Measuring Carbon-based Contaminant Mineralization Using Combined CO2 Flux and Radiocarbon Analyses

A method is described which uses the absence of radiocarbon in industrial chemicals and fuels made from petroleum feedstocks which frequently contaminatethe environment. This radiocarbon signal — or rather the absence of signal — is evenly distributed throughout a contaminantsource pool (unlike an added tracer) and is not impacted by biological, chemical or physical processes (e.g., the 14C radioactive decayrate is immutable). If the fossil-derived contaminantis fully degraded to CO2, a harmless end-product, that CO2 will contain no radiocarbon. CO2 derived from natural organic matter (NOM) degradation will reflect the NOM radiocarbon content (usually <30,000 years old). Given a known radiocarbon content for NOM (a site background), a two end-member mixing model can be used to determine the CO2 derived from a fossil source in a given soil gasor groundwater sample. Coupling the percent CO2 derived from the contaminantwith the CO2 respiration rate provides an estimate for the total amount of contaminantdegraded per unit time. Finally, determining a zone of influence (ZOI) representing the volume from which site CO2 is collected allows determining the contaminantdegradation per unit time and volume. Along with estimates for total contaminantmass, this can ultimately be used to calculate time-to-remediate or otherwise used by site managersfor decision-making.