In situ stabilization of persistent organic contaminants in marine sediments

This work addresses the addition of carbon sorbents to marine sediments to reduce the chemical and biological availability of persistent organic contaminants such as polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs). The sediment for all tests was obtained from the intertidal zone in South Basin, adjacent to the landfill at Hunters Point Naval Shipyard in San Francisco Bay, CA. Three major study activities were performed as part of the work reported here.; In the first study, PCB- and PAH-contaminated sediment from Hunters Point was contacted with coke and activated carbon for periods of one and six months. Sediment treated with 3.4% by weight activated carbon showed reductions in aqueous equilibrium PCB and PAH concentrations and uptake by semi-permeable membrane devices, and reductions in PCB flux to overlying water in quiescent systems. Adding coke to contaminated sediment did not significantly decrease aqueous equilibrium PCB concentrations nor PCB or PAH availability in SPMD measurements.; The second study showed that increasing the activated carbon dose reduced PCB and PAH aqueous concentrations, PCB and PAH uptake by semi-permeable membrane devices and quiescent flux of PCBs to overlying water. Decreasing activated carbon particle size decreased aqueous PCB concentrations. Collaborators at the Environmental Research and Development Center (ERDC) in Vicksburg, MS found that increasing the carbon dose increased the effectiveness in reducing PCB bioaccumulation.; The third study investigated how mixing activated carbon into cohesive sediment may affect the stability of sediment in the intertidal zone at South Basin, adjacent to Hunters Point. The results indicated for these sediments that mixing 3.4% by weight activated carbon into sediment does not significantly affect the stability of surface sediments, as measured by sediment erosion rate and critical shear stress for incipient motion. Hydrodynamic modeling of South Basin showed that bottom shear stresses caused by large waves under high-wind storm conditions are sufficient to erode surface sediments only for short periods of time.; The results from this investigation demonstrate that adding activated carbon to marine sediment can be an effective in situ stabilization method to reduce hydrophobic organic contaminant availability to surrounding water and biota.