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Understanding how changes in volumetric water content (theta) affect bacterial adsorption could help reduce transport of pathogenic and indicator bacteria that may be present in infiltrating wastewater. Three flow regimes that simulated infiltration from a household septic system were evaluated: saturated, unsaturated with a constant volumetric water content theta (constant unsaturated flow), and unsaturated with cyclic changes in theta (variable unsaturated flow). Escherichia coli was suspended in artificial sewage (AS) and applied as step inputs to sand columns, with regular interruptions in input for variable unsaturated flow. A transport model was fit to the saturated and constant unsaturated flow breakthrough curves to determine retardation (R), the first-order filtration coefficient (mu), and the maximum outflow relative concentration (Cmax). The total cells transported as a fraction of input (tau) in all three flow regimes was calculated. Constant unsaturated flow resulted in a significantly lower Cmax (0.633) in comparison with saturated flow (0.803, P < or = 0.05), although unsaturated mu (0.0693 h(-1)) was not significantly different from saturated mu (0.0259 h(-1)). Constant unsaturated flow also resulted in a significantly smaller tau (0.617) than saturated (0.806) or variable unsaturated flow (0.734). In variable unsaturated flow, cell concentrations were out of phase with theta--as the column drained, cell concentrations in the outflow increased; and when a pulse of suspension was applied, cell concentrations decreased. Constant unsaturated flow is probably the best for removal of pathogenic bacteria because this regime resulted in lower maximum concentrations of E. coli and greater cell removal, in comparison with saturated and variable unsaturated flow.

We reviewed literature results from 42 determinations of the fraction of methane oxidized and 30 determinations of methane oxidation rate in a variety of soil types and landfill covers. Both column measurements and in situ field measurements were included. The means for the fraction of methane oxidized on transit across the soil covers ranged from 22 to 55% from clayey to sandy material. Mean values for oxidation rate ranged from 3.7 to 6.4 mol m(-2) d(-1) (52-102 g m(-2) d(-1)) for the different soil types. The overall mean fraction oxidized across all studies was 36% with a standard error of 6%. The overall mean oxidation rate across all studies was 4.5 mol m(-2) d(-1) +/- 1.0 (72 +/- 16 g m(-2)d(-1)). For the subset of 15 studies conducted over an annual cycle the fraction of methane oxidized ranged from 11 to 89% with a mean value of 35 +/- 6%, nearly identical to the overall mean. Nine of these studies were conducted in north Florida at 30 degrees N latitude and had a fraction oxidized of 27 +/- 4%. Five studies were conducted in northern Europe ( approximately 50-55 degrees N) and exhibited an average of 54 +/- 14%. One study, conducted in New Hampshire, had a value of 10%. The results indicate that the fraction of methane oxidized in landfill greater than the default value of 10%. Of the 42 determinations of methane oxidation reported, only four report values of 10% or less.

Water with entrained disease‐causing virus entering soil normally passes through water‐saturated and unsaturated regions before reaching the groundwater. The effects of saturated and unsaturated flow on the survival and transport of a virus, MS‐2 bacteriophage, were compared. The viruses were added to well water and applied to soil columns 0.052 m in diameter and 1.05 m long. The soil material was Vint loamy fine sand (a sandy, mixed, hyperthermic Typic Torrifluvent) mixed with recent alluvium. Samples of the soil water were taken daily at 0.20, 0.40, and 0.80 m depths through porous stainless steel samplers and at 1.05 m from the percolate leaving the column. For saturated flow the virus concentrations reached the influent concentration in less than two pore volumes (PV). For unsaturated flow the concentrations remained at levels much lower than the influent, ranging from 27% of inflow at 0.20 m (18 PV) to 5% at 1.05 m (3.3 PV). At the end of the experiments soil samples from each depth were assayed to determine virus adsorption to the soil. The average distribution coefficient of the unsaturated columns, 0.27, indicates very little adsorption. The number balance showed that only 39% of the unsaturated flow virus were accounted for. It appears that under unsaturated flow conditions enhanced inactivation of this virus occurs.

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