In support for the North Coast Offshore Wind Feasibility Project, funded by the California Ocean Protection Council (OPC), this document provides an inventory of existing conditions and evaluates the potential effects of the project scenarios developed by Humboldt State University (HSU) and Mott MacDonald. These project scenarios (also referred to as the proposed action) represent different combinations of project scales and locations, as presented briefly below. The goal of this document is to inform the evaluation of project scenario feasibility and support future regulatory and permitting efforts.
The North Coast Offshore Wind Feasibility Project assesses two offshore wind farm locations with multiple build-out scenarios that differ in project size and the associated number of 12 MW turbines. The offshore wind farm locations consist of offshore Humboldt Bay (HB), which coincides with the Bureau of Ocean Energy Management’s Northern California Call Area, and the hypothetical Cape Mendocino area (CM). For HB, there are three project size scenarios: 50 MW (four turbines), 150 MW (12 turbines), and 1800 MW (153 turbines). At CM, there are two project size scenarios (150 MW and 1800 MW). Both locations would require the installation and operation of an export cable to convey the electricity to the shore cable landfall at the South Spit of Humboldt Bay. The segment of export cable between the South Spit cable landfall and the Humboldt Bay Substation would be installed using horizontal directional drilling under the bay.
All of the project scenarios would involve infrastructure improvements to the Humboldt Bay port. These improvements would include upgrades to Redwood Marine Terminal 1 and adjacent lands to support project construction and maintenance; potential changes to the timing and frequency of dredging within Humboldt Bay, and the potential addition of areas to be dredged in the bay. Power generated by the offshore wind farms will likely need to be distributed out of the area by overland transmission line route upgrades from the Humboldt Bay Substation to the east or south, or by a subsea cable route that extends south from the offshore wind farms to the San Francisco Bay area. All of the project scenarios (proposed action) would entail construction, operations and maintenance, and decommissioning that would result in effects on the marine and terrestrial environments. The potential short-term effects on the marine environment that would be associated with construction include: (1) disturbance of benthic habitat; (2) changes in water quality from sedimentation or contaminants; (3) increase in ambient acoustic levels underwater; (4) increase in the risk for vessel collisions with wildlife; and (5) wildlife disturbance from the use of artificial lighting (e.g., on decks or underwater). The potential longer-term effects associated with operations and maintenance include: (1) operational noise of turbines and maintenance vessels; (2) seabird and bat collision/avoidance with rotating turbine blades; (3) marine mammal interactions with underwater structure (e.g., cetacean collision or entanglement with lost fishing gear); (4) habitat changes associated with structure in the water column and on the seafloor; (5) perching and haul-out effects; and (6) electromagnetic field transmissions from the interarray cables, offshore substation, and export cable (see table below). The potential effects on the terrestrial environment associated with the transmission line upgrades include: (1) disturbance of threatened or endangered wildlife species from the noise associated with horizontal directional drilling and transmission line improvements; (2) removal of threatened or endangered plant species or sensitive natural communities during ground-disturbing activities; (3) loss of wildlife habitat (vegetation clearing); (3) hydrological interruption or the placement of fill in jurisdictional water bodies; (4) increased long-term risk of bird collision with transmission lines improvements; and (5) the introduction and spread of terrestrial invasive plant species (see table below).
The following are the key findings of this study.
- The potential effects of onshore and offshore construction will mostly be short-term and localized with opportunities for mitigation; however, major changes to existing habitat in Humboldt Bay (e.g., larger docks, dredging to increase channel size/depth beyond current channel configuration) will be a challenge to permit.
- The potential effects associated with the offshore project operations and maintenance will likely be an ongoing, long-term concern, primarily due to greater uncertainties about interactions with seabirds and marine mammals that may require extensive monitoring and adaptive management; these potential effects are scaled to project size and scenario.
- The long, linear improvements to existing overland transmission lines will also result in long-term effects on multiple terrestrial and freshwater biota and habitats, including those subject to state and federal regulations.
Permitting challenges are scaled to project size/scenario due to greater environmental uncertainties and potential risks: larger scale projects will not only affect a larger offshore footprint, but will include long terrestrial transmission line improvements that potentially affect a large number of threatened or endangered species and natural communities (e.g., wetlands and other waters). In addition, there are differences in the applicable regulatory agencies between the east and south transmission routes1.
Potential environmental effects associated with the installation and operation of a subsea transmission cable to the south and from Cape Mendocino to Humboldt Bay are not well understood when compared to the terrestrial transmission line improvements, and will require more extensive surveys to narrow down the cable route and improve understanding of environmental risks and permitting challenges. The routes for the export cables and the subsea transmission cable should avoid marine geological features (e.g., submarine canyons, faults), protected marine areas (e.g., Marine Protected Areas), and (where feasible) rocky or hard substrates, to minimize effects.
The potential effects, and their relative risks to the affected environment from stressors associated with the build-out scenarios were categorized as low, medium, and high. Stressors are considered to have a low risk if their potential effects are relatively well understood and/or they appear to present a low risk for harm to the affected environment (e.g., if only a small spatial scale or temporal scale of effect). If the potential environmental effects from stressors are not well understood (i.e., a higher level of uncertainty) and additional studies are required to improve understanding, the stressors are considered to have a medium risk. Stressors were classified as high risk if their potential effects are known to pose substantial risks to the affected environment (e.g., potential to have a negative effect over a longer term and spatial scale) and will require the implementation of avoidance, minimization, and/or mitigation measures.