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5.5 TOPOGRAPHY, SOILS AND GEOLOGY5.5.1 REGULATORY SETTINGTitle 25 Chapter 102 of the Pennsylvania State Code establishes permit requirements for construction activities involving earth disturbance activities and requires the preparation of an Erosion and Sedimentation Control Plan for site work. Although topography and soils are not strictly regulated there are various local zoning ordinances restricting development in steeply sloped areas or terrain. Geological conditions may also dictate the use of certain engineering design standards particularly in sinkhole-prone areas.5.5.2 METHODOLOGYTopographic information was obtained from project-specific photogrammetric mapping obtained for the conceptual engineering performed as part of the MIS. The quantity of rock and soil material that would be generated to accommodate the project footprint was estimated using the existing topography and placement of track with the required widening superimposed to determine the amount of cut and fill volume generated. A 2:1 slope was assumed for general soil conditions for both cut and fill areas with adjustments made in some areas of rock cuts or where retaining walls are proposed. Mapped geologic formations were obtained from the Pennsylvania Geologic Survey and added to the project GIS. Soils information was obtained from the U.S. Department of Agriculture, Soil Surveys for the counties of Philadelphia, Montgomery, Chester, and Berks. Hydric soils and prime agricultural soils were added to the project GIS database (see Section 5.6 and 5.13).5.5.3 AFFECTED ENVIRONMENTThe majority of existing alignment is topographically positioned on the edge of the Schuylkill River floodplain at the point where the alluvial floodplain meets the valley side. The floodplain, much of which is elevated approximately 10 feet above the river's average water surface elevation, is generally flat, with a slight undulating surface. The floodplain on the river side of the alignment ranges in width from a few tens of feet to over 300 feet. The valley side typically consists of gentle to moderate slopes. In several places the valley side consists of very steep cliffs or rock-cut highwalls.The alignment's geographic position with respect to the immediately adjacent land surface is a function of its position with respect to the edge of the floodplain. When the alignment is situated on the far edge of the floodplain, it is typically elevated on an embankment 5 to 15 feet above the adjacent floodplain surface and flush with the valley side. When the alignment is situated near, but not in the floodplain, it typically is situated in an excavated cut, with steep slopes on either side. When both sides of the alignment are bordered by low floodplain areas (as in the Conshohocken area), the alignment is typically at the same elevation as the bordering land. In the immediate vicinity of culverts and bridges, the alignment is typically on a berm elevated on both sides above the stream valley. The most notable aspect of the alignment geology is the extent of outcropping bedrock in the areas of steep valley sides and areas where the alignment is in a cut. These areas are prone to occasional rock falls and soil erosion. As shown in Exhibit 5.7-1 Groundwater, Wells, Surface Water Intakes and Sinkhole-Prone Areas [PDF], the alignment crosses sinkhole prone areas south of Reading and an area from King of Prussia to Plymouth Township and Conshohocken. As evidenced by the areas with steep hillsides and cut rock walls, bedrock along much of the alignment is capable of supporting steep slopes. Soils along the alignment and the station areas are typical of those found in the Pennsylvania piedmont. Soils in non-floodplain areas are typically shallow to bedrock, except in sinkhole prone areas where depth to bedrock varies greatly over very short distances (and can exceed 50 feet.) Soil in most of the area is moderately susceptible to erosion (and highly susceptible in areas of steep slopes). Bedrock typically underlies the floodplain soils at depths of approximately 10 feet. An unusual characteristic of the floodplain soils is the presence of fine-grained anthracite coal mixed in with the other, typical, locally derived sediments. In places, the floodplain soil is composed almost entirely of black coal fines. In certain areas, well drained Schuylkill River terrace deposit alluvial soils underlie the alignment area. Areas with these soils, particularly when proximate to both a tributary stream and the edge of the Schuylkill River floodplain, have a relatively high probability of bearing prehistoric artifacts (see Section 5.11). Where the alignment is elevated on a berm, the side slopes may contain both locally derived rock and soil fill. In places, stone and block retaining walls support the berm. 5.5.4 ENVIRONMENTAL CONSEQUENCES (IMPACTS)No-Build and TSM AlternativesThere are no impacts associated with the No-Build Alternative. Impacts associated with the TSM Alternative include footprint-related excavation and erosion issues between Port Kennedy and Norristown and erosion control issues at the park and ride facilities. Build Alternatives The new project footprint for the build alternatives will utilize and, in places, widen the existing graded alignment west of Norristown. The quantity of soil and rock to be excavated has been estimated as part of the conceptual engineering to be as much as 2.6 million cubic yards. It is anticipated that very little of this can be used as fill on the project due to the need to avoid placing unnecessary fill on the floodplain. Excavated soil and rock material unable to be used for grading elsewhere along the alignment, will have to be removed from the right-of-way and used offsite or disposed of in an appropriate landfill facility. No geologic formations traversed by the alignment footprint are unsuitable for railroad construction. Rock falls during or after construction are a worker safety issue and project operational concern. Blasting may be required in places. Should it be required, the requirements of PennDOT Publication 408 (or equivalent) will be followed. A pre-blast survey of the project area will be conducted prior to any blasting operations and they will be controlled so that no property or structural damage will occur. In some areas underlain by limestone, sinkholes can open up with little notice, resulting in land collapse and damage to the built environment. New and old construction can be equally susceptible to sinkhole activity. Erosion of soil from the area disturbed by construction is a concern of every construction project. Due to the crossing of numerous streams, proximity of the construction activities to the Schuylkill River and floodplain wetland areas, erosion control during construction is of considerable importance. 5.5.5 MITIGATIONDuring preliminary engineering, geotechnical testing will be performed to establish slope stability characteristics and subsurface stability conditions in areas of the project's footprint where widening will be necessary. This program will establish the maximum degree of slope that can be utilized in soil and rock cut areas so as to minimize the extent of the area disturbed and the quantity of material removed for off-site disposal. Minimizing the extent of area disturbed will also reduce the acreage of impacted forest, agricultural land, wetland areas, and reduce the number of impacted properties and the extent of those impacts. The program will also identify specific areas where precautions will be necessary so as to avoid rock falls and sinkhole impacts. As part of preliminary engineering, an excavated material management program will be developed. It will include an evaluation of measures to minimize the quantity of material to be excavated and the potential to haul the material by rail to minimize truck traffic, and examine whether some of the material can be sold as a product (e.g., crushed stone).The Erosion and Sediment Control (E&S) plans will include program elements and requirements associated with monitoring and maintaining the effectiveness of erosion and sediment control during and after construction. E&S pollution control practices, such as sediment traps, silt fences, sedimentation basins, interception channels, grassed swales, and seeding and mulching will be used to minimize the impacts of soil erosion on wetland areas, streams, and the Schuylkill River. Detailed E&S Plans will be prepared during final design in accordance with the guidelines provided by the Pennsylvania Department of Environmental Protection (PADEP) and the PennDOT Design Manual. The E&S Plans will be included in the NPDES Permit application. The permit application will meet the requirements of Chapter 102, Chapter 105, and Chapter 106 of PADEP's Rules and Regulations.
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