LESSONS LEARNED FROM IMPLEMENTATION OF MONITORED NATURALATTENUATION FOR AN AEROBIC TRICHLOROETHENE PLUMEAT THE IDAHO NATIONAL ENGINEERING AND ENVIRONMENTALLABORATORY

摘要

The Test Area North (TAN) Facility of the Idaho National Engineering and EnvironmentalrnLaboratory (INEEL) is the site of a 3-km-long trichloroethene (TCE) plume resulting from pastrnwaste injections into the deep fractured basalt aquifer. An in-depth natural attenuation fieldrnevaluation showed that aerobic TCE degradation was occurring with a half-life of 9 to 21 yearsrn(1) in the plume’s distal zone. Given the lack of precedent for the significance of thisrndegradation mechanism under intrinsic conditions, activity-dependent enzyme probe assays werernperformed on TAN field samples. Results showed that microbial enzymes known torncometabolize TCE are present and active in the TAN aquifer, both inside and outside of the TCErnplume. In addition, a multi-level sampling program was implemented to investigate thernthree-dimensional contaminant distribution in the distal zone. These results confirmed thernoriginal conceptual model for the distal zone by demonstrating that no previouslyrnuncharacterized zones of TCE flux exist in the distal zone.rnDespite the fact it was initially unexpected that intrinsic aerobic cometabolism would be anrnimportant degradation mechanism at TAN, the hypothesis was rigorously tested until sufficientrnevidence was collected to convince both the technical and regulatory members of the projectrnteam that intrinsic aerobic cometabolism of TCE was occurring. Ultimately, demonstration ofrnthis mechanism was the most important component of obtaining regulatory approval of thernmonitored natural attenuation (MNA) remedy. Given that this is the largest TCE plume forrnwhich the United States Department of Energy (DOE) has achieved regulatory acceptance ofrnMNA, other DOE sites could benefit from these lessons learned.