Surface Coal Mining Effects on Ground Water Recharge (1990) / Chapter Skim
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5. Mining: Methods and Impacts
5. Mining: Methods and Impacts
Pages 60-80
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From page 60... ...
provide comprehensive summaries of surface mining methods, impacts, and land -60
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From page 61... ...
Previously stored topsoil or a substitute material is placed over the spoil and is stabilized by mechanical compaction on sloping terrain, and the area is revegetated with herbaceous, shrub, and/or tree species. The main features of this mining method that influence recharge include initial vegetation removal, compaction of the reclaimed soil profile and the mine floor (e.g., clay material underlying the coal seam)
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From page 62... ...
- 6 2 9~__~y-~.t_~ ~.C3' ,~,j~,_.~ ~ o Ed En o o Cal Ed En .
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From page 63... ...
, southern Illinois, Indiana, and in western Kentucky, and is also being practiced in mountain areas of Appalachia where several mountaintop removal operations are combined. These operations have common features with the other mining methods in terms of vegetation removal, topsoil storage, blasting, overburden removal, coal extraction, landscape restructuring, and revegetation.
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From page 64... ...
-64, FIGURE 5.2 Surface mining mountaintop removal and valley fill method
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~ W~ ~i. GRADED AR:| HDISTURBED LAND ~.~ R ~ ~ ~ ~—~ Of —~ ~:——_ ~ '_·_~ FIGURE 5.3 Typical area mining method with s tr ipp ing shove 1 .
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From page 66... ...
. MINESOIL PROPERTIES Surface coal mining and other land disturbances often significantly change soil properties.
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From page 67... ...
Infiltration rates and saturated hydraulic conductivity of minesoils are highly variable and may be lower or higher than are those of contiguous native soils (Hnottavange, 1987; Pedersen et al., 1978~. Large macropores in some minesoils cause water to move rapidly through the profile, but compaction of clayey-textured material may cause water to move very slowly through the soil.
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From page 68... ...
Differences in mining effects on water-budget components for an eastern and a western coal region are given as examples. Appalachian Coal Basin Summer Operations Site preparation that is initiated in May, followed by mining, site reconstruction, and completion of revegetation by September may have a small impact on long-term recharge.
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From page 69... ...
Surface water diversion into sedimentation ponds and pond discharge into stream waters are the dominant impacts of summertime mining operations , replacing the normal evapotranspiration water-loss component of the water budget Winter Mining . Most recharge in eastern coal basins occurs during the winter and the spring into a natural fracture system within the outer rock zones of mountains.
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From page 70... ...
Mine operations often require dewatering of the intended mining area since the coal seams are usually a significant component of the aquifer system. Ground water pumping causes a drawdown of the aquifer, forming a cone of depression in the water table (Figure 5.4~.
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From page 71... ...
SOURCE: Office of Surface Mining Reclamation and Enforcement, 1988.
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lowered potentiometric levels pass unaffected beneath valley bottoms and perennial streams. SOURCE: Van Voast and Reiten, 1988.
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RECLAMATION EFFECTS ON RECHARGE AND ON WATER QUALITY Water Quantity Restoration of the mine site to approximately the pre-mining landscape by spoil placement, surface application of topsoil or other approved material, and revegetation can lead to an increase or decrease of recharge to aquifer systems relative to that of the original landscape. The factors contributing to an increase in post-mining recharge are Poor vegetation establishment.
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From page 74... ...
· Mine floor compaction -- limits recharge to deeper aquifers. o Elimination of surficial scoria or other high-recharge areas from within the mine site boundaries.
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From page 75... ...
Not all spoil materials exhibit favorable infiltration properties. In particular, spoils from a western Kentucky surface mine were shown to have extremely low infiltration rates that were associated with high bulk density and a well-graded particle size (Wells et al., 1982~.
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From page 76... ...
In most cases, the hydraulic-conductivity characteristics of the restored vadose zone are much higher than the corresponding pre-mining values due to the greater porosity of the reclaimed spoil materials relative to the original rocks and other geologic deposits and due to the breakup of layers of low hydraulic conductivity. Restoration of infiltration rates is needed to initiate the recharge process.
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From page 77... ...
Additionally, the requirements for revegetation specified in SMCRA favor the restoration of recharge capability by maintaining the integrity of the soil surface for infiltration as well as the permeability of the root zone for soil water drainage. Special attention needs to be given to evaluating compaction in reclaimed spoils as part of the post-mining assessment of recharge capability, particularly in areas with loess deposits, such as in western Kentucky.
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From page 78... ...
Exploration boreholes, drilled to determine the extent and quality of the coal seams, are, after data collection, now plugged as mandated by the Federal Surface Mining Control and Reclamation Act of 1977. This action is an important step in preventing contamination of deeper aquifers that often have better water quality than do shallower aquifers.
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From page 79... ...
During post-mining reclamation, considerable effort is devoted to minimizing the short- and long-term impacts of coal surface mining on ground water quality. Blending of spoils and selective placement of spoils are techniques now being developed rurcner, and in some cases practiced, to minimize the deterioration of water percolating through the backfill of reclaimed coal surface mines (Phelps and Saperstein, 1982; Groenewold et al., 1983; Caruccio and Geidel, 19891.
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From page 80... ...
Should recharge, however, be substantially reduced over a given area because of isolation practices, then artificial recharge through zones, engineered to assure good water quality, should be implemented. If isolation practices are required to protect water quality and the isolation technique reduces recharge and this reduction in recharge cannot be overcome by engineered recharge zones, then the area should be evaluated under the "unsuitable-for-mining" provision of SMCRA (Sect.
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