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FOOTPRINT: A COMPUTER APPLICATION FOR ESTIMATING PLUME AREAS OF BTEX COMPOUNDS IN GROUND WATER IMPACTED BY A SPILL OF GASOLINE CONTAINING ETHANOL
Citation:
AHSANUZZAMAN, A. AND J. T. WILSON. FOOTPRINT: A COMPUTER APPLICATION FOR ESTIMATING PLUME AREAS OF BTEX COMPOUNDS IN GROUND WATER IMPACTED BY A SPILL OF GASOLINE CONTAINING ETHANOL. Presented at 2005 NGWAa Conference on MTBE, San Francisco, CA, May 26 - 27, 2005.
Impact/Purpose:
To inform the public.
Description:
Ethanol has a potential negative impact on the natural biodegradation of other gasoline constituents, including BTEX compounds, in ground water. The impact of ethanol on the size of the BTEX plume should be considered in the risk evaluation of spills of gasoline containing ethanol. FOOTPRINT was developed as a simple and user-friendly computer application that can be used as a screening model to estimate the extent of the BTEX plume when the gasoline that is spilled contains ethanol. FOOTPRINT estimates the overall area of a plume of BTEX compounds that are contained within two biodegradation zones, one zone where ethanol is present and there is no biodegradation of BTEX compounds, surrounded by a second zone where the ethanol has been removed by natural biodegradation and the rate of biodegradation of BTEX compounds is constant. Existing simple models for BTEX compounds (such as BIOSCREEN) can not model this interaction between ethanol and BTEX compounds because these models are limited to a single biodegradation rate uniformly applied across the flow path. FOOTPRINT applies a 3-dimensional analytical solute transport model to estimate solute concentration at any location downgradient from a constant concentration source for a fixed first-order decay rate. It first uses an estimate of the rate of ethanol biodegradation to estimate the zone downgradient from the source where ethanol inhibits BTEX biodegradation. Within this zone, concentrations of BTEX compounds can only attenuate through dilution and dispersion. Downgradient from this zone, FOOTPRINT models BTEX biodegradation at a constant rate. FOOTPRINT assumes that the concentration of BTEX at the source is constant. It allows either a constant concentration or exponentially decaying source for ethanol. FOOTPRINT could also be applied to estimate the plume area of any single chemical compound downgradient from a constant concentration source for a constant decay rate. Finally, results obtained from simulating FOOTPRINT for a synthetic case study were verified by comparing with the results from a conceptually identical numerical model.