In-situ remediation with activated carbon amendment projects often actively mix AC with contaminated sediment to speed transfer of contaminants from the sediment and water to AC; however, actively mixing the AC into the sediment is often not feasible for deep water sediments or ecologically sensitive areas. We tested the efficacy of a thin layer of AC (0.3 cm) in reducing sediment-to-water flux and porewater, including in the event of additional deposition on top of the AC layer with clean and contaminated sediment. Our microcosms studies consisted of an underlying contaminated control sediment from our field study site and included five different treatment methods with thin caps and sediment deposition scenarios: 1) control, with no capping 2) simulated natural attenuation, comprising control sediment sublayer with simulated deposition events by placing thin layer (3 mm) of background sediment cap (0.03 mg/kg dw SDDT) on top of the AC at 30-day time points 3) a simulated AC in-situ treatment, comprising a control sediment sublayer, with a thin layer of virgin activated carbon (2 mm) 4) a simulated AC in-situ treament with three deposition events of background sediment, and 5) a simulated AC in-situ treatment without source control with three deposition events with control contaminanted sediment. For each sediment treatment method, we conducted a set of microcosm experiments with Lumbriculus variegatus and microcosms without worms. These experimental results show thin activated carbon placement above sediment can be effective in reducing the flux, with and without bioturbation.  Moreover, AC layer is effective in reducing flux when there is additional deposition of contaminated sediment, but requires some mixing mechanisms, like bioturbation to mix AC with the newly deposited contamination.

Thin-layer AC placement for sequestering DDT contaminated sediment facilitated by bioturbation

248th National Meeting (2014)

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