Microbial and Biogeochemical Indicators of Methane in Groundwater Aquifers of the Denver Basin, Colorado

The presence of methane and other
hydrocarbons in domestic-use
groundwater aquifers poses significant environmental and human health
concerns. Isotopic measurements are often relied upon as indicators
of groundwater aquifer contamination with methane. While these parameters
are used to infer microbial metabolisms, there is growing evidence
that isotopes present an incomplete picture of subsurface microbial
processes. This study examined the relationships between microbiology
and chemistry in groundwater wells located in the Denver-Julesburg
Basin of Colorado, a rapidly urbanizing area with active oil and gas
development. A primary goal was to determine if microbial data can
reliably indicate the quantities and sources of groundwater methane.
Comprehensive chemical and molecular analyses were performed on 39
groundwater well samples from five aquifers. Elevated methane concentrations
were found in only one aquifer, and both isotopic and microbial data
support a microbial origin. Microbial parameters had similar explanatory
power as chemical parameters for predicting sample methane concentrations.
Furthermore, a subset of samples with unique microbiology corresponded
with unique chemical signatures that may be useful indicators of methane
gas migration, potentially from nearby coal seams interacting with
the aquifer. Microbial data may allow for more accurate determination
of groundwater contamination and improved long-term water quality
monitoring compared solely to isotopic and chemical data in areas
with microbial methane.