The feasibility of phytoremediation to both remediate and hydraulically contain a methyl tert-butyl ether (MTBE)-contaminated groundwater plume was investigated in a three-phase study that included the following elements: (i) a laboratory bioreactor study that examined the fate and transport of 14C-radiolabeled MTBE in hybrid poplar trees, (ii) a novel approach for a mathematical modeling study that investigated the influence of deep-rooted trees on unsaturated and saturated groundwater flow, and (iii) a field study at a Houston site with MTBE-contaminated groundwater where hybrid poplar trees were planted. In the laboratory study, the predominant fate pathway was uptake and evapotranspiration of [14C]-MTBE from leaves and stems of poplar cuttings rooted in hydroponic solution. The modeling study demonstrates that phytohydraulic containment of MTBE in groundwater by deep-rooted trees can be achieved. The field study demonstrated significant groundwater uptake of groundwater by deep-rooted trees via direct measurement in the first three seasons. The use of vegetation may provide a cost-effective in-situ alternative for containment and remediation of MTBE-contaminated groundwater plumes.

Concentrations of NzO. NO" CO z• and O, were determined along the axis of coal, oil. and gas flames in a 3 MW experimental furnace, for both single-stage and two-stage combustion conditions. Concentrations of NO, and NzO were found to be strongly correlated along the flames and in the flue gas samples, with approximately one mole of N 20 produced for every three moles of NO,. The resulls suggested that most of the NO, and N 20 arose from oxidation of fuel nitrogen , with highest concentrations observed in coal flames and lowest levels in the natural gas flame. Appr oximately 12 percent of fuel nitrogen was converted to N20 in coal and oil flames.Two-stage combustion, which produces a fuel-rich zone near the burner, substantially lowered emissions of both NO, and N 20 in the experimental flames. In most cases the rates of decline were similar for the two gases, suggesting that related processes could account for the reduction of these nitrogen oxides in fuel-rich flames. Staged combustion is seen as an effective method for controlling both N 20 and NO, emissions.

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