Appalachian streams were buried by valley fills from 1985 to 2001. Blasting at a mountaintop removal mine expels dust and fly-rock into the air, which can then disturb or settle onto private property nearby. This dust may contain sulfur compounds, which some claim corrode structures and tombstones and is a health hazard. Although MTR sites are required to be reclaimed after mining is complete, reclamation has traditionally focused on stabilizing rock and controlling erosion, but not always on reforesting the area. Quick-growing, non-native grasses, planted to quickly provide vegetation on a site, compete with tree seedlings, and trees have difficulty establishing root systems in compacted backfill. Consequently, biodiversity suffers in a region of the United States with numerous endemic species. Erosion also increases, which can intensify flooding. In the eastern United States, the Appalachian Regional Reforestation Initiative works to promote the use of trees in mining reclamation. Dredging Dredging is a method for mining below the water table. It is mostly associated with gold mining. Small dredges often use suction to bring the mined material up from the bottom of a water body. Historical large-scale dredging operations often used a floating dredge; a barge-like vessel that scoops material up through a conveyor belt on the bow, filters out the desired component on board, and returns the unwanted material to the water via another conveyor belt on the stern. In gravel-filled river valleys with shallow water tables, a floating dredge can work its way through the loose sediment in a pond of its own making. Highwall mining Highwall mining is another form of mining sometimes conducted to recover additional coal adjacent to a surface-mined area. The method evolved from auger mining but does not meet the definition of surface mining since it does not involve the removal of overburden to expose the coal seam. CERB final report No. 2014-004 "Highwall Mining: Design Methodology, Safety, and Suitability" by Yi Luo characterizes it as a "relatively new semi-surface and semi-underground coal mining method that evolved from auger mining". In highwall mining, the coal seam is penetrated by a continuous miner propelled by a hydraulic pushbeam transfer mechanism (PTM). A typical cycle includes sumping (launch-pushing forward) and shearing (raising and lowering the cutterhead boom to cut the entire height of the coal seam). As the coal recovery cycle continues, the cutterhead is progressively launched into the coal seam for . Then, the PTM automatically