Side-by-side experiments were conducted in a sulfate-reducing aquifer at a former fuel station to evaluate the effect of ethanol on biodegradation of other gasoline constituents. On one side, for approximately 9 months we injected groundwater amended with 1-3 mg/L benzene, toluene, and o-xylene (BToX). On the other side, we injected the same, adding approximately 500 mg/L ethanol. Initially the BToX plumes on both sides ("lanes") extended approximately the same distance. Thereafter, the plumes in the "No Ethanol Lane" retracted significantly, which we hypothesize to be due to an initial acclimation period followed by improvement in efficiency of biodegradation under sulfate-reducing conditions. In the "With Ethanol Lane", the BToX plumes also retracted, but more slowly and not as far. The preferential biodegradation of ethanol depleted dissolved sulfate, leading to methanogenic/acetogenic conditions. We hypothesize that BToX in the ethanol-impacted lane were biodegraded in part within the methanogenic/acetogenic zone and, in part, within sulfate-reducing zones developing along the plume fringes due to mixing with sulfate-containing groundwater surrounding the plumes due to dispersion and/or shifts in flow direction. Overall, this research confirms that ethanol may reduce rates of biodegradation of aromatic fuel components in the subsurface, in both transient and near steady-state conditions.

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A new multilevel ground water monitoring system has been developed that uses custom‐extruded flexible 1.6‐inch (4.1 cm) outside‐diameter (O.D.) multichannel HOPE tubing (referred to as Continuous Multichannel Tubing or CMT) to monitor as many as seven discrete zones within a single borehole in either unconsolidated sediments or bedrock. Prior to inserting the tubing in the borehole, ports are created that allow ground water to enter six outer pie‐shaped channels (nominal diameter = 0.5 inch [1.3 cm]) and a central hexagonal center channel (nominal diameter = 0.4 inch [1 cm]) at different depths, facilitating the measurement of depth‐discrete piezometric heads and the collection of depth‐discrete ground water samples. Sand packs and annular seals between the various monitored zones can be installed using conventional tremie methods. Alternatively, bentonite packers and prepacked sand packs have been developed that are attached to the tubing at the ground surface, facilitating precise positioning of annular seals and sand packs. Inflatable rubber packers for permanent or temporary installations in bedrock aquifers are currently undergoing site trials. Hydraulic heads are measured with conventional water‐level meters or electronic pressure transducers to generate vertical profiles of hydraulic head. Ground water samples are collected using peristaltic pumps, small‐diameter bailers, inertial lift pumps, or small‐diameter canister samplers. For monitoring hydrophobic organic compounds, the CMT tubing is susceptible to both positive and negative biases caused by sorption, desorption, and diffusion. These biases can be minimized by: (1) purging the channels prior to sampling, (2) collecting samples from separate 0.25‐inch (0.64 cm) O.D. Teflon sampling tubing inserted to the bottom of each sampling channel, or (3) collecting the samples downhole using sampling devices positioned next to the intake ports. More than 1000 CMT multilevel wells have been installed in North America and Europe to depths up to 260 feet (79 m) below ground surface. These wells have been installed in boreholes created in unconsolidated sediments and bedrock using a wide range of drilling equipment, including sonic, air rotary, diamond‐bit coring, hollow‐stem auger, and direct push. This paper presents a discussion of three field trials of the system, demonstrating its versatility and illustrating the type of depth‐discrete data that can be collected with the system.

Side-by-side experiments were conducted in an aquifer contaminated with methyl-tert-butyl ether (MTBE) at a former fuel station to evaluate the effect of ethanol release on the fate of pre-existing MTBE contamination. On one side, for approximately 9 months we injected groundwater amended with 1-3 mg/L benzene, toluene, and o-xylene (BToX). On the other side, we injected the same, adding approximately 500 mg/L ethanol. The fates of BToX in both sides ("lanes") were addressed in a prior publication. No MTBE transformation was observed in the "No Ethanol Lane." In the "With Ethanol Lane", MTBE was transformed to tert-butyl alcohol (TBA) underthe methanogenic and/or acetogenic conditions induced by the in situ biodegradation of the ethanol downgradient of the injection wells. The lag time before onset of this transformation was less than 2 months and the pseudo-first-order reaction rate estimated after 7-8 months was 0.046 d(-1). Our results imply that rapid subsurface transformation of MTBE to TBA may be expected in situations where strongly anaerobic conditions are sustained and fluxes of requisite nutrients and electron donors allow development of an active acetogenic/methanogenic zone beyond the reach of inhibitory effects such as those caused by high concentrations of ethanol.