O.K. firstly a sharp reader will already have noticed something significant in the title above. This Master's degree requirement thesis is specific to DNAPLS in Bedrock! This research is NOT a comparison of Natural Attenuation between Bedrock Aquifers versus Overburden Aquifers. Overburden meaning sand, gravel, some silt and probably some kind of clay in an aquitard or two in the subsurface located above the Bedrock. Bedrock Aquifers do literally refer to sub-surface Bedrock whose fractures and openings are saturated with groundwater. Furthermore in the case of Guelph much of the shallower Bedrock consists of Dolomite made up of Calcium and Magnesium and more. The Bedrock Aquifers in Guelph as well as parts of Cambridge are located very close to the surface often with only a couple of metres of Overburden above them. Here in Elmira the Overburden however starts at the surface and goes eighty to one hundred feet (30 + metres) below ground surface.
So according to this research paper there are multiple different physical, chemical and microbial processes taking place in the Bedrock which either degrade Trichloroethylene (TCE) to other compounds such as cis DCE, trans DCE, VC, or dechlorinate it hence removing the chlorine from the TCE ending up with non toxic hydrocarbons such as ethene and ethane. This does of course take decades but it seems to me to be faster than what I was led to understand here in Elmira. Now there are specific bacteria that live and grow in Bedrock that can break down TCE (dechlorinate it). What I don't know yet is if these obviously pretty tough bacteria/microbes thrive in Bedrock conditions but are less available or effective in Overburden soils. If that is so then it explains the honest professionals stating in 2007 that DNAPL should be removed one way or the other up here in Elmira to speed up groundwater remediation.
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