During a study performed as part of the Tower Replacement Program, it was identified that multiple electrical transmission towers were in need of immediate repair. The San Francisco District U.S. Army Corps of Engineers (USACE) issued an emergency permit to replace three towers at risk of failure. According to the USACE, “A failure of one or more of these towers would lead to an extended outage affecting over 30,000 homes and a variety of schools and medical facilities for upwards of three to six months, causing an unacceptable hazard to life.” The project presented logistical challenges due to the extremely shallow Dutchman Slough with no terrain access.
Scope of Work
Ballard teamed with Lind Marine to utilize their fleet of specialized equipment to install 595-linear feet of sheet pile and dredge 32,000 cubic yards of sediment, permitting access to the towers for repair. In the original project scope, the dredge material was to be transported and hydraulically pumped into a containment area located three miles downstream from the dredge site. However, a second challenge arose when sediment sampling results revealed the sediment did not meet the required material disposal standards.
Due to the emergent nature of the project, Ballard and Lind Marine proposed alternative solutions to continue dredging while working to source an alternate disposal location. Those efforts resulted in transporting the dredge spoils to Lind Marine’s Shipyard on Mare Island and transloading the material into 1,800-2,400 cubic yard hopper barges for temporary storage. Additionally, the project team completed batch testing to dry and transport the dredge spoils for upland disposal. After many weeks of collaborative planning, agency approval was received to dispose of the material at Montezuma Wetlands, a nearly thirty-mile round trip by a tugboat.
Upon receiving the final disposal location, Ballard and Lind Marine began 24/7 operations to continue dredging and transporting material, exceeding daily production rates and accelerating the schedule. Daily bathymetric surveys were completed to calculate the dredge quantities, quantify the sediment infill, and calibrate the dredge positioning system. The final result provided the correct depth for equipment to access the tower locations for repair.
Client: Pacific Gas & Electric
Location: Napa River, CA