Evaluation of Uncertainty in Constituent Input Parameters for Modeling the Fate of RDX

The Training Range Environmental Evaluation and Characterization System (TREECS ) was reapplied for a previously validated model of Demolition Area 2 of the Massachusetts Military Reservation (MMR) on Cape Cod. The purpose of the exercise was to evaluate the importance of chemical-specific model input parameters, the impacts of their uncertainty, and the potential benefits of having improved estimates from the Environmental Fate Simulator (EFS). RDX migration to groundwater was the focus of the modeling. There were two chemical-specific inputs for RDX that were determined to be sensitive with relatively high uncertainty: these included the soil-water linear partitioning distribution coefficient (Kd, L/kg) and the half-life, which is related to the degradation rate. Testing revealed that results were only sensitive to Kd and half-life for the vadose zone. Results indicated that RDX degradation is very slow for the aerobic media of this site, resulting in half-life on the order of 100 years. The EFS does not presently have the capability to estimate degradation rates. Results also indicated that the organic carbon-to-water partitioning coefficient Koc can be used to estimate Kd, and log Koc of RDX is on the order of 1.0. The EFS can provide estimates of Koc for organic chemicals. The EFS values provided for log Koc of RDX were 1.72 and 1.95.