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Aerobic Degradation of Calcium Magnesium Acetate in Roadside Soils: Field Simulations from Soil Microcosms

Civil Engineering Dep., Univ. of Massachusetts, Amherst, MA 01003;
Microanalytical Lab., Univ. of Massachusetts, Amherst, MA 01003;
Research and Materials Section, Massachusetts Highway Dep., Wellesley, MA 02181.

^* Corresponding author.

ABSTRACT

Aseptic soil samples from the 0.2-m loamy sand cover and underlying sand fill of a state highway shoulder in southeastern Massachusetts were placed in sterile serum bottles at 5 °C, forming a series of aerobic soil microcosms. The sand fill belonged to the Carver coarse sand series (Mesic, uncoated Typic Quartzisamment), while the loamy sand was of unknown origin. The samples were dosed with reagent grade glacial acetic acid and commercially available calcium magnesium acetate [(CMA; Ca_0.3Mg_0.7(C₂H₃O₂)₂] solutions without acclimation, then sampled at various time intervals and analyzed by gas chromatography in a laboratory determination of the microbial degradation kinetics. The aerobic reaction rate varied strongly and directly with depth but was uniform with distance along and normal to the highway. A simple steady state transport simulation model balancing infiltration and degradation was derived and run with the observed microcosm kinetics for a range of assumed snowmelt rates. The resulting simulated profiles suggested that the loamy sand cover bad the potential to reduce O₂ demand by CMA on groundwater for slow (10^–7 m/s^–1 snowmelt rates at 5 °C under aerobic conditions. Shoulders with more rapid infiltration, colder temperatures, and thinner loamy sand covers would pass more CMA to the underlying aquifer.