Powder River Basin - Memorandum
TO: Jack Stults, Administrator
Water Resources Division
FROM: Kirk Waren, Hydrogeologist
Water Management Bureau
DATE: 10/4/1999
RE: Ground water assessment, monitoring and reporting recommendations for coalbed methane operations
The type of hydrologic assessment and monitoring that is needed for a particular coalbed methane project would best be determined on a case-by-case basis. It is imperative that hydrogeologists are involved with assessing the targeted coal beds, or aquifers and in determining an appropriate monitoring scheme. This would be beneficial to producers, the Board of Oil and Gas Conservation and any other party interested in knowing what is happening to aquifer pressures in the vicinity of coalbed methane operations and its relevance to water problems or issues that arise. A qualified review board, having expertise both in natural gas operations and in hydrogeology, is recommended to approve ground water assessment and monitoring plans, evaluate monitoring results and to recommend modifications if necessary.
The following is a general description of the type of assessment and monitoring that could be used to track groundwater conditions near coalbed methane operations. These are provided with the idea in mind that enough information would be available to confidently ascertain the impacts of coalbed methane operations on the potentiometric surface, or pressure, in the coal around the periphery of the operation. This may not be an all-inclusive description, but should provide a starting point for what type of assessment and monitoring should be required for coalbed methane projects.
Qualified personnel must conduct assessment and monitoring activities. Unless some public or private agency comes forth with funding or services, it must be conducted at the expense of the coalbed methane operators. The operators can hire qualified staff, use consultants, or contract with a public agency such as MBMG, US Bureau of Land Management, or US Geological Survey to acquire data. Regardless of who does the work, certain reporting criteria must be maintained. Ground water level or pressure measurements reported through required monitoring activities must be stored at the Ground Water Information Center at the Montana Bureau of Mines and Geology (MBMG) in Butte.
Groundwater Assessment
In the Controlled Ground Water Area Proposed Order, we specified that hydrogeologic conditions must be evaluated before extensive ground water pumping is implemented to reduce aquifer pressures. Such evaluation should include maps of the natural potentiometric surface of the targeted coal bed and an assessment of existing wells, springs and streamflow that could be impacted by the operation. The basic goal of such and evaluation or assessment is to determine the natural conditions in the area before extensive pumping of groundwater and lowering of pressure in coal beds gets underway. It is imperative to have such information to determine what changes take place as a result of ground water pumping associated with coalbed methane operations.
In an area about to be tested or developed for coalbed methane, a group of test wells could be drilled at a density of about one per section to determine the potentiometric surface elevations in the coal bed in the area before any production activity is started. These wells would later be converted to methane extraction wells. The predevelopment potentiometric surface of targeted coal beds would then be mapped and some data describing baseline conditions would be generated. Ideally, the potentiometric surface should be monitored for a year, to determine natural seasonal fluctuations, however because of the time involved, this may not be practical.
Dedicated monitoring wells should be placed outside of the operating area. Initially, these wells would be used to assess conditions outside of the coalbed methane operation. They would provide information on the structure and thickness of the coal beyond the area of exploration required for the methane project. These wells would provide baseline static potentiometric surface data for areas adjacent to, but just outside of the project limits. These should be completed as permanent, dedicated monitoring wells, fitted with an access port for water level measurements, or in the case of flowing artesian conditions, set up so that accurate pressure readings can be made.
For each targeted coal bed, a minimum of four such wells should be drilled in four different directions, e.g. north, south, east and west. Ideally, the orientation of the four monitoring wells or clusters of wells should be shifted to align with the predominant potentiometric surface gradient as shown in Figure 1. In addition to the dedicated coal bed monitoring wells, at least one dedicated monitoring well should be drilled to assess baseline conditions in the first significant aquifer both overlying and underlying the coal bed, unless none exist within some reasonable distance, say 500 vertical feet. These wells would best be placed within the area of operations, for example near one of the methane extraction wells.
For larger projects, or for a number of adjacent projects in the same coal bed creating essentially a larger coalbed methane operation, more than four well would be needed. The monitoring network should include wells outside of the operating area at a distance of about 1 to 2 miles from the nearest operating methane extraction well and such wells should be placed so that nowhere along the periphery of the operations does the distance between dedicated monitoring wells exceed about 4 miles.
An inventory should be conducted on all wells and springs within at least three miles distance from the outer bounds of a proposed methane operation. The inventory should include research of MBMG and DNRC records and topographic maps, as well as interviews with local landowners.
The inventory of wells should consist of a standard hydrogeologic well inventory such as that conduced by MBMG. A set of minimum data requirements needs to be assembled and would include basic data such as owner, location, static water level or pressure, depth, well log if available and specific conductance. The inventory of springs would have special requirements, such as flow measurement or estimates, and photographs to accompany the inventory should be considered.
