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METHANE EMISSIONS FROM ABANDONED
COAL MINES IN THE UNITED STATES:
EMISSION INVENTORY METHODOLOGY
AND 1990-2002 EMISSIONS ESTIMATES
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COALBED METHANE OUTREACH PROGRAM
The Coalbed Methane Outreach Program (CMOP) is a U.S. Environmental Protection Agency
(EPA) voluntary program. CMOP works with coal companies and related industries to identify
technologies, markets, and means of financing for the profitable recovery and use of coal mine
methane (a greenhouse gas) that would otherwise be vented to the atmosphere. CMOP assists
the coal industry by profiling coal mine methane project opportunities at the nation's gassiest
mines, by conducting mine-specific technical and economic assessments, and by identifying
private, federal, state, and local institutions and programs that could facilitate project
development.
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ACKNOWLEDGMENTS
This report was prepared under Environmental Protection Agency Contract 68-W-00-092 by
Raven Ridge Resources Incorporated. The principal authors are Mr. Michael Cote, Mr. Ronald
Collings, and Mr. Raymond Pilcher of Raven Ridge Resources, Incorporated, and Clark
Talkington and Pamela Franklin of U.S. EPA.
The authors and U.S. EPA gratefully acknowledge the contributions of several individuals that
contributed their time and expertise in reviewing drafts of the report and providing insightful and
invaluable comments.
Kashy Aminian, West Virginia University
Clemens Backhaus, Fraunhofer UMSICHT (Fraunhofer Institute for Environmental, Safety, and
Energy Technology - Germany)
Philip Cloues, U.S. National Park Service
llham Demir, Illinois Geologic Survey
Michiel Dusar, Geologic Survey of Belgium
Roger Fernandez, U.S. Environmental Protection Agency
Satya Harpalani, Southern Illinois University, Carbondale
David Kirchgessner, U.S. Environmental Protection Agency, Office of Research & Development
Les Lunarzewski, Lunagas Party Ltd (Australia)
Jim Penman, UK Department of Environment, Food & Rural Affairs
Patrick Rienks, Ingersoll-Rand Energy Systems
Abouna Saghafi, Commonwealth Scientific & Industrial Research Organization (Australia)
Elizabeth Scheehle, U.S. Environmental Protection Agency
Karl Schultz, Climate Mitigation Works LLC (United Kingdom)
Peet Soot, Northwest Fuels Development Inc.
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TABLE OF CONTENTS
Table of Contents i
List of Figures iii
List of Tables iv
Abbreviations and Acronyms v
EXECUTIVE SUMMARY 1
1.0-INTRODUCTION 4
1.1 GREENHOUSE GAS INVENTORY GUIDELINES AND PRACTICES 4
1.2 DEFINITION OF AN ABANDONED COAL MINE 5
1.3 PREVIOUS ATTEMPTS TO ESTIMATE ABANDONED MINE EMISSIONS 5
1.4 REPORT STRUCTURE 6
2.0 - ABANDONED MINES AS A SOURCE OF METHANE EMISSIONS 8
2.1 OVERVIEW OF COAL MINE METHANE 8
2.1.1 Active coal mine emissions 9
2.1.2 Abandoned coal mine emissions 9
2.2 FACTORS INFLUENCING METHANE EMISSIONS 9
2.2.1 Gas content and adsorption characteristics of coal 10
2.2.2 Methane flow capacity of the mine 12
2.2.3 Mine Flooding 13
2.2.4 Active Vents 14
2.2.5 Mine Seals 14
3.0 -COAL MINE EMISSIONS DATA 15
3.1 COAL MINE EMISSIONS DATA 15
3.2 MINE STATUS INFORMATION 17
4.0 -EMISSIONS ESTIMATION 19
4.1 OVERVIEW 19
4.2 FORECASTING ABANDONED MINE METHANE EMISSIONS USING
DECLINE CURVES 19
4.3 GENERATING DIMENSIONLESS DECLINE CURVES WITH FLOW
SIMULATION 22
4.4 DATA AVAILABILITY AND UNCERTAINTY 23
4.4.1 Adsorption isotherms 24
4.4.2 Permeability 26
4.4.3 Pressure at abandonment 26
4.4.4 Ventilation air emissions 26
4.5 SENSITIVITY ANALYSIS FOR ADSORPTION ISOTHERM,
PERMEABILITY, AND PRESSURE 26
4.6 ANNUAL EMISSION ESTIMATIONS AS A FUNCTION OF MINE STATUS 27
4.6.1 Venting mines 27
4.6.2 Flooded mines 27
4.6.3 Sealed mines 28
4.7 CALCULATING ANNUAL METHANE EMISSIONS INVENTORY 29
4.7.1 Mines of unknown status 30
4.7.2 Combining the known status and unknown status inventories 30
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TABLE OF CONTENTS (CONTINUED)
5.0 CALIBRATION THROUGH FIELD MEASUREMENTS 32
5.1 FIELD MEASUREMENT METHODOLOGY 32
5.2 COMPILATION OF DATA 33
6.0 ESTIMATING EMISSIONS FROM MINES CLOSED BEFORE 1972 35
6.1 HISTORICAL TRENDS IN GASSY MINE EMISSIONS 35
6.2 ESTIMATING LOCATIONS OF GASSY MINES ABANDONED BEFORE 1972 36
6.3 ESTIMATING DATE OF ABANDONMENT FOR PRE-1972 MINES 38
6.4 ESTIMATING INITIAL EMISSION RATES FOR PRE-1972 MINES 39
6.5 CALCULATING TOTAL ABANDONED MINE METHANE EMISSIONS FOR
MINES CLOSED PRIOR TO 1972 40
7.0 RESULTS OF THE 1990 - 2002 ABANDONED MINE METHANE EMISSIONS
INVENTORY 42
7.1 1990 BASELINE INVENTORY 42
7.2 EMISSIONS FOR 1991-2002 42
7.3 INVENTORY ADJUSTMENTS FOR 1990-2002 METHANE RECOVERY
PROJECTS 43
7.3.1 Summary of U.S. Emissions 44
7.4 KEY ASSUMPTIONS AND AREAS OF UNCERTAINTY 46
7.4.1 Limited data on mines abandoned before 1972 47
7.4.2 Biases in U.S. mine ventilation data 47
7.4.3 Lack of data on gasification prior to 1990 47
7.4.4 Exclusion of surface mines emissions 47
7.4.5 Total estimated uncertainty range 48
7.5 PROJECTING FUTURE EMISSIONS FROM ABANDONED COAL MINES 49
8.0 CONCLUSIONS 51
9.0 REFERENCES 53
APPENDIX A. U.S. Abandoned Coal Mine Database A-1
APPENDIX B. State Agencies and Organizations B-1
APPENDIX C. Combining Uncertain Parameters Using Monte Carlo Simulation C-1
APPENDIX D. Effect of Barometric Pressure on Mine Venting D-1
APPENDIX E. Sensitivity Analysis Calculations E-1
APPENDIX F. Emission Inventory: Sample Calculations According to Mine Type F-1
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LIST OF FIGURES
Figure 1. Abandoned Mine Methane Emissions Estimate (mmcf) for 1990 - 2002 3
Figure 2. Map of U.S. Gassy Coal Basins 8
Figure 3. Comparison of Methane Storage Capacity of Sandstone and Coal 11
Figure 4. Typical Adsorption Isotherms as a Function of Coal Rank 11
Figure 5. Methodology for calculating abandoned mine emissions 21
Figure 6. Cambria Mine Gob Well Decline Curve 22
Figure 7. Dimensionless decline curve for non-flooding, venting abandoned mines 23
Figure 8. Average methane adsorption isotherms for U.S. coal basins 25
Figure 9. Methane adsorption as a function of mine pressure for the Central
Appalachian Basin 25
Figure 10. Emission model for abandoned flooding mines 28
Figure 11. Emission model for abandoned mine with different degrees of sealing 29
Figure 12. Year 2000 emissions inventory: methane emissions from abandoned mines 31
Figure 13. Vented emissions from unflooded abandoned mines in U.S. coal basins 34
Figure 14. Active coal mine methane emissions from nine states, 1971-1980 36
Figure 15. Mine closures in Colorado and Illinois, 1910 - 1960 39
Figure 16. Active mine emission data for northern West Virginia 40
Figure 17. Emissions contribution from mines abandoned prior to 1972
for the 1990-2002 inventories 41
Figure 18. Gassy coal mines abandoned annually, 1990-2002 43
Figure 19. Abandoned mine methane emissions estimate, 1990-2002 45
Figure 20. Net Abandoned Mine Emissions (C02e and Gg methane) 45
Figure 21. Abandoned coal mine emissions from each U.S. coal basin, 1990 - 2002 46
Figure 22. Range of abandoned mine methane emissions estimates, 1990-2002 48
Figure 23. Trends in coal mine emissions from gassy U.S. mines 49
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LIST OF TABLES
Table 1. Data sources used to compile gassy abandoned coal mines database 16
Table 2. Abandoned coal mines by basin 17
Table 3. Status of abandoned mines 18
Table 4. Adsorption isotherms available for each coal basin 24
Table 5. Distribution of (known) types of abandoned mines for year 2000 30
Table 6. Year 2000 abandoned mine emissions by coal basin, Bcf 31
Table 7. Year 2000 abandoned mine emissions, tonnes of C02e 31
Table 8. Gassy abandoned mines located in 17 counties 38
Table 9. Distributions of methane emissions, 1971-1975 40
Table 10. Contribution of mines closed from 1920 - 1969 to the 1990 inventory 41
Table 11. Cumulative gassy coal mines abandoned, 1990-2002 42
Table 12. Abandoned mine methane recovery projects 44
Table 13. Summary of abandoned coal mine emissions by basin (Bcf/yr) 46
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ABBREVIATIONS AND ACRONYMS
Weights and Measures
cf cubic feet
Bcf billion cubic feet
Gg gigagrams = 109 grams
kg kilogram = 103 grams
km kilometer = 103 meter
km2 square kilometer
kPa kilopascals = 103 Pascals
mcf thousand cubic feet
mcfd thousand cubic feet per day
m3 cubic meter
md millidarcies = 10"3 Darcies
mmcf million cubic feet
PL Langmuir pressure
psia pounds per square inch absolute
psig pounds per square inch gauge
scf standard cubic feet
t short ton
tonne metric ton
VL Langmuir volume
Acronyms
AMDB Abandoned Mine Database
BHP Bottom hole pressure
C02e Carbon Dioxide global warming equivalent
CBM Coalbed Methane
CFD Computational fluid dynamics
CMM Coal Mine Methane
EIA Energy Information Administration
GHG Greenhouse gas
GRI Gas Research Institute
IPCC Intergovernmental Panel on Climate Change
MSHA U.S. Mine Safety and Health Administration
P Pressure
STP Standard temperature and pressure
USBM United States Bureau of Mines
U.S. EPA United States Environmental Protection Agency
V Volume
Conversion Factors
1 million m3 = 35.315 mmcf
1 tonne CC^e = 2.483 Mcf CH4
1 kPa = 0.145 psi
1 m3/tonne = 32.04 scf/t gas storage
1 mcf CH4 = 0.0001926 Gg CH4
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EXECUTIVE SUMMARY
Coal mine methane (CMM) emissions are one of the major sources of anthropogenic methane
emissions in the U.S., accounting for approximately 10 percent of total emissions. Current CMM
emission estimates, however, only include emissions from active, or working, mines and do not
account for methane vented from abandoned mines. The United States Environmental
Protection Agency (EPA) has recently completed an effort to quantify abandoned underground
mine methane (AMM) emissions both to improve the accuracy of the CMM emissions inventory
and to assess mitigation opportunities. According to these estimates, detailed in this report,
AMM emissions increased total U.S. coalmine methane emissions by about 13 billion cubic feet
(Bcf) in 2002, or about 5% of total U.S. CMM emissions.
U.S. EPA prepares an annual inventory to identify and quantify the country's anthropogenic
sources and sinks of greenhouse gas emissions. In addition to fulfilling its commitment to the
United Nations Framework Convention on Climate Change (UNFCCC) to publish and make
available a national inventory of greenhouse gas emissions, the U.S. develops the inventory
because systematically and consistently estimating national and international emissions is a
prerequisite for accounting for reductions and evaluating mitigation strategies.
Thousands of closed coal mines in the United States and other countries continue to emit
methane, contributing to the total greenhouse gas emissions from coal mining. The unique
features of abandoned mines, however, require a separate emissions estimation methodology
from that employed for operating mines. To date, the coal mine methane (CMM) emission
inventory is limited to operating (active) mines, in part because the Intergovernmental Panel on
Climate Change (IPCC) has not provided guidance on how to quantify emissions from
abandoned mines. This report proposes a credible methodology for determining methane
emissions from abandoned underground coal mines and uses this methodology to quantify
methane emissions from abandoned U.S. mines for each year from 1990 through 2002.
The method outlined in this report is consistent with the "Tier 2" approach for estimating
emissions from active mines as described in the Revised 1996 IPCC Guidelines for National
Greenhouse Gas Inventories (IPCC, 1997). Under this approach, data availability dictates
whether emissions estimates are based on a country- or basin-specific method. This method
consists of five steps, as described below:
Stepl: Create a database on abandoned gassy mines. Based on an analysis of
methane emissions at operating mines, 98% of all CMM emissions come from
mines that emit more than 100 mcfd (thousand cubic feet per day). Assuming
that emissions profiles for abandoned mines are correlated to their emissions
during active mining operations, EPA compiled a database containing information
on 374 abandoned coal mines that produced emissions greater than 100 mcfd
when they were active. The database includes the name, location, coal basin,
date of abandonment, emission rate at closure, and status (venting, flooded,
sealed, or unknown status) of each mine. For mines closing since 1990, the
emission rate includes both ventilation emissions and emissions from
degasification systems.
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Step 2: Identify the factors affecting methane emissions and develop coal basin-
specific decline curves. Several important factors impact mine methane
emissions, including the gas content of the coal, flow capacity in the coal seam
and the mine void, and the time since abandonment. The latter is especially
important because gas emissions decline significantly following closure and level
off over time. Coal basin-specific geological data and coal mine-specific emission
data were used to develop input parameters for a numerical model. Decline
curves were then used to forecast abandoned mine methane emissions as a
function of time since the mine was abandoned, given the characteristics of a
specific coal basin.
Step 3: Calibrate through field measurements. Field measurements are an important
tool used to verify whether theoretical calculations accurately reflect actual
emissions from abandoned mines. A series of field measurements were
conducted at seven abandoned mines across the country. The goal of the field
study was to determine the measurement interval and duration necessary to
accurately predict average methane emission rates from a mine vent. The field
measurements were also used to test the accuracy of the basin-specific decline
curves. Measurements from a previous EPA study (Kirchgessner, 2001) of
abandoned mine vents at 21 mines were used to validate these results.
Step 4: Calculate a national emissions inventory for each year. Once decline curves
were developed, emission estimates of each mine were calculated according to
their status: venting, flooded, sealed, or unknown. To arrive at a total abandoned
mine emission inventory in a given year, Monte Carlo simulations were used to
sum the probability distributions for the mines within each basin, and then to sum
the emission distributions for the basins.
Step 5: Adjust for methane recovery and determine the net total emissions.
Methane recovery projects are known to exist at about 20 abandoned mines in
the US. The quantity of gas recovered and used at the abandoned mine projects
is subtracted from the total emissions to determine the net total emissions.
Employing this methodology, abandoned mine emissions for 1990 were estimated to range from
6.9 to 10.1 billion cubic feet (Bcf), or 2.8 to 4.1 million tonnes C02 equivalent (C02e), with a best
estimate of 8.4 Bcf or 3.4 million tonnes C02e. For the year 2002, additional contributions of
emissions from 163 gassy mines that closed between 1991-2002, increases the range of
emissions estimates to 10.9 to 14.7 Bcf (4.4 to 5.9 million tonnes C02e), with a best estimate of
12.8 Bcf (5.2 million tonnes C02e). However, mine methane recovery projects reduce
abandoned mine methane emissions by approximately 2.6 Bcf (1.0 million tonnes C02e),
bringing the net emissions for 2002 to approximately 10.2 Bcf (4.1 million tonnes C02e). Figure
1 shows the estimated annual abandoned coal mine methane emissions for 1990 - 2002,
including emissions avoided due to methane recovery projects.
This methodology and the calculated emissions estimates are based on the best available data.
At a 95% confidence interval, the current level of uncertainty is approximately + 20%. This
uncertainty range accounts for four important areas of uncertainty that could significantly impact
the emissions inventory calculations: limited data on mines closed before 1972, biases in the
U.S. mine ventilation data, no data on mine drainage before 1990, and exclusion of surface
mine emissions. There are also important uncertainties associated with poor data availability for
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coal permeability, the condition of abandoned mines (whether sealed or flooded), and, where
applicable, the effectiveness of mine seals.
Figure 1. Abandoned Mine Methane Emissions Estimates, 1990-2002
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~ Emission Avoided
~ Net Emissions (Bcf)
1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002
The methodology and emission estimates presented in this report are a first attempt to quantify
emissions from abandoned coal mines in the U.S. EPA will continue to refine the methodology
to quantify abandoned mine emissions with greater certainty. Some important next steps
include:
Identifying all abandoned mine methane recovery projects in the U.S. that operated from
1990 to the present and obtaining data on emission reductions;
Obtaining more field data to verify methodological results and to serve as the basis for
refinements to the methodology;
Developing methodologies to set baselines and calculate emissions avoided on a
project-specific basis; and
Incorporating the abandoned mine emissions into the U.S. Inventory of Greenhouse Gas
Emissions and Sinks.
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1.0 Introduction
EPA prepares an annual inventory of its greenhouse gas (GHG) emissions to track U.S.
progress in meeting its commitments under the United Nations Framework Convention on
Climate Change (UNFCCC). Active coal mines, which account for nearly 10% of U.S.
anthropogenic methane emissions, are included in the U.S. inventory. Coal mines release
methane, a greenhouse gas over 20 times more potent than carbon dioxide, as a direct result of
the coal mining process. In 2002, operating coal mines liberated 174 billion cubic feet (Bcf) of
CMM. Of this amount, 44 Bcf was recovered, resulting in net emissions of 130 Bcf (53 million
metric tons of carbon dioxide equivalents, or million tonnes C02e) from active mines (EPA,
2002).1
In the U.S., extensive data availability has facilitated the development of emissions estimates for
active mines with a high degree of confidence. The location and operating status of the mines
are known; vent air emissions are measured by the Mine Safety & Health Administration
(MSHA) at least quarterly; and gas volumes sold are recorded by state tax authorities or oil and
gas boards. In addition, many coal mining companies in the U.S. voluntarily cooperate with
EPA to refine the methane emission estimates.
In contrast, quantifying emissions from thousands of abandoned mines across the country has
proven much more challenging. For many of these mines, there are few if any data, especially
for mines closed before 1972. Some of these abandoned mines continue to emit methane,
contributing to total greenhouse gas emissions from the coal sector. EPA conducted this study
to determine the magnitude of abandoned coal mine methane emissions and to assess the
technical feasibility of including this source in the U.S. greenhouse gas emissions inventory.
Consistent with the stated goals of the U.S. Greenhouse Gas Inventory, the purposes of this
study are twofold: 1) to develop a credible methodology for determining methane emissions
from abandoned underground coal mines, and 2) to quantify those emissions for each year from
1990 through 2002. The methodology developed in this report incorporates quantitative models
with coal basin-specific parameters, calibrated with field measurements at several mines.
These emission calculations were used in conjunction with a comprehensive database of U.S.
mines abandoned since 1972 to generate an aggregate estimate of U.S. abandoned mine
methane emissions for each year from 1990 to 2002.
1.1 Greenhouse Gas Inventory Guidelines and Practices
Current guidelines of the Intergovernmental Panel on Climate Change (IPCC, 1997) establish
three different methodological levels (called "tiers") for estimating greenhouse gas emissions
depending on the level of detail available. For coal mining, the three tiers are described as
follows:
Tier 1: the least accurate estimate; based on national coal production data and
global average emission factors.
1 130 Bcf CH4 = 130 x 109 ft3 CH4 x (0.04246 lb CH4 / ft3 CH4) x (21 lb C02 / lb CH4 )(GWP) x (1 kg C02 /
2.2 lb C02) x (metric tonne/1000 kg) = 52.7 million metric tonnes C02 equivalent (C02e). Here, the factor
of 21 lb C02 to 1 lb CH4 reflects the global warming potential (GWP) of CH4, which is 21 times greater
than C02 on a mass basis over a 100 year time frame.
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Tier 2: a more detailed estimate; based on national average emission factors, or if
more specific emission factors are available, on sub-national emission
factors.
Tier 3: the most detailed estimate; based on mine-specific emission measurements.
The methodology developed in this report is consistent with Tier 2 guidelines. Under this
approach, emissions estimates can be based on country- or basin-specific methods, depending
on data availability. In the U.S., data on the gas content of coal are readily available, both for
entire coal basins and within each basin. To implement the Tier 2 approach, EPA examined
emissions data from hundreds of gassy active mines, as well as a limited number of abandoned
mines. Computer simulation of post-mining emissions, together with the available emissions
data, produced basin-specific decline curves based on established mathematical equations for
gas rate declines. Following general IPCC guidance, EPA relied on both statistical analysis and
expert judgment to develop emissions factors for abandoned mine emissions in each U.S. coal
basin.
1.2 Definition of an Abandoned Coal Mine
In order to avoid double counting or undercounting of emissions, it is important to clearly define
the term "abandoned mine."2 The Mine Safety & Health Administration (MSHA) classifications
for inactive or non-producing mines are as follows:
1) Non-Producing, Men Working:
2) No One Working, Temporarily Abandoned:
3) No One Working, Permanently Abandoned:
No coal being produced, but persons
are maintaining equipment.
