Conclusions and Recommendations
The commercial potential of some coals to serve as a source of natural gas has been realized only in the past three decades in the form of coalbed methane (CBM) production. The energy value of this resource can often be achieved by pumping water from water-saturated coal seams to reduce the pressure in the seam, allowing methane to desorb and flow to the surface. Thus, CBM production requires management of two important resources—natural gas and CBM “produced water.”
Management of CBM produced water is a challenge for regulatory agencies, CBM operators, water treatment companies, policy makers, natural resource agencies, some landowners, and the public because produced water from CBM extraction represents a waste to some and is considered a beneficial byproduct of CBM activity by others. Furthermore, natural hydrogeological variations among and within CBM basins make a simple, single management approach to CBM produced water unrealistic. Presently, no collectively and clearly defined goals, objectives, management positions, or regulatory policies exist among federal and state agencies and other stakeholders regarding CBM produced water management and potential beneficial use.
The conclusions and recommendations in this chapter are directed toward identifying and resolving what the committee identifies as gaps—in data and information about CBM produced water geochemistry and basin hydrogeology, the effects of CBM production and produced water discharges on the environment, and the regulatory framework governing the management of CBM produced water. Resolving these gaps could increase the ability of stakeholders to continue to develop more effective and sound CBM development and produced water management practices. These recommendations also serve to reinforce efforts being made by individuals, regulatory authorities, operating companies, research institutions, and water treatment companies to monitor, analyze, regulate, and treat CBM produced water for disposal and/or beneficial use. The committee has examined the most prolific CBM basins—the Powder River, San Juan, Raton, Piceance, and Uinta located in five of the six western states identified for this study—New Mexico, Colorado, Utah, Wyoming, and Montana. North Dakota, which is also identified as a target for this study,
does not have active CBM production at present. In examining the known and potential effects of CBM produced water discharges on the environment, the committee focused its efforts on the Powder River Basin, with its relatively shallow coalbeds and less saline produced water and management of CBM produced water primarily through disposal in surface impoundments and surface water.
CBM PRODUCED WATER HYDROGEOLOGY: THE IMPORTANCE OF ESTABLISHING HYDRAULIC CONNECTIVITY
The degree of hydraulic connectivity between water-bearing coalbeds targeted for methane production and shallow alluvial or water table aquifers that support human activities and natural habitats is an important factor in determining the consequences of water withdrawal during CBM extraction. In this context the concept of the age of the water in a coalbed is also significant because the age, or length of time the water has resided in the coalbed, is one indication of the degree to which the coalbed aquifer is connected to surface water and shallow groundwater. “Old” or “fossil” water in coalbeds is water that has not been replenished in the coalbed by infiltrating precipitation within human lifetimes or even thousands to millions of years. This lack of natural recharge may be due to discontinuities within coalbeds or between a coalbed and associated geological units, and/or to the location of recharge areas far from downgradient portions of a coalbed. Such fossil water can be considered a “nonrenewable” resource.
Thorough in situ physical studies to determine the degree of hydraulic connectivity between CBM aquifers and shallow groundwater aquifers have been completed only in the San Juan Basin. The data, including geochemical analyses to determine the age of the water, establish a lack of hydraulic connectivity between CBM aquifers and shallow groundwater resources. The great depths from which CBM and water are extracted in the Uinta and Piceance basins, relative to shallow groundwater systems in these areas, make widespread hydraulic connectivity unlikely. Existing data in the Raton and Powder River basins suggest a lack of widespread hydraulic connectivity between CBM aquifers and other groundwater aquifers, but these studies have been limited in scope and have been generally site specific. Consequently, the connectivity between coalbed water and other water resources is not well defined in most western CBM basins and leads to uncertainty in the consequence of long-term produced water withdrawals on other aquifers.
Mathematical models have been used to characterize the effects of CBM water withdrawal on surface water flows and shallow groundwater levels but have not been calibrated using actual measurements of drawdown in the surface water bodies or shallow aquifers. Such measurements can provide reliable inputs against which model results can be tested. Current mathematical models cannot yet characterize complex water/rock interactions, differences in hydraulic properties, or boundary conditions present in CBM basins with con-
fidence, including the degree of interconnectivity between coalbeds, groundwater aquifers, and shallow alluvial aquifers.Therefore, mathematical models used to characterize the effects of CBM water extraction on the connections between surface water and shallow groundwater aquifers should include independent geological, geochemical (including age dating), and hydrological measurements in CBM basins and watersheds as inputs to provide a level of reliability for model results. When noncalibrated models are used to make water management and regulatory decisions, their uncertainties should be explicitly recognized.
