Field and Laboratory Evaluation of the Potential for Monitored Natural Attenuation of Perchlorate in Groundwater

Abstract : As an emerging technology, the promise of using monitored natural attenuation (MNA) as a remediation approach for perchlorate is significant. There is extensive laboratory documentation that perchlorate is biodegradable under anaerobic conditions and can be expected to naturally attenuate in some aquifers. However, besides an apparent decrease in concentrations often seen downgradient of many source areas, there are essentially no data showing mechanisms responsible for the observed changes and the conditions where attenuation is most likely to occur. Without clear, convincing evidence for the natural attenuation of perchlorate, there may be a tendency to push for aggressive remediation approaches whenever perchlorate is detected. While aggressive remediation is warranted at some sites, there are probably many other sites where MNA is a very appropriate approach. Before the MNA of perchlorate becomes an accepted technology, evidence must be obtained to confirm the informal observations in the field. In addition, the approach should be demonstrated in the field at multiple sites. The field and laboratory evaluation (treatability study) that is the subject of this report was conducted as a preliminary task in answering the question about the suitability and practicality of using MNA as a viable treatment remedy for perchlorate-contaminated groundwater. This report, funded by the Environmental Security Technology Certification Program (ESTCP) as part of a larger project (ESTCP ER-0428), describes the results of the process used to: 1) identify perchlorate sites; 2) select a subset of these contaminated sites for field characterization and sampling; 3) characterize the sites in the field, and 4) test the site conditions in the laboratory.