TECHNICAL SUPPORT DOCUMENT FOR UNDERGROUND COAL MINES: PROPOSED RULE FOR MANDATORY REPORTING OF GREENHOUSE GASES Office of Air and Radiation U.S. Environmental Protection Agency February 4, 2009 2/11/2009 ------- CONTENTS 1 Source Description a Total Emissions (based on Inventory) b. Types of Emissions to be Reported 2. Options for Reporting Thresholds a Options Considered b Emissions and Facilities Covered Per Option 3 . Existing Relevant Reporting Programs/Methodologies 4. Proposed Monitoring Methods Monitoring Methods Considered 5 Procedures for Estimating Missing Data 6. QA/QC and Verification Requirements 7. Reporting Procedures REFERENCES 3 3 4 8 8 9 9 13 13 17 18 19 21 2/11/2009 ------- 1. Source Description Coal production in the United States reached a record level in 2006, with production of 1,163 million short tons, according to the Energy Information Administration (EIA 2007). This was produced from 1,424 mines, of which, 612 were underground mines and 812 were surface mines.1 Two primary sources of greenhouse gas (GHG) emissions are of concern in the coal mining sector. The first and largest source of emissions is fugitive emissions of CH4 released from the coal and surrounding rock strata due to mining activities. There are five primary sources of fugitive CH4 emissions from coal mining operations: Ventilation air from underground mines, which contains dilute concentrations of CH4 Degasification systems at underground coal mines (also commonly referred to as drainage systems). These systems may employ vertical and/or horizontal wells to recover CH4 in advance of mining (known as "pre-mine drainage") or after mining (called "gob" or "goaf wells) Fugitive emissions from post-mining operations, during which coal continues to emit CH4 as it is stored in piles, processed, and transported Surface mines, from which CFLi in the coal seams is directly exposed to the atmosphere Abandoned or closed mines, from which CFLi may seep out through vent holes or through fissures or cracks in the ground. The second source of GHG emissions combustion-related CC>2 emissions are associated with the use of energy in mining operations, both from stationary and mobile sources, for both surface and underground mines. In some cases, CFLi produced from the coal mine itself is combusted as a source of energy. Total Emissions (based on Inventory) The annual Inventory of U.S. GHG Emissions and Sinks considers active coal mining-related fugitive CH4 emissions to the atmosphere from three sources: underground mining, surface mining, and post-mining (i.e., coal-handling) activities (EPA 2008). Total CFLi emissions from active mining operations in 2006 were estimated to be 58.5 million metric tons of CC>2 equivalent (CO2e) from these sources, a decline of 30% since 1990. Of this, underground mines accounted for 35.9 million metric tons of CC^e, surface mines accounted for 14.0 million metric tons of CO26, and post-mining emissions accounted for 8.6 million metric tons of CC^e. Fugitive CFLi emissions from inactive, closed (or abandoned) coal mines were estimated to contribute another 5.4 million metric tons of CC^e. The relative contribution of the various sources of coal mine emissions is illustrated in Figure 1. 1 An underground mine is where coal is produced by tunneling into the earth to the coalbed, which is then mined with equipment such as cutting machines and continuous, long wall, and shortfall mining machines. Underground mines are classified according to the type of opening used to reach the coal, i.e., drift (level tunnel), slope (inclined tunnel), or shaft (vertical tunnel). In contrast, surface mines are mines that are usually within a few hundred feet of the surface. Earth and rock above or around the coal (overburden) is removed to expose the coalbed, which is then mined with surface excavation equipment such as draglines, power shovels, bulldozers, loaders, and augers. Surface mines include: area, contour, open-pit, strip, and auger mines. 2/11/2009 ------- Figure 1 Estimated Fugitive CH4 Emissions from U.S. Coal Mines (2006) 5.40 35.9 (56%) n Underground mines (\«ntilation and degasification) Surface mines D Post mining (underground) D Post mining (surface) I Abandoned underground mines Source: Environmental Protection Agency, Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2006, USEPA#430-R-08-005, April 2008 Coal mining operations require a wide variety of equipment that uses coal, distillate, residual fuel oil, natural gas, gasoline, and purchased electricity, and hence, results in emissions from combustion. An estimated 9 million metric tons of CC>2 equivalent emissions were associated with energy use in coal mining operations in the United States in 2006 (see discussion below). Types of Emissions to be Reported i) Process Emissions Currently, only fugitive CH4 emissions from coal mining operations are addressed separately in the U.S. national inventory for the coal mining sector. Five categories of fugitive CFLi emissions are considered: Ventilation air from underground mines Degasification systems at underground coal mines Fugitive emissions from post-mining operations Surface mines Abandoned and/or closed mines. The nature of each of these sources of emissions, and considerations associated with various options for inclusion in the proposed rulemaking, are discussed in more detail below. Underground mines - mine ventilation emissions Mine ventilation emissions from underground coal mines account for the largest share of fugitive CH4 emissions 32.8 million metric tons of CC^e, or 56% of all U.S. coal mining fugitive emissions. In underground mines, CFLi can create an explosive hazard to coal miners. To ensure 2/11/2009 ------- mine safety, fresh air is circulated through underground coal mines using ventilation systems to dilute in-mine concentrations of CH4 to well below explosive levels. In the U.S., mine safety authorities at the Mine Safety and Health Administration (MSHA) regulate these concentrations. Typically, CH4 concentrations in ventilation air range from 0.1% to 1.0%. These ventilation systems can exhaust significant amounts of CH4 to the atmosphere in relatively low concentrations. MSHA field inspectors, as part of periodic mine safety inspections, conduct air sampling according to well-defined procedures. The results of this sampling currently provide the basis for estimating CH4 emission rates from ventilation systems at underground coal mines for the Inventory of U.S. Greenhouse Gas Emissions and Sinks. Underground mines - Degasification In many cases, it is necessary to supplement the mine ventilation with a CH4 degasification system. Methane drainage must be performed when the ventilation system cannot dilute CH4 emissions from the mine to below statutory levels. Mines that employ degasification systems also liberate large quantities of CH4 in relatively high concentrations. Degasification systems use wells drilled from the surface or boreholes drilled inside the mine to remove CH4 before, during, or after mining operations. These degasification systems usually consist of a network of boreholes, pumping systems, and gas gathering pipelines. The majority of the CH4 liberated from degasification systems is combusted by flaring or at energy projects. Of the 21.8 million metric tons CC^e of CH4 liberated by degasification systems in 2006, 18.7 million metric tons CO26 of CH4 was combusted, and 3.1 million metric tons were emitted to the atmosphere. In 2006, twenty U.S. coal mines supplemented their ventilation systems with active degasification systems. Thirteen coal mines collected CH4 from degasification systems and sold this gas to a pipeline. One coal mine used CH4 