&EPA
Roadmap for Incorporating Energy
Efficiency/Renewable Energy
Policies and Programs into State and Tribal
Implementation Plans
Appendix H: Weight of Evidence Pathway
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EPA-456/D-12-0011
July 2012
Roadmap for Incorporating Energy Efficiency/Renewable Energy
Policies and Programs into State and Tribal Implementation Plans
Appendix H: Weight of Evidence Pathway
By:
U.S. Environmental Protection Agency
Office of Air Quality Planning and Standards
Outreach and Information Division
Research Triangle Park, North Carolina
U.S. Environmental Protection Agency
Office of Air Quality Planning and Standards
Outreach and Information Division
Research Triangle Park, North Carolina
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ACKNOWLEDGMENTS
We would like to acknowledge substantial contributions from members of an inter-office EPA
team that included the Office of Atmospheric Programs, the Office of Policy Analysis and
Review, the Office of General Counsel and Regions 1 and 6. This document also reflects
comments received from a number of stakeholders, including state and local air quality
agencies.
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SECTION H.I: BASICS OF WEIGHT OF EVIDENCE H-4
Pathway Description H-4
Tradeoffs of Pathway H-4
Circumstances the Pathway is Best Suited For H-5
SECTION H.2: DOCUMENTATION AND ANALYSIS H-5
Documentation H-5
Objective Analysis of EE/RE Policy and/or Program Impacts H-6
Strengthening the WOE Analysis H-6
REFERENCES H-8
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SECTION H.I: BASICS OF WEIGHT OF EVIDENCE
Pathway Description
A weight of evidence determination (WOE) that accompanies air quality modeling results draws
from a variety of analyses - including the primary attainment test - to make a conclusion about
whether an area will reach attainment of a National Ambient Air Quality Standard (NAAQS) by
the appropriate year.1 Supplemental analyses of air quality, emissions and meteorological
data, and outputs from additional modeling runs may be used in a WOE determination to show
whether attainment is likely. The level of
detail required in a WOE submittal will
vary depending on the strengths and
weaknesses of the models used (e.g.,
model performance, degree of residual
nonattainment in the modeled
attainment test, amount of uncertainty
Task Checklist:
Weight-of-Evidence Pathway
Identify and describe the EE/RE policies and programs
that it wishes to include in the WOE demonstration
Ensure EE/RE policies and programs will be in place for
the duration of the planning period
Perform an objective analysis of the benefits expected
from the policies and programs
Ensure that any EE/RE emission reductions included in
the WOE demonstration are not double counted as
part of another pathway
in the model and its inputs, etc.). WOE
demonstrations are generally described
in guidance the U.S. Environmental
Protection Agency (EPA) has issued on
their use in State Implementation Plan
(SIP) attainment demonstrations.2
Tradeoffs of Pathway
State, tribal and local agencies can, of course, select more than one pathway for their
jurisdiction's different EE/RE policies and programs. Out of the four pathways, documentation
requirements for this pathway can vary the most depending on how rigorous an analysis the
state, tribal or local agency performs to support the WOE determination. For example, if the
primary test for attainment shows an area is close to meeting a NAAQS, a WOE determination
based on a qualitative analysis may be compelling. If the primary test shows an area is not
close to meeting a NAAQS, it is far less likely that qualitative arguments would be sufficient to
support a WOE determination that the NAAQS will be attained. In these instances, a
quantitative analysis is likely to be more compelling.
Unlike the control strategy and emerging/voluntary measures pathways, the WOE pathway
does not offer SIP/Tribal Implementation Plan (TIP) credit. In addition, unlike the control
strategy pathway, the WOE pathway does not include federal enforceability for the measures
included in the WOE demonstration.
1 Air quality modeling to show attainment of the NAAQS (and accompanying WOE demonstrations) primarily
applies to nonattainment areas for which modeling is needed, or desired. However, air quality modeling can be
performed in maintenance areas or to support other rules or sections of the Clean Air Act.
2 EPA (2007).
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Circumstances the Pathway is Best Suited For
State, tribal and local agencies can, of course, select more than one pathway for their
jurisdiction's different EE/RE policies and programs. The WOE pathway is applicable where a
state, tribal, or local agency has prepared an attainment demonstration based on modeling that
results in projected future air quality that is close to the NAAQS. In this case, an agency may
choose to submit a WOE determination, which may be based on, among other things,
alternative modeling results, emissions controls that were not modeled, and ambient data
trends and analyses. As part of the WOE determination, the agency may wish to take
advantage of EE/RE policies/programs adopted in its jurisdiction for purposes other than the
SIP/TIP. They may want to reflect the emission benefits of EE/RE policies/programs in the WOE
determination because they believe that these programs are likely to improve air quality in the
attainment year, but modeling the impact of the policy/program is either too resource intensive
or not feasible for other reasons and/or the jurisdiction is not interested in SIP/TIP credit.
