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MNA TO ACHIEVE SITE OBJECTIVES: BACK TO BASICS
Citation:
Wilson*, J T. MNA TO ACHIEVE SITE OBJECTIVES: BACK TO BASICS. Presented at AFCEE Technology Transfer Workshop, San Antonio, TX, August 16 - 18, 2004.
Impact/Purpose:
To inform the public.
Description:
The U.S. EPA recognizes a three-tiered approach to evaluate site specific data in support of monitored natural attenuation (1) historical groundwater and/or soil chemistry data that demonstrate a clean and meaningful trend of decreasing contaminant mass and/or concentration over time, (2) hydrogeologic and geochemical data that can be used to demonstrate indirectly the type(s) of natural attenuation processes active at the site, (3) data from field or microcosm studies which directly demonstrate the occurrence of a particular natural attenuation process at the site and its ability to degrade the contaminants of concern.
As a practical matter, it is difficult to provide hydrogeologic and geochemical data to demonstrate indirectly the type of processes and the rate at which the processes operate. Although microcosm studies are easy to interpret, they are expensive and tend to be time-consuming. An analysis of stable carbon isotope ratios in residual contaminants can provide irrefutable evidence of natural in situ biodegradation, and provide a useful supplement to the traditional data collected to evaluate monitored natural attenuation.