from its degasification system onsite to heat mine ventilation air. Two of the coal mines that sold gas to pipelines also used CH4 to generate electricity or fuel a thermal coal dryer on site (EPA 2005). Before mining, drainage wells are drilled through a coal seam or seams and cased to pre-drain the CH4 prior to mining. The wells are normally placed in operation 2 to 7 years ahead of mining and the coal seam is often hydraulically fractured to remove much of the CH4 and water from the seam. These pre-mine drainage wells can recover relatively high-quality gas from the coal seam and the surrounding strata in most cases because the CH4 is not diluted by ventilation from the mine. The total amount of CH4 recovered depends on site-specific conditions such as the gas content of the coal seams and surrounding strata, permeability of the geologic materials, the drainage time, the amount of pressure differential applied, and other characteristics of the geologic and extractive systems. Such pre-mine drainage wells can recover 50% to 90% of the gas content of the coal. Horizontal holes can also be drilled into the coal seam from development entries in the mine to drain CH4 from the unmined areas shortly before mining, reducing the flow of CH4 into the mining section. In this case, because CH4 drainage occurs only from the mined coal seam, and the period of drainage is relatively short, and the recovery efficiency of this technique is relatively low normally, about 10% to 20% of the CH4 is recovered from the drilled area. Higher recoveries can generally be achieved in room-and-pillar sections by drilling longer holes farther in advance of mining. 2/11/2009 ------- Gob wells and cross-measure bore holes recover CH4 from the overburden (i.e., gob area) after mining of the seam, primarily in longwall mines. The gob area is a fractured zone in a mine seam that is the result of the relaxation and collapse of strata surrounding the mined coal seam. Such "gobs" can be significant sources of CFLt emissions. Gob gas vent holes drilled into mine gobs after mining generally vent the degasified CH4 directly to the atmosphere. These are typically equipped with exhausters on the surface to draw the gas from the gob. Monitoring equipment may or may not be equipped as part of the surface infrastructure for these gob gas vent wells, but would be in place where the collected gas is sold or used onsite. In many cases, the CH4 recovered from degasification systems can be productively utilized. Methane emitted from coal mine ventilation systems constitutes an unused potential source of energy. Utilization technologies for recovered coal mine CH4 fall into three broad categories: 1) natural gas substitution, 2) direct use at or near the mine site, and 3) electricity generation and/or cogeneration. High quality coal mine gas may require only modest processing before compression and pipeline injection, while medium-quality coal mine gas may require some processing or upgrading, but then can be used in nearby boilers or furnaces, or in internal combustion engines and gas turbines. In cases where the sale and/or use of coal mine gas would not be profitable or feasible, an alternative to utilization for mitigating coal mine CH4 emissions is to destroy the CH4 via flaring, thus converting the higher global warming intensity CH4 into lower intensity CC>2. Procedures to estimate CH4 emissions from degasification will include estimating "emissions avoided." Estimating these "emissions avoided" has value in several respects. First, it provides a method for verifying emissions estimates for gassy mines. Second, it provides a mechanism for documenting current actions by operators to reduce emissions, even if these reductions were primarily implemented for safety, rather than GHG reduction, reasons. Emissions from post mining operations Other sources of CFLt emissions from the mining sector relate to activities after the coal is mined, and include coal piles and coal storage areas, coal transport operations, and the coal preparation plant. Estimated post-mining emissions accounted for 14% of all coal mining sector fugitive CFLt emissions in 2006, representing 8.6 million metric tons of CC^e. These emissions apply to both underground and surface coal mines. For these sources of fugitive emissions, emissions estimates are generally developed for emissions inventory purposes by using standard region or basin-specific emission factors, multiplied by rates of coal production, applied to all "post- mining" activities. Measuring and/or monitoring emissions from these operations would be difficult, since no robust monitoring methodology has been developed for these emissions. Moreover, existing emission factors are highly uncertain; and are established based on very sporadic data, if based on any emissions data at all. One category of post-mining emissions that perhaps could be considered for monitoring would be emissions from coal preparation plants. On April 16, 2008 (Federal Register: April 28, 2008, Vol. 73, No. 82, pp. 22901-22913), EPA proposed revisions to emissions control requirements for new coal preparation plants. These proposed new source performance standards (NSPS) would apply to new coal preparation plants that process more than 200 tons of coal per day. The proposed NSPS would apply to new, modified, and reconstructed coal preparation plants and reflect improvements in emission control technologies for particulate matter (PM) that have been developed since the original NSPS for these sources were issued in 1976. 2/11/2009 ------- As part of these new proposed NSPS requirements, EPA is proposing to require owners/operators of thermal dryers and pneumatic coal-cleaning equipment at constructed, modified, or reconstructed coal preparation plants to either install and operate a PM continuous emissions monitoring system (CEMS), or to conduct annual PM performance tests. A possible logical extension of this proposal would be to also include monitoring for fugitive CH4 emissions from these coal preparation plants. For the installation of a new CEMS, the incremental costs of adding CR4 monitoring capability to the PM monitoring capability would be quite small, since the dual monitoring capability can be designed within the same system. Retrofitting after the fact to add CH4 monitoring would cost more. It is important to note that fugitive emissions from coal preparation plants represent a small portion of the total emissions from the coal mining sector. In fact, the vast majority of GHG emissions from a coal preparation plant correspond to the fuel consumed for various operations such as coal drying. Fugitive CH4 emissions will only correspond to any remaining CH4 emitted from the coal during processing. Emissions from surface mines Surface coal mines release CH4 as the overburden is removed and the coal is exposed. The level of estimated emissions from surface mines is much lower than that from underground mines, representing 22% of all coal mine fugitive emissions, amounting to 14.0 million metric tons of CO26. Moreover, similar to that for post mining operations, emissions for surface mining are generally estimated for national inventory purposes by using standard region or basin-specific emission factors, multiplied by rates of coal production, applied to all surface mining activities. Monitoring emissions from these operations would be difficult, since; again, no robust methodology has been developed. Moreover, existing emission factors are highly uncertain; and are established based on very sporadic data, if based on any emissions data at all. Emissions from abandoned mines When coal mines are no longer operated to produce