May
14,
1998
(
AR­
18J)

Don
Smith
Permit
Unit
II
Air
Quality
Division
Minnesota
Pollution
Control
Agency
520
Lafayette
Road
St.
Paul,
Minnesota
55155
Dear
Mr.
Smith:

The
United
States
Environmental
Protection
Agency
(
USEPA)
has
reviewed
the
DRAFT
Air
Emission
Part
70
Permit
No.
03700003­
001
for
Northern
States
Power
(
NSP)
for
the
Black
Dog
facility
located
at
1400
Black
Dog
Road,
Burnsville,
Dakota
County,
Minnesota.
The
USEPA
has
comments
concerning
periodic
monitoring
with
respect
to
particulate
(
PM)
matter
and
opacity
emission
limits.
These
concerns
have
arisen
in
light
of
the
periodic
monitoring
guidance
being
developed
and
out
of
concern
for
national
consistency.

Periodic
monitoring
needs
to
be
addressed
for
each
particulate
matter
and
opacity
limit
where
there
is
not
a
performance
testing
requirement
listed
in
the
draft
permit.
This
is
the
case
for
SV
001
and
for
most,
if
not
all,
of
the
coal
and
ash
handling
and
storage
facilities.
Section
70.6(
a)(
3)(
B)
requires
each
Part
70
permit
to
contain
periodic
monitoring
sufficient
to
yield
reliable
data
from
the
relevant
time
period
that
are
representative
of
the
source's
compliance
with
the
permit,
if
the
underlying
applicable
requirements
do
not
otherwise
specify
such
monitoring.
This
is
a
"
gapfilling
provision
to
fill
in
any
"
holes"
that
allow
the
source
to
verify
compliance
with
any
or
all
applicable
requirements.
In
order
to
meet
this
"
gap­
filling"
provision,
the
periodic
monitoring
terms
for
each
emission
limit
in
the
permit
must
include
not
only
the
appropriate
method
of
monitoring,
but
also
the
minimum
frequency
at
which
the
monitoring
must
be
done
in
order
to
yield
sufficient
data
to
represent
the
source's
compliance
with
the
permit.
If
the
Part
70
permit's
monitoring
requirements
do
not
specify
frequency,
the
monitoring
methods
they
institute
can
not
be
considered
periodic.

The
emission
sources
affected
by
this
include
SV
001,
SV
006,
EU
006,
EU
007,
EU
008,
EU
011,
EU
012,
EU
013,
EU
014,
EU
015,
EU
016,
EU
017,
EU
018,
EU
019,
and
EU
021
for
PM;
EU
003,
EU
004,
EU
019,
and
EU
023
for
opacity.
(
See
enclosed
policy
on
periodic
monitoring
for
opacity
emissions.)
There
are
also
a
few
fugitive
emission
sources
that
may
need
monitoring
or
record
keeping
because
opacity
and
PM
emission
limits
apply
to
these
sources.
The
USEPA
is
also
aware
that
some
performance
tests
specified
in
the
draft
permit
are
one­
time
tests.
These
tests
are
on
emission
units
001,
003,
004,
024,
and
025.
The
USEPA
believes
this
is
too
infrequent
to
constitute
periodic
monitoring.
The
USEPA
is
submitting
an
attachment
which
lists
conditions
that
can
be
useful
for
periodic
monitoring
for
opacity.
Periodic
monitoring
for
PM
can
include,
but
is
not
limited
to,
stack
testing
using
method
5
or
any
other
test
conducted
at
the
source
that
will
assure
compliance
with
the
limits
in
the
permit.
The
frequency
of
monitoring
should
be
at
least
twice
during
the
permit
term
for
low­
emitting
sources,
and
more
frequent
for
higher
emitting
pollution
sources.
If
an
emission
limit
is
monitored
less
frequently,
the
reasons
for
this
should
be
given
in
the
technical
support
document
(
TSD).

The
TSD
of
the
permit
states
that
the
MPCA
utilities
permit
team
has
found
that
monitoring
of
control
equipment
parameters
such
as
pressure
drop
across
a
baghouse
or
voltage
and
amperage
of
an
electrostatic
precipitator
was
environmentally
insignificant
when
past
emissions
testing
clearly
shows
that
opacity,
and
not
mass
emissions,
is
the
limiting
parameter
for
PM­
10
and
the
emission
unit
is
continuously
monitored
for
opacity
with
it's
own
dedicated
opacity
monitor.
This
method
appears
to
be
used
for
SV
001.
However,
this
does
not
exempt
the
source
from
complying
with
its
PM
limit
for
SV
001,
and
the
permit
needs
to
specify
how
the
source
will
demonstrate
compliance
with
this
applicable
requirement.

The
USEPA
requests
that
the
NSP
part
70
permit
be
amended
to
address
the
above
comments,
and
corrected
before
the
permit
reaches
the
proposed
permit
stage.
We
appreciate
MPCA's
consideration
of
our
comments
and
efforts
to
improve
periodic
monitoring
requirements
in
their
Part
70
permits.
Although
this
comment
letter
is
specific
to
the
NSP
Black
Dog
facility,
the
periodic
monitoring
concept
should
be
addressed
in
all
your
Part
70
permits.
We
hope
that
the
information
outlined
in
this
letter
is
useful
to
you,
and
we
will
continue
to
work
with
you
to
develop
an
acceptable,
flexible
permit.
If
you
have
any
questions
on
this
letter,
please
contact
Shaheerah
Fateen
at
(
312)
353­
4779.

Sincerely,

/
s/

Robert
Miller,
Chief
Permits
and
Grants
Section
