A projectís environmental permit may include underwater sound thresholds and require hydroacoustic monitoring to ensure these thresholds are not exceeded. These thresholds typically apply to impact pile driving, but can also apply to vibratory pile driving. Monitoring may also be performed to verify the effectiveness of sound attenuation devices such as pile pads, bubble curtains, and coffer dams.
The National Marine Fisheries Service (NMFS) and United States Fish and Wildlife Service (USFWS) regional offices in Washington, Oregon and California typically require hydroacoustic monitoring, and requirements in Alaska and Idaho are becoming more common. The Endangered Species Act (ESA) and Marine Mammal Protection Act (MMPA) consultation for a project typically determines whether monitoring will be required. Generally monitoring is required for pile installation or proofing with an impact hammer in areas where fish and marine mammals are present.
Greenbusch can perform underwater noise monitoring to document background sound levels at a project site. Normally, the project must identify an ďaction areaĒ where underwater sound generated by the project is higher than the harassment and injury thresholds for marine life. For marine mammals, this is as low as 120 dB. The distance for noise to reach this level can be many miles. Often background sound levels are higher than this 120 dB requirement and measuring background sound levels can reduce the size of this ďaction area.Ē
Elliott Bay Seawall Replacement
Hydroacoustics monitoring was conducted during impact and vibratory pile driving. Greenbusch staff also worked with the Contractor during construction to implement effective underwater noise mitigation. Technical monitoring reports were generated for each season of construction. These monitoring reports included summaries of monitored airborne and underwater sound levels for vibratory and impact pile driving, ambient conditions, data acquisition procedures and monitoring equipment, predicted areas of influence on marine mammals (injury and disturbance regions for cetaceans and pinnipeds), and effectiveness of sound attenuation measures.
BNSF Bridge Number 24.8 Replacement
Greenbusch prepared an Underwater Noise Monitoring Plan outlining means and methods for underwater noise monitoring, signal processing and reporting requirements for submission to State and Federal Agencies/Services. The Projectís permits require hydroacoustic monitoring for all piles driven on-land and in-water with an impact hammer. Due to the Projectís duration and location, project specific equipment and deployment techniques were developed. Underwater sound levels are monitored in real time to ensure the distances for onset of injury to fish does not exceed the distances specified in the Projectís environmental permits. The data collected during these measurements was used to generate an Underwater Noise Monitoring Report summarizing; 1) The results of underwater sound levels from impact pile driving; 2) Effectiveness of underwater noise mitigation; 3) Data acquisition procedures, and 4) The predicted areas of influence on fish.
Morse Lake Pump Plant
North Bend, WA
Greenbusch is working closely with the Contractor to develop and implement an Underwater Noise Monitoring and Mitigation plan to satisfy Contract requirements for pile driving. Hydroacoustic monitoring occurred during the installation of steel sheet piles with a drop impact hammer. Underwater sound levels were measured in real time to assess compliance with the Projectís sound limits. The number of remaining pile strikes until the sound limits were reached was also calculated in real time. The approach allowed the Contractor to determine the type of mitigation to use to optimize their production. The Project will replace the current floating pump station at Chester Morse Lake; an essential water supply storage reservoir that is home to a unique genetic stock of bull trout and pygmy whitefish.