Field Testing of Activated Carbon Mixing and In Situ Stabilization of PCBs in Sediment

Abstract

We conducted the first field-scale test of in-situ activated carbon AC amendment for contaminated sediment remediation. Using commercial equipment devices, AC was successfully incorporated into the test plots to a nominal 1 foot depth at a dose of 2-3%. In-situ bioassays with Macoma nasuta showed the benefit of AC treatment, though at 18 months post-treatment the insitu assay results were confounded due to newly deposited sediment. Ex-situ M.nasuta bioassays showed about 50% reduction in PCB biouptake with 2% of AC dose. Field-exposed AC retained a strong stabilization capability to reduce aqueous equilibrium PCB concentrations by as much as 95%, which supports the long-term effectiveness of AC in the field at least up to 18 months. Neither PCB resuspension from the test plots nor adverse impacts to the benthic community were observed. Scaling-up the AC treatment method results in possible total cost savings of 70 to 75% less than sediment dredging and disposal for the Hunters Point South Basin test site. If ongoing contaminant sources are eliminated and freshly deposited sediments are clean, in-situ AC amendment of contaminated sediments can provide a suitable method for reducing contaminant exposure to the water column and biota.