Monitored natural attenuation (MNA) has been widely used as a remedial strategy, acknowledged by the EPA as the most appropriate technology for cost effective remediation under certain site conditions. Despite the widespread use of MNA, empirical methods are lacking to evaluate the sustainability of MNA at a site. The objective of this thesis is to investigate the natural attenuation capacity (NAC) as a quantitative metric for evaluating the sustainability of MNA for contaminants in groundwater systems. Five DoD sites were selected for this study, where the common thread between the sites is the existence of a mature chlorinated ethene groundwater plume and the use of MNA as the long-term remediation strategy. Constituent specific NAC values were quantified and statistically examined to determine past performance of MNA at the sites. A conceptual decision model was developed to be a framework of the statistical tools demonstrated in this thesis. Analyzing MNA sustainability at a site can be separated into two components; past performance of natural attenuation and evaluation of current MNA parameters. The former is the focus of this thesis where NAC is the screening metric and the temporal trend in the rate of natural attenuation being evaluated. Within the conceptual decision model, the use of NAC as a screening tool in combination with a specific analysis of MNA parameters allows engineers, regulators, and decision makers to clearly determine whether MNA at a site is sustainable and whether site specific remediation goals will be met. / Master of Science