Figure 1. Ideal configuration of dedicated monitoring wells around a coalbed methane operation
The coal bed structure should be compared with the topography of the area to determine where the coal crops out or forms subcrops beneath alluvium in the area, regardless of distance from the operation. Any such areas should be evaluated to determine whether the pressure reductions could impact springs or groundwater discharge. Distance, the potentiometric gradient and hydraulic properties of the coal will be factors that influence the potential for reducing discharges at springs or alluvial discharge areas. Such an evaluation would then form the basis for appropriate mitigation plans.
One standard, 24-hour, constant-rate aquifer test should performed at the site to determine aquifer parameters. As with monitoring wells, if the project is unusually large, an additional test or tests may be needed, especially if the thickness or hydraulic properties of the coal appear to vary considerably in the area. Aquifer parameters of trasmissivity and storage coefficient must be determined from data collected in an observation well. The test, data collection and reports need to follow conventional, hydrogeologic standards. This test would have various applications such as determining the radius of influence of the well, estimating well interference and use in analytical evaluations or groundwater models.
Initial, baseline water quality tests must be conducted for the peripheral monitoring wells and for those adjacent aquifers above and below the coal seam. These tests should include all major ions and should follow a standard groundwater sampling protocol.
Groundwater Monitoring
Groundwater pumped for coalbed methane operations should be measured and volumes of water pumped recorded and reported on a quarterly basis. Discharge of the groundwater is under the authority of the Department of Environmental Quality and sampling and other requirements of that agency.
Ground water monitoring plans should be designed to track drawdown outside of the area of operations. Dedicated monitoring wells to be placed outside of the coalbed methane extraction well grid, as described above, would be ideally suited to monitor conditions in the coal bed just outside of the area of operations. The same data collected for the nearest overlying and underlying aquifers would provide information concerning conditions in other strata sandwiching the coal beds right in the area of operations and would therefore likely indicate the worst-case impacts to other aquifers. Pumping water levels should be reported for all coal bed methane extraction wells, or if impractical, at least some subset of the wells that provides a representative indication of the pumping levels within the area of operations.
Although subject to modification, a quarterly monitoring scheme is recommended, in which groundwater levels or pressures in the dedicated monitoring wells and pumping water levels in selected coal bed methane wells are reported. Regardless of who gets such reports, a copy of the data must be delivered to the Ground Water Information Center at MBMG.
In addition to the dedicated monitoring wells, any existing wells within 3 miles of the project and completed in the same coal seam should be considered potential monitoring locations and any such well should be subject to required monitoring with landowner permission. Without details on the locations and density of such wells, selection would best be made on a project-specific basis. However, the basic idea would be to monitor more distant wells to determine if any measurable change occurs in areas away from the operation. As a guideline, existing wells a few miles apart would be sufficient and such activities should initially extend about 3 miles away from the coalbed methane operations. If significant, or unexpectedly large drawdown occurs at the most distant wells, the monitoring could be expanded outward. Depending on conditions observed in adjacent, underlying and overlying aquifers at the operation area, ground water monitoring in those materials should also be subject to expansion if a potential for problems is found.
The water-level or pressure information collected would be used to map and track changes in the potentiometric surface. This information would serve a variety of purposes. It would be used to determine drawdowns attributable to a particular project. It can be used to estimate potential impacts to springs. It can be used to evaluate how expansion of operations or a second project may affect groundwater levels. It provides the operators and the Board of Oil and Gas Conservation with reliable data that can used in dealing with complaints.
Ground water quality samples should taken periodically in the dedicated monitoring wells to determine whether the coalbed methane operations are affecting water quality in the coal. There are a variety of ways this could happen, such as migration of more mineralized water into the coal from adjacent aquitards. This sampling could probably be infrequent, perhaps every 2 years, unless it appears to be a significant problem.
Reporting and Verification
A standard reporting mechanism should be designed. One method would be to have operators responsible for quarterly reports that provide the data. Such reports would best include both raw data and interpreted data. The reports should contain project summaries in regards to water, including amounts pumped, ground water level or pressure measurements for all designated monitoring and pumping wells and water quality data if applicable. Ideally, the reports would provide maps of the drawdown impacts outside of the operation, if any. If multiple operators are running projects near each other, the data should be presented without regard to which company’s operation might be responsible for observed changes, as that may be impossible to determine. However, the presence of adjacent operations should be noted in the reports. Regardless of format, the data and reports must be compatible with and provided to, the MBMG Ground Water Information Center.
A system of verification is recommended. This could be accomplished through access agreements that allow MBMG, DNRC, or other agencies to take measurements in dedicated monitoring wells. Some type of funding mechanism may be required if the coal bed methane operations expand significantly.
