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1 Introduction . . Surface mining of coal affects large areas in the United States (3 million hectares so far). Currently, this figure is increasing by about 150,000 hectares per year and could eventually reach about 7 million hectares. Since 1977, when Congress passed the Surface Mining Control and Reclamation Act (SMCRA; P.L. 95-87), there have been strict federal rules for restoring the land to "approximately its original contours" and for minimizing degradation of the quality of surface and ground water (e.g., by controlling sediment content and acid or alkaline drainage). Although Congress's general goal in passing SMCRA may appear fairly clear for the water-related provisions, problems arise with some of the specifics that Congress mandated. The general goal is that in areas where there are usable surface water and/or ground water resources, those resources should be qualitatively and quantitatively suitable for post-mining land use. One of the specific provisions is the focus of this report. Congress mandated that the "recharge ~ capacity" of the surface-mined lands be restored to approximately pre-mining conditions. Congress provided no definition of recharge capacity, nor does one exist in either the legal or scientific literature. Yet several things are clear about - 1 -
-2- the recharge capacity requirement: (1) Congress was thinking about ground water and not surface water; ~ 2 ) this requirement was viewed as quantity and not quality related; and (3) it was conceived to prevent a lessened recharge capacity without indicating any concern for an increased recharge capacity . Intuitively, recharge capacity could be interpreted as the maximum capability of the land surface and underlying materials (vadose zone or unsaturated zone) to recharge ground water at some maximum rate as if, for example? the land were continuously flooded with water. The actual recharge, however, is primarily controlled by the climate (precipitation' evaporation from soil, transpiration from vegetation) and by rainfall-runoff relationships that may not be adversely affected by the mining operation if the land is properly restored and the vadose zones are sufficiently permeable to transmit the water to underlying aquifers. Desert alluvial fans in the southwestern United States have a high recharge capacity but very little actual ground water recharge because of the very low rainfall and high evaporation in those areas. On the contrary, soils and geologic profiles in more humid areas may be less permeable and have less recharge capacity, but ground water recharge rates are higher because of higher rainfall and lower evaporation. Thus recharge capacity, as such, is not a true indicator of actual ground water recharge rates. As a matter of fact, surface mining and restoration of the land conceivably could reduce recharge capacity but increase recharge of ground water, and vice versa! A better term than "recharge capacity," therefore, would simply be "ground water recharge." Tn the context of SMCRA, this would mean that restoration of surface-mined land must also restore long-term average ground water recharge rates to at least pre -mining levels ~ assuming, of course, that the climate does not change).
-3- Ground water recharge rates typically are expressed in centimeters or inches of water per year. Rates vary from year to year as annual rainfall (amount and distribution) and temperatures vary. Rates also vary from location to location as - ace; TV; ~C, ~T^~T^~-~;~= '^ - Harry Rear ~ a_. = ~ _~ i. Quantification of ground water recharge from atmospheric precipitation is difficult. Thus there is a paucity of good data. Studies in various parts of the world have shown that ground water recharge may range from 50 percent of precipitation or more in humid, temperate climates to 1 percent of . . . ~ . ~ ~ · . precipitation or less In cry, warm climates. Regional ground water recharge rates can sometimes be estimated from a simple analysis of rainfall, evapotranspiration, and surface runoff data. Such an estimate shows, for example, that the relatively dry, coal mining area of Gillette, Wyoming, may get less than 5 cm/year recharge out of 40 cm/year precipitation, or less than 12 percent. For the warm, humid area of Oak Ridge in eastern Tennessee, evapotranspiration is 73 cm/year, leaving a total recharge and runoff of 64 cm/year out of 137 cm/year precipitation, or 47 percent. Ground water recharge rates are very difficult to measure, and quantification may even be impractical for operational purposes, such as restoring ground water recharge rates to original levels after surface mining of coal. A more practical approach would be to require that surface-mined areas be restored in such a manner that the factors controlling ground water recharge are returned to condition that produces ground water recharge at rates that are not lower than those that existed before mining _ 17 a Water quality considerations also are very important. Depending on the particular geologic materials and geochemistry, water percolating through "reconstituted" vadose zones will leach more chemicals than it did when it moved through natural formations. In the eastern United States, acid drainage and leaching of trace elements can be a problem. In the western United States, salts,
