Bioenhanced In-Well Vapor Stripping to Treat Trichloroethylene (TCE)

Mark N. Goltz
Air Force Institute of Technology
Engineering and Environmental Management
E-mail: mark.goltz@afit.af.mil
Perry L. McCarty, Steve M. Gorelick and Gary D. Hopkins
Stanford University
E-mail: mccarty@cive.stanford.edu and gorelick@pangea.stanford.edu

Goal

The purpose of this study is to evaluate the potential for removal of chlorinated organic solvents at their source in an aquifer by combining two processes, in-well vapor stripping and in situ aerobic cometabolic biodegradation. The combined system is termed BioEnHanced In Well Vapor Stripping (BEHIVS). The system will be evaluated at full scale in the field at a trichloroethylene (TCE) contaminated groundwater site at Edwards Air Force Base.

Rationale

Removal of chlorinated solvent contaminants at their subsurface source is one of the most challenging problems for remediation of these prevalent contaminants. Here, the solvents are generally present as dense non-aqueous phase liquids (DNAPLs). The potential for application of innovative processes is thus of great interest. The BEHIVS system is believed to be applicable to this problem, at last at some sites. The efficacy of each of the two innovative remediation technologies that comprise BEHIVS were successfully demonstrated during field trials for TCE removal at Edwards AFB. Both technologies make use of groundwater recirculation wells, which may be defined as wells with injection and extraction screens that create groundwater circulation cells in the surrounding aquifer. The in-well vapor stripper established a vertical circulation cell in the aquifer, whereas the aerobic cometabolism system employed a pair of vertical recirculation wells, one operated in an upflow mode, the other in a downflow mode, to establish two horizontal cells. By combining the two in situ treatment systems, the advantages of each can be captured in a way that enhances the performance of the other.

Approach

Using the BEHIVS concept, an in-well vapor stripper, operating in an upflow mode, will be augmented by a biotreatment well that promotes aerobic cometabolic bioremediation, operating in a downflow mode. The well pair will be used to establish horizontal circulation cells to remediate the source of TCE in a single contaminated aquifer at Edwards AFB. Model simulations are being used to illustrate how this configuration may be applied to remediate a chlorinated solvent source area under typically encountered conditions of anisotropy. The model simulations are also being used for system design.

Status

A numerical fate and transport model of the technology is substantially complete and has been used to design the treatment wells and monitoring network for this demonstration. Extensive site characterization was accomplished in order to localize the TCE source location to help position the treatment wells and monitoring system. The characterization work involved application of 2-D refractive and 3-D reflective geophysical surveys. Based upon the results of the surveys, direct-push sampling at the site, and model simulations, the treatment well locations were determined. A work plan was submitted to Federal, California, and regional regulators, who gave preliminary approval to construct the site. Site construction has commenced.

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Last modified on: March 16, 2000.
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