coal, they are known as closed or "abandoned" mines. Even though active mining no longer occurs, these abandoned mines can still produce CH4 emissions from diffuse vents, fissures, or boreholes. This CH4 can be deliberately extracted and used to generate power or for other end uses. Methane liberated from abandoned mines is estimated to be 6.8 million metric tons of CC^e per year, of which an estimated 1.4 million metric tons of CC^e per year is recovered and used (EPA 2008). Therefore, an estimated 5.4 million metric tons of CC^e is emitted per year, representing 8% of all fugitive CH4 emissions from coal mines. There are several thousand abandoned coal mines in the United States. Of these, EPA has identified some 400 abandoned mines that are considered "gassy," and has developed profiles of potential projects at abandoned mines that may be good candidates for project development (EPA 2004). Measuring and/or monitoring emissions from abandoned mines would be difficult. There is currently no robust way to measure fugitive emissions from abandoned mines. Measuring at discrete borehole/wellhead sites would not adequately capture the emissions seeping out of various other fissures and leakage points. Moreover, in many cases, it can be quite difficult to identify owners of abandoned mine sites, i.e., it would be difficult to identify the responsible parties to monitor and report. Even where the owner is known, abandoned sites are unmanned 2/11/2009 ------- and often remote; and it would be burdensome to require company personnel to travel to each abandoned mine site to measure emissions, along with being expensive and resource-intensive, especially given the relatively small contribution abandoned mines make to total GHG emissions in the coal mining sector. ii) Combustion Emissions Estimates of fuel consumption in the mining sector are reported by the Bureau of the Census (Census, 2004a, 2004b, 2004c, 2004d) for 2002, which include coal consumed directly in mining operations, distillate, residual fuel oil, natural gas, gasoline, and purchased electricity. The 2002 fuel consumption estimates were updated to 2006 based on 2006 levels of coal production, and based on this, an estimated 9 million metric tons of CC>2 emissions were associated with energy use in coal mining operations in the United States in 2006. The majority of these emissions result from the generation of electricity purchased to support mining operations. The CC>2 emissions from only on-site combustion (the value used in this analysis) are estimated to be 3.62 million metric tons. 2. Options for Reporting Thresholds In general, MSHA samples (quarterly or more frequently) CH4 emissions for mines liberating more than 100,000 cubic feet of CH4 per day from ventilation systems,2 which is equivalent to about 15,000 metric tons CC^e per year. However, emissions rates from some mines emitting less than that threshold are included in the MSHA database. Of the over 600 underground coal mines operating in the U.S. according to EIA, ventilation air emissions based on MSHA inspections were reported and electronically accounted for in 128 mines in 2006. a. Options Considered Several different emissions thresholds were considered for fugitive CH4 emissions from underground coal mines based on the data in the MSHA databases and the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2006. The estimated emissions and facilities covered are summarized in Table 1 for different emissions threshold levels, based on 2006 emissions levels. Table 1 Threshold Analysis for Underground Coal Mining- Source Category Underground Coal Mining Underground Coal Mining Threshold Level (Metric tons CO2e per year) 100,000 50,000 Total National Emissions3 (Metric tons C02e) 39,520,000 39,520,000 Number of Facilities'1 612 612 Emissions Covered0 Process Emissions (Metric tons CO2e/yr) 30,649,815 32,316,726 Estimated Combustion CO2 Emissions (Metric tons/yr) 405,040 438,262 Metric tons (C02e/yr) 31,054,856 32,754,988 Percent 79% 83% Facilities Covered Number 53 77 Percent 9% 13% Personal communication, Fred H. Menke, Jr., Supervisory IT Specialist, Mine Safety and Health Administration, to Michael Codec, Advanced Resources International, April 25, 2008. 2/11/2009 ------- Underground Coal Mining Underground Coal Mining Underground Coal Mining Underground Coal Mining 25,000 MSHA quarterly reporting threshold 10,000 1,000 39,520,000 39,520,000 39,520,000 39,520,000 612 612 612 612 33,082,854 33,364,265 33,465,371 33,483,922 453,531 459,140 461,155 461,524 33,536,385 33,823,404 33,926,526 33,945,446 85% 86% 86% 86% 100 114 122 125 16% 19% 20% 20% a Estimated national fugitive CH4 emissions for underground mining from 2006 Annual Inventory (Table 3- 26) (http://epa.gov/climatechange/emissions/downloads/08 Energv.pdf): plus estimated combustion emissions of 3.62 million metric tons, excluding those associated with purchased electricity. b Number of active underground coal mines in the U.S. in 2006 according to the Energy Information Administration (EIA 2007). 0 Based on the fugitive CH4 emissions volumes reported for individual mines in the MSHA database "Analysis of 2006 Emissions Data for Active Underground Mines," along with estimated combustion-related emissions from these mine sites, but not including emissions associated with purchased electricity. Estimates made for fuel combustion emissions based on Bureau of Census data on fuel use as a % of coal mined (for gassiest mines) or as % of vented emissions for less gassy mines. Combustion emissions calculated as approximately 1% to 3% of vented emissions, on CO2e basis. b. Emissions and Facilities Covered Per Option The fugitive CH4 emissions from the 114 of the 128 underground coal mines reporting ventilation emissions in 2006 of over approximately 15,000 metric tons of CC^e per year (equivalent to the current MSHA threshold for accounting for emissions from gassy mines) accounts for 86% of the 39.5 million metric tons estimated to be emitted by underground coal mines (35.9 million metric tons from fugitive CH4 emissions and 3.6 million metric tons from combustion emissions, excluding those emissions associated with purchased electricity). These 114 mines represent 19% of the active underground mines in the United States. Increasing the reporting threshold to 25,000 metric tons of CC^e per year would reduce the number of reporting mines by 14 to 100 and would reduce the amount of total emissions reported from this sector by 3%. If no threshold is established, and all mines must report, this will add nearly 500 mines to the number required to report, but these 500 mines would only represent another 14% of the total GHG emissions from underground coal mines. Other options for establishing thresholds could be based on other factors, such as coal production. Alternative threshold levels for reporting could also be considered. However, since all underground coal mines are subject to MSHA inspections where CH4 concentration samples and ventilation air rate measurements are taken; and thresholds for reporting emissions above defined levels are already established by MSHA policies and procedures, maintaining this threshold is likely the most logical and least burdensome method for establishing GHG monitoring and reporting thresholds for the coal mining sector, while capturing a majority of GHG emissions from coal mining. 