TO: Jack Stults, Administrator
Water Resources Division
FROM: Kirk Waren, Hydrogeologist
Water Management Bureau
DATE: 10/4/1999
RE: Ground water assessment, monitoring and reporting recommendations for coalbed methane operations
The type of hydrologic assessment and monitoring that is needed for a particular coalbed methane project would best be determined on a case-by-case basis. It is imperative that hydrogeologists are involved with assessing the targeted coal beds, or aquifers and in determining an appropriate monitoring scheme. This would be beneficial to producers, the Board of Oil and Gas Conservation and any other party interested in knowing what is happening to aquifer pressures in the vicinity of coalbed methane operations and its relevance to water problems or issues that arise. A qualified review board, having expertise both in natural gas operations and in hydrogeology, is recommended to approve ground water assessment and monitoring plans, evaluate monitoring results and to recommend modifications if necessary.
The following is a general description of the type of assessment and monitoring that could be used to track groundwater conditions near coalbed methane operations. These are provided with the idea in mind that enough information would be available to confidently ascertain the impacts of coalbed methane operations on the potentiometric surface, or pressure, in the coal around the periphery of the operation. This may not be an all-inclusive description, but should provide a starting point for what type of assessment and monitoring should be required for coalbed methane projects.
Qualified personnel must conduct assessment and monitoring activities. Unless some public or private agency comes forth with funding or services, it must be conducted at the expense of the coalbed methane operators. The operators can hire qualified staff, use consultants, or contract with a public agency such as MBMG, US Bureau of Land Management, or US Geological Survey to acquire data. Regardless of who does the work, certain reporting criteria must be maintained. Ground water level or pressure measurements reported through required monitoring activities must be stored at the Ground Water Information Center at the Montana Bureau of Mines and Geology (MBMG) in Butte.
Groundwater Assessment
In the Controlled Ground Water Area Proposed Order, we specified that hydrogeologic conditions must be evaluated before extensive ground water pumping is implemented to reduce aquifer pressures. Such evaluation should include maps of the natural potentiometric surface of the targeted coal bed and an assessment of existing wells, springs and streamflow that could be impacted by the operation. The basic goal of such and evaluation or assessment is to determine the natural conditions in the area before extensive pumping of groundwater and lowering of pressure in coal beds gets underway. It is imperative to have such information to determine what changes take place as a result of ground water pumping associated with coalbed methane operations.
In an area about to be tested or developed for coalbed methane, a group of test wells could be drilled at a density of about one per section to determine the potentiometric surface elevations in the coal bed in the area before any production activity is started. These wells would later be converted to methane extraction wells. The predevelopment potentiometric surface of targeted coal beds would then be mapped and some data describing baseline conditions would be generated. Ideally, the potentiometric surface should be monitored for a year, to determine natural seasonal fluctuations, however because of the time involved, this may not be practical.
Dedicated monitoring wells should be placed outside of the operating area. Initially, these wells would be used to assess conditions outside of the coalbed methane operation. They would provide information on the structure and thickness of the coal beyond the area of exploration required for the methane project. These wells would provide baseline static potentiometric surface data for areas adjacent to, but just outside of the project limits. These should be completed as permanent, dedicated monitoring wells, fitted with an access port for water level measurements, or in the case of flowing artesian conditions, set up so that accurate pressure readings can be made.
For each targeted coal bed, a minimum of four such wells should be drilled in four different directions, e.g. north, south, east and west. Ideally, the orientation of the four monitoring wells or clusters of wells should be shifted to align with the predominant potentiometric surface gradient as shown in Figure 1. In addition to the dedicated coal bed monitoring wells, at least one dedicated monitoring well should be drilled to assess baseline conditions in the first significant aquifer both overlying and underlying the coal bed, unless none exist within some reasonable distance, say 500 vertical feet. These wells would best be placed within the area of operations, for example near one of the methane extraction wells.
For larger projects, or for a number of adjacent projects in the same coal bed creating essentially a larger coalbed methane operation, more than four well would be needed. The monitoring network should include wells outside of the operating area at a distance of about 1 to 2 miles from the nearest operating methane extraction well and such wells should be placed so that nowhere along the periphery of the operations does the distance between dedicated monitoring wells exceed about 4 miles.
An inventory should be conducted on all wells and springs within at least three miles distance from the outer bounds of a proposed methane operation. The inventory should include research of MBMG and DNRC records and topographic maps, as well as interviews with local landowners.
The inventory of wells should consist of a standard hydrogeologic well inventory such as that conduced by MBMG. A set of minimum data requirements needs to be assembled and would include basic data such as owner, location, static water level or pressure, depth, well log if available and specific conductance. The inventory of springs would have special requirements, such as flow measurement or estimates, and photographs to accompany the inventory should be considered.
