case Study 4 ........................................... 2-58

2.2.4 Discussion ............................................ 2-59

Benefits .............................................. 2-59

Limitations ............................................ 2-60

Efficiency ............................................. 2-60

2.2.5 Summary ............................................. 2-61

2.3 Induced Alkaline Recharge ...................................... 2-63

Theory ..................................................... 2-63

2.3.1 Implementation Guidelines ................................ 2-64

2.3.2 Verification of Success or Failure ........................... 2-65

2.3.3 Case Studies ........................................... 2-66

Case Study 1 ........................................... 2-66

Case Study 2 ........................................... 2-70

Case Study 3 ........................................... 2-74

2.3.4 Discussion ............................................ 2-74

Benefits .............................................. 2-74

Limitations ............................................ 2-75

Efficiency ............................................. 2-76

2.3.5 Summary ............................................. 2-77

2.4 Special Handling .............................................. 2-79

Theory ..................................................... 2-83

Sampling and Site Assessment ................................... 2-86

Geologic and Geochemical Considerations .................... 2-87

Hydrogeologic Considerations ............................. 2-87

Operational Considerations ................................ 2-90

2.4.1 Implementation Guidelines ................................ 2-90

Geologic and Geochemical Considerations .................... 2-90

Hydrogeologic Considerations ............................. 2-91

Operational Considerations ................................ 2-92

Discussion of Theory .................................... 2-96

Placement above the water table and encapsulation ........ 2-96

Capping ........................................ 2-102

Handling of Acid Materials Using the Submergence or “Dark and Deep”

Technique ...................................... 2-104

Handling of Acid and Alkaline Materials Using Blending Techniques and

Alkaline Redistribution ............................ 2-107

Operational Considerations ............................... 2-109

2.4.2 Verification of Success or Failure .......................... 2-111

Implementation Checklist ................................ 2-111

2.4.3 Case Studies .......................................... 2-112

Case Study 1 .......................................... 2-112

Case Study 2 .......................................... 2-117

Case Study 3 .......................................... 2-117
Coal Remining BMP Guidance Manual

Table of Contents v

Case Study 4 .......................................... 2-118

Case Study 5 .......................................... 2-118

Case Study 6 .......................................... 2-120

2.4.4 Discussion ........................................... 2-120

Benefits ............................................. 2-121

Limitations ........................................... 2-121

Efficiency ............................................ 2-122

2.4.5 Summary ............................................ 2-124

2.5 Bactericides ................................................ 2-127

Introduction ................................................ 2-127

Theory .................................................... 2-127

Site Assessment ............................................. 2-129

2.5.1 Implementation Guidelines ............................... 2-130

2.5.2 Verification of Success or Failure .......................... 2-131

2.5.3 Literature Review/Case Studies ............................ 2-131

Case Study 1 .......................................... 2-135

Case Study 2 .......................................... 2-136

Case Study 3 .......................................... 2-137

Case Study 4 .......................................... 2-137

Case Study 5 .......................................... 2-137

Case Study 6 .......................................... 2-138

2.5.4 Discussion ........................................... 2-138

Benefits ............................................. 2-139

Limitations ........................................... 2-139

Efficiency ............................................ 2-139

2.4.5 Summary ............................................ 2-140

References ........................................... 2-140

Section 3.0 Operational Best Management Practices .......................... 3-1

Introduction ........................................................ 3-1

Theory ............................................................ 3-1

Site Assessment ..................................................... 3-2

3.1 Implementation Guidelines ....................................... 3-4

Rapid Mining and Concurrent Reclamation ........................... 3-4

Off-Site Disposal of Acid-Forming Materials ......................... 3-8

Auger Mining ................................................ 3-11

Stockpiling of Coal ............................................ 3-12

Consideration of Overburden Quality .............................. 3-14

Coal Refuse Reprocessing or Cogeneration Usage .................... 3-16

Maximizing Daylighting ........................................ 3-18

Implementation Checklist ....................................... 3-22

3.2 Verification of Success or Failure ................................. 3-24

Implementation Checklist ...................................... 3-27

3.3 Literature Review / Case Studies ................................. 3-28

3.4 Discussion .................................................. 3-29
Coal Remining BMP Guidance Manual

vi Table of Contents

Benefits .................................................... 3-29

Limitations .................................................. 3-30

Efficiency ................................................... 3-30

3.5 Summary ................................................... 3-31

References .................................................. 3-32

Section 4.0 Passive Treatment Technologies ................................. 4-1

Introduction ....................................................... 4-1

Theory ............................................................ 4-2

Site Assessment ..................................................... 4-3

4.1 Implementation Guidelines ....................................... 4-4

Anoxic Limestone Drains ........................................ 4-4

Constructed Wetlands ........................................... 4-9

Successive Alkalinity-Producing Systems ........................... 4-14

Open Limestone Channels ...................................... 4-18

Oxic Limestone Drains ........................................ 4-21

The Pyrolusite® Process ........................................ 4-22

Alkalinity-Producing Diversion Well .............................. 4-24

Design Criteria ............................................... 4-28

4.2 Verification of Success or Failure ................................. 4-28

Implementation Checklist ....................................... 4-29

4.3 Case Studies ................................................. 4-32

Case Study 1 ................................................ 4-32

4.4 Discussion .................................................. 4-35

Benefits .................................................... 4-35

Limitations .................................................. 4-36

Efficiency ................................................... 4-36

4.5 Summary ................................................... 4-36

References .................................................. 4-37

Section 5.0 Integration of Best Management Practices ......................... 5-1

Regrading and Revegetation ............................................ 5-2

Daylighting ........................................................ 5-4

Coal Refuse Removal ................................................. 5-4

Special Handling with Surface and Ground Water Controls .................... 5-5

Miscellaneous BMP Combinations ....................................... 5-9

Summary ......................................................... 5-10

References ........................................................ 5-11

Section 6.0 Efficiencies of Best Management Practices ......................... 6-1

Limitations ................................................... 6-3

6.1 Pennsylvania DEP – Remining Site Study ............................ 6-5

6.2 Observed Results .............................................. 6-6

6.3 Predicted Efficiencies .......................................... 6-26

6.3.1 Statistical Approach ..................................... 6-26
Coal Remining BMP Guidance Manual

Table of Contents vii

6.3.2 Statistical Results ....................................... 6-28

Individual BMPs ........................................ 6-28

BMP Combinations ...................................... 6-38

6.4 Discussion .................................................. 6-59

6.4.1 Observed Results ....................................... 6-59

Acidity Loading ........................................ 6-60

Iron Loading ........................................... 6-61

Manganese Loading ..................................... 6-64

Aluminum Loading ..................................... 6-65

Sulfate Loading ........................................ 6-67

Flow Rate ............................................ 6-68

6.4.2 Predicted Results ....................................... 6-70

BMPs Implemented Alone ................................ 6-70

BMP Groups .......................................... 6-74

Regrading and Revegetation ......................... 6-75

Daylighting ...................................... 6-78

Regrading, Revegetation, and Daylighting ............... 6-80

Coal Refuse Removal .............................. 6-82

Overall Evaluation ................................. 6-84

Limitations ............................................ 6-85

6.5 Summary ................................................... 6-86

References .................................................. 6-89

Section 7.0 Best Management Practices - Costs ............................... 7-1

Table Summary ..................................................... 7-2

References ........................................................ 7-18
Coal Remining BMP Guidance Manual

viii Table of Contents
Coal Remining BMP Guidance Manual

List of Tables ix

List of Tables

Page

Introduction

Table 1: Number of Stream Miles Impacted by AMD ............................ 3

Table 2: AML Inventory Totals of 4 Major AML Problem Types in Appalachia 

and the U.S, as of September, 1998 ................................. 6

Table 3: Coal Production by State (Short Tons) ................................ 8

Table 4: State by State Profile of Remining Operations. ........................ 11

Table 5: Types of Remining Permits Issued by State ........................... 12

Table 6: Characteristics of Existing Remining Operations by State ................ 13

Table 7: Potential Remining Operations by State .............................. 14

Table 8: Pennsylvania Remining Permits Which Required Treatment, June, 1997 ...... 17

Section 1.0 Hydrologic and Sediment Control Best Management Practices

Table 1.1.3a: Synopsis of Water Quality Data at Case Study 1 Site .................. 1-23

Table 1.1.3b: Synopsis of Water Quality Data at Case Study 2 Site .................. 1-24

Table 1.1.3c: Synopsis of Flow and Pollutant Loading at Case Study 3 Site. ........... 1-27

Table 1.3.1a: Revegetation Practices and Maintenance ............................ 1-77

Section 2.0 Geochemical Best Management Practices

Table 2.1a: Minimum Overburden Analysis Drill Hole Spacing Requirements, by State. 2-15

Table 2.1b: Number of Acres per Overburden Analysis Hole. ..................... 2-17

Table 2.1c: Number of Acres per Overburden Analysis Hole Based on SOAP 

Applications Received in 1993. ................................... 2-17

Table 2.1d: Overburden Interval Sampling Requirements. ....................... 2-25

Table 2.1e: Compositing of Too Many 1-foot Intervals Can Underestimate Acid 

Producing Potential. ........................................... 2-26

Table 2.2.1a: Distribution, Type and Amount of Alkaline Materials Used. ............ 2-34

Table 2.2.1b: Example Analyses of Coal Ash. .................................. 2-35

Table 2.2.1c: Percentage of Sites Producing Net Alkaline Drainage by Net NP without

Thresholds. .................................................. 2-41

Table 2.2.1d: Percentage of Sites Producing Net Alkaline Drainage by Total NP without

Thresholds. .................................................. 2-41

Table 2.2.1e: Percentage of Sites Producing Net Alkaline Drainage by Net NP 

with Thresholds. .............................................. 2-41

Table 2.2.1f: Percentage of Sites Producing Net Alkaline Drainage by Total NP 

with Thresholds. .............................................. 2-42

Table 2.3.3a: Water Quality for Wells at the Case Study 2 Site .................... 2-73
Coal Remining BMP Guidance Manual

x List of Tables

Table 2.4a: EPA Remining Database (Appendix A), Special Handling of Toxic/Acid 

Forming Materials ........................................... 2-80

Table 2.4b: Saturated Thickness in Meters for Wells developed in Appalachian 

Mine Spoil ................................................. 2-89

Table 2.4.3a: Summary of Water Quality for Greene County Site Phases 1 and 2 . ...... 2-118

Table 2.4.3b: Summary of Water Quality Conditions, Alkaline Redistribution Site. ..... 2-119

Section 3.0 Operational Best Management Practices

Table 3.1a: Summary of Overburden Analysis Data from a Surface Mine 

Located in Logan County, West Virginia. ............................ 3-8

Table 3.1b: Total Sulfur in Stratigraphic Sections Enclosing the Coal at a 

Remining Site in Westmoreland County, Pennsylvania. ................. 3-10

Table 3.1c: Coal and Enclosing Strata Sulfur Values. ........................... 3-20

Table 3.1d: Overburden Analysis from an Acid-producing Underground Mine in 

Armstrong County, PA. ........................................ 3-21

Section 4.0 Passive Treatment

Table 4.1: OLC Sizing Calculations . ....................................... 4-20

Table 4.3: Summary of Water Quality Data at Various Points Along a 

Passive Treatment System. ...................................... 4-34

Section 5.0 Integration of Best Management Practices

Section 6.0 Efficiencies of Best Management Practices

Table 6.2a: Pennsylvania Remining Permits, Summary of Observed Water Quality 

Results by Individual BMP. ...................................... 6-8

Table 6.2b: PA Remining Study: Observed Effects of BMP Groupings on Discharges. . . 6-17

Table 6.3a: PA Remining Study: Predicted Odds of Acidity Improvement or Elimination. 6-32

Table 6.3b: PA Remining Study: Predicted Odds of Iron Improvement or Elimination. . . 6-33

Table 6.3c: PA Remining Study: Predicted Odds of Manganese Improvement 

 or Elimination. ............................................... 6-34

Table 6.3d: PA Remining Study: Predicted Odds of Aluminum Improvement 

 or Elimination. ............................................... 6-35

Table 6.3e: PA Remining Study: Predicted Odds of Sulfate Improvement

or Elimination . .............................................. 6-36

Table 6.3f: PA Remining Study: Predicted Odds of Flow Improvement. ............. 6-37

Table 6.3g: Analysis of Discrete Groups based on Observed Acidity Results Using

Regrading and Revegetation as Reference Group.. .................... 6-41

Table 6.3h: Analysis of Discrete Groups based on Observed Iron Results 

Using Regrading and Revegetation as Reference Group.. ............... 6-42
Coal Remining BMP Guidance Manual

List of Tables xi

Table 6.3i: Analysis of Discrete Groups based on Observed Manganese Results 

Using Daylighting as Reference Group. ............................ 6-43

Table 6.3j: Analysis of Discrete Groups based on Observed Aluminum Results 

Using Daylighting as Reference Group. ............................ 6-44

Table 6.3k: Analysis of Discrete Groups based on Observed Sulfate Results 

Using Daylighting as Reference Group. ............................ 6-45

Table 6.3l: Analysis of Discrete Groups based on Observed Flow Results 

Using Daylighting as Reference Group. ............................ 6-46

Table 6.3m: Analysis of Discrete Groups based on Observed Acidity Results Using 

Daylighting as Reference Group. ................................. 6-47

Table 6.3n: Analysis of Discrete Groups based on Observed Iron Results Using

Daylighting as Reference Group. ................................. 6-48

Table 6.3o: Analysis of Discrete Groups based on Observed Manganese Results

Using Daylighting as Reference Group.. ............................ 6-49

Table 6.3p: Analysis of Discrete Groups based on Observed Aluminum Results

Using Daylighting as Reference Group. ............................ 6-50

Table 6.3q: Analysis of Discrete Groups based on Observed Sulfate Results

Using Daylighting as Reference Group.. ............................ 6-51

Table 6.3r: Analysis of Discrete Groups based on Observed Flow Results

Using Daylighting as Reference Group.. ............................ 6-52

Table 6.3s: Analysis of Discrete Groups based on Observed Acidity Results

Using Regrading, Revegetation, and Daylighting as Reference Group. ..... 6-53

Table 6.3t: Analysis of Discrete Groups based on Observed Iron Results

Using Regrading, Revegetation, and Daylighting as Reference Group. ..... 6-54

Table 6.3u: Analysis of Discrete Groups based on Observed Manganese Results

Using Regrading, Revegetation, and Daylighting as Reference Group. ..... 6-55

Table 6.3v: Analysis of Discrete Groups based on Observed Aluminum Results

Using Regrading, Revegetation, and Daylighting as Reference Group. ..... 6-56

Table 6.3w: Analysis of Discrete Groups based on Observed Sulfate Results

Using Regrading, Revegetation, and Daylighting as Reference Group. ..... 6-57

Table 6.3x: Analysis of Discrete Groups based on Observed Flow Results

Using Regrading, Revegetation, and Daylighting as Reference Group. ..... 6-58

Table 6.4a: Types of Mining and Minimal BMPs. .............................. 6-74

Section 7.0 Unit Costs of Best Management Practices

Table 7a: Alkaline Addition. ............................................. 7-3

Table 7b: Anoxic Limestone Drains (ALDs) . ................................. 7-4

Table 7c: Ash Fill Placement . ............................................ 7-5

Table 7d: Bactericides . ................................................. 7-6

Table 7e: Check Dams . ................................................. 7-7

Table 7f: Constructed Wetlands . .......................................... 7-8

Table 7g: Daylighting .. ................................................. 7-9

Table 7h: Diversion Ditch . ............................................. 7-10
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xii List of Tables

Table 7i: Diversion Wells, Alkalinity Producing ............................. 7-11

Table 7j: Drains, Pit Floor . ............................................. 7-12

Table 7k: Regrading of Abandoned Mine Spoil/Highwalls . ..................... 7-13

Table 7l: Revegetation . ............................................... 7-14

Table 7m: Sealing and Rerouting of Mine Water from Abandoned Workings . ....... 7-15

Table 7n: Silt Fences . ................................................. 7-16

Table 7o: Special Handling for Toxic and Acid Forming Materials . ............... 7-17
Coal Remining BMP Guidance Manual

List of Figures xiii

List of Figures

Page

Introduction

Figure 1: Percentage of Total Number of Rahall Permits Issued by State ....... 15

Figure 2: Status of 260 Pennsylvania Remining Permits .................... 17

Figure 3: Percentage of Streams with a pH less than 6.0 for 24 Watersheds in the

Appalachian Basin ......................................... 28

Figure 4: Percentage of Surface Water Sample Stations with Sulfate Greater than 

75 mg/L for 24 Watersheds in the Appalachian Basin .............. 29

Figure 5: Statigraphic Variation of Sulfur Content of 34-Coal Beds of the Cental 

Appalachians ............................................. 30

Figure 6: Example of Steep Topography and High Relief in Southern West 

Virginia Showing Multiple Contour Strip Mines on Steep Slopes ..... 32

Figure 7: Example of Moderate Slopes and Broader Valleys and Hilltops in 

West-central Pennsylvania Showing Small Area Mines ............. 33

Figure 8: Topographic Map Illustrating Contour Surface Mining ............. 34

Figure 9: Topographic Map Illustrating Area Surface Mining ................ 35

Section 1.0 Hydrologic and Sediment Control Best Management Practices

Figure 1.1.1a: Diagram of the Location of Surface Cracks Between Highwall

and Backfill ............................................ 1-10

Figure 1.1.1b: Schematic Diagram of a Cap Instilled on a Reclaimed Surface Mine . . . 1-12

Figure 1.1.3a: Acidity Concentration at Discharge Point MD-12 Before and 

After Remining ......................................... 1-25

Figure 1.1.3b: Acidity Load at Discharge Point MD-12 Before and After Remining . 1-25

Figure 1.2a: Typical Correlation Between Discharge Flow and Pollutant Loading 

in Mine Drainage Discharges. .............................. 1-33

Figure 1.2.1a: Example of Mine Subsidence and Exposed Fractures ............ 1-36

Figure 1.2.1b: Exposed Auger Holes. ................................... 1-40

Figure 1.2.1c: Example of a Mine Entry Seal .............................. 1-41

Figure 1.2.1d: Example of a Virginia-Type Mine Entry Seal ................... 1-42

Figure 1.2.1e: Example of a Mine Drain System ........................... 1-43

Figure 1.2.1f: Cross Section of an Example Chimney Drain ................... 1-45

Figure 1.2.1g: Cross Section of Horizontal Highwall Drains .................. 1-46

Figure 1.2.1h: Pit Floor Drain Patterns .................................. 1-48

Figure 1.2.1i: Pit Floor Drain ......................................... 1-49

Figure 1.2.1j: Common Drilling Pattern for Pressure Grouting Wells. ........... 1-52

Figure 1.2.3a: Change in Flow Over Time (Case Study Discharge MP-1). ........ 1-61

Figure 1.2.3b: Change in Flow Over Time (Case Study Discharge MP-4) ........ 1-61
Coal Remining BMP Guidance Manual

xiv List of Figures

Figure 1.2.3c: Flow Rate Reduction, Pre- and Post-Remining Periods (Case Study

Discharge MP-4). ....................................... 1-62

Figure 1.2.3d: Flow Rate Reduction, Pre- and Post-Remining Periods (Case Study

Discharge MP-6) ........................................ 1-63

Figure 1.3.1a: Example of a Rock Check Dam ............................ 1-82

Figure 1.3.1b: Example of a Gabion Check Dam .......................... 1-83

Section 2.0 Geochemical Best Management Practices

Figure 2.2a: Solubility of Calcium Carbonate in Water at 25OC as a Function of 

Partial Pressure of CO2.. .................................. 2-32

Figure 2.2.3a: Water Quality Before and After Mining at the Keating #2 Site, 

Clinton, PA ............................................ 2-53

Figure 2.2.3b: Water Quality Before and After Mining at the Case Study 2 Site .... 2-54

Figure 2.2.3c: Water Quality at the Case Study 3 Site ....................... 2-56

Figure 2.3.1a: Alkaline Recharge Channels and Capped Acid-producing 

Material Pods .......................................... 2-65

Figure 2.3.3a: Topography, Location of Recharge Trenches and Funnels, and 

Locations of Seeps (Case Study 1, Upshur County, WV) ......... 2-67

Figure 2.3.3b: Plot of Acidity versus Time for Seep #2 at Case Study 1 Mine ..... 2-69

Figure 2.3.3c: Map of Case Study 2 Site ................................. 2-72

Figure 2.4a: Early Recommendation of the Pennsylvania Sanitary Water Board for

Handling Sulfuritic Material ............................... 2-85

Figure 2.4b: High and Dry Placement of Acidic Material .................... 2-86

Figure 2.4.1a: Overburden Handling Procedures Depending on the Stratigraphic 

Position of Acid-producing Materials ........................ 2-94

Figure 2.4.1b: Overburden Handling Procedures Depending on the Stratigraphic 

Position of Acid-producing Materials. ........................ 2-94

Figure 2.4.1c: Three-dimensional Conceptual View of High and Dry Placement 

of Acid-forming Materials.. ................................ 2-97

Figure 2.4.1d: Projected Target Zone Determination for Placement of Acid 

Forming Material within the Backfill ......................... 2-99

Figure 2.4.1e: Schematic of Special Handling of Acid-forming Materials by the

Submergence Technique ................................. 2-106

Figure 2.4.1f: Blending and Alkaline Redistribution Do Not Require the Isolation 

of Acid-forming Materials in Isolated Pads ................... 2-110

Figure 2.4.3a: Distribution of Sulfur and Neutralization Potential for Bedrock at 

the Special Handling Site in Clarion County, PA. .............. 2-112

Figure 2.4.3b: Distribution of Sulfur and Neutralization Potential for Spoil in the 

Northern Hilltop where Bulldozers and Loaders Were Used ...... 2-115

Figure 2.4.3c: Distribution of Sulfur and Neutralization Potential for Spoil in the 

Southern Hilltop Where a Dragline was Used ................. 2-116

Figure 2.5a: Rates of Pyrite Oxidation with and without Iron-oxidizing Bacteria . 2-128

Figure 2.5.3a: Effect of Anionic Detergents on Acid Production from Pyritic Coal. . 2-132
Coal Remining BMP Guidance Manual

List of Figures xv

Figure 2.5.3b: Measured Profiles of Oxygen in Unsaturated Spoil ............. 2-133

Figure 2.5.3c: Oxygen Cncentration with Depth in Coal Refuse in Pennsylvania

and Ohio ............................................. 2-134

Figure 2.5.3d: Effect of Sodium Lauryl Sulfate on Runoff Water Quality at an 8-acre

Active Coal Refuse Pile in Northern West Virginia ............. 2-136

Section 3.0 Operational Best Management Practices

Figure 3.1a: Relationship Between the Solubility of Calcium Carbonate and the 

Partial Pressure of Carbon Dioxide at 25EC. .................... 3-6

Figure 3.1b: Advective Impacts on Unreclaimed Mine Spoil .................. 3-6

Figure 3.1c: Potential Sources of Pit and Tipple Cleanings. ................... 3-9

Section 4.0 Passive Treatment

Figure 4.1a: Anoxic Limestone Drain Construction ......................... 4-6

Figure 4.1b: Commonly Constructed Wetland Diagram. .................... 4-12

Figure 4.1c: Typical Wetland Cell Cross Section. ......................... 4-13

Figure 4.1d: Example of a Successive Alkalinity-Producing System Cell. ....... 4-16

Figure 4.1e: Typical Alkalinity-Producing Diversion Wells. .................. 4-25

Figure 4.1f: Example of Water Intake Portion of an Alkalinity-Producing

Diversion Well. ......................................... 4-26

Section 5.0 Integration of Best Management Practices

Figure 5.0a: Water Table Suppression in Conjunction with Special Handling of 

Acidic Material. ......................................... 5-6

Figure 5.0b: Optimal Location for Special Handling of Acidic and Alkaline 

Materials.. .............................................. 5-8

Section 6.0 Efficiencies of Best Management Practices

Figure 6.4a: Impacts of BMP Combinations on Acidity Loading.. ............. 6-61

Figure 6.4b: Impacts of BMP Combinations on Iron Loading. ................ 6-63

Figure 6.4c: Impacts of BMP Combinations on Manganese Loading. .......... 6-65

Figure 6.4d: Impacts of BMP Combinations on Aluminum Loading. ........... 6-66

Figure 6.4e: Impacts of BMP Combinations on Sulfate Loading. ............. 6-68

Figure 6.4f: Impacts of BMP Combinations on Flow Rate. .................. 6-69

Section 7.0 Best Management Practices - Costs
Coal Remining BMP Guidance Manual

xvi List of Figures
Coal Remining BMP Guidance Manual

Glossary and Acronyms xvii

Glossary and Acronyms

Abiotic: Pertaining to the absence of plant and animal activity or mode of living.

Acid-Forming Materials (AFMs): Rocks (enclosing strata) and processed mine wastes that have

appreciable amounts of reactive sulfides. These sulfides are mainly iron disulfides in the form of

pyrite and marcasite, and will oxidize and subsequently combine with water to produce acidity

and yielding significant amounts of iron and sulfate ions.

Aerobic: A term used to describe organisms that only live in the presence of free oxygen. It is

also used to describe the activities of these organisms. 

Alkaline addition: The practice of adding alkaline-yielding material into a mine site where the

overburden analysis indicates that there is a net deficiency of natural alkalinity. Alkaline material

used to perform this task is commonly limestone, various lime wastes, or alkaline CCW.

Anaerobic: A term used to describe organisms that live in the absence of free oxygen. It is also

used to describe the activities of these organisms. 

Anoxic: An environment (gaseous or aqueous) with virtually no available free oxygen. Oxygen

required for chemical reactions or for organisms is severely limited. Little or no chemical and

biological activity that requires oxygen can occur. Water with less than 0.2 mg/L dissolved

oxygen may be considered anoxic.

Anoxic Limestone Drains (ALDs): Drains composed of limestone that are constructed and

covered to prevent the introduction of atmospheric oxygen to the system. Mine drainage is

diverted through these drains to increase the alkalinity and without the armoring of the limestone

by the iron in the water. The iron in the mine water must be in the ferrous state (Fe2+) and the

aluminum concentration must be relatively low in order for these systems to work properly over

the long term.

Anionic surfactants: Any of a number of cleansing detergents that act as bactericides, thus

inhibiting the presence of iron-oxidizing bacteria.

Anisotropic: A medium that exhibits different properties (e.g., hydraulic conductivity, porosity,

etc.) in each direction measurement. 

Anticline: A generally convex upward fold in sedimentary rocks where the rock in the core of the

fold is older than those on the flanks. The opposite of a syncline.
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xviii Glossary and Acronyms

Aquifer: A relatively permeable rock unit or stratigraphic sequence. Aquifers are saturated units

that are permeable enough to produce economic quantities of water at wells or springs.

Aquifer tests: A variety of hydraulic tests conducted with the use of a well to determine porosity,

permeability, and other properties of the rock unit tested. These tests usually involve the addition

or removal of a measured volume of water or a solid with respect to time, while the response of

the aquifer is measured in that well and/or other nearby wells.

Aquitard: Less permeable units in a stratigraphic sequence. These units are not impermeable, but

only permeable enough to be important on a regional ground-water system basis. Wells in

aquitards are not able to produce sufficient amounts of water for domestic or commercial use.

Auger mining: To extract coal from a highwall by drilling into the coal by the use of a horizontal

augering equipment. This is employed when removal of additional (thicker) overburden is not

economical.

Bactericide: Any of a number of materials that are used to kill bacteria, such as anionic

surfactants.

Baseline: Pre-mining environmental conditions, specifically, pre-mining pollutant loading in preexisting discharges. Baseline levels of pollutants can be used for comparison monitoring during

mining activity.

Bench: This term can be used in at least two distinct contexts in regards to mining. First it can

refer to a particular part of a coal seam split by a noncoal unit (e.g., shale, claystone), for example

a “lower bench”. A second definition can refer to a land form where a nearly flat level area is

created along a slope with steeper areas above and below.

Bentonite: An encompassing term for variety or mixture of clays (primarily montmorillonite) that

swell in water. Bentonite is used commercially used as a sealant in wells and for creating low

permeability barriers.

Best Management Practice (BMP): Relative to remining, and as used in this document, BMPs

are mining or reclamation procedures, techniques, and practices that, if properly implemented, will

(1) cause a decrease in the pollution load by reducing the discharge rate and/or the pollutant

concentration, (2) reduce erosion and sedimentation control problems, and/or (3) result in

improved reclamation and revegetation of abandoned mine lands. 

Biosolids: A general term for the residual solid fraction, primarily organic material, of processed

sewage sludge. A similar term is biosludge, which can be derived from other organic sources,

such as paper mill waste.

Biotic: Pertaining to plant and animal activity and mode of living.
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Glossary and Acronyms xix

Bone coal: A relatively hard high-ash coal grading toward a carbonaceous shale, a high-organic

content shale. 

Buffer: The ability of a solution to resist changes in pH with the addition of an acid or a base.

Calcareous shale: A shale with a significant calcium carbonate content. The calcium carbonate

content is sufficient to yield alkalinity with contact with ground water.

Carbonaceous: An organic-rich (carbon) rock, such as coal, “bone” coal, and organic-rich black

shale.

Cast-blasting: A method of directional overburden removal blasting.

Check dam: An above grade structure placed bank to bank across a channel/ditch (usually with

its central axis perpendicular to flow) for the purpose of controlling erosion. Check dams are

commonly composed of rip rap, earthen materials, or hay bales.

Chimney drain: A highly transmissive vertical drain composed of large rock fragments that will

intersect ground water coming in from the highwall or the surface and rapidly directing this water

through and away from the main body of the mine spoil.

Claystone: A clay-rich rock exhibiting the some of the induration of shales, but without the thin

layering (laminations) or fissility (splits easily into thin layers). 

Coal Combustion Wastes (CCW): The residual material remaining from the process of burning

coal for power generation and for other purposes. CCW includes fly ash, bottom ash, flue gas

desulfurization wastes, and other residues. CCW may also include the by-product of limestone

used for desulfurization during the combustion process. 

Coal Refuse: The waste material cleaned from freshly-mined coal after it is excavated from the

pit or brought from underground. Coal refuse is commonly composed of carbonaceous shale,

claystone, bone coal, and minor to substantial amounts of “good” coal. 

Confidence Interval: The range of values around a statistic (for example, the median) in which

the true population value of the statistic occurs with a given probability (often 95 percent).

Culm: Term used in the anthracite district of Pennsylvania when referring to coal refuse.

Daylighting: To surface mine through abandoned underground mine workings by the removal of

the overlying strata to access the remaining coal. Overburden removal exposes the remaining coal

pillars.
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xx Glossary and Acronyms

Diagenesis: The chemical, physical, and biologic actions (e.g., compaction, cementation,

crystallization, etc.) that alter sediments after deposition, exclusive of metamorphism and surficial

weathering.

Dragline: A large crane-like type of earth moving equipment that employs a heavy cable or line

to pull a excavating bucket through the material to be removed (overburden rock), thus filling it.

The bucket is then lifted, moved to away, and dumped. 

Drawdown: The measured lowering of the water level in a well ( or aquifer) from the withdrawal

of water. It is reported as the difference between the initial water level and the level during or

after the withdrawal.

Diversion ditch: A ditch engineered and installed to collect surface water runoff and transport it

away from down gradient areas. These ditches are commonly installed to control runoff.

Evapotranspiration: The water loss from the land surface to the atmosphere caused by direct

evaporation and transpiration from plants.

Exsolve: The process by which where two materials, such as a gas and a liquid, unmix. For

example, when carbon dioxide (CO2) comes out of solution from water into the atmosphere.

Geotextiles: Any of a variety of manufactured materials (e.g., plastic sheeting) that are used to

prevent or impede the movement of ground water vertically or laterally or prevent erosion.

Ground-Water diversion well: A water well installed and designed to intercept and collect a

significant amount ground water, thus preventing the ground water from reaching an undesirable

area down gradient.

Grout curtain: A low or nearly impermeable barrier created in strata or fill by the use of pressure

grouting via a series of injection wells. In theory, the fractures and other pore spaces are filled

with a low permeability grout thus impeding ground-water movement. 

Highwall: The highest exposed vertical face of the coal and overburden of a surface mine at any

given time during mining. The final highwall is the maximum extent of surface mining.

Hummocky: Used to describe highly uneven topography, commonly composed of a series of

small irregularly-rounded hills or hummocks.

Hydraulic conductivity: The flow rate of ground water through a permeable medium. The flow

rate is given in distance over time (velocity), such as meters per second (m/s). 

Hydrologic: Pertaining to ground and/or surface water systems.
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Glossary and Acronyms xxi

Hydrologic unit: A term used to describe an area where infiltrating waters will drain to a point or

a series of related points. The area is hydrologically distinct and isolated from adjacent hydrologic

units.

Hydrolyze: Chemical reactions involving water, where H+ or OH- ions are consumed in the

process.

Hydrothermal: Chemical and physical activity pertaining to hot ground water associated with

underlying igneous activity.

Induced Alkaline Recharge: Systems installed in surface mines to introduce recharge of alkaline

charged waters to treat or abate the production of acid mine drainage. Surface water is diverted to

where it contacts trenches or “funnels” filled or lined with alkaline rocks (e.g., limestone). These

trenches are closed systems that induce this water to infiltrate and recharge the spoil.

Infiltration: The downward flow of water into the land surface through the soil or lateral groundwater flow from one area to another.

Interaction: The effect of a variable (for example, the presence or absence of a BMP) on a

variable of interest (for example, the change in a discharge) is significantly effected by a third

variable (for example, the presence or absence of another BMP).

Interfluves: Regions of higher land lying between two streams that are in the same drainage

system.

Logistic Regression Model: A statistical method of evaluating the relationship between one or

more variables on a variable with a discrete (countable) number of outcomes.

Lowwall: A exposed vertical face of the coal and overburden generally representing the lowest

cover to be encountered. Common to mines where the coal is not mined completely out to the

coal outcrop and frequently spatially opposite to the location of the highwall.

Metamorphic: The mineralogical, chemical, and structural alteration of buried sediments and

rock from heat and pressure.

Mine spoil: Overburden strata (rock) broken up during the course of surface mining and replaced

once the coal is removed. Particle sizes in the backfill (spoil) range from clay-size to those

exceeding very large boulders.

Odds: The probability of an event occurring divided by the probability of an event not occurring.
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xxii Glossary and Acronyms

Odds ratio: The odds of an event occurring divided by the odds of a second event occurring,

used to compare how likely two different events are.

Oxic: An environment (gaseous or aqueous) with readily available free oxygen (oxygen not

limited for typical chemical reactions or for organisms that require it). 

Oxic Limestone Drains: These are limestone drains that are partially open to the atmosphere.

These drains induce elevated CO2 concentrations to build up, which in turn causes an aggressive

limestone dissolution and alkalinity production, thus preventing armoring from the iron in the

water. 

Open Limestone Channels: These are limestone drains that are open to the atmosphere. Some

research has indicated that even armored with iron these drains may impart 20 percent of the

alkalinity that unarmored limestone will yield.

Outcrop: The exposure where a specific rock unit intersects the earths surface. The outcrop can

be covered with a thin layer of surficial material such as colluvium. 

Parting: A noncoal unit that commonly separates parts (benches) of a coal seam. Parting rock

commonly consists of shale, claystone, or bone coal. Sometimes called a binder.

Passive treatment: Methods of mine drainage treatment requiring minimal maintenance after the

initial installation. Passive treatment systems include but are not limited to aerobic and anaerobic

wetlands, successive alkaline producing systems, and anoxic limestone drains.

Permeability: The ability of a rock or sediment to transmit a fluid (e.g., water). It is directly

related to interconnectedness of the void spaces and the aperture widths. 

Pillar: A solid block of coal remaining after conventional underground mining (room and pillar)

mining has occurred.

Piping: The action of substantial volumes of ground water transporting fine-grained sediments

through unconsolidated materials, such as mine spoil, leaving large conduits or voids in the

process. 

Pit Cleanings: Noncoal material (e.g., seat rock, roof rock or parting material) separated from

the saleable coal at the mine pit. This material commonly contains elevated sulfur values and is

usually potentially acid producing.

Pit floor drains: As the name implies, these are drains that are installed in or along the pit floor to

collect and rapidly transmit ground water through and away from the spoil. They are commonly

constructed of perforated drain pipe covered in limestone or sandstone gravel.
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Glossary and Acronyms xxiii

Pore gas: Gases located and stored in the interstitial or pore spaces in soil, spoil, or other earthen

materials above the water table.

Porosity: The ratio of open or void space volume compared to the total volume of rock or

sediment. Commonly given in units of percent.

Pozzolonic: A property of a material to be, to some degree, self-cementing.

Pre-existing discharge: Pollutional discharge resulting from mining activities prior to August 3,

1977 and not physically encountered during active mining operations. Under the Rahall

Amendment to the Clean Water Act, a pre-existing discharge is defined as any discharge existing

at the time of permit application.

Probability: On a scale of 0-100, how frequently a given event (for example, a discharge

improving) would occur.

Pyrolusite® systems: A large open limestone bed that mine water is allowed to slowly pass

through. The system is inoculated with “specially developed bacteria” to promote the formation

pyrolusite (an manganese oxide), thus removing manganese from solution. More recent research

indicates that the mineral formed is todorokite (a hydrated manganese, calcium, magnesium oxide)

and the bacteria that aid this mineral formation most likely exist within the system naturally

without inoculation.

Remining: Surface mining of abandoned surface and/or underground mines for which there were

no surface coal mining operations subject to the standards of the Surface Mining Control and

Reclamation Act. Remining operations implement pollution prevention techniques while

extracting coal that was previously unrecoverable.

Rill: Small erosional gully or channel created by runoff.

Rip rap: Materials (rock, cobbles, boulders, straw) placed on a stream bank, ditch or filter as

protection against erosion.

Rivulet: A small stream or streamlet that develops from rills, commonly located on steep slopes.

Sample Median: In a set of numbers, the value where the number of results above and below the

value are equal.

Scarification: The act of making a series of shallow incisions into the pit floor, topsoil, or other

surface to loosen or break up the material to foster beneficial actions, such as exposure of alkaline

material or promote plant growth.

Seep: A low-flowing surface discharge point for ground water. A low-flow spring.
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xxiv Glossary and Acronyms

Shoot and shove mining: A pre-SMCRA mining method that involved shooting or blasting the

overburden and pushing (shoving) it down the hillside. This type of operation was most common

in steeply-sloped regions, and resulted in abandoned highwalls, exposed pit surfaces, and

steep abandoned spoil piles below the mine.

Shotcrete: A mixure of portland cement, water, and sand that can be pumped under pressure

applied (sprayed) via a hose. It is commonly used for sealing in underground mines and for

surface features, such as streams. Also called gunite.

Special handling: A process where potentially acidic or alkaline material is segregated

(stockpiled) during surface mining and selectively placed during reclamation in lifts or pods the

backfill with respect to the projected post-mining water table and/or the final ground surface. 

Spoil swell: The increase in volume exhibited by mine spoil over the original volume the material

prior to mining. Swell values can approach 25 percent in some regions.

Stemming: Inert material placed in blast holes above and between the explosive material to

confine the energy of the explosion and maximize the breaking of the rock.

Stoichiometric: Used to describe the proportions of elements that combine during, or are yielded

by, a chemical reaction.

Stress-relief fractures: Fractures in rock which form at relatively shallow depths caused by

relaxation from the removal of the overlying rock mass from erosion. The retreat of glaciers in the

northern Appalachian Plateau also may have aided the formation of these fractures. They are most

common at depths of 200 feet or less.

Subaerial: Used to describe processes or resulting conditions from exposure to the atmosphere at

or near the lands surface.

Suboxic: An environment (gaseous or aqueous) with very low concentrations of free oxygen. The

levels are not low enough to be considered anoxic, but are suppressed to the degree that chemical

and biological activity are controlled and attenuated.

Successive Alkaline Producing System (SAPS): A series of passive treatment systems that mine

water is passed through by which alkalinity is imparted from sulfate reduction and limestone

dissolution.

Syncline: A generally concave upward fold in sedimentary rocks where the rocks in the core of

the fold are younger. The opposite of a anticline.

Tipple refuse (cleanings): The waste material left after raw coal is run through a “cleaning

plant”. It usually has an elevated sulfur content.
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Glossary and Acronyms xxv

Turbulent flow: Flow characterized by irregular, tortuous, and heterogeneous flow paths. 

Vadose zone: Zone of aeration above the water table, unsaturated zone.

Water year: According to the United States Geological Survey (USGS) a water year occurs

between October 1 and September 30.

Acronyms and Abbreviations

ABA: acid-base accounting

AFM: acid-forming material

ALD: anoxic limestone drains

AMD: acid mine drainage

AML: abandoned mine land

AMLIS: Abandoned Mine Land Inventory System

AOC: approximate original contour

ASTM: American Society for Testing and Materials

BAT: Best Available Technology Economically Achievable

BMP: Best Management Practice

BPJ: Best Professional Judgement

BPT: Best Practicable Control Technology

C: centigrade

CCW: coal combustion wastes

CFR: Code of Federal Regulations

cfs: cubic feet per second

CWA: Clean Water Act

cm: centimeter(s)

DO: dissolved oxygen

DOE: Department of Energy

ENR: Engineering News Record

EPA: Environmental Protection Agency

EPRI: Electric Power Research Institute

FIFRA: Federal Insecticide, Fungicide and Rodenticide Act

fps: feet per second

FRP: Federal Reclamation Program

gdm: grams per day per meter squared

GIS: Geographic Information System

gpm: gallons per minute

IMCC: Interstate Mining Compact Commission

L/min: liters per minute

lbs/day: pounds per day
Coal Remining BMP Guidance Manual

xxvi Glossary and Acronyms

lbs/ft3: pounds per cubic feet

mg/L: milligrams per liter

MPA: maximum potential acidity

m/s: meters per second

mt: metric tonnes

NNP: net neutralization potential

NP: neutralization potential

NPDES: National Pollutant Discharge Elimination System

NSPS: New Source Performance Standards

OBA: overburden analysis

OLD: oxic limestone drain

OLC: open limestone channel

OSMRE: Office of Surface Mining and Reclamation Enforcement

PA DEP: Pennsylvania Department of Environmental Protection

ppt: parts per thousand

psi: pounds per square inch

PVC: polyvinyl chloride

RAMP: Rural Abandoned Mine Program

RUSLE: Revised Universal Soil Loss Equation

SAPS: successive alkalinity-producing systems

SLS: sodium lauryl sulfate

SMCRA: Surface Mining Control and Reclamation Act

SOAP: Small Operator Assistance Program

SOS: Standard of Success

TCLP: Toxicity Characteristic Leaching Procedure

TMAT: Total Mined Area Triangle

TSS: total suspended solids

TVA: Tennessee Valley Authority

USBM: United States Bureau of Mines

USDA: United States Department of Agriculture

USGS: United States Geological Survey

USLE: Universal Soil Loss Equation

WPA: Works Progress Administration
Coal Remining BMP Guidance Manual

Executive Summary xxvii

Executive Summary

Purpose 

This manual was created to support EPA’s proposal of a Remining subcategory under existing

regulations for the Coal Mining industry. The purpose of this guidance manual is to assist

operators in the development and implementation of a best management practice (BMP) plan

specifically designed for a particular remining operation. This guidance manual also was

developed to give direction to individuals reviewing remining applications and associated BMP

plans. This document is not intended as a substitute for thoughtful and thorough planning and

decision making based on site-specific information and common sense.

Organization

This manual is organized to function as a user’s guide to meet remining plan requirements and to

improve abandoned mine land conditions during remining operations. The manual is divided into

the following sections: 

C Introduction - presenting state-specific abandoned mine land conditions, industry profile

information, the status of remining operations, and general information regarding remining

BMPs; the scope of pre-Surface Mining Control and Reclamation Act (SMCRA) mining

and associated acid mine drainage contamination

C Sections 1.0 through 5.0 - describing hydrologic, sediment and geochemical control BMP

implementation practices, site assessment required to determine implementation of these

practices, implementation guidelines, design considerations, and case studies; 
Coal Remining BMP Guidance Manual

xxviii Executive Summary

C Section 6.0 - detailing the efficiency of remining BMPs in regards to the water quality of

pre-existing discharges; 

C Section 7.0 - providing BMP implementation unit cost information;

C Appendix A - presenting EPA Coal Remining Database and including summary data and

information from 61 state remining and abandoned mine land (AML) project data

packages;

C Appendix B - presenting summary data from the Pennsylvania Remining Study of 112

closed remining operations affecting 248 pre-existing discharges; and

C Appendix C - presenting responses to the Interstate Mining Compact Commission (IMCC)

remining solicitation sheet from 20 member states.

Details of the contents of each section are provided in the Section Outline.

Limitations 

This manual provides information on many hydrologic and geochemical control BMPs which can

be used to prevent or reduce pollution loading from abandoned mine lands during remining

operations. This manual describes the best management practices and controls, provides guidance

on how, when, and where to use them, and recommends maintenance procedures. However, the

effectiveness of these controls lies fully in the hands of those individuals responsible for site

operations. Although specific recommendations are offered in the following chapters, careful

consideration must be given to selecting the most appropriate control measures based on sitespecific features and conditions, and on properly installing the controls in a timely manner. Finally,

although this manual provides guidelines for maintenance, it is up to the responsible party to make

sure controls are carefully maintained or they will prove to be ineffective.

This manual is not intended as a stand-alone document in terms of BMP plan development and

implementation. Additional information sources pertaining to remining and various aspects of 
Coal Remining BMP Guidance Manual

Executive Summary xxix

BMPs can and should be consulted. Many of these information sources are referenced throughout

this guidance manual. This manual is intended for use by individuals with the background or

experience to adequately understand the technical aspects detailed herein. Those individuals

charged with developing, reviewing, implementing, and enforcing remining BMP plans, must be

knowledgeable of all aspects of remining operations (e.g., hydrology, geochemistry, mining

operations, etc.), and must be able to modify them when appropriate.

Results Summary

Review of existing data and information that was used to prepare this document indicates that

remining operations accompanied by proper implementation of appropriate BMPs is highly

successful in reducing the pollution load of mine drainage discharges. The information also shows

that remining BMPs typically are used in combination as part of an overall and site-specific BMP

plan. Critical to the effectiveness of a BMP plan in terms of water quality and AML improvement

is that the plan is well designed and engineered, implemented as proposed, and that the

implementation and subsequent post-mining results are verifiable. 
Coal Remining BMP Guidance Manual

xxx Executive Summary
Coal Remining BMP Guidance Manual

Introduction 1

Introduction

Environmental Conditions

Acid drainage from abandoned underground and surface coal mines and coal refuse piles is the

most chronic industrial pollution problem in the Appalachian Coal Region of the Eastern United

States. It has been estimated that there are currently over 1.1 million acres of abandoned coal

mine lands, over 9,709 miles of streams polluted by acid mine drainage (AMD), 18,000 miles of

abandoned highwalls, 16,326 acres of dangerous spoil piles and embankments, and 874 dangerous

impoundments (IMCC, 1998; Lineberry and others, 1990; OSMRE, 1998). Prior to the passage

of the federal Surface Mining Control and Reclamation Act (SMCRA) of 1977 reclamation of

mining sites was not a federal requirement and therefore, often was not done. However, some

states did have reclamation requirements prior to 1977. Of the land disturbed by coal mining

between 1930 and 1971, roughly only 30 percent has been reclaimed (Lineberry and others,

1990). 

One of SMCRA’s goals was to promote the reclamation of mined areas left without adequate

reclamation prior to the enactment of SMCRA and which continue, in their unreclaimed

condition, to substantially degrade the quality of the environment, prevent or damage the

beneficial use of land or water resources, or endanger the health or safety of the public.

Waters Impacted by Pre-SMCRA Mining

Problematic mine drainage forms when air and water come into contact with certain minerals in

rocks associated with mining. Pyrite and other sulfide minerals in rocks associated with coal react

with oxygen and water to form acid and yield dissolved metals (such as aluminum, iron, and

manganese). The acidity and dissolved metals then contaminate surface and ground water. The

production of acid mine drainage can occur during several phases of the mining process, and 
Coal Remining BMP Guidance Manual

2 Introduction

can continue well after the mine has closed. In Great Britain, for example, Roman mine sites

dating back 2,000 years continue to generate acid mine drainage today (USGS, 1998).

Streams that are impacted by acid mine drainage characteristically have low pH levels (less than

6.0, standard units) and contain high concentrations of sulfate, acidity, dissolved iron, and other

metals. These conditions commonly will not support fish or other aquatic life. Even if the acid

was neutralized (pH raised), the metals will precipitate and coat the stream bed, making it

unsuitable for supporting aquatic life. Additionally, the impact of mine drainage on the waterway

aesthetics results in undesirable conditions for visitors and recreational users (EPA Region III and

OSM, 1997).

Acid mine drainage can result from both surface and underground coal mining and from coal

refuse piles. In surface mining, the rock overlying the coal (overburden) is excavated, and in the

process, broken into a range of large to small rock fragments which are replaced in the pit after

the coal is removed. This exposes the acid-forming minerals in some rocks to air and water

resulting in a high probability of AMD formation, if such minerals are present in sufficient

quantities. In underground mining, large reservoirs of AMD may form in the cavern-like

passageways below the earth surface. These reservoirs are constantly replenished by groundwater movement through the mineral-bearing rocks, creating more AMD. Water from these

“mine pools” seeps through the hillsides or flows freely from abandoned mine entries, enters

streams, and deposits metal-rich precipitates on the substrate downstream. Coal refuse piles often

contain excessive amounts of pyritic materials and water flowing through the piles can become

highly acidic.

Mine drainage discharges can be as small as an unmeasurable flow, or they may be huge torrents

of thousands of gallons per minute. Receiving streams frequently do not contain sufficient

alkalinity to neutralize the additional acid, thus its water quality may be adversely impacted and

the stream’s uses impaired. Even if the stream has sufficient alkalinity to improve pH, 

precipitation of iron, manganese, and/or aluminum may occur.
Coal Remining BMP Guidance Manual

Introduction 3

Ninety percent of AMD comes from abandoned coal mines (mostly underground mines) where no

individual or company is responsible for treating the water (Skousen and others, 1999). Acid

mine drainage impacts approximately 9,709 stream miles (IMCC, 1998). Table 1 provides a

breakdown by state of the 9,709 stream miles estimated to be impacted by AMD. 

303(d) List

Pursuant to Section 303(d) of the Clean Water Act, States biannually submit a list of water bodies

not presently supporting designated uses to the U.S. Environmental Protection Agency (EPA). 

As required by 40 CFR 130, 7(b)(4), States biannually compile a 303(d) list of streams affected by

such pollution sources as acid mine drainage. Priority and non-priority stream lists are generated

on the basis of analytical and benthic investigations. Table 1 contains a summary of the stream

miles affected by AMD according to the 1998 303(d) lists for each state.

Table 1: Number of Stream Miles Impacted by AMD

State Stream Miles

(Source A)

Stream Miles

(Source B)

Stream Miles

(Source C)*

Alabama 65 -- 50+440 acres

Illinois NA -- --

Indiana 0 -- --

Kentucky 600 -- 141+219 acres

Maryland 430 152 --

Missouri 139 -- --

Ohio 1,500 607 --

Pennsylvania 3,000 3,239 2,149

Tennessee 1,750 -- 726+ 510 acres

Virginia NA 17 44

West Virginia 2,225 1,100 2,019

 Totals >9,709 >5,115 >5,129 + 1,169 acres

* May include area of affected lakes and reservoirs

Source A: IMCC, 1998 NA = Not Available

Source B: Faulkner & Skousen, 1998

Source C: State 303(d) lists, 1998.
Coal Remining BMP Guidance Manual

4 Introduction

Abandoned Mine Land Program and AMLIS

Title IV of SMCRA established the Abandoned Mine Land (AML) program which provides for

the restoration of eligible lands and waters mined and abandoned or left inadequately restored. 

The AML program stipulates that a tax of $0.35 per ton of surface mined coal, $0.15 per ton for

underground mined coal, and $0.10 for lignite coal is paid into the AML fund. These funds are

deposited in an interest bearing Abandoned Mine Reclamation Fund which is used to pay

reclamation costs of AML projects. When Congress passed SMCRA, it realized that AML fees

would not generate enough revenue to address every eligible site, and left the States and Indian

Tribes the choice of which projects to select for funding. 

Expenditures from the AML fund are authorized through the regular congressional budgetary and

appropriations process. SMCRA specifies that 50 percent of the reclamation fees collected in

each state be allocated to that State for use in its reclamation program. SMCRA further specifies

that 50 percent of the reclamation fees collected annually with respect to Indian lands be allocated

to the Indian tribe having jurisdiction over such lands, subject to the Indian tribe having eligible

abandoned mine lands and an approved reclamation plan. The remaining 50 percent is used by the

Office of Surface Mining Reclamation Enforcement (OSMRE) to fund emergency projects and

high-priority projects in states and Indian tribes without approved AML programs under the

Federal Reclamation Program (FRP); to fund the Rural Abandoned Mine Program (RAMP); to

fund the Small Operator Assistance Program (SOAP); to supplement the State-share funding for

reclamation of abandoned mine problems through State/Indian tribe reclamation programs; and

for Federal expenses to collect the AML fee and administer the AML program.

The Office of Surface Mining’s Abandoned Mine Land Inventory System (AMLIS) catalogs AML

areas by problem type and estimated reclamation cost. The most serious problems are those

posing a threat to health, safety, and general welfare of people (Priority 1 and Priority 2, or “high

priority”). These are the only problems which the law requires to be inventoried. The 17 

Priority 1 and 2 types are:
Coal Remining BMP Guidance Manual

Introduction 5

• Clogged Streams • Clogged Stream Lands

• Dangerous Highwalls • Dangerous Impoundments

• Dangerous Piles & Embankments • Dangerous Slides

• Gases: Hazardous/Explosive • Hazard. Equip. & Facilities

• Hazardous Water Bodies • Ind./Residential Waste

• Portals • Polluted Water: Agri. & Ind.

• Polluted Water: Human Consump. • Subsidence

• Surface Burning • Underground Mine Fires

• Vertical Openings

AML problems impacting the environment are known as Priority 3 problems. While SMCRA

does not require OSMRE to inventory every unreclaimed Priority 3 problem, some states and

Indian Tribes have chosen to submit such information. There are twelve Priority 3 problem types

in AMLIS and they are:

• Benches • Industrial/Residential Waste

• Equipment/Facilities • Gob

• Highwalls • Haul Road

• Mine Openings • Slump

• Pits • Spoil Areas

• Slurry • Other

Of the $3.6 billion of high priority (Priority 1 and 2) coal related AML problems in the AML

inventory, $2.5 billion, or 69 percent, have yet to be funded and reclaimed. Priority 1 and 2 AML

problems are those that pose a significant health and safety problem, and does not include

environmental problems such as AMD. Current estimates indicate that ninety percent of the $1.7

billion coal related environmental problems (Priority 3) in the AML inventory are not funded and

reclaimed (OSMRE, 1999). An important note is that the AMLIS Priority 3 inventory represents

only a small part of the total environmental problem as states are not required to inventory

Priority 3 problems in general. In addition, the AML inventory is more complete for some states

than for others, and the frequency of occurrence of different types of problems varies widely
Coal Remining BMP Guidance Manual

6 Introduction

between states. Table 2 lists inventories of abandoned mine land conditions in nine Eastern Coal

Region states.

Table 2: AML Inventory Totals of 4 Major AML Problem Types in Appalachia and 

the U.S., as of September, 1998 (OSMRE, 1998)

State Clogged Stream

Lands

(acres)

Dangerous

Highwalls

(linear feet)

Dangerous Piles

or Embankments

(acres)

Dangerous slides

(acres)

Alabama 0 177,945 2,209 21

Indiana 0 1,650 25 0

Kentucky 7,936 64,718 1,137 1,519

Maryland 5 8,250 156 8

Ohio 11,850 56,453 29 99

Pennsylvania 570 1,116,071 5,294 7

Tennessee 0 36,560 779 92

Virginia 1,717 91,889 154 117

West Virginia 164 1,358,616 1,928 346

Appalachia Total 22,242 2,912,152 11,711 2,209

% of U.S. Total 93% 68% 72% 98%

U.S. Total 24,028 4,252,115 16,282 2,253

The cost of remediating AML problems far exceed the amounts that may ever be collected, hence,

alternative solutions should be found to reclaim remaining AML sites. 

AML funds fall far short for may states, especially for those that were extensively mined prior 

to SMCRA. For example, in Virginia, an estimated $432 million in Priority 1, 2, and 3 AML

liabilities remain while annual funding in recent years has been on the order of $ 5 million (Zipper

and Lambert, 1998). At current rates, it will take better than eighty years to reclaim Virginia’s

abandoned mine land problems.

Remining can be one of the tools used to help the AML funding shortfall. A report by Skousen

and others (1997) compared the cost of remining ten sites in Pennsylvania and West Virginia

with the costs of reclamation to AML standards. All ten remining operations resulted in 
Coal Remining BMP Guidance Manual

Introduction 7

environmental benefits. In all but two cases, the coal mined and sold from the remining operation

produced a net profit for the remining company. Remining of these ten sites saved the AML

program over $4 million (Skousen and others, 1997). 

Industry Profile

The U.S. coal mining industry has its commercial roots back to approximately 1750 when coal

was first mined from the James River coalfield near Richmond Virginia. More recently, U.S. coal

production set record levels in 1997, when a record 1.09 billion short tons were mined. The

electric power industry used a record 922 million short tons (85 percent of coal mined) that year. 

The three highest ranking coal producing states in 1997 were Wyoming (26 percent), West

Virginia (16 percent), and Kentucky (14 percent), which together accounted for 56 percent of the

coal produced in the United States (DOE, 1997). 

The most recent estimates available on coal production by state in the U.S. are summarized in

Table 3. In 1996, the Energy Information Administration estimated that the United States has

enough coal to last 250 years (USGS, 1996). They estimated the demonstrated reserve base of

coal in the United States was 474 billion short tons. Although recoverability rates differ from site

to site, an estimated 56 percent (or 265 billion tons) of the demonstrated reserve base is presently

recoverable (DOE, 1999).

Regulatory History

On October 13, 1982, EPA promulgated final effluent guidelines under the Clean Water Act to

limit the discharges from the coal mining industry point source category. The rule amended

previously promulgated effluent limitations guidelines based on “best practicable control

technology currently available” (BPT) and “new source performance standards” (NSPS), and

established new guidelines based on “best available technology economically achievable” (BAT).
Coal Remining BMP Guidance Manual

8 Introduction

Table 3: Coal Production by State (Short Tons) (DOE, 1997)

State Underground Surface Total 

Alabama 18,505,000 5,963,000 24,468,000 51

Alaska -- 1,450,000 1,450,000 1

Arizona -- 11,723,000 11,723,000 2

Arkansas -- 18,000 18,000 3

Colorado 17,820,000 9,628,000 27,449,000 14

Illinois 34,824,000 6,334,000 41,159,000 28

Indiana 3,530,000 31,967,000 35,497,000 39

Kansas -- 360,000 360,000 3

Kentucky 96,302,000 59,551,000 155,853,000 529

Louisiana -- 3,545,000 3,545,000 2

Maryland 3,301,000 859,000 4,160,000 18

Missouri -- 401,000 401,000 4

Montana 8,000 40,997,000 41,005,000 8

New Mexico -- 27,025,000 27,025,000 6

North Dakota -- 29,580,000 29,580,000 6

Ohio 16,949,000 12,205,000 29,154,000 81

Oklahoma 212,000 1,409,000 1,621,000 11

Pennsylvania

 Anthracite 419,000 4,259,000 4,678,000 131

 Bituminous 54,410,000 17,110,000 71,520,000 272

Tennessee 1,396,000 1,904,000 3,300,000 27

Texas -- 53,328,000 53,328,000 12

Utah 26,683,000 -- 26,683,000 12

Virginia 26,929,000 8,907,000 35,837,000 191

Washington -- 4,495,000 4,495,000 3

West Virginia 116,523,000 57,220,000 173,743,000 349

Wyoming 2,846,000 279,035,000 281,881,000 25

Appalachian Total 308,360,000 159,418,000 467,778,000 1,602

Interior Total 64,941,000 105,923,000 170,863,000 149

Western Total 47,357,000 403,934,000 451,291,000 77

East of Miss. 373,089,000 206,281,000 579,369,000 1,716

West of Miss. 47,569,000 462,994,000 510,563,000 112

U.S. Total 420,657,000 669,274,000 1,089,932,000 1,828
Coal Remining BMP Guidance Manual

Introduction 9

The October 1982 rule established four subcategories for promulgation of effluent limitations

based on BAT: (1) preparation plants and associated areas; (2) acid mine drainage; (3) alkaline

mine drainage; and (4) post-mining discharges. The limitations of acid mine drainage, post-mining

discharges at underground mines, and coal preparation plants and associated areas were based on

neutralization and settling technologies. The limits for alkaline mine drainage were based solely

on settling technology. For the coal mining category, BAT and BPT effluent limits were identical.

The issue of remining was raised during the comment period following the 1982 proposal of the

final rule. Comments addressed the fact that technology-based standards would likely serve as a

deterrent to remining activities, since the operator would have to assume responsibility for

treating effluent from previous operations that already may be significantly contaminated. 

However, the question of the appropriate effluent limitations for remining operations was not a

subject of the proposal, and was therefore not addressed in detail in the final rule. Instead, EPA

stated that generally, effluent limitations guidelines and standards are applicable to point source

discharges even if those discharges pre-dated the remining operation.

In 1987, the Clean Water Act (CWA) was amended to provide incentives for remining abandoned

mine lands that were mined prior to the 1977 passage of the Surface Mining Control and

Reclamation Act (SMCRA). The modification of the CWA (known as the Rahall Amendment)

established that BAT effluent limitations for iron, manganese, and pH are not required for

discharge conditions existing prior to remining activities. 

Remining

Development of modern surface-mining techniques has allowed for more efficient and effective

removal of coal deposits; consequently, mining is now feasible in areas where mining was

previously uneconomical. A report prepared for the U.S. Department of Energy estimates that
Coal Remining BMP Guidance Manual

10 Introduction

 460 million to 1.1 billion tons of coal could potentially be recovered from remining in mine states

(PA, WV, MD, VA, KY, TN, OH, IN, IL) (Veil, 1993).

In 1987 Congress passed the “Rahall Amendment” to the Clean Water Act. The CWA was

amended to include section 301(p) in order to provide remining incentives for permits containing

abandoned mine lands that pre-date the passage of SMCRA in 1977. The Rahall Amendment

established that BAT effluent limits for iron, manganese, and pH (40 CFR part 434) are not

required for pre-existing mine drainage discharges. Instead, site-specific BAT limits determined

by Best Professional Judgement (BPJ) are applicable to these pre-existing discharges, and the

permit effluent limits for iron, manganese, and pH (or acidity) may not exceed pre-existing

“baseline” levels. The Rahall Amendment established new effluent guidelines for pre-existing

discharges for remining operations potentially freeing the operators from the requirement to treat

degraded pre-existing discharges to the statutory BAT levels.

“Remining,” as defined in the 1987 Rahall Amendment and this document refers to “ a coal

mining operation which began after the enactment of the Rahall Amendment at a site on which

coal mining was conducted before the effective date of the Surface Mining Control and

Reclamation Act of 1977. 

On September 3, 1998, the Interstate Mining Compact Commission (IMCC) distributed a

Solicitation Sheet to member states in support of continuing efforts to collect data and

information required for proposal of a remining subcategory under 40 CFR 434. The solicitation

sheet was intended to gather information necessary to assess current industry remining activity

and potential. The results of the solicitation are summarized in numerous tables in this report.

IMCC member states have estimated that there are currently 150 mining companies in ten states

actively involved in remining activities. These companies are producing at least 25.1 million tons

of coal annually; and employing approximately 3,000 people (Table 4).
Coal Remining BMP Guidance Manual

Introduction 11

Table 4: State by State Profile of Remining Operations (IMCC, 1998)

 

Number of

mining

companies

with remining

permits

Total employment

at remining

operations

(Number of

employees)

Annual coal

production from

remining sites

(tons)

Estimated coal 

reserves

(tons)

Alabama 20 ND ND ND

Alaska 0 0 0 0

Colorado 0 0 0 ND

Illinois 35 70 200,000 10,000,000

Indiana 2 NA 720,000 NA

Kentucky 4 ND ND ND

Maryland 13 150 650,000 ND

Missouri 2 0 0 ND

Mississippi 0 0 0 ND

Montana 0 -- -- --

New Mexico 0 0 0 0

Ohio 3 ND ND ND

Pennsylvania 50 2,345 17,530,000 100,000,000+

Tennessee 10 75 - 100 3,000,000 50,000,000

Texas 0 0 0 0

Utah 0 0 0 ND

Virginia 3 300 3,000,000+ ND

West 8 ND ND ND

Wyoming 0 0 0 ND

 Totals 150 >2,940-2,965 >25,100,000 >160,000,000

NA = Not Available; -- = No Response; ND = No Data.

Currently there are approximately 1,072 active remining permits and 638 AML projects, (Table

5). Of these 1,072 permits, 330 (31 percent) are Rahall type permits where the effluent standards

for pH, iron, and manganese have been relaxed. 
Coal Remining BMP Guidance Manual

12 Introduction

Table 5: Types of Remining Permits Issued by State (IMCC, 1998)

State Number of

Rahall Permits

Number of NonRahall Permits

(a)

“Other”

Remining

Permits/Projects

(b)

Remining

Permits (% of

Total)

Alabama 10 61 1 ND

Alaska 0 0 0 0

Colorado 0 0 15 0

Illinois 0 41 0 0

Indiana 0 1 1 1

Kentucky 4 N/A 1 40

Maryland 2 21 0 30

Missouri 0 20 0 15

Mississippi 0 0 0 0

Montana 0 0 14 0

North Dakota 0 -- -- --

New Mexico 0 -- -- 0

Ohio 3 ND 101 60-70

Pennsylvania 300 40 3 95(c)/50(d)

Tennessee 0 350-450 0 60

Texas 0 0 0 0

Utah 0 0 0 0

Virginia 3 158 501 75-80

West Virginia 8 -- 1 0.4

Wyoming -- -- -- --

Totals 330 692-792 638

(a) Where operators accept liability for all discharges. N/A = Not Applicable

(b) (e.g., AML) -- = No Response

(c) Anthracite ND = No Data

(d) Bituminous

Table 6 provides information on the type of remining being conducted at the existing remining

operations (i.e., refuse piles, surface mine, or underground mines).
Coal Remining BMP Guidance Manual

Introduction 13

Table 6: Characteristics of Existing Remining Operations by State (IMCC, 1998)

Number of coal

refuse piles

Number of

surface mine sites

Number of

underground

sites

Number of

remining permits

meeting BAT 

State Active

Mines

Under

Permit

AML

Projects

Active

Mines

Under

Permit

AML

Projects

Active

Mines

Under

Permit

AML

Projects

Active

Mines

Under

Permit

AML

Projects

Alabama 4 1 54 -- 13 -- ND 1

Alaska 0 0 0 0 0 0 0 0

Colorado 0 4 0 12 0 2 0 0

Illinois 40 0 1 0 0 0 0 0

Indiana 1 0 34 -- 2 -- 0 --

Kentucky 3 1 1 -- 2 -- 5 --

Maryland 0 -- 17 -- 21 -- 2 --

Missouri 0 0 2 0 0 0 0 0

Mississippi 0 0 1 0 0 0 0 0

Montana 1 -- 11 -- 1 -- 0 --

New Mexico 0 0 0 0 0 0 0 0

Ohio 0 -- 2 1 1 -- 0 --

Pennsylvania 173 0 1,278 0 655 2 616 0

Tennessee 5-10 0 135-

180

0 210-

260

0 0 0

Texas 0 0 0 0 0 0 0 0

Utah 5 0 2 0 32 N/A 0 N/A

Virginia 33 38 77 117 107 104 0 2

West Virginia 1 -- 7 -- 1 -- 9 --

Wyoming -- -- -- -- -- -- -- --

 Totals 266-

271

44 1,622-

1,667

130 1,045-

1,095

108 632 3

N/A = Not Applicable; -- = No Response; ND = No Data. 
Coal Remining BMP Guidance Manual

14 Introduction

Best estimates of potential remining activities according to IMCC member states are provided in

Table 7.

Table 7: Potential Remining Operations by State (IMCC, 1998)

 Number of Number of Number of

coal refuse piles surface mine sites underground mined sites

Alabama 1 -- --

Alaska 3 5 1

Colorado ~400 ~50 ~850

Illinois 30 10 12

Indiana 150 453 615

Kentucky ~200 400-600 800 - 1,000

Maryland 10 75 75

Missouri 0 0 0

Mississippi 0 1 0

Montana 1 11 1

New Mexico N/A N/A N/A

Ohio (1,095 acres) (23,000 acres) 4,000

Pennsylvania 858 (158,960 acres) (31,587 acres)

Tennessee (182 acres) (46,000 acres) 800

Texas 0 0 0

Utah 5 2 32

Virginia 400-450 750 800

West Virginia -- 3 --

Wyoming 0 0 0

 Totals 2,058 - 2,108 and

1,277 acres

1,760 - 1,960 and

227,960 acres

7,986 - 8,186 and 

31,587 acres

-- = No Response

N/A = Not Applicable
Coal Remining BMP Guidance Manual

Introduction 15

OH (0.91%)

MD (0.61%)

KY (1.21%)

AL (3.03%)

VA (0.91%)

WV (2.42%)

PA (90.91%)

Existing State Remining Programs

After more than ten years of success with state remining permit programs, abandoned mine land

reclamation, and water quality improvements in Pennsylvania and other coal mining states, it is

time to re-evaluate the regulatory conditions that were originally developed, advance the process

by offering new remining incentives, and remove disincentives embedded in the current remining

program. The goal is to develop a more efficient remining permitting process, with design-based

permit standards, that incorporate critical BMPs. The permitting incentives should be integrated

with watershed scale approaches to abandoned mine land reclamation and AMD abatement; and

risk assessment protocols should be developed to minimize liability and risk concerns of mine

operators, state and federal regulatory agencies, watershed groups, and landowners.

The recent IMCC Solicitation indicates that 7 states have issued Rahall type permits (Refer to

Table 5). Pennsylvania’s remining program has issued more than 300 remining permits,

accounting for 91 percent of all the Rahall permits (Figure 1). The remaining states have issued

ten or less remining permits each. 

Figure 1: Percentage of Total Number of Rahall Permits Issued by State
Coal Remining BMP Guidance Manual

16 Introduction

Below is a brief history of the development and requirements of each state’s remining program.

Pennsylvania

Prior to the federal law changes in 1987, the Pennsylvania (PA) legislature amended PA SMCRA

in 1984 (Senate Bill 1309) to include remining incentives. Under the PA law and related

regulations [25 PA Code Chapter 87, Subchapter F (bituminous coal) and Chapter 88, Subchapter

G (anthracite coal)] a baseline pollution load is established, a pollution abatement plan is

submitted incorporating best technology, and the effluent limits for the pre-existing discharges are

determined by the BPJ process. From 1984 to 1988, PA Department of Environmental Resources

(PA DER), now PA Department of Environmental Protection (PA DEP), EPA, and OSMRE,

were involved in a cooperative research and development project with the Pennsylvania State

University and KRE Engineers concerning elements of the BPJ process. The project resulted in

the development of the REMINE computer program and related publications by Smith (1988),

and Pennsylvania Department Of Environmental Resources, and others (1988).

Between 1985 and June 1997, PADEP issued 260 remining permits (Table 8 and Figure 1), based

on the following three-step process: (1) development of baseline loads; (2) submittal of a

pollution abatement plan (technologies and BMPs); and (3) development of water quality

limitations and standards based on BPJ. Of the 260 facilities issued permits, only three are

required to treat pre-existing discharges on a long-term basis to achieve compliance with the

baseline pollutant levels. Treatment can also be required to treat short-term excursions from the

baseline. Only eleven permits (4.2 percent) have ever required treatment on a temporary or longterm basis in Pennsylvania. 

An independent evaluation of the success of the PA remining program was performed by 

Hawkins (1995) of the U.S. Bureau of Mines. As of 1995, the Pennsylvania remining program

successfully permitted for reclamation approximately 4,000 acres of abandoned mine land, which

led to the production of 36 million tons of coal from acres deemed “untouchable” under pre-
Coal Remining BMP Guidance Manual

Introduction 17

1% fo rfeiture sites

98% not treating

1% sites treating

remining regulations (Hawkins, 1995). Site specific data and a project description for a key

remining site (Fisher Mining Company, Lycoming County) are found in publications by Plowman

(1989) and Smith and Dodge (1995). The authors reported that pre-remining data from the main

discharge from the Game Land site showed a medium net acidity in excess of 100 mg/L. Post

remining data showed the same discharge to be net alkaline and the receiving stream now

supports brook trout. Another independent evaluation of water quality improvements and costs

of remining in Pennsylvania and West Virginia was performed by Skousen et al. (1997), including

data from ten sites, of which the largest and most significant is Solar mine near Pittsburgh. The

water quality improved at all ten sites. In all but two cases, coal mined and sold produced a net

profit for the mining company.

Table 8: Pennsylvania Remining Permits Which Required Treatment, June, 1997

(IMCC, 1997)

Bituminous Region Anthracite Region Totals

Permits Issued 248 12 260

Currently Treating 3 0 3

Forfeited due to AMD 2 0 2

Required Treatment 11 0 11

Figure 2: Status of 260 Pennsylvania Remining Permits (IMCC, 1997)
Coal Remining BMP Guidance Manual

18 Introduction

Pennsylvania has taken additional steps to encourage remining and reclamation of abandoned mine

lands. In 1997, SMCRA and 25 PA Code Chapter 86 were revised to authorize bonding

incentives, including reclamation bond credits and financial guarantees. A qualified mine operator

can earn bond credits by performing voluntary reclamation of additional mine lands. The credit is

the operator’s cost to reclaim the proposed area or DEP’s cost, whichever is less. Credits may

then be applied as bond on any coal mining permit, and may be transferred and used once after

their first use.

West Virginia

West Virginia has issued eight remining permits with modified water quality requirements. The

basic elements of their program are similar to those in Pennsylvania in that the applicant must

conduct water quality and quantity monitoring to establish a baseline pollutant load and must

submit an abatement plan. 

In order to receive remining approval, operators must demonstrate that their proposed abatement

plan represents the best available technology and that the operation will not cause additional

surface water pollution and will result in the potential for improved water quality. Effluent limits

in the remining permit do not allow a discharge of pollutants in excess of the baseline pollutant

load. Also, a remining water quality standard variance must be approved prior to issuing the

National Pollutant Discharge Elimination System (NPDES) remining permit. If the variance is

denied, the NPDES Remining Permit will also be denied.

Maryland

Although Maryland has a relatively small coal industry, the State actively implemented the 

Rahall amendment, which allows for a modified NPDES permit for remining operations. 

Maryland also implemented EPA revegetation standards allowing for bond release after 2 years,

and offers reduced bonding rates for an NPDES remining permit. Currently, Maryland has 
Coal Remining BMP Guidance Manual

Introduction 19

issued two remining permits with relaxed effluent limits. Maryland has numerous remining

operations on previously mined areas with no pre-existing discharges.

Virginia

Virginia has regulations for remining and has issued three permits with relaxed effluent limits for

remining operations. Operators must show that remining operations have the potential to improve

water quality. To obtain a remining permit, the applicant submits baseline monitoring data, a

module of REMINE, and an abatement and reclamation plan. Permits are based on BPJ

determined by the output of REMINE and must result in a reduction in pollutant loading to the

stream.

Kentucky

Kentucky has regulations for remining and has issued four permits with relaxed effluent limits for

remining activities. The Kentucky procedure is much like that described for the other states

above. The applicant submits baseline monitoring data, an abatement and reclamation plan, and

may submit a module of REMINE. Operators must show that remining operations have the

potential to improve water quality. Permit limits are based on BPJ and must result in a reduction

in pollutant loading to the stream (Veil, 1993). 

Tennessee

Tennessee does not administer its coal mining program. OSMRE maintains the authority to issue

coal mining permits. As of 1993, about 60 percent of all coal mining permits in the state involved

remining, however, no permits were issued with relaxed effluent limits.

Ohio

Ohio has regulations for remining and has issued three permits with relaxed effluent limits for 
Coal Remining BMP Guidance Manual

20 Introduction

remining activities. Remining approvals are limited to sites with pre-existing discharges. 

Operators must submit baseline monitoring data along with a pollution abatement plan and

supplemental hydrological information. Permit approval is contingent on the abatement plan

representing BAT and having the potential to reduce the baseline pollutant load (Veil, 1993).

Alabama

Alabama has issued 10 permits with relaxed effluent limits for remining operations. To qualify for

a remining permit an operator must show:

• Original mining/disturbance must have occurred prior to 1977.

• Subsequent permitted/legal disturbance could not have occurred after 1977.

• Areas that have had a SMCRA permit or bonding at anytime are not eligible. 

• Substantive showing must be made that water quality can be improved ( a

pollution abatement plan must be submitted).

• Effluent limits must at least meet ambient water quality standards.

Modified requirements for pH, iron and manganese must apply the best available technology

economically achievable on a case-by-case basis, using best professional judgement, to set specific

numerical effluent limits in each permit.

Regulatory agencies for states where remining is not currently practiced may be inclined to start

and promote remining programs if such programs can be shown to be successful in terms of

enhanced coal recovery, reclamation of abandoned mine lands, and reduction of (or no net

increase in) mine drainage. Mine operators also may be more inclined to enter into remining

projects with the knowledge that the potential of incurring liability for long-term treatment of

mine waters from prior mining activities is low.
 Coal Remining BMP Guidance Manual

Best Management Practices 21

 Introduction to Best Management Practices

Remining is the mining of abandoned surface mines, underground mines, and/or coal refuse piles

that were mined prior to the environmental standards imposed by the Surface Mining Control and

Reclamation Act of 1977. There are four types of abandoned mine lands available for remining

operations: (1) sites that were previously surface mined, (2) sites that were previously

underground mined, (3) sites that were previously surface mined and underground mined, and (4)

sites that had coal refuse deposited on the surface. These sites were typically left unreclaimed and

unvegetated, sometimes pose safety hazards and are often associated with pollutional discharges

or sedimentation problems. Because of associated environmental problems, these areas cannot be

re-affected or remined without the implementation of minimal best management practices (BMPs)

in an attempt to correct past problems.

BMPs implemented during the remining and reclamation of these sites are designed to reduce, if

not completely eliminate, these pre-existing environmental problems, particularly water pollution.

The types and scope of BMPs are tailored to specific operations based largely on pre-existing site

conditions, hydrology, and geology. BMPs are designed to function in a physical and/or

geochemical manner to reduce the pollution loadings.

In this guidance document, BMPs have been placed into four categories: hydrologic and sediment

control, geochemical, operational, and passive treatment, although there is some question whether

passive treatment is a true BMP. These categories have been designed for ease of discussion, and

each BMP has been placed in the category that is most appropriate. In several cases, a BMP

serves more than a single function. For example, induced alkaline recharge trenches are discussed

as a geochemical BMP, but also influence hydrology and are closely related to some passive

systems. Adding to this complexity is the fact that remining operations nearly always employ

multiple BMPs in an effort to abate pollution.
Coal Remining BMP Guidance Manual

22 Best Management Practices

Physically-performing BMPs function to limit the amount of ground water that is ultimately

discharged from the mine and by reducing erosion and subsequent off-site sedimentation by

controlling surface-water runoff. Discharge reduction is performed by limiting the amount of

ground and surface water that laterally or vertically infiltrates into the backfill. Water is routed

away from spoil via regrading, diversion ditches, low-permeability seals and caps, and highwall

and pit floor drains. Ground water that has entered the spoil is collected and drained away via

floor drains. Some physical BMPs are performed to reduce ground-water flow, some to reduce

erosion and sedimentation problems, and some serve both purposes. Physical BMPs are

addressed in Section 1.0 (Hydrologic and Sediment Control Best Management Practices). Below

is a list of physically performing BMPs and an indication whether they influence ground-water

hydrology (gw), erosion and sedimentation (e&s) or both (gw, e&s). 

• Regrading of spoil (gw, e&s)

• Revegetation (gw, e&s)

• Diversion ditch installation (gw, e&s)

• Installation of low-permeability caps (gw)

• Stream sealing (gw)

• Underground mine daylighting (gw)

• Mine entry and auger hole sealing (gw)

• Highwall and pit floor drains (gw)

• Grout curtains (gw)

• Ground water diversion wells (gw)

• Advanced erosion and sedimentation controls (e&s)

Geochemically-performing BMPs function to inhibit pyrite oxidation, reduce the contact of 

water with acid-producing materials, inhibit iron-oxidizing bacteria, or increase the amount of

alkalinity generated within the backfill. Pyrite oxidation is inhibited by limiting its exposure to 

the atmosphere and preventing the proliferation of iron-oxidizing bacteria with bactericides.

Acidic materials are special handled or capped to isolate them from the ground-water flow path.

Alkaline materials are imported, redistributed, and strategically placed in the ground-water 

flow path in order to increase and/or accelerate alkalinity production. Geochemical BMPs are 
 Coal Remining BMP Guidance Manual

Best Management Practices 23

discussed in Section 2.0 (Geochemical Best Management Practices). Geochemically-performing

BMPs include:

• Alkaline addition

• Alkaline redistribution

• Mining into highly-alkaline strata

• Induced alkaline recharge

• Special handling of acid-forming materials

• Special handling alkaline materials

• Use of bactericides

Operational BMPs are mining practices that can reduce the risk of pollution or erosion and

sedimentation problems. Rapid mining and concurrent reclamation limit the exposure of acidforming materials to weathering and promote rapid reclamation and revegetation that can reduce

erosion and sedimentation problems. Coal refuse reprocessing removes an acid-producing

material. This material is burned to produce electricity, and the ash that is produced, which is

frequently alkaline, is returned to the site where it can neutralize acid. Operational BMPs are

discussed in Section 3.0 (Operational BMPs). They include:

C Coal refuse reprocessing

C Rapid mining and concurrent reclamation

C Limited or no auger mining

C Off-site disposal of acid-forming coal cleanings, pit and tipple refuse

The last category, passive treatment, encompasses a variety of engineered treatment facilities that

require minimal maintenance, once constructed and operational. Passive treatment generally

involves natural physical, biological and geochemical actions and reactions. The systems are

commonly powered by water pressure created by differences in elevation between the mine

discharge point and the treatment facilities. Passive treatment does not meet the standard

definition of BMPs in that they are typically end-of-pipe (treatment) solutions. They are included

in this manual because they can be used as part of the overall abatement plan to reduce pollution
Coal Remining BMP Guidance Manual

24 Best Management Practices

loads discharging from remining sites. Passive treatment methods are discussed in Section 4.0

(Passive Treatment Technologies). Types of passive treatment include:

C anoxic limestone drains

C constructed wetlands

C successive alkalinity-producing systems

C open limestone channels

C oxic limestone drains

C alkalinity-producing diversion wells

C pyrolusite® systems 

Site Characteristics and BMP Selection

Factors that influence which BMPs can be employed effectively at remining sites include previous

types of mining activities, geologic and hydrologic characteristics of the site, the quality and

quantity of pre-existing discharges, economics, and regional differences. Listed below under these

categories are examples of associated BMPs and some of their limitations:

Previous mining history

• Daylighting only occurs where previous underground mining was conducted.

• Mine sealing is used where underground mines or auger holes are not completely

daylighted.

• Regrading and revegetation are performed on abandoned and reclaimed surface mines.

• Coal refuse reprocessing occurs where there are abandoned coal refuse piles.

Geologic and hydrologic characteristics

• Alkaline addition is conducted where there is an inadequate quantity of naturally-occurring

alkaline rocks.

• Alkaline redistribution takes place where only a portion of the site has a significant amount

of alkaline material which is then distributed more evenly across the site.
 Coal Remining BMP Guidance Manual

Best Management Practices 25

• Alkaline material that is located stratigraphically high above the coal may require mining

into higher cover to access it or may require a reorientation of the pit so that the alkaline

material is encountered with every mining cut.

• Special handling of acidic material occurs where there is a significant amount, but not an

over abundance, of this material that can be field-identified and segregated.

• Highwall drains are not an option where no up-gradient final highwall remains.

• Hydrologic controls, such as floor drains or ground-water diversion wells, are not

necessary unless lateral recharge is present.

• The site may be capped with a low-permeability material, if vertical recharge is predicted

to be the main source of water to the backfill and a low-permeability material is readily

available.

• Passive treatment may be used, if the topography to drive the system is present and

sufficient construction space is available.

Pre-remining water quality and quantity

• Large volumes of severely degraded water may not be suitable for a passive treatment

BMP. 

• High volumes of water flowing from underground mines that will not be completely

daylighted may be suited to rerouting (piping) through the spoil. 

• Highly acidic pre-remining discharges associated with pyritic overburden may require

substantial alkaline addition and/or special materials handling. 

Economics

Cost plays a substantial role in determination of which BMPs are employed and the degree to

which they are implemented. Remining sites are commonly economically marginal because of

reduced coal recovery rates compared to virgin sites. These sites also generally entail greater

reclamation costs due to pre-existing site conditions. Therefore, economics plays a significant role

in the development of a BMP plan. The BMP plan is weighed against these costs. If the cost of

BMP implementation is prohibitive the site will not be remined. Mining only occurs on sites where

a profit can be made.
Coal Remining BMP Guidance Manual

26 Best Management Practices

Regional Differences

There are also regional considerations that play into the decision of which BMPs to use at a

particular site. Differences in the geology, geochemistry, hydrology, and topography between coal

regions cause distinct problems requiring differing solutions. Regional differences include:

• Geologic conditions that effect the type (lithology) and chemistry/mineralogy of rocks and

the structure (e.g., folding, faulting, and fracturing).

• Hydrologic conditions, such as differences in local and regional ground-water flow

systems and precipitation amounts, frequency, and/or duration.

• Differences in topography (such as amount of relief and steepness of slopes).

• Differing surface and underground mining techniques, thus abandoned sites will exhibit

distinct problems regionally.

Acid Mine Drainage

It has been recognized for decades that acid mine drainage (AMD) is to a large extent a regional

problem that is most prevalent in the northern Appalachians. Upon closer examination it was

evident that the problem was frequently associated with the Allegheny Group coals (Appalachian

Regional Commission, 1969). Figure 3 illustrates the percentage of streams within various

Appalachian watersheds that had pH less than 6.0. Figure 4 shows the percentage of streams for

these same watersheds that have sulfate greater than 75 mg/L. The cut-offs of pH 6.0 and 75

mg/L sulfate were chosen by the US Geological Survey because low pH and elevated sulfate can

indicate impacts from coal mine drainage. 

Watersheds with 35 percent or more of streams with pH less than 6.0 occur in the northern

Appalachians and are associated with the outcrop areas of the Allegheny Group. Typically the

watersheds in the southern Appalachians have 10 percent or less of steams with pH less than 6.0. 
 Coal Remining BMP Guidance Manual

Best Management Practices 27

The distribution of watersheds with a high percentage of streams with greater than 75 mg/L

sulfate does not necessarily correspond with the low pH areas. For example, one of the

watersheds in eastern Kentucky had 57 percent of streams with sulfate greater than 75 mg/L, but

no stream measured had pH less than 6.0. Other watersheds show similarly high percentages of

streams with sulfate greater than 75 mg/L, but with few streams with pH less than 6.0. This type

of water is characteristic of neutralized acid mine drainage.

No full explanation as to the water quality differences within the Appalachian Basin has been

provided to date, but there is little question that it is due to geologic differences. Cecil and others

(1985) examined sulfur data for coals from southern West Virginia to Pennsylvania. The

stratigraphically older coals, which occur in southern West Virginia, have lower sulfur than the

younger coals that occur in the northern Appalachians (Figure 5). Cecil and others attribute these

differences to climatic factors at the time of peat (coal) deposition that influenced the chemistry of

the swamp, which ultimately influenced the sulfur content of the coal.

The production of acidity from pyritic sulfur is only half the story. The other half of the story is

the production of alkalinity from carbonate dissolution. Calcareous rocks neutralize acid and they

are the explanation for the water quality in streams that have pH greater than 6.0 and sulfate

greater than 75 mg/L (i.e., neutralized mine drainage).

It is evident that in some regions AMD is a significant problem, while in other areas it is rare. 

This difference is an important factor in remining. Where AMD is prevalent, water quality is an

important remining issue. Where AMD is rare, water quality typically less of a concern, with the

possible exception of sedimentation problems. 
Coal Remining BMP Guidance Manual

28 Best Management Practices

Figure 3: Percentage of Streams with pH < 6.0 for 24 Watersheds in the Appalachian

Basin (data from Wetzel and Hoffman, 1983).
 Coal Remining BMP Guidance Manual

Best Management Practices 29

Figure 4: Percentage of Surface Water Sample Stations with Sulfate Greater than 75

mg/L for 24 Watersheds in the Appalachian Basin (data from Wetzel and

Hoffman, 1983).
Coal Remining BMP Guidance Manual

30 Best Management Practices

Figure 5: Stratigraphic Variation of Sulfur Content of 34 Coal Beds of the Central

Appalachians. (Figure from Cecil and others, 1985).

Hydrology

The ground-water hydrology is similar throughout much of the Appalachian Plateau, however

there are some subtle differences region to region. Some of these differences are related to

changes in major rock types associated with the coal which in turn directly impacts the fracturing

density, interconnectedness of fractures, depth of fracturing, and aperture size of the fractures.

For example, experience has shown that in shallow cover (#200 ft), the massive, well-cemented

sandstones commonly associated with coals of eastern Kentucky tend to exhibit much less

fracturing than is observed in the more thinly-bedded, poorly-cemented sandstones associated
 Coal Remining BMP Guidance Manual

Best Management Practices 31

with the Pittsburgh coal in northern West Virginia. These differences will be reflected in the

ground-water flow systems (location of ground water, amounts in storage, and ground water

movement velocity) of the respective areas.

Additionally, the ground-water systems associated with the mid-Western coals in Indiana and

Illinois are primarily regional in nature and near surface. Whereas, ground-water systems in the

Appalachian Plateau are characterized by a series of limited-area perched aquifers underlain by

deeper more regional systems that discharge to the major rivers and creeks of the area (e.g.,

Monongahela, Kanawha, or Tug Fork rivers).

Topography and Geomorphology

Regional differences in topography and geomorphology can impact the types of BMPs employed.

For example, the topography of southern West Virginia, western Virginia, and eastern Kentucky

is generally steep with narrow V-shaped valleys and sharp-peaked hills and mountains. Figure 6

shows this type of topography in Kanawha and Raleigh Counties in southern West Virginia.

Whereas, the topography of northern West Virginia and western Pennsylvania is not nearly as

steep-sloped with broader valleys and more flat-topped hills and mountains. Figure 7 illustrates

this topography in Jefferson County in west-central Pennsylvania. These differences have resulted

in distinctive mining techniques and post-mining configurations. For example, the steep sloped

areas tended to promote contour surface mining (Figure 8), whereas in shallower sloped areas

block cut or area mining was used more frequently (Figure 9). 

Mining Methodology

Differences in mining methods in turn can result in greatly differing abandoned mine site

conditions, and thus may require distinct BMP engineering plans to effect water quality

improvement. For example the steep-sloped areas may require additional ditches, check dams 

and ponds for stabilizing, while regrading and revegetating a shallower sloped area may be

adequate to stabilize erosion. Abandoned mines in southern West Virginia, western Virginia, 

and eastern Kentucky frequently exhibit down slope spoil disposal, open pits, and exposed

highwalls making reclamation back to the approximate original contour (AOC) impractical in
Coal Remining BMP Guidance Manual

32 Best Management Practices

most cases. Abandoned mines in northern West Virginia and western Pennsylvania will have some

open pits and exposed highwalls, but are commonly characterized by a series of unreclaimed spoil

piles and ridges. Returning the site to AOC is generally more feasible on these sites. 

Figure 6: Example of Steep Topography and High Relief in Southern West Virginia

Showing Multiple Contour Strip Mines on Steep Slopes.
 Coal Remining BMP Guidance Manual

Best Management Practices 33

Figure 7: Example of Moderate Slopes and Broader Valleys and Hilltops in Westcentral Pennsylvania Showing Small Area Mines.
Coal Remining BMP Guidance Manual

34 Best Management Practices

Figure 8: Topographic Map Illustrating Contour Surface Mining.
 Coal Remining BMP Guidance Manual

Best Management Practices 35

Figure 9: Topographic Map Illustrating Area Surface Mining. 

The “shoot and shove” method of past mining on the steep slopes of the central Appalachian

Plateau has resulted in erosion and sedimentation problems.
Coal Remining BMP Guidance Manual

36 Best Management Practices

BMP Implementation

The best BMP plan may fail if it is not implemented as designed (e.g., conducted properly,

adequately, and on a timely basis) and as approved by the permitting authority. To facilitate field

implementation, the BMP plan should be clearly thought out and designed for site-specific

conditions during the permit application process. A well designed plan can eliminate the need for

revisions once the permit is issued and will provide guidance to ensure proper implementation.

