BUGS ON A SUGAR HIGH: ENHANCED BIOREMEDIATION FOR PESTICIDES AND PCBS AT THE SAVANNAH RIVER SITE

An enhanced bioremediation treatability study was conducted (October 2001 through May 2002) at the Chemicals, Metals, and Pesticides (CMP) Pits waste unit on the Savannah River Site to address soils contaminated with pesticides (including DDT) and PCBs. Disposition of the soil to an off-site facility proved cost-prohibitive. Enhanced bioremediation was selected as a more cost-effective strategy, provided the technology could be demonstrated to reduce contaminant levels to remedial goals under site specific conditions.

Contaminated soil was placed into four windrows. A windrow turner was used to mix the soils and add amendments. During the first six months of the study, the windrows were mixed biweekly with molasses, SuperCalTM, horse manure, and woodchips. During the final month of the study, the windrows were aggressively treated on a semiweekly basis with these same amendments plus cottonseed husks, lime, and cow manure. Temperature, pH, oxygen, and moisture were measured to monitor the bioremediation process and to adjust amendment additions as necessary.

During the first three months of treatment, PCB levels were reduced from over 5000 ppb to about 3000 ppb. PCB levels plateaued to around 2000 ppb, then dropped below 1000 ppb during the aggressive treatment phase. Accordingly, DDT levels dropped from about 13000 ppb to about 750 ppb over the course of the treatability study. The results indicate that through careful selection of nutrient components coupled with control of the redox, temperature, moisture, and pH it is possible to degrade PCBs and pesticides through enhanced bioremediation.