This report summarizes NESDI Project 537 activities to track in situ RDX biodegradation by adding small quantities of C-labeled RDX to the environment using groundwater push-pull tests and analyzing groundwater respiration products (CO and CH) over time. C-enrichment in CO and CH was observed at two RDX-contaminated field sites at the Naval Base Kitsap-Bangor in Washington. The C-enrichment was modeled and rate constants for RDX degradation were calculated. The technique was validated relative to RDX extinction models previously approved by federal and state regulators. A cost analysis for this technology relative to "standard" methods is included.