Coal production has ceased, mine
may reopen in near future.
Mine has been abandoned for more
than 90 days.
Although the MSHA definitions are practical from an operational perspective, they are not as
clear when defining mine emissions as active or abandoned. Often, a coal mine will stop
producing coal (e.g., Category 2 above), but it will continue to operate ventilation fans for
months or even years afterwards. During this time, the coal mine must report the methane
emissions to MSHA as part of the active coal mine emissions inventory. Thus, it would be
double-counting to include them as part of the abandoned coal mine emissions inventory.
Taking this into account for this methodology, the term "abandoned" is defined for purposes of
developing an emissions estimate as the time when active mine ventilation ceases.
1.3 Previous Attempts to Estimate Abandoned Mine Emissions
While the IPCC has recommended that emissions from abandoned mines be included in the
GHG emissions inventory, it has not yet provided any methodological guidance on how to
2 The Mine Safety & Health Administration (MSHA) catalogs information on individual mines using
Federal Information Processing Standards (FIPS) codes. For coal mines, MSHA assigns both an
operational and auxiliary status regarding mining activities; these codes are defined in the Code of
Federal Regulations (30 CFR Part 50, User's Handbook).
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calculate abandoned mine emissions, due in large part to the lack of reliable data (IPCC, 1997).
EPA's earlier efforts to develop a methodology for abandoned mine emissions resulted in wide-
ranging estimates, from 1 to 34 Bcf per year. In a separate EPA study on developing improved
methane emission estimates at coal mining operations, 1995 abandoned mine emissions were
estimated to be 7.4 Bcf, based on pre-abandonment data and vent pipe emissions measured at
21 abandoned underground coal mines in the Appalachian and Black Warrior basins
(Kirchgessner et al., 2001).
1.4 Report Structure
The report outlines a logical approach for estimating CMM emissions. An overview of each
major section is presented below.
Section 2.0 Abandoned Mines as a Source of Methane Emissions
This section describes the location of gassy underground mines in the U.S. and
introduces readers to the factors affecting methane emissions from abandoned
coal mines.
Section 3.0 Coal Mine Methane Emissions Data
This section describes the data sources for abandoned mines in the U.S.,
including data limitations, and summarizes these data.
Section 4.0 Emissions Estimation
This section outlines the quantitative procedures to estimate abandoned mine
methane emissions. Because methane emissions at abandoned mines will
decline over time, basin-specific decline curves were developed to calculate
emission estimates for individual mines. These mine-specific emissions were
then totaled to develop a national estimate. Because taking measurements at
every abandoned mine is not practical, the proposed methodology incorporates
a probabilistic analysis (Monte Carlo simulation) to develop a range of
emissions estimates with a high degree of confidence.
Section 5.0 Calibration Through Field Measurements
This section describes the field measurements EPA undertook to validate the
calculated estimates.
Section 6.0 Estimating Emissions from Mines Closed Before 1972
This section presents the results of EPA's efforts to gather data and quantify
abandoned mine emissions from mines closed before 1972. Unfortunately,
critical data are missing for mines closed prior to 1972, including the active
mine emissions data, time of abandonment, number of gassy mines, and mine
status. Therefore, this information was estimated based on extrapolations from
physical, geologic and hydrologic constraints that apply to mines closed after
1972.
Section 7.0 Results of the 1990-2002 Abandoned Mine Methane Emissions Inventory
This section presents the estimates of total methane liberated from abandoned
U.S. mines annually from 1990 through 2002. Net emission estimates include
adjustments for mine methane recovery projects. This section also discusses
the range of variability and uncertainty in the calculations.
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Section 8.0 Conclusions
This section presents conclusions and proposed next steps to set a roadmap
for possible future activities to improve these emissions estimates for
abandoned mines, and to develop methodologies for project-specific baselines.
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2.0 Abandoned Mines as a Source of Methane Emissions
2.1 Overview of Coal Mine Methane
Coalbed methane is formed during coalification, the process that transforms plant material into
coal. Organic matter accumulates in swamps as lush vegetation dies and decays. As this
organic matter becomes more deeply buried, the temperature and pressure increase, subjecting
the organic matter to extreme conditions that transform it into coal and methane, as well as
byproducts including carbon dioxide, nitrogen, and water. As heat and pressure continue to
increase, the carbon content ("rank") of the coal increases.
The methane trapped in coal seams is commonly referred to as coalbed methane (CBM) or coal
seam gas. Generally, the deeper the coal seam and/or higher the coal rank, the higher the
methane content. Coalbed methane is known as coal mine methane (CMM) when mining
activity releases the methane, a potent greenhouse gas.
Not all coal seams are gassy (generally defined as mineable seams capable of producing more
than 100 mcfd in coal mine ventilation emissions). In the U.S., gassy coals are located in the
Appalachian Basins in the East, Black Warrior Basin in the South, the Illinois Basin in the
Central U.S., and several western basins such as the San Juan and Powder River Basins.
Figure 2 shows the locations of gassy coal basins in the U.S.
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2.1.1 Active Coal Mine Emissions
To ensure mine safety, active underground coal mines must remove methane from the mine
using powerful ventilation systems. For particularly gassy mines, operators employ methane
drainage systems to supplement their ventilation systems. In the U.S., these drainage systems
consist of pre-mine vertical boreholes (drilled from the surface), in-mine horizontal boreholes
drilled prior to mining, or vertical or in-mine gob wells.3 The methane gas emitted through the
ventilation and drainage systems is either released directly to the atmosphere or recovered and
used.
2.1.2 Abandoned Coal Mine Emissions
As mines mature and coal seams are mined out, mines are closed and eventually abandoned.
Often, mines may be sealed by filling shafts or portals with gravel and capping them with a
concrete seal. Vent pipes and boreholes may be plugged in a similar manner to oil and gas
wells.
As active mining stops, the mine's gas production decreases, but the methane liberation does
not stop completely. Following an initial decline, abandoned mines can liberate methane at a
near-steady rate over an extended period of time. The gas migrates up through conduits,
particularly if they have not been sealed adequately. In addition, diffuse emissions can occur
when methane migrates to the surface through cracks and fissures in the strata overlying the
coal mine.
After they are abandoned, some mines may flood as a result of intrusion of groundwater or
surface water into the void. Flooded mines typically produce gas for only a few years.
2.2 Factors Influencing Mine Methane Emissions
Within a coalbed, methane is stored both as a free gas in coal's pores and fractures, as well as
on the coal surface through physical adsorption. As the partial pressure of methane in the
fracture (cleat) system of the coal decreases, the methane desorbs from the coal and moves
into the cleat system as free gas. The pressure differential between the cleat system and the
open mine void4 provides the energy to move the methane into the mine. Driven by this
pressure differential between the gas in the mine and atmospheric pressure, the methane will
eventually flow through existing conduits and will be emitted to the atmosphere.
Many factors can impact the rate of CMM emissions at both active and abandoned mines. The
most important factor is the total gas (methane) content of the coal, which has been directly
linked to methane emissions from mining activities (Grau, et al. 1981, EPA, 1990)
The time since abandonment is a critical factor affecting an abandoned mine's annual
emissions, as the mine's emissions decline steeply as a function of time elapsed.5 EPA has
developed a decline curve, which describes the rate at which methane continues to desorb from
3 A "gob" or "goaf is the rubble zone formed by collapsed roof strata caused by the removal of coal.
4 The mine void refers to the mined out area of the coal seam.
5 The decline of CMM emissions begins with the cessation of coal production, although abandoned mine
emissions officially begin only when active (forced) ventilation of the mine ceases.
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the coal after abandonment, moves into the mine void, and is eventually released to the
atmosphere. The decline curves are strong functions of time: the methane emissions rate
decreases rapidly in the years immediately after a mine closure, and flattens out after several
decades. The development of these decline curves is described in Section 4 of this report.
Other factors impacting the rate of methane emission include mine size, flooding, sealing, and
the coal's permeability, porosity, and water saturation.
The remainder of this section discusses in greater detail several additional factors influencing
abandoned mine emissions:
Gas content and adsorption characteristics of coal
Methane flow capacity of the mine
Mine flooding
Open (active) mine vents
Mine seals
Each of these factors can impact methane emissions independent of the other factors, but in
almost all cases several factors are important.
2.2.1 Gas Content and Adsorption Characteristics of Coal
Compared to many sedimentary rocks, coal beds have the capacity to store a large amount of
methane gas.6 Coal can hold a significant amount of methane in the adsorbed state because of
the extensive internal surface area of the coal matrix (up to 250 square meters/gram, or 2.4
billion square feet per ton).7 Figure 3 illustrates the methane storage capacity of a middle rank
coal compared with the storage capacity of a similar mass of (non-adsorbing) sandstone having
a porosity of 15%. This figure illustrates that coal can contain significant quantities of methane
even at very low pressures. The gas content of coal is generally expressed as standard cubic
feet per short ton (scf/ton), or cubic meters per metric ton (m3/tonne).8
This difference in storage capacity is due primarily to coal's internal pore structure. For
example, porosity in sedimentary rock (e.g. sandstone and limestone) is mostly in the mesopore
(20 to 500 angstroms) and macropore (>500 angstroms) range. In contrast, a significant fraction
of the coal matrix is in the micropore range (<20 angstroms).9 The methane content at a given
temperature and pressure generally increases with coal rank because of the increase in the
percentage of micropores and surface area available for methane adsorption (Figure 4).
6 The quantity of gas that can be stored in the pore space of most sedimentary rock is a function of
temperature and pressure as described by the real gas law.
7 The density of the adsorbed methane is approximately its liquid density at atmospheric pressure boiling
point (Yee et al., 1993).
32 scf/ton is approximately equal to 1 m3/tonne.
9 As coal increases in rank, the pore structure of the matrix changes. The percentage of the total matrix
porosity in the micropore range increases with increasing rank from about 30% for a lignite to about 80%
for an anthracite (Gan, et. al., 1972).
10
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Figure 3. Comparison of methane storage capacity of sandstone and coal
Pressure, psia
10
Figure 4. Typical adsorption isotherms as a function of coal rank (GRI, 1996)
Depth (ft)
1 1 i 1
0 140 280 420 560 700 840 980
Pressure (psia)
The curves shown in Figure 4 are called adsorption isotherms because they are measured at a
constant temperature.11 Adsorption isotherms can be characterized by mathematical functions
based on theoretical adsorption properties. One function commonly used for methane
10
Depth indicated in Figure 4 is derived from the fresh water pressure gradient of 0.43 psi/ft (GRI, 1996).
11 At constant pressure, increasing temperature decreases the amount of adsorbed methane.
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adsorption on coal is called the Langmuir Isotherm, which is based on the ideal case of a single
layer of molecules adsorbed on the coal surface.12 The Langmuir isotherm is generally
expressed as:
V = VL P / (P + Pl) (Equation 1)
where:
V = Volume of methane at standard temperature and pressure per ton of coal,
m3/tonne (or scf/t)
VL= Langmuir volume constant, m3/tonne (or scf/t)
P = Pressure in the coal cleat system, kPa (or psia)
PL = Langmuir pressure constant, kPa (or psia)
Both of the Langmuir constants VL and PL can be determined by fitting the function to
experimental adsorption data. The Langmuir volume VL represents the maximum storage
capacity of the coal. The Langmuir pressure PL is the pressure at which half of the Langmuir
volume is achieved. The lower the Langmuir pressure for a given Langmuir volume, the more
methane may be stored at lower pressures. The amount of gas stored at low pressures is
important for predicting abandoned mine emissions, where there is lower pressure in the coal
cleat (fracture) system due to depletion during active mining. The steeper the adsorption
isotherm at low pressures, the more gas will adsorb or desorb per unit pressure change.
2.2.2 Methane flow capacity of the mine
Methane moves from within the microporous matrix of the coal to the macroporous structure
and the cleat system via diffusion. This diffusion from the micropores into the cleat system is
almost always fast enough that it is not the rate-limiting step for gas production from coal.
Rather, the limiting factor is the ability of the gas to flow through the macropores and cleat
system (Seidle and Arri, 1990).
Once the methane reaches the macropores and cleat system, it exists primarily in the free gas
state. Here, its movement is determined by the laws of gas flow through porous media, such as
Darcy's Law. For linear flow of an incompressible liquid, Darcy's law is of the form
q = (kA/|j,)(dp/dl) (Equation 2)
where:
q = volumetric rate in cm3/sec
k = permeability in Darcys
A = the cross-sectional area perpendicular to flow in cm2
la, = the viscosity of the fluid in centipoises
dp/dl = the change in pressure per unit length or pressure gradient in atm/cm
The form of Darcy's law must be modified for gases, for which both viscosity and volume are
functions of pressure. Several key parameters for determining gas flow through a porous
medium such as a coal mine include the following:
12 The adsorbent refers to the solid surface; the adsorbate refers to the adsorbed gas.
12
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Permeability, k, a property of the porous media (coal) plays a major role in the rate at
which gas can flow from the unmined coal into the void space of the abandoned mine.
Unfortunately, measurements of the absolute permeability of coal are scarce.
The area, A, across which gas moves from the unmined coal into the void space can be
very large because of the large areas of exposed coal in an underground mine.
Determining the coal's surface area in an abandoned mine is very difficult.
The pressure gradient from the coal to the void space of the mine decreases over time
as the gas is released and the pressure in the coal seam is reduced. As a result, the
emissions rate from an abandoned mine decreases over time.
In an application related to coal mine methane production, gas production from oil and gas wells
is predicted using Darcy's Law together with material balance equations. In this context, the well
acts as a material sink whose rate of withdrawal (q) is a function of the difference between a
specified pressure at the well, (Pw), and the pressure at some outside boundary of the gas
reservoir (Pr). For a gas, this function takes the following form:
q = PI (Pw2. pr2)" (Equation 3)
where:
q = volumetric rate of gas production
Pw = pressure at the well
Pr = pressure of the gas reservoir
PI = Productivity Index
n = empirically derived exponent13
By convention, flow from the reservoir to the well (q) is a negative value. Equation 3 is
essentially the same as Equation 2, modified for a gas and combining the permeability of the
rock, the viscosity of the gas, the geometry and configuration of the pressure sink and outside
gas reservoir, and the thickness of the flow unit into the PI term.
By analogy, the coal mine and its connection to the atmosphere (via the vent shaft or
overburden fracture conduit) acts as the wellbore, and the unmined coal within and peripheral to
the mine is the reservoir of the stored methane. The PI can be considered a constant at the low
pressures involved in coal mining. The application of Equation 3 to abandoned mine methane
emission forecasting will be discussed later in this report.
2.2.3 Mine flooding
Over time, abandoned mines may partially or completely flood, which will decrease or
completely shut off gas flowing into the mine. The inhibition of gas flow depends on the
pressure balance between the gas within the coal and the water in the coal cleat system. Even if
the gas phase is at a higher pressure than the water phase, the presence of water will
substantially inhibit gas flow into the mine. As the water level rises in a mine, the gas flow will be
reduced more rapidly than it would have otherwise, because as the coal cleat becomes re-
saturated with water, its relative permeability to gas decreases. Thus, the presence of water in
the coal cleat system decreases the apparent permeability of the coal seam.
13 The exponent n accounts for turbulence and other non-ideal flow conditions (Slider, 1983).
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Mine flooding plays a critical role in methane emissions from abandoned coal mines. For
example, even if a coal mine contains a large quantity of methane and the coal is highly
permeable, if the mine rapidly floods the total methane emitted will be far less than if the mine
had remained dry.
2.2.4 Active vents
At some abandoned mines, vent pipes relieve the buildup of pressure resulting from desorption
and flow of methane into the mine void. These vents are installed to prevent methane from
migrating into surrounding strata. An abandoned mine with an open (or "active") vent will
behave very much like a natural gas well (at a much lower pressure regime).
Methane emissions from venting mines are a function of the pressure differential between the
vent and the gas in the coal bed. The surface opening of the vent is at atmospheric pressure,
while the gas within the unmined coal seam near the mine void will range from atmospheric
pressure (14.7 psi, or 1.01 bars) to tens of psi (more than 1 bar) above atmospheric pressure.
Mines with open vents are known to "breathe" with atmospheric changes. In other words, the
mines emit methane during times of low atmospheric pressure and pull air in during times of
high atmospheric pressure. The effect of barometric pressure on measured vent emission rates
is described in Section 5.2.
2.2.5 Mine seals
While many abandoned mines have active (open) vents, some mines are sealed in an attempt
to prevent unauthorized access or the escape of methane gas. Even during active mining, seals
are placed in worked-out areas of the mine to reduce fresh air ventilation requirements as a
cost-saving measure. Old shafts and drifts are commonly plugged with cement.
It is common, however, for gas to leak out around these plugs or to make its way through
fractures in the overlying strata. The seals are generally assumed to leak even at very low
pressure differentials (e.g., a few tenths of a psi), and they typically degrade over time. Although
mine seals can impact the rate of flow, they are not considered to be effective at preventing
atmospheric methane emissions over time.
14
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3.0 Coal Mine Methane Emissions Data
The first step in developing an emissions inventory is collecting information on abandoned
mines. There are numerous abandoned mines in the United States, and it is impractical to visit,
measure, and collect mine-specific data from individual mines. Thousands of U.S. coal mines
that operated during the 20th century have since closed.14 MSHA estimates that over 7,500
underground coal mines have been abandoned just since 1980 as a result of significant
restructuring in the coal industry (U.S. Department of Labor, 2000). Throughout the 1990s, on
average, 14 gassy mines were abandoned each year. Therefore, to estimate U.S. abandoned
mine emissions with a reasonable degree of confidence for this study, EPA relied on historical
emissions data, available MSHA databases, and information collected during field studies. EPA
emissions estimates are also based on known characteristics of coal basins, including lithology,
coal rank, coal depth, coal seam gas content, and hydrologic characteristics.
Emissions data for coal mines has been compiled only since 1971, originally by U.S. Bureau of
Mines (USBM), and currently by MSHA. Thus, gathering historical information for abandoned
mines in the U.S. is difficult for mines abandoned prior to 1972, for which very few data exist.
EPA has developed a methodology to estimate emissions contributions from these older
abandoned mines based on extrapolation from mines closed in and after 1972 (this
methodology is described in detail in Section 6). The remainder of this section and Section 4.0
describe data sources and methodology for estimating emissions from mines abandoned in or
after 1972.
3.1 Coal Mine Emissions Data
For mines abandoned in or after 1972, EPA compiled data from several key sources to
characterize abandoned mines and their emissions. Table 1 shows the data sources that EPA
used to compile a database of gassy abandoned mines.
Mine Safety and Health Administration (MSHA). The largest source of data assembled on
abandoned mines is the MSHA Coal Mine Information System (MIS) Database, which
contains information for over 7,500 coal mines abandoned since 1980, categorized on the
basis of average daily emissions. The MSHA MIS database lists 98 mine closures during the
1980s for mines that had active emissions greater than 200 mcfd. Since 1990, MSHA has
provided EPA with information on all coal mines with emissions greater than 100 mcfd.15
One limitation of this data set is that it includes only ranges of emissions data, rather than
more precise estimates.16
United States Bureau of Mines (USBM). The USBM produced a series of five information
circulars on coal mine emissions from 1971-1985. EPA used these reports to identify gassy
14
Only a small portion of all US mines are gassy. In 2001, for example, approximately 125 of nearly 600
operating underground coal mines (20%) contained detectable methane levels in ventilation air and were
considered gassy (methane emissions above 100,000 cubic feet per day). The percentage of gassy
mines was much lower during the early- and mid-twentieth century, when most coal mining occurred in
small shallower mines.
15 Except for the years 1991 and 1992, when ventilation fan data were not collected.
16 All mines reporting emissions greater than 200 mcfd were designated as one of three categories: 200 -
500 mcfd, 500-1,000 mcfd, or >1,000 mcfd.
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active mines with emissions greater than 100 mcfd that closed during this period.
Subsequently, EPA also used these data to establish average basin-specific emission rates
for gassy mines. To estimate emissions from individual mines that closed during the 1980s,
EPA extrapolated from the USBM information to determine basin-average emission rates for
the mines with emissions greater than 1 mmcfd.
State agencies. Some additional comprehensive mine opening and closure information was
obtained through state mine and mineral agencies. Mine maps were available for some
mines through coal mine operators and state geologic surveys.
Table 1. Data sources used to compile gassy abandoned coal mines database
Year
Data Source
Range of
Vent
Emissions
Degasifi cation
Data
Number
of Mines
1971
USBM
> 100 mcfd
No
199
1973
USBM
> 100 mcfd
No
178
1975
USBM
> 100 mcfd
No
196
1980
USBM
> 100 mcfd
No
200
1985
USBM (partial list)
> 100 mcfd
No
85
1980 -1990
MSHA MIS Database
> 200 mcfd
No
98
1990-2002
(excluding '91 & '92)
MSHA Quarterly
Reports
> 100 mcfd
Yes
95- 182
EPA used these data sets to compile a list of abandoned gassy mines that constitute the vast
majority of abandoned mine emissions. This was a multiple step process:
1. First, EPA was able to establish a national profile of abandoned active mines. The 1997
MSHA mine methane emissions dataset consisted of all (586) active coal mines with
detectable emissions, not just mines with emissions greater than 100 mcfd. Based on
these 1997 active mine data, EPA determined that mines emitting greater than 100 mcfd
comprised 98% of emissions for all mines with reportable emissions (EPA, 2002). The
USBM data showed similar results for the 1970s.
