Before a permit can be approved the RA must conduct an assessment of the cumulative hydrologic impacts (CHIA)of all anticipated mining on the hydrologic balance in the cumulative impact area (CIA) and must find that the proposed operation has been designed to prevent material damage to the hydrologic balance outside the permit area. CHIA preparation is an integrated process which embodies a specific application of hydrologic information management at each step of the process. An sample outline for the CHIA report is available for downloading.
With proper enforcement of surface mining regulations, the hydrologic impacts of individual mining operations should be minimized. The hydrologic impacts that cannot be mitigated through implementation of the hydrologic reclamation plan may be insignificant when considered individually. However, when the impacts from existing mines as well as from all anticipated mining within a specific area are considered, their additive effects may become significant and create the potential for material damage to the hydrologic balance. The CHIA is intended to assure that such additive impacts will not be overlooked in the approval of individual permit applications.
Any significant or major change in mining operations, such as the addition of a new area, a change in mining or reclamation methods, or the discovery of an unforeseen geologic or hydrologic condition necessitates a permit revision. This generally entails a reconfirmation of the accuracy of the PHC (Probable Hydrologic Consequences) and CHIA findings, or a revision and updating the findings.
The scope of a CHIA may initially include all components of the ground-water and surface-water systems in the CIA. This initial scope can then be systematically and logically reduced to those concerns of quantity and/or quality considered significant to maintaining the hydrologic balance of the area. The process should focus on those aspects of the hydrologic balance that are likely to affect designated uses of water available from the system.
Statutory and regulatory requirements allow the RA wide latitude in determining how to conduct the CHIA. Specific concerns, procedures, methods, and data requirements may vary with each CIA, and the RA has the flexibility to use those that best apply to the particular conditions of each site. While each new permit requires a CHIA finding, it need not be a totally new analysis. Appropriate information from previously prepared CHIA's, PHC's, and monitoring data may be used.
The CHIA predicts the type and magnitude of impacts to the hydrologic system attributable to the proposed operation in conjunction with existing and anticipated mining. Thus during the CHIA process the RA should:
The RA should address these elements in a logical sequence, based upon good hydrologic practice.
Define the cumulative impact area (CIA)
The CIA is an area where impacts from the proposed operation, in combination with other existing and anticipated operations may cause material damage. At a minimum, anticipated mining includes existing operations, proposed operations for which permit applications have been submitted to the RA, and operations required to meet diligent development requirements for leased Federal Coal for which there is actual mine development information available.
When establishing a CIA, the RA should be aware that boundaries should be flexible and can be changed if analyses or new data reveal conditions or concerns not previously identified. In the interim, a "working" CIA may be delineated based on estimates or calculations of the down-gradient extent of measurable impacts to surface water or ground water. As the analysis progresses for the various parameters being evaluated, the need may arise for adjustment of the "working" CIA boundary. A procedure for delineating the CIA is available.
The size and location of the CIA will depend on the surface- and ground-water system characteristics, the hydrologic resources of concern to the RA, and projected impacts from the operations included in the assessment. A ground-water CIA should extend from the up-gradient extent of impacts down-gradient to aquifer discharge points unless it can be demonstrated that measurable impacts do not extend that far. In some cases measurable ground-water impacts may extend down-gradient to surface-water bodies which receive ground water discharge.
Among other factors, two items generally of importance for ground-water CIA's are water-level drawdown areas and areas through which plumes of degraded water may migrate. Similarly, a surface-water CIA should extend from a downstream point at which all mining impacts can be cumulated, and upstream to either a watershed boundary or to a point at which upstream effects can be isolated from mining impacts such as at a stream gauging station.
The surface-water and ground-water systems should be described in sufficient detail to identify their significant characteristics and interactions. The description should focus on the hydrologic resources that may be affected by anticipated mining. This will enable the RA to focus the cumulative impact description and analysis on these same resources. Much of the data describing the hydrologic resources will be available in permit applications. However, areas outside permit boundaries may require additional data from other sources.