However, a well designed plan also provides a degree of flexibility to allow for “mid-stream”

changes caused by unforeseen circumstances. 

An effective BMP plan hinges greatly on a detailed site assessment. Site assessment data and

information should be sufficient to identify which strata will require handling, potential sources of

ground water, probable reasons for existing AMD, the scope of previous mining, and other salient

data. Site assessment will typically, at a minimum, require extensive field work and mapping,

multiple bore holes with appropriate vertical sampling, ground-water level measurements, surface

water flow measurements, and representative ground- and surface-water samples.

A BMP plan should be realistic. It should be appropriate to the site, workable in the field,

economically feasible, and based on sound scientific principles. Plans should be clearly designed

with appropriate maps, cross-sections and narrative. The ultimate viability of a BMP plan depends

heavily on the individual(s) that develops the BMP plan, the one(s) that review and approve it,

those who implement it, and those who enforce it. The BMP plan should be verifiable and

enforceable by those individuals who inspect the site. Implementation guidelines are provided for

each category of BMPs in the appropriate sections. 

Efficiency

The efficiencies of BMPs or groups of BMPs, in regards to decreasing pollution loadings, are

based on limiting one or more of the following factors: 
 Coal Remining BMP Guidance Manual

Best Management Practices 37

C amount of pyritic material

C availability of oxygen to the pyritic material

C contact of water with the pyritic material 

Previous studies (Smith, 1988 and Hawkins, 1995), have shown that controlling (decreasing) the

flow of AMD discharges exerts the largest influence on the reduction of pollution load. Flow

reduction is best accomplished by reducing surface- and ground-water infiltration. However,

prevention of additional acid formation by use of geochemically-based BMPs can also decrease

the pollutant concentration which will likewise decrease the associated loading. BMPs can also

function by treatment (neutralization) of AMD after it has formed. This treatment can be in-situ

neutralization from contact with additional alkaline materials or can be in the form of end-of-thepipe treatment performed by passive treatment systems. 

Some BMPs function in more than one way. Underground mine sealing will not only inhibit

ground-water movement, it will also attenuate oxygen infiltration. Alkaline addition can prevent

AMD through inhibition of iron-oxidizing bacteria and it can neutralize acidity once it has been

produced. Surface- and ground-water controls can reduce erosion and sedimentation, while

inhibiting infiltration into the spoil. 

Efficiencies of BMPs are discussed in the sections dealing with each BMP category and are

evaluated by the observed and statistical approaches described in Section 6.0 (Efficiencies of Best

Management Practices).

Verification

Proper implementation of BMPs can be critical to the environmental success or failure of a

remining site. Thus, it is imperative that the BMPs be implemented as planned. It is the role of the

regulatory inspection staff to verify and enforce the provisions outlined in the BMP plan of a

remining permit. The inspector generally does not need to be present at all times to assess the

implementation of the BMPs in this document. However, some BMPs will require more detailed
Coal Remining BMP Guidance Manual

38 Best Management Practices

and more frequent inspections than others. It is also incumbent on the mine operator to ensure

that the BMPs are implemented as designed and to provide the proper documentation (e.g.,

material weigh slips, receipts, laboratory analyses, etc.) where necessary. Guidelines for

verification for each BMP category are provided in the appropriate section of this manual. 

Monitoring of the water quality and quantity is the truest measure of BMP effectiveness. If the

discharges exhibit lower pollution loadings, this is an indication that the BMPs were successful

with all other factors being equal.

Monitoring and inspection of BMPs to verify site conditions and implementation should be a

requirement of any remining operation. Verification includes:

C Direct measurement of flow and water sampling for contaminant concentrations before,

during, and after reclamation.

C Monitoring should continue beyond the initial water table re-establishment period (e.g., at

least 2 years after backfilling).

C Evaluation of water quality and quantity data at hydrologically-connected units and/or

discrete individual discharges, so trends caused by remining can be assessed.

C Hydrologic data should be reviewed with respect to climatic (i.e. precipitation) conditions.

C Assessment of deviations from the approved implementation plan.

C Inspection of critical stages of the BMP implementation plan, such as during special

materials handling, alkaline addition, drain installation, or mine entry sealing.

C Inspection should assure, where required, proper maintenance is performed.

C Review of material weigh slips, receipts, laboratory analysis, and other necessary

documentation.

C Assessment of BMP stability over time.

C Periodic site evaluation to ensure the BMP plan is appropriate to on-site conditions. This

evaluation should include, at a minimum, assessment of water quality and quantity, site

physical and geologic conditions, and impacts of significant storm events.
 Coal Remining BMP Guidance Manual

Best Management Practices 39

Adequate inspection, hence verification, is necessary to ensure that BMPs are being performed as

proposed. Remining operation inspections will also provide information as to changing site

conditions (anticipated and unanticipated) as well as unexpected developments.

Verification also will provide additional data for on-going assessment of the efficiency of

individual BMPs as well as BMP combinations. The analyses of these data will foster continuing

improvement of the BMPs which will ultimately lead to more efficient ways of decreasing

pollution loadings.

This manual is designed to:

• describe the BMPs that are available for remining operations. 

• define the appropriate circumstances for the BMPs.

• explain how each BMP functions to diminish the pollution load.

• discuss how a BMP works or in conjunction with other BMPs.

• give details of BMP construction and installation specifics, size and scope of a particular

BMP, and the required materials.

• present actual data from remining case studies employing various BMPs.

• discuss relative frequency of use for each BMP.

• give estimates of the cost of employing each BMP.

• present projected efficiencies of specific BMPs based on a database of 116 completed sites

in Pennsylvania, case studies, and published research.

References 

Appalachian Regional Commission, 1969. Acid Mine Drainage in Appalachia. Appalachian

Regional Commission, Washington, DC, 210 p.

Brady, K.B.C., R.J. Hornburger, and G. Fleeger, 1998. Influence of Geology on Postmining

Water Quality: Northern Appalachian Basin. Chapter 8, Coal Mine Drainage Prediction and

Pollution Prevention in Pennsylvania. Pennsylvania Dept. of Environmental Protection. 
Coal Remining BMP Guidance Manual

40 Best Management Practices

Cecil, C.B., R.W. Stanton, S.G. Neuzil, F.T. DuLong and B.S. Pierce, 1985. Paleoclimate

controls on Late Paleozoic sedimentation and peat formation in the central Appalachian Basin. 

International Journal of Coal Geology, v. 5, p. 195-230.

Hawkins, J. W., 1995. Characterization and effectiveness of Remining Abandoned Coal Mines in

Pennsylvania. U.S. Bureau of Mines, Report of Investigations - 9562, 37 pp.

Interstate Mining Compact Commission (IMCC), 1997. Discussion Paper on Water Quality Issues

Related to Remining. Presented at the IMCC meeting conducted July 8, 1997, amended

September 1997 for presentation at IMCC annual meeting conducted September 15, 1997, 5 pp.

Interstate Mining Compact Commission (IMCC), 1998. Solicitation to Members, September 3,

1998.

Lineberry, G.T., K.F. Unrug, and D.E. Hinkle, 1990. Estimating Secondary Mining Potential of

Inactive and Abandoned Appalachian Highwalls. Int. J. Surf. Min. Reclam., v. 4, pp. 11-19.

Office of Surface Mining, Reclamation and Enforcement (OSMRE), 1998. Electronic copy of

AMLIS database, current as of September 23, 1998, dBase file format called ALLPADS.dbf,

14,307,960 bytes.

Office of Surface Mining, Reclamation and Enforcement (OSMRE), 1999. Unreclaimed

Problems. Abandoned Mine Land Program. http://www.osmre.gov/zintroun.htm Updated

11/13/98, 2pp.

Pennsylvania Dept. Of Environmental Resources, Penn. State Univ., and Kohlman Ruggiero

Engineers, 1988. Coal Remining - Best Professional Judgement Analysis. Prepared for USEPA

Office of Water and PA Dept. Of Envir. Res., November 1988.

Plowman, W., 1989. New Light on an Old Problem. Game News, May 1989, 6pp.

Skousen, J., R. Hedin, and B. Faulkner, 1997. Water Quality Changes and Costs of Remining in

Pennsylvania and West Virginia. Paper presented at the 1997 National Meeting of the American

Society for Surface Mining and Reclamation, Austin, Texas, May 10-15, 1997.

Skousen, J., T. Hilton, and B. Faulkner, 1999. Overview of Acid Mine Drainage Treatment with

Chemicals. West Virginia Extension Service, http://www.edu/~agexten/landrec/chemtrt.htm 15

pp.

Smith, M.W., 1988. Establishing Baseline Pollution Load from Pre-existing Pollutional

Discharges for Remining in Pennsylvania. Paper in Mine Drainage and Surface Mine

Reclamation. II. Mine Reclamation, Abandoned Mine Lands and Policy Issues. USBM IC 9184, 

pp.311-318.
 Coal Remining BMP Guidance Manual

Best Management Practices 41

Smith, M.W. and C.H. Dodge, 1995. Coal Geology and Remining, Little Pine Creek Coal Field,

Northwestern Lycoming County. PADEP Guidebook, pp. 13-26.

U.S. Environmental Protection Agency Region III and Office of Surface Mining, 1997. Cleaning

Up Appalachian Polluted Streams. 1996 Progress Report, USEPA Region III and OSM,

September 1997, 54 pp..

U.S. Department of Energy (DOE), 1997. Coal Industry Annual. Energy Information

Administration, DOE/EIA-0584(97), 256 pp.

U.S. Department of Energy (DOE), 1999. Annual Report of the Council on Environmental

Quality, http://ceq.eh.doe.gov/reports/1993/chap7.htm 24 pp.

USGS, 1996. Assessing the Coal Resources of the United States. Factsheet FS-157-96,

http://energy.usgs.gov/factsheets/nca.html, p.2.

USGS, 1998. Biology in Focus. Biological Resources Division, April 1998, 4 pp.

Veil, J.A., 1993. COAL REMINING: Overview and Analysis. Prepared for U.S. DOE under

Contract W-31-109-ENG-38, 37 pp.

Wetzel, K.L. and S.A. Hoffman, 1983. Summary of surface-water quality data, Eastern Coal

Province, October 1978 to September 1982. US Geological Survey Open-File Report 83-940,

p.67.

Zipper, C.E. and B. Lambert, 1998. Remining To Reclaim Abandoned Mined Lands: Virginia’s

Initiative. Presented at 15th Ann. Meeting of the Amer. Society for Surface Mining and

Reclamation. May 17-22, 1998. St. Louis, 8pp.

303(d)PA, 1998. Commonwealth of Pennsylvania Section 303(d) List. Pennsylvania Department

of Environmental Protection, July 23, 1998.

303(d)WV, 1998. West Virginia, Division of Environmental Protection, Office of Water

Resources, Supplement to West Virginia 303(d)

303(d)AL, 1998. Alabama Department of Environ. Management 303(d) List. August 26, 1998.

303(d)VA, 1998. Virginia 1998 303(d) Total Maximum Daily Load Priority List and Report.

Prepared by the Dept. Of Envir, Quality and the Dept. Of Conservation and Recreation,

Richmond, VA, October 1998.
Coal Remining BMP Guidance Manual

42 Best Management Practices

303(d)KY, 1998. 303(d) List of Waters for Kentucky. Kentucky Natural Resources and

Environmental Protection Cabinet, Division of Water, June 1998.

303(d)TN, 1998. Proposed Final 1998 303(d) List. Tennessee Department of Environment and

Conservation, Nashville, Tennessee, June 1998 (Revised July).
Coal Remining BMP Guidance Manual

Hydrologic Controls 1-1

Section 1.0: Hydrologic and Sediment Control BMPs

Introduction

Controlling physical hydrologic aspects constitutes a substantial portion of the Best Management

Practices (BMP) that are employed at remining sites. Reduction of the pollution load yielded from

abandoned mines by remining has shown that reduction of the flow rate is the most salient factor

(Smith, 1988; Hawkins, 1994). Where site conditions permit recharge to the ground-water system

to be controlled through mining practices and engineering techniques, the discharge flow rate will

likewise be reduced. The diminished flow rate will in a majority of cases cause a quantifiable

decrease in the pollution load. Although contaminant concentrations from coal mining sources

frequently exhibit an inverse relationship to flow, pollution load reductions are more commonly

recorded, even when moderate increases to the contaminant concentration occur in conjunction

with a discharge flow rate reduction.

BMPs that ultimately are responsible for reducing discharge flow rates include various means of

reducing the infiltration of precipitation and surface waters, impeding or intercepting the

movement of ground water from adjacent areas unaffected by remining activities, and providing a

means to collect and rapidly remove ground water (Hawkins, 1995a). There are a battery of BMP

methods that can be employed to impede recharge to mine spoil. These BMPs are subdivided into

two main categories: the exclusion of infiltrating surface water and the exclusion of laterallymigrating ground water.
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1.1 Control of Infiltrating Surface Water

Methods that decrease surface-water infiltration include, but are not limited to, spoil regrading

(for elimination of closed-contour depressions and the promotion of runoff), installation of

diversion ditches, capping the spoil with a low-permeability material, surface revegetation, and

stream sealing. Prior to remining, abandoned sites commonly have unreclaimed pits and closedcontour depressions in poorly-sorted spoil that serve as recharge zones for significant quantities

of infiltrating surface water. For many abandoned surface mines, the act of regrading, resoiling,

and revegetating spoil significantly reduces surface-water infiltration and increases runoff just by

the elimination of recharge zones and enhanced evapotranspiration. These three actions are the

more commonly employed BMPs during remining operations, because they are an integral part of

the remining and reclamation process. Additional means by which surface-water infiltration can be

restricted are prevention of surface water infiltration by the installation of diversion ditches,

stream reconstruction and sealing, and capping of the backfill with an low-permeability material. 

Theory

Initially after reclamation, diffuse recharge from the surface through soil is generally well below

pre-mining levels because of the destruction of soil structure, soil compaction by mining

equipment, and low-vegetative growth, all of which tend to promote surface-water runoff rather

than infiltration (Razem, 1983; Rogowski and Pionke, 1984). Wunsch and Dinger (1994) noted

that, during re-excavation, spoil within a few inches of the surface was dry indicating little

infiltration was occurring. Decreases in recharge also may be facilitated by increases in porosity in

the unsaturated zone (Razem, 1984). Flow-duration curves show that after mining receiving

streams have reduced base flows, which indicate that recharge is decreased (29 percent less than

pre-mining levels) and surface runoff is increased (Weiss and Razem, 1984). After this initial

period, as soil structure and vegetation re-establishes, diffuse recharge from the surface begins to

increase. This may coincide with observed increases in hydraulic conductivity after 30 months.

The slow recovery of the water table during this period may be linked to decreased recharge
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1-4 Hydrologic Controls

shortly after reclamation and to increased effective porosity and permeability of the spoil.

Increased porosity permits more of the infiltrating water to become stored within the aquifer.

Some of the recharge from the surface during this early period occurs through discrete openings

or voids that are exposed at the surface (Hawkins and Aljoe, 1991; Wunsch and Dinger, 1994).

Surface-exposed voids facilitating ground-water recharge also have been observed at a surface

mine in central Pennsylvania that has been reclaimed for over 15 years. Surface runoff flowing

across the mine surface enters the spoil through these exposed voids and flows rapidly downward

via conduits to the saturated zone. This observation illustrates that these exposed voids continue

to receive significant amounts of recharge long after final reclamation, re-establishment of the soil

structure, and successful revegetation.

Other researchers contend that mining may improve the recharge potential from undisturbed areas

(Cederstrom, 1971). Herring (1977) observed that overall recharge and surface water runoff to

reclaimed surface mines in the Illinois Basin were greatly increased. Herring attributes the

increased recharge to the dramatic increase in permeability of the cast overburden. Herring also

observed a four-fold increase in recharge from mining one half of a watershed in Indiana. It is

important to note that these two studies did not address the impact of mining on the soil horizon

as discussed by Razem (1983, 1984). Once infiltrating water has passed through the soil horizon,

it appears that the recharge potential is dramatically increased. In order for surface water

infiltration to be prevented, the water should be intercepted before it percolates through the soil

and enters the highly permeable spoil beneath.

Strock (1998) wrote: 

The practical reality of this is that in ... humid areas where precipitation exceeds

evapotranspiration, virtually all mine sites will receive ground water recharge and

generate drainage - acidic or alkaline. That there may be no obvious springs or seeps

does not imply that there is no drainage from the site. To illustrate what 15 inches (38

cm) of infiltration per year means in terms of the quantity of mine drainage which can

be generated, each acre of spoil surface would produce an average flow rate of 0.75

gpm (2.84 L/min). A 100-acre surface mine, then, would yield 75 gpm (284 L/min)

of ground water flow.
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Hydrologic Controls 1-5

Unreclaimed abandoned spoil piles and ridges may permit infiltration approaching 100 percent of

the precipitation falling on the site. Some of this water will be removed as direct evaporation, but

most will recharge the spoil. Infiltration rates and amounts are directly related to ground slopes,

particle sizes, sorting, lithology, and degree of weathering. Larger particles tend to create larger

pore spaces, thus permitting rapid infiltration of substantial volumes of water. Poorly-sorted spoils

likewise permit large volumes of water to infiltrate quickly, compared to well sorted fine-grained

spoils. Well-cemented sandstones tend to break into and remain as large fragments, thus forming a

relatively transmissive material. Conversely, many shales of the Appalachian Plateau tend to break

and weather rapidly to relatively small fragments and clays creating a somewhat poorly

transmissive environment (Hawkins, 1998a).

Mine spoil is a poorly sorted, unconsolidated material composed of angular particles ranging from

clay-sized (less than 2 microns) to those exceeding very large boulders (greater than 2 meters).

Because of the broad range of particle sizes and poor sorting, spoil tends to be highly porous and

transmissive. Testing in mine spoil has recorded porosity values exceeding 15 percent for mine

sites reclaimed for more than 10 years (Hawkins, 1995a). The porosity of recently reclaimed spoil

may approach a spoil swell factor of 20 to 25 percent (Cederstrom, 1971). Aquifer testing in the

Appalachian Plateau indicates that the transmissive properties of spoil tend to be more than two

orders of magnitude (100 times) greater than that of undisturbed parent rock (Hawkins, 1995a).

Some of the recharge from surface water occurs through discrete openings or voids exposed at

the surface across a backfill (Hawkins and Aljoe, 1991; Wunsch and Dinger, 1994). Surface

runoff from a precipitation event, flowing across the mine surface, will combine in rivulets, enter

the spoil through these exposed voids, and flow rapidly downward via conduits to the saturated

zone. The action of this water rapidly flowing in from the surface tends to increase the size and

conductivity of these holes through the piping of finer grained sediments. In some instances,

infiltrating water will reappear a short distance away (e.g., 300 feet) as a high-flowing ephemeral

spring, but in most cases the water recharges the spoil aquifer and is more slowly released at

perennial discharge points. Also aiding surface water infiltration is the characteristic high porosity

of mine spoil, which permits rapid acceptance and storage of relatively large quantities of ground

water.
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Site Assessment - Backfill Testing

Spoil characteristics, such as hydraulic conductivity, porosity, and infiltration rates, are by-andlarge dependent on site-specific conditions. Even with site-specific testing, these parameters can

vary widely and are only predictable within a broad range. A wide range of hydraulic conductivity

values (up to 3 orders of magnitude) can be recorded within a single mine site (Hawkins, 1998a).

Prediction of these values prior to mining is exceedingly difficult.

Hawkins (1998a) conducted aquifer tests on several mine sites across the northern Appalachian

Plateau in an attempt to predict mine spoil hydraulic properties. He found that the best correlation

occurs between the age of the spoil and the hydraulic conductivity. The impacts of other factors

(e.g., lithology, spoil thickness, and mining types) on spoil properties appear to be masked by a

variety of factors introduced during the operation.

Given the broad range of mining types, spoil lithology and age, and other factors, it is doubtful a

narrowly defined prediction model will ever be available. In addition to the aforementioned testing

problems, spoil will at times exhibit turbulent flow which does not obey Darcy’s Law, invalidating

the aquifer testing procedures. 

Materials used in sealing or grouting may require analysis to ascertain their hydraulic properties,

and thus, determine suitability of use. Field testing for compaction or density may also be needed.

This testing can be performed via a standard penetration test, using a penetrometer.

1.1.1 Implementation Guidelines

There are very few, if any, situations where the proper implementation of the surface water

infiltration reduction BMPs discussed in this chapter will not have a positive impact toward the

reduction of pollution loads. A reduction of recharge ultimately reduces discharge rate, and

discharge and pollution load rates commonly exhibit a strong positive correlation. Therefore,
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Hydrologic Controls 1-7

with a reduction in flow rate, pollution loads usually exhibit a reduction commensurate with the

decreased flow (Hawkins, 1995b). Until the present, however, these BMPs have been

implemented almost entirely with the intention of aesthetically-pleasing reclamation in mind. 

The prevention of surface water infiltration has not been a specifically targeted concern, thus

the true potential to reduce discharge rates with these BMPs has not been determined. 

Regrading Abandoned Mine Spoil

A significant amount of surface-water infiltration can be reduced by regrading abandoned mine

spoil. Abandoned spoil piles commonly exhibit poor drainage. Closed-contour depressions and

poorly vegetated surfaces facilitate the direct infiltration of precipitation and other surface

 waters. Closed-contour depressions permit the impounding of surface water which in turn

promotes infiltration into the spoil. Rough unreclaimed spoil ridges and valleys with exposed 

rock fragments facilitate the direct and immediate infiltration of precipitation as it occurs.

Removal of closed contour depressions, elimination of spoil ridges and valleys, and the 

resulting creation of runoff-inducing slopes greatly reduces surface-water infiltration into spoil. 

Skousen and others (1997) observed an average flow rate reduction of 43 percent of a 

discharge that averaged 188 gpm at a remining operation in Butler County, Pennsylvania. The

main BMP was regrading and reclamation of approximately 8.7 acres of abandoned surface 

mine land. A second remining operation in Butler County, Pennsylvania reclaimed about 12 

acres of abandoned spoil as its primary BMP. Flow reduction of the discharges ranged from

complete elimination of one, 70 percent reduction of two others, and 25 percent reduction of a

fourth. While regrading and revegetation were not the exclusive BMP employed, these flow

reductions are indicative of what can be achieved with these BMPs.

Regrading of abandoned mine spoil is one of the most frequently employed BMPs in the 

operation of remining permits. Older mining operations were not as efficient as present day

operations, and could not economically excavate as deeply as more modern equipment

allows. Regrading is an integral part of most remining permits. In order to achieve a minimum 
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1-8 Hydrologic Controls

reclamation standard as statutorily mandated, abandoned spoil piles are regraded to return the site

to the approximate original contour or to at least achieve a more natural looking post-mining

condition. In order to maximize the efficiency of this BMP, the spoil should be regraded in a

manner which promotes runoff of precipitation and other surface water. This is achieved by

creating slopes of a sufficient grade to induce runoff, but not to the degree that the runoff water

velocity causes undue erosion.

The application of topsoil or an available soil substitute to newly regraded spoil improves the

ability of spoil to impede surface-water infiltration. Several factors that directly impact changes in

the infiltration rate between bare spoil and top-soiled and revegetated spoil, are lithology of the

spoil material, composition, structure, roughness, and texture of the soil, density of vegetation,

and surface slope. Soil freshly replaced on spoil exhibits an infiltration rate that is considerably

less than that for unmined areas (Rogowski and Pionke, 1984; Jorgensen and Gardner, 1987).

Therefore, it is not unexpected that the infiltration rate in resoiled spoil will be significantly below

that in unreclaimed spoil. These low infiltration rates are related to the lack of soil structure,

reduced root density, and the lack of other naturally occurring infiltration pathways that are

present in undisturbed soils. Over time, the infiltration rate of mine soils increase. However, after

four years, Jorgensen and Gardner (1987) observed that infiltration rates for mine soil were still

below natural soils. Potter and others (1988) noted that significant differences between reclaimed

soil properties and those of undisturbed soils still exist 11 years after reclamation.

Potter and others (1988) observed that the saturated hydraulic conductivity of reclaimed topsoil

was approximately one fourth of that measured in undisturbed topsoil. Reclaimed subsoil

exhibited a hydraulic conductivity about a tenth of undisturbed subsoil. Silburn and Crow

observed that subsoils composed of shale and clay spoils are 10 and 100 times less permeable than

from natural subsoils, respectively. Thus, runoff from reclaimed mine spoils is much greater than

natural soils. The reasons for these differences are attributed to decreased percentage of large

pores resulting in density increases, loss of soil structure and reduced depths to low permeability

layers (Silburn and Crow, 1984).
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Hydrologic Controls 1-9

Effective regrading of “dead” spoils, commonly an integral part of reclamation, will reduce the

amount of surface water that will infiltrate into the backfill. However, there may be situations

where site conditions indicate that re-affecting the spoil could cause an increase in the pollution

load. These are sites where the original mining was conducted several decades earlier, the spoil

has been naturally revegetated and the backfill is in a state of geochemical equilibrium. Reaffecting the site would subaerially expose a significant portion of the backfill material, allowing

additional oxidation of pyritic material that was otherwise relatively stable. Remining (in this case,

regrading dead spoil) could reinvigorate the production of acid-mine drainage and cause more

problems than it abates. In these situations, the anticipated amount of reduced flow would have to

be weighed against the projected increase in contaminant concentration.

Installation of Surface Water Diversion Ditches

Diversion ditches can be constructed in two different locations, both of which reduce surfacewater infiltration into the backfill. First, diversion ditches can be constructed above the final

highwall or open pit to prevent surface water from adjacent unmined areas from entering the

reclaimed site and infiltrating into the subsurface. Second, diversion ditches can be constructed

within the backfill area to promote the efficient and rapid removal of direct precipitation prior to

infiltration into the spoil.

Diversion ditches can be installed on top of reclaimed mine spoil to control the rate and pathway

of runoff in the prevention of soil erosion. Diversion ditches also can be installed as part of a BMP

plan to reduce pollution load. These ditches should be constructed to collect as much surface

water as possible and to subsequently and expeditiously transport it from the site. Properly

constructed (lined and sloped) ditches installed on the backfill will transport runoff from the

backfill to the nearest drainage way. 

A significant potential for recharge exists at the interface of the highwall and the spoil. For years

and probably for decades after backfilling, spoil tends to settle, compact, and undergo other

volume-reducing actions. While this settling occurs, the adjacent unmined highwall does not
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1-10 Hydrologic Controls

appreciably change. Because of this differential settling, it is common for linear surface gaps or

cracks to run along or near this interface (Figure 1.1.1a). These cracks create an ideal infiltration

zone for surface water. If surface water from unmined areas can be intercepted prior to flowing

across a highwall and on to the spoil, a substantial amount of infiltration can be prevented. The

installation of diversion ditches above the highwall is an effective BMP to preclude recharge to

the spoil from adjacent surface water runoff.

Figure 1.1.1a: Diagram of the Location of Surface Cracks Between Highwall and Backfill

Because of the transmissive characteristics of mine spoil, diversion ditches need to be lined or

sealed to preclude infiltration of the water that they are designed to collect and transport away.

Lining of these ditches can be performed using a variety of natural and man-made materials, such

as existing on-site clays, bentonite, coal combustion wastes (CCW), sheet plastic or other

geotextiles, and cement (shotcrete). Regardless of the material used to line the ditches, it will need

to be durable. The integrity of these ditches should be maintained for a considerable length of time

or until the mine drainage discharges no longer exceed applicable effluent standards.
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Hydrologic Controls 1-11

By and large, there are very few situations where properly constructed diversion ditches will not

be beneficial in terms of reducing surface-water infiltration into the reclaimed site. Diversion

ditches constructed above the final highwall across undisturbed ground are unlikely to be

problematic in terms of leakage. The underlying subsoil and rock are less permeable than that

encountered in disturbed areas. Diversion ditches constructed across reclaimed spoil are more

prone to leak and allow substantial amounts of surface-water infiltration. The aforementioned

porous and permeable nature of spoil can facilitate rapid infiltration of significant amounts of

water over a short linear distance or at discrete points. Measures should be taken to insure the

integrity of these ditches. The emplacement of some type of ditch-lining material, natural or

manmade, is recommended. Where water velocities are sufficient to cause erosion, an erosionresistant material should be placed as a cover for the liner material.

Lining diversion ditches with a relatively impervious material reduces the amount of infiltration

through the bottom of the ditch, thus reducing recharge to the underlying strata. Reducing

recharge to areas adjacent to reclaimed mines can indirectly reduce the amount of recharge to the

mine spoil. When the adjacent strata receives increased recharge, some of this ground water will

flow toward and enter the spoil. Therefore, if surface-water infiltration from the diversion ditch is

impeded, recharge to adjacent spoil aquifers may also be reduced.

Low-Permeability Caps or Seals

There have been sporadic studies performed to determine the efficiency of sealing or capping the

surface of backfilled surface mines. The intention of sealing or capping is to preclude area-wide

surface-water infiltration by placing a low-permeability cap over the backfill material, before the

soil is replaced (Figure 1.1.1b). Because of the large surface area to be covered and the generally

low profit margin at remining sites, the capping material should be readily available and

inexpensive to make this BMP a viable option. Capping materials generally should be composed

of a locally-available waste product, such as pozzolonic (self-cementing) CCW or a naturallyoccurring clay within a short hauling distance.
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Figure 1.1.1b: Schematic Diagram of a Cap Installed on a Reclaimed Surface Mine

The installation of low-permeability caps over the top of mine backfills can be an effective BMP

for reducing surface-water infiltration. However, installation of these caps can be an expensive

operation. Before approving the use of this BMP, the reviewer needs to ascertain whether it is

economically feasible. The reviewer also needs to determine that the capping materials are readily

available and of sufficient quality to complete the operation. Additionally, because mine spoil

continues to subside with time, as has been observed beyond ten years after reclamation, the cap

should be made to withstand the expected subsidence as much as possible. 
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Hydrologic Controls 1-13

In order to prevent the movement of water and atmospheric oxygen, Broman and others (1991)

determined that capping materials need to have a hydraulic conductivity of 5 x 10-9 m/s or less.

Broman and others developed a mixture of 35 percent biosludge from a paper mill and 65 percent

coal fly ash. Lundgren and Lindahl (1991) specified a hydraulic conductivity of 1 x 10-9 m/s or less

for a capping material for waste rock piles in a copper-producing area of Sweden. They

successfully used a grouting cement-stabilized coal fly ash material, with a hydraulic conductivity

approximately one order of magnitude lower than this specified value. Hydraulic conductivity

values ranging from 10-10 to 10-12 m/s were recorded by Gerencher and others (1991) for shotcrete

used to cap and seal waste rock dumps in British Columbia. Based on these studies, the hydraulic

conductivity values necessary to create an effective cap are in the range of 10-9 to 10-10 m/s. These

values are similar to values recorded for extremely impervious igneous rock, such as dense

unfractured basalt (Freeze and Cherry, 1979). Spoil, on the other hand, is substantially more

transmissive exhibiting a median hydraulic conductivity of 2.8 x 10-5 m/s. However, the hydraulic

conductivity of spoil exhibits a very broad range, 10-9 to 10-1 m/s, depending on the parent rock

lithology and other geologic- and mining-related factors (Hawkins, 1998a).

A 20 hectare mine site in Upshur County, West Virginia was covered with PVC sheeting in an

effort to reduce the pollution load. The result was a 50 to 70 percent reduction of the acidity load.

Even though additional BMP techniques (e.g., special handling, lime and phosphate addition)

were employed at this site and may have contributed some to the acid load reduction, the bulk of

the pollution load reduction appeared to be directly related to the subsequent flow reduction

(Meek, 1994).

A layered-composite soil cover was used to cover waste rock piles near Newcastle, New

Brunswick, Canada in an attempt to preclude infiltration of atmospheric oxygen as well as water.

The system consisted of a sand base overlain by compacted glacial till covered with sand and

gravel. The top layer of cover consisted of 10 cm of well-graded gravel to prevent erosion. This

system permitted between 1 and 2 percent of precipitation falling on the site to infiltrate into the
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waste rock below the cap. The cap’s low-permeability material was glacial till with a hydraulic

conductivity of 1.0 x 10-8 m/s (Bell and others, 1994).

Yanful and others (1994) constructed a cover for tailings piles in Canada to prevent the

infiltration of surface water and atmospheric oxygen. A 60 cm compacted clay layer was placed

between two 30 cm sand layers. The clay had an initial hydraulic conductivity of 1.0 x 10-9 m/s,

which did not change during the 3 year monitoring period. A thin gravel layer was placed over the

top of the cap for protection. This cover excluded over 96 percent of the total precipitation from

infiltrating into the tailings. 

These studies indicate that if a cap is placed on top of a reclaimed backfill, a significant reduction

of surface-water infiltration can be achieved. For example, if a hypothetical unreclaimed and

unvegetated site permits infiltration of 75 percent of the precipitation (this number is likely higher)

and continues to allow 35 percent infiltration after it is regraded, the addition of an effective cap

should decrease the infiltration rate to between 2 and 4 percent. Let us assume that a 100 acre site

receives 40 inches of precipitation per year and all of the infiltrating water discharges at one point.

In the unreclaimed state, the average discharge rate would be 155 gpm. Once regraded the

discharge will yield approximately 72.3 gpm. If a cap is installed the discharge rate should be

reduced to 8.3 to 12.4 gpm. If the initial acidity concentration is 120 mg/L, the loading rate for

the unreclaimed site would be 225.4 lbs/day. However, with regrading and cap installation, even if

the acidity concentration increased by 10 percent to 132 mg/L, acidity loading would still show an

overall decrease to a range of 13.3 to 19.8 lbs/day or 91.2 to 94.1 percent.

Revegetation

Revegetation of mine spoil can dramatically reduce the amount of surface water that would

otherwise eventually make it to the underlying ground-water system. Vegetative cover also can 

decrease the amount of atmospheric oxygen that can enter the subsurface, because biological

activity in the soil, such as decay of organic matter, can create an oxygen sink. A well developed
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Hydrologic Controls 1-15

soil with a dense cover of vegetation can retain a significant amount of water. Eventually, this

water evaporates or is transpired by the plants and does not recharge the spoil aquifer. Because

this BMP is a statutory requirement of all mining permits, it is one of the most frequently

employed. However, attempts to specifically tailor the vegetative cover to maximize

evapotranspiration are rare to nonexistent.

Evapotranspiration of surface water entering mine spoil will be enhanced as the vegetative cover

is increased (Strock, 1998). A thick forested area will permit more than twice as much

evapotranspiration (35 inches per year) as barren rocky ground (15 inches per year) in the same

area (Strock, 1998). The actual water loss depends on several factors including density, type of

plants, and length of the growing season.

Revegetation of a reclaimed mine will in most cases be beneficial toward reducing surface-water

infiltration. Caution should be used to prevent vegetative cover from providing conductive

avenues for surface-water infiltration. In some cases, the root systems of plants will create areas

where water can infiltrate in to the spoil. However, a lush vegetative growth may allow for greatly

increased evapotranspiration rates that can offset the increased infiltration along root zones. 

Stream Sealing

The sealing of streams reconstructed across backfill areas is intended to preclude direct infiltration

into the spoil. The increased permeability and porosity of spoil by comparison to undisturbed

strata promotes streams that have been reconstructed in mine spoil to lose water to the underlying

aquifer. The water table in surface mine spoil is commonly suppressed compared to the water

table at the site prior to mining and/or in adjacent unmined areas (Hawkins, 1995a). A hydraulic

gradient from the reconstructed stream to the suppressed underlying water table is frequently

present, thus facilitating infiltration. Therefore, reconstruction of these streams should be

conducted with the assumption that they will leak unless sealed or lined.
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1-16 Hydrologic Controls

The primary and probably most inexpensive method of sealing streams is with plastic sheet lining.

Shotcrete can also be used for lining limited sections of stream beds in a relatively cost effective

manner. One of the problems associated with plastic lining is that the plastic sheeting eventually

breaks down chemically and ruptures or is punctured by sharp rock fragments. 

Stream sealing also has been performed by excavating and emplacing a clay liner along the stream

reach (Ackman and others, 1989). In this case, the stream was disrupted by subsidence from a

shallow abandoned underground mine. The effectiveness of the clay seal was less than 100

percent. The section of stream that was clay lined exhibited a 4 percent loss of flow over

approximately 170 feet, whereas, the preceding section of stream exhibited an 8 percent flow

decrease over a similar distance.

Another method of stream sealing involves injecting polyurethane to grout targeted sections of

streams. Similar grouting has been successfully conducted on losing streams situated over the top

of abandoned underground mine workings. In these cases, the underlying mine was relatively

shallow (25 to 50 feet) and losing stream sections were located by use of electromagnetic terrain

conductivity surveying equipment. Once located, zones of significant infiltration were targeted for

grouting (Ackman and Jones, 1988). Given the length of stream that would require grouting and

the high porosity of the spoil, it is doubtful that polyurethane grouting would be economically

viable for most remining operations.

Stream sealing as a BMP is appropriate only where a section of a stream is mined through and

subsequently reconstructed. Like diversion ditches that cross a reclaimed mine, these streams

should be rebuilt in such a manner that they do not leak water into the subsurface. The stream bed

should be underlain with a liner material to preclude surface water infiltration. However, erosionresistant material should be placed over the top of the liner to prevent future liner breaching.
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Hydrologic Controls 1-17

Design Criteria

The design and implementation plan of BMPs intended to reduce the infiltration of surface water

into mine spoil and adjacent undisturbed areas depends a great deal on site conditions (i.e. amount

of precipitation, location of surface water streams or drainage areas, original contour, indigenous

vegetation, soil type, and readily available materials. Recommended design criteria for the

implementation of surface-water infiltration control BMPs are included in the following list. This

list is by no means all-inclusive. Permit writers, regulatory authorities, and designers should

consider all site conditions with the intent of implementing the most cost effective means of

reducing pollutant loading during remining operations.

Regrading

C Promote controlled runoff of precipitation and other surface waters

C Return the site to the approximate original contour

C Performed along the contour to minimize erosion and instability

Diversion Ditches

C Divert runoff away from disturbed areas

C Promote rapid runoff from disturbed areas

C Adequate to pass the peak discharge of a defined storm event such as a 2-year, 24-hour

storm (temporary ditches) or a 10-year, 24-hour storm (permanent ditches)

C Diversion ditch construction in landslide prone areas or where severe erosion is possible

should be performed with extreme care, if at all

Caps or Seals

C Use readily available materials (e.g., on site clays or CCW)

C Material with hydraulic conductivity of 10-9 m/s or less

C Should be able to withstand anticipated subsidence without breaching
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1-18 Hydrologic Controls

Revegetation

C Root systems should retain water and not provide infiltration pathways

C Select local and native plant species that will thrive and create a lush cover

Stream Sealing

C Use chemically inert materials that are not prone to erosion or puncture damage

C Use readily available materials (e.g., on-site clays or CCW)

1.1.2 Verification of Success or Failure

Verification that BMPs have been properly and completely implemented during remining

operations is crucial to effective control or remediation of pollutant loading. In other words,

monitoring should ensure that the as-built product is the same as that originally proposed by the

operator and approved by the regulating authority. The importance of field verification of all

aspects of a BMP cannot be overstated. It is the role of the mine inspector to enforce the

provisions outlined in the permit. The mine inspector does not need to be present at all times to

assess the amount of regrading for dead spoils, the elimination of closed-contour depressions or

revegetation. The completion of these tasks should be evident from visual inspection or if

required, from a survey of the area.

The actual installation of diversion ditches or stream replacements should be self evident from a

visual inspection. However, whether the ditch or stream was properly constructed and will not

leak requires a bit more work on the part of the mine inspector or hydrologist. If a liner was

prescribed for proper stream installation, the inspector can require weigh slips or receipts for

material brought into the site. If on-site material is to be used, a marked material stock pile can be

required. An inspector also can require notification of liner installation and completion dates.

Failure of a ditch or a stream to hold water can be determined by conducting flow measurements.

If the flow shows a significant decrease (e.g., outside the known error of the flow measurement

method) or disappears altogether, there is an indication that water is infiltrating and recharging the

backfilled site.
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Hydrologic Controls 1-19

Determining the implementation level of some of the BMPs discussed in this chapter after the fact

is not always an easy procedure. Verification that a capping seal was installed properly, without

being present during the operation, can be difficult. However, if the capping material is trucked in

from an outside source, weigh slips or receipts can be obtained to confirm the amount of material

used. If on-site material is to be used, a marked stockpile of the material can be required. Given

the amount of work involved in spreading and compacting, it is likely a mine inspector will visit

the site at least once during the capping process. If there is great concern that the cap will not be

properly installed, the permit can be conditioned to require notification of the mine inspector at

predetermined salient points during the procedure.

The efficiencies of BMPs need to be monitored in order to improve and effect future refinements

of the processes. Not only does the type of BMP need to be assessed, but the scope and degree of

BMP implementation needs to be related to the degree of improvement (e.g., flow or pollution

load reduction). The mechanism to determine the effectiveness of BMPs discussed in this chapter

is similar to any abatement procedure research project. In the case of these surface water control

BMPs, a significant portion of the monitoring will consist of measuring the flow rates of

discharges emanating from the site. It is fully realized that the locations of discharges may, and

frequently do, move from their pre-remining locations. Therefore, a hydrologic-unit approach is

recommended. The mine site should be divided into hydrologic units, that is, portions of the mine

that contribute to one or more discharges. Discharge data (flow and/or loading rate) can be

mathematically combined to permit pre- versus post-mining comparisons.

Given the nature of mine spoil and the time that it takes for a water table to re-establish and reach

equilibrium, post-mining monitoring may need to continue for at least 3 to 5 years. In eastern

Ohio, water-table re-establishment at three reclaimed surface mines was observed to be nearly

complete approximately 22 months after reclamation was completed (Helgesen and Razem,

1980). Recovery of the water table after mining may take 24 months or longer in Pennsylvania

(Hawkins, 1998b). The rate of water-table recovery is related to several factors including

precipitation, infiltration and discharge rates, porosity, topography, and geologic structure.

Additionally, short-term changes in flow and/or contaminant concentration commonly occur
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during the initial 1-3 years after backfilling because of substantial physical and chemical flux

within the spoil aquifer. During this period, the water table is re-establishing and the spoil is

undergoing considerable subsidence, piping, and shifting. Sulfate salts, created by oxidation when

cast overburden is exposed to the atmosphere during mining, are flushed through the system

(Hawkins, 1995b). It is important to monitor these sites beyond the initial re-establishment period,

in order to accurately assess the true changes due to remining and BMP implementation. The

length of the post-mining monitoring period may vary from site to site depending on climatic

(e.g., precipitation) and hydrogeologic (spoil porosity and permeability, topography, etc.)

conditions, and should be at the discretion of the professional in charge of project oversight. 

Implementation Checklist

Monitoring and inspection of BMPs, in order to verify appropriate conditions and implementation,

should be a requirement of any remining operation. Though BMP effectiveness is highly sitespecific, it is recommended that implementation inspections of hydraulic control BMPs include the

following:

C Measurement of flow and sampling for contaminant concentrations (before, during, and

after mining)

C Monitoring should continue well beyond initial water table re-establishment period (e.g.,

about 2 years after backfilling)

C Assessment of hydrologically connected units as well as individual discharges

C Review or inspection of sealing-material weigh slips, receipts, or marked stockpiles

C Review of implementation initiation and completion dates

C Assessment of any deviation from an approved implementation plan

C Inspection of salient phases of the BMP implementation

C Inspection of diversion ditches, caps and seals for leakage

C Inspection of vegetation for viability
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Hydrologic Controls 1-21

1.1.3 Case Studies

Presented below are results from three completed remining operations for which a significant

portion of the site had dead spoils regraded, closed-contour depressions eliminated, and more

natural runoff-inducing slopes created. It is important to note that the full potential of these BMPs

may not have been realized because regrading was performed primarily as part of the perfunctory

reclamation process. These BMPs were not necessarily implemented with the minimization of

surface-water infiltration as a primary intention. Evaluation of these sites may tend to

underestimate the potential for infiltration reduction that can be achieved. Minor implementation

modifications can dramatically affect efficiency. Future efforts which employ these BMPs to their

greatest potential should be closely monitored and analyzed in an attempt to ascertain true BMP

efficacy and to develop methods for fine tuning and improvement.

There are several factors that make pre-mining versus post-mining comparison difficult. One of

the main pitfalls in comparing the discharge rates is the assumption that the pre- and post-mining

periods have had similar precipitation preceding the measurements. Precipitation amount,

duration, and intensity can vary widely from event to event, season to season, and year to year,

serving to complicate pre- to post-mining comparisons. This is especially true when the sampling

periods before and/or after mining are relatively short (e.g., a year or less). Another complicating

factor is that post-mining sampling often will include a period of time when the water table is reestablishing and much of the infiltrating water is going into storage. Under ideal conditions, an

evaluation of flow reduction from BMPs discussed in this chapter would entail similar climatic

conditions, preclude data collected during water table re-establishment, and include several years

of pre- and post-mining monitoring. These criteria are seldom met in real-world situations. The

location of the pre-existing discharges commonly move because of the physical disruption of the

yielding aquifer and ground-water flow paths, and the change of the flow system from a fractureflow dominated system to a dual-porosity system as exhibited in mine spoil. These caveats and

potential problems should be considered while reviewing the case studies below.
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1-22 Hydrologic Controls

Case Study 1 (Appendix A, EPA Remining Database, 1999, PA(6))

This mine was located in Armstrong County, Pennsylvania where the remining was performed on

abandoned surface mines in the Upper Freeport and Lower Kittanning coal seams. All 24.8 acres

of abandoned surface mined land within the permit boundary was reclaimed by the operation.

According to the permit application, the total area to be affected by mining operations was 126.5

acres. The operation also eliminated 1,700 feet out of a possible 2,600 feet of highwall. Originally,

two remining discharge points were included in the permit. However, a third discharge point was

added later. The BMPs listed in the permit included regrading of abandoned mine spoil (24.8

acres), underground mine daylighting (5 acres), special handling of acid-forming materials, and

revegetation. The most predominant BMP component by far was the regrading. The site was

completed in August of 1996 and post-mining water quality data has been collected since. A

synopsis of the data is shown in Table 1.1.3a.

The changes in flow rates from remining of this site are somewhat inconsistent. Discharge point

MD-2 exhibits a statistically significant increase in flow, but the acidity and iron loads are not

significantly higher. This is caused by decreases in concentrations and a relatively broad range of

values, resulting in a wide 95 percent confidence interval about the median, as is commonly

associated with mine drainage. Discharge points C-3A and C-17A exhibit only very minor

differences in the discharge rate after remining. The acidity concentration decreases caused the

median acidity loads to be substantially lower, but only the decrease in the median acidity load of

C-17A is statistically significant.
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Hydrologic Controls 1-23

Table 1.1.3a: Synopsis of Water Quality Data at Case Study 1 Site

Parameter

Discharge Points

MD-2 C-3A C-17A

Pre-Remining Post-Remining Pre-Remining Post-Remining Pre-Remining Post-Remining

Sample Number (n) 22 22 24 22 6 17

Flow (gpm) 2.4 27.1 14.2 16.3 12.5 9.1

Acidity Load (lbs/day) 1.93 4.76 16.17 0.75 8.56 0.07

Iron Load (lbs/day) 0.0016 0.0044 0.09 0.10 0.003 0.003

Sulfate Load (lbs/day) 5.57 85.78 23.15 60.01 21.06 25.45

All numbers are median values.

The lack of better flow reduction may predominantly be due to precipitation differences during

the two comparison periods and, to a lesser degree, to a rerouting of ground-water flow paths.

The reclamation area comprised a small amount (slightly under 20 percent) of the total area to be

disturbed by remining. In addition, the post-remining period is relatively short (less than 2 years)

in terms of allowing complete re-establishment of the water table and post-remining stabilization

of the entire hydrogeologic system. Additional monitoring of the site will likely illustrate more

clearly the true impacts of regrading and revegetation.

Case Study 2 (Appendix A, EPA Remining Database, 1999, PA(7))

This mine was located in Clearfield County, Pennsylvania. Remining was performed on 

abandoned surface mines in the Upper Freeport and Lower Kittanning coal seams. Ten acres 

(32 percent) of the 30.8 acres of abandoned surface-mined land within the permit boundary 

was reclaimed by the operation. Of the 101.1 acres of abandoned underground mines on the

Lower Freeport coal, 17.3 acres (17 percent) were daylighted during the remining operation.

According to the permit application, the total area to be affected was 139.3 acres. Two remining

discharge points were included in the permit. The BMPs listed in the permit included regrading of

abandoned mine spoil (10 acres), underground mine daylighting (17.3 acres), sealing of exposed

mine entries, special handling of toxic materials, and revegetation. The predominant BMP
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1-24 Hydrologic Controls

components were regrading, revegetation, and daylighting. The site was completed in May of

1996, and was assessed using monthly water-quality data collected through August 1997. A

synopsis of the data is shown in Table 1.1.3b.

Table 1.1.3b: Synopsis of Water Quality Data at Case Study 2 Site

Parameter

Discharge Points

MD-12 MD-13

Pre-Remining Post-Remining Pre-Remining Post-Remining

Sample Number (n) 44 16 47 16

Flow (gpm) 0.55 0.40 31.6 35.9

Acidity Load (lbs/day) 2.48 0.59 176.2 133.7

Iron Load (lbs/day) 0.047 0.006 9.99 6.31

Sulfate Load (lbs/day) 2.87 2.65 273.79 289.8

All numbers are median values.

Analysis of the data indicate that the flow rates of the two discharges were not significantly

changed by the remining (regrading and revegetation); there is no statistical difference. The acidity

and iron concentrations at MD-12 were significantly reduced, but the lack of significant flow

changes prevented concomitant acidity and iron load reductions. Figures 1.1.3a and 1.1.3b

illustrate an example of these observations. The lack of overlap of the notches indicating the 95

percent confidence intervals about the medians indicate that the medians of acidity data before and

after remining operations are significantly different, with a definitive decrease in acidity following

remining site closure. 
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Hydrologic Controls 1-25

MD-12

Acidity

mg/L

Pre-Remining Post-Remining

0

200

400

600

800

MD-12

Acidity Load

lbs/day

Pre-Remining Post-Remining

0

10

20

30

Figure 1.1.3a:Acidity Concentration at Discharge Point MD-12 Before and After 

Remining

Figure 1.1.3b:Acidity Load at Discharge Point MD-12 Before and After Remining
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1-26 Hydrologic Controls

Some of the same caveats that apply to Case Study 1 also apply to this site. The climatic

differences (e.g., precipitation) for the two sampling periods should be considered as part of the

overall evaluation of flow changes due to remining. For example, the period of pre-remining

sampling (12/86 through 9/89) averaged 2.83 inches of precipitation per month, while the postremining period (5/96 through 8/97) averaged 3.36 inches of precipitation per month. This is an

increase of about 19 percent. The precipitation values were compiled from the Pittsburgh

International Airport which is approximately 90 miles southwest of the site. However, the data

can be used for the general precipitation trends during pre- and post-remining sampling periods at

this site. The increase in flow from the combined discharges (about 13 percent) is not

commensurate with the recorded precipitation increase. Additionally, the post-remining period is

relatively short (less than 2 years) in terms of allowing complete re-establishment of the water

table and post-remining stabilization of the entire hydrogeologic system. Additional monitoring of

the site over a longer time period and with similar precipitation amounts will likely clarify the true

impacts of regrading and revegetation.

Case Study 3 (Appendix A, EPA Remining Database, 1999, PA(10))

This site is located in Somerset County, Pennsylvania. Remining was conducted on the Lower

Bakerstown coal seam. According to the permit application, a total of 85.8 acres was to be

affected by the operation and 48.8 acres of coal removed. BMPs employed at this site included

regrading of abandoned spoils, alkaline addition, hydrologic controls, revegetation, and

scarification of the calcareous pavement (seat rock). Of the 32.2 acres of abandoned mine lands

within the permit boundary, 15.6 acres, or 48 percent, were to be reclaimed. Approximately 

1,800 feet (84 percent) of a total of 2,150 feet of abandoned highwall was eliminated. The 

alkaline addition rate was 3 tons per acre applied at the interface of the spoil and the topsoil.

Hydrologic controls consisted of a clay barrier placed between remining operations and adjacent

unreclaimed areas. The seat rock was found to be alkaline and was scarified to increase the

surface area of the alkaline material exposed to ground water. Reclamation was completed by 
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Hydrologic Controls 1-27

November of 1995 and monitoring has continued since that time. Table 1.1.3c is a synopsis of the

flow and loading data for this site.

Table 1.1.3c: Synopsis of Flow and Pollutant Loading Data at Case Study 3 Site

Parameter

Discharge Points

SP-10 SP-11 SP12 SP-18 SP-23

Pre-Remining

Post-Remining

Pre-Remining

Post-Remining

Pre-Remining

Post-Remining

Pre-Remining

Post-Remining

Pre-Remining

Post-Remining

Sample Number (n) 8 34 8 34 8 34 8 35 4 34

Flow (gpm) 7.47 5.15 11.3 3.0 1.0 0.7 0.88 1.20 0 0

Acidity Load (lbs/day) 2.72 8.18 20.5 7.4 1.04 0.95 0.31 1.97 0 0

Iron Load (lbs/day) 0.006 0.008 0.03 0.01 0.004 0.003 0.003 0.004 0 0

Sulfate Load (lbs/day) 21.6 49.4 71.1 57.2 11.3 6.06 3.04 9.51 0 0

All numbers are median values.

This site exhibited an accumulative discharge median flow reduction of 10.6 gpm or slightly over

51 percent. However, only SP-11 exhibited a statistically significant flow reduction on an

individual basis. According to the precipitation history from the Pittsburgh International Airport,

precipitation during the two sampling periods was dissimilar, with precipitation during the postremining period (a mean of 3.29 inches per month) being about 15 percent below the background

sampling period (a mean of 3.85 inches per month). Roughly 15 percent of the flow reduction

may be attributable to reduced precipitation, but the remainder appears to be related to regrading,

highwall elimination, and revegetation. The same caveats discussed in Cases 1 and 2, on using

precipitation data from a site somewhat removed from the actual mine sites, apply here. These

results illustrate that substantial flow reduction (approximately 35 percent) may be realized by a

50 percent reduction in abandoned mine lands, even with additional mining of virgin areas (49

acres) occurring in conjunction with the operation. The post-mining monitoring period is

considerable, exceeding three years, but additional monitoring is required to determine whether

the trends observed are genuine and can be expected to continue. Additional flow reduction may
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1-28 Hydrologic Controls

be possible if regrading and revegetation are designed specifically with the intent of preventing

surface-water infiltration, rather than solely with the intent of returning the site to an aestheticallypleasing approximation of the original pre-mining contours and conditions. Specific operations to

reduce surface-water infiltration may include, but are not limited to, additional compaction of the

spoil to reduce permeability, final slopes that may differ from the approximate original contour but

are more efficient in promoting runoff, and plants that promote runoff and/or utilize substantial

amounts of the water that does manage to infiltrate into the soil horizon. 

Even with the aforementioned reductions in discharge flow, two of the discharges (SP-10 and SP18) exhibited a statistically significant increase in median acidity and sulfate loads. This difference

is caused by substantially higher acidity and sulfate concentrations after reclamation. Discharge

points SP-11 and SP-12 also exhibit significantly increased concentrations of acidity, but the

reduced flows prevent the median loadings from being significantly different from the baseline

levels. This indicates that the site may be producing more acidity, but the reduced flow moving

through the site has prevented the combined discharge acid load from exceeding baseline.

Geochemical conditions within this reclaimed operation have worsened, or become more acidic.

The causes of this possible failure will be discussed in detail in the section on alkaline addition.

To obtain a more definitive determination of the efficiency of regrading and revegetation to

reduce discharge rates, additional studies are needed on sites where these BMPs are employed

specifically to preclude surface-water infiltration. The case sites discussed above utilized these

BMPs during remining operations, but they did not specifically design or implement them to

minimize infiltration of surface water. Thorough evaluation of these studies also requires site

specific precipitation data for background sampling as well as post-mining sampling periods. A

sufficient post-mining sampling period of at least 3-5 years, depending on climatic and sitespecific conditions, is required to permit a true assessment of BMP efficiency. With these data,

prediction of load reduction based on the amount of regrading, revegetating, and other BMPs may

be possible. 
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Hydrologic Controls 1-29

1.1.4 Discussion

The BMPs discussed in this chapter, when properly employed under the right conditions, will

successfully reduce the infiltration of surface waters and should subsequently reduce the discharge

yield. However, these BMPs cannot be viewed as a panacea for all pre-existing problems at a site.

There are limits to what can be physically achieved and/or economically attempted. The two lists

below (Benefits and Limitations) include, but are not limited to, what can and cannot be expected

of these BMPs.

Benefits

C Reduces pollution loading from abandoned mine land

C Establishes a hydrologic balance to site 

C Restores land to approximate original contour and creates an aesthetically pleasing postremining configuration

C Requires little additional cost to the operation because they are often already implemented

as a statutory requirement during remining operations

Limitations

C Current implementation of hydraulic control BMPs focuses primarily on reclamation. A

complete evaluation of the effectiveness for pollution prevention, in terms of reducing the

discharge rate, is needed.

C Careful consideration should be made to the implementation of surface-water control

BMPs in areas abandoned for long periods or with some degree of natural remediation

(e.g. stabilized spoil, natural vegetative cover).

C Complete exclusion of infiltrating surface waters is not likely, therefore the discharges will

not be entirely eliminated.

Efficiency

Analysis of completed remining sites in Pennsylvania (Appendix B, PA Remining Site Study)

indicated that at sites with regrading as a BMP, 46.1 percent of 154 discharges were eliminated 
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1-30 Hydrologic Controls

or were significantly improved in terms of acidity loadings. Over half the discharges (53.2

percent) were unchanged and less than one percent (0.6 percent) were significantly degraded with

respect to acidity loadings. 

For iron loadings, 42.3 percent of 137 discharges were eliminated or significantly improved from

remining. Over half (52.6 percent) of the discharges were unchanged, while 5.1 percent showed

significant degradation for iron loadings.

The manganese loadings for 39.6 percent of the 111 discharges were significantly improved or

eliminated, while 52.3 percent were unchanged. The manganese loading failure rate was the

highest for the parameters analyzed, with 8.1 percent significantly degraded. This has been a

common trend for all the BMPs. Manganese loadings exhibited the highest failure rate (9.0

percent for 155 discharges) regardless of the BMP employed.

The bulk (60.7 percent) of the aluminum loadings for 84 discharges were unchanged, while 36.9

percent of the discharges were significantly improved or eliminated. Discharges that were

significantly degraded, in regards to aluminum loadings, amounted to 2.4 percent.

1.1.5 Summary

Studies have shown that the extent of pollution reduction from remining is largely dependent on

reducing the discharge rate, which in turn is dependent on controlling the infiltration of surface

water into the backfill. The commonly-observed positive correlation between flow and loading

rates illustrates the close relationship between the two. BMPs that are designed and implemented

to prevent surface-water infiltration will be successful in reducing the pollution load. 

The case studies above illustrate that regrading and revegetating can yield mixed results unless

differences in precipitation rates are taken into account and the post-mining monitoring period is

of sufficient length to accurately reflect site conditions. However, it is well known that these

BMPs, when properly implemented, will reduce the contaminant load from remining operations. 
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Hydrologic Controls 1-31

1.2 Control of Infiltrating Ground Water

Methods to control the lateral infiltration (recharge) of ground water into remining sites from

adjacent mines and undisturbed strata include, but are not limited to, daylighting of underground

mine workings, sealing exposed mine entries, auger holes, highwalls and pit floors, and installing

diversion drains, vertical highwall (chimney) drains, pit-floor drains, grout curtains and diversion

wells. These BMPs are designed to work in one of two ways to reduce the ultimate discharge

flow rate: (1) to preclude or divert the lateral movement of ground water; and (2) to intercept and

collect laterally-migrating ground water and channel it away from the backfilled areas. These

BMPs are effective singly or when used in conjunction with others, but are seldom used alone

during remining operations.

Currently, these BMPs are being used as a part of the general mining and reclamation processes,

but they are not being implemented with ground-water handling as the primary concern.

Therefore, the results of the case studies (discussed below) and other remining data (Appendix B:

Pennsylvania Remining Site Study) may tend to underestimate the potential for lateral infiltration

reduction that can be achieved. Minor implementation modifications toward ground-water

handling can dramatically effect the efficiency of these BMPs with little additional time or expense

introduced.

Theory

Ground-water modeling of reclaimed surface mines has shown that a substantial portion of

ground-water infiltration into mine spoil comes from adjacent areas. Infiltration from adjacent

areas can originate from other surface mines as well as from unmined strata. The nature of this

lateral recharge can be continuous or episodic. Adjacent areas tend to permit lateral groundwater movement somewhat continuously under baseflow conditions, long after the last

precipitation event. However, rapid, high-volume lateral recharge also can occur immediately
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1-32 Hydrologic Controls

following significant rainfall events (Hawkins and Aljoe, 1990). Fractures in the adjacent strata

can yield substantial amounts of water during or shortly after significant precipitation. The BMPs

discussed in this section need to be able to accommodate this bimodal, lateral ground- water

infiltration.

Unlike many of the BMPs implemented to prevent surface-water infiltration, most of the BMPs

for preventing lateral ground-water movement are implemented on and above standard

reclamation practices. These BMPs tend to be more labor and material intensive than standard

reclamation practices, and therefore, can be more costly. One exception is underground mine

daylighting, which is performed as a consequence of the remining process. However, the time and

effort required to clean the waste rock from around the remaining coal pillars entails additional

cost during mining, the percentage of coal recovery is less than that for virgin areas, and

additional acid-forming materials should be special handled. Some of the BMPs discussed in this

section are mandated by regulation, such as sealing of auger holes and exposed mine entries.

The effectiveness of many of the ground-water control BMPs relies largely on the use of proper

engineering techniques. As with BMPs implemented for the prevention of surface-water

infiltration, there are very few situations where these BMPs will fail. If the ultimate discharge

flow rate is reduced through reduced lateral infiltration, there is a high probability that the

pollution load will be diminished. Figure 1.2a shows the strong flow-versus-pollution-load

correlation commonly exhibited by mine drainage discharges. There are hydrogeologic conditions

where some of these BMPs could exacerbate the production of acid mine drainage (AMD). In

these cases, the BMP should be eliminated or modified to prevent additional pollution. In

situations where the BMP is an integral part of the entire operation (e.g., daylighting), additional

BMPs will need to be added or designed to compensate for possible deleterious side effects of the

others.
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Hydrologic Controls 1-33

Figure 1.2a: Typical Correlation Between Discharge Flow and Pollutant Loading in Mine

Drainage Discharges (Appendix A, EPA Remining Database, 1999 PA(6),

MP-A)

Site Assessment

Assessment of spoil characteristics is site-specific for each operation. Even with on-site testing,

spoil hydraulic parameters can be highly variable. Hawkins (1998a) observed that hydraulic

conductivity can range widely (up to 3 orders of magnitude) within a site. This makes prediction

of spoil characteristics prior to mining extremely difficult. However, there are some general

conclusions that can be drawn about mine spoil. 

Hawkins (1998a) conducted aquifer tests on several mine sites across the northern Appalachian

Plateau in an attempt to predict mine spoil hydraulic properties. He found that the best

correlation occurs between the hydraulic conductivity and age of the spoil. The impacts of other

factors (e.g., lithology, spoil thickness, and mining type) on spoil properties appear to be masked

by a variety of factors introduced during the operation.
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1-34 Hydrologic Controls

Given the broad range of mining types, spoil lithology and age, and other factors, it is doubtful a

narrowly-defined prediction model will be available. In addition to the aforementioned testing

problems, spoil will at times exhibit turbulent flow which does not conform to Darcy’s Law and

causes aquifer-testing procedures to become inapplicable. 

Prior to the engineering and installation of highwall and pit floor drains, an assessment as to the

amount of ground water to be collected and piped needs to be made. This determination can be

performed by empirical testing of observed recharge while the pit is open or can be performed by

conducting a hydrologic budget exercise. The hydrologic budget will require, at a minimum,

knowledge of the size of the recharge zone, precipitation and evapotranspiration rates, storage

capacity, and aquifer characteristics.

Materials used in sealing or grouting may require analysis to ascertain the hydraulic properties,

and thus, the suitability of use. Field testing for compaction also may be necessary. This testing

can be performed via a standard penetration test, using a penetrometer.

Assessment of ground-water diversion (interceptor) wells may require aquifer testing. Performing

a constant-discharge test while monitoring other wells will yield insight as to the efficiency of

these wells. Aquifer testing will also yield data on well and aquifer interconnection.

1.2.1 Implementation Guidelines

Daylighting of Underground Mines 

Underground mining has been conducted in some areas of the United States for over 200 years.

Although limited surface mining was conducted in the early part of the 20th century, surface

mining did not become prominent until after the Second World War. Surface mining into higher

cover coal (greater than 30 to 40 feet) only became commonplace in the 1960's with the

proliferation of mining equipment capable of moving large amounts of rock efficiently. Early

underground mining operations have left a considerable amount of abandoned underground 
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Hydrologic Controls 1-35

mines that are now candidates for remining. These underground mines have been producing

untreated mine drainage since abandonment and, if left unchecked, will continue to do so for

decades or even longer. Daylighting of abandoned underground mines is one of the more

frequently employed BMPs during remining operations. 

Daylighting operations are often economically marginal. This is because the same volume of

overburden associated with virgin coal needs to be removed, but the coal recovery rates are

greatly diminished. A coal recovery rate of 50 percent is usually the maximum observed at

daylighting operations, but this level is seldom achieved. Recovery rates are more commonly in

the range of 20 to 35 percent, because many of the mines were retreat mined (high coal

extraction from partially mining through pillars as the operation withdraws from the mine) prior to

abandonment. Because of this reduced recovery, the thickness of overburden that can be

removed economically is less than that for solid coal areas.

The act of daylighting is the removal of the strata above the coal (overburden), the removal of the

collapsed rock (gob) around the existing pillars, and the loading out of the coal. Once the coal is

removed, the site is reclaimed. Daylighting works to reduce lateral ground-water infiltration in

several ways. Abandoned underground mines are recharged, to a large degree, from fractures in

the overlying rock. The fractures are created primarily by stress relief of erosional rock mass

removal and to a lesser extent by tectonic (mountain building) activities (Wyrick and Borchers,

1981). One of the more prominent results of daylighting is that avenues for vertical recharge are

eliminated, and water that once recharged the underground mine is no longer available.

Daylighting of approximately one half a 380 acre abandoned mine in Allegheny County,

Pennsylvania reduced the flow by about 50 percent (Skousen and others, 1997).

Subsidence and collapse of abandoned mine workings can create additional fractures and increase

the size of existing fractures, also increasing their transmissive properties. Evidence of subsidence

is frequently observed at the surface as cracks, damage to surface structures (e.g., house

foundations, roads, and utilities), and sinkholes (closed contour depressions).
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1-36 Hydrologic Controls

Figure 1.2.1a is a photograph illustrating exposed fractures accentuated due to mine subsidence.

The degree of surface disturbance depends to a large extent on the thickness and lithology of the

overburden and the size of the mine void. Daylighting removes the highly transmissive avenues

for ground water to enter underground mine workings. Even when the underground mine has not

been completely eliminated, daylighting can dramatically reduce this recharge. Empirical

observations indicate that there is an exponential decrease in recharge to underground mines with

increasing overburden thickness. Shallow cover areas tend to yield more water to the mines than

deeper (thicker) cover areas and are more commonly eliminated through remining. In shallow

overburden, stress-relief fractures are more frequent and generally more transmissive than in

deeper overburden (Borchers and Wyrick, 1981; Hawkins and others, 1996). Because of more

extensive fracturing with shallow cover, the overlying rocks are more susceptible to the impacts

from mine subsidence. For example, daylighting 20 percent of a mine, which is the shallowest

cover, will likely reduce infiltration by an amount much greater than 20 percent.

Figure 1.2.1a: Example of Mine Subsidence and Exposed Fractures

The storage capacity of underground mines is considerable, and can approach 65 percent of the

original coal volume. However, a storage capacity of 20-40 percent is more likely. A 100-acre
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Hydrologic Controls 1-37

underground mine with 50 percent of the coal mined, a 5 foot thick coal seam, and no significant

subsidence has a potential storage volume of over 81 million gallons. If the mine workings are

only one third flooded, the mine water stored exceeds 27 million gallons. Storage of vast

amounts of mine water in underground mines allows for continuous lateral recharge to adjacent

operations, even during dry periods. Daylighting decreases the amount of storage available for

ground water and therefore prevents lateral movement into adjacent areas. 

Abandoned underground mines are commonly ideal environments for AMD formation. If acidic,

metal-laden ground water is infiltrating into an adjacent surface remining operation, it can cause

the formation of more AMD than the sum the two mines would produce separately. For example,

it is known that ferric iron (Fe3+), a product of acid-mine drainage formation, can become the

main oxidant of pyrite. Additional pyrite oxidation can occur even under suboxic or anoxic

conditions (Caruccio and Geidel, 1986). Therefore, AMD entering into pyritic-rich zones in spoil

can produce more pollution than the spoil would produce on its own. 

By and large, the water quality of underground mines is much poorer than that of surface mines

on the same seams (Hawkins, 1995b). AMD formation is facilitated by the configuration of an

underground mine which permits ground water to preferentially encounter commonly acidforming units (seat and roof rock and the coal). Over time, roof falls and pillar deterioration

continue to introduce additional acid-forming materials into the system. Daylighting is radically

different than the mining processes that allow the underground mine to create AMD, because the

coal mine entries are eliminated and the gob is mixed with the remainder of the overburden. The

post-remining configuration of the daylighted sections becomes that of a reclaimed surface mine. 

However, because of roof falls and pillar deterioration, there may be a higher amount of

unrecoverable coal mixed in with the spoil associated with daylighting than with remining surface

mines. After daylighting, and in the absence of selective spoil handling, ground water flowing

through the reclaimed portions will encounter acidic, alkaline, and/or relatively inert spoil

materials at a frequency based on the volumetric content of the spoil and on the ground-water

flow regime. With these changes to the ground-water flow and the materials contacted, 
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mine water is likely to be less acidic, especially with the presence of alkaline units in the

overburden.

Daylighting of an abandoned underground mine on the Pittsburgh Coal seam in Allegheny

County, Pennsylvania resulted in turning mine discharge water from “extremely acidic” to alkaline

with low metal concentrations. The areas of the mine that were not daylighted continued to

produce acidic mine water similar to the premining water quality (Skousen and others, 1997).

Daylighting of underground mines can reduce pollution loads through the reduction of groundwater infiltration and through changing the geochemical and physical properties of material that

the ground water contacts. Daylighting eliminates potential recharge sources by mining out

subsidence features. The original ground-water flow path is interrupted by the subsequent

installation of seals and/or drainage systems. The potential amount of mine water storage is

likewise reduced.

Before an underground mine is daylighted, the ground-water system exhibits primarily open

conduit flow with water encountering seat rock, roof rock, and coal. All three of these units are

typically pyritic, and thus possible acid generators. Once daylighting has occurred, the lithology

and particle size of the overburden, whether alkaline, acidic, or inert, is greatly modified. This

modification of the overburden strata substantially increases the amount of freshly-exposed rock

surfaces that are accessible to the ground water. Following daylighting, the ground-water flow

regime is a dual porosity system, where ground water is stored in large conduits and voids

between spoil fragments, but exhibits overall intergranular flow characteristics through the finergrained spoil (Hawkins, 1998a). With this change in the ground-water flow regime, the

probability of ground water encountering alkaline or acidic material is proportional to the volume

and surface area of that material in the spoil, whereas, prior to daylighting, the water almost

exclusively contacted acid-forming materials. The intergranular flow through the fine-grained

spoil exhibits the lowest transmissivity and is the controlling factor of the speed of ground-water

flow in the backfill. Therefore, contact time with rock surface areas also is altered, and generally
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Hydrologic Controls 1-39

lengthened by daylighting. These flow regime changes can have a significant impact on groundwater geochemistry.

Potential problems do exist with daylighting. Overburden material can be highly acidic, and

disturbing it would allow for additional pyrite exposure and oxidation, release additional acidity,

and possibly increase the pollution load. To prevent this scenario from occurring, potential acidproducing and alkaline-yielding zones, as well as the net acidity or alkalinity of the overburden,

should be determined prior to remining. If the overburden is acidic, the anticipated reduction in

flow that can result from daylighting may be offset by the additional acid production. In this case,

alkaline addition or some other ameliorating BMP would be required. In addition, coal itself can

be acidic (with total sulfur concentrations greater than 0.5 percent). The acidity potential of

unrecoverable coal needs to be included in the acid-base accounting conducted for the site. 

Additional coal mixed in with the spoil and left in the backfill can be problematic for marginal

sites. 

Another potential problem associated with daylighting is that underground mine workings have

often collapsed and pillars have crushed, causing coal to spall off. Under these situations,

separating coal from the waste rock can be difficult, and some of the coal will be unrecoverable.

Industry estimates range between 5 and 20 percent of the coal may be left during daylighting. 

Sealing and Rerouting of Mine Water from Abandoned Workings

As an integral part of daylighting, abandoned mine entries and auger holes exposed at the final

highwall are sealed with a low-permeability material. Sealing these abandoned workings inhibits

the infiltration of atmospheric oxygen. Sealing also prevents ground-water movement into these

workings from the mine spoil and from these mine workings into the mine spoil. Figure 1.2.1b

shows exposed auger holes that require sealing. The most common method of sealing an exposed

mine entry or auger hole is by pushing, and compacting as much as possible, a low-permeability

material into the abandoned workings with a bulldozer or other appropriate equipment. 

Compaction of the material is difficult to achieve because the inside of the seal is open ended. 
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1-40 Hydrologic Controls

When a material is pushed into the opening, there is nothing on the inside to push against to aid

compaction.

Figure 1.2.1b: Exposed Auger Holes

Achieving water-tight seals for auger holes and mine entries that have not been daylighted is

extremely important. If these seals leak, a fluctuating water table may be created for the

undaylighted portion of the underground mine. A fluctuating water table is possibly one of the

worst conditions in an underground mine environment. When the water table drops, pyritic

material is subaerially exposed, permitting oxidation. When the water table rises again, salts that

were created by the pyrite oxidation, are hydrolyzed and mobilized, creating additional AMD. The

importance of sealing these mine workings should not be taken for granted.

In some regions, constructed mine seals may be permitted. In Tennessee, a “brick wall” has been

approved as a means of sealing exposed underground mine entries (Appendix A, EPA Remining

Database, 1999). On a site-specific basis, other types of constructed water seals may be

approved.
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It is highly recommended, and in some states statutorily-mandated, to seal mine entries and auger

holes to a depth equaling three times the widest dimension of the opening. For example, if the

auger hole is 3 feet in diameter, the depth of the seal should be at least 9 feet. Figure 1.2.1c is a

schematic illustration of a mine entry seal. Determining the depth of a seal is extremely difficult, if

not impossible. It is doubtful that a mine entry that is 10 feet wide is sealed to a depth of 30 feet. 

Figure 1.2.1c: Example of a Mine Entry Seal

Not all states require that these mine workings be sealed to three times the widest dimension.

Some require that the sealing material be pushed into the entry as far as possible with a bulldozer

or other piece of equipment. Figure 1.2.1d illustrates this type of seal, as approved in Virginia. 
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Figure 1.2.1d: Example of a Virginia-Type Mine Entry Seal 

There are other problems with assessing the effectiveness of these seals. Daylighting abandoned

workings often exposes numerous mine entries. Sealing of all exposed entries can require a large

amount of material and is difficult to achieve because the inside of the seal is open ended. For

example, if daylighting exposes 20 entries with average dimensions of 10 feet wide and 5 feet

high, sealing will require over 1,100 cubic yards of material. This is a considerable amount of

material to stockpile and handle, even if it is locally available. If not locally available, the material

should be obtainable at a minimal cost.

The permeability of this material should be similar to that required for surface capping or stream

lining material. The material should exhibit hydraulic conductivities of 10-10 to 10-9 m/s or lower

to effectively inhibit ground-water movement. By comparison, coals in the northern Appalachian

Plateau may have hydraulic conductivity values ranging from 10-6 to 10-5 m/s (Miller and
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Hydrologic Controls 1-43

Thompson, 1974). If these mine workings are sealed properly with a low-permeability material,

ground-water movement is more likely to be through the more permeable coal than through the

entry seals.

Daylighting operations commonly encounter mine discharge points and/or water pathways during

mining operations. The mine water will continue to flow through portions of the mine that have

not been daylighted. Therefore, sealing of mine entries can cause extensive flooding of the

remaining mine workings behind the seals. Under these hydrogeologic conditions, considerable

hydrostatic head eventually will rest against these seals, causing a substantial amount of mine

water to infiltrate into the backfill. This infiltration can occur even when seals are properly

installed. These flooded areas can be dewatered by installation of a free-draining piping system to

collect and transport the water through the entry seals and bypassing the backfill. The drain

system prevents mine water from being exposed to the spoil. Figure 1.2.1e illustrates this

potential-sealing scenario with the drain system in place. The system should be designed to

accommodate the maximum flow anticipated.

Figure 1.2.1e: Example of a Mine Drain System
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Highwall Drains

There are two basic forms of highwall drains (horizontal and vertical) that work together or

separately to collect ground water entering the spoil from the highwall. Horizontal drains can be

installed to work on a stand alone basis. Vertical (chimney) drains usually are not installed as

stand alone, but are commonly tied into a horizontal drain. Highwall drain systems work to

minimize or prevent the contact between ground water and potentially acid-forming spoil by

interception, collection, and transport away from the spoil. If the water quality is within

compliance standards, the water can be discharged directly. If not, it will require treatment prior

to release.

Highwall-drain systems can also function to collect surface water prior to infiltration at the

interface between the highwall and spoil. This horizontal-pipe system is installed with a

perforated pipe running along the surface or just below the surface, parallel to the highwall. The

surface pipe is connected to a solid pipe that runs from the surface to the pit floor, where it is tied

into a horizontal highwall drain (Gardner, 1998). 

Chimney drains are highly-transmissive linear zones of rock installed vertically at the highwall.

Chimney drains collect ground water as it enters spoil from the highwall and channel it downward

toward the pit floor (Figure 1.2.1f). These drains are usually installed at a known inflow point

(observed during mining), such as a ground water-bearing fracture or fracture zone exposed at the

final highwall. Chimney drains are usually tied into a horizontal drain installed at the base of the

highwall in order to channel the water away from the bulk of the backfill. Water captured by a

chimney drain is channeled to an integral horizontal drain located at the base of the highwall. This

water is then drained laterally and is subsequently discharged away from the spoil. In some cases,

a highwall drain also be constructed of perforated pipe buried vertically at the highwall. If a pipe

drain is used, it should be surrounded by coarse rock to facilitate drainage.
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Hydrologic Controls 1-45

Figure 1.2.1f: Cross Section of an Example Chimney Drain

For chimney drains to work effectively, they need to be substantially more transmissive than that

anticipated for the spoil. A median hydraulic conductivity of 1.7 x 10-5 m/s was determined from

aquifer testing of 124 wells in mine spoil from 18 mines tested in the northern Appalachian

Plateau (Hawkins, 1998a). Drains should have a hydraulic conductivity two orders of magnitude

(100 times) higher than this value. The need for this difference in hydraulic conductivity is based

on the difference in the definitions of an aquifer and an aquitard. With a hydraulic conductivity

difference of two orders of magnitude, ground water tends to move through the aquifer and not

through the adjacent aquitard. The relatively-high hydraulic conductivity required for the drain

necessitates that the material is a uniform coarse-sized durable rock. Rock size can vary, but

should be large enough to ensure long term drain integrity and preclude piping of the drain

material. Drains comprised of rock one inch or larger have been successful. Inert, well-indurated

(cemented) sandstone or a limestone is frequently employed to ensure the desired life span.
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Horizontal drains are commonly installed at or near the base of the final highwall to collect

ground water entering from undisturbed strata or adjacent unrelated surface mine areas. Ground

and surface water often infiltrate into mine spoil at the highwall. If this water is not collected by a

chimney drain, it tends to migrate downward taking a path close to the highwall toward the pit

floor. Horizontal highwall drains are installed to intercept this water and remove it from the site

before the water encounters additional spoil. If present, chimney drains are tied into the

horizontal drain. 

Horizontal drains are either constructed directly on top of the pit floor or are incised a few feet

into the seat rock. The latter appears to be a more efficient method for collecting water. Figure

1.2.1g illustrates two common types of horizontal highwall-drain construction. These drains

consist of a perforated pipe placed into a core of coarse-grained rock. Rock composition and size

should be similar to that used for chimney drains. Pipe diameter should be large enough to easily

transmit more water than the predicted highest flow. Four or six inch diameter, flexible

perforated plastic pipes are the more common pipes used for horizontal drain construction. At

sites where extreme flows are anticipated, a larger pipe diameter may be necessary.

Figure 1.2.1g: Cross Section of Horizontal Highwall Drains
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Drain orientation depends to some degree on the structural dip of the pit floor. Horizontal

highwall drains, as with pit floor drains (discussed in a later section), need to have sufficient grade

to properly drain water from the spoil. Once ground water enters the drain, it should flow rapidly

through the pipe and be discharged away from the site. These drains are designed to prevent the

formation of a defined ground-water table. If the drain system is ineffective, a water table will

form and some of the ground water will bypass the drain, continue to flow through the spoil, and

eventually discharge as mine drainage at some point down gradient at or near the toe of the spoil. 

The drain outflow point should have an air trap installed to prevent atmospheric oxygen from

migrating back into the backfill and possibly oxidizing additional pyrite. 

An important factor in the implementation of highwall drains is the collection and transportation

offsite of as much water as possible, before it encounters the spoil. A clear understanding of the

surface water drainage system and the ground water-bearing zones or fractures is imperative. A

good idea of from where the water will be infiltrating is required to design and install an efficient

highwall drain system. However, some spoils are so highly conductive, a properly installed drain

will collect the water shortly after it enters the spoil, regardless of infiltration points or zones.

Care should be taken to ensure that the drains have sufficient grade to efficiently drain water away

from the spoil and discharge it freely. 

Pit Floor Drains

Pit-floor drains are similar in construction to and perform a similar function as horizontal highwall

drains. Depending on the dip of the pit floor, they can be tied into each other to create a common

drainage system. Pit-floor drains are designed to capture ground water that has entered the

backfill either through lateral or vertical infiltration. The water is then rapidly drained from the

site without intercepting additional spoil material.

Pit floor drainage patterns should be designed so that the majority of the ground water in the

backfill is collected and the ground-water table is greatly suppressed, if not eliminated.

Construction of pit floor drains is similar to construction of highwall drains, but the orientation

and layout design are substantially different. Figure 1.2.1h illustrates the cross-sectional view of
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Structural Dip of Strata

Outflow Point

Outflow Points

Structural Dip of Strata

Extent of Mining

Dendritic Pattern Linear Pattern

two common methods for constructing pit floor drains, and two of the more common pit floor

drainage patterns. Efficient pit floor drainage is not exclusive to these two patterns. There are a

multitude of drain plan view layout designs that should work effectively to collect ground water. 

The drainage pattern employed should be site specific.

Figure 1.2.1h: Pit Floor Drain Patterns

The dendritic pattern is similar to stream drainage patterns. There is a main stem with a series of

tributaries that intersect it at angles less than 90 degrees. This drainage pattern contains one

common outflow. Drain tributaries need to be positioned with respect to the dip of the pit floor

to allow water to drain freely. Tributaries also need to be at an oblique angle to the dip so they

will intercept as much ground water as possible, yet still drain properly. Air traps should be

placed at the outflow point to prevent atmospheric oxygen from migrating freely back into the

spoil. 

The linear pattern is composed of a series of evenly-spaced parallel drains with each drainpipe

having a discrete outflow point. These drains, like those of the dendritic pattern, need to be at an
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oblique angle to the dip, where a substantial amount of the ground water is intercepted, while

maintaining sufficient grade to allow free drainage off of the site. Air traps should be placed at

the outflow points to prevent atmospheric oxygen migrating freely back into the spoil.

Determination of the probable transmissive properties of spoil and the appropriate spacing of

drains is critical to the effectiveness of this BMP. Parallel pit floor drains installed on a site in

Westmoreland County, Pennsylvania, were spaced at roughly 500 to 600 foot intervals. Figure

1.2.1i shows the construction of a pit-floor drain at this site. Preliminary monitoring results

indicated that this spacing may be too broad. Monitoring wells indicated the presence of a

defined water table in parts of the backfill, and water levels in the monitoring wells were typically

3 to 5 feet above the pit floor. The drains installed were not completely suppressing the groundwater levels, but were keeping them lower than expected for nondrained spoil. The spoil at this

site is comprised almost entirely of shales, which caused the backfill to be less transmissive than

originally anticipated. Sandstone-rich spoils are expected to be more transmissive, requiring a

wider drain spacing than shale-rich spoils. In this case, the drain spacing was inadequate for the

given site conditions. Future operations should be specifically engineered to account for the

expected spoil hydraulic properties. 

Figure 1.2.1i: Example of a Pit Floor Drain
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The engineering and construction of pit-floor drains are critical to their efficient use. These drains

should be installed so they intercept the ground water flowing across the pit floor, with sufficient

grade to drain water freely. Too broad a spacing between drains with regard to the spoil

hydraulic conductivity and expected heterogeneity will permit the formation of a water table

between the drains. Drain spacing and configuration should be based on a forecast of the spoil

hydraulic conductivity and heterogeneity based on overburden lithology, mining equipment

employed, direction of mining, and direct aquifer testing on nearby reclaimed surface mines.

There is a caveat with incising drains in to the pit floor. Excavation into a pit floor can breach the

integrity of the seat rock and facilitate infiltration of mine water into underlying aquifers. Once

ground water infiltrates into underlying units, it is less controllable and can eventually discharge at

a point far removed from the site. 

Grout Curtains

Grout curtains are vertical or nearly vertical, tabular-shaped, low-permeability layers that are

emplaced to prevent or divert ground-water movement. In remining operations, grout curtains

can be installed at and against the highwall or they can be installed in the undisturbed strata above

the highwall. A limiting factor for the installation of grout curtains in remining situations is that

they tend to be more expensive than some of the alternative BMPs. It is doubtful that grout

curtains will be used often as a BMP, because the narrow profit margin in most remining

operations.

Grout curtains or barriers can be installed during reclamation by pushing and compacting a low

permeability material (grout, clay, coal combustion waste, and other materials) against the

highwall as reclamation progresses.

This is conducted in lifts with each lift tied into the previous one. Grout curtain material is

typically either an on-site material (clay) or an inexpensive waste material, such as CCW. Clays

commonly have hydraulic conductivities ranging between 10-12 to 10-8 m/s (Freeze and Cherry,

1979). Yanful and others (1994) recorded an initial hydraulic conductivity of 10-9 m/s for 
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compacted clay used to cap an acid-producing waste rock site. The importance of compaction of

the barrier material in the creation of a low-permeability barrier should not be overlooked. A

continuous barrier is needed to effectively prevent ground-water movement. Any breach in this

barrier can permit ground-water movement from the strata into the spoil.

The “haulback” of CCW to a mining operation is often a provision of the sale of coal to electrical

generating facilities. With the addition of water, CCW is often pozzolanic (self cementing). The

permeability of this material, once hardened, is sufficiently low to nearly preclude all groundwater flow. The Electric Power Research Institute (EPRI) reported a range of hydraulic

conductivities for “self-hardening ashes” of 3.2 x 10-9 to 1.8 x 10-7 m/s (EPRI, 1981). These

values were determined after a 28 day set-up period. Hellier (1998) reported a hydraulic

conductivity of 10-9 m/s for a fluidized bed combustion ash used for a surface mine capping

project in north central Pennsylvania.

At some mining locations, the installation of a grout curtain at the highwall after reclamation has

been completed. In these cases, the spoil directly adjacent to the highwall has to be re-excavated

and a slurry-type grout used to fill the trench. Though grout types can vary considerably, grouts

containing high percentages of CCWs and cement or bentonite and cement are frequent choices.

Potential problems can arise from highly-permeable spoil. If the grout is watery and flows too

freely, it will enter the spoil and construction of a continuous, effective barrier is difficult. This

after-the-fact grout curtain would be expensive and probably cost prohibitive for remining

operations.

Grout curtains also can be installed above the highwall in undisturbed strata by performing a

pressure grouting operation. A series of boreholes are drilled across the site parallel to the

highwall. These holes are often drilled in a staggered pattern to maximize the grouting potential

by accessing as many natural fractures as possible (Figure 1.2.1j). Spacing of boreholes varies

depending on fracture density and transmissivity and on the propagation characteristics of the

grout. Grout holes drilled on ten foot centers have been suggested for sealing underground mines

(U.S. Environmental Research Service, 1998). Given the common orientation and density of
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stress-relief fractures in the Appalachian Plateau, drilling grouting holes at a slight angle (up to 3

degrees) from vertical will help to optimize efficiency. A commonly-used pressure grouting

material is a commercially available polyurethane. The polyurethane is a two component material

that is injected simultaneously in equal amounts (Ackman and others, 1989). Other materials

suitable to this type of grouting, are neat cement or bentonite. 

Figure 1.2.1j: Common Drilling Pattern for Pressure Grouting Wells

Problems with the implementation of grout curtains are often related to the continuity of the

emplaced grout. Ground water is expected to impound behind a grout curtain and eventually flow

laterally away from the spoil. If the grout curtain is not continuous, ground water eventually will

flow through a breach, following the path of least resistance. Pressure grouting in fractured rock

aquifers is particularly problematic, because the fractures are not continuous, are not all

interconnected, and do not necessarily interact with one another. It has been observed that

individual fractures may represent discrete aquifer zones and may have distinctly different

piezometric surfaces (Booth, 1988). Rasmuson and Neretnieks (1986) estimated that only 5 to 
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Hydrologic Controls 1-53

20 percent of the fracture plane transmits 90 percent of the water. A study of overburden

material at a surface mine in Clearfield County, Pennsylvania, illustrated that only a few discrete

fractures intercepted by a borehole actually contributed to the well yield. The remainder of the

fractures appeared to be unconnected or poorly connected to these active fractures (Hawkins and

others, 1996). Grout hole spacing, grouting material, and grouting pressures need to be designed

to overcome these potential fracture discontinuity problems. It is recommended that grouting

wells be drilled at a slight angle from true vertical to increase the likelihood of encountering

vertical or near vertical water-bearing fractures. 

Ground-Water Diversion (Interceptor) Wells

Diversion wells are installed specifically to intercept and collect ground water prior to its

infiltrating into the reclaimed backfill. These wells are drilled up gradient of the backfill area and

can be oriented vertically or horizontally. Care should be taken not to over pump these wells,

which can cause a reversal of ground-water flow. If the water table is lowered to the point that

ground water is drawn from the reclaimed operation, the water may require treatment prior to

discharging. The intent of diversion wells is to prevent water movement into the strip, not to

create a pump-and-treat operation.

Vertical diversion wells require a pumping system operated by a consistent power supply. In order

for vertical diversion wells to effectively intercept ground water, a series of wells drilled normal

(perpendicular) to the structural dip and up gradient are required. Spacing of these wells depends

on site-specific conditions, such as fracture density, hydraulic conductivity, and structure. Well

depth is generally to or a short distance below the top of the seat rock. In relatively shallow wells

(less than 200 feet) of the Appalachian Plateau, the highest well production occurs at the

shallowest depths (Hawkins and others, 1996). However, there are circumstances where

substantial ground water flows in from deeper fractures. In competent rocks in the Appalachian

Plateau, the entire borehole should be left open to prevent restriction of any ground-water inflow

points. As with grouting boreholes, these wells may be more efficient if they are drilled at a slight

angle (1 to 3 degrees) to increase the probability of intercepting vertical fractures. 
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Diversion wells should be configured so that pumping will initiate when the water reaches a predefined level above the bottom of the coal and that pumping will cease once the water is drawn

down to second pre-defined level, commonly at or near the base of the coal. Pump cycling times

depend on the amount of ground water present, transmissivity of the strata, and the efficiency of

the well. Diversion wells are relatively inexpensive to drill, but can be expensive to complete and

maintain over a period of time. Therefore, they will seldom be an economically viable option for

remining. 

Horizontal diversion wells, when properly installed, may be more efficient and effective than a

series of vertical wells, depending on the size of the area to be dewatered.

The initial cost of a horizontal well will be dramatically more than the equivalent footage of

vertical wells. However, there are definite advantages to horizontal wells. They can be drilled to

allow for free drainage. No pumping system or power is required with a free-drainage system, and

thus, very little maintenance is required. Horizontal wells access water from a continuous

horizontal line, rather than from discrete well points, and are more likely to intersect waterbearing fractures. Because of the high cost of outfitting and maintaining the pumping systems of

vertical well sets and the initial high cost of drilling horizontal wells, it is doubtful that diversion

wells will be an economically viable option at more than a few remining operations.

