LT2ESWTR
Toolbox
Guidance
Manual
Proposal
Draft
June
2003
6­
1
6.0
Lime
Softening
6.1
Introduction
Lime
softening
is
a
drinking
water
treatment
process
that
uses
chemical
precipitation
with
lime
and
other
chemicals
to
reduce
hardness
and
to
enhance
clarification
prior
to
filtration.
Lime
softening
can
be
categorized
into
two
general
types:
(
1)
single
stage
softening
that
is
used
to
remove
calcium
hardness
and
(
2)
two­
stage
softening
that
is
used
to
remove
magnesium
hardness
and
high
levels
of
calcium
hardness.
A
single
stage
softening
plant
includes
a
primary
clarifier
and
filtration
components.
A
two
stage
softening
plant
has
an
additional
clarifier
located
between
the
primary
clarifier
and
filter.
Within
these
general
categories
there
are
several
possible
treatment
schemes;
however,
describing
each
is
beyond
the
scope
of
this
chapter.

This
toolbox
option
is
practical
for
lime
softening
plants
that
either
have
a
two
stage
process
or
could
upgrade
to
a
two
stage
process.
The
advantage
of
using
this
toolbox
option
to
achieve
compliance
with
the
LT2ESWTR
is
that
systems
will
have
the
treatment
process
in
place
or
if
an
upgrade
or
modification
is
needed,
it
could
benefit
the
treatment
of
other
contaminants.
A
disadvantage
for
softening
plants
is
a
potential
reduced
flexibility
in
the
treatment
train
since
all
water
must
be
treated
by
both
stages.

Since
the
water
systems
considering
this
toolbox
option
will
most
likely
have
a
lime
softening
process
in
place,
this
section
does
not
provide
design
or
operational
information.
Instead,
this
section
focuses
on
the
requirements
that
lime
softening
systems
must
meet
to
receive
Cryptosporidium
removal
credit
and
how
those
requirements
can
be
met
with
general
process
modifications.
The
chapter
is
organized
into
two
sections:

6.2
LT2ESWTR
Compliance
Requirements
­
describes
the
criteria
that
plants
must
meet
in
order
to
receive
additional
credit
for
Cryptosporidum
removal,
and
reporting
requirements
to
maintain
compliance.

6.3
Split
Flow
Processes
­
addresses
compliance
issues
for
split
flow
processes.
Chapter
6
­
Lime
Softening
1
For
purposes
of
compliance
with
the
lime­
softening
toolbox
option,
"
clarifier"
is
used
as
a
general
term
for
processes
with
settling.

LT2ESWTR
Toolbox
Guidance
Manual
Proposal
Draft
June
2003
6­
2
Flocculation
and
Sedimentation
Basin
Recarbonation
Flocculation
and
Sedimentation
Basin
Recarbonation
Filters
Lime
CO2
CO2
Primary
Clarifier
Secondary
Clarifier
coagulant
must
be
present
Soda
Ash
coagulant
must
be
present
6.2
LT2ESWTR
Compliance
Requirements
6.2.1
Credit
for
Cryptosporidium
Removal
The
LT2ESWTR
requires
plants
to
meet
the
following
criteria
in
order
to
receive
0.5
log
credit
towards
additional
Cryptosporidium
treatment
requirements
(
40
CFR
141.726(
b)):

°
The
plant
must
have
a
second
clarification
step
between
the
primary
clarifier1
and
filter
which
is
operated
continuously.
For
split
treatment
processes,
only
the
portion
of
flow
going
through
two
clarification
stages
can
receive
credit.
If
a
portion
of
flow
bypasses
one
stage,
additional
treatment
must
be
provided
to
the
bypassed
portion
(
see
section
6.3).

°
A
coagulant
must
be
present
in
both
clarifiers.
Precipitation
of
metal
salts
(
e.
g.,
magnesium
hydroxide
or
excess
lime)
could
be
considered
a
coagulant
for
the
second
clarifier.

Figure
6.1
shows
a
typical
two
stage
lime
softening
process.
Lime
or
lime
and
soda
ash
are
added
at
the
first
stage.
To
receive
treatment
credit
for
this
type
of
process,
both
stages
of
clarification
must
have
a
coagulant
present.

Figure
6.1
Typical
Two­
Stage
Lime
Softening
Process
Chapter
6
­
Lime
Softening
LT2ESWTR
Toolbox
Guidance
Manual
Proposal
Draft
June
2003
6­
3
6.2.2
Reporting
Requirements
The
LT2ESWTR
requires
monthly
verification
and
reporting
of
the
following
conditions
for
systems
using
the
lime
softening
option
(
40
CFR
141.730):

°
Continuous
operation
of
a
second
clarification
step
between
the
primary
clarifier
and
filter
°
Continuous
presence
of
coagulant
in
the
first
and
second
stage
clarifiers
°
Both
clarifiers
treat
100
percent
of
the
plant
flow
In
addition,
EPA
recommends
submitting
a
schematic
of
the
treatment
process
to
the
State,
clearly
identifying
the
two
stages
of
clarification.
EPA
also
recommends
that
systems
monitor
the
coagulant
dosages
(
or
concentration)
in
the
secondary
clarifier
on
a
daily
basis,
for
the
first
year,
and
record
the
average
and
minimum
coagulant
concentrations.
This
data
can
assist
the
State
in
assessing
whether
the
system
operates
in
compliance
at
all
times.

6.3
Spilt­
Flow
Processes
Split­
flow
processes
divert
a
portion
of
the
flow
from
either
the
first
or
second
stage
of
the
process
and
then
blend
the
two
streams
together
further
downstream.
Only
the
portion
of
flow
that
receives
the
two
stages
of
treatment
would
be
eligible
for
the
0.5
log
credit.
In
these
situations,
systems
would
either
have
to:
1)
eliminate
the
bypass
and
direct
the
entire
flow
through
both
stages,
or
2)
treat
the
bypassed
portion
with
another
toolbox
option,
such
as
chlorine
dioxide,
membranes,
or
ozone
to
receive
0.5
log
credit
for
that
stream.
