Methanogens/Archaea produce methane. They are often the dominant microbes in reduced environments. Methanogenesis is a requisite component of conventional anaerobic bioremediation.
If Archaea are not controlled, then in situ remedial actions employing conventional (i.e., no active control of Archaea) ERD amendments such as [emulsified] oils/lecithins, lactates/sugars, simple hydrogen release compounds or conventional ISCR reagents can generate excessive amounts of methane. At several sites where these conventional ERD/ISCR remedial amendments have been applied excessive methanogenesis (some yielding effervescent samples as shown below) has been observed, sometimes for many months — even years — after the amendments were applied.