2. EPA used an analogous assumption that the profile of abandoned mines is substantially
similar to the profile of active mine emissions: that is, that 98% of abandoned mine
emissions come from mines that produced 98% of their emissions when they were
active. In other words, mines that emitted more than 100 mcfd when they were active
will contribute more than 98% of the total abandoned mine emissions when they are
closed.
3. EPA determined which abandoned mines constitute a representative sample population
of abandoned mines. 393 mines that were abandoned between 1972 and 2002
produced emissions greater than 100 mcfd when they were active (Table 2). Analogous
to the known distribution of active mine methane emissions, these 393 abandoned
mines are assumed to account for 98% of all abandoned mine emissions. Thus, these
mines constitute the sample population used as the basis for estimating methane
emissions from all abandoned mines in the U.S..
16
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Table 2. Abandoned Coal Mines by Basin
Coal Basin
Total No. of
Abandoned Coal
Mines
Coal Mines That Had
Active Emissions
>100 mcfd
(Years 1972-2002)
Gassy
Mines as a
% of Total
Mines
Central Appalachian
6075
178
2.9
Northern Appalachian
834
101
12.1
Penn. Anthracite
312
0
0.0
Illinois
100
64
64.0
Black Warrior
68
14
17.9
Piceance
28
14
50.0
Uinta
28
15
54.0
San Juan
2
0
0.0
Other
135
8
6.0
Total
7582
393
5.0
From 2002 MSHA Data base
3. 2 Mine status information
Additional mine-specific information was collected on each of the targeted mines from state and
federal regulatory agencies and from the mine operators where possible. Information collected
included:
Mine-specific maps
Mined-out acreage
Locations of vents and shafts
Degree of flooding
Status of mine (e.g., sealed or venting to the atmosphere)
Table 3 shows the status of the 393 gassy abandoned mines in the database.17 The entire list of
393 coal mines in the database can be found in Appendix A, including the status of the mine (if
known), the date of abandonment, emissions at abandonment, and coal basin. Of the 393
mines, 244 (62%) of these abandoned mines were classified as either:
Vented to the atmosphere,
Sealed to some degree (either earthen or concrete seals), or
Flooded (enough to inhibit methane flow to the atmosphere).
The status of the remaining 149 mines (38%) is unknown. These "unknown" mines were
classified into one of these three categories by generalizing on the basis of other mines in a
given coal basin, using a probability distribution analysis. For example, in the Black Warrior
basin, 92% of the mines are known to flood once they are abandoned, but only 21% of the
mines in the Northern Appalachian basin do so (Table 3). As a result, one would expect a larger
17 Information regarding the status of abandoned mines was obtained from state government agencies in
ten states (Appendix B).
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percentage of the abandoned mines in the Black Warrior basin to be flooded compared with
abandoned mines in the Northern Appalachian basin.
Table 3. Status of Abandoned Mines in U.S. Database
Sealed
Vented
Flooded
Unknown
Status
Basin
(% of
(% of
(% of
Total Known
Total Mines
Known)
Known)
Known)
Central Appalachia
24 (25%)
25 (26%)
48 (49%)
97 (54%)
83 (46%)
180
Illinois Basin
18 (55%)
3 (9%)
12 (36%)
33 (52%)
31 (48%)
64
Northern Appalachia
36 (49%)
23 (31%)
15 (20%)
74 (74%)
26 (26%)
100
Warrior Basin
1 (8%)
0 (0%)
12 (92%)
13 (93%)
1 (7%)
14
Western Basins
20 (74%)
5 (19%)
2 (7%)
27 (77%)
8 (23%)
35
Total
99 (43%)
56 (16%)
89 (42%)
244 (62%)
149 (38%)
393
Data on adsorption isotherms, gas content, flow capacity and abandonment status are not
available for all of the 374 gassy U.S. underground coal mines known to be abandoned since
1972. However, the methane ventilation rate before abandonment and the date of abandonment
are available for the post-1971 abandoned mines. Mine degasification data are available from
1990 to present. Several adsorption isotherms for the most commonly mined coals in each coal
basin are documented (Masemore, et al., 1996), as described below in Section 4.4.1.
18
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4.0 Emissions Estimation
4.1 Overview
Once the database of abandoned mines is compiled, it is possible to calculate emissions based
on the factors described in Section 2.2. Figure 5 illustrates the steps involved in the calculation
procedure.
As Figure 5 indicates, the template for calculating abandoned mine methane emissions is based
primarily on the status of the mine, whether flooded, vented, sealed, or unknown. Emissions
calculations for each type follow a similar sequence of steps.
Vented mines. Closed mines are often intentionally left vented to the atmosphere to
allow methane to escape and prevent the dangerous or explosive buildup of methane
underground. Even after active ventilation measures (such as fans) cease and the mine
is officially abandoned, the open access to the atmosphere impacts the mine's methane
emissions. To estimate emissions from abandoned vented mines, this methodology
uses basin-specific decline curves to develop low, mid-range, and high emission factors
that are incorporated into probability distributions for annual emissions. The
methodology for calculating emissions from vented mines is described in Section 4.6.1.
Flooded mines. Abandoned mines frequently partially or completely fill with water from
surrounding strata. The water impedes the escape of the methane in the coal seam,
effectively trapping it. Emissions estimates for abandoned flooded mines are based on
emission factors (low, medium, and high) that are incorporated into probability
distributions for annual emissions. The methodology for calculating emissions from
flooded mines is described in Section 4.6.2.
Sealed mines. The efficiency of the seal impacts emissions from abandoned sealed
mines. Emission factors are based on low, mid-range, and high emission factors for
each seal type, which are incorporated into annual probability distributions. The
methodology for calculating emissions from sealed mines is described in Section 4.6.3.
Unknown mines. To estimate their emissions, abandoned mines of unknown status
must be assigned a classification as vented, flooded, or sealed. This apportionment,
based on the proportion of these types for abandoned mines that are known, is
described in Section 4.7.1.
4.2 Forecasting Abandoned Mine Methane Emissions Using Decline
Curves
The methane emission rate of a mine before abandonment is a function of the gas content of
the coal, the rate of coal mining, and the flow capacity of the mine. In this respect, methane
emissions from active mines are very similar to conventional gas wells, where the initial rate of a
water-free conventional gas well reflects both the gas content of the producing formation and
the productivity index of the well. Production from conventional gas wells as a function of time
US Environmental Protection Agency
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is commonly forecast using decline curve analysis. The physical basis for decline curve analysis
and its application to abandoned mine emission forecasting are described below.
Existing data on abandoned mine emissions through time, although sparse, appear to fit a
hyperbolic model of decline. For example, USBM measured daily emissions at the Cambria
Mine in Pennsylvania18 for over 3 years, including approximately 1.5 years after the gob area
was sealed (Garcia et al., 1994). As shown in Figure 6, a hyperbolic decline equation matches
this set of data with a correlation coefficient (R2) equal to 0.88, indicating a statistically
significant correlation.
An examination of Equation 3 (page 13) reveals why methane emission rates from abandoned
mines decline over time. As methane leaves the system, the reservoir pressure, Pr, declines as
described by the isotherm. At the same time, both the mine pressure (Pw ซ 1 atm for vented
mines) and the PI term are essentially constant at the pressures of interest (atmospheric to 30
psia). Thus, the flowrate q becomes smaller (q is defined as a negative number by convention).
Methane production from abandoned coal mines can be estimated based on the decline curve
(Equation 3) used in conjunction with material balances. Fetkovitch et al. (1994) have
generated a rate-time equation that can be used to predict future gas production. These
authors combined the pseudosteady state flow equation (Equation 3) with a material balance
equation that calculates the pressure loss as material is removed. The resulting expression for
gas production as a function of time clearly shows that gas production declines in a hyperbolic
fashion:
q = qi(1+bDjt)(1/b) (Equation 4)
Where:
q = the gas rate at time t in mcf/d
qi = the initial gas rate at time zero (t0) in mcf/d
b = the hyperbolic exponent, dimensionless
Di = the initial decline rate, 1/yr
t = elapsed time from t0 in years
The coefficients b and Di can be determined by fitting Equation 4 to measured rate data.
Unfortunately, historical information on methane emission rates from abandoned mines is very
rare. The only parameters in Equation 4 that are readily available from the abandoned mine
database are the emission rate at the time of abandonment (q^ and the date of abandonment
(t0). The values for the coefficients Di and b must be obtained in other ways. Once determined,
Equation 4 can be used to forecast future gas production. Several key parameters that affect
the flow of methane from a mine, including flow capacity, pressure in the coal at abandonment,
and the gas storage as a function of pressure (represented by the adsorption isotherm) are
implicitly incorporated into this equation's coefficients.
18 This particular well used a blower to maintain a constant low pressure on the wellhead, which
accelerated gas production but did not affect the hyperbolic nature of the decline curve.
20
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Figure 5. Methodology for Calculating Abandoned Mine Emissions
No
Select unknown
status
spreadsheet
Select Basin for
Decline Curve
Calculations
Generate emission
probability
distribution as
flooded, vented
and sealed
Add to unknown
mine status
summation
'
Generate unknown
mine status
emission inventory
probability
distribution
'
Determine fraction
of each status type
by basin
'
Multiply emission
inventory
distribution by
fraction of each
status type
'
Generate factored
unknown mine
status emission
inventory
probability
distribution
Select flooded
status spreadsheet
Calculate low, mid
and high emission
factors
Define distribution
type and assign
data
Generate yearly
emissions
probability
distribution
Add to flooded
status summation
Generate total
flooded status
emission inventory
probability
distribution
Select sealed
status spreadsheet
No
Select vented
status spreadsheet
Select Basin for
Decline Curve
Calculation
Calculate low, mid
and high emission
factors
Define distribution
type and assign
data
Generate yearly
emissions
probability
distribution
Add to vented
status summation
Generate total
vented status
emission inventory
probability
distribution
/tiombine all mine status probability
/ distributions through Monte Carlo
~( Simulation to generate probability
V distribution for the abandoned mine
emission inventory
Select Basin for
Decline Curve
Calculation
Calculate perm
based low, mid
and high factors
for each seal type
Calculate average
factor for each
seal type
Define distribution
type and assign
data
Generate yearly
emissions
probability
distribution
Add to sealed
status summation
Generate total
sealed status
emission inventory
probability
distribution
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Figure 6. Cambria Mine gob well decline curve
Days from Abandonment
4.3 Generating Dimensionless Decline Curves with Flow Simulation
To forecast methane emissions over time for a given mine, one must characterize the gas
production of that mine as a function of time (e.g, a decline function), and initiated at the time of
abandonment. To accomplish this, EPA has used a computational fluid dynamics (CFD) flow
simulation model.19
To illustrate how a decline curve can be built with the CFD simulator, a conceptual model of a
non-flooding, actively venting mine was built. The numerical model was configured such that the
volume of the mined-out areas, or void volume, was 10% of the model bulk volume.20 The
remaining volume was coal in communication with the void volume. This coal represents both
the coal remaining in the mined seam and unmined coal seams in communication with the void
volume because of roof and floor fracturing and relaxation.
The model was configured to simulate a single component (methane), single-phase (gas)
system for a period of 100 years. The model was initialized at 20 psia in the void with the outer
boundaries acting as barriers to flow. The coal permeability was set at 1 millidarcy and the
average adsorption isotherm for the Central Appalachian coal basin was used as the adsorbed
methane storage function. The minimum pressure was limited to one atmosphere.
19
CFD software uses the rate equations of gas flowing through a porous media (conservation of
momentum) with material balance equations (conservation of mass) in combination with an initial
pressure and boundary conditions that define the flow geometry.
0 The 10% void volume value was based on a proprietary study of several abandoned mine complexes,
which accounted for the volume of coal peripheral to the mine workings.
22
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According to the idealized case in the model, the gas from the mine void depletes rapidly,
reducing the methane pressure in the mine, which in turn allows desorption of methane from the
coal. This methane then migrates to the void area where it is removed from the system. In
generating the family of dimensionless emission decline curves, the conceptual model size was
held constant and the methane flow capacity (PI in Equation 3) was modified by adjusting the
permeability. Modifications of this procedure for flooded and sealed mines will be discussed in
following sections.
Figure 7 shows the resulting methane production decline curve for a non-flooded, actively
vented mine. This figure is normalized to the initial emission rate (q/qi), which allows this curve
to be applied to mines with differing initial emission rates, as long as they have similar initial
pressures, permeability and adsorption isotherms. This figure is based on an isotherm for the
Central Appalachian basin, a permeability of 1 md, and an initial pressure of 20 psia.
Figure 7. Dimensionless decline curve for non-flooded, actively venting abandoned mine
100%l
90% I
80%
a;
to
a.
S 60%
C
at
o
-------
For mines abandoned during or after 1972, two key data are generally available: average
methane emissions rate while mine was active, and the date of abandonment. The initial gas
flow rate at time t0 (closure) can be estimated, by assuming it is approximately equal to the
average methane liberation rate for each mine (ventilation plus drainage) while the mine was
active.21 Methane drainage information is available on a mine-specific basis since 1990.
To estimate mine-specific values for parameters such as coal adsorption isotherm coefficients,
permeability, and pressure at time of abandonment, a probability distribution was generated
based on the most likely value and the probable range of values for each parameter. This range
of values is not meant to capture extreme values; rather, the probability distribution helps to
select values that represent the highest and lowest quartile. Specifically, values are chosen at
the ten-percentile and the ninety-percentile of the cumulative probability density function of the
parameter. For example, 0.1, 1.0 and 10.0 md were selected as the low, mid and high values for
permeability. This means that 10% of all coal permeability values are less than 0.1 md, and 90%
are less than 10.0 md. Similarly, 50% of coal permeability values are expected to be above 1.0
md and 50% are below 1.0 md. Where measured data are lacking, values such as permeability
are selected based on expert opinion.
Once the low, mid-range, and high values are selected, they are applied to a probability density
function, using a Monte Carlo simulation to combine these distributions as either summations or
products. This technique combines the statistical distribution of the data by randomly sampling
values from each distribution, performing the mathematical operation, then repeating the task
numerous times. The Monte Carlo simulation provides a rigorous approach to combining
uncertainties expressed as probability distributions, but the calculated results ultimately depend
on the adequacy of the underlying statistical model. The uncertainties associated with combining
different probability distributions using Monte Carlo simulations are described in Appendix C.
4.4.1 Adsorption Isotherms
Masemore et al. (1996) compiled numerous adsorption isotherm parameters for each coal
basin. Table 4 lists the number of isotherms available by coal basin. Based on these datasets,
ranges could be determined for the PL and VL parameters of the adsorption isotherms, using the
low, mid and high values from the probability distribution. Average values of these isotherms are
shown in Figure 8. Figure 9 shows the adsorption isotherms for the Central Appalachian coal
basin at the low-pressure range of interest.
Table 4. Adsorption isotherms available for each coal basin
Basin
Central
Appalachia
Illinois
Northern
Appalachia
Black
Warrior
Western
# of Isotherms
11
4
22
16
41
21 While the actual emission rate at the time of closure may be somewhat more accurate than average
active mine emissions, these data are generally not available. Moreover, ventilation rates during a mine's
final closure would represent the ventilation of only a small part of the mine where the final work is
conducted, since presumably seals have already been installed throughout the mine workings.
24
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Figure 8. Average methane adsorption isotherm for U.S. coal basins
Figure 9. Methane adsorption as a function of mine pressure for the Central Appalachian Basin
160 n
140
120
100
80
60
40
20
/
/
s
S
s
*
*
*
*
*
CA High
" " " CA Mid
' 'CA Low
/
/
/
*
*
*
*
*
*
\
\
\
/
*
*
*
*
*
*
~
\ ^
\ \
\
*
*
*
*
X .
*
*
*
*
*
-
ฆ* '
* """
10 15 20 25 30 35 40 45
psia
50
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4.4.2 Permeability
Coal permeability data are limited. The few data that are available generally come from
borehole injection tests into unmined coal or from analysis of the production profile of coalbed
methane wells. These data are generally proprietary; therefore, a range of permeability values
was selected based on expert judgment. To ensure a sufficiently broad range for this parameter,
the low and high values for permeability were selected to be 0.1 and 10.0 millidarcy (md),
respectively with a mid case value of 1.0 md.
4.4.3 Pressure at abandonment
Mine pressure could be measured by closing a vent and allowing the void area to approach
equilibrium with the pressure in the surrounding unmined coal. Unfortunately, no data have
been published on the pressure within abandoned mines. Proprietary information on shut-in
pressures measured at some abandoned mines, range from essentially atmospheric up to 27
psia. The impact of barometric pressure on abandoned mine methane emissions is described
in Appendix D.
For this model, initial pressures of 17, 20, and 30 psia were used to represent the low, mid-
range, and high values.
4.4.4 Initial Emissions Rates: Ventilation Air Emissions
Ventilation air methane emissions rates from active mines are used as in indicator of a mine's
initial emission rate at time of abandonment. To calculate these initial rates, EPA used
emissions data from underground ventilation systems from active mines, obtained from USBM
and MSHA, based upon averages of quarterly instantaneous readings. The MSHA quarterly
readings for ventilation emissions were assigned a probability distribution, which became the
basis for the initial mine emissions rates used in this inventory.
Some errors are inherent in the measured ventilation emissions data. For example, a degree of
imprecision is introduced into the readings because the measurements are not continuous.
Mutmansky (2000) showed that individual mine emission measurements vary from +10% to
+20%. Additionally, the measurement equipment used by MSHA introduced a bias of +2% to
+16%, resulting in an average of 10% overestimation of annual methane emissions (Mutmansky
and Wang, 2000). The combination of these two measurements and calculation methods result
in the quarterly instantaneous readings ranging from 10% underestimated to 30%
overestimated.
4.5 Sensitivity Analysis for Adsorption Isotherm, Permeability, and
Pressure
A sensitivity analysis was performed to determine if the range of uncertainty for three
parameters (adsorption isotherm, represented by VL and PL; permeability; and pressure at
abandonment) is large enough to significantly affect the emissions inventory. If an individual
parameter does not have a significant effect on the outcome, the mid-case value of the
parameter can be used in the calculations. Conversely, if the sensitivity analysis indicates that
26
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the outcome is significantly affected by the parameter value, then three values of the parameter
(high, medium, and low values) are input into a probability distribution.
Sensitivity analysis calculations are presented in Appendix E. For example, the 1990
emissions for the Central Appalachian basin are much more sensitive to permeability than to
either initial pressure or the adsorption isotherm. Therefore, inventory calculations, use only
mid-case values for initial pressure and the mid-case basin-specific isotherm, but include the
range of values for permeability for the probabilistic analysis.
4.6 Annual Emission Estimations As a Function of Mine Status
Estimating emissions from an abandoned mine for any given year after its closure depends
upon the status of the mine: whether it is open to the atmosphere through one or several vents,
flooded, or partially sealed. Approaches for estimating emissions for each of these types of
mines are described below.
4.6.1 Venting Mines
Emissions from a vented mine are calculated using Equation 4 (page 19). Mine-specific values
are input for the known elapsed time since closure, the average active mine emission rate, and
three sets of decline constants for each basin (a low, mid and high case). These decline curves
are based on the simulated decline curves (see Figure 7) that were generated using the
average adsorption isotherm for the coal basin, an initial pressure of 20 psia, and permeability
values of 0.1, 1.0 and 10.0 md. The calculated emission rates represent the low, mid and high
values, with the low and high values representing an 80% range of certainty.
The time since abandonment is perhaps the most important determinant of mine emissions in
the early years after closure because of the rapid rate of emissions decline.
4.6.2 Flooded Mines
Empirical observations suggest that methane emissions from flooded mines decline rapidly, and
that the flooding process dominates the other factors affecting methane emissions. In fact, the
very rapid methane emissions decline rate for flooded mines suggests that their contribution to
long-term methane emissions will be insignificant.
Based on these considerations, no attempt was made to arrive at a theoretical model of this
process; rather, this approach uses measured data to fit a decline curve equation. An
exponential equation was developed from emissions data measured at eight abandoned mines,
located in two of the five major U.S. coal basins, known to be filling with water. Using a least
squares, curve-fitting algorithm, emissions data were matched to this exponential equation.
There were not enough data to establish basin-specific equations, as was done with the vented
and non-flooding mines. The following equation represents methane emissions from flooded
mines as a function of time:
q = qje ( Dt) (Equation 5)
where:
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q = the gas flow rate at time t in mcf/d
qi = the initial gas flow rate at time zero (t0) in mcf/d
D = the decline rate, 1/yr
t = elapsed time from t0 in years
Figure 10 shows the normalized emission rate compared to the initial emission rate as a
function of time since abandonment. The graph shows measured data from eight flooded
mines, the best-fit curve for those data points (solid line), and the 95% confidence interval
(dashed lines).
Figure 10. Emission model for abandoned flooding mines
4.6.3 Sealed Mines
Seals have an inhibiting effect on the rate of flow of methane into the atmosphere compared to
open-vented mines. The total volume of methane emitted will be the same, but it will occur over
a longer period. Accordingly, this methodology treats the emissions prediction from a sealed
mine in a similar manner to emissions from a vented mine, but using a lower initial emissions
rate that depends on the degree of sealing. The CFD simulator was again used with the
conceptual abandoned mine model to predict the decline curve for inhibited flow. The degree of
sealing, or the percent sealed (Xs), is defined by Equation 6:
Xs = 100 * (1 - qis / qi) (Equation 6)
where:
qis = initial emissions from abandoned mine at time to (after sealing)
qi = emission rate at abandonment prior to sealing
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Figure 11 shows a set of decline curves for several cases with different degrees of sealing for a
mine in the Black Warrior Basin. The emission rates are normalized to the emission rate of the
mine at the time of closure. This graph illustrates how the rate of decline decreases as the
degree of sealing (percent sealed) increases.
