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We measure bacterial density and acetate concentrations in 5 sets of aerobic soil microcosms from an infiltration basin in southeastern Massachusetts. The basin drains runoff from a highway deiced with calcium magnesium acetate (CMA), with the potential to sustain a biomass that exerts an oxygen demand on subsurface moisture. Acetate is measured by ion chromatograph, while biomass is estimated by most probable number analysis of serially sacrified soil microcosms. Monod kinetics calibrate the acetate and biomass data: the maximum specific reaction rate M is estimated as 0.0337 hr-1, the half saturation constant KS is 0.044 kg acetate/m3 soil moisture, and the yield Y is 0.133 kg biomass/kg substrate. The viable acetate degrading population collapses abruptly once the substrate is consumed, and an endogenous decay rate b of 0.166 hr-1 fits the data, with decay time set equal to zero at the time of observed maximum biomass concentration. The calibration supports a simple simulation which suggests that substrate and viable biomass persist about 1 m into the soil moisture if the biomass is mobile and the soil moisture oxygenated. The simulated, transient oxygen demand of 460 g oxygen/m2-s is an order of magnitude larger than the steady oxygen flux observed to enter the highway shoulder in the field.