-4- alkalinity, and leaching of trace elements are of concern. Restoring ground water recharge becomes meaningless if the quality of the resulting ground water is so poor that it becomes useless or degrades the quality of existing aquifers or streams. Thus protection of ground water quality in mined areas may actually require reduction of post-mining recharge for specified subareas. Aquifers differ in different coal mining regions. In eastern Kentucky, "aquifers" may be consolidated rock formations-that trap and convey water in vertical stress-relief fractures so that it may be pumped from small, mostly shallow, domestic wells. When these fractures are replaced by disturbed material due to surface mining and restoration of the land, the original "aquifer" system is also destroyed in the mine area. After reclamation, aquifers will then form in unconsolidated fill material. If local fracture systems are drained, deeper aquifers may have to be tapped if they are available. If coarser fill materials are placed on the mine floor and the finer ones on top, and if the fill is bowl-shaped or has a controlled outlet so that water can be stored in the coarse material, an "engineered" aquifer can be created. This is being done, for example, at the Starfire Mine in eastern Kentucky, where the engineered aquifer also is connected to the land surface with specially constructed rock shafts to enhance ground water recharge. In large coal fields of the West, the coal seams themselves may be the major aquifers. Removing the-coal seams, then, also removes the aquifers and replaces them with mine spoil. If the lower layers of this spoil become saturated, the spoils become the new aquifers. Apparently because of uncertainties about the definition of recharge capacity and the method for ascertaining or measuring its restoration, the regulatory authorities responsible for the implementation of SMCRA have generally not stressed its implementation. Or at least it was perceived
-5- by some that this aspect of SMCRA was among provisions not being implemented in Kentucky, the top coal-producing state in the United States. The supervisory agency for SMCRA is the Office of Surface Mining Reclamation and Enforcement (OSM) of the U.S. Department of the Interior. Basically OSM has three roles to perform: (1) promulgation of procedural and substantive regulations to carry out the provisions in SMCRA; (2) oversight of state administration of SMCRA and the regulations adopted under SMCRA by those states that have assumed primacy; and (3) administration of SMCRA and the regulations adopted under SMCRA to coal mining operations in those states that have not assumed primacy. It was alleged that the ground water recharge capacity provisions of SMCRA were not being addressed adequately in Kentucky. Because Kentucky had been granted primacy, it was sued for this alleged failure of administration and enforcement. The OSM, in turn, was sued for a failure in oversight. Eventually the suit against OSM was dismissed when the Kentucky suit was settled and OSM joined as a party to the settlement. That settlement, known as the Kentucky Settlement Agreement, included a requirement for hydrologic balance among other items. A steering committee was to be selected to advise OSM on a study of hydrologic balance. i__ _ =_ ~ , and specifically, that study was to undertake to "identify . . . cost-effective approaches to determination of the pre-mining recharge capacity for both eastern and western Kentucky coal field regimes." Thus at OSM's request the Committee on Ground Water Recharge in Surface-Mined Areas was established to clarify issues associated with the requirement of restoring "recharge capacity." Therefore, as a result of the Kentucky Settlement Agreement, this report was prepared to resolve a scientific uncertainty, namely how to measure in an efficient, cost-effective way whether the "recharge capacity" restoration requirement has been implemented. Before the scientific question can be
-6- addressed, it must be determined what "recharge capacity" means. Thus a somewhat detailed examination of the SMCRA language, its legislative history, and prior interpretation of the recharge capacity restoration provision follows in Chapter 2.