The installation of diversion wells encounters some of the same poor fracture interconnection

problems as are incurred during the installation of grout curtains. Because individual fractures

can represent discrete piezometric zones (Booth, 1988), diversion wells need to be drilled in a

configuration and at a spacing that accesses all of the discrete ground-water flow systems. A

common occurrence in the Appalachian Plateau is for shallow water wells (less than 200 feet) a

short distance apart (less than 100 feet) to show little interconnection based on an aquifer test.

Drawdown at a pumping well may exceed 100 feet while a well 50 to 80 feet away may only

exhibit a drawdown of a fraction of an inch over the length of a pumping test lasting 2 hours or

more. It is advised to drill to the vertical diversion wells at a slight angle from true vertical to

increase the likelihood of encountering vertical or near vertical water-bearing fractures. It is also
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Hydrologic Controls 1-55

recommended to drill horizontal diversion wells at an angle to the preferred orientation of the

vertical stress-relief fractures. Because vertical fractures are created by tensional forces and tend

to be oriented parallel to the strike of the adjacent valley (Borchers and Wyrick, 1981), horizontal

diversion wells should be drilled at an angle that is subparallel to the valley orientation. 

Design Criteria

These BMPs should be designed and implemented to preclude the lateral infiltration of ground

water into the backfill areas of reclaimed remining operations. Some of the salient design criteria

for each of the BMPs discussed in this chapter are included in the list below. Site-specific

conditions will ultimately dictate which BMPs should be used and the scope of BMP

implementation required in order to reduce or eliminate lateral ground-water inflow, discharge

rate and pollution load. It should be noted that although grout curtains can be employed as a

BMP, they are rarely used and the technology is unproven.

Daylighting

C Eliminate subsidence-induced ground-water infiltration zones.

C Eliminate vast ground-water storage areas.

C Reduce the amount of ground-water contact with acid-forming materials.

C Increase the possibility of ground water contacting alkaline materials.

C Facilitates special handling of acid-forming materials.

C Greatly reduce the oxygen flow to the subsurface.

Sealing and Ground Water Rerouting of Mine Workings

C Inhibit atmospheric oxygen infiltration into mine workings.

C Use low permeability sealing material (e.g., equal to or less than 10-9 m/s).

C Install seals to preclude ground-water movement into or out of the mine workings.

C Drain to control the ground-water buildup, bypass the spoil, and discharge off site.
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Highwall Drains

C Intercept and collect ground-water infiltration at the highwall.

C Quickly drain ground water from the spoil and discharge it off-site.

C Make drains more permeable than the surrounding spoil.

Pit Floor Drains

C Orient and construct the drains to collect ground water within the backfill.

C Suppress or eliminate the ground-water table within the backfill.

C Orient and construct the drains to quickly drain ground water from the spoil and discharge

it off site.

Grout Curtains

• Install to prevent or redirect ground water away from the backfill.

C Use low-permeability grouting material (e.g., equal to or less than 10-9 m/s).

• Ensure that continuity is maintained across the potential infiltration zone.

• Drill grout holes at an angle of up to 3 degrees (depending on site strata) to increase the

interception of vertical fractures.

Diversion Wells

C Locate and drill up-gradient of the mine to intercept ground-water flow.

• Make intersection of water-bearing fractures or zones a priority.

• Use low or no-maintenance systems, if possible.

• Install horizontal wells at an angle subparallel to valley orientation.

1.2.2 Verification of Success or Failure

The cumulative discharge rate of the post-reclamation discharges compared to pre-mining

discharges is, as with all of the physical hydrogeologic BMPs, the truest indication of the

effectiveness of ground-water control BMPs.
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Daylighting

Verification of the amount of daylighting that has occurred is relatively easy. The acreage

disturbed can be viewed during mining and after reclamation and compared to underground mine

maps. If there is uncertainty of the exact amount of daylighting that occurred, the area can be

surveyed. 

Sealing

Verification of the implementation of sealing of abandoned mine workings will require the

inspection staff to be present during different phases of the operation. Once seals are in place,

they will be covered. If there is concern that the mine workings will not be properly sealed, the

permit may be conditioned to require notification when sealing will occur or will be completed.

The material to be employed to seal the openings may need to be stockpiled on site to confirm the

type of material and the amount to be used. The stockpile should be marked to distinguish it from

spoil or topsoil piles. To be sure the material has a sufficiently low permeability, the relative

hydraulic conductivity also may need to be certified by laboratory testing. As previously stated, it

is extremely difficult to verify the depth to which the seal is emplaced. If this parameter is deemed

important enough, boreholes can be drilled behind the seal and a borehole video camera can be

lowered to view the seal from the inside and/or to monitor the flooding of the remaining mine

voids. It is doubtful that this step will be necessary.

Drains

If drains are installed in conjunction with the seals, drain piping can be viewed as it is installed.

Drain outflow can be monitored to determine if it is yielding the anticipated volume of mine

water. That is, does the drain yield a similar volume before and after mining. A mine consistently

yielding 300 gpm prior to mining and drain installation and a median flow of 85 gpm after

reclamation would indicate that the seals and/or the drain are not functioning properly. The

existence of toe-of-spoil seeps may also indicate that the drains are working improperly.

Pit floor drains are installed as mining progresses, and tend to be extended with each phase (cut)

of the mining operation. Pit floor drains can usually be inspected during several phases of the
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operation. Effectiveness of these drains can be determined once the backfilling is complete. If the

drains are yielding water and unexpected discharge points (seeps) are nonexistent, it is an

indication that the drains are effectively collecting ground water. Monitoring wells installed in the

backfill provide the best indication that the water table is being suppressed as designed. Site

monitoring should be continued for a period beyond the anticipated water table re-establishment,

and monitoring through several wet seasons is important. In the Appalachian Plateau, the backfill

water table can require at least two years to completely re-establish.

Grout Curtains

The type of grout curtain installation monitoring depends on the method used to install the grout

curtain. If the curtain is created as the site is backfilled, an inspection staff can review portions

(lifts) of the installation as it progresses. 

In situations where the installation of a grout or clay curtain along a significant portion of a

highwall takes a protracted period of time and the inspection staff cannot be present for every

stage implementation, estimates of the amount of material required should be submitted as part of

the reclamation plan. Marked stockpiles or weigh slips equaling the proposed volume can be used

to determine if the proper amount of material was used.

Determination of the success of grout curtains emplaced via pressure grouting drill holes is

substantially more difficult. Grouting effectiveness can be evaluated indirectly by comparing the

estimated porosity of the strata, the total volume of the strata, and the volume of grout employed.

The ultimate effectiveness of grout curtains, regardless of how they were installed, is whether they

preclude ground-water movement through them. To make this determination, monitoring wells

can be installed on each side of the grout curtain.

Diversion Wells

There is little that can be viewed at the surface during the installation and use of diversion wells to

ascertain their efficacy. 
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The effectiveness of diversion wells can be estimated by the amounts of water pumped from them

and monitored by the construction of monitoring wells both up and down gradient of the pumping

wells. If the down-gradient wells exhibit a suppressed ground-water table over the anticipated

levels, it is indicative that the diversion wells may be functioning properly. Ultimately, if

discharge rates are reduced, the diversion wells are effective.

Implementation Checklist

Monitoring a site for anticipated changes is a critical and inherent aspect of BMP implementation

and efficiency determination.

Monitoring should continue well beyond initial water table re-establishment period (e.g., about 2

years after backfilling). The list below is a recommended guideline for an inspection staff to

monitor and evaluate ground-water control BMPs.

• Measurement of flow and sampling for contaminant concentrations at time-consistent

intervals.

C Assessment of hydrologically-connected units, as well as individual discharges, for

pollution load changes.

C Review or inspection of sealing material weigh slips, receipts, or marked stockpiles.

C Review of implementation initiation and completion dates

C Assessment of any deviation from an approved implementation plan.

C Inspection of salient phases of the BMP implementation for:

a. integrity of seals.

b. drain construction, location, and orientation.

c. grout curtain integrity and continuity.

d. diversion well locations and productivity (yield).
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1.2.3 Case Studies

Case Study 1 (Appendix A, EPA Remining Database, 1999 PA(3))

Remining was performed on an abandoned surface mine and abandoned underground mines in the

Pittsburgh coal seam. A total of 33.8 acres (48 percent) of the 69.6 acres of abandoned surface

mine land within the permit boundary were reclaimed by the operation. Of the 90 acres of

abandoned underground mines in the Pittsburgh coal seam, at least 49 acres (54 percent) were

daylighted during the remining operation. More than 203 acres were impacted by the remining

operation. Fourteen pre-existing mine drainage discharge points were included in the permit.

BMPs listed in the permit included regrading of abandoned mine spoil and highwalls, underground

mine daylighting, sealing of exposed mine entries, special handling of toxic materials, and

revegetation. The most predominant BMP components were regrading/revegetation and

daylighting. The site was completed in June of 1998. Ten discharge points were used to

determine the impacts of remining. The remaining four discharges were low flow and discharged

intermittently during pre- and post-mining periods. 

Because this site has been reclaimed relatively recently and post-remining data are limited, the

resulting pollution load analysis is less than ideal and subject to change. However, this site is

worth evaluation because of the large percentage of daylighting that was implemented and

because it drains to a stream that is used as a public water supply. Additionally, considerable

discharge reductions were observed prior to final backfilling for several of the monitoring points.

Two of the main discharges (MP-1 and MP-4) began to exhibit significant flow reduction prior to

the completion of reclamation. Prior to October, 1992, MP-1 ranged in flow from 0 to 139 gpm

with a median of 18 gpm. Since October of 1992, MP-1 ceased to flow, except for one monthly

sample where the flow rate was 0.25 gpm. The flow rate of MP-4 ranged from 0 to 132 gpm

with a median of 6.9 gpm prior to April of 1994. After that time, the flow ranged from 0 to 18

gpm with a median of 0.1 gpm. Figures 1.2.3a and 1.2.3b illustrate the flow reduction exhibited

by these two discharges over time. 
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Figure 1.2.3a: Change in Flow Over Time (Case Study Discharge MP-1)

Figure 1.2.3b: Change in Flow Over Time (Case Study Discharge MP-4)
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These analyses indicate that a flow reduction was observed even prior to complete backfilling

(Figure 1.2.3c). MP-1 and MP-4 are directly down gradient from the first areas to be mined and

reclaimed, and down gradient of limited-sized recharge areas. Therefore, it should be expected

that these points would exhibit the greatest change during remining operations.

Figure 1.2.3c: Flow Rate Reduction, Pre- and Post-Remining Periods (Case Study 

Discharge MP-4)

Pre- and post-remining comparisons (discharge points MP-2, MP-3, MP-5, MP-6, and MP-D)

exhibited no apparent change in flow. However, flows for MP-A and MP-B appear to have

decreased slightly, although not significantly. Although MP-C shows a slight, but significant,

increase in median flow (from 0.5 to 2.9 gpm) from before to after November of 1994 , the actual

change in flow is relatively low by comparison to flow rate for most of other discharges.

Analysis of the post-mining data is, at this stage, preliminary. Only data for the first two months

after remining were submitted for four of the discharges (MP-4, MP-5, MP-C, and MP-D) and

these discharges have been excluded from the evaluation of pre- versus post-mining water 
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quality. Four of the remaining discharges (MP-1, MP-6, MP-A, and MP-B) exhibited a postremining median significantly below the background data at a 95 percent confidence interval. 

This improvement in water quality is illustrated in Figure 1.2.3d. Three of the discharges (MP-1,

MP-A, and MP-B) have been nearly or completely eliminated. The two remaining discharges

(MP-2 and MP-3) exhibited a median flow rate reduction that was not statistically significant.

Figure 1.2.3d: Flow Rate Reduction, Pre- and Post-Remining Periods (Case Study

Discharge MP-6)

The results discussed above should be tempered with the knowledge that precipitation for the 32

month baseline period was near average (i.e., a mean of +0.05 inches per month), while the brief

post-remining period (6 months) was significantly below the average (i.e. a mean of -0.50 inches

per month). Post remining monitoring should be continued until the precipitation has returned to

near average for several months (preferably 6 to 12 months) and the water table has been fully reestablished. Precipitation data were compiled from the Pittsburgh International Airport,

approximately 37 miles west of this mine site.
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Case Study 2 (Appendix A, EPA Remining Database, 1999, VA(7))

This site is located in Wise County, Virginia. The coal seams being remined are the Imboden

Marker, Lower Kelly, Upper Kelly, Kelly rider, Lower Standiford, Upper Standiford, Taggard

Marker, Bottom Taggart, Top Taggart, Owl, and Cedar Grove.

The permitted acreage is 1,140, with 149 acres to be regraded, 158 to be reclaimed, and a total of

498 acres to be disturbed. Daylighting will occur on previous augering of the Standiford seams.

Abandoned mine workings will be daylighted on the Upper Standiford. It is also probable the

abandoned mine workings on the Upper and Lower Kelly seams will be intersected and partially

daylighted. 

There are three discharge points (SB-5, SB-6, and SB-7) that were identified as pre-existing mine

discharges. Although this site was still active as of January 1999, it is worth evaluating because it

illustrates the type of remining occurring in Virginia and a substantial amount of daylighting and

sealing of abandoned mines and auger holes is being performed.

Preliminary analysis of flow data yielded mixed results, but indicates an overall flow decrease. A

comparison of baseline flow rates to flow rate during mining indicates that two of the three

discharges (SB-6 an SB-7) have a reduced median flow.

The reduced flow was significant at a 95 percent confidence level for SB-7. SB-5 exhibited an

insignificant increase in median flow for the same time periods. The sum of the median flows for

baseline was 97 gpm compared to a median 53.5 gpm during remining, yielding a possible flow

reduction of 45 percent. Evaluation of these results should acknowledge that climatic (e.g.,

precipitation) conditions were not considered during the analysis. Long term post-remining

monitoring with determinations of precipitation during the same period, as well as that for the

background period will yield a true assessment of the impact of remining on the pollution load.
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1.2.4 Discussion

The BMPs discussed in this chapter, when properly employed under the right conditions, will

successfully reduce the lateral infiltration of ground water into the backfill and should

subsequently reduce the discharge rates. However, these BMPs cannot be viewed as a panacea

for all of the pre-existing problems at a site. There are limits to what can be physically achieved

and/or economically attempted. The two lists below (Benefits and Limitations) include, but are

not limited to, what should and should not be expected of these BMPs.

Benefits

C Reduce pollution loading from abandoned mine land.

C Establish an alternate, improved hydrologic balance at the site.

C Eliminate surface subsidence features (e.g., sinkholes, disappearing streams, etc.).

C Highwall drains can be installed at the observed infiltration points.

C Control of the location of post-mining discharge points in case treatment is required.

C Daylighting often results in little profit, however, it is implemented as an integral part of

the mining operation.

C Special handling of acid-forming materials.

C Reduction of oxygen flow to the subsurface.

Limitations

C Current implementation of these BMPs lacks comprehensive evaluation of effectiveness

for pollution prevention.

C Previous use of some of these BMPs (pit floor and highwall drains, highwall sealing, and

diversion wells) has been limited, therefore the true extent of their effectiveness has not

been adequately determined.

C The true effectiveness of mine seals, drains, and grout curtains installation cannot be

determined prior to reclamation and establishment of the post-mining hydrologic regime.

C Given the highly heterogeneous and anisotrophic nature of surface mine spoil, the present

state of predictability of the post-mining ground-water flow system is limited. It is
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doubtful that an extremely high degree of predictability of the efficiency of highwall and

pit floor drains is possible.

C Complete exclusion of laterally-infiltrating ground waters is not likely, therefore there

needs to be a realization that the discharges will likely not be entirely eliminated.

C Diversion wells are costly and even the best planning may not provide an effective BMP

system, if the hydrologic system is poorly understood.

C Success of daylighting can be dependant on the geochemistry of overburden material and

special handling of acid-forming materials.

Efficiency

Analysis of completed remining sites in Pennsylvania (Section 6, BMP Efficiencies) indicated that

at least 90 percent of discharges impacted by ground-water control BMPs will either exhibit a

significant improvement, no change in the pollution load, or be completely eliminated (in the case

of manganese, 89.5% of the affected discharges were improved, eliminated or unchanged).

For a total of 164 discharges with elevated acidity levels from remining operations in the state of

Pennsylvania (Appendix B, PA Remining Site Study), slightly over 43 percent were improved or

eliminated, over 56 percent were unchanged, and less than one percent were significantly worse

from daylighting.

Of the 156 discharges with elevated iron, nearly 40 percent were improved or eliminated, about

55 percent were unchanged, and over 4 percent were significantly degraded from daylighting.

Similar results were yielded by analysis of aluminum and manganese loads. In regards to iron,

acidity, manganese, and aluminum, the percent of discharges that were degraded during

daylighting was never greater than 6.5.

Analysis of the implementation of special water handling facilities, tabulated in Appendix B,

yielded similar results. However, this category includes both surface and ground-water handling

facilities. Fifty percent of the 22 affected discharges exhibited an improvement or elimination for

acidity loading with the remainder showing no significant change. Almost 48 percent of 23
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discharges exhibited an improvement or elimination with an additional 48 percent showing no

significant change for iron loading. Slightly over 4 percent were significantly degraded in regards

to iron loads. Manganese loadings showed that 47 percent of the 20 affected discharges were

improved or eliminated and 42 percent were unchanged. The analysis indicated that slightly over

10 percent of the discharges had been degraded in regards to manganese loadings. Aluminum

loads exhibited similar results with the bulk of the discharges (73 percent) being unchanged and

none showing degradation.

Overall, the analyses of acidity, iron, manganese, and aluminum loading data from these

completed remining sites indicates that between 90 and 100 percent of the discharges will show

no degradation from daylighting or special water handling. Additionally, between 27 and 50

percent of the discharges will be improved or completely eliminated. These efficiency numbers

can be improved with the specific tailoring of the BMPs to reduce or exclude lateral ground-water

movement. 

1.2.5 Summary

Previous studies have shown that the extent of pollution reduction from remining is largely

dependent on reducing the discharge rate, which in turn is dependent on the controlling the

infiltration of ground water into the backfill. The commonly-observed positive correlation

between flow and loading rates illustrates this close relationship. BMPs designed and

implemented to prevent ground-water infiltration from adjacent areas will be successful in

reducing the pollution load and in some cases may completely eliminate the discharge.

Case Studies 1 and 2 illustrate that underground mine daylighting, entry and highwall sealing, and

other ground water-controlling BMPs can yield mixed results unless differences in precipitation

rates are taken into account and the post-remining monitoring period is of sufficient length to

accurately reflect site conditions. However, it is well known that these BMPs, when properly

implemented, will reduce the contaminant load from remining operations.
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1.3 Sediment Control and Revegetation

Erosion and sediment deposition caused by weathering and precipitation are natural processes that

can be accelerated in disturbed watersheds. Disturbances such as surface coal mining involve the

removal of vegetation, soil, and rock. Spoil or highwall surfaces create conditions highly

vulnerable to erosion and result in adverse sediment deposition that can clog streams, increase the

risk of flooding, damage irrigation systems, and destroy aquatic habitats. Sediment deposition in

downslope areas can have adverse environmental impacts on watershed soil and vegetation. 

Abandoned surface mine land, spoil refuse and gob piles often have exposed surfaces that are

vulnerable to erosion or conducive to high rates of storm water runoff resulting in increased

problems of sedimentation in receiving streams. Re-exposing these abandoned sites during

remining operations without concern for sediment control can cause serious solids loading and

hydrologic imbalance. Successful implementation of erosion and sediment control BMPs are

critical for ultimate landscape stability and receiving stream protection. 

Theory

The implementation of the BMPs discussed in this section for management of surface water and

ground water at remining operations also can form the basis for sediment control. If implemented

properly, site hydrologic controls can serve to prevent erosion, solids loading into receiving

waters, and unchecked sediment deposition. Likewise, if hydrologic controls are implemented

without consideration for potential sedimentation, conditions leading to discharge of solids and

sediment can rapidly increase and result in severe environmental degradation. 

Remining and reclamation of abandoned mine lands typically require techniques that involve

regrading to approximate original contour, replacing topsoil, applying vegetation amendments,

and constructing erosion-control structures. The resulting reclamation often is aesthetically

pleasing, but can result in an artificial drainage system that can be problematic and accelerate
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erosion as natural drainage systems are re-established. If reclamation techniques fail to consider

natural drainage patterns and surface water flow characteristics, conditions can become worse

than those that existed prior to implementation of these techniques. Sedimentation and erosion

problems can be alleviated by proper implementation of some or all of the BMPs discussed in this

section.

Site Assessment

Prior to implementation of BMPs to control erosion and suspended solids loading, sites should be

assessed to determine existing drainage patterns and topography, to quantify effects of storm

runoff and the yield of coarse- and fine-grained sediment, and to determine morphologic evolution

of gullies. Natural drainage patterns can be determined using before and after maps and profiles,

aerial photography, site mining history information and water quality data. Determinations should

also consider precipitation frequency, duration, and intensity. This information can be used to

indicate locations where the implementation of sediment control BMPs will be most effective.

In addition to determining sedimentation patterns, it is important to determine the quantity of

sedimentation that can be expected. An estimate of sediment erosion and deposition can be

derived over time using water samples, sediment traps or sediment accumulation markers. 

Empirical equations also can be used to estimate the potential for and expected rate of erosion.

The Universal Soil Loss Equation (USLE) was developed as a means to predict sediment loss

from watersheds and can be used to estimate sediment yield produced by rill or sheet erosion in

field areas. A Revised Universal Soil Loss Equation (RUSLE) was developed to estimate

quantities of soil that can be lost due to erosion in larger, steeply sloped areas. Predicted soil loss

is calculated using the following equation (OSMRE, 1998, PA DEP, 1999, Renard and others,

1997):
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A = RKLSCP

Where:

A = Computed Soil Loss (Annual Soil Loss as tons/acre/year)

R = Climatic Erosivity or Rainfall erosion index - a measure of the erosive

force and intensity of a specific rainfall or the normal yearly rainfall for

specific climatic regions

K = Soil Erodibility Factor - Ability of soils to resist erosive energy of rain. A

measure of the erosion potential for a specific soil type based on inherent

physical properties (particle size, organic matter, aggregate stability,

permeability). Soils with a K value of 0.17 or less are considered slightly

erodible, and those with a K value of 0.45 or higher are highly erodible.

Soils in disturbed areas can be more easily eroded regardless of the listed

K value for the soil type because the structure has been changed.

LS = Steepness Factor - Combination factor for slope length and gradient 

C = Cover and Management Factor - Type of vegetation and cover. The ratio

of soil loss from a field with specific cropping relative to that from the

fallow condition on which the factor K is evaluated.

P = Support Practice - Erosion control practice factor, the ratio of soil loss

under specified management practices. 

RUSLE can be used to predict soil loss from areas that have been subjected to a full spectrum of

land manipulation and reclamation activities and has been designed to accommodate undisturbed

soil, spoil, and soil-substitute material, percent rock cover, random surface roughness, mulches,

vegetation types, and mechanical equipment effects on soil roughness, hillslope shape, and surface

manipulation including contour furrows, terraces, and strips of close-growing vegetation and

buffers. It is important to note that RUSLE estimates soil loss caused by raindrop impact and

overland flow in addition to rill erosion, but does not estimate gully or stream-channel erosion. 
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To establish successful vegetation, the soil loss rate should be minimized. Keeping the soil loss

rate below 15 tons/acre for the first year after reclamation should, if surface water controls are

included, allow the establishment of successful vegetation (PA DEP, 1999). For successful

establishment of vegetative cover on abandoned mine land or redisturbed surfaces, the addition of

soil amendments (e.g., soil substitutes, biosolids, etc.) may be necessary. Following regrading,

final texture samples should be taken at a rate appropriate for site representation and analyzed for:

pH, acid-base account, and fertility ratings for phosphorous, potassium, nitrogen, and magnesium. 

The necessity of amendments such as limestone, nitrogen, available phosphorous (P2O5), and

potash (K2O) can be determined from these analytical results. Additional analyses that can be

performed for further determination of site characteristics include: percent sand, silt and clay,

textural classification, and water-holding capacity. This information can be used to assist in

determination of the extent of final grading, cover preparation, and soil water retention

amendments that should be implemented or added. 

1.3.1 Implementation Guidelines

The intention of BMPs for control of sedimentation is to minimize erosion caused by wind and

water. A remining sediment control plan should demonstrate that all exposed or disturbed areas

are stabilized to the greatest extent possible. Operational BMP measures that can be implemented

with this intent include: 

C Disturbing the smallest practicable area at any one time during the remining operation,

C Implementing progressive backfilling, grading, and prompt revegetation, 

C Stabilizing all exposed surface areas,

C Stabilizing backfill material to control the rate and volume of runoff, 

C Diverting runoff from undisturbed lands away from or through disturbed areas using

protected channels or pipes, and 

C Using terraces, check dams, dugout ponds, straw dikes, rip rap, mulch, and other

measures to control overland flow velocity and volume, trap sediment in runoff or protect

the disturbed land surface from erosion (e.g. silt fences and vegetative sediment filters).
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Construction of terraces, diversion ditches, and other grading/drainage control measures can be

utilized to help prevent erosion and ensure slope stability. It is recommended that drainage

ditches, spillways or channels are designed to be non-erodible, to carry sustained flows, or, if

sustained flows are not expected, to be earth or grass-lined and designed to carry short-term,

periodic flows at non-erosive velocities. Design should demonstrate that erosion will be

controlled, deepening or enlargement of stream channels will be prevented, and disturbance of the

hydrologic balance will be minimal. All slopes and exposed highwalls should be stable and

protected against surface erosion. Slopes and highwall faces should be vegetated, rip rapped, or

otherwise stabilized. Hydrologic diversions and flow controls should be free of sod, large roots,

frozen soil and acid- or toxic-forming coal processing waste, and should be compacted properly

according to applicable regulatory standards. Additional contributions of sediment to streamflow

and runoff outside the permit area should be prevented to the greatest extent possible. 

Certain sediment control BMPs already are an integral part of mining operations and do not

require additional engineering designs or construction. These BMPs are recommended for

implementation during pre-, active and post-remining activities, and often are incorporated into

remining BMP implementation plans (Appendix A, EPA Remining Database, 1999). These BMPs

include:

C Streams, channels, checks dams, diversion ditches, and drains should be inspected

regularly and accumulated sediment removed. Channels and ditches should be seeded and

mulched immediately after completion, if completion corresponds to regional growing

seasons.

C Backfilling and regrading should be concurrent with coal removal and should follow

removal as soon as is technically feasible. Final grading should be performed during

normal seeding seasons to eliminate spoil piles and depressions at a time expeditious for

prompt establishment of vegetation.
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C Exposed and rounded surfaces should be mulched and vegetated immediately following

final grading. It is recommended that mulch be anchored in the topsoil and that vegetation

be planted immediately after topsoil grading.

C Areas should be reclaimed to an appropriate grade (slopes should not exceed the angle of

repose or the slope necessary to achieve minimum long-term stability and prevent slides)

to prevent surface-water impounding and promote drainage and stability. All final grading

should be completed along the contour. Terrace-type backfilling and grading works to

prevent slides and sedimentation while promoting slope stability (this also maximizes coal

recovery and eliminates exposed highwalls and spoil piles).

C Unstable-abandoned spoil and highwalls should be eliminated to the greatest extent

possible. Care should be taken if the remining operation requires disturbance of existing

benches and highwalls that have well-established vegetation and drainage patterns. Reaffecting abandoned mine lands that are well-vegetated and stabilized should be avoided to

the greatest extent possible. 

C Overburden and topsoil stockpiles that are not being used for topsoil or the establishment

of vegetation should be located to minimize exposure and should be seeded with annual

plants when needed to prevent excessive erosion.

C Topsoil material should be redistributed on graded areas in a manner which protects the

material from wind and water erosion before it is seeded and planted. Compaction of

surface topsoil materials should be such as to minimize erosion and surface water

infiltration, yet promote establishment of vegetation.

C Streams and runoff should be directed away from spoil, refuse and overburden piles,

exposed surfaces, and unstable slopes.
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Site Stabilization

Minimization of the amount of disturbance during remining operations will decrease the amount

of soil and sediment eroding from the site, and can decrease the amount of additional controls or

BMPs that will be required. Operations should only disturb portions of the site necessary for coal

recovery. Operations also can be staged to ensure that only a small portion of the site is disturbed

at any given time. If possible, portions should be remined, regraded and seeded prior to

disturbance of the next area. 

Preserving existing vegetation or revegetating disturbed soil as soon as possible after disturbance

is the most effective way to control erosion (EPA, 1992). Vegetative and other site stabilization

practices can be either temporary or permanent. Temporary controls provide a cover for exposed

or disturbed areas for short periods of time or until permanent erosion controls are established. 

Erosion and sedimentation can be minimized by removing as little overburden or topsoil as

possible during remining operations, and by having sediment controls in place before operations

begin. Any possible preservation of natural vegetation should be planned before site disturbance

begins. The advantages of such preservation include the capacity for natural vegetation to handle

higher quantities of surface water runoff.

Revegetation

Revegetation can be one of the most effective BMPs for achieving erosion control. By

functioning to shield surfaces from precipitation, attenuate surface water runoff velocity, hold soil

particles in place and maintain the soil’s capacity to absorb water while preventing deeper

infiltration, the establishment of vegetation can stabilize disturbed areas with respect to erosion,

and surface water infiltration, and attenuate AMD formation. Implementation of revegetation

consists of seedbed preparation, fertilizing, liming, seeding, mulching, and maintenance. 
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Biosolids are a low-cost alternative to the use of commercially available lime and fertilizers. The

biosolids typically used on remining sites are sewage treatment sludge. However, other biosolids

can be obtained from paper mill waste and from other industries. Biosolids are available in various

forms, but the most common is anaerobically digested materials that require an additional lime

amendment. 

Abandoned mine lands frequently have large areas with little or no topsoil, devoid of organic

matter, and micro-organisms. Biosolids use is beneficial in terms of creating a soil substitute and

improving revegetation, but also in developing soil structure through the addition of organic

matter which will foster a microbial community needed for the decomposition of biomass and

other biochemical activities that take place in soil.

Vegetative cover can be grass, trees or shrubs, but grasses are the most frequently used because

they grow quickly, providing erosion protection sometimes within days. Permanent seeding and

planting is appropriate for any graded or cleared area where long-lived plant cover is desired, and

is especially effective in areas where soils may be unstable because of soil texture and structure, a

high water table, high winds, or steep slopes. 

Typical implementation and maintenance of revegetation operations at 51 mining sites in

Alabama, Kentucky, Pennsylvania, Tennessee, Virginia, and West Virginia, are summarized in

Table 1.3.1a. 
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Table 1.3.1a: Revegetation Practices and Maintenance (Appendix A, EPA Remining

Database, 1999)

Revegetation Plan

- Systematic sample collection and analysis of topsoil, subsoil, and overburden materials to

determine the type and amount of soil amendments necessary to maintain vegetative growth. 

- Topsoil placement and seeding occur no later than the first period of favorable planting after

backfilling and grading. Disturbed areas are seeded/planted as contemporaneously as practicable

with completion of backfilling and grading. Backfilled areas prepared for seeding during adverse

climatic conditions are seeded with an appropriate temporary cover until permanent cover is

established (cover of small grain, grasses, or legumes can be installed until a permanent cover is

established).

- Disturbed areas are seeded in such a manner as to stabilize erosion and establish a diverse,

effective and permanent vegetative cover, preferably of a native seasonal variety or species that

supports the approved post-mining land use.

- Regraded areas are disced prior to application of fertilizer, lime and seed mixture. Fertilizer

mixture is applied as determined necessary by soil sample analyses. Treatment to neutralize soil

acidity is performed by adding agricultural grade lime at a rate determined by soil tests.

Neutralizers are applied immediately after regrading. A minimum pH of 5.5 is maintained. 

- Mulch is applied to promote germination, control erosion, increase moisture retention, insulate

against solar heat, and supply additional organic matter. Straw, hay, or wood fiber mulch are

applied at approximately 1.0 to 2.5 tons/acre. Small cereal grains have been used in lieu of

mulch (small grains absorb moisture and act as a soil stabilizer and protective cover until a

suitable growing season).

- Conventional equipment is used: broadcast spreader, hay blower, hydroseeder, discs, cyclone

spreaders, grain drills, or hand broadcasting. Excess compaction is prevented by using only

tracked equipment. Rubber tired vehicles are kept off reconstructed seedbeds.

Maintenance

- Vegetative cover is inspected regularly. Areas are checked and maintained until permanent cover

is satisfactory. Bare spots are reseeded, and nutrients are added to improve growth and

coverage. Areas that are damaged due to abnormal weather conditions, disease, or pests are

repaired.

- Unwanted rills and gullies are repaired with soil material. If necessary, the area is scarified and

(in severe cases) back-bladed before reseeding and mulching. 

- Revegetation success is determined by systematic sampling, typically at a minimum of 1 percent

of the area. Aerial photography can be used to determine success (typically at the 1 percent

level - or higher if necessary). Standard of Success (SOS) for revegetation is based on percent of

existing ground cover or achievement of vegetation adequate to control erosion.
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Maintenance (cont.)

- Periodic mowing is performed to allow grasses and legumes a greater chance of growth and

survival. Plants are not grazed or harvested until well-established. 

- Previously seeded areas are reseeded as necessary, on an annual basis until covered with an

adequate vegetal cover to prevent accelerated erosion. Areas where herbaceous cover is bare or

sparsely covered after 6-12 months are re-limed and/or re-fertilized as necessary to promote

vegetative growth, then reseeded and mulched. 

The amount of runoff generated from well vegetated areas is considerably reduced and is of better

quality than from unvegetated areas. However, it is not possible, based on data currently

available, to quantify the water quality benefits of the vegetative coverings as a BMP (EPA,

1996).

Direct Revegetation

Direct revegetation is an alternative to reclamation techniques that are designed to resculpture the

existing topography. During direct revegetation, grading is avoided to prevent exposure of

deeper, unweathered acid-forming materials and emphasis is placed on preservation of the

weathered surficial materials and the network of natural drainage. Direct revegetation is generally

low-cost and eliminates the acidity and potential acidity remaining in exposed surface layers by

treatment with limestone or other alkaline materials. Once the surficial acidity is removed, natural

processes that are aided and accelerated by application of fertilizer, mulch, and other organic

amendments, can be relied upon to establish permanent vegetative cover (Nawrot and others,

1988). Work may be required for several (typically three) successive growing seasons, in order to

ensure the establishment of vegetation across the entire area to be reclaimed (Olyphant, 1995).

Direct revegetation commonly requires the addition of lime and fertilizers to mine spoil or coal

refuse piles that are devoid of vegetation. Biosolids can be easily employed in cases of direct

revegetation. The material can be spread by use of a hydroseeder or farm equipment. Areas

requiring direct revegetation are often poorly accessible due to steep and unstable slopes. 
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Therefore, the ability to spread biosolids from a secure distance makes it ideal for direct

revegetation application. Biosolids, in many cases, form the basis of soil material or augment what

little soil exists on the site. 

Biosolids were used at numerous remining sites in Pennsylvania where little soil existed prior to

remining or where, if soil did exist, it was lost due to burial or erosion from pre-SMCRA mining.

Increases in plant growth and density can be dramatically improved using biosolids.

Channel, Ditch and Gully Stabilization 

Stabilization of channels, ditches, and gullies at remining sites, whether constructed for surface

water and erosion control or unwanted, is imperative for controlling sedimentation. In general,

formation of unwanted gullies should be avoided. These BMPs are recommended when vegetative

stabilization practices are not practical and where stream banks are subject to heavy erosion from

increased flows or disturbances. If unwanted or naturally-formed gullies are well- established,

stabilization may prove more effective than removal. Gullies that are deeper than nine inches may

form in regraded areas and should be filled, graded, and reseeded. Rills or gullies of lesser size

may have a disruptive effect on post-mining land use or may add to erosion and sedimentation and

should be filled, graded, and seeded (Appendix A, EPA Remining Database, 1999 VA(2)). 

It is recommended that permanent channels and gullies be designed and constructed based on 100

year, 24 hour storm event. Channels and gullies can be stabilized and protected from eroding

forces by the implementation of linings and/or check dams. Linings can be constructed of grass,

rock, rip rap, or concrete. Check dams can be constructed with staked straw bales, wood, or

rock. Although channel linings and check dams can trap small amounts of sediment, their primary

purpose is to reduce the velocity of storm water flow, thus abating additional erosion. 
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Channel Linings 

Erosion is a serious problem associated with channels and other water control structures.

Sediment loads from eroded channels can cause numerous sediment and hydraulic problems and

decrease the effectiveness of other sediment control measures. Depending on flow velocities,

channel linings may be required to prevent channel erosion (MD DNR, 1989).

Due to the ease of construction and low cost, a vegetated channel lining is one of the most costeffective ways of reducing channel erosion and is frequently used on diversion ditches. A wellestablished grass can protect the channel from erosive flow velocities of up to 6 feet per second

(fps). Shorter meadow-type grasses with short, flexible blades can withstand a maximum

permissible velocity of 5 fps. Bunch grasses or sparse cover provides only marginally better

erosion protection than a well constructed earthen channel. For prevention of erosion, the

Commonwealth of Kentucky (Kentucky, 1996) recommends that channels having a peak

discharge design velocity of less than 5 fps be lined with grass species that are effective against

erosion (e.g. Tall Fescue, Reed Canarygrass, Bermudagrass, and Kentucky Bluegrass). Channels

having discharge velocities of 5 fps or greater should be lined with rip rap or other non-erodible,

non-degradable materials unless the ditch is located in solid rock. Pennsylvania DEP (PA DEP,

1999) recommends a maximum velocity of 3 fps if only sparse cover can be established or

maintained (because of shale, soils, or climate); a velocity of 3 to 4 fps if the vegetation is

established by seeding (under normal conditions); and a velocity of 4 to 5 fps only in areas where

a dense, vigorous sod is obtained quickly or if runoff can be diverted out of the waterway while

vegetation is being established.

Vegetative linings typically begin eroding the base of channels, and once started, will continue

until an erosion resistant layer is encountered. If it becomes evident that erosion of a channel

bottom is occurring, rock or stone rip rap lining should be placed in the eroded areas. Rip rap

lining should be durable and should be free of acid-forming materials. Generally, rip rap composed

of varying sizes of stones is preferred over rip rap that is uniform, not only because it is less

expensive, but because the varying stone size promotes natural settling and grading to form a
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better seal. In addition, rectangularly shaped stone is preferred for its durability. Smooth or

rounded stones should not be used (MD DNR, 1989). A good recommendation is the use of a

well-graded mixture down to the one-inch particle size such that 50 percent of the mixture by

weight is no larger than the median stone size. Rip rap layers should have a minimum thickness of

1.5 times the maximum stone diameter or no less than six inches, whichever is the lesser value. 

Channel banks should be protected to a height equal to the maximum depth of flow (Kentucky,

1996). Rip rap used in diversion ditches and pond spillways should consist of durable sandstone

or limestone exhibiting a Slake-Durability Index of 85 or greater. The rip rap should be wellgraded with the maximum stone size D(100) equal to the blanket thickness and the median stone

size DD(50) equal to one half the blanket thickness (Appendix A, EPA Remining Database, 1999

VA(7)).

Check Dams

The purpose of check dams is to reduce the velocity of concentrated surface-water flow until

diversion ditches or gullies are properly vegetated. Check dams can be constructed of straw bales,

logs, rocks (Figure 1.3.1a), or other readily available materials, and should be designed so that

water crosses only through a weir or other outlet and never flows along the top or the outside of

the dam (Kentucky, 1996). The distance between check dams varies depending on the slope, with

a closer spacing when slopes are steeper. Materials used should be relatively impermeable and of

appropriate size, angularity, and density. They should be contained in anchored wire mesh or

gabions, or staked to prevent flowing water from transporting them (Figure 1.3.1b). 

The material used depends on the size and type of flow that is expected. Straw bale check dams

generally are suitable for sediment control where concentrated flows do not develop. The

efficiency of straw bale dams is limited by slope length and gradient. Straw or hay bales should be

secured with stakes. Log check dams can be used in channels and generally are more effective

and stable than straw bale barriers. It is recommended that logs be four to six inches in diameter,

driven sufficiently beneath the channel floor, and stand perpendicular to the plane of the channel

cross section, with no space between logs (Kentucky, 1996). It also is recommended that rip rap
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or shorter, wider logs on the downstream side be installed for stability. Rock check dams and

straw bales allow water to pass through, controlling sediment movement through filtration and

flow control. The size of the stone used in a rock check dam varies, with rock size increasing as

flow velocity and discharge volume increase. For most rock check dams, the National Crushed

Stone Association no. R-4 stone (3 to 12 inches, 6 inch average) is a suitable stone size (PA DEP,

1999). Filter stone applied to the upstream face of check dams can improve sediment trapping

efficiency. Regular removal of sediment that accumulates behind the check dam is imperative for

maintenance of efficiency, control of surface water flow, and avoidance of worsening conditions.

Check dams also can be built in series, as necessary. 

Figure 1.3.1a: Example of a Rock Check Dam (Kentucky, 1996)
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Figure 1.3.1b: Example of a Gabion Check Dam (Kentucky, 1996)

Silt Fences

Silt fences are used as temporary sediment barriers and are commonly constructed of burlap or

synthetic materials stretched between and attached to supporting posts. The purpose of silt

fencing is to detain sediment-laden, overland (sheet) flow long enough to allow the larger size

particles to settle out and to filter out silt-sized particles. Because the screen sizes of synthetic

screen fences will vary according to the manufacturer, these fences usually do not have the

strength to support impounded water and are limited to control of overland runoff. Common

problems associated with silt or filter fabric fences usually result from inappropriate installation

such as placement in areas of concentrated flows or steep slopes and placement down rather than

along contours. These fences work best when placed on areas with zero slope. Because this

often is not possible, flow should be otherwise reduced by the downslope emplacement of hay

bales, mulching, or breaking the length of installation into separate sections that will not allow

significant flow volumes. Silt fencing is appropriate for sediment control immediately upstream of

the point(s) of runoff discharge, before a flow becomes concentrated, or below disturbed areas

where runoff may occur in the form of overland flow. 
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Gradient Terraces

Gradient terraces can be used to control slope lengths, minimize sediment movement, and, on a

site-specific basis, to address particular erosion problem spots according to need. Terraces are

typically earth embankments or ridge-and-channels constructed along the face of a slope at

regular intervals and at a positive grade. These BMPs often help stabilize steeply sloped areas

until vegetation can be established and reduce erosion damage by capturing surface runoff and

directing it to a stable outlet at a speed necessary to minimize erosion. Terrace locations and

spacing can be determined following general grading and location of problem areas. It is

recommended that terraces constructed on slopes are not excessive in width and have outer slopes

no greater than 50 percent.

Design Criteria

General

C Design should approximate natural drainage as closely as possible.

C Sediment-control structures should be chosen according to review of existing topography,

flow direction and volume, outlet location, and feasibility of construction.

C Sediment control structures should be constructed on stable ground.

C Use of costly earth-moving equipment should be minimized.

C Weathered, vegetated and highly established portions of landscape should be preserved to

the greatest extent possible.

Revegetation

C Volunteer, natural vegetation should be encouraged, and where possible, undisturbed.

Channel, Ditch and Gully Stabilization

C Liner materials should not contain acid-forming materials.
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C Stabilization should be supported properly. Potential for stream bottom and sides to erode

should be considered.

C Vegetation-lined ditches should be limited to velocities of 4 to 5 fps, unless documentation

is provided that runoff will be diverted elsewhere while vegetation is being established.

C Permanent structures should be designed to handle expected flood conditions.

Check Dams

C Should be used only in small open channels which will not be overtopped by flow once the

dams are constructed.

C Check dams should be anchored to prevent failure.

C Dams should be sized according to projected flows.

C The center of the dam should be lower than the edges.

C Straws bale barriers should be placed at zero percent grade, with the ends extended up the

side slopes so that all runoff above the barrier is contained in the barrier.

C Stones should be placed by hand or using appropriate machinery, and should not be

dumped in place.

Silt Fences

C Support posts should be strong and durable.

C Filter material should be able to retain at least 75 percent of the sediment.

C Fences should be installed in undisturbed ground, and stability should be reinforced with

rope or rip rap.

C Adjoining sections of filter fabric should be overlapped and folded.

C Bottom edge should be tied or anchored into the ground to prevent underflow.

C Maintenance should be performed as needed, and material replaced when bulges or tears

develop.
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Terraces

C Terraces, in general, should not be excessive in width or have outer slopes greater than 50

percent. 

C Utilize diversion ditches as necessary, while a vegetative cover is being established.

C Terraces should be designed with adequate outlets, such as a grassed waterway or

vegetated area, to direct runoff to a point not causing additional erosion.

1.3.2 Verification of Success or Failure

Implementation Checklist

Revegetation

C Vegetation should be maintained through cutting, fertilizing and reseeding if needed.

C Vegetative success should be determined by a systematic sampling and plant count, and if

necessary, aerial photography. Success should be measured on the basis of adequate

vegetative cover which shall be defined as a vegetative cover capable of self-regeneration

and plant succession, and sufficient to control soil erosion.

C Established vegetation should be inspected periodically for scouring. Scoured areas should

be reseeded immediately.

Channel, Ditch and Gully Stabilization

C Inspect regularly and after each major storm event for: sediment buildup, scouring,

blockage and lining damage or movement.

C If excessive scouring or erosion occurs in ditches or channels, they should be lined with

rock rip rap or netting immediately.

C Sediment build up usually occurs in areas of low-flow velocities allowing particles to

settle. Grade should be checked in these areas since low-flow velocities may mean the

channel is undersized.
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C Rip rap stones that have moved should be replaced and the rip rap fortified if undercutting

has occurred.

Check Dams

C Inspect check dams regularly and after significant precipitation events for damage and

sediment accumulation.

C Accumulated sediment should be removed from behind the dams and erosive damage

restored after each storm or when half the original dam height is reached.

C The length of straw bale barriers should be inspected on a periodic basis to look for

problem areas. Eroded areas should be regraded, accumulated sediment removed, and the

barrier repaired to maintain effectiveness.

C Stone should be replaced as necessary to maintain correct dam height.

Silt Fences

C Silt fences should be inspected daily during periods of prolonged rainfall, immediately after

each rainfall event, and weekly during periods of no rainfall.

C Required repairs should be made immediately.

C Sediment should be removed once it reaches one-third to one-half the height of the filter

fence.

C Filter fences should not be removed until the upslope area has been permanently stabilized. 

Sediment deposits remaining after the filter fence has been removed should be graded,

prepared and seeded.

Terraces

C Terraces should be inspected regularly at least once a year and after major storms.

C Proper vegetation and stabilization practices should be implemented during construction.
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1.3.3 Literature Review / Case Studies

Case Study 1 (Harper and Olyphant, 1993; Olyphant and Harper, 1995; Carlson and Olyphant,

1996)

Direct Revegetation

Coal refuse is often an acid-forming material containing high concentrations of pyrite (» 0.50

percent total sulfur). If present, the oxidation of pyrite causes acidification of the soil, and

acidification in turn, greatly inhibits vegetation. Substantial erosion and sedimentation occur due

to poor or complete lack of vegetation on abandoned surface mine lands and coal refuse piles. 

Erosion is further accelerated by steep slopes common to some abandoned mine sites. Olyphant

and Harper (1995) observed that direct revegetation of abandoned pyritic coal refuse piles can

successfully reduce the sediment load as well as improve the water quality of the runoff effluent

from abandoned mine lands. 

Direct revegetation was conducted on abandoned pre-SMCRA coal refuse piles located in

Sullivan County, Indiana (Harper and Olyphant, 1993; Olyphant and Harper, 1995; and Carlson

and Olyphant, 1996). Prior to revegetation, these piles were characterized by “severe and rapid

erosion” and high pyritic content (up to 4.4 percent by weight). The colluvial material “derived

from gully side slopes” built up through the winter months. This material was washed out during

the spring followed by “erosional downcutting” through the summer and fall. Yearly backcutting

of the gullies ranged from 2.5 to 4.6 centimeters with an interfluve lowering of 0.4 centimeters. 

The volume of sediment yielded by these gullies was approximately four fold that of the

watershed as a whole and about 10 times that of adjacent interfluve areas. Yearly sedimentation

yield was over 10 kg/m2 (Olyphant and Harper, 1995).

In order to treat the acidity of the surficial refuse and allow plant growth, limestone was directly

disced into the refuse without regrading the existing surface. Fertilizer was also broadcast over

portions of the site to promote the vegetative cover. Additionally, small rip rap check dams and

water bars were installed to prevent erosion and promote infiltration of precipitation. From 1990
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to 1992, 100 to 210 tons per acre of agricultural limestone was disced to a depth of 6 inches into

the refuse. Fertilizer was applied in the spring of 1991 and 1992 at rates of 100 lbs per acre of

N2, 150 lbs per acre of P2O2, and 350 lbs per acre of K2O. The refuse was initially planted with a

rye-nurse crop. Additionally, a permanent cover of Kentucky 31 fescue, bristly locust, and black

locust was highly successful. Direct vegetation of weathered, undisturbed refuse with a pH less

than 3.8 and pyrite concentrations less than 0.84 percent, resulted in successful stabilization

(Harper and Olyphant, 1993). Within 18 months, the site had a diverse dense growth of planted

and volunteer vegetation (Olyphant and Harper, 1995).

The rip rap check dams were installed by “end-dumping” between 5 and 185 tons of rock directly

into the upper parts of erosion gullies. Erosion netting and water bars were also used to control

erosion on steep-slope areas, where additional time and effort is required to achieve sufficient

vegetative cover to inhibit erosion. 

The remedial work (direct planting, check dams, and water bars) resulted in increased

precipitation infiltration (decreased runoff), reduced erosion and sedimentation, and an

improvement in the runoff-water quality. Runoff decreased by 56.7 percent, from 30 to 13

percent of the precipitation. The increased infiltration resulted in a higher moisture content in the

root zone, especially during dry periods. Coarse sediment yield prior to vegetation and the

implementation of sediment controls comprised more that 50 percent of the total sediment.

Afterward, coarse-grained sediments were virtually nonexistent. Fine-grained sediments declined

from 4.5 kg/m2 to 0.3 kg/m2, or 93.3 percent. The acidity of the runoff improved from being

occasionally over 700 mg/L to an average alkalinity of 75 mg/L (Olyphant and Harper, 1995). 

However, no alkalinity was observed in the refuse pore water below a depth of 1.7 feet (Harper

and Olyphant, 1993).

Case Study 2 - Keel Branch, VA (Zipper and others, 1992)

The study area was an abandoned surface and underground coal mining site in Dickenson County,

Virginia. The surface mining occurred between 1955 and 1958. “Shoot and shove” mining

operations of that period produced a terrain consisting of exposed highwalls, more or less 
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level benches, and steep spoiled outslopes. Abandoned mine land areas included approximately

170 acres and 8,000 linear feet of outslope-bench-highwall terrain. Highwalls from 50 to 100 feet

high remained easily visible with evidence of some sloughing of highwall materials. Vegetative

cover of the benches varied from dense to barren. The barren areas are associated with “burn

out” from acidic coal fines. The outslopes were the main source of major environmental

problems, with surface inclinations commonly exceeding 30E and extremely sloped areas nearing

40E. Adverse environmental impacts on watershed soil and vegetation was verified by the

deterioration of natural forest areas directly below outslopes, caused by sediment movement from

higher elevations downward toward the stream. A mining company was interested in remining

coal from abandoned deep mine pillars and solid-coal sections that had not been surface mined,

but was concerned about environmental liabilities (Zipper and others, 1992).

The goal of the study was to identify and compare the environmental effects of four remining and

reclamation options. The objective was to estimate the reduction in soil loss and sediment yield

likely to be achieved by various remining and reclamation strategies, relative to existing conditions

using a modified Universal Soil Loss Equation model in a Geographic Information System (GIS)

environment. The study evaluated three remining options and one AML-funded reclamation

option and compared them to a “do-nothing” strategy. The remining options considered were:

Remnant Recovery: a technique frequently used to mine the remaining coal reserves from

abandoned bench-highwall-outslope terrain in southwestern Virginia, eastern Kentucky and

southern West Virginia. The mine operator employs conventional second-cut remining, taking an

additional cut from the highwall to extract coal from the most profitable areas. Spoil from the

second-cut is used to reclaim the exposed highwall segment to the maximum extent technically

practical. The reclaimed site is characterized as a steeply sloped highwall backfill, which may be

adjacent to exposed highwalls remaining from unreclaimed pre-SMCRA operations. Existing

spoil in the outslope areas is not re-affected (Zipper and others, 1992). 
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Conventional Second-Cut Contour: is also commonly used in steeply-sloped Appalachian areas

and similar to remnant recovery, except rather than mining only the most profitable areas,

additional cuts are taken from a relatively long, continuous portion of the highwall. This method

also allows for reclamation of all exposed highwall to steeply sloped backfill contours. As with

remnant recovery, outslope spoils are avoided to the greatest extent possible (Zipper and others,

1992).

Innovative Remining: designed to maximize reclamation effectiveness as allowed by the scope of

the remaining minable coal reserves. The key to this plan is to apply virgin cuts to a coal seam at

the base of the spoil slope as well as additional cuts into the existing highwall of a higher coal

seam. In the process of reclamation, the spoil on the outslope will be eliminated. Critical to this

plan is that the highest portions of the upper highwall do not have to be completely reclaimed. 

This is important because such reclamation can be cost prohibitive for remining

operations. Much of the temporary sediment controls are placed down gradient in or near the

headwaters of the adjacent streams. The main benefit of this methodology is that the problems

caused by the spoil outslopes are eliminated (Zipper and others, 1992).

AML Reclamation: an option in which no additional coal is mined, the outslope area is regraded

and the spoil is replaced into the existing open pit. Complete highwall elimination is unlikely,

because the amount of spoil on the outslope is insufficient. However, the exposed strip bench is

covered. Actual AML reclamation is unlikely at the study site because is has been assigned the

lowest AML Fund priority number (3) (Zipper and others, 1992). 

Roughly 40 percent of the abandoned mined areas of the site (mainly the steep outslopes)

presently yield 95 percent of the sediment. Most of the study area (77 percent) has estimated soil

losses of “stable conditions”, which are 0 to 1 ton per year. Approximately 8 percent of the AML

area has soil loss potentials of between 20 and 50 tons per year. Soil losses exceeding 50 tons per

year were determined for 2.6 percent of the AML area. Of the total soil loss, 60 percent was

redeposited on the land surface, while the remaining 40 percent caused siltation of the streams.
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Remnant recovery and conventional second-cut contour were determined to be the least effective

reclamation techniques in terms of controlling erosion and sedimentation. Remnant recovery

showed a soil loss reduction of 8 to 23 percent depending on the amount of vegetative cover of

60 and 95 percent respectively. Conventional second-cut contour faired slightly higher with soil

loss reductions of 19 to 39 percent. The two reclamation methods that eliminate the outslope

spoil performed the best. Innovative remining has predicted soil loss reductions ranging from 38

to 86 percent, while AML reclamation would yield soil loss reductions from 52 to 75 percent.

Regardless of the reclamation technique analyzed the effectiveness improved with increasing

ground cover (Zipper and others, 1992). 

Critical to innovative reclamation is procurement of a variance to the complete highwall

elimination requirement. With this type of reclamation, sedimentation is greatly reduced, a coal

resource is utilized, and substantial reclamation is achieved. 

1.3.4 Discussion

Typical sedimentation control BMPs entail slope regrading, revegetation, sediment trapping, and

control of runoff. Successful control of erosion and sedimentation from remining operations may

require innovative practices and controls in addition to those normally implemented. Existing

unreclaimed conditions create distinct problems, especially in terms of erosion and sedimentation

on steeply sloped spoil. Innovative techniques for remining and reclamation can be employed to

mitigate erosion and sedimentation problems. 

Benefits

C Implementation can require minimal labor. Sediment control BMPs are typically low cost

and use conventional farming equipment.

C Can subsequently reduce availability or reactivity of acid-forming materials.

C Can subsequently be implemented to control site surface-water hydrology.

C Hydraulic and sediment control BMPs are often already permit requirements.
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C Biosolids can provide nutrients and organic mater on sites with poor or nonexistent soils,

thus enhancing plant growth. 

C These BMPs often improve site aesthetics and can provide wildlife habitats.

Limitations

C If not designed, implemented, and maintained properly, severe and rapid erosion can occur

as natural drainage networks are re-established.

C Steeply sloped areas may require intensive physical labor (not machine accessible).

C Establishment of vegetative covering should be coordinated with climatic conditions for

proper establishment.

C Biosolids application rates may be limited by metals concentrations.

C BMP success is often dependent on climate and weather.

1.3.5 Summary

There are remining situations where the primary water quality concern is not necessarily the

dissolved contaminant component or pH, but is instead suspended solids and the subsequent

deposition of sediment into receiving streams. Surface mining prior to SMCRA commonly left

unreclaimed spoil piles and open pits. Pre-SMCRA mining operations in steeply sloped areas

tended to spoil the overburden downslope of the operation. Abandoned spoil piles and exposed

surfaces have been weathering for decades and through natural processes, typically have been

partially to completely revegetated. Whether or not these spoil piles are reaffected, considerable

erosion and sedimentation may result during remining operations. Therefore, erosion and

sedimentation control BMPs frequently require additional measures in addition to the standard

controls.

Slope stabilization through control of precipitation runoff is a critical component of these BMP

practices. If erosion can be prevented, sedimentation will be controlled. Runoff and associated

erosion is controlled through the integration of engineered slopes (e.g., terraces), revegetation,
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surface-water diversion through or away from spoil areas, sediment traps (e.g., silt fences, check

dams, rip rap, dugout ponds), minimizing the amount of unreclaimed land at any given time,

concurrent reclamation, and elimination of existing unstable spoil areas. Although significant

sedimentation associated with remining is somewhat regional and is more prominent in steep slope

areas, the problem is an important one. The BMPs discussed in this section have been

successfully applied throughout the eastern Coalfields.

References

Ackman, T. E., J. R. Jones, and C. C. Hustwit, 1989. Stream Sealing to Reduce Infiltration into

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with the Office of Surface Mining Reclamation and Enforcement, Green Tree, PA, 108 p.

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Bell, A. V., M. D. Riley, and E. K. Yanful, 1994. Evaluation of a Composite Cover to Control

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Broman, P. G., P. Hagland, and E. Mattsson, 1991. Use of Sludge for Sealing Purposes in Dry

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Caruccio, F.T. and G Geidel, 1986. Geologic Factors Affecting Mine Drainage Quality, In the

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Cederstrom, D.J., 1971. Hydrologic Effects of Strip Mining West of Appalachia. Mining

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Mine Drainage Prediction and Pollution Prevention in Pennsylvania, Pennsylvania Department of

Environmental Protection, Harrisburg, PA, 11 p.

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the Proceedings of the Second International Conference on the Abatement of Acidic Drainage,

Monteal, Quebec, Canada, Tome 4, pp. 69-84.

Harper, Denver and Olyphant, Greg A, 1993. Direct Revegetation of Abandoned Coal-Refuse

Deposits in Indiana: Its Effects on Hydrology, Chemistry, and Erosion. Final Report to the

Indiana Division of Reclamation Concerning Research and Reclamation Feasibility Studies at the

Friar Tuck Site, Sullivan and Greene Counties, Indiana. Indiana Geological Survey, 41 p

Hawkins, J. W., 1998a. Hydraulic Properties of Surface Mine Spoils of the Northern Appalachian

Plateau. In the proceedings of 25th Anniversary and 15th Annual Meeting of the American Society

for Surface Mining and Reclamation, St. Louis, MO, pp. 32-40.

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to 3-11.

Hawkins, J. W., 1995a. Impacts on Ground Water Hydrology from Surface Coal Mining in

Northern Appalachia, Proceedings of the 1995 Annual Meeting of the American Institute of

Hydrology, Denver, CO.

Hawkins, J. W., 1995b. Characterization and Effectiveness of Remining Abandoned Coal Mines

in Pennsylvania. U.S. Bureau of Mines, Report of Investigations-9562, 37 p.

Hawkins, J. W., 1994. Modeling of a Reclaimed Surface Coal Mine Spoil Aquifer Using

MODFLOW. In Proceedings of the International Land Reclamation and Mine Drainage
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PA, Vol. 2, pp. 265-272.

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Drainage, Montreal, Quebec, Canada, Tome 1, pp. 47-68. 

Hawkins, J.W. and W.W. Aljoe, 1990. Hydrologic Characterization and Modeling of a

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Kentucky, Lexington Kentucky, pp. 43-52.

Hawkins, J.W., K.B.C. Brady, S. Barnes, and A.W. Rose, 1996, Shallow Ground Water Flow in

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Mine Water Assoc., v. 17, no. 1, pp. 28-40.

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the Fifth Symposium on Coal Mine Drainage Research, National Coal Association, Louisville,

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103.

Olyphant, Greg A. and Harper, Denver. Effects of direct revegetation on the hydrology, erosion

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Investigation Report 83-4155. Columbus, OH. 36 p.

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Small Watershed in Jefferson County, Ohio. U.S. Geological Survey, Water-Resources

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Rogowski, A. S. and H. B. Pionke, 1984. Hydrology and Water Quality on Stripmined Lands.

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American Society for Surface Mining and Reclamation, Austin, TX, pp. 64-73.

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Hydrologic Controls 1-99

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671-679.
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1-100 Hydrologic Controls
Coal Remining BMP Guidance Manual

Geochemical Controls 2-1

Section 2.0 Geochemical Best Management Practices

Introduction

The previous section discussed how hydrologic best management practices (BMPs) can reduce

pollution load from remining sites. This section will discuss BMPs that use geochemical approaches

to reduce pollution load. Effective use of geochemical BMPs requires at least a rudimentary

understanding of the acid-producing and acid-neutralizing chemical processes.

Acid mine drainage results from the oxidation of pyrite (FeS2). The following summary equation

shows the reactants and products:

FeS2 + 3.75 O2 + 3.5 H2O 6 Fe(OH)3(s) + 2 SO4

2- + 4 H+

(Equation 1)

Pyrite in the presence of oxygen and water will oxidize to form "yellowboy" [Fe(OH)3(s)], sulfate

(SO4

2-) and acidity (H+

). Equation 1 is a summary equation. The following reactions are important

intermediate steps:

FeS2 + 3.5 O2 + H2O 6 Fe2+ + 2 SO4

2- + 2 H+

 (Equation 2)

Fe2+ + 0.25 O2

 + H+ 6 Fe3+ + 0.5 H2O (Equation 3)

A product of Equations 2 and 3 is ferric iron (Fe3+). Ferric iron can oxidize pyrite in the absence of

oxygen:

FeS2 + 14 Fe3+ + 8 H2O 6 15 Fe2+ + 2 SO4

2- + 16 H+

(Equation 4)

The oxidation of pyrite by ferric iron can become cyclical and self-feeding (Stumm and Morgan,

1996). Chemical reactions represented by Equations 1 through 4 occur "naturally," but the rate of
Coal Remining BMP Guidance Manual

2-2 Geochemical Controls

reaction can be enhanced by orders of magnitude by the catalytic influence of bacteria, primarily

Thiobacillus ferrooxidans. The bacteria obtain energy for their metabolism from the above reactions.

Equally important to any of the above acid-producing reactions is the ability of certain minerals to

neutralize acid. This is illustrated by the dissolution of calcite:

CaCO3 + H+ 6 Ca2+ + HCO3

-

( Equation 5)

CaCO3 + 2 H+ 6 Ca2+ + CO2 + H2O (Equation 6)

In Equation 5, acidity (H+) is neutralized and alkalinity (HCO3

-

) is produced. In Equation 6 acidity

is neutralized, but no alkalinity is generated. Whether Equation 5 or 6 dominates depends on how

open or closed the system is to the atmosphere (Guo and Cravotta, 1996). In a more closed system

Equation 5 will dominate.

Two overall reactions can be written to describe pyrite oxidation (acid production) and carbonate

dissolution (acid neutralization) in a closed (Equation 7) and open (Equation 8) system:

FeS2 + 4 CaCO3 + 3.75 O2 + 3.5 H2O 6 Fe(OH)3 + 2 SO4

2- + 4 Ca2+ + 4 HCO3-

(Equation7)

FeS2 + 2 CaCO3 + 3.75 O2 + 1.5 H2O 6 Fe(OH)3 + 2 SO4

2- + 2 Ca2+ + 2 CO2

(Equation 8)

Chemical BMPs attempt to counter the acid-generating chemical reactions in one or more ways.

Approaches include the following:

C preventing pyrite from being oxidized

C keeping water away from pyrite

C neutralization of acid by dissolution of calcareous materials

C inhibition of the bacterial catalysis.

The chemical BMPs examined in this section are alkaline addition, induced alkaline recharge, special

handling of acid-forming materials, and bactericides. Alkaline addition can positively affect mine
Coal Remining BMP Guidance Manual

Geochemical Controls 2-3

drainage in several ways. It can neutralize acid generated from pyrite oxidation, it can elevate pH,

which can have an inhibitory effect on bacteria, and it can facilitate precipitation of ferric iron (Fe3+),

thus reducing its role in pyrite oxidation. Induced alkaline recharge is a hybrid of geochemical and

hydrologic controls. The geochemical aspect is largely neutralization of acid. Special handling can

be used to keep water or oxygen away from pyrite. Bactericides are used specifically for stopping

the influence of bacteria on the acid mine drainage (AMD)-generating process.
Coal Remining BMP Guidance Manual

2-4 Geochemical Controls
Coal Remining BMP Guidance Manual

Geochemical Controls 2-5

2.1 Sampling

Introduction

Proper planning for implementation of geochemical BMPs requires an adequate understanding of

overburden characterization and sampling. This discussion on sampling is primarily taken from

Tarantino and Shaffer (1998), and supplemented by data from Sames and others (in preparation). 

Sames and others surveyed all Appalachian coal mining states to determine sampling protocol and

interpretative techniques used by the various states.

The results of overburden analyses are generally used in two ways: 1) as a permitting decisionmaking tool (determining whether the permit is issuable), and 2) as a management tool (using the

information to design best management practices for avoidance or remediation of pollution).

This section will concentrate on using overburden sampling for providing insights into the design

of best management practices. Representative overburden sampling is used to:

C determine overall acid or alkaline-producing potential of a proposed mine;

C calculate alkaline addition rates;

C determine the distribution of pyritic zones that may require special handling or avoidance;

C identify alkaline zones which can be incorporated into a mining plan to prevent acidic

drainage (i.e., alkaline redistribution); and,

C determine the economic feasibility of mining without unacceptable environmental impacts.
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2-6 Geochemical Controls

Acid-Base Accounting

Overburden analysis (OBA) refers to determination of the acidity or alkalinity producing potential

of the rocks that will be disturbed by mining. OBA methods fall into two broad categories: static

and kinetic. Static tests are “whole rock analyses” that determine the concentration of elements

or minerals. Kinetic tests are simulated weathering procedures that attempt to reproduce

weathering. In short, static tests measure what is in the rock and kinetic tests measure what

comes out of the rock. By far the most commonly used overburden analysis method in the

Appalachian region is static “acid-base accounting” (ABA). 

Components of ABA

ABA is based on the premise that the propensity for a site to produce acid mine drainage can be

predicted by quantitatively determining the total amount of acidity and alkalinity contained in

samples representative of site overburden. The maximum potential acidity (expressed as a

negative concentration of CaCO3) and total potential alkalinity (termed neutralization potential

and expressed as concentration of CaCO3) are summed. If the result is positive, the site should

produce alkaline water. If it is negative, the site should produce acidic water. The maximum

potential acidity (MPA) is stoichiometrically calculated from the percent sulfur (S) in the

overburden. Sobek and others (1978), noting that 3.125 g of CaCO3 is theoretically capable of

neutralizing the acid produced from 1 g of S (in the form of FeS2 ), suggested that the amount of

potential acidity in 1000 tons of overburden could be calculated by multiplying the percent S

times 31.25. This factor is derived from the stoichiometric relationships in Equation 9 and carries

the assumption that the CO2 exsolves as a gas.

FeS2 + 2 CaCO3 + 3.75 O2 +1.5 H2O --> Fe(OH)3 + 2 SO4

2-+ 2 Ca2+ + CO2

(g) (Equation 9)
Coal Remining BMP Guidance Manual

Geochemical Controls 2-7

Cravotta and others, (1990) suggested that, in backfills where CO2 cannot readily exsolve, the

CO2 dissolves and reacts with water to form carbonic acid and that the maximum potential acidity

in 1000 tons of overburden should be derived by multiplying the percent S times 62.50. 

In short, however, it can be said that interpretation of ABA data is far more complicated than

simply summing the MPA and neutralization potential (NP) values. In addition to the percent

sulfur and NP determinations, two other measured parameters in an ABA overburden analysis are

paste pH and “fizz.” 

Paste pH

Paste pH has its origin in soil science, where weathered material (soil) is analyzed. A portion of

prepared sample is mixed with deionized water, and then tested with a pH probe after one hour. 

The paste pH test indicates the number of free hydrogen ions in the prepared sample, However,

since pyrite oxidation reactions are time dependent, the paste pH results provide little indication

of the propensity of a sample to produce acid mine drainage. In fact, the paste pH of a

unweathered, high-sulfur sample is likely to be near that of deionized water, while a weathered

sample with relatively low percent sulfur (but which includes a small amount of residual

weathering products) may have a significantly depressed paste pH. Thus, paste pH is of limited

use when dealing with unweathered rock.

Percent Sulfur

Since acid mine drainage results from weathering of sulfide minerals, the amount of sulfur in a

sample, or in an overburden column, is obviously an important component of ABA. 

Sulfur determinations for ABA are often performed for total sulfur only, however, determinations

for forms of sulfur are sometimes included. Sulfur generally occurs in one of three forms in the

rock strata associated with coals in Appalachia: sulfide sulfur, organic sulfur, and sulfate sulfur. 
Coal Remining BMP Guidance Manual

2-8 Geochemical Controls

Sulfide sulfur is that sulfur that reacts with oxygen and water to form acid mine drainage. 

The sulfide minerals most commonly associated with coal in Appalachia are pyrite and

marcasite, both of which have the formula FeS2. 

Organic sulfur is that sulfur which occurs in carbon-based molecules in coal and other

rocks with significant carbon content. Since organic sulfur is tied up in compounds that

are stable under surface conditions, it is generally not considered a contributor to AMD. 

Organic sulfur is only a small percentage of total sulfur for most rock types, but can be

significant in coal. 

Sulfate sulfur, in humid climates, is generally found in relatively small concentrations due

to its association with high-solubility minerals. However, when present in Appalachia,

sulfate sulfur often occurs in partially weathered samples as a reaction by-product of

sulfide-mineral oxidation. When solubilized, these by-products are the source of the

contaminants found in acid mine drainage. For that reason, when determinations for forms

of sulfur are performed, sulfate sulfur should be considered in the calculation of MPA. 

Alkaline earth sulfate minerals such as gypsum (CaSO4) can also contribute to the sulfate

sulfur fraction, but generally are not abundant in coal-bearing rocks in Appalachia. Where

they are present, the alkaline earth-sulfate minerals do not contribute to acidity and should

not be counted in the calculation of MPA (Brady, Hornberger, and Fleeger, 1998).

A review of the methods for sulfur determinations described in Noll and others, (1988) reveals

that the methods for total sulfur determinations have a relatively high degree of precision with few

notable interferences and precautions, while methods for determination of the forms of sulfur had

lesser degrees of precision and more numerous potential interferences. Stanton and Renton

(1981) examined the nitric acid dissolution procedure, which is the cornerstone of the most

frequently used methods for determining pyritic sulfur, including American Society for Testing

and Materials (ASTM) D2492. They found the procedure frequently does not succeed in
Coal Remining BMP Guidance Manual

Geochemical Controls 2-9

digesting all the pyrite, and thus underestimates the pyritic fraction of the sulfur. Brady and

others (1990) compared total sulfur and forms of sulfur determinations performed by various

laboratories. Their findings include:

C While the results generated by each laboratory were internally consistent in terms of the

ratio of pyritic sulfur to total sulfur, there were significant differences between laboratories

in the median percent pyritic sulfur/total sulfur. Where the same samples were analyzed

by different laboratories, differences were noted in the pyritic determinations, but total

sulfur determinations were comparable.

C There was no significant difference in the percent pyritic sulfur/total sulfur between rock

types (excluding coal). This contradicts one of the primary reasons for determining forms

of sulfur: that some rock types contain significant percentages of organic sulfur.

C With one exception, all laboratories used high temperature combustion for determining

weight percent total sulfur. The high temperature combustion results compared well on

duplicate samples, while the pyritic results on the same samples did not.

C Standards are available from the National Institute of Standards and Technology for total

sulfur but not for pyritic sulfur.

C A wide range of methods for determining pyritic sulfur were in use and individual

laboratories had their own variations of the methods.

C According to ASTM Committee D-5 on Coal and Coke, the most commonly used method

of pyritic sulfur determination, ASTM D2492, was developed for use on coal and is

probably not appropriate for determinations on rock overburden.
Coal Remining BMP Guidance Manual

2-10 Geochemical Controls

The above findings can be summarized as:

 

C Total sulfur determinations are typically simple to perform, are reproducible, and can be

calibrated and verified using available standards; 

C pyritic sulfur is determined using a variety of methods (the most common of which is

considered inappropriate for rock samples), 

C pyritic sulfur methods produce results which are often not reproducible between

laboratories, and cannot be calibrated and verified using available standards. 

Given these considerations, and that pyritic sulfur is the most abundant form in coal overburden

(but not necessarily in the coal), total sulfur determinations currently provide the best basis for

calculating MPA.

Fizz Rating

The fizz test is a subjective test measured visually and rated as to the amount of effervescence

when one to two drops of 25 percent HC1 is added to a small amount of finely-ground sample

(Sobek and others, 1978). Fizz ratings range from strong effervescence to none. The fizz test

serves two functions:

C as a check on the NP determination, since there should be a qualitative correlation

between the two. Calcareous rocks with high NP should show a strong fizz, whereas noncalcareous rocks should not; and 

C more importantly, the fizz rating determines the volume and the strength of the acid that is

used to digest samples for NP determinations. 
Coal Remining BMP Guidance Manual

Geochemical Controls 2-11

Neutralization Potential

The first step of the NP test is to conduct a qualitative fizz test on a small amount of the prepared

sample as described above. Based on the fizz test results, an appropriate volume and normality of

HCl is selected then added to 2.0 grams of prepared sample (Noll and others, 1988; Sobek and

others, 1978). The strength of the acid is chosen to assure complete digestion of acid-neutralizing

minerals. The neutralization potential is calculated by determining the amount of acid that has

been neutralized by the rock.

Carbonate minerals, such as calcite and dolomite, are known to be major contributors to groundwater alkalinity in the coal regions of the Appalachians. The acid-digestion step of the NP test is

suspected of dissolving various silicate minerals, which results in a NP determination that

overstates the amount of carbonate minerals in a sample. Lapakko (1993) noted that since this

dissolution will only take place at low pH values, it is unlikely to help maintain a drainage pH of

acceptable quality. 

Siderite (FeCO3) is common in Appalachian coal overburdens, and has long been suspected of

interfering with the accuracy of NP determinations and of complicating the interpretation of the

data (Skousen and others, 1997). If iron from siderite is not completely oxidized when the

titration is terminated, the calculated NP value will be overstated. Skousen and others (1997)

found that the addition of hydrogen peroxide (H2O2) following sample digestion can expedite

oxidation and precipitation of iron. Samples exposed to H2O2 digestion produced results similar

to those of samples containing little pyrite or siderite. The additional H2O2 digestion step provided

the lowest NP values for samples with significant siderite content and the best reproducibility

between laboratories. 

Net Neutralization Potential

Neutralization potential and maximum potential acidity are both expressed in units of tons CaCO3

equivalent per 1000 tons of material (e.g., parts per thousand CaCO3). Net neutralization
Coal Remining BMP Guidance Manual

2-12 Geochemical Controls

potential (NNP) is neutralization potential minus maximum potential acidity. Thus, if the NNP is

positive, there is an excess of neutralizers. If the NNP is negative there is a deficiency of

neutralizers.

Studies comparing ABA with post-mining water quality have consistently shown that although

NP and MPA have the same units of tons CaCO3 per thousand tons of material, and in theory

should be "equal," their relative importance is not equal. It takes an excess of NP to assure that

post-mining water will be alkaline (diPretoro, 1986; Erickson and Hedin, 1988; Brady and others,

1994; Perry, 1998). Post-mining water quality predictions should not be based on ABA alone,

but should employ an array of prediction techniques. The best decisions involve consideration of

as much data as is available (Kania, 1998b).

Information Needed to Conduct an Overburden Analysis

The site-specific data needed to properly plan an overburden analysis (OBA) includes:

C Mining limits: -boundaries of the proposed area to be affected by coal removal;

-proposed maximum highwall heights;

-type of mining (e.g., contour/block cut or hill top removal); and

-accessibility to drilling locations

C Geologic considerations such as coal-seam identification, depth of weathering, and

stratigraphic variation.

C Information available in state mining office permit files, such as water quality data from

previous permits or applications covering the same or adjacent areas.

C Overburden analyses from the same or adjacent areas.

C Publications of state geologic surveys, the US Geologic Survey (USGS), the former US

Bureau of Mines (USBM), US Army Corps of Engineers, and miscellaneous other state

specific publications (e.g. the Pennsylvania “Operation Scarlift” reports from the late

1960s and early 1970s). These publications can include information such as:
Coal Remining BMP Guidance Manual

Geochemical Controls 2-13

-coal-bed outcrop maps,

-generalized stratigraphic sections,

-coal seam thickness maps,

-structure contour maps.

Old and current deep mine maps are available from the Office of Surface Mining, Appalachian

Region Coordination Center, at 3 Parkway Center, Pittsburgh, PA, 15220, and various state

agencies. These agencies have map repositories containing prints, originals, and microfilm, and

copies can be readily obtained. These repositories include the Works Progress Administration 

(WPA) deep mine maps prepared in the 1930s, which cover an area that is 1/9 of a 15 minute

quadrangle. In addition to showing mining limits, deep mine maps frequently show structure

contours. This information can be very helpful in planning OBA drilling.

Other considerations in developing an OBA drilling plan include:

C Exploration equipment. It is important to understand the limitations that are inherent with

different types of drilling equipment. These limitations can have an impact on the ability

to obtain unbiased, representative samples. The choice of exploration equipment can

influence costs.

C The type of overburden analysis to be performed. This is important in determining how

much sample and what size fraction is required for the specific type of testing to be

employed.

C Time constraints. Air rotary drilling is normally faster than coring.

C Economic constraints. Air rotary drilling is generally less expensive than coring.
Coal Remining BMP Guidance Manual

2-14 Geochemical Controls

Preparing for Overburden Analysis Sampling

The obvious questions that need to be asked when planning an OBA drilling plan are:

C How many OBA holes are needed ?

C Where should the drill holes be located ? 

Once these details have been worked out, preliminary work can start.

The first step in the development of an OBA proposal is to plan for the drilling. While there may

appear to be savings associated with performing the drilling for the overburden analysis as part of

the initial exploration drilling, it is generally preferable to perform exploratory drilling throughout

the entire site before OBA drilling is initiated. This preliminary drilling enables the determination

of depth to coal and the lateral extent of strata. This information can then be used to locate

overburden holes best suited to represent the lithologic variation and degree of weathering within

the site. If research and exploration are done prior to drilling the OBA holes, it is less likely that

there will be a need to drill additional OBA holes later during the permitting process.

Areal Sampling-A Survey of State Practices

Sames and others (in preparation) surveyed Appalachian coal states to determine rules-of-thumb

for areal sample coverage. According to Sames and others (in preparation) “all the states

interviewed, except Virginia, have some minimum spatial distribution requirements for

overburden analysis that should be supplemented upon request from the reviewing

professional(s).” Table 2.1a shows the minimum drill hole spacing requirements by state.
Coal Remining BMP Guidance Manual

Geochemical Controls 2-15

Table 2.1a: Minimum Overburden Analysis Drill Hole Spacing Requirements by State

(Sames and others, in preparation)

State Minimum Requirement Comments

AL Two drill holes on small permit properties (<10 acres).

One drill hole per 160 acres, or one per property quarter

on larger permits.

-

KY Eastern KY: Drill holes should be distributed on a

staggered, one-quarter mile grid pattern.

Western KY: Drill holes should be distributed on a

staggered, one-half mile grid pattern.

-

MD One drill hole per site regardless of size -

PA Two drill holes per site regardless of size. However, a

rule-of-thumb of 2 drill holes per site plus 1 drill hole per

100 acres is usually requested.

On average, most applications

contain 1 overburden analysis hole

for every 20 permit acres.

TN One drill hole per 60 to 100 acres for permits to mine

coal beds considered a high risk for AMD, based on past

experience. One sample point per one-quarter mile in

coal beds considered a low risk for AMD.

-

VA

-

In general, accepts any information

submitted by the applicant,

considers the quantity, quality, and

consistency of the OBA for the

permit area, and decides whether a

reasonable characterization of the

site is possible based on the spatial

distribution provided.

WV One drill hole in low cover and one in high cover.

Otherwise, regulatory agency geologists to utilize Best

Professional Judgement when determining the number of

drill holes required for a permit.

In general, accepts any information

submitted by the applicant,

considers the quantity, quality, and

consistency of the OBA for the

permit area, and decides whether a

reasonable characterization of the

site is possible based on the spatial

distribution provided.
Coal Remining BMP Guidance Manual

2-16 Geochemical Controls

Areal Sampling Experience: Pennsylvania

Pennsylvania has grappled with the issue of drill hole distribution since the advent of overburden

sampling. A rule of thumb developed in Pennsylvania in the 1980s to determine a suggested

minimum number of overburden holes was:

Number of acres to be mined + 2 = Number of

100 Acres Overburden Holes

If the first part of the equation resulted in a fraction, it was rounded to the closest whole number. 

For example:

143 acres + 2 = 3 Overburden Holes

100 acres 

49.99 acres + 2 = 2 Overburden Holes

100 acres 

179 acres + 2 = 4 Overburden Holes

100 acres 

This equation assumes that, for mines where OBA was requested, at least two holes are needed

to determine whether the drilling was representative. This two-hole minimum is still in use. More

recent data show that the actual sampling density for acid base accounting drill holes is greater

than the “rule of thumb.” A recent survey of overburden hole coverage for 38 sites in

Pennsylvania revealed that on average, there is one OBA hole for every 15.5 acres of coal

removal (Table 2.1b).
Coal Remining BMP Guidance Manual

Geochemical Controls 2-17

Table 2.1b: Number of Acres per Overburden Analysis Hole (Brady and others, 1994)

n = 38 Coal Acreage Acres per OBA Hole

Mean 43.5 15.5

Median 30.3 11.9

Minimum 5.0 2.3

Maximum 172.5 44.9

Std. Deviation 38.0 10.6

A similar survey of 31 Small Operator Assistance Program (SOAP) applications received in

Pennsylvania during the 1993 calendar year revealed that on average, there was one hole for each

18.8 acres of coal removal (Table 2.1c).

Table 2.1c: Number of Acres per Overburden Analysis Hole Based on SOAP

Applications Received in 1993 (Tarantino and Shaffer, 1998)

n = 31 Coal Acres Acres per OBA Hole

Average 72.6 18.8

Median 55.0 15.7

Minimum 6.0 3.0

Maximum 220.0 53.5

Std. Deviation 54.6 12.3

The above tables give an idea of the range of overburden analysis sampling intensity used in

Pennsylvania. The ranges in the data are due to a multitude of factors including stratigraphic

complexity of the site, shape of the site, and availability of other prediction tools. Approximately

30 to 40 percent of applications in Pennsylvania do not require submittal of overburden analysis

because of the availability of equivalent prediction data. The data included in these tables apply

only to permit applications that included overburden analysis data.
Coal Remining BMP Guidance Manual

2-18 Geochemical Controls

Operational Considerations

The overburden analysis drilling program should accurately represent the overburden that will be

encountered during mining operations. Therefore, the overburden holes should be located within

the limits of the proposed mining area. Some holes should be located at maximum highwall

conditions (maximum overburden cover to be mined), and the holes should represent all of the

strata that will be encountered. Additional holes should be located under both low and average

cover conditions to provide representative sampling of the overburden where stratigraphic units

may be missing or the strata may have been chemically altered due to surface weathering.

Stratigraphic Variation

It is important to provide enough drill holes to adequately represent the site, including any spatial 

lithologic variation. One of the first references to the minimum overburden hole spacing is

contained in the West Virginia Surface Mine Drainage Task Force’s “Suggested Guidelines for

Surface Mining in Potentially Acid-Producing Areas” (1978), which recommended that all surface

mining in potentially acid-producing areas be within approximately 3300 feet of a sampled

overburden analysis hole or highwall. 

Donaldson and Renton (1984) and Donaldson and Eble (1991) indicated that although drill cores 

spaced up to two miles apart in the Pittsburgh coal seam were adequate to reflect major thickness

and sulfur trends for the coal seam, this spacing was not adequate for mine operation design. 

They felt that sampling at intervals on the order of 1200 to 1400 feet for the Pittsburgh coal and

sampling at intervals of less than 500 feet for the Waynesburg coal would be necessary to

determine small-scale sulfur content trends within the coal seams.

Representative Samples

Each OBA bore hole contains sample intervals representing various unit thicknesses of each

lithologic unit encountered. Vertical sample interval thicknesses are typically three feet. The
Coal Remining BMP Guidance Manual

Geochemical Controls 2-19

maximum thickness of each lithologic unit to be represented by one vertical sample interval will be

discussed under “Compositing and Laboratory Preparation.” It is also discussed on pages 29 to 30

of Part 1 “Collection and Preparation of Sample” in the “Overburden Sampling and Testing

Manual” (Noll and others, 1988).

Noll and others (1988) do not, however, discuss the complexity of ensuring that accurate, nonbiased, representative samples are collected. They do stress that it is critical that 100 percent of

the sample volume of each sample interval be included for compositing purposes, because of

possible geochemical variations within the 3-foot interval. The ultimate sample size used in ABA

is 1 gram for total percent sulfur and 2 grams for the neutralization potential (NP) test. Assuming

no loss or contamination of the zone being sampled, only 1 gram to 2 grams are tested out of a

25,550 gram sample (based upon a 4.5 inch diameter drill bit and using an average rock density of

170 lbs/ft3). Fortunately, sample preparation procedures have been developed to obtain

representative, small sample aliquots. These procedures are discussed below in “Preparation of

Samples.”

Extensive literature has been published, and a complete science has been developed to integrate

geology and statistics for spatial sampling and the determination of optimal sampling patterns for

estimating the mean value of spatially distributed geologic variables. Textbooks on the subject

include Journel and Huijbregts (1981), Webster and Burgress (1984), J.C. Davis (1986) and Koch

and Link (1970).

Fortunately, the geologic systems responsible for the deposition and alteration of sediments and

their chemical quality do not operate in a completely random fashion at the cubic centimeter level

and, thus, do not produce overburden samples that are statistically independent. Although there

are exceptions, most stratigraphic systems, especially those which produce calcareous material,

operate over large areas with some degree of order, and deposit laterally pervasive units

(Caruccio and others, 1980). Lateral continuity has also been observed in high-sulfur strata. 

Abrupt lateral changes in stratigraphy can occur such as where channel sandstones cut out and

replace other strata. Surface weathering also causes changes to the percent total sulfur and NP
Coal Remining BMP Guidance Manual

2-20 Geochemical Controls

over short distances. Therefore, it is imperative to know the areal extent of any alkaline or acidic

material, and adequate exploratory drilling is essential for a representative overburden sampling

plan.

Sample collection and handling

Sample Collection

Overburden sampling is accomplished by drilling or direct collection of the sample from an open

surface such as a highwall. Sample methods used to obtain overburden samples include air rotary

(normal circulation), air rotary (reverse circulation), diamond core, augering, and highwall

sampling.

Air rotary (normal circulation) - This type of drill is the method most commonly used for the

collection of overburden samples in Pennsylvania. Drilling in this manner uses air to blow rock

chips (cuttings) to the surface for collection. The most common disadvantage of normal

circulation air rotary drilling is that individual samples of stratum can be contaminated by an

overlying sample zone as the rock chips are blown up the annular space of the drill hole. Rock

chips traveling in this space can dislodge loose particles from an overlying source. Care should be

taken to stop the downward progression of the drill stem after each interval has been sampled and

allow any upper loose particles to blow out prior to continuing downward. 

Contamination of the sample can also occur at the surface from the pile of ejected material that

forms near the drill hole. These piled materials, if not removed during drilling, can slough back

into the open hole and the chip stream. This can be avoided by shoveling the materials away from

the hole during the period when drilling is stopped to blow out the hole. Another option is to add

a short length of casing to the top of the hole after the upper few feet or first sample interval has

been collected. 
Coal Remining BMP Guidance Manual

Geochemical Controls 2-21

Samples are collected by placing a shovel under the chip stream. Care should be taken to clean

the shovel of any accumulated materials from previous usage or sampling. This is particularly

important when sampling wet test holes where the ejected materials consist primarily of mud. 

Before drilling the overburden hole, the dust collector hood should be cleaned to remove any

accumulated materials that may dislodge and contaminate the samples being collected.

Air rotary (reverse circulation) - This type of drill rig is less commonly used for the collection of

overburden samples, primarily because of availability. A reverse circulation rig uses a doublewalled drill stem. Water or air is forced down the outer section of the drill stem and the

cuttings/chips are forced up the inner section of the drill stem. The cuttings and water or air are

brought into a separator and dropped near the rig where the samples can be collected. The

samples are isolated from contact with overlying strata, offering a much cleaner and quicker

means of obtaining overburden samples, without requiring that the drilling be stopped to blow out

the hole. If water is employed in the drilling process, the materials are also washed free of the fine

dust coating that can accumulate on the chips during drilling with air. This allows for much easier

rock type identification and logging.

Diamond core - Diamond core barrels can be used on both types of rotary drilling platforms. 

Coring provides a continuous record of the lithology and provides more information than can be

obtained through the collection of rock chips. Cores can provide a better overall view of the

lithology by providing information necessary to judge rock color, gross mineralogy, grain

size/texture, fossil content, and relative hardness. This type of information is not always readily

available from rock chips. Although a core provides an uncontaminated and better source of

reliable lithologic data, coring is very time consuming and costly, especially if the entire

overburden section is to be sampled. Diamond cores can be used as a secondary means of data

collection to target previously identified problem zones, or as a primary sampling tool in the coal

area (i.e. the interval 5 feet above and below the coal horizon). The entire sample interval from

the core should be collected and processed for analysis to ensure representative sampling, as

opposed to only collecting and analyzing a portion of the sample interval. 
Coal Remining BMP Guidance Manual

2-22 Geochemical Controls

A problem that can occur with coring is “core loss.” The problems of core loss can be reduced by

regulating the drilling speed, (i.e., rotational speed of the bit, and down pressure), diameter and

type of core bit, and amount of water; by minimizing the overbearing weight in the core barrel

through emptying it prior to drilling the coal, and by keeping the equipment in good condition. 

Knowing what drilling adjustments to make can prevent blocking of the core barrel.

Successful coring is dependent primarily upon the experience of the on-site geologist, project

engineer, or driller. Factors that are important include total years of core drilling experience,

experience with the drill being used, and previous drilling experience in the same region, including

exposure to the same rock formations and weathering characteristics. Having as much geologic

data as possible (e.g. approximate depth to the coal, extent of weathering) prior to drilling is also

particularly useful. It is especially useful to have air rotary pilot holes to evaluate the site prior to

the core drilling. These pilot holes allow particularly troublesome formations to be identified and

avoided. Particularly troublesome conditions include highly fractured rocks, joints or

intersections of joints or fractures. 

Mine voids, solution cavities, unconsolidated soil and rocks, and the transition through weathered

rock into competent rock are the zones most subject to core loss. Core recovery on the order of

only 50 to 60 percent or less in these situations is not unusual. When drilling is performed in

unweathered rock core recovery approaching 100 percent is the norm rather than the exception.

When coring into the coal, it is advisable to use a core barrel long enough to core the entire

thickness of the coal. The core barrel should be no more than 20 percent full when the coal is first

encountered. It is preferable to have a nearly empty core barrel containing 6 to 12 inches of

overburden before drilling into the coal. The small amount of overburden aids in determining if

the entire coal section has been sampled (i.e., knowing the starting point of the coal) and helps

protect the coal from being crushed by the “ram” when extracting the coal from the core barrel. 
Coal Remining BMP Guidance Manual

Geochemical Controls 2-23

In addition to actual core sample loss, drilling data can be lost due to improper handling of the

cores. Data loss causes include placing cores in the core boxes in the wrong order or upside

down, or damage caused to the core during handling and shipping.

Augering - Auger drilling is not recommended for general overburden sampling. The materials

lifted by the auger screw are in constant contact with the overlying stratum, thus providing for

intermixing and contamination. Augering is typically used for unconsolidated or highly weathered

sections. 

Highwall sampling - Direct collection of samples from an open source, such as a highwall, can be

used for overburden analysis, provided several caveats are understood. First, samples may be

weathered to such a degree that the strata to be mined is not accurately represented. Second,

there is limited availability and accessibility of highwalls. Care should be taken to collect only

unweathered samples in close proximity to and representative of the proposed mining. It is

recommended that open source (e.g. outcrop, highwall, etc.) samples be used primarily to

supplement drilled overburden samples.

