The EPA Guidance document on Natural Attenuation (NA) of chlorinated solvents primarily addressed PCE and TCE but not other chlorinated solvents (e.g. chloromethanes). Because of my involvement with observing novel processes, reviewing draft guidance documents and teaching regulators, I have been able to get NA remedies selected at sites where others could not, and at sites with chlorinated compounds other than TCE. To some extent, NA has fallen out of favor as enhanced bioremediation has blossomed, but NA is often where huge $$ can be saved for a client or is the only applicable answer for huge, dilute plumes.
The new trend in NA is looking at abiotic reactions mediated by aquifer minerals such as FeS, often to explain why DCE and vinyl chloride disappear with out the production of ethene. See the Abiotic Natural Attenuation project below as well as the following project as examples. Citations within the project descriptions are under ABOUT.