DCN
#
300­
017
MEMORANDUM
TO
MPP
RECORD
Date:
February
25,
2004
Derivation
of
Adjustment
Factor
for
Total
Nitrogen
Limits
As
described
further
in
the
Cost
Report,
EPA
used
a
denitrification
rate
of
0.171
mg
nitrate/
nitrite­
N
denitrified/
mg
MLVSS­
day
in
its
evaluation
of
different
nutrient
removal
technologies.
Using
this
nitrification
rate
in
its
cost
model,
EPA
determined
that
achieving
Option
2.5
nitrogen
removals
was
economically
achievable
and
cost­
effective
for
MPP
facilities.
EPA
recognizes,
however,
that
the
actual
denitrification
rate
will
vary
among
facilities
and
be
dependent
on
a
number
of
factors.
In
order
to
confirm
its
conclusion
about
the
economic
achievability
of
the
final
rule,
EPA
performed
a
sensitivity
analysis
to
determine
the
potential
impact
of
a
lower
denitrification
rate
on
the
costs
of
the
rule.
Based
on
data
and
information
collected
and
reviewed
for
the
final
rule,
EPA
has
concluded
that,
in
most
cases,
the
denitrification
rate
will
be
greater
than
0.05
mg
nitrate/
nitrite­
N
denitrified/
mg
MLVSS­
day.
This
is
consistent
with
the
Industry
Coalition's
view
that
"
the
denitrification
rate
is
slowest
with
endogenous
decay
as
food
source
(
0.06),
about
half
that
for
sewage..."
EPA
found
that
even
at
a
rate
of
0.05
mg
nitrate/
nitrite­
N
denitrified/
mg
MLVSS­
day,
the
final
rule
was
economically
achievable.

In
selecting
facilities
for
derivation
of
effluent
limitations,
EPA
chose
two
well­
operated
facilities
(
see
DCN
300001
for
discussion
of
how
EPA
selected
the
model
facilities).
Comments
were
provided
by
the
industry
stating
that
these
two
facilities
included
very
large
anoxic
tanks
that
result
in
very
long
detention
times,
and
that
the
cost
model
used
by
EPA
does
not
adequately
reflect
costs
required
to
achieve
the
NODA
nitrogen
target
effluent
concentrations
if
nitrification
rates
are
lower
then
EPA
assumed.
In
an
effort
to
determine
whether
adjustments
were
needed
to
EPA's
approach
to
calculating
final
limitations
based
on
data
from
two
facilities,
EPA
re­
ran
the
cost
model
for
the
two
facilities
using
a
lower
denitrification
rate
of
0.05
mg
nitrate/
nitrite­
N
denitrified/
mg
MLVSS­
day
and
a
less
stringent
total
nitrogen
LTA
based
on
only
these
two
model
facilities
to
see
how
the
modeled
anoxic
volume
compares
to
the
actual
anoxic
tank
volumes.
At
one
facility,
the
cost
model
calculated
that
the
facility
would
require
an
anoxic
volume
higher
than
the
actual
volume
to
meet
the
nitrogen
LTA
that
it
was
actually
achieving,
which
means
that
the
actual
denitrification
rate
was
higher
than
0.05.
However
for
the
other
facility,
the
modeled
anoxic
volume
was
lower
than
the
actual
volume
the
facility
required,
suggesting
that
the
actual
denitrification
rate
was
lower
than
0.05.

