Photo courtesy AGC of Washington General Construction used a closed, sealed and vented bucket to extract contaminated sediments at Todd Pacific Shipyards.

General Construction made sure oil absorbents were readily available during the course of dredging for the Todd Pacific Shipyards remediation project. Personnel were trained in detection and suppression of any event that could degrade water quality, and water and sediment quality tests were conducted throughout the project’s duration.

Cleaning the site without spreading contaminants off-site or redepositing was crucial. Clamshell digging was needed, a repetitive process that requires removing material from the bottom and bringing it up through the water column. By using best management practices, clamshell dredging contaminant risks were mitigated by slower bucket speeds and the use of a bucket that was closed, sealed and vented.

A hopper barge was used for off-site material transport. Typically, material is sent off on flat barges that allow excess water drainage. Since hopper barges are completely sealed, the risk of recontamination was again eliminated.

A decanting barge gave General Construction an on-site means of dealing with excess water. The barge was essentially a water treatment facility that used a series of weirs and settlement ponds to separate sediment from the water and return treated water to the site.

Another significant component of the project included the removal of two pier footprints. Regulatory agencies noted that shaded areas were not conducive to fish and benthic life. A habitat mitigation area was built to allow natural sunlight exposure. The construction of this are required careful placement of rip-rap and graded rock under water.