2006 Activated Carbon Pilot Study

Project Details

The technology implemented for this pilot study consists of the addition of activated carbon to the upper layer of the sediment. Laboratory and focused field studies conducted by Stanford University, University of Maryland Baltimore County, and others have demonstrated that mixing activated carbon into surface sediments is effective in reducing the bioavailability of PCBs in sediments to fish and other river-dwelling organisms. The carbon dose is not toxic to humans, fish, or other organisms. The PCBs sorb onto the carbon particles and become trapped, making them unavailable to fish and other organisms. This, in turn, is expected to result in the reduction of PCB levels in both water and fish of the lower Grasse River. Only a thin layer of carbon is necessary to achieve this result. The overall objective of the ACPS is to verify that the bioavailability of PCBs within lower Grasse River sediments can be effectively reduced at the field scale through the addition of activated carbon.

Tiller

Tiller
To evaluate the use of activated carbon, Arconic (formerly Alcoa) implemented a pilot demonstration that consisted of:
  1. Laboratory studies to evaluate the applicability of this technology to Grasse River sediments, and identifying the target application concentration of activated carbon that should be mixed into Grasse River surface sediment (2.5 percent by weight);
  2. Designing and developing specialty equipment for activated carbon placement including:
    • A "roto-tiller" or tiller – 7 x 12-foot enclosed device that first applied (via spraying) activated carbon onto the sediment surface, followed by mixing of the material into near-surface sediments using the roto-tiller (was used with and without mixing); and
    • Tine Sled

      Tine Sled
    • A "tine sled" – 7 x 10-foot tine sled device that included direct injection of activated carbon into near-surface sediments.
  3. Field-scale testing of the specialty equipment and placement methods on land to determine if equipment will work as intended;
  4. A field demonstration of the most promising equipment and placement methods in a 0.5-acre pilot area in the lower Grasse River (described in further detail below); and
  5. Monitoring activities prior to, during, and after the field demonstration (described in further detail below).

The ACPS field demonstration in the Grasse River was conducted in an approximate 0.5-acre area located in the main channel of the river approximately 2 miles downstream of the Route 131 Bridge. This area was divided into four separate test plots to evaluate the different application techniques and mixing methods. These areas, along with the equipment used to place activated carbon, included:

  • Initial Testing Area – tiller with and without mixing and tine sled;
  • Mixed Tiller Treatment Area – tiller with mixing;
  • Tine Sled Mixed Treatment Area – tine sled; and
  • Unmixed Tiller Treatment Area – tiller without mixing.

Activated Carbon Pilot Study Area

Study Area Map

A silt curtain was used on the downstream and center channel sides of the in-river work area to control any solids and PCBs that may be resuspended during the operation.

Collecting core samples as part

of the monitoring program

Collecting core samples

As indicated above, baseline, during-construction, and post-construction monitoring was conducted to evaluate potential impacts to the surrounding environment due to activated carbon placement (water column and noise monitoring) and to assess the amount of carbon placed (sediment sampling). Water column and noise monitoring results indicated little to no impacts resulted from implementation of the ACPS. Sediment cores collected immediately following application of activated carbon indicated that an overall average activated carbon increase of 2.5 percent or greater was successfully achieved in each of the treatment areas, although some variability was observed in the measurements. A summary presentation of ACPS activities and monitoring results was given at a community meeting in April 2007.

View of the Activated Carbon Pilot Study Activities

Study area activities

The ACPS includes a detailed 2-year post-implementation physicochemical and biological monitoring program to evaluate the longer-term effectiveness of the treatment. Ultimately, results of these studies will be incorporated into the modeling framework that has been developed for the lower Grasse River to determine the potential benefits associated with larger-scale application of this technology in the Grasse River.

Aerial View of ACPS

Study area activities