Background/Objectives: Treatability testing can be an effective tool to demonstrate activated carbon (AC) effectiveness and select the most cost-effective carbon amendment rate to reduce bioavailable polychlorinated biphenyl (PCB) and other hydrophobic organic compound (HOC) concentrations.
However, because the concentration of chemicals in bulk sediment does not change as result of AC amendment, and modeling of the effects of AC on chemical availability can often overpredict chemical availability, empirical measurement of chemical availability is needed for site-specific optimization of AC remedies and demonstration of remedial effectiveness. To address a 1-acre area of PCB impacted sediment in a near-shore embayment, an AC-amended remedy was proposed. This presentation details a bench-scale treatability test to optimize the AC loading rate to meet site-specific remedial goals for reducing PCB availability.
Approach: The project team conducted treatability testing in order to evaluate the reduction in availability that will be provided by the carbon amended sand layer. Sediment from the Site was collected and sent to SiREM Laboratories in Guelph, Ontario Canada where static microcosms were created to simulate Site sediments in contact with a bioturbated sand layer amended with 0%, 1%, 3%, 5% and 10% SediMite™ a powdered activated carbon containing amendment. Sediment pore water, which provides an indirect measure of bioavailability, was measured for PCB congeners using commercially available SP3 polyethylene passive samplers deployed in the mesocosms.
Results: Based on the results of the test, the project team optimized the thin-layer sand cover design with the activated carbon dosing indicated by the treatability testing results. Results showed that a 1% SediMite™ concentration (0.5% powdered activated carbon) resulted in an 80% reduction in PCB bioavailability, while a 3% concentration (1.5% PAC) resulted in a 98% reduction. The project team selected a SediMite™ dosing of 3% to ensure a greater level of confidence in achieving the remedy design performance goal of 75% or greater reduction in bioavailability from the carbon amendment. The project is now moving towards permitting and construction of the full-scale remedy with the treatability testing helping to provide Site specific confidence in the design leading to rapid implementation of the remedy. The benefits of the treatability test and confirmation of remedy success via empirical PCB availability measurements saved time and costs by enabling the project to quickly move from design to implementation, addressing regulatory concerns and uncertainties with regards to the site-specific performance of AC.