2.
Response
to
Comments
2.9
Individual
Responses
to
Comments
from
Organizations
casings
to
prevent
the
spread
of
leachates
from
the
landfill
into
groundwater.
See
for
discussion
of
the
Title
27
landfill
closure
review
and
approval
process
and
5
for
discussion
of
compliance
with
the
law
as
mitigation
under
CEQA.
Mitigation
Measure
4.G-2f
is
intended
to
address
the
potential
buildup
of
methane
from
landfill
gas
within
underground
utilities
and
utility
vaults.
In
addition,
Title
27
closure
of
the
portion
of
the
landfill
will
require
methane
collection
and
extraction
systems,
along
with
ongoing
monitoring
within
the
Baylands.
Specifically,
Mitigation
Measure
4.G-2h
requires
that
all
new
structures
within
the
former
landfill
footprint
and
within
and
as
well
as
on
site
areas
within
1,000
feet
of
the
waste
material
footprint,
shall
incorporate
sub-slab
vapor
barriers
to
minimize
potential
vapor
intrusion
into
buildings.
In
addition,
Mitigation
Measure
4.G-2h
requires
that
all
structures
built
within
1,000
feet
of
the
landfill
footprint
be
equipped
with
automatic
combustible
gas
sensors
in
sub-floor
areas
and
in
the
first
floor
of
occupied
interior
spaces
of
buildings.
Mitigation
Measure
4.G-2h
further
requires
provision
of
a
centralized
sensor
monitoring
and
recording
system.
In
addition,
any
installation
of
utilities
in
areas
that
have
adopted
soil
capping
remediation
strategies
are
required
to
be
located
above
the
contaminated
soil
and
groundwater
areas
in
accordance
with
RWQCB
and
DTSC
requirements.
Where
gravity
and
utility
force
mains
require
encroachment
into
contaminated
areas,
special
construction
details
and
mitigation
measures
are
required
to
be
developed
during
the
preparation
of
the
final
RAPs
for
and
as
approved
by
the
RWQCB
and
DTSC
and
in
accordance
with
Soil
and
Groundwater
Management
Plans.
Final
RAPs
will
include
regulatory
agency
(DTSC
or
RWQCB)
approved
Human
Health
Risk
Assessments
that
address
inhalation
risks.
In
accordance
with
the
requirements
of
Title
27,
monitoring
for
trace
gases
is
required
to
be
conducted
for
30
years
or
until
the
operator
receives
authorization
from
the
local
enforcement
agency
(LEA),
which
is
the
San
Mateo
County
Health
System,
and
CalRecycle
to
discontinue
monitoring
upon
demonstration
by
the
operator
that
there
is
no
potential
for
trace
gas
migration
into
onsite
structures.
See
for
discussion
regarding
the
efficacy
of
vapor
intrusion
mitigation.
See
Response
Methane
will
migrate
from
areas
where
it
is
present
at
higher
pressures
or
concentrations
to
areas
where
it
is
present
at
lower
pressures
or
concentrations.
Since
methane
is
lighter
than
air,
it
has
a
tendency
to
rise
toward
the
ground
surface
where
it
dissipates
into
the
atmosphere
as
it
moves
away
from
its
source.
Brisbane
Baylands
Final
EIR
2.9.1-86
May
2015