Grissom Air Reserve Base, Indiana --
The use of an innovative soil excavation approach at Grissom Air Reserve Base, Ind., as part of a larger environmental restoration effort, has resulted in significant cost and time savings for the Air Force.
In September 2009, AFCEE implemented a performance-based restoration project to address two Environmental Restoration Program sites at Grissom. One of the objectives of the project was to conduct interim remediation for the contamination sources at two sites.
The first site consists of a former oil and water separator associated with former Building 741, in addition to a concrete area formerly occupied by the engine test cell and blast shield. The 300-gallon capacity separator was located three feet below the surface and approximately 30 feet from the building. Reportedly, this site received petroleum products and solvents generated during engine maintenance activities, resulting in soil and groundwater contamination.
The separator had been removed in December 2003 and the groundwater treated through injection of Hydrogen Release Compound-X in 2007. HRC-X works by producing a long-term, controlled release of lactic acid, resulting in hydrogen distribution throughout the area. This, in turn, drives the rapid desorption, dissolution and degradation of the contaminants.
The second site consists of a low-point drain box connected to a jet fuel transfer pipeline, which was used from 1963 to 1985 to remove impurities within the pipeline. Water and impurities reportedly drained out of the box and into the surrounding soil. The fuel transfer pipeline is still in use to transfer jet propulsion fuel; however, the drain box is no longer used. Previous interim remediation activities at the site included free product removals in 1999 and 2000, and the in-situ biological oxidation of soils in 2004.
Many factors contributed to the complexity of the remediation at these sites. The locations of the sites were problematic, with one site lying adjacent to an active military airfield, and the other in close proximity to office buildings and several active utilities. Other considerations were the limited work space, water removal requirements, the amount of soil that needed to be hauled off site and the amount of backfill that was required to be hauled on site.
In response to these issues, the contractor for the performance-based project, Shaw Environmental, Inc., proposed an innovative solution for excavating the soil in these areas. A slide rail shoring system was suggested as an alternative to traditional excavation technologies, which was to be followed with targeted in-situ bioremediation to address tetrachloroethene and trichloroethene contamination in the soil.
Historically, slide rail shoring systems have been used for various utilities applications including pump stations, tank installations and removals, boring and tunnel shafts, retaining walls, and sewer, water, gas and hydro installations and repairs. While slide rail systems have been used in other industries for years, it is the first time this approach has been implemented for one of AFCEE's environmental remediation projects.
The areas to be excavated were divided up into sections to implement the system. The process from installation to removal of individual cells at the first site ranged from one to three working days, depending on cell size, soil type and weather conditions. Installation was completed with a relatively small crew.
Installation and removal of the slide-rail shoring system at the second location was considerably faster as a result of the operator experience gained during the first site's excavation and the site's shallower depth.
The most noticeable benefit of using the slide-rail shoring system was the reduced impact on the base's mission by protecting site infrastructure and minimizing the onsite duration.
"Shaw Environmental, Inc. worked seamlessly with the base airfield operations to achieve minimal impact to the flying mission," said Lisa Krawczyk, project coordinator at Grissom. "The slide rail shoring system aided them in removing approximately 4,900 tons of TCE-contaminated soil and 60,000 gallons of TCE-contaminated groundwater in less time than estimated. The speed, efficiency and professionalism of the operation was impressive."
Traditional excavation at the first site would have required removing part of the taxiway and generating a significantly larger footprint, due to the sloping and benching that would have been required. Also, traditional excavation could have required three times the duration to complete, and resulted in a much larger open pit.
Some of the other benefits that were realized during the various phases of this project included increased safety and easier segregation of soils with depth, since contaminant concentrations increased with depth.
From a safety standpoint, the slide rail systems minimized worker exposure to hazardous substances because workers and equipment were not required to enter the excavation. Traditional excavation methods would have required that equipment and workers enter the excavation area, thereby making it a more hazardous operation given the site PCE and TCE concentrations. It also would have increased the duration of the project, potentially taking two to three times longer, and further increasing cost.