Using Advanced Analysis Approaches to Complete Long-Term Evaluations of Natural Attenuation Processes on the Remediation of Dissolved Chlorinated Solvent Contamination

The methodology, case-study examples, and recommendations described in this report are intended to provide restoration program managers, their support staff, and the regulatory community with descriptions of methods and tools that can be used to advance the state-ofpractice for monitoring and documenting the long-term sustainability of monitored natural attenuation (MNA)-based remedies for chlorinated solvent-impacted groundwater. Specifically, this report 1) presents a strategy and framework for quantitatively assessing the sustainability of MNA-based remedies for groundwater at chlorinated solvent-impacted sites, 2) provides casestudy reviews using existing long-term monitoring (LTM) data sets from multiple United States Air Force (USAF) sites where chlorinated solvents exceed closure criteria, and 3) summarizes observations and recommendations that were developed when working through the case-study examples. The context for developing this report is summarized in the following general observations from a review of data from multiple USAF sites where MNA is either a primary or secondary remedy component for remediation of chlorinated solvents in groundwater.