Abiotic Degradation of TCE by Naturally Occurring Magnetite can be Important in Large Plumes
An empirical relationship has been established between the mass magnetic susceptibility of aquifer sediment and the rate constant for degradation of TCE and cis-DCE in the sediment. In a variety of aerobic unconsolidated sand aquifers, the magnetic susceptibility ranged from 2E-07 to 2E-06 m3 kg-1. Biological reductive dechlorination of TCE or cis-DCE would not be expected in these aquifers. However, the field-scale bulk rate constants for TCE or cis-DCE degradation varied from 0.1 per year to 0.7 per year with a median near 0.3 per year.
In large plumes, the rate constant for abiotic degradation of TCE by magnetite may be large enough that abiotic degradation is adequate to support monitored natural attenuation (MNA) as a remedy or part of a remedy at the site. If the concentration of TCE is 100 μg/L or less, and the degradation rate constant is 0.3 per year, the concentration can be brought to the MCL in 10 years of travel time along the flow path in the groundwater.