3. Existing Relevant Reporting Programs/Methodologies For this proposal, EPA reviewed several protocols and programs with guidance monitoring and/or estimating GHG from this source, including the 2006 IPCC GL, U.S. GHG Inventory, 2/11/2009 ------- California AB32 ("CARS rule"), EIA's 1605(b) program, EPA's Coalbed Methane Outreach Program (CMOP), MSHA, BLM, and Australia's National Mandatory GHG Reporting Program (draft). In general, there are three methods for monitoring emissions: the use of emission factors, periodic sampling of CH4 concentrations and flow, and direct measurement. This section presents the existing relevant monitoring methods by coal mine CH4 sources. Underground mines - mine ventilation To calculate emissions from ventilation at underground mines in the Inventory of U.S. Greenhouse Gas Emissions and Sinks, EPA uses CH4 emissions data collected through an MSHA sampling program, which also serves as the basis for EPA's CMOP emissions estimates from this source. MSHA regulatory requirements specify that qualified and trained MSHA field inspectors perform periodic mine safety inspections at all underground coal mines in the United States, and as part of these inspections, test CH4 emissions rates at each coal mine according to MSHA-approved sampling procedures.3 Air sampling is conducted by MSHA inspectors collecting air bottle samples at a mine's main fans, along with a total quantity air ventilation volume reading. Sampling procedures and equipment are approved by MSHA (NIOSH 2006). The sample bottles are sent to the MSHA lab for analysis and the results are provided back to the MSHA district offices for inclusion in the inspection report. The results are also maintained separately by the district ventilation group. In general, air sample readings with CH4 concentrations below 50 ppm are considered non- detectable. Annual air samples and ventilation readings are taken annually unless emission rates exceed 100,000 standard cubic feet per day, where quarterly sampling is conducted. MSHA electronically keeps track of emissions for mines liberating more than 100,000 cubic feet of CH4 per day,4 which is equivalent to about 15,000 metric tons CO26 per year. If emissions levels are greater that 200,000 cubic feet per day, according to Section 103 (i) of the Federal Mine Safety & Health Act of 1977 (Public Law 95-164), more frequent inspections are mandated, with the frequency determined by the daily CH4 liberation rate calculated for the mine. For the mines with emissions exceeding 100,000 cubic feet per day, annual ventilation emissions estimates are developed by averaging the four quarterly tests, and are accurate to the extent that the data collected are representative of actual emissions. In addition, for federal coal leases where degasification systems are in place, the Bureau of Land Management (BLM) requests that mine operators provide CH4 emissions rates from both degasification and ventilation systems to BLM. Operators currently provide this information voluntarily; it is not a requirement either by regulation or under their federal coal lease terms.5 3 MSHA requires that monitoring be performed by a qualified person using CH4 monitoring devices approved by MSHA (under 30 CFR Parts 18,21,22,23,27, and 29); and that are maintained in permissible and proper operating condition and calibrated with a known CH4-air mixture at least once every 31 days. 4 Personal communication, Fred H. Menke, Jr., Supervisory IT Specialist, Mine Safety and Health Administration, to Michael Codec, Advanced Resources International, April 25, 2008. 5 Personnel communication, Desty Dyer, U.S. Bureau of Land Management (BLM), Montrose Field Office, to Michael Codec, Advanced Resources International, Inc., June 6, 2008 2/11/2009 10 ------- For this source, the IPCC Guidelines recommend that where mine-specific measurement data are available, it is good practice to use a method comparable to that based on the MSHA sampling results. In situations when mine-specific measurement data are available only for a subset of underground mines (which generally should not be the case in the United States), the Guidelines specify that emissions from the remaining mines can be calculated with emission factors based on the mines with measurement data. These emission factors can be based on specific emission rates derived from operating mines within the same basin, or on the basis of mine-specific properties, such as the average depth of the coal mines. When no mine-specific data are available, but country- or basin-specific data are, the IPCC Guidelines suggest that it is good practice to employ a Tier 2 method. Where no data (or very limited data) are available, the Guidelines specify that it is good practice to use a Tier 1 approach, provided underground coal mining is not a key sub source category. DOE 1605(b) inventory reporting guidelines specify that mines with undetectable CH4 levels can calculate ventilation emissions by multiplying a flow rate of 3,000 cubic feet per minute by an assumed CH4 concentration of 0.05% to derive a CH4 emissions rate (DOE 2007). DOE 1605(b) guidelines otherwise provide the same methodology as the Inventory of U.S. Greenhouse Gas Emissions and Sinks and IPCC. Australia's National Mandatory GHG Reporting Program (draft) (Australia 2008) recommends a methodology comparable to that in the 2006 IPCC Guidelines. Recent draft regulations proposed by the California Air Resources Board (CARB 2008) do not prescribe any approach for estimating emissions from coal mining operations; these only propose the use of emission factors to estimate emissions from post-mining coal storage and handling activities (see discussion below). Underground mines - degasification As discussed above, of the 20 U.S. coal mines deploying degasification systems in 2006, 13 mines sold this gas to a pipeline. It is common practice for these mines to monitor the volume of gas produced and delivered to the pipeline (which also monitored these volumes). Coal mines using CH4 from degasification systems on site to heat mine ventilation air are also likely to monitor the volumes of CH4 produced. In contrast to CH4 emissions from ventilation systems, no agency requires mines to report the amount of CH4 they drain from degasification systems. MSHA collects information about the presence and type of degasification systems in some mines, but does not collect quantitative data on the amount of CH4 liberated. As mentioned above, BLM requests that mine operators on federal coal leases provide information on CH4 emissions from both ventilation and degasifications systems. In most instances, it would be relatively straightforward for operators to report the annual volumes of CH4 liberated from mine degasification systems, along with the disposition of the degasified CH4 (e.g.; vented, flared, sold, and/or consumed on-site). This is based on the fact that most mines already provide such information to EPA's CMOP program (and, in a few cases, to BLM), though perhaps not always on a regular basis. If not, they are still likely to have good measurements or estimates on hand. As part of the annual U.S. inventory (EPA 2008), EPA estimates the volume of CH4 drained assuming drainage efficiencies based on information obtained from MSHA district offices or 2/11/2009 11 ------- from information provided by operators. Some of the coal mines employing degasification systems have provided EPA with information regarding CH4 liberated from their degasification systems. In cases in which mines sell CH4 recovered from degasification systems to a pipeline, gas sales are used to estimate CH4 liberated from degasification systems. For those mines that do not sell CH4 to a pipeline and/or do not currently provide information to EPA, CH4 liberated from degasification systems is estimated by EPA based on the type of system employed. For example, for coal mines employing gob wells and horizontal boreholes, the methodology assumes that CH4 volumes liberated from