Unfortunately, no measurements of diffuse emissions are available to calibrate the sealed mine
emission rate calculations. Therefore, the decline curves shown in Figure 11 were used to
select the high, mid-range, and low values for sealed mine emissions. As 11 illustrates, the
difference in emission rates between an unsealed mine and a 50% sealed mine is insignificant
after a year of closure. However, significant differences are seen in the fractional emission rates
between cases for 50%, 80% and 95% closure achieved for sealed mines. Thus, these values
were selected as the low, mid-range, and high range values for the extent of mine sealing,
respectively.
Figure 11. Emission model for abandoned mines with different degrees of sealing
4.7 Calculating Annual Methane Emissions
To calculate annual methane emissions from abandoned mines, a spreadsheet workbook was
developed for each inventory year, containing data for 364 gassy mines abandoned since 1972.
These mines are estimated to account for 98% of abandoned mine emissions in those years.
For mines of known condition, the emissions are calculated according to the methods described
previously for each type (venting, flooded, or sealed). Probability distributions of total annual
emissions for each mine are summed to provide yearly emissions classified by mine status,
which are then aggregated to determine total annual emissions. Emissions for mines of
unknown status are calculated and incorporated into the total annual emissions inventory as
described below. Example calculations for each type of mine for the year 2000 are shown in
Appendix F.
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4.7.1 Mines of Unknown Status
To calculate emissions for mines whose status is unknown, it was assumed that the population
of these unknown status mines is similar to the population of mines that are known to be sealed,
venting, or flooded. That is, the percentage of sealed, venting, or flooded mines is assumed to
be consistent for all the mines in a given basin. This assumption is reasonable because
abandonment practices such as backfilling shafts and portals are uniform within a given state.
In addition, the hydrogeology and flooding characteristics of mines are similar within most of the
U.S. basins, although they can vary greatly in Central Appalachia.
Three probability density functions of the total emissions from these mines are calculated
assuming that they are either venting, flooding, or sealed. The probability density function for
each status type is then multiplied by the percentage of mines known to be vented, flooded or
sealed within each basin. Table 5 shows the percentage of each known status type for the year
2000 inventory.
Table 5. Distribution of (known) types of abandoned mines
for year 200C
Basin
Sealed %
Venting %
Flooded %
Central Appalachia
25%
26%
49%
Illinois Basin
56%
6%
38%
Northern Appalachia
48%
32%
21%
Warrior Basin
8%
0%
92%
Western Basins
76%
16%
8%
4.7.2 Combining the known status and unknown status inventories
To arrive at a total abandoned mine emission inventory, the distributions from the known and
unknown status mines are summed using Monte Carlo simulation. The distribution for the total
basin value for the year 2000 inventory is shown in Figure 12. From the distributions for each
basin, a probability table can be constructed, as shown in Table 6. The emission distributions of
the individual basins were added together using Monte Carlo simulation to produce the
probability distribution for the combined basins.22 Table 7 converts the emissions inventory for
all abandoned mines in the U.S. from units of cubic feet of methane to metric tons of carbon
dioxide equivalent (C02e).
22 The mean of the total basin distribution will equal the sum of the mean of the basin distributions. The
probability of the 2.5% values of all basins occurring is 0.025s = 1.0E-08, which is why the 2.5% value of
the total distribution is greater than the sum of the 2.5% values of each basin. Accordingly, the 97.5%
value of the total distribution is less than the sum of the 97.5% values of each zone.
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Figure 12. Year 2000 emissions inventory: Total methane emissions from abandoned mines
Distribution for All Basins for Year 2000
X-s-9.302 X ฐ^12.75
2 5% 97.5%
Mean = 11.06
8.0 9.0 10.0 11.0 12.0 13.0 14.0 15.0
Values (Bcf)
Table 6. Year 2000 abandoned mine emissions by coal basin, Bcf
Basin
2.5%
Probability
50%
Probability
97.5%
Probability
Mean
Central Appalachia
3.2
4.5
5.8
4.5
Illinois Basin
0.70
1.0
1.4
1.0
Northern Appalachia
2.2
2.7
3.2
2.7
Warrior Basin
0.27
0.94
1.8
0.97
Western Basins
1.3
1.8
2.5
1.9
Total
9.3
11.1
12.8
11.0
Table 7. Year 2000 Abandoned Mine Methane Emissions, Tonnes of C02e
Basin
2.5%
Probability
50%
Probability
97.5%
Probability
Mean
Central Appalachia
1,297,075
1,810,396
2,339,099
1,813,577
Illinois Basin
283,434
407,555
575,287
414,150
Northern Appalachia
872,747
1,087,689
1,297,761
1,087,483
Warrior Basin
110,154
376,608
723,240
390,591
Western Basins
530,668
745,404
1,008,743
751,990
Total
3,748,640
4,456,451
5,139,777
4,457,789
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5.0 Calibration through Field Measurements
In developing abandoned mine emission estimates, field measurements serve two important
roles. First, they provide empirical data for model inputs. One of the keys to estimating methane
emissions from an abandoned mine is determining the average methane emissions rate from
the mine in order to project future emissions rates. The field measurement program was
designed to determine the measurement interval and duration necessary to accurately calculate
an average methane emission rate from a mine vent. Second, field measurements verify
whether theoretical calculations serve as a reliable proxy for real outcomes or events. In this
case, field measurements tested the accuracy of the mathematical decline curves used for
basin-specific emissions estimates.
Previously, EPA's Office of Research and Development (ORD) initiated a field research
program in the early 1990s (Kirchgessner, et al., 2001), collecting data for 21 abandoned mines
located throughout the Northern and Central Appalachian, Black Warrior, and Illinois basins.
Seven of the mines that produced no methane were documented to be at least partially flooded.
Of the 14 mines that were producing methane, seven were also documented to be at least
partially flooded. This study was limited by the fact that only single or one-day measurements at
each borehole or vent pipe were recorded, and the results were not normalized for average
barometric pressure.
For the present study, EPA conducted a series of field measurements at abandoned mine vent
locations across the U.S., with the goal of measuring actual methane emissions at a
representative sample of mines with vent pipes. Vent pipes are the only feasible sites at an
abandoned mine to accurately measure methane emissions. Of the 393 abandoned mines in
the database, 55 (14%) are known to have vent pipes still in place. Unfortunately, limited
access to the mines precluded measurement of all but seven mines.23 Two of these seven
mines were nearly flooded at the time of the study and produced little methane.
5.1 Field Measurement Methodology
Between November 1998 and February 2000, EPA recorded measurements at five unflooded
abandoned mines to which the agency had access. Measurements were recorded at two
abandoned mines located in Ohio and Virginia continuously for 6-12 hours. EPA also measured
three additional mines located in Illinois and Colorado, recording measurements hourly for 3-4
days, normalizing them to average barometric pressures.
At the five abandoned mines where measurements were conducted, vane anemometers24 and
methane detectors were used to determine gas flow rates and concentrations, respectively.
Several correction factors are necessary to convert anemometer flow and methane
concentration measurements to standard methane emission values, to account for the blocking
factor of the vanes and provide an empirical correction for the velocity profile.25
23 EPA contacted mine operators and landowners that controlled over 50 of the candidate abandoned
mines, but attained access to only seven mines.
24 An anemometer measures the velocity of gas flow through a shaft or vent pipe of a known cross-
sectional area.
25 USBM conducted a series of measurements for pipes smaller than 12 inches in diameter (Garcia, et al.,
1987). Based on their work, method factors for 4-, 6-, and 8-inch diameter pipes are 0.68, 0.71 and 0.78,
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Corrections are also necessary for reporting gas emissions under standard temperature and
pressure (STP) conditions. However, because elevation and temperature conditions at most
mines do not vary greatly, these corrections are generally insignificant. According to the USBM
study, the effects of density changes due to methane concentrations using anemometers
calibrated in air are miniscule.
As part of this study, EPA monitored the effects of barometric pressure on mine venting, since
atmospheric pressure can impact the rate of methane release from abandoned mines. Results
of these measurements are shown in Appendix F.
5.2 Compilation of Data
Figure 13 shows EPA's measurements of abandoned mine methane emissions field data
collected during the two studies (1991-2000). The emission rate decline curves are shown
separately for each coal basin, with the dashed lines indicating the 10 and 90 percentile
emission predictions. The solid lines indicate the 50% emission predictions. As these graphs
illustrate, emission rates from nine of the ten abandoned mines that were measured fall very
close to the predicted mid-case decline rate for their respective basins.
Of the seven flooded mines with no methane emissions investigated, five mines had been
abandoned for less than 10 years, while the remaining two had been abandoned for over 15
years. Of the nine flooded mines that produced methane emissions, six (67%) fell within a 95%
predictive confidence interval of the exponential equation defined in Equation 5 (also shown in
Figure 10). These data suggest that most U.S. mines prone to flooding will become mostly
flooded within 8 years and after 14 years no longer have any measurable methane emissions.
Based on this assumption and until additional data can be collected, this methodology uses an
average U.S. decline rate for all flooding mines.
respectively. The National Coal Board of the United Kingdom had previously developed method factors
for correcting vane anemometer measurements for 12 to 30 inch diameter pipes (Northover, 1957).
Furthermore, results indicated that for pipes larger than 12 inches in diameter, a method factor of 0.85 is
sufficient for conversion purposes.
US Environmental Protection Agency
33
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Figure 13. Vented emissions from unflooded, abandoned mines in U.S. coal basins
Central Appalachian Basin Decline Curves for Active Vents
0.90
0.80
d)
0.70
ฃ
0.60
TO
"E
0.50
o
0.40
o
0.30
F
Li.
0.20
0.10
' " "High
Mid
' " "Low
A Measured
15
Years
0.90
0.80
Illinois Basin Decline Curves for Active Vents
15
Years
Black Warrior Basin Decline Curves for Active Vents
Northern Appalachian Basin Decline Curves for Active Vents
0.90
0.80
0.70
0.60
0.50
0.40
0.30
0.20
0.10
t
i
V
*
" " "High
Mid
" " "Low
A Measured
%
X
s
v
*
I
1
1
I
f
I
\
*
ซ
ฆ
ฆ
ฆ
I
I
1
1
1
1
15
Years
0.90
0.80
0.70
-2 0.60
Ql
75 0.50
0.40
'S
.1 ฐ-30
"u
ซ 0.20
u_
0.10
0.00
ฆ ฆ 'High
Mid
" ฆ 'Low
^ Measured
15 20
Years
Western Basins Decline Curves for Active Vents
0.90
0.80
0.70
0.60
0.50
0.40
0.30
0.20
0.10
" " "High
Mid
' " "Low
^ Measured
15
Years
34
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6.0 Estimating Emissions from Mines Closed Before 1972
For mines abandoned in or after 1972, data are readily available, including comprehensive
active mine emissions data, date of abandonment, number of gassy mines, mine status, and
even coal production on a state and county basis. In contrast, most of the information needed
to calculate emissions from abandoned mines is largely unknown for mines closed before
1972.
Emissions from the pre-1972 mines may be characterized using the dimensionless decline
curves described in this report. Key data needed to use a modified version of the post-1971
methodology for the pre-1972 mines include the number of suspected gassy mine closures, the
dates of closure, and the emissions rate at closure. For this report, EPA makes the reasonable
assumption that pre-1972 mines are governed by the same physical, geologic and hydrologic
constraints that apply to 1971, 1973, and 1975 coal mine datasets. The major reason for this is
that most mining methods at that time were still room and pillar mining.
To extrapolate emissions estimates for mines abandoned before 1972, EPA compiled
information from several USBM studies (1971, 1973, and 1975). In addition, EPA obtained
statewide mine closure dates for Colorado and Illinois throughout the 20th century, and used
this information for establishing national trends. EPA determined that most coal mine
emissions in the U.S. originate in relatively small geographic areas. For example, during the
1970s, nearly 80% of CMM emissions came from seventeen counties in seven states.
Based on these data, EPA applied basin-specific decline curve equations to 145 gassy coal
mines estimated to have closed between 1920 and 1971 in the U.S, representing 78% of the
active mine emissions during that time. Mines abandoned before 1972 are estimated to have
contributed 1.7 Bcf methane emissions to the 1990 abandoned mine emissions inventory.
6.1 Historical Trends in Gassy Mine Emissions
The gassy mine population in the U.S. is geographically limited to specific coal seams within a
few coal basins. The population of gassy mines (those with emissions >100 mcfd) in the U.S.
has remained stable since 1971, numbering between 100-200 mines. Based on several
historical observations, it is reasonable to assume that there were fewer gassy mines during
the early days of mining:
1) Historic trends in mine size indicate exponential growth in recent years. A USBM
study has shown that the average mine size in 1985 was one half of those in 1995.
Thus, extrapolating backward from this trend suggests that pre-1972 mine sizes
would be much smaller than those in 1985 would.
2) Many of the gassy mines closed after 1972 had operated since early in the 20th
century, particularly in the Pittsburgh coal seam, where the largest concentration of
gassy mines in the U.S. is located.
3) Coal mines operating in coal seams at depths up to 2000 feet in Virginia (e.g.,
Pocahontas #3) and Alabama (Mary Lee), which produced a significant portion of the
U.S. emissions in the 1970s, and even today, only began operating in the 1940s.
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4) Prior to the 1970's, all underground mining in the U.S. was through room and pillar
operations. Longwall production, associated with high gas production, was not
introduced widely until the 1970s. These historic production trends created smaller
mine voids that exposed less coal and other gassy strata, therefore probably emitting
less gas.
5) Historical records indicate that prior to 1920, there were far fewer gassy coal mines
(by current standards) operating at only a fraction of the production rates practiced
after 1920.
EPA estimates that emissions from mines closed before 1920 would emit less than 0.1 Bcf of
methane during 1990, making it an insignificant contribution to the 1990 emissions inventory
baseline. Thus, EPA's estimate of abandoned mine emissions in this inventory is based only on
mines that were closed since 1920.
6.2 Estimating the Locations of Gassy Mines Abandoned Before 1972
The geographic distribution of active mine methane emissions during the 1970s is assumed to
represent emissions from mines abandoned prior to 1972. The primary justification for this
assumption is that the room and pillar mining methods used in 1971 were similar to those used
in previous decades.
The oldest, most comprehensive dataset of underground coal mine emissions that EPA has
found is a 1972 USBM Circular listing emissions for all mines in the U.S. (>100 mcfd) during
1971 (Irani, 1972). Emissions from these coal mines originated in 64 counties located in eleven
states. Of these, the nine states shown in Figure 14 made up 95 - 99% of the total methane
emissions from active coal mines in 1971.
Figure 14. Active Coal Mine Methane Emissions from Nine States, 1971 - 1980
~KENTUCKY
ฆ OHIO
~ UTAH
~ COLO
ฆ ALABAMA
ฆ ILLINOIS
ฆ VIRGINIA
ฆ PENN
~ SO WVIR
~ NOWVIR
36
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Seven states (Pennsylvania, West Virginia, Virginia, Alabama, Illinois, Colorado, and Utah)
produced over 90% of the total U.S. active mine emissions from 1971-1980.
The Northern Appalachian basin states were by far the largest contributors during the
1970s, emitting approximately 50% of all U.S. emissions. Pennsylvania and northern West
Virginia are the principal representatives of the Northern Appalachian basin. 26
Central Appalachian Basin states contributed approximately 25% of U.S. mining emissions
during the 1970s. Southern West Virginia and Virginia are the principal contributors.27
The next highest group of producing states, Illinois, Alabama, and Colorado, each
contributed significantly to the U.S. total mining emissions.
Utah and Colorado represent the Western Basins.
U.S. coal mine emissions are even more concentrated than these numbers suggest. 78% of all
U.S. coal mine emissions originated from only 17 counties within seven states. Other counties
each accounted for less than 1% of the national emissions. Because of the relatively high
uncertainty associated with the pre-1972 data, identifying more mines would only reduce the
uncertainty incrementally. Therefore, EPA used these 17 counties as a representative sample
of coal mines in all five major U.S. coal basins that constituted the majority of coal production
from gassy underground mines. Emissions from these 17 counties have been scaled to
account for emissions from all U.S. mines.28
EPA compiled a list of 145 (suspected) gassy mines located in these 17 counties that had
closed prior to 1972. Table 8 lists the counties and the number of mines estimated to be in
each county.29
26 Emissions from abandoned mines in Ohio constitute 2% of the total emissions from this basin and are
considered negligible in comparison.
27 Kentucky mine emissions were only 2% of total emissions; Kentucky's emissions are divided between
the Central Appalachian and Illinois Basins. Kentucky was therefore considered negligible in comparison.
28 Since these mines represent 78% of the total emissions, they are multiplied by a scaling factor of 1.22
to account for all U.S. emissions.
oq
In Colorado, Utah, Illinois, Virginia, and Alabama, EPA obtained the information directly from state
agencies or from old state publications. In fact, Colorado and Illinois had databases that included mine
closure dates since the late 1800s. For Pennsylvania and West Virginia, the number of mines was
estimated using maps showing all the mines that had once operated.
US Environmental Protection Agency
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Table 8. Gassy Abandoned Mines Located in 17 Counties
County
State
Number of Mines
Franklin
IL
23
Pitkin
CO
18
Buchanan
VA
17
Raleigh
WV
15
McDowell
WV
12
Cambria
PA
12
Jefferson
AL
9
Washington
PA
9
Indiana
PA
7
Las Animas
CO
7
Marion
WV
4
Marshall
WV
3
Carbon
UT
3
Monongalia
WV
2
Greene
PA
2
Tuscaloosa
AL
1
Jefferson
IL
1
TOTAL
145
6.3 Estimating Date of Abandonment for Pre-1972 Mines
EPA was able to estimate the date of abandonment for mines closed prior to 1972 based on
extrapolation from historical records of gassy mine closures. While researching historical coal
mine information at the state level, EPA found that the states of Illinois and Colorado had
compiled historical coal mine opening and closure dates for each county dating back to the late
1800s. From these data, a histogram was developed of Illinois and Colorado mine closures in
counties known to have gassy mines. This subset of mines represents 34% of the total
number of pre-1972, gassy mines and 30% of the total abandoned mine emissions.
As Figure 15 illustrates, mine closures in the two states show consistent patterns since 1910,
including an increased number of mine closures following World Wars I and II. Based on a
reasonable assumption that mine closures in these two states followed national trends, EPA
used the average to estimate the approximate closure dates (decade) for mines in all 17
counties. The mid-decade date (e.g. 6/30/1925) was selected as the nominal "closure date" for
mines closed in a given decade.30
on
This selection of mid-decadal closure has a minimal impact on the estimated emissions rate. For
example, the incremental change in emission rates caused by adjusting the nominal closure date by up to
4 years will be less than 1% because of the extended time since abandonment (e.g., 20 to 70 years for
the 1990 emissions inventory).
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Figure 15. Mine Closures in Colorado and Illinois, 1910 - 1960
~ Illinois Mine Closures
ฆ Colorado Mine Closures
II Average
1910s 1920s 1930s 1940s 1950s 1960s
Decade
6.4 Estimating Initial Emission Rates for Pre-1972 Mines
Once the number of abandoned mines and their approximate closure dates have been
established, the next step is to determine the mine's initial emission rate at the time of
abandonment.
EPA conducted a statistical analysis of all the active mine emissions originating in the 17
counties for the years 1971, 1973, and 1975, based on data from the USBM circulars. The
data were aggregated to the state level in order to use larger samples of mine data.31 Table 9
summarizes the distributions for the seven states.
There were three key steps in determining the distribution of initial methane emission rates:
1) 100 mcfd was defined as the minimum emissions rate.
2) The maximum emission rate for each state was based on the USBM data sets.
3) Distribution functions were fitted to the datasets to calculate the probability distribution
of the statewide emission inventory. In most cases, the best fit was either a log-normal
or an inverse Gaussian distribution; however, in some cases other distributions were
found to be better fits. Figure 16 illustrates a function that was fitted to the northern
West Virginia dataset using a "log-logistic" distribution.
vJU /o
25%
TJ
0
5 20%
0
15%
0
a.
10%
5%
no/.
31 West Virginia was divided into two "states" because its mines occur in two coal basins.
US Environmental Protection Agency
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Table 9. Distributions of Methane Emissions from USBM Datasets from 1971-1975
STATE
AL |
I VA|
SWV
lUT |
CO
IL
I PA |
N WV
Minimum Emission
Rate (mmcfd)
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
Mean of Data
Distribution (mmcfd)
1.0
1.1
0.6
0.4
1.0
0.7
1.0
2.6
Maximum Emission
Rate (mmcfd)
6.1
8.5
5.0
1.9
3.5
2.4
6.0
12.2
Figure 16. Active mine emissions for northern West Virginia
0.40
-2 0 2 4 6 8 10 12 14
Methane Emissions, mmcf/d
6.5 Calculating Total Abandoned Mine Methane Emissions for Mines
Closed Prior to 1972
The initial emission rate distributions for mines in these gassy counties were used as inputs for
the post-1972 basin-specific decline equations. Emissions for each inventory year were
calculated for mines closed during each of the five decades (1920s through 1960s) and then
summed. Because it is unknown whether the mines are sealed or venting, a conservative
approach assumes that the mines could still be venting.
Based upon the presumed similarity of hydrologic conditions for mines abandoned before and
after 1972, a basin-specific factor was used to account for flooding. All mines abandoned prior
to 1972 that had flooded would have been closed for at least 19 years by 1990 and,
presumably, would have completely flooded out by then. To derive a net, or relative, emissions
number, emissions were reduced by the percentage of flooding mines in each of the basins
(summarized in Table 3).
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Table 10 shows the emissions contribution for all mines closed in each decade to the 1990
inventory of total abandoned mine emissions.
