Verification of Methods for Assessing the Sustainability of Monitored Natural Attenuation (MNA)

Abstract

Abstract : The requirement for sustainable monitored natural attenuation (MNA) is that energy and material inputs be available for efficient and consistent performance over the life-cycle of a project. Currently, the effectiveness of MNA at chlorinated solvent sites is typically assessed over short time periods (several years). However, when MNA becomes part of a long-term remediation strategy, it is assumed that natural attenuation processes documented during site assessment will continue over the operational life of the site. Regulators, however, are reluctant to approve such MNA-based remediation strategies in the absence of direct evidence that MNA will be sustained over the life-cycle of the site. The technology demonstrated and verified in this report is an approach to assessing MNA sustainability as applied to chlorinated solvents in groundwater, particularly at sites where microbially-mediated reductive dechlorination is the primary attenuation mechanism. The MNA sustainability assessment technology may be applied at sites where MNA has been adopted and approved as the primary remediation strategy for plume management or at a site where source zone remediation is planned and MNA is the projected follow-up remediation strategy. At a given site, the assumed starting point is that site characterization efforts and data analysis have proven that the proper environmental conditions for microbially-mediated reductive dechlorination exist in the groundwater and that ample evidence exists to confirm that the microbial community is reducing chlorinated compounds.