February
19,
2004
Question:

How
should
Weight
of
Evidence
(
WOE)
procedures
used
to
support
an
8­
hour
ozone
standard
attainment
demonstration
modeling
analysis
be
applied
for
areas
participating
in
the
8­
hour
ozone
Early
Action
Compact
(
EAC)
program?

Answer:

The
EPA's
draft
8­
hour
ozone
modeling
guidance,
which
EAC
areas
should
follow
in
developing
their
attainment
demonstrations,
refers
to
the
use
of
WOE
under
limited
circumstances
when
the
modeled
attainment
test
either
narrowly
passes
or
fails
to
pass.
The
draft
guidance
(
Table
2.1)
contains
rules
of
thumb
for
assessing
whether
a
WOE
determination
may
be
appropriate.
WOE
is
used
to
support
8­
hour
ozone
standard
attainment
demonstrations
for
State
implementation
plans
(
SIPs),
including
demonstrations
for
EACs.
Modeling
is
required
to
show
that
collective
control
strategies
will
reduce
ozone
to
concentrations
below
the
air
quality
standard
by
the
area's
attainment
date.
When
the
modeled
attainment
test
is
not
passed
or
narrowly
passes,
EPA's
draft
guidance
discusses
the
use
of
additional
corroborative
analyses
to
support
the
attainment
demonstration.

One
of
the
underlying
premises
of
the
voluntary
EAC
program
is
that
participating
areas
commit
to
early
action
implementing
control
measures
needed
for
attainment;
and
EPA's
expectation
is
that
compact
areas
will
commit
to
implement
quantifiable
local
control
strategies
to
reduce
the
emissions
of
ozone
precursors.
Use
of
WOE
procedures
is
not
intended
to
be
a
substitute
for
implementing
quantifiable
local
control
measures.
Section
C,
"
Modeling"
of
the
"
Protocol
for
Early
Action
Compact
Designed
to
Achieve
and
Maintain
the
8­
Hour
Ozone
Standard"
(
the
Protocol)
states
"
Quantifiable
emission
reduction
measures
will
be
integrated
into
the
future
case
to
produce
one
or
more
control
cases.
These
control
cases
will
be
used
to
indicate
the
relative
effectiveness
of
different
measures
and
aid
in
selecting
appropriate
measures."
Section
D,
"
Control
Strategies"
goes
on
to
state
that
"
The
local
plan
shall
include
measures
that
are
specific,
quantified,
and
permanent,
and
that
if
approved
by
EPA,
will
be
Federally
enforceable
SIP
revisions."

Clearly,
in
addition
to
federal
measures,
the
EAC
area
must
agree
to
implement
some
quantifiable
local
control
measures
to
better
ensure
attainment
by
2007.
Then,
if
modeling
that
includes
the
new
local
control
measures,
conducted
in
accordance
with
EPA
guidance
and
approval,
does
not
pass
the
attainment
test
for
2007,
the
area
may
apply
WOE
procedures
as
specified
in
EPA's
draft
guidance
as
part
of
the
attainment
demonstration.
The
further
the
attainment
test
is
from
being
passed,
the
more
compelling
contrary
evidence
produced
by
corroboratory
analyses
must
be
to
draw
a
conclusion
differing
from
that
implied
by
the
test
results.