Table 10. Contribution of mines closed from 1920-1969 (by decade) to the 1990 inventory
Total
emissions
from
mines
closed,
1920-1969
Decade of mine closure
1920s
1930s
1940s
1950s
1960s
Mine methane emissions in
1990 (Bcf)
0.258
0.277
0.279
0.611
0.286
1.712
Relative contribution of pre-
1970 closures to 1990
emissions inventory
15.1%
16.2%
16.3%
35.7%
16.7%
100.0%
The annual emissions inventory totals for 1990 - 2002 calculated in this report (Section 7)
include emissions from the 145 mines abandoned prior to 1972. The pre-1972 mines
contributed 1.7 Bcf (0.7 million tonnes C02e) to the 1990 emissions inventory (20% of the
total), and declined to 1.4 Bcf (0.6 million tonnes C02e) by the year 2000 (10% of the total).
Figure 17 shows the emissions contribution for each coal basin from mines abandoned prior to
1972 for the 1990-2002 inventories The range of uncertainty associated with the pre-1972
emissions analysis is discussed in Section 7.4.
Figure 17. Emissions contribution from mines abandoned prior to 1972
to the 1990-2002 inventories
C*
ซ 1.20-
1.00-
w
w
Q)
C
(0
-C
"q> 0.60 -
II
ฆ Illinois
ฆ Western
Basins
~ Warrior
Basin
~ Northern
Appl
~ Central
Appl
1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002
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7.0 Results of the 1990 - 2002 Abandoned Mine Methane Emissions
Inventory
7.1 1990 Baseline Inventory
For the 1990 baseline year, the abandoned mines emissions inventory was based on emissions
from 145 suspected gassy mines that closed from 1920 - 1971 (estimated as described in the
previous section) as well as 249 mines closed after 1972 that are known to have active mine
methane ventilation emission rates greater than 100 mcfd at the time of abandonment.
As described previously, EPA used estimated initial emission rates (based on MSHA reports for
post-1972 mines), time of abandonment, and basin-specific decline curves to calculate annual
emissions for each mine in the database. Because coal mine degasification data is not available
for years prior to 1990, the estimated initial emission rates reflect ventilation emissions only.
The gassy mines for which emissions were calculated are assumed to account for 98% of total
national emissions. Therefore, to account for total post-1971 abandoned mine emissions, this
estimate was multiplied by 1.02. EPA estimates that 1990 methane emissions from post-1971
U.S. abandoned coal mines range from 5.6 to 7.9 Bcf (2.3 to 3.2 million tonnes C02e), with a
median value of 6.6 Bcf (2.7 million tonnes C02e) at the 95% confidence level.
7.2 Emissions for 1991 -2002
To determine the post-1971 abandoned mine emissions for 1991 through 2002, EPA used
several sources of information. Using MSHA data and EPA annual coal mine emissions
inventory data, EPA identified and calculated the ventilation emissions and degasification
volumes from 144 mines that were closed from 1991-2002 (Figure 18).32 Table 11 shows the
number of gassy mines closed each year by coal basin.
For nearly all mines closed between 1990 and 2002, the initial methane emission rate at time of
abandonment reflects ventilation emissions only. However, for 14 mines that closed between
1992 and 2002, degasification data were available, so the initial emissions rate for these 14
mines includes the total methane liberation rate (ventilation plus degasification).
Table 11. Cumulative Number of Gassy Coal Mines Abandoned Annually, 1990 - 2002
Coal Basin
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
Central Appalachian
105
108
114
119
131
143
157
162
164
166
168
176
180
Illinois Basin
35
37
38
40
44
47
53
56
59
59
61
62
64
Northern Appalachian
60
64
68
74
80
82
94
97
97
97
98
99
100
Black Warrior
9
9
9
10
10
10
11
12
13
14
14
14
14
Western U.S.
21
22
23
23
23
25
27
28
30
31
33
35
35
U. S. Total
230
240
252
266
288
306
342
355
363
367
374
386
393
32 An additional 17 mines closed from 1991-2002, but they were reopened for coal mining activity.
Emissions from these mines were never added to the abandoned mine database.
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Figure 18. Gassy Coal Mines Abandoned Annually (1990-2002)
Year
7.3 Inventory Adjustments for 1990 - 2002 Methane Recovery Projects
Once the total methane emissions for 1990 - 2002 were calculated, they were adjusted to reflect
abandoned mine methane emissions that are recovered and used. No known or reported
abandoned mine methane recovery projects were in operation from 1990 - 1992, and therefore
emissions inventories for these years have not been adjusted.
Conceptually, estimating annual emissions for abandoned mines with recovery projects
consists of two key steps: (1) calculating the estimated emission rate without the recovery
project, and (2) subtracting the project-specific emissions estimate for individual mines as
appropriate.33 The total annual "avoided" emissions are determined by subtracting the total
project-specific emissions from the annual total that was calculated assuming no recovery
projects.
Table 12 shows the number of abandoned mine methane recovery projects that were operating
from 1990-2002, and the emissions avoided as a consequence of those projects. It is important
to note that the emissions avoided values do not represent the amount of gas produced from
each project, but rather the amount of emissions that would have occurred had the project not
been in place. Recovery projects often rely on blowers and other equipment that may pull more
methane out of the mine than likely would be vented naturally.34 Therefore, some of the CMM
captured at an abandoned mine recovery project is not always considered an avoided emission.
In actuality, the emissions avoided were integrated as part of the Monte Carlo simulation, rather than
subtracted at the end of the calculation.
34 For this analysis, it is assumed that the negative pressure applied to the mine void to facilitate methane
recovery would negate any additional diffuse emissions from the mine.
US Environmental Protection Agency
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Furthermore, EPA assumes that the projects produce gas equal to or greater than the
emissions avoided value; therefore, the presence of the project reduces the mine emissions to
zero.35
Table 12. Abandoned Mine Methane Recovery Projects
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
# of Recovery Projects
Emissions Avoided (mmcf)
0
0
0
1
2
3
4
11
13
14
15
17
21
0
0
0
34
190
779
1,214
2,899
3,244
2,975
2,587
2,487
2,625
7.3.1 Summary of U.S. Emissions
Figure 19 shows that gross abandoned mine emissions ranged from 8.4 to 16.8 Bcf during the
decade, varying by as much as 2 Bcf from year to year. Fluctuations were due to the number of
mines closed during a given year as well as the magnitude of the emissions from those mines
when active. Abandoned mine emissions peaked in 1996 due to the large number of mine
closures from 1994 to 1996 (76 gassy mines closed during this three-year period). Abandoned
mine emissions have declined since 1996, due primarily to the decreased number of closures;
fewer than twelve gassy mine closures occurred during each of the years from 1998-2002. The
abandoned mine emissions estimate for the year 2002 had declined to 12.9 Bcf (5.2 million
tonnes C02e, excluding recovery projects), compared to a peak of nearly 16.7 Bcf (6.7 million
tonnes C02e) in 1996. Figure 20 shows the net emissions in units of C02e and Gg of methane.
Table 13 summarizes the abandoned coal mine emissions for each basin from 1990 to 2002.
The majority of abandoned mine emissions originate from mines located in the Central and
Northern Appalachian basins. On average, mines abandoned in these two basins make up 72%
of the mines in the database and between 65-75% of the U.S. abandoned mine emissions.
Figure 21 shows that the Central Appalachian basin is by far the largest contributor to the post-
1971 abandoned mines emission inventory. Interestingly, the overall ranking of the basins
differed only slightly up until 1997, but since that time emissions contributions from the Central
and Northern Appalachian basins have declined, while emissions from the Western and Warrior
basins have risen. This change reflects the geographical shift in U.S. coal production away from
the Appalachian basin.
The only exception known is the Blue Creek Mine project, which was an active mine project until 1999.
It produced only 0.2bcf in 2002, but the emissions avoided potential was 0.6 Bcf. The reason is that, for
now, the recovery project is simply a continuation of the small number of active mine gas wells that were
operating prior to closure.
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Figure 19. Abandoned Mine Methane Emissions Estimate for 1990-2002
14.0 -
.2 12.0
t/i
w
E
m 10.0-
0) c
^ O
m
ai 8.0 -
2.0 -
0.0 -
~ Emission Avoided
~ Net Emissions (Bcf)
1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002
Figure 20. Net Abandoned Mine Emissions (C02e and Gg Methane)
~ 4.0-
v
TO wT
> c
IT H
m ฃ 3.0 -
0) ฃ
"O d)
P
o o
1990 1991 1992 1993
1994 1995 1996 1997
Year
2000 2001 2002
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Table 13. Summary of Abandoned Coal Mine Emissions by Basin (Bcf/yr)
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
Central Appalachian
Basin
Methane Liberated
3.12
3.51
4.23
4.57
5.17
6.17
7.06
6.87
6.47
5.81
5.21
5.05
5.08
Emissions Avoided
0.00
0.00
0.00
0.00
0.16
0.75
0.63
0.96
1.49
1.27
1.02
0.95
0.89
Net Emissions (Bcf)
3.12
3.51
4.23
4.57
5.01
5.42
6.43
5.91
4.98
4.54
4.19
4.11
4.19
Illinois Basin
Methane Liberated
0.71
0.70
0.99
0.93
1.12
1.27
1.69
1.81
1.63
1.46
1.30
1.29
1.51
Emissions Avoided
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.06
0.05
0.04
0.04
0.26
Net Emissions (Bcf)
0.71
0.70
0.99
0.93
1.12
1.27
1.69
1.81
1.57
1.41
1.25
1.24
1.25
Northern
Appalachian Basin
Methane Liberated
3.09
2.85
2.83
3.63
3.63
4.43
5.34
5.79
4.53
3.82
3.41
3.37
3.28
Emissions Avoided
0.00
0.00
0.00
0.03
0.03
0.03
0.59
1.47
1.30
1.31
1.18
1.08
1.00
Net Emissions (Bcf)
3.09
2.85
2.83
3.59
3.59
4.40
4.75
4.32
3.23
2.51
2.22
2.28
2.28
Warrior Basin
Methane Liberated
0.19
0.11
0.07
0.05
0.03
0.06
0.14
0.38
0.49
0.77
1.17
0.89
0.77
Emissions Avoided
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.02
0.12
0.20
Net Emissions (Bcf)
0.19
0.11
0.07
0.05
0.03
0.06
0.14
0.38
0.49
0.77
1.15
0.77
0.57
Western Basins
Methane Liberated
1.34
1.35
1.40
1.56
1.50
1.48
1.77
1.90
2.17
2.13
2.51
2.32
2.21
Emissions Avoided
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.47
0.40
0.35
0.32
0.29
0.27
Net Emissions (Bcf)
1.34
1.35
1.40
1.56
1.50
1.48
1.77
1.44
1.77
1.78
2.19
2.03
1.94
U. S. Total
Methane Liberated
8.44
8.53
9.53
10.74
11.46
13.40
15.99
16.75
15.28
13.98
13.59
12.93
12.86
Emissions Avoided
0.00
0.00
0.00
0.03
0.19
0.78
1.21
2.90
3.24
2.97
2.59
2.49
2.62
Net Emissions (Bcf)
8.44
8.53
9.53
10.71
11.27
12.62
14.78
13.85
12.04
11.00
11.00
10.44
10.23
Figure 21. Abandoned Coal Mine Emissions from U.S. Coal Basins, 1990 - 2002
Central Appl
Northern Appl
-ฆ-Western Basins
-ฆ-Illinois Basin
--Warrior Basin
ซ E 30%
3 LU
ฆ2 .=
O
ฆD
V
c
o
ฆD
c
re
n
<
20%
1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
Year
7.4 Key Assumptions and Areas of Uncertainty
Uncertainties in the emission inventory results from data gaps, methodology, and key
assumptions made in developing an estimate of abandoned mine emissions. This section
identifies and attempts to quantify these uncertainties.
Four important areas of uncertainty described in this report could significantly impact the
emissions inventory calculations:
46
US Environmental Protection Agency
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1) Limited data on mines closed before 1972
2) Biases in U.S. mine ventilation data
3) Lack of data on mine drainage before 1990
4) Exclusion of surface mine emissions.
Each of these key areas of uncertainty is discussed briefly below.
7.4.1 Limited data on mines abandoned before 1972
The limitations on data available for mines abandoned prior to 1972 have been dealt with in this
emissions inventory using the methodology described in Section 6.
7.4.2 Biases in U.S. mine ventilation data
U.S. mine ventilation data, as received from MSHA, has inherent limitations because it is
reported in broad classification ranges. In addition, research has suggested that the MSHA
data is inherently biased to overestimate ventilation emissions, with estimated error of +30% to
- 10% (Mutmansky and Wang 2000).
7.4.3 Lack of data on degasification prior to 1990
Comprehensive data on degasification systems prior to 1990 are not available. Therefore,
EPA's estimates of pre-1990 mine methane emissions includes only mine ventilation emissions.
For mines closed since 1990, EPA compiled estimates of methane liberated using
degasification systems in addition to ventilation. For mines using degasification systems for
which no data are available, EPA assigned default recovery efficiencies.
Because methane liberated from degasification systems prior to 1990 was not incorporated in
this inventory, the total active mine emissions estimate used from 1972-1989 for this inventory
may be underestimated by approximately 6.5%. This figure is based on USBM's estimate for
1973, that total coal mine ventilation emissions accounted for 93.5% of the total methane
liberated from U.S. coal mines (Irani, et al, 1974).
However, the overall impact on the emissions inventory of not accounting for degasification
systems may be less than 6.5%, since many of the mines are suspected to be flooded or
sealed, which would dramatically decrease their emissions. Abandoned mine emissions rapidly
decline during the early years after abandonment, further mitigating the impact of potential
marginal increases in the initial emissions rate.
7.4.4 Exclusion of surface mine emissions
Surface mines are included in the U.S. inventory of active coal mine methane emissions, but
have not been included in this abandoned mine emissions inventory. In 2002, active surface
mines emitted 25.4 Bcf (10.2 million tonnes of C02), or 19% of total U.S. coal mine methane
emissions. Although some abandoned surface mines may contribute methane emissions, it is
assumed that they constitute a negligible share of abandoned mine emissions. The coal seams
mined at the surface are shallow, and therefore less likely to have a high gas content. In
US Environmental Protection Agency
47
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addition, regulations often require reclamation of the mined void, which for surface mining may
involve leveling and covering the mined-out area.
7.4.5 Total estimated uncertainty range
These key uncertainties, as well as those associated with coal permeability, mine seal
effectiveness, abandonment status, and the Monte Carlo simulation36 result in an estimated
range of certainty of + 20%. Figure 22 shows the high and low estimate range within a 95%
confidence interval for net emissions. For each of the years in this inventory, the estimated
mean-value emissions varied from the 50% case (the most likely case) by only +3%. The 50%
case was developed from an uncertainty analysis with a 95% confidence interval. Statistically,
the closeness of the calculated mean to the probability distribution analysis results indicates that
the sample population of gassy mines used for the analysis has a normal distribution.
The IPCC considers an uncertainty level of + 20% to 55% acceptable for Tier 2 coal mine
methane emissions inventories (IPCC, 1997). When compared to other IPCC Tier 2 emission
inventories, the methodology used in this report produced a fairly narrow range of values. The
range is relatively narrow in part because mine-specific data (required for a Tier 3 inventory) is
used. The largest degree of uncertainty is associated with abandoned mines of unknown status,
(which account for 36% of the mines), which have an overall uncertainty of + 60%.
Figure 22. Range of Abandoned Mine Methane Emissions (net) Estimates for 1990-2002
36 Uncertainties associated with the Monte Carlo simulation are described in Appendix B.
48 US Environmental Protection Agency
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7.5 Projecting future emissions from abandoned coal mines
The total methane liberated from active underground mines continues to decrease for U.S.
mines.37 Yet active mine emissions (and therefore initial emission rates for mines at time of
abandonment) continue to increase from individual mines. As more mines incorporate longwall
mining techniques, ventilation equipment becomes more sophisticated, and mining depths
increase, the emissions from active coal mines are likely to continue to increase. Figure 23
shows that the per-mine average ventilation emissions for gassy coal mines that were closed
from 1991-1999 nearly doubled from the 1990 inventory. Furthermore, average ventilation
emissions for currently operating mines (with emissions greater than 100 mcfd) are more than
double that of the active-mine emissions for mines closed from 1991-1999.
Although the specific emissions of active gassy mines in the U.S. are increasing, the actual
number of active mines has decreased. For example, fewer than 125 gassy mines have been
operating in the U.S. since 1995 (EPA, 2002), and only 95 gassy mines were active in 2002.
Underground coal production in the U.S. has been declining since 1997, with a corresponding
decrease in the associated mine methane emissions. As a result of these trends, the downward
trend in total abandoned mine emissions since 1996, shown in Figure 22, is expected continue
as fewer gassy mines remain to close.
Figure 23. Trends in Coal Mine Emissions from Active Gassy U.S. Mines
a)
c
(0
-C
a>
Average U.S. Coal Mine Emissions for
Mines >100 mcfd
2 2,500
o
~ 2,000
c
| 1.500
tfl
E 1,000
111
500
2,250
1,440
750
Mines Closed Mines Closed
1990 or 1991-1999
before
Mines
Currently
Operating
(2002 Data)
The methodology for creating this inventory allows estimation of future abandoned mine
emissions, by coupling predicted decline curves with presumed closure dates for currently
active mines. Abandoned mine emissions could then be forecasted for any given year. In
37
According to Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990 - 2000, the methane
liberated from underground mines decreased by 13.5 million tonnes of C02 equivalent, from 67.6 million
tonnes to 51.1 million tonnes. This equates to a reduction of 32.4 Bcf or slightly less than 1 Bm3.
US Environmental Protection Agency
49
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addition, this estimation methodology allows coal mining regions with high emissions or
emission anomalies to be identified. Most importantly, this methodology may be used to
determine the effect that abandoned mine emissions may have on the U.S. Greenhouse Gas
Inventory in future years.
50
US Environmental Protection Agency
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8.0 Conclusions
EPA's Inventory of U.S. Greenhouse Gas Emissions and Sinks includes methane emission
estimates for underground mining, surface mining, and post-mining activities at active mines.38
The emissions estimation methodology and results described in this report enables the
quantification of emissions from abandoned mines, for which there is currently no recognized
methodology.
This methodology has been designed to produce robust estimates and to incorporate new data
as available. It allows annual emissions inventories to be readily updated, because it is flexible
enough to allow additional mines to be included in the inventory as information becomes
available. In addition, the method can be used to predict future emissions from existing
underground coal mines for any given year. Furthermore, the mine database is thorough and
representative of the majority of methane emissions from abandoned mines in the U.S. Finally,
the method requires minimal inputs: active mine emissions, mine closure dates, and coal
adsorption isotherm data. Thus, it could potentially be used to estimate coal mine methane
emissions in other nations.
The methodology and emission estimates presented in this report are the first attempt to
systematically quantify emissions from abandoned coal mines in the U.S.. EPA will continue to
refine the methodology to quantify abandoned mine emissions with greater certainty. Important
next steps include:
Researching additional sources for data on mines closing before 1972 to further refine
estimates for emissions from the pre-1972 mines
Developing more accurate estimates of the percentage of gas liberated by drainage
systems before 1990
Identifying all abandoned mine methane recovery projects in the U.S. that operated from
1990 to the present and obtaining data on emission reductions
Considering the results of any additional work being conducted with regard to the
uncertainty in MSHA ventilation emission data
Obtaining more field data to verify methodological results or serve as the basis for
refinements to the methodology
Developing methodologies to set baselines and calculate emissions avoided on a
project-specific basis
Incorporating the abandoned mine emissions into the U.S. Inventory of Greenhouse Gas
Emissions and Sinks
Evaluating the method for its application to other countries, and if not, developing a more
universal methodology
38 Post-mining emissions are emissions from coal during storage (e.g. in piles) and transportation (e.g.
while in train cars) prior to the coal's usage as fuel.
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Several other countries have also begun to quantify their abandoned mine emissions. As EPA
continues refining its methodology and estimates, we welcome comments and suggestions on
this report and the methodology, as there are many potential gains from critical input and
coordination.
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9.0 References
IPCC/UNEP/OECD/IEA, 1997, Revised 1996 IPCC Guidelines for National Greenhouse Gas
Inventories, Paris: Intergovernmental Panel on Climate Change; J. T. Houghton, L.G. Meiro
Filho, B.A. Callander, N. Harris, A. Kattenberg, and K. Maskell, eds.; Cambridge University
Press, Cambridge, U.K.
Fetkovich, M.J., Fetkovich, E. J., and Fetkovich, M.D.: "Useful Concepts for Decline Curve
Forecasting, Reserve Estimation and Analysis," paper SPE 28628 presented at the 1994 SPE
69th Annual Technical Conference and Exhibition
Gan, H., Nandi, S.P., and Walker, P.L. Jr., 1972, Nature of the Porosity in American Coals:
Fuel, v. 51, p. 272-277
Garcia, Fred, and J. Cervik, 1987, Method Factors for Anemometer Measurement at Pipe
Outlets, U.S. Bureau of Mines, Rl 9061, Pittsburgh, PA.
Garcia, Fred, Frank E. McCall, and Michael A. Trevits, 1994, Proceedings of the 7th U.S. Mine
Ventilation Symposium, A Case Study of Methane Gas Migration Through Sealed Mine Gob
Into Active Mine Workings, U.S. Bureau of Mines, Pittsburgh, PA.
Gas Research Institute, 1996, A Guide To Coalbed Methane Reservoir Engineering, GRI
Reference No.GRI-94/0397, Chicago, IL.
