FATE AND TRANSPORT OF RDX AND ITS DEGRADATION PRODUCTS IN SOILS OF THE BANDELIER TUFT, LOS ALAMOS NEW MEXICO

High explosive compounds including hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) were used extensively in weapons research and testing at Los Alamos National Laboratory (LANL). Waste from the manufacture and testing of weapons components containing RDX was released directly to the surface of Canon de Valle at LANL’s Technical Area 16, resulting in the contamination of the alluvial, intermediate and regional groundwater aquifers. Monitoring of groundwater wells within Canon de Valle have shown persistent RDX contamination in deep perched intermediate groundwater, located between 650 and 1200 feet below ground surface. Batch and column experiments were conducted to determine the extent of adsorption-desorption and transport of RDX and its degradation products MNX, DNX, and TNX in three subsurface materials that intercept segments of the RDX plume. The three core segments examined are representatives of the Otowi member of the Bandelier tuff, and the underlying alluvial fan deposits of the Puye formation. All experiments were performed using water obtained from a well located at the center of the plume, which is fairly oxic and has a neutral pH of 7.5. Transport results for RDX, MNX, DNX and TNX were fairly consistent and showed significant retardation of these compounds relative to a bromide tracer. Preliminary processing of the data revealed retardation factors up to 3.3, which are significantly higher than those observed in studies of the movement of RDX though shallow groundwater aquifers. The most significant retardation factors for these compounds were observed in the pumice-rich Otowi material. A reactive transport model is being developed to predict the subsurface migration of RDX in the vadose zone and in groundwater utilizing the first-order sorption and degradation parameters. Recommendations for future work include conducting laboratory and field studies of in-situ treatment options to remediate RDX in groundwater.