Sample Description (Log)

For each sample or composite of sample intervals collected, an accurate description of the gross

lithology should be determined. This lithologic description should include the rock type (e.g. 

shale, sandstone, etc.), rock color (as determined by comparison with the Munsell Rock Color

Chart), texture/grain size, moisture conditions, and relative degree of weathering. Where

applicable, a description of the gross mineralogy should be included with particular emphasis on

the presence of any calcite (CaCO3), siderite (FeCO3), or pyrite (FeS2). In addition, fossils should

be noted to provide insights into coal seam correlations and depositional environment

interpretations. The sample description should include the relative degree of fizz (effervescence)

when doused with a 10 percent solution of hydrochloric acid (HCl). A field fizz based on a scale

of " none, slight, moderate, or strong" should be used. A dilute (10 percent) HCl solution is

widely used by field geologists to differentiate calcium carbonate (CaCO3) from other carbonate
Coal Remining BMP Guidance Manual

2-24 Geochemical Controls

rocks. Fizz determinations are highly subjective and should be made by the same individual for

every sample on every hole for a particular site. Extreme care should be exercised to be sure that

the displacement of trapped air is not mistaken for CO2 evolution. It is also important to identify

whether the fizz is from the matrix or from the cementing material. It is recommended that

logging of test holes, including sample descriptions, be performed by a qualified geologist.

Sample Preparation and Compositing

Proper sample preparation techniques are essential for maintaining sample integrity. Preparation

is divided into steps that occur in the field and steps that occur in the laboratory. Field

preparation of samples is discussed in Tarantino and Shaffer (1998), Noll and others (1988), and

Sobek and others (1978). Procedures discussed in these publications include the use of proper

containers, labeling, preservation, and field logs. Field sample preparation will not be discussed

further in this section.

Sample compositing and laboratory preparation techniques are just as important to the integrity of

a sample. The purpose of compositing overburden samples is to reduce the cost of overburden

analysis by minimizing the volume and number of samples to be tested, without sacrificing the

accuracy and precision needed to predict post-mining water quality. Sobek and others (1978), in

the first generally accepted “manual” on overburden sampling, recommend that most rock types

should not be combined into composites representing more than 3 feet. They suggest that

sandstone can be composited into 5-ft increments. Experience in some regions, such as

Pennsylvania, has indicated that it is often prudent to sample sandstone at the same resolution as

other rock types (Tarantino and Shaffer, 1998). As with any well-intended cost-saving procedure,

if not done properly, the real long-term costs might far outweigh the small cost saving.

Table 2.1d lists vertical sampling practices of Appalachian coal-producing states. 
Coal Remining BMP Guidance Manual

Geochemical Controls 2-25

Table 2.1d: Overburden Interval Sampling Requirements (Sames and others, in

preparation).

STATE INTERVAL SAMPLING REQUIREMENTS

AL One sample every 5 feet or at a significant lithologic change, whichever comes

first. Sample compositing is not allowed. Regulatory agency reserves the right

to request core drilling in permit areas where there are known acid-forming

lithologic units.

KY Same treatment required for samples from eastern and western region. 

One sample for suspected acid-producing strata and coal seams less than one

foot thick; smaller strata and seams may be grouped with the next lower unit. 

One sample within the lithologic unit for strata one to five feet thick. 

Two samples for strata ranging from five to ten feet thick.

One sample every 5 feet for strata more than ten feet thick.

MD For rotary drill cuttings, one sample every 1 foot or at a significant lithologic

change; for core samples, 3 foot composite samples or at a significant

lithologic change.

PA One sample per 3 vertical feet or at a lithologic change plus 1 foot above and

below the coal bed. Rotary drill samples should be collected in 1-foot

increments that then can be composited up to 3 feet. Core sample composites

also limited to 3-foot increments regardless of the unit thickness; an equal

portion of the entire core length should also be crushed and split for analysis. 

TN One sample every 3 feet or at a significant lithologic change, whichever comes

first.

VA Sobek and others (1978) protocol: 

One sample every 5 feet for sandstone units.

One sample every 3 feet for other lithologies.

WV One sample every 5 feet or at a significant lithologic change, whichever comes

first. Sample compositing is not allowed.

Sobek and others (1978) followed as the official guide. Permit geologists also

refer to NPDES, DMR discharge data, and other historical data from adjacent

operations in the same seam. 

Some sandstones, such as portions with significant coal inclusions, may need to be sampled at a

greater resolution. Till, when from separate glaciations, should be sampled separately. The 

reason for the 1-foot sample intervals above and below the coal (Pennsylvania) is that these are
Coal Remining BMP Guidance Manual

2-26 Geochemical Controls

frequently the highest sulfur strata present. Mixing of these strata with overlying strata can result

in dilution and a falsely low-percent sulfur, or make a thicker zone (e.g., 3 feet) resemble a high

sulfur zone. The coal seam may also require greater sample resolution than the suggested 3-feet if

a portion of the coal will be left in the pit as pit cleanings or unmarketable coal. The coal that

remains behind should be sampled separately.

As can be seen from Table 2.1e, if too many 1 foot intervals are composited or too large a vertical

sampling interval is chosen, a high total sulfur, potentially acid-producing zone can be masked by

dilution with adjacent low sulfur strata. The net effect is an underestimation of the potential for a

site to produce acid mine drainage. Compositing one foot of 2.34 percent sulfur black shale with

an overlying four feet of low-sulfur sandstone results in a 0.48 percent total sulfur for the

composited five-foot zone. If, for example, 0.5 percent sulfur is the “threshold” above which a

unit is considered acid producing and thus targeted for special handling; this dilution effect would

underestimate the acid-producing potential of the black shale and result in the strata not being

specially handled.

Table 2.1e: Compositing of Too Many 1-foot Intervals Can Underestimate Acid

Producing Potential (Tarantino and Schafer, 1998)

Thickness

(feet)

Lithology Total % S Average % S of Interval

1 sandstone 0.01 0.48

1 sandstone 0.01 0.59

1 sandstone 0.01 0.79

1 sandstone 0.01 1.18

1 black shale 2.34
Coal Remining BMP Guidance Manual

Geochemical Controls 2-27

Sobek and others (1978) suggested that for core samples, a 5-inch section of the core could be

extracted from the middle of a 1 foot interval to represent the entire one-foot interval. The best

way to ensure representativeness of an interval is to sample the entire interval. In order to avoid

bias, one of the following two methods is recommended:

1) The entire core interval whether it be a 1, 2, or 3 foot interval, should be entirely crushed

and reduced in size via a riffle or rotating sectorial splitter until a suitable amount of

sample remains for analysis.

2) The entire core length should be bisected longitudinally using a core-splitter or saw. One

half of the core is retained for historical records and possible additional testing. The entire

other half of the core is crushed for the entire sampling interval. After crushing, the

sample is divided and reduced in volume via a riffle or rotating sectorial splitter. 

There are three reasons for splitting and crushing samples: 

1) To reduce the bulk (amount) of a geological sample.

2) To provide an unbiased, statistically representative sample of small quantity, which can be

analyzed to evaluate percent sulfur and NP for acid base accounting. 

3) To reduce samples to a small size fraction that maximizes surface area and minimizes the

analytical time.
Coal Remining BMP Guidance Manual

2-28 Geochemical Controls
Coal Remining BMP Guidance Manual

Geochemical Controls 2-29

2.2 Alkaline Addition

It is widely recognized that mine sites with an abundance of naturally-occurring limestone or

alkaline strata produce alkaline water, even in the presence of high sulfur. However, many sites

contain little or no alkaline material and, as a consequence, often produce acidic drainage even

when sulfur contents are relatively low. One approach to improving alkaline deficient sites is to

import alkaline material to amend the spoil in order to obtain alkaline drainage.

Before implementing an alkaline addition BMP, the following factors should be considered: How

much material should be added and how and where should it be applied to the backfill? When is

additional alkaline material needed? What are the prospects of obtaining alkaline drainage for a

given application rate and how much risk of acidic drainage is acceptable? Ultimately, whether or

not alkaline addition is a feasible alternative is driven by the economics of the operation. 

Therefore, it is important that an alkaline addition project be carefully evaluated and designed

before it is implemented. This section reviews theoretical and practical aspects of alkaline

addition and summarizes the current state-of-the-art in the use of alkaline addition to prevent acid

mine drainage.

Theory

AMD is formed when pyrite and other iron disulfide minerals present in coal and overburden are

exposed to oxygen and water by mining. The oxidation of pyrite releases dissolved iron,

hydrogen ions (acidity), and sulfate (Equation 1). Although this process occurs very slowly in

undisturbed natural conditions, it can be greatly accelerated by both surface and underground

mining.

Pyrite oxidation is further accelerated by the iron-oxidizing bacterium Thiobacillus ferrooxidans,

which thrives in a low-pH environment and oxidizes ferrous iron to ferric iron (Kleinmann and

others, 1980). Under low pH conditions, ferric iron remains in solution and can directly oxidize
Coal Remining BMP Guidance Manual

2-30 Geochemical Controls

pyrite. Thus, once AMD formation gets started, the reaction is further accelerated by bacteria and

the production of ferric iron. The result can be severe acid mine drainage.

Acidity produced by acid mine drainage can be neutralized in the presence of sufficient carbonate

minerals. This reaction is shown by Equation 6, for which it is assumed that CO2 will be

produced and will exsolve from solution. Using this equation, it takes 31.25 tons of CaCO3 to

neutralize 1000 tons of material with 1 percent sulfur. This is the traditional method used for

acid-base accounting calculations. The main shortcoming of this equation is that there is no

"alkalinity" (bicarbonate or HCO3

-

) produced. Under normal conditions, not all CO2 escapes to

the atmosphere. Some CO2 dissolves in water producing acidity. If the reaction product is 

HCO3

-

 alkalinity (Equation 5), twice as much carbonate will be required to neutralize the same

amount of material (Cravotta and others, 1990). Whether it is the process in Equation 5 or

Equation 6 that is dominant depends on the extent of how open or closed the mine is to the

atmosphere.

Where neutralization occurs, the pH can remain near-neutral, inhibiting bacterial catalysis of iron

oxidation and keeping ferric iron relatively insoluble. Thus, the quality of drainage produced by 

a given mine is largely dependent not only on the presence or absence of pyritic sulfur, but also 

on the availability of calcium carbonate or other neutralizing agents in the coal and overburden.

Brady and others (1994) and diPretoro and Rauch (1988) found a strong relationship between

the neutralization potential of surface coal mine overburden and the alkalinity or neutrality of

post-mining drainage. Sites with more than 3 percent naturally occurring carbonates produced

alkaline drainage. Sites with less than 1 percent carbonate generally produced acidic drainage. 

Perry and Brady (1995) attribute this effect not only to neutralization but also to near-neutral

conditions limiting bacterial catalysis of ferrous iron oxidation and oxidation of pyrite by ferric

iron. 

NP was found to be a much better predictor of whether a mine would produce alkaline or acidic

water than was the maximum potential acidity, calculated from the overburden sulfur content,
Coal Remining BMP Guidance Manual

Geochemical Controls 2-31

thus demonstrating the importance of carbonates on mine drainage quality (diPretoro, 1986;

Brady and Hornberger, 1990; Brady and others, 1994; Perry and Brady 1995). For mines which

are naturally deficient in carbonates, and therefore likely producers of acidic drainage, the

implication is obvious. If sufficient alkaline material is imported from off-site to make up the

deficiency in NP, the site will produce alkaline rather than acidic drainage.

The solubility of calcium carbonate also plays an important role in whether a site can generate

sufficient neutralization to prevent acidic drainage. Calcite (CaCO3) solubility is dependent on the

partial pressure of CO2 (Figure 2.2a). At atmospheric conditions, the solubility of calcite is

limited to approximately 20 mg/L Ca (50 mg/L as CaCO3 or 61 mg/L as HCO3

-

 alkalinity)

assuming a CO2 content of the pore gases of only 0.03 percent. At 20 percent CO2 content,

which has been measured in some backfill environments (Cravotta and others, 1994a), calcite

solubility exceeds 200 mg/L Ca (500 mg/L as CaCO3 or 610 mg/L as HCO3

-

 alkalinity). Guo and

Cravotta (1996) note that CO2 partial pressures vary from mine site to mine site depending on

rock type and backfill configuration. Shallow backfills on steep slopes with blocky overburden

and thin soil cover, for example, tend to "breathe," thereby reducing CO2 partial pressures (Pco2). 

Deeply buried backfills or sites with restricted airflow or thick soil covers would tend to have

higher CO2 levels, enhancing calcite dissolution. At these sites, Pco2 tends to increase with depth. 

The Pco2 has implications for the placement of alkaline materials within the backfill. Near-surface

placement of alkaline material, where CO2 partial pressures approach atmospheric conditions, may

not be as desirable as distribution deeper within the backfill.

In theory, almost any acid-prone site could be transformed into an alkaline site, if enough

carbonate material is imported. For this to be achieved, however, it is necessary to determine: (1)

how much alkaline material should be applied to ensure a successful result; and (2) the optimum

place within the backfill where the alkaline material should be applied.
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2-32 Geochemical Controls

Figure 2.2a: Solubility of Calcium Carbonate (Calcite) in Water at 25OC as a Function of

Partial Pressure of CO2 (Hem, 1985)
Coal Remining BMP Guidance Manual

Geochemical Controls 2-33

2.2.1 Implementation Guidelines

Fifteen years of research has shown that alkaline addition can improve water quality and prevent

AMD production, but that failures are common, especially where alkaline addition rates are too

low. Based on these studies, any alkaline addition project should consider: 

C how much and what type of alkaline material should be applied, 

C how should the alkaline material should be emplaced in the backfill, and 

C when is alkaline addition appropriate? 

Seventeen of sixty-one mining site data packages submitted by Appalachian coal mining states

(Appendix A, EPA Remining Database, 1999) had alkaline addition listed as a BMP. Alkaline

addition, like any other BMP, is seldom used alone. Table 2.2.1a lists additional significant BMPs

that were used in conjunction with alkaline addition at these sites. In a Pennsylvania study of

closed remining sites (Appendix B, PA Remining Site Study), alkaline addition was always used in

conjunction with some other BMP. Other BMPs included daylighting of deep mines, special

handling of acidic materials, surface regrading, ground-water handling, and surface revegetation.
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2-34 Geochemical Controls

Table 2.2.1a: Distribution, Type and Amount of Alkaline Materials Used (Appendix A,

EPA Remining Database, 1999)

Mine,

Type

Placement Type of Alkaline

Material

Other Major BMPs

PA(1) S 30 tons/acre applied to pit floor Crushed limestone

(>95% CaCO3)

Daylighting

PA(2) R* Alternate refuse & coal ash. 1,650,000

tons of reject refuse, 1,350,000 tons ash

Power plant coal

ash. 5.8% CaCO3

Removal of Acid-Forming

materials, Revegetation

PA(7) S10ft thick layer in backfill. Compacted/set

as cement. Above post-mining water table

Coal ash Daylighting, Regrading

Revegetation, Special

Handling

PA(8) S* 360 tons/acre applied to pit floor. 240

tons/acre in blast holes; dispersed

throughout spoil

Limestone

Screenings

Daylighting

Special Handling

PA(10) S Ripping of calcareous pit floor material Pit floor rock is 15

to 20% CaCO3

Bactericide, Special Handling

Regrading

PA(11) S* 50 tons/acre applied to pit floor Agricultural Lime Regrading, Revegetation

PA(12) S* Within spoil. Compacted to 90%

maximum dry density

Coal Ash Daylighting, Regrading,

Revegetation

PA(14) A* In abandoned strip pit. 5 million yds3

compacted to min. 90% dry density

Coal Ash Revegetation

PA(18) A* Coal Ash, pH 11 Daylighting, Regrading,

Revegetation

PA(19) S* 100 tons/acre applied to surface and pit

floor. Approx. 800 tons/acre in spoil

Lime processing 

flue dust

Regrading

Revegetation

TN(3) S Limestone

TN(4) S* “Spoil side” of dragline bench Limestone Special Handling, 

Chimney Drains, Regrading, 

Backfill Innundation

WV(3) S* 2 ft lifts through overburden Coal Ash

WV(5) S* 2 ft applied to surface. Mixed through

overburden

Coal Ash Anoxic Limestone Drains

WV(6) S* 12 to 18 inches applied to pit floor.

2 ft applied to surface

Coal Ash, 

pH 10.5 to 12

WV(8) S* Min. 1 ft thick, 30 ft wide channel Regrading

AL(10) S20 tons/acre applied to pit floor Regrading

* Mine is still active S Surface

A

 Anthracite R Refuse Reprocessing
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Geochemical Controls 2-35

Alkaline Materials

A variety of alkaline materials are available as alkaline additives. Traditionally alkaline addition

projects use crushed limestone or limestone-based waste products. Limestone-based waste

products include crusher waste, kiln dust, partially burnt lime and "off-spec" lime products. More

recently alkaline waste products from other sources have been considered. Chief among these is

fluidized-bed combustion fly ash and bottom ash. An examination of Table 2.2.1b shows the

range of products being used and the current trend in using coal combustion ash.

Table 2.2.1b: Example Analyses of Coal Ash. (Units are percentages) (Scheetz and others,

1997)

Oxide Coal Ash with

< 10% CaO a

Coal Ash with 

> 20% CaO b

High BTU

Coal c

Anthracite

Culm c

Bituminous

Refuse c

SiO2 52.5 ± 9.6 36.9 ± 4.7 24 58 34

Al2O3 22.8 ± 5.4 17.6 ± 2.7 6.05 20.4 2.15

Fe2O3 7.5 ± 4.3 6.2 ± 1.1 2.05 5.74 5.98

CaO 4.9 ± 2.9 25.2 ± 2.8 42 4.11 30

MgO 1.3 ± 0.7 5.1 ± 1.0 0.045 0.62 0.62

Na2O 1.0 ± 1.0 1.7 ± 1.2 0.07 0.59 0.11

K2O 1.3 ± 0.8 0.6 ± 0.6 0.51 2.56 1.49

SO3 0.6 ± 0.5 2.9 ± 1.8 20.8 1.1 13.0

Moisture 0.11± 0.14 0.06 ± 0.06 + 0.25 + 0.49 3.70

LOI 2.6 ± 2.4 0.33 ± 0.35 2.03 3.31 10.0

aCharacteristics of eastern bituminous and anthracite coal

bCharacteristics of western lignitic and sub-bituminous coals

cAsh resulting from burning coal, culm and refuse with limestone

LOI = Loss on ignition
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2-36 Geochemical Controls

Limestone and Limestone-Based Products

The chemical principles of neutralization by limestone are presented above in the section "Theory

of Alkaline Addition" and the neutralization reactions are shown in Equations 5 and 6. 

Limestone, which is composed mainly of the mineral calcite (CaCO3), occurs naturally on many

mine sites. An advantage of limestone is that it dissolves more slowly than quick lime or hydrated

lime, thus lasting longer. A disadvantage is that its solubility is limited, such that alkalinity higher

than ~400 mg/L as CaCO3 is rarely achieved. At atmospheric pressures of CO2, calcite will

produce an alkalinity of <100 mg/L CaCO3 (Hornberger and Brady, 1998). Another mineral that

has neutralizing properties and occurs naturally in coal overburden is dolomite [CaMg(CO3)2]. 

Neutralization by dolomite is similar to that shown in Equations 5 and 6, but the reaction rate in

slower than limestone.

"Quick lime" (calcium oxide, CaO) and "hydrated lime" [calcium hydroxide, Ca(OH)2] are

produced by heating limestone and driving off CO2. These are more soluble than calcite and can

produce a pH as high as 11 or 12. The advantage of quick lime or hydrated lime is its high

solubility and ability to generate high pH. The disadvantage is that because of its high solubility it

may be consumed quickly. The neutralization processes are represented by Equations 6 and 7

(Cravotta and others, 1990).

Ca(OH)2 + 2 H+ 6 Ca2+ + 2H2O (Equation 9)

CaO + 2 H+ 6 Ca2+ + H2O (Equation 10)

The neutralization of acid generated from pyrite oxidation by hydrated lime is represented by

Equation 11 (Cravotta and others, 1990):

FeS2 + 2 Ca(OH)2 + 3.75 O2 6 Fe(OH)3 + 2 SO4

2- + 2 Ca2+ + 0.5 H2O (Equation 11)

The purity of limestone or other alkaline additives is an important factor. Many rocks with the

potential to generate alkaline water are not limestones, but calcareous shales or other rock. If a
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Geochemical Controls 2-37

rock that is not nearly pure calcite is used, alkaline addition rates should be adjusted to

compensate for the lack of purity. For example, if the material that is proposed for alkaline

addition has a NP of 500 tons CaCO3/1000 tons of material (50 percent purity), twice as much

material would be required to provide the necessary amount of CaCO3. Regardless of the alkaline

material to be used, the application rate should be adjusted to reflect the material's neutralization

potential as calcium carbonate equivalent. 

Coal Ash

Coal ash has been used in a variety of ways for abatement of mine drainage pollution, including

the following:

C injection into underground mines with the intention of abating acid mine drainage by sealing

(Aljoe, 1999; Canty and Everett, 1999; and Rafalko and Petzrick, 1999), 

C as an additive to help create a suitable soil substitute out of acidic spoil (Stehouwer and

others, 1999),

C as an impermeable cap for reduction of infiltration into acidic surface mine spoil (Hellier,

1998). Ash has been mixed with reprocessed coal refuse for AMD abatement (Foster Wheeler

Corp., 1998; Panther Creek Energy Facility, n.d.),

C as a grout to isolate acidic material in surface mine spoil (Schueck and others, 1994), 

C as fill material for abandoned surface mines and anthracite region "crop falls" (Scheetz and

others, 1997), and 

C as an alkaline additive to neutralize acidic mine spoil. 

The use of coal ash as an alkaline additive will be discussed in this section. The use of ash for

low-permeability caps and seals is discussed in Section 1.1 and its use for grout curtains is

discussed in Section 1.2.

The popularity of using coal ash as an alkaline additive is demonstrated by the fact that it is being

practiced by eight of the 17 mines listed in Table 2.2.1a. The alkalinity generating properties of

coal ash vary depending on the type of power plant producing the ash. Most alkaline ashes are
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2-38 Geochemical Controls

generated by fluidized bed combustion (FBC) power plants. These plants burn high-sulfur coal or

coal reject material as fuel. Limestone is used to absorb the sulfur. The limestone calcines

leaving calcium oxide. According to Skousen and others (1997), about one-half of the CaO

reacts with sulfur dioxide to form gypsum and the rest remains unreacted. The ash can be 10 to

20 percent calcium carbonate equivalent. The amount of limestone used can be substantial. For

example, the Colver, Pennsylvania, power plant burns 600,000 tons of "gob" (coal refuse)

annually, requiring 120,000 tons of limestone to remove the sulfur (Foster Wheeler Corp., 1998).

Table 2.2.1b shows the neutralizing properties of various coal ashes. As can be seen, not all coal

ash is alkaline. In fact, some ash has to have alkaline material added for proper disposal. 

A problem that exists with using coal ash as an alkaline additive is that it can exhibit 

cementitious behavior. The cementitious behavior is activated by alkali materials. The making 

of cement from ash (volcanic ash) dates back to the time of the Romans. Many of these

structures are still standing today (Scheetz and others, 1993) which is testimony to its durability. 

Cementitious behavior is an advantage if one is proposing ash as a grout or an impermeable cap. 

Scheetz and others (1993) list the following "advantages" for the use of coal ash for cementitious

material:

C low cost of raw materials

C grouts can be formulated to gain strength rapidly

C grouts have low heats of hydration

C grouts are less soluble than portland cement-based materials

C grouts can be less permeable than portland cement-based materials

C grouts can be activated with alkali chlorides and sulfates.

Many of these same properties that are advantageous for impermeable grouts and caps are a

disadvantage for its use as an alkaline additive. For example, low solubility and low 

permeability are not properties that are desirable for an alkaline additive. Pulverized coal

combustion fly ash exhibits a pozzolonic reactivity "that is directly correlated to the calcium
Coal Remining BMP Guidance Manual

Geochemical Controls 2-39

content of the ash" (Scheetz and others, 1997). In other words, the lime portion of the ash is an

activator that can make the ash into cement.

Coal combustion ash, if it is to be used as an alkaline additive, should be evaluated for its calcium

carbonate equivalency and its cementitious properties. It should be spread and mixed with spoil

so as to maximize its surface area. If not adequately mixed, the ash may set up as large blocks of

cement with minimal surface area for reactivity, thus resulting in an ineffective alkaline additive.

Coal ash, even with pozzolanic properties, has potential as an effective "seal" on acidic pit floors. 

This application would also provide an alkaline substrate for spoil waters. 

Other Alkaline Additives

Information on other alkaline sources is scarce. Skousen and others (1997) briefly discusses the

use of steel slags and states that these slags often have NPs from 45 to 90 percent, but warns that

slags "are produced by a number of processes so care is needed to ensure candidate slags will not

leach metal ions such as Cr, Mn, Ni, or Pb." Phosphate rock has been proposed for use as an

alkaline additive, but no full-scale field projects have been commenced and the cost is high

(Skousen and others, 1997). Phosphate rock can contain significant quantities of calcium

carbonate. Thus it may be difficult to determine the relative effectiveness of the phosphate

relative to the carbonate. Other alkaline additives or alkaline-producing additives mentioned by

Skousen and others (1997) are AMD sludge and organic wastes. AMD sludge is the waste

product from mine drainage treatment. Lime-treated flocs can contain up to 50 percent 

unreacted lime. Field results are limited. Organic waste is different from the other alkaline

generating processes in that it does not directly impart alkalinity. Several species of bacteria can

obtain metabolic energy by reacting sulfate with simple organic compounds. In the process

sulfate is reduced and bicarbonate is created (i.e., alkalinity). Stalker, Rose and Michaud (1996)

performed laboratory studies on a variety of organic materials. The rates of sulfate reduction for
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2-40 Geochemical Controls

cellulose materials (sawdust, pulped newspaper & mushroom compost) were slow, but for milk

products (cheese whey and lactate) the rates were more rapid. 

Application Rates

Published studies on alkaline addition primarily examine mines in the northern Appalachian. The

transferability of this research to the southern Appalachians is not fully known. The overburden in

the southern Appalachians is typically lower in sulfur than overburden in the northern

Appalachians. Field studies of alkaline addition in the northern Appalachians appear to be

converging on required application rates. The amount needed to produce alkaline drainage is

approximately 1.5 to 3 percent CaCO3 equivalent for sites with low to moderate pyrite content. 

This application rate appears deceptively low. One percent CaCO3 equates to approximately 37

tons of CaCO3 for each acre-foot of overburden. A 100-acre surface mine with an average

overburden thickness of 50 feet needing 1 percent additional CaCO3 would require 183,500 tons

of added alkaline material or 1,835 tons/acre. Thus, the feasibility of an alkaline addition project

usually becomes a matter of economics as well as science. The challenge is to determine the

minimum alkaline addition rate which will still be effective in preventing acidic drainage.

Using data from Brady and others (1994) and Perry and Brady (1995), Tables 2.2.1c - 2.2.1f

show overall NP and NNP requirements in order to produce alkaline drainage using acid-base

accounting data. In all cases, NP and NNP calculations are made using the method described by

Smith and Brady (1990). Total weights of overburden, NP, and MPA are determined for each

drill hole interval, based on an approximation of the areal extent of that interval and unit weights

for overburden materials. The total weights of the coal intervals are multiplied by a pit loss 

factor of 0.1, assuming approximately 10 percent of the coal will be lost in the pit and not

removed. A higher or lower pit loss factor can be used if warranted by site-specific conditions. 

The uppermost 0.5 feet of strata underlying the bottom coal seam is also included in the

calculation. These quantities are summed to determine the total tonnage of overburden, NP,

MPA and to represent the overall NP, MPA and NNP in parts per thousand as CaCO3 for the site. 
Coal Remining BMP Guidance Manual

Geochemical Controls 2-41

Multiple overburden holes are combined by considering an area of influence of each hole using the

Theissen polygon method (Smith and Brady, 1990).

Table 2.2.1c: Percentage of Sites Producing Net Alkaline Drainage by Net NP without

Thresholds

Net NP (ppt CaCO3) Number of Sites (n) % with Net Alkaline Drainage

< -10 1 0.0

-10 to 0 11 18.2

0 to 12 17 58.8

>12 10 100.0

Table 2.2.1d: Percentage of Sites Producing Net Alkaline Drainage by Total NP without

Thresholds

Total NP (ppt CaCO3) Number of Sites (n) % with Net Alkaline Drainage

<5 3 0.0

5 to 10 9 33.3

10 to 18 10 50.0

18 to 22 7 71.4

>22 10 100.0

Table 2.2.1e: Percentage of Sites Producing Net Alkaline Drainage by Net NP with

Thresholds

Net NP (ppt CaCO3) Number of Sites (n) % with Net Alkaline Drainage

< -2 14 28.6

-2 to 6 14 57.1

>6 11 100.0
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2-42 Geochemical Controls

Table 2.2.1f: Percentage of Sites Producing Net Alkaline Drainage by Total NP with

Thresholds

Total NP (ppt CaCO3) Number of Sites (n) % with Net Alkaline Drainage

<2 12 16.7

2 to 9 12 50.0

>9 15 100.0

When all acid base accounting data are considered (i.e., there are no significance thresholds), an

overall NNP greater than 12 ppt CaCO3 or a NP greater than 22 ppt CaCO3 is very likely to

assure alkaline drainage. Based on these data, a conservative approach to determining alkaline

addition rates would require application of alkaline material at a rate equal to the difference

between an overall NNP of 12 ppt CaCO3 or a NP of 22 ppt CaCO3 and the actual premining

overall NP or NNP. A site having a NNP of 2 ppt CaCO3, for example, would require the

application of an additional 1 percent CaCO3 (10 ppt). An example calculation is shown below:

Tons of overburden: 1,000,000 tons

Acres of mining: 20 acres 

Average Net NP: 2 ppt CaCO3

Deficiency: (12 - 2) ppt CaCO3

 = 10 ppt CaCO3 = 1%

Tons additional NP required for Net NP of 12: 1% X 1,000,000 tons overburden = 10,000 tons

Tons per acre required: 10,000 tons / 20 acres = 500 ton/acre

Adjusted for alkaline material with 80% CaCO3 equivalent: 500 tons/acre / 80% = 625 ton/acre

Similarly, where significance thresholds are used to analyze ABA data, a "safe" alkaline addition

rate would bring the overall NP value above 9 ppt CaCO3 or the NNP above 6 ppt CaCO3. 

Traditionally, the Commonwealth of Pennsylvania has required most alkaline addition sites to

produce an overall NNP of 0 ppt CaCO3 with thresholds. The success rate for sites with this

application rate is risky at best with only 59 percent of sites in this class producing alkaline
Coal Remining BMP Guidance Manual

Geochemical Controls 2-43

drainage (Smith and Brady, 1990). To a great extent, the selection of the appropriate alkaline

addition rate is determined by the risk of failure that can be tolerated, as well as by the availability

and cost of alkaline additives.

As more data are compiled, the ability to accurately determine minimum alkaline addition rates

needed to obtain alkaline drainage should improve. Also, based on the limited experience to date,

most alkaline addition projects using more than 500 tons/acre as CaCO3 have been successful. 

Except for sites with very low sulfur, alkaline addition rates less than 500 tons/acre have

consistently failed to produce alkaline drainage. This is based on a small population of alkaline

addition sites (~5), none of which contained the worst possible overburden. It would be

premature to conclude that alkaline addition of more than 500 ton/acre will ensure success on all

sites or that lower addition rates guarantee failure.

Materials Handling and Placement

Most successful alkaline addition sites have employed thorough mixing of alkaline material

throughout the backfill. This can be done using various methods. One innovative and effective

approach is to use the alkaline material as blast hole stemming (Smith and Dodge, 1995). 

Depending on the material being used and how well it packs, it may also result in more effectively

directing the blast energy at breaking overburden. Alternately, alkaline material can be placed on

the surface of the overburden where it will be subsequently redistributed following excavation and

placement.

Another method of alkaline addition is to place the material on the surface of regraded spoil and

disk it into the upper portion of the spoil. This approach usually is used either in combination

with mixing in the backfill or as a remedial measure after the site has already been backfilled. 

Although it was originally thought that this method would take advantage of the added alkalinity

in the most active zone of AMD production and create an alkaline environment, inhibiting AMD

formation, most projects employing only surface application have not been successful. There are

at least three possible explanations: (1) Dissolution of CaCO3 and the production of alkalinity at
Coal Remining BMP Guidance Manual

2-44 Geochemical Controls

near surface conditions is limited by the partial pressure of CO2. Typically, the maximum

alkalinity which can be achieved under thin soil cover is approximately 75 to 150 mg/L, (Rose and

Cravotta, 1998). This greatly limits the effectiveness of near-surface alkaline material and usually

does not produce enough alkalinity to neutralize acidity generated elsewhere in the backfill; (2)

Mine spoils do not transmit water as a uniform wetting front (Caruccio and Geidel, 1989). 

Rather, surface waters tend to preferentially infiltrate the spoils at the most conductive areas,

effectively bypassing much of the near-surface alkaline material; and (3) Contact of limestone with

acid-producing materials is very limited in the surface environment.

The earliest alkaline addition projects involved spreading all of the alkaline material on the pit

floor, prior to backfilling. The assumption was that this portion of backfill was the most likely to

be saturated, allowing the alkaline material to neutralize all of the acidity produced. These sites

tended to produce alkaline drainage initially, which soon changed to acidic drainage. This is

presumably because the pit floor environment was not anoxic and the alkaline material became

ineffective due to armoring with ferric hydroxide precipitate. Alkaline addition to the pit floor still

has utility, however, when there is a need to neutralize a high-sulfur pit floor. If the pit floor is

saturated, and iron remains ferrous, calcite on the pit floor should function as an anoxic drain

neutralizing acidity. Putting most of the material on the pit floor fails to take advantage of the

inhibitory effect of maintaining a near-neutral pH within the spoil environment. There probably is

little utility in application rates of more than 100 tons/acre to the pit floor, although at least 20

tons/acre should be applied to provide complete coverage. Again, the key appears to be getting

the alkaline material mixed throughout the spoil, especially throughout the more pyritic material.

 

Alkaline addition is frequently implemented in conjunction with special handling of high-sulfur

zones, where high sulfur material is placed in pods and isolated from percolating ground water. 

Alkaline material can be mixed with the high-sulfur material to prevent AMD formation within the

pod and can be placed in conjunction with a cap to enhance hydraulic isolation and to help

maintain an alkaline environment near the pod. Observations at the Kauffman project suggest that

lime kiln dust may actually cement the material, inhibiting ground-water flow (Rose and others,

1995).
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Geochemical Controls 2-45

The use of alkaline addition as part of special materials handling has not yet been fully 

evaluated although some demonstration projects are underway. Recommended procedures for

handling imported alkaline materials have undergone continuous modification as more is learned

about AMD prevention and the interaction between acid-forming materials and neutralizing

agents. Currently, the recommended procedure is to first ensure that enough alkaline material

 is thoroughly mixed within the backfill. In addition, smaller amounts of imported alkaline

material should be applied to the surface of the regraded backfill. Applications to the pit floor

should be limited to conditions requiring isolation or neutralization of a high-sulfur pavement, 

and to no more than is needed to provide sufficient coverage. Unless the remaining spoil is 

clearly alkaline, sufficient alkaline material also should be retained for distribution throughout the

backfill.

Alkaline Redistribution

A practice similar to alkaline addition is the redistribution of alkaline materials to alkaline-deficient

areas from areas of the same or adjacent mine sites which have more than ample alkaline strata. 

This procedure is practical where sufficient quantities of alkaline material are present, but

distribution is so uneven that some portions of the backfill do not contain enough neutralizers to

prevent or neutralize AMD. Alkaline redistribution then becomes largely an exercise in materials

handling. Alkaline stratigraphic units should be clearly identified, segregated, transported to the

alkaline-deficient area, and incorporated into the backfill. Depending on the quantity and

characteristics of the alkaline material available, it may also be necessary to crush the material

prior to redistribution. The obvious advantage to redistribution, if it can be done, is the ready

availability of the material and the low or zero cost of transportation.

Michaud (1995) developed a mining plan for a proposed surface mine where alkaline

redistribution was fully integrated into the operation, minimizing the need for stockpiling and

rehandling of alkaline overburden. Through the implementation of a complex series of selective

sequencing of cuts and multiple benches, the handling plan provided for redistribution of 

alkaline strata, which existed only in limited areas and stratigraphic intervals throughout the site. 
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2-46 Geochemical Controls

Through this approach, thorough mixing of alkaline material could be achieved while avoiding the

need to identify, segregate, and redistribute specific geologic units, usually the most difficult part

of a spoil redistribution plan.

Alkaline redistribution has been successfully employed on several surface mining sites that are

currently producing alkaline drainage. The Bridgeview "Morrison" site in Township, Fayette

County, PA, had abundant calcareous rock over most of the site with NPs as high as 700 ppt

CaCO3, but more typically in the 100 to 300 ppt CaCO3 range. The site included two areas of

about 5 acres each, containing shallow overburden and lacking calcareous rock due to erosion and

weathering. Alkaline material from the high cover area was transported to these low cover areas. 

The resulting post-mining water quality from the areas was alkaline.

The Amerikohl "Schott" site in Westmoreland County, Pennsylvania, had calcareous rock on only

about 8 acres of the 38 acre site. Originally four acid-base accounting holes were drilled. These

were supplemented by additional holes drilled to determine the lateral distribution of the

calcareous rock. The calcareous rock was removed during mining operations and incorporated

into the spoil on all portions of the mine. Waste limestone was also placed on the pit floor at the

rate of 100 tons/acre. Four years of post-mining water quality monitoring data shows the water

to be net alkaline with alkalinity ranging from 10 ppt to 138 ppt CaCO3.

Alkaline Addition as a Best Management Practice on Shallow Overburden

In many cases, relatively low (less than 300 ton/acre) alkaline addition rates have been employed

on mine sites that indicated a relatively minor potential to produce acid mine drainage, but were

lacking in significant calcareous strata. Although these sites commonly have low sulfur contents,

they frequently produce mildly acidic drainage due the lack of any significant NP. In other cases,

alkaline addition was used as an added safety factor to assure alkaline drainage. Alkaline addition

has proven to be an effective "best management practice" for these types of sites.
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Geochemical Controls 2-47

Often, mine sites with shallow (less than 40 feet) overburden have had calcareous minerals and

pyrite leached out by weathering (Brady and others, 1988). Since easily weatherable minerals

have been removed, water flowing through the overburden material picks up very little dissolved

solids and emerges essentially with the characteristics of rain water. In Pennsylvania, 

precipitation typically has a pH less than 6.0. Thus, post-mining water from weathered

overburden may also have a pH of 6.0 or less. The addition of alkaline material is needed to

ensure alkaline post-mining drainage. An example of this implementation is described in Case

Study 1, Section 2.2.3. 

2.2.2 Verification of Success or Failure

A critical step in successful alkaline addition is to ensure that the alkaline addition plan is properly

implemented. Both the amount of material to be applied and its distribution throughout the site

should be appropriate. Because of the large quantities of materials involved, careful record

keeping of each shipment of alkaline material and calculation of the quantities of material

distributed is required. Depending on the method of mining, quantities of alkaline material to be

applied or distributed should be tabulated for each individual cut or phase of the operation.

It is necessary also to periodically retest the neutralization potential of the alkaline material being

used, with a frequency determined by the variability of the material. 

Inspections by the regulatory agency of sites with alkaline addition as a BMP should be frequent

and detailed enough to document compliance with the mining plan. An inspection checklist

identifying key aspects of the plan will be useful in many cases.

Implementation Checklist

Recommended items to be considered during the permit review process include:

C Site-specific overburden data should be available for determination of the amount of alkaline

material.
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2-48 Geochemical Controls

C The site-specific overburden data should be representative of the mine overburden. This will

typically require multiple holes and appropriate vertical sampling.

C Plans should be clearly designed with appropriate maps, cross-sections and narrative.

C The plan should be feasible in the field, not just on paper.

C The plan should be enforceable.

Recommended items to consider in an alkaline addition implementation inspection checklist

include:

C Does what is being done in the field correspond with the plan that is specified in the permit

plans, as shown on maps, cross-sections, and in the narrative? 

C Is the appropriate equipment available? 

C Is the alkaline material being placed where specified? 

C Is the alkaline material being brought to the site the material that was specified in the

permit plan?

C Are weigh slips or other records available to verify the amount of materials being

imported? Are they up to date? Do these records match what can be observed on the site,

in terms of material stored and applied?

C Is water-monitoring data being submitted?

2.2.3 Literature Review and Case Studies

There has been an extensive body of literature published on alkaline addition. This literature is

discussed below along with selected case studies. An early published report regarding the use of

imported alkaline material as a method of preventing the formation of acidic drainage was in the

West Virginia Surface Mine Drainage Task Force’s Suggested Guidelines for Method of

Operation in Surface Mining of Areas With Potentially Acid-Producing Materials (1979). The

Guidelines recommend that alkaline material be added to the backfill at the rate of one third of any

net deficiency in neutralization potential as determined by acid-base accounting. However, it is

uncertain as to why this rate was selected. Many sites with alkaline application rates based on this

recommendation have subsequently failed and are producing acidic drainage.
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Geochemical Controls 2-49

Waddell and others (1986) used alkaline addition to abate acidic drainage resulting from the

construction of Interstate 80 in north central Pennsylvania. The Waddell study involved surface

application of limestone crusher waste and lime flue dust at the rate of 267 tons/acre. It improved

pH values from 3.9 to 4.4. Sulfate concentrations were also reduced, indicating that the alkaline

addition not only neutralized AMD, but slowed its production.

Geidel and Caruccio (1984) examined the selective placement of high-sulfur material in

combination with the application of limestone to a pit floor at the rate of 39 tons/acre. Although

the treated site initially produced alkaline drainage, the drainage soon became acidic. An

untreated control site produced acidic drainage throughout the same period.

Attempting to abate acidic drainage from a Clarion County, Pennsylvania mine site, Lusardi and

Erickson (1985) applied high-calcium crushed limestone at the rate of 120 tons/acre. Although

NNP deficiencies at the site ranged from 25 to 590 tons/acre, they assumed that most acid

production occurred near the surface and that it was necessary to add only enough limestone to

balance the NP deficiency in the upper two meters of spoil. The limestone was disced into the

upper 1.0 feet of the spoil surface. One year after application, no substantial neutralization or

inhibition of acid formation was noted.

O’Hagan and Caruccio (1986) used leaching columns to examine the effect of varying rates of

limestone application on alkaline and non-alkaline shales. A sulfur-bearing (1.07 percent)

noncalcareous shale produced acidic drainage when no limestone was added, mixed neutral/

slightly acidic drainage when 1 to 2 percent limestone was added, and alkaline drainage when 3

percent or greater limestone was added. Following longer periods of leaching, the shale with 1 to

2 percent limestone produced consistently acidic drainage. The alkaline shale produced alkaline

drainage regardless of whether or not any limestone was added.

By 1990, there were enough well-documented surface mining operations that had employed

alkaline addition to allow an extensive review of the effectiveness of alkaline addition in

preventing or ameliorating acid mine drainage. Brady and others (1990) examined 10
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2-50 Geochemical Controls

Pennsylvania mine sites. Of these 10 sites, 8 employed alkaline addition as a means of preventing

postmining AMD. Six of the eight alkaline-addition plans failed to prevent AMD. The sites

which were successful in preventing or at least ameliorating AMD had several things in common:

(1) alkaline addition rates were among the highest (500 to 648 tons/acre) and exceeded permit

requirements, (2) pyritic materials were special handled, (3) backfilling was performed in a timely

manner, and (4) some potentially acid-forming materials were removed from the mine site. The

study concluded that most unsuccessful attempts at alkaline addition were too conservative in

terms of the application rate, particularly the practice of applying one-third the calculated

deficiency. Further, alkaline addition is most effective when incorporated into the backfill

concurrently with mining and reclamation and when implemented in conjunction with other best

management practices.

A study of the use of acid-base accounting for predicting surface coal mine drainage quality

(Brady and others, 1994) showed a strong relationship between the presence of neutralizing

minerals in the overburden (generally carbonates) and the alkalinity of post-mining discharges. 

Critical values of NP and NNP were identified. Mines with NP values greater than about 15 ppt

and NNP greater than 10 ppt CaCO3 had net alkaline drainage. Sulfur content alone was not a

reliable predictor of post-mining water quality, except where calcareous strata were absent. The

implication for alkaline addition is clear. If it is assumed that imported alkaline material behaves

no differently than native alkaline strata, the application of alkaline material at a rate that simulates

a naturally alkaline site should assure alkaline post-mining water quality.

Skousen and Larew (1995) studied an alkaline addition project that imported alkaline shale from a

nearby mining operation to an operation that was deficient in neutralizers. Although the

deficiency calculated from ABA data was equivalent to a one-foot thick layer of the alkaline shale,

3 to 4 feet of shale were actually imported. Significantly, for this discussion, the alkaline addition

project successfully prevented AMD. 

 

Perry and Brady (1995) found that overall NP values in excess of 21 ppt CaCO3 and NNP values

greater than 12 ppt CaCO3 would produce net alkaline water. Overall NP and NNP values less
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Geochemical Controls 2-51

than 10 ppt CaCO3 and 0 ppt CaCO3, respectively, produced net acidic water. Variable water

quality was found for NP and NNP levels between these limits. The same water quality data were

examined using significance thresholds. Sulfur contents less than 0.5 percent and NP values less

than 30 ppt CaCO3 for individual strata were considered to be insignificant producers of acidity or

alkalinity, hence, values which do not exceed these thresholds are assigned a value of zero for the

NP and NNP calculations. Applying significance thresholds, overall (the entire volume of

overburden to be mined) NP and NNP values greater than 10 ppt and 5 ppt CaCO3 produced

consistently alkaline water. NP and NNP values less than 1 ppt and -5 ppt CaCO3 produced

consistently acidic drainage. Noting decreased sulfate concentrations with increasing NP, they

concluded that the presence of carbonate minerals in amounts as low as 1 to 3 percent (10 to 30

ppt of NP) inhibit pyrite oxidation. Moreover, maintenance of the alkaline conditions created by

carbonate dissolution is not conducive to bacterial catalysis or ferrous iron oxidation and greatly

limits the activity of dissolved ferric iron, thus interrupting the self-propagating acid cycle.

Case Study 1 (West Keating Township, Clinton County, Pennsylvania)

Unfortunately, actual mine sites having adequate acid-base accounting data, water quality

monitoring, and records of mining practices (including alkaline addition rates and placement of

materials) are difficult to find. One such site, however, is located in West Keating Township,

Clinton County, Pennsylvania. The area had been previously mined on a rider seam 10 feet 

above the main bench of the middle Kittanning (MK) coal, and had not been reclaimed. The

recent operation mined the remaining MK coal and reclaimed the previously mined area. The

total area affected by MK coal removal was 11.5 acre and the maximum highwall height,

including old spoil, was about 20 feet. Overburden analysis was performed on five drill holes, 

but only sulfur was determined. The deepest hole was 18 feet to the bottom of the coal and 

seam and the shallowest was 5 feet. Rock between the rider coal and the MK was described as

"soft brown shale," indicating weathering. The coal had the highest sulfur of any of the strata

encountered, ranging from 0.28 to 0.50 percent. Sulfur in the rest of the overburden was 0.13

percent or less. No NP was determined, however, based on experience with other sites with 
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2-52 Geochemical Controls

shallow overburden in the same region, it can be assumed that no significant carbonates were

present.

Mining began in January 1988, and the site was backfilled by the end of March 1988. Some

alkaline material was added during mining, but the precise amount is not clear. The operation

permit required 10 tons/acre of limestone to be added to the pit floor, and there would have been

another 5 to 10 tons/acre of limestone added to the reclaimed surface for revegetation purposes. 

It is suspected that these alkaline addition amounts are minimums, and the actual amount added

was probably several times greater.

A downgradient discharge from an unreclaimed pit (K1) was monitored before and after mining. 

Following mining, the location of the discharge moved down hill to a lower seam that also had

been mined. It is unclear why this point was not monitored during mining, although it may have

gone dry. Figure 2.2.3a shows water quality over time for net alkalinity and sulfate. Water

quality improved following mining. Because the overburden contained virtually no source of

alkalinity, the increase in alkalinity would not have been possible without the importation of

limestone. The added material was adequate to maintain net alkaline conditions from 1990

through sometime in 1994. The sulfate concentrations, mostly less than 40 mg/L, confirm that

there was little pyrite available for oxidation. These concentrations are typical of premining

sulfate within the Appalachian Plateau (Brady and others, 1996). Comparatively small amounts

(perhaps around 40 tons/acre) of alkaline addition may have been sufficient because of the small

amount and highly weathered nature of overburden present at this site.
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Geochemical Controls 2-53

Mine Discharge K1, Keating #2 Site

-20

-10

0

10

20

30

40

50

60

1986 1988 1990 1992 1994 1996

YEARS

Net Alkalinity (mg/L)

Figure 2.2.3a: Water Quality Before and After Mining at the Keating #2 Site, Clinton,

PA

The Case Study 1 site illustrates that a surface mine with weathered overburden that lacks pyrite

can produce alkaline drainage with a minimal quantity of alkaline material added as a safety factor.

Without the addition of alkaline material, there would have been little or no alkalinity produced.
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2-54 Geochemical Controls

Backfill Well Manganese Concentrations

0.01

0.10

1.00

10.00

100.00

1000.00

1993 1994 1995 1996 1997 1998

Period of Sampling

Manganese Concentrations (mg/L)

BF1 Mang

BF2 Mang

BF3 Mang

Case Study 2 (Boggs Township, Clearfield County, PA)

This study site is just to the south of the PA(19) site (Appendix A, EPA Remining Database,

1999). The alkaline addition measures used on PA(19) were partly derived from experience

gained from this site. Rose and others (1995) reported results from an ongoing alkaline addition

demonstration project in Clearfield County, Pennsylvania that indicated positive but preliminary

results. More recent data from monitoring wells in the backfill show mixed results. Baghouse

lime, a lime production waste product, was applied at rates ranging from 150 to 1,080 tons/acre,

adjusted to 100 percent CaCO3 content, based on ABA calculations using significance thresholds

and correcting for deficiencies in NP. Areas with the highest alkaline addition rate (and the most

acidic overburden) were successful in producing alkaline drainage with low concentrations of

dissolved iron and manganese (Figure 2.2.3b). Backfill wells in areas which received lower

alkaline addition rates showed both alkaline and acidic water and relatively high levels of

dissolved iron and manganese. Post-reclamation sulfate levels of 300 to 800 ppt in all of the

monitoring wells indicate that AMD is being produced but neutralized.

Figure 2.2.3b: Water Quality Before and After Mining at the Case Study 2 Site
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Geochemical Controls 2-55

Based on the experience from this demonstration project, it is probably unrealistic to adjust

alkaline addition rates based on minor overburden quality variations between drill holes. Unless

there is a corresponding change in stratigraphy, alkaline addition rates should reflect aggregate

(average) overburden quality.

Evans and Rose (1995) also reported the results of alkaline addition to large test cells 

constructed solely of high-sulfur overburden from this site. Cells were constructed of 2 percent

pyritic sulfur mixed with different amounts of alkaline material. Although alkaline addition

reduced the generation of acidity by as much as 96 percent, even the highest alkaline addition

amount, equivalent to 3.4 percent CaCO3, was insufficient to prevent AMD formation. Two

important considerations resulted from this study. First, the high-sulfur overburden was 

exposed to weathering for a considerable time period before cell construction and application 

of alkaline material. Test cells remained exposed without a soil cover for an extended time 

period thereafter. More rapid application of alkaline material and timely covering may have

reduced the likelihood of AMD formation. In other words, once AMD generation starts, it is

much more difficult to slow its formation than to keep it controlled in the first place. Second,

because complete mixing of alkaline material may be difficult or impossible to achieve,

microenvironments within the spoil can still allow acid production and bacterial activity. AMD

formation in very high-sulfur mine sites or areas of concentrated high-sulfur refuse, represented 

by the concentration of highly pyritic material in the cells, may be impossible to ameliorate using

alkaline addition rates which have otherwise been successful in mines with more typical sulfur

values.

Case Study 3 (Appendix A, EPA Remining Database, 1999 (PA (8))

Smith and Dodge (1995) reported on an alkaline addition site in Lycoming County, PA, which

was part of the original Brady and others (1990) study. Alkaline addition rates of 600 tons/acre

and daylighting of an underground mine resulted in dramatic improvements in water quality 

from the underground mine discharge (Figure 2.3.3c). Pre-mining net acidity values exceeded

100 mg/L. After remining, the discharge was predominately alkaline. Increased sulfate
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2-56 Geochemical Controls

concentrations indicated that the improvement in water quality could be attributed to

neutralization by imported alkaline material rather than daylighting. No naturally occurring

alkaline material was present. This operation is one of the oldest successful alkaline addition sites. 

It has exhibited improved water quality since the onset of large-scale alkaline addition in 1986 and

produced predominately alkaline water since 1989, suggesting that the impact of alkaline addition

will be long-term or permanent.

Figure 2.2.3c: Water Quality at the Case Study 3 Site

Backfill Well Net Alkalinity Concentrations

-800.0

-600.0

-400.0

-200.0

0.0

200.0

400.0

600.0

1993 1994 1995 1996 1997 1998

Period of Sampling

Net Alkalinity Concentrations (mg/L)BF1 NetAlk

BF2 NetAlk

BF3 NetAlk
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Geochemical Controls 2-57

Figure 2.2.3c: Water Quality at the Case Study 3 Site (continued)

Backfill Well Manganese Concentrations

0.01

0.10

1.00

10.00

100.00

1000.00

1993 1994 1995 1996 1997 1998

Period of Sampling

Manganese Concentrations (mg/L)

BF1 Mang

BF2 Mang

BF3 Mang

Backfill Well Sulfate Concentrations

10.0

100.0

1000.0

10000.0

1993 1994 1995 1996 1997 1998

Period of Sampling

Sulfate Concentrations (mg/L)

BF1 Sulf

BF2 Sulf

BF3 Sulf
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2-58 Geochemical Controls

Figure 2.2.3c: Water Quality at the Case Study 3 Site (continued)

Backfill Well Iron Concentrations

0.01

0.10

1.00

10.00

100.00

1000.00

1993 1994 1995 1996 1997 1998

Period of Sampling

Iron Concentrations (mg/L)

BF1 Iron

BF2 Iron

BF3 Iron

Case Study 4 (Sequatchie County, Tennessee)

Most of the published research in alkaline addition has taken place in northern Appalachian states. 

An exception is the work done by Wiram and Naumann (1996) on an AMD-producing surface

mine in Sequatchie County, Tennessee. This site is adjacent to the TN(4) site (Appendix A, EPA

Remining Database, 1999) and the pollution prevention measures used on TN(4) were first

applied at this study site. Alkaline addition was implemented as the principal component of a

toxic materials handling plan that also included selective overburden placement and the

construction of chimney drains and alkaline recharge basins. Alkaline addition rates were

determined for individual stratigraphic intervals having a NNP less than -5, however, a modified

NP test was used in order to exclude the apparent NP contribution from siderite (FeCO3).
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Geochemical Controls 2-59

Previous overburden analysis results erroneously predicted alkaline drainage due to the presence

of siderite that falsely indicated the presence of significant alkaline strata. The role that siderite

plays in mine drainage and acid-base accounting are explained by Skousen and others (1997). 

Limestone application rates for each of these intervals were summed to determine the application

rate for the area around each bore hole. Net neutral zones were not factored into the alkaline

addition calculations.

Results of the Wiram and Naumann study were favorable. Monitoring wells on the site in the

backfill spoil area that had alkaline addition have higher alkalinities than wells into areas that did

not have alkaline addition.

2.2.4 Discussion

It has long been known that mines with sufficient naturally occurring calcareous strata produce

alkaline mine drainage. It is a logical next step that sites without sufficient naturally occurring

alkaline strata can be made to produce alkalinity by importing the appropriate amount of alkaline

material. The questions are: how much alkaline material should be added, and where should it be

placed? Another question that can be of equal importance, especially in sensitive watersheds, is

how much risk of failure can be tolerated. The literature and the case studies cited above provide

some insights into these questions and identify benefits and limitations of the methods. 

Benefits

C Alkaline materials are an effective means of neutralizing and preventing acid mine drainage.

C Alkaline materials are generally readily available, and in some cases available as waste

products that would otherwise be landfilled.

C Alkaline addition is probably the best understood "chemical" BMP, and there are natural

analogues (i.e., calcareous mines) for comparison.

C The amount of material required to assure alkaline drainage for low to moderate sulfur sites

is well understood.
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2-60 Geochemical Controls

C The chemistry of the alkalinity generating processes of carbonate minerals is well

understood.

C Site-specific data can be obtained to determine the amount of alkaline material that needs

to be added.

Limitations

C Alkaline addition is not generally effective at fixing a problem once it has been created.

C Alkalinity from carbonate dissolution is limited and may not be adequate for high sulfur

mines and coal refuse materials.

C Alkaline materials can armor with iron precipitates and become ineffective. Proper

placement of alkaline materials to avoid high iron water is a way to prevent this problem.

C Ensuring that a site produces alkaline water does not guarantee that effluent limitations for

metals will be met.

C Siderite can produce overburden analyses that falsely predict alkaline drainage. A modified

method for determination of neutralization potential can greatly reduce this risk.

Efficiency

C Alkaline addition has proven to be an effective mine drainage prevention technique for

mines with low to moderate sulfur content. 

C Studies show that mines with net neutralization potentials greater than 12 produce alkaline

drainage. 

C For sites with moderate sulfur, alkaline addition rates below 500 tons/acre typically have

not produced alkaline drainage.

C Alkaline addition rates at less than 500 tons/acre can be effective for low sulfur sites that

would not otherwise produce alkaline water because of a lack of naturally occurring

carbonates.

C More work needs to occur in the southern Appalachians to determine appropriate addition

rates for those geologic conditions.
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Geochemical Controls 2-61

2.2.5 Summary

The addition of alkaline material to surface mine backfill can be an effective method of

compensating for overburden that is naturally deficient in neutralizers and thus, reduce the

potential for acid mine drainage. Two categories of alkaline additives currently are being used on

Appalachian mine sites, limestone (and its derivatives) and coal ash. Coal ash addition was

proposed for 8 of the 17 alkaline addition sites in the BMP-site data packages. 

To successfully prevent the formation of acid mine drainage, a sufficient quantity of alkaline

material should be added to the backfill. Most successful alkaline addition sites to date have used

substantial application rates, exceeding 500 ton/acre. Lower rates have proven to be effective

only for low-cover overburden with very low sulfur content. Alkaline material is best applied by

distributing and thoroughly mixing it throughout the backfill. It also may be useful to place up to

100 ton/acre on the pit floor. Surficial applications of alkaline material are less effective due to

low solubility of calcite and limited contact with acid-producing materials deeper in the backfill. 

Most failed alkaline addition sites either had used application rates that were too low or employed

ineffective placement of the alkaline material.
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2-62 Geochemical Controls
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Geochemical Controls 2-63

2.3 Induced Alkaline Recharge

Constructed recharge infiltration pathways composed of limestone within mine backfill have been

used to increase alkalinity in mine spoil and to increase oxygen availability within spoil. These

pathways can be near surface features (trenches) or deeper structures that extend from the surface

to the base of the spoil (funnels). Surface runoff is directed into these pathways where it contacts

the limestone and generates alkalinity. The pathway is positioned such that infiltrating water

would not contact potentially acid-generating rock. As originally envisioned, the goal is net

alkaline water in the mine spoil. A second goal at some sites is to induce oxygen into the backfill

with the purpose of precipitating iron from solution. The principal studies on this subject have

been conducted by Caruccio and Geidel (1984, 1985, 1989 and 1996) and Wiram and Naumann

(1996). 

Theory

Pyrite oxidation can result in significant quantities of soluble, acid-producing oxidation products. 

In fact, mine drainage acidities in the hundreds or even thousands of milligrams per liter are not

uncommon. Calcite dissolution on the other hand is much more limited in terms of alkalinity

generation. At surface conditions the maximum alkalinity is less than 100 mg/L. Carbonates are

more soluble at elevated partial pressures of carbon dioxide and under high Pco2 they can 

produce alkalinity as high as 500 mg/L, a condition that can occur in mine spoil. Alkalinity and

acidity are both reported in the same units of calcium carbonate equivalent and, for example, 100

mg/L of alkalinity will neutralize the acid from 100 mg/L of acidity. A good discussion on the

chemistry of pyrite oxidation and carbonate dissolution at coal mines is in Rose and Cravotta

(1998).

It has been proposed that one way to offset the frequently unequal generation of acidity in

comparison to alkalinity was to increase the load of alkalinity. Load is concentration times flow
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2-64 Geochemical Controls

and is reported in units of mass per time period (e.g., pounds per day). The means proposed to

do this was to divert surface runoff into trenches and/or funnels filled with limestone. This water

would contact and dissolve some of the limestone. Thus the water flowing from these structures

into the spoil would be alkalinity enriched. It was hoped that the increase in the volume of water,

even with limited alkalinity, would result in a large enough alkalinity load to offset the spoil

water's acid load. It has been estimated that it would require 3 to 8 times more water in contact

with the calcareous material than the water in contact with the acidic material. This concept was

developed by Caruccio and Geidel (1984) based on laboratory work by Geidel (1979). 

A second purpose for recharge pathways is to promote the inflow of oxygen into the spoil. 

Oxygen could enter the spoil in three ways, dissolved in the infiltrating water, entrapped in the

infiltrating water, and with air directly entering the recharge structure. This would be used where

waters are already alkaline or only slightly acidic and where the water is iron-rich. Reduced iron

(Fe2+) precipitation is very slow even at neutral pH, however, oxidized iron (Fe3+) precipitates

rapidly under alkaline conditions. The additional oxygen would help to enhance oxidation and

precipitation of iron within the backfill. 

2.3.1 Implementation Guidelines

Caruccio and Geidel (1984) suggest a refinement to the above concept which would incorporate

special handling and capping of acidic material. Acid-producing material is placed in pods and

capped with clay. Alkaline recharge channels are located such that infiltrating water enters

"neutral" or alkaline spoil located between the pods of acidic material. This concept is depicted in

Figure 2.3.1a. The purpose is to minimize the amount of acidic water and maximize the amount

of alkaline water that reaches the water table in the spoil.
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Geochemical Controls 2-65

Figure 2.3.1a: Alkaline Recharge Channels and Capped Acid-producing Material

Pods (Caruccio and Geidel, 1984)

If recharge trenches are installed for the purpose of inducing oxygen into the backfill the

limestone (or other type of rock) should be of sufficient size and sorting to be easily permeable to

air. 

2.3.2 Verification of Success or Failure

C The BMP should be constructed as designed and the on-site construction plan should be

documented. Means of documentation include:

- Engineer’s certification of construction.

- Photographs of the structure as it is being constructed. 

- Locations of the recharge structures accurately located by survey or global

positioning system.

- Verification of the amount of imported alkaline material by weigh slips or another

accounting method. Weigh slips would be submitted to the regulatory authority at

specified intervals. A copy should also be available for inspection at the mine site

by the mine inspector. 
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2-66 Geochemical Controls

C Increased inspection frequency may be needed to verify that a BMP is being constructed

as designed. Inspections can include examination of limestone weigh slips and verification

of the size and type of imported material. 

C Photographs of the construction process can be taken by the mine inspector, company

engineer or other qualified person. Copies would be placed in the state permit file. A

narrative, including date and location, should accompany each photograph.

C Water quality monitoring should include both concentration and flow at discharge points. 

This is especially critical for remining sites where the intent and purpose is to reduce loads

of constituents. Because alkaline recharge structures increase flow into the ground- water

system, being able to determine load is critical. 

Monitoring for concentration and flow, as well as other accurate documentation of construction,

will allow for future improvements in design and determination of the efficiency of alkaline

recharge structures. 

2.3.3 Case Studies

The case studies discussed below are examples of sites where the alkaline recharge concept has

been applied. 

Case Study 1 (Caruccio and Geidel, 1984, 1985 and 1996)

A site in Upshur County, WV is approximately 20 acres and was mined in the early 1970s. 

Acidic discharges developed following reclamation. Four post-mining discharges from the toe-ofspoil had acidities between 400 and 600 mg/L. Caruccio and Geidel have attempted, over the

course of more than a decade, various means of reducing the acidity, most of which involved

alkaline recharge structures. Figure 2.3.3a shows the topography, location of recharge trenches

and funnels, and locations of the seeps at the site. 
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Geochemical Controls 2-67

Figure 2.3.3a: Topography, Location of Recharge Trenches and Funnels, and

Locations of Seeps (Case Study 1, Upshur County, WV) (Caruccio

and Geidel, 1984).

Fifteen alkaline recharge trenches were installed to divert surface water into the ground water

system in the summer of 1983. The trenches averaged 10 feet wide, 3 feet deep, and 75 to 725

feet long. Trench floors were capped with sodium carbonate briquettes (0.5 lbs/ft2) and covered

with two feet of limestone reject. Halogen tracers (KI and KBr) were placed at the base of the

trenches to serve as tracers for infiltrating water. Eight months after installation, the tracers

appeared at the seeps. At this time the acidity decreased to a range of 75 to 125 mg/L. Because

the water was still acidic, fine limestone (up to 1⁄2 inch) was broadcast over the site at a rate of

100 tons/acre in 1984. The acidity continued to hover at around 100 mg/L.

In February 1994 eight funnels were installed adjacent to or within the trenches. These funnels

were excavations of approximately 4 feet x 7 feet x 8 feet, and were filled with a total of 60 to 80
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2-68 Geochemical Controls

tons of coarse limestone having a CaCO3 equivalent of ~70 percent. The purpose of the funnels

was to transmit water directly from the surface to the water table. Following funnel installation

acidity was 50 to 100 mg/L.

Figure 2.3.3b shows acidity concentrations for Seep #2 and time lines showing when the alkaline

recharge trenches and funnels were installed. The data indicates a decrease in acidity

concentration following the installation of each BMP. Flow was not measured, thus load could

not be calculated. Without flow information it can not be determined how much of the decrease

in acidity was due to dilution from infiltrating precipitation and how much was due to

neutralization. Water quality data for the seeps following funnel installation shows alkalinity is

occasionally at measurable concentrations, and in a few instances is greater than acidity. This

measured alkalinity indicates that, at least occasionally, alkalinity is being generated by the

trenches/funnels and sometimes is enough to neutralize all of the acid.
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Geochemical Controls 2-69

Figure 2.3.3b Plot of Acidity versus Time for Seep #2 at Case Study 1 Mine. (Vertical lines

indicate when recharge trenches and funnels were installed.)

There are four possible interpretations of the observed decrease in acidity concentration:

1. Trenches and funnels provided alkalinity to the ground water and thereby

neutralized existing acidity.

2. The trenches and funnels increased rain water infiltration into the ground water

system, thus diluting the ground water and lowering concentration.

3. Some natural attenuation occurred through time. A control area with similar

overburden would have to be monitored to account for the effects of this factor.
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2-70 Geochemical Controls

4. The decrease in acidity concentration is the result of two or three of the above factors.

If the decreased concentrations are due simply to dilution, increased infiltration could result in an

increased acid load and exacerbate the problem. For example if:

Before construction of funnels: 

Average flow is 10 gpm and concentration is 250 mg/L.

10 gpm x 250 mg/L x 0.012 = 30 lbs/day acidity

After construction of funnels: 

Average flow is 30 gpm and concentration is 150 mg/L.

30 gpm x 150 mg/L x 0.012 = 54 lbs/day acidity

An evaluation of whether this BMP was effective requires a knowledge of both flow and

concentration.

Case Study 2 (Wiram and Naumann, 1996; Wiram, 1996).

This site is located in Sequatchie County, Tennessee. Mining began in September 1987 and

mining used loaders and trucks. Once the initial box cut was in place a dragline was used. Castblasting was later employed along with the dragline operation. 

In mid-1990 pollutional seepage began to enter a receiving stream. The mine discharge water 

had pH from 3.4 to 7.5, alkalinity from 0 to 121 mg/L, iron from 4.8 to 48.6 mg/L, manganese

from 2.3 to 34 mg/L, and sulfate from 8 to 812 mg/L. The coal company embarked on an

extensive investigation to determine the source of the problem and effective methods for resolving

the problem. Alkaline recharge structures were just one of several BMPs that were ultimately

used. Other BMPs included special handling of overburden and alkaline addition in the backfill. 

Although special handling and alkaline addition will be touched on in this discussion, the focus is

on the alkaline recharge structures.
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Geochemical Controls 2-71

The alkaline recharge structures were approximately 150 x 50 feet, with a depth of 12 feet, and

were often placed over chimney drains which had been constructed in the backfill. The recharge

structures were filled with four feet of "crusher-run" limestone (0 to 1.25 inches) overlain by four

feet of limestone gravel (2 to 2.25 inches). The remaining four feet was for "free storage." The

purpose of these recharge drains was different from that of Case Study 1. In this case, the drains

were installed to enhance "the alkaline/oxygen loading" of the backfill ground water. The key

objective was to induce metal precipitation within the backfill.

This site can be divided into two areas in terms of BMPs. Most of the site (the southern seveneighths) was mined conventionally without incorporation of special BMPs to prevent water

quality problems. The northern one-fifth was mined using special handling and alkaline addition. 

Both areas had alkaline recharge structures installed. A map of the site showing the location of

alkaline recharge structures, monitoring wells and the area where alkaline addition and special

handling were part of the mining plan are shown in Figure 2.3.3c. Monitoring wells OW-2, OW5, and OW-8 were placed downgradient from recharge trenches. Table 2.3.3a shows the range of

water quality in terms of pH, alkalinity, iron and manganese for these wells, as well as water

quality for wells OW-7 and OW-10.
Coal Remining BMP Guidance Manual

2-72 Geochemical Controls

Figure 2.3.3c: Map of Case Study 2 Site
Coal Remining BMP Guidance Manual

Geochemical Controls 2-73

Table 2.3.3a: Water Quality for Wells at the Case Study 2 Site (data interpreted from

graphs by Wiram, 1996)

Well OW-2 OW-5 OW-7 OW-8 OW-10

Date 10/90 to

4/93

1995 7/92 to

4/93

1995 7/92 to

4/93

1995 11/92

to 4/93

1995 11/92

to 4/93

1995

pH 6.0 6.0 6.0 6.0 6.5 6.4 6.5 6.3 6.0 6.0

Alk.

mg/L

100-175 125-

150

~100 150-

200

~450 ~450 50-500 400-

450

150-

200

100-

200

Fe

mg/L

15-30 <1-

15

<10 10-20 <1-7 <1-6 <1-5 <1-4 15-30 40-90

Mn

mg/L

10-20 8-18 ~10 ~10 5-8 2-8 2-4 3-8 ~10 10-20

Water quality data from the monitoring wells prior to construction of the alkaline recharge

structures do not exist. Thus pre- and post-construction data cannot be compared. For purposes

of evaluation the data in Table 2.3.3a has been divided into early monitoring data (April 1993 and

earlier) and late monitoring data (1995). The differences between early and late monitoring data,

overall, are not significant. The biggest differences in water quality is observed when the wells

drilled into the area without special handling and alkaline addition are compared with the wells

located near the area of alkaline addition and special handling. Wells OW-2 and OW-5 were not

influenced by special handling and alkaline addition, whereas there were indications that OW-7

and OW-8 were influenced. The water in OW-7 and OW-8 is more alkaline than in the other

wells and in general has lower metal concentrations than wells OW-2, OW-5 and OW-10. Well

OW-10 is upgradient from any BMPs and serves as a "control." The water in OW-10 has higher

metal concentrations than the other wells. If OW-10 is representative of mine spoil water in the

absence of BMPs, then the BMPs do appear to have resulted in water quality improvement. 
Coal Remining BMP Guidance Manual

2-74 Geochemical Controls

Case Study 3 (Appendix A, EPA Remining Database, 1999, TN(4))

This site was submitted as one of the 61 state data packages. It is located in Sequatchie County,

Tennessee and is immediately to the east of the Case Study 2 site. The same company is mining

both sites and experience gained at the Case Study 2 site was incorporated at the Case Study 3

site. This site incorporated numerous BMPs in addition to alkaline recharge structures, including

alkaline addition, special handling, compaction of spoil, backfill hydrology routing, backfill water

inundation, and stream buffer zone expansions. Only the induced alkaline recharge structures will

be discussed here. The surface feature is a depression that is about 150 feet long by 75 feet wide

and 12 feet deep. The area filled with limestone is somewhat smaller and the depth of limestone is

about 8 feet. As with the Case Study 2 site one of the goals is to promote the flow of oxygen into

the spoil for in situ precipitation of metals. The effectiveness of the measures used at this site can

not be evaluated because the site is still active. 

2.3.4 Discussion

The theory of increasing alkaline load by increasing the amount of water that is in contact with

calcareous materials is a valid concept, although it is not without potential problems and is not

applicable to all mine sites. The benefits and limitations of implementation of this BMP are

highlighted below. Most of the potential problems have not been discussed in previous literature.

 

Benefits

C Surface water is preferentially directed to calcareous material that can produce alkalinity. 

The water will flow through the limestone in the recharge structure and avoid contact with

acidic material. 

C Water flowing into the structures will be surface runoff (i.e., essentially rainwater) that is

low in dissolved solids, and more importantly, has low metals concentration. Water

containing high concentrations of metals, such as mine drainage, can coat (armor)

limestone and other calcareous materials rendering them ineffective. 
Coal Remining BMP Guidance Manual

Geochemical Controls 2-75

C Limestone recharge structures are passive and require little, if any, maintenance.

C Recharge structures can introduce oxygen into the backfill to facilitate oxidation and, if

the water is sufficiently alkaline, metals will precipitate in the backfill rather than at a

surface water discharge point.

Limitations

C Limestone only dissolves when in contact with water, thus only during precipitation events

is the limestone in contact with water. 

C Permeable trenches can increase the flow of air into and out of spoil. This could increase

oxygen availability and decrease carbon dioxide within the spoil. Increases in oxygen can

be desirable (as in Case Studies 2 and 3 where the goal was/is to precipitate iron in the

backfill), or undesirable (if the spoil is highly pyritic). Retention of carbon dioxide (CO2)

in spoil can be important if calcareous minerals are present because carbonates are more

soluble when CO2 is elevated, a condition that often exists in surface coal mines (for

examples of mine sites where elevated CO2 has been measured see Guo and Cravotta,

1996, Lusardi and Erickson, 1985, and Jaynes and others, 1983). This is the reason that

many mine waters have alkalinities greater than 200 mg/L (for examples, see Hornberger

and Brady, 1998; and Brady and others, 1998, Table 8.2).

C The increased flow into spoil could potentially increase load of undesirable constituents

such as acidity, metals and sulfate, especially if the water entering the spoil flushes

oxidation products that have built up between precipitation events. 

C To reach saturation with respect to alkalinity, water should be in contact with calcareous

minerals for a sufficient length of time. If contact time is not enough, sufficient alkalinity

may not be generated. 
Coal Remining BMP Guidance Manual

2-76 Geochemical Controls

C Intentional diversion of surface water into the ground water system can result in a

fluctuating water table. This could adversely affect water quality if pyrite oxidation

products, which can build up between flushing cycles, are flushed during this fluctuation. 

The effects of induced alkaline recharge structures have been studied at few sites. Thus there are

unanswered questions regarding the effectiveness of this BMP. Although concentrations

decreased at the Case Study 1 site, flow data was not evaluated, and BMP effects on acid load

can not be assessed. The Case Study 2 site lacked pre-installation ground water monitoring data,

but contained a single well in an area that was not affected by the BMPs. This control well has

higher metal concentrations than wells below the recharge trenches. The recharge structures may

have been effective at in-situ metal removal. Water in all the wells in Case Study 2 was alkaline. 

An evaluation of the effectiveness of alkaline recharge structures at the Case Study 3 site cannot

be made at this time because the site is still active.

Efficiency

Until efficiency can be further demonstrated, it would be prudent to restrict the use of alkaline

recharge structures as a BMP to the following scenarios:

C Sites where the overburden contains very little acid-producing material and there is a lack

of calcareous rocks. In other words, this BMP should be implemented on "marginal" sites

that would not create severe acid mine drainage in the absence of alkaline recharge

structures, but likewise would not produce alkaline drainage. In cases where this

technology is implemented and where selective handling of acidic materials has occurred,

the acid material should be placed above the highest water table anticipated to occur

during a recharge event. Otherwise the acidic material may be in a zone of water table

fluctuation.

C This BMP has potential use at sites with alkaline or near-alkaline ground water with

elevated metals. The purpose at these sites is to enhance the amount of oxygen that will

reach the ground water and this in turn will promote in-situ precipitation of metals. 
Coal Remining BMP Guidance Manual

Geochemical Controls 2-77

2.3.5 Summary

Although alkaline recharge structures have the potential to induce alkalinity in mine spoil,

experience is limited and there are possible drawbacks that have not been evaluated, such as the

potential for increasing the load of undesirable chemical constituents. The Case Study 1 site had

several acid seeps which had resulted from mining. Following installation of recharge trenches

and funnels there were decreases in acidity concentration. Flow data, however, was not available

so it can not be determined whether acidity load decreased. The mine spoil monitoring wells at

the Case Study 2 site lack pre-installation data. A single control well in an area where BMPs

were not applied is of poorer quality than wells in areas with induced alkaline recharge trenches. 

At this site, the primary problem was the discharge of metals offsite. The recharge trenches were

constructed with the intent of causing precipitation of metals in the backfill by increasing alkalinity

and oxygen availability. If a comparison between the control well and the other wells is valid, this

could indicate that the efforts at the Case Study 2 site did result in better water quality. The Case

Study 3 mine incorporated most of the measures adopted at the adjacent Case Study 2 site

including using the recharge structures to enhance the flow of oxygen into the backfill. The Case

Study 3 mine is still active and it is too early to evaluate effectiveness.

The number of sites where alkaline recharge structures have been constructed as a BMP are few

and many questions remain as to their effectiveness. Some implementation considerations can be

suggested, the most important being that it should be certain that an increase in surface infiltration

will not also result in an increase in acid load. The methodology will probably be most effective

on sites with minimal amounts of pyrite and a lack of naturally occurring calcareous rocks. 

Recharge structures may also be effective where the goal is increased oxygen in the backfill, so as

to precipitate metals within the backfill.

Measures should be taken to ensure that plans were carried out as designed, including increased

inspection frequency and engineer certification of on-site design. Monitoring of ground water

discharges should include flow as well as concentration so that load can be determined. 
Coal Remining BMP Guidance Manual

2-78 Geochemical Controls
Coal Remining BMP Guidance Manual

Geochemical Controls 2-79

2.4 Special Handling

Special handling at surface mines encompasses the selection, handling, and controlled placement

of acid-producing and/or calcareous rock. The primary purpose of special handling is to place

acidic or alkaline strata in such a way as to minimize acid production and transport, and to

maximize the alkalinity generation within the mine spoil water. 

Special handling is often used in conjunction with other acid mine drainage prevention techniques

such as alkaline addition, water management (e.g., pit floor drains), and surface reclamation (e.g.,

slope grading to promote runoff) to improve the water quality. For example, special handling, in

the absence of calcareous material, cannot by itself produce alkaline drainage. Thus, where

calcareous strata are absent, offsite calcareous material can be imported to offset these natural

deficiencies in acid-neutralizing rocks. Pit floor drains can be used to engineer where the postmining water table will re-establish within the spoil, thus assuring that special handled material

will remain above the water table.

Special handling is a common practice, occurring on at least 35 of the 61 mines included in the

EPA Remining Database (Appendix A and Table 2.4a). It affected at least 78 of 231 discharges

in Pennsylvania (Appendix B, Pennsylvania Remining Site Study). An examination of both

databases shows that special handling is not a “stand-alone” BMP. It is always used in

conjunction with other BMPs.
Coal Remining BMP Guidance Manual

2-80 Geochemical Controls

Table 2.4a: EPA Remining Database (Appendix A), Special Handling of Toxic/Acid

Forming Materials

ID Type of

Mine

Mine

Closure

Date

Cover

Material

Placement Blending 

of

Overburden

Other Major

BMPs

Comments

AL

(2)

Surface 3/90 Regrading

Revegetation

Terraces

AL

(7)

Surface 5/92 4' Non-toxic Regrading

Revegetation

AL

(10)

Surface

Auger

12/95 Yes Regrading

Revegetation

Temp.

Diversions

AL

(11)

Surface No

mining

taking

place.

Yes On pit floor Old washer

fines to be

relocated.

Alkaline

addition

Reclamation

will occur

through a

party other

than the

mining

company

AL

(14)

Surface 

Coal

Refuse

Disp.

10/89 4' clay over

fines

4' over rest

Regrading

Revegetation

KY

(1)

Surface

Coal

Refuse

Repr.

Active 4' Non-toxic On pit floor Regrading

Revegetation

KY

(2)

Surface

Auger

Active 4' Against

Highwall

Regrading

Revegetation

Daylighting

KY

(3)

Surface

Auger

Refuse

Storage

Shut

down - 

11/98

4' Non-toxic Regrading

Revegetation

Shut down due

to low coal

demand. Will

be reopened.

KY

(4)

Surface

Auger

Active 4' Non-toxic Regrading

Revegetation

Seals

Acid material

minimal

PA

(1)

Surface 10/98 5' Non-toxic 10' above pit

floor; 10'

from

highwall

Revegetation

Daylighting

Alk. Addition

Clay Seals

Alternating

layers of 2 ft

"toxic", 2 ft

clean spoil
Coal Remining BMP Guidance Manual

ID Type of

Mine

Mine

Closure

Date

Cover

Material

Placement Blending 

of

Overburden

Other Major

BMPs

Comments

Geochemical Controls 2-81

PA

(3)

Surface 6/98 4' Non-toxic 10' above pit

floor

Regrading

Revegetation

Daylighting

Clay Seals

Alternating

layers of 2 ft

"toxic", 2 ft

clean spoil

PA

(5)

Surface 4/98 4' Non-toxic 20' above

ground water;

10' from

highwall

Yes Regrading

Revegetation

Alternating

layers of 2 ft

"toxic", 2 ft

clean spoil

PA

(6)

Surface

Auger

8/96 Regrading

Revegetation

Daylighting

PA

(7)

Surface

Auger

Coal

Refuse

5/96 15' Neutral

Spoil;

2' Clay

Shield

15' above pit

floor;

15' from

highwall

Regrading

Revegetation

Daylighting

Alk. Addition

PA

(8)

Surface Active Regrading

Revegetation

Daylighting

Alk. Addition

PA

(9)

Surface 

Rock

Active Regrading

Revegetation

Daylighting

Alk. Addition

Biosolids

PA

(10)

Surface 11/95 Yes Above

ground water

Regrading

Revegetation

Scarification

Bactericide

PA

(11)

Surface

Auger

Active 4' Clean Fill 25' above pit

floor

Regrading

Revegetation

Daylighting

Alk. Addition

25 T/ac Lime

added 24"

Toxic

30" Clean

PA

(13)

Surface

Auger

1996 70' above

ground water

PA

(19)

Surface Active 10' 10' Regrading

Revegetation

Alk. Addition

TN

(1)

Surface

Auger

Active Non-acid

strata

On pit floor Backfill

Drains

TN

(4)

Surface

Auger

Active Alk. Addition

Backfill Inun.
Coal Remining BMP Guidance Manual

ID Type of

Mine

Mine

Closure

Date

Cover

Material

Placement Blending 

of

Overburden

Other Major

BMPs

Comments

2-82 Geochemical Controls

VA

(1)

Surface

Auger

10/98 Yes Regrading

Revegetation

Daylighting

Excess of NP

VA

(2)

Surface

Auger

12/93 4' Non-toxic Regrading

Revegetation

Topsoil Repl. 

VA

(3)

Surface

Auger

4/92 4' Non-toxic Regrading

Revegetation

VA

(4)

Surface 88/90 Yes Regrading

Revegetation

Bactericide

Underdrains

VA

(6)

Surface Active 4' Non-toxic Regrading

Revegetation

Underdrains

Diversions

Compaction

VA

(7)

Surface Active 4' Non-toxic 4' above pit

floor; 4' from

highwall; not

in bottom

fills

Regrading

Revegetation

Daylighting

Drainage 

WV

(1)

Surface

Deep

Active 6' Non-toxic Regrading

Revegetation

Daylighting

Alk. Addition

WV

(4)

Surface 11/95 Calcareous

rock

On pit floor

Against

highwall

Surround

w/calcareous

rock

Regrading

Revegetation

Sed. Ditches

WV

(5)

Surface

Ash

Disposa

l

Active Blend

w/calcareous

rock

Regrading

Revegetation

ALD

Alk. Addition

WV

(6)

Surface Active 1' non-toxic On pit floor Surround

w/calcareous

rock

Regrading

Revegetation

Alk. Addition

WV

(7)

Surface 6/87 10' 12-15' Regrading

Revegetation

24" Acid
Coal Remining BMP Guidance Manual

ID Type of

Mine

Mine

Closure

Date

Cover

Material

Placement Blending 

of

Overburden

Other Major

BMPs

Comments

Geochemical Controls 2-83

WV

(8)

Surface

Deep 

Ash

Disp.

Active 4' Non-toxic 4' above pit

floor

Regrading

Revegetation

Alk. Addition

Underdrains

Add Alkaline

Mat’l

WV

(9)

Surface 1/91 Yes Yes Mixed w/

calcareous 

Regrading

Revegetation

Theory

There are essentially four methods of special handling:

C Blending: mixing of naturally occurring calcareous and acid producing rocks.

C Dark and deep: placement of acidic materials consistently below the water table

C High and dry: placement of acidic materials consistently above the water table

C Alkaline redistribution: distributing alkaline material from areas with an excess to areas with 

a deficiency of neutralizing rock.

These four processes rely on different methods of avoiding acid production. Blending relies 

on the presence of a sufficient amount of calcareous rock throughout the overburden to produce

enough alkalinity to offset acidity production from pyritic rocks. “Dark and deep,” or

submergence, relies on the fact that water can contain only a small amount of dissolved oxygen 

(at most ~10 mg/L) and that water is therefore an effective barrier to atmospheric oxygen

(Watzlaf, 1992). This lack of oxygen reduces the potential for the pyrite to oxidize and produce

acid mine drainage. “High and dry” is based on the premise that ground water plays a role in the

chemical reaction that takes place to form AMD and also acts as a transport medium. Placement

above the water table cannot preclude the contact of water with pyritic material. Even in the

unsaturated zone, there is gaseous water in the pore gases and ground water can adhere to particle

surfaces hydroscopically. Thus, the primary effect of high and dry is avoidance of the transport 

of pyrite weathering products. Alkaline redistribution takes advantage of naturally occurring 
Coal Remining BMP Guidance Manual

2-84 Geochemical Controls

alkaline strata where portions of the mine site lack sufficient neutralizers. This alkaline material is

redistributed such that all parts of the site have sufficient alkaline material to prevent or neutralize

AMD. 

Blending is being used on at least 5 of the special handling sites listed in Table 6.4a. Blending

takes advantage of naturally-occurring calcareous strata. In its simplest form, mixing of the strata

occurs in the coarse of overburden removal. Blending plans can be more intentional with specific

strata targeted to assure adequate mixing.

Typically, in the Appalachians, acidic material is placed above the post-mining water table to

minimize water contact. Calcareous materials, on the other hand, are placed such that their

dissolution will be maximized, which can mean placement below the ground-water table. 

Combinations of special handling, alkaline addition, water management, and surface reclamation

can allow the mine operator some control over acid- and alkaline-generating processes.

Probably the first special handling concept involved the recognition of black or very dark colored

rocks and coal reject (“gob,” “bone coal”) as potential acid formers. Initially, it was proposed that

the material be buried on the pit floor. Deep burial was thought to prevent contact with oxygen,

and hence shut off acid production. This approach was discussed as early as 1952 by the

Pennsylvania Sanitary Water Board and is shown in Figure 2.4a. The Sanitary Water Board also

recommended highwall diversion ditches, pit floor drains, contemporaneous backfilling, and

grading topography to limit water infiltration.
Coal Remining BMP Guidance Manual

Geochemical Controls 2-85

Figure 2.4a: Early Recommendation of the Pennsylvania Sanitary Water Board for

Handling Sulfuritic Material (suggested placement was on the pit floor

under the unreclaimed spoil piles).

Experience with deep burial of potential acid-forming materials in Pennsylvania showed that water

quality problems were not always eliminated and sometimes were more severe. This is because of

difficulties maintaining a sufficient water table to keep the material submerged. In most

Appalachian states, special handling strategies began to evolve towards isolation of material above

the post-mining water table with isolation from preferred ground-water flow paths. This remains

the most common special handling technique used in the Appalachians and is illustrated

conceptually in Figure 2.4b.
Coal Remining BMP Guidance Manual

2-86 Geochemical Controls

Figure 2.4b: High and Dry Placement of Acidic Material (commonly used method of

special handling in Appalachia). 

Sampling and Site Assessment

Special handling plans are site specific and should include consideration of the following factors:

C Geologic and Geochemical Conditions: identifying acidity- and alkalinity-generating rocks

in the overburden and determining the distribution, location, and volume of these rocks.

C Hydrogeologic Conditions: identifying ground- and surface-water conditions on the site. 

This would include examination of the geologic structure in relationship to the area to be

mined; the occurrence, quantity, and quality of surface and ground water; and estimating the
Coal Remining BMP Guidance Manual

Geochemical Controls 2-87

highest post-mining ground-water elevation in the backfill based on projected spoil

transmissive properties.

C Operational Considerations: determining an appropriate mining method(s), sequence of

mining, area to be mined, equipment to be used, and placement and amount of acidic and

alkaline materials.

C Field Identification: determination of whether the alkalinity- or acidity-producing rocks be

identified in the field so that they can be properly handled.

Geologic and Geochemical Considerations

Development of a special handling plan requires knowledge of the stratigraphic position, aerial

extent, and total volume of acidity- and alkalinity-generating rocks (See Section 2.1). Horizontal

sampling should be sufficient to define the lateral distribution of calcareous or high-sulfur strata. 

Likewise, vertical sampling should be of adequate resolution to discriminate calcareous and high

sulfur strata. Too large a sample interval can result in loss of resolution and an inability to

determine acidic or alkaline rocks. Acid-base accounting (ABA) is the overburden analysis

procedure most commonly used for these determinations, and is discussed in Section 2.1.

Hydrogeologic Conditions

Hydrologic conditions are an important consideration in the design of a special handling plan. The

position of the post-mining water table has bearing on where materials are placed, and is an

important consideration in whether materials should be submerged below the water table or placed

above the water table. Whichever method is chosen, the goal is typically to keep the material out

of the zone of water table fluctuation.
Coal Remining BMP Guidance Manual

2-88 Geochemical Controls

The information needed to predict the post-mining water table includes a determination of the type

of ground-water system (regional, perched, unsaturated zone). Considerations include premining

ground-water levels, examination of ground-water conditions on nearby mined areas, relationship

to adjacent streams, geologic structure, and water management designs in the mine plan and pit

design. Overburden lithology and mining methods also play a role in the hydrologic characteristics

of mine spoil, which ultimately impacts the post-mining water table.

Table 2.4b is a statistical summary of saturated thickness of ground water in spoil wells. The

summary represents data from Kentucky, Ohio, West Virginia and Pennsylvania, with 5, 9, 27, and

83 wells, respectively. Data are from measurements made by Hawkins (1999). The data have

been split into two categories, wells that were developed in spoil less than 15 meters thick and

wells in spoil greater than 15 meters thick. The median saturated thickness for the deeper wells is

twice that for the shallower wells (4 and 2 meters). This difference is significant at the 95 percent

confidence limit. The range, however, in both categories is extreme, ranging from a fraction of a

meter to 8 and 11 meters, respectively. The significance for special handling is profound. The

“dark and deep” method will not work where the saturated thickness is a fraction of a meter. 

Conversely, “high and dry” will not work where the overburden is less than 15 meters and the

saturated thickness is 8 meters. With a water table this high special handled acidic material would

be near the surface, thus exposing it to oxygen and placing it near or within the rooting zone. The

values in Table 2.4b are a “snapshot” in time. They were a one-time sampling event and do not

represent seasonal and climatic variations which would extend the range. These data, however,

provide insights into the variability of saturated thickness in mine spoil.
Coal Remining BMP Guidance Manual

Geochemical Controls 2-89

Table 2.4b. Saturated Thickness in Meters for Wells Developed in Appalachian Mine Spoil. 

(Hawkins, 1999).

