In-water Pile Driving Impact Hammer use

If it is determined that impact hammers are required and/or underwater sound monitoring demonstrates that thresholds are being exceeded, the contractor shall implement sound dampening or attenuation devices to reduce levels to the extent feasible; these may include the following:
o A cushioning block shall be used between the hammer and pile.
o A confined or unconfined air bubble curtain shall be used.
o If feasible, pile driving could be done in the dry area (dewatered) behind the cofferdam