Each year, several wood pile dolphin clusters are identified by VDOT for replacement due to damage and wear from normal ferry operations. The removal and replacement of the dolphin clusters requires the use of a vibratory hammer to remove old timber piles, and the use of a drop (impact) hammer and/or vibratory hammer to install new timber piles. Pile driving activities have the potential to create underwater sound pressure levels that may adversely affect aquatic species.
In 2012, two distinct population segments of the Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus) were listed as endangered by the National Marine Fisheries Service (NMFS), National Oceanic and Atmospheric Administration (NOAA), under the Endangered Species Act (ESA) of 1973, as amended. As a result of this action, the Virginia Department of Transportation (VDOT) found that it had to address potential noise impacts to the species due to construction-related activities for a proposed dolphin pier replacement project at each terminal of the Jamestown-Scotland Ferry on the James River.
HMMH performed a hydroacoustic assessment of pile driving activities to estimate the geographic range (within the James River) at which the estimated thresholds for the onset of behavioral effects and physical harm would be exceeded. Recommended Best Management Practices (BMP) for the project included the use of pile caps to reduce the transmission of impact energy to the pile during a hammer strike.