degasification systems account for 40% of total CH4 liberated from the mine. This is also the recommended method presented in the DOE 1605(b) Guidelines. The IPCC Guidelines suggest a similar approach. Where ventilation can be measured (or can be estimated from measurements from similar mines in the same basin or region), but not degasification volumes, they suggest that reporters estimate the amount degasified (although no methodology is specified) and use appropriate methods for accounting for the disposition of the degasified CFLt (e.g.; vented, flared, sold, consumed on-site). Several suggested approaches are provided in the Guidelines. Australia's National Mandatory GHG Reporting Program (draft) (Australia 2008) recommends a methodology comparable to that in IPCC Guidelines. Post mining operations For post-mining operations, since mine-specific emissions measurements are not available, emissions estimates for the U.S. inventory are developed by using basin-specific coal production multiplied by a basin-specific emission factor. Emission factors for surface mined coal were developed from the in situ CFLt content of the surface coal in each basin. Furthermore, the post- mining emission factors used were estimated to be 25 to 40% of the average in situ CFLt content in the basin. Thus, for the current inventory, the post-mining emission factor was determined to be 32.5% of the in situ CH4 content in the basin. The IPCC Guidelines and the DOE 1605(b) guidelines also recommend this approach for inventory development purposes, and CARB recommends this approach (for coal storage) as part of its mandatory greenhouse gas reporting program. Australia's National Mandatory GHG Reporting Program (draft) (Australia 2008) recommends a methodology comparable to that in IPCC Guidelines. Surface mines Similarly, surface mining emissions estimates for the U.S. inventory are also developed by using basin-specific coal production multiplied by a basin-specific emission factor. Emission factors for surface mined coal were developed from the in situ CH4 content of the surface coal in each basin. Surface mining emission factors were estimated to be from 1 to 3 times the average in situ CFLt content in the basin. For the current inventory, the surface mining emission factor was determined to be twice the in situ CFLt content in the basin. Again, the IPCC Guidelines and the DOE 1605(b) guidelines also recommend this approach for inventory development purposes, as does Australia's National Mandatory GHG Reporting Program (draft). Abandoned mines EPA (EPA 2004) and the IPCC (IPCC 2006) have developed emissions estimation methodologies for abandoned underground mines for emissions inventory purposes. EPA (EPA 2/11/2009 12 ------- 2004) has developed emissions estimation methodologies for abandoned or closed underground mines for emissions inventory purposes based on the time since abandonment; gas content and adsorption characteristics of the coal, CH4 flow capacity of the mine; mine flooding; the presence of vent holes, and mine seals. The IPCC methodology is based on the elapsed time since abandonment, the mine's initial gassiness, and the extent to which the mines have become flooded. Similarly, the EPA methodology is based on the time since abandonment; gas content and adsorption characteristics of coal, CH4 flow capacity of the mine; mine flooding; the presence of vent holes, and mine seals. Both methodologies recommend default assumptions and approaches for calculating emission factors for abandoned underground and surface mines and the portion of mines that are gassy. The current methodologies (EPA and IPCC) use an estimation technique based on modeling; thus it is not very accurate unless considerable data are available to make site-specific estimates. Australia's National Mandatory GHG Reporting Program (draft) (Australia 2008) recommends a methodology comparable to that in IPCC Guidelines. DOE 1605(b) guidelines contain no specific recommendations for estimating emissions from abandoned coal mines. 4. Proposed Monitoring Methods a. Monitoring Methods Considered Emissions in Ventilation Air i. Option 1: Direct Measurement (Annual Reporting) The direct measurement option considered would involve implementing a continuous monitoring program in underground U.S. coal mines, focused specifically on monitoring the emissions from underground coal mine ventilation shafts. This option builds upon the fact that continuous monitors are already in place throughout all underground coal mines. For compliance with this GHG emissions monitoring rule, such monitoring devices could be placed at or near the mine vent outflows where the air samples are taken my MSHA inspectors. Federal safety standards6 mandate that, "when 1.0 percent or more CH4 is present in a working place or an intake air course [...] electrically powered equipment in the affected area shall be de- energized, and other mechanized equipment shall be shut off." A flammable mixture of CH4 and air can be ignited by electric arcs and sparks, open flames, or by the heat of friction between the cutting bits of mining equipment and the mine rock immediately above or below the coal. To ensure that CH4 levels in underground coal mines remain below combustible levels, continuous monitoring devices are already in operation within underground coal mines. MSHA regulations require that wall and/or machine-mounted CH4 monitors are mounted at various locations and on certain types of machinery to continuously monitor mine air quality. These 6 Code of Federal Regulations. Title 30, Part 75: Mandatory safety standards-underground coal mines 2/11/2009 13 ------- monitors are certified under 30 CFR Part 27,7 which requires monitoring system design and operation that prevents the mining equipment from operating unless the CH4 monitoring system is functioning. The CH4 monitoring system has a warning device that activates when the CH4 concentration is above 1.0% to 1.5%, and has a means to shut off power to the equipment when the CH4 concentration is above 2.0%. The advantage of continuous monitoring is that it takes into consideration any variability in emissions from mining operations that may not be represented in periodic sampling. Moreover, since such devices are already used within the mine, mine operator personnel are familiar with their operation. Methane detectors fall into two categories: portable CH4 detectors and wall or machine-mounted monitors. Most CH4 detectors used in mining use a catalytic heat of combustion sensor to detect CH4 and other combustible gases. These have been proven reliable through many years of operation. For detection of CH4, proper operation of catalytic heat of combustion sensors requires both a CH4 concentration below 8% (by volume) and oxygen content above 10% - requirements that are usually satisfied in mining applications. Some detectors measure the CH4 concentration by using infrared absorption as an operating method. These infrared detectors can measure accurately without oxygen and at concentrations up to 100% CH4. However, water vapor and dust can cause operating difficulties. In some mines, the CH4 may be accompanied by ethane, which can produce an exaggerated infrared detector response. Machine-mounted CH4 monitors are usually mounted on mining and tunnel-boring machines. They are designed to have their readout display separated from the sensing head so that the readout is visible to the machine operator and the sensing head is placed in a location where CH4 is most likely to accumulate. Machine and wall-mounted monitors operate continuously and can identify emission peaks. Using machine or wall-mounted monitors could likely improve