AEROBIC DEGRADATION POTENTIAL ASSESSMENT FROM OXYGEN AND CARBON-DIOXIDE SOIL-GAS CONCENTRATIONS IN ROADSIDE SOIL

The application of calcium magnesium acetate [CMA; Ca0.3Mg0.7-(C2H3O2) (2)] to highways as a deicing agent induces aerobic acetate degradatio n by microorganisms in the capillary fringe, which may reduce O-2 dema nd in the underlying groundwater. We assessed this aerobic degradation potential by computing the diffusive fluxes of O-2 and CO2 from measu red soil gas concentrations in the unsaturated zone of a mildly acidic roadside soil. The fluxes were relevant to the potential assessment b ecause O-2 is consumed and CO2 is generated by the aerobic degradation of organic substrates such as acetate, Soil gas O-2 and CO2 were meas ured on a monthly basis in tubing clusters in the unsaturated zone ove r a 2-yr period using portable meters, Quasi-steady gaseous diffusion models were calibrated with the data, shelving that O-2 diffused into the fringe at a rate that was proportional to the exiting diffusive fl ux of CO2. The modeled fluxes were consistent with an independent esti mate of acetate-based microcosm reaction rates in the capillary fringe . Roadside soils have the potential to significantly degrade CMA under aerobic conditions before the deicing agent reaches the water table, thus reducing O-2 demand in the groundwater.