Fe(III)-reducing isolates were recovered from two aquifers in which Fe(III) reduction is known to be important. Strain BemT was enriched from subsurface sediments collected in Bemidji, MN, USA, near a site where Fe(III) reduction is important in aromatic hydrocarbon degradation. Strains P11, P35T and P39 were isolated from the groundwater of an aquifer in Plymouth, MA, USA, in which Fe(III) reduction is important because of long-term inputs of acetate as a highway de-icing agent to the subsurface. All four isolates were Gram-negative, slightly curved rods that grew best in freshwater media. Strains P11, P35T and P39 exhibited motility via means of monotrichous flagella. Analysis of the 16S rRNA and nifD genes indicated that all four strains are δ-proteobacteria and members of the Geobacter cluster of the Geobacteraceae. Differences in phenotypic and phylogenetic characteristics indicated that the four isolates represent two novel species within the genus Geobacter. All of the isolates coupled the oxidation of acetate to the reduction of Fe(III) [iron(III) citrate, amorphous iron(III) oxide, iron(III) pyrophosphate and iron(III) nitrilotriacetate]. All four strains utilized ethanol, lactate, malate, pyruvate and succinate as electron donors and malate and fumarate as electron acceptors. Strain BemT grew fastest at 30 °C, whereas strains P11, P35T and P39 grew equally well at 17, 22 and 30 °C. In addition, strains P11, P35T and P39 were capable of growth at 4 °C. The names Geobacter bemidjiensis sp. nov. (type strain BemT=ATCC BAA-1014T=DSM 16622T=JCM 12645T) and Geobacter psychrophilus sp. nov. (strains P11, P35T and P39; type strain P35T=ATCC BAA-1013T=DSM 16674T=JCM 12644T) are proposed.

We use Monod kinetics to calibrate previously published data that documentthe aerobic biodegradation of hydrocarbon vapors in soil microcosms from a weathered petroleum spill site. Monod kinetics offer insight into biodegradation mechanics because they address biomass growth as well as substrate depletion. A blend of five aromatics and five alkanes dose the microcosm sets at four strengths, and a finite difference model describes the response superimposed across the constituent substrates. An observed initial biomass X0 of 125 g biomass/m(3) soil moisture and an endogendous decay rate b of 0.102 day(-1) calibrate all four dosages and agree with heterotrophic plate counts. Common maximum specific growth rates microMJ and half saturation constants KSJ calibrate each constituent across the four dosages. The biodegradable alkanes exhibit microMJ values ranging from 0.0190 to 0.0996 day(-1), while the aromatic rates vary from 0.0946 to 0.322 day(-1). One of the alkanes (2,2,4-trimethylpentane) is recalcitrant. The half saturation constants range from 0.000083 to 0.000355 g substrate/m(3) soil moisture for the biodegradable alkanes, which imply zero-order kinetics. The aromatic KSJ values vary from 5.02 to 14.3 g substrate/m(3) soil moisture, and suggest first-order kinetics. The yield YJ increases with dosage concentration for all the biodegradable constituents, varying from 0.0533 to 1.58 g biomass/g substrate.

This research documents the seasonal variation of de-icing agent contamination by measuring the specific conductivity of runoff and groundwater from an infiltration basin that serves a highway drainage system in southeast Massachusetts. The order of magnitude of the winter maxima of the runoff and groundwater specific conductivities over a 9 year period of record is lOmScm"'. The groundwater specific conductivity decreases by 1-2 orders of magnitude to its fail minimum, which is an order of magnitude higher than the fall minimum of the runoff. This warm weather source behaviour impiies slow, seasonal dissolution of de-icing agent soiids deposited in the infiitration basin during the winter. A completely mixed reactor idealization of the basin models this postuiate as a coupled balance of dissolved and solid de-icing agents. The data suggest that 13% of the de-icing agent soiids applied to the highway deposits in the basin, where it dissolves into the infiltrating groundwater with a first order decay rate of 0.0035day \

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Abstract. We calibrate a stoichiometrically coupled soil gas diffusion model with spatially resolved observations of oxygen, carbon dioxide, total hydrocarbon, and trichloroethylene vapor concentrations in the unsaturated zone above a weathered jet fuel/solvent spill at Plattsburgh Air Force Base in upstate New York. The calibration suggests that aerobic microorganisms in the capillary fringe degrade jet fuel vapor at a steady rate of 9.5 hydrocarbons (m -2 s-l). The solvent does not degrade in the fringe, however, and the model and data estimate a steady evaporation rate of 1.2 x 10 -2/xg TCE (m -2 s-•).Barometric pumping slightly alters the steady concentration profile at Plattsburgh, although the transient advective flux is the same order of magnitude as the steady diffusive flux. We derive a simple perturbation theory for the second-order transient concentration corrections and include it in the calibration. The perturbation theory is valid at Plattsburgh because the soil is uniform and permeable with a relatively deep capillary fringe. 1.Introduction 0 0 at (O•c + OC) + •zz (v•c + vC)We use concentration data and a set of steady and transient, stoichiometrically coupled, one-dimensional, analytical transport models to estimate the flux of soil gas constituents through a uniform, permeable, unsaturated zone. We postulate aerobic biodegradation of hydrocarbons in the contaminated capillary fringe, so that, to leading order, oxygen diffuses steadily down from the atmospheric source at the ground surface, while carbon dioxide and hydrocarbon vapors diffuse steadily upward from a separate phase source at the edge of the fringe. The steady carbon dioxide and oxygen fluxes are evaluated above a jet fuel/solvent spill at Plattsburgh Air Force Base and found to be consistent with steady values found by Lahvis and Baehr [1996] and Lahvis et al. [1999] over automobile gasoline spills.Wallach [1998] applies perturbation theory to the reactive term of a groundwater contaminant transport model. We compliment this approach by considering perturbations to the transport mechanisms of a soil gas constituent. Gaseous diffusion is assumed to dominate the steady profile and barometric pressure fluctuations drive the transient profile. The barometric pressure distribution is described by a diffusion equation [Shah, 1995] and induces a second-order, transient correction to the steady concentration profiles if the capillary fringe is uniform and relatively deep. The constraints validating the perturbation theory are easily satisfied at Plattsburgh. Soil Gas Transport Theory Steady and Transient Soil Gas Transport EquationsWe assume that the advective, dispersive, and diffusive vertical flux of a dissolved and gaseous phase constituent through the unsaturated zone is balanced by a reaction and the temporal change of aqueous c and soil gas C concentrations