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

Draft Supplemental Environmental Impact StatementKeystone XL ProjectThe HDD method could also be used to bore beneath terrestrial areas that contain specialresources that require avoidance. Additional HDD crossings could be incorporated into theproposed Project as a result of resource agency, landowner, or land manager concerns, as well asdue to construction-related issues.The HDD method involves drilling a pilot hole under the waterbody and banks, then enlargingthe hole through successive ream borings with progressively larger bits until the hole is largeenough to accommodate a pre-welded segment of pipe. Throughout the process of drilling andenlarging the hole, a water-bentonite slurry would be circulated to lubricate the drilling tools,remove drill cuttings, and provide stability to the drilled holes. Pipe sections long enough to spanthe entire crossing would be staged and welded along the construction work area on the oppositeside of the waterbody and then pulled through the drilled hole.The welded drill string would be hydrostatically tested for 4 hours prior to being pulled intoplace. Depending on the angle of approach of the pipeline alignment to the water crossing, a“false ROW” may need to be cleared on the pull back side to allow pipe placement at theappropriate angle to the waterbody. Keystone has created Site-Specific Waterbody CrossingPlans (Appendix G, CMRP) that describe the procedures to be used at each perennial waterbodycrossed using the HDD method. Keystone would use industry standard procedures to ensure pipeand coating integrity are maintained during HDD installations.During HDD operations, the hole that is reamed to allow the pipeline to be pulled through ismuch larger than the pipe diameter (approximately a 42-inch-diameter hole or larger for the 36­inch-diameter pipe). As noted above, bentonite drilling mud would be used to reduce friction andprovide lubrication and buoyancy for the pipe during the pull back, assuring minimal contactwith the walls of the drill hole. 5 An abrasion-resistant overcoat would be applied to the FBEcoating on the pipe joints designated for HDDs. This overcoat prevents damage to the corrosionresistant FBE coating as the pipe is pulled through the bored hole. After installation, Keystonewould conduct CP and in-line inspection surveys to determine if any damage may have resultedto the pipe coating during the construction process.There is a potential for HDD frac-outs (accidental releases of pressurized drilling mud from theborehole) to occur during construction. A frac-out could release bentonite drilling mud into theaquatic environment. Bentonite is non-toxic; the released drilling mud would disperse in flowingwater or eventually settle in standing water. The proposed minimum depth for HDD pipelinesections is 25 feet below the streambed. In some instances, the pressurized fluids and drillinglubricants used in the HDD process may escape the active bore, migrate through the soils, andcome to the surface at or near the construction site, an event commonly known as a frac-out.While the HDD method poses a small risk of frac-out (i.e., release of bentonite-based drillingfluids), potential releases would be contained by best management practices that are describedwithin the HDD Contingency Plans required for drilled crossings and prepared by the pipelinecontractor prior to construction. These practices include monitoring of the directional drill,monitoring downstream for evidence of drilling fluids, and mitigation measures to address a fracoutshould one occur.Most leaks of HDD drilling fluids occur near the entry and exit locations for the drill and arequickly contained and cleaned up. Frac-outs that may release drilling fluids into aquatic5See Section 4.3, Water Resources.Project Description 2.1-59 March 2013