Management of large, dilute groundwater plumes of comingled chlorinated volatile organic compounds (CVOCs) and 1,4-dioxane (dioxane) is problematic due to chemical, hydrogeologic and economic concerns. The US Environmental Protection Agency (US EPA) has conducted research on the management of CVOC plumes for many years, and more recently dioxane. US EPA research on monitored natural attenuation (MNA) of CVOC plumes was reviewed by a science advisory board in 2001. Specific additional research was recommended and has been addressed in a series of US EPA reports produced over almost two decades. These reports are summarized in this document along with supporting information including evidence of biological degradation of dioxane. Based on the summarized reports, US EPA work documented elsewhere, and the work of others, under appropriate conditions MNA or augmented MNA remain viable management options for these plumes. Unlike MNA of plumes containing only CVOCs, however, MNA of large dilute comingled plumes should be expected to occur by cometabolic oxidation rather than direct metabolic processes.