Determining the age of CBM produced water—whether the water should be considered “fossil” water and thereby a nonrenewable resource—is a corollary benefit to conducting these kinds of measurements prior to modeling. The scientifically established age of CBM produced water, and therefore its “renewability,” should be considered in the development and implementation of CBM produced water management regulations.
CBM PRODUCED WATER EFFECTS ON SURFACE WATER AND GROUNDWATER RESOURCES AND THE ENVIRONMENT
The potential effects on the environment of pumping and eventual disposal or use of CBM produced water relate to water quantity, through potential water drawdown or volume addition, and changes in water quality. Baseline water quantity or quality (conditions before CBM extraction begins) could change as a result of CBM operations and produced water management practices, depending on the relative quality of CBM produced water and baseline groundwater or surface water and whether produced water is being extracted or discharged in a given environment.
Groundwater Quantity and Quality
In the Powder River Basin, evidence of drawdown of water levels and hydrostatic heads has been documented in coalbed aquifers as a result of CBM production. However, drawdown effects on shallow groundwater aquifers as a result of CBM production have not, to the committee’s knowledge, been publicly documented and substantiated. This lack of documented effect may be due, in part, to lack of hydraulic connection between coalbed aquifers and shallower aquifers that may be used for domestic water supplies, and in part to a lack of reliable baseline water level data. Thus, resource management or regulatory agencies should require or continue to require collection of baseline groundwater level and quality information for domestic water wells in advance of new CBM drilling activities to protect well operators and residents. These data can be compared against groundwater level and quality measurements made during and after CBM development.
Effects on groundwater quality from CBM produced water impoundments relate largely
to leaching of salts, metals, or metalloids, such as sulfate, selenium, arsenic, manganese, barium, and total dissolved solids (TDS), which occur naturally in soils in or under many impoundments but may be dissolved and mobilized by CBM produced water infiltrating beneath the impoundments. Changes to groundwater quality in the Powder River Basin below and downgradient from CBM produced water impoundments were found in approximately one-third of the currently monitored impoundments. Changes involved increased levels of TDS, selenium, and sulfate. Some impoundments (lined and unlined) are also used in the Raton Basin in Colorado, and state authorities have reported leaks or seepage from the impoundments, either to surface water or groundwater. However, the committee was not able to identify specific data on the extent of any effects from impoundment seepage in the Raton Basin. The committee notes that few baseline data (prior to CBM development) on groundwater quality are available and that more time may have to elapse in the western CBM basins for effects on groundwater to be observed.
Groundwater monitoring networks and the capacity to maintain and analyze results from such networks are considered important for use and management of CBM produced water impoundments that are used for more than temporary storage. Groundwater monitoring downgradient of impoundments used for disposal of CBM produced water before, during, and after water storage in the impoundments should be conducted and the data from these installations should be enhanced with (1) data on the volumes and chemistry of water discharged into impoundments, and (2) evaluation of the effects of impoundment infiltration or seepage on downgradient groundwater and nearby surface water.
In the San Juan and Raton basins, no existing documentation shows adverse affects to groundwater quality from long-term reinjection of CBM produced waters. No empirical evidence was available from the Uinta and Piceance basins, but the committee concludes that the great vertical separation between sites of deep reinjection and groundwater aquifers, as well as the compartmentalization of the hydrogeological system in these basins, makes adverse effects unlikely.
Surface Water Quantity and Quality
Current surface water discharge permitting requires consideration of the quantity and quality of water in that receiving stream or river and the quantity and quality of discharged produced water. Measurements of the effects of CBM produced water discharges on the receiving stream or river quantity and quality are made periodically and can be used to regulate the discharge quantity and quality, if needed, to comply with permitted levels. Measurements of the effects of CBM produced water discharges on receiving stream quality and quantity should be continued and rigorously used in setting regulatory requirements and permit limits by the appropriate state and federal authorities.
