Marietta, GA: Bio-Polymer Slurry Trench, Permeable Reactive Barrier Installation at Air Force Plant 6
Air Force plant 6 is located in Marietta, GA and is utilized by the federal government for the manufacture and assembly of military aircraft. The F-22 Raptor is currently manufactured at the site. The Air Force Center for Engineering Excellence (AFCEE) tasked GSI's client, the engineering firm of CH2M Hill, Inc. with the installation of a permeable reactive barrier to mitigate chlorinated solvent contamination in the groundwater along the eastern perimeter of the site. The contaminant present in the groundwater and soil in this area is due to releases from a former plating shop operation on post. A permeable reactive barrier is an underground slurry-trench installation that when complete, leaves behind a permeable lens. This lens is oriented so that potentially contaminated groundwater will flow through. The addition of an environmental reagent to the permeable lens creates a matrix by which the contaminated groundwater undergoes remedial action. In this case the permeable lens was constructed of sand. This sand matrix was outfitted with a well-point system designed to allow the operator to inject a liquid carbon source.
CH2M Hill turned to GSI to design and construct the PRB, taking good advantage of our expertise in slurry trenching methodologies. Work on this project took place in two distinct phases. First excavation from the ground surface to approximately 77-feet below grade was performed with a standard long-stick hydraulic excavator. Thereafter, a clamshell excavator was utilized to reach depths of up to 94-feet. All of this work was completed while the trench was kept full of natural bio-polymer slurry. The slurry has the proper physical characteristics to hold open the trench as well as being easily metabolized to a viscosity near that of water via simple enzymatic reaction. The slurry percolates naturally along with the ground water at the site once metabolized.
Two 30-inch storm sewer mains were rerouted to accommodate the work. One 48-inch sewer main had to remain in place during construction. GSI crews fashioned a support system and monitored movement of this sewer main throughout the rainy season. All sewer mains were put back into service at projects end. Sand was introduced into the trench excavation to act as the aforementioned permeable lens and the project completed with the installation of the well-point system and site restoration activities. Work on this project was predicated on a fast track schedule and completed accordingly.