the accuracy of emissions measurements in underground mines, when operated and calibrated properly, compared to just periodic sampling. The accuracy of such devices is acceptable for emissions monitoring purposes, since they are sufficient for purposes of ensuring mine safety. The resolution of these monitors can be specified - in general, the higher the resolution, the higher the cost. Resolutions at levels lower than the 50 ppm limit, which characterizes the current MSHA sampling protocol, are certainly achievable. Nonetheless, emissions at levels below the resolution of the monitors, if assumed to be zero, whatever the threshold, could correspond to an underestimation of emissions. However, as shown above in Table 1, 85% of the GHG emissions from U.S. coal mines (including combustion emissions) occur in just 100 of the over 600 coal mines in the United States, so increased accuracy does not necessarily provide much improvement in capturing GHG emissions from this sector. A disadvantage would be the larger costs associated with purchasing and maintaining these continuous emissions monitoring systems (CEMS) devices for this application. ii. Option 2: Quarterly Sampling of CH4 Content and Gas Flow 7 A list of approved gas monitors for U.S. mines is available from MSHA's Approval and Certification Center (http://www.msha.gov/TECHSUPP/ACC/lists/27mthmon.pdf) 2/11/2009 14 ------- Under this option, coal mine operators would be required to duplicate the MSHA process of collecting air samples and ventilation rates, submitting the samples to a lab for analysis, and developing estimates of emissions on their own. The advantage of this option would be that the responsibility for monitoring would rest with the mine operator, which is consistent with most, if not all, of the other industrial sectors likely to be affected by the rule. Moreover, it would not involve EPA imposing regulatory responsibilities on another federal agency. However, it would require mine operators to purchase sampling equipment, train personnel in their use, develop emissions estimates based on the data collected, and report the results. If this option is pursued, the operator would have to incur the capital and O&M costs involved in purchasing and maintaining the air sampling equipment, and in sending air samples to an independent lab for analysis. Alternatively, the results of MSHA inspections could be used to estimate ventilation air emissions. In this case, either the mines would obtain data from MSHA (it is not currently shared with the mine), or sampling and reporting would be the responsibility of MSHA. An advantage of MSHA sampling and reporting is that MSHA inspectors have procedures in place, and a high level of QA/QC established for this process. No additional training of operator personnel would be required, the implementation period could be almost instantaneous, and the accuracy of emissions estimates would most likely be higher. iii. Option 2: More Frequent Sampling Sampling could be done more frequently than quarterly. This could provide a more consistent, reliable, and representative characterization of fugitive CH4 mine emissions, but at a higher cost. iv. Option 3: Simplified Emission Calculation This option would involve utilizing the same procedures as recommended by the IPCC and DOE 1605(b) Guidelines, assuming no mine-specific data were available. For inventory reporting purposes, the IPCC Guidelines recommend that when ventilation emissions cannot be measured, they can be estimated from measurements from similar mines in the same basin or region. If analogous mine-specific data are unavailable, they recommend using basin/region-specific emission factor multiplied by production, and representative emissions factors are provided in the Guidelines. Since mine-specific data is available in the U.S. from MSHA inspections, Option 3 represents a more simplified, and considerably less accurate, methodology compared to that currently used in U.S. underground coal mines. Degasification Systems (i) Option 1: Direct Measurement This option involves continuous monitoring of gas recovered from mine degasification systems. This option would apply to all degasification wells, including gob gas vent holes and other degasification wells that are currently not monitored. Approaches for monitoring the volumes of CH4 produced from coal mine degasification systems prior to mining use the same general techniques for monitoring gas flows from natural gas production wells. Recommendations for improved approaches for both degasification systems and monitoring gas flow specifically from degasification wells date back to the mid-1970s (Lambert and Trevits, 1978; Diamond, 1994). Degasification systems operate in conjunction 2/11/2009 15 ------- with the ventilation system and overall mining operations, generally requiring coordinated management (using measuring instruments, monitoring, controls, and good communications) to optimize overall operations.8 The advantages to this approach are that continuous monitoring provides accurate data and can captures seasonal changes in gas flow and concentrations, and that most degasification systems already have continuous monitoring in place. The disadvantage would be the costs incurred by mines that do not currently have these systems in place. ii) Option 2: Sampling of CFU Content and Gas Flow This option would involve continuous monitoring for those wells already deploying such systems, but would allow periodic sampling and reporting for those that do not. For example, gob gas vent holes that are currently not monitored could conduct periodic sampling, as could perhaps any other degasification borehole, rather than installing continuous monitoring. For example, weekly or monthly sampling at each gob gas vent hole/well could be conducted. While such an approach would involve less capital costs, greater labor costs would be involved with traveling to each (often remote) well/vent site to take samples. If direct measurements of gas volumes are not available for degasification wells, other options could be to: (1) use gas sales data, and/or (2) apply an assumed degasification efficiency based on the technology used. This is the procedure suggested in the IPCC and DOE 1605(b) Guidelines, and is the method currently used in the U.S. inventory if underground coal mine degasification volumes are not available. For example, for coal mines employing gob wells and horizontal boreholes, the methodology assumes that degasification emissions account for 40% of total CH4 liberated from the mine. Gas sales data, if available, should be a direct proxy for the volume of methane produced from degasification systems, and is clearly better than a assumed degasification efficiency should sales data be available. While simple in application, the use of an assumed degasification efficiency is highly uncertain, since such an efficiency is clearly a function of many mine-specific parameters that can vary considerably from mine-to-mine. Option 3: Simplified Emission Calculation This option would involve utilizing the same procedures as recommended by the IPCC and/or DOE 1605(b) Guidelines, assuming no mine-specific data were available. For GHG inventory reporting purposes, the IPCC Guidelines recommend that when recovered gas from degasification systems cannot be measured, they can be estimated from measurements from similar mines in the same basin or region. If analogous mine-specific data are unavailable, they recommend using basin/region-specific emission factor multiplied by production, and representative emissions factors are provided in the Guidelines. Again, similar to that discussed above, while simple in