United States Department of Transportation
i
Impact of new diesel fuels used in port operations on subsurface quality
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2008-04-01
[PDF-512.85 KB]
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Abstract:Diesel is widely used as fuel for operations in the port of Los Angeles - Long
Beach as well as for transport of goods to and from the port. Conventional diesel fuel
contributes disproportional to air pollution (particulate matter, NOx, CO, and
hydrocarbons). The arrival of low-sulfur diesel, which is already widely available in
Japan and Europe, and other improvements in fuel and engine technology should
greatly decrease the adverse impact of diesel on air quality. Examples of modifications
are the use of diesel with ethanol as oxygenate (“diesohol”), biodiesel, and diesel with
catalytic additives. Each fuel has some merits that need to be weighed against potential
disadvantages. This proposal considers diesohol. Diesohol is already used in Europe
and Brazil and is being investigated for wider use in the United States and Australia. In
the past, scientists and decision makers were mainly concerned with the impact of
diesel and gasoline on air quality. However, even under the best of circumstances
release of diesel and fuel additives to the surface and subsurface environment cannot
be ruled out. Accidental spillage and leakage may occur during production, transport,
storage, handling, or use.
In this study we quantified the impact of the release of a potential new diesel fuel
on the movement and fate of contaminants in the aqueous phase of the unsaturated
(vadose) and saturated zone of the subsurface. Existing software was modified to
model subsurface flow in the vadose zone. The model accounts for the effect of
surfactants (ethanol and other fuel additives) on flow properties, and the dissolution of
diesel components (benzene in this case). The impact of ethanol on dissolution and
degradation of fuels compounds and pre-existing organic contaminants in the
groundwater has been analyzed using a model based on analytical solutions.
The results of the study for the unsaturated zone suggest that, for the most
common scenario of a particular water flux at the surface, water and dissolved
substances will move somewhat farther in the underground. Ethanol reduces the
amount of water that is retained by the porous medium. Furthermore, the concentration
of contaminants such as benzene may be greatly increased due to the enhanced
aqueous solubility. The analysis conducted for the saturated zone illustrated changes in
contaminant plumes due to enhanced solubility and reduced biodegradation caused by
ethanol. Contaminants such as benzene are more persistent in groundwater and the
plume area exhibits a moderate increase if ethanol is present.
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