Grau, Roy H. Ill, and John C. LaScola, 1981, Methane Emissions From U.S. Coal Mines in
1980, U.S. Bureau of Mines, Information Circular 8987, Pittsburgh, PA.
Irani, M. C., E. D. Thimons, T. G. Bobick, Maurice Deul, and M. G. Zabetakis, 1972, Methane
Emissions From U.S. Coal Mines, A Survey, U.S. Bureau of Mines, Information Circular 8558,
Pittsburgh, PA.
Irani, M. C., P. W. Jeran, and Maurice Deul, 1974, Methane Emissions From U.S. Coal Mines in
1973, A Survey, (A Supplement to IC 8558), U.S. Bureau of Mines, Information Circular 8659,
Pittsburgh, PA.
Irani, M. C., J. H. Jansky, P. W. Jeran, and G. L. Hassett, 1977, Methane Emissions From U.S.
Coal Mines in 1975, A Survey, (A Supplement to ICs 8558 and 8659), U.S. Bureau of Mines,
Information Circular 8733, Pittsburgh, PA.
Masemore, S., S. Piccot, E. Ringler, and W. P. Diamond, 1996, Evaluation and Analysis of Gas
Content and Coal Properties of Major Coal Bearing Regions of the United States, EPA-600/R-
96-065, Washington, D.C.
Mutmansky, Jan M., and Yanbei Wang, 2000, Analysis of Potential Errors in Determination of
Coal Mine Annual Methane Emissions, Pennsylvania State University, Department of Energy
and Geo-Environmental Engineering, University Park, PA.
US Environmental Protection Agency
53
-------
Kirchgessner, D.A., Piccot, S. D., and Masemore, S.S., 2001, An Improved Inventory of
Methane Emissions from Coal Mining in the U.S., Journal of Air and Waste Management
Association, Volume 50:1904-1919, March 2001.
Northover, E.W., Vane Anemometer Measurements of the Quantity of Air Entering and Leaving
Auxiliary Systems, National Coal Board, M.R.E. Rep. 2061, March 1957, London.
Seidle, J.P. and L.E. Arri, "Use of Conventional Reservoir Models for Coalbed Methane
Simulation," Paper CIM/SPE 90-118, presented at the CIM/SPE International Technical
Meeting, Calgary, Alberta (June 10-13, 1990)
Slider, H.C. Worldwide Practical Petroleum Reservoir Engineering Methodsi PennWell
Publishing Company, Tulsa, Oklahoma, 1983, (P. 45)
Soot, Peet, Northwest Fuel Development, Inc., Various Emissions Databases and Field
Measurement Results.
U.S. Environmental Protection Agency, 1990, Methane Emissions From Coal Mining, EPA
400/9-90/008, Washington D.C.
U.S. Environmental Protection Agency, 2002, Greenhouse Gas Emissions and Sinks: 1990-
2001, EPA 236-R-00-001, Washington D.C.
U.S. Department of Labor, 2000, Mine Safety and Health Administration, Coal Mine Safety and
Health, Coal MIS Data Base, Arlington, WV
Yee, D., Seidle, J.P. and Hanson, W.B. "Gas Sorption on Coal and Measurement of Gas
Content" in Hydrocarbons from Coal, AAPG Studies In Geology #38, 1993.
54
US Environmental Protection Agency
-------
APPENDIX A. U. S. Abandoned Coal Mine Database
State
County
Coal Basin
Mine Name
Current Emissions
Status
Date
Abandoned
Active
Mine
Emissions
(mmcfd)
OK
Haskell
Arkoma
Choctaw Coal
10/29/90
0.35
OK
Le Flore
Arkoma
Howe No 1
06/10/72
1.6
OK
Okmulgee
Arkoma
Pollyanna No 4
10/11/96
0.35
KY
Harlan
Central Appl.
No. 10 Wisconsin Steel
Mine
6/10/1972
0.1
KY
Harlan
Central Appl.
Creech No 1
6/15/1995
0.2
KY
Harlan
Central Appl.
Harlan No.1
7/10/1995
0.2
KY
Harlan
Central Appl.
Arch No. 37
1/21/1999
1
KY
Henderson
Central Appl.
Retiki
Sealed
02/03/95
0.35
KY
Johnson
Central Appl.
White Ash No 1
06/10/77
0.35
KY
Leslie
Central Appl.
No 2
08/29/96
0.35
KY
Leslie
Central Appl.
Unicorn No.2
8/29/1996
0.2
KY
Leslie
Central Appl.
No. 60
05/07/01
0.3
KY
Letcher
Central Appl.
Scotia Mine
06/10/82
0.4
KY
Martin
Central Appl.
Peter Cave No 1
06/10/77
0.15
KY
Martin
Central Appl.
Wolf Creek No.3
Sealed
06/10/77
0.75
KY
Martin
Central Appl.
Wolf Creek No 4
Flooded
10/2/1995
1
KY
MeCreary
Central Appl.
Justus
06/15/94
0.35
KY
Pike
Central Appl.
Big Creek No 2
06/10/81
0.15
KY
Pike
Central Appl.
Leslie
Sealed
06/10/81
0.75
KY
Pike
Central Appl.
Scotts Branch
06/10/81
0.35
KY
Pike
Central Appl.
No. 1 Mine (D)
10/20/82
0.35
KY
Pike
Central Appl.
No. 2 Mine (D)
12/16/82
0.35
KY
Pike
Central Appl.
No. 6 Mine (D)
03/04/83
0.35
KY
Pike
Central Appl.
No. 1 Mine (D)
06/14/83
0.35
KY
Pike
Central Appl.
No. 1 Mine
11/14/88
0.35
KY
Pike
Central Appl.
Ovenfork Mine
1/15/1992
2.4
KY
Pike
Central Appl.
Mate Creek No 2
06/10/94
0.75
KY
Pike
Central Appl.
No 3
06/10/94
0.35
KY
Pike
Central Appl.
No.9
8/25/1995
0.1
KY
Whitley
Central Appl.
No. 1
08/15/86
0.35
KY
Whitley
Central Appl.
Blue Gem No 1
02/27/97
0.35
TN
Clearborne
Central Appl.
Matthews Mine
12/29/1990
0.2
TN
Rosedale
Central Appl.
Volunteer No 1
06/10/74
2.5
TN
Sequatchie
Central Appl.
Kelly's Creek No. 63
2/18/1994
0.1
VA
Buchanan
Central Appl.
Jewell No 18
06/10/82
0.15
VA
Buchanan
Central Appl.
LAMBERT FORK
Flooded
06/18/85
0.75
VA
Buchanan
Central Appl.
WINSTON MINE NO 10
Sealed
02/25/92
0.35
VA
Buchanan
Central Appl.
No 1
Flooded
04/23/93
0.35
VA
Buchanan
Central Appl.
1 -A Mine
Venting/
partially Flooded
06/10/93
0.35
VA
Buchanan
Central Appl.
VIRGINIA POCAHONTAS 4
Sealed/
Recovering Methane
8/9/1993
2.4
VA
Buchanan
Central Appl.
Raven No. 1
Flooded
6/10/1994
0.1
VA
Buchanan
Central Appl.
VP 1
Recovering Methane
06/10/94
7.5
VA
Buchanan
Central Appl.
Big Creek Seaboard No. 1
Venting
8/18/1995
2.4
VA
Buchanan
Central Appl.
Beatrice Mine
Sealed
12/5/1995
6.8
VA
Buchanan
Central Appl.
No 4
Flooded
03/21/96
0.35
VA
Buchanan
Central Appl.
Virginia Pocahontas No 2
Sealed/
Recovering Methane
12/11/1996
2.8
VA
Buchanan
Central Appl.
VP No 3
Recovering Methane
12/10/1997
7.3
US Environmental Protection Agency
A-1
-------
APPENDIX A. U. S. Abandoned Coal Mine Database
State
County
Coal Basin
Mine Name
Current Emissions
Status
Date
Abandoned
Active
Mine
Emissions
(mmcfd)
VA
Buchanan
Central Appl.
1 -A
3/12/2001
0.25
VA
Dickenson
Central Appl.
Splashdam
Partially Flooded
09/27/95
0.35
VA
Dickenson
Central Appl.
McClure No 1
Flooded
8/20/1996
1.4
VA
Dickerson
Central Appl.
Moss No 3
Flooded
06/10/76
1.4
VA
Lee
Central Appl.
No. 1 Mine
04/28/92
0.35
VA
Lee
Central Appl.
#1
03/24/94
0.75
VA
Lee
Central Appl.
Holton
Flooded
01/23/97
0.35
VA
Russell
Central Appl.
Chaney Creek No 2
Flooded
06/10/74
0.35
VA
Russell
Central Appl.
MOSS NO. 2
Flooded
07/15/83
1.3
VA
Russell
Central Appl.
HURRICANE CREEK
Flooded
06/29/87
0.35
VA
Russell
Central Appl.
Moss No 3A2
Flooded
03/18/88
0.75
VA
Russell
Central Appl.
Moss No 4
Adjacent to strip
mine
01/11/89
0.75
VA
Tazewell
Central Appl.
Amonate No 31
09/26/94
2.2
VA
Tazewell
Central Appl.
No 1
Flooded
06/10/95
0.35
VA
Wise
Central Appl.
PRESCOTT NO 1
Flooded
02/20/81
0.35
VA
Wise
Central Appl.
No 7
06/10/82
0.15
VA
Wise
Central Appl.
Virginia No 1
06/10/82
0.15
VA
Wise
Central Appl.
Wentz B Portal
Flooded
06/10/82
0.35
VA
Wise
Central Appl.
Osaka No 2
06/16/89
0.35
VA
Wise
Central Appl.
Prescott No 2 Mine
Sealed
01/11/94
0.35
VA
Wise
Central Appl.
No 1
Flooded
04/08/94
0.35
VA
Wise
Central Appl.
No. 2
Flooded
5/24/1995
0.1
VA
Wise
Central Appl.
Bullitt Mine
Venting
08/01/95
0.75
VA
Wise
Central Appl.
Wentz No 1
Flooded
01/25/96
0.35
VA
Wise
Central Appl.
Pierre
Venting
01/31/96
0.35
VA
Wise
Central Appl.
Har-Lee No 3
Sealed
04/29/96
0.35
VA
Wise
Central Appl.
No 1
Flooded
05/08/96
0.35
VA
Wise
Central Appl.
Deep No 20
Venting
01/08/97
0.35
VA
Wise
Central Appl.
#12
5/21/1999
0.1
VA
Wise
Central Appl.
Sargent Hollow
7/12/2001
0.2
WV
Boone
Central Appl.
Ferrell No 17
Flooded
06/10/82
0.35
WV
Boone
Central Appl.
HAMPTON NO 3 MINE
Flooded
02/02/87
0.35
WV
Boone
Central Appl.
Wharton No. 4
3/23/1987
0.2
WV
Boone
Central Appl.
HAMPTON NO 4
Flooded
01/23/91
0.35
WV
Boone
Central Appl.
Birchfield No 1
Venting
06/10/92
1.5
WV
Boone
Central Appl.
Oasis No. 1
06/10/96
1.1
WV
Boone
Central Appl.
Lightfoot No. 1
2/9/2000
0.2
WV
Brooke
Central Appl.
Beech Bottom
06/10/74
0.35
WV
Brooke
Central Appl.
Valley Camp No 1
06/10/82
0.35
WV
Fayette
Central Appl.
Royal No 5
Sealed
06/10/77
0.35
WV
Fayette
Central Appl.
Siltix
Flooded
10/23/87
0.35
WV
Kanawha
Central Appl.
No 34
06/10/72
0.35
WV
Kanawha
Central Appl.
Cannelton No 8
Venting
04/05/83
0.35
WV
Kanawha
Central Appl.
MADISON NO 1 MINE
06/14/84
0.35
WV
Kanawha
Central Appl.
Lady Dunn No 105
Flooded
11/12/87
0.75
WV
Lincoln
Central Appl.
Five Block No 4 Mine
09/26/80
0.75
WV
Logan
Central Appl.
Guyan No 5
Flooded
06/10/74
0.35
WV
Logan
Central Appl.
No 4-H
Sealed
06/10/74
0.35
A-2
US Environmental Protection Agency
-------
APPENDIX A. U. S. Abandoned Coal Mine Database
State
County
Coal Basin
Mine Name
Current Emissions
Status
Date
Abandoned
Active
Mine
Emissions
(mmcfd)
WV
Logan
Central Appl.
Paragon
Flooded
06/10/74
0.15
wv
Logan
Central Appl.
NO 1 CEDAR GROVE
Flooded
09/26/80
2.4
WV
Logan
Central Appl.
Dehue
Sealed
11/14/85
0.35
wv
Logan
Central Appl.
Guyan No 1
Flooded
07/03/90
0.35
wv
McDowell
Central Appl.
Cannelton No 3 & 4
Venting /
Partially Flooded
06/10/74
0.35
wv
McDowell
Central Appl.
Pocahontas No 7
06/10/74
0.15
wv
McDowell
Central Appl.
Maitland
Venting /
Partially Flooded
06/10/77
1
wv
McDowell
Central Appl.
U.S. Steel No 14-4
Venting /
Partially Flooded
06/10/77
1.4
wv
McDowell
Central Appl.
NEWHALL NO 6 MINE
Venting/
Partially Flooded
10/01/79
0.75
wv
McDowell
Central Appl.
SHANNON BRANCH MINE
Flooded
11/05/82
1.3
wv
McDowell
Central Appl.
GARY NO 10
Sealed
02/28/84
0.75
wv
McDowell
Central Appl.
Little B Mine No 2
Sealed
12/19/85
2.4
wv
McDowell
Central Appl.
Keystone No 1 Mine
04/01/87
0.35
wv
McDowell
Central Appl.
Ogla
Flooded
06/17/88
1.6
wv
McDowell
Central Appl.
No 4 Mine
Sealed
06/27/88
2.4
wv
McDowell
Central Appl.
U.S. Steel No 2
Venting/
Partially Flooded
06/10/91
0.9
wv
McDowell
Central Appl.
ANGUS
Venting
10/24/95
0.35
wv
Mingo
Central Appl.
National No 25
06/10/74
0.35
wv
Mingo
Central Appl.
Gary No 20-B
06/10/82
0.15
wv
Mingo
Central Appl.
No 19
07/02/90
0.35
wv
Mingo
Central Appl.
Rocky Hollow
11/19/94
0.35
wv
Nicholas
Central Appl.
Sewell No 4
06/10/72
0.75
wv
Nicholas
Central Appl.
Coalbank Fork No 9
02/27/82
2.4
wv
Nicholas
Central Appl.
Mine #3
04/26/82
2.4
wv
Nicholas
Central Appl.
Mine No 4
07/27/82
2.4
wv
Nicholas
Central Appl.
No 24 Mine
09/15/82
2.4
wv
Nicholas
Central Appl.
Mine No 4
09/20/82
2.4
wv
Nicholas
Central Appl.
Hewett Fork No 1A
01/05/83
2.4
wv
Nicholas
Central Appl.
Big Foot Coal 4-B Mine
03/21/83
2.4
wv
Nicholas
Central Appl.
Stone Run 6A
06/14/83
2.4
wv
Nicholas
Central Appl.
SEWELL #1A
04/22/86
0.35
wv
Nicholas
Central Appl.
SEWELL NO 1
09/06/88
0.35
wv
Nicholas
Central Appl.
Donegan No 10
06/14/90
0.35
wv
Nicholas
Central Appl.
Mine No 1
06/24/93
2.4
wv
Nicholas
Central Appl.
Long Run Deep Mine No 1
04/17/96
2.4
wv
Nicholas
Central Appl.
Hutchinsons Branch Mine
No. 1
06/26/00
0.25
wv
Raleigh
Central Appl.
East Gulf
Flooded
06/10/74
1
wv
Raleigh
Central Appl.
Bethlehem No 46
Flooded
06/10/77
0.15
wv
Raleigh
Central Appl.
Macalpin #3
Flooded
10/19/79
0.3
wv
Raleigh
Central Appl.
ECCLES NO 5
Flooded
10/01/81
0.75
wv
Raleigh
Central Appl.
KEYSTONE NO 4-A MINE
Flooded
07/21/82
0.35
wv
Raleigh
Central Appl.
SLAB FORK NO 8
Flooded
02/06/84
0.75
wv
Raleigh
Central Appl.
SLAB FORK NO. 10 MINE
Flooded
02/06/84
0.75
wv
Raleigh
Central Appl.
WINDING GULF #4
Flooded
02/06/84
0.35
wv
Raleigh
Central Appl.
ECCLES NO 6
Flooded
06/28/85
0.35
wv
Raleigh
Central Appl.
KEYSTONE NO 4 MINE
Flooded
10/01/85
0.35
US Environmental Protection Agency
A-3
-------
APPENDIX A. U. S. Abandoned Coal Mine Database
State
County
Coal Basin
Mine Name
Current Emissions
Status
Date
Abandoned
Active
Mine
Emissions
(mmcfd)
WV
Raleigh
Central Appl.
KEYSTONE NO 5 MINE
Flooded
12/31/85
0.35
wv
Raleigh
Central Appl.
SKELTON MINE
Flooded
12/08/86
0.35
WV
Raleigh
Central Appl.
Macalpin
Flooded
07/06/89
0.35
wv
Raleigh
Central Appl.
Bonny
Sealed/
Recovery Pending
06/10/90
3.4
wv
Raleigh
Central Appl.
No 4 Mine
Venting/
Partially Flooded
1/29/1991
2.9
wv
Raleigh
Central Appl.
Beckley
Flooded
7/1/1992
3.7
wv
Raleigh
Central Appl.
KEYSTONE NO 2 MINE
Flooded
5/7/1993
0.6
wv
Raleigh
Central Appl.
Tommy Creek #1
Flooded
03/20/96
0.35
wv
Raleigh
Central Appl.
Maple Meadow Mine
Sealed/
Recovery Pending
7/10/1998
2.6
wv
Upshur
Central Appl.
Adrian Mine
6/10/1977
0.2
wv
Upshur
Central Appl.
Queen # 14 Mine
11/05/82
2.4
wv
Upshur
Central Appl.
Grand Badger No 1A Mine
08/08/83
2.4
wv
Webster
Central Appl.
Smoot
01/22/97
0.35
wv
West
Central Appl.
Dixianna
06/10/72
0.35
wv
Wyoming
Central Appl.
Buckeye Coll.
Sealed
06/10/74
0.15
wv
Wyoming
Central Appl.
Kepler
Venting/
Partially Flooded
06/10/74
0.75
wv
Wyoming
Central Appl.
Otsego
06/10/74
0.15
wv
Wyoming
Central Appl.
Itmann No 4
Flooded
06/10/76
1
wv
Wyoming
Central Appl.
GASTON NO 2 MINE
01/15/82
0.35
wv
Wyoming
Central Appl.
Beckley No 1
Venting/Partially
Flooded
2/9/1982
0.7
wv
Wyoming
Central Appl.
National Pocahontas
Venting/Partially
Flooded
01/31/84
0.75
wv
Wyoming
Central Appl.
ITMANN #3
Sealed
05/20/87
1.4
wv
Wyoming
Central Appl.
Beckley No 2
Venting/Partially
Flooded
6/21/1988
1
wv
Wyoming
Central Appl.
ITMANN# 1 AND SHOP
Sealed
06/12/92
0.35
wv
Wyoming
Central Appl.
Shawnee Mine
Venting/Partially
Flooded
11/7/1994
2.4
wv
Wyoming
Central Appl.
KOPPERSTON NO. 1
Sealed
01/10/96
0.35
wv
Central Appl.
Mine No 1
12/13/82
2.4
wv
Central Appl.