Saturated Thickness (meters)

Summary Statistics All Wells Spoil < 15 m Thick Spoil > 15 m Thick

Median 2.94 2.08 4.08

Minimum 0.18 0.26 0.18

Maximum 11.03 8.08 11.03

Lower Quartile 1.44 1.30 2.55

Upper Quartile 4.52 3.22 5.49

Number of Wells 124 69 55

It is also important to understand the sources of ground-water recharge. These sources include

infiltrating precipitation, ground-water recharge through the final highwall or adjacent mined 

area, and upward flow through the pit floor. Monitoring wells, piezometers and aquifer tests may

be necessary to provide insight into ground-water conditions. However, one should be cognizant

that ground-water flow in the coal fields of the Appalachians, is largely fracture controlled and 

that wells not located in fractures may underestimate the amount of water present and it’s

stratigraphic location. Another technique that can be used to estimate the amount of water present

is the determination of flows from cropline springs. Insights can also be gained by looking at 

post-mining water conditions at nearby mines with similar geologic, hydrologic, and mining

conditions. 

Ground-water conditions are not “static” and vary seasonally and in response to recharge events. 

Monitoring should be sufficient to account for these variations. If, for example, the chosen

placement technique is submergence below the ground-water table, and monitoring occurred 

only during the period of seasonally-high water, there may be times of the year when the water

table would be below the placement position, and the special handled material would not be

submerged. Alternatively, if the design is “high and dry” and monitoring only took place when 
Coal Remining BMP Guidance Manual

2-90 Geochemical Controls

the water table was low, there may be times of the year when the material is within or below the

ground-water table.

Operational Considerations

Implementation of a special handling plan is also dependent on operational considerations. These

considerations include: the amount of area to be mined, total overburden thickness, amount of

material to be special handled, sequence of mining, time needed to complete mining, the need for

blasting, the mining method, and equipment. The equipment should be appropriate for the special

handling plan and site conditions. For example, truck and loader operations are able to easily

remove distinct portions of overburden and to transport the overburden from one area of a mine to

another. This type of segregation is not performed as easily with a dragline. Operational

considerations will be discussed in more detail under Section 2.4.1.

2.4.1 Implementation Guidelines

Prior to developing a special handling plan the overburden should be sampled and acid- and

alkaline-forming strata should be identified. Ground-water conditions should be well understood. 

The shape of the area to be mined should be considered. Only then can a plan be designed and the

appropriate mining methods determined. Special handling plans should be clear, simple, and easily

implemented by field personnel. Maps and cross-sections should show the positions of the

materials to be special handled, and locations where these materials are to be placed. The

materials should be readily identifiable in the field by color, position or rock type. The plan should

be logistically feasible and field verifiable. 

Geologic and Geochemical Considerations

Stratigraphic position of the material is an important planning consideration. If the material lies

immediately above or below the coal seam to be mined, segregation is usually not a problem.

Segregating strata located in other positions above a coal seam may be more problematic. 
Coal Remining BMP Guidance Manual

Geochemical Controls 2-91

Feasibility will require consideration of equipment and blasting plans, how readily identifiable the

strata is in the field, and costs of implementing the plan. “Fizz tests” using dilute hydrochloric acid

can be performed in the field to identify alkaline strata. Unfortunately there is no comparable filed

test for acid-forming strata. 

Hydrogeologic Conditions

In situations where the operator is attempting to special handle acid-forming material by

submergence, the length of time required for the post-mining water table to re-establish is

important. If the operator wishes to place this material above the post-mining water table timing

of water table reestablishment is not important. 

The contribution to the post-mining water table from infiltrating precipitation during the first few

years following reclamation will be less than that for unmined areas. Jorgensen and Gardner

(1987), Guebert and Gardner (1992), and Ritter and Gardner (1993) investigated infiltration and

runoff on newly reclaimed surface mines in central Pennsylvania. They found that infiltration rates

on newly reclaimed mine soils are an order of magnitude lower than adjacent, undisturbed soil. 

However, within four years after reclamation, infiltration rates on some mine surfaces approach

pre-mined rates (8 cm/hr). During the topsoiling operation, the soil is compacted by the

equipment. This compaction promotes runoff. During freeze/thaw and wet/dry cycles,

macropores develop in the surface soils which promote infiltration. The reestablishment of soil

structure and plants also promotes infiltration.

Re-establishment of a post-mining water table will probably occur most rapidly for those mines

where the lowest seam mined lies beneath the regional water table. Once the pumps are shut off,

the regional water table will typically re-establish itself in a relatively short period of time. It

becomes somewhat more difficult to predict the configuration and rate of rebound of the postmining water table for mines with aquifers perched above the regional water table.
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Where the mine is situated above the regional ground-water table, the hydraulic characteristics of

the pit floor will determine whether a post-mining water table will be intermittent or permanent. If

the pit floor material is a thick underclay, it will tend to serve as an aquitard inhibiting further

downward migration. In other cases, the floor might be massive, fractured sandstone, which will

allow the downward percolation of ground water. The post-mining, ground-water table is

dependent on the structure of the lowest mined coal seam and the final highwall configuration. 

Where a down-dip highwall remains after mining and the pit floor retards vertical percolation,

ground water may become impounded on the pit floor against the highwall, resulting in a higher

post-mining water table than is typically the case with an up-dip highwall. In the case where a

downdip highwall remains after mining and conditions are present which promote impounding of

the ground water against the highwall, the "rule of thumb" placement 10 to 20 feet above the pit

floor may be inadequate. If the intention is to keep the ground-water table low, it may be desirable

to change the orientation and/or location of the final highwall to avoid impounding water, or to

incorporate underdrains to minimize ground-water buildup in the backfill.

Spoil hydrology plays a role in the configuration of the water table. Low-permeability spoil will

tend to maintain a higher water table than high permeability spoil. However, most mine spoil is

highly permeable compared to undisturbed strata.

Operational Considerations

The mining plan is often based on the configuration of the land that is to be mined rather than the

optimum configuration for overburden and coal removal. The stratigraphic and areal distribution

of the acid- and alkaline-forming materials, as they relate to the mining plan, are important in

determining how these strata can be special handled and how much is to be segregated. However,

several pit orientations are often possible, and some may be more efficient for a particular handling

plan.

Typically, when blasting, the total overburden column above the coal is broken up in one shot

(lift). However, if the strata to be segregated lies at some distance above the coal, it will 
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Geochemical Controls 2-93

probably be necessary to blast in multiple lifts. The first lift removes the overburden above the

unit to be special handled, and the unit to be special handled is removed separately. The remaining

overburden above the coal is then removed. This process can easily increase blasting costs by

more than 50 percent, and may result in poor rock breakage at the top of the lift because of

stemming requirements (Getto, 1998). Blast hole “stemming” refers to material that is placed in

the shot hole above the explosive. Stemming confines the energy of the explosion to the area

around the explosive. 

When potentially acid-forming strata are exposed, rapidly covering the strata helps prevent the

onset of acid-forming reactions (Skousen and others, 1987). Perry and others (1997) examined

seven sites with special handling and found timeliness of reclamation to have some influence on

water quality. Extended exposure of unreclaimed spoil to infiltration and circulation of water and

to oxygen apparently allows accelerated acid production.

In general, segregation of spoil material is more difficult when using a dragline. In many cases,

dragline operators do not have visual contact with the spoil that is being loaded. Also, typically,

for a dragline to remove material it has to be “shot” and this often results in random material

mixing. Even without mixing, draglines are not good at separating discrete stratigraphic layers. 

“Blending” of overburden is often appropriate where the alkaline and acidic overburden occur in

proximity. Blending may not require anything out of the ordinary and may occur simply as a

consequence of overburden removal and replacement. 

Two overburden removal plans are shown in Figures 6.4.1a and 6.4.1b. In Figure 6.4.1a, acidic

material is located in the upper part of the rock column and requires separate removal. In Figure

6.1.4b, acid material is located directly above the coal. In the later scenario the entire overlying

rock column can be blasted and removed in one lift, resulting in a blending of the alkaline- and

acid-forming material.
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Figures 2.4.1a and 2.4.1b: Overburden Handling Procedures Depending on

Stratigraphic Position of Acid-producing Materials (figures

show the types of equipment that may be appropriate for

handling the overburden).
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Geochemical Controls 2-95

Another operational constraint occurs when the alkaline material is located beneath the coal being

mined. Ripping (disaggregating) the pit floor can be done to incorporate alkaline material into the

mine backfill at sites where alkaline strata exist below the lowest coal seam to be mined. This

method involves removing the coal and ripping the pit floor to expose the alkaline strata to ground

water on the pit floor. It is a suitable practice if the pit floor or underclay is not acid forming. The

operator should have equipment capable of ripping the pit floor to the needed depth and

sufficiently breaking up the alkaline zone. Typically, an average size dozer can rip to a depth of

approximately 3 feet (1 m), while a D-11 dozer is capable of ripping to greater depths. If the

alkaline material is at a depth greater than the depth accessible by ripping, the overlying material

will need to be removed prior to ripping.

Limestone is generally a durable rock and is resistant to abrasion. When ripped, limestone tends to

be of a much larger size than is normally associated with alkaline addition or redistribution, hence,

increased surface area is limited. This method is adequate for mines where alkaline deficiencies are

small, as it may have a limited effect on ground-water quality when compared to alkaline addition

of fine-grained material or alkaline redistribution in the spoil. Section 2.4.4, Case Study 6

discusses a mine where the pit floor was ripped to expose alkaline material. This site is a rare case

in which a Pennsylvania remining site resulted in degradation of water quality.

Special handling is an overburden management technique by which acidic and alkaline materials

are selectively placed in the backfill. Special handling is rarely used alone and is typically used

with other BMPs. Special handling techniques and associated BMPs include:

C Relocation of potentially acid-forming strata above the anticipated post-mining ground-water

table,

C Constructing "pods" of acid-forming materials

C Capping the acid-forming material

C Submergence or flooding;

C Blending including alkaline redistribution; 

C Operational considerations; and
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2-96 Geochemical Controls

C Incorporation with other BMPs such as alkaline addition, daylighting and surface- and groundwater management.

Discussion of Theory

Placement above the water table and encapsulation

Placement of acidic materials above the water table using segregation, isolation, and encapsulation

techniques minimizes contact between acid-forming material and ground water. Special placement

usually occurs in "pods" or discrete piles that are located above the expected post-mining water

table in the backfill; thus it is often referred to as the "high and dry" method. 

A few mines have constructed liners and caps that are designed to prevent ground-water contact

with the acid-forming materials. This method is encapsulation. Segregation and isolation from the

ground-water system does not totally prevent pyrite oxidation. Oxygen, microbes and water are

still present in the pods. Segregation and isolation are directed at preventing massive downward

leaching, or upward migration of oxidation products. The technique is illustrated and described in

Figure 2.4.1c.
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Geochemical Controls 2-97

Figure 2.4.1c: Three-dimensional Conceptual View of High and Dry Placement of Acidforming Materials

Construction of acid-forming material pods is one of the oldest techniques used to isolate

potentially acidic strata. The purpose is to inhibit percolation or recharge of ground water 

through the potentially acid-forming strata. Pods are constructed in compacted layers, sometimes

with potentially acid-forming material alternated with alkaline strata. Pods are placed above the

highest anticipated ground-water elevation in the backfill, and usually at least 25 feet away from

the final highwalls and lowwalls and 10 feet from the surface. Potentially acid-forming material
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needs to be rapidly excavated and covered to prevent prolonged exposure of the materials to

oxygen and water.

Cravotta and others (1994a and 1994b) compared the abilities of a dragline versus trucks and

front-end loaders on two areas of the same mine to special handle acid-forming strata. Both

handling methods tended to invert the original rock column. Where loaders were used, pyritic

shale was selectively placed in pods near the final surface, and only low sulfur material was near

the pit floor. On the area mined with a dragline, the overburden with the highest-sulfur content

was placed near the surface, but the sulfur contents for the material at the bottom of the spoil were

higher than they were for the area mined with loaders. A special handling study in Montana with

dragline mining also reported that the overburden profile was inverted (Dollhopf and others,

1977a, 1977b, 1978, and 1979). Both studies compared chemical and lithologic properties of

drillholes in mine spoil to premining conditions.

Improper construction of pods, especially the failure to construct an impervious cap over the top

of the pod, can result in conditions favorable to the formation of AMD. High and dry burial places

pyritic material closer to the surface where atmospheric oxygen is more abundant. This, in

conjunction with percolating precipitation and the high concentrations of pyrite, creates an

environment that can allow the bacteria Thiobacillus ferrooxidans to thrive. Schueck (1998)

found severe AMD formation associated with segregated, but improperly isolated pyritic material. 

Subsequent drilling and ground-water sampling confirmed that the AMD associated with these

improperly constructed pods was more severe than AMD generated elsewhere on the site. In

many cases, the operator confirmed that the pods were segregated acid-forming materials, often

pit cleanings, but that impervious caps were not constructed on top of the pod.

Placement of acidic material into a contour surface mine backfill should fall within a projected

target zone (See Figure 2.4.1d). The bounds of this zone are established by the distance from the

highwall, height above the pit floor, post-mining water table, the depth below the root zone, the

distance from the outcrop, and the distance from reestablished drainageways and various barrier
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Geochemical Controls 2-99

areas. In the example provided in Figure 2.4.1d, a simplistic approach is demonstrated to indicate

the maximum amount of acid material that can be placed in the target zone. 

Figure 2.4.1d: Projected Target Zone Determination for Placement of Acid Forming

Material within the Backfill
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The values used for the Total Mined Area Triangle (TMAT) include:

Maximum Highwall Height 60 feet

Coal Thickness 4 feet

Stripping Ratio 15:1

Landslope 30%

Calculated Maximum Pit Floor Width 200 feet

The values for the Acid Material Target (Area Triangle TMAT) include:

Distance from the highwall 20 feet

Distance above the pit floor 10 feet

Depth below the root zone 10 feet

Distance above the post-mining water table Variable

Away from re-established surface drains Variable

The TMAT square footage value is 6000 feet2 using the maximum pit floor width and highwall

height. The maximum height of the TMAT to which the acid material could be placed (and still

meet the segregation and isolation disposal conditions) is 34 feet on the side nearest the highwall. 

The maximum width of the TMAT is 112 feet. At most, only 32 percent (roughly one third) of the

total mined area can be used for acid material placement. This value will change depending on

highwall height, land slope and placement constraints. As a general rule, as land slope increases,

the size of the target area for acidic material will decrease.

Further reductions in the amount of acidic material placement result from the practicalities of

handling and construction of the top portion of the TMAT. If the material is dumped at the angle

of repose (assumed to be 30E) before being compacted, a portion of the TMAT would not be

available for use during placement. This zone (cross-hatched area in Figure 2.4.4b) represents

about 5 percent of the fill cross section. Under these conditions, no more than approximately 27

percent of the total backfill is available for acidic material placement. This target triangle area for

acidic material placement is not continuous around a hill (along the contour) because of the 

natural drainageways, which occur every few hundred feet in the Appalachian Plateau. Other

obstacles such as gas wells, gas lines, power lines, and houses may further reduce available 
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Geochemical Controls 2-101

placement area, and further limit the lateral extent of placement. A high water table will often

require placement more than 10 feet above the pit floor. Due to these constraints, the acid

material should be less than 20 percent of the material to be backfilled.

Meek (1994) monitored acid production on surface mined areas with segregation and several

different alkaline amendments. Acid load, on an area with segregation, was reduced about 50

percent compared to a control area with no segregation or alkaline addition. 

Phelps and Saperstein (1982) suggested that pods should have a bulk density of 1.1 to 1.5 times

the surrounding spoil to minimize infiltration. These investigators also observed that the highest

spoil bulk densities occurred at 50 to 80 percent depth of spoil for most mining methods. They

suggested that the high density spoil zones should be favorable locations for pods, if hydrologic

requirements are satisfied.

Schueck and others (1996) reported on attempts to grout buried refuse with fluidized bed

combustion ash as a method of isolating pods after the fact. This was done on a site where the

lower Kittanning coal seam was mined and most of the overburden is apparently acid-forming. 

Grout was injected directly into the buried pods to fill the void spaces and directly coat the refuse. 

Grout caps were also constructed over several of the pods. Combined grouting affected only 5

percent of the site but resulted in a 50 to 60 percent decrease in acid concentration in

downgradient monitoring wells.

Short exposure time before burial and reclamation can reduce weathering and acid generation. As

the acid-forming material remains exposed, rocks break down exposing more surface area, and

weathering proceeds to produce acid products along with the subsequent buildup of soluble acid

salts. In practice, potentially acid-forming materials are often stockpiled until enough material to

start pod construction is accumulated. To reduce exposure, some mines in Pennsylvania construct

temporary stockpiles covered with soil and vegetation, or cover the material with lime for

neutralization. 
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When acid-forming material is handled from a cut, the construction of pods should be concurrent

with mining and backfilling. This ensures that acid-forming material is rapidly buried. Rose and

others (1995) reported on experimental test pods where the high-sulfur material was stockpiled for

several months before construction of the pods. Some pods unexpectedly produced very acidic

drainage even though they had been amended with alkaline materials. Delay in construction of the

pods may have allowed significant acid generation to start even before the acid material was

placed in pods. 

Capping: A cap refers to an overlying low-permeability zone created through placement of

compacted, fine-grained soil material (clay), combustion byproducts (fly ash, fluidized bed

wastes), kiln dust, or synthetic (plastic or geotextile) fabric. The cap is significantly less permeable

(at least two orders of magnitude difference) than the surrounding material. Caps inhibit or

prevent the infiltration of water into acidic material from above.

The term liner is normally used in the context of an underlying low-permeability zone created

through placement of an earthen or synthetic material which is at least two orders of magnitude

less permeable than the surrounding units. However, materials used for liner construction can also

be used as a cap over the specially handled pod. Liners restrict or prevent the adjacent and

underlying ground water from encountering the acid-forming material. Caps and liners can also

restrict diffusion of atmospheric oxygen; a key component of acid generation.

A detailed study of special handling at a Montana surface coal mine included the construction of 

a 3-feet-thick clay cap over special handled material (Dollhopf et al., 1977a, 1977b, 1978, and

1979). Construction of the cap required several pieces of equipment, including pans and

bulldozers. Maintaining clay at optimum moisture content for maximum compaction was 

difficult; water sometimes had to be added to the clay material. The region in which the mine 

was located was semi-arid. Cost of special handling with the clay cap was about 1.5 times

"normal" operations due in large part to idling the dragline at certain stages of cap construction. 

An experienced mining engineer was needed on-site to supervise operations and schedule 
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Geochemical Controls 2-103

equipment. Special handled material was maintained in a dry state, and the investigators

concluded that capping was successful. 

Synthetic plastic and geotextile “liners” are a technology borrowed from the waste management

industry. Thick, high-strength plastics of 20, 30, 40 or even 80 mil thickness can be used to isolate

acid-forming material from infiltrating precipitation and ground-water interflow. The liners are

designed to be resistant to a wide range of leachate conditions. They are laid out in sheets with

the seams welded by heat or solvent or stapled. Synthetic liners require a smooth, firm base to

avoid puncture or stretching. A potential area of weakness is the seams which should be joined

properly to avoid leakage or failure. The cost of synthetic liners is high in comparison to other

capping methods. Refuse piles may be amenable to capping with liners due to their engineered

structure and more controlled particle size distribution. Meek (1994) reported that a plastic cap

reduced acid load by about 70 percent compared to no special handling and that a cap was one of

the most effective treatment measures evaluated in that study.

Caruccio and Geidel (1983) used a 20-mil liner at a 40-acre site in West Virginia as an infiltration

barrier. The acid load from two highly acidic seeps was reduced such that the liner would pay for

itself in 6 years. Because of a steep outslope, the liner only covered the flatter, upper portion of

the mined area. Recharge along the outslope area probably accounted for most of the remaining

flow to the seeps.

Earthen materials can be placed and compacted to form relatively impervious-flow barriers. 

Cap thickness is frequently an issue, but a rule-of-thumb from the solid waste industry is a 2-

foot minimum. Little information, directly applied to mining, is available to determine if 2 feet is

adequate. Permeability of a cap is affected by grain size, mineralogy, and moisture content of 

the earthen material, the degree of compaction, and the thickness of the lifts (lifts of 6 inches 

are frequently required). Bowders and others (1994) tested mixtures of flyash, sand, and clay 

as candidate hydraulic barriers in minespoil. They found that a mix of particle sizes and materials

provided the highest packing density and lowest permeability, rather than flyash alone. Hydraulic

conductivity varied about 2 orders of magnitude from 10-5 to 10-7 cm/sec over different 
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2-104 Geochemical Controls

mixes and moisture contents. Rubber tired equipment or a sheepsfoot roller is required for good

compactive efforts. Caps constructed of earthen material can shrink and crack if allowed to dry

out. Caps can also be damaged by differential settlement of spoil, which commonly continues for

over 10 years after backfilling.

Design geometry of the cap may enhance or reduce the volume of water passing through the cap. 

A dome shape tends to "shed" water, while flat caps could impound water. 

Handling of Acid Materials Using the Submergence or "Dark and Deep" Technique

Submergence involves the placement of special handled material below the lowest level of the

water table. This method is expected to exclude oxygen from pyrite and is similar in concept to

sealing and flooding of underground mines to reduce acid generation. Watzlaff (1992) showed that

complete submergence will virtually shut down pyrite oxidation, even with maximum dissolved

oxygen. Submergence or "dark and deep" generally requires a relatively flat area with a thick

saturated zone. A stationary water table helps to produce a near stagnant condition. The

technique is not widely used in Appalachian states because of thin and seasonally variable

saturated zones. It is used in Canada and elsewhere for tailings disposal at hard rock mines

(Fraser and Robertson, 1994; Robertson and others, 1997) and in the Interior Coal Basin of the

United States where thick and stable saturated zones are more conducive to this method.

In Canada, tailings disposal in lakes usually involves water bodies with minimal circulation and

anoxic conditions at depth. Tailings may also be buried on the lake floor by naturally

accumulating sediment and organic debris, providing a further barrier to oxygen. In the US midcontinent, topographic relief is low, water tables tend to be near ground surface, and flow

gradients are small. Surface mining is conducted mainly by area mining methods, and the final cut

is often allowed to flood at reclamation, leaving a relatively deep narrow lake incised into the

terrain.
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Geochemical Controls 2-105

Leach and Caruccio (1991) characterized backfill materials as consisting of three broad hydrologic

zones. The first zone is the vadose (unsaturated) zone or zone of high oxygen concentration. 

Next is the zone of water-table fluctuation with alternately higher and lower oxygen concentration. 

The final zone is saturated, with very low oxygen concentration. Leaching experiments

representing the three zones showed acid load under saturated conditions to be about 5 percent of

that produced in the unsaturated zone. They recommended that acid-forming material should be in

the saturated portion of the backfill to restrict oxidation.

Submergence has not been widely documented as a disposal technique in the Appalachian coal

fields. Perry and others (1997) found that submergence of acid material buried on the pit floor

produced very poor quality drainage at one Appalachian surface mine. In the Interior Coal Basin

of the central United States, flooding of final pits and development of a thick saturated zone

occurs on many sites. The water quality of most flooded last cut lakes is alkaline; some also have

elevated concentrations of dissolved solids and sulfate (Gibb and Evans, 1978). The alkalinity is

due to calcareous bedrock and till. A typical submergence scenario for the Interior Coal Basin is

shown in Figure 2.4.1e.
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Figure 2.4.1e: Schematic of Special Handling of Acid-forming Materials by the

Submergence Technique

Submergence in the Appalachians entails some risk. If post-mining hydrology is not correctly

anticipated, substantially more acid may be generated. Weathering products are leached or

mobilized by flowing ground water. Therefore, it is imperative that the site hydrology be well

understood. Information necessary to characterize the ground-water flow system includes:

C Estimates of ground-water recharge to ensure a permanent and sufficiently thick water table.

C Determination of how isolated the site is hydrologically from adjacent ground-water systems.
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Geochemical Controls 2-107

C Determination of whether the backfill can be constructed to produce a reservoir that will keep

the acid-forming material continually submerged.

This type of disposal during the mining operation should involve handling the acid-forming

material only one time before permanent placement (such as on the pit floor of a previously

excavated pit). 

A possible disadvantage of submergence is that pyrite oxidation may have already begun before

the material is submerged, forming ferric-sulfate salts. This can occur during storage and while

the water table is rebounding. Upon dissolution, these salts release ferric iron that can oxidize

pyrite and sustain acid generation in the absence of atmospheric oxygen. If material handling is

unsuccessful (i.e., the water table is not stagnant or thick enough), resultant drainage problems

can be large scale. This technique might require a relatively long lag time before success/failure

can be determined and large areas can be impacted before the results are known.

Handling of Acid and Alkaline Materials Using Blending Techniques and Alkaline

Redistribution

Blending is the mixing of rocks on a mine site to promote the generation of alkaline drainage. The

term "blending" has been used widely in the past to refer to the mixing that occurs during the

routine mining process. This technique has been recognized since at least the mid 1970s. 

Anecdotal information exists to suggest that it is an effective practice. It can be effective if

sufficient carbonates are present and can maximize the contribution of carbonates by mixing them

with acid-forming rock. This can inhibit oxidation of pyrite as well as neutralize acidity. In

theory, it is possible to blend rocks from virtually any position in the overburden column, but the

actual practice is dependent on the mining method and spoil handling equipment. 

A spoil mixing experiment with dragline mining was conducted in Montana where saline or

 “toxic” overburden was present in varying amounts across a mined area (Dollhopf et al., 1977a,

1977b, 1978, and 1979). Premining distribution and properties of the toxic material were
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determined from overburden analyses. Systematic drilling and sampling of the reclaimed spoil

after mining showed:

C When the toxic material constituted about 5 percent or less of the overburden, the material

was undetectable in the regraded spoil.

C When the toxic material constituted 5 to 15 percent of the overburden, partial to complete

mixing occurred.

C At concentrations greater than 15 percent toxic material, partial mixing occurred.

Special handling and spoil mixing were conducted on this mine primarily to protect the root zone. 

It should be kept in mind that the potential problem was saline overburden, not pyritic overburden. 

Dilution is not always a solution when dealing with pyritic materials. Dilution of pyritic materials

with inert materials frequently does not prevent the formation of AMD. Broadly

disseminating a substantial amount of reactive, acid-forming rock throughout relatively inert

material can allow for widespread generation of AMD.

Alkaline redistribution is a special handling strategy that is used when only a portion of a mine site

contains and large portions are devoid of calcareous materials. Without redistribution or off-site

importation of alkaline materials (alkaline addition), the portions of the site lacking calcareous

materials will produce acidic mine drainage. Examples of sites where alkaline redistribution was

used are given in Case Studies 2 and 5 in Section 2.4.4. 

General considerations for use of alkaline redistribution include:

C Areal distribution of alkaline materials,

C Position of alkaline materials within the overburden section,

C Volume present at the mine site, and

C Calcium carbonate content of the material.
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Location and available volume of alkaline material largely determine the feasibility and

effectiveness of alkaline redistribution. If the material is present as a discrete identifiable unit, it

can be moved as such. However, if the alkaline material is laterally discontinuous, or dispersed

through the column, a plan to isolate and move this material will be difficult to implement.

Alkaline redistribution strategies can include:

C Determining the proportions of alkaline material to be placed on the pit floor, mixed into the

spoil, and added to the spoil/soil interface,

C Determining the methods for incorporating the alkaline material into the backfill,

C Choosing the best pit orientation to minimize haulage of the alkaline material,

C Designing a multiple pit operation to facilitate redistribution of alkaline material, and

C Ripping the pit floor to expose alkaline material (when present) beneath the coal.

Actual implementation of alkaline redistribution generally requires the use of rock trucks, since the

alkaline amendment is not an integral part of coal overburden removal. The amount of alkaline

amendment per acre is calculated via overburden analysis and mass balance equations.

Operational Considerations

When special handling is part of the mine plan, keeping the pit clean (e.g., removing pit cleanings)

and quickly covering acid-forming strata are simple and important activities to reduce the potential

for acid production. Removing pit cleanings, will ensure that any ground water that reaches the

pit floor will encounter reduced amounts of potentially acid-forming material.

Equipment availability is an important consideration in the development of the special handling

plan. If the proposal is to move discrete rock units, a truck-shovel operation may be necessary. 

In addition, if two pits are open at once, a truck-shovel operation facilitates the movement of

overburden from one pit to another. However, if large sections of strata are to be removed, a

skilled dragline operator may be required.
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If an alkaline stratum lies adjacent to a potentially acid-forming stratum, the strata may become mixed

without additional effort during the overburden removal operation, and separation of the potentially

acid-forming strata may not be needed.

Generally an excess of neutralizers dispersed throughout the overburden profile is necessary to offset

both acid production and imprecise mixing. A simple blending plan is shown in Figure 2.4.1f.

Figure 2.4.1f: Blending and Alkaline Redistribution Do Not Require the Isolation of Acidforming Materials in Isolated Pods
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Geochemical Controls 2-111

2.4.2 Verification of Success or Failure

A critical step in successful special handling is to ensure that the special handling plan is properly

implemented. It may be necessary to periodically perform additional testing of the overburden to

assure that the proper material is being handled.

Inspections by the regulatory agency, of sites with special handling as a BMP, should be frequent

and detailed enough to document compliance with the mining plan. An inspection implementation

checklist identifying key aspects of the plan will be useful.

Implementation Checklist

Recommended items to be considered during the permit review process include:

C The overburden data should be sufficient enough to identify which strata will require handling.

C The overburden data should be sufficient enough to provide representative sampling for the

mine. This will typically require multiple bore holes and appropriate vertical sampling.

C Plans should be clearly designed with appropriate maps, cross-sections and narrative.

C Plans should be feasible in the field and not just on paper. For example, the strata to be special

handled should be easily identifiable in the field.

C The plan should be enforceable.

Recommended items to consider in a special handling implementation inspection checklist 

include:

C Field implementation should correspond with the plans in the permit application (e.g,

agreement with the permit maps, cross-sections and narrative)

C The appropriate equipment should be available.

C The blasting method should be appropriate.
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C The material to be special handled should be identifiable in the field by the equipment

operators.

C The water monitoring data should be submitted.

2.4.3 Case Studies

Case Study 1

Cravotta and others (1994b) compared the distribution of sulfur and neutralization potential in

undisturbed overburden strata (Figure 2.4.4a) with the post-mining redistribution of these

parameters in the disaggregated mine spoil (Figures 2.4.4b and 2.4.4c) for two mining methods. 

The mine site studied was a reclaimed surface mine on two adjoining hilltops in Clarion County,

Pennsylvania. The southern area was mined with a 45 yd3 dragline. The northern area was mined

with bulldozers and front-end loaders, which selectively handled the high-sulfur strata near the

coal.
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Geochemical Controls 2-113

Figure 2.4.3a: Distribution of Sulfur and Neutralization Potential for Bedrock at the

Special Handling Site in Clarion County, PA. (Drill logs are to scale. 

Most sample intervals for N1-0 are five feet.)
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The original plan for the 16-acre northern area called for placing the high-sulfur rock in pods 10

feet above the pit floor, with low-sulfur material placed between the pods and the pit floor. Drill

holes N2-0 and N2-2, located 5 feet apart, encountered one of the specially handled pods. The

other drill logs show that mining, in general, inverted the high-sulfur (>0.5 percent) material and

located it near the spoil surface. Most logs show low-sulfur (<0.15 percent) material near the pit

floor. Maximum saturated thickness of spoil in the northern area was 18 feet and in the area of

N2-0 the saturated thickness was 10 feet. The spoil sulfur data and spoil water level data suggests

that the high-sulfur spoil was successfully placed above the water table within the northern area. 

The permit specification for placement 10 feet above the pit floor, however, would have been

inadequate to keep the high-sulfur material above the spoil water table.

Spoil in the 34-acre southern area was also inverted, with the highest sulfur rock predominantly in

the upper part of the spoil. The sulfur in the lower part of the spoil is typically between 0.25 and

0.4 percent, higher than typical on the northern area where the spoil was selectively handled. The

highest saturated thickness in the spoil was about 20 feet. Thus the highest sulfur material in the

southern area was also placed above the water table.

Spoil handled by bulldozers and loaders can be expected to have a more uniform particle-size

distribution, exhibit similar or greater compaction, and exhibit lesser hydraulic conductivity than

that handled by the dragline (Hawkins, 1998; Phelps and Saperstein, 1982; and Phelps, 1983). Air

circulation commonly was lost in shallow spoil during air rotary drilling in the dragline-mined

southern area. However, no air losses occurred in the bulldozer-mined northern area, suggesting

greater compaction and more uniform particle size distribution from bulldozers and loaders than

from a dragline. Nonetheless, hydraulic conductivities for saturated mine spoil were similar

among the two areas. For saturated spoil, median hydraulic conductivities were 10-3.8 to 10-3.6 m/s

in each area. The similarity in hydraulic conductivities could result from similar lithologies, and

piping and settling processes (Hawkins, 1998, and Pionke and Rogowski, 1982) by which fines

are transported downward and large voids fill or collapse. Mine spoil in the southern area is

several years older than that in the northern area, so a longer time has elapsed for these processes

to occur.
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Geochemical Controls 2-115

Figure 2.4.3b: Distribution of Sulfur and Neutralization Potential for Spoil in the

Northern Hilltop Where Bulldozers and Loaders Were Used (Note the

“pod” of selectively handled high sulfur material in N2-0 and N2-2.

Sample interals are five feet.)
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Figure 2.4.3c: Distribution of Sulfur and Neutralization Potential for Spoil in the

Southern Hilltop Where a Dragline was Used (Sample intervals are five

feet.)

Alkalinity, sulfate, iron, and manganese concentrations in the spoil ground water produced by the

selective-handling method was similar to that in spoil produced by the dragline method. Median

values for alkalinity of ground water in the saturated zone were between 100 and 400 mg/L. 

Sulfate ranged from 600 to over 1000 mg/L (Cravotta and others, 1994b).
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Geochemical Controls 2-117

Case Study 2 (West Virginia)

Skousen and Larew (1994) describe the redistribution of alkaline material from separate but

adjacent mine sites. Calcareous rock was hauled from a mine extracting Bakerstown coal to a

mine on the upper Freeport coal. Alkaline redistribution consisted of placement of about 3 feet of

calcareous shale on the pit floor, partial backfilling, then placement of acidic material about 20 feet

high in the spoil, followed by capping with more calcareous shale. A pre-existing, mildly acidic

discharge (acidity about 75 mg/L CaCO3) was ameliorated and made alkaline.

Case Study 3 (Clearfield Co., PA)

A cementitious cap constructed of fluidized bed combustion (FBC) ash mixed with waste lime has

been placed on a 97 acre reclaimed mine site in Clearfield County, Pennsylvania. Hellier (1998)

reports on the successful efforts of the operator. Surface mining on the lower and

middle Kittanning coal seams began in the 1940s on this site. Upon completion of the mining in

1991, the operator was required to pump and treat an acidic post-mining discharge. Treatment

costs threatened to bankrupt the operator. Most of the mining on the site predated special

handling techniques. The operator removed the top 3 feet of material and spread a 3-feet layer of

FBC ash mixed with 10 percent waste lime. Water was added to increase the moisture content. 

The ash/lime mixture hardened to form a low-strength cement. The top material was then

replaced and revegetated. The cap served to inhibit infiltration, which was thought to be the

primary source of water at this site. The cap would also inhibit oxygen from entering the backfill. 

At 80 percent completion, the operator no longer has to provide chemical treatment, pumps

significantly less water, and the chemistry of the water remaining in the backfill has improved. A

passive treatment system, which is in place, is adequate to mitigate the reduced flows of AMD.
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Case Study 4 (Green Co., PA)

A mine in Greene County, Pennsylvania produced both alkaline and acid water on two segment

phases (Perry and others, 1997). The two segments had similar geology and hydrology, and were

mined by the same company. Alkaline drainage was produced on the segment where mining was

completed without stoppage and where a special-handling plan was followed. Acidic drainage

was produced from the Phase 2 segment where mining ceased for an extended period before the

site was completely reclaimed. The poor quality drainage on the Phase 2 segment was attributed

to weathering of partly reclaimed material during mining cessation and poor adherence to the

special handling plan. Median water quality data for the two sites is summarized in Table 2.4.4a.

Table 2.4.3a: Summary Water Quality for Greene County Site Phases 1 and 2

Monitoring Point pH Net Alkalinity 

(mg/L CaCO3 Eq.)

Total Fe

(mg/L)

Total Mn

(mg/L)

Sulfate

(mg/L)

Phase 1, Mining 6.5 176 0.3 6.5 606

Phase 2, Mining 3.6 - 488 71.4 105 2233

Phase 1, Post Mining 7.2 151 1.88 16.35 1197

Phase 2, Post Mining 4.0 - 128 18.7 62.7 1770

Case Study 5 (Westmoreland Co., PA)

A mine in Westmoreland County, Pennsylvania used alkaline redistribution to amend a portion of

the site that was deficient in carbonate-bearing rocks. Acid-forming materials were laterally

continuous and had 0.5 to over 2 percent total sulfur. A zone of calcareous materials, with

carbonate content exceeding 20 percent, was present over a small area of the site. Special

handling consisted of moving excess calcareous strata from the upper end of the mine and

redistributing it in the alkaline deficient areas. Three pits were operated simultaneously. 

Operations were timed so alkaline material was available and cut and fill balances could be

maintained. Material placement and backfilling included crushed limestone on the pit floor,
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Geochemical Controls 2-119

“neutral” spoil backfill, placement of potentially acid material in lifts covered by more “neutral”

spoil, and finally topsoil.

Wells and springs have been monitored for four years after reclamation at the alkaline

redistribution site (Table 2.4.4b). In Well MW-6 (located downgradient of the site), median

sulfate concentration decreased by approximately 70 percent, and net alkalinity rose above zero

after reclamation was completed. MP-10 (a spring located downgradient of the mine) is

representative of shallow ground-water conditions and contains negligible alkalinity. Overburden

rocks in the recharge area for MP-10 and well MW-6 were likely acid forming. Post-mining water

quality for MP-10 and MW-6 show a small but significant increase in net alkalinity. Sulfate

concentrations indicate a lesser amount of oxidation and leaching is continuing within the spoil.

Table 2.4.3b: Summary of Water Quality Conditions, Alkaline Redistribution Site

Monitoring Point pH Net Alkalinity 

(mg/L CaCO3 Eq.)

Specific

Conductance

(umhos/cm)

Sulfate

(mg/L)

Total Fe

(mg/L)

MW-6, Mining 6.1 - 8 855 398 0.15

MW-6, Post Mining 6.1 24 404 115 1.5

MP-10, Mining 6.5 6 N/A 19.5 0.04

MP-10, Post Mining 7.1 20 280 90 0.09

Key factors influencing post-mining water quality are the redistribution of calcareous rock to

alkaline-deficient areas, and rapid completion of mining and reclamation. Responses in water

chemistry are attributed to placement of acid-forming materials above the water table to minimize

leaching, while the calcareous rocks are dissolving and producing alkalinity.
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Case Study 6 (EPA Remining Database, PA(10))

The PA(10) is also discussed in Section 1.1.4, Case Study 3. This site included the following

BMPs: regrading of abandoned spoil, alkaline addition, hydrologic controls, revegetation and

scarification of the calcareous pavement, and application of bactericides. The only calcareous

stratum was the underclay beneath the lowest coal seam. There was a significant amount of high

sulfur rock above the coal. To counter the lack of calcareous rock above the coal, the coal

company proposed scarifying the pit floor (to expose the calcareous underclay) and a negligible

alkaline addition rate of 3 tons/acre (applied to the spoil surface). Bactericide was added to

prevent oxidation of pyrite through the retardation of the pyrite-oxidizing bacteria. Scarifying of

the underclay is the form of special handling implemented at this site.

This site is one of only a handful of remining sites in Pennsylvania that have resulted in poorer

post-mining water quality (see Section 1.1.4, Case Study 3). Several factors may have worked

together to contribute to poor water quality. Failures have been observed at other, non-remining

sites, where the bulk of the alkaline material was located on the pit floor (Smith and Brady, 1998). 

Scarifying may not have broken the rock sufficiently to allow for exposure of adequate surface

area of the calcareous strata. Perhaps this plan would have been more successful if the calcareous

material had been mixed through the spoil. 

2.4.4 Discussion

Despite years of implementation, few studies of special handling and its effect on post-mining

water quality have been performed. Special handling is almost always used in conjunction with

other BMPs, thus separation of the effects of special handling alone is often not possible. For 

sites lacking calcareous strata, special handling alone will not create alkaline water. For this

reason, special handling is often combined with alkaline addition. For a site to be a remining site,

the area has to have been previously affected by mining. This previous mining and the type of

associated remining is of three types: deep mining and subsequent daylighting, strip mining and

subsequent regrading and revegetation, and coal refuse removal and subsequent regrading 
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Geochemical Controls 2-121

and revegetation. Thus remining sites with special handling do not occur without one of these

additional BMPs.

Special handling methods fall into four categories: 1) blending, 2) high and dry, 3) dark and deep,

and 4) alkaline redistribution. Blending is generally used where both calcareous and acidproducing rocks occur within the stratigraphic column. Mining is done in such a way as to blend

the two materials together such that AMD should be prevented. “High and dry” and “dark and

deep” are intended to limit the amount of water and oxygen in contact with the special handled

material, respectively. Limitation of water will be most effectively accomplished if the surface of

the special handled pod is sloped to achieve ground-water runoff, the pod is capped with a low

permeability material, and the material is placed above the post-mining water table (“high and

dry”). Limitation of oxygen can probably only realistically be achieved by submergence below the

water table (“dark and deep”). Alkaline redistribution is used where calcareous materials occur on

only part of a site. Excess alkaline material is redistributed to the portions of the site lacking

alkaline materials. 

Benefits

C Blending of calcareous material in the spoil has the advantage of being accomplished during

the regular course of mining.

C Dark and deep (i.e., submergence below the water table) has the benefit of limiting oxygen

available for pyrite oxidation.

C Alkaline redistribution results in calcareous rocks being distributed to parts of the mine where

they did not occur naturally, thus providing the benefits inherent in calcareous rocks.

C High and dry, if material is capped and placed above the water table, should reduce the

transport of pyrite-weathering products.

Limitations

C Blending is only effective if the calcareous material is can be adequately mixed in the spoil.
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2-122 Geochemical Controls

C Sites that can satisfy the requirements for “dark and deep” do not always exist in the

Appalachians due to thin saturated zones and fluctuating water tables.

C High and dry technology has been inadequately studied and some of the studies are

inconclusive. Without capping and proper placement it may be ineffective. The post-mining

hydrology should be well understood.

Efficiency

Blending is the most common handling method, but is not strictly “special handling” because it

does not require additional selective handling of materials and is accomplished as part of the

routine mining process. The many sites in the Appalachians that have compliant post-mining water

quality demonstrate its success. The key is to have sufficient calcareous strata present. The

success of this method is probably reflected in the fact that mines that had regrading and

revegetation as their only BMPs (Section 6.0, Table 6.3g) had 50 percent of discharges improve in

acidity load, with the other 50 percent remaining unchanged. As discussed in Section 6, remining

operations in the Pennsylvania Remining Site Study (Appendix B) that implemented these minimal

BMPs, probably contained better overburden quality than many of the sites that employed multiple

BMPs. 

The effectiveness of high and dry placement is not as clear. Studies that have been performed 

are few and some are inconclusive. High and dry is the most commonly used special handling

method in Pennsylvania, and it can be assumed that most of the sites listing special handling as a

BMP in the Pennsylvania Remining Site Study were using this method. Data from this study 

were used to predict the effectiveness of special handling for improving water quality during

remining operations. Section 6.0, Table 6.3a shows special handling can be predicted to result in

slightly lower water quality improvement in regards to acidity loading than can be predicted if no

BMPs are implemented. Section 6.0, Table 6.3g provides some different insight into the

effectiveness of special handling. Special handling in conjunction with the minimal BMPs of

regrading and revegetation, resulted in the same effectiveness rating as did the combination of

regrading and revegetation alone. As other BMPs were added (regrading, revegetation, special
Coal Remining BMP Guidance Manual

Geochemical Controls 2-123

handling, plus other BMPs), efficiency generally declined, with less discharges showing

improvement in acidity load. This is probably due to the presence of greater amounts of acidproducing overburden and/or lesser amounts of calcareous overburden, with the additional BMPs

added to offset the effects of the poorer overburden. 

When deep mines are daylighted, there is often acidic material that requires special handling. This

acidic material is typically unrecoverable coal and roof-rock. Section 6.0, Table 6.3m compares

the implementation of daylighting alone to seven other BMP combinations. Four of these seven

BMP combinations involve special handling. Three of the four resulted in a higher percentage of

discharge water quality improvement than daylighting alone. Two of these three successful BMP

combinations included the addition of alkaline materials. The fourth BMP group included a

combination of five BMPs that routinely produced the poorest results. It is suspected that this is

because additional BMPs were implemented in an attempt to counter poor quality overburden. 

The dark and deep method of special handling has been shown to be a good means of AMD

prevention. Its usefulness in the Appalachians, however, is often limited because of a thin

saturated zone and a fluctuating water table that allows the acidic material to be exposed part of

the year. The effectiveness of dark and deep cannot be evaluated using the Pennsylvania data

because it is used so seldom.

Alkaline redistribution has had a high degree of success. Evaluation of the Pennsylvania data

(Section 6.0 and Appendix B) suggests that alkaline redistribution has been a very successful

special handling practice. Section 6.0, Table 6.3a shows that the predicted odds for improvement

of acidity load when alkaline redistribution is used is eight times greater than when no BMPs are

implemented. The only other BMP that gave a greater odds of improving discharges was mining

of alkaline strata (nearly 19 times greater than when no BMPs are implemented). 

Special handling by itself may reduce acid production, but it can not produce alkalinity in the

absence of calcareous materials. Special handling in conjunction with alkaline addition or other
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2-124 Geochemical Controls

means of incorporating alkaline strata can result in better water quality than using special handling

alone.

2.4.5 Summary

C Special handling practices used in the Appalachians include: blending of acid and alkaline

materials, the segregation and isolation of acidic materials (high and dry), and alkaline

redistribution.

C Special handling is often used in conjunction with other BMPs such as management of ground

water and alkaline addition. 

C Submergence (dark and deep) is seldom used in much of the Appalachians because the

saturated thickness of the water table is generally thin and the water table can undergo large

seasonal fluctuations.

C Special handling in the absence of alkaline materials cannot produce alkaline drainage.

C Special handling often involves both acid and alkaline materials and may also include clay

materials for capping and lining pods of acidic materials.

C Special handling is most effective in conjunction with other BMPs such as alkaline addition

and surface- and ground-water management techniques.

C Alkaline redistribution and mining of high-alkaline strata (which often involves special

handling) have been very successful in improving post-remining water quality.

C The volume of the material to be special handled should generally be less than 20 percent of

the mine backfill volume because of the need to keep acidic materials away from the surface,

water table, highwalls, etc.
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Geochemical Controls 2-125

C Special handling is not necessary on all mine sites.

C Identification and segregation of acid material is extremely difficult if multiple zones exist in

the stratigraphic section, unless these zones are persistent laterally and vertically, of uniform

thickness, and distinctive in appearance.

C Special handling requires that the proper earth-moving equipment be used at the mine site.

C Monitoring during and after mining is necessary to evaluate special handling techniques.
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Geochemical Controls 2-127

2.5 Bactericides

Introduction

Bacteria can play an important role in pyrite oxidation. They can cause pyrite to oxidize at a

much faster rate at low oxygen levels than would occur in the absence of bacteria under the same

conditions. Bactericides attempt to block the catalytic effects of certain bacteria on the pyrite

oxidation process. 

Theory

Pyrite-oxidizing bacteria, in particular Thiobacillus ferrooxidans, are responsible for the increased

oxidation of pyrite over what would occur abiotically (Figure 2.5a), especially at low oxygen

concentrations. Although numerous bactericides have been tested against pyrite-oxidizing

bacteria, the bactericides of choice for mine sites have been anionic surfactants. These

bactericides occur in household cleansers and soap products. At near-neutral pH these surfactants

generally are considered to be poor bactericides, but they are markedly more inhibitory at low pH

(Kleinmann, 1998). T. ferrooxidans has a near-neutral pH internally, but it can exist in low pH

conditions (in fact, the conditions that it creates by oxidizing pyrite) because of a coating that

protects the cell from the externally low pH environment. Anionic surfactants dissolve the

protective coating, thus subjecting the bacteria cell to low pH conditions, conditions under which

it can not survive unprotected. 
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2-128 Geochemical Controls

Figure 2.5a: Rates of Pyrite Oxidation with and without Iron-oxidizing Bacteria (In small

columns maintained at different oxygen partial pressures) (Hammack and

Watzlaf, 1990).

The amount of oxygen present within the pore gas of mine spoil or coal refuse is an important

factor when considering the use of bactericides. Figure 2.5a shows pyrite oxidation rates under

biotic and abiotic conditions. At oxygen levels of approximately 14 percent, biotic and abiotic

rates are about equal. Below oxygen levels of 14 percent, pyrite oxidation rates are considerably

slower when bacteria are absent. In the presence of bacteria, pyrite oxidation can be significant

even at oxygen concentrations as low as one percent. Thus bactericides are most advantageous

where oxygen concentrations are low. 

Bactericides have a limited period of effectiveness, and typically are only effective for up to four

months. This limitation can be compensated for by repeated application or by application of timerelease pellets.
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Geochemical Controls 2-129

Cations such as calcium and magnesium can cause water "hardness" which can reduce the

effectiveness of surfactants in much the same way that hardness reduces the effectiveness of soap.

Calcite and dolomite, which contain calcium and magnesium, are common minerals in coal

overburden. Kleinmann (1999) felt that this surfactant inhibition would be greatest with highlysoluble neutralizers such as quick lime (CaO) and hydrated lime (CaOH2

). Something to keep in

mind is that bactericides in-and-of-themselves do not produce alkalinity, and compounds that

produce alkalinity frequently contain calcium and magnesium which may inhibit the effectiveness

of bactericides. That is, the minerals that result in acid neutralization can retard the effectiveness

of bactericides. 

Site Assessment

The initial site assessment for bactericides is similar to that for other geochemical BMPs. First,

the acidity- and alkalinity-generating potential of the site should be determined by evaluating

overburden and water-quality data. If the site has little or no potential to produce acidity,

bactericides are not necessary.

Kleinmann (1998) points out that application rates of anionic surfactants are site-specific, and

heavily dependent on the adsorptive capacity of the material being treated. He suggests that pilotscale field tests in plastic 55-gallon drums be used to determine the adsorptive properties of the

surfactant. He cautions that small test piles may not accurately simulate larger sites because of

higher oxygen concentrations in the small piles (Kleinmann, 1998). Determination of the amount

of adsorption is important to assure that there will be adequate bactericide available to combat the

bacteria on the surfaces where it is needed.

It is important to estimate the oxygen concentration in the mine spoil or coal refuse. For

bactericides to be effective the oxygen concentration should be relatively low (<10 percent). 

Most experiments with bactericides have been done on compacted coal refuse. This material,

because it is compacted (and often contains a high percentage of fine materials) can have low

concentrations of oxygen. The use of bactericides at surface coal mines is potentially less

effective because of likely higher concentrations of oxygen. If oxygen levels are high (>10
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2-130 Geochemical Controls

percent) there may be very little benefit from bactericides because abiotic pyrite oxidation is

sufficient to create significant amounts of acid. 

Spoil pore gas oxygen concentrations can be related to the type of rock that was mined, or

disposed of (in the case of coal refuse). Some examples of oxygen levels in pore gas, which can

serve as guidelines, are given below in the literature review/case study section. 

Site evaluation should include assessment of:

C the acid-producing potential of the site

C the adsorptive capacity of the overburden

C prediction of the percent oxygen in spoil or coal refuse pore gas

2.5.1 Implementation Guidelines

The following guidelines are recommended for application of bactericides:

C Surfactants should be targeted to treat unweathered acid-forming material, such as coal

refuse, that can be quickly buried.

C They should be applied at a rate higher than the rate they are adsorbed by the rock.

C They should not be applied to soils if the intention is to treat spoil, because soils will

adsorb the surfactant leaving little to act on the underlying spoil.

C They are probably only effective where oxygen content is low (< 10 percent), thus an

estimation of pore gas oxygen should be made.

C Surfactant solutions can be applied to acid-producing materials prior to their disposal. 

Time release pellets can be mixed with the spoiled material. Both methods may be needed

for long-term effectiveness. If used in solution form, the surfactant may need to be

applied 3 to 4 times per year.

C Carbonate content may also be important. Kleinmann (personal communication, June 28,

1999) says that high calcium water can inhibit the effectiveness of some anionic

surfactants. More soluble neutralizers such as hydrated lime and quick limes are most
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Geochemical Controls 2-131

problematic. Essentially calcium can cause hard water and inhibit the effectiveness of the

surfactant. 

2.5.2 Verification of Success or Failure

As with all BMPs, bactericide application should be implemented as described in the plans. 

Means of documentation include:

C Engineer's certification and increased inspection frequency to verify that the bactericide

was implemented as planned

C Photographs of the bactericide application

C Locations of bactericide applications being accurately recorded through surveying or

global positioning systems

C Verification of the amount of bactericide used by submittal of receipts.

C Laboratory analyses of the acid-forming materials to assure proper placement of

bactericides

C Water-quality monitoring for flow and concentration of mine drainage parameters and

bactericide.

Monitoring of water quality and flow, as well as accurate documentation of implemented plan,

will allow for future improvements in design and determination of the efficiency of bactericides.

2.5.3 Literature Review/Case Studies

There are a variety of substances that can inhibit pyrite-oxidizing bacteria, but Kleinmann (1998)

states that only anionic surfactants proved to be cost effective. Kleinmann tested, in the

laboratory, the relative effectiveness of three anionic surfactants in preventing acid formation. He

found sodium lauryl sulfate (SLS) to be the most effective (Figure 2.5.3a). Higher concentrations

of the other surfactants were required to get the same effect.
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Figure 2.5.3a: Effect of Anionic Detergents on Acid Production from Pyritic Coal. 

(SLS = sodium lauryl sulfate, ABS = alkyl benzene sulfonate, AOS =

alpha olefin sulfonate) (from Kleinmann, 1998).

As mentioned earlier, an important consideration as to the effectiveness of bactericides is pore gas

concentration of oxygen. Oxygen concentrations in pore gas have been measured for refuse

material and for surface mines. Guo and Cravotta (1996) reported oxygen concentrations with

depth for two surface mines in Pennsylvania (Figure 2.5.3b). Mine 1 contained predominantly

shale/siltstone overburden and Mine 4 contained predominantly sandstone overburden. Mine 1

shows significant decreases in oxygen with depth, with concentrations as low as 2 to 4 percent at

11 meters. By contrast, oxygen was never below 18 percent at Mine 4, even at depths of 17
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Geochemical Controls 2-133

meters. This is probably due to the blocky nature of the sandstone which allows more atmospheric

exchange than the smaller-sized rubble resulting from shale/siltstone. 

Figure 2.5.3b: Measured Profiles of Oxygen in Unsaturated Spoil (after Guo and

Cravotta, 1996) (At Mine 1 gas transport is by diffusion and at Mine

4 it is by convection. Mine 1 has shale/siltstone overburden and Mine

4 has sandstone overburden.)

Erickson and Campion (1982) report on oxygen concentrations with depth in coal refuse for sites 

in Pennsylvania and Ohio. The results of their measurements are shown in Figure 2.5.3c. All gas

probes were installed at less than one meter deep. Three of the four plots show similar declines in

oxygen concentration with depth (PA Fine, OH 3 and OH 4). The "PA Course" refuse had

substantially higher oxygen concentrations at a depth of 36 cm than did the other refuse. The

courser nature of the refuse apparently allowed for greater exchange with the atmosphere.
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2-134 Geochemical Controls

0 5 10 15 20 25

Percent Oxygen

0

20

40

60

80

100

Depth (cm)

PA Fine

PA Course

OH 3

OH 4

Figure 2.5.3c: Oxygen Concentration with Depth in Coal Refuse in Pennsylvania

and Ohio.

The course refuse had less than 1 percent oxygen at less than 1 meter, whereas oxygen

concentrations in surface mines had 12 percent and greater at one meter depth. At 7 meters, the

surface mines had at least 4 percent oxygen, even where the overburden was shale (a rock that

breaks into small sizes). There are a couple of explanations for these results. First, coal refuse is
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Geochemical Controls 2-135

generally composed of highly pyritic material that will consume and deplete oxygen near the

surface. Surface mine spoil, by comparison, is lower in sulfur and oxygen consumption is not as

great. Second, coal refuse is typically finer-grained and more compacted than mine spoil. This

permits less oxygen exchange between the pore gas and the atmosphere.

Case Study 1 (Preston Co., WV) (Kleinmann and Erickson, 1983)

This site was an 8-acre active coal refuse disposal area. Because the area lacked background

water quality data, a pond was constructed to collect runoff for monitoring purposes. Adsorption

tests indicated that an application rate of one 55-gallon drum of 30 percent SLS would be needed

per acre. The bactericide was diluted with water by a factor of 50:1. A larger dilution factor

would have been preferred, but good-quality water was limited. 

Water quality improved dramatically within a month of the SLS application. Acidity, sulfate and

iron were reduced by 95 percent and remained low for approximately four months following

application (Figure 2.5.3d). A complicating factor with this study was that coal refuse not treated

with bactericide was added during the study period. It is thus impossible to separate out whether

the increases in acidity starting at 120 days was due to this untreated refuse or diminishing effects

of SLS.
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Figure 2.5.3d: Effect of Sodium Lauryl Sulfate on Runoff Water Quality at an 8-acre

Active Coal Refuse Pile in Northern West Virginia (Application rate: 

55 gal/ac of 30 percent solution, diluted 50:1 (Kleinmann and

Erickson, 1983))

Effluent concentrations of surfactant remained extremely low (consistently less than 0.1 mg/L)

throughout application with none being detected in the receiving stream.

Case Study 2 Ohio (Kleinmann, 1998)

This site provides a long-term evaluation of bactericide application to a refuse pile. The initial

field test was conducted in 1984 by the Ohio Department of Environmental Resources. A 2.5
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Geochemical Controls 2-137

acre area was treated with SLS and an adjacent 2.2 acre area served as an untreated control. SLS

was applied in solution at a rate of 200 lbs/acre and as pellets composed of a rubber matrix at a

rate of 500 lbs/acre (containing 16 to 28 percent SLS). Both areas were covered with 6 to 8

inches of topsoil which was fertilized, limed, seeded and mulched.

Five years after reclamation, biomass production on the treated area was 9 times greater than the

untreated area. Acidity in the vadose zone in the treated area was 80 percent lower than in the

untreated area. After 10 years, 35 to 40 percent of the control area was barren and eroding,

whereas the treated area showed no significant erosion and the vegetative cover was dense.

Case Study 3 West Virginia (Skousen and others, 1997)

A 35-acre coal refuse pile was first regraded. Controlled release surfactant pellets were applied to

the surface, which was then topsoiled, limed and revegetated. The treated area had a pH of 6.2

compared with a pH of 2.9 in a 1.2-acre untreated control area. Acidity was as low as 1 mg/L

compared to 1680 mg/L, and reductions in iron and manganese were equally significant.

Case Study 4 Ohio (Skousen and others, 1997)

Bactericides were applied to an abandoned surface mine that was poorly vegetated. The

application was in the form of slow-release pellets that were spread by a hydroseeder. The

overburden was predominantly sandstone with abundant pyrite. Seeps with acidity of 1000 to

3000 mg/L have remained acidic, showing little sign of improvement.

Case Study 5 Appendix A, EPA Coal Remining Database (PA (10)), Somerset Co., PA

Details on the specifics of this site are presented under Section 1.1 Case Study 3 in regards to

Control of Infiltrating Surface Water. Multiple BMPs were implemented at this site including

surface regrading, scarification of calcareous pavement (seat rock), alkaline addition, hydrologic
Coal Remining BMP Guidance Manual

2-138 Geochemical Controls

controls, and bactericides. The bactericides were applied in the form of time release pellets on the

spoil surface prior to spreading of topsoil.

Two of four seeps have had increases in acid and sulfate post-mining loads compared to baseline

loads. The other two seeps show no significant statistical difference in load. In all cases the

concentrations of acidity have increased. 

Case Study 6 Remining Database VA (4), Wise Co., VA

A blend of polymers and a bacteria inhibiting agent were formulated to retard acid soil formation. 

The bactericides were used as part of a plan to reduce the thickness of topsoil from four feet to

one foot. In addition to bactericide use, the topsoil was limed, seeded, fertilized and hay mulched. 

Erosion control blankets were applied to reduce erosion and to protect the seed. Tree seedlings

were planted on slope areas. Vegetation remains successful after more than a decade. 

2.5.4 Discussion

The literature review and case studies suggest that bactericides have been successfully used on

fresh (unweathered) coal refuse to inhibit pyrite oxidation (Case Studies 1, 2 and 3) and for

revegetation purposes (Case Studies 2 and 6). Case Studies 4 and 5 concern application of

bactericides at remining sites, and in both cases the water quality was not improved. This lack of

improvement at remining sites containing abandoned surface mines may be due to the high oxygen

concentrations present in spoil pore gas, the large volume of material that needs to be treated, and

adsorption of much of the bactericide on non-acidic rock. An additional complication with

surface mines is that calcareous strata or alkaline amendments may cause water hardness that can

decrease the effectiveness of bactericides.

Bactericides are regulated under the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA). 

Only bactericides registered under FIFRA can be legally used.
Coal Remining BMP Guidance Manual

Geochemical Controls 2-139

Benefits

C Can inhibit pyrite oxidation in low oxygen environments

C Can assist in revegetation efforts by acting as a wetting agent.

Limitations

C Limited to low oxygen environments, such as coal refuse disposal

C The bactericide will be adsorbed onto rock and soil, thus an excess should be applied

C Bactericides have a limited period of effectiveness and should continually be replenished

C Works best on fresh materials

C Limited by the presence of certain cations (Ca, Mg)

Efficiency

Not enough data regarding the application of bactericide is available for statistical analysis. 

However, review of the case studies cited above allows for some tentative efficiency statements to

be made:

C Bactericides appear to have successfully reduced acidity at active refuse piles where it can

be applied directly to fresh refuse.

C Very few studies exist for surface coal mines. The two case studies cited above were not

successful. This may be due to oxygen availability in surface mine spoil. Another

complicating factor is "hard water," due to the high concentration of calcium and

magnesium. Much of the bactericide may be adsorbed on non-acid-producing rocks, thus

diminishing its availability for acid-producing rocks 

C Can be effective for enhancement of revegetation efforts by acting as a wetting agent
Coal Remining BMP Guidance Manual

2-140 Geochemical Controls

2.5.5 Summary

As a remining BMP, the evidence to date does not support the use of bactericides for prevention

of acid water on surface coal mines. It appears, however, that bactericides have assisted in

enhancement of revegetation efforts and bactericides have successfully reduced acid production

from active coal refuse piles.

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Stehouwer, R.C., D.A. Kost, J. P. Vimmerstedt, J.H. Beeghly, 1999. Reclamation of acidic coal

minespoils using flue gas desulfurization by-product and sewage sludge. In: Proceedings 13th

International Symposium on Use and Management of Coal Combustin Products (CCPs), Vol. 3,

January 11-15, 1999, Orlando, FL American Coal Ash Assoc and EPRI, Palo Alto, CA, paper 76.

Tarantino, J.M. and D.J. Shaffer, 1998. Planning the overburden analysis. Chapter 5 of Coal

Mine Drainage Prediction and Pollution Prevention in Pennsylvania, PADEP, Harrisburg, pp. 5.1-

5.8.

Waddell, R.K., R.R. Parizek, and D.R. Buss, 1986. Acidic Drainage Abatement Through

Surficial Application of Limestone Quarry Waste and Limeplant Flue Dust, Jonathan Run, Centre

County, PA. Proceedings 7th Annual West Virginia Surface Mine Drainage Task Force

Symposium, 45 p.

Webster, R. and Burgess, T. M., 1984. Sampling and bulking strategies for estimating soil

properties in small regions. Journal of Soil Science, v.35, pp. 127-140.

West Virginia Surface Mine Drainage Task Force, 1979. Suggested Guidelines for Method of

Operation in Surface Mining of Areas With Potentially Acid-Producing Materials, 20 p.

West Virginia Surface Mine Drainage Task Force, 1978. Suggested Guidelines for Method of

Operation in Surface Mining of Areas with Potentially Acid-Producing Materials. WV Dept. of

Natural Resources, Elkins, WV, 20 p.

Wiram, V.P., 1996. Unpublished notes distributed during a field trip for the American Society for

Surface Mining and Reclamation to the Skyline Glady Fork Mine, May 23, 1996. 
Coal Remining BMP Guidance Manual

2-150 Geochemical Controls

Wiram, V.P. and H.E. Naumann, 1996. Improving ground water quality in the backfill with

alkaline additions. In: Successes and Failures: Applying Research Results to Insure Reclamation

Success. Proceedings 13th Annual Meeting American Society for Surface Mining and

Reclamation, pp. 336-354.

 
Coal Remining BMP Guidance Manual

Operational BMPs 3-1

Section 3.0: Operational Best Management Practices

Introduction

Some remining Best Management Practices (BMP) are operational procedures that specifically

should or should not be implemented during mining. Other operational BMPs pertain to how,

where, and under what circumstances a certain procedure should be employed or to what areal

extent it should be implemented. The BMPs discussed in this chapter deal with a broad range of

mining practices such as: the rate of mining and the speed of reclamation, handling and disposal

of pit and tipple cleanings, auger mining, onsite coal stockpiling, issuance of permits with acidforming overburden, coal refuse reprocessing, and the scope of underground mine daylighting.

In certain mine sites the proposed remining operation is within a “gray area” with regard to

whether the pollution load will be reduced or increased. In these marginal situations, there are

operational procedures that, if implemented, can improve the likelihood of pollution load

reduction. These operational BMP procedures are generally sound environmental practices even

when the site is not considered marginal.

Theory

The production of acid mine drainage (AMD) requires three basic components: a sulfide mineral

(i.e., pyrite), oxygen, and water. If any one of these components is missing or controlled, AMD

production will not occur. In the production of AMD, pyrite is oxidized to form hydrous iron

sulfates (salts). Pyrite oxidation is catalyzed to a high degree by the iron-oxidizing bacteria

Thiobacillus ferrooxidans (Erickson and others, 1985). These salts are subsequently dissolved in

water and a hydrolysis reaction occurs yielding acidity (H+), iron (Fe2+), and sulfate (SO4

2-). 

AMD production can be attenuated or prevented if:
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3-2 Operational BMPs

• Pyrite is not present in significant quantities.

• The contact of oxygen with pyrite is limited or prevented.

• The proliferation of iron-oxidizing bacteria is prevented.

• The contact of ground water with pyritic materials is prevented.

The BMPs discussed in this chapter are based on limiting one or more of the basic components

that cause the formation of AMD. 

Site Assessment

The mining operation should be reviewed in terms of whether or not the concurrent reclamation is

an viable option. Will the topography, type of surface mining, number of coal seams, mining

equipment allow for concurrent reclamation? Are there other factors that may impact the speed

of reclamation? If so, the question of how these factors be mitigated to ensure concurrent

reclamation should be addressed.

As part of site assessment, determination should be made of the amount of tipple refuse material

that the remining will produce. This determination will require lithologic logs and chemical

analyses of the coal, partings, and enclosing strata. Information should be provided on how this

material will be segregated and temporarily stored onsite. The type and location of an offsite

disposal facility also should be given.

Information on the hydrogeologic properties of the site should be obtained. The location,

direction, and depth of auger mining needs to be delineated on mine maps. Depth of the overlying

cover also needs to be determined from drill holes. Using monitoring wells and boreholes, the

stratigraphic location of aquifers can be determined. Aquifer tests (e.g., slug or constantdischarge tests) will yield information on the hydraulic properties (transmissivity and hydraulic

conductivity) of the aquifers. Water levels in the monitoring wells should be measured at 

least monthly to determine seasonal variations and response to precipitation. A literature review

of spoil testing and/or onsite testing of existing spoils, where present, will provide data on 
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Operational BMPs 3-3

the projected hydrologic properties of the post-mining backfill. Analysis of the hydrogeologic

data will yield insight into the potential post-mining water levels with respect to the auger holes.

Assessment of onsite coal stockpiling will require information on coal sulfur values, location and

construction details of the stockpile pad, and determination of pad construction material (e.g.,

clay or other low-permeability substance). Engineering specifications on the pad material

compactibility, permeability, and stability should be available. Available space to construct a

treatment facility down gradient for any stockpile leachate should be demonstrated. If onsite

stockpiling is deemed undesirable, an operational plan to haul offsite the coal as soon as it is

excavated should be required.

Assessment of the additional overburden to be disturbed by remining requires that the overlying

rocks be analyzed using standard overburden analysis techniques as described in Section 2.0

Geochemical BMPs. The drill holes need to be distributed in a manner to ensure that the entire

site is characterized. The overburden analysis can be used to calculate alkaline addition rates, if

needed.

Refuse piles commonly contain areas where burning has occurred in the past from spontaneous

combustion or ignition by trash fires. If these areas are extensive, they can dramatically impact

the economics of the operation. The refuse pile needs to be drilled to the extent that an accurate

assessment of the amount of recoverable coal can be made. Once reprocessed, some type of

cover material that will support vegetative growth is required. Availability of enough topsoil 

or a soil substitute to reclaim the site also needs to be determined. A survey of support areas

surrounding the pile will yield information regarding the onsite availability of topsoil materials.

A pre-remining assessment of the amount of daylighting that will occur should be performed. 

This assessment is based on the amount of cover to be disturbed and perhaps more importantly,

on the amount of recoverable coal. Determination of the recoverable coal reserves needs to be

accurate. This level of accuracy is achieved by an extensive drilling program. It is not 

uncommon for different sections of an underground mine to contain significantly different
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3-4 Operational BMPs

recoverable percentages. If these differences exist they need to be delineated. If the entries are

relatively open, a borehole camera can also be used to visually inspect the remaining pillars. The

amount of cover can likewise be determined by drilling.

3.1 Implementation Guidelines

Rapid Mining and Concurrent Reclamation

In recent years, many mine operators have come to the realization that expedient reclamation

reduces the potential for AMD production. Concurrent reclamation thus, has become an integral

part of mining operations. The speed at which mining and subsequent reclamation are conducted

can have a substantial impact on the resulting post-mining water quality. Accelerated pyrite

oxidation occurs when the overburden is broken up and exposed to atmospheric oxygen. The

process of overburden removal during mining breaks the rocks into clay- to large boulder-sized

particles, which increases the exposed surface area by several orders of magnitude. This greater

exposed surface area, in turn greatly increases the potential amount of pyrite that is freshly

exposed to the atmosphere and is susceptible to oxidation. A certain amount of pyrite oxidation

is expected and inevitable in the course of surface mining. However, when a mine spoil is

permitted to remain exposed to the atmosphere for a protracted period of time prior to

reclamation, accelerated and extraordinary oxidation of the pyrite-rich (>0.5 percent total sulfur)

rocks in the overburden can occur.

The scale and scope of acid mine drainage formation from mining cessations depends on several

factors, including but not limited to:

• length of the cessation period,

• amount and sizes of pyrite-rich rocks that are exposed,

• concentration of the pyrite in the exposed rocks, and

• the form of the pyrite (e.g., massive versus widely disseminated).
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Other geochemical factors also come into play in the protracted cessation scenario. The chemical

reactions that create acid mine drainage are accelerated by protracted subaerial exposure. The

chemical reactions that can prevent or ameliorate AMD are attenuated by this exposure. If

present, alkaline materials (e.g., calcium carbonate-rich rocks) will yield alkalinity to water when

exposed. At atmospheric carbon dioxide (CO2) concentrations (mean 0.03 percent by volume or

0.0003 atmosphere), an approximate maximum of 61 mg/L as bicarbonate (HCO3

-

) alkalinity or

20 mg/L calcium can be released into water (Hem, 1989; Smith and Brady, 1998). When alkaline

rocks are buried, they can yield substantially more alkalinity through calcium carbonate

dissolution. The release of alkalinity is governed by several factors, including to a large extent 

the CO2 concentration in the surrounding atmosphere. Figure 3.1a illustrates the relationship

between the solubility of calcium carbonate in water at 25BC and the partial pressure of CO2

(Pco2) in atmospheres. Lusardi and Erickson (1985) and Cravotta and others (1994) recorded

CO2 concentrations in mine backfills exceeding 20 percent by volume. A Pco2 of 0.2 (20 percent)

is capable of yielding calcium concentrations up to and exceeding 200 mg/L, which yield

substantially higher bicarbonate alkalinities (610 mg/L) than produced at atmospheric CO2

concentrations. Unreclaimed spoil will likely produce much less alkalinity than the same spoil

after reclamation has occurred and once the natural background levels of gases in the vadose zone

are re-established. Carbon dioxide is produced in soils from plant root respiration and bacterial

decay of organic matter. Concentrations of 1 to 2 percent in soil are common. However, higher

concentrations can occur (Jennings, 1971). When spoil is unreclaimed there is no soil cover to aid

CO2 production and retard its escape. Exposed spoil is highly subject to advective forces driven

by winds, temperature gradients, and other factors, which permit the flow of the surrounding

atmosphere through the piles. With continual advection, near atmospheric levels of CO2 are

maintained within the spoil. Figure 3.1b illustrates advective impacts on unreclaimed mine spoil. 

The relatively low permeability of a soil cover slows the rate of gases released from the backfill,

thus preventing the escape of CO2 once it is introduced into the subsurface. Infiltration of

atmospheric gases into the spoil is likewise impeded by the soil cover. 
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3-6 Operational BMPs

Calcuim Carbonate Solubility in mg/L

Partial Pressure of CO2 in Atmospheres

10 100 1000

0.00001

0.0001

0.001

0.01

0.1

1

10

100

Figure 3.1a: Relationship Between the Solubility of Calcium Carbonate and the Partial

Pressure of Carbon Dioxide at 25EC (modified after Hem (1989))

Figure 3.1b: Advective Impacts on Unreclaimed Mine Spoil
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The reaction rate of sulfide (pyrite) oxidation and subsequent hydrolysis to form AMD is

generally much faster than the dissolution of calcium carbonate to yield alkalinity under normal

backfill conditions. With prolonged atmospheric exposure of spoil, this inequity of reaction rates

is accentuated even more. The rate-determining step for AMD production at low pH is the

oxidation of ferrous iron (Fe2+) to ferric iron (Fe3+) which is facilitated (catalyzed) by certain iron

oxidizing bacteria (Stumm and Morgan, 1996) that thrive under acidic conditions. Then, because

the Fe3+ will oxidize pyrite much faster than O2 (atmospheric oxygen) in a low pH environment

(Rose and Cravotta, 1998), the AMD production greatly increases once a low pH is established. 

Substantial pyrite oxidation from protracted mining cessation and associated spoil exposure, can

accelerate the progression to this higher phase of AMD production. With accelerated AMD

production, any alkalinity that is released may be overwhelmed, resulting in a net acidic discharge. 

If the backfill is prevented from reaching this high rate of AMD production, alkalinity released

from the spoil may be able to prevent or neutralize AMD. 

There are some possible exceptions to the necessity of this operational BMP. These include but

may not be limited to:

• Situations where the pyritic content of the overburden material is extremely low, there are

no disturbed rock units with any significant pyrite concentrations, or most overburden

samples are well below the threshold of concern (0.5 percent total sulfur). For example,

overburden associated with many of the coals in the southern West Virginia coalfields fall

in to this category. Table 3.1a summarizes overburden analysis data from a surface mine

located in Logan County, West Virginia. These data are indicative of the low-sulfur

values common to these coalfields, but are not necessarily representative of the quality of

the entire coalfields. 

• It is possible that the application of massive amounts of bactericides on the unreclaimed

spoil may temporarily prevent the deleterious effects of a protracted cessation. 

Bactericides can, for a time, dramatically slow the rate of pyrite oxidation. However, the

use of bactericides on surface mines in the past has been less than successful. Some
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3-8 Operational BMPs

success has been observed for the temporary stockpiling of coal refuse subsequent to

burial (Sobek and others, 1990). Additionally, the use of bactericides is expensive, thus

may not be economically feasible for many remining operations.

Table 3.1a: Summary of Overburden Analysis Data from a Surface Mine Located in

Logan County, West Virginia

Coal Seam

Total

Overburden

Thickness

( feet)

Sample

Thickness

Range

( feet)

Highest Sulfur

Value 

(percent)

Lowest Sulfur

Value

( percent)

Median Sulfur

Value

( percent)

Lower Stockton 44.70 1.30-15.00* 0.10 <0.01 <0.01

Lower Stockton

Leader

14.95 0.95-3.65 0.09 0.02 0.04

Upper Stockton

“A”

16.40 1.60-3.40 0.06 <0.01 0.03

Lower Stockton

“B”

95.10 0.30-5.00 0.10 <0.01 <0.01

Coalburg 91.05 0.30-5.00 2.21** <0.01 0.01

* The first 15 feet of soil and subsoil was grouped.

** This was a 1.45 foot thick unit and the only one to exceed 0.50 percent total sulfur.

Off-Site Disposal of Acid-Forming Materials

In the course of a remining operation, quantities of acid-forming rocks associated with the coal

(e.g., pit and tipple cleanings) are separated out and frequently stockpiled for later disposal within

the spoil. These rocks include rocks immediately overlying the coal (commonly a black shale or

pyritic sandstone), parting or binder (usually a carbonaceous black shale or bone coal), immediate

seat rock (carbonaceous and/or pyritic shales or claystones) removed along with the coal,

unsaleable rider or split seams, and other acid-forming materials separated from the coal during

loading out of the pit or during the initial coal cleaning at the tipple/breaker. See Figure 

3.1b for examples of sources for pit and tipple cleanings. Total sulfur concentrations of several

percent are common in these rocks. Table 3.1c contains total sulfur values for stratigraphic
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Operational BMPs 3-9

sections surrounding the coal in an overburden analysis hole drilled on a remining site is located in

Westmoreland County, Pennsylvania (Appendix A, EPA Remining Database, 1999, PA(3)).

Figure 3.1c: Potential Sources of Pit and Tipple Cleanings

Remining operations typically occur on abandoned mine sites that are already producing AMD

from prior coal mining activities. Therefore, it is generally a sound practice to remove acidforming materials from the remining site and dispose of them elsewhere. Disposal of materials

that have been identified as acid-producers within backfill that is already producing AMD, has the

potential to accentuate or aggravate the existing problem.
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Table 3.1b: Total Sulfur in Stratigraphic Sections Enclosing the Coal at a Remining Site

in Westmoreland County, Pennsylvania (Appendix A, EPA Remining

Database, PA(3))

Lithology

Interval Thickness

(feet)

Total Sulfur 

(Percent)

medium gray claystone 1 0.80

black shale 1 1.86

coal 1 2.31

grayish black shale with coal layers 3 1.16

coal 6 1.01

medium dark gray calcareous fireclay 1 1.48

There are a few circumstances that would allow onsite disposal of acidic pit and tipple cleanings

while limiting the potential to produce more acid. These conditions include, but may not be

limited to:

• Sites where the overburden is composed to a great extent of calcareous (alkaline) material. 

Any potentially acidic material can be entirely encapsulated within this material. In these

situations, the production of alkalinity will most likely either preclude acid production

(iron oxidizing bacteria do not thrive in an alkaline environment) or overwhelm any acidity

that is produced. 

• Sites where the amount of pit and tipple cleanings are relatively small in volume and

insignificant compared to the entire volume of the spoil. In these cases, the acidic material

can be specially handled (e.g., strategically placed, capped, encapsulated, etc.) to prevent

additional acid production. Care should be taken in these situations to ensure that the

special handling technique is physically viable (See Section 2.4, Special Handling of AcidForming Materials). For example, if the special handling plan is to place the acid-forming

materials above the water table, the backfill should be thick enough allow material

placement well above the anticipated highest level of the post-mining water table.
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Auger Mining

Similar to onsite disposal of pit and tipple cleanings, auger mining during a remining operation is

generally not recommended. Auger holes, depending on the hydrologic system of the site and the

sulfur content of the coal, have a high potential to create additional AMD. Because remining sites

are usually already yielding AMD, it is generally not a good practice to permit auger mining.

Auger holes can create similar environmental conditions to those previously described for

underground mine workings, creating a substantial increase in exposed surface areas in potentially

acidic strata. Ground water entering the auger holes contacts primarily coal and perhaps a minor

amount of roof and seat rock. All three of these rock units are composed of potentially acidforming materials as illustrated in Table 3.1c. At the final highwall, auger holes typically are

sealed with a low-permeability material to a depth up to three times the diameter of the hole. The

sealed holes are then covered with spoil. A large portion of the holes remain empty, allowing the

exposure and possible oxidation of pyrite. Ground water entering auger holes will dissolve the

salts created by the pyrite oxidation and subsequently hydrolyze, creating AMD.

The amount of increased surface area caused by auger holes can be considerable compared to

exposure of the remaining coal at a final highwall. For example, a mine with a 1000 foot final

highwall, no augering, and a 4 foot coal seam would have 4000 ft2 of coal exposed prior to

reclamation. If the same site incurred augering, the exposed surface area would include the area

defined by the auger holes plus the remaining coal exposed at the highwall. If the auger holes

were 3.5 feet in diameter, spaced on 8 foot centers (leaving 1 foot between holes) and augered to

a depth of 400 feet, the additional area is equal to 549,750 ft2 or an increase in exposed surface

area of over two orders of magnitude (137 fold).

In addition to the increased exposure of acid-forming materials, the hydrologic system of the

auger holes is drastically different from spoil that is simply backfilled against a highwall. These
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3-12 Operational BMPs

differences in the hydrology can result in differences in the types of drainage produced. The

nature of many surface mines may permit the auger holes to experience alternate dewatering and

flooding, which allows oxidation of pyrite followed by flushing from the influx of ground water.

Depending on the dip of the strata, overlying topography, aquifer characteristics, and other

hydrogeologic factors, it is possible that the coal will be below the water table. If the water table

levels are somewhat stable and the coal lies below water level, the coal seam will be essentially

inert in terms of AMD production because of the exclusion of atmospheric oxygen. Thus,

depending on the hydrologic system, auger holes can become AMD generating systems.

There are circumstances where auger mining may be permissible at remining operations with little

chance of increasing the pollution load. These include, but are not limited to:

• If the hydrologic system is such that the auger holes are likely to be flooded and remain so

permanently, auger mining may be acceptable. Permanent flooding will preclude the

introduction of atmospheric oxygen, thus the acid mine drainage production should cease.

Watzlaf (1992) and Watzlaf and Hammack (1989) observed that subaqueous positioning

of pyrite virtually stops the oxidation. Even if the ground water is saturated with

dissolved oxygen (12.75 mg/L at 5EC (Hem, 1989)), pyrite oxidation is halted by

submersion. Augering below the regional drainage system will likely allow for complete

and permanent inundation the auger holes.

• Augering above regional drainage may be permissible if auger hole sealing can be achieved

to a degree that precludes the infiltration of atmospheric oxygen and/or inhibits groundwater drainage from the holes. If the auger holes, once sealed, flood and the flooded

conditions are maintained, AMD production should be prevented.

Stockpiling of Coal

Stockpiling of coal onsite for extended periods is not recommended. Coal is often the most 

acidic material encountered during mining and therefore can produce the worst water quality. 
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Operational BMPs 3-13

Leaving a large stockpile of acidic material exposed to the atmosphere and precipitation will

create extremely acidic, metal-laden water that can infiltrate into the backfill and foster additional

AMD production.

Often the least saleable coal is the coal with the highest sulfur concentration. This lower quality

coal is commonly held until it can be blended with a higher quality (lower sulfur) coal to promote

sales. This coal is the most frequently stockpiled and held for extended periods of time, prior to

sale. This coal also creates some of the worst water quality associated with coal mining.

Acidity concentrations in the thousands of milligrams per liter are not uncommon for water

draining from these stockpiles. Concentrations exceeding even 10,000 mg/L have been recorded.

Total iron concentrations frequently exceed 300 mg/L. If drainage of this quality enters the

ground-water system, AMD production within the backfill can greatly accelerate. Thus, it is

probable that more AMD will be produced under this scenario than would be produced if the two

sources (stockpile and backfill areas) remained hydrologically separate. Additionally, if stockpile

runoff infiltrates into the spoil, it may overwhelm any natural alkalinity in the backfill. The

alkalinity in the backfill may be able to ameliorate acid production from the spoil, but not from the

additional high-acid source. Exceptions to this BMP include, but are not limited to, sites where:

• The coal has an extremely low reactive sulfur (pyritic and sulfate) concentration (<0.5

percent).

• The stockpile and associated treatment facilities are underlain by a liner material to prevent

infiltration and the runoff is treated to effluent standards prior to discharging. The liner

material, commonly an onsite clay, should be nonacidic and have a sufficiently low

permeability (e.g., less than 10-8 m/s).

• A bactericide is used to prevent or delay the oxidation of the pyrite. This is only a short

term solution, and the bactericide may have to be reapplied periodically.
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3-14 Operational BMPs

• The stockpile is covered or otherwise sheltered to prevent the infiltration of precipitation.

• The amount of time the coal is permitted to stay onsite (e.g., 1 or 2 weeks) and perhaps

the size of the stockpile are greatly limited.

Consideration of Overburden Quality

There are cases where hydrogeologic conditions inherent to specific sites will (with remining)

cause the pollution load to be increased. Permits for these sites are not issuable. The potential

for reclaiming abandoned mine lands should not override the potential to increase the pollution

load. The decision of whether or not to issue a remining permit to some extent hinges on the

quality of the overburden material. The associated strata for some coal seams in certain areas of

the coalfields are going to produce AMD if disturbed by surface mining. When mining occurs on

these sites, there is little that can be done to prevent AMD.

AMD emanating from abandoned and unreclaimed surface mines does not necessarily have to be

caused by poor mining and reclamation practices in the past, such as, improper handling of acidforming materials, poor ground- and surface-water handling practices, open pits, exposed

highwalls, unclaimed and unvegetated spoil piles, and protracted onsite coal stockpiling. The

cause of the AMD can in some cases be due to the fact that the overburden quality is such that

AMD production was almost inevitable. The overburden is simply net acidic.

A particular rock unit in a coal overburden is considered acidic if the net potential acidity, based

on the total sulfur content, exceeds the net potential alkalinity, based on the neutralization

potential. Both these values are given in terms of calcium carbonate equivalency. The threshold

for significant acid-producing potential of a particular rock unit has been empirically derived as

0.5 percent total sulfur by weight (Brady and Hornberger, 1990). At or above this value, the rock

unit has a good potential to produce acid mine drainage. The threshold for significant alkalinity

generation has been empirically defined as a neutralization potential of 20 to 30 (tons per
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Operational BMPs 3-15

thousand tons calcium carbonate equivalent) with a noticeable “fizz” (Brady and Hornberger,

1990; Perry, 1998). A fizz is the effervescence that is released when a few drops of a 25 percent

solution of hydrochloric acid is applied on sufficiently alkaline material (Kania, 1998). For a

comprehensive and detailed discussion on overburden analysis and mine drainage prediction the

reader is directed to, “Coal Mine Drainage Prediction and Pollution Prevention in Pennsylvania”

(1998), published by the Pennsylvania Department of Environmental Protection.

In situations where the overburden quality is such that additional AMD production is predicted

and BMPs will not effectively offset additional AMD production, remining should not take place.

In some cases, where it is economically feasible, other BMPs can be increased to compensate for

and prevent the increased acid-production. BMPs that can be used to offset the effects of acidic

overburden include, but are not limited to:

• Alkaline addition based on the net acidity of the material. Alkaline addition rates above

the net acidity for the spoil are recommended to provide a margin of safety and offset the

inequity of the reaction rates (See Section 2.2, Alkaline Addition). 

• Removal and off-site disposal of delineated acidic material (See Section 2.4, Special

Handling of Acid-Forming Materials).

• Encapsulation of the acidic material within an alkaline or a low-permeability material (See

Section 2.4, Special Handling of Acid-Forming Materials).

• Physical ground-water controls such that either the water will not contact the acidic spoil

or the forecasted decrease in post-mining flow rates are more than sufficient to offset the

projected increase in concentration (See Section 1.2, Exclusion of Infiltrating Ground

Water).

If the proposed BMPs are sufficient to overcome the acid potential expressed by the overburden,

remining without contributing to AMD production may be possible. This evaluation will have to
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3-16 Operational BMPs

be made on a case-by-case basis. A significant decrease in the flow rate may be able to more than

compensate for a predicted increase in concentration. For example:

An extensive daylighting operation is forecasted to decrease the discharge rate

from a median of 300 gpm to a median of 80 gpm. The pre-mining median acidity

concentration is 120 mg/L, which yields a median pollution load of 433 lbs/day of

acidity. The overburden, which has been identified as potentially acidic, will be

disturbed by the daylighting. This scenario could accommodate an increase in the

median acidity concentration to 450 mg/L without a concomitant acidity load

increase. 

It is recommended that remining permits, where the contaminant concentrations are predicted to

be increased, either be amended to include BMPs to prevent additional pollution or be

reconsidered for issuance. However, the opportunity to gain significant reclamation without truly

increasing the pollution load may bear heavily on the final permitting decision. 

Coal Refuse Reprocessing or Cogeneration Usage

Remining operations where abandoned coal refuse piles are reprocessed to glean out the

remaining coal or the entire pile is excavated and hauled to a electricity-producing cogeneration

plant are almost without exception highly beneficial. These operations remove a significant

portion of the acid-forming materials in addition to regrading and vegetating the remaining

material to inhibit water infiltration. All reprocessing activities work to greatly reduce, if not

eliminate, the pollution load.

Abandoned coal refuse piles are common in areas with historic mining. In the past, the coal

cleaning process was not nearly as rigorous or technologically advanced as it is today and large

piles of waste material were dumped at the surface. Older coal refuse piles tend to have

commercially recoverable quantities of coal or enough burning ability for use in newer technology,

such as electrical cogeneration.
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These piles, even though some may be approaching 100 years old, are still producing AMD. The

coal and true refuse material (e.g., carbonaceous black shales, some roof and seat rock) that

comprise refuse piles usually have a significant sulfur content (> 0.50 percent total sulfur) making

acid generation almost inevitable. Acid production is additionally facilitated by the fact that coal

refuse does not readily support vegetation. The acidic nature of the refuse inhibits plant growth

and the commonly dark color generates considerable heat in the summer causing heat toxicity. 

Without vegetation, the infiltration of atmospheric oxygen and surface water into the pile is

virtually unimpeded promoting continual acid generation within the pile. If these piles can be

reduced in size and in the amount of acid-forming material, regraded, topsoiled, and vegetated,

the volume of acid generation will be reduced. In the case of refuse used in cogeneration, the

entire pile is commonly removed for burning, and ash from the cogeneration plant is frequently

returned to the site. This ash, depending on the type of cogeneration plant and original sulfur

content of the refuse, may be highly alkaline.

It is not uncommon for refuse piles located in the bituminous regions of western Pennsylvania,

eastern Ohio, and northern West Virginia to have rates for recovery of coal from coal refuse piles

exceeding 20 percent. Similar values are found elsewhere in the coalfields. Some positions within

individual piles have reportedly had recoveries exceeding 50 percent. Much of this coal is

economically recoverable using modern coal processing techniques and many of these piles

(anthracite and bituminous) have overall burning abilities of several thousand BTUs. This refuse is

commonly burned in conjunction with oil, natural gas and other materials to produce heat or

electricity. Because of the relatively high sulfur content, limestone is frequently burned with the

refuse to aid in desulfurization of the smoke stack emissions. The ash created is commonly

alkaline and can be returned to the site or used at other sites to add alkalinity.

The operation of reprocessing performs several functions that work toward reducing the pollution

load. First, a significant portion of the pile, hence acid-forming materials, is removed. Second,

the refuse material is crushed to a much finer particle size and, when replaced, the pore space

percentage is dramatically reduced. Thus, water will move through the piles more slowly and

much less water will be stored. It is also more difficult for water to initially infiltrate. These piles
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are regraded to promote surface water runoff and reduce infiltration. The piles are topsoiled and

vegetated, which also reduces surface-water infiltration and inhibits the infiltration of oxygen into

the pile. In other words, reprocessing has the ability to reduce the rate of acid generation, reduce

the amount total amount of acidity generated, and reduce the discharge rate from the pile.

Use of refuse piles for cogeneration has the potential to completely eliminate acid generation from

these piles. Complete removal, removes the acid-generating source. Additionally, if alkaline coal

combustion waste (CCW) is returned, the site may begin yielding alkaline waters offsetting acid

generation elsewhere in the basin from other piles not economically remineable.

Very few limitations exist for coal refuse reprocessing or cogeneration use. However, the

potential exists that if a relatively stable (physically and geochemically) pile is excavated, acid

generation may be reactivated or accelerated. The sediment load could also be increased, albeit

temporarily. In the case where CCW is returned to the site, care should be taken to ensure that

higher amounts of trace metals will not be liberated from the ash. Testing of the CCW, for

example by using the Toxicity Characteristic Leaching Procedure (TCLP), should performed to

establish the potential for trace metals leaching. 

Maximizing Daylighting

In general, daylighting as much area of an abandoned underground mine as possible yields positive

results in terms of reducing pollution loads. Daylighting can work both physically and

geochemically to effect a pollution load reduction.

