Implementation of In Situ Activated Carbon
Remedies at Contaminated Sediment Sites



Two of the earliest pilot projects with GAC utilized heavy equipment to inject and/or mix the placed GAS into the contaminated sediments.

Actuated Rototillers
The first field demonstration of activated carbon as a sediment remedial alternative took place in 2005 on the mudflats at the Hunters Point Naval Shipyard pilot project in San Francisco, CA. Conducted as part of ESTCP Project ER-200510, a commercially-available amphibious-mounted rototiller, the "Aquamog" was used to place and mix the AC into one of the treatment plots.

At Hunters Point, the Aquamog was deployed on the water during high tide and allowed to settle onto the sediment surface at low tide to place the PAC. The PAC was manually deployed on the surface of the plot at low tide and then mixed into sediment by the rotovator arm for about half an hour total over the plot. The depth of the mixing was controlled by the speed and downward pressure of the rotovator. The overall operation by Aquamog was reported as being very successful; the AC-sediment mixing was immediately visually confirmed (ESTCP Project ER-200510). The limitation to the equipment for PAC placement was that the treatable sediment area was limited to a 6-foot swath (the swing-length of the rotorvator) per one tidal cycle, because the barge units its mobility was limited to high tides. A second limit was that a second amphibious support vehicle was necessary to support placement onto the demonstration site.

Excavator_Mounted Rake Injectors
A second system tested in the 2005 Hunters Point project was an excavator-mounted rake injection system. The injector-rake system was adapted from a commercially available soil/sediment stabilization that uses a set of hollow "forks" to inject and then mix ("rake") cement grout. For Hunters Point, the rake was equipment was mounted to a track-mounted conventional excavator, which mobilized out into the intertidal test plots during low tides. The PAC slurry was mixed onshore, and pumped to the rig, and then injected and mixed into the upper one foot of tidal zone sediments.


An advantage of the system used at the 2005 Hunters Point placement was that the contractor was able to record data such as slurry flow rate, slurry density, pump time, and slurry volume pumped into each test plot; this provided the data necessary to demonstrate that the requisite carbon mass has been added to test plot. This disadvantage of this equipment was that the equipment was restricted to intertidal areas, and that the total weight of the equipment limited the application to areas where the sediment was sufficiently stable to support the equipment weight.

Injection and Mixing Systems
Custom systems for injecting and mixing GAC were developed and tested for the 2006 Alcoa Grasse River pilot project (Beckingham and Ghosh, 2011; Patmont et al 2015). GAC (particle size 75-300 µm) was added to sediments at a target dose of 3.75% by dry weight to the top~15 cm of surficial sediment as a slurry by three modes of amendment: (1) mixed using an enclosed tilling device, (2) layered without mixing, and (3) injected into surficial sediments using two rows of hollow tines. Two types of GAC were also tested at this site: bituminous coal-based AC, and a coconut shell-based AC.

Additional Resources
ALCOA 2006 Grasse River Activated Carbon Pilot Study. ALCO Grass River Project web page.

In situ sediment treatment using activated carbon: A demonstrated sediment cleanup technology. Patmont et al., 2014.