The Project is limited to replacing two existing power line structures (Structures 04/37 and 04/38) on the IgnacioAlto-Sausalito 60 kV alignment, decommissioning portions of an access boardwalk, building portions of an access boardwalk, placing and removing temporary access and construction matting, and placing and removing a
temporary access bridge. In-water work will be limited to: 1) installation and removal of the temporary access bridge, 2) moving the center portion of the temporary access bridge to allow vessel access, 3) installation and removal of temporary access matting across small streams, 4) installation and removal of boardwalks across small
streams. Temporary access matting will be lowered by a crane or other large equipment such as an excavator or loader. The edges of matting segments interlock; segments will be lowered into place and not require further joining. The same
technique will be used to install the temporary bridge and to move the center piece periodically for vessel access. An excavator using a screwdriver attachment will be used to place up to twelve helical piles in Gallinas Creek to support the bridge. To remove the temporary bridge, the piles will be slowly unscrewed and lifted onto the bridge, after which the piles and bridge segments will be removed from the channel.
Four, four-foot diameter steel pipe piles will be driven into the ground approximately 60 feet landward of the existing towers and used as foundations for each replacement tower. Once driven to depth, each pile will be reinforced internally with rebar cage and concrete. A steel pipe cap will be installed to connect the pipe piles to the tower leg.
Concrete is anticipated to be transferred by truck to the construction staging areas on the construction mats where it will be pumped into each pile. The new steel lattice towers will be constructed following completion of the new foundations. The towers will be assembled on site, either in upland staging areas or on the construction matting and erected with cranes. Once the electric conductors for both circuits are relocated to the replacement towers, and the circuits have been fully energized, the existing towers will be removed. The steel lattice will be removed first in segments using mechanical hand tools such as saws and torch cutters in combination with helicopters and cranes to remove pieces of steel for disposal. Following tower removal, footings and associated support piles will be removed to six inches
below the mudline. The existing towers each have four footings measuring 22.5 square feet. Mechanical methods such as hoe rams and diamond wire saws will be used to remove tower footings. Existing tower components will be completely removed from the site using trucks, barges, or helicopters and disposed at an appropriate upland facility.To facilitate construction access and installation of the temporary construction matting, existing boardwalk access to Towers 04/37 and 04/38 will be removed from the tower replacement work areas. Boardwalk removal will occur with hand tools, beginning with above ground planks and handrails. Support pilings will be cut at ground level or the mud line, and aboveground portions removed. Removed boardwalk materials will then be disposed of at an appropriate off-site facility. After the towers are replaced, the removed boardwalk sections will be rebuilt. Boardwalk construction will occur using hand tools, and no excavation will be required. All materials and tools will be transported by foot with no vehicle or machinery necessary for construction. Four-inch by four-inch wooden support pilings will be installed at approximately 10-foot spacing and driven directly into the mud. A 9-foot-wide work area is required to construct and decommission boardwalk. Final layout will be determined during final design. Because replacement Tower 04/37 will be set north of the existing tower, 82 feet of boardwalk will be removed and 194 feet will be built. At Tower 04/38, the new boardwalk will be constructed approximately 415 feet west to the Buck’s Landing parking lot, using the same alignment as the temporary construction matting. This new alignment will allow approximately 1,421 feet of existing boardwalk south of the tower to removed. At Tower 05/39, where no
tower repairs will occur, approximately 67 feet of boardwalk will be replaced in the same location and approximately 91 feet of new boardwalk extending west to N. San Pedro Road will be built. The project will result in approximately 2.34 acres and 450 linear feet of temporary impacts to salt marsh habitat hydrologically connected to Gallinas Creek. The Project will result in approximately 0.58 acres and 80 linear feet of temporary impacts to aquatic habitat in Gallinas Creek associated with the temporary bridge. The Project will result in approximately 2,222 square feet and 420 linear feet of permanent impacts associated with building new tower footings and access boardwalk, and 3,186 square feet of restored salt marsh habitat associated with removing old footings and access boardwalk for a net permanent salt marsh habitat increase of approximately 964 square feet and a net loss of 420 linear feet of salt marsh habitat. No trees will be removed by the Project.