First, and perhaps the most salient mechanism that works toward reducing pollutant loads, is the

reduction of potential surface water infiltration zones. As previously discussed in Section 1.2,

daylighting tends to eliminate large portions of subsided mine sections where considerable 

vertical ground-water infiltration into the mines occurs. The reduced infiltration rates in turn

facilitate reduced loads. Surface-expressed subsidence features, such as exposed fractures and

sinkholes, tend to collect surface and ground water and divert it directly into the mine. When
Coal Remining BMP Guidance Manual

Operational BMPs 3-19

surface mining eliminates these subsidence features, water infiltration into the mine is significantly

reduced. Daylighting also eliminates substantial void spaces that serve as mine water storage

areas, which tend to facilitate a more continuous source of lateral recharge to the adjacent

reclaimed remining operation.

Daylighting dramatically changes the ground-water flow system from open conduit-type of

underground mines to the double-porosity system exhibited by mine spoils (Hawkins, 1998). In

underground mines, ground water, once it has entered the workings, tends to contact only seat

rock, roof rock, and coal. All of these units are commonly sulfur-rich, hence, potentially acidproducing (Table 3.1c). The data in Table 3.1c is from a mine in Donegal Township,

Westmoreland County (Appendix A, EPA Remining Database, 1999 (PA(5)). The strata that the

ground water will contact in this mine, based on this drillhole, have a total sulfur range of 0.574 to

1.637 percent. In short, everything the water contacts is potentially acidic (i.e. <0.50 percent).

Once in the underground mine, ground water tends to follow the path of least resistance, which is

through the open void areas. Therefore, the ground water continues to contact acidic rock units

until it exits the mine via a discharge point or infiltrates into other ground-water systems (e.g.,

adjacent surface mine spoil or undisturbed strata).

Once surface mining and reclamation have occurred, the ground-water flow system changes

dramatically, and the strata encountered is reflective of the entire overburden quality. Rather than

only encountering acidic strata exposed in the underground mine, ground water will contact strata

in the spoil that can be potentially alkaline or acidic or relatively inert. The amount of each type

of rock intersected by the ground water is directly related to the volume of the material in the

spoil, and to some degree, the mining and reclamation methods. Daylighting operations may need

to have special conditions to require mining to a predetermined overburden thickness to ensure

that a sufficient amount of alkaline strata are encountered and spoiled.
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Table 3.1c: Coal and Enclosing Strata Sulfur Values (Appendix A, EPA Remining

Database, 1999, PA(5) hole OB-5)

Interval Lithology Total Sulfur

(percent)

95-97 light gray shale and interbedded

sandstone

0.344

97-98 medium dark gray clay shale 0.574

98-101 coal -Lower Kittanning 1.637

101-104 light gray fireclay 1.201

Table 3.1d summarizes overburden analysis data from an acid-producing underground mine in

Armstrong County, Pennsylvania, on the Upper Freeport Coal. The data illustrate that the coal

itself is the acid-producing rock unit, with total sulfur ranging from 1.60 to 2.78 percent.

Remining will remove most of the coal. As is common with most daylighting, some of the coal

will be unrecoverable. On the other hand, the overburden itself exhibits relatively low total sulfur

values (i.e. <0.50 percent). Total sulfur in the overburden ranges from 0 to 0.32 percent with the

bulk of the strata being less than 0.10 percent. However, the overburden does exhibit several

zones of significant alkaline material with neutralization potential (NP) of up to 209.7 tons of

calcium carbonate equivalent per thousand tons. About 22 feet or 26 percent of the overburden

exhibited NPs exceeding 30. When the overburden is removed and then replaced, this material is

highly broken up, increasing the exposed surface area, and it is mixed to some degree in the

backfill. Ground water should contact each stratum to a degree similar to the volumetric content

of that rock unit. Therefore, in the aforementioned site, roughly one fourth (26 percent) of the

time during transit through the spoil the ground water should be contacting alkaline strata. Most

of the remaining time, the material encountered by the ground water will be relatively inert in

terms of acidity and/or alkalinity production. Thus, once mining has occurred at this site, the

ground water will contact very little acid-producing materials. This illustrates how daylighting

has the potential to greatly improve the quality of the material that the ground water will

potentially contact. 
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Operational BMPs 3-21

Table 3.1d: Overburden Analysis from an Acid-producing Underground Mine in

Armstrong County, PA (Appendix A, EPA Remining Database, 1999, PA(6)

hole OB-4).

Interval Lithology Total Sulfur

(percent)

Neutralization Potential

(tons per 1000 tons of CaCO3

equivalent)

0-1 soft light brown sandstone 0.02 0.47

1-5 medium light gray clay 0.02 3.15

5-10 dark yellowish brown sandstone 0.01 5.29

10-17 pale yellowish brown sandstone 0.04 9.63

17-20 dark to medium brown sandy shale 0.16 6.41

20-25 moderate brown shale 0.04 8.77

25-28 medium gray shale 0.14 3.73

28-31 pale red to grayish red shale 0.02 3.50

31-33 moderate yellowish brown shale 0.02 40.1

33-35 moderate yellowish brown shale 0.03 44.07

35-38 pale brown sandstone 0.00 29.85

38-40 pale brown sandstone 0.02 29.85

40-42 pale brown sandstone 0.02 209.70

42-45 dark yellowish brown shale 0.04 4.66

45-48 dark yellowish brown shale 0.00 7.00

48-51 dark yellowish brown shale 0.04 82.05

51-54 dark yellowish brown shale 0.00 125.82

54-56 dark yellowish brown shale 0.02 7.46

56-58 dark yellowish brown shale 0.02 5.60

58-61 medium light gray shale 0.18 3.96

61-64 medium light gray shale 0.14 16.90

64-67 medium light gray sandstone 0.10 16.21

67-69 medium light gray sandstone 0.06 8.74

69-71 medium light gray sandstone 0.06 11.31

71-74 brownish gray sandstone 0.04 77.19

74-77 medium light gray sandstone 0.06 31.61

77-80 medium light gray sandstone 0.02 44.37

80-82 medium gray sandy shale 0.14 12.82

82-84 medium gray sandy shale 0.11 3.38

84-85 medium gray sandy shale 0.32 9.09

85-88 coal 1.60 0.82

88-90 coal 2.78 0.12

90-91 medium gray clay 0.11 4.20

91-93 medium gray clay 0.10 10.73
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If the entire mine is not daylighted, the remaining underground mine entries need to be adequately

sealed to restrict or prevent ground-water movement between the underground mine and the

backfill and to preclude oxygen infiltration into the mine entries. 

Daylighting underground mines does not always yield a decrease in the pollution load. The

predicted decrease in flow rates and the change in the ground-water flow system, as described in

Section 1.2, can be offset by the increased exposure of highly acidic overburden material to

atmospheric oxidation and subsequent contact of ground water. This situation could in turn

produce a higher pollution load (acidity and/or metals) than previously existed. Reed (1980)

observed that daylighting of a underground mine in Tioga County, Pennsylvania, on the Bloss

Coal seam, increased the acidity concentrations. In fact, he observed a direct relationship

between the amount of daylighting and the acidity concentration. The overburden of the Bloss

Coal was “mostly shale containing pyrite” indicating the potential for acid production. However,

this site is an exception, rather than the rule. In most cases, daylighting successfully decreases the

pollution loads. 

Implementation Checklist

The efficiency of these operational BMPs is related to a large degree to the restraint of certain

activities, the promotion of others, and effective management operation activities. All have the

specific goal of reducing the pollution load; however, these BMPs are somewhat diverse in

regards to how this goal is achieved. The following list includes some recommended

implementation guidelines for these BMPs.

Rapid Mining and Concurrent Reclamation

• Minimize the amount of time the spoil is sub-aerially exposed.

• Regrade and revegetate as soon as possible after coal removal.
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Operational BMPs 3-23

Off-Site Disposal of Acid-Forming Materials

• Note high-sulfur strata and segregate it.

• Stockpile and haul acid-forming materials off-site.

Auger Mining

• Avoid auger mining above water table.

• If augering is necessary for economic reasons, be sure all holes are properly sealed to

preclude ground-water movement and oxygen infiltration.

Stockpiling of Coal

• Do not permit uncontrolled drainage.

• Cover or line under the stockpile to prevent drainage.

• Set maximum time allowed prior to removal or completely preclude stockpiling.

Consideration of Overburden Quality

• Determine the net acidity/alkalinity for the entire volume of overburden to be affected.

• If the overburden is acidic, other BMPs should be employed to compensate for the

negative impacts of disturbance.

Coal Refuse Reprocessing or Cogeneration Use

• Regrade and vegetate to promote runoff and inhibit infiltration.

• Where possible return alkaline coal combustion waste (CCW) to the site.

Maximizing Daylighting

• Eliminate as many of the existing water-infiltration areas as possible.

• Remove or decrease contact between acid-forming materials and ground water.

• Mine to a point where as much alkaline overburden as possible will be disturbed.

• Be certain unmined entries are properly sealed.
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3.2 Verification of Success or Failure

As with all BMPs, verification of proper implementation during remining operations is crucial to

effective control or remediation of the discharge pollution loadings. The importance of field

verification of all aspects of a BMP cannot be overstated. It is the role of the inspection staff to

enforce the provisions outlined in the permit. The inspector generally does not need to be present

at all times to assess the implementation of the BMPs in this chapter. However, some BMPs will

require closer and more frequent field reviews than others. Monitoring of water quality and

quantity will be the truest measure of BMP effectiveness.

During rapid mining and concurrent reclamation, inspection staff needs to verify that the site is

reclaimed shortly after the coal is removed. It is possible for permits to require notification by the

operator of certain reclamation phases and/or require certification by an engineer or registered

surveyor that the reclamation occurred within the predefined guidelines. An inspector should be

able to visually assess that reclamation is occurring concurrently during each site visit.

The removal of pit and tipple cleanings can be verified using a lined stockpile area and review of

weigh slips from the waste disposal facility. The refuse material may be stockpiled for short time

periods, until it is hauled to the waste disposal site. Copies of the weigh slips from the waste

disposal site and an estimate of the amount of material stockpiled should be submitted to the

inspector for comparison of the amount of material sent to the waste site to the amount previously

stockpiled. The amount of material stockpiled can be estimated from the dimensions of the pile or

from company-supplied records. The total amount of refuse to be removed from the site can be

estimated from the overburden analysis and volumetric calculations based on the strata thickness

and the area mined. This estimated amount then can be compared to the total amount that was

actually shipped off-site. The inspection staff should also observe the segregation of the acidic

material during overburden removal.
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Verification that no auger mining has taken place is relatively straight forward; either it does or

does not. If augering is permitted, affirmative proof should be submitted that all of the augering

occurred below drainage and/or the holes were sealed as approved. The determination that

augering is below drainage is initiated during the permitting stage. The operator should submit

hydrologic data showing that the coal where the augering is proposed is below the regional

drainage. Data needed for this determination include, but are not limited to:

• pre-mining water levels

• stratigraphic location of aquifers

• transmissive properties of the aquifers

• dip of the strata

• projected post-mining water table

• anticipated post-mining recharge rates

• the location of potential nearby dewatering sources

• the location and relative elevation of adjacent streams

• specifics of the auger mining plan (e.g., location, direction, depth, etc.)

Once mining operations have begun, an inspector should make certain that the augering is

conducted in the locations and in the manner indicated in the approved permit. Verification that

the auger holes have been properly sealed is a difficult procedure and is discussed in detail in

Section 1.2, Control of Infiltrating Ground Water. If verification that the auger holes are below

the water table and flooded after reclamation is deemed important, monitoring wells can be

installed in and adjacent to the holes to monitor the ground-water conditions.

Verification that coal is not being stockpiled is accomplished by a simple visual inspection.

However, where stockpiles are allowed under limited circumstances, slightly more effort is

required. Verification will be needed to ensure that a liner was installed, the pile is usually

covered, or that there is a limited onsite holding time.
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The sulfur concentration (acid-producing potential) of coal can be determined from the analysis of

the coal quality or the overburden analysis. An inspector will need to verify that a liner was

constructed for the stockpile area and require stockpiling of the liner material prior to placement.

This determination can be performed onsite during construction or after installation, but before

use. An inspector can also verify that the runoff is collected and routed to a treatment facility. If

there is a discharge visible at the base of the pile, but it is not reaching the treatment facility, this is

an indication that the leachate may be infiltrating into the ground and will eventually reach the

water table. If no drainage is observed from the stockpile during or immediately following a wet

period, it is also an indication that the liner is leaking, and steps will need to be taken to remedy

the situation. Elimination of coal storage or reconstruction of the liner may be required. 

Verification of the application of a bactericide can be performed by reviewing sales receipts or

being present when the material is applied and reapplied. Stockpile covering is accomplished by

visual inspection. The lack of any runoff from the pile is an indication that the cover is being used

consistently and effectively. Verification of short-term stockpiling can be performed by

comparing the amount of coal removed from the pit to the amount shipped to the buyer. The

amount taken from the pit is a simple calculation:

Coal Thickness x Acreage x 1750 tons per acre/foot of Thickness = Coal Tonnage

Verification of the amount trucked off-site is available from dated weigh slips or sales receipts.

The inspector can also observe the removal of coal from the stockpile while no coal is being

actively excavated from the pit.

The delineation of acid-forming materials is verified by review of the overburden analysis

submitted with the permit application and discussed in Section 2.0. However, it is recommended

that the inspector periodically examine the exposed highwall to ensure the lithology expressed 

by the overburden drill hole logs does not appreciably change across the site. Channel samples 

(a vertical series of overburden samples collected by hand, comprising the entire exposed strata)
Coal Remining BMP Guidance Manual

Operational BMPs 3-27

may need to be collected at the highwall and analyzed to verify that the overburden quality has not

changed laterally from the nearest overburden hole.

Visual inspection will permit the determination that the amount of reprocessing, or refuse

removal, taking place matches the original plan. The amount of CCW returned to the site can be

determined from weigh slips and volumetric calculations. The quality of the CCW and potential

to leach toxic trace metals can be determined from laboratory analysis. Adequate post-mining

slopes and vegetation can be measured in the field and compared to those proposed in the permit.

To ensure that the maximum amount of daylighting is completed, certification from an engineer or

registered surveyor may be needed. The inspector can visually estimate the daylighted acreage to

a reasonable degree of accuracy. The operator may need to flag the site to define the limits of the

daylighting on the surface.

Implementation Checklist

Monitoring and inspection of BMPs in order to verify appropriate conditions and implementation

should be a requirement of any remining operation. Though BMP effectiveness is highly sitespecific, it is recommended that implementation inspections of Operational BMPs include the

following:

C Measurement of flow and sampling for contaminant concentrations before, during, and

after mining.

C Monitoring should continue well beyond initial water table re-establishment period (e.g.,

about 2 years after backfilling).

C Assessment of hydrologically-connected units and/or individual discharges.

C Review of liner material weigh slips or receipts and/or inspection of marked stockpiles.

C Assessment of any deviation from an approved implementation plan.

C Inspection of salient phases of the BMP implementation.

• Frequent inspection to determine reclamation concurrency.
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3-28 Operational BMPs

• Frequent observation of the handling of pit and tipple cleanings and stockpiled coal.

• Inspection of augering operation or lack thereof.

• Review of coal recovery or refuse shipping records.

• Monitoring scope of daylighting.

3.3 Literature Review / Case Studies

Perry and others (1997) discussed the impacts of operational cessations on post-mining discharge

water quality for several surface mines in Pennsylvania and West Virginia. Their conclusions

were that rapid mining without delays generally yielded improved post-mining water quality

compared to similar mines that experienced delays or cessations during mining. One site in

particular (the Greene Mine) had two discrete mining phases. Mining and reclamation on Phase 1

proceeded without delays, while the mining on Phase 2 was interrupted by a two and a half year

cessation of operations. The two phases were also hydrologically separate. Phase 1 was mined

without any work stoppage. While Phase 2 was idle reclamation was incomplete and the acidforming overburden material was exposed to atmospheric oxidation. The post-mining water

quality of the two phases was distinctly different. The net alkalinity for Phase 1 was 151 mg/L,

while that of Phase 2 was -128 mg/L (net acidic). Iron concentration for Phase 1 was 1.88 mg/L,

while Phase 2 yielded 18.7 mg/L. Manganese concentration for Phase 1 was 16.4 mg/L, while the

concentration for Phase 2 was 62.7 mg/L (Perry and others, 1997). Sulfate concentration, while

not a regulated effluent parameter, it is a viable and direct indicator of acid mine drainage

production. The sulfate ion is released as part of the mine drainage reactions and except under

extreme conditions sulfate remains in solution. The sulfate values for the two phases of the

Greene mine also differed significantly, indicating a difference in the volume and rate of mine

drainage production. Phase 1 had a sulfate concentration of 1197 mg/L, while that of Phase 2

was 1770 mg/L or an increase of 48 percent. The lack of acid production at several other sites

included in the study was attributed to the rapid mining followed by concurrent reclamation of the

sites (Perry and others, 1997). 
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Operational BMPs 3-29

3.4 Discussion

The operational BMPs discussed in this section are recommended during remining for controlling

the effects of the mining activities. Rapid and concurrent reclamation, appropriate location of

auger mining (if allowed at all), off-site disposal of acid-forming materials, control of coal

stockpiling, and thorough daylighting are operational procedures that should be implemented as

part of the mining plan. Coal refuse reprocessing is a type of remining that should be encouraged. 

These BMPs do not preclude application of other BMPs discussed in this guidance document or

required for environmental maintenance or improvement. 

Benefits

• Rapid/concurrent reclamation reduces the risk of the operator falling behind which often

results in incomplete reclamation and promotes AMD formation.

• Off-site disposal of pit and tipple cleanings may transform a remining site from producing

additional acidity to producing less acidity. 

• Appropriate implementation of auger mining can maximize the amount of coal recovered

while reducing the risk of increased AMD production.

• Short-term or no coal stockpiling reduces the risk of accentuating AMD production.

• Reviewing the overburden quality and making a decision on permit issuance or denial

based on this review will lessen the likelihood of making the pollution loads worse and the

operator assuming treatment liability.

• Removal of significant amounts of acid-forming materials from refuse piles and

introduction of alkaline material decreases acid and metal loads.

• Daylighting radically changes the geochemistry and hydrology of the site, reducing the

amount of acidic material, increasing the potential for ground water to encounter alkaline

material, and reducing the water infiltration volume.
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3-30 Operational BMPs

Limitations

C Unscheduled or unforeseen circumstances may prevent maintenance of concurrent

reclamation.

• Off-site disposal of pit and tipple cleanings may not be economically feasible.

• Without the approval to auger mine, some abandoned mines may not be economically

viable to remine, because of the limited coal recovery.

• Auger mining above drainage areas may not be permissible.

• The coal market may dictate whether or not the coal may need to be stockpiled.

Avoidance of stockpiling may induce coal sales at below anticipated prices, possibly

compromising the economics of the operation.

• Redisturbance of a refuse pile may reactivate or accelerate acid production.

• In many cases, it may not be economically feasible to daylight large amounts of an

underground mine. The low coal recovery rates and higher cover may make additional

daylighting unprofitable.

Efficiency

Analysis of sites with Coal Refuse Removal or off-site disposal of pit and tipple cleanings showed

that two thirds of the discharges were eliminated or significantly improved in terms of acidity

loading (Appendix B, PA Remining Site Study). The remaining one third were unchanged. 

Almost 86 percent of the discharges exhibited either no change or a significant improvement in

the iron loading with about 14 percent exhibiting some degradation. Most (83 percent) of the

discharges were unchanged for manganese load with the remainder being significantly worse. No

discharge was degraded in terms of aluminum load. All were unchanged or significantly better.

The success of Mining of Highly Alkaline Strata is directly related to the overburden quality. At

sites where alkaline overburden existed, no discharges were made worse by remining, while over

67 percent were significantly better or completely eliminated in regard to acidity load. Twenty
Coal Remining BMP Guidance Manual

Operational BMPs 3-31

three percent of the discharges exhibited significantly higher iron loads. Another 39 percent were

unchanged and the remaining 38 percent were significantly better or eliminated. None of the

discharges exhibited degradation in terms of manganese or aluminum loads.

Less than one percent of the 170 discharges analyzed for Daylighting showed degradation due to

acidity loading. Over 58 percent were unchanged, with the rest being eliminated or significantly

better. Iron, manganese, and aluminum loads exhibited similar results with a slightly higher

degradation rate (about 4 to 6.5 percent).

3.5 Summary

In general, operational BMPs are “rules-of-thumb” for good mining procedures. Research and

experience has demonstrated that these BMPs will minimize the potential for additional AMD

production; and thus, increase the likelihood of reduced pollution loads.

These recommendations are intended to prevent unchecked, large-scale pyrite oxidation within

the spoil and adjacent areas. Once accelerated oxidation has occurred, abatement or treatment of

the acidic drainage becomes increasingly difficult, if not impossible. In general:

• Rapid, concurrent reclamation is a good practice regardless of the overburden quality. 

• Off-site disposal of pit and tipple cleanings reduces the probability of additional AMD

production. 

• Auger mining should only be permitted below drainage or where effective auger hole

sealing will preclude AMD production. 

• Unless the drainage is controlled, extended onsite coal stockpiling is discouraged.

• Overburden quality should be a consideration during permitting remining operations. 

• There are very few, if any, problems associated with coal refuse pile utilization. 

• The greater amount of daylighting during remining will produce the most positive

reduction in pollution loads.
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References

Brady, K.B.C. and R.J. Hornburger, 1990, The Prediction of Mine Drainage Quality in

Pennsylvania, Water Pollution Control Association of Pennsylvania Magazine, pp.8-15.

Cravotta, C.A, D.L. Dugas, K.B.C. Brady, and T.E. Kovalchuk, 1994. Effects of Selective

Handling of Pyritic, Acid-Forming Materials on the Chemistry of Pore Gas and Ground Water at

a Reclaimed Surface Coal Mine, in Proceedings of the International Land Reclamation and Mine

Drainage Conference and the Third International Conference on the Abatement of Acidic

Drainage, Pittsburgh PA, pp. 365-374.

Erickson, P.M., R.L.P. Kleinmann, and S.J. Onysko, 1985. Control of Acid Mine Drainage by

Application of Bactericidal Materials, Control of Acid Mine Drainage: Proceedings of Technology

Transfer Seminar, U.S. Bureau of Mines Information Circular 9027, pp. 25-34.

Hawkins, J.W., 1998. Hydraulic Properties of Surface Mine Spoils of the Northern Appalachian

Plateau. in Proceedings of 25th Anniversary and 15th Annual Meeting of the American Society for

Surface Mining and Reclamation, St. Louis, MO, pp. 32-40.

Hem, J.D. , 1989. Study and Interpretation of Chemical Characteristics of Natural Water, Third

Edition, U.S. Geological Survey, Water-Supply Paper 2254, 263 p.

Jennings, J.N., 1971. Karst. The M.I.T. Press, Cambridge, MA, 252 p.

Kania, T., 1998. Laboratory Methods for Acid-Base Accounting: An Update. Chapter 6 of Coal

Mine Drainage Prediction and Pollution Prevention in Pennsylvania, PA DEP, Harrisburg, pp. 6-1

to 6-9.

Lusardi, P.J. and P.M. Erickson, 1985. Assessment and Reclamation of an Abandoned AcidProducing Strip Mine in Northern Clarion County, Pennsylvania, in Proceedings of the 1985

Symposium on Surface Mining, Hydrology, Sedimentology, and Reclamation, Lexington, KY, pp.

313-321.

Pennsylvania Department of Environmental Protection, 1998. Coal Mine Drainage Prediction and

Pollution Prevention in Pennsylvania, K.B.C. Brady, M.W. Smith, and J. Schueck, Technical

Editors, Harrisburg, PA.

Perry, E.F., 1998. Interpretation of Acid-Base Accounting, Chapter 11 of Coal Mine Drainage

Prediction and Pollution Prevention in Pennsylvania, PA DEP, Harrisburg, pp. 11-1 to 11-18.

Perry, E.F., M.D. Gardner, and R.S. Evans, 1997. Effects of Acid Material Handling and Disposal

on Coal Mine Drainage Quality, Proceedings of Fourth International Conference on Acid Rock

Drainage, Vancouver, B.C. Canada, Vol. III, pp. 1007-1025.
Coal Remining BMP Guidance Manual

Operational BMPs 3-33

Reed, L.A., 1980. Effects of Strip Mining the Abandoned Deep Anna S Mine on the Hydrology

of Babb Creek, Tioga County, Pennsylvania, U.S. Geological Survey, Water Resources

Investigations 80-53, 41 p.

Rose, A.W. and C.A. Cravotta, 1998. Geochemistry of Coal Mine Drainage, Chapter 1 of Coal

Mine Drainage Prediction and Pollution Prevention in Pennsylvania, PA DEP, Harrisburg, pp. 1-1

to 1-22.

Smith, M.W. and K.B.C. Brady, 1998. Alkaline Addition, Chapter 13 of Coal Mine Drainage

Prediction and Pollution Prevention in Pennsylvania, PA DEP, Harrisburg, pp. 13-1 to 13-13.

Sobek, A.A., D.A. Benedetti, An V. Rastogi, 1990. Successful Reclamation Using Controlled

Release Bactericides: Two Case Studies, In the Proceedings of the 1990 Mining and Reclamation

Conference and Exhibition, Vol. 1, Charleston, WV, pp. 33-41. 

Stumm, W. and J.J. Morgan, 1996. AQUATIC CHEMISTRY Chemical Equilibria and Rates in

Natural Waters, John Wiley & Sons, Inc. 1022 p.

Watzlaf, G.R., 1992. Pyrite Oxidation in Saturated and Unsaturated Coal Waste, In the

Proceedings of the 1992 National Meeting of the American Society for Surface Mining and

Reclamation, Duluth, MN, pp. 191-205.

Watzlaf, G.R. and R. W. Hammack, 1989. The Effect of Oxygen, Iron-Oxidizing Bacteria, and

Leaching Frequency on Pyrite Oxidation. In the Proceedings of the Ninth Annual West Virginia

Surface Mine Drainage Task Force Symposium, Morgantown, WV.
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Coal Remining BMP Guidance Manual

Passive Treatment 4-1

Section 4.0 Passive Treatment Technologies

Introduction

Passive treatment encompasses a series of engineered treatment facilities that require very little to

no maintenance once constructed and operational. Passive water treatment generally involves

natural physical, biochemical, and geochemical actions and reactions, such as calcium carbonate

dissolution, sulfate/iron reduction, bicarbonate alkalinity generation, metals oxidation and

hydrolysis, and metals precipitation. The systems are commonly powered by existing water

pressure created by differences in elevation between the discharge point and the treatment

facilities.

Passive treatment does not meet the standard definition of a Best Management Practice (BMP). 

In general, BMPs consist of abatement, remediation, and/or prevention techniques that are

conducted within the mining area (at the source) during active remining operations. Passive

treatment, by its nature, is an end-of-the-pipe solution to acid mine drainage (AMD); it is

treatment. These systems are frequently installed after reclamation to treat AMD. BMPs, on the

other hand, are performed as part of the mining or reclamation process, generally not after the

fact. If treatment, passive or conventional, is required for a discharge to meet effluent standards

(BAT or some alternate standard), the operator is held liable and treatment continues,

theoretically, until the discharges naturally meet the applicable effluent standards.

Regardless of whether or not passive treatment fits the definition of a BMP, it can be used as part

of the overall abatement plan to reduce pollution loads discharging from remining sites. There are

situations where passive treatment may be employed to improve water quality above what was

accomplished by the BMPs. Therefore, a detailed discussion of the use of passive treatment

technology to treat AMD in this manual is warranted. Passive treatment includes, but is not

limited to:
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4-2 Passive Treatment

• Anoxic limestone drains (ALDs)

• Constructed wetlands

• Successive alkalinity-producing systems (SAPS)

• Open limestone channel (OLCs)

• Oxic limestone drains (OLDs)

• Pyrolusite® systems

• Alkalinity-Producing Diversion wells

Passive treatment technologies also can be incorporated into the reclamation plan along with more

traditional BMPs. For example, ALDs can be installed within the backfill as a type of pit floor

drain. This has been done at a remining site on the Shaw Mines Complex in Somerset County,

Pennsylvania, where an ALD 2,500 feet long, 30 feet wide, and 10 feet deep was installed within

the backfill (Ziemkiewicz and Brant, 1997). Wetlands can be constructed where returning the site

completely to the approximate original contour is not economical. Discharges can be routed

through these wetlands for treatment. Open limestone channels can be used in the construction of

diversion ditches or as pond outflow structures. Additionally, passive treatment can be employed

on AMD-yielding discharges that would not otherwise be impacted by the operation or by integral

BMPs. These discharges are hydrologically discrete from the operation.

Theory

Once installed, passive treatment systems require little maintenance through the projected life of

the system. They are a low-cost method of treating mine water. However, these systems have a

finite life and may require rebuilding or rejuvenation over the life of treatment. The period of

treatment can be considerable; some mines have continually yielded AMD for well over a century. 

The power to run these systems is generated by changes in elevation that creates sufficient head

and forces the water flow through them. The treatment is performed by natural, biological,

geochemical, and physical actions.
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Passive Treatment 4-3

Frequently, more than one type of passive treatment or an integrated system of passive treatment

technologies are employed to treat mine drainage. These facilities, like conventional treatment

facilities, are typically designed to raise the pH and remove metals (e.g., iron, manganese, and

aluminum) of acid mine drainage.

Site Assessment

In order to determine the feasibility of integrating passive treatment into a remining operation

BMP plan, there are several factors that need to be assessed. The most critical is the

determination of the water quality and discharge rates. These data need to be collected and

analyzed on a seasonal basis to completely characterize discharge(s). Sampling at least once per

month, for a complete year, is recommended. Additional monitoring may be required, if the

precipitation has been substantially above or below normal. These data directly relate to the sizing

of passive systems.

Of particular importance in selecting the type of passive treatment system(s) is the water quality

characteristics of the discharge. Dissolved oxygen (DO) concentration in the water as it

emanates, speciation of the dissolved iron (i.e. ferrous and ferric) concentrations, dissolved

aluminum concentration, net acidity or alkalinity, and pH are all important parameters. The

concentrations of dissolved manganese and sulfate are of lesser importance (less problematic), but

should also be determined.

Determination of the discharge flow rate is perhaps the most critical data for the sizing and

selection of passive treatment technologies. Without accurate flow data, an improperly sized

passive treatment system may either under treat the water or be much larger, and thus more

expensive, than needed. Flow measurements should be determined at the time water samples are

collected and should be performed using standard scientifically accepted means. A weir (e.g., vnotch) or flume (e.g., H-type), timed-volumetric (e.g., bucket and stopwatch), or flow meter 

and cross sectional area are acceptable and commonly used methods to determine flow. It is

recommended that at least one extreme high flow and low flow be sampled during the 
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4-4 Passive Treatment

monitoring period. If the flow is too low or too erratic, some types of passive treatment (e.g.,

wetlands, SAPS) may not be suitable. 

Most passive treatment systems require a sufficient gradient to create the desired head to drive the

water flow through the treatment systems. Therefore, implementation of these systems requires a

large enough area for construction sufficiently down gradient of the discharge. 

4.1 Implementation Guidelines

Anoxic Limestone Drains

In general, attempts to use limestone to treat acidic ferruginous mine drainage at the ground

surface commonly fail after a short time period. These failures are caused by the low dissolution

rate of limestone at atmospheric levels of CO2 and by iron (ferric) hydroxide (FeOH3) armoring of

the limestone. Limestone armoring virtually halts all bicarbonate alkalinity production from the

dissolution of calcium carbonate. Once exposed to the atmosphere, the iron in mine drainage

rapidly oxidizes from ferrous (Fe2+) to the ferric state (Fe3+). Once oxidized, the ferric iron will

quickly precipitate out of solution, coating the limestone, and creating an iron hydroxide

precipitate sludge known as “yellow boy”. However, if mine drainage is maintained in a low

oxygen (anoxic) environment, the iron will remain in the ferrous state and will not readily

precipitate from solution. Anoxic mine water passing through limestone drains allows for the

production of alkalinity without iron armoring and precipitation. For these drains to function

properly, the mine drainage dissolved oxygen content should be less than 1 mg/L (Kepler and

McCleary, 1994). Cravotta (1998) states that dissolved oxygen in the water should be less than

0.3 mg/L to preclude iron oxidation.

Anoxic limestone drains are designed to generate alkalinity in acid mine drainage without

atmospheric exposure. In addition to preventing iron hydroxide precipitation, the closed

environment of an ALD fosters increased CO2 concentrations, which in turn facilitates higher

alkalinity production. Alkalinity production in ALDs is much greater than what can be expected
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Passive Treatment 4-5

at atmospheric CO2 levels. CO2 partial pressures ranging from 0.022 to 0.268 atmospheres were

calculated for 21 ALDs (Hedin and Watzlaf, 1994). The production of 61 mg/L alkalinity under

atmospheric conditions can quickly be increased to over 450 mg/L within an ALD (Hem, 1989;

Hedin and Watzlaf, 1994). The mechanism for the increased alkalinity production from higher

CO2 concentrations is discussed in Section 2.0 and 3.0. Removal of acidity from mine water

flowing through ALDs ranges from 0 to over 5900 mg/L. The higher levels of acidity removal are

attributed to loss of mineral acidity from detention of ferric iron and aluminum within the drains.

This detention of ferrous iron was observed at two sites using ALDs with the detention times

exceeding 25 hours (Hedin and Watzlaf, 1994). The lower acidity and higher alkalinity of the

water once it leaves the drain cause the pH of the water to rise, which in turn significantly

increases the precipitation rate of iron and other metals.

ALDs are often installed to aid the efficiency of constructed wetlands. These wetlands work

more effectively to remove metals if the pH of the water is raised by ALD pretreatment. Most

metals associated with AMD will precipitate more readily from solution in a high pH environment. 

Nairn and others (1991) stated that a pH of 6.0 (standard units) and a net alkalinity allow passive

treatment systems (constructed wetlands and settling ponds) to work much more effectively.

Design and construction of an ALD should be based on the required detention time for the

maximum flow anticipated for the discharge over the effective life of the facility. The discharge

water quality should also be considered. It is recommended that an environmental safety factor be

employed in design to cover the worst case scenario. The discharges should be monitored for at

least one year prior to system installation to determine the range of flows anticipated and the

variability of water quality. Precipitation records during the monitoring period should be

compared to average years to determine the representativeness of the flow and water quality data.

Configuration and size of ALDs are based on the flow rate, projected life of the system, purity of

the limestone, and desired water quality. The ALD should be able to treat the water to the

desired levels under all flow conditions. Design details of ALDs can vary, but the general

configuration is relatively consistent. Figure 4.1a illustrates the basic construction of an ALD.
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4-6 Passive Treatment

Figure 4.1a: Typical Anoxic Limestone Drain Construction

Hedin and Watzlaf (1994) analyzed water quality and flow data from 21 completed ALDs treating

AMD in Appalachia to determine their efficiency. They determined that an in-drain detention time

of at least 15 hours and perhaps as high as 23 hours is required to produce the maximum

alkalinity. ALD sizing criteria were developed based on the discharge rate, a minimum 15 hour

detention time, the desired life of the drain, and physical and chemical properties of the limestone

used. The equation derived is as follows:

M (Equation 1)

Qp

V

QCT

v x

= +

b d t

Where: M = mass of the limestone

Q = discharge rate

pb = bulk density of the limestone

td = the detention time

Vv = bulk void volume expressed as a decimal (20 percent voids is

expressed as 0.20)

C = predicted concentration of alkalinity of drain effluent

T = designed life of drains in years

x = calcium carbonate content of the limestone in decimal form
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Passive Treatment 4-7

An example calculation of drain size in metric tonnes (mt) is as follows. The calculation assumes

a discharge rate of 30 L/min, limestone bulk density of 1600 kg/m3, bulk void volume of 40

percent, a projected alkalinity of 300 mg/L, a limestone calcium carbonate content of 95 percent,

and a life of 25 years. 

M

(30 L / min x 60 min / hr) (1600 kg / m

3

 x m3/ 1000L x mt / 1000 kg) (15 hr)

0.40

=

+ =

(30 L / min x 60 min / hr) (300 mg / L x mt / 109 mg) (25yr x 8766 hr / yr)

0.95

232.6mt

ALDs are located down gradient of the discharge point to allow for a free-flowing, gravity-driven

system. A sufficiently wide and deep trench is dug to accommodate the amount of limestone

needed to provide the desired detention time to yield the maximum alkalinity. Dimensions of

ALDs commonly range from 2 to 9 feet wide and 150 to 1500 feet long; however, much larger

drains have been constructed. Drain depth should be enough to hold a 2 to 6 feet thick layer of

limestone with sufficient cover to preclude infiltration of oxygen (Nairn and others, 1991). Once

excavated, the trench is filled with crushed limestone. Brodie and others (1991) recommended

that the size of the limestone be 0.75 to 1.5 inches to give both the needed surface area and

needed drain hydraulic conductivity. Purity of the limestone should be as high as possible to

prolong the functional life. Use of a low-purity limestone would require the drain to be larger and

more limestone material to be used. 

Mine drainage is piped into the ALD directly from the source, before it has been exposed to the

atmosphere. It is common to dig into the discharge point and install a buried collection and piping

system. The drain inlet is usually at the base of the drain to maximize limestone contact. The

limestone is covered with 10 to 20 mil (0.01 to 0.02 inches) thick sheet plastic followed by

geosynthetic fabric to prevent puncturing of the plastic. The fabric is then covered with lightly

compacted clay. The plastic and clay are emplaced to inhibit the infiltration of atmospheric
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4-8 Passive Treatment

oxygen. Clay is then covered with soil. The clay and soil should be at least 2 feet thick to

effectively prevent oxygen infiltration. The surface should be crowned (mounded) to inhibit

erosion and water infiltration and to accommodate long-term subsidence as the limestone

dissolves. Brodie and others (1991) recommend that the drain should be rip rapped or vegetated

with a plant species that will discourage the growth of trees, such as sericea or crown vetch. Tree

roots could breach the drain seal and allow oxygen infiltration. The outflow pipe is installed at

the top of the limestone trench opposite to the inflow point. The outflow pipe is equipped with an

air trap to prevent oxygen migration into the drain. The elevation of the outflow pipe should be

below the head elevation driving water through the drain. The inflow and outflow piping size

should be large enough to permit unrestricted flow for the highest projected discharge rates. 

Once the water exits the drain and is subaerially exposed, dissolved iron and most other dissolved

metals in the water will rapidly oxidize and begin to precipitate out. It is recommended that the

water be diverted to a settling basin or pond sized for this purpose. The settling basin will greatly

extend the life of a constructed wetland or other subsequent treatment facility. Ideally, the

alkalinity yielded by the drain will be high enough to neutralize the existing mine water acidity as

it enters the drain and to neutralize the mineral acidity created subsequently by the oxidation and

hydrolysis of the iron and metals after the water exits the drain.

There are some restrictions to using ALDs to treat AMD. Most are related to the mine water

quality. If the dissolved iron in the discharge water has been oxidized to the ferric state prior to

entering the drain, the drain will eventually fail. Ferric iron will readily precipitate in the drain

once the pH of the water is sufficiently raised, armoring the limestone and clogging the void

spaces. This precipitation decreases the drain efficiency and eventually causes failure in terms of

limestone dissolution rate and/or water not flowing through the drain. The introduction of DO to

the mine water will allow iron oxidation to the ferric state. Therefore, the available atmospheric

oxygen should be restricted. These drains are not recommended to treat mine water with high

concentrations of dissolved aluminum, because aluminum will also precipitate out in the drain

once the pH is raised with or without oxidation. It is not recommended to use a dolomitic

limestone, because the dissolution rate of dolomite (CaMg(CO3)2) is much slower than calcium
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Passive Treatment 4-9

carbonate. Therefore, the effectiveness of the drain would be diminished or the drain size would

have to be increased to accommodate the lower reaction rates. If sulfate concentrations exceed

2000 mg/L, it is possible for gypsum (CaSO4 + 2H2O) to precipitate within the drain once the pH

is raised and calcium concentration is increased (Ziemkiewicz and others, 1994).

Constructed Wetlands

The possibility of using constructed wetlands to treat AMD was first indicated by observations

made on the treatment of mine drainage by naturally-existing wetlands. The flow of AMD

through Sphagnum moss bogs illustrated that iron and acidity concentrations could be reduced

without degrading the wetland. Studies on naturally-formed wetlands treating mine drainage

were initially conducted in Ohio and West Virginia. Both studies showed that iron and acidity

were substantially decreased and the pH of the water was raised after flowing through the

wetlands (Kleinmann, 1985).

Because of the beneficial effects observed at natural wetlands, numerous wetlands have been

constructed in attempts to treat acid mine waters passively. Sphagnum moss was used initially

because it was observed to be successful in natural wetlands and preliminary studies showed that

it can remove large quantities of iron (Kleinmann, 1985). Near surface oxidation and sulfate

reduction in deeper organic-rich zones also decrease the amount of iron in wetlands. Later, cattail

(Typha) wetlands were constructed to treat mine drainage. This change in vegetation appears to

be related to limited iron detention from cation exchange by Sphagnum moss and the high

sensitivity of the moss to wetland water levels. Studies showed that most of the iron detention in

constructed wetlands was due to binding to the organic matter and the direct precipitation of iron

hydroxides (Wieder, 1988).

There are two ways that constructed wetlands treat AMD. First, aerobic reactions cause oxidation

and hydrolysis of the metals forming metal hydroxide precipitates. This removal of metals has a

tendency to release mineral acidity and lower the pH of the water. Aerobic wetlands work

primarily with mine water flowing through at or very near the surface. The subaerial exposure
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4-10 Passive Treatment

permits oxidation of iron and other metals. However, in order for these wetlands to work most

efficiently, the water needs to have a pH of 6.0 or higher and a net alkalinity. At a pH of 6.0 or

higher, the rate of iron oxidation dramatically increases. At pH levels below 6.0, manganese

oxidation virtually halts. As these metals oxidize and hydrolyze, mineral acidity is released and

the pH will decrease. Therefore, the more efficient wetland systems will have an excess net

alkalinity in the water prior to the precipitation of the metals to buffer (the ability to hold the pH

relatively steady with the addition of an acid or a base) the release of mineral acidity.

Second, anaerobic reactions that occur under anoxic conditions cause sulfate reduction. Under

anaerobic conditions, metals are removed in reduced forms (metal sulfides), and bicarbonate

alkalinity is created. Anaerobic wetlands, also called compost wetlands, support reducing

conditions within the substrate. Sulfate reduction by sulfate reducing bacteria (e.g., Desulfovibrio

and Desulfomaculatum) is one of the primary anaerobic reactions (Smith, 1982). Sulfate-reducing

bacteria thrive in anoxic environments, feed on organic material, and utilize sulfate in their

respiration processes. The organic substrate acts as an oxygen sink in natural and constructed

wetlands, creating suboxic or anoxic conditions from the bacterial decomposition of the organic

matter. Oxygen in water flowing through the organic substrate is rapidly removed. With sulfate

reduction, hydrogen sulfide gas (H2S) is created and a variety of metal sulfides (e.g., pyrite (FeS2),

iron monosulfides (FeS)) are formed and deposited within the substrate. Wetland flow systems

designed to force water through the organic substrate promote sulfate reduction on a larger scale. 

In the process of sulfate reduction, bacteria use organic carbon (CH2O) and sulfate (SO4

 2-),

producing hydrogen sulfide (H2S) and bicarbonate alkalinity (HCO3

-

) (McIntire and Edenborn,

1990) as shown in Equation 2. The production of bicarbonate alkalinity neutralizes acidity and

raises the pH of the water.

2CH2O + SO4

2- = H2S + 2HCO3-

 (Equation 2)

There are a multitude of configurations for constructed wetlands. However, a few researchers

have developed criteria for wetlands sizing and design to maximize AMD treatment. Kleinmann

(1985) suggested that 200 ft3 of wetland are required for each gallon per minute of discharge.
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Passive Treatment 4-11

Kleinmann indicated that constructed wetlands may be most applicable to discharges of no more

than 10 gpm, a pH over 4.0, and iron concentration of 50 mg/L or less. Attempted uses of

wetlands to treat discharges with water quality or quantity exceeding those criteria were mostly

unsuccessful.

Hedin and Nairn (1990) determined that loading (mass/time) directly related to the wetland

treatment area was a more appropriate criteria for wetland engineering. They developed a sizing

formula based on iron grams per day per meter squared (Fe g/day/m2 or gdm) of wetland area.

The method also factored in pH, flow, and iron concentration. A sizing criterion of 10 gdm of

iron was determined for water with a pH of 4.0. For water with a pH of 3.0, the efficiency drops

to 4 gdm of iron. 

Kepler (1990) observed that there may be other factors that also play a role in the efficiency of

wetlands to treat mine water. He noted seasonal variations in the treatment effectiveness related

to variations in influent iron loadings as well as treatment area and biological efficiency. An

inverse relationship was observed between the iron load (ferrous and ferric iron ratio) and the

efficiency of the wetland. This is related to the flow system through the wetland allowing time for

aerobic and anaerobic reactions to occur. He indicated that the flow system may be as important

as the surface area or vegetation types. For overall effectiveness, a value of 15 gdm was

determined for year round treatment. A sizing safety factor of 1.25 was also recommended

(Kepler, 1990).

Stark and others (1990) in a study of a Typha wetland near Coshocton, Ohio, observed a

consistent treatment efficiency at 10 gdm. However, the site averaged over 13.5 gdm. They

likewise recommended that wetlands be sized to treat the maximum loads anticipated. 

It is critical that accurate discharge flow and water quality background data are collected for at

least one water year (October 1st through September 30th). Extreme care should be taken to

ensure that flows are accurately measured. Wetlands should be sized for the maximum forecasted

flow, concentration, and load, so extreme conditions can be successfully treated.
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4-12 Passive Treatment

Although configuration of constructed wetlands can vary widely, there are some basic common

components. Figure 4.1b is a schematic diagram of a typically constructed wetland system. In

many instances, the mine discharge is initially diverted to a small settling pond. Depending on the

pH and alkalinity of the water, some iron will precipitate within the pond, extending the working

life of the wetland. The water then flows from the pond into a large wetland cell or series of cells. 

The water course is designed so the detention time is as long as possible to yield maximum

treatment. This is usually accomplished by the inclusion of a series of baffles to divert the water

along a circuitous path. The last wetland cell is followed by a final “polishing” pond to allow for

precipitation of any appreciable remaining iron. After the final pond, the water, if meeting

applicable effluent standards, is discharged to the receiving stream. If effluent standards are not

being met, additional treatment may be required. 

Figure 4.1b: Commonly Constructed Wetland Diagram

Construction design of individual wetland cells is directly dependent on the amount of flow and

water chemistry. Brodie and others (1988a) based the size and number of cells on the projected

flow from a 10-year, 24-hour storm event. The cell size is based on the area required to treat the

flow for iron concentration, according to grams/day/m2 of iron, as discussed above. Cell
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Passive Treatment 4-13

dimensions are based on the treatment area needed, maximization of the flow path, site

topography, and configuration of the available space down gradient of the discharge. 

Wetland cells are frequently lined with an initial thin layer of crushed limestone that is usually

about 6 inches thick (Figure 4.1c). The limestone is covered with a thicker organic layer, usually

12 to 18 inches. Mushroom compost is the most common material used for the organic substrate.

The cell is subsequently flooded with 6 to 12 inches (15 to 30 cm) of water and planted with

vegetation. Cattails are by far the most commonly planted vegetation in constructed wetlands.

Other plants used include, but are not limited to, cattail-rice cutgrass, sphagnum moss, rushes, and

bulrushes (Brodie, 1990; Brodie and others, 1988b). Various types of blue-green algae

(Cyanobacteria) have also been introduced into wetlands in attempts to improve efficiency for

manganese reduction (Spratt and Wieder, 1988).

Figure 4.1c: Typical Wetland Cell Cross Section

There are limits to which wetlands can be used to treat mine water. One of the most salient

problems is the amount of area required. A high-flowing, high-iron discharge requires a huge 

area for treatment. A low pH (<4.0) water will require more treatment sizing (4 gdm) than 

a higher pH (>4.0) water (10 gdm). Using the sizing criteria developed by Hedin and Nairn
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4-14 Passive Treatment

(1990), a mine discharge of 600 gpm, 75 mg/L of iron, and a pH greater than 4.0 would require a

wetland area of at least 6.1 acres and an area of 15 acres for a pH under 4.0. However, Hedin

and Nairn (1990) stated that for “highly contaminated drainage,” a larger wetland sizing criterion

may be required. At a pH of 3.0, the wetland sizing may need to be increased by 300 percent.

The performance of aerobic wetlands is greatly hampered by low-pH water. Raising the pH prior

to piping the water into the wetland will greatly improve iron removal. ALDs have been used

successfully in conjunction with wetland treatment. The increased alkalinity buffers the decrease

in pH caused by release of mineral acidity from iron hydrolysis. This buffering in turn improves

the treatment ability of the wetland (Brodie and others, 1991).

By design, iron hydroxide will precipitate within constructed wetlands. This precipitation will

eventually cause iron hydroxide sludge buildup in the cells, which will cause changes to the water

levels. These changes will adversely impact the vegetation and decrease the wetland treatment

ability. Also organic material will eventually be depleted through bacterial action, and require

replacement. Depending on the flow system, the limestone may also need to be replenished as

dissolution occurs. Therefore, over time, wetlands require periodic maintenance to remove the

iron hydroxide sludge and replace substrate materials.

Successive Alkalinity-Producing Systems 

Successive alkalinity-producing systems utilize the alkalinity production of anaerobic wetlands

and ALDs to remove metals from mine water, while greatly increasing the alkalinity production

over either of the two systems working singly. With SAPS, the ALD criteria for anoxic mine

water and the requirement of ferrous iron does not apply. An oxygen sink is created by anaerobic

sulfate reduction which will reduce any ferric iron (Fe3+) to ferrous.

Construction of individual SAPS cells is similar to that of a constructed wetland cell, but the flow

system differs and no vegetation is required. Because SAPS work on the concept of a series of

steps that produce alkalinity, there are several configurations for the entire system. Kepler and
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Passive Treatment 4-15

McCleary (1994) suggested a configuration of an ALD followed by an aerobic wetland or settling

pond, which is then followed by a SAPS cell that discharges into a second aerobic wetland or

settling pond.

An individual SAPS cell is designed to accept water inflow at the surface and drain from the

bottom. The basal layer in a SAPS cell is crushed limestone covering perforated underdrain pipes

(Figure 4.1d). Skousen and others (1995) suggested that the underdrain pipes be covered with 12

to 24 inches of limestone. However, Kepler and McCleary (1994) indicate that the thickness of

the limestone layer is based on the detention time required for maximum alkalinity production. A

similar amount of detention time as that required for an ALD is recommended. Four SAPS

constructed in Pennsylvania had limestone layers ranging in thickness from 18 to 24 inches

(Kepler and McCleary, 1995). A layer of organic matter, usually mushroom compost, is placed

over the limestone. The thickness of the organic layer, like the limestone layer, is based to a large

extent on the required detention time. Kepler and McCleary (1995) observed four sites in

Pennsylvania where the organic layers were 18 inches thick. Skousen and others (1995)

recommended 12 to 18 inches of organic material. Overlying the organic layer is free-standing

mine water. The depth of the water is dependent on the head (pressure) required to drive the

water through the organic and limestone layers at a rate that to adequately achieve the required

the biochemical and chemical reactions (discussed below). Kepler and McCleary (1995) indicated

a depth range of 5.25 to 6.23 feet was adequate at the four study sites in Pennsylvania; whereas,

Skousen and others (1995) suggested a water depth of 4 to 8 feet. Size of the SAPS is based on

the required water detention time, which is related to the flow rate, more so than the water

quality. The rate of atmospheric oxygen diffusion into a body of water is relatively constant and

should be used in determining the areal size of the SAPS cell.
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4-16 Passive Treatment

Figure 4.1d: Example of a Successive Alkalinity-Producing System Cell

SAPS function through a series of chemical and biochemical reactions to remove iron and other

metals from the water, while increasing the alkalinity. When mine water is initially discharged into

the SAPS cell, it does not matter if the water has been oxygenated or the iron has been oxidized

to the ferric state. Some of these metals, especially iron, will oxidize in the shallower water and

precipitate on top of the organic layer. Kepler and McCleary (1994) observed 2 inches (5 cm) of

iron hydroxide deposited in a SAPS at a mine site in northwestern Pennsylvania.

Once in the cell, the water flows downward toward the organic layer and the water is rapidly

stripped of dissolved oxygen by microbial decomposition of the organic material. Bacteria 

utilize the DO in the mine water to metabolize the organics. These reactions occur near the

interface of the organic material and the water. Kepler and McCleary (1994) reported that water

nearly saturated with dissolved oxygen (~10 mg/L) entering the cell was virtually anoxic (<0.2

mg/L) after passing through the system. Oxygen can only infiltrate several centimeters into the

organic substrate (Kepler and McCleary, 1994). Once the dissolved oxygen is removed,
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Passive Treatment 4-17

anaerobic sulfate-reducing bacteria in the organic layer will chemically reduce the metals as well

as the sulfate ions, yielding hydrogen sulfide (H2S) gas and metal sulfides. The H2S will be

released into the atmosphere, where it subsequently oxidizes to form water and native sulfur (S)

(Lehr and others, 1980). When these systems are working properly, considerable H2S is yielded

and the systems tend to have an offensive smell. H2S smells similar to rotten eggs and is

unpleasant even at very low concentrations (0.05 mg/L). Metal sulfides are deposited within the

organic material, but some of the reduced metals will remain dissolved and pass through the

organic layer. 

This reduction process also yields bicarbonate alkalinity to the water as described in the preceding

wetlands section. This process, in turn, will neutralize acidity, add alkalinity, and raise the pH of

the water. 

Once the water has passed through the organic layer, it enters the underlying limestone gravel.

Because the oxygen has been stripped from the water, and any metals that are not precipitated are

in a reduced state, the limestone layer functions as an ALD. Passage through the limestone adds

additional alkalinity to the water through dissolution of the calcium carbonate, as described above

under ALDs. If the SAPS are properly sized, the effluent should have a pH of 6.0 or higher

(Skousen and others, 1995). Aluminum tends to pass through the organic layer and is

precipitated in the limestone. Because aluminum precipitate does not armor the limestone, but

instead remains as loose precipitate, it can eventually plug the limestone layer. Therefore, a

piping system that will allow a periodic forced flushing of the limestone layer is needed to

maintain the efficiency of the system (Kepler and McCleary, 1997). 

The SAPS cell effluent is typically piped into a conventional aerobic wetland or settling pond.

With the excess alkalinity yielded by the SAPS, much of the remaining metals (mainly iron) will

quickly precipitate out of solution in the wetland or pond. The process of iron oxidation and

hydrolysis will, as discussed earlier, yield acidity. However, the excess alkalinity in water from a

well-designed SAPS should perform a buffering action and be sufficient to maintain a net

alkalinity throughout this secondary precipitation process. If the alkalinity is insufficient to
Coal Remining BMP Guidance Manual

4-18 Passive Treatment

neutralize the acidity produced by the iron precipitation, the water can be piped through a second

SAPS. This process can be repeated until the mine water meets the applicable effluent standards.

Limitations on SAPS construction, use, and maintenance are similar to those for wetlands and

ALDs. Restrictions to the use of SAPS include, but are not limited to:

• Engineering and sizing should be determined by the discharge flow rate. The highest

anticipated flow rates should be used as an engineering guideline.

• Topography should be such that the system will function (flow) properly without the need

for additional power.

• The organic material and limestone will eventually be exhausted and will need to be

replaced.

• The water level needs to be deep enough that significant continued diffusion of dissolved

oxygen at depth is prevented. 

• There should be some mechanism to control the water level in the SAPS cell. This is

important during extremely low flow periods, because the organic material could be

subaerially exposed and dry out, thus shutting down oxygen removal and sulfate

reduction. At high flows, the system could be overwhelmed. 

• Iron sludge can eventually fill the pre- and post-SAPS ponds and will require periodic

cleaning. If the iron precipitation within the SAPS is substantial, this will also require a

periodic cleaning.

• Calcium carbonate purity of the limestone should be the highest available to prolong the

life and maximize alkalinity production.

• Aluminum tends to precipitate in the limestone layer just as with ALDs. Therefore, a

system is required to permit periodic flushing of the aluminum floc from the limestone.

Open Limestone Channels

In contrast to treating AMD with limestone in an anoxic environment, more recent research 

has been conducted on this treatment in an environment open to the atmosphere (oxic). As

previously stated, when dissolved iron is oxidized, it will precipitate, armoring limestone and
Coal Remining BMP Guidance Manual

Passive Treatment 4-19

creating an iron hydroxide sludge. In theory, limestone, even if completely armored with iron,

will continue to yield some alkalinity. Ziemkiewicz and others (1994) indicated that CaCO3 in

fully armored limestone is 20 percent as soluble as that in unarmored limestone. However,

Ziemkiewicz and others (1996) reported that armored limestone may exhibit 25 to 33 percent of

the CaCO3 solubility of unarmored limestone. They observed an acidity reduction of 0.029 to

1.77 percent per foot of open limestone channel (OLC). Though rapid neutralization of acidity by

armored limestone is observed initially, it slows with time, and exhibits a logarithmic decay of the

neutralization rate (Ziemkiewicz and others, 1996).

Limestone channels are sized based on a projected 90 percent acidity neutralization with one hour

of contact time or 100 percent acidity neutralization with three hours of contact time.

Construction criteria are determined from the flow rate, channel slope, and acidity concentration.

This information will determine the mass of limestone, the cross-sectional area and length of the

drain, and ultimately, the in-channel detention time. Channels are constructed with an initial damlike structure at the up-stream end to trap sediment and other debris and keep it from clogging the

pore spaces between the limestone material throughout the remainder of the channel

(Ziemkiewicz and others, 1994). OLCs also require sufficient slope, hence water velocity, to

prevent clogging of the interstitial pore spaces with iron, manganese, and aluminum floc. If the

pore spaces are substantially filled with metal floc, the water will flow over the top and be

precluded from contacting the armored limestone, greatly attenuating, if not eliminating predicted

dissolution rates.

Table 4.1 presents examples of limestone tonnage calculated to treat mine drainage with 1000

mg/L acidity, in an OLC with a cross section 3 feet deep by 10 feet wide. A mine discharge of

200 gpm and 1000 mg/L acidity would require a channel 3 feet deep, 10 feet wide, and 401 feet

long filled with 5,085 tons of armored limestone to treat 100 percent of the acidity.
Coal Remining BMP Guidance Manual

4-20 Passive Treatment

Table 4.1: OLC Sizing Calculations

Channel Length in feet

Tons of Limestone Required

100% Dissolution 20% Dissolution

Flow in

gpm

1 hour

contact time

3 hour

contact time

1 hour, 90%

Treatment

3 hour, 100%

Treatment

1 hour, 90%

Treatment

3 hour, 100%

Treatment

100 67 201 169 508 847 2,542

200 134 401 339 1,017 1,695 5,085

500 334 1003 847 2,542 4,237 12,712

1000 669 2006 1,695 5,085 8,475 25,424

Modified after Ziemkiewicz and others (1994)

A recommended size of limestone gravel for use in these channels is greater than 4 inches in

diameter (Ziemkiewicz and others, 1994). Optimal efficiency may be reached with limestone in

the 6 to 12 inch diameter range. A channel grade exceeding 10 percent is also recommended to

facilitate flushing of the metal floc from the drain, preventing a clogging of the pore spaces.

Channels with less than a 9 percent grade were shown to be much less effective than channels

with steeper grades (Ziemkiewicz and others, 1996). Because these channels are designed to

flush out the metal floc, settling ponds are often constructed at the outlet point. These ponds will

allow the metal floc to be concentrated at one point and should permit discharging the compliance

water to the receiving stream. However, ponds will require periodic cleaning to maintain

efficiency.

Open limestone channels are relatively simple and inexpensive systems to construct. However,

there are some limitations to their use. Neutralization ability of these channels is greatly limited by

the dissolution rate of armored limestone, atmospheric CO2 concentrations, and contact time.

Additionally, the reported dissolution rates (Ziemkiewicz and others, 1994; 1996) may be greater

than what is chemically possible. Acidity reduction of up to 5 percent may occur due the

formation of the minerals swartzmanite and jarosite, which store acidity (H+). Calcium

concentrations indicate the limestone dissolves at a rate considerably below 5 percent (Rose,
Coal Remining BMP Guidance Manual

Passive Treatment 4-21

1999). In order to treat relatively large discharges with considerable acidity concentrations, very

long drains (>3000 feet) with thousands of tons of limestone would be required. Therefore, these

channels may not be applicable to space-limited mine sites. These channels require at least a 10

percent slope to prevent clogging, so they cannot be constructed in areas without the required

topography or where the receiving stream is too near.

Oxic Limestone Drains

An oxic limestone drain, unlike an ALD, is designed to treat water containing appreciable

dissolved oxygen and iron that has been oxidized (ferric). Like ALDs, OLDs are designed to

promote higher limestone dissolution, hence alkalinity production, by concentrating the partial

pressure of CO2 (Pco2). The Pco2 is increased because the drain is covered, hampering its escape.

The limestone dissolves rapidly enough to make the surface an unstable substrate for iron

armoring, because the chemical reactions within the drain cause the dissolution of 2 moles of

CaCO3 for each mole of Fe(OH)3 produced. The iron hydroxide (Fe(OH)3) and aluminum

hydroxide (Al(OH)3) will precipitate to some extent within the drain. However, Cravotta (1998)

observed that some of the metal flocs were “loosely bound” and were eventually carried down

through the drain with water velocities 0.33 to 1.31 feet per minute and residence times #3.1

hours (Cravotta and Trahan, 1999). Additionally, the drains can be designed for periodic flushing

to preclude buildup of these metal hydroxides.

There has been limited research on the use of OLDs to treat mine drainage. AMD with a

moderate acidity concentration (< 90 mg/L), a pH of less than 4.0, and moderately low dissolved

metal (iron, manganese, and aluminum) concentrations (1 to 5 mg/L) was treated using an OLDs

(Cravotta, 1998).

The drains studied exhibited decreased iron and aluminum concentrations of up to 95 percent.

Initially (first 6 months), manganese concentrations were unaffected by the drains. After the

initial 6 months, the manganese concentrations were lowered by 50 percent, because of

coprecipitation with the Fe(OH)3 facilitated by higher pH (>5.0) of the water. The higher pH was
Coal Remining BMP Guidance Manual

4-22 Passive Treatment

due to increased alkalinity production as the water flowed through the drain. The rate of

alkalinity production was greatest initially and decreased as the water traveled through the drain

(Cravotta, 1998). This observation was likely caused by the more aggressive nature of the water

as acidity (H+) is released with the formation of Fe(OH)3.

Drain sizing criteria are based largely on the discharge rate and desired alkalinity production. The

discharge rate relates to in-drain residence time, which in turn is related to treatment effectiveness.

Cravotta (1998) recommends that a perforated-pipe under drain be installed to permit periodic

flushing of the precipitated metal hydroxides.

Although the research and use of OLDs are limited at this time, these drains may be a low cost

method of treating low-level mine drainage. These drains will likely fail to effectively treat if:

• The flow rates are too high for the required detention time.

• The acidity is higher than the limited reaction rates allowed by the drain .

• The metal concentrations of the inflowing water are well above those previously tested.

• Drain clogging cannot be prevented or abated.

• The Pco2 cannot be maintained at a high level.

The Pyrolusite® Process

Manganese removal from AMD is extremely difficult and has been historically costly. 

Manganese does not precipitate as easily as iron, and certain manganese oxides are soluble in 

the presence of ferrous iron. For these reasons, many operators should raise the pH to above 10

in order to effectively precipitate it out of solution (Kleinmann and others, 1985). The elevated 

pH then becomes problematic, because it is out of compliance (6.0 to 9.0 standard units) and

extremely costly in terms of reagent and facility sizing. The manganese effluent standards were

originally established as a surrogate rather than establishing standards for a series of toxic metals

at mine treatment facilities, to some extent due to the detriment of manganese on the stream

quality, and the best practicable control technology (BPT) of existing water treatment facilities

(Kleinmann and Watzlaf, 1986). However, the toxicity of manganese on aquatic life has not 
Coal Remining BMP Guidance Manual

Passive Treatment 4-23

been conclusively established. An effective and inexpensive passive method to treat manganese in

AMD has been actively pursued for several years.

Vail and Riley (1997) reported on a biologically-driven patented process to remove iron and

especially manganese from mine drainage, while raising the alkalinity of the water. In this

process, a bed of crushed limestone is inoculated with “cultured microorganisms” that oxidize

iron and manganese in the water contacting the bed. These aerobic microorganisms produce

relatively “insoluble metal oxides” while yielding alkalinity by “etching” the limestone hosting

medium. The microorganisms are environmentally safe and are not biologically engineered (Vail

and Riley, 1997). The metal oxides formed during this process are believed to be manganese

dioxide or pyrolusite (MnO2) and hematite (Fe2O3). Both metal oxides are relatively stable and

insoluble in alkaline water.

The system is designed so that the water has a protracted contact with the limestone with a

recommended minimum residence time of 2.5 to 3.0 days. The engineered treatment cell size

should be based on a projected maximum peak flow. The purity of the limestone should be at 87

percent CaCO3 or greater (Vail and Riley, 1997). The hydraulics of the cell should be managed to

maximize water contact with the limestone substrate.

Results from a Pyrolusite® process cell monitored over a 5 year period showed a dramatic

reduction in metals and an increase in the pH. An average influent of 30 mg/L manganese was

reduced to below 0.05 mg/L in the effluent. Inflowing iron ranged from near 1 to over 115 mg/L,

while the effluent was consistently below 1 mg/L. The pH of the water was raised over 2 orders

of magnitude from about 4.5 to over 7.0. The pH improvement is directly attributable to a

dramatic increase in the alkalinity from about 10 mg/L or less to an average of nearly 80 mg/L

(Vail and Riley, 1997).

Restrictions on the use of Pyrolusite® cells stem to some extent from the limited knowledge of

these systems and details on precisely how they function. The mineral created may in fact be

todorokite (i.e. delatorreite), which is a more complex manganese oxide (Cravotta, 1999). The
Coal Remining BMP Guidance Manual

4-24 Passive Treatment

microorganisms that oxidize the metals may be inherent in nature. Therefore, culturing and

inoculation procedures may not be necessary. There are size considerations in the construction of

these systems due to the relatively long residence times recommended (2.5 to 3.0 days). A large

flow rate would require a fairly large system for successful treatment. It is also uncertain how

highly acidic (pH < 4.0) metal-laden water would affect the treatment process.

Alkalinity-Producing Diversion Wells

Alkalinity-producing diversion wells, a low maintenance method for treating acidic water, were

developed in Norway and Sweden using a water pressure-driven, fluidized limestone bed. This

technology has been modified for use in treating AMD and streams contaminated by AMD

(Arnold, 1991).

Typically, these diversion wells are large cylinders (commonly 5 to 6 feet in diameter and 6 to 8

feet high) composed of reinforced concrete or other erosion resistant material (Figure 4.1e). Two

manhole sections, one on top of the other, are frequently used. The bottom of the well should be

equally strong and erosion resistant and is commonly formed from reinforced concrete. Water is

piped into the center of the well with the end of the pipe just above the well bottom (2 to 3

inches). The outlet point can also be fitted with a metal collar with holes drilled in the sides. This

will direct the water sideways and appears to be more efficient than directing the water

downward. An 8 or 10 inch pipe size is recommended to provide the required flow rate. The

water is fed from a point up gradient, where the water is dammed to yield a consistent 8 feet of

head above the well surface (Arnold, 1991). A driving head of 10-12 feet was suggested by

McClintock and others (1993). Only a portion of the stream flow is diverted, while the rest

continues to flow normally downgradient. The recommended flow rate should average about

2,244 gpm (Arnold, 1991), however, observations of working wells in eastern Pennsylvania,

indicate that a flow rate of 112 to 224 gpm may sufficiently operate diversion wells. McClintock

and others (1993) stated that stream flows as low as 100 gpm can be treated with diversion wells. 

At low-flow streams virtually all of the flow will be routed through the well. Crushed limestone 

is dumped into the well. The optimum size of the limestone is one-half to three-quarters of an
Coal Remining BMP Guidance Manual

Passive Treatment 4-25

inch. Smaller size particles tend to easily wash out and larger particle sizes require higher flow

rates to maintain a fluidized bed. The rapid upward movement of the water through the well

causes the limestone chips to roil creating a fluidized bed. The top of the well is flared to

accommodate an energy reduction in the upward flow which inhibits limestone from washing out. 

The well is maintained to be consistently approximately half full of limestone (Arnold, 1991).

Figure 4.1e: Typical Alkalinity-Producing Diversion Wells

The water intake point needs to be constructed to inhibit the uptake of leaves, sticks, and other

debris, which tend to clog the plumbing. Arnold (1991) recommends a tee with each side fitted

with an elbow open toward downstream (Figure 4.1f). Air vents drilled into the tee are

recommended to allow the bleeding off of entrained air from vortex action and from air entrained

during low flow periods (Arnold, 1991).
Coal Remining BMP Guidance Manual

4-26 Passive Treatment

Figure 4.1f: Example of a Water Intake Portion of an Alkalinity-Producing Diversion

Well

These wells yield alkalinity from acidic water that reacts directly with the limestone and by the

churning action of the fluidized bed grinding the limestone into fine particles. The finer limestone

particles will also react with the water in the well, imparting additional alkalinity and are carried

out of the well and to the stream to react with the remaining acidic water that is not piped through

the well. The constant churning and surface abrasion of the limestone prevents armoring by

dissolved iron in the mine drainage. Limestone consumption rates vary with flow rate, well size,

limestone purity and hardness, and to a lesser extent water quality. However, these wells are

generally designed to use approximately 0.92 yd3 of limestone per week. Purer limestones are

recommended, because highly dolomitic, very hard limestones tend to react too slowly (Arnold,

1991). It is important to note limestones that are too soft will break up too easily, rapidly wash

out of the well, and require more frequent replenishment.
Coal Remining BMP Guidance Manual

Passive Treatment 4-27

The turbulent action within the wells preclude in-situ iron deposition. Any dissolved iron present,

above 0.3 mg/L, will likely precipitate after leaving the well. It may be prudent to have a settling

pond constructed between the well and the receiving stream to collect much of the precipitating

iron and other metals.

Arnold (1991) recorded an increase of one to two pH units (orders of magnitude) of the water

leaving the diversion well at 5 cfs. McClintock and others reported a pH increase of up to 3

orders of magnitude. Arnold anticipated a rise in alkalinity proportional to the pH increase, and

which alkalinity was increased somewhat, but the concentrations remained relatively low. No

detrimental impacts on the in-stream aquatic life were noted with the use of diversion wells

(Arnold, 1991). The limited alkalinity production is due primarily to the low (atmospheric) levels

of CO2, which govern the rate of limestone dissolution. Watten and Schwartz (1996) proposed

pretreating the mine water by injecting CO2 under pressure (100 psi), which increases CO2

saturation by 22,000 fold. This CO2 saturation increases the potential alkalinity production to

1,000 mg/L (Watten and Schwartz, 1996). However, CO2 injection is not passive in nature and

would dramatically increase the cost and labor of the operation.

There are some restrictions in the use of diversion wells. These include, but are not limited to:

• Sufficient grade is required to maintain the 8 to 12 feet of head.

• Sufficient flow is required to keep the well functioning properly.

• Waters with high acidity concentrations will not be completely treated by one pass through

a well. The water may need to be piped through a battery of wells to achieve complete

neutralization.

• There is more maintenance required for these wells than is needed for other passive

treatment systems. Recharging of the limestone may need to be performed on a weekly

basis.

• If considerable dissolved iron is present, an additional settling pond may be required.

• Intake clogging may be a problem during certain times of the year. Keeping the intake

clear and unclogging of the entire piping system are periodic maintenance requirements.
Coal Remining BMP Guidance Manual

4-28 Passive Treatment

Design Criteria

Passive treatment systems are designed to inexpensively treat AMD with very little to no

maintenance once constructed. These systems are engineered to raise the alkalinity and pH while

facilitating the precipitation of metals. The mechanisms of AMD treatment rely on metals

oxidation or reduction and the production of alkalinity by sulfate reduction or limestone

dissolution. The design of these treatment systems varies according to the type, but there are

some basic requirements that are common to all. The following list includes basic criteria of

passive treatment systems:

• Data are required to determine anticipated flow rates and water quality.

• The size of the facility is based to a large extent on flow rates and detention time. 

• The type of system to be employed is directly dependent on water quality (e.g., pH,

ferrous vs ferric iron, dissolved oxygen content, net alkalinity, etc.).

• The highest CaCO3 purity limestone is recommended.

• Considerable area is generally required to construct these systems.

• Sufficient grade is required to permit gravity-driven water flow through these systems.

• Flow through these systems needs to be consistent. An interruption of flow can cause the

treatment efficacy to be compromised.

• ALDs require low levels of dissolved oxygen, dissolved iron to be virtually all ferrous, and

low levels of dissolved aluminum.

• Aerobic wetlands work best when the pH is elevated and there is a net alkalinity.

• To maintain efficiency, SAPS, oxic limestone drains, and open limestone channels require

periodic flushing to wash out the loose metal precipitates.

4.2 Verification of Success or Failure

As with all BMPs, verification of proper implementation is crucial to effective control or

remediation of the discharge pollution loadings. Monitoring of the water quality and quantity 

will be the truest measure of the effectiveness of these BMPs. The importance of field 
Coal Remining BMP Guidance Manual

Passive Treatment 4-29

verification of all aspects of a BMP cannot be overstated. It is the role of the inspection staff to

enforce the provisions outlined in the permit. The inspector generally does not need to be present

at all times to assess the implementation of the BMPs in this chapter. However, during

installation, some passive BMPs will require closer and more frequent field reviews than others.

The truest test of the success of passive treatment is the water quality of the effluent compared to

the influent. This assessment is determined through sampling and analysis of the water and

measurement of the flow rate. A sampling and measurement port is needed to access the

discharge prior to treatment. An assessment of influent verses effluent flow rates is also

necessary. Greater outflow than inflow is indicative that the system is gaining unaccounted-for

water within the system. If the outflow is less than the inflow, the system is likely leaking. If the

treatment system is gaining or losing unaccounted-for water, it should be repaired. Topographic

maps or surveying can be used to determine if sufficient grade exists to adequately drive the flow

of these systems.

Implementation Checklist

There are several items that should be monitored to ensure these treatment systems are adequately

engineered and installed. This list includes but is not limited to:

• Measurement of flow rate and analysis of the water quality of the discharge. Treatment

system engineering is based on these data. Water should be especially analyzed for DO,

ferrous and ferric iron, acidity, pH, alkalinity, dissolved aluminum, and dissolved

manganese.

• Measurement of the flow rate and analysis of the water quality of the system effluent.

Compare effluent quality to raw water for efficiency determinations.

• Monitor the amounts, size, and purity of any limestone used. Limestone purity should be

determined from laboratory analysis. Monitor the type and amount of organic materials.

The amount of limestone can be determined from reviewing the weigh slips or estimated

from the stockpile dimensions.
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4-30 Passive Treatment

• Review background data, especially flow, iron concentration, and acidity concentration, to

determine the adequate sizing of the treatment systems.

• Monitor crucial portions of the system installation.

• Check for unwanted water infiltration and/or leaks.

• Determine if sufficient grade exists to create the head required to run these systems.

Many of the verification techniques are common to several passive treatment types, while others

may be system-specific. The following list include implementation verification techniques for

passive treatment systems:

ALDs

• The size of the trench can be measured during excavation for comparison to the calculated

amount of crushed limestone required for treatment. A cubic yard of crushed limestone

(1.5 to 2.0 inch) weighs about 2,300 pounds (Nichols, 1976).

• Cover material (e.g., plastic and clays) can be inspected prior to use or can be viewed

during installation. If there is a concern as to the adequacy of this material, certification of

the strength, permeability, and other properties can be required.

• The DO and/or iron oxidation state of the effluent can be analyzed to ascertain the ability

of the drain to preclude atmospheric oxygen.

• A lack of drain outflow and/or the existence of unanticipated discharge points are

indicative that the drain is clogged and/or cannot handle the amount of water piped into it.

• Drains should be sized to permit at least a 15 hour, preferably 23 hour, detention time.

Constructed Wetlands

• Sizing of wetlands can be directly measured and compared to the flow rate to determine if

they were sized adequately to properly treat the water. It is recommended to use a sizing

factor of 10 gdm for water with a pH of greater than 4.0 and 4 gdm if the pH is less than

3.0 (Hedin and Nairn, 1990). However, a sizing factor of 15 gdm may provide reasonable

results (Kepler, 1990). 
Coal Remining BMP Guidance Manual

Passive Treatment 4-31

• the optimal flow through the wetland can be determined from visual observation or by use

of tracing dyes . 

• Lack of vegetation may be an indication that the water level is too high or too low.

SAPS

• The size of the system can be measured during excavation for comparison to the

calculated amount of crushed limestone required for treatment. 

• Sizing of SAPS can be directly measured and compared to the flow rate, (using the above

referenced sizing criteria) to determine if it is adequate for proper treatment.

• Effluent water quality can be monitored to determine if the iron is being reduced and the

DO is being removed.

• The water level should be monitored to ensure that the SAPS will not be dewatered or

overflow. Either situation will impede the effectiveness of the system.

• SAPS should be sized to permit a detention time similar to ALDs (15 to 23 hours).

Open Limestone Channels

• The size of the trench can be measured during excavation and compared to the calculated

amount of crushed limestone required for treatment. 

• Sizing of channels can be directly measured and compared to the flow, using the above

referenced sizing criteria, to determine if it is adequate for proper treatment.

• Visual inspection or inadequate flow rate will indicate if the metal floc is clogging the pore

spaces in the limestone. 

• Flow-through rate and average detention time can be determined by use of dye tracing.

• Recommended detention time is at least 3 hours to effect 100 percent acidity

neutralization.

Oxic Limestone Drains

• The size of the trench can be measured during excavation and compared to the calculated

amount of crushed limestone required for treatment. 
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4-32 Passive Treatment

• Proper sizing of drains can be directly measured and compared to the flow, using the

above-referenced sizing criteria, to determine if it is adequate for proper treatment.

• A lack of outflow and/or unanticipated discharge points are indicative that the drain is

clogged and/or cannot handle the amount of water piped into it.

• Drain residence times of #3.1 hours and water velocities of 0.33 to 1.31 feet per minute

are adequate to effect treatment and flush out the metal flocs.

• Flow through rate and average detention time can be determined by use of dye tracing.

The Pyrolusite®

 Process

• The size of the trench can be measured during excavation and compared to the calculated

amount of crushed limestone required for treatment. 

• Sizing of beds can be directly measured and compared to the flow, using the above

referenced sizing criteria, to determine if it is adequate for proper treatment.

• A minimum detention time of 2.5 to 3.0 days is recommended.

Alkalinity-Producing Diversion Wells

• The size of the well can be measured during excavation. 

• Sizing of well can be directly measured and compared to the flow, using the abovereferenced sizing criteria, to determine if it is adequate for proper treatment.

• The in-stream improvement as well as the quality of the well effluent are indicative of the

efficiency of these systems.

• A head of 10 to 12 feet is required to run the system. Flow rates of 100 gpm to over 2,000

gpm can be treated. 

4.3 Case Studies

Case Study 1 (Appendix A, EPA Remining Database, 1999 TN (5))

This site is located in Campbell County, Tennessee, approximately 4 miles north of Caryville. 

The operation was permitted for 201 acres adjacent to Interstate 75 with roughly 108 acres of
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Passive Treatment 4-33

coal removal. This was a conventional SMCRA permit, for non Rahall-type remining, and

accessed the Coal Creek coal seam. Passive treatment was used effectively to treat the postmining effluent. Problems arose at this site when operations were ceased, due to a fatal fly rock

incident from blasting of the overburden. After approximately 80 percent of the mining had been

completed, the operation was ceased and never reactivated. The performance bonds were

eventually forfeited and a mine drainage problem developed from flooding of the pit, lack of

proper handling of acid-forming materials, no contemporaneous reclamation, and other

undesirable conditions.

In order to remediate the problem, the Tennessee Valley Authority (TVA), owner of the mineral

rights, undertook the task of reclaiming the site and installed a series of passive treatment systems

to treat the water. They elected to install an ALD followed by staged aerobic wetlands. 

An underdrain was installed across the pit floor as part of the mining process. The outflow of the

underdrain was intercepted and an ALD was tied into it. The ALD was designed for a 30 year

lifespan with almost 3,200 tons of limestone used. Prior to entering the drain, the discharge was

slightly net alkaline (~50 mg/L), with around 40 mg/L dissolved ferrous iron, and an expected

flow estimated at 160 gpm. The drain was designed to yield 250 mg/L alkalinity. 

The discharge of the ALD was piped to the staged wetlands. The wetlands were designed to

remove 20 gdm of iron and 0.5 gdm of manganese. Based on these removal rates, the wetlands

were sized at 3.45 acres. Initially, the ALD effluent was piped to an oxidation pond to permit

primary treatment (abiotic oxidation of metals, hydrolysis, and subsequent precipitation) and to

prolong the effective life of the wetland. The pond was 0.77 acres with a detention time of about

24 hours. Following the pond, the mine water flowed into a 2.7 acre wetland. The wetland was

divided into five cells with different water levels and vegetation. The first cell had an average of 

3 feet of water and was planted with rice cutgrass, wool grass, and arrowhead. The area of the

first cell was 1.02 acres. The second cell had an average of 18 inches of water over 0.59 acres

and was planted with cattail, rice cutgrass, and bulrush. The third cell was 0.44 acres with an

average water depth of 8 inches and was planted with wool grass, arrowhead, and burreed. The
Coal Remining BMP Guidance Manual

4-34 Passive Treatment

fourth cell was 0.35 acres with an average of 10 inches of water and planted with wool grass,

arrowhead, bulrush, burreed, and sedge. The last cell was 0.3 acres with an average depth of 12

inches of water and was planted with cattails. Following the last wetland cell, the water was

channeled to an existing basin for final polishing prior to discharging.

The water of the underdrain discharge prior to the ALD installation (given by the TVA) had a pH

of 6.0, 40 mg/L iron, 7 mg/L manganese, 15 mg/L acidity, and 65 mg/L alkalinity. The flow was

given as 160 gpm. These values were used for treatment system design criteria. Once the passive

system was installed, the raw discharge water could no longer be sampled. Table 4.3a is a

summary of the water quality at various points as it flows through the treatment system from

November 1996 through August 1998. 

Table 4.3: Summary of Water Quality Data at Various Points Along a Passive

Treatment System

Sample Point

Median Flow

 ( gpm)

Median pH

(Standard

Units)

Median

Alkalinity

Concentration

(mg/L)

Median Iron

Concentration

(mg/L)

Median

Manganese

Concentration

(mg/L)

ALD Effluent 186.5 6.2 196 59.50 24.8

Fourth Wetland

Effluent

197.5 6.9 106 0.88 22.6

Last Settling Pond

Effluent

197.0 7.0 100 0.82 11.1

It appears that initial flow estimates used in sizing the system were too low. The median flow

through the system was about 23 percent above the pre-installation estimate. However, the

system has effectively raised the alkalinity. The alkalinity after the ALD is over three times

greater than the underdrain inflow value. The alkalinity is lowered as the water flows through the

wetland by release of mineral acidity as iron and manganese are oxidized and hydrolyze. The final

effluent alkalinity remains over 50 percent above the levels exhibited by the underdrain. The final

pH (~7.0) is significantly above the pH of the ALD influent (~6.0). Iron concentrations are

dramatically reduced from near 60 mg/L to well below BAT effluent standards (<1.0 mg/L).
Coal Remining BMP Guidance Manual

Passive Treatment 4-35

Manganese is reduced by greater than 50 percent, but continues to be well above effluent

standards. The continued manganese problem may be due to the apparent undersizing of the

system. It is uncertain how the 160 gpm was determined for the discharge prior to sizing the

treatment system. Analysis of the existing data indicates that the median flow prior to installation

of the treatment system was nearly 190 gpm. 

4.4 Discussion

The remining Best Management Practice discussed in this section relates to improvement of

effluent by end-of-the-pipe treatment of mine water. Because these systems can be considered as

treatment of mine water, they may not necessarily be categorized as true BMPs. There are

exceptions where a passive treatment technology or system may qualify as an integral BMP. If an

ALD is incorporated within the backfill as a pit floor drain, it can be considered a traditional

BMP. If a passive treatment system is installed to treat a discharge that is adjacent to the

remining operation and outside of the permit boundary, but is not hydrologically connected to the

operation, this also could be considered a BMP. In other words, the operator installs passive

treatment on an adjacent discharge, not legally associated with the remining site, to improve the

overall watershed water quality.

Benefits

• Low maintenance method to reduce the pollution load of mine water.

• Means of gaining additional water quality improvement on and above what is capable with

traditional BMPs.

• Some systems are capable of yielding very high amounts of alkalinity and thus, additional

buffering capacity, by maintaining elevated CO2 concentrations.

Limitations

• Generally require a substantial construction area for moderate to high-flow discharges.

• Require topography that provides sufficient gradient for gravimetric flow.
Coal Remining BMP Guidance Manual

4-36 Passive Treatment

• Need to be refurbished periodically for cleaning out or replenishment of the reactive

materials.

• Certain water quality parameters (e.g., ferric iron, aluminum, or low pH) can cause some

systems to fail or to perform below peak efficiency.

• Metals removal and alkalinity are limited by detention times and chemical reaction rates.

Efficiency

Very few of completed remining sites in Pennsylvania (Appendix B: PA Remining Site Study,

1999) utilized passive treatment as an integral part of their BMP plan. In this study, 2 out of a

total of 231 discharges were effected by passive treatment BMPs. However, only one discharge

was treated with a passive treatment BMP for a manganese problem. A statistical evaluation of

these data is not powerful, because of the extremely limited data. However, no discharge

exhibited significantly degraded water quality for acidity, iron, manganese, or aluminum loadings.

One discharge was significantly improved for acidity, iron, manganese, and aluminum loadings.

The other discharge was unchanged for acidity, iron, and aluminum loadings. 

Additional remining sites are required to conclusively evaluate the use of passive treatment BMPs

in improving effluent pollution loads. However, the research into passive treatment indicates that

in most cases a water quality improvement can be anticipated. 

4.5 Summary

Passive treatment technology, although not generally a traditional BMP, can be used to augment

pollution load reduction achieved by implementation of true BMPs. Passive treatment provides

low cost and minimum labor methods to treat AMD for acidity and certain metals. Research into

passive treatment illustrates that a variety of systems can be used to treat a broad range in water

quality. The type of systems to be employed should be tailored specifically to the mine water

quality. 
Coal Remining BMP Guidance Manual

Passive Treatment 4-37

References

Arnold, D.E., 1991. Diversion Wells - A Low-Cost Approach to Treatment of Acid Mine

Drainage, In the Proceedings of the 12th West Virginia Surface Mine Drainage Task Force

Symposium, Morgantown, WV.

Brodie, G.A., 1990. Treatment of Acid Drainage Using Constructed Wetlands Experiences of the

Tennessee Valley Authority, In the Proceedings of the 1990 Mining and Reclamation Conference

and Exhibition, Charleston, WV, pp. 77-83.

Brodie, G.A., C.R. Britt, T.M. Tomaszewski, and H.N. Taylor, 1991. Use of Passive Anoxic

Limestone Drains to Enhance Performance of Acid Drainage Treatment Wetlands, In the

Proceedings of the 1991 National Meeting of the American Society for Surface Mining and

Reclamation, Durango, CO, pp. 211-228.

Brodie, G.A., D.A. Hammer, and D.A. Tomljanovich, 1988a. Constructed Wetlands for Acid

Drainage Control in the Tennessee Valley, U.S. Bureau of Mines Information Circular, IC9183,

pp. 325-331.

Brodie, G.A., D.A. Hammer, and D.A. Tomljanovich, 1988b. An Evaluation of Substrate Types

in Constructed Wetlands Acid Drainage Treatment Systems, U.S. Bureau of Mines Information

Circular, IC9183, pp. 389-398.

Cravotta, C.A., personal communication with Jay Hawkins, 1999. Details available from the U.S.

Environmental Protection Agency Sample Control Center, operated by DynCorp I&ET, 6101

Stevenson Avenue, Alexandria, VA, 22304.

Cravotta, C.A., 1998. Oxic Limestone Drains for Treatment of Dilute, Acidic Mine Drainage.

Proceedings of the 19th West Virginia Surface Mine Drainage Task Force Symposium,

Morgantown, WV.

Cravotta, C.A. and M.K. Trahan, 1999. Limestone Drains to Increase pH and Remove Dissolved

Metals from Acidic Mine Drainage, Applied Geochemistry, vol. 14, pp. 581-606.

Hedin, R.S. and R.W. Nairn, 1990. Sizing and Performance of Constructed Wetland: Case

Studies, In the Proceedings of the 1990 Mining and Reclamation Conference and Exhibition,

Charleston, WV, pp. 385-392.

Hedin, R.S. and G.R. Watzlaf, 1994. The Effects of Anoxic Limestone Drains on Mine Water

Chemistry, Proceedings of the International Land Reclamation and Mine Drainage Conference

and the Third International Conference on the Abatement of Acidic Drainage, Volume 1,

Pittsburgh, PA, pp. 185-194.
Coal Remining BMP Guidance Manual

4-38 Passive Treatment

Hem, J.D. , 1989. Study and Interpretation of Chemical Characteristics of Natural Water, Third

Edition, U.S. Geological Survey, Water-Supply Paper 2254, 263 p.

Kepler, D.A., 1990. Wetland Sizing, Design, and Treatment Effectiveness for Coal Mine

Drainage, In the Proceedings of the 1990 Mining and Reclamation Conference and Exhibition,

Charleston, WV, pp. 403-408.

Kepler, D.A. and E.C. McCleary, 1994. Successive Alkalinity-Producing Systems (SAPS) for the

Treatment of Acidic Mine Drainage. Proceedings of the International Land Reclamation and Mine

Drainage Conference and the Third International Conference on the Abatement of Acidic

Drainage, Volume 1, Pittsburgh, PA, pp. 195-204.

Kepler, D.A. and E.C. McCleary, 1995. Successive Alkalinity-Producing Systems (SAPS). In the

Proceedings of the 16th West Virginia Surface Mine Drainage Task Force Symposium,

Morgantown, WV.

Kepler, D.A. and E.C. McCleary, 1997. Passive Aluminum Treatment Successes, In the

Proceedings of the 18th West Virginia Surface Mine Drainage Task Force Symposium,

Morgantown, WV.

Kleinmann, R.L.P., 1985. Treatment of Acid Mine Water by Wetlands, In Control of Acid Mine

Drainage, U.S. Bureau of Mines Information Circular 9027. pp. 48-52.

Kleinmann, R.L.P. and G.R. Watzlaf, 1986. Should the Discharge Standards for Manganese Be

Reexamined?, In the Proceedings on Surface Mining, Hydrology, Sedimentology, and

Reclamation, Lexington, KY, pp. 173-179.

Kleinmann, R.L.P., G.R. Watzlaf, and T.E. Ackman, 1985. Treatment of Mine Water to Remove

Manganese. In the Proceedings on Surface Mining, Hydrology, Sedimentology, and Reclamation,

Lexington, KY, pp. 211-217.

Lehr, J.H., T.E. Gass, W.A. Pettyjohn, and J. DeMarre, 1980. Domestic Water Treatment,

McGraw-Hill Book Company, 264 p.

McClintock, S.A., D.E. Arnold, and A.J. Gaydos, 1993. An Installation and Operations Manual

for Diversion Wells: A Low-Cost Approach for Treatment of Acidic Streams. Unpublished

manual. 23 p.

McIntire, P.E. and H.M. Edenborn, 1990. The Use of Bacterial Sulfate Reduction in the

Treatment of Drainage from Coal Mines. In the Proceedings of the 1990 Mining and Reclamation

Conference and Exhibition, Charleston, WV, pp. 409-415.

Nairn, R.W., R.S. Hedin, and G.R. Watzlaf, 1991. A Preliminary Review of the Use of Anoxic

Limestone Drains in the Passive Treatment of Acid Mine Drainage. In the Proceedings of the 12th

West Virginia Surface Mine Drainage Task Force Symposium, Morgantown, WV.
Coal Remining BMP Guidance Manual

Passive Treatment 4-39

Nichols, H.L. 1976. Moving the Earth. North Castle Books, Greenwich, Connecticut.

Rose, Arthur, personal communication with Jay Hawkins, 1999. Details available from the U.S.

Environmental Protection Agency Sample Control Center, operated by DynCorp I&ET, 6101

Stevenson Avenue, Alexandria, VA, 22304.

Skousen, J., B. Faulkner, and P. Sterner, 1995. Passive Treatment Systems and Improvement of

Water Quality, In the Proceedings of the 16th West Virginia Surface Mine Drainage Task Force

Symposium, Morgantown, WV.

Smith, S., 1982 Sulfur Bacterial Problems Revisited, Water Well Journal, NWWA, pp. 44-45.