application, the use of simplified emissions calculation approach is highly uncertain, since emission are a function of many mine-specific parameters that can vary considerably from mine-to-mine. Methane Combustion at Ventilation or Degasification Systems (i) Option 1: Direct Measurement 1 http://www.epa. gov/cmop/docs/ggasrecpv.pdf 2/11/2009 16 ------- This option involves continuous monitoring of the disposition of gas recovered from coal mines. Although this measurement is continuous, reporting would only be annual. This option would apply to all degasification wells, including gob gas vent holes and other degasification wells that are currently not monitored. Approaches for monitoring the volumes of CH4 produced from coal mine degasification systems prior to mining use the same general techniques for monitoring gas flows from natural gas production wells. Recommendations for improved approaches for both degasification systems and monitoring gas flow specifically from degasification wells date back to the mid-1970s (Lambert and Trevits, 1978; Diamond, 1994). Degasification systems operate in conjunction with the ventilation system and overall mining operations, generally requiring coordinated management (using measuring instruments, monitoring, controls, and good communications) to optimize overall operations.9 The advantages to this approach are that continuous monitoring provides accurate data and can captures seasonal changes in gas flow and concentrations, and that most degasification systems already have continuous monitoring in place. The disadvantage would be the costs incurred by mines that do not currently have these systems in place. iii) Option 2: Sampling of CFU Content and Gas Flow This option would involve continuous monitoring for those wells already deploying such systems, but would allow periodic sampling and reporting for those that do not. For example, gob gas vent holes that are currently not monitored could conduct periodic sampling, as could perhaps any other degasification borehole, rather than installing continuous monitoring. For example, weekly or monthly sampling at each gob gas vent hole/well could be conducted. While such an approach would involve less capital costs, greater labor costs would be involved with traveling to each (often remote) well/vent site to take samples. If direct measurements of gas volumes are not available for degasification wells, other options could be to: (1) use gas sales data, and/or (2) apply an assumed degasification efficiency based on the technology used. This is the procedure suggested in the IPCC and DOE 1605(b) Guidelines, and is the method currently used in the U.S. inventory if underground coal mine degasification volumes are not available. For example, for coal mines employing gob wells and horizontal boreholes, the methodology assumes that degasification emissions account for 40% of total CH4 liberated from the mine. iv) Option 3: Simplified Emission Calculation This option would involve utilizing the same procedures as recommended by the IPCC and/or DOE 1605(b) Guidelines, assuming no mine-specific data were available. For GHG inventory reporting purposes, the IPCC Guidelines recommend that when recovered gas from degasification systems cannot be measured, they can be estimated from measurements from similar mines in the same basin or region. If analogous mine-specific data are unavailable, they recommend using basin/region-specific emission factor multiplied by production, and representative emissions factors are provided in the Guidelines. 5. Procedures for Estimating Missing Data 9 http://www.epa. gov/cmop/docs/ggasrecpv.pdf 2/11/2009 17 ------- Options and considerations for missing data vary will vary depending on the proposed monitoring method. In general, each option would require a complete record of all measured parameters and parameters determined from company records that are used in the GHG emissions calculations (e.g., carbon contents, monthly fuel consumption, etc.). Therefore, whenever a quality-assured value of a required parameter is unavailable (e.g., if a monitor or CEMS malfunctions during unit operation or if a required fuel input parameter is not obtained), a substitute data value for the missing parameter must be used in the calculations. In addition, since periodic inspections are performed on all underground coal mines, data on CH4 concentrations (above 50 ppm) and ventilation rates exist for all mines. For mines below the 50 ppm "detectable" threshold, estimates could be made for emission rates assuming some value for CH4 concentrations (say 25 ppm). However, it again should be emphasized that the vast majority of emissions from underground coal mines come from roughly 1/6 of the gassiest underground coal mines. For emissions avoided from degasification systems, methods are described above for estimating volumes for CFLi recovered (Option 3) should recovered volumes not be known. For missing gas flow or gas recovery data, the substitute data value could be the arithmetic average of the quality-assured values of that parameter immediately preceding and immediately following the missing data incident. If, for a particular parameter, no quality-assured data are available prior to the missing data incident, the substitute data value shall be the first quality- assured value obtained after the missing data period. EPA considered not deducting CFLi combustion that was not recorded, but not including CFLi recovery could greatly overestimate an entity's emissions. On the other hand, allowing extended periods of missing data provides a disincentive to repairing the monitoring system. 6. QA/QC and Verification Requirements In addition, mines should conduct quality assurance and quality control of emission estimates reported. Facilities are encouraged to prepare an in-depth quality assurance and quality control plan which would include checks on the data collected, and the calculations performed to estimate GHG emissions. MSHA has established specific regulatory requirements for maintaining and ensuring the accuracy of mine sampling processes and for the operation of in-mine monitors. In particular, 30 CFR Part 75 specifies requirements for the maintenance and use of in-mine CFLt monitors and for portable air quality detectors and measurement devices. The section also sets forth requirements for ensuring that MSHA inspectors are trained and certified to take samples, and operators responsible for in-mine monitoring systems must also be certified. In general, since their primary current applications are for ensuring mine safety, the accuracy of existing CH4 detectors and emission measurement devices provide a level of accuracy and performance that is acceptable for GHG emissions monitoring applications. Similarly, since they are used to register volumes for gas sales, existing monitors for measuring gas produced from degasification systems are considered to be accurate, and both sellers and buyers of the gas produced have a vested interest in ensuring that the volumes recovered are accurate. 