FIELD DEMONSTRATION OF IN SITU BIODEGRADATION OF HE IN SOILS

摘要

The first field pilot-scale demonstration of a technology for in situ remediation of vadose zone soils contaminated with high explosives (HE) has been performed at the Department of Energy's Pantex Plant. The HE of concern at the demonstration site were RDX and 1,3,5-TNB, with concentrations ranging from 5 to 35 ppm, above the risk reduction clean-up criteria of 2.6 and 0.51 ppm, respectively. The shallow (<10 m depth) soils at the site could not be excavated due to the presence of buried utilities. Based on previous laboratory studies, it was found that the impacted soils had indigenous microbial populations that could be encouraged to reduce the RDX and TNB. A five-spot well pattern, with injection at the central well and extraction at the four outer wells (each 4.6 m from the injection well), was used to flood the target vadose zone soils with nitrogen gas with the intent of stimulating the HE degraders. The system was monitored periodically for gas composition as well as HE concentrations and microbial activity in retrievable soil samples. After 295 days of treatment, the target HE concentrations dropped by 40 percent from the initial site. Operation of the site continues.