Regulation of Fuels and Fuel Additives: Renewable Fuel Standard ...

estimate the true impacts of increases in renewable fuels on fossil fuel use, modelers
attempt to take many or all these steps into account. Similarly, energy is used and GHGs
emitted in the pumping of oil, transporting the oil to the refinery, refining the crude oil
into finished transportation fuel, transporting the refined gasoline or diesel fuel to the
consumer and then burning the fuel in the vehicle. Such analyses are termed lifecycle or
well-to-wheels analyses.
A variety of approaches are available to conduct lifecycle analysis. This variety
largely reflects different assumptions about (1) the boundary conditions and (2) the
estimates of input factors. The boundary conditions determine the scope of the analysis.
For example, a lifecycle analysis could include energy required to make farm equipment
as part of the estimate of energy required to grow corn. The agency chose a lifecycle
analytic boundary that encompasses the fuel-cycle and does not include the example used
above. Differing estimates on input factors (e.g. amount of fertilizer to grow corn) can
also affect the results of the lifecycle analysis.
For this proposed rulemaking, we have made use of a fuel-cycle model,
GREET, 87 developed at Argonne National Laboratory (ANL) under the sponsorship of
the U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy
(EERE). GREET has been under development for several years and has undergone
extensive peer review through multiple updates. Of the available sources of information
on lifecycle analyses of energy consumed and emissions generated, we believe that
GREET offers the most comprehensive treatment of the transportation sector. For
instance, GREET provides lifecycle assessments for ethanol made from corn and
cellulosic materials, biodiesel made from soybean oil, and petroleum-based gasoline and
diesel fuel. Thus GREET provides a means for calculating the relative greenhouse gas
(GHG) and petroleum impacts of renewable fuels that displace conventional motor
vehicle fuels. For this proposal, we used version 1.7 of the GREET model, with a few
modifications to its input assumptions as described in more detail below.
We do not believe that it would be appropriate at this time to base the regulatory
provisions for this rule on lifecycle modeling, as described in more detail in Section
III.B.4. Although the GREET model does provide a peer-reviewed source for lifecycle
modeling, a consensus on all the assumptions, including point estimates, that are used as
inputs into that model does not exist. 88 Also, given the short timeframe available for the
development of this proposal, we have not had the opportunity to initiate the type of
public dialogue on lifecycle modeling that would be necessary before such analyses could
be incorporated into a regulatory framework. We have therefore chosen to use lifecycle
modeling only as a means to estimate the impacts of the increased use of renewable fuel.
In addition to the GREET model tool, EPA has also developed a lifecycle
modeling tool that is specific to individual fuel producers. This FUEL-CO2 model is
87 Greenhouse gases, Regulated Emissions, and Energy use in Transportation.
88 See Chapter 6.1.2 of the RIA for further discussion of input assumptions used for the GREET modeling.
Also see IX.A.2 of this preamble section for a discussion about the differing estimates.
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