Mid-Atlantic Power Pathway Chalk Point Substation to Indian River ...

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Mid-Atlantic Power Pathway Environmental Review Document Chalk Point Substation to Indian River Substation Volume II – Environmental Analysis of April 13, 2011 Chalk Point Substation to MD/DE State Line Table 1.2-1 (continued) Soil Series Within the Project Right-of-Way and Project Boundaries Soil Series Description Wist The Wist series consists of deep well drained soils on uplands. They formed in Coastal Plain sediments containing moderate amounts of glauconite. Typically these soils have a dark brown sandy loam surface layer 11 inches thick over 2 inches of brown sandy loam. The dark brown subsoil from 13 to 29 inches is sandy clay loam and from 29 to 32 inches is sandy loam. The dark brown substratum from 32 to 44 inches is sandy loam and from 44 to 80 inches is loose sand. The parent material consists of glauconite bearing loamy fluviomarine deposits. Depth to a root restrictive layer is greater than 60 inches. Water movement in the most restrictive layer is moderately high. Available water to a depth of 60 inches is moderate. Shrink-swell potential is low. This soil is not flooded. It is not ponded. A seasonal zone of water saturation is at 45 inches during January. Organic matter content in the surface horizon is about 4 percent. This soil does not meet hydric criteria. Woodstown The Woodstown series consists of deep, moderately well-drained soils on uplands and terraces. They formed in marine and alluvial Coastal Plain sediments. Typically, these soils have a dark grayish-brown sandy loam surface layer 7 inches thick and a subsurface layer from 7 to 11 inches of light yellowish-brown sandy loam. The light olive brown sandy clay loam subsoil, from 11 to 29 inches, is mottled in the lower part. The substratum layers from 29 to 70 inches are sandy loam and loamy sand. This soil is moderately well drained. The slowest permeability within 60 inches is moderately slow. Available water capacity is very high and shrink swell potential is low. This soil is not flooded and is not ponded. The top of the seasonal high water table is at 30 inches. There are no saline horizons. This component is not a hydric soil. Zekiah The Zekiah series consists of very deep poorly drained soils located on flood plains of the Mid-Atlantic Coastal Plain. They formed in loamy fluvial sediments overlying sandy sediments. Typically these soils have dark brown silt loam surface 3 inches thick. The subsurface is mottled dark grayish brown silt loam 17 inches thick. The substratum is mottled and is dark gray and grayish brown sandy loam then stratified sand down to 72 inches. The parent material consists of loamy alluvium. Depth to a root restrictive layer is greater than 60 inches. Water movement in the most restrictive layer is moderately high. Available water to a depth of 60 inches is high. Shrink-swell potential is low. This soil is frequently flooded. It is frequently ponded. A seasonal zone of water saturation is at 5 inches year-round. Organic matter content in the surface horizon is about 4 percent. This soil meets hydric criteria. 1.2.1.1 Description of Potential Soil Limitations Some soil types have characteristics (e.g., erosion potential, hydric soils, compaction potential) that make them more susceptible to certain impacts or that make them valuable for specific purposes (e.g., farmland). These various “soil limitations” are discussed for each of the Project components in the following sections. In addition, Tables 1.2-2 through 1.2-7, respectively, present the known soil limitations of the soil map units for each Project component. Note that the acreages presented in the tables below are estimates based on projected disturbance areas and available soil mapping data (USDA- NRCS 2010). The actual soil conditions at a given location might vary from the generalized soil mapping presented by this data. Potential impacts discussed below are limited only to those areas where there would be temporary and/or permanent ground disturbance [construction entrances, tower foundations, 1-28
Mid-Atlantic Power Pathway Environmental Review Document Chalk Point Substation to Indian River Substation Volume II – Environmental Analysis of April 13, 2011 Chalk Point Substation to MD/DE State Line buildings, trenching for underground installation (and the associated roads), manholes, etc.]. The subsections following the tables provide brief discussions of these soil limitations relevant to these portions of the Project right-of-way that would be disturbed. The “Soil Unit Composition” column in these tables lists the soil series which represent at least 10 percent of the indicated map unit; soil series which represent less than 10 percent of the map unit are not listed. 1.2.1.1.1 Erosion Potential The potential erosion of soil can be a concern whenever vegetation is removed as a result of clearing and grading activities. Concern is increased further if the vegetation is slow to become re-established. However, leaving root systems in place as the Company has proposed, where practical, would tend to limit erosion and promote revegetation along with re-seeding. The “Erosion Potential” column of Tables 1.2-2 through 1.2-7 presents the water-related erosion potential and the wind-related erosion potential, respectively. The water-related erosion potential (“Slight”, “Moderate”, “Severe”, or “Very Severe”) is based on slope and on the soil erodibility. The wind erodibility group (1 to 8, with 1 indicating highly erodible soils and 8 indicating soils not susceptible to wind erosion) indicates the soil’s susceptibility to blowing by wind in cultivated areas. 1.2.1.1.2 Compaction and Rutting Potential Soil rutting and compaction can occur in response to the pressure exerted by the weight of the construction equipment that would be used to perform the underground or aerial installation of transmission lines and construction of new converter stations. Soil compaction increases soil density by packing the particles closer together, decreasing pore spaces in the soil, reducing soil porosity, and decreasing water and air movement into and through the soil. The result is poor soil aeration, poor root penetration, limited water movement, and reduced activity of soil organisms involved in nutrient cycling. Soil compaction can also increase surface water runoff which may lead to soil erosion and increased sedimentation in the watershed. Rutting and compaction of soils is more likely when the soils are moist or wet. The potential risk for compaction is also influenced by soil texture, with fine texture soils having higher compaction potential than coarse textured soils; soils with greater than 70 percent fragments have very low potential for compaction. The information presented in the “Compaction Potential” column of Tables 1.2-2 through 1.2-7 is the USDA-NRCS soil rutting hazard, stated as “Slight” (the soil is subject to little or no rutting), “Moderate” (rutting is likely), or “Severe” (ruts form readily). The rutting hazard and compaction potential for soils correspond well with one another; therefore, the rutting hazard information presented there also indicates the degree to which soil compaction can be considered a potential limitation for the indicated soil map units. 1.2.1.1.3 Prime Farmland There are four USDA-NRCS classifications for farmland soils: prime farmland, farmland of statewide importance, farmland of local importance, and unique farmland. USDA-NRCS defines prime farmland as “land that has the best combination of physical and chemical characteristics for producing food, feed, forage, fiber, and oilseed crops and that is available for these uses.” The designation of prime farmland is generally independent of the current land use, but it cannot be applied to areas of water or urban or builtup land. Areas designated as “farmland of statewide importance” are nearly prime farmland that economically produces high yields of crops when treated and managed according to acceptable farming methods. Farmland classifications for the soil map units in the Project area are listed in Tables 1.2-2 through 1.2-7. 1-29
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