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OCR for page 95
Conclusions and Recommendations The committee's mission was basically to assist the Office of Surface Mining Reclamation and Enforcement (OSM) concerning interpretation of the term "ground water recharge capacity" in the context of the Surface Mining Control and Reclamation Act of 1977 and to advise OSM in regard to its estimation or assessment before and after mining. The committee expresses the results of its deliberations in terms of the following several sets of conclusions and recommendations that correspond generally to the items of its charge, outlined in the Preface. These conclusions and recommendations are of three general types: (1) those that should clarify the meaning of the term "ground water recharge capacity"; (2) those that should provide operational guidance to the OSM and their constituents; and (3) those concerning research and development that may produce more long-term and general benefits to the evaluation of the hydrologic functions of surface-mined areas in the future. GROUND WATER RECHARGE CAPACITY INTERPRETED CONCLUSION: "Ground water recharge capacity"~has no clear -95-
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-96- scientific meaning. This committee's legal interpretation is that the term means ground water recharge capability, as concluded in Chapter 2. Again, this term has no scientific definition but is an indicator of the "ability of soils and underlying materials to allow precipitation and runoff to infiltrate and reach the zone of ." Notwithstanding the issue of definition, for reasons stated in Chapter 1 both terms ("capacity" and "capability") are nebulous and are poor indicators of actual ground water saturation " recharge. RECOMMENDATION: For the above reasons, the term "ground water recharge capacity" should be interpreted to mean ground water recharge, which is the movement of surface water to ground water or the addition of precipitation or surface water to ground water, the real issue of concern. The rates of this movement are controlled by precipitation, infiltration, surface and subsurface runoff, evapotranspiration, and site stratigraphy and structure. All of these parameters exhibit spatial and temporal variabilities, making accurate measurement of pre- and post-mining recharge rates for mine-scale areas difficult. HYDROLOGI C EVALUATIONS CONCLUSION: The several parameters relevant to ground water recharge can, in principle, be measured for a given point. However, spatial and temporal variabilities would require intensive instrumentation at high costs, and these variabilities and the uncertainty in measurement techniques would generally preclude accurate extrapolation to mine-scale areas. Nonpoint methods for estimating ground water recharge, made by hydrograph separation, tracer techniques, and regional water budgets, are also
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-97- not exact. The errors in resulting estimates of ground water recharge may exceed the change in recharge due to mining. RECOMMENDATION: No single technique or set of techniques for assessing recharge at required as rat provision of SMCRA. v surface coal mines should be Dart of the "recharge-cacacitY" CONCLUSION: Although accurate determination of differences between pre- and post-mining recharge rates is not practical, the committee concluded that enforcement of existing OSM regulations concerning mine reclamation will, in the vast majority of situations, result in post-mining recharge rates that equal or exceed pre-mining rates. This conclusion is based on the following currently required conditions: 1. The land surface is recontoured and stabilized to the approximate pre-mining topography; ' the committee concluded 2. The site is typically revegetated with plants using less or approximately the same quantity of water as the pre-mining species; 3. Compaction of surface soils and vadose zone materials Is avolueu; and 4. Restricting layers in the original vadose ~ ~ ~ ~ the zone are broken up and alspersea in reconstituted vadose zone by the mining and reclamation process. RECOMMENDATION: No additional instrumentation and measurement, over and above that already required by other sections of the SMCRA and justified solely on the grounds of establishing whether or not differences exist in pre- and post-minin~ recharge, should be required as part of surface coal mining, because Suck measurement cannot be justified rationally given the present state of recharge measurement technology. ~ ~ , the permitting process for . . .
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-98- CONCLUSION: Isolation practices can be implemented to preserve water quality in surface mine restoration projects. These practices can have an impact on the process of ground water recharge. RECOMMENDATION: When practices implemented to preserve water quality substantially reduce recharge over a given area, recharge should be restored through other areas that are especially engineered to assure good quality and quantity of water. But if isolation practices substantially reduce mine-site recharge and this recharge cannot be restored by engineered zones, the area should be reconsidered in respect to its suitability for mining. There is an "unsuitable-for-mining" provision of SMCRA (Sect. 5221. CONCLUSION: The impacts of mining on the hydrology of a region with many mining operations may be substantial but are currently not well known, because cumulative hydrologic impact studies currently are difficult to conduct in a meaningful manner due to the lack of a central digitized data base. RECOMMENDATION: Each state regulatory authority should be encouraged to produce and maintain a Geographic Information Systems data base of all mined areas Such data bases should be uniform across states. RESEARCH AND DEVELOPMENT . CONCLUSION: The long-term cumulative consequences of large surface coal mining projects on the ground and surface water parameters are unknown. RECOMMENDATION: A long-term research program of hydrologic monitoring should be provided for such sites. This monitoring may have to continue well beyond the current bond-release dates.
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- 9 9 - CONCLUSION: No single current technique or combination of current techniques can provide a sufficiently accurate characterization of ground water recharge at mine scale. Improvement in our ability to determine site recharge rates is needed to allow for better quantification of pre- and post-mining hydrologic systems so as to improve our ability to predict the effects of mining and reclamation on the surface and ground water resources of an area. RECOMMENDATION: Research should be undertaken in eastern and western coal provinces to help improve our understanding of the recharge process, its spatial and temporal variability, and the accuracy of individual measurement techniques. CONCLUSION: Issues of hydrologic balance, recharge, and pre- and post-mining monitoring need to be addressed in a more coherent hydrologic framework. RECOMMENDATION: In conjunction with research to improve hydrologic methods and information, annual water budgets should be developed based on available monthly records representative of the pre-mining landscapes in the permitting areas. Several water budgets may be needed because the rates and timing of recharge can differ between and within the coal mining areas of each state. As part of each permit application, the applicant should qualitatively describe the anticipated changes in water-budget components (evapotranspiration, runoff, infiltration, soil water storage, drainage, and recharge) during mining operations and the reclamation period. (A written review of the reclamation project could take place at the time of bond release.) All the above data should be incorporated into the above mentioned Geographic Information System data base for use in subsequent cumulative hydrologic impact studies.
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-100- CONCLUSION: Soil compaction can be a major factor affecting the restoration of the recharge process in a reclaimed landscape. RECOMMENDATION: Innovative methods should be developed for overcoming compaction problems in reclaimed spoil materials and minesoils, particularly in surface-mined areas with identified compaction problems.
Representative terms from entire chapter: