Measuring Carbon-based Contaminant Mineralization Using Combined CO(2) 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 contaminate the environment. This radiocarbon signal — or rather the absence of signal — is evenly distributed throughout a contaminant source pool (unlike an added tracer) and is not impacted by biological, chemical or physical processes (e.g., the (14)C radioactive decay rate is immutable). If the fossil-derived contaminant is fully degraded to CO(2), a harmless end-product, that CO(2) will contain no radiocarbon. CO(2) 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 CO(2) derived from a fossil source in a given soil gas or groundwater sample. Coupling the percent CO(2) derived from the contaminant with the CO(2) respiration rate provides an estimate for the total amount of contaminant degraded per unit time. Finally, determining a zone of influence (ZOI) representing the volume from which site CO(2) is collected allows determining the contaminant degradation per unit time and volume. Along with estimates for total contaminant mass, this can ultimately be used to calculate time-to-remediate or otherwise used by site managers for decision-making.