Decontamination Methods for Explosives-Contaminated Lagoon Rock

The U.S. Army Environmental Center has conducted a field demonstration of composting explosives-contaminated soils from Explosives Washout Lagoons at Umatilla Depot Activity (UMDA) in Hermiston, Oregon. The lagoons are lined with gravel and rocks which may have to be separated from soils prior to composting. Consequently, USAEC conducted this study to evaluate methods for decontaminating lagoon gravel and rocks. This testing was conducted in two phases. In the first test phase, aqueous washing using spray/screen and tumbler methods was evaluated. In the second phase, the potential enhancement achievable by the use of chemical washing solutions (aqueous solutions of surfactants or other reagents) was evaluated. The results of Phase I testing showed that aqueous washing alone could remove the majority of explosives contamination from lagoon gravel and rock. Hot washwater (140 degrees F) may be more effective than lower temperature washwater (70 degrees F) in removing explosives from the rock. The site specific cleanup criteria for UMDA (30 mg/kg TNT and 30 mg/kg RDX) were not achieved by water washing alone. However, testing in Phase II showed that a variety of chemical reagents, including biodegradable surfactants, could be used following initial water washing to achieve the lower required explosives levels on the rock and gravel. Initial explosives levels were lower in Phase 2 than in Phase 1. In addition to these rock and gravel washing tests, a preliminary desk top evaluation of Hot Gas Decontamination for contaminated rock and gravel was conducted. This evaluation indicated that several existing equipment configurations may be adaptable to this use. Further testing of candidate equipment may be useful in confirming performance and developing design and operating criteria.