Achieving
a
particular
LTA
concentration
for
nitrate/
nitrite­
N
will
vary
depending
on
both
the
denitrification
rate
and
the
anoxic
tank
volume.
Consequently,
prediction
of
the
anoxic
tank
volume
for
a
facility
is
dependent
on
the
denitrification
rate.
Use
of
a
higher
denitrification
rate
results
in
lower
anoxic
tank
volume.
For
the
above
two
selected
facilities,
a
denitrification
rate
of
0.08
mg
nitrate/
nitrite­
N
denitrified/
mg
MLVSS­
day
may
be
appropriate
for
the
facility
that
currently
has
an
anoxic
tank
volume
less
than
that
predicted
by
the
cost
model
(
using
a
rate
of
0.05),
while
a
denitrification
rate
of
0.03
mg
nitrate/
nitrite­
N
denitrified/
mg
MLVSS­
day
should
be
used
for
the
facility
that
currently
has
an
anoxic
tank
volume
greater
than
that
predicted
by
the
cost
model
As
stated
earlier,
EPA
concluded
that
it
had
correctly
determined
that
the
final
rule
was
economically
achievable
based
on
both
its
primary
cost
model,
and
its
sensitivity
analysis
that
assessed
costs
assuming
a
denitrification
rate
of
0.05
mg
nitrate/
nitrite­
N
denitrified/
mg
MLVSSday
Costing
facilities
with
a
denitrification
rate
of
0.05
mg
nitrate/
nitrite­
N
denitrified/
mg
MLVSS­
day
will
normally
represent
a
high
end
of
the
cost.
Nevertheless,
EPA
recognizes
that
this
assessment
may
not
fully
account
for
likely
actual
costs,
given
the
information
showing
that,
in
the
case
of
one
of
the
model
facilities,
the
actual
denitrification
rate
appeared
to
be
lower
than
0.05,
given
the
larger
than
predicted
anoxic
tank.
Thus,
in
order
to
account
for
potential
underestimation
of
costs
and
resulting
overestimation
of
the
achievable
removals,
EPA
adjusted
the
final
effluent
limits
of
total
nitrogen
as
described
below.

EPA
derived
the
final
monthly
average
effluent
limitations
for
total
nitrogen
for
Subcategory
K
using
data
from
two
well­
operated
BAT
plants
based
on
a
long­
term
average
of
45.5
mg/
L
and
a
variability
factor
of
1.8.
The
resulting
monthly
average
effluent
limitation
was
81.9
mg/
L.
Assuming
a
denitrification
rate
of
0.05
mg
nitrate/
nitrite­
N
denitrified/
mg
MLVSS­
day,
EPA
estimated
with
the
cost
model
that
a
2.8
million
gallon
anoxic
tank
would
be
required
for
one
of
the
facilities
to
achieve
this
final
monthly
average
effluent
limitations
for
total
nitrogen.
However,
as
stated
earlier,
the
facility
actually
has
an
unusually
low
denitrification
rate
of
0.03
mg
nitrate/
nitrite­
N
denitrified/
mg
MLVSS­
day.
With
a
denitrification
rate
of
0.03
mg
nitrate/
nitrite­
N
denitrified/
mg
MLVSS­
day
and
with
the
projected
(
and
costed)
volume
of
the
anoxic
tank
(
2.8
million
gallon),
the
facility
would
be
projected
to
actually
achieve
a
maximum
monthly
average
of
104
mg/
L
of
total
nitrogen
in
the
effluent.
A
total
nitrogen
effluent
concentration
of
104
mg/
L
reflects
an
approximately
25
percent
increase
over
the
unadjusted
monthly
average
effluent
limits
for
the
subcategory
derived
from
the
two
BAT
facilities.
Therefore,
to
ensure
that
the
final
limitations
are
achievable
by
the
two
BAT
facilities
selected
by
EPA
to
serve
as
the
basis
for
limit
development
(
and
by
all
other
facilities
in
the
subcategory
that
install
the
model
technology
as
EPA
costed
it),
EPA
increased
the
effluent
total
nitrogen
limits
for
Subcategory
K
facilities
by
25
percent
over
the
unadjusted
limits.

For
red
meat
facilities,
EPA
based
the
unadjusted
limits
on
a
single
poultry
facility,
because
it
did
not
identify
any
meat
facilities
that
had
both
installed
option
2.5
technology
and
were
operating
it
as
BAT.
Because
average
influent
nitrogen
concentrations
in
red
meat
facility
wastewaters
are
significantly
higher
than
the
average
influent
nitrogen
concentrations
in
poultry
facility
wastewaters,
EPA
chose
to
use
only
one
of
the
two
BAT
facilities
that
it
used
for
Subcategory
K,
specifically
the
one
that
had
influent
wastewaters
closer
in
nitrogen
concentration
to
those
in
the
meat
subcategories.
This
is
also
the
facility
where
the
actual
denitrification
rate
appears
to
be
lower
than
the
0.05
rate
used
in
the
costing
sensitivity
analysis,
so
the
same
25%
adjustment
factor
is
applied
to
the
unadjusted
limitations
derived
from
this
facility.
The
adjusted
monthly
nitrogen
limitation
for
the
meat
subcategories
based
on
this
facility
is
130
mg/
L.