2/11/2009 18 ------- 7. Reporting Procedures For the coal mining industrial sector, the issues to consider with regard to reporting relate both to the party responsible for reporting emissions to EPA, and to the frequency of reporting. In the case of the reporting party, options to consider include whether MSHA does the reporting to EPA (of emissions from ventilation systems), or if the operator should be responsible for reporting. Recovered CFLi volumes from degasifications systems (emissions avoided) will be reported by the operator. In terms of frequency, options to consider include annual, quarterly, and, perhaps, even more frequent reporting. EPA considered quarterly reporting. The issues (other than frequency, as noted above) to consider are somewhat different for reporting of emissions from ventilation systems or emissions avoided from degasification systems, so each of these two areas are discussed separately below. Emissions in Ventilation Air With regard to mine CFLi ventilation emissions, the information currently collected by MSHA (CFLt concentration, ventilation flow rates, major changes in mine activity, etc.) should be sufficient to support implementation of Options 2, 3, or 4, discussed above. However, current CH4 emissions data collection and reporting are conducted by MSHA field inspectors, with the results reported to and maintained by MSHA district offices. In general, mine operators are currently not provided a copy of the results of the sampling or the estimates made for CH4 emissions, unless emission levels are of concern to MSHA. As discussed above, MSHA currently voluntarily provides EPA with its mine-by-mine estimates of annual CH4 emissions for the gassiest mines. This provides the basis for both EPA's estimates of coal sector emissions in the national inventory (EPA 2008), as well as providing the Coalbed Methane Outreach Program (CMOP) its basis for identifying opportunities for CH4 recovery at U.S. coal mines (EPA 2005). However, in developing is annual emission estimates, MSHA develops these estimates by averaging the sample data results from quarterly inspections. Several options are available for reporting the results of GHG emissions monitoring in the coal mining sector. These are: MSHA continues to collect ventilation air samples and rates, and from these develop estimates of GHG emissions for all mines that exceed a defined emissions threshold (currently 100,000 cubic feet per day). Then, MSHA would be responsible for reporting emissions estimates directly to EPA. Under this option, the incremental burden on both coal mine operators and MSHA would be small. MSHA continues to collect ventilation air samples and rates, and from these develop estimates of GHG emissions for all mines that exceed the defined emissions threshold. Then, MSHA would make these emissions estimates available to mine operators, and the operators would be responsible for reporting emissions levels to EPA. Under this option, the burden on MSHA would be the same - it would now just provide its emissions 2/11/2009 19 ------- estimates back to the operator, rather than EPA. In this case, the burden on the operator would be greater, since it would now need to report to EPA. MSHA would continue to collect ventilation air samples and rates, but provide just the sampling results to the operator, and the operator would develop its own estimates of GHG emissions from these sample results, and report emissions estimates to EPA. Here, the burden on MSHA would actually be reduced somewhat (though it would still need to send the operators the sampling results), but the burden on the operator would be considerably greater. Coal mine operators would duplicate the MSHA process, by collecting air samples and ventilation rates, submitting the samples to a commercial lab for analysis, developing estimates of emissions, and reporting this information to EPA. This would impose a burden on the operators. The extent of the burden reduction for MSHA will depend on whether or not MSHA continues to do its own sampling under its mine inspection program, which, presumably, it would still do. Currently, although MSHA collects samples quarterly for the gassy mines, emissions estimates are only developed on an annual basis. If quarterly reporting is implemented, this would require that MSHA develop quarterly, rather than annual, CH4 emissions estimates, and report these either to EPA or to the mine operator. This would result in an increase in responsibility for MSHA as a result of regulatory requirements to mandate industrial GHG emissions monitoring, under any of the reporting options listed above. If mine air ventilation emissions are monitored using a CEMS, the operator would be responsible for reporting, at the frequency specified (annual, quarterly, etc.). Under any of the reporting options, it would also be expected that operators should also report any CH4 emissions from ventilation air that are destroyed or utilized. This data is presumably automatically collected by the installed equipment. It is also recommended that operators report the number of days in a quarter that the mine is shut down. Degasification Systems With regard to coal mine degasification systems, even when continuous monitoring of CH4 recovered from degasification systems, reporting is done on an annual or quarterly basis. Operators would be responsible for reporting the volumes of CH4 recovered from these systems, along with the disposition of the CH4 (sold, used on site, and/or destroyed/flared. Reporting would be directly to EPA. 2/11/2009 20 ------- REFERENCES Australian Government, Department of Climate Change, National Greenhouse and Energy Reporting (Measurement) Technical Guidelines 2008 vl. 0, July 2008 California Air Resources Board, Second 15-Day Modified Regulatory Language For Public Comment, Regulation For The Mandatory Reporting Of Greenhouse Gas Emissions, May 15, 2008 (http ://www.arb.ca.gov/cc/reporting/ghg-rep/ghg-rep.htm) Diamond, William P., Methane Control for Underground Coal Mines, Bureau of Mines Information Circular 9395, 1994 United States Department of Energy, Office of Policy and International Affairs, Technical Guidelines Voluntary Reporting of Greenhouse Gases (1605(B)) Program, January 2007 http://www.pi. energy. gov/enhancingghgregistry/documents/january2007_1605btechnicalguideli nes.pdf Environmental Protection Agency, Methane Emissions from Abandoned Coal Mines in the United States: Emission Inventory Methodology and 1990-2002 Emissions Estimates, Coalbed Methane Outreach Program, April 2004 (http ://www. epa. gov/coalbed/docs/amm_final_report.pdf) Environmental Protection Agency, Identifying Opportunities for Methane Recovery at U.S. Coal Mines: Profiles of Selected Gassy Underground Coal Mines: 1999-2003, EPA 430-K-04-003, September 2005 (http://www.epa.gov/coalbed/docs/profiles_2003_final.pdf) Environmental Protection Agency, Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2006, USEPA#430-R-08-005, April 2008 (http://www.epa.gov/climatechange/emissions/usinventoryreport.htmn Energy Information Administration, Annual Coal Report: 2006, DOE/EIA-0584 (2006), November 2007 (http://www.eia.doe.gov/cneaf/coal/page/acr/acr_sum.html) Intergovernmental Panel on Climate Change (IPCC), 2006IPCC Guidelines for National Greenhouse Gas Inventories, Gas Inventories, National Greenhouse Gas Inventories Programme, Eggleston H.S., Buendia L., Miwa K., Ngara T. and Tanabe K. (eds.)., 2006 (http://www.ipcc- nggip.iges.or.jp/public/2006gl/index.htm) Lambert, S.W., and M.A. Trevits, "Improved Methods for Monitoring Production from Vertical Degasification Wells, U.S. Bureau of Mines, Report of Investigations 8309, 1978 (http://www.cdc.gov/niosh/mining/pubs/pdfs/ri8309.pdf National Institute for Occupational Safety and Health (NIOSH), Handbook for Methane Control in Mining, CDC Information Circular (1C) 9486, June 2006 U.S. Census Bureau, Bituminous Coal Underground Mining: 2002, 2002 Economic Census, December 2004a U.S. Census Bureau, Bituminous Coal and Lignite Surface Mining: 2002, 2002 Economic Census, December 2004b U.S. Census Bureau, Anthracite Mining: 2002, 2002 Economic Census, December 2004c U.S. Census Bureau, Support Activities for Coal Mining: 2002, 2002 Economic Census, December 2004d 2/11/2009 21 ------- 2/11/2009 22 ------- |