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Full‐scale demonstration of in situ cometabolic biodegradation of trichloroethylene in groundwater 2. Comprehensive analysis of field data using reactive transport modeling
Author(s) -
Gandhi Rahul K.,
Hopkins Gary D.,
Goltz Mark N.,
Gorelick Steven M.,
McCarty Perry L.
Publication year - 2002
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/2001wr000380
Subject(s) - aquifer , trichloroethylene , groundwater , environmental chemistry , biodegradation , contamination , cometabolism , environmental science , environmental engineering , aeration , hydrogen peroxide , chemistry , geology , bioremediation , ecology , geotechnical engineering , organic chemistry , biology
We present an analysis of an extensively monitored full‐scale field demonstration of in situ treatment of trichloroethylene (TCE) contamination by aerobic cometabolic biodegradation. The demonstration was conducted at Edwards Air Force Base in southern California. There are two TCE‐contaminated aquifers at the site, separated from one another by a clay aquitard. The treatment system consisted of two recirculating wells located 10 m apart. Each well was screened in both of the contaminated aquifers. Toluene, oxygen, and hydrogen peroxide were added to the water in both wells. At one well, water was pumped from the upper aquifer to the lower aquifer. In the other well, pumping was from the lower to the upper aquifer. This resulted in a “conveyor belt” flow system with recirculation between the two aquifers. The treatment system was successfully operated for a 410 day period. We explore how well a finite element reactive transport model can describe the key processes in an engineered field system. Our model simulates TCE, toluene, oxygen, hydrogen peroxide, and microbial growth/death. Simulated processes include advective‐dispersive transport, biodegradation, the inhibitory effect of hydrogen peroxide on biomass growth, and oxygen degassing. Several parameter values were fixed to laboratory values or values from previous modeling studies. The remaining six parameter values were obtained by calibrating the model to 7213 TCE concentration data and 6997 dissolved oxygen concentration data collected during the demonstration using a simulation‐regression procedure. In this complex flow field involving reactive transport, TCE and dissolved oxygen concentration histories are matched very well by the calibrated model. Both simulated and observed toluene concentrations display similar high‐frequency oscillations due to pulsed toluene injection approximately one half hour during each 8 hour period. Simulation results indicate that over the course of the demonstration, 6.9 kg of TCE was degraded and that in the upper aquifer a region 40 m wide extending 25 m down gradient of the treatment system was cleaned up to less than 100 μg L −1 from initial concentrations of approximately 700 μg L −1 . A smaller region was cleaned up to less than 30 μg L −1 . Simulations indicate that the cleaned up area in the upper aquifer would continue to expand for as long as treatment was continued.