SECTION H.2: DOCUMENTATION AND ANALYSIS
Weight of evidence demonstrations are generally a set of analyses of air quality, emissions,
meteorological data and modeling data that state, tribal and local agencies can use as
supporting evidence to show that attainment of a NAAQS is likely. State, tribal and local
agencies should weigh each type of analysis according to its credibility, as well as its ability to
address the question being posed (i.e., whether the strategy is adequate for meeting the
NAAQS by a defined deadline). The conclusions will help make an overall assessment of
whether meeting the air quality goal is likely. The last step is a qualitative one. If the
jurisdiction concludes that a strategy is inadequate to demonstrate attainment, a new strategy
is selected for review, and the process is repeated. State, tribal and local agencies should
provide a written rationale documenting how and why the conclusion is reached regarding the
adequacy of the final selected strategy. Results obtained with air quality models are an
essential part of a WOE determination and should ordinarily be very influential in deciding
whether the NAAQS will be met. The EPA's guidance includes guidelines for assessing when
corroborating analyses and/or WOE determinations may be appropriate.3
Documentation
EE/RE policies and programs that are included in a WOE determination to show attainment of a
NAAQS is likely despite inconclusive air quality modeling should reference the policies and
programs adopted for purposes other than the SIP that will be in place by the area's attainment
date. During public review of the SIP, it must be clear what analyses were included in the WOE
determination, including the additional state and local policies and programs whose benefits
were reflected therein. A typical WOE determination would describe the impact from these
EE/RE policies and programs and point out that they were not factored into the nonattainment
area's modeling analysis; had they been, the results would have been more likely to show the
area could meet the relevant NAAQS by its attainment date. The WOE determination should
include the following:
3 EPA (2007).
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• A description of the EE/RE policies and programs reflected in the WOE determination.
• A statement that the benefits of the EE/RE policy/program will occur in the attainment
planning timeframe for the nonattainment area in question.
• A statement that any emission reductions expected from the EE/RE policies/programs
are not being double counted. (Avoiding double counting means that the emission
reductions accounted for in the WOE demonstration are not incorporated in any of the
other pathways.)
Each WOE determination will be subject to area-specific conditions and data availability. Area-
specific factors may also affect the types of analyses that are feasible for a nonattainment area,
as well as the significance of each analysis. Thus, those making the WOE determination need to
make decisions about which analyses to perform and how much weight to place on each
analysis on a case-by-case basis. EPA encourages state, tribal and local agencies to consult their
EPA regional office before doing supplemental analyses to determine which analyses may be
most appropriate for a particular area.
Objective Analysis of EE/RE Policy and/or Program Impacts
WOE demonstrations can include qualitative or quantitative analysis. If a state, tribal or local
agency chooses to include a quantitative analysis they can refer to Appendix I for emission
quantification approaches for EE/RE policies and programs.
State, tribal and local agencies need to perform an objective analysis of the air quality impacts
expected from the EE/RE policies and programs reflected in the WOE demonstration. If the
state, tribal or local agency chooses to quantify emission reductions, EPA has four approaches
described in Appendix I that are available to help:
• Dispatch or Capacity Expansion Model Approach
• Historical Hourly Emission Rate Approach
• Capacity Factor Approach
• The eGRID Subregion Emission Rates Approach
In addition, EPA is providing energy savings estimates for state-mandated EE policies that could
be used in a WOE demonstration (see Appendix J). For example, if the policies included in EPA's
analysis are reflected in the WOE demonstration, then the estimate of energy savings could be
used to estimate expected emission reductions from those policies. Generally, the more robust
the analysis supporting the demonstration, then the stronger the case is that the
nonattainment area will attain the NAAQS.
Strengthening the WOE Analysis
State, tribal and local agencies can strengthen the WOE analysis by providing a quantitative
estimate of emission reductions resulting from EE/RE policies and programs. State, tribal and
local agencies can carry out two tasks when including quantitative analyses:
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• Estimate the energy savings that an EE policy will produce, or for an RE policy, the
amount of energy generation that will occur and that will displace fossil fuel-fired
generation. (Appendix I discusses approaches for accomplishing this task.)
• Quantify displaced electric generating unit emissions from energy impacts of an EE
policy or RE policy using one of the four approaches described in Appendix I or other
comparable techniques. Using the most rigorous emission quantification approach will
strengthen the WOE analysis.
o For example, including an analysis of whether the EE/RE policies and programs
incorporated in the WOE demonstration are likely to result in emission reductions
that will improve air quality in the area at the times of day and year when the area
experiences air quality problems.
State, tribal and local agencies can also strengthen the WOE demonstration by obtaining
commitments from state energy offices and/or public utility commissions to help achieve
expected emission reductions. These state offices typically administer state EE/RE policies and
programs. Making sure these offices understand that the emission reductions from EE/RE
policies and programs are in the WOE demonstration and that they commit to helping achieve
them should help ensure that the reductions occur.
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REFERENCES
EPA (2007). Guidance on the Use of Models and Other Analyses for Demonstrating Attainment of Air
Quality Goals for Ozone, PM2.5, and Regional Haze. April 2007. Available online at
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United States Office of Air Quality Planning and Standards Publication No. EPA-456/D-12-001J
Environmental Protection Outreach and Information Division July 2012
Agency Research Triangle Park, NC
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