Long-term Monitoring to Ob- Serve Natural Attenuation in the Laboratory

Long-term studies to observe natural attenuation have been described for many field locations. Often the attenuation can only be inferred to be biodegradation, based on, for instance, the presence of cis-dichloroethylene (DCE) where only trichloroethylene (TCE) was a known contaminant. Because in several instances we had observed such transitions in the presence of plants, an unplanted control was set up to see if natural attenuation may arise " spontaneously. " A cylinder 12 cm in diameter and 33 cm high was packed with a natural, sandy soil. The surface-volatilized gas phase was sampled intermittently over more than 1.5 years. Soil water was analyzed for contaminants on several occasions. Continuous feeding of TCE-contaminated water from the bottom resulted in release of only DCE, and relatively little of that. Both methanogenesis and methanotrophy were observed within the contaminated column. Surface monitoring currently indicates disappearance of >95% of the input TCE.