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BIOENHANCED IN-WELL VAPOR STRIPPING TO TREAT TRICHLOROETHYLENE(TCE)
Impact/Purpose:
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.
Description:
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.
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.
The numerical fate and transport model of the technology is complete and has been used to design the treatment wells and monitoring network for this demonstration. Extensive site characterization was accomplished using 2-D refractive and 3-D reflective geophysical survey as well as more traditional methods. A work plan was submitted to Federal, California, and regional regulators, and construction of the treatment system and monitoring wells has been completed. The system is now undergoing site testing, and operation will begin sometime during the first month or two of 2001. Six months of continuous operation is planned in order to reach steady-state operation within the treatment zone. This will be followed with three months of shut down for the treatment system, with continuous monitoring of samples from the many groundwater locations to determine the location and extent of TCE rebound in groundwater that might result.