Aerobic natural attenuation of trichloroethene (TCE) is being evaluated on a groundwater contaminant plume at the Paducah Gaseous Diffusion Plant. The hydrologic system is considered perturbed due to ongoing remedial actions (pump and treat operations) over the past twelve years. However, the plume remains relatively stable. First-order rate estimation methods were used to calculate attenuation rates after monitoring well data were statistically evaluated to determine which locations near extraction wells could be used for the analyses. The method used to determine an attenuation rate was a “tracer corrected” approach using a co-contaminant [technetium-99 (⁹⁹Tc)] that would allow to distinguish between dispersion and degradation processes. Since the hydrologic system was perturbed, the ratio of TCE to ⁹⁹Tc for each sampling event was used in the evaluation (actual concentrations of either TCE or ⁹⁹Tc near extraction wells were less than in the surrounding plume but the ratios remained similar). The degradation half-life for TCE was calculated to range between 16.6 and 6.2 years for average groundwater flow rates between 550 and 910 feet/year, respectively. Ongoing analytical work is being conducted at the site to determine if the observed TCE attenuation is due to aerobic cometabolism, or if some other process (e.g., sorption) is attenuating TCE at greater rates than the ⁹⁹Tc.