Potential Consequences of Excessive Methane Production Following ERD and Conventional ISCR Treatment: Case Studies and Remedial
At some sites, excessive production of methane has been observed following the addition of organic hydrogen donors such as (emulsified) oils, lecithin, sugars and conventional ISCR reagents. This is because methanogens are commonly the most ubiquitous indigenous microbes in anoxic aquifer settings. And given that methanogens replicate in 1 to 2 hours (whereas Dehalococcoides spp. for example double in 24 to 48 hours), they often bloom and dominate following the addition of organic hydrogen donors, thereby liberating large amounts of methane gas. There are at least three important consequences of this response: i) By utilizing hydrogen, the methanogens compete with dechlorinating microbes thus making inefficient use of the remedial amendment (just 20 ppm methane in groundwater represents about 35% “waste” of material – this is a common and tangible detriment); ii) Rapid growth of methanogens consumes alkalinity while generating acids thereby having the potential for aquifer acidification (which may liberate heavy metals causing secondary contaminant issues); and iii) Elevated methane concentrations can exceed current and pending regulations of < 10 to <28 ppm in groundwater and/or 0.5% v/v methane in soil gas (e.g., 10% of the LEL) and/or indoor air (methane is flammable between 5% and 15% v/v). Five case studies will be reviewed where methane production was problematic: i) Subsurface fires next to an industrial facility at a site in the Midwest USA immediately following the application of a convention Read More >>