Summary Report for Evaluation of Compost Sample Drying Methods

The U.S. Army Environmental Center (USAEC), formerly the U.S. Army Toxic and Hazardous Materials Agency, has evaluated composting methods for treatment of explosive-contaminated soils and sediments at Army installations. Previous work in Support of these efforts developed a compost sample preparation scheme, consisting of air drying followed by milling, to reduce analytical variability in the heterogeneous compost matrix. While this procedure successfully reduced variability, USAEC determined that the time required for air drying results in undesirable delays in analytical results turnaround. The time required to air dry compost samples was typically 3 to 5 days. As a result of this determination, this study on alternative drying methods was conducted. Three drying methods were examined in this test: (1) air drying as used in previous work, (2) oven drying at 60 deg C, and (3) convection oven drying at 60 deg C. The maximum drying temperature of 60 deg C was based upon the low melting points of the target explosives. Drying methods were compared in terms of time required to achieve specified dryness levels and potential effects on residual explosives levels. The results of this testing indicate that convection oven drying at 60 deg C results in rapid and satisfactory drying of compost samples. Required dryness levels (greater than 95% solids) were achieved in approximately 12 hours with this drying method. These tests demonstrate that conventional, commercially available convection ovens can be used for compost sample preparation during field operations.