2. Alternative 1: Partial Undergrounding of Proposed Antelope-Pardee Line
For Alternative 1, the proposed 500 kV transmission line would be constructed underground in two specific high-impact segments: along Del Sur Ridge in the ANF, and within the City of Santa Clarita. Underground construction was considered in the ANF to reduce visual impacts, conflicts with Forest Management activities (e.g., wildland fire suppression), and the potential for avian collision associated with overhead lines and related infrastructure. In the City of Santa Clarita, underground construction was considered in response to the City's request to minimize visual impacts.
This alternative would generally follow the same route (and use similar proposed improvements and remove the existing 66 kV line) as the proposed Project, with the exception of the underground segment in Santa Clarita, which would occur within city streets. Underground construction along the Del Sur Ridge would begin just south of Mile 11.0 and continue until just south of Mile 15.0. (See, Figure B.4-1a in the Final EIR/EIS.) A transition station, approximately 80 feet high and with a footprint of approximately 2 to 3 acres, would be required at each end of the underground segment to transfer the 500 kV transmission lines from overhead to underground and vice versa. In Santa Clarita, underground construction would begin at Mile 22.7 and continue until Mile 25.6 (Pardee Substation). (See, Figure B.4-1b in the Final EIR/EIS.) Upon leaving the ANF, the transmission line would continue to follow the proposed Project route; however, at Mile 20.3, where the proposed Project enters the existing Pardee-Vincent ROW, new single-circuit 500kV towers would be placed in the vacant position of this existing ROW, rather than replacing the existing single-circuit 500 kV towers with double-circuit towers to keep the vacant position open. At Mile 22.7, the overhead transmission line would exit the existing Pardee-Vincent ROW and tie into a new transition station, which would be located west of the corridor on the east side of San Francisquito Canyon Road, near Copper Hill Drive. The transmission line would exit the transition station underground and travel south in a new ROW along San Francisquito Canyon Road for 0.3 miles, head west on Copper Hill Drive for 3.0 miles, where San Francisquito Creek would be crossed by installing casings directly on to an existing bridge (or an independent support structure, if it is determined that the existing bridge would be structurally unsound with the additional infrastructure attached), then turn west on Newhall Ranch Road for 0.2 miles before connecting to the Pardee Substation (Mile 26.2). For the underground connection to Pardee Substation, the transition station would take the place of the substation "dead-end" structure required for overhead line terminations.
The technology that would be used for the underground portions of this alternative would consist of Solid Dielectric Cables (XLPE) installed in concrete-encased ductbanks. To date, only one 500 kV XLPE cable system of significant length (several consecutive miles) has been installed in the world. Therefore, this technology has little operating history that can serve as a basis for demonstrating reliability at 500 kV. However, XLPE cable has been successfully installed and operated for long lengths at lower voltages and has been shown to be technically feasible for a 500 kV installation since the fundamental technology is the same.
For Alternative 1, as for the proposed project, the USFS would issue a 50-year term Special Use Easement authorizing the construction, use, and maintenance of the long-term transmission line and infrastructure, 12.6 miles long, within a 160-foot-wide ROW, on ANF lands. Any ground-disturbing activities during construction on ANF lands and outside the proposed 160-foot-wide ROW easement would be authorized by one or more temporary Special Use Permits. Additional resource studies would be necessary to authorize the temporary Special Use Permit for work outside the proposed 160-foot-wide ROW (e.g., secondary marshalling yards, pulling and splicing set up sites, helicopter staging areas).
In addition, this alternative would require several amendments to the ANF Land Management Plan, including changing the Scenic Integrity Objectives along the proposed utility corridor (see, Table A.5-3 in the Final EIR/EIS); relocating approximately 1.9 miles of the 1,000-foot wide Saugus-Del Sur utility corridor to follow the Alternative 1 underground portion of the route on ANF lands (the underground cables would be placed at the centerline of the relocated utility corridor); and modifying the Forest Standard relating to the Pacific Crest Trail (S1) as regards this Project.
A detailed discussion of the facilities needed to construct the project under Alternative 1 is set forth at pages B-67 to B-85 of the Final EIR/EIS.