Bells Creek Mine No. 1
6/10/1998
0.50
IL
Christian
Illinois
Peabody No. 10
7/10/1994
0.75
IL
Clinton
Illinois
Monterey No 2
07/25/96
0.75
IL
Douglas
Illinois
Zeigler#5
Sealed
05/27/87
0.35
IL
Douglas
Illinois
Murdock
11/1/1996
0.75
IL
Franklin
Illinois
Old Ben No 27
02/05/87
0.75
IL
Franklin
Illinois
Old Ben No 25
Venting Methane
9/10/1994
1
IL
Franklin
Illinois
Old Ben No 21
11/13/95
1.4
IL
Franklin
Illinois
Old Ben No 24
Sealed
7/10/1998
1.2
IL
Franklin
Illinois
Old Ben No 26
Sealed
7/10/1998
1.6
IL
Gallatin
Illinois
Eagle No. 2
06/10/94
0.75
IL
Gallatin
Illinois
Eagle No 1
05/15/96
0.35
IL
Hamilton
Illinois
Inland No 2
06/10/82
0.35
IL
Jefferson
Illinois
Inland No 1
06/10/82
1.1
IL
Jefferson
Illinois
Orient #3
Sealed
02/01/84
1.5
IL
Jefferson
Illinois
Orient #5
Sealed
02/01/84
1.5
IL
Jefferson
Illinois
Wheeler Creek
04/04/88
0.75
IL
Jefferson
Illinois
Orient No 6
Sealed /
3/13/1997
1
A-4
US Environmental Protection Agency
-------
APPENDIX A. U. S. Abandoned Coal Mine Database
State
County
Coal Basin
Mine Name
Current Emissions
Status
Date
Abandoned
Active
Mine
Emissions
(mmcfd)
Recovering Methane
IL
Montgomery
Illinois
Crown
Sealed
06/10/72
1
IL
Montgomery
Illinois
Crown #2
Sealed
06/10/82
1.1
IL
Montgomery
Illinois
HILLSBORO MINE
12/02/83
0.35
IL
Perry
Illinois
Kathleen
08/23/95
0.35
IL
Randolph
Illinois
Baldwin No 1
06/10/82
0.35
IL
Randolph
Illinois
No 11
06/10/82
0.15
IL
Randolph
Illinois
Spartan
Sealed
12/10/97
0.35
IL
Saline
Illinois
No 16
Flooded
06/10/72
0.15
IL
Saline
Illinois
No 5
Flooded
06/10/72
0.15
IL
Saline
Illinois
Sahara No 20
Flooded
06/10/82
0.35
IL
St. Clair
Illinois
River King Underground
05/11/90
0.35
IL
Williamson
Illinois
ZEIGLER #4 UG
Sealed
11/14/80
0.75
IL
Williamson
Illinois
ORIENT NO. 4
Sealed
09/01/87
0.75
IL
Illinois
Big Ridge Mine
3/15/1997
0.60
IN
Gibson
Illinois
Kings
Sealed
06/10/74
0.35
IN
Sullivan
Illinois
Thunderbird
Sealed
06/10/72
0.75
IN
Sullivan
Illinois
Buck Creek
2/2/1998
0.35
KY
Hopkins
Illinois
East Diamond
Venting/Flooded
06/10/72
0.35
KY
Hopkins
Illinois
Island Creek No 9
Venting/Flooded
06/10/74
0.35
KY
Hopkins
Illinois
FIES MINE
Venting/Flooded
01/11/80
1.1
KY
Hopkins
Illinois
ZEIGLER NO 9 MINE
01/11/80
0.75
KY
Hopkins
Illinois
Drake No 4
Flooded
04/27/82
0.35
KY
Hopkins
Illinois
Providence No 1
Venting/Flooded
06/10/83
0.35
KY
Hopkins
Illinois
Busick Mine
06/29/83
0.35
KY
Hopkins
Illinois
Green River No.9
5/1/1992
1.2
KY
Hopkins
Illinois
West Hopkins
Sealed/Filled
06/10/94
0.35
KY
Hopkins
Illinois
Richland Mine
9/21/2000
0.2
KY
Muhlenberg
Illinois
Drake No 1
Sealed/Filled
06/10/72
0.35
KY
Muhlenberg
Illinois
Crescent
Flooded
06/10/77
0.75
KY
Muhlenberg
Illinois
River Queen Underground
No 1
Flooded
02/02/81
0.35
KY
Muhlenberg
Illinois
Star Underground
Flooded
05/15/96
0.35
KY
Ohio
Illinois
ALSTON NO 3 MINE
02/06/81
0.35
KY
Ohio
Illinois
Peacock Coal Mine No.
02/01/83
0.75
KY
Ohio
Illinois
KEN NO 4 MINE
09/01/84
0.35
KY
Union
Illinois
Pyro No 2
Sealed
06/10/74
0.35
KY
Union
Illinois
Peabody Camp No 2
Sealed
06/10/83
0.35
KY
Union
Illinois
Pyro No. 11 Highway
11/15/1991
0.2
KY
Union
Illinois
Pyro No. 9 Slope Wlliam
Station
11/15/1991
1.2
KY
Union
Illinois
Camp No.2
8/20/1993
0.4
KY
Union
Illinois
Hamilton No 2
Venting/Flooded
03/18/94
0.35
KY
Union
Illinois
Hamilton No 1
Venting/Flooded
05/14/96
0.35
KY
Webster
Illinois
Dorea
Sealed/Filled
01/29/93
0.35
KY
Webster
Illinois
Wheatcroft #9
06/10/96
1.9
KY
Webster
Illinois
Smith U/G mine
9/21/2000
0.35
OH
Belmont
Northern
Appl.
Powhatan No 4
Venting
06/10/78
0.75
OH
Belmont
Northern
Appl.
POWHATAN NO 5 MINE
Venting
03/31/81
0.35
US Environmental Protection Agency
A-5
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APPENDIX A. U. S. Abandoned Coal Mine Database
State
County
Coal Basin
Mine Name
Current Emissions
Status
Date
Abandoned
Active
Mine
Emissions
(mmcfd)
OH
Belmont
Northern
Appl.
POWHATAN NO 1
Sealed
02/16/82
0.75
OH
Belmont
Northern
Appl.
Powhatan No 3
Venting
03/18/83
0.35
OH
Belmont
Northern
Appl.
ALLISON MINE
Venting
01/11/84
0.35
OH
Belmont
Northern
Appl.
Saginaw no 1
Venting
06/17/93
0.35
OH
Harrison
Northern
Appl.
Nelms #1
Sealed/
Recovering Methane
06/10/77
1.9
OH
Harrison
Northern
Appl.
Rose Valley No. 6
8/28/1980
0.5
OH
Harrison
Northern
Appl.
VAIL
Venting
01/04/84
0.35
OH
Harrison
Northern
Appl.
Oak Park No 7
Sealed/
Recovering Methane
05/13/88
0.75
OH
Harrison
Northern
Appl.
NELMS NO 2
Venting
2/29/1996
1.5
OH
Jefferson
Northern
Appl.
Jensie
Venting
06/10/74
0.35
OH
Monroe
Northern
Appl.
POWHATAN 7 MINE
Temporary Seal
08/03/92
0.35
OH
Perry
Northern
Appl.
Sunnyhill No. 9 South
7/10/1991
0.1
OH
Vinton
Northern
Appl.
Raccoon #3
09/25/89
0.35
PA
Allegheny
Northern
Appl.
Oakmont
05/01/80
0.35
PA
Allegheny
Northern
Appl.
HARMAR MINE
Sealed
01/13/89
0.35
PA
Allegheny
Northern
Appl.
Renton Mine
10/23/1992
0.7
PA
Allegheny
Northern
Appl.
Allegheny No. 2 & Portal
No. 3
10/25/1993
0.1
PA
Allegheny
Northern
Appl.
Newfield
Sealed
06/26/95
0.75
PA
Allegheny
Northern
Appl.
OCEAN #5 MINE
Sealed
03/18/97
0.35
PA
Armstrong
Northern
Appl.
Harold No 1
06/10/74
0.15
PA
Armstrong
Northern
Appl.
Jane Nos 1 & 2
06/10/84
0.75
PA
Armstrong
Northern
Appl.
DAVID MINE
Sealed/Adjacent to
Dianne Mine
02/27/96
0.35
PA
Armstrong
Northern
Appl.
Jane
Sealed
08/22/96
0.75
PA
Cambria
Northern
Appl.
Bethlehem No 31
Sealed
06/10/78
0.35
PA
Cambria
Northern
Appl.
Bethlehem No 77
Flooded/
Pumping Water
06/10/78
0.35
PA
Cambria
Northern
Appl.
Nanty Glo No 31
Sealed
06/10/84
0.35
PA
Cambria
Northern
Appl.
Bethlehem No 32
Sealed/
Recovering Methane
09/17/85
4.5
PA
Cambria
Northern
Appl.
Lancashire No 25
Sealed
03/05/86
0.35
PA
Cambria
Northern
Appl.
Lancashire No 20
Sealed
09/09/88
0.9
PA
Cambria
Northern
Appl.
Cambria Slope No 33
Recovering Methane
7/15/1994
8.5
PA
Centre
Northern
Appl.
Rushton
12/31/1992
0.4
PA
Fayette
Northern
Appl.
Isabella
Sealed
06/10/74
0.35
A-6
US Environmental Protection Agency
-------
APPENDIX A. U. S. Abandoned Coal Mine Database
State
County
Coal Basin
Mine Name
Current Emissions
Status
Date
Abandoned
Active
Mine
Emissions
(mmcfd)
PA
Greene
Northern
Appl.
WARWICK MINE NO. 2
Sealed
05/01/80
0.35
PA
Greene
Northern
Appl.
ROBENA MINE
Flooded
02/12/84
2.1
PA
Greene
Northern
Appl.
GATEWAY MINE
Venting
12/9/1992
2.6
PA
Greene
Northern
Appl.
Nemacolin Mine
3/25/1996
0.6
PA
Greene
Northern
Appl.
Shannopin Mine
Sealed
3/25/1996
1
PA
Greene
Northern
Appl.
Lazarus
6/13/1996
0.6
PA
Greene
Northern
Appl.
Monongahela Resource
Venting
06/13/96
0.35
PA
Greene
Northern
Appl.
Warwick Mine No 2
Flooded/Pumping
Water
3/10/1997
1.1
PA
Indiana
Northern
Appl.
CONEMAUGH NO. 1
09/23/82
0.35
PA
Indiana
Northern
Appl.
Greenwich Collieries No 1
8/1/1988
0.3
PA
Indiana
Northern
Appl.
Urling No. 1
Venting
12/18/1989
0.7
PA
Indiana
Northern
Appl.
Florence No. 1
3/7/1990
0.2
PA
Indiana
Northern
Appl.
Urling No. 3
Venting
1/3/1991
0.7
PA
Indiana
Northern
Appl.
Greenwich Collieries No 2
03/13/93
1.2
PA
Indiana
Northern
Appl.
Homer City
6/30/1993
1.7
PA
Indiana
Northern
Appl.
Florence No. 2
10/4/1994
0.3
PA
Indiana
Northern
Appl.
Lucerne No 8
03/31/95
0.35
PA
Indiana
Northern
Appl.
Lucerne No. 9
Sealed/
Partially Flooded
8/23/1995
0.35
PA
Indiana
Northern
Appl.
Marion
Sealed*
01/23/97
0.75
PA
Indiana
Northern
Appl.
Lucerne No. 6 Extension
5/24/2000
0.3
PA
Luzerne
Northern
Appl.
Forge Slope
06/10/72
1.5
PA
Luzerne
Northern
Appl.
No. 19 Wanamie Colliery
6/10/1972
0.2
PA
Somerset
Northern
Appl.
BIRD #2
Flooded
10/30/91
0.75
PA
Somerset
Northern
Appl.
BIRD #3
Flooded
10/30/91
0.4
PA
Somerset
Northern
Appl.
Grove No. 1
12/21/1994
0.35
PA
Washington
Northern
Appl.
VESTA #4 MINE
Sealed
04/14/80
0.35
PA
Washington
Northern
Appl.
Beth Ellsworth No 51
Flooded
06/10/83
0.75
PA
Washington
Northern
Appl.
WESTLAND #2
Sealed
09/27/83
0.35
PA
Washington
Northern
Appl.
Marianna No 58
Sealed/
Partially Flooded
8/31/1988
2.2
PA
Washington
Northern
Appl.
Clyde
12/9/1994
0.1
PA
Washington
Northern
Appl.
VESTA #5 MINE
04/17/96
1.6
PA
Washington
Northern
Appl.
MONTOUR#4
Flooded
05/22/96
3
US Environmental Protection Agency
A-7
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APPENDIX A. U. S. Abandoned Coal Mine Database
State
County
Coal Basin
Mine Name
Current Emissions
Status
Date
Abandoned
Active
Mine
Emissions
(mmcfd)
PA
Washington
Northern
Appl.
Westland
05/22/96
0.75
PA
Westmoreland
Northern
Appl.
Banning No 4
Flooded
06/10/83
0.75
PA
Westmoreland
Northern
Appl.
DELMONT
Flooded
03/04/88
0.35
PA
Northern
Appl.
Hutchinson
Flooded
06/10/74
0.35
WV
Barbour
Northern
Appl.
Boulder Mine
Sealed
03/17/83
2.2
WV
Barbour
Northern
Appl.
BADGER NO. 15 MINE
Sealed
02/26/84
0.35
WV
Barbour
Northern
Appl.
BADGER NO 14 MINE
Sealed
08/28/85
0.35
WV
Gilmer
Northern
Appl.
Kanawha #1
Sealed
09/15/82
2.2
WV
Gilmer
Northern
Appl.
Kanawha #2
Sealed
11/02/82
2.2
WV
Grant
Northern
Appl.
Potomac
Sealed
04/07/80
0.35
WV
Harrison
Northern
Appl.
Compass No 2
Sealed
06/10/74
0.75
WV
Harrison
Northern
Appl.
Mars No 2
Flooded
06/10/74
0.75
WV
Harrison
Northern
Appl.
Williams
Venting/
Partially Flooded
06/10/78
2.2
WV
Harrison
Northern
Appl.
Pioneer Mine
Venting/
Partially Flooded
11/12/82
2.2
WV
Marion
Northern
Appl.
Consol No 9
Venting/
Recovering Gas
06/10/77
1.4
WV
Marion
Northern
Appl.
No 93
Venting
06/10/78
1
WV
Marion
Northern
Appl.
Phillip Sporn No 1
06/10/79
0.35
WV
Marion
Northern
Appl.
Bethlehem No 44
Venting
10/1/1979
0.3
WV
Marion
Northern
Appl.
Consol No. 20
Venting/
Recovering Gas
10/1/1982
1.1
WV
Marion
Northern
Appl.
Bethlehem No 41
Venting/
Partially Flooded
02/15/83
0.75
WV
Marion
Northern
Appl.
JOANNE MINE
Venting
03/10/83
1.3
WV
Marion
Northern
Appl.
Federal No 1
Venting
03/24/87
1.8
WV
Marion
Northern
Appl.
Tygart River
Flooded/
Pumping Water
08/26/93
0.35
WV
Marshall
Northern
Appl.
Alexander
Venting/
Partially Flooded
7/10/1981
2.2
WV
Marshall
Northern
Appl.
Ireland
Venting
06/10/94
1.5
WV
Mason
Northern
Appl.
Putnam
06/10/72
0.35
WV
Monongalia
Northern
Appl.
Pursglove No. 15
9/14/1989
2.1
WV
Monongalia
Northern
Appl.
Blacksville No 1
06/10/93
2.9
WV
Monongalia
Northern
Appl.
Arkwright No 1
Sealed/Recovering
Methane
5/24/1996
4.2
WV
Monongalia
Northern
Appl.
Osage No. 3
5/25/1996
5.3
WV
Preston
Northern
Appl.
#1
Sealed
09/14/82
2.2
WV
Preston
Northern
Appl.
H & H Mine No 2
Sealed
03/22/83
2.2
A-8
US Environmental Protection Agency
-------
APPENDIX A. U. S. Abandoned Coal Mine Database
State
County
Coal Basin
Mine Name
Current Emissions
Status
Date
Abandoned
Active
Mine
Emissions
(mmcfd)
WV
Preston
Northern
Appl.
#3 Mine
Sealed
07/19/83
2.2
wv
Taylor
Northern
Appl.
Keg No 1
11/15/82
2.2
CO
Delta
Piceance
Hawks Nest East
Venting
1/3/1986
0.9
CO
Delta
Piceance
Somerset Mine
Sealed
2/16/1989
0.7
CO
Delta
Piceance
Bowie No 1
Venting Methane
12/10/1998
1.2
CO
Gunnison
Piceance
Bear Creek Mine
10/12/79
0.7
CO
Gunnison
Piceance
BEAR MINE
Sealed
05/27/82
0.75
CO
Gunnison
Piceance
Bear No 3
Flooded
04/01/97
0.35
CO
Mesa
Piceance
Roadside North Portal
Sealed
2/25/2000
0.7
CO
Mesa
Piceance
Roadside South Portal
Venting/
Partially Flooded
4/25/2000
0.4
CO
Moffat
Piceance
Eagle No 5
03/04/96
0.35
CO
Pitkin
Piceance
COAL BASIN
Sealed
02/27/81
1.6
CO
Pitkin
Piceance
L.S.Wood
Sealed
12/02/85
2.4
CO
Pitkin
Piceance
Thompson Creek No. 1
Sealed
09/01/86
0.35
CO
Pitkin
Piceance
Dutch Creek No. 2
Sealed
7/1/1988
1.7
CO
Pitkin
Piceance
Dutch Creek No 1
Sealed
10/4/1992
2.9
CO
Fremont
Raton
Southfield Mine
5/10/2001
0.35
CO
Las Animas
Raton
Allen
06/10/84
0.75
CO
Las Animas
Raton
Golden Eagle
Sealed/
Recovering Methane
5/30/1996
4.5
NM
Colfax
Raton
York Canyon Mine
3/3/1986
0.3
NM
Colfax
Raton
Cimarron
Sealed
10/10/98
0.75
UT
Carbon
Uinta
Carbon No 2
06/10/74
0.35
UT
Carbon
Uinta
Kennilworth
Sealed
06/10/74
0.75
UT
Carbon
Uinta
Braztah No 3
06/10/79
0.35
UT
Carbon
Uinta
Price River No. 3
06/10/82
0.9
UT
Carbon
Uinta
Price River No. 5
06/10/82
0.3
UT
Carbon
Uinta
Beehive
Sealed
03/27/87
1.7
UT
Carbon
Uinta
Castle Gaste Portal #5
Sealed
03/31/88
1.7
UT
Carbon
Uinta
Sunnyside Mine No. 3
Sealed
09/20/90
1.7
UT
Carbon
Uinta
Castle Gate Mine
Sealed
10/23/91
0.75
UT
Carbon
Uinta
Sunnyside Mine No. 1
Sealed
6/27/1994
1.7
UT
Carbon
Uinta
Soldier Canyon
Venting
10/10/1999
2.6
UT
Emery
Uinta
Trail Mountain Mine
6/29/2001
0.85
UT
Grand
Uinta
Wlberg
Sealed
02/05/90
1.7
UT
Sevier
Uinta
Emery
Sealed
08/01/95
0.35
AL
Jefferson
Warrior
Flat Top
Flooded
06/10/79
1
AL
Jefferson
Warrior
Bessie Mine
06/10/82
1
AL
Jefferson
Warrior
Concord No 1
Flooded
06/10/84
4.5
AL
Jefferson
Warrior
Mulga
Flooded
06/10/84
1.2
AL
Jefferson
Warrior
MAXINE MINE
Flooded
10/02/89
0.35
AL
Jefferson
Warrior
NEBO MINE
Flooded
10/02/89
0.35
AL
Jefferson
Warrior
Chetopa
Flooded
06/10/96
0.75
AL
Jefferson
Warrior
Blue Creek No. 3
Sealed/
Recovering Methane
10/1/1999
12.3
AL
Shelby
Warrior
Segco No 2
Flooded
06/10/72
0.35
AL
Shelby
Warrior
BOONE NO. 1
12/10/1998
1.3
AL
Walker
Warrior
Gorges No 7
Flooded
06/10/79
0.35
US Environmental Protection Agency
A-9
-------
APPENDIX A. U. S. Abandoned Coal Mine Database
State
County
Coal Basin
Mine Name
Current Emissions
Status
Date
Abandoned
Active
Mine
Emissions
(mmcfd)
AL
Walker
Warrior
Segco No 1
Flooded
06/10/84
0.75
AL
Walker
Warrior
Mary Lee No 2
Flooded
06/10/93
0.35
AL
Walker
Warrior
Mary Lee No 1
Flooded
5/10/1997
1.5
A-10
US Environmental Protection Agency
-------
APPENDIX B. State Agencies and Organizations with Information on
Abandoned Coal Mines and Regulations
Geological Survey of Alabama
420 Hackberry Lane (W.B. Jones Hall)
The University of Alabama
Tuscaloosa, Alabama 35486-6999
(205) 349-2852
Colorado Department of Natural Resources
Division of Minerals and Geology
1313 Sherman St., Rm. 215
Denver, CO 80203
(303) 866-3567
Illinois Department of Natural Resources
Illinois Office of Mines and Minerals
300 W. Jefferson, Suite 300
Springfield, IL 62701-1787
(217) 782-6791
Illinois State Geological Survey
615 E. Peabody
Champaign, IL 61820
(217) 333-4747
Indiana Department of Natural Resources
Bureau of Mine Reclamation
402 W. Washington St., Rm. W295
Indianapolis, IN 46204
(317) 232-1547
Geological Survey
Indiana University
Energy Resources Division
611 North Walnut Grove
Bloomington, IN 47405-2208
(812) 855-7636
Kentucky Department of Mines and Minerals
P.O. Box 2244
Frankfort, KY 40602
(502) 573-0140
Ohio Department of Natural Resources
Division of Mines and Reclamation
1855 Fountain Square, Bldg. H-3
Columbus, Ohio 43224
(614) 265-6633
Pennsylvania Dept. of Environmental Protection
Bureau of Abandoned Mine Reclamation
Rachel Carson State Office Building
PO Box 8476
Harrisburg, PA 17105-8476
(717) 783-2267
Pennsylvania Dept. of Environmental Protection
Bureau of Abandoned Mine Reclamation
Rachel Carson State Office Building
P.O. Box 8461
Harrisburg, PA 17105-8461
(717) 787-5103
Utah Department of Natural Resources
Division of Oil, Gas, and Mining
Abandoned Mine Reclamation
1594 West North Temple, Suite 1210
P.O. Box 145801
Salt Lake City, Utah 84114-5801
(801) 538-5349
Virginia Dept. of Mines, Minerals, and Energy
PO Box 900
U.S. Route 23 South
Big Stone Gap, VA 24219
(540) 523-8100
West Virginia Dept. of Environmental Protection
Office of Abandoned Mine Lands & Reclamation
PO Box 6064, NRCCE Bldg.
Morgantown, WV 26505
(304) 293-2867 ext. 5460
West Virginia Dept. of Environmental Protection
Office of Mining & Reclamation
10 McJunkin Road
Nitro, WV 25143
(304) 759-0510
US Environmental Protection Agency
B-1
-------
-------
Appendix C. Combining Uncertain Parameters Using Monte Carlo
Simulation
The IPCC guidelines for GHG inventory reporting require that the values be reported to within a
95% confidence interval. In other words, that there is a 95% probability that the true value will lie
within a specified interval (or, conversely, a 5% chance that the true value will lie outside of this
interval). Because the methodology presented in this report relies on combining variables with
uncertain values, a technique was needed that allowed the statistical uncertainty of those values
to be captured in the calculated abandoned mine methane emission value for a given inventory
year. One way to do this type of analysis is through Monte Carlo simulation.
