Jeffrey Cange This is Me

 Web References

1. 1. RTDF - Permeable Reactive Barriers Action Team Meeting - February 16-17, 2000

   www.rtdf.org/public/permbarr/m - [Cached]

   Published on: 2/16/2000   Last Visited: 12/11/2007

   Jeff Cange, Bechtel Environmental, Inc.
   
   Jeff Cange said that his presentation would focus on a PRB system that has been installed at Pease AFB. This site, he said, has a large chlorinated solvent plume that extends for more than 1,300 feet. The plume contains TCE, cis-1,2-DCE, and vinyl chloride; total VOCs have been detected above 1,000 ppb. Although a discrete source has never been found, investigators suspect that the contaminants originated from Pease AFB's Site 73. Cange described the geology that underlies the site: a stratified silty sand and till that overlies fractured bedrock. The plume is migrating downward; as a result, it has penetrated the upper portions of the bedrock at locations starting about 325 feet away from the source. Ground-water flow patterns and the site's water table are influenced by the pumping action of a soil vapor extraction system. This system, installed to extract petroleum hydrocarbons, appears to be causing the plume to bend. Much remains to be learned about the plume. For example, Cange said, additional work needs to be performed to identify the plume's downgradient edge.
   
   Cange said that a Record of Decision (ROD) that outlines a preferred remedy for the site has been signed. After closer evaluation, however, site managers agreed that the preferred remedy would not work at the site. They started searching for alternatives, and agreed to participate in a PRB demonstration project. If the PRB proves to be a success, Cange said, it will be added to the list of potential remedial options for the site. The goals of the demonstration are twofold: (1) study the application of ZVI barriers at Pease AFB, and (2) assess potential application at other Air Force sites.
   
   Before designing the PRB, Cange said, investigators conducted a siting study to determine where to install it. This proved to be challenging. The Air Force decided to place the barrier downgradient of the source area and upgradient of the point where ground water enters bedrock. Cange said that he had reservations about this decision because he was not sure whether there would be anything in the subsurface for the PRB to key into. Nevertheless, activities progressed forward.
   
   After identifying the location for the PRB, Cange said, investigators conducted supplemental site investigations in the selected area and used ground-water models to gain a better understanding of local three-dimensional flow fields. (This information had to be obtained, in part, to make sure that introducing a PRB would not disrupt flow fields and drive the plume into the bedrock.) Also, a bench-scale treatability study was conducted to ensure that the site's ground water could be remediated with ZVI.
   
   After a PRB had been designed for the site, Cange said, a performance-based specification and bid package was sent out to installation contractors.
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   PRB installation was performed within a one-month period, Cange said. Activities included:
   
   Mobilizing and grading the site.
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   Cange said that it is important to make sure that contractors understand that they must stay on site until the trench is adequately flushed.
   
   Installing a non-woven geosynthetic material and restoring the site. A non-woven geosynthetic material was placed on top of the reactive barrier and then covered with fill.
   
   Cange said that a rigorous monitoring program has been initiated at the site.
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   Cange is hopeful that this TCE will be dechlorinated as it passes through the PRB.
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   Jeffrey Cange Remediation Manager