This project demonstrated the placement and quantitative integration of a suite of common and novel monitoring tools to evaluate amendment stability and performance in deep water (15 meters) at an active Naval shipyard with high vessel traffic. A key goal of this project was to extend pilot-scale efforts to larger scale footprints in active Department of Defense (DoD) harbor areas. This study demonstrated that reactive amendments are a viable tool for solving contaminated sediment challenges at DoD sites.
The sorbent material, AquaGate+PACTM (AquaGate, AquaBlok, Limited, Toledo, Ohio) was specifically manufactured by coating an aggregate core with PAC held in a bentonite clay binder, to enable deep water placement of the material on the sediment surface. The AquaGate, which is denser than water, sinks rapidly through the water column directly to the surface of the sediment. Over a short period of time (days), the PAC coating of the AquaGate releases from the aggregate and becomes mixed with the underlying sediment. Natural mixing, specifically bioturbation, incorporates the PAC into the surface sediments over time. AquaGate was placed with a conveyor belt-type equipment, which demonstrated the ability to rapidly and evenly place the material both in the open water and areas under structures such as piers and between pilings.
In this study, in situ remediation of surface sediment contaminated with hydrophobic organic compounds (HOCs) was demonstrated by placing a reactive amendment consisting of powdered activated carbon (PAC) at a site contaminated with polychlorinated biphenyls (PCBs) located at the Puget Sound Naval Shipyard & Intermediate Maintenance Facility (PSNS&IMF), Bremerton, WA. The PAC was successfully placed on the seafloor of a half-acre target site to sorb PCBs in sediments, thereby reducing bioavailability and limiting bioaccumulation of contaminants into the tissues of benthic invertebrates, and subsequently the food web.
For contaminated sediment sites such as those near infrastructure (i.e. piers and bulkheads), in harbors, ports and shipyards that present challenges to dredging and capping as remedies, in situ remediation may be a preferred alternative. In addition, in situ remediation may be suitable in areas where dredging will cause destruction of sensitive habitat or where contaminant concentrations do not warrant removal. Also, conventional sand capping may not be possible at sites where water depths must be maintained for navigational channels and berthing areas as well as where there are concerns with propeller wash. Implementation of remedies in deep water and active areas present cost and logistical challenges for many remedies. Prior to this project, the majority of the in situ sediment amendment efforts have been small, pilot-scale efforts in areas without significant limitations to access and generally targeted to low velocity waters with minimal vessel traffic or harbor activities.