Vantage to Pomona FEIS Index 34 - Laserfiche WebLink

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Vantage to Pomona Heights Chapter 2 230 kV Transmission Line Project FEIS Proposed Action and Alternatives PAGE 2-40 The Wisconsin Public Service Commission (WPSC), an independent regulatory agency, issued a report in 2011 titled Underground Electric Transmission Lines (WPSC 2011). According to the report, the varying circumstances of an underground line failure dictate the duration of an outage. Repair person availability and skill level, as well the availability of parts, all contribute to the length of time it takes to repair an underground line failure. On the average, it takes between 5 and 9 days to repair an outage on a XLPE underground transmission line. Repair time for a high pressure, gas-filled GIL underground transmission often takes longer (8 to 12 days). Depending on the extent of the damage, repairing a fault in a HPFF system can take from 2 to 9 months. The duration of an outage and the time it takes to repair the line increases with the number of splices in the system. Allowing quick and easy access to the system via concrete vaults at splice locations can reduce the duration of an outage. Outages tend to be longer when a splice is directly buried, as is occasionally seen with suburban and rural XLPE lines. For pipe-type lines, the line must be de-energized and the pipe pressure reduced below 60 pounds per square inch before any probes are put into the pipe to locate a leak. The line must be out of service for a day, for some leak probes, before the tests can begin. The fluid on each side of the line failure is frozen approximately 25 feet out from the failure point in order to repair a pipe-type line. The pipe would be opened and the line inspected. Repairs may include a new splice or cable replacement and splicing. Upon completion of the repair, the fluid in the pipe would be thawed and the line would be slowly re- pressurized, tested, and put back in service. As a result, a couple of extra days are required before the line can be reenergized (WPSC 2011). Emergency response time for underground transmission lines is often affected because hampered by the fact most of the underground transmission material suppliers are located in Europe. Horizontal Directional Drilling (HDD) As an alternative to open trenching or the use of overhead transmission lines and transition stations, horizontal directional drilling (HDD) is a trenchless method of installing transmission lines and other utilities where surface and near-surface features must remain undisturbed. HDD would be technically feasible as an alternative construction method of the Underground Design Option instead of the use of transition stations, such as the crossing of I-82 for the proposed Project. HDD is a process where a conduit pipe is placed in a hole drilled along an underground arc between insertion and reception pits on each end using a bore machine, which is essentially a specialized drilling rig placed at a horizontal angle. A boring machine pushes and guides a drilling head connected to hollow pipe into the ground at a designated angle based on site conditions. As each joint of drill pipe advances into the ground through the “pilot hole”, a new one is added behind it. When the bore head and rod emerge on the opposite side of the crossing, a special cutter, called a back reamer, is attached and pulled back through the pilot hole. The reamer bores out the pilot hole so that the pipe can be pulled through. Once the drilling is complete and the conduit is in place, the underground cable (e.g., solid dielectric cable) may be fed through the conduit. HDD requires extensive geotechnical study to identify soil formations at the potential bore sites of the drilling area to determine appropriate design and drilling techniques. This must be conducted before decisions on the pipe design or installation techniques can be made. The purpose of the investigation is not only to determine if HDD is feasible, but to establish the most efficient implementation procedures. The study would identify soil types, rock inclusions, areas of hardpan, soil strength and stability characteristics, and potential groundwater occurrence. Based on the study, the best boring route can be determined, drilling tools and procedures would be selected, and the pipe designed. The extent of the geotechnical investigation depends on the pipe diameter, bore length, and the nature of the crossing. Drilling fluid or drilling mud, typically a mixture of water, and bentonite (clay) or polymer, is used during the drilling process to aid in stabilizing the bore hole, cooling the cutting head, removing cuttings, and