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Great Falls of the Passaic River at Paterson, N.J

Great Falls of the Passaic River at Paterson, N.J.




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EPA biofules and drinking water suupplies

Project Title:EPA biofules and drinking water suupplies
Project Number: LJ00EGY
Project Chief:
Project Start Date: 01-MAR-2011
Project End Date:

Project Objectives

Refine an existing Modpath MODFLOW model of the Opequon Creek watershed (see Figure 1) to adequately show flow paths and travel times of water through the system from hypothetical new releases of biofuels at all existing gasoline service stations  in the model domain to the point of extraction at water supply wells, or the point of discharge to surface water.

Incorporate the conceptual model of FOOTPRINT into the existing MODFLOWModpath model to evaluate the potential impact of releases of biofuels on groundwater supplies.  The evaluation will consider various compositions of biofuels, including E10, E15, E20 and E85.

Including a measure of uncertainty of the simulations based on parameter uncertainty from the calibration process.

Statement of Problem

In response to the requirements of the renewable fuel standard (RFS), established by the Energy Policy Act of 2005 and amended by the Energy Independence and Security Act of 2007, biofuels will provide a greater contribution to the fuel supply in the United States.  With increased use, there is increased risk that the production, transportation, and storage of biofuels might impact municipal water supplies.  The US EPA Office of Research and Development is carrying out a comprehensive evaluation of the potential impacts on water quality and water supply resulting from the increased use of biofuels.

Contamination resulting from releases of biofuel from underground storage tanks may impact ground water that is available for municipal water supply.  This concern is greatest for regions of the country that rely on ground water from an urban landscape for municipal water supply.

Strategy and Approach

Groundwater flow models constructed using the program Modflow (McDonald and Harbaugh, 1988, Harbaugh, 2005) will be used to simulate water levels, flow volumes, paths of water, and travel times through the groundwater system. Automated parameter estimation programs such as Ucode (Poeter and Hill, 2005) or PEST (Dougherty, 2005) will be used to find parameter values that best match observations of heads, head gradients, base flows in streams, and
concentrations of age tracers.  The statistics on parameter uncertainty provided by the parameter estimation programs will then be used to translate the uncertainty in parameter values to the uncertainty in predicted values (Starn, 2010). The groundwater flow models will be coupled with a particle tracking program, Modpath (Pollock, 1994) to estimate concentrations of benzene in groundwater, and to estimate concentrations of benzene produced by water supply wells. Uncertainty in flow will be used to estimate uncertainty in the simulations of concentrations.

Public-supply wells typically draw water from a large areas resulting in dilution which can lessen the impact of a plume reaching a well.  This approach will allow for quantification of this dilution. In contrast, smaller communities with fewer wells and domestic-supply wells have more limited areas that contribute recharge to them. The limited areas result in lower probability of intersecting plumes but would also lead to higher concentrations when a plume is intersected compared to the public-supply wells since the dilution effect would be less.

Maps will be produced from the simulations that areas that could be impacted by spills from current gas station locations or areas in which a spill could impact existing wells. Rather than classify areas in a binary manner as would be the result of a single parameter set, probability maps will be developed that are based on multiple parameter sets derived from parameter uncertainty analysis.  A range of biofuel compositions would be used in the vulnerability analyses including a base case with conventional gasoline with no ethanol added.


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