The RA's task in the CHIA is to estimate the magnitude and importance of changes to hydrologic resources as a result of mining. Lumb (1982) provides guidance and examples for determining the magnitude and significance of mining impacts. Lumb, A.M., 1982, Procedures for Assessment of Cumulative Impacts of Surface Mining on the Hydrologic Balance: U.S. Geological Survey Open File Report, 82-334, 50 pp. The hydrologic considerations differ greatly in the different coal regions of the United States primarily due to regional variations in rainfall, temperature, water use, topography, and geology. For example, typical hydrologic concerns in areas associated with the coal fields of the western United States may include:
Typical examples of hydrologic concerns in areas associated with coal mining in the eastern United States may include:
These are only typical hydrologic concerns and represent only a small number of possible impacts. At each site and within individual CIAs, the hydrologic considerations should be determined on the basis of water usage in the area, existing water-quality standards, and local hydrologic conditions.
Material damage is any long-term or permanent change in the available quantity or quality of a water source that will preclude its use or reduce its utility to an existing water user within the CIA. In terms of the hydrologic balance, material damage would occur when postmining levels exceed defined limits. These defined limits thus become the criteria or standards against which material damage will be evaluated.
The increased public concern for the quality of the Nation's water supplies has led to the establishment of water-quality standards by various regulatory agencies. These standards generally are based on the maintenance and protection of specified water uses such as public and domestic water supply, agriculture, industry, aquatic life, and recreation. Although standards for surface water are most common, some states also have established standards for protection of ground water. Material damage criteria for both ground-water and surface-water quality should be related to existing standards; sources of information available to RAs as guidance are listed in Appendix B. In addition, standards may exist for water quantity, such as State laws governing water rights for both surface-water and ground-water supplies. Such standards may be based on critical surface flow rates or aquifer storage capacity that support identified uses. At a minimum, when such standards have not been established, it must be assumed that premining yields must be maintained. A water supply system will be deemed to have been impacted when it can no longer meet these pre-existing needs, all other variables such as precipitation, inflow, evaporation, etc., being equal.
Material damage considerations must be consistent with existing laws, standards or regulations. The RA should assemble the existing standards that apply to the hydrologic resources in areas in which mining will occur. Included is a list of agencies in each State that may have information regarding water-quality standards. County and city governments may also have established standards for water protection and use, especially in metropolitan areas, and should be considered a possible source of information. It may be expedient to develop a listing of known standards during the initial CHIA in order to reduce the time it takes to prepare subsequent assessments.
In addition to the existing standards that may be fairly general in scope, the RA should consider developing material damage standards for specific parameters that generally reflect mining impacts such as iron, manganese, sulfate, and total dissolved solids, as well as parameters of local significance to water use.
There are two general categories of cumulative impact predictions:
Qualitative methods rely heavily on the experience and qualifications of the user and minimize the need for numerical calculations. Results are more general in content and require less detailed information than quantitative methods. On the other hand, quantitative methods include a variety of numerical analyses, some fairly simple, while others may involve very complex calculations requiring large amounts of data.
Qualitative and quantitative methods may vary greatly in information requirements and cost per analysis. The RA should consider the accuracy and precision needed for a particular impact analysis, the information available for the CIA, the number of permits to be approved, and the time and resources available to do the analysis. While quantitative methods may be more precise than qualitative methods, this does not guarantee greater prediction accuracy. Also, as discussed for PHC strategies earlier, high precision will not be warranted for CHIA assessments in all cases. In some cases, long-term monitoring may be the only way to determine the accuracy of CHIA methods.
After the cumulative impact assessment has been made, the projected impacts for the parameters of concern (projected indicator parameters) are compared to the material damage criteria. The material damage finding for permit approval or denial under section 510(b)(3) of SMCRA requires that hydrologic impacts be evaluated to determine whether the proposed operation has been designed to prevent material damage to the hydrologic balance outside the permit area. Therefore, the RA should include the rationale and the standards by which the potential for material damage has been assessed. These standards are needed for comparison with the quantitatively or qualitatively predicted impacts of mining that will be obtained through the CHIA. The required material damage finding has no prescribed format or content. This in no way reduces the importance of the finding in the permit approval process but rather emphasizes the flexibility provided to the RA in meeting this requirement.
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