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Abstract
In situ aerobic cometabolic transformations of ethylene, propylene, and cis-1,2-dichloroethylene
(c-DCE), by microorganisms stimulated on propane, were examined in groundwater contaminated
with c-DCE and trichloroethylene (TCE). In situ measurements were performed by conducting
field push-pull tests, which consisted of injecting site groundwater amended with
a bromide tracer and combinations of propane, dissolved oxygen (DO), nitrate, ethylene,
propylene, c-DCE, and TCE into existing monitoring wells and sampling the same wells
over time. Mass balance and transformation rate calculations were performed after
adjusting for dilution losses using measured tracer concentrations. Initial rates
of propane utilization were very low; rates increased substantially following sequential
additions of propane and DO. Evidence that propane and DO additions had stimulated
organisms expressing a propane monoxygenase enzyme system and that had the capability
to transform chlorinated aliphatic hydrocarbons (CAHs) included: (1) the transformation
of injected ethylene and propylene to the cometabolic byproducts ethylene oxide and
propylene oxide, (2) the transformation of c-DCE, and (3) the inhibition of these
transformations in the presence of coinjected acetylene, a known monoxygenase mechanism-based
inactivator. These results suggest that a series of push-pull tests performed with
nontoxic chemical probes can be useful for detecting and monitoring in situ aerobic
cometabolism of CAHs.