In Wyoming, discharge volumes of CBM produced water at outfalls (end-of-pipe) are
recorded periodically and some data are also collected at CBM outfalls in Montana. Actual volumes of water being discharged at most CBM outfalls in the basins studied vary as a normal function of CBM well operations. Produced water volume and chemistry data at outfalls are at present either infrequently collected, or are not available in an easily-accessible database. Knowledge of produced water volumes and chemistry at CBM produced water outfalls would allow operators and regulators to work in concert to monitor and predict anticipated needs for treatment, disposal, management and use of produced water. In monitoring compliance, in modifying discharge allowances and permitted conditions, and in setting regulatory requirements, measurement of CBM produced water volumes and chemistry at outfalls should be collected regularly, reported, and made publicly accessible as a collaborative endeavor among industry, and state and federal authorities. More regular monitoring and reporting would provide regulatory agencies, compliance officers, and researchers with more useful information than the periodic instantaneous data that are generally required at present.
Little evidence exists to substantiate that surface water has been depleted by pumping water during CBM production at the large watershed scale in the San Juan or Powder River basins. Managed-by-permit discharge of CBM produced water to ephemeral and perennial streams and rivers occurs only in the Powder River and Raton basins. At present, too few data, including background (historical) information on streamflows and climatic conditions, exist to evaluate positive or negative effects on water flows in streams and rivers in these two basins as a result of CBM produced water discharge.
Other physical effects to ephemeral or perennial streams and rivers, such as bank scouring, increased bottom sedimentation, or channel erosion, and to landscapes due to regulated, controlled, and managed, or unregulated and/or unmanaged CBM produced water discharges have been registered on private lands in the Powder River and Raton basins. Regulatory authorities have required operators to control and discontinue practices that have been shown to contribute to these physical effects. Regulated (managed and controlled) releases to perennial and ephemeral streams and rivers and directly to the landscape should be accompanied by pre-release monitoring of landscape features, including stream channels. Regular monitoring of the same landscapes is necessary after releases have commenced.
In parts of some perennial streams and rivers in the Powder River Basin, managed CBM produced water discharge has changed water chemistry. These changes are demonstrated by measurements of isotopic compositions of some solutes. However, the majority of studies on perennial drainages (Powder and Tongue rivers) found no discernable changes in surface water quality resulting from CBM inputs, using inorganic constituents, especially SAR and TDS, even when adjustments were made for changing climatic conditions. Specific conductance (as measure by TDS) and SAR may not be the most diagnostic measures of CBM produced water influence on receiving water bodies, particularly in the Powder River
Basin where rivers have natural salinity values close to those in CBM produced waters. A larger array of chemical parameters, including major, minor and trace constituents and isotopes, should be used to evaluate the potential effects of CBM discharges on stream water quality. The occurrence of comingling or presence of deep-injected CBM produced water in shallow groundwater in the San Juan, Raton, Piceance, or Uinta basins has not been documented.
Use of some CBM produced waters for site-specific irrigation appears practical given appropriate conditions including availability of produced water and use of various combinations of selective application to nondispersive soils, treatment, dilution or blending of CBM produced water with other water sources; amendment of produced water and soils to be irrigated; and appropriate timing of irrigation practices. However, in the event that CBM produced water is discharged to perennial or ephemeral streams and rivers for the purpose of supplementing irrigation water supplies, careful consideration needs to be given to potential effects on instream water qualities. Suitability of CBM produced water for irrigation is site specific, thus necessitating identification of the most sensitive irrigable soils within the watershed and managing produced water discharges accordingly. After use of CBM produced water ceases, additional soil management will be required to restore impoundment sites and may be required to restore some soil agricultural resources to conditions that existed prior to CBM produced water application. Although CBM produced water does not represent an inexhaustible supply of water for irrigation, consideration may be given to use of CBM produced water as a supplement to irrigation, given appropriate conditions and management.
A number of controlled laboratory benchtop greenhouse studies and modeling efforts to examine potential effects of CBM produced water on some aquatic organisms have been published. These studies have indicated that water containing TDS and other ionic species above specific baseline levels may cause chronic distress in or be toxic to some organisms. However, widespread adverse effects on indigenous organisms and vegetation as a result of changes in surface water chemistry due to CBM produced water discharges in CBM basins have not been documented. At present, only limited published peer-reviewed research findings on in situ short- and long-term impacts of CBM produced water discharges on ephemeral and perennial stream channel ecology exist. Studies to evaluate the extent and persistence of changes in water chemistry and ecological effects on indigenous species and hydrological systems in the field, including perennial riparian vegetation, stream
hydrological function, stream channel geomorphology, macroinvertebrates, nutrient loading, and fisheries, should be conducted and the results used as input to review and enhance, as needed, CBM produced water management, treatment, and disposal requirements.
