Pile driving noise and mitigation
The Cape Disappointment experiments by Jim Laughlin of WADOT assessed mitigation potential of bubble curtains and different cap materials. He found mean peak and RMS SPLs of 179 and 193 dB, respectively (average over all cap materials), were reduced 8 dB on average by the bubble curtain (see Google spreadsheet with SPLs of common Salish Sea sounds). The min and max values associated with different combinations of cap materials and bubble curtains were 165 and 208 dB.
Recordings made via Salish Sea Hydrophone Network: