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Posted 4/24/2013

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By Carlos J. Lazo

SACRAMENTO, Calif. – At Fort Hunter Liggett, the largest U.S. Army Reserve post in the nation, the U.S. Army Corps of Engineers Sacramento District is about to test its green thumb.

But instead of farming fruits or vegetables, the district will be farming soil - using the sun to naturally clean up soil contaminated with gasoline at a former fueling station on the installation.

“We will be using a cleanup method called ‘landfarming’ that uses the power of the sun to naturally heat the soil,” said Nicholas Kent, a geologist with the Sacramento District working on the project.

“Gasoline volatilizes readily in warm weather. Instead of using expensive chemicals, energy-intensive vapor treatment systems, or trucking waste to a landfill, we're using the sun to help us out,” Kent said. “Since the summers at Fort Hunter Liggett are quite hot, this cleanup method is perfectly suited for use at the installation.”

The project requires the excavation and treatment of about 6,500 cubic yards of contaminated soil near building 258, located in the main garrison area of Fort Hunter Liggett.

The contaminated soil will be stockpiled outside of the main garrison area, spread by tractor to a thickness of several feet and tilled regularly to ensure all the gasoline evaporates. As of mid-April 2013, roughly 1,200 cubic yards of soil has been excavated.

“Soil samples will be taken periodically to monitor the progress of the remediation, but it is expected to take less than a year to completely clean up,” Kent said.

Excavating the soil presented its own challenges.

“The area was surrounded by operational buildings and roads which would be needed to be removed if we used a standard excavation process,” said David Eisen, the project manager with the Sacramento District. “It would have cost substantially more and taken a much longer period to complete.”

Due to the active nature of the site, limited work area access and the depth of the contamination, the Sacramento District and its contractor decided instead to use a large-diameter auger excavation technique for the targeted removal of impacted soil.

“Auger excavation is not a typical method for remediation of impacted soil,” said Kent, “but all other methods were less likely to completely remediate the site and would have taken multiple years to see results.”

Landfarming shortens remediation time, but it is just one of the ways the project is contributing to the Army’s sustainability goals.

Fort Hunter Liggett has been selected as a net-zero waste installation by the Department of the Army, with a goal to eliminate or reuse waste produced on the installation. In support of this goal, the Sacramento District and its contractor will reclaim as much project-related materials as possible for eventual reuse. Materials expected to be reclaimed include pavement and cinder blocks from a building removed to gain access to the soil, as well as the soil itself.

“The removed pavement and cinder blocks were stockpiled for processing into future roadway materials and the soil will be used as fill material for future building pad construction,” said Kent. “We were at first concerned that the (net zero) program would complicate the cleanup process, but it turned out to be very easy to meet the installation's goals.”

california Corps of Engineers environmental fort hunter liggett military restoration sacramento district U.S. Army USACE