The requirements associated with leasing and permitting CBM operations on federal and tribal lands through BLM and protecting water resources on federal, state, tribal, or private lands through the CWA and SDWA under EPA’s jurisdiction are relatively broad, but clear. Specific provisions under the NPDES permitting process apply to disposal of produced waters to the surface, and the UIC program, under the SDWA, applies if subsurface reinjection of produced water for disposal is used. Federal agencies work in concert with state and tribal authorities to enforce the federal standards and regulations, and EPA has delegated primacy for some of these permitting and regulatory functions to relevant state and tribal authorities in the six western states examined in this study.
Regulations regarding treatment and management of CBM produced water differ among the states examined in this study, as do the degree to which the states have been delegated primacy by federal agencies for permitting and regulation of CBM produced water management. Recognizing the jurisdiction of Indian tribes in regulating CBM development and managing CBM produced water is also important. Although different approaches have been taken by states and tribes, the various governing authorities generally appear to try to work in concert in their efforts to negotiate the complexities of these interleaved regulations for the protection and preservation of clean and safe surface water and groundwater resources and environmental protection.
At present, a challenge to effective management of produced water is inconsistency in the definition and consideration of CBM produced water as either a waste or a “beneficial use” in the six western states. Identifiable beneficial opportunities for use of CBM water include irrigation, rangeland habitat improvement, livestock watering, alluvial aquifer recharge, aquifer storage, wildlife habitat enhancement, reclamation of well pads, industry applications, and potentially municipal use or consumption. CBM produced water volumes change over time and eventually decrease to near zero as development of CBM fields mature, making sustainability or long-term dependability of this water supply an issue in consideration of these beneficial use opportunities.
The committee concludes that management of CBM produced water is presently driven by regulations and economics of disposal and treatment costs relative to revenues generated from the sale of methane rather than consideration of the potential for beneficial use. Additionally, efforts to direct produced water management based on uncalibrated models need to be avoided.
Given that produced water can be treated to any water quality with current technologies but at widely varying costs, future regulation of CBM produced water management should consider the age of the CBM produced water. Careful management of nonrenewable “fossil” water, after extraction, for best nonrenewable resource use should be considered a priority.
Costs of water treatment, storage, and transport are not negligible, but current regulations and water law do not allow CBM operating companies or other stakeholders many options to consider other than disposal of fossil (nonrenewable) CBM produced water of relatively poor quality through deep-well injection. This kind of water management is not and should not be considered a beneficial use of the water resource. Even in cases such as the Powder River Basin where CBM produced water contains relatively low dissolved solids concentrations, the full range of beneficial use options is not exercised, partly due to economics and partly due to the restrictions of existing water law.
Each beneficial use aligns with a set of criteria and acceptable or appropriate criteria for one beneficial use of CBM produced water may be in direct conflict with the criteria for another beneficial use. Additional complications are introduced when consideration is given to liability, water rights regulations, and sustainability of supply issues. These circumstances, in addition to the general decrease in volume of CBM produced water over the lifetime of a well, make CBM produced water an uncertainty and only a temporary source of water for beneficial use. This uncertainty contributes to the difficulty of addressing opportunities for beneficial use.
Recent litigation and changing case law in some western states related to CBM produced water management signal that various stakeholders now recognize the fact that water resources traverse state, legal, and geological boundaries. CBM production in the United States currently constitutes about 10 percent of annual domestic dry natural gas production and is predicted to grow as the nation considers the transition to a less carbon intensive energy resource base, of which natural gas is considered a cornerstone. Integrated approaches toward water and energy use and conservation are increasingly being considered as environmentally and economically sound. Multiple potential users and uses of limited water resources, a concern by the public for protection of these limited resources, the complexities of hydrogeological systems, and the renewability or nonrenewability of water resources require increasingly sophisticated approaches to CBM produced water management. These approaches require a basis in scientifically grounded studies and consistent monitoring and should allow for a greater range of economically and environmentally viable options for CBM produced water management.