2.1 Overview of the Proposed Project - Keystone XL pipeline - US ...

Draft Supplemental Environmental Impact StatementKeystone XL ProjectFor some crossings, the owner of the utility or buried feature may require the facility to beexcavated and exposed by their own employees prior to the Keystone contractor getting to thelocation. In those cases, Keystone would work with owners to complete work to the satisfactionof the owner. Where the owner of the utility does not require pre-excavation, generally, thepipeline contractor would locate and expose the utility before excavating the trench.2.1.8.3 Steep TerrainSteep slopes traversed by the proposed route would be graded to reduce slope angles, thusallowing safer operation of construction equipment and reducing the degree of pipe bendingrequired. In areas where the pipeline route crosses side slopes, cut-and-fill grading may beemployed to obtain a safe working terrace. Keystone would install the pipeline to maintain therequired depth of cover of 48 inches in cultivated areas and 42 inches in all other areas, includingon side slope cuts and perpendicular slope crossings, except in bedrock areas where theminimum depth would be 36 inches.Prior to cut-and-fill grading on steep terrain, topsoil would be stripped from the ROW andstockpiled. If soil and slope conditions permit, soil from the high side of the ROW would beexcavated and moved to the low side to create a safer and more level working surface. Afterpipeline installation, soil from the low side of the ROW would be returned to the high side andthe contour of the slope would be restored to its pre-construction condition to the degreepracticable.Temporary sediment barriers, such as silt fences and straw bales, would be installed whereappropriate to prevent erosion and siltation of wetlands, waterbodies, or other environmentallysensitive areas. During grading, temporary slope breakers consisting of mounded and compactedsoil would be installed across the ROW. In the cleanup phase, permanent slope breakers wouldbe installed where appropriate. Section 4.5 of the CMRP (Appendix G) presents additionalinformation on the use of sediment barriers and slope breakers.After regrading and installation of erosion control devices, seed would be applied to steep slopesand mulch consisting of hay or non-brittle straw would be placed on the ROW, or the ROWwould be protected with erosion control geofabrics. MDEQ requires that geofabric mesh size be2 inches or greater to avoid animal entanglement. Sediment barriers would be maintained acrossthe ROW until permanent vegetation is established. Additional temporary workspaces may berequired for storage of graded material and/or topsoil during construction.2.1.8.4 Unstable SoilsSpecial construction techniques and environmental protection measures would be applied toareas with unstable soils and to areas with high potential for landslides, erosion, and masswasting. Construction in these areas could require additional temporary workspace areas.Topsoil piles would be protected from erosion through matting, mulching, watering, ortackifying (making slightly sticky by applying resin adhesives) to the extent practicable.Photodegradable matting would be placed on steep slopes or areas prone to extreme windexposure, such as north- or west-facing slopes and ridge tops. Biodegradable pins would be usedin place of metal staples to hold the matting in place.Reseeding would be carried out using native seed mixes that are certified noxious weed-free, ifpossible. Land imprinting may be employed to create impressions in the soil to reduce erosion,Project Description 2.1-53 March 2013