Spratt, A.K. and R.K. Wieder, 1988. Growth Responses and Iron Uptake in Sphagnum Plants and

Their Relation to Acid Mine Drainage Treatment, U.S. Bureau of Mines Information Circular,

IC9183, pp. 279-290.

Stark, L.R., S.E. Stevens, H.J. Webster, and W.R. Wenerick, 1990. In the Proceedings of the

1990 Mining and Reclamation Conference and Exhibition, Charleston, WV, pp. 393-401.

Vail, W.J. and R.K. Riley, 1997. The Abatement of Acid Mine Pollution Using the Pyrolusite®

Process, In the Proceedings of the 19th Annual Conference of the Association of Abandon Mine

Land Programs, Canaan Valley, WV.

Watten, B.J. and M.F. Schwartz, 1996. Carbon Dioxide Pretreatment of AMD for Limestone

Diversion Wells. Proceedings of the 17th West Virginia Surface Mine Drainage Task Force

Symposium, Morgantown, WV. pp. J-1 to J-10.

Wieder, R.K., 1988. Determining the Capacity for Metal Retention in Man-Made Wetlands

Constructed for Treatment of Coal Mine Drainage. U.S. Bureau of Mines Information Circular,

IC9183, pp. 375-381.

Ziemkiewicz, P.F., and D.L. Brant, 1997. The Casselman River Restoration Project, In the

Proceedings of the 18th West Virginia Surface Mine Drainage Task Force Symposium,

Morgantown, WV. 

Ziemkiewicz, P., J. Skousen, and R. Lovett, 1994. Open Limestone Channels for Treating Acid

Mine Drainage: A New Look at an Old Idea. Green Lands, NMLRC, pp. 36-41.

Ziemkiewicz, P.F., D.L. Brant, and J.G. Skousen, 1996. Acid Mine Drainage Treatment with

Open Limestone Channels. Passive Treatment Systems and Improvement of Water Quality, In the

Proceedings of the 17th West Virginia Surface Mine Drainage Task Force Symposium,

Morgantown, WV. pp. M-1 to M-15.
Coal Remining BMP Guidance Manual

4-40 Passive Treatment
Coal Remining BMP Guidance Manual

Integration of BMPs 5-1

Section 5.0 Integration of Best Management Practices

As the preceding sections have illustrated, Best Management Practices (BMP) are seldom

employed singly. Furthermore, it is virtually impossible for some BMPs to be employed without

the use of other integral and complementary BMPs. For example, if regrading of dead spoils is

performed, corresponding revegetation would also be needed; partial underground mine

daylighting requires sealing of undisturbed mine entries at the final highwall; and daylighting

commonly entails the cleanup of acid-forming materials surrounding the remaining pillars, which

in turn need to be special handled. The efficiency of many BMPs can be augmented by employing

others which complement them. The ability of regrading of dead spoils to preclude surface water

infiltration can be improved when combined with diversion ditches, lined channels, stream sealing,

or spoil capping. The efficacy of special materials handling of acid-forming materials can be aided

by special water handling facilities and alkaline addition.

Past mining practices, prior to the initiation of the Surface Mining Control and Reclamation Act

(SMCRA), dealt mainly with extracting coal as inexpensively as possible. Little attention was

paid to the environmental impacts of the active operation, much less the condition of the site after

mining was completed. The need for employing multiple BMPs is driven by site characteristics

such as the condition and amount of prior land disturbance, acidity of overburden, and the extent

of abandoned deep mines, and by requirements to prevent further degradation by taking

additional, pollutional countermeasures. These abandoned mines often require multiple BMPs to

effect adequate reclamation and pollution mitigation.

There are two basic mechanisms by which BMPs work to decrease the contaminant load: 1) by

physically decreasing the flow of the discharge, and 2) by geochemically improving the water

quality (decrease the contaminant concentration). Some BMPs perform both functions to 

varying degrees simultaneously. Sealing of deep mine entries will inhibit the flow of ground water

as well as prevent the infiltration of oxygen into the mine. Revegetation will inhibit water and 
Coal Remining BMP Guidance Manual

5-2 Integration of BMPs

oxygen infiltration into the backfill as well as impede erosion and sedimentation. It can also

increase the amount of CO2 available in spoil and therefore can positively influence carbonate

dissolution. The choice of which BMPs are needed to decrease the pollutant loads is site-specific

and cannot be determined using cookbook methodology. The experience and knowledge of

permit preparers and reviewers are the major factors in the successful selection, design, and

implementation of remining BMPs.

Some of the BMP combinations have been discussed in preceding sections. This section will

discuss these combinations in more detail, as well as cover BMP combinations not previously

discussed. This section was written to cover the benefits of combining BMPs. It is not the

intention of this section to discuss the benefits of all possible BMP combinations, but rather to

discuss the overall benefits of combining BMPs. It is likely that there are some beneficial

combinations not specifically addressed.

Regrading and Revegetation

Regrading and revegetation work hand-in-hand to decrease pollution loadings both physically and

geochemically. This BMP combination functions physically by reducing the amount of surface

water introduced into the backfill and, geochemically by altering spoil pore gas composition that

impacts the weathering of carbonates and pyrite. Spoil regrading eliminates exposed, highly

permeable material and closed contour depressions, both of which, when unchecked, facilitate

direct infiltration into the spoil of surface water, and promote surface runoff.

The addition of soil and vegetative cover over regraded spoil also works to enhance the inhibition

of surface water infiltration. Soils will allow some surface water infiltration, but a great deal of

the infiltrating water will be held in the soil horizon until it is used by plants. The structure of soil

cover is such that significant quantities of water are preferentially retained. The soil holds water

near the ground surface which permits direct evaporation. The addition of vegetative cover

further inhibits water infiltration into the underlying spoil. The plants, during the growing 
Coal Remining BMP Guidance Manual

Integration of BMPs 5-3

season, will take up the water in the soil and transpire it back into the atmosphere. Certain types

of plants will promote additional runoff, especially during high intensity precipitation events. Use

of biosolids can greatly enhance the vegetative growth and cover percentage, which in turn, will

promote greater water use by the plants. However, biosolids should be applied with the provision

that the nutrients that they provide may promote significant growth of iron-oxidizing bacteria,

thus possibly increasing acid production. However, this effect may be transient and relatively

insignificant (Cravotta, 1998). The application of biosolids in Pennsylvania’s Remining Site Study

appears to have resulted in a positive influence on water quality (Section 6, Table 6.3a).

The more stable regraded surfaces will also function geochemically by inhibiting the introduction

of oxygen at depth and by retaining carbon dioxide. Regrading of several spoil piles into one

large backfilled area results in less surface area and fewer slopes for atmospheric exchange. In

addition, thicker spoil will make it more difficult for oxygen penetration at depth. Soil cover and

plant growth tend to further preclude oxygen infiltration and retention of carbon dioxide in the

underlying spoil. In addition, the decay of organic matter in the soil utilizes oxygen, further

suppressing deeper oxygen infiltration. 

Combining implementation of diversion ditches and stream sealing above the mined area and/or

across the surface of the backfill (typically implemented on sites with severely acidic overburden)

can augment the efficiency of regrading and revegetation. Capping the site with a low

permeability material can also reduce surface water as well as oxygen infiltration. 

There are cases where regrading and revegetation alone are not adequate for pollution reduction. 

If the regraded spoil is determined to be inherently acidic and the acid-forming materials are

widely disseminated, other BMPs such as alkaline addition, mining into alkaline strata (if present),

or alkaline redistribution may be necessary. Another BMP that has been used in these

circumstances is the installation of induced alkaline recharge structures. 
Coal Remining BMP Guidance Manual

5-4 Integration of BMPs

Daylighting

There are several BMPs that can be implemented in conjunction with daylighting to enhance the

impact on discharge pollution loadings. Daylighting commonly generates considerable acidforming materials (waste coal, immediate roof rock, etc.) when the area around pillars is cleaned

prior to the excavation of the coal. This acidic material generally requires special handling to

further prevent AMD formation. If the amount of acid-forming materials removed from around

the coal pillars is significant, this material may need to be removed from the site and disposed of

off-site. Additionally, because of the fair amount of acid-forming material that is usually spoiled,

alkaline addition may be needed to offset the acidity potential. The alkaline material may also

require special handling. Depending on the situation, alkaline material may need to be placed

either above the acidic material to prevent AMD formation, or below or within the acidic material

to neutralize AMD already formed. Alternatively, mining may need to progress to a predefined

overburden thickness to allow disturbance of significant quantities of naturally occurring alkaline

rocks above the coal.

If the daylighting does not eliminate all of the abandoned underground mine, other BMPs may be

used to aid pollution abatement. The mine entries will need to be sealed to exclude the lateral

infiltration or discharge of ground water as described in Section 1.0. Mine entry seals also inhibit

the infiltration of atmospheric oxygen to or from the underground mine. If considerable water is

stored in and is flowing through the underground mine, a drain may need to be piped from behind

the seals through the backfill, thus diverting the water away from the site.

Coal Refuse Removal

Coal refuse removal or reprocessing is a special case of remining. The acidic material is partially

or completely removed from the site. In either coal refuse removal or reprocessing, the potential

for AMD production is greatly reduced, because the sulfur source is diminished. 
Coal Remining BMP Guidance Manual

Integration of BMPs 5-5

Other BMPs can also be employed to further the pollution abatement. In cases where the coal is

reprocessed on-site and the waste rock is returned, bactericides may be an option to inhibit pyrite

oxidation prior to covering and revegetating the pile. Bactericides can be applied as the waste

material is transported via a conveyor belt. Sites involving coal refuse removal or reprocessing are

also prime candidates for alkaline addition. Coal refuse seldom has any natural alkalinityproducing ability, therefore any alkaline material added should be beneficial in AMD prevention or

neutralization. 

Prior to remining, coal refuse piles commonly allow considerable water and oxygen infiltration. 

These piles are poorly vegetated and typically do not promote runoff. Regrading, soiling and

revegetation of the waste material will prove beneficial in many respects, not the least of which is

to promoting runoff and reducing water and oxygen infiltration. Surface water control structures

(e.g., diversion ditches) and the capping of the refuse with a low permeability material can also aid

the reduction of pollution loads. 

Remining operations involving complete removal of the coal refuse will nearly completely

eliminate the AMD production. However, all of the refuse is seldom removed. Refuse is

screened and the fine material, which contains most of the coal, is sent to the power plant. The

larger materials remain behind. There are usually minor amounts of refuse left in place. Other

BMPs that can prove useful with these types of operations are alkaline addition, regrading and

revegetation, and surface water control. Coal combustion waste (CCW), a byproduct of burning

the refuse, is often returned to these sites. CCWs typically contain some alkaline material

resulting from the addition of limestone during the burning process, thus providing some acidneutralization potential. 

Special Handling with Surface and Ground-Water Controls

A critical component of successful special handling of acidic and alkaline material is understanding

the ground-water system. If the ground water can be controlled, special handling will more likely

prove successful. 
Coal Remining BMP Guidance Manual

5-6 Integration of BMPs

In cases where the acidic material is placed in pods in the backfill and are intended to be located

above the fluctuating water table, ground-water control and, to some extent, surface water

control can be used to suppress the water table and dampen water table fluctuations. Highwall

drains and highwall diversion wells can be employed to intercept laterally infiltrating ground

water, and floor drains can be used to collect and rapidly remove ground water. Both of these

BMPs will work to suppress the water table (Figure 5.0a). Mine entry sealing and diversion

(piping or channeling) of underground mine waters will also aid in this respect. The use of

surface water diversion ditches, spoil capping, and/or stream sealing will aid in suppressing the

water table through reduced vertical infiltration. Capping and revegetation may aid geochemically

by inhibiting atmospheric oxygen infiltration into acidic pods, reducing pyrite oxidation, and

reducing the amount of water available for transport of acid materials. 

Figure 5.0a: Water Table Suppression in Conjunction with Special Handling of Acidic

Material 
Coal Remining BMP Guidance Manual

Integration of BMPs 5-7

Conversely, if alkaline material is specially handled within the backfill, it may be beneficial to

divert extra water through these areas to generate additional alkalinity. This is similar to induced

alkaline recharge (Section 2.3). In cases of special handling of alkaline materials, there are

ground- and surface-water controls that can be employed to increase the amount of water that

encounters the alkaline material. Chimney drains can be used to funnel water from the surface

toward alkaline zones. Additionally, the drains themselves can be comprised of limestone or other

alkaline rock. The surface of the reclaimed site can be configured to promote selective

infiltration. Small impoundment areas can be created to allow surface water to collect and

infiltrate in areas above alkaline-rich areas.

Alkaline material can be placed in areas that will be within the main ground-water flow paths. 

Ground water will flow primarily along the path of least resistance, which in mine spoil is

commonly the buried spoil valleys. The larger spoil particles tend to roll off the sides and collect

at the valleys between spoil piles. Thus, these valleys tend to be highly transmissive zones that

facilitate significant ground-water flow (Hawkins, 1998). Placing alkaline material in these

valleys, prior to reclamation, will likely enhance increased alkalinity production. Conversely, the

acid-rich pods would be best placed in the center of the ridges as far away, both vertically and

horizontally, from the highly transmissive zones as possible, but such that they will not be too near

the surface. These optimal placement locations are illustrated in Figure 5.0b.
Coal Remining BMP Guidance Manual

5-8 Integration of BMPs

Figure 5.0b: Optimal Location for Special Handling of Acidic and Alkaline Materials

For selected sites where acidic material placement is below the water table, the use of water

infiltration control BMPs can be beneficial. It is critical to keep this acidic material under

saturated conditions and out of contact with atmospheric oxygen. Given the hydrogeologic

conditions within the Appalachian Plateau, many surface mines are located above the regional

water table and local water tables are relatively thin. Keeping acidic material under saturated

conditions is extremely difficult. However, if large amounts of water can be induced to infiltrate

into and held within spoil, it can help maintain a minimum water level in the backfill. Chimney

drains and induced alkaline recharge structures can be used to promote infiltration. In addition,

the surface of the reclaimed site can be configured to promote direct infiltration, and small

impoundment areas can be created to allow surface water to collect and infiltrate into the spoil. 

Engineered highwalls can also be created to aid infiltration. For example, bench slopes can be

designed to induce infiltration by directing water back toward the highwall, permitting small

impoundments or infiltration zones rather than promoting runoff. Once ground water has
Coal Remining BMP Guidance Manual

Integration of BMPs 5-9

infiltrated the backfill, as much ground water as possible should be stored to maintain a high water

table and saturated conditions. Surface mining below the regional ground-water flow system

should allow acidic material submergence, because the water table will commonly re-establish

itself and be maintained at a sufficient level. Because it is common in the Appalachian Plateau for

undisturbed strata to have hydraulic conductivity values two orders of magnitude lower than the

associated spoil (Hawkins, 1995), if the final highwall is down dip from the mining operations,

substantial ground water should impound behind it. In these situations, acidic material should be

placed against the highwall to maximize the potential for continual submergence. If the highwall

is up dip of the mining operations or the strata are nearly level, maintaining a high water table will

be extremely difficult, because the ground water will tend to drain more freely at the toe of the

spoil. Therefore, subaqueous placement of acidic materials will likely not be an option. If

hydrologic controls (e.g., low permeability zones) can be installed in the backfill to inhibit groundwater movement and subsequent discharge, subaqueous placement of acid-forming materials may

be viable through maintenance of an elevated water table. A thorough knowledge of site

hydrogeologic conditions is required to attempt a “dark and deep” placement or saturated

condition of acid-forming materials. However, even with these ground-water controls, a

protracted drought may cause the water table to drop below the level of the acidic material, which

will likely make worsen the water qualitiy.

Alkaline addition also can be combined with the use of low permeability CCW. CCW, when used

as a capping, entry seal, or grouting material, can be used with other BMPs to inhibit water

movement and provide the ground water with some alkalinity. CCW also can be beneficial when

applied to acidic pit floors by sealing the pit floor from ground water.

Miscellaneous BMP Combinations

The use of passive treatment systems can be beneficial to virtually all remining sites with

continuing post-remining AMD discharges, regardless of the BMPs employed during mining. 

However, some types of passive treatment can be integrated into the reclamation plan. These
Coal Remining BMP Guidance Manual

5-10 Integration of BMPs

passive treatment systems include installing an ALD as a pit floor underdrain through the backfill

and configuring the regrading and revegetation to create a wetland.

Mining into enough cover to encounter alkaline strata can also be beneficial for special handling of

acidic materials. Acidic materials, when strategically placed above the water table, commonly

need to be well above the pit floor (e.g., >15 to 20 feet) and deep enough to be removed from the

impacts of infiltrating atmospheric oxygen. Therefore, a substantially thick backfill is required to

maintain the acid-forming materials within these narrow guidelines. Mining into additional cover

may yield the necessary spoil thickness to properly handle acid-forming materials.

Capping of mine spoil with a low permeability material can aid the alkalinity production of

inherent, redistributed, and added alkaline materials in the backfill. These caps can inhibit the

exchange of gases from the backfill to the atmosphere and vice versa. Therefore, the caps will

prevent CO2 in the vadose zone from escaping, which will promote higher alkalinity production.

Summary

BMPs are seldom employed alone. Because of the frequently multifaceted nature of abandoned

surface and underground mines, BMP combinations are required to enhance reclamation and to

preclude the potential for greater pollution loadings due to remining. Some BMPs, when used in

conjunction with others can enhance the pollution load reduction efficacy. 

This section does not cover all potential BMP combinations, but does review some of the more

common combinations being implemented during remining operations. BMP plans do not lend

themselves to a preset methodology or cookbook formula. Each remining operation requires a

BMP plan that stems from site-specific conditions that are contingent on the background and

experience of the remining permit and BMP plan preparer and reviewer. Factors such as the 

extent of previous mining, configuration of the abandoned site, geochemistry of the overburden,

site hydrology, and topography all impact the formulation of an effective BMP plan.
Coal Remining BMP Guidance Manual

Integration of BMPs 5-11

References

Cravotta, C.A., 1998. Effect of Sewage Sludge on Formation of Acidic Ground Water at a

Reclaimed Coal Mine. Ground Water, vol. 36, no. 1, pp. 9-19.

Hawkins, J.W., 1998. Hydrogeologic Characteristics of Surface-Mine Spoil, Chapter 3 of Coal

Mine Drainage Prediction and Pollution Prevention in Pennsylvania, Pennsylvania Department of

Environmental Protection, Harrisburg, PA, 11 p.

Hawkins, J.W., 1995. Impacts on Ground Water Hydrology from Surface Coal Mining in

Northern Appalachia. In the Proceedings of the 1995 Annual Meeting of the American Institute of

Hydrology, Denver, CO. pp. IMWA-32 - IMWA-43.
Coal Remining BMP Guidance Manual

5-12 Integration of BMPs
 Coal Remining BMP Guidance Manual

Efficiencies of BMPs 6-1

Section 6.0 Efficiencies of Best Management Practices

Determination of the efficiencies of Best Management Practices (BMP) is best performed using

data that accurately represent water quality and pollution loading before, during, and after

remining has occurred. Water quality and flow data that are used to determine baseline pollution

loading for pre-existing discharges can be compared to data collected to monitor the same

discharges after mining operations have been completed. Because the effects of both remining

operations and associated BMPs are generally not immediate and can continue well beyond mine

closure, it is important to consider water quality and flow conditions for a period of time (e.g., > 2

years) following site closure. 

Site-specific efficiency statements for BMPs have been included in each section of this Guidance

Manual. The purpose of this section is to: 1) present observed results of the effects of the

implementation of 12 BMPs at over 100 remining sites in Pennsylvania using existing data, and 2)

analyze these data, using statistical methods, in order to predict BMP efficiencies at remining sites

throughout the Appalachian coal region. Efficiencies are presented for the following BMPs, as

implemented individually or in combination:

Regrading: the restoration of positive drainage to pre-Surface Mining Control and Reclamation

Act (SMCRA) surface mined areas. Regrading can be to approximate original contour (if

adequate spoil is available) or terraced (if existing spoil is inadequate or if terracing will result in a

higher land use).

Revegetation: the establishment of a diverse and permanent vegetative cover on inadequately

vegetated pre-SMCRA surface-mined areas that is adequate to control surface-water infiltration

and erosion.

Daylighting: the exposure by surface mining of a deep-mined coal seam, with the purpose of

removal of the remaining coal.

Special Handling of Acid-Producing Materials: the selective placement of acid-generating

overburden rock at a position within the backfill that is advantageous for reducing the amount of

acid that would otherwise be generated from that rock.
Coal Remining BMP Guidance Manual

6-2 Efficiencies of BMPs

Alkaline Addition: the importation of off-site calcareous material to a mine site. Alkaline

addition is used in a variety of circumstances, particularly where a mine lacks sufficient

naturally-occurring calcareous rock, but does contain a sufficient amount of pyritic material

that could produce mine drainage pollution in the absence of neutralizers. Alkaline addition is

measured as tons of CaCO3 equivalent/acre. 

Water Handling Systems: refers to any BMP that is specifically designed to: 1) reduce the

amount of surface water that could infiltrate into the spoil and become ground water, or 2)

channel ground water through spoil with the purpose of reducing water contact time with spoil

and/or lowering the ground water table or preventing ground water from entering the spoil.

Passive Treatment: means of treating polluted mine drainage chemically and/or biologically

such that metals concentrations are oxidized or reduced and acidity is neutralized. Compared

with conventional chemical treatment (the typical alternative), passive methods generally

require more surface area, but use less costly reagents, and require less operational attention,

power, and maintenance.

Coal Refuse Removal: the elimination or reduction of abandoned coal waste piles. This

material is typically sent to power plants for generation of electricity. In addition to the

elimination or reduction of the size of the pile, the site of disturbance is regraded and

revegetated.

Biosolids Addition: the application of nutrient-rich organic materials resulting from the

treatment of sewage sludge (a solid, semi-solid or liquid residue generated during the

treatment of domestic sewage in a treatment works) as a soil amendment for enhancement of

plant growth on surface mines.

Mining of Highly Alkaline Strata: the encountering and mixing of naturally-occurring

calcareous rock during the mining process. The mining plan may have to be adjusted to

ensure that sufficient calcareous rock is encountered.

Alkaline Redistribution: the process of taking excess calcareous material from a portion of a

mine and placing it in areas of the mine that lack calcareous materials. Typically, these areas

lacking calcareous materials would not produce acceptable post-mining water quality without

the addition of the calcareous material.

BMP efficiencies presented in this section are based on data provided by Pennsylvania

Department of Environmental Protection (PA DEP) as a remining site study (PA Remining Site

Study). The database from this study existed prior to the initiation of this evaluation, and

includes summary water quality information and associated BMPs only. Therefore, factors that

may have affected discharges in addition to the associated BMPs (such as compliance history)
 Coal Remining BMP Guidance Manual

Efficiencies of BMPs 6-3

 were not considered in this evaluation. The PA Remining Study was not specifically designed

for the purposes of evaluating or determining the BMP efficiencies presented in this section. It

is, however, the largest database available on completed remining sites and includes baseline

data, post-mining data, and a record of BMPs used on 113 mine sites.

In spite of certain limitations of the data evaluated, these data include 231 discharges from 112

closed remining operations, and are the most comprehensive compiled to date regarding the

efficiency of remining. These data are considered highly suited for the determination of BMP

efficiencies, and the BMP efficiencies that have been predicted using these data can be

considered the best available at this time. The advantages of this data set include:

C Over 100 different remining sites and over 230 pre-existing discharges are represented.

C Baseline data include monthly samples, typically for one year.

C Post-mining data include at least one year of monthly sample results.

C Post-mining data represent conditions following reclamation of remining sites.

C BMPs implemented are identified for each discharge.

C Water quality data represent ground-water discharges that are hydrologically connected

to the mine. 

Limitations

It is important to note while reviewing this section that, although the data set used is the most

extensive available on remining at this time, there are some limitations to its use for evaluating

BMP efficiencies. 

C The data is specific and exclusive to remining operations in the Pennsylvania

bituminous coal regions. Although hydrologically and geologically very similar,

remining in other parts of the Appalachian coalfields may exhibit slight differences.
Coal Remining BMP Guidance Manual

6-4 Efficiencies of BMPs

C All permits were State-approved, Rahall remining permits and sites have been

reclaimed to at least Stage II bond release standards. During permit application review,

for operations thought to be potentially environmentally detrimental (i.e., resulting in

increased pollution loadings), permits are either denied or amended to preclude

degradation. 

C This data set does not include non Rahall-type remining operations where pre-existing

discharges are subject to statutory effluent limitations. 

C No discharge data from mining on areas previously unmined, or discharge data from

areas unaffected by BMPs (i.e., control data) were included. 

C All sites all had at least monthly water quality analysis and flow measurement

requirements for determining baseline, as well as during-mining and post-mining

monitoring data. However, no compensation has been applied for sampling through

periods of abnormal precipitation (well above or below the average). 

C At this time, only contaminant loading and flow data are available. Review of

concentration data would permit a more rigorous determination of BMP efficiency. 

Determination of whether a change in flow or contaminant concentration effected the

change in load would permit determinations as to whether a specific BMP made a

physical (flow) and/or geochemical (concentration) difference. These data may be

available in the near future and an in-depth analysis and discussion may follow. 

C For mines reclaimed only recently, the post-mining data may not be fully representative

of equilibrium conditions. During this early period (~ 2 years), the water table is

rebounding and discharge rates may be below those that will occur once the water table

has reached equilibrium. Because the most recently collected 12 months of data (at the

time of database compilation) was used in this study, most sites have been reclaimed

for a number of years and the water table should have stabilized in the backfill.
 Coal Remining BMP Guidance Manual

Efficiencies of BMPs 6-5

6.1 Pennsylvania DEP - Remining Site Study

In 1998, Pennsylvania DEP evaluated water-quality and flow data for 248 pre-existing

discharges from 112 remining sites that had been reclaimed to at least Stage II bond release

standards (completely backfilled and revegetated). The remining sites were scattered

throughout the bituminous coal region of the state and most heavily concentrated in the

southwestern counties. The most recently available 12 months of pollution loading and flow

data were compared against baseline loading and flow data (usually 12 months) for each preexisting discharge. The same statistical test used to detect significant increases in pollution

load (Tukey, 1976; PA DER, 1988) was used to determine whether there were significant

decreases in pollution load. In addition, the current (or most recently available) median

pollution load was calculated in order to quantify the actual increase or decrease in pollution

load. This analysis was conducted for acidity, total iron, total manganese, and total aluminum

loadings. 

Results of the analysis for each individual discharge or discharges identified by and combined

into hydrologically-connected units were entered into a database. The database also identified

the best management practices employed during remining operations that were expected to

have an impact on the water quality of that discharge. A single surface mining permit, more

often than not, includes several individual discharges or hydrologic units and implements

multiple BMPs. Some or all of the employed BMPs may be applicable to each discharge or

hydrologic unit. Therefore, analysis of BMP effect on discharges was performed at the

discharge or hydrologic-unit level, not at the permit level. 

Of the 248 discharges included in the database, some could not be used for BMP efficiency

analyses due to missing or unavailable information or data. Six monitoring points did not have

baseline water quality data for any parameter, most likely due to an absence of flow. Ten other

discharges did not have any associated BMP information. Therefore, the total number of

discharges used in the BMP efficiency analyses was 231, from 109 permits. 
Coal Remining BMP Guidance Manual

6-6 Efficiencies of BMPs

Sulfate loadings and flow rates were also analyzed in this section to yield insight as to which

BMPs may have caused the observed loadings changes. Sulfate loading trends may indicate if

changes in loading rates of acidity, iron, manganese, and/or aluminum are due to geochemical

changes in acid mine drainage (AMD) production (increases or decreases in pyrite oxidation). 

Sulfate ions are a conservative indicator of AMD production. Flow rate data may indicate

whether changes to contaminant loadings are due to changes in the flow rate. These two

parameters can in turn indicate if an improvement in water quality is related to a particular

geochemically-based or physically-based BMP.

6.2 Observed Results

The database was used to summarize the number of discharges which showed statistically

significant increases, decreases, or no change in pollution load and to compare the aggregate

(combined) median pollution load. Statistical significance is determined by comparing the

baseline upper and lower confidence limits about the median pollution load against the upper

and lower confidence limits about the post-mining median. BMP effects on discharges were

rated as follows:

C No significant difference - If the baseline and post-mining confidence intervals overlap,

then there is no statistically significant difference and the median pollutant loading of

the discharge is considered unchanged. 

C Significantly degraded - If the post-mining lower confidence limit exceeds the baseline

upper confidence limit, then there is a significant increase in median load. 

C Significantly improved - If the post-mining upper confidence limit is lower than the

baseline lower confidence limit, there is a significant decrease in median load. 

C Eliminated - If the post-mining upper confidence limit was zero, the pollution load was

considered to have been eliminated. This does not necessarily mean that the discharge
 Coal Remining BMP Guidance Manual

Efficiencies of BMPs 6-7

was physically eliminated, only that with 95 percent confidence, the median pollution loads

were zero. 

This analysis was performed for each discharge affected by any of the 12 specific BMPs listed

earlier in this section. The results of the observed BMP effects on pre-existing discharges are

summarized by BMP and parameter in Table 6.2a.

Most discharges (or hydrologic units) were affected by multiple BMPs. For that reason, BMP

effects on a single discharge may be represented in Table 6.2a under several different BMPs. For

example, surface regrading, revegetation, and daylighting may have been implemented in an area

affecting a single discharge. In Table 6.2a, the water quality results for that discharge would be

represented in the summary results for each of these BMPs separately. Therefore, changes in

pollution-loading rates may not be attributed solely to that BMP, but may have been affected by a

group of BMPs. Table 6.2b summarizes the observed effects of BMPs on discharges by BMP

group and parameter.
Coal Remining BMP Guidance Manual

6-8 Efficiencies of BMPs

Table 6.2a: Pennsylvania Remining Permits, Summary of Observed Water

Quality Results by Individual BMP (Appendix B, Pennsylvania

Remining Site Study)

Water Quality Results - Overall

Acidity #

Discharges

Percent of

Discharges

Manganese #

Discharges

Percent of

Discharges

Discharge eliminated 43 19.1% Discharge eliminated 32 20.6%

Significantly improved 57 25.3% Significantly improved 31 20.0%

No significant difference 123 54.7% No significant difference 78 50.3%

Significantly degraded 2 0.9% Significantly degraded 14 9.0%

 Total for parameter 225 Total for parameter 155

Iron Aluminum

Discharge eliminated 49 23.7% Discharge eliminated 21 17.9%

Significantly improved 37 17.9% Significantly improved 23 19.7%

No significant difference 110 53.1% No significant difference 69 59.0%

Significantly degraded 11 5.3% Significantly degraded 4 3.4%

 Total for parameter 207 Total for parameter 117

Sulfate Flow

Discharge eliminated 43 18.7% Discharge eliminated 42 18.2%

Significantly improved 47 20.4% Significantly improved 54 23.4%

No significant difference 116 50.4% No significant difference 122 52.8%

Significantly degraded 24 10.4% Significantly degraded 13 5.6%

 Total for parameter 230 Total for parameter 231
 Coal Remining BMP Guidance Manual

Efficiencies of BMPs 6-9

Water Quality Results by BMP - Alkaline Addition > 100 tons/acre

Acidity #

Discharges

Percent of

Discharges

Manganese #

Discharges

Percent of

Discharges

Discharge eliminated 4 36.4% Discharge eliminated 1 16.7%

Significantly improved 3 27.3% Significantly improved 0 0.0%

No significant difference 3 27.3% No significant difference 3 50.0%

Significantly degraded 1 9.1% Significantly degraded 2 33.3%

 Total for parameter 11 Total for parameter 6

Iron Aluminum

Discharge eliminated 5 45.5% Discharge eliminated 0 0.0%

Significantly improved 1 9.1% Significantly improved 0 0.0%

No significant difference 4 36.4% No significant difference 1 100.0%

Significantly degraded 1 9.1% Significantly degraded 0 0.0%

 Total for parameter 11 Total for parameter 1

Sulfate Flow

Discharge eliminated 5 45.5% Discharge eliminated 4 36.4%

Significantly improved 1 9.1% Significantly improved 3 27.3%

No significant difference 4 36.4% No significant difference 3 27.3%

Significantly degraded 1 9.1% Significantly degraded 1 9.1%

 Total for parameter 11 Total for parameter 11

Water Quality Results by BMP - Alkaline Addition < 100 tons/acre

Acidity #

Discharges

Percent of

Discharges

Manganese #

Discharges

Percent of

Discharges

Discharge eliminated 11 16.9% Discharge eliminated 8 20.5%

Significantly improved 11 16.9% Significantly improved 5 12.8%

No significant difference 43 66.2% No significant difference 22 56.4%

Significantly degraded 0 0.0% Significantly degraded 4 10.3%

 Total for parameter 65 Total for parameter 39

Iron Aluminum

Discharge eliminated 13 21.7% Discharge eliminated 5 19.2%

Significantly improved 9 15.0% Significantly improved 2 7.7%

No significant difference 37 61.7% No significant difference 19 73.1%

Significantly degraded 1 1.7% Significantly degraded 0 0.0%

 Total for parameter 60 Total for parameter 26

Sulfate Flow

Discharge eliminated 14 20.9% Discharge eliminated 14 20.9%

Significantly improved 11 16.4% Significantly improved 9 13.4%

No significant difference 36 53.7% No significant difference 41 61.2%

Significantly degraded 6 9.0% Significantly degraded 3 4.5%

 Total for parameter 67 Total for parameter 67
Coal Remining BMP Guidance Manual

6-10 Efficiencies of BMPs

Water Quality Results by BMP - On-site Alkaline Redistribution

Acidity #

Discharges

Percent of

Discharges

Manganese #

Discharges

Percent of

Discharges

Discharge eliminated 5 83.3% Discharge eliminated 4 100.0%

Significantly improved 0 0.0% Significantly improved 0 0.0%

No significant difference 1 16.7% No significant difference 0 0.0%

Significantly degraded 0 0.0% Significantly degraded 0 0.0%

 Total for parameter 6 Total for parameter 4

Iron Aluminum

Discharge eliminated 2 66.7% Discharge eliminated 3 100.0%

Significantly improved 0 0.0% Significantly improved 0 0.0%

No significant difference 1 33.3% No significant difference 0 0.0%

Significantly degraded 0 0.0% Significantly degraded 0 0.0%

 Total for parameter 3 Total for parameter 3

Sulfate Flow

Discharge eliminated 4 66.7% Discharge eliminated 4 66.7%

Significantly improved 1 16.7% Significantly improved 1 16.7%

No significant difference 1 16.7% No significant difference 1 16.7%

Significantly degraded 0 0.0% Significantly degraded 0 0.0%

 Total for parameter 6 Total for parameter 6

Water Quality Results by BMP - Biosolids application

Acidity #

Discharges

Percent of

Discharges

Manganese #

Discharges

Percent of

Discharges

Discharge eliminated 0 0.0% Discharge eliminated 3 60.0%

Significantly improved 5 83.3% Significantly improved 0 0.0%

No significant difference 1 16.7% No significant difference 2 40.0%

Significantly degraded 0 0.0% Significantly degraded 0 0.0%

 Total for parameter 6 Total for parameter 5

Iron Aluminum

Discharge eliminated 3 50.0% Discharge eliminated 2 66.7%

Significantly improved 1 16.7% Significantly improved 1 33.3%

No significant difference 2 33.3% No significant difference 0 0.0%

Significantly degraded 0 0.0% Significantly degraded 0 0.0%

 Total for parameter 6 Total for parameter 3

Sulfate Flow

Discharge eliminated 2 33.3% Discharge eliminated 2 33.3%

Significantly improved 3 50.0% Significantly improved 3 50.0%

No significant difference 1 16.7% No significant difference 1 16.7%

Significantly degraded 0 0.0% Significantly degraded 0 0.0%

 Total for parameter 6 Total for parameter 6
 Coal Remining BMP Guidance Manual

Efficiencies of BMPs 6-11

Water Quality Results by BMP - Coal Refuse Removal

Acidity #

Discharges

Percent of

Discharges

Manganese #

Discharges

Percent of

Discharges

Discharge eliminated 2 22.2% Discharge eliminated 0 0.0%

Significantly improved 4 44.4% Significantly improved 0 0.0%

No significant difference 3 33.3% No significant difference 5 83.3%

Significantly degraded 0 0.0% Significantly degraded 1 16.7%

 Total for parameter 9 Total for parameter 6

Iron Aluminum

Discharge eliminated 0 0.0% Discharge eliminated 0 0.0%

Significantly improved 2 28.6% Significantly improved 2 33.3%

No significant difference 4 57.1% No significant difference 4 66.7%

Significantly degraded 1 14.3% Significantly degraded 0 0.0%

 Total for parameter 7 Total for parameter 6

Sulfate Flow

Discharge eliminated 0 0.0% Discharge eliminated 0 0.0%

Significantly improved 2 22.2% Significantly improved 1 11.1%

No significant difference 7 77.8% No significant difference 8 88.9%

Significantly degraded 0 0.0% Significantly degraded 0 0.0%

 Total for parameter 9 Total for parameter 9

Water Quality Results by BMP - Construction of Special Water Handling Facilities

Acidity #

Discharges

Percent of

Discharges

Manganese #

Discharges

Percent of

Discharges

Discharge eliminated 5 22.7% Discharge eliminated 5 26.3%

Significantly improved 6 27.3% Significantly improved 4 21.1%

No significant difference 11 50.0% No significant difference 8 42.1%

Significantly degraded 0 0.0% Significantly degraded 2 10.5%

 Total for parameter 22 Total for parameter 19

Iron Aluminum

Discharge eliminated 7 30.4% Discharge eliminated 2 18.2%

Significantly improved 4 17.4% Significantly improved 1 9.1%

No significant difference 11 47.8% No significant difference 8 72.7%

Significantly degraded 1 4.3% Significantly degraded 0 0.0%

 Total for parameter 23 Total for parameter 11

Sulfate Flow

Discharge eliminated 6 26.1% Discharge eliminated 6 26.1%

Significantly improved 4 17.4% Significantly improved 5 21.7%

No significant difference 12 52.2% No significant difference 10 43.5%

Significantly degraded 1 4.3% Significantly degraded 2 8.7%

 Total for parameter 23 Total for parameter 23
Coal Remining BMP Guidance Manual

6-12 Efficiencies of BMPs

Water Quality Results by BMP - Daylighting

Acidity #

Discharges

Percent of

Discharges

Manganese #

Discharges

Percent of

Discharges

Discharge eliminated 28 17.1% Discharge eliminated 21 19.4%

Significantly improved 39 23.8% Significantly improved 23 21.3%

No significant difference 96 58.5% No significant difference 57 52.8%

Significantly degraded 1 0.6% Significantly degraded 7 6.5%

 Total for parameter 164 Total for parameter 108

Iron Aluminum

Discharge eliminated 27 17.3% Discharge eliminated 17 18.5%

Significantly improved 35 22.4% Significantly improved 13 14.1%

No significant difference 87 55.8% No significant difference 58 63.0%

Significantly degraded 7 4.5% Significantly degraded 4 4.3%

 Total for parameter 156 Total for parameter 92

Sulfate Flow

Discharge eliminated 28 16.6% Discharge eliminated 28 16.5%

Significantly improved 33 19.5% Significantly improved 35 20.6%

No significant difference 87 51.5% No significant difference 96 56.5%

Significantly degraded 21 12.4% Significantly degraded 11 6.5%

 Total for parameter 169 Total for parameter 170

Water Quality Results by BMP - Mining of highly alkaline strata

Acidity #

Discharges

Percent of

Discharges

Manganese #

Discharges

Percent of

Discharges

Discharge eliminated 3 25.0% Discharge eliminated 0 0.0%

Significantly improved 5 41.7% Significantly improved 2 50.0%

No significant difference 4 33.3% No significant difference 2 50.0%

Significantly degraded 0 0.0% Significantly degraded 0 0.0%

 Total for parameter 12 Total for parameter 4

Iron Aluminum

Discharge eliminated 3 23.1% Discharge eliminated 0 0.0%

Significantly improved 2 15.4% Significantly improved 0 0.0%

No significant difference 5 38.5% No significant difference 3 100.0%

Significantly degraded 3 23.1% Significantly degraded 0 0.0%

 Total for parameter 13 Total for parameter 3

Sulfate Flow

Discharge eliminated 2 15.4% Discharge eliminated 2 15.4%

Significantly improved 4 30.8% Significantly improved 6 46.2%

No significant difference 6 46.2% No significant difference 5 38.5%

Significantly degraded 1 7.7% Significantly degraded 0 0.0%

 Total for parameter 13 Total for parameter 13
 Coal Remining BMP Guidance Manual

Efficiencies of BMPs 6-13

Water Quality Results by BMP - Passive Treatment System Construction

Acidity #

Discharges

Percent of

Discharges

Manganese #

Discharges

Percent of

Discharges

Discharge eliminated 0 0.0% Discharge eliminated 1 100.0%

Significantly improved 0 0.0% Significantly improved 0 0.0%

No significant difference 1 100.0% No significant difference 0 0.0%

Significantly degraded 0 0.0% Significantly degraded 0 0.0%

 Total for parameter 1 Total for parameter 1

Iron Aluminum

Discharge eliminated 1 50.0% Discharge eliminated 0 0.0%

Significantly improved 0 0.0% Significantly improved 0 0.0%

No significant difference 1 50.0% No significant difference 1 100.0%

Significantly degraded 0 0.0% Significantly degraded 0 0.0%

 Total for parameter 2 Total for parameter 1

Sulfate Flow

Discharge eliminated 0 0.0% Discharge eliminated 0 0.0%

Significantly improved 1 50.0% Significantly improved 1 50.0%

No significant difference 1 50.0% No significant difference 1 50.0%

Significantly degraded 0 0.0% Significantly degraded 0 0.0%

 Total for parameter 2 Total for parameter 2

Water Quality Results by BMP - Special handling of acid-forming material

Acidity #

Discharges

Percent of

Discharges

Manganese #

Discharges

Percent of

Discharges

Discharge eliminated 11 14.1% Discharge eliminated 12 23.5%

Significantly improved 17 21.8% Significantly improved 8 15.7%

No significant difference 48 61.5% No significant difference 28 54.9%

Significantly degraded 2 2.6% Significantly degraded 3 5.9%

 Total for parameter 78 Total for parameter 51

Iron Aluminum

Discharge eliminated 11 15.7% Discharge eliminated 6 15.8%

Significantly improved 15 21.4% Significantly improved 6 15.8%

No significant difference 39 55.7% No significant difference 25 65.8%

Significantly degraded 5 7.1% Significantly degraded 1 2.6%

 Total for parameter 70 Total for parameter 38

Sulfate Flow

Discharge eliminated 11 13.8% Discharge eliminated 11 13.8%

Significantly improved 15 18.8% Significantly improved 16 20.0%

No significant difference 42 52.5% No significant difference 47 58.8%

Significantly degraded 12 15.0% Significantly degraded 6 7.5%

 Total for parameter 80 Total for parameter 80
Coal Remining BMP Guidance Manual

6-14 Efficiencies of BMPs

Water Quality Results by BMP - Surface Regrading

Acidity

#

Discharges

Percent of

Discharges Manganese

#

Discharges

Percent of

Discharges

Discharge eliminated 30 19.5% Discharge eliminated 21 18.9%

Significantly improved 41 26.6% Significantly improved 23 20.7%

No significant difference 82 53.2% No significant difference 58 52.3%

Significantly degraded 1 0.6% Significantly degraded 9 8.1%

 Total for parameter 154 Total for parameter 111

Iron Aluminum

Discharge eliminated 33 24.1% Discharge eliminated 14 16.7%

Significantly improved 25 18.2% Significantly improved 17 20.2%

No significant difference 72 52.6% No significant difference 51 60.7%

Significantly degraded 7 5.1% Significantly degraded 2 2.4%

 Total for parameter 137 Total for parameter 84

Sulfate Flow

Discharge eliminated 27 17.4% Discharge eliminated 26 16.7%

Significantly improved 32 20.6% Significantly improved 42 26.9%

No significant difference 81 52.3% No significant difference 78 50.0%

Significantly degraded 15 9.7% Significantly degraded 10 6.4%

 Total for parameter 155 Total for parameter 156

Water Quality Results by BMP - Surface Revegetation

Acidity

#

Discharges

Percent of

Discharges Manganese

#

Discharges

Percent of

Discharges

Discharge eliminated 35 20.1% Discharge eliminated 26 20.5%

Significantly improved 46 26.4% Significantly improved 25 19.7%

No significant difference 93 53.4% No significant difference 67 52.8%

Significantly degraded 0 0.0% Significantly degraded 9 7.1%

 Total for parameter 174 Total for parameter 127

Iron Aluminum

Discharge eliminated 40 25.3% Discharge eliminated 17 17.3%

Significantly improved 29 18.4% Significantly improved 20 20.4%

No significant difference 82 51.9% No significant difference 58 59.2%

Significantly degraded 7 4.4% Significantly degraded 3 3.1%

 Total for parameter 158 Total for parameter 98

Sulfate Flow

Discharge eliminated 34 19.3% Discharge eliminated 33 18.6%

Significantly improved 40 22.7% Significantly improved 46 26.0%

No significant difference 85 48.3% No significant difference 88 49.7%

Significantly degraded 17 9.7% Significantly degraded 10 5.7%

 Total for parameter 176 Total for parameter 177
 Coal Remining BMP Guidance Manual

Efficiencies of BMPs 6-15

Of the 12 BMPs assessed, only 3 were reported to be used singly, accounting for effects on 8.7

percent (20) of 231 discharges. The BMPs reported as being implemented singly were regrading

(affecting 1 discharge), revegetation (affecting 5 discharges), and daylighting (affecting 14

discharges). However, the possibility that regrading was implemented alone, without

revegetation, is doubtful. The pollution abatement of the remaining discharges was affected by

BMP groups containing up to 6 BMPs. Table 6.2b lists the observed effects of the various BMP

groupings implemented on 231 pre-existing discharges or hydrologic units.
Coal Remining BMP Guidance Manual

6-16 Efficiencies of BMPs

Table 6.2b: PA Remining Study - Observed Effects of BMP Groupings on Discharges

BMP Group Code Ratings Code

(a) Regrading 4 Eliminated

(b) Revegetation 3 Improved

(c) Daylighting 2 Unchanged

(d) Special Handling 1 Got Worse

(e) Alkaline Addition < 100 tons/acre

(f) Special Water Handling Facilities

(g) Passive Treatment

(h) Coal Refuse Removal

(i) Biosolids Application

(j) Mining High Alkaline Strata

(k) Alkaline Addition > 100 tons/acre

(l) On-Site Alkaline Redistribution

Rating

BMP Group Discharges

Affected

Parameter 1 2 3 4 Improved or

Eliminated

%

Got

Worse

%

c 14 acidity 0 9 3 1 30.8% 0.0%

iron 0 5 4 3 58.3% 0.0%

manganese 1 4 4 2 54.5% 9.1%

aluminum 1 5 2 2 40.0% 10.0%

flow 0 12 1 1 14.3% 0.0%

sulfate 2 8 3 1 28.6% 14.3%

b 5 acidity 0 3 2 0 40.0% 0.0%

iron 1 3 1 0 20.0% 20.0%

manganese 0 4 1 0 20.0% 0.0%

aluminum 0 2 3 0 60.0% 0.0%

flow 0 2 3 0 60.0% 0.0%

sulfate 1 1 3 0 60.0% 20.0%

a 1 acidity 0 0 1 0 100.0% 0.0%

iron 0 1 0 0 0.0% 0.0%

manganese 1 0 0 0 0.0% 100.0%

aluminum 0 0 1 0 100.0% 0.0%

flow 0 1 0 0 0.0% 0.0%

sulfate 0 1 0 0 0.0% 0.0%

c, l 1 acidity 0 1 0 0 0.0% 0.0%

iron 0 1 0 0 0.0% 0.0%

manganese 0 0 0 0 - -

aluminum 0 0 0 0 - -

flow 0 1 0 0 0.0% 0.0%

sulfate 0 1 0 0 0.0% 0.0%
 Coal Remining BMP Guidance Manual

BMP Group Discharges

Affected

Parameter 1 2 3 4 Improved or

Eliminated

%

Got

Worse

%

Efficiencies of BMPs 6-17

c, h 1 acidity 0 1 0 0 0.0% 0.0%

iron 0 1 0 0 0.0% 0.0%

manganese 0 0 0 0 - -

aluminum 0 1 0 0 0.0% 0.0%

flow 0 1 0 0 0.0% 0.0%

sulfate 0 1 0 0 0.0% 0.0%

c, e 12 acidity 0 8 3 1 33.3% 0.0%

iron 0 8 2 1 27.3% 0.0%

manganese 0 1 0 0 0.0% 0.0%

aluminum 0 1 0 0 0.0% 0.0%

flow 1 8 1 2 25.0% 8.3%

sulfate 0 9 1 2 25.0% 0.0%

c, d 5 acidity 1 4 0 0 0.0% 20.0%

iron 1 3 0 0 0.0% 25.0%

manganese 1 0 0 0 0.0% 100.0%

aluminum 0 1 0 0 0.0% 0.0%

flow 1 4 0 0 0.0% 20.0%

sulfate 3 2 0 0 0.0% 60.0%

b, i 1 acidity 0 0 1 0 100.0% 0.0%

iron 0 0 0 1 100.0% 0.0%

manganese 0 0 0 1 100.0% 0.0%

aluminum 0 0 0 1 100.0% 0.0%

flow 0 0 0 1 100.0% 0.0%

sulfate 0 0 0 1 100.0% 0.0%

b, c 5 acidity 0 1 2 2 80.0% 0.0%

iron 0 1 2 2 80.0% 0.0%

manganese 0 2 1 2 60.0% 0.0%

aluminum 1 2 0 2 40.0% 20.0%

flow 0 1 2 2 80.0% 0.0%

sulfate 0 1 2 2 80.0% 0.0%

a, b 18 acidity 0 9 2 7 50.0% 0.0%

iron 0 6 2 2 40.0% 0.0%

manganese 2 4 2 3 45.5% 18.2%

aluminum 0 3 2 1 50.0% 0.0%

flow 0 6 5 7 66.7% 0.0%

sulfate 1 7 3 7 55.6% 5.6%
Coal Remining BMP Guidance Manual

BMP Group Discharges

Affected

Parameter 1 2 3 4 Improved or

Eliminated

%

Got

Worse

%

6-18 Efficiencies of BMPs

c, h, j 1 acidity 0 0 0 1 100.0% 0.0%

iron 0 1 0 0 0.0% 0.0%

manganese 0 1 0 0 0.0% 0.0%

aluminum 0 0 0 0 - -

flow 0 1 0 0 0.0% 0.0%

sulfate 0 1 0 0 0.0% 0.0%

c, e, f 1 acidity 0 0 0 1 100.0% 0.0%

iron 0 0 0 1 100.0% 0.0%

manganese 0 0 0 1 100.0% 0.0%

aluminum 0 0 0 1 100.0% 0.0%

flow 0 0 0 1 100.0% 0.0%

sulfate 0 0 0 1 100.0% 0.0%

c, d, k 1 acidity 0 1 0 0 0.0% 0.0%

iron 0 1 0 0 0.0% 0.0%

manganese 1 0 0 0 0.0% 100.0%

aluminum 0 0 0 0 - -

flow 0 1 0 0 0.0% 0.0%

sulfate 0 1 0 0 0.0% 0.0%

c, d, j 3 acidity 0 0 2 0 100.0% 0.0%

iron 2 1 0 0 0.0% 66.7%

manganese 0 0 0 0 - -

aluminum 0 0 0 0 - -

flow 0 1 2 0 66.7% 0.0%

sulfate 0 2 1 0 33.3% 0.0%

c, d, e 5 acidity 0 3 0 2 40.0% 0.0%

iron 0 3 0 2 40.0% 0.0%

manganese 0 3 0 2 40.0% 0.0%

aluminum 0 3 0 0 0.0% 0.0%

flow 0 3 0 2 40.0% 0.0%

sulfate 2 1 0 2 40.0% 40.0%

b, d, l 1 acidity 0 0 0 1 100.0% 0.0%

iron 0 0 0 1 100.0% 0.0%

manganese 0 0 0 1 100.0% 0.0%

aluminum 0 0 0 0 - -

flow 0 0 0 1 100.0% 0.0%

sulfate 0 0 0 1 100.0% 0.0%
 Coal Remining BMP Guidance Manual

BMP Group Discharges

Affected

Parameter 1 2 3 4 Improved or

Eliminated

%

Got

Worse

%

Efficiencies of BMPs 6-19

b, d, k 1 acidity 0 0 1 0 100.0% 0.0%

iron 0 0 1 0 100.0% 0.0%

manganese 0 1 0 0 0.0% 0.0%

aluminum 0 0 0 0 - -

flow 0 1 0 0 0.0% 0.0%

sulfate 0 1 0 0 0.0% 0.0%

b, d, e 1 acidity 0 1 0 0 0.0% 0.0%

iron 0 1 0 0 0.0% 0.0%

manganese 0 1 0 0 0.0% 0.0%

aluminum 0 0 0 0 - -

flow 0 1 0 0 0.0% 0.0%

sulfate 0 1 0 0 0.0% 0.0%

b, c, k 1 acidity 0 0 0 1 100.0% 0.0%

iron 0 0 0 1 100.0% 0.0%

manganese 0 0 0 0 - -

aluminum 0 0 0 0 - -

flow 0 0 0 1 100.0% 0.0%

sulfate 0 0 0 1 100.0% 0.0%

b, c, g 1 acidity 0 0 0 0 - -

iron 0 0 0 1 100.0% 0.0%

manganese 0 0 0 1 100.0% 0.0%

aluminum 0 0 0 0 - -

flow 0 0 1 0 100.0% 0.0%

sulfate 0 0 1 0 100.0% 0.0%

b, c, f 1 acidity 0 1 0 0 0.0% 0.0%

iron 0 1 0 0 0.0% 0.0%

manganese 1 0 0 0 0.0% 100.0%

aluminum 0 0 1 0 100.0% 0.0%

flow 1 0 0 0 0.0% 100.0%

sulfate 1 0 0 0 0.0% 100.0%

b, c, e 4 acidity 0 2 0 2 50.0% 0.0%

iron 0 2 0 1 33.3% 0.0%

manganese 1 1 1 1 50.0% 25.0%

aluminum 0 2 0 1 33.3% 0.0%

flow 0 3 0 1 25.0% 0.0%

sulfate 0 3 0 1 25.0% 0.0%
Coal Remining BMP Guidance Manual

BMP Group Discharges

Affected

Parameter 1 2 3 4 Improved or

Eliminated

%

Got

Worse

%

6-20 Efficiencies of BMPs

b, c, d 2 acidity 0 1 1 0 50.0% 0.0%

iron 0 1 1 0 50.0% 0.0%

manganese 0 2 0 0 0.0% 0.0%

aluminum 0 1 0 0 0.0% 0.0%

flow 0 1 1 0 50.0% 0.0%

sulfate 0 0 2 0 100.0% 0.0%

a, d, k 1 acidity 1 0 0 0 0.0% 100.0%

iron 1 0 0 0 0.0% 100.0%

manganese 1 0 0 0 0.0% 100.0%

aluminum 0 0 0 0 - -

flow 1 0 0 0 0.0% 100.0%

sulfate 0 1 0 0 0.0% 0.0%

a, d, e 1 acidity 0 1 0 0 0.0% 0.0%

iron 0 1 0 0 0.0% 0.0%

manganese 0 1 0 0 0.0% 0.0%

aluminum 0 0 0 0 - -

flow 0 1 0 0 0.0% 0.0%

sulfate 0 1 0 0 0.0% 0.0%

a, c, j 2 acidity 0 1 1 0 50.0% 0.0%

iron 0 0 1 1 100.0% 0.0%

manganese 0 1 1 0 50.0% 0.0%

aluminum 0 0 0 0 - -

flow 0 0 2 0 100.0% 0.0%

sulfate 0 1 1 0 50.0% 0.0%

a, c, d 1 acidity 0 0 0 1 100.0% 0.0%

iron 0 0 0 0 - -

manganese 0 0 0 1 100.0% 0.0%

aluminum 0 0 0 1 100.0% 0.0%

flow 0 0 0 1 100.0% 0.0%

sulfate 0 0 0 1 100.0% 0.0%

a, b, k 2 acidity 0 0 0 2 100.0% 0.0%

iron 0 0 0 2 100.0% 0.0%

manganese 0 0 0 0 - -

aluminum 0 0 0 0 - -

flow 0 0 1 1 100.0% 0.0%

sulfate 0 0 0 2 100.0% 0.0%
 Coal Remining BMP Guidance Manual

BMP Group Discharges

Affected

Parameter 1 2 3 4 Improved or

Eliminated

%

Got

Worse

%

Efficiencies of BMPs 6-21

a, b, h 3 acidity 0 1 2 0 66.7% 0.0%

iron 1 1 0 0 0.0% 50.0%

manganese 1 1 0 0 0.0% 50.0%

aluminum 0 2 0 0 0.0% 0.0%

flow 0 2 1 0 33.3% 0.0%

sulfate 0 2 1 0 33.3% 0.0%

a, b, g 1 acidity 0 1 0 0 0.0% 0.0%

iron 0 1 0 0 0.0% 0.0%

manganese 0 0 0 0 - -

aluminum 0 1 0 0 0.0% 0.0%

flow 0 1 0 0 0.0% 0.0%

sulfate 0 1 0 0 0.0% 0.0%

a, b, f 4 acidity 0 0 3 1 100.0% 0.0%

iron 0 0 2 2 100.0% 0.0%

manganese 0 0 2 2 100.0% 0.0%

aluminum 0 0 0 0 - -

flow 0 1 2 1 75.0% 0.0%

sulfate 0 1 2 1 75.0% 0.0%

a, b, e 4 acidity 0 4 0 0 0.0% 0.0%

iron 0 3 1 0 25.0% 0.0%

manganese 1 3 0 0 0.0% 25.0%

aluminum 0 0 0 0 - -

flow 0 3 1 0 25.0% 0.0%

sulfate 0 4 0 0 0.0% 0.0%

a, b, d 4 acidity 0 2 2 0 50.0% 0.0%

iron 0 2 2 0 50.0% 0.0%

manganese 0 1 2 0 66.7% 0.0%

aluminum 0 1 2 0 66.7% 0.0%

flow 0 2 2 0 50.0% 0.0%

sulfate 0 4 0 0 0.0% 0.0%

a, b, c 37 acidity 0 20 10 6 44.4% 0.0%

iron 2 22 4 9 35.1% 5.4%

manganese 1 19 7 3 33.3% 3.3%

aluminum 1 12 7 4 45.8% 4.2%

flow 3 18 11 5 43.2% 8.1%

sulfate 3 19 9 5 38.9% 8.3%
Coal Remining BMP Guidance Manual

BMP Group Discharges

Affected

Parameter 1 2 3 4 Improved or

Eliminated

%

Got

Worse

%

6-22 Efficiencies of BMPs

c, e, f, j 2 acidity 0 0 1 1 100.0% 0.0%

iron 0 1 0 1 50.0% 0.0%

manganese 0 0 0 0 - -

aluminum 0 0 0 0 - -

flow 0 0 0 2 100.0% 0.0%

sulfate 0 0 0 2 100.0% 0.0%

c, d, e, f 1 acidity 0 0 0 0 - -

iron 0 0 1 0 100.0% 0.0%

manganese 0 0 1 0 100.0% 0.0%

aluminum 0 0 0 0 - -

flow 0 0 1 0 100.0% 0.0%

sulfate 0 0 1 0 100.0% 0.0%

b, c, d, e 5 acidity 0 5 0 0 0.0% 0.0%

iron 0 4 0 1 20.0% 0.0%

manganese 0 0 0 0 - -

aluminum 0 0 0 0 - -

flow 0 3 0 2 40.0% 0.0%

sulfate 0 2 1 2 60.0% 0.0%

a, c, i, k 1 acidity 0 1 0 0 0.0% 0.0%

iron 0 1 0 0 0.0% 0.0%

manganese 0 0 0 0 - -

aluminum 0 0 0 0 - -

flow 0 0 1 0 100.0% 0.0%

sulfate 0 1 0 0 0.0% 0.0%

a, b, i, k 2 acidity 0 0 2 0 100.0% 0.0%

iron 0 1 0 1 50.0% 0.0%

manganese 0 1 0 1 50.0% 0.0%

aluminum 0 0 0 0 - -

flow 0 0 1 1 100.0% 0.0%

sulfate 0 0 1 1 100.0% 0.0%

a, b, e, f 1 acidity 0 1 0 0 0.0% 0.0%

iron 1 0 0 0 0.0% 100.0%

manganese 1 0 0 0 0.0% 100.0%

aluminum 0 0 0 0 - -

flow 0 0 1 0 100.0% 0.0%

sulfate 0 0 1 0 100.0% 0.0%
 Coal Remining BMP Guidance Manual

BMP Group Discharges

Affected

Parameter 1 2 3 4 Improved or

Eliminated

%

Got

Worse

%

Efficiencies of BMPs 6-23

a, b, d, l 3 acidity 0 0 0 3 100.0% 0.0%

iron 0 0 0 1 100.0% 0.0%

manganese 0 0 0 3 100.0% 0.0%

aluminum 0 0 0 2 100.0% 0.0%

flow 0 0 1 2 100.0% 0.0%

sulfate 0 0 1 2 100.0% 0.0%

a, b, d, k 1 acidity 0 1 0 0 0.0% 0.0%

iron 0 1 0 0 0.0% 0.0%

manganese 0 1 0 0 0.0% 0.0%

aluminum 0 1 0 0 0.0% 0.0%

flow 0 1 0 0 0.0% 0.0%

sulfate 0 1 0 0 0.0% 0.0%

a, b, d, j 1 acidity 0 1 0 0 0.0% 0.0%

iron 0 0 1 0 100.0% 0.0%

manganese 0 0 1 0 100.0% 0.0%

aluminum 0 0 0 0 - -

flow 0 0 1 0 100.0% 0.0%

sulfate 0 0 1 0 100.0% 0.0%

a, b, d, h 3 acidity 0 1 1 1 66.7% 0.0%

iron 0 1 1 0 50.0% 0.0%

manganese 0 2 0 0 0.0% 0.0%

aluminum 0 1 1 0 50.0% 0.0%

flow 0 3 0 0 0.0% 0.0%

sulfate 0 3 0 0 0.0% 0.0%

a, b, d, f 1 acidity 0 1 0 0 0.0% 0.0%

iron 0 1 0 0 0.0% 0.0%

manganese 0 0 0 0 - -

aluminum 0 0 0 0 - -

flow 1 0 0 0 0.0% 100.0%

sulfate 0 1 0 0 0.0% 0.0%

a, b, c, l 1 acidity 0 0 0 1 100.0% 0.0%

iron 0 0 0 0 - -

manganese 0 0 0 0 - -

aluminum 0 0 0 1 100.0% 0.0%

flow 0 0 0 1 100.0% 0.0%

sulfate 0 0 0 1 100.0% 0.0%
Coal Remining BMP Guidance Manual

BMP Group Discharges

Affected

Parameter 1 2 3 4 Improved or

Eliminated

%

Got

Worse

%

6-24 Efficiencies of BMPs

a, b, c, k 1 acidity 0 0 0 1 100.0% 0.0%

iron 0 0 0 1 100.0% 0.0%

manganese 0 0 0 0 - -

aluminum 0 0 0 0 - -

flow 0 0 0 1 100.0% 0.0%

sulfate 0 0 0 1 100.0% 0.0%

a, b, c, j 1 acidity 0 0 0 1 100.0% 0.0%

iron 1 0 0 0 0.0% 100.0%

manganese 0 0 0 0 - -

aluminum 0 0 0 0 - -

flow 0 1 0 0 0.0% 0.0%

sulfate 1 0 0 0 0.0% 100.0%

a, b, c, i 1 acidity 0 0 1 0 100.0% 0.0%

iron 0 0 0 1 100.0% 0.0%

manganese 0 0 0 1 100.0% 0.0%

aluminum 0 0 0 1 100.0% 0.0%

flow 0 0 1 0 100.0% 0.0%

sulfate 0 0 1 0 100.0% 0.0%

a, b, c, f 4 acidity 0 1 2 1 75.0% 0.0%

iron 0 1 1 2 75.0% 0.0%

manganese 0 1 1 1 66.7% 0.0%

aluminum 0 1 0 0 0.0% 0.0%

flow 0 3 0 1 25.0% 0.0%

sulfate 0 3 0 1 25.0% 0.0%

a, b, c, e 14 acidity 0 8 3 2 38.5% 0.0%

iron 0 8 2 2 33.3% 0.0%

manganese 1 7 3 1 33.3% 8.3%

aluminum 0 9 1 1 18.2% 0.0%

flow 2 8 2 2 28.6% 14.3%

sulfate 3 7 2 2 28.6% 21.4%

a, b, c, d 18 acidity 0 11 7 0 38.9% 0.0%

iron 1 8 5 2 43.8% 6.3%

manganese 0 4 4 1 55.6% 0.0%

aluminum 1 9 2 0 16.7% 8.3%

flow 3 10 5 0 27.8% 16.7%

sulfate 5 9 4 0 22.2% 27.8%
 Coal Remining BMP Guidance Manual

BMP Group Discharges

Affected

Parameter 1 2 3 4 Improved or

Eliminated

%

Got

Worse

%

Efficiencies of BMPs 6-25

a, b, c, e, j 3 acidity 0 2 1 0 33.3% 0.0%

iron 0 2 0 1 33.3% 0.0%

manganese 0 0 0 0 - -

aluminum 0 3 0 0 0.0% 0.0%

flow 0 2 1 0 33.3% 0.0%

sulfate 0 2 1 0 33.3% 0.0%

a, b, c, d, f 8 acidity 0 7 0 1 12.5% 0.0%

iron 0 7 0 1 12.5% 0.0%

manganese 0 7 0 1 12.5% 0.0%

aluminum 0 7 0 1 12.5% 0.0%

flow 0 6 1 1 25.0% 0.0%

sulfate 0 7 0 1 12.5% 0.0%

a, b, c, d, e 12 acidity 0 8 2 2 33.3% 0.0%

iron 0 4 2 3 55.6% 0.0%

manganese 0 4 0 3 42.9% 0.0%

aluminum 0 1 0 2 66.7% 0.0%

flow 0 8 2 2 33.3% 0.0%

sulfate 1 6 3 2 41.7% 8.3%

a, b, d, e, h, i 1 acidity 0 0 1 0 100.0% 0.0%

iron 0 0 1 0 100.0% 0.0%

manganese 0 1 0 0 0.0% 0.0%

aluminum 0 0 1 0 100.0% 0.0%

flow 0 1 0 0 0.0% 0.0%

sulfate 0 0 1 0 100.0% 0.0%
Coal Remining BMP Guidance Manual

6-26 Efficiencies of BMPs

6.3 Predicted Efficiencies

The ratings of BMP effects presented in Table 6.2b were used to predict the effects that individual

BMPs would have on pollution loadings of acidity, iron, manganese, aluminum and sulfate and on

flow rates of pre-existing discharges. 

6.3.1 Statistical Approach

Because the effect of BMPs on pollutant loadings in each discharge were summarized using a 

rating on a four point scale (got worse, no difference, improved, eliminated), the effects of the

various BMPs on discharges were assessed statistically using a logit-link logistic regression model

(Agresti, 1990). This model is based on the assumption that the natural logarithm of the odds of

an event (in this case, that a discharge at least improves) is linearly related to certain predictor

variables (in this case, 10-12 BMP variables, each indicating whether a specific BMP affected a

discharge). The model can be used to predict the odds of an event’s occurrence (i.e. the odds of

a BMP improving or eliminating a discharge pollution load). In this way, the model can be used

to evaluate the effect of each BMP separately, and make predictions of the likelihood of a

discharge pollution load improving or being eliminated for a given BMP. 

A number of assumptions were made while applying this model in order to predict BMP effects

and determine BMP efficiencies. These assumptions include:

• The number of discharges that were observed to be significantly degraded by BMPs or

BMP groups was so low that these discharges could not be used for meaningful statistical

analyses. For example, the occurrences of “significantly degraded” in regards to acidity

and aluminum loading were infrequent (occurred with acidity in 2 out of 225 discharges

and occurred with aluminum in 4 out of 117 discharges). This is illustrative of how

successful remining and the use of appropriate BMPs can be when properly implemented.
 Coal Remining BMP Guidance Manual

Efficiencies of BMPs 6-27

• It was assumed that both elimination and improvement of discharge pollution loadings are

measures of success and could be combined into a single rating (i.e., “at least improved”). 

C The ratings of “no significant difference” and “significantly degraded” were not combined. 

Rahall permits stipulate that pollution loadings in pre-existing discharges must at least

maintain baseline levels.

C The ratings “significantly improved” and “eliminated” were combined and assessed against

“no significant difference.” Therefore, the prediction variable had two possible outcomes

(no difference or at least improved) and a logit model for a binary outcome was used. 

C Summary data for the effects of passive treatment were only available for one discharge for

acidity, manganese or aluminum. Summary data for alkaline addition greater than 100

tons/acre were only available for one discharge for aluminum. Therefore, passive treatment

was not assessed in regards to acidity, manganese or aluminum, and alkaline addition

greater than 100 tons/acre was not assessed in regards to aluminum. 

C All discharges or hydrologic units were treated independently regardless of hydrologic

connection or proximity to other discharges. It is probable that ratings for multiple

discharges within the same permit would correlate more highly with each other than

discharges from different permits. However, due to the wide range in numbers of

discharges per permit (from one to ten), and the two-category nature of the outcome

variable, a reliable estimate of this correlation could not be made.
Coal Remining BMP Guidance Manual

6-28 Efficiencies of BMPs

6.3.2 Statistical Results

Model prediction results for individual BMP efficiencies in regards to acidity, iron, manganese,

aluminum, sulfate, and flow, are reported in Tables 6.3a through 6.3f. Tables 6.3e and 6.3f

present sulfate loadings and flow rate, respectively. As previously stated, sulfate and flow typically

are not regulated, but but can provide insight into the causes of BMP effectiveness or

ineffectiveness. The prediction results are indicated as follows:

Probability: Out of 100 events, how frequently would discharges be improved with

implementation of this BMP(s)

Ratio of Odds: What are the odds of improvement if the BMP(s) is implemented vs. if the

BMP(s) is not implemented (odds are the probability of at least improvement divided by

the probability of no improvement). Due to the low number of discharges made

significantly worse, this calculation does not include the possibility of degradation.

Odds Ratio for Interaction Terms: Compares odds when both BMPs are implemented to

odds when only one of the two BMPs is implemented.

Intercept term: Estimated by separately assessing discharges both with and without each

BMP, and extrapolating to the case where no BMPs are present. The intercept term

estimates odds or probability of at least improvement when no BMPs are implemented.

6.3.2.1 Individual BMPs

The first column of Tables 6.3a through 6.3f identifies the BMP assessed including the intercept

term. The first row of of this column reports the intercept term that was used to predict odds

ratios and probabilities, and reports the predicted probability of at least improvement given the

situation where no BMPs are implemented. Because no discharges existed that were not affected
 Coal Remining BMP Guidance Manual

Efficiencies of BMPs 6-29

by at least one BMP, the intercept was estimated by assessing the effect of the presence of each

BMP individually, and extrapolating to the case where all those effects are absent.

The second column (Probability of at Least Improvement) of Tables 6.3a through 6.3f gives the

model-predicted percentage of discharges that would be improved or eliminated in all discharges

affected by that BMP. Since no data for discharges getting significantly worse were used, the

percentages should be interpreted as the predicted percentage of discharges that would at least

improve, as compared to those that would remain unchanged. The third column (Ratio of Odds)

lists the ratio of odds of at least improvement where the given BMP is used with or without other

BMPs compared with the odds of at least improvement where the BMP is not used. For example,

a ratio of 2.0 indicates that the odds of at least improvement are two times higher when the BMP

is used. Column 4 lists the number of discharges (n) that were affected by the particular BMP in

regards to the parameter being assessed (i.e., acidity, iron, manganese, aluminum, sulfate, or flow). 

Statistical Significance

Because some BMPs affected a small number of discharges, the odds ratios were reviewed for

statistical significance. Column 5 lists the p-values calculated from the Wald Chi-square test for

the statistical significance of odds ratios (i.e., that the corresponding odds ratio in Column 3 was

significantly different from 1.0) tested at the 95 percent significance level (i.e., " = 0.05) (Agresti,

1990). The value of " denotes the probability of a false positive, or the probability (based on the

Wald test) that the model would determine that a BMP will have a significant effect on the odds of

at least improvement, when in actuality the BMP does not have an effect. An odds ratio (from

Column 3) significantly greater than one is an indication that inclusion of that BMP would

significantly increase the odds of improvement. An odds ratio significantly less than one is an

indication that inclusion of that BMP would significantly decrease the odds of improvement. 

The p-values reported in Column 5 give the probability of observing (in a similar data set) an odds

ratio equal to or greater than that in Column 3, if in truth that BMP does not have an effect 
Coal Remining BMP Guidance Manual

6-30 Efficiencies of BMPs

on the odds of at least improvement. If the odds ratio in Column 3 is less than 1.0, the p-value

gives the probability of observing an odds ratio equal to or less than the predicted odds ratio in

Column 3. If the calculated p-value is less than the designated " (0.05), it can be concluded that

the BMP has a significant effect on the odds of at least improvement at " = 0.05. In other words,

the " level of 0.05 indicates that with 95 percent confidence, the BMP has an effect on the

discharge. For example, the calculated odds ratio for mining of high alkaline strata in regards to

sulfate loading is 5.081 (based on 13 discharges that were affected). This means that, with 95

percent confidence, the odds of at least improvement are greater than 1.0 when mining of high

alkaline strata is applied. This is an indication that the mining of high alkaline strata appears to

have a significant positive effect on the chances of a discharge improving in regards to sulfate.

The last rows of Tables 6.3a through 6.3f (except for Table 6.3d) list significant interaction terms. 

These interaction terms state that the combined effect of the two BMPs is different from what

would be expected given the sum of the predicted effects for those BMPs individually. For

example, the significant interaction between special handling and water handling for acidity (Table

6.3a) shows that the odds of discharges at least improving are significantly less than would be

expected given the combined positive effects of the two separate BMPs. Two odds ratios are

listed for interaction terms in this table. Each term gives the odds ratio comparing the odds when

both BMPs are present compared to the odds when only one of the two BMPs is present. 

The presence of a significant interaction term alters the interpretation of the two BMP included in

that interaction. For example, because there is a significant interaction between special handling

and water handling for acidity (Table 6.3a), the odds ratio of 4.013 for water handling holds for all

cases when water handling is implemented except when combined with special handling. 

Likewise, the odds ratio of 0.755 for special handling holds for all cases when special handling is

implemented except when combined with water handling. In addition, the odds of at least

improvement are 0.186 times higher (5.38 times lower) when water handling is used in conjunction

with a BMP group that includes mining of high-alkaline strata than when a BMP group that

includes special handling is used without water handling. Because the odds ratio for a 
 Coal Remining BMP Guidance Manual

Efficiencies of BMPs 6-31

BMP present in a significant interaction does not apply in situations when the second BMP of the

interaction is present, the test for significant interactions cannot lead to the conclusion that the

BMP is significant in all cases, merely that it is significant when the second BMP is not present.
Coal Remining BMP Guidance Manual

6-32 Efficiencies of BMPs

Table 6.3a: PA Remining Study - Predicted Odds of Acidity Improvement or Elimination

BMP or BMP Group Probability of

at Least

Improvement 

Ratio of Odds with

BMP(s) vs. Odds without

BMP(s)

Discharges

Affected

(n)

p-value of

Wald test

(at "=0.05)

None (Intercept term) 37.3 1.00 ---- ----

Regrading 34.7 0.893 154 0.783

Revegetation 50.1 1.684 174 0.279 *

Daylighting 37.1 0.991 164 0.981

Special Handling 31.0 0.755 78 0.387 *

Alkaline Addition 

<100 tons/acre

25.4 0.570 65 0.098

Water Handling 71.4 4.182 22 0.040 *

Passive Treatment Passive treatment affected only 1 discharge / discharge was unchanged

Coal Refuse Removal 57.6 2.283 9 0.285

Biosolids Addition 71.5 4.216 6 0.215

Mining of Alk. Strata 64.2 3.005 12 0.098 *

Alkaline Addition 

>100 tons/acre

56.6 2.190 11 0.312

Alkaline Redistribution 80.9 7.127 6 0.083

1Special Handling/

Water Handling

7.7 vs. Spec. Hand.: 0.186

vs. Water Hand.: 0.020

9 0.018

* Assessment of significance not meaningful due to presence in significant interaction term

Interaction terms: 1 Combined effect is less than expected from combining single effects

2 discharges got worse: These discharges were not used in statistical assessments of improvement or elimination

of acidity. No predictions regarding discharges getting worse were made.

Discharge BMPs Affecting Discharge

1 Daylighting, Special Handling

2 Regrading, Special Handling, Alkaline Addition >100 tons/acre
 Coal Remining BMP Guidance Manual

Efficiencies of BMPs 6-33

Table 6.3b: PA Remining Study - Predicted Odds of Iron Improvement or Elimination

BMP or BMP Group Probability of

at Least

Improvement

Ratio of Odds with

BMP(s) vs. Odds without

BMP(s)

Discharges

Affected

(n)

p-value of

Wald test

(at "=0.05)

None (Intercept term) 40.3 1.00 ---- ----

Regrading 36.0 0.831 137 0.657

Revegetation 51.3 1.559 158 0.359

Daylighting 37.7 0.896 156 0.775

Special Handling 42.1 1.075 70 0.833 *

Alk. Add.<100 tons/ac. 32.2 0.703 60 0.311

Water Handling 73.1 4.013 23 0.049 *

Passive Treatment 42.6 1.010 2 0.947

Coal Refuse Removal 26.2 0.525 7 0.492

Biosolids Addition 62.9 2.504 6 0.348

Mining of Alk. Strata 49.7 1.463 13 0.590

Alk. Add. >100 tons/ac 48.6 1.400 11 0.649

Alkaline Redistribution 61.3 2.340 3 0.505

1Special Handling/

Water Handling

18.3 vs. Spec. Hand.: 0.308

vs. Water Hand.:0.083

10 0.021

* Assessment of significance not meaningful due to presence in significant interaction term

Interaction terms: 1Combined effect is less than expected from combining single effects

11 discharges got worse: These discharges were not used in statistical assessments of improvement or elimination

of iron. No predictions regarding discharges getting worse were made.

Discharge BMPs Affecting Discharge

1 Revegetation

2 Daylighting, Special Handling

3-4 Daylighting, Special Handling, Mining of High Alkaline Strata

5 Regrading, Special Handling, Alkaline Addition >100 tons/acre

6 Regrading, Revegetation, Coal Refuse Removal

7-8 Regrading, Revegetation, Daylighting

9 Regrading, Revegetation, Alkaline Addition <100 tons/acre, Water Handling

10 Regrading, Revegetation, Daylighting, Mining of High Alkaline Strata

11 Regrading, Revegetation, Daylighting, Special Handling
Coal Remining BMP Guidance Manual

6-34 Efficiencies of BMPs

Table 6.3c: PA Study - Predicted Odds of Manganese Improvement or Elimination

BMP or BMP Group Probability of

at Least

Improvement

Ratio of Odds with

BMP(s) vs. Odds without

BMP(s)

Discharges

Affected 

(n)

p-value of

Wald test

(at "=.05)

None (Intercept term) 54.0 1.00 ---- ----

Regrading 50.0 0.850 111 0.717 *

Revegetation 44.6 0.685 127 0.493

Daylighting 55.1 1.043 108 0.923 *

Special Handling 60.3 1.290 51 0.534

Alk. Add.<100 ton/ac 42.3 0.624 39 0.250

Water Handling 90.4 8.010 19 0.024

Passive Treatment Passive treatment affected only 1 discharge/discharge was eliminated

Coal Refuse Removal 2.8 0.024 6 0.047

Biosolids Addition 96.1 21.150 5 0.060

Mining of Alk. Strata 68.8 1.877 4 0.551

Alk.Add>100ton/ac 6.2 0.056 6 0.098

Alkaline Redistribution 92.6 10.597 4 0.130

1Special Handling/

Water Handling

39.5 vs. Special Handling: 0.43

vs. Water Handling: 0.069

9 0.016

* Assessment of significance not meaningful due to presence in significant interaction term

Interaction terms: 1Combined effect is less than expected from combining single effects

14 discharges got worse: These discharges were not used in statistical assessments of improvement or elimination of

manganese. No predictions regarding discharges getting worse were made.

Discharges BMPs Affecting Discharge

1 Daylighting

2 Regrading

3 Daylighting, Special Handling

4, 5 Regrading, Revegetation

6 Daylighting, Special Handling, Alkaline Addition >100 tons/acre

7 Revegetation, Daylighting, Water Handling

8 Revegetation, Daylighting, Alkaline Addition <100 tons/acre

9 Regrading, Special Handling, Alkaline Addition >100 tons/acre

10 Regrading, Revegetation, Coal Refuse Removal

11 Regrading, Revegetation, Alkaline Addition <100 tons/acre

12 Regrading, Revegetation, Daylighting

13 Regrading, Revegetation, Alkaline Addition <100 tons/acre, Water Handling

14 Regrading, Revegetation, Daylighting, Alkaline Addition <100 tons/acre
 Coal Remining BMP Guidance Manual

Efficiencies of BMPs 6-35

Table 6.3d: PA Remining Study - Predicted Odds of Aluminum Improvement or

Elimination

BMP or BMP Group Probability of

at Least

Improvement

Ratio of Odds with

BMP(s) vs. Odds

without BMP(s)

Discharges

Affected 

(n)

p-value of

Wald test

(at "=0.05)

None (Intercept term) 59.1 1.00 ---- ----

Regrading 61.2 1.094 84 0.862

Revegetation 55.0 0.847 98 0.784

Daylighting 43.0 0.522 92 0.198

Special Handling 47.5 0.625 38 0.278

Alkaline Addition 

<100 tons/acre

49.9 0.690 26 0.446

Water Handling 59.5 1.017 11 0.980

Passive Treatment Passive treatment affected only 1 discharge/discharge was unchanged

Coal Refuse Removal 34.0 0.356 6 0.257

Biosolids Addition 96.4 18.587 3 0.074

Mining of Alk. Strata 26.1 0.245 3 0.372

Alkaline Addition 

>100 tons/acre

Alkaline addition >100 affected only 1 discharge/discharge was unchanged

Alkaline Redistribution 93.3 9.711 3 0.139

4 discharges got worse: These discharges were not used in statistical assessments of improvement or elimination of

aluminum. No predictions regarding discharges getting worse were made.

Discharges BMPs Affecting Discharge

1 Daylighting

2 Revegetation, Daylighting

3 Regrading, Revegetation, Daylighting

4 Regrading, Revegetation, Daylighting, Special Handling
Coal Remining BMP Guidance Manual

6-36 Efficiencies of BMPs

Table 6.3e: PA Remining Study - Predicted Odds of Sulfate Improvement or Elimination

BMP or BMP Group Probability of

at Least

Improvement 

Ratio of Odds with

BMP(s) vs. Odds without

BMP(s)

Discharges

Affected

(n)

p-value of

Wald test

(at "=0.05)

None (Intercept term) 27.1 1.00 ---- ----

Regrading 12.3 0.377 155 0.030 

Revegetation 75.1 8.113 176 0.002 *

Daylighting 24.1 0.852 169 0.678

Special Handling 10.8 0.326 80 0.010 *

Alk. Add.<100 tons/ac 38.9 1.708 67 0.457 *

Water Handling 31.8 1.251 23 0.660

Passive Treatment 17.9 0.585 2 0.716

Coal Refuse Removal 9.0 0.267 9 0.167

Biosolids Addition 76.0 8.492 6 0.106

Mining of Alk. Strata 65.4 5.081 13 0.022 

Alk. Add.>100 tons/ac 37.0 1.579 11 0.599

Alkaline Redistribution 80.1 10.794 6 0.041

1 Revegetation/

Alk. Add.<100 tons/ac

44.8 vs. Revegetation: 0.269

vs. Alk. Add.: 1.277 

45 0.029

2Special Handling/

Alk. Add.<100 tons/ac

63.4 vs. Spec. Hand.: 14.275

vs. Alk. Add.: 2.721

26 0.004

* Assessment of significance not meaningful due to presence in significant interaction term.

Interaction terms: 1Combined effect is less than expected from combining single effects.

 

2Combined effect is more than expected from combining single effects .

24 discharges got worse: These discharges were not used in statistical assessments of improvement or elimination of sulfate. No

predictions regarding discharges getting worse were made.

Discharges BMPs Affecting Discharge

1, 2 Daylighting

3, 4, 5 Daylighting, Special Handling

6, 7 Daylighting, Special Handling, Alkaline Addition <100 tons/acre

8 Revegetation

9 Revegetation, Daylighting, Water Handling

10 Regrading, Revegetation

11 Regrading, Revegetation, Special Handling, Alkaline Addition >100 tons/acre

12-14 Regrading, Revegetation, Daylighting

15 Regrading, Revegetation, Daylighting, Mining of High Alkaline Strata

16-18 Regrading, Revegetation, Daylighting, Alkaline Addition <100 tons/acre

19-23 Regrading, Revegetation, Daylighting, Special Handling

24 Regrading, Revegetation, Daylighting, Special Handling, Alk. Add. < 100 tons/acre
 Coal Remining BMP Guidance Manual

Efficiencies of BMPs 6-37

Table 6.3f: PA Remining Study - Predicted Odds of Flow Improvement or Elimination

BMP or BMP Group Probability of

at Least

Improvement 

Ratio of Odds with BMP(s)

vs. Odds without BMP(s)

Discharges

Affected

(n)

p-value of

Wald test

(at "=.05)

None (Intercept term) 19.5 1.00 ---- ----

Regrading 16.4 0.807 156 0.621

Revegetation 66.0 8.009 177 0.005 *

Daylighting 13.3 0.631 170 0.212

Special Handling 12.7 0.601 80 0.121

Alk.Add.<100 ton/ac 52.3 4.529 67 0.054 *

Water Handling 21.3 1.118 23 0.827

Passive Treatment 14.9 0.721 2 0.821

Coal Refuse Removal 1.4 0.061 9 0.025

Biosolids Addition 80.4 16.897 6 0.072

Mining of Alk. Strata 88.7 32.367 13 0.002 *

Alkaline Addition 

>100 tons/acre

30.4 1.798 11 0.489

Alk. Redistribution 66.3 8.109 6 0.082 *

1Revegetation/

Alk.Add.100tons/ac

50.7 vs. Revegetation: 0.529

vs. Alk. Addition: 0.935 

45 0.014

1

 Revegetation/

Mining of Alk. Strata

65.8 vs. Revegetation: 0.989

vs. Mining Alk.Strata:

0.245

12 0.019

* Assessment of significance not meaningful due to presence in significant interaction term.

Interaction terms: 1Combined effect is less than expected from combining single effects.

13 discharges got worse: These discharges were not used in statistical assessments of improvement or elimination of

sulfate. No predictions regarding discharges getting worse were made.

Discharges BMPs Affecting Discharge

1 Daylighting, Alkaline Addition < 100 tons/acre

2 Daylighting, Special Handling

3 Revegetation, Daylighting, Water Handling

4 Regrading, Special Handling, Alkaline Addition > 100 tons/acre

5 Regrading, Revegetation, Special Handling, Water Handling

6, 7, 8 Regrading, Revegetation, Daylighting

9, 10 Regrading, Revegetation, Daylighting, Alkaline Addition <100 tons/acre

11-13 Regrading, Revegetation, Daylighting, Special Handling
Coal Remining BMP Guidance Manual

6-38 Efficiencies of BMPs

6.3.2.2 BMP Combinations

Selection of BMP combinations that are regularly employed during remining operations allows for

a true determination of the efficiencies, rather than projected efficiencies for BMP combinations

not presently occurring in the real world. BMP groups were selected for evaluation based on the

observed implementation of the combinations in the Pennsylvania Remining Study. A secondary

BMP group selection criterion was that each group affected a minimum of four discharges that

were not significantly degraded. With under four discharges impacted by a BMP combination, the

data subset is too small to allow credible conclusions and predictions based on the results. This

selection of BMP combinations affecting four or more discharges allows study of the most

frequently used combinations, by default.

The BMP groups of: (1) regrading and revegetation, (2) daylighting, and (3) regrading,

revegetation, and daylighting were employed as control (reference) groups for comparison with

groups containing additional BMPs. These three reference groups were selected for control

because they are implemented as part of remining and occur as stand-alone BMPs. An operation

would not be considered to be a remining operation unless one or more of these BMPs is

conducted or coal refuse reprocessing is performed. These three BMP reference groups are

directly related to the re-affecting of previously mined areas, because regrading and revegetation

are used at abandoned surface-mined lands and daylighting is used for abandoned underground

mines. Coal refuse reprocessing is seldom conducted (affected 9 out of 231 total discharges in the

data set) and therefore was excluded as a control BMP.

This BMP group selection precluded the determination of potential efficacy of some BMP groups

that, based on experience, may be highly successful in reducing pollution loads. Some BMPs,

including mining into alkaline strata and alkaline addition (>100 tons per acre), are used

infrequently, but have been shown to be quite successful when implemented. 
 Coal Remining BMP Guidance Manual

Efficiencies of BMPs 6-39

The observed results were used to compare the three reference groupings to the selected BMP

combinations. Performances of selected BMP combinations were compared to BMP reference

groups using the observed study results (number of discharges eliminated, improved or

unchanged) presented in Table 6.2b. This comparison provides an indication of relative observed

performance, and does not necessarily predict BMP group efficiencies. Each reference group was

compared to only those BMP groups that included the reference group (although groups did not

need to include revegetation when compared to the reference group containing regrading and

revegetation). Again, only those BMP groups that affected at least four non-worsening discharges

were used in the calculation.

Observed Percent Improved: For each group, the percent of discharges that at least improved

was determined by dividing the number of discharges that were improved or eliminated, by the

number that were improved, eliminated, or did not significantly change (significantly degraded

discharges were not included in the calculations because of their small number) and multiplying by

100. 

Observed Odds of Improvement: For each group, the odds of at least improvement were

calculated as the number of improved or eliminated discharges affected, divided by the number of

discharges that did not significantly change. 

Observed Odds Ratio Compared to Reference: The odds ratio for a given group represents the

odds of at least improvement for that group, divided by the odds of at least improvement for the

reference group. 

Percent Improved minus Reference Percent Improved: The last column in Tables 6.3g

through 6.3x gives the difference between the percentage of discharges affected by the BMP

group that at least improved minus the percentage of discharges at least improved by the reference

group.
Coal Remining BMP Guidance Manual

6-40 Efficiencies of BMPs

For example, in Table 6.3m, Daylighting (reference group) improved or eliminated acidity loading

in 4 discharges, and did not change acidity loading in 9 other discharges. Therefore, the observed

percentage of discharges that at least improved is 4/13 x 100 = 30.8 percent, and the observed

odds of at least improvement is 4/9 = 0.444. The group of Daylighting and Alkaline Addition

<100 tons/acre affected 4 discharges that were improved or eliminated, and affected 8 discharges

that did not significantly change. Therefore, the observed percentage of discharges that at least

improved is 4/12 x 100 = 33.3 percent, and the observed odds of at least improvement was 4/8 =

0.500. The odds ratio comparing Daylighting and Alkaline Addition <100 tons/acre to the

reference group (Daylighting) is 0.500/0.444 = 1.125. According to the observed data, the odds

of at least improvement is 1.125 times higher when Daylighting and Alkaline Addition <100

tons/acre were used compared to when Daylighting was used alone.

For some BMP groups (i.e., Regrading, Revegetation, and Water Handling for acidity and iron),

all discharges affected were improved or eliminated. This yields infinite odds, since the number of

discharges improved or eliminated is divided by 0. Therefore, an odds ratio cannot be calculated

for these groups.
 Coal Remining BMP Guidance Manual

Efficiencies of BMPs 6-41

Table 6.3g: Analysis of Discrete Groups based on Observed Acidity Results Using

Regrading and Revegetation as Reference Group

BMP Group Number 

of

Discharges

Affected

Number of

Discharges

Improved or

Eliminated

Number of

Discharges

Unchanged

Observed

Percent

Improved

Observed

Odds Ratio

compared

to

Reference

Percent

Improved 

minus

Reference

Percent

Improved

Regrading, Revegetation 

(Reference)

18 9 9 50.0 --- ---

Regrading, Revegetation,

Daylighting

36 16 20 44.4 0.800 -5.6

Regrading, Revegetation,

Special Handling

4 2 2 50.0 1.000 0.0

Regrading, Revegetation,

Alkaline Addition <100

4 0 4 0.0 0.0 -50.0

Regrading, Revegetation,

Water Handling

4 4 0 100.0 4 * 50.0

Regrading, Revegetation,

Daylighting, Special

Handling

18 7 11 38.9 0.636 -11.1

Regrading, Revegetation,

Daylighting, Alkaline

Addition <100

13 5 8 38.5 0.625 -11.5

Regrading, Revegetation,

Daylighting, Special

Handling, Alkaline

Addition <100

12 4 8 33.3 0.500 -16.7

Regrading, Revegetation,

Daylighting, Special

Handling, Water

Handling

8 1 7 12.5 0.143 -37.5

Observed Percentage Improvement: On a scale of 0-100, how frequently were discharges improved with 

implementation of this BMP grouping

Observed Odds of Improvement: Number improved or eliminated divided by number with no significant

difference

Ratio of Odds: What are the odds of improvement if BMP grouping is implemented vs.

if reference grouping (Regrading & Revegetation) is implemented

* Because all discharges for this grouping were improved, the odds of improvement would be 4 divided by 0. 

