Ignacio Mare Island Phase 2 Tower Replacement (Notification of Lake or Streambed Alteration, No. EPIMS-SON-38861-R3)

Ignacio Mare Island Phase 2 Tower Replacement (Notification of Lake or Streambed Alteration, No. EPIMS-SON-38861-R3)

The Project is limited to removing and replacing an existing tower (Tower 3/29) on the Ignacio-Mare Island alignment, replacing and building portions of an access boardwalk, placing and removing temporary access matting, and placing and removing one temporary access landing. In-water work will be limited to: 1) installation and removal of the temporary barge landing, 2) barge operation, 3) installation and removal of temporary access matting across small streams, 4) installation and removal of boardwalks extending into the Petaluma River and across small streams, and 5) removal of existing piles. Due to access restrictions, large equipment such as cranes and piles cannot be moved to Tower 3/28 over land. As such, this equipment will be delivered to the tower via barge from the Petaluma River. A temporary barge landing will be built on the south bank of the Petaluma River (Site 1). The landing will provide a stable transition for the crane from the barge to the temporary access matting and staging area. Prior to or during installation of the barge landing, approximately 10 existing 8-inch to 1-foot diameter wood piles will be removed by cutting them at or below the mud line. The barge landing will consist of 56, 24-inch diameter piles installed in the Petaluma River using a crane-mounted vibratory hammer. One pile, located approximately 25 feet inland from the mean lower-low tide line, will be driven using an impact hammer for approximately 15 impacts to collect data for a safety analysis for the barge landing. A 40-foot-wide steel trestle will be placed on and connected to the piles. The trestle will be 200 feet long. When work is complete, the trestle will be removed. The piles will be vibrated out from the substrate and removed from the site or will be cut at or below the mudline and the larger portion removed from the site. Roads consisting of temporary access matting will connect the landing to the staging area at Site 1 and will connect the land access point to the staging area at Site 2. 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. Four, five-foot diameter steel pipe piles will be driven into the ground approximately 60 feet south-southwest of Tower 3/29 and used as foundations for the replacement tower. Once driven to depth, each pile will be reinforced internally with rebar cage and concrete. Base plate will be installed to connect the pipe piles to the tower legs. The new steel lattice tower will be constructed following completion of the new foundations. The tower will be assembled on site, either in upland staging areas or on the construction matting and erected using cranes or helicopters. Once the electric conductors for both circuits are relocated to the replacement Tower 3/29 and the circuits have been fully energized, the existing tower will be removed. The existing Tower 3/28 will also be removed and replaced, however this activity is outside of the stream and not subject to this Agreement. 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 3/29 removal, footings and associated support piles will be removed to 36 inches below the mudline or to the top of the second foundation tier, estimated to be 2- to 3- feet below grade. The existing Tower 3/29 has four footings measuring 22.5 square feet each. Mechanical methods such as hoe rams and diamond wire saws will be used to remove tower footings. Existing Tower 3/29 components will be 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, approximately 100 feet of existing boardwalk access to Tower 3/29 will be removed and reinstalled following tower installation. 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 tower 3/29 is replaced, approximately 315 feet of boardwalk connecting the tower to the Petaluma River will be built, 12 feet of which will extend into the Petaluma River for boat access. 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 composite support pilings will be installed at approximately 10-foot spacing and driven directly into the mud. A 10-foot-wide work area is required to construct and decommission boardwalk. Final layout will be determined during final design. The project will result in approximately 0.03 acres of permanent impacts and 2.65 acres of temporary impacts to salt marsh habitat, including sloughs, hydrologically connected to the Petaluma River. The Project will result in approximately 48 square feet of permanent impacts and 0.18 acres of temporary impacts to aquatic habitat in the Petaluma River associated with a boardwalk extension and the temporary landing. No dewatering will occur and no trees will be removed by the Project.

Unincorporated area

Marin, Sonoma

Northern California, San Francisco Bay Area

Sonoma