Electronic Field Guide » Restoration & Goals » Topographic Reconstruction
Prepared by Patrick Drohan (Ecosystem Science and Management)
When a gas company reclaims a Marcellus site, first they remove the gravel surface of the drill pad. In some cases a sealed surface of mixed soil and concrete may be broken up and turned under (some may be hauled away). Next, the land shape is returned to the original contour (or better, depending on the intended land use) and the stockpiled
topsoil is replaced; lease negotiation proves critical here for determining exactly what is done. In the case of steep topography or if slope excavation occurs and a high wall was created adjacent to the pad, ordering fill appropriately, and monitoring of fill settling and stabilization will be important.
Slope stabilization, stormwater control, and road restoration are also critical. Companies
are required to meet Pennsylvania DEP requirements regarding earth moving and
disturbance. From our experience, companies are proactive and careful that state and federal laws are followed.
Slope reconstruction should in general follow 3:1 or better (4:1) (meaning 3 feet of horizontal surface for every 1 foot gain in elevation) reconstruction profiles, which minimize the potential for surface water to generate erosion. Stabilization of slopes with geofabric in the subsurface, trenching, French drains, and other best management practices (see Pennsylvania Stormwater Best Management Practices Manual) can all help to make sure land reshaping is successful.
When a site is first developed, substantial excavation occurs. In some cases, excavation may also result in fractured rock being moved and stockpiled. When this fractured rock is replaced at the end of the project, settling may often occur. Adequate stabilization and the creation of a soil suitable for plant growth can occur in several ways. Currently, we recommend that a process outlined by the Appalachian Regional Reforestation Initiative be followed (Forest Reclamation Advisory No. 3, Sweigard et al., 2007). Layers of soil material placed back onto the site must be mixed to minimize the risk of discontinuities (two distinctly different particle sizes or compaction zones). One way to prevent discontinuities is to avoid travelling across a newly placed surface more than once. In addition, it is best to avoid incorporating rock fragments into a soil mix if the percentage of rocks to soil will exceed 50%. The more rocks found in a mantle of soil, the less soil, and less water-holding capacity. If a large percentage of rock fragments (> 50%) is not present, one can simply dump soil materials in piles across the site (as suggested by Sweigard et al. (2007)) or one can mix materials with a harrow between additions of soil material. If discontinuities are created, water can pond or sit at the boundary between two kinds of soil material and develop an oxygen-free (anaerobic) condition. This condition can make plant growth (for non-wetland plants) unlikely.
To provide the best medium for tree growth, at least 4 feet of soil should be placed on a rehabilitated site (Sweigard et al., 2007). Note that this may not be possible given that much of Pennsylvania, especially on ridge-top plateaus, may not have 4 feet of unobstructed soil material to begin with. Thus, rehabilitation of a site may actually improve soil potential by enhancing low bulk density and removing restricting soil horizons such as a very hard fragipan. To improve the success of a rehabilitated site, one may wish to add a soil amendment that adjusts a soil nutrient or pH problem. Soil amendments added to the new topsoil may include compost; municipal wastewater treatment products that have been composted or treated; lime; gypsum; and/or fertilizer. Lime can help adjust soil pH; gypsum can help promote aggregation of particles (soil stability) and relieve potential aluminum toxicity in soil. A boost of nutrients applied via a fertilizer can give plants a jump-start--a needed advantage over potential invasive species. Long-term slower release nutrient sources such as compost also build valuable organic matter; more organic matter can help hold precious water in the soil. However, it is important not to create too dissimilar a soil chemistry from that of native soils in the area. For example, many Appalachian Plateau soils have a low surface pH to begin with (3.9–5). If ample lime is added, the pH of the surface soil may increase to near 7, which may than become a more favorable environment for nonnative species or invasive species. If an active construction site used limestone rock on the Allegheny Plateau, a landowner may actually wish to apply sulfur or aluminum sulfate to help lower the soil pH. Note, though, that simply adding fertilizer will slowly lower the soil pH too.
Accelerated vegetation recovery will minimize erosion and help ensure slope stability. If vegetation cannot be planted right away because of low temperatures or site wetness, it’s important to apply a geofabric cover until planting can occur. See the Pennsylvania Stormwater Best Management Practices Manual for further ideas on site stabilization.
Remember--do not rush the site reconstruction process. Years of benefits can be lost if site reconstruction is rushed. Working a soil when it is wet, driving across a reclaimed area when it is wet, or repeatedly driving over the same reclaimed areas can all result in failed reclamation.