Therefore, the odds ratio is infinite.
Coal Remining BMP Guidance Manual

6-42 Efficiencies of BMPs

Table 6.3h: Analysis of Discrete Groups based on Observed Iron Results Using Regrading

and Revegetation as Reference Group

BMP Group Number of

Discharges

Affected

Number of

Discharges

Improved

or

Eliminated

Number of

Discharges

Unchanged

Observed

Percent

Improved

Observed

Odds Ratio

compared

to

Reference

Percent

Improved 

minus

Reference

Percent

Improved

Regrading, Revegetation 

(Reference)

12 6 6 50.0 --- ---

Regrading, Revegetation,

Daylighting

37 13 22 37.1 0.591 -12.9

Regrading, Revegetation,

Special Handling

4 2 2 50.0 1.000 0.0

Regrading, Revegetation,

Alkaline Addition <100

4 1 3 25.0 0.333 -25.0

Regrading, Revegetation,

Water Handling

4 4 0 100.0 4 * 50.0

Regrading, Revegetation,

Daylighting, Special

Handling

16 7 8 46.7 0.875 3.3

Regrading, Revegetation,

Daylighting, Alkaline

Addition <100

12 4 8 33.3 0.500 -16.7

Regrading, Revegetation,

Daylighting, Special

Handling, Alkaline

Addition <100

9 5 4 55.6 1.250 5.6

Regrading, Revegetation,

Daylighting, Special

Handling, Water Handling

8 1 7 12.5 0.143 -37.5

Observed Percentage Improvement: On a scale of 0-100, how frequently were discharges improved with 

implementation of this BMP grouping

Observed Odds of Improvement: Number improved or eliminated divided by number with no significant

difference

Ratio of Odds: What are the odds of improvement if BMP grouping is implemented vs.

if reference grouping (Regrading & Revegetation) is implemented

* Because all discharges for this grouping were improved, the odds of improvement would be 5 divided by 0. 

Therefore, the odds ratio is infinite.
 Coal Remining BMP Guidance Manual

Efficiencies of BMPs 6-43

Table 6.3i: Analysis of Discrete Groups based on Observed Manganese Results Using

Regrading and Revegetation as Reference Group

BMP Group Number of

Discharges

Affected

Number of

Discharges

Improved

or

Eliminated

Number of

Discharges

Unchanged

Observed

Percent

Improved

Observed

Odds Ratio

compared

to

Reference

Percent

Improved 

minus

Reference

Percent

Improved

Regrading, Revegetation 

(Reference)

11 5 4 55.6 --- ---

Regrading, Revegetation,

Daylighting

30 10 19 34.5 0.421 -21.1

Regrading, Revegetation,

Alkaline Addition <100

4 0 3 0.0 0.0 -55.6

Regrading, Revegetation,

Water Handling

4 4 0 100.0 4 * 44.4

Regrading, Revegetation,

Daylighting, Special

Handling

 9 5 4 55.6 1.000 -0.0

Regrading, Revegetation,

Daylighting, Alkaline

Addition <100

12 4 7 36.4 0.457 -19.2

Regrading, Revegetation,

Daylighting, Special

Handling, Alkaline

Addition <100

7 3 4 42.9 0.600 -12.7

Regrading, Revegetation,

Daylighting, Special

Handling, Water Handling

8 1 7 12.5 0.114 -43.1

Observed Percentage Improvement: On a scale of 0-100, how frequently were discharges improved with 

implementation of this BMP grouping

Observed Odds of Improvement: Number improved or eliminated divided by number with no significant

difference

Ratio of Odds: What are the odds of improvement if BMP grouping is implemented vs.

if reference grouping (Regrading & Revegetation) is implemented

* Because all discharges for this grouping were improved, the odds of improvement would be 5 divided by 0. 

Therefore, the odds ratio is infinite.
Coal Remining BMP Guidance Manual

6-44 Efficiencies of BMPs

Table 6.3j: Analysis of Discrete Groups based on Observed Aluminum Results Using

Regrading and Revegetation as Reference Group

BMP Group Number of

Discharges

Affected

Number of

Discharges

Improved

or

Eliminated

Number of

Discharges

Unchanged

Observed

Percent

Improved

Observed

Odds Ratio

compared

to

Reference

Percent

Improved 

minus

Reference

Percent

Improved

Regrading, Revegetation 

(Reference)

6 3 3 50.0 --- ---

Regrading, Revegetation,

Daylighting

24 11 12 47.8 0.917 -2.2

Regrading, Revegetation,

Daylighting, Special

Handling

 12 2 9 18.2 0.222 -31.8

Regrading, Revegetation,

Daylighting, Alkaline

Addition <100

11 2 9 18.2 0.222 -31.8

Regrading, Revegetation,

Daylighting, Special

Handling, Water Handling

8 1 7 12.5 0.143 -37.5

Observed Percentage Improvement: On a scale of 0-100, how frequently were discharges improved with 

implementation of this BMP grouping

Observed Odds of Improvement: Number improved or eliminated divided by number with no significant

difference

Ratio of Odds: What are the odds of improvement if BMP grouping is implemented vs.

if reference grouping (Regrading & Revegetation) is implemented
 Coal Remining BMP Guidance Manual

Efficiencies of BMPs 6-45

Table 6.3k: Analysis of Discrete Groups based on Observed Sulfate Results Using

Regrading and Revegetation as Reference Group

BMP Group Number 

of

Discharges

Affected

Number of

Discharges

Improved or

Eliminated

Number of

Discharges

Unchanged

Observed

Percent

Improved

Observed

Odds Ratio

compared

to

Reference

Percent

Improved 

minus

Reference

Percent

Improved

Regrading, Revegetation 

(Reference)

18 10 7 58.8 --- ---

Regrading, Revegetation,

Daylighting

36 14 19 42.4 0.516 -16.4

Regrading, Revegetation,

Special Handling

4 0 4 0.0 0.000 -58.8

Regrading, Revegetation,

Alkaline Addition <100

4 0 4 0.0 0.000 -58.8

Regrading, Revegetation,

Water Handling

4 3 1 75.0 2.099 16.2

Regrading, Revegetation,

Daylighting, Special

Handling

18 4 9 30.8 0.311 -28.0

Regrading, Revegetation,

Daylighting, Alkaline

Addition <100

14 4 7 36.4 0.400 -22.4

Regrading, Revegetation,

Daylighting, Special

Handling, Alkaline

Addition <100

12 5 6 45.5 0.583 -13.3

Regrading, Revegetation,

Daylighting, Special

Handling, Water

Handling

8 1 7 12.5 0.100 -46.3

Observed Percentage Improvement: On a scale of 0-100, how frequently were discharges improved with 

implementation of this BMP grouping

Observed Odds of Improvement: Number improved or eliminated divided by number with no significant

difference

Ratio of Odds: What are the odds of improvement if BMP grouping is implemented vs.

if reference grouping (Regrading & Revegetation) is implemented
Coal Remining BMP Guidance Manual

6-46 Efficiencies of BMPs

Table 6.3l: Analysis of Discrete Groups based on Observed Flow Results Using

Regrading and Revegetation as Reference Group

BMP Group Number 

of

Discharges

Affected

Number of

Discharges

Improved or

Eliminated

Number of

Discharges

Unchanged

Observed

Percent

Improved

Observed

Odds Ratio

compared

to

Reference

Percent

Improved 

minus

Reference

Percent

Improved

Regrading, Revegetation 

(Reference)

18 12 6 66.7 --- ---

Regrading, Revegetation,

Daylighting

37 16 18 47.1 0.444 -19.6

Regrading, Revegetation,

Special Handling

4 2 2 50.0 0.500 -16.7

Regrading, Revegetation,

Alkaline Addition <100

4 1 3 25.0 0.167 -41.7

Regrading, Revegetation,

Water Handling

4 3 1 75.0 1.500 8.3

Regrading, Revegetation,

Daylighting, Special

Handling

18 5 10 33.3 0.250 -33.3

Regrading, Revegetation,

Daylighting, Alkaline

Addition <100

14 4 8 33.3 0.250 -33.3

Regrading, Revegetation,

Daylighting, Special

Handling, Alkaline

Addition <100

12 4 8 33.3 0.250 -33.3

Regrading, Revegetation,

Daylighting, Special

Handling, Water

Handling

8 2 6 25.0 0.167 -41.7

Observed Percentage Improvement: On a scale of 0-100, how frequently were discharges improved with 

implementation of this BMP grouping

Observed Odds of Improvement: Number improved or eliminated divided by number with no significant

difference

Ratio of Odds: What are the odds of improvement if BMP grouping is implemented vs.

if reference grouping (Regrading & Revegetation) is implemented
 Coal Remining BMP Guidance Manual

Efficiencies of BMPs 6-47

Table 6.3m: Analysis of Discrete Groups based on Observed Acidity Results Using

Daylighting as Reference Group

BMP Group Number of

Discharges

Affected

Number of

Discharges

Improved

or

Eliminated

Number of

Discharges

Unchanged

Observed

Percent

Improved

Observed

Odds

Ratio

compared

to

Reference

Percent

Improved 

minus

Reference

Percent

Improved

Daylighting 

(Reference)

13 4 9 30.8 --- ---

Daylighting, Alkaline

Addition <100

12 4 8 33.3 1.125 -2.5

Regrading, Revegetation,

Daylighting

36 16 20 44.4 1.800 13.6

Daylighting, Special

Handling, Alkaline

Addition <100

5 2 3 40.0 1.500 9.2

Regrading, Revegetation,

Daylighting, Special

Handling

18 7 11 38.9 1.432 8.1

Regrading, Revegetation,

Daylighting, Alkaline

Addition <100

13 5 8 38.5 1.406 7.7

Regrading, Revegetation,

Daylighting, Special

Handling, Alkaline

Addition <100

12 4 8 33.3 1.125 2.5

Regrading, Revegetation,

Daylighting, Special

Handling, Water Handling

8 1 7 12.5 0.321 -18.3

Observed Percentage Improvement: On a scale of 0-100, how frequently were discharges improved with 

implementation of this BMP grouping

Observed Odds of Improvement: Number improved or eliminated divided by number with no significant

difference

Ratio of Odds: What are the odds of improvement if BMP grouping is implemented vs.

if reference grouping (Daylighting) is implemented

* Because all discharges for this grouping were improved, the odds of improvement would be 4 divided by 0. 

Therefore, the odds ratio is infinite.
Coal Remining BMP Guidance Manual

6-48 Efficiencies of BMPs

Table 6.3n: Analysis of Discrete Groups based on Observed Iron Results Using

Daylighting as Reference Group

BMP Group Number of

Discharges

Affected

Number of

Discharges

Improved or

Eliminated

Number of

Discharges

Unchanged

Observed

Percent

Improved

Observed

Odds Ratio

compared

to

Reference

Percent

Improved 

minus

Reference

Percent

Improved

Daylighting 

(Reference)

12 7 5 58.3 --- ---

Daylighting, Alkaline

Addition <100

11 3 8 27.3 0.268 -31.0

Regrading,

Revegetation,

Daylighting

37 13 22 37.1 0.422 -21.2

Daylighting, Special

Handling, Alkaline

Addition <100

5 2 3 40.0 0.476 -18.3

Regrading,

Revegetation,

Daylighting, Special

Handling

16 7 8 46.7 0.625 -11.6

Regrading,

Revegetation,

Daylighting, Alkaline

Addition <100

12 4 8 33.3 0.357 -25.0

Regrading,

Revegetation,

Daylighting, Special

Handling, Alkaline

Addition <100

9 5 4 55.6 0.893 -2.7

Regrading,

Revegetation,

Daylighting, Special

Handling, Water

Handling

8 1 7 12.5 0.102 -45.8

Observed Percentage Improvement: On a scale of 0-100, how frequently were discharges improved with 

implementation of this BMP grouping

Observed Odds of Improvement: Number improved or eliminated divided by number with no significant

difference

Ratio of Odds: What are the odds of improvement if BMP grouping is implemented vs.

if reference grouping (Daylighting) is implemented
 Coal Remining BMP Guidance Manual

Efficiencies of BMPs 6-49

Table 6.3o: Analysis of Discrete Groups based on Observed Manganese Results Using

Daylighting as Reference Group

BMP Group Number of

Discharges

Affected

Number of

Discharges

Improved

or

Eliminated

Number of

Discharges

Unchanged

Observed

Percent

Improved

Observed

Odds

Ratio

compared

to

Reference

Percent

Improved 

minus

Reference

Percent

Improved

Daylighting 

(Reference)

11 6 4 60.0 --- ---

Regrading, Revegetation,

Daylighting

30 10 19 34.5 0.351 -25.5

Daylighting, Special

Handling, Alkaline

Addition <100

5 2 3 40.0 0.444 -20.0

Regrading, Revegetation,

Daylighting, Special

Handling

9 5 4 55.6 0.833 -4.4

Regrading, Revegetation,

Daylighting, Alkaline

Addition <100

12 4 7 36.4 0.381 -23.6

Regrading, Revegetation,

Daylighting, Special

Handling, Alkaline

Addition <100

7 3 4 42.9 0.500 -17.1

Regrading, Revegetation,

Daylighting, Special

Handling, Water

Handling

8 1 7 12.5 0.095 –47.5

Observed Percentage Improvement: On a scale of 0-100, how frequently were discharges improved with 

implementation of this BMP grouping

Observed Odds of Improvement: Number improved or eliminated divided by number with no significant

difference

Ratio of Odds: What are the odds of improvement if BMP grouping is implemented vs.

if reference grouping (Daylighting) is implemented
Coal Remining BMP Guidance Manual

6-50 Efficiencies of BMPs

Table 6.3p: Analysis of Discrete Groups based on Observed Aluminum Results Using

Daylighting as Reference Group

BMP Group Number of

Discharges

Affected

Number of

Discharges

Improved or

Eliminated

Number of

Discharges

Unchanged

Observed

Percent

Improved

Observed

Odds Ratio

compared

to

Reference

Percent

Improved 

minus

Reference

Percent

Improved

Daylighting 

(Reference)

10 4 5 44.4 --- ---

Regrading,

Revegetation,

Daylighting

24 11 12 47.8 1.146 3.4

Regrading,

Revegetation,

Daylighting, Special

Handling

12 2 9 18.2 0.278 -26.2

Regrading,

Revegetation,

Daylighting, Alkaline

Addition <100

11 2 9 18.2 0.278 -26.2

Regrading,

Revegetation,

Daylighting, Special

Handling, Water

Handling

8 1 7 12.5 0.179 –31.9

Observed Percentage Improvement: On a scale of 0-100, how frequently were discharges improved with 

implementation of this BMP grouping

Observed Odds of Improvement: Number improved or eliminated divided by number with no significant

difference

Ratio of Odds: What are the odds of improvement if BMP grouping is implemented vs.

if reference grouping (Daylighting) is implemented
 Coal Remining BMP Guidance Manual

Efficiencies of BMPs 6-51

Table 6.3q: Analysis of Discrete Groups based on Observed Sulfate Results Using

Daylighting as Reference Group

BMP Group Number of

Discharges

Affected

Number of

Discharges

Improved

or

Eliminated

Number of

Discharges

Unchanged

Observed

Percent

Improved

Observed

Odds

Ratio

compared

to

Reference

Percent

Improved 

minus

Reference

Percent

Improved

Daylighting 

(Reference)

14 4 8 33.3 --- ---

Daylighting, Alkaline

Addition <100

12 3 9 25.0 0.666 -8.3

Regrading, Revegetation,

Daylighting

36 14 19 42.4 0.516 9.1

Regrading, Revegetation,

Daylighting, Special

Handling

18 4 9 30.8 0.889 -2.5

Regrading, Revegetation,

Daylighting, Alkaline

Addition <100

14 4 7 36.4 1.143 3.1

Regrading, Revegetation,

Daylighting, Special

Handling, Alkaline

Addition <100

12 5 6 45.5 1.667 12.2

Regrading, Revegetation,

Daylighting, Special

Handling, Water Handling

8 1 7 12.5 0.286 -20.8

Observed Percentage Improvement: On a scale of 0-100, how frequently were discharges improved with 

implementation of this BMP grouping

Observed Odds of Improvement: Number improved or eliminated divided by number with no significant

difference

Ratio of Odds: What are the odds of improvement if BMP grouping is implemented vs.

if reference grouping (Daylighting) is implemented
Coal Remining BMP Guidance Manual

6-52 Efficiencies of BMPs

Table 6.3r: Analysis of Discrete Groups based on Observed Flow Results Using

Daylighting as Reference Group

BMP Group Number of

Discharges

Affected

Number of

Discharges

Improved

or

Eliminated

Number of

Discharges

Unchanged

Observed

Percent

Improved

Observed

Odds

Ratio

compared

to

Reference

Percent

Improved 

minus

Reference

Percent

Improved

Daylighting 

(Reference)

14 2 12 14.3 --- ---

Daylighting, Alkaline

Addition <100

12 3 9 25.0 2.000 10.7

Regrading, Revegetation,

Daylighting

37 16 18 47.1 5.333 32.8

Daylighting, Special

Handling, Alkaline

Addition <100

5 2 3 40.0 4.000 25.7

Regrading, Revegetation,

Daylighting, Special

Handling

18 5 10 33.3 3.000 19.0

Regrading, Revegetation,

Daylighting, Alkaline

Addition <100

14 4 8 33.3 3.000 19.0

Regrading, Revegetation,

Daylighting, Special

Handling, Alkaline

Addition <100

12 4 8 33.3 3.000 19.0

Regrading, Revegetation,

Daylighting, Special

Handling, Water Handling

8 2 6 25.0 2.000 10.7

Observed Percentage Improvement: On a scale of 0-100, how frequently were discharges improved with 

implementation of this BMP grouping

Observed Odds of Improvement: Number improved or eliminated divided by number with no significant

difference

Ratio of Odds: What are the odds of improvement if BMP grouping is implemented vs.

if reference grouping (Daylighting) is implemented
 Coal Remining BMP Guidance Manual

Efficiencies of BMPs 6-53

Table 6.3s: Analysis of Discrete Groups based on Observed Acidity Results Using

Regrading, Revegetation, and Daylighting as Reference Group

BMP Group Number of

Discharges

Affected

Number of

Discharges

Improved

or

Eliminated

Number of

Discharges

Unchanged

Observed

Percent

Improved

Observed

Odds

Ratio

compared

to

Reference

Percent

Improved 

minus

Reference

Percent

Improved

Regrading, Revegetation,

Daylighting (Reference)

36 16 20 44.4 — ---

Regrading, Revegetation,

Daylighting, Special

Handling

18 7 11 38.9 0.795 -5.5

Regrading, Revegetation,

Daylighting, Alkaline

Addition <100

13 5 8 38.5 0.781 -5.9

Regrading, Revegetation,

Daylighting, Special

Handling, Alkaline

Addition <100

12 4 8 33.3 0.625 -11.1

Regrading, Revegetation,

Daylighting, Special

Handling, Water

Handling

8 1 7 12.5 0.179 -31.9

Observed Percentage Improvement: On a scale of 0-100, how frequently were discharges improved with 

implementation of this BMP grouping

Observed Odds of Improvement: Number improved or eliminated divided by number with no significant

difference

Ratio of Odds: What are the odds of improvement if BMP grouping is implemented vs.

if reference grouping (Regrading, Revegetation & Daylighting) is

implemented
Coal Remining BMP Guidance Manual

6-54 Efficiencies of BMPs

Table 6.3t: Analysis of Discrete Groups based on Observed Iron Results Using

Regrading, Revegetation, and Daylighting as Reference Group

BMP Group Number of

Discharges

Affected

Number of

Discharges

Improved

or

Eliminated

Number of

Discharges

Unchanged

Observed

Percent

Improved

Observed

Odds

Ratio

compared

to

Reference

Percent

Improved 

minus

Reference

Percent

Improved

Regrading, Revegetation,

Daylighting (Reference)

37 13 22 37.1 --- ---

Regrading, Revegetation,

Daylighting, Special

Handling

16 7 8 46.7 1.481 9.6

Regrading, Revegetation,

Daylighting, Alkaline

Addition <100

12 4 8 33.3 0.846 -3.8

Regrading, Revegetation,

Daylighting, Special

Handling, Alkaline

Addition <100

9 5 4 55.6 2.115 18.5

Regrading, Revegetation,

Daylighting, Special

Handling, Water

Handling

8 1 7 12.5 0.242 -24.6

Observed Percentage Improvement: On a scale of 0-100, how frequently were discharges improved with 

implementation of this BMP grouping

Observed Odds of Improvement: Number improved or eliminated divided by number with no significant

difference

Ratio of Odds: What are the odds of improvement if BMP grouping is implemented vs.

if reference grouping (Regrading, Revegetation & Daylighting) is

implemented
 Coal Remining BMP Guidance Manual

Efficiencies of BMPs 6-55

Table 6.3u: Analysis of Discrete Groups based on Observed Manganese Results Using

Regrading, Revegetation and Daylighting as a Reference Group

BMP Group Number of

Discharges

Affected

Number of

Discharges

Improved

or

Eliminated

Number of

Discharges

Unchanged

Observed

Percent

Improved

Observed

Odds

Ratio

compared

to

Reference

Percent

Improved 

minus

Reference

Percent

Improved

Regrading, Revegetation,

Daylighting (Reference)

30 10 19 34.5 --- ---

Regrading, Revegetation,

Daylighting, Special

Handling

 9 5 4 55.6 2.376 21.1

Regrading, Revegetation,

Daylighting, Alkaline

Addition <100

12 4 7 36.4 1.086 1.9

Regrading, Revegetation,

Daylighting, Special

Handling, Alkaline

Addition <100

7 3 4 42.9 1.426 8.4

Regrading, Revegetation,

Daylighting, Special

Handling, Water

Handling

8 1 7 12.5 0.272 -22.0

Observed Percentage Improvement: On a scale of 0-100, how frequently were discharges improved with 

implementation of this BMP grouping

Observed Odds of Improvement: Number improved or eliminated divided by number with no significant

difference

Ratio of Odds: What are the odds of improvement if BMP grouping is implemented vs.

if reference grouping (Regrading, Revegetation & Daylighting) is

implemented
Coal Remining BMP Guidance Manual

6-56 Efficiencies of BMPs

Table 6.3v: Analysis of Discrete Groups based on Observed Aluminum Results Using

Regrading, Revegetation and Daylighting as Reference Group

BMP Group Number of

Discharges

Affected

Number of

Discharges

Improved

or

Eliminated

Number of

Discharges

Unchanged

Observed

Percent

Improved

Observed

Odds Ratio

compared

to

Reference

Percent

Improved 

minus

Reference

Percent

Improved

Regrading, Revegetation,

Daylighting (Reference)

24 11 12 47.8 --- ---

Regrading, Revegetation,

Daylighting, Special

Handling

 12 2 9 18.2 0.242 -29.6

Regrading, Revegetation,

Daylighting, Alkaline

Addition <100

11 2 9 18.2 0.242 -29.6

Regrading, Revegetation,

Daylighting, Special

Handling, Water

Handling

8 1 7 12.5 0.156 -35.3

Observed Percentage Improvement: On a scale of 0-100, how frequently were discharges improved with 

implementation of this BMP grouping

Observed Odds of Improvement: Number improved or eliminated divided by number with no significant

difference

Ratio of Odds: What are the odds of improvement if BMP grouping is implemented vs.

if reference grouping (Regrading, Revegetation & Daylighting) is

implemented
 Coal Remining BMP Guidance Manual

Efficiencies of BMPs 6-57

Table 6.3w: Analysis of Discrete Groups based on Observed Sulfate Results Using

Regrading, Revegetation, and Daylighting as Reference Group

BMP Group Number of

Discharges

Affected

Number of

Discharges

Improved

or

Eliminated

Number of

Discharges

Unchanged

Observed

Percent

Improved

Observed

Odds

Ratio

compared

to

Reference

Percent

Improved 

minus

Reference

Percent

Improved

Regrading, Revegetation,

Daylighting (Reference)

36 14 19 42.4 --- ---

Regrading, Revegetation,

Daylighting, Special

Handling

18 4 9 30.8 0.603 -11.6

Regrading, Revegetation,

Daylighting, Alkaline

Addition <100

14 4 7 36.4 0.775 -6.0

Regrading, Revegetation,

Daylighting, Special

Handling, Alkaline

Addition <100

12 5 6 45.5 1.131 3.1

Regrading, Revegetation,

Daylighting, Special

Handling, Water

Handling

8 1 7 12.5 0.194 -29.9

Observed Percentage Improvement: On a scale of 0-100, how frequently were discharges improved with 

implementation of this BMP grouping

Observed Odds of Improvement: Number improved or eliminated divided by number with no significant

difference

Ratio of Odds: What are the odds of improvement if BMP grouping is implemented vs.

if reference grouping (Regrading, Revegetation & Daylighting) is

implemented
Coal Remining BMP Guidance Manual

6-58 Efficiencies of BMPs

Table 6.3x: Analysis of Discrete Groups based on Observed Flow Results Using

Regrading, Revegetation, and Daylighting as Reference Group

BMP Group Number of

Discharges

Affected

Number of

Discharges

Improved

or

Eliminated

Number of

Discharges

Unchanged

Observed

Percent

Improved

Observed

Odds

Ratio

compared

to

Reference

Percent

Improved 

minus

Reference

Percent

Improved

Regrading, Revegetation,

Daylighting (Reference)

37 16 18 47.1 --- ---

Regrading, Revegetation,

Daylighting, Special

Handling

18 5 10 33.3 0.563 -13.8

Regrading, Revegetation,

Daylighting, Alkaline

Addition <100

14 4 8 33.3 0.563 -13.8

Regrading, Revegetation,

Daylighting, Special

Handling, Alkaline

Addition <100

12 4 8 33.3 0.563 -13.8

Regrading, Revegetation,

Daylighting, Special

Handling, Water

Handling

8 2 6 25.0 0.375 -22.1

Observed Percentage Improvement: On a scale of 0-100, how frequently were discharges improved with 

implementation of this BMP grouping

Observed Odds of Improvement: Number improved or eliminated divided by number with no significant

difference

Ratio of Odds: What are the odds of improvement if BMP grouping is implemented vs.

if reference grouping (Regrading, Revegetation & Daylighting) is

implemented
 Coal Remining BMP Guidance Manual

Efficiencies of BMPs 6-59

6.4 Discussion

6.4.1 Observed Results

The combinations of BMPs affecting the most discharges at the completed Pennsylvania remining

sites in order of decreasing frequency of occurrence are as follows:

Group # Discharges Affected

1 Daylighting, Regrading, Revegetation 37

2 Regrading, Revegetation 18

3 Daylighting, Regrading, Revegetation, Special

Materials Handling 18

4 Daylighting, Regrading, Revegetation, Special 

Materials Handling, Alkaline Addition (<100 

tons/acre) 12

5 Daylighting, Regrading, Revegetation, Alkaline 

Addition (<100 tons/acre) 14

6 Daylighting, Alkaline Addition (<100 tons

CaCO3 equivalent/acre)

12

7 Daylighting, Regrading, Revegetation, Special 

Materials Handling, Special Water Handling 

Facilities 8
Coal Remining BMP Guidance Manual

6-60 Efficiencies of BMPs

Acidity Loading

Only three BMPs (regrading, revegetation, and daylighting) were reported to be used singly at the

Pennsylvania study remining sites (Table 6.2b). Of these BMPs, only daylighting impacted acidity

loading in a significant number of discharges (13). Daylighting alone significantly improved 30.8

percent of the discharges for acidity loading with no discharges significantly degraded. 

Revegetation used singly significantly improved acidity loading in 40 percent of 5 discharges

affected with the remainder unchanged. Regrading used singly affected one discharge which was

shown to be significantly improved. However, it is doubtful that regrading was used without

corresponding revegetation.

The seven most common BMP groups (listed previously) were highly successful in not degrading

the discharges in terms of acidity loadings. All of the discharges affected by these BMP groups

were either significantly improved or unchanged (Figure 6.4a) with improvement ranging from

12.5 to 50 percent of the discharges depending on BMP group. No discharges were significantly

degraded. The most successful BMP combination was regrading and revegetation (#2), followed

by daylighting, regrading, and revegetation (#1), and daylighting, regrading, revegetation, and

alkaline addition (#5). BMP group #2 significantly improved 50 percent of the discharges and had

no significant effect on 50 percent of the discharges. Over 44 percent of the discharges were

improved under BMP group #1 with the remainder unchanged. The success of these BMP

combinations (#1 and #2) in decreasing acidity loading may be due to the fact that these BMP

groups are generally used for remining operations that are environmentally uncomplicated and do

not require elaborate BMP plans to effect improvement. Additionally, these BMPs greatly impact

the amount of water moving through the reclaimed site and, to a lesser extent, effect the water

quality. This may be an indication that flow-reducing BMPs may be more effective in reducing

loads than those that work primarily geochemically. This determination is supported by Smith

(1988) and Hawkins (1995) who both observed flow to be the predominant determinant of

pollution loadings (see Section 1.2, Figure 2.1a).
 Coal Remining BMP Guidance Manual

Efficiencies of BMPs 6-61

Figure 6.4a: Impacts of BMP Combinations on Acidity Loading

Iron Loading

As previously stated, only three BMPs (regrading, revegetation, and daylighting) were reported to

be used singly at the Pennsylvania study remining sites and of these BMPs, only daylighting

impacted a significant number of discharges (12) for iron loadings. Daylighting singly improved

more than half (58 percent) of the discharges for iron loading and had no effect on the remaining

42 percent. No discharges were significantly degraded. Revegetation alone significantly improved

20 percent of discharges (1 discharge), significantly degraded 20 percent of the discharges and did

not affect the remaining discharges. Regrading alone was shown to be used for one discharge

which was unchanged. However, as previously stated, it is doubtful that regrading was used

without corresponding revegetation.
Coal Remining BMP Guidance Manual

6-62 Efficiencies of BMPs

 The seven BMP combinations quite successfully left most of the discharges improved or

unchanged in terms of the iron load. The two most successful BMP combinations for discharge

iron load improvement were daylighting, regrading, revegetation, special materials handling, and

alkaline addition (#4) which improved 55.6 percent of the discharges and regrading, revegetation,

and alkaline addition (#8) which improved 50 percent of the discharges. The remaining discharges

affected by those two BMP groups were unchanged. Implementation of two other BMP groups

(daylighting, regrading, and revegetation (#1) and daylighting, regrading, revegetation and special

materials handling (#3)), resulted in a few discharges exhibiting higher iron loadings (failures).

The failure rates were 5.4 and 6.7 percent, respectively. However, the actual number of degraded

discharges for either BMP group was small, a total of 2. The impact of the seven BMP groups on

iron loading rates is illustrated in Figure 6.4b.

The two BMP groups with the highest iron loading improvement rates (#4 and #2) included

alkaline addition (<100 tons per acre), which may have raised the pH of the water enough to

permit some of the iron to precipitate within the backfill. However, two other BMP groups with

that level of alkaline addition (#5 and #6) did not exhibit similar rates of iron loading

improvement. This situation can occur in cases where a large amount of acidic material is

encountered during daylighting and naturally occurring alkaline material was not present in the

overburden. The amount of alkaline addition may have been insufficient to offset the acidity

production.
 Coal Remining BMP Guidance Manual

Efficiencies of BMPs 6-63

Figure 6.4b: Impacts of BMP Combinations on Iron Loading
Coal Remining BMP Guidance Manual

6-64 Efficiencies of BMPs

Manganese Loading

Of the three BMPs (regrading, revegetation, and daylighting) used singly at the Pennsylvania

study remining sites, only daylighting impacted manganese loading in a significant number of

discharges (11). Daylighting singly improved 54.5 percent of the discharges for manganese

loading with 9.1 percent (one discharge) significantly degraded. Revegetation significantly

improved one (20 percent) of five discharges and did not affect the remaining discharges.

Implementation of regrading affected one discharge which was significantly degraded.

Two of the BMP groups induced some of the highest improvement rates observed for any of the

contaminant loadings (see Figure 6.4c). The combinations of regrading and revegetation (#2) and 

daylighting, regrading, revegetation and special materials handling (#3) exhibited discharge

improvement rates for manganese of 45.5 and 55.6 percent, respectively. It is difficult to

determine what may have allowed these two BMP combinations to be so effective. Manganese

concentrations are extremely difficult to predict. Exactly where manganese originates is unclear.

However, the main source of manganese appears to be as a solid-solution replacement of iron in

siderite (FeCO3) (Rose and Cravotta, 1998). The actual amount of manganese replacement is

quite low (~1 percent) (Rose, 1999). Ongoing research may improve the predictive capabilities. 

The highest rates of discharge degradation (failure) for the seven BMP groups were exhibited for

manganese loadings. Three of seven BMP combinations had at least one discharge that was

degraded with respect to manganese loadings. BMP groups regrading and revegetation (#2) and

regrading, revegetation, daylighting, and alkaline addition (#5) exhibited the highest failure rates

of 18.2 and 8.3 percent, respectively. It is interesting to note that the highest discharge failure

rate for manganese loading occurred with BMP group #2, which also had the second highest

manganese loading improvement rate. This illustrates the problematic nature of manganese

effluent predictions.
 Coal Remining BMP Guidance Manual

Efficiencies of BMPs 6-65

Figure 6.4c: Impacts of BMP Combinations on Manganese Loading

Aluminum Loading

Of the three BMPs (regrading, revegetation, and daylighting) reported to be used singly at the

Pennsylvania study remining permits, only daylighting impacted a significant number of discharges

(10) for aluminum loadings. Daylighting implemented alone significantly improved 40 percent of

the affected discharges for aluminum loading and significantly degraded 10 percent (one

discharge). Revegetation significantly improved 60 percent of the five affected discharges and had

no effect on the remaining two discharges. Regrading implemented alone affected one discharge

which was shown to be significantly improved.

The most successful BMP group in improving the aluminum loads was daylighting, regrading,

revegetation, special materials handling, and alkaline addition (#4) with 66.7 percent of the
Coal Remining BMP Guidance Manual

6-66 Efficiencies of BMPs

N = 24 6 12 3 11 1 8

 1 2 3 4 5 6 7

BMP Group #

Aluminum Load

Better or Eliminated

Unchanged

Worse

0

20

40

60

80

100

discharges exhibiting significant improvement. This was the highest improvement rate exhibited by

any of the BMP groups for any of the contaminants, although this group affected only 3

discharges in terms of aluminum loading. BMP groups of daylighting, regrading, and revegetation

(#1) and regrading and revegetation (#2) were the next most successful in improving the

aluminum loadings with 45.8 and 50 percent improvement, respectively.

Figure 6.4d: Impacts of BMP Combinations on Aluminum Loading

Sulfate Loading

As previously stated, sulfate loading is not a regulated effluent parameter, but is included herein to

permit a clearer analysis of the effectiveness of BMPs to geochemically reduce the acidity, iron,

manganese, and aluminum loadings. Of the three BMPs (regrading, revegetation, and daylighting)

reported to be used singly at the Pennsylvania study remining sites, only daylighting impacted

sulfate loading in a significant number of discharges (14). Daylighting singly improved 28.6

percent of the discharges for sulfate loading with 14.3 percent (two discharges) significantly
 Coal Remining BMP Guidance Manual

Efficiencies of BMPs 6-67

degraded. Revegetation significantly improved three (60 percent) of five discharges, did not affect

one discharge, and significantly degraded one discharge. Implementation of regrading affected one

discharge which was improved.

The most successful BMP group in improving sulfate loading was regrading and revegetation (#2)

with 55.6 percent. The next two most successful BMP combinations were daylighting, regrading,

revegetation, special materials handling, alkaline addition < 100 tons/acre (#4) and daylighting,

regrading, and revegetation (#1) exhibiting improvements of 41.7 and 38.9 percent, respectively. 

The presence of regrading and revegetation in the three most successful groups indicates that

simply reclaiming an abandoned site may greatly decrease acid production.

Figure 6.4e: Impacts of BMP Combinations on Sulfate Loading
Coal Remining BMP Guidance Manual

6-68 Efficiencies of BMPs

Flow Rate

As previously stated, flow rate is not a regulated effluent parameter, but is included herein to

permit a clearer analysis of the effectiveness of BMPs that work to physically reduce the pollution

loadings. Of the three BMPs (regrading, revegetation, and daylighting) used singly at the

Pennsylvania study remining sites, only daylighting impacted flow rate in a significant number of

discharges (14). Daylighting singly improved (decreased or eliminated flow) 28.6 percent of the

discharges, with none of the discharges significantly increasing in flow. Revegetation significantly

improved three (60 percent) of five discharges and effected no change of the remaining

discharges. Implementation of regrading affected one discharge which was unchanged.

The most successful BMP group in improving flow rate was regrading and revegetation (#2) with

66.7 percent, followed by daylighting, regrading, and revegetation (#1) and daylighting,

regrading, revegetation, special materials handling, alkaline addition < 100 tons/acre (#4)

exhibiting improvements of 43.2 and 33.3 percent, respectively. As with sulfate, the presence of

regrading and revegetation in both these groups, indicates that simply reclaiming a site will reduce

infiltration into the spoil, which ultimately reduces the outflow. 
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Efficiencies of BMPs 6-69

Figure 6.4f: Impacts of BMP Combinations on Flow Rate

6.4.2 Predicted Results

The data obtained from the Pennsylvania study remining sites were statistically analyzed using the

methodology described in Section 6.3.1. These analyses, applied to single BMPs, determined the

predicted percentage of discharges that would be improved, the odds that a discharge would be

improved, and the odds of improvement over doing nothing at all in terms of BMPs. The results

of these analyses are listed in Tables 6.3a through 6.3d (BMPs implemented alone). Tables 6.3e

and 6.3f are the same analyses conducted for sulfate loadings and flow rate to allow for an in

depth determination of the possible impacts (physical or geochemical) of specific BMPs and BMP

combinations. 
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6-70 Efficiencies of BMPs

6.4.2.1 BMPs Implemented Alone

Acidity Loading

The predicted probabilities of improvement for all of the single-use BMPs (Revegetation,

Regrading, and Daylighting) range from 27.4 to 50.1 percent. The remaining BMPs were not

implemented alone, and therefore, do not have associated observed results. However, the

statistical analyses can provide some insight into their efficiency. Alkaline redistribution (80.9

percent) and biosolids addition (71.5 percent) exhibit the highest predicted probabilities of

improvement of acidity loading of all of the BMPs followed by special water handling (71.4

percent), mining alkaline strata (64.2 percent) and coal refuse removal (57.6 percent). It is

interesting to note that alkaline addition of <100 tons per acre yielded the lowest predicted

improvement probability of 25.4 percent, while half of the four highest predicted percentages also

deal with increasing the amount of alkaline material in the backfill. The results may indicate that

the amount of alkaline material added (<100 tons per acre) was too low. Brady and others (1990)

observed that alkaline addition application rates at surface mines frequently are too low to

improve the water quality.

The significant interaction between special handling and water handling indicates that the positive

effect of water handling on the odds of at least improvement is greatly diminished when special

handling is also present. This can be best explained by comparing the observed results for water

handling with and without special handling (see Table 6.2b). When water handling and special

handling both affect a discharge, the result is at least improvement 11 percent (1 out of 9

discharges) of the time. However, when water handling but not special handling affect a

discharge, the result is at least improvement 77 percent (10 out of 13 discharges) of the time. It is

worth noting that these two BMPs never affect a discharge without being combined with other

BMPs. Eight of the nine discharges affected by both water handling and special handling were

affected additionally by regrading, revegetation and daylighting. The failure of special handling
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Efficiencies of BMPs 6-71

may be because it is frequently employed where a substantial amount of acid-forming materials is

present, perhaps too much to be offset by any single BMP or group of BMPs.

Iron Loading

Predicted probabilities of improvement in iron loading for all of the single-use BMPs range from

36.0 to 51.3 percent. Special water handling facilities (73.1 percent) and biosolids addition (62.9

percent) exhibit the highest predicted improvement percentages followed by alkaline redistribution

(61.3 percent), revegetation (51.3 percent) and mining of alkaline strata (49.7 percent). The

lowest predicted probability of improvement is coal refuse removal (26.2 percent). The relatively

low number of discharges affected (7) may bring into question the usefulness of this prediction

value. In addition, the low predicted discharge improvement may be due to a delayed response in

regards to water quality, compared with other BMPs. Refuse is typically acid-producing and

when removed, fresh refuse is exposed to weathering or flushing of existing weathered products. 

It may take more time than the limited monitoring periods available to see improvements in some

water quality parameters. 

The significant interaction between special handling and water handling indicates that the positive

effect of water handling on the odds of at least improvement is greatly diminished when special

handling is also present. This can be best explained by comparing the observed results for water

handling with and without special handling (see table 6.2b). When water handling and special

handling both affect a discharge, the result is at least improvement 20 percent (2 out of 10

discharges) of the time. However, when water handling but not special handling affect a

discharge, the result is at least improvement 75 percent (9 out of 12 discharges). It is worth

noting that these two BMPs never affect a discharge without being combined with other BMPs. 

Eight of the ten discharges affected by both water handling and special handling were also

affected by regrading, revegetation and daylighting.
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6-72 Efficiencies of BMPs

Manganese Loading

Predicted probabilities of discharge improvement for single-use BMPs range from 44.6 to 54.0

percent. Alkaline material redistribution (92.6 percent) and biosolids application (96.1 percent)

exhibit the highest predicted improvement, followed by water handling (90.4 percent), mining

alkaline strata (68.8 percent) and special handling (60.3 percent). The lowest probabilities of

improvement were predicted for coal refuse removal (2.8 percent) and alkaline addition >100 tons

per acre (6.2 percent). However, these BMPs each affected 6 discharges and the strength of the

prediction is weak. In addition, an improvement in manganese loading in discharges affected by

coal refuse removal may be delayed as explained in regards to iron loading.

The significant interaction between special handling and water handling indicates that the positive

effect of water handling on the odds of at least improvement is greatly diminished when special

handling is also present. This can be best explained by comparing the observed results for water

handling with and without special handling (see table 6.2b). When water handling and special

handling both affect a discharge, the result is at least improvement 22 percent (2 out of 9

discharges) of the time. However, when water handling but not special handling affect a discharge,

the result is at least improvement 88 percent (7 out of 8 discharges) of the time. It is worth noting

that these two BMPs never affect a discharge without being combined with other BMPs.

Aluminum Loading

The number of discharges (117) analyzed for aluminum loading is considerably lower than for 

any of the other contaminants. Therefore, the results of the statistical analyses are much less

definitive. The predicted probabilities of improvement for single-use BMPs ranges from 43.0 to

61.2 percent. Biosolids application (96.4 percent) and alkaline material redistribution (93.3

percent) exhibit the highest improvement predictions, followed by regrading (21.2 percent), 

special water handling (59.5 percent) and revegetation (55.0 percent). The lowest improvement 
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Efficiencies of BMPs 6-73

predictions are for coal refuse removal (34.0 percent) and mining of high-alkaline strata (26.1

percent). However, these BMPs impacted 6 and 3 discharges respectively, and the strength of the

prediction is questionable. In addition, an improvement in aluminum loading in discharges affected

by coal refuse removal may be delayed as explained in regards to iron and manganese loading.

Sulfate Loading

Predicted probabilities of discharge improvement for single-use BMPs range from 12.3 to 75.1

percent. Alkaline material redistribution (80.1 percent) and biosolids application (76.0 percent)

exhibit the highest predicted improvement of all of the BMPs, followed by mining alkaline strata

(65.4 percent). The lowest probabilities of improvement were predicted for coal refuse removal

(9.0 percent) and special handling (10.8 percent).

Flow Rate

Predicted probabilities of discharge improvement for single-use BMPs range from 19.5 to 66.0

percent. Mining of alkaline strata (88.7 percent), biosolids addition (80.4 percent), and alkaline

redistribution (66.3 percent) exhibit the highest predicted improvement of all of the BMPs,

followed by alkaline addition < 100 tons per acre with 52.3 percent. The lowest probabilities of

improvement were predicted for coal refuse removal (1.4 percent) and special handling (12.7

percent).

6.4.2.2 BMP Groups

The term “remining” implies that mining will be occurring on an area that has been previously

mined. Specifically, for the sake of this manual, it also implies that the area was mined prior to

implementation of SMCRA (1977) and modern reclamation standards. There are four basic types

of abandoned mine lands that are remined: (1) sites that were previously surface mined, (2) sites

that were previously underground mined, (3) sites that were previously surface mined and
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6-74 Efficiencies of BMPs

underground mined, and (4) sites that had coal refuse deposited on the surface. These areas

cannot be reaffected or remined without implementation of some minimal BMPs. Table 6.4a

shows the type of previous mining and the associated minimal BMP(s). 

 Table 6.4a: Types of Mining and Minimal BMPs

Type of Previous Mining Minimal Best Management Practices

Surface Mining Regrading, Revegetation

Underground Mining Daylighting

Surface and Underground Mining Regrading, Revegetation and Daylighting

Refuse Disposal Refuse Removal, Regrading, Revegetation

Of the discharges affected by remining, 156 were affected by regrading, 170 by daylighting and

only 9 by coal refuse removal. There were also a large number of discharges that were affected by

both regrading and daylighting. Nearly all discharges affected by regrading were also affected by

revegetation. The group of regrading and revegetation and the group of daylighting occurred

enough times that it was possible to compare the effectiveness of these minimum BMPs against the

minimum BMPs plus other select BMPs (Tables 6.3g through 6.3r). Likewise, the group of

regrading and revegetation combined with daylighting, together, affected enough discharges for

similar evaluation (Table 6.3s through 6.3x). These minimum BMP combinations were compared

against the minimum combination plus select other BMPs. The BMP groups were selected based

on their having affected at least four discharges that did not get significantly worse. The BMP

groups were evaluated for effects on flow and for effects on acidity, iron, manganese, aluminum

and sulfate loadings. 

Unfortunately some BMPs that had a high rate of success (i.e., alkaline redistribution, mining of

alkaline strata and alkaline addition at application rates greater than 100 tons per acre, Table 6.3a)

could not be evaluated because they affected too few discharges. 

Results of the evaluations of BMP groups are reported in Tables 6.3g through 6.3x. Interpretation

of these tables is as follows:
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Efficiencies of BMPs 6-75

C The first BMP group represents the reference BMP(s).

C If the observed percent improved is greater than the percent improved by the reference

group. This suggests that the combined BMPs may have been more effective than the

reference group.

C If the observed odds ratio is greater than one, the combined BMPs were possibly more

effective than the reference BMP group.

C If the observed odds ratio is less than one, the combined BMPs were possibly less effective

than the reference BMP group.

C If the percent improved minus the reference group percent improved is positive, the

combined BMPs may have been more effective than the reference group used alone. If

negative, the combined BMPs were possibly less effective.

Interpretation of these results cannot be made blindly. A combination of BMPs that is less

effective than the reference does not necessarily imply that the "added" BMP(s) are detrimental. It

should also be kept in mind that the comparisons are between discharges that had pre- and postmining water quality that was not statistically different versus pre- and post-mining water quality

that showed at least a statistically significant improvement (improved or eliminated) after remining. 

Failures were not evaluated because they were so infrequent. Climatic differences also were not

taken into account.

Regrading and Revegetation

Regrading and revegetation, as mentioned above, are the basic BMPs required for reclamation of

previously surface mined land. They occur together, but without other BMPs, to affect at least 18

discharges. Tables 6.3g through 6.3l compare the success of regrading and revegetation, against

regrading and revegetation in addition to other select BMPs for acidity, iron, manganese and

aluminum loading. Tables 6.3k and 6.3l show the analysis of sulfate loadings and flow rate.

Acidity Loading (Table 6.3g): Of the discharges affected by this BMP reference group, the 

number of discharges that stayed the same and that at least improved, in regards to acidity, were 
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6-76 Efficiencies of BMPs

the same. One other BMP group (regrading revegetation, and special handling) had similar

results, although the sample size was the minimum of four. Only one BMP combination

(regrading, revegetation, and water handling) performed better than the reference. Again the

sample size was the minimum, but all four samples improved or were eliminated. All other BMP

combinations performed less effectively than the reference group. The least effective BMP

combination was regrading, revegetation, daylighting, special handling, and water handling, with

only one of eight discharges improving.

Iron Loading (Table 6.3h): Two of seven BMP combinations were more effective than the

reference group, and one was as effective, in regards to at least improving iron loading, than the

control. The most effective BMP group was water handling combined with the reference BMPs. 

Iron in all four of the discharges effected, either was improved or eliminated. The least effective

BMP combination was that of regrading, revegetation, daylighting, special handling, and water

handling, where only one of eight discharges improved.

Manganese Loading (Table 6.3i): Again, the combination of regrading, revegetation and water

handling proved the most effective BMP combination, with all four discharges showing

improvement or elimination. This was the only combination that was more successful than the

reference BMP group. The combination of regrading, revegetation, daylighting, special handling,

and water handling, again proved least effective. In general, manganese had the most failures

(resulted in the most discharges with loadings that were significantly unchanged) of any parameter. 

As discussed in Section 6.4.1, the ability to predict manganese is severely limited.

Aluminum Loading (Table 6.3j): Results for aluminum loading were reported less often than were

results for the other parameter loadings, and less BMP combinations are available for comparison

to the reference. Although all BMP combinations performed less effectively than the reference

group in regards to aluminum loading, the combination of regrading, revegetation, daylighting,

special handling and water handling was the least effective.
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Efficiencies of BMPs 6-77

Sulfate Loading (Table 6.3k): As for other parameters, the combination of regrading, revegetation

and water handling proved the most effective BMP combination, with three of four discharges

(75.0 percent) showing improvement or elimination. This was the only combination that was more

successful than the reference BMP group with 58.8 percent. The combinations of regrading,

revegetation, and special handling and regrading, revegetation, and alkaline addition < 100 tons

proved least effective with no discharges exhibiting improvement.

Flow Rate (Table 6.3l): As for other parameters, the combination of regrading, revegetation and

water handling proved the most effective BMP combination, with three of four discharges (75.0

percent) showing improvement or elimination. This was the only combination that was more

successful than the reference BMP group with 66.7 percent. The BMP combination of regrading,

revegetation, daylighting, special handling and water handling was the least effective.

Overall

The BMP reference group of regrading and revegetation includes BMPs that are effective for

reducing pollution load by reducing flow. This is reflected by the fact that half the discharges

using only these BMPs showed improvement (Tables 6.3g through 6.3l). Most of the other 

BMPs in the groupings are BMPs that are typically applied to sites that have acidic materials

and/or a lack of calcareous rocks. These BMPs are "geochemical" and affect water chemistry

rather than flow. The reference group out-performed 6 of the 8 other groupings that were

compared. This is probably because, in cases where regrading and revegetation were used alone,

the overburden was of good quality and there was no need for additional BMPs. The

implementation of special handling and alkaline addition imply that there was acidic material

present and a lack of calcareous rocks. Special handling of acidic materials, alone, may reduce

acid production, but cannot produce alkaline drainage. Alkaline addition, where it does occur in a

comparison group, is always less than 100 tons/acre. It has been shown by various studies, that

addition rates less than 100 tons/acre are not generally capable of producing alkaline drainage. It

should be kept in mind that alkaline drainage is not necessarily a goal of remining sites, the goal is

that the water not get worse. The BMP comparisons with alkaline addition at less than 100 tons 
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6-78 Efficiencies of BMPs

per acre do suggest that alkaline addition rates greater than 100 tons per acre could result in more

improvements.

For acidity, iron, and manganese, the most effective BMP combination that included the reference

group was that of regrading, revegetation, and water handling. Water handling is a physical BMP

and may have further reduced flow which would further reduce load. The BMP combination that

consistently performed the worst was regrading, revegetation, daylighting, special handling, and

water handling. This combination performed poorly for each parameter and for each evaluation

of reference BMPs. There is no intuitive explanation for this. Daylighting generally results in

acidic materials that need to be handled, and the inclusion of special handling implies that this was

the case. 

Daylighting

Daylighting is the minimum BMP required when an abandoned underground mine exists within a

coal seam proposed for surface mining. Daylighting by itself occurred 14 times and was

associated with 7 other BMP combinations that occurred at least 4 times. 

Acidity Loading (Table 6.3m): Daylighting implemented alone improved or eliminated acidity

loading in four affected discharges, and resulted in no change in nine discharges. Six of the seven

BMP combinations were more effective than the reference combination. The least effective

performance was for the same least effective combination in respect to regrading and revegetation

(regrading, revegetation, daylighting, special handling, and water handling). 

 

Iron Loading (Table 6.3n): Daylighting implemented alone resulted in the improvement of seven

discharges, and resulted in no change in the remaining five discharges. None of the 7 BMP

combinations were as effective as the control. The least effective combination was the same as

the least effective combination in regards to acidity (regrading, revegetation, daylighting, special

handling, and water handling).
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Efficiencies of BMPs 6-79

Manganese Loading (Table 6.3o): Six of the discharges affected by the reference group in terms

of manganese loading, improved or were eliminated and four remained unchanged. No BMP

combination was more effective than the reference combination. The least effective combination

was the same as the least effective combination in regards to acidity and iron (regrading,

revegetation, daylighting, special handling, and water handling).

Aluminum Loading (Table 6.3p): Because fewer data were available in regards to aluminum,

there are only four BMP combinations that were compared to the reference group. One of these

combinations (regrading, revegetation, and daylighting), was slightly more effective than the

control group. The other three combinations were less effective, with the least effective

combination being the same as the least effective combination in regards to acidity and iron and

manganese (regrading, revegetation, daylighting, special handling, and water handling).

Sulfate Loading (Table 6.3q): Four of the discharges (33.3 percent) affected by the reference

group in terms of sulfate loading, improved or were eliminated and eight remained unchanged.

Three BMP groups (regrading, revegetation, and daylighting; regrading, revegetation, daylighting,

and alkaline addition < 100 tons/acre; and regrading, revegetation, daylighting, special handling

and alkaline addition < 100 tons/acre) were more effective than the reference combination. The

least effective combination was the same as the least effective combination in regards to the other

parameters (regrading, revegetation, daylighting, special handling, and water handling) with 12.5

percent.

Flow Rate (Table 6.3r): Two of the discharges (14.3 percent) affected by the reference group in

terms of flow, improved or were eliminated and 12 remained unchanged. All of the seven BMP

combinations were more effective than the reference group. The least effective BMP group other

than the reference group, was daylighting, regrading, and revegetation and regrading,

revegetation, daylighting, special handling, and water handling.
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6-80 Efficiencies of BMPs

Overall

The percentage of discharges that improved in regards to acidity from the implementation of

daylighting alone (Table 6.3m), is less than the percentage that improved from the implementation

of regrading and revegetation alone (Table 6.3g). Percentages of improved discharges were 30.8

and 50 respectively. This result is not surprising because, daylighting often results in a large

amount of acidic material that is spoiled. It is interesting that six of the seven groupings, when

compared to the reference group, were more effective in regards to acidity loading. This suggests

that many of the BMPs, such as special handling and alkaline addition (even applied at lower

rates), helped to offset some of the natural potential of these sites to produce acidic water. 

The least effective BMP group was again the combination of regrading, revegetation, daylighting,

special handling and water handling.

Regrading, Revegetation, and Daylighting

A large number of remining operations encountered both abandoned surface mines and

underground mines. Therefore, the minimum BMPs implemented at these sites, are a combination

of those in the first two reference groups, namely regrading, revegetation, and daylighting. 

Acidity Loading (Table 6.3s): A total of 36 discharges were affected by the reference BMP group. 

Sixteen discharges were improved or eliminated and twenty remained unchanged. Four other

BMP combinations affected enough discharges to be compared to the reference group. None

were as effective as the reference group (although three of the four were only slightly less

effective). The least effective, as in all cases cited thus far, was the combination of regrading,

revegetation, daylighting, special handling, and water handling.
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Efficiencies of BMPs 6-81

Iron Loading (Table 6.3t): Thirty-seven discharges were affected by the reference BMP group. 

Thirteen were improved or eliminated and 22 remained unchanged. Two of the four BMP groups

(regrading, revegetation, daylighting and special handling; and regrading, revegetation,

daylighting, special handling, and alkaline addition less then 100 tons per acre) were more

effective than the reference group. A third group (regrading, revegetation, daylighting, and

alkaline addition less than 100 tons/acre) was almost as effective as the reference group. The

least effective, again, was the combination of regrading, revegetation, daylighting, special

handling, and water handling.

Manganese Loading (Table 6.3u): Thirty discharges were affected by the reference BMP group

in terms of manganese loading. Ten were improved or eliminated and 19 remained unchanged. 

Three of the four BMP groups were more effective than the reference group. The least effective,

again, was the combination of regrading, revegetation, daylighting, special handling, and water

handling.

Aluminum Loading (Table 6.3v): Twenty-four discharges were affected by the reference BMP

group in regards to aluminum loading. Eleven were improved or eliminated and 12 remained

unchanged. All three other BMP combinations that affected enough discharges to allow

comparison to the reference group, were less effective than the reference group in terms of at

least improving aluminum loading. The least effective, again, was the combination of regrading,

revegetation, daylighting, special handling, and water handling.

Sulfate Loading (Table 6.3w): Thirty-six discharges were affected by the reference BMP group in

regards to sulfate loading. Fourteen (42.4 percent) were improved or eliminated and 19 remained

unchanged. Four other BMP groups affected enough discharges to allow for a comparison. Only

one of these four BMP groups (regrading, revegetation, daylighting, special handling, and alkaline

addition < 100 tons/acre) exceeded the reference group for effectiveness by improving 45.5

percent of the discharges. The group of regrading, revegetation, daylighting, special handling, and

water handling was the least effective improving only 12.5 percent. 
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6-82 Efficiencies of BMPs

Flow Rate (Table 6.3x): Thirty-seven discharges were affected by the reference BMP group in

regards to flow rate. Sixteen (47.1 percent) were improved or eliminated and 18 remained

unchanged. Four BMP combinations affected enough discharges to allow for a comparison.

None of these four BMP groups exceeded the effectiveness of the reference group. The BMP

group of regrading, revegetation, daylighting, special handling, and water handling was the least

effective in reducing the flow rate at 25.0 percent improvement. 

Overall

The effectiveness of the four BMP groups in terms of acidity compared to the reference grouping

was always less than that of the reference grouping (Tables 6.3s through 6.3x). The last grouping

(regrading, revegetation, daylighting, special handling, and water handling) was again,

substantially less effective. Daylighting of underground mines adds additional acidic material to

the mine spoil and as discussed under the reference group of regrading and revegetation, if other

BMPs are not used the overburden was probably of good quality. If other BMPs are used, the

overburden was probably considered problematic (acidic and/or a lack of calcareous strata). 

Coal Refuse Removal

Coal refuse removal is the minimum BMP implemented when mining coal refuse, although an

examination of coal refuse removal sites indicates that regrading and revegetation also are

typically implemented. BMP groups that included coal refuse removal did not affect a sufficient

number of discharges to compare with a reference set. Four discharges were affected by 

special handling in addition to coal refuse removal, one by biosolids application in addition to

coal refuse removal, and one by alkaline addition in addition to coal refuse removal. Special

handling of coal refuse, a material that is generally acid producing, is not easy to perform,

because it would require special handling of 100 percent of the material. Isolation of 100 percent

of the material is not possible. Implementation of biosolids application or alkaline addition are

more reasonable. Abandoned coal refuse disposal areas are typically characterized by sparse

vegetation and lack of "topsoil." Biosolids could aid in the establishment of a growth medium. 
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Efficiencies of BMPs 6-83

Because refuse is, more often than not, acid producing, the addition of alkaline material would be

an appropriate additional BMP. The results of the implementation of coal refuse removal are

presented in Table 6.2a, and are discussed below. 

Acidity Loading: Coal refuse removal affected only 9 discharges in regards to acidity loading. Six

discharges were improved or eliminated and three remained unchanged.

Iron Loading: Coal refuse removal affected 7 discharges in regards to iron loading. Two

discharges were significantly improved or eliminated, four remained the same, and one became

significantly worse.

Manganese Loading: Coal refuse removal affected 6 discharges in terms of manganese loading. 

No discharges improved, five remained the same and one was significantly degraded.

Aluminum Loading: Coal refuse removal affected 6 discharges in terms of aluminum loading. 

Two discharges improved, four remained the same and none were degraded.

Sulfate Loading: Coal refuse removal affected 9 discharges in terms of sulfate loading. Of these

discharges 2 improved and the remainder were unchanged. None exhibited increased loadings

(possible increase in acid production).

Flow Rate: Coal refuse removal affected 9 discharges in terms of flow rate. One discharge

exhibited an improvement (reduced flow rate), while the remaining discharges were unchanged.

None showed an increase in flow.

Overall

Two thirds of the 9 discharges showed improvements in acidity load. This is not surprising

because the removal of coal refuse can only be beneficial. Coal refuse is typically an acidproducing material and is often associated with severe acid mine drainage. Removal of the coal

refuse is the removal of an acid-producing material. The two BMPs that typically accompany
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6-84 Efficiencies of BMPs

coal refuse removal are regrading and revegetation. Both of these BMPs tend to decrease water

infiltration into the refuse material and thus, tend to decrease load.

Overall Evaluation

Many of the multiple BMP groups when compared with the reference BMP group were not as

effective as the reference group. This should not be interpreted to mean that the addition of

BMP(s) to the reference groups were not effective or that discharges would have improved if the

additional BMPs had not been implemented. The very nature of many of the BMPs that were

implemented indicates that they were added to counter either the potential for acid production or

to compensate for a lack of naturally-calcareous material. For example, special handling

generally implies that acid-forming materials are present; alkaline addition <100 tons per acre

suggests that naturally calcareous materials were lacking. Conversely, discharges affected by the

minimum BMPs, may have had better quality overburden, and thus, not required additional

BMPs. Also, some BMPs listed in Tables 6.3a through 6.3d, that were shown to positively

influence water quality (e.g., alkaline redistribution and mining high-alkaline strata), were not

used for comparison because of small number of discharges they affected. 

In addition, although many of the BMP groups were not as effective as the control group, it is not

an indication that they were not successful. The fact is that very few sites in the entire data set

got worse. This may not have been the case if these additional BMPs were not used.

The least effective BMP combination was regrading, revegetation, daylighting, special handling

and water handling. Only one of eight discharges affected by this BMP combination improved.

None of the BMPs in this group will add alkalinity to the mine site and it is known that special

handling, in the absence of calcareous rock, will not in-and-of-itself produce alkaline water. 

Perhaps this should be taken as a sign that alkaline-deficient sites can benefit from alkaline

addition. The failure of this group may be due to these sites having considerable problems in

terms of contaminant loadings and in order to offset these existing and potential future problems,
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Efficiencies of BMPs 6-85

a variety of BMPs are applied. This sort of a “shotgun approach” to pollution abatement on

marginal sites may not be viable.

The low success rate of the BMP group of regrading, revegetation, daylighting, special handling,

and water handling also was seen in the significant interaction terms presented in Tables 6.3a,

6.3b, and 6.3c. For acidity, iron, and manganese, there was a significant negative interaction

between water handling and special handling. These interactions suggest that the positive effect

of water handling on the odds of at least improvement is diminished when special handling is also

present. For 89 percent of the discharges (in regards to acidity and manganese) and 80 percent of

the discharges (in regards to iron) that were affected by water handling and special handling, the

discharges were also affected by regrading, revegetation and daylighting. Of these five BMPs,

water handling was the most efficient in dealing with acidity and iron loadings for other

discharges. Since special handling and water handling rarely occurred together in BMP groups,

the percentage of discharges affected by the combination of the two, that at least improved, was

very low. Therefore, the statistical models for acidity and iron isolated these two BMPs as

interacting significantly. However, since the interaction was significant, mainly due to this fiveBMP group, conclusions about the behavior of these two BMPs combined alone should not be

made without first examining why the five-BMP group yielded such low results. 

Studies cited earlier by Smith (1988) and Hawkins (1995) showed that reduction in flow is the

most significant influence on load reduction. Regrading and revegetation are both significant

BMPs in terms of reducing flow. The other BMPs evaluated, with the exception of water

handling, are predominantly geochemical BMPs, which would have a less marked effect on flow

reduction. 

Limitations

As previously stated, this remining water quality data set for pre-existing discharges is the most

comprehensive available at this time. However, the results of these analyses should be considered

with the following limitations in mind: 
Coal Remining BMP Guidance Manual

6-86 Efficiencies of BMPs

C Once the actual subsets of the 231 discharges that were impacted by specific BMPs or

BMP combinations are separated out, the number impacted, in some cases, becomes

relatively small. In cases where smaller subsets of data represent each BMP or BMP

group, the number of results that are statistically significant at the 95 percent confidence

level are few.

C The data collected for pre-, during, and post-mining does not take into consideration the

variability of precipitation during the sampling periods. Water quality and flow data

recorded during unusually low or high precipitation periods can greatly impact 

determined efficiency results.

C No consideration has been given to the probability that, some discharges within a mine

site have gained some or all of the flow that previously went to another. One discharge

may appear to have been degraded, while others may appear to have significantly

improved. However, the overall pollution load for the hydrologic unit may not have

changed or may have substantially improved. With the anticipated changes in the ground

water flow system, this scenario is not uncommon.

C Data evaluated included contaminant loading and flow rate information, and did not

include contaminant concentration data. For this reason, it is not possible at this time, to

determine whether discharge improvement is in terms of water volume, contaminant

concentration or both. The effects of geochemical BMPs verses hydrologic control BMPs

are difficult to determine. With the evaluation of concentration data, efficiency

determinations of individual BMPs and BMP combinations are expected to improve.

6.5 Summary

Even with the aforementioned limitations, the analyses strongly indicate the high rate of success

of BMPs and BMP combinations implemented at remining operations throughout Pennsylvania.

Very few of the single-use BMPs or BMP combinations had less than a 90 percent success rate.
 Coal Remining BMP Guidance Manual

Efficiencies of BMPs 6-87

Those BMPs that exhibited a significant failure rate for any pollutant had no more than 2

discharges with significantly higher loadings. The most efficient BMPs varied according to the

target contaminant. The number of discharges that were observed to be made worse during

remining was so low that they could not be used for meaningful statistical analyses. This is

illustrative how successful remining and the use of appropriate BMPs can be when properly

implemented. 

Remining falls into four categories: (1) reaffecting previously surface mined areas, (2) daylighting

of underground mines, (3) refuse removal, and (4) reaffecting previously surface mined areas and

daylighting underground mines. Each of these remining activities has minimum BMP(s)

associated with them. For example, remining of previously surface mined areas requires

regrading and revegetation and where deep mines are present the minimal BMP is

daylighting. Minimal BMP groups were determined for each of the above four remining

categories. Frequently, in addition to the minimum BMPs, other BMPs were also employed

during each of the four remining operations. This allowed a comparison between the minimum

BMPs for a category against situations were other BMPs were also used (minimum plus other

BMPs). In many instances, the discharges affected by the minimum BMPs plus additional BMPs

were less effective (had less "improved" discharges) than the minimal BMPs used alone. This is

attributed to the fact that, in situations where more than the minimum number of BMPs were

implemented, it was probably due to the presence of acid-forming materials and/or a lack of

naturally occurring calcareous rock. In these cases, additional BMPs were added to counter

negative characteristics of the mine site overburden. In contrast, remining operations that

implemented the minumum BMPs, probably had overburden that was of better quality.

The BMPs predicted to be most efficient for acidity load were those that added alkalinity to the

operation, such as mining into alkaline strata and alkaline redistribution. However, when the

amount of alkaline material added was small (< 100 tons per acre), the predicted success rate (at

least improvement) was one of the lowest (25.4 percent). This amount of added alkalinity was

insufficient to successfully prevent or treat AMD production. The finding that BMPs that

incorporate calcareous materials into mine spoil have a positive influence on acidity load (i.e., a
Coal Remining BMP Guidance Manual

6-88 Efficiencies of BMPs

reduction in load) may seem obvious, but is significant. Previous studies of remining have

emphasized the role of physical BMPs in reducing load through a reduction of flow. Chemical

BMPs, such as alkaline addition or alkaline redistribution, are unlikely to have much, if any,

influence on flow. Therefore, the positive effects are almost certainly due to added alkalinity and

neutralization of acid contributed from the calcareous materials. 

The BMPs that were predicted to be most effective in terms of iron loadings were special water

handling (73.1 percent) and biosolids addition (62.9 percent). Special water handling is primarily

a physically effective BMP, whereas, biosolids addition functions geochemically and perhaps

physically, through increased plant growth and density which may increase water consumption. 

Therefore, no common causation trend between these BMPs, in terms of how they functioned to

improve iron loadings, was definite. The BMPs that were predicted to be most effective in terms

of manganese loadings were alkaline redistribution (92.6 percent) and biosolids application (96.1

percent). The total number of discharges affected by each of these BMPs was low (5 for biosolids

and 4 for alkaline redistribution). Therefore, these conclusions are not definitive. As with

manganese loadings, the most successful predicted single-use BMPs dealing with aluminum

loadings were biosolids application (96.4 percent) and alkaline redistribution (93.3 percent).

Again, the number of discharges affected by each of these BMPs was low (<4), and these

conclusions are not definitive.

The efficiency predictions of BMPs indicate that most BMPs, if properly employed, will improve

contaminant loadings. No BMP was shown to be overall detrimental in terms of increasing

contaminant loadings. With further analysis of flow and concentration data, the determination of

whether the change in loadings was physical or geochemical is expected to be more definite. 
 Coal Remining BMP Guidance Manual

Efficiencies of BMPs 6-89

References

Agresti, Alan, 1990. Categorical Data Analysis. John Wiley & Sons, Inc., New York, NY, 558 p.

Brady, K.B.C., M.W. Smith, R.L. Beam, and C.A. Cravotta, 1990. Effectiveness of the Addition

of Alkaline Materials at Surface Coal Mines in Preventing or Abating Acid Mine Drainage: Part

2. Mine Site Case Studies, In the Proceedings of the 1990 Mining and Reclaimation Conference

and Exhibition, Charleston, WV, pp. 227-241.

Hawkins, J.W., 1995. Characterization and Effectiveness of Remining Abandoned Coal Mines in

Pennsylvania. U.S. Bureau of Mines, Report of Investigations-9562, 37 p.

Pennsylvania Department of Environmental Resources, Pennsylvania State University, and

Kuhlmann Ruggiero Engineers, 1988. Coal Remining – Best Professional Judgement Analysis

(REMINE).

Rose, Arthur, personal communication with Jay Hawkins, 1999. Details available from the U.S.

Environmental Protection Agency Sample Control Center, operated by DynCorp I&ET, 6101

Stevenson Avenue, Alexandria, VA, 22304.

Rose, A.W. and C.A.Cravotta, 1998. Geochemistry of Coal Mine Drainage, Chapter 1 of Coal

Mine Drainage Prediction and Pollution Prevention in Pennsylvania, Pennsylvania Department of

Environmental Protection, Harrisburg, PA, 22 p.

Smith, M.W., 1988. Establishing Baseline Pollution Load from Pre-existing Pollutional

Discharges for Remining in Pennsylvania. U.S. Bureau of Mines IC 9184, p. 311-318.

Tukey, J.W., 1976. Exploratory Data Analysis. Addison-Wesley Publ., Reading, MA, 638 p.
Coal Remining BMP Guidance Manual

6-90 Efficiencies of BMPs
Coal Remining BMP Guidance Manual

BMP Costs 7-1

Section 7.0 Best Management Practices - Costs

This section provides a summary of the Best Management Practice (BMP) cost information

obtained during the preparation of this document. Although not specifically requested, a

significant amount of BMP cost information was obtained. This information should provide mine

engineers and permitters with at least preliminary or “ballpark” costs for the BMPs. This cost

information should not preclude detailed engineering analysis and design efforts to include such

things as location, climate, and site limitations. 

When sufficient data were available, a least-squares-best-fit linear regression was done on the data

to come up with a cost equation. When limited data were available unit costs were developed and

presented. 

The primary source of information used in the preparation of this section was 61 data packages

gathered from six states and representing remining or reclamation activities during which these

BMPs were implemented (Appendix A: EPA Remining Database). A limited amount of cost

information was found in the literature. Abatement plans from several state’s mining permit

applications require the applicant to define which BMPs will be used to abate or ameliorate

pollutional discharges, and estimate what the BMP implementation cost would be. This cost

information has been summarized in this Section in table form. Very little has been done with the

cost information other than indexing to today’s dollars with the aid of the Engineering News

Record (ENR) Construction Cost Index (ENR, 1999).

Unless otherwise noted, the costs were considered current with the date of permit application and

have been indexed to January 1999 dollars with the use of ENR’s Construction Cost Index. 

January 1999 has an ENR index value of 6000. For example, the index for September 1995 is

5491. Dividing the January 1999 index by the September 1995 index yields a factor of 1.09. 

Costs in September 1995 were multiplied by this factor to derive costs in January 1999 dollars.
Coal Remining BMP Guidance Manual

7-2 BMP Costs

The cost information has been summarized alphabetically by BMP. Within each BMP the cost

information is summarized by mine followed by assumptions underlying the costs, and finally, cost

equations generated from the available cost information (if possible). Cost information for the

following BMPs are summarized in the following tables:

BMP Table

 1. Alkaline Addition . . . . . . . . . . . 7a

 2. Anoxic Limestone Drains . . . . . . . . . 7b

 3. Ash Fill Placement . . . . . . . . . . . 7c

 4. Bactericides . . . . . . . . . . . 7d

 5. Check Dams . . . . . . . . . . . 7e

 6. Constructed Wetlands . . . . . . . . . 7f

 7. Daylighting . . . . . . . . . . . . . 7g

 8. Diversion Ditches . . . . . . . . . . . 7h

 9. Diversion Wells, Alkalinity Producing . . . . . 7i

10. Drains, Pit Floor . . . . . . . . . . . 7j

11. Regrading of Abandoned Mine Spoil . . . . . . . 7k

12. Revegetation . . . . . . . . . . . . . 7l

13. Sealing and Rerouting of Mine Water from Abandoned 

Workings . . . . . . . . . . . . . 7m

14. Silt Fences . . . . . . . . . . . . . 7n

15. Special Handling of Acid Forming Materials . . . . . 7o
Coal Remining BMP Guidance Manual

BMP Costs 7-3

Table 7a: Alkaline Addition

Mine Acres Alkaline

Material

(tons/acre)

Location Alkaline

Addition

Cost

($/ton)

Cost (Date) Unit Cost

ENR 6000

($/ton)

Lime Addition

PA (10) 28.6 3 Spoil $ 17.50 $1,501 (2/90) $ 22.40

PA(1) 26.1 30 Pit Floor $ 16.852$13,194 (3/90) $ 21.55

PA(11) 61.3 50 Pit Floor $ 6.00 $18,390 (9/89) $ 7.73

PA (8) 22.68 403-493 Blast Holes, 

& Pit Floor

$ 5.003$68,040 (2/93) NA

PA (19) 9.8 1050 NA $ 10.00 $102,900(12/97) $ 10.24

Ash Addition

PA (2) 501$2,608,000(8/88) $ 2.55

NA = Not Available.

1

 Ash and refuse will be placed in alternating two foot lifts, reconstructed pile estimated to

 contain 1,650,000 tons of refuse and 1,350,000 tons of ash.

2

 Cost includes $2.25/ton handling, $6.00/ton trucking, and $8.60/ton lime.

3

 Cost includes $1.00/ton handling, $1.00/ton trucking, and $3.00/ton lime.

Assumptions:

• Costs include lime, trucking, and spreading.

Cost Equation: Not developed.
Coal Remining BMP Guidance Manual

7-4 BMP Costs

Table 7b: Anoxic Limestone Drains (ALDs)

Mine Design

Flow

(gpm)

Loss of

Limestone

(mg/L)

Design

Life

(Years)

Design Loading

(tons

CaCO3/gal·min)

Cost (Date) Unit Cost

ENR 6000

($/Ton of

Limestone)

TN

(3)

8 250 40 33 NA NA

TN

(5)

160 250 30 201$ 90,014

(5/94)

$ 31.42

TN

(2)

200 370 10 20 $ 230,0002

(1995)

NA

NA = Not Available.

1

 Design loading required 4,000 tons of limestone; 5,000 actually used to provide safety factor.

2

 Costs are for a 5,000 ton ALD and a 2.35 acre oxidation pond.

Assumptions:

• TN(2) - 5,000 tons of limestone used; loss of limestone 370 mg/L; design life 10

years.

• TN(3) - 264 tons of limestone used; loss of limestone 250 mg/L; design life 40

years; safety factor 1.5.

• TN(5) - 3,180 tons of limestone used; loss of limestone 250 mg/L; design life 30

years; safety factor 1.2.

Cost Equation: Not developed, only one point available.
Coal Remining BMP Guidance Manual

BMP Costs 7-5

Table 7c: Ash Fill Placement

Mine Cubic Yards Cost

($/cu. Yd.)

Cost (Date) Unit Cost

ENR 6000

($/ cu.yd.)

PA (18) 15,000,000 $ 0.25 $ 3,750,000 (12/96) $ 0.26

Assumptions:

• Cost are for handling ash only (hauling, spreading, and compacting)

Cost Equation: Not developed, only one point available.
Coal Remining BMP Guidance Manual

7-6 BMP Costs

Table 7d: Bactericides

Mine Acres Cost/Acre Cost (Date) Unit Cost

ENR 6000

($/acre)

PA (10) 13.0 $ 2,100 $ 27,300 (2/90) $ 2,689

Assumptions:

• Use B.F. Goodrich’s “ProMac”

• Applied before top cover is spread and revegetated

Cost Equation: Not developed, only one point available.
Coal Remining BMP Guidance Manual

BMP Costs 7-7

Table 7e: Check Dams

Source Cost (Date) Cost

ENR 6000

Ref. (USEPA, 1992) See Below

Assumptions:

• Check dams are appropriate for use in the following locations:

1. Across swales or drainage ditches to reduce the velocity of flow.

2. Where velocity should be reduced because a vegetated channel lining has

 not yet been established.

• Check dams may never be used in a live stream unless approved by the appropriate

government agency.

• The drainage area above the check dam should be between 2 and 10 acres.

• The dams should be spaced so that the toe of the upstream dam is never any higher

than the top of the downstream dam.

• The center of the dam must be 6 inches to 9 inches lower than either edge, and the

maximum height of the dam should be 24 inches.

• The check dam should be as much as 18 inches wider than the banks of the channel

to prevent undercutting as overland flow water re-enters the channel.

• Excavating a sump immediately upstream from the check dam improves its

effectiveness.

• Provide outlet stabilization below the lowest check dam where the risk of erosion

is greatest.

• Consider the use of channel linings or protection such as plastic sheeting or rip rap

where there may be significant erosion or prolonged submergence.

Cost Equation:

The costs for the construction of check dams varies with the material used. Rock costs about

$100 per dam ($ 119 => ENR = 6000). Log check dams are usually slightly less expensive than

rock check dams. All costs vary depending on the width of the channel to be checked.
Coal Remining BMP Guidance Manual

7-8 BMP Costs

Wetlands

$10

$100

$1,000

1 10 100

Acres

Cost ($1000)

y = 6.41x1.405

r2 = 0.93

 ENR = 6000

Table 7f: Constructed Wetlands

Mine Fe Loading

(gr/day/m2)

Mn

Loading

(gr/day/m2)

Ox.

Pond

(acres)

Marsh

(acres)

Total

Acres

(acres)

Cost

(Date)

Cost

ENR 

6000

($1,000)

TN (5)120 0.5 0.7622.69 3.45 $ 21,559 

( 5/94)

$ 23.93

VA (8) 14.2 14.2 $ 284,000

( 9/96)

$ 299.84

TN (2) 17.2 2.3532.0 4.35 $ 21,0004$ 23.03

NA = Not Available

1

 This wetlands design includes areas for an oxidation pond and marshes in the calculation for

 required area of wetland. Oxidation pond designed for 24 hours retention at 160 gpm and 5 

 foot depth of 6,160 sq. ft. (Actually used 33,450 sq. ft. At 6 ft. depth). The remainder of the

 wetland will be marsh (150,790 sq.ft. - 33,450 sq.ft = 117,340 sq.ft.).

2

 Twenty-four hour retention minimum.

3

 Minimum 1 to 2 days retention; 11.0 actual.

4

 Costs are for the 2.0 acre marsh area only.

Assumptions:

• Refer to design criteria in table above.

Cost Equation:

Least Squares Best Fit Linear Regression expressed as y = axb, (ENR = 6000):

Equation:

 y = 6.41x1.405

where: x = acres

y = Cost ($1,000)

n = 3

r2 = 0.93
Coal Remining BMP Guidance Manual

BMP Costs 7-9

Daylighting

1

10

100

1,000

1 10 100 1,000

Tons of Coal Recovered (1,000)

Cost ($1,000)

 ENR = 6000

y = 0.60x1.21

r2 = 0.91

Table 7g: Daylighting

Mine Acres

Daylighted

Recoverable

Coal

 (1,000 tons)

Cost/Ton

of

Recovered

Coal

Cost (Date) Cost

ENR 6000

($1,000)

PA (6) 5.0 9.72 $ 0.25 $ 2,430 ( 9/89) $ 3.13

PA (1) 3.6 8.957 $ 1.21 $ 10,880 ( 4/90) $ 13.91

PA (7) 15.1 26.550 $ 1.54 $ 40,770 ( 10/89) $ 52.52

PA (11) 23.7 47.988 $ 1.67 $79,988 ( 10/93) $ 91.17

PA (9) 103.5 229.767 $ 2.00 $ 459,534 ( 8/94) $ 508.33

PA (3) 90 550.785 $ 1.21 $ 666,450 (12/88) $ 875.37

1

 Complete.

2

 Partial.

Assumptions:

• Mining ratio cannot exceed 18:1 or 60 ft max. Highwall

• 60 ft. Max. Highwall

Cost Equation:

Least Squares Best Fit Linear Regression expressed as y = axb, (ENR=6000):

Equation:

y = 0.60x1.21

where: x = Tons of 

 Recov. Coal

 (1,000)

y = Cost ($1,000)

n = 6

r2 = 0.91
Coal Remining BMP Guidance Manual

7-10 BMP Costs

Table 7h: Diversion Ditch

Mine Length (Ft.) Design Flow

(cfs)

Cost (Date) Cost

ENR 6000

Unit Cost

ENR 6000

($/Ft.)

TN (5) 8751195 $ 7,925 (5/94) $ 8,797 $10.05

1

 Estimated.

Assumptions:

• Bottom Width 20'

• Side Slopes 2H:1V

• Ditch Slope 1%

• Constructed Depth 3'

• Flow Depth (Design) 1.85'

• Lining Rip rap for a 2.25' flow depth

Cost Equation: Not developed, only one point available.
Coal Remining BMP Guidance Manual

BMP Costs 7-11

Table 7i: Diversion Wells, Alkalinity Producing

Reference Materials Labor Total Cost ENR 6000

McClintock, 1993 $ 5,000 $ 6,000 $ 11,000 ea.

Assumptions:

• From page ten of the reference: “A rough estimate is about $5,000 for the materials and

equipment rental.”

• From page 7 of the reference;” About 8 to 10 people working 8 hour per day for 2 to 3

days are needed for construction of a diversion well.”

(10 people x 8 hours/day x 3 days x $ 25.00/hr = $ 6,000) 

Cost Equation: Not developed, only one point available.
Coal Remining BMP Guidance Manual

7-12 BMP Costs

Table 7j: Drains, Pit Floor 

Mine Total Length

(Ft.)

Cost (Date) Unit Cost

ENR 6000

($/Ft.)

PA (8) 2,600 $ 132,500 (2/93) $ 60.31

Assumptions:

• Details not available in permit file.

Cost Equation: Not developed, only one point available.
Coal Remining BMP Guidance Manual

BMP Costs 7-13

Regrading

$10

$100

$1,000

$10,000

$100,000

10.00 100.00 1,000.00 10,000.00 100,000.00

Cubic Yards (1,000 cu. yd.)

Costs ($1,000)

y=0.136x1.217

r2=0.92

ENR=6000

Table 7k: Regrading of Abandoned Mine Spoil/Highwalls

Mine Cubic Yards

(1,000)

Cost/cu.yd. Cost (Date) Cost ENR 6000

($ 1,000)

PA(7) 76.550 $ 0.16 $ 12,060 (10/89) $ 15.545

PA (10) 138.905 $ 0.25 $ 34,171 ( 2/90) $ 43.76

PA (11) 304.944 $ 0.16 $ 48,150 (10/93) $ 54.88

KY (4) 332.046 $ 0.23 $ 76,039 ( 9/94) $ 83.91

PA (6) 136.660 $0.65 $ 88,829 ( 9/89) $ 114.42

PA (5) 178.100 $ 0.75 $ 133,575 ( 9/94) $ 147.76

PA (19) 321.376 $ 0.50 $ 160,688 (12/97) $ 164.58

PA (3) 1,090.613 $ 0.90 $ 981,552 (12/88) $ 1,289.25

PA (18) 4,000 $ 0.65 $ 2,600,000 (9/97) $ 2,666.21

PA (9) 7,743 $ 0.45 $ 3,484,350 (8/94) $ 3,854.37

WV (4) 3,630 $ 1.00 $ 3,630,000 ( 2/90) $ 4,648.88

KY (3) 17,250.378 $ 0.23 $ 3,950,378 ( 8/91) $ 4,845.11

WV (9) 5,488.314 $ 1.00 $ 5,488,314 (10/81) $ 8,997.24

WV (7) 5,848 $ 1.00 $ 5,848,000 ( 9/83) $ 8,471.27

WV (10) 7,139 $ 1.00 $ 7,139,000 ( 3/85) $ 10,318.96

WV (2) 12,100 $ 1.00 $ 12,100,000 ( 1981) $ 20,537.48

Assumptions:

• Regrading of abandoned mine spoil

• Elimination of abandoned highwalls

Cost Equation:

Least Squares Best Fit Linear Regression expressed as y = axb, (ENR=6000):

Equation:

 

y=0.136x1.217

where: x = Cu.Yds. 

 (1,000)

 y = Cost 

 ($1,000)

n = 16

r2 = 0.92
Coal Remining BMP Guidance Manual

7-14 BMP Costs

Revegetation

$1

$10

$100

$1,000

1 10 100 1,000 10,000

Acres

Costs ($1,000)

ENR=6000

y=0.772x0.961

r2=0.96

Table 7l: Revegetation

Mine Acres Cost/Acre Cost (Date) Cost ENR 6000

($ 1,000)

PA (7) 10 $ 450 $ 4,500 (10/89) $ 5.80

PA (10) 13 $ 550 $ 7,150 ( 2/90) $ 9.16

KY (4) 23.4 $ 409 $ 9,570 ( 9/94) $10.56

PA (6) 17 $ 600 $ 10,200 ( 9/89) $ 13.14

VA (6) 15 $ 750 $ 11,250 (10/91) $ 13.80

PA(11) 25.2 $ 450 $ 11,340 ( 9/89) $ 14.61

PA (8) 21 $ 720 $ 16,200 (12/94) $ 17.87

PA (19) 30.3 $ 650 $ 19,695 (12/97) $ 20.17

PA (4) 45 $ 800 $ 36,000 ( 2/93) $ 42.60

KY (1) 195.7 $ 625 $ 69,264 ( 7/97) $ 69.60

PA (18) 500 $ 1,000 $ 500,000 ( 9/97) $ 512.73

KY (3) 1,215.7 $ 409 $ 497,221 ( 8/91) $ 609.84

 Assumptions:

 • Lime

 • Fertilizer

 • Seed

 • Mulch

 • Handling and spreading of above.

Cost Equation:

Least Squares Best Fit Linear Regression expressed as y = axb, (ENR=6000).

 Equation:

y = 0.772x0.961

where: x = Acres

 y = Cost 

($1,000)

r2 = 0.96

n = 12
Coal Remining BMP Guidance Manual

BMP Costs 7-15

Table 7m: Sealing and Rerouting of Mine Water from Abandoned Workings

Mine Lin. Ft.

(1000)

Cost/

Lin. Ft.

Clay 

(Cu. Yd.)

Cost/ 

Cu. Yd.

Cost (Date) Cost

ENR 6000

($ 1,000)

Highwall Seal

PA (1) 1.75 $ 4.69 4,111 $ 2.00 $ 8,222 ( 3/90) $ 10.52

PA(3) 10.50 $ 3.80 20,000 $ 2.00 $ 40,000 (12/88) $ 52.54

Clay Barrier

PA (10) 1.75 $ 0.67 583 $ 2.00 $ 1,166 ( 9/96) $ 1.23

Auger Holes

KY (4) 1.88 $ 0.20 1,671 $ 0.23 $ 380 ( 9/94) $ 0.42

KY (3) 11.16 $ 0.20 9,920 $ 0.23 $ 2,275 ( 8/91) $ 2.79

Assumptions:

Highwall Seal

• 10' - 12' at base

• 8' high

• slope away from highwall face

• Mine void to be filled with clay to a width and depth of a minimum of 3

times the diameter of the exposed opening.

• Clay available on-site.

Clay Barrier

• 3' high

• 3' wide

• Clay available on-site

Auger Hole Seals

• 4' high

• 6' wide

• Clay available on-site

Cost Equations:

Least Squares Best Fit Linear Regression expressed as y = axb, (ENR=6000):

Highwall Seal ==> y = 6.37x0.90 where: x = Linear Feet (1,000) r2 = 1.0

 y = Cost ($1,000) n = 2

Clay Barrier ==> y = 0.703x 1.0 where: x = Linear Feet (1,000)

 y = Cost ($1,000)

Auger Hole Seal ==> y = 0.215x1.06 where: x = Linear Feet (1,000) r2 = 1.0

 y = Cost ($1,000) n = 2
Coal Remining BMP Guidance Manual

7-16 BMP Costs

Table 7n: Silt Fences

Source Unit Cost (Date) Unit Cost

ENR 6000

($/Ft.)

Ref.(USEPA, 1992) $ 6.00/Ft. (1992) $ 7.221

1 Installation costs only.

Assumptions:

• Silt fences are appropriate at the following general locations:

(1) Immediately upstream of point(s) of runoff discharge from a site before

 flow becomes concentrated (maximum design flow rate should not

 exceed 0.5 cubic feet per second).

(2) Below disturbed areas where runoff may occur in the form of overland

 flow.

• Ponding should not be allowed behind silt fences since they will collapse under

high pressure; the design should provide sufficient outlets to prevent overtopping.

• The drainage area should not exceed 0.25 acre per 100 feet of fence length.

• For slopes between 50:1 and 5:1, the maximum allowable upstream flow path

length to the fence is 100 feet; for slopes 2:1 and steeper, the maximum is 20 feet.

• The maximum up slope grade perpendicular to the fence line should not exceed

1:1.

• Synthetic silt fences should be designed for six months of service; burlap is only

acceptable for periods of up to 60 days.

Cost Equation: Not developed with only one point available.
Coal Remining BMP Guidance Manual

BMP Costs 7-17

Special Handling

$1

$10

$100

$1,000

$10,000

10 100 1,000 10,000

Cubic Yards (1,000 cu. yds.)

Cost ($1,000)

ENR = 6000

y = 0.309x1.129

r2=0.94

Table 7o: Special Handling for Toxic and Acid Forming Materials

Mine Cubic

Yards

(1,000)

Cost/cu.yd. Cost (Date) Cost

ENR 6000

($ 1,000)

PA (11) 17.58 $ 0.20 $ 3,516 ( 9/89) $ 4.53

PA (19) 15.81 $ 1.00 $ 15,811 (12/97) $16.19

PA (7) 216.13 $ 0.25 $ 54,032 ( 6/88) $ 71.64

PA (3) 2,468.4 $ 0.90 $2,221,560 (12/88) $2,917.99

Assumptions:

• Material placed 25' above floor

• Placed in 2' layers

• Up to 30" clean fill in between

• 25 tons/acre of lime on top

• 25' from outcrops

• 4' clean cover

Cost Equation:

Least Squares Best Fit Linear Regression expressed as y = axb, (ENR=6000):

y = 0.309x1.129 where: x = Cubic Yards (1,000) r2 = 0.94

 y = Cost ($1,000) n = 4
Coal Remining BMP Guidance Manual

7-18 BMP Costs

References

ENR, 1999. Engineering New Record Construction Cost Index (1908-1999).

http://www.enr.com/cost/costcci.asp, 2 p.

McClintock, S.A., D.E. Arnold and A.J. Gaydos, 1993. An Installation and Operations Manual

for Diversion Wells: A Low Cost Approach for Treatment of Acidic Streams. Pennsylvania State

University, 23 p.

USEPA, 1992. Storm Water Management for Construction Activities, Office of Water, Report

No. EPA 832-R-92-005.