Impacts of ethanol on natural attenuation of BTEX and MTBE extrapolation of findings of the Vandenberg controlled-release field experiment to other release scenarios and background geochemical environments

Side-by-side field experiments were conducted to evaluate the impact of ethanol on the natural attenuation of BTEX and MTBE at Site 60, Vandenberg Air Force Base, CA, at which leaking UST and/or piping resulted in the generation of a plume of petroleum hydrocarbons and MTBE. In Lane A, groundwater spiked with dissolved BTX was injected, while groundwater spiked with the same concentrations of BTX and ∼ 400 mg/L ethanol was injected in Lane B. There was rapid and preferential degradation of ethanol in Lane B, which consumes all of the sulfate and creates methanogenic conditions immediately downgradient of the injection wells in Lane B. In Lane A, conditions remained sulfate-reducing downgradient of the injection wells. The natural attenuation of BTX was significantly slower in Lane B than Lane A. The ultimate extent of the benzene plume in Lane B was controlled by the lateral mixing of the benzene plume with the sulfate-rich water surrounding it, resulting in natural attenuation under sulfate-reducing conditions along the sides of the Lane B plume. The concentrations of TBA increased significantly in the aquifer along the path of the water injected into Lane B after the initiation of ethanol injection. Results of a study carried out to determine whether the TBA plume produced by transformation of the MTBE in Lane B is naturally attenuating under the sulfate-reducing conditions prevalent from the injection wells are presented. This is an abstract of a paper presented at the Petroleum Hydrocarbons and Organic Chemicals in Ground Water: Prevention, Assessment, and Remediation Conference (Costa Mesa, CA 8/8-19/2005).