Roger Painter, Tom Byl, Lonnie Sharpe1, Valetta Watson and Tony Patterson
It is widely perceived that karst groundwater often has insufficient residence time for significant biodegradation of contaminants to occur. It is perhaps due to these perceptions that less research has been conducted for quantitative modeling of biodegradation in karst as compared to consolidated aquifers. Modeling biodegradation in karst is in the domain of non-ideal chemical reaction kinetics. The residence time distribution function (RTD) for tracer molecules in a single karst conduit or a complex system of conduits is a probability density function which can be interpreted to define the probability that contaminant molecules present at the influent at time equals zero will arrive at the effluent after a particular amount of time. To demonstrate this methodology the biodegradation rate of a contaminant (toluene) in raw karst groundwater from a BTEX impacted site in central Kentucky was quantitatively measured in batch microcosm studies and the extent of biodegradation of toluene in the same groundwater was measured for a complex flow system.The values of the pseudo first order rate constant (k’) obtained ranged from 0.017 (hr)-1 to 0.0210 (hr)-1 compared to 0.0186 (hr)-1 for the microcosm experiments. The close agreement between the values of k’ obtained from the static microcosms and the ADE model indicate that the model adequately describes the RTD for modeling biodegradation in karst aquifers. The values of k’ obtained correspond to a half-life of less than two days for toluene and this has major
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