Figure 1. Ideal configuration of dedicated monitoring wells around a coalbed methane operation
The coal bed structure should be compared with the topography of the area to determine where the coal crops out or forms subcrops beneath alluvium in the area, regardless of distance from the operation. Any such areas should be evaluated to determine whether the pressure reductions could impact springs or groundwater discharge. Distance, the potentiometric gradient and hydraulic properties of the coal will be factors that influence the potential for reducing discharges at springs or alluvial discharge areas. Such an evaluation would then form the basis for appropriate mitigation plans.
One standard, 24-hour, constant-rate aquifer test should performed at the site to determine aquifer parameters. As with monitoring wells, if the project is unusually large, an additional test or tests may be needed, especially if the thickness or hydraulic properties of the coal appear to vary considerably in the area. Aquifer parameters of trasmissivity and storage coefficient must be determined from data collected in an observation well. The test, data collection and reports need to follow conventional, hydrogeologic standards. This test would have various applications such as determining the radius of influence of the well, estimating well interference and use in analytical evaluations or groundwater models.
Initial, baseline water quality tests must be conducted for the peripheral monitoring wells and for those adjacent aquifers above and below the coal seam. These tests should include all major ions and should follow a standard groundwater sampling protocol.
Groundwater Monitoring
Groundwater pumped for coalbed methane operations should be measured and volumes of water pumped recorded and reported on a quarterly basis. Discharge of the groundwater is under the authority of the Department of Environmental Quality and sampling and other requirements of that agency.
Ground water monitoring plans should be designed to track drawdown outside of the area of operations. Dedicated monitoring wells to be placed outside of the coalbed methane extraction well grid, as described above, would be ideally suited to monitor conditions in the coal bed just outside of the area of operations. The same data collected for the nearest overlying and underlying aquifers would provide information concerning conditions in other strata sandwiching the coal beds right in the area of operations and would therefore likely indicate the worst-case impacts to other aquifers. Pumping water levels should be reported for all coal bed methane extraction wells, or if impractical, at least some subset of the wells that provides a representative indication of the pumping levels within the area of operations.
Although subject to modification, a quarterly monitoring scheme is recommended, in which groundwater levels or pressures in the dedicated monitoring wells and pumping water levels in selected coal bed methane wells are reported. Regardless of who gets such reports, a copy of the data must be delivered to the Ground Water Information Center at MBMG.
In addition to the dedicated monitoring wells, any existing wells within 3 miles of the project and completed in the same coal seam should be considered potential monitoring locations and any such well should be subject to required monitoring with landowner permission. Without details on the locations and density of such wells, selection would best be made on a project-specific basis. However, the basic idea would be to monitor more distant wells to determine if any measurable change occurs in areas away from the operation. As a guideline, existing wells a few miles apart would be sufficient and such activities should initially extend about 3 miles away from the coalbed methane operations. If significant, or unexpectedly large drawdown occurs at the most distant wells, the monitoring could be expanded outward. Depending on conditions observed in adjacent, underlying and overlying aquifers at the operation area, ground water monitoring in those materials should also be subject to expansion if a potential for problems is found.
The water-level or pressure information collected would be used to map and track changes in the potentiometric surface. This information would serve a variety of purposes. It would be used to determine drawdowns attributable to a particular project. It can be used to estimate potential impacts to springs. It can be used to evaluate how expansion of operations or a second project may affect groundwater levels. It provides the operators and the Board of Oil and Gas Conservation with reliable data that can used in dealing with complaints.
Ground water quality samples should taken periodically in the dedicated monitoring wells to determine whether the coalbed methane operations are affecting water quality in the coal. There are a variety of ways this could happen, such as migration of more mineralized water into the coal from adjacent aquitards. This sampling could probably be infrequent, perhaps every 2 years, unless it appears to be a significant problem.
Reporting and Verification
A standard reporting mechanism should be designed. One method would be to have operators responsible for quarterly reports that provide the data. Such reports would best include both raw data and interpreted data. The reports should contain project summaries in regards to water, including amounts pumped, ground water level or pressure measurements for all designated monitoring and pumping wells and water quality data if applicable. Ideally, the reports would provide maps of the drawdown impacts outside of the operation, if any. If multiple operators are running projects near each other, the data should be presented without regard to which company’s operation might be responsible for observed changes, as that may be impossible to determine. However, the presence of adjacent operations should be noted in the reports. Regardless of format, the data and reports must be compatible with and provided to, the MBMG Ground Water Information Center.
A system of verification is recommended. This could be accomplished through access agreements that allow MBMG, DNRC, or other agencies to take measurements in dedicated monitoring wells. Some type of funding mechanism may be required if the coal bed methane operations expand significantly.