The purpose of this appendix is to explain the process of combining probability distributions
within mathematical functions, such as products and sums, using Monte Carlo simulation and to
help provide an understanding of the nature of the results. The stepwise calculation of the
volume of methane emitted from a vented abandoned mine for the inventory year 1992, and its
associated confidence interval, will be used as an example to illustrate the process. The
methane emissions for several mines will then be summed using Monte Carlo simulation to
provide a frequency distribution, and hence the confidence interval, for the emission inventory of
those abandoned mines.
Quantifying uncertainty
The term "variables with uncertain
values" means that if the variable of
interest is measured repeatedly, the
value of that variable will be different
with each measurement. This
difference can be related to
measurement error or variations
through time or by sample location. If
the value is measured numerous
times, the frequency of occurrence of
a value or range of values can be
determined and an experimental
frequency histogram is created.
Figure C-1 is an example of a
frequency histogram of gas content
data from a coal basin in the United States. A continuous probability distribution function can be
fitted to the frequency histogram of the measured data. It is generally the probability distribution
function that is used within mathematical expressions to generate a frequency histogram of the
result. A lognormal distribution function is the best fit to the histogram in Figure C-1, but there
are several functions available to choose from, each with a different general shape. The
@Riskฎ add-in to Microsoft Excel used in this inventory contains a subroutine that fits a set of
probability distribution functions to the experimental frequency histogram and then ranks each
function by the goodness of fit using three different statistical tests.
Figure C-1. Histogram of Gas Content Data and the Best Fit
of the Lognormal Distribution Function to the Data
X <= 7.6 X <= 93.2
5.0% 95.0%
-20 0 20 40 60 80 100 120 140
scf/ton
US Environmental Protection Agency
C-1
-------
Another way that data distributions are
often presented is by the cumulative
frequency diagram. Figure C-2 is a
cumulative frequency diagram of the
data shown in Figure C-1 including the
lognormal cumulative probability
function. Both of these figures show
delimiters at the 5% and 95%
frequency. The meaning of these
values is best understood from Figure
C-2. The 5% value of 7.6 scf/t means
that 5% of the time a sampled value
will be 7.6 scf/t or less or, conversely,
that 95% of the time a sampled value
will be 7.6 scf/t or more. There is a
95% chance that a sampled value will
be 93.0 scf/t or less, or a 5% chance that it will be 93.0 scf/t or greater. These values represent
the 90% confidence interval. In other words, there is a 90% chance that a sampled value will lie
between 7.6 and 93.0 scf/t.
Figure C-2. Cumulative Probability of Gas Content Data and
Best Fit of the Lognormal Distribution Function to the Data
X <= 7.6 X<= 93.2
1 5.0% Q5._0%_
0.9-
40 60 80
Gas Content, scf/t
Methodology review
The methodology for determining the methane emissions from an abandoned underground coal
mine for a particular inventory year uses mathematical prediction techniques based on material
balance and the behavior of gas flowing through a porous adsorptive media, coal, to the
atmosphere. Section 4.2 in the main body of the report describes how a set of dimensionless
emission rate decline curves were generated for each U.S. coal basin based on these
principles. These decline curves were then fitted to a hyperbolic equation of the form:
(-1/b)
Where:
q/qi = (1+bDjt)
q is the gas rate at time t in mmcf/d
qi is the initial gas rate at time zero (t0) in mmcf/d
b is the hyperbolic exponent, dimensionless
Di is the initial decline rate,
1/day
t is elapsed time from t0, days
Based on these decline curves and the
time since abandonment, the emissions
for a given inventory year are
determined.
Using probability
distributions as variables
A single value of the yearly emissions
can be calculated from the single values
of the initial emission rate and the decline
Figure C-3. Uncertainty of the Initial Emission Rate at
Abandonment for a Mine
X<= 0.7000
2.
C-2
US Environmental Protection Agency
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coefficients, b and Dj. The initial emission rate (qi), however, is uncertain. The measured
emissions have an estimated uncertainty of plus 10% and minus 30% within a 95% confidence
interval (as discussed in Section 4.4.4). In the example above, the measured emissions at
closure was 1.0 mmcf/d, plus 0.1 mmcf/d or minus 0.3 mmcf/d. This information can be
characterized as a triangular probability function with a mean value of 0.925 as shown in Figure
C-3. Using this function in place of the single value for initial emission rate will result in a
frequency histogram of the yearly methane emission for this mine in 1992.
Unfortunately, the initial emission rate is not the only uncertainty in the hyperbolic equation. The
hyperbolic decline coefficients are also uncertain. The decline coefficients for the Central
Appalachian Basin are listed in Table C-1. The low, mid and high cases relate to low, mid and
high permeability uncertainty (see section 4.4.2). The range of values is not meant to capture
the extreme values, but values that represent the highest and lowest quartile of the data
distribution. These are specified as the values at the ten-percentile and the ninety-percentile of
the cumulative probability function of the parameter.
Table C-1. Central Appalachian Hyperbolic Decline
Coefficients
Case
b
Dj, 1/day
Low (P10)
1.079
0.00892
Mid (P50)
1.834
0.00874
High (P90)
1.014
0.00077
Figure C-4 shows the three emissions decline profiles based on these coefficients for the
example mine data in Table C-2. Given an abandonment date and an emission rate at the time
of closure, as in Table C-2, the mid-range case emission estimate for the inventory year 1992
can be calculated using the following function.
q = 63.4 = 365 * 0.925 (1+1.83 * 0.0087 * 1278)(1/183)
Table C-2. Sample inventory calculation for a vented mine
Coal
Basin
Mine Name
Status
Date of
Abn.
Active
Mine
Emissions
(mmcf/d)
Time
Since
Closure,
days
Mid
Emission
(mmcf/yr)
High
Emission
(mmcf/yr)
Low
Emission
(mmcf/yr)
CA
Example
Venting
06/21/88
0.925
1278
63.4
170.7
30.7
Calculating the emission rate
probability function for the low, mid or
high permeability case for an inventory
year can be done on a personal
computer using a spreadsheet program
with "add-in" Monte Carlo simulation
software such as @Riskฎ. The
software randomly selects a value for
the initial emission rate variable based
on the probability of this value
occurring as described by the triangular
probability function (Figure C-3). This
value is used to calculate a value of the
Figure C-4. Single Abandoned Mine Emissions Through
Time Based on Permeability Uncertainty
Days Since Abandonment
US Environmental Protection Agency
C-3
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yearly emissions for the inventory year of interest. This sampling process is repeated numerous
times (the number of times is set by the user) producing the probability function for the emission
rate for that inventory year. This is shown by Figure C-5, which represents sampling the
triangular probability function and calculating the result 5,000 times for the low, mid and high
emissions estimates shown in Table C-2. Each of the forecasted distributions has an
uncertainty range of plus 10% and minus 30% relative to the mode as shown in Table C-3.
Table C-3. 95% confidence intervals and percent difference for example mine emissions for 1992
by permeability case, mmcf
Case
P2.5%
Mode
P97.5%
% Difference Low
% Difference High
Low Permeability
48.0
68.1
75.4
-30%
10%
Mid Permeability
23.2
33.1
36.5
-30%
10%
High Permeability
129.2
184.3
203.0
-30%
10%
Distributions within
distributions
In order to generate a single
probability density function of the
emissions for this mine for 1992,
the low, mid and high distributions
need to be combined. Here the
probability density function depicts
the frequency of occurrence of the
range of values that potentially may
occur, plotted versus the probability
of any given outcome occurring.
Generating this probability density
function is accomplished by
selecting the low, mid and high
emission distributions as the low,
mid and high points in another triangular distribution shown in Figure C-6. The endpoints (which
are specified as the means of each distribution) are defined as the P10, mode and P90 because
this is how the permeability ranges were characterized when generating the decline curves. A
condition must be applied to this
distribution so that no negative
emission values are returned in the
final distribution. The final
distribution is shown in Figure C-7.
This distribution shows that the
emission for inventory year 1992 is
between 12.3 and 210.7 mmcf at a
95% confidence interval with a
mean of 96.5 mmcf. This is a range
of plus 118% and minus 87%
relative to the mean of the
distribution. Figure C-8 shows the
mean predicted for yearly
emissions for this mine with the
95% confidence interval.
Figure C-5. Yearly Emission Volumes Based on
Permeability and Emission Rate At Closure Uncertainties
Low Permeability
310 Mean='
30 7
__ Mid Permeability
ฆfli
P
50 Mean=63
4
i
l
High Permeabilihs-ri_
^0 lllhi
0 50 100 150 200 250
mmcf/yr
Figure C-6. Static Triangular Distribution for
Uncertainty
5--
4--
3--
2 -
1 --
X <= 30.7
10.0%
0-4
US Environmental Protection Agency
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Figure C-7. Initial Rate Distribution and Permeability
Distribution Combined
X <=12.3 X <=210.7
I
i
Mean = 96.5
100 150
mmcf/yr
Figure C-8. Single Abandoned Mine Emissions
Uncertainty over Time with Initial Rate Uncertainty
x x
X X X
X X
0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
Days Since Abandonment
Summing distributions
The probability distribution of the emissions and their associated confidence intervals will be
different for each mine for any given inventory year. Summing these distributions is an
appropriate way to determine the basin total emissions and the associated uncertainty.
Intuitively, one might expect that the range of uncertainty of a combination of highly uncertain
predictions would yield an even more uncertain result, while, in fact, the opposite is true. Table
C-4 lists a subset of vented Central Appalachian basin mines for inventory year 1992 with the
mean value of their calculated yearly emissions, the 2.5% and 97.5% probability values, and
their percent difference relative to the mean. The result of the summed distributions is also
shown on the bottom line of Table C-4. The sum of the mean values for each mine's emission
distribution is the same as the mean of the summed distributions. However, the summation of
the values of the 2.5% probabilities is much smaller than the 2.5% probability value of the
summed distributions. Similarly, the sum of the 97.5% probability values is much larger than the
97.5% probability value of the summed distributions. The range of uncertainty of the summed
distributions is significantly smaller than the range of uncertainty of the individual distributions
for a given confidence interval.
US Environmental Protection Agency
C-5
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Table C-4. Partial list or Central Appalachian abandoned coal mines and their mean emission
estimate with the 95% confidence interval bounding values
Mine Name
Mean
2.5%
Prob.
97.%
Prob.
%Diff
Low
%Diff
High
Std
Dev
Coefficient of
Variation
Cannelton No 8
18.6
1.8
40.8
-90%
119%
10.4
56%
U.S. Steel No 14-4
52.1
4.9
113.1
-91%
117%
28.8
55%
Maitland
37.3
3.5
81.2
-91%
118%
20.8
56%
Beckley No 2
89.4
10.6
195.3
-88%
118%
49.6
55%
Beckley No 1
34.3
3.3
76.0
-90%
121%
19.3
56%
Kepler
19.4
1.9
41.7
-90%
115%
10.6
55%
Newhall No. 6 Mine
21.1
2.0
45.6
-91%
116%
11.8
56%
Sewell No 4
14.9
1.5
31.5
-90%
112%
8.1
54%
Sums (
of Values
287.2
29.0
625.2
Sum of
Distributions
287.2
165.4
429.6
-42%
50%
68.0
24%
Conclusions
This process may seem counterintuitive. For example, an individual mine in Table C-4 (Beckley
#1) located in the Central Appalachian Basin had an uncertainty range of plus 121% and minus
90% for the 1992 inventory. After that mine is combined into a larger group of mines (classified
by coal basin), the resulting range of uncertainty for the Central Appalachian Basin mine group
is plus 41% and minus 32%. Furthermore, the range of uncertainty associated with the entire
population of abandoned mines compiled for the 1992 inventory results in an even lower range
of plus or minus 20%. The above example illustrates the phenomenon, supported by the central
limits theorem, that the coefficient of variation (standard deviation divided by the mean) of the
sum of distributions is smaller than the coefficient of variation of the component distributions.
C-6
US Environmental Protection Agency
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APPENDIX D. Effect of Barometric Pressure
During the spring of 1999, EPA collected gas flow and quality data from an abandoned mine
vent in the Illinois basin to correlate flow rates with barometric pressure.39 The mine selected
for the study had been closed since 1962, but a three-inch vent pipe remained intact and
continued to vent methane into the atmosphere. This mine is considered representative of
gassy abandoned mines in the Illinois basin region.40
Figure D-1, which shows all three data sets taken, clearly illustrates the strong inverse
relationship between barometric pressure and methane emissions from the mine vent. As
barometric pressure increases, mine emissions decrease. As the graph illustrates, the 72-hour
and 96-hour studies resulted in roughly the same average emission rate. Based on these
measurements, EPA determined that 72-hour flow measurements are sufficient for determining
a mine's average flow rate.41
Figure D-1. Illinois Basin field measurements of barometric pressure and mine emissions
Correlating gas flow rates to barometric pressure is critical for obtaining representative field
measurements for decline curve validation. The correlation between gas flow and barometric
pressure is shown in Figure D-2. The linear regression equation describing the relationship
resulted in a correlation coefficient (R2) equal to 0.92.
OQ
Flow measurements were recorded at the vent pipe every hour over three 2-4 day periods to determine
the minimum time necessary to obtain representative emissions data. Corresponding hourly barometric
pressure data obtained from the Midwestern Climate Center indicates that the average annual barometric
pressure for this county was 30.03 inches of mercury. Variations in barometric pressure during the study
were typical of the annual variation. The calculated average methane emissions rate for the vent pipe
equaled 316.5 mcfd; daily readings ranged from 195 to 365 mcfd.
40 This mine is of room and pillar type, 500 to 600 feet deep, and includes the Herrin #6 coal seam.
41 Daily variations in the flow rate mean that daily measurements may not be reflective of the average flow
rate.
US Environmental Protection Agency
D-1
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For this study, only field-measured gas flow rates were normalized to account for average
annual barometric pressure. Emission rates derived from numerical modeling were based on a
constant barometric pressure of one atmosphere.
Ideally, one would measure diffuse emissions from sealed mines, through surface cracks and
fissures, to more accurately determine the degree to which mines are sealed (referred to in
terms of percentage sealed). Some techniques exist to measure these diffuse emissions (e.g.,
using infrared detectors), but resource limitations prohibited their use for this study.
Of the 374 mines in the U.S. abandoned mines database, only about 14% maintain vents to the
atmosphere. Therefore, basing emissions estimates on field data alone would result in an
unrepresentative and biased estimate. Therefore, additional field measurements could be used
to further calibrate emission estimates. It would be particularly useful to extend such
measurements to sealed mines since they comprise such a significant component of the
inventory.
Figure D-2. Correlation between mine methane emissions and barometric pressure
Barometric Pressure (in. Hg)
D-2
US Environmental Protection Agency
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Appendix E. Sensitivity Analysis Calculations
To test the sensitivity of emissions calculations to three parameters (adsorption isotherm, as
represented by VL and PL, permeability, and pressure at abandonment) involves 27 calculations
for each mine for each inventory year, since three values of each parameter must be tested
(high, low, and mid-range). A sensitivity analysis was performed to determine if the range of
uncertainty of these three parameters is large enough to make a significant difference in the
outcome of the calculation. If a parameter does not have a significant effect on the outcome, the
probability analysis is not necessary and the mid-case value of the parameter can be used in
the calculations.
To test the sensitivity of the calculations to the range of uncertainty, seven cases were
generated using the values shown in Table E-1. Gas content of coal mines at low pressures is
most sensitive to the value of the Langmuir Pressure, to which it is inversely proportional. The
Langmuir Volume has little effect.
Table E-1. Parameter values used in sensitivity analysis
Parameter
High
Mid
Low
Permeability, md
10
1
0.1
Pressure, psia
30
20
17
Pl, psia
176
286
667
VL, scf/ton
712
911
1093
These values were combined and used in the CFD model to calculate an emission inventory
number using a set of mine data from the Central Appalachian basin. Table E-2 lists the results,
which are shown graphically in Figure E-1. The mine is assumed to be emitting methane to the
atmosphere through one or several vents as opposed to being sealed or flooded.
Table E-2. Results of parameter sensitivity test
Permeability
Pressure
Isotherm
Emissions,
Bcf/yr
High
Mid
Mid
8.877
Mid
Mid
Mid
4.259
Low
Mid
Mid
1.627
Mid
High
Mid
4.970
Mid
Low
Mid
4.049
Mid
Mid
High
4.504
Mid
Mid
Low
3.546
US Environmental Protection Agency
E-1
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Figure E-1. Range of uncertainty for 1990 methane emissions for the Central Appalachian basin
associated with key parameters.
I 8.877
i 4.y /u
1
4.504
1 3.546
I 1.627
Permeability Pressure Isotherm
Figure E-1 shows that the calculated emissions for 1990 for the Central Appalachian basin are
much more sensitive to permeability than to either initial pressure or the adsorption isotherm.
Inventory calculations, therefore, use mid-case values for initial pressure and the mid-case
basin isotherm, but include the range of values for permeability for the probabilistic analysis.
E-2
US Environmental Protection Agency
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APPENDIX F. Emissions Inventory: Sample Calculations According To
Mine Types
Venting Mines
The low, mid and high emission calculations are based on decline equations derived from the
simulation model using the mid case adsorption isotherm for the basin, using permeability
values of 1.0, 10.0 and 0.1 md, respectively. Table F-1 shows the results from the spreadsheet
for the year 2000 inventory.
Table F-1. Sample inventory calculation for a venting mine
Coal
Basin
Mine Name
Status
Date of
Abn.
Active
Mine
Emissions
(mmcf/yr)
Time
Since
Closure,
days
Mid
Emission
(mmcf/yr)
High
Emission
(mmcf/yr)
Low
Emission
(mmcf/yr)
Central
Appl.
Cannelton
No 8
Venting
04/05/83
323.644
6480
9.349
20.146
3.533
The mid case equation for Central Appalachian Basin (shown below) is based on Equation 4:
q = qi(1+bDjt)(1/b)
q = 9.349 = 323.64(1+1.83 * 0.0087 * 6480)(1/183)
Different decline curve equation sets are used for each coal basin, because each basin has a
unique adsorption isotherm, which affects the decline curves calculated for each permeability
value.
The resulting three emissions estimates for each basin are then used to define a triangular
distribution for each mine (Figure F-1). The 10% and 90% probabilities shown in Table F-1 and
Figure F-1 are used to represent the lower and upper quartiles of the distribution.
This methodology uses the entire triangular distribution of emissions for each mine as input for a
Monte Carlo simulation. This produces a probability distribution of emissions for the population
of all venting abandoned mines (Figure F-2).
The frequency histogram shown in Figure F-2 is the result of randomly sampling the triangular
distribution of emissions for each mine (e.g., in Figure F-1) one thousand times and adding
them together. Additional trials did not significantly change the mean or the variance of the
distribution. The brackets on the x-axis show the 95% certainty bounds.
US Environmental Protection Agency
F-1
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Figure F-1. Distribution of Year 2000 Emissions for a vented abandoned mine
xCWltฐn #8 Mine, Central Appa^chjgujiJJasin
Emissions for Year 2000 in mmcf
Figure F-2. Probability density function for vented abandoned mines emissions for the year 2000
Distribution for Known Vented Mines for Year 2000
X <=2.112 X <=3.425
2.
5%
97.5%
Me a
n = 2.721
>
o
c
0)
3
O-
ฃ
ฆ
LL
nl-J
|k
1.5 2.0
2.5
3.0 3.5 4.0
Values in Bcf
F-2
US Environmental Protection Agency
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Flooded Mines
The calculation procedure for flooded, but still venting, mines is very similar to that for dry
venting mines except that an exponential function is used rather than a hyperbolic function. For
the mid-range case shown in Table F-2 below, emissions are calculated using Equation 5:
0.223 = 1022exp(- 0.672(4580/365))
For flooded mines, the exponential constant D in Equation 5 is the same for all basins because
it is a simple empirical curve fit to measured data. The low, mid and high emission values, as
shown in Table F-2, are used to define a triangular distribution. The triangular distributions for
all flooded mines are summed to generate a probability distribution for the emissions inventory
for the year 2000 (Figure F-3).
Table F-2. Sample inventory calculation for a flooded mine
Coal
Basin
Mine
Name
Status
Date of
Abn.
Active
Mine
Emissions
(mmcf/yr)
Time Since
Closure,
days
Mid
Emission
(mmcf/yr)
Low
Emission
(mmcf/yr)
High
Emission
(mmcf/yr)
Central
Appl.
Ogla
Flooded
06/17/88
1022
4580
0.206
0.039
1.106
Figure F-2. Probability density function for flooded abandoned mines emissions
for the year 2000
Distribution for Known Flooded Mines for Year 2000
X <=229.48 X <=374.53
2.5% 97.5%
US Environmental Protection Agency
F-3
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Sealed Mines
The sealed mine calculations average the low, mid-range, and high emission factors based on
the permeability uncertainty for each of the "percent sealed" cases of 50%, 80%, and 95%.
Here, the 80% sealed case is treated as the most likely or mid-range case. The average
emission factor for each of the three values of percentage sealed is used to define a triangular
distribution, which is then used in the Monte Carlo simulation to create a probability density
function for emissions from sealed abandoned mines. The probability density plot for the year
2000 emissions inventory for sealed mines is shown in Figure F-4.
Figure F-4. Probability density function for year 2000 emissions from sealed abandoned mines
Distribution for Known Sealed Mines for Year 2000
X <=4.415 X <=6.684
2 5% 97 5%
5.0 5.5 6.0
Values in Bcf
F-4
US Environmental Protection Agency
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