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Enhanced Biodegradation of TCE by Groundwater Recirculation in a Shallow Aquifer with Dramatic Seasonal Groundwater Elevation Fluctuations
Author: Greg Menna, Jeff Bold, Tim Crummett, Guy Graening, Brian Timmins
Date: 7/111
Preprint, Battelle's 2011 Bioremediation and Sustainable Environmental Technologies Symposium, Reno, NV, June 27-30, 2011

Brown and Caldwell conducted a pilot test to remediate trichloroethylene (TCE) in groundwater associated with past operation of a Formerly Used Defense Site (FUDS) communication station in Northern California. The TCE in shallow groundwater had not degraded significantly in more than 40 years, likely due to oxidizing conditions. A mobile treatment system was installed that extracted groundwater, treated it with granular activated carbon (GAC), amended it with a carbon substrate plus macronutrients (N and P) and injected the amended water. The treatment system induced recirculation in the shallow aquifer accomplishing two important objectives: 1) extract and treat TCE in the dissolved phase in the source area; and 2) thoroughly distribute the amendment to enhance biodegradation of TCE adsorbed to carbon in the subsurface. A bench scale test was conducted prior to the pilot test to determine dosage of the amendment and effectiveness of enhanced biodegradation. The pilot test established reducing conditions and reduced TCE concentrations by 50% during initial operation in 2009; TCE was reduced from 86 ug/L to 0.51 ug/L. The pilot test continued in 2010/2011 with baseline groundwater sampling. The baseline event indicated that the rise in water table and period of inactivity resulted in a rebound in TCE to 160 ug/L in source area wells and a return to oxidative conditions. Operation of the pilot test in 2010/2011 resulted in TCE decreasing steadily to non-detect (<0.5 g/L) and 4 g/L in two performance monitoring wells, based on February 11, 2011 results.