Excess spoil generated during surface mining in southern West Virginia is generally placed in headwater valleys. Known as valley fills, these structures are designed to move water rapidly through constructed drains to maximize geotechnical stability using the conventional design method termed Approximate Original Contour (AOC). Seepage from valley fills tends to be elevated with respect to calcium, magnesium, alkalinity and sulfates and there is evidence that, in high concentrations, these ions can contribute to stream degradation. New fluvial geomorphic principals are being researched to aid in reclamation alternatives to AOC designs. Geomorphic designs have proven successful in semi-arid regions; however, there has been little research performed into the application of this approach for eastern surface mining reclamation.
Geomorphic reclaimed landforms aim to improve groundwater movement and diminish contaminant transport through increased runoff and reduced groundwater infiltration. The objective of this research was to determine if geomorphic reclamation techniques result in improved selenium concentrations of discharge water as compared to conventional reclamation for valley-fills constructed of blasted rock. Comparisons investigated if groundwater and contaminant desorption could be improved by altering valley-fill construction. Three-dimensional finite-element groundwater modelling was performed on two valley-fill geometries and was coupled with laboratory testing of selenium leaching from blasted-rock overburden. Selenium desorption characteristics and distributions were compared. Lower water volumes and shorter contact times with overburden fill resulted in lower masses of selenium desorbed from geomorphic fills as compared to conventional techniques. When results were normalized by varying fill areas and volumes, the geomorphic valley-fill exhibited 23% lower surface infiltration, 27% lower discharge volumes and 39% lower selenium discharge loads as compared to the conventional reclamation. To achieve these advantages in geomorphic reclamation, infiltration must be reduced through both the construction of curvilinear slopes of the fill surface and the creation of a low infiltration-capacity reclaimed stream.
This research aimed to evaluate the potential of applying geomorphic landform design (GLD) principles to valley fill reclamation, specifically in southern West Virginia, central Appalachia, USA. When constructing reclaimed landforms, GLD aims to mimic the geomorphology of reference landforms that are stable and in erosive and hydrologic equilibrium. Challenges with the technique have been identified related to use in central Appalachia. Reference landform design values vary by location and need to be quantified at a local scale for site-specific design. Due to the steep slopes of existing valleys, constructing engineered landforms that naturally blend in with the surrounding environment may not ensure stability. Less steep, more stable slopes of geomorphic landforms could create greater stream disturbance to maintain fill volumes. Potential benefits of GLD with respect to groundwater movement and contaminant desorption have also not been quantified. This research presents three major objectives to assess geomorphic landform design in central Appalachia: 1) define the geomorphic characteristics of mature landform reference sites in southern West Virginia; 2) quantify the issues associated with implementing geomorphic reclamation on a field scale at an existing valley fill; and, 3) compare models of groundwater movement and desorption of selenium in reclamation alternatives for a southern WV surface mine. Geomorphic properties of drainage length and drainage density for mature landforms in central Appalachia were 408 ft and 62 ft/ac, respectively. Slopes were steep (>20%), aspects were well distributed in all directions, vegetation was predominately dense core forest, and ephemeral channel heads developed where erosive surface processes created concentrated flow and sediment transport. Potential issues associated with implementing GLD in central Appalachia with respect to landform stability, stable channel mitigation, and mass balance were confirmed. No geomorphic design was able to satisfy all three criteria when the permitted area of impact was maintained. Expanding the area of impact beyond permit boundaries promoted more success in meeting design criteria, but did not comply with reclamation regulations governing excess spoil placement and constructed hillslopes. A quantitative comparison of the groundwater movement and selenium desorption between alternative reclamation designs confirmed potential benefits to geomorphic reclamation. Selenium desorption was reduced by 23-39% in geomorphic fills and was attributed to improved groundwater movement. Geomorphic reclaimed landforms exhibited 23-45% lower infiltration volumes, 12-63% lower groundwater discharge volumes, and approximately 50% shorter groundwater residence times. These findings will be used to provide recommendations to government agencies and the surface mining industry on the practicality of implementing geomorphic reclamation as an alternative to conventional valley fill reclamation in central Appalachia.
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