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

The Training Range Environmental Evaluation and Characterization System (TREECSTM) 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. OBJECTIVE: TREECSTM (http://el.erdc.usace.army.mil/treecs/) was developed by the U.S. Army Engineer Research and Development Center (ERDC) for the Army. TREECSTM has varying levels of capability to forecast the fate of munitions constituents (MC), such as high explosives (HE), metals, and other contaminants found within and transported from firing/training ranges (and other types of source zones) to surface water and groundwater. The overall purpose of TREECSTM is to provide environmental specialists with tools to assess the potential for MC and contaminant migration into surface water and groundwater systems and to assess range management strategies for ensuring protection of human health and the environment. TREECSTM is being applied as part of the Environmental Security Technology Certification Program (ESTCP) work unit ER-201435 entitled “Field Demonstration and Validation of the Training Range Environmental Evaluation and Characterization System (TREECSTM) and Environmental Fate Simulator (EFS) for the Risk Assessment of Contaminants on DoD Ranges.” The EFS provides improved estimates of chemical-specific fate parameters required for fate and transport models such as those within TREECSTM. The objective of the present investigation is to evaluate the importance of chemical-specific model input parameters, the impacts of their uncertainty, and the potential benefits of having improved estimates from EFS. TECHNICAL APPROACH: Chemical-specific properties that affect constituent fate include factors such as solubility, Henry’s law constant, soil and sediment partitioning distribution Report Documentation Page Form Approved