Mitigation measures to avoid or reduce acoustical impacts (noise) from hydrokinetic energy development.
The following are examples of mitigation measures that could be applied to reduce the project noise impacts depending upon site- and project-specific conditions. Noise impacts are related to the source of the noise (e.g., vehicles, construction equipment, workers, blasting, and project facility components), the proximity to sensitive noise receptors (e.g., humans and wildlife), and the time of day at which noise-producing activities occur. Many impacts can be reduced or avoided when considered during the siting and design phase.
Develop a final set of mitigation measures for the project in consultation with the appropriate tribal, federal, and state resource management agencies, and with stakeholders. Conduct these consultations early in the project development process, preferably prior to final project siting and design.
Siting and Design Mitigation Measures
Siting and design considerations that mitigate impacts include:
Proponents of a hydrokinetic energy facility should take measurements to assess the existing background noise levels at a given site (onshore and offshore, both above and below the ocean or river surface) and compare them with the anticipated noise levels associated with the proposed project. Nearby residences, marine wildlife, and likely sensitive receptors should be identified at this time.
Locate the hydrokinetic energy facility to avoid marine wildlife feeding areas, commercial fishing areas, and marine- or river- protected areas.
To the extent practicable, site the transmission lineright-of-way (ROW) to avoid residential areas and important wildlife habitat areas (e.g., rookeries, raptor nesting areas, calving areas).
General Mitigation Measures
General mitigation practices and principles that could apply to any or all phases of a hydrokinetic energy project include:
Limit noisy activities (including pile driving) to the least noise-sensitive times of day (weekdays between 7 a.m. and 10 p.m.).
All equipment should have sound-control devices no less effective than those provided on the original equipment. Motorized equipment should be adequately muffled and maintained.
Notify nearby residents in advance if blasting or other noisy activities are required during the construction period.
Whenever feasible, schedule different noisy activities (e.g., pile driving and transmission line excavation) to occur at the same time, since additional sources of noise generally do not increase the total noise level significantly, i.e., less-frequent noisy activities would be less annoying than frequent less-noisy activities.
To the extent feasible, route heavy-truck traffic supporting construction activities away from residences and other sensitive receptors.
Project Phase-Specific Mitigation Measures
Mitigation measures specific to a particular phase of a hydrokinetic energy project include:
Employ a bubble curtain during pile driving to reduce underwater noise transmission.
Surround substations with noise-reducing fencing, earthen berms, shrubs or trees, or other noise barriers.